Fluid retention and vascular effects of rosiglitazone in obese, insulin-resistant, nondiabetic subjects

Identification of Novel PPARγ Partial Agonists Based on Virtual Screening Strategy: In Silico and In Vitro Experimental Validation

Thiazolidinediones (TZDs) including rosiglitazone and pioglitazone function as peroxisome proliferator-activated receptor gamma (PPARγ) full agonists, which have been known as a class to be among the most effective drugs for the treatment of type 2 diabetes mellitus (T2DM). However, side effects of TZDs such as fluid retention and weight gain are associated with their full agonistic activities toward PPARγ induced by the AF-2 helix-involved "locked" mechanism. Thereby, this study aimed to obtain novel PPARγ partial agonists without direct interaction with the AF-2 helix. Through performing virtual screening of the Targetmol L6000 Natural Product Library and utilizing molecular dynamics (MD) simulation, as well as molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) analysis, four compounds including tubuloside b, podophyllotoxone, endomorphin 1 and paliperidone were identified as potential PPARγ partial agonists. An in vitro TR-FRET competitive binding assay showed podophyllotoxone displayed the optimal binding affinity toward PPARγ among the screened compounds, exhibiting IC50 and ki values of 27.43 µM and 9.86 µM, respectively. Further cell-based transcription assays were conducted and demonstrated podophyllotoxone's weak agonistic activity against PPARγ compared to that of the PPARγ full agonist rosiglitazone. These results collectively demonstrated that podophyllotoxone could serve as a PPARγ partial agonist and might provide a novel candidate for the treatment of various diseases such as T2DM.

Oral magnesium supplementation does not affect insulin sensitivity in people with insulin-treated type 2 diabetes and a low serum magnesium: a randomised controlled trial

AIMS/HYPOTHESIS

Hypomagnesaemia has been associated with insulin resistance and an increased risk of type 2 diabetes. Whether magnesium supplementation improves insulin sensitivity in people with type 2 diabetes and a low serum magnesium level is unknown.

METHODS

Using a randomised, double-blind (both participants and investigators were blinded to the participants' treatment sequences), placebo-controlled, crossover study design, we compared the effect of oral magnesium supplementation (15 mmol/day) for 6 weeks with that of matched placebo in individuals with insulin-treated type 2 diabetes (age ≥18 years, BMI 18-40 kg/m2, HbA1c <100 mmol/mol [11.3%], serum magnesium ≤0.79 mmol/l). Participants were recruited from the outpatient clinic and through advertisements. Randomisation to a treatment sequence order was done using a randomisation list. We used block randomisation and the two possible treatment sequences were evenly distributed among the trial population. The primary outcome was the mean glucose infusion rate during the final 30 min of a hyperinsulinaemic-euglycaemic clamp (i.e. M value). Secondary outcomes included variables of glucose control, insulin need, BP, lipid profile and hypomagnesaemia-related symptoms during follow-up.

RESULTS

We recruited 14 participants (50% women, 100% White, mean ± SD age 67±6 years, BMI 31±5 kg/m2, HbA1c 58±9 mmol/mol [7.4±0.9%]) with insulin-treated type 2 diabetes. Magnesium supplementation increased both mean ± SEM serum magnesium level (0.75±0.02 vs 0.70±0.02 mmol/l, p=0.016) and urinary magnesium excretion (magnesium/creatinine ratio, 0.23±0.02 vs 0.15±0.02, p=0.005), as compared with placebo. The M value of the glucose clamp did not differ between the magnesium and placebo study arms (4.6±0.5 vs 4.4±0.6 mg kg-1 min-1, p=0.108). During the 6 weeks of treatment, continuous glucose monitoring outcomes, HbA1c, insulin dose, lipid profile and BP also did not differ, except for a lower HDL-cholesterol concentration after magnesium compared with placebo (1.14±0.08 vs 1.20±0.09 mmol/l, p=0.026). Symptoms potentially related to hypomagnesaemia were similar for both treatment arms.

CONCLUSIONS/INTERPRETATION

Despite an albeit modest increase in serum magnesium concentration, oral magnesium supplementation does not improve insulin sensitivity in people with insulin-treated type 2 diabetes and low magnesium levels.

TRIAL REGISTRATION

EudraCT number 2021-001243-27.

FUNDING

This study was supported by a grant from the Dutch Diabetes Research Foundation (2017-81-014).

