Pelargonidin alleviates acrolein-induced inflammation in human umbilical vein endothelial cells by reducing COX-2 expression through the NF-κB pathway.

Acrolein, a common environmental pollutant, is linked to the development of cardiovascular inflammatory diseases. Pelargonidin is a natural compound with anti-inflammation activity. In this study, we aimed to explore the effects of pelargonidin on inflammation induced by acrolein in human umbilical vein endothelial cells (HUVECs). MTT assay was utilized for assessing cell viability in HUVECs. LDH release in HUVECs was measured using the LDH kit. Western blot was used to detect the protein expression of p-p65, p65 and COX-2. Inflammation was evaluated through determining the levels of PGE2, IL-1ß, IL-6, IL-8 and TNF-α in HUVECs after treatment. COX-2 mRNA expression and COX-2 content were examined using RT-qPCR and a human COX-2 ELISA kit, respectively. Acrolein treatment at 50 µM resulted in a 45% decrease in the viability and an increase in LDH release (2.2-fold) in HUVECs. Pelargonidin at 5, 10, 20, and 40 µM alleviated acrolein-caused inhibitory effect on cell viability (increased to 1.3-, 1.5-, 1.8-, and 1.9-fold, respectively, compared to acrolein treatment group) and promoting effect on LDH release (decreased to 82%, 75%, 62%, and 58%, respectively, compared to acrolein treatment group) in HUVECs. Moreover, pelargonidin or pyrrolidine dithiocarbamate (PDTC; an NF-κB pathway inhibitor) inhibited acrolein-induced activation of the NF-κB pathway. Acrolein elevated the levels of PGE2, IL-1ß, IL-6, IL-8 and TNF-α (from 40.2, 27.3, 67.2, 29.0, 24.8 pg/mL in control group to 224.0, 167.3, 618.3, 104.6, and 275.1 pg/mL in acrolein treatment group, respectively), which were retarded after pelargonidin (decreased to 134.8, 82.3, 246.2, 70.2, and 120.8 pg/mL in acrolein + pelargonidin treatment group) or PDTC (decreased to 107.9, 80.1, 214.6, 64.0, and 96.6 pg/mL in acrolein + PDTC treatment group) treatment in HUVECs. Pelargonidin inactivated the NF-κB pathway to reduce acrolein-induced COX-2 expression. Furthermore, pelargonidin relieved acrolein-triggered inflammation through decreasing COX-2 expression by inactivating the NF-κB pathway in HUVECs. In conclusion, pelargonidin could protect against acrolein-triggered inflammation in HUVECs through attenuating COX-2 expression by inactivating the NF-κB pathway.

Acrolein suppresses anticancer drug-induced toxicity mediated by activating claudin-1 and Nrf2 axis in a spheroid model of human lung squamous cell carcinoma cells.

Tobacco smoke contains various carcinogenic ingredients such as nicotine, acrolein, and benzopyrene; however, their effects on cancer treatment are not fully understood. Claudin-1 (CLDN1), a component of tight junctions, is involved in the increased resistance to anticancer drugs. In this study, we found that acrolein increases the mRNA and protein levels of CLDN1 in RERF-LC-AI cells derived from human lung squamous cell carcinoma (SCC). Acrolein increased the p-extracellular signal-regulated kinase (ERK) 1/2 levels without affecting the p-Akt level. The acrolein-induced elevation of CLDN1 expression was attenuated by U0126, a mitogen-activated protein kinase kinas (MEK) inhibitor. These results indicate that the activation of MEK/ERK pathway is involved in the acrolein-induced elevation of CLDN1 expression. In a spheroid model, acrolein suppressed the accumulation and toxicity of doxorubicin (DXR), which were rescued by CLDN1 silencing. The acrolein-induced effects were also observed in lung SCC-derived EBC-1 and LK-2 cells. Acrolein also increased the expression level of nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor that regulates antioxidant and detoxifying genes, which were inhibited by CLDN1 silencing. In spheroid cells, the levels of reactive oxygen species were enhanced by acrolein, which was inhibited by CLDN1 silencing. Taken together, acrolein may reduce the anticancer drug-induced toxicity in human lung SCC cells mediated by high CLDN1 expression followed by the upregulation of Nrf2 signaling pathway.

Serum metabolome and liver transcriptome reveal acrolein inhalation-induced sex-specific homeostatic dysfunction.

