Effects of atorvastatin and pravastatin on glucose tolerance in diabetic rats mildly induced by streptozotocin

Effects of atorvastatin and pravastatin on signal transduction related to glucose uptake in 3T3L1 adipocytes

A number of patients with hyperlipidemia are prescribed 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors that are concomitantly used along with the treatment of diabetes mellitus. The effects of atorvastatin and pravastatin on insulin-induced glucose uptake and the related signal transduction in 3T3L1 adipocytes were studied. 3T3L1 fibroblasts were differentiated into adipocytes, pretreated with atorvastatin or pravastatin, and then exposed to insulin. Glucose uptake and the amount of insulin signal proteins were measured. Atorvastatin significantly decreased insulin-stimulated 2-deoxyglucose uptake in 3T3L1 adipocytes associated with the prevention of translocation of GLUT4 into the plasma membrane. The amounts of Rab4 and RhoA that required lipid modification with farnesyl or geranylgeranyl pyrophosphate, in the membrane fraction were decreased by atorvastatin. Insulin-induced tyrosine phosphorylation of IRS-1 and serine/threonine phosphorylation of Akt were reduced by atorvastatin. Pravastatin did not modify these insulin-induced changes in the signal transduction. Inhibitors of the RhoA/Rho kinase system, C3 and Y27632, as well as atorvastatin reduced insulin-induced changes in signal transduction. Atorvastatin and pravastatin did not affect messenger RNA expression, protein level, and tyrosine phosphorylation of insulin receptors. In conclusion, hydrophobic atorvastatin decreases the glucose uptake by 3T3L1 adipocytes since it can enter the cell and prevents lipid modification of some proteins that are involved in the insulin signal transduction process.

Simvastatin improves flow-mediated dilation but reduces adiponectin levels and insulin sensitivity in hypercholesterolemic patients

OBJECTIVE

We hypothesized that simvastatin may reduce adiponectin levels and insulin sensitivity in hypercholesterolemic patients.

RESEARCH DESIGN AND METHODS

This was a randomized, double-blind, placebo-controlled, parallel study. Age, sex, and BMI were matched. Thirty-two patients were given placebo, and 30, 32, 31, and 31 patients were given daily 10, 20, 40, and 80 mg simvastatin, respectively, during a 2-month treatment period.

RESULTS

Simvastatin doses of 10, 20, 40, and 80 mg significantly reduced total cholesterol (mean changes 27, 25, 37, and 38%), LDL cholesterol (39, 38, 52, and 54%), and apolipoprotein B levels (24, 30, 36, and 42%) and improved flow-mediated dilation (FMD) (68, 40, 49, and 63%) after 2 months of therapy compared with baseline (P < 0.001 by paired t test) or compared with placebo (P < 0.001 by ANOVA). Simvastatin doses of 10, 20, 40, and 80 mg significantly decreased plasma adiponectin levels (4, 12, 5, and 10%) and insulin sensitivity (determined by the Quantitative Insulin-Sensitivity Check Index [QUICKI]) (5, 8, 6, and 6%) compared with baseline (P < 0.05 by paired t test) or compared with placebo (P = 0.011 for adiponectin and P = 0.034 for QUICKI by ANOVA). However, the magnitudes of these percent changes (FMD, adiponectin, and QUICKI) were not significantly different among four different doses of simvastatin despite dose-dependent changes in the reduction of apolipoprotein B levels.

CONCLUSIONS

Simvastatin significantly improved endothelium-dependent dilation, but reduced adiponectin levels and insulin sensitivity in hypercholesterolemic patients independent of dose and the extent of apolipoprotein B reduction.

Simvastatin enhances induction of inducible nitric oxide synthase in 3T3-L1 adipocytes

The present study was designed to determine whether hydroxymethylglutaryl-CoA reductase inhibitors (statins) modulate the NO production via iNOS in adipocytes stimulated by lipopolysaccharide (L) and tumour necrosis factor-alpha (T). Well-differentiated 3T3-L1 adipocytes significantly produced NO by LT-treatment. Pre-incubation with simvastatin, a lipophilic statin, pravastatin, a hydrophilic one, or Y27632, an inhibitor of Rho kinase, further enhanced the production of NO. The effect of simvastatin was offset by mevalonate and geranylgeranyl pyrophosphate (GGPP) but not by squalene. The mRNA level for iNOS parallelled the NO production. The NF-kappaB was activated by the LT-treatment and was further enhanced by simvastatin, pravastatin or Y27632 addition. Mevalonate and GGPP completely offset the effect of simvastatin. Statins and Y27632 also further increased the interleukin-6 secretion in the LT-treated 3T3-L1 adipocytes. These results suggest that statins, especially lipophilic type, enhance induction of iNOS by inhibiting the small GTP-binding protein signal in adipocytes.

Activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) by atorvastatin is mediated by 15-deoxy-delta-12,14-PGJ2

Several studies suggested that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) activate peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Atorvastatin (ATV) increases myocardial levels of prostaglandins (PG) by upregulating and activating cytosolic-phospholipase-A(2) and cycloxygenase-2 (COX2). We investigated whether ATV activates PPAR-gamma via 15-deoxy-delta-12,14-PGJ(2) (15DPGJ(2)) an endogenous ligand of PPAR-gamma and a product of PGD(2), and to compare the effects of pioglitazone (PIO), a known direct PPAR-gamma activator, to that of ATV. First we measured myocardial 15DPGJ(2) levels in the rat heart after a 3-day pretreatment with oral ATV (10 mg/(kg d)), PIO (10 mg/(kg d)), ATV+PIO, ATV+COX1 inhibitor, and ATV+COX2 inhibitor. We also assessed in human umbilical venous endothelial cells (HUVEC) whether ATV and PIO activate PPAR-gamma via 15DPGJ(2) using siRNA targeted to PGD(2) synthase. Both 15DPGJ(2) levels and PPAR-gamma activation were assessed. ATV and PIO increased myocardial 15DPGJ(2) levels in the rat myocardium and HUVEC. siRNA inhibited this increase in both groups. Both ATV and PIO augmented PPAR-gamma activation while co-treatment with siRNA completely blocked the ATV effect but only partially inhibited the PIO effect. In conclusion, both ATV and PIO activate PPAR-gamma and increase myocardial 15DPGJ(2) levels. Activation of PPAR-gamma by ATV is mediated solely by 15DPGJ(2), whereas PIO activates PPAR-gamma both directly and indirectly via 15DPGJ(2).

Effects of pravastatin in murine collagen-induced arthritis

Here we evaluated whether 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have beneficial effects for collagen-induced arthritis (CIA). DBA/1 mice were immunized with bovine type-II collagen and administered 100 mg/kg of pravastatin interperitoneally. We measured the effects of pravastatin for CIA including infiltration of macrophages at the synovial membrane and production of anti-type-II collagen antibodies and cytokines. Adverse reactions of pravastatin were also measured. The pravastatin-treated mice had delayed onset of CIA compared with the controls. The involvement of inflammatory cells in the synovial membrane and the expression of monocyte chemotactic protein-1 (MCP-1) mRNA in the joint were reduced. Moreover, some cytokines (TNF-alpha, IL-6, IFN-gamma) and MCP-1 levels in the supernatants of spleen cells cultured with pravastatin decreased. Meanwhile, adverse reactions of pravastatin, such as peritonitis, were not detected. Pravastatin may have good prospects for treating some anti-inflammatory effects on human rheumatoid arthritis.

Pravastatin improves insulin resistance in dyslipidemic patients

To evaluate the effect of pravastatin on both lipid and glucose metabolism, twenty-two consecutive dyslipidemic patients treated with pravastatin at 10 mg/day for one year were enrolled in this study. The meal test, which consisted of 115 g of cookies (energy 560 kcal; glucose 75 g; protein 7 g; fat 24 g), was conducted before and after one year of treatment. Insulin resistance was assessed by the homeostasis model assessment of insulin resistance (HOMA-IR), by the area under the IRI curve (AUC-IRI), and by the formula AUC-IRI x AUC-PG. After one year of treatment with pravastatin, the plasma glucose (PG), immunoreactive insulin (IRI) and C-peptide levels were unchanged after fasting and at 120 minutes after the meal test; however, PG, IRI and C-peptide levels at 60 minutes after the meal were all significantly decreased from baseline (p < 0.05). AUC-IRI and AUC-IRI x AUC-PG were also significantly decreased (p < 0.05). HOMA-IR was reduced by 26.8%, but the reduction was not significant. The triglyceride (TG) level was decreased after fasting and increased at 60 and 120 minutes after the meal test, but not significantly. This study demonstrated that pravastatin not only reduced serum lipids, but also improved the glucose metabolism, including insulin resistance, of dyslipidemic patients.

Influences of Statins on Glucose Tolerance in Patients with Type 2 Diabetes Mellitus

Atorvastatin is frequently administered for the treatment of hypercholesterolemia associated with type 2 diabetes mellitus. However, a marked deterioration of glycemic control has been reported in some patients treated with atorvastatin. No study has been done to determine whether atorvastatin adversely affects glycemic control. In this study, we retrospectively compared an atorvastatin-treated group (Group A, n = 76) with a pravastatin-treated group (Group P, n = 78) to examine the effects of the 2 statins on glycemic control from the onset of administration to 3 months thereafter. No change occurred in the antidiabetic drug dose in 62 patients of Group A and 68 patients of Group P. In those patients, arbitrary blood glucose levels increased from 147 +/- 50 (mean +/- SD) mg/dL to 177 +/- 70 mg/dL in Group A and from 140 +/- 38 mg/dL to 141 +/- 32 mg/dL in Group P. HbA(1c) increased from 6.8 +/- 0.9% to 7.2 +/- 1.1% in Group A and from 6.9 +/- 0.9% to 6.9 +/- 1.0% in Group P. The increase was significant only in Group A, and the extent of the increase was also significantly greater in Group A. These results suggest a predisposition to a deterioration of glycemic control in type 2 diabetic patients treated with atorvastatin.

