[A clinical performance study of modified CT angiography in detecting bronchial artery-pulmonary artery fistula].

Objective: To evaluate the clinical value of modified computed tomography angiography(CTA) in detecting bronchial artery-pulmonary artery fistula(BPF). Methods: Retrospective analysis was performed on 246 patients with hemoptysis admitted to the First Affiliated Hospital of Wenzhou Medical University from July 2017 to December 2018, who underwent modified CTA and DSA examination at the same time. CT was performed with Toshiba Aquilion one 320 row 640-slice spiral CT scanner. All modified CTA images were read blindly by two radiologists above the attending doctors. The sensitivity, specificity and accuracy of the modified CTA in diagnosing BPF were calculated with the DSA results as the reference,and the consistency of the two tests was analyzed. Results: DSA detected 186 cases of positive and 60 cases of negative, modified CTA detected 160 cases of positive and 86 cases of negative. The sensitivity,specificity and accuracy of modified CTA for BPF diagnosis was 85.5%(159/186),98.3%(59/60), 88.6%(218/246) respectively, and they were with high consistency with DSA examination results (kappa=0.73,P<0.01). Conclusion: Modified CTA has high diagnostic specificity for BPF,which can be used as the preferred method for non-invasive screening of suspected BPF patients.

Characterization and phylogenomics of the complete mitochondrial genome of the polyzoic cestode Gangesia oligonchis (Platyhelminthes: Onchoproteocephalidea).

The order Onchoproteocephalidea (Eucestoda) was recently erected to accommodate the hook-bearing tetraphyllideans and the proteocephalideans, which are characterized by internal proglottization and a tetra-acetabulate scolex. The recognized subfamilies in the Proteocephalidae appeared to be non-monophyletic based on 28S recombinant DNA (rDNA) sequence data. Other molecular markers with higher phylogenetic resolution, such as large mitochondrial DNA fragments and multiple genes, are obviously needed. Thus the mitochondrial genome of Gangesia oligonchis, belonging to the putative earliest diverging group of the Proteocephalidae, was sequenced. The circular mitogenome of G. oligonchis was 13,958 bp in size, and contained the standard 36 genes: 22 transfer RNA genes, two rRNA genes and 12 protein-coding genes, as well as two major non-coding regions. A short NCR and a large NCR (lNCR) region were 216 bp and 419 bp in size, respectively. Highly repetitive regions in the lNCR region were detected with that of 11 repeat units. The mitogenome of G. oligonchis shared 71.1% nucleotide identity with Testudotaenia sp. WL-2016. Phylogenetic analyses of the complete mitochondrial genomes with Bayesian inference and maximum likelihood methods indicated that G. oligonchis formed a sister clade with Testudotaenia sp. WL-2016 with maximum support. The ordinal topology is (Caryophyllidea, (Diphyllobothriidea, (Bothriocephalidea, (Onchoproteocephalidea, Cyclophyllidea)))). The mitogenomic gene arrangement of G. oligonchis was identical to that of Testudotaenia sp. WL-2016. Both mitogenomic and nuclear sequence data for many more taxa are required to effectively explore the inter-relationships among the Onchoproteocephalidea.

Tuning nano-skyrmions and nano-skyrmioniums in Janus magnets.

We study non-trivial spin textures, nanoscale magnetic skyrmions and skyrmioniums, in two-dimensional (2D) Janus magnets, such as MnSTe and MnSeTe, based on the micromagnetism approach and Landau-Lifshitz-Gilbert (LLG) equation. It is found that the Janus magnetic structures can host stable Néel nano-skyrmions with sub-10 nm diameters, and skyrmioniums with zero topological charge. The skyrmion size can be squeezed by external magnetic fields, and even the topological charge can be changed. The diameters of the skyrmioniums are about twice the size of the skyrmions. Moreover, the switching of the topological charge Q = ±1 can be realized by changing the direction of the external magnetic fields. Our results clearly show that magnetic skyrmions in Janus magnets can be used to construct new types of efficient spintronic nanodevices.

