Quercetin exerts radioprotective effects against radiation-induced intestinal injury with involvement of the PI3K-AKT/Caspase-3 axis.

Radiation-induced intestinal injury (RIII) significantly limits the efficacy of abdominal and pelvic radiotherapy while also impairing patient quality of life. This condition is primarily driven by excessive reactive oxygen species (ROS) and dysregulation of Caspase-dependent apoptosis. Quercetin (QUE), a natural antioxidant flavonoid, exhibits radioprotective potential; however, the key signaling pathways it employs to regulate radiation-induced apoptosis remain to be elucidated. In vitro studies, IEC-6 cells (1-10 µg/mL QUE pretreatment followed by 0-8 Gy X-ray exposure) were conducted to analyze proliferation, clonogenic survival, ROS levels, apoptosis, and expression of RIII-related proteins and genes. Network pharmacology identified 47 overlapping targets associated with QUE and RIII, with AKT1 and CASP3 identified as hub targets, and the PI3K-AKT pathway recognized as a key regulatory pathway. A Caspase-3/7 inhibitor (HY-103346, H10) and AutoDock-Vina docking analysis were used to explore the involvement of Caspase-3-related apoptotic signaling. In vivo experiments using Drosophila melanogaster (W1118) involved groups subjected to control, 50 Gy irradiation alone, or 50 Gy combined with 1/5/10/50 µg/mL QUE. Lifespan, locomotor capacity, and intestinal ROS levels were assessed, including validation with DCP-1RNAi transgenic flies (DCP-1: Drosophila Caspase-3 homolog). In vitro findings revealed that QUE enhanced the viability of irradiated IEC-6 cells, reduced ROS and apoptosis, upregulated anti-apoptotic markers (p-AKT, p-PI3K and p-mTOR), and downregulated pro-apoptotic markers (cleaved-Caspase-3 and Cytochrome C), while H10 inhibited the effects of QUE. Molecular docking suggested a potential interaction between QUE and Caspase-3 through hydrogen bonds and hydrophobic interactions to inhibit its activation. In vivo, pre-irradiation gavage of 10 µg/mL QUE mitigated RIII in Drosophila, an effect that was abolished in DCP-1 knockdown flies. In summary, QUE protects against RIII by scavenging ROS and modulating apoptosis-related signaling, with evidence supporting the involvement of the PI3K-AKT/Caspase-3 axis, with the PI3K-AKT/Caspase-3 axis identified as central to these protective effects. This study underscores the clinical potential of QUE for RIII and offers insights into the targeting of apoptosis for radioprotection.