A systematic review of transgender male rodent model methodology

Robust preclinical models of transgender male (TGM) gender-affirming hormone therapy (GAHT) can inform clinicians of the isolated effects of GAHT; however existing models vary significantly in approach. We aimed to assess existing methodology and how it influences circulating sex-hormone levels in rodent models of TGM GAHT to provide recommendations of best practise. PubMed, Embase, and Scopus databases were systematically searched for studies that investigated GAHT in rodent models and were published from inception to the 1st of August 2024. Study characteristics and methodology were extracted and compared. Post-intervention circulating sex hormone concentrations were the primary outcome used to determine whether successful gender affirming hormone therapy had been achieved. Sixteen experimental rodent studies were included. Studies were performed on mice (n = 11) and rats (n = 5). Subcutaneous (SC) pellets and SC silastic implants were featured in some studies but weekly SC injections of testosterone enanthate was the preferred method. Sesame oil was the preferred solvent for injected testosterone formulations. Weekly doses of ~450 μg (mice) and ~420-900 μg (rats) consistently induced the testosterone levels of the male counterpart. Similarly, 10 mg of unesterified testosterone in a SC silastic implant in mice or 10 mg/100 g in rats were also successful methods. Most studies administered hormones for 6-8 weeks before performing post-treatment assessments. This review demonstrates that methods largely varied across studies and successfully identifies the effective methodological approaches that improve the reproducibility and accuracy of preclinical models. Representing an integral step forward to bridging gaps in preclinical transgender healthcare research.