Molecular mechanisms of action of styrene toxicity in blood plasma and liver

Single-chemical and mixture effects of multiple volatile organic compounds exposure on liver injury and risk of non-alcoholic fatty liver disease in a representative general adult population

Evidence on liver injury and non-alcoholic fatty liver disease (NAFLD) from volatile organic compounds (VOCs) exposure is insufficient. A cross-sectional study including 3011 US adults from the National Health and Nutrition Examination Survey was conducted to explore the associations of urinary exposure biomarkers (EBs) for 13 VOCs (toluene, xylene, ethylbenzene, styrene, acrylamide, N,N-dimethylformamide, acrolein, crotonaldehyde, 1,3-butadiene, acrylonitrile, cyanide, propylene oxide, and 1-bromopropane) with liver injury biomarkers and the risk of NAFLD by performing single-chemical (survey weight regression) and mixture (Bayesian kernel machine regression [BKMR] and weighted quantile sum [WQS]) analyses. We found significant positive associations of EBs for toluene and 1-bromopropane with alanine aminotransferase (ALT), EBs for toluene, crotonaldehyde, and 1,3-butadiene with asparate aminotransferase (AST), EBs for 1,3-butadiene and cyanide with alkaline phosphatase (ALP), EBs for xylene and cyanide with hepamet fibrosis score (HFS), EBs for the total 13 VOCs (except propylene oxide) with United States fatty liver index (USFLI), and EBs for xylene, N,N-dimethylformamide, acrolein, crotonaldehyde, and acrylonitrile with NALFD; and significant inverse associations of EBs for ethylbenzene, styrene, acrylamide, acrolein, crotonaldehyde, 1,3-butadiene, acrylonitrile, cyanide, and propylene oxide with total bilirubin, EBs for ethylbenzene, styrene, acrylamide, acrolein, 1,3-butadiene, acrylonitrile, and cyanide with albumin (ALB), EBs for ethylbenzene, styrene, acrylamide, N,N-dimethylformamide, acrolein, crotonaldehyde, 1,3-butadiene, acrylonitrile, cyanide, and propylene oxide with total protein (TP), and EB for 1-bromopropane with AST/ALT (all P-FDR<0.05). In BKMR and WQS, the mixture of VOC-EBs was significantly positively associated with ALT, AST, ALP, HFS, USFLI, and the risk of NAFLD, while significantly inversely associated with TBIL, ALB, TP, and AST/ALT. VOCs exposure was associated with liver injury and increased risk of NAFLD in US adults. These findings highlight that great attention should be paid to the potential risk of liver health damage from VOCs exposure.

Long-term effect of styrene and ethylbenzene exposure on fasting plasma glucose: A gene-environment interaction study

Styrene and ethylbenzene (S/EB) are hazardous pollutants that have attracted worldwide concern. In this prospective cohort study, S/EB exposure biomarker (the sum of mandelic acid and phenylglyoxylic acid [MA+PGA]) and fasting plasma glucose (FPG) were repeatedly measured three times. The polygenic risk score (PRS) based on 137 single nucleotide polymorphisms for type 2 diabetes mellitus (T2DM) was calculated to evaluate cumulative genetic effect. In repeated-measures cross-sectional analyses, MA+PGA (β [95% confidence interval]: 0.106 [0.022, 0.189]) and PRS (0.111 [0.047, 0.176]) were significantly related to FPG. For long-term effect assessment, participants with sustained high MA+PGA or with high PRS had 0.021 (95% CI: -0.398, 0.441) or 0.465 (0.064, 0.866) mmol/L increase in FPG, respectively, over 3 years follow-up, and had 0.256 (0.017, 0.494) or 0.265 (0.004, 0.527) mmol/L increase in FPG, respectively, over 6 years follow-up. We further detected a significant interaction effect between MA+PGA and PRS on FPG change, compared with participants with sustained low MA+PGA and low PRS, those with sustained high MA+PGA and high PRS had 0.778 (0.319, 1.258) mmol/L increase in FPG (P for interaction=0.028) over 6 years follow-up. Our study provides the first evidence that long-term exposure to S/EB potentially increases FPG, which might be aggravated by genetic susceptibility.

