The tobacco smoke component, acrolein, suppresses innate macrophage responses by direct alkylation of c-Jun N-terminal kinase

Acrolein produced by glioma cells under hypoxia inhibits neutrophil AKT activity and suppresses anti-tumoral activities

Acrolein, which is the most reactive aldehyde, is a byproduct of lipid peroxidation in a hypoxic environment. Acrolein has been shown to form acrolein-cysteine bonds, resulting in functional changes in proteins and immune effector cell suppression. Neutrophils are the most abundant immune effector cells in circulation in humans. In the tumor microenvironment, proinflammatory tumor-associated neutrophils (TANs), which are termed N1 neutrophils, exert antitumor effects via the secretion of cytokines, while anti-inflammatory neutrophils (N2 neutrophils) support tumor growth. Glioma is characterized by significant tissue hypoxia, immune cell infiltration, and a highly immunosuppressive microenvironment. In glioma, neutrophils exert antitumor effects early in tumor development but gradually shift to a tumor-supporting role as the tumor develops. However, the mechanism of this anti-to protumoral switch in TANs remains unclear. In this study, we found that the production of acrolein in glioma cells under hypoxic conditions inhibited neutrophil activation and induced an anti-inflammatory phenotype by directly reacting with Cys310 of AKT and inhibiting AKT activity. A higher percentage of cells expressing acrolein adducts in tumor tissue are associated with poorer prognosis in glioblastoma patients. Furthermore, high-grade glioma patients have increased serum acrolein levels and impaired neutrophil functions. These results suggest that acrolein suppresses neutrophil function and contributes to the switch in the neutrophil phenotype in glioma.

The Tobacco Smoke Component, Acrolein, as a Major Culprit in Lung Diseases and Respiratory Cancers: Molecular Mechanisms of Acrolein Cytotoxic Activity

Acrolein, a highly reactive unsaturated aldehyde, is a ubiquitous environmental pollutant that seriously threatens human health and life. Due to its high reactivity, cytotoxicity and genotoxicity, acrolein is involved in the development of several diseases, including multiple sclerosis, neurodegenerative diseases such as Alzheimer’s disease, cardiovascular and respiratory diseases, diabetes mellitus and even the development of cancer. Traditional tobacco smokers and e-cigarette users are particularly exposed to the harmful effects of acrolein. High concentrations of acrolein have been found in both mainstream and side-stream tobacco smoke. Acrolein is considered one of cigarette smoke’s most toxic and harmful components. Chronic exposure to acrolein through cigarette smoke has been linked to the development of asthma, acute lung injury, chronic obstructive pulmonary disease (COPD) and even respiratory cancers. This review addresses the current state of knowledge on the pathological molecular mechanisms of acrolein in the induction, course and development of lung diseases and cancers in smokers.

Origin and Fate of Acrolein in Foods

Acrolein is a highly toxic agent that may promote the occurrence and development of various diseases. Acrolein is pervasive in all kinds of foods, and dietary intake is one of the main routes of human exposure to acrolein. Considering that acrolein is substantially eliminated after its formation during food processing and re-exposed in the human body after ingestion and metabolism, the origin and fate of acrolein must be traced in food. Focusing on molecular mechanisms, this review introduces the formation of acrolein in food and summarises both in vitro and in vivo fates of acrolein based on its interactions with small molecules and biomacromolecules. Future investigation of acrolein from different perspectives is also discussed.

Acid-Catalyzed Isomerization of Carbonyls-2,4- dinitrophenylhydrazone in Mainstream Smoke of Heat-Not-Burn Tobacco Product for HPLC Analysis

