Search

Exposure to environmental pollutants and human microbiome composition are important predisposition factors for tumour development 1,2 . Similar to drug molecules, pollutants are typically metabolized in the body, which can change their carcinogenic potential and affect tissue distribution through altered toxicokinetics 3 . Although recent studies demonstrated that human-associated microorganisms can chemically convert a wide range of xenobiotics and influence the profile and tissue exposure of resulting metabolites 4,5 , the effect of microbial biotransformation on chemical-induced tumour development remains unclear. Here we show that the depletion of the gut microbiota affects the toxicokinetics of nitrosamines, which markedly reduces the development and severity of nitrosamine-induced urinary bladder cancer in mice 6,7 . We causally linked this carcinogen biotransformation to specific gut bacterial isolates in vitro and in vivo using individualized bacterial culture collections and gnotobiotic mouse models, respectively. We tested gut communities from different human donors to demonstrate that microbial carcinogen metabolism varies between individuals and we showed that this metabolic activity applies to structurally related nitrosamine carcinogens. Altogether, these results indicate that gut microbiota carcinogen metabolism may be a contributing factor for chemical-induced carcinogenesis, which could open avenues to target the microbiome for improved predisposition risk assessment and prevention of cancer., (© 2024. The Author(s).)

Dibenzo[def,p]chrysene (DBC) is an environmental polycyclic aromatic hydrocarbon (PAH) that causes tumors in mice and has been classified as a probable human carcinogen by the International Agency for Research on Cancer. Animal toxicity studies often utilize higher doses than are found in relevant human exposures. Additionally, like many PAHs, DBC requires metabolic bioactivation to form the ultimate toxicant, and species differences in DBC and DBC metabolite metabolism have been observed. To understand the implications of dose and species differences, a physiologically based pharmacokinetic model (PBPK) for DBC and major metabolites was developed in mice and humans. Metabolism parameters used in the model were obtained from experimental in vitro metabolism assays using mice and human hepatic microsomes. PBPK model simulations were evaluated against mice dosed with 15 mg/kg DBC by oral gavage and human volunteers orally microdosed with 29 ng of DBC. DBC and its primary metabolite DBC-11,12-diol were measured in blood of mice and humans, while in urine, the majority of DBC metabolites were obeserved as conjugated DBC-11,12-diol, conjugated DBC tetrols, and unconjugated DBC tetrols. The PBPK model was able to predict the time course concentrations of DBC, DBC-11,12-diol, and other DBC metabolites in blood and urine of human volunteers and mice with reasonable accuracy. Agreement between model simulations and measured pharmacokinetic data in mice and human studies demonstrate the success and versatility of our model for interspecies extrapolation and applicability for different doses. Furthermore, our simulations show that internal dose metrics used for risk assessment do not necessarily scale allometrically, and that PBPK modeling provides a reliable approach to appropriately account for interspecies differences in metabolism and physiology., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Potential consequences of combined exposure to the selected food-borne alkenylbenzenes safrole and estragole or their proximate carcinogenic 1'-hydroxy metabolites were evaluated in vitro and in silico. HepG2 cells were exposed to 1'-hydroxyestragole and 1'-hydroxysafrole individually or in equipotent combination subsequently detecting cytotoxicity and DNA adduct formation. Results indicate that concentration addition adequately describes the cytotoxic effects and no statistically significant differences were shown in the level of formation of the major DNA adducts. Furthermore, physiologically based kinetic modeling revealed that at normal dietary intake the concentration of the parent compounds and their 1'-hydroxymetabolites remain substantially below the Km values for the respective bioactivation and detoxification reactions providing further support for the fact that the simultaneous presence of the two carcinogens or of their proximate carcinogenic 1'-hydroxy metabolites may not affect their DNA adduct formation. Overall, these results point at the absence of interactions upon combined exposure to selected food-borne alkenylbenzenes at realistic dietary levels of intake., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Studies demonstrate that with sufficient dose and duration, 1,4-dioxane (1,4-DX) induces liver tumors in laboratory rodent models. The available evidence aligns with a threshold-dependent, tumor promotion mode of action (MOA). The MOA and key events (KE) in rats are well developed but less so in the mouse. Therefore, we conducted a 90-day drinking water study in female mice to evaluate early KE at 7, 28, and 90 days. Female B6D2F1/Crl mice consumed drinking water containing 0, 40, 200, 600, 2000 or 6000 ppm 1,4-DX. 1,4-DX was detected in blood at 90-days of exposure to 6000 ppm, but not in the other exposure groups, indicating a metabolic clearance threshold between 2000 and 6000. Early events identified in this study include glycogen-like vacuolization, centrilobular hypertrophy, centrilobular GST-P staining, apoptosis, and pan-lobular increase in cell proliferation observed after 90-days of exposure to 6000 ppm 1,4-DX. There was minimal evidence of hepatotoxicity over the duration of this study. These findings demonstrate a previously unreported direct mitogenic response following exposures exceeding the metabolic clearance threshold of 1,4-DX. Collectively, the information generated in this study supports a threshold MOA for the development of liver tumors in mice after exposure to 1,4-DX., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: The tradition of khat chewing has been deep-rooted in the African and Arabian Peninsula for centuries. Due to its amphetamine-like psycho-stimulant or euphoric effect, khat has been used by millions in Somalia, Ethiopia, Saudi Arabia and Yemen. The long-term use of khat can induce many major health outcomes, which may be serious and irreversible., Objective: Prolonged use of khat constituents has been associated with different types of cancers such as prostatic, breast and ovarian cancer. However, it has been very difficult to identify the molecular targets involved in khat carcinogenesis that interact with the Khat constituents by in vitro/in vivo experimental tools., Methods: In silico tools were used to predict potential targets involved in the carcinogenesis of khat. Pass on-line prediction server was used for the prediction of a potential molecular target for khat constituents. Molecular Dynamics simulation and MM-GBSA calculation of the predicted target were carried out., Results: Molecular Dynamics simulation and MM-GBSA calculation revealed that among khat constituents, β-sitosterol showed a high binding affinity towards 17β-HSD5. On the other hand, this study highlights for the first time some new interactions, which were observed in the case of cathine, cathinone and nerol during the simulation., Conclusion: In silico molecular dynamic simulation tools were used for the first time to investigate the molecular mechanism of widely used leaves of psychoactive khat (Catha edulis) constituent. The present study provides deep insight to understand the effect of khat constituents involved in the impairment of the reproductive system and its binding to 17β-HSD5. ADMET profiling also suggested that few khat constituents do not fulfill the requirements of the Lipinski rule of five i.e. poor absorption and blood-brain barrier impermeability., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Chronic inhalation of naphthalene causes nasal olfactory epithelial tumors in rats and benign lung adenomas in mice. The available human data do not establish an association between naphthalene and increased respiratory cancer risk. Therefore, cancer risk assessment of naphthalene in humans depends predominantly on experimental evidence from rodents. The United States Environmental Protection Agency's (US EPA) Toxicity Forecaster (ToxCast™) database contains data from 710 in vitro assays for naphthalene, the majority of which were conducted in human cells. Of these assays, only 18 were active for naphthalene, and all were in human liver cells. No assays were active in human bronchial epithelial cells. In our analysis, all of the active naphthalene ToxCast assay data were reviewed and used to: 1) determine naphthalene human inhalation concentrations corresponding to relevant activity concentrations for all active naphthalene assays, using a physiologically based pharmacokinetic (PBPK) model; and 2) evaluate the transcriptional responses for active assays in the context of consistency with the larger naphthalene data set and proposed modes of action (MoAs) for naphthalene toxicity and carcinogenicity. The transcriptional responses in liver cells largely reflect cellular activities related to oxidative stress and chronic inflammation. Overall, the results from our analysis of the active ToxCast assays for naphthalene are consistent with conclusions from our earlier weight-of-evidence evaluation for naphthalene carcinogenesis., Competing Interests: Declaration of Competing Interest The authors' affiliation during the course of this work is as shown on the first page. This paper was prepared with financial support to Gradient from the American Petroleum Institute (API). The work reported in the paper was conducted during the normal course of employment by Gradient. The API was given the opportunity to comment on the manuscript. The authors retained final decision-making and have the sole responsibility for the writing and content of this paper. The views and opinions expressed are not necessarily those of API., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Chlorophyll, a phytochemical responsible for the green pigmentation in plants, has been studied for almost 100 years for its biological activities in humans. Over the past 30 years, the potential chemopreventative activities of both natural chlorophylls and their processed induced derivatives as well as the semisynthetic forms, such as sodium copper chlorophyllin, have been the focus of many research efforts. Established as potential chemopreventative agents with little to no bioavailability themselves, the activities of chlorophyll derivatives were generally ascribed to their ability to modulate mutagen/carcinogen bioavailability, their metabolism, and ultimately their ability to decrease the "exposure" to these carcinogens for humans at risk. More recently, systemic activities of chlorophyll derivatives have been reported to include modulation of oxidative stress and regulation of xenobiotic metabolizing systems and gene expression of systems critical to prevention of initiation and/or progression of cancer including NFE2-related factor 2, nuclear factor kappa B, TGF-β, and β-catenin pathways. With this in mind, the goals of this review are to provide an update to the comprehensive review of Ferruzzi and Blakeslee (2007) to include new insights into the behavior of chlorophyll derivatives in the gut as well as evidence of the systemic bioavailability of chlorophyll derivatives and their metabolites in support of potential impacts in prevention of cancer throughout the body., (Copyright © 2020 Elsevier Inc. All rights reserved.)

