Rosiglitazone short-term monotherapy lowers fasting and post-prandial glucose in patients with type II diabetes

Peroxisome proliferator-activated receptors--from active regulators of macrophage biology to pharmacological targets in the treatment of cardiovascular disease

Altered macrophage functions contribute to the pathogenesis of many infectious, immunological and inflammatory disease processes. Pharmacological modulation of macrophage activities therefore represents an important strategy for the prevention and treatment of inflammation-related diseases, such as atherosclerosis. This review focuses on recent advances on the role of the peroxisome proliferator-activated receptor transcription factor family in the modulation of lipid homeostasis and the inflammatory response in macrophages and the potential participation of these actions in the modulation of metabolic and cardiovascular disease.

Peroxisome proliferator-activated receptor-gamma agonists and diabetes: current evidence and future perspectives

Since their initial availability in 1997, the thiazolidinediones (TZDs) have become one of the most commonly prescribed classes of medications for type 2 diabetes. In addition to glucose control, the TZDs have a number of pleiotropic effects on myriad traditional and non-traditional risk factors for diabetes. TZDs may benefit cardiovascular parameters, such as lipids, blood pressure, inflammatory biomarkers, endothelial function and fibrinolytic state. In this review, we summarise the experimental, preclinical and clinical data regarding the effects of the TZDs in conditions for which they are indicated and discuss their potential in the treatment of other conditions.

Insulin signaling and glucose transport in insulin resistant human skeletal muscle

Insulin increases glucose uptake and metabolism in skeletal muscle by signal transduction via protein phosphorylation cascades. Insulin action on signal transduction is impaired in skeletal muscle from Type 2 diabetic subjects, underscoring the contribution of molecular defects to the insulin resistant phenotype. This review summarizes recent work to identify downstream intermediates in the insulin signaling pathways governing glucose homeostasis, in an attempt to characterize the molecular mechanism accounting for skeletal muscle insulin resistance in Type 2 diabetes. Furthermore, the effects of pharmaceutical treatment of Type 2 diabetic patients on insulin signaling and glucose uptake are discussed. The identification and characterization of pathways governing insulin action on glucose metabolism will facilitate the development of strategies to improve insulin sensitivity in an effort to prevent and treat Type 2 diabetes mellitus.

Measuring biomarkers to assess the therapeutic effects of PPAR agonists?

The metabolic syndrome is defined as a clustering of cardiovascular risk factors with insulin resistance, including dyslipidemia, coagulation disturbances and hypertension. Activators of the peroxisome proliferator-activated receptors (PPARs) modulate several of the metabolic risk factors predisposing to atherosclerosis. Fibrates are hypolipidemic drugs acting through activation of PPARα, whereas glitazones are insulin sensitizers activating PPARγ. In addition, these drugs exert pleiotropic anti-inflammatory actions. In this review, we will focus on the effects of fibrates and glitazones on biomarker modulation and their usefulness in the treatment of cardiovascular disease.

Ala12 variant of the peroxisome proliferator-activated receptor-gamma gene (PPARG) is associated with higher polyunsaturated fat in adipose tissue and attenuates the protective effect of polyunsaturated fat intake on the risk of myocardial infarction

BACKGROUND

Intake of polyunsaturated fat is protective against the development of coronary heart disease. Less is known about the genetic variation modulating this association. The Ala12 allele of the peroxisome proliferator-activated receptor-gamma gene (PPARG) decreases the lipolysis of triacylglycerols in adipose tissue, which results in the accumulation of fatty acids in adipocytes.

OBJECTIVE

We aimed to determine whether the Pro12Ala polymorphism interacts with polyunsaturated fat intake to affect the risk of myocardial infarction (MI).

DESIGN

Cases (n = 1805) with a first nonfatal acute MI and population-based controls matched by age, sex, and area of residence (n = 1805) living in Costa Rica were genotyped for the PPARG Pro12Ala genetic polymorphism. Polyunsaturated fat intake was determined by use of a validated food-frequency questionnaire and by gas chromatography analysis of adipose tissue. Odds ratios and 95% CIs for MI were estimated by use of logistic regression.

RESULTS

The relative allele frequencies of the Ala12 allele were 10% in controls and 11% in cases. Odds ratios (95% CI) for MI per each 5% increase in energy from polyunsaturated fat were 0.66 (0.53, 0.82) in Pro12/Pro12 subjects and 0.93 (0.61, 1.42) in carriers of the Ala12 allele (P for interaction = 0.03). Increments (95% CI) of polyunsaturated fat in adipose tissue per 5% increment in dietary intake were 5.4% (4.9%, 5.9%) in Pro12/Pro12 homozygotes, 6.9% (6.0%, 7.9%) in Pro12/Ala12 heterozygotes, and 7.7% (3.2%, 12.2%) in Ala12/Ala12 homozygotes (P for interaction = 0.016).

CONCLUSIONS

The protective effect of polyunsaturated fat intake on MI is attenuated in carriers of the Ala12 allele of PPARG.

The different mechanisms of insulin sensitizers to prevent type 2 diabetes in OLETF rats

OBJECTIVE

To investigate the effects of pioglitazone and metformin treatment during pre-diabetic period for the prevention of diabetes in a rat model.

METHODS

OLETF rats aged 18-weeks, were treated with pioglitazone (10 mg/kg/day) and metformin (300 mg/kg/day) for 10 weeks from their pre-diabetic period. We measured weight, lipid profiles, fat distribution, glucose tolerance, and pancreatic insulin content.

RESULTS

Prominent weight gain (mostly subcutaneous fat area) was observed in the pioglitazone-treated OLETF (O-P) rats versus significant weight loss was observed in the metformin-treated OLETF (O-M) rats. Pioglitazone reversed the serum triglyceride (TG) and FFAs levels to normal (TG 0.46 +/- 0.04 vs 0.88 +/- 0.05 mmol/l in LETO). At the age of 28 weeks, the O-P rats showed completely normal glucose tolerance, and the glucose disposal rate (GDR) was markedly improved (25.6 +/- 0.4 vs 20.6 +/- 0.5 mg/min/kg in O-C, p < 0.05). The O-M rats also showed an improved fasting glucose and GDR level, but not as much as those with O-P rats. The pancreas insulin contents were much improved in the O-P rats (22.9 +/- 1.2 vs 18.8 +/- 1.3 nmol/pancreas in O-M rats, p < 0.05) with histological improvement.

CONCLUSION

The pre-diabetic treatment with pioglitazone, despite significant weight gain, completely prevents to develop diabetes and enhances beta cell function with preservation of islet cell changes. Metformin treatment was also effective, but mainly by ameliorating the insulin resistance with marked reduction in body weight. The reversal of dyslipidaemia and the fat redistribution might contribute to the greater improvement of pioglitazone treatment compared to metformin in OLETF rats.

A one-year study comparing the efficacy and safety of rosiglitazone and glibenclamide in the treatment of type 2 diabetes

BACKGROUND AND AIM

This study was designed to compare the efficacy of rosiglitazone and glibenclamide in individuals with type 2 diabetes over a 12-month period.

METHODS AND RESULTS

A total of 598 patients were randomized to double-blind treatment for 52 weeks with rosiglitazone 4 mg/d (n=200), rosiglitazone 8 mg/d (n=191) or glibenclamide (n=207; dose adjusted up to 15 mg/d over the first 12 weeks according to clinical response). Changes in fasting plasma glucose (FPG), haemoglobin A1c (HbA1c), fasting insulin and its precursor peptides, and lipids were measured and safety was evaluated. Significant reductions in HbA1c levels at 52 weeks compared with baseline were seen in all treatment groups (rosiglitazone 4 mg/d=-0.3%, P=0.0003; rosiglitazone 8 mg/d=-0.5%, P<0.0001; glibenclamide=-0.7%, P<0.0001). Mean FPG levels were also significantly reduced in all treatment groups (rosiglitazone 4 mg/d=-1.4 mmol/l; rosiglitazone 8 mg/d=-2.3 mmol/l; glibenclamide=-1.7 mmol/l; P<0.0001 vs. baseline for all treatments). Rosiglitazone therapy reduced plasma insulin, proinsulin, split proinsulin and free fatty acid levels compared with glibenclamide. Rosiglitazone improved insulin resistance while a worsening was seen with glibenclamide. Total:high-density lipoprotein cholesterol ratios were reduced with glibenclamide and unchanged with rosiglitazone. All treatments were generally well tolerated.

CONCLUSIONS

The efficacy of rosiglitazone 8 mg/d in improving glycaemic control in patients with type 2 diabetes is comparable to that of glibenclamide. However, rosiglitazone reduced insulin resistance and proinsulin levels whereas glibenclamide use was associated with an increase in fasting insulin and proinsulin. This suggests that in the long term, rosiglitazone may protect the beta-cell whereas glibenclamide is likely to increase the burden.

