Neuropeptide regulation of human dermal microvascular endothelial cell ICAM-1 expression and function

Recent advances in the role of neuroregulation in skin wound healing

Neuroregulation during skin wound healing involves complex interactions between the nervous system and intricate tissue repair processes. The skin, the largest organ, depends on a complex system of nerves to manage responses to injury. Recent research has emphasized the crucial role of neuroregulation in maximizing wound healing outcomes. Recently, researchers have also explained the interactive contact between the peripheral nervous system and skin cells during the different phases of wound healing. Neurotransmitters and neuropeptides, once observed as simple signalling molecules, have since been recognized as effective regulators of inflammation, angiogenesis, and cell proliferation. The significance of skin innervation and neuromodulators is underscored by the delayed wound healing observed in patients with diabetes and the regenerative capabilities of foetal skin. Foetal skin regeneration is influenced by the neuroregulatory environment, immature immune system, abundant growth factors, and increased pluripotency of cells. Foetal skin cells exhibit greater flexibility and specialized cell types, and the extracellular matrix composition promotes regeneration. The extracellular matrix composition of foetal skin promotes regeneration, making it more capable than adult skin because neuroregulatory signals affect skin regeneration. The understanding of these systems can facilitate the development of therapeutic strategies to alter the nerve supply to the skin to enhance the process of wound healing. Neuroregulation is being explored as a potential therapeutic strategy for enhancing skin wound repair. Bioelectronic strategies and neuromodulation techniques can manipulate neural signalling, optimize the neuroimmune axis, and modulate inflammation. This review describes the function of skin innervation in wound healing, emphasizing the importance of neuropeptides released by sensory and autonomic nerve fibres. This article discusses significant discoveries related to neuroregulation and its impact on skin wound healing.

Neural Regulation of Innate Immunity in Inflammatory Skin Diseases

As the largest barrier organ of the body, the skin is highly innervated by peripheral sensory neurons. The major function of these sensory neurons is to transmit sensations of temperature, pain, and itch to elicit protective responses. Inflammatory skin diseases are triggered by the aberrant activation of immune responses. Recently, increasing evidence has shown that the skin peripheral nervous system also acts as a regulator of immune responses, particularly innate immunity, in various skin inflammatory processes. Meanwhile, immune cells in the skin can express receptors that respond to neuropeptides/neurotransmitters, leading to crosstalk between the immune system and nervous system. Herein, we highlight recent advances of such bidirectional neuroimmune interactions in certain inflammatory skin conditions.

Genetic variants affecting chemical mediated skin immunotoxicity

The skin is an immune-competent organ and this function may be impaired by exposure to chemicals, which may ultimately result in immune-mediated dermal disorders. Interindividual variability to chemical-induced skin immune reactions is associated with intrinsic individual characteristics and their genomes. In the last 30-40 years, several genes influencing susceptibility to skin immune reactions were identified. The aim of this review is to provide information regarding common genetic variations affecting skin immunotoxicity. The polymorphisms selected for this review are related to xenobiotic-metabolizing enzymes (CYPA1 and CYPB1 genes), antioxidant defense (GSTM1, GSTT1, and GSTP1 genes), aryl hydrocarbon receptor signaling pathway (AHR and ARNT genes), skin barrier function transepidermal water loss (FLG, CASP14, and SPINK5 genes), inflammation (TNF, IL10, IL6, IL18, IL31, and TSLP genes), major histocompatibility complex (MHC) and neuroendocrine system peptides (CALCA, TRPV1, ACE genes). These genes present variants associated with skin immune responses and diseases, as well as variants associated with protecting skin immune homeostasis following chemical exposure. The molecular and association studies focusing on these genetic variants may elucidate their functional consequences and contribution in the susceptibility to skin immunotoxicity. Providing information on how genetic variations affect the skin immune system may reduce uncertainties in estimating chemical hazards/risks for human health in the future.

Sympathetic and Sensory-Motor Nerves in Peripheral Small Arteries

Small arteries, which play important roles in controlling blood flow, blood pressure, and capillary pressure, are under nervous influence. Their innervation is predominantly sympathetic and sensory motor in nature, and while some arteries are densely innervated, others are only sparsely so. Innervation of small arteries is a key mechanism in regulating vascular resistance. In the second half of the previous century, the physiology and pharmacology of this innervation were very actively investigated. In the past 10-20 yr, the activity in this field was more limited. With this review we highlight what has been learned during recent years with respect to development of small arteries and their innervation, some aspects of excitation-release coupling, interaction between sympathetic and sensory-motor nerves, cross talk between endothelium and vascular nerves, and some aspects of their role in vascular inflammation and hypertension. We also highlight what remains to be investigated to further increase our understanding of this fundamental aspect of vascular physiology.

Elevated serum substance P during simian varicella virus infection in rhesus macaques: implications for chronic inflammation and adverse cerebrovascular events

Varicella and zoster, produced by varicella-zoster virus (VZV), are associated with an increased risk of stroke that may be due to persistent inflammation and hypercoagulability. Because substance P is associated with inflammation, hypercoagulability, and atherosclerotic plaque rupture that may contribute to increased stroke risk after VZV infection, we measured serum substance P in simian varicella virus-infected rhesus macaques. We found significantly increased and persistent serum substance P concentrations during varicella and zoster compared with pre-inoculation, supporting the hypothesis that VZV-induced increases in serum substance P may contribute to increased stroke risk associated with VZV infection.

Capsaicin-induced rapid neutrophil leukocyte activation in the rat urinary bladder microcirculatory bed

AIMS

This study was initiated to investigate the involvement of neutrophil leukocyte activation in neurogenic inflammation, a process also involved in human urinary pathologies, elicited in the rat urinary bladder by the local administration of capsaicin, the archetypal TRPV1 agonist. The contribution of afferent nerves and sensory neuropeptides to leukocyte activation in the urinary bladder microcirculatory bed was examined.

METHODS

Following a 15-min topical application of capsaicin (50 μM), leukocyte-endothelial interactions were examined for an observation period of 45 min with intravital microscopy. Expression of adhesion molecules E-selectin and ICAM-1 implicated in these interactions was assessed by immunohistochemistry. Selective sensory denervation was performed by neonatal treatment with capsaicin. The role of the TRPV1 receptor and two sensory neuropeptides (CGRP and substance P [SP]) were studied using the selective antagonists capsazepine, CGRP_8-37 and RP67580, respectively.

RESULTS

Capsaicin induced rapid increases in leukocyte rolling and adhesion and increased the expression of E-selectin and ICAM-1 in the postcapillary venules. Sensory chemodenervation via capsaicin and also TRPV1 receptor antagonism effectively prevented these changes. A similar reduction was observed in leukocyte adhesion after topical application of CGRP_8-34 or RP67580, but only CGRP_8-34 reduced the capsaicin-evoked leukocyte rolling.

CONCLUSIONS

Topical application of capsaicin induces early neurogenically mediated cellular microcirculatory inflammatory reactions via the activation of the TRPV1 receptor and the release of CGRP and SP from sensory nerves in the bladder. Co-administration of SP and CGRP receptor antagonists may ameliorate microcirculatory inflammatory changes elicited by capsaicin in the urinary bladder.

