Suppression of endotoxin-induced inflammation by taxol.

The pathogenesis of acute lung injury includes transendothelial diapedesis of leukocytes into lung tissues and disruption of endothelial/epithelial barriers leading to protein-rich oedema. In vitro studies show that the microtubule network plays a role in the regulation of endothelial permeability as well as in neutrophil locomotion. It was hypothesised that the microtubule-stabilising agent, taxol, might attenuate inflammation and vascular leak associated with acute lung injury in vivo. The effect of intravenously delivered taxol was assessed using a model of murine lung injury induced by intratracheal lipopolysaccharide (LPS) administration. Parameters of lung injury and inflammation were assessed 18 h after treatment. Intravenously delivered taxol significantly reduced inflammatory histological changes in lung parenchyma and parameters of LPS-induced inflammation: infiltration of proteins and inflammatory cells into bronchoalveolar lavage fluid, lung myeloperoxidase activity, and extravasation of Evans blue-labelled albumin into lung tissue. Taxol alone (in the absence of LPS) had no appreciable effect on these parameters. In addition to lung proteins, intravenous taxol reduced accumulation of leukocytes in ascitic fluid in a model of LPS-induced peritonitis. Taken together, the present data demonstrate that microtubule stabilisation with taxol systemically attenuates lipopolysaccharide-induced inflammation and vascular leak.     

Opposite effects of ANP receptors in attenuation of LPS-induced endothelial permeability and lung injury

Atrial natriuretic peptide (ANP) has been recently identified as a modulator of acute lung injury (ALI) induced by pro-inflammatory agonists. While previous studies tested effects of exogenous ANP administration, the role of endogenous ANP in the course of ALI remains unexplored. This study examined regulation of ANP and its receptors NPR-A, NPR-B and NPR-C by LPS and involvement of ANP receptors in the modulation of LPS-induced lung injury. Primary cultures of human pulmonary endothelial cells (EC) were used in the in vitro tests. Expression of ANP and its receptors was determined by quantitative RT-PCR analysis. Agonist-induced cytoskeletal remodeling was evaluated by immunofluorescence staining, and EC barrier function was characterized by measurements of transendothelial electrical resistance. In the murine model of ALI, LPS-induced lung injury was assessed by measurements of protein concentration and cell count in bronchoalveolar lavage fluid (BAL). LPS stimulation significantly increased mRNA expression levels of ANP and NPR-A in pulmonary EC. Pharmacological inhibition of NPR-A augmented LPS-induced EC permeability and blocked barrier protective effects of exogenous ANP on LPS-induced intercellular gap formation. In contrast, pharmacological inhibition of ANP clearance receptor NPR-C significantly attenuated LPS-induced barrier disruptive effects. Administration of NPR-A inhibitor in vivo exacerbated LPS-induced lung injury, whereas inhibition of NPR-C suppressed LPS-induced increases in BAL cell count and protein content. These results demonstrate for the first time opposite effects of NPR-A and NPR-C in the modulation of ALI and suggest a compensatory protective mechanism of endogenous ANP in the maintenance of lung vascular permeability in ALI.     

Phosphoramidon, an endothelin-converting enzyme inhibitor, attenuates lipopolysaccharide-induced acute lung injury

Phosphoramidon blocks the formation of endothelin-1 (ET-1), a proinflammatory mediator implicated in the pathogenesis of a variety of lung diseases. To determine whether phosphoramidon can ameliorate pulmonary inflammation, our laboratory undertook a series of experiments involving treatment of hamsters with either intraperitoneal (i.p.) or aerosolized phosphoramidon prior to induction of acute lung injury by intratracheal administration of lipopolysaccharide (LPS). The results indicate that phosphoramidon significantly reduces LPS-induced pulmonary inflammation as measured by lung histology, neutrophil content of bronchoalveolar lavage (BAL) fluid, percent tumor necrosis factor receptor 1 (TNFR1)-labeled BAL macrophages, and alveolar septal cell apoptosis. In additional experiments, i.p. administration of a novel endothelin A receptor anatgonist (HJP272) similarly decreased BAL neutrophils, whereas i.p. administration of either ET-1, or its precursor peptide, "big" ET-1, had the opposite effect. These findings support further evaluation of phosphoramidon and other ET-1 suppressors as potential treatments for human inflammatory lung disease.     

