Current views on the mechanism of action of thiazolidinedione insulin sensitizers

Metabolic and other effects of pioglitazone as an add-on therapy to metformin in the treatment of polycystic ovary syndrome (PCOS)

Insulin resistance is a key pathogenic defect of the clustered metabolic disturbances seen in polycystic ovary syndrome (PCOS). Metformin is an insulin sensitizer acting in the liver and the peripheral tissues that ameliorates the metabolic and reproductive defects in PCOS. In addition, pioglitazone is an insulin sensitizer used in diabetes mellitus type 2 (T2DM), improving insulin resistance (IR) in adipose tissue and muscles. In T2DM, these drugs are also used as a combined treatment due to their "add-on effect" on insulin resistance. Although the beneficial role of troglitazone (a member of the thiazolidinediones (TZDs) family) in PCOS has been shown in the past, currently only pioglitazone is available in the market. A few small randomized controlled trials have directly compared the effectiveness of pioglitazone in women with PCOS, while there are a limited number of small studies that support the beneficial metabolic add-on effect of pioglitazone on metformin-treated PCOS women as compared to metformin or pioglitazone monotherapy. These findings suggest a potentially promising role for combined pioglitazone/metformin treatment in the management of PCOS in metformin-resistant patients. In view of recent concerns regarding pioglitazone usage and its associated health risk, we aim to compare the pros and cons of each drug regarding their metabolic and other hormonal effects in women with PCOS and to explore the possible beneficial effect of combined therapy in certain cases, taking into consideration the teratogenic effect of pioglitazone. Finally, we discuss the need for a randomized controlled trial that will evaluate the metabolic and other hormonal effects of combined metformin/pioglitazone treatment in PCOS with selective treatment targets.

PPAR-gamma agonists and their role in type 2 diabetes mellitus management

Type 2 diabetes mellitus and obesity are the most frequent endocrine-metabolic diseases in the world and their pathogenic basis are characterized by insulin resistance and insulin secretion defects that can be demonstrated through several alterations in carbohydrates, lipids, and protein metabolism. The peroxisome proliferator-activated receptors have been identified as key regulators of glucose and lipid metabolism, because they act as transcription factors that stimulate protein synthesis in a wide variety of processes (energetic metabolism, proliferation, and cellular differentiation), of which have been identified 3 types (alpha, beta/delta, gamma). The thiazolidenediones are compounds that act as agonists of the peroxisome proliferator-activated receptor-gamma increasing the tissues sensibility (muscle, adiposity tissue, and liver) to the insulin action; that is why they are used nowadays in treatment of type 2 diabetes mellitus. These drugs produce several of adverse effects, such as weight increased, edema, anemia, pulmonary edema, and congestive cardiac failure. Even their use have been related for some studies to an increased in the myocardium infarct risk; this correlation has not been a strong determinant to remove them from the market.

The nuts and bolts of subcutaneous insulin therapy in non-critical care hospital settings

In non-critical care settings, patients with hyperglycemia experience increased morbidity and mortality. Despite an increased recognition of the importance of treating inpatient hyperglycemia, many patients are still not adequately controlled. Insulin offers flexibility to address varying glucose levels and therefore is the preferred therapy to achieve recommended targets and manage hyperglycemia. Traditional sliding-scale insulin regimens often ineffectively control blood glucose levels as they are unable to mimic physiologic insulin secretion. Basal-bolus insulin regimens are recognized as a more effective way to correct hyperglycemia in non-critical care settings and a systematic glycemic control program is necessary to address hyperglycemia while minimizing hypoglycemia. Critical components of these programs include addressing barriers to glycemic control, understanding varying needs of different types of patients, and developing standardized subcutaneous insulin orders to achieve target glucose levels. This article provides strategies for using insulin in non-critical care settings to facilitate glycemic control.

The effects of rosiglitazone and metformin on insulin resistance and serum androgen levels in obese and lean patients with polycystic ovary syndrome

AIM

The aim of this study was to assess the effects of metformin and rosiglitazone on insulin resistance and serum androgen levels in both obese and lean patients with polycystic ovary syndrome (PCOS).

MATERIALS AND METHODS

Forty lean [body mass index (BMI) < 25 kg/m2] and 40 overweight and obese (BMI > 25 kg/m2) patients were included in the study. Waist and hip measurements, serum sex steroid levels, insulin response to 75-g oral glucose tolerance test, fasting insulin, fasting C-peptide levels and homeostasis model assessment of insulin resistance (HOMA-IR) were determined in all patients. The degree of hirsutism was determined by the Ferriman-Gallwey scoring system. Patients were divided into two groups, with 40 (20 overweight and obese; 20 non-obese) patients each. One group was treated with metformin (MET group) 850 mg bid while the other received rosiglitazone (ROSI group) 4 mg/day for 12 weeks. All measurements were repeated at the end of this period.

