Endometriotic cells are resistant to interferon-gamma-induced cell growth inhibition and apoptosis: a possible mechanism involved in the pathogenesis of endometriosis

Simvastatin inhibits the proliferation and the contractility of human endometriotic stromal cells: a promising agent for the treatment of endometriosis

Simvastatin significantly inhibited the proliferation of endometriotic stromal cells, attenuated the collagen gel contraction mediated by these cells, and suppressed endometriotic stromal cell attachment to collagen fibers. Simvastatin is considered to be a promising agent for the treatment of endometriosis-associated fibrosis, which is among the major pathologies caused by endometriosis.

Inverse regulation of the interferon-gamma receptor and its signaling in human endometrial stromal cells during decidualization

OBJECTIVE

To investigate whether human endometrial stromal cells (ESCs) express the interferon-gamma-receptor (IFN-gamma R) and whether the process of decidualization or human chorionic gonadotropin (hCG) regulate the IFN-gamma R and its signaling pathway.

DESIGN

In vitro experiment.

SETTING

Research laboratory at a medical university center.

PATIENT(S)

Premenopausal women undergoing hysterectomy for benign reasons.

INTERVENTION(S)

Isolation and incubation of ESCs from hysterectomy specimens with 17beta-estradiol, progesterone, recombinant hCG, and IFN-gamma as well as an IFN-gamma R-blocking antibody.

MAIN OUTCOME MEASURE(S)

We analyzed IFN-gamma R and the phosphorylation of signal transducer and activator of transcription 1 (STAT-1) by flow cytometry. We measured IFN-gamma R and interferon response factor 1 (IRF-1) mRNA using semiquantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR).

RESULT(S)

The IFN-gamma R is up-regulated in human ESCs during decidualization without affecting the phosphorylation of STAT-1. Stimulation of IRF-1 by IFN-gamma is reduced in decidualized ESCs. We found that hCG neither regulates the IFN-gamma R nor its signaling pathway.

CONCLUSION(S)

These results show an inverse regulation of the IFN-gamma R and its signaling response via STAT-1 and IRF-1 in human ESCs during decidualization. The early embryonic signal hCG has no effect on this process. This mechanism may finely modulate the reactivity of ESCs to IFN-gamma-mediated signals from immune cells at the implantation site.

Pathogenesis of endometriosis: the role of defective 'immunosurveillance'

OBJECTIVE

To analyse the aetiopathogenesis and the role of defective 'immunosurveillance' in endometriosis.

METHOD

Review of studies on the pathogenesis of endometriosis, focusing particularly on novel molecules which express adhesive or proteolytic properties. Hypotheses addressing the role of oxidative stress in endometriosis were also reviewed.

RESULTS

Endometriosis is a multifactorial disease associated with a general inflammatory response aiming to clear the peritoneal cavity from the ectopic endometriotic cells and tissue. Modern theories suggest that this inflammatory response creates an environment that may promote implantation and proliferation due to defective 'immunosurveillance'.

CONCLUSION

The modern interpretation of the theory of reflux menstruation holds that women destined to develop endometriosis have a deficient immune system, which cannot defend against regurgitated endometrial cells. New findings on genetics, immune modulation, and secreted products of endometriotic lesions of affected women have given insight into the pathogenesis of this disorder and may serve as the background for new treatments of endometriosis-associated pain and infertility.

Alteration of focal adhesion kinase expression in eutopic endometrium of women with endometriosis

OBJECTIVE

To investigate whether focal adhesion kinase (FAK) expression is altered in eutopic endometrium of women with endometriosis.

DESIGN

Experimental study using human endometrial tissue.

SETTING

Academic research center.

PATIENT(S)

Women with or without endometriosis who were undergoing surgery for benign indications.

INTERVENTION(S)

Endometrial biopsy.

MAIN OUTCOME MEASURE(S)

Expression of FAK was assessed by immunohistochemistry, Western blotting analysis, and reverse-transcription polymerase chain reaction.

RESULT(S)

At secretory phase, the average level of endometrial FAK expression of women with endometriosis was significantly higher than that of controls, but no significant difference was found between the two groups at proliferative phase. There was a positive correlation between FAK expression in secretory endometrial tissues and disease stage and pelvic pain in women with endometriosis. Furthermore, the endometrial FAK protein expression varied with the serum E(2) at proliferative phase and with the ratio of E(2) to P at secretory phase.

