Fractional intestinal absorption of magnesium is directly proportional to dietary magnesium intake in rats

Modeling calcium and magnesium balance: Regulation by calciotropic hormones and adaptations under varying dietary intake

Magnesium (Mg2+) is crucial for several cellular and physiological processes and is tightly regulated due to health risks associated with imbalances. Mg2+, calcium (Ca2+), parathyroid hormone, and vitamin D3 are tightly coupled, ensuring proper bone metabolism and intestinal and renal absorption of Mg2+ and Ca2+. While several Ca2+ homeostasis models exist, no computational model has been developed to study Mg2+ homeostasis. We developed a computational model of Mg2+ homeostasis in male rats, integrating it with an existing Ca2+ homeostasis model, to understand the interconnected physiological processes regulating their homeostasis. We then analyzed adaptations in these interconnected processes under (1) dietary Mg2+ deficiency, (2) low/high dietary Ca2+ with Mg2+ deficiency, and (3) vitamin D3 deficiency. Model simulations predicted severe hypomagnesemia and mild hypocalcemia with significant dietary Mg2+ deficiency. Low dietary Ca2+ improved, while high dietary Ca2+ worsened Mg2+ deficiency. Finally, vitamin D3 deficiency caused severe hypocalcemia, with minimal impact on Mg2+ homeostasis.

Identification of TRPM6 and TRPM7 expression changes in response to a diet supplemented with inulin in porcine kidney

Abstract. Magnesium is the fourth most abundant mineral element in vertebrates and the second most common intracellular cation. Recently identified Mg2+-specific channels – TRPM6 and TRPM7 – have been shown to be essential for whole-body and cellular Mg2+ homeostasis. The aim of the study was to determine the effect of inulin on the expression of TRPM6 and TRPM7 in the renal cortex and medulla of growing pigs. The study was carried out on 16 Danbred  ×  Duroc castrated male piglets fed a cereal-based diet without inulin or with 2 % addition of inulin from chicory root from the 10th day of life. In pigs fed a diet with inulin, TRPM6 expression was greater in both the renal cortex and medulla compared to the control group. The expression of TRPM7 in both the renal cortex and medulla in the control group and in piglets fed a diet enriched with inulin was relatively stable. To our knowledge, this is the first study aimed at the identification of TRPM6 and TRPM7 in the kidneys of pig. It is proposed that inulin addition to fodder resulted not only in a magnesium absorption increase, but also, due to prolonged low plasma Mg concentration of examined piglets, renal magnesium retention. Therefore, higher magnesium reabsorption via increased TRPM6 expression in the kidney was probably observed in order to supplement deficiencies of this element. Diet-unresponsive expression of TRPM7 supports the concept that this channel is not involved in the extracellular magnesium homeostasis.

Health-promoting effects of a dietary fiber concentrate from the soybean byproduct okara in rats

Okara (a byproduct of the soy milk industry) is rich in proteins (24.5-37.5 g/100 g of dry matter (dm)), lipids (9.3-22.3 g/100 g of dm), and dietary fiber (DF) (14.5-55.4 g/100 g of dm). It also contains isoflavones (0.14 g/100 g of dm). In the present study we fed female healthy Wistar rats either a standard rat diet or a supplemented 10% DF-rich okara (DFRO) diet for 4 weeks, and then we assessed several health parameters in the serum and the cecum compartments. In comparison to the control group, rats fed DFRO showed a significant decrease in weight gain (5.00 +/- 1.22 g vs 2.00 +/- 1.46 g, P < 0.03, during week 4) and in total cholesterol (65 +/- 8 mg/dL vs 51 +/- 5 mg/dL, P < 0.05) and a significantly increased antioxidant status (36.71 +/- 15.31 micromol of Trolox equivalents (TEs)/g vs 69.75 +/- 16.11 micromol of TEs/g, P < 0.0003) and butyrogenic effect (39.37%, P < 0.003) in the cecum. In addition, a significant enhancement in the apparent absorption (41.89 +/- 1.64% vs 47.02 +/- 2.51%, P < 0.004) and in the true retention (41.62 +/- 1.60% vs 46.68 +/- 2.55%, P < 0.005) of calcium was appreciated. In summary, these findings show for the first time that a concentrate DF from a soybean byproduct protects the gut environment in terms of antioxidant status and prebiotic effect. These results may highlight the development of an innovative soybean byproduct rich in DF which could be useful as a functional ingredient with health-promoting attributes.

Excess calcium increases bone zinc concentration without affecting zinc absorption in rats

We examined zinc (Zn) metabolism in rats given diets containing excess calcium (Ca). Rats were given phytate-free diet containing 5 g Ca/kg (control), 12.5 g Ca/kg, or 25 g Ca/kg for 4 wk in Experiment 1. The dietary treatment did not affect Zn concentration in the plasma, testis, kidney, spleen and liver; however, Zn concentration in the femur and its cortex was significantly higher in rats given diet containing 25 g Ca/kg than in other rats. Rats were given phytate-free diet containing 5 g Ca /kg or 25 g Ca /kg for 4 wk in Experiment 2. After 12-h food deprivation, rats were given a diet extrinsically labeled by 67Zn with dysprosium as a fecal marker for 4 h. Feces were collected from 1 d before administration of the labeled diet to 5 d after administration. Excess Ca did not affect the true absorption of Zn and its endogenous excretion but increased femoral Zn. These results suggest that excess Ca improves Zn bioavailability without affecting Zn absorption when diets do not contain phytate.

