Metabolism of benzo(a)pyrene by subcellular fractions of gastrointestinal (GI) tract and liver in Apc Min mouse model of colon cancer

The Role of Autophagy and Pyroptosis in Liver Disorders

Pyroptosis is a programmed cell death caused by inflammasomes, which can detect cell cytosolic contamination or disturbance. In pyroptosis, caspase-1 or caspase-11/4/5 is activated, cleaving gasdermin D to separate its N-terminal pore-forming domain (PFD). The oligomerization of PFD forms macropores in the membrane, resulting in swelling and membrane rupture. According to the different mechanisms, pyroptosis can be divided into three types: canonical pathway-mediated pyroptosis, non-canonical pathway-mediated pyroptosis, and caspase-3-induced pyroptosis. Pyroptosis has been reported to play an important role in many tissues and organs, including the liver. Autophagy is a highly conserved process of the eukaryotic cell cycle. It plays an important role in cell survival and maintenance by degrading organelles, proteins and macromolecules in the cytoplasm. Therefore, the dysfunction of this process is involved in a variety of pathological processes. In recent years, autophagy and pyroptosis and their interactions have been proven to play an important role in various physiological and pathological processes, and have gradually attracted more and more attention to become a research hotspot. Therefore, this review summarized the role of autophagy and pyroptosis in liver disorders, and analyzed the related mechanism to provide a basis for future research.

E-waste polycyclic aromatic hydrocarbon (PAH) exposure leads to child gut-mucosal inflammation and adaptive immune response

Polycyclic aromatic hydrocarbon (PAH) exposure alters immunological responses. Research concerning PAH exposure on intestinal immunity of children in electronic waste (e-waste) areas is scarce. The aim of this study was to evaluate the effects of polycyclic aromatic hydrocarbon (PAH) pollutants on intestinal mucosal immunity of children in e-waste areas. Results showed higher hydroxylated PAH (OH-PAH) concentrations in e-waste-exposed children, accompanied with higher sialyl Lewis A (SLA) level, absolute lymphocyte and monocyte counts, decreased of percentage of CD4⁺ T cells, and had a higher risk of diarrhea. OH-PAH concentrations were negative with child growth. 1-OHNap mediated through WBCs, along with 1-OHPyr, was correlated with an increase SLA concentration. 2-OHFlu, 1-OHPhe, 2-OHPhe, 1-OHPyr, and 6-OHChr were positively correlated with secretory immunoglobulin A (sIgA) concentration. Our results indicated that PAH pollutants caused inflammation, affected the intestinal epithelium, and led to transformation of microfold cell (M cell). M cells initiating mucosal immune responses and the subsequent increasing sIgA production might be an adaptive immune respond of children in the e-waste areas. To our knowledge, this is the first study of PAH exposure on children intestinal immunity in e-waste area, showing that PAH exposure plays a negative role in child growth and impairs the intestinal immune function.

Curcumin Suppresses the Lipid Accumulation and Oxidative Stress Induced by Benzo[a]pyrene Toxicity in HepG2 Cells

Benzo[a]pyrene (B[a]P) is a potentially hepatotoxic group-1 carcinogen taken up by the body through ingestion of daily foods. B[a]P is widely known to cause DNA and protein damages, which are closely related to cell transformation. Accordingly, studies on natural bioactive compounds that attenuate such chemical-induced toxicities have significant impacts on public health. This study aimed to uncover the mechanism of curcumin, the major curcuminoid in turmeric (Curcuma longa), in modulating the lipid accumulation and oxidative stress mediated by B[a]P cytotoxicity in HepG2 cells. Curcumin treatment reduced the B[a]P-induced lipid accumulation and reactive oxygen spicies (ROS) upregulation and recovered the cell viability. Cytochrome P450 family 1 subfamily A polypeptide 1 (CYP1A1) and Cytochrome P450 subfamily B polypeptide 1 (CYP1B1) downregulation resulting from decreased aryl hydrocarbon receptor (AhR) translocation into nuclei attenuated the effects of B[a]P-induced lipid accumulation and repressed cell viability, respectively. Moreover, the curcumin-induced reduction in ROS generation decreased the nuclear translocation of Nuclear factor erythroid-2-related factor 2 (Nrf2) and the expression of phase-II detoxifying enzymes. These results indicate that curcumin suppresses B[a]P-induced lipid accumulation and ROS generation which can potentially induce nonalcoholic fatty liver disease (NAFLD) and can shed a light on the detoxifying effect of curcumin.