RESULTS

After the 12-week treatment period, HOMA-IR, area under the curve of insulin, fasting insulin and C-peptide levels were observed to have be decreased significantly in all groups. The decrease in the parameters mentioned above was similar in the four groups. The serum levels of free testosterone, androstenedione and DHEA-S decreased in all groups, but the decrease was statistically significant only in the ROSI groups. Within the lean MET group one patient became pregnant and was hence excluded from the final data analysis. Menstruations became regular after metformin therapy in 41.6% of lean and 35.7% of obese patients who had menstrual disturbance prior to the study. Rosiglitazone therapy improved menstrual disturbance in 61.5 % of lean and 53.8% of obese patients.

CONCLUSIONS

Our data showed that both metformin and rosiglitazone increased insulin sensitivity in obese patients with PCOS as expected, and in lean patients as well. Rosiglitazone seemed to be more effective in decreasing the androgen levels and in achieving slightly greater improvement in menstrual disturbance than metformin.

The effects of rosiglitazone and metformin on menstrual cyclicity and hirsutism in polycystic ovary syndrome

OBJECTIVE

The aim of the present study was to assess the effects of metformin and rosiglitazone on menstrual cyclicity and hirsutism in patients with polycystic ovary syndrome (PCOS).

MATERIALS AND METHODS

Ninety-six patients were included in the study. Serum sex steroids, serum fasting glucose and insulin levels, and insulin response to a 75-g oral glucose tolerance test were assessed in all patients. Menstrual cyclicity, with recording of menses in the 6-month periods before the study and during treatment, was evaluated in each patient. Patients were divided into two groups: one was treated with metformin (MET group, n = 48), while the other received rosiglitazone (ROSI group, n = 48). At baseline and after 24 weeks of treatment all patients underwent hormonal and clinical assessments, including body mass index (BMI), waist and hip measurements and Ferriman - Gallwey (FG) scores.

RESULTS

Of the 96 patients included in the study, 88 (91.7%) were able to complete it and yielded data for analyses. After the 24-week treatment period, fasting insulin levels and area under the curve for serum insulin decreased significantly, while the glucose/insulin ratio increased in both groups. The degree of reduction in serum free testosterone and androstenedione levels was similar in the two groups. The decreases in luteinizing hormone/follicle-stimulating hormone ratio and serum dehydroepiandrosterone sulfate levels were significantly greater in the ROSI group compared with the MET group. BMI increased in the ROSI group, while it decreased in the MET group. In patients with menstrual disturbance treated with rosiglitazone, menstrual cycles became regular in 87.8%, while improvement occurred in 79.3% of the patients treated with metformin. FG score decreased in both ROSI and MET groups, but the degree of decrease was significantly greater in the ROSI group than in the MET group.

CONCLUSION

Our data show that both metformin and rosiglitazone improve ovarian function and hirsutism in patients with PCOS. Rosiglitazone appears better than metformin in the treatment of hirsutism and has better patient tolerance.

The effects of rosiglitazone and metformin on oxidative stress and homocysteine levels in lean patients with polycystic ovary syndrome

BACKGROUND

Oxidative stress and hyperhomocysteinaemia are risk factors for cardiovascular diseases. The aim of this study was to assess the effects of rosiglitazone and metformin on cardiovascular disease risk factors such as insulin resistance, oxidative stress and homocysteine levels in lean patients with polycystic ovary syndrome (PCOS).

METHODS

Fifty lean patients (BMI <25 kg/m2) with PCOS and 35 healthy subjects were included this study. Serum homocysteine, sex steroids, fasting insulin, fasting glucose and lipid levels were measured. Total antioxidant status (TAS; combines concentrations of individual antioxidants) and malonyldialdehyde concentration (MDA) were determined. Insulin resistance was evaluated by using the homeostasis model insulin resistance index (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), Area under the curve insulin (AUCI) and the insulin sensitivity index (ISI). Patients were divided into two groups. One group was treated with metformin (n = 25) and the other received rosiglitazone (n = 25) for 12 weeks. All measurements were repeated at the end of 12 weeks.

