Overexpression of nerve growth factor in peritoneal fluid from women with endometriosis may promote neurite outgrowth in endometriotic lesions

Targeting NGF but not VEGFR1 or BDNF signaling reduces endometriosis-associated pain in mice

INTRODUCTION

Endometriosis is a chronic inflammatory disease that affects ∼ 10 % of women. A significant fraction of patients experience limited or no efficacy with current therapies. Tissue adjacent to endometriosis lesions often exhibits increased neurite and vascular density, suggesting that disease pathology involves neurotrophic activity and angiogenesis.

OBJECTIVES

We aim to evaluate the potential for key tyrosine-kinase-receptor-coupled neurotrophic molecules to contribute to endometriosis-associated pain in mice.

METHODS

Peritoneal fluid was collected from endometriosis patients undergoing surgery and the levels of NGF and VEGFR1 regulators (VEGFA, VEGFB, PLGF, and sVEGFR1) were quantified by ELISA. VEGFR1 regulator concentrations were used to calculate VEGFR1 occupancy. We used genetic depletion, neutralizing antibodies, and pharmacological approaches to specifically block neurotrophic ligands (NGF or BDNF) or receptors (VEGFR1, TRKs) in a murine model of endometriosis-associated pain. Endometriosis-associated pain was measured using von Frey filaments, quantification of spontaneous abdominal pain-related behavior, and thermal discomfort. Disease parameters were evaluated by lesion size and prevalence. To evaluate potential toxicity, we measured the effect of entrectinib dose and schedule on body weight, liver and kidney function, and bone structure (via micro-CT).

RESULTS

We found that entrectinib (pan-Trk inhibitor) or anti-NGF treatments reduced evoked pain, spontaneous pain, and thermal discomfort. In contrast, even though calculated receptor occupancy revealed that VEGFR1 agonist levels are sufficient to support signaling, blocking VEGFR1 via antibody or tamoxifen-induced knockout did not reduce pain or lesion size in mice. Targeting BDNF-TrkB with an anti-BDNF antibody also proved ineffective. Notably, changing dosing schedule to once weekly eliminated entrectinib-induced bone-loss without decreasing efficacy against pain.

CONCLUSIONS

This suggests NGF-TrkA signaling, but not BDNF-TrkB or VEGF-VEGFR1, mediates endometriosis-associated pain. Moreover, entrectinib blocks endometriosis-associated pain and reduces lesion sizes. Our results also indicated that entrectinib-like molecules are promising candidates for endometriosis treatment.

Musculoskeletal evaluation of the lower pelvic complex in women with endometriosis: A case-control study

OBJECTIVE

Use clinical pain measurement tools to investigate and compare the prevalence of pelvic loin disoders in women with and without endometriosis.

STUDY DESIGN

Chronic pelvic pain (CPP) associated with endometriosis has diverse origins, including musculoskeletal factors. Musculoskeletal dysfunction in the pelvic region is theorized to result from sustained muscular contraction, triggered by altered visceral stimuli and adoption of antalgic postures, causing secondary damage to muscles, ligaments, and joints. CPP significantly impacts quality of life, relationships, sexuality, and mental health. However, limited data exists on musculoskeletal impacts of endometriosis and CPP. It was made a case-control study at Maternidade Escola Assis Chateaubriand from August 2017 to January 2021. Evaluated 71 women: 41 in endometriosis group (EG) and 30 in control group (CG). Data collection included sociodemographic questionnaires, musculoskeletal physiotherapeutic evaluations, pain mapping, pressure pain thresholds, kinesiophobia, and disability measurements. Statistical analysis was performed using Spearman's Rho test to determine correlations.

RESULTS

Mean age of participants was 31 years. EG exhibited lower pain threshold variations in lumbopelvic trigger points than CG (P < .05). Significant muscle flexibility differences between groups were observed; EG had reduced flexibility (P < .05). Most common pain areas were hypogastrium in EG (48.78 %) and left lumbar in CG (30 %). EG had higher kinesiophobia values (P = .009). There was a weak association between kinesiophobia-pressure threshold association observed in CG's lumbar pelvic region.

CONCLUSION

Women with Endometriosis and CPP exhibit higher prevalence of musculoskeletal disorder, lower pain thresholds, decreased lumbopelvic muscle range of motion, higher kinesiophobia scores, and increased disability indices with low back pain compared to healthy women.

Endometriosis, Pain, and Related Psychological Disorders: Unveiling the Interplay among the Microbiome, Inflammation, and Oxidative Stress as a Common Thread

Endometriosis (EM), a chronic condition in endometrial tissue outside the uterus, affects around 10% of reproductive-age women, significantly affecting fertility. Its prevalence remains elusive due to the surgical confirmation needed for diagnosis. Manifesting with a range of symptoms, including dysmenorrhea, dyschezia, dysuria, dyspareunia, fatigue, and gastrointestinal discomfort, EM significantly impairs quality of life due to severe chronic pelvic pain (CPP). Psychological manifestations, notably depression and anxiety, frequently accompany the physical symptoms, with CPP serving as a key mediator. Pain stems from endometrial lesions, involving oxidative stress, neuroinflammation, angiogenesis, and sensitization processes. Microbial dysbiosis appears to be crucial in the inflammatory mechanisms underlying EM and associated CPP, as well as psychological symptoms. In this scenario, dietary interventions and nutritional supplements could help manage EM symptoms by targeting inflammation, oxidative stress, and the microbiome. Our manuscript starts by delving into the complex relationship between EM pain and psychological comorbidities. It subsequently addresses the emerging roles of the microbiome, inflammation, and oxidative stress as common links among these abovementioned conditions. Furthermore, the review explores how dietary and nutritional interventions may influence the composition and function of the microbiome, reduce inflammation and oxidative stress, alleviate pain, and potentially affect EM-associated psychological disorders.

GPR30-mediated non-classic estrogen pathway in mast cells participates in endometriosis pain via the production of FGF2

Pain is one of the main clinical symptoms of endometriosis, but its underlying mechanism is still not clear. Recent studies have shown that the secretory mediators of mast cells activated by estrogen are involved in the pathogenesis of endometriosis-related pain, but how estrogen-induced mast cell mediators are involved in endometriosis-related pain remains unclear. Here, mast cells were found to be increased in the ovarian endometriotic lesions of patients. They were also closely located closely to the nerve fibers in the ovarian endometriotic lesions from of patients with pain symptoms. Moreover, fibroblast growth factor 2 (FGF2)-positive mast cells were upregulated in endometriotic lesions. The concentration of FGF2 in ascites and the protein level of fibroblast growth factor receptor 1 (FGFR1) were higher in patients with endometriosis than in those without endometriosis, and they were correlated with pain symptoms. In vitro, estrogen could promote the secretion of FGF2 through G-protein-coupled estrogen receptor 30 (GPR30) via the MEK/ERK pathway in rodent mast cells. Estrogen-stimulated mast cells enhanced the concentration of FGF2 in endometriotic lesions and aggravated endometriosis-related pain in vivo. Targeted inhibition of the FGF2 receptor significantly restrained the neurite outgrowth and calcium influx in dorsal root ganglion (DRG) cells. Administration of FGFR1 inhibitor remarkably elevated the mechanical pain threshold (MPT) and prolonged the heat source latency (HSL) in a rat model of endometriosis. These results suggested that the up-regulated production of FGF2 by mast cells through non-classic estrogen receptor GPR30 plays a vital role in the pathogenesis of endometriosis-related pain.

Cracking the enigma of adenomyosis: an update on its pathogenesis and pathophysiology

In brief

Traditionally viewed as enigmatic and elusive, adenomyosis is a fairly common gynecological disease but is under-recognized and under-researched. This review summarizes the latest development on the pathogenesis and pathophysiology of adenomyosis, which have important implications for imaging diagnosis of the disease and for the development of non-hormonal therapeutics.