Polarizability and aromaticity index govern AhR-mediated potencies of PAHs: A QSAR with consideration of freely dissolved concentrations

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants associated with adverse human effects including cancer, and the aryl hydrocarbon receptor (AhR) is a key ligand-activated transcription factor mediating their toxicity. However, there is presently a lack of data on AhR potencies of PAHs. Simple, transparent, interpretable and predictive quantitative structure-activity relationship (QSAR) models are helpful, especially with the consideration of freely dissolved concentrations linked to bioavailability. Here, QSAR models on AhR-mediated luciferase activity of PAHs were developed with nominal median effect concentrations (EC₅₀, _nom) and freely dissolved concentration (EC_{50, free}) as endpoints, and quantum chemical and Dragon descriptors as predictor variables. Results indicated that only the EC_{50, free} model met the acceptable criteria of QSAR model (determination coefficient (R²) > 0.600, leave-one-out cross validation (Q_LOO²) > 0.500, and external validation coefficient (Q_EXT²) > 0.500), implying that it has good goodness-of-fit, robustness and external predictive power. Molecular polarizability and aromaticity index reflecting the partition behavior and intermolecular interactions can effectively predict AhR-mediated potencies of PAHs. The results highlight the necessity of adoption of the freely dissolved concentration in the QSAR modeling and more in silico models need to be further developed for different animal models (in vivo or in vitro).

6-Gingerol delays tumorigenesis in benzo[a]pyrene and dextran sulphate sodium-induced colorectal cancer in mice

Colorectal cancer (CRC) has been linked to dietary consumption of benzo[a]pyrene (B[a]P). 6-Gingerol (6-G), a component of ginger has been reported to possess anti-inflammatory and antioxidant activities, but little is known regarding the mechanism of 6-G in CRC chemoprevention. We therefore investigated the effect of 6-G on B[a]P. and dextran sulphate sodium (DSS) induced CRC in mice. Mice in Group I and Group II received corn oil and 6-G orally at 2 ml/kg and 100 mg/kg, respectively for 126 days. Group III were administered 125 mg/kg of B[a]P for 5 days followed by 3 cycles of 4% dextran sulphate sodium (DSS). Group IV received 6-G for 7 days followed by co-administration with 125 mg/kg of B[a]P. for 5 days and 3 cycles of 4% DSS. Tumor formation was reduced and expression of Ki-67, WNT3a, DVL-2 and β-catenin following 6-G exposure. Also, 6-G increases expression of APC, P53, TUNEL positive nuclei and subsequently decreased the expression of TNF-α, IL-1β, INOS, COX-2 and cyclin D1. 6-G inhibited angiogenesis by decreasing the concentration of VEGF, Angiopoietin-1, FGF and GDF-15 in the colon of B[a]P. and DSS exposed mice. Overall, 6-G attenuated B[a]P and DSS-induced CRC in mice via anti-inflammatory, anti-proliferative and apoptotic mechanisms.

Modulatory Effects of Silymarin on Benzo[a]pyrene-Induced Hepatotoxicity

Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon, is a group 1 carcinogen that introduces mutagenic DNA adducts into the genome. In this study, we investigated the molecular mechanisms underlying the involvement of silymarin in the reduction of DNA adduct formation by B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), induced by B[a]P. B[a]P exhibited toxicity in HepG2 cells, whereas co-treatment of the cells with B[a]P and silymarin reduced the formation of BPDE-DNA adducts, thereby increasing cell viability. Determination of the level of major B[a]P metabolites in the treated cells showed that BPDE levels were reduced by silymarin. Nuclear factor erythroid 2-related factor 2 (Nrf2) and pregnane X receptor (PXR) were found to be involved in the activation of detoxifying genes against B[a]P-mediated toxicity. Silymarin did not increase the expression of these major transcription factors, but greatly facilitated their nuclear translocation. In this manner, treatment of HepG2 cells with silymarin modulated detoxification enzymes through NRF2 and PXR to eliminate B[a]P metabolites. Knockdown of Nrf2 abolished the preventive effect of silymarin on BPDE-DNA adduct formation, indicating that activation of the Nrf2 pathway plays a key role in preventing B[a]P-induced genotoxicity. Our results suggest that silymarin has anti-genotoxic effects, as it prevents BPDE-DNA adduct formation by modulating the Nrf2 and PXR signaling pathways.

