Oxidative damage to surfactant protein D in pulmonary diseases

Oxidative stress and aging: synergies for age related diseases

Aging is characterized by a progressive decline in physiological function and underlies several disabilities, including the increased sensitivity of cells and tissues to undergo pathological oxidative stress. In recent years, efforts have been made to better understand the relationship between age and oxidative stress and further develop therapeutic strategies to minimize the impact of both events on age-related diseases. In this work, we review the impact of the oxidant and antioxidant systems during aging and disease development and discuss the crosstalk of oxidative stress and other aging processes, with a focus on studies conducted in elderly populations.

Countermeasures against Pulmonary Threat Agents

Inhaled toxicants are used for diverse purposes, ranging from industrial applications such as agriculture, sanitation, and fumigation to crowd control and chemical warfare, and acute exposure can induce lasting respiratory complications. The intentional release of chemical warfare agents (CWAs) during World War I caused life-long damage for survivors, and CWA use is outlawed by international treaties. However, in the past two decades, chemical warfare use has surged in the Middle East and Eastern Europe, with a shift toward lung toxicants. The potential use of industrial and agricultural chemicals in rogue activities is a major concern as they are often stored and transported near populated areas, where intentional or accidental release can cause severe injuries and fatalities. Despite laws and regulatory agencies that regulate use, storage, transport, emissions, and disposal, inhalational exposures continue to cause lasting lung injury. Industrial irritants (e.g., ammonia) aggravate the upper respiratory tract, causing pneumonitis, bronchoconstriction, and dyspnea. Irritant gases (e.g., acrolein, chloropicrin) affect epithelial barrier integrity and cause tissue damage through reactive intermediates or by direct adduction of cysteine-rich proteins. Symptoms of CWAs (e.g., chlorine gas, phosgene, sulfur mustard) progress from airway obstruction and pulmonary edema to acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which results in respiratory depression days later. Emergency treatment is limited to supportive care using bronchodilators to control airway constriction and rescue with mechanical ventilation to improve gas exchange. Complications from acute exposure can promote obstructive lung disease and/or pulmonary fibrosis, which require long-term clinical care. SIGNIFICANCE STATEMENT: Inhaled chemical threats are of growing concern in both civilian and military settings, and there is an increased need to reduce acute lung injury and delayed clinical complications from exposures. This minireview highlights our current understanding of acute toxicity and pathophysiology of a select number of chemicals of concern. It discusses potential early-stage therapeutic development as well as challenges in developing countermeasures applicable for administration in mass casualty situations.

Mammals' humoral immune proteins and peptides targeting the bacterial envelope: from natural protection to therapeutic applications against multidrug‐resistant Gram ‐negatives

Mammalian innate immunity employs several humoral ‘weapons’ that target the bacterial envelope. The threats posed by the multidrug‐resistant ‘ESKAPE’ Gram‐negative pathogens (Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) are forcing researchers to explore new therapeutic options, including the use of these immune elements. Here we review bacterial envelope‐targeting (peptidoglycan and/or membrane‐targeting) proteins/peptides of the mammalian immune system that are most likely to have therapeutic applications. Firstly we discuss their general features and protective activity against ESKAPE Gram‐negatives in the host. We then gather, integrate, and discuss recent research on experimental therapeutics harnessing their bactericidal power, based on their exogenous administration and also on the discovery of bacterial and/or host targets that improve the performance of this endogenous immunity, as a novel therapeutic concept. We identify weak points and knowledge gaps in current research in this field and suggest areas for future work to obtain successful envelope‐targeting therapeutic options to tackle the challenge of antimicrobial resistance.

A Novel Nonhuman Primate Model of Nonatopic Asthma

Nonhuman primate models have an essential role in understanding progressive respiratory disease pathogenesis. Immune and physiologic parameters in the nonhuman primate closely reflect the complexity of human systems and provide an exceptional translational impact for the investigation of the mucosal immune changes in response to environmental exposures. This potential warrants the development of novel models that will clarify the interaction of respiratory disease and the inhalable environment and the potential of novel therapies to alleviate the untoward results of these interactions. Nonhuman primate models of asthma can be spontaneous, induced, or experimentally manipulated by various exposures. Here we describe a model of exacerbation of airway hyperreactivity induced by exposure to an air pollutant, ozone, in a cohort of young adult asthmatic rhesus macaques.

