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Bioavailability of Pyridoxine-5'-ß-D-Glucoside Determined in Humans by Stable-Isotopic Methods^{1 ,2 ,3}

Food Science and Human Nutrition Department ^* Department of Medicine, University of Florida, Gainesville, FL 32610

Stable-isotopic methods were employed to evaluate the utilization of dietary pyridoxine-5'-ß-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 ß-glucosidase(s) of the intestinal mucosa, microflora, or both in the release of free PN from dietary PN-glucoside.

KEY WORDS: • vitamin B-6 • pyridoxine glucoside • stable isotopes • bioavailability • humans

¹ Presented in part at the 1988 and 1989 meetings of the Federation of American Societies for Experimental Biology, Washington, D.C., and New Orleans, LA, respectively [Trumbo, P. R., Gregory, J. F., Sartain, D. B., Toth, J. P., Bailey, L. B. & Cerda, J. J. (1988) The bioavailability of pyridoxine-beta-glucoside in the rat and human. FASEB J. 2: A1086 (abs. #4591); Gregory, J. F., Trumbo, P. R., Bailey, L.B., Toth, J. P., Cerda, J. J. & Baumgartner, T. G. (1989) Bioavailability of oral and intravenous deuterium-labeled pyridoxine-beta-glucoside in human subjects. FASEB J. 3: A454. (abs. #1325)].

² Supported by grant DK37481 from the National Institutes of Health. Preliminary studies concerning the development of stable-isotopic methods were supported by grant 83-CRCR-1-1240 from the U.S. Department of Agriculture Competitive Grants Program. Paula R. Trumbo was supported in part by NIH grant 1F32 DK08179-01.

³ Florida Agricultural Experiment Station Journal Series Number R-00552.

Manuscript received 12 March 1990. Revision accepted 17 July 1990.

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