EM is a chronic inflammatory disorder in females that is dependent on estrogen. It is characterized by the presence of endometrial glands and stroma outside the uterine cavity [1,2]. The exact cause and pathogenesis of EM are still not well understood. However, proinflammatory cytokines have been detected in the peritoneal fluid of EM patients and are believed to be actively involved in the EM progression [3,4]. Therefore, it is essential to investigate the potential molecular mechanisms contributing to altered inflammatory responses to improve both the diagnosis and treatment of EM [5].

The inflammasome is a cytosolic multimeric protein complex that serves as a platform for producing and releasing inflammatory cytokine interleukin-1 (IL-1) by activating caspase-1 [6]. Among the inflammasome components, NLRP3 plays a crucial role, and its overactivation in response to certain disease-related stimuli is associated with the pathogenesis of several inflammatory diseases [7,8]. In the context of EM, it has been proposed that NLRP3, in particular, plays a significant role in the initiation and progression of the disease. Han et al. [9] demonstrated in a mouse model of EM that the deletion of NLRP3 led to a remarkable decrease in the number of ectopic EM lesions. Furthermore, they found that estrogen upregulates NLRP3 concentration and inflammasome activation, promoting increased inflammation in endometriotic lesions.

Conversely, the deficiency of estrogen receptor (ERb) reduces NLRP3 concentration. Additionally, in vitro studies on endometrial cancer cells showed that estrogen enhances inflammation induced by NLRP3 concentration through the augmentation of Erb. These findings indicate that estrogen signaling causes the concentration of NLRP3, which is a critical mediator of estrogen's proinflammatory effects [9].

In a healthy endometrium, progesterone binds to its receptor and counteracts estrogen signaling, leading to an anti-inflammatory effect. However, the functional pathway through which progesterone inhibits NLRP3 in endometrial cells remains unknown. Previous studies have shown that progesterone regulates the secretory phase process and induces autophagy in endometrial stromal cells. Autophagy has been found to have a negative regulatory effect on the inflammasome. Conversely, it has been reported that estrogen inhibits the activation of autophagy in endometrial stromal cells. Therefore, progesterone may induce autophagy in endometrial stromal cells during the secretory phase, thereby preventing estrogen-induced activation of NLRP3 [10], [11], [12], [13], [14]. DNG is a selective progesterone receptor agonist commonly used to treat EM [15]. However, it has not yet been determined whether DNG affects NLRP3 concentration, which is the focus of this study.

Simply put, individuals with EM exhibit resistance to progesterone in their endometrial cells, resulting in unchanged autophagy induction and uninterrupted NLRP3 activity. This resistance leads to an increase in the cytokine IL-1β, subsequently causing inflammation [16].

Recent research has highlighted oxidative stress (OS) as a prominent factor in EM development. Consequently, there has been a significant focus on investigating antioxidant therapies to control reactive oxygen species (ROS) and inflammation. Evidence suggests that the peritoneal cavity, peritoneal fluid, endometriotic lesions, and the peritoneum of women with EM experience oxidative stress due to inflammation. Various antioxidant systems function within cells to eliminate excess free radicals and neutralize them, thereby preventing cellular damage. The oxidative stress observed in EM may arise from an imbalance between ROS production and antioxidant levels [17]. Intracellular pathways have demonstrated that the NLRP3 concentration levels increase with elevated ROS production. Conversely, as antioxidant levels rise, ROS levels and, subsequently NLRP3 concentration decrease [18]. Although the impact of antioxidants on this disease has been extensively studied, no research has been conducted on the effect of DNG on the balance between oxidants and antioxidants in these patients, which is the primary focus of this study.

Thus, this study aims to investigate whether regulating NLRP3 by DNG in the blood plasma of patients with EM can influence oxidant and antioxidant markers.