Abstract

Traditionally considered as an enigmatic disease, adenomyosis is a uterine disease that affects many women of reproductive age and is a contributing factor for pelvic pain, heavy menstrual bleeding (HMB), and subfertility. In this review, the new development in the pathogenesis and pathophysiology of adenomyosis has been summarized, along with their clinical implications. After reviewing the progress in our understanding of the pathogenesis and describing the prevailing theories, in conjunction with their deficiencies, a new hypothesis, called endometrial-myometrial interface disruption (EMID), which is backed by extensive epidemiologic data and demonstrated by a mouse model, is reviewed, along with recent data implicating the role of Schwann cells in the EMI area in the genesis of adenomyosis. Additionally, the natural history of adenomyotic lesions is elaborated and underscores that, in essence, adenomyotic lesions are fundamentally wounds undergoing repeated tissue injury and repair (ReTIAR), which progress to fibrosis through epithelial-mesenchymal transition, fibroblast-to-myofibroblast transdifferentiation, and smooth muscle metaplasia. Increasing lesional fibrosis propagates into the neighboring EMI and endometrium. The increased endometrial fibrosis, with ensuing greater tissue stiffness, results in attenuated prostaglandin E2, hypoxia signaling and glycolysis, impairing endometrial repair and causing HMB. Compared with adenomyosis-associated HMB, the mechanisms underlying adenomyosis-associated pain are less understood but presumably involve increased uterine contractility, hyperinnervation, increased lesional production of pain mediators, and central sensitization. Viewed through the prism of ReTIAR, a new imaging technique can be used to diagnose adenomyosis more accurately and informatively and possibly help to choose the best treatment modality.

Is primary dysmenorrhea a precursor of future endometriosis development?

Primary dysmenorrhea (PD) is the most common gynecologic disorder during adolescence and it is characterized by crampy lower abdominal pain that occurs during menstruation. Secondary dysmenorrhea, in contrast, has the same clinical features but occurs in women with a disease that could account for their symptoms (endometriosis, adenomyosis, uterine fibroids, pelvic inflammatory disease). Endometriosis is the most common cause of secondary dysmenorrhea and it should be considered in patients with persistent and clinically significant dysmenorrhea despite treatment. It is often diagnosed after a long delay, increasing the likelihood of pain chronicity and fertility problems at a later age. Women who suffer from dysmenorrhea in adolescence have higher risk of endometriosis in future. The open question is if endometriosis was already present at the onset of dysmenorrhea but undiagnosed or if PD favors subsequent development of endometriosis-associated pain. Since PD is associated with higher risk for developing chronic pain state and shares some of the same pain pathways of endometriosis (prostaglandins overproduction, inflammation, peripheral sensitization, central sensitization and abnormal stress responses), a correlation between PD and endometriosis is suggested. To know whether it is a risk factor for the development of endometriosis-associated pain may provide an opportunity for early intervention and prevention. The present review aims to investigate the clinical and pathogenetic features of PD and endometriosis in order to identify a possible association between the two conditions.

Widespread Pain Hypersensitivity and Lumbopelvic Impairments in Women Diagnosed with Endometriosis

OBJECTIVE

To explore hypersensitivity to pain and musculoskeletal impairments in the lumbopelvic area in women with and without endometriosis.

METHODS

This cross-sectional study included 66 women (41 women with endometriosis and 25 healthy women). Pain and related catastrophizing thoughts were assessed through a numeric rating scale, pressure pain thresholds (PPTs), the slump test, and the Pain Catastrophizing Scale. Lumbopelvic muscles were evaluated through ultrasound imaging, flexor/extensor resistance tests, and the lumbopelvic stability test.

RESULTS

Women with endometriosis showed increased self-reported intensity of current pelvic pain (CuPP), reduced local PPTs (42.8-64.7% in the affected area, P-value <.001) and higher prevalence of lumbar nerve root impingement/irritation pain and catastrophizing thoughts (P-value ≤.002). Moreover, affected women showed decreased thickness of transversus abdominis, reduced resistance of flexor and extensor trunk muscles and lower lumbopelvic stability (P-values <.030). Endometriosis stage and severity of CuPP were related to worse results in these parameters.

CONCLUSIONS

The presence of pain sensitization signs and lumbopelvic impairments, more pronounced in patients with stage IV endometriosis and moderate/severe CuPP, warrants the development of rehabilitation interventions targeting pain and lumbopelvic impairments in women with endometriosis.

When and how should peritoneal endometriosis be operated on in order to improve fertility rates and symptoms? The experience and outcomes of nearly 100 cases

Purpose

To analyze the follow-up results of patients suffering from symptomatic early-stage endometriosis after a consistent laparoscopic peritoneal stripping of the altered peritoneum (peritoneal endometriosis and surrounding inflamed tissue) was performed. This type of endometriosis is resistant to medical therapy and/or impairs fertility.

Methods

Using our prospectively maintained database, we were able to identify all symptomatic women with the suspicion of only peritoneal endometriosis who underwent laparoscopy at our endometriosis center over a period of 5 years. All procedures were carried out in a standardized fashion by one single surgeon, who is highly experienced in minimal invasive surgery, and included a suspended hormonal pretreatment for 2 months. Postoperative outcomes including complications, fertility and recurrence rates were analysed.

Results

Laparoscopic peritonectomy was performed on 94 women. Follow-up data were available in 87% of these cases. At the time of surgery, almost all patients tested showed signs of stage I or II endometriosis (44.7 and 48.9%, respectively). More than three-quarters of the women reported pain relief, inter alia, due to the post-surgical hormonal therapy. About one-third of the patients wanted to have children after the procedure. 62% of them became pregnant and the majority did so without the need for assisted reproductive therapy. In seven women a re-operation was performed.

Conclusion

According to our data, a consistent excision of altered peritoneum followed by adjuvant hormonal therapy and multimodal concepts results in better outcomes for the patient, particularly in regards to pregnancy and recurrence rates.

Novel Medicine for Endometriosis and Its Therapeutic Effect in a Mouse Model

Current therapeutic medicines for endometriosis cannot be administered during assisted reproductive technology (ART) because they have bad effects during pregnancy. In this study, we created an animal model of endometriosis and evaluated the therapeutic effect of progestin (Dienogest), dopamine agonist (Cabergoline), and their combination (Dienogest + Cabergoline). We established a mouse model mimicking human endometriosis. The mice with endometriosis were then treated with a single drug (Dienogest or Cabergoline) or both drugs (Dienogest + Cabergoline) for 14 days. An immunohistological study was then performed to analyze inflammatory lesions in the recipient mice. Real-time polymerase chain reaction (RT-PCR) and Western blotting were also performed to determine the levels of genes and proteins in inflammatory lesions to assess the recovery of endometriosis. Histologic staining showed that all medication groups showed a clear decrease in the inflammatory phenotype in the uterus, peritoneum, and intestine. Gene and protein expression analysis showed a therapeutic effect in all medication groups. In conclusion, Cabergoline had a therapeutic effect similar to that of Dienogest and could be used as an alternative to Dienogest during ART for patients with infertility; compared to the individual drugs, the combination treatment has a synergistic effect on endometriosis.

Expression of nerve growth factor (NGF) in endometrium as a potential biomarker for endometriosis - Single tertiary care centre study

OBJECTIVE

to identify novel biomarkers for peritoneal endometriosis in eutopic endometrium thus giving an oportunity for non-invasive diagnosis.

DESIGN

A cross-sectional single-center study SETTING: tertiary care hospital PATIENTS: 49 patients subjected to laparoscopy because of suspected endometriosis, 33 patients out of the group qualified to the study had sufficient endometrial tissue taken and were in their follicular phase of menstrual cycle.

