DL-methionine supplementation of rice-and-bean diets affects gamma-glutamyltranspeptidase activity and glutathione content in livers of growing rats

Abstract

Gamma-glutamyltranspeptidase (GGT-EC 2.3.2.2) activity and glutathione (GSH) content were measured in livers of female weanling Wistar rats (N = 5-18), submitted to rice-and-bean diets (13 and 6% w/ w protein), both supplemented or not with DL-methionine (0.5 and 0.23 g/100 g dry diet, respectively). After 28 days, the rats on the riceand-bean diets showed significantly higher levels (four times higher) of liver GGT activity and a concomitant 50% lower concentration of liver GSH in comparison with control groups feeding on casein. The addition of DL-methionine to rice-and-bean diets significantly increased the liver GSH content, which reached levels 50% higher than those found in animals on casein diets. The increase in GSH was accompanied by a decrease in liver GGT activity, which did not reach levels as low as those observed in the control groups. No significant correlation could be established between GGT and GSH changes under the present experimental conditions. Linear correlation analysis only revealed that in animals submitted to unsupplemented rice-andbean diets GSH concentration was positively associated (P<0.05) with weight gain, food intake and food efficiency. GGT, however, was negatively correlated (P<0.05) with food intake only, and exclusively for supplemented rice-and-bean diets. The high levels of GGT activity observed in the present study for rats receiving a rice-and-bean mixture could be a result of the poor quality of these diets associated with their deficiency in sulfur amino acids. The results also suggest that diet supplementation with methionine could be important in the reduction of the deleterious effects of GSH depletion by restoring the intracellular concentration of this tripeptide.

Human papillomavirus infection and cervical cancer precursor lesions in women living by Amazon rivers: investigation of relations with markers of oxidative stress

“…Just as GSSG, which is thought to be the most powerful antioxidant in the body, GSH is part of the total glutathione pool and may be regulated by diet. 24 , 25 Fish is a major dietary component among people living in this Amazon region, and may contain minerals with antioxidative potential, such as selenium. 17 Selenium may mitigate toxic metal (and mercury) toxicity via oxidative and antioxidative mechanisms, thereby contributing to cell defense against free radicals.…”