Comparison of large single and small multiple doses of cyclophosphamide exposure in mice during early prepubertal age on fertility outcome

Cyclophosphamide (CY) exposure is known to affect the ovary and impair fertility. Clinically, treatment is generally given over multiple doses, but research models have generally used single doses. The relative effects of administering multiple small doses of CY in the prepubertal period are not elucidated. Two-week-old early-prepubertal Swiss albino female mice were administered with either large single (200 mg/Kg x 1; CY200X1) or small multiple (75 mg/Kg x 4; CY75X4) CY doses, thus a 50% higher total dose. Surviving females were assessed for estrous cyclicity, ovarian follicle reserve, oocyte functional competence, and postnatal assessment of first-generation (F1) pups. Exposure to CY75X4 reduced the loss of ovarian follicles (p < 0.05), and body weight (p < 0.001), and resulted in a larger population of cycling females (p < 0.01) with higher oocyte yield (p < 0.05) compared to CY200X1. Although CY200X1 exposed cycling females had comparable oocyte quality, and fertility index, the postnatal mortality was higher in F1 pups (p < 0.05) in comparison to the CY75X4 group. Although both strategies affect oocyte quality and functional competence similarly, CY75X4, despite the higher overall dose, results in reduced follicle loss, produces higher oocyte/blastocyst yield, and exhibits lower postnatal mortality rates, suggesting a potential advantage over CY200X1 for later fertility and offspring health. The differences in effects of the two treatment models show the need for designing animal model studies that more closely mimic the clinical administration of gonadotoxic therapies such as cyclophosphamide.