Effect of vanadate on glycogen synthesis in dexamethasone-treated 3T3 adipocytes: evidence for a novel insulin sensitizing action.

AIM: Type 2 diabetes is characterized by peripheral tissue insulin resistance. The present study was carried out to determine the insulin sensitizing action of vanadium using dexamethasone-treated 3T3 adipocytes as an in-vitro model of insulin resistance. METHODS: Fully differentiated 3T3 adipocytes were incubated with or without 100 nM dexamethasone in the presence or absence of 200 nM insulin for 6 days. Sodium orthovanadate (0-1000 microM) was added on day 2 and was present during the last 4 days. At the end, insulin (100 nM) stimulated glycogen synthesis was determined. RESULTS: Vanadate treatment for 4 days, caused 2-3-fold increase in glycogen synthesis in dexamethasone treated adipocytes. At 100 microM, vanadate completely reversed dexamethasone-induced insulin resistance (by increasing the levels from 9.65 +/- 0.80 to 28.4 +/- 4.9 nmol/h). In cells treated with dexamethasone and insulin, vanadium was partially active and it caused only 30% increase in glycogen synthesis. Exposure of dexamethasone treated cells for 24 h with vanadium did not affect glycogen synthesis. Under identical condition, vanadium had no significant effect in the normal insulin sensitive adipocytes. Vanadium at 100 microM had no effect on 125I-insulin binding to insulin-resistant adipocytes. Glycogen synthesis in the normal and insulin-resistant adipocytes was stimulated by lithium, an inhibitor of glycogen synthase kinase 3 beta, suggesting the involvement of phosphorylation events in dexamethasone-induced insulin resistance. CONCLUSIONS: Since vanadium was active only in the insulin-resistant adipocytes it is likely that vanadium acts by relieving dexamethasone actions rather than having independent effects. These results provide evidence for the novel insulin sensitizing action of vanadium which might be of future clinical relevance.

Troglitazone prevents and reverses dexamethasone induced insulin resistance on glycogen synthesis in 3T3 adipocytes.

Troglitazone lowers blood glucose levels in Type II diabetic patients. To evaluate the insulin sensitizing action of troglitazone on glycogen synthesis we have used dexamethasone-treated 3T3 adipocytes as an in vitro model. Differentiated 3T3 adipocytes were incubated with 100 nM dexamethasone for 6 days. Troglitazone (1.0 microM) or metformin (1.0 mM) with or without 200 nM insulin was added during the last 4 days. At the end, insulin (100 nM) stimulated glycogen synthesis was determined using (14)C-glucose. Dexamethasone caused a 50% reduction in glycogen synthesis. Troglitazone caused an approximately 3 fold increase in glycogen synthesis from 43.9+/-3.4 to 120+/-16.2 nmols h(-1). Under identical conditions metformin had no significant effect. When cells were incubated with troglitazone and dexamethasone simultaneously for 6 days, troglitazone but not metformin completely prevented dexamethasone-induced insulin resistance. RU 486 (1.0 microM) also completely prevented the insulin resistance. Chronic incubation with dexamethasone and insulin resulted in a 73% reduction in glycogen synthesis. In these adipocytes, troglitazone was partially active with glycogen synthesis rising from 23.1+/-3.0 to 44.4+/-4.5 nmol h(-1), P<0.01 while metformin was inactive. Troglitazone stimulated 2-deoxyglucose uptake by 2 - 3 fold in dexamethasone-treated adipocytes. Metformin also increased glucose uptake significantly. Troglitazone did not affect insulin binding while a 2 fold increase was observed in normal adipocytes where it exhibited a modest effect. Since the effect of troglitazone was greater in dexamethasone-treated adipocytes, troglitazone is likely to act by preventing dexamethasone-induced alterations which may include (i) binding to glucocorticoid receptor and (ii) effect on glucose uptake. These data demonstrate the direct insulin sensitizing action of troglitazone on glycogen synthesis and suggest a pharmacological profile different from metformin.

Association of insulin resistance to electrocardiographic changes in non obese Asian Indian subjects with hypertension.

To investigate the relationship between insulin resistance and electrocardiographic changes in hypertension in the absence of confounding influences, plasma glucose and insulin responses to oral glucose were studied in 26 normotensive and 38 hypertensive subjects. Resting ECG was taken and classified into normal or abnormal using the Minnesota code. Among the 38 subjects, 16 had ECG abnormalities. All the hypertensive subjects had normal glucose tolerance. Serum insulin response of hypertensive subjects with ECG changes was 43% higher than those of hypertensive subjects without ECG changes and of normotensive subjects. The ratio AUC glucose/AUC insulin, a measure of insulin sensitivity was significantly reduced in subjects with abnormal ECG. Serum LDL cholesterol was significantly elevated and was the highest in hypertensive subjects with abnormal ECG. The ratio, Total Cholesterol/HDL Cholesterol was elevated to 5.81+/-0.47. I(125)-insulin binding to erythrocytes from 6 normotensive subjects, and 16 hypertensive subjects (8 with and 8 without ECG abnormalities) indicated 50% reduction in insulin receptor number in both the groups of hypertensive subjects compared to normotensive subjects. Multiple logistic regression analysis using mean blood pressure, serum total cholesterol, LDL cholesterol/HDL cholesterol, sex, insulin level at 60 min in OGTT, treatment, serum triglyceride, presence of family history of diabetes, CHD, hypertension and tobacco as independent variables causing ECG changes, revealed correct classification in 84% of cases. Among the variables, insulin level in OGTT contributed the most to ECG abnormalities. The data suggest that in the non obese, non diabetic Asian Indian hypertensive subjects, the presence of electrocardiographic abnormalities might be partly related to hyperinsulinemia or insulin resistance in them.