Primary Outcomes of a Randomized Controlled Crossover Trial to Explore the Effects of a High Chlorophyll Dietary Intervention to Reduce Colon Cancer Risk in Adults: The Meat and Three Greens (M3G) Feasibility Trial

Preclinical and observational research suggests green leafy vegetables (GLVs) may reduce the risk of red meat (RM)-induced colonic DNA damage and colon cancer (CC). We sought to determine the feasibility of a high GLV dietary intervention in adults with an increased risk of CC (NCT03582306) via a 12-week randomized controlled crossover trial. Participants were randomized to immediate or delayed (post-4-week washout) intervention groups. During the 4-week intervention period, participants were given frozen GLVs and counseled to consume one cooked cup equivalent daily. The primary outcomes were: accrual—recruiting 50 adults in 9 months; retention—retaining 80% of participants at completion; and adherence—meeting GLV intake goals on 90% of days. Adherence data were collected twice weekly and 24-h dietary recalls at each time point provided nutrient and food group measures. The Food Acceptability Questionnaire (FAQ) was completed to determine acceptability. On each of the four study visits, anthropometrics, stool, saliva, and blood were obtained. Fifty adults were recruited in 44 days. Participants were 48 ± 13 years of age, 62% female, and 80% Caucasian, with an average BMI at screening of 35.9 ± 5.1. Forty-eight (96%) participants were retained and completed the study. During the intervention phase, participants consumed GLVs on 88.8% of days; the adherence goal of one cup was met on 73.2% of days. Dietary recall-derived Vitamin K and GLVs significantly increased for all participants during the intervention periods. Overall satisfaction did not differ between intervention and control periods (p = 0.214). This feasibility trial achieved accrual, retention and acceptability goals, but fell slightly short of the benchmark for adherence. The analysis of biological specimens will determine the effects of GLVs on gut microbiota, oxidative DNA damage, and inflammatory cytokines.

Benzo[a]pyrene induces pyroptotic and autophagic death through inhibiting PI3K/Akt signaling pathway in HL-7702 human normal liver cells

Benzo(α)pyrene (BaP) possesses a forceful hepatotoxicity, and is ubiquitous in foods and ambient air. Our previous study found that BaP induced pyroptotic and autophagic death in HL-7702 human liver cells; the relevant mechanisms, however, remain unknown. This work was therefore to unravel the effects of the PI3K/Akt signaling pathway on pyroptotic and autophagic death triggered by BaP. Cells were treated with or without LY294002 (PI3K/Akt inhibitor) and IGF-1 (PI3K/Akt activator) before BaP exposure, and the results showed that compared with the control, the protein expression of p-Akt was markedly decreased by BaP (p < 0.05). IGF-1 did not subvert this inhibitive effect of BaP, while LY294002 enhanced it. Furthermore, the protein expression of pyroptosis (Cleaved Caspase-1, NO, IL-1β, IL-18), as well as LDH and the relative electrical conductivity were significantly augmented by BaP. The levels of these indices were increased by LY294002 pretreatment, and decreased by IGF-1. Similarly, LY294002 enhanced BaP-induced increase in the key protein expression of autophagy (Beclin-1 and LC3II), while IGF-1 weakened it. Finally, the phosphorylation of FOXO4 was clearly (p < 0.01) inhibited by BaP, and LY294002 suppressed this inhibitive effect of BaP, while IGF-1 strengthened it. In conclusion, BaP was able to induce pyroptotic and autophagic death via blocking the PI3K/Akt signaling pathway in HL-7702 liver cells.

[6]-Gingerol modulates spermatotoxicity associated with ulcerative colitis and benzo[a]pyrene exposure in BALB/c mice

BACKGROUND

The deterioration of male reproductive health may represent an outcome of an active disease and environmental factors. The present study investigated the modulatory role of [6]-gingerol in spermatotoxicity resulting from colitis and benzo[a]pyrene (B[a]P), an environmental and food-borne pollutant.

METHODS

Group I (control) mice received corn oil alone, while group II ([6]-gingerol alone) mice orally received [6]-gingerol alone at 100 mg/kg body weight. Group III [benzo[a]pyrene+dextran sulfate sodium (BDS) alone] mice were orally exposed to B[a]P at 125 mg/kg for 7 days followed by three cycles of 4% dextran sulfate sodium (DSS) in drinking water. A cycle consisted of seven consecutive days of exposure to DSS-treated water followed by 14 consecutive days of normal drinking water. Group IV (BDS+[6]-gingerol) mice were orally treated daily with 100 mg/kg of [6]-gingerol during exposure to B[a]P and DSS in the same manner as those of group III.

RESULTS

[6]-Gingerol significantly abrogated BDS-mediated increase in disease activity index and restored the colon wet weight, colon length and colon mass index to near normal when compared to BDS alone group. Moreover, [6]-gingerol significantly prevented BDS-induced decreases in the daily sperm production (DSP), testicular sperm number (TSN), epididymal sperm number, sperm progressive motility and sperm membrane integrity when compared with the control. [6]-Gingerol markedly increased the sperm antioxidant enzymes activities and decreased the sperm head, mid-piece and tail abnormalities as well as suppressed oxidative stress and inflammatory biomarkers in BDS-exposed mice.