INTERVENTIONS

biopsy sampling of eutopic endometrial tissue during diagnostic or diagnostic and terapeutic laparoscopy, questionaires, MAIN OUTCOME MEASURE(S): qRT-PCR to evaluate the mRNA expression of selected candidate marker genes in endometrium: ARO1 (aromatase), CXCL8 (interleukin 8), NGF (nerve growth factor), VEGF-A (vascular endothelial growth factor A), PDGF-A (platelet-derived growth factor A).

RESULTS

mRNA expression of ARO1, CXCL8, VEGF-A and PDGF-A did not differ significantly between women with and without endometriosis. NGF mRNA expression was decreased in women with endometriosis.

CONCLUSIONS

Observed preliminary results suggest a possible role of NGF in early diagnosis of peritoneal endometriosis. The role of NGF changes in eutopic endometrium of patients with peritoneal endometriosis needs further evaluation.

Challenges in uncovering non-invasive biomarkers of endometriosis

Endometriosis affects up to 10% of women of childbearing age, causing symptoms that can include chronic pelvic pain and reduced fertility. The symptoms are not specific to the disease and can be confused with other gynecological conditions or normal menstruation. Currently, the disease can be only definitively diagnosed by laparoscopy, as no clinically accepted biomarker exists. Biomarker discovery can either follow a hypothesis-driven approach selecting targets to be tested based on current knowledge of the disease, or take an unbiased high-throughput screening “omics” approach, such as transcriptomics or proteomics, to identify markers that are unique or elevated in accessible bodily fluids of patients with the disease. Numerous studies have been conducted using these approaches to try and identify endometriosis biomarkers, but variabilities in study design, cohort selection, and analysis, together with the fact that most studies were small-scale, have made independent validation of biomarker candidates difficult. Therefore, efforts are underway to standardize cohort selection, patient data, and sample collection to allow better cross-study comparisons. Large scale multi-center studies using this standardized approach are necessary to validate existing endometriosis biomarker candidates and uncover potential new markers. Given the complexity and heterogeneity of the disease, it is likely that a panel of biomarkers will be necessary to diagnose and categorize endometriosis.

Endometriosis-Associated Pain - Do Preclinical Rodent Models Provide a Good Platform for Translation?

Pelvic pain is a common symptom of endometriosis. Our understanding of its etiology remains incomplete and medical management is limited by poor translation from preclinical models to clinical trials. In this review, we briefly consider the evidence, or lack thereof, that different subtypes of lesion, extra-uterine bleeding, and neuropathic pathways add to the complex and heterogeneous pain experience of women with the condition. We summarize the studies in rodent models of endometriosis that have used behavioral endpoints (evoked and non-evoked) to explore mechanisms of endometriosis-associated pain. Lesion innervation, activation of nerves by pronociceptive molecules released by immune cells, and a role for estrogen in modulating hyperalgesia are key endometriosis-associated pain mechanisms replicated in preclinical rodent models. The presence of ectopic (full thickness uterus or endometrial) tissue may be associated with changes in the spinal cord and brain, which appear to model changes reported in patients. While preclinical models using rats and mice have yielded insights that appear relevant to mechanisms responsible for the development of endometriosis-associated pain, they are limited in scope. Specifically, most studies are based on models that only resulted in the formation of superficial lesions and use induced (evoked) behavioral 'pain' tests. We suggest that translation for patient benefit will be improved by new approaches including models of ovarian and deep infiltrating disease and measurement of spontaneous pain behaviors. Future studies must also capitalize on new advances in the wider field of pain medicine to identify more effective treatments for endometriosis-associated pain.

Pathogenesis of pelvic pain syndrome associated with endometriosis in patients resistant to surgical treatment

AIM

Endometriosis is one of the most common gynecological diseases diagnosed in almost 70% of patients with chronic pelvic pain (CPP). However, a quarter of women with pelvic pain is diagnosed with external genital endometriosis (EGE) during laparoscopy. A special group is represented by patients with PP that did not stop after the removal of endometrial foci. The mechanisms of the pathogenesis of the formation of pain syndrome are not completely explored yet. According to several authors, a significant role in the pathogenesis of pelvic pain recurrence after surgical treatment of EGE is played by active neuroangiogenesis, both in ectopic and eutopic endometrium. The aim of the study was to expand the understanding of the pathogenesis of pelvic pain that did not stop (recurrence) after surgical treatment of external genital endometriosis.

MATERIAL AND METHODS

The study involved 2 stages. At the first stage (algological), data from B&B, NRS and VRS algological questionnaires, which were completed by patients with recurrent PP after surgical treatment of EGE, were analyzed (n = 130, aged 18-45 years old, average age 32.5 ± 7.6 years). All women were operated on for EGE no later than 3-6 months after assessing the patients by the algological questionnaires; they did not receive drug therapy after surgical treatment and sought medical attention for recurrent pelvic pain. Materials for the study of the endometrium were obtained by the pipelle biopsymethod. The control group was formed from a number of women with EGE without PP, who applied for surgical treatment of infertility (n = 30).

RESULTS

The results of the study have shown that the basis of pathogenesis of pelvic pain recurrence in patients who did not receive medical therapy after surgical treatment of EGE is the activation of neuro-angiogenesis processes and reduction of apoptosis. The results show a statistically significant 1.6 times increasing expression of NGF in eutopic endometrium (57.9 ± 2.5 vs 35.3 ± 2.1% of patients with the silent form of the gene and its receptor NTRK1 1.8 times (2.78 ± 0.25 versus 1.56 ± 0.21.e. respectively). Conclusion: The pathogenesis of pelvic pain in patients who did not receive medical therapy after surgical treatment of endometriosis compared to no pain form of the disease is the activation of the processes of neurogenesis in the eutopic endometrium.

Postmenopausal endometriosis, where are we now?

PURPOSE OF REVIEW

Postmenopausal endometriosis is a gynecologic disease, affecting 2-5% of postmenopausal woman. Current literature assessing the prevalence, pathogenesis, and treatment of this uncommon condition is limited, stressing the necessity for future research. This review examines the current literature on postmenopausal endometriosis to help inform clinical decision-making and point to novel approaches for treatment and management.

RECENT FINDINGS

Although one unifying theory to explain the pathogenesis of endometriotic lesions has not been elucidated, estrogen dependence is central to the pathophysiological process. The total quantity of estrogen production is mediated by multiple enzymes in complex pathways. Recent studies have confirmed the presence of these necessary enzymes in endometriotic lesions thereby suggesting a local source of estrogen and a likely pathogenic contributor. More research is needed to fully elucidate the mechanism of local estrogen biosynthesis; however, the current data provide possible explanations for the presence of postmenopausal endometriosis in an otherwise systemically hypoestrogenic environment.

SUMMARY

All suspected endometriosis lesions should be surgically excised for optimization of treatment and prevention of malignant transformation. If hormone replacement therapy is initiated, combined estrogen and progestin is recommended, even in the setting of previous hysterectomy, given the risk of disease reactivation and malignant transformation of endometriotic lesions. Further research is needed to understand the true prevalence, cause, and progression in this patient demographic. Histologic studies evaluating tissue lesions and peritoneal fluid for estrogen receptors, estrogen metabolizing enzymes, immune cells, and nerve fibers will aide in clinical management and treatment planning.

