Mutagenicity of acrolein and acrolein-induced DNA adducts

AlkA Glycosylase and AlkB Dioxygenase Constitute an Effective Protective System for Endogenously Arising Acrolein: E. coli AlkA Glycosylase Excises Acrolein Adduct to Adenine

Acrolein (ACR) is a ubiquitous environmental pollutant but also formed endogenously as a metabolite in oxidative stress conditions. Its adduct to adenine 1,N6-α-hydroxypropanoadenine (HPA) is a mutagenic lesion effectively repaired by the AlkB dioxygenase. Here, we provide in vivo, in vitro, and in silico evidence that it is also the substrate for the AlkA glycosylase. We studied the role of AlkA and AlkB in E. coli cells under conditions of induced adaptive response. Both alkA and alkB defective strains were not more sensitive to exogenous ACR than the wild type was. To simulate endogenously arising adducts, we used acrolein-modified plasmids, allowing monitoring of all kinds of substitutions originating from the acrolein modification of adenine. Both the AlkA and AlkB proteins were engaged in alleviating HPA-induced mutagenesis. Moreover, HPA was effectively repaired by AlkA and AlkB in vivo, even without induction of adaptive response. These findings suggest that the main contribution to acrolein mutagenicity comes from its endogenous sources, whereas AlkA and AlkB can play an additional role in controlling the level of DNA adducts of endogenous origin. Acrolein does not induce the adaptive response. HPA contains an asymmetric carbon atom in the hydroxypropano ring and exists as two stereoisomers. AlkA excises both of them in vitro. Molecular modelling demonstrated how dsDNA carrying both HPA stereoisomers could be properly bound at the AlkA catalytic centre. So, in contrast to the reaction catalyzed by AlkB, the HPA repair by AlkA is not expected to be stereoselective.

ALDH3A1-mediated detoxification of reactive aldehydes contributes to distinct muscle responses to denervation and Amyotrophic Lateral Sclerosis progression

Different muscles exhibit varied susceptibility to degeneration in Amyotrophic Lateral Sclerosis (ALS), a fatal neuromuscular disorder. Extraocular muscles (EOMs) are particularly resistant to ALS progression and exploring the underlying molecular nature may deliver great therapeutic value. Reactive aldehyde 4-hydroxynonenal (HNE) is implicated in ALS pathogenesis and ALDH3A1 is an inactivation-resistant intracellular detoxifier of 4-HNE protecting eyes against UV-induced oxidative stress. Here we detected prominently higher levels of ALDH3A1 in mouse EOMs than other muscles under normal physiological conditions. In an ALS mouse model (hSOD1G93A) reaching end-stage, ALDH3A1 expression was sustained at high level in EOMs, whereas substantial upregulation of ALDH3A1 occurred in soleus and diaphragm. The upregulation was less pronounced in extensor digitorum longus (EDL) muscle, which endured the most severe pathological remodeling as demonstrated by unparalleled upregulation of a denervation marker ANKRD1 expression. Interestingly, sciatic nerve transection in wildtype mice induced ALDH3A1 and ANKRD1 expression in an inverse manner over muscle type and time. Adeno-associated virus enforced overexpression of ALDH3A1 protected myotubes from 4-HNE-induced DNA fragmentation, plasma membrane leakage and restored MG53-mediated membrane repair. Our data indicate that ALDH3A1 may contribute to distinct muscle resistance to ALS through detoxifying reactive aldehydes.

Post-harvest processed parsnip showed improved anti-oxidative capacity and protective potential against acrolein-induced inflammation in vitro and in vivo

Introduction

Post-harvest processing plays a crucial role in enhancing the bioactive properties of vegetables. This study aimed to investigate the impact of post-harvest aging on parsnip's bioactive profile and its protective effects against acrolein (Acr)-induced inflammation, a common pollutant and irritant linked to respiratory inflammation.

Methods

Parsnips (Pastinaca sativa L.) were aged at 60°C for up to 30 days, with extracts collected at intervals. Total phenolic content (TPC) and antioxidant capacity were assessed using DPPH assays. Key bioactive compounds, including falcarindiol, DDMP, and 5-HMF, were quantified. In vitro studies used BEAS-2B cells to evaluate anti-inflammatory effects, while in vivo tests involved treating Acr-exposed mice with aged parsnip extract to observe cytokine responses.

Results

Aged parsnip extracts showed a 9.96-fold increase in TPC and a 4.25-fold increase in antioxidant capacity after 30 days. Bioactive compounds significantly increased in aged samples, especially falcarindiol and 5-HMF. In vitro, aged parsnip reduced Acr-induced TNF-α and IL-1β expression. In vivo, treated mice showed reduced bronchial inflammation, goblet cell hyperplasia, and cytokine expression compared to controls.

Discussion

These findings suggest that post-harvest aging enhances parsnip's antioxidant and anti-inflammatory properties, highlighting its potential as a functional food ingredient for managing inflammation and respiratory health.

