Bioavailability of Pyridoxine-5′-β-D-Glucoside Determined in Humans by Stable-Isotopic Methods

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Abstract
Stable-isotopic methods were employed to evaluate the utilization of dietary pyridoxine-5′-β-D-glucoside (PN-glucoside), a major form of vitamin B-6 in plant-derived foods, as a source of available vitamin B-6 for adult men (20–35 y old, n = 5). Deuterium-labeled forms of free pyridoxine (PN) and PN-glucoside were compared using the urinary excretion of labeled forms of the vitamin B-6 metabolite 4-pyridoxic acid as the main index of absorption and metabolism. When comparing orally administered, isotopically labeled PN and PN-glucoside in separate groups of subjects, similar bioavailability was observed although within-group variability was high. A dual-label study designed to examine the bioavailability of these compounds when administered simultaneously indicated that the utilization of deuterated PN-glucoside was 58 ± 13% (mean ± SEM) relative to that of deuterated PN. PN-glucoside was detected in all urine samples, which provided additional evidence of incomplete metabolic utilization. In contrast, intravenously administered PN-glucoside underwent approximately half the metabolic utilization of oral PN-glucoside. These studies indicate that the bioavailability of dietary PN-glucoside, although incomplete, is substantially greater in humans than previously found in rats. In addition, the difference between oral and intravenous routes suggests a role of β-glucosidase(s) of the intestinal mucosa, microflora, or both in the release of free PN from dietary PN-glucoside.

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