Neuropeptides Substance P and Calcitonin Gene Related Peptide Accelerate the Development and Fibrogenesis of Endometriosis

Endometriotic lesions are known to be hyperinnervated, especially in lesions of deep endometriosis (DE), which are frequently in close proximity to various nerve plexuses. DE lesions typically have higher fibromuscular content than that of ovarian endometriomas (OE) lesions, but the underlying reason remains elusive. Aside from their traditional role of pain transduction, however, whether or not sensory nerves play any role in the development of endometriosis is unclear. Here, we show that, thorough their respective receptors neurokinin receptor 1 (NK1R), calcitonin receptor like receptor (CRLR), and receptor activity modifying protein 1 (RAMP-1), neuropeptides substance P (SP) and calcitonin gene related peptide (CGRP) induce epithelial-mesenchymal transition (EMT), fibroblast-to-myofibroblast transdifferentiation (FMT) and further turn stromal cells into smooth muscle cells (SMCs) in endometriotic lesions, resulting ultimately in fibrosis. We show that SP and CGRP, or the rat dorsal root ganglia (DRG) supernatant, through the induction of NK1R and CGRP/CRLR/RAMP-1 signaling pathways, promoted EMT, FMT and SMM in endometriosis, resulting in increased migratory and invasive propensity, cell contractility, production of collagen, and eventually to fibrosis. Neutralization of NK1R and/or CGRP/CRLR/RAMP-1 abrogated these processes. Extended exposure of endometriotic stromal cells to SP and/or CGRP or the DRG supernatant induced increased expression of α-SMA, desmin, oxytocin receptor, and smooth muscle myosin heavy-chain. Finally, we show that DE lesions had significantly higher nerve fiber density, increased staining levels of α-SMA, NK1R, CRLR, and RAMP-1, concomitant with higher lesional fibrotic content than that of OE lesions. The extent of lesional fibrosis correlated positively with the staining levels of NK1R, CRLR, and RAMP-1, as well as the nerve fiber density in lesions. Thus, this study provides another piece of evidence that sensory nerves play an important role in promoting the development and fibrogenesis of endometriosis. It explains as why DE frequently have higher fibromuscular content than that of OE, highlights the importance of lesional microenvironment in shaping the lesional fate, gives more credence to the idea that ectopic endometrium is fundamentally wounds that go through repeated tissue injury and repair, and should shed much needed light into the pathophysiology of endometriosis.

Partners in Crime: NGF and BDNF in Visceral Dysfunction

Neurotrophins (NTs), particularly Nerve Growth Factor (NGF) and Brain-Derived Neurotrophic Factor (BDNF), have attracted increasing attention in the context of visceral function for some years. Here, we examined the current literature and presented a thorough review of the subject. After initial studies linking of NGF to cystitis, it is now well-established that this neurotrophin (NT) is a key modulator of bladder pathologies, including Bladder Pain Syndrome/Interstitial Cystitis (BPS/IC) and Chronic Prostatitis/Chronic Pelvic Pain Syndrome (CP/CPPS. NGF is upregulated in bladder tissue and its blockade results in major improvements on urodynamic parameters and pain. Further studies expanded showed that NGF is also an intervenient in other visceral dysfunctions such as endometriosis and Irritable Bowel Syndrome (IBS). More recently, BDNF was also shown to play an important role in the same visceral dysfunctions, suggesting that both NTs are determinant factors in visceral pathophysiological mechanisms. Manipulation of NGF and BDNF improves visceral function and reduce pain, suggesting that clinical modulation of these NTs may be important; however, much is still to be investigated before this step is taken. Another active area of research is centered on urinary NGF and BDNF. Several studies show that both NTs can be found in the urine of patients with visceral dysfunction in much higher concentration than in healthy individuals, suggesting that they could be used as potential biomarkers. However, there are still technical difficulties to be overcome, including the lack of a large multicentre placebo-controlled studies to prove the relevance of urinary NTs as clinical biomarkers.

The Expression and Cellular Localisation of Neurotrophin and Neural Guidance Molecules in Peritoneal Ectopic Lesions

Endometriosis is a gynaecological disorder characterised by the presence of endometrial-like tissue outside the uterus. It affects 10-15% of women during their reproductive age. The existence of close and complex relationship between chronic pelvic pain and endometriosis are widely recognised. However, the mechanisms of pain generation in women with endometriosis remain poorly understood. Immunohistochemistry was used to assess the density of nerve fibres stained with protein gene product 9.5 (PGP9.5) and the expression of various neurotrophins including glial cell derived neurotrophic factor (GDNF), persephin, neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) and neuronal guidance molecules semaphorin 3E and Slit-2 and their receptors Plexin-D1 and Robo4 in peritoneal ectopic lesions from women with endometriosis and uninvolved peritoneum samples. Neurotrophins and neuronal guidance molecules and their receptors are synthesised in situ within peritoneal ectopic lesion which suggest their role in facilitating and maintaining the growth of nerve fibres. These molecules were found to be overall most highly expressed in the glands of endometriotic peritoneal lesions. In addition, the presence of ectopic lesions within the peritoneal cavity may affect the environment; in turn, the peritoneum altered appeared to play a role in the growth of nerve fibres and their development and maintenance in peritoneal lesions. Through exploring different neuronally active factors in and around ectopic lesions which may be contributing to pain generation, this study provides an insight and better understanding of the pain mechanisms associated with peritoneal endometriosis.

Redox regulation of microRNAs in endometriosis-associated pain

Endometriosis is a chronic, painful condition with unknown etiology. A differential expression of microRNAs in the endometriotic tissues from women with endometriosis with pain compared to those without suggested a plausible role for miRNA or epigenetic mechanisms in the etiology of endometriotic pain. The peritoneal milieu is involved in maintenance of endometriotic lesion and nociception. We recently showed the mechanistic role for oxidized-lipoproteins (ox-LDLs) present in peritoneal fluid (PF) in endometriosis and pain. We explored the possibility of ox-LDLs modulating the expression of miRNAs in a manner similar to PF from women with endometriosis. Expression levels of miRNAs and their predicted nociceptive and inflammatory targets were determined in PF and ox-LDL treated human endometrial cell-lines. Samples from IRB-approved and consented patients with and without endometriosis or pain were used. These were compared to endometrial cell-lines treated with various forms of oxidized-lipoproteins. RNA (including miRNAs) were isolated from treated endometrial cells and expression levels were determined using commercial miRNome arrays. Cell lysates were used in immunoblotting for inflammatory proteins using a protein array. Twenty miRNAs including isoforms of miR-29, miR-181 and let-7 were mutually differentially expressed in cells treated with PF from endometriosis patients with pain and those treated with ox-LDL components. The ox-LDLs and endo-PF treatment also produced significant overexpression of microRNA predicted target genes nerve growth factor, interleukin-6 and prostaglandin E synthase and overexpression of their downstream protein targets Mip1α and MCP1. This study showed similarities between miRNA regulation in PF from endometriotic women and ox-LDLs present in abundance in the PF of these women. Key miRNAs responsible for targeting nociceptive and inflammatory molecules were downregulated in the presence of ox-LDLs and endo-PF, thus playing a role in the etiology of endometriotic pain. These redox-sensitive miRNAs can be of potential use as targets in the treatment of endometriosis-associated pain.

Pain Mechanisms in Peritoneal Diseases Might Be Partially Regulated by Estrogen

To identify factors influencing the differential pain pathogenesis in peritoneal endometriosis (pEM) and peritoneal carcinomatosis in ovarian cancer (pOC), we undertook an experimental study. Tissue samples of 18 patients with pEM, 15 patients with pOC, and 15 unaffected peritoneums as controls were collected during laparoscopy or laparotomy. Immunohistochemical stainings were conducted to identify nerve fibers and neurotrophins in the tissue samples. Additionally, 23 pEM fluids, 25 pOC ascites fluids, and 20 peritoneal fluids of patients with myoma uteri as controls were collected. In these fluids, the expression of neurotrophins was evaluated. The effects of peritoneal fluids and ascites on the neurite outgrowth of chicken sensory ganglia were estimated by using a neuronal growth assay. An electrochemiluminescence immunoassay was carried out to determine the expression of estrogen in the peritoneal fluids and ascites. The total and sensory nerve fiber density was significantly higher in pEM than in pOC ( P < .001 and P < .01). All neurotrophins tested were present in tissue and fluid samples of pEM and pOC. Furthermore, the neurotrophic properties of pEM and pOC fluids were demonstrated, leading to sensory nerve fiber outgrowth. Estrogen concentration in the peritoneal fluids of pEM was significantly higher compared to ascites of pOC ( P < .001). The total and sensory nerve fiber density in the tissue samples as well as the estrogen expression in the peritoneal fluid of pEM was considerably higher than that in pOC, representing the most notable difference found in both diseases. This might explain the differential pain perception in pEM and pOC. Therefore, estrogen might be a key factor in influencing the genesis of pain in endometriosis.

