Metabolism of carcinogenic urethane to nitric oxide is involved in oxidative DNA damage

Structure-guided engineered urethanase from Candida parapsilosis with pH and ethanol tolerance to efficiently degrade ethyl carbamate in Chinese rice wine

Urethane hydrolase can degrade the carcinogen ethyl carbamate (EC) in fermented food, but its stability and activity limit its application. In this study, a mutant G246A and a double mutant N194V/G246A with improved cpUH activity and stability of Candida parapsilosis were obtained by site-directed mutagenesis. The catalytic efficiency (Kcat/Km) of mutant G246A and double mutant N194V/G246A are 1.95 times and 1.88 times higher than that of WT, respectively. In addition, compared with WT, the thermal stability and pH stability of mutant G246A and double mutant N194V/G246A were enhanced. The ability of mutant G246A and double mutant N194V/G246A to degrade EC in rice wine was also stronger than that of WT. The mutation increased the stability of the enzyme, as evidenced by decreased root mean square deviation (RMSD) and increased hydrogen bonds between the enzyme and substrate by molecular dynamics simulation and molecular docking analysis. The molecule modification of new cpUH promotes the industrial process of EC degradation.

A Nationwide Survey and Risk Assessment of Ethyl Carbamate Exposure Due to Daily Intake of Alcoholic Beverages in the Chinese General Population

Ethyl carbamate (EC) is carcinogenic, and, in China, oral intake of EC mainly occurs as a result of the consumption of alcoholic beverages. To obtain the latest EC intake and risk analysis results for the general population in China, the China National Center for Food Safety Risk Assessment (CFSA) conducted the sixth total diet study (TDS) as a platform to analyze EC contents and exposure due to the intake of alcoholic beverages. A total of 100 sites in 24 provinces were involved in the collection and preparation of alcohol mixture samples for the sixth TDS. There were 261 different types of alcohol collected across the country, based on local dietary menus and consumption survey results. Ultimately, each province prepared a mixed sample by mixing their respective samples according to the percentage of local consumption. The EC levels of these twenty-four mixed samples were determined using our well-validated gas chromatography-mass spectrometry (GC-MS) method. The values ranged from 1.0 μg/kg to 33.8 μg/kg, with 10.1 μg/kg being the mean. China's EC daily intake ranged from 0.001 ng/kg bw/d to 24.56 ng/kg bw/d, with a mean of 3.23 ng/kg bw/d. According to the margin of exposure (MOE), virtually safe dose (VSD), and T25 risk assessments of the carcinogenicity of EC, the mean lifetime cancer risk for the Chinese population was 9.8 × 104, 1.5 × 10-7, and 8.6 × 10-8, respectively. These data show that the carcinogenicity of EC in the general Chinese population due to alcoholic intake is essentially minimal.

The Screening and Isolation of Ethyl-Carbamate-Degrading Strains from Fermented Grains and Their Application in the Degradation of Ethyl Carbamate in Chinese Baijiu

Ethyl carbamate (EC), a 2A carcinogen produced during the fermentation of foods and beverages, primarily occurs in distilled spirits. Currently, most studies focus on strategies for EC mitigation. In the present research, we aimed to screen strains that can degrade EC directly. Here, we report two Candida ethanolica strains (J1 and J116), isolated from fermented grains, which can reduce EC concentrations directly. These two yeasts were grown using EC as the sole carbon source, and they grew well on different carbon sources. Notably, after immobilization with chitosan, the two strains degraded EC in Chinese Baijiu by 42.27% and 27.91% in 24 h (from 253.03 ± 9.89 to 146.07 ± 1.67 and 182.42 ± 5.05 μg/L, respectively), which was better than the performance of the non-immobilized strains. Furthermore, the volatile organic compound content, investigated using gas chromatography-mass spectrometry, did not affect the main flavor substances in Chinese Baijiu. Thus, the yeasts J1 and J116 may be potentially used for the treatment and commercialization of Chinese Baijiu.

