Oxidative stress and genotoxicity in 1,4-dioxane liver toxicity as evidenced in a mouse model of glutathione deficiency

Altered oxidative stress and antioxidant biomarkers concentrations in pregnant individuals exposed to oil and gas sites in Northeastern British Columbia

Northeastern British Columbia is a region of prolific unconventional oil and gas (UOG) activity. UOG activity can release volatile organic compounds (VOCs) which can elevate oxidative stress and disrupt antioxidant activity in exposed pregnant individuals, potentially increasing the risk of adverse pregnancy outcomes. This study measured biomarkers of oxidative stress and antioxidant activity in pooled urine samples of 85 pregnant individuals living in Northeastern British Columbia, to analyze associations between indoor air VOCs, oil and gas well density and proximity metrics, and biomarker concentrations. Concentrations of catalase, superoxide dismutase (SOD), glutathione S-transferase, total antioxidant capacity, 6-hydroxymelatonin sulfate (aMT6s), malondialdehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OHdG), and 8-isoprostane were measured using assay kits. Associations between exposure metrics and biomarker concentrations were determined using multiple linear regression models adjusted for biomarker-specific covariables. UOG proximity was associated with decreased SOD and 8-OHdG. Decreased 8-OHdG was associated with increased proximity to all wells. Decreased aMT6s were observed with increased indoor air hexanal concentrations. MDA was negatively associated with indoor air 1,4-dioxane concentrations. No statistically significant associations were found between other biomarkers and exposure metrics. Although some associations linked oil and gas activity to altered oxidative stress and antioxidant activity, the possibility of chance findings due to the large number of tests cannot be discounted. This study shows that living near UOG wells may alter oxidative stress and antioxidant activity in pregnant individuals. More research is needed to elucidate underlying mechanisms and to what degree UOG activity affects oxidative stress and antioxidant activity.

CYP2E1 in 1,4-dioxane metabolism and liver toxicity: insights from CYP2E1 knockout mice study

1,4-Dioxane (DX), an emerging water contaminant, is classified as a Group 2B liver carcinogen based on animal studies. Understanding of the mechanisms of action of DX liver carcinogenicity is important for the risk assessment and control of this environmental pollution. Previous studies demonstrate that high-dose DX exposure in mice through drinking water for up to 3 months caused liver mild cytotoxicity and oxidative DNA damage, a process correlating with hepatic CYP2E1 induction and elevated oxidative stress. To access the role of CYP2E1 in DX metabolism and liver toxicity, in the current study, male and female Cyp2e1-null mice were exposed to DX in drinking water (5000 ppm) for 1 week or 3 months. DX metabolism, redox and molecular investigations were subsequently performed on male Cyp2e1-null mice for cross-study comparisons to similarly treated male wildtype (WT) and glutathione (GSH)-deficient Gclm-null mice. Our results show that Cyp2e1-null mice of both genders were resistant to DX-induced hepatocellular cytotoxicity. In male Cyp2e1-null mice exposed to DX for 3 months, firstly, DX metabolism to β-hydroxyethoxyacetic acid was reduced to ~ 36% of WT levels; secondly, DX-induced hepatic redox dysregulation (lipid peroxidation, GSH oxidation, and activation of NRF2 antioxidant response) was substantially attenuated; thirdly, liver oxidative DNA damage was at a comparable level to DX-exposed WT mice, accompanied by suppression of DNA damage repair response; lastly, no aberrant proliferative or preneoplastic lesions were noted in DX-exposed livers. Overall, this study reveals, for the first time, that CYP2E1 is the main enzyme for DX metabolism at high dose and a primary contributor to DX-induced liver oxidative stress and associated cytotoxicity. High dose DX-induced genotoxicity may occur via CYP2E1-independent pathway(s), potentially involving impaired DNA damage repair.

