High fructose consumption combined with low dietary magnesium intake may increase the incidence of the metabolic syndrome by inducing inflammation.

The metabolic syndrome is a cluster of common pathologies: abdominal obesity linked to an excess of visceral fat, insulin resistance, dyslipidemia and hypertension. This syndrome is occurring at epidemic rates, with dramatic consequences for human health worldwide, and appears to have emerged largely from changes in our diet and reduced physical activity. An important but not well-appreciated dietary change has been the substantial increase in fructose intake, which appears to be an important causative factor in the metabolic syndrome. There is also experimental and clinical evidence that the amount of magnesium in the western diet is insufficient to meet individual needs and that magnesium deficiency may contribute to insulin resistance. In recent years, several studies have been published that implicate subclinical chronic inflammation as an important pathogenic factor in the development of metabolic syndrome. Pro-inflammatory molecules produced by adipose tissue have been implicated in the development of insulin resistance. The present review will discuss experimental evidence showing that the metabolic syndrome, high fructose intake and low magnesium diet may all be linked to the inflammatory response. In many ways, fructose-fed rats display the changes observed in the metabolic syndrome and recent studies indicate that high-fructose feeding is associated with NADPH oxidase and renin-angiotensin activation. The production of reactive oxygen species results in the initiation and development of insulin resistance, hyperlipemia and high blood pressure in this model. In this rat model, a few days of experimental magnesium deficiency produces a clinical inflammatory syndrome characterized by leukocyte and macrophage activation, release of inflammatory cytokines, appearance of the acute phase proteins and excessive production of free radicals. Because magnesium acts as a natural calcium antagonist, the molecular basis for the inflammatory response is probably the result of a modulation of the intracellular calcium concentration. Potential mechanisms include the priming of phagocytic cells, the opening of calcium channels, activation of N-methyl-D-aspartate (NMDA) receptors, the activation of nuclear factor-kappaB (NFkB) and activation of the renin-angiotensin system. Since magnesium deficiency has a pro-inflammatory effect, the expected consequence would be an increased risk of developing insulin resistance when magnesium deficiency is combined with a high-fructose diet. Accordingly, magnesium deficiency combined with a high-fructose diet induces insulin resistance, hypertension, dyslipidemia, endothelial activation and prothrombic changes in combination with the upregulation of markers of inflammation and oxidative stress.

Magnesium deficiency modulates hepatic lipogenesis and apolipoprotein gene expression in the rat.

The present study was performed to determine the effects of magnesium (Mg) deficiency upon plasma lipoproteins and hepatic apolipoprotein gene expression in the rat. The most obvious effect of Mg-deficiency on plasma lipids is a marked increase in post-prandial triacylglycerol concentration. This increased triglyceridemia persists in fasted rats. Density gradient ultracentrifugation analysis revealed marked alterations in the distribution of plasma lipoproteins in Mg-deficient rats. An increase in triacylglycerol-rich lipoproteins (TGRLP) was associated with a significant increase in plasma apolipoprotein B (apo B) concentration and was accompanied by selective accumulation of apo B-48. A decrease in high-density lipoproteins (HDL) was accompanied by a corresponding decrease in plasma apo E concentration and a concordant decrease in hepatic apo E mRNA abundance and biosynthesis. Hepatic apo B-100 synthesis was reduced by over 75% in Mg-deficient animals despite an increase in hepatic apo B mRNA abundance. However, this change in hepatic apo B gene expression was not associated with alterations in posttranscriptional apo B mRNA editing. These changes in apolipoprotein gene expression were associated with increased hepatic lipogenesis, despite the observation that net triacylglycerol secretion rates were not different between Mg-deficient and control animals. Taken together, the data demonstrate a complex pattern of alterations in hepatic lipid metabolism and apolipoprotein gene expression in the Mg-deficient rat and suggest a defect in the catabolism rather than secretion of TGLRP as the major factor underlying the altered plasma lipoprotein profile.

Enhanced tumor necrosis factor-alpha production following endotoxin challenge in rats is an early event during magnesium deficiency.