Carbonyls (such as acrolein, acetaldehyde, and formaldehyde) are the critical type of carcinogens and toxicants contained within the heat-not-burn (HNB) tobacco products. Using HNB products can have negative effects on human health; therefore, it is important to measure carbonyl contents within the HNB mainstream smoke. Typically, the 2,4-dinitrophenylhydrazine (DNPH) approach involves forming the 2,4-dinitrophenylhydrazone derivatives, which is the most extensively adopted approach to qualitatively and quantitatively analyze carbonyl compounds. However, the approach can result in analytical error because 2,4-dinitrophenylhydrazones contains the E-stereoisomer as well as the Z-stereoisomer. Only an E-isomers exists in the purified carbonyls-2,4-dinitrophenylhydrazone, but when acid is added, the E-isomer and Z-isomer can be observed. For propionaldehyde-, acetaldehyde-, crotonaldehyde-, acrolein-, and 2-butanone-2,4-dinitrophenylhydrazones, their equilibrium Z/E isomer ratios are 0.143, 0.309, 0.093, 0.028, and 0.154. In the case of adding trace water into hydrazone derivatives dissolved within the acetonitrile solution, the derivative contents decrease, whereas the free DNPH content increases. Therefore, catalytic acid should be added in the low content. To determine carbonyls-2,4-dinitrophenylhydrazones through HPLC, the optimal approach is adding phosphoric acid into the samples and the standard reference solution to form the 0.02–1.0% acid solution.

Redox Dysregulation in Aging and COPD: Role of NOX Enzymes and Implications for Antioxidant Strategies

With a rapidly growing elderly human population, the incidence of age-related lung diseases such as chronic obstructive pulmonary disease (COPD) continues to rise. It is widely believed that reactive oxygen species (ROS) play an important role in ageing and in age-related disease, and approaches of antioxidant supplementation have been touted as useful strategies to mitigate age-related disease progression, although success of such strategies has been very limited to date. Involvement of ROS in ageing is largely attributed to mitochondrial dysfunction and impaired adaptive antioxidant responses. NADPH oxidase (NOX) enzymes represent an important enzyme family that generates ROS in a regulated fashion for purposes of oxidative host defense and redox-based signalling, however, the associations of NOX enzymes with lung ageing or age-related lung disease have to date only been minimally addressed. The present review will focus on our current understanding of the impact of ageing on NOX biology and its consequences for age-related lung disease, particularly COPD, and will also discuss the implications of altered NOX biology for current and future antioxidant-based strategies aimed at treating these diseases.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Preventive effect of Nigella sativa on M1/M2 ratio, reducing risk of endothelial dysfunction in cigarette smoked Wistars

Background: Smoking is one of the top three causes of cardiovascular disease (CVD). Natural antioxidants including black cumin ( Nigella sativa) may inhibit the pathogenesis of initial process of atherosclerosis. The aim of this study was to determine the effect of black cumin (Nigella sativa) in preventing endothelial dysfunction mainly through macrophage M1/M2 inflammatory response in cigarette smoked male Wistars. Methods: In total, 50 Wistar rats were randomly allocated to five experimental groups: two control groups, namely no intervention (K-) and exposure to smoke of 40 cigarettes each day (K+); and three treatment groups: rats given a dose of 0.3 g (P1), 0.6 g (P2) or 1.2 g (P3) black cumin per kilograms bodyweight/ day, respectively, and exposed to smoke of 40 cigarettes each day. After 28 days of cigarette smoke exposure, macrophage M1/M2 ratio was evaluated by counting total M1 and M2 in ten microscope field of view. Data were analysed by Mann-Whitney test. Results: The M1 / ​​M2 ratio on K (-) was 0.9 7 ± 0.9 8 (<1) which means M2 was dominant, while the M1 / ​​M2 ratio on K (+) was of 4.97 ± 3.42 (> 1) which means M1 dominant. There was no significant difference in the number of M1 count in treatment groups P1, P2, P3 (p value = 0.996; 0.170; 0.884, respectively) when compared with K+. Additionally, P2 group has the lower M1 number with the highest significance value when compared to K+. The number of M1 counts on P1 did not differ significantly when compared to P2 with p = 0.121 and P3 with p = 0.936. Conclusions: In sum, ethanol extract of black cumin prevents endothelial dysfunction by inhibiting increase in macrophages M1 / M2 ratio in rats  Wistar exposed to sub-chronic cigarette smoke.

Tobacco use and neurogenesis: A theoretical review of pathophysiological mechanism affecting the outcome of peripheral nerve regeneration

Peripheral nerve injury often requires medical intervention. Unfortunately, many patients never have a full recovery, despite a multi-disciplinary approach, including operative intervention and physical and/or occupational therapy. Outcomes are multifactorial, but are largely affected by the original injury severity, and patient comorbidities. A lcoholism, diabetes mellitus and ageing may detrimentally affect the outcomes of nerve injury; however little is known about tobacco's potential impact on nerve regeneration. Tobacco has known immunomodulatory effects, which suggests that it might affect peripheral nerve regeneration and functional recovery following injury. This review characterizes the effects of tobacco use on the complex cellular and chemokine interactions in peripheral nerve regeneration.