Non-glycemic Adverse Effects of Insulin

Insulin is primarily considered for its glycemic effects in patients with diabetes. There are, however, non-glycemic adverse effects of insulin that may significantly impact patient health and interfere with glycemic control. Insulinogenic edema primarily occurs with rapid improvement in glycemic control either in patients with newly discovered diabetes or in patients with poorly-controlled diabetes. Insulin-induced sympathetic activation, vasodilation, changes in vascular permeability, and most importantly, sodium retention play significant etiologic roles in the development of edema. Clinically, it is usually self-limited, but significant complications can develop. Allergic reactions to all insulin preparations and various compounds used in insulin formulations with a wide range of severity have been reported. Frequently, changing the type of insulin or delivery method is sufficient, but more advanced treatments such as insulin desensitization and anti-IgE antibody treatment may be needed. Lipohypertrophy and lipoatrophy frequently develop with the overuse of injection sites. Lipohypertrophy can affect tissue insulin absorption and glycemic control.

Endothelial Cell-Targeted Deletion of PPARγ Blocks Rosiglitazone-Induced Plasma Volume Expansion and Vascular Remodeling in Adipose Tissue

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor γ (PPARγ) agonists that represent an effective class of insulin-sensitizing agents; however, clinical use is associated with weight gain and peripheral edema. To elucidate the role of PPARγ expression in endothelial cells (ECs) in these side effects, EC-targeted PPARγ knockout (Pparg ΔEC) mice were placed on a high-fat diet to promote PPARγ agonist-induced plasma volume expansion, and then treated with the TZD rosiglitazone. Compared with Pparg-floxed wild-type control (Pparg f/f) mice, Pparg ΔEC treated with rosiglitazone are resistant to an increase in extracellular fluid, water content in epididymal and inguinal white adipose tissue, and plasma volume expansion. Interestingly, histologic assessment confirmed significant rosiglitazone-mediated capillary dilation within white adipose tissue of Pparg f/f mice, but not Pparg ΔEC mice. Analysis of ECs isolated from untreated mice in both strains suggested the involvement of changes in endothelial junction formation. Specifically, compared with cells from Pparg f/f mice, Pparg ΔEC cells had a 15-fold increase in focal adhesion kinase, critically important in EC focal adhesions, and >3-fold significant increase in vascular endothelial cadherin, the main component of focal adhesions. Together, these results indicate that rosiglitazone has direct effects on the endothelium via PPARγ activation and point toward a critical role for PPARγ in ECs during rosiglitazone-mediated plasma volume expansion.

Does Thiazolidinedione therapy exacerbate fluid retention in congestive heart failure?

The ever-growing global burden of congestive heart failure (CHF) and type 2 diabetes mellitus (T2DM) as well as their co-existence necessitate that anti-diabetic pharmacotherapy will modulate the cardiovascular risk inherent to T2DM while complying with the accompanying restrictions imposed by CHF. The thiazolidinedione (TZD) family of peroxisome proliferator-activated receptor γ (PPARγ) agonists initially provided a promising therapeutic option in T2DM owing to anti-diabetic efficacy combined with pleiotropic beneficial cardiovascular effects. However, the utility of TZDs in T2DM has declined in the past decade, largely due to concomitant adverse effects of fluid retention and edema formation attributed to salt-retaining effects of PPARγ activation on the nephron. Presumably, the latter effects are potentially deleterious in the context of pre-existing fluid retention in CHF. However, despite a considerable body of evidence on mechanisms responsible for TZD-induced fluid retention suggesting that this class of drugs is rightfully prohibited from use in CHF patients, there is a paucity of experimental and clinical studies that investigate the effects of TZDs on salt and water homeostasis in the CHF setting. In an attempt to elucidate whether TZDs actually exacerbate the pre-existing fluid retention in CHF, our review summarizes the pathophysiology of fluid retention in CHF. Moreover, we thoroughly review the available data on TZD-induced fluid retention and proposed mechanisms in animals and patients. Finally, we will present recent studies challenging the common notion that TZDs worsen renal salt and water retention in CHF.

