# Cardioprotective response of remote ischemic preconditioning: Revealing possible role of cannabinoid type 2 receptor and AMPK-mediated autophagy in rats

## TL;DR

This study shows that remote ischemic preconditioning protects the heart by activating the cannabinoid type 2 receptor and AMPK-mediated autophagy in rats.

## Contribution

The study identifies CB2R and AMPK-mediated autophagy as key mechanisms underlying the cardioprotective effects of RIPC.

## Key findings

- RIPC significantly reduced infarct size and cardiac marker levels in rats with myocardial injury.
- Blocking CB2R or AMPK-mediated autophagy eliminated the cardioprotective effects of RIPC.
- RIPC improved hemodynamic and biochemical parameters associated with heart injury and stress.

## Abstract

Remote ischemic preconditioning (RIPC) is a non-invasive, practically acceptable and applicable conditioning technique reported to confer cardioprotection in myocardial ischemia-reperfusion injury (MIRI). It is documented that cannabinoid B2 receptor (CB2R) plays crucial role in providing cardioprotection in various cardiovascular pathologies.

MIRI was induced in the isolated hearts of Wistar rats by exposing them to global ischemia of 30 minutes followed by subsequent reperfusion with Kreb’s Henseleit (KH) buffer solution of 120 minutes after mounting on the Langendorff Power Lab apparatus. RIPC was applied by providing four alternate inter-spread cycles of 5 min non-lethal ischemia and 5 min reperfusion by tying the pressure cuff at the hind limb of the rats before isolation of hearts.

Ischemia-reperfusion injury (IRI) induced myocardial damage was manifested in terms of significant increase in infarct size, elevated levels of cardiac specific markers i.e. Lactate dehydrogenase-1 (LDH-1), Creatine kinase-MB (CK-MB), Cardiac troponin-I (C-tPn-I), altered hemodynamic parameters i.e. decreased heart rate (HR), coronary flow rate (CFR), left ventricular developed pressure (LVDP), rate pressure product (RPP),+dp/dtmax, and -dp/dtmin and other biochemical markers including increased thiobarbituric acid reactive species (TBARS), decreased glutathione reductase (GSH), and catalase; markers of oxidative stress, increased tumor necrosis factor-α (TNF-α); inflammatory marker, transforming growth factor-β (TGF-β); fibrosis marker, Bax, and caspase-3; markers of apoptosis. RIPC significantly reduced the infarct size, LDH-1, and CK-MB release and C-tPn-I content. Moreover, RIPC significantly improved series of aforementioned hemodynamic as well as biochemical parameters. Pre-administration of AM-630 (selective CB2R antagonist; 0.5 and 1 mg/kg;i.p.) and BML-275 i.e. AMP activated protein kinase (AMPK) mediated autophagy inhibitor; 1.5 and 3 mg/kg;i.p.) substantially abrogated the cardioprotective response of RIPC.

The current findings highlight the pivotal role of CB2R activation and AMPK activated autophagy in cardioprotective mechanism of RIPC against MIRI.