Influence of dietary methionine with or without adequate dietary vitamins on hyperhomocysteinemia in rats

Information on the effects of dietary vitamins involved in homocysteine metabolism on the dietary methionine (Met)-induced hyperhomocysteinemia is limited. Thus, a six-wk study was conducted to investigate the effects of dietary Met with or without adequate vitamins on plasma total homocysteine (tHcy) in rats. Four levels of supplemental L-Met (0, 5, 10 and 20 g/kg) and two levels of vitamins (adequate and deficient in folate plus B-12) were tested in the casein-based diets. The plasma tHcy values in males were higher (p < 0.05) than in females (8.1± 0.6 vs. 6.0±0.6 μmol/L for adequate diet; 66.5± 1.4 vs. 45.5±0.9 μmol/L for folate-B-12 deficient diet). In males, supplementation of the adequate (control) diet with 5, 10 and 20 g/kg Met, increased tHcy to 1.3, 1.9 and 7.9 times control, respectively. In females, the corresponding values were 1.3, 1.7 and 5.6 times control. In rats fed folate-B-12 deficient diets, supplemental Met, however, generally caused reductions in plasma tHcy values in both sexes. These disparate responses to supplementary Met could be partly due to increases in hepatic S-adenosylmethionine (SAM)/S-adenosylhomocysteine (SAH) ratios in folate-B-12 deficient rats.