Skeletal Muscle Vascular Function: A Counterbalance of Insulin Action

Insulin is a vasoactive hormone that regulates vascular homeostasis by maintaining balance of endothelial-derived NO and ET-1. Although there is general agreement that insulin resistance and the associated hyperinsulinemia disturb this balance, the vascular consequences for hyperinsulinemia in isolation from insulin resistance are still unclear. Presently, there is no simple answer for this question, especially in a background of mixed reports examining the effects of experimental hyperinsulinemia on endothelial-mediated vasodilation. Understanding the mechanisms by which hyperinsulinemia induces vascular dysfunction is essential in advancing treatment and prevention of insulin resistance-related vascular complications. Thus, we review literature addressing the effects of hyperinsulinemia on vascular function. Furthermore, we give special attention to the vasoregulatory effects of hyperinsulinemia on skeletal muscle, the largest insulin-dependent organ in the body. This review also characterizes the differential vascular effects of hyperinsulinemia on large conduit vessels versus small resistance microvessels and the effects of metabolic variables in an effort to unravel potential sources of discrepancies in the literature. At the cellular level, we provide an overview of insulin signaling events governing vascular tone. Finally, we hypothesize a role for hyperinsulinemia and insulin resistance in the development of CVD.

Peroxisome Proliferator-Activated Receptors and the Heart: Lessons from the Past and Future Directions

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear family of ligand activated transcriptional factors and comprise three different isoforms, PPAR-α, PPAR-β/δ, and PPAR-γ. The main role of PPARs is to regulate the expression of genes involved in lipid and glucose metabolism. Several studies have demonstrated that PPAR agonists improve dyslipidemia and glucose control in animals, supporting their potential as a promising therapeutic option to treat diabetes and dyslipidemia. However, substantial differences exist in the therapeutic or adverse effects of specific drug candidates, and clinical studies have yielded inconsistent data on their cardioprotective effects. This review summarizes the current knowledge regarding the molecular function of PPARs and the mechanisms of the PPAR regulation by posttranslational modification in the heart. We also describe the results and lessons learned from important clinical trials on PPAR agonists and discuss the potential future directions for this class of drugs.

Effect of Rosiglitazone and Insulin Combination Therapy on Inflammation Parameters and Adipocytokine Levels in Patients with Type 1 DM

AIM

To investigate the efficacy of combined therapy of insulin and rosiglitazone on metabolic and inflammatory parameters, insulin sensitivity, and adipocytokine levels in patients with type 1 diabetes mellitus (type 1 DM).

MATERIAL AND METHODS

A total of 61 adults with type 1 DM were randomly and prospectively assigned in open-label fashion to take insulin and rosiglitazone 4 mg/day (n = 30) or insulin alone (n = 31) for a period of 18 weeks while undergoing insulin therapy without acute metabolic complications.

RESULTS

Combination therapy did not significantly improve metabolic and inflammatory parameters, insulin sensitivity, and adiponectin levels. While leptin and resistin levels decreased in both groups (group 1: resistin 6.96 ± 3.06 to 4.99 ± 2.64, P = 0.006; leptin 25.8 ± 17.6 to 20.1 ± 12.55, P = 0.006; group 2: resistin 7.16 ± 2.30 to 5.57 ± 2.48, P = 0.031; leptin 16.72 ± 16.1 to 14.0 ± 13.4, P = 0.007) Hgb and fibrinogen levels decreased only in group 1 (Hgb 13.72 ± 1.98 to 13.16 ± 1.98, P = 0.015, and fibrinogen 4.00 ± 1.08 to 3.46 ± 0.90, P = 0.002). Patients in both groups showed weight gain and the incidence of hypoglycemia was not lower.

DISCUSSION

The diverse favorable effects of TZDs were not fully experienced in patients with type 1 DM. These results are suggesting that insulin sensitizing and anti-inflammatory characteristics of TZDs were likely to be more pronounced in patients who were not totally devoid of endogenous insulin secretion.

Lipocalin 2 is a selective modulator of peroxisome proliferator-activated receptor-gamma activation and function in lipid homeostasis and energy expenditure

We have previously identified lipocalin 2 (Lcn2) as a cytokine playing a critical role in the regulation of body fat mass, lipid metabolism, and insulin resistance. Lcn2 deficiency reduces PPARγ gene expression in adipocytes. In this study, we investigated the role of Lcn2 in PPARγ activation and function via assessing the insulin sensitization and fatty acid (FA) homeostasis of PPARγ agonist in high-fat diet (HFD)-induced obesity in Lcn2(-/-) mice. We found that rosiglitazone (Rosi) significantly improved insulin sensitivity in Lcn2(-/-) mice as effectively as in wild-type (WT) mice; unfed-state levels of blood glucose, free FAs, and triglycerides (TGs) were significantly reduced after a 25-d treatment of Rosi in Lcn2(-/-) mice. However, Rosi action on fat deposition and FA homeostasis was altered; Rosi-induced body weight and subcutaneous fat gain and liver lipid accumulation were markedly lessened in Lcn2(-/-) mice. The results of in vivo metabolic labeling showed that Rosi markedly reduced de novo lipogenesis in adipose tissue of Lcn2(-/-) mice. In brown adipose tissue (BAT), the expression of the genes functioning in TG hydrolysis and mitochondrial oxidation was up-regulated more in Lcn2(-/-) than in WT mice. Most strikingly, Rosi stimulated significantly higher levels of uncoupling protein-1 expression in BAT, and completely rescued cold intolerance in Lcn2(-/-) mice. We demonstrate that Lcn2 is a critical selective modulator of PPARγ activation and function in lipid homeostasis and energy expenditure.