Tackling Challenges of Long-Term Electrode Stability in Electrochemical Treatment of 1,4-Dioxane in Groundwater

Electrochemical advanced oxidation is an appealing point-of-use groundwater treatment option for removing pollutants such as 1,4-dioxane, which is difficult to remove by using conventional separation-based techniques. This study addresses a critical challenge in employing electrochemical cells in practical groundwater treatment─electrode stability over long-term operation. This study aims to simulate realistic environmental scenarios by significantly extending the experimental time scale, testing a flow-through cell in addition to a batch reactor, and employing an electrolyte with a conductivity equivalent to that of groundwater. We first constructed a robust titanium suboxide nanotube mesh electrode that is utilized as both anode and cathode. We then implemented a pulsed electrolysis strategy in which reactive oxygen species are generated during the anodic cycle, and the electrode is regenerated during the cathodic cycle. Under optimized conditions, single-pass treatment through the cell (effective area: 2 cm2) achieved a remarkable 65-70% removal efficiency for 1,4-dioxane in the synthetic groundwater for over 100 h continuous operation at a low current density of 5 mA cm-2 and a water flux of 6 L m-2 h-1. The electrochemical cell and pulse treatment scheme developed in this study presents a critical advancement toward practical groundwater treatment technology.

Comparative antioxidant and metabolomic analysis for the identification of differential response of mussel (Mytilus coruscus) to four succinate dehydrogenase inhibitor fungicides

Succinate dehydrogenase inhibitor fungicides (SDHIs) are frequently detected in the marine environment. However, studies on the toxicity of SDHIs to marine organisms, Mytilus coruscus (M. coruscus), are poorly reported. Therefore, the antioxidant activities and metabolomic response of four SDHIs, namely, boscalid (BC), thifluzamide (TF), fluopyram (FO), and bixafen (BIX), to (M. coruscus), were comprehensively investigated. The antioxidant activity of BC and TF was significantly increased (p<0.05), whereas those of FO and BIX were significantly decreased. Furthermore, metabolite discriminations among M. coruscus to four SDHIs were illustrated by an untargeted metabolomics approach. A total of 52, 50, 93, and 129 differential metabolites were obtained for BC, TF, FO, and BIX. KEGG of the different metabolites show that the four SDHIs had differential effects on the metabolic pathways of M. coruscus. The current study demonstrated four SDHIs triggered glucose metabolism, lipid metabolism, tricarboxylic acid cycle, and oxidative phosphorylation processes and caused the disruption of nutrient and energy conversion processes in mussels. Finally, five biomarkers were screened by analyzing common differential metabolites that emerged from the four SDHI exposures, which could be used for risk assessment of marine ecosystem exposure to SDHIs. Our results demonstrated the use of metabolomics to understand the potential mechanisms of toxicity of four SDHIs to mussels and to identify potential targets for future targeted risk assessment.

Comparative role of acetaminophen, carbon tetrachloride and thioacetamide in development of fibrosis in rats

Background

Several hepatotoxicants such as acetaminophen, carbon tetrachloride, and thioacetamide are repeatedly used to develop hepatic fibrosis to mimic the histological and hemodynamic characteristics of human illness. It may be a good idea to establish a better model among these hepatotoxicants to develop hepatic fibrosis.

Aim

The present study evaluated comparative toxic effects of three model hepatotoxicants for experimental progression of fibrosis or cirrhosis.

Materials and methods

Acetaminophen (200 mg/kg), carbon tetrachloride (200 µl/kg) and thioacetamide (200 mg/kg) were administered orally, thrice in a week for 8 weeks in different groups. After 8 weeks of exposure, animals were euthanized, blood and tissues were collected for various hematological, serological, tissue biochemical analysis and histological observations for comparative assessment of toxic consequences.

Results

Significant deviation was noted in liver function tests, lipid peroxidation, glutathione, activities of superoxide dismutase, catalase, and GSH cycle enzymes; aniline hydroxylase, amidopyrine-N-demethylase, DNA fragmentation and level of hydroxyproline when compared with control group. Histology also depicted damage in liver histoarchitecture with exposure to acetaminophen, carbon tetrachloride and thioacetamide. Tukey's HSD post hoc test confirmed that thioacetamide produced severe toxic effects in comparison to carbon tetrachloride and acetaminophen.

Conclusion

In conclusion, toxic effects were noted in ascending order as acetaminophen.

From imbalance to impairment: the central role of reactive oxygen species in oxidative stress-induced disorders and therapeutic exploration

Increased production and buildup of reactive oxygen species (ROS) can lead to various health issues, including metabolic problems, cancers, and neurological conditions. Our bodies counteract ROS with biological antioxidants such as SOD, CAT, and GPx, which help prevent cellular damage. However, if there is an imbalance between ROS and these antioxidants, it can result in oxidative stress. This can cause genetic and epigenetic changes at the molecular level. This review delves into how ROS plays a role in disorders caused by oxidative stress. We also look at animal models used for researching ROS pathways. This study offers insights into the mechanism, pathology, epigenetic changes, and animal models to assist in drug development and disease understanding.

