Circulating Markers of Cardiovascular Health in Hypogonadism Before and After Testosterone Therapy: Molecular Aspects and Formulation Comparison

Hypogonadism is increasingly recognized as an independent cardiovascular risk factor, with testosterone deficiency associated with endothelial dysfunction, increased thrombotic risk, and adverse cardiovascular outcomes. Circulating biomarkers provide valuable insights into the vascular health status of hypogonadal men and the cardiovascular effects of testosterone replacement therapy (TRT). This comprehensive review examines the molecular basis of testosterone action on the cardiovascular system and synthesizes evidence on circulating cardiovascular biomarkers in hypogonadism, including endothelial progenitor cells (EPCs), endothelial microparticles (EMPs), platelet markers, endothelial activators, adhesion molecules, and inflammatory/oxidative stress markers. We also compare the cardiovascular safety profiles of transdermal versus intramuscular testosterone formulations. Hypogonadal men exhibit reduced circulating EPCs, elevated EMPs, increased platelet reactivity, higher levels of endothelial activators (ICAM-1, VCAM-1, E-selectin, von Willebrand factor, endothelin-1, ADMA), and increased inflammatory markers (hsCRP, IL-6, TNF-α). TRT improves most of these biomarkers through androgen receptor (AR)-dependent and AR-independent mechanisms involving PI3K/Akt/eNOS signaling, VEGF upregulation, CXCL12/CXCR4 axis modulation, and NF-κB pathway suppression. Current evidence suggests that transdermal testosterone formulations may offer advantages regarding hematological safety and more stable testosterone exposure; however, definitive evidence demonstrating superior cardiovascular outcomes compared with intramuscular formulations remains limited. Circulating cardiovascular biomarkers are significantly altered in hypogonadism and improve with TRT. Available data suggest that transdermal testosterone formulations may offer a more favorable cardiovascular safety profile than intramuscular preparations, particularly with respect to erythrocytosis and pharmacokinetic stability, although head-to-head randomized trials with hard cardiovascular endpoints are still needed. Understanding the molecular mechanisms underlying these changes is essential for optimizing TRT in hypogonadal men with cardiovascular risk factors. The cardiovascular safety advantage of transdermal formulations is currently supported primarily by pharmacokinetic and hematological evidence; direct comparative evidence from randomized trials with hard cardiovascular endpoints remains unavailable.