Interaction of riboflavin with zinc bioavailability

Effect of different dietary zinc levels on hepatic antioxidant and micronutrients indices under oxidative stress conditions

Dietary zinc (Zn) status exerts a powerful influence on the degree of oxidative damage caused by free radicals. We examined the effect of dietary Zn variations with oxidative stress (OS) treatment on antioxidant status, liver function, and status of vitamins in male Wistar rats. Oxidative stress was generated by intraperitoneal injections of tert-butyl hydroperoxide; and dietary Zn variations done were Zn deficient, normal, and excess, with 8, 30, and 60 mg Zn per kilogram diet, respectively. After 21-day dietary regimen, the animals were killed; and plasma aspartate aminotransferase, alanine aminotransferase, hepatic antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), Zn, reduced glutathione, lipid peroxidation (LPO), and hepatic riboflavin, nicotinic acid, and ascorbic acid estimations were done. The alanine aminotransferase and aspartate aminotransferase levels were elevated in rats with OS and Zn-deficient diet, which were restored to normal levels with excess dietary Zn. Hepatic antioxidant enzymes and reduced glutathione levels were significantly decreased with concomitant increase in LPO due to OS induction in animals with Zn-deficient diet. Corresponding enhanced enzyme activities, higher hepatic Zn, and lowered LPO were observed in animals with normal- and excess-Zn diet. A dose-dependent increase in hepatic nicotinic acid accumulation was observed as the dietary Zn level increased from deficient to excess; however, there was no influence on riboflavin and ascorbic acid status. The results suggest that Zn may have a therapeutic potential in treatment of oxidative liver damage along with enhanced nicotinic acid absorption.

Predicting Bioavailable Zinc from Lower Phytate Forms, Folic Acid and Their Interactions with Zinc in Vegetarian Meals

OBJECTIVE

To develop a statistical model for predicting zinc bioavailability from cereal-based vegetarian meals using relative proportion of nutrients, non-nutrients and their interactive effects.

METHODS

A database on in vitro zinc dialysability (by isotopic tracer, 65Zn) of vegetarian meals (266 out of 326) from Asia, Africa, Europe /US and Latin America was used to develop a model for estimating zinc bioavailability. A multiple regression analysis adjusted for energy content was carried out for net bioavailable zinc from a meal with the predictor variables as meal contents of iron, zinc, copper, ascorbic acid, beta-carotene, riboflavin, thiamine, folic acid, tannic acid, fiber, phytate degradation products (IP6 to IP1), along with their interaction terms. Reproducibility of the model was tested with remaining 60 meals. Validation of the model was done with zinc absorption data of i) 12 young adults on 24 meals and ii) 5 adults with ileostomy on 7 meals.

RESULTS

Folic acid, IP3 and IP5 were significant influencing factors for bioavailable zinc. Weighted multiple regression equation was: ln (bioavailable zinc in mg) = -1.701 + 1.285 x ln [(IP5 in mg] x (Zn in mg)] -1.222 x ln(IP5 in mg) -0.0078 x folic acid in microg -0.137 x ln [(IP3 in mg) x (Zn in mg)] with adjusted R--[2] = 0.64, p = 0.0001. The correlation between predicted and observed dialysability of meals was found to be 0.96 (p < 0.01). A significant correlation between observed and predicted amount of absorbed zinc (r = 0.85, p < 0.01) was obtained for the human data of zinc absorption in 12 healthy and 5 subjects with ileostomy.

CONCLUSIONS

Bioavailable amount of zinc from vegetarian meals was influenced by IP3, IP5 and folic acid content and their interactive effect with zinc content.

Intestinal absorption in health and disease: micronutrients

The main theme of this chapter concerns the precise biochemical mechanisms involved in stages up to, and including, gastrointestinal absorption of vitamins and certain selected minerals. Essential data regarding sequential events, immediately following absorption of these micronutrients, are also included. There is reference to water-soluble vitamins that are, in general, either coenzymes in various metabolic reactions or carriers of certain biochemical groupings. In contrast, fat-soluble vitamins frequently function as integral components of cell membranes; they, too, receive ample attention. It is appropriate, nevertheless, to recognize that some minerals required in very small amounts are closely allied biochemically with particular vitamins; these specific associations are apportioned emphasis at relevant places in the text. Although predominant discussion centres on the physiological state, clinical reference is necessarily made to gastrointestinal disorders in which imbalance of vitamins and minerals consequently results in an additional detrimental impact on health.

Effect of riboflavin supplementation on zinc and iron absorption and growth performance in mice

Diets prevalent in vegetarian populations using rice and other whole grains as staples with little consumption of yellow vegetables are low in riboflavin. These diets have poor bioavailability of iron and zinc because metals are present as inorganic salts with low solubility. Riboflavin has the capacity to form complexes, and supplementation of riboflavin may result in increased absorption of zinc and iron, thus increasing the cellular transport. Therefore, riboflavin may have direct as well as indirect effects on growth. Using this as the conceptual basis, experiments were conducted on pregnant and lactating mice. Two groups, each of 12 mice (9 females and 3 males), were observed on a low-riboflavin rice-based diet (adequate in all other nutrients), one with and one without supplementation of 10 mg riboflavin/kg diet. There was significant improvement in the growth parameters like percent conception, mean weight gain in pregnancy, mean weight of pups at the age of 21 d, and percentage hemoglobin due to riboflavin supplementation (p < 0.05). Percent zinc absorption, for the low-riboflavin diet, the supplemented diet, and the synthetic control diet were 16.4+/-5.7, 33.7+/-8.9, and 44.6+/-4.0, respectively, indicating the beneficial effect of riboflavin supplementation on iron and zinc utilization.