Improving ethanol tolerance of ethyl carbamate hydrolase by diphasic high pressure molecular dynamic simulations

Ethyl carbamate (EC) is mainly found in fermented foods and fermented alcoholic beverages, which could cause carcinogenic potential to humans. Reducing EC is one of the key research priorities to address security of fermented foods. Enzymatic degradation of EC with EC hydrolase in food is the most reliable and efficient method. However, poor tolerance to ethanol severely hinders application of EC hydrolase. In this study, the mutants of EC hydrolase were screened by diphasic high pressure molecular dynamic simulations (dHP-MD). The best variant with remarkable improvement in specific activity and was H68A/K70R/S325N, whose specific activity was approximately 3.42-fold higher than WT, and relative enzyme activity under 20% (v/v) was 5.02-fold higher than WT. Moreover, the triple mutant increased its stability by acquiring more hydration shell and forming extra hydrogen bonds. Furthermore, the ability of degrading EC of the immobilized triple mutant was both detected in mock wine and under certain reaction conditions. The stability of immobilized triple mutant and WT were both improved, and immobilized triple mutant degraded nearly twice as much EC as that of immobilized WT. Overall, dHP-MD was proved to effectively improve enzyme activity and ethanol tolerance for extent application at industrial scale.

The effect of Moringa oleifera leaf extracts against urethane-induced lung cancer in rat model

Lung cancer is one of the most common malignancies in the world, and chemotherapy can have unfavorable side effects. The aim of the present study is to evaluate the therapeutic anticancer role of Moringa oleifera leaf extracts (MLE) in urethane-induced lung cancer in adult male albino rats as compared to standard chemotherapy. Rats were categorized into four groups (10 rats/group), including negative control rats, urethane lung cancer model rats, MLE-treated lung cancer rats, and cisplatin-treated rats. Estimation of lung index, some biochemical markers of oxidative stress, quantitative real-time polymerase chain reaction (qRT-PCR), and histopathology and transmission electron microscopy were performed. The lung index was significantly increased about one-fold in urethane lung cancer model rats, but it decreased after MLE treatment. Also, MLE was able to improve the induced changes in glutathione, superoxide dismutase, and malondialdehyde concentration to be 3.8 ± 0.4 mg/g, 900.6 ± 58 U/g, and 172 ± 24 nmol/g, respectively. Additionally, after MLE treatment, the expression of EGFR-mRNA increased by about 50%. Our light and electron microscopic examination revealed that urethane group showed abnormally distributed excessive collagen fibers and the development of papillary adenocarcinoma from hyperplastic Clara cells in the lumen of terminal bronchiole with bronchiolar wall thickening, alveolar collapse, and inflammation. MLE group has moderate amount of collagen fiber and absence of tumor mass and provided more or less restoration of normal lung histology. Moreover, MLE was able to ameliorate the induced changes in mucin and PCNA positive cells in the lung by 10.8 ± 2.3%. Collectively, the current study showed that MLE could be used as anticancer agents alleviating changes associated with lung cancer in a urethane-induced lung cancer bearing rats thereby representing alternative options to toxic chemotherapy.

Assessing cytochrome P450 function using genetically engineered mouse models

The ability to knock out and/or humanize different genes in experimental animals, globally or in cell- and tissue-specific patterns, has revolutionized scientific research in many areas. Genetically engineered mouse models, including knockout models, transgenic models, and humanized models, have played important roles in revealing the in vivo functions of various cytochrome P450 (CYP) enzymes. These functions are very diverse, ranging from the biotransformation of drugs and other xenobiotics, events that often dictate their pharmacokinetic or toxicokinetic properties and the associated therapeutic or adverse actions, to the metabolism of endogenous compounds, such as steroid hormones and other bioactive substances, that may determine susceptibility to many diseases, such as cancer and metabolic diseases. In this review, we provide a comprehensive list of Cyp-knockout, human CYP-transgenic, and CYP-humanized mouse models that target genes in the CYP1-4 gene families, and highlight their utility in assessing the in vivo metabolism, bioactivation, and toxicity of various xenobiotic compounds, including therapeutic agents and chemical carcinogens. We aim to showcase the advantages of utilizing these mouse models for in vivo drug metabolism and toxicology studies, and to encourage and facilitate greater utility of engineered mouse models to further improve our knowledge of the in vivo functions of various P450 enzymes, which is integral to our ability to develop safer and more effective therapeutics and to identify individuals predisposed to adverse drug reactions or environmental diseases.