Dual PPAR α/γ Agonists: Promises and Pitfalls in Type 2 Diabetes

Type 2 diabetes mellitus is a disease of complex pathogenesis and pleiotropic clinical manifestations. The greatest clinical challenge in this disease is the prevention of the long-term complications, many of which involve cardiovascular outcomes. The peroxisome proliferator-activated receptor (PPAR) alpha and gamma isoforms of the family of nuclear transcription factors are pharmaceutical targets for therapeutic intervention because they can potentially ameliorate not only the hyperglycemia of diabetes, but also the dyslipidemia that is characteristic of this disorder (low high-density lipoprotein cholesterol, high triglycerides, small, dense low-density lipoprotein particles). Novel drugs with dual PPAR alpha and gamma activity have been under clinical development for type 2 diabetes, and they have shown promise in early studies with regard to glucose lowering and improved lipid profile when compared with the PPAR-gamma-specific thiazolidinediones. Unfortunately, the dual PPARs available to date have some of the PPAR-gamma-associated side effect profile, including fluid retention and weight gain, which have limited the further clinical development of higher doses that show improved efficacy. This review will briefly summarize our understanding of the pathogenesis of type 2 diabetes, the role of the PPAR family of receptors, and the potential for clinical use of this novel emerging class of agents that serve as dual activators of both PPAR-alpha and PPAR-gamma.

Effects of eicosapentaenoic acid on the early stage of type 2 diabetic nephropathy in KKA(y)/Ta mice: involvement of anti-inflammation and antioxidative stress

Eicosapentaenoic acid (EPA) has been reported to have beneficial effects on the progression of various renal diseases including diabetic nephropathy; however, the precise mechanisms are not completely understood. We examined the effects of EPA on the early stage of type 2 diabetic nephropathy in KKA(y)/Ta mice and the possible role of inflammation, oxidative stress, and growth factor in this process. KKA(y)/Ta mice were divided into 2 groups. The treatment group was injected with EPA ethyl ester at 1 g/kg per day intraperitoneally from 12 to 20 weeks of age and the control group was injected with saline. Renal morphologic examinations were performed after 8 weeks of treatment. Glomerular macrophage infiltration and expression of monocyte chemoattractant protein 1, malondialdehyde (MDA), nitrotyrosine, transforming growth factor beta1 (TGF-beta1), and type I collagen were evaluated. Eicosapentaenoic acid decreased the levels of urinary albumin, serum triglyceride and MDA, and improved glucose intolerance in KKA(y)/Ta mice. Morphometric analysis showed that accumulation of extracellular matrix and the tubulointerstitial fibrosis area were significantly decreased after treatment. Immunohistochemistry revealed that glomerular macrophage infiltration and the expression of MDA and nitrotyrosine in KKA(y)/Ta mice were increased and were inhibited by EPA treatment. Protein and gene expression levels of monocyte chemoattractant protein 1, TGF-beta1, and type I collagen, which were evaluated by immunohistochemistry and real-time reverse transcriptase-polymerase chain reaction, were down-regulated in the EPA treatment group. In conclusion, EPA improves type 2 diabetic nephropathy in KKA(y)/Ta mice. This beneficial effect might be mediated by attenuation of metabolic abnormalities and inhibition of renal inflammation, oxidative stress, and TGF-beta expression.

Factors associated with the effect-size of thiazolidinedione (TZD) therapy on HbA(1c): a meta-analysis of published randomized clinical trials

OBJECTIVE

To examine factors affecting the size of the HbA(1c) response to thiazolidinedione (TZD) therapy.

RESEARCH DESIGN AND METHODS

Meta-analysis of randomized TZD controlled trials which were identified using PubMed, EBSCO and Sci-lit databases and were published in English. Sociodemographic and clinical data were extracted from each trial. HbA(1c) effect size was defined as either a placebo-subtracted change in HbA(1c) or a change in HbA(1c) from baseline. Weighted multivariable regression was used to examine factors associated with changes in HbA(1c). Bootstrapped smearing estimates were computed to obtain reliable estimates of HbA(1c) effect size.

RESULTS

Forty-two trials yielded 60 trial arms which represented 8322 patients treated with thiazolidinediones. Weighted placebo-subtracted change in HbA(1c) was -0.99% +/- 0.02% with an average baseline HbA(1c) of 9.1% +/- 1.0%. Weighted bootstrapped smearing estimate of the placebo-subtracted change in HbA(1c) was -1.02% +/- 0.004%. After controlling for other variables, the baseline HbA(1c) level had a significant negative association with placebo-subtracted HbA(1c) change (p = 0.004) and also with change in HbA(1c) from baseline (p = 0.002). Longer trial duration was associated with greater placebo-subtracted HbA(1c) change (p = 0.01) but not with the change in HbA(1c) from baseline. The multivariable models explained 72% of the variation in placebo-subtracted HbA(1c) change. It was not possible to estimate effects of the run-in period and obesity on TZD effect size.

CONCLUSION

Baseline HbA(1c) and trial duration significantly impacted the effect size of TZD therapy on HbA(1c). Age, gender, duration of diabetes and prior use of anti-diabetic therapy were not associated with the TZD effect size.

The long-term effects of rosiglitazone on serum lipid concentrations and body weight

OBJECTIVE

Although rosiglitazone, an insulin sensitizer, is known to have beneficial effects on high density lipoprotein cholesterol (HDL-C) concentrations and low density lipoprotein (LDL) particle size, it has unwanted effects on total cholesterol (TC) and LDL cholesterol (LDL-C) concentrations and body weight in some short-term studies. The aim of this study was to evaluate the long-term effects of rosiglitazone on serum lipid levels and body weight.

DESIGN

Open labelled clinical study.

PATIENTS AND MEASUREMENTS

We prospectively evaluated fasting serum glucose, haemoglobin A(1c) (HbA(1c)), lipid profiles and body weight at baseline and every 3 months after the use of rosiglitazone (4 mg/day) for 18 months in 202 type 2 diabetic patients.

RESULTS

TC levels increased maximally at 3 months and decreased thereafter. However, overall, TC levels remained significantly higher at 18 months than those at baseline. LDL-C levels from the 3-month to the 12-month timepoint were significantly higher than those at baseline. However, after 15 months, LDL-C concentrations were not significantly different from basal LDL-C concentrations. HDL-C levels increased after the first 3 months and these levels were maintained. The increment of change in HDL-C was more prominent in patients with low basal HDL-C concentrations than in patients with high basal HDL-C concentrations. Body weight increased after the first 3 months and these levels were maintained.

CONCLUSIONS

HDL-C and body weight increased and remained elevated for the duration of the study. There was an initial increase in LDL-C but this attenuated and by the end of the study was not significantly elevated above baseline levels.

Rosiglitazone versus bedtime insulin in the treatment of patients with conventional oral antidiabetic drug failure: a 1-year randomized clinical trial

This study was conducted to evaluate the efficacy and tolerability of rosiglitazone in the treatment of patients with secondary oral antidiabetic drug (OAD) failure and to directly compare its use with bedtime insulin. A total of 112 Chinese patients with type 2 diabetes and conventional OAD failure were recruited. Patients were randomly assigned to treatment with rosiglitazone or bedtime isophane insulin; they continued to take their original oral antidiabetic drugs. Glycemic index, other clinical profiles, and tolerability were assessed during treatment and 1 y after add-on treatment was provided. Among the 112 patients, mean age (+/-SD) was 58.2+/-11.0 y (median, 58 y; range, 37 to 84 y). Both rosiglitazone (n=56) and insulin (n=56) significantly improved fasting glucose (2.4 and 3.7 mmol/L, respectively) and hemoglobin A1c concentrations (1.1% and 1.3%, respectively). Both therapies increased body mass index after 1 y of treatment (0.9 and 0.8 kg/m2, respectively). Only rosiglitazone increased high-density lipoprotein cholesterol concentrations (0.1 mmol/L). Four patients (7.1%) who were given rosiglitazone developed adverse effects (2, ankle edema, and 2, gastrointestinal disturbance). Six insulin-treated patients (10.7%) described adverse effects (5, early morning hypoglycemia, and 1, anxiety). Investigators concluded that in Chinese patients with type 2 diabetes and secondary conventional OAD failure, 1 y of treatment with rosiglitazone or bedtime insulin added to the regular regimen resulted in similar improvements in glycemic control. Rosiglitazone was also associated with improved high-density lipoprotein cholesterol levels. The addition of rosiglitazone may offer a safe and effective alternative to bedtime insulin treatment.

