Abundance of DNA adducts of 4-oxo-2-alkenals, lipid peroxidation-derived highly reactive genotoxins

Reactivity of the 2-Methylfuran Phase I Metabolite 3-Acetylacrolein Toward DNA

2-Methylfuran (2-MF) is a well-known industrial chemical and also formed via thermal treatment of food. One main source of 2-MF in the human diet is coffee. 2-MF is known to form 3-acetylacrolein (AcA, 4-oxopent-2-enal) via cytochrome P 450 metabolism and further reacts with amino acids in vivo. Still the reactivity toward other biomolecules is rather scarce. Therefore, AcA was synthesized, and its reaction with 2'-deoxyadenosine (dA), 2'deoxyguanosine (dG), 2'deoxycytosine (dC), and 2'-deoxythymidine (dT) was tested. For this purpose, adduct formation was performed by acid hydrolysis of 2,5-dihydro-2,5-dimethoxy-2-methylfuran (DHDMMF) as well as pure AcA. The structures of these adducts were confirmed by UPLC-ESI+-MS/MS fragmentation patterns and 1H-/13CNMR spectra. Except for dT, which showed no reactivity, all adducts of AcA were characterized, which enabled the development of sensitive quantification methods via (U)HPLC-ESI±-MS/MS. Pure AcA was synthesized by oxidation of 2-MF using dimethyldioxirane (DMDO), and its behavior in aqueous medium was studied. Incubations of AcA and isolated DNA of primary rat hepatocytes (pRH) showed time- and dose-dependent formation of the identified DNA adducts dA-AcA, dG-AcA, or dC-AcA. In contrast, the DNA adducts dA-AcA, dG-AcA, or dC-AcA were not detected on a cellular level when pRH were incubated with 2-MF or AcA. This indicates an efficient detoxification or reaction with biomolecules in the cell, although the induction of other DNA damage, possibly also by other metabolites, cannot be ruled out in principle.

Metabolic Activation of 2-Methylfuran to Acetylacrolein and Its Reactivity toward Cellular Proteins

2-Methylfuran (2-MF) is a process-related contaminant found primarily in heat-treated foods, such as coffee or canned food. The oxidative metabolic activation of 2-MF is supposed to follow the pathway established for furan, which is known to generate the highly reactive metabolite butenedial (BDA). In the case of 2-MF, generation of the BDA homologue 3-acetylacrolein (AcA) is to be expected. 2-MF metabolism to AcA was investigated in two model systems: commercial microsomal preparations and primary rat hepatocytes (pRH). To scavenge the generated 2-MF, two model nucleophils, N-acetyl-l-cysteine (AcCys) and N-α-acetyl-l-lysine (AcLys), were used, and the formation of the corresponding adducts was measured in the supernatants. The metabolic activation of 2-MF to AcA was studied using human liver microsomes as well as rat liver microsomes. Incubation of 2-MF in Supersomes allowed to identify the cytochrome P450 isoenzyme primarily responsible for 2-MF. In addition, primary rat hepatocytes were incubated with 2-MF or AcA and AcLys adduct of AcA (N-α-acetyl-l-lysine-acetylacrolein, AcLys-AcA) determined in the cell supernatants by UHPLC-MS/MS. In model experiments, AcA formed adducts with AcCys and AcLys. The structures of both adducts were characterized. For incubations in biological activating systems, CYP 2E1 was found to be a key enzyme for the conversion of 2-MF to AcA in Supersomes. When pRH were incubated with 2-MF and AcA, AcLys-AcA was detected in the cell supernatants in a time- and dose-dependent manner. The results showed that AcA was indeed formed at the cellular level. In contrast to the AcLys-AcA adduct, no N-acetyl-l-cysteine-acetylacrolein (AcCys-AcA) adduct could be detected in pRH. AcA was determined as a reactive metabolite of 2-MF in vitro, and its adduct formation with nucleophilic cellular components was evaluated. The metabolites were characterized, and AcLys-AcA was identified as potential biomarker.

Lipid peroxidation: Reactive carbonyl species, protein/DNA adducts, and signaling switches in oxidative stress and cancer

Under the exposure of lipids to reactive oxygen species (ROS), lipid peroxidation proceeds non-enzymatically and generates an extremely heterogeneous mixture of reactive carbonyl species (RCS). Among them, HNE, HHE, MDA, methylglyoxal, glyoxal, and acrolein are the most studied and/or abundant ones. Over the last decades, significant progress has been achieved in understanding mechanisms of RCS generation, protein/DNA adduct formation, and their identification and quantification in biological samples. In our review, we critically discuss the advancements in understanding the roles of RCS-induced protein/DNA modifications in signaling switches to provide adaptive cell response under physiological and oxidative stress conditions. At non-toxic concentrations, RCS modify susceptible Cys residue in c-Src to activate MAPK signaling and Cys, Lys, and His residues in PTEN to cause its reversible inactivation, thereby stimulating PI3K/PKB(Akt) pathway. RCS toxic concentrations cause irreversible Cys modifications in Keap1 and IKKβ followed by stabilization of Nrf2 and activation of NF-κB, respectively, for their nuclear translocation and antioxidant gene expression. Dysregulation of these mechanisms causes diseases including cancer. Alterations in RCS, RCS detoxifying enzymes, RCS-modified protein/DNA adducts, and signaling pathways have been implicated in various cancer types.