Protective effects of sphingosine 1-phosphate in murine endotoxin-induced inflammatory lung injury

Our prior in vitro studies indicate that sphingosine 1-phosphate (S1P), a phospholipid angiogenic factor, produces endothelial cell barrier enhancement through ligation of endothelial differentiation gene family receptors. We hypothesized that S1P may reduce the vascular leak associated with acute lung injury and found that S1P infusion produced a rapid and significant reduction in lung weight gain (more than 50%) in the isolated perfused murine lung. The effect of S1P was next assessed in a murine model of LPS-mediated microvascular permeability and inflammation with marked increases in parameters of lung injury at both 6 and 24 hours after intratracheal LPS. Each parameter assessed was significantly reduced by intravenous S1P (1 microM final) and in selected experiments by the S1P analogue FTY720 (0.1 mg/kg, intraperitoneally) delivered 1 hour after LPS. S1P produced an approximately 40-50% reduction in LPS-mediated extravasation of Evans blue dye albumin, bronchoalveolar lavage protein content, and lung tissue myeloperoxidase activity (reflecting phagocyte infiltration). Consistent with systemic barrier enhancement, S1P significantly decreased Evans blue dye albumin extravasation and myeloperoxidase content in renal tissues of LPS-treated mice. These studies indicate that S1P significantly decreases pulmonary/renal vascular leakage and inflammation in a murine model of LPS-mediated acute lung injury and may represent a novel therapeutic strategy for vascular barrier dysfunction.     

Influence of hyperbaric oxygen on tumor necrosis factor-alpha and nitric oxide production in endotoxin-induced acute lung injury in rats

We previously demonstrated that hyperbaric oxygen (HBO) treatment alleviated lipopolysaccharide (LPS)-induced acute lung injury in rats. However, the mechanisms responsible for the protective effect are still not fully understood. To obtain further information on the protective effect of HBO, in this study we investigated the role of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in intratracheal spraying LPS-induced acute lung injury in rats after HBO or hyperoxia treatment. The results showed that HBO but not hyperoxia attenuated the TNF-alpha level in plasma and bronchoalveolar lavage (BAL) fluid, NO concentration in BAL and plasma, and inducible NO synthase protein expression in lung tissue based on the Western blotting and immunohistochemical staining.     

Altered lung function relates to inflammation in an acute LPS mouse model

Preclinical in vivo models of lipopolysaccharide (LPS) -induced acute lung injury are commonly used to recapitulate pathophysiological features of chronic obstructive pulmonary disease and acute exacerbations. The LPS-induced lung inflammation is well described; however, whether the inflammatory response relates temporally to specific alterations in lung function has not been elucidated.We have investigated the effects of acute LPS inhalation in mice up to 96 h post LPS. Quantitation of inflammatory cells and inflammatory mediators in bronchoalveolar lavage fluid and non-invasive and invasive lung function measurements were performed at corresponding time points. The inhibitory effect of the glucocorticoid, budesonide, on LPS-induced lung inflammation and lung function was determined.LPS inhalation induced distinct histopathological changes, and infiltration of inflammatory cells to the lungs peaked at 48 h. At this time point, significantly increased inflammatory mediators and significantly altered lung capacity and mechanics parameters were observed. Budesonide given per os prevented the LPS-induced lung inflammation and lung dysfunction.These results demonstrate a temporal relationship between the peak of inflammatory cell influx and significant impairment of lung function, suggestive of a causative role of inflammation. These results allow better understanding of the functional consequences of lung inflammation in respiratory diseases.     

The effects of acute and chronic alcoholism on tumor necrosis factor and the inflammatory response

Ethanol intoxication has been shown to suppress selected functions of the immune system, thereby compromising host defenses against bacterial infections. Because the macrophage secretory protein, tumor necrosis factor (TNF), plays a central role in the inflammatory cascade, the effect of acute and chronic alcoholism on lipopolysaccharide (LPS)-induced TNF activity was studied. Saline or ethanol was given intraperitoneally to normal or chronic alcoholic rats followed 30 min later by either intravenous or intratracheal LPS. Intravenous LPS caused a substantial increase in serum TNF at 90 min in both normal and chronic alcoholic rats. In marked contrast, peak serum TNF levels were significantly suppressed in normal and chronic alcoholic rats given an acute injection of ethanol. When LPS was instilled intratracheally into normal rats, high levels of TNF appeared in the bronchoalveolar lavage fluid. Similar levels of TNF were found in chronic alcoholic rats after intratracheal LPS. However, acute ethanol intoxication significantly inhibited LPS-induced TNF in bronchoalveolar lavage fluid. In a similar manner, acute ethanol intoxication, but not chronic alcohol consumption, markedly inhibited both systemic and intrapulmonary polymorphonuclear leukocyte aggregation in response to either intravenous or intratracheal LPS. Alcohol-induced inhibition of TNF is a potential mechanism of the antiinflammatory effects of ethanol.     

