New advances in the protective mechanisms of acidic pH after ischemia: Participation of NO.

BACKGROUND: It has been previously demonstrated that the maintenance of ischemic acidic pH or the delay of intracellular pH recovery at the onset of reperfusion decreases ischemic-induced cardiomyocyte death. OBJECTIVE: To examine the role played by nitric oxide synthase (NOS)/NO-dependent pathways in the effects of acidic reperfusion in a regional ischemia model. METHODS: Isolated rat hearts perfused by Langendorff technique were submitted to 40 min of left coronary artery occlusion followed by 60 min of reperfusion (IC). A group of hearts received an acid solution (pH = 6.4) during the first 2 min of reperfusion (AR) in absence or in presence of l-NAME (NOS inhibitor). Infarct size (IS) and myocardial function were determined. In cardiac homogenates, the expression of P-Akt, P-endothelial and inducible isoforms of NOS (P-eNOS and iNOS) and the level of 3-nitrotyrosine were measured. In isolated cardiomyocytes, the intracellular NO production was assessed by confocal microscopy, under control and acidic conditions. Mitochondrial swelling after Ca2+ addition and mitochondrial membrane potential (Δψ) were also determined under control and acidosis. RESULTS: AR decreased IS, improved postischemic myocardial function recovery, increased P-Akt and P-eNOS, and decreased iNOS and 3-nitrotyrosine. NO production increased while mitochondrial swelling and Δψ decreased in acidic conditions. l-NAME prevented the beneficial effects of AR. CONCLUSIONS: Our data strongly supports that a brief acidic reperfusion protects the myocardium against the ischemia-reperfusion injury through eNOS/NO-dependent pathways.

Chronic GPER activation prevents ischemia/reperfusion injury in ovariectomized rats.

During menopause women are exposed to an increase in cardiovascular risk. G protein-coupled estrogen receptor (GPER) is known to mediate several of the protective effects of such hormones. G1 was described as a selective and synthetic agonist for GPER. The aim of the present research is to evaluate the effect of a chronic treatment with G1 in ovariectomized (OVX) rats exposed to ischemia/reperfusion (I/R). Considering the hypothesis that an impaired mitochondrial state could be involved in the alterations produced in OVX rats, other objective of this study was to investigate it in an isolated preparation. Three months old rats were assigned to undergo either bilateral ovariectomy or sham operation. The OVX rats were randomly treated during one month with either G1 or vehicle. Cardiac mitochondria from OVX rats showed a depolarized membrane potential and a decreased calcium retention capacity in comparison with Sham rats, which were prevented by chronic G1 treatment. I/R caused a higher decrease of left ventricular developed pressure and a higher increase of left ventricular end diastolic pressure in OVX compared to Sham hearts. These altered mechanical parameters were prevented by G1. The induced infarct size was significantly higher in OVX, which was reduced by G1 treatment. These results indicate that the mitochondrial state in OVX rats is impaired, accompanied by an altered mechanical response after ischemia and reperfusion injury, which was effectively prevented with chronic treatment with G1. The present study may provide further insights for the potential development of a therapy based on the GPER modulation.

Cyclosporine-A mimicked the ischemic pre- and postconditioning-mediated cardioprotection in hypertensive rats: Role of PKCε.

Our aim was to assess the action of cyclosporine-A (CsA) against reperfusion injury in spontaneously hypertensive rats (SHR) compared to the effects of ischemic pre- (IP) and postconditioning (IPC), examining the role played by PKCε. Isolated hearts were submitted to the following protocols: IC: 45 min global ischemia (GI) and 1h reperfusion (R); IP: a cycle of 5 min GI and 10 min of R prior to 45 min-GI; and IPC: three cycles of 30s-GI/30s-R at the start of R. Other hearts of the IC, IP and IPC groups received CsA (mitochondrial permeability transition pore inhibitor) or chelerythrine (Che, non-selective PKC inhibitor). Infarct size (IS) was assessed. TBARS and reduced glutathione (GSH) content - as parameters of oxidative damage, the expression of P-Akt, P-GSK-3ß, P-PKCε and cytochrome c (Cyc) release - as an index of mitochondrial permeability and the response of isolated mitochondria to Ca(2+) were also measured. IS similarly decreased in preconditioned, postconditioned and CsA treated heart showing the highest values in the combinations IP+CsA and IPC+CsA. TBARS decreased and GSH was partially preserved after all interventions. The content of P-Akt, P-GSK-3ß and P-PKCε increased in cytosol and decreased in mitochondria after IP and IPC. In CsA treated hearts these enzymes increased in both fractions reaching the highest values. Cyc release was attenuated and the response of mitochondria to Ca(2+) was improved by the interventions. The beneficial effects of IP and IPC were annulled when PKC was inhibited with Che. A PKCε/VDAC association was also detected. These data show that, in SHR, the CsA treatment mimicked and reinforced the cardioprotective action afforded by IP and IPC in which PKCε-mediated attenuation of mitochondrial permeability appears as the main mechanism involved.