Acrolein and Human Disease: Untangling the Knotty Exposure Scenarios Accompanying Several Diverse Disorders

Understanding How Chemical Pollutants Arise and Evolve in the Brewing Supply Chain: A Scoping Review

In this study, a critical review was carried out using the Web of ScienceTM Core Collection database to analyse the scientific literature published to date to identify lines of research and future perspectives on the presence of chemical pollutants in beer brewing. Beer is one of the world's most popular drinks and the most consumed alcoholic beverage. However, a widespread challenge with potential implications for human and animal health is the presence of physical, chemical, and/or microbiological contaminants in beer. Biogenic amines, heavy metals, mycotoxins, nitrosamines, pesticides, acrylamide, phthalates, bisphenols, microplastics, and, to a lesser extent, hydrocarbons (aliphatic chlorinated and polycyclic aromatic), carbonyls, furan-derivatives, polychlorinated biphenyls, and trihalomethanes are the main chemical pollutants found during the beer brewing process. Pollution sources include raw materials, technological process steps, the brewery environment, and packaging materials. Different chemical pollutants have been found during the beer brewing process, from barley to beer. Brewing steps such as steeping, kilning, mashing, boiling, fermentation, and clarification are critical in reducing the levels of many of these pollutants. As a result, their residual levels are usually below the maximum levels allowed by international regulations. Therefore, this work was aimed at assessing how chemical pollutants appear and evolve in the brewing process, according to research developed in the last few decades.

Diet as a Source of Acrolein: Molecular Basis of Aldehyde Biological Activity in Diabetes and Digestive System Diseases

Acrolein, a highly reactive α,β-unsaturated aldehyde, is a compound involved in the pathogenesis of many diseases, including neurodegenerative diseases, cardiovascular and respiratory diseases, diabetes mellitus, and the development of cancers of various origins. In addition to environmental pollution (e.g., from car exhaust fumes) and tobacco smoke, a serious source of acrolein is our daily diet and improper thermal processing of animal and vegetable fats, carbohydrates, and amino acids. Dietary intake is one of the main routes of human exposure to acrolein, which is a major public health concern. This review focuses on the molecular mechanisms of acrolein activity in the context of its involvement in the pathogenesis of diseases related to the digestive system, including diabetes, alcoholic liver disease, and intestinal cancer.

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.

The Role of Acrolein in Neurodegenerative Diseases and Its Protective Strategy

Neurodegenerative diseases are characterized by a massive loss of specific neurons, which can be fatal. Acrolein, an omnipresent environmental pollutant, is classified as a priority control contaminant by the EPA. Evidence suggests that acrolein is a highly active unsaturated aldehyde related to many nervous system diseases. Therefore, numerous studies have been conducted to identify the function of acrolein in neurodegenerative diseases, such as ischemic stroke, AD, PD, and MS, and its exact regulatory mechanism. Acrolein is involved in neurodegenerative diseases mainly by elevating oxidative stress, polyamine metabolism, neuronal damage, and plasma ACR-PC levels, and decreasing urinary 3-HPMA and plasma GSH levels. At present, the protective mechanism of acrolein mainly focused on the use of antioxidant compounds. This review aimed to clarify the role of acrolein in the pathogenesis of four neurodegenerative diseases (ischemic stroke, AD, PD and MS), as well as protection strategies, and to propose future trends in the inhibition of acrolein toxicity through optimization of food thermal processing and exploration of natural products.

Electrophile versus oxidant modification of cysteine residues: Kinetics as a key driver of protein modification

Humans have widespread exposure to both oxidants, and soft electrophilic compounds such as alpha,beta-unsaturated aldehydes and quinones. Electrophilic motifs are commonly found in a drugs, industrial chemicals, pollutants and are also generated via oxidant-mediated degradation of biomolecules including lipids (e.g. formation of 4-hydroxynonenal, 4-hydroxyhexenal, prostaglandin J2). All of these classes of compounds react efficiently with Cys residues, and the particularly the thiolate anion, with this resulting in Cys modification via either oxidation or adduct formation. This can result in deleterious or beneficial effects, that are either reversible (e.g. in cell signalling) or irreversible (damaging). For example, acrolein is a well-established toxin, whereas dimethylfumarate is used in the treatment of multiple sclerosis and psoriasis. This short review discusses the targets of alpha,beta-unsaturated aldehydes, and particularly two prototypic cases, acrolein and dimethylfumarate, and the factors that control the selectivity and kinetics of reaction of these species. Comparison is made between the reactivity of oxidants versus soft electrophiles. These rate constants indicate that electrophiles can be significant thiol modifying agents in some situations, as they have rate constants similar to or greater than species such as H₂O₂, can be present at higher concentrations, and are less efficiently removed by protective systems when compared to H₂O₂. They may also induce similar or higher levels of modification than highly reactive oxidants, due to the very low concentrations of oxidants formed in most in vivo situations.

