Zinc (Zn) is required as a catalytic, structural and regulatory ion for enzymes, proteins and transcription factors and is thus a key trace element in many homeostatic mechanisms of the body. Vitamins like riboflavin, nicotinic acid, thiamine, folic acid and ascorbic acid have functional groups capable of forming complexes with Zn. However, the interaction of water-soluble vitamins with Zn has not received much attention. Methods: We have examined the Zn-vitamin interactions at a variety of conditions like different Zn concentrations, different cell and protein models and under normal and oxidative stress (OS) conditions. The interactions were studied in vitro, by using erythrocytes under deficient, normal and excess Zn states. Results: Under Zn-deficient state, thiamine significantly enhanced the erythrocyte Zn uptakes (p<0.05), whereas ascorbic acid and riboflavin inhibited it (p<0.05). In another study, an in vitro erythrocyte Zn uptake was compared among healthy and diabetic subjects and it was found that Zn uptakes of healthy subjects were 17-52% higher than those for diabetic subjects. Furthermore, erythrocyte super oxide dismutase, plasma ascorbic acid and status of riboflavin were negatively correlated with Zn uptakes in healthy subjects (p<0.01). These interactions were also studied in precision cut rat liver slices, where it was found that folic acid showed inhibitory effect on Zn uptake under both normal and OS conditions as seen by dose response curves. Ascorbic acid showed marked enhancing effect on Zn uptake under OS. These in vitro interactions were confirmed in vivo using male Wistar rats. The 21 days old rats were used to examine the effect of niacin supplementation on Zn absorption under chronic OS generated by tert-butyl hydro peroxide at a dose of 0.2 mM/Kg body weight. Niacin supplementation increased the Zn absorption and improved antioxidant enzyme profile. The albumin being the major Zn carrier protein in plasma and the albumin bound Zn (ABZn) comprises 80% plasma Zn. Folic acid and thiamine significantly enhanced the ABZn (p<0.010), while nicotinic acid inhibited Zn binding to albumin. Conclusions: These results collectively suggest that vitamins are playing an important role in distribution of circulating Zn among albumin, blood cells and liver and giving a new dimension to their functionality in Zn metabolism in health and disease conditions.

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