Investigação dos efeitos tóxicos, mutagênicos e genotóxicos do herbicida Trifluralina, utilizando Allium cepa e Oreochromis niloticus como sistemas-testes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Otimização, validação e aplicação de método para análise de diuron e seus metabólitos em urina de ratos utilizando SPE e HPLC-DAD

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Desenvolvimento de imunossensores para aflatoxina B1

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influência da fuligem da queima de palha de cana-de-açucar na presença de HPA em hortaliças de consumo humano

Pós-graduação em Química - IQ

Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Modeling, design and experimental characterization of Micro-Electro-Mechanical-Systems for gas chromatographic applications

Design parameters, process flows, electro-thermal-fluidic simulations and experimental characterizations of Micro-Electro-Mechanical-Systems (MEMS) suited for gas-chromatographic (GC) applications are presented and thoroughly described in this thesis, whose topic belongs to the research activities the Institute for Microelectronics and Microsystems (IMM)-Bologna is involved since several years, i.e. the development of micro-systems for chemical analysis, based on silicon micro-machining techniques and able to perform analysis of complex gaseous mixtures, especially in the field of environmental monitoring. In this regard, attention has been focused on the development of micro-fabricated devices to be employed in a portable mini-GC system for the analysis of aromatic Volatile Organic Compounds (VOC) like Benzene, Toluene, Ethyl-benzene and Xylene (BTEX), i.e. chemical compounds which can significantly affect environment and human health because of their demonstrated carcinogenicity (benzene) or toxicity (toluene, xylene) even at parts per billion (ppb) concentrations. The most significant results achieved through the laboratory functional characterization of the mini-GC system have been reported, together with in-field analysis results carried out in a station of the Bologna air monitoring network and compared with those provided by a commercial GC system. The development of more advanced prototypes of micro-fabricated devices specifically suited for FAST-GC have been also presented (silicon capillary columns, Ultra-Low-Power (ULP) Metal OXide (MOX) sensor, Thermal Conductivity Detector (TCD)), together with the technological processes for their fabrication. The experimentally demonstrated very high sensitivity of ULP-MOX sensors to VOCs, coupled with the extremely low power consumption, makes the developed ULP-MOX sensor the most performing metal oxide sensor reported up to now in literature, while preliminary test results proved that the developed silicon capillary columns are capable of performances comparable to those of the best fused silica capillary columns. Finally, the development and the validation of a coupled electro-thermal Finite Element Model suited for both steady-state and transient analysis of the micro-devices has been described, and subsequently implemented with a fluidic part to investigate devices behaviour in presence of a gas flowing with certain volumetric flow rates.

Etablierung eines high content imaging-basierten in vitro Testsystems zur Evaluierung genotoxischer Substanzen

