Technical Verification and Assessment of Independent Validation of Biomarker Models for Endometriosis.

There is a great need for a noninvasive diagnosis for endometriosis. Several biomarkers and biomarker panels have been proposed. Biomarker models consisting of CA-125, VEGF, Annexin V, and glycodelin/sICAM-1 were previously developed by our group. The objective of our current study was to assess the impact of technical and biological variability on the performance of those previously developed prediction models in a technical verification and a validation setting. The technical verification cohort consisted of peripheral blood plasma samples from a subset of the patients included in the original study of Vodolazkaia et al. (99 women with and 37 women without endometriosis). The validation study was done in plasma samples of an independent patient cohort (170 women with and 86 women without endometriosis). Single immunoassays were used for CA-125, VEGF-A, sICAM-1, Annexin V, and glycodelin. Statistical analyses were done using univariate and multivariate (logistic regression) approaches. The previously reported prediction models for endometriosis had a low performance in both the technical verification and validation setting. New prediction models were developed, which included CA-125, Annexin V, and sICAM-1, but CA-125 was the only marker that was retained in the models across the technical verification and validation study. Overall, successful validation of a biomarker model depends on several factors such as patient selection, collection methods, assay selection/handling, stability of the marker, and statistical analysis and interpretation. There is a need for standardized studies in large, well-defined patient cohorts with robust assay methodologies.

Telomerase Reverse Transcriptase Expression in Mouse Endometrium During Reepithelialization and Regeneration in a Menses-Like Model.

The regenerative capacity of the endometrium has been attributed to resident stem/progenitor cells. A number of stem/progenitor markers have been reported for human endometrial stem/progenitor cells; however, the lack of convenient markers in the mouse has made experimental investigation into endometrial regeneration difficult. We recently identified endometrial epithelial, endothelial, and immune cells, which express a reporter for the stem/progenitor marker, mouse telomerase reverse transcriptase (mTert). In this study, we investigate the expression pattern of a green fluorescent protein (GFP) reporter for mTert promoter activity (mTert-GFP) in endometrial regeneration following a menses-like event. mTert-GFP expression marks subepithelial populations of T cells and mature macrophages and may play a role in immune cell regulated repair. Clusters of mTert-GFP-positive epithelial cells were identified close to areas of reepithelialization and possibly highlight a role for mTert in the repair and regeneration of the endometrial epithelium.

Functional Expression of TRP Ion Channels in Endometrial Stromal Cells of Endometriosis Patients.

Endometriosis is a common gynecological disease that is characterized by the presence of functional endometrial-like lesions in the abdominal cavity. Aside from epithelial cells, these lesions consist of stromal cells that have the capacity to migrate, adhere, proliferate, and induce neuro- and lymphangiogenesis, which allows them to survive at ectopic locations. However, the exact underlying mechanisms that regulate these changes are yet to be elucidated. The common ground of these processes, however, is the second messenger, calcium. In this regard, members of the superfamily of transient receptor potential (TRP) ion channels, which are known to be calcium-permeable and expressed in the endometrium, have emerged as key regulators. Here, we assessed the molecular and functional expression of TRP channels in stromal cells isolated from the eutopic endometrium of endometriosis patients and controls. Using RT-qPCR, high mRNA levels of TRPV2, TRPV4, TRPM4, TRPM7, TRPC1, TRPC3, TRPC4, and TRPC6 were observed in the whole endometrium throughout the menstrual cycle. Additionally, and in line with previous reports of control patients, TRPV2, TRPV4, TRPC1/4, and TRPC6 were present in human endometrial stromal cells (hESC) from endometriosis patients both at the molecular and functional level. Moreover, proliferation and migration assays illustrated that these parameters were not affected in stromal cells from endometriosis patients. Furthermore, comparison between eutopic and ectopic endometrial samples revealed that the RNA expression pattern of TRP channels did not differ significantly. Collectively, although a functional expression of specific ion channels in hESCs was found, their expression did not correlate with endometriosis.

Noninvasive diagnosis of endometriosis: Review of current peripheral blood and endometrial biomarkers.

