Arsenite and methylarsonite inhibit mitochondrial metabolism and glucose-stimulated insulin secretion in INS-1 832/13 ß cells.

Growing evidence suggests that exposure to environmental contaminants contributes to the current diabetes epidemic. Inorganic arsenic (iAs), a drinking water and food contaminant, is one of the most widespread environmental diabetogens according to epidemiological studies. Several schemes have been proposed to explain the diabetogenic effects of iAs exposure; however, the exact mechanism remains unknown. We have shown that in vitro exposure to low concentrations of arsenite (iAsIII) or its trivalent methylated metabolites, methylarsonite (MAsIII) and dimethylarsinite (DMAsIII), inhibits glucose-stimulated insulin secretion (GSIS) from isolated pancreatic islets, with little effect on insulin transcription or total insulin content. The goal of this study was to determine if exposure to trivalent arsenicals impairs mitochondrial metabolism, which plays a key role in the regulation of GSIS in ß cells. We used a Seahorse extracellular flux analyzer to measure oxygen consumption rate (OCR), a proxy for mitochondrial metabolism, in cultured INS-1 832/13 ß cells exposed to iAsIII, MAsIII, or DMAsIII and stimulated with either glucose or pyruvate, a final product of glycolysis and a substrate for the Krebs cycle. We found that 24-h exposure to 2 µM iAsIII or 0.375-0.5 µM MAsIII inhibited OCR in both glucose- and pyruvate-stimulated ß cells in a manner that closely paralleled GSIS inhibition. In contrast, 24-h exposure to DMAsIII (up to 2 µM) had no effects on either OCR or GSIS. These results suggest that iAsIII and MAsIII may impair GSIS in ß cells by inhibiting mitochondrial metabolism, and that at least one target of these arsenicals is pyruvate decarboxylation or downstream reactions.

Effect of selenium and vitamin E supplements on tissue lipids, peroxides, and fatty acid distribution in experimental diabetes.

The protective role of selenium (Se), given as a Se-rich yeast, selenomethionine or selenomethionine + vitamin E supplement, toward changes in lipid, peroxide, and fatty acid distribution in tissues of streptozotocin-induced diabetic rats, was investigated, after 24 wk of disease. Diabetes increased liver thiobarbituric acid-reactive substances and conjugated dienes; Se supplement completely corrected these changes. In kidney, as in heart, the peroxide levels were not significantly changed by diabetes. In diabetic rat liver, a significant drop in triglycerides and phospholipids (P < 0.05) was observed; this was modulated by Se + vitamin E supplementation. Se + vitamin E supplementation also inhibited the decrease in 18:2n-6 and the increase in 22:6n-3 observed in liver of diabetic rats, changes which reflect altered glycemic control. In kidney, heart, and aorta, diabetes produced some changes in lipid content and fatty acid distribution, especially an increase in heart triglycerides which was also corrected by the Se supplement. Se supplementation to diabetic rats also increased 18:0 ether-linked alcohol, 20:4 n-6, and 22:5 n-3 in cardiac lipids. In aorta, Se + vitamin E significantly increased 20:5 n-3. These polyunsaturated fatty acids are precursors, in situ, of prostaglandin I2 (PGI2) and PGI3 which may protect against cardiovascular dysfunction. In kidney, conversely, Se decreased 20:4 n-6, the precursor of thromboxane A2 implicated in diabetic glomerular injury. Thus Se, and more efficiently Se + Vitamin E supplementation, in experimental diabetes could play a role in controlling oxidative status and altered lipid metabolism in liver, thereby maintaining favorable fatty acid distribution in the major tissues affected by diabetic complications.

Effect of selenium and vitamin E supplementation on lipid abnormalities in plasma, aorta, and adipose tissue of Zucker rats.