Zur Registrierung von Pharmazeutika ist eine umfassende Analyse ihres genotoxischen Potentials von Nöten. Aufgrund der Vielzahl genotoxischer Mechanismen und deren resultierenden Schäden wird ein gestaffeltes Testdesign durch die ICH-Richtlinie S2(R1) „Guidance on genotoxicity testing and data interpretation for pharmaceuticals intended for human use S2(R1)“ definiert, um alle genotoxischen Substanzen zu identifizieren. Die Standardtestbatterie ist in der frühen Phase der Arzneimittelentwicklung aufgrund des geringen Durchsatzes und des Mangels an verfügbarer Substanzmenge vermindert anwendbar. Darüber hinaus verfügen in vitro Genotoxizitätstests in Säugerzellen über eine relativ geringe Spezifität. Für eine vollständige Sicherheitsbeurteilung wird eine in vivo Testung auf Kanzerogenität benötigt. Allerdings sind diese Testsysteme kosten- und zeitintensiv. Aufgrund dessen zielen neue Forschungsansätze auf die Verbesserung der Prädiktivität und die Erfassung des genotoxischen Potentials bereits in der frühen Phase der Arzneimittelentwicklung ab. Die high content imaging (HCI)-Technologie offeriert einen Ansatz zur Verbesserung des Durchsatzes verglichen mit der Standardtestbatterie. Zusätzlich hat ein Zell-basiertes Modell den Vorteil Daten relativ schnell bei gleichzeitig geringem Bedarf an Substanzmenge zu generieren. Demzufolge ermöglichen HCI-basierte Testsysteme eine Prüfung in der frühen Phase der pharmazeutischen Arzneimittelentwicklung. Das Ziel dieser Studie ist die Entwicklung eines neuen, spezifischen und sensitiven HCI-basierten Testsytems für Genotoxine und Progenotoxine in vitro unter Verwendung von HepG2-Zellen gewesen. Aufgrund ihrer begrenzten metabolischen Kapazität wurde ein kombiniertes System bestehend aus HepG2-Zellen und einem metabolischen Aktivierungssystem zur Testung progenotoxischer Substanzen etabliert. Basierend auf einer vorherigen Genomexpressionsprofilierung (Boehme et al., 2011) und einer Literaturrecherche wurden die folgenden neun unterschiedlichen Proteine der DNA-Schadensantwort als putative Marker der Substanz-induzierten Genotoxizität ausgewählt: p-p53 (Ser15), p21, p-H2AX (Ser139), p-Chk1 (Ser345) p-ATM (Ser1981), p-ATR (Ser428), p-CDC2 (Thr14/Tyr15), GADD45A und p-Chk2 (Thr68). Die Expression bzw. Aktivierung dieser Proteine wurde 48 h nach Behandlung mit den (pro-) genotoxischen Substanzen (Cyclophosphamid, 7,12-Dimethylbenz[a]anthracen, Aflatoxin B1, 2-Acetylaminofluoren, Methylmethansulfonat, Actinomycin D, Etoposid) und den nicht-genotoxischen Substanzen (D-Mannitol, Phenforminhydrochlorid, Progesteron) unter Verwendung der HCI-Technologie ermittelt. Die beste Klassifizierung wurde bei Verwendung der folgenden fünf der ursprünglichen neun putativen Markerproteine erreicht: p-p53 (Ser15), p21, p-H2AX (Ser139), p-Chk1 (Ser345) und p-ATM (Ser1981). In einem zweiten Teil dieser Arbeit wurden die fünf ausgewählten Proteine mit Substanzen, welche von dem European Centre for the Validation of Alternative Methods (ECVAM) zur Beurteilung der Leistung neuer oder modifizierter in vitro Genotoxizitätstests empfohlen sind, getestet. Dieses neue Testsystem erzielte eine Sensitivität von 80 % und eine Spezifität von 86 %, was in einer Prädiktivität von 84 % resultierte. Der synergetische Effekt dieser fünf Proteine ermöglicht die Identifizierung von genotoxischen Substanzen, welche DNA-Schädigungen durch eine Vielzahl von unterschiedlichen Mechanismen induzieren, mit einem hohen Erfolg. Zusammenfassend konnte ein hochprädiktives Prüfungssystem mit metabolischer Aktivierung für ein breites Spektrum potenziell genotoxischer Substanzen generiert werden, welches sich aufgrund des hohen Durchsatzes, des geringen Zeitaufwandes und der geringen Menge benötigter Substanz zur Substanzpriorisierung und -selektion in der Phase der Leitstrukturoptimierung eignet und darüber hinaus mechanistische Hinweise auf die genotoxische Wirkung der Testsubstanz liefert.

Assessment of in vivo genotoxicity of the rodent carcinogen furan: evaluation of DNA damage and induction of micronuclei in mouse splenocytes

In recent years, several surveys have highlighted the presence of the rodent carcinogen furan in a variety of food items. Even though the evidence of carcinogenicity of furan is unequivocal, the underlying mechanism has not been fully elucidated. In particular, the role of genotoxicity in furan carcinogenicity is still not clear, even though this information is considered pivotal for the assessment of the risk posed by the presence of low doses of furan in food. In this work, the genotoxic potential of furan in vivo has been investigated in mice, under exposure conditions similar to those associated with cancer onset in the National Toxicology Program long-term bioassay. To this aim, male B6C3F1 mice were treated by gavage for 4 weeks with 2, 4, 8 and 15 mg furan/kg b.w./day. Spleen was selected as the target organ for genotoxicity assessment, in view of the capability of quiescent splenocytes to accumulate DNA damage induced by repeat dose exposure. The induction of primary DNA damage in splenocytes was evaluated by alkaline single-cell gel electrophoresis (comet assay) and by the immunofluorescence detection of foci of phosphorylated histone H2AX (gamma-H2AX). The presence of cross-links was probed in a modified comet assay, in which cells were irradiated in vitro with gamma-rays before electrophoresis. Chromosome damage was quantitated through the detection of micronuclei in mitogen-stimulated splenocytes using the cytokinesis-block method. Micronucleus induction was also assessed with a modified protocol, using the repair inhibitor 1-beta-arabinofuranosyl-cytosine to convert single-strand breaks in micronuclei. The results obtained show a significant (P < 0.01) increase of gamma-H2AX foci in mitogen-stimulated splenocytes of mice treated with 8 and 15 mg furan/kg b.w. and a statistically significant (P < 0.001) increases of micronuclei in binucleated splenocytes cultured in vitro. Conversely, no effect of in vivo exposure to furan was observed when freshly isolated quiescent splenocytes were analysed by immunofluorescence and in comet assays, both with standard and radiation-modified protocols. These results indicate that the in vivo exposure to furan gives rise to pre-mutagenic DNA damage in resting splenocytes, which remains undetectable until it is converted in frank lesions during the S-phase upon mitogen stimulation. The resulting DNA strand breaks are visualized by the increase in gamma-H2AX foci and may originate micronuclei at the subsequent mitosis.

