Effect of Mg2+ on Na(+)-dependent inositol transport. Role for Mg2+ in etiology of diabetic complications

Oral Magnesium Supplementation Improved Lipid Profile but Increased Insulin Resistance in Patients with Diabetic Nephropathy: a Double-Blind Randomized Controlled Clinical Trial

Low serum magnesium concentrations were associated with development of renal failure. We aimed to determine whether magnesium supplementation improves renal function, insulin resistance, and metabolic profiles in patients with diabetic nephropathy. A total of 80 hypomagnesemic patients diagnosed with type 2 diabetes and early-stage nephropathy were recruited. Subjects received either daily magnesium oxide or placebo for 12 weeks. Biochemical and anthropometric variables were measured. Physical activity and dietary intakes were also recorded. This study was approved by the ethics committee of Isfahan University of Medical Sciences and was registered on the Iranian Registry of Clinical Trials website (IRCT registration no. IRCT201404271485N12). Serum magnesium levels were not changed significantly. Although the supplementation did not influence glycemic indices, patients in the magnesium group had greater insulin resistance compared with the placebo group after intervention (0.3 ± 2.3 μIU/mL vs. - 0.04 ± 2.05, P = 0.04). No significant changes were observed in serum total cholesterol, triglycerides, HDL, LDL, and total cholesterol/HDL cholesterol ratio. Furthermore, magnesium did not affect inflammation, serum levels of creatinine, and blood urine nitrogen. However, a marginal decrease in microalbuminuria (- 3.1 ± 2.2 mg/L vs. - 14 ± 9.9, P = 0.09) was observed. Oral magnesium supplementation slightly improved microalbuminuria but resulted in increased insulin resistance in patients with diabetic nephropathy.

Hypomagnesemia in persons with type 1 diabetes: associations with clinical parameters and oxidative stress

BACKGROUND

Among persons with type 1 diabetes mellitus (T1DM) low concentrations of magnesium have been reported. Previous (small) studies also suggested a relation of hypomagnesemia with (poor) glycaemic control and complications. We aimed to investigate the magnitude of hypomagnesemia and the associations between magnesium with parameters of routine T1DM care in a population of unselected outpatients.

METHODS

As part of a prospective cohort study, initially designed to measure quality of life and oxidative stress, data from 207 patients with a mean age of 45 [standard deviation (SD) 12] years, 58% male, diabetes duration 22 [interquartile range (IQR) 16, 31] years and glycated haemoglobin (HbA1c) of 60 (SD 11) mmol/mol [7.6 (SD 1.0)%] were examined. Hypomagnesemia was defined as a concentration below <0.7 mmol/l.

RESULTS

Mean magnesium concentration was 0.78 (SD 0.05) mmol/l. A deficiency was present in 4.3% of participants. Among these persons, mean concentration was 0.66 (SD 0.03) mmol/l. There was no correlation between magnesium and HbA1c at baseline (r = -0.014, p = 0.843). In multivariable analysis, free thiols (reflecting the degree of oxidative stress) were significantly and negatively associated with magnesium concentrations.

CONCLUSION

In this cohort of T1DM outpatients, the presence of hypomagnesemia was infrequent and, if present, relative mild. Magnesium was not associated with glycaemic control nor with presence of micro- and macrovascular complications. Although these results need confirmation, in particular the negative association of magnesium with free thiols, this suggests that hypomagnesemia is not a relevant topic in routine care for people with T1DM.

Low serum magnesium levels are associated with impaired peripheral nerve function in type 2 diabetic patients

The aim of this study was to explore the relationship between serum magnesium and peripheral nerve function in patients with type 2 diabetes (T2DM). A total of 978 T2DM patients were included in the study. Patients were divided into tertiles according to serum magnesium concentration (low tertile: ≤0.85 mmol/L; medium tertile: 0.85 to 0.92 mmol/L; and high tertile: >0.92 mmol/L). All participants underwent nerve conduction (NC) studies. Composite z scores of conduction velocity, latency, and amplitude were constructed, respectively. The serum magnesium levels were significantly lower in patients with abnormal NC than in those with normal NC (0.87 [0.82, 0.92] vs. 0.88 [0.83, 0.93] mmol/L, P = 0.048). The composite z score of amplitude significantly increased with increasing tertiles of magnesium (−0.60 ± 0.02 vs. −0.57 ± 0.02 vs. −0.48 ± 0.03, P for trend = 0.001). After adjusting for all potential confounders, lower serum magnesium levels were still associated with lower composite z score of amplitude (β = 0.095, P = 0.014). In patients with T2DM, lower serum magnesium levels were significantly associated with lower composite z score of amplitude, indicating magnesium might affect peripheral nerve function through axonal degeneration.

