Visualization of Acrolein Upregulation during Ferroptosis by a Ratiometric Fluorescent Probe

Ferroptosis is a pattern of cell death caused by iron-dependent accumulation of lipid peroxides and is closely associated with the occurrence and development of multiple diseases. Acrolein (ACR), one of the final metabolites of lipid peroxidation, is a reactive carbonyl species with strong biotoxicity. Effective detection of ACR is important for understanding its role in the progression of ferroptosis and studying the specific mechanisms of ferroptosis-mediated diseases. However, visualization detection of ACR during ferroptosis has not yet been reported. In this work, the first ratiometric fluorescent probe (HBT-SH) based on 2-(2'-hydroxyphenyl) benzothiazole (HBT) was designed for tracing endogenous ACR with an unprecedented regiospecific ACR-induced intramolecular cyclization strategy, which employs 2-aminoethanethiol as an ACR-selective recognition receptor. The experimental results showed that HBT-SH has excellent selectivity, high sensitivity (LOD = 0.26 μM) and good biocompatibility. More importantly, the upregulation of ACR levels was observed during ferroptosis in HeLa cells and zebrafish, indicating that ACR may be a specific active molecule that plays an essential biological role during ferroptosis or may serve as a potential marker of ferroptosis, which has great significance for studying the pathological process and treatment options of ferroptosis-related diseases.

Theanine Capture of Reactive Carbonyl Species in Humans after Consuming Theanine Capsules or Green Tea

Acrolein (ACR), methylglyoxal (MGO), and glyoxal (GO) are a class of reactive carbonyl species (RCS), which play a crucial role in the pathogenesis of chronic and age-related diseases. Here, we explored a new RCS inhibitor (theanine, THE) and investigated its capture capacity on RCS in vivo by human experiments. After proving that theanine could efficiently capture ACR instead of MGO/GO by forming adducts under simulated physiological conditions, we further detected the ACR/MGO/GO adducts of theanine in the human urine samples after consumption of theanine capsules (200 and 400 mg) or green tea (4 cups, containing 200 mg of theanine) by using ultraperformance liquid chromatography-time-of-flight-high-resolution mass spectrometry. Quantitative assays revealed that THE-ACR, THE-2ACR-1, THE-MGO, and THE-GO were formed in a dose-dependent manner in the theanine capsule groups; the maximum value of the adducts of theanine was also tested. Furthermore, besides the RCS adducts of theanine, the RCS adducts of catechins could also be detected in the drinking tea group. Whereas, metabolite profile analysis showed that theanine could better capture RCS produced in the renal metabolic pathway than catechins. Our findings indicated that theanine could reduce RCS in the body in two ways: as a pure component or contained in tea leaves.

Acrolein Induces Changes in Cell Membrane and Cytosol Proteins of Erythrocytes

High concentrations of acrolein (2-propenal) are found in polluted air and cigarette smoke, and may also be generated endogenously. Acrolein is also associated with the induction and progression of many diseases. The high reactivity of acrolein towards the thiol and amino groups of amino acids may cause damage to cell proteins. Acrolein may be responsible for the induction of oxidative stress in cells. We hypothesized that acrolein may contribute to the protein damage in erythrocytes, leading to the disruption of the structure of cell membranes. The lipid membrane fluidity, membrane cytoskeleton, and osmotic fragility were measured for erythrocytes incubated with acrolein for 24 h. The levels of thiol, amino, and carbonyl groups were determined in cell membrane and cytosol proteins. The level of non-enzymatic antioxidant potential (NEAC) and TBARS was also measured. The obtained research results showed that the exposure of erythrocytes to acrolein causes changes in the cell membrane and cytosol proteins. Acrolein stiffens the cell membrane of erythrocytes and increases their osmotic sensitivity. Moreover, it has been shown that erythrocytes treated with acrolein significantly reduce the non-enzymatic antioxidant potential of the cytosol compared to the control.