Acrolein in cigarette smoke attenuates the innate immune responses mediated by surfactant protein D

BACKGROUND

Surfactant proteins (SP) A and D belong to collectin family proteins, which play important roles in innate immune response in the lung. We previously demonstrated that cigarette smoke (CS) increases the acrolein modification of SP-A, thereby impairing the innate immune abilities of this protein. In this study, we focused on the effects of CS and its component, acrolein, on the innate immunity role of another collectin, SP-D.

METHODS

To determine whether aldehyde directly affects SP-D, we examined the lungs of mice exposed to CS for 1 week and detected aldehyde-modified SP-D using an aldehyde reactive probe. The structural changes in CS extract (CSE) or acrolein-exposed recombinant human (h)SP-D were determined by western blot, liquid chromatography-electrospray ionization tandem mass spectrometry, and blue native-polyacrylamide gel electrophoresis analyses. Innate immune functions of SP-D were determined by bacteria growth and macrophage phagocytosis.

RESULTS

Aldehyde-modified SP-D as well as SP-A was detected in the lungs of mice exposed to CS for 1 week. Exposure of hSP-D to CSE or acrolein induced an increased higher-molecular -weight of hSP-D and acrolein induced modification of five lysine residues in hSP-D. These modifications led to disruption of the multimer structure of SP-D and attenuated its ability to inhibit bacterial growth and activate macrophage phagocytosis.

CONCLUSION

CS induced acrolein modification in SP-D, which in turn induced structural and functional defects in SP-D.

GENERAL SIGNIFICANCE

These results suggest that CS-induced structural and functional defects in SP-D contribute to the dysfunction of innate immune responses in the lung following CS exposure.

Smoking-induced iron dysregulation in the lung

Iron is one of the most abundant transition elements and is indispensable for almost all organisms. While the ability of iron to participate in redox chemistry is an essential requirement for participation in a range of vital enzymatic reactions, this same feature of iron also makes it dangerous in the generation of hydroxyl radicals and superoxide anions. Given the high local oxygen tensions in the lung, the regulation of iron acquisition, utilization, and storage therefore becomes vitally important, perhaps more so than in any other biological system. Iron plays a critical role in the biology of essentially every cell type in the lung, and in particular, changes in iron levels have important ramifications on immune function and the local lung microenvironment. There is substantial evidence that cigarette smoke causes iron dysregulation, with the implication that iron may be the link between smoking and smoking-related lung diseases. A better understanding of the connection between cigarette smoke, iron, and respiratory diseases will help to elucidate pathogenic mechanisms and aid in the identification of novel therapeutic targets.

Cigarette Smoking-Mediated Macrophage Reprogramming: Mechanistic Insights and Therapeutic Implications

Macrophages, the mature form of the monocytes, play a significant role in tissue homeostasis and immunity. In response to environmental cues, they can undergo classical or alternative activation, polarizing into specialized functional subsets. A common hallmark of the pathologic environment is represented by cigarette smoking. Although the contribution of cigarette smoke to various cellular processes has been extensively studied, its roles in macrophage polarization have been conflicting. This review discusses the molecular and functional differences of cigarette smoke-exposed macrophages that exist between pro-inflammatory and anti-inflammatory states. We also highlight the most recent advances in therapeutic potential of targeting signaling molecules associated with smoking to modulate macrophage plasticity and polarized activation.

Tuberculosis and cigarette smoke exposure: An update of in vitro and in vivo studies

Tuberculosis (TB) has been declared the first cause of death by an infectious agent. Annually, 10.4 million people suffer active TB. Most infected individuals live in low-income countries, where social and economic conditions enhance the dissemination and progression of the disease. These countries have a high percentage of smokers. Thousands of studies have linked cigarette smoke (CS) with increased risk of many diseases, such as cancer and lung diseases. Numerous in vitro studies have been conducted to evaluate the general and specific toxic effects of CS in lung immune function. Smoke exposure increases the risk of TB development three-fold. However, until now, only few animal studies have been performed to analyze the association between smoke and TB. In the present work, we review in vitro and in vivo studies whose aim was to analyze the molecular basis of TB susceptibility caused by exposure to CS.

