Identification of a Novel Antagonist of BRS-3 from Natural Products and Its Protective Effects Against H(2)O(2)-Induced Cardiomyocyte Injury.

The identification of exogenous ligands from natural products is an alternative strategy to explore the unrevealed physiological functions of orphan G-protein-coupled receptors (GPCRs). In this study, we have successfully identified and pharmacologically characterized licoisoflavone A (LIA) as a novel selective antagonist of BRS-3, an orphan GPCR. Functional studies showed that pretreatment with LIA ameliorated hydrogen peroxide (H(2)O(2))-induced cardiomyocyte injury. Furthermore, LIA pretreatment significantly restored the activities of malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT), as well as lactate dehydrogenase (LDH) levels, in H9c2 cells following H(2)O(2) exposure. The protective effect of LIA was also evident in primary cardiomyocytes from rats and mice against H(2)O(2)-induced cell injury but was absent in primary cardiomyocytes derived from bombesin receptor subtype-3 knockout (Brs3(-/y)) mice, strongly confirming the mechanism of LIA's action through BRS-3 antagonism. Proteomics studies further revealed that LIA exerted its protective effects via activating the integrin/ILK/AKT and ERK/MAPK signaling pathways. Complementary findings from Bantag-1, a well-recognized antagonist of BRS-3, in human embryonic kidney 293 mBRS-3 (HEK293-mBRS-3) stable cells and B16 cell lines, which demonstrated resistance to H(2)O(2)-induced damage, further supported the pivotal role of BRS-3 in oxidative stress-induced cell injury. Our study contributes to expanding our understanding of the potential pharmacological functions of BRS-3, unveiling previously unknown pharmacological functionality of this orphan receptor.