Metal(loid) bioaccessibility and children's health risk assessment of soil and indoor dust from rural and urban school and residential areas

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.

Derivation of a No significant risk level (NSRL) for acrylamide

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.

Fate of ptaquiloside-A bracken fern toxin-In cattle

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.

Concentration Levels, Biological Enrichment Capacities and Potential Health Risk Assessment of Trace Elements in Eichhornia crassipes from Honghu Lake, China

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.

The impact of chemotherapeutic drugs on the CYP1A1-catalysed metabolism of the environmental carcinogen benzo[a]pyrene: Effects in human colorectal HCT116 TP53(+/+), TP53(+/-) and TP53(-/-) cells

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.

S-(3-Aminobenzanthron-2-yl)cysteine in the globin of rats as a novel type of adduct and possible biomarker of exposure to 3-nitrobenzanthrone, a potent environmental carcinogen

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.

Skin permeation of polycyclic aromatic hydrocarbons: A solvent-based in vitro approach to assess dermal exposures against benzo[a]pyrene and dibenzopyrenes

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.

Predicting lung dosimetry of inhaled particleborne benzo[a]pyrene using physiologically based pharmacokinetic modeling

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.

Neurobehavioral alterations in rats exposed to acrylonitrile in drinking water

This study was carried out on rodents, to explore the neurobehavioral effects of acrylonitrile (AN) administered in drinking water. Thirty, male, Sprague-Dawley rats were randomly divided into three groups: two exposure groups (50 and 200 ppm AN), and one control group (tap water without AN). Three tests, including the open field test, rotarod test and spatial water maze, were applied to evaluate locomotor activities, motor co-ordination and learning and memory, respectively, prior to initiation of the treatment, and at Week 4, 8 and 12 postexposure. There were no consistent changes in the open field test, except for locomotion and grooming episodes. In the rotarod test, AN significantly decreased the latencies to fall in a dose and time-dependent manner. In the spatial water maze test, rats exposed to AN for 12 weeks had significantly more training times and longer escape latencies than control animals. These findings indicate that oral exposure to AN induces neurobehavioral alterations in rats.

Species difference in the disposition of acrylonitrile: quantitative whole-body autoradiographic study in rats and mice

Previous studies from this and other laboratories have indicated the role of species difference in acrylonitrile (VCN) toxicity and its metabolism to cyanide. Our recent studies also indicated a more pronounced elimination of VCN following oral as compared to i.v. administration. To further characterize the mechanism of these differences on the distribution of VCN, quantitative whole-body autoradiographic distribution and elimination studies were conducted at various time points (0.08, 8, 24, 48 h) following the administration of an equivalent i.v. dose of 2-[14C]-VCN to male Fischer rats and male CD-1 mice. Whole-body autoradiographs obtained from freeze-dried and acid-extracted sections of rats and mice demonstrated a rapid uptake of 14C in liver, lungs, spleen and bone marrow at early time intervals. Quantitatively, the uptake, retention and covalent interaction of 14C were higher in organs of rats as compared to mice, over 48 h. Mice eliminated 74% of the total administered dose of 2-[14C]-VCN (expired air 4%, urine 16% and feces 54%), while rats eliminated only 26% of the dose (expired air 2%, urine 4% and feces 20%). Species differences in VCN toxicity seem to be correlated with its rate of elimination. The distribution and elimination data demonstrated that mice divest VCN more rapidly than rats. The study also demonstrated that administration of VCN in rats resulted in covalent interactions and retention of 2-[14C]-VCN/metabolites in the tissues thus exerting more chronic toxicity to rats than to mice.

Genotoxic and carcinogenic products arising from reductive transformations of the azo dye, Disperse Yellow 7

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.

Physiologically-based pharmacokinetic modelling of immune, reproductive and carcinogenic effects from contaminant exposure in polar bears (Ursus maritimus) across the Arctic

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<RQ<1.4), whereas PFOS was the second highest effect contributor for carcinogenic (genotoxic) effects (0.35<RQ<2.5). The results from this study corroborate and lend further support to previous assessments of the possible adverse health effects of exposure to known and measured OHCs in polar bears. We therefore suggest that Critical Daily Doses (CDD) should be investigated in "ex vivo" dose-response studies on polar bears to replace laboratory studies on rats (Rattus rattus) to reveal whether high RQs are maintained.

Evaluation of carcinogenic potential of the herbicide glyphosate, drawing on tumor incidence data from fourteen chronic/carcinogenicity rodent studies

Abstract Glyphosate, an herbicidal derivative of the amino acid glycine, was introduced to agriculture in the 1970s. Glyphosate targets and blocks a plant metabolic pathway not found in animals, the shikimate pathway, required for the synthesis of aromatic amino acids in plants. After almost forty years of commercial use, and multiple regulatory approvals including toxicology evaluations, literature reviews, and numerous human health risk assessments, the clear and consistent conclusions are that glyphosate is of low toxicological concern, and no concerns exist with respect to glyphosate use and cancer in humans. This manuscript discusses the basis for these conclusions. Most toxicological studies informing regulatory evaluations are of commercial interest and are proprietary in nature. Given the widespread attention to this molecule, the authors gained access to carcinogenicity data submitted to regulatory agencies and present overviews of each study, followed by a weight of evidence evaluation of tumor incidence data. Fourteen carcinogenicity studies (nine rat and five mouse) are evaluated for their individual reliability, and select neoplasms are identified for further evaluation across the data base. The original tumor incidence data from study reports are presented in the online data supplement. There was no evidence of a carcinogenic effect related to glyphosate treatment. The lack of a plausible mechanism, along with published epidemiology studies, which fail to demonstrate clear, statistically significant, unbiased and non-confounded associations between glyphosate and cancer of any single etiology, and a compelling weight of evidence, support the conclusion that glyphosate does not present concern with respect to carcinogenic potential in humans.

Human in Vivo Pharmacokinetics of [(14)C]Dibenzo[def,p]chrysene by Accelerator Mass Spectrometry Following Oral Microdosing

Dibenzo(def,p)chrysene (DBC), (also known as dibenzo[a,l]pyrene), is a high molecular weight polycyclic aromatic hydrocarbon (PAH) found in the environment, including food, produced by the incomplete combustion of hydrocarbons. DBC, classified by IARC as a 2A probable human carcinogen, has a relative potency factor (RPF) in animal cancer models 30-fold higher than benzo[a]pyrene. No data are available describing the disposition of high molecular weight (>4 rings) PAHs in humans to compare to animal studies. Pharmacokinetics of DBC was determined in 3 female and 6 male human volunteers following oral microdosing (29 ng, 5 nCi) of [(14)C]-DBC. This study was made possible with highly sensitive accelerator mass spectrometry (AMS), capable of detecting [(14)C]-DBC equivalents in plasma and urine following a dose considered of de minimus risk to human health. Plasma and urine were collected over 72 h. The plasma Cmax was 68.8 ± 44.3 fg·mL(-1) with a Tmax of 2.25 ± 1.04 h. Elimination occurred in two distinct phases: a rapid (α)-phase, with a T1/2 of 5.8 ± 3.4 h and an apparent elimination rate constant (Kel) of 0.17 ± 0.12 fg·h(-1), followed by a slower (β)-phase, with a T1/2 of 41.3 ± 29.8 h and an apparent Kel of 0.03 ± 0.02 fg·h(-1). In spite of the high degree of hydrophobicity (log Kow of 7.4), DBC was eliminated rapidly in humans, as are most PAHs in animals, compared to other hydrophobic persistent organic pollutants such as, DDT, PCBs and TCDD. Preliminary examination utilizing a new UHPLC-AMS interface, suggests the presence of polar metabolites in plasma as early as 45 min following dosing. This is the first in vivo data set describing pharmacokinetics in humans of a high molecular weight PAH and should be a valuable addition to risk assessment paradigms.

