Pathways of Helium Postconditioning induced Cardioprotection
Short cycles of ventilation with anesthetic gases prior to or after prolonged cardiac ischemia, called anesthetic pre- or postconditioning, are known to reduce cardiac damage. The underlying mechanisms include the reperfusion injury salvage (RISK) pathway and involve recruitment of molecular signaling via caveolin (Cav) modulation. Postconditioning with helium (HePoc) mimics cardioprotective effects. In the present study using a rat model, we investigated whether (1) HePoc alters protein or mRNA expression of Cav-1 and -3 and (2) activation of RISK pathway and (3) autophagy associated proteins. Heliox ventilation (70% He, 30% O2) was applied after 25 min of ischemia and tissue from ischemic area at risk (AAR), non-ischemic not area at risk (NAAR), and serum was obtained. Cell fractions of Sham, I/R, I/R+He treated animals were separated and investigated for changes of Cav-1 and Cav-3 protein levels and mRNA expression. Phosphorylation levels were measured to determine RISK pathway activation (Erk1/2, PI3K, PKCε and Akt). Protein levels of autophagy proteins Bcl-1 and sequestosome-1 were also measured. HePoc lead to an increase of Cav-1 mRNA expression compared to I/R only and additionally elevated levels of Cav-1 (P<0.01) and Cav-3 (P<0.05) in the membrane fraction of ischemic myocardium (AAR). RISK pathway kinase Akt was activated more in AAR and NAAR tissue of the HePoc group (both P<0.05). Erk1/2 phosphorylation was higher in AAR (P<0.05) after HePoc. However in NAAR tissue of I/R and HePoc treated animals, pErk1/2 was lower compared to Sham (both P<0.001). PKCε and PI3K showed no significant changes in phosphorylation. Bcl-1 was significantly elevated in the mitochondrial fraction after HePoc in AAR (P<0.05) as well as NAAR (P<0.05), while sequestosome-1 levels showed no difference between groups. We propose that HePoc induces cardioprotection through a network of signalling. Respective mediators may include caveolins, the RISK pathway and autophagic processes.