This study focused on the oral bioaccessibility and children health risks of metal(loid)s (As, Cd, Cr, Cu, Ni, Pb and Zn) in soil/indoor dust of school and households from Lanzhou, China. The simple bioaccessibility extraction test method was applied to assess bioaccessibility, and children's health risk was assessed via statistical modeling (hazard quotients, hazard index and incremental lifetime carcinogenic risk). Metal(loid) content and bioaccessibility in indoor dust samples were significantly higher than those in corresponding soil samples (p < 0.05). The order for mean values of bioaccessibility of the elements in soil was as follows: Cd (57.1%) > Zn (44.6%) > Pb (39.9%) > Cu (33.2%) > Ni (12.4%) > Cr (5.3%) > As (4.4%), while for indoor dust, the order was: As (73.0%) > Cd (68.4%) > Pb (63.3%) > Zn (60.4%) > Cu (36.5%) > Ni (25.2%) > Cr (13.6%). The Pearson correlation coefficient showed that metal(loid) bioaccessibility was in general significantly negatively correlated to the Al, Fe and Mn contents. Neither noncarcinogenic nor carcinogenic risks exceeded the tolerance interval for 3-5- and 6-9-year-old children for all elements. They both were mostly attributed to As considering metal(loid)s types and to school indoor dust considering sources. Therefore, maintaining interior sanitation would be an effective measure to reduce the potential health effects of indoor dust on children.

Benzene is a known hematotoxic and leukemogenic agent with hematopoietic stem cells (HSCs) niche being the potential target. Occupational and environmental exposure to benzene has been linked to the incidences of hematological disorders and malignancies. Previous studies have shown that benzene may act via multiple modes of action targeting HSCs niche, which include induction of chromosomal and micro RNA aberrations, leading to genetic and epigenetic modification of stem cells and probable carcinogenesis. However, understanding the mechanism linking benzene to the HSCs niche dysregulation is challenging due to complexity of its microenvironment. The niche is known to comprise of cell populations accounted for HSCs and their committed progenitors of lymphoid, erythroid, and myeloid lineages. Thus, it is fundamental to address novel approaches via lineage-directed strategy to elucidate precise mechanism involved in benzene-induced toxicity targeting HSCs and progenitors of different lineages. Here, we review the key genetic and epigenetic factors that mediate hematotoxicological effects by benzene and its metabolites in targeting HSCs niche. Overall, the use of combined genetic, epigenetic, and lineage-directed strategies targeting the HSCs niche is fundamental to uncover the key mechanisms in benzene-induced hematological disorders and malignancies.

A study was conducted to determine the cytosolic in vitro hepatic enzymatic kinetic parameters V max , K M , and intrinsic clearance (CL int ) for aflatoxin B 1 (AFB 1 ) reductase [aflatoxicol (AFL) production] and AFL dehydrogenase (AFB 1 production) in four commercial poultry species (chicken, quail, turkey and duck). Large differences were found in AFB 1 reductase activity, being the chicken the most efficient producer of AFL (highest CL int value). Oxidation of AFL to AFB 1 showed only slight differences among the different poultry species. On average all species produced AFB 1 from AFL at a similar rate, except for the turkey which produced AFB 1 from AFL at a significantly lower rate than chickens and quail, but not ducks. Although the turkey and duck showed differences in AFL oxidation V max and K M parameters, their CL int values did not differ significantly. The ratio AFB 1 reductase/AFL dehydrogenase enzyme activity was inversely related to the known in vivo sensitivity to AFB 1 being highest for the chicken, lowest for the duck and intermediate for turkeys and quail. Since there is no evidence that AFL is a toxic metabolite of AFB 1 , these results suggest that AFL production is a detoxication reaction in poultry. Conversion of AFB 1 to AFL prevents the formation of the AFB 1 -8,9-exo-epoxide which, upon conversion to AFB 1 -dihydrodiol, is considered to be the metabolite responsible for the acute toxic effects of AFB 1 .

1,3-Dichloropropene (1,3-D) showed a statistically increased incidence of bronchioloalveolar adenomas in male B6C3F1 mice at 60 ppm air concentration during previous chronic inhalation testing. No tumors were observed in female mice, nor in either sex of F344 rats up to 60 ppm, the highest dose tested. Therefore, to understand if lung tumors observed in high dose male mice are due to saturation of metabolic clearance, the linearity of 1,3-D concentrations in mouse blood was investigated on day 15 of repeated nose-only inhalation exposure to 0, 10, 20, 40, 60, 90, and 120 ppm (6 h/d, 7 d/week). Additional groups were included at 20, 60, and 120 ppm for blood collection at 1.5 and 3 h of exposure and up to 25 or 40 min post-exposure to determine area-under-the-curve. The data provide multiple lines of evidence that systemic exposures to 1,3-D in the mouse become nonlinear at inhalation exposure levels of 30 ppm or above. A reduction in minute volume occurred at the highest exposure concentration. The glutathione (GSH)-dependent metabolism of 1,3-D results in significant depletion of GSH at repeated exposure levels of 30 ppm and above. This loss of GSH results in decreased metabolic clearance of this test material, with a concomitant increase of the 1,3-D isomers in circulating blood at exposure concentrations ≥30 ppm. Shifts in the ratio of cis- and trans-1,3-D also support nonlinear toxicokinetics well below 60 ppm. Based on this data, a kinetically derived maximum dose for 1,3-D in mice for repeated exposures should be at or below 30 ppm. These results support non-relevance of 1,3-D-induced benign pulmonary tumorigenicity in mice for human health risk assessment., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Acrylamide is included on the State of California's Proposition 65 list as a carcinogen. Acrylamide is found in cigarette smoke and in many types of foods, including breads, cereals, coffee, cookies, French fries, and potato chips. In 1990, California's Office of Environmental Health Hazard Assessment (OEHHA) established a no significant risk level (NSRL) of 0.2 μg/day for acrylamide. Since then, multiple cancer studies have been published. In this report, we developed an updated NSRL for acrylamide. Using benchmark dose modeling and a weight-of-evidence, non-threshold approach to identify the most sensitive species, cancer slope factors (CSFs) were derived based on combined incidences of statistically significant neoplastic lesions in the Harderian gland, lung, and stomach in male mice. We then used a toxicokinetic (TK)-based scaling approach to convert the animal CSF to a human equivalent CSF, which served as the basis for the NSRL of 1.1 μg/day at the cancer risk level of 1 in 100,000. This NSRL can be used in quantitative exposure assessments to assess compliance with Proposition 65 to ascertain either the need for or exemption from the Proposition 65 labeling requirement and drinking water discharge prohibition., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Areca Nut (AN), the seed of tropical palm tree Areca catechu, is a widely chewed natural product with estimated 600 million users across the world. Various AN products, thriving in the market, portray 'Areca nut' or 'Supari' as mouth freshener and safe alternative to smokeless tobacco. Unfortunately, AN is identified as a Group 1 human carcinogen by International Agency for Research on Cancer (IARC). Wide variation in the level of alkaloids, broadly ranging from 2 to 10 mg/gm dry weight, is observed in diverse variety of AN sold worldwide. For the first time, various factors influencing the formation of carcinogenic alkaloids in AN at various stages, including during the growth, processing, and storage of the nut, are discussed. Current review illustrates the mechanism of cancer induction by areca alkaloids in humans and also compiles dose-dependent pharmacology and toxicology data of arecoline, the most potent carcinogenic alkaloid in AN. Careful monitoring of the arecoline content in AN can potentially be used as a tool in product surveillance studies to identify the variations in characteristics of various AN sample sold worldwide. The article will help to generate public awareness and sensitize the government bodies to initiate campaigns against AN use and addiction., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Arsenic, a metalloid and naturally occurring element, is one of the most abundant elements in the earth's crust. Water is contaminated by arsenic through natural sources (underground water, minerals and geothermal processes) and anthropogenic sources such as mining, industrial processes, and the production and use of pesticides. Humans are exposed to arsenic mainly by drinking contaminated water, and secondarily through inhalation and skin contact. Arsenic exposure is associated with the development of vascular disease, including stroke, ischemic heart disease and peripheral vascular disease. Also, arsenic increases the risk of tumors of bladder, lungs, kidneys and liver, according to the International Agency for Research on Cancer and the Food and Drug Administration. Once ingested, an estimated 70-90% of inorganic arsenic is absorbed by the gastrointestinal tract and widely distributed through the blood to different organs, primarily to the liver, kidneys, lungs and bladder and secondarily to muscle and nerve tissue. Arsenic accumulates in the organs, especially in the liver. Its excretion mostly takes place through urination. The toxicokinetics of arsenic depends on the duration of exposure, pathway of ingestion, physicochemical characteristics of the compound, and affected biological species. The present review outlines of arsenic toxic effects focusing on different cancer types whit highest prevalence's by exposure to this metalloid and signaling pathways of carcinogenesis., (Copyright © 2019 Elsevier Inc. All rights reserved.)

