Oral N-acetyl-L-cysteine is a safe and effective precursor of cysteine

¹ Department of Animal Sciences and Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801

^* To whom correspondence should be addressed. E-mail: dhbaker{at}uiuc.edu.

	Abstract

Relative bioavailability and toxicity of N-acetyl-L-cysteine (NAC) were evaluated in 9-d chick growth assays. The bioavailability of NAC relative to Cys was determined by feeding young chicks a highly purified, crystalline AA diet singly deficient in Cys. Bioavailability estimates were obtained using standard slope-ratio methodology. N-acetyl-L-cysteine was shown to be as effective as Cys in supporting chick growth, and was assigned a relative bioavailability value of 100%. To assess toxicity, a nutritionally-adequate, corn-soybean meal diet was supplemented with graded concentrations of NAC (isomolar to 10, 20, 30, or 40 g/kg Cys). When NAC supplied 10 or 20 g/kg Cys, chick growth performance was unaffected, but NAC supplying 30 or 40 g/kg Cys reduced (P < 0.05) weight gain 13% and 34%, respectively, relative to the unsupplemented control diet. Only plasma free NAC was substantially increased (P < 0.05) due to excess dietary NAC; plasma free Cys was unaltered. It was concluded that dietary NAC is completely efficacious in supplying Cys in support of chick growth, and only large excesses of NAC are growth depressing. Hence, the human clinical benefits of oral NAC likely result from its ability to deliver Cys safely and effectively to the portal circulation.

Key Words: N-Acetyl-L-cysteine, Bioavailability, Chick, Cysteine, Toxicity

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