Magnesium deficiency regulates vitamin D metabolizing enzymes and type II sodium-phosphate cotransporter mRNA expression in rats.

A magnesium (Mg) deficiency induces changes in calcium (Ca) and phosphorus (P) metabolism; however, the mechanisms responsible for these effects remain unclear. Since 1,25-dihydroxyvitamin D3 and type II sodium-phosphate (Na/Pi) cotransporters are essential regulators of Ca and P metabolism, this study examined the effects of Mg deficiency on the mRNA expression of vitamin D metabolizing enzymes (25-hydroxyvitamin D-1α-hydroxylase (1α(OH)ase) and 25-hydroxyvitamin D-24-hydroxylase (24(OH)ase)), and Na/Pi cotransporters (type IIa and IIc) in the rat kidney. Rats were divided into two groups and fed a control diet (Mg concentration: 0.05%) or a Mg-deficient diet (Mg concentration: Mg-free) for 21 days. 1α(OH)ase mRNA levels were significantly decreased in rats fed the Mg-deficient diet, while 24(OH)ase mRNA levels were significantly increased, compared to rats fed the control diet. Type IIa and IIc Na/Pi cotransporter mRNA levels in rats fed the Mg-deficient diet were significantly decreased compared to rats fed the control diet. These results suggest that Mg deficiency induces downregulation of 1α(OH)ase and type IIa and IIc Na/Pi cotransporters, and upregulation of 24(OH)ase in the kidney.

Magnesium deficiency increases serum fibroblast growth factor-23 levels in rats.

A magnesium (Mg)-deficient diet results in decreased serum phosphorus (P) levels and increased urinary P excretion; however, the mechanisms responsible for these effects are unclear. Fibroblast growth factor-23 (FGF-23) is a potent regulator of P homeostasis. To determine the mechanisms responsible for the change in serum levels and urinary excretion of P with Mg deficiency, the present study examined the effects of Mg deficiency on serum FGF-23 levels. Male rats were randomized by weight into two groups and fed a control diet (Mg concentration: 0.05%) or a Mg-deficient diet (Mg concentration: Mg-free) for 21 days. Serum P levels in rats fed the Mg-deficient diet were significantly lower than in rats fed the control diet. Furthermore, urinary P excretion was significantly higher in rats fed the Mg-deficient diet compared to rats fed the control diet. Conversely, the tubular reabsorption rate of P was significantly lower in rats fed the Mg-deficient diet than in the controls. Serum FGF-23 levels in rats fed the Mg-deficient diet were significantly higher than those in animals fed the control diet. The results from the present study indicate that 1) Mg deficiency increases serum FGF-23 levels; and 2) Mg deficiency causes increased urinary P excretion via inhibition of renal P reabsorption, resulting in a lowering of serum P levels. Moreover, we suggest that the high serum FGF-23 levels induced by Mg deficiency contribute to the decrease in renal P reabsorption.

Effects of a high-calcium diet on serum insulin-like growth factor-1 levels in magnesium-deficient rats.

In order to clarify the effects of a high-calcium (Ca) diet on bone formation in magnesium (Mg)-deficient rats, this study focused on the effects of a high-Ca diet on serum insulin-like growth factor-1 (IGF-1) levels. Male rats were randomized by weight into four groups, and fed one of four experimental diets containing two different Mg concentrations (0.05% (normal-Mg) or Mg-free (Mg-deficient)), and two different Ca concentrations (0.5% (normal-Ca) or 1.0% (high-Ca)) for 14 days. Serum concentrations of osteocalcin and IGF-1 were significantly lower in rats fed the Mg-deficient diet than in rats fed the normal-Mg diet. On the other hand, dietary Ca concentration had no significant influence on serum concentrations of osteocalcin and IGF-1. This study suggested that: 1) a high-Ca diet has no preventive effects on the decreased bone formation seen in Mg-deficient rats; and 2) a high-Ca diet does not enhance serum IGF-1 levels in Mg-deficient rats. Moreover, unchanged serum IGF-1 concentrations may contribute to the decreased bone formation seen in Mg-deficient rats receiving a high-Ca diet.

Dietary magnesium supplementation suppresses bone resorption via inhibition of parathyroid hormone secretion in rats fed a high-phosphorus diet.

