Rosiglitazone improves insulin sensitivity, glucose tolerance and ambulatory blood pressure in subjects with impaired glucose tolerance

RhoBTB1 protects against hypertension and arterial stiffness by restraining phosphodiesterase 5 activity

Mice selectively expressing PPARγ dominant negative mutation in vascular smooth muscle exhibit RhoBTB1-deficiency and hypertension. Our rationale was to employ genetic complementation to uncover the mechanism of action of RhoBTB1 in vascular smooth muscle. Inducible smooth muscle-specific restoration of RhoBTB1 fully corrected the hypertension and arterial stiffness by improving vasodilator function. Notably, the cardiovascular protection occurred despite preservation of increased agonist-mediated contraction and RhoA/Rho kinase activity, suggesting RhoBTB1 selectively controls vasodilation. RhoBTB1 augmented the cGMP response to nitric oxide by restraining the activity of phosphodiesterase 5 (PDE5) by acting as a substrate adaptor delivering PDE5 to the Cullin-3 E3 Ring ubiquitin ligase complex for ubiquitination inhibiting PDE5. Angiotensin-II infusion also caused RhoBTB1-deficiency and hypertension which was prevented by smooth muscle specific RhoBTB1 restoration. We conclude that RhoBTB1 protected from hypertension, vascular smooth muscle dysfunction, and arterial stiffness in at least two models of hypertension.

Klotho and PPAR Gamma Activation Mediate the Renoprotective Effect of Losartan in the 5/6 Nephrectomy Model

Renin angiotensin system (RAS) blockade reduces the progression of chronic kidney disease (CKD) independently of its antihypertensive effect. Ang II-induced fibrosis can be mediated by molecules such as klotho, peroxisome proliferator-activate receptor γ (PPAR-γ), and the Wnt/β-catenin pathway; however, the interaction among these molecules and RAS activation is not completely known. The aim of this study was to investigate a possible link between RAS, PPAR-γ, and Klotho in the 5/6 nephrectomy (NX) animals. NX rats presented hypertension that was blunted by both losartan and propranolol, however, only losartan was able to reduce the expression levels of fibronectin FSP1 and TGF-β in the remnant kidney. The anti-fibrotic Klotho and PPAR-γ were reduced in the remnant kidney, and losartan, but not propranolol, restored their levels. In contrast, the profibrotic Wnt 7a and Wnt 3 were upregulated and losartan prevented the increase in Wnts. In vitro, Ang II induced a decrease in both klotho and in PPAR-γ in Madin-Darby canine kidney (MDCK) cells, and this effect was blunted by losartan. However, klotho expression was increased by pioglitazone, an agonist of PPAR-γ, and suppressed by BADGE, an antagonist of PPAR-γ, suggesting that the effect of Ang II downregulating klotho is mediated by PPAR-γ. These data suggest that activation of the Wnt pathway together with downregulation of PPAR-γ that in turn suppresses klotho contribute to potentiating the profibrotic effect of Ang II.

Sildenafil does not enhance but rather attenuates vasorelaxant effects of antidiabetic agents

Type 2 diabetic men commonly experience erectile dysfunction for which phosphodiesterase-5 (PDE5) inhibitors like sildenafil (Viagra) are often recommended. By preventing degradation of cyclic guanosine monophosphate (cGMP) in vascular smooth muscle, these inhibitors also enhance arterial vasorelaxant effects of nitric oxide donors (which stimulate cGMP synthesis). In the present work, we confirmed this enhancing effect after co-administration of sildenafil with nitroprusside to freshly-isolated rat tail arterial tissues. However, in the same tissues we also observed that sildenafil does not enhance but rather attenuates vasorelaxant effects of three commonly-used antidiabetic drugs, i.e. the biguanide metformin and the thiazolidinediones pioglitazone and rosiglitazone. Indeed, sildenafil completely blocked vasorelaxant effects of low concentrations of these drugs. In addition, we found that this same novel anti-vasorelaxant interaction of sildenafil with these agents was abolished by either 1) omitting extracellular glucose or 2) inhibiting specific smooth muscle glycolytic pathways; pathways known to preferentially utilize extracellular glucose to fuel certain adenosine triphosphate (ATP)-dependent ion transporters: e.g. ATP-sensitive K channels, sarcoplasmic reticulum Ca-ATPase, plasma membrane Ca-ATPase and Na/K-ATPase. Accordingly, we suspect that altered activity of one or more of these ion transporters mediates the observed attenuating (anti-vasorelaxant) interaction of sildenafil with the antidiabetic drugs. The present results are relevant because hypertension is so common and difficult to control in Type 2 diabetes. The present data suggest that sildenafil might interfere with the known antihypertensive potential of metformin and the thiazolidinediones. However, they do not suggest that it will interact with them to cause life-threatening episodes of severe hypotension, as can occur when it is co-administered with nitrates.

Early Clinical Detection of Pharmacologic Response in Insulin Action in a Nondiabetic Insulin-Resistant Population

Background

Insulin resistance heightens the risk for type 2 diabetes mellitus and cardiovascular disease. Amelioration of insulin resistance may reduce this risk. The thiazolidinedone class of insulin sensitizers improves insulin action in individuals with insulin-resistant diabetes and nondiabetic individuals. However, there are few reports on the time of onset of such effects independent of reversal of glucotoxicity.

Objective

The goal of our study was to test whether the thiazolidinedione pioglitazone has prominent early metabolic effects that can be detected in an obese, nondiabetic, insulin-resistant population.

Methods

We conducted a randomized, double-blind, placebo-controlled, parallel-group trial in men with nondiabetic insulin resistance using a hyperinsulinemic euglycemic clamp technique (at low and high doses of insulin at 10 and 40 mU/m²/min, respectively). The patients were given 30 mg daily oral pioglitazone or placebo for 28 days. Patients underwent a baseline clamp before initiation of treatment, and again at 14 and 28 days of treatment.

Results

Compared with placebo, under high-dose hyperinsulinemia, pioglitazone led to significant increases in glucose disposal rates (GDR) of 1.29 mg/kg/min (90% CI, 0.43–2.15; 39%; P=0.008) that were detectable at 2 weeks of treatment and persisted at 4 weeks of treatment. Under low-dose hyperinsulinemia, significant increases in GDR of 0.40 mg/kg/min (90% CI, 0.17–0.62; 95%; P=0.003) were observed at 4 weeks of treatment. These responses were accompanied by robust suppression of free fatty acids under hyperinsulinemic conditions, and by significant increases in circulating basal total adiponectin at 2 and 4 weeks of treatment.

Conclusions

Significant changes in insulin action across multiple insulin-sensitive tissues can be detected within 2 weeks of initiation of insulin-sensitizing therapy with pioglitazone in obese patients with nondiabetic insulin resistance. ClinicalTrials.gov identifier: NCT01115712.

Prevention of type 2 diabetes; a systematic review and meta-analysis of different intervention strategies

AIM

Different intervention strategies can prevent type 2 diabetes (T2DM). Aim of the present systematic review and meta-analysis was to evaluate the effectiveness of different strategies.

METHODS

Studies were grouped into 15 different strategies: 1: diet plus physical activity; 2: physical activity; 3-6: anti-diabetic drugs [glitazones, metformin, beta-cell stimulating drugs (sulphanylureas, glinides), alfa-glucosidase inhibitors]; 7-8: cardiovascular drugs (ACE inhibitors, ARB, calcium antagonists); 9-14 [diets, lipid-affecting drugs (orlistat, bezafibrate), vitamins, micronutrients, estrogens, alcohol, coffee]; 15: bariatric surgery. Only controlled studies were included in the analysis, whether randomized, non-randomized, observational studies, whether primarily designed to assess incident cases of diabetes, or performed with other purposes, such as control of hypertension, of ischemic heart disease or prevention of cardiovascular events. Appropriate methodology [preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement] was used. Seventy-one studies (490 813 subjects), published as full papers, were analysed to identify predictors of new cases of T2DM, and were included in a meta-analysis (random-effects model) to study the effect of different strategies. Intervention effect (new cases of diabetes) was expressed as odds ratio (OR), with 95% confidence intervals (C.I.s). Publication bias was formally assessed.

