Abstract
Since vitamin B6 is required for taurine synthesis, this study intended to reduce taurine bile acid conjugation in the cebus monkey, an obligate taurine conjugator, through dietary restriction of vitamin B6. Subsequently, the effect of vitamin B6 deficiency on lipoprotein 3H-cholesterol incorporation into biliary sterols was evaluated. Two groups of cebus monkeys were each fed a taurine-free soy-protein semi-purified diet for 9 months with (n=5) or without (n=5) 4mg of vitamin B6 per kg of diet. Bile acid conjugation, pool size and basal synthesis rate, and cholesterol solubility in bile were determined. After total bile acid pool washout, monkeys were injected with a mixture of 3H-cholesterol LDL and HDL, and the specific activity (SA) of biliary cholesterol and primary bile acids was calculated with the percent radioactivity retained by the liver and spleen. The cebus monkey remained an obligate taurine conjugator regardless of taurine and vitamin B6 status. Neither bile acid conjugation profile or pool size, cholesterol solubility in bile, nor the percent radioactivity retained in liver and spleen were affected by vitamin B6 deficiency. However, lower B6-dependent enzyme activity (γ-cystathionase and cysteinesulfinic acid decarboxylase), elevated cystathione, and reduced taurine levels were demonstrated in the B6-deficient monkeys. Further, the basal synthesis rate of primary bile acids, and the SA of all biliary sterols were significantly reduced in B6-deficient monkeys. In addition, vitamin B6 deficiency tended to elevate the plasma cholesterol concentration, which inversely correlated with the incorporation of lipoprotein 3H-cholesterol into biliary cholesterol.