Extracellular regulated kinase/mitogen activated protein kinase is up-regulated in pulmonary emphysema and mediates matrix metalloproteinase-1 induction by cigarette smoke

The interstitial collagenase matrix metalloprotein-ase-1 (MMP-1) is up-regulated in the lung during pulmonary emphysema. The mechanisms underlying this aberrant expression are poorly understood. Although cigarette smoking is the predominant cause of emphysema, only 15-20% of smokers develop the disease. To define the signaling pathways activated by smoke and to identify molecules responsible for emphysema-associated MMP-1 expression, we performed several in vitro and in vivo experiments. In this study, we showed that cigarette smoke directly induced MMP-1 mRNA and protein expression and increased the collagenolytic activity of human airway cells. Treatment with various chemical kinase inhibitors revealed that this response was dependent on the extracellular regulated kinase-1/2 (ERK) mitogen activated protein kinase pathway. Cigarette smoke increased phosphorylation of residues Thr-202 and Tyr-204 of ERK in airway lining cells and alveolar macrophages in mice at 10 days and 6 months of exposure. Moreover, analysis of lung tissues from emphysema patients revealed significantly increased ERK activity compared with lungs of control subjects. This ERK activity was evident in airway lining and alveolar cells. The identification of active ERK in the lungs of emphysema patients and the finding that induction of MMP-1 by cigarette smoke in pulmonary epithelial cells is ERK-dependent reveal a molecular mechanism and potential therapeutic target for excessive matrix remodeling in smokers who develop emphysema.     

The Receptor for Advanced Glycation End Products (RAGE) Contributes to the Progression of Emphysema in Mice

Several recent clinical studies have implied a role for the receptor for advanced glycation end products (RAGE) and its variants in chronic obstructive pulmonary disease (COPD). In this study we have defined a role for RAGE in the pathogenesis of emphysema in mice. RAGE deficient mice (RAGE-/-) exposed to chronic cigarette smoke were significantly protected from smoke induced emphysema as determined by airspace enlargement and had no significant reduction in lung tissue elastance when compared to their air exposed controls contrary to their wild type littermates. The progression of emphysema has been largely attributed to an increased inflammatory cell-mediated elastolysis. Acute cigarette smoke exposure in RAGE-/- mice revealed an impaired early recruitment of neutrophils, approximately a 6-fold decrease compared to wild type mice. Hence, impaired neutrophil recruitment with continued cigarette smoke exposure reduces elastolysis and consequent emphysema.     

TLR4 protein contributes to cigarette smoke-induced matrix metalloproteinase-1 (MMP-1) expression in chronic obstructive pulmonary disease

Cigarette smoke is the major risk factor associated with the development of chronic obstructive pulmonary disease and alters expression of proteolytic enzymes that contribute to disease pathology. Previously, we reported that smoke exposure leads to the induction of matrix metalloproteinase-1 (MMP-1) through the activation of ERK1/2, which is critical to the development of emphysema. To date, the upstream signaling pathway by which cigarette smoke induces MMP-1 expression has been undefined. This study demonstrates that cigarette smoke mediates MMP-1 expression via activation of the TLR4 signaling cascade. In vitro cell culture studies demonstrated that cigarette smoke-induced MMP-1 was regulated by TLR4 via MyD88/IRAK1. Blockade of TLR4 or inhibition of IRAK1 prevented cigarette smoke induction of MMP-1. Mice exposed to acute levels of cigarette smoke exhibited increased TLR4 expression. To further confirm the in vivo relevance of this signaling pathway, rabbits exposed to acute cigarette smoke were found to have elevated TLR4 signaling and subsequent MMP-1 expression. Additionally, lungs from smokers exhibited elevated TLR4 and MMP-1 levels. Therefore, our data indicate that TLR4 signaling, through MyD88 and IRAK1, plays a predominant role in MMP-1 induction by cigarette smoke. The identification of the TLR4 pathway as a regulator of smoke-induced protease production presents a series of novel targets for future therapy in chronic obstructive pulmonary disease.     