RESULTS

Body mass index was in the overweight range for 13 groups, obese or morbidly obese in lipid-affecting drugs and in bariatric surgery. Non-surgical strategies, except for beta-cell stimulating drugs, estrogens and vitamins, were able to prevent T2DM, with different effectiveness, from 0.37 (C.I. 0.26-0.52) to 0.85 (C.I. 0.77-0.93); the most effective strategy was bariatric surgery in morbidly obese subjects [0.16 (C.I. 0.11,0.24)]. At meta-regression analysis, age of subjects and amount of weight lost were associated with effectiveness of intervention.

CONCLUSIONS

These data indicate that several strategies prevent T2DM, making it possible to make a choice for the individual subject.

Induction of peroxisome proliferator-activated receptor γ (PPARγ)-mediated gene expression by tomato (Solanum lycopersicum L.) extracts

Since beneficial effects related to tomato consumption partially overlap with those related to peroxisome proliferator-activated receptor γ (PPARγ) activation, our aim was to test extracts of tomato fruits and tomato components, including polyphenols and isoprenoids, for their capacity to activate PPARγ using the PPARγ2 CALUX reporter cell line. Thirty tomato compounds were tested; seven carotenoids and three polyphenols induced PPARγ2-mediated luciferase expression. Two extracts of tomato, one containing deglycosylated phenolic compounds and one containing isoprenoids, also induced PPARγ2-mediated expression at physiologically relevant concentrations. Furthermore, enzymatically hydrolyzed extracts of seven tomato varieties all induced PPARγ-mediated expression, with a 1.6-fold difference between the least potent and the most potent variety. The two most potent varieties had high flavonoid content, while the two least potent varieties had low flavonoid content. These data indicate that extracts of tomato are able to induce PPARγ-mediated gene expression in vitro and that some tomato varieties are more potent than others.

Oral antidiabetic drugs and regression from prediabetes to normoglycemia: a meta-analysis

BACKGROUND

Impaired glucose tolerance, impaired fasting glucose, and elevated hemoglobin A(1c) are intermediate stages, considered prediabetes, a precursor to overt type 2 diabetes mellitus. Prediabetes is associated with increased risk for cardiovascular disease, independent of diabetes development. Data have shown that various oral antidiabetic drugs can help people regress from prediabetes to normoglycemia.

OBJECTIVE

To evaluate the efficacy of oral antidiabetic drugs in promoting regression from prediabetes to normoglycemia.

METHODS

MEDLINE (1950-November 2011), EMBASE (1990-November 2011), and Cochrane Central Register of Controlled Trials (indexed September 2011) were systematically searched. A manual search of references from reports of clinical trials and review articles was performed to identify additional relevant studies. Randomized controlled trials 12 weeks or more in duration evaluating any of the oral antidiabetic drugs and studying regression from prediabetes to normoglycemia were included. A random-effects model was used to calculate pooled odds ratios with 95% confidence intervals.

RESULTS

Thirteen studies (N = 11,600 participants) were included in the meta-analysis. Use of oral antidiabetic drugs in prediabetic patients was shown to double the odds of achieving normoglycemia compared to controls (OR 2.03, 95% CI 1.54 to 2.67). When individual classes of oral antidiabetic drugs were evaluated, use of thiazolidinediones (OR 2.33, 95% CI 1.93 to 2.81) and α-glucosidase inhibitors (OR 2.02, 95% CI 1.26 to 3.24) was associated with significantly increased odds. However, biguanides (OR 2.04) and sulfonylureas (OR 1.84) failed to reach statistical significance (p = 0.06 and p = 0.39, respectively).

CONCLUSIONS

In patients with prediabetes, oral antidiabetic drugs were associated with increased odds of regression to normoglycemia versus placebo/control. Only thiazolidinediones and α-glucosidase inhibitors provided a statistically significant increase in odds of regressing to normoglycemia.

Effects of pioglitazone and rosiglitazone combined with metformin on body weight in people with diabetes

Currently, pioglitazone and rosiglitazone are the thiazolidinediones available for clinical use. In the literature, there are different studies concerning the efficacy, safety and tolerability of thiazolidinediones as add-on therapy to metformin in patients with type 2 diabetes inadequately controlled with metformin alone. Metformin and thiazolidinediones are both antihyperglycaemic drugs, both lower blood glucose concentrations in type 2 diabetes without causing overt hypoglycaemia and both require the presence of insulin to generate their therapeutic effects, but act without stimulating insulin secretion. Some authors reported that the improved glycaemic control obtained with thiazolidinediones is associated with an increase in body weight with an estimated 2-3 kg weight gain for every 1% decrease in HbA(1c) which could negate some of the benefits of the improved metabolic control. Some other authors, instead, reported that thiazolidinediones give a better improvement in the glycaemic control compared with metformin alone without giving weight gain. The emerging discrepancies from these studies could be because of the study design, the patient selection, the degree of glycaemic control and/or the methods to measure body weight. We have undertaken a thorough literature search on Medline and Embase to evaluate the effects of thiazolidinediones plus metformin combination in people with diabetes on the body weight.

Effect of rosiglitazone, metformin and medical nutrition treatment on arterial stiffness, serum MMP-9 and MCP-1 levels in drug naive type 2 diabetic patients

The aim of the study was to evaluate the long-term effect of rosiglitazone and metformin monotherapy with medical nutrition treatment (MNT) and of MNT alone on arterial stiffness, serum monocyte chemoattractant protein (MCP)-1 and matrix metalloproteinase (MMP)-9 in drug naive patients with type 2 diabetes mellitus. Fifty type 2 diabetic patients were randomized to receive rosiglitazone 4 mg/day (n=19) or metformin 850 mg/day (n=16) with MNT or MNT alone (n=15), for 52 weeks. Arterial stiffness was assessed by using large and small artery elasticity index (SAEI and LAEI, respectively). SAEI, LAEI, serum MCP-1 and MMP-9 levels were measured at baseline and following 52 weeks of treatment. SAEI was improved only in the rosiglitazone group, and the difference was still statistically significant when the three groups were compared (p=0.024). There were no differences in LAEI in inter- and intragroup comparisons at the end of the study. Serum MMP-9 levels were decreased in the metformin (-13.5+/-34.8%, p=0.02) and rosiglitazone (-27.2+/-51.0%, p=0.023) groups compared with baseline values, whereas no significant change was seen in serum MCP-1 levels. These results suggest that rosiglitazone monotherapy has favorable effects on arterial stiffness compared with metformin monotherapy independent of glycemic control.

Insulin Resistance and Inflammation in the Early Phase of Type 2 Diabetes: Potential for Therapeutic Intervention

Prospective studies of prediabetic subjects have shown that obesity and its duration are major risk factors for type 2 diabetes. Longitudinal studies are consistent with an etiologic role of subclinical inflammation in the pathogenesis of type 2 diabetes, primarily as a mediator of obesity-induced insulin resistance. Inflammation is closely associated with endothelial dysfunction and is recognized as one of the cardiovascular risk factors clustering in the Insulin Resistance Syndrome or Metabolic Syndrome. The adipose tissue has been recognized as an important source of metabolically active secretory products (adipocytokines), free fatty acids, leptin, TNF-alpha, Iinterleucin-6, plasminogen activator inhibitor-1, adiponectin and resistin. Prevention of insulin resistance by weight loss, diet and exercise is very effective in reducing the progression from glucose intolerance to type 2 diabetes in obese subjects. Since insulin resistance is a key disturbance in early type 2 diabetes additional drug treatment with insulin-sensitizing drugs might be helpful to reduce the progression to both beta-cell failure and macrovascular late complications. The PROACTIVE study will determine if the effects of improving insulin sensitivity and reducing inflammation will translate into clinical benefits and reduce the cardiovascular morbidity and mortality associated with insulin resistance and Type 2 diabetes.

