Dietary Fiber-Induced Changes in Bile Acid Conjugation and Taurine Metabolism in Rats

Abstract

Effect of types of dietary fiber on biliary bile acid glycine/taurine ratio (G/T) and activities of hepatic enzymes in bile acid conjugation (bile acid-CoA:amino acid N-acyltransferase) and taurine synthesis (cysteine dioxygenase and cysteine sulfinate decarboxylase) was examined in the rats. Dietary pectin compared to cellulose greatly increased the G/T accompanying the decrease in the concentration of hepatic taurine. However, the N-acyltransferase reaction produced taurine- but little glycine-conjugated bile acids when both taurine and glycine were coexisted at the concentrations of physiological ranges in the assay media both in rats fed cellulose and pectin. Dietary pectin relative to cellulose greatly decreased the activity of cysteine dioxygenase but rather increased that of cysteine sulfinate decarboxylase. A taurine-lowering agent (guanidinoethyl sulfonate) severely decreased activities of these enzymes in taurine synthesis accompanying the decreases in hepatic taurine concentrations both in rats fed cellulose and pectin. This drug like as pectin profoundly increased the G/T irrespective of the dietary fiber sources. Although there was no consistent relationship between the G/T and hepatic concentration of taurine, an inverse relationship between the activity of cysteine dioxygenase and the G/T was observed among the groups of rats. It was suggested that the alterat ion in the activity of hepatic cysteine dioxygenase and thus the taurine synthesis is the factor to modify the G/T in rats fed different types of dietary fiber.