New feelings about the role of sensory nerves in inflammation

Chronic itch in African Americans: an unmet need

Chronic pruritus carries a significant burden of disease and is associated with a negative impact on quality of life. African Americans are disproportionately burdened by chronic pruritic disorders, including but not limited to atopic dermatitis, prurigo nodularis, inflammatory scalp dermatoses, pathologic scarring, and HIV-related dermatoses. Racial differences in skin structure and function may contribute to the pathogenesis of itch in African Americans. Itch perception and response to treatment in African Americans remain understudied and not well understood. As such, there is a large unmet need with regard to the knowledge and management of pruritus in African Americans. This review highlights notable differences in the epidemiology, pathophysiology, genetic predisposition, clinical presentation, and response to treatment for select pruritic skin conditions. By addressing itch as an unmet need in African Americans, we hope to improve patient outcomes and lessen disparities in dermatologic care.

Vulvar Pruritus: A Review of Clinical Associations, Pathophysiology and Therapeutic Management

Vulvar pruritus is an unpleasant sensation and frequent symptom associated with many dermatologic conditions, including infectious, inflammatory and neoplastic dermatoses affecting the female genitalia. It can lead to serious impairment of quality of life, impacting sexual function, relationships, sleep and self-esteem. In this review, common conditions associated with vulvar itch are discussed including atopic and contact dermatitis, lichen sclerosus, psoriasis and infectious vulvovaginitis. We review the potential physiologic, environmental and infectious factors that contribute to the development of vulvar itch and emphasize the importance of addressing their complex interplay when managing this disruptive and challenging symptom.

Investigational drugs for pruritus

INTRODUCTION

Chronic pruritus (CP), defined as itch lasting for > 6 weeks, is a burdensome symptom of several different diseases, dermatological and systemic, with a high negative impact on the quality of life of patients. Given the manifold aetiologies of CP, therapy is often difficult. In recent years, however, novel substances have been developed for treatment of certain CP entities and identified targets.

AREAS COVERED

In this review, the authors present a survey of targets currently believed to be promising (H4R, IL-31, MOR, KOR, GRPR, NGF, NK-1R, TRP channels) and related investigational drugs that are in the preclinical or clinical stage of development. Some substances have already undergone clinical testing, but only one of them (nalfurafine) has been licensed so far. Many of them are most likely to exert their effects on the skin and interfere there with the cutaneous neurobiology of CP.

EXPERT OPINION

Currently, the most promising candidates for new therapeutic agents in CP are neurokinin-1 receptor antagonists and substances targeting the kappa- or mu-opioid receptor, or both. They have the potential to target the neuronal pathway of CP and are thus of interest for several CP entities. The goal for the coming years is to validate these concepts and move forward in developing new drugs for the therapy of CP.

Psychological stress and the severity of post-inflammatory visceral hyperalgesia

OBJECTIVES

Lowered visceral sensory thresholds are a key finding in at least a subgroup of patients with functional bowel disorders. Stress and inflammation contribute to this altered visceral sensory function. We aimed to elucidate the role of repetitive stress and acute mucosal inflammation, alone and in combination, on sensory function.

METHODS

In randomized order, trinitrobenzenesulfonic acid (TNBS) plus the equal amount of ethanol or saline were instilled into the colorectum of female Lewis rats. Colorectal distensions (CRD) were performed with a barostat device (3 min/40 mmHg); to quantify the visceromotor response (VMR) to CRD, electromyographic activity (EMG) of the abdominal muscles was recorded. In randomized order, equal numbers of both treatment groups underwent either seven days (1 h/day) repetitive water avoidance stress (WAS) or sham WAS. CRD's were conducted 28 days later. Colonic tissue samples were obtained to characterize inflammation and blood samples were taken at day 28 to measure plasma IL-2 levels by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Compared to controls (662+/-114 microV) TNBS (1081+/-227 microV), WAS (1366+/-125 microV) and the combination of both (1477+/-390 microV) significantly augmented the VMR to CRD. TNBS and/or WAS caused significant inflammatory changes at day 5, while only TNBS+WAS also showed signs of mucosal inflammation on day 14 and significantly elevated IL-2 levels on day 28.

CONCLUSIONS

Stress and inflammation cause long lasting alterations of visceral sensory function. Concomitant stress further increases post-inflammatory visceral hyperalgesia.