Autonomic neuropathy predisposes to rosiglitazone-induced vascular leakage in insulin-treated patients with type 2 diabetes: a randomised, controlled trial on thiazolidinedione-induced vascular leakage

AIMS/HYPOTHESIS

The mechanism of fluid-related complications caused by thiazolidinedione derivatives is unclear. One potential mechanism is thiazolidinedione-induced arterial vasodilatation, which results in vascular leakage and a fall in blood pressure, normally counterbalanced by sympathetic activation and subsequent renal fluid retention. We hypothesised that thiazolidinedione-induced vascular leakage will be particularly prominent in patients with autonomic neuropathy.

METHODS

We conducted a randomised, double-blind, placebo-controlled, parallel study in 40 patients with type 2 diabetes on insulin treatment recruited from a university medical centre. The randomisation was performed by a central office using a randomisation schedule. Both treatment groups, placebo (n = 21) and rosiglitazone (n = 19), were stratified for sex and level of autonomic neuropathy as assessed by Ewing score (<2.5 or >or=2.5). We investigated the effects of 16 weeks of treatment with rosiglitazone 4 mg twice daily on vascular leakage (transcapillary escape rate of albumin, TERalb), body weight, extracellular volume and plasma volume.

RESULTS

Thirty-nine patients were included in the analysis. In patients with high Ewing scores (n = 16), rosiglitazone increased TERalb significantly (DeltaTERalb: rosiglitazone +2.43 +/- 0.45%/h, placebo -0.11 +/- 0.15%/h, p = 0.002), while rosiglitazone had no effect in the patients with low Ewing scores (n = 23). Rosiglitazone-induced increases in TERalb and Ewing score at baseline were correlated (r = 0.65, p = 0.02). There was no correlation between Ewing score and rosiglitazone-induced changes in fluid variables. One subject was withdrawn from the study because of atrial fibrillation.

CONCLUSIONS/INTERPRETATION

Rosiglitazone may increase vascular leakage in insulin-treated patients with type 2 diabetes with autonomic neuropathy. Autonomic neuropathy did not exaggerate rosiglitazone-induced fluid retention. Therefore, autonomic neuropathy should be considered as a risk factor for thiazolidinedione-induced oedema, not for thiazolidinedione-induced fluid retention.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00422955.

FUNDING

GlaxoSmithKline.

Fluid compartmental shifts with efficacious pioglitazone therapy in overweight monkeys: implications for peroxisome proliferator-activated receptor-gamma agonist use in prediabetes

Pioglitazone is prescribed to improve insulin sensitivity in type 2 diabetes mellitus patients and has been discussed as a therapy for metabolic syndrome. Pioglitazone and other thiazolidinediones are associated with fluid retention and edema that may exacerbate existing or developing congestive heart failure, which is often present in these patients. Using a nonhuman primate model, our aims were to evaluate (1) whether fluid shifts were detectable in normoglycemic monkeys, (2) which fluid compartment changed, and (3) whether fluid retention was dose dependent. Seventeen adult male cynomolgus macaques (Macaca fascicularis) were studied in a Latin square design such that all animals received 0, 1, 2, and 5 mg/kg pioglitazone for 6 weeks with 2 weeks of washout between dosing intervals. Doses approximated human exposures achieved with 30, 45, and 60 mg. At the end of each period, animals were weighed and underwent dual-absorption x-ray absorption scanning for body composition measurements. Fluid volumes were quantitated by Evans blue dilution for plasma volume, equilibration of sodium bromide for extracellular water, and deuterated water for total body water. Significant (P < .05) effects were seen with expansion of PV at both the 2- and 5-mg/kg doses, along with reduced plasma sodium at 5 mg/kg; however, surrogate end points used to indicate fluid retention (body weight, hematocrit, total protein, and albumin) did not change significantly. Significant trends toward increases in interstitial fluid and extracellular water with increasing dose were apparent. Pioglitazone effectively improved metabolic status by significantly decreasing fasting glucose and triglycerides and increasing adiponectin. We conclude that thiazolidinedione-related plasma volume expansion occurs in nondiabetic primates and that fluid retention is detectable when compartments are directly measured.

