PGP9.5-immunoactive Nerve Fibers In Peritoneal Endometriotic Lesions In Women With Endometriosis

BACKGROUNDEndometriosis is a common gynaecological disease and is frequently associated with recurrent and serious pelvic pain such as dysmenorrhoea and dyspareunia, but the mechanisms by which these symptoms are generated are not well understood. Endometriosis can be divided into the different types of peritoneal endometriosis (PE), ovarian endometriosis and deep infiltrating endometriosis(DIE) according to the distribution of lesions, clinical manifestations and treatment. All these three types can cause a series of pain symptoms, but DIE does the best, Therefore, the research into the associations of DIE and pain is also the most. However, the research on the pathophysiological basis for PE-associated pelvic pain and the innervation of peritoneal endometriotic lesions is the less.The associations of PE and pelvic pain remain unclear up to date because the severity of PE-associated pelvic pain does not always correlate closely with the disease stage,lesion type or site. Recently, Tokushige et al. have found that pain-conducting substance P-positive nerve fibers were present in human peritoneal endometriotic lesions. These nerve fibers could be characterized as sensory AS, sensory C, cholinergic,and adrenergic nerve fibers, and were more frequently seen near endometriotic glands. Moreover, there were more nerve fibres in peritoneal endometriotic lesions in women with endometriosis than in normal peritoneum. Consquently, Tokushige considered these nerve fibers as endometriosis-associated nerve fibers..Mechsner et al. have found that Growth-associated protein 43 (GAP-43), a marker molecule for neurite outgrowth and regeneration, is expressed in endometriosis-associated nerve fibers but not in peritoneal nerve fibers distant to the endometriotic lesion. These findings suggest that nerve fibers in peritoneal endometriotic lesions are newborn and may play an important role in the etiology of PE-associated pelvic pain. The PE-associated nerve fibers are accompanied by immature blood vessels within the stroma. This may be due to the interaction of nerve growth factor(NGF) and vascular endothelial growth factor(VEGF).NGF involvements in the regulation of blood vessel and neurite sprouting. VEGF can act both as a angiogenic factor and a neurotrophic factor stimulating the growth of blood vessels and nerve fibres. These data suggest that peritoneal endometriotic cells exhibit neurotrophic properties and imply that the fibers play an important role in the etiology of endometriosis-associated pelvic pain.Recently, some researchers suggest that in peritoneal endometriotic lesions of patients with severe symptoms there were significantly more endometriosis-associated nerve fibers than in those of patients with only a few of pain symptoms.They also demonstrated that the density of nerve fibers in peritoneal endometriotic lesions was statistically higher in endometriosis women with chronic pelvic pain and/or dysmenorrheoa than in endometriosis women with other pain . However, they did not find any differences of the density of nerve fibers in peritoneal endometriotic lesions among the type and site of endometriotic lesions as well as the disease stage. In a rat model of surgically induced endometriosis, it has been shown that ectopic endometrial growth induces its own autonomic and sensory innervation. In rodents, the sensory and sympathetic nerve supply seem to develop within ectopic endometrial implants. These data suggest that pain-associated nerve fibers in peritoneal endometriotic lesions may play an important role in the mechanism of pain generation in women with endometriosis.PGP9.5 is a highly specific pan-neuronal marker for both myelinated and unmyelinated nerve fibres, including Aα,Aβ,Aγ,Aδ,B and C fibres, Immunohistochemistry studies have demonstrated the wide distribution of PGP9.5 in the central and peripheral nervous systems, and the localization of PGP9.5 in all neurons and nerve fibres at all levels of the central and peripheral nervous system as well as in cells of the diffuse neuroendocrine system. In fact, PGP9.5 has recently been considered as a good diagnostic marker when using endometrial biopsy for investigating endometriosisIn the present study, we use PGP9.5 to investigate the association of nerve fibres in peritoneal endometriotic lesions in women with endometriosis and the disease-associated pain symptoms.MATERIALS AND METHODS1. Objects: Thirty-two peritoneal endometriotic lesions from women with PE (Stages I- IV,with pain, n=16; without pain, n=16) and 20 normal peritoneal tissues from women without endometriosis ( with uterine leiomyoma and without pain symptoms).2.Methods:2.1 Determination of nerve fibres in peritoneal endometriotic lesionsEnvision immunohistochemistry: All samples were stained immunohistochemically for the highly specific polyclonal rabbit anti-protein gene product 9.5 (PGP9.5) to demonstrate both myelinated and unmyelinated nerve fibers.2.2 Evaluation of pain degree and typesUsing a standardized questionnaire with a visual analogue scale(VAS), the severity of pain symptoms, such as pelvic pain and dysmenorrhea, was documented before surgery. The pain scale was subdivided into 10 grades. "No pain" was indicated at the left side of the scale and "the maximum pain you could imagine" at the right side of the scale. The patient should point out the severity of pain and the type of pain. We define patients with pelvic pain during menstruation as dysmenorrhea, and with persistent pelvic pain lasting more than six month as chronic pelvic pain.3.Statistical analysis:All data were managed with SPSS 15.0 for windows. Kruskal-Wallis H,chi-square,Mann-Whitney U,Wilcoxon and Spearman rank correlation analysis were used for statistical analysis. Two-tailed test with p<0.05 were considered significance.RESULTS1. The positive rate and the density of PGP9.5-immunoreactive nerve fibers were both significantly higher in peritoneal endometriotic lesions in PE women with pain than in PE women without pain (P<0.05), and in normal peritoneal tissues in women without endometriosis (P<0.05) although no differences were found between peritoneal endometriotic lesions in endometriosis women without pain and normal peritoneal tissues in women without endometriosis (P>0.05)2. The density of PGP9.5-immunoreactive nerve fibers in peritoneal endometriotic lesions in PE women with pain was significantly correlated with the severity of pain (P<0.001).3. The density of PGP9.5-immunoreactive nerve fibers in peritoneal endometriotic lesions was statistically higher in PE women with chronic pelvic pain and/or dysmenorrheoa than in PE women with other pain(P<0.05). However, we did not found any differences of the density of PGP9.5-immunoreactive nerve fibers in peritoneal endometriotic lesions among the type and site of endometriotic lesions as well as the disease stage.CONCLUSIONThese results suggest that pain-associated PGP9.5-immunoreactive nerve fibers in peritoneal endometriotic lesions may play an important role in the mechanisms of pain generation in women with PE.