Lung inflammation induced by endotoxin is enhanced in rats depleted of alveolar macrophages with aerosolized clodronate

Clodronate liposomes were given to rats via intratracheal inhalation to investigate the importance of alveolar macrophages (AMs) in inhaled endotoxin-induced lung injury. When AM depletion was maximal (87% to 90%), rats were exposed to lipopolysaccharide (LPS) or saline. Neither clodronate nor saline liposomes induced an influx of neutrophils (PMNs) into the lungs. However, depleted LPS-exposed rats had 5- to 8-fold higher numbers of lavage PMNs and greater lavage cell reactive oxygen species release compared to undepleted rats. Although AM depletion by itself did not significantly increase inflammatory cytokine expression in lung tissue, LPS-induced message levels for interleukin (IL)-1alpha, IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha were approximately 2-fold higher in AM-depleted rats compared to undepleted rats. These results indicate that cells other than AMs can recruit inflammatory cells into the lungs during acute LPS-induced injury and that AMs play an important suppressive role in the innate pulmonary inflammatory response.     

Signal transduction pathways activated in human pulmonary endothelial cells by OxPAPC, a bioactive component of oxidized lipoproteins

The bioactive component of mildly oxidized low-density lipoproteins, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC), activates tissue factor expression and monocyte adhesion to endothelial cells (EC) from systemic circulation, but blocks expression of inflammatory adhesion molecules (VCAM, E-selectin) and neutrophil adhesion associated with EC acute inflammatory response to bacterial lypopolysacharide (LPS). Due to constant exposure to oxygen free radicals, lipids in the injured lung are especially prone to oxidative modification and increased OxPAPC generation. In this study, we focused on OxPAPC-mediated intracellular signaling mechanisms that lead to physiological responses in pulmonary endothelial cells. Our results demonstrate that OxPAPC treatment activated in a time-dependent fashion protein kinase C (PKC), protein kinase A (PKA), Raf/MEK1,2/Erk-1,2 MAP kinase cascade, JNK MAP kinase and transient protein tyrosine phosphorylation in human pulmonary artery endothelial cells (HPAEC), whereas nonoxidized PAPC was without effect. Pharmacological inhibition of PKC and tyrosine kinases blocked activation of Erk-1,2 kinase cascade upstream of Raf. OxPAPC did not affect myosin light chain (MLC) phosphorylation, but increased phosphorylation of cofillin, a molecular regulator of actin polymerization. Finally, OxPAPC induced p60Src-dependent tyrosine phosphorylation of focal adhesion proteins paxillin and FAK. Our results suggest a critical involvement of PKC and tyrosine phosphorylation in OxPAPC-induced activation of Erk-1,2 MAP kinase cascade associated with regulation of specific gene expression, and demonstrate rapid phosphorylation of cytoskeletal proteins, which indicates OxPAPC-induced EC remodeling.     

肺组织 Treg 细胞反应性降低加重 LPS 诱导的老龄小鼠急性肺损伤

目的：本研究旨在对老龄和年轻小鼠 ALI 病理变化过程中 Treg (regulatory T cell, Treg)细胞的变化进行观察,以期进一步揭示老龄鼠肺组织损伤和修复的机制。方法使用3~4月龄和18~22月龄雄性 C57BL/6小鼠,通过气管内给药建立脂多糖(LPS)诱导 ALI 模型,分别观察两组小鼠在肺损伤急性炎症期和损伤修复期的病理表现。取造模后1、3、5、7和10 d 小鼠 BALF 和肺组织单细胞悬液,流式细胞术检测 Treg 细胞百分比变化。结果在肺损伤急性炎症期,与年轻小鼠相比,老龄小鼠 BALF 及肺组织中 Treg 细胞反应均明显低于年轻小鼠。在肺损伤的修复期,老龄小鼠 BALF 和肺组织内 Treg 细胞的百分比和绝对值仍低于年轻小鼠。结论本研究结果提示,经 LPS刺激后老龄小鼠 Treg 细胞反应性降低,同时伴随老龄小鼠炎症反应加重。     

Interferon-gamma enhances the pulmonary CXC chemokine response to intratracheal lipopolysaccharide challenge

