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Objective  This study aims to systematically evaluate the protective role of quercetin (QCT), a naturally occurring flavonoid, against oxidative damage in human endometrial stromal cells (HESCs) induced by hydrogen peroxide (H₂O₂). Oxidative stress, such as that induced by H₂O₂, is known to contribute significantly to cellular damage and has been implicated in various reproductive health issues. The study is focused on investigating how QCT interacts with specific molecular pathways to mitigate this damage. Special attention was given to the p38 MAPK/NOX4 signaling pathway, which is crucial to the regulation of oxidative stress responses in cellular systems. By elucidating these mechanisms, the study seeks to confirm the potential of QCT not only as a protective agent against oxidative stress but also as a therapeutic agent that could be integrated in treatments of conditions characterized by heightened oxidative stress in endometrial cells.

Methods  In vitro cultures of HESCs were treated with QCT at different concentrations (0, 10, 20, and 40 μmol/L) for 24 h to verify the non-toxic effects of QCT on normal endometrial cells. Subsequently, 250 μmol/L H₂O₂ was used to incubate the cells for 12 h to establish an H₂O₂-induced HESCs injury model. HESCs were pretreated with QCT for 24 h, which was followed by stimulation with H₂O₂. Then, CCK-8 assay was performed to examine the cell viability and to screen for the effective intervention concentration. HESCs were divided into 3 groups, the control group, the H₂O₂ model group, and the H₂O₂+QCT group. Intracellular levels of reactive oxygen species (ROS) were precisely quantified using the DCFH-DA fluorescence assay, a method known for its accuracy in detecting and quantifying oxidative changes within the cell. The mitochondrial membrane potential was determined by JC-1 staining. Annexin Ⅴ/PI double staining and flow cytometry were performed to determine the effect of QCT on H₂O₂-induced apoptosis of HESCs. Furthermore, to delve deeper into the cellular mechanisms underlying the observed effects, Western blot analysis was conducted to measure the expression levels of the critical proteins involved in oxidative stress response, including NADPH oxidase 4 (NOX4), p38 mitogen-activated protein kinase (p38 MAPK), and phosphorylated p38 MAPK (p-p38 MAPK). This analysis helps increase understanding of the specific intracellular signaling pathways affected by QCT treatment, giving special attention to its potential for modulation of the p38 MAPK/NOX4 pathway, which plays a significant role in cellular defense mechanisms against oxidative stress.

Results  In this study, we started off by assessing the toxicity of QCT on normal endometrial cells. Our findings revealed that QCT at various concentrations (0, 10, 20, and 40 μmol/L) did not exhibit any cytotoxic effects, which laid the foundation for further investigation into its protective roles. In the H₂O₂-induced HESCs injury model, a significant reduction in cell viability was observed, which was linked to the generation of ROS and the resultant oxidative damage. However, pretreatment with QCT (10 μmol/L and 20 μmol/L) significantly enhanced cell viability after 24 h (P<0.05), with the 20 μmol/L concentration showing the most substantial effect. This suggests that QCT can effectively reverse the cellular damage caused by H₂O₂. Furthermore, the apoptosis assays demonstrated a significant increase in the apoptosis rates in the H₂O₂ model group compared to those in the control group (P<0.01). However, co-treatment with QCT significantly reversed this trend (P<0.05), indicating QCT’s potential protective role in mitigating cell apoptosis. ROS assays showed that, compared to that in the control group, the average fluorescence intensity of ROS in the H₂O₂ model group significantly increased (P<0.01). QCT treatment significantly reduced the ROS fluorescence intensity in the H₂O₂+QCT group compared to the that in the H₂O₂ model group, suggesting an effective alleviation of oxidative damage (P<0.05). JC-1 staining for mitochondrial membrane potential changes revealed that compared to that in the control, the proportion of cells with decreased mitochondrial membrane potential significantly increased in the H₂O₂ model group (P<0.01). However, this proportion was significantly reduced in the QCT-treated group compared to that of the H₂O₂ model group (P<0.05). Finally, Western blot analysis indicated that the expression levels of NOX4 and p-p38 MAPK proteins were elevated in the H₂O₂ model group compared to those of the control group (P<0.05). Following QCT treatment, these protein levels significantly decreased compared to those of the H₂O₂ model group (P<0.05). These results suggest that QCT may exert its protective effects against oxidative stress by modulating the p38 MAPK/NOX4 signaling pathway.

Conclusion  QCT has demonstrated significant protective effects against H₂O₂-induced oxidative damage in HESCs. This protection is primarily achieved through the effective reduction of ROS accumulation and the inhibition of critical signaling pathways involved in the oxidative stress response, notably the p38 MAPK/NOX4 pathway. The results of this study reveal that QCT’s ability to modulate these pathways plays a key role in alleviating cellular damage associated with oxidative stress conditions. This indicates not only its potential as a protective agent against cellular oxidative stress, but also highlights its potential for therapeutic applications in treating conditions characterized by increased oxidative stress in the endometrium, thereby offering the prospect of enhancing reproductive health. Future studies should explore the long-term effects of QCT and its clinical efficacy in vivo, thereby providing a clear path toward its integration into therapeutic protocols.