Exposure of primary porcine urothelial cells to benzo(a)pyrene: in vitro uptake, intracellular concentration, and biological response

A pilot study exploring time- and dose-dependent DNA damage and chromosomal instability caused by benzo[a]pyrene in two urothelial cell types

Environmental and occupational exposure to polycyclic aromatic hydrocarbons (PAHs) is associated with adverse health effects in humans. Uncertainty exists regarding the causation of urinary bladder cancer by benzo[a]pyrene (B[a]P) due to a lack of sufficient data. In this work, we focused on in-vitro DNA damage and the formation of micronuclei and chromosomal aberrations as predictors of cancer risk, applying a wide range of dosages and time periods to quantify the onset, intensity, and duration of the response. We chose two urothelial cell types to compare susceptibility and the ability to increase the malignity of a pre-existing bladder cancer: a cancer cell line (T24) and a pooled sample of primary urinary bladder epithelia cells (PUBEC) from pigs. The highest level of DNA damage assessed by comet assay was observed following 24-h treatment in both cell types, whereas PUBEC cells were clearly more susceptible. Even 4-h treatment induced DNA damage in PUBEC cells with benchmark doses of 0.0027 µM B[a]P and 0.00023 µM after 4-h and 24-h exposure, respectively. Nearly no effect was observed for periods of 48 h. The frequency of micronucleus formation increased more markedly in T24 cells, particularly with 24-h treatment. In PUBEC cells, 48-h exposure notably induced the formation of nucleoplasmic bridges and nuclear buds. Even though only one biological replicate was studied due to the sophisticated study design, our results give a strong indication of the potential of B[a]P to induce and increase malignity in human-relevant cell types.

Resveratrol: A Potential Protector Against Benzo[a]pyrene- Induced Lung Toxicity

<b>Background and Objective:</b> Benzo[a]pyrene (B[a]P), a major component of lipophilic pollutants then can be translated to diffluent substances. The aim of t he present article was to investigate protective activity of resveratrol against lung toxicity induced by B[a]P. Material and Methods: Male Sprague-Dawley rats were randomly assigned to 6 groups (6 animals/group): 3 negative control groups, control positive, B[a]P (20 mg kg<sup></sup><sup>1</sup> b.wt., resveratrol (50 mg kg<sup></sup><sup>1</sup> b.wt.)-B[a]P and vitamin C (1 g kg<sup></sup><sup>1</sup> b.wt.)-B[a]P groups. <b>Results:</b> The daily oral administration of the resveratrol (50 mg kg<sup></sup><sup>1</sup> b.wt.) and vitamin C (1 g kg<sup></sup><sup>1</sup> b.wt.) for 30 days to rats treated with B[a]P (20 mg kg<sup></sup><sup>1</sup> b.wt.) resulted in a significant improve plasma cholesterol, triglyceride and HDL-C as well as serum TNF-α, TBARS, IL-2,IL-6, haptoglobin, histamine, IgA, Ig E,Ig G and Ig M in B[a]P treated rats. On the other hand oral administration of resveratrol elevated the SOD, GPx and GR gene expression in lung rats treated with B[a]P. Furthermore, resveratrol and vitamin C nearly normalized these effects in lung histoarchitecture. <b>Conclusion:</b> The obtained biochemical, molecular biology and histological results of this study proved the lung protective activity of resveratrol against B[a]P induced lung toxicity in rats.

MP-SeNPs; A Promising Cytokines Suppressor in Benzo[a]pyrene-Induced Mammal Tissue Injury in Rats

<b>Background and Objective:</b> <i>Moringa peregrina</i> (family Moringaceae) is a common flowering plant found in the Arabian Peninsula, Horn of Africa and Southern Sinai, Egypt. The purpose of this study was to investigate the protective activity of MP-SeNPs against BaP-induced mammal tissue injury in rats. <b>Materials and Methods:</b> MP-SeNPs were prepared and characterized in terms of particle size and zeta potential. Furthermore, the IC<sub>50</sub> of MP-SeNPs against the Mcf7 breast carcinoma cell line and LD<sub>50</sub> was evaluated. Adult albino rats weighing approximately 187±10 g was used to assess the lung protective activity of MP-SeNPs (28.7 and 71.75 mg kg<sup>1</sup> b.wt.) against BaP-induced mammal tissue injury in rats. <b>Results:</b> The mean particle size of MP-SeNPs was 134.69±8.24 nm with negative zeta potential of +26.04 with the observed shapes of nano particle was spherical. Also, IC<sub>50</sub> of MP-SeNPs against Mcf7 breast carcinoma cell line = 89.57 μg mL<sup>1</sup> and LD<sub>50</sub> equals and 1435 mg kg<sup>1</sup> b.wt., respectively. The daily oral administration of MP-SeNPs at concentrations of 28.7 and 71.75 mg kg<sup>1</sup> b.wt. for 30 days to rats treated with BaP (20 mg kg<sup>1</sup> b.wt.) resulted in a significant improvement of IL-2, IL-6 and IL-10. Oral administration of MP-SeNPs, on the other hand, increased the levels of SOD, GPx, TNF-α, iNOs and GSH as well as decreased the level of MDA in mammal tissue of BaP-treated rats. Furthermore, MP-SeNPs almost normalized these effects in mammal tissue histoarchitecture and MRI examination. <b>Conclusion:</b> The biochemical, histological and MRI findings incurrent study demonstrated that MP-SeNPs have protective activity against BaP-induced mammal tissue injury in rats.