Pulmonary surfactant: a unique biomaterial with life-saving therapeutic applications

Pulmonary surfactant is a complex lipoprotein mixture secreted into the alveolar lumen by type 2 pneumocytes, which is composed by tens of different lipids (approximately 90% of its entire mass) and surfactant proteins (approximately 10% of the mass). It is crucially involved in maintaining lung homeostasis by reducing the values of alveolar liquid surface tension close to zero at end-expiration, thereby avoiding the alveolar collapse, and assembling a chemical and physical barrier against inhaled pathogens. A deficient amount of surfactant or its functional inactivation is directly linked to a wide range of lung pathologies, including the neonatal respiratory distress syndrome. This paper reviews the main biophysical concepts of surfactant activity and its inactivation mechanisms, and describes the past, present and future roles of surfactant replacement therapy, focusing on the exogenous surfactant preparations marketed worldwide and new formulations under development. The closing section describes the pulmonary surfactant in the context of drug delivery. Thanks to its peculiar composition, biocompatibility, and alveolar spreading capability, the surfactant may work not only as a shuttle to the branched anatomy of the lung for other drugs but also as a modulator for their release, opening to innovative therapeutic avenues for the treatment of several respiratory diseases.

Ozone-Induced Oxidative Stress, Neutrophilic Airway Inflammation, and Glucocorticoid Resistance in Asthma

Despite recent advances in using biologicals that target Th2 pathways, glucocorticoids form the mainstay of asthma treatment. Asthma morbidity and mortality remain high due to the wide variability of treatment responsiveness and complex clinical phenotypes driven by distinct underlying mechanisms. Emerging evidence suggests that inhalation of the toxic air pollutant, ozone, worsens asthma by impairing glucocorticoid responsiveness. This review discusses the role of oxidative stress in glucocorticoid resistance in asthma. The underlying mechanisms point to a central role of oxidative stress pathways. The primary data source for this review consisted of peer-reviewed publications on the impact of ozone on airway inflammation and glucocorticoid responsiveness indexed in PubMed. Our main search strategy focused on cross-referencing "asthma and glucocorticoid resistance" against "ozone, oxidative stress, alarmins, innate lymphoid, NK and γδ T cells, dendritic cells and alveolar type II epithelial cells, glucocorticoid receptor and transcription factors". Recent work was placed in the context from articles in the last 10 years and older seminal research papers and comprehensive reviews. We excluded papers that did not focus on respiratory injury in the setting of oxidative stress. The pathways discussed here have however wide clinical implications to pathologies associated with inflammation and oxidative stress and in which glucocorticoid treatment is essential.

Progressive Lung Injury, Inflammation, and Fibrosis in Rats Following Inhalation of Sulfur Mustard

Sulfur mustard (SM) inhalation causes debilitating pulmonary injury in humans which progresses to fibrosis. Herein, we developed a rat model of SM toxicity which parallels pathological changes in the respiratory tract observed in humans. SM vapor inhalation caused dose (0.2-0.6 mg/kg)-related damage to the respiratory tract within 3 days of exposure. At 0.4-0.6 mg/kg, ulceration of the proximal bronchioles, edema and inflammation were observed, along with a proteinaceous exudate containing inflammatory cells in alveolar regions. Time course studies revealed that the pathologic response was biphasic. Thus, changes observed at 3 days post-SM were reduced at 7-16 days; this was followed by more robust aberrations at 28 days, including epithelial necrosis and hyperplasia in the distal bronchioles, thickened alveolar walls, enlarged vacuolated macrophages, and interstitial fibrosis. Histopathologic changes were correlated with biphasic increases in bronchoalveolar lavage (BAL) cell and protein content and proliferating cell nuclear antigen expression. Proinflammatory proteins receptor for advanced glycation end product (RAGE), high-mobility group box protein (HMGB)-1, and matrix metalloproteinase (MMP)-9 also increased in a biphasic manner following SM inhalation, along with surfactant protein-D (SP-D). Tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS), inflammatory proteins implicated in mustard lung toxicity, and the proinflammatory/profibrotic protein, galectin (Gal)-3, were upregulated in alveolar macrophages and in bronchiolar regions at 3 and 28 days post-SM. Inflammatory changes in the lung were associated with oxidative stress, as reflected by increased expression of heme oxygenase (HO)-1. These data demonstrate a similar pathologic response to inhaled SM in rats and humans suggesting that this rodent model can be used for mechanistic studies and for the identification of efficacious therapeutics for mitigating toxicity.

