Substance P and alveolar macrophages: effects on oxidative metabolism and eicosanoid production

TRPV1: Receptor structure, activation, modulation and role in neuro-immune interactions and pain

In the 1990s, the identification of a non-selective ion channel, especially responsive to capsaicin, revolutionized the studies of somatosensation and pain that were to follow. The TRPV1 channel is expressed mainly in neuronal cells, more specifically, in sensory neurons responsible for the perception of noxious stimuli. However, its presence has also been detected in other non-neuronal cells, such as immune cells, β- pancreatic cells, muscle cells and adipocytes. Activation of the channel occurs in response to a wide range of stimuli, such as noxious heat, low pH, gasses, toxins, endocannabinoids, lipid-derived endovanilloid, and chemical agents, such as capsaicin and resiniferatoxin. This activation results in an influx of cations through the channel pore, especially calcium. Intracellular calcium triggers different responses in sensory neurons. Dephosphorylation of the TRPV1 channel leads to its desensitization, which disrupts its function, while its phosphorylation increases the channel's sensitization and contributes to the channel's rehabilitation after desensitization. Kinases, phosphoinositides, and calmodulin are the main signaling pathways responsible for the channel's regulation. Thus, in this review we provide an overview of TRPV1 discovery, its tissue expression as well as on the mechanisms by which TRPV1 activation (directly or indirectly) induces pain in different disease models.

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

Regulation of Carcinogenesis by Sensory Neurons and Neuromediators

Interactions between the immune system and the nervous system are crucial in maintaining homeostasis, and disturbances of these neuro-immune interactions may participate in carcinogenesis and metastasis. Nerve endings have been identified within solid tumors in humans and experimental animals. Although the involvement of the efferent sympathetic and parasympathetic innervation in carcinogenesis has been extensively investigated, the role of the afferent sensory neurons and the neuropeptides in tumor development, growth, and progression is recently appreciated. Similarly, current findings point to the significant role of Schwann cells as part of neuro-immune interactions. Hence, in this review, we mainly focus on local and systemic effects of sensory nerve activity as well as Schwann cells in carcinogenesis and metastasis. Specific denervation of vagal sensory nerve fibers, or vagotomy, in animal models, has been reported to markedly increase lung metastases of breast carcinoma as well as pancreatic and gastric tumor growth, with the formation of liver metastases demonstrating the protective role of vagal sensory fibers against cancer. Clinical studies have revealed that patients with gastric ulcers who have undergone a vagotomy have a greater risk of stomach, colorectal, biliary tract, and lung cancers. Protective effects of vagal activity have also been documented by epidemiological studies demonstrating that high vagal activity predicts longer survival rates in patients with colon, non-small cell lung, prostate, and breast cancers. However, several studies have reported that inhibition of sensory neuronal activity reduces the development of solid tumors, including prostate, gastric, pancreatic, head and neck, cervical, ovarian, and skin cancers. These contradictory findings are likely to be due to the post-nerve injury-induced activation of systemic sensory fibers, the level of aggressiveness of the tumor model used, and the local heterogeneity of sensory fibers. As the aggressiveness of the tumor model and the level of the inflammatory response increase, the protective role of sensory nerve fibers is apparent and might be mostly due to systemic alterations in the neuro-immune response. Hence, more insights into inductive and permissive mechanisms, such as systemic, cellular neuro-immunological mechanisms of carcinogenesis and metastasis formation, are needed to understand the role of sensory neurons in tumor growth and spread.

Sensory denervation increases potential of bisphosphonates to induce osteonecrosis via disproportionate expression of calcitonin gene-related peptide and substance P

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a serious side effect of systematic administration of bisphosphonates (BPs). Sensory innervation is crucial for bone healing. We established inferior alveolar nerve injury (IANI) and inferior alveolar nerve transection (IANT) models characterized by disorganized periosteum, increased osteoclasts, and unbalanced neuropeptide expression. Zoledronate injection disrupted neuropeptide expression in the IANI and IANT models by decreasing calcitonin gene-related peptide (CGRP) and increasing substance P (SP); associated with this, BRONJ prevalence was significantly higher in the IANT model, followed by the IANI model and the sham control. CGRP treatment significantly reduced BRONJ occurrence, whereas SP administration had the opposite effect. In vitro, RAW 264.7 cells were treated with BPs and then CGRP and/or SP to study changes in zoledronate toxicity; combined application of CGRP and SP decreased zoledronate toxicity, whereas CGRP or SP applied alone showed no effects. These results demonstrate that sensory denervation facilitates the occurrence of BRONJ and that CGRP used therapeutically may prevent BRONJ progression, provided that SP is also present. Further studies are necessary to determine the optimal ratio of CGRP to SP for promoting bone healing and to uncover the mechanism by which CGRP and SP cooperate.

Neuroimmune communication in infection and pain: Friends or foes?