Identification of a cinnamoyl-CoA reductase from Cinnamomum cassia involved in trans-cinnamaldehyde biosynthesis

MAIN CONCLUSION

The identification of a functional cinnamoyl-CoA reductase enzyme from Cinnamomum cassia involved in trans-cinnamaldehyde biosynthesis offers the potential for enhancing trans-cinnamaldehyde production through genetic engineering. A significant accumulation of trans-cinnamaldehyde has been found in the bark tissues of C. cassia, used in traditional Chinese medicine. trans-Cinnamaldehyde exhibits various pharmacological properties such as anti-inflammatory, analgesic, and protection of the stomach and the digestive tract. However, further elucidation and characterization of the biosynthetic pathway for trans-cinnamaldehyde is required. In this study, we conducted an integrated analysis of trans-cinnamaldehyde accumulation profiles and transcriptomic data from five different C. cassia tissues to identify the genes involved in its biosynthesis. The transcriptome data we obtained included nearly all genes associated with the trans-cinnamaldehyde pathway, with the majority demonstrating high abundance in branch barks and trunk barks. We successfully cloned four C. cassia cinnamoyl-CoA reductases (CcCCRs), a key gene in trans-cinnamaldehyde biosynthesis. We found that the recombinant CcCCR1 protein was the only one that more efficiently converted cinnamoyl-CoA into trans-cinnamaldehyde. CcCCR1 exhibited approximately 14.7-fold higher catalytic efficiency (kcat/Km) compared to the Arabidopsis thaliana cinnamoyl-CoA reductase 1 (AtCCR1); therefore, it can be utilized for engineering higher trans-cinnamaldehyde production as previously reported. Molecular docking studies and mutagenesis experiments also validated the superior catalytic activity of CcCCR1 compared to AtCCR1. These findings provide valuable insights for the functional characterization of enzyme-coding genes and hold potential for future engineering of trans-cinnamaldehyde biosynthetic pathways.

Mitochondrial DNA is a key driver in cigarette smoke extract-induced IL-6 expression

Smoking is an independent risk factor for atherosclerosis, the primary pathogenesis of which is inflammation. We recently reported that cigarette smoke extract (CSE) causes cytosolic and extracellular accumulation of both nuclear (n) and mitochondrial (mt) DNA, which leads to inflammation in human umbilical vein endothelial cells (HUVECs). In this study, we examined whether inflammation induction depends more on cytosolic nDNA or mtDNA, and which chemical constituents of CSE are involved. Acrolein (ACR), methyl vinyl ketone (MVK), and 2-cyclopenten-1-one (CPO) were used in the experiments, as these are the major cytotoxic factors in CSE in various cell types. Stimulation with ACR, MVK, or CPO alone resulted in the accumulation of DNA double-strand breaks (DSBs), but not oxidative DNA damage, accumulation of cytosolic DNA, or increased expression of inflammatory cytokines. Simultaneous administration of all three constituents (ALL) resulted in oxidative DNA damage in both the nucleus and mitochondria, accumulation of DSBs, reduced mitochondrial membrane potential, induction of minority mitochondrial outer membrane permeabilization, accumulation of cytosolic free DNA, and increased expression of inflammatory cytokines such as IL-6 and IL-1α. Treatment with N-acetyl-L-cysteine, a reactive oxygen species scavenger, suppressed oxidative DNA damage and the increased expression of IL-6 and IL-1α induced by ALL or CSE. The ALL- or CSE-induced increase in IL-6 expression, but not that of IL-1α, was suppressed by mtDNA depletion. In conclusion, ACR, MVK, and CPO may strongly contribute to CSE-induced inflammation. More importantly, cytosolic free mtDNA is thought to play an important role in IL-6 expression, a central mediator of inflammation.

Bulk and In Situ Quantification of Coniferaldehyde Residues in Lignin

Lignin is a group of cell wall localised heterophenolic polymers varying in the chemistry of the aromatic and aliphatic parts of its units. The lignin residues common to all vascular plants have an aromatic ring with one para hydroxy group and one meta methoxy group, also called guaiacyl (G). The terminal function of the aliphatic part of these G units, however, varies from alcohols, which are generally abundant, to aldehydes, which represent a smaller proportion of lignin monomers. The proportions of aldehyde to alcohol G units in lignin are, nevertheless, precisely controlled to respond to environmental and development cues. These G aldehyde to alcohol unit proportions differ between each cell wall layer of each cell type to fine-tune the cell wall biomechanical and physico-chemical properties. To precisely determine changes in lignin composition, we, herein, describe the various methods to detect and quantify the levels and positions of G aldehyde units, also called coniferaldehyde residues, of lignin polymers in ground plant samples as well as in situ in histological cross-sections.