I first became acquainted with the Ames test at the very beginning of my career in 1978, when my task at the National Institute of Health Sciences (Tokyo) was to screen for mutagenicity of food additives used in Japan, using the Ames test. I also used this test to research the metabolic activation mechanisms of chemical carcinogens, in particular, the analgesic drug, phenacetin. This chemical was not mutagenic in Salmonella typhimurium TA100 with standard 9000 × g supernatant of liver homogenates (S9) from rat but was mutagenic with hamster S9. It was revealed that hamster S9 had much higher deacetylation activities than rat S9, which accounts for the species difference. Then, my work was focused on molecular biology. We cloned the genes encoding nitroreductase and acetyltransferase in Salmonella typhimurium TA1538. Plasmids carrying these genes made strain TA98 more sensitive to mutagenic nitroarenes and aromatic amines. Because of their high sensitivity, the resulting strains such as YG1021 and YG1024 are widely used to monitor mutagenic nitroarenes and aromatic amines in complex mixtures. Later, we disrupted the genes encoding DNA polymerases in TA1538 and classified chemical mutagens into four classes depending on their use of different DNA polymerases. I was also involved in the generation of gpt delta transgenic rodent gene mutation assays, which examine the results of the Ames test in vivo. I have unintentionally developed my career under the influence of Dr. Ames and I would like to acknowledge his remarkable achievements in the field of environmental mutagenesis and carcinogenesis., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Potassium octatitanate fibers (K 2 O•8TiO 2 , POT fibers) are used as an asbestos substitute. Their physical characteristics suggest that respirable POT fibers are likely to be carcinogenic in the lung and pleura. However, previous 2-year inhalation studies reported that respired POT fibers had little or no carcinogenic potential. In the present study ten-week old male F344 rats were left untreated or were administered vehicle, 0.25 or 0.5 mg rutile-type nano TiO 2 (r-nTiO 2 ), 0.25 or 0.5 mg POT fibers, or 0.5 mg MWCNT-7 by intra-tracheal intra-pulmonary spraying (TIPS), and then observed for 2 years., Results: There were no differences between the r-nTiO 2 and control groups. The incidence of bronchiolo-alveolar cell hyperplasia was significantly increased in the groups treated with 0.50 mg POT and 0.50 mg MWCNT-7. The overall incidence of lung tumors, however, was not increased in either the POT or MWCNT-7 treated groups. Notably, the carcinomas that developed in the POT and MWCNT-7 treated rats were accompanied by proliferative fibrous connective tissue while the carcinomas that developed in the untreated rats and the r-nTiO 2 treated rats were not (carcinomas did not develop in the vehicle control rats). In addition, the carcinoma that developed in the rat treated with 0.25 mg POT was a squamous cell carcinoma, a tumor that develops spontaneously in about 1 per 1700 rats. The incidence of mesothelial cell hyperplasia was 4/17, 7/16, and 10/14 and the incidence of malignant mesothelioma was 3/17, 1/16, and 2/14 in the 0.25 mg POT, 0.5 mg POT, and MWCNT-7 treated groups, respectively. Neither mesothelial cell hyperplasia nor mesothelioma developed in control rats or the rats treated with r-nTiO 2 . Since the incidence of spontaneously occurring malignant mesothelioma in rats is extremely low, approximately 1 per 1000 animals (Japan Bioassay Research Center [JBRC] historical control data), the development of multiple malignant mesotheliomas in the POT and MWCNT-7 treated groups was biologically significant., Conclusion: The incidence of pleural mesotheliomas in male F344 rats administered POT fibers and MWCNT-7 was significantly higher than the JBRC historical control data, indicating that the incidence of pleural mesothelioma in the groups administered POT fibers and MWCNT-7 fibers via the airway using TIPS was biologically significant. The incidence of type II epithelial cell hyperplasia and the histology of the carcinomas that developed in the POT treated rats also indicates that respirable POT fibers are highly likely to be carcinogenic in the lungs of male F344 rats.

Aromatic amines are an important class of human carcinogens found ubiquitously in our environment. It is estimated that 1 in 8 of all known or suspected human carcinogens is or can be converted into an aromatic amine, making the elucidation of their mechanisms of toxicity a top public health priority. Decades of research into aromatic amine carcinogenesis revealed a complex bioactivation process where Phase I and Phase II drug metabolizing enzymes catalyze N-oxidation and subsequent conjugation reactions generating the highly electrophilic nitrenium intermediate that reacts with and forms adducts on cellular macromolecules. Although aromatic amine-DNA adducts were believed to be the main driver of cancer formation, several studies have reported a lack of correlation between levels of DNA adducts and tumors. Using genetically modified mouse models, our laboratory and others observed several instances where levels of conventionally measured DNA adducts failed to correlate with liver tumor incidence following exposure to the model aromatic amine procarcinogen 4-aminobiphenyl. In this review we first provide a historical overview of the studies that led to a proposed mechanism of carcinogenesis caused by aromatic amines, where their bioactivation to form DNA adducts represents the central driver of this process. We then highlight recent mechanistic studies using 4-aminobiphenyl that are inconsistent with this mechanism which suggest novel drivers of aromatic amine carcinogenesis., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Ptaquiloside is a natural toxin present in bracken ferns (Pteridium sp.). Cattle ingesting bracken may develop bladder tumours and excrete genotoxins in meat and milk. However, the fate of ptaquiloside in cattle and the link between ptaquiloside and cattle carcinogenesis is unresolved. Here, we present the toxicokinetic profile of ptaquiloside in plasma and urine after intravenous administration of ptaquiloside and after oral administration of bracken. Administered intravenously ptaquiloside, revealed a volume of distribution of 1.3 L kg-1 with a mean residence-time of 4 hours. A large fraction of ptaquiloside was converted to non-toxic pterosin B in the blood stream. Both ptaquiloside and pterosin B were excreted in urine (up to 41% of the dose). Oral administration of ptaquiloside via bracken extract or dried ferns did not result in observations of ptaquiloside in body fluids, indicating deglycosolidation in the rumen. Pterosin B was detected in both plasma and urine after oral administration. Hence, transport of carcinogenic ptaquiloside metabolites over the rumen membrane is indicated. Pterosin B recovered from urine counted for 7% of the dose given intravenously. Heifers exposed to bracken for 7 days (2 mg ptaquiloside kg-1) developed preneoplastic lesions in the urinary bladder most likely caused by genotoxic ptaquiloside metabolites., Competing Interests: The authors have declared that no competing interests exist.

