Phosphate-induced chondrocyte apoptosis is linked to nitric oxide generation

Abstract

An elevation in inorganic phosphate (Pi) concentration activates epiphyseal chondrocyte apoptosis. To determine the mechanism of apoptosis, tibial chondrocytes were treated with Pi, and nitrate/nitrite (NO[Formula: see text]/NO[Formula: see text]) levels were determined. Piinduced a threefold increase in the NO[Formula: see text]/NO[Formula: see text] concentration; inhibitors of nitric oxide (NO) synthase activity and Pitransport significantly reduced NO[Formula: see text]/NO[Formula: see text]levels and prevented cell death. Furthermore, a dose-dependent increase in cell death was observed after exposure of chondrocytes to S-nitrosoglutathione. Piincreased caspase 3 activity 2.7-fold. Both caspase 1 and caspase 3 inhibitors protected chondrocytes from Pi-induced apoptosis. Picaused a significant decrease in the mitochondrial membrane potential, while NO synthase inhibitors maintained mitochondrial function. While Picaused thiol depletion, inhibition of Piuptake or NO generation served to maintain glutathione levels. The results suggest that NO serves to mediate key metabolic events linked to Pi-dependent chondrocyte apoptosis.