Clinically, a variety of micro-organisms cause painful infections. Before seen as bystanders in the context of infections, recent studies have demonstrated that, as immune cells, nociceptors can sense pathogen-derived products. Nociceptors and immune cells, therefore, have evolved to communicate with each other to control inflammatory and host responses against pathogens in a complementary way. This interaction is named as neuroimmune communication (or axon-axon immune reflex) and initiates after the release of neuropeptides, such as CGRP and VIP by neurons. By this neurogenic response, nociceptors orchestrate the activity of innate and adaptive immune cells in a context-dependent manner. In this review, we focus on how nociceptors sense pathogen-derived products to shape the host response. We also highlight the new concept involving the resolution of inflammation, which is related to an active and time-dependent biosynthetic shift from pro-inflammatory to pro-resolution mediators, the so-called specialized pro-resolving lipid mediators (SPMs). At very low doses, SPMs act on specific receptors to silence nociceptors, limit pain and neurogenic responses, and resolve infections. Furthermore, stimulation of the vagus nerve induces SPMs production to regulate immune responses in infections. Therefore, harnessing the current understanding of neuro-immune communication and neurogenic responses might provide the bases for reprogramming host responses against infections through well balanced and effective immune response and inflammation resolution.

Neuropeptide substance P and the immune response

Substance P is a peptide mainly secreted by neurons and is involved in many biological processes, including nociception and inflammation. Animal models have provided insights into the biology of this peptide and offered compelling evidence for the importance of substance P in cell-to-cell communication by either paracrine or endocrine signaling. Substance P mediates interactions between neurons and immune cells, with nerve-derived substance P modulating immune cell proliferation rates and cytokine production. Intriguingly, some immune cells have also been found to secrete substance P, which hints at an integral role of substance P in the immune response. These communications play important functional roles in immunity including mobilization, proliferation and modulation of the activity of immune cells. This review summarizes current knowledge of substance P and its receptors, as well as its physiological and pathological roles. We focus on recent developments in the immunobiology of substance P and discuss the clinical implications of its ability to modulate the immune response.

Substance P alters the in vitro LPS responsiveness of bovine monocytes and blood-derived macrophages

Neuromediators like substance P have a decisive influence on inflammatory processes via the neuroendocrine regulation circuit. The aim of the present study was therefore to evaluate the expression of the main substance P receptor NK-1R in cattle as well as the modulatory properties of substance P for bovine macrophages. The expression of NK-1R was detected in subsets of lymphocytes, granulocytes, monocytes and in vitro-generated macrophages (MdM). Stimulation of monocytes and MdM with lipopolysaccharide (LPS) for 3h did not alter the expression level of NK-1R. In vitro, the modulatory potential of substance P for monocytes and in vitro-generated blood-derived macrophages (MdM) was analysed. In MdM, generated in the presence of substance P, mRNA expression of chemokines, which are crucial for the attraction and activation of granulocytes and monocytes (CXCL8, CCL5) as well as the expression of IL-1beta, a classically pro-inflammatory cytokine were significantly elevated. After stimulation with LPS, MdM generated in the presence of substance P showed an elevated expression of CXCL8 and IL-1beta, while in SP-influenced monocytes only the expression of CCL5 was significantly upregulated after LPS stimulation. In addition, supernatants of MdM cultured in the presence of substance P induced neutrophil migration and inhibited both necrosis and apoptosis of neutrophil granulocytes. Thus, it has been shown that the modulation of the expression pattern of chemokines and cytokines in MdM by substance P has also functional relevance for the attraction and activation of other immune cells. In general, the modulation of sensor and effector functions by substance P suggests, that this neuromediator can alter the course of an inflammatory disease in cattle.

Bovine alveolar macrophage neurokinin-1 and response to substance P

In this study bovine alveolar macrophage neurokinin-1 (NK-1) and the in vitro response to substance P (SP) exposure were investigated. Bovine alveolar macrophage membrane extracts separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotted using anti-NK-1 antiserum demonstrated the presence of an approximately 60kDa band. Phagocytosis of fluorescent bioparticles by SP-exposed macrophages was 39% greater than that of non-exposed macrophages (P=0.0089). Likewise, there was 28% greater TNF production by macrophages following SP exposure compared to non-exposed controls (P=0.116). These results suggest that bovine alveolar macrophages respond to SP at least in part by enhancing phagocytosis and TNF production.

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.