Here we evaluate a multiplicative (relative) risk model for improved cancer risk estimation of genotoxic compounds. According to this model, cancer risk is proportional to the background tumor incidence and to the internal dose of the genotoxic compound. Furthermore, the relative risk coefficient per internal dose is considered to be approximately the same across tumor sites, sex, and species. In the present study, we demonstrate that the relative risk model is valid for cancer risk estimation of glycidol, a common food contaminant. Published tumor data from glycidol carcinogenicity studies in mice and rats were evaluated in combination with internal dose estimates from hemoglobin adduct measurements in blood from mice and rats treated with glycidol in short-term studies. A good agreement between predicted and observed tumor incidence in responding sites was demonstrated in the animals, supporting a relative risk coefficient that is independent of tumor site, sex, and species. There was no significant difference between the risk coefficients for mice (5.1% per mMh) and rats (5.4% per mMh) when considering internal doses of glycidol. Altogether, this mechanism-based risk model gives a reliable risk coefficient, which then was extrapolated to humans considering internal dose, and background cancer incidence., (Copyright © 2019. Published by Elsevier Ltd.)

The aim of this study was to determine the heavy metals content of milk from cows fed with forage irrigated with waste water from industrial sources and the health risk to children. Milk samples were taken from milk collection tanks of eight localities in the state of Puebla. On average, the heavy metals in the milk had the following order Zn> As> Pb > Cr> Cu > Ni. Pb (0.03 mg kg -1 ) exceeded the Codex limits. For As the hazard index was 8.0 ± 0.4, which is far above 1. On the other hand, the individual risk of cancer showed a descending order Cr> As > Pb, while the risk of total cancer (0.004 ± 0.002) indicated that the combined effect of heavy metals created a serious risk for girls and children.

This study investigated the concentrations of Zn, Cu, Cr, Pb, As and Cd in different tissues of E. crassipes from Honghu Lake. The total concentrations of trace elements in E. crassipes were observed in descending order: Zn (111.6162) > Cu (15.7494) > Cr (7.0466) > Pb (5.6251) > As (3.6831) > Cd (0.1941) mg/kg. The order of the bioconcentration factor (BCF) measured in E. crassipes was Zn > As > Cr > Cu > Pb > Cd > 1, indicating that E. crassipes possessed a strong biological enrichment ability to accumulate a variety of trace elements. The translocation factor (TF) values decreased in the order of Cu > Zn > Cr > As > Pb > Cd, all of which were lower than 1, which showed that the absorption of the trace elements by E. crassipes was mainly accomplished in the roots. Moreover, the health risk assessments showed that the carcinogenic and noncarcinogenic risks of the edible parts of E. crassipes were 26.1 and 4.6 times higher than the maximum acceptable value recommended by the USEPA for adults and children of approximately 39.2- and 6.9-fold, respectively. Children were more sensitive than adults. The main trace elements that led to noncarcinogenic risks were As, Cr and Cu, while Cr and As led to carcinogenic risks. The results of the Pearson correlation showed positive correlations with the concentrations of Zn, Cr and As between E. crassipes and the water as well as negative correlations of the contents of all six trace elements between E. crassipes and the sediment.

Competing Interests: Nil.

Benzo[a]pyrene (BaP), is a known human carcinogen (International Agency for Research on Cancer (IARC) class 1). The remarkable sensitivity (zepto-attomole 14 C in biological samples) of accelerator mass spectrometry (AMS) makes possible, with de minimus risk, pharmacokinetic (PK) analysis following [ 14 C]-BaP micro-dosing of humans. A 46 ng (5 nCi) dose was given thrice to 5 volunteers with minimum 2 weeks between dosing and plasma collected over 72 h. [ 14 C]-BaP eq PK analysis gave plasma T max and C max values of 1.25 h and 29-82 fg/mL, respectively. PK parameters were assessed by non- compartment and compartment models. Intervals between dosing ranged from 20 to 420 days and had little impact on intra-individual variation. DNA, extracted from peripheral blood mononuclear cells (PBMCs) of 4 volunteers, showed measurable levels (LOD ~ 0.5 adducts/10 11 nucleotides) in two individuals 2-3 h post-dose, approximately three orders of magnitude lower than smokers or occupationally-exposed individuals. Little or no DNA binding was detectable at 48-72 h. In volunteers the allelic variants CYP1B1 *1/*⁎1 , *1/*3 or *3/*3 and GSTM1 * 0/0 or *1 had no impact on [ 14 C]-BaP eq PK or DNA adduction with this very limited sample. Plasma metabolites over 72 h from two individuals (one CYP1B1 *1/*1 and one CYP1B1 *3/*3 ) were analyzed by UPLC-AMS. In both individuals, parent [ 14 C]-BaP was a minor constituent even at the earliest time points and metabolite profiles markedly distinct. AMS, coupled with UPLC, could be used in humans to enhance the accuracy of pharmacokinetics, toxicokinetics and risk assessment of environmental carcinogens., (Copyright © 2018 Elsevier Inc. All rights reserved.)

The 6-month Tg.rasH2 mouse carcinogenicity model provides an acceptable alternative to the 2-year carcinogenicity study in CD-1 mice. However, key questions related to the use of this model for testing antisense oligonucleotides (ASOs) include the similarity in the biologic response between mouse strains and the feasibility of using data from the CD-1 mouse to set doses and dose schedules for a Tg.rasH2 carcinogenicity study. To evaluate the potential strain differences, four distinct 2'- O-(2-methoxyethyl) ASOs were administered to CByB6F1 (wild type), Tg.rasH2 (hemizygous), and CD-1 mice. There were no meaningful differences in clinical signs, body weight, food consumption, or serum chemistry and hematology parameters. Histopathology evaluation indicated little to no difference in the spectrum or magnitude of changes present. The cytokine/chemokine response was also not appreciably different between the strains. This was consistent with the similarity in ASO concentration in the liver between the mouse strains tested. As the class effects of the ASOs were not meaningfully different between CD-1, CByB6F1, or Tg.rasH2 mice, data from nonclinical studies in CD-1 mice can be used for dose selection and expectation of effect in the Tg.rasH2 mouse.

Based on 13 chronic studies, styrene exposure causes lung tumors in mice, but no tumor increases in other organs in mice or rats. Extensive research into the mode of action demonstrates the key events and human relevance. Key events are: metabolism of styrene by CYP2F2 in mouse lung club cells to ring-oxidized metabolites; changes in gene expression for metabolism of lipids and lipoproteins, cell cycle and mitotic M-M/G1 phases; cytotoxicity and mitogenesis in club cells; and progression to preneoplastic/neoplastic lesions in lung. Although styrene-7,8-oxide (SO) is a common genotoxic styrene metabolite in in vitro studies, the data clearly demonstrate that SO is not the proximate toxicant and that styrene does not induce a genotoxic mode of action. Based on complete attenuation of styrene short-term and chronic toxicity in CYP2F2 knockout mice and similar attenuation in CYP2F1 (humanized) transgenic mice, limited metabolism of styrene in human lung by CYP2F1, 2 + orders of magnitude lower SO levels in human lung compared to mouse lung, and lack of styrene-related increase in lung cancer in humans, styrene does not present a risk of cancer to humans., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Afidopyropen is a novel insecticide that acts as a TRPV channel modulator in chordotonal organs of target insects. In two carcinogenicity studies with Fischer rats, an increased incidence of uterine adenocarcinomas was observed at 1000 and 3000 ppm. This finding prompted an investigation of the mechanism of the tumor formation as well as the relevance of this mechanism to humans. The mechanistic work took parallel paths: one path investigated the pharmacokinetic properties of the test substance at the doses where the tumors were found; while the second path examined the key mechanistic events that culminated in uterine adenocarcinomas. The results of the investigation indicated that the tumors only occurred at doses where excretion of test substance was saturated - indicating that homeostatic biological and/or physiological processes were overwhelmed. At the doses where these processes were overwhelmed, the test substance acted through a mechanism of dopamine agonism, triggering a cascade key events that resulted in uterine adenocarcinomas. An analysis of these mechanisms observed in rat showed that they are both quantitatively (pharmacokinetic mechanism) and qualitatively (dopamine agonism mechanism) not relevant to humans. Therefore the uterine adenocarcinomas observed in the rat associated with high doses of Afidopyropen are not expected to pose a carcinogenic risk to humans., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Benzo[a]pyrene (BaP), a polycyclic aromatic hydrocarbon (PAH), is a known human carcinogen. In non-smoking adults greater than 95% of BaP exposure is through diet. The carcinogenicity of BaP is utilized by the U.S. EPA to assess relative potency of complex PAH mixtures. PAH relative potency factors (RPFs, BaP = 1) are determined from high dose animal data. We employed accelerator mass spectrometry (AMS) to determine pharmacokinetics of [ 14 C]-BaP in humans following dosing with 46 ng (an order of magnitude lower than human dietary daily exposure and million-fold lower than animal cancer models). To assess the impact of co-administration of food with a complex PAH mixture, humans were dosed with 46 ng of [ 14 C]-BaP with or without smoked salmon. Subjects were asked to avoid high BaP-containing diets and a 3-day dietary questionnaire given to assess dietary exposure prior to dosing and three days post-dosing with [ 14 C]-BaP. Co-administration of smoked salmon, containing a complex mixture of PAHs with an RPF of 460 ng BaP eq , reduced and delayed absorption. Administration of canned commercial salmon, containing very low amounts of PAHs, showed the impacts on pharmacokinetics were not due to high amounts of PAHs but rather a food matrix effect., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BaP) can induce cytochrome P450 1A1 (CYP1A1) via a p53-dependent mechanism. The effect of different p53-activating chemotherapeutic drugs on CYP1A1 expression, and the resultant effect on BaP metabolism, was investigated in a panel of isogenic human colorectal HCT116 cells with differing TP53 status. Cells that were TP53(+/+), TP53(+/-) or TP53(-/-) were treated for up to 48 h with 60 μM cisplatin, 50 μM etoposide or 5 μM ellipticine, each of which caused high p53 induction at moderate cytotoxicity (60-80% cell viability). We found that etoposide and ellipticine induced CYP1A1 in TP53(+/+) cells but not in TP53(-/-) cells, demonstrating that the mechanism of CYP1A1 induction is p53-dependent; cisplatin had no such effect. Co-incubation experiments with the drugs and 2.5 μM BaP showed that: (i) etoposide increased CYP1A1 expression in TP53(+/+) cells, and to a lesser extent in TP53(-/-) cells, compared to cells treated with BaP alone; (ii) ellipticine decreased CYP1A1 expression in TP53(+/+) cells in BaP co-incubations; and (iii) cisplatin did not affect BaP-mediated CYP1A1 expression. Further, whereas cisplatin and etoposide had virtually no influence on CYP1A1-catalysed BaP metabolism, ellipticine treatment strongly inhibited BaP bioactivation. Our results indicate that the underlying mechanisms whereby etoposide and ellipticine regulate CYP1A1 expression must be different and may not be linked to p53 activation alone. These results could be relevant for smokers, who are exposed to increased levels of BaP, when prescribing chemotherapeutic drugs. Beside gene-environment interactions, more considerations should be given to potential drug-environment interactions during chemotherapy., (Copyright © 2018 The Author(s). Published by Elsevier B.V. All rights reserved.)