The effects of thiazolidinediones on blood pressure levels – A systematic review

Insulin resistance has been proposed to be the underlying disorder of the so-called metabolic or insulin resistance syndrome, which represents the clustering in the same individual of several cardiovascular risk factors, such as type 2 diabetes mellitus, hypertension, abdominal obesity, elevated triglycerides and low high-density lipoprotein-cholesterol. As far as the connection of insulin resistance and compensatory hyperinsulinaemia with hypertension is concerned, a number of mechanisms possibly linking these disturbances have been described, such as activation of sympathetic nervous system, enhancement of renal sodium reabsorption, or impairment of endothelium-dependent vasodilatation. Thiazolidinediones (TZDs) constitute a class of oral antihyperglycaemic agents that act by decreasing insulin resistance, and apart from their action on glycaemic control, they have been also reported to exert beneficial effects on other parameters of the metabolic syndrome. In particular, during recent years a considerable number of animal and human studies have shown that the use of TZDs was associated with usually small but significant reductions of blood pressure (BP) levels. Since a possible beneficial action of these compounds on BP could be of particular value for patients with the metabolic syndrome, this review aimed to summarize and evaluate the literature data in the field, derived either from studies that just examined BP levels among other parameters or from studies that were specifically designed to determine the effect of a TZD on BP.

Relation of severe coronary artery narrowing to insulin or thiazolidinedione use in patients with type 2 diabetes mellitus (from the Bypass Angioplasty Revascularization Investigation 2 Diabetes Study)

Patients with diabetes continue to die of coronary artery disease (CAD) at rates 2 to 4 times higher than patients without diabetes, despite advances in treatment of cardiovascular disease. The role of glycemic control therapies, independent of their glucose-lowering effects, on cardiovascular disease is a recurring question. We examined the association of glycemic control therapies with extent of CAD as measured by coronary angiogram obtained at baseline in 1,803 subjects in the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) trial who had type 2 diabetes mellitus, documented moderate to severe CAD, and no previous cardiac revascularization procedures. The association between glycemic control therapy use recorded at baseline and percent coronary artery stenosis and myocardial jeopardy index was analyzed by multiple regression models. Insulin use at study entry was associated with 23% fewer highly stenotic lesions (> or =70%) (p <0.001) and a significantly lower myocardial jeopardy index compared with subjects not on insulin, despite a worse cardiac risk factor profile, more unstable angina, and increased inflammatory markers in insulin users. Subjects taking thiazolidinediones (TZDs) for > or =6 months had 17% fewer highly stenotic lesions (p = 0.02) and significantly lower C-reactive protein, fibrinogen, and plasminogen activator inhibitor-1 levels compared with those not taking TZDs. In conclusion, this cross-sectional study of patients with type 2 diabetes mellitus and CAD showed that treatment with insulin or TZDs was associated with fewer highly stenotic lesions, independent of disease duration, glycemic control, and other risk factors.

Thiazolidinediones in type 2 diabetes: a cardiology perspective

OBJECTIVE

To examine the cardiovascular effects of thiazolidinediones (TZDs), discuss concerns regarding this drug class and its relation to heart failure (HF) and myocardial infarction (MI), and address the clinical implications of HF and MI.

DATA SOURCES

Literature was accessed through MEDLINE (1979-April 2008) using the search terms type 2 diabetes mellitus, thiazolidinediones, cardiovascular events, heart failure, myocardial infarction, and edema. Reviews, meta-analyses, clinical trials, observational studies (case-control, cohort), and descriptive studies (case reports, case series) were included.

STUDY SELECTION AND DATA EXTRACTION

All articles that were written in English and identified from the data sources were reviewed.

DATA SYNTHESIS

The American Diabetes Association recommends metformin as first-line therapy for type 2 diabetes, with the subsequent addition of a TZD, sulfonylurea, or insulin if the target is not met. Beyond glucose lowering, TZDs improve various factors associated with cardiovascular risk. Whether the effects translate into beneficial cardiovascular outcomes is controversial. In PROactive (Prospective Pioglitazone Clinical Trial in Macrovascular Events), pioglitazone did not produce a significant reduction in the primary endpoint that included a composite of coronary and vascular deaths, but the secondary composite endpoint of all-cause mortality, MI, or stroke was significantly reduced. Concerns related to HF have led to warnings in the labeling of TZDs. The drugs are contraindicated in patients with New York Heart Association Class III or IV HF. Rosiglitazone, but not pioglitazone, is associated with an increased risk of myocardial ischemic events, although the absolute magnitude is extremely small.

CONCLUSIONS

Although the glycemic efficacy of TZDs is comparable to that of metformin, adverse effects and higher costs make TZDs less appealing for initial therapy. Among the TZDs, pioglitazone should be considered based on cardiovascular safety data. In combination with metformin, pioglitazone may be particularly beneficial for patients with diabetes and metabolic syndrome. For patients on rosiglitazone who are achieving glycemic goals and tolerating the therapy without apparent complications, rosiglitazone may be continued.

Effects of ramipril and rosiglitazone on cardiovascular and renal outcomes in people with impaired glucose tolerance or impaired fasting glucose: results of the Diabetes REduction Assessment with ramipril and rosiglitazone Medication (DREAM) trial

OBJECTIVE

Impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) are risk factors for diabetes, cardiovascular disease (CVD), and kidney disease. We determined the effects of ramipril and rosiglitazone on combined and individual CVD and renal outcomes in people with IGT and/or IFG in the Diabetes REduction Assessment With ramipril and rosiglitazone Medication (DREAM) trial.

RESEARCH DESIGN AND METHODS

A total of 5,269 people aged >or=30 years, with IGT and/or IFG without known CVD or renal insufficiency, were randomized to 15 mg/day ramipril versus placebo and 8 mg/day rosiglitazone versus placebo. A composite cardiorenal outcome and its CVD and renal components were assessed during the 3-year follow-up.

RESULTS

Compared with placebo, neither ramipril (15.7% [412 of 2,623] vs. 16.0% [424 of 2,646]; hazard ratio [HR] 0.98 [95% CI 0.84-1.13]; P = 0.75) nor rosiglitazone (15.0% [394 of 2,635] vs. 16.8% [442 of 2,634]; 0.87 [0.75-1.01]; P = 0.07) reduced the risk of the cardiorenal composite outcome. Ramipril had no impact on the CVD and renal components. Rosiglitazone increased heart failure (0.53 vs. 0.08%; HR 7.04 [95% CI 1.60-31.0]; P = 0.01) but reduced the risk of the renal component (0.80 [0.68-0.93]; P = 0.005); prevention of diabetes was independently associated with prevention of the renal component (P < 0.001).

CONCLUSIONS

Ramipril did not alter the cardiorenal outcome or its components. Rosiglitazone, which reduced diabetes, also reduced the development of renal disease but not the cardiorenal outcome and increased the risk of heart failure.

Effect of the addition of rosiglitazone to metformin or sulfonylureas versus metformin/sulfonylurea combination therapy on ambulatory blood pressure in people with type 2 diabetes: a randomized controlled trial (the RECORD study)

Background

Hypertension and type 2 diabetes are common co-morbidities. Preliminary studies suggest that thiazolidinediones reduce blood pressure (BP). We therefore used ambulatory BP to quantify BP lowering at 6–12 months with rosiglitazone used in combination with metformin or sulfonylureas compared to metformin and sulfonylureas in people with type 2 diabetes.

