Thiazolidinediones

A Narrative Review of Diabetic Macroangiopathy: From Molecular Mechanism to Therapeutic Approaches

Diabetic macroangiopathy, a prevalent and severe complication of diabetes mellitus, significantly contributes to the increased morbidity and mortality rates among affected individuals. This complex disorder involves multifaceted molecular mechanisms that lead to the dysfunction and damage of large blood vessels, including atherosclerosis (AS) and peripheral arterial disease. Understanding the intricate pathways underlying the development and progression of diabetic macroangiopathy is crucial for the development of effective therapeutic interventions. This review aims to shed light on the molecular mechanism implicated in the pathogenesis of diabetic macroangiopathy. We delve into the intricate interplay of chronic inflammation, oxidative stress, endothelial dysfunction, and dysregulated angiogenesis, all of which contribute to the vascular complications observed in this disorder. By exploring the molecular mechanism involved in the disease we provide insight into potential therapeutic targets and strategies. Moreover, we discuss the current therapeutic approaches used for treating diabetic macroangiopathy, including glycemic control, lipid-lowering agents, and vascular interventions.

Cardiovascular Outcomes in Patients With Previous Myocardial Infarction and Mild Diabetes Mellitus Following Treatment With Pioglitazone: Reports of a Randomised Trial From The Japan Working Group for the Assessment Whether ioglitazone rotects DM Patients gainst e-Infarction (PPAR Study)

BACKGROUND

Secondary prevention in patients with myocardial infarction (MI) is critically important to prevent ischaemic heart failure and reduce social burden. Pioglitazone improves vascular dysfunction and prevents coronary atherosclerosis, mainly via anti-inflammatory and antiatherogenic effects by enhancing adiponectin production in addition to antihyperglycemic effects, thus suggesting that pioglitazone attenuates cardiovascular events in patients with mild (HbA1c levels < 6·5%) diabetes mellitus (DM). Therefore, we evaluated the effects of pioglitazone on cardiovascular events in patients with both previous MI and mild DM.

METHODS

In this multicentre, prospective, randomised, open, blinded-endpoint trial, we randomly assigned 630 patients with mild DM with a history of MI to undergo either DM therapy with (pioglitazone group) or without (control group) pioglitazone. DM was diagnosed using the 75-g oral glucose tolerance test, and mild DM was defined if HbA1c level was < 6·5%. The primary endpoint was the composite of cardiovascular death and hospitalisation caused by acute MI, unstable angina, coronary revascularisation (including percutaneous coronary intervention and cardiac bypass surgery), and stroke.

FINDINGS

HbA1C levels were 5·9 and 5·8% (p = 0·71) at baseline and 6·0 and 5·8% (p < 0·01) at 2 years for the control and pioglitazone groups, respectively.The primary endpoint was observed in 14·2% and 14·1% patients in the control and pioglitazone groups during two years (95% confidential interval (CI):0.662-1·526, p = 0·98), respectively; the incidence of MI and cerebral infarction was 0·3% and 2·2% (95%CI: 0·786-32·415, p = 0·09) and 1·0% and 0·3% (95%CI: 0·051-3·662, p = 0·44), respectively. Post-hoc analyses of the 7-year observation period showed that these trends were comparable (21·9% and 19·2% in the control and pioglitazone groups, 95%CI: 0.618-1·237, p = 0·45).

INTERPRETATION

Pioglitazone could not reduce the occurrence of cardiovascular events in patients with mild DM and previous MI.

Pharmacological interventions for preventing or delaying onset of type 2 diabetes mellitus

Prevention or delay of onset of type 2 diabetes in individuals at varying risk across the dysglycaemia continuum before overt diabetes becomes clinically manifest constitutes a leading objective of global disease prevention schemes. Pharmacological intervention has been suggested as a means to help prevent diabetes and reduce the global burden of this chronic condition. However, there is no credible evidence that early pharmacological intervention leads to long-term benefit in reducing diabetes-related complications or preventing early mortality, compared to treating people with diagnosed diabetes who have crossed the glycaemic threshold. In this review, we examine published evidence from trials using pharmacological agents to delay or prevent progression to diabetes. We also explore the benefit/risk impact of such therapies, safety issues and relevant off-target effects. Current evidence suggests none of the drugs currently available sustainably lower cumulative diabetes incidence, none provides a durable delay in diabetes diagnosis and none provides a convincing concomitant excess benefit for microvascular or macrovascular risk.

Can C-peptide mediated anti-inflammatory effects retard the development of microvascular complications of type 1 diabetes?