The carcinogenic potential of roxadustat (FG-4592), a novel orally active, heterocyclic small molecule inhibitor of hypoxia-inducible factor prolyl hydroxylase (HIF-PH) enzymes in clinical development for treatment of anemia, was evaluated in CD-1 mice and Sprague Dawley rats. Inhibition of HIF-PH by roxadustat leads to a rapid increase in cytoplasmic HIF-α concentrations, followed by translocation of HIF-α to the nucleus and upregulation of HIF-responsive genes, including erythropoietin. Roxadustat was dosed by oral gavage 3 times weekly (TIW) for up to 104 weeks in mice at 0, 15, 30, and 60 mg/kg and in rats at 0, 2.5, 5, and 10 mg/kg. Treatment-associated changes in hematology parameters were consistent with the pharmacologic activity of roxadustat and included elevations in hematocrit in mice at 30 and 60 mg/kg TIW and elevations in erythrocyte count, hemoglobin, hematocrit, and red cell distribution width in rats at 10 mg/kg TIW. No increase in mortality or neoplastic effects compared with vehicle controls was observed after roxadustat treatment in either species. No treatment-related nonneoplastic findings were observed in mice, whereas nonneoplastic microscopic findings in rats were limited to atrial/aortic thromboses at 10 mg/kg TIW males and bone marrow hypercellularity in all treated male and female groups, consistent with the pharmacology of roxadustat. In conclusion, roxadustat administered by oral gavage to mice and rats TIW for up to 104 weeks resulted in dose-dependent exposure and hematologic effects with no effect on survival or development of neoplastic lesions at up to 60 mg/kg in mice and up to 10 mg/kg in rats.

3-Nitrobenzanthrone (3-NBA), a potent environmental mutagen and carcinogen, is known to be activated in vivo to 3-benzanthronylnitrenium ion which forms both NH and C2-bound adducts with DNA and also reacts with glutathione giving rise to urinary 3-aminobenzanthron-2-ylmercapturic acid. In this study, acid hydrolysate of globin from rats dosed intraperitoneally with 3-NBA was analysed by HPLC/MS to identify a novel type of cysteine adduct, 3-aminobenzanthron-2-ylcysteine (3-ABA-Cys), confirmed using a synthesised standard. The 3-ABA-Cys levels in globin peaked after single 3-NBA doses of 1 and 2 mg/kg on day 2 to attain 0.25 and 0.49 nmol/g globin, respectively, thereafter declining slowly to 70-80% of their maximum values during 15 days. After dosing rats for three consecutive days with 1 mg 3-NBA/kg a significant cumulation of 3-ABA-Cys in globin was observed. 3-ABA-Cys was also found in the plasma hydrolysate. Herein, after dosing with 1 and 2 mg 3-NBA/kg the adduct levels peaked on day 1 at 0.15 and 0.51 nmol/ml plasma, respectively, thereafter declining rapidly to undetectable levels on day 15. In addition, sulphinamide adducts were also found in the exposed rats, measured indirectly as 3-aminobenzanthrone (3-ABA) split off from globin by mild acid hydrolysis. Levels of both types of adducts in the globin samples parallelled very well with 3-ABA/3-ABA-Cys ratio being around 1:8. In conclusion, 3-ABA-Cys is the first example of arylnitrenium-cysteine adduct in globin representing a new promising class of biomarkers to assess cumulative exposures to aromatic amines, nitroaromatics and heteroaromatic amines.

The rabbit was the initial animal model to investigate the acetylation polymorphism expressed in humans. Use of the rabbit model is compromised by lack of a rapid non-invasive method for determining acetylator phenotype. Slow acetylator phenotype in the rabbit results from deletion of the N-acetyltransferase 2 (NAT2) gene. A relatively quick and non-invasive method for identifying the gene deletion was developed and acetylator phenotypes confirmed by measurement of N- and O-acetyltransferase activities in hepatic cytosols. Rabbit liver cytosols catalyzed the N-acetylation of sulfamethazine (p = 0.0014), benzidine (p = 0.0257), 4-aminobiphenyl (p = 0.0012), and the O-acetylation of N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP; p = 0.002) at rates significantly higher in rabbits possessing NAT2 gene than rabbits with NAT2 gene deleted. In contrast, hepatic cytosols catalyzed the N-acetylation of p-aminobenzoic acid (an N-acetyltransferase 1 selective substrate) at rates that did not differ significantly (p > 0.05) between rabbits positive and negative for NAT2. The new NAT2 genotyping method facilitates use of the rabbit model to investigate the role of acetylator polymorphism in the metabolism of aromatic and heterocyclic amine drugs and carcinogens.

Introduction: Meat consumption is a risk factor for colorectal cancer. This research investigated the relationship between meat-derived carcinogen exposure and bulky DNA adduct levels, a biomarker of DNA damage, in colon mucosa., Methods: Least squares regression was used to examine the relationship between meat-derived carcinogen exposure (PhIP and meat mutagenicity) and bulky DNA adduct levels in normal-appearing colon tissue measured using 32 P-postlabelling among 202 patients undergoing a screening colonoscopy. Gene-diet interactions between carcinogen exposure and genetic factors relevant to biotransformation and DNA repair were also examined. Genotyping was conducting using the MassARRAY ® iPLEX ® Gold SNP Genotyping assay., Results: PhIP and higher meat mutagenicity exposures were not associated with levels of bulky DNA adducts in colon mucosa. The XPC polymorphism (rs2228001) was found to associate with bulky DNA adduct levels, whereby genotypes conferring lower DNA repair activity were associated with higher DNA adduct levels than the normal activity genotype. Among individuals with genotypes associated with lower DNA repair (XPD, rs13181 and rs1799179) or detoxification activity (GSTP1, rs1695), higher PhIP or meat mutagenicity exposures were associated with higher DNA adduct levels. Significant interactions between the XPC polymorphism (rs2228000) and both dietary PhIP and meat mutagenicity on DNA adduct levels was observed, but associations were inconsistent with the a priori hypothesized direction of effect., Conclusion: Exposure to meat-derived carcinogens may be associated with increased DNA damage occurring directly in the colon among genetically susceptible individuals., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Considering the rapid developments in food safety in the past decade in China, it is of importance to obtain insight into what extent safety and risk assessments of chemicals performed for the Caucasian population apply to the Chinese population. The aim of the present study was to determine physiologically based kinetic (PBK) modeling-based predictions for differences between Chinese and Caucasians in terms of metabolic bioactivation and detoxification of the food-borne genotoxic carcinogen estragole. The PBK models were defined based on kinetic constants for hepatic metabolism derived from in vitro incubations using liver fractions of the two ethnic groups, and used to evaluate the inter-ethnic differences in metabolic activation and detoxification of estragole. The models predicted that at realistic dietary intake levels, only 0.02% of the dose was converted to the ultimate carcinogenic metabolite 1'-sulfooxyestragole in Chinese subjects, whereas this amounted to 0.09% of the dose in Caucasian subjects. Detoxification of 1'-hydroxyestragole, mainly via conversion to 1'-oxoestragole, was similar within the two ethnic groups. The 4.5-fold variation in formation of the ultimate carcinogenic metabolite of estragole accompanied by similar rates of detoxification may indicate a lower risk of estragole for the Chinese population at similar levels of exposure. The study provides a proof of principle for how PBK modeling can identify differences in ethnic sensitivity and provide a more refined risk assessment for a specific ethnic group for a compound of concern.

