Estrogen elicits dorsal root ganglion axon sprouting via a renin-angiotensin system

The proteus effect on human pain perception through avatar muscularity and gender factors

The Proteus effect, which occurs when using an avatar in virtual reality, influences user behavior, changes attitudes, and improves physical performance. Here, we show that human pain perception can be alleviated by the Proteus effect. To investigate the pain alleviation effect of using an avatar in a virtual environment, we conducted two experiments using a head-mounted display and a thermal pain stimulator to induce acute pain. The first experiment involved 20 adult participants, while the second experiment involved 44 adult participants. Experimental results show that participants reported significantly lower pain scores (15.982% reduction), as measured by the Pain Assessment Scale (PAS), when using a muscular avatar than when using a normal avatar. The experiments also revealed several significant gender factors. For example, participants reported significantly lower pain scores when using a gender-congruent avatar. In addition, the use of a muscular avatar was particularly effective for male participants. In contrast, female participants consistently reported lower pain scores when using the avatar regardless of its body type (muscular/normal). To further our understanding, we also measured participants' gender-related pain stereotypes using the Gender Role Expectations of Pain (GREP) questionnaire, as well as participants' sense of embodiment. The results of these questionnaires are consistent with the results of the PAS, suggesting possible relationships between stereotypes and the Proteus effect on pain perception, and between the degree of immersion in an avatar and the user's perception of pain.

Perinatal exposure to pesticides alters synaptic plasticity signaling and induces behavioral deficits associated with neurodevelopmental disorders

Increasing evidence from animal and epidemiological studies indicates that perinatal exposure to pesticides cause developmental neurotoxicity and may increase the risk for psychiatric disorders such as autism and intellectual disability. However, the underlying pathogenic mechanisms remain largely elusive. This work was aimed at testing the hypothesis that developmental exposure to different classes of pesticides hijacks intracellular neuronal signaling contributing to synaptic and behavioral alterations associated with neurodevelopmental disorders (NDD). Low concentrations of organochlorine (dieldrin, endosulfan, and chlordane) and organophosphate (chlorpyrifos and its oxon metabolite) pesticides were chronically dosed ex vivo (organotypic rat hippocampal slices) or in vivo (perinatal exposure in rats), and then biochemical, electrophysiological, behavioral, and proteomic studies were performed. All the pesticides tested caused prolonged activation of MAPK/ERK pathway in a concentration-dependent manner. Additionally, some of them impaired metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD). In the case of the pesticide chlordane, the effect was attributed to chronic modulation of MAPK/ERK signaling. These synaptic alterations were reproduced following developmental in vivo exposure to chlordane and chlorpyrifos-oxon, and were also associated with prototypical behavioral phenotypes of NDD, including impaired motor development, increased anxiety, and social and memory deficits. Lastly, proteomic analysis revealed that these pesticides differentially regulate the expression of proteins in the hippocampus with pivotal roles in brain development and synaptic signaling, some of which are associated with NDD. Based on these results, we propose a novel mechanism of synaptic dysfunction, involving chronic overactivation of MAPK and impaired mGluR-LTD, shared by different pesticides which may have important implications for NDD.

Estrogen Mediates the Sexual Dimorphism of GT1b-Induced Central Pain Sensitization

We have previously reported that the intrathecal (i.t.) administration of GT1b, a ganglioside, induces spinal cord microglia activation and central pain sensitization as an endogenous agonist of Toll-like receptor 2 on microglia. In this study, we investigated the sexual dimorphism of GT1b-induced central pain sensitization and the underlying mechanisms. GT1b administration induced central pain sensitization only in male but not in female mice. Spinal tissue transcriptomic comparison between male and female mice after GT1b injection suggested the putative involvement of estrogen (E2)-mediated signaling in the sexual dimorphism of GT1b-induced pain sensitization. Upon ovariectomy-reducing systemic E2, female mice became susceptible to GT1b-induced central pain sensitization, which was completely reversed by systemic E2 supplementation. Meanwhile, orchiectomy of male mice did not affect pain sensitization. As an underlying mechanism, we present evidence that E2 inhibits GT1b-induced inflammasome activation and subsequent IL-1β production. Our findings demonstrate that E2 is responsible for sexual dimorphism in GT1b-induced central pain sensitization.

Sexual Dimorphism in the Expression of Cardiac and Hippocampal Renin-Angiotensin and Kallikrein–Kinin Systems in Offspring from Mice Exposed to Alcohol during Gestation

Prenatal alcohol exposure (PAE) impairs fetal development. Alcohol consumption was shown to modulate the renin–angiotensin system (RAS). This study aimed to analyze the effects of PAE on the expression of the renin–angiotensin system (RAS) and kallikrein–kinin system (KKS) peptide systems in the hippocampus and heart of mice of both sexes. C57Bl/6 mice were exposed to alcohol during pregnancy at a concentration of 10% (v/v). On postnatal day 45 (PN45), mouse hippocampi and left ventricles (LV) were collected and processed for messenger RNA (mRNA) expression of components of the RAS and KKS. In PAE animals, more pronounced expression of AT1 and ACE mRNAs in males and a restored AT2 mRNA expression in females were observed in both tissues. In LV, increased AT2, ACE2, and B2 mRNA expressions were also observed in PAE females. Furthermore, high levels of H2O2 were observed in males from the PAE group in both tissues. Taken together, our results suggest that modulation of the expression of these peptidergic systems in PAE females may make them less susceptible to the effects of alcohol.

On the Relationship between Diabetes and Obstructive Sleep Apnea: Evolution and Epigenetics

This review offers an overview of the relationship between diabetes, obstructive sleep apnea (OSA), obesity, and heart disease. It then addresses evidence that the traditional understanding of this relationship is incomplete or misleading. In the process, there is a brief discussion of the evolutionary rationale for the development and retention of OSA in light of blood sugar dysregulation, as an adaptive mechanism in response to environmental stressors, followed by a brief overview of the general concepts of epigenetics. Finally, this paper presents the results of a literature search on the epigenetic marks and changes in gene expression found in OSA and diabetes. (While some of these marks will also correlate with obesity and heart disease, that is beyond the scope of this project). We conclude with an exploration of alternative explanations for the etiology of these interlinking diseases.

Shedding Light on the Pharmacological Interactions between μ-Opioid Analgesics and Angiotensin Receptor Modulators: A New Option for Treating Chronic Pain

The current protocols for neuropathic pain management include µ-opioid receptor (MOR) analgesics alongside other drugs; however, there is debate on the effectiveness of opioids. Nevertheless, dose escalation is required to maintain their analgesia, which, in turn, contributes to a further increase in opioid side effects. Finding novel approaches to effectively control chronic pain, particularly neuropathic pain, is a great challenge clinically. Literature data related to pain transmission reveal that angiotensin and its receptors (the AT1R, AT2R, and MAS receptors) could affect the nociception both in the periphery and CNS. The MOR and angiotensin receptors or drugs interacting with these receptors have been independently investigated in relation to analgesia. However, the interaction between the MOR and angiotensin receptors has not been excessively studied in chronic pain, particularly neuropathy. This review aims to shed light on existing literature information in relation to the analgesic action of AT1R and AT2R or MASR ligands in neuropathic pain conditions. Finally, based on literature data, we can hypothesize that combining MOR agonists with AT1R or AT2R antagonists might improve analgesia.