Magnesium in Prevention and Therapy

Magnesium is the fourth most abundant mineral in the body. It has been recognized as a cofactor for more than 300 enzymatic reactions, where it is crucial for adenosine triphosphate (ATP) metabolism. Magnesium is required for DNA and RNA synthesis, reproduction, and protein synthesis. Moreover, magnesium is essential for the regulation of muscular contraction, blood pressure, insulin metabolism, cardiac excitability, vasomotor tone, nerve transmission and neuromuscular conduction. Imbalances in magnesium status—primarily hypomagnesemia as it is seen more common than hypermagnesemia—might result in unwanted neuromuscular, cardiac or nervous disorders. Based on magnesium’s many functions within the human body, it plays an important role in prevention and treatment of many diseases. Low levels of magnesium have been associated with a number of chronic diseases, such as Alzheimer’s disease, insulin resistance and type-2 diabetes mellitus, hypertension, cardiovascular disease (e.g., stroke), migraine headaches, and attention deficit hyperactivity disorder (ADHD).

Magnesium modifies the association between serum phosphate and the risk of progression to end-stage kidney disease in patients with non-diabetic chronic kidney disease

It is known that magnesium antagonizes phosphate-induced apoptosis of vascular smooth muscle cells and prevents vascular calcification. Here we tested whether magnesium can also counteract other pathological conditions where phosphate toxicity is involved, such as progression of chronic kidney disease (CKD). We explored how the link between the risk of CKD progression and hyperphosphatemia is modified by magnesium status. A post hoc analysis was run in 311 non-diabetic CKD patients who were divided into four groups according to the median values of serum magnesium and phosphate. During a median follow-up of 44 months, 135 patients developed end-stage kidney disease (ESKD). After adjustment for relevant clinical factors, patients in the lower magnesium-higher phosphate group were at a 2.07-fold (95% CI: 1.23-3.48) risk for incident ESKD and had a significantly faster decline in estimated glomerular filtration rate compared with those in the higher magnesium-higher phosphate group. There were no significant differences in the risk of these renal outcomes among the higher magnesium-higher phosphate group and both lower phosphate groups. Incubation of tubular epithelial cells in high phosphate and low magnesium medium in vitro increased apoptosis and the expression levels of profibrotic and proinflammatory cytokine; these changes were significantly suppressed by increasing magnesium concentration. Thus, magnesium may act protectively against phosphate-induced kidney injury.

Hypomagnesemia in type 2 diabetic nephropathy: a novel predictor of end-stage renal disease

OBJECTIVE

There is now growing evidence that magnesium (Mg) deficiency is implicated in type 2 diabetes and its complications. However, it has not been fully elucidated whether hypomagnesemia is a predictor of end-stage renal disease (ESRD) in type 2 diabetic nephropathy.

RESEARCH DESIGN AND METHODS

This retrospective cohort study included 455 chronic kidney disease (CKD) patients (144 with type 2 diabetic nephropathy and 311 with nondiabetic CKD) who were hospitalized at Osaka General Medical Center for a CKD educational program between April 2001 and December 2007. The primary outcome was progression to renal replacement therapy. Participants were categorized based on serum Mg level into Low-Mg (serum Mg level ≤1.8 mg/dL) and High-Mg (serum Mg level >1.8 mg/dL) groups with the previously published normal lower limit chosen as the cutoff point.

RESULTS

Of the subjects with type 2 diabetic nephropathy, 102 progressed to ESRD during follow-up (median, 23 months). A multivariate Cox proportional hazards model showed that after adjustment for various demographic factors and laboratory data, the Low-Mg group had a 2.12-fold higher risk of ESRD than the High-Mg group (95% CI 1.28-3.51; P = 0.004). In contrast, 135 of the nondiabetic CKD subjects progressed to ESRD during follow-up (median, 44 months). No significant difference in outcome was found between the Low- and High-Mg groups of this population (adjusted hazard ratio, 1.15; 95% CI 0.70-1.90; P = 0.57).

CONCLUSIONS

Hypomagnesemia is a novel predictor of ESRD in patients with type 2 diabetic nephropathy.