Targeting postprandial hyperglycemia

In healthy individuals, blood glucose levels in the fasting state are maintained by the continuous basal-level insulin secretion. After a meal, the rise in postprandial glucose (PPG) is controlled by the rapid pancreatic release of insulin, stimulated by both glucose and the intestinal production of the incretins glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1. In diabetic individuals, postprandial insulin secretion is insufficient to suppress an excessive rise in PPG. There is increasing evidence that elevated PPG exerts a more deleterious effect on the vascular system than elevation of fasting plasma glucose. In particular, individuals with normal fasting plasma glucose but impaired glucose tolerance have significantly increased risk of cardiovascular events. With the recognition of the importance of PPG and the availability of new pharmacologic options, management of diabetes will shift to greater attention to PPG levels. The prototype for such an approach is in the treatment of gestational diabetes and diabetic pregnancies where PPG is the primary target of efforts at glycemic control. These efforts have been extremely successful in improving the outlook for diabetic pregnant women. There are many approaches to reduction of PPG; dietary management and promotion of exercise are very effective. Sulfonylureas, meglitinides, metformin, thiazolidinediones, and disaccharidase inhibitors all counteract PPG elevation. The development of glucagon-like peptide 1 agonists such as exendin and dipeptidyl peptidase IV inhibitors such as vildagliptin offers a new approach to suppression of PPG elevation. New semisynthetic insulin analogues permit a more aggressive response to postprandial glucose elevation, with lower risk of hypoglycemia, than with regular insulin. Inhaled insulin also has a rapid onset of action and offers benefits in PPG control. It is proposed that an aggressive treatment approach focusing on PPG, similar to the current standards for diabetic pregancies, be directed at individuals with diabetes and impaired glucose tolerance.

Peroxisome proliferator-activated receptor gamma agonists: their role as vasoprotective agents in diabetes

Both type 1 and type 2 diabetes melitius are associated with increased cardiovascular morbidity, and now affect more than 170 million individuals worldwide. The incidence of type 2 diabetes is growing rapidly and now accounts for 90 to 95 percent of all diabetes cases. Thiazolidinediones (TZDs) a class of insulin sensitizing agents commonly used in the treatment of patients who have type 2 diabetes, improve endothelial dysfunction and exert beneficial effects on lipid profiles by activating the nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR-gamma). In addition, TZDs exhibit antiatherogenic effects, independent of their antidiabetic and lipid-lowering properties, by attenuating proinflammatory processes. The combination of increased insulin sensitivity, improved lipid profile, and reduced inflammation may explain the cardiovascular benefits of this class of drugs

Insulin resistance--a common link between type 2 diabetes and cardiovascular disease

Evidence suggests that diabetes and cardiovascular disease (CVD) may share an underlying cause(s), a theory known as the 'common soil' hypothesis. Insulin resistance is central both to the progression from normal glucose tolerance to type 2 diabetes and to a constellation of cardiovascular risk factors known as the metabolic syndrome. These risk factors include visceral obesity and dyslipidaemia characterized by low levels of high-density lipoprotein cholesterol, hypertriglyceridaemia and raised small dense low-density lipoprotein particle levels. Changes in adipose tissue mass and metabolism may link insulin resistance and visceral obesity, a condition that is common in type 2 diabetes. Furthermore, weight reduction, increased physical activity, metformin and acarbose have been shown to reduce the development of type 2 diabetes in genetically predisposed subjects and may decrease the high cardiovascular risk of patients with diabetes. Some fatty acid derivatives can affect energy metabolism by activating peroxisome proliferator-activated receptors (PPARs), nuclear receptors that play a key role in energy homeostasis. These receptors represent an ideal therapeutic target for reducing cardiovascular risk, because they are involved in the regulation of both insulin action and lipid metabolism. In addition to lifestyle changes, PPARgamma agonists such as thiazolidinediones are frequently beneficial and have been shown to ameliorate insulin resistance, while activation of PPARalpha (e.g. by fibrates) can lead to improvements in free fatty acid oxidation and lipid profile, and a reduction in cardiovascular events. The development of agents with both PPARalpha and PPARgamma activity promises added benefits with amelioration of insulin resistance, delayed progression to and of type 2 diabetes and a reduction of CVD.

PPAR gamma and human metabolic disease

The nuclear receptor family of PPARs was named for the ability of the original member to induce hepatic peroxisome proliferation in mice in response to xenobiotic stimuli. However, studies on the action and structure of the 3 human PPAR isotypes (PPARalpha, PPARdelta, and PPARgamma) suggest that these moieties are intimately involved in nutrient sensing and the regulation of carbohydrate and lipid metabolism. PPARalpha and PPARdelta appear primarily to stimulate oxidative lipid metabolism, while PPARgamma is principally involved in the cellular assimilation of lipids via anabolic pathways. Our understanding of the functions of PPARgamma in humans has been increased by the clinical use of potent agonists and by the discovery of both rare and severely deleterious dominant-negative mutations leading to a stereotyped syndrome of partial lipodystrophy and severe insulin resistance, as well as more common sequence variants with a much smaller impact on receptor function. These may nevertheless have much greater significance for the public health burden of metabolic disease. This Review will focus on the role of PPARgamma in human physiology, with specific reference to clinical pharmacological studies, and analysis of PPARG gene variants in the abnormal lipid and carbohydrate metabolism of the metabolic syndrome.

Effect of Rosiglitazone Treatment on Plaque Inflammation and Collagen Content in Nondiabetic Patients

Background— Therapeutic strategies to stabilize advanced arteriosclerotic lesions may prevent plaque rupture and reduce the incidence of acute coronary syndromes. Thiazolidinediones (TZDs), like rosiglitazone, are oral antidiabetic drugs with additional antiinflammatory and potential antiatherogenic properties. In a randomized, placebo-controlled, single-blind trial, we examined the effect of 4 weeks of rosiglitazone therapy on histomorphological characteristics of plaque stability in artery specimen of nondiabetic patients scheduled for elective carotid endarterectomy.

Methods and Results— A total of 24 nondiabetic patients with symptomatic carotid artery stenosis were randomly assigned to rosiglitazone (4 mg BID) or placebo in addition to standard therapy. In this population of nondiabetic patients, rosiglitazone treatment did not significantly change fasting blood glucose, fasting insulin, or lipid parameters. In contrast, rosiglitazone significantly reduced CD4-lymphocyte content as well as macrophage HLA-DR expression in the shoulder region, reflecting less inflammatory activation of these cells by lymphocyte interferon-γ. Moreover, rosiglitazone significantly increased plaque collagen content (7.7±1.6% versus 3.7±0.7% of plaque area; P =0.036) compared with placebo, suggesting that TZD treatment may stabilize arteriosclerotic lesions. In addition, rosiglitazone reduced serum levels of 2 inflammatory arteriosclerosis markers: C-reactive protein and serum amyloid A.

Conclusions— Four weeks of treatment with rosiglitazone significantly reduces vascular inflammation in nondiabetic patients, leading to a more stable type of arteriosclerotic lesion.

Effect of rosiglitazone on plasma adiponectin levels and arterial stiffness in subjects with prediabetes or non-diabetic metabolic syndrome

OBJECTIVE

Thiazolidinediones have favorable influences on surrogate markers of atherosclerosis such as adiponectin, and arterial stiffness in diabetic patients. However, it is not well known whether these beneficial effects occur in subjects without diabetes, such as prediabetes or the non-diabetic metabolic syndrome (MetS). The present study was therefore designed to evaluate the effectiveness of the insulin-sensitizing agent rosiglitazone on circulating adipocytokine levels and brachial-ankle pulse wave velocity (baPWV) in non-diabetics.

DESIGN AND METHODS

Ninety-nine subjects with prediabetes or non-diabetic MetS were randomly assigned to either rosiglitazone or an untreated control group (50 and 49 subjects respectively). The rosiglitazone group was treated daily for 12 weeks with 4 mg rosiglitazone. All subjects received a 75 g oral glucose test (OGTT) before and after treatment. In addition, baPWV, together with the levels of adiponectin, resistin, and high sensitivity C-reactive protein (hsCRP) were determined.

RESULTS

Rosiglitazone treatment significantly increased circulating adiponectin levels (P < 0.001) relative to the control group (P = 0.21). Plasma resistin levels were unchanged in both the rosiglitazone-treated and -untreated groups, but baPWV and hsCRP were significantly decreased (P < 0.001 and P = 0.003 respectively) in the rosiglitazone group only. Multiple linear regression analysis showed that changes in plasma adiponectin and baPWV were significantly affected by rosiglitazone treatment.

CONCLUSIONS

These data suggest that rosiglitazone may have an anti-atherogenic effect in subjects with prediabetes or non-diabetic MetS.

Endocrine and metabolic effects of rosiglitazone in overweight women with PCOS: a randomized placebo-controlled study

BACKGROUND

The objective of the study was to assess the therapeutic effects of rosiglitazone in overweight women with polycystic ovary syndrome (PCOS).

METHODS

A double-blind, placebo-controlled study was conducted on 30 (BMI > 25 kg/m2, mean age 29.1 +/- 1.2 years) overweight women with PCOS treated with rosiglitazone or placebo for 4 months. Waist-to-hip ratios (WHRs), serum concentrations of sex hormones and binding proteins, blood glucose, serum insulin and serum C-peptide during a 75-g oral glucose tolerance test (OGTT), first-phase insulin secretion as determined by an intravenous glucose tolerance test (IVGTT), M values (expressing insulin sensitivity using a euglycaemic clamp) and calorimetric data were assessed at 0 and 4 months of treatment.