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

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

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

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

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

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

Hydralazine Promotes Central Nervous System Recovery after Spinal Cord Injury by Suppressing Oxidative Stress and Inflammation through Macrophage Regulation

OBJECTIVE

This study aims to investigate the effects of hydralazine on inflammation induced by spinal cord injury (SCI) in the central nervous system (CNS) and its mechanism in promoting the structural and functional recovery of the injured CNS.

METHODS

A compressive SCI mouse model was utilized for this investigation. Immunofluorescence and quantitative real-time polymerase chain reaction were employed to examine the levels of acrolein, acrolein-induced inflammation-related factors, and macrophages at the injury site and within the CNS. Western blotting was used to evaluate the activity of the phosphoinositide 3-kinase (PI3K)/AKT pathway to study macrophage regulation. The neuropathic pain and motor function recovery were evaluated by glutamic acid decarboxylase 65/67 (GAD65/67), vesicular glutamate transporter 1 (VGLUT1), paw withdrawal response, and Basso Mouse Scale score. Nissl staining and Luxol Fast Blue (LFB) staining were performed to investigate the structural recovery of the injured CNS.

RESULTS

Hydralazine downregulated the levels of acrolein, IL-1β, and TNF-α in the spinal cord. The downregulation of acrolein induced by hydralazine promoted the activation of the PI3K/AKT pathway, leading to M2 macrophage polarization, which protected neurons against SCI-induced inflammation. Additionally, hydralazine promoted the structural recovery of the injured spinal cord area. Mitigating inflammation and oxidative stress by hydralazine in the animal model alleviated neuropathic pain and altered neurotransmitter expression. Furthermore, hydralazine facilitated motor function recovery following SCI. Nissl staining and LFB staining indicated that hydralazine promoted the structural recovery of the injured CNS.

CONCLUSION

Hydralazine, an acrolein scavenger, significantly mitigated SCI-induced inflammation and oxidative stress in vivo, modulated macrophage activation, and consequently promoted the structural and functional recovery of the injured CNS.

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

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

Cinnamaldehyde Resist Salmonella Typhimurium Adhesion by Inhibiting Type I Fimbriae

Salmonella Typhimurium (S. Typhimurium), a common foodborne pathogen, severely harms the public and food security. Type I fimbriae (T1F) of S. Typhimurium, plays a crucial role in the pathogenic processes; it mediates the adhesion of bacteria to the mannose receptor on the host cell, assists the bacteria to invade the host cell, and triggers an inflammatory response. Cinnamaldehyde is the main ingredient in cinnamon essential oil. In this study, cinnamaldehyde was demonstrated to inhibit the expression of T1F by hemagglutination inhibition test, transmission electron microscopy, and biofilms. The mechanism of cinnamaldehyde action was studied by proteomics technology, PCR and Western blotting. The results showed that cinnamaldehyde can inhibit T1F in S. typhimurium without the growth of bacteria, by regulating the level of expression and transcription of fimA, fimZ, fimY, fimH and fimW. Proteomics results showed that cinnamaldehyde downregulated the subunits and regulators of T1F. In addition, the invasion assays proved that cinnamaldehyde can indeed reduce the ability of S. typhimurium to adhere to cells. The results of animal experiments showed that the colonization in the intestinal tract and the expression levels of inflammatory cytokine were significantly decreased, and the intestinal mucosal immune factors MUC1 and MUC2 were increased under cinnamaldehyde treatment. Therefore, cinnamaldehyde may be a potential drug to target T1F to treat Salmonella infections.