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.

Angiotensin receptors and neuropathic pain

Growing evidence implicates the renin-angiotensin system (RAS) in multiple facets of neuropathic pain (NP). This narrative review focuses primarily on the major bioactive RAS peptide, Angiotensin II (Ang II), and its receptors, namely type 1 (AT1R) and type 2 (AT2R). Both receptors are involved in the development of NP and represent potential therapeutic targets. We first discuss the potential role of Ang II receptors in modulation of NP in the central nervous system. Ang II receptor expression is widespread in circuits associated with the perception and modulation of pain, but more studies are required to fully characterize receptor distribution, downstream signaling, and therapeutic potential of targeting the central nervous system RAS in NP. We then describe the peripheral neuronal and nonneuronal distribution of the RAS, and its contribution to NP. Other RAS modulators (such as Ang (1-7)) are briefly reviewed as well. AT1R antagonists are analgesic across different pain models, including NP. Several studies show neuronal protection and outgrowth downstream of AT2R activation, which may lead to the use of AT2R agonists in NP. However, blockade of AT2R results in analgesia. Furthermore, expression of the RAS in the immune system and a growing appreciation of neuroimmune crosstalk in NP add another layer of complexity and therapeutic potential of targeting this pathway. A growing number of human studies also hint at the analgesic potential of targeting Ang II signaling. Altogether, Ang II receptor signaling represents a promising, far-reaching, and novel strategy to treat NP.

The Angiotensin II Type 2 Receptor, a Target for Protection and Regeneration of the Peripheral Nervous System?

Preclinical evidence, accumulated over the past decade, indicates that the angiotensin II type 2 receptor (AT2R) stimulation exerts significant neuroprotective effects in various animal models of neuronal injury, notably in the central nervous system. While the atypical G protein-coupled receptor superfamily nature of AT2R and its related signaling are still under investigation, pharmacological studies have shown that stimulation of AT2R leads to neuritogenesis in vitro and in vivo. In this review, we focus on the potential neuroprotective and neuroregenerative roles of AT2R specifically in the peripheral nervous system (PNS). The first section describes the evidence for AT2R expression in the PNS and highlights current controversies concerning the cellular distribution of the receptor. The second section focuses on AT2R signaling implicated in neuronal survival and in neurite outgrowth. The following sections review the relatively few preclinical studies highlighting the putative neuroprotective and neuroregenerative effects of AT2R stimulation in the context of peripheral neuropathy.

Mechanisms Involved in Superiority of Angiotensin Receptor Blockade over ACE Inhibition in Attenuating Neuropathic Pain Induced in Rats

Although previous reports described the beneficial role of angiotensin-converting enzyme inhibitors (ACE-Is) or AT1 receptor blockers (ARBs) in attenuating neuropathic pain (NP), no study has yet explored the exact underlying mechanisms, as well as the superiority of using centrally versus peripherally acting renin-angiotensin-aldosterone system (RAAS) drugs in NP. We investigated the effects of 14 days of treatment with centrally (telmisartan and ramipril) or peripherally (losartan and enalapril) acting ARBs and ACE-Is, respectively, in attenuating peripheral NP induced by sciatic nerve chronic constriction injury (CCI) in rats. We also compared these with the effects of pregabalin, the standard treatment for NP. Behavioral changes, inflammatory markers (NFкB, TNF-α, COX-2, PGE2, and bradykinin), oxidative stress markers (NADPH oxidase and catalase), STAT3 activation, levels of phosphorylated P38-MAPK, ACE, AT1 receptor (AT1R), and AT2 receptor (AT2R), as well as histopathological features, were assessed in the brainstem and sciatic nerve. CCI resulted in clear pain-related behavior along with increased levels of inflammatory and oxidative stress markers, and STAT3 activity, as well as increased levels of phosphorylated P38-MAPK, ACE, AT1R, and AT2R, along with worsened histopathological findings in both the brainstem and sciatic nerve. ARBs improved both animal behavior and all measured parameters in CCI rats and were more effective than ACE-Is. At the tested doses, centrally acting ARBs or ACE-Is were not superior to the peripherally acting drugs of the same category. These findings suggest that ARBs (centrally or peripherally acting) are an effective treatment modality for NP.

Differential role of specific cardiovascular neuropeptides in pain regulation: Relevance to cardiovascular diseases

In many instances, the perception of pain is disproportionate to the strength of the algesic stimulus. Excessive or inadequate pain sensation is frequently observed in cardiovascular diseases, especially in coronary ischemia. The mechanisms responsible for individual differences in the perception of cardiovascular pain are not well recognized. Cardiovascular disorders may provoke pain in multiple ways engaging molecules released locally in the heart due to tissue ischemia, inflammation or cellular stress, and through neurogenic and endocrine mechanisms brought into action by hemodynamic disturbances. Cardiovascular neuropeptides, namely angiotensin II (Ang II), angiotensin-(1-7) [Ang-(1-7)], vasopressin, oxytocin, and orexins belong to this group. Although participation of these peptides in the regulation of circulation and pain has been firmly established, their mutual interaction in the regulation of pain in cardiovascular diseases has not been profoundly analyzed. In the present review we discuss the regulation of the release, and mechanisms of the central and systemic actions of these peptides on the cardiovascular system in the context of their central and peripheral nociceptive (Ang II) and antinociceptive [Ang-(1-7), vasopressin, oxytocin, orexins] properties. We also consider the possibility that they may play a significant role in the modulation of pain in cardiovascular diseases. The rationale for focusing attention on these very compounds was based on the following premises (1) cardiovascular disturbances influence the release of these peptides (2) they regulate vascular tone and cardiac function and can influence the intensity of ischemia - the factor initiating pain signals in the cardiovascular system, (3) they differentially modulate nociception through peripheral and central mechanisms, and their effect strongly depends on specific receptors and site of action. Accordingly, an altered release of these peptides and/or pharmacological blockade of their receptors may have a significant but different impact on individual sensation of pain and comfort of an individual patient.

