Malondialdehyde-acetaldehyde adducts decrease bronchial epithelial wound repair

Malondialdehyde Acetaldehyde-Adduction Changes Surfactant Protein D Structure and Function

Alcohol consumption with concurrent cigarette smoking produces malondialdehyde acetaldehyde (MAA)-adducted lung proteins. Lung surfactant protein D (SPD) supports innate immunity via bacterial aggregation and lysis, as well as by enhancing macrophage-binding and phagocytosis. MAA-adducted SPD (SPD-MAA) has negative effects on lung cilia beating, macrophage function, and epithelial cell injury repair. Because changes in SPD multimer structure are known to impact SPD function, we hypothesized that MAA-adduction changes both SPD structure and function. Purified human SPD and SPD-MAA (1 mg/mL) were resolved by gel filtration using Sephadex G-200 and protein concentration of each fraction determined by Bradford assay. Fractions were immobilized onto nitrocellulose by slot blot and assayed by Western blot using antibodies to SPD and to MAA. Binding of SPD and SPD-MAA was determined fluorometrically using GFP-labeled Streptococcus pneumoniae (GFP-SP). Anti-bacterial aggregation of GFP-SP and macrophage bacterial phagocytosis were assayed by microscopy and permeability determined by bacterial phosphatase release. Viral injury was measured as LDH release in RSV-treated airway epithelial cells. Three sizes of SPD were resolved by gel chromatography as monomeric, trimeric, and multimeric forms. SPD multimer was the most prevalent, while the majority of SPD-MAA eluted as trimer and monomer. SPD dose-dependently bound to GFP-SP, but SPD-MAA binding to bacteria was significantly reduced. SPD enhanced, but MAA adduction of SPD prevented, both aggregation and macrophage phagocytosis of GFP-SP. Likewise, SPD increased bacterial permeability while SPD-MAA did not. In the presence of RSV, BEAS-2B cell viability was enhanced by SPD, but not protected by SPD-MAA. Our results demonstrate that MAA adduction changes the quaternary structure of SPD from multimer to trimer and monomer leading to a decrease in the native anti-microbial function of SPD. These findings suggest one mechanism for increased pneumonia observed in alcohol use disorders.

Aldehyde Trapping by ADX-102 Is Protective against Cigarette Smoke and Alcohol Mediated Lung Cell Injury

Most individuals diagnosed with alcohol use disorders smoke cigarettes. Large concentrations of malondialdehyde and acetaldehyde are found in lungs co-exposed to cigarette smoke and alcohol. Aldehydes directly injure lungs and form aldehyde protein adducts, impacting epithelial functions. Recently, 2-(3-Amino-6-chloroquinolin-2-yl)propan-2-ol (ADX-102) was developed as an aldehyde-trapping drug. We hypothesized that aldehyde-trapping compounds are protective against lung injury derived from cigarette smoke and alcohol co-exposure. To test this hypothesis, we pretreated mouse ciliated tracheal epithelial cells with 0-100 µM of ADX-102 followed by co-exposure to 5% cigarette smoke extract and 50 mM of ethanol. Pretreatment with ADX-102 dose-dependently protected against smoke and alcohol induced cilia-slowing, decreases in bronchial epithelial cell wound repair, decreases in epithelial monolayer resistance, and the formation of MAA adducts. ADX-102 concentrations up to 100 µM showed no cellular toxicity. As protein kinase C (PKC) activation is a known mechanism for slowing cilia and wound repair, we examined the effects of ADX-102 on smoke and alcohol induced PKC epsilon activity. ADX-102 prevented early (3 h) activation and late (24 h) autodownregulation of PKC epsilon in response to smoke and alcohol. These data suggest that reactive aldehydes generated from cigarette smoke and alcohol metabolism may be potential targets for therapeutic intervention to reduce lung injury.

