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Critical control points in the impact of the proinflammatory immune response on growth and metabolism^1,2

T. H. Elsasser^*,3, T. J. Caperna^*, C-J. Li^*, S. Kahl^* and J. L. Sartin

^* United States Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705; and and Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL 36849

	Abstract

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 
Intrinsic in the equation for successful animal production is the efficiency of nutrient use for assimilation into useful animal-derived products. However, when young growing animals encounter various stressors that activate the proinflammatory response (PR), the biochemical effects of the resulting cascade of PR mediators [cytokines, prostaglandin and prosta-cyclin derivatives, nitric oxide (NO), superoxide anion (O₂·), etc.] override the regulatory signals normally ascribed to anabolic tissue accretion and growth. The efficiency of energy and nutrient use will proportionally decrease for growth rate due to the redirection of nutrient use to support immune defense processes. These proinflammatory events can develop in association with infectious disease but also are apparent in and a part of the natural response to birth, parturition, and weaning. If growth patterns are tracked during the PR, growth deficits are often apparent. Some growth deficits are relatively transient in duration, whereas others are quite long lasting, persisting although traditional clinical markers of PR are no longer evident. Recent evidence indicates that the PR cascades initiated by cytokines like tumor necrosis factor- play a major role in these growth deficits. Perturbations in mitochondrial energetics and NO and O₂· interactions further affect metabolic balance. Free radicals and reactive nitrogen intermediates interact with select molecular targets in proteins (i.e., enzymes, histone proteins, and signal transduction proteins), causing the nitration and nitrosylation of select amino acids. If these posttranslational modifications occur in proteins associated with control points critical in metabolic stability, the resulting altered protein structure blocks its functionality. Attenuation of these overt posttranslational protein modifications at their site of production offers a strategy to minimize their detrimental impact while preserving needed cytokine, NO, and O₂· functions.

Key Words: cytokine • metabolism • nitric oxide • peroxynitrite • proinflammatory response • tyrosine nitration

	INTRODUCTION

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 
The proinflammatory response (PR) is a process initiated by the body’s internal recognition of threats to stability and well-being. This response begins with the release of immune system hormones termed proinflammatory cytokines [i.e., tumor necrosis factor- (TNF-), IL-1, IL-1β, IL-6, and transforming growth fractor (TGF) that set into motion the cascade of factors that ultimately bring about the clinical signs of inflammation. The main effectors of this process change mitochondrial function and electron transport chain efficiency, alter capillary permeability and regional blood flow, channel a progression of white blood cells to the affected regions, and redirect metabolism and nutrient utilization (progressively more toward catabolism as the magnitude of the immune challenge escalates) by many different tissue beds (Elsasser et al., 2000b; Zhang et al., 2000; Pober and Min, 2006). In general, the response to stressors that initiate the PR range from mild and brief to overt and intense. The larger responses above a so-called break-point are usually associated with clinical signs and progressively impact on greater growth and metabolism (Elsasser et al., 2000b). This is especially true in the younger animal at a time in its life when a relatively large biological priority is given to growth via the assimilation of nutrients into tissue proteins, bone, and lipid.

On a molecular basis, a major underlying cause for the perturbed metabolic profiles of proinflammatory stress is observed in one form or another in terms of altered protein function. Historically, this has been attributed to the effects of cytokines on differential gene expression (activation and repression), protein synthesis and degradation, or posttranslational modifications in proteins including phosphorylation, myristylation, carbonylation, and ubiquitination (Janssen-Heininger et al., 2000; Andrassy et al., 2006). Newer data, however, indicate that perturbations in the interactions between nitric oxide (NO) and superoxide anion (O₂·) promote the posttranslational nitration of amino acids, such as tyrosine, serine, and cysteine, with severe consequences to the affected protein’s functionality. The objective of this review, therefore, is to illustrate how the specific proinflammatory modification to proteins termed tyrosine nitration affects signal transduction within the growth hormone axis and to suggest how this might impact growth and metabolism during bouts of immune stress.

	A PERSPECTIVE ON THE ORIGINS OF METABOLIC DYSFUNCTION IN THE PROINFLAMMATORY RESPONSE

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 
Three fundamental defining features of life are that: 1) component systems of an organism are maintained in some manner physically separated from the surrounding environment (i.e., a barrier, such as a membrane); 2) there is an inherent drive to survive, and 3) the process of survival is a cumulative end result of what can be termed life cycle transitions, processes through which the intrinsic information and molecular interactions necessary to make more copies of the organism are coordinated and distributed or passed on (Bishop and Brandhorst, 2003; Hulbert, 2003). The ancient origins of the basic mechanisms that facilitated life cycle transitions and, therefore, the capacity to survive have been the focus of philogenetic detectives and have been revealed through detailed, pathway-based chemical fingerprinting. If one tracks the phylogenetic relationships among divergent and disparate organisms back to a point where some level of commonality was present among them, it becomes evident that the processes surrounding the chemistry of NO, its decay products, and the resulting NO signaling were key in the evolutionary processes of defense and communication (Bishop and Brandhorst, 2003). In their earliest potential uses, NO and compounds that rapidly release NO have been characterized as defensive weapons, similar in scope to superoxide anion. In effect, a noxious chemical mediator generated to discourage the assimilation of one organism (i.e., becoming a food source) into another by a predator or competitive organism (Durner et al., 1999). Even as far back as single-celled organisms, the chemical characteristics of NO as a signaling molecule were quite applicable towards survival and communication. Whether for defense or communication, NO was rapidly generated, rapidly diffused, and differed in solubility between aqueous and lipid environments. In high concentrations, NO was highly reactive (especially in the presence of superoxide anion) with other molecules causing nitration and nitrosylation inhibition and dysfunction (Greenacre and Ischiropoulos, 2001; Ischiropoulos and Gow, 2005). The relative toxicity of NO could be great when generated quickly and present in high concentrations similar to what is now observed in the monocyte burst production and its impact on bacterial killing (Xia and Zweier, 1997; Vazquez-Torres et al., 2000). Toxicity is moderated and attenuated by the rapidity of NO diffusion, its brief reactive half-life, and short physical distance of diffusion before degradation (Thomas et al., 2001).

Within mammals, NO is made by the enzymatic cleavage of the guanido N of arginine by any of 4 isoforms of nitric oxide synthase (NOS, Goligorsky et al., 2002; Liochev and Fridovich 2002). The different isoforms are, for the most part, compartmentally distinct within and between cells and consist of 1) a membrane-bound endothelial form (eNOS, found in numerous cell types like hepatocytes, vascular endothelium, and enterocytes); 2) an inducible high output form (iNOS, highly functional in monocytes, neutrophils, and Kupffer cells); 3) a neuronal form (mNOS), and 4) a form specific to inner regions of mitochondria (mNOS). It is well recognized that NO plays multiple roles in practically all tissues of the body. Immune function is no exception and NO generation is a key component of both the rapid response arm of the PR defense system we call the innate immune system as well as the more highly evolved adaptive immune system (Bogdan et al., 2000). Although an in-depth discussion of the character of innate and acquired immunity falls outside the scope of this review, it serves a good purpose to point out a few significant features of each to better understand why some physiological systems become pathologically perturbed when the immune system becomes activated.

The fight to maintain a constant or stabile internal environment through what has evolved as immune surveillance has, on the one hand, linked the cooperating mechanisms of quick general response (innate immunity) with the specificity of a tuned response (acquired immunity). Several evolutionary markers indicate that the closely regulated generation of NO plays a key role in coordinating innate and acquired immune responses (Bayne, 2003). However, the very nature of the chemical reactivity of NO and its metabolites demands that for the biological actions of NO-supported functions to occur in the absence of adverse side effects (e.g., function-stopping posttranslational reactions between NO-derived compounds and proteins), the generation and reactivity of NO needs to be confined spatially and temporally to succinct compartments and time frames within and between cells (Greenacre and Ischiropoulos, 2001; Goligorsky et al., 2002; Ischiropoulos and Gow, 2005). In effect, a conflict develops when the more ancient innate systems of defense over-respond to proinflammatory challenges. Biochemically, and now recognized in clinical medicine, nitration-based protein and enzyme dysfunction (Greenacre and Ischiropoulos, 2001) develops in circumstances where the generation of NO and its decay products is too great or it reacts with unintended target molecules.

	THE PROINFLAMMATORY RESPONSE: IMPACTS ON NUTRIENT AVAILABILITY AND USE

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 
Recognizing the Impact
In a practical and applied industry perspective, the comprehensive review by Larson (2005) summarized the economic impact of the negative effects of disease on cattle carcass traits and, by inference, the economic impact of proinflammatory stress. In essence, the following 3 key potential hypotheses were presented to suggest a mechanistic cause for the observed economic losses: 1) cytokine-driven changes in endocrine signaling with respect to the thyroid, insulin, and GH-IGF-I axes; 2) disease-related decreases in feed intake with accompanying further impacts on the GH-IGF-I axis, and 3) the number of effective feeding days for sick animals were less than healthy penmates. However, a conclusion reached was that there were few data that specifically demonstrated a clear mechanistic link between disease processes and how they impact carcass traits. Recent work from our laboratory has addressed this very concern, and we now can make inferences about how alterations in disease-mediated metabolism occur at the molecular and, in some aspects, at the atomic level. With this depth of insight, the intent is to be better able to suggest science-driven interventions that can be applied to animal management scenarios to prevent the magnitude of response to disease as well as to facilitate the recovery from such disease.