Acrolein, a respiratory irritant, induces systemic neuroendocrine stress. However, peripheral metabolic effects have not been examined. Male and female WKY rats were exposed to air (0 ppm) or acrolein (3.16 ppm) for 4 h, followed by immediate serum and liver tissue collection. Serum metabolomics in both sexes and liver transcriptomics in males were evaluated to characterize the systemic metabolic response. Of 887 identified metabolites, > 400 differed between sexes at baseline. An acrolein biomarker, 3-hydroxypropyl mercapturic acid, increased 18-fold in males and 33-fold in females, indicating greater metabolic detoxification in females than males. Acrolein exposure changed 174 metabolites in males but only 50 in females. Metabolic process assessment identified higher circulating free-fatty acids, glycerols, and other lipids in male but not female rats exposed to acrolein. In males, acrolein also increased branched-chain amino acids, which was linked with metabolites of nitrogen imbalance within the gut microbiome. The contribution of neuroendocrine stress was evident by increased corticosterone in males but not females. Male liver transcriptomics revealed acrolein-induced over-representation of lipid and protein metabolic processes, and pathway alterations including Sirtuin, insulin-receptor, acute-phase, and glucocorticoid signaling. In sum, acute acrolein inhalation resulted in sex-specific serum metabolomic and liver transcriptomic derangement, which may have connections to chronic metabolic-related diseases.

The mechanism of acrolein exposure inhibited the release of neutrophil extracellular traps: By reducing respiratory burst and Raf/MEK/ERK pathway and promote cell apoptosis.

Acrolein (AC) is a highly toxic volatile substance in the environment, and studies have found that excessive AC had a toxic effect on the immune system. Neutrophils are the first line of defense against pathogen invasion. The release of neutrophil extracellular traps (NETs) is a protective mechanism for neutrophils, and its release is affected by environmental pollutants. However, the effect of AC on NETs release and its mechanism remains unclear. In this study, chicken peripheral blood neutrophils were pretreated with 20 µM AC and treated with 5 µM Phorbol 12-myristate 13-acetate (PMA) to stimulate the release of NETs. The results showed that AC exposure significantly inhibited the release of NETs induced by PMA, respiratory burst, and the expression levels of phospho-rapidly accelerated fibrosarcoma (p-Raf), phospho-mitogen-activated extracellular signal-regulated kinase (p-MEK) and phospho-extracellular regulated protein kinases (p-ERK). In addition, AC exposure significantly inhibited the expression of B-cell lymphoma-2 (Bcl-2) and promoted the expression of apoptotic factors Bcl2-Associated X (Bax), cytochrome c (Cyt C), cysteinyl aspartate specific proteinase 9 (Casp 9) and cysteinyl aspartate specific proteinase 3 (Casp 3). Further inhibition of neutrophil apoptosis significantly improved the release of NETs. The above results indicated that AC exposure led to a decrease in the formation of NETs, which is caused by excessive AC-induced neutrophil apoptosis. Our study clarified the immune toxicity mechanism of AC on chickens, which is of great significance and reference value for protecting the ecological environment and poultry health.

Acrolein Induces Retinal Abnormalities of Alzheimer's Disease in Mice.

It is reported that retinal abnormities are related to Alzheimer's disease (AD) in patients and animal models. However, it is unclear whether the retinal abnormities appear in the mouse model of sporadic Alzheimer's disease (sAD) induced by acrolein. We investigated the alterations of retinal function and structure, the levels of ß-amyloid (Aß) and phosphorylated Tau (p-Tau) in the retina, and the changes in the retinal vascular system in this mouse model. We demonstrated that the levels of Aß and p-Tau were increased in the retinas of mice from the acrolein groups. Subsequently, a decreased amplitudes of b-waves in the scotopic and photopic electroretinogram (ERG), decreased thicknesses of the retinal nerve fiber layer (RNFL) in the retina, and slight retinal venous beading were found in the mice induced by acrolein. We propose that sAD mice induced by acrolein showed abnormalities in the retina, which may provide a valuable reference for the study of the retina in sAD.

Acrolein increases the concentration of intracellular Zn2⁺ by producing mitochondrial reactive oxygen species in A549 cells.