Gastrin-releasing peptide induces monocyte adhesion to vascular endothelium by upregulating endothelial adhesion molecules

Gastrin-releasing peptide (GRP) is a neuropeptide that plays roles in various pathophysiological conditions including inflammatory diseases in peripheral tissues; however, little is known about whether GRP can directly regulate endothelial inflammatory processes. In this study, we showed that GRP promotes the adhesion of leukocytes to human umbilical vein endothelial cells (HUVECs) and the aortic endothelium. GRP increased the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by activating nuclear factor-κB (NF-κB) in endothelial cells. In addition, GRP activated extracellular signal-regulated kinase 1/2 (ERK1/2), p38MAPK, and AKT, and the inhibition of these signaling pathways significantly reduced GRP-induced monocyte adhesion to the endothelium. Overall, our results suggested that GRP may cause endothelial dysfunction, which could be of particular relevance in the development of vascular inflammatory disorders.

Substance P enhances the activation of AMPK and cellular lipid accumulation in 3T3‑L1 cells in response to high levels of glucose

The rescue of glucose tolerance and insulin-sensitivity in peripheral tissues, including adipose tissue, is essential in therapeutic strategies for diabetes. The present study demonstrated that substance P (SP) increases the accumulation of lipids in 3T3-L1 cells during their differentiation into adipocytes in response to a high concentration of glucose. SP reciprocally regulated the activities of AMP-activated protein kinase (AMPK) and Akt: SP enhanced the activation of AMPK, although the activity of Akt was downregulated. Notably, SP induced an increase in the expression level of glucose transporter 4 in the 3T3-L1 adipocytes. Therefore, it is possible that SP leads to an increase in glucose uptake and the accumulation of lipids in adipocytes, and may contribute towards the rescue of insulin-sensitivity in diabetes.

Non-human primate and rat cardiac fibroblasts show similar extracellular matrix-related and cellular adhesion gene responses to substance P

BACKGROUND

The sensory nerve neuropeptide substance P (SP) regulates cardiac fibrosis in rodents under pressure overload conditions. Interestingly, SP induces transient increased expression of specific genes in isolated rat cardiac fibroblasts, without resultant changes in cell function. This suggests that SP 'primes' fibroblasts, but does not directly activate them. We investigated whether these unusual findings are specific to rodent fibroblasts or are translatable to a larger animal model more closely related to humans.

METHODS

We compared the effects of SP on genes associated with extracellular matrix (ECM) regulation, cell-cell adhesion, cell-matrix adhesion and ECM in cardiac fibroblasts isolated from a non-human primate and Sprague-Dawley rats.

RESULTS

We found that rodent and non-human primate cardiac fibroblasts showed similar responses in genes that relate to ECM regulation and cell adhesion in response to SP. There were large discrepancies in ECM component genes, however, this did not result in collagen or laminin synthesis in rat or non-human primate fibroblasts in response to SP.

CONCLUSIONS

This study further supports the notion that SP serves as a 'primer' for fibroblasts rather than initiating direct effects and suggests that rodent fibroblasts are a suitable model for studying gene and functional responses to SP in the absence of human or non-human primate fibroblasts.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.

The role of cytokines in skin aging

Cutaneous aging is one of the major noticeable menopausal complications that most women want to fight in their quest for an eternally youthful skin appearance. It may contribute to some maladies that occur in aging which, despite not being life-threatening, affect the well-being, psychological state and quality of life of aged women. Skin aging is mainly affected by three factors: chronological aging, decreased levels of estrogen after menopause, and environmental factors. Aged skin is characterized by a decrease in collagen content and skin thickness which result in dry, wrinkled skin that is easily bruised and takes a longer time to heal. Cytokines play a crucial role in the manifestation of these features of old skin. The pro-inflammatory cytokine tumor necrosis factor-alpha inhibits collagen synthesis and enhances collagen degradation by increasing the production of MMP-9. It also lowers the skin immunity and thus increases the risk of cutaneous infections in old age. Deranged levels of several interleukins and interferons also affect the aging process. The high level of CCN1 protein in aged skin gives dermal fibroblasts an 'age-associated secretory phenotype' that causes abnormal homeostasis of skin collagen and leads to the loss of the function and integrity of skin. Further research is required especially to establish the role of cytokines in the treatment of cutaneous aging.

Modern methods and approaches to studying the role of neurotransmitters in the pathogenesis of chronic inflammatory skin diseases accompanied with itching

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Differentiation state determines neural effects on microvascular endothelial cells

Growing evidence indicates that nerves and capillaries interact paracrinely in uninjured skin and cutaneous wounds. Although mature neurons are the predominant neural cell in the skin, neural progenitor cells have also been detected in uninjured adult skin. The aim of this study was to characterize differential paracrine effects of neural progenitor cells and mature sensory neurons on dermal microvascular endothelial cells. Our results suggest that neural progenitor cells and mature sensory neurons have unique secretory profiles and distinct effects on dermal microvascular endothelial cell proliferation, migration, and nitric oxide production. Neural progenitor cells and dorsal root ganglion neurons secrete different proteins related to angiogenesis. Specific to neural progenitor cells were dipeptidyl peptidase-4, IGFBP-2, pentraxin-3, serpin f1, TIMP-1, TIMP-4 and VEGF. In contrast, endostatin, FGF-1, MCP-1 and thrombospondin-2 were specific to dorsal root ganglion neurons. Microvascular endothelial cell proliferation was inhibited by dorsal root ganglion neurons but unaffected by neural progenitor cells. In contrast, microvascular endothelial cell migration in a scratch wound assay was inhibited by neural progenitor cells and unaffected by dorsal root ganglion neurons. In addition, nitric oxide production by microvascular endothelial cells was increased by dorsal root ganglion neurons but unaffected by neural progenitor cells.

Involvement of the peripheral sensory and sympathetic nervous system in the vascular endothelial expression of ICAM-1 and the recruitment of opioid-containing immune cells to inhibit inflammatory pain

Endogenous opioids are known to be released within certain brain areas following stressful stimuli. Recently, it was shown that also leukocytes are a potential source of endogenously released opioid peptides following stress. They activate sensory neuron opioid receptors and result in the inhibition of local inflammatory pain. An important prerequisite for the recruitment of such leukocytes is the expression of intracellular adhesion molecule-1 (ICAM-1) in blood vessels of inflamed tissue. Here, we investigated the contribution of peripheral sensory and/or sympathetic nerves to the enhanced expression of ICAM-1 simultaneously with the increased recruitment of opioid peptide-containing leukocytes to promote the inhibition of inflammatory pain. Selective degeneration of either peripheral sensory or sympathetic nerve fibers by their respective neurotoxins, capsaicin or 6-hydroxydopamime, significantly reduced the subcutaneous immigration of β-endorphin- (END-) and met-enkephalin- (ENK-)-containing polymorphonuclear leukocytes (PMN) (in the early phase) and mononuclear cells (in the late phase) during painful Freund's complete adjuvant (FCA) rat hind paw inflammation. In contrast, this treatment did not alter the percentage of opioid peptide-containing leukocytes in the circulation. Calcitonin gene-related peptide- (CGRP-) and tyrosine hydroxylase- (TH-) immunoreactive (IR) nerve fibers were in close contact to ICAM-1 IR blood vessels within inflamed subcutaneous tissue. The selective degeneration of sensory or sympathetic nerve fibers attenuated the enhanced expression of vascular endothelial ICAM-1 after intraplantar (i.pl.) FCA and abolished endogenous opioid peptide-mediated peripheral analgesia. Our results suggest that, during localized inflammatory pain, peripheral sensory and sympathetic nerve fibers augment the expression of vascular endothelial ICAM-1 simultaneously with the increased recruitment of opioid peptide-containing leukocytes which consequently promotes the endogenous opioid peptide-mediated inhibition of inflammatory pain. They support existing evidence about a close link between the nervous and the immune system.

