Growth-associated protein 43–positive sensory nerve fibers accompanied by immature vessels are located in or near peritoneal endometriotic lesions

Prolactin and pain of endometriosis

Women experience chronic pain more often than men with some pain conditions being specific to women while others are more prevalent in women. Prolactin, a neuropeptide hormone with higher serum levels in women, has recently been demonstrated in preclinical studies to sensitize nociceptive sensory neurons in a sexually dimorphic manner. Dysregulation of prolactin and prolactin receptors may be responsible for increased pain especially in female predominant conditions such as migraine, fibromyalgia, and pelvic pain. In this review, we focus on the role of prolactin in endometriosis, a condition characterized by pelvic pain and infertility that affects a large proportion of women during their reproductive age. We discuss the symptoms and pathology of endometriosis and discuss how different sources of prolactin secretion may contribute to this disease. We highlight our current understanding of prolactin-mediated mechanisms of nociceptor sensitization in females and how this mechanism may apply to endometriosis. Lastly, we report the results of a systematic review of clinical studies conducted by searching the PubMed and EMBASE databases to identify association between endometriosis and blood levels of prolactin. The results of this search strongly indicate that serum prolactin levels are increased in patients with endometriosis and support the possibility that high levels of prolactin may promote pelvic pain in these patients and increase vulnerability to other comorbid pain conditions likely by dysregulating prolactin receptor expression. Targeting of prolactin and prolactin receptors may improve management of pain associated with endometriosis.

Potential link between the nerve injury-induced protein (Ninjurin) and the pathogenesis of endometriosis

Endometriosis remains a widespread but severe gynecological disease in women of reproductive age, with an unknown etiology and few treatment choices. The menstrual reflux theory is largely accepted as the underlying etiology but does not explain the morbidity or unpleasant pain sensations of endometriosis. The neurological and immune systems are both involved in pain mechanisms of endometriosis, and interlinked through a complex combination of cytokines and neurotransmitters. Numerous pieces of evidence suggest that the nerve injury-inducible protein, Ninjurin, is actively expressed in endometriosis lesions, which contributes to the etiology and development of endometriosis. It may be explored in the future as a novel therapeutic target. The aim of the present review was to elucidate the multifaceted role of Ninjurin. Furthermore, we summarize the association of Ninjurin with the pain mechanism of endometriosis and outline the future research directions. A novel therapeutic pathway can be discovered based on the potential pathogenic variables.

Nonsurgical mouse model of endometriosis-associated pain that responds to clinically active drugs

Endometriosis is an estrogen-dependent inflammatory disease that affects approximately 10% of women. Debilitating pelvic or abdominal pain is one of its major clinical features. Current animal models of endometriosis-associated pain require surgery either to implant tissue or to remove the ovaries. Moreover, existing models do not induce spontaneous pain, which is the primary symptom of patients with chronic pain, including endometriosis. A lack of models that accurately recapitulate the disease phenotype must contribute to the high failure rate of clinical trials for analgesic drugs directed at chronic pain, including those for endometriosis. We set out to establish a murine model of endometriosis-associated pain. Endometriosis was induced nonsurgically by injecting a dissociated uterine horn into a recipient mouse. The induced lesions exhibited histological features that resemble human lesions along with an increase in proinflammatory cytokines and recruitment of immune cells. We also observed the presence of calcitonin gene-related peptide-, TRPA1-, and TRPV1-expressing nerve fibers in the lesions. This model induced mechanical allodynia, spontaneous abdominal pain, and changes in thermal selection behavior that indicate discomfort. These behavioral changes were reduced by drugs used clinically for endometriosis, specifically letrozole (aromatase inhibitor) and danazol (androgen). Endometriosis also induced neuronal changes as evidenced by activation of the NF-κB signaling pathway in TRPA1- and TRPV1-expressing dorsal root ganglion neurons. In conclusion, we have established a model of endometriosis-associated pain that responds to clinically active drugs and can, therefore, be used to identify novel therapies.

A deep insight into pelvic pain and endometriosis: a review of the literature from pathophysiology to clinical expressions

Endometriosis is a chronic inflammatory disease that affects approximately 10% of women of reproductive age. Its clinical manifestations are highly heterogeneous, but pelvic pain is the most frequent, causing functional disability. Cyclic or acyclic chronic pelvic pain (CPP), dysmenorrhea and dyspareunia are frequent symptoms which often compromise all aspects of the women's quality of life (QoL). The pathophysiology of endometriosis-related pain is extremely complex and not always clear. The aim of this literature review is to focus on recent updates on the clinical presentation, the pathophysiology and the most important mechanisms involved in the pathogenesis of pelvic pain in endometriosis. A literature search in the Cochrane library, PubMed, Scopus and web of Science databases has been performed, identifying articles from January 1995 to November 2020. Several processes seem to be involved in the pathogenesis of pain, but many aspects are still unclear. Scientific evidence has shown that a correlation between pain severity and stage of endometriosis rarely occurs, whereas there is a significant correlation between pain and the presence of deep endometriosis. Onset and intensity of pain may be due to a complex process involving central sensitization and peripheral activation of nociceptive pathways as well as dysfunction of the immune system and of the hypothalamic-pituitary-adrenal (HPA) axis. A deeper understanding of these different pathogenetic mechanisms may improve future treatments in women with painful endometriosis.

Inflammatory Mediators and Pain in Endometriosis: A Systematic Review

BACKGROUND

pain is one of the main symptoms of endometriosis and it has a deleterious effect on a patients' personal and social life. To date, the clinical management of pain includes prolonged medication use and, in some cases, surgery, both of which are disruptive events for patients. Hence, there is an urgency for the development of a sufficient non-invasive medical treatment. Inflammation is one of the causative factors of pain in endometriosis. It is well established that inflammatory mediators promote angiogenesis and interact with the sensory neurons inducing the pain signal; the threshold of pain varies and it depends on the state and location of the disease. The inhibition of inflammatory mediators' synthesis might offer a novel and effective treatment of the pain that is caused by inflammation in endometriosis.

