A systematic review of transgender male rodent model methodology

Abstract

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.

Keywords

animal model / endocrinology / hormone therapy / methodology / transgender

References

[1] Flores A, Herman J, Gates G, Brown T. How many adults identify as transgender in the united states? 2016.

[2] Reisner SL, Poteat T, Keatley J, et al. Global health burden and needs of transgender populations: a review. Lancet. 2016;388(10042):412-436.

[3] Joseph A, Cliffe C, Hillyard M, Majeed A. Gender identity and the management of the transgender patient: a guide for non-specialists. J R Soc Med. 2017;110(4):144-152.

[4] Coleman E, Bockting W, Botzer M, et al. Standards of Care for the Health of transsexual, transgender, and gender-nonconforming people, version 7. Int J Transgenderism. 2012;13(4):165-232.

[5] Colizzi M, Costa R, Todarello O. Transsexual patients' psychiatric comorbidity and positive effect of cross-sex hormonal treatment on mental health: results from a longitudinal study. Psychoneuroendocrinology. 2014;39:65-73.

[6] Cundill P. Hormone therapy for trans and gender diverse patients in the general practice setting. Aust J Gen Pract. 2020;49:385-390.

[7] Government A. Pharmaceutical Benefits Scheme – Testosterone 2024. https://www.pbs.gov.au/pbs/search?term=testosterone.

[8] Government US. Drug Coverage (Part D). https://www.medicare.gov/drug-coverage-part-d

[9] Douglas Gordon John M, O'Nions E, Bailey J, Hobbs L, Gillespie F, Petersen I. Transgender identity in young people and adults recorded in UK primary care electronic patient records: retrospective, dynamic, cohort study. BMJ Med. 2023;2(1):e000499.

[10] Dela Cruz C, Kinnear HM, Hashim PH, et al. A mouse model mimicking gender-affirming treatment with pubertal suppression followed by testosterone in transmasculine youth. Hum Reprod. 2023;38(2):256-265.

[11] Godiwala P, Uliasz TF, Lowther KM, Kaback D, Mehlmann LM. Puberty suppression followed by testosterone therapy does not impair reproductive potential in female mice. Endocrinology. 2023;164(11):1-10.

[12] Goetz TG, Mamillapalli R, Devlin MJ, Robbins AE, Majidi-Zolbin M, Taylor HS. Cross-sex testosterone therapy in ovariectomized mice: addition of low-dose estrogen preserves bone architecture. Am J Physiol Endocrinol Metab. 2017;313(5):E540-E551.

[13] Goetz TG, Mamillapalli R, Sahin C, et al. Addition of estradiol to cross-sex testosterone therapy reduces atherosclerosis plaque formation in female ApoE−/− mice. Endocrinology. 2018;159(2):754-762.

[14] Hashim PH, Kinnear HM, Cruz CD, Padmanabhan V, Moravek MB, Shikanov A. Pharmacokinetic comparison of three delivery systems for subcutaneous testosterone administration in female mice. Gen Comp Endocrinol. 2022;327:114090.

[15] Kinnear HM, Constance ES, David A, et al. A mouse model to investigate the impact of testosterone therapy on reproduction in transgender men. Hum Reprod. 2019;34(10):2009-2017.

[16] Kinnear HM, Hashim PH, Dela Cruz C, et al. Reversibility of testosterone-induced acyclicity after testosterone cessation in a transgender mouse model. F S Sci. 2021;2(2):116-123.

[17] Kinnear HM, Hashim PH, Dela Cruz C, et al. Presence of ovarian stromal aberrations after cessation of testosterone therapy in a transgender mouse model†. Biol Reprod. 2023;108(5):802-813.

[18] Santos JD, Oliveira-Neto JT, Barros PR, et al. Th17 cell-linked mechanisms mediate vascular dysfunction induced by testosterone in a mouse model of gender-affirming hormone therapy. Am J Phys Heart Circ Phys. 2022;323(2):H322-H335.

[19] Schwartz A, Xu M, Henderson N, et al. Impaired IVF outcomes following testosterone treatment improve with washout in a mouse model of gender-affirming hormone treatment. Am J Obstet Gynecol. 2023;229:419.e1-419.e10.

[20] Bartels CB, Uliasz TF, Lestz L, Mehlmann LM. Short-term testosterone use in female mice does not impair fertilizability of eggs: implications for the fertility care of transgender males. Hum Reprod. 2021;36(1):189-198.

[21] Craft RM, Sewell CM, Taylor TM, Vo MS, Delevich K, Morgan MM. Impact of continuous testosterone exposure on reproductive physiology, activity, and pain-related behavior in young adult female rats. Horm Behav. 2024;158:105469.

[22] Tassinari R, Tammaro A, Lori G, et al. 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. Cells. 2023;12(3):474.

