Sphingosine-1-phosphate and its mimetic FTY720 do not protect against radiation-induced ovarian fibrosis in the nonhuman primate^†

Oocytes are highly radiosensitive, so agents that prevent radiation-induced ovarian follicle destruction are important fertility preservation strategies. A previous study in rhesus macaques demonstrated that ovarian treatment with antiapoptotic agents, sphingosine-1-phosphate (S1P) and FTY720, its long-acting mimetic, preserved follicles following a single dose of 15 Gy X-ray radiation, and live offspring were obtained from FTY720-treated animals. However, it is unknown whether these antiapoptotic agents also protected the ovarian stroma from late effects of radiation, including vascular damage and fibrosis. Using ovarian histological sections from this study, we evaluated the vasculature and extracellular matrix in the following cohorts: Vehicle + sham irradiation, vehicle + irradiation (OXI), S1P + irradiation (S1P), and FTY720 + irradiation (FTY720). One ovary from each animal was harvested prior to radiation whereas the contralateral ovary was harvested 10 months post-treatment. We assessed vasculature by immunohistochemistry with a PECAM1 antibody, hyaluronan by a hyaluronan binding protein assay, and collagen by picrosirius red and Masson's trichrome staining. Disorganized vessels were observed in the medulla in the OXI and S1P cohorts relative to the sham, but the vasculature in the FTY720 cohort appeared intact, which may partially explain fertoprotection. There were no differences in the hyaluronan matrix among the cohorts, but there was thickening of the tunica albuginea and fibrosis in the OXI cohort relative to the sham, which was not mitigated by either S1P or FTY720 treatment. Thus, the fertoprotective properties of S1P and FTY720 may be limited given their inability to protect the ovarian stroma against the late effects of radiation-induced fibrosis.