Magnesium (Mg) plays an essential role in fundamental cellular reactions and the importance of the immuno-inflammatory processes in the pathology of Mg deficiency has been recently reconsidered. The purpose of the present study was to assess the effect of different stages of Mg deficiency on endotoxin response and tumor necrosis factor-alpha (TNF alpha) production. Weaning male Wistar rats were pair fed either a Mg-deficient or a control diet. At day 7, lipopolysaccharide (LPS) induced no lethal effects in control rats but resulted in 70% mortality in Mg-deficient rats within 3 h. The vulnerability of Mg-deficient rats to LPS was associated with higher TNF alpha plasma values. Mg-deficient animals that received magnesium supplementation before endotoxin challenge had significantly increased survival. At day 2, control and Mg-deficient rats were also subjected to endotoxin challenge with or without magnesium pre-treatment. A significant increase in TNF alpha plasma level was observed in Mg-deficient rats compared to rats fed the control diet. Mg-deficient rats that received magnesium replacement therapy before endotoxin challenge had significantly lower TNF alpha plasma values than those receiving saline before endotoxin. Thus, the results of this experiment suggest that the activated or primed state of immune cells is an early event occurring in Mg deficiency.

Inflammatory response following acute magnesium deficiency in the rat.

The importance of inflammatory processes in the pathology of Mg deficiency has been recently reconsidered but the sequence of events leading to the inflammatory response remains unclear. Thus, the purpose of the present study was to characterize more precisely the acute phase response following Mg deficiency in the rat. Weaning male Wistar rats were pair-fed either a Mg-deficient or a control diet for either 4 or 8 days. The characteristic allergy-like crisis of Mg-deficient rats was accompanied by a blood leukocyte response and changes in leukocytes subpopulations. A significant increase in interleukin-6 (IL-6) plasma level was observed in Mg-deficient rats compared to rats fed a control diet. The inflammatory process was accompanied by an increase in plasma levels of acute phase proteins. The concentrations of alpha2-macroglobulin and alpha1-acid glycoprotein in the plasma of Mg-deficient rats were higher than in control rats. This was accompanied in the liver by an increase in the level of mRNA coding for these proteins. Moreover, Mg-deficient rats showed a significant increase in plasma fibrinogen and a significant decrease in albumin concentrations. Macrophages found in greater number in the peritoneal cavity of Mg-deficient rats were activated endogenously and appeared to be primed for superoxide production following phorbol myristate acetate stimulation. A high plasma level of IL-6 could be detected as early as day 4 for the Mg-deficient diet. Substance P does not appear to be the initiator of inflammation since IL-6 increase was observed without plasma elevation of this neuropeptide. The fact that the inflammatory response was an early consequence of Mg deficiency suggests that reduced extracellular Mg might be responsible for the activated state of immune cells.

Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach.

Literature data on the bioavailability of various Mg forms provide scarce information on the best Mg salt to be used in animal and human supplementation. This study aimed to investigate the bioavailability of different forms of Mg in rats using Mg stable isotopes. Eighty male Wistar rats aged 6 weeks were fed a semi-purified Mg-depleted diet for three weeks. The rats were then randomised into ten groups and received, for two more weeks, the same diet repleted with Mg (550 mg Mg/kg) as: oxide, chloride, sulphate, carbonate, acetate, pidolate, citrate, gluconate, lactate or aspartate. After 10 days of Mg-repleted diet, the rats received orally 1.8 mg of an enriched 26Mg. Faeces and urine were then collected for 4 consecutive days. Isotope ratios in faeces and urine were determined. The Mg absorption values obtained varied from 50% to 67%. Organic Mg salts were slightly more available than inorganic Mg salts. Mg gluconate exhibited the highest Mg bioavailability of the ten Mg salts studied. Urinary 26Mg excretion varied from 0.20 mg to 0.33 mg, and feeding with the organic pidolate, citrate, gluconate and aspartate salts resulted in higher urinary 26Mg excretion than with inorganic salts. Ultimately, 26Mg retention was higher in the rats receiving the organic salts such as gluconate, lactate and aspartate than in those receiving the inorganic salts. Taken together, these results indicate that 26Mg is sufficiently bioavailable from the ten different Mg salts studied in the present experiment, although Mg gluconate exhibited the highest bioavailability under these experimental conditions.

Erythrocyte magnesium influx and efflux in solid tumor bearing mice.