Ozone-induced enhancement of airway hyperreactivity in rhesus macaques: Effects of antioxidant treatment

BACKGROUND

Ozone (O3) inhalation elicits airway inflammation and impairs treatment responsiveness in asthmatic patients. The underlying immune mechanisms have been difficult to study because of the lack of relevant experimental models. Rhesus macaques spontaneously have asthma and have a similar immune system to human subjects.

OBJECTIVES

We sought to investigate mucosal immune changes after O3 inhalation in a clinically relevant nonhuman primate asthma model and to study the effects of an antioxidant synthetic lignan (synthetic secoisolariciresinol diglucoside [LGM2605]).

METHODS

A cohort of macaques (n = 17) previously characterized with airway hyperreactivity (AHR) to methacholine was assessed (day 1). Macaques were treated (orally) with LGM2605 (25 mg/kg) or placebo twice per day for 7 days, exposed to 0.3 ppm O3 or air for 6 hours (on day 7), and studied 12 hours later (day 8). Lung function, blood and bronchoalveolar lavage (BAL) fluid immune cell profile, and bronchial brushing and blood cell mRNA expression were assessed.

RESULTS

O3 induced significant BAL fluid neutrophilia and eosinophilia and increased AHR and expression of IL6 and IL25 mRNA in the airway epithelium together with increased BAL fluid group 2 innate lymphoid cell (ILC2s), CD1c+ myeloid dendritic cell, and CD4+ T-cell counts and diminished surfactant protein D expression. Although LGM2605 attenuated some of the immune and inflammatory changes, it completely abolished O3-induced AHR.

CONCLUSION

ILC2s, CD1c+ myeloid dendritic cells, and CD4+ T cells are selectively involved in O3-induced asthma exacerbation. The inflammatory changes were partially prevented by antioxidant pretreatment with LGM2605, which had an unexpectedly disproportionate protective effect on AHR.

Surfactant Protein D in Respiratory and Non-Respiratory Diseases

Surfactant protein D (SP-D) is a multimeric collectin that is involved in innate immune defense and expressed in pulmonary, as well as non-pulmonary, epithelia. SP-D exerts antimicrobial effects and dampens inflammation through direct microbial interactions and modulation of host cell responses via a series of cellular receptors. However, low protein concentrations, genetic variation, biochemical modification, and proteolytic breakdown can induce decomposition of multimeric SP-D into low-molecular weight forms, which may induce pro-inflammatory SP-D signaling. Multimeric SP-D can decompose into trimeric SP-D, and this process, and total SP-D levels, are partly determined by variation within the SP-D gene, SFTPD. SP-D has been implicated in the development of respiratory diseases including respiratory distress syndrome, bronchopulmonary dysplasia, allergic asthma, and chronic obstructive pulmonary disease. Disease-induced breakdown or modifications of SP-D facilitate its systemic leakage from the lung, and circulatory SP-D is a promising biomarker for lung injury. Moreover, studies in preclinical animal models have demonstrated that local pulmonary treatment with recombinant SP-D is beneficial in these diseases. In recent years, SP-D has been shown to exert antimicrobial and anti-inflammatory effects in various non-pulmonary organs and to have effects on lipid metabolism and pro-inflammatory effects in vessel walls, which enhance the risk of atherosclerosis. A common SFTPD polymorphism is associated with atherosclerosis and diabetes, and SP-D has been associated with metabolic disorders because of its effects in the endothelium and adipocytes and its obesity-dampening properties. This review summarizes and discusses the reported genetic associations of SP-D with disease and the clinical utility of circulating SP-D for respiratory disease prognosis. Moreover, basic research on the mechanistic links between SP-D and respiratory, cardiovascular, and metabolic diseases is summarized. Perspectives on the development of SP-D therapy are addressed.