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

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

DNA Damage and Oxidative Stress of Tobacco Smoke Condensate in Human Bladder Epithelial Cells

Smoking is a major risk factor for bladder cancer (BC), with up to 50% of BC cases being attributed to smoking. There are 70 known carcinogens in tobacco smoke; however, the principal chemicals responsible for BC remain uncertain. The aromatic amines 4-aminobiphenyl (4-ABP) and 2-naphthylamine (2-NA) are implicated in BC pathogenesis of smokers on the basis of the elevated BC risk in factory workers exposed to these chemicals. However, 4-ABP and 2-NA only occur at several nanograms per cigarette and may be insufficient to induce BC. In contrast, other genotoxicants, including acrolein, occur at 1000-fold or higher levels in tobacco smoke. There is limited data on the toxicological effects of tobacco smoke in human bladder cells. We have assessed the cytotoxicity, oxidative stress, and DNA damage of tobacco smoke condensate (TSC) in human RT4 bladder cells. TSC was fractionated by liquid-liquid extraction into an acid-neutral fraction (NF), containing polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, phenols, and aldehydes, and a basic fraction (BF) containing aromatic amines, heterocyclic aromatic amines, and N-nitroso compounds. The TSC and NF induced a time- and concentration-dependent cytotoxicity associated with oxidative stress, lipid peroxide formation, glutathione (GSH) depletion, and apurinic/apyrimidinic (AP) site formation, while the BF showed weak effects. LC/MS-based metabolomic approaches showed that TSC and NF altered GSH biosynthesis pathways and induced more than 40 GSH conjugates. GSH conjugates of several hydroquinones were among the most abundant conjugates. RT4 cell treatment with synthetic hydroquinones and cresol mixtures at levels present in tobacco smoke accounted for most of the TSC-induced cytotoxicity and the AP sites formed. GSH conjugates of acrolein, methyl vinyl ketone, and crotonaldehyde levels also increased owing to TSC-induced oxidative stress. Thus, TSC is a potent toxicant and DNA-damaging agent, inducing deleterious effects in human bladder cells at concentrations of <1% of a cigarette in cell culture media.

Acrolein plays a culprit role in the pathogenesis of diabetic nephropathy in vitro and in vivo

OBJECTIVE

Diabetic nephropathy (DN), also known as diabetic kidney disease (DKD), is a major chronic complication of diabetes and is the most frequent cause of kidney failure globally. A better understanding of the pathophysiology of DN would lead to the development of novel therapeutic options. Acrolein, an α,β-unsaturated aldehyde, is a common dietary and environmental pollutant.

DESIGN

The role of acrolein and the potential protective action of acrolein scavengers in DN were investigated using high-fat diet/ streptozotocin-induced DN mice and in vitro DN cellular models.

METHODS

Acrolein-protein conjugates (Acr-PCs) in kidney tissues were examined using immunohistochemistry. Renin-angiotensin system (RAS) and downstream signaling pathways were analyzed using quantitative RT-PCR and Western blot analyses. Acr-PCs in DN patients were analyzed using an established Acr-PC ELISA system.

RESULTS

We found an increase in Acr-PCs in kidney cells using in vivo and in vitro DN models. Hyperglycemia activated the RAS and downstream MAPK pathways, increasing inflammatory cytokines and cellular apoptosis in two human kidney cell lines (HK2 and HEK293). A similar effect was induced by acrolein. Furthermore, acrolein scavengers such as N-acetylcysteine, hydralazine, and carnosine could ameliorate diabetes-induced kidney injury. Clinically, we also found increased Acr-PCs in serum samples or kidney tissues of DKD patients compared to normal volunteers, and the Acr-PCs were negatively correlated with kidney function.

CONCLUSIONS

These results together suggest that acrolein plays a role in the pathogenesis of DN and could be a diagnostic marker and effective therapeutic target to ameliorate the development of DN.

ROS-derived lipid peroxidation is prevented in barley leaves during senescence

Senescence in plants enables resource recycling from senescent leaves to sink organs. Under stress, increased production of reactive oxygen species (ROS) and associated signalling activates senescence. However, senescence is not always associated with stress since it has a prominent role in plant development, in which the role of ROS signalling is less clear. To address this, we investigated lipid metabolism and patterns of lipid peroxidation related to signalling during sequential senescence in first-emerging barley leaves grown under natural light conditions. Leaf fatty acid compositions were dominated by linolenic acid (75% of total), the major polyunsaturated fatty acid (PUFA) in galactolipids of thylakoid membranes, known to be highly sensitive to peroxidation. Lipid catabolism during senescence, including increased lipoxygenase activity, led to decreased levels of PUFA and increased levels of short-chain saturated fatty acids. When normalised to leaf area, only concentrations of hexanal, a product from the 13-lipoxygenase pathway, increased early upon senescence, whereas reactive electrophile species (RES) from ROS-associated lipid peroxidation, such as 4-hydroxynonenal, 4-hydroxyhexenal and acrolein, as well as β-cyclocitral derived from oxidation of β-carotene, decreased. However, relative to total chlorophyll, amounts of most RES increased at late-senescence stages, alongside increased levels of α-tocopherol, zeaxanthin and non-photochemical quenching, an energy dissipative pathway that prevents ROS production. Overall, our results indicate that lipid peroxidation derived from enzymatic oxidation occurs early during senescence in first barley leaves, while ROS-derived lipid peroxidation associates weaker with senescence.

