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.
- acute lung injury
- neurokinin-1 receptor
- neurogenic inflammation
it is widely held that substance P (SP), an 11-amino acid neuropeptide mostly synthesized in the predominantly C sensory neurons and released in the nerve endings, elicits a variety of neuro-immune effects on target cells expressing neurokinin-1 receptor (NK-1R; 1–3, 5, 6, 8, 9, 11, 15, 41). Among them, particular changes are microvascular plasma leakage, neutrophil recruitment, and inflammatory mediator synthesis following environmental stimuli, collectively known as neurogenic inflammation. The response is highly regulated by neutral endopeptidase (NEP), a major membrane-bound enzyme responsible for controlling SP in the lungs, whereas uncontrolled or exaggerated response is mostly similar to the pathogenesis of patients with fire smoke (FS)-induced acute lung injury (ALI)/acute respiratory distress syndrome (ARDS; 4, 35, 49). The response exhibits airway hyperresponsiveness (30, 31, 36) but also induces a rather complex interplay of multiple inflammatory mediators, including chemokines, cytokines, reactive oxygen/nitrogen species, arachidonic acid products, and others (7, 19, 24, 26, 38, 46) due to airway irritation and/or damage. As observed in numerous human and experimental animal models, the response may be attributed to smoke combustion products, heat, and hypoxia environment. Detailed examinations have indicated the characterized airway damage induced by FS could be reproduced by the airway nebulization of acrolein, one of numerous aldehydes among smoke combustion products (18, 25). These are some of the chemicals that have been recognized to have obvious sensory neurotoxicity in the lungs (27, 48). However, the role of sensory SP in the pathogenesis of ALI/ARDS remains unclear following smoke inhalation.
Considering that SP is an important mediator in signaling transduction within a complex inflammatory network, we initially measured SP levels in the lungs of an established rabbit model of ALI/ARDS-like injury. FS inhalation induced a significant increase in SP in lung tissue, but not in bronchoalveolar lavage (BAL) fluid (BALF), at 1 h after FS exposure (48). The change in SP level was accompanied by increases in BALF concentrations of tumor necrosis factor-α (TNF-α), 6-keto-prostaglandin F1-α, superoxide anion, and gene and protein expression for TNF-α, increased BAL cell number/differentials, extensive alveolar hypoventilation (PaO2/FiO2 <200), and pulmonary edema (44–47). Sloughing and necrosis of epithelial cells were apparent in the respiratory tract above the bronchioles of the FS-exposed animals (46). Due to the pervasive presence of NEP, it is possible that FS-induced membrane damage of airway epithelial cells could result in potentiation of microvascular permeability and inflammatory cell infiltration evoked by endogenous SP. It was then hypothesized that the magnitude of NEP disruption may be of primary importance in shifting neurogenic response from their normal physiological functions to detrimental pathophysiological roles in the development of ALI/ARDS.
In current studies, consequently, we examined a temporal pattern within 24 h of FS exposure and dose-dependent involvement of SP, NK-1R, and NEP activity in a rat model of ALI/ARDS-like injury. Furthermore, we examined the receptor-mediated mechanism of SP using an NK-1R antagonist. Our data suggest that a combination of the high persistent level of SP and substantial loss of NEP activity is a potential and critical determinant of an uncontrolled inflammatory response in the acute phase of ALI/ARDS.
MATERIALS AND METHODS
Specific pathogen-free Fischer 344/NH rats (F344/NH, half each sex and ∼4 wk old), weighing ∼175 g, were utilized for a series of designs in this study. The procedures involving animals were reviewed and approved by the Institutional Animal Care and Use Committee. All rats were housed in the American Association of Animal Laboratory and Care-approved animal facility at the University of Arizona Health Sciences Center. In rats, SP-immunoreactive nerves have been found in the airways from the pharynx down to the terminal bronchioles and even the alveolar septal level (20). The rats were on a 12:12-h light-dark cycle and were given a standard rat chow diet/tap water ad libitum.