OBJECTIVES

patients with endometriosis experience chronic pelvic pain, which is moderate to severe in terms of intensity. The objective of this systematic review is to highlight the inflammatory mediators that contribute to the induction of pain in endometriosis and present their biological mechanism of action. In addition, the authors aim to identify new targets for the development of novel treatments for chronic pelvic pain in patients with endometriosis.

DATA SOURCES

three databases (PubMed, Scopus, and Europe PMC) were searched in order to retrieve articles with the keywords 'inflammation, pain, and endometriosis' between the review period of 1 January 2016 to 31 December 2020. This review has been registered with PROSPERO (registry number: CRD42020171018). Eligibility Criteria: only original articles that presented the regulation of inflammatory mediators and related biological molecules in endometriosis and their contribution in the stimulation of pain signal were included.

DATA EXTRACTION

two authors independently extracted data from articles, using predefined criteria.

RESULTS

the database search yielded 1871 articles, which were narrowed down to 56 relevant articles of interest according to the eligibility criteria.

CONCLUSIONS

inflammatory factors that promote angiogenesis and neuroangiogenesis are promising targets for the treatment of inflammatory pain in endometriosis. Specifically, CXC chemokine family, chemokine fractalkine, and PGE₂ have an active role in the induction of pain. Additionally, IL-1β appears to be the primary interleukin (IL), which stimulates the majority of the inflammatory factors that contribute to neuroangiogenesis along with IL-6. Finally, the role of Ninj1 and BDNF proteins needs further investigation.

Macrophage-derived netrin-1 contributes to endometriosis-associated pain

Background

Endometriosis-associated pain can be considered a type of neuropathic pain. Netrin-1 is an axon guidance cue that regulates axonal attraction or rejection in neural injury and regeneration. However, whether netrin-1 plays a role in endometriosis-associated pain remains unclear. This study aimed to determine the role of netrin-1 in endometriosis-related pain.

Methods

Peripheral blood, peritoneal fluid, and endometrial tissues were sampled from women with (n=37) and without endometriosis (n=23). Lipopolysaccharide (LPS) and interferon gamma (IFN-γ) were used to stimulate human monocytic cell lines (THP-1) and rat alveolar macrophage-derived cell lines (NR8383) to induce M1 phenotype macrophages. Serum netrin-1 concentrations, endometrial expression levels of netrin-1, and its receptors including deleted in colorectal cancer (DCC), A2B adenosine receptor (A2BAR), uncoordinated B receptor (UNC5B), uncoordinated C receptor (UNC5C) and Down’s syndrome cell adhesion molecule (DSCAM) were assessed. The polarization phenotypes of the peritoneal macrophages were identified by detecting the marker expression of M1/M2 macrophages via flow cytometry. The expression levels of M1 markers and netrin-1 in THP-1/NR8383 cells were determined.

Results

The expression levels of netrin-1 in serum and endometriotic lesions were significantly higher in women with endometriosis, and were positively correlated with the severity of endometriosis-associated pain. Netrin-1 was co-expressed with CD68 (a macrophage marker) in endometriotic lesions and was synthesized and secreted by THP-1 and NR8383 cells in the process of M1 polarization. In women with endometriosis, peritoneal macrophages were polarized towards the M1 phenotype. In addition, increased expression of DCC and A2BAR, and decreased expression of UNC5B, UNC5C and DSCAM were found in endometriotic lesions.

Conclusions

These results suggest that netrin-1 production by macrophages in endometriotic lesions may play an important role in endometriosis-associated pain.

The establishment of a mouse model of deep endometriosis

STUDY QUESTION

Is it possible to establish a mouse model of deep endometriosis (DE)?

SUMMARY ANSWER

A mouse DE model that is macroscopically and microscopically similar to nodular lesions in humans can be constructed in as short as 3 weeks by intraperitoneal injection of uterine fragments along with the infusion of substance P (SP) and/or calcitonin gene-related peptide (CGRP).

WHAT IS KNOWN ALREADY

Although a baboon DE model was reported 5 years ago, its prohibitive cost and demand for facilities and expertise associated with the use of non-human primates put its use out of reach for most laboratories.

STUDY DESIGN, SIZE, DURATION

A total of 48 female Balb/C mice were used for this study. Among them, 16 were randomly selected as donors that contributed uterine fragments, and the remaining 32 were recipient mice. The mice with induced endometriosis were followed up for 3-4 weeks.

PARTICIPANTS/MATERIALS, SETTING, METHODS

One day before the induction of endometriosis by intraperitoneal injection of uterine fragments, osmotic pumps were inserted into equal groups of recipient mice to infuse either sterile saline, SP, CGRP, or both SP and CGRP. The hotplate test was administrated to all mice at the baseline and before and after induction of endometriosis. Four (3 for the SP+CGRP group) weeks after induction, all mice were sacrificed. Their endometriotic lesions were excised, weighed and processed for histopathologic examination, and histochemistry, immunohistochemistry and immunofluorescence analyses of markers of proliferation, angiogenesis, epithelial-mesenchymal transition (EMT), fibroblast-to-myofibroblast transdifferentiation (FMT), smooth muscle metaplasia (SMM), mesothelial-mesenchymal transition (MMT) and endothelial-mesenchymal transition (EndoMT) were done. The extent of lesional fibrosis was evaluated by Masson trichrome staining. To further evaluate surrounding organ/tissue invasion, the peritoneal areas adhesive to the lesions were excised for immunohistochemical analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

Endometriotic lesions in mice treated with SP and/or CGRP satisfied all requirements for DE, i.e. presence of endometrial epithelial and stromal cells, abundance of fibromuscular content, and encapsulation in surrounding tissues or organs. The lesion weight in the CGRP, SP and SP+CGRP groups was 1.62, 2.14 and 2.18-fold, respectively, heavier than that of control group. Concomitantly, the SP, CGRP and SP+CGRP groups had significantly shorter hotplate latency than that of control group. Lesions in mice treated with SP and/or CGRP, especially with SP+CGRP, exhibited characteristics consistent with EMT, FMT, SMM and extensive fibrosis, along with signs of MMT and EndoMT. Lesional invasion into surrounding tissues/organs was found to be 25.0, 75.0 and 87.5% in mice treated with CGRP, SP and SP+CGRP, but none in control mice.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study is limited by the use of histologic and immunohistochemistry analyses only and lacks molecular data.

