Betaine analogues alter homocysteine metabolism in rats

Abstract

Glycine betaine supplementation lowers homocysteine levels in homocystinuria and in chronic renal failure patients through methylation catalysed by betaine-homocysteine methyltransferase (BHMT). The aim of this study was to determine the effect of glycine betaine analogues on homocysteine metabolism in Lewis rats. Glycine betaine, proline betaine, trigonelline, dimethylsulfoniopropionate (DMSP) or dimethylthetin (1.5 mmoles) was subcutaneously administered to rats fed a low betaine diet. The effect of each betaine on total plasma homocysteine and urinary and plasma betaine concentrations was monitored for 24 h following administration. Baseline plasma homocysteine was 8.5±0.2 μmol/l (S.E.M., n=44) and compared to controls concentrations decreased following glycine betaine (0.8±0.4 μmol/l, P=0.064), DMSP (1.0±0.5 μmol/l, P=0.041) and dimethylthetin (1.5±0.7 μmol/l, P=0.033) treatment, while concentrations increased following proline betaine (2.2±0.7 μmol/l, P=0.002) and trigonelline (1.6±0.3 μmol/l, P<0.001) treatment. The effect of glycine betaine, DMSP and dimethylthetin on circulating homocysteine concentrations was thought to be mediated by BHMT in vivo. This hypothesis was supported by the finding that circulating glycine betaine concentrations increased following DMSP and dimethylthetin treatment. Proline betaine and trigonelline appeared to be poor BHMT substrates, being largely excreted in the urine unchanged, yet increased circulating homocysteine levels. This suggests they are inhibitors of BHMT. Urinary excretion of glycine betaine increased following treatment with all betaines, suggesting that the resorption of glycine betaine in the kidney was inhibited. The study shows that glycine betaine analogues have multiple effects on homocysteine metabolism (250).