Cutaneous inflammation differentially regulates the expression and function of Angiotensin-II types 1 and 2 receptors in rat primary sensory neurons

Neuropathic and inflammatory pain results from cellular and molecular changes in dorsal root ganglion (DRG) neurons. The type-2 receptor for Angiotensin-II (AT2R) has been involved in this type of pain. However, the underlying mechanisms are poorly understood, including the role of the type-1 receptor for Angiotensin-II (AT1R). Here, we used a combination of immunohistochemistry and immunocytochemistry, RT-PCR and in vitro and in vivo pharmacological manipulation to examine how cutaneous inflammation affected the expression of AT1R and AT2R in subpopulations of rat DRG neurons and studied their impact on inflammation-induced neuritogenesis. We demonstrated that AT2R-neurons express C- or A-neuron markers, primarily IB4, trkA, and substance-P. AT1R expression was highest in small neurons and co-localized significantly with AT2R. In vitro, an inflammatory soup caused significant elevation of AT2R mRNA, whereas AT1R mRNA levels remained unchanged. In vivo, we found a unique pattern of change in the expression of AT1R and AT2R after cutaneous inflammation. AT2R increased in small neurons at 1 day and in medium size neurons at 4 days. Interestingly, cutaneous inflammation increased AT1R levels only in large neurons at 4 days. We found that in vitro and in vivo AT1R and AT2R acted co-operatively to regulate DRG neurite outgrowth. In vivo, AT2R inhibition impacted more on non-peptidergic C-neurons neuritogenesis, whereas AT1R blockade affected primarily peptidergic nerve terminals. Thus, cutaneous-induced inflammation regulated AT1R and AT2R expression and function in different DRG neuronal subpopulations at different times. These findings must be considered when targeting AT1R and AT2R to treat chronic inflammatory pain. Cover Image for this issue: doi: 10.1111/jnc.14737.

Inflammatory Renin-Angiotensin System Disruption Attenuates Sensory Hyperinnervation and Mechanical Hypersensitivity in a Rat Model of Provoked Vestibulodynia

Vestibulodynia is characterized by perivaginal mechanical hypersensitivity, hyperinnervation, and abundant inflammatory cells expressing renin-angiotensin system proteins. We developed a tractable rat model of vestibulodynia to further assess the contributions of the renin-angiotensin system. Complete Freund's adjuvant injected into the posterior vestibule induced marked vestibular hypersensitivity throughout a 7-day test period. Numbers of axons immunoreactive for PGP9.5, calcitonin gene-related peptide, and GFRα2 were increased. Numbers of macrophages and T cells were also increased whereas B cells were not. Renin-angiotensin-associated proteins were abundant, with T cells as well as macrophages contributing to increased renin and angiotensinogen. Media conditioned with inflamed vestibular tissue promoted neurite sprouting by rat dorsal root ganglion neurons in vitro, and this was blocked by the angiotensin II receptor type 2 receptor antagonist PD123319 or by an angiotensin II function blocking antibody. Sensory axon sprouting induced by inflamed tissue was dependent on activity of angiotensin-converting enzyme or chymase, but not cathepsin G. Thus, vestibular Complete Freund's adjuvant injection substantially recapitulates changes seen in patients with provoked vestibulodynia, and shows that manipulation of the local inflammatory renin-angiotensin system may be a useful therapeutic strategy.

PERSPECTIVE

This study provides evidence that inflammation of the rat vestibule induces a phenotype recapitulating behavioral and cytological features of human vestibulodynia. The model confirms a crucial role of the local inflammatory renin-angiotensin system in hypersensitivity and hyperinnervation. Targeting this system holds promise for developing new nonopioid analgesic treatment strategies.

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.

A Local Inflammatory Renin-Angiotensin System Drives Sensory Axon Sprouting in Provoked Vestibulodynia

Vestibulodynia is a form of provoked vulvodynia characterized by profound tenderness, hyperinnervation, and frequently inflammation within well-defined areas of the human vestibule. Previous experiments in animal models show that inflammatory hypersensitivity and hyperinnervation occur in concert with establishment of a local renin-angiotensin system (RAS). Moreover, mechanical hypersensitivity and sensory axon sprouting are prevented by blocking effects of angiotensin II on angiotensin II receptor type 2 (AT2) receptors. This case-control study assessed whether a RAS contributes to hyperinnervation observed in human vestibulodynia. Vestibular biopsies from asymptomatic controls or patients' nontender areas showed moderate innervation and small numbers of inflammatory cells. In women with vestibulodynia, tender areas contained increased numbers of mechanoreceptive nociceptor axons, T-cells, macrophages, and B-cells, whereas mast cells were unchanged. RAS proteins were increased because of greater numbers of T cells and B cells expressing angiotensinogen, and increased renin-expressing T cells and macrophages. Chymase, which converts angiotensin I to angiotensin II, was present in constant numbers of mast cells. To determine if tender vestibular tissue generates angiotensin II that promotes axon sprouting, we conditioned culture medium with vestibular tissue. Rat sensory neurons cultured in control-conditioned medium showed normal axon outgrowth, whereas those in tender tissue-conditioned medium showed enhanced sprouting that was prevented by adding an AT2 antagonist or angiotensin II neutralizing antibody. Hypersensitivity in provoked vestibulodynia is therefore characterized by abnormal mechanonociceptor axon proliferation, which is attributable to inflammatory cell-derived angiotensin II (or a closely related peptide) acting on neuronal AT2 receptors. Accordingly, reducing inflammation or blocking AT2 represent rational strategies to mitigate this common pain syndrome.

PERSPECTIVE

This study provides evidence that local inflammation leads to angiotensin II formation, which acts on the AT2 to induce nociceptor axon sprouting in vulvodynia. Preventing inflammation and blocking AT2 therefore present potential pharmacological strategies for reducing vestibular pain.

Nociceptor-like rat dorsal root ganglion neurons express the angiotensin-II AT2 receptor throughout development

AT2 receptor (AT2R) plays a functional role in foetal development. Its expression declines in most tissues soon after birth but stays high in sensory areas of the adult nervous system. In the dorsal root ganglia (DRG) the expression pattern of AT2R during development and the identity of the subpopulation expressing it remain unknown. Using a combination of semi-quantitative PCR, western blotting and immunohistochemistry we examined the expression of AT2R at mRNA and protein levels in rat DRGs from embryonic day 15 (E15) until postnatal day 30 (PN30). We found that both AT2R mRNA and protein levels exhibited only minor (statistically non-significant) fluctuations from E15 to PN30. Detailed quantitative analysis of ABC/DAB AT2R staining showed a) that the receptor was present in most neurons at E15 and E18 and b) that postnatally it was predominantly expressed by small DRG neurons. Given that small neurons are putative C-nociceptors and the proposed role of AT2R in neuropathic pain, we next examined whether these AT2R-positive neurons co-localized with Ret and trkA embryonically and with IB4-binding postnatally. Most AT2R-positive neurons expressed trkA embryonically and bound IB4 postnatally. We found strong positive statistically highly significant correlations between AT2R cytoplasmic%intensities and trkA at E15/E18 and with Ret only at E18. Cytoplasmic AT2R also strongly and positively correlated with IB4-binding at PN3, 15 and 30. Our demonstration that a subpopulation of C-nociceptor-like neurons expresses AT2R during development supports a role for this receptor in neuropathic pain.