Oxidative stress decreases functional airway mannose binding lectin in COPD

We have previously established that a defect in the ability of alveolar macrophages (AM) to phagocytose apoptotic cells (efferocytosis) and pathogens is a potential therapeutic target in COPD. We further showed that levels of mannose binding lectin (MBL; required for effective macrophage phagocytic function) were reduced in the airways but not circulation of COPD patients. We hypothesized that increased oxidative stress in the airway could be a cause for such disturbances. We therefore studied the effects of oxidation on the structure of the MBL molecule and its functional interactions with macrophages. Oligomeric structure of plasma derived MBL (pdMBL) before and after oxidation (oxMBL) with 2,2′-azobis(2-methylpropionamidine)dihydrochroride (AAPH) was investigated by blue native PAGE. Macrophage function in the presence of pd/oxMBL was assessed by measuring efferocytosis, phagocytosis of non-typeable Haemophilus influenzae (NTHi) and expression of macrophage scavenger receptors. Oxidation disrupted higher order MBL oligomers. This was associated with changed macrophage function evident by a significantly reduced capacity to phagocytose apoptotic cells and NTHi in the presence of oxMBL vs pdMBL (eg, NTHi by 55.9 and 27.0% respectively). Interestingly, oxidation of MBL significantly reduced macrophage phagocytic ability to below control levels. Flow cytometry and immunofluorescence revealed a significant increase in expression of macrophage scavenger receptor (SRA1) in the presence of pdMBL that was abrogated in the presence of oxMBL. We show the pulmonary macrophage dysfunction in COPD may at least partially result from an oxidative stress-induced effect on MBL, and identify a further potential therapeutic strategy for this debilitating disease.

Pressurized whey protein can limit bacterial burden and protein oxidation in Pseudomonas aeruginosa lung infection

BACKGROUND

Lung infection caused by Pseudomonas aeruginosa is associated with an exuberant inflammatory response, oxidative stress, and lung damage. Whey protein is a rich source of cysteine, and anti-inflammatory and immune-enhancing peptides. Anti-inflammatory and antioxidant properties of whey are augmented by hyperbaric pressure treatment. In this study, we tested whether dietary supplementation with pressurized whey protein enhances the host ability to clear P. aeruginosa infection compared with native (i.e., unpressurized) whey.

METHODS

Using a minimally invasive, non-lethal model of murine (female C57Bl/6) model of P. aeruginosa infection (mucoid strain embedded in agar beads), we studied kinetics of infection, inflammation, and oxidative stress at d 1, 3, and 7 postinfection. A parallel set of mice were fed for 4 wk a semipurified diet containing either native or pressurized whey and subsequently infected with P. aeruginosa. In these mice, the parameters mentioned previously were studied at d 1 and 3 postinfection.

RESULTS

Infection with P. aeruginosa resulted in inflammation and protein oxidation sustained beyond bacterial clearance. Animals that were fed pressurized whey had fewer bacteria at day 3 than mice on native whey. Weight loss or broncho-alveolar lavage cell content were comparable. Airway protein oxidation was attenuated, whereas airway leukocyte bacterial killing ability and oxidative burst in response to opsonized bacteria were increased in the pressurized whey-fed animals.

CONCLUSIONS

Use of nutritionally derived substances with anti-inflammatory and antioxidant properties, such as pressurized whey, aids in limiting airway bacterial infection, particularly, under conditions of ongoing oxidative stress.

