Absorption Of Divalent Cations Research Articles

Effect of co-exposure to multiple metals (Pb, Cd, Cr, Hg, Fe, Mn and Ni) and metalloid (As) on liver function in Swiss albino mice.

The study examined the cumulative toxic effect of multiple elements, As, Pb, Cd, Cr, Hg, Fe, Mn and Ni on the liver function and their association with inflammation and apoptosis. To explore the health consequence of simultaneous exposure to multiple metals and metalloid, male and female Swiss Albino mice were randomly divided into 14 groups and subjected to different doses [MPL (maximum permissible limit), 1×, 5×, 10×, 50× or 100×] of metal(loid)s mixture via drinking water for 8weeks. Data showed that combined effect of multiple elements impaired the liver function. This was associated with significant decrease in the antioxidant enzymes and the elevation in lipid peroxidation for high exposure dose of 50× and 100× (p < 0.05). The metal(loid)s mixture exposure led to significant increase (p < 0.05) in cytokines, TNF-α, IL-6 and effector caspases (3 and 6) in exposure groups above 10× dose. Histopathological observation also revealed significant damage in the hepatic tissue on exposure to high dose. Dose dependent accumulation of respective elements (As, Cd, Cr, and Pb) in the liver was observed in each of the exposure groups. However, similar dose related increment was not observed for essential metals such as Ni, Fe and Mn. Differential accumulation of metals in the liver may be attributed to the effect of co-contaminant exposure, which could affect the divalent cation absorption due to antagonism and competitive transport process. Overall findings in this study manifest the complexity of possible joint effect of co-exposure to multiple metals and metalloid on the liver function.

Butyrate reduces cellular magnesium absorption independently of metabolic regulation in Caco-2 human colon cells

Digestion of dietary fibers by gut bacteria has been shown to stimulate intestinal mineral absorption [e.g., calcium (Ca2+) and magnesium (Mg2+)]. Although it has been suggested that local pH and short-chain fatty acid (SCFA) concentrations determine divalent cation absorption, the exact molecular mechanisms are still unknown. Therefore, this study aimed to determine the effects of SCFAs on intestinal Mg2+ absorption. We show that the butyrate concentration in the colon negatively correlates with serum Mg2+ levels in wildtype mice. Moreover, Na-butyrate significantly inhibited Mg2+ uptake in Caco-2 cells, while Ca2+ uptake was unaffected. Although Na-butyrate significantly lowered total ATP production rate, and resulted in increased phosphorylation of AMP-activated protein kinase (AMPK), inhibition of Mg2+ uptake by butyrate preceded these consequences. Importantly, electrophysiological examinations demonstrated that intracellular butyrate directly reduced the activity of the heteromeric Mg2+ channel complex, transient receptor potential melastatin (TRPM)6/7. Blocking cellular butyrate uptake prevented its inhibitory effect on Mg2+ uptake, demonstrating that butyrate acts intracellularly. Our work identified butyrate as novel regulator of intestinal Mg2+ uptake that works independently from metabolic regulation. This finding further highlights the role of microbial fermentation in the regulation of mineral absorption.

Doses of iron in prevention and treatment of anemia in pregnant women: an ongoing debate

Iron supplementation during pregnancy, both as a preventive and therapeutic measure has been a matter of debate. The guiding principles behind supplementation include availability of adequate iron stores before pregnancy, diet during pregnancy and concomitant infections. No country performs routine screening of iron stores by measuring ferritin and the decision to supplement iron is largely based on haemoglobin (Hb) levels. Evidence suggests that Hb content of the mother’s blood between 95 and 105 g/l in the third trimester correlates with the best clinical outcome. Effectiveness of routine iron supplementation during pregnancy for improving maternal hematological indices exists, but the clinical significance for both pregnant women and infants remains unclear. In the absence of conclusive evidence, several developed nations follow an individual based approach by evaluating the iron stores and then deciding on the course of treatment. On the other hand, in developing countries, where the baseline prevalence of anemia is high, existing data supports routine iron supplementation as a safe strategy to prevent maternal anemia. Controversies exist around the most appropriate dosage and frequency (daily v/s weekly) of iron supplementation for both preventive and therapeutic purposes because increased doses does not necessary yield better haematological and clinical outcomes. On the contrary, excess doses may be associated with more side effects and also may produce oxidative stress, release of free radicals, may interfere with the absorption of divalent cations, may block iron absorption by upregulating hepcidin and may result in hemoconcentration further leading to adverse outcomes. This document gives a snapshot of the existing evidence and provides a case for further deliberations on the most appropriate dosage for iron supplementation during pregnancy giving due weightage to epidemiological, physiological and clinical requirements.