Effect of urethan anesthesia on cigarette smoke-induced airway injury in guinea pigs

The effect of urethan anesthesia on cigarette smoke-induced airway responsiveness and permeability was studied in the guinea pig. Airway responsiveness was determined by measuring changes to airway resistance to graded doses of aerosolized histamine, and mucosal permeability was determined by measuring the appearance of fluorescein isothiocyanate-dextran (FITC-D) in the blood and examining its distribution in lung tissue after it had been delivered to the lung in an aerosol. The results confirm previous studies that smoke exposure increased airway responsiveness and mucosal permeability. They also show that urethan anesthesia administered before smoke exposure prevented the smoke-related changes in airway reactivity and mucosal permeability. In animals that remained conscious during the smoke exposure, there was increased deposition of the dextran in the regions of the bronchioloalveolar junctions with a more rapid uptake of FITC-D into the blood. We postulate that, when urethan anesthesia is administered before smoke exposure, the exudative phase of the inflammatory reaction produced by smoke exposure is suppressed.     

Cigarette Smoke-Induced Emphysema and Pulmonary Hypertension Can Be Prevented by Phosphodiesterase 4 and 5 Inhibition in Mice

Rationale

Chronic obstructive pulmonary disease (COPD) is a widespread disease, with no curative therapies available. Recent findings suggest a key role of NO and sGC-cGMP signaling for the pathogenesis of the disease. Previous data suggest a downregulation/inactivation of the cGMP producing soluble guanylate cyclase, and sGC stimulation prevented cigarette smoke-induced emphysema and pulmonary hypertension (PH) in mice. We thus aimed to investigate if the inhibition of the cGMP degrading phosphodiesterase (PDE)5 has similar effects. Results were compared to the effects of a PDE 4 inhibitor (cAMP elevating) and a combination of both.

Methods

C57BL6/J mice were chronically exposed to cigarette smoke and in parallel either treated with Tadalafil (PDE5 inhibitor), Piclamilast (PDE4 inhibitor) or both. Functional measurements (lung compliance, hemodynamics) and structural investigations (alveolar and vascular morphometry) as well as the heart ratio were determined after 6 months of tobacco smoke exposure. In addition, the number of alveolar macrophages in the respective lungs was counted.

Results

Preventive treatment with Tadalafil, Piclamilast or a combination of both almost completely prevented the development of emphysema, the increase in lung compliance, tidal volume, structural remodeling of the lung vasculature, right ventricular systolic pressure, and right ventricular hypertrophy induced by cigarette smoke exposure. Single, but not combination treatment prevented or reduced smoke-induced increase in alveolar macrophages.

Conclusion

Cigarette smoke-induced emphysema and PH could be prevented by inhibition of the phosphodiesterases 4 and 5 in mice.     

Cigarette smoke-induced lung emphysema in mice is associated with prolyl endopeptidase, an enzyme involved in collagen breakdown

There is increasing evidence that the neutrophil chemoattractant proline-glycine-proline (PGP), derived from the breakdown of the extracellular matrix, plays an important role in neutrophil recruitment to the lung. PGP formation is a multistep process involving neutrophils, metalloproteinases (MMPs), and prolyl endopeptidase (PE). This cascade of events is now investigated in the development of lung emphysema. A/J mice were whole body exposed to cigarette smoke for 20 wk. After 20 wk or 8 wk after smoking cessation, animals were killed, and bronchoalveolar lavage fluid and lung tissue were collected to analyze the neutrophilic airway inflammation, the MMP-8 and MMP-9 levels, the PE activity, and the PGP levels. Lung tissue degradation was assessed by measuring the mean linear intercept. Additionally, we investigated the effect of the peptide L-arginine-threonine-arginine (RTR), which binds to PGP sequences, on the smoke-induced neutrophil influx in the lung after 5 days of smoke exposure. Neutrophilic airway inflammation was induced by cigarette smoke exposure. MMP-8 and MMP-9 levels, PE activity, and PGP levels were elevated in the lungs of cigarette smoke-exposed mice. PE was highly expressed in epithelial and inflammatory cells (macrophages and neutrophils) in lung tissue of cigarette smoke-exposed mice. After smoking cessation, the neutrophil influx, the MMP-8 and MMP-9 levels, the PE activity, and the PGP levels were decreased or reduced to normal levels. Moreover, RTR inhibited the smoke-induced neutrophil influx in the lung after 5 days' smoke exposure. In the present murine model of cigarette smoke-induced lung emphysema, it is demonstrated for the first time that all relevant components (neutrophils, MMP-8, MMP-9, PE) involved in PGP formation from collagen are upregulated in the airways. Together with MMPs, PE may play an important role in the formation of PGP and thus in the pathophysiology of lung emphysema.     