Advanced glycation end products (AGEs) and other adducts in aging-related diseases and alcohol-mediated tissue injury

Advanced glycation end products (AGEs) are potentially harmful and heterogeneous molecules derived from nonenzymatic glycation. The pathological implications of AGEs are ascribed to their ability to promote oxidative stress, inflammation, and apoptosis. Recent studies in basic and translational research have revealed the contributing roles of AGEs in the development and progression of various aging-related pathological conditions, such as diabetes, cardiovascular complications, gut microbiome-associated illnesses, liver or neurodegenerative diseases, and cancer. Excessive chronic and/or acute binge consumption of alcohol (ethanol), a widely consumed addictive substance, is known to cause more than 200 diseases, including alcohol use disorder (addiction), alcoholic liver disease, and brain damage. However, despite the considerable amount of research in this area, the underlying molecular mechanisms by which alcohol abuse causes cellular toxicity and organ damage remain to be further characterized. In this review, we first briefly describe the properties of AGEs: their formation, accumulation, and receptor interactions. We then focus on the causative functions of AGEs that impact various aging-related diseases. We also highlight the biological connection of AGE-alcohol-adduct formations to alcohol-mediated tissue injury. Finally, we describe the potential translational research opportunities for treatment of various AGE- and/or alcohol-related adduct-associated disorders according to the mechanistic insights presented.

Second hits exacerbate alcohol-related organ damage: an update

Chronic and excessive alcohol abuse cause direct and indirect detrimental effects on a wide range of body organs and systems and accounts for ~4% of deaths worldwide. Many factors influence the harmful effects of alcohol. This concise review presents newer insights into the role of select second hits in influencing the progression of alcohol-induced organ damage by synergistically acting to generate a more dramatic downstream biological defect. This review specifically addresses on how a lifestyle factor of high fat intake exacerbates alcoholic liver injury and its progression. This review also provides the mechanistic insights into how increasing matrix stiffness during liver injury promotes alcohol-induced fibrogenesis. It also discusses how hepatotropic viral (HCV, HBV) infections as well as HIV (which is traditionally not known to be hepatotropic), are potentiated by alcohol exposure to promote hepatotoxicity and fibrosis progression. Finally, this review highlights the impact of reactive aldehydes generated during alcohol and cigarette smoke coexposure impair innate antimicrobial defense and increased susceptibility to infections. This review was inspired by the symposium held at the 17th Congress of the European Society for Biomedical research on Alcoholism in Lille, France entitled 'Second hits in alcohol-related organ damage'.

Dual Substance Use of Electronic Cigarettes and Alcohol

Electronic cigarettes (ECs) are a modern nicotine delivery system that rapidly grew in widespread use, particularly in younger populations. Given the long history of the comorbidity of alcohol and nicotine use, the rising prevalence of ECs raises the question as to their role in the consumption of alcohol. Of the numerous models of ECs available, JUUL is the most popular. This narrative review aims to determine current trends in literature regarding the relationship between EC and alcohol dual use, as well as hypothesize potential pathogenic tissue damage and summarize areas for future study, including second-hand vapor exposure and calling for standardization among studies. In summary, EC users are more likely to participate in hazardous drinking and are at higher risk for alcohol use disorder (AUD). We surmise the pathogenic damage of dual use may exhibit an additive effect, particularly in pathogen clearance from the lungs, increased inflammation and decreased immune response, physical damage to epithelial cells, and exacerbation of chronic obstructive pulmonary disease (COPD)-like illnesses. A better understanding of pathogenic damages is critical to understand the risks placed on dual users when exposed to respiratory pathogens, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Dimethylarginine dimethylaminohydrolase (DDAH) overexpression enhances wound repair in airway epithelial cells exposed to agricultural organic dust

OBJECTIVE

Workers exposed to dusts from concentrated animal feeding operations have a high prevalence of pulmonary diseases. These exposures lead to chronic inflammation and aberrant airway remodeling. Previous work shows that activating cAMP-dependent protein kinase (PKA) enhances airway epithelial wound repair while activating protein kinase C (PKC) inhibits wound repair. Hog barn dust extracts slow cell migration and wound repair via a PKC-dependent mechanism. Further, blocking nitric oxide (NO) production in bronchial epithelial cells prevents PKA activation. We hypothesized that blocking an endogenous NO inhibitor, asymmetric dimethylarginine, by overexpressing dimethylarginine dimethylaminohydrolase mitigates the effects of hog dust extract on airway epithelial would repair.

MATERIALS/METHODS

We cultured primary tracheal epithelial cells in monolayers from both wild-type (WT) and dimethylarginine dimethylaminohydrolase overexpressing C57Bl/6 (DDAH₁ transgenic) mice and measured wound repair using the electric cell impedance sensing system.

