Magnesium deficiency modulates the insulin signaling pathway in liver but not muscle of rats

Magnesium increases insulin-dependent glucose uptake in adipocytes

Background

Type 2 diabetes (T2D) is characterized by a decreased insulin sensitivity. Magnesium (Mg2+) deficiency is common in people with T2D. However, the molecular consequences of low Mg2+ levels on insulin sensitivity and glucose handling have not been determined in adipocytes. The aim of this study is to determine the role of Mg2+ in the insulin-dependent glucose uptake.

Methods

First, the association of low plasma Mg2+ with markers of insulin resistance was assessed in a cohort of 395 people with T2D. Secondly, the molecular role of Mg2+ in insulin-dependent glucose uptake was studied by incubating 3T3-L1 adipocytes with 0 or 1 mmol/L Mg2+ for 24 hours followed by insulin stimulation. Radioactive-glucose labelling, enzymatic assays, immunocytochemistry and live microscopy imaging were used to analyze the insulin receptor phosphoinositide 3-kinases/Akt pathway. Energy metabolism was assessed by the Seahorse Extracellular Flux Analyzer.

Results

In people with T2D, plasma Mg2+ concentration was inversely associated with markers of insulin resistance; i.e., the lower Mg2+, the more insulin resistant. In Mg2+-deficient adipocytes, insulin-dependent glucose uptake was decreased by approximately 50% compared to control Mg2+condition. Insulin receptor phosphorylation Tyr1150/1151 and PIP3 mass were not decreased in Mg2+-deficient adipocytes. Live imaging microscopy of adipocytes transduced with an Akt sensor (FoxO1-Clover) demonstrated that FoxO1 translocation from the nucleus to the cytosol was reduced, indicting less Akt activation in Mg2+-deficient adipocytes. Immunocytochemistry using a Lectin membrane marker and at the membrane located Myc epitope-tagged glucose transporter 4 (GLUT4) demonstrated that GLUT4 translocation was diminished in insulin-stimulated Mg2+-deficient adipocytes compared to control conditions. Energy metabolism in Mg2+ deficient adipocytes was characterized by decreased glycolysis, upon insulin stimulation.

Conclusions

Mg2+ increases insulin-dependent glucose uptake in adipocytes and suggests that Mg2+ deficiency may contribute to insulin resistance in people with T2D.

Association of magnesium consumption with type 2 diabetes and glucose metabolism: A systematic review and pooled study with trial sequential analysis

Prevention of type 2 diabetes (T2D) with diet or diet supplementation is challenging. This article aims to draw conclusive associations between magnesium intake and T2D incidence and evaluate the effect of magnesium supplementation on glucose metabolism. Databases were searched for related articles from inception to May 15, 2019. Prospective cohort studies investigating the relevant relationship as well as randomized controlled trials (RCTs) assessing the effect of magnesium supplementation were eligible. We conducted trial sequential analysis (TSA) to prove the sufficiency of the current evidence. Twenty-six publications involving 35 cohorts were included in the analysis. Compared to the lowest magnesium intake, the highest level was associated with a 22% lower risk for T2D; the risk was reduced by 6% for each 100 mg increment in daily magnesium intake. Additional analysis of 26 RCTs (1168 participants) was performed, revealing that magnesium supplementation significantly reduced the fasting plasma glucose (FPG) level (SMD, -0.32 [95% CI, -0.59 to -0.05], 2-hour oral glucose tolerance test (2-h OGTT) result (SMD, -0.30 [-0.58 to -0.02]), fasting insulin level (SMD, -0.17 [-0.30 to -0.04]), homeostatic model assessment-insulin resistance (HOMA-IR) score (SMD, -0.41 [-0.71 to -0.11]), triglyceride (TG) level, systolic blood pressure (SBP) and diastolic blood pressure (DBP). TSA showed an inverse association, with most benefits of magnesium supplementation on glucose metabolism being stable. In conclusion, magnesium intake has an inverse dose-response association with T2D incidence, and supplementation appears to be advisable in terms of glucose parameters in T2D/high-risk individuals.