Comparative analysis of the relationship between trichloroethylene metabolism and tissue-specific toxicity among inbred mouse strains: kidney effects

Trichloroethylene (TCE) is a well-known environmental and occupational toxicant that is classified as carcinogenic to humans based on the epidemiological evidence of an association with higher risk of renal-cell carcinoma. A number of scientific issues critical for assessing human health risks from TCE remain unresolved, such as the amount of kidney-toxic glutathione conjugation metabolites formed, interspecies and interindividual differences, and the mode of action for kidney carcinogenicity. It was postulated that TCE renal metabolite levels are associated with kidney-specific toxicity. Oral dosing with TCE was conducted in subacute (600 mg/kg/d; 5 d; 7 inbred mouse strains) and subchronic (100 or 400 mg/kg/d; 1, 2, or 4 wk; 2 inbred mouse strains) designs. The quantitative relationship was evaluated between strain-, dose, and time-dependent formation of TCE metabolites from cytochrome P-450-mediated oxidation (trichloroacetic acid [TCA], dichloroacetic acid [DCA], and trichloroethanol) and glutathione conjugation [S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2-dichlorovinyl)glutathione], and various kidney toxicity phenotypes. In subacute study, interstrain differences in renal TCE metabolite levels were observed. In addition, data showed that in several strains kidney-specific effects of TCE included induction of peroxisome proliferator-marker genes Cyp4a10 and Acox1, increased cell proliferation, and expression of KIM-1, a marker of tubular damage and regeneration. In subchronic study, peroxisome proliferator-marker gene induction and renal toxicity diminished while cell proliferative response was elevated in a dose-dependent manner in NZW/LacJ but not C57BL/6J mice. Overall, data demonstrated that renal TCE metabolite levels are associated with kidney-specific toxicity and that these effects are strain dependent.

Comparative analysis of the relationship between trichloroethylene metabolism and tissue-specific toxicity among inbred mouse strains: liver effects

Trichloroethylene (TCE) is a widely used organic solvent. Although TCE is classified as carcinogenic to humans, substantial gaps remain in our understanding of interindividual variability in TCE metabolism and toxicity, especially in the liver. A hypothesis was tested that amounts of oxidative metabolites of TCE in mouse liver are associated with hepatic-specific toxicity. Oral dosing with TCE was conducted in subacute (600 mg/kg/d; 5 d; 7 inbred mouse strains) and subchronic (100 or 400 mg/kg/d; 1, 2, or 4 wk; 2 inbred mouse strains) designs. The quantitative relationship was evaluated between strain-, dose-, and time-dependent formation of TCE metabolites from cytochrome P-450-mediated oxidation (trichloroacetic acid [TCA], dichloroacetic acid [DCA], and trichloroethanol) and glutathione conjugation [S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2-dichlorovinyl)glutathione] in serum and liver, and various hepatic toxicity phenotypes. In subacute study, interstrain variability in TCE metabolite amounts was observed in serum and liver. No marked induction of Cyp2e1 protein levels in liver was detected. Serum and hepatic levels of TCA and DCA were correlated with increased transcription of peroxisome proliferator-marker genes Cyp4a10 and Acox1 but not with degree of induction in hepatocellular proliferation. In subchronic study, serum and liver levels of oxidative metabolites gradually decreased over time despite continuous dosing. Hepatic protein levels of CYP2E1, ADH, and ALDH2 were unaffected by treatment with TCE. While the magnitude of induction of peroxisome proliferator-marker genes also declined, hepatocellular proliferation increased. This study offers a unique opportunity to provide a scientific data-driven rationale for some of the major assumptions in human health assessment of TCE.

Essentiality and toxicity of vanadium supplements in health and pathology

The biological properties of vanadium complexes have become an object of interest due to their therapeutic potential in several diseases. However, the mechanisms of action of vanadium salts are still poorly understood. Vanadium complexes are cofactors for several enzymes and also exhibit insulin-mimetic properties. Thus, they are involved in the regulation of glucose metabolism, including in patients with diabetes. In addition, vanadium salts may also normalize blood pressure and play a key role in the metabolism of the thyroid and of iron as well as in the regulation of total cholesterol, cholesterol HDL and triglyceride (TG) levels in blood. Moreover, in cases of hypoxia, vanadium compounds may improve cardiomyocytes function. They may also exhibit both carcinogenic and anti-cancer properties. These include dose- and exposure-time-dependent induction and inhibition of the proliferation and survival of cancer cells. On the other hand, the balance between vanadium's therapeutic properties and its side effects has not yet been determined. Therefore, any studies on the potential use of vanadium compounds as supplements to support the treatment of a number of diseases must be strictly monitored for adverse effects.

In vitro metabolism of benzo[a]pyrene and dibenzo[def,p]chrysene in rodent and human hepatic microsomes

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and often carcinogenic contaminants released into the environment during natural and anthropogenic combustion processes. Benzo[a]pyrene (B[a]P) is the prototypical carcinogenic PAH, and dibenzo[def,p]chrysene (DBC) is a less prevalent, but highly potent transplacental carcinogenic PAH. Both are metabolically activated by isoforms of the cytochrome P450 enzyme superfamily to form reactive carcinogenic and cytotoxic metabolites. Metabolism of B[a]P and DBC was studied in hepatic microsomes of male Sprague-Dawley rats, naïve and pregnant female B6129SF1/J mice, and female humans, corresponding to available pharmacokinetic data. Michaelis-Menten saturation kinetic parameters including maximum rates of metabolism (VMAX, nmol/min/mg microsomal protein), affinity constants (KM, μM), and rates of intrinsic clearance (CLINT, ml/min/kg body weight) were calculated from substrate depletion data. CLINT was also estimated from substrate depletion data using the alternative in vitro half-life method. VMAX and CLINT were higher for B[a]P than DBC, regardless of species. Clearance for both B[a]P and DBC was highest in naïve female mice and lowest in female humans. Clearance rates of B[a]P and DBC in male rat were more similar to female human than to female mice. Clearance of DBC in liver microsomes from pregnant mice was reduced compared to naïve mice, consistent with reduced active P450 protein levels and elevated tissue concentrations and residence times for DBC observed in previous in vivo pharmacokinetic studies. These findings suggest that rats are a more appropriate model organism for human PAH metabolism, and that pregnancy's effects on metabolism should be further explored.

Use of mode of action data to inform a dose-response assessment for bladder cancer following exposure to inorganic arsenic

In the recent National Research Council report on conducting a dose-response assessment for inorganic arsenic, the committee remarked that mode of action data should be used, to the extent possible, to extrapolate below the observed range for epidemiological studies to inform the shape of the dose-response curve. Recent in vitro mode of action studies focused on understanding the development of bladder cancer following exposure to inorganic arsenic provide data to inform the dose-response curve. These in vitro data, combined with results of bladder cancer epidemiology studies, inform the dose-response curve in the low-dose region, and include values for both pharmacokinetic and pharmacodynamic variability. Integration of these data provides evidence of a range of concentrations of arsenic for which no effect on the bladder would be expected. Specifically, integration of these results suggest that arsenic exposures in the range of 7-43 ppb in drinking water are exceedingly unlikely to elicit changes leading to key events in the development of cancer or noncancer effects in bladder tissue. These findings are consistent with the lack of evidence for bladder cancer following chronic ingestion of arsenic water concentrations <100 ppb in epidemiological studies.

The influence of dicoumarol on the bioactivation of the carcinogen aristolochic acid I in rats

Aristolochic acid I (AAI) is the major toxic component of the plant extract AA, which leads to the development of nephropathy and urothelial cancer in human. Individual susceptibility to AAI-induced disease might reflect variability in enzymes that metabolise AAI. In vitro

NAD(P)H

quinone oxidoreductase (NQO1) is the most potent enzyme that activates AAI by catalyzing formation of AAI-DNA adducts, which are found in kidneys of patients exposed to AAI. Inhibition of renal NQO1 activity by dicoumarol has been shown in mice. Here, we studied the influence of dicoumarol on metabolic activation of AAI in Wistar rats in vivo. In contrast to previous in vitro findings, dicoumarol did not inhibit AAI-DNA adduct formation in rats. Compared with rats treated with AAI alone, 11- and 5.4-fold higher AAI-DNA adduct levels were detected in liver and kidney, respectively, of rats pretreated with dicoumarol prior to exposure to AAI. Cytosols and microsomes isolated from liver and kidney of these rats were analysed for activity and protein levels of enzymes known to be involved in AAI metabolism. The combination of dicoumarol with AAI induced NQO1 protein level and activity in both organs. This was paralleled by an increase in AAI-DNA adduct levels found in ex vivo incubations with cytosols from rats pretreated with dicoumarol compared to cytosols from untreated rats. Microsomal ex vivo incubations showed a lower AAI detoxication to its oxidative metabolite, 8-hydroxyaristolochic acid (AAIa), although cytochrome P450 (CYP) 1A was practically unchanged. Because of these unexpected results, we examined CYP2C activity in microsomes and found that treatment of rats with dicoumarol alone and in combination with AAI inhibited CYP2C6/11 in liver. Therefore, these results indicate that CYP2C enzymes might contribute to AAI detoxication.