WIDER IMPLICATIONS OF THE FINDINGS

The establishment of a mouse DE model supports the idea that endometriotic lesions are wounds undergoing repeated tissue injury and repair and underscores the importance of microenvironments in shaping the lesions' destiny. In addition, signs consistent with MMT and EndoMT indicate that there may be more culpable factors that still remain unidentified and should be pursued in the future. Moreover, the close correlation between the extent of lesional fibrosis and markers of EMT, MMT, EndoMT, FMT and SMM as shown here should facilitate our understanding of the molecular mechanisms underlying the DE pathophysiology. Since this DE model is based on a biologically plausible and evidence-backed theory, it should shed much needed insight into the molecular mechanisms underlying the pathophysiology of DE.

STUDY FUNDING/COMPETING INTEREST(S)

This research was supported by Grants 81471434 (S.W.G.), 81530040 (S.W.G.), 81771553 (S.W.G.), 81671436 (X.S.L.) and 81871144 (X.S.L.) from the National Natural Science Foundation of China. None of the authors has any conflict of interest to disclose.

Eutopic stromal cells of endometriosis promote neuroangiogenesis via exosome pathway†

Endometriosis is a common multifactorial gynecological disorder defined as the proliferation of endometrial tissue outside of the uterine cavity. Neuroangiogenesis (co-recruitment of nerves and blood vessels) is believed to play an integral part in the establishment and growth of endometriotic lesions. We hypothesized that exosomes derived from abnormal endometrium may serve as the second identifier of endometriosis and play an important role in the development of endometriosis by regulating neuroangiogenesis. Primary human endometrial stromal cells (ESCs) were isolated from eutopic endometrium (EmESC, n = 22) with endometriosis and normal endometrium (CoESC, n = 6). Exosomes were isolated from ESCs using the "standard" ultracentrifugation method, and the characterization of exosomes was identified through transmission electron microscopy, nanoparticle tracking analysis, and western blot. The role of exosomes in regulating neuroangiogenesis was determined through in vitro tube formation assay, neurite outgrowth assay, and dorsal root ganglion (DRG) neuron apoptosis analysis. The data showed that EmESCs could secrete exosomes with a diameter of approximately 100 nm and a biconcave morphological feature; they were internalized by human umbilical vein endothelial cells and DRG neurons and enhanced neuroangiogenic effects. We further validated the role of exosomes through blocking experiments. We found that when the exosome secretion was blocked, the pro-neuroangiogenesis effects were decreased. In conclusion, these data suggested that exosomes may play a key role in endometriosis by promoting neuroangiogenesis.

Macrophage-derived netrin-1 is critical for neuroangiogenesis in endometriosis

Netrin-1 is an extracellular guidance cue of neuronal navigation, mediated through interaction with its main receptors, and is known to be crucial in the development of multiple chronic inflammatory diseases. However, the expression pattern and mechanism of netrin-1 in endometriosis are currently undefined. Here we report that netrin-1 expression peaked in peritoneal macrophages found in endometriosis. Netrin-1 induced angiogenesis in ovarian endometriomas through interaction with CD146 in vascular endothelial cells. Through another receptor, neogenin, netrin-1 promoted neurite growth and sensitization in endometriosis through the up-regulation of MAP4, TAU, and CGRP. Targeted knockdown of neogenin in dorsal root ganglion (DRG) nerve cells compromised its response to netrin-1 through inhibiting phosphorylation of ERK1/2. The inhibition of netrin-1 using a neutralizing antibody reduced vascular and nerve infiltration in rat endometriotic lesions. In summary, our results suggest that netrin-1 is an important factor that promotes neuroangiogenesis in 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.

Novel Drug Targets with Traditional Herbal Medicines for Overcoming Endometriosis

Endometriosis is a disease in which the lining of the endometrium is found outside of the uterus. Recent medical treatments for endometriosis have adverse effects, limiting their long-term use. Furthermore, the recurrence of the disease after the cessation of therapy is quite common, and most patients need to continue treatment to maintain a hypoestrogenic environment till conception. Notwithstanding recent advances in computational and chemical practices, traditional medicines are considered the most consistent sources for the discovery of new drugs. Numerous medicinal plants and plantderived compounds have been tested against gynecological disorders, mainly endometriosis. This review aimed to describe the pharmacological activity profile of the medicinal plants and their active ingredients and draw attention to the discovery of multitargeted drug molecules for rational therapy.

Effect of Dehydrocostus Lactone Isolated from the Roots of Aucklandia lappa on the Apoptosis of Endometriotic Cells and the Alternative Activation of Endometriosis-Associated Macrophages

The roots of Aucklandia lappa have been used in traditional medicine in Asia to treat inflammation and diseases associated with pain, including endometriosis. The aim of this study was to investigate the anti-endometriotic effect of dehydrocostus lactone, an active compound in A. lappa roots, using human endometriotic cells and macrophages stimulated by these cells. Dehydrocostus lactone induced apoptotic cell death in 12Z human endometriotic cells. Dehydrocostus lactone stimulated the activation of caspase-3, -8, and -9, while caspase inhibitors significantly reversed the dehydrocostus lactone-induced cell death in 12Z cells. In addition, dehydrocostus lactone decreased the production of PGE₂ and neurotrophins (BDNF, NGF, NT3, and NT4/5), which are regarded as endometriosis-associated pain factors in human endometriotic cells. Moreover, dehydrocostus lactone inhibited the expression of M2 markers (CD206, and Trem-2), IL-10, VEGF, and MMP-2/-9 in endometriosis-associated macrophages (EAMs). Furthermore, dehydrocostus lactone inhibited the Akt and NFκB pathways in both endometriotic cells and EAMs. Taken together, our findings suggest that dehydrocostus lactone, an active compound of A, lappa, has anti-endometriotic activities via induction of apoptosis and downregulation of pain factors in endometriotic cells and inhibition of the alternative activation of EAMs.