Pathophysiological Rearrangement of Cellular Metabolism During Proinflammatory Stress
If there is one overriding principle that can be associated with the metabolic response to proinflammatory stress, it is the concept that it is never appropriate to consider that "one size fits all"; each tissue in the body differs in and changes over time with respect to its sensitivity and responsiveness to the signal mediators that are evolved during the PR and impact metabolism. To aid in our grasp of redirected metabolism during the proinflammatory state, we need to accept the assumption that surviving the immune insult takes priority over any other biological need, especially growth and tissue accretion in the young animal (Elsasser et al., 2000b). The needed shifts in nutrient use by tissues during the PR are, therefore, affected by the intensity of the perceived immune challenge and the potential contribution of a tissue to the recovery process at the time of the challenge. We can adapt some of the fundamental features of Hammond’s model of differential nutrient use (metabolic priority) by tissues (Hammond, 1952) to help us comprehend this concept.

The Hammond model initially related a tissue’s priority to acquire and use nutrients to its metabolic rate and biological priority toward survival (Hammond, 1944). In his vision, the concept of survival was that of the species, and in that regard a relatively high priority in females was assigned to tissues and processes supporting fetal development, lactation, etc., processes not relevant to nutrient partitioning in the male. Because the fetal and placental tissues that developed early in pregnancy were of very high metabolic rate, these "new" sources of tissue were in high competition with maternal tissues to receive nutrients. In fact, as depicted in Figure 1, the fetal-placental priority of early gestational development was ranked by Hammond in a position just slightly lower than that of the central nervous system tissues of the dam. However, with fetal maturation and development, the later stage tissues were of lower metabolic rate than the early stage tissues and were therefore reassigned a lower partitioning priority than the early stage tissues (as reflected in the lower intensity arrows for "fetal-placental". For the mother and the fetus this inferred that a given tissue’s metabolic priority changed with physiological status. This dynamic and changing competition for maternal nutrients was reflected in Hammond’s summarization of priorities (1944) when he stated that "At the onset of pregnancy the foetus comes into the picture with at first a very high metabolic rate and competes with the maternal tissues on a level, as far as can be judged, slightly below that of the (maternal) central nervous system... In other words, the later developing parts of the foetus are less able to compete with the maternal tissues than the early developing parts, and especially is this so when the mother herself is not yet fully grown". Intuitively, therefore, we see that the priorities for nutrient partitioning between tissues and the regulation of such in males is more straightforward than those which occur in females.

View larger version (22K): [in this window] [in a new window]   Figure 1. Sir John Hammond (1944) ranked the relative ability of a tissue to obtain and utilize nutrients as a function of its metabolic rate, its contribution to the higher biological function of survival, and the availability of nutrients within the environment. For example, in states of health, the assimilation of nutrients into adipose tissue is viewed as a low priority, a so-called luxury of excess, where the availability of calories is not limiting to metabolic processes and the excess nutrients are stored. Defined through the integration of signals in the endocrine-immune gradient, this calorie storage depot as well as some muscle protein locations can achieve states of higher biological importance as they are called on (in part via the increased catabolic influence of proinflammatory cytokine signals) as first responders to be catabolized to yield energy and amino acids for immune defense purposes, especially in the face of reduced voluntary intake. TNF- = tumor necrosis factor-; LPS = lipopolysaccharide. Adapted from Hammond (1952) and Elsasser et al. (2000b).

The manner in which metabolism gets redirected during the PR is far more complicated than ordinarily attributed to easily measured changes in plasma and tissue concentrations of hormones and cytokines. In fact, there are as many as 10 interrelated regulatory processes that set and reset cellular responses during the onset of and recovery from the immune challenge. These are summarized in Table 1 and described in detail elsewhere (Elsasser and Kahl, 2002). At the onset of the PR, several of the first responder cytokines are purely catabolic in character, setting a physiological state of readiness to retrieve needed energy substrates from storage depots like fat and muscle. These are subsequently downregulated and reversed back toward anabolic functions as the later-arriving anti-inflammatory cytokines and acute phase proteins reestablish normal function. These initial responses are generally catabolic for 2 main reasons: 1) when fever is present, the caloric demand can increase as much as 30% for each 1°C increase in core body temperature (Baracos et al., 1987) and 2) if this is accompanied by the normal decrease in feed intake (anorexia and inappetance) that occurs during proinflammatory stress, the needed calories are channeled away from other resources and processes in a prioritized manner proportional to the severity of the response (Elsasser et al., 1998). Examples of how the nature of proinflammatory effectors impact metabolic processes are illustrated in Table 2 in its summarization of TNF- effects on different hormonal, metabolic, and tissue systems.

View this table: [in this window] [in a new window]   Table 1. Ten influences that impact tissue metabolic responses to proinflammatory challenge (adapted from Elsasser and Kahl, 2002)

The role of mitochondrial dysfunction as a major contributor to the metabolic consequences of proinflammatory stress cannot be stated too strongly. In particular, the cellular density of mitochondria may be a major reason why some cells within specific architecturally arranged tissue regions (i.e., pericentral venous cells in the liver and islets in the pancreas) are significantly more affected by proinflammatory stress than other areas. The reason why functional mitochondrial stability should be considered a major critical control point in metabolic perturbations of disease stress is the simple fact that a very small change in mitochondrial efficiency results in a functionally large increase in free radical generation and release into the cell. This is reflected in some examples of just how much chemical work is accomplished by mitochondria in normal healthy states of function. In the normal human, to process the turnover of the 65 kg of ATP generated and cleaved daily requires that more than 3 x 10²¹ protons be pumped per second with a corresponding consumption of 380 L of O₂ (Rich, 2003). In the energy transfer events that regenerate ATP, it has been estimated that 1 to 2% of the electrons passing through the electron transport chain escape the chain and participate in the reactions that form free radicals (Nijtmans et al., 2004). This is largely the results of perturbations to the oxidative phosphorylation system termed Complex I, NADH-ubiquinone oxidoreductase and the associated accessory proteins. The damaging effects of cytokine-driven proinflammatory stress are presumed to largely be initiated and channeled through a cascade of events starting with the elaboration of the proinflammatory-initiating cytokine, TNF-, which further triggers increased cellular NO.

In the early years of NO research, the origin of pathology-associated effects of NO was thought to be a manifestation of the high output cytokine-inducible isoform of nitric oxide called Type 2 or iNOS (MacMicking et al., 1997). It is readily acknowledged now, however, that the constitutive, lower output Type 3 isoform, endothelial eNOS [especially ₁₁₇₇-SER-phosphorylation-activated endothelial eNOS (Elsasser et al., 2004; Connelly et al., 2005)] as well as the unique mitochondrial NOS (Giulivi et al., 2006), contribute significantly to pathology associated with NO. Rather than purely a function of the amount of NO generated, the main cause of NO-related side effects resides in aberrant temporal patterns and sites of production that place NO in spatial proximity to molecular targets with which it readily interacts (Goligorski et al., 2002). The generation of NO outside of its normal temporal and spatial intracellular limits largely results in the formation of intermediary oxynitrogen species with high reactivity. When these oxynitrogen compounds interact with targets, such as the phenolic ring of tyrosine or cysteine sulfur, the result is a chemical nitration or nitrosylation, respectively. If this occurs in molecules that are pivotal regulatory points in a given metabolic pathway, the normal progression of this pathway becomes perturbed and is apparent in clinical manifestations of disease. Post-translational chemical modifications like these impact several intracellular signaling molecules and regulatory enzymes resulting in more than 50 defined clinical pathologies ranging from atherosclerosis to clotting defects (Greenacre and Ischiropoulos, 2001; Gow et al., 2004).

The other chemical culprit associated with aberrant proinflammatory stress perturbations on metabolism is superoxide anion. Overproduction of superoxide anion during the proinflammatory response affects metabolic processes in 2 main areas: decreased intracellular energetic efficiency (Frisard and Ravussin, 2006) and post-translational modification of metabolic regulatory proteins leading to carbonyl proteins (Frein et al., 2005). Superoxide anion is generated from mitochondrial and nonmitochondrial (xanthine oxidase, XO) sources and the interplay between these derived sources and other reactive compounds, such as hydrogen peroxide, set the stage for the level of pathology associated with proinflammatory stress (Witting et al., 2007). In these situations, the generation of superoxide anion is not the large outpouring typical of the neutrophil oxidative burst needed for pathogen killing (Burvenich et al., 2003), but rather the comparatively low intracellular levels that leak from mitochondria or are generated in the cytoplasm by XO in a variety of cells including hepatocytes. Under appropriate spatial limits and proximities, NO and superoxide anion combine to form a highly reactive oxynitrogen species called peroxynitrite, ON-OO^– (Greenacre and Ischiropoulos, 2001). Peroxynitrite directly reacts with several biomolecules leading to the nitration of several protein amino acid (the phenolioc ring of tyrosines in particular), DNA, and lipid targets. The generation of protein tyrosine nitration can be tracked now relatively easily through immunohistochemical procedures using primary antibodies to 3'-nitrotyrosine (Gow et al., 1998). Indeed, some of the ONOO^– targets are also mitochondrial molecules, such as respiratory Complex I (Murray et al., 2002). The impact on mitochondrial Complex I is a cascading process that leads to further impairment of the electron transport chain and ultimately more free radical production and more tissue damage (Nijtmans et al., 2004).