Hyperglycemia is considered to be the major cause of microvascular complications of diabetes. Growing evidence highlights the importance of hyperglycemia-mediated inflammation in the initiation and progression of microvascular complications in type 1 diabetes. We hypothesize that lack of proinsulin C-peptide and lack of its anti-inflammatory properties contribute to the development of microvascular complications. Evidence gathered over the past 20 years shows that C-peptide is a biologically active peptide in its own right. It has been shown to reduce formation of reactive oxygen species and nuclear factor-κB activation induced by hyperglycemia, resulting in inhibition of cytokine, chemokine and cell adhesion molecule formation as well as reduced apoptotic activity. In addition, C-peptide stimulates and induces the expression of both Na⁺, K⁺-ATPase and endothelial nitric oxide synthase. Animal studies and small-scale clinical trials in type 1 diabetes patients suggest that C-peptide replacement combined with regular insulin therapy exerts beneficial effects on kidney and nerve dysfunction. Further clinical trials in patients with microvascular complications including measurements of inflammatory markers are warranted to explore the clinical significance of the aforementioned, previously unrecognized, C-peptide effects.

Regulation of lipoprotein lipase gene expression by insulin and troglitazone in rainbow trout (Oncorhynchus mykiss) adipocyte cells in culture

Adipose tissue plays a central role regulating the balance between deposition and mobilization of lipid reserves. Lipoprotein lipase (LPL) is a key enzyme controlling lipid accumulation in mammals and fish. In the present study, we have examined the expression of LPL in rainbow trout cultured adipocytes and we have investigated the effect of troglitazone, a member of thiazolidinediones (TZDs), and insulin on its expression. LPL gene expression increased from day 1 until day 12 of culture, and the level was maintained up to day 21. The addition of insulin at 10 nM and 1.7 μM increased significantly LPL gene expression in undifferentiated cells (days 7 to 12 maintained in growth medium). Nevertheless, treatment of day 7 cells incubated in growth medium with troglitazone (5 μM) or troglitazone plus insulin (1 μM each), tended to enhance LPL expression. In addition, LPL mRNA levels increased significantly in the presence of 1 μM and 5 μM of troglitazone (days 7 to 12) when the cells were induced to differentiate by addition of differentiation medium. Although troglitazone alone (1 μM) did not stimulate lipid accumulation in the cells neither in growth nor in differentiation medium, the simultaneous presence of troglitazone (1 μM) and insulin (1 μM) increased significantly the content of triglycerides in adipocyte cells maintained in growth medium (days 7 to 12). These results indicate that insulin and troglitazone regulate LPL gene expression during adipocyte differentiation and suggest that both factors may have combined effects in the modulation of adipogenesis.

Treatment of diabetic vasculopathy with rosiglitazone and ramipril: Hype or hope?

Cardiovascular diseases are responsible for increased morbidity and mortality in people with diabetes. Diabetic macrovasculopathy is associated with structural and functional changes in large arteries, which causes endothelial dysfunction, increased arterial stiffness, or decreased arterial distensability. Diabetic complications can be controlled and avoided by strict glycemic control, maintaining normal lipid profiles, regular physical exercise, adopting a healthy lifestyle and pharmacological interventions. Treatment goals for patients with type 2 diabetes specify targets for glycemia and other cardiometabolic risk factors, for example, hypertension and dyslipidemia. In recent years, special attention has been devoted to both thiazolidindiones (TZDs) and angiotensin converting enzyme (ACE) inhibitors as clinical trials revealed that these drugs may reduce the rate of progression to diabetes or delay the onset of diabetes, regression of impaired glucose tolerance (IGT) to normoglycemia and reduces the composite of all-cause mortality, nonfatal myocardial infarction and stroke in patients with diabetes. This review focuses on the potential roles of rosiglitazone, a member of TZD class of antidiabetic agents, and ramipril, an ACE inhibitor, in preventing the preclinical macrovasculopathy in diabetes and IGT population.