UGT2B gene expression analysis in multiple tobacco carcinogen-targeted tissues

The UDP-glucuronosyltransferase (UGT) 2B subfamily of enzymes plays an important role in the metabolism of numerous endogenous and exogenous compounds, including various carcinogens present in tobacco smoke. The goal of the present study was to examine the levels of expression of individual UGT2B genes in various tissues that are targets for tobacco carcinogenesis. Using MT-ATP6 as the experimentally validated housekeeping gene, the highest extrahepatic expression of UGT2B genes was observed in human tonsil, with UGT2B expression levels similar to that observed in human liver. UGT2B17 exhibited high relative expression in most tissues examined, including lung, most tissues of the aerodigestive tract, and pancreas. UGT2B7 expression was highest in pancreas but low or undetectable in most other tissues examined. UGT2B10 expression was high in both tonsil and tongue. There was wide variability between individuals in the magnitude of expression in each tissue site, and there were strong correlations between UGT2B expression levels in different individuals within many of the tissue sites, suggesting coordinated regulation of UGT2B gene expression in extrahepatic tissues. In the liver, UGTs 2B4, 2B7, 2B10, and 2B15 were significantly correlated with each other (all r(2) > 0.70, P < 0.0001). In all examined tissues of the aerodigestive tract, UGTs 2B10, 2B11, and 2B17 exhibited a strong correlation with each other (all r(2) > 0.75, P < 0.05). UGTs 2B7 and 2B10 exhibited a strong inverse correlation in the pancreas (r(2) = -0.95, P < 0.01). These data suggest that specific UGT2B enzymes important in tobacco carcinogen metabolism are expressed and coordinately regulated in various target sites for tobacco-related cancers.

An immunochromatographic assay for rapid and direct detection of 3-amino-5-morpholino-2-oxazolidone (AMOZ) in meat and feed samples

BACKGROUND

Furaltadone (FTD) is a type of nitrofuran and has been banned in many countries as a veterinary drug in food-producing animals owing to its potential carcinogenicity and mutagenicity. FTD is unstable in vivo, rapidly metabolizing to 3-amino-5-methylmorpholino-2-oxazolidinone (AMOZ); thus AMOZ can be used as an indicator for illegal usage of FTD. Usually, for the determination of nitrofurans, the analyte is often a derivative of the metabolite rather than the metabolite itself. In this study, based on the monoclonal antibody (mAb) against AMOZ, a competitive immunochromatographic assay (ICA) using a colloidal gold-mAb probe for rapid and direct detection of AMOZ without a derivatization step in meat and feed samples was developed.

RESULTS

The intensity of red color in the test line is inversely related to the analyte concentration and the visual detection limit was found to be 10 ng mL⁻¹. The performance of this assay was simple and convenient because the tedious and time-consuming derivatization step was avoided. The ICA detection was completed within 10 min. The ICA strips could be used for 7 weeks at room temperature without significant loss of activity. The AMOZ spiked samples were detected by ICA and confirmed by enzyme-linked immunosorbent assay. The results of the two methods were in good agreement.

CONCLUSION

The proposed ICA provides a feasible tool for simple, sensitive, rapid, convenient and semi-quantitative detection of AMOZ in meat and feed samples on site. To our knowledge, this is the first report of the ICA for direct detection of AMOZ.

Bcrp1;Mdr1a/b;Mrp2 combination knockout mice: altered disposition of the dietary carcinogen PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) and its genotoxic metabolites

The multidrug transporters breast cancer resistance protein (BCRP), multidrug-resistance protein 1 (MDR1), and multidrug-resistance-associated protein (MRP) 2 and 3 eliminate toxic compounds from tissues and the body and affect the pharmacokinetics of many drugs and other potentially toxic compounds. The food-derived carcinogen PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) is transported by BCRP, MDR1, and MRP2. To investigate the overlapping functions of Bcrp1, Mdr1a/b, and Mrp2 in vivo, we generated Bcrp1;Mdr1a/b;Mrp2(-/-) mice, which are viable and fertile. These mice, together with Bcrp1;Mrp2;Mrp3(-/-) mice, were used to study the effects of the multidrug transporters on the pharmacokinetics of PhIP and its metabolites. Thirty minutes after oral or intravenous administration of PhIP (1 mg/kg), the PhIP levels in the small intestine were reduced 4- to 6-fold in Bcrp1;Mdr1a/b;Mrp2(-/) (-) and Bcrp1;Mrp2;Mrp3(-/-) mice compared with wild-type mice. Fecal excretion of PhIP was reduced 8- to 20-fold in knockouts. Biliary PhIP excretion was reduced 41-fold in Bcrp1;Mdr1a/b;Mrp2(-/-) mice. Biliary and small intestine levels of PhIP metabolites were reduced in Bcrp1;Mrp2-deficient mice. Furthermore, in both knockout strains, kidney levels and urinary excretion of genotoxic PhIP-metabolites were significantly increased, suggesting that reduced biliary excretion of PhIP and PhIP metabolites leads to increased urinary excretion of these metabolites and increased systemic exposure. Bcrp1 and Mdr1a limited PhIP brain accumulation. In Bcrp1;Mrp2;Mrp3(-/-), but not Bcrp1;Mdr1a/b;Mrp(-/-) mice, the carcinogenic metabolites N2-OH-PhIP (2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine) and PhIP-5-sulfate (a genotoxicity marker) accumulated in liver tissue, indicating that Mrp3 is involved in the sinusoidal secretion of these compounds. We conclude that Bcrp1, Mdr1a/b, Mrp2, and Mrp3 significantly affect tissue disposition and biliary and fecal elimination of PhIP and its carcinogenic metabolites and may affect PhIP-induced carcinogenesis as a result.

Role of CYP2A13 in the bioactivation and lung tumorigenicity of the tobacco-specific lung procarcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone: in vivo studies using a CYP2A13-humanized mouse model

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is abundant in tobacco smoke, is a potent lung procarcinogen. The present study was aimed to prove that transgenic expression of human cytochrome P450 2A13 (CYP2A13), known to be selectively expressed in the respiratory tract and be the most efficient enzyme for NNK bioactivation in vitro, will enhance NNK bioactivation and NNK-induced tumorigenesis in the mouse lung. Kinetic parameters of NNK bioactivation in vitro and incidence of NNK-induced lung tumors in vivo were determined for wild-type, Cyp2a5-null and CYP2A13-humanized (CYP2A13-transgenic/Cyp2a5-null) mice. As expected, in both liver and lung microsomes, the loss of CYP2A5 resulted in significant increases in Michaelis constant (K m) values for the formation of 4-oxo-4-(3-pyridyl)-butanal, representing the reactive intermediate that can lead to the formation of O(6)-methylguanine (O(6)-mG) DNA adducts; however, the gain of CYP2A13 at a fraction of the level of mouse lung CYP2A5 led to recovery of the activity in the lung, but not in the liver. The levels of O(6)-mG, the DNA adduct highly correlated with lung tumorigenesis, were significantly higher in the lungs of CYP2A13-humanized mice than in Cyp2a5-null mice. Moreover, incidences of lung tumorigenesis were significantly greater in CYP2A13-humanized mice than in Cyp2a5-null mice, and the magnitude of the differences in incidence was greater at low (30mg/kg) than at high (200mg/kg) NNK doses. These results indicate that CYP2A13 is a low K m enzyme in catalyzing NNK bioactivation in vivo and support the notion that genetic polymorphisms of CYP2A13 can influence the risks of tobacco-induced lung tumorigenesis in humans.