Oral lichenoid contact lesions induced by areca nut and betel quid chewing: a mini review

Betel quid (BQ) and areca nut chewing is widely prevalent in many parts of Asia and Asian-migrant communities throughout the world. Global reports estimate 600 million users. Sufficient evidence of carcinogenicity has been found for BQ and its main ingredient, areca nut. BQ areca nut users have an increased risk of potentially malignant disorders. Among chewers, BQ remains in contact with the oral mucosa for prolonged periods. This review examines the clinical and pathological aspects of lichenoid lesions caused by areca nut and BQ, a condition that has received little attention in the published literature.

Abnormal expression of REST/NRSF and Myc in neural stem/progenitor cells causes cerebellar tumors by blocking neuronal differentiation.

Medulloblastoma, one of the most malignant brain tumors in children, is thought to arise from undifferentiated neural stem/progenitor cells (NSCs) present in the external granule layer of the cerebellum. However, the mechanism of tumorigenesis remains unknown for the majority of medulloblastomas. In this study, we found that many human medulloblastomas express significantly elevated levels of both myc oncogenes, regulators of neural progenitor proliferation, and REST/NRSF, a transcriptional repressor of neuronal differentiation genes. Previous studies have shown that neither c-Myc nor REST/NRSF alone could cause tumor formation. To determine whether c-Myc and REST/NRSF act together to cause medulloblastomas, we used a previously established cell line derived from external granule layer stem cells transduced with activated c-myc (NSC-M). These immortalized NSCs were able to differentiate into neurons in vitro. In contrast, when the cells were engineered to express a doxycycline-regulated REST/NRSF transgene (NSC-M-R), they no longer underwent terminal neuronal differentiation in vitro. When injected into intracranial locations in mice, the NSC-M cells did not form tumors either in the cerebellum or in the cerebral cortex. In contrast, the NSC-M-R cells did produce tumors in the cerebellum, the site of human medulloblastoma formation, but not when injected into the cerebral cortex. Furthermore, the NSC-M-R tumors were blocked from terminal neuronal differentiation. In addition, countering REST/NRSF function blocked the tumorigenic potential of NSC-M-R cells. To our knowledge, this is the first study in which abnormal expression of a sequence-specific DNA-binding transcriptional repressor has been shown to contribute directly to brain tumor formation. Our findings indicate that abnormal expression of REST/NRSF and Myc in NSCs causes cerebellum-specific tumors by blocking neuronal differentiation and thus maintaining the "stemness" of these cells. Furthermore, these results suggest that such a mechanism plays a role in the formation of human medulloblastoma.