Evolution of surfactant protein-D levels in children with ventilator-associated pneumonia

RATIONALE

The pathobiology of ventilator-associated pneumonia (VAP) in children is poorly understood; investigation has been limited by lack of universally applied diagnostic criteria and reliable biomarkers for this condition.

OBJECTIVES

We evaluated the clinical pulmonary infection score (CPIS) in diagnosing VAP and prospectively characterized the relationship between surfactant protein-D (SP-D) metabolism and VAP.

METHODS

Children admitted to an Egyptian PICU requiring intubation were screened for the absence of primary pulmonary pathology. Thirty-nine children underwent two evaluations: during the first 36 hr following intubation and after 4 days of mechanical ventilation. During both, bronchoalveolar lavage fluid (BALF) was obtained for culture and SP-D assay. CPIS was computed during the second evaluation.

RESULTS

Optimum performance of the CPIS against BALF culture occurred at a cutoff value of 6, (ROC AUC of 0.89 ± 0.05). Children who developed VAP had significantly higher SP-D levels, both preceding (129.9 ± 33.5 ng/ml at the 1st BAL)-and following positive BALF culture (249.5 ± 51.2 ng/ml at the 2nd BAL), compared to children whose BALF remained sterile (62.6 ± 18.1 ng/ml and 64.9 ± 9.4 ng/ml; P < 0.001). This increase in SP-D levels was most evident in children infected with Pseudomonas aeruginosa compared to children with Klebsiella pneumonia or S. aureus.

CONCLUSIONS

The CPIS performed well against BALF culture. We observed a bacterial species-specific difference in SP-D levels in children who developed VAP; this change preceded detection of infection by CPIS or BALF culture.

Pulmonary Collectins in Diagnosis and Prevention of Lung Diseases

Pulmonary surfactant is a complex mixture of lipids and proteins, and is synthesized and secreted by alveolar type II epithelial cells and bronchiolar Clara cells. It acts to keep alveoli from collapsing during the expiratory phase of the respiratory cycle. After its secretion, lung surfactant forms a lattice structure on the alveolar surface, known as tubular myelin. Surfactant proteins (SP)-A, B, C and D make up to 10% of the total surfactant. SP-B and SPC are relatively small hydrophobic proteins, and are involved in the reduction of surface-tension at the air-liquid interface. SP-A and SP-D, on the other hand, are large oligomeric, hydrophilic proteins that belong to the collagenous Ca²⁺-dependent C-type lectin family (known as “Collectins”), and play an important role in host defense and in the recycling and transport of lung surfactant (Awasthi 2010) (Fig. 43.1). In particular, there is increasing evidence that surfactant-associated proteins A and -D (SP-A and SP-D, respectively) contribute to the host defense against inhaled microorganisms (see 10.1007/978-3-7091-1065_24 and 10.1007/978-3-7091-1065_25). Based on their ability to recognize pathogens and to regulate the host defense, SP-A and SP-D have been recently categorized as “Secretory Pathogen Recognition Receptors”. While SP-A and SP-D were first identified in the lung; the expression of these proteins has also been observed at other mucosal surfaces, such as lacrimal glands, gastrointestinal mucosa, genitourinary epithelium and periodontal surfaces. SP-A is the most prominent among four proteins in the pulmonary surfactant-system. The expression of SP-A is complexly regulated on the transcriptional and the chromosomal level. SP-A is a major player in the pulmonary cytokine-network and moreover has been described to act in the pulmonary host defense. This chapter gives an overview on the understanding of role of SP-A and SP-D in for human pulmonary disorders and points out the importance for pathology-orientated research to further elucidate the role of these molecules in adult lung diseases. As an outlook, it will become an issue of pulmonary pathology which might provide promising perspectives for applications in research, diagnosis and therapy (Awasthi 2010).

Comprehensive characterisation of pulmonary and serum surfactant protein D in COPD

Background

Pulmonary surfactant protein D (SP-D) is considered as a candidate biomarker for the functional integrity of the lung and for disease progression, which can be detected in serum. The origin of SP-D in serum and how serum concentrations are related to pulmonary concentrations under inflammatory conditions is still unclear.