烟草烟雾暴露对哮喘大鼠气道CCR6 mRNA及其蛋白表达的影响

目的研究烟草烟雾暴露对支气管哮喘（简称哮喘）大鼠气道chemokine receptor 6（CCR6）表达的影响,探讨吸烟加重哮喘气道炎症的免疫学机制。方法雄性Wistar大鼠40只,随机分为对照组、烟雾暴露组、哮喘组和哮喘＋烟雾暴露组,每组10只。建立哮喘大鼠模型和哮喘大鼠烟草烟雾暴露模型,采集大鼠支气管肺泡灌洗液（BALF）行白细胞计数及分类,采用逆转录-聚合酶链式反应（RT-PCR）方法及免疫组织化学法检测各组大鼠气道CCR6 mRNA及蛋白的表达。结果①哮喘组（69.0±3.5;4.1±1.0;8.9±2.0）、哮喘＋烟雾暴露组（86.7±5.2;2.2±1.0;19.0±2.8）BALF中白细胞总数、嗜酸粒细胞、中性粒细胞均高于对照组（10.1±3.8;1.3±0.7;2.2±1.1）、烟雾暴露组（47.7±6.8;0.5±0.3;2.7±1.4）（P均〈0.05）;哮喘＋烟雾暴露组BALF中白细胞总数和中性粒细胞高于哮喘组,嗜酸粒细胞低于哮喘组（P均〈0.05）。②哮喘组（8.15±0.88;0.452±0.013）、哮喘＋烟雾暴露组（15.16±0.87;0.531±0.024）CCR6 mRNA及其蛋白表达水平均明显高于对照组（1.01±0.52;0.299±0.027）、烟雾暴露组（5.55±0.54;0.442±0.018）（均P〈0.01）;哮喘＋烟雾暴露组明显高于哮喘组（均P〈0.01）。结论烟草烟雾暴露可通过促使气道CCR6 mRNA及其蛋白高表达,加重哮喘大鼠气道慢性炎症。     

Alpha 1 anti-trypsin: one protein, many functions

α-1 anti-trypsin (AAT) is the most abundant circulating serine protease inhibitor (serpin) and an acute phase reactant. Systemic deficiency in AAT (AATD) due to genetic mutations can result in liver failure and chronic lung disease such as emphysema. Considered the prototypic serpin, the emphysema observed in patients with AATD, consisting of progressive destruction of the alveoli and small airway structures, formed the basis of the protease/anti-protease imbalance theory of chronic obstructive pulmonary disease (COPD). Over the past decade, however, investigations of AATD have described multiple functions of AAT beyond those generally attributed to its antiprotease activity. Evidence now suggests that AAT plays an important role in modulating immunity, inflammation, proteostasis, apoptosis, and possibly cellular senescence programs. When integrated in vivo, these processes contribute to the lung maintenance program which preserves the lung despite a constant bombardment by damage associated molecular patterns (DAMPs) and/or pathogenassociated molecular patterns (PAMPs) initiated by cigarette smoke, pollutants, or infections. In this review, we discuss the clinical aspects of AATD as they pertain to emphysema; including similarities and differences to cigarette smoke-induced emphysema. Examining the lung maintenance program, we next consider the multiple mechanisms of airspace destruction and explore the role AATD contributes. Finally, we consider the data regarding treatment of AATD, including AAT supplementation and its current limitations, and suggest further avenues of research informed by the multiple functions of AAT.     