Selection and dosing of medications for management of diabetes in patients with advanced kidney disease

Diabetes mellitus is a leading cause of kidney disease worldwide. A large and expanding array of treatments for diabetes is available to improve glycemic control, including newer classes of drugs, such as thiazolidinediones and incretin-based therapies. The presence of impaired kidney function with reduced glomerular filtration rate should influence choices, dosing, and monitoring of hypoglycemic agents, as some agents require a dosing adjustment in patients with kidney disease and some are entirely contraindicated. This article reviews the clinical use of insulin and other antidiabetic therapies, focusing on pharmacokinetic properties and dosing in patients with advanced kidney disease.

Effects of intensive insulin therapy alone and with added pioglitazone on renal salt/water balance and fluid compartment shifts in type 2 diabetes

OBJECTIVE

To evaluate the effects of intensive insulin therapy alone or with added pioglitazone on renal salt/water balance and body fluid compartment shifts in type 2 diabetes.

METHODS

A total of 25 insulin-treated, obese patients with type 2 diabetes were randomized to pioglitazone 45 mg (n = 12) or placebo (n = 13) and treated intensively for 12-16 weeks to achieve equivalent glycaemic control. We measured total body water (TBW) and extracellular/intracellular fluid by bioimpedance analysis; plasma/RBC volume with I(131)albumin; sodium handling by fractional excretion of sodium/lithium (FeNa/FeLi) and other renal/hormonal parameters.

RESULTS

Intensification of insulin therapy and the addition of pioglitazone significantly improved glycaemia (HbA1C 7.8-7.2% and 7.6-7.1%) and increased body weight (1.7 and 4.9 kg) respectively. TBW increased 1.7 l with insulin alone (65% intracellular) and 1.6 l with added pioglitazone (75% extracellular) (p = 0.06 and 0.09 respectively). Plasma volume increased 0.2 +/- 0.1 l with insulin alone (p = 0.05) and 0.4 +/- 0.1 l with added pioglitazone (p < 0.05). Extravascular, extracellular (interstitial) fluid increased significantly and more with added pioglitazone (0.8 +/- 0.2 l, p < 0.01) than with insulin alone (0.4 +/- 0.2 l, p = ns). At steady-state, FeLi (marker of proximal-tubular sodium delivery to the distal nephron) increased significantly with added pioglitazone (12.4 +/- 1.3 to 18.0 +/- 3.2%) vs. no significant change with insulin alone (15.4 +/- 1.2 to 14.5 +/- 2.3%). There were no significant changes in the other parameters.

CONCLUSION

In intensively insulin-treated obese type 2 diabetic patients, at equivalent glycaemic control, the addition of pioglitazone causes greater weight gain, but a similar increase in body water that is mainly extracellular and interstitial compared with intracellular increase with insulin therapy alone. Pioglitazone also increases the filtered load of sodium reabsorbed at the distal nephron with no net change in FeNa.

Evaluation of rosiglitazone administration on cardiovascular function in severe obesity

BACKGROUND

Obese patients have myocardial structural and functional alterations related to insulin resistance.

HYPOTHESIS

The purpose of the study was to analyze the effects of rosiglitazone, an insulin sensitizer agent, on cardiac morphometry and functioning.

METHODS

In 2 groups of sex- and age-matched, nondiabetic, obese patients (5 men and 7 women, age 19-51 y; group A: body mass index [BMI] 40.6 +/- 3.4 kg/m(2); group B: BMI 42.6 +/- 2.7 kg/m(2)), we evaluated the basal insulin sensitivity index (HOMA[IS]), body composition by bioelectrical impedance analysis and 24-h blood pressure monitoring. Furthermore, all patients underwent conventional 2-Dimensional and color Doppler echocardiography, and pulsed-wave tissue Doppler imaging (TDI). After the baseline evaluation, all patients were put on a hypocaloric diet (70% basal metabolic rate) plus placebo if they were in group A, or plus rosiglitazone (4 mg twice daily; Avandia [GlaxoSmithKline plc., Brentford, Middlesex, United Kingdom]) if they were in group B, for 6 mo.