Stereoselectivity of rat liver microsomal enzymes in the metabolism of 7-fluorobenz(a)anthracene and mutagenicity of metabolites.

7-Fluorobenz(a)anthracene (7-FBA) was metabolized by rat liver microsomes predominantly to 4-hydroxy-7-FBA and 7-FBA trans-3,4-, 5,6-, 8,9-, and 10,11-dihydrodiols. Proton nuclear magnetic resonance spectral analyses indicated that the fluoro substituent causes 7-FBA trans-5,6- and 8,9-dihydrodiols to adopt preferentially quasidiaxial conformations (Chiu, P.-L., Fu, P. P., and Yang, S. K. Biochem. Biophys. Res. Commun., 106: 1405-1411, 1982). The major enantiomers of the quasidiaxial trans-5,6- and trans-8,9-dihydrodiols have been determined by the exciton chirality method to have R,R absolute stereochemistries. By comparing with the circular dichroism spectra of BA 3R,4R- and 10R,11R-dihydrodiols, the major enantiomers of the quasidiequatorial 7-FBA trans-3,4- and trans-10,11-dihydrodiols were also found to have R,R absolute configurations. All four 7-FBA trans-dihydrodiol metabolites obtained from incubations of 7-FBA with liver microsomes prepared from untreated and 3-methylcholanthrene-, phenobarbital-, and polychlorinated biphenyl-treated male Sprague-Dawley rats were enriched in R,R enantiomers, differing only in optical purities. Pretreatment of rats with phenobarbital, 3-methylcholanthrene, and polychlorinated biphenyls changed the rate of 7-FBA metabolism by 0.47-, 1.14-, and 1.70-fold, respectively. Pretreatment of rats with enzyme inducers also altered the quantitative distribution of metabolites formed. The relative mutagenic activities of metabolites toward Salmonella typhimurium TA 100 were: 7-FBA trans-3,4-dihydrodiol greater than 7-FBA trans-10,11-dihydrodiol greater than 7-methyl-BA approximately equal to 7-FBA greater than 7-FBA trans-8,9-dihydrodiol approximately equal to 7-methyl-BA trans-10,11-dihydrodiol greater than 7-FBA trans-5,6-dihydrodiol approximately equal to 4-hydroxy-7-FBA. The relatively high mutagenic activities of 7-FBA trans-3,4- and trans-10,11-dihydrodiols suggest that both 7-FBA trans-3,4-dihydrodiol 1,2-epoxide(s) and 7-FBA trans-10,11-dihydrodiol 8,9-epoxide(s) may be the major metabolites which contribute to the carcinogenic properties of 7-FBA.

Metabolism of 6-methylbenz[a]anthracene by rat liver microsomes and mutagenicity of metabolites.

6-Methylbenz[a]anthracene (6-MBA) is metabolized by rat liver microsomes to form 3-hydroxy-6-MBA, 4-hydroxy-6-MBA, 5-hydroxy-6-MBA, 6-MBA trans-3,4-, 5,6-, 8,9-, and 10,11-dihydrodiols, and 4-hydroxy-6-MBA trans-10,11-dihydrodiol as the identifiable metabolites. 6-Hydroxymethylbenz[a]anthracene and its phenolic and dihydrodiol metabolites are also formed. The unique metabolites identified in 6-MBA metabolism are 6-MBA trans-5,6-dihydrodiol and 4-hydroxy-6-MBA trans-10,11-dihydrodiol. Metabolites were isolated by reversed-phase and normal-phase high-performance liquid chromatographies and identified by UV-visible absorption, mass, and proton nuclear magnetic resonance spectral analyses. Metabolites formed by low and high concentrations of liver microsomal enzymes from untreated, phenobarbital-treated, and 3-methylcholanthrene-treated male Sprague-Dawley rats were quantified by using [3H]6-MBA, with the tritium labeled at the methyl carbon, and liquid scintillation counting of fractions collected from reversed-phase high-performance liquid chromatography. Metabolic formations of 6-hydroxymethylbenz[a]anthracene, 6-MBA trans-dihydrodiols, and 4-hydroxy-6-MBA trans-10,11-dihydrodiol are highly dependent on the contents of cytochrome P-450 isozymes present in liver microsomes. The relative mutagenic activities of metabolites toward Salmonella typhimurium TA100 are: 6-MBA trans-3,4-dihydrodiol greater than 6-MBA trans-8,9-dihydrodiol greater than 6-MBA greater than 6-MBA trans-10,11-dihydrodiol greater than 4-hydroxy-6-MBA congruent to 4-hydroxy-6-MBA trans-10,11-dihydrodiol. The relatively high mutagenic activities of 6-MBA trans-3,4-dihydrodiol and 6-MBA trans-8,9-dihydrodiol suggest that both 6-MBA trans-3,4-dihydrodiol 1,2-epoxide(s) and 6-MBA trans-8,9-dihydrodiol 10,11-epoxide(s) may be the major metabolites which contribute to the carcinogenic properties of 6-MBA.

