Calcium and Magnesium in the Regulation of Smooth Muscle Function and Blood Pressure

Cytotoxicity Analysis of Morphologically Different Sol-Gel-Synthesized MgO Nanoparticles and Their In Vitro Insulin Resistance Reversal Ability in Adipose cells

Insulin resistance is one of the major factors that leads to type 2 diabetes. Although insulin therapies have been shown to overcome insulin resistance, overweight and hypoglycemia are still observed in most cases. The disadvantages of insulin therapies have driven the interest in developing novel curative agents with enhanced insulin resistance reversibility. Magnesium deficiency has also been recognized as a common problem which leads to insulin resistance in both type 1 and 2 diabetes. Oxide nanoparticles demonstrate highly tunable physicochemical properties that can be exploited by engineers to develop unique oxide nanoparticles for tailored applications. Magnesium supplements for diabetic cells have been reported to increase the insulin resistance reversibility. Hence, it is hypothesized that magnesium oxide (MgO) nanoparticles could be molecularly engineered to offer enhanced therapeutic efficacy in reversing insulin resistance. In the present work, morphologically different MgO nanoparticles were synthesized and evaluated for biophysical characteristics, biocompatibility, cytotoxicity, and insulin resistance reversibility. MTT assay revealed that hexagonally shaped MgO nanoparticles are less toxic to 3T3-L1 adipose cells (diabetic) compared with spherically and rod-shaped MgO nanoparticles. MTT assays using VERO cells (normal, non-diabetic) showed that 400 μg/ml of hexagonal MgO nanoparticles were less toxic to both diabetic and non-diabetic cells. DNS glucose assay and western blot showed that hexagonally shaped MgO nanoparticles had reversed 29.5% of insulin resistance whilst fluorescence microscopy studies indicated that the insulin resistance reversal is due to the activation of intracellular enzymes. The probable mechanism for MgO nanoparticles to induce cytotoxic effect and insulin resistance reversal is discussed.

Cellular ionic alterations with age: relation to hypertension and diabetes

BACKGROUND

Cytosolic free calcium (Cai) and magnesium (Mgi) are vital to cellular homeostasis and function.

OBJECTIVE

To evaluate cellular divalent cations in normal subjects at different ages and their relationship to ion levels in essential hypertension and diabetes.

DESIGN

A cross-sectional study.

SETTING

A university hospital in New York.

PARTICIPANTS

A total of 103 subjects (32 older, 71.1 +/- 1.2 y/o, and 71 young/middle aged subjects, 51.1 +/- 2.3 y/o).

INTERVENTION

Oral glucose tolerance test.

MEASUREMENTS

19F and 31P NMR spectroscopy were used to measure Cai and Mgi levels in erythrocytes from normal (>65 y/o, n = 11; <65 y/o, n = 26), hypertensive (EH) (>65 y/o, n = 9; <65 y/o, n = 30), and type 2 diabetic (DM) (>65 y/o, n = 12; <65 y/o, n = 15) subjects; these levels were also compared with glucose and insulin levels before and after oral glucose loading.

RESULTS

Fasting Mgi levels were lower (207 +/- 7.8 vs 236 +/- 7.5 microM; P < .05) and Cai higher (32.2 +/- 3.0 vs 20.3 +/- 1.8 nM; P < .05) in older than in younger normal subjects. For all normal subjects, the greater the age, the higher the Cai (r = 0.622, P = .004) and the lower the Mgi (r = -0.423; P = .011). However, no significant (P = NS) differences in Mgi or Cai levels were observed between older normal and young/middle-aged subjects with EH (Mgi = 189.7 +/- 5.9 vs 182.6 +/- 9.8 microM; Cai = 33.8 +/- 4.9 vs 35.6 +/- 4.0 nM) or DM (Mgi = 182.8 +/- 10.9 vs 180.8 +/- 8.1 microM; Cai = 33.6 +/- 4.3 vs 39.7 +/- 5.9 nM). Significant relationships were also found between cellular ion content, blood pressure, and glycemic indices.

CONCLUSIONS

Aging is associated with the onset of altered Cai and Mgi levels, indistinguishable from those observed in hypertension and diabetes, independent of age. We suggest that these ionic changes may be clinically significant, underlying the predisposition of older subjects to cardiovascular and metabolic diseases.