RESULTS

Wound closure in epithelial cells from WT mice occurred within 24 h in vitro. In contrast, treatment of the WT cell monolayers with 5% hog dust extract prevented significant NO-stimulated wound closure. In cells from DDAH₁ transgenic mice, control wounds were repaired up to 8 h earlier than seen in WT mice. A significant enhancement of wound repair was observed in DDAH cells compared to WT cells treated with hog dust extract for 24 h. Likewise, cells from DDAH₁ transgenic mice demonstrated increased NO and PKA activity and decreased hog dust extract-stimulated PKC.

DISCUSSION/CONCLUSION

Preserving the NO signal through endogenous inhibition of asymmetric dimethylarginine enhances wound repair even in the presence of dust exposure.

Cigarette Smoke Impairs A2A Adenosine Receptor Mediated Wound Repair through Up-regulation of Duox-1 Expression

Cigarette smoke (CS) exposure and intrinsic factors such as the NADPH oxidases produce high levels of reactive oxygen species (ROS), ensuing inflammatory tissue injury. We previously demonstrated that CS-generated ROS, particularly hydrogen peroxide (H2O2), impaired adenosine stimulated wound repair. We hypothesized that CS exposure modulates expression of Dual oxidase 1 (Duox-1), a NADPH oxidases known to generate H2O2. To test this hypothesis, we used human bronchial epithelial cell line Nuli-1 and C57BL/6 mice. Cells were treated with 5% CS extract (CSE) for various periods of time, and mice were exposed to whole body CS for six weeks. Both CSE and CS treatment induced increased expression of Duox-1, and silencing of Doux-1 improved the rate of cell wound repair induced by CSE treatment. Nuli-1 cells pretreated with thapsigargin but not calcium ionophore exhibited increased Duox-1 mRNA expression. CSE treatment stimulated PKCα activation, which was effectively blocked by pretreatment with diphenylene iodonium, a NADPH oxidase inhibitor. Compared to control, lungs from CS-exposed mice showed a significant increase in PKCα activity and Duox-1 expression. Collectively, the data demonstrated that CS exposure upregulates expression of Duox-1 protein. This further leads to H2O2 production and PKCα activation, inhibiting A2AAR-stimulated wound repair.

Malondialdehyde-acetaldehyde (MAA) adducted surfactant protein induced lung inflammation is mediated through scavenger receptor a (SR-A1)

Background

Co-exposure to cigarette smoke and alcohol leads to the generation of high concentrations of acetaldehyde and malondialdehyde in the lung. These aldehydes being highly electrophilic in nature react with biologically relevant proteins such as surfactant protein D (SPD) through a Schiff base reaction to generate SPD adducted malondialdehyde-acetaldehyde adduct (SPD-MAA) in mouse lung. SPD-MAA results in an increase in lung pro-inflammatory chemokine, keratinocyte chemoattractant (KC), and the recruitment of lung lavage neutrophils. Previous in vitro studies in bronchial epithelial cells and macrophages show that scavenger receptor A (SR-A1/CD204) is a major receptor for SPD-MAA. No studies have yet examined the in vivo role of SR-A1 in MAA-mediated lung inflammation. Therefore, we hypothesize that in the absence of SR-A1, MAA-induced inflammation in the lung is reduced or diminished.

Methods

To test this hypothesis, C57BL/6 WT and SR-A1 KO mice were nasally instilled with 50 μg/mL of SPD-MAA for 3 weeks (wks). After 3 weeks, bronchoalveolar lavage (BAL) fluid was collected and assayed for a total cell count, a differential cell count and CXCL1 (KC) chemokine. Lung tissue sections were stained with hematoxylin and eosin (H&E) and antibodies to MAA adduct.

Results

Results showed that BAL cellularity and influx of neutrophils were decreased in SR-A1 KO mice as compared to WT following repetitive SPD-MAA exposure. MAA adduct staining in the lung epithelium was decreased in SR-A1 KO mice. In comparison to WT, no increase in CXCL1 was observed in BAL fluid from SR-A1 KO mice over time.

Conclusions

Overall, the data demonstrate that SR-A1/CD204 plays an important role in SPD-MAA induced inflammation in lung.