Evaluation of BTS 67 582, a novel antidiabetic agent, in normal and diabetic rats.

1. The effect of BTS 67 582, a novel antidiabetic agent, has been evaluated on plasma glucose and plasma insulin in normal and streptozotocin-induced diabetic rats. 2. BTS 67 582 (3 to 300 mg kg-1, p.o.) caused a dose- and time-dependent reduction in plasma glucose and an increase in plasma insulin in both fasted and glucose-loaded normal rats. The ED50 for the glucose lowering effect of BTS 67 582 in fasted rats was 37.6, 18.4 and 18.5 mg kg-1 at 1, 2 and 4 h after administration respectively. 3. In streptozotocin-induced (50 mg kg-1, i.v.) diabetic rats, BTS 67 582 (37-147 mg kg-1, p.o.) caused significant reductions of plasma glucose following a glucose load, whereas glibenclamide (100 mg kg-1, p.o.) was ineffective. BTS 67 582 significantly increased plasma insulin compared to controls whereas glibenclamide did not. 4. BTS 67 582 did not displace [3H]-glibenclamide from its binding sites in rat brain, guinea-pig ventricle or the HIT-T15 insulinoma beta-cell line. BTS 67 582 does not therefore appear to modulate its action via an effect on the 'sulphonylurea' receptor. 5. In fasted rats, the glucose lowering effect of BTS 67 582 (100 mg kg-1 p.o.) and glibenclamide (1 mg kg-1, p.o.) were antagonized by diazoxide (30 mg kg-1, i.p.). In addition BTS 67 582, like glibenclamide, caused a dose-dependent rightward shift of cromakalim-induced relaxation of noradrenaline precontracted rat aortic strips, suggesting the involvement of KATP channels. 6. In summary, BTS 67 582 produces a blood glucose-lowering effect in normal and streptozotocin-induced diabetic rats associated with increased insulin concentrations. This effect appears to be due to a blockade of ATP-sensitive potassium channel activity via a different binding site to that of glibenclamide.

Anna Pavala Sindhooram, a novel hypolipidemic agent reduces phospholipid levels in atherosclerosis.

Anna Pavala Sindhooram (APS) was investigated in rabbits during atherosclerosis. Changes in the metabolism of plasma and aortic phospholipids were studied by fractionation into individual lipids by tlc and following the incorporation of radiolabel from 14C-acetate into phospholipids. In these studies APS was found to lower the levels of plasma lecithin and aortic sphingomyelin. The effect of APS on plasma lecithin could be partly attributed to its action on synthesis from acetate while synthesis does not account for the effect observed in aortic sphingomyelin levels.

Plasma cholesterol and lipoprotein lowering effect of Anna Pavala Sindhooram.

Plasma lipid and lipoprotein lowering effect of Anna Pavala Sindhooram (APS), a Sidha medicinal preparation was investigated in normal rabbits, chicken and men, and in hypercholesterolemic rabbits. The drug exhibited a marked hypolipaemic and hypocholesterolemic action in the three species studied. In rabbits, marked reduction was observed in very low density lipoprotein cholesterol, while in chicks and in humans low density lipoprotein cholesterol was also reduced significantly when compared to the levels measured before the administration of the drug. The drug enhances faecal elimination of lipids and bile acids in atherosclerotic rabbits.

Effect of Anna Pavala Sindhooram on plasma and aortic lipids in experimental atherosclerosis.

The effect of orally administered Anna Pavala Sindhooram (APS), a herbo-mineral Sidha formulation was investigated on experimental atherosclerosis. Rabbits were fed a cholesterol rich (0.5%) diet for 6 months to induce atherosclerosis. These animals were then divided into six groups and given 50 mg of APS powder/day/animal for a further 6 months. At the end of the experimental period the animals were killed, and their plasma and aortic lipid components estimated. Atherosclerotic lesions of the aorta were quantified and examined histologically. Synthesis of lipids using [14C]acetate as a precursor was studied after i.v. injection. APS was found to be hypolipidemic and induced partial regression of rabbit atheroma and decreased lipogenesis. The results indicate that APS may play an anti-atherogenic role if used in larger doses.