Novel functional aspect of antihistamines: the impact of bepotastine besilate on substance p-induced events

Besides histamine, substance P (SP) has been demonstrated to play a crucial role in pruritic skin diseases. Although antihistamines are frequently used for pruritic skin diseases, little is known concerning the effect on an SP-induced event such as mast cell degranulation and the upregulation of adhesion molecules or the nitric oxide (NO) synthesis in endothelial cells. Our aim was to study the effect of bepotastine besilate on SP-induced degranulation of rat basophillic leukemia (RBL-2H3) cells and expression of adhesion molecules and NO synthesis in human dermal microvascular endothelial cells (HMVECs). Bepotastine besilate significantly inhibited SP-induced degranulation of RBL-2H3 cells and NO synthesis in HMVECs. Bepotastine besilate significantly inhibited expression of adhesion molecules in HMVESs, while it failed to suppress SP-induced upregulation of the adhesion molecules in HMVECs. Therefore, bepotastine besilate is assumed to act favorably on SP-induced basophil degranulation and NO synthesis in HMVECs.

Endothelin-converting enzyme 1 promotes re-sensitization of neurokinin 1 receptor-dependent neurogenic inflammation

BACKGROUND AND PURPOSE

The metalloendopeptidase endothelin-converting enzyme 1 (ECE-1) is prominently expressed in the endothelium where it converts big endothelin to endothelin-1, a vasoconstrictor peptide. Although ECE-1 is found in endosomes in endothelial cells, the role of endosomal ECE-1 is unclear. ECE-1 degrades the pro-inflammatory neuropeptide substance P (SP) in endosomes to promote recycling and re-sensitization of its neurokinin 1 (NK(1)) receptor. We investigated whether ECE-1 regulates NK(1) receptor re-sensitization and the pro-inflammatory effects of SP in the endothelium.

EXPERIMENTAL APPROACH

We examined ECE-1 expression, SP trafficking and NK(1) receptor re-sensitization in human microvascular endothelial cells (HMEC-1), and investigated re-sensitization of SP-induced plasma extravasation in rats.

KEY RESULTS

HMEC-1 expressed all four ECE-1 isoforms (a-d), and fluorescent SP trafficked to early endosomes containing ECE-1b/d. The ECE-1 inhibitor SM-19712 prevented re-sensitization of SP-induced Ca2+ signals in HMEC-1 cells. Immunoreactive ECE-1 and NK(1) receptors co-localized in microvascular endothelial cells in the rat. SP-induced extravasation of Evans blue in the urinary bladder, skin and ears of the rat desensitized when the interval between two SP injections was 10 min, and re-sensitized after 480 min. SM-19712 inhibited this re-sensitization.

CONCLUSIONS AND IMPLICATIONS

By degrading endocytosed SP, ECE-1 promotes the recycling and re-sensitization of NK(1) receptors in endothelial cells, and thereby induces re-sensitization of the pro-inflammatory effects of SP. Thus, ECE-1 inhibitors may ameliorate the pro-inflammatory actions of SP.

The angiotensin-converting enzyme insertion/deletion and the endothelin -134 3A/4A gene polymorphisms in patients with chronic plaque psoriasis

BACKGROUND

Psoriasis is a common chronic inflammatory skin disease. Vasoactive peptides such as endothelin-1 (ET-1) and bradykinin have previously been implicated in the pathogenesis of chronic plaque psoriasis. The angiotensin-converting enzyme (ACE) gene carries a 287-base pair insertion/deletion (I/D) gene polymorphism, which is associated with plasma concentrations of bradykinin-degrading ACE. A functional polymorphism (EDN1 -134 3A/4A) in the gene encoding ET-1 has been shown to affect ET-1 expression. The purpose of the present study was thus to investigate a hypothesized association between these gene polymorphisms and the presence of chronic plaque psoriasis.

METHODS

The present case-control study comprised 207 patients with chronic plaque psoriasis (136 with early onset and 71 with late onset disease) and 182 control subjects. Genotypes of EDN1 and ACE were determined by a 5' exonuclease assay (Taqman).

RESULTS

The prevalence of the homozygous ACE II genotype was significantly higher in patients with early-onset psoriasis than among control subjects (30.9% vs 19.2%, P = 0.016), yielding an odds ratio of 1.88 [95% confidence interval (CI): 1.12-3.15] for early-onset disease. For late-onset psoriasis, presence of the ACE II genotype was associated with a non-significant odds ratio 1.54 (95% CI: 0.81-2.92). As for the EDN1 -134 3A/4A gene polymorphism, no significant differences in genotype distributions were found between patients with either early- or late-onset psoriasis and control subjects (EDN1 -134 4A/4A: 9.6% in early-onset and 5.6% late-onset psoriasis vs 7.7% in controls; P > 0.05).

CONCLUSIONS

Our data suggest that homozygosity for the ACE I allele may affect susceptibility to early-onset psoriasis.

Making sense of hypertrophic scar: a role for nerves

Healed partial thickness wounds including burns and donor sites cause hypertrophic scar formation and patient discomfort. For many patients with hypertrophic scars, pruritus is the most distressing symptom, which leads to wound excoriation and chronic wound formation. In spite of the clinical significance of abnormal innervation in scars, the nervous system has been largely ignored in the pathophysiology of hypertrophic scars. Evidence that neuropeptides contribute to inflammatory responses to injury include inflammatory cell chemotaxis, cytokine and growth factor production. The neuropeptide substance P, which is released from nerve endings after injury, induces inflammation and mediates angiogenesis, keratinocyte proliferation, and fibrogenesis. Substance P activity is tightly regulated by neutral endopeptidase (NEP), a membrane bound metallopeptidase that degrades substance P at the cell membrane. Altered substance P levels may contribute to impaired cutaneous healing responses associated with diabetes mellitus or hypertrophic scar formation. Topical application of exogenous substance P or an NEP inhibitor enhances wound closure kinetics in diabetic murine wounds suggesting that diabetic wounds have insufficient substance P levels to promote a neuroinflammatory response necessary for normal wound repair. Conversely, increased nerve numbers and neuropeptide levels with reduced NEP levels in human and porcine hypertrophic scar samples suggest that excessive neuropeptide activity induces exuberant inflammation in hypertrophic scars. Given these observations about the role of neuropeptides in cutaneous repair, neuronal modulation of repair processes at two extremes of abnormal wound healing, chronic non-healing ulcers in type II diabetes mellitus and hypertrophic scars in deep partial thickness wounds, may provide therapeutic targets.

Substance P regulates migration in rat intestinal epithelial cells

OBJECTIVE

The current study examined the effect of substance P (SP) upon intestinal epithelial cells and the mechanistic details of this interaction.