Polychlorinated biphenyls (PCBs) are suspected of carcinogenic, neurotoxic and immunotoxic effects in animals and humans. Although background levels of PCBs have been slowly decreased after their ban, they are still among the most persistent and ubiquitous pollutants in the environment, remaining the subject of great concern. PCB 28 is a trichlorinated PCB found in high concentrations not only in human plasma but also in indoor air in Europe, yet little is known about its metabolic pathway and potential metabolites in humans. The present study aims to elucidate the kinetics of metabolite formation and elimination by analyzing four hydroxylated PCBs (OH-PCBs) in human plasma as potential metabolites of the PCB 28 congener. For this purpose, the study was conducted in plasma samples of highly PCB-exposed individuals (N=268), collected from 2010 to 2014 as a representation of a real case scenario with longitudinal data. OH-PCBs have been predicted, synthesized in the course of this study and further identified and quantitated in human plasma. This is the first time that previously unknown PCB 28 metabolites have been measured in human plasma and half-lives have been estimated for PCB metabolites, which could then provide further understanding in the toxicological consequences of exposure to PCBs in humans., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The detoxification of toxic substances is of general relevance in all biological systems. The plethora of exogenous xenobiotic compounds and endogenous toxic metabolic products explains the evolutionary pressure of all organisms to develop molecular mechanisms to detoxify and excrete harmful substances from the body. P-glycoprotein and other members of the ATP-binding cassette (ABC) transporter family extrude innumerous chemical compounds out of cells. Their specific expression in diverse biological contexts cause different phenotypes: (1) multidrug resistance (MDR) and thus failure of cancer chemotherapy, (2) avoidance of accumulation of carcinogens and prevention of carcinogenesis in healthy tissues, (3) absorption, distribution, metabolization and excretion (ADME) of pharmacological drugs in human patients, (4) protection from environmental toxins in aquatic organisms (multi-xenobiotic resistance, MXR). Hence ABC-transporters may have opposing effects for organismic health reaching from harmful in MDR of tumors to beneficial for maintenance of health in MXR. While their inhibition by specific inhibitors may improve treatment success in oncology and avoid carcinogenesis, blocking of ABC-transporter-driven efflux by environmental pollutants leads to ecotoxicological consequences in marine biotopes. Poisoned seafood may enter the food-chain and cause intoxications in human beings. As exemplified with ABC-transporters, joining forces in interdisciplinary research may, therefore, be a wise strategy to fight problems in human medicine and environmental sciences.

In cancer bioassays, inhalation, but not drinking water exposure to ethyl tertiary-butyl ether (ETBE), caused liver tumors in male rats, while tertiary-butyl alcohol (TBA), an ETBE metabolite, caused kidney tumors in male rats following exposure via drinking water. To understand the contribution of ETBE and TBA kinetics under varying exposure scenarios to these tumor responses, a physiologically based pharmacokinetic model was developed based on a previously published model for methyl tertiary-butyl ether, a structurally similar chemical, and verified against the literature and study report data. The model included ETBE and TBA binding to the male rat-specific protein α2u-globulin, which plays a role in the ETBE and TBA kidney response observed in male rats. Metabolism of ETBE and TBA was described as a single, saturable pathway in the liver. The model predicted similar kidney AUC 0-∞ for TBA for various exposure scenarios from ETBE and TBA cancer bioassays, supporting a male-rat-specific mode of action for TBA-induced kidney tumors. The model also predicted nonlinear kinetics at ETBE inhalation exposure concentrations above ~2000 ppm, based on blood AUC 0-∞ for ETBE and TBA. The shift from linear to nonlinear kinetics at exposure concentrations below the concentration associated with liver tumors in rats (5000 ppm) suggests the mode of action for liver tumors operates under nonlinear kinetics following chronic exposure and is not relevant for assessing human risk. Copyright © 2016 The Authors Journal of Applied Toxicology Published by John Wiley & Sons Ltd., (Copyright © 2016 The Authors Journal of Applied Toxicology Published by John Wiley & Sons Ltd.)

Okadaic acid (OA), Dinophysistoxins (DTX1 and DTX2) and their acyl-derivatives (DTX3) are marine toxins responsible for the human diarrhetic shellfish poisoning. To date the amount of toxins ingested from consumption of shellfish has been considered equal to the amount of toxins available for uptake by the human body. The aim of this study is to assess the OA, DTX2 and DTX3 fractions released from raw and steamed mussels and cockles into the digestive fluids (bioaccessibility) using a static in vitro digestion model. Higher bioaccessibility was found in mussels (86 ± 4%) than in cockles (59 ± 9%). A significant reduction of ester derivatives of OA and an increase of OA were observed in the bioaccessible fraction of mussel samples, suggesting that DTX3 undergo conversion into their more toxic parent compounds during human digestion. However, similar increase of DTX2 and reduction of the respective acyl derivatives was not observed. Steaming lead to significant reduction of OA and analogues bioaccessibility in both species even though increased concentrations of toxins are obtained after this treatment. Risk assessment based solely on DSP toxins occurrence in seafood can conduct to an overestimation of the exposure and lead to more conservative regulatory measures., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The present study describes physiologically based kinetic (PBK) models for the alkenylbenzene myristicin that were developed by extension of the PBK models for the structurally related alkenylbenzene safrole in rat and human. The newly developed myristicin models revealed that the formation of the proximate carcinogenic metabolite 1'-hydroxymyristicin in liver is at most 1.8 fold higher in rat than in human and limited for the ultimate carcinogenic metabolite 1'-sulfoxymyristicin to (2.8-4.0)-fold higher in human. In addition, a comparison was made between the relative importance of bioactivation for myristicin and safrole. Model predictions indicate that for these related compounds, the formation of the 1'-sulfoxy metabolites in rat and human liver is comparable with a difference of <2.2-fold over a wide dose range. The results from this PBK analysis support that risk assessment of myristicin may be based on the BMDL 10 derived for safrole of 1.9-5.1 mg/kg bw per day. Using an estimated daily intake of myristicin of 0.0019 mg/kg bw per day resulting from the use of herbs and spices, this results in MOE values for myristicin that amount to 1000-2700, indicating a priority for risk management. The results obtained illustrate that PBK modeling provides insight into possible species differences in the metabolic activation of myristicin. Moreover, they provide an example of how PBK modeling can facilitate a read-across in risk assessment from a compound for which in vivo toxicity studies are available to a related compound for which tumor data are not reported, thus contributing to alternatives in animal testing., Competing Interests: Prof. IMCM Rietjens declares she is a member of the Expert Panel of the Flavour and Extract Manufacturers Association (FEMA). Other authors declare that no conflict of interest exists.