Methods

Participants (n = 759) in the multicentre RECORD study were studied. Those taking metformin were randomized (open label) to add-on rosiglitazone or sulfonylureas, and those on sulfonylurea to add-on rosiglitazone or metformin.

Results

24-Hour ambulatory BP was measured at baseline, 6 months and 12 months. At 6 and 12 months, reductions in 24-hour ambulatory systolic BP (sBP) were greater with rosiglitazone versus metformin (difference at 6 months 2.7 [95% CI 0.5–4.9] mmHg, p = 0.015; 12 months 2.5 [95% CI 0.2–4.8] mmHg, p = 0.031). Corresponding changes for ambulatory diastolic BP (dBP) were comparable (6 months 2.7 [95% CI 1.4–4.0] mmHg, p < 0.001; 12 months 3.1 [95% CI 1.8–4.5] mmHg, p < 0.001). Similar differences were observed for rosiglitazone versus sulfonylureas at 12 months (sBP 2.7 [95% CI 0.5–4.9] mmHg, p = 0.016; dBP 2.1 [95% CI 0.7–3.4] mmHg, p = 0.003), but differences were smaller and/or not statistically significant at 6 months (sBP 1.5 [95% CI -0.6 to 3.6] mmHg, p = NS; dBP 1.3 [95% CI 0.0–2.5] mmHg, p = 0.049). Changes in BP were not accompanied by compensatory increases in heart rate, did not correlate with basal insulin sensitivity estimates and were not explained by changes in antihypertensive therapy between the various strata.

Conclusion

When added to metformin or a sulfonylurea, 12-month treatment with rosiglitazone reduces ambulatory BP to a greater extent than when metformin and a sulfonylurea are combined.

Trial registration

NCT00379769

Management of type 2 diabetes mellitus: is it time for a paradigm shift?

Type 2 diabetes mellitus is a multi-organ disease that results from the combination of insulin resistance and a beta-cell secretory defect. The worldwide prevalence of type 2 diabetes has increased substantially during the past decade, and patients with this disease continue to experience a high incidence of morbidity and mortality. Because the complications associated with this disease affect multiple organ systems and have a dramatic impact on daily life, the importance of lowering glycosylated hemoglobin (HbA(1c)) levels to within the normal range cannot be overemphasized. The introduction in the past decade of several new classes of pharmacological agents to treat patients with type 2 diabetes now provides the opportunity to focus therapy on treating the underlying disease process instead of just reacting to the blood glucose levels. The thiazolidinediones are unique in their ability to modulate free fatty acid metabolism and to improve insulin sensitivity. These agents also exert numerous nonglycemic effects on the vasculature and lipid metabolism and may improve many of the risk factors associated with metabolic syndrome. Data from the United Kingdom Prospective Diabetes Study (UKPDS) group showed that conventional methods of managing type 2 diabetes, including the use of sulfonylureas or biguanides, do not provide long-term glycemic control. Consequently, new treatment paradigms stressing the earlier use of thiazolidinediones, either alone or in combination with metformin, may lead to more durable glycemic control, thus facilitating the reduction of complications in patients with type 2 diabetes.

Effects of thiazolidinediones on blood pressure

Peroxisome-proliferator-activated receptor-gamma (PPAR-gamma) agonists (known as thiazolidinediones; TDZs) activate nuclear receptors that regulate gene expression; they were developed as insulin-sensitizing drugs to treat type 2 diabetes mellitus. Although the prototypic TZD troglitazone was withdrawn from the market due to hepatic toxicity, rosiglitazone and pioglitazone are mainstays in managing type 2 diabetes mellitus. TZDs exert their hypoglycemic effect by reducing insulin resistance, hence improving insulin sensitivity. However, TZDs also exhibit a broad range of cardiovascular actions, with the clinical consequence of reduction in blood pressure (BP), observed in animal models and human diabetic subjects. The magnitude of reduction appears to be about 4 to 5 mm Hg in systolic and 2 to 4 mm Hg in diastolic BP--sufficient to significantly reduce subsequent cardiovascular event rates. But these BP-reducing properties, which are not present with metformin or sulfonylureas, are particularly important when viewed in conjunction with hypoglycemic effects. A significant proportion of patients with type 2 diabetes mellitus and BP mildly above target range might be successfully treated for both processes with a single drug.

Interference with PPAR gamma function in smooth muscle causes vascular dysfunction and hypertension

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor that plays a critical role in metabolism. Thiazolidinediones, high-affinity PPARgamma ligands used clinically to treat type II diabetes, have been reported to lower blood pressure and provide other cardiovascular benefits. Some mutations in PPARgamma (PPARG) cause type II diabetes and severe hypertension. Here we tested the hypothesis that PPARgamma in vascular muscle plays a role in the regulation of vascular tone and blood pressure. Transgenic mice expressing dominant-negative mutations in PPARgamma under the control of a smooth-muscle-specific promoter exhibit a loss of responsiveness to nitric oxide and striking alterations in contractility in the aorta, hypertrophy and inward remodeling in the cerebral microcirculation, and systolic hypertension. These results identify PPARgamma as pivotal in vascular muscle as a regulator of vascular structure, vascular function, and blood pressure, potentially explaining some of the cardioprotective effects of thiazolidinediones.

Insulin resistance and impaired functional vasodilation in obese Zucker rats

Individuals with metabolic syndrome exhibit insulin resistance and an attenuated functional vasodilatory response to exercise. We have shown that impaired functional vasodilation in obese Zucker rats (OZRs) is associated with enhanced thromboxane receptor (TP)-mediated vasoconstriction. We hypothesized that insulin resistance, hyperglycemia/hyperlipidemia, and the resultant ROS are responsible for the increased TP-mediated vasoconstriction in OZRs, resulting in impaired functional vasodilation. Eleven-week-old male lean Zucker rats (LZRs) and OZRs were fed normal rat chow or chow containing rosiglitazone (5 mg.kg(-1).day(-1)) for 2 wk. In another set of experiment, LZRs and OZRs were treated with 2 mM tempol (drinking water) for 7-10 days. After the treatments, spinotrapezius muscles were prepared, and arcade arteriolar diameters were measured following muscle stimulation and arachidonic acid (AA) application (10 muM) in the absence and presence of the TP antagonist SQ-29548 (1 muM). OZRs exhibited higher insulin, glucose, triglyceride, and superoxide levels and increased NADPH oxidase activity compared with LZRs. Functional and AA-induced vasodilations were impaired in OZRs. Rosiglitazone treatment improved insulin, glucose, triglyceride, and superoxide levels as well as NADHP oxidase activity in OZRs. Both rosiglitazone and tempol treatment improved vasodilatory responses in OZRs with no effect in LZRs. SQ-29548 treatment improved vasodilatory responses in nontreated OZRs with no effect in LZRs or treated OZRs. These results suggest that insulin resistance and the resultant increased ROS impair functional dilation in OZRs by increasing TP-mediated vasoconstriction.

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.