RESULTS

Rosiglitazone improved menstrual cyclicity, increased serum sex hormone-binding globulin (SHBG) levels and decreased serum levels of androstenedione, 17-hydroxyprogesterone (17-OHP), dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEA-S). Glucose tolerance [expressed as AUC(glucose) during the OGTT] improved (P = 0.002) and peripheral insulin response (expressed as AUC(insulin)) decreased (P = 0.004) in the rosiglitazone group (ROSI group). M value improved in the ROSI group from 33.4 +/- 3.27 to 40.0 +/- 5.51 micromol/kg min (P = 0.04).

CONCLUSION

Rosiglitazone, by improving menstrual cyclicity, hyperandrogenism, insulin resistance and hyperinsulinaemia, represents an alternative treatment for overweight anovulatory women with PCOS and no pregnancy desire.

Old World Nonhuman Primate Models of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a major health problem of increasing incidence. To better study the pathogenesis and potential therapeutic agents for this disease, appropriate animal models are needed. Old World nonhuman primates (NHPs) are a useful animal model of type 2 diabetes; like humans, the disease is most common in older, obese animals. Before developing overt diabetes, NHPs have a period of obesity-associated insulin resistance that is initially met with compensatory insulin secretion. When either a relative or absolute deficiency in pancreatic insulin production occurs, fasting glucose concentrations begin to increase and diabetic signs become apparent. Pathological changes in pancreatic islets are also similar to those seen in human diabetics. Initially there is hyperplasia of the islets with abundant insulin production typically followed by replacement of islets with islet-associated amyloid. Diabetic NHPs have detrimental changes in plasma lipid and lipoprotein concentrations, lipoprotein composition, and glycation, which may contribute to progression of atherosclerosis. As both the prediabetic condition (similar to metabolic syndrome in humans) and overt diabetes become better defined in monkeys, their use in pharmacological studies is increasing. Likely due to their genetic similarity to humans and the similar characteristics of the disease in NHPs, NHPs have been used to study recently developed agonists of the peroxisome proliferators-activated receptors. Importantly, agonists of the different receptor subclasses elicit similar responses in both humans and NHPs. Thus, Old World NHPs are a valuable animal model of type 2 diabetes to study disease progression, associated risk factors, and potential new treatments.

Obesity, peroxisome proliferator-activated receptor, and atherosclerosis in type 2 diabetes

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. The 3 PPAR isotypes, PPAR-alpha, PPAR-gamma, and PPAR-delta, play a key role in the regulation of lipid and glucose metabolism. Obesity and the interrelated disorders of the metabolic syndrome have become a major worldwide health problem. In this review, we summarize the critical role of PPARs in regulating inflammation, lipoprotein metabolism, and glucose homeostasis and their potential implications for the treatment of obesity, diabetes, and atherosclerosis.

Rosiglitazone Reduces Insulin Requirement and C-Reactive Protein Levels in Type 2 Diabetic Patients Receiving Peritoneal Dialysis

BACKGROUND

Glycemic control is important in determining the outcome of patients with diabetes on dialysis therapy. However, the choice of oral hypoglycemia agent is limited in these patients. Very often, a high dose of insulin is required because of the uremia-associated insulin-resistant state. Rosiglitazone (RSG), a thiazolidinedione, can improve insulin resistance, and its excretion does not rely on renal function. Moreover, it has an anti-inflammatory effect that might be beneficial in patients with renal failure.

METHODS

An open-label randomized study was performed in which 52 patients with type 2 diabetes on peritoneal dialysis therapy administered a constant dosage of subcutaneous insulin with stable glycemic control were randomly assigned to the administration of either RSG (fixed dose, 4 mg) plus insulin or insulin alone. Insulin was titrated to maintain hemoglobin A1c (HbA1c) and blood glucose at pretreatment levels. Study duration was 24 weeks.

RESULTS

Both groups had similar baseline demographic characteristics, HbA1c and glucose levels, insulin requirement, and C-reactive protein (CRP) levels. Insulin requirement was decreased significantly in the RSG group (27.88 +/- 17.6 to 22.4 +/- 15.21 U/d; P < 0.001). There was a significantly greater decrease in insulin dosage in the RSG than control group (-21.5% versus +0.5%; P = 0.03), whereas glycemic control was similar between groups. At the end of the study, the RSG group also had significantly lower CRP levels than the control group (2.21 versus 8.59 mg/L; P = 0.03). No significant increase in such adverse effects as hypoglycemia, liver impairment, and fluid overload was observed in the RSG group. However, the RSG group was associated with more weight gain. Multivariate regression analysis (using decrease in HbA1c and lipid levels, change in insulin dosage, and treatment with RSG, with lipid-lowering agents) showed that only treatment with RSG was an independent predictor for posttreatment CRP level (P = 0.016).

CONCLUSION

RSG in combination with insulin is well tolerated and beneficial in the treatment of patients with type 2 diabetes on peritoneal dialysis therapy by improving insulin sensitivity and decreasing inflammatory response.

Rapid Effects of Rosiglitazone Treatment on Endothelial Function and Inflammatory Biomarkers

Background— Antidiabetic thiazolidinediones (TZDs), like rosiglitazone or pioglitazone, improve endothelial function in patients with type 2 diabetes or metabolic syndrome, but it is currently unknown, whether these beneficial effects of TZDs depend on their metabolic action or may be caused by direct effects on the endothelium. Therefore, the present study examined whether short-term rosiglitazone treatment influences endothelium-dependent vasodilation as well as serum levels of vascular disease biomarkers in healthy, nondiabetic subjects.

Methods and Results— Short-term treatment (21 days) of healthy subjects (n=10) did not significantly change blood glucose levels or lipid profile. In contrast, rosiglitazone significantly increased flow-mediated, endothelium-dependent vasodilation already within the first day from 5.3±2.7% at baseline to 7.8±2.6%, further increasing it to 9.4±3.0% at day 21. In addition, the early improvement of endothelium-dependent vasodilation was paralleled by a rapid reduction of serum levels of the biomarkers C-reactive protein (CRP), serum amyloid A (SAA), and sE-selectin. Moreover, after drug withdrawal all markers remained suppressed for the whole follow-up period of 7 days. In contrast, rosiglitazone treatment did not significantly affect tumor necrosis factor (TNF)-α, interleukin (IL)-6, sICAM-1, sVCAM-1, and sCD40L levels.

Conclusions— Our study suggests a direct effect of TZD treatment on endothelial function and inflammatory biomarkers of arteriosclerosis, promoting the concept that TZDs, independent of their metabolic action, may exhibit protective effects in the vessel wall.

Rosiglitazone protects against cyclosporine-induced pancreatic and renal injury in rats

Rosiglitazone (RGTZ) has protective effect against various types of injury. This study was performed to evaluate the effect of RGTZ on pancreatic and renal injury caused by cyclosporine (CsA). CsA (15 mg/kg) and RGTZ (3 mg/kg) were administered alone and together to the rats for 28 days. The effect of RGTZ on CsA-induced pancreatic injury was evaluated by intraperitoneal glucose tolerance test (IPGTT), plasma insulin concentrations and pancreatic beta-cell morphology. The effect of RGTZ on CsA-induced renal injury was evaluated by assessing renal function and pathology; mediators of inflammation and fibrosis such as angiotensin II (AngII), osteopontin (OPN) and transforming growth factor-beta1 (TGF-beta1) and apoptotic cell death. Four weeks of CsA treatment caused diabetes, renal dysfunction, typical pathologic lesions (arteriolopathy, interstitial fibrosis and inflammatory cells infiltration) and apoptotic cell death. RGTZ treatment decreased blood glucose concentration, increased plasma insulin concentration and preserved pancreatic beta islet mass. RGTZ treatment improved renal function and histopathology. Pro-inflammatory and pro-fibrotic molecules such as AngII, OPN and TGF-beta1, and apoptotic cell death also decreased with RGTZ treatment. These data suggest that RGTZ has a protective effect against CsA-induced pancreatic and renal injury.

The effect of metformin and rosiglitazone on postprandial lipid metabolism in obese insulin-resistant subjects

INTRODUCTION

Obese insulin-resistant individuals exhibit a dyslipidaemia due to raised levels of both hepatically and intestinally derived lipoproteins. However, little is known about the related dysregulation of intestinally derived lipoproteins. We examined whether the insulin-sensitizing agents, metformin and rosiglitazone, improve intestinal lipoprotein metabolism in obese insulin-resistant individuals.

METHODS

Thirty male obese (body mass index > 26; waist circumference > 100 cm) insulin-resistant [homeostasis model assessment (HOMA) score > 2.0] subjects were randomized to either a metformin (1 g bd), rosiglitazone (4 mg bd) or control treatment group for a period of 8 weeks. Fasting and postprandial lipid metabolism was studied before and after the intervention period.

RESULTS

Metformin and rosiglitazone both significantly improved insulin sensitivity, but this was not paralleled by improvement in dyslipidaemia. With rosiglitazone relative to control there was a significant (p < 0.05) increase in the area under the apolipoprotein (apo) B48 curve following the oral fat load and a decrease in the ratio of triglyceride to apo B48 levels postprandially following rosiglitazone treatment.