Metabolism and DNA binding of 2-nitropyrene in the rat.

2-Nitropyrene (2-NP), a contaminant of ambient air, is a potent bacterial mutagen in the Ames assay and induces leukemia/lymphoma in female Sprague-Dawley rats. To understand the mechanistic basis for its tumorigenic activity, it is essential to elucidate the metabolic pathways of 2-NP in vivo. Such knowledge will also assist in developing analytical methods for monitoring human exposure to nitropolynuclear aromatic hydrocarbons in ambient air. Thus, 2-nitro[U-4,5,9,10-14C]pyrene was synthesized and administered to male F344 rats by intragastric gavage at a dose of 30 mg (0.4 mCi/mM)/kg body weight. During the first 48 h, 57.5% of the dose was eliminated in the feces and 9.7% was eliminated in the urine. Correspondingly, after 168 h, 58.9 and 10.6% were excreted in feces and urine, respectively. Fecal metabolites (isolated amounts) included 6-hydroxy-2-acetylaminopyrene (19.5%), 6-hydroxy-2-aminopyrene (10.4%), 2-aminopyrene (10.0%), 2-acetylaminopyrene (0.8%), and unmetabolized 2-nitropyrene (10.0%). 6-Hydroxy-2-acetylaminopyrene, 6-hydroxy-2-aminopyrene, and 2-aminopyrene were identified as their acetyl derivatives by comparison of their chromatographic retention times, mass spectra, and UV spectra to those of synthetic standards. Urinary metabolites included 6-hydroxy-2-acetylaminopyrene (2.0%); glucuronide conjugates were tentatively identified (3.2%). The results of this study indicate that nitroreduction and ring oxidation are metabolic pathways in vivo. For DNA binding studies, rats were treated with 2-nitro[4,5,9,10-3H]pyrene [1.6 mg (598 mCi/mM)/kg body weight]. The levels of binding (pM bound/mg DNA) were as follows: 1.3, liver; 1.14, mammary tissue; 0.65, lung; 1.67, kidney; and 1.8, bladder. Upon high-performance liquid chromatographic analysis of the DNA hydrolysate (liver, mammary, and kidney), approximately 2.0% of the radioactivity coeluted with the synthetic markers derived from nitroreduction, N-(deoxyguanosin-8-yl)-2-aminopyrene and N-(deoxyadenosin-8-yl)-2-aminopyrene. Thus, simple nitroreduction of 2-NP does not significantly contribute to the total DNA binding of 2-NP metabolites in vivo. The significance of each pathway for the tumorigenic effects of 2-NP remains to be examined.

Molecular structure of the K-region cis-dihydrodiol of 7,12-dimethylbenz[a]anthracene.