SUMMARY BACKGROUND DATA

Intestinal epithelial cells must be capable of migration to reseal mucosal wounds for several vital intestinal functions. This process is incompletely understood; however, recent evidence implicates the neurotransmitter SP in this process.

METHODS

Normal rat intestinal epithelial cells (IEC-6 cells) were studied to identify the presence of the SP receptor (NK-1 subtype) and then exposed to physiologic doses of SP and antagonists to assess for increased migration.

RESULTS

Examination IEC-6 cells revealed the presence of the SP receptor. Wounding of these cells followed by subsequent exposure to SP (10 mol/L) resulted in increased migration. Similarly, SP-induced increases in intracellular calcium concentration and actomyosin stress fiber formation. These effects were all blocked through specific NK-1 receptor antagonists.

CONCLUSIONS

These results indicate that SP stimulates intestinal epithelial migration and increases in calcium concentration. These data support a beneficial role for SP in the maintenance of intestinal mucosal homeostasis.

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.

Trichinella spiralis: histamine secretion induced by TSL-1 antigens from unsensitized mast cells

Mast cells' hyperplasia and activation are prominent features in Trichinella spiralis infection. Recently, it was shown that TSL-1 antigens from T. spiralis muscle larvae induce IL-4 and TNF release by unsensitized, normal mast cells (MC) involving an Ig-independent mechanism. In this study, we characterized histamine secretion induced by TSL-1 antigens from normal, unsensitized rat peritoneal MC. Maximum histamine secretion (30+/-5.3% SEM, n=13) was achieved with 30 ng/mL TSL-1 antigens. However, TSL-1 did not induce an increase in beta-hexosaminidase release or NADPH oxidase activity by MC. Interestingly, histamine secretion by TSL-1 was completed at 10s, and was inhibited by both Bordetella pertussis toxin and neuraminidase V, characteristics similar to those involved in substance P-induced histamine secretion. However, in contrast to substance P, TSL-1 induced histamine secretion in the absence of detectable changes in intracellular Ca(2+). We are investigating the molecular pathways involved in MC activation by TSL-1.

Functional Characterization and Expression Analysis of the Proteinase-Activated Receptor-2 in Human Cutaneous Mast Cells

Proteinase-activated receptor-2 (PAR2) belongs to a new G protein-coupled receptor subfamily activated by serine proteinases. PAR2 has been demonstrated to play a role during inflammation and immune response in different tissues including the skin. We examined whether PAR2 is functionally expressed by cutaneous human primary skin mast cells (HPMC) and the human mast cell line 1 (HMC-1). Reverse transcription-polymerase chain reaction and FACS analysis show expression of PAR2 both at the RNA and protein level. HPMCs and HMC-1 also express PAR1, PAR3, and PAR4. Ca-mobilization studies demonstrate functional PAR2 expressed by human skin mast cells, as shown by natural and synthetic PAR2 agonists. PAR2 agonists induced histamine release from HPMC indicating a role of PAR2 in regulating inflammatory and immune responses by skin mast cells. Double-immunofluorescence staining reveals colocalization of PAR2 with tryptase in the majority of human skin mast cells. In conclusion, trypsin and tryptase as well as specific agonists for PAR2 were able to induce Ca2+ mobilization in HPMCs, and agonists of PAR2 induce the release of histamine from these cells. Thus, PAR2 may be an important regulator of skin mast cell function during cutaneous inflammation and hypersensitivity.

Pivotal role of endogenous tachykinins and the NK1 receptor in mediating leukocyte accumulation, in the absence of oedema formation, in response to TNFα in the cutaneous microvasculature

Tachykinins including substance P (SP) are well known to play a role in influencing oedema formation and leukocyte accumulation during tissue insult and inflammation. Cutaneous inflammatory models to characterize a TNFalpha-dependent mechanism where endogenous SP act via the NK1 receptor to promote leukocyte accumulation in the absence of oedema formation were used. We found that TNFalpha induced dose-dependent leukocyte accumulation at 4 h, which returned towards basal levels at 8 h in NK1+/+ mice. This response was absent in both the NK1+/+ mice treated with an NK1 receptor antagonist and NK1-/- mice. At the highest dose IL-6 induced a significant accumulation in NK1+/+ and NK1-/- mice but IL-12 was ineffective. SP induced skin oedema but none of the cytokines did. Either co-injection of SP with low dose of TNFalpha (0.3 pmol/site) or SP previously injected (30 min) to TNFalpha evoked a significant increase in MPO activity when compared with that induced by the cytokine alone. In contrast, SP injected i.d. 3.5 h after TNFalpha failed to produce additive response. Control, but not capsaicin-pretreated rats (to deplete sensory nerves), exhibited a marked increase in MPO activity in response to TNFalpha. Histological analysis showed that TNFalpha caused tissue infiltrate of leukocytes in NK1+/+ mice, whilst leukocytes accumulated at intravascular sites in NK1-/- mice, but did not appear to emigrate, suggesting a defect in trans-endothelial migration. Interestingly, monocytes in addition to neutrophils accumulated 4 h post TNFalpha injection. In conclusion, the NK1 receptor plays a functional role in mediating leukocyte accumulation independently of the historically important NK1 mediated oedema formation. It seems that TNFalpha directly activates sensory nerve in addition to its chemoattractant activity. The NK1 receptor agonist influences the accumulation of monocytes in addition to that of PMN by 4 h, thus revealing an important influence of the NK1 receptor on TNFalpha mediated events in mouse skin.

Without nerves, immunology remains incomplete -in vivo veritas

Interest in the interactions between nervous and immune systems involved in both pathological and homeostatic mechanisms of host defence has prompted studies of neuroendocrine immune modulation and cytokine involvement in neuropathologies. In this review we concentrate on a distinct area of homeostatic control of both normal and abnormal host defence activity involving the network of peripheral c-fibre nerve fibres. These nerve fibres have long been recognized by dermatologists and gastroenterologists as key players in abnormal inflammatory processes, such as dermatitis and eczema. However, the involvement of nerves can all too easily be regarded as that of isolated elements in a local phenomenon. On the contrary, it is becoming increasingly clear that neural monitoring of host defence activities takes place, and that involvement of central/spinal mechanisms are crucial in the co-ordination of the adaptive response to host challenge. We describe studies demonstrating neural control of host defence and use the specific examples of bone marrow haemopoiesis and contact sensitivity to highlight the role of direct nerve fibre connections in these activities. We propose a host monitoring system that requires interaction between specialized immune cells and nerve fibres distributed throughout the body and that gives rise to both neural and immune memories of prior challenge. While immunological mechanisms alone may be sufficient for local responsiveness to subsequent challenge, data are discussed that implicate the neural memory in co-ordination of host defence across the body, at distinct sites not served by the same nerve fibres, consistent with central nervous mediation.

Mobilisation of specific T cells from lymph nodes in contact sensitivity requires substance P

Capsaicin-mediated depletion of neuropeptides in the skin was previously shown to abolish a dinitrocholorobenzene (DNCB)-induced contact sensitivity (CS) response. To understand the basis for this disruption, we explored whether nerve fibres innervating the draining lymph node (LN) could be involved. As expected, removal of the draining LN after DNCB sensitisation abolished the CS response. Furthermore, the CS response could be abolished by destroying the nerve fibres in the draining LN and could be restored by providing the LN with the neuropeptide substance P. The size of the CS response restored by substance P was dose dependent. The response was also inhibited by exposing the lymph node to a neurokinin-1 receptor antagonist which blocks binding of substance P. The results suggest that an afferent signal from the skin via the sympathetic arm of the central nervous system evokes an efferent signal to the LN which combines to regulate the CS response. The efferent signal may serve to control or release from the LN primed effector lymphocytes into the circulation.