Smoking or occupational exposure leads to low concentrations of acrolein on the surface of the airways. Acrolein is involved in the pathophysiological processes of various respiratory diseases. Reports showed that acrolein induced an increase in mitochondrial reactive oxygen species (mROS). Furthermore, exogenous H2O2 was found to increase intracellular Zn2⁺ concentration ([Zn2⁺]ᵢ). However, the specific impact of acrolein on changes in intracellular Zn2⁺ levels has not been fully investigated. Therefore, this study aimed to investigate the effects of acrolein on mROS and [Zn2⁺]ᵢ in A549 cells. We used Mito Tracker Red CM-H2Xros (MitoROS) and Fluozin-3 fluorescent probes to observe changes in mROS and intracellular Zn2⁺. The results revealed that acrolein increased [Zn2⁺]ᵢ in a time- and dose-dependent manner. Additionally, the production of mROS was observed in response to acrolein treatment. Subsequent experiments showed that the intracellular Zn2⁺ chelator TPEN could inhibit the acrolein-induced elevation of [Zn2⁺]ᵢ but did not affect the acrolein-induced mROS production. Conversely, the acrolein-induced elevation of mROS and [Zn2⁺]ᵢ were significantly decreased by the inhibitors of ROS formation (NaHSO3, NAC). Furthermore, external oxygen free radicals increased both [Zn2⁺]ᵢ levels and mROS production. These results demonstrated that acrolein-induced elevation of [Zn2⁺]ᵢ in A549 cells was mediated by mROS generation, rather than through a pathway where [Zn2⁺]ᵢ elevation leads to mROS production.

Toxicological effects of ocular acrolein exposure to eyelids in rabbits in vivo.

Acrolein is a highly reactive volatile toxic chemical that injures the eyes and many organs. It has been used in wars and terrorism for wounding masses on multiple occasions and is readily accessible commercially. Our earlier studies revealed acrolein's toxicity to the cornea and witnessed damage to other ocular tissues. Eyelids play a vital role in keeping eyes mobile, moist, lubricated, and functional utilizing a range of diverse lipids produced by the Meibomian glands located in the upper and lower eyelids. This study sought to investigate acrolein's toxicity to eyelid tissues by studying the expression of inflammatory and lipid markers in rabbit eyes in vivo utilizing our reported vapor-cap model. The study was approved by the institutional animal care and use committees and followed ARVO guidelines. Twelve New Zealand White Rabbits were divided into 3 groups: Naïve (group 1), 1-min acrolein exposure (group 2), or 3-min acrolein exposure (group 3). The toxicological effects of acrolein on ocular health in live animals were monitored with regular clinical eye exams and intraocular pressure measurements and eyelid tissues post-euthanasia were subjected to H&E and Masson's trichrome histology and qRT-PCR analysis. Clinical eye examinations witnessed severely swollen eyelids, abnormal ocular discharge, chemosis, and elevated intraocular pressure (p < 0.001) in acrolein-exposed eyes. Histological studies supported clinical findings and exhibited noticeable changes in eyelid tissue morphology. Gene expression studies exhibited significantly increased expression of inflammatory and lipid mediators (LOX, PAF, Cox-2, and LTB4; p < 0.001) in acrolein-exposed eyelid tissues compared to naïve eyelid tissues. The results suggest that acrolein exposure to the eyes causes acute damage to eyelids by altering inflammatory and lipid mediators in vivo.

Transient Receptor Potential Ankyrin 1 (TRPA1) Channel Mediates Acrolein Cytotoxicity in Human Lung Cancer Cells.

Transient receptor potential ankyrin 1 (TRPA1) is a nonselective ion channel implicated in thermosensation and inflammatory pain. It has been reported that expression of the TRPA1 channel is induced by cigarette smoke extract. Acrolein found in cigarette smoke is highly toxic and known as an agonist of the TRPA1 channel. However, the role of TRPA1 in the cytotoxicity of acrolein remains unclear. Here, we investigated whether the TRPA1 channel is involved in the cytotoxicity of acrolein in human lung cancer A549 cells. The IC50 of acrolein in A549 cells was 25 µM, and acrolein toxicity increased in a concentration- and time-dependent manner. When the effect of acrolein on TRPA1 expression was examined, the expression of TRPA1 in A549 cells was increased by treatment with 50 µM acrolein for 24 h or 500 µM acrolein for 30 min. AP-1, a transcription factor, was activated in the cells treated with 50 µM acrolein for 24 h, while induction of NF-κB and HIF-1α was observed in the cells treated with 500 µM acrolein for 30 min. These results suggest that acrolein induces TRPA1 expression by activating these transcription factors. Overexpression of TRPA1 in A549 cells increased acrolein sensitivity and the level of protein-conjugated acrolein (PC-Acro), while knockdown of TRPA1 in A549 cells or treatment with a TRPA1 antagonist caused tolerance to acrolein. These findings suggest that acrolein induces the TRPA1 channel and that an increase in TRPA1 expression promotes the cytotoxicity of acrolein.