Magnesium attenuates chronic hypersensitivity and spinal cord NMDA receptor phosphorylation in a rat model of diabetic neuropathic pain

Neuropathic pain is a common diabetic complication affecting 8-16% of diabetic patients. It is characterized by aberrant symptoms of spontaneous and stimulus-evoked pain including hyperalgesia and allodynia. Magnesium (Mg) deficiency has been proposed as a factor in the pathogenesis of diabetes-related complications, including neuropathy. In the central nervous system, Mg is also a voltage-dependent blocker of the N-methyl-d-aspartate receptor channels involved in abnormal processing of sensory information. We hypothesized that Mg deficiency might contribute to the development of neuropathic pain and the worsening of clinical and biological signs of diabetes and consequently, that Mg administration could prevent or improve its complications. We examined the effects of oral Mg supplementation (296 mg l(-1) in drinking water for 3 weeks) on the development of neuropathic pain and on biological and clinical parameters of diabetes in streptozocin (STZ)-induced diabetic rats. STZ administration induced typical symptoms of type 1 diabetes. The diabetic rats also displayed mechanical hypersensitivity and tactile and thermal allodynia. The level of phosphorylated NMDA receptor NR1 subunit (pNR1) was higher in the spinal dorsal horn of diabetic hyperalgesic/allodynic rats. Magnesium supplementation failed to reduce hyperglycaemia, polyphagia and hypermagnesiuria, or to restore intracellular Mg levels and body growth, but increased insulinaemia and reduced polydipsia. Moreover, it abolished thermal and tactile allodynia, delayed the development of mechanical hypersensitivity, and prevented the increase in spinal cord dorsal horn pNR1. Thus, neuropathic pain symptoms can be attenuated by targeting the Mg-mediated blockade of NMDA receptors, offering new therapeutic opportunities for the management of chronic neuropathic pain.

Role of dietary magnesium in cardiovascular disease prevention, insulin sensitivity and diabetes

PURPOSE OF REVIEW

This review summarizes the evidence for benefits of magnesium on metabolic abnormalities, inflammatory parameters, and cardiovascular risk factors and related-potential mechanisms. Controversy due to contrasting results in the literature is also discussed.

RECENT FINDINGS

Increased dietary magnesium intake confers protection against the incidence of diabetes, metabolic syndrome, hypertension, and cardiovascular disease. It ameliorates insulin resistance, serum lipid profiles, and lowers inflammation, endothelial dysfunction, oxidative stress, and platelet aggregability. Magnesium acts as a mild calcium antagonist on vascular smooth muscle tone, and on postreceptor insulin signaling; it is critically involved in energy metabolism, fatty acid synthesis, glucose utilization, ATPase functions, release of neurotransmitters, and endothelial cell function and secretion. Prospective studies, however, have found only a modest effect for dietary magnesium on incident pathologies. Furthermore, magnesium supplementation on glucose metabolism, blood lipid levels, and ischemic heart disease has given inconsistent results.

SUMMARY

There is strong biological plausibility for the direct impact of magnesium intake on metabolic and cardiovascular risk factors, but in-vivo magnesium deficiency might play only a modest role. Reverse causality, the strong association between magnesium and other beneficial nutrients, or the possibility that people who choose magnesium-rich foods are more health-conscious may be confounding factors.

Role of glucose in modulating Mg2+ homeostasis in liver cells from starved rats

Alpha1- and beta-adrenoceptor stimulation elicits Mg2+ extrusion from liver cells in conjunction with hepatic glucose output (T. Fagan and A. Romani. Am J Physiol Gastrointest Liver Physiol 279: G943-G950, 2000.). To characterize the role of intrahepatic glucose on Mg2+ transport, male Sprague-Dawley rats were starved overnight before being anesthetized and used as organ donors. Perfused livers or collagenase-dispersed hepatocytes were stimulated by alpha1 (phenylephrine)- or beta (isoproterenol)-adrenergic agonists. Mg2+ extrusion was assessed by atomic absorbance spectrophotometry. In both experimental models, the administration of pharmacological doses of adrenergic agonists did not elicit Mg2+ extrusion. The determination of cellular Mg2+ indicated an approximately 9% decrease in total hepatic Mg2+ content in liver cells after overnight fasting, whereas the ATP level was unchanged. Hepatocytes from starved rats accumulated approximately four times more Mg2+ than liver cells from fed animals. This enlarged Mg2+ accumulation depended in part on extracellular glucose, since it was markedly reduced in the absence of extracellular glucose or in the presence of the glucose transport inhibitor phloretin. The residual Mg2+ accumulation observed in the absence of extracellular glucose was completely abolished by imipramine or removal of extracellular Na+. Taken together, these data indicate 1) that hepatic glucose mobilization is essential for Mg2+ extrusion by adrenergic agonist and 2) that starved hepatocytes accumulate Mg2+ via two distinct pathways, one of which is associated with glucose transport, whereas the second can be tentatively identified as an imipramine-inhibited Na+-dependent pathway.

Hypomagnesemia in acute and chronic illness

Magnesium deficit is associated with several acute and chronic illnesses. Of major concern is the association between cardiovascular problems, such as myocardial infarction, hypertension, congestive heart failure, and hypomagnesemia. In addition, evidence is mounting regarding the relationship between Type II Diabetes Mellitus, and magnesium deficit. The American diet is low in magnesium, and with modern water systems, very little is ingested in the drinking water. A review of the state of the science in relation to literature on magnesium follows, as well as nursing interventions crucial to managing magnesium deficit.