β-Propeller Phytase Hydrolyzes Insoluble Ca2+-Phytate Salts and Completely Abrogates the Ability of Phytate To Chelate Metal Ions

Phytate is an antinutritional factor that influences the bioavailability of essential minerals by forming complexes with them and converting them into insoluble salts. To further our understanding of the chemistry of phytate's binding interactions with biologically important metal cations, we determined the stoichiometry, affinity, and thermodynamics of these interactions by isothermal titration calorimetry. The results suggest that phytate has multiple Ca(2+)-binding sites and forms insoluble tricalcium- or tetracalcium-phytate salts over a wide pH range (pH 3.0-9.0). We overexpressed the β-propeller phytase from Hahella chejuensis (HcBPP) that hydrolyzes insoluble Ca(2+)-phytate salts. Structure-based sequence alignments indicated that the active site of HcBPP may contain multiple calcium-binding sites that provide a favorable electrostatic environment for the binding of Ca(2+)-phytate salts. Biochemical and kinetic studies further confirmed that HcBPP preferentially recognizes its substrate and selectively hydrolyzes insoluble Ca(2+)-phytate salts at three phosphate group sites, yielding the final product, myo-inositol 2,4,6-trisphosphate. More importantly, ITC analysis of this final product with several cations revealed that HcBPP efficiently eliminates the ability of phytate to chelate several divalent cations strongly and thereby provides free minerals and phosphate ions as nutrients for the growth of bacteria. Collectively, our results provide significant new insights into the potential application of HcBPP in enhancing the bioavailability and absorption of divalent cations.

Absorption of calcium and magnesium in patients with intestinal resections treated with medium chain fatty acids

BACKGROUNDSteatorrhoea is associated with increased faecal loss of calcium and magnesium. Medium chain C8-C10 triglycerides (MCTs) improve fat absorption in patients with small bowel resections but the effects on intestinal...

Calcium and magnesium transport in the cortical thick ascending limb of Henle's loop: influence of age and gender.

Previous studies from our laboratory have shown that Ca2+ and Mg2+ absorption in the mouse cortical thick ascending limb of Henle's loop (cTAL) is a passive, paracellular process driven by the transepithelial voltage. The passive permeability of the epithelium is enhanced by peptide hormones. The present study investigated whether divalent cation absorption in the cTAL is influenced by cell maturation and/or gender. For this purpose, mouse cTAL segments were microdissected from kidneys of female and male animals aged 4 and 8 weeks. The microdissected tubules were perfused in vitro at a luminal flow rate of 1.5 to 2.5 nl/min. Transepithelial Na+, Cl-, Ca2+ and Mg2+ net fluxes (JX, pmol.min-1.mm-1) were measured using electron microprobe analysis, and the transepithelial potential difference (PDte) was measured continuously. No differences were found in the PDte, JNa and JCl of the various animal groups but the transepithelial Ca2+ and Mg2+ transport capacity of the cTAL was higher in adults (8 weeks) than in young animals (4 weeks). Furthermore, irrespective of age, transepithelial Ca2+ net absorption was greater in male than in female animals. In contrast, the NaCl transport was maximal at 4 weeks in both genders. We conclude therefore that transepithelial divalent cation absorption in the mouse cTAL is an inductive process influenced by cell maturation and gender. The molecular basis of these inductions remains to be elucidated.