The role of acrolein for E-cigarette vapour condensate mediated activation of NADPH oxidase in cultured endothelial cells and macrophages.

Electronic cigarettes (E-cigarettes) have recently become a popular alternative to traditional tobacco cigarettes. Despite being marketed as a healthier alternative, increasing evidence shows that E-cigarette vapour could cause adverse health effects. It has been postulated that degradation products of E-cigarette liquid, mainly reactive aldehydes, are responsible for those effects. Previously, we have demonstrated that E-cigarette vapour exposure causes oxidative stress, inflammation, apoptosis, endothelial dysfunction and hypertension by activating NADPH oxidase in a mouse model. To better understand oxidative stress mechanisms, we have exposed cultured endothelial cells and macrophages to condensed E-cigarette vapour (E-cigarette condensate) and acrolein. In both endothelial cells (EA.hy 926) and macrophages (RAW 264.7), we have observed that E-cigarette condensate incubation causes cell death. Since recent studies have shown that among toxic aldehydes found in E-cigarette vapour, acrolein plays a prominent role, we have incubated the same cell lines with increasing concentrations of acrolein. Upon incubation with acrolein, a translocation of Rac1 to the plasma membrane has been observed, accompanied by an increase in oxidative stress. Whereas reactive oxygen species (ROS) formation by acrolein in cultured endothelial cells was mainly intracellular, the release of ROS in cultured macrophages was both intra- and extracellular. Our data also demonstrate that acrolein activates the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway and, in general, could mediate E-cigarette vapour-induced oxidative stress and cell death. More mechanistic insight is needed to clarify the toxicity associated with E-cigarette consumption and the possible adverse effects on human health.

Acrolein produced during acute kidney injury promotes tubular cell death.

Acute kidney injury is an important global health concern as it is associated with high morbidity and mortality. Polyamines, essential for cell growth and proliferation, are known to inhibit cardiovascular disease. However, under conditions of cellular damage, toxic acrolein is produced from polyamines by the enzyme spermine oxidase (SMOX). We used a mouse renal ischemia-reperfusion model and human proximal tubule cells (HK-2) to investigate whether acrolein exacerbates acute kidney injury by renal tubular cell death. Acrolein visualized by acroleinRED was increased in ischemia-reperfusion kidneys, particularly in tubular cells. When HK-2 cells were cultured under 1% oxygen for 24 h, then switched to 21% oxygen for 24 h (hypoxia-reoxygenation), acrolein accumulated and SMOX mRNA and protein levels were increased. Acrolein induced cell death and fibrosis-related TGFB1 mRNA in HK-2 cells. Administration of the acrolein scavenger cysteamine suppressed the acrolein-induced upregulation of TGFB1 mRNA. Cysteamine also inhibited a decrease in the mitochondrial membrane potential observed by MitoTrackerCMXRos, and cell death induced by hypoxia-reoxygenation. The siRNA-mediated knockdown of SMOX also suppressed hypoxia-reoxygenation-induced acrolein accumulation and cell death. Our study suggests that acrolein exacerbates acute kidney injury by promoting tubular cell death during ischemia-reperfusion injury. Treatment to control the accumulation of acrolein might be an effective therapeutic option for renal ischemia-reperfusion injury.

Sex-specific respiratory and systemic endocrine effects of acute acrolein and trichloroethylene inhalation.