Acrolein: formation, health hazards and its controlling by dietary polyphenols

Acrolein, a highly reactive toxic aldehyde, is a common dietary and environmental contaminant which can also be generated endogenously. Exposure to acrolein has been positively associated with some pathological conditions, such as atherosclerosis, diabetes mellitus, stroke, and Alzheimer's disease. At the cellular level, acrolein induces various harmful effects, particularly protein adduction and oxidative damages. Polyphenols are a group of secondary plant metabolites ubiquitously presented in fruits, vegetables, and herbs. Recent evidence has gradually solidified the protective role of polyphenols by working as acrolein scavengers and regulator of acrolein toxicities. This was largely attributed to the ability of polyphenols as antioxidants and sacrificial nucleophiles in trapping acrolein. This review discussed the exposure and toxicity of acrolein, summarized the known and anticipated contribution of polyphenols in ameliorating acrolein contamination and its health hazards.

Cigarette Smoke-Induced Respiratory Response: Insights into Cellular Processes and Biomarkers

Cigarette smoke (CS) poses a significant risk factor for respiratory, vascular, and organ diseases owing to its high content of harmful chemicals and reactive oxygen species (ROS). These substances are known to induce oxidative stress, inflammation, apoptosis, and senescence due to their exposure to environmental pollutants and the presence of oxidative enzymes. The lung is particularly susceptible to oxidative stress. Persistent oxidative stress caused by chronic exposure to CS can lead to respiratory diseases such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), and lung cancer. Avoiding exposure to environmental pollutants, like cigarette smoke and air pollution, can help mitigate oxidative stress. A comprehensive understanding of oxidative stress and its impact on the lungs requires future research. This includes identifying strategies for preventing and treating lung diseases as well as investigating the underlying mechanisms behind oxidative stress. Thus, this review aims to investigate the cellular processes induced by CS, specifically inflammation, apoptosis, senescence, and their associated biomarkers. Furthermore, this review will delve into the alveolar response provoked by CS, emphasizing the roles of potential therapeutic target markers and strategies in inflammation and oxidative stress.

Low Level of Advanced Glycation End Products in Serum of Patients with Allergic Rhinitis and Chronic Epstein-Barr Virus Infection at Different Stages of Virus Persistence

Advanced glycation end products (AGEs) are formed in a nonenzymatic reaction of the reducing sugars with amino groups of proteins, lipids, and nucleic acids of different tissues and body fluids. A relatively small number of studies have been conducted on the role of AGEs in allergic inflammation. In this study, patients with allergic rhinitis (AR) were examined for the presence of Epstein-Barr virus and the content of fluorescent and nonfluorescent AGEs. We have also determined the level of a unique epitope (AGE10) which was recently identified in human serum using monoclonal antibodies against synthetic melibiose-derived AGE (MAGE). The levels of AGE10 determined with an immunoenzymatic method revealed no significant difference in the patients' blood with intermittent AR and chronic EBV persistence in the active and latent phases. It has been shown that there is a statistically significantly smaller amount of AGEs and pentosidine in groups of patients, both with and without viremia, than in healthy subjects. In turn, higher levels of immune complexes than of AGE10 were detected in the groups of patients, in contrast to the control group, which had lower levels of complexes than AGE10 concentration. In patients with active infection, there is even more complexes than of noncomplexed AGE10 antigen. The lower level of AGE in allergic rhinitis patient sera may also be due, besides complexes, to allergic inflammation continuously activating the cells, which effectively remove glycation products from the body.

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.

A H2O2-activatable nanoprobe for diagnosing interstitial cystitis and liver ischemia-reperfusion injury via multispectral optoacoustic tomography and NIR-II fluorescent imaging

Developing high-quality NIR-II fluorophores (emission in 1000-1700 nm) for in vivo imaging is of great significance. Benzothiadiazole-core fluorophores are an important class of NIR-II dyes, yet ongoing limitations such as aggregation-caused quenching in aqueous milieu and non-activatable response are still major obstacles for their biological applications. Here, we devise an activatable nanoprobe to address these limitations. A molecular probe named BTPE-NO₂ is synthesized by linking a benzothiadiazole core with two tetraphenylene groups serving as hydrophobic molecular rotors, followed by incorporating two nitrophenyloxoacetamide units at both ends of the core as recognition moieties and fluorescence quenchers. An FDA-approved amphiphilic polymer Pluronic F127 is then employed to encapsulate the molecular BTPE-NO₂ to render the nanoprobe BTPE-NO₂@F127. The pathological levels of H₂O₂ in the disease sites cleave the nitrophenyloxoacetamide groups and activate the probe, thereby generating strong fluorescent emission (950~1200 nm) and ultrasound signal for multi-mode imaging of inflammatory diseases. The nanoprobe can therefore function as a robust tool for detecting and imaging the disease sites with NIR-II fluorescent and multispectral optoacoustic tomography (MSOT) imaging. Moreover, the three-dimensional MSOT images can be obtained for visualizing and locating the disease foci.

Impact of manipulation of glycerol/diol dehydratase activity on intestinal microbiota ecology and metabolism

Glycerol/diol dehydratases (GDH) are enzymes that catalyse the production of propionate from 1,2-propanediol, and acrolein from glycerol. Acrolein reacts with dietary carcinogenic heterocyclic amines (HCA), reducing HCA mutagenicity, but is itself also an antimicrobial agent and toxicant. Gut microbial GDH activity has been suggested as an endogenous acrolein source; however, there is limited information on the potential of the intestinal microbiota to have GDH activity, and what impact it can have on the intestinal ecosystem and host health. We hypothesized that GDH activity of gut microbiota is determined by the abundance and distribution of GDH-active taxa and can be enhanced by supplementation of the GDH active Anaerobutyricum hallii, and tested this hypothesis combining quantitative profiling of gdh, model batch fermentations, microbiota manipulation, and kinetic modelling of acrolein formation. Our results suggest that GDH activity is a common trait of intestinal microbiota shared by a few taxa, which was dependent on overall gdh abundance. Anaerobutyricum hallii was identified as a key taxon in GDH metabolism, and its supplementation increased the rate of GDH activity and acrolein release, which enhanced the transformation of HCA and reduced fermentation activity. The findings of this first systematic study on acrolein release by intestinal microbiota indicate that dietary and microbial modulation might impact GDH activity, which may influence host health.

