The interaction between inflammation and estrogen in adenomyosis : from molecular mechanisms to therapeutic strategies

In the widely studied mechanism of tissue damage and repair, it is believed that endometrial peristalsis causes chronic self-injury to produce an inflammatory reaction, activates IL-1, and promotes estrogen production via COX-2 and prostaglandins; additionally, an abnormal increase in estrogen can elicit hyperactivity of endometrial peristalsis and aggravate the inflammatory reaction. Therefore, an increase in estrogen can aggravate the inflammatory response in a variety of ways and that the inflammatory response can maintain the local high estrogen state in many ways. Thus, there is a complex interaction between estrogen and inflammation, which jointly promotes the occurrence and development of adenomyosis. (Fig.  5 ) Fig. 5 The interaction between inflammation and estrogen affects the pathogenesis of adenomyosis. Estrogen aggravates the inflammatory response by interacting with inflammatory cells, inflammatory factors and inflammatory pathways, and the inflammatory response can also maintain a high estrogen state in adenomyosis, which promotes the pathogenesis of adenomyosis. This figure was created by Figdraw. JNK  C-Jun N-terminal kinase, IDO1  indoleamine 2,3-dioxygenase-1, FGF2  fibroblast growth factor 2, MEK/ERK  mitogen-activated protein kinase kinase/extracellular signal-regulated kinase, PGE2  prostaglandin E2, COX2  cyclooxygenase 2, NLRP3  NOD-like receptor hot protein domain-related protein 3, GPR30  G protein-coupled estrogen receptor 30, NGF  nerve growth factor, NFκB  nuclear factor kappa-B, ERβ  estrogen receptor β, GRIM-19  gene associated with retinoid-IFN-induced mortality-19, TGF-β1/Smad3  transforming growth factor-β1/small mothers against decapentaplegic, STAT3  signal transducer and activator of transcription 3, PI3K/AKT, phosphatidylinositol 3 kinase/protein kinase B The interaction between inflammation and estrogen affects the pathogenesis of adenomyosis. Estrogen aggravates the inflammatory response by interacting with inflammatory cells, inflammatory factors and inflammatory pathways, and the inflammatory response can also maintain a high estrogen state in adenomyosis, which promotes the pathogenesis of adenomyosis. This figure was created by Figdraw. JNK  C-Jun N-terminal kinase, IDO1  indoleamine 2,3-dioxygenase-1, FGF2  fibroblast growth factor 2, MEK/ERK  mitogen-activated protein kinase kinase/extracellular signal-regulated kinase, PGE2  prostaglandin E2, COX2  cyclooxygenase 2, NLRP3  NOD-like receptor hot protein domain-related protein 3, GPR30  G protein-coupled estrogen receptor 30, NGF  nerve growth factor, NFκB  nuclear factor kappa-B, ERβ  estrogen receptor β, GRIM-19  gene associated with retinoid-IFN-induced mortality-19, TGF-β1/Smad3  transforming growth factor-β1/small mothers against decapentaplegic, STAT3  signal transducer and activator of transcription 3, PI3K/AKT, phosphatidylinositol 3 kinase/protein kinase B Estrogen can promote the secretion of chemokines in peripheral nerves and enhance the recruitment and polarization of macrophages in endometriosis. Studies have shown that the coculture of macrophages with estrogen increases the concentration of neurotrophic factor 3, which stimulates nerve growth [ 237 ]. Under the influence of estrogen, the coexistence of macrophages and nerves induces a new type of neuroimmune communication. The continuous stimulation of inflammatory cytokines from macrophages to peripheral nerve nociceptors aggravates neuroinflammation by releasing inflammatory neurotransmitters, which eventually leads to neuropathic pain [ 238 ]. In addition, previous studies have shown that the expression of estrogen receptors in the macrophages of women with endometriosis is significantly greater than that in the control group, which was demonstrated by detecting the estrogen receptors of macrophages in the peritoneal fluid of patients with endometriosis [ 239 ]. The estrogen receptor also has a recruitment effect on macrophages. Gou et al. reported that the high expression of estrogen receptor β can produce CCL2 via the signal transduction of NF-κB and recruit macrophages to the ectopic environment of the endometrium, whereas the recruited macrophages can promote the proliferation and colony formation of endometrial stromal cells [ 240 ]. CD200 is an immunomodulatory factor and a type I glycosylated protein that is located on the cell surface. Studies have shown that the CD200 protein can be induced by estrogen; moreover, with increasing CD200 concentration, the phagocytosis rate of macrophages decreases, which leads to an impaired macrophage-mediated immune response in endometriosis [ 241 ], thereby potentially leading to the development of adenomyosis. The number of mast cells in ectopic lesions of adenomyosis is significantly increased. Studies have shown that the levels of the proinflammatory factors IL-6 and IL-8 are increased in human endometrial stromal cells cultured in the conditioned medium of endometrial ectopic epithelial cells and human mast cells. A high estrogen environment can promote the recruitment of mast cells and aggravate the inflammatory response to promote the pathogenesis of adenomyosis [ 242 ]. Nerve growth factor (NGF) plays an important role in the generation of pain, nerve plasticity and the release of inflammatory factors. Studies have shown that NGF is significantly upregulated in tamoxifen-induced adenomyosis mice [ 12 ]. In addition, 17β-estradiol can stimulate the production of NGF in endometrial stromal cells in adenomyomas and subsequently induce the expression of cyclooxygenase in mast cells, increase the production of prostaglandin E2, and promote the proliferation of endometrial stromal cells in adenomyomas and the synthesis of aromatase [ 243 , 244 ]. Moreover, it can also induce the production of TNF-α and IL-6 to further promote the development of adenomyosis [ 244 ]. Studies have shown that estrogen can promote the secretion of fibroblast growth factor 2 in endometriosis lesions via the G protein-coupled estrogen receptor 30 (GPR30) and MEK/ERK pathways in mast cells. Specifically, a previous study showed that the concentration of fibroblast growth factor 2 in the pelvic fluid of the mild pain group and severe pain group was greater than that in the pelvic fluid of patients without endometriosis-related pain, thereby indicating that the increase in fibroblast growth factor (FGF2) secretion in mast cells