Our FS exposure protocol and the chemical characteristics of this particular type of smoke have been described in detail in previous studies (44, 48). Briefly, 30 ml of diesel fuel were placed in a ceramic crucible and burned in a stainless steel smoke chamber. This system produces a very consistent fire temperature (°C) as shown by mean (± SE) fire temperature readings of 330 (± 6), 395 (± 3), 407 (± 3), and 386 (± 4) at 5, 10, 15, and 20 min of FS, respectively. Smoke temperatures were recorded by a thermistor connected to the animal exposure chamber, and the mean smoke temperature for all exposures was calculated to be 27.3 (± 1.4)°C. The fire smoke was drawn through a 24-port nose-only exposure chamber (IN-TOX, Albuquerque, NM) by a constant vacuum (2.5 l/min). The smoke was analyzed for its respective CO2, CO (ZRH Fuji Electronics Infrared Gas Analyzer), NOx (Chemiluminescent Analyzer series 10, ThermoElectron), and particulate (IN-TOX seven-stage cascade impactor) concentrations. The mean concentrations of gases in the smoke the animals were exposed to contained 1.24 ppm CO2, 2.0 ppm NOx, and 99.5 mg/l particulate matter (in time-integrated mass concentrations). In the time-course design, animals in the groups with either the high level (20 min) of FS or room air were each sampled at 1, 6, 12, and 24 h, respectively. Room air control (sham smoke exposure) rats had the same protocol as FS exposure except that ambient air was drawn through an empty smoke chamber. In a separate dose-response study, three groups of animals were exposed to either 0 (air), low (10 min), or high (20 min) levels of FS and sampled at 1 h after insult. Then, using an NK-1R antagonist, we conducted two separated intervention studies and characterized lung injury at 1 and 24 h following 20-min FS exposure, respectively.
Blood Gas Values
Abdomen aorta blood (0.5 ml) was taken 24 h after FS inhalation and blood gas values were analyzed with a System 1620 pH/Blood Gas Analyzer. The blood gas values were adjusted to standard atmospheric pressure and temperature.
At the end of the experiments, the rats were anesthetized with ketamine HCl (50 mg/kg im; Research Biochemicals International, Natick, MA), xylazine (8 mg/kg im; Fort Dodge Laboratories, Fort Dodge, IA), and acepromazine maleate (1 mg/kg im, Fort Dodge Laboratories) and killed by exsanguination of the inferior vena cava. The heart-lung block was removed immediately for BAL with 3-ml aliquots of sterile 0.85% saline solution for pathological studies. Cell number was determined with a hemacytometer, and we performed cell differentials on a Diff-Quick-stained (Baxter Diagnostics, McGaw Park, IL) cytocentrifuged slide preparation by counting 300 cells per slide. BALF was centrifuged at 4°C for 15 min at 500 g, and albumin in the supernatant was determined with a commercial kit (Pierce Chemical, Rockford, IL).
Enzyme Immunoassay of SP
SP in the supernatant of BALF (n = 6) was quantified with a commercial enzyme immunoassay (EIA) kit as directed by the kit supplier (Cayman Chemical, Ann Arbor, MI). The procedure is based on the competition between free SP, derived from the unknown sample, and an SP tracer (SP linked to an acetylcholinesterase molecule) for a limited number of SP-specific rabbit antiserum binding sites. Briefly, 2 ml of BALF supernatant were then purified through an activated C-18 reverse phase cartridge and evaporated by vacuum. The test samples and standards were run in triplicate in 96-well microplates. The absorbance was determined at 412 nm with a BIO-TEK Elx808 automated microplate reader (BIO-TEK Instruments, Winooski, VT). The concentrations of SP in BALF were expressed in pg/ml calculated following the manufacturer's instructions.