Synthesis and cellular evaluation of click-chemistry probes to study the biological effects of alpha, beta-unsaturated carbonyls

Humans are commonly exposed to α,β-unsaturated carbonyls as both environmental toxins (e.g. acrolein) and therapeutic drugs (e.g. dimethylfumarate, DMFU, a front-line drug for the treatment of multiple sclerosis and psoriasis). These compounds undergo rapid Michael addition reactions with amine, imidazole and thiol groups on biological targets, with reaction at protein Cys residues being a major reaction pathway. However, the cellular targets of these species (the ‘adductome’) are poorly understood due to the absence of readily identifiable tags or reporter groups (chromophores/fluorophores or antigens) on many α,β-unsaturated carbonyls. Here we report a ‘proof of concept’ study in which we synthesize novel α,β-unsaturated carbonyls containing an alkyne function introduced at remote sites on the α,β-unsaturated carbonyl compounds (e.g. one of the methyl groups of dimethylfumarate). The presence of this tag allows ‘click-chemistry’ to be used to visualize, isolate, enrich and characterize the cellular targets of such compounds. The probes show similar selectivity and reactivity to the parent compounds, and compete for cellular targets, yielding long-lived (stable) adducts that can be visualized in intact cells (such as primary human coronary artery smooth muscle cells), and extracted and enriched for subsequent target analysis. It is shown using this approach that dimethylfumarate forms adducts with multiple intracellular targets including cytoskeletal, organelle and nuclear species, with these including the rate-limiting glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). This approach should be amenable to use with multiple α,β-unsaturated carbonyls and a wide variety of targets containing nucleophilic sites.

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Humans are widely exposed to α,β-unsaturated carbonyls via drugs and environmental toxins.

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These compounds react with cellular targets, and particularly Cys residues, via Michael addition.

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Alkyne tagged derivatives have been synthesized to allow click chemistry detection.

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These tags allow visualization, extraction, enrichment and identification of adducted proteins.

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GAPDH reacts with dimethylfumarate, with adducts detected in both the cytosol and nucleus.

Metabolic Investigation on the Interaction Mechanism between Dietary Dihydrochalcone Intake and Lipid Peroxidation Product Acrolein Reduction

SCOPE

Acrolein (ACR), a lipid peroxidation product, pathologically participates in various chronic diseases. In vitro evidence suggestes that dietary dihydrochalcones (DHCs) potentiate safe and alternative therapeutics to synthetic pharmaceuticals for ACR scavenging. Here, to investigate whether ingested DHCs could trap ACR and thereof result in reductions in endogenous ACR in mice is aimed.

METHODS AND RESULTS

Three doses of phloretin (25, 100, and 400 mg kg-1 ), a major dietary DHC, are orally administrated to mice and 24 h urine and fecal samples are collected, respectively. High-resolution MS-based targeted metabolomics reveal for the first time that phloretin and its oxidized metabolite are able to trap endogenous ACR via formation of ACR conjugates. Quantification further demonstrate that a) more than 13% of ingested phloretin can dose-dependently trap 0.77-9.92 nmol of ACR within 24 h; b) phloretin ingestion leads to marked reductions in both free ACR and ACR metabolites in mouse urine compared to control; and c) trapping reactions by phloretin can account for up to 20.1% of the total decreases in endogenous ACR, depending on the administration doses.

CONCLUSION

Findings from this study indicate that regular consumption of DHCs-rich diets holds great promise to alleviate the development of ACR-associated chronic diseases.