Under normal circumstances the production of ROS in cells that do not generate the oxidative burst, as does the neutrophil, is handled and eliminated by superoxide dismutase, wherein H₂O₂ is generated from superoxide anion. Hydrogen peroxide is processed further to H₂O via catalase and glutathione peroxidase. However, an interesting feature of the total free radical generating and disposal system is that when sufficient ONOO^– is present (i.e., a high intracellular site-localized concentration), superoxide dismutase (Quijano et al., 2001; Demicheli et al., 2007) and glutathione peroxidase (Sies and Arteel, 2000) themselves become targets for nitration. The result is diminished protective capacity, which then further increases the impact of the nitro-oxidative stress on metabolism (Elsasser et al., 2000a, 2004).

One mechanism that functions to downregulate the progressive surge of free radical production and tissue metabolic impairment is the eventual decrease in the functioning number of active mitochondria, a mitochondrial atresia, so to speak. The fact that the nitration or other chemical modification of Complex I leads to its own demise was illustrated in the experiments conducted by Chandel et al. (2000) where the use of rote-none, a potent Complex I inhibitor, blocked the further generation of ROS, thereby attenuating the magnitude of proinflammatory impact.

Interestingly, however, the discriminating difference between a regulatory process and pathology may relate to how much and where in the cell free radical generation develops during an inflammatory episode, how long the episode continues before downregulating, and what intracellular molecules become targets for these free radical reactions. Nitric oxide is itself a free radical, and it now appears that, under normal circumstances, it participates in a type of feedback regulation on mitochondrial function. Nitric oxide was identified as a physiologic regulator of electron transfer and ATP synthesis through its capacity to interact with and inhibit cytochrome oxidase. Additionally, NO stimulates the mitochondrial production of O₂·-active species, primarily O₂^– and H₂O₂, and depending on NO matrix concentration, the generation of ONOO^–. In proper spatial and temporal production and diffusion limits (ONOO^– reactivity is very short-lived, so an interaction with a target molecule is a probability function defined by how much is produced and over what distance it diffuses before either chemically modifying a target or being neutralized), which is responsible for the nitrosylation and nitration of mitochondrial and cytosolic molecules. In this manner, alterations in mitochondrial complex function restrict energy output, further increases O₂· active species and changes cell signaling for proliferation and apoptosis (Carreras et al., 2004). Furthermore, and as a direct impact on hormone signal transduction processes that ordinarily regulate metabolic processes, the decreased ATP-generating potential of affected mitochondria decrease cytosolic phosphorylation potential where the activity of many signal transduction intermediates is dictated by the state of phosphorylation of specific tyrosine and serine residues (Gellerich et al., 2002).

The loss of mitochondrial numbers and processes is not a one-way street, however. Recently, the converse of this mitochondrial atresia, a process called mitochondrial biogenesis, has been described as a prosurvival mechanism following needed metabolic adjustments to the onset of proinflammatory stress, mitochondrial biogenesis restores oxidative metabolism and increases in ATP needed for homeostatic stability (Haden et al., 2007) as the PR resolves back to a state of health. Whereas high output levels of NO are detrimental to mitochondrial processing and cytochrome oxidase activity, chronic low level increases appear to be a major regulatory stimulus toward increased mitochondrial biogenesis (Nisoli and Carruba, 2006; Kato and Giulivi, 2006). This dynamic response in mitochondrial numbers and functionality during critical illness, as it impacts on protection and survival, has also been reviewed extensively by Protti and Singer (2007).

	PHYSIOLOGICAL STATUS: MODULATING CYTOKINE RESPONSE CASCADES

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 
To better establish courses of action in the treatment and management of the proinflammatory response, it is critical to realize that the prevailing physiological and metabolic status at the time of immunological encounter has a significant impact on how large or severe some aspects of the proinflammatory cascade develop. Originally thought of as animal-to-animal variability in host response to pathogen infection or challenge with bacterial endotoxin, the varying nature of several components of the proinflammatory response between animals was demonstrated to actually reflect the modulation of the initiating cytokine release by such factors as sex and reproductive state, diet, subclinical infection, and nutritional and metabolic status. For several years, our laboratory has developed research strategies to test and manage aspects of the variability in cytokine response that are affected by commonly encountered physiological states in cattle. We did this for 2 main reasons. First, changes in many of the subcomponents of the proinflammatory cascade are so subtle that unless the magnitude of the background variability is minimized, the response cannot be adequately measured and evaluated. Second, in real-life situations, no immune stimulus is ever encountered as a single entity. There is usually a main or primary insult that launches some level of a proinflammatory response, but there are always additional viral, bacterial, and parasitic pathogens in the background, mostly undetected, that are lumped into the category of subclinically infected. This is particularly true with respect to the multiplicity of factors that shape the magnitude of the proinflammatory response during mastitis (Burvenich et al., 2003). Figure 2 summarizes results from several studies in our laboratory that addressed the impact of commonly encountered health and metabolic factors that could affect maximum plasma concentrations and area under the concentration x time curve for the elaboration of TNF- following i.v. challenge with E. coli O55L:5 endotoxin (i.e., lipopolysaccharide, LPS) in calves.

View larger version (22K): [in this window] [in a new window]   Figure 2. Different physiological, environmental, and genetic influences shape and determine the magnitude of some proinflammatory cytokine responses like that of tumor necrosis factor- (TNF-). Reproductive hormones such as testosterone, estrogen, and progesterone (panel A) affect both cytokine receptor numbers as well as endotoxin binding protein concentrations in plasma and signal transduction responses to determine in part the intensity of the cytokine release. Other naturally occurring toxicants derived from fungus infection of plants (panel B) impact both cytokine production and further perturb the regulatory set point of the hypothalamus that determined internal core body temperature. Certain subclinical infections (panel C) can augment otherwise rather benign proinflammatory responses to bacterial toxins, where the outcome is more severe than either immune challenge alone. Finally, some genetic parameters (panel D) cause natural mechanisms of cytokine downregulation and accommodation to terminate the proinflammatory response to remain active and prolong the chance for tissue damage from free radical generation. LPS = lipopolysaccharide. Adapted, in part, from Filipov et al. (1999), Elsasser et al. (2005), and Kahl and Elsasser (2006).

2

Prevailing climate largely dictates the type of grasses that cattle graze and, in the southeastern United States, tall fescue is a major nutritional source. However, one aspect of fescue that makes it superior in its growth resilience and insect resistance is the same feature that causes the health problems collectively called fescue syndrome. The active agent formed by the fungus growing in the grass is a mixture of loline alkyloids, similar in pharmacological properties to ergot, including its effects as a dopaminergic modulator of endocrine function. Collaboratively with researchers at the University of Georgia, we asked whether the underlying presence of fescue syndrome might further exacerbate the clinical response to proinflammatory challenge in cattle. As summarized in Figure 2B, the intensity of the proinflammatory response was affected by underlying ergot-like toxicosis. When cattle that were grazed on endophyte-infected or endophyte-free fescue grass were additionally challenged with endotoxin, the increase in plasma levels of TNF- was significantly increased (3-fold greater) in the cattle consuming the toxic forage (Filipov et al., 1999). From a pathophysiological point of view, the implications are that any underlying fescue syndrome-associated complications in body temperature regulation and the localized redistribution of blood flow to peripheral tissues may be perturbed substantially further with the onset of a proinflammatory episode arising from bacterial infection.

Figure 2C illustrates the consequences of underlying subclinical disease in the face of a mild immune challenge, as modeled with the administration of a low level of E. coli endotoxin. In a 2-by-2 factorial arrangement of treatments, we measured plasma TNF- concentrations in young Holstein steer calves (Elsasser et al., 1999). Treatments were noninfected control, endotoxin-challenged, subclinically infected with the coccidian-like protozoa Sarcocystis cruzi, and endotoxin-positive subclinical infection. Pathogens such as S. cruzi are interesting as a model in which to study the effects of subclinical infection because the onset of clinical signs of disease stemming from the S. cruzi is well timed to the day (Fayer and Elsasser, 1991), and so one knows that the schizogonous eruption of the organism that triggers the proinflammatory cascade is occurring, even though the outward signs of disease are not readily observable. The results indicate that the presence of subclinical parasitic infection alone had a marginal, if any, effect on plasma concentrations of TNF-. However, where LPS administration stimulated the typical proinflammatory surge in TNF- levels, the underlying presence of the subclinical parasitic infection caused significant further increases in the cytokine. The molecular basis for this upregulation of the proinflammatory response may be related to observations by McCall et al. (2007) and Bafica et al. (2006), in which toll-like receptor (TLR) interactions associated with modulation of TLR-2, TLR-4, and TLR-9 by Trypanasoma cruzi primed the immune system of infected animals for an augmented proinflammatory response. In our study, additional data demonstrated that the NO cascade was also augmented by the presence of subclinical infection in LPS-challenged calves, and that measures of glucose metabolism, insulin responses to feeding, and pancreatic islet immunohistopathology were significantly more perturbed in animals exposed to the combined stimuli. The level to which viral, bacterial, and parasitic pathogens shape and affect the host’s ability to mount a TNF- response is far beyond the scope of this review; more details on this topic can be found in Rahman and McFadden, 2006.