Underlying Mechanisms for the Sex- and Chemical-Specific Hepatotoxicity of Perfluoroalkyl Phosphinic Acids in Common Carp (Cyprinus carpio)

The hepatotoxicities of perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been extensively investigated, while little is known about the sex-specific differences. In this study, common carp were exposed to the emerging perfluoroalkyl phosphinic acids (6:6 and 8:8 PFPiAs) for 14 days to disclose sex-specific hepatotoxicity. Apparent hepatotoxicity, including cell necrosis, apoptosis, and steatosis, was observed in both male and female carp liver. The observed hepatocyte steatosis was predominantly attributed to the dysregulation of hepatic lipid metabolism but was based on sex-specific mechanisms. It was manifested as inhibited oxidative decomposition of fatty acids (FAs) in the female liver, whereas it enhanced the uptake of FAs into the male liver, both of which led to excessive lipid accumulation. Untargeted lipidomics validated that the metabolism pathways of FA, sphingolipid, glycerolipid, and glycerophospholipid were disrupted by both compounds, leading to the generation of reactive oxygen species and oxidative stress. The oxidative stress further evolved into inflammation, manifested as promoted expression of proinflammatory cytokines and repressed expression of anti-inflammatory cytokines. Consistently, all of the changes were more noticeable in male carp, suggesting that male fish were more susceptible to PFPiA disruption. 8:8 PFPiA was less accumulated but caused stronger hepatotoxicity than 6:6 PFPiA, possibly because of the stronger binding capacity of 8:8 PFPiA to nuclear transcription factors mediating lipid metabolism and inflammation. The findings of this study highlight the significance of sex- and chemical-dependent bioaccumulation and the toxicity of PFASs in organisms.

An integrated assessment of the 1,4-dioxane cancer mode of action and threshold response in rodents

1,4-Dioxane is an environmental contaminant that has been shown to cause cancer in rodents after chronic high dose exposures. We reviewed and integrated information from recently published studies to update our understanding of the cancer mode of action of 1,4-dioxane. Tumor development in rodents from exposure to high doses of 1,4-dioxane is preceded by pre-neoplastic events including increased hepatic genomic signaling activity related to mitogenesis, elevation of Cyp2E1 activity and oxidative stress leading to genotoxicity and cytotoxicity. These events are followed by regenerative repair and proliferation and eventual development of tumors. Importantly, these events occur at doses that exceed the metabolic clearance of absorbed 1,4-dioxane in rats and mice resulting in elevated systemic levels of parent 1,4-dioxane. Consistent with previous reviews, we found no evidence of direct mutagenicity from exposure to 1,4-dioxane. We also found no evidence of CAR/PXR, AhR or PPARα activation resulting from exposure to 1,4-dioxane. This integrated assessment supports a cancer mode of action that is dependent on exceeding the metabolic clearance of absorbed 1,4-dioxane, direct mitogenesis, elevation of Cyp2E1 activity and oxidative stress leading to genotoxicity and cytotoxicity followed by sustained proliferation driven by regenerative repair and progression of heritable lesions to tumor development.

Environmentally relevant concentrations of butyl benzyl phthalate triggered oxidative stress and apoptosis in adult zebrafish (Danio rerio) liver: Combined analysis at physiological and molecular levels

Butyl benzyl phthalate (BBP), a typical phthalate plasticizer, is frequently detected in aquatic environments, but its possible effects on fish liver are unknown. In this study, adult zebrafish were exposed to 5-500 μg/L BBP and cultured for 28 days. The toxicity mechanism of environmentally relevant concentrations of BBP in the liver was explored using integrated biomarker response (IBR), molecular docking, and histopathological analysis, based on the tests of oxidative stress, apoptosis, and tissue damage, respectively. The results revealed that exposure to 500 μg/L BBP caused lipid peroxidation and DNA damage and induced inflammatory responses in the liver and intestinal tissues. The accumulation of reactive oxygen species (ROS) is the primary manifestation of BBP toxicity and is accompanied by changes in the activities of antioxidant and detoxification enzymes. Notably, the pro-apoptotic genes (p53 and caspase-3) were still significantly upregulated in the 50 μg/L and 500 μg/L treatment groups on day 28. Moreover, BBP interfered with apoptosis by forming a stable complex with apoptosis proteins (P53 and Caspase-3). Our findings are helpful for understanding the toxicity mechanisms of BBP, which could further promote the assessment of the potential environmental risks of BBP.