Thoracic Vagal Efferent Nerve Stimulation Evokes Substance P-Induced Early Airway Bronchonstriction and Late Proinflammatory and Oxidative Injury in the Rat Respiratory Tract

Electrical stimulation of efferent thoracic vagus nerve (TVN) evoked neurogenic inflammation in respiratory tract of atropine-treated rats by an undefined mechanism. We explored whether efferent TVN stimulation via substance P facilitates neurogenic inflammation via action of nuclear factor-kappaB (NF-kappaB) activation and reactive oxygen species (ROS) production. Our results showed that increased frequency of TVN stimulation concomitantly increased substance P-enhanced hypotension, and bronchoconstriction (increases in smooth muscle electromyographic activity and total pulmonary resistance). The enhanced SP release evoked the appearance of endothelial gap in silver-stained leaky venules, India-ink labeled extravasation, and accumulations of inflammatory cells in the respiratory tract, contributing to trachea plasma extravasation as well as increases in blood O (2)(-) and H(2)O(2) ROS amount. L-732138 (NK(1) receptor antagonist), SR-48968 (NK(2) receptor antagonist), dimethylthiourea (H(2)O(2) scavenger) or catechins (O (2)(-) and H(2)O(2) scavenger) pretreatment reduced efferent TVN stimulation-enhanced hypotension, bronchoconstriction, and plasma extravasation. Increased frequency of TVN stimulation significantly upregulated the expression of nuclear factor-kappaB (NF-kappaB) in nuclear protein and intercellular adhesion molecule-1 (ICAM-1) in total protein of the lower respiratory tract tissue. The upregulation of NF-kappaB and ICAM-1 was attenuated by NK receptor antagonist and antioxidants. In conclusion, TVN efferent stimulation increases substance P release to trigger NF-kappaB mediated ICAM-1 expression and O (2)(-) and H(2)O(2) ROS production in the respiratory tract.

Coexpression of preprotachykinin A and B transcripts in the bovine corpus luteum and evidence for functional neurokinin receptor activity in luteal endothelial cells and ovarian macrophages

Nonneuronal cell sources of tachykinins, such as substance P (SP) and neurokinin B (NKB), have been demonstrated in leukocytes, endothelial cells and endocrine cells, and may play a role in corpus luteum (CL) development. For this reason, we analyzed mRNA presence for the two tachykinin precursors together with the neurokinin-1 receptor and the neurokinin-3 receptor (NK-1R and NK-3R, preferred by SP and NKB, respectively) in bovine CL at various stages in the luteal phase. Using the RT-PCR technique, we detected coexpression for the preprotachykinin A gene (PPT-A), which encodes SP and neurokinin A (NKA), and the preprotachykinin B gene (PPT-B) for NKB in the CL at the development, secretion and regression stages. Coexpression was also noted for NK-1R and NK-3R gene transcripts. Cultures of endothelial cells (ECs) derived from bovine CL expressed NK-1R and NK-3R mRNA, as did ovarian macrophages. Agonist treatment induced a stronger intracellular calcium ([Ca2+]i) increase after activation of NK-1R compared to NK-3R, a result that we verified by calcium imaging. This is the first evidence for functional tachykinin receptor activity in luteal ECs and ovarian macrophages from bovine CL.

Cutaneous allergic contact dermatitis responses are diminished in mice deficient in neurokinin 1 receptors and augmented by neurokinin 2 receptor blockage

Sensory neuropeptides such as neurokinin A (NKA) or particularly substance P (SP) by neurokinin receptor (NK-R) activation modulate skin and immune cells functions during neurogenic inflammation. In this study, we examined the relative importance of SP/NK-1Rs or NKA/NK-2Rs in a murine model for allergic contact dermatitis (ACD) and tested if the functional absence of NK-Rs will impair inflammatory response in vivo. Mice lacking NK-1Rs (C57BL/6J-NK-1R-/-) displayed a significantly reduced ACD inflammatory ear swelling response to dinitrofluorobenzene (DNFB) with histological less edema and 50% fewer infiltrating leukocytes compared with the ACD response in wild-type (+/+) animals. In NK-1R+/+ mice, transient NK-1R inhibition impaired ACD sensitization. In vitro haptenized bone marrow-derived dendritic cells from NK-1R+/+ mice matured in the presence of an NK-1R antagonist displayed a reduced capability to induce T cell proliferation in vitro and ACD after adoptive transfer into naïve wild-type mice in vivo. By contrast, NK-2R inhibition significantly enhanced the ACD response in NK-1R null or in wild-type mice, whereas epicutaneous application of NK-2R agonists diminished the ACD inflammation. In conclusion, NK-1R and SP are required for antigen sensitization and a full inflammatory response to cutaneous allergens and NKA and the NK-2R mediate a contrasting anti-inflammatory role in ACD. Thus, SP, NKA, NK-1R, and NK-2R have important but differential roles in the regulation of cutaneous inflammatory responses.

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.

Substance P increases neutrophil adhesion to human umbilical vein endothelial cells

1. Adhesion of neutrophils (PMNs) to vascular endothelial cells (EC) is a critical step in recruitment and infiltration of leukocytes into tissues during inflammation. Substance P (SP), a neuropeptide released from sensory nerves, evoked PMN adhesion to EC. The NK receptor subtype(s) and the cell type(s) involved were investigated. 2. SP was coincubated with human PMNs and EC from the human umbilical vein (HUVEC); adhesion was quantitated by computerised microimaging fluorescence analysis. 3. The proadhesive effects of SP (range 10(-18)-10(-6) M) were illustrated in a biphasic dose-response curve, with a maximum at 10(-15) M (276+/-16% adhesion vs control; P<0.01) and another one at 10(-10) M (200+/-18% adhesion vs control; P<0.01). Neurokinin A was less active and neurokinin B was inactive. The adhesion molecules LFA-1 and OKM-1, but not selectins, were involved according to results with selective mAbs. 4. The NK(1) agonist [Sar(9),Met(O(2))(11)]SP reproduced the effects of SP, whereas the NK(2) agonist [betaAla(8)]-neurokininA (4-10) acted at 10(-13)-10(-8) M only. The NK(3) agonist, senktide, was ineffective. 5. The NK(1) antagonists, CP 96,345 and L 703,606 (both 10(-6) M), abolished the effect of 10(-15) M SP and inhibited that of 10(-10) M SP by 56+/-5% (P<0.01). By comparison, the NK(2) antagonist, SR 48,968 (10(-7) M), partially antagonised the adhesion evoked by 10(-10) M SP (% inhibition: 61+/-6; P<0.05). 6. Since preincubation of PMNs and HUVEC with SP gave the same results it is clear that both cell types contributed to its proadhesive effects. 7. These results indicate that SP induced a proadhesive effect during inflammatory processes, which was mediated by NK(1) and NK(2) receptors.

