The Tissue Renin-Angiotensin System and Its Role in the Pathogenesis of Major Human Diseases: Quo Vadis?

Evidence has arisen in recent years suggesting that a tissue renin-angiotensin system (tRAS) is involved in the progression of various human diseases. This system contains two regulatory pathways: a pathological pro-inflammatory pathway containing the Angiotensin Converting Enzyme (ACE)/Angiotensin II (AngII)/Angiotensin II receptor type 1 (AGTR1) axis and a protective anti-inflammatory pathway involving the Angiotensin II receptor type 2 (AGTR2)/ACE2/Ang1-7/MasReceptor axis. Numerous studies reported the positive effects of pathologic tRAS pathway inhibition and protective tRAS pathway stimulation on the treatment of cardiovascular, inflammatory, and autoimmune disease and the progression of neuropathic pain. Cell senescence and aging are known to be related to RAS pathways. Further, this system directly interacts with SARS-CoV 2 and seems to be an important target of interest in the COVID-19 pandemic. This review focuses on the involvement of tRAS in the progression of the mentioned diseases from an interdisciplinary clinical perspective and highlights therapeutic strategies that might be of major clinical importance in the future.

Immune activation enhances epithelial nerve growth in provoked vestibulodynia.

BACKGROUND: Provoked vestibulodynia manifests as allodynia of the vulvar vestibular mucosa. The exact mechanisms that result in altered pain sensation are unknown. Recently, we demonstrated the presence of secondary lymphoid tissue, which is the vestibule-associated lymphoid tissue in the vestibular mucosa, and showed that this tissue becomes activated in provoked vestibulodynia. OBJECTIVE: The purpose of this study was to examine whether expression of intraepithelial nerve fibers and nerve growth factor are related to immune activation in provoked vestibulodynia. STUDY DESIGN: Vestibular mucosal specimens were obtained from 27 patients with severe provoked vestibulodynia that was treated by vestibulectomy and from 15 control subjects. We used antibodies against the protein gene product 9.5, the neuron specific neurofilament, and nerve growth factor for immunohistochemistry to detect intraepithelial nerve fibers and nerve growth factor expressing immune cells in the vestibular mucosa. For intraepithelial nerve fibers, we determined their linear density (fiber counts per millimeter of the outer epithelial surface, protein gene product 9.5) or presence (neuron specific neurofilament). Nerve growth factor was analyzed by counting the staining-positive immune cells. Antibodies against CD20 (B lymphocytes) and CD3 (T lymphocytes) were used to identify and locate mucosal areas with increased density of lymphocytes and the presence of germinal centers (ie, signs of immune activation). B-cell activation index was used to describe the overall intensity of B-cell infiltration. RESULTS: We found more protein gene product 9.5-positive intraepithelial fibers in vestibulodynia than in the control samples (6.3/mm [range, 0.0-15.8] vs 2.0/mm [range, 0.0-12.0]; P=.006). Neuron specific neurofilament -positive intraepithelial fibers were found in 17 of 27 vestibulodynia cases (63.0%) and in none of the control cases. Protein gene product 9.5-positive intraepithelial fibers were more common in samples with more pronounced immune activation. The density of these fibers was higher in samples with than without germinal centers (6.1/mm [range, 4.3-15.8] vs 3.0/mm [range, 0.0-13.4]; P=.020). A positive correlation between the fiber density and B-cell activation index score of the sample was found (Spearman's Rho, 0.400; P=.004; R2=0.128). No significant difference, however, was found in the density or presence of nerve fibers between samples with high and low T-cell densities. We identified areas of minor and major vestibular glands in 16 of the patient samples and in 1 control sample. Protein gene product 9.5-positive nerve fibers were found more often in glandular epithelium surrounded by B-cell infiltration than in glands without B cells (P=.013). Also, the presence of neuron specific neurofilament-positive fibers in glandular epithelium was associated with B-cell infiltrates (P=.053). Nerve growth factor-positive immune cells were more common in mucosal areas with than without B-cell infiltration and intraepithelial nerve fibers. CONCLUSION: Excessive epithelial nerve growth in provoked vestibulodynia is associated with increased B-cell infiltration and the presence of germinal centers. This supports the fundamental role of immune activation in provoked vestibulodynia.

Mast cell infiltrates in vulvodynia represent secondary and idiopathic mast cell hyperplasias.

Mast cell infiltrates in tissues of vulvodynia are common, but they have not been characterized for criteria of neoplastic mast cell disease or correlated with patient's concomitant diseases associated with increased mast cells. Formalin-fixed specimens of 35 patients with vulvodynia were evaluated immunohistochemically with antibodies to CD 3,4,8,20,117c and human mast cell tryptase, and for WHO-criteria of neoplastic mastocytosis (>25% spindled mast cell, CD25 expression, point mutations of the c-kit gene (D816V), and chronically elevated serum tryptase levels). Only 20/35 specimens showed a T-lymphocyte dominant inflammatory infiltrate on HE-stained sections, but all showed mast cells. 4/35 biopsies showed <10 mast cells/mm(2) , 15/35 specimens 40-60 mast cells/mm(2) and 16/35 specimens >60 mast cells/mm(2) (average 80/mm(2) ). Control tissue contained typically <10 mast cells/mm(2) . Spindling, CD25-expression, c-kit gene mutations, or increased serum tryptase levels were not detected. 26/35 (74%) patients had concomitant autoimmune diseases, psoriasis, atopy, various allergies, preceding infections. Independent of the subtype of vulvodynia, the majority of mast cell rich biopsies with >40 mast cells/mm(2) were classified as a secondary mast cell disorder reflecting an activated immune system in 75% of vulvodynia patients. Patients with increased mast cells may benefit from medical therapy targeting mast cells.