CONCLUSIONS

[6]-Gingerol protected against spermatotoxicity in experimental model of interaction of colitis with environmental pollutant B[a]P.

Western diet enhances benzo(a)pyrene-induced colon tumorigenesis in a polyposis in rat coli (PIRC) rat model of colon cancer

Consumption of Western diet (WD), contaminated with environmental toxicants, has been implicated as one of the risk factors for sporadic colon cancer. Our earlier studies using a mouse model revealed that compared to unsaturated dietary fat, the saturated dietary fat exacerbated the development of colon tumors caused by B(a)P. The objective of this study was to study how WD potentiates B(a)P-induced colon carcinogenesis in the adult male rats that carry a mutation in the Apc locus - the polyposis in the rat colon (PIRC) rats. Groups of PIRC rats were fed with AIN-76A standard diet (RD) or Western diet (WD) and received 25, 50, or 100 μg B(a)P/kg body weight (wt) via oral gavage for 60 days. Subsequent to exposure, rats were euthanized; colons were retrieved and preserved in 10% formalin for counting the polyp numbers, measuring the polyp size, and histological analyses. Blood samples were collected and concentrations of cholesterol, triglycerides, glucose, insulin and leptin were measured. Rats that received WD + B(a)P showed increased levels of cholesterol, triglycerides, and leptin in comparison to RD + B(a)P groups or controls. The colon tumor numbers showed a B(a)P dose-response relationship. Adenomas with high grade dysplasia were prominent in B(a)P + WD rats compared to B(a)P + RD rats and controls (p < 0.05). The larger rat model system used in this study allows for studying more advanced tumor phenotypes over a longer duration and delineating the role of diet - toxicant interactions in sporadic colon tumor development.

Benzo[a]pyrene Induces Autophagic and Pyroptotic Death Simultaneously in HL-7702 Human Normal Liver Cells

As a common polycyclic aromatic hydrocarbon compound, benzo[a]pyrene (BaP) is readily produced in processing of oil and fatty foods. It is not only a strong carcinogen but also a substance with strong immunotoxicity and reproduction toxicity. Autophagy and pyroptosis are two types of programmed cell death. Whether or not BaP damages body tissues via autophagy or pyroptosis remains unknown. The present study investigated the effects of BaP on autophagy and pyroptosis in HL-7702 cells. The results showed that BaP induced cell death in HL-7702 cells enhanced the intracellular levels of ROS and arrested the cell cycle at the S phase. Additionally, BaP resulted in cell death through autophagy and pyroptosis. Compared with the BaP group, the autophagy inhibitor 3-MA significantly (p < 0.01) inhibited the release of LDH by 70.53% ± 0.46 and NO by 50.36% ± 0.80, the increase of electrical conductivity by 12.08% ± 0.55, and the expressions of pyroptotic marker proteins (Caspase-1, Cox-2, IL-1β, IL-18). The pyroptosis inhibitor Ac-YVAD-CM also notably (p < 0.01) blocked BaP-induced autophagic cell death characterized by the increase of autophagic vacuoles and overexpression of Beclin-1 and LC3-II. In conclusion, BaP led to injury by inducing autophagy and pyroptosis simultaneously, the two of which coexisted and promoted each other in HL-7702 cells.

Metabolism of benzo(a)pyrene by aortic subcellular fractions in the setting of abdominal aortic aneurysms

As exposure to polycyclic aromatic hydrocarbons (PAHs; a family of environmental toxicants) have been implicated in cardiovascular diseases, the ability of the aortic tissue to process these toxicants is important from the standpoint of abdominal aortic aneurysms and atherosclerosis. Benzo(a)pyrene (B(a)P), a representative PAH compound is released into the environment from automobile exhausts, industrial emissions, and considerable intake of B(a)P is also expected in people who are smokers and barbecued red meat eaters. Therefore, knowledge of B(a)P metabolism in the cardiovascular system will be of importance in the management of vascular disorders. Toward this end, subcellular fractions (nuclear, cytosolic, mitochondrial, and microsomal) were isolated from the aortic tissues of Apo E mice that received a 5 mg/kg/week of B(a)P for 42 days and 0.71 mg/kg/day for 60 days. The fractions were incubated with 1 and 3 μM B(a)P. Post incubation, samples were extracted with ethyl acetate and analyzed by reverse-phase HPLC. Microsomal B(a)P metabolism was greater than the rest of the fractions. The B(a)P metabolite levels generated by all the subcellular fractions showed a B(a)P exposure concentration-dependent increase for both the weekly and daily B(a)P treatment categories. The preponderance of B(a)P metabolites such as 7,8-dihydrodiol, 3,6-, and 6,12-dione metabolites are interesting due to their reported involvement in B(a)P-induced toxicity through oxidative stress.