Methods

In a cross-sectional study comprising non-smokers (n = 10), young - (n = 10), elderly smokers (n = 20), and smokers with COPD (n = 20) we simultaneously analysed pulmonary and serum SP-D levels with regard to pulmonary function, exercise, repeatability and its quaternary structure by native gel electrophoresis. Statistical comparisons were conducted by ANOVA and post-hoc testing for multiple comparisons; repeatability was assessed by Bland-Altman analysis.

Results

In COPD, median (IQR) pulmonary SP-D levels were lower (129(68) ng/ml) compared to smokers (young: 299(190), elderly: 296(158) ng/ml; p < 0.01) and non-smokers (967(708) ng/ml; p < 0.001). The opposite was observed in serum, with higher concentrations in COPD (140(89) ng/ml) as compared to non-smokers (76(47) ng/ml; p < 0.01). SP-D levels were reproducible and correlated with the degree of airway obstruction in all smokers. In addition, smoking lead to disruption of the quaternary structure.

Conclusions

Pulmonary and serum SP-D levels are stable markers influenced by smoking and related to airflow obstruction and disease state. Smaller subunits of pulmonary SP-D and the rapid increase of serum SP-D levels in COPD due to exercise support the translocation hypothesis and its use as a COPD biomarker.

Trial registration

no interventional trial

Effect of single vs bilateral lung transplantation on plasma surfactant protein D levels in idiopathic pulmonary fibrosis

BACKGROUND

Serum levels of surfactant protein D (SP-D) have been suggested as reflecting epithelial damage in acute lung injury, COPD, and idiopathic pulmonary fibrosis (IPF). However, little is known about SP-D levels in the setting of lung transplantation.

METHODS

We examined plasma SP-D levels in 104 subjects from a prospective, multicenter cohort study of lung allograft recipients. Plasma SP-D was measured by enzyme-linked immunosorbent assay prior to transplant and daily for 3 days after transplant.

RESULTS

Subjects undergoing transplant for IPF had higher baseline SP-D levels (median, 325 ng/mL) compared with subjects with cystic fibrosis, COPD, and pulmonary hypertension (median, 100, 80, and 82 ng/mL, respectively; P = .0001). Among subjects with IPF undergoing bilateral transplant, SP-D levels declined rapidly postoperatively. In contrast, SP-D levels in subjects undergoing single lung transplant for IPF remained significantly higher than those of bilateral allograft recipients. Among subjects undergoing single lung transplant for IPF, the development of primary graft dysfunction (PGD) was associated with a subsequent rise in SP-D levels, whereas SP-D levels in IPF subjects undergoing bilateral transplant declined, even in the presence of grade 3 PGD. Importantly, single lung allograft recipients without PGD had higher postoperative SP-D levels than bilateral allograft recipients with PGD.

CONCLUSIONS

Subjects undergoing lung transplant for IPF have significantly higher baseline plasma SP-D levels compared with those with other diagnoses. Plasma SP-D is likely a biomarker of the air-blood barrier integrity in the native IPF lung, but may be less useful as a biomarker of PGD after transplant.

Involvement of type II pneumocytes in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality, but the cellular and molecular mechanisms are still not fully understood. Type II pneumocytes are identified as the synthesizing cells of the alveolar surfactant, which has important properties in maintaining alveolar and airway stability. Lung surfactant can reduce the surface tension and prevent alveolar collapse and the airway walls collapse. Pulmonary surfactant components play important roles in normal lung function and inflammation in the lung. Surfactant has furthermore been shown to modulate the process of innate host defense, including suppression of cytokine secretion and transcription factor activation, in the inflammatory network of COPD. Abnormalities of lung surfactant might be one of the mechanisms leading to increased airway resistance in COPD. The increased expression of Granzyme A and B was found in lung tissues of patients with COPD and type II pneumocytes was proposed to be involved in the pathogenesis of COPD. These novel findings provide new sights into the role of the type II pneumocytes in the pathogenesis of COPD.