Preprotachykinin-A gene deletion protects mice against acute pancreatitis and associated lung injury

Impaired lung function in severe acute pancreatitis is the primary cause of morbidity and mortality in this condition. Preprotachykinin-A (PPT-A) gene products substance P and neurokinin (NK)-A have been shown to play important roles in neurogenic inflammation. Substance P acts primarily (but not exclusively) via the NK1 receptor. NKA acts primarily via the NK2 receptor. Earlier work has shown that knockout mice deficient in NK1 receptors are protected against acute pancreatitis and associated lung injury. NK1 receptors, however, bind other peptides in addition to substance P, not all of which are derived from the PPT-A gene. To examine the role of PPT-A gene products in acute pancreatitis, the effect of PPT-A gene deletion on the severity of acute pancreatitis and the associated lung injury was investigated. Deletion of PPT-A almost completely protected against acute pancreatitis-associated lung injury, with a partial protection against local pancreatic damage. These results show that PPT-A gene products are critical proinflammatory mediators in acute pancreatitis and the associated lung injury.

Neuronal plasticity in relation to nociception and healing of rat achilles tendon

Nerve regeneration and the occurrence of three neuropeptides; i.e. substance P (SP), calcitonin gene related peptide (CGRP) and galanin (GAL), were studied during healing of tendon rupture in the rat by semi-quantitative immunohistochemistry. The neuronal findings were related to nociception as assessed by hindpaw withdrawal latencies at thermal and mechanical tests. Experimental rupture of rat Achilles tendon--normally devoid of nerves--elicited extensive nerve ingrowth into the rupture site in the early phase of healing followed by almost complete fiber disappearance (weeks 12-16). The ingrowth of SP and CGRP positive fibers, seen already at weeks 1-2, was associated with increased nociception. Subsequently, the occurrence of GAL positive fibers at weeks 4-6 was associated with decreased nociception. An even stronger relationship to nociception during healing was observed when the rate of change in neuropeptide expression instead of the expression in absolute terms was considered, according to the "cascade" formula of SP(')+CGRP(')-GAL(').It may prove that the observed temporal occurrence of different neuropeptides reflects a role of the peripheral nervous system in regulating synchronously nociception and healing.

Alpha-melanocyte stimulating hormone prevents lipopolysaccharide-induced vasculitis by down-regulating endothelial cell adhesion molecule expression

The neuroendocrine hormone alpha-melanocyte stimulating hormone (MSH) has profound antiinflammatory and immunomodulating properties. Here we have examined the possibility that alpha-MSH may interfere with the expression and function of cell adhesion molecules (CAMs) expressed by human dermal microvascular endothelial cells (HDMECs) in response to lipopolysaccharide (LPS) or TNFalpha in vitro and in vivo. In HDMEC, alpha-MSH (10(-8)/10(-12) M) profoundly reduced the mRNA and protein expression of E-selectin, vascular CAM (VCAM)-1, and intercellular CAM (ICAM)-1 induced by LPS or TNFalpha as determined by semiquantitative RT-PCR, ELISA, and fluorescence-activated cell sorter analysis. In addition, alpha-MSH significantly impaired the LPS-induced ICAM-1 and VCAM-1-mediated adhesion of lymphocytes to HDMEC monolayer in a functional adhesion assay. Likewise, alpha-MSH effectively inhibited the transcription factor nuclear factor-kappaB activation in HDMEC, which is required for CAM gene expression. Importantly in vivo, in murine LPS-induced cutaneous vasculitis (local Shwartzman reaction), a single ip injection of alpha-MSH significantly suppressed the deleterious vascular damage and hemorrhage by inhibiting the sustained expression of vascular E-selectin and VCAM-1. This persistent expression has been implicated in the dysregulation of diapedesis and activation of leukocytes, which subsequently leads to hemorrhagic vascular damage. Our findings indicate that alpha-MSH may have an important therapeutical potential for the treatment of vasculitis, sepsis, and inflammatory diseases.

Substance P enhances the production of interferon-induced protein of 10 kDa by human keratinocytes in synergy with interferon-gamma

A neuropeptide substance P is related to skin inflammation. Interferon-induced protein of 10 kDa (IP-10) chemoattracts T helper 1 cells, and interferon-induced protein of 10 kDa production by keratinocytes is enhanced in inflammatory skin diseases such as psoriasis. We examined the in vitro effects of substance P on interferon-induced protein of 10 kDa production by human keratinocytes. Though substance P alone did not induce interferon-induced protein of 10 kDa production, it enhanced interferon-induced protein of 10 kDa secretion, mRNA expression, and promoter activity induced by suboptimal concentrations of interferon-gamma. Interferon-stimulated response element and two nuclear factor-kappaB sites on interferon-induced protein of 10 kDa promoter were responsible for the enhancement by substance P. Substance P alone enhanced transcriptional activity and transcription factor binding through the two nuclear factor-kappaB sites, whereas it did not alter interferon-gamma-induced transcriptional activity and transcription factor binding through interferon-stimulated response element. The effects of substance P on interferon-induced protein of 10 kDa production and nuclear factor-kappaB activation were inhibited by neurokinin-1 receptor antagonist, phospholipase C inhibitor, intracellular Ca2+ chelator, and anti-oxidant. These results suggest that substance P may induce nuclear factor-kappaB activation and interferon-induced protein of 10 kDa production in synergy with interferon-gamma via neurokinin-1 receptor on keratinocytes. These effects of substance P may be mediated via phospholipase C activation, intra-cellular Ca2+ signal, and reactive oxygen intermediates.

Neutral endopeptidase activity is increased in the skin of subjects with diabetic ulcers

Cutaneous sensory nerves mediate inflammation and wound healing by releasing neuropeptides, such as substance P, which stimulates pro-inflammatory responses by keratinocytes, fibroblasts, and endothelial cells. The cell surface enzyme, neutral endopeptidase, degrades substance P, thereby regulating its biologic actions. We hypothesized that neutral endopeptidase enzymatic activity is increased in chronic wounds and skin from subjects with diabetes. We compared cutaneous neutral endopeptidase expression and enzymatic activity between normal controls and diabetic subjects with neuropathy and chronic wounds. Skin samples from subjects with diabetes were taken at the time of amputation for nonhealing ulcers. Skin taken from the ulcer margin, 1 cm from the ulcer (adjacent), and from the most proximal region of the amputated leg were studied. Skin biopsies from the leg of healthy control subjects were also studied. Neutral endopeptidase was localized by immunohistochemistry in all tissue sections. Neutral endopeptidase activity was measured using a fluorimetric assay. The median neutral endopeptidase activity of the ulcer margin was 1.21 x higher (p>0.2) than adjacent skin, 5.26 (p<0.001) than proximal skin, and 15.22 x higher (p<0.001) than control skin. Adjacent skin had a median neutral endopeptidase activity 4.34 x higher (p<0.001) than proximal skin and 12.58 x higher (p<0.001) than control skin. The median neutral endopeptidase activity of proximal skin was 2.90 x higher (p<0.001) than control skin. This elevated neutral endopeptidase activity in the skin and chronic ulcers of subjects with diabetes combined with peripheral neuropathy may contribute to deficient neuroinflammatory signaling and may impair wound healing in subjects with diabetes.