CONCLUSION

In obese insulin-resistant subjects metformin and rosiglitazone both improve insulin sensitivity, as measured by HOMA, without improvement in lipid metabolism. Rosiglitazone may have a detrimental effect on chylomicron metabolism by an increase in postprandial apo B48 levels, and this requires further investigation.

A comparison of lipid and glycemic effects of pioglitazone and rosiglitazone in patients with type 2 diabetes and dyslipidemia

OBJECTIVE

Published reports suggest that pioglitazone and rosiglitazone have different effects on lipids in patients with type 2 diabetes. However, these previous studies were either retrospective chart reviews or clinical trials not rigorously controlled for concomitant glucose- and lipid-lowering therapies. This study examines the lipid and glycemic effects of pioglitazone and rosiglitazone.

RESEARCH DESIGN AND METHODS

We enrolled subjects with a diagnosis of type 2 diabetes (treated with diet alone or oral monotherapy) and dyslipidemia (not treated with any lipid-lowering agents). After a 4-week placebo washout period, subjects randomly assigned to the pioglitazone arm (n = 400) were treated with 30 mg once daily for 12 weeks followed by 45 mg once daily for an additional 12 weeks, whereas subjects randomly assigned to rosiglitazone (n = 402) were treated with 4 mg once daily followed by 4 mg twice daily for the same intervals.

RESULTS

Triglyceride levels were reduced by 51.9 +/- 7.8 mg/dl with pioglitazone, but were increased by 13.1 +/- 7.8 mg/dl with rosiglitazone (P < 0.001 between treatments). Additionally, the increase in HDL cholesterol was greater (5.2 +/- 0.5 vs. 2.4 +/- 0.5 mg/dl; P < 0.001) and the increase in LDL cholesterol was less (12.3 +/- 1.6 vs. 21.3 +/- 1.6 mg/dl; P < 0.001) for pioglitazone compared with rosiglitazone, respectively. LDL particle concentration was reduced with pioglitazone and increased with rosiglitazone (P < 0.001). LDL particle size increased more with pioglitazone (P = 0.005).

CONCLUSIONS

Pioglitazone and rosiglitazone have significantly different effects on plasma lipids independent of glycemic control or concomitant lipid-lowering or other antihyperglycemic therapy. Pioglitazone compared with rosiglitazone is associated with significant improvements in triglycerides, HDL cholesterol, LDL particle concentration, and LDL particle size.

Spotlight on rosiglitazone in the management of type 2 diabetes mellitus

Rosiglitazone, a thiazolidinedione with a different side chain from those of troglitazone and pioglitazone, reduces plasma glucose levels and glucose production and increases glucose clearance in patients with type 2 diabetes mellitus. Insulin sensitivity, pancreatic beta-cell function and surrogate markers of cardiovascular risk factors are significantly improved by rosiglitazone. Double-blind trials of 8 to 26 weeks of rosiglitazone 4 or 8 mg/day monotherapy indicate significant decreases in fasting plasma glucose (-2 to -3 mmol/L with 8 mg/day) and glycosylated hemoglobin levels [HbA(1c); -0.6 to -0.7% (-0.8 to -1.1% in drug-naive patients) with 8 mg/day]. Significant decreases in hyperglycemic markers occurred when rosiglitazone was combined with metformin (HbA(1c) -0.8 to -1.0%), a sulfonylurea (-1.4%) or insulin (-1.2%) for 26 weeks versus little change with active comparator monotherapy. Efficacy was maintained in trials of < or =2 years, and was also apparent in various ethnic subgroups, elderly patients and both obese and nonobese patients. Rosiglitazone is currently not indicated in combination with injected insulin. It should be administered in conjunction with diet and exercise regimens. Rosiglitazone is generally well tolerated. Despite rare individual reports of liver function abnormalities in rosiglitazone recipients, the incidence of these in clinical trials (< or =2 years' duration) was similar to that in placebo and active comparator groups. Fluid retention associated with rosiglitazone may be the cause of the increased incidence of anemia in clinical trials, and also means that patients should be monitored for signs of heart failure during therapy. Although bodyweight is increased overall with rosiglitazone therapy, increases are in subcutaneous, not visceral, fat; hepatic fat is decreased. The pharmacokinetic profile of rosiglitazone is not substantially altered by age or renal impairment, nor are there important drug interactions. Rosiglitazone is not indicated in patients with active liver disease or increased liver enzymes.

CONCLUSIONS

Oral rosiglitazone 4 or 8 mg/day provides significant antihyperglycemic efficacy and is generally well tolerated, both as monotherapy and in combination with other antihyperglycemic agents, in patients with type 2 diabetes mellitus who do not have active liver disease. Long-term data are required before conclusions can be drawn about the clinical significance of positive changes to surrogate markers of cardiovascular disease risk and improvements to pancreatic beta-cell function. Rosiglitazone significantly improves insulin sensitivity and, as such, is a welcome addition to the treatment options for patients with type 2 diabetes mellitus.

Role of insulin secretagogues and insulin sensitizing agents in the prevention of cardiovascular disease in patients who have diabetes

In the absence of clinical trial evidence to compare the secretagogues with sensitizers, it is difficult to make recommendations about which class of drug is more important to prescribe for the prevention of cardiovascular disease in diabetes mellitus. Epidemiologic data supports insulin resistance as a major factor in cardiovascular disease through a variety of mechanisms. Because sensitizers improve insulin sensitivity and correct many of the vascular abnormalities that are associated with insulin resistance, it is tempting to suggest that they may be superior for this purpose. Conversely, meeting the goals that are recommended for glycemia also are important and achieving them may not be always possible with sensitizers, particularly in the later stages of the disease when insulin levels are not high,despite insulin resistance. In such situations,combination therapy may be needed with both types of drugs. No data are available on the cardiovascular effects of such combinations;some retrospective data suggest a possibility of increased events with the combination of sulfonylureas and metformin. Thus, further prospective studies in this area are necessary.

Rosiglitazone improves, while Glibenclamide worsens blood pressure control in treated hypertensive diabetic and dyslipidemic subjects via modulation of insulin resistance and sympathetic activity

BACKGROUND

Type II diabetes is often associated with high blood pressure, elevated sympathetic activity, and high plasma insulin levels. Hypoglycemic agents may negatively interfere with blood pressure control, sympathetic activity, and plasma insulin level; therefore the choice of treatment in type II diabetes may be crucial. We aimed to compare the effects of two hypoglycemic drugs on blood glucose, blood pressure, sympathetic activity, and insulin levels in type II diabetic and hypertensive patients.

METHODS

Forty-eight (24M, 24F) type II diabetic, hypertensive, and hyperlipidemic subjects were enrolled and treated for 4 weeks with an ACE inhibitor (Cilazapril) and a statin (Simvastatin). They were then randomized into two groups to receive a thiazolidinedione (Rosiglitazone; ROS) or a sulfonylurea (Glibenclamide; GLB) for 8 weeks. Blood biochemistry, blood pressure, plasma insulin, endothelial function, and sympathetic skin activity were measured before and after treatment.

RESULTS

A significant drop in systolic and diastolic blood pressure by 6.1 +/- 4.1 mm Hg and 4.2 +/- 1.9 mm Hg respectively; a reduction in plasma insulin concentration by 4.3 +/- 1.9 mU/L and a decline in skin sympathetic activity were observed in the group receiving ROS. The GLB group showed an increase in systolic blood pressure by 3.1 +/- 2.5 mm Hg, no change in diastolic blood pressure, significant elevation in plasma insulin concentration by 2.3 +/- 1.4 mu/L, and augmentation of sympathetic activity. No significant changes in endothelial function were observed in either group.

CONCLUSIONS

Rosiglitazone improved both plasma glucose and blood pressure levels, probably by attenuation of hyperinsulinemia and sympathetic activity, while Glibenclamide worsened blood pressure control possibly by elevation of insulin levels and activation of the sympathetic system.

The role of thiazolidinediones in the treatment of patients with type 2 diabetes mellitus

Diabetes mellitus is a significant and growing health concern worldwide. Unfortunately, type 2 diabetes mellitus is generally under-managed, and this may explain the increasing prevalence of diabetic complications throughout the world. The introduction of newer classes of antihyperglycemic agents should enhance the ability of clinicians to achieve optimal blood glucose control. One recent addition to the pharmacologic armamentarium is the thiazolidinedione class. The main effect of thiazolidinediones is amelioration of insulin resistance. These agents may also preserve beta-cell function, although evidence in favor of this effect is still inconclusive. The mechanism of action of thiazolidinediones is not completely understood. Similarly, the current state of knowledge cannot explain the differences in the lipid effects of pioglitazone and rosiglitazone. Thiazolidinediones are commonly used as add-on therapy for those requiring large daily doses of insulin therapy, or in addition to sulfonylurea agents and metformin for those reluctant to start insulin therapy. The potential role of thiazolidinediones as first-line therapy is now emerging. It is possible that in certain subgroups, particularly patients with renal failure, elderly individuals or those with corticosteroid-induced diabetes mellitus, the use of thiazolidinediones as a first-line therapy is justifiable. However, the lack of a long-term safety record, and the cost, would limit the widespread acceptance of this class of agents as first-line therapy.