Targeted delivery of acrolein scavenger hydralazine in spinal cord injury using folate-linker-drug conjugation

Oxidative stress has been shown to play a critical pathogenic role in functional loss after spinal cord injury (SCI). As a direct result of oxidative stress, lipid peroxidation-derived aldehydes have emerged as key culprits that sustain secondary injury and contribute significantly to pathological outcomes. Acrolein, a neurotoxin, has been shown to be elevated in SCI and can result in post-SCI neurological deficits. Reducing acrolein has therefore emerged as a novel and effective therapeutic strategy in SCI. Previous studies have revealed that hydralazine, an FDA approved blood pressure lowering medication, when administered after SCI shows strong acrolein scavenging capabilities and significantly improves cellular and behavioral outcomes. However, while effective at scavenging acrolein, hydralazine's blood pressure lowering activity can have a detrimental impact on neurotrauma patients. Here, our goal was to preserve the acrolein scavenging capability while mitigating the effect of hydralazine on blood pressure. We accomplished this using a folate-targeted delivery system to deploy hydralazine to the folate receptor positive inflammatory site of the cord injury. Using a model of rat SCI, we found that this system is effective for targeting the injury site, and that folate targeted hydralazine can scavenge acrolein without significantly impacting blood pressure.

Critical role of mitochondrial aldehyde dehydrogenase 2 in acrolein sequestering in rat spinal cord injury

Lipid peroxidation-derived aldehydes, such as acrolein, the most reactive aldehyde, have emerged as key culprits in sustaining post-spinal cord injury (SCI) secondary pathologies leading to functional loss. Strong evidence suggests that mitochondrial aldehyde dehydrogenase-2 (ALDH2), a key oxidoreductase and powerful endogenous anti-aldehyde machinery, is likely important for protecting neurons from aldehydes-mediated degeneration. Using a rat model of spinal cord contusion injury and recently discovered ALDH2 activator (Alda-1), we planned to validate the aldehyde-clearing and neuroprotective role of ALDH2. Over an acute 2 day period post injury, we found that ALDH2 expression was significantly lowered post-SCI, but not so in rats given Alda-1. This lower enzymatic expression may be linked to heightened acrolein-ALDH2 adduction, which was revealed in co-immunoprecipitation experiments. We have also found that administration of Alda-1 to SCI rats significantly lowered acrolein in the spinal cord, and reduced cyst pathology. In addition, Alda-1 treatment also resulted in significant improvement of motor function and attenuated post-SCI mechanical hypersensitivity up to 28 days post-SCI. Finally, ALDH2 was found to play a critical role in in vitro protection of PC12 cells from acrolein exposure. It is expected that the outcome of this study will broaden and enhance anti-aldehyde strategies in combating post-SCI neurodegeneration and potentially bring treatment to millions of SCI victims. All animal work was approved by Purdue Animal Care and Use Committee (approval No. 1111000095) on January 1, 2021.

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.

Kinetic assessment of Michael addition reactions of alpha, beta-unsaturated carbonyl compounds to amino acid and protein thiols

Humans have extensive adverse exposure to alpha,beta-unsaturated carbonyl compounds (ABuCs) as these are major toxins in smoke and exhaust fumes, as well as products of lipid peroxidation. In contrast, another ABuC, dimethylfumarate, is used to treat psoriasis and multiple sclerosis. ABuCs undergo Michael adduction with amine, imidazole and thiol groups, with reaction at Cys residues predominating. Here we report rate constants, k₂, for ABuCs (acrolein, crotonaldehyde, dimethylfumarate, cyclohex-1-en-2-one, cyclopent-1-en-2-one) with Cys residues present on N-Ac-Cys, GSH, bovine serum albumin, creatine kinase, papain, glyceraldehyde-3-phosphate dehydrogenase, and both wild-type and the C151S mutant of Keap-1. k₂ values for N-Ac-Cys and GSH vary by > 250-fold, indicating a marked ABuC structure dependence, with acrolein the most reactive. There is also considerable variation in k₂ between protein Cys groups, with these significantly greater than for GSH. A linear inverse correlation for acrolein with the thiol pK_a indicates that the thiolate anion is the reactive species. The modest k₂ for GSH rationalizes the detection of protein adducts of ABuCs in cells. The k₂ values for dimethylfumarate also vary markedly, with the Cys151 residue on Keap-1 being particularly reactive, with the C151S mutant giving a much lower k₂ value. The data for crotonaldehyde, dimethylfumarate, and cyclohex-1-en-2-one show little correlation with the Cys pK_a values, indicating that steric/electronic interactions, rather than Cys ionization are important. These data indicate that protein Cys residues, and particularly Cys151 on Keap-1, react readily with dimethylfumarate, and this may help rationalize the use of this compound as a therapeutic agent.

