Effects of pioglitazone on the components of diabetic dyslipidaemia: results of double-blind, multicentre, randomised studies

Pioglitazone — an oral antidiabetic agent and metabolic syndrome modulator. Can theory translate into practice?

The metabolic syndrome, associated with insulin resistance, is a cluster of cardiovascular risk factors which results in premature morbidity and mortality from atherosclerotic vascular disease. Pioglitazone, a peroxisome-proliferator-activated receptor gamma (PPARγ) agonist, is an insulin sensitiser with the ability to address key features of the metabolic syndrome: glucose intolerance including type 2 diabetes, hypertension, dyslipidaemia, the pro-coagulant state, endothelial dysfunction, inflammation and atherosclerosis. The greatest potential benefit of pioglitazone is to influence atherogenesis itself through its pleiotrophic effects on vascular risk factors. This has been tested by the PROactive study, results of which are published in September 2005.

Oral Antidiabetic Drugs: Bioavailability Assessment of Fixed-Dose Combination Tablets of Pioglitazone and Metformin. Effect of Body Weight, Gender, and Race on Systemic Exposures of Each Drug

Bioavailability of pioglitazone and metformin, in 2 dose strengths, given either as a fixed-dose combination tablet or as coadministration of commercial tablets (coad), was studied in young healthy subjects in 2 separate studies. In study I (n = 63), single oral doses of 15-mg pioglitazone/500-mg metformin fixed-dose combination tablets or equivalent doses of commercial tablets were administered, in a fasting state, in an open-label, randomized, crossover study with a 7-day washout period between treatments. Study II (n = 61) was similar in design to study I, except the 15/850-mg fixed-dose combination tablet and coad treatments were evaluated. Least squares mean (fixed-dose combination/coad) ratios and 90% confidence intervals of the ratios for the 15/500-mg dose strength for the maximum observed serum concentration (Cmax) and area under the serum concentration-time curve from time 0 to infinity (AUC(infinity)) were 0.95 (0.86-1.05) and 1.02 (0.98-1.08), respectively, for pioglitazone and 0.99 (0.95-1.03) and 1.03 (0.98-1.08), respectively, for metformin. Bioequivalency for pioglitazone and metformin between fixed-dose combination tablets and coad treatments was met for both strengths of fixed-dose combination tablets. In a post hoc meta-analysis of combined data from the 2 studies (n = 124), there was considerable overlapping in AUC(infinity) values between gender and race (Caucasians, Blacks, and Hispanics), making neither gender- nor racial-based dosing of pioglitazone or metformin necessary.

Long-term lipid effects of pioglitazone by baseline anti-hyperglycemia medication therapy and statin use from the PROactive experience (PROactive 14)

Studies have shown that pioglitazone treatment in patients with type 2 diabetes mellitus can improve parameters of diabetic dyslipidemia. The aim of this study was to examine the effect of pioglitazone on triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol levels in patients from the Prospective Pioglitazone Clinical Trial in Macrovascular Events (PROactive) to determine whether pioglitazone-induced lipid effects were altered by different baseline antihyperglycemia medication or statin use. PROactive was a long-term, randomized, double-blind, cardiovascular outcomes study in patients with type 2 diabetes at high cardiovascular risk who had pioglitazone or placebo added to existing treatment. The present post hoc study analyzed lipid results from patients who received different baseline antihyperglycemia regimens and the presence or absence of baseline statin use. Independent of antihyperglycemia medication and statin use, triglyceride levels decreased in all subgroups treated with pioglitazone (-9.9% to -12.3%), whereas little change was observed in placebo groups. High-density lipoprotein cholesterol increased nearly twice as much with pioglitazone (18.1% to 20.3%) as with placebo (8.1% to 11.8%) across all subgroups. Low-density lipoprotein cholesterol increased moderately with pioglitazone (5.2% to 9.6%) compared with placebo (3.3% to 7.6%) (placebo-adjusted range 1.11% to 4.37%). In conclusion, long-term pioglitazone therapy led to durable improvements in triglyceride and high-density lipoprotein cholesterol levels, irrespective of baseline antihyperglycemia therapy or statin use.

Targeting the pathophysiology of type 2 diabetes: rationale for combination therapy with pioglitazone and exenatide

OBJECTIVE

The objectives of this article are to review the pathophysiology of type 2 diabetes mellitus (T2DM), present the rationale for a pathophysiologically based treatment approach for patients with T2DM and discuss the role of the therapeutic combination of pioglitazone and exenatide in the management of T2DM.

