Antidiabetic agent pioglitazone increases insulin receptors on 3T3-L1 adipocytes

Thiazolidinedione-induced effects beyond glycaemic control

The thiazolidinediones exert their insulin sensitising effect by binding to the nuclear receptors (transcription factors) peroxisome proliferator activated receptor (PPAR) γ and, to varying degrees, to PPARα. Several different genes are activated by thiazolidinediones, many of which contribute to the increase in insulin sensitivity (eg. an increase in glucose uptake and utilisation, a decrease in gluconeogenesis and in insulin-antagonistic cytokines, such as tumour necrosis factor α). Activation of other genes indirectly reduces insulin resistance by, for example, increasing free fatty acid (FFA) uptake and oxidation resulting in lower circulating FFA levels. The action of thiazolidinediones at PPARγ is generally responsible for their insulin sensitising effects while action at PPARα contributes to their lipid lowering effects. Therefore, the relative affinities of the different thiazolidinediones for PPARγ and PPARα will also lead to a different spectrum of actions for each agent.

Relationship between plasma hANP level and pretibial edema by pioglitazone treatment

Pioglitazone is an insulin-sensitizer with a thiazolidinedione structure. It is used to reduce hyperglycemia and is frequently prescribed to type 2 diabetic patients. However, it causes edema as an adverse effect in some patients. Although the mechanism of edema is unclear, it may bring an increased risk of congestive heart failure. We investigated whether pioglitazone correlates with the level of plasma human atrial natriuretic peptide (hANP), a marker for congestive heart failure. We administered 15 mg/day of pioglitazone for 3 months to 49 patients (34 men and 15 women; mean age: 64+/-12 years) with type 2 diabetes and no history of pretibial edema. Three of the patients complained of pretibial edema during the 3-month period, and their plasma hANP levels were higher than those of the other 46 before and during the treatment. We therefore suspect that pretibial edema appearing after administration of low-doses of pioglitazone coincides with the level of plasma hANP, and that the appearance of pretibial edema may reflect an increase in circulating blood volume induced by pioglitazone.

Troglitazone enhances glycolysis and improves intracellular glucose metabolism in rat mesangial cells

To clarify the action of the new antidiabetic agent, troglitazone, on rat mesangial cells, we assessed its effect on the uptake and intracellular metabolism of glucose. Troglitazone increased the uptake of 2-deoxyglucose (2DOG) in a dose-dependent manner with an upregulation of glucose transporter 1 (GLUT1) mRNA, whereas it had no effect on the uptake of alpha-methyl glucoside (AMG). This troglitazone-induced glucose uptake was not suppressed by phlorizin. In 5 mmol/L glucose, 2 microg/mL (4.5 micromol/L) troglitazone increased glucose consumption 2.9-fold, similar to that in 20 mmol/L glucose. Troglitazone increased the production of pyruvate and lactate as a consequence of the increase in glycolysis, but did not increase the cellular ATP content. Troglitazone improved the high-glucose-induced accumulation of intracellular sorbitol and fructose and elevation of the cellular redox potential. These data suggest that troglitazone enhances glucose uptake through GLUT1 with an acceleration of glycolysis, and improves the abnormal intracellular glucose metabolism under high-glucose conditions in rat mesangial cells.