Enzyme Activity of NEP
Lung tissues (n = 6) were washed with saline and stored at −70°C for later analysis. To obtain a cell-free extract, we homogenized lung tissue in 10 ml of T-PER tissue protein extraction reagent (Pierce, Rockford, IL). The residue was removed from the extract by centrifuge at 12,000 g for 15 min at 4°C. Cell-free NEP activity in tissue lysate was measured spectrophotometrically as had been reported earlier (48). Briefly, 5 μl of cell-free extract were incubated with 1 mM succinyl-Ala-Ala-Phe-p-nitroanilide (Suc-Ala-Ala-Phe-pNA; Bachem Bioscience, King of Prussia, PA) as a substrate in 0.1 M Tris·HCl (pH 7.6) in the presence of 1 μl (0.14 units/μl) porcine kidney aminopeptidase AP-N (Sigma, St. Louis, MO). The reaction (total volume, 250 μl) was measured in duplicate in a 96-well microtiter plate. In this coupled activity assay, NEP cleaves Suc-Ala-Ala-Phe-pNA between Ala and Phe, yielding Phe-pNA. AP-N subsequently cleaves Phe-pNA, generating pNA as the final product. The increase in specific absorbance at 405 nm (as a result of the accumulation of free p-nitroaniline) was determined after incubation at 37°C for 30 min with a plate reader (BIO-TEK Instruments). Substrate alone and substrate with AP-N and Tris buffer blanks were run in parallel. We determined protein concentration by a Coomassie Plus Protein assay (Pierce, Rockford, IL) using BSA as a standard.
Immunohistochemical Analyses of NK-1R and NEP
Immunohistochemical analyses were adopted from published methods (46, 50). Briefly, after dissecting the esophagus and cardiovascular structures from the heart-lung bloc, we weighed the tracheopulmonary bloc on an electronic scale, and wet lung/body wt ratio was calculated (n = 6). The lungs were fixed with 4% formaldehyde and 12.5% picric acid (pH 6.9) at 20 cmH2O pressure for 24 h at 4°C. Sections (2–3 mm in thickness) from the fixed lungs were taken from each of the left and right inferior lobes. Sections were first treated with blocker buffer for 15 min to block any nonspecific background. Primary antiserum, raised in rabbits, was then applied overnight at 4°C (NK-1R, 1:4,000, NEP 1:1,000). After rinses in phosphate-buffered saline, sections were treated with the Zymed Histostain kit (Zymed Laboratories, San Francisco, CA). Briefly, this included secondary biotinylated goat anti-rabbit serum followed by horseradish peroxidase-labeled streptavidin and subsequent development in a diaminobenzidine-substrate solution, yielding a permanent reddish brown reaction product. All slides were coverslipped permanently with crystal-mount (Biomeda, Foster City, CA). Slides were visualized by confocal microscopy with a MRC-1024ES laser scanning confocal (Bio-Rad) equipped with a Nikon TE-300 research microscope with objectives for both bright field and fluorescence (NK-1R and NEP). Images were captured using a Spot digital camera, imported to a Dell computer, and printed on photo-grade paper.
Comparisons of means between groups were made by ANOVA. Because the measures are independent variables, we evaluated mean changes when appropriate using post hoc linear contrasts, adjusting for multiple comparisons made by both Bonferroni and Fisher's paired least significant difference-corrected significance levels. To determine whether these changes were induced dose dependently by FS exposures, we also calculated Pearson correlation coefficients. All tests were two-sided tests, and P < 0.05 was considered to be significant. Data were collected and analyzed on a Macintosh computer with the Statview IV statistical program and expressed as means ± SE (n = 6).
Neither FS exposure nor NK-1R antagonist treatment was found to be acutely lethal to any of the animals during the 24 h following insult in these experiments. As shown in our previous studies (44–48), exposure of animals to FS induced a typical ALI/ARDS-like injury, as shown by a rapid increase in microvascular permeability, presence of alveolar edema rich in serum proteins, and severe hypoxemia (PaO2/FiO2, 154–163).
To elucidate the involvement of neurogenic response as the onset pathogenesis of ALI/ARDS, we initially analyzed the 24-h temporal pattern of the related changes in the lungs following 20-min FS inhalation.
BALF concentrations of SP were significantly increased, in a temporal manner, at all of the time points of 1, 6, 12, and 24 h after FS inhalation (Fig. 1). Obviously, the changes occurred within 1 h after insult, persisting over 24 h.
NK-1R immunoreactivity in the FS-exposed lungs, either density or distribution, did not exhibit any significant change compared with room air controls in this time-course study (data not shown).
