Modulation of adult rat benzo(a)pyrene (BaP) metabolism and DNA adduct formation by neonatal diethylstilbestrol (DES) exposure

Imprinting and Reproductive Health: A Toxicological Perspective

This overview discusses the role of imprinting in the development of an organism, and how exposure to environmental chemicals during fetal development leads to the physiological and biochemical changes that can have adverse lifelong effects on the health of the offspring. There has been a recent upsurge in the use of chemical products in everyday life. These chemicals include industrial byproducts, pesticides, dietary supplements, and pharmaceutical products. They mimic the natural estrogens and bind to estradiol receptors. Consequently, they reduce the number of receptors available for ligand binding. This leads to a faulty signaling in the neuroendocrine system during the critical developmental process of 'imprinting'. Imprinting causes structural and organizational differentiation in male and female reproductive organs, sexual behavior, bone mineral density, and the metabolism of exogenous and endogenous chemical substances. Several studies conducted on animal models and epidemiological studies provide profound evidence that altered imprinting causes various developmental and reproductive abnormalities and other diseases in humans. Altered metabolism can be measured by various endpoints such as the profile of cytochrome P-450 enzymes (CYP450's), xenobiotic metabolite levels, and DNA adducts. The importance of imprinting in the potentiation or attenuation of toxic chemicals is discussed.

Influence of polycyclic aromatic hydrocarbon exposure on IVF: now is the time to focus on women

RESEARCH QUESTION

Is polycyclic aromatic hydrocarbon (PAH) exposure associated with the reproductive outcomes of IVF treatment?

DESIGN

A prospective, small-scale monocentric cohort study of couples who underwent IVF treatment between January 2018 and June 2019. Both members of each couple answered a questionnaire on PAH exposure and provided urine samples to measure urinary 1-hydroxypyrene (1-OHP) the day before oocyte retrieval and semen collection for fertilization. To assess the specific PAH exposure of gamete cells, immunostaining was conducted on both spermatozoa and granulosa cells obtained during IVF with an anti-benzo(a)pyrene diol epoxide (BPDE) monoclonal antibody that recognizes BDPE-DNA adducts. To assess DNA damage, a comet assay on spermatozoa was conducted. The PAH exposure was compared between couples who had positive HCG and couples who had negative HCG on day 14 after embryo transfer.

RESULTS

Eighteen couples were included. The mean 1-OHP level in women whose HCG tests were positive (n = 6) was significantly lower than that in women with negative HCG tests (0.098 [0.042-0.170] versus 0.177 [0.067-0.812] μg/g creatinine; P = 0.048). The presence of BPDE-DNA adducts in granulosa cells of women with a negative (29.7 [16.2-57.5] arbitrary units) or positive HCG test (20.3 [9.3-23.3] arbitrary units) were not significantly different (P = 0.092). The urinary 1-OHP levels of men and BPDE-DNA adducts in spermatozoa showed no differences between groups.

CONCLUSIONS

This exploratory research should encourage further studies to determine the effect of women's exposure to PAHs on reproductive outcomes of IVF treatment.

Alteration of benzo(a)pyrene biotransformation by resveratrol in ApcMin/+ mouse model of colon carcinogenesis

Epidemiological surveys have revealed that environmental and dietary factors contribute to most of the human cancers. Our earlier studies have shown that resveratrol (RVT), a phytochemical reduced the tumor number, size and incidence of dysplasias induced by benzo(a)pyrene (BaP), an environmental toxicant in the Apc^Min/+ mouse model of colon cancer. In this study we investigated to ascertain whether the preventive effects of RVT on BaP-induced colon carcinogenesis is a result of altered BaP biotransformation by RVT. For the first group of mice, 100 μg BaP/kg bw was administered in peanut oil via oral gavage over a 60 day period. For the second group, 45 μg RVT/kg bw was co-administered with BaP. For the third group, RVT was administered for 1 week prior to BaP exposure. Blood, colon and liver were collected from control and BaP/RVT-treated mice at 60 days post-BaP & RVT exposure. We have assayed activities and expression (protein & mRNA) of drug metabolizing enzymes such as cytochrome P4501A1 (CYP1A1), CYP1B1, and glutathione-S-transferase (GST) in colon and liver samples from the treatment groups mentioned above. An increased expression of CYP1A1 in liver and colon and of CYP1B1 in liver of BaP-treated mice was seen, while RVT inhibited the extent of biotransformation mediated by these enzymes in the respective tissue samples. In the case of GST, an increased expression in colon of BaP alone-treated mice was noted when RVT was administered prior to BaP or simultaneously with BaP. However, there is no change in liver GST expression between BaP and RVT treatment groups. The concentrations of BaP aqueous (phase II) metabolites were found to be greater than the organic (phase I) metabolites, suggesting that RVT slows down the phase I metabolism (metabolic activation) of BaP, while enhancing phase II metabolism (detoxification). Additionally, the BaP-DNA adduct concentrations measured in colon and liver of BaP + RVT-treated mice were low relative to their BaP counterparts. Taken together, our findings strongly suggest that RVT alleviates BaP-induced colon carcinogenesis by impairing biotransformation pathways and DNA adduct formation, and therefore holds promise as a chemopreventive agent.