In vitro dosimetry analyses for acrolein exposure in normal human lung epithelial cells and human lung cancer cells

Establishing accurate dosimetry is important for assessing the toxicity of xenobiotics as well as for comparing responses between different test systems. In this study, we used acrolein as a model toxicant and defined the concentration-response relationships of the key adverse responses in normal human bronchial epithelial (NHBE) cells and human mucoepidermoid pulmonary carcinoma (NCI-H292) cells. Direct trace analysis of intracellular free acrolein is extremely challenging, if not impossible. Therefore, we developed a new method for indirectly estimating the intracellular uptake of acrolein. A 10-min treatment was employed to capture the rapid occurrence of the key alkylation reactions of acrolein. Responses, including protein carbonylation, GSH depletion, and GSH-acrolein (GSH-ACR) adduct formation, were all linearly correlated with acrolein uptake in both cell types. Compared to the NCI-H292 mucoepidermoid carcinoma cells, NHBE cells were more sensitive to acrolein exposure. Furthermore, results from the time-course studies demonstrated that depletion and conjugation of GSH were the primary adverse events and directly associated with the cytotoxicity induced by acrolein. In summary, these data suggest that cell susceptibility to acrolein exposure is closely associated with acrolein uptake and formation of GSH-ACR adducts. The dosimetric analysis presented in this study may provide useful information for computational modeling and risk assessment of acrolein using different test systems.

Trapping of Acrolein by Curcumin and the Synergistic Inhibition Effect of Curcumin Combined with Quercetin

Acrolein (ACR) is a toxic unsaturated aldehyde that is formed during different steps of thermal food processing. Here, we explored the kinetics of curcumin and ACR and elucidated the pathway of curcumin trapping ACR by preparing a mono-adduct of ACR (CMA-1) conjugated with curcumin. The synergistic scavenging effect and mechanism of curcumin combined with quercetin on ACR was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Comparing the uses of curcumin and quercetin both individually and in combination, we found that quercetin in combination resulted in more curcumin being transformed into CMA-2, while curcumin in combination made the amount of di-ACR conjugated to quercetin (QDA) increase. We also added combined curcumin and quercetin into grilled chicken wings to demonstrate that curcumin and quercetin could scavenge ACR by forming their own ACR adducts and antioxidant activity during the process. Our results have noted a new strategy, in which some combinations of dietary polyphenols might contribute to the removal of toxic ACR produced during thermal food processing.

Acrolein: A Potential Mediator of Oxidative Damage in Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of vision loss among working-age adults. Extensive evidences have documented that oxidative stress mediates a critical role in the pathogenesis of DR. Acrolein, a product of polyamines oxidation and lipid peroxidation, has been demonstrated to be involved in the pathogenesis of various human diseases. Acrolein’s harmful effects are mediated through multiple mechanisms, including DNA damage, inflammation, ROS formation, protein adduction, membrane disruption, endoplasmic reticulum stress, and mitochondrial dysfunction. Recent investigations have reported the involvement of acrolein in the pathogenesis of DR. These studies have shown a detrimental effect of acrolein on the retinal neurovascular unit under diabetic conditions. The current review summarizes the existing literature on the sources of acrolein, the impact of acrolein in the generation of oxidative damage in the diabetic retina, and the mechanisms of acrolein action in the pathogenesis of DR. The possible therapeutic interventions such as the use of polyamine oxidase inhibitors, agents with antioxidant properties, and acrolein scavengers to reduce acrolein toxicity are also discussed.

Acrolein-Trapping Mechanism of Theophylline in Green Tea, Coffee, and Cocoa: Speedy and Successful

Increasing evidence has identified the unsaturated aldehyde acrolein (ACR) as the potential factor that causes deoxyribonucleic acid cross-linking and the development of chronic diseases. The objective of this study was to investigate the mechanism by which theophylline (TP) scavenges ACR for the first time. TP efficiently scavenged ACR through forming adducts, which was demonstrated in a system in which TP was incubated with ACR at different ratios for different times for liquid chromatography with tandem mass spectrometry. Then, the mono- and di-ACR-TP adducts were purified, and their structures were elucidated by high-resolution mass spectrometry and nuclear magnetic resonance analysis. We found that the ACR residue on mono-ACR-TP further trapped one more ACR and formed di-ACR-TP adducts. Furthermore, mono- and di-ACR-TP had similar time-dependent ACR-scavenging activity to TP. Finally, we demonstrated that green tea, coffee, and cocoa inhibited ACR by trapping ACR to form mono- and di-ACR-TP adducts during the incubation of green tea, coffee, and cocoa with ACR.