Alda-1 Protects Against Acrolein-Induced Acute Lung Injury and Endothelial Barrier Dysfunction

Inhalation of acrolein, a highly reactive aldehyde, causes lung edema. The underlying mechanism is poorly understood and there is no effective treatment. In this study, we demonstrated that acrolein not only dose-dependently induced lung edema but also promoted LPS-induced acute lung injury. Importantly, acrolein-induced lung injury was prevented and rescued by Alda-1, an activator of mitochondrial aldehyde dehydrogenase 2. Acrolein also dose-dependently increased monolayer permeability, disrupted adherens junctions and focal adhesion complexes, and caused intercellular gap formation in primary cultured lung microvascular endothelial cells (LMVECs). These effects were attenuated by Alda-1 and the antioxidant N-acetylcysteine, but not by the NADPH inhibitor apocynin. Furthermore, acrolein inhibited AMP-activated protein kinase (AMPK) and increased mitochondrial reactive oxygen species levels in LMVECs-effects that were associated with impaired mitochondrial respiration. AMPK total protein levels were also reduced in lung tissue of mice and LMVECs exposed to acrolein. Activation of AMPK with 5-aminoimidazole-4-carboxamide-1-β-4-ribofuranoside blunted an acrolein-induced increase in endothelial monolayer permeability, but not mitochondrial oxidative stress or inhibition of mitochondrial respiration. Our results suggest that acrolein-induced mitochondrial dysfunction may not contribute to endothelial barrier dysfunction. We speculate that detoxification of acrolein by Alda-1 and activation of AMPK may be novel approaches to prevent and treat acrolein-associated acute lung injury, which may occur after smoke inhalation.

Disruption of the structural and functional features of surfactant protein A by acrolein in cigarette smoke

The extent to which defective innate immune responses contribute to chronic obstructive pulmonary disease (COPD) is not fully understood. Pulmonary surfactant protein A (SP-A) plays an important role in regulating innate immunity in the lungs. In this study, we hypothesised that cigarette smoke (CS) and its component acrolein might influence pulmonary innate immunity by affecting the function of SP-A. Indeed, acrolein-modified SP-A was detected in the lungs of mice exposed to CS for 1 week. To further confirm this finding, recombinant human SP-A (hSP-A) was incubated with CS extract (CSE) or acrolein and then analysed by western blotting and nanoscale liquid chromatography-matrix-assisted laser desorption/ionisation time-of-flight tandem mass spectrometry. These analyses revealed that CSE and acrolein induced hSP-A oligomerisation and that acrolein induced the modification of six residues in hSP-A: His39, His116, Cys155, Lys180, Lys221, and Cys224. These modifications had significant effects on the innate immune functions of hSP-A. CSE- or acrolein-induced modification of hSP-A significantly decreased hSP-A's ability to inhibit bacterial growth and to enhance macrophage phagocytosis. These findings suggest that CS-induced structural and functional defects in SP-A contribute to the dysfunctional innate immune responses observed in the lung during cigarette smoking.

Acrolein enhances epigenetic modifications, FasL expression and hepatocyte toxicity induced by anti-HIV drug Zidovudine

Zidovudine (AZT) remains the mainstay of antiretroviral therapy against HIV in resource-poor countries; however, its use is frequently associated with hepatotoxicity. Not all HIV patients on AZT develop hepatotoxicity, and the determining factors are unclear. Alcohol consumption and cigarette smoking are known risk factors for HIV hepatotoxicity, and both are significant sources of acrolein, a highly reactive and toxic aldehyde. This study examines the potential hepatotoxic interactions between acrolein and AZT. Our data demonstrate that acrolein markedly enhanced AZT-induced transcriptionally permissive histone modifications (H3K9Ac and H3K9Me3) allowing the recruitment of transcription factor NF-kB and RNA polymerase II at the FasL gene promoter, resulting in FasL upregulation and apoptosis in hepatocytes. Notably, the acrolein scavenger, hydralazine prevented these promoter-associated epigenetic changes and inhibited FasL upregulation and apoptosis induced by the combination of AZT and acrolein, as well as AZT alone. Our data strongly suggest that acrolein enhancement of promoter histone modifications and FasL upregulation are major pathogenic mechanisms driving AZT-induced hepatotoxicity. Moreover, these data also indicate the therapeutic potential of hydralazine in mitigating AZT hepatotoxicity.