Relevant human tissue resources and laboratory models for use in endometriosis research

Endometriosis is characterized by the growth of endometrium‐like tissue outside the uterus, most commonly on the pelvic peritoneum and ovaries. Although it may be asymptomatic in some women, in others it can cause debilitating pain, infertility or other symptoms including fatigue. Current research is directed both at understanding the complex etiology and pathophysiology of the disorder and at the development of new nonsurgical approaches to therapy that lack the unwanted side effects of current medical management. Tools for endometriosis research fall into two broad categories; patient‐derived tissues, and fluids (and cells isolated from these sources) or models based on the use of cells or animals. In this review, we discuss the literature that has reported data from the use of these tools in endometriosis research and we highlight the strengths and weaknesses of each. Although many different models are reported in the literature, hypothesis‐driven research will only be facilitated with careful experimental design and selection of the most appropriate human tissue from patients with and without endometriosis and combinations of physiologically relevant in vitro and in vivo laboratory models.

How to Understand the Complexity of Endometriosis-Related Pain

Pain is the most important symptom in patients with endometriosis, and its management is truly challenging. Due to the different localization of the endometriotic lesions in the pelvis, patients suffer from visceral and somatic pain or both at the same time. There are specific and unspecific symptoms characterized by endometriosis. Specific symptoms include dysmenorrhea, cyclic and acyclic pelvic pain, dyschezia, dysuria and dyspareunia. There is also a wide range of unspecific symptoms, such as unspecific bowel and bladder complaints, the emission of pain in the legs, vegetative concomitants like vomiting, emesis, gastric disorders, headaches, dizziness, painful ovulation, irregular pelvic pain, lower back pain, chronic fatigue. These symptoms can be both cyclic and acyclic, and in most cases, they are permanent.

Visceral and somatic pain are completely different pain subtypes and can therefore be an explanation for the wide variety of symptoms. The close interaction between visceral sensory nerve fibers and the autonomic ganglia explain the high rate of concomitant vegetative reactions, such as vomiting and orthostatic dysregulation. In general, pain generation is a complex interplay of peripheral and central sensitization mechanisms. Accordingly, the pain produced in endometriotic lesions is the result of mediating substances, nerve fibers, cytokine-releasing immune cells and macrophages synthesis. These interactions seem to stimulate the neurogenic inflammatory process and sensitization of the peripheral nerves.

Furthermore, the disruption of the input on the level of the spinal cord and the recognition of the pain in the brain may lead to exaggerated responses known as central hyperalgesia. Hormones and psychological factors influence the pain sensation and make the status of each patient very individual. Consequently, the involvement of professional pain management along with an implementation of pain-coping strategies in the patient's everyday life are obligatory in chronic pain situations. An additional osteopathic treatment with a manual resolve of muscle blockades to avoid secondary “pain intensifying” changes of the pelvic floor (tension) or malposition through relieving posture, is also recommended.

Pain management in patients with endometriosis is very complex and requires an individual treatment strategy for each patient to avoid unnecessary surgical procedures. This information proves that it is hard to break the cycle of pain when chronic pain syndrome is already apparent.

New developments in the medical treatment of endometriosis

Endometriosis affects 1 in 10 women of reproductive-age. The current treatments are surgical and hormonal but have limitations, including the risk of recurrence, side effects, contraceptive action for women who desire pregnancy, and cost. New treatments include gonadotropin-releasing hormone analogues, selective progesterone (or estrogen) receptor modulators, aromatase inhibitors, immunomodulators, and antiangiogenic agents. Further research is needed into central sensitization, local neurogenesis, and the genetics of endometriosis to identify additional treatment targets. A wider range of medical options allows for the possibility of precision health and a more personalized treatment approach for women with endometriosis.

New developments in the pharmacotherapy of neuropathic chronic pelvic pain

Advancements in further understanding the pathophysiology of chronic pelvic pain syndromes continue to direct therapy. The mechanisms of chronic pelvic pain are often multifactorial and therefore require a multidisciplinary approach. The final treatment plan is often an accumulation of organ-specific treatment and chronic pain medications directed to the CNS and PNS. This article is a review of commonly used medications for chronic pelvic neuropathic pain disorders as well as an introduction to recent innovative developments in pain medicine.

Reinnervation of rat endometrium in the anterior eye chamber model of experimental endometriosis: Old methods for new questions

Endometriosis is a benign estrogen-dependent chronic gynecological disease characterized by the presence of endometrial-like tissue outside the uterine cavity. In both women and experimental endometriotic rats, endometriosis lesions endow autonomic and sensory nerves, which are thought to contribute to the disease-associated pain. Some evidence indicates that the reinnervation of lesions is regulated by factors produced by the endometrial tissue as well as by environmental factors from the peritoneum. In this study, we examined the reinnervation of the rat endometrial tissue in an ectopic environment different from the peritoneum employing the anterior eye chamber model of experimental endometriosis. At 3 and 6weeks following transplantation, endometrial grafts retained many histological features of the eutopic tissue. Both sympathetic and sensory nerves reinnervated endometrial grafts and distributed in the stroma-like tissue, around blood vessels and in close proximity to the glands and lining epithelium. Sympathetic innervation was more robust than sensory innervation. No significant topographical relationship between sympathetic nerves and macrophages was observed. These results suggest that the rat endometrium possesses intrinsic neuritogenic capacities and can be reinnervated by sympathetic and sensory nerves in ectopic sites different from the peritoneum.

Endometriosis-Derived Thromboxane A2 Induces Neurite Outgrowth

Hyperinnervation in endometriosis is now well documented, but so far only a few neurotrophins have been identified. Since endometriotic stromal cells secrete thromboxane A2 (TXA₂), we sought to determine whether TXA₂, derived from endometriotic stromal cells, induces neurite outgrowth. Using primary sensory neurons derived from rat dorsal root ganglia (DRG) and ectopic endometrial stromal cells (EESCs) derived from human ovarian endometrioma tissues, we treated the primary neurons with different concentrations of U-46619, a stable TXA₂ mimetic, and performed a neuronal growth assay. The primary neurons were also cocultured with a vehicle, nerve growth factor (NGF, serving as a positive control), the supernatant of EESC culture medium, or the supernatant of EESCs pretreated with ozagrel, a thromboxane synthase inhibitor, and a neuronal growth assay was performed. The total neurite length was evaluated through immunofluorescence microscopy. We found that U-46619 significantly increased the neurite outgrowth in DRG neurons in a concentration-dependent fashion ( P < .001). It also increased the number of neurite ends in a concentration-dependent fashion. Ozagrel treatment alone had no effect on the neurite growth ( P > .05), and the treatment with the supernatant of EESCs induced neurite outgrowth just as potently as that treated with NGF (positive control; P > .05). Remarkably, treatment with the EESC supernatant increased the neurite outgrowth by nearly 3-fold as compared with the control ( P < .01), but the pretreatment with ozagrel abolished the stimulatory effect of the EESC by 31.3% ( P < .05). These findings indicate that EESCs potently induce neurite outgrowth, and endometriosis-derived TXA₂ is responsible, at least in part, for this neurotrophic effect.