TLR and NKG2D Signaling Pathways Mediate CS-Induced Pulmonary Pathologies

Long-term exposure to cigarette smoke (CS) can have deleterious effects on lung epithelial cells including cell death and the initiation of inflammatory responses. CS-induced cell injury can elaborate cell surface signals and cellular byproducts that stimulate immune system surveillance. Our previous work has shown that the expression of ligands for the cytotoxic lymphocyte activating receptor NKG2D is enhanced in patients with COPD and that the induction of these ligands in a mouse model can replicate COPD pathologies. Here, we extend these findings to demonstrate a role for the NKG2D receptor in CS-induced pathophysiology and provide evidence linking nucleic acid-sensing endosomal toll-like receptor (TLR) signaling to COPD pathology through NKG2D activation. Specifically, we show that mice deficient in NKG2D exhibit attenuated pulmonary inflammation and airspace enlargement in a model of CS-induced emphysema. Additionally, we show that CS exposure induces the release of free nucleic acids in the bronchoalveolar lavage and that direct exposure of mouse lung epithelial cells to cigarette smoke extract similarly induces functional nucleic acids as assessed by TLR3, 7, and 9 reporter cell lines. We demonstrate that exposure of mouse lung epithelial cells to TLR ligands stimulates the surface expression of RAET1, a ligand for NKG2D, and that mice deficient in TLR3/7/9 receptor signaling do not exhibit CS-induced NK cell hyperresponsiveness and airspace enlargement. The findings indicate that CS-induced airway injury stimulates TLR signaling by endogenous nucleic acids leading to elevated NKG2D ligand expression. Activation of these pathways plays a major role in the altered NK cell function, pulmonary inflammation and remodeling related to long-term CS exposure.     

Differential induction of apoptosis by cigarette smoke extract in primary human lung fibroblast strains: implications for emphysema

Cigarette smoke is the principal cause of emphysema. Recent attention has focused on the loss of alveolar fibroblasts in the development of emphysema. Fibroblasts may become damaged by oxidative stress and undergo apoptosis as a result of cigarette smoke exposure. Not all smokers develop lung diseases associated with tobacco smoke, a fact that may reflect individual variation among human fibroblast strains. We hypothesize that fibroblasts from different human beings vary in their ability to undergo apoptosis after cigarette smoke exposure. This could account for emphysematous changes that occur in the lungs of some but not all smokers. Primary human lung fibroblast strains were exposed to cigarette smoke extract (CSE) and assessed for viability, morphological changes, and mitochondrial transmembrane potential as indicators of apoptosis. We also examined the generation of intracellular reactive oxygen species (ROS), 4-hydroxy-2-nonenal, and changes in glutathione (GSH) and glutathione disulfide (GSSG) levels. Each human lung fibroblast strain exhibited a differential sensitivity to CSE as judged by changes in mitochondrial membrane potential, viability, ROS generation, and glutathione production. Interestingly, the thiol antioxidants N-acetyl-L-cysteine and GSH eliminated CSE-induced changes in fibroblast morphology such as membrane blebbing, nuclear condensation, and cell size and prevented alterations in mitochondrial membrane potential and the generation of ROS. These findings support the concept that oxidative stress and apoptosis are responsible for fibroblast death associated with exposure to tobacco smoke. Variations in the sensitivity of fibroblasts to cigarette smoke may account for the fact that only some smokers develop emphysema.     

Role of CXCR2 in cigarette smoke-induced lung inflammation

It has been hypothesized that the destruction of lung tissue observed in smokers with chronic obstructive pulmonary disease and emphysema is mediated by neutrophils recruited to the lungs by smoke exposure. This study investigated the role of the chemokine receptor CXCR2 in mediating neutrophilic inflammation in the lungs of mice acutely exposed to cigarette smoke. Exposure to dilute mainstream cigarette smoke for 1 h, twice per day for 3 days, induced acute inflammation in the lungs of C57BL/6 mice, with increased neutrophils and the neutrophil chemotactic CXC chemokines macrophage inflammatory protein (MIP)-2 and KC. Treatment with SCH-N, an orally active small molecule inhibitor of CXCR2, reduced the influx of neutrophils into the bronchoalveolar lavage (BAL) fluid. Histological changes were seen, with drug treatment reducing perivascular inflammation and the number of tissue neutrophils. beta-Glucuronidase activity was reduced in the BAL fluid of mice treated with SCH-N, indicating that the reduction in neutrophils was associated with a reduction in tissue damaging enzymes. Interestingly, whereas MIP-2 and KC were significantly elevated in the BAL fluid of smoke exposed mice, they were further elevated in mice exposed to smoke and treated with drug. The increase in MIP-2 and KC with drug treatment may be due to the decrease in lung neutrophils that either are not present to bind these chemokines or fail to provide a feedback signal to other cells producing these chemokines. Overall, these results demonstrate that inhibiting CXCR2 reduces neutrophilic inflammation and associated lung tissue damage due to acute cigarette smoke exposure.     

