Excess Dietary l-Cysteine, but Not l-Cystine, Is Lethal for Chicks but Not for Rats or Pigs

Abstract

A comparative species investigation of the relative pharmacologic effects of sulfur amino acids was conducted using young chicks, rats, and pigs. Ingestion of excess Met, Cys, or Cys-Cys supplemented at 2.5-, 5.0-, 7.5-, or 10 times the dietary requirement in a corn-soybean meal diet depressed chick growth to varying degrees. Strikingly, ingestion of excess Cys at 30 g/kg Cys (7.5-times the dietary requirement) caused a chick mortality rate of 50% after only 5 d of feeding. Growth was restored and chick mortality was reduced by supplementing diets containing 25 g/kg excess Cys with KHCO3 at 10 g/kg. Additionally, mortality was prevented by supplementing the drinking water of chicks receiving 25 g/kg supplemental Cys with H2O2 (0.05% final concentration). After young rats and pigs consumed excess Cys or Cys-Cys up to 40 g/kg for 14 d, weight gain was severely depressed, but we observed no mortality. An excess of dietary Cys-Cys>or=48 g/kg caused some mortality in rats. Pigs exhibited rapid recovery from growth-depressing excesses of Cys or Cys-Cys. These results lend credence to the acute toxic effects associated with the ingestion of excess sulfur amino acids and highlight the potential for excess dietary cyst(e)ine to be more pernicious than Met in certain species.

DietaryL-Cysteine Improves the Antioxidative Potential and Lipid Metabolism in Rats Fed a Normal Diet

“…20) In contrast, excessive dietary cysteine is known to cause oxidative stress. 32,33) It has even been reported that extreme doses of sulfur amino acid caused mortality in rats. 33) However, a low level of L-cysteine also had an adverse effect with regard to oxidative damage, although it increased hepatic GSH in mice fed a normal or high-fat diet.…”

“…32,33) It has even been reported that extreme doses of sulfur amino acid caused mortality in rats. 33) However, a low level of L-cysteine also had an adverse effect with regard to oxidative damage, although it increased hepatic GSH in mice fed a normal or high-fat diet. 34) Nevertheless, there was no significant difference in hepatic TBARS level among the groups of rats in this study, a finding similar to that in the report of Yang et al 35) Nor did the hepatic GSH level show any significant difference among the groups, this being similar to the finding of Weisse et al 17) However, we found increases in the hepatic catalase and GR activities in the Cys2 group.…”

Animal Models in Nutrition Research ,

“…Use of diets containing mixed ingredients and with normal protein levels is probably more relevant in terms of extrapolation to humans. Our work with chicks and pigs, therefore, involved individual amino acid excesses in diets containing 20% to 23% protein from corn and soybean meal (11,12,14,(40)(41)(42)(43). This work showed that a large dietary excess (4 g/100 g) of methionine, cysteine, or tryptophan was more growth depressing than the same excess of other amino acids.…”

Scientific Opinion on the safety and efficacy of L‐cysteine hydrochloride monohydrate as a flavouring additive for pets

“…L-Cystine did not cause mortality even at the highest tested dose (40 g/kg feed) in broilers or in pigs (receiving 6.5-and 13-fold, corresponding to 20 and 40 g/kg cyst(e)ine), whereas some deaths occurred in rats receiving a dose of 72 g/kg feed (corresponding to a 24-fold increase with respect to dietary requirements). It should be noted that the experiments were of a relatively short duration (9-17 days with broilers, 14 days with other species) (Dilger et al, 2007).…”