Worldwide, cancers of the oral cavity and pharynx comprise the sixth most common malignancies. Histologically, more than 90% of oral cancers are squamous cell carcinoma (SCC). Epidemiologic data strongly support the role of exogenous factors such as tobacco, alcohol, and human papilloma virus infection as major causative agents. Avoidance of risk factors has only been partially successful, and survival rates have not improved despite advances in therapeutic approaches. Therefore, new or improved approaches to prevention and/or early detection are critical. Better understanding of the mechanisms of oral carcinogenesis can assist in the development of novel biomarkers for early detection and strategies for disease prevention. Toward this goal, several animal models for carcinogenesis in the oral cavity have been developed. Among these are xenograft, and transgenic animal models, and others employing the synthetic carcinogens such as 7,12-dimethylbenz[a]anthracene in hamster cheek pouch and 4-nitroquinoline-N-oxide in rats and mice. Additional animal models employing environmental carcinogens such as benzo[a]pyrene and N'-nitrosonornicotine have been reported. Each model has certain advantages and disadvantages. Models that (1) utilize environmental carcinogens, (2) reflect tumor heterogeneity, and (3) accurately represent the cellular and molecular changes involved in the initiation and progression of oral cancer in humans could provide a realistic platform. To achieve this goal, we introduced a novel nonsurgical mouse model to study oral carcinogenesis induced by dibenzo[a,l]pyrene (DB[a,l]P), an environmental pollutant and tobacco smoke constituent, and its diol epoxide metabolite (±)-anti-11,12-dihydroxy-13,14-epoxy-11,12,13,14-tetrahydrodibenzo[a,l]pyrene [(±)-anti-DB[a,l]PDE]. On the basis of a detailed comparison of oral cancer induced by DB[a,l]P with that induced by the other above-mentioned oral carcinogens with respect to dose, duration, species and strain, cellular and molecular targets, and relative carcinogenic potency, our animal model may offer a more realistic platform to study oral carcinogenesis. In this perspective, we also discuss our preclinical studies to demonstrate the potential of black raspberry extracts on the prevention of OSCC. Specifically, we were the first to demonstrate that black raspberry inhibited DB[a,l]P-DNA binding and of particular importance its capacity to enhance the repair of DB[a,l]P-induced bulky lesions in DNA. We believe that the information presented in this perspective will stimulate further research on the impact of environmental carcinogens in the development of oral cancer and may lead to novel strategies toward the control and prevention of this disease.

Pyrrolizidine alkaloids (PAs) and PA N-oxides are a class of phytochemical carcinogens contained in over 6000 plant species spread around the world. It has been estimated that approximately half of the 660 PAs and PA N-oxides that have been characterized are cytotoxic, genotoxic, and tumorigenic. It was recently determined that a genotoxic mechanism of liver tumor initiation mediated by PA-derived DNA adducts is a common metabolic activation pathway of a number of PAs. We proposed this set of PA-derived DNA adducts could be a common biological biomarker of PA exposure and a potential biomarker of PA-induced liver tumor formation. We have also found that several reactive secondary pyrrolic metabolites can dissociate and interconvert to other secondary pyrrolic metabolites, resulting in the formation of the same exogenous DNA adducts. This present perspective reports the current progress on these new findings and proposes future research needed for obtaining a greater understanding of the role of this activation pathway and validating the use of this set of PA-derived DNA adducts as a biological biomarker of PA-induced liver tumor initiation.

Consumer products with high contents of polycyclic aromatic hydrocarbons (PAHs) were repeatedly identified by market surveillance authorities. Since several of the individual compounds have been identified as genotoxic carcinogens, there might be health risks associated with the usage of these items. It therefore becomes reasonable to argue to reduce PAH contents in consumer products to a level as low as possible. This study presents data on the migration of PAHs from consumer products into aqueous sweat simulant or aqueous ethanol and on its combined migration and penetration into human skin. Product specimens were either submerged in simulant, or placed directly on test skins in Franz cell chambers to simulate dermal contacts. Migration of hexacyclic dibenzopyrenes became detectable by using ethanolic simulant, but not in aqueous sweat simulant. Similarly, migration of the pentacyclic model carcinogen benzo[a]pyrene (B[a]P) into aqueous sweat simulant was significantly lower when compared with human skin or skin models. The results point to a gross underestimation (about two orders of magnitude) when using aqueous sweat simulant instead of human skin for assessing PAH migration. On the other side, the usage of 20% ethanol as simulant revealed good agreement to the actual exposure of human skin against B[a]P migrating out of contaminated products. Our results underline that aqueous sweat simulant is not suitable to study dermal migration of highly lipophilic compounds.

Benzo[a]pyrene (BaP) is a by-product of incomplete combustion of fossil fuels and plant/wood products, including tobacco. A physiologically based pharmacokinetic (PBPK) model for BaP for the rat was extended to simulate inhalation exposures to BaP in rats and humans including particle deposition and dissolution of absorbed BaP and renal elimination of 3-hydroxy benzo[a]pyrene (3-OH BaP) in humans. The clearance of particle-associated BaP from lung based on existing data in rats and dogs suggest that the process is bi-phasic. An initial rapid clearance was represented by BaP released from particles followed by a slower first-order clearance that follows particle kinetics. Parameter values for BaP-particle dissociation were estimated using inhalation data from isolated/ventilated/perfused rat lungs and optimized in the extended inhalation model using available rat data. Simulations of acute inhalation exposures in rats identified specific data needs including systemic elimination of BaP metabolites, diffusion-limited transfer rates of BaP from lung tissue to blood and the quantitative role of macrophage-mediated and ciliated clearance mechanisms. The updated BaP model provides very good prediction of the urinary 3-OH BaP concentrations and the relative difference between measured 3-OH BaP in nonsmokers versus smokers. This PBPK model for inhaled BaP is a preliminary tool for quantifying lung BaP dosimetry in rat and humans and was used to prioritize data needs that would provide significant model refinement and robust internal dosimetry capabilities.

The H2-receptor antagonist, ranitidine, is among the most widely used pharmaceuticals to treat gastroesophageal reflux disease and peptic ulcers. While previous studies have demonstrated that amines can form N-nitrosamines when exposed to nitrite at stomach-relevant pH, N-nitrosamine formation from ranitidine, an amine-based pharmaceutical, has not been demonstrated under these conditions. In this work, we confirmed the production of N-nitrosodimethylamine (NDMA), a potent carcinogen, by nitrosation of ranitidine under stomach-relevant pH conditions in vitro We also evaluated the urinary NDMA excretion attributable to ingestion of clinically used ranitidine doses. Urine samples collected from five female and five male, healthy adult volunteers over 24-h periods before and after consumption of 150mg ranitidine were analyzed for residual ranitidine, ranitidine metabolites, NDMA, total N-nitrosamines and dimethylamine. Following ranitidine intake, the urinary NDMA excreted over 24h increased 400-folds from 110 to 47 600ng, while total N-nitrosamines increased 5-folds. NDMA excretion rates after ranitidine intake equaled or exceeded those observed previously in patients with schistosomiasis, a disease wherein N-nitrosamines are implicated as the etiological agents for bladder cancer. Due to metabolism within the body, urinary NDMA measurements represent a lower-bound estimate of systemic NDMA exposure. Our results suggest a need to evaluate the risks attributable to NDMA associated with chronic consumption of ranitidine, and to identify alternative treatments that minimize exposure to N-nitrosamines., (© The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Selected aromatic azo and benzidine based dyes are priority compounds under the Government of Canada's Chemical Management Plan (CMP) for environmental risk assessments. Organic compounds undergo chemical and biological transformations when they interact with environmental matrices and biotic species; identifying the transformation products is thus a critical component of the risk assessment process. Here, we used zero valent iron (ZVI) to initiate the reduction of the diazo compound dye Disperse Yellow 7 (DY 7). Using state-of-the-art accurate mass Liquid Chromatography-Quadrupole Time of Flight-Mass Spectroscopy (LC-QToF-MS), four transformation products were conclusively identified, while a fifth product was tentatively ascertained. The conclusively established transformation products included p-phenylenediamine (p-PDA, a known genotoxin), 4-aminoazobenzene (4-AAB, a category 2 carcinogen) and 4-aminobiphenyl (4-ABP, a category 1 human carcinogen). 4-ABP is thought to form via a benzidine rearrangement; this is the first report of DY 7 undergoing a benzidine rearrangement. Given the importance of reduction processes in the metabolism of organic contaminants by aquatic species, we used LC-MS/MS to analyze sediment samples that had been generated previously upon exposure of Western clawed frogs (Silurana tropicalis) to DY 7 (at exposure levels where cellular stress was observed in S. tropicalis). We found p-PDA, 4-AAB, and 4-ABP were present in all exposures, but not in any of the sediment controls, demonstrating that upon release of DY 7 to the aquatic environment, sediment dwelling organisms will metabolize DY 7 to generate known (and suspected) human carcinogens, including through a previously unreported in vivo benzidine rearrangement to produce 4-ABP., (Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.)