The molecular structure and conformation of the cis-5,6-dihydrodiol of 7,12-dimethylbenz[a]anthracene has been determined by an X-ray crystallographic analysis. The compound crystallizes in the space group P21/a with cell dimensions a equals 17.799(6), b equals 33.211(8), c equals 5.241(1) A, beta equals 91.88(2)degrees. There are two molecules, designated A and B in the asymmetrical unit, that are not related to each other by crystallographic symmetry. Their conformations are almost identical, and there are no significant differences in their bond lengths or angles. In both molecules the 5-hydroxyl group is equatorial while the 6-hydroxyl group is axial. This conformation is probably forced by steric hindrance between the hydroxyl group, 0-6, and the hydrogen atoms of the 7-methyl group. The molecules pack in the crystal by forming hydrogen bonds between the hydroxyl groups of adjacent molecules, A with A, B, with B, and A with B. The ring system of the cis-5,6-dihydrodiol is much more buckled than is that in 7,12-dimethylbenz[a]anthracene itself. The angle between the two outermost rings is 36 degrees, the deviation from planarity being primarily a consequence of the partial saturation in the ring containing the two hydroxyl groups. Extrapolation of these results to other dihydrodiol derivatives of carcinogenic hydrocarbons permits some predictions of preferred molecular geometry. Thus, the 8,9-dihydrodiol-10,11-epoxide of 7,12-dimethylbenz]a[anthracene, analogous to the biologically active 7,8-dihydrodiol-9,10-epoxide of benzo]a[pyrene, a mutagen that is believed to be an active intermediate in carcinogenesis by benzo]a[pyrene, should probably exist preferentially in a conformation bearing the8-hydroxyl group in the axial orientation.

Carcinogen-DNA adduct formation in the lungs and livers of preweanling CD-1 male mice following administration of [3H]-6-nitrochrysene, [3H]-6-aminochrysene, and [3H]-1,6-dinitropyrene.

6-Nitrochrysene (NC) and 6-aminochrysene (AC) have been shown to be potent lung and liver carcinogens when administered in multiple i.p. doses to preweanling mice. 1,6-Dinitropyrene has been shown to be a strong hepatocarcinogen but a weak lung carcinogen in this same bioassay. We have examined carcinogen-DNA adduct profiles in the target tissues of preweanling male CD-1 mice following administration of single or multiple doses of these compounds. Depending on the tissue and the dosing schedule, the total level of DNA modification in animals dosed with [3H]NC was 2- to 9-fold higher than in animals dosed with [3H]AC. Regardless of the dosing schedule, DNA isolated from the lungs and livers of both [3H]NC- and [3H]AC-treated preweanling male mice contained a single major and chromatographically identical adduct. This major adduct, which accounted for as much as 90% of the total carcinogen-DNA adducts in enzymatic hydrolysates from treated animals, was chromatographically distinct from the major C8-purine-substituted adducts formed from the reaction of N-hydroxy-AC with calf thymus DNA. In contrast to the results obtained with NC and AC, the major carcinogen-DNA adduct formed in the livers of mice treated with [3H]-1,6-dinitropyrene was found to cochromatograph with 1-N-(deoxyguanosin-8-yl)amino-6-nitropyrene, a product derived from N-hydroxy-1-amino-6-nitropyrene. Since NC and its nitro-reduced derivative, AC, yielded an identical carcinogen-DNA adduct in vivo and this adduct was not derived from N-hydroxy-AC, we conclude that the metabolic activation of NC in the neonatal mouse must involve some previously undescribed combination of ring-oxidation and nitro-reduction pathways. This activation pathway could be an important factor in determining the potency of NC and AC as carcinogens in this bioassay system.

Comparative metabolism of 1-, 2-, and 4-nitropyrene by human hepatic and pulmonary microsomes.

