Acylated Ghrelin Protects Rat Hearts from Doxorubicin-Induced Apoptosis via PKA and Akt Signaling

Doxorubicin (DOX) is a highly effective chemotherapy agent, but its use is limited by severe cardiotoxicity, often leading to heart failure. The primary mechanism of this damage involves the induction of apoptosis (programmed cell death) in cardiomyocytes, partly through the Fas/FasL pathway, and disruption of intracellular calcium (Ca+2) balance. Current cardioprotective strategies are insufficient, creating a need for novel therapies. Acylated ghrelin (AG), an orexigenic peptide, is being investigated for its potential protective effects on the heart, specifically its ability to modulate cell death pathways and restore calcium homeostasis, potentially by stimulating the SERCA2a pump which is crucial for Ca+2 reuptake into the sarcoplasmic reticulum.

Adult male Wistar rats were divided into four groups (20 rats each): control, control + AG, DOX, and DOX + AG. Acylated ghrelin was co-administered to all rats consecutively for 35 days. An in vitro component used isolated cardiomyocytes treated with AG in the presence or absence of DOX, with or without pre-incubation with a ghrelin receptor antagonist ([D-Lys3]-GHRP-6), an Akt inhibitor (VIII), or a PKA inhibitor (KT-5720). Key endpoints included left ventricular systolic pressure (LVSP), dp/dtmax, dp/dtmin, cardiac ultrastructure, and intracellular levels of ROS and Ca2+.

Acylated ghrelin (AG) demonstrated significant cardioprotective effects. In both control and DOX-treated rats, AG increased key cardiac function metrics including LVSP, dp/dtmax, and dp/dtmin. For animals exposed to doxorubicin, AG lowered left ventricular end-diastolic pressure (LVEDP) and improved cardiac ultrastructure. AG also significantly reduced intracellular reactive oxygen species (ROS) and Ca2+ levels and decreased calcineurin activity in the left ventricles of DOX-treated rats. This led to an inhibition of NFAT-4 nuclear translocation and a downregulation of the apoptotic proteins Fas and FasL.

Mechanistically, AG upregulated SERCA2a levels and increased the activity of protein kinase A (PKA) and Akt, which enhanced the phosphorylation of phospholamban at sites Ser16 and Thr17. These protective effects were independent of food intake or the GH/IGF-1 axis and were completely abolished by the co-administration of ghrelin receptor, PKA, or Akt inhibitors, confirming the pathway's critical role.