Selective small molecule angiotensin II type 2 receptor antagonists for neuropathic pain: preclinical and clinical studies

Neuropathic pain affects up to 10% of the general population, but drug treatments recommended for the treatment of neuropathic pain are associated with modest efficacy and/or produce dose-limiting side effects. Hence, neuropathic pain is an unmet medical need. In the past 2 decades, research on the pathobiology of neuropathic pain has revealed many novel pain targets for use in analgesic drug discovery programs. However, these efforts have been largely unsuccessful as molecules that showed promising pain relief in rodent models of neuropathic pain generally failed to produce analgesia in early phase clinical trials in patients with neuropathic pain. One notable exception is the angiotensin II type 2 (AT2) receptor that has clinical validity on the basis of a successful double-blind, randomized, placebo-controlled, clinical trial of EMA401, a highly selective, orally active, peripherally restricted AT2 receptor antagonist in patients with postherpetic neuralgia. In this study, we review research to date on target validation, efficacy, and mode of action of small molecule AT2 receptor antagonists in rodent models of peripheral neuropathic pain and in cultured human sensory neurons, the preclinical pharmacokinetics of these compounds, and the outcome of the above clinical trial.

Menopause and Parkinson's disease. Interaction between estrogens and brain renin-angiotensin system in dopaminergic degeneration

The neuroprotective effects of menopausal hormonal therapy in Parkinson's disease (PD) have not yet been clarified, and it is controversial whether there is a critical period for neuroprotection. Studies in animal models and clinical and epidemiological studies indicate that estrogens induce dopaminergic neuroprotection. Recent studies suggest that inhibition of the brain renin-angiotensin system (RAS) mediates the effects of estrogens in PD models. In the substantia nigra, ovariectomy induces a decrease in levels of estrogen receptor-α (ER-α) and increases angiotensin activity, NADPH-oxidase activity and expression of neuroinflammatory markers, which are regulated by estrogen replacement therapy. There is a critical period for the neuroprotective effect of estrogen replacement therapy, and local ER-α and RAS play a major role. Astrocytes play a major role in ER-α-induced regulation of local RAS, but neurons and microglia are also involved. Interestingly, treatment with angiotensin receptor antagonists after the critical period induced neuroprotection.

Piperazine derivatives for therapeutic use: a patent review (2010-present)

INTRODUCTION

Piperazine, a six membered nitrogen containing heterocycle, is of great significance to the rational design of drugs. This moiety can be found in a plethora of well-known drugs with various therapeutic uses, such as antipsychotic, antihistamine, antianginal, antidepressant, anticancer, antiviral, cardio protectors, anti-inflammatory, and imaging agents. Slight modification to the substitution pattern on the piperazine nucleus facilitates a recognizable difference in the medicinal potential of the resultant molecules.

AREAS COVERED

Scifinder was the main source used to search for patents containing piperazine compounds with therapeutic uses. The article describes a variety of molecular designs bearing piperazine entity furnishing CNS agents, anticancer, cardio-protective agents, antiviral, anti-tuberculosis, anti-inflammatory, antidiabetic, and antihistamine profiles, as well as agents relieving pain and useful in imaging applications.

EXPERT OPINION

The great interest gathered to explore piperazine based molecules in relatively few years reflects the broad potential of the entity. Earlier, this scaffold was considered to express CNS activity only. However, a significant increase in research covering studies of several different activities of piperazine ring suggest a successful emergence of the pharmacophore. Certain patents outlined in the present article recommend that piperazines can be a flexible building block to discover drug-like elements and modification of substituents present on the piperazine ring may have a significant impact on the pharmacokinetic and pharmacodynamics factors of the resulting molecules. This article aims to provide insights to piperazine based molecular fragments that would assist drug discoverers to rationally design molecules for various diseases. We anticipate, and highly recommend, further therapeutic investigations on this motif.

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

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

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Mechanisms underlying clinical efficacy of Angiotensin II type 2 receptor (AT2R) antagonist EMA401 in neuropathic pain: clinical tissue and in vitro studies

Background

The clinical efficacy of the Angiotensin II (AngII) receptor AT₂R antagonist EMA401, a novel peripherally-restricted analgesic, was reported recently in post-herpetic neuralgia. While previous studies have shown that AT₂R is expressed by nociceptors in human DRG (hDRG), and that EMA401 inhibits capsaicin responses in cultured hDRG neurons, the expression and levels of its endogenous ligands AngII and AngIII in clinical neuropathic pain tissues, and their signalling pathways, require investigation. We have immunostained AngII, AT₂R and the capsaicin receptor TRPV1 in control post-mortem and avulsion injured hDRG, control and injured human nerves, and in cultured hDRG neurons. AngII, AngIII, and Ang-(1-7) levels were quantified by ELISA. The in vitro effects of AngII, AT₂R agonist C21, and Nerve growth factor (NGF) were measured on neurite lengths; AngII, NGF and EMA401 effects on expression of p38 and p42/44 MAPK were measured using quantitative immunofluorescence, and on capsaicin responses using calcium imaging.

Results

AngII immunostaining was observed in approximately 75% of small/medium diameter neurons in control (n = 5) and avulsion injured (n = 8) hDRG, but not large neurons i.e. similar to TRPV1. AngII was co-localised with AT₂R and TRPV1 in hDRG and in vitro. AngII staining by image analysis showed no significant difference between control (n = 12) and injured (n = 13) human nerves. AngII levels by ELISA were also similar in control human nerves (4.09 ± 0.36 pmol/g, n = 31), injured nerves (3.99 ± 0.79 pmol/g, n = 7), and painful neuromas (3.43 ± 0.73 pmol/g, n = 12); AngIII and Ang-(1-7) levels were undetectable (<0.03 and 0.05 pmol/g respectively). Neurite lengths were significantly increased in the presence of NGF, AngII and C21 in cultured DRG neurons. AngII and, as expected, NGF significantly increased signal intensity of p38 and p42/44 MAPK, which was reversed by EMA401. AngII mediated sensitization of capsaicin responses was not observed in the presence of MAP kinase inhibitor PD98059, and the kinase inhibitor staurosporine.

Conclusion

The major AT₂R ligand in human peripheral nerves is AngII, and its levels are maintained in injured nerves. EMA401 may act on paracrine/autocrine mechanisms at peripheral nerve terminals, or intracrine mechanisms, to reduce neuropathic pain signalling in AngII/NGF/TRPV1-convergent pathways.