Loss of Fibroblast Growth Factor Receptor 2 (FGFR2) Leads to Defective Bladder Urothelial Regeneration after Cyclophosphamide Injury

Cyclophosphamide may cause hemorrhagic cystitis and eventually bladder urothelial cancer. Genetic determinants for poor outcomes are unknown. We assessed actions of fibroblast growth factor receptor (FGFR) 2 in urothelium after cyclophosphamide exposure. Conditional urothelial deletion of Fgfr2 (Fgfr2KO) did not affect injury severity or proliferation of keratin 14⁺ (KRT14⁺) basal progenitors or other urothelial cells 1 day after cyclophosphamide exposure. Three days after cyclophosphamide exposure, Fgfr2KO urothelium had defective regeneration, fewer cells, larger basal cell bodies and nuclei, paradoxical increases in proliferation markers, and excessive replication stress versus controls. Fgfr2KO mice had evidence of pathologic basal cell endoreplication associated with absent phosphorylated ERK staining and decreased p53 expression versus controls. Mice with conditional deletion of Fgfr2 in urothelium enriched for KRT14⁺ cells reproduced Fgfr2KO abnormalities after cyclophosphamide exposure. Fgfr2KO urothelium had defects up to 6 months after injury versus controls, including larger basal cells and nuclei, more persistent basal and ectopic lumenal KRT14⁺ cells, and signs of metaplasia (attenuated E-cadherin staining). Mice missing one allele of Fgfr2 also had (less severe) regeneration defects and basal cell endoreplication 3 days after cyclophosphamide exposure versus controls. Thus, reduced FGFR2/ERK signaling apparently leads to abnormal urothelial repair after cyclophosphamide exposure from pathologic basal cell endoreplication. Patients with genetic variants in FGFR2 or its ligands may have increased risks of hemorrhagic cystitis or urothelial cancer from persistent and ectopic KRT14⁺ cells.

DNA polymerase eta: A potential pharmacological target for cancer therapy

In the last two decades, intensive research has been carried out to improve the survival rates of cancer patients. However, the development of chemoresistance that ultimately leads to tumor relapse poses a critical challenge for the successful treatment of cancer patients. Many cancer patients experience tumor relapse and ultimately die because of treatment failure associated with acquired drug resistance. Cancer cells utilize multiple lines of self-defense mechanisms to bypass chemotherapy and radiotherapy. One such mechanism employed by cancer cells is translesion DNA synthesis (TLS), in which specialized TLS polymerases bypass the DNA lesion with the help of monoubiquitinated proliferating cell nuclear antigen. Among all TLS polymerases (Pol η, Pol ι, Pol κ, REV1, Pol ζ, Pol μ, Pol λ, Pol ν, and Pol θ), DNA polymerase eta (Pol η) is well studied and majorly responsible for the bypass of cisplatin and UV-induced DNA damage. TLS polymerases contribute to chemotherapeutic drug-induced mutations as well as therapy resistance. Therefore, targeting these polymerases presents a novel therapeutic strategy to combat chemoresistance. Mounting evidence suggests that inhibition of Pol η may have multiple impacts on cancer therapy such as sensitizing cancer cells to chemotherapeutics, suppressing drug-induced mutagenesis, and inhibiting the development of secondary tumors. Herein, we provide a general introduction of Pol η and its clinical implications in blocking acquired drug resistance. In addition; this review addresses the existing gaps and challenges of Pol η mediated TLS mechanisms in human cells. A better understanding of the Pol η mediated TLS mechanism will not merely establish it as a potential pharmacological target but also open possibilities to identify novel drug targets for future therapy.

A Comprehensive Review on Source, Types, Effects, Nanotechnology, Detection, and Therapeutic Management of Reactive Carbonyl Species Associated with Various Chronic Diseases

Continuous oxidation of carbohydrates, lipids, and amino acids generate extremely reactive carbonyl species (RCS). Human body comprises some important RCS namely hexanal, acrolein, 4-hydroxy-2-nonenal, methylglyoxal, malondialdehyde, isolevuglandins, and 4-oxo-2- nonenal etc. These RCS damage important cellular components including proteins, nucleic acids, and lipids, which manifests cytotoxicity, mutagenicity, multitude of adducts and crosslinks that are connected to ageing and various chronic diseases like inflammatory disease, atherosclerosis, cerebral ischemia, diabetes, cancer, neurodegenerative diseases and cardiovascular disease. The constant prevalence of RCS in living cells suggests their importance in signal transduction and gene expression. Extensive knowledge of RCS properties, metabolism and relation with metabolic diseases would assist in development of effective approach to prevent numerous chronic diseases. Treatment approaches for RCS associated diseases involve endogenous RCS metabolizers, carbonyl metabolizing enzyme inducers, and RCS scavengers. Limited bioavailability and bio efficacy of RCS sequesters suggest importance of nanoparticles and nanocarriers. Identification of RCS and screening of compounds ability to sequester RCS employ several bioassays and analytical techniques. Present review describes in-depth study of RCS sources, types, properties, identification techniques, therapeutic approaches, nanocarriers, and their role in various diseases. This study will give an idea for therapeutic development to combat the RCS associated chronic diseases.