FS disrupted 51.4, 55.6, 46.3, and 43.0% of NEP activity in lung tissue at all of the time points of 1, 6, 12, and 24 h, respectively, indicating ∼50% NEP activity loss as early as in 1 h after insult (Fig. 2). To further evaluate the potential effects of FS on lung cell population that express NEP, we immunolabeled tissue slides from control and FS rats at 1 h postexposure by a specific antibody directed against NEP (Fig. 3). In controls, NEP-like immunoreactivity appears largely as a reddish brown color on airway epithelial cells (Fig. 3A) but is also present in airway smooth muscle cells, submucosal gland cells, and fibroblasts (data not shown). In contrast, immunolabelings largely disappeared in the airway epithelium above the bronchioles of the FS-exposed animals (Fig. 3B).
Cell count and differentials.
Animals with FS inhalation showed 2.3-fold and 3.0-fold increases in BALF total cell count at 1 and 6 h, respectively, compared with controls (Fig. 4). However, at 12 h after FS insult, total cell count returned to the baseline level and then proceeded to increase again over the remaining 24 h. FS significantly induced both a decrease in macrophage percentage and an increase in granulocyte percentage during the first 6 h, and both remained at these altered levels up to 24 h. Lymphocyte differential increased slowly and significantly during the 24 h after FS inhalation.
BALF albumin increased significantly at all of the time points of 1, 6, 12, and 24 h, peaking at 6 h, after FS inhalation (Fig. 5).
To examine the sensitivity and specificity of tachykininergic responses at acute phase (1-h) after FS inhalation, we exposed rats to 0 (air controls), low (10 min), and high (20 min) levels of FS, respectively, in a dose-effect design.
Exposure of rats to the low level of FS did not induce any change in BALF SP compared with controls (Fig. 6). However, there was the same significant increase in rats exposed to the high level of FS as observed in the time-course experiment mentioned above.
No significant change in NK-1R immunoreactivity was observed in rats exposed to any time period of FS compared with controls.
NEP activity in the lung tissue decreased significantly in a dose-dependent manner, i.e., 25.4 and 32.1% of NEP activity loss, respectively, following low and high levels of FS inhalation (Fig. 7). Immunohistochemistry showed that, after exposure to the high level of FS, NEP activity followed the same trend of NEP distribution or density in airway epithelium as that of the time-course experiment (data not shown). This noticed change did not occur, however, for the low level of FS exposure.
NK-1R Antagonist Study
To examine the role of the receptor-mediated mechanism in the development of FS-induced ALI/ARDS-like injury, we utilized the NK-1R antagonist (SR-140333B) in this model (Table 1). Treatment with SR-140333B (10 mg/kg im) immediately following 20-min FS inhalation significantly improved FS-induced changes in PaO2, total cells/granulocyte infiltration, and the ratio of wet lung/body wt at 24 h after insult.
Further effort was made to determine whether the protective effect of SR-140333B is mediated by blockage of the SP-induced vascular permeability that may lead to pulmonary edema and hypoxemia. Treatment with SR-140333B (1.0–10.0 mg/kg im) immediately following 20-min FS inhalation significantly abolished early plasma extravasation at 1 h after insult (Fig. 8).
This paper illustrates the involvement of tachykininergic mechanisms in a rat model of ALI/ARDS-like injury following FS inhalation. Data from a series of experiments revealed that the enhanced release and prolonged existence of SP in airways and/or alveoli could be a critical factor in leading to acute pulmonary edema due to both overstimulation of C-fibers and substantial loss of NEP activity. Considering that SP is a potent proinflammatory mediator mediating multiple pathways in signaling transduction within a complex inflammatory network, this study may provide an insight into the role of SP/tachykinins in the onset and progress of FS-induced ALI/ARDS.
