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

Abstract

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. Ca(2+)-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.

Excessive Na+/H+ Exchange in Disruption of Dendritic Na+ and Ca2+ Homeostasis and Mitochondrial Dysfunction following in Vitro Ischemia

“…Taken together, these studies demonstrate a conserved role of the NHE-1 signaling mechanism in ischemic reperfusion injury among multiple cell types. Moreover, it has been suggested that NHE-1 inhibitors, including HOE 642, have a direct effect on reactive oxygen species production and mitochondrial permeability transition pore formation (13). In the current study, it is unknown whether any protective effects mediated by HOE 642 result from its direct actions on mitochondria.…”

Mitochondrial Permeability Transition Pore Opening as a Promising Therapeutic Target in Cardiac Diseases

“…Moreover, the antihypertrophic effects of NHE-1 inhibitors were associated with the inhibition of pore opening in isolated cardiomyocytes in response to phenylephrine (Javadov et al, 2006a), angiotensin II, and endothelin-1 (Garciarena et al, 2008). It should be pointed out that mitochondrial ROS accumulation in response to prohypertrophic agents was abrogated in the presence of NHE-1 inhibitors (Javadov et al, 2006a;De Giusti et al, 2008;Garciarena et al, 2008).…”

“…Long-term (12 and 18 weeks) treatment of rats with the NHE-1 inhibitor EMD87580 reduced postinfarction remodeling, which was associated with inhibition of MPTP opening, as well as improved mitochondrial respiration (Javadov et al, 2005) and biogenesis (Javadov et al, 2006b). Moreover, the antihypertrophic effects of NHE-1 inhibitors were associated with the inhibition of pore opening in isolated cardiomyocytes in response to phenylephrine (Javadov et al, 2006a), angiotensin II, and endothelin-1 (Garciarena et al, 2008). It should be pointed out that mitochondrial ROS accumulation in response to prohypertrophic agents was abrogated in the presence of NHE-1 inhibitors (Javadov et al, 2006a;De Giusti et al, 2008;Garciarena et al, 2008).…”

Myocardial Mineralocorticoid Receptor Activation by Stretching and Its Functional Consequences

“…[1][2][3] Previous studies demonstrated that inhibiting the NHE1 either pharmacologically or by silencing its expression also prevents these stretch-triggered actions [2][3][4] and decreases the production of mitochondrial reactive oxygen species (ROS). 5,6 However, pharmacological inhibition is not always deprived of nonspecific unwanted effects. Spironolactone is a nonselective compound that also blocks receptors other than the MR. 7 Furthermore, both spironolactone and eplerenone have been described as having an inverse agonist activity on the MR. 8 Therefore, we examined whether conclusive evidence about MR activation after myocardial stretch could be obtained using biomolecular techniques to silence MR expression in rat hearts.…”