Nerve fibers and endometriotic lesions: partners in crime in inflicting pains in women with endometriosis

One of major objectives in treating endometriosis is to alleviate pain since dysmenorrhea and other types of pain top the list of complaints from women with endometriosis who seek medical attention. Indeed, endometriosis-associated pain (EAP) is the most debilitating of the disease that negatively impacts on the quality of life in affected women, contributing significantly to the burden of disease and adding to the substantial personal and societal costs. Unfortunately, the mechanisms underlying the EAP are still poorly understood. In the last two decades, one active research field in endometriosis is the investigation on the distribution and genesis of nerve fibers in eutopic and ectopic endometrium, and the attempt to use endometrial nerve fiber density for diagnostic purpose. Since EAP presumably starts with the terminal sensory nerves, in or around endometriotic lesions, that transduce noxious mediators to the central nervous system (CNS) which ultimately perceives pain, this field of research holds the promise to elucidate the molecular mechanisms underlying the EAP, thus opening new avenues for novel diagnostics and therapeutics. In this review, we shall first briefly provide some basic facts on nerve fibers, and then provide an overview of some major findings in this filed while also note some conflicting results and expose areas in need of further research. We point out that since recently accumulated evidence suggests that endometriotic lesions are wounds undergoing repeated tissue injury and repair, the relationship between endometriotic lesions and nerve fibers is not simply unidirectional, i.e. lesions promote hyperinnervations. Rather, it is bidirectional, i.e. endometriotic lesions and nerve fibers engage active cross-talks, resulting in the development of endometriosis and pain. That is, nerve fibers and endometriotic lesions are actually partners in crime in inflicting pains in women with endometriosis, aided and abetted possibly by other culprits, some yet to be identified. We provide a list of possible perpetrators likely to be involved in this crime. Finally, we discuss possible implications when viewing the relationship from this vista.

Potential role of estrogen in maintaining the imbalanced sympathetic and sensory innervation in endometriosis

Endometriosis, one of the most common benign gynecological diseases, affects millions of women of childbearing age. Endometriosis-associated pain is a major cause of disability and compromised quality of life in women. Neuropathic mechanisms are believed to play an important role. An imbalanced sympathetic and sensory innervation (reduced sympathetic innervation, with unchanged or increased sensory innervation in endometriotic lesions) has been demonstrated in endometriosis in recent studies. And it is believed to contribute to the pathogenesis of endometriosis-associated pain. It is primarily considered to be a natural adaptive program to endometriosis-associated inflammation. However, it is important to further clarify whether other potential modulating factors are involved in this dysregulation. It is generally accepted that endometriosis is an estrogen dependent disease. Higher estrogen biosynthesis and lower estrogen inactivation in endometriosis can lead to an excess of local estrogen in endometriotic lesions. In addition to its proliferative and anti-inflammatory actions, local estrogen in endometriosis also exerts potential neuromodulatory effects on the innervation in endometriosis. The aim of this review is to highlight the role of estrogen in mediating this imbalanced sympathetic and sensory innervation in endometriosis, through direct and indirect mechanisms on sympathetic and sensory nerves. Theoretical elaboration of the underlying mechanisms provides new insights in supporting the therapeutic role of estrogen in endometriosis-associated pain.

Are endometrial nerve fibres unique to endometriosis? A prospective case-control study of endometrial biopsy as a diagnostic test for endometriosis in women with pelvic pain

STUDY QUESTION

Can the presence of endometrial nerve fibres be used as a diagnostic test for endometriosis in women with pelvic pain?

SUMMARY ANSWER

Endometrial fine nerve fibres were seen in the endometrium of women both with and without endometriosis, making their detection a poor diagnostic tool for endometriosis.

WHAT IS KNOWN ALREADY

Laparoscopy and biopsy are currently the gold standard for making a diagnosis of endometriosis. It has been reported that small density nerve fibres in the functional layer of the endometrium are unique to women with endometriosis and hence nerve fibre detection could function as a less invasive diagnostic test of endometriosis. However, it may be that other painful conditions of the pelvis are also associated with these nerve fibres. We therefore focused this prospective study on women with pelvic pain to examine the efficacy of endometrial nerve fibre detection as a diagnostic test for endometriosis.

STUDY DESIGN, SIZE, DURATION

This prospective case-control study conducted between July 2009 and July 2013 included 44 women with pelvic pain undergoing laparoscopic examination for the diagnosis of endometriosis. Immunohistochemical nerve fibre detection in endometrial curettings and biopsies using anti-protein gene product 9.5 was compared with surgical diagnosis.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Paired endometrial biopsies and curettings were taken from patients with (n = 22, study group) and without (n = 22, control group) endometriosis. Tissue was analysed by immunohistochemistry and nerve fibres were counted whenever they were present in the functional layer of the endometrium.

MAIN RESULTS AND THE ROLE OF CHANCE

Fine nerve fibres were present in the eutopic endometrium of patients both with and without endometriosis. The presence of nerve fibres in curettings was not effective for either diagnosing or excluding endometriosis; sensitivity and specificity were 31.8 and 45.5% respectively, positive predictive value was 36.8% and negative predictive value was 40.0%. Few endometrial biopsy specimens were found to have nerve fibres present; sensitivity and specificity for endometrial biopsy were 13.6 and 68.2% respectively, positive predictive value was 30.0% and negative predictive value was 44.1%.

LIMITATIONS, REASONS FOR CAUTION

This was a relatively small sample size and studies like this are subject to the heterogeneous nature of the patient population and tissue samples, despite our best efforts to regulate these parameters.

WIDER IMPLICATIONS OF THE FINDINGS

Our results demonstrate that fine nerve fibres are present in women with and without endometriosis. Future work should focus on the function of endometrial nerves and whether these nerves are involved with the subfertility or pain that endometriosis sufferers experience. Our study does not support the detection of endometrial nerve fibres as a non-invasive diagnostic test of endometriosis in women with pelvic pain.

Impact of medical and surgical treatment of endometriosis on the cure of endometriosis and pain

This endometriosis study evaluates three different treatment strategies (hormonal medication, surgical, or combined treatment) and discusses the influence of endometriosis on the cure of this disease and pain relief. Four hundred and fifty patients with genital endometriosis, aged 18-44 years, were randomly distributed to three treatment groups at the first laparoscopy. They were reevaluated at a second-look laparoscopy (D 426/10), one to two months after the three-month hormonal therapy for groups 1 and 3 and five to six months later for group 2 (surgical treatment alone). Outcome data focussed on the recurrence of symptoms and pain. The three treatment options independent of the initial endoscopic endometriosis classification (EEC) stage including deep infiltrating endometriosis (DIE) achieved an overall cure rate of 50% or higher. The highest cure rate of 60% was achieved by the combined treatment, 55% by the exclusively hormonal therapy, and 50% by the exclusively surgical treatment. An overall pregnancy rate between 55% and 65% was achieved with no significant difference in relation to the therapeutical option.

Estrogen and female reproductive tract innervation: cellular and molecular mechanisms of autonomic neuroplasticity

The female reproductive tract undergoes remarkable functional and structural changes associated with cycling, conception and pregnancy, and it is likely advantageous to both individual and species to alter relationships between reproductive tissues and innervation. For several decades, it has been appreciated that the mammalian uterus undergoes massive sympathetic axon depletion in late pregnancy, possibly representing an adaptation to promote smooth muscle quiescence and sustained blood flow. Innervation to other structures such as cervix and vagina also undergo pregnancy-related changes in innervation that may facilitate parturition. These tissues provide highly tractable models for examining cellular and molecular mechanisms underlying peripheral nervous system plasticity. Studies show that estrogen elicits rapid degeneration of sympathetic terminal axons in myometrium, which regenerate under low-estrogen conditions. Degeneration is mediated by the target tissue: under estrogen's influence, the myometrium produces proteins repulsive to sympathetic axons including BDNF, neurotrimin, semaphorins, and pro-NGF, and extracellular matrix components are remodeled. Interestingly, nerve depletion does not involve diminished levels of classical sympathetic neurotrophins that promote axon growth. Estrogen also affects sympathetic neuron neurotrophin receptor expression in ways that appear to favor pro-degenerative effects of the target tissue. In contrast to the uterus, estrogen depletes vaginal autonomic and nociceptive axons, with the latter driven in part by estrogen-induced suppression of BMP4 synthesis. These findings illustrate that hormonally mediated physiological plasticity is a highly complex phenomenon involving multiple, predominantly repulsive target-derived factors acting in concert to achieve rapid and selective reductions in innervation.