Ethyl carbamate in Chinese liquor (Baijiu): presence, analysis, formation, and control

Ethyl carbamate (EC) is a genotoxic and carcinogenic compound that is also a by-product of fermented foods (bread, sour milk, soy cheese, etc.) and alcoholic beverages (wine, sake, distilled liquor, etc.). Studies have showed that ethyl carbamate is ingested by humans primarily through the consumption of alcoholic beverages. Many countries have thus established EC limits for alcoholic beverages. Chinese liquor (Baijiu) is a traditional and unique distilled liquor, which has a huge consumption in China due to its excellent color, flavor, and taste. Therefore, the control of EC in Chinese liquor is of great significance. This review summarized for the first time the progress in presence level, analysis method, formation mechanism, and elimination strategy of EC of Chinese liquor in recent decades. KEY POINTS: • GC-MS and HPLC are the main methods to quantify EC in Chinese liquor. • EC is formed in the fermentation, distillation, and storage stage. • EC content can be reduced from raw material, microorganism, and production process.

Bifenthrin induces DNA damage and autophagy in Spodoptera frugiperda (Sf9) insect cells

Bifenthrin is one of the most commonly used synthetic pyrethroid insecticides. It targets the nervous system of insects, mainly acting on sodium channels in nerve cell membranes. The high use of bifrenthrin may lead to an increase in pest insect resistance. Additionally, there are only a few studies describing its cytotoxic action. A series of bioassays were carried out, and the results showed that bifenthrin has a significant ability to induce DNA damage and the inhibition of viability in Spodoptera frugiperda (Sf9) cells. Monodansylcadaverine staining and transmission electron microscope assays were used to observe significant levels of autophagosomes and mitochondrial dysfunction in the cytoplasm. Additionally, western blot analysis showed an upregulation in LC3-II and beclin-1 protein expression and a downregulation in p62 expression, which contributed to the cytotoxic effect of bifenthrin on Sf9 cells. Overall, bifenthrin significantly impacts the viability of Sf9 cells by inducing DNA damage and autophagy. These results provide a theoretical basis for understanding bifrenthin's mechanism of cytotoxicity.

Renal Transcriptomics Reveals the Carcinogenic Mechanism of Ethyl Carbamate in Musalais

INTRODUCTION

Musalais is a traditional fermented wine produced in southern Xinjiang (a province of China) and is protected as a form of national intangible cultural heritage. However, ethyl carbamate (EC), which is naturally produced during the fermentation process, has been shown to induce carcinogenesis and was classified as a group 2A carcinogen by The World Health Organization's International Agency for Research on Cancer.

METHODS

In this work, rats were treated with musalais containing EC at varying contents (0.1, 1, or 10 mg/kg). To evaluate the toxicity of EC in musalais, the liver and kidney of the rats were subjected to transcriptomics sequencing. Differentially expressed genes (DEGs) between treated and untreated rats were identified, and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were performed on these genes to investigate the biological functions affected by EC in musalais.

RESULTS

The results demonstrated that high EC content in musalais is possibly involved in the regulation of cytochrome P450 metabolism, chemical carcinogenesis, metabolism of xenobiotics by cytochrome P450, Wnt signaling, and p53 signaling by targeting Mgst1, Gstp1, Gsta5, Gsta1, Adh1, Gsta2, and Ccnd1, thereby inducing cancer.

CONCLUSION

The present work predicted the potential carcinogenic mechanism of high EC content in musalais, providing a reference for its safety evaluation.