CONCLUSION(S)

The study showed a significant increase of FAK expression in the secretory endometrial tissues of women with endometriosis, a relationship between FAK expression and disease stage, pelvic pain, and serum steroid hormones. Those results suggest that FAK may play a role in the pathogenesis of endometriosis and be regulated by steroid hormones.

Targeting mast cells in endometriosis with janus kinase 3 inhibitor, JANEX-1

Endometriosis (EMS) is a chronic inflammatory disease of multifactorial etiology characterized by implantation and growth of endometrial glands and stroma outside the uterine cavity. EMS is a significant public health issue as it affects 15-20% of women in their reproductive age. Clinical symptoms may include pelvic pain, dysmenorrhea, dyspareunia, pelvic/abdominal masses, and infertility. Symptomatic treatments such as surgical resection and/or hormonal suppression of ovarian function and analgesics are not as effective as desired. Consequently, there is an enormous unmet need to develop effective medical therapy capable of preventing the occurrence and recurrence of EMS without undesirable side-effects. EMS-associated intra-abdominal bleeding episodes, local inflammation, adhesions, and i.p. immunologic dysfunction leads to pelvic nociception and pelvic pain. Increasing evidence supports the involvement of allergic-type inflammation in EMS. Invasion of mast cells, degranulation, and proliferation of interstitial component are observed in endometriotic lesions. Presence of activated and degranulating mast cells within the nerve structures can contribute to the development of pain and hyperalgesia by direct effects on primary nociceptive neurons. Therefore, treatments targeting endometrial mast cells may prove effective in preventing or alleviating EMS-associated symptoms. The Janus kinase 3 (JAK3) is abundantly expressed in mast cells and is required for the full expression of high-affinity IgE receptor-mediated mast cell inflammatory sequelae. JANEX-1/WHI-P131 is a rationally designed novel JAK3 inhibitor with potent anti-inflammatory activity in several cellular and in vivo animal models of inflammation, including mouse models of peritonitis, colitis, cellulitis, sunburn, and airway inflammation with favorable toxicity and pharmacokinetic profile. We hypothesize that JAK3 inhibitors, especially JANEX-1, may prove useful to prevent or alleviate the symptoms of EMS.

Effect of interferon-gamma treatment on the expression of interleukin-1beta at the maternal-fetal interface of pregnant rats

In the present study, the possible mechanisms by which interferon (IFN)-gamma affects pregnancy were investigated using the cytokine network model. The IFN-gamma-induced expression of interleukin (IL)-1beta was examined using western blotting, immunohistochemistry and immunofluorescence. The results showed that IFN-gamma treatment significantly decreased the expression of uterine IL-1beta protein during the preimplantation, post-implantation and mid-gestation periods. The expression of IL-1beta protein was increased after IFN-gamma treatment compared with the control group in late pregnancy. In the placenta, IL-1beta protein levels were significantly increased after IFN-gamma treatment in early and mid-pregnancy. In late pregnancy, IFN-gamma treatment significantly decreased placental IL-1beta protein levels. IL-1beta was mainly expressed in the myometrium, uterine arteries, decidua basalis, trophospongium of the junctional layer and trophoblastic epithelium of the labyrinthine layers. IL-1beta was mainly located in the cytoplasm of in vitro cultured endometrial stromal cells (ESCs). IFN-gamma treatment did not affect the distribution of IL-1beta, only the expression of IL-1beta. The effects of IFN-gamma on the proliferation of ESCs were determined using an MTS (a novel tetrazolium compound) assay. IFN-gamma treatment inhibited the proliferation of ESCs and decreased the weight of the fetus and placenta. These results indicate that exogenous IFN-gamma affects the expression of IL-1beta and inhibits ESC proliferation.