Estrogen receptor (ER) agonists differentially regulate neuroangiogenesis in peritoneal endometriosis via the repellent factor SLIT3

Endometriosis is an estrogen-dependent neurovascular disorder characterized by growth of endometrial tissue (lesions) outside the uterine cavity. Patients suffer chronic pelvic pain, and it has been proposed that co-recruitment of nerves/blood vessels (neuroangiogenesis) into the lesions is fundamental to the development of painful symptoms. We hypothesized that estrogen-dependent regulation of axonal guidance molecules of the SLIT/ROBO (Roundabout) family could play a role in neuroangiogenesis occurring in endometriosis lesions found on the peritoneal wall. In tissue samples from human patients and a mouse model of endometriosis, concentrations of mRNA encoded by SLIT3 were significantly higher in lesions than normal peritoneum. Estrogen regulation of SLIT3 was investigated using 17β-estradiol and selective agonists for each subtype of estrogen receptor (ER) (ERα agonist, 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-tryl) trisphenol; ERβ agonist, 2,3-bis(4-hydroxy-phenyl)-propionitrile [DPN]). In mice, DPN (EC50 0.85) increased Slit3 mRNA concentrations compared with hormone-depleted and 17β-estradiol-treated (EC50 0.1) animals and decreased the density of nerves but not vessels in endometriosis lesions. SLIT3 mRNA concentrations were increased in DPN-treated human endometrial endothelial cells and in 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-tryl) trisphenol-treated (EC50 200) rat dorsal root ganglia neurons. Functional assays (neurite outgrowth, network formation) revealed that SLIT3 promotes angiogenesis but decreases neurogenesis. In conclusion, these data suggest that estrogen-dependent expression of SLIT3 may play a key role in regulating nerve-vessel interactions within the complex microenvironment of endometriosis lesions.

Resolvins RvD1 and 17(R)-RvD1 alleviate signs of inflammation in a rat model of endometriosis

OBJECTIVE

To study the effects of two resolvins of D series, RvD1 and 17(R)-RvD1, on inflammatory signs associated with endometriosis (ENDO).

DESIGN

In vivo research study.

SETTING

Research laboratory.

ANIMAL(S)

Female Sprague-Dawley rats.

INTERVENTION(S)

Intravenous or intraperitoneal injections of RvD1 (300 ng/kg) or 17(R)-RvD1 (300 and 900 ng/kg) in rats with surgically induced ENDO.

MAIN OUTCOME MEASURE(S)

Vascular permeability of ectopic endometrial growths was assessed by Evans Blue extravasation; vaginal hyperalgesia was assessed with telemetered visceromotor response.

RESULT(S)

Both resolvins, but not vehicle, significantly decreased vascular permeability in ectopic endometrial tissue. 17(R)-RvD1 also significantly alleviated severity of vaginal hyperalgesia.

CONCLUSION(S)

Our results suggest that RvD1 and 17(R)-RvD1 can be considered for further investigation of their therapeutic potential for treating ENDO.

Screening the role of pronociceptive molecules in a rodent model of endometriosis pain

Chronic pain is a major symptom in patients with endometriosis, a common gynecologic condition affecting women in their reproductive years. Although many proalgesic substances are produced by endometriosis lesions, experimental evidence supporting their relative roles is still lacking. Furthermore, it is unclear whether these proalgesic agents directly activate nociceptors to induce endometriosis pain. To determine their relative contribution to pain associated with endometriosis, we evaluated the intrathecal administration of oligodeoxynucleotides (ODNs) antisense to messenger RNA for receptors for 3 pronociceptive mediators known to be produced by the ectopic endometrium. Two weeks after the implant of autologous uterine tissue onto the gastrocnemius muscle, local mechanical hyperalgesia was observed in operated rats. Intrathecal antisense ODN targeting messenger RNA for the interleukin 6 receptor-signaling complex subunit glycoprotein 130 and the nerve growth factor tyrosine kinase receptor A, but not their mismatch ODNs, reversibly attenuated mechanical hyperalgesia at the implant site. In contrast, intrathecal antisense ODN targeting the tumor necrosis factor receptor 1, at a dose that markedly inhibited intramuscularly injected tumor necrosis factor alpha, had only a small antihyperalgesic effect in this model. These results indicate the relative contribution of pronociceptive mediators produced by ectopic endometrial tissue to endometriosis pain. The experimental approach presented here provides a novel method to evaluate for the differential contribution of mediators produced by other painful lesions as well as endometriosis lesions as targets for novel treatment of pain syndromes.

PERSPECTIVE

This article presents evidence for the relative contribution of proalgesic mediators to primary hyperalgesia displayed by rats submitted to a model of endometriosis pain. This approach can be used to identify potential targets for the treatment of endometriosis pain.

Peripheral changes in endometriosis-associated pain

BACKGROUND

Pain remains the cardinal symptom of endometriosis. However, to date, the underlying mechanisms are still only poorly understood. Increasing evidence points towards a close interaction between peripheral nerves, the peritoneal environment and the central nervous system in pain generation and processing. Recently, studies demonstrating nerve fibres and neurotrophic and angiogenic factors in endometriotic lesions and their vicinity have led to increased interest in peripheral changes in endometriosis-associated pain. This review focuses on the origin and function of these nerves and factors as well as possible peripheral mechanisms that may contribute to the generation and modulation of pain in women with endometriosis.

METHODS

We conducted a systematic search using several databases (PubMed, MEDLINE, EMBASE and CINAHL) of publications from January 1977 to October 2013 to evaluate the possible roles of the peripheral nervous system in endometriosis pathophysiology and how it can contribute to endometriosis-associated pain.

RESULTS

Endometriotic lesions and peritoneal fluid from women with endometriosis had pronounced neuroangiogenic properties with increased expression of new nerve fibres, a shift in the distribution of sensory and autonomic fibres in some locations, and up-regulation of several neurotrophins. In women suffering from deep infiltrating endometriosis and bowel endometriosis, in which the anatomical distribution of lesions is generally more closely related to pelvic pain symptoms, endometriotic lesions and surrounding tissues present higher nerve fibre densities compared with peritoneal lesions and endometriomas. More data are needed to fully confirm a direct correlation between fibre density in these locations and the amount of perceived pain. A better correlation between the presence of nerve fibres and pain symptoms seems to exist for eutopic endometrium. However, this appears not to be exclusive to endometriosis. No correlation between elevated neurotrophin levels and pain severity appears to exist, suggesting the involvement of other mediators in the modulation of pain.

CONCLUSIONS

The increased expression of neurotrophic factors and nerve fibres in endometriotic lesions, eutopic endometrium and the peritoneum imply a role of such peripheral changes in the pathogenesis of endometriosis-associated pain. However, a clear link between these findings and pain in patients with endometriosis has so far not been demonstrated.