Neuromediators--a crucial component of the skin immune system

There is increasing evidence that the cutaneous nervous system modulates physiological and pathophysiological effects including cell growth and differentiation, immunity and inflammation as well as tissue repair. Both cutaneous nervous fibers and inflammatory cells are able to release neuromediators and thereby activate specific receptors on target cells in the skin or transient immunocompetent cells. Cutaneous neuromediators include classical neurotransmitters such as catecholamines and acetylcholine being released from the automatic nervous system or cutaneous cells. On the other hand neuropeptides including substance P, calcitonin gene related peptide (CRGP), vasointestinal peptide (VIP) or proopiomelanocortin (POMC) derived peptides such as alpha melanocyte stimulating hormone (alphaMSH) may be released from sensory or autonomic nerve fibers and several epidermal as well as dermal cells. Neuropeptides are known to activate a variety of cutaneous cells through high affinity neuropeptide receptors or by direct activation of intracellular G-protein signalling cascades. Via the modulation of transcription factor activation (NF-kappaB, AP-1, STAT-3) they regulate the expression of adhesion molecules and proinflammatory cytokines in different cells and thereby function as modulators of immune and inflammatory reactions. Accordingly, neuropeptides such as CGRP or alphaMSH in vitro were found to downregulate costimulatory molecule expression on dendritic cells and in vivo via the generation of suppressor T-lymphocytes to induce hapten specific tolerance. Proteinases such as tryptase or neural endopeptidase inactivate neuropeptides in the extracellular space or at the cell surface thereby terminating neuropeptide induced inflammatory or immune responses. Proteinase-activated receptors (PAR) are recently described receptors that may have high impact in regulating cutaneous neurogenic inflammation. In the skin PAR-2 being expressed on sensory neurons and endothelial cells is self activated by tethered peptide ligands that are exposed after extracellular amino-terminal cleavage by trypsin or mast cell tryptase. PAR-2 agonists were found to induce the release of CGRP and SP which mediate vasodilation, plasma extravasation as well as the expression of adhesion molecules on vascular endothelial cells and thus elicit neurogenic inflammation. These findings indicate that the neuromediator network including neuropeptide receptors as well as proteinases play an important role in the maintenance of tissue integrity and the regulation of inflammatory and immune responses in the skin.

Diminished neuropeptide levels contribute to the impaired cutaneous healing response associated with diabetes mellitus

Background. Patients with diabetic sensory neuropathy have significant risk of chronic ulcers. Insufficient nerve-derived mediators such as substance P (SP) may contribute to the impaired response to injury. Mutant diabetic mice (db/db), which develop neuropathy and have delayed healing, may provide a model to study the role of nerves in cutaneous injury.Methods. Skin from human chronic nonhealing ulcers and age-matched control skin was immunohistochemically evaluated for nerves. Nerve counts were also compared in murine diabetic (C57BL/KsJ-m+/+ Lepr(db); db/db) and nondiabetic (db/-) skin. Excisional wounds on the backs of db/db and db/- mice were grouped as: (a) untreated db/- mice; (b) untreated db/db mice; (c) db/db mice with polyethylene glycol (PEG); (d) db/db mice with PEG and SP 10(-9) M; or (e) db/db mice with PEG and SP 10(-6) M.Results. We demonstrated fewer nerves in the epidermis and papillary dermis of skin from human subjects with diabetes. Likewise, db/db murine skin had significantly fewer epidermal nerves than nondiabetic littermates. We confirmed increased healing times in db/db mice (51.7 days) compared to db/- littermates (19.8 days; P </= 0.001). SP 10(-6) M (44 days; P = 0.02) and SP 10(-9) M (45 days; P = 0.03) shortened time to closure compared to PEG treatment alone (68 days). Since there was no difference in the percentage contraction in these treatment groups, SP may favorably promote wound epithelization.Conclusions. Our data support the use of db/db murine excisional wounds to evaluate the role of nerves in healing. We have demonstrated that exogenous SP improves wound healing kinetics in an animal model.

Neutral endopeptidase inhibition in diabetic wound repair

In response to cutaneous injury, sensory nerves release substance P, a proinflammatory neuropeptide. Substance P stimulates mitogenesis and migration of keratinocytes, fibroblasts, and endothelial cells. Neutral endopeptidase (NEP), a cell surface metallopeptidase, degrades substance P. Chronic nonhealing wounds and skin from patients with diabetes mellitus show increased NEP localization and activity. We hypothesized that increased NEP may retard wound healing and that NEP inhibition would improve closure kinetics in an excisional murine wound model. NEP enzyme activity was measured in skin samples from mutant diabetic mice (db/db) and nondiabetic (db/-) littermates by degradation of glutaryl-ala-ala-phe-4-methoxy-2-naphthylamine. Full-thickness 6-mm dorsal excisional wounds treated with normal saline or the NEP inhibitor thiorphan (10 microM or 25 microM) for 7 days were followed until closure. Histological examination and NEP activity were evaluated in a subset of wounds. NEP activity in unwounded db/db skin (20.6 pmol MNA/hr/ microg) significantly exceeded activity in db/-skin (7.9 pmol MNA/hr/ microg; p = 0.02). In db/db mice, 25 microM thiorphan shortened time to closure (18.0 days; p < 0.05) compared to normal saline (23.5 days). NEP inhibition did not alter closure kinetics in db/-mice. While the inflammatory response appeared enhanced in early wounds treated with thiorphan, blinded histological scoring of healed wounds using a semiquantitative scale showed no difference in inflammation. Unwounded skin from diabetic mice shows increased NEP activity and NEP inhibition improved wound closure kinetics without affecting contraction, suggesting that its principal effect was to augment epithelialization.

Human keratinocytes express functional CD14 and toll-like receptor 4

CD14 and the toll-like receptor 4 have been known to play an important role in lipopolysaccharide-induced cellular responses in bacterial infections. Although CD14 and toll-like receptor 4 expression has been demonstrated in a number of myeloid cells, much less is known about the expression and function of these lipopolysaccharide receptors on nonleukocytes. In this study, we demonstrate that human keratinocytes are capable of expressing functional CD14 and toll-like receptor 4. Keratinocytes were found to constitutively express CD14 and toll-like receptor 4 mRNA that was augmented by exposure to lipopolysaccharide. Cell surface expression of keratinocyte CD14 and toll-like receptor 4 was detected by flow cytometry. Lipopolysaccharide binding to keratinocyte CD14 and toll-like receptor 4 resulted in a rapid intracellular Ca2+ response, nuclear factor-kappaB nuclear translocation, and the secretion of proinflammatory cytokines and chemokines. These results have important implications for our understanding of cutaneous innate immunity to bacterial infections of the skin.

Triptans reduce the inflammatory response in bacterial meningitis

Severe headache and meningism provide clear evidence for the activation of trigeminal neurotransmission in meningitis. The authors assessed the antiinflammatory potential of 5HT1B/D/F receptor agonists (triptans), which inhibit the release of proinflammatory neuropeptides from perivascular nerve fibers. In a 6-hour rat model of pneumococcal meningitis, zolmitriptan and naratriptan reduced the influx of leukocytes into the cerebrospinal fluid, and attenuated the increase of regional cerebral blood flow. Elevated intracranial pressure as well as the brain water content at 6 hours was reduced by triptans. These effects were partially reversed by a specific 5HT1D as well as by a specific 5HT1B receptor antagonist. Meningitis caused a depletion of calcitonin gene-related peptide (CGRP) and substance P from meningeal nerve fibers, which was prevented by zolmitriptan and naratriptan. In line with these findings, patients with bacterial meningitis had significantly elevated CGRP levels in the cerebrospinal fluid. In a mouse model of pneumococcal meningitis, survival and clinical score at 24 hours were significantly improved by triptan treatment. The findings suggest that, besides mediating meningeal nociception, meningeal nerve fibers contribute to the inflammatory cascade in the early phase of bacterial meningitis. Adjunctive treatment with triptans may open a new therapeutic approach in the acute phase of bacterial meningitis.