Cytokine upregulation, such as that which is observed and measured in animals challenged with natural gram-negative bacterial infection or gram-negative endotoxin, is a necessary evil; however, one side of the so-called 2-edged sword referred to by Aggarwal (2003) to start the immune response ball rolling, measured counterinflammatory responses usually soon begin that constrain this early response and attenuate further increases in the elaboration of TNF-. This counterregulatory process has been termed "endotoxin tolerance" and has been characterized as an essential component of the survival aspects of the response to infection (West and Heagy, 2002). If the proinflammartory cascade were to further progress unchecked, the results would culminate in the stark over-production of nitrogen and oxygen free radicals, overt localized ischemia and the development of multiorgan failure and death (Crouser et al., 2000). The data shown in Figure 2D illustrate this downregulated elaboration of TNF-, for which 2 endotoxin challenges were administered to each calf and the challenges separated by 5 d. The area under the response curve was calculated through the first 4 h after the administration of the endotoxin. The interesting feature of this tolerance feature is that we have defined a subpopulation of cattle with a distinct phenotypic departure from the customary downregulated TNF- response to repeated endotoxin challenge. We have tracked this phenomenon to polymorphisms in the promoter region of the TNF- gene and the feature is an inheritable characteristic (Elsasser et al., 2005). A significant characteristic of these animals is that when they are unstressed, they grow and present metabolic profiles consistent with normal calves. However, the onset of the proinflammatory immune response with repeated LPS challenges exacerbates aspects of perturbed metabolism as reflected in significantly more weight loss, longer time to recover, severe impairment of the somatotropic axis and increased nitration of liver proteins (Elsasser et al., 2005, 2007b). The significance of these examples of TNF- variability resides in the fact that each has defined impacts on metabolism that largely stem from the inherent associated variability in NO and superoxide anion response.

	CRITICAL CONTROL POINTS IMPACTING TISSUE PROTEIN NITRATION

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 
While NO generation by cells is recognized as essential to life, a comprehensive review of the functions of NO in normal physiological processes and regulation is beyond the scope of the present topic. However, for relevant and recent information in this area, readers are directed to other extensive reviews (Perrotta et al., 2005; Moncada and Bolaños, 2006; Valko et al., 2007). For the purposes of discussion herein, the concerns regarding NO are largely those surrounding the consequences of overstimulated production of NO and the localized interaction of NO with other reactive molecules, such as superoxide anion. It is well documented that during the proinflammatory response, NO and superoxide anion interact (and more so in the presence of increased tissue pCO₂ associated with poor tissue oxygenation; Goldstein et al., 2004), resulting in the production of the highly reactive oxynitrogen species, peroxynitrite (ONOO^– ; Pryor and Squadrito, 1995; Greenacre and Ischiropoulos, 2001; Liochev and Fridovich, 2002). Under physiological concentrations of reactants and conditions, ONOO^– chemically nitrates in vivo several molecular targets, including phenolic ring-containing compounds like tyrosine (forming 3-nitrotyrosine; Greenacre and Ischiropoulos, 2001), amino acid residues critical to phosphorylation activation of several signal transduction proteins. Posttranslational nitration modifications, such as these, largely have been defined as pathology-associated biomarkers of disease in situations ranging from host responses to immune stimuli (Greenacre and Ischiropoulos, 2001; Gow et al., 2004) to drug metabolism toxicities (James et al., 2003). Whereas several changes in protein function have been associated with tyrosine nitration, the majority of changes have been considered an impairment to protein function, especially where conformational change or steric hindrance in protein structure coincides with the site of nitration (Pryor and Squadrito, 1995; Greenacre and Ischiropoulos, 2001; Liochev and Fridovich, 2002; Ischiropoulos, 2003). Some of the more severe impacts on proteins that become nitrated are that their biological effectiveness is shortened due to rapid ubiquitination and channeled degradation in the proteosome (Souza et al., 2000). Many of these proteins can escape normal immunorecognition as self-proteins and elicit antibody production resembling autoimmunopathies (Ohmori and Kanayama, 2005) with harmful consequences to tissues and cells.

Our laboratory recently has tracked the biochemical progressions leading to generation of these nitrated proteins as a consequence of the formation of ONOO^– in the liver of endotoxin-challenged calves (Elsasser et al., 2004; Kahl and Elsasser, 2004). The responses of several pathway elements to a proinflammatory stimulus with E. coli lipopolysaccharide (2.5 µg/kg, BW, i.v.) in beef calves were examined, several of which were identified as critical control points, sites to which intervention strategies might be targeted in the attempt to minimize pathological associations of the proinflammatory response. These significant control points are summarized across publications and localized to specifically numbered structures and processes depicted in Figure 3 as a representative stylized hepatocyte.

View larger version (59K): [in this window] [in a new window]   Figure 3. Critical control points in the progression from proinflammatory cytokine (TNF-) binding to its caveolar-localized receptor to the generation of the potent protein tyrosine-nitrating anion peroxynitrite, ONOO–. As detailed in the accompanying text, in each of the 7 key elements, these critical control points are pathway locations toward which effective intervention strategies might be directed to minimize aberrant pathology from the ONOO– and free radicals produced, all the while maintaining an efficient immune response against the pathogen. CAT-2 = cationic amino acid transporter-2; eNOS = endothelial nitric oxide (NO) synthase.

	METABOLIC PERTURBATIONS: PROINFLAMMATORY UNCOUPLING OF THE GH AXIS AT THE LEVEL OF SIGNAL TRANSDUCTION

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In states of health, the actions of GH and IGF-I to regulate metabolic activities in young animals largely are geared toward anabolic processes. However, in coordination with the immune system recognition of a challenge that culminates in the proinflammatory cascade, these anabolic properties are progressively more constrained as the severity of the insult is perceived as more severe and life threatening. Functionally, especially in terms of a septic crisis, this manifests itself as an inability for tissues and cells to respond to GH signals, and many aspects of this active repression are driven through the effects of the proinflammatory cytokines IL-1 (Cooney and Shumate, 2006) and TNF- and the differential effect of these cytokines to regulate, in turn, the release patterns of GH in numerous species. All-in-all, this cellular inability to respond to endogenous or exogenous GH is similar in scope to the refractory state described by Jenkins and Ross (1998) as GH resistance. As a compounding factor, GH resistance is further amplified where voluntary food intake is decreased in the febrile state by what Thissen et al. (1999) defined as uncoupling of the somatatropic axis.

Growth hormone resistance and axis uncoupling has been attributed to multiple actions of proinflammatory cytokines like TNF- and IL-1 and downstream effectors on both the regulation of GH release from the pituitary (inhibition of the GH release stimulating properties of growth hormone releasing hormone and thyrotropin releasing hormone; Elsasser et al., 1991; Fry et al., 1998; Daniel et al., 2002), as well as many direct actions at peripheral target cells such as JAK-STAT (signal transducer and activators of transcription) signaling in hepatocytes. These effects on target cells include decreased GH receptor (GHR) content, altered activity of STAT proteins, increased activity of suppressors of cytokine signaling (SOCS) proteins by TNF-, and a generalized decrease in IGF-I message transcription (Thissen and Verniers, 1997; Defalque et al., 1999; Colson et al., 2000; Lang et al., 2005). Furthermore, the metabolic actions of IGF-I are redirected, not only in terms of IGF-I message transcription and tissue and plasma concentrations, but also through the redistribution IGF-I to tissues as affected by proinflammatory patterns of the IGFBP. Again using a model of proinflammatory response based on LPS administration to well-fed rapidly growing cattle, we observed that the pattern of change in IGFBP-2 and -3 concentrations were differentially affected over time where the plasma concentration of IGF-I progressively declined through 24 h following the LPS challenge (Figure 4). Whereas plasma IGFBP-3 (the major bulk carrier protein for IGF-I in plasma) levels declined through 8 h after LPS and then rebounded toward normal content by 24 h, IGFBP-2 (an IGF carrier facilitating transendothelial IGF-I transfer) levels were significantly increased at 4 h post-LPS and remained elevated through 24 h. Data from in vitro modeling of the changes in IGFBP production by cultured bovine cells (Elsasser et al., 2007a) indicate that these differential effects on IGFBP-2 and -3 are an intricate balance between changes in IGFBP gene transcription and translation and the increased production and release of proteases that selectively degrade specific binding proteins under the control of cytokines like TNF- (Elsasser et al., 1995; Holly and Perks, 2006).