Fat redistribution preferentially reflects the anti-inflammatory benefits of pioglitazone treatment

Thiazoledinedione is known to have an anti-inflammatory effect besides a hypoglycemic effect. We investigated changes in high-sensitivity C-reactive protein (hsCRP), a proinflammatory marker, after pioglitazone treatment in association with the resulting changes in various metabolic and anthropometric parameters. A total of 93 type 2 diabetes mellitus patients (47 men and 46 women; mean age, 50.0 ± 10.8 years) who were being treated with a stable dose of sulfonylurea or metformin were enrolled in the study. Pioglitazone (15 mg/d) was added to their treatment regimen for 12 weeks, and metabolic and anthropometric measurements were taken before and after pioglitazone treatment. Pioglitazone treatment for 12 weeks decreased serum hsCRP levels (0.83 [1.14] to 0.52 [0.82] mg/L, P < .001) and improved glycemic control (fasting glucose, P < .001; glycosylated hemoglobin, P < .001) and lipid profiles (triglyceride, P = .016; high-density lipoprotein cholesterol, P < .001). Between responders and nonresponders to the hsCRP-lowering effect of pioglitazone, there were significant differences in baseline hsCRP levels and changes in the postprandial glucose and the ratio of visceral fat thickness (VFT) to subcutaneous fat thickness (SFT) (P = .004, .011, and .001, respectively). The percentage change in hsCRP levels after treatment was inversely correlated with baseline hsCRP levels (r = -0.497, P < .001) and directly correlated with the change in postprandial glucose (r = 0.251, P = .021), VFT (r = 0.246, P = .030), and VFT/SFT ratio (r = 0.276, P = .015). Logistic regression analysis revealed that the hsCRP-lowering effect of pioglitazone was affected by baseline hsCRP levels (odds ratio [OR] = 7.929, P = .007) as well as changes in postprandial 2-hour glucose (OR = 0.716, P = .025) and VFT/SFT ratio (OR = 0.055, P = .009). In conclusion, treatment with pioglitazone produced an anti-inflammatory effect, decreasing serum hsCRP levels; and a decrease in the VFT/SFT ratio was independently and most strongly associated with the hsCRP-decreasing effect. These results suggest that abdominal fat redistribution preferentially reflects the anti-inflammatory benefits of pioglitazone treatment.

Pro12Ala polymorphism of the peroxisome proliferator-activated receptor γ2 in patients with fatty liver diseases

AIM: To test the occurrence of the Pro12Ala mutation of the peroxisome proliferator-activated receptor-γ (PPARγ)2-gene in patients with non-alcoholic fatty liver disease (NAFLD) or alcoholic fatty liver disease (AFLD).

METHODS: DNA from a total of 622 specimens including 259 blood samples of healthy blood donors and 363 histologically categorized liver biopsies of patients with NAFLD (n = 263) and AFLD (n = 100) were analyzed by Real-time polymerase chain reaction using allele-specific probes.

RESULTS: In the NAFLD and the AFLD collective, 3% of the patients showed homozygous occurrence of the Ala12 PPARγ2-allele, differing from only 1.5% cases in the healthy population. In NAFLD patients, a high incidence of the Ala12 mutant was not associated with the progression of fatty liver disease. However, we observed a significantly higher risk (odds ratio = 2.50, CI: 1.05-5.90, P = 0.028) in AFLD patients carrying the mutated Ala12 allele to develop inflammatory alterations. The linkage of the malfunctioning Ala12-positive PPARγ2 isoform to an increased risk in patients with AFLD to develop severe steatohepatitis and fibrosis indicates a more prominent anti-inflammatory impact of PPARγ2 in progression of AFLD than of NAFLD.

CONCLUSION: In AFLD patients, the Pro12Ala single nuclear polymorphism should be studied more extensively in order to serve as a novel candidate in biomarker screening for improved prognosis.

Cardiovascular risk and thiazolidinediones--what do meta-analyses really tell us?

Meta-analyses of clinical trials suggest that the use of the thiazolidinedione (TZD), rosiglitazone, in patients with type 2 diabetes mellitus may increase the risk of myocardial ischaemic events by 30-40%. Although these controversial data must be interpreted with caution, in the absence of definitive prospective cardiovascular (CV) outcomes data, they represent a prominent source of evidence concerning the CV safety of rosiglitazone. The results of meta-analyses and a large randomized-controlled CV outcomes trial provide strong evidence that pioglitazone does not increase the risk of coronary events. This article clarifies the clinical significance of these meta-analytical findings alongside other sources of evidence and assesses their impact on evolving treatment guidelines and recommendations for the use of TZDs in patients with type 2 diabetes.

Cytokine and cytokine-like inflammation markers, endothelial dysfunction, and imbalanced coagulation in development of diabetes and its complications

CONTEXT

Recent developments indicate that pathophysiological mechanisms leading to beta-cell damage, insulin resistance, and the vascular complications of diabetes include an activation of the inflammation cascade, endothelial dysfunction, and procoagulant imbalance. Their circulating biomarkers may therefore provide opportunities for early diagnosis and targets for novel treatments.

