K.Madhavan Nair

Oral repletion of iron induces free radical mediated alterations in the gastrointestinal tract of rat

Free radical mediated effects on the gastrointestinal (GI) tract were studied by supplementing 8 mg of iron orally for 15 days to groups of both control (C+) and iron deficient (D+) rats. They were compared with their respective unsupplemented groups C and D. Incorporation of 3H-thymidine into the isolated mucosal cells, as a measure of cell turn over, was lowered significantly in both the D+ and C+ groups compared to their respective controls D and C. It was observed that a single dose of 8 mg of iron given orally to control rats could cause apoptosis of GI tract mucosal cells as shown by the ladder pattern of DNA on electrophoresis. Continuous administration of the same dose of iron for a period of 15 days resulted in necrosis of the GI tract absorptive surface in D+ and C+ rats. In addition to this, a reduction of microvillus height in C+ and complete erosion of the same in D+ were observed by the transmission electron microscopy. EPR spectroscopy identified production of hydroxyl and methoxyl radicals in both the luminal and mucosal contents in the GI tract of rats. These results suggest that when iron is orally administered, free radicals are formed at the site of absorption causing damage to the GI tract mucosa.

In vitro bioavailability of iron from wheat flour fortified with ascorbic acid, EDTA and sodium hexametaphosphate, with or without iron

Abstract A laboratory scale technology was developed to fortify wheat flour with absorption promoters of iron, such as ascorbic acid, disodium ethylenediaminetetraacetic acid (NaEDTA) and with a stabilizer, sodium hexametaphosphate (SHMP), with or without iron. The in vitro bioavailability of iron in food (Indian bread, chapathi) prepared with the wheat flour fortified at 60 mg of iron/kg in the presence (1:1 molar ratio) or absence of the three chemical additives was tested. NaEDTA and ascorbic acid enhanced the in vitro bioavailability of native iron from Indian bread while SHMP had no effect. All three additives showed a trend of enhancing the in vitro bioavailabilty of total iron (native and added iron) from iron fortified chapathis. The predicted bioavailability of iron in man from Indian bread containing ascorbic acid or NaEDTA was twice as high than that with wheat flour alone or that with SHMP (8%). Similar enhancing effects of these two compounds were shown with iron-fortified wheat flour. It is concluded that wheat flour fortified with ascorbic acid or NaEDTA, either with or without iron, can enhance the predicted bioavailability of both native and added iron in man.

Polyphenol-Rich Beverages Enhance Zinc Uptake and Metallothionein Expression in Caco-2 Cells

The effect of red wine (RW), red grape juice (RGJ), green tea (GT), and representative polyphenols on Caco-2 cell (65)Zn uptake was explored. RW, RGJ, and GT enhanced the uptake of zinc from rice matrix. Fractionation of RW revealed that enhancing activity of zinc uptake was exclusively resided in the polyphenol fraction. Among the polyphenols tested, only tannic acid and quercitin stimulated the uptake of zinc while others did not influence the uptake. In tune with these results, only tannic acid and quercitin competed with zinquin (a zinc selective fluorophore) for zinc in vitro. Although all the polyphenols tested appear to enhance the expression of metallothionein (MT), the induction was higher with tannic acid, quercitin, and RW extract. Furthermore, phytic acid abrogated the tannic acid-induced MT expression. These results suggest that polyphenol-rich beverages, tannic acid, and quercitin bind and stimulate the zinc uptake and MT expression in Caco-2 cells.

Coordinate expression and localization of iron and zinc transporters explain iron–zinc interactions during uptake in Caco-2 cells: implications for iron uptake at the enterocyte ☆