Mg metabolism is modified in tumors and tumor-bearing organisms. In particular cancer patients often display elevated erythrocyte Mg levels. For a better understanding of the increased erythrocyte Mg content, we attempted to determine Mg fluxes in erythrocytes from tumor-bearing mice by Mg stable isotopes, using a method developed in our laboratory. To characterize the animal Mg status, blood and tissue Mg levels and hematological parameters were assayed. Results showed that in tumor-bearing mice total erythrocyte Mg was about 46% higher than in controls, whereas plasma and tissues Mg levels were not modified; red blood cells and hemoglobin as well as hematocrits were significantly decreased, while mean corpuscular volume and mean corpuscular hemoglobin were slightly but significantly increased in tumor-bearing mice compared to controls (by 3% and 4%, respectively), a picture corresponding to a normochromic, slightly macrocytic anemia. Erythrocyte Mg efflux was about 20% higher (404 + 59 versus 330 + 45 micromol/L, respectively, p < 0.05) in tumor-bearing mice compared to controls, whereas influx was not significantly modified (130 + 11 versus 122 + 19 micromol/L, respectively). Our data therefore exclude that the increased Mg content observed in erythrocytes of tumor-bearing mice is due to decrease of Mg efflux, or to an increase of Mg influx. On the other hand, the increased Mg content observed in erythrocytes of tumor-bearing mice could simply result from an increase of young Mg-enriched erythrocytes produced by the enhanced erythropoiesis which follows tumor-induced anemia.

Hepatic apolipoprotein B synthesis in copper-deficient rats.

The present study was designed to examine if induction of apolipoprotein B synthesis is associated with hypercholesterolemia in copper-deficient rats. This hypercholesterolemia mainly resides in an increase in the HDL-1 and LDL and is associated with a significant increase in plasma apoB concentration. Liver apoB mRNA levels were not significantly modified in deficient animals as compared to control rats. Studies on liver apolipoprotein synthesis indicated that apoB100 synthesis was increased in deficient animals whereas apoB48 synthesis was unchanged. Thus, it appears that the increase in apoB synthesis in the liver of copper-deficient rats occurs at the posttranscriptional level. The selective increase in apoB100 synthesis indicates the possible impact of this deficiency on the editing of apoB. An increase in apoB100 synthesis by the liver in copper-deficient rats may significantly contribute to the increase in plasma concentration of LDL.

Apolipoprotein B gene expression in rat intestine. The effect of dietary fiber.

The effect of the dietary fiber on apo B mRNA level was studied in the intestine of rats that were fed either fiber-free or high-fiber (30% sugar-beet fiber) low-fat diets for 3 weeks. The fiber diet studied does not affect jejunal apo B mRNA levels but decreases the level of ileal apo B mRNA. In the rat cecum, in both fiber-free and fiber groups, we failed to detect the apo B mRNA. The test fiber diet feeding markedly increased fecal bile salt and cholesterol excretions. We suggest that dietary fiber can modify apo B expression in the intestine. The increased fecal bile salt excretion might be involved in such a modification.

Functional alterations in sarcoplasmic reticulum membranes of magnesium-deficient rat skeletal muscle as consequences of free radical-mediated process.

Free radical-induced physiopathologies are generally thought to be mediated by membrane injuries. Using a pro-oxidant model induced by dietary magnesium deficiency, we have recently shown that skeletal muscle lesions occurred with a rise in the calcium level and enhanced free radical production. In this study, we investigated the physicochemical and biochemical properties of sarcoplasmic reticulum membranes isolated from hind limb muscles of weanling male rats pair fed magnesium-deficient or control diets for 12 d. The calcium-induced calcium efflux from preloaded vesicles was increased in membranes isolated from Mg-deficient rat muscle. In agreement with this latter observation, we demonstrated increased ryanodine binding affinity of the calcium channel. The Ca2(+)-ATPase activity of the pump was shown to be reduced. The viscosity state of the membranes, assessed by 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy, was significantly increased in Mg-deficient membranes. Moreover, these membranes demonstrated an increased content of protein carbonyls as compared with controls. These functional as well as structural changes are closed to those described in sarcoplasmic reticulum membranes oxidatively modified in vitro. Together, these data fitted well with the concept that free radical-induced membrane damages resulting in calcium overload may be at the origin of skeletal muscle lesion during Mg-deficiency.