Application of the nuclear factor-kappaB inhibitor BAY 11-7085 for the treatment of endometriosis: an in vitro study

Most of the current medical treatments for endometriosis aim to downregulate estrogen activity. However, a high recurrence rate after medical treatment has been the most significant problem. BAY 11-7085, a soluble inhibitor of NK-kappaB activation, has been shown to inhibit cell proliferation and induce apoptosis of a variety of cells. To examine the potential application of BAY 11-7085 in the treatment of endometriosis, we investigated the effects of this agent on the cell proliferation and apoptosis of cultured ovarian endometriotic cyst stromal cells (ECSCs) by a modified methylthiazole tetrazolium assay, a 5-bromo-2'-deoxyuridine incorporation assay, and internucleosomal DNA fragmentation assays. The effect of BAY 11-7085 on the cell cycle of ECSCs was also determined by flow cytometry. The expression of apoptosis-related molecules was examined in ECSCs with Western blot analysis. BAY 11-7085 significantly inhibited the cell proliferation and DNA synthesis of ECSCs and induced apoptosis and the G0/G1 phase cell cycle arrest of these cells. Additionally, downregulation of the B-cell lymphoma/leukemia-2 (Bcl-2) and Bcl-X(L) expression with simultaneous activation of caspase-3, -8, and -9 was observed in ECSCs after treatment with BAY 11-7085. These results suggest that BAY 11-7085 induces apoptosis of ECSCs by suppressing antiapoptotic proteins, and that caspase-3-, -8-, and -9-mediated cascades are involved in this mechanism. Therefore, BAY 11-7085 could be used as a therapeutic agent for the treatment of endometriosis.

Serum cytokines as biomarkers for nonsurgical prediction of endometriosis

OBJECTIVE

To test the ability of a group of serum cytokines, either individually or in combination, to serve as biomarkers for the nonsurgical diagnosis of endometriosis.

STUDY DESIGN

Subjects were allocated to two groups according to their laparoscopic diagnosis. The first group consisted of patients with endometriosis and the second group was made up of infertile women with no pelvic pathology (controls). Blood samples were collected preoperatively and stored. Cytokines were measured in the serum of all participants using the Bio-Plex Protein Array System. Nonparametric statistics and the Mann-Whitney test were used to compare groups. Subjects were seen at the Gynecologic endoscopy unit.

RESULTS

Three cytokines were significantly higher in the serum of subjects with endometriosis than in the control group: interleukin-6 (IL-6) [4.41 pg/ml (range: 1.47-15.01) versus 0.97 pg/ml (range: 0.29-2.98), respectively; p<0.001], monocyte chemotactic protein-1 (MCP-1) [37.91 pg/ml (range: 24.54-94.74) versus 22.13 pg/ml (range: 13.85-39.45), respectively; p<0.001], and interferon-gamma (INF-gamma) [19.01 pg/ml (range: 1.19-73.52) versus 0.30 pg/ml (range: 0.00-13.05), respectively; p<0.001]. There was no statistically significant difference between subjects with endometriosis and controls in the serum concentration of vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha (TNF-alpha), or granulocyte macrophage colony stimulating factor (GM-CSF). Interleukin-2 (IL-2), interleukin-8 (IL-8), and interleukin-15 (IL-15) were undetectable in the serum of both groups. None of the measured cytokines showed significant correlation with the cycle phase or stage of endometriosis. In a multivariate analysis, serum interleukin-6 provided a sensitivity of 71% and a specificity of 66% to discriminate between endometriosis patients and controls at a cutoff point of 1.9 pg/ml. Adding monocyte chemotactic protein-1 and interferon-gamma to interleukin-6 did not increase the discriminative ability over that achieved by measuring serum interleukin-6 alone.

CONCLUSIONS

Serum of subjects with endometriosis contains significantly higher levels of interleukin-6, monocyte chemotactic protein-1, and interferon-gamma than control women. Serum interleukin-6 measurements discriminate between women with endometriosis and controls. Interleukin-6 provides a promising serum marker for the nonsurgical prediction of endometriosis.

A system-wide analysis of differentially expressed genes in ectopic and eutopic endometrium

BACKGROUND

Decades of research suggest that endometriosis is a complex disorder, with varying severity, onset and progression. Many genes have been associated with endometriosis through a number of studies and now microarray analyses have added to the list of perturbed or differentially regulated genes. Thus, it is difficult to see 'the big picture' without first integrating these multiple, heterogeneous sources of high-quality information for analysis.

METHODS

The goal of this study was to infer correlative and/or causal trends by combining empirical microarray analysis with a historical knowledge base of genetic relationships in endometriosis via a program called IRIDESCENT.

RESULTS

Importantly, we found a number of genes, which may have a central role in endometriosis, despite the fact that few or no past studies have reported these associations.