View larger version (27K): [in this window] [in a new window]   Figure 4. Plasma concentrations of IGF-I as well as the respective major IGFBP change over time after the onset of a proinflammatory challenge. The plasma concentration reductions in IGF-I reflect a part of the mechanism needed to spare nutrients for immune defense purposes by arresting some anabolic actions of IGF-I on muscle and bone. The changing milieu of binding proteins (BP) as well as localized paracrine tissue production of IGF-I ensure that the needed IGF-I signals to the immune cells are maintained. Panel (A) represents a 125I-IGF-I ligand blot of plasma IGF binding proteins from calves challenged with endotoxin (i.e., lipopolysaccharide; LPS). Panel (B) summarizes the change over time in plasma content of IGF-I, and IGFBP-2 and IGFBP-3 in these calves. Adapted from Elsasser et al. (1991, 2007a).

The nitration of JAK-2 and the associated decrease in phospo-STAT5b translocation to the nucleus were consistent with much of the GH resistance associated with endotoxemia. Because this specific nitration was localized to membrane-associated caveolae regions in association with the localization of a source of NO (caveolin-1-bound eNOS), the spatial and temporal criteria for nitration by ONOO^– were satisfied. Some important characteristics of this site-localization of ONOO^– generation and reactivity are presented in Figure 5.

View larger version (43K): [in this window] [in a new window]   Figure 5. When endotoxin [lipopolysaccharide (LPS), Escherichia coli O55:B5, 2.5 µg/kg of BW] is used as a provocative i.v. immune challenge, several intracellular communication links are altered. As seen in panel (A) and quantified in panel (B), which represents Western blot analysis of cell caveolin-1-immunoprecipitated cell proteins, early in the proinflammatory response a decrease in membrane content of caveolin-1 occurs accompanied by an increase in the phosphorylation activation of endothelial nitric oxide synthase (eNOS) and an increase in the epitope-specific nitration of Janus kinase (JAK)-2 (a feature that impairs its enzymatic protein kinase activity). Confocal immunomicroscopy (panel C) clearly indicates that these JAK-2 nitrations occur in and are localized to caveolae, wherein reside many of the proinflammatory cytokine receptors as well as the constitutive isoform of nitric oxide synthase (NOS), eNOS.b From Elsassser et al. (2007b).

Experiments by Lanone et al. (2002) indicated that the molecular probability for in vivo tyrosine nitration to take place in proteins was increased by the nature of the molecular microenvironment immediately surrounding the nitration target. They discovered a commonality between many nitrated proteins and this was shown to be the patterned amino acid sequence where the critical affected tyrosines were flanked on each side by aspartate, glutamate, and glutamine. We looked at the consequences of nitration at the 3' phenolic position of either or both tyrosine residues at the 1007 and 1008 residue locations by subjecting a series of natural or nitrated 20 amino acid peptide analogs of this JAK-2 phosphorylation site to high field magnetic resonance analysis and substitution molecular modeling based on Gasteiger-Marsili electronegativity changes (Elsasser et al., 2007c). In addition, we tested the ability for these peptides to become phosphorylated by subjecting them to in vitro tyrosine kinase peptide phosphorylation reactions and measuring the product by Western blot using anti-phosphotyrosine antibody. As depicted in Figure 6A, the phosphorylation target tyrosines located at the 1007 and 1008 amino acid sites are situated within a hydrophobic compartment stabilized through hydrophobic bonds to glutamic and aspartic acid residues in close spatial proximity. In Figure 6B, substitution molecular modeling combined with high field magnetic resonance analysis of synthesized 20-mer peptides spanning this phosphorylation site revealed that the presence of nitrate at the 3' tyrosine phenolic position resulted in significant changes in the spatial planar orientation of the tyrosines, destabilization of hydrophobic bonding between 1007 tyrosine and its complementary 1006 glutamic acid residue and the 1008 tyrosine and its stabilizing 1004 aspartic acid residue. The reordered intramolecular forces result in the inability for this epitope to rotate from its sequestered hydrophobic region in the JAK-2 (protein database designation 2B7A; Lucet et al., 2006) molecule to the more hydrophilic orientation needed for the transfer of the high energy phosphate from ATP. It was especially significant that the nitration in the 1008 tyrosine led to such a large counterclockwise rotation in the presentation of the tyrosine at the adjacent 1007 site. The presence of either nitration led to a complete inhibition of capacity for this site to be phosphorylated when these peptides were used as substrates for the kinase-ATP reaction (Figure 6C). Additional results indicate that nitration may be a signal for protein ubiquitination, the key signal that directs affected proteins into the proteosome degradation pathway functionally shortening the half-life of the protein in the cell (Souza et al., 2000).

View larger version (52K): [in this window] [in a new window]   Figure 6. Modeling the effects of specific tyrosine nitration at the tyrosine residues 1007 and 1008 of Janus kinase (JAK)-2, the major phosphorylation activation domain of this tyrosine kinase. Panel (A) shows the proper spatial folding of a 20-amino acid synthetic peptide surrounding the 1007 to 1008 tyrosine epitope of JAK-2 (1001LPQDKE-1007Y- 1008Y-KVKEPGESPIFW1020) as assessed by Gasteiger-Marsali molecular modeling and high-field magnetic resonance analysis. The effects of nitration at the 3' position on the phenolic ring of either tyrosine (LPQDKE-1007YONO2-Y-KVKEPGESPIFW or LPQDKE-Y-1008YONO2-KVKEPGESPIFW; panel B) causes large perturbations in the spatial orientation of these residues, reordered hydrophobic bonding to stabilizing neighbor amino acids, and an inability for this site to rotate into a favorable hydrophobic environment for phosphorylation. In panel (C), in vitro kinase reactions using these natural and nitrotyrosine-substituted peptides as substrates show that these peptides fail to phosphorylate, thus ending the progression of intracellular signal transduction processes. From Elsasser et al. (2007c).

View larger version (81K): [in this window] [in a new window]   Figure 7. Hepatocytes in biopsy samples from calves respond to proinflammatory i.v. challenge with endotoxin [lipopolysaccharide (LPS), Escherichia coli 055:B5, 2.5 µg/kg of BW,] with decreased IGF-I mRNA expression in cells in which the ONOO– mediated nitration of Janus kinase (JAK)-2 is present. In panel (A), before LPS challenge tricolor fluorescent confocal microscopy revealed that nitrated JAK-2 (red pixels, immunohistochemistry) was sparsely present in low abundance, whereas mRNA for IGF-I (green pixels, in situ hybridization) was actively expressed in the majority of the cells. After LPS challenge (panel B), on a cell by cell basis, where nitration of JAK-2 was increased in the cells, the presence of IGF-I mRNA was largely absent. When quantified by color-specific image analysis algorithms (panel C), LPS challenge resulted in a 4.5-fold increase in JAK-2 nitration (red bars, P < 0.03 vs. pre-LPS) accompanied by a 63% decrease in IGF-I mRNA (blue bars, P < 0.02 vs. pre-LPS).

	TARGETING INTERVENTION STRATEGIES TO LIMIT THE METABOLIC IMPACT OF ABERRANT PROTEIN NITRATION: A ROLE FOR VITAMIN E

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

View larger version (61K): [in this window] [in a new window]   Figure 8. The ability of vitamin E to modulate and moderate the effects of tissue protein nitration may be beneficial as a preemptive strategy to control the adverse impacts of proinflammatory free radical and reactive oxynitrogen species on metabolism. When calves were treated with GH to force the increase in plasma concentrations of IGF-I (panel A), and then exposed to 2 endotoxin (lipopolysaccharide; LPS) challenges separated by 48 h (LPS-1 and LPS-2, 2.5 µg Escherichia coli O55:B5 LPS/kg BW), the change in plasma concentrations of IGF-I was maintained within a normal range of variability in calves pretreated (5 d) with 800 to 1,000 IU of mixed isomer natural vitamin E (gray bars) in contrast to significant reductions in IGF-I measured in endotoxemic calves not pretreated with the vitamin E (black bars). Consistent with this observation, immunohistochemical examination (anti-nitrotyrosine, panel B, brown pixels) of liver biopsy tissue (samples collected by biopsy 24 h after injection of LPS-2) from these calves showed the effect of LPS to increase overall tissue protein nitration and the ability of vitamin E to counter this aberrant reaction. Similarly, the specific nitration of Janus kinase (JAK)-2 (panel C, computer-enhanced red pixels) was significantly reduced in liver cells after LPS challenge of calves, as shown in panel (D).

	CONCLUSIONS

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

	Footnotes

 
¹ This article is a US government work under the auspices of the US Department of Agriculture and, as such, is in the public domain in the United States of America. Mention of a brand name or product does not constitute an endorsement of that product by the US government where other suitably related products are adequately functional in a similar application.

² Presented at the Triennial Growth symposium at the annual meeting of the American Society of Animal Science, San Antonio, TX, July 8 to 12, 2007.

³ Corresponding author: theodore.elsasser{at}ars.usda.gov

Received for publication October 4, 2007. Accepted for publication February 22, 2008.

