Dietary vitamin B 6 effects on the distribution of intestinal mucosal and microbial β-glucosidase activities toward pyridoxine-5′-β- d-glucoside in the guinea pig

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Guinea pigs utilize dietary pyridoxine-5′-β- d-glucoside (PN-glucoside) as a source of vitamin B 6 more extensively than other species studied to date, including rats, mice, hamsters, and humans. In this study, we evaluated the sources of β-glucosidase activity involved in the hydrolysis and utilization of dietary PN-glucoside and the potential influence of vitamin B 6 nutritional status. Male guinea pigs (∼400 g, 3 to 6/diet group) were fed a sucrose/casein based diet containing 0, 1, or 3 mg/kg pyridoxine (as pyridoxine · HCl) for 4 wk. Animals fed diets containing the two lower concentrations of pyridoxine exhibited loss of body weight, although plasma pyridoxal 5′-phosphate did not vary as a function of dietary pyridoxine concentration. However, significant differences in plasma and muscle taurine and erythrocyte aspartate aminotransferase activity among diets indicated functional differences in vitamin B 6 status. β-glucosidase activity (pmol/hr/mg protein), as measured using [ 3H] pyridoxine-glucoside as the substrate, was higher in lumenal contents than mucosal cytosol. Specific activity in mucosal cytosol was significantly higher in animals fed diets containing 0 mg/kg pyridoxine than either 1 or 3 mg/kg. In contrast, the specific β-glucosidase activity of lumenal contents was significantly lower in guinea pigs fed 0 mg/kg pyridoxine versus 1 or 3 mg/kg pyridoxine diets. Although the absolute quantity of the mammalian and microbial enzyme available for in vivo small intestinal hydrolysis of dietary pyridoxine-glucoside cannot be directly determined, these data indicate that both mucosal and microbial β-glucosidase activities may contribute to the intestinal hydrolysis of pyridoxine-glucoside, and that the distribution of these activities is influenced by the concentration of dietary vitamin B 6.