CONCLUSIONS

Several genes listed as non-responders on the microarray were found to be regulated post-transcriptionally, illustrating the importance of integrating multiple data sources.

Molecular profiling of experimental endometriosis identified gene expression patterns in common with human disease

OBJECTIVE

To validate a rat model of endometriosis using complimentary DNA (cDNA) microarrays by identifying common gene expression patterns between experimental and natural disease.

DESIGN

Autotransplantation rat model.

SETTING

Medical school department.

ANIMALS

Female Sprague-Dawley rats.

INTERVENTION(S)

Endometriosis was surgically induced by suturing uterine horn implants next to the small intestine's mesentery. Control rats received sutures with no implants. After 60 days, endometriotic implants and uterine horn were obtained.

MAIN OUTCOME MEASURE(S)

Gene expression levels determined by cDNA microarrays and real-time quantitative polymerase chain reaction (qPCR). The Cy5-labeled cDNA was synthesized from total RNA obtained from endometriotic implants. The Cy3-labeled cDNA was synthesized using uterine RNA from a control rat. Gene expression levels were analyzed after hybridizing experimental and control labeled cDNA to PIQOR (Parallel Identification and Quantification of RNAs) Toxicology Rat Microarrays (Miltenyi Biotec, Cologne, Germany) containing 1,252 known genes. The Cy5/Cy3 ratios were determined, and genes with >2-fold higher or <0.5-fold lower expression levels were selected. Microarray results were validated by QRT-PCR.

RESULT(S)

We observed differential expression of genes previously shown to be up-regulated in patients, including growth factors, inflammatory cytokines/receptors, tumor invasion/metastasis factors, adhesion molecules, and antiapoptotic factors.

CONCLUSION(S)

This study presents evidence in support of using this rat model to study the natural history of endometriosis and to test novel therapeutics for this incurable disease.

Endometriosis: an inflammatory disease with a Th2 immune response component

BACKGROUND

Efforts have been made to correctly characterize the role of the immune response in endometriosis. The objective of this study was to analyse the interaction between Th1 and Th2 immune response patterns and endometriosis by evaluating a panel of cytokines.

METHODS

Between January 2004 and November 2005, 98 patients, classified into two groups according to the histologically confirmed presence (Group A) or absence of endometriosis (Group B), were evaluated. Interleukins (IL) 2, 4 and 10, tumour necrosis factor-alpha and interferon-gamma (IFN-gamma) were measured by flow cytometry in the peripheral blood and peritoneal fluid of all patients.

RESULTS

IFN-gamma and IL-10 levels were significantly higher in the peritoneal fluid of patients with endometriosis compared to those without endometriosis (P < 0.05). There was a significant alteration in the IL-4/IFN-gamma (P < 0.001), IL-4/IL-2 (P = 0.006), IL-10/IFN-gamma (P < 0.001) and the IL-10/IL-2 ratios (P < 0.001) in the peritoneal fluid of patients with endometriosis, with a predominance of IL-4 and IL-10, reflecting a shift towards Th2 immune response despite the increase in IFN-gamma concentrations.

CONCLUSIONS

Endometriosis is an inflammatory disease involving a possible shift towards Th2 immune response component, as demonstrated by the relative increase in cytokines characteristic of this pattern of immune response.

Altered apoptosis and proliferation in endometrial stromal cells of women with adenomyosis

BACKGROUND

The eutopic endometrium in a woman suffering from adenomyosis is known to be biologically different from that of healthy women. The aim of this study was to examine the apoptosis and proliferation of eutopic endometrium from women with adenomyosis.

METHODS

We enrolled 23 women with adenomyosis (study group) and 21 without (control group). Eutopic endometrium was obtained and separated into single endometrial stromal cells (ESCs). ESCs were treated in vitro with hydrogen peroxide (H(2)O(2)) to examine their apoptosis using a fluorescence-activated cell sorter. Cells were also treated with estradiol (E(2)), medroxyprogesterone acetate, interleukin (IL)-6, lipopolysaccharide and interferon-gamma (IFN-gamma) to test their proliferation using a non-radioactive cell proliferation assay.