Studies of the mechanism of daunorubicin carcinogenesis: Modulation by vitamin E

Daunorubicin (DNR) is an anthracycline antibiotic used as a cancer chemotherapeutic agent. However, it causes mammary adenocarcinomas in female Sprague-Dawley (SD) rats. Vitamin E (E) has been found to reduce DNR carcinogenicity. I investigated the mechanism of DNR carcinogenicity and its interaction with E in SD rats by studying DNR-DNA adduct formation and the influence of E status on DNR clearance and free radical producing and detoxifying enzymes.^ The hypothesis was that DNR exerts its tumorigenic effect via free radicals generated during redox cycling and production of reactive intermediates capable of forming DNA adducts. E was postulated to act as a protective agent through a combination of its antioxidant property, modulation of drug clearance and levels of free radical producing and detoxifying enzymes.^ DNA adduct formation was measured by the nuclease P1 $\sp{32}$P-post labeling assay. In vitro, DNR was activated by rat liver microsomes and either NADPH or cumene hydrogen peroxide (CuOOH). Rat liver DNA incubated with this mixture formed two adducts when the cofactor was NADPH and three adducts when CuOOH was used. In vivo, SD rats were treated with i.v. doses of DNR. No detectable DNR-DNA adducts were formed in liver or mammary DNA in vivo, although there was an intensification of endogenous DNA adducts.^ Groups, 1, 2, 3 and 4 of weanling female SD rats were fed 0, 100, 1,000 and 10,000 mg $\alpha$-tocopheryl acetate/kg diet respectively. A comparison of Groups 1 and 4 showed no effect of E status on clearance of 10 mg tritiated DNR/kg body weight over 72 hours. However, liver cleared DNR at a faster rate than mammary epithelial cells (MEC).^ Xanthine oxidase, which catalyzes DNR redox cycling, was significantly decreased in liver and MEC of rats in group 4 compared to groups 1, 2, and 3. Detoxifying enzymes were not dramatically affected by E supplementation. Quinone reductase in MEC was significantly increased in group 4 compared to other groups. Overall, the liver had higher levels of free radical detoxifying enzymes compared to MEC.^ These data support a role of free radicals in DNR carcinogenicity because (1) endogenous DNA adducts formed due to free radical insult are further intensified by DNR treatment in vivo, (2) MEC, the specific target of DNR carcinogenicity, cannot rapidly clear DNR and have a lower free radical detoxifying capability than liver, (3) E supplementation caused lowering of free radical generating potential via xanthine oxidase, and increased DNR detoxification due to elevation of quinone reductase in MEC. ^

AN ANALYSIS OF THE DNA DAMAGE INDUCED BY NICKEL COMPOUNDS IN CHINESE HAMSTER OVARY CELLS (CARCINOGENESIS, HETEROCHROMATIN, CYTOTOXICITY, REPLICATION, PROTEIN CROSSLINKING)

The carcinogenic activity of water-insoluble crystalline nickel sulfide requires phagocytosis and lysosome-mediated intracellular dissolution of the particles to yield Ni('2+). This study investigated the extent and nature of the DNA damage in Chinese hamster ovary cells treated with various nickel compounds using the technique of alkaline elution. Crystalline NiS and water-soluble NiCl(,2) induced single strand breaks that were repaired quickly and DNA-protein crosslinks that persisted up to 24 hr after exposure to nickel. The induction of single strand breaks was concentration dependent at both noncytotoxic and lethal amounts of nickel. The induction of DNA-protein crosslinks was concentration dependent but was absent at lethal amounts of nickel. The cytoplasmic and nuclear uptake of nickel was concentration dependent even at the toxic level of nickel. However, the induction of DNA-protein crosslinks by nickel required active cell cycling and occurred predominantly in mid-late S phase of the cell cycle, suggesting that the lethal amounts of nickel inhibited DNA-protein crosslinking by inhibiting active cell cycling. Since the DNA-protein crosslinking induced by nickel was resistant to DNA repair, the nature of this lesion was investigated using various methods of DNA isolation and chromatin fractionation in combination with SDS-polyacrylamide gel electrophoresis. High molecular weight, non-histone chromosomal proteins and possibly histone 1 were preferentially crosslinked to DNA by nickel. The crosslinked proteins were concentrated in a magnesium-insoluble fraction of sonicated chromatin (5% of the total) that was similar to heterochromatin in solubility and protein composition. Alterations in DNA structure and function, brought about by the effect of nickel on protein-DNA interactions, may be related to the carcinogenicity of nickel compounds. ^

Secondary malignancies in chronic myeloid leukemia patients after imatinib-based treatment: long-term observation in CML Study IV.

Treatment of chronic myeloid leukemia (CML) has been profoundly improved by the introduction of tyrosine kinase inhibitors (TKIs). Long-term survival with imatinib is excellent with a 8-year survival rate of ∼88%. Long-term toxicity of TKI treatment, especially carcinogenicity, has become a concern. We analyzed data of the CML study IV for the development of secondary malignancies. In total, 67 secondary malignancies were found in 64 of 1525 CML patients in chronic phase treated with TKI (n=61) and interferon-α only (n=3). The most common malignancies (n⩾4) were prostate, colorectal and lung cancer, non-Hodgkin's lymphoma (NHL), malignant melanoma, non-melanoma skin tumors and breast cancer. The standardized incidence ratio (SIR) for all malignancies excluding non-melanoma skin tumors was 0.88 (95% confidence interval (0.63-1.20)) for men and 1.06 (95% CI 0.69-1.55) for women. SIRs were between 0.49 (95% CI 0.13-1.34) for colorectal cancer in men and 4.29 (95% CI 1.09-11.66) for NHL in women. The SIR for NHL was significantly increased for men and women. An increase in the incidence of secondary malignancies could not be ascertained. The increased SIR for NHL has to be considered and long-term follow-up of CML patients is warranted, as the rate of secondary malignancies may increase over time.Leukemia advance online publication, 26 February 2016; doi:10.1038/leu.2016.20.