Knockout and humanized mice as suitable tools to identify enzymes metabolizing the human carcinogen aristolochic acid

1. Aristolochic acid I (AAI) is the predominant component in plant extract of Aristolochia genus that is involved in development of aristolochic acid nephropathy, Balkan endemic nephropathy and urothelial cancer. The diseases do not develop in all individuals exposed to AAI and patients exhibit different clinical outcomes. Differences in the activities of enzymes catalyzing the metabolism of AAI might be one of the reasons for this individual susceptibility. 2. Understanding which human enzymes are involved in reductive activation of AAI generating AAI-DNA adducts, and/or its detoxication to the O-demethylated metabolite, aristolochic acid Ia (AAIa), is necessary in the assessment of the susceptibility to this compound. 3. This review summarizes the results of the latest studies utilizing genetically engineered mouse models to identify which human and rodent enzymes catalyze the reductive activation of AAI to AAI-DNA adducts and its oxidative detoxication to AAIa in vivo. 4. The use of hepatic cytochrome P450 (Cyp) reductase null (HRN) mice, in which NADPH:Cyp oxidoreductase (Por) is deleted in hepatocytes, Cyp1a1((-/-)), Cyp1a2((-/-)) single-knockout, Cyp1a1/1a2((-/-)) double-knockout and CYP1A-humanized mice revealed that mouse and human CYP1A1 and 1A2, besides mouse

NAD(P)H

quinone oxidoreductase, were involved in the activation of AAI but CYP1A1 and 1A2 also oxidatively detoxified AAI.

Tanshinone I protects mice from aristolochic acid I-induced kidney injury by induction of CYP1A

Hepatic CYP1A especially CYP1A2 plays an important role in the reduction of aristolochic acid I (AAI) nephrotoxicity. In this study, we investigated the effects of tanshinone I, a strong inducer of Cyp1a, on the nephrotoxicity induced by AAI. Histopathology and blood biochemistry assays showed that tanshinone I could reduce AAI-induced acute kidney injury. Pharmacokinetics analysis revealed that tanshinone I markedly decreased AUC of AAI in plasma and the content of AAI in both liver and kidney, indicating the enhancement of AAI metabolism. Real-time PCR and Western blot analysis confirmed that tanshinone I effectively increased the mRNA and protein levels of hepatic CYP1A1 and CYP1A2 in vivo. Luciferase assay showed that tanshinone I strongly increased the transcriptional activity of CYP1A1 and CYP1A2 in the similar extent. In summary, our data suggested that tanshinone I facilitated the metabolism of AAI and prevented AAI-induced kidney injury by induction of hepatic CYP1A 1/2 in vivo.

Toxicology and carcinogenesis of 3´-azido-3´-deoxythymidine (AZT) (CAS No. 30516-87-1) in genetically modified C3B6.129F1-Trp53(tm1Brd) N12 haploinsufficient mice (in utero and postnatal gavage studies)

Antiviral therapy is essential for treatment and prevention of human immunodeficiency virus (HIV) disease in adults and children and to prevent mother-to-child transmission of HIV during pregnancy and labor. The studies described in this report were designed to determine possible long-term sequelae from 3´-azido-3´-deoxythymidine (AZT) treatment, often used in combination with other antivirals, in preventing mother-to-child transmission of HIV. AZT is the most widely used and evaluated chemotherapeutic agent for the treatment of persons with acquired immune deficiency syndrome (AIDS). Male and female heterozygous F1 p53+/- mice were exposed, by maternal gavage, to AZT in utero on gestation days (GD) 12 through 18, then administered AZT by gavage from postnatal day (PND) 1 through 30 weeks of age (30-week study), 45 weeks of age (45-week study), or PND 8 (45-week stop-study). Mice in the 0 mg/kg groups received only an aqueous solution containing 0.2% methylcellulose and 0.1% Tween® 80. Mice were dosed once daily until PND 28, then 5 days per week. Genetic toxicology studies were conducted in mouse peripheral blood erythrocytes. 30-WEEK STUDY: Pregnant dams were administered 0 or 240 mg AZT/kg body weight per day on GDs 12 through 18. Groups of 26 or 27 male and 26 or 27 female pups were administered 0 or 120 mg/kg by gavage on PNDs 1 through 10, then 0 or 240 mg/kg until the end of the study. Survival of 240/120/240 mg/kg males was significantly less than that of 0/0/0 mg/kg males. Mean body weights of dosed males and females were less than those of the 0/0/0 mg/kg groups, and absolute kidney weights of dosed males and females were significantly less than those of the 0/0/0 mg/kg groups. Mean cell volume and mean cell hemoglobin in dosed females and mean cell volume in dosed males were significantly increased, suggesting moderately severe macrocytic anemia. The incidence of malignant lymphoma was increased in male mice administered 240/120/240 mg/kg. The increase was significant when adjusted for litter correlations. 45-WEEK STUDY: Pregnant dams were administered 0, 80, 160, or 240 mg/kg on GDs 12 through 18. Corresponding groups of 27 male and 26 or 27 female pups were administered 0, 40, 80, or 120 mg/kg on PNDs 1 through 10, then 0, 80, 160, or 240 mg/kg until the end of the study. There was no effect of AZT administration on the survival of dosed mice. Mean body weights of dosed males and females were generally less than those of the 0/0/0 mg/kg groups. Absolute brain weights of males and females administered 240/120/240 mg/kg were significantly less than those of the 0/0/0 mg/kg groups. Mean cell volume and mean cell hemoglobin at 160 days were increased in 240/120/240 mg/kg males and females, suggesting moderately severe macrocytic anemia. The incidences of hepatocellular adenoma occurred with a positive trend in males, and the incidence in the 240/120/240 mg/kg group was significantly increased. In females, there was a positive trend in the incidences of malignant lymphoma, and the increased incidence in the 240/120/240 mg/kg group was significant when adjusted for litter correlations. 45-WEEK STOP-STUDY: Pregnant dams were administered 0 or 240 mg/kg on GDs 12 through 18. Groups of 24 or 25 male and 26 female pups were administered 0 or 40 mg/kg on PNDs 1 through 8; pups were then maintained on study until 45 weeks of age without dosing. There was no effect of AZT administration on the survival of dosed mice. Mean body weights of dosed males were generally less than those of the 0/0 mg/kg group. Absolute, but not relative, brain weights of dosed males and females were significantly less than those of the 0/0 mg/kg groups. The incidences of hepatocellular adenoma and hepatocellular adenoma or carcinoma (combined) were slightly increased in 240/40 mg/kg males.

GENETIC TOXICOLOGY

Micronucleated normochromatic erythrocytes and reticulocyte frequencies were generally significantly increased relative to the corresponding 0, 0/0, or 0/0/0 mg/kg group values in 1-day-old pups exposed to AZT in utero at 160 or 240 mg/kg, in 10-day-old pups administered 80/40, 160/80, or 240/120 mg/kg, in 28-day-old pups administered 80/40/80, 160/80/160, or 240/120/240 mg/kg, and in 30-week-old mice administered 240/120/240 mg/kg.

CONCLUSIONS

Under the conditions of these gavage studies, there was clear evidence of carcinogenic activity of of AZT in male heterozygous F1 p53+/- mice based on the occurrence of hepatocellular neoplasms (predominantly adenomas) after 45 weeks of administration. The occurrence of malignant lymphoma may have been related to AZT administration for 30 weeks. There was equivocal evidence of carcinogenic activity of AZT in female heterozygous F1 p53+/- mice based on the occurrence of malignant lymphoma after 45 weeks of administration. Synonyms: AZT; 3´-azido-2´,3´-dideoxythymidine; azidodeoxythymidine; azidothymidine; 3´-azidothymidine; 3´-deoxy-3´-azidothymidine; 3´-deoxy-(8CI) (9CI); BW A509U; Compound S; ZDV; zidovudine Trade Name: Retrovir®

Report on Carcinogens Monograph on 1-Bromopropane: RoC Monograph 01

The National Toxicology Program conducted a cancer evaluation on 1 bromopropane for possible listing in the Report on Carcinogens (RoC). The cancer evaluation is captured in the RoC monograph, which was peer reviewed in a public forum. The monograph consists of two components: (Part 1) the cancer evaluation, which reviews the relevant scientific information, assesses its quality, applies the RoC listing criteria to the scientific information, and provides the NTP recommendation for listing status for 1 bromopropane in the RoC, and (Part 2) the substance profile proposed for the RoC, containing the NTP's listing status recommendation, a summary of the scientific evidence considered key to reaching that decision, and data on properties, use, production, exposure, and Federal regulations and guidelines to reduce exposure to 1-bromopropane. This monograph provides an assessment of the available scientific information on 1 bromopropane, including human exposure and properties, disposition and toxicokinetics, cancer studies in experimental animals, and studies of mechanisms and other related effects, including relevant toxicological effects, genetic toxicology, and mechanisms of carcinogenicity. From this assessment, the NTP recommended that 1 bromopropane be listed as reasonably anticipated to be a human carcinogen in the RoC based on sufficient evidence from studies in experimental animals, which found inhalation exposure to 1-bromopropane caused skin tumors in male rats, large intestine tumors in female and male rats, and lung tumors in female mice. Also noted was that 1 bromopropane, either directly or via reactive metabolites, caused molecular alterations that typically are associated with carcinogenesis, including genotoxicity, oxidative stress, and glutathione depletion. These alterations, observed in mainly in vitro and toxicity studies in rodents, are relevant to possible mechanisms of human carcinogenicity and support the relevance of the cancer studies in experimental animals to humans.