RESULTS

The percentage of annexin V ( + )/7-amino-actinomycin D ( + ) ESCs was much lower in women with adenomyosis after 24 h culture with and without H(2)O(2) treatment when compared with the control group. ESCs of adenomyosis proliferated more rapidly than those of the control group, whether they were cultured alone or were treated with E(2), MPA, IL-6 or IFN-gamma. The immunocytochemical Ki-67 labelling index was much more prominent in adenomyotic ESCs than that of the control group (7.7% versus 1.1%, P < 0.001).

CONCLUSIONS

Altered apoptosis and proliferation of eutopic endometrium possibly elucidate some aspects of the pathophysiology of adenomyosis. A high Ki-67 labelling index in immunocytochemistry might be a potential indicator in predicting the occurrence of adenomyosis.

Collagen gel contractility is enhanced in human endometriotic stromal cells: a possible mechanism underlying the pathogenesis of endometriosis-associated fibrosis

BACKGROUND

Excessive fibrosis is frequently associated with endometriosis. To evaluate the involvement of the extracellular matrix contractility of endometriotic stromal cells (ECSCs) in the pathogenesis of endometriosis-associated fibrosis, we compared the collagen gel contractility of cultured ECSCs with that of normal endometrial stromal cells. To clarify the mechanism underlying collagen gel contraction by ECSCs, we also evaluated the effect of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride, monohydrate (Y-27632), a selective Rho-associated coiled-coil-forming protein kinase (ROCK) inhibitor, on the collagen gel contraction by ECSCs.

METHODS AND RESULTS

ECSCs showed enhanced collagen gel contractility in comparison with NESCs. Myofibroblastic differentiation and the increased expression of fibronectin, RhoA, ROCK-I and ROCK-II proteins were observed with ECSCs using the 3D culture. Y-27632 significantly inhibited the collagen gel contractility of ECSCs without cytotoxicity.

CONCLUSIONS

The present findings suggest that the enhanced collagen contractility in ECSCs is associated with myofibroblastic differentiation, the increased expression of fibronectin and the activation of the Rho-ROCK-mediated signalling pathway, all of which may be involved in the pathogenesis of endometriosis-associated fibrosis. These results suggest that the inhibition of the Rho-ROCK-mediated signalling pathway may provide a novel strategy for the treatment of this disease. In addition, our experimental system of ECSCs using 3D collagen gel culture would be suitable for evaluating novel treatments for endometriosis.

Activation of mammalian target of rapamycin in postmenopausal ovarian endometriosis

The purpose of this study was to determine whether Akt and mammalian target of rapamycin (mTOR), downstream targets of phosphatidylinositol 3-kinase, are activated in endometriosis and ovarian cancer specimens. We measured total and phosphorylated levels of Akt and mTOR from 17 frozen ovarian cancers and 15 benign endometriosis specimens (nine from premenopausal women and six from postmenopausal women) by quantitation of signals from western blots using antibodies against these proteins. Elevated phospho-Akt was detected in ovarian cancer versus endometriosis specimens from premenopausal women and endometriosis specimens from postmenopausal women (2.3 +/- 0.45 versus 0.10 +/- 0.06 and 0.17 +/- 0.11; P < 0.05) when the western blot signal of activated kinase was normalized to total kinase levels. Elevated phospho-mTOR was detected in ovarian cancer and postmenopausal endometriosis versus premenopausal endometriosis (0.52 +/- 0.19 and 0.46 +/- 0.29 versus 0.13 +/- 0.08; P < 0.05). Expression of total kinases (normalized to beta-actin) was higher in carcinoma versus endometriosis specimens. Elevation of the active mTOR was specifically detected in postmenopausal endometriosis.

Comparison of RCAS1 and metallothionein expression and the presence and activity of immune cells in human ovarian and abdominal wall endometriomas

BACKGROUND

The coexistence of endometrial and immune cells during decidualization is preserved by the ability of endometrial cells to regulate the cytotoxic immune activity and their capability to be resistant to immune-mediated apoptosis. These phenomena enable the survival of endometrial ectopic cells. RCAS1 is responsible for regulation of cytotoxic activity. Metallothionein expression seems to protect endometrial cells against apoptosis. The aim of the present study was to evaluate RCAS1 and metallothionein expression in human ovarian and scar endometriomas in relation to the presence of immune cells and their activity.

