Effects of troglitazone on dexamethasone-induced insulin resistance in rats

Anti-Atherosclerotic Potential of Aqueous Extract of Cinnamomum Zeylanicum Bark against Glucocorticoid Induced Atherosclerosis in Wistar Rats

INTRODUCTION

Atherosclerosis is one of the major causes of disability of blood vessels which can result in development of many cardiovascular disorders. There is a strong association between atherosclerosis and insulin resistance and dyslipidemia.

AIM

To study the anti-atherosclerotic potential of C. zeylanicum bark extract in insulin resistance associated atherosclerosis and worsened Atherogenic Index (AI) associated with dyslipidemia, which are the predominant complications of steroid diabetes in Wistar rats.

MATERIALS AND METHODS

A sum of 36 rats were categorized into five study groups and one plain control. In a 12 day study period, respective drug treatments were given every day throughout the study period whereas, dexamethasone dosage was started from day seven onwards. On day 12, fasting blood samples were collected and processed for lipid estimation and the determined values were also used to assess AI further. Animals were sacrificed under ether anaesthesia and the aorta was dissected away for its measurement and histopathological findings. One-way ANOVA was used to analyse the data and multiple comparison was done, interpreted based on Post-Hoc Scheffe test.

RESULTS

High dose of dexamethasone (8 mg/kg/i.p) in Dexa Control (DC) group produced significant dyslipidemia, increased risk of atherogenicity (p<0.05) and caused severe thickening (78.5% compared to Plain Control (PC) of wall of aorta. Rosiglitazone (ROSI) (8 mg/kg and 16 mg/kg) and C. zelanicum (CZE) extract treatments (500 mg/kg and 250 mg/kg) significantly prevented dyslipidemia, well maintained AI compared to dexa control (p<0.05). However, both the CZE treatments protected the aorta from atherosclerosis (40.3% and 30.2% compared to DC) and significantly prevented the dyslipidemia and reduced the risk of atherogenicity compared to ROSI treatment (p<0.05). Although, the CZE did not show difference in significance in maintaining very low density lipoprotein when compared to ROSI (p>0.05). The atherosclerotic changes were completely absent in both the CZE treatments whereas, ROSI treatments did not prevented the atherosclerosis of aorta completely as they showed moderate and mild atherosclerotic changes in the aorta.

CONCLUSION

The aqueous extract of C. zelanicum bark exhibited marked protection against dexamethasone induced atherosclerosis and also minimized the atherogenic risk in Wistar rats.

Thiazolidinediones attenuate lipolysis and ameliorate dexamethasone-induced insulin resistance

BACKGROUND

Elevated levels of circulating free fatty acids induce insulin resistance and often occur in obese and diabetic conditions. One pharmacological basis for the antidiabetic effects of thiazolidinediones (TZDs) is that TZDs reduce levels of circulating FFAs by accelerating their uptake and reesterification from plasma into adipocytes. Here, we investigated whether TZDs affect adipose lipolysis, a process controlling triglyceride hydrolysis and FFA efflux to the bloodstream.

METHODS

The effects of TZDs on lipolysis were investigated in primary rat adipocytes in vitro and in rats in vivo.

RESULTS

In rat primary adipocytes, the TZDs pioglitazone, rosiglitazone and troglitazone inhibited the lipolytic reaction dose- and time-dependently and in a post-receptor pathway by decreasing cAMP level and total lipase activity. TZDs increased the phosphorylation of Akt/protein kinase B, an action required for activating cyclic-nucleotide phosphodiesterase 3B, a major enzyme responsible for cAMP hydrolysis in adipocytes. Furthermore, rosiglitazone inhibited the lipolytic action in dexamethasone-stimulated adipocytes, thereby preventing the increased level of circulating FFAs, and ameliorated insulin resistance in vivo in dexamethasone-treated rats.

CONCLUSIONS

TZDs may attenuate lipolysis and FFA efflux by activating Akt signaling to decrease cAMP level and hence reduce lipase activity in adipocytes. Inhibiting lipolysis and FFA efflux with TZDs could be a pharmacological basis by which TZDs antagonize diabetes, particularly in patients with hypercortisolemia or glucocorticoid challenge.

Dose Dependent Hepatic and Endothelial Changes in Rats Treated with Dexamethasone

AIMS AND OBJECTIVES

To study the effect of dexamethasone on liver and endothelium, and to determine the optimum dose which induces the abnormal changes in liver and endothelium in Wistar rats.