Report on Carcinogens Monograph on 1-Bromopropane: RoC Monograph 01

The National Toxicology Program conducted a cancer evaluation on 1 bromopropane for possible listing in the Report on Carcinogens (RoC). The cancer evaluation is captured in the RoC monograph, which was peer reviewed in a public forum. The monograph consists of two components: (Part 1) the cancer evaluation, which reviews the relevant scientific information, assesses its quality, applies the RoC listing criteria to the scientific information, and provides the NTP recommendation for listing status for 1 bromopropane in the RoC, and (Part 2) the substance profile proposed for the RoC, containing the NTP's listing status recommendation, a summary of the scientific evidence considered key to reaching that decision, and data on properties, use, production, exposure, and Federal regulations and guidelines to reduce exposure to 1-bromopropane. This monograph provides an assessment of the available scientific information on 1 bromopropane, including human exposure and properties, disposition and toxicokinetics, cancer studies in experimental animals, and studies of mechanisms and other related effects, including relevant toxicological effects, genetic toxicology, and mechanisms of carcinogenicity. From this assessment, the NTP recommended that 1 bromopropane be listed as reasonably anticipated to be a human carcinogen in the RoC based on sufficient evidence from studies in experimental animals, which found inhalation exposure to 1-bromopropane caused skin tumors in male rats, large intestine tumors in female and male rats, and lung tumors in female mice. Also noted was that 1 bromopropane, either directly or via reactive metabolites, caused molecular alterations that typically are associated with carcinogenesis, including genotoxicity, oxidative stress, and glutathione depletion. These alterations, observed in mainly in vitro and toxicity studies in rodents, are relevant to possible mechanisms of human carcinogenicity and support the relevance of the cancer studies in experimental animals to humans.

Impact of pregnancy on the pharmacokinetics of dibenzo[def,p]chrysene in mice

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants generated during combustion. Dibenzo[def,p]chrysene (DBC) is a high molecular weight PAH classified as a 2B carcinogen by the International Agency for Research on Cancer. DBC crosses the placenta in exposed mice, causing carcinogenicity in offspring. We present pharmacokinetic data of DBC in pregnant and nonpregnant mice. Pregnant (gestational day 17) and nonpregnant female B6129SF1/J mice were exposed to 15mg/kg DBC by oral gavage. Subgroups of mice were sacrificed up to 48h postdosing, and blood, excreta, and tissues were analyzed for DBC and its major diol and tetrol metabolites. Elevated maximum concentrations and areas under the curve of DBC and its metabolites were observed in blood and tissues of pregnant animals compared with naïve mice. Using a physiologically based pharmacokinetic (PBPK) model, we found observed differences in pharmacokinetics could not be attributed solely to changes in tissue volumes and blood flows that occur during pregnancy. Measurement of enzyme activity in naïve and pregnant mice by activity-based protein profiling indicated a 2- to 10-fold reduction in activities of many of the enzymes relevant to PAH metabolism. Incorporating this reduction into the PBPK model improved model predictions. Concentrations of DBC in fetuses were one to two orders of magnitude below maternal blood concentrations, whereas metabolite concentrations closely resembled those observed in maternal blood.

Report on Carcinogens Monograph on Cumene: RoC Monograph 02

The National Toxicology Program conducted a cancer evaluation on cumene for possible listing in the Report on Carcinogens (RoC). The cancer evaluation is captured in the RoC monograph, which was peer reviewed in a public forum. The monograph consists of two components: (Part 1) the cancer evaluation, which reviews the relevant scientific information, assesses its quality, applies the RoC listing criteria to the scientific information, and provides the NTP recommendation for listing status for cumene in the RoC, and (Part 2) the substance profile proposed for the RoC, containing the NTP's listing status recommendation, a summary of the scientific evidence considered key to reaching that decision, and data on properties, use, production, exposure, and Federal regulations and guidelines to reduce exposure to cumene. This monograph provides an assessment of the available scientific information on cumene, including human exposure and properties, disposition and toxicokinetics, cancer studies in experimental animals, and studies of mechanisms and other related effects, including relevant toxicological effects, genetic toxicology, and mechanisms of carcinogenicity. From this assessment, the NTP recommended that cumene be listed as reasonably anticipated to be a human carcinogen in the RoC based on sufficient evidence from studies in experimental animals, which found that cumene exposure caused lung tumors in male and female mice and liver tumors in female mice. Several proposed mechanisms of carcinogenesis support the relevance to humans of the lung and liver tumors observed in experimental animals. Specifically, there is evidence that humans and experimental animals metabolize cumene through similar metabolic pathways. In addition, mutations of the K-ras oncogene and p53 tumor-suppressor gene observed in cumene-induced lung tumors in mice, along with altered expression of many other genes, resemble molecular alterations found in human lung and other cancers.

Longitudinal study of [D10]phenanthrene metabolism by the diol epoxide pathway in smokers

The extent of metabolism of [D10]phenanthrene to [D(10)]r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetradeuterophenanthrene ([D10]PheT) could be a biomarker of human metabolic activation of carcinogenic polycyclic aromatic hydrocarbons, leading to identification of smokers particularly susceptible to lung cancer. The longitudinal stability of [D10]PheT was evaluated in 24 cigaret smokers given 7-8 oral doses of [D10]phenanthrene (10 µg) over 5.5 months. [D10]PheT in 6 h urine was quantified after each dose. The overall coefficient of variation for 24 subjects was (mean ± S.D.) 27.4% ± 8.83%. Thus, a single administration of [D10]phenanthrene is likely sufficient to determine a smoker's ability to metabolize it to [D10]PheT.

Identification and functional characterization of a novel UDP-glucuronosyltransferase 2A1 splice variant: potential importance in tobacco-related cancer susceptibility

UDP-glucuronosyltransferase (UGT) 2A1 is a respiratory and aerodigestive tract-expressing phase II detoxifying enzyme that metabolizes various xenobiotics including polycyclic aromatic hydrocarbons (PAHs). In the present study, a novel exon 3 deletion splice variant was identified for UGT2A1 (UGT2A1Δexon3). As determined by reverse transcription-polymerase chain reaction (PCR), UGT2A1Δexon3 was shown to be expressed in various tissues including lung, trachea, larynx, tonsil, and colon. The ratio of UGT2A1Δexon3/wild-type UGT2A1 expression was highest in colon (0.79 ± 0.08) and lung (0.42 ± 0.12) as determined by real-time PCR; an antibody specific to UGT2A1 showed splice variant protein (UGT2A1_i2) to wild-type protein (UGT2A1_i1) ratios in the range of 0.5 to 0.9 in these tissues. Using ultra-pressure liquid chromatography, we found that homogenates prepared from UGT2A1_i2-overexpressing human embryonic kidney 293 cells exhibited no glucuronidation activity against PAHs, including benzo[a]pyrene-7,8-dihydrodiol (B[a]P-7,8-diol). An inducible in vitro system was created to determine the effect of UGT2A1_i2 expression on UGT2A1_i1 activity. Increasing UGT2A1_i2 levels resulted in a significant (p < 0.01) decrease in the UGT2A1_i1 V(max) against 1-hydroxy (OH)-pyrene, 3-OH-benzo[a]pyrene, and B[a]P-7,8-diol; no significant changes in K(M) were observed for any of the three substrates. Coimmunoprecipitation experiments suggested the formation of UGT2A1_i1 and UGT2A1_i2 hetero-oligomers and UGT2A1_i1 homo-oligomers; coexpression of UGT2A1_i1 or UGT2A1_i2 with other UGT1A or UGT2B enzymes caused no change in UGT1A or UGT2B glucuronidation activity. These data suggest that a novel UGT2A1 splice variant regulates UGT2A1-mediated glucuronidation activity via UGT2A1-specific protein-protein interactions, and expression of this variant could play an important role in the detoxification of carcinogens within target tissues for tobacco carcinogenesis.