Linalool acts as a fast and reversible anesthetic in Hydra

The ability to make transgenic Hydra lines has allowed for quantitative in vivo studies of Hydra regeneration and physiology. These studies commonly include excision, grafting and transplantation experiments along with high-resolution imaging of live animals, which can be challenging due to the animal’s response to touch and light stimuli. While various anesthetics have been used in Hydra studies, they tend to be toxic over the course of a few hours or their long-term effects on animal health are unknown. Here, we show that the monoterpenoid alcohol linalool is a useful anesthetic for Hydra. Linalool is easy to use, non-toxic, fast acting, and reversible. It has no detectable long-term effects on cell viability or cell proliferation. We demonstrate that the same animal can be immobilized in linalool multiple times at intervals of several hours for repeated imaging over 2–3 days. This uniquely allows for in vivo imaging of dynamic processes such as head regeneration. We directly compare linalool to currently used anesthetics and show its superior performance. Linalool will be a useful tool for tissue manipulation and imaging in Hydra research in both research and teaching contexts.

XPC protects against smoking- and carcinogen-induced lung adenocarcinoma

Cigarette smoke (CS) contains hundreds of carcinogens and is a potent inducer of oxidative and bulky DNA damage, which when insufficiently repaired leads to activation of DNA damage response and possibly mutations. The DNA repair protein xeroderma pigmentosum group C (XPC) is primed to play an important role in CS-induced DNA damage because of its function in initiating repair of both bulky oxidative DNA damage. We hypothesized that loss of XPC function will increase susceptibility to developing CS- and carcinogen-induced lung cancer through impaired repair of oxidative DNA damage. Mice deficient in XPC (XPC-/-) exposed to chronic CS developed lung tumors whereas their wild-type littermates (XPC+/+) did not. XPC-/- mice treated with the CS-carcinogen urethane developed lung adenocarcinomas representing progressive stages of tumor development, with lung tumor number increased 17-fold compared with XPC+/+ mice. Mice heterozygous for XPC (XPC+/-) demonstrated a gene-dose effect, developing an intermediate number of lung tumors with urethane treatment. Treatment of XPC-/- mice with the carcinogen 3-methylcholanthrene followed by the proliferative agent butylated hydroxytoluene resulted in a 2-fold increase in lung adenocarcinoma development. Finally, tumor number decreased 7-fold in the lungs of XPC-/- mice by concurrent treatment with the antioxidant, N-acetylcysteine. Altogether, this supports a mechanism by which decreased XPC expression promotes lung adenocarcinoma development in response to CS-carcinogen exposure, due in part to impaired oxidative DNA damage repair.

The Management of Compounds that Influence Human Health in Modern Winemaking from an HACCP Point of View

The undesirable effects of some hazardous compounds involved in the different steps of the winemaking process may pose health risks to consumers; hence, the importance of compliance with recent international food safety standards, including the Hazard Analysis and Critical Control Point (HACCP) standards. In recent years, there has been a rise in the development of new technologies in response to the hazardous effects of chemical compounds detected during the winemaking process, whether naturally produced or added during different winemaking processes. The main purpose was to reduce the levels of some compounds, such as biogenic amines, ethyl carbamate, ochratoxin A, and sulfur dioxide. These technological advances are currently considered a necessity, because they produce wines free of health-hazardous compounds and, most importantly, help in the management and prevention of health risks. This review shows how to prevent and control the most common potential health risks of wine using a HACCP methodology.

Simultaneous determination of ethyl carbamate and urea in Korean rice wine by ultra-performance liquid chromatography coupled with mass spectrometric detection

In this study, a rapid method for simultaneous detection of ethyl carbamate (EC) and urea in Korean rice wine was developed. To achieve quantitative analysis of EC and urea, the conditions for Ultra-performance liquid chromatography (UPLC) separation and atmospheric-pressure chemical ionization tandem mass spectrometry (APCI-MS/MS) detection were first optimized. Under the established conditions, the detection limit, relative standard deviation and linear range were 2.83μg/L, 3.75-5.96%, and 0.01-10.0mg/L, respectively, for urea; the corresponding values were 0.17μg/L, 1.06-4.01%, and 1.0-50.0μg/L, respectively, for EC. The correlation between the contents of EC and its precursor urea was determined under specific pH (3.5 and 4.5) and temperature (4, 25, and 50°C) conditions using the developed method. As a result, EC content was increased with greater temperature and lower pH. In Korean rice wine, urea was detected 0.19-1.37mg/L and EC was detected 2.0-7.7μg/L. The method developed in this study, which has the advantages of simplified sample preparation, low detection limits, and good selectivity, was successfully applied for the rapid analysis of EC and urea.