Malondialdehyde Epitopes as Targets of Immunity and the Implications for Atherosclerosis

Accumulating evidence suggests that oxidation-specific epitopes (OSEs) constitute a novel class of damage-associated molecular patterns (DAMPs) generated during high oxidative stress but also in the physiological process of apoptosis. To deal with the potentially harmful consequences of such epitopes, the immune system has developed several mechanisms to protect from OSEs and to orchestrate their clearance, including IgM natural antibodies and both cellular- and membrane-bound receptors. Here, we focus on malondialdehyde (MDA) epitopes as prominent examples of OSEs that trigger both innate and adaptive immune responses. First, we review the mechanisms of MDA generation, the different types of adducts on various biomolecules and provide relevant examples for physiological carriers of MDA such as apoptotic cells, microvesicles, or oxidized low-density lipoproteins. Based on recent insights, we argue that MDA epitopes contribute to the maintenance of homeostatic functions by acting as markers of elevated oxidative stress and tissue damage. We discuss multiple lines of evidence that MDA epitopes are proinflammatory and thus important targets of innate and adaptive immune responses. Finally, we illustrate the relevance of MDA epitopes in human pathologies by describing their capacity to drive inflammatory processes in atherosclerosis and highlighting protective mechanisms of immunity that could be exploited for therapeutic purposes.

Aldehyde-modified proteins as mediators of early inflammation in atherosclerotic disease

Inflammation is widely accepted to play a major role in atherosclerosis and other cardiovascular diseases. However, the exact mechanism(s) by which inflammation exerts its pathogenic effect remains poorly understood. A number of oxidatively modified proteins have been associated with cardiovascular disease. Recently, attention has been given to the oxidative compound of malondialdehyde and acetaldehyde, two reactive aldehydes known to covalently bind and adduct macromolecules. These products have been shown to form stable malondialdehyde-acetaldehyde (MAA) adducts that are reactive and induce immune responses. These adducts have been found in inflamed and diseased cardiovascular tissue of patients. Antibodies to these adducted proteins are measurable in the serum of diseased patients. The isotypes involved in the immune response to MAA (i.e., IgM, IgG, and IgA) are predictive of atherosclerotic disease progression and cardiovascular events such as an acute myocardial infarction or coronary artery bypass grafting. Therefore, it is the purpose of this article to review the past and current knowledge of aldehyde-modified proteins and their role in cardiovascular disease.

Alcohol, Aldehydes, Adducts and Airways

Drinking alcohol and smoking cigarettes results in the formation of reactive aldehydes in the lung, which are capable of forming adducts with several proteins and DNA. Acetaldehyde and malondialdehyde are the major aldehydes generated in high levels in the lung of subjects with alcohol use disorder who smoke cigarettes. In addition to the above aldehydes, several other aldehydes like 4-hydroxynonenal, formaldehyde and acrolein are also detected in the lung due to exposure to toxic gases, vapors and chemicals. These aldehydes react with nucleophilic targets in cells such as DNA, lipids and proteins to form both stable and unstable adducts. This adduction may disturb cellular functions as well as damage proteins, nucleic acids and lipids. Among several adducts formed in the lung, malondialdehyde DNA (MDA-DNA) adduct and hybrid malondialdehyde-acetaldehyde (MAA) protein adducts have been shown to initiate several pathological conditions in the lung. MDA-DNA adducts are pre-mutagenic in mammalian cells and induce frame shift and base-pair substitution mutations, whereas MAA protein adducts have been shown to induce inflammation and inhibit wound healing. This review provides an insight into different reactive aldehyde adducts and their role in the pathogenesis of lung disease.

Pattern recognition scavenger receptor A/CD204 regulates airway inflammatory homeostasis following organic dust extract exposures

Exposure to agriculture organic dusts, comprised of a diversity of pathogen-associated molecular patterns, results in chronic airway diseases. The multi-functional class A macrophage scavenger receptor (SRA)/CD204 has emerged as an important class of pattern recognition receptors with broad ligand binding ability. The objective was to determine the role of SRA in mediating repetitive and post-inflammatory organic dust extract (ODE)-induced airway inflammation. Wild-type (WT) and SRA knockout (KO) mice were intra-nasally treated with ODE or saline daily for 3 weeks and immediately euthanized or allowed to recover for 1 week. Results show that lung histopathologic changes were increased in SRA KO mice as compared to WT following repetitive ODE exposures marked predominately by increased size and distribution of lymphoid aggregates. After a 1-week recovery from daily ODE treatments, there was significant resolution of lung injury in WT mice, but not SRA KO animals. The increased lung histopathology induced by ODE treatment was associated with decreased accumulation of neutrophils, but greater accumulation of CD4(+) T-cells. The lung cytokine milieu induced by ODE was consistent with a TH1/TH17 polarization in both WT and SRA KO mice. Overall, the data demonstrate that SRA/CD204 plays an important role in the normative inflammatory lung response to ODE, as evidenced by the enhanced dust-mediated injury viewed in the absence of this receptor.