METHODS

References were identified from searches of the PubMed database that were conducted in May 2007, October 2007 and March 2008 and updates to product labeling that occurred between May 2007 and December 2007. Information was selected for inclusion on the basis of its relevance to the pathophysiology of T2DM or the clinical use of thiazolidinediones or exenatide. Discussion of other anti-diabetic treatment strategies is not included.

RESULTS

T2DM results from a combination of insulin resistance and beta-cell dysfunction. The combination of a thiazolidinedione and an incretin mimetic offers a combination of characteristics (e.g., glycemic control, reduced insulin resistance, decreased weight, potential cardiovascular benefits, beta-cell preservation) that addresses many of the pathophysiologic underpinnings of T2DM. A recent small placebo-controlled study assessed the effects of exenatide used with a thiazolidinedione (TZD; pioglitazone or rosiglitazone) with or without metformin. Exenatide demonstrated a greater incidence of glycosylated hemoglobin (HbA(1c)) < 7%; greater reductions in fasting blood glucose, postprandial plasma glucose and body weight; and improved beta-cell function versus the TZD/placebo group. However, exenatide was associated with a high dropout rate, and the 16-week duration of treatment in this study precluded evaluation of the long-term effects of the exenatide/pioglitazone combination. Furthermore, exenatide/pioglitazone has not been compared with any other anti-diabetic combination in a head-to-head clinical study.

CONCLUSIONS

Dual effects on insulin sensitivity (TZD) and insulin secretion (exenatide) make the TZD/exenatide combination a rational treatment option for patients who do not attain glycemic control with a single agent. Studies undertaken to evaluate the effects on cardiovascular outcomes and the potential for prevention of T2DM with impaired glucose tolerance may reveal additional advantages of this combination approach.

The altered homeostatic theory: A hypothesis proposed to be useful in understanding and preventing ischemic heart disease, hypertension, and diabetes – including reducing the risk of age and atherosclerosis

Evidence will be presented to support the usefulness of the altered homeostatic theory in understanding basic pathogenetic mechanisms of ischemic heart disease (IHD), hypertension, and diabetes, and in improving prevention of these disorders. The theory argues that: IHD, hypertension, and diabetes share the same basic pathogenesis; risk factors favor a sympathetic homeostatic shift; preventative factors favor a parasympathetic homeostatic shift; risk and preventative factors oppose each other through a dynamic risk/prevention balance; and prevention should be based on improving the risk/prevention balance. Prevention based on improving the risk/prevention balance should be more effective, as this method is regarded as reflecting more accurately basic pathogenetic mechanisms. As example, the theory argues that the risk of supposedly nonmodifiable risk factors as age and the risk of relatively nonmodifiable atherosclerosis can be reduced significantly. The possible validity of the altered homeostatic theory was tested by a study based on multiple associations. Findings support a common pathogenesis for IHD, hypertension, and diabetes based on a sympathetic homeostatic shift, and the usefulness of prevention based on improving the risk/prevention balance by using standard pharmaceutical and lifestyle preventative measures. The same set of multiple and diverse risk factors favored IHD, hypertension, and diabetes, and the same set of multiple and diverse pharmaceutical and lifestyle preventative measures prevented these disorders. Also, the same set of preventative agents generally improved cognitive function and bone density, and reduced the incidence of Alzheimer's disease, atrial fibrillation, and cancer. Unexpectedly, evidence was developed that four major attributes of sympathetic activation represent four major risk factors; attributes of sympathetic activation are a tendency toward thrombosis and vasoconstriction, lipidemia, inflammation, and hyperglycemia, and corresponding risk factors are endothelial dysfunction (which expresses thrombosis/vasoconstriction and epitomizes this tendency), dyslipidemia, inflammation, and insulin resistance. These findings, plus other information, provide evidence that dyslipidemia acts mainly as a marker of risk of IHD, rather than being the basic mechanism of this disorder. However, prevention generally is based solely on improvement of dyslipidemia; basing prevention on dyslipidemia relatively underemphasizes the importance of other significant risk factors and, by certifying its validity, discourages alternate pathogenetic approaches. Also, development of myocardial infarction is approached differently. It seems generally accepted that dyslipidemia results rather automatically in infarction through the sequence of atherosclerosis, atherosclerotic complications, and thrombosis. In contrast, distinction is made between development of atherosclerosis and acute induction of infarction--where atherosclerosis is only one of multiple risk factors.