Substance P and neutral endopeptidase in development of acute respiratory distress syndrome following fire smoke inhalation

To characterize the tachykininergic effects in fire smoke (FS)-induced acute respiratory distress syndrome (ARDS), we designed a series of studies in rats. Initially, 20 min of FS inhalation induced a significant increase of substance P (SP) in bronchoalveolar lavage fluid (BALF) at 1 h and persisted for 24 h after insult. Conversely, FS disrupted 51.4, 55.6, 46.3, and 43.0% enzymatic activity of neutral endopeptidase (NEP, a primary hydrolyzing enzyme for SP) 1, 6, 12, and 24 h after insult, respectively. Immunolabeling density of NEP in the airway epithelium largely disappeared 1 h after insult due to acute cell damage and shedding. These changes were also accompanied by extensive influx of albumin and granulocytes/lymphocytes in BALF. Furthermore, levels of BALF SP and tissue NEP activity dose dependently increased and decreased, respectively, following 0, low (10 min), and high (20 min) levels of FS inhalation. However, neither the time-course nor the dose-response study observed a significant change in the highest affinity neurokinin-1 receptor (NK-1R) for SP. Finally, treatment (10 mg/kg im) with SR-140333B, an NK-1R antagonist, significantly prevented 20-min FS-induced hypoxemia and pulmonary edema 24 h after insult. Further examination indicated that SR-140333B (1.0 or 10.0 mg/kg im) fully abolished early (1 h) plasma extravasation following FS. Collectively, these findings suggest that a combination of sustained SP and NEP inactivity induces an exaggerated neurogenic inflammation mediated by NK-1R, which may lead to an uncontrolled influx of protein-rich edema fluid and cells into the alveoli as a consequence of increased vascular permeability.

Immune parameters in patients with anxiety or depression during psychotherapy

BACKGROUND

Numerous studies have described distinctive immunological findings in patients with depression. In contrast, only very little is known about the possible influence of anxiety disorders on the immune system. It is also unknown whether treatment with psychotherapy alone has any influence on immunological variations in patients with psychiatric disorders.

METHODS

We measured immunological and psychological parameters in patients with minor depression (N=10) or anxiety disorder (N=13) over an 8-week course of inpatient psychotherapy. Data for patients and a group of healthy controls (N=11) were recorded three times in 4-week intervals. A FACS analysis revealed the composition of lymphocyte subpopulations. The production of reactive oxygen species (ROS) by phagocytes was analyzed using lucigenin-enhanced chemiluminescence.

RESULTS

On admission, patients with anxiety disorder showed a markedly elevated ratio of CD4(+) (T helper) versus CD8(+) (T suppressor/cytotoxic) lymphocytes compared to healthy controls (P<0.001) and minor depressives (P<0.01). The increased ratio in patients with anxiety disorder could mainly be attributed to a reduced count in CD8(+) T cells compared to healthy controls (P<0.01) and depressives (P<0.05). There were no differences between patients with depression and healthy controls with respect to the CD4(+)/CD8(+) ratio. We did not observe any differences in the production of ROS by phagocytes in patients compared to healthy controls. The CD4(+)/CD8(+) ratio remained elevated in patients with anxiety disorders during the following 8 weeks. There were no significant changes in this parameter over the course of the inpatient treatment.

LIMITATIONS

As a pilot study on the immune status in patients with anxiety disorders, the study's main limitation is the relatively low number of patients observed.

CONCLUSIONS

In this study we demonstrated for the first time marked immunological changes in patients with anxiety disorders. In addition, our results provide preliminary evidence that these immunological variations are not reversible by an 8-week course of inpatient psychotherapy alone.

Acute psychological stress induces a prolonged suppression of the production of reactive oxygen species by phagocytes

Possible effects of psychological stress on the function of phagocytic cells have thus far hardly been investigated. In this study, we examined the phagocytic production of reactive oxygen species (ROS) in 10 healthy subjects undergoing a brief mental stressor. In a crossover design, the same subjects served as their own unstressed controls on a second experimental date. The acute laboratory stress resulted in a suppressed circadian rhythm of ROS production and in a decreased overall formation of ROS throughout the day. Especially under conditions of chronic stress, this finding may be of importance for the host's defense against infectious diseases.

Reactive oxygen species in sustained airway constriction induced by citric acid aerosol inhalation

We tested if there is a direct relationship between reactive oxygen species and citric acid-induced airway constriction. Guinea pigs were divided into two groups: control and dimethylthiourea (a hydroxyl radical scavenger). The animals in each group were further separated into four subgroups: baseline, recovery 2-3 min, recovery 10 min, and recovery 20 min. Each animal was anesthetized, cannulated, paralyzed, and artificially ventilated. Citric acid aerosol inhalation caused the following significant changes in the control group during the recovery period: airway constriction for at least 20 min, increases in luminol-amplified t-butyl hydroperoxide-initiated chemiluminescence counts in the bronchoalveolar lavage samples at 2-3 and 20 min, an increase in bronchoalveolar lavage fluid substance P level at 2-3 min, and elevations in the bronchoalveolar lavage fluid total cell and neutrophil numbers at 20 min. All citric acid-induced alterations were prevented by dimethylthiourea pretreatment. These results suggest that citric acid inhalation induces the initial release of reactive oxygen species and tachykinins, which causes further cellular infiltration and sustained airway constriction.