Gut fermentation products of inulin-type fructans modulate the expression of xenobiotic-metabolising enzymes in human colonic tumour cells

Epidemiological studies suggest that nutrition plays an important role in colonic cancer prevention. A possible mechanism of this prevention may be the modulation of carcinogen metabolism and scavenging of reactive intermediates. In particular, dietary fibres are discussed as potentially protective food ingredients. Therefore, the aim of this study was to analyse if the expression of genes related to biotransformation is modulated by fermentation samples of dietary fibres. HT29 (human colonic carcinoma) and LT97 (human adenoma) cells were incubated with fermentation supernatant (SFS), produced by in vitro fermentation of inulin enriched with oligofructose. Possible mechanisms of de-toxification were investigated by analysing the expression of catalase and glutathione-S-transferase (GST) A4 mRNA and the enzyme activity of catalase and GST. In addition, protection of both cell lines against DNA damage, induced by H(2)O(2) or 4-hydroxynonenal (HNE), was analysed using the comet assay. Incubation with SFS resulted in significantly increased GSTA4 mRNA expression, significantly enhanced catalase activity and a significant reduction in the amount of H(2)O(2)-induced DNA damage in HT29 cells. Our results show that complex fermentation samples of inulin-type fructans favourably modulate expression of genes related to biotransformation in carcinoma cells, which in turn supports the important role of dietary fibres in primary chemoprevention.

Benzo[a]pyrene-induced transcriptomic responses in primary hepatocytes and in vivo liver: toxicokinetics is essential for in vivo-in vitro comparisons

The traditional 2-year cancer bioassay needs replacement by more cost-effective and predictive tests. The use of toxicogenomics in an in vitro system may provide a more high-throughput method to investigate early alterations induced by carcinogens. Recently, the differential gene expression response in wild-type and cancer-prone Xpa (-/-) p53 (+/-) primary mouse hepatocytes after exposure to benzo[a]pyrene (B[a]P) revealed downregulation of cancer-related pathways in Xpa (-/-) p53 (+/-) hepatocytes only. Here, we investigated pathway regulation upon in vivo B[a]P exposure of wild-type and Xpa (-/-) p53 (+/-) mice. In vivo transcriptomics analysis revealed a limited gene expression response in mouse livers, but with a significant induction of DNA replication and apoptotic/anti-apoptotic cellular responses in Xpa (-/-) p53 (+/-) livers only. In order to be able to make a meaningful in vivo-in vitro comparison we estimated internal in vivo B[a]P concentrations using DNA adduct levels and physiologically based kinetic modeling. Based on these results, the in vitro concentration that corresponded best with the internal in vivo dose was chosen. Comparison of in vivo and in vitro data demonstrated similarities in transcriptomics response: xenobiotic metabolism, lipid metabolism and oxidative stress. However, we were unable to detect cancer-related pathways in either wild-type or Xpa (-/-) p53 (+/-) exposed livers, which were previously found to be induced by B[a]P in Xpa (-/-) p53 (+/-) primary hepatocytes. In conclusion, we showed parallels in gene expression responses between livers and primary hepatocytes upon exposure to equivalent concentrations of B[a]P. Furthermore, we recommend considering toxicokinetics when modeling a complex in vivo endpoint with in vitro models.

Phenanthrene metabolism in smokers: use of a two-step diagnostic plot approach to identify subjects with extensive metabolic activation

Polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke are among the most likely causes of lung cancer. PAHs require metabolic activation to initiate the carcinogenic process. Phenanthrene (Phe), a noncarcinogenic PAH, was used as a surrogate of benzo[α]pyrene and related PAHs to study the metabolic activation of PAHs in smokers. A dose of 10 μg of deuterated Phe ([D₁₀]Phe) was administered to 25 healthy smokers in a crossover design, either as an oral solution or by smoking cigarettes containing [D₁₀]Phe. Phe was deuterated to avoid interference from environmental Phe. Intensive blood and urine sampling was performed to quantitate the formation of deuterated r-1,t-2,3,c-4-tetrahydroxy-1,2,3,4-tetrahydrophenanthrene ([D₁₀]PheT), a biomarker of the diol epoxide metabolic activation pathway. In both the oral and smoking arms approximately 6% of the dose was metabolically converted to diol epoxides, with a large intersubject variability in the formation of [D₁₀]PheT observed. Two diagnostic plots were developed to identify subjects with large systemic exposure and significant lung contribution to metabolic activation. The combination of the two plots led to the identification of subjects with substantial local exposure. These subjects produced, in one single pass of [D₁₀]Phe through the lung, a [D₁₀]PheT exposure equivalent to the systemic exposure of a typical subject and may be an indicator of lung cancer susceptibility. Polymorphisms in PAH-metabolizing genes of the 25 subjects were also investigated. The integration of phenotyping and genotyping results indicated that GSTM1-null subjects produced approximately 2-fold more [D₁₀]PheT than did GSTM1-positive subjects.

UDP-glucuronosyltransferase-mediated metabolic activation of the tobacco carcinogen 2-amino-9H-pyrido[2,3-b]indole

2-Amino-9H-pyrido[2,3-b]indole (AαC) is a carcinogenic heterocyclic aromatic amine (HAA) that arises in tobacco smoke. UDP-glucuronosyltransferases (UGTs) are important enzymes that detoxicate many procarcinogens, including HAAs. UGTs compete with P450 enzymes, which bioactivate HAAs by N-hydroxylation of the exocyclic amine group; the resultant N-hydroxy-HAA metabolites form covalent adducts with DNA. We have characterized the UGT-catalyzed metabolic products of AαC and the genotoxic metabolite 2-hydroxyamino-9H-pyrido[2,3-b]indole (HONH-AαC) formed with human liver microsomes, recombinant human UGT isoforms, and human hepatocytes. The structures of the metabolites were elucidated by (1)H NMR and mass spectrometry. AαC and HONH-AαC underwent glucuronidation by UGTs to form, respectively, N(2)-(β-D-glucosidurony1)-2-amino-9H-pyrido[2,3-b]indole (AαC-N(2)-Gl) and N(2)-(β-D-glucosidurony1)-2-hydroxyamino-9H-pyrido[2,3-b]indole (AαC-HON(2)-Gl). HONH-AαC also underwent glucuronidation to form a novel O-linked glucuronide conjugate, O-(β-D-glucosidurony1)-2-hydroxyamino-9H-pyrido[2,3-b]indole (AαC-HN(2)-O-Gl). AαC-HN(2)-O-Gl is a biologically reactive metabolite and binds to calf thymus DNA (pH 5.0 or 7.0) to form the N-(deoxyguanosin-8-yl)-AαC adduct at 20-50-fold higher levels than the adduct levels formed with HONH-AαC. Major UGT isoforms were examined for their capacity to metabolize AαC and HONH-AαC. UGT1A4 was the most catalytically efficient enzyme (V(max)/K(m)) at forming AαC-N(2)-Gl (0.67 μl·min(-1)·mg of protein(-1)), and UGT1A9 was most catalytically efficient at forming AαC-HN-O-Gl (77.1 μl·min(-1)·mg of protein(-1)), whereas UGT1A1 was most efficient at forming AαC-HON(2)-Gl (5.0 μl·min(-1)·mg of protein(-1)). Human hepatocytes produced AαC-N(2)-Gl and AαC-HN(2)-O-Gl in abundant quantities, but AαC-HON(2)-Gl was a minor product. Thus, UGTs, usually important enzymes in the detoxication of many procarcinogens, serve as a mechanism of bioactivation of HONH-AαC.