Compartmental analysis of magnesium kinetics in Mg-sufficient and Mg-deficient rats.

In this study, we determined magnesium kinetic values in normal rats using stable-isotope techniques. Additionally, we calculated the mass of the exchangeable pools of Mg in Mg-deficient rats to determine whether it can be used as a marker of Mg status. Rats were fed either a control diet (1,000 mg Mg/kg) or a Mg-deficient diet (60 mg Mg/kg). After 2 weeks on the experimental diets, each rat received an intravenous injection of 26Mg. The plasma Mg disappearance curve over the next 7 days was used to measure the mass and fractional transport rate of 3 rapidly exchanging Mg metabolic pools. In control rats, the mass of pool 1 (1.37 mg) was half that of pool 2 (2.46 mg), and pool 3 (47.7 mg) accounted for greater than 90% of exchangeable Mg. In Mg-deficient rats, we observed a significant decrease in the size of the 3 exchangeable pools of Mg (0.36, 0.72, and 20.2 mg, respectively) relative to the control rats. Furthermore, the fractional transport rate of Mg from pool 1 to pool 3 in Mg-deficient rats was 3 times the rate in the control rats, and the rate of irreversible loss from pool 1 was lower in Mg-deficient rats. In summary, this study allows us to establish Mg kinetic data in Mg-sufficient and Mg-deficient rats. The present experiment supports the conclusion that the isotopic test identifies animals with severe Mg deficiency.

Stability of brain content of magnesium in experimental hypomagnesemia.

Magnesium is important in cerebral function. If there is a deficiency and neurological symptoms accrue, we hypothesised that Mg2+ deficiency causes neurological symptoms by decreasing the level of Mg2+ in cerebral tissue. The content of magnesium was determined in 12 brain structures in magnesium-deficient rats. Experiments were carried out for 40 days in two groups of Wistar male rats made magnesium-deficient (MD) by a well-controlled diet (50 mg of Mg2+/kg of food), and a control group (CG) rats fed normal diet (1 g of Mg2+/kg of food). At the end of the 40 days, the clinical signs of hypomagnesemia were sought in the MD rats and Mg2+ concentration levels were measured in the blood and brain. The results showed variable distribution of Mg2+ in the different brain structures, both in CG and MD rats; in the MD rats there is an important stability of global Mg2+ content of the brain. Although the global values for Mg2+ in the brain did not decline in MD rats, there was a significant decrease in Mg2+ in the brainstem. We conclude that the brain is able to maintain a stable concentration of Mg2+ during chronic hypomagnesemia, but its topographic variations could account for some of neurological signs accompanying this condition.

Oxidative modification of triglyceride-rich lipoproteins in hypertriglyceridemic rats following magnesium deficiency.

Hypertriglyceridemia observed in magnesium (Mg)-deficient rats was associated with a significant increase in the very low-density lipoprotein (VLDL) plus low-density lipoprotein (LDL) fractions. The results from in vitro copper-induced lipid peroxidation, expressed in terms of conjugated dienes and thiobarbituric acid reactive substances content, showed that VLDL + LDL particles from Mg-deficient rats were more susceptible to oxidative damage than lipoproteins from control rats. These results suggest that the mechanism responsible for the atherogenicity and tissue damage characteristic of Mg deficiency may be mediated by an increased susceptibility of triglyceride-rich lipoproteins to peroxidation in hypertriglyceridemic animals.

Apolipoprotein A-I, A-IV and E synthesis in the liver of copper-deficient rats.

Copper deficiency induces hypercholesterolemia in the rat. This hypercholesterolemia is mainly due to an increase in apo E-rich high density lipoproteins (HDL1). The present study was undertaken to determine whether the HDL increase could be explained by altered low-molecular weight apolipoprotein (apo) synthesis in the liver. The effect of copper deficiency on apo A-I, apo A-IV and apo E concentrations in plasma, as well as on respective mRNA levels and synthesis in the liver, were therefore investigated. We observed that the increased HDL1 levels in the plasma of copper-deficient rats were associated with a significant rise in plasma apo E concentrations; however, plasma apo A-I and apo A-IV concentrations remained unchanged. Liver apo synthesis and respective apo mRNA levels were not significantly altered in copper-deficient animals when compared to control rats. No changes in apo E mRNA levels in various tissues from copper-deficient, as compared to control rats, were noted. Based on the data obtained, it was concluded that the observed changes in plasma lipoprotein and apo concentrations are not related to changes in low-molecular weight apo synthesis in the liver. The mechanisms of the impaired catabolism of HDL1 should be further evaluated to possibly explain the observed increase in this fraction in copper-deficient rats.