MATERIALS AND METHODS

Albino Wistar rats were divided into 7 groups (n=6). Control group rats received normal saline. Graded doses of dexamethasone (0.5,1,2,4,8 and 16mg/kg/ i.p.) was administered to the groups for six days. Liver and aorta were dissected at the end of the study and examined for histopathological changes under microscope.

RESULTS

Intraperitoneal administration of dexamethasone (4,8 and 16mg/kg) for six days resulted in fatty changes in liver and same doses have shown thickening of endothelial layers in aorta, in comparison to control group. There were not much significant changes seen in low doses of dexamethasone (0.5, 1 and 2mg/kg).

CONCLUSION

It is concluded that the acute high doses of dexamethasone (4,8 and 16mg/kg) for six days caused hepatic steatosis and showed mild to moderate arteriosclerosis in aorta. These changes may be secondary consequences of insulin resistance. Hence, it can be used as new animal model to screen the various plants and medicines in the treatment of insulin resistance.

Chronic prednisolone treatment aggravates hyperglycemia in mice fed a high-fat diet but does not worsen dietary fat-induced insulin resistance

Synthetic glucocorticoids such as prednisolone have potent antiinflammatory actions. Unfortunately, these drugs induce severe adverse effects in patients, many of which resemble features of the metabolic syndrome, such as insulin resistance. In this study, we investigated whether adverse effects of prednisolone on glucose homeostasis are aggravated in mice with compromised insulin sensitivity due to a high-fat diet by applying various methods to analyze changes in insulin sensitivity in mice. C57BL/6J mice were fed a high-fat diet for 6 wk and treated with either prednisolone (10 mg/kg · d) or vehicle for the last 7 d. Insulin sensitivity and blood glucose kinetics were analyzed with state-of-the-art stable isotope procedures in different experimental conditions. Prednisolone treatment aggravated fasting hyperglycemia and hyperinsulinemia caused by high-fat feeding, resulting in a higher homeostatic assessment model of insulin resistance. In addition, prednisolone-treated high-fat diet-fed mice appeared less insulin sensitive by detailed analysis of basal glucose kinetics. Remarkably, using hyperinsulinemic-euglycemic or hyperglycemic clamp techniques, neither hepatic nor peripheral insulin resistance was worsened in the group that was treated with prednisolone. Yet analysis of hepatic glucose metabolism revealed that prednisolone did alter glycogen balance by reducing glycogen synthase flux under hyperinsulinemic as well as hyperglycemic conditions. In addition to elevated insulin levels, prednisolone-treated mice showed a major rise in plasma leptin and fibroblast growth factor 21 levels. Our data indicate that prednisolone-induced adverse effects on glucose metabolism in high-fat diet-fed mice do not reflect impaired insulin sensitivity but may be caused by other changes in the hormonal regulatory network controlling glucose metabolism such as fibroblast growth factor 21 and leptin.

Evaluation of weekly-reduction regimen of glucocorticoids in combination with cyclophosphamide for anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis in Japanese patients

The current therapeutic regimen recommended by the European League against Rheumatism (EULAR) for anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) is continuation of initially administered doses of glucocorticoids (GCs) in combination with cyclophosphamide (CYC) for 1 month followed by gradual tapering. Considering the adverse effects of GCs, another tapering regimen of GCs with CYC, which was characterized by tapering GCs weekly, was reported by the British Society of Rheumatology (weekly-reduction regimen). The aim of the present study is to evaluate the safety and efficacy of this weekly-reduction regimen for Japanese AAV patients in comparison with the monthly-reduction regimen recommended by the EULAR. We retrospectively reviewed medical records of adult patients newly diagnosed with AAV during the period from April 2000 to December 2010. The outcome measures were rates of remission, relapse, infection, and GC-induced diabetes mellitus during the first 12 months. Clinical data in the two groups and categorial variables with a possible relation to the outcomes were compared by using the t test and chi-square test, respectively. Twenty-four patients were enrolled in our study. All of the patients achieved remission, and the rates of relapse during the first 12 months were not statistically different between the two groups (P = 0.16). Patients treated with the weekly-reduction regimen were less liable to have infection (P = 0.03) and impaired glucose tolerance (P = 0.017), compared with those treated with the monthly-reduction regimen. A therapeutic strategy using the weekly-reduction regimen of GCs would be effective and would have fewer side effects than the monthly-reduction regimen.