The Effect of Iodine-Containing Nano-Micelles, FS-1, on Antibiotic Resistance, Gene Expression and Epigenetic Modifications in the Genome of Multidrug Resistant MRSA Strain Staphylococcus aureus ATCC BAA-39

Application of supplementary drugs which increase susceptibility of pathogenic bacteria to antibiotics is a promising yet unexplored approach to overcome the global problem of multidrug-resistant infections. The discovery of a new drug, an iodine-containing nano-molecular complex FS-1, which has proven to improve susceptibility to antibiotics in various pathogens, including MRSA strain Staphylococcus aureus ATCC BAA-39TM, allowed studying this phenomenon. Chromosomal DNA and total RNA samples extracted from the FS-1 treated strain (FS) and from the negative control (NC) cultures were sequenced by PacBio SMRT and Ion Torrent technologies, respectively. PacBio DNA reads were used to assemble chromosomal DNA of the NC and FS variants of S. aureus BAA-39 and to perform profiling of epigenetically modified nucleotides. Results of transcriptional profiling, variant calling and detection of epigenetic modifications in the FS variant were compared to the NC variant. Additionally, the genetic alterations caused by the treatment of S. aureus BAA-39 with FS-1 were compared to the results of a similar experiment conducted with another model organism, E. coli ATCC BAA-196. Several commonalities in responses of these phylogenetically distant microorganisms to the treatment with FS-1 were discovered, which included metabolic transition toward anaerobiosis and oxidative/osmotic stress response. S. aureus culture appeared to be more sensitive to FS-1 due to a higher penetrability of cells by iodine bound compounds, which caused carbonyl stress associated with nucleotide damaging by FS-1, abnormal epigenetic modifications and an increased rate of mutations. It was hypothesized that the disrupted pattern of adenine methylated loci within methicillin-resistance chromosome cassettes (SCCmec) may promote excision of this antibiotic resistance determinant from chromosomes while the altered pattern of cytosine methylation was behind the adaptive gene regulation in the culture FS. The selection against the antibiotic resistance in bacterial populations caused by abnormal epigenetic modifications exemplifies possible mechanisms of antibiotic resistance reversion induced by iodine-containing compounds. These finding will facilitate development of therapeutic agents against multidrug-resistant infections.

Characterization and Validation of a Chronic Model of Cyclophosphamide-Induced Interstitial Cystitis/Bladder Pain Syndrome in Rats

Interstitial cystitis/Bladder Pain Syndrome (IC/BPS) is a chronic inflammatory disease characterized by visceral pain and voiding symptoms. IC/BPS is still an unsolved enigma with ineffective diagnosis criteria and treatment. A main limitation in IC/BPS understanding is the lack of appropriate preclinical model. Cyclophosphamide (CYP) is commonly used as an experimental model for IC/BPS in rodent. However, the proposed models are very aggressive, contrasting with what occurs in clinic, and often associated with severe toxicity and high mortality rate. In addition, visceral pain, the hallmark symptom of IC/BPS, has been validated in only few of them. In this study, we developed a chronic model of CYP-induced IC/BPS in female rat. In our protocol, no severe weight loss occurred and the survival rate was 100%. In accordance to human pathology, chronic CYP-injected rats developed severe painful behavior whereas only sparse inflammation was observed. Inflammatory response was characterized by bladder edema and focal urothelial damage but absence of massive infiltrate. This chronic model showed persistent symptoms indicative for a central sensitization mechanism. We further demonstrate that CYP-induced chronic visceral pain was significantly reduced by curative treatment with clinically relevant compounds (gabapentin, ibuprofen, and Ialuril^®). We therefore developed and validated a rat model of chronic cystitis that shares strong similarity with human non-ulcerative IC/BPS features without overtly affecting the animal health. This model will thus provide mechanistic insights of the disease and help to evaluate therapeutic agents for IC/BPS.

Interaction of Acrylamide, Acrolein, and 5-Hydroxymethylfurfural with Amino Acids and DNA

Acrylamide, acrolein, and 5-hydroxymethylfurfural (HMF) are food-borne toxicants produced during the thermal processing of food. The α,β-unsaturated carbonyl group or aldehyde group in their structure can react easily with the amino, imino, and thiol groups in amino acids, proteins, and DNA via Michael addition and nucleophilic reactions in food and in vivo. This work reviews the interaction pathways of three toxins with amino acids and the cytotoxicity and changes after the digestion and absorption of the resulting adducts. Their interaction with DNA is also discussed. Amino acids ubiquitously exist in foods and are added as nutrients or used to control these food-borne toxicants. Hence, the interaction widely occurring in foods would greatly increase the internal exposure of these toxins and their derived compounds after food intake. This review aims to encourage further investigation on toxin-derived compounds, including their types, exposure levels, toxicities, and pharmacokinetics.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Interaction of volatile organic compounds and underlying liver disease: a new paradigm for risk