RESULTS

Significant decreases in body weight, total fat mass, BMI, and systolic blood pressure were registered in both groups. Rosiglitazone administration appeared more efficient in improving HOMA(IS) (mean difference: 0.30 +/- 0.19 versus 0.11 +/- 0.21, p < 0.05). Left ventricular (LV) diastolic diameter (49.4 +/- 7.7 versus 52.3 +/- 5.4 mm, p < 0.05) and E wave (0.89 +/- 0.18 versus 0.99 +/- 0.20 m/sec, p < 0.05) increased in the rosiglitazone group due to a rise in preload and water content without peripheral edema. The increase in systolic (Sa) wave velocity in both groups was probably a result of the general improvement in insulin metabolism and the decrease in blood pressure.

CONCLUSIONS

We confirmed the positive effect of rosiglitazone on glucose metabolism in obese, nondiabetic patients, but changes in insulin sensitivity did not explain the cardiac effects produced by further mechanisms.

Confusion over thiazolidinedione-induced heart failure: need for a better definition of heart failure

Evaluation of: Erdmann E, Wilcox RG. Weighing up the cardiovascular benefits of thiazolidinedione therapy: the impact of increased risk of heart failure. Eur. Heart J. 29(1), 12-20 (2008). Thiazolidinediones (TZDs) reduce insulin resistance through the modulation of peroxisome proliferator-activated receptor (PPAR)-gamma activity and are, therefore, used for the treatment of individuals with Type 2 diabetes. TZDs have been blamed for inducing heart failure (HF) and are contraindicated in patients with impaired ventricular function. Whether precipitation of HF by TZDs is overestimated or not remains hotly debated in the scientific community. One message from the TZD-HF debacle is that current definitions of HF lack scientific rigour as they fail to assess cardiac organ function directly using a representative and reliable method. Once cardiologists reappraise and update the current definition of HF, appropriate steps can then be taken to answer the question of whether TZDs really induce true HF.

Rosiglitazone is more effective than metformin in improving fasting indexes of glucose metabolism in severely obese, non-diabetic patients

AIM

In obese patients, the diet-induced weight loss markedly improves glucose tolerance with an increase in insulin sensitivity and a partial reduction of insulin secretion. The association with metformin treatment might potentiate the effect of diet alone.

METHODS

From patients admitted to our Nutritional Division for diet programme, we selected obese, non-diabetic, uncomplicated patients with age 18-65 years and body mass index 35-50 kg/m(2) and studied the effects of a 6-month pharmacological treatment with either metformin (850 mg twice daily) or rosiglitazone (4 mg twice daily) on possible changes in body weight, fat mass, glucose and lipids metabolism.

RESULTS

A significant weight loss and reduction of fat mass was demonstrated with metformin (-9.7 +/- 1.8 kg and -6.6 +/- 1.1 kg) and also with rosiglitazone (-11.0 +/- 1.9 kg and -7.2 +/- 1.8 kg), without fluid retention in either treatment group. Rosiglitazone administration induced a significant decrease in glucose concentration (4.7 +/- 0.1 vs. 4.4 +/- 0.1 mmol/l, p < 0.005) and insulin-circulating level (13.6 +/- 1.5 vs. 8.0 +/- 0.,7 microU/ml, p < 0.005), an increase in insulin sensitivity as measured by homeostatic model assessment (HOMA) of insulin sensitivity (68.9 +/- 8.8 vs. 109.9 +/- 10.3, p < 0.005) with a concomitant decrease in beta-cell function as measured by HOMA of beta-cell function (163.2 +/- 16.1 vs. 127.4 +/- 8.4, p < 0.005). In contrast, metformin did not produce any significant effect on blood glucose concentration, insulin level and HOMA2 indexes. No adverse events were registered with pharmacological treatments.

CONCLUSION

Our study shows that in severely obese, non-diabetic, hyperinsulinaemic patients undergoing a nutritional programme, rosiglitazone is more effective than metformin in producing favourable changes in fasting-based indexes of glucose metabolism, with a reduction of both insulin resistance and hyperinsulinaemia. In spite of previous studies reporting rosiglitazone-induced body weight gain, in our study the joint treatment with diet and rosiglitazone was accompanied by weight loss and fat mass reduction.

Thiazolidinedione insulin sensitizers and the heart: a tale of two organs?