Effect of rosiglitazone on factors related to endothelial dysfunction in patients with type 2 diabetes mellitus

The effect of the insulin sensitizer rosiglitazone (RSG) on biological markers of endothelial dysfunction in subjects with type 2 diabetes mellitus (T2DM) was investigated in a 12-week, multi-center, randomized, double-blind study. One hundred and thirty-six subjects aged 40-70 years, with FPG > or = 7.0 and < or = 15.0 mmol/l, previously treated with a single oral anti-diabetic agent or diet/exercise, were randomized to RSG 8 mg/day (n=65) or placebo (PBO, n=71). Results revealed that RSG significantly reduced soluble (s)E-selectin by -10.9% (P=0.004) compared with PBO, but did not significantly alter soluble vascular cell adhesion molecule-1 (+0.6%, P=NS). Compared with PBO, RSG also significantly reduced plasminogen activator inhibitor-1 (-36.9%, P<0.001), tissue plasminogen activator antigen (-22.7%, P<0.001), FPG (-2.8 mmol/l, P<0.001), fasting fructosamine (-42.0 mg/dl, P<0.001). Post-prandial AUC(0-4h) for free fatty acids (FFAs) reduced by -6.5 mg/dl*h from baseline (P=0.03), a change that positively and significantly correlated with changes in sE-selectin (r=0.22, P=0.05). The incidence of adverse events was similar in the two groups (RSG: 35.4%; PBO: 40.8%); the majority mild or moderate. These data support the hypothesis that, in patients with T2DM, rosiglitazone has beneficial effects on biological markers of endothelial dysfunction. Improvements in insulin sensitivity and decreases in FFAs may play a role in these effects.

beta-cell function and anti-diabetic pharmacotherapy

Type 2 diabetes is a chronic disease characterized by progressive worsening of glycaemic control as indicated by the United Kingdom Prospective Diabetes Study (UKPDS). The progressive nature of the disease is mainly due to continuous loss of beta-cell mass and function. Though much of this loss is due to intrinsic defects of the beta-cell several factors may accelerate such process. These include the metabolic environment where hyperglycaemia and increased circulating free-fatty acid exert a toxic effect on the beta-cell. Therefore, tight metabolic control may prevent not only the risk of long-term diabetic complication but also preserve beta-cell function. Several therapeutic agents are currently used for treatment of type 2 diabetic patients. However, their effect on maintenance of beta-cell function has not been yet systematically reviewed. By literature searching we have then analysed in detail the effect of sulfonylureas and non-sulfonylureic secretagogues, incretin-mimetics, insulin sensitizers, alpha-glucosidase inhibitors, and insulin on beta-cell function. Moreover, promising future approaches aiming at preserving beta-cell function and mass are discussed.

Rosiglitazone reduces office and diastolic ambulatory blood pressure following 1-year treatment in non-diabetic subjects with insulin resistance

OBJECTIVE

Rosiglitazone (RSG) has been reported to reduce blood pressure (BP) in patients with type-2 diabetes, but similar effects in non-diabetic people with insulin resistance is less clear. Our aim was to test the long-term BP-lowering effects of RSG compared with placebo.

METHODS

We recruited participants for BP evaluation of RSG treatment from a larger intervention trial. Office BP was recorded in 355 non-diabetic subjects with insulin resistance randomized to receive either RSG or placebo for 52 weeks. Ambulatory BP monitoring (ABPM; Spacelab 90207) was performed in a subgroup of 24 subjects (RSG: n = 11; placebo n = 13).

RESULTS

After 1 year, the office BP decreased by -3.1 mmHg systolic (p<0.05) and -3.8 mmHg diastolic (p<0.001) in the RSG group versus placebo. In patients treated with RSG, at 1 year there was a trend for a reduction from baseline for mean 24-h diastolic BP (DBP), daytime DBP and night-time DBP (-4.39, -5.26 and -2.93 mmHg, respectively). However, only daytime DBP was significantly lower in the RSG group compared with control (adjusted mean difference: -4.41 mmHg, p = 0.007). There was also a non-significant trend for a reduction in mean 24-h systolic BP (SBP), daytime SBP and night-time SBP (-2.70, -2.51 and -3.35 mmHg, respectively).

CONCLUSIONS

RSG treatment for 1 year was associated with a small but significant decrease in diastolic 24-h ambulatory diastolic BP, and both systolic and diastolic office BPs in non-diabetic people with insulin resistance.

Metformin/rosiglitazone combination pill (Avandamet) for the treatment of patients with Type 2 diabetes

More than 150 million people worldwide have diabetes, the prevalence of which is increasing so rapidly that the number of adults with diabetes in the world will rise to 300 million by the year 2025. In the US, approximately 21 million people have diabetes and in some areas of the country, the prevalence is as high as 50%. The pathophysiologic hallmarks consist of insulin resistance and progressive pancreatic beta-cell dysfunction. An increased metabolic demand for insulin due to increased insulin resistance usually precedes the development of hyperglycemia. At early stages, pancreatic beta cells compensate for insulin resistance by hypersecretion of insulin. However, the period of beta-cell compensation is followed by beta-cell failure, in which the pancreas fails to secrete sufficient insulin and diabetes ensues. Biguanides and thiazolidinediones (TZDs) are two unique classes of oral antidiabetic agents that are the most commonly used medications to improve insulin sensitivity. They have no direct effect on beta-cell function, although some indirect mechanisms of actions may help to preserve beta-cell function or slow beta-cell apoptosis. Their glucose-lowering effect results from improving insulin sensitivity in a complementary fashion: metformin reduces hepatic glucose production and TZDs increase skeletal muscle glucose use. The combination of metformin and rosiglitazone in a single pill (Avandamet), was approved by the FDA in October 2002 for the treatment of diabetes. As insulin resistance is a pathophysiologic cornerstone of diabetes and cardiovascular disease, the use of Avandamet represents an optimal approach to the treatment of diabetes. This manuscript reviews the pharmacology, safety and benefits of the combination pill Avandamet.

Rosiglitazone and carotid IMT progression rate in a mixed cohort of patients with type 2 diabetes and the insulin resistance syndrome: main results from the Rosiglitazone Atherosclerosis Study

OBJECTIVE

Insulin resistance is associated with progression of atherosclerosis. We assessed the effect of 12 months of treatment with rosiglitazone (RSG) on the progression of carotid intima-media thickness (IMT) in people with type 2 diabetes mellitus (T2DM) or the insulin resistance syndrome (IRS).

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Malmö University Hospital, Malmö, Sweden.

SUBJECTS

555 subjects (200 with T2DM and 355 nondiabetics with IRS according to EGIR criteria), aged 35-80 years. 447 subjects (165 T2DM and 282 IRS) completed the study.

INTERVENTION

Participants were allocated to placebo or RSG 4 mg for 2 months and then 8 mg daily.

MAIN OUTCOME MEASURE

Change in composite IMT [mean IMT in the common carotid artery (CCA) and maximal IMT in the bulb] was the primary and various other IMT measures were secondary outcome variables.

RESULTS

There was no effect of RSG treatment in the mixed population. In T2DM patients there was a reduced progression of the composite IMT (mean change: 0.041 vs. 0.070 mm, P = 0.07), and of the mean IMT CCA (mean change: -0.005 mm vs. 0.021 mm, P = 0.007). RSG treatment led to significant reductions of HOMA-IR, fasting plasma glucose, HbA1c, PAI-1 activity, fibrinogen, C-reactive protein and matrix metalloproteinase-9.

CONCLUSIONS

In a mixed study population of patients with T2DM and IRS RSG treatment was not associated with a statistically significant reduction of carotid IMT progression rate. Separate analyses of these two patient groups indicated, however, a significant beneficial effect on CCA IMT in T2DM patients but no similar effect in subjects with IRS.

Thiazolidinediones for the treatment of type 2 diabetes

Thiazolidinediones (TZD), or glitazones, represent a new generation of antidiabetic drugs that have recently been introduced in Europe. They improve insulin resistance, one of the key anomalies involved in the pathogenesis of type 2 diabetes mellitus, by activating the nuclear peroxoxisome proliferator activated receptor-gamma (PPAR-gamma), leading to crucial metabolic alterations in adipose tissue. Rosiglitazone and pioglitazone have been shown to be active as monotherapy, in combination therapy with metformin or sulfonylureas, and even in triple therapy. They are generally well tolerated but can induce fluid retention. Cardiac failure is a contraindication for the use of TZDs, as is the concomitant administration of insulin. Aside from their effect on glycemic control, TZDs act on several cardiovascular risk factors and may protect pancreatic beta cells from apoptosis. The cardiovascular protective effect of TZDs has recently been demonstrated with the results of the PROactive study, and long-term preservation of beta-cell function is currently under further investigation.