Novel Insights on Intake of Fish and Prevention of Sarcopenia: All Reasons for an Adequate Consumption

Sarcopenia is defined as a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength and it is diagnosed by measurements of muscle mass, muscle strength, and physical performance. Sarcopenia affects quality of life and is associated with several adverse health effects. Muscle decline is aggravated by a sedentary lifestyle and can be prevented through proper nutrition, together with adequate physical activity. Fish contains biologically active compounds, such as omega-3 polyunsaturated fatty acids, proteins, vitamin D, magnesium, and carnitine, which are able to intervene positively on muscle metabolism. This narrative literature review was performed to evaluate evidence regarding the actual benefit of fish consumption in the prevention of sarcopenia and the positive action on the muscle mass of the biological compounds present in fish. The results demonstrated that fish consumption has a protective and anti-inflammatory function on skeletal muscle and that its biologically active compounds help to maintain good muscle performance, preventing sarcopenia. Considering the nutritional and health benefits, elderly with sarcopenia should consume at least three servings per week of fish in order to have a minimum intake of 4-4.59 g daily of omega 3, and reaching the 50% RDA in Vitamin E and D. High biological value of proteins in 150 g of fish and its high available magnesium (20% of RDA in 150 g of fish) are an added value that could suggest fish as a "functional food" in order to prevent and treat sarcopenia.

Low serum magnesium is associated with faster decline in kidney function: the Dallas Heart Study experience

Hypomagnesemia associates with inflammation and risk of diabetes and hypertension, which may contribute to kidney function decline. We hypothesized that low serum magnesium (SMg) levels independently associate with a significant decline in estimated glomerular filtration rate (eGFR). We analyzed SMg levels in 2056 participants from the Dallas Heart Study, a longitudinal, population-based, multiethnic, cohort study involving residents of Dallas County, Texas, USA. The primary study outcome was the change in eGFR using multivariable linear regression models adjusted for demographics, anthropometric and biochemical parameters, medications, C reactive protein levels, prevalent hypertension and diabetes. During a median follow-up of 7.0 years (25th, 75th percentile: 6.5, 7.6), the median decrease in eGFR was -0.71 (25th, 75th percentile: -2.43, +0.68) mL/min/1.73 m² per year in the entire cohort. In a fully adjusted model, the lowest SMg quintile (≤1.9 mg/dL or ≤0.8 mM) was associated with a -0.50 mL/min/1.73 m² per year drop in eGFR (95% CI -0.95 to -0.05; p=0.028) compared with the highest SMg quintile (≥2.3 mg/dL or ≥1.0 mM). Every 0.2 mg/dL (0.08 mM) decrease in SMg was associated with an eGFR decline of -0.23 mL/min/1.73 m² per year (95% CI -0.38 to -0.08; p=0.003), a decline that was more pronounced in participants with prevalent diabetes compared with patients without diabetes (-0.51 vs -0.18 mL/min/1.73 m² per year, respectively). In conclusion, low SMg was independently associated with eGFR decline. Further studies are needed to determine whether Mg repletion can ameliorate inflammation, lower blood pressure and serum glucose and ultimately prevent or retard kidney function decline.

Hypomagnesemia in Type 2 Diabetes: A Vicious Circle?

Over the past decades, hypomagnesemia (serum Mg(2+) <0.7 mmol/L) has been strongly associated with type 2 diabetes mellitus (T2DM). Patients with hypomagnesemia show a more rapid disease progression and have an increased risk for diabetes complications. Clinical studies demonstrate that T2DM patients with hypomagnesemia have reduced pancreatic β-cell activity and are more insulin resistant. Moreover, dietary Mg(2+) supplementation for patients with T2DM improves glucose metabolism and insulin sensitivity. Intracellular Mg(2+) regulates glucokinase, KATP channels, and L-type Ca(2+) channels in pancreatic β-cells, preceding insulin secretion. Moreover, insulin receptor autophosphorylation is dependent on intracellular Mg(2+) concentrations, making Mg(2+) a direct factor in the development of insulin resistance. Conversely, insulin is an important regulator of Mg(2+) homeostasis. In the kidney, insulin activates the renal Mg(2+) channel transient receptor potential melastatin type 6 that determines the final urinary Mg(2+) excretion. Consequently, patients with T2DM and hypomagnesemia enter a vicious circle in which hypomagnesemia causes insulin resistance and insulin resistance reduces serum Mg(2+) concentrations. This Perspective provides a systematic overview of the molecular mechanisms underlying the effects of Mg(2+) on insulin secretion and insulin signaling. In addition to providing a review of current knowledge, we provide novel directions for future research and identify previously neglected contributors to hypomagnesemia in T2DM.