Effect of magnesium deficiency on post-heparin lipase activity and tissue lipoprotein lipase in the rat.

Previous studies have provided evidence that Mg deficiency affects lipid metabolism. The present experiments were designed to assess whether the hypertriglyceridemia associated with Mg deficiency was related to alterations in post-heparin lipase activity (PHLA). Mg-deficient and control diets were pair-fed to weanling Wistar rats for eight days and plasma lipoproteins were separated into various density classes by sequential preparative ultracentrifugation. Triglycerides were significantly increased in chylomicrons and in the very low density lipoprotein, low density lipoprotein and high density lipoprotein (HDL) fractions. Cholesterol and phospholipid levels were significantly lower in the HDL fraction. PHLA in deficient rat was substantially lower than in control rats. The inverse correlation between plasma triglyceride concentration and PHLA strongly suggests that hypertriglyceridemia is the result of defective lipolysis of plasma triglycerides in Mg-deficient rats. Further examination of the PHLA was carried out by salt-mediated inhibition of lipoprotein lipase (LPL) and by heparin sepharose affinity chromatography and purified rat LPL antiserum. The results indicate that hepatic lipase is significantly decreased in Mg-deficient rats but the low PHLA is due mainly to a decline in LPL. However, total LPL activity, that is, both the intracellular and the extracellular pools of LPL in adipose tissue, heart and diaphragm, were unaffected by Mg deficiency. The results suggest that the decrease of LPL activity in the plasma of Mg-deficient rats may be due to a selective decrease in the heparin-releasable pool of enzyme.

Plasma lipoproteins and fatty liver in dairy cows.

Dairy cows were classified on the basis of a histological study after a hepatic biopsy conducted in the second week post partum (mild fatty liver, moderate fatty liver, severe fatty liver). Plasma lipoproteins were separated into various density classes by repeated ultracentrifugation. The results indicate that the beginning of lactation is associated with a low concentration of the 1.006 to 1.063 g ml-1 lipoprotein fraction. The lowest concentrations occurred in cows with severe steatosis or during the evolution of moderate steatosis.

The effect of dietary copper on rat plasma apolipoprotein B, E plasma levels, and apolipoprotein gene expression in liver and intestine.

The plasma levels of apo B and apo E, and the level of hepatic and intestinal mRNA coding for these apolipoproteins were investigated in weanling male rats pair-fed for 6 wk with a control or copper-deficient diet. Plasma cholesterol, triglycerides, and phospholipids were significantly increased, and plasma apo B and apo E levels were also markedly increased in copper-deficient rats as compared to control rats. Copper deficiency significantly increased triglyceride levels and decreased cholesterol levels in the liver. No major differences in the levels of hepatic and intestinal apo B and apo E mRNA occurred between control and copper-deficient rats. These data imply that hypertriglyceridemia dn hypercholesterolemia owing to the copper deficiency are not accompanied by modifications in the gene expression at the mRNA level in the liver and intestine of the apolipoproteins studied.

Protective effect of severe magnesium deficiency on Plasmodium chabaudi infection.

Mice were fed for 30 days on purified diets containing 50 (severely Mg deficient diet), 100 (moderately Mg deficient diet) and 1300 mg/kg (control diet). An additional group raised on stock UAR diet was also used for the experiment. The mice were maintained on the experimental diets for 12 days before being inoculated with P. chabaudi. Infection evolved similarly in mice fed the control purified diet, moderately Mg deficient diet and the stock diet whereas the severely Mg deficient diet induced a 50% decrease in malarial infection as shown by the decrease in the percentage of parasitized red blood cells (RBC). In control mice, RBC Mg values increased significantly during P. chabaudi infection; however RBC Mg values were significantly lower in Mg-deficient than in control animals.