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.

Thiazolidinediones, insulin resistance and obesity: Finding a balance

The clinical efficacy of currently available thiazolidinediones (TZDs) in improving glycaemic control and ameliorating several risk factors for cardiovascular disease (linked to their insulin-sensitising actions as well as direct vascular effects) is well established. Treatment-associated weight gain, however, which has been identified as a class effect of the TZDs, is seen in a number of patients. The magnitude of weight gain correlates in part with improved metabolic control, i.e. better responders are more prone to increases in body weight. The cardiovascular risk associated with obesity appears to be depot specific; while peripheral obesity is associated with a low risk of cardiovascular complications, central obesity confers a greater degree of risk. Evidence is reviewed that increases in body weight associated with TZD treatment are associated with neutral effects (or even, decreases) in visceral fat, the adipose depot that is associated with central obesity.

Rosiglitazone is effective and well-tolerated in a range of therapeutic regimens during daily practice in patients with type 2 diabetes

Subjects (N = 22,808) with inadequately controlled type 2 diabetes mellitus (T2DM) were included in a large 6-month observational study in Germany. Rosiglitazone (RSG) was added to existing therapy in line with daily practice, with 19,962 subjects evaluated for efficacy by treatment group: RSG monotherapy (n = 1017), RSG plus metformin (MET) (n = 7160), RSG plus sulphonylurea (n = 5033), triple oral therapy (n = 4247), and the remaining subject population (n = 2505). Overall, RSG significantly reduced median HbA(1c) and fasting blood glucose by 1.3% and 50 mg/dl over 6 months (p < 0.001 for both). The proportion of subjects achieving glycaemic goals of <or= 6.5% and <or= 7.0% increased from 5.7% to 33.8%, and from 13.9% to 55.5%, respectively (p < 0.001 for both). Mean systolic and diastolic blood pressures were reduced in the total subject population by 6 mmHg and 2 mmHg, respectively (p < 0.001 for both). RSG had a neutral or reductive effect on mean weight of most (69%) subjects. Consistent with clinical trial data, RSG mono- or combination therapy improved glycaemic control when used in daily clinical practice and is generally well-tolerated.

Can thiazolidinediones delay disease progression in type 2 diabetes?

BACKGROUND

Type 2 diabetes results from increasing insulin resistance coupled with progressive loss of beta-cell function. Further deterioration of beta-cell function is associated with progression of diabetes and the potential development of microvascular and macrovascular complications.

SCOPE

This review examines current knowledge of beta-cell function and uses this information to assess how the results of ongoing trials could increase our understanding of disease progression and potential interventions. Data were derived from a Medline search using the search terms 'beta-cell dysfunction', 'IGT', 'thiazolidinediones', 'metformin', and 'sulfonylurea'.

RESULTS

The mechanisms that underlie beta-cell dysfunction are complex and most likely involve the interplay of a range of factors that reduce both beta-cell mass and secretory function. These include detrimental effects associated with hyperglycemia itself, elevated free fatty acids, and inflammatory responses linked to adipocyte-derived cytokines, with apoptosis a key underlying mechanism. Early intervention with treatments that address these defects, and preserve beta-cell function while improving insulin sensitivity, may delay disease progression in patients with type 2 diabetes and also prevent the development of diabetes in 'at-risk' individuals. Two of the studies examining the effects of interventions on development and progression of diabetes that are due to report shortly are ADOPT (A Diabetes Outcome Progression Trial), comparing a thiazolidinedione, metformin and a sulfonylurea in patients with type 2 diabetes not previously treated with oral hypoglycemic agents, and DREAM (Diabetes REduction Assessment with ramipril and rosiglitazone Medication), assessing the effects of a thiazolidinedione and an angiotensin-converting enzyme inhibitor in subjects with impaired glucose tolerance and/or impaired fasting glucose.

CONCLUSIONS

Although we do not have a full understanding of the mechanisms driving progression of type 2 diabetes, there is growing evidence that we may be able to modulate them and thereby improve patient outcomes.

A meta-analysis of the effect of thiazolidinediones on blood pressure

In epidemiologic studies, insulin resistance is associated with hypertension. Thiazolidinediones (TZDs) are antidiabetic agents that decrease insulin resistance. Multiple clinical trials have evaluated the effect of TZDs on blood pressure (BP) with inconsistent results. The aim of this study was to estimate the effect of TZDs on BP. The authors searched PubMed for clinical trials published in English. A total of 37 clinical trials that reported a change in BP were included in the analysis. Trials with independent-group design and trials with pre-post design were evaluated separately. When compared with baseline, TZDs lowered systolic BP by 4.70 mm Hg (95% confidence interval, -6.13 to -3.27) and diastolic BP by 3.79 mm Hg (95% confidence interval, -5.82 to -1.77). When compared with placebo, TZDs lowered systolic BP by 3.47 mm Hg (95% confidence interval, -4.91 to -2.02) and diastolic BP by 1.84 mm Hg (95% confidence interval, -3.43 to -0.25). Thus, TZDs lower both systolic and diastolic BP, albeit the BP-lowering effect is small and may not be of clinical significance.

Thiazolidinediones and progression of renal disease in patients with diabetes

OBJECTIVE

Thiazolidinediones (TZDs) are used in the treatment of type 2 diabetes mellitus (T2DM) and appear to have beneficial effects on markers of cardiovascular or renal risk that are independent of glycemic control. We examined the effects of TZDs on renal survival in a predominantly black population with T2DM.

METHODS

We performed a retrospective case-control study in patients with T2DM seen in our nephrology clinic in 2001 to 2002. Cases had T2DM and were on a TZD at presentation or for >or= 6 months over follow-up. Controls were matched for sex, age, duration of T2DM, and initial creatinine. Reaching end-stage renal disease (ESRD) was the primary end point.

RESULTS

From 387 records, 43 cases (34 blacks, 31 females) and 106 controls (96 blacks, 83 females) were identified. The baseline characteristics were similar for both groups. Both groups had moderate renal disease (estimated glomerular filtration rate approximately 40-45 mL/min). Cases had lower systolic blood pressure over follow-up (p=.02), but there was no difference in glycemic control or use of insulin. Renal survival was better among cases (age- and gender-adjusted odds ratio for reaching ESRD 0.17 [95% confidence interval 0.03-0.8]; p=.03). When adjusted for systolic blood pressure over follow-up, the tendency for improved renal survival in cases remained but was no longer significant.

CONCLUSION

We conclude that TZDs may protect against the progression of renal disease in T2DM. Prospective studies are required to determine the effects of TZDs on renal survival in T2DM.

Peroxisome proliferator-activated receptor-gamma and its agonists in hypertension and atherosclerosis : mechanisms and clinical implications

Cardiovascular diseases are the leading cause of morbidity and mortality in the US. Proper management and/or prevention of atherosclerosis and hypertension, two complex and chronic disorders, would significantly reduce the risk for cardiovascular events such as myocardial infarction and stroke, but this requires an understanding of the mechanisms underlying their development and progression. Whereas a great deal has been learned and applied toward the management of these disorders, especially hypertension, morbidity and mortality remains unacceptably high, most likely because there are disease-causing mechanisms that have yet to be fully recognized. Understanding these disease mechanisms is necessary so that novel management strategies can be developed. One of these novel mechanisms centers on peroxisome proliferator-activated receptor (PPAR)-gamma. PPAR-gamma is a member of the nuclear receptor superfamily of ligand-activated transcription factors known to play a role in glucose homeostasis and adipocyte differentiation and, more recently, has been shown to have anti-inflammatory, antiatherogenic, and antihypertensive effects. Thiazolidinediones, a class of drugs used in the treatment of type 2 diabetes mellitus, are high-affinity ligands for PPAR-gamma. In this review, the anti-inflammatory, anti-atherosclerotic, and anti-hypertensive mechanisms by which PPAR-gamma and its agonists are thought to exert protective effects on the cardiovascular system are discussed. Ongoing clinical trials using PPAR-gamma activators for the management of cardiovascular diseases, especially in patients with type 2 diabetes mellitus, are summarized.

