Estrogen elicits ferroptosis-related myocardial oxidative stress and dysfunction in male rats.

Clinical evidence showed estrogen (E2)-mediated adverse cardiac effects in transgender women. This study aimed to determine if this paradoxical cardiac effect occurs in male rats and to elucidate the mechanisms for this unexplained detrimental cardiac effect of E2. Male Sprague-Dawley rats were divided into 2 groups: one group received E2, whereas the other received vehicle. Blood pressure and echocardiographic assessments were performed over 8 weeks following chronic E2 or vehicle administration. At the conclusion of the study, hearts were collected for ex vivo biochemical and molecular analyses. E2-treated male rats exhibited significant cardiac dysfunction, as evidenced by reduced heart rate, ejection fraction, and fractional shortening. Ex vivo molecular analyses of cardiac tissues from E2-treated rats, compared to vehicle-treated controls, revealed (1) a significant downregulation of the circadian clock protein Per2 and cardiac-specific miRNAs (1, 133a, 208a, and 499); (2) marked suppressions of key redox enzymes, including mitochondrial aldehyde dehydrogenase 2, catalase, along with nuclear factor erythroid 2-related factor 2 expression; and (3) increases in cardiac ferroptosis, pro-oxidant heme oxygenase-1 levels, and oxidative stress, indicating disrupted redox homeostasis and heightened oxidative damage. Our novel findings corroborated the clinical paradoxical adverse cardiac effects of chronic E2 in transgenders. The suppressions in interrelated cardioprotective factors, including Per2, miRNAs, and redox enzymes, along with the upregulation of ferroptosis, may contribute to the disrupted cardiac redox homeostasis and impaired cardiac function in E2-treated male rats. SIGNIFICANCE STATEMENT: The study findings reveal the paradoxical adverse effects of chronic estrogen treatment on cardiac redox status and function in male rats. Estrogen-treated male rats exhibited reduced cardiac function, decreased expression of the circadian clock protein Period 2, impaired redox balance, and elevated levels of ferroptosis mediators. These preclinical findings are highly relevant to the sex-specific adverse cardiac effects associated with gender-affirming estrogen therapy in transgender women, offering insights into their increased cardiovascular risk.