Acrolein and trichloroethylene (TCE) are priority hazardous air pollutants due to environmental prevalence and adverse health effects; however, neuroendocrine stress-related systemic effects are not characterized. Comparing acrolein, an airway irritant, and TCE with low irritancy, we hypothesized that airway injury would be linked to neuroendocrine-mediated systemic alterations. Male and female Wistar-Kyoto rats were exposed nose-only to air, acrolein or TCE in incremental concentrations over 30 min, followed by 3.5-hr exposure to the highest concentration (acrolein - 0.0, 0.1, 0.316, 1, 3.16 ppm; TCE - 0.0, 3.16, 10, 31.6, 100 ppm). Real-time head-out plethysmography revealed acrolein decreased minute volume and increased inspiratory-time (males>females), while TCE reduced tidal-volume. Acrolein, but not TCE, inhalation increased nasal-lavage-fluid protein, lactate-dehydrogenase activity, and inflammatory cell influx (males>females). Neither acrolein nor TCE increased bronchoalveolar-lavage-fluid injury markers, although macrophages and neutrophils increased in acrolein-exposed males and females. Systemic neuroendocrine stress response assessment indicated acrolein, but not TCE, increased circulating adrenocorticotrophic hormone, and consequently corticosterone, and caused lymphopenia, but only in males. Acrolein also reduced circulating thyroid-stimulating hormone, prolactin, and testosterone in males. In conclusion, acute acrolein inhalation resulted in sex-specific upper respiratory irritation/inflammation and systemic neuroendocrine alterations linked to hypothalamic-pituitary-adrenal axes activation, which is critical in mediating extra-respiratory effects.

Hydrogen sulfide protects Sertoli cells against toxicant Acrolein-induced cell injury.

Acrolein (ACR), a highly toxic α,ß-unsaturated aldehyde, is considered to be a common mediator behind the reproductive injury induced by various factors. However, the understanding of its reproductive toxicity and prevention in reproductive system is limited. Given that Sertoli cells provide the first-line defense against various toxicants and that dysfunction of Sertoli cell causes impaired spermatogenesis, we, therefore, examined ACR cytotoxicity in Sertoli cells and tested whether hydrogen sulfide (H2S), a gaseous mediator with potent antioxidative actions, could have a protective effect. Exposure of Sertoli cells to ACR led to cell injury, as indicated by reactive oxygen species (ROS) generation, protein oxidation, P38 activation and ultimately cell death that was prevented by antioxidant N-acetylcysteine (NAC). Further studies revealed that ACR cytotoxicity on Sertoli cells was significantly exacerbated by the inhibition of H2S-synthesizing enzyme cystathionine γ-lyase (CSE), while significantly suppressed by H2S donor Sodium hydrosulfide (NaHS). It was also attenuated by Tanshinone IIA (Tan IIA), an active ingredient of Danshen that stimulated H2S production in Sertoli cells. Apart from Sertoli cells, H2S also protected the cultured germ cells from ACR-initiated cell death. Collectively, our study characterized H2S as endogenous defensive mechanism against ACR in Sertoli cells and germ cells. This property of H2S could be used to prevent and treat ACR-related reproductive injury.

Chitooligosaccharides Derivatives Protect ARPE-19 Cells against Acrolein-Induced Oxidative Injury.

Age-related macular degeneration (AMD) is the leading cause of vision loss among the elderly. The progression of AMD is closely related to oxidative stress in the retinal pigment epithelium (RPE). Here, a series of chitosan oligosaccharides (COSs) and N-acetylated derivatives (NACOSs) were prepared, and their protective effects on an acrolein-induced oxidative stress model of ARPE-19 were explored using the MTT assay. The results showed that COSs and NACOs alleviated APRE-19 cell damage induced by acrolein in a concentration-dependent manner. Among these, chitopentaose (COS-5) and its N-acetylated derivative (N-5) showed the best protective activity. Pretreatment with COS-5 or N-5 could reduce intracellular and mitochondrial reactive oxygen species (ROS) production induced by acrolein, increase mitochondrial membrane potential, GSH level, and the enzymatic activity of SOD and GSH-Px. Further study indicated that N-5 increased the level of nuclear Nrf2 and the expression of downstream antioxidant enzymes. This study revealed that COSs and NACOSs reduced the degeneration and apoptosis of retinal pigment epithelial cells by enhancing antioxidant capacity, suggesting that they have the potential to be developed into novel protective agents for AMD treatment and prevention.

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.

A search for acrolein scavengers among food components.