CXC chemokines are major chemoattractants for pulmonary polymorphonuclear leukocyte (PMNL) recruitment. To study the effects of interferon (IFN)-gamma on the pulmonary chemokine response to lipopolysaccharide (LPS) challenge, rats were treated with intratracheal IFN-gamma (1x10(5) U/rat) 24 h before an intratracheal LPS (100 microg/rat) challenge. Intratracheal LPS caused significant increases in both cytokine-induced neutrophil chemoattractant (CINC) and macrophage inflammatory protein-2 in bronchoalveolar lavage (BAL) fluid and pulmonary PMNL recruitment. IFN-gamma enhanced these responses. IFN-gamma also increased LPS-induced tumor necrosis factor (TNF)-alpha in BAL fluid. LPS-induced TNF-alpha and CINC mRNA expression in alveolar macrophages was increased by IFN-gamma. CD11b/c and CD18 expression on circulating PMNLs was not affected by IFN-gamma, nor was the chemotaxis of these cells. IFN-gamma increases the pulmonary CXC chemokine response, which may serve as one mechanism underlying enhanced PMNL delivery into the lung.     

Effects of intratracheal tumor necrosis factor-alpha plasmid vector on lipopolysaccharide lethality and lung injury in mice

Bacterial lipopolysaccharide (LPS) causes acute lung injury (ALI) and contributes to inflammation in the acute respiratory distress syndrome (ARDS) and sepsis, making mechanisms of resistance to LPS critically important in clinical settings. The authors postulated that intratracheal administration of a plasmid (pcDNA3. 0-rTNFalpha) encoding rat tumor necrosis factor-alpha (TNF-alpha) would increase resistance of mice to LPS-induced ALI or mortality. They investigated the time course and dose-response for development of LPS-induced ALI in C57/BL6 mice and sought possible protective effects of 100 microg pcDNA3.0-rTNFalpha intratracheally 1, 2, or 3 weeks before LPS challenge. Lung myeloperoxidase (MPO) activity and alveolar lavage fluid (BALF) cell counts increased significantly 48 hours after intraperitoneal (IP) LPS challenges. After pcDNA3.0-rTNFalpha pretreatment, mice challenged with LPS had lower lung/body weight ratios than mice treated with pcDNA3.0; however, other indices of lung injury did not differ. Survival of mice challenged with lethal IP LPS 2 weeks after intratracheal pcDNA3.0-rTNFalpha vector improved significantly, compared to mice pretreated with the control vector, pcDNA3.0. However, pcDNA3.0-pretreated mice tolerated LPS challenge less well than saline-pretreated controls. LPS causes neutrophilic lung injury and mortality, but pcDNA3.0-TNFalpha does not prevent ALI due to LPS. Intratracheal pcDNA3.0-rTNFalpha pretreatment significantly improves survival of mice after LPS challenge, compared to those pretreated with pcDNA3.0.     

KL4-surfactant prevents hyperoxic and LPS-induced lung injury in mice

KL(4)-surfactant contains the novel KL(4) peptide, sinapultide, which mimics properties of the hydrophobic pulmonary surfactant protein SP-B, in a phospholipid formulation and may be lung protective in experimental acute respiratory distress syndrome/acute lung injury. Our objective was to determine the protective role of airway delivery of KL(4)-surfactant in murine models of hyperoxic and lipopolysaccharide (LPS)-induced lung injury and further explore the mechanisms of protection. For the hyperoxic injury model, mice exposed to 80% O(2) for 6 days received an intranasal bolus of vehicle, beractant, or KL(4)-surfactant on days 3, 4, 5, and 6 of the exposure, and lungs were evaluated on day 7. Mice in the LPS-induced lung injury model received an intratracheal bolus of LPS followed by an intranasal bolus of KL(4)-surfactant or control at 1, 3, and 19 hr post-LPS challenge, and lungs were evaluated after 24 hr. To explore the mechanisms of protection, in vitro assays were performed with human and murine endothelial cell monolayers, and polymorphonuclear leukocyte (PMN) transmigration in the presence or absence of KL(4)-surfactant or lipid controls was evaluated. Based on morphology, histopathology, white blood cell count, percentage of PMNs, and protein concentration in bronchoalveolar lavage fluid, our data showed KL(4)-surfactant, unlike vehicle or beractant, blocked neutrophil influx into alveoli and suppressed lung injury. Furthermore, in vitro assays showed KL(4)-surfactant decreased neutrophil transmigration at the endothelial cell level. KL(4)-surfactant decreased inflammation and lung permeability compared with controls in both mouse models of lung injury. Evidence suggests the anti-inflammatory mechanism of the KL(4)-peptide is through inhibition of PMN transmigration through the endothelium.     