Implications of Rosiglitazone and Pioglitazone on Cardiovascular Risk in Patients with Type 2 Diabetes Mellitus

Clinical data suggest that thiazolidinediones--specifically, rosiglitazone and pioglitazone--may improve cardiovascular risk factors through multiple mechanisms. Low insulin sensitivity has been described as an independent risk factor for coronary artery disease and cerebrovascular disease. Patients with insulin resistance often have several known risk factors, such as obesity, dyslipidemia, and hypertension. Other emerging risk factors may be prevalent in patients with insulin resistance, such as hyperinsulinemia, elevated C-reactive protein, elevated plasminogen activator inhibitor levels, and small, dense, low-density lipoproteins. The only available drug class that primarily targets insulin resistance is the thiazolidinediones. These drugs have shown efficacy in affecting surrogate markers of cardiovascular risk in patients with diabetes mellitus. Alterations in these risk factors are likely due to their effects on improving insulin sensitivity and/or glycemic control. Trials to assess whether thiazolidinediones actually reduce cardiovascular outcomes are continuing.

Thiazolidinediones in patients with diabetes mellitus and heart failure : implications of emerging data

Individuals with diabetes mellitus have an increased risk of developing heart failure, usually as a consequence of coronary artery disease, although a specific diabetic cardiomyopathy, secondary to a microangiopathy, may also exist. The thiazolidinediones, a relatively new class of insulin-sensitizing agents used in the management of type 2 diabetes mellitus, have a number of complex metabolic actions on surrogate markers of atherogenesis, supported by the results of the recently published PROACTIVE (PROspective pioglitAzone Clinical Trial In macroVascular Events) trial. Unfortunately, the use of thiazolidinediones in individuals with diabetes mellitus and heart failure is limited because of a propensity to cause fluid retention. The underlying mechanisms of fluid retention have yet to be fully elucidated, but appear to be a dose-related class effect, exacerbated by combination therapy with insulin, and in some cases may be localized to peripheral edema. In parallel, echocardiographic studies show no significant effect of thiazolidinediones on cardiac structure or function. The design of epidemiologic studies describing an increased risk of developing heart failure in individuals with type 2 diabetes mellitus prescribed thiazolidinediones has been questioned, and a study of 'new users' of antihyperglycemic treatments found no increased risk of hospitalization for heart failure with thiazolidinedione therapy. There is also increasing evidence for the potential benefits of insulin sensitization in patients with diabetes mellitus and known heart failure, and a large observational study of over 16 000 patients with a principal discharge diagnosis of heart failure found a reduced mortality (hazard ratio [HR] 0.87; 95% CI 0.80, 0.94) in those prescribed thiazolidinediones. This benefit was offset by an increased risk of readmission with heart failure (HR 1.06; 95% CI 1.00, 1.09). Despite an increase in fluid-related events, recent studies suggest that individuals with type 2 diabetes mellitus and heart failure (New York Heart Association grade I/II) can be treated with thiazolidinediones with appropriate monitoring and adjustment of heart failure therapies. These findings would suggest the need for large-scale, prospective trials to investigate the safety and potential benefits of thiazolidinedione use in patients with diabetes mellitus and heart failure.

Treating insulin resistance in type 2 diabetes with metformin and thiazolidinediones

Insulin resistance underlies the pathogenesis of hyperglycaemia and cardiovascular disease in most people with type 2 diabetes. Metformin and thiazolidinediones (pioglitazone and rosiglitazone) counter insulin resistance by different cellular mechanisms and with complementary effects, making them suited for use in combination. Metformin exerts a stronger suppression of hepatic glucose output, while thiazolidinediones produce a greater increase in peripheral glucose uptake, enabling metformin-thiazolidinedione combinations to improve glycaemic control in type 2 diabetes with additive efficacy. Basal insulin concentrations are not raised by metformin or thiazolidinediones, so there is minimal risk of hypoglycaemia, and metformin can reduce the weight gain associated with thiazolidinediones. There are overlapping effects of metformin and thiazolidinediones against a range of athero-thrombotic factors and markers. These include decreased plasminogen activator inhibitor-1, reduced platelet aggregation, reductions of several vascular adhesion molecules, and reduced markers of low-grade inflammation such as C-reactive protein. Additionally, thiazolidinediones increase adiponectin and slightly reduce blood pressure. Both metformin and thiazolidinediones can improve components of the lipid profile: thiazolidinediones consistently reduce free fatty acid concentrations and decrease the proportion of small dense low-density-lipoprotein, and pioglitazone also decreases triglycerides. During co-administration, metformin and thiazolidinediones do not interfere with each other's pharmacokinetics, and lower doses of the two agents together can achieve efficacy with fewer side effects. Metformin-thiazolidinedione combinations require attention to the precautions for both agents, especially renal, cardiac and hepatic status. Thus, metformin and thiazolidinediones can be used in combination to address the hyperglycaemia and vascular risk in type 2 diabetes.

Rosiglitazone plus metformin is effective and well tolerated in clinical practice: results from large observational studies in people with type 2 diabetes

This study investigated the efficacy during daily practice of rosiglitazone (RSG) added to metformin (MET) in poorly controlled type 2 diabetes mellitus. Two post-marketing observational studies were conducted in Germany over 6 months. RSG (4 mg/day titrated to 8 mg/day as required) was added to existing MET in 11,014 subjects. Subjects were maintained on diet and exercise. Addition of RSG to MET significantly reduced median HbA 1c by 1.3% (8.1 vs. 6.8%; p < 0.0001) and median fasting blood glucose (FBG) by 47.0 mg/dl (171.0 vs. 124.0 mg/dl; p < 0.0001) after 6 months. The proportion of subjects achieving HbA(1c) targets of < or = 6.5 and < or = 7.0% increased from 3.5 to 38.8% and from 13.5 to 63.7%, respectively. Mean systolic and diastolic blood pressure decreased by 7 and 3 mmHg, respectively (p < 0.0001). Mean weight decreased by 1.7 kg and was constant or reduced in most (74.1%) subjects. Addition of RSG to MET significantly reduces median HbA 1c and FBG in clinical practice and is generally well tolerated.

Beta-cell preservation: a potential role for thiazolidinediones to improve clinical care in Type 2 diabetes

Type 2 diabetes is caused by progressively increasing insulin resistance coupled with deteriorating beta-cell function, and there is a growing body of evidence to suggest that both of these defects precede hyperglycaemia by many years. Several studies have demonstrated the importance of maintaining beta-cell function in patients with Type 2 diabetes. This review explores parameters used to indicate beta-cell dysfunction, in Type 2 diabetes and in individuals with a predisposition to the disease. A genetic element undoubtedly underlies beta-cell dysfunction; however, a number of modifiable components are also associated with beta-cell deterioration, such as chronic hyperglycaemia and elevated free fatty acids. There is also evidence for a link between pro-inflammatory cytokines and impairment of insulin-signalling pathways in the beta-cell, and the potential role of islet amyloid deposition in beta-cell deterioration continues to be a subject for debate. The thiazolidinediones are a class of agents that have demonstrated clinical improvements in indices of beta-cell dysfunction and have the potential to improve beta-cell function. Data are accumulating to show that this therapeutic group offers a number of advantages over traditionally employed oral agents, and these data demonstrate the growing importance of thiazolidinediones in Type 2 diabetes management.