TLR2 controls intestinal carcinogen detoxication by CYP1A1

Intestinal cytochrome P450 subclass 1A1 (CYP1A1) contributes to a metabolic “shield” protecting the host from ingested carcinogens such as polycyclic aromatic hydrocarbons (PAH). The expression of CYP1 (including CYP1A2 and CYP1B1) is considered to depend solely on a heterodimeric transcription factor consisting of the arylhydrocarbon receptor (AHR) and the AHR nuclear translocator (ARNT). So far, no interference has been noted between the regulation of CYP1 and the activation of Toll-like receptor 2 (TLR2), which modulates the inflammatory response to bacterial cell wall components in immune cells and enterocytes. Here we report that intestinal CYP1A1 is silenced in TLR2-deficient mice, even when under exposure to the carcinogenic PAH benzo[a]pyrene (BaP). In contrast, hepatic CYP1A1 was moderately induced in TLR2-deficient mice without restoring their ability to clear BaP from systemic circulation, as present in wild-type animals. After feeding of BaP for 21 days, only TLR2^−/− mice, but not their wild type littermates developed polyps in the colon. Gene expressions and protein concentrations of AHR and ARNT in the intestine did not differ between the genotypes. In conclusion, the presence of ligands for TLR2 of bacterial origin seems to be crucial for detoxication of luminal carcinogens by CYP1A1 in the intestine. This unprecedented finding indicates a complex interplay between the immune system of the host and intestinal bacteria with detoxication mechanisms. This highlights the relevance of intestinal microbiota when trying to unravel pathways present in mammals and opens new perspectives for research in human health.

Cytochrome P450-mediated metabolism and DNA binding of 2-amino-1,7-dimethylimidazo[4,5-g]quinoxaline and its carcinogenic isomer 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in mice

2-Amino-1,7-dimethylimidazo[4,5-g]quinoxaline (MeIgQx) is a recently discovered heterocyclic aromatic amine (HAA) that is formed during the cooking of meats. MeIgQx is an isomer of 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline (MeIQx), a rodent carcinogen and possible human carcinogen that also occurs in cooked meats. MeIgQx is a bacterial mutagen, but knowledge about its metabolism and carcinogenic potential is lacking. Metabolism studies on MeIgQx and MeIQx were conducted with human and mouse liver microsomes, and recombinant human P450s. DNA binding studies were also investigated in mice to ascertain the genotoxic potential of MeIgQx in comparison to MeIQx. Both HAAs underwent comparable rates of N-oxidation to form genotoxic N-hydroxylated metabolites with mouse liver microsomes (0.2-0.3 nmol/min/mg protein). The rate of N-oxidation of MeIQx was 4-fold greater than the rate of N-oxidation of MeIgQx with human liver microsomes (1.7 vs 0.4 nmol/min/mg protein). The rate of N-oxidation, by recombinant human P450 1A2, was comparable for both substrates (6 pmol/min/pmol P450 1A2). MeIgQx also underwent N-oxidation by human P450s 1A1 and 1B1 at appreciable rates, whereas MeIQx was poorly metabolized by these P450s. The potential of MeIgQx and MeIQx to form DNA adducts was assessed in female C57BL/6 mice given [(14)C]-MeIgQx (10 μCi, 9.68 mg/kg body wt) or [(14)C]-MeIQx (10 μCi, 2.13 mg/kg body wt). DNA adduct formation in the liver, pancreas, and colorectum was measured by accelerator mass spectrometry at 4, 24, or 48 h post-treatment. Variable levels of adducts were detected in all organs. The adduct levels were similar for both HAAs, when adjusted for dose, and ranged from 1 to 600 adducts per 10(7) nucleotides per mg/kg dose. Thus, MeIgQx undergoes metabolic activation and binds to DNA at levels that are comparable to MeIQx. Given the high amounts of MeIgQx formed in cooked meats, further investigations are warranted to assess the carcinogenic potential of this HAA.

Tissue specificities of tumor induction by aromatic amines

Certain aryl compounds that have nitrogen substitutions on their ring structures are, following metabolic conversion to reactive derivatives, able to elicit toxic responses by virtue of their modifications of protein and nucleic acid. This group of compounds is often referred to as aromatic amines (AA), although from a structural perspective, compounds that can be converted metabolically to crucial AA derivatives are also capable of producing the same adverse biological effects. These effects include cellular death, mutagenic events and tumor induction. Importantly, in humans, AA can induce tumors in the urinary tract, and possibly other tissues. This contribution addresses the mechanisms by which AA are likely to produce these carcinogenic consequences.

Subchronic thyroid toxicity evaluation of 4,4'-methylenebis(N,N'-dimethyl)aniline in Fischer 344 rats

Female F344 rats were exposed to 4,4'-methylenebis(N,N'-dimethyl)aniline (MDA) by dietary feed at concentrations of 0, 50, 200, 375, 500, or 750 ppm for 5 d, 2 wk, 4 wk, and 13 wk duration. Endpoints evaluated included clinical observations, body weights, thyroid weights, serum thyroid hormones, blood MDA, gross pathology, and thyroid histopathology. There were no MDA exposure-related clinical signs of toxicity. Mean body weight decreased 5% compared to control in the 750 ppm group during study wk 6 through 13. Serum TSH increased and serum T4 and T3 levels decreased with increasing feed concentrations of MDA and time of exposure. Thyroid weight increases were both concentration- and exposure time-dependent and statistically significant at ≥375 ppm. Incidence and severity of decreased colloid, follicular cell hypertrophy and follicular cell hyperplasia were also related to MDA concentration and exposure time. A no-observed-adverse-effect level (NOAEL) of 200 ppm was selected based on the statistically significant increase in incidence of follicular cell hyperplasia at concentrations ≥375 ppm.

Activation and detoxification metabolism of urban air pollutants 2-nitrobenzanthrone and carcinogenic 3-nitrobenzanthrone by rat and mouse hepatic microsomes

OBJECTIVES

2-Nitrobenzanthrone (2-NBA) has recently been detected in ambient air particulate matter. Its isomer 3-nitrobenzanthrone (3-NBA) is a potent mutagen and suspected human carcinogen identified in diesel exhaust. Understanding which enzymes are involved in metabolism of these toxicants is important in the assessment of individual susceptibility. Here, metabolism of 2-NBA and 3-NBA by rat and mouse hepatic microsomes containing cytochromes P450 (CYPs), their reductase (NADPH:CYP reductase), and NADH:cytochrome b5 reductase was investigated under anaerobic and aerobic conditions. In addition, using the same microsomal systems, 2-NBA and 3-NBA were evaluated to be enzymatically activated under anaerobic conditions to species generating 2-NBA- and 3-NBA-derived DNA adducts.

METHODS

High performance liquid chromatography (HPLC) with ultraviolet (UV) detection was employed for the separation and characterization of 2-NBA and 3-NBA metabolites formed by hepatic microsomes of rats and mice under the anaerobic and aerobic conditions. Microsomal systems isolated from the liver of the control (untreated) rats and rats pretreated with Sudan I, β-naphthoflavone (β-NF), phenobarbital (PB), ethanol and pregnenolon 16α-carbonitrile (PCN), the inducers of cytochromes P450 (CYP) 1A1, 1A1/2, 2B, 2E1 and 3A, respectively, were used in this study. Microsomes of mouse models, a control mouse line (wild-type, WT) and Hepatic Cytochrome P450 Reductase Null (HRN) mice with deleted gene of NADPH:CYP reductase in the liver, thus absenting this enzyme in their livers, were also employed. To detect and quantify the 2-NBA- and 3-NBA-derived DNA adducts, the 32P postlabeling technique was used.

RESULTS

Both reductive metabolite of 3-NBA, 3-aminobenzanthrone (3-ABA), found to be formed predominantly under the anaerobic conditions, and two 3-NBA oxidative metabolites, whose structures have not yet been investigated, were formed by several microsomal systems used in the study. Whereas a 3-NBA reductive metabolite, 3-ABA, was found only in the microsomal systems of control rats, the rats treated with β-NF and PB, and microsomes of WT and HRN mice, all hepatic microsomes tested in the study were capable of activating this carcinogen under the reductive conditions to form DNA adducts. A stability of a reactive intermediate of 3-NBA, N-hydroxy-3-aminobenzanthrone that is formed during 3-NBA reduction to 3-ABA, to form nitrenium (and/or carbenium) ions binding to DNA in individual microsomes as well as binding of these ions to proteins of these microsomes, might be the reasons explaining this phenomenon. In contrast to 3-NBA, its isomer 2-NBA was not metabolized by any of the used enzymatic systems both under the anaerobic and aerobic conditions. Likewise, no DNA adducts were detectable after reaction of 2-NBA in these systems with DNA.