Occupational and environmental exposures to industrial chemicals are known to cause hepatotoxicity and liver injury, in humans and in animal models. Historically, research has focused on severe acute liver injury (e.g. fulminant liver failure) or endstage diseases (e.g. cirrhosis and HCC). However, it has become recently recognized that toxicants can cause more subtle changes to the liver. For example, toxicant-associated steatohepatitis, characterized by hepatic steatosis, and inflammation, was recently recognized in an occupational cohort exposed to vinyl chloride. At high occupational levels, toxicants are sufficient to cause liver damage and disease even in healthy subjects with no comorbidities for liver injury. However, it is still largely unknown how exposure to toxicants initiate and possibly more importantly exacerbate liver disease, when combined with other factors, such as underlying non-alcoholic fatty liver disease caused by poor diet and/or obesity. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of toxicant-induced liver disease, rational targeted therapy can be developed to better predict risk, as well as to treat or prevent this disease. The purpose of this review is to summarize established and proposed mechanisms of volatile organic compound-induced liver injury and to highlight key signaling events known or hypothesized to mediate these effects.

Oxidative stress and hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths worldwide. There are two major challenges for HCC, the first being that early detection is generally not applicable, and secondly, it is usually fatal within several months after diagnosis. HCC is an inflammation-induced cancer. It is known that chronic inflammation leads to oxidative/nitrosative stress and lipid peroxidation, generating excess oxidative stress, together with aldehydes which can react with DNA bases to form promutagenic DNA adducts. In this review, the evidence between oxidative stress and liver carcinogenesis is summarized. We focused on the potential of using DNA adducts as oxidative stress biomarkers for liver carcinogenesis.

Genotoxicity of lipid oxidation compounds

Lipid peroxidation, the oxidative degradation of membrane lipids by reactive oxygen species generates a large variety of breakdown products such as alkanes, aldehydes, ketones, alcohols, furans and others. Due to their reactivity aldehydes (alkanals, 2-alkenals, 2,4-alkadienals, 4-hydroxyalkenals) received a lot of attention, in particular because they can diffuse from the site of formation and interact with proteins and nucleic acids thus acting as second toxic messengers. The major aldehydic peroxidation product of membrane lipids is 4-hydroxynonenal (HNE). Since HNE and other 4-hydroxyalkenals are strong alkylating agents they have therefore been considered to be the biologically most important peroxidation products. Although initially research focused on the toxicological potential of these compounds it is now well known that they play also a crucial role in cell signaling under physiological and pathophysiological conditions. Thus, it is obvious that the biological effects will be determined by the intracellular concentrations which can trigger adaptation, DNA damage and cell death. This review will not cover all these aspects but will concentrate on the genotoxic properties of selected lipid oxidation products important in the context of pathophysiological developments together with a chapter on epigenetic modifications.

Acrolein measurement and degradation in Dulbecco's Modified Eagle Medium: an examination of in-vitro exposure metrics

Acrolein is a reactive α,β-unsaturated aldehyde known for its adduction to endogenous biomolecules, resulting in initiation or exacerbation of several disease pathways. In-vitro systems are routinely used to elucidate the cytotoxic or mechanistic role(s) of acrolein in pathogenesis. Nevertheless, the half-life of acrolein in biological or in-vitro systems, e.g. blood or culture media, has not been well characterized. Since in-vitro cytotoxic and mechanistic investigations routinely expose cultures to acrolein from 1 hour to 72 hours, we aimed to characterize the half-life of acrolein in culture medium to ascertain the plausible exposure window. Half-life determinations were conducted in low-serum DMEM at room temperature and 37 °C, both with and without H9c2 cells. For quantitative assessment, acrolein was derivatized to a fluorescent 7-hydroxyquinoline method validated in-house and assessed via fluorescent spectroscopy. In closed vessel experiments at room temperature, acrolein in DMEM was reduced by more than 40% at 24 hours, irrespective of the initial concentration. Expectedly, open vessel experiments demonstrated accelerated depletion over time at room temperature, and faster still at 37 °C. The presence of cells tended to further accelerate degradation by an additional 15-30%, depending on temperature. These results undermine described experimental exposure conditions stated in most in-vitro experiments. Recognition of this discrepancy between stated and actual exposure metrics warrant examination of novel alternative objective and representative exposure characterization for in-vitro studies to facilitate translation to in-vivo and in-silico methods.

Mechanisms Underlying Acrolein-Mediated Inhibition of Chromatin Assembly

Acrolein is a major component of cigarette smoke and cooking fumes. Previously, we reported that acrolein compromises chromatin assembly; however, underlying mechanisms have not been defined. Here, we report that acrolein reacts with lysine residues, including lysines 5 and 12, sites important for chromatin assembly, on histone H4 in vitro and in vivo Acrolein-modified histones are resistant to acetylation, suggesting that the reduced H4K12 acetylation that occurs following acrolein exposure is probably due to the formation of acrolein-histone lysine adducts. Accordingly, the association of H3/H4 with the histone chaperone ASF1 and importin 4 is disrupted and the translocation of green fluorescent protein-tagged H3 is inhibited in cells exposed to acrolein. Interestingly, in vitro plasmid supercoiling assays revealed that treatment of either histones or ASF1 with acrolein has no effect on the formation of plasmid supercoiling, indicating that acrolein-protein adduct formation itself does not directly interfere with nucleosome assembly. Notably, exposure of histones to acrolein prior to histone acetylation leads to the inhibition of remodeling and spacing factor chromatin assembly, which requires acetylated histones for efficient assembly. These results suggest that acrolein compromises chromatin assembly by reacting with histone lysine residues at the sites critical for chromatin assembly and prevents these sites from physiological modifications.

