Alterations in the metabolomics of sulfur-containing substances in rat kidney by betaine

Earlier studies have shown that betaine administration may modulate the metabolism of sulfur amino acids in the liver. In this study, we determined the changes in the metabolomics of sulfur-containing substances induced by betaine in the kidney, the other major organ actively involved in the transsulfuration reactions. Male rats received betaine (1 %) in drinking water for 2 weeks before killing. Betaine intake did not affect betaine–homocysteine methyltransferase activity or its protein expression in the renal tissue. Expression of methionine synthase was also unchanged. However, methionine levels were increased significantly both in plasma and kidney. Renal methionine adenosyltransferase activity and S-adenosylmethionine concentrations were increased, but there were no changes in S-adenosylhomocysteine, homocysteine, cysteine levels or cystathionine β-synthase expression. γ-Glutamylcysteine synthetase expression or glutathione levels were not altered, but cysteine dioxygenase and taurine levels were decreased significantly. In contrast, betaine administration induced cysteine sulfinate decarboxylase and its metabolic product, hypotaurine. These results indicate that the metabolomics of sulfur-containing substances in the kidney is altered extensively by betaine, although the renal capacity for methionine synthesis is unresponsive to this substance unlike that of the liver. It is suggested that the increased methionine availability due to an enhancement of its uptake from plasma may account for the alterations in the metabolomics of sulfur-containing substances in the kidney. Further studies need to be conducted to clarify the physiological/pharmacological significance of these findings.