The role of aryl hydrocarbon receptor-regulated cytochrome P450 enzymes and their arachidonic acid metabolites in the pathogenesis of cardiac hypertrophy

Abstract

Introduction: Cardiac hypertrophy is an adaptive response to chronic hemodynamic and neurohormonal stress that initially preserves cardiac output but can progress to maladaptive remodeling and heart failure. Pressure overload and angiotensin II (Ang II) signaling drive pathological hypertrophy by promoting cardiomyocyte growth, fetal gene reactivation, inflammation and fibrosis. Current therapies mainly target systemic hemodynamics and neurohormonal activation but do not directly address metabolic mechanisms regulating cardiomyocyte growth. Arachidonic acid (AA) metabolism through cytochrome P450 (CYP) enzymes has emerged as an important regulator of cardiac remodeling. CYP1A1 preferentially produces 19-hydroxyeicosatetraenoic acid (19-HETE), whereas CYP1B1 and lipoxygenase pathways generate midchain HETEs, including 5-, 12-, and 15-HETEs, which promote pro-hypertrophic and pro-inflammatory signaling. Because these metabolites exist as stereoisomers, enantioselective analysis is important for understanding their biological functions. The aryl hydrocarbon receptor (AhR) regulates CYP1 family enzymes and links endogenous and environmental ligands to AA metabolism. This thesis tested the hypothesis that selective modulation of AhR-CYP1A1 signaling shifts AA metabolism toward cardioprotection by increasing 19(S)-HETE while suppressing pro-hypertrophic midchain-HETEs. Methods: Complementary in vitro and in vivo models of cardiac hypertrophy were used. In adult human ventricular cardiomyocytes (AC16), Ang II induced hypertrophic remodeling. The effects of the endogenous AhR ligand 6-formylindolo[3,2-b]carbazole (FICZ), cannabistilbene I and cannflavin-C were evaluated. Hypertrophic responses were assessed by hypertrophic gene expression and cardiomyocyte surface area. AhR, CYP1A1 and CYP1B1 expression, protein levels and catalytic activity were measured to determine involvement of AhR-regulated CYP pathways. Enantioselective AA metabolism was analyzed using chiral LC-MS/MS. In vivo, a rat abdominal aortic constriction (AAC) model was used to examine the chronic effects of FICZ on cardiac structure, hypertrophic markers, CYP expression, AA metabolite profiles and GPR31 expression. Results: In AC16 cardiomyocytes, Ang II induced hypertrophy and altered enantioselective AA metabolism by increasing midchain-HETEs and reducing 19(S)-HETE. FICZ attenuated hypertrophy by stabilizing AhR protein, reducing proteasomal degradation and selectively inducing CYP1A1 expression and activity. This increased 19(S)-HETE, suppressed hypertrophic gene expression and reduced cardiomyocyte surface area, identifying an AhR-CYP1A1-19(S)-HETE axis that limits hypertrophic growth. In the AAC model, chronic FICZ administration reduced left ventricular hypertrophy, wall thickness and heart weight-to-tibial length ratios. These protective effects were accompanied by selective CYP1A1 induction, increased 19(S)-HETE formation and suppression of CYP1B1, 12-lipoxygenase and pro-hypertrophic midchain-HETEs. AAC-induced GPR31 upregulation was also attenuated by FICZ. Moreover, cannabistilbene I reduced Ang II-induced hypertrophy by inducing CYP1A1 activity, increasing 19(S)-HETE and reducing midchain-HETEs, whereas cannflavin-C exerted anti-hypertrophic effects mainly through selective inhibition of CYP1B1 and subsequent suppression of midchain-HETE formation. Conclusion: This thesis establishes enantioselective AA metabolism as an important determinant of cardiac hypertrophy and identifies 19(S)-HETE as an endogenously generated cardioprotective mediator. AhR-mediated CYP1A1 induction together with CYP1B1 suppression shifts AA metabolism away from pro-hypertrophic midchain-HETEs toward protective 19(S)-HETE. These findings identify the AhR-CYP-AA metabolic axis as a promising therapeutic target for pathological cardiac hypertrophy.