Comparison of toxicogenomics and traditional approaches to inform mode of action and points of departure in human health risk assessment of benzo[a]pyrene in drinking water

Toxicogenomics is proposed to be a useful tool in human health risk assessment. However, a systematic comparison of traditional risk assessment approaches with those applying toxicogenomics has never been done. We conducted a case study to evaluate the utility of toxicogenomics in the risk assessment of benzo[a]pyrene (BaP), a well-studied carcinogen, for drinking water exposures. Our study was intended to compare methodologies, not to evaluate drinking water safety. We compared traditional (RA1), genomics-informed (RA2) and genomics-only (RA3) approaches. RA2 and RA3 applied toxicogenomics data from human cell cultures and mice exposed to BaP to determine if these data could provide insight into BaP's mode of action (MOA) and derive tissue-specific points of departure (POD). Our global gene expression analysis supported that BaP is genotoxic in mice and allowed the development of a detailed MOA. Toxicogenomics analysis in human lymphoblastoid TK6 cells demonstrated a high degree of consistency in perturbed pathways with animal tissues. Quantitatively, the PODs for traditional and transcriptional approaches were similar (liver 1.2 vs. 1.0 mg/kg-bw/day; lungs 0.8 vs. 3.7 mg/kg-bw/day; forestomach 0.5 vs. 7.4 mg/kg-bw/day). RA3, which applied toxicogenomics in the absence of apical toxicology data, demonstrates that this approach provides useful information in data-poor situations. Overall, our study supports the use of toxicogenomics as a relatively fast and cost-effective tool for hazard identification, preliminary evaluation of potential carcinogens, and carcinogenic potency, in addition to identifying current limitations and practical questions for future work.

Multiphoton spectral analysis of benzo[a]pyrene uptake and metabolism in a rat liver cell line

Dynamic analysis of the uptake and metabolism of polycyclic aromatic hydrocarbons (PAHs) and their metabolites within live cells in real time has the potential to provide novel insights into genotoxic and non-genotoxic mechanisms of cellular injury caused by PAHs. The present work, combining the use of metabolite spectra generated from metabolite standards using multiphoton spectral analysis and an "advanced unmixing process", identifies and quantifies the uptake, partitioning, and metabolite formation of one of the most important PAHs (benzo[a]pyrene, BaP) in viable cultured rat liver cells over a period of 24 h. The application of the advanced unmixing process resulted in the simultaneous identification of 8 metabolites in live cells at any single time. The accuracy of this unmixing process was verified using specific microsomal epoxide hydrolase inhibitors, glucuronidation and sulfation inhibitors as well as several mixtures of metabolite standards. Our findings prove that the two-photon microscopy imaging surpasses the conventional fluorescence imaging techniques and the unmixing process is a mathematical technique that seems applicable to the analysis of BaP metabolites in living cells especially for analysis of changes of the ultimate carcinogen benzo[a]pyrene-r-7,t-8-dihydrodiol-t-9,10-epoxide. Therefore, the combination of the two-photon acquisition with the unmixing process should provide important insights into the cellular and molecular mechanisms by which BaP and other PAHs alter cellular homeostasis.