Acute Acrolein Exposure Induces Impairment of Vocal Fold Epithelial Barrier Function

Acrolein is a ubiquitous pollutant abundant in cigarette smoke, mobile exhaust, and industrial waste. There is limited literature on the effects of acrolein on vocal fold tissue, although there are clinical reports of voice changes after pollutant exposures. Vocal folds are responsible for voice production. The overall objective of this study was to investigate the effects of acrolein exposure on viable, excised vocal fold epithelial tissue and to characterize the mechanism underlying acrolein toxicity. Vocal fold epithelia were studied because they form the outermost layer of the vocal folds and are a primary recipient of inhaled pollutants. Porcine vocal fold epithelia were exposed to 0, 50, 100, 500, 900 or 1300 μM of acrolein for 3 hours; the metabolic activity, epithelial resistance, epithelial permeability, tight junction protein (occludin and claudin 3) expression, cell membrane integrity and lipid peroxidation were investigated. The data demonstrated that acrolein exposure at 500 μM significantly reduced vocal fold epithelial metabolic activity by 27.2% (p≤0.001). Incubation with 100 μM acrolein caused a marked increase in epithelial permeability by 130.5% (p<0.05) and a reduction in transepithelial electrical resistance (TEER) by 180.0% (p<0.001). While the expression of tight junctional protein did not change in acrolein-treated samples, the cell membrane integrity was significantly damaged with a 45.6% increase of lipid peroxidation as compared to controls (p<0.05). Taken together, these data provide evidence that acute acrolein exposure impairs vocal fold epithelial barrier integrity. Lipid peroxidation-induced cell membrane damage may play an important role in reducing the barrier function of the epithelium.

Dark Hydrazone Fluorescence Labeling Agents Enable Imaging of Cellular Aldehydic Load

Aldehydes are key intermediates in many cellular processes, from endogenous metabolic pathways like glycolysis to undesired exogenously induced processes such as lipid peroxidation and DNA interstrand cross-linking. Alkyl aldehydes are well documented to be cytotoxic, affecting the functions of DNA and protein, and their levels are tightly regulated by the oxidative enzyme ALDH2. Mutations in this enzyme are associated with cardiac damage, diseases such as Fanconi anemia (FA), and cancer. Many attempts have been made to identify and quantify the overall level of these alkyl aldehydes inside cells, yet there are few practical methods available to detect and monitor these volatile aldehydes in real time. Here, we describe a multicolor fluorogenic hydrazone transfer ("DarkZone") system to label alkyl aldehydes, yielding up to 30-fold light-up response in vitro. A cell-permeant DarkZone dye design was applied to detect small-molecule aldehydes in the cellular environment. The new dye design also enabled the monitoring of cellular acetaldehyde production from ethanol over time by flow cytometry, demonstrating the utility of the DarkZone dyes for measuring and imaging the aldehydic load related to human disease.

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.

Mechanism of repair of acrolein- and malondialdehyde-derived exocyclic guanine adducts by the α-ketoglutarate/Fe(II) dioxygenase AlkB

The structurally related exocyclic guanine adducts α-hydroxypropano-dG (α-OH-PdG), γ-hydroxypropano-dG (γ-OH-PdG), and M₁dG are formed when DNA is exposed to the reactive aldehydes acrolein and malondialdehyde (MDA). These lesions are believed to form the basis for the observed cytotoxicity and mutagenicity of acrolein and MDA. In an effort to understand the enzymatic pathways and chemical mechanisms that are involved in the repair of acrolein- and MDA-induced DNA damage, we investigated the ability of the DNA repair enzyme AlkB, an α-ketoglutarate/Fe(II) dependent dioxygenase, to process α-OH-PdG, γ-OH-PdG, and M₁dG in both single- and double-stranded DNA contexts. By monitoring the repair reactions using quadrupole time-of-flight (Q-TOF) mass spectrometry, it was established that AlkB can oxidatively dealkylate γ-OH-PdG most efficiently, followed by M₁dG and α-OH-PdG. The AlkB repair mechanism involved multiple intermediates and complex, overlapping repair pathways. For example, the three exocyclic guanine adducts were shown to be in equilibrium with open-ring aldehydic forms, which were trapped using (pentafluorobenzyl)hydroxylamine (PFBHA) or NaBH₄. AlkB repaired the trapped open-ring form of γ-OH-PdG but not the trapped open-ring of α-OH-PdG. Taken together, this study provides a detailed mechanism by which three-carbon bridge exocyclic guanine adducts can be processed by AlkB and suggests an important role for the AlkB family of dioxygenases in protecting against the deleterious biological consequences of acrolein and MDA.