Translating In Vitro Acrolein-Trapping Capacities of Tea Polyphenol and Soy Genistein to In Vivo Situation is Mediated by the Bioavailability and Biotransformation of Individual Polyphenols

SCOPE

Acrolein (ACR) is a highly toxic unsaturated aldehyde. Humans are both endogenously and exogenously exposed to ACR. Long-term exposure to ACR leads to various chronic diseases. Dietary polyphenols have been reported to be able to attenuate ACR-induced toxicity in vitro via formation of ACR-polyphenol conjugates. However, whether in vitro ACR-trapping abilities of polyphenols can be maintained under in vivo environments is still unknown.

METHODS AND RESULTS

Two most commonly consumed dietary polyphenols, (-)-epigallocatechin-3-gallate (EGCG) from tea and genistein from soy, are evaluated for their anti-Acrolein behaviors both in vitro and in mice. Tea EGCG exerts a much higher capacity to capture ACR than soy genistein in vitro. But translation of in vitro anti-ACR activity into in vivo is mainly mediated by bioavailability and biotransformation of individual polyphenols. It is found that 1) both absorbed EGCG and genistein can trap endogenous ACR by forming mono-ACR adducts and eventually be excreted into mouse urine; 2) both absorbed EGCG and genistein can produce active metabolites, methyl-EGCG (MeEGCG) and orobol, to scavenge endogenous ACR; 3) both MeEGCG and non-absorbed EGCG show ability to trap ACR in the gut; 4) considerable amounts of microbial metabolites of genistein display enhanced anti-ACR capacity both in the body and in the gut, compared to genistein; and 5) biotransformation of genistein is able to boost its in vivo anti-ACR capacity, compared to EGCG.

CONCLUSION

The findings demonstrate that in vivo anti-ACR ability of dietary polyphenols cannot be reflected solely based on their in vitro ability. The bioavailability and biotransformation of individual polyphenols, and especially the gut microbiome, contribute to in vivo anti-ACR ability of dietary polyphenols.

Scavenging of Acrolein by Food-Grade Antioxidant Propyl Gallate in a Model Reaction System and Cakes

Reactive carbonyl species (RCS), such as acrolein (ACR), glyoxal (GO), and methylglyoxal (MGO), have received extensive attention recently as a result of their high activity and toxicity in vitro and in vivo. In the present study, propyl gallate (PG), a common food antioxidant, was found to effectively trap more ACR than butylated hydroxytoluene and butylated hydroxyanisole through the formation of mono-ACR adducts (PG-ACR) and di-ACR adducts (PG-2ACR). The two adducts were successfully purified, and their structures were elucidated on the basis of their high-resolution mass spectrometry and ¹H, ¹³C, and two-dimensional nuclear magnetic resonance data. We further identified that PG-ACR had the ability to continue to trap GO and MGO to form PG-ACR-GO and PG-ACR-MGO, respectively, by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Furthermore, we verified that PG could inhibit the production of ACR, GO, and MGO via trapping these RCS simultaneously to form the corresponding adducts in pound cakes using LC-MS/MS.

Mechanisms of soft and hard electrophile toxicities

Electron-deficient chemicals (electrophiles) react with compounds that have one or more unshared valence electron pairs (nucleophiles). The resulting covalent reactions between electrophiles and nucleophiles (e.g., Michael addition, SN2 reactions) are important, not only to Organic Chemistry, but also to the fields of Molecular Biology and Toxicology. Specifically, covalent bond formation is the operational basis of many critically important cellular processes; e.g., enzyme function, neurotransmitter release, and membrane-vesicle fusion. Given this context it is understandable that these reactions are also relevant to Toxicology, since a significant number of xenobiotic chemicals are toxic electrophiles that can react with endogenous nucleophilic residues. Therefore, the purpose of this Review is to discuss electrophile-nucleophile chemistry as it pertains to cell injury and resulting organ toxicity. Our discussion will involve an introduction to the Hard and Soft, Acids and Bases (HSAB) theory of Pearson. The HSAB concept provides a framework for calculation of quantum chemical parameters that classify the electrophile and nucleophile covalent components according to their respective electronic nature (softness/hardness) and reactivity (electrophilicity/nucleophilicity). The calculated quantum indices in conjunction with corroborative in vivo, in chemico (cell free) and in vitro research can offer an illuminating approach to mechanistic discovery. Accordingly, we will provide examples that demonstrate how this approach has been used to discern mechanisms and sites of electrophile action.