may be a potential cause of related pain caused by endometriosis in women [ 245 ]. Estrogen can lead to an increase in the rate of degranulation of mast cells, and the degranulation of mast cells is related to endometriosis-related dysmenorrhea, which itself is related to estrogen promoting the release of nerve growth factor. These effects consequently promote the growth of neurites in PC12 cells and upregulate the expression levels of Nav1.8 and transient receptor potential cation channels to increase dorsal root ganglion cell sensitivity [ 246 ], which may also be a related factor leading to the occurrence of pain in adenomyosis. Estrogen promotes the activation of mast cells, and the expression of NOD-like receptor hot protein domain-related protein 3 (NLRP3) in mast cells is significantly increased after estrogen treatment. NLRP3 is an intracellular receptor that interacts with caspase-1 to form the NLRP3 inflammasome, and estrogen can strongly activate the inflammasome via potassium efflux in mast cells [ 247 ], thereby enhancing the pathogenesis of adenomyosis. Studies have shown that estrogen can promote the expansion of Tregs and the production of cytokines such as IL-10 and TGF-β; moreover, the mRNA expression of ERα in amplified Tregs is increased. An increase in Tregs promotes the invasion and survival of endometrial stromal cells [ 248 ]. In addition, indoleamine 2,3-dioxygenase-1 (IDO1) is highly expressed in ectopic endometrial stromal cells. This molecule is a rate-limiting enzyme that catalyzes the synthesis of tryptophan and can promote the survival, proliferation and invasion of endometrial stromal cells via the c-Jun N-terminal kinase (JNK) signaling pathway [ 249 ] Estrogen can upregulate the expression of IDO1 and participate in the differentiation of Tregs, thus affecting the ability of the immune system to eliminate ectopic endometrial tissue [ 250 ]. The increased expression of galectin-3 can be induced by estrogen, and studies have shown that galectin-3 can impair the toxicity of natural killer cells in the peritoneal cavity to endometrial stromal cells, enhance the peritoneal implantation of endometrial stromal cells, and ultimately promote the adhesion and migration of endometrial stromal cells to the lesion [ 251 , 252 ], which promotes the occurrence of adenomyosis. Similarly, studies have shown that galectin-1, −3 and − 9 are overexpressed in the endometria of women with endometriosis and are related to the development of endometriosis-related tumors [ 253 , 254 ]. Therefore, the development of adenomyosis cannot be ignored with respect to this factor. IL-17 A is a proinflammatory cytokine that is closely related to the estrogen-COX-2 axis. IL-17 A has been found to promote the survival of endometrial cells by upregulating antiapoptotic genes, and IL-17 A can also inhibit natural killer cell-mediated cytotoxicity and promote angiogenesis and the proinflammatory environment in the peritoneal cavity [ 255 , 256 ]. IL-17 A also enhances the expression of COX-2 mRNA and plays a role in the development of endometriosis by promoting the proliferation of ectopic stromal cells [ 257 ]. In addition, elevated estrogen levels promote the production of IL-15 in the ectopic endometrium, thereby stimulating the growth and invasion of endometrial stem cells and inhibiting the cytotoxic activity of natural killer cells [ 258 , 259 ]. The Toll-like receptor 4 (TLR4) signaling pathway is essential for the pathogenesis of adenomyosis [ 260 ]. TLR4 signals that are activated by endogenous ligands promote the secretion of various cytokines and growth factors, stimulate the proliferation of endometrial cells, and recruit and activate immune cells (such as macrophages, DCs, and NK cells), estrogen is also involved in promoting the activation of TLR4, the proliferation and invasion of stromal cells further induce and amplify the local inflammatory response, thus ultimately leading to the development of adenomyosis [ 261 – 264 ]. The mechanism of tissue damage and repair in adenomyosis is physiologically associated with the local production of IL-1. IL-1 activates COX-2 and induces the production of prostaglandin E2; subsequently, steroids produce acute regulatory proteins, aromatase is activated, and testosterone is aromatized into estradiol, which helps in maintaining local estrogen overproduction [ 15 , 58 , 59 , 265 – 268 ]. Prostaglandin E2 also promotes angiogenesis through its effects on estrogen and the upregulation of vascular endothelial growth factor [ 269 ]. Elevated levels of prostaglandins in the peritoneal fluid and the expression of aromatase in the endometrium are considered to exert specific impacts on endometriosis-associated infertility [ 267 , 270 ]. In addition, the combination of IL-4 and prostaglandin E2 enhances estrogen production in the ectopic endometrium [ 271 ]. Hyperestrogenemia has also been shown to stimulate the production of IL-10, which is a cytokine exhibiting an immunosuppressive ability. IL-10 is highly expressed in the eutopic and ectopic endometria of women with adenomyosis. This observation may explain the persistence of ectopic lesions in the myometrium without the elimination of the host immune system [ 183 ]. Studies have shown that estrogen can increase the activity of NF-κB in ectopic endometrial cells. Estradiol can activate the PI3K/AKt pathway via the NF-κB/PTEN-dependent pathway, thereby promoting the proliferation of ectopic endometrial cells [ 272 ]. Estradiol has proinflammatory and antiapoptotic effects on endometrial cells. Moreover, estradiol can induce inflammatory responses mediated by local chemokines at normal physiological concentrations and enhance cell survival mechanisms mediated by extracellular signal-regulated kinases and Bcl-2. These effects seem to be exacerbated in women with endometriosis [ 273 ]. Furthermore, platelets have also been demonstrated to upregulate aromatase by activating the NF-κB and/or TGF-β1 pathways, thereby increasing estrogen production [ 274 ]. In addition, estrogen can promote the release of inflammatory factors by inducing the expression of GATA-3, thereby promoting the development of endometriosis [ 275 ]. In the investigation of the mechanism of adenomyosis, we observed that the occurrence of estrogen abnormalities and inflammation is closely related, and a variety of evidence shows that there is an interaction between estrogen and inflammation, which is of far-reaching significance for further guiding clinical medication use.