One of the more important findings in this study was that FS inhalation induced a dose-dependent reduction in pulmonary NEP activity beginning as early as 1 h after insult. Immunohistochemistry indicates in detail that the effect was mainly attributed to FS-induced damage of the epithelial lining, such as membrane disruption, necrosis, and sloughing of epithelial cells in the airways from trachea to bronchioles of the FS-exposed animals. It is well known that pulmonary NEP, as a membrane-bound enzyme, is mainly located at the surface of airway epithelial cells but is also present in airway smooth muscle cells, submucosal gland cells, and fibroblasts. As observed in our previous histopathological analysis, the airway epithelial lining showed conspicuous lesions, which were consistent in their severity with the airways subjected to FS exposure (46). In addition, the cause of NEP activity loss in this model may also include inhibition of NEP activity by oxidants (10, 23). It is recognized that smoke-induced oxidative damage could come not only from smoke combustion products such as nitrogen dioxide, ozone, and particulates, but also from the thermal denaturing of plasma proteins and from inflammatory cell activation (13, 18, 24, 26, 38). The in vivo efficacy of antioxidative products such as nitric oxide synthase inhibition (13) and oxygen free radical scavengers (44–47) has been reported in animal models of smoke inhalation. Therefore, the substantial NEP inactivation as an early consequence of smoke inhalation could lead to a persistent increase in endogenous SP, which may in turn lead to exaggerated microvascular permeability, edema, and severe hypoxia. This conclusion is supported by previous experimental observations that showed the removal of the airway epithelium (32) or inhibition of NEP (10, 23) could obviously induce airway hyperresponsiveness to SP. NEP is therefore a critical enzyme in limiting and constricting the activity of endogenously released SP to prevent abnormal involvement in the pathogenesis of ALI/ARDS.
The nature and pattern of increased SP in BALF following FS inhalation were observed in the dose-response/time-course studies. A significant elevation of BALF SP occurred within the first hour and persisted for 24 h, which is inversely correlated with the temporal pattern of pulmonary NEP activity. It suggests that FS not only triggered sensory bronchopulmonary C-fiber endings to release SP but also induced NEP dysfunction in airway epithelial cells. An earlier finding has reported that it is the concentration of SP, not the respective concentrations of vasoactive intestinal peptide or calcitonin gene-related peptide (CGRP), that significantly increased in pulmonary edema fluids of seven patients with ARDS, indicating involvement of SP in the pathogenesis of this syndrome (14). It should be noted that, in the dose-effect study, the increases in BALF SP were not conversely correlated with pulmonary NEP activity loss. Despite a 25.4% reduction of pulmonary NEP activity after the low level of FS exposure, BALF concentration of SP remained unchanged compared with controls. It seems that a partial significant loss of pulmonary NEP activity did not affect its regulatory capability for SP. However, as there was considerable NEP inactivation after prolonged exposure to FS, BALF level of SP begins to be increased. Therefore, it is a substantial disruption of NEP that develops a critical condition of inflammatory cascade leading to high microvascular permeability and pulmonary edema. This damage may eventually compromise the tachykininergic mechanisms that switch neurogenic responses from their physiological reflexes to a detrimental inflammatory role that perpetuates and intensifies lung injury (5, 6, 34, 43). As mentioned earlier, SP, as a potent proinflammatory mediator, has numerous pathways in signaling transduction within a complex network involving chemokines (12, 28, 29, 39, 40, 51), cytokines (1, 2, 11), reactive oxygen/nitrogen species (33, 37, 39), and other mediators (17, 37, 51). SP at large in airways may abnormally signal immunoinflammatory cells to generate these mediators through “silent NK receptors” that may not be involved in the cellular responses to SP under the normal physiological condition. The affected cell populations that have been characterized are mainly neutrophils (8, 21, 22, 51), eosinophils (21), lymphocytes (42), macrophages (9), and others (1, 28) that all express NK-1R on their cell membranes. Once these cells are activated, the uncontrolled inflammatory cascades with involvements of multiple immunoinflammatory cells and their mediators are abruptly started and rapidly progress, which is similar to the early pathophysological processes of ALI/ARDS (4, 35, 49).