Evaluating Mode of Action of Acrolein Toxicity in an In Vitro Human Airway Tissue Model

Acrolein is a reactive unsaturated aldehyde and is found at high concentrations in both mainstream and side-stream tobacco smoke. Exposure to acrolein via cigarette smoking has been associated with acute lung injury, chronic obstructive pulmonary diseases (COPDs), and asthma. In this study, we developed an in vitro treatment strategy that resembles the inhalation exposure to acrolein experienced by smokers and systematically examined the adverse respiratory effects induced by the noncytotoxic doses of acrolein in a human airway epithelial tissue model. A single 10-min exposure to buffered saline containing acrolein significantly induced oxidative stress and inflammatory responses, with changes in protein oxidation and GSH depletion occurring immediately after the treatment whereas responses in inflammation requiring a manifestation time of at least 24 h. Repeated exposure to acrolein for 10 consecutive days resulted in structural and functional changes that recapitulate the pathological lesions of COPD, including alterations in the beating frequency and structures of ciliated cells, inhibition of mucin expression and secretion apparatus, and development of squamous differentiation. Although some of the early responses caused by acrolein exposure were reversible after a 10-day recovery, perturbations in the functions and structures of the air-liquid-interface (ALI) cultures, such as mucin production, cilia structures, and morphological changes, failed to fully recover over the observation period. Taken together, these findings are consistent with its mode of action that oxidative stress and inflammation have fundamental roles in acrolein-induced tissue remodeling. Furthermore, these data demonstrate the usefulness of analytical methods and testing strategy for recapitulating the key events in acrolein toxicity using an in vitro model.

Carbonyl compounds in different stages of vinification and exposure risk assessment through Merlot wine consumption

The objective of this research was to estimate for the first time the transformations that the free form of some target carbonyl compounds may undergo during winemaking and assess the exposure risk to these compounds through the consumption of the Merlot commercial wines under study. Acrolein and furfural were found in grapes and the respective wines, although levels were observed to decline throughout the winemaking process. Formaldehyde was found in all stages of wine production in levels lower than the limit of quantification of the method and ethyl carbamate was not found in samples. Acetaldehyde seems to be a precursor of acetoin and 2,3-butanediol, since the levels of this aldehyde decreased along winemaking and the formation of the ester and alcohol was verified. Furfural levels decreased, while the occurrence of furan-containing compounds increased during winemaking. The formation of acetaldehyde during alcoholic fermentation and the potential environmental contamination of grapes with acrolein and furfural are considered as the critical points related to the presence of toxic carbonyl compounds in the wine. Acrolein was found in the samples under study in sufficient quantities to present risk to human health, while other potentially toxic carbonyl compounds did not result in risk. This study indicated for the first time the presence of acrolein in grapes suggesting that environmental pollution can play an important role in the levels of this aldehyde detected in wines. Reduction of the emission of this aldehyde to the environment may be achieved by replacing wood burning by another heat source in fireplaces or wood stones, and abandoning the practice of burning garbage and vegetation.

Exercise and β-alanine supplementation on carnosine-acrolein adduct in skeletal muscle

Previous studies have demonstrated that exercise results in reactive aldehyde production and that β-alanine supplementation increases carnosine content in skeletal muscle. However, little is known about the influence exercise and β-alanine supplementation have on the formation of carnosine-aldehydes. The goal of the present study was to monitor the formation of carnosine-aldehyde adducts, following high-intensity intermittent exercise, before and after β-alanine supplementation. Vastus lateralis biopsy samples were taken from 14 cyclists, before and after a 28 day β-alanine supplementation, following 4 bouts of a 30 s all-out cycling test, and carnosine and CAR-aldehyde adducts [carnosine-acrolein, CAR-ACR (m/z 303), carnosine-4-hydroxy-2-hexenal, CAR-HHE (m/z 341) and carnosine-4-hydroxy-2-nonenal, CAR-HNE (m/z 383)] were quantified by HPLC-MS/MS. β-alanine supplementation increased muscle carnosine content by ~50% (p = 0.0001 vs. Pre-Supplementation). Interestingly, there was a significant increase in post-exercise CAR-ACR content following β-alanine supplementation (p < 0.001 vs. post-exercise before supplementation), whereas neither exercise alone nor supplementation alone increased CAR-ACR formation. These results suggest that carnosine functions as an acrolein-scavenger in skeletal muscle. Such a role would be relevant to the detoxification of this aldehyde formed during exercise, and appears to be enhanced by β-alanine supplementation. These novel findings not only have the potential of directly benefiting athletes who engage in intensive training regimens, but will also allow researchers to explore the role of muscle carnosine in detoxifying reactive aldehydes in diseases characterized by abnormal oxidative stress.