Adenomyosis is an estrogen-dependent disease [ 35 ] that is related to the biological effects of estrogen and its receptor binding to the response elements of the target gene in the nucleus, thereby initiating the ‘genomic effect’ to induce the transcription of the target gene [ 36 ]. The increased level of estrogen in the endometrium enhances the growth ability of the myometrium and ectopic tissue in the junctional zone of endometrial infiltration, which leads to excessive growth and invasion of endometrial stromal cells and promotes the epithelial-mesenchymal transition of endometrial epithelial cells and angiogenesis [ 10 , 35 , 37 – 43 ]. Studies have shown that abnormal estrogen-related biological effects caused by the overexpression of estrogen receptors and aromatase in adenomyosis are closely related to the pathogenesis of adenomyosis [ 36 , 44 ]. Aromatase is a type of cytochrome P450 enzyme system. Moreover, it can synthesize estrogen by catalyzing testosterone, androstenedione and other components, thus directly affecting the expression level of estrogen. An examination of the activity of aromatase and estrone sulfatase in the ectopic endometrium revealed that estrogen is synthesized in the endometrial tissue of women with adenomyosis and may affect the occurrence and development of adenomyosis [ 45 ]. Studies have shown that women with adenomyosis had the highest menstrual blood estradiol levels, which were higher than those in the normal and endometriosis groups [ 46 ]. Polymorphisms in genes that lead to increased estrogen production, such as the expression of aromatase and COX-2, and the catechol-O-methyltransferase (COMT) 158G/A gene, which leads to decreased estrogen metabolism, are associated with an increased risk of developing adenomyosis [ 47 – 52 ]. Therefore, excessive estrogen is considered to be due to the overexpression of local aromatases and the reduction in local estrogen metabolism in the eutopic and ectopic endometria of patients with adenomyosis. Kitawaki et al. reported that aromatase is not present in the endometria of disease-free uteri but is observed in the ectopic endometria of adenomyosis patients [ 53 ]. This enzyme aromatizes circulating androgens into estradiol, promotes estrogen biosynthesis and increases estrogen bioavailability [ 53 ]. In addition, studies have shown that the presence of complete aromatase genes and aromatase activity are essential for the growth of ectopic uterine tissue in a mouse model of endometriosis [ 54 ]. Therefore, data suggests that aromatase should be used as a preliminary screening method for adenomyosis [ 55 , 56 ]. COX-2 is overexpressed in the eutopic endometrium and ectopic endometrium of patients with adenomyosis [ 57 ], and the local high estrogen state of patients with adenomyosis stimulates the activity of COX-2, thereby promoting prostaglandin synthesis [ 58 ]. Increased prostaglandins upregulate STAR and aromatase to increase estrogen synthesis [ 59 ]. Therefore, COX-2 can promote the high estrogen state caused by adenomyosis. Estrogen stimulation can promote the proliferation of the deep perivascular matrix in adenomyosis [ 60 ]. Estradiol activates the Slug- vascular endothelial growth factor (VEGF) axis in endometrial epithelial cells and promotes angiogenesis in vascular endothelial cells [ 43 ]. Slug is a zinc finger transcription factor and an important inducer of the epithelial-mesenchymal transition [ 61 ]. Moreover, VEGF is a major angiogenic factor that plays a role in mediating angiogenesis during the development of adenomyosis [ 62 ]. Previous studies have shown that estrogen can upregulate Slug in adenomyosis to induce the epithelial-mesenchymal transition, which subsequently produces VEGF to promote angiogenesis [ 43 ]. (Fig. 2 ). Fig. 2 The related signaling pathways by which estrogen affects the pathogenesis of adenomyosis. Estrogen leads to the migration, invasion and proliferation of endometrial stromal cells through a variety of signaling pathways and induces epithelial-mesenchymal transition of endometrial stromal cells, which can lead to adenomyosis. This figure was created by Figdraw. PGF2α prostaglandin F2α, COX-2  cyclooxygenase-2, PEG2  prostaglandin E2, STAR  steroidogenic acute regulatory protein, SGK1  serum and glucocorticoid-induced kinase 1, LPAR2  lysophosphatidic acid receptor 2, PI3K/AKT  phosphatidylinositol 3 kinase/protein kinase B, NRP1  neuropilin 1, VEGF  vascular endothelial growth factor, HIF-1α  hypoxia inducible factor-1α, EMT  endometrial epithelial-mesenchymal transition The related signaling pathways by which estrogen affects the pathogenesis of adenomyosis. Estrogen leads to the migration, invasion and proliferation of endometrial stromal cells through a variety of signaling pathways and induces epithelial-mesenchymal transition of endometrial stromal cells, which can lead to adenomyosis. This figure was created by Figdraw. PGF2α prostaglandin F2α, COX-2  cyclooxygenase-2, PEG2  prostaglandin E2, STAR  steroidogenic acute regulatory protein, SGK1  serum and glucocorticoid-induced kinase 1, LPAR2  lysophosphatidic acid receptor 2, PI3K/AKT  phosphatidylinositol 3 kinase/protein kinase B, NRP1  neuropilin 1, VEGF  vascular endothelial growth factor, HIF-1α  hypoxia inducible factor-1α, EMT  endometrial epithelial-mesenchymal transition Zhou et al. reported that estrogen can significantly upregulate the expression of annexin A2 in the endometrium. The overexpression of annexin A2 has been confirmed to exist in the ectopic lesions of human adenomyosis. Moreover, the high expression of annexin A2 can not only induce epithelial-mesenchymal transition by changing cell structure and function to mesenchymal-like cells via β-catenin/T cytokine signal transduction but also enhance the angiogenesis ability of human endometrial cells via the HIF-1α/VEGF-A pathway [ 63 ]. Talin1 can also synergize with estradiol to induce angiogenesis and endometrial stromal cell proliferation in human adenomyosis by triggering the Wnt/β-catenin pathway [ 64 – 66 ]. Talin1 is a macromolecular protein that mainly functions as a key regulator of integrin activation. Previous studies have demonstrated that Talin1-dependent