RESULTS

Compared with healthy women, those with PCOS had significantly elevated serum MDA, homocysteine, HOMA-IR, AUCI and lipoprotein a levels, and significantly decreased serum TAS, QUICKI and ISI. Serum free testosterone levels showed a significant positive correlation with MDA, AUCI and HOMA-IR, and a negative correlation with TAS, ISI and QUICKI in PCOS patients. HOMA-IR and AUCI significantly decreased, while QUICKI and ISI significantly increased after treatment in both groups. Serum TAS level increased and serum MDA level decreased after the rosiglitazone treatment, but these parameters did not change after the metformin treatment. Serum homocysteine and lipid levels did not change in either group, while serum androgen levels and LH/FSH ratio significantly decreased after the treatment period in only the rosiglitazone-treated group.

CONCLUSION

Elevated insulin resistance, oxidative stress and plasma homocysteine levels and changes in serum lipid profile (risk factors for cardiovascular disease) were observed in lean PCOS patients. Rosiglitazone seemed to decrease elevated oxidative stress when compared with metformin treatment in lean PCOS patients.

Elevated plasma levels of the atherogenic mediator soluble CD40 ligand in diabetic patients: a novel target of thiazolidinediones

BACKGROUND

Considerable evidence implicates the proinflammatory cytokine CD40 ligand (CD40L) in atherosclerosis and accumulating data link type 1 and 2 diabetes, conditions associated with accelerated atherosclerosis, to inflammation. This study therefore evaluated the hypothesis that diabetic patients have elevated plasma levels of soluble CD40L (sCD40L) and that treatment with the insulin-sensitizing thiazolidinediones lowers this index of inflammation.

METHODS AND RESULTS

Subjects with type 1 (n=49) or type 2 diabetes (n=48) had higher (P<0.001) sCD40L plasma levels (6.56+/-3.27 and 6.67+/-2.90 ng/mL, respectively) compared with age-matched control groups (1.40+/-2.21 and 1.32+/-2.68 ng/mL, respectively). Multiple regression analysis demonstrated a significant (P<0.001) association between plasma sCD40L and type 1 as well as type 2 diabetes, independent of total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, blood pressure, body mass index, gender, C-reactive protein, and soluble intracellular adhesion molecule-1. Furthermore, in a pilot study, administration of troglitazone (12 weeks, 600 mg/day), but not placebo, to type 2 diabetics (n=68) significantly (P<0.001) diminished sCD40L plasma levels by 29%. The thiazolidinedione lowered plasma sCD40L in type 2 diabetic patients with long-standing disease (>3 years) with or without macrovascular complications (-34% and -29%, respectively) as well as in type 2 diabetic patients with more recent (<3 years) onset of the disease (-27%; all P<0.05).

CONCLUSIONS

This study provides new evidence that individuals with type 1 or 2 diabetes have a proinflammatory state as indicated by elevated levels of plasma sCD40L. Troglitazone treatment of type 2 diabetic patients diminishes sCD40L levels, suggesting a novel antiinflammatory mechanism for limiting diabetes-associated arterial disease.

Are the metabolic effects of rosiglitazone influenced by baseline glycaemic control?

OBJECTIVE

To compare the metabolic effects of rosiglitazone, an antidiabetic agent of the thiazolidinedione class, in patients with type 2 diabetes with fair to moderate glycaemic control (glycosylated haemoglobin (HbA(lc)) < 9%) and poor glycaemic control (HbA(lc) > or = 9%).

RESEARCH DESIGN AND METHODS

Data were pooled from two 26-week, randomised, placebo-controlled, double-blind studies of rosiglitazone (4 and 8 mg/day).

RESULTS

After 26 weeks of treatment, HbA(lc) was significantly reduced (p < 0.05) compared with baseline and placebo in patients taking rosiglitazone 8 mg/day for both HbA(lc) stratifications, with greater reductions in patients with baseline HbA(lc) > or = 9%. After 26 weeks of treatment, reductions in fasting plasma glucose (FPG) were significant (p < 0.05) compared with baseline and placebo in both rosiglitazone treatment groups for both HbA(lc) stratifications, with greater reductions in the group with poor glycaemic control. Rosiglitazone significantly improved insulin sensitivity (p < 0.05) compared with baseline in patients with baseline HbA(lc) < 9%. Rosiglitazone significantly improved beta-cell function (p < 0.05) compared with baseline with more improvement in the group with baseline HbA(lc) > or = 9%. These improvements were statistically significant compared with placebo, regardless of HbA(lc) stratification.

CONCLUSION

Rosiglitazone significantly improved HbA(lc) and FPG levels in patients with type 2 diabetes, with the greatest improvements observed in patients with baseline HbA(lc) levels > or =9%.