Rosiglitazone is a safe and effective treatment option of new-onset diabetes mellitus after renal transplantation

The purpose of this study was to assess the safety and efficacy of the insulin sensitizer rosiglitazone in patients with new-onset diabetes mellitus (NODM) after renal transplantation. Twenty-two patients with NODM after renal transplantation were selected to receive rosiglitazone therapy. All patients received prednisone, 15 patients were treated with tacrolimus and seven patients received cyclosporine A. For 16 of the 22 patients treatment with rosiglitazone therapy was successful and mean fasting blood glucose decreased from 182 +/- 17 to 127 +/- 7 mg/dl. Six patients were not treated successfully with rosiglitazone alone, one patient needed a second oral antidiabetic agent and four patients insulin therapy. In one patient rosiglitazone was stopped because of edema after 5 days. There were no changes either in serum creatinine concentrations, or cyclosporine and tacrolimus blood levels respectively. Treatment with rosiglitazone appears to be safe and effective in patients with NODM after renal transplantation.

PPARgamma-mediated insulin sensitization: the importance of fat versus muscle

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a nuclear hormone receptor that functions as a transcriptional regulator in a variety of tissues. PPARgamma activation, e.g., through binding of the synthetic glitazones or thiazolidinediones (TZD), results in a marked improvement in type 2 diabetic patients of insulin and glucose parameters resulting from an improvement of whole body insulin sensitivity. The role of different metabolic tissues (fat, skeletal muscle, liver) in mediating PPARgamma function in glucose and insulin homeostasis is still unclear. Recently, the function of PPARgamma in adipose tissue and skeletal muscle has been intensively characterized by using targeted deletion of PPARgamma in those tissues. In those studies, adipose PPARgamma has been identified as an essential mediator for the maintainance of whole body insulin sensitivity. Two major mechanisms have been described. 1) Adipose PPARgamma protects nonadipose tissue against excessive lipid overload and maintains normal organ function (liver, skeletal muscle); and 2) adipose PPARgamma guarantees a balanced and adequate production of secretion from adipose tissue of adipocytokines such as adiponectin and leptin, which are important mediators of insulin action in peripheral tissues. In contrast to studies in adipose-specific PPARgamma-deficient mice, the data in muscle-specific PPARgamma(-/-) mice demonstrate that whole body insulin sensitivity is, at least in part, relying on an intact PPARgamma system in skeletal muscle. Finally, these early and elegant studies using tissue-specific PPARgamma knockout mouse models pinpoint adipose tissue as the major target of TZD-mediated improvement of hyperlipidemia and insulin sensitization.

Peroxisome proliferator-activated receptor gamma; Its role in atherosclerosis and restenosis

Cellular proliferation and migration are fundamental processes that contribute to the injury response in major blood vessels. The resultant pathologies are atherosclerosis and restenosis. As we begin to understand the cellular changes associated with vascular injury, it is critical to determine whether the inhibition of growth and movement of cells in the vasculature could serve as a novel therapeutic strategy to prevent atherosclerosis and restenosis.

Influence of Rosiglitazone on Flow-Mediated Dilation and Other Markers of Cardiovascular Risk in HIV-Infected Patients with Lipoatrophy

Background

Antiretroviral therapy for HIV infection is commonly complicated by lipoatrophy, insulin resistance and dyslipidaemia. In HIV-uninfected adults with insulin resistance or type 2 diabetes, thiazolidinediones can lower blood pressure and improve both insulin sensitivity and endothelial function. This study sought to investigate the effects of rosiglitazone on endothelial function and other markers of cardiovascular risk in patients with HIV-related lipoatrophy.

Methods

HIV-infected, lipoatrophic adults receiving anti-retroviral therapy were randomized to receive either rosiglitazone 4 mg or matched placebo, twice daily. Percentage flow-mediated forearm arterial dilation (FMD%) was measured at weeks 0, 12, 24 and 48, together with other markers of vascular risk (blood pressure, lipids, glycaemic parameters, adiponectin and leptin).

Results

Out of 64 enrolled adults, 44 (69%) attended all visits (23 rosiglitazone, 21 placebo). Relative to placebo, at week 48, rosiglitazone decreased systolic blood pressure (8 mmHg, P=0.03), insulin (3 μIU/ml, P=0.02), insulin resistance ( P=0.03) and leptin (0.6 ng/ml, P=0.02), whilst adiponectin was increased (3.3 μg/ml, P<0.0001). However, rosiglitazone increased total cholesterol (49.1 mg/dl, P=0.001), low-density lipoprotein cholesterol (23.5 mg/dl, P=0.01) and triglycerides (146 mg/dl, P=0.06). Mean baseline FMD% for the entire cohort was moderately impaired (4.5%). Compared with baseline, mean on-treatment FMD% increased by 0.8% with rosiglitazone and decreased by 0.3% with placebo (mean difference 1.1%, 95% CI -0.2 to 2.5, P=0.09).

Conclusions

Rosiglitazone has minimal effect on flow-mediated dilation in HIV-infected lipoatrophic adults. However, despite worsening of the lipid profile, the overall effect of rosiglitazone on the cardiovascular risk profile in these subjects was positive.

The effects of rosiglitazone on fatty acid and triglyceride metabolism in type 2 diabetes

AIMS/HYPOTHESIS

We investigated the effects of rosiglitazone on NEFA and triglyceride metabolism in type 2 diabetes.

METHODS

In a double-blind, placebo-controlled, cross-over study of rosiglitazone in diet-treated type 2 diabetic subjects, we measured arteriovenous differences and tissue blood flow in forearm muscle and subcutaneous abdominal adipose tissue, used stable isotope techniques, and analysed gene expression. Responses to a mixed meal containing [1,1,1-(13)C]tripalmitin were assessed.

RESULTS

Rosiglitazone induced insulin sensitisation without altering fasting NEFA concentrations (-6.6%, p=0.16). Postprandial NEFA concentrations were lowered by rosiglitazone compared with placebo (-21%, p=0.04). Adipose tissue NEFA release was not decreased in the fasting state by rosiglitazone treatment (+24%, p=0.17) and was associated with an increased fasting hormone-sensitive lipase rate of action (+118%, p=0.01). Postprandial triglyceride concentrations were decreased by rosiglitazone treatment (-26%, p<0.01) despite unchanged fasting concentrations. Rosiglitazone did not change concentrations of triglyceride-rich lipoprotein remnants. Adipose tissue blood flow increased with rosiglitazone (+32%, p=0.03). Postprandial triglyceride [(13)C]palmitic acid concentrations were unchanged, whilst NEFA [(13)C]palmitic acid concentrations were decreased (p=0.04). In muscle, hexokinase II mRNA expression was increased by rosiglitazone (+166%, p=0.001) whilst the expression of genes involved in insulin signalling was unchanged. Adipose tissue expression of FABP4, LPL and FAT/CD36 was increased.

CONCLUSIONS/INTERPRETATION

Rosiglitazone decreases postprandial NEFA and triglyceride concentrations. This may represent decreased spillover of NEFAs from adipose tissue depots. Decreased delivery of NEFAs to the liver may lead to lowered postprandial triglyceride concentrations. Upregulation of hexokinase II expression in muscle may contribute to insulin sensitisation by rosiglitazone.

Short-term treatment with rosiglitazone improves glucose tolerance, insulin sensitivity and endothelial function in renal transplant recipients

BACKGROUND

Insulin resistance (IR) contributes to the development of glucose intolerance (post-transplant diabetes mellitus or impaired glucose tolerance) following renal transplantation. Furthermore, endothelial dysfunction (ED) is associated with IR. Glucose intolerance, IR and ED are all independent risk factors for cardiovascular disease. Therefore, treatment with insulin sensitizers may benefit glucose-intolerant renal transplant recipients. The main objectives of the present study were to investigate the effect of 4 weeks' treatment with the PPAR-gamma agonist rosiglitazone on insulin sensitivity, plasma glucose and endothelial function in renal transplant recipients with glucose intolerance. Safety parameters were also addressed.

METHODS

A total of 10 glucose-intolerant renal transplant recipients were treated with rosiglitazone (initially 4 mg/day increasing to 8 mg/day after 1 week). A hyperinsulinaemic euglycaemic glucose clamp, an oral glucose tolerance test and endothelial function assessment with laser Doppler flowmetry were performed both at baseline and at follow-up.

RESULTS

Treatment with rosiglitazone was followed by a significantly improved mean glucose disposal rate (from 6.5 to 9.1 g/kg/min; P = 0.02) and a significant decline in fasting and 2 h plasma glucose (from 6.4 to 5.8 mmol/l, P = 0.01 and from 14.2 to 10.6 mmol/l, P = 0.03, respectively). Furthermore, a significant improvement in endothelial function was demonstrated (AUC(ACh); from 389 to 832 AU x min, P = 0.04). No serious adverse events or hypoglycaemic episodes were observed.

CONCLUSIONS

Four weeks' treatment with rosiglitazone was associated with increased insulin sensitivity, lowered fasting and 2 h plasma glucose and improved endothelial function in renal transplant recipients with glucose intolerance. The drug was well tolerated and may be a good alternative for treating these patients.