Acrolein induction of oxidative stress and degranulation in mast cells

Increases in asthma worldwide have been associated epidemiologically with expanding urban air pollution. The mechanistic relationship between airway hyper-responsiveness, inflammation, and ambient airborne triggers remains ambiguous. Acrolein, a ubiquitous aldehyde pollutant, is a product of incomplete combustion reactions. Acrolein is abundant in cigarette smoke, effluent from industrial smokestacks, diesel exhaust, and even hot oil cooking vapors. Acrolein is a potent airway irritant and can induce airway hyper-responsiveness and inflammation in the lungs of animal models. In the present study, we utilized the mast cell analog, RBL-2H3, to interrogate the responses of cells relevant to airway inflammation and allergic responses as a model for the induction of asthma-like conditions upon exposure to acrolein. We hypothesized that acrolein would induce oxidative stress and degranulation in airway mast cells. Our results indicate that acrolein at 1 ppm initiated degranulation and promoted the generation of reactive oxygen species (ROS). Introduction of antioxidants to the system significantly reduced both ROS generation and degranulation. At higher levels of exposure (above 100 ppm), RBL-2H3 cells displayed signs of severe toxicity. This experimental data indicates acrolein can induce an allergic inflammation in mast cell lines, and the initiation of degranulation was moderated by the application of antioxidants.

Rapamycin inhibits acrolein-induced apoptosis by alleviating ROS-driven mitochondrial dysfunction in male germ cells

OBJECTIVES

Acrolein (Acr) is a highly reactive α, β-unsaturated aldehyde, which can induce reactive oxygen species (ROS) generation. Several factors, including lipid peroxidation, clinical use of cyclophosphamide, fried foods, automobile exhausts, smoking and aging can increase its concentration in blood serum. Mounting evidence has suggested that Acr-induced ROS might reduce quality of sperm. Thus, the aim of this study was to examine reproductive toxicity of Acr-caused ROS in vitro and find a means to alleviate it.

MATERIALS AND METHODS

We investigated the effects of Acr on male germ cell (MGC)-derived GC-1 cells in vitro. Dihydroethidium and DCFH-DA fluorescent dyes were used to determine generation of intracellular ROS.

RESULTS

We found that Acr induced ROS generation, which was accompanied by reduced Bcl2/Bax ratio, substantial decline in mitochondrial membrane potential, and further promoted apoptosis of MGCs. Furthermore, Rapamycin was capable of alleviating Acr-induced ROS, reducing ROS-induced apoptosis by increasing ratio of Bcl2/Bax mRNA and proteins, and protecting MGC mitochondrial membranes.

CONCLUSION

Rapamycin inhibited Acr-induced apoptosis by alleviating ROS-driven mitochondrial dysfunction in MGCs.

Reactive carbonyl species in vivo: generation and dual biological effects

Reactive carbonyls are widespread species in living organisms and mainly known for their damaging effects. The most abundant reactive carbonyl species (RCS) are derived from oxidation of carbohydrates, lipids, and amino acids. Chemical modification of proteins, nucleic acids, and aminophospholipids by RCS results in cytotoxicity and mutagenicity. In addition to their direct toxicity, modification of biomolecules by RCS gives rise to a multitude of adducts and cross links that are increasingly implicated in aging and pathology of a wide range of human diseases. Understanding of the relationship between metabolism of RCS and the development of pathological disorders and diseases may help to develop effective approaches to prevent a number of disorders and diseases. On the other hand, constant persistence of RCS in cells suggests that they perform some useful role in living organisms. The most beneficial effects of RCS are their establishment as regulators of cell signal transduction and gene expression. Since RCS can modulate different biological processes, new tools are required to decipher the precise mechanisms underlying dual effects of RCS.

Thermally induced process-related contaminants: the example of acrolein and the comparison with acrylamide: opinion of the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG)

α,β-Unsaturated aliphatic carbonyl compounds are naturally widespread in food, but are also formed during the thermal treatment of food. This applies, for example, to the genotoxic carcinogen acrylamide (AA), but also to acrolein (AC), the simplest α,β-unsaturated aldehyde. First observations indicate that human exposure to AC may be higher than the exposure to AA. The DFG Senate Commission on Food Safety therefore compared data on AC and AA available in the scientific literature, evaluating current knowledge on formation, occurrence, exposure, metabolism, biological effects, toxicity, and carcinogenicity and defined knowledge gaps as well as research needs in an opinion on November 19, 2012, in German. The English version was agreed on April 17, 2013.

Acetaldehyde-induced cytotoxicity involves induction of spermine oxidase at the transcriptional level

Ethanol consumption causes serious liver injury including cirrhosis and hepatocellular carcinoma. Ethanol is metabolized mainly in the liver to acetic acid through acetaldehyde. We investigated the effect of ethanol and acetaldehyde on polyamine metabolism since polyamines are essential factors for normal cellular functions. We found that acetaldehyde induced spermine oxidase (SMO) at the transcriptional level in HepG2 cells. The levels and activities of ornithine decarboxylase (ODC) and spermidine/spermine acetyltransferase (SSAT) were not affected by acetaldehyde. Spermidine content was increased and spermine content was decreased by acetaldehyde treatment. Knockdown of SMO expression using siRNA reduced acetaldehyde toxicity. Acetaldehyde exposure increased free acrolein levels. An increase of acrolein by acetaldehyde was SMO dependent. Our results indicate that cytotoxicity of acetaldehyde involves, at least in part, oxidation of spermine to spermidine by SMO, which is induced by acetaldehyde.

Involvement of the endogenous hydrogen sulfide/Ca(v) 3.2 T-type Ca2+ channel pathway in cystitis-related bladder pain in mice

BACKGROUND AND PURPOSE

Hydrogen sulfide (H(2) S), generated by enzymes such as cystathionine-γ-lyase (CSE) from L-cysteine, facilitates pain signals by activating the Ca(v) 3.2 T-type Ca(2+) channels. Here, we assessed the involvement of the CSE/H(2) S/Ca(v) 3.2 pathway in cystitis-related bladder pain.