β-d-Glucosidase as "key enzyme" for sorghum cyanogenic glucoside (dhurrin) removal and beer bioflavouring

Sorghum malt used during African beer processing contains a high level of cyanogenic glucoside (dhurrin), up to 1375 ppm. In traditional sorghum malting and mashing, dhurrin is not sufficiently hydrolyzed due to uncontrolled germination and a high gelatinization temperature. The cyanide content of traditional African beers (11 ppm) is higher than the minimum dose (1 ppm) required to form carcinogenic ethyl carbamate during alcoholic fermentation. In the detoxification process, aryl-β-d-glucosidase (dhurrinase) is the "key component". For significant dhurrin hydrolysis during mashing, optimizing dhurrinase synthesis during malting is a good solution to reduce dhurrin completely to below the harmful dose in the sorghum wort. Lactic acid bacteria which exhibit aryl-β-d-glucosidase prior to alcoholic fermentation may help to reduce ethyl carbamate content in alcoholic beverages. Moreover, some specific β-d-glucosidases have a dual property, being able to cleave and synthesize glucosides bonds and thereby generating good precursors for beer bioflavouring.

Reduced production of ethyl carbamate for wine fermentation by deleting CAR1 in Saccharomyces cerevisiae

Ethyl carbamate (EC), a pluripotent carcinogen, is mainly formed by a spontaneous chemical reaction of ethanol with urea in wine. The arginine, one of the major amino acids in grape musts, is metabolized by arginase (encoded by CAR1) to ornithine and urea. To reduce the production of urea and EC, an arginase-deficient recombinant strain YZ22 (Δcarl/Δcarl) was constructed from a diploid wine yeast, WY1, by successive deletion of two CAR1 alleles to block the pathway of urea production. The RT-qPCR results indicated that the YZ22 almost did not express CAR1 gene and the specific arginase activity of strain YZ22 was 12.64 times lower than that of parent strain WY1. The fermentation results showed that the content of urea and EC in wine decreased by 77.89 and 73.78 %, respectively. Furthermore, EC was forming in a much lower speed with the lower urea during wine storage. Moreover, the two CAR1 allele deletion strain YZ22 was substantially equivalent to parental strain in terms of growth and fermentation characteristics. Our research also suggested that EC in wine originates mainly from urea that is produced by the arginine.

Intraperitoneal co-administration of low dose urethane with xylazine and ketamine for extended duration of surgical anesthesia in rats

Procedures involving complex surgical techniques in rats, such as placement of abdominal aortic graft require extended duration of surgical anesthesia, which often can be achieved by repeated administrations of xylazine-ketamine combination. However such repeated anesthetic administration, in addition to being technically challenging, may be associated with potential adverse events due to cumulative effects of anesthesia. We report here the feasibility of using urethane at low dose (~1/10 the recommended anesthetic dose) in combination with a xylazine-ketamine mix to achieve an extended duration of surgical anesthesia in rats. The anesthesia induction phase was quick and smooth with an optimal phase of surgical anesthesia achieved for up to 90 minutes, which was significantly higher compared to that achieved with use of only xylazine-ketamine combination. The rectal temperature, heart rate and respiratory rate were within the physiological range with an uneventful recovery phase. Post surgery the rats were followed up to 3 months without any evidence of tumor or any other adverse effects related to the use of the urethane anesthetic combination. We conclude that low dose urethane can be effectively used in combination with xylazine and ketamine to achieve extended duration of surgical anesthesia up to 90 minutes in rats.