Long-term treatment with rosiglitazone and metformin reduces the extent of, but does not prevent, islet amyloid deposition in mice expressing the gene for human islet amyloid polypeptide

Islet amyloid deposition in type 2 diabetes is associated with reduced beta-cell mass. Therefore, interventions aimed at reducing islet amyloid formation may help preserve beta-cell mass in type 2 diabetes. Rosiglitazone and metformin act by different mechanisms to improve insulin sensitivity and thereby reduce beta-cell secretory demand, resulting in decreased release of insulin and islet amyloid polypeptide (IAPP), the unique constituent of islet amyloid deposits. We hypothesized that this reduced beta-cell secretory demand would lead to reduced islet amyloid formation. Human IAPP (hIAPP) transgenic mice, a model of islet amyloid, were treated for 12 months with rosiglitazone (1.5 mg.kg(-1).day(-1), n = 19), metformin (1 g.kg(-1).day(-1), n = 18), or control (n = 17). At the end of the study, islet amyloid prevalence (percent islets containing amyloid) and severity (percent islet area occupied by amyloid), islet mass, beta-cell mass, and insulin release were determined. Islet amyloid prevalence (44 +/- 8, 13 +/- 4, and 11 +/- 3% for control, metformin-, and rosiglitazone-treated mice, respectively) and severity (9.2 +/- 3.0, 0.22 +/- 0.11, and 0.10 +/- 0.05% for control, metformin-, and rosiglitazone-treated mice, respectively) were markedly reduced with both rosiglitazone (P < 0.001 for both measures) and metformin treatment (P < 0.001 for both measures). Both treatments were associated with reduced insulin release assessed as the acute insulin response to intravenous glucose (2,189 +/- 857, 621 +/- 256, and 14 +/- 158 pmol/l for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin vs. control and P < 0.005 for rosiglitazone vs. control), consistent with reduced secretory demand. Similarly, islet mass (33.4 +/- 7.0, 16.6 +/- 3.6, and 12.2 +/- 2.1 mg for control, metformin-, and rosiglitazone-treated mice, respectively) was not different with metformin treatment (P = 0.06 vs. control) but was significantly lower with rosiglitazone treatment (P < 0.05 vs. control). When the decreased islet mass was accounted for, the islet amyloid-related decrease in beta-cell mass (percent beta-cell mass/islet mass) was ameliorated in both rosiglitazone- and metformin-treated animals (57.9 +/- 3.1, 64.7 +/- 1.4, and 66.1 +/- 1.6% for control, metformin-, and rosiglitazone-treated mice, respectively; P < 0.05 for metformin or rosiglitazone vs. control). In summary, rosiglitazone and metformin protect beta-cells from the deleterious effects of islet amyloid, and this effect may contribute to the ability of these treatments to alleviate the progressive loss of beta-cell mass and function in type 2 diabetes.

Thiazolidinediones, peripheral oedema and congestive heart failure: what is the evidence?

Cardiovascular disease is the most common complication of type 2 diabetes mellitus (type 2 DM), accounting for approximately 80% of deaths. While atherosclerotic vascular disease accounts for much of the cardiovascular morbidity and mortality among diabetic patients, congestive heart failure (CHF) is another key complication associated with diabetes, with an incidence three to five times greater in diabetic patients than in those without diabetes. One of the most promising developments in the treatment of type 2 DM has been the introduction of the thiazolidinedione (TZD) class of drugs, which appear to have pleiotropic effects beyond glycaemic control. Enthusiasm has been tempered, however, by concerns for safety in patients with CHF, given reports of worsening heart failure symptoms and peripheral oedema. With the growing epidemic of type 2 DM and the increasing use of TZDs, such concern has important therapeutic implications for a population of patients with a high prevalence of often subclinical systolic and diastolic dysfunction. This review provides an overview of the currently available data regarding the effects of TZDs on fluid retention and cardiac function. Particular emphasis is placed on the mechanisms of development of peripheral oedema and its significance in patients with impaired left ventricular function. TZDs are well known to cause an expansion in plasma volume; there has also been concern that TZDs may have direct toxic effects on the myocardium, leading to impaired cardiac function. Studies to date do not support this hypothesis and in fact there is growing evidence from animal models and human trials that treatment with TZDs actually improves cardiac function. There are also preclinical data to suggest TZDs may protect the myocardium in the setting of ischaemic insult or the toxic effects of myocardial lipid deposition. Ongoing clinical trials examining the use of these agents in patients at risk for heart failure will probably provide further insight into the aggregate cardiovascular effects of this promising class of medications.

Insulin-Mediated Upregulation of the Renin Angiotensin System in Human Subcutaneous Adipocytes Is Reduced by Rosiglitazone

Background— Obesity-associated hypertension is likely to be due to multiple mechanisms. Identification of the renin-angiotensin system (RAS) within adipose tissue does, however, suggest a potential causal role for it in obesity-associated hypertension. Obese patients are often hyperinsulinemic, but mechanisms underlying insulin upregulation of the RAS in adipose tissue are unclear. Tumor necrosis factor-α (TNF-α), an inducer of angiotensinogen in hepatocytes, is elevated in hyperinsulinemic, obese individuals and may provide a link in mediating insulin upregulation of the RAS in adipose tissue. Furthermore, thiazolidinediones lower blood pressure in vivo, and downregulation of the RAS in adipose tissue may contribute to this effect. We therefore examined the effect of rosiglitazone (RSG) on the insulin-mediated upregulation of the RAS.

Methods and Results— Sera were obtained from the arterial circulation and from venous blood by draining subcutaneous abdominal adipose tissue. Isolated human abdominal subcutaneous adipocytes (n=12) were treated with insulin (1 to 1000 nmol/L), insulin in combination with RSG (10 nmol/L), and RSG (10 nmol/L) alone to determine angiotensinogen expression and angiotensin II, bradykinin, and TNF-α secretion. Subcutaneous adipocytes were also treated with TNF-α (10 to 100 ng/mL) to examine the direct effect on angiotensinogen expression and angiotensin II secretion. The findings showed that the arteriovenous difference in angiotensin II levels was significant (>23%; P <0.001). Insulin increased TNF-α secretion in a concentration-dependent manner ( P <0.01), whereas RSG (10 nmol/L) significantly reduced the insulin-mediated rise in TNF-α ( P <0.001), as well as angiotensin and angiotensin II. TNF-α also increased angiotensinogen and angiotensin II in isolated adipocytes.

Conclusions— The present in vivo data suggest that human subcutaneous adipose tissue is a significant source of angiotensin II. This study also demonstrates a potential TNF-α–mediated mechanism through which insulin may stimulate the RAS and may contribute to explain obesity-associated hypertension. RSG downregulates the RAS in subcutaneous adipose tissue, and this effect may contribute to the long-term effect of RSG on blood pressure.

Potential cardiovascular benefits of insulin sensitizers

A multiple risk factor approach is needed in patients who have type 2 diabetes. Because many risk factors are linked with IR, treatment with insulin sensitizers has the potential to modulate these risk factors favorably. TZDs 'have many important effects beyond lowering blood glucose. By targeting IR, they improve many cardiovascular risk factors that are associated with the IR syndrome. In particular, they increase HDL-C, have anti-inflammatory effects, improve endothelial function and fibrinolysis, and decrease carotid intimal thickness; however, no evidence-based studies on cardiovascular outcomes are available to substantiate the potential cardioprotective effects of TZDs. Several clinical trials that were designed to investigate the effect that these agents have on reducing cardiovascular events are well under way.

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.