Recent nutritional studies have indicated prevalent marginal deficiency of vitamin B6 in many segments of the American population. While the consequences of long-term 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) may be a major determinant of the bioavailability of dietary vitamin B6. This research will involve further characterization of the nutritional properties of PN-G, which comprises a major portion of the vitamin B6 of plant-derived foods. The following objectives will be addressed: (1) Whether the utilization of labelled PN-G is influenced by adaptation to the level of chronic PN-G ingestion in the rat and in human subjects; (2) Whether PN- G ingested simultaneously with labelled pyridoxine (PN) may inhibit the metabolic utilization of PN in the rat, in human subjects, and in vitro with key enzymes in vitamin B6 metabolism and function; (3) The nutritional properties of three naturally occurring derivatives of PN-G will also be determined, relative to PN and PN-G, in a rat bioassay with long-term (3-week) administration of the tested compounds. All studies with human subjects will be conducted with deuterium-labelled (d2 and/or d5) forms of the vitamin to permit specific evaluation of metabolism and excretion without concerns of radioisotopic methods. The urinary excretion of deuterated or radiolabelled forms of 4- pyridoxic acid will be a major criterion of the utilization of the ingested labelled compound(s) in vitamin B6 metabolism in 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 derivatives of PN-glucoside, as well potential variation in the extent of metabolic utilization of PN-glucoside, and its potential inhibitory effect on the metabolism of non-glycosylated vitamin B6.
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