Iron and zinc have diverse and important physiological functions. Yet, the mechanism of their absorption at the intestine remains controversial and is confounded by the fact that many studies have shown, to varying extents, that they inhibit the absorption of each other. We have studied the expression of iron and zinc transporters and storage proteins, and their regulation, in Caco-2 cells, an established enterocyte model, under normal culture conditions and under conditions of iron and zinc depletion and supplementation using a combination of immunoblotting, confocal microscopy and reverse transcriptase polymerase chain reaction. We show that divalent metal transporter-1 (DMT-1) delocalizes from the plasma membrane upon iron or zinc depletion, but its apical abundance increases with zinc supplementation. This translocation of DMT-1 coincides with an increase in iron uptake upon zinc supplementation, as previously reported by us. FPN-1 expression increases upon zinc supplementation and decreases with iron or zinc depletion, effluxing the excess sequestered iron and thus maintaining cellular iron homeostasis. Zinc influx transporters Zip-1 and Zip-14 and efflux transporters ZnT-1 and ZnT-4 are coordinately regulated under conditions of zinc supplementation and depletion to ensure cellular zinc homeostasis. We have previously reported that iron uptake can entail two transporters and that zinc noncompetitively inhibits iron uptake in Caco-2 cells. We now provide evidence that this inhibition is independent of DMT-1 and that Zip-14 may be a relevant iron transporter. These new observations provide experimental support to this two-transporter model of iron uptake and give mechanistic insight to iron-zinc interactions during uptake at the enterocyte.

Dietary ligands as determinants of iron-zinc interactions at the absorptive enterocyte.

Iron and zinc interact at the enterocyte and influence the absorption of one another. We have previously reported that zinc noncompetitively inhibits iron uptake in Caco-2 cells, a widely accepted model of the absorptive enterocyte. However, the determinants of this interaction, such as the effect of dietary ligands, remain uncharacterized. Dietary ligands selectively chelate iron and zinc in definite stoichiometric proportions and thus alter the bioavailability from food matrices. Here, we have used common dietary ligands, such as ascorbic acid, phytic acid, tannic acid, tartaric acid, cysteine, histidine, and methionine to characterize iron, zinc uptake individually and in combination, using Caco-2 cells. Selective chelation of zinc, using cysteine, decreased the magnitude of inhibition of iron uptake but could not reverse the inhibition. On the other hand, selective increase in iron uptake in the presence of methionine resulted in increased zinc uptake, rather than inhibition. Taken together, these in vitro results suggest that dietary ligands can modulate iron-zinc interaction and that zinc cannot competitively inhibit iron uptake.

Vitamin A deficiency in infants: Effects of postnatal maternal vitamin A supplementation on the growth and vitamin A status

Abstract The effects of early postpartum maternal vitamin A supplementation (200,000 IU) on vitamin A status and growth of healthy breastfed infants were examined using a double blind controlled prospective study design. Vitamin A status during infancy was determined using a cross sectional study in infants. A retrospective analysis of case records of hospitalised children was used to define the extent of corneal lesions in infants. Serum vitamin A, retinol binding protein (RBP) and molar ratio of retinol to RBP in infants at birth, 6 wk, 3,6,9 & 12 months of age and vitamin A levels in breast milk were determined. Vitamin A status of infants at birth was low with mean serum retinol and RBP being 0.51 and 0.83 μmoles/L, respectively with a molar ratio of 0.59. Mean serum retinol was significantly increased in both the groups of infants by 6 wk of age (0.91 in the control and 0.82 μmoles L in the experimental group). Nevertheless, nearly 30% of infants continued to have serum retinol 1.05 μmoles/L upto 1 year of lactation in unsupplemented women. Supplemented mothers had significantly higher retinol content during the first 30 days of lactation. However, no impact of increased vitamin A intake could be observed on serum retinol levels and growth of their infants. In view of these data, the functional significance of low retinol levels among young infants and justification of supplementing lactating women with vitamin A to improve the vitamin A status of their newborns and young infants needs to be critically re-examined.

Pharmacokinetics of levonorgestkel in Indian women belonging to low socio-economic group

This study attempted to evaluate the effect of nutritional factors on the disposition of levonorgestrel (LN), as administered in a combination oral pill. Plasma samples from 11 low socioeconomic women were measured by radioimmunoassay after oral doses of 2 types of combination oral formulations, Primovlar-30 (500 mcg of LN and 30 mcg of ethinyl estradiol) and WHO-LNB (150 mcg of LN and 50 mcg of ethinyl estradiol). The following data suggest that nutritional status as reflected by anthropometry can modify the disposition of LN in women. With both preparations, plasma levels of LN reached a peak from 1-2 hours after administration and ranged from 4.6-16.2 ng/ml with Primovlar-30 and 2.8-14.4 ng/ml with LNB. The amount of LN in circulation at 48 hours was found to be more than .5 ng/ml. A triphasic decline in plasma levels of the steroid was established. Pharmacokinetic parameters calculated by graphical and regression analyses showed that the elimination half-life of the LN had a positive correlation and the peak plasma concentration a negative correlation with the 2 anthropometric indexes: weight/height sq. times 100 and skin-fold at triceps.