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Lipid peroxidation generates electrophilic reactive aldehydes.

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β-Alanine supplementation increases muscle carnosine content in skeletal muscle.

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The carnosine-acrolein levels were higher in muscle following β-alanine supplementation in post-exercise.

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This acrolein-scavenger role for muscle carnosine may contribute to its ergogenic and therapeutic effects.

Response of DNA damage genes in acrolein-treated lung adenocarcinoma cells

Acrolein is a α-β-unsaturated aldehyde and is toxic to human upon its exposure from the environment. Sources of exposure to acrolein can be from heating cooking oil, automobile exhaust, tobacco smoke, and plastic waste. Acrolein exposure to lung is a major concern because of its volatile nature and due to its presence in the urban atmospheric air. Acrolein being highly reactive forms DNA and protein adducts, thereby making the cells vulnerable to long-term damage. Such long-term effect can lead to high susceptibility towards malignant transformation as has been reported in cigarette smokers. The response of DNA damaging genes by acrolein can perhaps give an insight to the cause of damage in the DNA by acrolein. The aim of this study was to examine the response of the DNA damage responsive genes by acrolein in A549 lung adenocarcinoma cells. Acrolein treatment at IC50 concentration showed a robust response of the DNA repair genes but eventually failed to rescue the cells from undergoing apoptosis. The cells pretreated with acrolein and followed by growing the same cells in fresh medium in the absence of acrolein did not help the cells to proliferate. These results conclude that exposure to acrolein marks long-lasting damage to DNA, irrespective of the DNA repair response.

Carbonyl scavengers as pharmacotherapies in degenerative disease: Hydralazine repurposing and challenges in clinical translation

During cellular metabolism, spontaneous oxidative damage to unsaturated lipids generates many electrophilic carbonyl compounds that readily attack cell macromolecules, forming adducts that are potential drivers of tissue dysfunction. Since such damage is heightened in many degenerative conditions, researchers have assessed the efficacy of nucleophilic carbonyl-trapping drugs in animal models of such disorders, anticipating that they will protect tissues by intercepting toxic lipid-derived electrophiles (LDEs) within cells. This Commentary explores recent animal evidence for carbonyl scavenger efficacy in two disparate yet significant conditions known to involve LDE production, namely spinal cord injury (SCI) and alcoholic liver disease (ALD). Primary emphasis is placed on studies that utilised hydralazine, a clinically-approved "broad-spectrum" scavenger known to trap multiple LDEs. In addition to reviewing recent studies of hydralazine efficacy in animal SCI and ALD models, the Commentary reviews new insights concerning novel lifespan- and healthspan-extending properties of hydralazine obtained during studies in model invertebrate organisms, since the mechanisms involved seem of likely benefit during the treatment of degenerative disease. Finally, noting that human translation of the histoprotective properties of hydralazine have been limited, the final section of the Commentary will address two obstacles that hamper clinical translation of LDE-trapping therapies while also suggesting potential strategies for overcoming these problems.

Acrolein-mediated neuronal cell death and alpha-synuclein aggregation: Implications for Parkinson's disease

Growing evidence suggests that oxidative stress plays a critical role in neuronal destruction characteristic of Parkinson's disease (PD). However, the molecular mechanisms of oxidative stress-mediated dopaminergic cell death are far from clear. In the current investigation, we tested the hypothesis that acrolein, an oxidative stress and lipid peroxidation (LPO) product, is a key factor in the pathogenesis of PD. Using a combination of in vitro, in vivo, and cell free models, coupled with anatomical, functional, and behavioral examination, we found that acrolein was elevated in 6-OHDA-injected rats, and behavioral deficits associated with 6-OHDA could be mitigated by the application of the acrolein scavenger hydralazine, and mimicked by injection of acrolein in healthy rats. Furthermore, hydralazine alleviated neuronal cell death elicited by 6-OHDA and another PD-related toxin, rotenone, in vitro. We also show that acrolein can promote the aggregation of alpha-synuclein, suggesting that alpha-synuclein self-assembly, a key pathological phenomenon in human PD, could play a role in neurotoxic effects of acrolein in PD models. These studies suggest that acrolein is involved in the pathogenesis of PD, and the administration of anti-acrolein scavengers such as hydralazine could represent a novel strategy to alleviate tissue damage and motor deficits associated with this disease.