Cross-sectional and longitudinal associations of acrolein exposure with pulmonary function alteration: Assessing the potential roles of oxidative DNA damage, inflammation, and pulmonary epithelium injury in a general adult population

BACKGROUND

Acrolein is a significant high priority hazardous air pollutant with pulmonary toxicity and the leading cause of most noncancer adverse respiratory effects among air toxics that draws great attention. Whether and how acrolein exposure impacts pulmonary function remain inconclusive.

OBJECTIVES

To assess the association of acrolein exposure with pulmonary function and the underlying roles of oxidative DNA damage, inflammation, and pulmonary epithelium integrity.

METHODS

Among 3,279 Chinese adults from the Wuhan-Zhuhai cohort, associations of urinary acrolein metabolites (N-Acetyl-S-(2-carboxyethyl)-L-cysteine, CEMA; N-Acetyl-S-(3-hydroxypropyl)-L-cysteine, 3HPMA) as credible biomarkers of acrolein exposure with pulmonary function were analyzed by linear mixed models. Joint effects of biomarkers of oxidative DNA damage (8-hydroxy-deoxyguanosine), inflammation (C-reactive protein, CRP), and pulmonary epithelium integrity (Club cell secretory protein, CC16) with acrolein metabolites on pulmonary function and the mediating roles of these biomarkers were assessed. Besides, a subgroup (N = 138) was randomly recruited from the cohort to assess the stabilities of acrolein metabolites and their longitudinal associations with pulmonary function change in three years.

RESULTS

Significant inverse dose-response relationships between acrolein metabolites and pulmonary function were found. Each 10-fold increment in CEMA, 3HPMA, or ΣUACLM (CEMA + 3HPMA) was cross-sectionally related to a 68.56-, 40.98-, or 46.02-ml reduction in FVC and a 61.54-, 43.10-, or 50.14-ml reduction in FEV₁, respectively (P < 0.05). Furthermore, acrolein metabolites with fair to excellent stabilities were found to be longitudinally associated with pulmonary function decline in three years. Joint effects of acrolein metabolites with 8-hydroxy-deoxyguanosine, CRP, and CC16 on pulmonary function were identified. CRP significantly mediated 5.97% and 5.51% of CEMA-associated FVC and FEV₁ reductions, respectively. 8-hydroxy-deoxyguanosine significantly mediated 6.78%, 6.88%, and 7.61% of CEMA-, 3HPMA-, and ΣUACLM-associated FVC reductions, respectively.

CONCLUSIONS

Acrolein exposure of general adults was cross-sectionally and longitudinally related to pulmonary function decline, which was aggravated and/or partly mediated by oxidative DNA damage, inflammation, and pulmonary epithelium injury.

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.

•

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.

•

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.

Acrolein inhalation acutely affects the regulation of mitochondrial metabolism in rat lung