Involvement of tachykinin NK(1) and NK(2) receptors in changes in lung mechanics and airway microvascular leakage during the early phase of endotoxemia in Guinea pigs

We investigated the role of tachykinins in airway neurogenic responses occurring in the early phase of endotoxemia. Forty-eight anesthetized guinea pigs were evenly divided into six groups pretreated with either saline vehicle, CP-96,345 (a tachykinin NK(1) receptor antagonist), SR-48,968 (a tachykinin NK(2) receptor antagonist) or CP-96,345 and SR-48,968 in combination. Animals then received an intravenous injection of either saline (the vehicle for endotoxin) or endotoxin (30 mg/kg). Total lung resistance (R(L)) and dynamic lung compliance (C(dyn)) were continuously measured before and 30 min after administration of saline or endotoxin. Airway microvascular leakage was assessed at the end of the observation period. Endotoxin significantly increased R(L) and decreased C(dyn) 10 min after intravenous endotoxin injection. Plasma extravasation significantly increased in the trachea, main bronchi and intrapulmonary airways with endotoxin administration. These changes in lung mechanics were abolished by SR-48,968, but were unaffected by CP-96,345. The plasma extravasation was largely attenuated by CP-96,345 and/or SR-48,968. We conclude that (1) endogenous tachykinins play an important role in producing changes in lung mechanics and airway microvascular leakage during the early phase of endotoxemia and (2) activation of tachykinin NK(2) receptors is responsible for the former response, while activation of both tachykinin NK(1) and NK(2) receptors is involved in the latter response.

Acute psychological stress simultaneously alters hormone levels, recruitment of lymphocyte subsets, and production of reactive oxygen species

Very little is known about the effects of acute psychological stress on the production of reactive oxygen species (ROS) by human phagocytic cells and the interplay between subjectively perceived stress, mediating hormones, variations in the number of peripheral leukocytes and ROS production. We measured psychological reactions, cardiovascular parameters, plasma catecholamines, plasma prolactin and cortisol as well as peripheral lymphocyte subsets in 13 experimental subjects undergoing a brief psychological stressor, and production of ROS, as indicated by chemiluminescence (CL), in stressed subjects and in healthy controls. The stressor elevated anger (p<0.01) and cardiovascular activation (p<0.01). There were significant changes in plasma levels of cortisol (p<0.01) and prolactin (p<0.001). During psychological stress natural killer (NK) cells (p<0.01) and CD8/CD38 cells (p<0.05) increased and returned to baseline only 25 minutes later. Significant changes in the number of naive CD4+/CD45RA+ (p<0.01) and antigen-experienced CD8+/CD45RO+ T cells (p<0.05) occurred. Subjects with stronger cardiovascular reaction showed higher stress-related plasma levels of norepinephrine (p<0.05) and were mainly responsible for the increase in NK cells. We observed a significantly reduced production of ROS following the stress test (p<0.05). Our results show that psychological stress is expressed simultaneously on psychological, hormonal and immunological levels of the organism. We show the existence of a circadian rhythm leading to a pronounced increase in CL during the morning hours. This first study taking this circadian rhythm in account revealed a significant suppressive effect of stress on ROS production.

Alleviation of wood smoke-induced lung injury by tachykinin receptor antagonist and hydroxyl radical scavenger in guinea pigs

We recently reported that wood smoke inhalation initially (within 5 min) causes airway injury and subsequently produces both airway and parenchymal injury after a delay (within 2 h). In this study, we investigated the mediator mechanisms of this delayed smoke-induced lung injury in 126 anesthetized and artificially ventilated guinea pigs who received challenges of either air or 40 tidal breaths of wood smoke. Two hours after inhalation, wood smoke produced various injurious responses, including increases in alveolar-capillary permeability, microvascular permeabilities, and histological injury scores, in airway and parenchymal tissues. Pre-treatment given before smoke challenge with CP-96,345 [a tachykinin NK1 receptor antagonist; (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-aza bicyclo(2.2.2.)-octan-3-amine], dimethylthiourea (a hydroxyl radical scavenger), or a combination of these two drugs largely alleviated both the airway and parenchymal responses, whereas pre-treatment with SR-48,968 [a tachykinin NK2 receptor antagonist; (S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)-butyl)benzamide] or a combination of CP-96,344 and SR-48,965 (inactive enantiomers) failed to do so. Post-treatment given at 5 min after smoke challenge with CP-96,345 or dimethylthiourea significantly alleviated the parenchymal responses, while having no effect on the airway responses. Pre-treatment with dimethylthiourea prevented the smoke-induced reduction in airway neutral endopeptidase activity (an enzyme for tachykinin degradation). We concluded that (1) tachykinins and hydroxyl radical play important roles in producing smoke-induced delayed lung injury in guinea pigs, and both may be involved in the spread of injury from the airways to the pulmonary parenchyma, and (2) the contribution of tachykinins is mediated via the activation of tachykinin NK1 receptors, and is associated with the hydroxyl radical-induced inactivation of airway neutral endopeptidase.