METHODS

Metallothionein, RCAS1, CD25, CD69, CD56, CD16, CD68 antigen expression was assessed by immunohistochemistry in ovarian and scar endometriomas tissue samples which were obtained from 33 patients. The secretory endometrium was used as a control group (15 patients).

RESULTS

The lowest metallothionein expression was revealed in ovarian endometriomas in comparison to scar endometriomas and to the control group. RCAS1 expression was at the highest level in the secretory endometrium and it was at comparable levels in ovarian and scar endometriomas. Similarly, the number of CD56-positive cells was lower in scar and ovarian endometriomas than in the secretory endometrium. The highest number of macrophages was found in ovarian endometriomas. RCAS1-positive macrophages were observed only in ovarian endometriomas. CD25 and CD69 antigen expression was higher in scar and ovarian endometriomas than in the control group.

CONCLUSION

The expression of RCAS1 and metallothionein by endometrial cells may favor the persistence of these cells in ectopic localization both in scar following cesarean section and in ovarian endometriosis.

β-Hydroxyisovalerylshikonin induces apoptosis and G0/G1 cell-cycle arrest of endometriotic stromal cells: a preliminary in vitro study

BACKGROUND

Most of the current medical treatments for endometriosis aim to down-regulate the estrogen activity. However, a high recurrence rate after medical treatments has been the most significant problem. Beta-hydroxyisovalerylshikonin (beta-HIVS) is an ATP non-competitive inhibitor of protein-tyrosine kinases and is considered an apoptosis-inducing agent. The aim of this study is to evaluate the effects of beta-HIVS on the proliferation, cell cycle and apoptosis of endometriotic stromal cells.

METHODS

We investigated the effects of beta-HIVS on cultured ovarian endometriotic cyst stromal cells (ECSC) by a modified methylthiazoletetrazolium (MTT) assay, a 5-bromo-2'-deoxyuridine (BrdU) incorporation assay and internucleosomal DNA fragmentation assays. The effect of beta-HIVS on the cell cycle of ECSC was determined by flow cytometry. The expression of apoptosis-related molecules was examined in ECSC using western blot analysis.

RESULTS

Beta-HIVS significantly inhibited the proliferation and DNA synthesis of ECSC and induced apoptosis and G0/G1 phase cell-cycle arrest of these cells. Down-regulation of the B-cell lymphoma/leukaemia-2 (Bcl-2) expression with the activation of caspase-3, caspase-8 and caspase-9 was observed in ECSC after beta-HIVS treatment.

CONCLUSIONS

These results suggest that beta-HIVS induces apoptosis of ECSC by suppressing anti-apoptotic proteins. Although our present findings are preliminary, beta-HIVS could potentially be a therapeutic agent for the treatment of endometriosis.

Bufalin induces apoptosis and the G0/G1 cell cycle arrest of endometriotic stromal cells: a promising agent for the treatment of endometriosis

Most of the current medical treatments for endometriosis aim to down-regulate the estrogen activity. However, a high recurrence rate after medical treatments has been the most significant problem. Bufalin is a major digoxin-like immunoreactive component isolated from the skin and parotid venom glands of toad and is considered an apoptosis-inducing agent. To apply bufalin to the medical treatment of endometriosis, we investigated the effects of this agent on the cell proliferation and apoptosis of cultured ovarian endometriotic cyst stromal cells (ECSC) by a modified methylthiazoletetrazolium (MTT) assay, a 5-bromo-2'-deoxyuridine (BrdU) incorporation assay and internucleosomal DNA fragmentation assays. The effect of bufalin on the cell cycle of ECSC was also determined by flow cytometry. The expression of apoptosis- and cell cycle-related molecules was also examined in ECSC using Western blot analysis. Bufalin significantly inhibited the cell proliferation and DNA synthesis of ECSC and induced apoptosis and the G0/G1 phase cell cycle arrest of these cells. The down-regulation of the cyclin A, Bcl-2, and Bcl-X(L) expression with the simultaneous up-regulation of the p21 and Bax expression, and caspase-9 activation was observed in ECSC after bufalin treatment. It is suggested that bufalin induces apoptosis of ECSC by simultaneously suppressing anti-apoptotic proteins and inducing pro-apoptotic proteins. Caspase-9-mediated cascade is involved in this mechanism. Therefore, bufalin could be used as a therapeutic agent for the treatment of endometriosis.