Protective role of CYP2E1 inhibitor diallyl disulfide (DADS) on alcohol-induced malondialdehyde-deoxyguanosine (M1dG) adduct formation

BACKGROUND

Alcohol use disorders are often associated with lung disease. Alcohol exposure leads to the production of reactive oxygen species, lipid peroxidation, and formation of malondialdehyde (MDA) as well as to induce the expression of cytochrome p450 2E1 (CYP2E1). Likewise, cigarette smoking can lead to lung lipid peroxidation and formation of MDA. MDA can bind to DNA forming MDA-deoxyguanosine (M1dG) adducts, which have been implicated in alcohol-related cancers and cardiovascular disease. Because CYP2E1 regulates MDA production, and our previous studies have shown that alcohol and cigarette smoke can lead to MDA formation, we hypothesized that CYP2E1 would modulate M1dG adduct formation and single-strand DNA damage in alcohol- and cigarette smoke-exposed lung cells and tissue.

METHODS

Normal human bronchial epithelial cells (HBECs) were pretreated with 10 μM diallyl disulfide (DADS) for 1 hour and treated with 80 mM ethanol (EtOH) ± 5% cigarette smoke extract (CSE) for 3 hours for comet assay and 6 hours for CYP2E1, MDA, and M1dG adduct assays. C57BL/6 mice were administered 20% EtOH ad libitum in drinking water for 8 weeks and exposed to whole-body cigarette smoke for 5 weeks. Mice were also fed a CYP2E1 inhibitor, DADS, at 1 μM/g of feed in their daily diet for 7 weeks. Whole lung tissue homogenate was used for CYP2E1, MDA, and M1dG adduct assays.

RESULTS

EtOH exposure significantly increased HBEC olive tail moment. DADS pretreatment of HBECs attenuated this EtOH effect. EtOH also induced MDA and M1dG adduct formation, which was also significantly reduced by DADS treatment. CSE ± EtOH did not enhance these effects. In lung tissue homogenate of 8-week alcohol-fed mice, MDA and M1dG adduct levels were significantly elevated in comparison with control mice and mice fed DADS while consuming alcohol. No increase in MDA and M1dG adduct formation was observed in 5-week cigarette smoke-exposed mice.

CONCLUSIONS

These findings suggest that CYP2E1 plays a pivotal role in alcohol-induced M1dG adducts, and the use of DADS as dietary supplement can reverse the effects of alcohol on M1dG formation.

Smoke extract impairs adenosine wound healing: implications of smoke-generated reactive oxygen species

Adenosine concentrations are elevated in the lungs of patients with asthma and chronic obstructive pulmonary disease, where it balances between tissue repair and excessive airway remodeling. We previously demonstrated that the activation of the adenosine A2A receptor promotes epithelial wound closure. However, the mechanism by which adenosine-mediated wound healing occurs after cigarette smoke exposure has not been investigated. The present study investigates whether cigarette smoke exposure alters adenosine-mediated reparative properties via its ability to induce a shift in the oxidant/antioxidant balance. Using an in vitro wounding model, bronchial epithelial cells were exposed to 5% cigarette smoke extract, were wounded, and were then stimulated with either 10 μM adenosine or the specific A2A receptor agonist, 5'-(N-cyclopropyl)-carboxamido-adenosine (CPCA; 10 μM), and assessed for wound closure. In a subset of experiments, bronchial epithelial cells were infected with adenovirus vectors encoding human superoxide dismutase and/or catalase or control vector. In the presence of 5% smoke extract, significant delay was evident in both adenosine-mediated and CPCA-mediated wound closure. However, cells pretreated with N-acetylcysteine (NAC), a nonspecific antioxidant, reversed smoke extract-mediated inhibition. We found that cells overexpressing mitochondrial catalase repealed the smoke extract inhibition of CPCA-stimulated wound closure, whereas superoxide dismutase overexpression exerted no effect. Kinase experiments revealed that smoke extract significantly reduced the A2A-mediated activation of cyclic adenosine monophosphate-dependent protein kinase. However, pretreatment with NAC reversed this effect. In conclusion, our data suggest that cigarette smoke exposure impairs A2A-stimulated wound repair via a reactive oxygen species-dependent mechanism, thereby providing a better understanding of adenosine signaling that may direct the development of pharmacological tools for the treatment of chronic inflammatory lung disorders.