Determining the capability of humans to metabolize the mononitropyrene (mono-NP) isomers 1-, 2-, and 4-NP and understanding which human cytochrome P450 (P450) enzymes are involved in their activation and/or detoxification is important in the assessment of individual susceptibility to these environmental carcinogens. We compared the ability of 15 human hepatic and 8 pulmonary microsomal samples to metabolize each of the three isomers. Human hepatic microsomes were competent in metabolizing all three isomers. Qualitatively similar metabolic patterns were observed, although at much lower levels, upon incubating mono-NP with pulmonary microsomes. Ring-oxidized metabolites (phenols and trans-dihydrodiols) were produced from all three isomers. However, the nitroreductive metabolism leading to the formation of aminopyrene was evident only with 4-NP. The role of specific P450 enzymes in the human hepatic microsomal metabolism of mono-NP was investigated by correlating the P450-dependent catalytic activities in each microsomal sample with the levels of individual metabolites formed by the same microsomes and by examining the effects of agents that can either inhibit or stimulate specific P450 enzymes in mono-NP metabolism. On the basis of these studies, we attribute most of the hepatic microsomal metabolism of 1- and 4-NP to P450 3A4, although a minor role for P450 1A2 cannot be ruled out. Specifically, P450 3A4 was responsible for the formation of 3-hydroxy-1nitropyrene from 1-NP and the formation of trans-9,10-dihydro-9,10dihydroxy-4-nitropyrene, 9(10)-hydroxy-4-nitropyrene, and 4-aminopyrene from 4-NP. None of the P450 enzymes examined (P450s 3A4, 1A2, 2E1, 2A6, 2D6, and 2C9) appeared to be involved in catalyzing the formation of trans-4,5-dihydro-4,5-dihydroxy-2-nitropyrene and 6-hydroxy-2-nitropyrene from 2-NP in human hepatic microsomes. These results, the first report on the comparative metabolism of mono-NP in humans, clearly demonstrate that the role of specific human P450 enzymes in catalyzing oxidative and reductive pathways of mono-NP is dependent upon the position of the nitro group.

Molecular structure of benzo(a)pyrene 4,5-oxide.

An X-ray crystallographic study of benzo(a)pyrene 4,5-oxide, a metabolite of the carcinogen benzo(a)pyrene (BP), as given information on the geometry of this molecule. The carbon skeleton of BP itself has been shown by others to be early planar; the planarity of the carbon skeleton has been shown by this work to be perturbed very little by epoxidation of the 4,5-double bond. Epoxidation has, however, increased the double bond character of C-11--C-12, C-9--C-10, and C-7--C-8. The hydrogen atom on C-3 points directly toward the oxygen atom of another molecule. This C--H... O interaction, although weak, suggests that C-3 might be slightly acidic. An analysis of the experimentally determined bond lengths indicates that, after the highly reactive epoxide ring, the most reactive positions are at C-1, C-6, C-7, C-11, and C-12. The oxide ring of BP, unlike that for the K-region oxide of 7,12-dimethylbenz(a)anthracene, is symmetrical (with C--O distances equivalent within experimental error). The C--O distances are longer than those found in most oxides, including those in 7,12-dimethylbenz(a)anthracene-5,6-oxide. Thus it has been shown that the oxide rings of the K-region oxides of the two potent carcinogens BP and 7,12-dimethylbenz(a)anthracene are not similar in dimensions.

Metabolic activation and carcinogen-DNA adduct detection in human larynx.

Putative carcinogen-DNA adducts in human larynx tissues (n = 25) from smoker and non/ex-smoker patients were examined by 32P-postlabeling and compared with the metabolic activation capacity of larynx microsomes and cytosols from the same tissues. Hydrophobic DNA adducts were evident only in smokers, and chromatographic profiles of the adducts were similar using either the butanol extraction or nuclease P1 enhancement method, which suggested that the adducts may be derived from polycyclic aromatic hydrocarbons but not aromatic amines. Immunoblots of larynx microsomes using anti-cytochrome P450 1A1/1A2, 2C, 3A4, 2E1, and 2A6 antibodies showed intensities ranging from 1-10% of that typically observed with human liver microsomes. Enzymatic assays of larynx microsomes showed appreciable activity for benzo(a)pyrene hydroxylation (P450 1A1 and 2C) but not for 4-aminobiphenyl N-oxidation (P450 1A2), which indicated that the observed immunoreactivity was for P450 1A1; this represents the highest level of this P450 yet detected in human extrahepatic tissues. Accordingly, total DNA adduct levels in the larynx correlated strongly with levels of P450 2C, 1A1, and 3A4 but not with P450 2E1 or 2A6. Larynx cytosols also showed appreciable aromatic amine N-acetyl-transferase activity for p-aminobenzoic acid (NAT-1) but not for sulfamethazine (NAT-2); however, NAT-1 activity was not correlated with total DNA adducts, which is again consistent with the lack of aromatic amine-DNA adducts detected by 32P-postlabeling. Thus, these results suggest that the DNA adducts detected in human larynx are largely derived from metabolic activation of polycyclic aromatic hydrocarbons in cigarette smoke by P450 2C, 3A4, and/or 1A1.