A noninvasive biomarker-based test could help shorten the diagnostic delay for endometriosis. The most investigated biomarker sources are peripheral blood and endometrium. Discovery of endometriosis biomarkers is often hypothesis-driven, i.e. when one or a few biomarkers are investigated based on their role in the disease pathogenesis. Alternatively, a hypothesis-generating approach has been followed using the "omics" technologies. A variety of biomarkers for endometriosis have been investigated, but no biomarker has been validated for clinical use. Many challenges lie ahead in the endometriosis biomarker field. In the future, harmonized collection and reporting methods should allow large-scale international collaboration for highly powered studies.

Endometrial stem/progenitor cells and their role in the pathogenesis of endometriosis.

Human endometrium regenerates on a cyclical basis each month, likely mediated by endometrial stem/progenitor cells. Several types of stem/progenitor cells have been identified: CD140b+CD146+ or SUSD2+ endometrial mesenchymal stem cells (eMSCs), N-cadherin+ endometrial epithelial progenitor cells (eEPs), and side population (SP) cells, a heterogeneous population predominantly comprising endothelial cells. eMSCs reside in a perivascular niche and likely mediate angiogenesis and stromal regeneration. Human eEPs are located in the bases of glands in the basalis and are likely more primitive than SSEA-1+ basalis epithelial cells. Endometrial stem/progenitor cells may contribute to the pathogenesis of endometriosis by their retrograde shedding into the pelvic cavity, either after menarche or as a result of neonatal uterine bleeding. eMSCs may have a role in the generation of progesterone-resistant phenotype of endometrial stromal fibroblasts (eSFs) in endometriosis. In future clinical practice, endometrial stem/progenitor cells may be used to establish diagnosis of endometriosis or as therapeutic targets.

Of Mice and Women: A Laparoscopic Mouse Model for Endometriosis.

STUDY OBJECTIVE: To demonstrate how a novel laparoscopic approach allows the development of a mouse model for endometriosis after seeding menstrual endometrium from donor mice into the abdominal cavity of syngeneic recipient mice. DESIGN: A step-by-step video description of the techniques used to adapt the estrous cycle of mice towards a menstrual cycle and to subsequently induce endometriosis via laparoscopic seeding of menstrual endometrium. SETTING: University research institute. ETHICS: All animal experiments were ethically approved by KU Leuven, Belgium (ethical approval number: P031/2013). INTERVENTIONS, MEASUREMENTS, AND MAIN RESULTS: Oophorectomized female C57BL/6JRj mice received a series of estrogen injections. Next, a progesterone pellet was administered, together with a second series of estrogen injections. In addition, decidualization of the endometrium was induced with an intrauterine sesame oil stimulus. Four days later the progesterone pellet was removed and menstruation started [1]. Five hours after the progesterone pellet was removal the uterus was harvested, and the menstrual endometrium was dissected and seeded into the abdominal cavity of syngeneic recipient mice to induce endometriosis [2] using a laparoscopic approach [3]. Uterus and lesions were removed from the recipient mice 1 week after induction, and tissues were immunohistochemically stained for H&E, vimentin, and cytokeratin. CONCLUSION: In this video we show a novel methodology to induce endometriosis in mice using laparoscopic inoculation of syngeneic menstrual endometrium, mimicking Sampson's theory of retrograde menstruation [4]. Compared with currently available rodent models, our model offers a less invasive and more physiologic way for fundamental and preclinical endometriosis research, with a high endometriosis incidence and lesion take rate.

Evaluation of Total, Active, and Specific Myeloperoxidase Levels in Women with and without Endometriosis.

Myeloperoxidase (MPO) is a proinflammatory enzyme and a marker for neutrophil activation and oxidative stress. Since oxidative stress and inflammation are linked to the pathogenesis of endometriosis, we hypothesized that the total, active, and specific (active/total) MPO levels were significantly different in plasma of women with and without endometriosis. Samples were selected from our biobank from women with endometriosis (n = 212) and controls without endometriosis (n = 121) across the menstrual cycle. Total MPO plasma levels were measured by immunoassay and MPO activity by enzymatic assay. Total and active MPO levels did not differ significantly among endometriosis cases and controls, whereas the specific MPO activity was significantly lower in women with endometriosis than that in controls (p = 0.0159). After the subdivision of control patients into women with a normal pelvis and women with other benign gynecological disorders, a significant difference was observed only between women with endometriosis and women with other benign gynecological disorders (p = 0.0266). In conclusion, systemic MPO levels may not be suited as a single biomarker for endometriosis. Our data support the involvement of MPO in other gynecological disorders but do not provide any evidence for an association with endometriosis.