Adverse outcome pathway development from protein alkylation to liver fibrosis

In modern toxicology, substantial efforts are undertaken to develop alternative solutions for in vivo toxicity testing. The adverse outcome pathway (AOP) concept could facilitate knowledge-based safety assessment of chemicals that does not rely exclusively on in vivo toxicity testing. The construction of an AOP is based on understanding toxicological processes at different levels of biological organisation. Here, we present the developed AOP for liver fibrosis and demonstrate a linkage between hepatic injury caused by chemical protein alkylation and the formation of liver fibrosis, supported by coherent and consistent scientific data. This long-term process, in which inflammation, tissue destruction, and repair occur simultaneously, results from the complex interplay between various hepatic cell types, receptors, and signalling pathways. Due to the complexity of the process, an adequate liver fibrosis cell model for in vitro evaluation of a chemical's fibrogenic potential is not yet available. Liver fibrosis poses an important human health issue that is also relevant for regulatory purposes. An AOP described with enough mechanistic detail might support chemical risk assessment by indicating early markers for downstream events and thus facilitating the development of an in vitro testing strategy. With this work, we demonstrate how the AOP framework can support the assembly and coherent display of distributed mechanistic information from the literature to support the use of alternative approaches for prediction of toxicity. This AOP was developed according to the guidance document on developing and assessing AOPs and its supplement, the users' handbook, issued by the Organisation for Economic Co-operation and Development.

Cigarette smoke represses the innate immune response to asbestos

Both cigarette smoke (CS) and asbestos cause lung inflammation and lung cancer, and at high asbestos exposure levels, populations exposed to both of these carcinogens display a synergistic increase in the development of lung cancer. The mechanisms through which these two toxic agents interact to promote lung tumorigenesis are poorly understood. Here, we begin to dissect the inflammatory signals induced by asbestos in combination with CS using a rodent inhalation model and in vitro cell culture. Wild‐type C57BL/6 mice were exposed to room air as a control, CS, and/or asbestos (4 days per week to CS and 1 day per week to asbestos for 5 weeks). Bronchoalveolar lavage (BAL) fluid was collected following exposure and analyzed for inflammatory mediators. Asbestos‐exposed mice displayed an increased innate immune response consistent with NLRP3 inflammasome activation. Compared to mice exposed only to asbestos, animals coexposed to CS + asbestos displayed attenuated levels of innate immune mediators and altered inflammatory cell recruitment. Histopathological changes in CS + asbestos‐exposed mice correlated with attenuated fibroproliferative lesion development relative to their counterparts exposed only to asbestos. In vitro experiments using a human monocyte cell line (THP‐1 cells) supported the in vivo results in that coexposure to cigarette smoke extract repressed NLRP3 inflammasome markers in cells treated with asbestos. These observations indicate that CS represses central components of the innate immune response to inhaled asbestos.

Airway epithelial dual oxidase 1 mediates allergen-induced IL-33 secretion and activation of type 2 immune responses

BACKGROUND

The IL-1 family member IL-33 plays a critical role in type 2 innate immune responses to allergens and is an important mediator of allergic asthma. The mechanisms by which allergens provoke epithelial IL-33 secretion are still poorly understood.

OBJECTIVE

Based on previous findings indicating involvement of the NADPH oxidase dual oxidase 1 (DUOX1) in epithelial wound responses, we explored the potential involvement of DUOX1 in allergen-induced IL-33 secretion and potential alterations in airways of asthmatic patients.

METHODS

Cultured human or murine airway epithelial cells or mice were subjected to acute challenge with Alternaria alternata or house dust mite, and secretion of IL-33 and activation of subsequent type 2 responses were determined. The role of DUOX1 was explored by using small interfering RNA approaches and DUOX1-deficient mice. Cultured nasal epithelial cells from healthy subjects or asthmatic patients were evaluated for DUOX1 expression and allergen-induced responses.