integrin activation can regulate VE-cadherin localization and endothelial cell barrier function, which are essential for angiogenesis and development [ 67 , 68 ]. In addition, mutations in the Wnt/β-catenin pathway can lead to the abnormal activation of epithelial-mesenchymal transition and elicit the occurrence of adenomyosis. For instance, Wang et al. discovered in an in vitro experiment that Talin1 induced the epithelial-mesenchymal transition of human endometrial cells and the migration and invasion of ectopic endometrial epithelial cells, achieving this through the activation of the classical β-catenin pathway [ 65 ]. Serum and glucocorticoid-induced kinase 1 (SGK1) is an important Akt-independent mediator of the PI3K signaling pathway. Studies have shown that SGK1 is an additional PI3K effector and plays a key role in the PI3K pathway [ 69 ]. Additionally, FGF18 is a member of the FGF family, which is located on chromosome 14p11. FGF18 plays a major role in the manipulation of tumor cell growth and invasion [ 70 , 71 ]. Estrogen can directly act on nearby endometrial stromal cells, studies have shown that estrogen can induce FGF18 to promote the proliferation of endometrial cancer cells and transmit proliferation signals via the AKt pathway [ 72 ]. In addition, estradiol affects the abnormal activation of the PI3K/AKT signaling pathway related to tumor cell invasion and migration in most tumors by upregulating SGK1 in endometrial cells [ 69 , 73 , 74 ]. This upregulation results in increased expression of N-cadherin, matrix metalloproteinase 2, matrix metalloproteinase 9 and other proteins, thereby promoting the migration and invasion of human interstitial endometrial stromal cells and the epithelial-mesenchymal transition of endometrial cells [ 75 , 76 ]. Neuropilin 1 (NRP1) is a transmembrane glycoprotein that is involved in the occurrence and metastasis of various cancer cells [ 77 , 78 ]. Previous studies have shown that NRP1 can be targeted by miR-124-3p. Moreover, miR-124-3p downregulates the expression of NRP1 in adenomyosis and reduces the migratory activity of endometrial cells. Estrogen can also promote the migration and epithelial-mesenchymal transition of endometrial stromal cells by upregulating the expression of NRP1 [ 79 , 80 ]. B-cell lymphoma-2 (Bcl-2) is an anti-apoptotic factor. From the perspective of apoptosis, the inhibition of apoptosis and the abnormal accumulation of cells are common characteristics of tumors, and studies have shown that the expression of Bcl-2 is increased in various malignant tumors [ 81 ]. The investigation of Bcl-2 in adenomyosis revealed that the expression of Bcl-2 in the endometria and stromal cells of adenomyosis patients was significantly greater than that in normal control patients, which enhanced the antiapoptotic ability of endometrial cells and reduced their sensitivity to apoptosis; consequently, the cells escaped apoptosis, which resulted in the implantation of ectopic sites, thereby eventually leading to the formation of ectopic lesions [ 81 ]. The increase in local estrogen in adenomyosis can upregulate the expression of the oxytocin receptor, cause uterine hyperactivity and stimulate uterine peristalsis. Excessive peristalsis can lead to uterine trauma and the infiltration and growth of the basal endometrium into the uterine layer, which eventually leads to the occurrence of adenomyosis [ 15 , 82 ]. Moreover, oxytocin, which is mediated by the oxytocin receptor, is involved in the release of prostaglandin F2α (PGF2α) from endometrial cells. The increased production of PGF2α promotes the production of prostaglandins and upregulates COX-2, which correspondingly promotes the production of estrogen [ 83 – 88 ]. (Fig. 3 ) Fig. 3 Estrogen promotes the development of adenomyosis by stimulating uterine smooth muscle contraction. Estrogen stimulates uterine peristalsis by up-regulating the expression of oxytocin receptor, resulting in obvious uterine trauma. Estrogen can also promote the contraction of uterine smooth muscle by affecting ion channels and RhoA/Rock signaling pathway, thereby exacerbating adenomyosis Estrogen promotes the development of adenomyosis by stimulating uterine smooth muscle contraction. Estrogen stimulates uterine peristalsis by up-regulating the expression of oxytocin receptor, resulting in obvious uterine trauma. Estrogen can also promote the contraction of uterine smooth muscle by affecting ion channels and RhoA/Rock signaling pathway, thereby exacerbating adenomyosis The development of adenomyosis caused by estrogen may be related to changes in ion channels. For example, excessive estrogen can lead to the abnormal expression of potassium channels in the uterine smooth muscle cells of adenomyosis patients and may lead to progesterone resistance [ 89 ]. Similarly, estrogen can induce an increase in calcium ions in smooth muscle cells at the endometrial-myometrial interface, thus resulting in abnormal muscle contraction at the endometrial-myometrial interface, which is also related to the pathogenesis of adenomyosis [ 90 – 92 ]. The RhoA/ROCK signaling pathway has been investigated in many tumors, and it is believed that this pathway can promote the invasion of tumor cells. Many studies have confirmed that the RhoA/ROCK signaling pathway can promote the invasion and growth of adenomyosis and is widely involved in the pathophysiological process of adenomyosis [ 93 – 95 ]. The role of the RhoA/ROCK signaling pathway is closely related to estrogen. Specifically, estrogen can enhance RhoA/ROCK-1 signal transduction to affect smooth muscle contraction in the junction area of adenomyotic lesions, and excessive proliferation of uterine smooth muscle cells aggravates the process of adenomyosis [ 96 , 97 ]. The abovementioned findings demonstrate that estrogen plays an important role in the occurrence and development of adenomyosis; however, with respect to clinical medication, the effect of the simple use of antiestrogen drugs is not ideal, which indicates that the occurrence and development of adenomyosis includes not only the pathological phenomenon of an abnormal increase in estrogen but also other important pathological phenomena.

