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 -synthase activity was not enhanced by these amino acids. When the methioninesupplemented 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.

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.

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 methionineinduced enhancement of plasma homocysteine concentrations, but the mechanisms underlying the effect of these amino acids are thought not to be identical.

No abstract

The carbothermic reduction of NiO was carried out by microwave irradiation at 2.45 GHz under a constant rate of temperature rise. The state of reaction was analyzed by means of non-equilibrium thermodynamics. The rates of the dominant reaction was the Boudouard reaction followed by NiO + CO ¼ Ni + CO 2 , differing from that by conventional radiant heating. The uncompensated heat of reactions and the enthalpy change of reactions were almost same amount. The activation energy was 141 kJ/mol for the carbothermic reduction of NiO, 115 kJ/mol for the NiO reduction by CO gas and 166 kJ/mol for the Boudouard reaction. The former two values were smaller than conventional radiant heating.