Cigarette smoke extract induces oxidative stress and apoptosis in human lung fibroblasts

Cigarette smoke is a mixture of chemicals having direct and/or indirect toxic effects on different lung cells. We investigated the effect of cigarette smoke on human lung fibroblasts (HFL-1) oxidation and apoptosis. Cells were exposed to various concentrations (1, 5, and 10%) of cigarette smoke extract (CSE) for 3 h, and oxidative stress and apoptosis were assessed by fluorescence-activated cell sorting and confocal laser fluorescence microscopy. Both oxidative stress and apoptosis exhibited a dose-response relationship with CSE concentrations. Lung fibroblasts also showed marked DNA fragmentation at the Comet assay after exposure to 10% CSE. Coincubation of HLF-1 cells with N-acetylcysteine (1 mM) during CSE exposure significantly reduced oxidative stress, apoptosis, and DNA fragmentation, whereas preincubation (3 h) with the glutathione-depleting agent buthionine sulfoximine (125 microM) produced a significant increase of oxidative stress. Cigarette smoke is a potent source of oxidative stress, DNA damage, and apoptosis for HFL-1 cells, and we speculate that this could contribute to the development of pulmonary emphysema in the lungs of smokers.     

Cigarette smoke extract increases albumin flux across pulmonary endothelium in vitro

Cigarette smoking causes lung inflammation, and a characteristic of inflammation is an increase in vascular permeability. To determine if cigarette smoke could alter endothelial permeability, we studied flux of radiolabeled albumin across monolayers of porcine pulmonary artery endothelium grown in culture on microporous membranes. Extracts (in either dimethylsulfoxide or phosphate-buffered saline) of cigarette smoke in a range estimate of concentrations simulating cigarette smoke exposure to the lungs in vivo caused a dose-dependent increase in albumin flux that was dependent on extracellular divalent cations and associated with polymerization of cellular actin. The effect was reversible, independent of the surface of endothelial cells exposed (either luminal or abluminal), and due primarily to components of the vapor phase of smoke. The effects occurred without evidence of cell damage, but subtle morphological changes were produced by exposure to the smoke extracts. These findings suggest that cigarette smoke can alter permeability of the lung endothelium through effects on cytoskeletal elements.     

CD8+ T Cells are required for inflammation and destruction in cigarette smoke-induced emphysema in mice

Increased numbers of T lymphocytes are observed in the lungs of patients with chronic obstructive pulmonary disease, but their role in the disease process is not known. We investigated the role of CD8+ T cells in inflammatory cell recruitment and lung destruction in a cigarette smoke-induced murine model of emphysema. In contrast to wild-type C57BL/6J mice that displayed macrophage, lymphocyte, and neutrophil recruitment to the lung followed by emphysema in response to cigarette smoke, CD8+ T cell-deficient (CD8-/-) mice had a blunted inflammatory response and did not develop emphysema when exposed to long-term cigarette smoke. Further studies supported a pathogenetic pathway whereby the CD8+ T cell product, IFN-gamma-inducible protein-10, induces production of macrophage elastase (matrix metalloproteinase 12) that degrades elastin, both causing lung destruction directly and generating elastin fragments that serve as monocyte chemokines augmenting macrophage-mediated lung destruction. These studies demonstrate a requirement for CD8+ T cells for the development of cigarette smoke-induced emphysema and they provide a unifying pathway whereby CD8+ T cells are a central regulator of the inflammatory network in chronic obstructive pulmonary disease.     

Cigarette smoke-induced pulmonary inflammation is TLR4/MyD88 and IL-1R1/MyD88 signaling dependent

Acute cigarette smoke exposure of the airways (two cigarettes twice daily for three days) induces acute inflammation in mice. In this study, we show that airway inflammation is dependent on Toll-like receptor 4 and IL-1R1 signaling. Cigarette smoke induced a significant recruitment of neutrophils in the bronchoalveolar space and pulmonary parenchyma, which was reduced in TLR4-, MyD88-, and IL-1R1-deficient mice. Diminished neutrophil influx was associated with reduced IL-1, IL-6, and keratinocyte-derived chemokine levels and matrix metalloproteinase-9 activity in the bronchoalveolar space. Further, cigarette smoke condensate (CSC) induced a macrophage proinflammatory response in vitro, which was dependent on MyD88, IL-1R1, and TLR4 signaling, but not attributable to LPS. Heat shock protein 70, a known TLR4 agonist, was induced in the airways upon smoke exposure, which probably activates the innate immune system via TLR4/MyD88, resulting in airway inflammation. CSC-activated macrophages released mature IL-1beta only in presence of ATP, whereas CSC alone promoted the TLR4/MyD88 signaling dependent production of IL-1alpha and pro-IL-1beta implicating cooperation between TLRs and the inflammasome. In conclusion, acute cigarette exposure results in LPS-independent TLR4 activation, leading to IL-1 production and IL-1R1 signaling, which is crucial for cigarette smoke induced inflammation leading to chronic obstructive pulmonary disease with emphysema.     