Endometriotic lesions

Endometriosis is a complex gynaecological condition affecting women of reproductive age. It is characterised by the presence of lesions containing endometrial glands and stroma outside the uterus. The disease is typically associated with pelvic pain (including dysmenorrhoea and dyspareunia), infertility and bowel-related symptoms. Endometriotic lesions have a highly variable presentation and most commonly occur in the abdominal cavity. These lesions are broadly classified into peritoneal, ovarian and deep infiltrating endometriosis. There have been observations of increased density of nerve fibres and neurological molecules in the endometriotic lesions compared to the uninvolved peritoneum of women without endometriosis and the presence of unmyelinated nerve fibres were higher near the glands. The lesion sites are characterised by a range of immunological alterations, and specific immune cell populations have also been known to synthesise and secrete neurogenic factors. Endometriotic lesions are capable of producing prostaglandins which are direct generators of pain and are capable of inducing inflammation. Diagnosing the disease involves direct visualisation of the lesions through a laparoscopic or laparotomy, which is followed by histopathological examination of biopsied or excised lesions. The staging of endometriosis due to its complexity is highly variable as presentation and gaps in knowledge pose a great challenge in the classification of the disease. The medical management of endometriosis aims at providing adequate analgesia and suppression of the activity of the lesion. A better understanding of endometriotic lesion relationships between innervations and specific clinical characteristics may elucidate aspects of pain mechanisms and infertility in endometriosis and facilitate the development of novel therapeutic approaches.

Nerve fibre infiltration and expression in peritoneal lesions of endometriosis in a nonhuman primate model of endometriosis

Baboon ( Papio anubis) models of endometriosis are thought to mimic the early stages of spontaneous human peritoneal endometriotic disease. The objective of this study was to investigate the presence and course of nerve fibre ingrowth during peritoneal lesion formation in specimens collected at 3 months (early stage of lesion development) and 15 months (late stage of lesion development) after disease initiation compared to pelvic peritoneum (control). Five-micron sections of paraffin-embedded peritoneal lesions were obtained from normally cycling baboons with 3-month (n = 12), 15-month (n = 12) induced endometriosis and pelvic peritoneum (n = 10) from baboons with no endometriosis. Immunohistochemical staining was performed with specific antibodies: protein gene product 9.5 – broad marker of nerve fibres and neurones, neuropeptide Y – sympathetic neurones, substance P – sensory neurones, vasoactive intestinal peptide – parasympathetic neurones, nerve growth factor – development of new neurones and high-affinity receptor for nerve growth factor (tropomyosin receptor kinase A) – neuronal differential. Significantly, more nerve fibres were identified in peritoneal endometriotic lesions collected 15 months after the initiation of experimental protocols compared with 3-month and control samples (p < 0.001). Nerve fibres were immunoreactive for all the tested markers – protein gene product 9.5, neuropeptide Y, substance P, vasoactive intestinal peptide, nerve growth factor and tropomyosin receptor kinase A – indicating the presence of different types of nerve fibres. In conclusion, peritoneal lesions of endometriosis in a nonhuman primate model of endometriosis were found to be progressively and spontaneously innervated by both myelinated and unmyelinated sensory nerve fibres, parasympathetic and sympathetic neurones. These nerve fibres may play an important role in the mechanisms of pain generation in this condition.

Perineural invasion in endometriotic lesions contributes to endometriosis-associated pain

Purpose

Recent studies have shown that abnormal distribution of pelvic nerves contributes to endometriosis-associated pain. However, the relationship between neurogenesis and pain severity in endometriosis still remains uncertain, which makes it an enigma for both gynecologists as well as neuropathologists. In this study, we tried to explore a special phenomenon, perineural invasion (PNI), in deep infiltrating endometriosis (DIE) and investigated the correlation between PNI- and DIE-associated pain.

Patients and methods

The study was conducted in the Department of Obstetrics and Gynecology of the First Affiliated Hospital of Sun Yat-sen University from June 2012 to January 2015. In total, 64 patients with DIE were enrolled. They received laparoscopically surgical resection of endometriotic lesions. The Kruskal–Wallis and Mann–Whitney tests were used for comparisons of enumeration data. Spearman rank correlation was used for linear analysis.

Results

Immunohistochemical analysis demonstrated that PNI was commonly found in DIE lesions. Patients were divided into PNI (+) group and PNI (−) group. The visual analog scale scores of dysmenorrhea, dyspareunia, and chronic pelvic pain were higher in PNI (+) group than in PNI (−) group. Also, we found significantly increased density of newly formed nerve fibers as well as microvessels in lesions of PNI (+) group. Further, double immunofluorescence showed a closely spatial nerve–vessel network in the endometriotic lesion of PNI (+) group. More importantly, correlation analysis revealed positive relation between the density of newly formed nerve fibers in the lesion and the density of microvessels in lesions of PNI (+) group.

Conclusion

This study suggests that PNI in endometriotic lesions plays an important role in endometriosis-associated pain, mainly through a mechanism named “neuroangiogenesis”.

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.

Endometriosis-associated Pain in Patients with and without Hormone Therapy

Introduction

Endometriosis is associated with both cyclic and non-cyclic pelvic pain. Many patients do not remain symptom free, even after guideline-oriented treatment. This study aimed to identify differences in endometriosis-associated pain and test for possible associations with hormone therapy.

Methods

The results presented here are based on a cross-sectional study conducted at the Charité Endometriosis Center in Berlin in which pain profile data were collected via a questionnaire from women with a confirmed diagnosis of endometriosis. The questionnaire contained items concerning cyclic and non-cyclic pain, pain intensity, and pain duration. SPSS software was used to perform the statistical analysis, including descriptive and analytical statistics.

Results

Of 239 women surveyed, 121 (50.6%) reported current hormone therapy, and 185 (77.4%) reported previous hormone therapy. Moreover, 84% had current (cyclic and non-cyclic) pain symptoms, which were severe enough to warrant treatment in nearly 70% of all cases. Hormone therapy was only found to be associated with a slight, non-significant advantage in patients with “cyclic pain”. The reverse was true of non-cyclic pain: women on hormone therapy reported a greater incidence of pain, greater pain intensity, more frequent need for treatment, and more pain days.