Insulin Modulates the Na+/Mg2+ Exchanger SLC41A1 and Influences Mg2+ Efflux from Intracellular Stores in Transgenic HEK293 Cells

BACKGROUND

Magnesium deficiency is a common complication of diabetes with an unclear molecular background.

OBJECTIVE

We investigated the effect of the insulin (INS)-signaling pathway (ISP) on the regulation of Mg(2+) efflux (Mg(2+)E) conducted by solute carrier family 41, member A1 (SLC41A1; activated by protein kinase A) in transgenic human embryonic kidney (HEK) 293 cells.

METHODS

HEK293 cells overexpressing SLC41A1 were loaded with the Mg(2+) fluorescent indicator mag-fura-2 and Mg(2+). Measurements of Mg(2+)E were conducted in Mg(2+)-free buffer by using fast-filter fluorescence spectrometry. We examined the effects of INS, inhibitors of ISP or p38 mitogen-activated protein kinase (p38 MAPK), an activator of adenylate cyclase (ADC), and their combinations on SLC41A1-attributed Mg(2+)E.

RESULTS

The application of 400 μU/mL INS inhibited SLC41A1-mediated Mg(2+)E by up to 50.6% compared with INS-untreated cells (P < 0.001). Moreover, INS evoked the early onset of Mg(2+) release from intracellular stores. The application of 0.1 μM wortmannin or 10 μM zardaverine (both ISP inhibitors) restored SLC41A1 Mg(2+)E capacity in the presence of INS to the same levels in INS-untreated cells. The simultaneous application of 10 μM forskolin, an ADC activator, and INS resulted in a reduction of Mg(2+)E of up to 59% compared with untreated cells (P < 0.001), which was comparable to that in cells treated with INS alone. Inhibition of p38 MAPK with 10 μM SB 202190 (SB) in the absence of INS resulted in a decrease (P < 0.001) of SLC41A1-dependent Mg(2+)E (by up to 49%) compared with Mg(2+)E measured in untreated cells. Simultaneous exposure of cells to SB and INS had a stronger inhibitory effect on SLC41A1 activity than INS alone (P < 0.05).

CONCLUSIONS

INS affects intracellular Mg(2+) concentration in transgenic HEK293 cells by regulating SLC41A1 activity (via ISP) and by influencing the compartmentalization and cellular distribution of Mg(2+). In addition, p38 MAPK activates SLC41A1 independently of INS action.

Magnesium basics

As a cofactor in numerous enzymatic reactions, magnesium fulfils various intracellular physiological functions. Thus, imbalance in magnesium status-primarily hypomagnesaemia as it is seen more often than hypermagnesaemia-might result in unwanted neuromuscular, cardiac or nervous disorders. Measuring total serum magnesium is a feasible and affordable way to monitor changes in magnesium status, although it does not necessarily reflect total body magnesium content. The following review focuses on the natural occurrence of magnesium and its physiological function. The absorption and excretion of magnesium as well as hypo- and hypermagnesaemia will be addressed.