Resolvin D1 protects mice from LPS-induced acute lung injury

Resolvin D1 (RvD1), an endogenous lipid molecule derived from docosahexaenoic acid (DHA), has been described to promote inflammatory resolution. The present study aimed to determine the protective effects and the underlying mechanisms of RvD1 on lipopolysaccharide (LPS)-induced acute lung injury (ALI). Pretreatment RvD1 to mice 30 min before inducing ALI by LPS decreased the mortality and improved lung pathological changes, inhibited LPS-induced increases in polymorphonulear and mononuclear leukocytes recruitment, total proteins content, tumor necrosis factor (TNF-α) and interleukin-6 (IL-6) production in the bronchoalveolar lavage fluids (BALFs). In addition, RvD1 markedly reduced LPS-induced the expression of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and adhesion molecules, as well as myeloperoxidase (MPO) activity. Moreover, RvD1 markedly inhibited LPS-induced the activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB). Furthermore, pretreatment with Boc, a lipoxin A4 receptor (ALX) antagonist, significantly reversed these beneficial effects of RvD1 on LPS-induced acute lung injury in mice. Taken together, our study showed that RvD1 improved survival rate and attenuated ALI in mice induced by LPS, and the protective mechanisms might be related to selective reaction with ALX, which inhibits MAPKs and NF-κB pathway.     

The prevention of lipopolysaccharide-induced pulmonary vascular injury by pretreatment with cepharanthine in rats

Cepharanthine, a biscoclaurine alkaloid, has been shown to inhibit leukocyte activation in vitro. To determine whether cepharanthine may be of use in the treatment of acute respiratory distress syndrome (ARDS), we investigated its effect on lipopolysaccharide (LPS)-induced pulmonary vascular injury in rats, in which activated leukocytes have been implicated. Intravenous administration of LPS (5 mg/kg) induced pulmonary vascular injury, as indicated by increases in both the pulmonary vascular permeability and the lung wet/dry weight ratio. LPS-induced pulmonary vascular injury was significantly less in animals given cepharanthine (10 mg/kg) intraperitoneally. Cepharanthine significantly inhibited the LPS-induced increases in plasma tumor necrosis factor-alpha (TNF-alpha) concentrations in vivo and significantly inhibited the production of TNF-alpha by LPS-stimulated monocytes in vitro. Cepharanthine also inhibited the functions of activated neutrophils in vitro such as neutrophil elastase release, oxygen radical generation, and neutrophil aggregation, probably by inhibiting a rise in the intracellular free calcium concentration. These findings suggest that cepharanthine prevents LPS-induced pulmonary vascular injury by inhibiting leukocyte activation.     

RIP3介导的程序性坏死通路在LPS诱导的小鼠急性肺损伤模型中的作用

目的研究受体相互作用蛋白(RIP3)介导的程序性坏死通路在脂多糖(LPS)诱导的小鼠急性肺损伤模型(ALI)中的作用。方法将野生小鼠和RIP3敲除小鼠各30只分为四组:(a)Control RIP3-KO,(b)LPS RIP3-KO,(c)Control RIP3-WT,(d)LPS RIP3-WT。每组各15只,脂多糖组(LPS组)经小鼠气管套管滴入30mg/kg LPS,对照组经气管套管滴入等体积磷酸盐缓冲液(PBS),然后观察比较四组小鼠肺部病理损伤,小鼠直肠温度和生存率,并检测小鼠肺组织冰冻切片中坏死细胞计数和肺泡灌洗液中高迁移率族蛋白B1(HMGB1)水平。结果 RIP3敲除后,小鼠肺部病理损伤减轻,低体温症状得到明显改善,且死亡率降低。冰冻切片显示的肺组织坏死细胞计数减少,且支气管肺泡灌洗液中HMGB1表达水平也降低。结论 RIP3敲除能一定程度保护小鼠免受LPS诱导的急性肺损伤,并能减少肺组织细胞坏死的发生。     

Clara cell specific protein (CC16) expression after acute lung inflammation induced by intratracheal lipopolysaccharide administration