RESULTS

In vitro or in vivo allergen challenge resulted in rapid airway epithelial IL-33 secretion, which depended critically on DUOX1-mediated activation of epithelial epidermal growth factor receptor and the protease calpain-2 through a redox-dependent mechanism involving cysteine oxidation within epidermal growth factor receptor and the tyrosine kinase Src. Primary nasal epithelial cells from patients with allergic asthma were found to express increased DUOX1 and IL-33 levels and demonstrated enhanced IL-33 secretion in response to allergen challenge compared with values seen in nasal epithelial cells from nonasthmatic subjects.

CONCLUSION

Our findings implicate epithelial DUOX1 as a pivotal mediator of IL-33-dependent activation of innate airway type 2 immune responses to common airborne allergens and indicate that enhanced DUOX1 expression and IL-33 secretion might present important contributing features of allergic asthma.

The tobacco smoke component acrolein induces glucocorticoid resistant gene expression via inhibition of histone deacetylase

Chronic obstructive pulmonary disease (COPD) is the leading cause of cigarette smoke-related death worldwide. Acrolein, a crucial reactive electrophile found in cigarette smoke mimics many of the toxic effects of cigarette smoke-exposure in the lung. In macrophages, cigarette smoke is known to hinder histone deacetylases (HDACs), glucocorticoid-regulated enzymes that play an important role in the pathogenesis of glucocorticoid resistant inflammation, a common feature of COPD. Thus, we hypothesize that acrolein plays a role in COPD-associated glucocorticoid resistance. To examine the role of acrolein on glucocorticoid resistance, U937 monocytes, differentiated with PMA to macrophage-like cells were treated with acrolein for 0.5h followed by stimulation with hydrocortisone for 8h, or treated simultaneously with LPS and hydrocortisone for 8h without acrolein. GSH and nuclear HDAC activity were measured, or gene expression was analyzed by qPCR. Acrolein-mediated TNFα gene expression was not suppressed by hydrocortisone whereas LPS-induced TNFα expression was suppressed. Acrolein also significantly inhibited nuclear HDAC activity in macrophage-like cells. Incubation of recombinant HDAC2 with acrolein led to the formation of an HDAC2-acrolein adduct identified by mass spectrometry. Therefore, these results suggest that acrolein-induced inflammatory gene expression is resistant to suppression by the endogenous glucocorticoid, hydrocortisone.

Molecular mechanisms of acrolein toxicity: relevance to human disease

Acrolein, a highly reactive unsaturated aldehyde, is a ubiquitous environmental pollutant and its potential as a serious environmental health threat is beginning to be recognized. Humans are exposed to acrolein per oral (food and water), respiratory (cigarette smoke, automobile exhaust, and biocide use) and dermal routes, in addition to endogenous generation (metabolism and lipid peroxidation). Acrolein has been suggested to play a role in several disease states including spinal cord injury, multiple sclerosis, Alzheimer's disease, cardiovascular disease, diabetes mellitus, and neuro-, hepato-, and nephro-toxicity. On the cellular level, acrolein exposure has diverse toxic effects, including DNA and protein adduction, oxidative stress, mitochondrial disruption, membrane damage, endoplasmic reticulum stress, and immune dysfunction. This review addresses our current understanding of each pathogenic mechanism of acrolein toxicity, with emphasis on the known and anticipated contribution to clinical disease, and potential therapies.

Tobacco exposure and susceptibility to tuberculosis: is there a smoking gun?

In many regions of the world, there is a great overlap between the prevalence of cigarette smoke exposure and tuberculosis. Despite the large body of epidemiologic evidence that tobacco smoke exposure is associated with increased tuberculosis infection, active disease, severity of disease, and mortality from tuberculosis, these studies cannot distinguish whether the mechanism is principally through direct impairment of anti-tuberculosis immunity by cigarette smoke or due to potential confounders that increase risk for tuberculosis and are commonly associated with smoking--such as poverty, malnutrition, and crowded living conditions. While there are several in vivo murine and in vitro macrophage studies showing cigarette smoke impairs control of tuberculous infection, little is known of the molecular and cellular mechanisms by which this impairment occurs. Herein, we highlight the key findings of these studies. Additionally, we review key immune cells that play critical roles in host-defense or pathogenesis of tuberculosis and generate a hypothesis-driven discussion of the possible mechanisms by which cigarette smoke impairs or enhances their functions, respectively, ultimately resulting in compromised immunity against tuberculosis.