A luminescent Eu@SOF film fabricated by electrophoretic deposition as ultrasensitive platform for styrene gas quantitative monitoring through fluorescence sensing and ANNs model

Styrene is a harmful gas widely existing in the air, which can damage human organs. Therefore, it is very crucial to develop a sensitive, portable and simple sensor for monitoring styrene. Herein, we design and fabricate a luminescent Eu@TMA-ME/FTO film (F) through EPD method. F emits bright red light of Eu(III) ions and shows superior fluorescence response to styrene gas as a sensor, which enable real-time and quantitative monitoring for styrene gas. More importantly, F exhibits a linear response to styrene gas in a wide concentration range of 10^-7 to 10^-2 M and a low DL with 0.20 ppm. The efficient PET process to styrene induced by ME and the competitive absorption between styrene and F are responsible for the sensing mechanism. Besides, the detection of styrene solution is also investigated in deionized water, tap water and river water. For the further application, an intelligent ANNs model has been constructed to process the fluorescence sensing results, which can convert fluorescence sensing images to the concentration of styrene gas. The data demonstrates that ANNs model can accurately monitor the concentration of styrene gas via deep ML without tedious data processing.

Screening and validation of biomarkers for cadmium-induced liver injury based on targeted bile acid metabolomics

Although cadmium (Cd) is a toxic heavy metal that reportedly causes liver injury, few studies have investigated biomarkers of Cd-induced liver injury. The purpose of this study is to investigate the role of bile acid (BA) in Cd-induced liver injury and determine reliable and sensitive biochemical parameters for the diagnosis of Cd-induced liver injury. In this study, 48 Sprague-Dawley rats were randomly divided into six groups and administered either normal saline or 2.5, 5, 10, 20, and 40 mg/kg/d cadmium chloride for 12 weeks. A total of 403 subjects living in either a control area (n = 135) or Cd polluted area (n = 268) of Dongdagou-Xinglong (DDGXL) cohort were included, a population with long-term low Cd exposure. The BA profiles in rats' liver, serum, caecal contents, faeces, and subjects' serum were detected using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Changes in rats' and subjects' liver injury indices, rats' liver pathological degeneration, and rats' liver and subjects' blood Cd levels were also measured. Cadmium exposure caused cholestasis and an increase in toxic BAs, leading to liver injury in rats. Among them, glycoursodeoxycholic acid (GUDCA), glycolithocholic acid (GLCA), taurolithocholic acid (TLCA), and taurodeoxycholate acid (TDCA) are expected to be potential biomarkers for the early detect of Cd-induced liver injury. Serum BAs can be used to assess Cd-induced liver injury as a simple, feasible, and suitable method in rats. Serum GUDCA, GLCA, TDCA, and TLCA were verified to be of value to evaluate Cd-induced liver injury and Cd exposure in humans. These findings provided evidence for screening and validation of additional biomarkers for Cd-induced liver injury based on targeted BA metabolomics.

Dual role of cadmium in rat liver: Inducing liver injury and inhibiting the progression of early liver cancer

The heavy metal cadmium (Cd) can induce damage in liver and liver cancer cells; however, the mechanism underlying its toxicity needs to be further verified in vivo. We daily administered CdCl₂ to adult male rats at different dosages via gavage for 12 weeks and established rat liver injury model and liver cancer model to study the dual role of Cd in rat liver. Increased exposure to Cd resulted in abnormal liver function indicators, pathological degeneration, rat liver cell necrosis, and proliferation of collagen fibres. Using immunohistochemistry, we found that the area of GST-P-positive precancerous liver lesions decreased in a dose-dependent manner. Real-time quantitative polymerase chain reaction, western blot, immunohistochemistry, and transmission electron microscopy revealed that Cd induced mitophagy, as well as mitophagy blockade, as evidenced by the downregulation of TOMM20 and upregulation of LC3II and P62 with increasing Cd dose. Next, the expression of PINK1/Parkin, a classic signalling pathway protein that regulates mitophagy, was examined. Cd was found to promote PINK1/Parkin expression, which was proportional to the Cd dose. In conclusion, Cd activates PINK1/Parkin-mediated mitophagy in a dose-dependent manner. Mitophagy blockade likely aggravates Cd toxicity, leading to the dual role of inducing liver injury and inhibiting the progression of early liver cancer.

