Received for publication November 8, 2006.
Revised May 12, 2007.
Accepted for publication May 15, 2007.

GLITAZONES INDUCE ASTROGLIOMA CELL DEATH BY RELEASING REACTIVE OXYGEN SPECIES FROM MITOCHONDRIA: MODULATION OF CYTOTOXICITY BY NITRIC OXIDE

Abstract

The glitazones (or thiazolidinediones) are synthetic compounds used in type-2 diabetes, but they also have broad anti-proliferative and anti-inflammatory properties still not well understood. Previously we described the apoptotic effects of glitazones on astroglioma cells (J. Biol. Chem., 279, 8976-8985). At certain concentrations, we found a selective lethality on glioma cells versus astrocytes, which was dependent on a rapid production of reactive oxygen species (ROS) and seemed unrelated to the receptor PPAR. The present study was aimed at characterizing the oxygen derivatives induced by ciglitazone, rosiglitazone and pioglitazone in C6 glioma cells and to investigate their intracellular source. We examined the interaction of ROS with nitric oxide (NO) and its consequences for glioma cell survival. Fluorescence microscopy and flow cytometry showed that glitazones induced superoxide anion, peroxynitrite and hydrogen peroxide, ciglitazone being the most active. ROS production was completely prevented by uncoupling of the electron transport chain and by removal of glucose as energy substrate, whereas it was unaffected by inhibition of NADPH-oxidase and xanthine-oxidase. Moreover, glitazones inhibited state 3 respiration in permeabilized cells, and experiments with mitochondrial inhibitor suggested that Complex-I was the likely target of glitazones. Therefore, these results point to the mitochondrial electron transport chain as the source of glitazone-induced ROS in C6 cells. Glitazones also depolarized mitochondria and reduced mitochondrial pH. NO synthase inhibitors revealed that superoxide anion combines with NO to yield peroxynitrite, and that the latter contributes to the cytotoxicity of glitazones in astroglioma cells. Future anti-tumoral strategies may take advantage of these findings.

Key words: Nitric oxide synthases, PPARs, Fluorescence techniques, Mitochondrial toxins, Reactive intermediates, Mechanisms of cell killing/apoptosis

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