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

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

Effects of rosiglitazone and metformin on inflammatory markers and adipokines: decrease in interleukin-18 is an independent factor for the improvement of homeostasis model assessment-beta in type 2 diabetes mellitus

OBJECTIVE

We examined the individual pharmacological effects of the addition of rosiglitazone and metformin to glimepiride on inflammatory markers and adipokines in patients with type 2 diabetes mellitus. We analysed the relationships between these variables, the measurements of insulin sensitivity and beta-cell function in patients treated with rosiglitazone plus glimepiride.

DESIGN AND PATIENTS

One hundred twenty (120) patients with type 2 diabetes mellitus were randomized and treated with glimepiride plus rosiglitazone or glimepiride plus metformin for 12 weeks. The plasma concentrations of the inflammatory markers and adipokines were measured at baseline and after 12 weeks.

MEASUREMENTS

Markers of insulin sensitivity and beta-cell function were determined by the quantitative insulin sensitivity check index (QUICKI) and the homeostasis model assessment of beta-cell function (HOMA-beta), respectively. Plasma concentrations of adiponectin were measured by radioimmunoassay. Plasma concentrations of resistin, tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-18 (IL-18) were measured using ELISA.

RESULTS

Improvements in fasting insulin level, QUICKI and HOMA-beta were noted in the rosiglitazone-treated group. Only the QUICKI value improved in the metformin-treated group. Adiponectin concentrations significantly increased in the rosiglitazone-treated group after 12 weeks. Significant decreases in resistin, C-reactive protein, TNF-alpha, IL-6 and IL-18 were seen in the rosiglitazone-treated patients but not in the metformin-treated patients. The independent risk factor for the HOMA-beta change according to stepwise multivariate regression analysis was a change in IL-18.

CONCLUSIONS

Rosiglitazone, but not metformin, improved the plasma concentrations of inflammatory markers and adipokines in patients with type 2 diabetes mellitus. A decrease in IL-18 is an independent factor for the improvement of HOMA-beta in type 2 diabetes mellitus.

Diabetes and cardiovascular risk markers

BACKGROUND

People with type 2 diabetes generally carry an array of risk factors for cardiovascular disease (CVD), including hyperglycaemia, dyslipidaemia, alterations in inflammatory mediators and coagulation/thrombolytic parameters, as well as other 'non-traditional' risk factors, many of which may be closely associated with insulin resistance. Consequently, rates of CVD mortality and morbidity are particularly high in this population. Targeting hyperglycaemia alone does not reduce the excess risk in diabetes, highlighting the need for aggressive treatment of other risk factors.

SCOPE

This is a review of cardiovascular risk markers in diabetes, based on MEDLINE and EMBASE literature searches (1994-2004).

FINDINGS

Although, the current use of statin therapy is effective at reducing low-density lipoprotein (LDL)-cholesterol, residual risk remains from other independent lipid and non-lipid factors. The peroxisome proliferator-activated receptor-gamma(PPARgamma) appears to be intimately involved in regulating risk markers at multiple levels. Ligands that activate PPARgamma, which include the thiazolidinedione (TZD) insulin-sensitizing agents used to manage type 2 diabetes, display a number of potential anti-atherogenic properties, including effects on high-density lipoprotein (HDL) cholesterol and triglycerides, as well as other beneficial non-lipid effects, such as regulating levels of mediators involved in inflammation and endothelial dysfunction. Data from several sources suggest that simple strategies combining TZDs and statins could have complementary effects on CVD risk factors profiles in diabetes, alongside the ability to control glycaemia.

CONCLUSION

It is hoped that studies currently underway will provide insights into the value of such treatment approaches in terms of reducing the excess CVD risk, morbidity and mortality associated with type 2 diabetes.

The roles of insulin resistance, hyperinsulinemia, and thiazolidinediones in cardiovascular disease

Although it is difficult to distinguish between the relative effects of insulin resistance and hyperinsulinemia, insulin resistance is clearly associated with significantly increased cardiovascular and cerebrovascular risk. This effect is consistent across the spectrum of worsening glycemic control, from the onset of impaired glucose tolerance to the development of clinical diabetes. It is more difficult to discriminate between the roles of elevated circulating insulin and proinsulin levels; the association between insulin levels and cardiovascular risk is weak. The thiazolidinediones (TZDs) significantly improve insulin sensitivity and exert numerous effects on the vascular bed, including improved endothelial function, decreased vascular inflammation, decreased plasma free fatty acid levels, improved dyslipidemic profiles, and inhibition of vascular smooth muscle proliferation. These findings provide increasing evidence to suggest that the TZDs may have a beneficial effect on atherosclerosis and may reduce the incidence and severity of adverse cardiovascular outcomes. These effects remain to be substantiated by the results of large outcomes studies to evaluate the impact of glycemic control and reversal of insulin resistance on cardiovascular events.