Twenty-nine obese female Zucker rats (fa/fa) were fed with a laboratory chow supplemented or not with a selenium-rich yeast (Selenion), or Selenion + vitamin E, or vitamin E alone. Twelve lean female Zucker rats (Fa/Fa) of the same littermates fed with the same diet were used as control. After 32 wk of diet, obesity induced a large increase in plasma insulin and lipid levels. A significant decrease in the plasma vitamin E/triglycerides ratio (p<0.005) and an increase in plasma thiobarbituric reactive substances (TBARS) (p<0.005) were also observed. Plasma selenium and vitamin E increased in all supplemented rats. The plasma insulin level was decreased by selenion supplementation and the vitamin E/triglycerides ratio was completely corrected by double supplementation with Selenion + vitamin E. TBARS were also efficiently decreased in two obese groups receiving vitamin E. In plasma, adipose tissue and aorta, obesity induced an increase in palmitic acid (C16:0), a very large increase in monounsaturated fatty acids (palmitoleic acid C16:1, stearic acid C18:1) associated with a decrease in polyunsaturated n-6 fatty acids (linoleic acid C18:2 n-6, arachidonic C20:4 n-6). These alterations in fatty acid distribution were only partly modulated by Se and vitamin E supplements. However, in the aorta, antioxidant treatment in obese rats significantly reduced the increase in C16:0 and C16:1 (p<0.05 and p<0.01, respectively) and the decrease in arachidonic acid (p<0.05). These changes could be beneficial in the reduction of insulin resistance and help to protect the vascular endothelium.

In vitro and in vivo effects of selenium and selenium with vitamin E on platelet functions in diabetic rats relationship to platelet sorbitol and fatty acid distribution.

In vitro 30 min of incubation with selenomethionine (Sm) + vitamin E multiplied by about five platelet selenium (Se) decreased significantly platelet thrombin and ADP-induced aggregation decrease. Four groups of streptozotocin-induced diabetic rats were fed with a supplemented purified diet with an Se-rich yeast (Selenion): DSel, Sm: DSm, Sm alpha-tocopherol: DSmE or unsupplemented diet: D. After 24 wk of supplementation, only a decrease in thrombin-induced aggregation in group DSel compared to DSm and DSmE and D was observed. However, after 24 wk of diet compared to 14 wk, in group D and DSm, a significant increase in thrombin-induced aggregation occurred (p < 0.0001), whereas a significant decrease in groups DSel and DSmE (p < 0.0001, p < 0.03) was noted. After 21 wk of diet, in DSmE, platelet adhesion to fibronectin was significantly decreased compared to group D (p < 0.05). These changes in DSmE were associated with a significant decrease in platelet sorbitol (p < 0.02) and a very significant increase in platelet Se (p < 0.0005). Sm associated with vitamin E would appear more efficient to prevent oxidative damage of diabetic platelet membrane and thus to modulate its hyperactivity.

A selenium supplement associated or not with vitamin E delays early renal lesions in experimental diabetes in rats.

Seventy rats were separated into five groups: one group of 12 was used as a control and received a purified diet, and four groups of streptozotocin-induced diabetic rats, totalling 58, were fed the same diet without or with selenium (Se) supplementation. Of the noncontrol rats, 14 were without supplementation (Group D), 14 were fed a Se-rich yeast diet (i.e., selenion) (Group DSel), 14 received selenomethionine (Group DSm), and 16 received selenomethionine + tocopherol acetate (Group DSmE). Supplementation with Se in all groups was 0.99 micromole/100g of diet and with tocopherol acetate was 0.145 micromole/100 g. All diabetic rats were mildly balanced by insulin. After 24 weeks of diet, plasma glucose tended to decrease in diabetic Se-supplemented groups DSmE > DSm > DSel versus Group D. In DSm and DSmE groups, plasma lipid peroxides also decreased compared with Group D, but this decrease reached significance only for DSmE (P < 0.01 for both TBARS and conjugated dienes). Plasma triglycerides also decreased in DSm and DSmE groups versus Group D (P < 0.01; P < 0.05, respectively). At the same time, Se increased significantly in kidneys of Groups DSel and DSm versus D and more weakly in Group DSmE, but in this case was associated with a large increase of vitamin E. These beneficial effects of selenium supplement and more so of selenium combined with vitamin E were associated with a protection of kidneys in diabetic rats which found expression in a significant correction of renal hyperfiltration (P < 0.05) and in a diminution of the number and severity of glomerular lesions (P < 0.0005).