Acetaldehyde disrupts tight junctions in Caco-2 cell monolayers by a protein phosphatase 2A-dependent mechanism

Acetaldehyde is accumulated at high concentrations in the colonic lumen following ethanol administration. Previous studies demonstrated that acetaldehyde disrupts intestinal epithelial tight junctions and increases paracellular permeability. In the present study, we investigated the role of PP2A in the acetaldehyde-induced disruption of intestinal epithelial tight junctions. Caco-2 cell monolayers were exposed to 200-600 μM acetaldehyde for varying times, and the epithelial barrier function was evaluated by measuring transepithelial electrical resistance and inulin permeability. Acetaldehyde treatment resulted in a time-dependent increase in inulin permeability and redistribution of occludin and ZO-1 from the intercellular junctions. Treatment of cells with fostriecin (a PP2A-selective inhibitor) or knockdown of PP2A by siRNA blocked acetaldehyde-induced increase in inulin permeability and redistribution of occludin and ZO-1. The effects of fostriecin and acetaldehyde were confirmed in mouse intestine ex vivo. Acetaldehyde-induced tight junction disruption and barrier dysfunction were also attenuated by a PP2A-specific inhibitory peptide, TPDYFL. Coimmunoprecipitation studies showed that acetaldehyde increased the interaction of PP2A with occludin and induced dephosphorylation of occludin on threonine residues. Fostriecin and TPDYFL significantly reduced acetaldehyde-induced threonine dephosphorylation of occludin. Acetaldehyde failed to change the level of the methylated form of PP2A-C subunit. However, genistein (a tyrosine kinase inhibitor) blocked acetaldehyde-induced association of PP2A with occludin and threonine dephosphorylation of occludin. These results demonstrate that acetaldehyde-induced disruption of tight junctions is mediated by PP2A translocation to tight junctions and dephosphorylation of occludin on threonine residues.

Knowledge translation: airway epithelial cell migration and respiratory diseases

Airway epithelial cell migration is essential for lung development and growth, as well as the maintenance of respiratory tissue integrity. This vital cellular process is also important for the repair and regeneration of damaged airway epithelium. More importantly, several lung diseases characterized by aberrant tissue remodeling result from the improper repair of damaged respiratory tissue. Epithelial cell migration relies upon extracellular matrix molecules and is further regulated by numerous local, neuronal, and hormonal factors. Under inflammatory conditions, cell migration can also be stimulated by certain cytokines and chemokines. Many well-known environmental factors involved in the pathogenesis of chronic lung diseases (e.g., cigarette smoking, air pollution, alcohol intake, inflammation, viral and bacterial infections) can inhibit airway epithelial cell migration. Further investigation of cellular and molecular mechanisms of cell migration with advanced techniques may provide knowledge that is relevant to physiological and pathological conditions. These studies may eventually lead to the development of therapeutic interventions to improve lung repair and regeneration and to prevent aberrant remodeling in the lung.

Co-exposure to cigarette smoke and alcohol decreases airway epithelial cell cilia beating in a protein kinase Cε-dependent manner

Alcohol use disorders are associated with increased lung infections and exacerbations of chronic lung diseases. Whereas the effects of cigarette smoke are well recognized, the interplay of smoke and alcohol in modulating lung diseases is not clear. Because innate lung defense is mechanically maintained by airway cilia action and protein kinase C (PKC)-activating agents slow ciliary beat frequency (CBF), we hypothesized that the combination of smoke and alcohol would decrease CBF in a PKC-dependent manner. Primary ciliated bronchial epithelial cells were exposed to 5% cigarette smoke extract plus100 mmol/L ethanol for up to 24 hours and assayed for CBF and PKCε. Smoke and alcohol co-exposure activated PKCε by 1 hour and decreased both CBF and total number of beating cilia by 6 hours. A specific activator of PKCε, DCP-LA, slowed CBF after maximal PKCε activation. Interestingly, activation of PKCε by smoke and alcohol was only observed in ciliated cells, not basal bronchial epithelium. In precision-cut mouse lung slices treated with smoke and alcohol, PKCε activation preceded CBF slowing. Correspondingly, increased PKCε activity and cilia slowing were only observed in mice co-exposed to smoke and alcohol, regardless of the sequence of the combination exposure. No decreases in CBF were observed in PKCε knockout mice co-exposed to smoke and alcohol. These data identify PKCε as a key regulator of cilia slowing in response to combined smoke and alcohol-induced lung injury.