Endometriosis is associated with aberrant metabolite profiles in plasma.

OBJECTIVE: To identify metabolites that are associated with and predict the presence of endometriosis. DESIGN: Metabolomics study using state-of-the-art mass spectrometry approaches. SETTING: University hospital and universities. PATIENT(S): Twenty-five women with laparoscopically confirmed endometriosis (cases) and 19 women with laparoscopically documented absence of endometriosis (controls). None of the women included in this study had received oral contraception or GnRH agonists for a minimum of 1 month before blood collection. INTERVENTION(S): Plasma collection. MAIN OUTCOME MEASURE(S): Metabolite profiles were generated and interrogated using multiple mass spectrometry methods, that is, high performance liquid chromatography coupled with negative mode electrospray ionization tandem mass spectrometry, UPLC-MS/MS, and ultra performance liquid chromatography-electroSpray ionization-quadrupole time-of-flight (UPLC-ESI-Q-TOF). Metabolite groups investigated included phospholipids, glycerophospholipids, ether-phospholipids, cholesterol-esters, triacylglycerol, sphingolipids, free fatty acids, steroids, eicosanoids, and acylcarnitines. RESULT(S): A panel of acylcarnitines predicted the presence of endometriosis with 88.9% specificity and 81.5% sensitivity in human plasma, with a positive predictive value of 75%. However, due to data limitations the outcome of the receiver operating characteristic curve analysis was not significant. CONCLUSION(S): A diagnostic model based on acylcarnitines has the potential to predict the presence and stage of endometriosis.

The Presence of Endometrial Cells in Peritoneal Fluid of Women With and Without Endometriosis.

To reinforce Sampson's theory of retrograde menstruation in the pathogenesis of endometriosis, proof should be provided that during menstruation endometrial cells are present in peritoneal fluid (PF). We hypothesize that the prevalence of PF samples containing endometrial cells is higher in patients with endometriosis than in controls without endometriosis during menstruation. We selected from our biobank PF samples of 17 reproductive-age women with (n = 9) or without (n = 8) endometriosis who had received a diagnostic laparoscopy for investigation of pain/infertility. Peritoneal fluid had been collected during laparoscopy in the menstrual phase of the cycle, centrifuged, and the resulting pellet was stored at -80°C. About 5-µm sections of frozen PF pellets were stained using the Dako Envision Flex system with primary antibodies against epithelial cell adhesion molecule (Ep-CAM; endometrial epithelial cells), CD10 (endometrial stromal cells), prekeratin (epithelial/mesothelial cells), vimentin (endometrial/mesothelial/immune cells), calretinin (mesothelial cells), and CD68 (macrophages). The PF cells positive for Ep-CAM were detected in 5 of 9 patients with endometriosis and 6 of 8 controls ( P = .62). CD10 stained positively in 6 of the 9 patients with endometriosis and 3 of the 8 controls ( P = .35). Calretinin and prekeratin staining showed the presence of mesothelial cells in all pellets. Vimentin stained approximately 100% of the PF cells. CD68+ macrophages represented >50% of cells in all pellets. The prevalence of PF samples containing endometrial epithelial and stromal cells was not higher in patients with endometriosis than in controls without endometriosis during menstruation. Our findings question the relevance of endometrial cells in PF for the pathogenesis of endometriosis and support the importance of other mechanisms such as immune dysfunction and/or endometrial stem cells.

Multiplex immunoassays in endometriosis: An array of possibilities.