Dietary fibers from mushroom sclerotia. 4. In vivo mineral absorption using ovariectomized rat model

The effect of three novel dietary fibers (DFs) prepared from mushroom sclerotia, namely, Pleurotus tuber-regium, Polyporus rhinocerus, and Wolfiporia cocos, on calcium and magnesium absorption was evaluated in ovariectomized (OVX) rats fed with sclerotial DF based and low Ca (0.3%) diets for 14 days. The animals in the W. cocos DF diet group possessed significantly (p < 0.05) higher levels of cecal total short-chain fatty acids (204 mumol/g of cecal content) and had an acidic pH (5.88) in their cecum when compared with those of the cellulose control group. Such an acidic environment was found to promote the ionization of the unabsorbed Ca and Mg in their cecum, which in turn significantly (p < 0.05) increased the concentrations of cecal soluble Ca (2.56-fold) and Mg (1.22-fold). Besides, the apparent Ca and Mg absorptions of the W. cocos DF group were also significantly (p < 0.05) enhanced (Ca, 16.5%; Mg, 15.3%) together with significantly (p < 0.05) higher serum Ca (3.61 mmol/L) and Mg (1.07 mmol/L) levels when compared with those of the cellulose control group. These data suggest that ingestion of W. cocos DF could improve the overall Ca and Mg absorptions of the OVX rats fed a low Ca diet. The potential use of sclerotial DFs as a functional food ingredient for enhancing mineral absorption is also discussed.

The effect of aging on intestinal absorption and status of calcium, magnesium, zinc, and copper in rats: a stable isotope study

Many investigators have reported changes in mineral status with age but conflicting observations were done concerning mineral absorption. This study was conducted to clarify the effect of aging on intestinal absorption and status of minerals, using a stable isotope approach. To do so, 40 rats of different ages: 9, 22, 44, and 88 weeks were fed with a semi-purified diet for a total of 30 days. At the beginning of the 4th week, the rats received a stable isotope solution containing (44)Ca, (25)Mg, (67)Zn, and (65)Cu. Individual feces and urine were then collected during 4 consecutive days in order to measure stable isotopes by inductively coupled plasma/mass spectrometry (ICP/MS) and blood and tissues were sampled for mineral status determination. Intestinal absorption of (44)Ca and (67)Zn considerably decreased with age, whereas intestinal (25)Mg absorption decreased only moderately and intestinal (65)Cu absorption was unaffected. Plasma and bone calcium (Ca) were not modified with age whereas urinary Ca excretion considerably increased. Plasma and erythrocyte magnesium (Mg) levels were unaffected with age whereas urinary Mg excretion and Mg bone level decreased. Plasma zinc (Zn) level decreased and bone Zn level increased with age whereas red blood cell and liver Zn level and urinary Zn excretion remained unchanged. Plasma Cu level increased with age whereas liver and bone Cu levels and urinary Cu excretion remained unchanged. These results show that the effect of aging on the intestinal mineral absorption and status differ largely according to the mineral considered. Further studies are required under different nutritional conditions to explore the underlying mechanisms during aging and to adjust a better nutrition of the elderly.

Effect of potassium salts in rats adapted to an acidogenic high-sulfur amino acid diet

Low-grade metabolic acidosis, consecutive to excessive catabolism of sulfur amino acids and a high dietary Na:K ratio, is a common feature of Western food habits. This metabolic alteration may exert various adverse physiological effects, especially on bone, muscle and kidneys. To assess the actual effects of various K salts, a model of the Westernised diet has been developed in rats: slight protein excess (20 % casein); cations provided as non-alkalinising salts; high Na:K ratio. This diet resulted in acidic urine (pH 5.5) together with a high rate of divalent cation excretion in urine, especially Mg. Compared with controls, K supplementation as KCl accentuated Ca excretion, whereas potassium bicarbonate or malate reduced Mg and Ca excretion and alkalinised urine pH (up to 8). In parallel, citraturia was strongly increased, together with 2-ketoglutarate excretion, by potassium bicarbonate or malate in the diet. Basal sulfate excretion, in the range of 1 mmol/d, was slightly enhanced in rats fed the potassium malate diet. The present model of low-grade metabolic acidosis indicates that potassium malate may be as effective as KHCO3 to counteract urine acidification, to limit divalent cation excretion and to ensure high citrate concentration in urine.

