Comparative study of pyridoxine-alpha, beta-glucosides, and phosphopyridoxyl-lysine as a vitamin B6 nutrient

The nutritional effects of pyridoxine-alpha-glucoside (PN-alpha-Glc), pyridoxine-5' beta-glucoside (PN-5' beta-Glc) and epsilon-N-(phosphopyridoxyl)-lysine (PNP-Lys) were examined by means of: 1) transport across the intestinal wall using everted rat intestine, 2) metabolic conversion by liver or kidney homogenate, and 3) oral administration of the compound to B6-deficient rats and the subsequent analysis of B6 derivatives found in plasma. Using everted sacs prepared from rat small intestine, PN-alpha-Glc was transported into the serosal side in its intact form. On the other hand, a part of PN-5' beta-Glc was found as PN on the serosal side (PN-5' beta-Glc: PN = 2:1). When PN-alpha-Glc, PN-5' beta-Glc or PNP-Lys was incubated with liver or kidney homogenate for 3 h at pH 6.0, PN-alpha-Glc was hydrolyzed to PN (6%), while there was no hydrolysis of PN-5' beta-Glc. After 30 min of administration of each B6 derivative to B6-deficient rats, blood was collected from the heart, and the B6-derivatives found in plasma were analyzed. It was ascertained that PN-alpha-Glc served as well as PN as a B6 nutrient, while PN-5' beta-Glc and PNP-Lys were not easily metabolized to the coenzyme form, pyridoxal 5'-phosphate.