Thiazolidinediones: a review of their mechanisms of insulin sensitization, therapeutic potential, clinical efficacy, and tolerability

The thiazolidinediones (TZDs) rosiglitazone and pioglitazone are newer additions to the antidiabetic armamentarium and are indicated for the treatment of type 2 diabetes mellitus (T2DM) in the United States. The TZDs are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists that provide clinically effective glycemic control and unique pharmacologic effects on multiple risk factors for T2DM-related morbidity, including improvement of insulin sensitivity and endothelial dysfunction, reduction of blood pressure, and amelioration of dyslipidemia. Weight gain and fluid retention occur with TZD therapy, especially when they are administered in higher doses and in combination with insulin. Although fluid retention associated with the use of TZDs is generally mild and reversible, these agents should not be used in patients with New York Heart Association Class III or IV heart failure symptoms. The findings of ongoing, long-term, prospective studies will clarify the role of the TZDs in the treatment of T2DM, particularly in terms of the durability of improvements in glycemic control, insulin sensitivity, pancreatic beta- cell function, and cardiovascular health.

[The place of thiazolidinediones in the treatment of type 2 diabetes]

SUPPLEMENTARY ORAL ANTIDIABETICS: Thiazolidinediones or glitazones are a new class of oral antidiabetics, the effects on blood sugar control of which are mediated by the sensitivity of the peripheral tissue to the effect of insulin. Hence, their effect is complementary to that of the insulin secreting agents and that of metformin, which acts by blocking the hepatic production of glucose. OTHER BENEFICIAL EFFECTS: Other than their effect on blood glucose, thiazolidinediones have a favorable influence upon the cardiovascular risk factors or markers such as blood pressure, C-reactive protein and metalloproteinase-9. They also appear to induce long term preservation of the beta-cell capital. Principle side effects are salt-water retention with a risk of decompensation of a pre-existing heart failure and weight gain with regard to the subcutaneous adipose tissue, without deleterious effects on blood glucose control.

The 161TT genotype in the exon 6 of the peroxisome-proliferator-activated receptor γ gene is associated with premature acute myocardial infarction and increased lipid peroxidation in habitual heavy smokers

PPAR (peroxisome-proliferator-activated receptor) is a nuclear receptor. Activation of PPARγ by its ligands could modulate gene transcription, thereby leading to multiple anti-atherogenic and fibrinolytic effects. However, the association between the 161T allele in exon 6 of the PPARγ gene and premature AMI (acute myocardial infarction) is not clear. We recruited 146 patients with premature AMI (onset age ≤50 years) and 146 controls. The C161T polymorphism was examined using PCR and restriction-fragment-length polymorphism. Plasma levels of Ab-ox-LDL (antibody against oxidized low-density lipoprotein) were measured in 27 male smokers, whose genotypes have been identified. The frequency of the PPARγ TT genotype among patients with AMI was significantly higher than that in controls [13% compared with 5.5%; OR (95% CI) 2.7, (1.1–6.5), where OR and CI are odds ratio and confidence interval respectively]. This association was not observed in CC or CT genotypes. Using multivariate logistic regression analyses, we found that the homozygous TT genotype [OR (95% CI), 3.1 (1.2–7.9)], smoking [OR (95% CI), 3.5, (2.1–6.0)], hypertension [OR (95% CI), 3.6, (1.9–6.9)] and diabetes mellitus [OR (95% CI), 3.5 (1.5–8.4)] were independent risk factors for premature AMI. Plasma levels of Ab-ox-LDL were significantly higher in healthy volunteers with the TT genotype compared with those with the CC genotype (49.3±18.1 compared with 24.2±15.2 units/l respectively; P=0.02). Therefore in our study we observed an association between the PPARγ 161 TT genotype and premature AMI. Lipid peroxidation was significantly influenced by the 161T allele.

Peroxisome proliferator-activated receptors and atherogenesis: regulators of gene expression in vascular cells

A large body of data gathered over the past couple of years has identified the peroxisome proliferator-activated receptors (PPAR) alpha, gamma, and beta/delta as transcription factors exerting modulatory actions in vascular cells. PPARs, which belong to the nuclear receptor family of ligand-activated transcription factors, were originally described as gene regulators of various metabolic pathways. Although the PPARalpha, gamma, and beta/delta subtypes are approximately 60% to 80% homologous in their ligand- and DNA-binding domains, significant differences in ligand and target gene specificities are observed. PPARalpha is activated by polyunsaturated fatty acids and oxidized derivatives and by lipid-modifying drugs of the fibrate family, including fenofibrate or gemfibrozil. PPARalpha controls expression of genes implicated in lipid metabolism. PPARgamma, in contrast, is a key regulator of glucose homeostasis and adipogenesis. Ligands of PPARgamma include naturally occurring FA derivatives, such as hydroxyoctadecadienoic acids (HODEs), prostaglandin derivatives such as 15-deoxyDelta12,14-prostaglandin J2, and glitazones, insulin-sensitizing drugs presently used to treat patients with type 2 diabetes. Ligands for PPARbeta/delta are polyunsaturated fatty acids, prostaglandins, and synthetic compounds, some of which are presently in clinical development. PPARbeta/delta stimulates fatty acid oxidation predominantly acting in muscle. All PPARs are expressed in vascular cells, where they exhibit antiinflammatory and antiatherogenic properties. In addition, studies in various animal models as well as clinical data suggest that PPARalpha and PPARgamma activators can modulate atherogenesis in vivo. At present, no data are available relating to possible effects of PPARbeta/delta agonists on atherogenesis. Given the widespread use of PPARalpha and PPARgamma agonists in patients at high risk for cardiovascular disease, the understanding of their function in the vasculature is not only of basic interest but also has important clinical implications. This review will focus on the role of PPARs in the vasculature and summarize the present understanding of their effects on atherogenesis and its cardiovascular complications.

Targeting insulin resistance and beta-cell dysfunction: the role of thiazolidinediones

Insulin resistance and beta-cell dysfunction are fundamental defects that contribute to the development of type 2 diabetes, and as such are targets for primary prevention of disease progression. The two parameters are linked by several factors, including glucotoxicity and lipotoxicity, and recent research has enlightened understanding of the molecular mechanisms underlying the development and progression of the disease. Historically, type 2 diabetes has been managed by controlling hyperglycemia, using agents that increase insulin levels or reduce hepatic glucose production, as exemplified by the United Kingdom Prospective Diabetes Study. The thiazolidinediones control hyperglycemia by targeting the fundamental defects of the disease, and have shown well-documented improvements in insulin sensitivity and beta-cell function, both in monotherapy and in combination with other oral antidiabetic agents. TRoglitazone In the Prevention Of Diabetes (TRIPOD) has demonstrated the potential for thiazolidinediones to delay progression to type 2 diabetes. Prospective studies such as Diabetes REduction Approaches with ramipril and rosiglitazone Medications (DREAM) are currently evaluating the long-term effects of thiazolidinediones on metabolic status and disease progression.

Rosiglitazone treatment improves insulin regulation and dyslipidemia in type 2 diabetic cynomolgus monkeys

Impairment of peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a nuclear receptor that regulates genes involved in lipid and glucose metabolism, may contribute to the onset of metabolic disorders such as diabetes and the accompanying dyslipidemia. Fat-derived tumor necrosis factor alpha (TNF-alpha) and the acute-phase response protein, C-reactive protein (CRP), may also have a role in the development of obesity-related insulin resistance and type 2 diabetes mellitus. In this study, a group of 14 naturally occurring, insulin-requiring, type 2 diabetic cynomolgus monkeys were used to evaluate the effects of the PPAR-gamma agonist, rosiglitazone, on glycemic and lipid parameters and serum levels of TNF-alpha and CRP. The animals were randomized into 2 groups of 7. One group was treated with 0.5 mg/kg rosiglitazone orally once a day for 7 weeks. Blood was collected for evaluation at baseline, at 2 and 7 weeks during the treatment period, and at 7 and 13 weeks after treatment. Daily insulin requirements were recorded during the entire study. Results showed daily exogenous insulin requirements were significantly reduced (P <.01) in those treated with rosiglitazone, while glycemic control was maintained. Plasma triglyceride concentrations were significantly lower (P <.01) whereas plasma cholesterol levels tended to be lower and high-density lipoprotein (HDL) concentrations tended to be higher after treatment. No significant differences were noted in TNF-alpha and CRP serum levels during the treatment period. Body weights remained steady in both groups during the study. These results suggest overall improvement in insulin regulation and lipid profiles during treatment with rosiglitazone.

Outcomes of initiation of therapy with once-daily combination of a thiazolidinedione and a biguanide at an early stage of type 2 diabetes

CONTEXT

Utilization of the biguanide metformin and a thiazolidinedione (TZD) with new onset diabetes has the benefit of lowering A1cs into the normal range without the problem of severe hypoglycaemia.