Conclusions

With a very broad interpretation of our findings, it can be concluded that hormone therapy achieves some degree of pain reduction via down-regulation of the ovarian cycle, at least in the case of cyclic pain, whereas non-cyclic pain does not respond or no longer responds to hormones.

Human microvascular endothelial cell promotes the development of dorsal root ganglion neurons via BDNF pathway in a co-culture system

Our previous study found that co-culture with human vascular endothelial cells (HMVECs) is beneficial for dorsal root ganglion cells (DRGCs). The goal of the present study is to investigate whether co-culture with HMVECs could promote the development of DRGCs, and whether this effect is induced by the secretion of BDNF by HMVECs. DRGCs were mono-cultured, co-cultured with HMVECs or co-cultured with HMVECs that pre-transfected with BDNF siRNA, the expression of neurite formation and branching factors were determined. The results showed that transfecting with BDNF siRNA inhibited BDNF expression and reduced BDNF secretion. Co-culture with HMVECs increased the expression of Etv4, Etv5, FN-L, FN-M, and GAP-43 in DRGCs that accompanied by the activation of ERK pathway. However, these changes were all reversed by the inhibition of BDNF in HMVECs. In conclusion, our data demonstrate that HMVECs potentiated DRGCs development at least partly by the secretion of BDNF in the co-culture system.

Macrophage and nerve interaction in endometriosis

Dysregulation of the immune system in endometriotic milieus has been considered to play a pivotal role in the pathogenesis of endometriosis. Macrophage recruitment and nerve fiber infiltration are the two major characteristics of this aberrant immune environment. First, the recruitment of macrophages and their polarization phenotype within the endometriotic lesion have been demonstrated to facilitate the development and maintenance of endometriosis. M1 phenotype of macrophages has the capacity to secrete multiple cytokines for inflammatory response, while M2 macrophage possesses an opposite property that can mediate the process of immunosuppression and neuroangiogenesis. Upon secretion of multiple abnormal signal molecules by the endometriotic lesion, macrophages could alter their location and phenotype. These changes facilitate the accommodation of the aberrant microenvironment and the exacerbation of disease progression. Second, the infiltration of nerve fibers and their abnormal distribution are proved to be involved in the generation of endometriosis-associated pain and inflammatory response. An imbalance in sensory and sympathetic innervation and the abnormal secretion of different cytokines could mediate neurogenesis and subsequent peripheral neuroinflammation in endometriosis. Although endometriosis creates an inflammatory milieu promoting macrophage infiltration and an imbalanced innervation, interaction between macrophages and nerve fibers in this process remains unknown. The aim of this review is to highlight the role of macrophage and nerve interaction in endometriosis, where macrophage recruitment and neurogenesis can be the underlying mechanism of neuroinflammation and pathogenesis of endometriosis.

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.

Research Priorities for Endometriosis

The 3rd International Consensus Workshop on Research Priorities in Endometriosis was held in São Paulo on May 4, 2014, following the 12th World Congress on Endometriosis. The workshop was attended by 60 participants from 19 countries and was divided into 5 main sessions covering pathogenesis/pathophysiology, symptoms, diagnosis/classification/prognosis, disease/symptom management, and research policy. This research priorities consensus statement builds on earlier efforts to develop research directions for endometriosis. Of the 56 research recommendations from the 2011 meeting in Montpellier, a total of 41 remained unchanged, 13 were updated, and 2 were deemed to be completed. Fifty-three new research recommendations were made at the 2014 meeting in Sao Paulo, which in addition to the 13 updated recommendations resulted in a total of 66 new recommendations for research. The research recommendations published herein, as well as those from the 2 previous papers from international consensus workshops, are an attempt to promote high-quality research in endometriosis by identifying and agreeing on key issues that require investigation. New areas included in the 2014 recommendations include infertility, patient stratification, and research in emerging nations, in addition to an increased focus on translational research. A revised and updated set of research priorities that builds on this document will be developed at the 13th World Congress on Endometriosis to be held on May 17-20, 2017, in Vancouver, British Columbia, Canada.

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 Semaphorin 3A and Its Receptors in Regulating Aberrant Sympathetic Innervation in Peritoneal and Deep Infiltrating Endometriosis

Previous studies have demonstrated the involvement of nerve repellent factors in regulation of the imbalanced innervation of endometriosis. This prospective study aims to explore the role of Sema 3A in regulating aberrant sympathetic innervation in peritoneal and deep infiltrating endometriosis. Ectopic endometriotic lesion were collected from patients with peritoneal endometriosis (n = 24) and deep infiltrating endometriosis of uterosacral ligament (n = 20) undergoing surgery for endometriosis. Eutopic endometrial samples were collected from patients with endometriosis (n = 22) or without endometriosis (n = 26). Healthy peritoneum (n = 13) from the lateral pelvic wall and healthy uterosacral ligament (n = 13) were obtained from patients who had no surgical and histological proof of endometriosis during hysterectomy for uterine fibroids. Firstly, we studied the immunostaining of Sema 3A, Plexin A1 and NRP-1 in all the tissues described above. Then we studied the nerve fiber density (NFD) of endometriosis-associated (sympathetic) nerve and para-endometriotic (sympathetic) nerve by double immunofluorescence staining. Finally we analyzed the relationship between expression of Sema 3A in stromal cells of endometriotic lesion and the aberrant innervation of endometriosis. Semi-quantitative immunostaining demonstrated that (1) Higher immunostaining of Sema 3A were found in the eutopic endometrial glandular epithelial cells from patients with endometriosis (p = 0.041) than those without endometriosis; (2) Sema 3A immunostaining was higher in glandular epithelial cells of peritoneal endometriosis (P<0.001) and deep infiltrating endometriotic lesions of uterosacral ligament (P = 0.028)compared with glandular epithelial cells of the endometrium from women with endometriosis, while its expression in ectopic stormal cells in both groups were significantly lower than that from eutopic endometrium of women without endometirosis (P<0.001, P<0.001, respectively). NFDs of Anti-TH (+) endometriosis-associated sympathetic nerve of peritoneal endometriosis (p<0.001) and deep endometriosis of uterosacral ligament (p<0.001) were significantly lower than NFDs of para-endometriotic sympathetic nerve. Our results suggest that Sema 3A may contribute to the regulation of aberrant sympathetic innervation in peritoneal and deep infiltrating endometriosis.

