P-408 The ovarian tissues outside of the radiation field could be damaged by radiation-induced abscopal effects in mice: an experimental study.
Authors: Du Y 
Published: June 2023

Abstract

Study question
Could irradiation-induced abscopal effects (RIAEs) induce structural and functional damage in the distal ovary in female mice, and what is its mechanism?

Summary answer
The RIAEs can induce an inflammatory reaction and inhibit the growth and development of ovarian follicles in mice leading to a decrease in ovarian reserve.

What is known already
The irradiated tumor could induce cell and tissue injury in the organs distant from the radiation site, referred to as the radiation-induced abscopal effects (RIAEs). Many pieces of research have shown out-of-field tumor regression effects of radiation therapy. However, RIAEs is a double-edged sword and may cause serious side effects on normal tissues. Premature ovarian insufficiency (POI) is one of the main side effects of radiotherapy, but the relationship between RIAE and POI has not been clarified.

Study design, size, duration
C57BL/6J mice were used to establish a RIAEs model by irradiating the thorax and the abdomens were shielded. Sixteen C57BL/6J female mice were randomly allocated to sham and experimental groups (n = 8/group) according to the presence or absence of irradiation with an 8 Gy X-ray on the local area of the chest every day for three days. After irradiation for twenty-one days, The effect and possible mechanism of RIAEs on non-irradiated ovarian were discussed.

Participants/materials, setting, methods
After irradiation, the estrous cyclicity, serum steroid hormones, and pro-inflammatory factors were compared between groups. Furthermore, RNA-seq was used to detect the expression of transcriptional levels in ovarian tissues in both groups. The differentially expressed genes (DEGs) were screened and analyzed by gene ontology-biological process (GO_BP) between irradiated and sham groups. The expression and localization of spermatogenesis-and oogenesis-specific basic helix-loop-helix-containing protein 1(SOHLH1) and neutrophil elastase (NE) in ovarian tissues were detected by immunohistochemistry(IHC).

Main results and the role of chance
Compared with mice in the sham group, the irradiation group had disordered estrous cycles, reduced primordial follicles (P&lt;0.001)] and growing follicles (P&lt;0.001), significantly increased atretic follicles (P&lt;0.001). Levels of serum estradiol [(70.28 ± 5.27) pmol/L] and AMH [(104.00±6.98) ng/L] in the irradiation group were significantly lower than those in the sham group [estradiol (97.58±7.25) pmol/L, P=0.016; AMH [(129.70±8.39) ng/mL, P=0.046], but FSH levels in the irradiation group were not significantly different from those in the sham group (P=0.996). Compared with the sham group, Serum levels of TNF-α [(488.30±36.20) ng/L vs. (31.61±12.89) ng/L, P&lt;0.001] and IL-1β [(62.37±2.50) ng/L vs. (52.75±2.06) ng/L, P=0.018)] in the irradiation group were significantly increased. Serum levels of IL-6 in the irradiation group were also increased compared with the sham group, but the difference was not statistically significant (P=0.301). The results of GO_BP analysis showed that down-regulated DGEs were mainly involved in the process of follicular development, and up-regulated DGEs were involved in the inflammation process. The IHC results showed that the positive expression area of SOHLH1 in the irradiation group was significantly lower than in the sham group (P=0.005). In comparison, the positive expression area of NE was significantly higher than that of the Sham group(P=0.024).

Limitations, reasons for caution
This study was performed using a short, 3-day irradiation treatment condition. Therefore, the results need to be cautiously interpreted concerning radiation-associated chronic toxicity. Moreover, further studies in mouse tumor models are required to determine the clinical relevance of the role of RIAE.

Wider implications of the findings
Although the precise molecular mechanisms of these distal effects on the genital system are still unclear, the current discovery might pave the way for establishing novel fertility preservation protocols. The research offers hope to women with POI related to cancer therapy through the modulation of abscopal effects associated with radiotherapy.

Trial registration number
not applicable