Mechanistic Considerations in 1,4-Dioxane Cancer Risk Assessment

The risk assessment of many carcinogens involves extrapolation across large exposure differences between the dose levels used in animal studies and the much lower human exposures. This is true for 1,4-dioxane which has a consistent liver carcinogenic effect in both genders of rats and mice. These data have been applied to risk assessment assuming a linear low dose extrapolation in some cases but non-linear or threshold models have been used in others. This choice hinges on our understanding of the 1,4-dioxane cancer mechanism. While 1,4-dioxane is not genotoxic in standard test batteries and has non-linear toxicokinetics, the mechanism for its carcinogenic effect remains unknown and is an active area of research. This review summarizes the possible modes of action for this chemical, data gaps and application to risk assessment. We find that the cytotoxicity/hyperplasia and metabolic saturation hypotheses do not explain the carcinogenic response and do not take into account 1,4-dioxane's induction of its own metabolism, leading to less likelihood for saturation during chronic exposure. There is evidence for other mechanisms, especially oxidative stress associated with the induction of CYP2E1 and in vivo genotoxicity that is not seen in vitro. The dose response for these effects needs further exploration compared to the time course and dose response for 1,4-dioxane-induced carcinogenesis. An additional consideration is the manner in which these 1,4-dioxane effects may augment naturally occurring and disease-related processes that contribute to the increasing rate of human liver cancer. These factors add to the rationale for using a non-threshold linear approach for extrapolating to low dose for this carcinogen, which is consistent with the default for carcinogens which do not have a clearly defined mode of action.

Oxidative stress, glutathione, and CYP2E1 in 1,4-dioxane liver cytotoxicity and genotoxicity: insights from animal models

1,4-Dioxane (DX) is an emerging drinking water contaminant worldwide, which poses a threat to public health due to its demonstrated liver carcinogenicity and potential for human exposure. The lack of drinking water standards for DX is attributed to undetermined mechanisms of DX carcinogenicity. This mini-review provides a brief discussion of a series of mechanistic studies, wherein unique mouse models were exposed to DX in drinking water to elucidate redox changes associated with DX cytotoxicity and genotoxicity. The overall conclusions from these studies support a direct genotoxic effect by high dose DX and imply that oxidative stress involving CYP2E1 activation may play a causal role in DX liver genotoxicity and potentially carcinogenicity. The mechanistic data derived from these studies can serve as important references to refine the assessment of carcinogenic pathways that may be triggered at environmentally relevant low doses of DX in future animal and human studies.

Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens.

Borax relieved the acrylamide-induced hematotoxic, hepatotoxic, immunotoxic and genotoxic damages in rainbow trout by regulating apoptosis and Nrf2 signaling pathway

Acrylamide(AA) is a compound with wide usage areas including paper, dyes, and plastics industries. Due to its broad spectrum and water solubility suggest that this vinyl compound may cause serious environmental problems. AA was shown to exhibit neurotoxic, immunotoxic, reproductive toxicant as well as carcinogenic potency on animals. Especially in recent years, the therapeutic effects of boron and boron containing compounds like borax(BX), ulexite(ULX) and colemanite(COL) had been reported. However, the ameliorative potential by boron compounds against AA-induced toxicities had not been investigated yet. Therefore, in this investigation rainbow trout were exposed acutely to AA in the presence and absence of BX. The hematological indices and genotoxic end-points were examined in the fish blood tissue. In addition to oxidative stress response, the levels of DNA damage, CASP3, TNF-α, Nrf-2 as well as IL-6 amounts were determined in both blood and liver tissues of fish. The obtained results executed that AA induced toxic conditions in both tissues. In fact, an increase in the amount of oxidative stress and ROS, and a decrease in GSH levels were observed. AA exposure led to an increase in CASP3levels and 8-OHdG formation. It was also found that Nrf-2 pathway contributed to the initiation of oxidative stress that associated with AA-induced toxicity. On the contrary, our findings indicated that co-exposure of BX with AA elicited oxidative stress and cell death. In a conclusion BX was suggested as a useful and effective natural agent for the prevention and early treatment of AA toxicity in fish.