IL-4 and IFN-gamma up-regulate substance P receptor expression in murine peritoneal macrophages

While the ability of macrophages to express authentic substance P receptors (i.e., NK-1 receptors) has been inferred from radioreceptor binding assays and functional assays and, most recently, by identification of NK-1 receptor mRNA expression, we know little about NK-1 expression at the protein level or what host factors might up-regulate expression of this receptor. In the present study we demonstrate that the cytokines IL-4 and IFN-gamma can increase the expression of NK-1 receptors on murine peritoneal macrophages. Specifically, we show that IL-4 and IFN-gamma can elicit increases in the level of mRNA encoding the NK-1 receptor by up to 12- and 13-fold, respectively. Furthermore, these cytokines can significantly increase the expression of the NK-1 receptor protein as measured by Western blot and FACS analysis using specific Abs developed in our laboratory. In addition, we have demonstrated the ability of both IL-4 and IFN-gamma to enhance the ability of macrophages to bind substance P as measured by radiolabeled binding assay. The observation that the level of expression of this receptor protein can be enhanced by cytokines that promote either cell-mediated (Th1) or humoral (Th2) immune responses supports the idea that this receptor can be induced during either type of immune response. As such, these results may point to a more ubiquitous role for substance P in the generation of optimal immune responses than previously appreciated.

Acute neurogenic airway plasma exudation and edema induced by inhaled wood smoke in guinea pigs: role of tachykinins and hydroxyl radical

We studied the mechanisms underlying the wood smoke-induced acute airway injury in 120 anaesthetized guinea pigs. Five minutes after airway exposure, various doses of wood smoke produced a dose-dependent increase in Evans blue dye contents at all airway levels measured. Additionally, inhaled wood smoke produced submucosal edema of the trachea and bronchus, and peribronchial edema. These acute airway responses were nearly abolished by pretreatment with CP-96,345 alone [a tachykinin NK(1) receptor antagonist; (2S, 3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-azabicyc lo( 2.2.2.)-octan-3-amine] or with a combination of CP-96,345 and dimethylthiourea (a hydroxyl radical scavenger), and were attenuated by pretreatment with dimethylthiourea alone, yet were not affected by pretreatment with SR-48,968 [a tachykinin NK(2) receptor antagonist; (S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3, 4-dichlorophenyl)-butyl)benzamide], with a combination of CP-96,344 and SR-48,965 (inactive enantiomers), with MK-886 [a leukotriene biosynthesis inhibitor; L-663, 536(3-(1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl)-2, 2-dimethylpropanoic acid], with indomethacin (a cyclooxygenase inhibitor), or with N(G)-nitro-L-arginine methyl ester (a nitric oxide (NO) synthase inhibitor). The activity of airway neutral endopeptidase (an enzyme for tachykinin degradation) was not influenced by wood smoke at 5-min post-exposure. We conclude that both endogenous tachykinins and hydroxyl radical play an important role in producing smoke-induced acute airway plasma exudation and airway edema in guinea pigs. The contribution of tachykinins to these neurogenic responses is mediated via the activation of tachykinin NK(1) receptors and partly via a hydroxyl radical mechanism, and is not associated with inactivation of neutral endopeptidase.

Role of tachykinins in asthma

The sensory neuropeptides substance P (SP) and neurokinin A (NKA) are localized to sensory airway nerves, from which they can be released by a variety of stimuli, including allergen, ozone, or inflammatory mediators. Sensory nerves containing these peptides are relatively scarce in human airways, but it is becoming increasingly evident that inflammatory cells such as eosinophils, macrophages, lymphocytes, and dendritic cells can produce the tachykinins SP and NKA. Moreover, immune stimuli can boost the production and secretion of SP and NKA. SP and NKA have potent effects on bronchomotor tone, airway secretions, and bronchial circulation (vasodilation and microvascular leakage) and on inflammatory and immune cells. Following their release, tachykinins are degraded by neutral endopeptidase (NEP) and angiotensin-converting enzyme. The airway effects of the tachykinins are largely mediated by tachykinin NK1 and NK2 receptors. Tachykinins contract smooth muscle mainly by interaction with NK2 receptors, while the vascular and proinflammatory effects are mediated by the NK1 receptor. In view of their potent effects on the airways, tachykinins have been put forward as possible mediators of asthma, and tachykinin receptor antagonists are a potential new class of antiasthmatic medication.