Adenomyosis is an estrogen-dependent disease, and abnormalities in estrogen are highly important for its pathogenesis. Estradiol can enhance the excessive growth and invasion of endometrial stromal cells and vascular proliferation by activating various protein pathways, such as the glucocorticoid-regulated kinase 1, transmembrane glycoprotein neuropilin 1, annexin A2 and Slug-VEGF axes. It can also cause abnormal muscle contraction at the endometrial-myometrial interface via ion channels. Aromatase P-450 can aromatize local androgens in the circulation, thereby promoting estrogen biosynthesis and increasing estrogen bioavailability, which is highly important for the pathogenesis of adenomyosis. The occurrence of inflammation is also highly important for the pathogenesis of adenomyosis. The endometria of patients with adenomyosis exhibit an abnormal accumulation of immune cells, and patients with endometriosis demonstrate changes in the peritoneal inflammatory environment. Proinflammatory cytokines such as IL-6, IL-1β and IL-8 are increased in patients with adenomyosis. The occurrence of inflammation can affect the angiogenesis, invasion and migration of endometrial cells. The overexpression of HMGB1, protease-activated receptor 1, protease-activated receptor 2, lipoxygenase-5 and cyclooxygenase-2 in the endometrium is positively correlated with various inflammatory factors, such as IL-6 and IL-8, which are related to cell proliferation and dysmenorrhea in adenomyosis. Moreover, the expression of inflammatory signaling pathway components, such as NF-κB p65 and PI3K/AKT, leads to increased levels of inflammatory factors and cell proliferation, as well as the inhibition of apoptosis. It also plays an important role in adenomyosis. Therefore, the incidence of adenomyosis is closely related to the occurrence of estrogen abnormalities and inflammation, and a variety of evidence demonstrates that the interaction between estrogen and inflammation can also affect the incidence of adenomyosis. Estrogen can promote the secretion of chemokines by peripheral nerves and enhance the recruitment and polarization of macrophages in ectopic endometrial tissues, which ultimately leads to pain. Furthermore, estrogen plays a regulatory role in the recruitment, proliferation, differentiation and function of uterine natural killer cells, thereby enhancing the peritoneal implantation of endometrial stromal cells. The expression of inflammatory factors such as IL-17 A and MMP is also related to estrogen, which leads to the migration and proliferation of endometrial epithelial cells. Estrogen can also activate the expression of inflammatory pathways such as the NF-κB and PI3K/Akt pathways in ectopic endometrial cells, thereby promoting the proliferation of ectopic endometrial cells. The interaction between estrogen and the inflammatory response has practical importance for the treatment of adenomyosis. The combined treatment strategy of anti-inflammatory drugs and antiestrogen drugs shows the synergistic advantages of improving symptoms and controlling lesion development by targeting the dual pathological mechanism of the inflammatory response and hormone dependence of adenomyosis and provides a more potential multidimensional intervention plan for clinical treatment. Although the combination of antiestrogen drugs and anti-inflammatory drugs may have been widely used to treat adenomyosis in clinical practice, the mechanism of their combined action is not yet clear, and research attention is insufficient. Therefore, more high-quality clinical trials with large samples and long-term follow-up are still needed to clarify the optimal dose, course of treatment and individualized applicable population of different drug combinations. Moreover, the molecular biological mechanism of drug synergy should be further explored, and the potential risks and drug resistance associated with long-term treatment should be analyzed. In the future, with the deepening of the concept of precision medicine and breakthroughs in pathogenesis research, the combined application of anti-inflammatory drugs and antiestrogen drugs may become an important development direction for the clinical treatment of adenomyosis.

Adenomyosis is a common gynecological disease, with a prevalence of 20.9% to 34% [ 1 – 5 ]. It exhibits clinical manifestations such as uterine hypertrophy, excessive menstruation, pelvic pain and infertility [ 6 , 7 ]. Additionally, adenomyosis is characterized by the presence of abnormal endometrial epithelial cells and stromal fibroblasts in the myometrium and the proliferation and hypertrophy of surrounding smooth muscle cells, thereby leading to diffuse uterine enlargement [ 8 ]. Microscopically, nonneoplastic ectopic endometrial glands and stroma are surrounded by hypertrophic and proliferative myometrium [ 9 , 10 ]. However, the pathogenesis of adenomyosis is not yet clear. At present, the widely studied pathogenesis mainly includes : the endometrial invagination mechanism [ 11 – 14 ];the mechanism of tissue injury and repair [ 15 , 16 ]; the stem cell metaplasia theory [ 17 , 18 ];the menstrual retrograde theory [ 14 ]. (Fig. 1 ) Adenomyosis is often associated with endometriosis. The characteristics of these two diseases are the presence of endometrial glands and stroma outside the normal position. Endometriosis and adenomyosis are estrogen-dependent diseases, usually accompanied by inflammatory processes. Both estrogen abnormalities and inflammatory processes are essential for the establishment and growth of ectopic endometrium [ 19 ]. Fig. 1 There are four theories concerning the pathogenesis of adenomyosis. ( A ) The endometrial invagination mechanism. ( B ) The mechanisms of tissue injury and repair. ( C ) The stem cell metaplasia theory. ( D ) The menstrual retrograde theory. This figure was created by Figdraw There are four theories concerning the pathogenesis of adenomyosis. ( A ) The endometrial invagination mechanism. ( B ) The mechanisms of tissue injury and repair. ( C ) The stem cell metaplasia theory. ( D ) The menstrual retrograde theory. This figure was created by Figdraw The theory of endometrial invagination mainly involves structural changes in the junctional tissue between the endometrium and the myometrium. The influence of high estrogen status causes cohesion of smooth muscle cells, thus