Benzyl alcohol-benzyl benzoate clearing reveals the dose-dependent effect of cyclophosphamide on follicle damage in mice

Abstract

Objective: Cyclophosphamide (CTX), which is commonly used in clinical chemotherapy, has a damaging effect on ovarian follicles. This study aimed to establish a new method to count the number of follicles in mouse ovaries using benzyl alcohol–benzyl benzoate (BABB)-based tissue-clearing technology and evaluate the follicle-damaging effects of different doses of CTX. Methods: C57BL/6 mice were divided into four groups and administered intraperitoneal injections of 0, 40, 80, or 120 mg/kg CTX. The serum levels of estradiol (E2) and follicle-stimulating hormone (FSH) were detected using an ELISA kit. Mouse ovaries were subjected to BABB clearing and labeled with DAPI, β-actin, and DDX4 to observe the ovarian structure and follicles. A three-dimensional software, Imaris, was used to reconstruct the ovarian structure and automatically count the number of follicles. The effects of different CTX doses on the total follicle number and estrous cycle were determined. Results: As the CTX dose increased, E2 levels in CTX mice declined from 212.3 to 57.7 pg/mL; the FSH levels increased from 3.2 to 29 ng/mL. Mouse ovaries became transparent after BABB treatment. After fixation, microscopy, and Imaris processing, immunofluorescence signals of β-actin and DAPI from all levels in intact ovaries could be obtained and follicle number in half ovaries could be automatically counted using anti-DDX4 antibody labeling. In the NC, CTX40, CTX80, and CTX120 groups, the proportion of mice in the diestrus phase was 26.67%, 51.67%, 73.33%, and 95.00%, respectively, and the total follicle number was 2,603, 1,761, 1,043, and 262, respectively. E2 levels were positively correlated with follicle number and FSH levels were negatively correlated with follicle number, indicating that the damaging effect of CTX on follicle number may be dose dependent. Conclusion: BABB can be used to clear intact ovaries from adult mice, and follicle number in half ovaries can be automatically counted. The damaging effect of CTX on follicles and the endocrine system is dose dependent.

Keywords

• benzyl alcohol–benzyl benzoate; cyclophosphamide; follicle damage; tissue-clearing technology