Brain stroke is a major cause of being bedridden for elderly people, and preventing stroke is important for maintaining quality of life (QOL). Acrolein is a highly reactive aldehyde and causes tissue damage during stroke. Decreasing acrolein toxicity ameliorates tissue injury during brain stroke. In this study, we tried to identify food components which decrease acrolein toxicity. We found that 2-furanmethanethiol, cysteine methyl and ethyl esters, alliin, lysine and taurine decreased acrolein toxicity. These compounds neutralized acrolein by direct interaction. However, the interaction between acrolein and taurine was not so strong. Approximately 30 mM taurine was necessary to interact with 10 µM acrolein, and 2 g/kg taurine was necessary to decrease the size of mouse brain infarction. Taurine also slightly increased polyamine contents, which are involved in decrease in the acrolein toxicity. Mitochondrial potential damage by acrolein was also protected by taurine. Our results indicate that daily intake of foods containing 2-furanmethanethiol, cysteine methyl and ethyl esters, alliin, lysine and taurine may prevent severe injury in brain stroke and improve the quality of life for elderly people.

Impact of sub-acute acrolein inhalation on the molecular regulation of mitochondrial metabolism in rat lung.

Nowadays, mitochondria are recognized as key players in the pathogenesis of a variety of smoking-associated lung diseases. Acrolein, a component of cigarette smoke, is a known driver of biological mechanisms underlying smoking-induced respiratory toxicity. The impact of sub-acute acrolein inhalation in vivo on key processes controlling mitochondrial homeostasis in cells of the airways however is unknown. In this study, we investigated the activity/abundance of a myriad of molecules critically involved in mitochondrial metabolic pathways and mitochondrial quality control processes (mitochondrial biogenesis and mitophagy) in the lungs of Sprague-Dawley rats that were sub-acutely exposed to filtered air or 3 ppm acrolein by whole-body inhalation (5 h/day, 5 days/week for 4 weeks). Acrolein exposure induced a general inflammatory response in the lung as gene expression analysis revealed an increased expression of Icam1 and Cinc1 (p < 0.1; p < 0.05). Acrolein significantly decreased enzyme activity of hydroxyacyl-Coenzyme A dehydrogenase (p < 0.01), and decreased Pdk4 transcript levels (p < 0.05), suggestive of acrolein-induced changes in metabolic processes. Investigation of constituents of the mitochondrial biogenesis pathways and mitophagy machinery revealed no pronounced alterations. In conclusion, sub-acute inhalation of acrolein did not affect the regulation of mitochondrial metabolism and quality control, which is in contrast to more profound changes after acute exposure in other studies.

Disruption of the Molecular Regulation of Mitochondrial Metabolism in Airway and Lung Epithelial Cells by Cigarette Smoke: Are Aldehydes the Culprit?

Chronic obstructive pulmonary disease (COPD) is a devastating lung disease for which cigarette smoking is the main risk factor. Acetaldehyde, acrolein, and formaldehyde are short-chain aldehydes known to be formed during pyrolysis and combustion of tobacco and have been linked to respiratory toxicity. Mitochondrial dysfunction is suggested to be mechanistically and causally involved in the pathogenesis of smoking-associated lung diseases such as COPD. Cigarette smoke (CS) has been shown to impair the molecular regulation of mitochondrial metabolism and content in epithelial cells of the airways and lungs. Although it is unknown which specific chemicals present in CS are responsible for this, it has been suggested that aldehydes may be involved. Therefore, it has been proposed by the World Health Organization to regulate aldehydes in commercially-available cigarettes. In this review, we comprehensively describe and discuss the impact of acetaldehyde, acrolein, and formaldehyde on mitochondrial function and content and the molecular pathways controlling this (biogenesis versus mitophagy) in epithelial cells of the airways and lungs. In addition, potential therapeutic applications targeting (aldehyde-induced) mitochondrial dysfunction, as well as regulatory implications, and the necessary required future studies to provide scientific support for this regulation, have been covered in this review.

Smoking-Associated Exposure of Human Primary Bronchial Epithelial Cells to Aldehydes: Impact on Molecular Mechanisms Controlling Mitochondrial Content and Function.