OBJECTIVE

To assess the effectiveness of once-daily combined metformin and TZD therapy compared with other therapeutic regimens typically utilized at later stages of type 2 diabetes.

METHODS

A random chart review of 300 type 2 diabetic patients and extraction of data for body mass index (BMI), duration of diabetes and C-peptide and A1c was performed. In the 210 type 2 diabetic subjects in whom this information was currently available, the data were analysed.

RESULTS

Eighty-six patients on once-daily metformin and rosiglitazone had an average A1c of 6.2% (group A), and 58 subjects on triple therapy (metformin, rosiglitazone and glimepiride) (group B) had an average haemoglobin A1c (HbA1c) of 6.9%. The 22 subjects on one injection of insulin per day in addition to triple therapy (group C) had an average HbA1c of 7.6%, and the 44 subjects on more than one insulin injection per day plus metformin and/or rosiglitazone (group D) had an average HbA1c of 8.3%. HbA1cs below 7.0% were found in 91.9% of group A, 21.7% of group B, 36.4% of group C and 56.8% of group D. HbA1cs below 6.5% were found in 78.2% in group A, 15.5% in group B, 22.7% in group C and 31.8% in group D. HbA1cs below 6.0% were found in 41.9% in group A, 6.9% in group B, 9.1% in group C and 13.6% in group D. On univariate analyses, the HbA1c was positively associated with the duration of diabetes and the BMI and negatively associated with random C-peptide levels. Alternatively, on multiple regression analysis, there was no statistical correlation between the duration of diabetes or BMI with the HbA1c. However, there was a strong statistical correlation between the random C-peptide level and the HbA1c (p = 0.002).

CONCLUSION

Early initiation of therapy for type 2 diabetes with a once-daily combination of metformin and rosiglitazone provides the greatest opportunity to achieve A1cs within the normal range. The level of achieved glycaemic control is not dependent on the number or potency of the therapies utilized but is dependent on the level of endogenous insulin production. The use of a TZD as part of initial therapy of type 2 diabetes with its documented ability to preserve or improve beta-cell function has the potential to achieve prolonged normoglycaemia in the type 2 diabetic patient.

Hormone therapy impairs endothelial function in postmenopausal women with type 2 diabetes mellitus treated with rosiglitazone

Diabetes and ovarian senescence are associated with impaired endothelial function and altered arterial mechanical properties. Alterations in normal vascular structure and functioning are the primary cause of mortality and morbidity with type 2 diabetes. Similarly, after menopause, women experience an increase in the rate of cardiovascular disease. Thiazolidinediones have exhibited a number of antiatherogenic actions in populations with type 2 diabetes. The effect of thiazolidinediones in combination with hormone therapy (HT) in postmenopausal women is, however, unknown. To assess whether HT (transdermal estradiol 50 microg and micronized progesterone (100 mg/d) affects vascular function, 21 women receiving rosiglitazone were randomly assigned to receive HT or placebo for 12 wk in a double-blind crossover design. Measures of glycemic control, lipids, blood pressure, flow-mediated dilation, and distensibility index were undertaken at baseline and after each treatment. As a result, flow-mediated dilation was significantly reduced (15.3 +/- 3.8 to 6.6 +/- 1.6%, P = 0.02) with HT, whereas lipids, blood pressure, and distensibility index were unchanged. Placebo had no significant affect on any variables. Thus, the addition of HT to rosiglitazone treatment attenuates endothelial function without altering other cardiovascular risk factors. Caution should, therefore, be exercised when considering combined treatment with thiazolidinedione and HT.

Effects of rosiglitazone on gene expression in subcutaneous adipose tissue in highly active antiretroviral therapy-associated lipodystrophy

Highly active antiretroviral therapy (HAART) has improved the prognosis of human immunodeficiency virus (HIV)-infected patients but is associated with severe adverse events, such as lipodystrophy and insulin resistance. Rosiglitazone did not increase subcutaneous fat in patients with HAART-associated lipodystrophy (HAL) in a randomized, double-blind, placebo-controlled trial, although it attenuated insulin resistance and decreased liver fat content. The aim of this study was to examine effects of rosiglitazone on gene expression in subcutaneous adipose tissue in 30 patients with HAL. The mRNA concentrations in subcutaneous adipose tissue were measured using real-time PCR. Twenty-four-week treatment with rosiglitazone (8 mg/day) compared with placebo significantly increased the expression of adiponectin, peroxisome proliferator-activated receptor-gamma (PPARgamma), and PPARgamma coactivator 1 and decreased IL-6 expression. Expression of other genes involved in lipogenesis, fatty acid metabolism, or glucose transport, such as acyl-CoA synthase, adipocyte lipid-binding protein, CD45, fatty acid transport protein-1 and -4, GLUT1, GLUT4, keratinocyte lipid-binding protein, lipoprotein lipase, PPARdelta, and sterol regulatory element-binding protein-1c, remained unchanged. Rosiglitazone also significantly increased serum adiponectin concentration. The change in serum adiponectin concentration was inversely correlated with the change in fasting serum insulin concentration and liver fat content. In conclusion, rosiglitazone induced significant changes in gene expression in subcutaneous adipose tissue and ameliorated insulin resistance in patients with HAL. Increased expression of adiponectin might have mediated most of the favorable insulin-sensitizing effects of rosiglitazone in these patients.

Rosiglitazone improves intestinal lipoprotein overproduction in the fat-fed Syrian Golden hamster, an animal model of nutritionally-induced insulin resistance

We have recently shown that the fructose-fed Syrian Golden hamster, a non-diabetic animal model of nutritionally-induced insulin resistance and hyperlipidemia, is characterized by intestinal lipoprotein overproduction. In order to determine whether intestinal lipoprotein overproduction is specific to fructose feeding or applies generally to other models of insulin resistance, we studied intestinal lipoprotein production and the response to insulin sensitization in the high fat-fed Syrian Golden hamster. Syrian Golden Hamsters were fed either (1). chow (CHOW), (2). 60% fat (FAT) or (3). 60% fat with rosiglitazone, 20 micromol/kg per day (FAT + RSG) for 5 weeks. Euglycemic hyperinsulinemic clamp studies confirmed that FAT is a good model of insulin resistance and rosiglitazone treatment resulted in a significant improvement in insulin sensitivity. In addition, there was a significant approx. two- to four-fold increase in intestinal apoB48 particle production in FAT. Rosiglitazone treatment resulted in partial normalization of apoB48-containing intestinal lipoprotein secretion. In summary: (1). the fat-fed Syrian Golden Hamster is a good model of nutritionally-induced insulin resistance, (2). intestinal overproduction of lipoproteins appear to contribute to the hypertriglyceridemia of insulin resistance in this animal model and (3). insulin sensitization with rosiglitazone ameliorates intestinal apoB48 particle overproduction in the fat-fed Syrian Golden Hamster. These data further support the link between insulin resistance and intestinal lipoprotein overproduction.

Drug treatment of combined hyperlipidemia

Combined hyperlipidemia is increasing in frequency and is the most common lipid disorder associated with obesity, insulin resistance and diabetes mellitus. It is associated with other features of the metabolic syndrome including hypertension, hyperuricemia, hyperinsulinemia and highly atherogenic subfractions of lipoprotein remnant particles including small dense low density lipoprotein-cholesterol. This review examines the mechanisms by which combined hyperlipidemia arises and the various drugs including fibric acid derivatives, hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, and nicotinic acid which can be used either as monotherapy or in combination to manage it and to improve prognosis from atherosclerotic disease in diabetes mellitus, insulin resistant states and primary combined hyperlipidemia. The therapeutic approach to combined hyperlipidemia involves determination of whether the cause is hepatocyte damage or metabolic derangements. Combined hyperlipidemia due to hepatocyte damage should be treated by attention to the primary cause. In the case of metabolic dysfunction because of imbalance in glucose and fat metabolism, therapy of diabetes mellitus and obesity should be optimised prior to commencement of lipid lowering drugs. Both fibric acid derivatives and HMG-CoA reductase inhibitors can be used in the treatment of combined hyperlipidemia with fibric acid derivatives having greater effects on triglycerides and HMG-CoA reductase inhibitors on LDL-C though both have effects on the other cardiovascular risk factors. There is some evidence of benefit with both interventions in mild combined hyperlipidemias and large scale trials are underway. Fibric acid derivatives and HMG-CoA reductase inhibitor therapy can be combined with care, provided that gemfibrozil is avoided, fibric acid derivatives are given in the mornings and shorter half -life HMG-CoA reductase inhibitors are used at night. Combined hyperlipidemia emergencies occur with predominant hypertriglyceridemia in pregnancy or as a cause of pancreatitis. Therapy in the former should aim to reduce chylomicron production by a low fat diet and intervention to suppress VLDL-C secretion using omega-3 fatty acids. In the latter case, fluid therapy alone and medium chain plasma triglyceride infusions usually reduce levels satisfactorily though apheresis may be required. Blood glucose levels also need aggressive management in these conditions. Combined hyperlipidemia is likely to become an increasing problem with the increase in the prevalence of obesity and diabetes mellitus and needs aggressive management to reduce cardiovascular risk.