Aldehyde-Associated Mutagenesis─Current State of Knowledge

Aldehydes are widespread in the environment, with multiple sources such as food and beverages, industrial effluents, cigarette smoke, and additives. The toxic effects of exposure to several aldehydes have been observed in numerous studies. At the molecular level, aldehydes damage DNA, cross-link DNA and proteins, lead to lipid peroxidation, and are associated with increased disease risk including cancer. People genetically predisposed to aldehyde sensitivity exhibit severe health outcomes. In various diseases such as Fanconi's anemia and Cockayne syndrome, loss of aldehyde-metabolizing pathways in conjunction with defects in DNA repair leads to widespread DNA damage. Importantly, aldehyde-associated mutagenicity is being explored in a growing number of studies, which could offer key insights into how they potentially contribute to tumorigenesis. Here, we review the genotoxic effects of various aldehydes, focusing particularly on the DNA adducts underlying the mutagenicity of environmentally derived aldehydes. We summarize the chemical structures of the aldehydes and their predominant DNA adducts, discuss various methodologies, in vitro and in vivo, commonly used in measuring aldehyde-associated mutagenesis, and highlight some recent studies looking at aldehyde-associated mutation signatures and spectra. We conclude the Review with a discussion on the challenges and future perspectives of investigating aldehyde-associated mutagenesis.

The Combination of Cigarette Smoking and Alcohol Consumption Synergistically Increases Reactive Carbonyl Species in Human Male Plasma

Cigarette smoking and alcohol consumption are major risk factors for lifestyle-related diseases. Although it has been reported that the combination of these habits worsens risks, the underlying mechanism remains elusive. Reactive carbonyl species (RCS) cause chemical modifications of biological molecules, leading to alterations in cellular signaling pathways, and total RCS levels have been used as a lipid peroxidation marker linked to lifestyle-related diseases. In this study, at least 41 types of RCS were identified in the lipophilic fraction of plasma samples from 40 subjects using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Higher levels of 10 alkanals, 5 trans-2-alkenals, 1 cis-4-alkenal, and 3 alkadienals were detected in the smoking/drinking group (N = 10) as compared to those with either habit (N = 10 each) or without both habits (N = 10) in the analysis of covariances adjusted for age and BMI. The levels of 3 alkanals, 1 trans-2-alkenal, 1 alkadienal, and 1 4-hydroxy-2-alkenal in the smoking/drinking group were significantly higher than those in the no-smoking/drinking and no-smoking/no-drinking groups. These results strongly indicate that the combination of cigarette smoking and alcohol drinking synergistically increases the level and variety of RCS in the circulating blood, and may further jeopardize cellular function.

Regulation of arachidonic acid oxidation and metabolism by lipid electrophiles

Arachidonic acid (AA) is a precursor of enzymatic and non-enzymatic oxidized products such as prostaglandins, thromboxanes, leukotrienes, lipoxins, and isoprostanes. These products may exert signaling or damaging roles during physiological and pathological conditions, some of them being markers of oxidative stress linked to inflammation. Recent data support the concept that cyclooxygenases (COX), lipoxygenases (LOX), and cytochrome P450 (CYP450) followed by cytosolic and microsomal dehydrogenases can convert AA to lipid-derived electrophiles (LDE). Lipid-derived electrophiles are fatty acid derivatives bearing an electron-withdrawing group that can react with nucleophiles at proteins, DNA, and small antioxidant molecules exerting potent signaling properties. This review aims to describe the formation, sources, and electrophilic anti-inflammatory actions of key mammalian LDE.