Wood smoke-induced airway hyperreactivity in guinea pigs: time course, and role of leukotrienes and hydroxyl radical

A prior airway exposure to wood smoke induces a tachykinin-dependent increase in airway responsiveness to the subsequent smoke inhalation in guinea pigs (Life Sci. 63: 1513, 1998). To further investigate the time course of, and the contribution of other chemical mediators to, this smoke-induced airway hyperresponsiveness (SIAHR), two smoke challenges (each 10 ml) separated by 30 min were delivered into the lungs of anesthetized guinea pigs by a respirator. In the control animals, the SIAHR was evidenced by the bronchoconstrictive response to the second smoke challenge (SM2) which was approximately 5.2-fold greater than that to the first challenge (SM1). This SIAHR was alleviated by shortening the elapsed time between SM1 and SM2 to 10 min or by extending it to 60 min, and was abolished by extending it to 120 min. This SIAHR was reduced by pretreatment with either MK-571 (a leukotriene D4-receptor antagonist) or dimethylthiourea (a hydroxyl radical scavenger), but was not affected by pretreatment with either pyrilamine (a histamine H1-receptor antagonist) or indomethacin (a cyclooxygenase inhibitor). The smoke-induced reduction in the neutral endopeptidase activity (a major enzyme for tachykinin degradation) measured in airway tissues excised 30 min post SM1 was largely prevented by pretreatment with dimethylthiourea. However, this reduction was not seen in airway tissues excised 120 min post SM1. These results suggest that 1) the SIAHR to inhaled wood smoke has a rapid onset time following smoke inhalation and lasts for less than two hours, 2) leukotrienes and hydroxyl radical may play contributory roles in the development of this SIAHR, and 3) hydroxyl radical is the major factor responsible for the smoke-induced inactivation of airway neutral endopeptidase, which may possibly participate in the development of this SIAHR.

Substance P activates NF-kappaB independent of elevations in intracellular calcium in murine macrophages and dendritic cells

Professional antigen presenting cells, such as macrophages, can be activated by intracellular calcium-dependent as well as calcium-independent mechanisms, depending upon the stimulus used. In this report, we addressed the mechanism of substance P-induced intracellular signalling in murine macrophages and dendritic cells. While no increases in intracellular calcium concentration were detected in macrophages or dendritic cells using sensitive fluorimetric techniques, substance P did induce rapid enhanced activation of NF-kappaB, a transcriptional activator known to regulate pro-inflammatory cytokines. These data provide an important mechanism by which substance P may augment the production of pro-inflammatory molecules.

Tachykinin receptor modulators: novel therapeutics for rheumatoid arthritis

The activation of a cellular immune response in a genetically susceptible individual is widely recognised as a main step in triggering rheumatoid arthritis (RA). The tachykinins, substance P (SP) and neurokinin A (NKA), can play a major role in different immune diseases. In patients with inflammatory joint disease, elevated levels of SP have been demonstrated in the synovial fluid of affected joints. It is well known that SP and, to a lesser extent, NKA are deeply involved in the processing of nociceptive signals and exert many pro-inflammatory actions, which may be elicited by an increased neuronal neurokinin release in arthritis; the mechanism behind this increase remains to be fully elucidated. Different observations suggest that one approach to the treatment of RA might be to inhibit the local effects of neurokinins in the affected joints. This review will summarise the more relevant aspects of this topic.

A substance p agonist acts as an adjuvant to promote hapten-specific skin immunity

Because substance p (SP) has been reported to be released from cutaneous sensory nerve endings after hapten application, we determined whether SP participates in contact hypersensitivity (CH) induction by using a SP agonist, GR73632 or delta-Aminovaleryl [Pro9, N-Me-Leu10]-substance P(7-11) and a SP antagonist, spantide I. When injected intradermally, SP agonist enhanced CH induced by conventional, but not optimal, sensitizing doses of hapten. By contrast, SP antagonist inhibited the induction of CH by optimal sensitizing doses of hapten. Moreover, SP agonist promoted CH induction and prevented tolerance when hapten was painted on skin exposed to acute, low-dose ultraviolet-B radiation. Intradermally injected SP agonist altered neither the density nor the morphology of epidermal Langerhans cells, implying that SP agonist enhanced the generation of hapten-specific immunogenic signals from the dermis. It is proposed that SP is a natural "adjuvant" that promotes the induction of CH within normal skin. Although exogenous SP agonist can prevent impaired CH and tolerance after ultraviolet-B radiation, the susceptibility of native SP to local neuropeptidases renders the neuropeptide unable to prevent the deleterious effects of ultraviolet-B radiation on cutaneous immunity.