Ultrasensitive UPLC-MS/MS method for analysis of etheno-DNA adducts in human white blood cells.

Etheno-DNA adducts are generated by interaction of cellular DNA with exogenous environmental carcinogens and end products of lipid peroxidation. It has been determined that 1,N(6)-etheno-2'-deoxyadenosine (εdA) and 3,N(4)-etheno-2'-deoxycytidine (εdC) adducts formed in human white blood cells can be used to serve as biomarkers of genetic damage mediated by oxidative stress. In this study, we developed an ultrasensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method used to detect and quantify εdA and dC adducts in human white blood cells. The percent recoveries of εdA and dC adducts were found to be 88.9% ± 2.8 and 95.7% ± 3.7, respectively. The detection limits were ∼ 1.45 fmol for εdA and ∼ 1.27 fmol for εdC in 20 µg of human white blood cell DNA samples, both εdA and εdC adducts could be detected using only ∼ 5 µg of DNA per sample. For validation of the method, 34 human blood cell DNA samples were assayed and the results revealed a significant difference (P < 0.01) between levels (fmol/µg DNA) of 0.82 ± 0.83 (standard deviation [SD]) (range: 0.15-3.11) for εdA, 3.28 ± 3.15 (SD) (range: 0.05-9.6) for εdC in benzene-exposed workers; and 0.04 ± 0.08 (SD) (range: 0.0-0.27) for εdA and 0.77 ± 1.02 (SD) (range: 0.10-4.11) for εdC in non-benzene-exposed workers. Our method shows a high sensitivity and specificity when applied to small amounts of human white blood cell DNA samples; background levels of εdA and εdC could be reproducibly detected. The ultrasensitive and simple detection method is thus suitable for applications in human biomonitoring and molecular epidemiology studies.

Synthesis, spectral analysis, and mutagenicity of 1-, 3-, and 6-nitrobenzo[a]pyrene.

The mutagenic environmental pollutants 1-, 3-, and 6-nitrobenzo[a]pyrene were synthesized. Nitration of 7,8,9,10-tetrahydrobenzo[a]pyrene with sodium nitrate in trifluoroacetic acid and acetic anhydride at ambient temperature gave a mixture of 1-, 3-, and 6-nitro-7,8,9,10-tetrahydrobenzo[a]pyrene, which was separated by chromatography. Dehydrogenation of the isolated nitrotetrahydrobenzo[a]pyrenes with 2,3-dichloro-4,5-dicyano-1,6-benzoquinone produced 1-, 3-, and 6-nitrobenzo[a]pyrene in high yield. Comparison of the spectral data of these compounds with those obtained from direct nitration of benzo[a]pyrene confirmed that 1- and 3-nitrobenzo[a]pyrenes are indeed the minor products of the latter reaction. This confirmation also verifies that 1- and 3-nitrobenzo[a]pyrene were the minor nitrated products of benzo[a]pyrene formed in model air atmospheres. The 1-, 3-, and 6-nitrobenzo[a]pyrene were mutagenic in Salmonella typhimurium tester strains TA98 and TA100 in the presence of a mammalian microsomal (S9) activating system. Both 1- and 3-nitrobenzo[a]pyrene, but not 6-nitrobenzo[a]pyrene, were also direct-acting mutagens in these strains. However, only 6-nitrobenzo[a]pyrene exhibited weak mutagenic activity when tested in Chinese hamster ovary cells, while only 3-nitrobenzo[a]pyrene produced a concentration-dependent decrease in cellular survival.

Comparative carcinogenicity of 4-aminobiphenyl and the food pyrolysates, Glu-P-1, IQ, PhIP, and MeIQx in the neonatal B6C3F1 male mouse.