CX3CR1+ lung mononuclear phagocytes spatially confined to the interstitium produce TNF-α and IL-6 and promote cigarette smoke-induced emphysema

Increased numbers of macrophages are found in the lungs of smokers and those with chronic obstructive pulmonary disease. Experimental evidence shows the central role of macrophages in elaboration of inflammatory mediators such as TNF-α and the progression toward cigarette smoke-induced emphysema. We investigated the role of CX3CR1 in recruitment of mononuclear phagocytes, inflammatory cytokine responses, and tissue destruction in the lungs after cigarette smoke exposure. Using mice in which egfp is expressed at the locus of the cx3cr1 gene, we show that alveolar macrophages increased transmembrane ligand CX3CL1 expression and soluble CX3CL1 was detectable in the airspaces, but cx3cr1(GFP/GFP) and cx3cr1(GFP/+) mice failed to show recruitment of CX3CR1(+) cells into the airspaces with cigarette smoke. In contrast, cigarette smoke increased the accumulation of CX3CR1(+)CD11b(+) mononuclear phagocytes that were spatially confined to the lung interstitium and heterogenous in their expression of CD11c, MHC class II, and autofluorescent property. Although an intact CX3CL1-CX3CR1 pathway amplified the percentage of CX3CR1(+)CD11b(+) mononuclear phagocytes in the lungs, it was not essential for recruitment. Rather, functional CX3CR1 was required for a subset of tissue-bound mononuclear phagocytes to produce TNF-α and IL-6 in response to cigarette smoke, and the absence of functional CX3CR1 protected mice from developing tissue-destructive emphysema. Thus, CX3CR1(+) "tissue resident" mononuclear phagocytes initiate an innate immune response to cigarette smoke by producing TNF-α and IL-6 and are capable of promoting emphysema.     

A Novel Anti-Inflammatory and Pro-Resolving Role for Resolvin D1 in Acute Cigarette Smoke-Induced Lung Inflammation

Introduction

Cigarette smoke is a profound pro-inflammatory stimulus that contributes to acute lung injuries and to chronic lung disease including COPD (emphysema and chronic bronchitis). Until recently, it was assumed that resolution of inflammation was a passive process that occurred once the inflammatory stimulus was removed. It is now recognized that resolution of inflammation is a bioactive process, mediated by specialized lipid mediators, and that normal homeostasis is maintained by a balance between pro-inflammatory and pro-resolving pathways. These novel small lipid mediators, including the resolvins, protectins and maresins, are bioactive products mainly derived from dietary omega-3 and omega-6 polyunsaturated fatty acids (PUFA). We hypothesize that resolvin D1 (RvD1) has potent anti-inflammatory and pro-resolving effects in a model of cigarette smoke-induced lung inflammation.

Methods

Primary human lung fibroblasts, small airway epithelial cells and blood monocytes were treated with IL-1β or cigarette smoke extract in combination with RvD1 in vitro, production of pro-inflammatory mediators was measured. Mice were exposed to dilute mainstream cigarette smoke and treated with RvD1 either concurrently with smoke or after smoking cessation. The effects on lung inflammation and lung macrophage populations were assessed.

Results

RvD1 suppressed production of pro-inflammatory mediators by primary human cells in a dose-dependent manner. Treatment of mice with RvD1 concurrently with cigarette smoke exposure significantly reduced neutrophilic lung inflammation and production of pro-inflammatory cytokines, while upregulating the anti-inflammatory cytokine IL-10. RvD1 promoted differentiation of alternatively activated (M2) macrophages and neutrophil efferocytosis. RvD1 also accelerated the resolution of lung inflammation when given after the final smoke exposure.