NK1-receptor activation prevents hydrocarbon-induced lung injury in mice

Recent evidence suggests that neurokinin (NK)-receptor activation may have a protective role in maintaining lung integrity when challenged by airborne toxicants such as sulfur dioxide, ozone, acrolein, or hydrocarbons. To investigate the effect of NK1-receptor activation on hydrocarbon-induced lung injury, B6.A.D. (Ahr d/Nats) mice received subchronic exposures to JP-8 jet fuel (JP-8). Lung injury was assessed by the analysis of pulmonary physiology, bronchoalveolar lavage fluid, and morphology. Hydrocarbon exposure to target JP-8 concentrations of 50 mg/m3, with saline treatment, was characterized by enhanced respiratory permeability to 99mTc-labeled diethylenetriaminepentaacetic acid, alveolar macrophage toxicity, and bronchiolar epithelial damage. Mice administered [Sar9,Met(O2)11]substance P, an NK1-receptor agonist, after each JP-8 exposure had the appearance of normal pulmonary values and tissue morphology. In contrast, endogenous NK1-receptor antagonism by CP-96345 administration exacerbated JP-8-enhanced permeability, alveolar macrophage toxicity, and bronchiolar epithelial injury. These data indicate that NK1-receptor activation may have a protective role in preventing the development of hydrocarbon-induced lung injury, possibly through the modulation of bronchiolar epithelial function.

Smoke-induced airway hyperresponsiveness to inhaled wood smoke in guinea pigs: tachykininergic and cholinergic mechanisms

The smoke-induced airway hyperresponsiveness (SIAHR) to inhaled wood smoke was investigated in anesthetized guinea pigs. Two smoke challenges (each 10 ml) separated by 30 min were delivered into the lungs by a respirator. In control animals, SIAHR was evidenced by an average bronchoconstrictive response (an increase in total lung resistance) to the second smoke challenge (SM2) that was approximately 4.3-fold greater than that to the first challenge (SM1). Pretreatment with CP-96,345 and SR-48,968 (neurokinin-1 and -2 receptor antagonists; each 1 mg/kg) in combination totally prevented this SIAHR, while pretreatment with CP-96,344 and SR48,965 (inactive enantiomers of CP-96,345 and SR-48,968, each 1 mg/kg) in combination failed to do so. Pretreatment with CP-96,345 (1 mg/kg), SR48,968 (1 mg/kg), or atropine (50 microg/kg) significantly alleviated this SIAHR. Pretreatment with phosphoramidon [an inhibitor of neutral endopeptidase (NEP); 2 mg/kg], which suppresses the degradation of tachykinins, induced an increase in airway reactivity that largely mimicked this SIAHR. The NEP activity measured in airway tissues excised 30 min after SM1 was significantly lower than that in air control value. These results suggest that 1) a prior wood smoke exposure induces an airway hyperresponsiveness to the subsequent wood smoke inhalation, 2) a tachykininergic mechanism involving both neurokinin-1 and -2 receptors is essential for, and a cholinergic mechanism is also involved in the development of this SIAHR, and 3) inactivation of airway NEP by wood smoke may contribute to this SIAHR.

Effects of SR 140333 and SR 48968 on antigen and substance P-induced activation of guinea-pig alveolar macrophages

BACKGROUND

Tachykinins, such as substance P, might be involved in the development of airway hyperresponsiveness and airway inflammation.

OBJECTIVE

This study was designed to investigate the effects of the tachykinin NK1 receptor antagonist SR 140333 (Nolpitantium) and the NK2 receptor antagonist SR 48968 (Saredutant) on the activation of alveolar macrophages in the guinea-pig.

METHODS

Guinea-pigs sensitized and challenged by ovalbumin administered by aerosol or naive guinea-pigs were exposed by aerosol to the neutral endopeptidase, phosphoramidon and, 15 min later, to substance P. Twenty-four hours later, bronchoalveolar lavages were performed and the cell composition of bronchoalveolar lavage fluids and the arachidonate release from alveolar macrophages stimulated in vitro with fMLP were evaluated.

RESULTS

Antigen challenge in sensitized guinea-pigs induced an increase in the total number of cells and granulocytes in the bronchoalveolar lavage fluids that was not reduced by pre-treatment of guinea-pigs with a single dose of SR 140333 or SR 48968 (1 mg/kg). Substance P exposure in phosphoramidon-pretreated guinea-pigs did not induce an increase in the total number of cells. In contrast, antigen or substance P exposure induced a significant increase in the in vitro fMLP-induced arachidonate release from alveolar macrophages. Pre-treatment of the guinea pigs with SR 140333 or SR 48968 did not reduce the increase in arachidonate release from fMLP-stimulated alveolar macrophages from sensitized and challenged guinea-pigs. Pre-treatment of the animals by SR 140333 and SR 48968 reduced the enhanced arachidonate release induced by fMLP from substance P-exposed guinea-pigs.

CONCLUSION

The present data demonstrate the importance of NK1- and NK2-receptor stimulation in the development of substance P-induced increased reactivity of alveolar macrophages.