In vivo effects of 1,4-dioxane on genotoxic parameters and behavioral alterations in Drosophila melanogaster

1,4-Dioxane (DXN) is used as solvent in different consumer products including cosmetics, paints, surfactants, and waxes. In addition, DXN is released as an unwanted contaminating by-product as a result of some reactions including ethoxylation of alcohols, which occurs with in personal care products. Consequently, DXN pollution was detected in drinking water and is considered as an environmental problem. At present, the genotoxicity effects attributed to DXN are controversial. The present study using an in vivo model organism Drosophila melanogaster aimed to determine the toxic/genotoxic, mutagenic/recombinogenic, oxidative damage as evidenced by ROS production, phenotypic alterations as well as behavioral and developmental alterations that are closely related to neuronal functions. Data demonstrated that nontoxic DXN concentration (0.1, 0.25, 0.5, or 1%) induced mutagenic (1%) and recombinogenic (0.1, 0.25, or 0.5%) effects in wing spot test and genotoxicity in hemocytes using comet assay. The nontoxic concentrations of DXN (0.1, 0.25, 0.5, or 1%) significantly increased oxidative stress, climbing behavior, thermal sensivity and abnormal phenotypic alterations. Our findings show that in contrast to in vitro exposure, DXN using an in vivo model Drosophila melanogaster this compound exerts toxic and genotoxic effects. Data suggest that additional studies using other in vivo models are thus warranted.

Au@MnSe2 Core-Shell Nanoagent Enabling Immediate Generation of Hydroxyl Radicals and Simultaneous Glutathione Deletion Free of Pre-Reaction for Chemodynamic-Photothermo-Photocatalytic Therapy with Significant Immune Response

As a typical tumor microenvironment-responsive therapy, chemodynamic therapy (CDT), producing hydroxyl radicals (^• OH) to eliminate tumor cells, has demonstrated great promise. Nevertheless, there are still major challenges: ^• OH generated from endogenous H₂ O₂ is usually insufficient; the CDT effect is strongly dependent on the pre-reaction with glutathione. Addressing the challenges, Au@MnSe₂ core-shell nanoagent for synergetic chemodynamic-photothermo-photocatalytic therapy combined with tetramodal imaging, including magnetic resonance imaging, computed tomography, photoacoustic, and infrared thermal imaging is reported. Distinct from the reported glutathione-depleting agents, Mn²⁺ in MnSe₂ allows immediate generation of ^• OH, independent of pre-reaction. Meanwhile, Mn³⁺ consumes glutathione by its conversion to Mn²⁺ . The Au-MnSe₂ combination promotes photothermal conversion and photocatalytic reaction, resulting in largely enhanced ^• OH generation from endogenous H₂ O₂ and significant hyperthermia. Meanwhile, immune response is effectively activated: the intratumoral expression of programmed cell death-1 and proinflammatory cytokines increase to 4-7 folds; the cytotoxic and helper T lymphocytes cells in the tumor area increase to more than 2.5-folds; an evident, temporary systemic immunostimulatory effect is demonstrated. High tumor inhibition rate (≈97.3%) and greatly prolonged survival are obtained. This highly-integrated design coordinating three different therapies with four different imaging modals provide new possibilities for high-performance theranostic nanoagents.

Role of Mitochondrial Cytochrome P450 2E1 in Healthy and Diseased Liver

Cytochrome P450 2E1 (CYP2E1) is pivotal in hepatotoxicity induced by alcohol abuse and different xenobiotics. In this setting, CYP2E1 generates reactive metabolites inducing oxidative stress, mitochondrial dysfunction and cell death. In addition, this enzyme appears to play a role in the progression of obesity-related fatty liver to nonalcoholic steatohepatitis. Indeed, increased CYP2E1 activity in nonalcoholic fatty liver disease (NAFLD) is deemed to induce reactive oxygen species overproduction, which in turn triggers oxidative stress, necroinflammation and fibrosis. In 1997, Avadhani’s group reported for the first time the presence of CYP2E1 in rat liver mitochondria, and subsequent investigations by other groups confirmed that mitochondrial CYP2E1 (mtCYP2E1) could be found in different experimental models. In this review, we first recall the main features of CYP2E1 including its role in the biotransformation of endogenous and exogenous molecules, the regulation of its expression and activity and its involvement in different liver diseases. Then, we present the current knowledge on the physiological role of mtCYP2E1, its contribution to xenobiotic biotransformation as well as the mechanism and regulation of CYP2E1 targeting to mitochondria. Finally, we discuss experimental investigations suggesting that mtCYP2E1 could have a role in alcohol-associated liver disease, xenobiotic-induced hepatotoxicity and NAFLD.