Magnesium in man: implications for health and disease

Magnesium (Mg(2+)) is an essential ion to the human body, playing an instrumental role in supporting and sustaining health and life. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Although Mg(2+) availability has been proven to be disturbed during several clinical situations, serum Mg(2+) values are not generally determined in patients. This review aims to provide an overview of the function of Mg(2+) in human health and disease. In short, Mg(2+) plays an important physiological role particularly in the brain, heart, and skeletal muscles. Moreover, Mg(2+) supplementation has been shown to be beneficial in treatment of, among others, preeclampsia, migraine, depression, coronary artery disease, and asthma. Over the last decade, several hereditary forms of hypomagnesemia have been deciphered, including mutations in transient receptor potential melastatin type 6 (TRPM6), claudin 16, and cyclin M2 (CNNM2). Recently, mutations in Mg(2+) transporter 1 (MagT1) were linked to T-cell deficiency underlining the important role of Mg(2+) in cell viability. Moreover, hypomagnesemia can be the consequence of the use of certain types of drugs, such as diuretics, epidermal growth factor receptor inhibitors, calcineurin inhibitors, and proton pump inhibitors. This review provides an extensive and comprehensive overview of Mg(2+) research over the last few decades, focusing on the regulation of Mg(2+) homeostasis in the intestine, kidney, and bone and disturbances which may result in hypomagnesemia.

Relaxatory effect of magnesium on mesenteric vascular beds differs from normal and streptozotocin induced diabetic rats

Magnesium deficiency has recently been proposed as a novel factor implicated in the pathogenesis of diabetes complications. Previous studies have shown that magnesium decreases basal tone in normal isolated aortic rings and reduces phenylephrine-induced contraction. The mechanism of this magnesium action is not very well known. The present study was designed to determine the role of endothelium and nitric oxide in magnesium sulfate-induced vasorelaxation in diabetic rat vessels. Diabetes was induced by a single tail injection of streptozotocin. Eight weeks later, superior mesenteric arteries of control and diabetic animals were isolated and perfused according to the McGregor method. Prepared vascular beds were constricted with phenylephrine to induce 70-75% of maximal constriction. Magnesium sulfate at concentrations of 0.001 M to 0.1 M was added into the medium and perfusion pressure was then recorded. Mesenteric bed baseline perfusion pressure in intact and denuded endothelium of diabetic groups was higher than controls. In all groups, relaxant response to magnesium in mesenteric bed was attenuated after endothelium removal, but a relaxatory effect appears at high concentration. In the presence of N (omega)-nitro-L-arginine methyl ester (L-NAME), magnesium-induced relaxation was significantly suppressed in intact mesenteric bed of control animals but in diabetics, the relaxant response was slightly inhibited. From the results of this study, it can be concluded that magnesium-induced endothelium dependent and endothelium independent vasorelaxation are mediated by nitric oxide in control rats while in diabetic animals other mechanisms may be involved.

Dietary Boron Decreases Peak Pancreatic In Situ Insulin Release in Chicks and Plasma Insulin Concentrations in Rats Regardless of Vitamin D or Magnesium Status

Because dietary boron deprivation induces hyperinsulinemia in vitamin D-deprived rats, the influence of dietary boron on insulin metabolism as modified by nutritional stressors was examined in two animal models. Male weanling Sprague-Dawley rats were assigned to each of four (Experiment 1) or 8 (Experiment 2) dietary groups for 35 d: the basal diet (< 0.2 mg B; <1.0 mg Mg/kg) was supplemented with boron (as orthoboric acid) to contain <0.2 or 2.0 (a physiologic amount) mg B/kg; with magnesium (as magnesium acetate), at 100 (inadequate) or 360-400 (adequate) mg/kg; and with cholecalciferol [vitamin D-3; 25 microg/kg for study length (Experiment 2), or, depleted for 16-17 d then repleted until end of experiment (Experiments 1 and 2)]. In the rat model, boron reduced plasma insulin (Experiment 1, P < 0.002; Experiment 2, P < 0.03), but did not change glucose concentrations regardless of vitamin D-3 or magnesium status. Cockerels (1 d old) were fed a ground corn, high protein casein and corn oil-based basal diet (low boron; 0.3 mg B/kg) supplemented with boron as orthoboric acid to contain 0.3 or 1.65 mg/kg (a physiologic amount) and vitamin D-3 at 3.13 (inadequate) or 15.60 (adequate) microg/kg. In the chick model, boron decreased (P < 0.045) in situ peak pancreatic insulin release at 26-37 d of age regardless of vitamin D-3 nutriture. These results suggest that physiologic amounts of boron may help reduce the amount of insulin required to maintain plasma glucose.