Persistent genital hyperinnervation following progesterone administration to adolescent female rats

Provoked vestibulodynia, a female pelvic pain syndrome affecting substantial numbers of women, is characterized by genital hypersensitivity and sensory hyperinnervation. Previous studies have shown that the risk of developing provoked vestibulodynia is markedly elevated following adolescent use of oral contraceptives with high progesterone content. We hypothesized that progesterone, a steroid hormone with known neurotropic properties, may alter genital innervation through direct or indirect actions. Female Sprague Dawley rats received progesterone (20 mg/kg subcutaneously) from Days 20-27; tissue was removed for analysis in some rats on Day 28, while others were ovariectomized on Day 43 and infused for 7 days with vehicle or 17beta estradiol. Progesterone resulted in overall increases in vaginal innervation at both Day 28 and 50 due to proliferation of peptidergic sensory and sympathetic (but not parasympathetic) axons. Estradiol reduced innervation in progesterone-treated and untreated groups. To assess the mechanisms of sensory hyperinnervation, we cultured dissociated dorsal root ganglion neurons and found that progesterone increases neurite outgrowth by small unmyelinated (but not myelinated) sensory neurons, it was receptor mediated, and it was nonadditive with NGF. Pretreatment of ganglion with progesterone also increased neurite outgrowth in response to vaginal target explants. However, pretreatment of vaginal target with progesterone did not improve outgrowth. We conclude that adolescent progesterone exposure may contribute to provoked vestibulodynia by eliciting persistent genital hyperinnervation via a direct effect on unmyelinated sensory nociceptor neurons and that estradiol, a well-documented therapeutic, may alleviate symptoms in part by reducing progesterone-induced sensory hyperinnervation.

Targeting angiotensin II type 2 receptor pathways to treat neuropathic pain and inflammatory pain

INTRODUCTION

Neuropathic pain and chronic inflammatory pain are large unmet medical needs. Over the past two decades, numerous 'pain targets' have been identified for analgesic drug discovery. Despite promising results in rodent pain models, many compounds modulating such targets lacked efficacy in clinical trials. An exception is oral EMA401, a small-molecule angiotensin II type 2 receptor (AT2R) antagonist.

AREAS COVERED

Herein, angiotensin II/AT2R signaling-induced hyperexcitability and abnormal sprouting of cultured dorsal root ganglion neurons, together with radioligand binding, pharmacokinetics, analgesic efficacy and mode of action of small-molecule AT2R antagonists in rodent models of peripheral neuropathic and chronic inflammatory pain, are reviewed. The findings of a successful Phase IIa clinical trial of EMA401 in patients with neuropathic pain are presented in brief.

EXPERT OPINION

The functional importance of angiotensin II/AT2R signaling has remained enigmatic for decades, and there are no clinically available medications that target the AT2R. However, on the basis of preclinical findings and recent clinical trial data showing that the peripherally restricted, small-molecule AT2R antagonist, EMA401, successfully alleviated neuropathic pain in a Phase II clinical trial, the AT2R is receiving considerable attention as a new therapeutic target with human validation for the relief of peripheral neuropathic and chronic inflammatory pain conditions.

Trophic factor and hormonal regulation of neurite outgrowth in sensory neuron-like 50B11 cells

Sensory axon integrity and regenerative capacity are important considerations in understanding neuropathological conditions characterized by hyper- or insensitivity. However, our knowledge of mechanisms regulating axon outgrowth are limited by an absence of suitable high-throughput assay systems. The 50B11 cell line generated from rat embryonic dorsal root ganglion neurons offers a promising model for screening assays. Prior characterization shows that these cells express cytoskeletal proteins and genes encoding ion channels and neurotrophin receptors in common with sensory nociceptor neurons. In the present study we further characterized 50B11 cells in regard to their phenotypes and responsiveness to neurotrophic and hormonal factors. 50B11 cells express neuronal cytoplasmic proteins including beta-3 tubulin, peripherin (a marker of unmyelinated neurons), and the pan-neuronal ubiquitin hydrolase, PGP9.5. Only PGP9.5 immunoreactivity was uniformly distributed throughout soma and axons, and therefore presents the best means for visualizing the entire axon arbor. All cells co-express both NGF and GDNF receptors and addition of ligands increased neurite length. 50B11 cells also showed immunoreactivity for the estrogen receptor-α and the angiotensin receptor type II, and both 17-β estradiol and angiotensin II increased outgrowth by differentiated cells. 50B11 cells therefore show features reported previously for primary unmyelinated nociceptor neurons, including responsiveness to classical neurotrophins and hormonal modulators. Coupled with their ease of culture and predictable differentiation, 50B11 cells represent a promising cell line on which to base assays that more clearly reveal mechanisms regulating axon outgrowth and integrity.

Analgesic efficacy and mode of action of a selective small molecule angiotensin II type 2 receptor antagonist in a rat model of prostate cancer-induced bone pain

OBJECTIVE

The pathobiology of prostate cancer (PCa)-induced bone pain (PCIBP) has both inflammatory and neuropathic components. Previously, we showed that small molecule angiotensin II type 2 receptor (AT2 R) antagonists with >1,000-fold selectivity over the angiotensin II type 1 receptor produced dose-dependent analgesia in a rat model of neuropathic pain. Here, we assessed the analgesic efficacy and mode of action of the AT2 R antagonist, EMA200, in a rat model of PCIBP.

METHODS

At 14-21 days after unilateral intratibial injection of AT3B PCa cells, rats exhibiting hindpaw hypersensitivity received single intravenous bolus doses of EMA200 (0.3-10 mg/kg) or vehicle, and analgesic efficacy was assessed. The mode of action was investigated using immunohistochemical, Western blot, and/or molecular biological methods in lumbar dorsal root ganglia (DRGs) removed from drug-naïve and EMA200-treated PCIBP rats relative to sham-control rats.

RESULTS

Intravenous bolus doses of EMA200 produced dose-dependent analgesia in PCIBP rats. Lumbar DRG levels of angiotensin II, nerve growth factor (NGF), tyrosine kinase A (TrkA), phospho-p38 mitogen-activated protein kinase (MAPK), and phospho-p44/p42 MAPK, but not the AT2 R, were increased significantly (P < 0.05) in PCIBP rats, c.f. the corresponding levels for sham controls. EMA200 produced analgesia in PCIBP rats by reducing elevated angiotensin II levels in the lumbar DRGs to attenuate augmented angiotensin II/AT2 R signaling. This in turn reduced augmented NGF/TrkA signaling in the lumbar DRGs. The net result was inhibition of p38 MAPK and p44/p42 MAPK activation.

CONCLUSION

Small molecule AT2 R antagonists are worthy of further investigation as novel analgesics for relief of intractable PCIBP and other pain types where hyperalgesia worsens symptoms.

Angiotensin II type 2 receptor (AT2 R) localization and antagonist-mediated inhibition of capsaicin responses and neurite outgrowth in human and rat sensory neurons

BACKGROUND

The angiotensin II (AngII) receptor subtype 2 (AT2 R) is expressed in sensory neurons and may play a role in nociception and neuronal regeneration.

METHODS

We used immunostaining with characterized antibodies to study the localization of AT2 R in cultured human and rat dorsal root ganglion (DRG) neurons and a range of human tissues. The effects of AngII and AT2 R antagonist EMA401 on capsaicin responses in cultured human and rat (DRG) neurons were measured with calcium imaging, on neurite length and density with Gap43 immunostaining, and on cyclic adenosine monophosphate (cAMP) expression using immunofluorescence.