EVIDENCE

Circulating biomarkers of these pathways such as TNFalpha, IL-6, C-reactive protein (CRP) (inflammation), vascular cellular adhesion molecule-1, interstitial cellular adhesion molecule-1, E-selectin, von Willebrand factor (endothelial dysfunction), plasminogen activator inhibitor-1, fibrinogen, P-selectin (procoagulant state), and adiponectin (antiinflammation) may be associated with development of both type 1 and type 2 diabetes and some studies, particularly in type 2 diabetes, have demonstrated that certain biomarkers may have independent predictive value. Similarly studies have shown that these biomarkers may be associated with development of diabetic nephropathy and retinopathy, and again, particularly in type 2 diabetes, with cardiovascular events as well. Finally, the comorbidities of diabetes, namely obesity, insulin resistance, hyperglycemia, hypertension and dyslipidemia collectively aggravate these processes while antihyperglycemic interventions tend to ameliorate them.

CONCLUSIONS

Increased CRP, IL-6, and TNFalpha, and especially interstitial cellular adhesion molecule-1, vascular cellular adhesion molecule-1, and E-selectin are associated with nephropathy, retinopathy, and cardiovascular disease in both type 1 and type 2 diabetes. Whereas further work is needed, it seems clear that these biomarkers are predictors of increasing morbidity in prediabetic and diabetic subjects and should be the focus of work testing their clinical utility to identify high-risk individuals as well as perhaps to target interventions.

The influence of thiazolidinediones on adipogenesis in vitro and in vivo: Potential modifiers of intramuscular adipose tissue deposition in meat animals1,2

Thiazolidinediones (TZD) are insulin sensitizing agents currently used for the treatment of type 2 diabetes and are widely used as adipogenic agents because they are ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), a key adipogenic transcription factor. In vivo and in vitro studies of TZD as potential modifiers of intramuscular or marbling adipogenesis are reviewed. Thiazolidinedione-induced adipogenesis has been reported in numerous cell culture systems, including rodent, human, bovine, and porcine adipose tissue stromal-vascular (S-V) cell cultures. Studies of porcine S-V cell cultures derived from semitendinosus muscle show that TZD can potentially modify intramuscular or marbling adipogenesis. Preadipocyte recruitment was TZD-dependent in muscle S-V cultures but TZD-independent in adipose S-V cultures. There appear to be differences between adipocytes in muscle and subcutaneous adipose tissue, reminiscent of differences observed in adipocytes from different adipose tissue depots. Troglitazone, a TZD, induces marbling adipogenesis without inhibiting myogenesis when cells are grown on laminin precoated culture dishes. Additionally, troglitazone treatment does not increase lipid content in porcine adipose tissue or muscle S-V cell cultures. Thiazolidinedione treatment increases lipid content of muscle in rodents and humans; however, rosiglitazone treatment for 49 d in pigs did not influence muscle lipid content and meat quality, but several significant changes in muscle fatty acid composition were observed. Although timing of treatment with TZD needs to be optimized, evidence suggests these compounds may enhance marbling deposition in swine.

Diabetes-associated macrovasculopathy: pathophysiology and pathogenesis

The complications associated with diabetic vasculopathy are commonly grouped into two categories: microvascular and macrovascular complications. In diabetes, macrovascular disease is the commonest cause of mortality and morbidity and is responsible for high incidence of vascular diseases such as stroke, myocardial infarction and peripheral vascular diseases. Macrovascular diseases are traditionally thought of as due to underlying obstructive atherosclerotic diseases affecting major arteries. Pathological changes of major blood vessels leading to functional and structural abnormalities in diabetic vessels include endothelial dysfunction, reduced vascular compliance and atherosclerosis. Besides, advanced glycation end product formation interacts with specific receptors that lead to overexpression of a range of cytokines. Haemodynamic pathways are activated in diabetes and are possibly amplified by concomitant systemic hypertension. Apart from these, hyperglycaemia, non-enzymatic glycosylation, lipid modulation, alteration of vasculature and growth factors activation contribute to development of diabetic vasculopathy. This review focuses on pathophysiology and pathogenesis of diabetes-associated macrovasculopathy.