NOD-like receptor signaling pathway activation: A potential mechanism underlying negative effects of benzo(α)pyrene on zebrafish

Benzo(α)pyrene (BaP) is one of typical polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and has been shown to cause toxic effects to aquatic animals. Although the negative effects of BaP have been investigated, the potential toxic mechanisms remain uncharacterized. To explore the potential mechanisms mediating the toxic effects of BaP, zebrafish (Danio rerio) were exposed to BaP for 15 days and the toxic effects of BaP in zebrafish liver were investigated using physiological and transcriptomic analyses. After 15-day BaP exposure, zebrafish liver exhibited abnormalities including increased cytoplasmic vacuolation, inflammatory cell infiltration, swelled nuclei and irregular pigmentation. BaP exposure also induced oxidative stress to the liver of zebrafish. Transcriptomic profiles revealed 5129 differentially expressed genes (DEGs) after 15-days of BaP exposure, and the vast majority of DEGs were up-regulated under BaP treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that genes related to immune response were significantly dysregulated. Furthermore, the nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway was significantly enriched and most of the genes in this pathway exhibited enhanced expression after BaP exposure. These results partially explained the mechanisms underlying the toxic effects of BaP on zebrafish liver. In conclusion, BaP has the potential to induce physiological responses in zebrafish liver through altering associated genes.

Benzo[a]pyrene-induced metabolic shift from glycolysis to pentose phosphate pathway in the human bladder cancer cell line RT4

Benzo[a]pyrene (B[a]P), a well-known polyaromatic hydrocarbon, is known for its lung carcinogenicity, however, its role in bladder cancer development is still discussed. Comparative two-dimensional blue native SDS-PAGE analysis of protein complexes isolated from subcellular fractions of 0.5 µM B[a]P-exposed cells indicated a differential regulation of proteins involved in carbohydrate, fatty acid, and nucleotide metabolism, suggesting a possible metabolic flux redistribution. It appeared that B[a]P exposure led to a repression of enzymes (fructose-bisphosphate aldolase A, glucose-6-phosphate isomerase, lactate dehydrogenase) involved in glycolysis, and an up-regulation of proteins (glucose-6-phosphate 1-dehydrogenase, 6-phosphogluconolactonase) catalyzing the pentose phosphate pathway and one carbon metabolism (10-formyltetrahydrofolate dehydrogenase, bifunctional purine biosynthesis protein). Untargeted metabolomics further supported the proteomic data, a lower concentration of glycolytic metabolite was observed as compared to glutamine, xylulose and fatty acids. The analysis of the glutathione and NADPH/NADP⁺ content of the cells revealed a significant increase of these cofactors. Concomitantly, we did not observe any detectable increase in the production of ROS. With the present work, we shed light on an early phase of the metabolic stress response in which the urothelial cells are capable of counteracting oxidative stress by redirecting the metabolic flux from glycolysis to pentose phosphate pathway.

Live cell imaging of the intracellular compartmentalization of the contaminate benzo[a]pyrene

This study investigates the cellular response of murine hepatoma cells to the polycyclic aromatic hydrocarbon benzo[a]pyrene (B[a]P) using two-photon and confocal laser scanning microscopy. The intracellular distribution of B[a]P and the B[a]P/AhR complex was visualized time- and concentration-dependent for up to 48 h of exposure. B[a]P was predominantly found in lipid droplets, endoplasmic reticulum and lysosomes, where B[a]P is collected and forms large aggregates. Changes in mitochondrial membrane potential and bleb formation due to high B[a]P concentrations were observed. The imaging data presented in this study provide new insights into the systemic cellular regulation following B[a]P exposure.