Clara cell secretory protein (CC16, CC10, or CCSP), the major secretory protein of the Clara cell, presents several biologic properties, suggesting that it may play a protective role against intrapulmonary inflammatory processes. The aim of the present study was to investigate the changes of CC16 concentrations in the lung, bronchoalveolar lavage fluid (BALF), and serum of rats with acute lung injury induced by lipopolysaccharide (LPS). These changes were compared with Clara cell density, CC16 mRNA level in the lung and classic indices of inflammation in BALF. Injected at doses of 10, 100, or 200 microgram/100 g body weight, LPS induced an acute lung inflammation as estimated by an increased influx of cells and albumin in the BALF. This inflammatory response was associated with a marked reduction of CC16 concentrations in BALF and lung homogenate as well as of the CC16 mRNA levels in the lung. At the highest dose of LPS, the CC16-positive cell density in the bronchiolar epithelium was also decreased. In serum, by contrast, the concentration of CC16 was elevated as a consequence of increased airway permeability. Pretreating rats intraperitoneally with dexamethasone (2 mg/kg) significantly lowered the leukocyte influx and attenuated the albumin increase in BALF. Dexamethasone, however, failed to prevent the increased airway permeability to CC16, suggesting that during inflammation different mechanisms regulate the leakage of proteins across the alveolocapillary barrier depending on the direction of passage and/or the size of the protein. Our results show a marked decrease of the secretion and synthesis of CC16 during LPS-induced acute lung inflammation.     

Therapeutic potential of a new phosphodiesterase inhibitor in acute lung injury.

The effects of LASSBio596, a phosphodiesterase type-4 and -5 inhibitor, were tested in Escherichia coli lipopolysaccharide (LPS)-induced acute lung injury. Twenty-four BALB/c mice were randomly divided into four groups. In the control group, saline (0.05 mL) was injected intratracheally (i.t.). The LPS group received LPS (10 microg i.t., 0.05 mL). In the LASSBio596 groups, LASSBio596 (10 mg x kg(-1), 0.2 mL) was injected intraperitoneally 1 h before or 6 h after LPS administration. After 24 h, in vivo (lung resistive and viscoelastic pressures, and static and dynamic elastances) and in vitro (tissue resistance, elastance and hysteresivity) pulmonary mechanics, lung morphometry and collagenous fibre content were computed. Neutrophils and tumour necrosis factor (TNF)-alpha levels were evaluated in the bronchoalveolar lavage fluid. LASSBio596 prevented the changes in lung mechanics, and inhibited neutrophilic recruitment, TNF-alpha release, bronchoconstriction, alveolar collapse and the increment of collagen fibre content induced by LPS, independently of the moment of injection. In conclusion, LASSBio596 modulated the lung inflammatory process and had the potential to block fibroproliferation. Thus, agents that inhibit phosphodiesterase 4 and 5 simultaneously may be a useful adjunct therapy for acute lung injury.     

Hyperbaric oxygen increases the lung's susceptibility to inhaled lipopolysaccharide in mice

Hyperbaric oxygen (HBO2) has been shown to inhibit the adhesion function of b2-integrin, which is important in mediating cell-to-cell adhesion and extravasation of inflammatory cells. In the present study, we examined the effects of HBO2 exposure on neutrophil infiltration and tissue injury in a model of acute lung inflammation induced by lipopolysaccharide (LPS) inhalation. Male C57BL/6 mice of 8 weeks old were exposed to 3 atmosphere absolute (ATA) 100% HBO2, 3 ATA hyperbaric air (HBA), or room air for 90 min. After exposure, they were exposed to aerosolized LPS solution (1 mg/ml) or saline in a plexiglass chamber for 10 min. Four hours after inhalation, bronchoalveolar lavage (BAL) was performed to determine protein concentration, LDH activity, total cells, and differential cell counts in the lavage fluid (BALF). Myeloperoxidase (MPO) content, lung histopathology, and plasma nitric oxide (NO) metabolite concentrations were also determined in separate sets of animals. We observed that LPS inhalation increased neutrophil number in the BALF, which was significantly inhibited by HBO2 but not HBA pre-exposure. However, MPO content in the lung was prominently increased by HBO2 pre-exposure, which correlated with increased PMN infiltration in lung tissues. Further, HBO2 plus LPS, but not saline inhalation caused a significant increase in the BALF protein level and LDH activity compared with that of LPS inhalation alone. LPS exposure induced significant increase in plasma NO metabolites, which was not potentiated by HBO2 pre-exposure. The inducible nitric oxide synthase inhibitor, aminoguanidine, significantly attenuated the increases in plasma NO metabolites and tissue MPO content as well as lung injuries. In summary, our data suggest that HBO2 pre-exposure increases the lung's susceptibility to inhaled LPS, which may be related to increased tissue neutrophil infiltration and dependent on interaction(s) between HBO2 exposure with LPS-induced nitric oxide production.