Exposure of the airways to cigarette smoke (CS) is the primary risk factor for developing several lung diseases such as Chronic Obstructive Pulmonary Disease (COPD). CS consists of a complex mixture of over 6000 chemicals including the highly reactive α,β-unsaturated aldehyde acrolein. Acrolein is thought to be responsible for a large proportion of the non-cancer disease risk associated with smoking. Emerging evidence suggest a key role for CS-induced abnormalities in mitochondrial morphology and function in airway epithelial cells in COPD pathogenesis. Although in vitro studies suggest acrolein-induced mitochondrial dysfunction in airway epithelial cells, it is unknown if in vivo inhalation of acrolein affects mitochondrial content or the pathways controlling this. In this study, rats were acutely exposed to acrolein by inhalation (nose-only; 0-4 ppm), 4 h/day for 1 or 2 consecutive days (n = 6/group). Subsequently, the activity and abundance of key constituents of mitochondrial metabolic pathways as well as expression of critical proteins and genes controlling mitochondrial biogenesis and mitophagy were investigated in lung homogenates. A transient decreasing response in protein and transcript abundance of subunits of the electron transport chain complexes was observed following acrolein inhalation. Moreover, acrolein inhalation caused a decreased abundance of key regulators associated with mitochondrial biogenesis, respectively a differential response on day 1 versus day 2. Abundance of components of the mitophagy machinery was in general unaltered in response to acrolein exposure in rat lung. Collectively, this study demonstrates that acrolein inhalation acutely and dose-dependently disrupts the molecular regulation of mitochondrial metabolism in rat lung. Hence, understanding the effect of acrolein on mitochondrial function will provide a scientifically supported reasoning to shortlist aldehydes regulation in tobacco smoke.

Apiaceous vegetables protect against acrolein-induced pulmonary injuries through modulating hepatic detoxification and inflammation in C57BL/6 male mice

Acrolein (Acr) is a reactive aldehyde in the environment. Acr causes oxidative stress and a cascade of catalytic events and has, thereby, been associated with increased risk of pulmonary diseases. Whether apiaceous vegetables (API) consumption can prevent Acr-induced pulmonary toxicity has not yet been explored hence, we investigated the effects of API on Acr-induced pulmonary damages in C57BL/6J mice. The mice were assigned into either negative control [NEG group; American Institute of Nutrition (AIN)-93G diet only], positive control (POS group; AIN-93G+Acr) or API intervention group (API group; AIN-93G+21% API+Acr). After 1 week of dietary intervention, the POS and API mice were exposed to Acr (10 µmol/kg body weight/day) for 5 days. During the exposure period, assigned diets remained the same. Prominent indicators lung of toxicity of POS mice were found, including mucus accumulation, macrophage infiltration, and hemorrhage, all of which were ameliorated by the API. Serum and lung inflammation markers, such as a tumor necrosis factor alpha were also increased by Acr while reduced by API. In the liver, API upregulated expression of glutathione S-transferases, which enhanced the metabolism of Acr into water-soluble 3-hydroxypropyl mercapturic acid for excretion. This is consistent with observed reductions in serum Acr-protein adducts. Taken together, our results suggest that API may provide protection against Acr-induced pulmonary damages and inflammation via enhancement of the hepatic detoxification of Acr.

Acrolein, an endogenous aldehyde induces Alzheimer's disease-like pathologies in mice: A new sporadic AD animal model

Alzheimer's disease (AD) is a common neurodegenerative disease that mainly affects elderly people. However, the translational research of AD is frustrating, suggesting that the development of new AD animal models is crucial. By gavage administration of acrolein, we constructed a simple sporadic AD animal model which showed classic pathologies of AD in 1 month. The AD-like phenotypes and pathological changes were as followed. 1) olfactory dysfunctions, cognitive impairments and psychological symptoms in C57BL/6 mice; 2) increased levels of Aβ1-42 and Tau phosphorylation (S396/T231) in cortex and hippocampus; 3) astrocytes and microglia proliferation; 4) reduced levels of postsynaptic density 95(PSD95) and Synapsin1, as well as the density of dendritic spines in the CA1 and DG neurons of the hippocampus; 5) high-frequency stimulation failed to induce the long-term potentiation (LTP) in the hippocampus after exposure to acrolein for 4 weeks; 6) decreased blood oxygen level-dependent (BOLD) signal in the olfactory bulb and induced high T2 signals in the hippocampus, which matched to the clinical observation in the brain of AD patients, and 7) activated RhoA/ROCK2/ p-cofilin-associated pathway in hippocampus of acrolein-treated mice, which may be the causes of synaptic damage and neuroinflammation in acrolein mice model. Taken together, the acrolein-induced sporadic AD mouse model closely reflects the pathological features of AD, which will be useful for the research on the mechanism of AD onset and the development of anti-AD drugs.