providing an optimal condition for the endometrium to sink, moreover, high estrogen levels reduce the degree of apoptosis of ectopic endometrial cells and promote their proliferation, thus resulting in the development of adenomyosis [ 20 – 24 ]. The mechanism of tissue damage and repair is mainly due to the chronic self-injury state that is caused by endometrial peristalsis, which elicits an inflammatory response, activates interleukin-1 (IL-1) and induces cyclooxygenase-2 (COX-2) to promote prostaglandin production, which in turn activates steroidogenic acute regulatory protein (STAR) and the P450 aromatase, thereby resulting in a local high estrogen environment. Estrogen can cause endometrial peristaltic hyperfunction and increase the inflammatory response [ 25 – 30 ]. The activation of endometrial stem cells or stem cells deposited by retrograde menstruation is closely related to uterine injury. Endometrial stem cells or stem cells deposited by retrograde menstruation are activated after endometrial–myometrial junction injury, which may lead to abnormal alterations in the stem cell niche, allowing their differentiating progeny to move toward the myometrium rather than the endometrial functional area [ 13 , 18 , 26 ]. It suggests that the pathogenesis of adenomyosis is closely related to estrogen and inflammatory responses, and there is an interaction between inflammation and estrogen in adenomyosis, which together promotes the development of the disease. At present, the clinical drugs that have been reported to treat adenomyosis mainly include nonsteroidal anti-inflammatory drugs and gonadotropin-releasing hormone agonists, which can relieve adenomyosis; however, their curative effects are limited. For example, nonsteroidal anti-inflammatory drugs are effective for treating menstrual pain caused by adenomyosis, but their therapeutic effect with respect to abnormal bleeding is not as good as that of hormone therapy. Additionally, drugs that can maintain estrogen levels are not ideal for pain relief [ 7 , 31 – 34 ]. Therefore, the combination of estrogen inhibition and anti-inflammatory methods may achieve better therapeutic effects than single treatment does, and this article summarizes the existing evidence to provide reliable evidence for the clinical use of estrogen inhibition and anti-inflammatory methods in adenomyosis.

Adenomyosis is a chronic, hormone-related disease characterized by the presence of endometrial glands and stroma within the myometrium. The most common symptoms include chronic pelvic pain, dysmenorrhea, menorrhagia, and postmenopausal bleeding, but these symptoms are not specific and cannot be used for clinical diagnosis. With the advancement of diagnostic techniques, transvaginal ultrasound and magnetic resonance imaging can help in the early diagnosis of adenomyosis and distinguish it from other gynecological diseases. Based on these two examination methods, it can be classified into: diffuse adenomyosis; focal adenomyosis; and cystic adenomyosis. Early diagnosis is crucial for individualized treatment management, and drug therapy is the preferred treatment option. Selecting appropriate drugs based on the patient’s pathogenesis for intervention is extremely important [ 19 , 276 ]. Currently, abnormal estrogen levels, the occurrence of inflammatory responses, and their interaction play a prominent role in the pathogenesis of adenomyosis. Therefore, we have summarized the currently applied treatment drugs targeting abnormal estrogen levels and inflammatory responses and analyzed the existing two-drug combination treatment methods. Gonadotropin-releasing hormone (GnRH) is a hormone released by the hypothalamus that regulates reproductive function by stimulating the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The continuous administration of GnRH-as has been shown to initially cause a ‘flare-up’ effect, after which this administration inhibited the secretion of FSH and LH, thereby resulting in the production of ovarian-blocking steroids. Therefore, GnRH-as can improve symptoms by inducing a low estrogen status and regression of endometriosis implants [ 277 ]. Studies using GnRH-as to treat endometriosis have shown that these agonists can maintain the bone mineral density of the lumbar spine, reduce angiogenesis, relieve pain, and reduce subjective side effects [ 278 – 280 ]. GnRH-ants act by blocking the GnRH receptor in the pituitary gland and immediately inhibit reproductive function by inhibiting the secretion of FSH and LH by the pituitary gland. At present, elagolix is an oral, nonpeptide gonadotropin-releasing hormone antagonist that is considered for the treatment of uterine leiomyoma complicated with adenomyosis. This drug type has a dose-dependent and fast reversible effect on the pituitary-gonadal axis. Moreover, it can effectively improve dysmenorrhea and nonmenstrual pelvic pain, reduce excessive menstrual volume and improve the quality of life of patients [ 281 , 282 ]. In addition, linzagolix is a new type of GnRH-ant that is being investigated for the treatment of adenomyosis and endometriosis. Linzagolix significantly reduces the patient’s pain and excessive menstrual flow, reduces the size of the lesion, improves the patient’s quality of life, and demonstrates good safety [ 31 , 283 – 285 ]. Aromatase inhibitors specifically target aromatase. Aromatase functions by converting androgen into estrogen. In women with endometriosis, adenomyosis or leiomyoma, abnormal aromatase expression is stimulated by prostaglandin E2. This phenomenon appears to lead to increased estrogen production and further expression of prostaglandin E2, thereby leading to inflammation in ectopic endometriosis implants [ 265 ]. The selective inhibition of aromatase via drugs such as anastrozole or letrozole (used either alone or in combination with GnRH-as) has shown good efficacy in adenomyosis and endometriosis [ 286 – 289 ]. Badawy et al. randomly assigned patients to receive oral letrozole (2.5 mg/day) or subcutaneous injections of GnRH-as (goserelin, 3.6 mg) for 12 weeks and reported that aromatase inhibitors are as effective as GnRH agonists in reducing the volume of uterine adenomyoma and improving symptoms [ 286 ]. Kimura et al. used the aromatase inhibitor anastrozole combined with GnRH-as to treat severe adenomyosis in premenopausal women. After 