The tumorigenic activities of four representative heterocyclic amine food pyrolysates, 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), were assessed in the neonatal male B6C3F1 mouse and were compared with that of the potent human carcinogen, 4-amino-biphenyl (4-ABP). These aromatic amines were administered by i.p. injection at two dose levels on days 1, 8, and 15 after birth; and the incidence of tumors was examined at 8 and 12 months. Glu-P-1, IQ, PhIP, MeIQx, and 4-ABP each induced a significant incidence of hepatic adenomas, as compared to the solvent-treated (DMSO) control. Hepatocellular carcinomas were also observed with 4-ABP, SO, and MeIQx. Overall tumorigenicity was in the order: 4-ABP greater than Glu-P-1 greater than IQ approximately PhIP greater than MeIQx greater than DMSO. In the neonatal B6C3F1 mouse, these heterocyclic aromatic amines showed potent tumorigenicity after 8 and 12 months at total doses that were 5-10,000-fold less than those employed in standard chronic bioassays.

Potent tumorigenicity of 7-chlorobenz[a]anthracene and 7-bromobenz[a]anthracene in the neonatal B6C3F (1) male mouse.

The tumorigenicity of 7-chlorobenz[a]anthracene (7-Cl-BA, and environmental contaminant, and 7 bromobenz[a]anthracene (7-Br-BA) was determines in the male B6C3F(1) newborn mouse. Mice receiving 7-Cl-BA and 7-Br-BA by i.p. injections at a dose of 1600 nmol per mouse on 1, 8, and 15 days after birth developed 92 and 96% hepatocellular adenomas, and 100 and 83% hepatocellular carcinoma, respectively. Metabolism by liver microsomes of 15-day-old mice each produced the corresponding trans-3,4-dihydrodiol. Analysis by (32)P-postlabeling/HPLC indicated the presence of DNA adducts derived from 7-Cl-BA trans-3,4-dihydrodiol and 7-Br-BA trans-3,4-dihydrodiol. Our results indicate that both 7-Cl-BA and 7-Br-BA are potent carcinogens and that bay-region diol epoxides are the ultimate metabolites that lead to DNA adduct formation and tumor initiation.

Inhibitory effect of caloric restriction on tumorigenicity induced by 4-aminobiphenyl and 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine (PhIP) in the CD1 newborn mouse bioassay.

The tumorigenicity of 4-aminobiphenyl (4-ABP) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were studied in combination with caloric restriction in the male neonatal CD1 mouse bioassay. 4-ABP and PhIP exhibited moderate and weak tumorigenicity, respectively, in ad libitum fed mice; however, none of the caloric restricted mice developed tumors. These results indicate that caloric restriction, even when begun 3 months after the conclusion of compound treatment, markedly inhibited 4-ABP- and PhIP-induced tumors in the CD1 mouse.

Tumorigenicity and liver tumor ras-protooncogene mutations in CD-1 mice treated neonatally with 1- and 3-nitrobenzo[a]pyrene and their trans-7,8-dihydrodiol and aminobenzo[a]pyrene metabolites.

The environmental pollutants 1- and 3-nitrobenzo[a]pyrene (1- and 3-NBaP) are metabolized by mammalian microsomes through ring oxidation to 1-NBaP trans-7,8-dihydrodiol and 3-NBaP trans-7,8-dihydrodiol, and by nitroreduction to 1- and 3-aminobenzo[a]pyrene. To determine if these compounds are tumorigenic, 1- and 3-NBaP, along with several of their metabolites and the parent benzo[a]pyrene (BaP) and its trans-7,8-dihydrodiol metabolite, were tested in the neonatal CD-1 mouse bioassay. Male mice were administered i.p. injections at a total dose of 100 or 400 nmol per mouse on 1, 8 and 15 days after birth. While the liver tumor incidences for BaP, BaP trans-7,8-dihydrodiol, and the positive control 6-nitrochrysene (6-NC) were significantly higher than in the solvent control animals, all the other tested compounds exhibited no tumorigenicity. The frequency of Ha- and Ki-ras mutations in liver tumors of mice treated with BaP, BaP trans-7,8-dihydrodiol, and 6-NC were higher than in the few liver tumors isolated from control mice or mice treated with the NBaPs or their metabolites. Since 1- and 3-NBaP and their metabolites are potent mutagens in the Salmonella assay and moderate mutagens in the Chinese hamster ovary (CHO) mammalian mutagenicity assay, our results indicate that the in vitro mutagenicity of these compounds does not correlate with their tumorigenicity.