	LITERATURE CITED

Top Abstract INTRODUCTION A PERSPECTIVE ON THE... THE PROINFLAMMATORY RESPONSE:... PHYSIOLOGICAL STATUS: MODULATING... CRITICAL CONTROL POINTS... METABOLIC PERTURBATIONS:... TARGETING INTERVENTION... CONCLUSIONS LITERATURE CITED

 


Aggarwal, B. B. 2003. Signalling pathways of the TNF superfamily: A double-edged sword. Nat. Rev. Immunol. 3:745–756.[CrossRef][Medline]

Andrassy, M., J. Igwe, F. Autschbach, C. Volz, A. Remppis, M. F. Neurath, E. Schleicher, P. M. Humpert, T. Wendt, B. Liliensiek, M. Morcos, S. Schiekofer, K. Thiele, J. Chen, R. Kientsch-Engel, A. M. Schmidt, W. Stremmel, D. M. Stern, H. A. Katus, P. P. Nawroth, and A. Bierhaus. 2006. Posttranslationally modified proteins as mediators of sustained intestinal inflammation. Am. J. Pathol. 169:1223–1237.[Abstract/Free Full Text]

Bafica, A., H. C. Santiago, R. Goldszmid, C. Ropert, R. T. Gazzinelli, and A. Sher. 2006. Cutting edge: TLR9 and TLR2 signaling together account for MyD88-dependent control of parasitemia in Trypanosoma cruzi infection. J. Immunol. 177:3515–3519.[Abstract/Free Full Text]

Baracos, V. E., W. T. Whitmore, and R. Gale. 1987. The metabolic cost of fever. Can. J. Physiol. Pharmacol. 65:1248–1254.[Medline]

Barsacchi, R., C. Perrotta, S. Bulotta, S. Moncada, N. Borgese, and E. Clementi. 2003. Activation of endothelial nitric-oxide synthase by tumor necrosis factor-alpha: A novel pathway involving sequential activation of neutral sphingomyelinase, phosphatidylinositol-3' kinase, and Akt. Mol. Pharmacol. 63:886–895.[Abstract/Free Full Text]

Bayne, C. J. 2003. Origins and evolutionary relationships between innate and adaptive arms of immune systems. Integr. Comp. Biol. 43:293–299.[Abstract/Free Full Text]

Bishop, C. D., and B. P. Brandhorst. 2003. On nitric oxide signaling, metamorphosis, and the evolution of biphasic life cycles. Evol. Dev. 5:542–550.[CrossRef][Medline]

Bogdan, C., M. Röllinghoff, and A. Diefenbach. 2000. Reactive oxygen and reactive nitrogen intermediates in innate and specific immunity. Curr. Opin. Immunol. 12:64–76.[CrossRef][Medline]

Burvenich, C., V. Van Merris, J. Mehrzad, A. Diez-Fraile, and L. Duchateau. 2003. Severity of E. coli mastitis is mainly determined by cow factors. Vet. Res. 34:521–564.[CrossRef][Medline]

Carreras, M. C., M. C. Franco, J. G. Peralta, and J. J. Poderoso. 2004. Nitric oxide, complex I, and the modulation of mitochondrial reactive species in biology and disease. Mol. Aspects Med. 25:125–139.[CrossRef][Medline]

Carter-Su, C., and L. S. Smit. 1998. Signaling via JAK tyrosine kinases: Growth hormone receptor as a model system. Recent Prog. Horm. Res. 53:61–82.[Medline]

Chandel, N. S., W. C. Trzyna, D. S. McClintock, and P. T. Schumacker. 2000. Role of oxidants in NF-kappa B activation and TNF-alpha gene transcription induced by hypoxia and endotoxin. J. Immunol. 165:1013–1021.[Abstract/Free Full Text]

Clementi, E., and E. Nisoli. 2005. Nitric oxide and mitochondrial biogenesis: A key to long-term regulation of cell metabolism. Comp. Biochem. Physiol Mol. Integr. Physiol. 142:102–110.[CrossRef]

Cohen, A. W., R. Hnasko, W. Schubert, and M. P. Lisanti. 2004. Role of caveolae and caveolins in health and disease. Physiol. Rev. 84:1341–1379.[Abstract/Free Full Text]

Colson, A., A. Le Cam, D. Maiter, M. Edery, and J. P. Thissen. 2000. Potentiation of growth hormone-induced liver suppressors of cytokine signaling messenger ribonucleic acid by cytokines. Endocrinology 141:3687–3695.[Abstract/Free Full Text]

Connelly, L., M. Madhani, and A. J. Hobbs. 2005. Resistance to endotoxic shock in endothelial nitric-oxide synthase (eNOS) knockout mice: A proinflammatory role for eNOS-derived no in vivo. J. Biol. Chem. 280:10040–10046.[Abstract/Free Full Text]

Cooney, R. N., and M. Shumate. 2006. The inhibitory effects of interleukin-1 on growth hormone action during catabolic illness. Vitam. Horm. 74:317–340.[Medline]

Crouser, E. D., M. W. Julian, D. M. Weinstein, R. J. Fahy, and J. A. Bauer. 2000. Endotoxin-induced ileal mucosal injury and nitric oxide dysregulation are temporally dissociated. Am. J. Respir. Crit. Care Med. 161:1705–1712.[Abstract/Free Full Text]

Daniel, J. A., B. K. Whitlock, C. G. Wagner, and J. L. Sartin. 2002. Regulation of the GH and LH response to endotoxin in sheep. Domest. Anim. Endocrinol. 23:361–370.[CrossRef][Medline]

Defalque, D., N. Brandt, J. M. Ketelslegers, and J. P. Thissen. 1999. GH insensitivity induced by endotoxin injection is associated with decreased liver GH receptors. Am. J. Physiol. 276:E565–E572.[Medline]

Demicheli, V., C. Quijano, B. Alvarez, and R. Radi. 2007. Inactivation and nitration of human superoxide dismutase (SOD) by fluxes of nitric oxide and superoxide. Free Radic. Biol. Med. 42:1359–1368.[CrossRef][Medline]

Durner, J., A. J. Gow, J. S. Stamler, and J. Glazebrook. 1999. The ancient origins of nitric oxide signaling in biological systems. Proc. Natl. Acad. Sci. USA 96:14206–14207.[Free Full Text]

Elsasser, T., R. Rosebrough, T. Rumsey, and W. M. Moseley. 1996. Hormonal and nutritional modulation of arginase activity in growing cattle. Domest. Anim. Endocrinol. 13:219–228.[CrossRef][Medline]

Elsasser, T. H., J. W. Blum, and S. Kahl. 2005. Characterization of calves exhibiting a novel inheritable TNF-alpha hyperresponsiveness to endotoxin: Associations with increased pathophysiological complications. J. Appl. Physiol. 98:2045–2055.[Abstract/Free Full Text]

Elsasser, T. H., T. J. Caperna, and R. Fayer. 1991. TNF-alpha affects growth hormone secretion by a direct pituitary interaction. Proc. Soc. Exp. Biol. Med. 198:547–554.[CrossRef][Medline]

Elsasser, T. H., T. J. Caperna, and T. S. Rumsey. 1995. Endotoxin administration decreases plasma insulin-like growth factor (IGF)-I and IGF-binding protein-2 in Angus x Hereford steers independent of changes in nutritional intake. J. Endocrinol. 144:109–117.[Abstract/Free Full Text]

Elsasser, T. H., T. J. Caperna, P. J. Ward, J. L. Sartin, B. P. Steele, C. Li, and S. Kahl. 2007a. Mechanisms regulating growth factor activity during proinflammatory stress: Cytokine modulation of IGF binding proteins released by cultured bovine kidney epithelial cells. Domest. Anim. Endocrinol. 33:390–399.[CrossRef][Medline]

Elsasser, T. H., and S. Kahl. 2002. Adrenomedullin has multiple roles in disease stress: Development and remission of the inflammatory response. Microsc. Res. Tech. 57:120–129.[CrossRef][Medline]

Elsasser, T. H., S. Kahl, C. J. Li, J. L. Sartin, W. M. Garrett, and J. Rodrigo. 2007b. Caveolae nitration of Janus kinase-2 at the 1007Y–1008Y site: Coordinating inflammatory response and metabolic hormone readjustment within the somatotropic axis. Endocrinology 148:3803–3813.[Abstract/Free Full Text]

Elsasser, T. H., S. Kahl, C. MacLeod, B. Nicholson, J. L. Sartin, and C. Li. 2004. Mechanisms underlying growth hormone effects in augmenting nitric oxide production and protein tyrosine nitration during endotoxin challenge. Endocrinology 145:3413–3423.[Abstract/Free Full Text]

Elsasser, T. H., S. Kahl, T. S. Rumsey, and J. Blum. 2000a. Modulation of growth performance in disease: Reactive nitrogen compounds and their impact on cell proteins. Domest. Anim. Endocrinol. 19:75–84.[CrossRef][Medline]

Elsasser, T. H., K. C. Klasing, N. Filipov, and F. Thompson. 2000b. The metabolic consequences of stress: Targets for stress and priorities of nutrient use. Pages 77–110 in The Biology of Animal Stress. G. Moberg and J. Mench, ed. CABI Publ., New York, NY.