Impact of thiazolidenediones on serum lipoprotein levels

The thiazolidinediones, acting through peroxisome proliferator-activated receptor chi (PPARchi), affect multiple areas of metabolism. Of increasing importance is the recognition that these agents affect lipoprotein metabolism and cause changes in serum lipid and lipoprotein levels. All three thiazolidinediones, including troglitazone (which was withdrawn in the year 2000), rosiglitazone, and pioglitazone, tend to increase high-density lipoprotein (HDL) cholesterol, increase the size/decrease the density of low-density lipoprotein (LDL) particles, and raise the level of lipoprotein(a). In addition, troglitazone and pioglitazone, but not rosiglitazone, lower triglyceride levels modestly, thereby further contributing to increases in LDL and HDL size. The mechanism for these effects is still being clarified, but may involve enhancement of triglyceride clearance (in the case of pioglitazone), alteration of apolipoprotein C-III levels, reduction of hepatic lipase, and increase in ATP binding cassette A1 (ABCA1) activity. The clinical implications of these effects need further exploration.

Pioglitazone for type 2 diabetes mellitus

BACKGROUND

Diabetes has long been recognised as a strong, independent risk factor for cardiovascular disease, a problem which accounts for approximately 70% of all mortality in people with diabetes. Prospective studies show that compared to their non-diabetic counterparts, the relative risk of cardiovascular mortality for men with diabetes is two to three and for women with diabetes is three to four. The two biggest trials in type 2 diabetes, the United Kingdom Prospective Diabetes Study (UKPDS) and the University Group Diabetes Program (UGDP) study did not reveal a reduction of cardiovascular endpoints through improved metabolic control. Theoretical benefits of the newer peroxisome proliferator activated receptor gamma (PPAR-gamma) activators like pioglitazone on endothelial function and cardiovascular risk factors might result in fewer macrovascular disease events in people with type 2 diabetes mellitus.

OBJECTIVES

To assess the effects of pioglitazone in the treatment of type 2 diabetes.

SEARCH STRATEGY

Studies were obtained from computerised searches of MEDLINE, EMBASE and The Cochrane Library. The last search was conducted in August 2006.

SELECTION CRITERIA

Studies were included if they were randomised controlled trials in adult people with type 2 diabetes mellitus and had a trial duration of at least 24 weeks.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. Pooling of studies by means of random-effects meta-analysis could be performed for adverse events only.

MAIN RESULTS

Twenty-two trials which randomised approximately 6200 people to pioglitazone treatment were identified. Longest duration of therapy was 34.5 months. Published studies of at least 24 weeks pioglitazone treatment in people with type 2 diabetes mellitus did not provide convincing evidence that patient-oriented outcomes like mortality, morbidity, adverse effects, costs and health-related quality of life are positively influenced by this compound. Metabolic control measured by glycosylated haemoglobin A1c (HbA1c) as a surrogate endpoint did not demonstrate clinically relevant differences to other oral antidiabetic drugs. Occurrence of oedema was significantly raised. The results of the single trial with relevant clinical endpoints (Prospective Pioglitazone Clinical Trial In Macrovascular Events--PROactive study) have to be regarded as hypothesis-generating and need confirmation.

AUTHORS' CONCLUSIONS

Until new evidence becomes available, the benefit-risk ratio of pioglitazone remains unclear. Different therapeutic indications for pioglitazone of the two big U.S. and European drug agencies should be clarified to reduce uncertainties amongst patients and physicians.

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.

Inflammatory Markers and the Metabolic Syndrome

Inflammation in the vasculature might be an important pathogenic link between cardiovascular diseases and the metabolic syndrome. Inflammation can be reduced by a variety of approaches including diet, exercise, cardiovascular drugs, and insulin sensitizers. Importantly, these different measures improve vascular function and reduce inflammation by distinct mechanisms. Therefore, combination therapy including lifestyle modifications and multiple drugs from separate classes might produce additive beneficial outcomes. We review plausible mechanisms for effects of combination therapy to reduce inflammation, improve endothelial dysfunction, and decrease insulin resistance in atherosclerosis, coronary heart disease, and hypertension in the context of insulin-resistant states including diabetes, obesity, and the metabolic syndrome.