The importance of pelvic nerve fibers in endometriosis

Several lines of recent evidence suggest that pelvic innervation is altered in endometriosis-affected women, and there is a strong presumption that nerve fibers demonstrated in eutopic endometrium (of women with endometriosis) and in endometriotic lesions play roles in the generation of chronic pelvic pain. The recent observation of sensory C, sensory A-delta, sympathetic and parasympathetic nerve fibers in the functional layer of endometrium of most women affected by endometriosis, but not demonstrated in most women who do not have endometriosis, was a surprise. Nerve fiber densities were also greatly increased in myometrium of women with endometriosis and in endometriotic lesions compared with normal peritoneum. Chronic pelvic pain is complex, and endometriosis is only one condition which contributes to this pain. The relationship between the presence of certain nerve fibers and the potential for local pain generation requires much future research. This paper reviews current knowledge concerning nerve fibers in endometrium, myometrium and endometriotic lesions, and discusses avenues of research that may improve our knowledge and lead to enriched understanding and management of endometriotic pain symptoms.

Innervation in women with uterine myoma and adenomyosis

Objective

To determine if neurofilament (NF) is expressed in the endometrium and the lesions of myomas and adenomyosis, and to determine their correlation.

Methods

Histologic sections were prepared from hysterectomies performed on women with adenomyosis (n=21), uterine myoma (n=31), and carcinoma in situ of the uterine cervix. Full-thickness uterine paraffin blocks, which included the endometrium and myometrium histologic sections, were stained immunohistochemically using the antibodies for monoclonal mouse antihuman NF protein.

Results

NF-positive cells were found in the endometrium and myometrium in 11 women with myoma and in 7 with adenomyosis, but not in patients with carcinoma in situ of uterine cervix, although the difference was statistically not significant. There was no significant difference between the existence of NF-positive cells and menstrual pain or phases. The NF-positive nerve fibers were in direct contact with the lesions in nine cases (29.0%) of myoma and in five cases (23.8%) of adenomyosis. It was analyzed if there was a statistical significance between the existence of NF positive cells in the endometrium and the expression of NF-positive cells in the uterine myoma/adenomyosis lesions. When NF-positive cell were detected in the myoma lesions, the incidence of NF-positive nerve cells in the eutopic endometrium was significantly high. When NF-positive cell were detected in the basal layer, the incidence of NF-positive nerve cells in the myoma lesions and adenomyosis lesions was significantly high.

Conclusion

We assume that NF-positive cells in the endometrium and the myoma and adenomyosis lesions might play a role in pathogenesis. Therefore, more studies may be needed on the mechanisms of nerve fiber growth in estrogen-dependent diseases.

Dual suppression of estrogenic and inflammatory activities for targeting of endometriosis

Estrogenic and inflammatory components play key roles in a broad range of diseases including endometriosis, a common estrogen-dependent gynecological disorder in which endometrial tissue creates inflammatory lesions at extrauterine sites, causing pelvic pain and reduced fertility. Current medical therapies focus primarily on reducing systemic levels of estrogens, but these are of limited effectiveness and have considerable side effects. We developed estrogen receptor (ER) ligands, chloroindazole (CLI) and oxabicycloheptene sulfonate (OBHS), which showed strong ER-dependent anti-inflammatory activity in a preclinical model of endometriosis that recapitulates the estrogen dependence and inflammatory responses of the disease in immunocompetent mice and in primary human endometriotic stromal cells in culture. Estrogen-dependent phenomena, including cell proliferation, cyst formation, vascularization, and lesion growth, were all arrested by CLI or OBHS, which prevented lesion expansion and also elicited regression of established lesions, suppressed inflammation, angiogenesis, and neurogenesis in the lesions, and interrupted crosstalk between lesion cells and infiltrating macrophages. Studies in ERα or ERβ knockout mice indicated that ERα is the major mediator of OBHS effectiveness and ERβ is dominant in CLI actions, implying involvement of both ERs in endometriosis. Neither ligand altered estrous cycling or fertility at doses that were effective for suppression of endometriosis. Hence, CLI and OBHS are able to restrain endometriosis by dual suppression of the estrogen-inflammatory axis. Our findings suggest that these compounds have the desired characteristics of preventive and therapeutic agents for clinical endometriosis and possibly other estrogen-driven and inflammation-promoted disorders.

Inflammation and nerve fiber interaction in endometriotic pain

Endometriosis is an extremely prevalent estrogen-dependent condition characterized by the growth of ectopic endometrial tissue outside the uterine cavity, and is often presented with severe pain. Although the relationship between lesion and pain remains unclear, nerve fibers found in close proximity to endometriotic lesions may be related to pain. Also, women with endometriosis pain develop central sensitization. Endometriosis creates an inflammatory environment and recent research is beginning to elucidate the role of inflammation in stimulating peripheral nerve sensitization. In this review, we discuss endometriosis-associated inflammation, peripheral nerve fibers, and assess their potential mechanism of interaction. We propose that an interaction between lesions and nerve fibers, mediated by inflammation, may be important in endometriosis-associated pain.

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.

Role of nociceptor estrogen receptor GPR30 in a rat model of endometriosis pain

Endometriosis, the most common cause of chronic pelvic pain, is an estrogen-dependent disease in which classic estrogen receptors (ERα, ERβ) play an important role. Although recent evidence suggests that the novel G protein-coupled estrogen receptor (GPR30) also plays a key role in the progression of endometriosis, whether it is also involved in endometriosis pain is still unknown. Here we tested the hypothesis that GPR30 expressed by nociceptors contributes to endometriosis pain. Intramuscular injection of the GPR30 agonists raloxifene or 17β-estradiol produced a fast-onset, persistent, mechanical hyperalgesia at the site of the injection. Intrathecal antisense (AS) oligodeoxynucleotides (ODN), but not mismatch (MM) ODN, targeting mRNA for GPR30 markedly inhibited its protein expression in nociceptors and attenuated the mechanical hyperalgesia induced by local raloxifene or 17β-estradiol. Pretreatment with the GPR30 antagonist G-36 also inhibited the hyperalgesia induced by raloxifene or 17β-estradiol in naive control rats. Surgical implant of autologous uterine tissue onto the gastrocnemius muscle, which induces endometriosis-like lesions, produced local mechanical hyperalgesia. Intrathecal AS, but not MM, ODN targeting GPR30 mRNA reversibly inhibited the mechanical hyperalgesia at the site of endometriotic lesions. Finally, intralesional injection of the GPR30 antagonist G-36 also inhibited the mechanical hyperalgesia at the site of ectopic uterine tissue. We conclude that local GPR30 agonists produce persistent mechanical hyperalgesia in naive female rats, whereas local GPR30 antagonists inhibit mechanical hyperalgesia in a model of endometriosis pain. Thus, GPR30 expressed by nociceptors innervating ectopic uterine lesions might play a major role in endometriosis pain.