8 weeks of treatment, the reduction rate in uterine volume was observed to be 60% based on magnetic resonance imaging and ultrasonography [ 287 ]. Machado et al. reported that clotrimazole interferes with the estrogen production pathway by downregulating aromatase, thereby reducing serum estrogen levels, which indicates that clotrimazole can reduce the size of endometriosis lesions, thus decreasing disease progression [ 290 ]. Progesterone exhibits a wide range of contraceptive effects. In addition, due to the fact that progesterone can inhibit the secretion of FSH and LH and ultimately inhibit the formation of ovarian steroids and alleviate the excessive estrogen production associated with adenomyosis, this hormone is also used for the treatment of adenomyosis [ 291 ]. Dienogest is an oral progesterone drug. Hirata et al. evaluated 15 patients who were treated with dienogest for 24 weeks and reported that dienogest effectively alleviated the pain of adenomyosis patients and had an inhibitory effect on estradiol; however, 5 patients experienced anemia symptoms due to uterine bleeding [ 292 ]. Uterine bleeding is the most common side effect of this treatment, according to clinical trials of the long-term use of dienogest [ 293 , 294 ]. Ulipristal acetate (UPA) is a selective progesterone receptor modulator that delays ovulation and endometrial maturation by reducing serum estradiol levels [ 295 ]. This modulator has been used to treat adenomyosis symptoms; however, only limited clinical evidence supports its use. Gracia et al. reported that UPA significantly reduced bleeding and pain caused by adenomyosis through the performance of clinical trials and achieved a high amenorrhea rate in women with uterine fibroids. UPA may be a good alternative therapy for treating adenomyosis [ 296 ]. After 12 weeks of treatment with 10 mg UPA every day for patients with adenomyosis, Capmas et al. reported that UPA exhibited positive effects on abnormal uterine bleeding caused by adenomyosis, thereby reducing the pain of patients and improving their quality of life [ 297 ]. (Table 1 ) Table 1 Medications for estrogen therapy Drugs Category Effects References Leuprolide acetate Gonadotrophin-releasing hormone agonist A hypo-estrogenic effect Khaleque Newaz Khan (2009) Letrozole Aromatase inhibitor Reduce adenomyoma volume and improving symptoms Ahmed M Badawy (2012) Anastrozole Aromatase inhibitor Reduce uterine volume Fuminori Kimura (2007) Dienogest Progestin Reduce adenomyosis-associated pelvic pain、 CA-125 and CA19-9 levels; A modest Suppression of estradiol Tetsuya Hirata (2014) Ulipristal acetate A selective progesterone receptor modulator A significant reduction in the clinical symptoms of adenomyosis (bleeding and pain) Meritxell Gracia (2018) Medications for estrogen therapy Menstrual pain is one of the common clinical symptoms of adenomyosis, and nonsteroidal anti-inflammatory drugs are the most commonly used drugs for the treatment of dysmenorrhea. Their efficacy is acceptable; however, they are prone to adverse side effects when widely used. Nonsteroidal anti-inflammatory drugs can block cyclooxygenase, inhibit prostaglandins, and relieve excessive uterine contraction; therefore, they can relieve menstrual pain [ 291 , 298 ]. Regarding the treatment of excessive menstrual flow, a systematic review revealed that nonsteroidal anti-inflammatory drugs can reduce the excessive menstrual flow of patients; however, the therapeutic effect of NSAIDs is not as good as that of tranexamic acid, danazol and other drugs [ 33 ]. Mifepristone is one of the most widely used selective progesterone receptor modulators (SPRMs). It has become a long-term treatment for adenomyosis because of its various advantages, including fewer adverse reactions, good tolerance and low price [ 299 ]. Studies have shown that the addition of mifepristone to the endometrium exposed to long-acting medroxyprogesterone acetate can significantly reduce the number of mast tryptase-positive cells and that mifepristone is related to the inhibition of mast cell activity [ 300 ]. Che et al. reported that mifepristone can reduce the secretion of IL-6 and TNF-α by endometrial epithelial cells and stromal cells, limit the infiltration and degranulation of mast cells in the endometrium and ectopic endometrium, and reduce the density of nerve fibers by inhibiting the migration ability of nerve cells in adenomyosis. These findings indicate that mifepristone exhibits anti-inflammatory activity in the treatment of adenomyosis and that mifepristone can improve dysmenorrhea symptoms in patients [ 123 , 301 ]. In addition, mifepristone can increase the expression of caspase 3 in the ectopic endometrium and initiate apoptosis, thus inhibiting the development of adenomyosis [ 302 ]. Combined oral contraceptives (COCs) block follicular development and endometrial proliferation by inhibiting FSH and LH. Therefore, COCs can be used to treat the symptoms of adenomyosis [ 303 ]. In addition, COCs can also exert anti-inflammatory effects by inhibiting the expression of cyclooxygenase-2 in adenomyosis [ 304 ]. Shaaban et al. used COCs to treat 62 patients with adenomyosis for 6 months and reported that COCs reduced pain and menstrual bleeding associated with adenomyosis; however, the effect was slightly weaker than that of levonorgestrel treatment [ 305 ]. Hassanin et al. reported that COCs can effectively treat pain, bleeding and other related symptoms in patients with adenomyosis. Compared with dienogest, the therapeutic effect of dienogest is better than that of COCs; however, its side effects are greater [ 306 ]. Li et al. reported that Sanjie Zhentong capsules can treat adenomyosis by inhibiting IL-6 and IL-10 to exert anti-inflammatory effects, and the therapeutic mechanism of these capsules involves the inflammatory response, hormone regulation, cell adhesion, proliferation and angiogenesis [ 307 ]. Intravenous injections of dexamethasone can effectively reduce inflammation and pain within 24 h after uterine artery embolization in patients with adenomyosis [ 308 ]. Additionally, Feng et al. reported that the Rhein protein can dose-dependently weaken the proliferative and hypertrophic myometrium and improve adenomyosis, which is achieved by inhibiting p-p65, p-AKT and active Rac1. Moreover, in vitro experiments have revealed that the Rhein