Multiplex immunoassays range from small-scaled multiplex sandwich ELISAs in a planar or bead-based format to the more expanded antibody arrays employing direct sample labeling. The plethora of data generated from these arrays could be of great interest to understand a complex disorder such as endometriosis. Multiplex immunoassay analysis may provide information on disease pathology and may lead to improved, timely diagnosis. Until now, the use of multiplex immunoassays has been limited in endometriosis. With the constant development of multiplex technologies, future studies should focus on implementing these techniques, and combining them with multivariate statistical analysis. In this review, we provide an overview of multiplex immunoassay methods used in endometriosis studies and the data sets acquired by these methodologies. These data and future studies might provide novel insights for biomarker discovery and investigation of the pathogenesis in endometriosis.

Laparoscopic Surgery: A New Technique to Induce Endometriosis in a Mouse Model.

BACKGROUND: This prospective pilot study was designed to induce endometriosis in a mouse model using laparoscopy, a less invasive and more precise approach than laparotomy. We aimed to achieve a peritoneal implant rate of at least 50% by varying both duration of anesthesia and intra-abdominal insufflation pressure. METHODS: Female BALB/cANnCrl mice in metestrus or diestrus were used as donors (n = 5) or recipients (n = 20) of uterine transplant tissue. Each recipient mouse was laparoscopically inoculated with 10 uterine pieces (range: 10-12) from donor mice into the abdominal cavity. Before starting the study, recipient mice were randomly assigned to 4 groups with variable duration of anesthesia (ketamine/xylazine or pentobarbital) and variable intra-abdominal pressure (5 or 15 mm Hg). One week after laparoscopy, endometriosis incidence and peritoneal implant take rate were documented visually during laparotomy. The retrieved lesions were histologically analyzed. RESULTS: Laparoscopic inoculation of uterine pieces in recipient mice resulted in an endometriosis incidence of 100% (20/20 animals) and an individual peritoneal implant take rate of 60% (121/206), ranging from 17% (2/12) till 83% (10/12), without differences between the 4 subgroups, and with a histological confirmation rate of 92% (58/63). CONCLUSIONS: To the best our knowledge, this is the first report showing that endometriosis can be induced by laparoscopic surgery in rodents, with a 100% incidence and a median peritoneal implant take rate of 60%. This laparoscopic model offers important advantages over traditional laparotomy models that are limited by surgery-associated trauma and/or adhesion formation.

Update on Biomarkers for the Detection of Endometriosis.

Endometriosis is histologically characterized by the displacement of endometrial tissue to extrauterine locations including the pelvic peritoneum, ovaries, and bowel. An important cause of infertility and pelvic pain, the individual and global socioeconomic burden of endometriosis is significant. Laparoscopy remains the gold standard for the diagnosis of the condition. However, the invasive nature of surgery, coupled with the lack of a laboratory biomarker for the disease, results in a mean latency of 7-11 years from onset of symptoms to definitive diagnosis. Unfortunately, the delay in diagnosis may have significant consequences in terms of disease progression. The discovery of a sufficiently sensitive and specific biomarker for the nonsurgical detection of endometriosis promises earlier diagnosis and prevention of deleterious sequelae and represents a clear research priority. In this review, we describe and discuss the current status of biomarkers of endometriosis in plasma, urine, and endometrium.

Sox9 reprogrammed dermal fibroblasts undergo hypertrophic differentiation in vitro and trigger endochondral ossification in vivo.

Strategies for bone regeneration are undergoing a paradigm shift, moving away from the replication of end-stage bone tissue and instead aiming to recapture the initial events of fracture repair. Although this is known to resemble endochondral bone formation, chondrogenic cell types with favorable proliferative and hypertrophic differentiation properties are lacking. Recent advances in cellular reprogramming have allowed the creation of alternative cell populations with specific properties through the forced expression of transcription factors. Herein, we investigated the in vitro hypertrophic differentiation and in vivo tissue formation capacity of induced chondrogenic cells (iChon cells) obtained through direct reprogramming. In vitro hypertrophic differentiation was detected in iChon cells that contained a doxycycline-inducible expression system for Klf4, cMyc, and Sox9. Furthermore, endochondral bone formation was detected after implantation in nude mice. The bone tissue was derived entirely from host origin, whereas cartilage tissue contained cells from both host and donor. The results obtained highlight the promise of cellular reprogramming for the creation of functional skeletal cells that can be used for novel bone healing strategies.