Atorvastatin induces insulin sensitization in Zucker lean and fatty rats

BACKGROUND

The 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors ('statins') have been implicated in preventing new onset type 2 diabetes, whereas the mechanism of this effect is not known. We investigated the effects of an HMG-CoA reductase inhibitor, atorvastatin, on insulin sensitization in Zucker lean and fatty rats.

METHODS AND RESULTS

In vivo studies of insulin sensitization were performed in chow fed Zucker lean and fatty rats treated with atorvastatin 50mg/kg/day (ATORVA_50) and results were compared to Zucker lean and fatty rats treated with drug vehicle only (CONT). Additional Zucker lean rats were treated with an intermediate dose of atorvastatin 25mg/kg/day (ATORVA_25). Treatment with atorvastatin resulted in a dose-dependent improvement in whole body insulin sensitivity in both lean and fatty rats, with an approximately two-fold increase in glucose infusion rate and glucose disposal (Rd) in ATORVA_50 versus CONT (p<0.01). Atorvastatin 50mg/kg/day resulted in an increase in 2-deoxyglucose (2-DOG) uptake by skeletal muscles (approximately two-fold increase in 2-DOG uptake in quadriceps (p=0.06) and gastrocnemius (p<0.01)) in lean Zucker rats. Insulin-stimulated phosphorylation of Akt/PKB was significantly increased in skeletal muscle of ATORVA_50 versus CONT in both lean and fatty rats.

CONCLUSION

Atorvastatin induces insulin sensitization in Zucker lean and fatty rats. This may be a clinically important pleiotropic effect if confirmed in insulin resistant humans.

Diabetes: insulin resistance and derangements in lipid metabolism. Cure through intervention in fat transport and storage

We present multiple findings on derangements in lipid metabolism in type 2 diabetes. The increase in the intracellular deposition of triglycerides (TG) in muscles, liver and pancreas in subjects prone to diabetes is well documented and demonstrated to attenuate glucose metabolism by interfering with insulin signaling and insulin secretion. The obesity often associated with type 2 diabetes is mainly central, resulting in the overload of abdominal adipocytes with TG and reducing fat depot capacity to protect other tissues from utilizing a large proportion of dietary fat. In contrast to subcutaneous adipocytes, the central adipocytes exhibit a high rate of basal lipolysis and are highly sensitive to fat mobilizing hormones, but respond poorly to lipolysis restraining insulin. The enlarged visceral adipocytes are flooding the portal circulation with free fatty acids (FFA) at metabolically inappropriate time, when FFA should be oxidized, thus exposing nonadipose tissues to fat excess. This leads to ectopic TG accumulation in muscles, liver and pancreatic beta-cells, resulting in insulin resistance and beta-cell dysfunction. This situation, based on a large number of observations in humans and experimental animals, confirms that peripheral adipose tissue is closely regulated, performing a vital role of buffering fluxes of FFA in the circulation. The central adipose tissues tend to upset this balance by releasing large amounts of FFA. To reduce the excessive fat outflow from the abdominal depots and prevent the ectopic fat deposition it is important to decrease the volume of central fat stores or increase the peripheral fat stores. One possibility is to downregulate the activity of lipoprotein lipase, which is overexpressed in abdominal relatively to subcutaneous fat stores. This can be achieved by gastrointestinal bypass or gastroplasty, which decrease dietary fat absorption, or by direct means that include surgical removal of mesenteric fat. Indirect treatment consists of the compliant application of drastic lifestyle change comprising both diet and exercise and pharmacotherapy that reduces mesenteric fat mass and activity. The first step should be an attempt to effectively induce a lifestyle change. Next comes pharmacotherapy including acarbose, metformin, PPARgamma, or PPARgammaalpha agonists, statins and orlistat, estrogens in postmenopausal women or testosterone in men. Among surgical procedures, gastric bypass has been proven to produce beneficial results in advance of other surgical techniques, the evidence basis of which still needs strengthening.

HMG-CoA Reductase Inhibitors Do Not Improve Glucose Intolerance in Spontaneously Diabetic Goto-Kakizaki Rats

We examined whether 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) improve glucose intolerance in spontaneously diabetic Goto-Kakizaki (GK) rats or not. The fasting blood glucose, plasma insulin, and serum cholesterol levels were significantly higher in GK rats than those in age-matched Wistar rats. All rats were given orally once a day 0.5% carboxymethylcellulose, pravastatin 8 mg/kg, simvastatin 8 mg/kg, or atorvastatin 8 mg/kg. An oral glucose tolerance test (OGTT) was performed before and 3, 6 and 12 weeks after statin treatments. The hyperglycemic response to OGTT in GK rats significantly exceeded that in Wistar rats. The plasma insulin level in GK rats increased with age until 14-week-old (treated for 6 weeks), and then decreased. Glucose intake significantly increased the plasma insulin in almost all rats. The increment of plasma insulin due to OGTT in GK rats appeared to be less than that in Wistar rats, because the basal level was already high in GK rats. Pravastatin, simvastatin, and atorvastatin did not modify changes in blood glucose and plasma insulin induced by glucose intake. In conclusion, long-term treatments of GK rats with statins did not improve glucose intolerance observed during OGTT.