EXPERIMENTAL APPROACH

Cystitis was induced by i.p. administration of cyclophosphamide in mice. Bladder pain-like nociceptive behaviour was observed and referred hyperalgesia was evaluated using von Frey filaments. Phosphorylation of ERK in the spinal dorsal horn was determined immunohistochemically following intravesical administration of NaHS, an H(2) S donor.

KEY RESULTS

Cyclophosphamide caused cystitis-related symptoms including increased bladder weight, accompanied by nociceptive changes (bladder pain-like nociceptive behaviour and referred hyperalgesia). Pretreatment with DL-propargylglycine, an inhibitor of CSE, abolished the nociceptive changes and partly prevented the increased bladder weight. CSE protein in the bladder was markedly up-regulated during development of cystitis. Mibefradil or NNC 55-0396, blockers of T-type Ca(2+) channels, administered after the symptoms of cystitis appeared, reversed the nociceptive changes. Further, silencing of Ca(v) 3.2 protein by repeated intrathecal administration of mouse Ca(v) 3.2-targeting antisense oligodeoxynucleotides also significantly attenuated the nociceptive changes, but not the increased bladder weight. Finally, the number of cells staining positive for phospho-ERK was increased in the superficial layer of the L6 spinal cord after intravesical administration of NaHS, an effect inhibited by NNC 55-0396.

CONCLUSION AND IMPLICATIONS

Endogenous H(2) S, generated by up-regulated CSE, caused bladder pain and referred hyperalgesia through the activation of Ca(v) 3.2 channels, one of the T-type Ca(2+) channels, in mice with cyclophosphamide-induced cystitis.

Acrolein effects in pulmonary cells: relevance to chronic obstructive pulmonary disease

Acrolein (2-propenal) is a highly reactive α,β-unsaturated aldehyde and a respiratory irritant that is ubiquitously present in the environment but that can also be generated endogenously at sites of inflammation. Acrolein is abundant in tobacco smoke, which is the major environmental risk factor for chronic obstructive pulmonary disease (COPD), and elevated levels of acrolein are found in the lung fluids of COPD patients. Its high electrophilicity makes acrolein notorious for its facile reaction with biological nucleophiles, leading to the modification of proteins and DNA and depletion of antioxidant defenses. As a consequence, acrolein results in oxidative stress as well as altered intracellular signaling and gene transcription/translation. In pulmonary cells, acrolein, at subtoxic concentrations, can activate intracellular stress kinases, alter the production of inflammatory mediators and proteases, modify innate immune response, induce mucus hypersecretion, and damage airway epithelium. A better comprehension of the mechanisms underlying acrolein effects in the airways may suggest novel treatment strategies in COPD.

Differences in susceptibility to inactivation of human aldehyde dehydrogenases by lipid peroxidation byproducts

Aldehyde dehydrogenases (ALDHs) are involved in the detoxification of aldehydes generated as byproducts of lipid peroxidation. In this work, it was determined that, among the three most studied human ALDH isoforms, ALDH2 showed the highest catalytic efficiency for oxidation of acrolein, 4-hydroxy-2-nonenal (4-HNE), and malondialdehyde. ALDH1A1 also exhibited significant activity with these substrates, whereas ALDH3A1 only showed activity with 4-HNE. ALDH2 was also the most sensitive isoform to irreversible inactivation by these compounds. Remarkably, ALDH3A1 was insensitive to these aldehydes even at concentrations as high as 20 mM. Formation of adducts of ALDH1A1 and ALDH2 with acrolein increased their K(d) values for NAD(+) by 2- and 3-fold, respectively. NADH exerted a higher protection than propionaldehyde to the inactivation by acrolein, and this protection was additive. These results suggested that both binding sites, those for aldehyde and NAD(+) in ALDH2, are targets for the inactivation by lipid peroxidation products. Thus, with the advantage of being relatively inactivation-insensitive, ALDH1A1 and ALDH3A1 may be actively participating in the detoxification of these aldehydes in the cells.

DNA damage induced by endogenous aldehydes: current state of knowledge

DNA damage plays a major role in various pathophysiological conditions including carcinogenesis, aging, inflammation, diabetes and neurodegenerative diseases. Oxidative stress and cell processes such as lipid peroxidation and glycation induce the formation of highly reactive endogenous aldehydes that react directly with DNA, form aldehyde-derived DNA adducts and lead to DNA damage. In occasion of persistent conditions that influence the formation and accumulation of aldehyde-derived DNA adducts the resulting unrepaired DNA damage causes deregulation of cell homeostasis and thus significantly contributes to disease phenotype. Some of the most highly reactive aldehydes produced endogenously are 4-hydroxy-2-nonenal, malondialdehyde, acrolein, crotonaldehyde and methylglyoxal. The mutagenic and carcinogenic effects associated with the elevated levels of these reactive aldehydes, especially, under conditions of stress, are attributed to their capability of causing directly modification of DNA bases or yielding promutagenic exocyclic adducts. In this review, we discuss the current knowledge on DNA damage induced by endogenously produced reactive aldehydes in relation to the pathophysiology of human diseases.