Magnesium deprivation or short-term essential fatty acid deficiency in rats: effects on serum lipids, platelet fatty acid composition and arachidonic acid incorporation into platelet phospholipids.

The aim of this study was to evaluate the effect of short-term magnesium or essential fatty acid (EFA) deficiencies on plasma lipids, platelet fatty acid composition and [1-14C] arachidonic acid incorporation into platelet phospholipids. Weanling rats were fed purified diets (casein 20%, sucrose 70.5%, lipid 5%) for two weeks. The control and magnesium-deficient diets included corn oil as lipid source. The EFA-deficient diet included hydrogenated coconut oil. The fatty acid composition of serum lipids confirmed the linoleic acid deprivation in the EFA-deficient group. Significant changes in platelet fatty acid composition occurred in this limited period of time and arachidonic acid incorporation into platelet lipids was markedly increased. Magnesium deficiency induced hyperlipaemia. A significant decrease in the percentage of arachidonic acid in total serum lipids was observed, but fatty acid profile appeared quite different in the two deficiencies. In magnesium-deficient rats, the alteration in fatty acid composition of serum lipids was not associated with similar changes in fatty acid composition of platelet lipids. Arachidonic acid incorporation into platelet lipids was markedly increased in magnesium deficient animals as compared to control group. Relatively more arachidonic acid was incorporated into phosphatidylcholine and phosphatidylinositol when magnesium-deficient or EFA-deficient animals were compared to the control group.

Magnesium and ageing. I. Experimental data: importance of oxidative damage.

Magnesium status may be compromised with ageing for two reasons: insufficient intake (magnesium deficiency) or alterations in magnesium metabolism (magnesium depletion). There is a large volume of literature suggesting that magnesium deficit contributes to the ageing process and to the vulnerability to age-related diseases. One of the biological changes associated with ageing is an increase in free radical formation with subsequent damage to cellular processes. Prime targets of the more reactive free radicals are unsaturated lipids in cell membranes, amino acids in proteins, and nucleotides in DNA. The accumulation of unrepaired oxidative damage products may be a major factor in cellular ageing. Magnesium-deficient animals show an increased susceptibility to an in vivo oxidative stress and their tissues are more susceptible to in vitro peroxidation. Moreover, the protective properties of various antioxidant drugs and nutrients suggest that free radicals are involved in the injury process of magnesium deficiency. The consequences on stress susceptibility, defective membrane functions and perturbation of intracellular calcium metabolism, inflammation, cardiovascular diseases including atherosclerosis and ischaemia/reoxygenation injury, diabetes, fibrosis, immune dysfunction and other diseases associated with ageing are presented and discussed.

Stress protein expression cDNA array study supports activation of neutrophils during acute magnesium deficiency in rats.

Recent studies underline the importance of the immunoinflammatory processes in the pathology of acute magnesium (Mg)-deficiency. The aim of this study was to assess the effect of acute experimental Mg-deficiency in the rat on neutrophil activity. Weaning male Wistar rats were fed either a Mg-deficient or a control diet for 8 days. In this experiment, we measured neutrophil respiratory burst by chemiluminescence; then, to examine the molecular events associated with acute Mg-deficiency, we applied cDNA array technology to define the transcription response in neutrophils of Mg-deficient rats in comparison with controls. In Mg-deficient rats, the characteristic inflammatory response was accompanied by a marked increase in the number of neutrophils. Moreover, as shown by chemiluminescence studies, basal neutrophil activity from Mg-deficient rats was significantly elevated when compared to neutrophils from control rats. Moreover, the chemiluminescence of neutrophils from Mg-deficient rats was significantly higher than that of control rats following phorbol myristate acetate or opsonized zymosan activation. Using cDNA array which includes 207 known rat genes of stress proteins, 102 genes were found to be expressed in neutrophils. Among expressed genes, 78 per cent of genes were found to be expressed more than twofold in neutrophils from Mg-deficient rats compared to control rats. Acute Mg-deficiency was characterized by an induction of genes encoding for proteins involved in apoptosis, heat shock proteins, protein belonging to the cytoskeleton, proteins implicated as stress response regulators and effectors and enzyme implicated in thromboxane synthesis. Then, this experimental strategy allowed to identify a series of genes implicated in the immunoinflammatory process of Mg-deficiency.