RESULTS

AT2 R expression was localized in small-/medium-sized cultured neurons of human and rat DRG. Treatment with the AT2 R antagonist EMA401 resulted in dose-related functional inhibition of capsaicin responses (IC50  = 10 nmol/L), which was reversed by 8-bromo-cAMP, and reduced neurite length and density; AngII treatment significantly enhanced capsaicin responses, cAMP levels and neurite outgrowth. The AT1 R antagonist losartan had no effect on capsaicin responses. AT2 R was localized in sensory neurons of human DRG, and nerve fibres in peripheral nerves, skin, urinary bladder and bowel. A majority sub-population (60%) of small-/medium-diameter neuronal cells were immunopositive in both control post-mortem and avulsion-injured human DRG; some very small neurons appeared to be intensely immunoreactive, with TRPV1 co-localization. While AT2 R levels were reduced in human limb peripheral nerve segments proximal to injury, they were preserved in painful neuromas.

CONCLUSIONS

AT2 R antagonists could be particularly useful in the treatment of chronic pain and hypersensitivity associated with abnormal nerve sprouting.

Angiotensin II receptor type 2 activation is required for cutaneous sensory hyperinnervation and hypersensitivity in a rat hind paw model of inflammatory pain

Many pain syndromes are associated with abnormal proliferation of peripheral sensory fibers. We showed previously that angiotensin II, acting through its type 2 receptor (AT2), stimulates axon outgrowth by cultured dorsal root ganglion neurons. In this study, we assessed whether AT2 mediates nociceptor hyperinnervation in the rodent hind paw model of inflammatory pain. Plantar injection of complete Freund's adjuvant (CFA), but not saline, produced marked thermal and mechanical hypersensitivity through 7 days. This was accompanied by proliferation of dermal and epidermal PGP9.5-immunoreactive (ir) and calcitonin gene-related peptide-immunoreactive (CGRP-ir) axons, and dermal axons immunoreactive for GFRα2 but not tyrosine hydroxylase or neurofilament H. Continuous infusion of the AT2 antagonist PD123319 beginning with CFA injection completely prevented hyperinnervation as well as hypersensitivity over a 7-day period. A single PD123319 injection 7 days after CFA also reversed thermal hypersensitivity and partially reversed mechanical hypersensitivity 3 hours later, without affecting cutaneous innervation. Angiotensin II-synthesizing proteins renin and angiotensinogen were largely absent after saline but abundant in T cells and macrophages in CFA-injected paws with or without PD123319. Thus, emigrant cells at the site of inflammation apparently establish a renin-angiotensin system, and AT2 activation elicits nociceptor sprouting and heightened thermal and mechanical sensitivity.

PERSPECTIVE

Short-term AT2 activation is a potent contributor to thermal hypersensitivity, whereas long-term effects (such as hyperinnervation) also contribute to mechanical hypersensitivity. Pharmacologic blockade of AT2 signaling represents a potential therapeutic strategy aimed at biologic mechanisms underlying chronic inflammatory pain.

Bone morphogenetic protein 4 mediates estrogen-regulated sensory axon plasticity in the adult female reproductive tract

Peripheral axons are structurally plastic even in the adult, and altered axon density is implicated in many disorders and pain syndromes. However, mechanisms responsible for peripheral axon remodeling are poorly understood. Physiological plasticity is characteristic of the female reproductive tract: vaginal sensory innervation density is low under high estrogen conditions, such as term pregnancy, whereas density is high in low-estrogen conditions, such as menopause. We exploited this system in rats to identify factors responsible for adult peripheral neuroplasticity. Calcitonin gene-related peptide-immunoreactive sensory innervation is distributed primarily within the vaginal submucosa. Submucosal smooth muscle cells express bone morphogenetic protein 4 (BMP4). With low estrogen, BMP4 expression was elevated, indicating negative regulation by this hormone. Vaginal smooth muscle cells induced robust neurite outgrowth by cocultured dorsal root ganglion neurons, which was prevented by neutralizing BMP4 with noggin or anti-BMP4. Estrogen also prevented axon outgrowth, and this was reversed by exogenous BMP4. Nuclear accumulation of phosphorylated Smad1, a primary transcription factor for BMP4 signaling, was high in vagina-projecting sensory neurons after ovariectomy and reduced by estrogen. BMP4 regulation of innervation was confirmed in vivo using lentiviral transduction to overexpress BMP4 in an estrogen-independent manner. Submucosal regions with high virally induced BMP4 expression had high innervation density despite elevated estrogen. These findings show that BMP4, an important factor in early nervous system development and regeneration after injury, is a critical mediator of adult physiological plasticity as well. Altered BMP4 expression may therefore contribute to sensory hyperinnervation, a hallmark of several pain disorders, including vulvodynia.

Effects of estradiol on voltage-gated sodium channels in mouse dorsal root ganglion neurons

Estrogen has multiple actions in the brain to modulate homeostasis, synaptic plasticity, neuroprotection and pain sensitivity. Previous studies have demonstrated that estradiol may affect the ion channel function. The role of voltage-gated sodium channels in the transmission of nociceptive and neuropathic pain messages is well-established. Herein, we report the effects of estradiol (E2) on TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na(+) currents, using a conventional whole-cell patch clamp technique from acutely isolated mouse dorsal root ganglion neurons. We found that the extracellularly 17β-E2 inhibited TTX-S Na(+) currents and TTX-R Na(+) currents; the effects were rapid, reversible and in a concentration-dependent manner. Moreover, 17β-E2 did not significantly affect the activation curve for Na(+) channel, and shifted the steady-state inactivation curve for TTX-S and TTX-R Na(+) channels in the hyperpolarizing direction. We also found that the membrane impermeable E2-BSA was as efficacious as 17β-E2, whereas 17α-E2 had no effect. Blockers of PKC (GÖ-6983) and PKA (H-89) abrogated these acute effects of 17β-E2. In conclusion, E2 inhibited voltage-gated Na(+) channels in mouse DRG neurons through a membrane ER-activated PKC-PKA signaling pathway. Through the modulation of voltage-gated sodium currents, estradiol could affect cell excitability, firing properties.

The Angiotensin II Type 2 Receptor in Brain Functions: An Update

Angiotensin II (Ang II) is the main active product of the renin-angiotensin system (RAS), mediating its action via two major receptors, namely, the Ang II type 1 (AT₁) receptor and the type 2 (AT₂) receptor. Recent results also implicate several other members of the renin-angiotensin system in various aspects of brain functions. The first aim of this paper is to summarize the current state of knowledge regarding the properties and signaling of the AT₂ receptor, its expression in the brain, and its well-established effects. Secondly, we will highlight the potential role of the AT₂ receptor in cognitive function, neurological disorders and in the regulation of appetite and the possible link with development of metabolic disorders. The potential utility of novel nonpeptide selective AT₂ receptor ligands in clarifying potential roles of this receptor in physiology will also be discussed. If confirmed, these new pharmacological tools should help to improve impaired cognitive performance, not only through its action on brain microcirculation and inflammation, but also through more specific effects on neurons. However, the overall physiological relevance of the AT₂ receptor in the brain must also consider the Ang IV/AT₄ receptor.