Activation of vestibule-associated lymphoid tissue in localized provoked vulvodynia.

OBJECTIVE: Localized provoked vulvodynia (LPV) may have inflammatory etiology. We wanted to find out whether the cell-mediated immune system becomes activated in the vestibular mucosa in LPV. STUDY DESIGN: This was a controlled cross-sectional study. Vestibular mucosal specimens were obtained from 27 patients with severe LPV and 15 controls. Detailed clinical history of the patients was obtained. For immunohistochemistry, antibodies against CD3 (T cells), CD20 (B cells), IgA (mucosal plasma cells), CD163 (dendritic cells [DCs]), CD68 (macrophages), and CD117 (mast cells) were employed. Mann-Whitney U test and χ(2) test were used for statistical analyses. RESULTS: More B lymphocytes and mature mucosal IgA-plasma cells were found in patients than in controls (P < .001 and P < .001, respectively). In LPV samples, B and T cells were arranged into germinal centers representing local immune activation. Germinal centers were not seen in controls. Antigen-presenting DCs and macrophages were found both in patients and controls with similar densities. DCs were found to extend their dendrites into the luminal space through an intact epithelium. Similar amounts of mast cells were found evenly scattered throughout the stroma of vestibular mucosa of both patients and controls. CONCLUSION: We demonstrate here local organized vestibule-associated lymphoid tissue analogous to mucosa-associated lymphoid tissue. Vestibule-associated lymphoid tissue may emerge as a response to local infection or inflammation in LPV.

CD4-positive T-cell recruitment in primary-provoked localized vulvodynia: potential insights into disease triggers.

OBJECTIVE: To better understand the potential disease triggers of neurogenic inflammation in provoked localized vulvodynia (PLV), our objective was to determine whether the types of infiltrating lymphocytes were different in vestibular biopsies from women with primary PLV, secondary PLV, and unaffected controls. METHODS: Secondary retrospective analysis of archived vestibular biopsies from a series of adult premenopausal women with primary PLV (n = 10), secondary PLV (n = 10), and unaffected controls (n = 4) was performed. All study patients had severe entry dyspareunia for more than 1 year. Subjects were excluded if pregnant, or they had a known infection, or history of generalized vulvodynia. Biopsies were performed during the midfollicular phase. Lymphocyte subtypes were highlighted in histologic sections using antibodies against CD3, CD4, and CD8 and scored as the mean number of T-cell subtypes per high-power field. Flow cytometry was also used to test fresh biopsies from a de novo prospective series of primary PLV (n = 4) and unaffected controls (n = 2). RESULTS: Unaffected control biopsies showed more CD8-positive than CD4-positive T cells, similar to previous reports of the gynecologic tract. In contrast, biopsies from women with primary PLV showed significantly more CD4-positive T cells than those from women with secondary PLV and unaffected controls (p = .003). This observation was further supported by flow cytometry. CONCLUSIONS: CD4-positive T cells are more numerous in vestibular biopsies from premenopausal women with primary PLV. This may be important because subtypes of CD4-positive T cells are specifically recruited by infectious, allergic, or autoimmune triggers. Future studies distinguishing these subtypes may lead to new insights into this common disease.

Allergic reactions and risk of vulvodynia.

PURPOSE: A recent histological study of vestibular tissue from women with localized vulvodynia found universal presence of mast cells compared to no presence in vestibular tissue among controls. Since histamine is generated by mast cells, and mast cells contribute to the production of cytokines during chronic inflammation, we assessed the association between conditions that elicit a clinically relevant histamine response and vulvodynia. METHODS: We studied 239 women with and 239 women without vulvodynia to assess the influence of self-reported allergic reactions antecedent to first development of vulvar pain symptoms among cases, and a matched reference age among controls. RESULTS: Women with self-reported hives prior to first report of vulvar pain or reference age among controls were 2.5 times more likely to develop vulvodynia (95% confidence interval [CI], 1.7-4.4). Those reporting a history of allergic reactions to insect bites were 2.1 times more likely (95%CI, 1.1-4.0), and those reporting a history of seasonal allergies were 2.0 times (95%CI, 1.3-3.2) more likely to develop vulvodynia. Findings were similar in a restricted subset of clinically confirmed cases and matched controls. CONCLUSIONS: An altered immuno-inflammatory response to environmentally induced allergic reactions may predispose women to the development of vulvodynia or may be markers of an already heightened immuno-inflammatory response.

Immunological and genetic characterization of women with vulvodynia.

Vulvodynia is a complex disorder and described as discomfort or intense burning pain in the vulvar area. Such chronic pain affects 5 to 15% of women and many suffer of misdiagnosis. For sure the aetiology is multifactorial. Through few studies we consider the inflammatory response plays a major role. There is a genetic profile of women suffering of vulvodynia, especially genetic polymorphisms from genes coding for cytokines, Interleukin-1 receptor antagonist and Interleukin-1 beta, and gene coding for mannose-binding lectin (MBL). These polymorphisms result in a stronger inflammatory response and lay these women in a susceptibility situation. Histological analysis showed a chronic no specific inflammation. We have also demonstrated that these patients present in normal state or under infectious induction an inadequate inflammatory response. But there is still a variety of mechanisms which can interact with the inflammatory response. Management of such vulvar pain syndrome could be very frustrating, but the first step for improvement is to get the right diagnosis.