Elsasser, T. H., C. J. Li, T. J. Caperna, S. Kahl, and W. F. Schmidt. 2007c. Growth hormone (GH)-associated nitration of Janus kinase-2 at the 1007Y–1008Y epitope impedes phosphorylation at this site: Mechanism for and impact of a GH, AKT, and nitric oxide synthase axis on GH signal transduction. Endocrinology 148:3792–3802.[Abstract/Free Full Text]

Elsasser, T. H., J. L. Sartin, A. Martínez, S. Kahl, L. Montuenga, R. Pío, R. Fayer, M. J. Miller, and F. Cuttitta. 1999. Underlying disease stress augments plasma and tissue adrenomedullin (AM) responses to endotoxin: Colocalized increases in AM and inducible nitric oxide synthase within pancreatic islets. Endocrinology 140:5402–5411.[Abstract/Free Full Text]

Elsasser, T. H., J. L. Sartin, C. McMahon, G. Romo, R. Fayer, S. Kahl, and B. Blagburn. 1998. Changes in somatotropic axis response and body composition during growth hormone administration in progressive cachectic parasitism. Domest. Anim. Endocrinol. 15:239–255.[CrossRef][Medline]

Fayer, R., and T. H. Elsasser. 1991. Bovine sarcocystis: How parasites negatively affect growth. Parasitol. Today 7:250–255.[Medline]

Feng, J., B. A. Witthuhn, T. Matsuda, F. Kohlhuber, I. M. Kerr, and J. N. Ihle. 1997. Activation of Jak-2 catalytic activity requires phosphorylation of Y1007 in the kinase activation loop. Mol. Cell. Biol. 17:2497–2501.[Abstract]

Filipov, N. M., F. N. Thompson, J. A. Stuedemann, T. H. Elsasser, S. Kahl, R. P. Sharma, C. R. Young, L. H. Stanker, and C. K. Smith. 1999. Increased responsiveness to intravenous lipopolysaccharide challenge in steers grazing endophyte-infected tall fescue compared with steers grazing endophyte-free tall fescue. J. Endocrinol. 163:213–220.[Abstract]

Frein, D., S. Schildknecht, M. Bachschmid, and V. Ullrich. 2005. Redox regulation: A new challenge for pharmacology. Biochem. Pharmacol. 70:811–823.[CrossRef][Medline]

Frisard, M., and E. Ravussin. 2006. Energy metabolism and oxidative stress: Impact on the metabolic syndrome and the aging process. Endocrine 29:27–32.[CrossRef][Medline]

Fry, C., D. R. Gunter, C. D. McMahon, B. Steele, and J. L. Sartin. 1998. Cytokine-mediated GH release from cultured ovine pituitary cells. Neuroendocrinology 68:192–200.[CrossRef][Medline]

Gellerich, F. N., S. Trumbeckaite, Y. Chen, M. Deschauer, T. Miller, and S. Zierz. 2002. Energetic depression caused by mitochondrial dysfunction. Eur. Cytokine Netw. 13:397–399.

Giulivi, C., K. Kato, and C. E. Cooper. 2006. Nitric oxide regulation of mitochondrial oxygen consumption I: cellular physiology. Am. J. Physiol. Cell Physiol. 291:C1225–C1231.[Abstract/Free Full Text]

Goldstein, S., A. Samuni, and G. Merenyi. 2004. Reactions of nitric oxide, peroxynitrite, and carbonate radicals with nitroxides and their corresponding oxoammonium cations. Chem. Res. Toxicol. 17:250–257.[CrossRef][Medline]

Goligorsky, M. S., H. Li, S. Brodsky, and J. Chen. 2002. Relationships between caveolae and eNOS: Everything in proximity and the proximity of everything. Am. J. Physiol. Renal Physiol. 283:F1–F10.[Abstract/Free Full Text]

Gow, A. J., C. R. Farkouh, D. A. Munson, M. A. Posencheg, and H. Ischiropoulos. 2004. Biological significance of nitric oxide-mediated protein modifications. Am. J. Physiol. Lung Cell. Mol. Physiol. 287:L262–L268.[Abstract/Free Full Text]

Gow, A. J., M. McClelland, S. E. Garner, S. Malcolm, and H. Ischiropoulos. 1998. The determination of nitrotyrosine residues in proteins. Methods Mol. Biol. 100:291–299.[Medline]

Greenacre, S. A., and H. Ischiropoulos. 2001. Tyrosine nitration: Localisation, quantification, consequences for protein function and signal transduction. Free Radic. Res. 34:541–581.[Medline]

Guo, D., J. D. Dunbar, C. H. Yang, L. M. Pfeffer, and D. B. Donner. 1998. Induction of Jak/STAT signaling by activation of the type-1 TNF receptor. J. Immunol. 160:2742–2750.[Abstract/Free Full Text]

Haden, D. W., H. B. Suliman, M. S. Carraway, K. E. Welty-Wolf, A. S. Ali, H. Shitara, H. Yonekawa, and C. A. Piantadosi. 2007. Mitochondrial biogenesis restores oxidative metabolism during Staphylococcus aureus sepsis. Am. J. Respir. Crit. Care Med. 176:768–777.[Abstract/Free Full Text]

Hammond, J. 1944. Physiological factors affecting birth weight. Proc. Nutr. Soc. 2:8–14.

Hammond, J. 1952. Physiological limits to intensive production in animals. Br. Agric. Bulletin 4:222–225.

Holly, J., and C. Perks. 2006. The role of insulin-like growth factor binding proteins. Neuroendocrinology 83:154–160.[CrossRef][Medline]

Hulbert, A. J. 2003. Life, death, and membrane bilayers. J. Exp. Biol. 206:2303–2311.[Abstract/Free Full Text]

Ischiropoulos, H. 2003. Biological selectivity and functional aspects of protein tyrosine nitration. Biochem. Biophys. Res. Commun. 305:776–783.[CrossRef][Medline]

Ischiropoulos, H., and A. Gow. 2005. Pathophysiological functions of nitric oxide-mediated protein modifications. Toxicology 208:299–303.[CrossRef][Medline]

James, L. P., P. R. Mayeux, and J. A. Hinson. 2003. Acetaminophen-induced hepatotoxicity. Drug Metab. Dispos. 31:1499–1506.[Abstract/Free Full Text]

Janssen-Heininger, Y. M., M. E. Poynter, and P. A. Baeuerle. 2000. Recent advances towards understanding redox mechanisms in the activation of nuclear factor kappa-B. Free Radic. Biol. Med. 28:1317–1327.[CrossRef][Medline]

Jenkins, R. C., and R. J. Ross. 1998. Acquired growth hormone resistance in adults. Baillieres Clin. Endocrinol. Metab. 12:315–329.[Medline]

Kahl, S., and T. H. Elsasser. 2004. Endotoxin challenge increases xanthine oxidase activity in cattle: Effect of GH and vitamin E treatment. Domest. Anim. Endocrinol. 26:315–328.[CrossRef][Medline]

Kahl S. and T. H. Elsasser. 2005. Tumor necrosis factor-a (TNF-a), nitric oxide (NO), and xanthine oxidase (XO) responses to endotoxin (LPS) challenge in heifers: Effect of estrus cycle phase. J. Anim. Sci. 83(Suppl. 1):7.

Kahl, S., and T. H. Elsasser. 2006. Exogenous testosterone modulates tumor necrosis factor- alpha and acute phase protein responses to repeated endotoxin challenge in steers. Domest. Anim. Endocrinol. 31:301–311.[CrossRef][Medline]

Kahl S. and T.H. Elsasser. 2007. Tumor necrosis factor-a (TNF-a), nitric oxide (NO), and xanthine oxidase (XO) responses to endotoxin (LPS) challenge in steers: Effect of progesterone (P₄) and estradiol (E₂) treatment. J. Anim. Sci. 85(Suppl. 1):467.

Kahl, S., T. H. Elsasser, and J. Blum. 1997. Nutritional regulation of plasma tumor necrosis factor– and plasma and urinary nitrite/nitrate responses to endotoxin in cattle. Proc. Soc. Exp. Biol. Med. 215:370–376.[CrossRef][Medline]

Kato, K., and C. Giulivi. 2006. Critical overview of mitochondrial nitric oxide synthase. Front. Biosci. 11:2725–2738.[Medline]

Ko, Y. G., J. S. Lee, S. Y. Kang, J. H. Ahn, and J. S. Seo. 1999. TNF-alpha-mediated apoptosis is initiated in caveolae-like domains. J. Immunol. 162:7217–7223.[Abstract/Free Full Text]

Lang, C. H., L. Hong-Brown, and R. A. Frost. 2005. Cytokine inhibition of JAK-STAT signaling: a new mechanism of GH resistance. Pediatr. Nephrol. 20:306–312.[CrossRef][Medline]

Lanone, S., P. Manivet, J. Callebert, J. M. Launay, D. Payden, M. Aubier, J. Boczkowski, and A. Mebazza. 2002. Inducible nitric oxide synthase (NOS2) expressed in septic patients is nitrated on selected tyrosine residues; implications for enzymic activity. Biochem. J. 366:399–404.[CrossRef][Medline]

Larson, R. L. 2005. Effect of cattle disease on carcass traits. J. Anim. Sci. 83 (E. Suppl.): 37–43.