Effects of vitamin E and glutathione on glucose metabolism: role of magnesium

Vitamin E is an antioxidant that has been demonstrated to improve insulin action. Glutathione, another natural antioxidant, may also be important in blood pressure and glucose homeostasis, consistent with the involvement of free radicals in both essential hypertension and diabetes mellitus. Our group has recently suggested that the effects of reduced glutathione on glucose metabolism may be mediated, at least in part, by intracellular magnesium levels (Mg([i])). Recent evidence suggests that vitamin E enhances glutathione levels and may play a protective role in magnesium deficiency-induced cardiac lesions. To directly investigate the effects of vitamin E supplementation on insulin sensitivity in hypertension, in relation to the effects on circulating levels of reduced (GSH) and oxidized (GSSG) glutathione and on Mg([i]), we performed a 4-week, double-blind, randomized study of vitamin E administration (600 mg/d) versus placebo in 24 hypertensive patients and measured whole-body glucose disposal (WBGD) by euglycemic glucose clamp, GSH/GSSG ratios, and Mg([i]) before and after intervention. The relationships among WBGD, GSH/GSSG, and Mg([i]) in both groups were evaluated. In hypertensive subjects, vitamin E administration significantly increased WBGD (25.56+/-0.61 to 31.75+/-0.53 micromol/kg of fat-free mass per minute; P<0.01), GSH/GSSG ratio (1.10+/-0.07 to 1.65+/-0.11; P<0.01), and Mg([i]) (1.71+/-0.042 to 1.99+/-0.049 mmol/L; P<0.01). In basal conditions, WBGD was significantly related to both GSH/GSSG ratios (r=0.58, P=0.047) and Mg([i]) (r=0.78, P=0.003). These data show a clinical link between vitamin E administration, cellular magnesium, GSH/GSSG ratio, and tissue glucose metabolism. Further studies are needed to explore the cellular mechanism(s) of this association.

Effects of aging on serum ionized and cytosolic free calcium: relation to hypertension and diabetes

Elevated cytosolic free calcium (Ca(i)) and reciprocally reduced, extracellular ionized calcium (Ca-ion) levels are observed in both hypertension and non-insulin-dependent diabetes mellitus (NIDDM). Because the changes of vascular function and insulin sensitivity in these conditions resemble the changes associated with "normal" aging, we wondered to what extent similar alterations in calcium metabolism occur with aging per se in the absence of overt hypertension or diabetes. We therefore measured platelet Ca(i) levels by spectrofluorometry and serum Ca-ion levels in normotensive, nondiabetic, healthy, normal, elderly (>65 years old) subjects, mean age +/-SEM, 72.2+/-1.5 years old (n=11); in healthy, normal, young (<65 years old) adults, 46.1+/-2.3 years old (n=12); in 10 young adult hypertensives, 48.6+/-1.9 years old; and in 10 normotensive NIDDM subjects, 49.2+/-1.6 years old. Platelet Ca(i) levels were higher (104.5+/-4.9 versus 80.2+/-1.8 nmol/L, P<0.01) and Ca-ion levels lower (1.212+/-0.010 versus 1.236+/-0.011 mmol/L, P<0.05) in normal elderly compared with young control subjects, but normal elderly Ca(i) and Ca-ion levels were indistinguishable from those in hypertensive (Ca(i) 107.5+/-3.6 nmol/L, Ca-ion 1.210+/-0.009 mmol/L) and NIDDM (Ca(i) 110.7+/-4.7 nmol/L, Ca-ion 1.204+/-0.014 mmol/L) subjects. In normal subjects, significant correlations were found between platelet Ca(i) levels and age (r=0.655, P<0.01) and between Ca(i) levels and systolic blood pressure (r=0.733, P<0.001). We conclude that aging is associated with alterations of Ca(i) and Ca-ion levels resembling those changes present at any age in hypertension and type 2 diabetes. We hypothesize that these alterations of calcium metabolism underlie the predisposition to the alterations of blood pressure and insulin sensitivity characteristic of "normal" aging. The data also suggest that studies of the aging process should be limited to subjects with normal blood pressure and glucose tolerance.

Effects of glutathione on red blood cell intracellular magnesium: relation to glucose metabolism

Recent evidence suggests that the endogenous antioxidant glutathione may play a protective role in cardiovascular disease. To directly investigate the role of glutathione in the regulation of glucose metabolism in hypertension, we studied the acute effects of in vivo infusions of this antioxidant (alone or in combination with insulin) on whole body glucose disposal (WBGD) using euglycemic glucose clamp and the effects on total red blood cell intracellular magnesium (RBC-Mg) in hypertensive (n=20) and normotensive (n=30) subjects. The relationships among WBGD, circulating reduced/oxidized glutathione (GSH/GSSG) levels, and RBC-Mg in both groups were evaluated. The in vitro effects of glutathione (100 micromol/L) on RBC free cytosolic magnesium (Mg(i)) were also studied. In vivo infusions of glutathione (15 mg/minx120 minutes) increased RBC-Mg in both normotensives and hypertensives (1.99+/-0.02 to 2.13+/-0.03 mmol/L, P<0.01, and 1.69+/-0.03 to 1.81+/-0.03 mmol/L, P<0.01, respectively). In vitro GSH but not GSSG increased Mg(i) (179+/-3 to 214+/-5 micromol/L, P<0.01). In basal conditions, RBC-Mg values were related to GSH/GSSG ratios (r=0.84, P<0.0001), and WBGD was directly, significantly, and independently related to both GSH/GSSG ratios (r=0.79, P<0.0001) and RBC-Mg (r=0.89, P<0.0001). This was also true when hypertensive and control groups were analyzed separately. On multivariate analysis, basal RBC-Mg (t=6.81, P<0.001), GSH/GSSG (t=3. 67, P<0.02), and blood pressure (t=2.89, P<0.05) were each independent determinants of WBGD, with RBC-Mg explaining 31% of the variability of WBGD. These data demonstrate a direct action of glutathione both in vivo and in vitro to enhance intracellular magnesium and a clinical linkage between cellular magnesium, GSH/GSSG ratios, and tissue glucose metabolism.