Na+/H+ exchanger-1 inhibitors decrease myocardial superoxide production via direct mitochondrial action

Garciarena CD, Caldiz CI, Correa MV, Schinella GR, Mosca SM, Chiappe de Cingolani GE, Cingolani HE, Ennis IL. Na+/H+ exchanger-1 inhibitors decrease myocardial superoxide production via direct mitochondrial action. J Appl Physiol 105: 1706-1713, 2008. First published September 18, 2008; doi:10.1152/japplphysiol.90616.2008. - The possibility of a direct mitochondrial action of Na+/H+ exchanger-1 (NHE-1) inhibitors decreasing reactive oxygen species (ROS) production was assessed in cat myocardium. Angiotensin II and endothelin-1 induced an NADPH oxidase (NOX)-dependent increase in anion superoxide (O-2(-)) production detected by chemiluminescence. Three different NHE-1 inhibitors [cariporide, BIIB-723, and EMD-87580] with no ROS scavenger activity prevented this increase. The mitochondria appeared to be the source of the NOX-dependent ROS released by the "ROS-induced ROS release mechanism" that was blunted by the mitochondrial ATP-sensitive potassium channel blockers 5-hydroxydecanoate and glibenclamide, inhibition of complex I of the electron transport chain with rotenone, and inhibition of the permeability transition pore (MPTP) by cyclosporin A. Cariporide also prevented O-2(-) production induced by the opening of mK(ATP) with diazoxide. Ca2+-induced swelling was evaluated in isolated mitochondria as an indicator of MPTP formation. Cariporide decreased mitochondrial swelling to the same extent as cyclosporin A and bongkrekic acid, confirming its direct mitochondrial action. Increased O-2(-) production, as expected, stimulated ERK1/2 and p90 ribosomal S6 kinase phosphorylation. This was also prevented by cariporide, giving additional support to the existence of a direct mitochondrial action of NHE-1 inhibitors in preventing ROS release. In conclusion, we report a mitochondrial action of NHE-1 inhibitors that should lead us to revisit or reinterpret previous landmark observations about their beneficial effect in several cardiac diseases, such as ischemia-reperfusion injury and cardiac hypertrophy and failure. Further studies are needed to clarify the precise mechanism and site of action of these drugs in blunting MPTP formation and ROS release.