Fat feeding potentiates the diabetogenic effect of dexamethasone in Wistar rats

Background

The role of cortisol and its increased action/availability is implicated in the pathogenesis of insulin resistance associated with obesity and metabolic syndrome but the mechanism of increased action/availability is not known. Availability of several other lipophilic hormones, drugs and pollutants are also reported to be increased in obesity. Increased lipids in the circulation are reported to alter the fluidity and permeability of membranes. Hyperlipidemia is also reported to alter the pharmacokinetics and pharmacodynamics of lipophilic molecules and also membrane fluidity and permeability. In this context we assumed that the hyperlipidemia associated with human obesity might play a role in the altered action/availability of cortisol and this in turn might have initiated the metabolic complications. To evaluate our assumption we have administered dexamethasone [low [50 μg/kg/day] or high [250 μg/kg/day] dose] to high-fat [coconut oil & vanaspati] fed rats and the results were compared with rats administered with either dexamethasone or high-fat.

Results and Discussion

Within two weeks, the rats co-administered with high-fat and dexamethasone developed severe hyperglycemia, hyperlipidemia and insulin resistance compared to rats treated either of them alone. High-fat fed rats treated with higher dose of dexamethasone were presented with severe hyperglycemia, insulin resistance and also severe glycosuria. The hyperlipidemia caused by high-fat feeding might have altered the transport and distribution of dexamethasone, probably by altering the physical state of membranes and transport proteins.

Conclusion

From the results obtained, it can be speculated that the altered lipid and cortisol metabolism could affect one another, forming a vicious cycle.

Effect of dexamethasone on glucose tolerance and fat metabolism in a diet-induced obesity mouse model

Prolonged exposure to elevated glucocorticoid levels is known to produce insulin resistance (IR), a hallmark of diabetes mellitus. Although not fully elucidated, the underlying molecular mechanisms by which glucocorticoids induce IR may provide potential targets for pharmacological interventions. Here we characterized muscle lipid metabolism in a dexamethasone-aggravated diet-induced obesity murine model of IR. Male C57BL/6 mice on a high-fat diet for 2 months when challenged with dexamethasone showed elevated food consumption and weight gain relative to age and diet-matched animals dosed with saline only. Dexamethasone treatment impaired glucose tolerance and significantly increased the intramyocellular lipid content in the tibialis anterior muscle (TA). A good correlation (r = 0.76, P < 0.01) was found between accumulation in intramyocellular lipid content in the TA and visceral adiposity. The linoleic acid (18:2) to polyunsaturated acid ratio was increased in the dexamethasone-treated animals (+29%; P < 0.01), suggesting a possible increase in stearoyl-CoA desaturase 2 activity, as reported in Sertoli cells. The treatment was also accompanied by a reduction in the percent fraction of omega-3 and long-chain polyunsaturated fatty acids in the TA. Analysis of the low-molecular-weight metabolites from muscle extracts showed that there was no dysregulation of muscle amino acids, as has been associated with dexamethasone-induced muscle proteolysis. In conclusion, dexamethasone-induced insulin resistance in diet-induced obese mice is associated with a profound perturbation of lipid metabolism. This is particularly true in the muscle, in which an increased uptake of circulating lipids along with a conversion into diabetogenic lipids can be observed.

Effective use of thiazolidinediones for the treatment of glucocorticoid-induced diabetes

We evaluated the efficacy of a thiazolidinedione in the treatment of diabetes induced by glucocorticoids. We examined the effectiveness of troglitazone in seven patients with long-standing steroid-induced diabetes. Five of the seven subjects were treated with insulin alone, one was treated with both insulin and oral therapy and one was treated with oral therapy alone. The mean insulin dose in six of the seven subjects was 0.66+/-0.09 units/kg per day. Diabetes status was assessed by measuring serum fructosamine, HgbA1c, oral glucose and meal tolerance tests (OGTT and MTT) at baseline and after treatment for 5-8 weeks with troglitazone 400 mg/day. Troglitazone caused a significant decrease in fructosamine (274+/-32 vs. 217+/-22 mmol/l; P<0.01) and HgbA1C (7.8+/-0.4 vs. 7.2+/-0.4%; P<0.01) as well as decrements in the areas under the OGTT 2,308+/-156 vs. 1,937+/-127 mmol/l; P<0.05) and MTT glucose curves (4694+/-449 vs. 4057+/-437 mmol/l; P<0.05). In addition, the area under the insulin curve for the oral glucose tolerance test showed a significant increase from 27,438+/-4,488 to 41,946+/-6,048 pmol/l (P<0.05). Total and LDL cholesterol were also significantly decreased (6.4+/-0.9 vs. 5.0+/-0.6 mmol/l and 3.8+/-0.7 vs. 2.7+/-0.4 mmol/l, respectively, P<0.05). Fasting leptin values decreased by 23% despite an increase in body weight. Troglitazone is effective in the treatment of glucocorticoid-induced diabetes as manifested by lower measures of glycemia, HgbA1c, and post-prandial glucose values, while the doses of other diabetes medications remained unchanged or were reduced. The insulin-sensitizing drug also produced a marked increase in endogenous insulin secretion in response to glucose, lower total and LDL cholesterol, and decreased fasting leptin despite weight gain. Thiazolidinediones may improve diabetes-related parameters by antagonizing pathways of glucocorticoid-induced insulin resistance and by reversing adverse effects of glucocorticoids on beta cell function.