Protein alkylation by the α,β-unsaturated aldehyde acrolein. A reversible mechanism of electrophile signaling?

Acrolein, a reactive aldehyde found in cigarette smoke, is thought to induce its biological effects primarily by irreversible adduction to cellular nucleophiles such as cysteine thiols. Here, we demonstrate that acrolein rapidly inactivates the seleno-enzyme thioredoxin reductase (TrxR) in human bronchiolar epithelial HBE1 cells, which recovered over 4-8h by a mechanism depending on the presence of cellular GSH and thioredoxin 1 (Trx1), and corresponding with reversal of protein-acrolein adduction. Our findings indicate that acrolein-induced protein alkylation is not necessarily a feature of irreversible protein damage, but may reflect a reversible signaling mechanism that is regulated by GSH and Trx1.

Acrolein exposure suppresses antigen-induced pulmonary inflammation

Background

Adverse health effects of tobacco smoke arise partly from its influence on innate and adaptive immune responses, leading to impaired innate immunity and host defense. The impact of smoking on allergic asthma remains unclear, with various reports demonstrating that cigarette smoke enhances asthma development but can also suppress allergic airway inflammation. Based on our previous findings that immunosuppressive effects of smoking may be largely attributed to one of its main reactive electrophiles, acrolein, we explored the impact of acrolein exposure in a mouse model of ovalbumin (OVA)-induced allergic asthma.

Methods

C57BL/6 mice were sensitized to ovalbumin (OVA) by intraperitoneal injection with the adjuvant aluminum hydroxide on days 0 and 7, and challenged with aerosolized OVA on days 14–16. In some cases, mice were also exposed to 5 ppm acrolein vapor for 6 hrs/day on days 14–17. Lung tissues or brochoalveolar lavage fluids (BALF) were collected either 6 hrs after a single initial OVA challenge and/or acrolein exposure on day 14 or 48 hrs after the last OVA challenge, on day 18. Inflammatory cells and Th1/Th2 cytokine levels were measured in BALF, and lung tissue samples were collected for analysis of mucus and Th1/Th2 cytokine expression, determination of protein alkylation, cellular thiol status and transcription factor activity.

Results

Exposure to acrolein following OVA challenge of OVA-sensitized mice resulted in markedly attenuated allergic airway inflammation, demonstrated by decreased inflammatory cell infiltrates, mucus hyperplasia and Th2 cytokines. Acrolein exposure rapidly depleted lung tissue glutathione (GSH) levels, and induced activation of the Nrf2 pathway, indicated by accumulation of Nrf2, increased alkylation of Keap1, and induction of Nrf2-target genes such as HO-1. Additionally, analysis of inflammatory signaling pathways showed suppressed activation of NF-κB and marginally reduced activation of JNK in acrolein-exposed lungs, associated with increased carbonylation of RelA and JNK.

Conclusion

Acrolein inhalation suppresses Th2-driven allergic inflammation in sensitized animals, due to direct protein alkylation resulting in activation of Nrf2 and anti-inflammatory gene expression, and inhibition of NF-κB or JNK signaling. Our findings help explain the paradoxical anti-inflammatory effects of cigarette smoke exposure in allergic airways disease.

A direct and continuous assay for the determination of thioredoxin reductase activity in cell lysates

Thioredoxin reductase (TR) is an oxidoreductase responsible for maintaining thioredoxin in the reduced state, thereby contributing to proper cellular redox homeostasis. The C-terminal active site of mammalian TR contains the rare amino acid selenocysteine, which is essential to its activity. Alterations in TR activity due to changes in cellular redox homeostasis are found in clinical conditions such as cancer, viral infection, and various inflammatory processes; therefore, quantification of thioredoxin activity can be a valuable indicator of clinical conditions. Here we describe a new direct assay, termed the SC-TR assay, to determine the activity of TR based on the reduction of selenocystine, a diselenide-bridged amino acid. Rather than being an end-point assay as in older methods, the SC-TR assay directly monitors the continuous consumption of NADPH at 340 nm by TR as it reduces selenocystine. The SC-TR assay can be used in a cuvette using traditional spectrophotometry or as a 96-well plate-based format using a plate reader. In addition, the SC-TR assay is compatible with the use of nonionic detergents, making it more versatile than other methods using cell lysates.