Effects of pioglitazone on lipid and lipoprotein metabolism

Type 2 diabetes is associated with an increased risk of cardiovascular disease (CVD). A major contributing factor to this risk is the abnormal lipid profile known as dyslipidaemia, which is characterized by low HDL cholesterol (HDL-C), raised triglycerides (TGs) and a predominance of small, dense LDL cholesterol (LDL-C) particles. Statins are now widely used first-line in patients with type 2 diabetes due to their proven efficacy in reducing LDL-C and cardiovascular risk. However, despite the use of statins, the absolute risk of CVD in patients remains elevated, highlighting the need to target all aspects of the diabetic lipid profile such as raised TGs or low HDL-C levels. Insulin resistance is thought to be central in the pathogenesis of diabetic dyslipidaemia; therefore, improving insulin sensitivity with a thiazolidinedione offers an attractive treatment option. Indeed, pioglitazone, a member of the peroxisome proliferator-activated receptor-gamma family, has been shown in clinical trials to improve both blood glucose levels and the lipid profile when used either as monotherapy or in combination with other oral antidiabetic agents. In the monotherapy setting, pioglitazone has been associated with greater decreases in TGs and increases in HDL-C when compared with glibenclamide or metformin. Studies investigating the effects of pioglitazone add-on therapy to either metformin or sulphonylurea treatments have shown sustained improvements in serum levels of TGs and HDL-C and favourable effects on LDL-C particle size. In comparison with rosiglitazone, pioglitazone has different and potentially favourable effects on plasma lipids. The recent PROspective pioglitAzone Clinical Trial In macroVascular Events study has given weight to the hypothesis that the beneficial metabolic effects of pioglitazone may be associated with reductions in cardiovascular risk in patients with type 2 diabetes.

Effect of rosiglitazone/ramipril on preclinical vasculopathy in newly diagnosed, untreated diabetes and IGT patients: 1-year randomised, double-blind, placebo-controlled study

OBJECTIVE

To investigate whether pharmacological interventions with rosiglitazone/ramipril can reverse preclinical vasculopathy in newly diagnosed untreated patients with type 2 diabetes (T2DM) and impaired glucose tolerance (IGT).

METHODS

In this randomised, double-blind, placebo-controlled study, 33 T2DM and 33 IGT patients were randomised to 4 mg rosiglitazone or 5 mg ramipril or placebo for 1 year. The subjects were newly diagnosed, untreated, normotensive, nonobese, nonsmoker, and nonhyperlipidaemic. Haemodynamic variables were measured at three treatment phases and pulse wave velocity (PWV) and augmentation index (AI) were measured throughout the treatment period.

RESULTS

Rosiglitazone showed a significant reduction in PWV (p=0.039) and AI (p=0.031) and ramipril demonstrated a significant reduction of AI (p=0.025) in IGT in comparison to placebo on the 12th month of treatment. No significant difference was observed in PWV and AI in T2DM with rosiglitazone/ramipril in comparison to placebo during overall treatment period.

CONCLUSIONS

Rosiglitazone significantly reversed preclinical vasculopathy in IGT as evident by significant decrease in PWV and AI after 1 year of treatment. Ramipril also reduced large artery stiffness as shown by significant decrease of AI after 1 year of treatment in IGT. Further trials are needed for a longer period of time, maybe with higher doses, to show whether rosiglitazone/ramipril can reverse preclinical vasculopathy in T2DM.

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.

Managing psychiatric disorders with antidiabetic agents: translational research and treatment opportunities

The objective of this paper is to synthesise extant studies describing the neurotherapeutic effects of antidiabetic agents in neuropsychiatric disorders. The authors conducted a MedLine search of all English-language articles published between 1966 and March 2006. The search terms were the nonproprietary names of established and putative antidiabetic agents (e.g., insulin, insulin secretagogues and sensitisers) cross-referenced with the individual names of Diagnostic and Statistical Manual of Mental Disorders (DSM)-III-R/IV/-TR-defined mood, psychotic, anxiety and dementing disorders. The search was augmented with a manual review of article reference lists. Contemporary models of disease pathophysiology in major depressive disorder, bipolar disorder and several dementing disorders (e.g., Alzheimer's disease) emphasise alterations in cellular plasticity and cytoarchitecture, with associated regional abnormalities in neuronal and glial density and morphology. Antidiabetic treatments (e.g., thiazolidinediones) may be capable of attenuating this pathological process via disparate mechanisms (e.g., neuroprotective, neurotrophic, anti-inflammatory). Enhanced insulin signalling with antidiabetic treatments may preserve and/or augment cognitive function in several neuropsychiatric disorders. Antidiabetic treatments, which maintain euglycaemia, hold promise as potent and clinically significant therapeutic interventions for several neuropsychiatric disorders.