Genotoxic effects of drospirenone and ethinylestradiol in human breast cells (in vitro) and bone marrow cells of female mice (in vivo)

Estrogen and progesterone congeners as found in various oral contraceptive formulations have been implicated as the cause of cancer in sex and tissue-specific targets. The mechanism of carcinogenesis by sex steroids is still debatable. In this study, we evaluated the genotoxicity induced by two components of one of the commonly used oral contraceptive formulation; drospirenone and ethinylestradiol in human breast cells (MCF-7) in vitro and in bone marrow cells of female mice in vivo. DNA damage was assessed by alkaline comet assay. Both of the drugs produced DNA damage in human breast cells at exposure concentrations which are about 100-fold and above than normally found in human blood after their lowest recommended doses. The DNA damage was produced only after metabolic activation by mice liver S-9 fraction in both cases. The co-exposure with both the compounds at median exposure levels resulted in potentiation of DNA damage. In bone marrow cells of adult female mice, both the compounds produced DNA damage at human equivalent doses after exposure was carried out repeatedly for approximately one estrus cycle (5 days). The co-administration with the compounds resulted in potentiation of DNA damage as indicated by percent tail DNA in comet assay. Thus it is concluded that drospirenone and ethinylestradiol cause DNA damage in certain target specific tissue (mammary epithelial cells) and in female bone marrow cells. The co-exposure with drospirenone and ethinylestradiol results in potentiation of genotoxicity which may pose a threat of cancer development in women taking these drugs for long periods.

Effects of histamine and sodium hypochlorite on prooxidand state in the rats erytrocytes

We studied the simultaneous influence of histamine and sodium hypochlorite (SH) on lipid peroxidation processes, as well as the level of structural changes in membranes (via the content of sialic acid) in rat erythrocytes. We established that histamine affects lipid peroxidation processes with the formation of lipid hydroperoxides, damages proteins and reduces the content of sialic acids, which leads to changes in the surface charge of red blood cells. However, the simultaneous action of histamine and low SH concentration has a positive effect in that it corrects the pro-oxidant state of erythrocytes. Hence, the content of lipid hydroperoxides, TBA-active products, carbonyl groups of proteins and sialic acids were mainly reduced after the simultaneous action of histamine and SH at all studied concentrations during the rehabilitation period.

Revisiting Oxidative Stress and the Use of Organic Selenium in Dairy Cow Nutrition

In commercial animals production, productive stress can negatively impact health status and subsequent productive and reproductive performance. A great body of evidence has demonstrated that as a consequence of productive stress, an overproduction of free radicals, disturbance of redox balance/signaling, and oxidative stress were observed. There is a range of antioxidants that can be supplied with animal feed to help build and maintain the antioxidant defense system of the body responsible for prevention of the damaging effects of free radicals and the toxic products of their metabolism. Among feed-derived antioxidants, selenium (Se) was shown to have a special place as an essential part of 25 selenoproteins identified in animals. There is a comprehensive body of research in monogastric species that clearly shows that Se bioavailability within the diet is very much dependent on the form of the element used. Organic Se, in the form of selenomethionine (SeMet), has been reported to be a much more effective Se source when compared with mineral forms such as sodium selenite or selenate. It has been proposed that one of the main advantages of organic Se in pig and poultry nutrition is the non-specific incorporation of SeMet into general body proteins, thus forming an endogenous Se reserve that can be utilized during periods of stress for additional synthesis of selenoproteins. Responses in ruminant species to supplementary Se tend to be much more variable than those reported in monogastric species, and much of this variability may be a consequence of the different fates of Se forms in the rumen following ingestion. It is likely that the reducing conditions found in the rumen are responsible for the markedly lower assimilation of inorganic forms of Se, thus predisposing selenite-fed animals to potential Se inadequacy that may in turn compromise animal health and production. A growing body of evidence demonstrates that organic Se has a number of benefits, particularly in dairy and beef animals; these include improved Se and antioxidant status and better Se transfer via the placenta, colostrum, and milk to the newborn. However, there is a paucity in the data concerning molecular mechanisms of SeMet assimilation, metabolism and selenoprotein synthesis regulation in ruminant animals, and as such, further investigation is required.

High Risk of Hepatocellular Carcinoma Development in Fibrotic Liver: Role of the Hippo-YAP/TAZ Signaling Pathway

Liver cancer is the fourth leading cause of cancer-related death globally, accounting for approximately 800,000 deaths annually. Hepatocellular carcinoma (HCC) is the most common type of liver cancer, making up about 80% of cases. Liver fibrosis and its end-stage disease, cirrhosis, are major risk factors for HCC. A fibrotic liver typically shows persistent hepatocyte death and compensatory regeneration, chronic inflammation, and an increase in reactive oxygen species, which collaboratively create a tumor-promoting microenvironment via inducing genetic alterations and chromosomal instability, and activating various oncogenic molecular signaling pathways. In this article, we review recent advances in fields of liver fibrosis and carcinogenesis, and consider several molecular signaling pathways that promote hepato-carcinogenesis under the microenvironment of liver fibrosis. In particular, we pay attention to emerging roles of the Hippo-YAP/TAZ signaling pathway in stromal activation, hepatic fibrosis, and liver cancer.