Modeling the antioxidant properties of the eye reduces the false-positive rate of a nonanimal eye irritation test (OptiSafe)

We recently identified a group of chemicals that are misclassified by most, if not all, in vitro alternative ocular irritation tests, suggesting that nonanimal tests may not fully model the ocular environment in which these chemicals interact. To address this, we evaluated the composition of tears, the first defense against foreign substances, and identified the presence of antioxidants that could detoxify reactive chemicals that otherwise may be falsely identified as irritants in alternative irritation tests. In this study, we evaluated the effects of tear antioxidants on the ocular irritation scoring of commonly overclassified chemicals (false positives) using the OptiSafe™ ocular irritation test. Six tear-related antioxidants were individually added to the OptiSafe formulation, and the effects on test outcome were determined. Ascorbic acid, the most abundant water-soluble antioxidant in tears, specifically reduced the OptiSafe false-positive rate. Titration curves showed that this reduction occurs at in vivo concentrations and is specific to chemicals identified either as producing reactive oxygen species or as crosslinkers. Importantly, the addition of tear antioxidants did not impact the detection of true negatives, true positives, or other false positives unassociated with reactive oxygen species or crosslinking. These results suggest that the addition of tear antioxidants to in vitro alternative test systems may substantially reduce the false-positive rate and improve ocular irritant detection.

Cadmium causes hepatopathy by changing the status of DNA methylation in the metabolic pathway

Toxicity caused by the heavy metal Cadmium leads to liver diseases; this finding has generated interest among researchers. We detected DNA methylation using Whole Genome Bisulfite Sequencing (WGBS) to study the relationship between Cadmium exposure and liver damage. Forty-eight Sprague-Dawley rats were randomly divided into six groups, and given normal saline or 2.5, 5, 10, 20, and 40 mg/kg body weight per day CdCl₂ by gavage. Twelve weeks later, their liver tissues were collected for pathological examination and DNA extraction. Increased exposure to Cadmium led to a reduction in the amount of weight gain as well as pathological degeneration and necrosis of liver cells of the rats. Using WGBS, we found that DNA methylation changes in the high-dose exposure group were more remarkable, and most of the changes occurred in the gene promoter region. GO enrichment analysis showed that the genes were enriched in the biological process of "response to stimulus." KEGG analysis revealed that metabolic pathways, like MAPK, PI3K-Akt and cAMP, had the largest number of enriched genes. Using Integrative Genomics Viewer (IGV), the demethylation of F2rl3 after Cadmium poisoning was established. This finding may explain why there are changes in liver metabolism after Cadmium poisoning.

A ratiometric fluorescent probe for the quantitative detection of styrene in air

A ratiometric fluorescent probe (N-butyl-4-(4-amino-styryl)-1,8-naphthalimide) was developed for the quantitative detection of styrene in air. The sensing mechanism was found to involve a Heck reaction between the pretreated probe (diazotization) and styrene. A probe solution absorption method was established to detect gaseous styrene quantitatively.

Exposure to microplastics impairs digestive performance, stimulates immune response and induces microbiota dysbiosis in the gut of juvenile guppy (Poecilia reticulata)

Microplastics (MPs) are widely distributing in aquatic environment. They are easily ingested by aquatic organisms and accumulate in digestive tract especially of intestine. To explore the potential effects of MPs on intestine, here we, using juvenile guppy (Poecilia reticulata) as experimental animal, investigated the response characteristics of digestion, immunity and gut microbiota. After exposure to 100 and 1000 μg/L concentrations of MPs (polystyrene; 32-40 μm diameters) for 28 days, we observed that MPs could exist in guppy gut and induce enlargement of goblet cells. Activities of digestive enzymes (trypsin, chymotrypsin, amylase and lipase) in guppy gut generally reduced. MPs stimulated the expression of immune cytokines (TNF-α, IFN-γ, TLR4 and IL-6). Through high throughput sequencing of 16S rRNA gene, decreases in diversity and evenness and changed composition of microbiota were found in guppy gut. PICRUSt analysis revealed that MPs might have effects on intestinal microbiota functions, such as inhibition of metabolism and repair pathway. Our findings suggested that MPs could retain in the gut of juvenile guppy, impair digestive performance, stimulate immune response and induce microbiota dysbiosis in guppy gut. The results obtained here provide new insights into the potential risks of MPs to aquatic animals.