Thiazolidinediones (TZDs) are relatively new agents for the treatment of type 2 diabetes. They act as agonists at the PPAR-gamma nuclear receptor and their therapeutic effects include decreased insulin resistance and hyperglycaemia, an improved plasma lipid, inflammation and pro-coagulant profile, and amelioration of hypertension, microalbuminuria and hepatic steatosis. The most common side effects of TZDs include weight gain and oedema, with occasional reports of congestive heart failure (CHF). This review discusses the benefit-risk profile of TZDs in treating patients with type 2 diabetes, with particular reference to the heart. To provide context, we explore briefly the epidemiology and pathophysiology of heart failure in patients with type 2 diabetes, touch on the association of heart disease and cardiovascular mortality with antihyperglycaemic treatment modalities other than TZDs, and then focus on the effects of TZDs on the heart, cardiovascular risk factors and outcomes. We describe the cluster of host factors, which seems to predispose patients with type 2 diabetes to TZD-induced or TZD-exacerbated oedema and CHF and then provide an overview of the putative mechanisms of these TZD-related side effects. We also propose that certain diuretics (amiloride and spironolactone), by targeting the distal nephron that expresses PPARgamma in collecting duct cells, might be of benefit in ameliorating the fluid retention and oedema associated with TZDs.

Antioxidant supplemention in the treatment of skeletal muscle insulin resistance: potential mechanisms and clinical relevance

The incidence of type 2 diabetes has increased dramatically over the past several decades and this trend is projected to continue into the foreseeable future. Skeletal muscle insulin resistance is thought to be a key development in the pathogenesis of type 2 diabetes. Given this fact, interventions that prevent or reverse impairments in skeletal muscle action can have profound effects on whole-body glucose homeostasis. Traditional approaches used in this regard include exercise, weight loss, and insulin-sensitizing drugs such as thiazolidinediones (TZDs). Although these interventions have proven effective in improving glucose homeostasis, there are adherence issues seen with lifestyle interventions and undesirable side effects have been reported with TZDs. With these points in mind, the development of alternative strategies to maintain or improve skeletal muscle insulin sensitivity is warranted. In this context, the purpose of the present review is to highlight the role of antioxidant compounds in the prevention and treatment of skeletal muscle insulin resistance. Specifically, we will briefly describe the mechanisms of insulin-stimulated skeletal muscle glucose uptake and the potential mediators of oxidative stress induced insulin resistance, highlight data suggesting that antioxidant compounds can have beneficial effects on skeletal muscle insulin action, and discuss potential mechanisms mediating this effect.

Efficacy, safety and tolerability of tesaglitazar when added to the therapeutic regimen of poorly controlled insulin-treated patients with type 2 diabetes

This randomised, double-blind, parallel-group study assessed the effects of addition of the dual peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist, tesaglitazar, for 24 weeks to the therapeutic regimen of 392 poorly controlled (glycosylated haemoglobin [HbA1C] 7.5-10%) insulin-treated, type 2 diabetes patients. At 24 weeks, tesaglitazar 0.5 mg resulted in a 0.66% (95% confidence intervals: -0.85, -0.47; p<0.0001) reduction from baseline in HbA1C, and reduced fasting plasma glucose (p<0.0001) and daily insulin dose (p=0.014) versus placebo. After 24 weeks, tesaglitazar caused greater improvements from baseline in triglycerides (p<0.0001), high-density lipoprotein cholesterol (HDL-C) (p<0.001), non-HDL-C (p<0.05), apolipoprotein (apo)A-I (p<0.05) and apoB levels (p<0.01) than placebo. Tesaglitazar was generally well tolerated but was associated with a greater increase in serum creatinine level than placebo. The clinical development of tesaglitazar is no longer continuing; its effects on the glucose and lipid abnormalities of type 2 diabetes suggest that the concept of dual PPARalpha/gamma agonism is worthy of further investigation.

Vascular effects of PPARgamma activators - from bench to bedside

Activation of the nuclear transcription factor peroxisome proliferator-activated receptor-gamma (PPARgamma) plays an important role in adipogenesis, insulin resistance, and glucose homeostasis. Activators of PPARgamma include the anti-diabetic thiazolidinediones (TZDs), drugs that are in clinical use to treat patients with type 2 diabetes mellitus. Experimental as well as clinical data gathered over the last decade suggest that PPARgamma activators may exert direct modulatory function in the vasculature in addition to their metabolic effects. PPARgamma is expressed in all vascular cells, where its activators exhibit anti-inflammatory and anti-atherogenic properties, suggesting that PPARgamma ligands could influence important processes in all phases of atherogenesis. Results from clinical trials demonstrated that TZDs reduce blood levels of inflammatory biomarkers of arteriosclerosis, improve endothelial function, and directly influence lesion morphology and plaque stability, underscoring that PPAR activators may have direct effects in the vasculature in humans. This review will focus on the vascular effects of PPARgamma activators and summarize the current knowledge of their modulatory function on atherogenesis and vascular disease.