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.

Elevated peritoneal expression and estrogen regulation of nociceptive ion channels in endometriosis

CONTEXT

Ovarian suppression is a common treatment for endometriosis-associated pelvic pain. Its exact mechanism of action is poorly understood, although it is assumed to reflect reduced production/action of estrogens.

OBJECTIVE

The objective of the study was to measure the expression of mRNAs encoded by nociceptive genes in the peritoneum of women with chronic pelvic pain (CPP) with or without endometriosis and to investigate whether estrogens alter nociceptive gene expression in human sensory neurons.

DESIGN

The study was performed using human tissue analysis and cell culture.

SETTING

The study was conducted at a university research institute.

PATIENTS

Peritoneal biopsies were obtained from women with CPP and endometriosis (n = 12), CPP and no endometriosis (n = 10), and no pain or endometriosis (n = 5). Endometriosis lesions were obtained from women with endometriosis (n = 18).

MAIN OUTCOME MEASURES

mRNAs encoding ion channels (P2RX3, SCN9A, SCN11A, TRPA1, TRPV1) and the neurotransmitter TAC1 were measured in human tissue samples and in human embryonic stem cell-derived sensory neurons treated with estrogens.

RESULTS

TRPV1, TRPA1, and SCN11A mRNAs were significantly higher in the peritoneum from women with endometriosis (P < .001, P < .01). TRPV1, SCN9A, and TAC1 were elevated in endometriosis lesions (P < .05). P2RX3 mRNA was increased in the peritoneum of women with CPP, with and without endometriosis (P < .05). Incubation of sensory neurons with 17β-estradiol increased TRPV1 mRNA (P < .01). The estrogen receptor-β-selective agonist 2,3-bis(4-hydroxy-phenyl)-propionitrile increased concentrations of TRPV1, P2RX3, SCN9A, and TAC1 mRNAs.

CONCLUSIONS

Estrogen-dependent expression of TRPV1 in sensory neurons may explain why ovarian suppression can reduce endometriosis-associated pain. Strategies directly targeting ion channels may offer an alternative option for the management of CPP.

An Investigation of the Relationship between Pelvic Pain and Density of Nerve Fibers in Peritoneal Lesions of Endometriosis

Purpose

Endometriosis is a gynecological disease often characterized by severe pelvic pain, including perimenstrual and intermenstrual pain and dyspareunia. Sensory nerve fibers within peritoneal lesions have previously been shown to contribute to generation of pain in endometriosis; however, their association with different types of pelvic pain is currently uncertain.

Methods

Peritoneal endometriotic lesions (n = 30) were sectioned and stained immunohistochemically with protein gene product 9.5 (PGP 9.5; pan-neuronal marker), neuropeptide Y (NPY; sympathetic), vasoactive intestinal polypeptide (VIP; parasympathetic), substance P (SP; sensory) and nerve growth factor (NGF) to identify nerve fibers and neurotrophin levels. Densities were assessed within stroma of the lesions and in the adjacent peritoneum. Pelvic pain scores were obtained using a visual analogue scale (VAS), and correlation analysis was performed.

Results

Increased density of nerve fibers was observed within the stroma of lesions. NGF expression was significantly increased in glandular epithelium, compared with stromal regions (p = 0.026) and correlated inversely with menstrual pain scores (p = 0.05). Sympathetic nerve fiber density (NPY) in stroma showed a significant positive correlation with intensity of menstrual pain (p = 0.04). Parasympathetic nerve fiber density (VIP) also showed a strong trend toward a positive correlation with menstrual pain intensity (p = 0.056).

Conclusions

There is increased neurogenesis in the stromal region. Innervation of lesions correlates to intensity of menstrual pain. NGF in glandular epithelium may promote growth of nerve fibers into the core of lesions; however, the inverse correlation between NGF expression in glandular epithelium and menstrual pain indicates that mechanisms of pain generation in endometriosis are complex.

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.

Glucose transporter expression in eutopic endometrial tissue and ectopic endometriotic lesions

Endometriosis is an extremely prevalent disorder characterized by the growth of endometrial tissue at ectopic locations. Glycolysis is an energy-producing mechanism that occurs in almost all cells and requires an adequate uptake of glucose mediated by glucose transporter (GLUT) proteins. At present, however, very little is known about their expression in either the endometrium or the endometriotic lesions. The objective of this study was to examine the expression of SLC2A genes in the endometrium of women with and without endometriosis and in the matching ectopic tissue, and to confirm the presence of the GLUT proteins in ectopic lesions. There was a significantly higher expression of SLC2A3 and a significantly lower expression of SLC2A4 in women with endometriosis compared with those without. In women with endometriosis, the ectopic expression of SLC2A3, SLC2A4 and SLC2A5 was significantly higher than that observed in the matching eutopic tissue. GLUT1 protein expression was present in both epithelial and stromal cells and GLUT3 was confined to CD45-positive leukocytes. GLUT4 expression was strong in both ectopic epithelial and stromal cells and localized to the cellular membrane in epithelial cells. These results show that GLUT expression is altered between eutopic and ectopic tissue and between women with and without endometriosis, and that GLUT4 may represent a significant entry route for glucose into the endometriotic epithelial cells. The inducible nature of GLUT4 and its limited cellular expression may make GLUT4 an attractive target for non-hormone-based treatments of endometriosis.

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.

