The prevalence of inadequate vitamin B6 nutrition has been well documented in many segments of the American population. For example, the median intake is only about half of the RDA for women in recent USDA studies. While the consequences of longterm marginal status are unclear, vitamin B6 nutriture is known to affect the efficiency of many physiological processes and host defense mechanisms. Because of a lack of knowledge of the bioavailability of vitamin B6, the adequacy of human diets in meeting the nutritional requirement often cannot be determined. Recent studies indicate that the proportion of pyridoxine beta-glucoside (PN-G), which comprises a major portion of the vitamin B6 in plant-derived foods, is a major determinant of the bioavailability of dietary vitamin B6 because of its incomplete utilization in humans (ca 58% relative to free B6). Dietary PN-G also exerts a weak antagonistic action on the utilization of other forms of B6. The proposed research will involve further characterization of the nutritional properties of PN-G. The following objectives will be addressed: (1) the manner in which PN-G inhibits the metabolic utilization of pyridoxine as assessed by examination of excretion kinetics and metabolite distributions in studies with rats and human subjects; (2) whether the metabolic utilization of PN-G changes as a function of the stage of development in rats, and whether such changes are related to changes of beta-glucosidase activity intestinal mucosa, intestinal contents, and liver and other tissues; (3) the relative bioavailability of PN-G in the absence of interactive effects of pyridoxine in human subjects. All studies with human subjects will be conducted with deuterium-labeled forms of the vitamin to permit specific evaluation of metabolism and excretion without concerns of radioisotopic methods. The urinary excretion of deuterated or radiolabeled forms of 4-pyridoxic acid will be a major criterion of the utilization of the ingested labeled B6 compound(s) during in vivo studies. The results of these studies will permit a more accurate evaluation of vitamin B6 nutrition by providing detailed information concerning the nutritional activity of PN-G, and its inhibitory effect on the metabolism of nonglycosylated vitamin B6.
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