The inhibitory effect of rosiglitazone on agonist-induced or spontaneous regulation of contractility

The present study was undertaken to determine whether rosiglitazone treatment influences on the agonist-induced or spontaneous regulation of vascular smooth muscle contraction and, if so, to investigate the related mechanism. Stimulants were directly added without any preanesthetic stress or spontaneous vasoconstriction was induced by preanesthetic physical stress where rat aortic ring preparations isolated from rat exposed to preanesthetic stress such as pinch or prick for 30 min were mounted in organ baths and then exposed to contractile agents. Previously and subchronically ingested rosiglitazone decreased Rho-kinase activating agonist-induced contraction but not depolarization- or alpha adrenergic agonist-induced contraction. Moreover, preanesthetic stress induced the stress-induced spontaneous contraction and previously and subchronically ingested rosiglitazone abolished the stress-induced spontaneous contraction. In conclusion, this study provides the evidence and possible related mechanism concerning the vasorelaxing effect of an antidiabetic rosiglitazone as an antihypertensive on the agonist-induced contraction or stress-induced spontaneous vasoconstriction in rat aortic rings regardless of endothelial function.

Peroxisome proliferator-activated receptors as transcriptional nodal points and therapeutic targets

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in the transcriptional regulation of key metabolic pathways such as lipid metabolism, adipogenesis, and insulin sensitivity. More recent work implicates all 3 PPAR isotypes (alpha, gamma, and delta, also known as beta or beta/delta) in inflammatory and atherosclerotic pathways. Because these nuclear receptors are activated by extracellular signals and control multiple gene targets, PPARs can be seen as nodes that control multiple inputs and outputs involved in energy balance, providing insight into how metabolism and the vasculature may be integrated. The ongoing clinical use of fibrates, which activate PPARalpha, and thiazolidinediones, which activate PPARgamma, establishes these receptors as viable drug targets, whereas considerable in vitro animal model and human surrogate marker studies suggest that PPAR activation may limit inflammation and atherosclerosis. Together, these various observations have stimulated intense interest in PPARs as therapeutic targets and led to large-scale cardiovascular end-point trials with PPAR agonists. The first of these studies has generated mixed results that require careful review, especially in anticipation of additional clinical trial data and ongoing attempts to develop novel PPAR modulators. Such analysis of the existing PPAR data, the appropriate use of currently approved PPAR agonists, and continued progress in PPAR therapeutics will be predicated on a better understanding of PPAR biology.

Thiazolidinediones and their Fluid-Related Adverse Effects

Thiazolidinediones (TZDs) or glitazones are agents that are widely used for the treatment of type 2 diabetes mellitus. These drugs have a multitude of therapeutic effects including reduction in insulin resistance and hyperglycaemia, anti-inflammatory effects and amelioration of hypertension, microalbuminuria and hepatic steatosis. The TZD molecular target, peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear transcription factor, is expressed diffusely in humans, including many tissues comprising the cardiovascular and renal systems. This suggests a potential for TZDs to elicit perturbing effects on these systems, which are independent of their effects on glucose and lipid metabolism. One of the most common adverse effects of TZDs is fluid retention, which can result in, or exacerbate, oedema and congestive heart failure (CHF). The frequency of peripheral oedema is approximately 5% when TZDs are used in mono- or combination oral therapy, and about 15% when used with insulin. Patients with type 2 diabetes are at high risk of myriad morbid complications, including CHF. The development of CHF, particularly in the elderly, is a harbinger of premature mortality. TZD-induced oedema is largely peripheral, may have its origins in changes in haemodynamics, with some contribution from molecules, which regulate cell and tissue permeability (e.g. vascular endothelial growth factor and protein kinase Cbeta), and remains the preponderant manifestation of TZD-induced fluid retention even in those with existing heart failure. Preclinical and pilot clinical data attest to the fact that at least part of the fluid retention derives from a direct effect of TZDs on sodium reabsorption via the renal medullary collecting duct, a mechanism that is sensitive to diuretic agents that have this nephron segment as their site of action, in whole or in part (spironolactone, amiloride and hydrochlorothiazide). Our review suggests various potential clinical strategies by which TZD-induced fluid retention might be effectively monitored and addressed.