The Multitasking Mast Cell: Positive and Negative Roles in the Progression of Autoimmunity

Among the potential outcomes of an aberrantly functioning immune system are allergic disease and autoimmunity. Although it has been assumed that the underlying mechanisms mediating these conditions are completely different, recent evidence shows that mast cells provide a common link. Mast cells reside in most tissues, are particularly prevalent at sites of Ag entry, and act as sentinel cells of the immune system. They express many inflammatory mediators that affect both innate and adaptive cellular function. They contribute to pathologic allergic inflammation but also serve an important protective role in bacterial and parasite infections. Given the proinflammatory nature of autoimmune responses, it is not surprising that studies using murine models of autoimmunity clearly implicate mast cells in the initiation and/or progression of autoimmune disease. In this review, we discuss the defined and hypothesized mechanisms of mast cell influence on autoimmune diseases, including their surprising and newly discovered role as anti-inflammatory cells.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Frontiers in pruritus research: scratching the brain for more effective itch therapy

This Review highlights selected frontiers in pruritus research and focuses on recently attained insights into the neurophysiological, neuroimmunological, and neuroendocrine mechanisms underlying skin-derived itch (pruritogenic pruritus), which may affect future antipruritic strategies. Special attention is paid to newly identified itch-specific neuronal pathways in the spinothalamic tract that are distinct from pain pathways and to CNS regions that process peripheral pruritogenic stimuli. In addition, the relation between itch and pain is discussed, with emphasis on how the intimate contacts between these closely related yet distinct sensory phenomena may be exploited therapeutically. Furthermore, newly identified or unduly neglected intracutaneous itch mediators (e.g., endovanilloids, proteases, cannabinoids, opioids, neurotrophins, and cytokines) and relevant receptors (e.g., vanilloid receptor channels and proteinase-activated, cannabinoid, opioid, cytokine, and new histamine receptors) are discussed. In summarizing promising new avenues for managing itch more effectively, we advocate therapeutic approaches that strive for the combination of peripherally active antiinflammatory agents with drugs that counteract chronic central itch sensitization.

Pathophysiology and diagnostic value of urinary trypsin inhibitors

Inflammation is an important indicator of tissue injury. In the acute form, there is usually accumulation of fluids and plasma components in the affected tissues. Platelet activation and the appearance in blood of abnormally increased numbers of polymorphonucleocytes, lymphocytes, plasma cells and macrophages usually occur. Infectious disorders such as sepsis, meningitis, respiratory infection, urinary tract infection, viral infection, and bacterial infection usually induce an inflammatory response. Chronic inflammation is often associated with diabetes mellitus, acute myocardial infarction, coronary artery disease, kidney diseases, and certain auto-immune disorders, such as rheumatoid arthritis, organ failures and other disorders with an inflammatory component or etiology. The disorder may occur before inflammation is apparent. Markers of inflammation such as C-reactive protein (CRP) and urinary trypsin inhibitors have changed our appraisal of acute events such as myocardial infarction; the infarct may be a response to acute infection and (or) inflammation. We describe here the pathophysiology of an anti-inflammatory agent termed urinary trypsin inhibitor (uTi). It is an important anti-inflammatory substance that is present in urine, blood and all organs. We also describe the anti-inflammatory agent bikunin, a selective inhibitor of serine proteases. The latter are important in modulating inflammatory events and even shutting them down.

Proteinase-activated receptors: transducers of proteinase-mediated signaling in inflammation and immune response

Serine proteinases such as thrombin, mast cell tryptase, trypsin, or cathepsin G, for example, are highly active mediators with diverse biological activities. So far, proteinases have been considered to act primarily as degradative enzymes in the extracellular space. However, their biological actions in tissues and cells suggest important roles as a part of the body's hormonal communication system during inflammation and immune response. These effects can be attributed to the activation of a new subfamily of G protein-coupled receptors, termed proteinase-activated receptors (PARs). Four members of the PAR family have been cloned so far. Thus, certain proteinases act as signaling molecules that specifically regulate cells by activating PARs. After stimulation, PARs couple to various G proteins and activate signal transduction pathways resulting in the rapid transcription of genes that are involved in inflammation. For example, PARs are widely expressed by cells involved in immune responses and inflammation, regulate endothelial-leukocyte interactions, and modulate the secretion of inflammatory mediators or neuropeptides. Together, the PAR family necessitates a paradigm shift in thinking about hormone action, to include proteinases as key modulators of biological function. Novel compounds that can modulate PAR function may be potent candidates for the treatment of inflammatory or immune diseases.

Aging and the endothelium

One link between aging and endothelial function is the inflammatory response. On one hand, the latter shortens the biological engaged by activated leukocytes against invaders or stressing agents. On the other hand, the surveyed tissues become targets of the toxicity of reactive oxygen species, ROS. The ensuing regeneration is source of transcriptional infidelity, leading to the alteration of the repaired tissue. Hence, the toll of inflammatory stress consists in premature senescence of cell and tissues. This hypothesis is discussed in the present review, which focuses on the molecular targets relevant for cancer and degenerative diseases, both tributary to an inflammatory environment and taking advantage from the consequences of cell and tissue dysfunctions characteristic of aging. Eventually, adaptation to stress, whatever its origin -inflammatory and/or psychosocial-is discussed. Basal nitric oxide (NO) release, such as provided through moderate exercise, seems to be the most potent guardian against immune, nervous and cardiovascular over-stimulation. Tissue regeneration is also obtained by circulating endothelial progenitors able to recognize the damaged tissue. To avoid post-inflammatory alterations resulting in detrimental changes of tissues and organs, the pharmacological protection of endothelium by agents able to modulate its activation seems crucial to us.

