Hypoxic preconditioning protects rat hearts against ischemia-reperfusion injury via the arachidonate12-lipoxygenase/ transient receptor potential vanilloid 1 pathway

Hypoxic preconditioning (HPC) protects rat hearts against ischemia-reperfusion (IR) injury. However, the role of transient receptor potential vanilloid 1 (TRPV1) in HPC-mediated cardioprotection remains unknown. TRPV1 is activated by endovanilloid 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], which is synthesized by arachidonate 12-lipoxygenase (ALOX12). Therefore, we examined whether HPC protects the myocardium against IR via the ALOX12/TRPV1 pathway. Compared to hearts of rats kept in room air, the hearts of rats kept in air with 10 % oxygen for 4 weeks had better post-ischemic recovery and less tissue damage when subjected to 30-min global ischemia and 4-h reflow in a Langendorff apparatus. Capsazepine, a specific TRPV1 blocker, administered 5 min before reperfusion markedly attenuated the effects of HPC, confirming that TRPV1 is a downstream effector in HPC-mediated cardioprotection. HPC resulted in the upregulation of ALOX12 and myocardial 12(S)-HETE, and prevented IR-induced 12(S)-HETE reduction. In addition, sarcolemmal ALOX12 expression in HPC hearts mainly co-localized with TRPV1 expression. Blockade of ALOX12 by cinnamyl-3,4-dihydroxy-a-cyanocinnamate or baicalein abrogated the effects of HPC, baicalein also decreased 12(S)-HETE expression. Mimicking HPC by given 12(S)-HETE or capsaicin to baicalien-treated hearts enhanced cardiac recovery during reperfusion. The cardiac protein kinase C (PKC) isoforms a, d, e, and f were preferentially expressed in the sarcolemmal membrane of HPC-treated hearts, indicating their high intrinsic activation state. Capsazepine or co-treatment with baicalein attenuated translocation of PKCa, PKCd and PKCe, but not that of PKCf. We conclude that HPC reduces heart susceptibly to IR via ALOX12/TRPV1/PKC pathway, as shown by increased 12(S)-HETE expression in HPC hearts.