Body, metabolic and renal changes following cross-sex estrogen/progestogen therapy in a rodent model simulating its use by transwomen

A Review of Animal Models Investigating the Reproductive Effects of Gender-Affirming Hormone Therapy

Gender-affirming hormone therapy (GAHT) is an important component in the process of transitioning for many transgender and gender-diverse (TGD) individuals. Multiple medical organizations recommend fertility preservation counseling prior to initiation of GAHT; however, there remains little high-quality data regarding the impact of GAHT on fertility and reproductive function. A PubMed literature review was performed using Boolean search operators linking keywords or phrases such as "mouse", "rat", "primate", "animal model", "transgender", "gender", "estrogen", "testosterone", "fertility", and "fertility preservation". Recent research has produced a number of animal models of GAHT that utilize similar hormonal regimens and produce similar phenotypic results to those used and observed in human patients. Specific to testosterone(T)-containing GAHT, animals demonstrate loss of menstrual cyclicity with therapy, resumption of menses on cessation of therapy, suppression of gonadotropin levels, and physical changes such as clitoromegaly. Models mimicking GAHT for transmasculine individuals in the peripubertal period demonstrate that pretreatment with GnRHa therapy does not modify the effects of subsequent T administration, which were similar to those described in adult models. Both models suggest promising potential for future fertility with cessation of T. With estradiol (E)-containing GAHT, animals exhibit decreased size of testicles, epididymis, and seminal vesicles, as well as ongoing production of spermatocytes, and seminiferous tubule vacuolization. Given the ethical challenges of conducting human studies in this area, high-fidelity animal models represent a promising opportunity for investigation and could eventually transform clinical counseling about the necessity of fertility preservation. Future studies should better delineate the interactions (if any exist) between treatment attributes such as dosing and duration with the extent of reversibility of reproductive perturbations. The development of models of peripubertal feminizing GAHT is an additional area for future work.

The Utility of Preclinical Models in Understanding the Bone Health of Transgender Individuals Undergoing Gender-Affirming Hormone Therapy

PURPOSE OF REVIEW

To summarise the evidence regarding the effects of gender-affirming hormone therapy (GAHT) on bone health in transgender people, to identify key knowledge gaps and how these gaps can be addressed using preclinical rodent models.

RECENT FINDINGS

Sex hormones play a critical role in bone physiology, yet there is a paucity of research regarding the effects of GAHT on bone microstructure and fracture risk in transgender individuals. The controlled clinical studies required to yield fracture data are unethical to conduct making clinically translatable preclinical research of the utmost importance. Novel genetic and surgical preclinical models have yielded significant mechanistic insight into the roles of sex steroids on skeletal integrity. Preclinical models of GAHT have the potential inform clinical approaches to preserve skeletal integrity and prevent fractures in transgender people undergoing GAHT. This review highlights the key considerations required to ensure the information gained from preclinical models of GAHT are informative.

Testosterone Restores Body Composition, Bone Mass, and Bone Strength Following Early Puberty Suppression in a Mouse Model Mimicking the Clinical Strategy in Trans Boys

Transgender youth increasingly present at pediatric gender services. Some of them receive long-term puberty suppression with gonadotropin-releasing hormone analogues (GnRHa) before starting gender-affirming hormones (GAH). The impact of GnRHa use started in early puberty on bone composition and bone mass accrual is unexplored. It is furthermore unclear whether subsequent GAH fully restore GnRHa effects and whether the timing of GAH introduction matters. To answer these questions, we developed a mouse model mimicking the clinical strategy applied in trans boys. Prepubertal 4-week-old female mice were treated with GnRHa alone or with GnRHa supplemented with testosterone (T) from 6 weeks (early puberty) or 8 weeks (late puberty) onward. Outcomes were analyzed at 16 weeks and compared with untreated mice of both sexes. GnRHa markedly increased total body fat mass, decreased lean body mass, and had a modest negative impact on grip strength. Both early and late T administration shaped body composition to adult male levels, whereas grip strength was restored to female values. GnRHa-treated animals showed lower trabecular bone volume and reduced cortical bone mass and strength. These changes were reversed by T to female levels (cortical bone mass and strength) irrespective of the time of administration or even fully up to adult male control values (trabecular parameters) in case of earlier T start. The lower bone mass in GnRHa-treated mice was associated with increased bone marrow adiposity, also reversed by T. In conclusion, prolonged GnRHa use started in prepubertal female mice modifies body composition toward more fat and less lean mass and impairs bone mass acquisition and strength. Subsequent T administration counteracts GnRHa impact on these parameters, shaping body composition and trabecular parameters to male values while restoring cortical bone architecture and strength up to female but not male control levels. These findings could help guide clinical strategies in transgender care. © 2023 American Society for Bone and Mineral Research (ASBMR).

A Mouse Model to Investigate the Impact of Gender Affirming Hormone Therapy with Estradiol on Reproduction

Gender-affirming hormone therapy (GAHT) can help transgender and/or gender diverse (TGD) individuals achieve emobidment goals that align with their transition needs. Clinical evidence from estradiol (E)-GAHT patients indicate widespread changes in tissues sensitive to E and testosterone (T), particularly in the reproductive system. Notably, E-GAHTs effects on hormones and reproduction vary greatly between patients. With the goal of informing clinical research and practice for TGD individuals taking E, this study examines intact male mice implanted with capsules containing one of three different E doses (low 1.25 mg; mid 2.5 mg; high 5 mg), or a blank control capsule. All E-GAHT doses suppress T and follicle stimulating hormone levels while elevating E levels. Only the high E-GAHT dose significantly supresses luteinizing hormone levels. All E-GAHT doses affect epididymis tubule size similarly while seminiferous tubule morphology and bladder weight changes are dose-dependent. E-GAHT does not alter the presence of mature sperm, though E-exposed sperm have altered motility. These data represent the first evidence that mouse models offer an effective tool to understand E-GAHTs impact on reproductive health and the dose-dependent effects of this model permit examinations of diverse patient outcomes.

Risk Assessment of Transgender People: Development of Rodent Models Mimicking Gender-Affirming Hormone Therapies and Identification of Sex-Dimorphic Liver Genes as Novel Biomarkers of Sex Transition

Transgender (TG) describes individuals whose gender identity differs from the social norms. TG people undergoing gender-affirming hormone therapy (HT) may be considered a sub-group of the population susceptible to environmental contaminants for their targets and modes of action. The aim of this study is to set appropriate HT doses and identify specific biomarkers to implement TG animal models. Four adult rats/group/sex were subcutaneously exposed to three doses of HT (plus control) selected starting from available data. The demasculinizing-feminizing models (dMF) were β-estradiol plus cyproterone acetate, at 0.09 + 0.33, 0.09 + 0.93 and 0.18 + 0.33 mg, respectively, five times/week. The defeminizing-masculinizing models (dFM) were testosterone (T) at 0.45, 0.95 and 2.05 mg, two times/week. Clitoral gain and sperm count, histopathological analysis of reproductive organs and liver, hormone serum levels and gene expression of sex-dimorphic CYP450 were evaluated. In the dMF model, the selected doses-leading to T serum levels at the range of the corresponding cisgender-induced strong general toxicity and cannot be used in long-term studies. In the dFM model, 0.45 mg of T represents the correct dose. In addition, the endpoints selected are considered suitable and reliable to implement the animal model. The sex-specific CYP expression is a suitable biomarker to set proper (de)masculinizing/(de)feminizing HT and to implement TG animal models.