A G4·K+ hydrogel made from 5′-hydrazinoguanosine for remediation of α,β-unsaturated carbonyls

A G₄·KCl hydrogel with a nucleophilic 5′ sidechain absorbs α,β-unsaturated carbonyls via formation of cyclic adducts.

Exposure assessment of process-related contaminants in food by biomarker monitoring

Exposure assessment is a fundamental part of the risk assessment paradigm, but can often present a number of challenges and uncertainties. This is especially the case for process contaminants formed during the processing, e.g. heating of food, since they are in part highly reactive and/or volatile, thus making exposure assessment by analysing contents in food unreliable. New approaches are therefore required to accurately assess consumer exposure and thus better inform the risk assessment. Such novel approaches may include the use of biomarkers, physiologically based kinetic (PBK) modelling-facilitated reverse dosimetry, and/or duplicate diet studies. This review focuses on the state of the art with respect to the use of biomarkers of exposure for the process contaminants acrylamide, 3-MCPD esters, glycidyl esters, furan and acrolein. From the overview presented, it becomes clear that the field of assessing human exposure to process-related contaminants in food by biomarker monitoring is promising and strongly developing. The current state of the art as well as the existing data gaps and challenges for the future were defined. They include (1) using PBK modelling and duplicate diet studies to establish, preferably in humans, correlations between external exposure and biomarkers; (2) elucidation of the possible endogenous formation of the process-related contaminants and the resulting biomarker levels; (3) the influence of inter-individual variations and how to include that in the biomarker-based exposure predictions; (4) the correction for confounding factors; (5) the value of the different biomarkers in relation to exposure scenario's and risk assessment, and (6) the possibilities of novel methodologies. In spite of these challenges it can be concluded that biomarker-based exposure assessment provides a unique opportunity to more accurately assess consumer exposure to process-related contaminants in food and thus to better inform risk assessment.

Rapid and Convenient Oxidative Release of Thiol-Conjugated Forms of Microcystins for Chemical Analysis

Microcystins are potent cyclic heptapeptide toxins found in some cyanobacteria, and usually contain an α,β-unsaturated carbonyl group that is readily conjugated to thiol-containing amino acids, peptides, and proteins in vivo and in vitro. Methods for deconjugating these types of adducts have recently been reported, but the reactions are slow or result in derivatized microcystins. Mercaptoethanol derivatives of a range of microcystins were therefore used as model compounds to develop deconjugation procedures in which the dialkyl sulfide linkage was oxidized to a sulfoxide or sulfone that, when treated with base, rapidly eliminated the adducted thiol as its sulfenate or sulfinate via β-elimination to afford free microcystins with the α,β-unsaturated carbonyl group intact. These free microcystins can be analyzed by LC/MS to determine the toxin profile of bound microcystins. The method was tested on Cys- and GSH-derivatives of [Dha⁷]MC-LR. In solution, the deconjugation reactions were complete within minutes at pH 10.7 and within a few hours at pH 9.2. Oxidation of sulfides to sulfoxides is easier and more rapid than oxidation to sulfones, allowing the use of milder oxidants and shorter reaction times. Oxidation of any methionine residues present in the microcystins occurs inevitably during these procedures, and interpretation of the microcystin profile obtained by LC/MS analysis needs to take this into account. Oxidation of tryptophan residues and degradation of microcystins by excess oxidant were circumvented by the addition of Me₂SO as a sacrificial reducing agent. These methods may be useful for other compounds that undergo conjugation via thia-Michael addition, such as acrylamide and deoxynivalenol. Oxidation of sulfides to sulfoxides can occur in vivo and could affect the bioavailability of toxins and drugs conjugated via thia-Michael addition, potentially exacerbating oxidative stress by catalytically converting GSH to its sulfenate via conjugation, oxidation, and elimination to regenerate the free toxin.