Malondialdehyde-acetaldehyde-adducted protein inhalation causes lung injury

In addition to cigarette smoking, alcohol exposure is also associated with increased lung infections and decreased mucociliary clearance. However, little research has been conducted on the combination effects of alcohol and cigarette smoke on lungs. Previously, we have demonstrated in a mouse model that the combination of cigarette smoke and alcohol exposure results in the formation of a very stable hybrid malondialdehyde-acetaldehyde (MAA)-adducted protein in the lung. In in vitro studies, MAA-adducted protein stimulates bronchial epithelial cell interleukin-8 (IL-8) via the activation of protein kinase C epsilon (PKCɛ). We hypothesized that direct MAA-adducted protein exposure in the lungs would mimic such a combination of smoke and alcohol exposure leading to airway inflammation. To test this hypothesis, C57BL/6J female mice were intranasally instilled with either saline, 30μL of 50μg/mL bovine serum albumin (BSA)-MAA, or unadducted BSA for up to 3 weeks. Likewise, human lung surfactant proteins A and D (SPA and SPD) were purified from human pulmonary proteinosis lung lavage fluid and successfully MAA-adducted in vitro. Similar to BSA-MAA, SPD-MAA was instilled into mouse lungs. Lungs were necropsied and assayed for histopathology, PKCɛ activation, and lung lavage chemokines. In control mice instilled with saline, normal lungs had few inflammatory cells. No significant effects were observed in unadducted BSA- or SPD-instilled mice. However, when mice were instilled with BSA-MAA or SPD-MAA for 3 weeks, a significant peribronchiolar localization of inflammatory cells was observed. Both BSA-MAA and SPD-MAA stimulated increased lung lavage neutrophils and caused a significant elevation in the chemokine, keratinocyte chemokine, which is a functional homologue to human IL-8. Likewise, MAA-adducted protein stimulated the activation of airway and lung slice PKCɛ. These data support that the MAA-adducted protein induces a proinflammatory response in the lungs and that the lung surfactant protein is a biologically relevant target for malondialdehyde and acetaldehyde adduction. These data further implicate MAA-adduct formation as a potential mechanism for smoke- and alcohol-induced lung injury.

Hybrid malondialdehyde and acetaldehyde protein adducts form in the lungs of mice exposed to alcohol and cigarette smoke

BACKGROUND

Most alcohol abusers smoke cigarettes and approximately half of all cigarette smokers consume alcohol. However, no animal models of cigarette and alcohol co-exposure exist to examine reactive aldehydes in the lungs. Cigarette smoking results in elevated lung acetaldehyde (AA) and malondialdehyde (MDA) levels. Likewise, alcohol metabolism produces AA via the action of alcohol dehydrogenase and MDA via lipid peroxidation. A high concentration of AA and MDA form stable hybrid protein adducts known as malondialdehyde-acetaldehyde (MAA) adducts. We hypothesized that chronic cigarette smoke and alcohol exposure in an in vivo mouse model would result in the in vivo formation of MAA adducts.

METHODS

We fed C57BL/6 mice ad libitum ethanol (20%) in drinking water and exposed them to whole-body cigarette smoke 2 h/d, 5 d/wk for 6 weeks. Bronchoalveolar lavage fluid and lung homogenates were assayed for AA, MDA, and MAA adduct concentrations. MAA-adducted proteins were identified by Western blot and ELISA.

RESULTS

Smoke and alcohol exposure alone elevated both AA and MDA, but only the combination of smoke+alcohol generated protein-adducting concentrations of AA and MDA. MAA-adducted protein (~500 ng/ml) was significantly elevated in the smoke+alcohol-exposed mice. Of the 5 MAA-adducted proteins identified by Western blot, 1 protein band immunoprecipitated with antibodies to surfactant protein D. Similar to in vitro PKC stimulation by purified MAA-adducted protein, protein kinase C (PKC) epsilon was activated only in tracheal epithelial extracts from smoke- and alcohol-exposed mice.

CONCLUSIONS

These data demonstrate that only the combination of cigarette smoke exposure and alcohol feeding in mice results in the generation of significant AA and MDA concentrations, the formation of MAA-adducted protein, and the activation of airway epithelial PKC epsilon in the lung.