Chronic obstructive pulmonary disease (COPD) is a devastating lung disease primarily caused by exposure to cigarette smoke (CS). During the pyrolysis and combustion of tobacco, reactive aldehydes such as acetaldehyde, acrolein, and formaldehyde are formed, which are known to be involved in respiratory toxicity. Although CS-induced mitochondrial dysfunction has been implicated in the pathophysiology of COPD, the role of aldehydes therein is incompletely understood. To investigate this, we used a physiologically relevant in vitro exposure model of differentiated human primary bronchial epithelial cells (PBEC) exposed to CS (one cigarette) or a mixture of acetaldehyde, acrolein, and formaldehyde (at relevant concentrations of one cigarette) or air, in a continuous flow system using a puff-like exposure protocol. Exposure of PBEC to CS resulted in elevated IL-8 cytokine and mRNA levels, increased abundance of constituents associated with autophagy, decreased protein levels of molecules associated with the mitophagy machinery, and alterations in the abundance of regulators of mitochondrial biogenesis. Furthermore, decreased transcript levels of basal epithelial cell marker KRT5 were reported after CS exposure. Only parts of these changes were replicated in PBEC upon exposure to a combination of acetaldehyde, acrolein, and formaldehyde. More specifically, aldehydes decreased MAP1LC3A mRNA (autophagy) and BNIP3 protein (mitophagy) and increased ESRRA protein (mitochondrial biogenesis). These data suggest that other compounds in addition to aldehydes in CS contribute to CS-induced dysregulation of constituents controlling mitochondrial content and function in airway epithelial cells.

Impairment of Endothelial Function by Cigarette Smoke Is Not Caused by a Specific Smoke Constituent, but by Vagal Input From the Airway.

BACKGROUND: Exposure to tobacco or marijuana smoke, or e-cigarette aerosols, causes vascular endothelial dysfunction in humans and rats. We aimed to determine what constituent, or class of constituents, of smoke is responsible for endothelial functional impairment. METHODS: We investigated several smoke constituents that we hypothesized to mediate this effect by exposing rats and measuring arterial flow-mediated dilation (FMD) pre- and post-exposure. We measured FMD before and after inhalation of sidestream smoke from research cigarettes containing normal and reduced nicotine level with and without menthol, as well as 2 of the main aldehyde gases found in both smoke and e-cigarette aerosol (acrolein and acetaldehyde), and inert carbon nanoparticles. RESULTS: FMD was reduced by all 4 kinds of research cigarettes, with extent of reduction ranging from 20% to 46% depending on the cigarette type. While nicotine was not required for the impairment, higher nicotine levels in smoke were associated with a greater percent reduction of FMD (41.1±4.5% reduction versus 19.2±9.5%; P=0.047). Lower menthol levels were also associated with a greater percent reduction of FMD (18.5±9.8% versus 40.5±4.8%; P=0.048). Inhalation of acrolein or acetaldehyde gases at smoke-relevant concentrations impaired FMD by roughly 50% (P=0.001). However, inhalation of inert carbon nanoparticles at smoke-relevant concentrations with no gas phase also impaired FMD by a comparable amount (P<0.001). Bilateral cervical vagotomy blocked the impairment of FMD by tobacco smoke. CONCLUSIONS: There is no single constituent or class of constituents responsible for acute impairment of endothelial function by smoke; rather, we propose that acute endothelial dysfunction by disparate inhaled products is caused by vagus nerve signaling initiated by airway irritation.

E-cigarettes and their lone constituents induce cardiac arrhythmia and conduction defects in mice.

E-cigarette use has surged, but the long-term health effects remain unknown. E-cigarette aerosols containing nicotine and acrolein, a combustion and e-cigarette byproduct, may impair cardiac electrophysiology through autonomic imbalance. Here we show in mouse electrocardiograms that acute inhalation of e-cigarette aerosols disturbs cardiac conduction, in part through parasympathetic modulation. We demonstrate that, similar to acrolein or combustible cigarette smoke, aerosols from e-cigarette solvents (vegetable glycerin and propylene glycol) induce bradycardia, bradyarrhythmias, and elevations in heart rate variability during inhalation exposure, with inverse post-exposure effects. These effects are slighter with tobacco- or menthol-flavored aerosols containing nicotine, and in female mice. Yet, menthol-flavored and PG aerosols also increase ventricular arrhythmias and augment early ventricular repolarization (J amplitude), while menthol uniquely alters atrial and atrioventricular conduction. Exposure to e-cigarette aerosols from vegetable glycerin and its byproduct, acrolein, diminish heart rate and early repolarization. The pro-arrhythmic effects of solvent aerosols on ventricular repolarization and heart rate variability depend partly on parasympathetic modulation, whereas ventricular arrhythmias positively associate with early repolarization dependent on the presence of nicotine. Our study indicates that chemical constituents of e-cigarettes could contribute to cardiac risk by provoking pro-arrhythmic changes and stimulating autonomic reflexes.