Moderate decrease of pH by sourdough fermentation is sufficient to reduce phytate content of whole wheat flour through endogenous phytase activity

Whole wheat bread is an important source of minerals but also contains considerable amounts of phytic acid, which is known to impair their absorption. An in vitro trial was performed to assess the effect of a moderate drop of the dough pH (around 5.5) by way of sourdough fermentation or by exogenous organic acid addition on phytate hydrolysis. It was shown that a slight acidification of the dough (pH 5.5) with either sourdough or lactic acid addition allowed a significant phytate breakdown (70% of the initial flour content compared to 40% without any leavening agent or acidification). This result highlights the predominance of wheat phytase activity over sourdough microflora phytase activity during moderate sourdough fermentation and shows that a slight drop of the pH (pH value around 5.5) is sufficient to reduce significantly the phytate content of a wholemeal flour. Mg "bioaccessibility"of whole wheat dough was improved by direct solubilization of the cation and by phytate hydrolysis.

Stable isotopes in studies of intestinal absorption, exchangeable pools and mineral status: the example of magnesium

Magnesium (Mg) is a biologically essential mineral and Mg deficiency is known to lead to severe biochemical and symptomatic disorders. Radioactive isotopes and, more recently, stable isotopes have been used as research tools to determine intestinal Mg absorption in humans and animals under different nutritional and physiological conditions. Mg isotopes are given orally or orally plus intravenously and analysed in faeces and/or in plasma and urine in order to calculate intestinal Mg absorption and possibly endogenous Mg excretion. Mg isotopes have been used to assess exchangeable pools of Mg under nutritional and physiopathological conditions. Mg isotopes are given intravenously and are analysed in plasma and urine to calculate the size and half-life of the various Mg exchangeable pools. More recently, in vitro isotopic tests have been developed to study the need of cells for Mg in different nutritional and genetic conditions. Whole blood is incubated with Mg isotopes and isotopic blood cell enrichment is measured, which reflects the avidity of cells for Mg and thus its initial status. This paper is a report on the use of stable Mg isotopes and their advantages in these different fields of Mg absorption and metabolism. The studies available have clearly demonstrated that stable isotopes provide a useful research tool for determining intestinal Mg absorption, and represent a precious research tool for the study of Mg metabolism and the assessment of Mg status.

Magnesium and potassium homeostasis during cisplatin treatment

PURPOSE

Administration of cisplatin causes changes in magnesium and potassium metabolism. The purpose of this study was to investigate day-to-day changes in renal and intestinal homeostasis of magnesium (Mg) and potassium (K) during repeated cisplatin treatments in rats to provide guidelines for human supplementation studies.

EXPERIMENTAL DESIGN

Rats were housed in metabolic cages with access to a diet containing excess Mg and K. Treatment was administered once a week for 3 weeks and comprised either cisplatin 2.5 mg/kg body weight i.p or, as sham treatment, isotonic NaCl 2.5 ml/kg body weight i.p. Urine and feces were collected every 24 h. Blood samples for measurement of plasma Mg and K were obtained from a permanent arterial catheter prior to each treatment cycle and at the termination of the study.

RESULTS

Cisplatin exerted a significant negative effect on total Mg balance. This effect was cumulative with repeated doses of cisplatin. The observed difference was mainly due to the difference in Mg balance between the treatment day and the following 2-3 days. The cumulated urinary excretion of Mg did not differ significantly between the two groups at the end of follow-up. A significant decrease was observed in cumulated intestinal absorption in treated rats compared to control rats at the end of follow-up. Lowered intestinal absorption accounted for 90% of the difference in total Mg balance between the two groups as compared to the renal loss. Cisplatin treatment also exerted a negative effect on total K balance, although the difference between cisplatin-treated and control rats was not significant at the end of follow-up.

CONCLUSIONS

The Mg loss associated with cisplatin treatment was mainly the result of lowered intestinal absorption and not, as presently thought, the result of increased renal elimination. Instead, an increased renal reabsorption capacity was observed in response to decreased intestinal absorption. The study further showed that Mg and K metabolism are subject to predictable changes in intestinal absorption and renal excretion with each cisplatin treatment, and that knowledge of these changes can be used in planning supplementation. Thus, the experimental observations support intravenous supplementation on the day of treatment and 2-3 days after treatment followed by oral supplementation until the next treatment.

Effects of dietary fibers on magnesium absorption in animals and humans

There is overwhelming evidence that dietary fibers are an important component of human and animal diets and play an important role in human health. Because dietary fibers and some associated substances, such as phytate, have in vitro mineral-binding capacities, they have been thought to impair absorption of minerals such as calcium, iron and zinc, although magnesium absorption seems to be less affected. Indeed, the effect of dietary fibers depends largely on their own nature and characteristics, and also on mineral homeostasis. In 1977 it was observed that resistant starch, a fermentable dietary fiber, could improve Mg absorption in rats. More recently, attention has been focused on other fermentable substrates such as inulin and oligo- or polysaccharides, for their potential prebiotic and health effects. Studies conducted on different types of fermentable carbohydrates have confirmed their beneficial effect on Mg absorption in different animal species. The majority of these studies have also sought to determine the effects of fibers on other minerals such as calcium, iron and zinc. In contrast to the studies with Mg, these studies did not show a consistent effect on the absorption of these minerals. This is due to the particularities of sites and mechanism of Mg absorption. To date, four human studies have been carried out that generally confirmed the enhancing effect of fermentable oligo- or polysaccharides on Mg absorption.