Alterações do metabolismo da glicose na deficiência de magnésio

O magnésio é um cátion essencial o qual age como co-fator para adenosina trifosfatases em inúmeras reações enzimáticas. Vários estudos mostram seu envolvimento na ação e secreção de insulina e os efeitos deste hormônio sobre o metabolismo e transporte do magnésio. Entretanto, os resultados são conflitantes. Sugerem que a deficiência de magnésio está implicada direta ou indiretamente com a resistência à insulina no diabetes mellitus, enquanto outros descrevem uma relação inversa ou, ainda, um aumento da captação de glicose decorrente da falta de magnésio. A interação deste cátion com outros íons, os mecanismos hormonais e neuro-hormonais compensadores e possivelmente a duração da deficiência são alguns dos fatores descritos como responsáveis pelas variações na regulação glicêmica observadas durante a deficiência de magnésio.

Magnesium deficiency improves glucose homeostasis in the rat: studies in vivo and in isolated islets in vitro

The serum mineral levels, glucose disappearance rate (kg), total area under the glucose (DeltaG) and insulin (DeltaI) curves, and static insulin secretion were compared among rats fed a Mg-deficient diet for 6 (DF-6) or 11 (DF-11) weeks, and rats fed a control diet for the same periods (CO-6 and CO-11 groups). No change in glucose homeostasis was observed among DF-6, CO-6 and CO-11 rats. DF-11 rats showed an elevated kg and a reduced DeltaG and DeltaI. For evaluating the effect of supplementation, rats fed a control or Mg-deficient diet for 6 weeks were then fed a Mg- supplemented diet for 5 weeks (SCO and SDF groups respectively). The serum Mg levels in SDF rats were similar to those in CO-11 and SCO rats, but higher than in the DF-11 group. SDF rats showed similar kg, DeltaG and DeltaI compared with the CO-11 and SCO groups. However, a significantly lower kg and higher DeltaG and DeltaI were observed in SDF compared with DF-11 rats. Basal and 8.3 mmol glucose/l-stimulated insulin secretion by islets from DF-11 rats were higher than by islets from CO-11 rats. These results indicate that moderate Mg depletion for a long period may increase the secretion and sensitivity to insulin, while Mg supplementation in formerly Mg-deficient rats may prevent the increase in sensitivity and secretion of insulin.

Effect of hypomagnesemia and cold exposure on tissue responsiveness to insulin in sheep given a low magnesium and high potassium diet

Hypomagnesemia in ruminants has been shown to be associated with cold stress and with altered insulin secretion and sensitivity. However, the relationship between hypomagnesemia and tissue responsiveness to insulin in ruminants exposed to cold environment is still unclear. The hyperinsulinemic euglycemic clamps, four insulin infusion rates (1, 2, 4 and 8 mU x kgBW(-1) x min(-1) for four sequential periods of 2-h each) were performed to determine combined effects of hypomagnesemia and cold exposure (0 degrees C) on tissue responsiveness to insulin in sheep. The low magnesium (0.05% Mg) and high potassium (4.20% K) diet and cold exposure decreased (P <.05) plasma Mg levels compared with those of the control diet (0.28% Mg/0.52% K) and the thermoneutral environment (20 degrees C). In the euglycemic clamps, cold exposure increased (P <.01) the pooled glucose infusion rate (GIR) across various insulin infusion rates in both diet treatments, though the increases in GIR were small for the low Mg/high K diet. In the cold environment, the GIR was lower (P <.01) for the low Mg/high K diet-fed sheep than for the control diet-fed sheep. The maximal insulin-induced increase in GIR was lower (P <.01) in the hypomagnesemic sheep than in the control sheep during cold exposure, and the insulin level resulting in half-maximal GIR tended to be higher in the hypomagnesemic sheep than in the control sheep. These results indicated that hypomagnesemia in ruminants depressed the enhanced tissue responsiveness to insulin in the cold environment, and decreased insulin-mediated glucose disposal.