Proinflammatory role of proteinase-activated receptor-2 in humans and mice during cutaneous inflammation in vivo

Proteinase-activated receptor-2 belongs to a new subfamily of G-protein-coupled receptors. Its precise role during inflammation and the underlying mechanisms is still unclear. Our study establishes that PAR-2 plays a direct proinflammatory role during cutaneous inflammation in mice and humans in vivo. In a model of experimentally induced allergic (ACD) and toxic (ICD) contact dermatitis (CD) we show that ear swelling responses, plasma extravasation, and leucocyte adherence were significantly attenuated in PAR-2 null mutant (PAR-2-/-) mice compared with wild-type (PAR-2+/+) mice, especially at early stages. The proinflammatory effects by PAR-2 activation were significantly diminished using nitric oxide-synthase inhibitors, while NF-kappaB and neuropeptides appear to play a minor role in these mechanisms. PAR-2-mediated up-regulation of E-selectin and cell adhesion molecule ICAM-1; enhanced plasma extravasation was observed in humans and mice and of interleukin-6 in mice in vivo. Thus, PAR-2 may be a beneficial therapeutic target for the treatment of inflammatory skin diseases.

Break excitation alone does not explain the delay and amplitude of anodal current-induced vasodilatation in human skin

In iontophoresis experiments, a 'non-specific' current-induced vasodilatation interferes with the effects of the diffused drugs. This current-induced vasodilatation is assumed to rely on an axon reflex due to excitation of cutaneous nociceptors and is weaker and delayed at the anode as compared to the cathode. We analysed whether these anodal specificities could result from a break excitation of nociceptors. Break excitation is the generation of action potentials at the end of a square anodal DC current application, which are generally weaker than those observed at the onset of a same application at the cathode. In eight healthy volunteers, we studied forearm cutaneous laser Doppler flow (LDF) responses to: (1) anodal and cathodal 100 microA current applications of 1, 2, 3, 4 or 5 min; (2) 100 microA anodal applications of 3 min with a progressive ending over 100 s (total charge 23 mC); these were compared to square-ended 100 microA anodal applications of the same total charge (23 mC) or duration (3 min); (3) a 4 min 100 microA anodal application with a 333 msec break at half time. Results (mean +/- S.D.) are expressed as percentage of heat-induced maximal vasodilatation (%MVD). Onset (T(vd)) and amplitude (LDF(peak)) of vasodilatation were determined. We observed that: T(vd) was linearly related to the duration of current application at the anode (slope = 1.01, r(2) = 0.99, P < 0.0001) but not at the cathode (slope = 0.03, r(2) = 0.02, n.s.). Progressive ending of anodal current did not decrease LDF(peak) (63.3 +/- 24.6 %MVD) as compared to square-ending of current application of the same duration (36.9 +/- 22.2 %MVD) or the same total charge (57.1 +/- 23.5 %MVD). A transient break of anodal current did not allow for the vasodilatation to develop until current was permanently stopped. We conclude that, during iontophoresis, anodal break excitation alone cannot account for the delay and amplitude of the vascular response.

A polymorphic protease-activated receptor 2 (PAR2) displaying reduced sensitivity to trypsin and differential responses to PAR agonists

Protease-activated receptor 2 (PAR2) is a trypsin-activated member of a family of G-protein-coupled PARs. We have identified a polymorphic form of human PAR2 (PAR(2)F240S) characterized by a phenylalanine to serine mutation at residue 240 within extracellular loop 2, with allelic frequencies of 0.916 (Phe(240)) and 0.084 (Ser(240)) for the wild-type and mutant alleles, respectively. Elevations in intracellular calcium were measured in permanently transfected cell lines expressing the receptors. PAR(2)F240S displayed a significant reduction in sensitivity toward trypsin ( approximately 3.7-fold) and the PAR2-activating peptides, SLIGKV-NH(2) ( approximately 2.5-fold) and SLIGRL-NH(2) ( approximately 2.8-fold), but an increased sensitivity toward the selective PAR2 agonist, trans-cinnamoyl-LIGRLO-NH(2) ( approximately 4-fold). Increased sensitivity was also observed toward the selective PAR-1 agonist, TFLLR-NH(2) ( approximately 7-fold), but not to other PAR-1 agonists tested. Furthermore, we found that TLIGRL-NH(2) and a PAR4-derived peptide, trans-cinnamoyl-YPGKF-NH(2), were selective PAR(2)F240S agonists. By introducing the F240S mutation into rat PAR2, we observed shifts in agonist potencies that mirrored the human PAR(2)F240S, suggesting that Phe(240) is involved in determining agonist specificity of PAR2. Finally, differences in receptor signaling were paralleled in a cell growth assay. We suggest that the distinct pharmacological profile induced by this polymorphism will have important implications for the design of PAR-targeted agonists/antagonists and may contribute to, or be predictive of, an inflammatory disease.