Mutagenicity study of the urinary metabolites of 2-aminonaphthalene

The mutagenicity study of the urinary metabolites of 2-aminonaphthalene was conducted to determine whether differences in metabolism between different acetylator phenotypes could account for a proposed mechanism of bladder carcinogenesis. This required the use of fast and slow acetylator rabbits with phenotypic similarities to humans. In the absence of available slow acetylators, it was necessary to inhibit fast acetylators. The proposed mechanism was that slow acetylators were at greater potential risk of bladder carcinogenesis due to low rates of acetylation, a detoxification mechanism for certain aromatic amines. The alternate metabolic pathway will be hydroxylation. The fast acetylators were proposed to exhibit lower risk of bladder carcinogenicity as a result of higher acetylation rates and less mutagenic metabolites.^ This hypothesis was approached by determining from in vitro mutagenicity assays with Salmonella typhimurium strains TA98 and TA100 whether different metabolites were mutagenic. The acetylation rate of each rabbit and a suitable method of acetylation inhibition were determined through oral exposure to dapsone and the acetylation inhibitor, K-p-aminosalicylic acid. Residues of dapsone and its acetylated metabolite were extracted from blood samples and analyzed by ultra-violet spectrometry using standard curves for each metabolite. The urine samples were concentrated on XAD-2 resin and analyzed both as whole urine concentrates and as isolated metabolites from spots on high performance thin layer chromatography plates. The major isolated spots were identified and quantified through extraction and analysis by high performance liquid chromatography when possible.^ Acetylation rate determination and inhibition were successfully demonstrated in rabbits. Significant mutagenicity was noted for several critical metabolites. None of the mutagenic metabolites were detected in higher concentration in the inhibited acetylators and thus, no clear relationship of metabolite concentration to bladder carcinogenesis was evident for the compounds analyzed. There was some evidence that the inhibitor may have affected critical enzyme systems other than acetylation alone. This would account for the lower concentrations of mutagenic hydroxylated compounds observed. ^

Cytochrome P450 CYP1B1 determines susceptibility to 7,12-dimethylbenz[a]anthracene-induced lymphomas

CYP1B1-null mice, created by targeted gene disruption in embryonic stem cells, were born at the expected frequency from heterozygous matings with no observable phenotype, thus establishing that CYP1B1 is not required for mouse development. CYP1B1 was not detectable in cultured embryonic fibroblast (EF) or in different tissues, such as lung, of the CYP1B1-null mouse treated with the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin whereas the equivalent wild-type EF cells express basal and substantial inducible CYP1B1 and lung expresses inducible CYP1B1. CYP1A1 is induced to far higher levels than CYP1B1 in liver, kidney, and lung in wild-type mice and is induced to a similar extent in CYP1B1-null mice. 7,12-dimethylbenz[a]anthracene (DMBA) was toxic in wild-type EFs that express CYP1B1 but not CYP1A1. These cells effectively metabolized DMBA, consistent with CYP1B1 involvement in producing the procarcinogenic 3,4-dihydrodiol as a major metabolite, whereas CYP1B1-null EF showed no significant metabolism and were resistant to DMBA-mediated toxicity. When wild-type mice were administered high levels of DMBA intragastrically, 70% developed highly malignant lymphomas whereas only 7.5% of CYP1B1-null mice had lymphomas. Skin hyperplasia and tumors were also more frequent in wild-type mice. These results establish that CYP1B1, located exclusively at extrahepatic sites, mediates the carcinogenicity of DMBA. Surprisingly, CYP1A1, which has a high rate of DMBA metabolism in vitro, is not sufficient for this carcinogenesis, which demonstrates the importance of extrahepatic P450s in determining susceptibility to chemical carcinogens and validates the search for associations between P450 expression and cancer risk in humans.