The combined toxicity of dibutyl phthalate and benzo(a)pyrene on the reproductive system of male Sprague Dawley rats in vivo

Our previous studies revealed more than 100 pollutants, most of which were endocrine disruptors (EDs) in two Chinese rivers, the Jialing and the Yangtze near Chongqing. Most EDs, such as dibutyl phthalate (DBP) and benzo(a)pyrene (BaP), are known to act individually as reproductive toxicants. However, little is known about the combined toxicity of DBP and BaP. In the current study, male Sprague Dawley rats were subchronically exposed to single doses of DBP (250 mg/kg), single doses of BaP (5 mg/kg) and combined doses of DBP and BaP. Significant adverse effects were observed on the reproductive system, including decreased sperm count, increased production of abnormal sperm, changes in serum testosterone levels and irregular arrangements of the seminiferous epithelium. Biochemical analyses showed that the activities of superoxide dismutase and glutathione peroxidase decreased after exposure to these EDs. Therefore, our data suggest that exposure to DBP and BaP, in either separate or combined doses, can affect the reproductive system of male rats adversely via oxidative stress-related mechanisms. No significant additive effect was observed after combined exposure. These results indicate that exposure to mixtures of EDs have unexpected and elusive effects. Our findings provide preliminary but important data for assessing water safety in China.

Ovarian susceptibility to benzo[a]pyrene: tissue burden of metabolites and DNA adducts in F-344 rats

Exposure to environmental toxicants has been implicated as one of the causative factors for infertility in mammals. The objective of this study was to determine the amount of ingested benzo[a]pyrene (BaP), an environmental toxicant that reaches the reproductive tissues (internal dose) subsequent to a single acute exposure. Toward this end, the concentrations of BaP reactive metabolites and BaP-DNA adducts were measured throughout the course of BaP's residence in the body. Ten-week-old female Fischer-344 rats weighing approximately 220 g were administered 5 mg BaP/kg body weight orally. 1, 7, 14, 2,1 and 28 d post BaP exposure, BaP parent compound and metabolites from plasma, ovaries, and liver tissues were extracted using liquid-liquid extraction. The extracts were analyzed by reverse-phase highperformance liquid chromatography (HPLC). DNA was isolated and analyzed for BaP-induced DNA adducts by (32)P-postlabeling method. The BaP total metabolite concentrations in plasma, ovaries, and liver showed a gradual decrease from d 1 to 28 post BaP administration. The BaP-DNA adducts concentrations in ovaries and liver tissues from the treatment group demonstrated a trend similar to that observed for metabolites. Ovaries showed greater concentrations of DNA adducts compared to liver. However, with an increase in time post cessation of exposure, the adduct concentrations in liver tissue started declining rapidly, from d 1 to 28. For ovaries, the adduct concentrations demonstrated a significant decline from d 1 to 7 and a gradual fall thereafter. A concordance between BaP reactive metabolite levels and adduct concentrations indicates that the bioavailability of reactive metabolites determines the binding with DNA and consequently the formation and persistence of adducts in an acute exposure regimen.

Dose-dependent benzo(a)pyrene [B(a)P]-DNA adduct levels and persistence in F-344 rats following subchronic dietary exposure to B(a)P

In order to investigate the relationship between BaP-DNA adduct formation and long-term exposure to benzo(a)pyrene (BaP), DNA adduct levels in liver and lung tissues of male and female F-344 rats subchronically exposed to BaP were determined. Doses of 0, 5, 50, and 100mg/kg BaP, representing control, low, intermediate, and high doses, respectively, were administered in the animal diet over a 90-day period. After dosing, animals were sacrificed, liver and lung tissues were removed, DNA was isolated and analyzed for BaP-induced DNA adducts by the (32)P-postlabeling method using a four-directional thin-layer chromatography system. At low and intermediate BaP doses, DNA adduct levels in the tissues were significantly correlated with exposure. However, at high BaP doses, the dose-DNA adduct relationship became non-linear. Similarly, the relative DNA adducts persistence at intermediate and high doses were significantly higher than that measured at low dose. The low and intermediate dose linearity and high dose non-linearity may be due to saturation of metabolic activation and detoxification enzymes, and DNA repair processes.

Polycyclic aromatic hydrocarbon-DNA adduct formation in prostate carcinogenesis

The evidence for polycyclic aromatic hydrocarbons (PAH) playing a role in prostate carcinogenesis comes mainly from associations between reported PAH exposures and prostate cancer in epidemiologic studies. Associations between prostate cancer and DNA repair genotypes and phenotypes have also been reported, lending further credence to a PAH-induced carcinogenesis pathway in prostate cancer. Recent work that demonstrates the human prostate has metabolic enzyme activity necessary for PAH activation and will form DNA adducts upon exposure to PAH further supports PAH carcinogenesis. We have demonstrated the presence of PAH-DNA adducts in prostate cancer cases, but further validation of this biomarker as a carcinogenic agent in human prostate is needed.