The cardiovascular subtleties of testosterone on gender-affirming hormone therapy.

The growing number of people who identify themselves as transgender has gained increased attention in recent years and will certainly impact personalized clinical practices and healthcare worldwide. Transgender and gender-nonconforming individuals frequently undergo gender-affirming hormone therapy (GAHT), i.e., they use sex hormones to align their gender identity with their biological characteristics. Testosterone is the main compound used in GAHT by transmasculine people, leading to the development of male secondary sexual characteristics in these individuals. However, sex hormones, testosterone included, also influence hemodynamic homeostasis, blood pressure, and cardiovascular performance by direct effects in the heart and blood vessels, and by modulating several mechanisms that control cardiovascular function. In pathological conditions and when used in supraphysiological concentrations, testosterone is associated with harmful cardiovascular effects, requiring close attention in its clinical use. The present review summarizes current knowledge on the cardiovascular impact of testosterone in biological females, focusing on aspects of testosterone use by transmasculine people (clinical goals, pharmaceutical formulations, and impact on the cardiovascular system). Potential mechanisms whereby testosterone may increase cardiovascular risk in these individuals are discussed, and the influence of testosterone on the main mechanisms that control blood pressure and that potentially lead to hypertension development and target-organ damage are also reviewed. In addition, current experimental models, which are key to reveal testosterone mechanistic aspects and potential markers of cardiovascular injury, are reviewed. Finally, research limitations and the lack of data on cardiovascular health of transmasculine individuals are considered, and future directions for more appropriate clinical practices are highlighted.

Th17 cell-linked mechanisms mediate vascular dysfunction induced by testosterone in a mouse model of gender-affirming hormone therapy.

Clinical data point to adverse cardiovascular events elicited by testosterone replacement therapy. Testosterone is the main hormone used in gender-affirming hormone therapy (GAHT) by transmasculine people. However, the cardiovascular impact of testosterone in experimental models of GAHT remains unknown. Sex hormones modulate T-cell activation, and immune mechanisms contribute to cardiovascular risk. The present study evaluated whether testosterone negatively impacts female cardiovascular function by enhancing Th17 cell-linked effector mechanisms. Female (8 wk old) C57BL/6J mice received testosterone (48 mg/kg/wk) for 8 wk. Male mice were used for phenotypical comparisons. The hormone treatment in female mice increased circulating testosterone to levels observed in male mice. Testosterone increased lean body mass and body mass index, and decreased perigonadal fat mass, mimicking clinical findings. After 8 wk, testosterone decreased endothelium-dependent vasodilation and increased peripheral Th17 cells. After 24 wk, testosterone increased blood pressure in female mice. Ovariectomy did not intensify phenotypical or cardiovascular effects by testosterone. Female mice lacking T and B cells [Rag1 knockout (-/-)], as well as female mice lacking IL-17 receptor (IL-17Ra-/-), did not exhibit vascular dysfunction induced by testosterone. Testosterone impaired endothelium-dependent vasodilation in female mice lacking γδ T cells, similarly to the observed in wild-type female mice. Adoptive transfer of CD4+ T cells restored testosterone-induced vascular dysfunction in Rag1-/- female mice. Together, these data suggest that CD4+ T cells, most likely Th17 cells, are central to vascular dysfunction induced by testosterone in female mice, indicating that changes in immune-cell balance are important in the GAHT in transmasculine people.NEW & NOTEWORTHY Sex hormone-induced cardiovascular events are important undesirable effects in transgender people under GAHT. Studies addressing the cardiovascular impact of GAHT will certainly contribute to improve healthcare services offered to this population. Our study showing that vascular dysfunction, via Th17 cell-related mechanisms, precedes increased blood pressure induced by testosterone in a GAHT mouse model, reveals potential mechanisms involved in GAHT-related cardiovascular events and may provide new markers/targets for clinical practices in transmasculine people.