Heterologous regulation of trafficking and signaling of G protein-coupled receptors: beta-arrestin-dependent interactions between neurokinin receptors

Cells express multiple G protein-coupled receptors that are simultaneously or sequentially activated by agonists. The consequences of activating one receptor on signaling and trafficking of another receptor are unknown. We examined the effects of selective activation of the neurokinin 1 receptor (NK1R) on signaling and trafficking of the NK3R and vice versa. Selective agonists of NK1R and NK3R induced membrane translocation of beta-arrestins (beta-ARRs). Dominant negative beta-ARR(319-418) inhibited endocytosis of NK1R and NK3R. Whereas an NK1R agonist caused sequestration of NK1R with beta-ARR in the same endosomes, thereby depleting them from the cytosol, beta-ARRs did not prominently sequester with the activated NK3R and rapidly returned to the cytosol. In cells coexpressing both receptors, prior activation of the NK1R inhibited endocytosis and homologous desensitization of the NK3R, which was dose-dependently reversed by overexpression of beta-ARR1. Similar results were obtained in enteric neurons that naturally coexpress the NK1R and NK3R. In contrast, activation of the NK3R did not affect NK1R endocytosis or desensitization. Thus, the high-affinity and prolonged interaction of the NK1R with beta-ARRs depletes beta-ARRs from the cytosol and limits their role in desensitization and endocytosis of the NK3R. Because beta-ARRs are critical for desensitization, endocytosis, and mitogenic signaling of many receptors, this sequestration is likely to have important and widespread implications.

Nerve outgrowth and neuropeptide expression during the remodeling of human burn wound scars. A 7-month follow-up study of 22 patients

Increasing data suggest that the skin nerve system is involved in wound healing. The objective of this study was to investigate the outgrowth of nerve fibers during the burn wound remodeling process and to analyze possible differences between normotrophic and hypertrophic burn wounds. In a prospective study, biopsies were taken from 22 patients with spontaneously healed partial-thickness burns at 1, 4 and 7-month post-burn. Nerve outgrowth and the expression of the neuropeptides substance P, neurokinin A, calcitonin gene-related peptide, vasoactive intestinal peptide and neuropeptide Y was monitored using immunohistochemistry. Our results showed that the number of nerve fibers gradually increased in both the dermis and the epidermis, but that they did not reach the levels of expression present in matched unburned skin of the same patient. A significantly higher number of nerve fibers were observed in normotrophic scars compared with hypertrophic scars. The number of neuropeptides-containing nerves in normotrophic and hypertrophic scars were similar.

IN CONCLUSION

7 months after wound closure, burn wound scars contain less nerve fibers than unburned skin. The significantly higher number of nerve fibers in normotrophic, compared with hypertrophic scars suggests a regulatory role for the skin nerve system in the outcome of burn wound healing.

Inhibition of neurogenic inflammation by the Amazonian herbal medicine sangre de grado

This study was designed to determine if the Amazonian medicinal sangre de grado, confers benefit by suppressing the activation of sensory afferent nerves.

METHODS

(i) vasorelaxation of rat mesenteric arteries in response to calcitonin gene-related peptide; (ii) rat paw edema in response to protease- activating peptide receptor 2-activating peptide; (iii) rat paw hyperalgesia in response to low-dose protease-activating peptide receptor 2-activating peptide or prostaglandin E2; (iv) gastric hyperemia in response luminal capsaicin; (v) a clinical trial of a sangre de grado balm in pest control workers. The parent botanical was fractionated for evaluation of potential active components. In preconstricted rat mesenteric arteries, highly diluted sangre de grado (1:10,000) caused a shift to the right of the calcitonin gene-related peptide dose-response curve (p < 0.01). Paw edema in response to protease-activating peptide receptor 2-activating peptide (500 microg) was reduced by as single topical administration sangre de grado balm (1% concentration, p < 0.01) for at least 6 h. Hyperalgesia induced by either low-dose protease-activating peptide receptor 2-activating peptide (50 microg) or prostaglandin E2 was prevented by sangre de grado balm. A fraction possessing analgesic and capsaicin antagonistic properties was isolated and high-performance liquid chromatography and gas chromatography-mass spectrometry analysis indicated that it was a proanthocyandin oligomer. In pest control workers, sangre de grado balm (Zangrado) was preferred over placebo, for the relief of itching, pain, discomfort, edema, and redness in response to wasps, fire ants, mosquitoes, bees, cuts, abrasions, and plant reactions. Subjects reported relief within minutes. We conclude that sangre de grado is a potent inhibitor of sensory afferent nerve mechanisms and supports its ethnomedical use for disorders characterized by neurogenic inflammation.

The trigeminovascular system in bacterial meningitis

Headache as a cardinal symptom of acute meningitis reflects activation of trigeminal afferents from the meninges. With their perivascular endings, these fibers form the so-called trigeminovascular system (TVS), which releases proinflammatory neuropeptides upon nociceptive stimulation. In the present article, we review a role of the TVS in enhancing the early inflammatory response of bacterial meningitis. Furthermore, we discuss inhibition of neuropeptide release from the TVS using 5HT(1B/D) agonists as a potential new anti-inflammatory treatment strategy for early bacterial meningitis.

Neural regulation of endothelial cell-mediated inflammation

There is increasing evidence that the cutaneous neurosensory system can directly modulate inflammatory responses in the skin by the release of neuropeptides such as substance P (SP). Dermal microvascular endothelial cell (DMEC) cellular adhesion molecule (CAM) expression plays a key role in directing leukocyte trafficking during cutaneous inflammatory responses. In recent studies, our laboratory examined the direct effect of SP on DMEC CAM expression and function in vitro and in vivo. Our studies indicate that DMEC express high affinity functional receptors for SP. After exposure to SP, DMEC expressed significant levels of both intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), which was accompanied by increased binding to leukocytes expressing the appropriate integrin counter receptors for these CAM. We then determined the in vivo effect of released neuropeptides on DMEC CAM expression. Our results indicate that the topical cutaneous application of the neuropeptide-releasing agent capsaicin resulted in increased ICAM-1 and VCAM-1 immunostaining of microvascular cells in the skin of human volunteers. Little is known regarding the cellular regulatory events by which SP modulates DMEC CAM expression. Our studies indicate that SP-induced cellular Ca+2 signals led to the activation of the NF-kappaB pathway, resulting in nuclear translocation of p65/p50 heterodimers that bind to high-affinity tandem kappaB sites on the VCAM-1 promoter, whereas SP activation induced NF-AT activation and ICAM-1 DNA binding. Thus, these studies further support the role of the cutaneous neurologic system in modulating inflammatory processes in the skin.