Reappraisal of the pharmacologic approach to treatment of type 2 diabetes mellitus

Nearly 16 million adults in the United States have diabetes mellitus, and the incidence of type 2 diabetes, the most prevalent form of diabetes, has steadily increased during the past decade. Patients with diabetes are at increased risk for microvascular and macrovascular complications and experience significant morbidity and mortality. Diabetes is the leading cause of blindness, end-stage renal disease, and nontraumatic amputations in adults. Because diabetes is a progressive disorder, the importance of early and appropriate treatment cannot be overemphasized. Present therapeutic strategies for the management of type 2 diabetes are adequate but are not maximally effective. Clearly, reappraisal of the pharmacologic approach to the optimal management of patients with type 2 diabetes is needed. A number of oral hypoglycemic agents, including thiazolidinediones, biguanides, sulfonylureas, and alpha-glucosidase inhibitors, may be used to normalize glucose levels in patients with type 2 diabetes. Because insulin resistance is an underlying pathologic defect in patients with type 2 diabetes, agents that increase insulin sensitivity should be used early in the course of therapy. By using a multifaceted approach to target insulin resistance, many patients with type 2 diabetes may achieve normoglycemia and improved long-term outcomes.

Insulin resistance as the core defect in type 2 diabetes mellitus

Insulin resistance is a major contributor to the pathogenesis of type 2 diabetes and plays a key role in associated metabolic abnormalities, such as dyslipidemia and hypertension. Obesity, especially visceral adiposity, is negatively correlated with insulin sensitivity. The release of free fatty acids from adipocytes can block insulin-signaling pathways and lead to insulin resistance. In addition, recently identified adipocyte-specific chemical messengers, the adipocytokines, such as tumor necrosis factor-alpha, adiponectin, and resistin, appear to modulate the underlying insulin resistance. When insulin resistance is combined with beta-cell defects in glucose-stimulated insulin secretion, impaired glucose tolerance, hyperglycemia, or type 2 diabetes can result. The thiazolidinediones are potent peroxisome proliferator-activated receptor-gamma agonists and directly improve insulin resistance and glycemic control in patients with type 2 diabetes. Increasing evidence supports the early use of thiazolidinediones for preventing, delaying, or treating diabetes by improving insulin sensitivity and beta-cell insulin secretion.

Peroxisome proliferator-activated receptor ligands as antiatherogenic agents: panacea or another Pandora's box?

Peroxisome proliferator activated receptors (PPARs) are members of the nuclear receptor super family that modulate gene expression upon ligand activation. They are 3 major subtypes of PPARs: alpha, delta (also called beta), and gamma. PPAR-gamma is widely expressed in the cardiovascular system and is involved in the regulation of tissue inflammation and smooth muscle cell growth pathways as well as in lipoprotein metabolism and coagulation cascades. PPAR-gamma ligands of (e.g., rosigitazone and pioglitazone) have been shown to exert antiatherogenic effects both in vitro and in vivo. PPAR-alpha ligands (e.g., clofibrate and benzofibrate) modulate lipoprotein metabolism, and affect inflammation and coagulation cascade. These effects may be helpful in resolving the dilemma arising from studies that showed significant mortality and morbidity benefits of fibrates in the face of minimal changes in HDL-cholesterol levels. The role of PPAR-delta in atherogenesis remains largely unknown, although it appears that PPAR-delta activation affects lipoprotein metabolism. PPAR ligands appear to be promising agents in limiting atherosclerosis; however, large-scale clinical trials are required to assess their safety and efficacy before they can be added to the clinicians' arsenal of antiatherosclerotic agents.

Potential Utility of Insulin Sensitizers in the Treatment of Patients with Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a form of functional ovarian hyperandrogenism. It is one of the most common endocrinologic disorders in women of reproductive age. Women with PCOS may present with menstrual irregularities, chronic anovulation, infertility, obesity and hyperandrogenism. PCOS is associated with insulin resistance and hyperinsulinemia in most, if not all, patients. Besides its gynecological manifestations, PCOS is also associated with increased metabolic and cardiovascular risks. These risks are strongly linked to insulin resistance, and during recent years a novel therapeutic approach using insulin-sensitizing agents has been extensively investigated. In most studies conducted to date, metformin and the thiazolidinedione agent troglitazone have resulted in improved insulin sensitivity, resumption of regular menses and decreased serum androgen levels. Insulin-sensitizing agents may be a useful adjuvant therapy for women with PCOS.