Parallel stimulation of glucose and Mg(2+) accumulation by insulin in rat hearts and cardiac ventricular myocytes

The stimulation of beta-adrenoceptors in cardiac cells results in a rapid loss of cellular Mg(2+). Because insulin physiologically counteracts several of the cellular effects mediated by the activation of beta-adrenoceptors and the elevation of cytosolic cAMP levels, we investigated whether insulin administration could prevent Mg(2+) mobilization from rat hearts and ventricular myocytes. Rat hearts were perfused in a retrograde Langendorff system, and the changes in extracellular Mg(2+) were measured by atomic absorbance spectrophotometry. Pretreatment of the hearts with 6 nmol/L insulin completely prevented the Mg(2+) extrusion induced by the beta-adrenergic agonist isoproterenol. Furthermore, the administration of insulin per se induced an accumulation of Mg(2+) by the heart. This accumulation was small but detectable in the presence of 25 to 35 micromol/L [Mg(2+)](o) and increased in proportion to [Mg(2+)](o). Insulin-mediated Mg(2+) accumulation was not observed in hearts perfused with a medium devoid of glucose or with a medium containing the inhibitors of glucose transport, cytochalasin B and phloretin. Insulin-stimulated [(3)H]2-deoxyglucose accumulation was measured in collagenase-dispersed cardiac ventricular myocytes in the presence of varying levels of [Mg(2+)](o). Glucose transport was not observed below 25 micromol/L [Mg(2+)](o), and it also increased in proportion to [Mg(2+)](o). Taken together, these results indicate the presence of a major uptake of Mg(2+) into cardiac cells that is stimulated by insulin and may require the insulin-induced operation of a glucose transporter. Hence, extracellular and/or intracellular Mg(2+) may modulate glucose transport and/or utilization.

Regulation of myo-inositol transport during the growth and differentiation of thyrocytes: a link with thyroid-stimulating hormone-induced phospholipase A2 activity

The Vmax of myo-inositol transport increased 3-fold during epidermal growth factor (EGF)-induced growth and thyroid-stimulating hormone. (TSH)-induced differentiation in primary cultures of sheep and human thyrocytes. The Km remained unaltered. This up-regulation required the presence of insulin. The TSH-induced rise in myo-inositol transport commenced 8 to 16 h after the initial stimulus and achieved a plateau at 24 h. In human thyrocytes the change in Vmax was accompanied by an increase in the steady-state levels of mRNA for the myo-inositol transporter following treatment with either ligand. Examination of the metabolites of myo-inositol showed few significant changes after treatment of sheep thyrocytes with EGF for 24 h. This is consistent with maintenance of the intracellular concentration of myo-inositol as the cells enlarge in preparation for cell division. In TSH-treated cells, however, up-regulation of myo-inositol transport was linked with increased myo-inositol cycling across the cell membrane, increased phospholipase A2-mediated turnover of phosphatidylinositol and a concomitant increase in arachidonic acid turnover. Increased levels of myo-inositol phosphates were also noted 24 h after TSH treatment. These results indicate the initiation of secondary signalling events many hours after the primary stimulus.

Diabetes mellitus: a disease of abnormal cellular calcium metabolism?

Although the pathogenesis of the diabetes mellitus syndrome remains poorly understood, both insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus predispose the individual to a similar spectrum of complications, including hypertension, macrovascular and microvascular disease, cataracts cardiomyopathy, neuropathy, and premature aging, suggesting that these complications develop along a pathway common to both diabetic conditions. Yet not all diabetic persons are affected by all of these complications or to the same degree. What causes this marked variability in the clinical manifestations of the diabetes syndrome remains an enigma. Accumulating data from animal models of diabetes and from studying patients with diabetes reveal that intracellular calcium levels are increased in most tissues. The activities of the membrane, adenosine triphosphatase (ATPase) associated cation pumps, which determine intracellular calcium level (i.e., calcium-ATPase and [sodium + potassium]-ATPase), are also altered. The nature of the alteration is often tissue specific and may depend on the level of blood glucose or insulin, or both. In this review we discuss the potential contribution of these changes in intracellular calcium regulation, whether acquired or genetically determined, to the pathogenesis of the diabetes syndrome, to the abnormalities in insulin secretion and action (mainly in non-insulin-dependent diabetes), and to the complications of both diabetes syndromes. Altered intracellular calcium metabolism may represent a common, underlying abnormality linking the metabolic, cardiovascular, ocular, and neural manifestations of the diabetic disease process.