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Mode of action

Thiazolidinediones act by binding to PPARs (peroxisome proliferator-activated receptors), a group of receptor molecules inside the cell nucleus, specifically PPARγ (gamma). The normal ligands for these receptors are free fatty acids (FFAs) and eicosanoids. When activated, the receptor migrates to the DNA, activating transcription of a number of specific genes.
Genes upregulated by PPARγ can be found in the main article on peroxisome proliferator-activated receptors.

By activating PPARγ:

• insulin resistance is decreased
• adipocyte differentiation is modified
• VEGF-induced angiogenesis is inhibited (abstract).
• Leptin levels decrease (leading to an increased appetite)
• Levels of certain interleukins (e.g. IL-6) fall
• Adiponectin levels rise

Members of the class

These include:

• rosiglitazone (Avandia)
• pioglitazone (Actos)
Troglitazone was withdrawn from the market due to an increased incidence of drug-induced hepatitis in patients who were using the drug. It is now common practice that liver enzymes are monitored during the first year of treatment with the "newer" thiazolidinediones.
Experimental agents include MCC-555, a powerful antidiabetic agent and the early non-marketed thiazolidinedione ciglitazone.


Uses

The only registered use of the thiazolidinediones is in diabetes mellitus type 2.
It is being investigated experimentally in polycystic ovary syndrome (PCOS) and non-alcoholic steatohepatitis (NASH).
Several forms of lipodystrophy cause insulin resistance, which has responded favorably to thiazolidinediones.


Side effects and contraindications

The withdrawal of troglitazone has led to concerns of other thiazolidinediones increasing the risk of hepatitis. Guidelines now mention that for the first year of thiazolidinedione therapy, a two- or three-monthly check of liver enzymes is conducted to ascertain that no liver damage is occurring.
The main side effect of all thiazolidinediones is fluid retention, leading to edema, weight gain, and potentially aggravating heart failure. Therefore, thiazolidinediones cannot be prescribed in patients with decreased ventricular function (NYHA grade III and IV heart failure)

(Wikipedia free encyclopedia, 2006).