protein has a negative regulatory effect on β-catenin in stromal cells and that stimulation with IL-1β can significantly increase the nuclear translocation of β-catenin and increase the expression of its target genes. However, Rhein has an inhibitory effect on β-catenin; thus, Rhein may improve adenomyosis via anti-inflammatory pathways [ 184 ]. Animal experiments have demonstrated that berberine downregulates the expression of TRPV1, COX-2, VEGF and other pain-related genes in mice with adenomyosis. Berberine can inhibit inflammation by inhibiting the activation of NF-κB; moreover, it can reduce hyperalgesia and exert analgesic and therapeutic effects on mice with adenomyosis [ 309 ]. The abovementioned drugs that are used for inflammation or estrogen treatment can alleviate adenomyosis; however, there are deficiencies with respect to these drugs in clinical practice, and these drugs cannot achieve the ideal therapeutic effect. Therefore, the combination of estrogen inhibition and anti-inflammatory methods should be considered in the treatment of adenomyosis to achieve better therapeutic effects than the use of a single treatment. (Table  2 ) Table 2 Drugs for the treatment of inflammation Drugs Category Effects References Non-steroidal anti-inflammatory drugs Non-steroidal anti-inflammatory drugs Blocks cox-2 and inhibits PGE2 Stella Iacovides(2015) Mifepristone Selective progesterone receptor modulators Anti-inflammatory; Improves menstrual cramps Xuan Che (2020) Combined oral contraceptives Steroid hormone Blocks cox-2; Anti-inflammatory Hugo Maia Jr (2013) Sanjie Zhentong capsule Proprietary chinese medicines Anti-inflammatory Li Du (2020) Drugs for the treatment of inflammation The current management of adenomyosis mainly focuses on drug intervention, but some studies have shown that appropriate lifestyle intervention can also alleviate the pain symptoms of women with adenomyosis caused by inflammation due to tissue damage. Research has shown that after 3 or 6 months of a Mediterranean diet intervention with increased fruit and vegetable intake, the levels of substances such as vitamins, folic acid, and zinc in the body increase, which directly or indirectly inhibit the occurrence of inflammatory responses and relieve pain [ 310 , 311 ]. The prevalence of adenomyosis in patients with endometriosis and the prevalence of endometriosis in patients with adenomyosis are approximately 80%, and estrogen is essential for the establishment and growth of the ectopic endometrium. Endometriosis and adenomyosis are both estrogen-dependent diseases. Moreover, endometriosis and adenomyosis are often accompanied by related inflammatory processes. In the clinical treatment of endometriosis, it has been treated by combination therapy. Xue et al. reported that the total effective rate of mifepristone combined with gestrinone in the treatment of endometriosis was 90.7%, which was significantly higher than the 77.3% reported for gestrinone alone; follow-up also revealed a higher pregnancy rate in the combined drug group(Xue et al., 2016). For the treatment of pain caused by endometriosis, the combination of aromatase inhibitors with compound oral contraceptives has also yielded good results. For example, Zhao et al. treated the pain symptoms of endometriosis by using letrozole combined with oral contraceptives and reported that the pain intensity of patients was significantly reduced after combined treatment(Zhao et al., 2021). Similarly, Amsterdam et al. used a combination of anastrozole and oral contraceptives to treat 15 patients with refractory endometriosis. Among them, 14 patients experienced significant pain relief, and no adverse reactions occurred(Amsterdam et al., 2005). These findings indicate that the combination of antiestrogen and anti-inflammatory agents has potential clinical value in the treatment of endometriosis and is worthy of further study. Similarly, in adenomyosis, patients undergoing frozen-thawed embryo transfer were pretreated with GnRH agonists and hormone replacement therapy, whereas Liu et al. used anti-inflammatory TNF-α inhibitors for peri-implantation treatment. The implantation rate and pregnancy rate of the treatment group were significantly greater than those of the untreated group(Liu et al., 2025). This finding shows that the combined application also has potential benefits in adenomyosis. Similarly, Zhu et al. evaluated the efficacy of high-intensity focused ultrasound ablation combined with mifepristone and the levonorgestrel-releasing intrauterine system in the treatment of adenomyosis and reported that the combined treatment can reduce uterine volume, effectively improve symptoms, and reduce serum CA125 levels. The efficacy of combined application is better than that of high-intensity focused ultrasound ablation alone, high-intensity focused ultrasound ablation combined with mifepristone and high-intensity focused ultrasound combined with the levonorgestrel-releasing intrauterine system(Zhu et al., 2023). These findings show that the combined application of antiestrogen and anti-inflammatory agents has positive effects on adenomyosis patients undergoing high-intensity focused ultrasound ablation. Therefore, in the treatment of adenomyosis, the combination of antiestrogen drugs and anti-inflammatory drugs has certain advantages and application potential. Anti-inflammatory drugs can relieve the pain symptoms caused by adenomyosis and improve the quality of life of patients by inhibiting the release of inflammatory factors, reducing the local inflammatory response of the lesion, and promoting the proliferation of endometrial cells. Antiestrogen drugs reduce the excessive growth and invasion of endometrial stromal cells and vascular proliferation by inhibiting estradiol. The synergistic effect of the two can not only cut through the two key pathological pathways of inflammation and hormones and block the progression of the disease in multiple dimensions but also control the development of the disease while alleviating symptoms. Compared with single drug treatment, combination therapy can significantly improve the therapeutic effect and provide a more optimized and comprehensive treatment strategy for patients with adenomyosis. It has the potential to become an important development direction for the clinical treatment of this disease in the future.