Effects of Addition of Sulfur-containing Amino Acids and Their Catabolites to a Low Protein Diet on Liver Fat Content in Rats

Abstract

To investigate the effects of catabolites of sulfur-containing amino acids on the liver fat content, rats fed a protein-free or 10% casein diet were orally or intraperitoneally administered sulfur-containing amino acids and their catabolites. Force-feeding of the proteinfree diet supplemented with 0.01 and 0.05% methionine reduced the excretion of urinary nitrogen, but it did not affect the liver fat content. Supplementation with 0.2% methionine induced significant liver fat accumulation accompanied with remarkable increases in the concentrations of nonprotein sulfhydryl (NP-SH) and taurine in the liver. The effects of the addition of 0.2% cystine HCI to the protein-free diet were similar to those of 0.2% methionine. Forcefeeding of the protein-free diet supplemented with 0.2% cysteine sulfinic acid or 0.2% thiopyruvate did not bring about any changes in the concentrations of sulfur-containing metabolites and fat content in the liver and the excretion of urinary nitrogen. On the contrary supplementation with 0.2% hypotaurine remarkably increased the liver fat content and taurine concentration without any changes in NP-SH concentration. The effects of injection of methionine, cysteine and hypotaurine to rats fed 10% casein diet on the fat content and sulfurcontaining metabolites in the liver were similar to those of oral administration of these compounds. These findings supported the possibility that the excess of catabolites of sulfurcontaining amino acids might be one of the factors which cause the liver fat accumulation.