Liver tumors induced in B6C3F1 mice by 7-chlorobenz[a]anthracene and 7-bromobenz[a]anthracene contain K-ras protooncogene mutations.

We previously examined the tumorigenicity of 7-chlorobenz[a]anthracene (7-Cl-BA) and 7-bromobenz[a]anthracene (7-Br-BA) in the neonatal mouse bioassay and found that 7-Cl-BA and 7-Br-BA induced hepatocellular adenoma in 92 and 96% of the mice and hepatocellular carcinoma in 100 and 83% of the mice, respectively. In the present study, mRNA was isolated from each of the liver tumors induced by the two compounds and reverse-transcribed to cDNA. Portions of the K- and H-ras oncogene coding sequences were then amplified and analyzed for DNA sequence alterations. Eighty-three percent (20/24) of 7-Cl-BA-induced and 91% (20/22) of 7-Br-BA-induced liver tumors had activated ras protooncogenes. In contrast to the general finding of H-ras mutations in B6C3F1 mouse liver tumors, both compounds had 95% (19/20) of the mutations located at the first base of K-ras codon 13, resulting in a pattern of GGC --> CGC. Thus, our results demonstrate that 7-Cl-BA and 7-Br-BA induce a unique type of ras (K-ras) oncogene activation in liver tumors of B6C3F1 mice.

Cell and microsome mediated binding of 7,12-dimethylbenz(a)anthracene to DNA studied by fluorescence spectroscopy.

Fluorescence spectra of DNA isolated from hamster embryo cells incubated with 7,12-dimethylbenz(a)anthracene, or DNA modified in a microsomal system by reaction with this carcinogen or its 7-hydroxymethyl derivative, were compared to various model compounds. The spectra indicate that the DMBA derivative bound to DNA, in all 3 cases, has a 9,10-dimethylanthracene-like chromophore. They also provide the first evidence of the similarity in structure of the DNA-bound products between 7,12-dimethylbenz(a)anthracene and its 7-hydroxymethyl derivative. Our results are consistent with an activation mechanism that involves saturation of the 1,2,3,4-ring positions.

Tumorigenicity of nitropolycyclic aromatic hydrocarbons in the neonatal B6C3F1 mouse bioassay and characterization of ras mutations in liver tumors from treated mice.

The nitropolycyclic aromatic hydrocarbons (nitro-PAHs) 1-, 2-, and 3-nitrobenzo[a]pyrene, 1- and 3-nitrobenzo[e]pyrene, 2- and 3-nitrofluoranthene, 9-nitrodibenz[a,c]anthracene, and two of the parent PAHs fluoranthene and dibenz[a,c]anthracene were tested for tumorigenicity in the neonatal male B6C3F1 mouse. 6-Nitrochrysene was used as a positive control. Mice were administered three intraperitoneal injections of test agent (400 nmol total) on 1, 8, and 15 days after birth and evaluated for liver and lung tumors at 12 months of age. 2-Nitrobenzo[a]pyrene and 6-nitrochrysene induced a high incidence of liver tumors (91-100%), while the remaining test compounds did not induce tumors at a rate significantly higher than the solvent control. 6-Nitrochrysene was the only test agent to produce a significant increase in the frequency of lung tumors. K- and H-ras mutations were analyzed in liver tumors of treated mice and mainly occurred at the first base of K-ras codon 13, resulting in GGC --> CGC transversion. Since most of the tested nitro-PAHs are mutagens in vitro, the results of this study indicate that the in vitro mutagenicity of these compounds does not correlate with their tumorigenicity in the neonatal B6C3F1 mouse bioassay. Also, the results indicate that liver tumors from mice treated with nitro-PAHs possess ras mutations typical of PAHs and their derivatives.