Some Serum Mineral Profiles in Response to a Slimming Regime Containing Pectin.

Because of the controversy among reports as to whether dietary fiber interferes with mineral absorption or not, we investigated the effect of dietary citrus pectin in a low-caloric, processed formula on serum calcium (Ca), zinc (Zn), copper (Cu), and iron (Fe) in 14 healthy obese Egyptian women undergoing weight reduction over a four-week period. The total caloric supply was 1, 000kcal/day. There was no difference between pre- and post-study values in the serum Ca. This was ascribed to the fact that water-soluble dietary fibers are fermented in the colon with the generation of short-chain fatty acids, which besides being absorbed, also enhance colonic divalent cation absorption. There was a numerical non significant decrease well within the reference values of Zn (-4.87%), Cu(-6.42%), and Fe(-19.65%). These results were discussed in light of the suggestion that the Zn, Cu, and Fe status is one aspect of an integrated acute-phase response. The response might have been triggered earlier by obesity, and later on augmented by the nutritional and psychological stress superimposed by the slimming diet. Hence, we conclude that dieters should be supplemented with minerals to replenish the body resources before embarking on low-energy diets. These diets should be of short duration, and must be interrupted by periods of normal alimentation if the need calls for their repetition.

Control of magnesium transport in the thick ascending limb.

The mammalian renal thick ascending limb of Henle (TAL) reabsorbs approximately 55% of the filtered magnesium; accordingly, it is the major segment involved in control of renal Mg balance. This review discusses recent evidence for passive and active transport of Mg through the paracellular and transcellular pathways of the TAL, respectively. The properties of these pathways provide a basis for understanding the factors influencing magnesium reabsorption and hormonal controls regulating Mg balance. Normally, Mg absorption is load dependent, whether delivery is altered by increasing luminal Mg concentration or increasing the flow rate into the thick ascending limb. In contrast to the luminal concentration, elevation of peritubular (plasma) Mg and Ca inhibit divalent cation absorption by mechanisms that are not entirely clear. Magnesium reabsorption in the TAL is also closely associated with NaCl absorption so that factors that influence NaCl also affect magnesium. Magnesium deficiency results in a specific and apparently intrinsic cellular adaptation to increase Mg absorption in the TAL. Our greatest understanding of hormonal controls for Mg absorption have come from recent studies using a "hormone deprived" animal model. Parathyroid hormone, calcitonin, glucagon, and antidiuretic hormone act through a common second messenger, adenosine 3',5'-cyclic monophosphate, to limit Mg excretion by enhancing active Mg transport in the TAL. The integrated actions of these hormones and possibly others provide a sensitive means of control. Clearly, recent observations, using in vivo and in vitro microperfusion studies, have altered our thinking of TAL function and indicate that Mg transport is sensitively and specifically controlled within this segment.

Nutritional absorption in short bowel syndrome

Eight patients with a short bowel resulting from intestinal resection and clinically stable for at least one year were studied for 10 days. The diet chosen was lactose-free with a low fiber content and contained 22% of total calories as protein, 32% as carbohydrate, and 46% as fat. Total fluid volume was kept constant, and all patients were in positive nitrogen balance. During the 10-day period, blood chemical concentrations, stool, and/or ostomy volume, urine volume, electrolyte excretion, and calorie and divalent cation absorption were measured. In addition it was determined that fluid restriction during meals did not affect these parameters. In these patients the absorptions of fat, carbohydrate, protein, and total calories were 54%, 61%, 81%, and 62%, respectively. Similarly the absorption of the divalent cations, calcium, magnesium, and zinc, were 32%, 34%, and 15%, respectively. We suggest that patients with short bowel syndrome, who have been stable for at least one year and who can tolerate oral diets, do not need to restrict fat or to separate fluids from solids during their meals. Furthermore, they should increase their oral intake to 35-40 kcal/kg ideal body weight in order to counteract their increased losses. The diet should contain 80-100 g protein/day in order to maintain a positive nitrogen balance and a large margin of safety. In addition, these patients may take oral supplementation of calcium, magnesium, and zinc to maintain divalent cation balance.