Cigarette smoking and mechanisms of susceptibility to infections of the respiratory tract and other organ systems

The predisposition of cigarette smokers for development of oral and respiratory infections caused by microbial pathogens is well recognised, with those infected with the human immunodeficiency virus (HIV) at particularly high risk. Smoking cigarettes has a suppressive effect on the protective functions of airway epithelium, alveolar macrophages, dendritic cells, natural killer (NK) cells and adaptive immune mechanisms, in the setting of chronic systemic activation of neutrophils. Cigarette smoke also has a direct effect on microbial pathogens to promote the likelihood of infective disease, specifically promotion of microbial virulence and antibiotic resistance. In addition to interactions between smoking and HIV infection, a number of specific infections/clinical syndromes have been associated epidemiologically with cigarette smoking, including those of the upper and lower respiratory tract, gastrointestinal tract, central nervous and other organ systems. Smoking cessation benefits patients in many ways, including reduction of the risk of infectious disease.

Acrolein-induced activation of mitogen-activated protein kinase signaling is mediated by alkylation of thioredoxin reductase and thioredoxin 1

Cigarette smoking remains a major health concern worldwide, and many of the adverse effects of cigarette smoke (CS) can be attributed to its abundant electrophilic aldehydes, such as acrolein (2-propenal). Previous studies indicate that acrolein readily reacts with thioredoxin reductase 1 (TrxR1), a critical enzyme involved in regulation of thioredoxin (Trx)-mediated redox signaling, by alkylation at its selenocysteine (Sec) residue. Because alkylation of Sec within TrxR1 has significant implications for its enzymatic function, we explored the potential importance of TrxR1 alkylation in acrolein-induced activation or injury of bronchial epithelial cells. Exposure of human bronchial epithelial HBE1 cells to acrolein (1–30 μM) resulted in dose-dependent loss of TrxR thioredoxin reductase activity, which coincided with its alkylation, as determined by biotin hydrazide labeling, and was independent of initial GSH status. To test the involvement of TrxR1 in acrolein responses in HBE1 cells, we suppressed TrxR1 using siRNA silencing or augmented TrxR1 by cell supplementation with sodium selenite. Acrolein exposure of HBE1 cells induced dose-dependent activation of the MAP kinases, extracellular regulated1 kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, and activation of JNK was markedly enhanced after selenite-mediated induction of TrxR1, and was associated with increased alkylation of TrxR1. Conversely, siRNA silencing of TrxR1 significantly suppressed the ability of acrolein to activate JNK, and also appeared to attenuate acrolein-dependent activation of ERK and p38. Alteration of initial TrxR1 levels by siRNA or selenite supplementation also affected initial Trx1 redox status and acrolein-mediated alkylation of Trx1, but did not significantly affect acrolein-mediated activation of HO-1 or cytotoxicity. Collectively, our findings indicate that alkylation of TrxR1 and/or Trx1 may contribute directly to acrolein-mediated activation of MAP kinases such as JNK, and may therefore be important in acrolein-induced alterations in airway epithelial function, as a contributing mechanism in tobacco-related respiratory disease.

Cigarette smoke dissociates inflammation and lung remodeling in OVA-sensitized and challenged mice

We evaluated the effects of cigarette smoke (CS) on lung inflammation and remodeling in a model of ovalbumin (OVA)-sensitized and OVA-challenged mice. Male BALB/c mice were divided into 4 groups: non-sensitized and air-exposed (control); non-sensitized and exposed to cigarette smoke (CS), sensitized and air-exposed (OVA) (50 μg+OVA 1% 3 times/week for 3 weeks) and sensitized and cigarette smoke exposed mice (OVA+CS). IgE levels were not affected by CS exposure. The increases in total bronchoalveolar fluid cells in the OVA group were attenuated by co-exposure to CS, as were the changes in IL-4, IL-5, and eotaxin levels as well as tissue elastance (p<0.05). In contrast, only the OVA+CS group showed a significant increase in the protein expression of IFN-γ, VEGF, GM-CSF and collagen fiber content (p<0.05). In our study, exposure to cigarette smoke in OVA-challenged mice resulted in an attenuation of pulmonary inflammation but led to an increase in pulmonary remodeling and resulted in the dissociation of airway inflammation from lung remodeling.