High dosage vitamin E effect on oxidative status and serum lipids distribution in streptozotocin-induced diabetic rats.

This study was performed to determine whether vitamin E supplementation in streptozotocin-induced diabetic rats treated by insulin could reduce serum oxidation markers (malondialdehyde: MDA, Schiff bases, anti-protein-MDA adduct antibodies) and modulate lipid changes. After 10 weeks, diabetes induced in rats a significant increase in Schiff bases (P < 0.006) and anti-protein-MDA adduct antibodies (P < 0.01). These alterations were accompanied by a significant rise in serum free fatty acids (225%), triglycerides (35%), and phospholipids (30%) and changes in fatty acid distribution in these fractions and in cholesterol esters. Vitamin E supplementation in diabetic rats reduced Schiff bases and anti-protein-MDA adduct antibodies and tended to restore the fatty acid profile close to control rats without decreasing quantitatively serum lipids enhanced by diabetes. Concerning fatty acids, vitamin E chiefly reduced stearic acid (C18:0) in free fatty acids, cholesterol esters, and phospholipids and cancelled the decrease in low molecular triglycerides observed in diabetic rats. Furthermore, vitamin E maintained the ratio of monounsaturated and polyunsaturated fatty acids, particularly with respect to oleic acid (C18:1), dihomo-gamma-linolenic acid (C20:3 n-6), eicosapentaenoic (C20:5 n-3), and docosapentaenoic acid (C22:5 n-3), in serum phospholipids. These changes observed in vitamin E supplemented rats, compared to vitamin E-untreated diabetic rats, could favor prevention of accelerated atherogenesis. Particularly, the decrease of serum peroxides and enhancement in phospholipid fatty acids (C20:3 n-6, C20:5 n-3, and C22:5 n-3) could induce the preferential formation of prostaglandins (PGE1, PGI2, PGI3) which are protective in cardiovascular diseases.

Mechanisms by which bradykinin promotes fibrosis in vascular smooth muscle cells: role of TGF-beta and MAPK.

Accumulation of extracellular matrix (ECM) is a hallmark feature of vascular disease. We have previously shown that hyperglycemia induces the expression of B(2)-kinin receptors in vascular smooth muscle cells (VSMC) and that bradykinin (BK) and hyperglycemia synergize to stimulate ECM production. The present study examined the cellular mechanisms through which BK contributes to VSMC fibrosis. VSMC treated with BK (10(-8) M) for 24 h significantly increased alpha(2)(I) collagen mRNA levels. In addition, BK produced a two- to threefold increase in alpha(2)(I) collagen promoter activity in VSMC transfected with a plasmid containing the alpha(2)(I) collagen promoter. Furthermore, treatment of VSMC with BK for 24 h produced a two- to threefold increase in the secretion rate of tissue inhibitor of metalloproteinase 1 (TIMP-1). The increase in alpha(2)(I) collagen mRNA levels and alpha(2)(I) collagen promoter activity, as well as TIMP-1 secretion, in response to BK were blocked by anti-transforming growth factor-beta (anti-TGF-beta) neutralizing antibodies. BK (10(-8) M) increased the endogenous production of TGF-beta1 mRNA and protein levels. Inhibition of the mitogen-activated protein kinase (MAPK) pathway by PD-98059 inhibited the increase of alpha(2)(I) collagen promoter activity, TIMP-1 production, and TGF-beta1 protein levels observed in response to BK. These findings provide the first evidence that BK induces collagen type I and TIMP-1 production via autocrine activation of TGF-beta1 and implicate MAPK pathway as a key player in VSMC fibrosis in response of BK.