Systemic and topical hormone therapies reduce vaginal innervation density in postmenopausal women

OBJECTIVE

Menopause is often accompanied by vaginal discomfort including burning, itching, dryness, and spontaneous or provoked pain. Although the direct effects of estrogen withdrawal on vaginal cells are implicated, surgical menopause in rodents causes autonomic and sensory nerves to proliferate, suggesting that indirect effects mediated by changes in vaginal innervation may contribute. We assessed whether postmenopausal women display hormone-dependent changes in vaginal innervation.

METHODS

Vaginal biopsies from 20 postmenopausal women undergoing surgery for stress urinary incontinence and pelvic organ prolapse were fixed and immunostained for the pan-neuronal marker protein gene product 9.5, sympathetic marker tyrosine hydroxylase, parasympathetic marker vasoactive intestinal polypeptide, and sensory nociceptor marker calcitonin gene-related peptide. Innervation density was measured as an apparent percentage of the section area occupied by immunofluorescent axons. Specimens were grouped according to whether participants received systemic hormone therapy (HT), topical (vaginal) HT, or no HT.

RESULTS

Women not receiving HT showed relatively high levels of total innervation, with most axons expressing tyrosine hydroxylase or vasoactive intestinal polypeptide immunoreactivity. In women receiving systemic HT, overall innervation was reduced, as were presumptive parasympathetic, sympathetic, and sensory axon populations. Topical HT elicited more dramatic reductions in innervation than in systemic HT.

CONCLUSIONS

Hormone therapy reduces autonomic and sensory vaginal innervation density, which may, in part, contribute to relief from vaginal discomfort. Moreover, topical therapy is more effective than systemic therapy, which may help explain the greater improvement reported with topical compared with systemic HT.

Molecular mechanisms involved in the regulation of neuritogenesis by estradiol: Recent advances

This review analyzes the signaling mechanisms activated by estradiol to regulate neuritogenesis in several neuronal populations. Estradiol regulates axogenesis by the activation of the mitogen activated protein kinase (MAPK) cascade through estrogen receptor α located in the plasma membrane. In addition, estradiol regulates MAPK signaling via the activation of protein kinase C and by increasing the expression of brain derived neurotrophic factor and tyrosine kinase receptor B. Estradiol also interacts with the signaling of insulin-like growth factor-I receptor through estrogen receptor α, modulating the phosphoinositide-3 kinase signaling pathway, which contributes to the stabilization of microtubules. Finally, estradiol modulates dendritogenesis by the inhibition of Notch signaling, by a mechanism that, at least in hippocampal neurons, is mediated by G-protein coupled receptor 30. This article is part of a Special Issue entitled 'Neurosteroids'.

The p21-activated kinase PAK 5 is involved in formalin-induced nociception through regulation of MAP-kinase signaling and formalin-specific receptors

p21-activated kinases (PAKs) are involved in signal cascades relevant for nociceptive processing and neuropathic pain. Particularly, the recently described group B PAKs 4, 5 and 6 regulate MAP-kinases and the rearrangement of the actin cytoskeleton, both of which have been linked to pain processing. However, a specific role of these PAKs in nociception has not yet been demonstrated. We found PAK 4, 5 and 6 expression in pain-relevant tissues in peripheral and CNS. Since viable knock-out mice only exist for the PAK isoform 5, we further assessed the impact of this PAK on acute and chronic pain using different behavioral models in mice. PAK 5 knock-out mice showed normal acute nociception and did not differ from wild type mice in their neuropathic pain behavior. However, the nociceptive response in formalin-induced paw inflammation was significantly reduced in knock-out mice associated with inhibition of MAP-kinase activation and a decreased number of formalin-induced c-Fos positive neurons in the spinal cord. Furthermore, in isolated neurons, we found a significantly reduced calcium response after stimulation of TRPA1-channels in PAK 5(-/-)- compared to PAK 5(+/+)-cells. Our results indicate that PAK 5 is involved in formalin-induced inflammatory nociception through regulation of MAPK-induced c-Fos-activation and formalin-specific TRP-channels.

17β-Estradiol regulates the gene expression of voltage-gated sodium channels: role of estrogen receptor α and estrogen receptor β

Estradiol (E2) plays a key role in pain modulation, and the biological effects of E2 are transduced by binding estrogen receptors (ERs). Voltage-gated sodium (Nav) channels are responsible for the generation and propagation of action potentials in the membranes of most neurons and excitable cells. Adult dorsal root ganglion (DRG) neurons can express the ERs (ERα and ERβ), and Nav channels (TTX-S: Nav1.1, Nav1.6, and Nav1.7; and TTX-R: Nav1.8, and Nav1.9). Although E2 modulates Nav channel currents, little is known about the molecular mechanisms involved. In this study, we investigate the mRNA expressions of Nav channel subtypes mediated differentially by the ERs in the DRGs of wild-type (WT) and estrogen receptor knockout (αERKO and βERKO) mice. By means of quantitative real-time PCR, we found that the expressions of Nav1.1, Nav1.7, Nav1.8, and Nav1.9 subtypes were elevated in αERKO and βERKO mice, whereas Nav1.6 mRNA decreased in αERKO, but not in βERKO mice. The mRNA expressions of Nav subtypes were increased in E2-treated WT ovariectomized animals. We also found that E2-regulation of Nav1.1 and Nav1.9 mRNA expressions is dependent on ERα, ERβ, and another ER, whereas E2-regulation of Nav1.8 appears to be in an ERβ-dependent manner.

Multiple sclerosis: neuroprotective alliance of estrogen-progesterone and gender

The potential of 17β-estradiol and progesterone as neuroprotective factors is well-recognized. Persuasive data comes from in vitro and animal models reflecting a wide range of CNS disorders. These studies have endeavored to translate findings into human therapies. Nonetheless, few human studies show promising results. Evidence for neuroprotection was obtained in multiple sclerosis (MS) patients. This chronic inflammatory and demyelinating disease shows a female-to-male gender prevalence and disturbances in sex steroid production. In MS-related animal models, steroids ameliorate symptoms and protect from demyelination and neuronal damage. Both hormones operate in dampening central and brain-intrinsic immune responses and regulating local growth factor supply, oligodendrocyte and astrocyte function. This complex modulation of cell physiology and system stabilization requires the gamut of steroid-dependent signaling pathways. The identification of molecular and cellular targets of sex steroids and the understanding of cell-cell interactions in the pathogenesis will offer promise of novel therapy strategies.