Toxicological Parameters of a Formulation Containing Cinnamaldehyde for Use in Treatment of Oral Fungal Infections: An In Vivo Study

OBJECTIVE

We aimed to define the safety and toxicity of both isolated and embedded cinnamaldehyde using a pharmaceutical formulation for the treatment of oral fungal infections in an in vivo study.

MATERIALS AND METHODS

Acute toxicity was assessed in studies with Galleria mellonella larvae and Danio rerio embryos (zebrafish), and genotoxicity was assessed in a mouse model. The pharmaceutical formulation (orabase ointment) containing cinnamaldehyde was evaluated for verification of both in vitro antifungal activity and toxicity in keratinized oral rat mucosa.

RESULTS

In Galleria mellonella larvae, cinnamaldehyde was not toxic up to the highest dose tested (20 mg/kg) and presented no genotoxicity up to the dose of 4 mg/kg in the model using mice. However, it was found to be toxic in zebrafish embryos up to a concentration of 0.035 μg/mL; LC50 0.311; EC50 0.097 (egg hatching delay); and 0.105 (Pericardial edema). In the orabase antifungal susceptibility test, cinnamaldehyde exhibited activity in concentrations greater than 200 μg/mL. As for safety in the animal model with rats, the orabase ointment proved to be safe for use on keratinized mucosa up to the maximum concentration tested (700 μg/mL).

CONCLUSIONS

At the concentrations tested, cinnamaldehyde was not toxic in vertebrate and invertebrate animal models and did not exhibit genotoxic activity. In addition, when used in the form of an ointment in orabase, having already recognized antifungal activity, it was shown to be safe up to the highest concentration tested.

Functional roles of polyamines and their metabolite acrolein in eukaryotic cells

Among low molecular weight substances, polyamines (spermidine, spermine and their precursor putrescine) are present in eukaryotic cells at the mM level together with ATP and glutathione. It is expected therefore that polyamines play important roles in cell proliferation and viability. Polyamines mainly exist as a polyamine-RNA complex and regulate protein synthesis. It was found that polyamines enhance translation from inefficient mRNAs. The detailed mechanisms of polyamine stimulation of specific kinds of protein syntheses and the physiological functions of these proteins are described in this review. Spermine is metabolized into acrolein (CH2 = CH-CHO) and hydrogen peroxide (H2O2) by spermine oxidase. Although it is thought that cell damage is mainly caused by reactive oxygen species (O2-, H2O2, and •OH), it was found that acrolein is much more toxic than H2O2. Accordingly, the level of acrolein produced becomes a useful biomarker for several tissue-damage diseases like brain stroke. Thus, the mechanisms of cell toxicity caused by acrolein are described in this review.

Reduced Acrolein Detoxification in akr1a1a Zebrafish Mutants Causes Impaired Insulin Receptor Signaling and Microvascular Alterations

Increased acrolein (ACR), a toxic metabolite derived from energy consumption, is associated with diabetes and its complications. However, the molecular mechanisms are mostly unknown, and a suitable animal model with internal increased ACR does not exist for in vivo studying so far. Several enzyme systems are responsible for acrolein detoxification, such as Aldehyde Dehydrogenase (ALDH), Aldo-Keto Reductase (AKR), and Glutathione S-Transferase (GST). To evaluate the function of ACR in glucose homeostasis and diabetes, akr1a1a-/- zebrafish mutants are generated using CRISPR/Cas9 technology. Accumulated endogenous acrolein is confirmed in akr1a1a-/- larvae and livers of adults. Moreover, a series of experiments are performed regarding organic alterations, the glucose homeostasis, transcriptome, and metabolomics in Tg(fli1:EGFP) zebrafish. Akr1a1a-/- larvae display impaired glucose homeostasis and angiogenic retina hyaloid vasculature, which are caused by reduced acrolein detoxification ability and increased internal ACR concentration. The effects of acrolein on hyaloid vasculature can be reversed by acrolein-scavenger l-carnosine treatment. In adult akr1a1a-/- mutants, impaired glucose tolerance accompanied by angiogenic retina vessels and glomerular basement membrane thickening, consistent with an early pathological appearance in diabetic retinopathy and nephropathy, are observed. Thus, the data strongly suggest impaired ACR detoxification and elevated ACR concentration as biomarkers and inducers for diabetes and diabetic complications.