Modification of surfactant protein D by reactive oxygen-nitrogen intermediates is accompanied by loss of aggregating activity, in vitro and in vivo

Surfactant protein D (SP-D) is an important effector of innate immunity. We have previously shown that SP-D accumulates at sites of acute bacterial infection and neutrophil infiltration, a setting associated with the release of reactive species such as peroxynitrite. Incubation of native SP-D or trimeric SP-D lectin domains (NCRDs) with peroxynitrite resulted in nitration and nondisulfide cross-linking. Modifications were blocked by peroxynitrite scavengers or pH inactivation of peroxynitrite, and mass spectroscopy confirmed nitration of conserved tyrosine residues within the C-terminal neck and lectin domains. Mutant NCRDs lacking one or more of the tyrosines allowed us to demonstrate preferential nitration of Tyr314 and the formation of Tyr228-dependent cross-links. Although there was no effect of peroxynitrite or tyrosine mutations on lectin activity, incubation of SP-D dodecamers or murine lavage with peroxynitrite decreased the SP-D-dependent aggregation of lipopolysaccharide-coated beads, supporting our hypothesis that defective aggregation results from abnormal cross-linking. We also observed nitration, cross-linking of SP-D, and a significant decrease in SP-D-dependent aggregating activity in the lavage of mice acutely exposed to nitrogen dioxide. Thus, modification of SP-D by reactive oxygen-nitrogen species could contribute to alterations in the structure and function of SP-D at sites of inflammation in vivo.

Protective effects of low-dose carbon monoxide against renal fibrosis induced by unilateral ureteral obstruction

Tubulointerstitial fibrosis is a hallmark of chronic progressive kidney disease leading to end-stage renal failure. An endogenous product of heme oxygenase activity, carbon monoxide (CO), has been shown to exert cytoprotection against tissue injury. Here, we explored the effects of exogenous administration of low-dose CO in an in vivo model of renal fibrosis induced by unilateral ureteral obstruction (UUO) and examined whether CO can protect against kidney injury. UUO in mice leads to increased extracellular matrix (ECM) deposition and tubulointerstitial fibrosis within 4 to 7 days. Kidneys of mice exposed to low-dose CO, however, had markedly reduced ECM deposition after UUO. Moreover, low-dose CO treatment inhibited the induction of alpha-smooth muscle actin (alpha-SMA) and major ECM proteins, type 1 collagen and fibronectin, in kidneys after UUO. In contrast, these anti-fibrotic effects of CO treatment were abrogated in mice carrying null mutation of Mkk3, suggesting involvement of the MKK3 signaling pathway in mediating the CO effects. Additionally, in vitro CO exposure markedly inhibited TGF-beta(1)-induced expression of alpha-SMA, collagen, and fibronectin in renal proximal tubular epithelial cells. Our findings suggest that low-dose CO exerts protective effects, via the MKK3 pathway, to inhibit development of renal fibrosis in obstructive nephropathy.

Immunomodulatory roles of surfactant proteins A and D: implications in lung disease

Surfactant, a lipoprotein complex, was originally described for its essential role in reducing surface tension at the air-liquid interface of the lung; however, it is now recognized as being a critical component in lung immune host defense. Surfactant proteins (SP)-A and -D are pattern recognition molecules of the collectin family of C-type lectins. SP-A and SP-D are part of the innate immune system and regulate the functions of other innate immune cells, such as macrophages. They also modulate the adaptive immune response by interacting with antigen-presenting cells and T cells, thereby linking innate and adaptive immunity. Emerging studies suggest that SP-A and SP-D function to modulate the immunologic environment of the lung so as to protect the host and, at the same time, modulate an overzealous inflammatory response that could potentially damage the lung and impair gas exchange. Numerous polymorphisms of SPs have been identified that may potentially possess differential functional abilities and may act via different receptors to ultimately alter the susceptibility to or severity of lung diseases.