Dopaminergic neuroprotection of hormonal replacement therapy in young and aged menopausal rats: role of the brain angiotensin system

There is a lack of consensus about the effects of the type of menopause (surgical or natural) and of oestrogen replacement therapy on Parkinson's disease. The effects of the timing of replacement therapy and the female's age may explain the observed differences in such effects. However, the mechanisms involved are poorly understood. The renin-angiotensin system mediates the beneficial effects of oestrogen in several tissues, and we have previously shown that dopaminergic cell loss is enhanced by angiotensin via type 1 receptors, which is activated by ageing. In rats, we compared the effects of oestrogen replacement therapy on 6-hydroxydopamine-induced dopaminergic degeneration, nigral renin-angiotensin system activity, activation of the nicotinamide adenine dinucleotide phosphate oxidase complex and levels of the proinflammatory cytokine interleukin-1β in young (surgical) menopausal rats and aged menopausal rats. In young surgically menopausal rats, the renin-angiotensin system activity was higher (i.e. higher angiotensin converting enzyme activity, higher angiotensin type-1 receptor expression and lower angiotensin type-2 receptor expression) than in surgically menopausal rats treated with oestrogen; the nicotinamide adenine dinucleotide phosphate oxidase activity and interleukin-1β expression were also higher in the first group than in the second group. In aged menopausal rats, the levels of nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity were similar to those observed in surgically menopausal rats. However, oestrogen replacement therapy significantly reduced 6-hydroxydopamine-induced dopaminergic cell loss in young menopausal rats but not in aged rats. Treatment with oestrogen also led to a more marked reduction in nigral renin-angiotensin and nicotinamide adenine dinucleotide phosphate oxidase activity in young surgically menopausal rats (treated either immediately or after a period of hypo-oestrogenicity) than in aged menopausal rats. Interestingly, treatment with the angiotensin type-1 receptor antagonist candesartan led to remarkable reduction in renin-angiotensin system activity and dopaminergic neuron loss in both groups of menopausal rats. This suggests that manipulation of the brain renin-angiotensin system may be an efficient approach for the prevention or treatment of Parkinson's disease in oestrogen-deficient females, together with or instead of oestrogen replacement therapy.

Vitamin D deficiency promotes skeletal muscle hypersensitivity and sensory hyperinnervation

Musculoskeletal pain affects nearly half of all adults, most of whom are vitamin D deficient. Previous findings demonstrated that putative nociceptors ("pain-sensing" nerves) express vitamin D receptors (VDRs), suggesting responsiveness to 1,25-dihydroxyvitamin D. In the present study, rats receiving vitamin D-deficient diets for 2-4 weeks showed mechanical deep muscle hypersensitivity, but not cutaneous hypersensitivity. Muscle hypersensitivity was accompanied by balance deficits and occurred before onset of overt muscle or bone pathology. Hypersensitivity was not due to hypocalcemia and was actually accelerated by increased dietary calcium. Morphometry of skeletal muscle innervation showed increased numbers of presumptive nociceptor axons (peripherin-positive axons containing calcitonin gene-related peptide), without changes in sympathetic or skeletal muscle motor innervation. Similarly, there was no change in epidermal innervation. In culture, sensory neurons displayed enriched VDR expression in growth cones, and sprouting was regulated by VDR-mediated rapid response signaling pathways, while sympathetic outgrowth was not affected by different concentrations of 1,25-dihydroxyvitamin D. These findings indicate that vitamin D deficiency can lead to selective alterations in target innervation, resulting in presumptive nociceptor hyperinnervation of skeletal muscle, which in turn is likely to contribute to muscular hypersensitivity and pain.

Axonal protection by 17β-estradiol through thioredoxin-1 in tumor necrosis factor-induced optic neuropathy

Axonal degeneration often leads to the death of neuronal cell bodies. Previous studies demonstrated the substantial protective role of 17β-estradiol (E2) in several types of neuron. However, most studies examined cell body protection, and the role of 17β-E2 in axonal degeneration of retinal ganglion cells (RGC) remains unclear. In this study, we showed the presence of thioredoxin-1 (Trx1) in the optic nerve axons and found that the levels of Trx1 protein were significantly decreased in isolated RGC and the optic nerve after intravitreal injection of TNF, which was shown previously to induce optic nerve degeneration and subsequent loss of RGC. These changes were concomitant with disorganization of the microtubules with neurofilament accumulation, which were blocked by 17β-E2 implantation. 17β-E2 treatment also totally abolished TNF-induced decreases in Trx1 protein levels in isolated RGC and the optic nerve. The induction of Trx1 by 17β-E2 in the optic nerve was significantly inhibited by simultaneous injection of Trx1 small interfering RNA (siRNA) with TNF. Up-regulation of Trx1 by 17β-E2 in RGC-5 cells was prevented by Trx1 siRNA treatment. 17β-E2 significantly prevented TNF-induced axonal loss, and this axonal-protective effect was inhibited by intravitreal injection of Trx1 siRNA. This finding was also supported by the quantification of microtubules and neurofilaments. These results suggest that a Trx1 decrease in RGC bodies and their axons may be associated with TNF-induced optic nerve axonal degeneration. Axonal protection by 17β-E2 may be related to its regulatory effect on Trx1 induction.

Notch/neurogenin 3 signalling is involved in the neuritogenic actions of oestradiol in developing hippocampal neurones

The ovarian hormone oestradiol promotes neuritic outgrowth in different neuronal types, by mechanisms that remain elusive. Recent studies have shown that the Notch-regulated transcription factor neurogenin 3 controls neuritogenesis. In the present study, we assessed whether oestradiol regulates neurogenin 3 in primary hippocampal neurones. As expected, neuritogenesis was increased in the cultures treated with oestradiol. However, the neuritogenic action of oestradiol was not prevented by ICI 182,780, an antagonist of classical oestrogen receptors (ERs). Oestradiol decreased the expression of Hairy and Enhancer of Split-1, a Notch-regulated gene that negatively controls the expression on neurogenin 3. Furthermore, oestradiol increased the expression of neurogenin 3 and regulated its distribution between the neuronal cell nucleus and the cytoplasm. The effect of oestradiol on neurogenin 3 expression was not blocked by antagonists of classical nuclear ER-mediated transcription and was not imitated by selective agonists of nuclear ERs. By contrast, G1, a ligand of G protein receptor 30/G protein-coupled ER, fully reproduced the effect of oestradiol on neuritogenesis, neurogenin 3 expression and neurogenin 3 subcellular localisation. Moreover, knockdown of neurogenin 3 in neurones by transfection with small interference RNA for neurogenin 3 completely abrogated the neuritogenic actions of oestradiol and G1. These results suggest that oestradiol regulates neurogenin 3 in primary hippocampal neurones by a nonclassical steroid signalling mechanism, which involves the down-regulation of Notch activity and the activation of G protein receptor 30/G protein-coupled ER or of other unknown G1 targets. In addition, our findings indicate that neurogenin 3 participates in the neuritogenic mechanisms of oestradiol in hippocampal neurones.