RETENTION OF CALCIUM SUPPLEMENTATION ESTIMATED BY MEANS OF FULL BALANCES IN THE LOW BIRTH WEIGHT INFANT

Net absorption of Ca,Mg and P was measured in three low birth-weight babies with no major problems, during periods of 3 days in the 3rd week of life. Their formula was supplemented with 800 mg of calcium-magnesium lactate. Five control babies were on the same formula,the mineral content (mean± SD) of which was:Ca 76.26±5.44 mg/dl,Mg 10.23± 2.06 mg/dl and P 53.40± 6.94. In this control group the absorption (intake-faeces) was: Ca 89.98 ± 18.73 mg/kg/day; Mg 14.19±2.08 mg/kg/day and P 88.59± ± 13.96 mg/kg/day. Serum calcium, magnesium,phosphate, lipids,cholesterol and triglycerides were normal on all ocassions. In supplemented group the absorption in each baby was: Ca 202.17; 232.29 and 216.63 mg/kg/day; Mg 20.59; 19.77 and 17.99 mg/kg/day and P 80.05; 100.40 and 83.19 mg/kg/day.Calcemia increases in two cases (11mg/dl) on the 4th day, but no hypo or hypermagnesemia appeared. As previous experiences has suggested the supplementation considerabily increases the absorption of divalent cations.

Inhibition of Ca2+ and Zn2+ Uptake by Mn2+ in Excised Rice Roots

The effects of varying concentrations of Mn2+ on the absorption of divalent cations, viz., Ca2+ and Zn2+ from 2 concentrations were studied. Mn2+ at all concentrations tested were inhibitory to Ca2+ uptake from 0.1 and 5 mᴍ CaCl2 . However, when Ca2+ uptake was measured at concentrations ranging from 0.05 to 10 mᴍ CaCl2, MnCl2 only at high concentration of 5 mᴍ, inhibited Ca ab­sorption. Zn2+ uptake from 0.1 mᴍ ZnCl2 was decreased by all concentrations of Mn2+.

Surface dipoles, surface charges and negative steady-state resistance in biological membranes

A theoretical expression for the steady-state current-voltage characteristic of biological membranes is given, justifying various assumptions which are usually made in the framework of the electrodiffusion theory, and taking into account the effect of surface charges and surface dipoles. It is shown that the orientation of the dipoles can be treated by a two-state model. But a comparison with the experimental curves of Gilbert and Ehrenstein leads to the conclusion that the observed negative resistances cannot be explained by a reorientation of the dipoles alone. An additional modification of the surface charges could be sufficient. Some features can be well explained by an absorption of divalent cations on the “outside” surface.

Influence of calcium and magnesium on manganese absorption.

Mutual effects between Mn, Ca, and Mg were studied during steady-state absorption experiments with excised barley roots. Calcium appeared to enhance the rate of Mn absorption; whereas, Mg had a highly depressive effect. The combination of both Ca and Mg was even more inhibitory to Mn absorption than Mg alone. Manganese had no effect on the usual negligible Ca absorption by this tissue, but effectively inhibited the absorption of Mg. Although divalent cation absorption from the Ca-Mg-Mn system was essentially nil, K absorption was greatly stimulated in the presence of these cations. These mutual effects and others reported in the literature are explained by the hypothesis that selectivity in ion absorption results from cation-induced conformational changes in the structure of the carrier molecule.

Divalent Cation Absorption and Interaction in Atriplex

The absorption of calcium and magnesium from solutions of chloride salts by Atriplex spp. and tomato was investigated. In Atriplex divalent cation uptake to leaves remained constant when external concentration was low (1-10 m-equiv/l) but thereafter uptake increased in proportion to� concentration. This response was in contrast to that of tomato where divalent cation uptake was saturated at relatively low concentrations (10-20 m-equiv/l).