Substance P diminishes lipopolysaccharide and interferon-gamma-induced TGF-beta 1 production by cultured murine macrophages

Recent evidence has demonstrated the importance of substance P and its receptor in macrophage-mediated inflammatory responses. While previous studies have shown that substance P can augment proinflammatory monokine production, little is known about the effects of this neuropeptide on the production of monokines that might limit inflammation. In the present study we have investigated the effect of substance P treatment on the production of transforming growth factor-beta 1 (TGF-beta 1) in cultured murine macrophages. We report that, while substance P agonist alone elicited increases in TGF-beta 1 mRNA expression and modest increases in TGF-beta 1 secretion, substance P dramatically diminished LPS- or IFN-gamma-induced TGF-beta 1 production. These results suggest a previously unrecognized mechanism where substance P may act as a proinflammatory mediator by limiting the production of excessive levels of TGF-beta 1 by LPS- or IFN-gamma-activated macrophages.

Cromolyn sodium prevents bronchoconstriction and urinary LTE4 excretion in aspirin-induced asthma

BACKGROUND

Inhalation of cromolyn sodium protects against sulpyrine-induced bronchoconstriction and prevents urinary leukotriene E4 (u-LTE4) excretion in aspirin-induced asthma.

OBJECTIVE

This study was designed to investigate the protective effect of cromolyn sodium on airway responsiveness to the sulpyrine provocation test, and to investigate whether this protective activity is associated with a reduction in aspirin-induced urinary excretion of LTE4, a marker of the cysteinyl leukotriene overproduction that participates in the pathogenesis of aspirin-induced asthma.

METHODS

We evaluated the effects of pretreatment with cromolyn sodium on bronchoconstriction precipitated by inhalation of sulpyrine in ten adult patients with mild aspirin-induced asthma. Those who were in stable clinical condition and were hyperresponsive to sulpyrine provocation test were allocated to this study. Urinary leukotriene E4 was measured using combined reverse phase high performance liquid chromatography (rp-HPLC)/enzyme immunoassay.

RESULTS

Inhaled cromolyn sodium protects against aspirin-induced attacks of asthma through mechanisms not related to the bronchodilator property, but related to the improvement of the bronchial hypersensitivity, almost completely in all patients (P < .001). By contrast, after cromolyn sodium the maximum level of u-LTE4 was significantly lower than control (P < .05).

CONCLUSION

Our results suggest for the first time that inhaled cromolyn sodium is one of the most useful inhibitors of aspirin-induced bronchoconstriction, probably acting by inhibiting the release of cysteinyl leukotrienes, and possibly other chemical mediators, by bronchial inflammatory cells.

The effects of tachykinins on inflammatory and immune cells

The aim of this article is to provide an up-dated overview of the available information on the role played by tachykinins in recruiting/regulating the function of immune/inflammatory cells, an issue which has received considerable input from the recent availability of potent and selective antagonists for tachykinin receptors. It appears that NK1 receptors play a role in mediating the extravascular migration of granulocytes into inflamed tissues in response to various inflammatory stimuli, although this effect may not be due to the expression of NK1 receptors by granulocytes themselves. Several data also imply a role for NK1 and NK2 receptors in regulating immune function. No data are available to suggest the expression of NK3 receptors by inflammatory/immune cells. Mast cell degranulation by substance P appears to be a non-receptor dependent response which may take place in vivo during intense stimulation. An emerging concept in the field relates to the ability of certain immune cell types to synthesize and possibly release tachykinins. Immune cells could represent an additional source of tachykinins in inflamed tissues, providing a non-neurogenic tachykininergic contribution to the local inflammatory process.

Tachykinin activation of human alveolar macrophages in tobacco smoke and sarcoidosis: a phenotypical and functional study

Substance P (SP) and neurokinin A (NKA), which exert bronchoconstrictor effects on human airways, are known to interact with inflammatory and immune cells, including monocyte macrophages. We have evaluated the effects of SP, NKA and the NK2 selective agonist [beta-Ala8]-NKA(4-10) on alveolar macrophages (AM) isolated from 4 healthy smokers and 4 non-smoker active pulmonary sarcoid patients. An accumulation of activated mononuclear phagocytes, as well as elevated angiotensin-converting enzyme (ACE) activity, has been evidenced in both clinical conditions. The phenotype of AMs in the studied subjects was characterized by an elevated expression of CD68+, HLA-DR+ and CD14+, CD14+ being significantly less in sarcoidosis as compared to smokers. SP, NKA and the NK2 selective agonist evoked superoxide anion (O2-) production in AMs obtained from sarcoid patients or healthy smokers. While SP acted in a non-dose-dependent manner in both conditions, NKA and [beta-Ala8]-NKA(4-10) evoked a dose-dependent respiratory burst (ED50 = 0.25 and 0.26 nM, respectively) in smokers, but not in sarcoidosis. The more marked phenotypical expression correlated well with the ability of NK2 receptors to activate AMs in smoker subjects.