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.

Pharmacological peroxisome proliferator-activated receptorgamma ligands: emerging clinical indications beyond diabetes

The discovery of peroxisome proliferator-activated receptor gamma (PPARgamma) as the molecular target for antidiabetic thiazolidinediones has heralded a new era in the approach to understanding the pathophysiology of insulin resistance and its relationship to cardiovascular disease. However, the subsequent discovery of PPARgamma-dependent modulation of immune function and the cell cycle has led to a new paradigm in the approach to treating proliferative, inflammatory diseases. Moreover, PPARgamma agonists can promote apoptosis, block angiogenesis and inhibit pathological remodelling in a variety of malignant and non-malignant pathological states. These findings imply that the pharmacological modulation of this key nuclear transcription factor and its co-factors could be important tools in understanding the relationships between multigenic diseases, and pave the way to a focused interventional approach in their treatment. With the availability of the PPARgamma protein crystal structure, the ligand binding domain co-ordinates and a better knowledge of the interaction of PPARgamma with co-factor assemblies, libraries of simple synthetic organic PPARgamma ligands can be constructed. High throughput screening can identify the best candidates for targeting cellular phenotypic transition, cell cycle control, inflammation and apoptosis. Instead of single agents for single pathologies, one can envisage the development of multifunctional therapeutic agents that target the multiple cellular processes that contribute to multifactorial diseases such as diabetes, hypertension, atherosclerosis, psoriasis and other inflammatory diseases, and carcinogenesis. The considerable potential of PPARgamma ligands in the treatment of diseases other than diabetes is the subject of this review.

Differential effects of troglitazone and D-chiroinositol on glucosamine-induced insulin resistance in vivo in rats

Troglitazone and D-chiroinositol have been shown to exert antidiabetic effects by either potentiating or mimicking insulin action. We studied whether pretreatment with these compounds can prevent the deleterious effects of glucosamine on insulin action that may play an important role in hyperglycemia-induced insulin resistance. Normal Wistar rats were pretreated with troglitazone (100 mg/kg/d), D-chiroinositol (100 mg/kg/d), or placebo (saline) for 7 days. Glucosamine (50 micromol/kg/min) was then infused for 210 minutes, and a euglycemic glucose clamp was performed during the last 120 minutes. Pretreatment with troglitazone or D-chiroinositol had no effect on fasting plasma glucose or insulin or basal hepatic glucose output (HGO). Under the euglycemic-hyperinsulinemic (956+/-93 pmol/L) clamp condition, HGO in glucosamine-infused placebo-treated rats was not suppressed, but instead was increased over the basal level, indicative of hepatic insulin resistance. In contrast, HGO failed to increase during glucosamine infusion in rats pretreated with troglitazone but was not normally suppressed. This may indicate a partial improvement in the hepatic insulin resistance. D-Chiroinositol pretreatment had no effect on the glucosamine-induced increase in HGO. The glucose disposal rate (GDR) was 25% lower in rats infused with glucosamine versus saline-infused rats (25.5+/-2.5 v 34.1+/-2.0 mg/kg/min), indicative of peripheral insulin resistance. Pretreatment with D-chiroinositol (34.5+/-2.3 mg/kg/min) prevented the glucosamine-induced decrease in the GDR, indicating an improvement in peripheral insulin resistance. Troglitazone (25.2+/-3.3 mg/kg/min) was without effect. In conclusion, (1) in normal control rats, glucosamine infusion induced hepatic and peripheral insulin resistance; (2) D-chiroinositol, but not troglitazone, pretreatment prevented glucosamine-induced peripheral insulin resistance; and (3) troglitazone, but not D-chiroinositol, partially blocked the glucosamine-induced hepatic insulin resistance. D-Chiroinositol may provide a novel pharmacological approach to hexosamine-induced peripheral insulin resistance.