Inhibitory action of benzo[α]pyrene on hepatic lipoprotein receptors in vitro and on liver lipid homeostasis in mice

BACKGROUND

Dyslipidemia associated with obesity often manifests as increased plasma LDL and triglyceride-rich lipoprotein levels suggesting changes in hepatic lipoprotein receptor status. Persistent organic pollutants have been recently postulated to contribute to the obesity etiology by increasing adipogenesis, but little information is available on their potential effect on hepatic lipoprotein metabolism.

OBJECTIVE

The objective of this study was to investigate the effect of the common environmental pollutant, benzo[α]pyrene (B[α]P) on two lipoprotein receptors, the LDL-receptor and the lipolysis-stimulated lipoprotein receptor (LSR) as well as the ATP-binding cassette transporter A1 (ABCA1) using cell and animal models.

RESULTS

LSR, LDL-receptor as well as ABCA1 protein levels were significantly decreased by 26-48% in Hepa1-6 cells incubated (<2 h) in the presence of B[α]P (≤1 µM). Real-time PCR analysis and lactacystin studies revealed that this effect was due primarily to increased proteasome, and not lysosomal-mediated degradation rather than decreased transcription. Furthermore, ligand blots revealed that lipoproteins exposed to 1 or 5 µM B[α]P displayed markedly decreased (42-86%) binding to LSR or LDL-receptor. B[α]P-treated (0.5 mg/kg/48 h, i.p. 15 days) C57BL/6J mice displayed higher weight gain, associated with significant increases in plasma cholesterol, triglycerides, and liver cholesterol content, and decreased hepatic LDL-receptor and ABCA1 levels. Furthermore, correlational analysis revealed that B[α]P abolished the positive association observed in control mice between the LSR and LDL-receptor. Interestingly, levels of other proteins involved in liver cholesterol metabolism, ATP-binding cassette transporter G1 and scavenger receptor-BI, were decreased, while those of acyl-CoA:cholesterol acyltransferase 1 and 2 were increased in B[α]P-treated mice.

CONCLUSIONS

B[α]P demonstrates inhibitory action on LSR and LDL-R, as well as ABCA1, which we propose leads to modified lipid status in B[α]P-treated mice, thus providing new insight into mechanisms underlying the involvement of pollutants in the disruption of lipid homeostasis, potentially contributing to dyslipidemia associated with obesity.

The extreme variety of genotoxic response to benzo[a]pyrene in three different human cell lines from three different organs

Polycyclic aromatic hydrocarbons (PAHs) are associated with occupational exposure and urban atmospheric pollution. Determination of the genotoxic properties of these compounds is thus of outmost importance. For this purpose a variety of cellular models have been widely used. Reliable results can however only be obtained with models reflecting the specific sensitivity of different organs towards PAHs. In this work, we compared the response to benzo[a]pyrene in cell lines from human lungs (A549) and bladder (T24); two important target organs for PAHs-induced cancer. Human hepatocytes (HepG2) were used as a reference, although liver is not a concern for PAHs carcinogenesis. Adducts arising from the ultimate diol-epoxide metabolite of B[a]P, BPDE, were found to be produced in a dose-dependent manner in HepG2. BPDE DNA adducts were not detected in T24 and in A549 their formation was found to be most efficient at the lowest concentration studied (0.2 µM). These results are probably explained by differences in induction and activity of phase I metabolization enzymes, as well as by proteins eliminating the B[a]P epoxide in A549. In addition to BPDE adducts, oxidative DNA damage, namely strand breaks and oxidized purines were measured and found to be produced only in minute amounts in all three cell lines. In summary, our results emphasize the large differences in the response of cells originating from different organs. Our data also point out the importance of carefully selecting the doses used in in vitro toxicological experiments. The example of A549 shows that working at high doses may lead to an underestimation of the risk. Finally, the choice of method for evaluating genotoxicity appears to be of crucial importance. The comet assay does not seem to be the best method for a compound like B[a]P which induces stable adducts causing limited oxidative damage.

Oral chemoprevention with acetyl salicylic Acid, vitamin D and calcium reduces the risk of tobacco carcinogen-induced bladder tumors in mice

Bladder cancer is a common urological malignancy with high recurrence rate, which may be reduced by chemoprevention. The aim was to evaluate chemoprevention in a mouse model of tobacco carcinogen-induced bladder tumors. A total of 60 A/J mice were randomized to normal diet, diet with low calcium, and diet with chemoprevention (acetyl salicylic acid, 1-alpha 25(OH)2-vitamin D3 and calcium). There were significantly fewer tumors (0 (0-0) vs. 0 (0-2), p = .045) and fewer animals with tumors (0/20 vs. 5/20, p = .045) in the chemoprevention group compared with controls. Thus, chemoprevention diet effectively reduced the tumor promoting effect of tobacco carcinogens in the mouse bladder.