Hog barn dust slows airway epithelial cell migration in vitro through a PKCalpha-dependent mechanism

Agricultural work and other occupational exposures are responsible for approximately 15% of chronic obstructive pulmonary disease (COPD). COPD involves airway remodeling in response to chronic lung inflammatory events and altered airway repair mechanisms. However, the effect of agricultural dust exposure on signaling pathways that regulate airway injury and repair has not been well characterized. A key step in this process is migration of airway cells to restore epithelial integrity. We have previously shown that agents that activate the critical regulatory enzyme protein kinase C (PKC) slow cell migration during wound repair. Based on this observation and direct kinase measurements that demonstrate that dust extract from hog confinement barns (HDE) specifically activates the PKC isoforms PKCalpha and PKCepsilon, we hypothesized that HDE would slow wound closure time in airway epithelial cells. We utilized the human bronchial epithelial cell line BEAS-2B and transfected BEAS-2B cell lines that express dominant negative (DN) forms of PKC isoforms to demonstrate that HDE slows wound closure in BEAS-2B and PKCepsilon DN cell lines. However, in PKCalpha DN cells, wound closure following HDE treatment is not significantly different than media-treated cells. These results suggest that the PKCalpha isoform is an important regulator of cell migration in response to agricultural dust exposure.

Scavenger receptor class-A is a novel cell surface receptor for double-stranded RNA

Double-stranded RNA (dsRNA) is a potent signal to the host immune system for the presence of an ongoing viral infection. The presence of dsRNA, intracellularly or extracellularly, leads to the induction of innate inflammatory cytokines in many cell types including epithelial cells. However, the cell surface receptor for recognition of extracellular dsRNA is not yet determined. Here, we report that extracellular dsRNA is recognized and internalized by scavenger receptor class-A (SR-A). Treatment of human epithelial cells with specific antagonists of SR-A or with an anti-SR-A antibody significantly inhibited dsRNA induction of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-8, and regulated on activation normal T-cell expressed and secreted (RANTES). Furthermore, intranasal dsRNA treatment of SR-A-deficient (SR-A(-/-)) mice showed a significant decrease in the expression of inflammatory cytokines and a corresponding decrease in the accumulation of polymorphonuclear leukocytes (PMNs) in lungs. These data provide direct evidence that SR-A is a novel cell surface receptor for dsRNA, and therefore, SR-A may play a role in antiviral immune responses.

Adenosine A2A receptors promote adenosine-stimulated wound healing in bronchial epithelial cells

Adenosine produces a wide variety of physiological effects through the activation of specific adenosine receptors (A(1), A(2A), A(2B), A(3)). Adenosine, acting particularly at the A(2A) adenosine receptor (A(2A)AR), is a potent endogenous anti-inflammatory agent and sensor of inflammatory tissue damage. The complete healing of wounds is the final step in a highly regulated response to injury. Recent studies on epidermal wounds have identified the A(2A)AR as the main adenosine receptor responsible for altering the kinetics of wound closure. We hypothesized that A(2A)AR promotes wound healing in bronchial epithelial cells (BECs). To test this hypothesis, the human BEC line BEAS-2B and bovine BECs (BBECs) were used. Real-time RT-PCR of RNA from unstimulated BEAS-2B cells revealed transcriptional expression of A(1), A(2A), A(2B) and A(3) receptors. Western blot analysis of lysates from BEAS-2B cells and BBECs detected a single band at 44.7 kDa in both the BECs, indicating the presence of A(2A)AR. In a wound healing model, we found that adenosine stimulated wound repair in cultured BBECs in a concentration-dependent manner, with an optimal closure rate observed between 4 and 6 h. Similarly, the A(2A)AR agonist 5'-(N-cyclopropyl)carboxamidoadenosine (CPCA) augmented wound closure, with a maximal closure rate occurring between 4 and 6 h. Inhibition of A(2A)AR with ZM-241385, a known A(2A)AR antagonist, impeded wound healing. In addition, ZM-241385 also attenuated adenosine-mediated wound repair. Kinase studies revealed that adenosine-stimulated airway repair activates PKA by ligating A(2A)AR. Collectively, the data suggest that the A(2A)AR is involved in BEC adenosine-stimulated wound healing and may prove useful in understanding purinergic-mediated actions on airway epithelial repair.