Moreover, pulmonary hyperresponsiveness to SP due to NEP inactivation, especially on alveolar endothelial and epithelial cells underlying the increased capillary-alveolar permeability, may cause considerable pathophysiological processes, which could lead to alveolar edema and dysfunction of gas exchange. It has been suggested that SP leads to plasma leakage as a result of granulocytes acting through NK-1R situated on capillary and postcapillary venules. Experiments have also demonstrated that SP can transfer polymorphonuclear neutrophils (PMNs) from a resting to a primed state, thus allowing for an enhanced response to a given stimulus. In this study, we have observed that the pathogenesis is similar following FS inhalation. The increased microvascular permeability followed the same pattern as that of BALF SP with extensive influx of albumin and granulocytes/lymphocytes in BALF. However, these responses may also include secondary responses of SP through broad inflammatory cell activation. It has been reported that SP works as a priming agent for PMNs triggered by various stimuli that are able to evoke different responses, such as the production of reactive oxygen/nitrogen species, the generation of cytokines/chemokines, and the formation of leukotriene B4 and 5-hydroxyeicosatetranoic acid (8, 33, 39, 40, 51). For example, previous experimental evidence has been provided that a single concentration of SP (3 × 10−5 M) stimulated a significant release of IL-8 from PMNs (39). SP also primes IL-8-activated PMNs, thus amplifying the cell response to the chemokine (12). However, the recent studies have demonstrated the critical role of IL-8 in causing injury to the alveolar epithelial barrier and the lung endothelium (29) or neutrophil-dependent ALI after smoke inhalation (13). Combined with these data, it is clearly necessary to define the effects of SP on other mediators, including proinflammatory cytokines (chemokines in response to FS inhalation).
Furthermore, we hypothesized that FS-induced injury could primarily occur in a receptor-mediated fashion, since microvascular permeability was abolished by pretreatment with pharmacological NK-1R antagonists in other models (9, 42). There is strong evidence that shows that gene-targeted disruption of the NK-1R (NK-1R−/−) protects the lung from immune complex injury (6). Numerous other studies have also reported that activation of NK-1R could induce multiple forms of inflammatory mediators, characterized by inflammatory amplification (16, 37, 39, 40). Consistent with previous findings, treatment (10 mg/kg im) of rats with SR-140333B, an NK-1R antagonist, immediately following FS inhalation significantly improved hypoxemia, decreased inflammatory cell infiltration, and reduced the ratio of wet lung/body weight at 24 h after FS insult. This suggests that intervention of NK-1R may be a novel therapeutic strategy to prevent or ameliorate the development of ALI/ARDS following FS inhalation. Further effort was made to determine whether the protective effect of SR-140333B is mediated by blockage of the SP-induced microvascular permeability that may lead to pulmonary edema and hypoxemia. At 1 h after treatment of rats with SR-140333B (1.0–10.0 mg/kg im), it was observed that fully abolished FS-induced plasma extravasation occurred. This finding indicates that the early rapid increase of microvascular permeability abnormally trigged by the SP may be one of the more important events that result in the influx of protein-rich edema fluid and inflammatory cells into the alveolar spaces.
On the basis of this series of experiments, we have concluded that a high persistent level of SP along with a substantial disruption of NEP activity lead to a critical physiological condition that alters neurogenic responses from their normal physiological reflexes to a detrimental inflammatory role that increases and perpetuates lung injury. The changes in SP signaling may be present during the early pathophysiological event in the pathogenesis of ALI/ARDS, particularly affecting alveolar permeability. However, additional studies are needed to clarify the role(s) and mechanism of neurogenic inflammation as a trigger factor. We therefore recommend two courses of further studies: first, the intervention studies should be performed utilizing capsaicin (to delete C-fibers) and gene knockdown/-out models of NK-1R or inhibitors and antibody directed against NEP. That will aid in confirming the data in this study and will provide an opportunity to examine the mechanism of neurogenic inflammation. Second, an additional study should be extended to include other neuropeptides in neurons and nonneuron sources, such as CGRP, NKA, and NKB, all of which may be involved in FS-induced pathogenesis. It is hoped that the results of these experiments and future studies will lead to novel therapeutic strategies to prevent or ameliorate FS-induced ALI/ARDS.
This research was partially funded by national and local American Lung Association Research Awards GR-013-N and GR-012-N (to S. S. Wong).
The authors gratefully acknowledge Dr. Robert Berg for support in analysis of gas exchange and Dr. Richard J. Lemen for critically reviewing the manuscript. The authors also wish to thank Sanofi-Synthelabo Reserche (French) for providing NK-1R antagonist RS-140333B. This work was presented, in part, at the Experimental Biology Annual Meeting, San Diego, California, April 11–15, 2003.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
- Copyright © 2004 the American Physiological Society