[23] Zhang Q, Wei H, Lee A, Felmlee MA. Sex and cross-sex testosterone treatment alters gamma-Hydroxybutyrate acid Toxicokinetics and Toxicodynamics in rats. Pharmaceutics. 2024;16(1):143.

[24] Lichtenecker DCK, Argeri R, Castro CHM, Dias-da-Silva MR, Gomes GN. Cross-sex testosterone therapy modifies the renal morphology and function in female rats and might underlie increased systolic pressure. Clin Exp Pharmacol Physiol. 2021;48(7):978-986.

[25] Perez-Laso C, Cerdan S, Junque C, et al. Effects of adult female rat Androgenization on brain morphology and Metabolomic profile. Cereb Cortex. 2017;28(8):2846-2853.

[26] Kelleher S, Howe C, Conway AJ, Handelsman DJ. Testosterone release rate and duration of action of testosterone pellet implants. Clin Endocrinol. 2004;60(4):420-428.

[27] Pirtea P, Ayoubi JM, Desmedt S, T'Sjoen G. Ovarian, breast, and metabolic changes induced by androgen treatment in transgender men. Fertil Steril. 2021;116(4):936-942.

[28] Ikeda K, Baba T, Noguchi H, et al. Excessive androgen exposure in female-to-male transsexual persons of reproductive age induces hyperplasia of the ovarian cortex and stroma but not polycystic ovary morphology. Hum Reprod. 2013;28(2):453-461.

[29] Ghofranian A, Estevez SL, Gellman C, et al. Fertility treatment outcomes in transgender men with a history of testosterone therapy. F&S Reports. 2023;4(4):367-374.

[30] Fighera TM, Ziegelmann PK, Rasia da Silva T, Spritzer PM. Bone mass effects of cross-sex hormone therapy in transgender people: updated systematic review and meta-analysis. J Endocr Soc. 2019;3(5):943-964.

[31] Fukao T, Ohi K, Shioiri T. Gray matter volume differences between transgender men and cisgender women: a voxel-based morphometry study. Aust N Z J Psychiatry. 2022;56(5):535-541.

[32] Maheshwari A, Dines V, Saul D, Nippoldt T, Kattah A, Davidge-Pitts C. The effect of gender-affirming hormone therapy on serum creatinine in transgender individuals. Endocr Pract. 2022;28(1):52-57.

[33] Gulanski BI, Flannery CA, Peter PR, Leone CA, Stachenfeld NS. Compromised endothelial function in transgender men taking testosterone. Clin Endocrinol. 2020;92(2):138-144.

[34] van Zijverden LM, Wiepjes CM, van Diemen JJK, Thijs A, den Heijer M. Cardiovascular disease in transgender people: a systematic review and meta-analysis. Eur J Endocrinol. 2024;190(2):S13-S24.

[35] Ford K, Huggins E, Sheean P. Characterising body composition and bone health in transgender individuals receiving gender-affirming hormone therapy. J Hum Nutr Diet. 2022;35(6):1105-1114.

[36] McFarland J, Craig W, Clarke NJ, Spratt DI. Serum testosterone concentrations remain stable between injections in patients receiving subcutaneous testosterone. J Endocr Soc. 2017;1(8):1095-1103.

[37] Unger CA. Hormone therapy for transgender patients. Transl Androl Urol. 2016;5(6):877-884.

[38] Byrne MM, Nieschlag E. Androgens: pharmacological use and abuse. Reference Module in Neuroscience and Biobehavioral. Elsevier; 2017.

[39] Callies F, Kollenkirchen U, von zur Mühlen C, Tomaszewski M, Beer S, Allolio B. Testosterone undecanoate: a useful tool for testosterone administration in rats. Exp Clin Endocrinol Diabetes. 2003;111(4):203-208.

[40] Kobayashi H, Shirasawa N, Naito A. Estrogen synthesis in the stomach of Sprague-Dawley rats: comparison to Wistar rats. Exp Anim. 2021;70(1):63-72.

[41] Madsen LW, Knauf JA, Gotfredsen C, et al. GLP-1 receptor agonists and the thyroid: C-cell effects in mice are mediated via the GLP-1 receptor and not associated with RET activation. Endocrinology. 2012;153(3):1538-1547.

[42] Pasternak B, Wintzell V, Hviid A, et al. Glucagon-like peptide 1 receptor agonist use and risk of thyroid cancer: Scandinavian cohort study. BMJ. 2024;385:e078225.

[43] Nagendra L, Bg H, Sharma M, Dutta D. Semaglutide and cancer: a systematic review and meta-analysis. Diabetes Metab Syndr. 2023;17(9):102834.

RIGHTS & PERMISSIONS

2025 The Author(s). Animal Models and Experimental Medicine published by John Wiley & Sons Australia, Ltd on behalf of The Chinese Association for Laboratory Animal Sciences.