This study examined the effects of dietary magnesium (Mg) supplementation on bone turnover and serum parathyroid hormone (PTH) levels in rats fed a high-phosphorus (P) diet. Male rats were randomized by weight into three groups, and fed a control diet (control), a high-P diet (HP) or a high-P and high-Mg diet (HPHMg) for 14 days. Serum osteocalcin levels were significantly higher in the HP and HPHMg groups than in the control group. Serum CTx levels were significantly higher in the HP and HPHMg groups than in the control group, while the levels in the HPHMg group were significantly lower than in the HP group. Serum PTH levels were significantly higher in the HP group than in the control and HPHMg groups. Dietary Mg supplementation had a significant influence on serum PTH levels in the HP and HPHMg groups. These results suggest that dietary Mg supplementation suppresses the high bone resorption induced by a high-P diet via inhibition of PTH secretion. Moreover, our results suggest that dietary Mg supplementation may be beneficial for the prevention of bone loss with high-P diet administration.

High-phosphorus diet induces osteopontin expression of renal tubules in rats.

High-phosphorus (P) diet induces nephrocalcinosis in rats; however, the mechanism for onset of this disorder is unclear. The calcium (Ca) deposits in kidney are a form of hydroxyapatite, while osteopontin is combined with hydroxyapatite. Based on these observations, we speculated that the osteopontin play an important role in the formation of the Ca deposits induced by high-P diet. This study was investigated the effect of high-P diet on osteopontin expression in kidney. Female Wistar rats were fed diets containing P concentrations of either 0.3% (control diet) or 1.5% (high-P diet) for 14 days. On von Kossa staining, Ca deposits were seen in the tubules of the cortex, outer medulla and inner medulla in rats fed on the high-P diet. Expression of osteopontin was confirmed in rats fed on the high-P diet by immunohistochemical staining, and the localization of this protein was in the same region as the Ca deposits. On the other hand, no evidence of Ca deposits and osteopontin expression was observed in the tubules of the cortex, outer medulla or inner medulla of rats fed on the control diet. These results suggest that high-P diet induces osteopontin expression in the renal tubules. Moreover, our results suggest that increase in osteopontin expression in the renal tubules is presumably involved in the formation of Ca deposits induced by high-P diet.

Dietary calcium supplementation suppresses bone formation in magnesium-deficient rats.

The purpose of this study was to clarify the effects of dietary calcium (Ca) supplementation on bone metabolism of magnesium (Mg)-deficient rats. Male Wistar rats were randomized by weight into three groups, and fed a control diet (control group), a Mg-deficient diet (Mg- group) or a Mg-deficient diet having twice the control Ca concentrations (Mg-2Ca group) for 14 days. Trabecular bone volume was significantly lower in the Mg- and Mg-2Ca groups than in the control group. Trabecular number was also significantly lower in the Mg- and Mg-2Ca groups than in the control group. Mineralizing bone surface, mineral apposition rate (MAR), and surface referent bone formation rate (BFR/BS) were significantly lower in the Mg- and Mg-2Ca groups than in the control group. Furthermore, MAR and BFR/BS were significantly lower in the Mg-2Ca group than in the Mg- group. These results suggest that dietary Ca supplementation suppresses bone formation in Mg-deficient rats.

Quantitative determination of urinary 8-hydroxy-2'-deoxyguanosine level in healthy Japanese volunteers.

8-hydroxy-2'-deoxyguanosine (8-OHdG), as a measure of oxidative stress, was measured in healthy Japanese volunteers using an ELISA (New 8-OHdG Check, JICA). Analysis of daytime spot urine of 83 healthy male subjects and smoking habit, exercise and age revealed significant correlation only between the urinary level of 8-OHdG and age. As the inter-individual variation of 8-OHdG of the daytime spot urine was relatively high, we next determined inter-and intra-individual variation of 5 healthy volunteers. The levels of 8-OHdG/creatinine in morning spot urine significantly correlated with 8-OHdG levels in 24-h pool urine. Thus, a morning spot urine sample can be used for the measurement of 8-OHdG instead of inconvenient 24-h sampling.

Oral administration of swine gastric mucin alters levels of serum and urine nitric oxide, and lipid metabolism in mice.

Mice were fed with swine gastric mucin in a basal diet for 5 weeks. In 5 week-old mice, a 2% mucin diet significantly decreased nitric oxide levels of serum and liver. Reduction of serum total cholesterol and triglyceride and increase of HDL-cholesterol level were also significant with the mucin diet. In 14 month-old mice, the mucin diet was less effective.

Inhibition of Clostridium botulinum Okra B by N-Acyl Amino Acid Ester (Nα-Cocoil Arginine Ethylester•DL-Pyrrolidone Carbonate).

An amino acid ester, Nα-cocoil-L-arginine ethylester·DL-pyrrolidone carbonate (CAE), was inhibitory to growth and toxin production of Clostridium botulinum okra in peptone-yeast extract-glucose (PYG) medium, pH 7.0, at 30°C. Addition of 10 mg of CAE/L to PYG medium delayed toxin production and 25 mg of CAE/L inhibited growth and toxin production, whereas 5 mg of CAE/L had no effect on both growth and toxin production.