Alterations of the composition and metabolism of pulmonary surfactant phospholipids induced by experimental peritonitis in rats

Pulmonary complications often accompany the development of acute peritonitis. In this study, we analyzed the alterations of alveolar surfactant phospholipids in rats with experimentally induced peritonitis. The results showed a reduction of almost all phospholipid fractions in pulmonary surfactant of experimental animals. The most abundant alveolar phospholipids-phosphatidylcholine and phosphatidylglycerol were reduced significantly in surfactant of rats with experimental peritonitis. In addition, analysis of the fatty acid composition of these two phospholipids revealed marked differences between experimental and control animals. The activity of phospholipase A2, which is localized in the hydrophyllic phase of alveolar surfactant, was higher in rats with experimental peritonitis compared to sham-operated ones. Also, a weak acyl-CoA:lysophospholipid acyltransferase activity was detected in alveolar surfactant of rats with experimental peritonitis, whereas in control animals this activity was not detectable. The lipid-transfer activity was quite similar in pulmonary surfactant of control and experimental rats. The total number of cells and the percentage of neutrophils were strongly increased in broncho-alveolar lavage fluid from rats with peritonitis. Thus, our results showed that the development of peritonitis was accompanied by pulmonary pathophysiological processes that involved alterations of the phospholipid and fatty acid composition of alveolar surfactant. We suggest that the increased populations of inflammatory cells, which basically participate in internalization and secretion of surfactant components, contributed to the observed alterations of alveolar phospholipids. These studies would be useful for clarification of the pathogenic mechanisms underlying the occurrence of pulmonary disorders that accompany acute inflammatory conditions, such as peritonitis and sepsis.

Surfactant protein A and surfactant protein D variation in pulmonary disease

Surfactant proteins A (SP-A) and D (SP-D) have been implicated in pulmonary innate immunity. The proteins are host defense lectins, belonging to the collectin family which also includes mannan-binding lectin (MBL). SP-A and SP-D are pattern-recognition molecules with the lectin domains binding preferentially to sugars on a broad spectrum of pathogen surfaces and thereby facilitating immune functions including viral neutralization, clearance of bacteria, fungi and apoptotic and necrotic cells, modulation of allergic reactions, and resolution of inflammation. SP-A and SP-D can interact with receptor molecules present on immune cells leading to enhanced microbial clearance and modulation of inflammation. SP-A and SP-D also modulate the functions of cells of the adaptive immune system including dendritic cells and T cells. Studies on SP-A and SP-D polymorphisms and protein levels in bronchoalveolar lavage and blood have indicated associations with a multitude of pulmonary inflammatory diseases. In addition, accumulating evidence in mouse models of infection and inflammation indicates that recombinant forms of the surfactant proteins are biologically active in vivo and may have therapeutic potential in controlling pulmonary inflammatory disease. The presence of the surfactant collectins, especially SP-D, in non-pulmonary tissues, such as the gastrointestinal tract and genital organs, suggest additional actions located to other mucosal surfaces. The aim of this review is to summarize studies on genetic polymorphisms, structural variants, and serum levels of human SP-A and SP-D and their associations with human pulmonary disease.

Proteome analysis of bronchoalveolar lavage in lung diseases

The proteomic approach is complementary to genomics and enables protein composition to be investigated under various clinical conditions. Its application to the study of bronchoalveolar lavage (BAL) is extremely promising. BAL proteomic studies were initially based on two-dimensional electrophoretic separation of complex protein samples and subsequent identification of proteins by different methods. With the techniques available today it is possible to attain many different research objectives. BAL proteomics can contribute to the identification of proteins in alveolar spaces with possible insights into pathogenesis and clinical application for diagnosis, prognosis and therapy. Many proteins with different functions have already been identified in BAL. Some could be biomarkers that need to be individually confirmed by correlation with clinical parameters and validation by other methods on larger cohorts of patients. The standardization of BAL sample preparation and processing for proteomic studies is an important goal that would promote and facilitate clinical applications. Here, we review the principal literature on BAL proteomic analysis applied to the study of lung diseases.