The peritoneum--an important factor for pathogenesis and pain generation in endometriosis

Endometriosis (EM) is an oestrogen-dependent disease affecting 10-15 % of women during reproductive age. It is characterised by the presence of endometrial glands, stromal- and smooth muscle-like cells outside of the uterine cavity. Fifty to sixty per cent of women and teenage girls with pelvic pain suffer from EM. EM causes disability and compromises the quality of life in women and young girls significantly. Pain generation in EM is an intricate interplay of several factors such as the endometriotic lesions themselves and the pain-mediating substances, nerve fibres and cytokine-releasing immune cells such as macrophages. These interactions seem to induce a neurogenic inflammatory process. Recently published data demonstrated an increased peptidergic and decreased noradrenergic nerve fibre density in peritoneal lesions. These data could be substantiated by in vitro analyses demonstrating that the peritoneal fluids of patients suffering from EM induced an enhanced sprouting of sensory neurites from chicken dorsal root ganglia and decreased neurite outgrowth from sympathetic ganglia. These findings might be directly involved in the perpetuation of inflammation and pain. Furthermore, the evidence of EM-associated smooth muscle-like cells seems another important factor in pain generation. The peritoneal endometriotic lesion leads to reactions in the surrounding tissue and, therefore, is larger than generally believed. The identification of EM-associated nerve fibres and smooth muscle-like cells fuel discussions on the mechanisms of pain generation in EM, and may present new targets for innovative treatments.

Dienogest inhibits nerve growth factor expression induced by tumor necrosis factor-α or interleukin-1β

OBJECTIVE

Dienogest (DNG), a selective P receptor (PR) agonist, is used to treat endometriosis. To investigate whether DNG affects nerve growth factor (NGF) expression, we stimulated human endometrial epithelial cells (hEECs) with inflammatory cytokines.

DESIGN

Prospective basic research study using immortalized hEEC lines.

SETTING

Development Research, Mochida Pharmaceutical Co., Ltd., Japan.

PATIENT(S)

None.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

In immortalized hEECs, NGF production induced by tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β) was evaluated in the presence or absence of the synthetic progestin DNG or endogenous P. The NGF messenger RNA (mRNA) and protein were measured using real-time reverse transcriptase-polymerase chain reaction (PCR) and ELISA, respectively. The NGF bioactivity in the culture medium was measured by assaying neurite outgrowth of PC-12 cells.

RESULT(S)

Tumor necrosis factor-α and IL-1β induced NGF mRNA and protein and increased NGF bioactivity in the culture medium. These activities were inhibited by DNG in a hEEC line that stably expresses PR. In contrast, in an hEEC line that constitutively expresses faint levels of PR, no inhibitory effect of DNG on NGF mRNA was detected. The NGF mRNA was also inhibited in hEEC lines that express only PR-A or only PR-B.

CONCLUSION(S)

Nerve growth factor is one of the key mediators that generates the pain associated with endometriosis. Dienogest inhibits NGF expression through PR-A and PR-B in hEEC, which may contribute to the pharmacological mechanisms of how DNG relieves pain in endometriosis.

Effect of siRNA against β-NGF on nerve fibers of a rat model with endometriosis

OBJECTIVE

This study examines whether silencing specific β-nerve growth factor small interfering RNA (β-NGF siRNA) can affect the growth of ectopic endometriotic implants, generalized hyperalgesia, and nerve fiber density in endometriosis.

METHODS

Four specific β-NGF siRNAs were detected by Western blot analysis, and the most efficient specific siRNA was transferred into rats with surgically induced endometriosis through gene transfer. The length × width × height of each ectopic transplant that survived from 2 groups were measured at pre-and postbombardment after 2 weeks. The transplants were collected 2 weeks after bombardment. Warm-water tail flick test was performed before the rats were sacrificed. The specimens were sectioned and stained immunohistochemically with antibodies against the types of nerve fibers to compare the presence of different nerve fibers in the treatment and control groups. The serums and supernatants of the peritoneal washings in the treatment and control groups were collected for enzyme-linked immunosorbent assay (ELISA) analysis. The extra rats were successfully induced with endometriosis and through gene transfer as described above. The spherical volumes of the transplants and tail flick latency post-bombardment after 4, 6, 8, and 10 weeks were measured.

RESULTS

The spherical volumes in the treatment group were much smaller than those in the control group, and tail flick latency significantly increased in the treatment group postbombardment after 2 weeks. The ELISA analysis showed that the concentrations of β-NGF in the serums and supernatants of the peritoneal fluid decreased in the treatment group unlike in the control group. Less sympathetic and sensory innervation was observed in the treatment group postbombardment after 2 weeks. The outcomes of the spherical volumes of the transplants and tail flick latency postbombardment after 4, 6, 8, and 10 weeks showed that the sizes of the transplants did not return to their previous size and that the treatment had some effects on generalized hyperalgesia.

CONCLUSION

Specific siRNA-mediated silencing of the β-NGF gene expression after gene transfer suppressed the growth of ectopic endometriotic implants resulted in a significant improvement in generalized hyperalgesia as well as reduced sympathetic and sensory nerve fiber density in the treatment group.

Calcium-binding protein expression in peritoneal endometriosis-associated nerve fibres

BACKGROUND

Recent studies demonstrated the potential involvement of nerve fibres in the chronic inflammatory process of endometriosis. We aimed to characterize nerve fibres in the proximal and distal areas of the peritoneal endometriotic lesions in order to understand the chronic inflammatory process in endometriosis.

METHODS

Peritoneal endometriotic lesions (proximal area) (n = 17), the matching unaffected peritoneum (distal area) and healthy peritoneum of patients without endometriosis (n = 15) were analysed with the neuronal markers PGP 9.5, calbindin, calretinin and parvalbumin. Peritoneal fluids of women with and without endometriosis were used for Western blot analysis and for the neuronal growth assay. The protein expression of neuronal PC-12 cells incubated with peritoneal fluids was analysed.

RESULTS

The overall nerve fibre density was significantly reduced in the distal area of the lesion when compared with the proximal area or with healthy peritoneum. The density of calbindin-, calretinin- and parvalbumin-positive nerve fibres was significantly increased in the endometriosis group. Calretinin expression was elevated in the peritoneal fluid of women with symptomatic endometriosis when compared with women with asymptomatic endometriosis. Furthermore, PC-12 cells incubated with peritoneal fluid of women with endometriosis showed a higher proliferation rate and a stronger neurite outgrowth than the control group. PC-12 cells incubated in peritoneal fluids of women with endometriosis expressed less calretinin but more calbindin than the control group.

CONCLUSIONS

Calcium-binding proteins seem to be increased in endometriosis-associated nerve fibres and might play an important role in the chronic inflammatory condition and the pain pathogenesis of endometriosis.

Nerve Fibers are Absent in Disease-Free and Eutopic Endometrium, but Present in Endometriotic (Especially Deep) Lesions

Objective

Detection of nerve fibers in endometrial biopsies was recently proposed as a noninvasive diagnostic tool for endometriosis. However, their occurrence in the functional layer of endometrium still remains controversial. Nerve fibers were found to be present in endometriotic lesions themselves, which may account for some of the pain experienced by patients, but their origin is not clear. The objective of the present study was to reevaluate the presence of nerve fibers in endometrium and in different types of endometriotic lesions.

Patients and Methods

Nerve fiber density (PGP9.5 immunohistochemical analysis), unmyelinated nerve fiber presence (neurofilament immunohistochemical detection) and nerve growth factor expression were evaluated in endometrial (disease free: n = 20; endometriotic: n = 26) and endometriotic (peritoneal lesions: n = 11; ovarian lesions: n = 16; rectovaginal lesions: n = 27) samples.

Results

Endometrial biopsies were found to be mostly negative for nerve fibers. Nerve fiber density was higher in deep nodular lesions than in peritoneal (p<0.01) or ovarian (p<0.001) lesions. Around 30% of PGP9.5-positive nerve fibers were confirmed by neurofilament staining. Nerve growth factor expression was detected at higher levels in the stroma of deep-infiltrating lesions (p<0.05).

Conclusions

No nerve fibers were detected in endometrial biopsies (from healthy or endometriosis patients). However, nerve fibers were detected in endometriotic lesions. Most of them were found to be unmyelinated, suggesting they could be implicated in pain. Deep nodular lesions may be more neuroattractive through the action of nerve growth factor.