Conclusions

RvD1 has potent anti-inflammatory and pro-resolving effects in cells and mice exposed to cigarette smoke. Resolvins have strong potential as a novel therapeutic approach to resolve lung injury caused by smoke and pulmonary toxicants.     

Vitamin C prevents cigarette smoke-induced oxidative damage in vivo

Our recent in vitro results [4] indicate that cigarette smoke induces oxidation of human plasma proteins and extensive oxidative degradation of the guinea pig lung, heart, and liver microsomal proteins, which is almost completely prevented by ascorbic acid. In this paper, we substantiate the in vitro results with in vivo observations. We demonstrate that exposure of subclinical or marginal vitamin C-deficient guinea pigs to cigarette smoke causes oxidation of plasma proteins as well as extensive oxidative degradation of the lung microsomal proteins. Cigarette smoke exposure also results in some discernible damage of the heart microsomal proteins. The oxidative damage has been manifested by SDS-PAGE, accumulation of carbonyl and bityrosine, as well as loss of tryptophan and protein thiols. Cigarette smoke exposure also induces peroxidation of microsomal lipids as evidenced by the formation of conjugated dienes, malondialdehyde, and fluorescent pigment. Cigarette smoke-induced oxidative damage of proteins and peroxidation of lipids are accompanied by marked drop in the tissue ascorbate levels. Protein damage and lipid peroxidation are also observed in cigarette smoke-exposed pair-fed guinea pigs receiving 5 mg vitamin C/animal/day. However, complete protection against protein damage and lipid peroxidation occurs when the guinea pigs are fed 15 mg vitamin C/animal/day. Also, the cigarette smoke-induced oxidative damage of proteins and lipid is reversed after discontinuation of cigarette smoke exposure accompanied by ascorbate therapy. The results, if extrapolated to humans, indicate that comparatively large doses of vitamin C may protect the smokers from cigarette smoke-induced oxidative damage and associated degenerative diseases.     

Mechanisms of cigarette smoke-induced COPD: insights from animal models

Cigarette smoke-induced animal models of chronic obstructive pulmonary disease support the protease-antiprotease hypothesis of emphysema, although which cells and proteases are the crucial actors remains controversial. Inhibition of either serine or metalloproteases produces significant protection against emphysema, but inhibition is invariably accompanied by decreases in the inflammatory response to cigarette smoke, suggesting that these inhibitors do more than just prevent matrix degradation. Direct anti-inflammatory interventions are also effective against the development of emphysema, as are antioxidant strategies; the latter again decrease smoke-induced inflammation. There is increasing evidence for autoimmunity, perhaps directed against matrix components, as a driving force in emphysema. There is intriguing but controversial animal model evidence that failure to repair/failure of lung maintenance also plays a role in the pathogenesis of emphysema. Cigarette smoke produces small airway remodeling in laboratory animals, possibly by direct induction of fibrogenic growth factors in the airway wall, and also produces pulmonary hypertension, at least in part through direct upregulation of vasoactive mediators in the intrapulmonary arteries. Smoke exposure causes goblet cell metaplasia and excess mucus production in the small airways and proximal trachea, but these changes are not good models of either chronic bronchitis or acute exacerbations. Emphysema, small airway remodeling, pulmonary hypertension, and mucus production appear to be at least partially independent processes that may require different therapeutic approaches.     

The role of short-chain fatty acids in orchestrating two types of programmed cell death in colon cancer

Autophagy serves a critical function in cellular homeostasis by prolonging survival during nutrient deprivation. Although primarily characterized as a cell survival mechanism, the relationship between autophagy and cell death pathways remains incompletely understood. Autophagy has heretofore not been studied in the context of human pulmonary disease. We have recently observed increased morphological and biochemical markers of autophagy in human lung tissue from patients with chronic obstructive pulmonary disease (COPD). Similar observations of increased autophagy were also made in mouse lung tissue subjected to chronic cigarette smoke exposure, a primary causative agent in COPD, and in pulmonary cells exposed to aqueous cigarette smoke extract. Since knockdown of autophagic regulator proteins inhibited apoptosis in response to cigarette smoke exposure in vitro, we concluded that increased autophagy was associated with increased cell death in this model. We hypothesize that increased autophagy contributes to COPD pathogenesis by promoting epithelial cell death. Further research will examine whether autophagy plays a causative, correlative, or protective role in specific lung pathologies.