Effects of various amino acids on methionine-induced hyperhomocysteinemia in rats.

Rats were fed diets supplemented with 1% L-methionine with and without 2.5% various amino acids for 7 d to determine what amino acids other than glycine, serine, and cystine can suppress methionine-induced hyperhomocysteinemia. L-Glutamic acid, L-histidine, and L-arginine significantly suppressed methionine-induced enhancement of plasma homocysteine concentrations, but the mechanisms underlying the effect of these amino acids are thought not to be identical.

Dietary eritadenine suppresses guanidinoacetic Acid-induced hyperhomocysteinemia in rats.

We assessed the effect of eritadenine, a hypocholesterolemic factor isolated from the edible mushroom Lentinus edodes, on plasma homocysteine concentration using methyl-group acceptor-induced hyperhomocysteinemic rats. Male Wistar rats were fed a control diet or diets supplemented with a methyl-group acceptor or a precursor of methyl-group acceptor. Diets were supplemented with guanidinoacetic acid (GAA) at 2.5, 5, 7.5, and 10 g/kg, nicotinic acid (NiA) or ethanolamine (EA) at 5 and 10 g/kg, or glycine at 25 and 50 g/kg, and the rats were fed for 10 d (Expt. 1). Plasma total homocysteine concentration was increased 255 and 421% by 5 and 10 g/kg GAA, respectively, and 39 and 58% by 5 and 10 g/kg NiA, respectively, but not by EA or glycine. GAA supplementation dose-dependently decreased the hepatic S-adenosylmethionine (SAM) concentration and the activity of cystathionine beta-synthase (CBS) and increased the hepatic S-adenosylhomocysteine (SAH) and homocysteine concentrations. In another study in which rats were fed 5 g/kg GAA-supplemented diet for 1-10 d, plasma homocysteine and the other variables affected in Expt. 1 were affected in rats fed the GAA-supplemented diet (Expt. 2). We investigated the effect of supplementation of 5 g/kg GAA-supplemented diet with eritadenine (50 mg/kg) on plasma homocysteine concentration (Expt. 3). Eritadenine supplementation significantly suppressed the GAA-induced increase in plasma homocysteine concentration. Eritadenine also restored the decreased SAM concentration and CBS activity in the liver, whereas it further increased hepatic SAH concentration, suggesting that eritadenine might elicit its effect by both slowing homocysteine production and increasing cystathionine formation. The results confirm that GAA is a useful compound to induce experimental hyperhomocysteinemia and indicate that eritadenine can effectively counteract the hyperhomocysteinemic effect of GAA.

Suppression of methionine-induced hyperhomocysteinemia by glycine and serine in rats.

The hyperhomocysteinemia induced by a dietary addition of 1% methionine was significantly suppressed by the concurrent addition of 1% glycine or 1.4% serine to the same degree. The methionine-induced increase in the hepatic concentration of methionine metabolites was significantly suppressed by glycine and serine, but the hepatic cystathionine beta-synthase activity was not enhanced by these amino acids. When the methionine-supplemented diet was changed to the methionine plus glycine or serine diet, the plasma homocysteine concentration rapidly decreased during and after the first day. The hyperhomocysteinemia induced by an intraperitoneal injection with methionine was also suppressed by concurrent injection with glycine or serine, although the effect of serine was significantly greater than that of glycine. These results indicate that glycine and serine were effective for suppressing methionine-induced hyperhomocysteinemia: serine and its precursor glycine are considered to have elicited their effects mainly by stimulating cystathionine synthesis by supplying serine, another substrate for cystathionine synthesis.

Suppression of methionine-induced hyperhomocysteinemia by dietary eritadenine in rats.

The effect of dietary eritadenine on the plasma homocysteine concentration was investigated in methionine-induced hyperhomocysteinemic rats. The rats were fed on the control or eritadenine-supplemented (50 mg/kg) diet for 10 d. The animals were then injected with saline or methionine at a level of 100 or 300 mg/kg of body weight, and sacrificed 2 h or a more appropriate time after injection. The methionine injection increased the post-2 h concentration of plasma homocysteine in a dose-dependent manner in the control rats, this increase being significantly suppressed in the eritadenine-fed rats. This effect persisted up to 8 h after the methionine injection. The hepatic concentrations of S-adenosylmethionine and S-adenosylhomocysteine were increased by eritadenine, whereas the hepatic homocysteine concentration was inversely decreased. The cystathionine beta-synthase activity in the liver was increased by eritadenine. It is suggested from these results that eritadenine might suppress the methionine-induced increase in plasma homocysteine concentration by dual mechanisms: slowing the homocysteine production from S-adenosylhomocysteine and increasing the removal of homocysteine due to the enhanced activity of cystathionine beta-synthase.