Bladder endometriosis: characterization by magnetic resonance imaging and the value of documenting ureteral involvement

OBJECTIVES

To characterize bladder endometriosis by MRI and assess aspects of ureteral involvement.

STUDY DESIGN

From 2007 to 2013, bladder endometriosis was diagnosed, surgically treated and histopathologically verified in 18 patients (mean age 31.7±4.6 years) retrospectively enrolled under a published MRI protocol at our hospital's Endometriosis Center. Preoperatively, to diagnose disease spread, cystoscopy was performed and MRI in the following sequences: T2-TSE and T1-SE with and without fat saturation in the sagittal and transversal planes after rectovaginal opacification. Nine patients additionally underwent a diffusion-weighted sequence, including calculation of the apparent diffusion coefficient (ADC). By consensus, two experienced radiologists, without prior knowledge of the surgical or cystoscopic findings, retrospectively characterized bladder endometriosis on the MRI scans, also determining anatomic position, size, sequence-dependent features and incidence of hemorrhages, and calculating ADC. The scans were also investigated to determine if MRI could detect ureteral involvement intercurrent with bladder endometriosis.

RESULTS

Endometriosis localizations were bladder roof, n=1 (5.6%) and back wall, n=17 (94.4%). Mean lesion size was 3.65±1.5ml. Lesions exhibited a lower signal intensity in T2- than in T1-weighted images. High-signal-intensity spots showed an occurrence of 72.2% in fat-suppressed T1-weighted and 61.1% in T2-weighted sequences. Mean ADC was 1251.6±220.9mm(2)/s. By MRI, it was not possible to differentiate wall layers and hence infiltration depth. The bladder endometriosis of two women showed direct involvement with the right ureter. Furthermore, one woman had endometriosis of the left distal ureter in addition to bladder endometriosis. All cases of ureteral involvement were detected by MRI.

CONCLUSIONS

Characteristic MRI features of bladder endometriosis were found to be low signal intensity in T2-weighted and high-signal-intensity spots in T1- and T2-weighted sequences. Standard-sequence MRI was capable of detecting ureteral involvement, but not bladder wall infiltration depth.

L1 cell adhesion molecule as a potential therapeutic target in murine models of endometriosis using a monoclonal antibody approach

Background/Aims

The neural cell adhesion molecule L1CAM is a transmembrane glycoprotein abnormally expressed in tumors and previously associated with cell proliferation, adhesion and invasion, as well as neurite outgrowth in endometriosis. Being an attractive target molecule for antibody-based therapy, the present study assessed the ability of the monoclonal anti-L1 antibody (anti-L1 mAb) to impair the development of endometriotic lesions invivo and endometriosis-associated nerve fiber growth.

Methods and Results

Endometriosis was experimentally induced in sexually mature B6C3F1 (n=34) and CD-1 nude (n=21) mice by autologous and heterologous transplantation, respectively, of endometrial fragments into the peritoneal cavity. Transplantation was confirmed four weeks post-surgery by invivo magnetic resonance imaging and laparotomy, respectively. Mice were then intraperitoneally injected with anti-L1 mAb or an IgG isotype control antibody twice weekly, over a period of four weeks. Upon treatment completion, mice were sacrificed and endometrial implants were excised, measured and fixed. Endometriosis was histologically confirmed and L1CAM was detected by immunohistochemistry. Endometriotic lesion size was significantly reduced in anti-L1-treated B6C3F1 and CD-1 nude mice compared to mice treated with control antibody (P<0.05). Accordingly, a decreased number of PCNA positive epithelial and stromal cells was detected in autologously and heterologously induced endometriotic lesions exposed to anti-L1 mAb treatment. Anti-L1-treated mice also presented a diminished number of intraperitoneal adhesions at implantation sites compared with controls. Furthermore, a double-blind counting of anti-neurofilament L stained nerves revealed significantly reduced nerve density within peritoneal lesions in anti-L1 treated B6C3F1 mice (P=0.0039).

Conclusions

Local anti-L1 mAb treatment suppressed endometriosis growth in B6C3F1 and CD-1 nude mice and exerted a potent anti-neurogenic effect on induced endometriotic lesions invivo. The findings of this preliminary study in mice provide a strong basis for further testing in invivo models.

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.

Induction of the neurokinin 1 receptor by TNFα in endometriotic tissue provides the potential for neurogenic control over endometriotic lesion growth

CONTEXT

Endometriosis is characterized by the growth of ectopic endometrial tissue. Nerve fibers are frequently associated with ectopic lesions, and neurogenic inflammation may play a role in endometriosis.

OBJECTIVE

The purpose of this study was to determine the presence of tachykinin receptors in endometriotic lesions and the role of TNFα on their expression.

DESIGN

This study was an assessment of matching eutopic and ectopic endometrial tissue and peritoneal fluid from patients with endometriosis and an in vitro analysis of primary endometrial cells.

SETTING

The setting was a university hospital.

PATIENTS

Participants were premenopausal women undergoing laparoscopy.

INTERVENTIONS

Endometriotic lesions were removed surgically.

MAIN OUTCOME MEASURES

Tachykinin mRNA (TACR1/2) and protein (neurokinin 1 receptor [NK1R]) expression in both eutopic and ectopic endometrial tissue from patients with endometriosis and the correlation to peritoneal fluid TNFα were measured. Primary endometrial epithelial and stromal cells were assessed in vitro to determine the induction of TACR1/2 and NK1R expression after TNFα treatment. Cell viability of endometrial stromal cells after substance P exposure was also assessed.

RESULTS

Expression of both TACR1 and TACR2 mRNA was significantly higher in the ectopic than in the eutopic tissue. Both TACR1 mRNA and NK1R protein expression was significantly correlated with peritoneal fluid TNFα, and in vitro studies confirmed that TNFα treatment induced both TACR1 mRNA and NK1R protein expression in endometrial stromal cells. In endometrial stromal cells, substance P treatment enhanced cell viability, which was inhibited by a specific NK1R antagonist.

CONCLUSIONS

NK1R expression is induced in ectopic endometrial tissue by peritoneal TNFα. Induction of NK1R expression may permit endometriotic lesion maintenance via exposure to substance P.

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.