Styrene Oxide Caused Cell Cycle Arrest and Abolished Myogenic Differentiation of C2C12 Myoblasts

Contaminations of chemicals in foods and drinks are raising public concerns. Among these, styrene, a monomer for plastic production, receives increasing interest due to its ability to leach from the packaging and contaminate in foods and drinks causing many health problems. The present study was designed to investigate the effects of styrene monomer (STR) and its metabolite styrene oxide (STO) on C2C12 myoblast proliferation and differentiation. Based on an MTT assay, both STR and STO showed no cytotoxic effect at 10-100 μM. However, at 50-100 μM STO, but not STR, significantly inhibited cell proliferation. The STO-treated cells were accumulated in S-phase of cell cycles as revealed by flow cytometry. The antioxidant enzyme (catalase and superoxide dismutase) activities and the gene expressing these enzymes of the arrested cells were decreased and ultimately led to nuclear condensation and expression of apoptotic markers such as cleaved caspase-3 and-9, but not cleaved caspase-8. In addition, STO significantly suppressed myogenic differentiation by decreasing both the number and size of differentiated myotubes. Biochemical analysis showed attenuations of total protein synthesis and myosin heavy chain (MHC) protein expression. In conclusion, a metabolite of styrene, STO, leached from plastic packaging of foods and beverages suppressed both myoblast proliferation and differentiation, which would affect skeletal muscle development and regeneration.

Microplastics induce transcriptional changes, immune response and behavioral alterations in adult zebrafish

Microplastics have become pervasive environmental pollutants in both freshwater and marine ecosystems. The presence of microplastics have been recorded in the tissues of many wild fish species, and laboratory studies have demonstrated that microplastics can exert adverse health effects. To further investigate the biological mechanisms underlying microplastics toxicity we applied an integrated approach, analyzing the effects of microplastics at transcriptomic, histological and behavioral level. Adult zebrafish have been exposed to two concentrations of high-density polyethylene and polystyrene microplastics for twenty days. Transcriptomic results indicate alterations in the expression of immune system genes and the down-regulation of genes correlated with epithelium integrity and lipid metabolism. The transcriptomic findings are supported by tissue alterations and higher occurrence of neutrophils observed in gills and intestinal epithelium. Even the daily rhythm of activity of zebrafish appears to be affected, although the regular pattern of activity is recovered over time. Considering the transcriptomic and histological findings reported, we hypothesize that the effects on mucosal epithelium integrity and immune response could potentially reduce the organism defense against pathogens, and lead to a different utilization of energy stores.

Protein carbonylation in human bronchial epithelial cells exposed to cigarette smoke extract

Cigarette smoke is a well-established exogenous risk factor containing toxic reactive molecules able to induce oxidative stress, which in turn contributes to smoking-related diseases, including cardiovascular, pulmonary, and oral cavity diseases. We investigated the effects of cigarette smoke extract on human bronchial epithelial cells. Cells were exposed to various concentrations (2.5-5-10-20%) of cigarette smoke extract for 1, 3, and 24 h. Carbonylation was assessed by 2,4-dinitrophenylhydrazine using both immunocytochemical and Western immunoblotting assays. Cigarette smoke induced increasing protein carbonylation in a concentration-dependent manner. The main carbonylated proteins were identified by means of two-dimensional electrophoresis coupled to MALDI-TOF mass spectrometry analysis and database search (redox proteomics). We demonstrated that exposure of bronchial cells to cigarette smoke extract induces carbonylation of a large number of proteins distributed throughout the cell. Proteins undergoing carbonylation are involved in primary metabolic processes, such as protein and lipid metabolism and metabolite and energy production as well as in fundamental cellular processes, such as cell cycle and chromosome segregation, thus confirming that reactive carbonyl species contained in cigarette smoke markedly alter cell homeostasis and functions.