Alternate strategies for improving iron nutrition: lessons from recent research.

Strategies such as dietary diversification and food fortification have yielded significant results in controlling iron deficiency anaemia in developed countries. Reducing the prevalence of iron deficiency anaemia in developing countries is still a matter of importance. The major factors responsible for iron deficiency anaemia in the vulnerable segments of developing countries are reduced intake and poor bioavailability of dietary iron. Dietary diversification and food-based approaches pose considerable challenges before they can be implemented on a wide scale. Anaemia control programmes based on the administration of prophylactic doses of iron and folic acid tablets have been widely implemented. As the programmes were not effective in countries such as India, the dosage of iron was increased. The role of excess iron in causing intestinal oxidative stress has drawn attention to other approaches of iron supplementation. Prophylactic administration of iron along with antioxidants like vitamins E and C or foods rich in these vitamins is one such strategy. To reduce the intestinal oxidative stress, intermittent supplementation of iron is being considered. The potential benefits and shortcomings of these approaches are reviewed.

Impact of iron-fortified foods on Hb concentration in children (<10 years): a systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE To combine evidence from randomized controlled trials to assess the effect of Fe-fortified foods on mean Hb concentration in children (<10 years). DESIGN We conducted a meta-analysis of randomized, controlled, Fe-fortified feeding trials that evaluated Hb concentration. The weighted mean difference was calculated for net changes in Hb by using random-effects models. Meta-regression and covariate analyses were performed to explore the influence of confounders on the net pooled effect. SETTING Trials were identified through a systematic search of PubMed, the Cochrane Library and secondary references. SUBJECTS Eighteen studies covering 5142 participants were identified. The duration of feeding of fortified foods ranged from 6 to 12 months in these studies. RESULTS Eighteen studies were included and evaluated in the meta-analysis. The overall pooled estimate of Hb concentration showed a significant increase in the fortification group compared with the control group (weighted mean difference = 5·09 g/l; 95% CI 3·23, 6·95 g/l; I 2 = 90%, τ 2 = 18·37, P < 0·0001). Meta-regression analysis indicated that duration of feeding was positively related to the effect size (regression coefficient = 0·368; 95% CI 0·005, 0·731; P < 0·05). The net pooled effect size after removing the confounders was 4·74 (95% CI 3·08, 6·40) g/l. CONCLUSIONS We observed an association between intake of Fe-fortified foods and Hb concentration in children aged <10 years. Fe-fortified foods could be an effective strategy for reducing Fe-deficiency anaemia in children.

Bioavailability of Iron and Zinc from Multiple Micronutrient Fortified Beverage Premixes in Caco‐2 Cell Model

Iron and zinc deficiencies are the most prevalent nutrient deficiencies worldwide. They often coexist as the dietary factors, especially phytate, which impairs iron absorption also affects zinc absorption. Therefore, suitable strategies are required to control multiple micronutrient deficiencies in populations that subsist on high-phytate foods such as the whole wheat flour based Indian bread (chapatti). The objective of the study, therefore, was to test the bioavailability of iron and zinc in 2 multiple micronutrient beverage premixes in the absence and presence of chapatti. The premix-1 contained iron, zinc, and vitamin A while premix-2 contained all micronutrients in premix-1, plus folic acid and ascorbic acid. Ferritin induction and (65)Zn uptake were assessed using coupled in vitro digestion/Caco-2 cell line model as the surrogate markers of iron and zinc bioavailability, respectively. The results show that iron bioavailability from premixes-1 and 2 was similar in the absence of chapatti. However, premix-2 showed significantly higher iron bioavailability compared to premix-1 in the presence of chapatti. In contrast, the zinc uptake was similar from both premixes-1 and 2 in the absence or presence of chapatti. These results suggest that both the premixes provide bioavailable minerals, but premix-2 appears to be promising in the presence of foods that have high phytate.