CONCLUSIONS

The results found in this study, the first report on the metabolism of 2-NBA and 3-NBA by rat and mouse hepatic microsomes demonstrate that 3-NBA, in contrast to 2-NBA, is reductively activated to form 3-NBA-derived DNA adducts by these enzymatic systems. NADPH:CYP reductase can be responsible for formation of these DNA adducts in rat livers, while NADH:cytochrome b5 reductase can contribute to this process in livers of HRN mice.

Acute treatment with kerosene damages the dermal barrier and alters the distribution of topically applied benzo(a)pyrene in mice

The dermal route is important in many occupational exposures. Some materials may reduce the barrier function of the skin to enhance absorption and effect on internal organs. We have reported previously that kerosene cleaning following treatment with used engine oil increased DNA adduct levels in the lungs of mice compared with animals treated with used oil alone. To investigate what other physiological parameters might be affected by kerosene, we conducted in vitro and in vivo measurements of skin barrier function. We also topically applied (3)H-BAP(100 nM in 25 μL acetone) and washed half the mice with 25 μL kerosene 1 hr after carcinogen application. Groups of four mice were euthanized from 1 to 72 hr after treatment. Skin, lungs, and livers were harvested from each animal and stored separately. Kerosene application reduced the barrier function of the skin in vitro beyond the effect of the acetone vehicle and the vehicle plus BAP. In vivo studies indicated that kerosene treatment reduced the barrier function at 4 and 8 hr post application and that the barrier function recovered at 24 hr after a single treatment. The fraction of the radiolabel remaining in the skin of animals treated with (3)H-BAP and washed with kerosene was significantly less than those not washed, beginning at 24 hr (p< 0.05). Fractional distribution to the lungs and livers of these animals became significantly elevated at this time. Kerosene treatment compromises dermal barrier function and the ability of the skin to retain water, enhances carcinogen absorption, and alters organ distribution. This appears to contribute to the increase in BAP DNA adducts we reported earlier.

[Dependence of carcinogenic properties of benzene derivatives on structure of their substituents adjusted for biotransformation]

An oxenoid model of the effect of cytochrome P450 and quantum chemical calculations were used to study a relationship of the carcinogenic activity of the benzene derivatives C6H5-X and C6H4-XY to the nature of the substituents X and Y For mono- and disubstituted benzenes, the methods based on the neglect of diatomic differential overlap was used to calculate the minimal values of AE for this compound, which is the minimum difference in the complete energies of the arenoxide intermediate OC6-H5-X or OC6H4-XY with one tetraedrically coordinated carbon atom in the benzene ring in reference to the initiar molecule of substituted benzene. The boundary value of the parameter deltaE min' which separated cancerogenic compounds from noncancerogenous ones was determined. A classification for nitrosubstituted benzenes was clarified using the parameter characterizing bioactivation via nitro group reduction to form phenylhydroxylamines and then nitrenic ions.

Nicotine, carbon monoxide, and carcinogen exposure after a single use of a water pipe

BACKGROUND

Smoking tobacco preparations in a water pipe (hookah) is widespread in many places of the world, including the United States, where it is especially popular among young people. Many perceive water pipe smoking to be less hazardous than cigarette smoking. We studied systemic absorption of nicotine, carbon monoxide, and carcinogens from one water pipe smoking session.

METHODS

Sixteen subjects smoked a water pipe on a clinical research ward. Expired carbon monoxide and carboxyhemoglobin were measured, plasma samples were analyzed for nicotine concentrations, and urine samples were analyzed for the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and polycyclic aromatic hydrocarbon (PAH) metabolite biomarker concentrations.

RESULTS

We found substantial increases in plasma nicotine concentrations, comparable to cigarette smoking, and increases in carbon monoxide levels that are much higher than those typically observed from cigarette smoking, as previously published. Urinary excretion of NNAL and PAH biomarkers increased significantly following water pipe smoking.

CONCLUSIONS

Absorption of nicotine in amounts comparable to cigarette smoking indicates a potential for addiction, and absorption of significant amounts of carcinogens raise concerns of cancer risk in people who smoke tobacco products in water pipes.

IMPACT

Our data contribute to an understanding of the health impact of water pipe use.

Influence of mercury bioaccessibility on exposure assessment associated with consumption of cooked predatory fish in Spain

BACKGROUND

Predatory fish tend to accumulate high levels of mercury (Hg). Food safety assessment of these fish has been carried out on the raw product. However, the evaluation of the risk from Hg concentrations in raw fish might be modified if cooking and bioaccessibility (the contaminant fraction that solubilises from its matrix during gastrointestinal digestion and becomes available for intestinal absorption) were taken into account. Data on Hg bioaccessibility in raw predatory fish sold in Spain are scarce and no research on Hg bioaccessibility in cooked fish is available. The aim of the present study was to evaluate Hg bioaccessibility in various kinds of cooked predatory fish sold in Spain to estimate their health risk.

RESULTS

Both Hg and bioaccessible Hg concentrations were analysed in raw and cooked fish (swordfish, tope shark, bonito and tuna). There were no changes in Hg concentrations during cooking. However, Hg bioaccessibility decreased significantly after cooking (42 ± 26% in raw fish and 26 ± 16% in cooked fish), thus reducing in swordfish and tope shark the Hg concentration to which the human organism would be exposed.

CONCLUSION

In future, cooking and bioaccessibility should be considered in risk assessment of Hg concentrations in predatory fish.

Polychlorinated biphenyls: persistent pollutants with immunological, neurological, and endocrinological consequences

Polychlorinated biphenyls (PCBs) are considered "persistent organic pollutants;" fat-soluble compounds that bioaccumulate in individuals and bio-magnify in the food chain. PCBs were the first industrial compounds to experience a worldwide ban on production because of their potent toxicity. These compounds are still present in our food supply (fish, dairy, hamburger, and poultry being the most contaminated) and our bodies. Once in the body, they can cause long-term problems, especially for those exposed in utero. PCB bioaccumulation can lead to reduced infection fighting ability, increased rates of autoimmunity, cognitive and behavioral problems, and hypothyroidism. Some research also links PCBs to increased rates of type 2 diabetes. Testing is currently available for some of the most damaging PCBs. The testing compares individual levels to national reference values and can be interpreted to determine current exposure. Dietary measures can be enacted that will reduce PCB half-lives in humans by increasing excretion.

Human risk assessment of heavy metals: principles and applications

Humans are exposed to a number of "heavy metals" such as cadmium, mercury and its organic form methylmercury, uranium, lead, and other metals as wel as metalloids, such as arsenic, in the environment, workplace, food, and water supply. Exposure to these metals may result in adverse health effects, and national and international health agencies have methodologies to set health-based guidance values with the aim to protect the human population. This chapter introduces the general principles of chemical risk assessment, the common four steps of chemical risk assessment: hazard identification, hazard characterization, exposure assessment, risk characterization, and toxicokinetic and toxicity aspects. Finally, the risk assessments performed by international health agencies such as the World Health Organisation, the Environmental Protection Agency of the United States, and the European Food Safety Authority are reviewed for cadmium, lead, mercury, uranium, and arsenic.

Mixtures and their risk assessment in toxicology

For communities generally and for persons living in the vicinity of waste sites specifically, potential exposures to chemical mixtures are genuine concerns. Such concerns often arise from perceptions of a site's higher than anticipated toxicity due to synergistic interactions among chemicals. This chapter outlines some historical approaches to mixtures risk assessment. It also outlines ATSDR's current approach to toxicity risk assessment. The ATSDR's joint toxicity assessment guidance for chemical mixtures addresses interactions among components of chemical mixtures. The guidance recommends a series of steps that include simple calculations for a systematic analysis of data leading to conclusions regarding any hazards chemical mixtures might pose. These conclusions can, in turn, lead to recommendations such as targeted research to fill data gaps, development of new methods using current science, and health education to raise awareness of residents and health care providers. The chapter also provides examples of future trends in chemical mixtures assessment.