Li, C. J., S. Kahl, D. Carbaugh, and T. H. Elsasser. 2007. Temporal response of liver signal transduction elements during in vivo endotoxin challenge in cattle: Effects of growth hormone treatment. Domest. Anim. Endocrinol. 32:79–92.[CrossRef][Medline]

Liochev, S. I., and I. Fridovich. 2002. Superoxide and nitric oxide: Consequences of varying rates of production and consumption: A theoretical treatment. Free Radic. Biol. Med. 33:137–141.[Medline]

Lucet, I. S., E. Fantino, M. Styles, R. Bamert, O. Patel, S. E. Broughton, M. Walter, C. J. Burns, H. Treutlein, A. F. Wilks, and J. Rossjohn. 2006. The structural basis of Janus Kinase 2 inhibition by a potent and specific pan-Janus Kinase inhibitor. Blood 107:176–183.[Abstract/Free Full Text]

MacMicking, J., Q. W. Xie, and C. Nathan. 1997. Nitric oxide and macrophage function. Annu. Rev. Immunol. 15:323–350.[CrossRef][Medline]

McCall, M. B., M. G. Netea, C. C. Hermsen, T. Jansen, L. Jacobs, D. Golenbock, A. J. van der Ven, and R. W. Sauerwein. 2007. Plasmodium falciparum infection causes proinflammatory priming of human TLR responses. J. Immunol. 179:162–171.[Abstract/Free Full Text]

Moncada, S., and J. P. Bolaños. 2006. Nitric oxide, cell bioenergetics and neurodegeneration. J. Neurochem. 97:1676–1689.[CrossRef][Medline]

Mori, M. 2007. Regulation of nitric oxide synthesis and apoptosis by arginase and arginine recycling. J. Nutr. 137(Suppl 2):1616S–1620S.[Abstract/Free Full Text]

Murray, J., S. W. Taylor, B. Zhang, S. S. Ghosh, and R. A. Capaldi. 2002. Oxidative damage to mitochondrial Complex I due to peroxynitrite. J. Biol. Chem. 278:37223–37230.[CrossRef]

Nijtmans, L. G. J., C. Ugalde, L. P. Van den Heuvel, and J. A. M. Smeitnik. 2004. Function and dysfunction in the oxidative phosphorylation system. Pages 149–167 in Mitochondrial function and biogenesis. C. M. Koehler and M. F. Bauer, ed. Springer Publ., New York, NY.

Nisoli, E., and M. O. Carruba. 2006. Nitric oxide and mitochondrial biogenesis. J. Cell Sci. 119:2855–2862.[Abstract/Free Full Text]

Oh, Y. S., K. A. Cho, S. J. Ryu, L. Y. Khil, H. S. Jun, J. W. Yoon, and S. C. Park. 2006. Regulation of insulin response in skeletal muscle cell by caveolin status. J. Cell. Biochem. 99:747–758.[CrossRef][Medline]

Ohmori, H. and N. Kanayama. 2005. Immunogenicity of an inflammation-associated product, tyrosine nitrated self-proteins. Autoimmun. Rev. 4:224–229.[CrossRef][Medline]

Perrotta, C., C. De Palma, S. Falcone, C. Sciorati, and E. Clementi. 2005. Nitric oxide, ceramide and sphingomyelinase-coupled receptors: A tale of enzymes and messengers coordinating cell death, survival and differentiation. Life Sci. 77:1732–1739.[CrossRef][Medline]

Pober, J. S., and W. Min. 2006. Endothelial cell dysfunction, injury and death. Handb. Exp. Pharmacol. 176:135–156.[CrossRef][Medline]

Protti, A., and M. Singer. 2007. Strategies to modulate cellular energetic metabolism during sepsis. Novartis Found. Symp. 280:7–16.[Medline]

Pryor, W. A., and G. L. Squadrito. 1995. The chemistry of peroxynitrite: A product from the reaction of nitric oxide with superoxide. Am. J. Physiol. 268:L699–L722.[Medline]

Quijano, C., D. Hernandez-Saavedra, L. Castro, J. M. McCord, B. A. Freeman, and R. Radi. 2001. Reaction of peroxynitrite with Mn-superoxide dismutase. Role of the metal center in decomposition kinetics and nitration. J. Biol. Chem. 276:11631–11638.[Abstract/Free Full Text]

Raha, S., and B. H. Robinson. 2001. Mitochondria, oxygen free radicals, and apoptosis. Am. J. Med. Genet. 106:62–70.[CrossRef][Medline]

Rahman, M. M., and G. McFadden. 2006. Modulation of TNF- by microbial pathogens. PLoS Pathog. 2:66–77.[CrossRef]

Rich, P. 2003. Chemiosmotic coupling: The cost of living. Nature 421:583–587.[CrossRef][Medline]

Sartin, J. L., T. H. Elsasser, D. R. Gunter, and C. D. McMahon. 1998. Endocrine modulation of physiological responses to catabolic disease. Domest. Anim. Endocrinol. 15:423–429.[CrossRef][Medline]

Sartin, J. L., T. H. Elsasser, S. Kahl, J. Baker, J. A. Daniel, D. D. Schwartz, B. Steele, and B. K. Whitlock. 2003. Estradiol plus progesterone treatment modulates select elements of the proinflammatory cytokine cascade in steers: Attenuated nitric oxide and thromboxane B₂ production in endotoxemia. J. Anim. Sci. 81:1546–1551.[Abstract/Free Full Text]

Sies, H., and G. E. Arteel. 2000. Interaction of peroxynitrite with selenoproteins and glutathione peroxidase mimics. Free Radic. Biol. Med. 28:1451–1455.[CrossRef][Medline]

Simionescu, M., and F. Anthone. 2006. Functional ultrastructure of the vascular endothelium: Changes in various pathologies. Handb. Exp. Pharmacol. 176:41–69.[CrossRef][Medline]

Souza, J. M., I. Choi, Q. Chen, M. Weisse, E. Daikhin, M. Yudkoff, M. Obin, J. Ara, J. Horwitz, and H. Ischiropoulos. 2000. Proteolytic degradation of tyrosine nitrated proteins. Arch. Biochem. Biophys. 380:360–366.[CrossRef][Medline]

Thissen, J. P., L. E. Underwood, and J. M. Ketelslegers. 1999. Regulation of insulin-like growth factor-I in starvation and injury. Nutr. Rev. 57:167–176.[Medline]

Thissen, J. P., and J. Verniers. 1997. Inhibition by interleukin-1 and tumor necrosis factor- of the insulin-like growth factor-I messenger ribonucleic acid response to growth hormone in rat hepatocyte primary culture. Endocrinology 138:1078–1084.[Abstract/Free Full Text]

Thomas, D. D., X. Liu, S. P. Kantrow, and J. R. Lancaster. 2001. The biological lifetime of nitric oxide: Implications for the perivascular dynamics of NO and O₂. Proc. Natl. Acad. Sci. USA 98:355–360.[Abstract/Free Full Text]

Valko, M., D. Leibfritz, J. Moncol, M. T. Cronin, M. Mazur, and J. Telser. 2007. Free radicals and antioxidants in normal physiological functions and human disease. Int. J. Biochem. Cell Biol. 39:44–84.[CrossRef][Medline]

Vazquez-Torres, A., J. Jones-Carson, P. Mastroeni, H. Ischiropoulos, and F. C. Fang. 2000. Antimicrobial actions of the NADPH phagocyte oxidase and inducible nitric oxide synthase in experimental salmonellosis. I. Effects on microbial killing by activated peritoneal macrophages in vitro. J. Exp. Med. 192:227–236.[Abstract/Free Full Text]

West, M. A., and W. Heagy. 2002. Endotoxin tolerance: A review. Crit. Care Med. 30:64–73.[CrossRef]

Witting, P. K., B. S. Rayner, B. J. Wu, N. A. Ellis, and R. Stocker. 2007. H₂O₂ promotes endothelial dysfunction by stimulating multiple sources of superoxide anion production and decreasing nitric oxide bioavailability. Cell. Physiol. Biochem. 20:255–268.[Medline]

Xia, Y., and J. L. Zweier. 1997. Superoxide and peroxynitrite generation from inducible nitric oxide synthase in macrophages. Proc. Natl. Acad. Sci. USA 94:6954–6959.[Abstract/Free Full Text]

Yang, N., Y. Huang, J. Jiang, and S. J. Frank. 2004. Caveolar and lipid raft localization of the growth hormone receptor and its signaling elements: Impact on growth hormone signaling. J. Biol. Chem. 279:20898–20905.[Abstract/Free Full Text]

Zhang, P., W. R. Summer, G. J. Bagby, and S. Nelson. 2000. Innate immunity and pulmonary host defense. Immunol. Rev. 173:39–51.[CrossRef][Medline]

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