A non-linear approach, consistent with available mode of action (MOA) data, is most scientifically defensible for assessing the carcinogenicity of oral exposure to hexavalent chromium (CrVI). Accordingly, the current paper builds upon previous studies (Haney, 2015a, 2015b) to first develop a non-linear, non-threshold approach as well as a non-linear threshold approach for assessing the oral carcinogenicity of CrVI, and then utilizes available MOA analyses and information for selection of the most scientifically-supported approach. More specifically, a non-linear, non-threshold dose-response function was developed that adequately describes the non-linearity predicted for potential human excess risk versus oral dose due to the sub-linear relationship between oral dose and internal dose (added mg Cr/kg target tissue) across environmentally-relevant doses of regulatory interest. Additionally, benchmark dose modeling was used to derive a reference dose (RfD of 0.003 mg/kg-day) with cytotoxicity-induced regenerative hyperplasia as a key precursor event to carcinogenesis in the mouse small intestine. This RfD value shows remarkable agreement with that published previously (0.006 mg/kg-day) based on a more scientifically-sophisticated, physiologically-based pharmacokinetic modeling approach (Thompson et al., 2013b). The RfD approach is the most scientifically-defensible approach based on the weight-of-evidence of available MOA information and analyses conducted for the most scientifically-supported MOA., (Copyright © 2015 The Author. Published by Elsevier Inc. All rights reserved.)

A unit risk factor (URF) was developed for isoprene based on evaluation of three animal studies with adequate data to perform dose-response modeling (NTP, 1994, 1999; Placke et al., 1996). Ultimately, the URF of 6.2E-08 per ppb (2.2E-08 per μg/m(3)) was based on the 95% lower confidence limit on the effective concentration corresponding to 10% extra risk for liver carcinoma in male B6C3F1 mice after incorporating appropriate adjustment factors for species differences in target tissue metabolite concentrations and inhalation dosimetry. The corresponding lifetime air concentration at the 1 in 100,000 no significant excess risk level is 160 ppb (450 μg/m(3)). This concentration is almost 4400 times lower than the lowest exposure level associated with statistically increased liver carcinoma in B6C3F1 mice in the key study (700 ppm in Placke et al., 1996) and is above typical isoprene breath concentrations reported in the scientific literature. Continuous lifetime environmental exposure to the 1 in 100,000 excess risk level of 160 ppb would be expected to raise the human blood isoprene area under the curve (AUC) less than one-third of the standard deviation of the endogenous mean blood AUC. The mean for ambient air monitoring sites in Texas (2005-2014) is approximately 0.13 ppb., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

Drug metabolism is the crucial part of pharmaco- and toxicokinetics and consequently is associated with both desirable and adverse effects of most xenobiotics, compounds foreign to the body. This minireview follows some advances of the field over the last 50 years or so through the experiences and work of one scientist. Thus, this minireview represents a rather personal view of research in one research field. Drug metabolism is affected and controlled by a huge number of factors and conditions such as individual development, species differences, drug-drug interactions and various environmental, host and genetic factors working via a variable set of regulatory mechanisms. All these different factors create wide individual, population and species variability with obvious repercussions to clinical drug therapy and chemical risk assessment. This minireview also provides glimpses to methodological developments over recent decades and ends up presenting a few promising approaches and techniques such as various omics and high-content and high-throughput techniques feeding huge amounts of data to computational integration and modelling, which constitute the basis for systems or network pharmacology and toxicology., (© 2015 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).)

The effect of route of exposure on the kinetics of key biomarkers of exposure to benzo[a]pyrene (BaP), a known human carcinogen, was studied. Rats were exposed to an intravenous, intratracheal, oral and cutaneous dose of 40 µmol kg(-1) BaP. BaP and several metabolites were measured in blood, urine and feces collected at frequent intervals over 72 h post-treatment, using high-performance liquid chromatography/fluorescence. Only BaP and 3-hydroxyBaP (3-OHBaP) were detectable in blood at all time points. There were route-to-route differences in the excreted amounts (% dose) of metabolites but the observed time courses of the excretion rate were quite similar. In urine, total amounts of BaP metabolites excreted over the 0-72 h period followed the order: trans-4,5-dihydrodiolBaP (4,5-diolBaP) ≥ 3-OHBaP > 7-OHBaP ≥ 7,8-diolBaP after intravenous injection and intratracheal instillation; 3-OHBaP ≈ 7-OHBaP ≥ 4,5-diolBaP > 7,8-diolBaP after cutaneous application; 3-OHBaP ≥ 4,5-diolBaP ≈ 7-OHBaP > 7,8-diolBaP following oral administration. In feces, total amounts of BaP metabolites recovered were: 7-OHBaP ≈ 3-OHBaP > 4,5-diolBaP > 7,8-diolBaP > BaP-7,8,9,10-tetrol following all administration routes. For all exposure routes, excretion of 4,5- and 7,8-diolBaP was almost complete over the 0-24 h period in contrast with that of 3- and 7-OHBaP. This study confirms the interest of measuring multiple metabolites due to route-to-route differences in the relative excretion of the different biomarkers and in the time courses of diolBaPs versus OHBaPs. Concentration ratios of the different metabolites may help indicate time and main route of exposure., (Copyright © 2014 John Wiley & Sons, Ltd.)

Polar bears (Ursus maritimus) consume large quantities of seal blubber and other high trophic marine mammals and consequently have some of the highest tissue concentrations of organohalogen contaminants (OHCs) among Arctic biota. In the present paper we carried out a risk quotient (RQ) evaluation on OHC-exposed polar bears harvested from 1999 to 2008 and from 11 circumpolar subpopulations spanning from Alaska to Svalbard in order to evaluate the risk of OHC-mediated reproductive effects (embryotoxicity, teratogenicity), immunotoxicity and carcinogenicity (genotoxicity). This RQ evaluation was based on the Critical Body Residue (CBR) concept and a Physiologically-Based Pharmacokinetic Modelling (PBPK) approach using OHC concentrations measured in polar bear adipose or liver tissue. The range of OHC concentrations within polar bear populations were as follows for adipose, sum polychlorinated biphenyls ∑PCBs (1797-10,537 ng/g lw), sum methylsulphone-PCB ∑MeSO2-PCBs (110-672 ng/g lw), sum chlordanes ∑CHLs (765-3477 ng/g lw), α-hexachlorocyclohexane α-HCH (8.5-91.3 ng/g lw), β-hexachlorocyclohexane β-HCH (65.5-542 ng/g lw), sum chlorbenzenes ∑ClBzs (145-304 ng/g lw), dichlorodiphenyltrichloroethane ∑DDTs (31.5-206 ng/g lw), dieldrin (69-249 ng/g lw), polybrominated diphenyl ethers ∑PBDEs (4.6-78.4 ng/g lw). For liver, the perfluorooctanesulfonic acid (PFOS) concentrations ranged from 231-2792 ng/g ww. The total additive RQ from all OHCs ranged from 4.3 in Alaska to 28.6 in East Greenland bears for effects on reproduction, immune health and carcinogenicity, highlighting the important result that the toxic effect threshold (i.e. RQ>1) was exceeded for all polar bear populations assessed. PCBs were the main contributors for all three effect categories, contributing from 70.6% to 94.3% of the total risk and a RQ between 3.8-22.5. ∑MeSO2-PCBs were the second highest effect contributor for reproductive and immunological effects (0.17

Dose-dependent changes in target tissue absorption have important implications for determining the most defensible approach for developing a cancer-based oral toxicity factor for hexavalent chromium (CrVI). For example, mouse target tissue absorption per unit dose is an estimated 10-fold lower at the CrVI dose corresponding to the federal maximum contaminant level (MCL) than at the USEPA draft oral slope factor (SFo) point of departure dose. This decreasing target tissue absorption as doses decrease to lower, more environmentally-relevant doses is inconsistent with linear low-dose extrapolation. The shape of the dose-response curve accounting for this toxicokinetic phenomenon would clearly be non-linear. Furthermore, these dose-dependent differences in absorption indicate that the magnitude of risk overestimation by a linear low-dose extrapolation approach (e.g., SFo) increases and is likely to span one or perhaps more orders of magnitude as it is used to predict risk at progressively lower, more environmentally-relevant doses. An additional apparent implication is that no single SFo can reliably predict risk across potential environmental doses (e.g., doses corresponding to water concentrations⩽the federal MCL). A non-linear approach, consistent with available mode of action data, is most scientifically defensible for derivation of an oral toxicity factor for CrVI-induced carcinogenesis., (Copyright © 2015 The Author. Published by Elsevier Inc. All rights reserved.)