Caryocar brasiliense camb protects against genomic and oxidative damage in urethane-induced lung carcinogenesis

The antioxidant effects of Caryocar brasiliense Camb, commonly known as the pequi fruit, have not been evaluated to determine their protective effects against oxidative damage in lung carcinogenesis. In the present study, we evaluated the role of pequi fruit against urethane-induced DNA damage and oxidative stress in forty 8-12 week old male BALB/C mice. An in vivo comet assay was performed to assess DNA damage in lung tissues and changes in lipid peroxidation and redox cycle antioxidants were monitored for oxidative stress. Prior supplementation with pequi oil or its extract (15 µL, 60 days) significantly reduced urethane-induced oxidative stress. A protective effect against DNA damage was associated with the modulation of lipid peroxidation and low protein and gene expression of nitric oxide synthase. These findings suggest that the intake of pequi fruit might protect against in vivo genotoxicity and oxidative stress.

Decreased tumorigenesis in mice with a Kras point mutation at C118

KRAS, NRAS, or HRAS genes are mutated to encode an active oncogenic protein in a quarter of human cancers. Redox-dependent reactions can also lead to Ras activation in a manner dependent upon the thiol residue of cysteine 118 (C118). Here, to investigate the effect of mutating this residue on tumorigenesis, we introduce a C118S mutation into the endogenous murine Kras allele and expose the resultant mice to the carcinogen urethane, which induces Kras mutation-positive lung tumors. We report that Kras^+/C118S and Kras^C118S/C118S mice develop fewer lung tumors. Although the Kras^C118S allele does not appear to affect tumorigenesis when the remaining Kras allele is conditionally oncogenic, there is a moderate imbalance of oncogenic mutations favoring the native Kras allele in tumors from Kras^+/C118S mice treated with urethane. We conclude that the Kras^C118S allele impedes urethane-induced lung tumorigenesis.

Interactions of sulforaphane and dimethyl sulfoxide with methyl methanesulfonate, urethane, 4-nitroquinoline-1-oxide and hydrogen peroxide in the Drosophila melanogaster wing spot test

Sulforaphane (SF) is an isothiocyanate present in Brassicaceae, vegetables that induce the detoxification of electrophiles and reactive oxygen species. SF has been correlated with chemoprevention mechanisms against degenerative diseases. We tested if the SF had an effect against methyl methanesulfonate (MMS), urethane (URE), 4-NQO and H(2)O(2). SF (>95% purity, 0.14, 0.28, 0.56 mM) was diluted in a DMSO/Tw80/EtOH mixture (DTE) corresponding to 25, 50, 100% of lyophilized broccoli. The SF treatment (0.14 mM) was positive for small spots in the ST cross and negative in the HB cross. In the HB cross, SF (0.28 mM) was genotoxic. In the ST cross, the SF treatments showed a tendency to reduce the genotoxic damage caused by MMS, which could be explained by the radical scavenging action of the DTE mixture. In the ST cross, the frequency of small spots in the SF 0.14 mM/URE treatment was similar to that of Water/URE, which can be explained by a DTE and SF scavenger action. In both crosses, the results for the direct oxidants, 4-NQO and H(2)O(2), were different and must be related to differential modulation of CYPs expression and the SF and DTE scavenger properties.

Urethane and N-nitrosodiethylamine are mutagenic for the Syrian hamster fetus

Urethane and N-nitrosodiethylamine are soluble environmental carcinogens that initiate tumors transplacentally, but have a mixed history of effectiveness in mutagenesis assays in vitro or in vivo with adult rodents. To test for their transplacental mutagenicity, Syrian hamster fetuses at 12 days in gestation were exposed transplacentally to urethane or N-nitrosodiethylamine at 0.5 or 1.0 mM/kg. The fetal cells were isolated on day 13 of gestation and tested for diphtheria toxin resistance as a mutation marker. Both compounds were significantly mutagenic, at both doses, causing 6- to 20-fold increases in mutations compared with controls. Compared with N-nitrosodiethylamine, urethane was somewhat more effective as a mutagen with a more marked dose-response. These results are consistent with mutagenesis as part of the mechanism of transplacental carcinogenicity of urethane and N-nitrosodiethylamine.

Glutathione transferase pi plays a critical role in the development of lung carcinogenesis following exposure to tobacco-related carcinogens and urethane

Human cancer is controlled by a complex interaction between genetic and environmental factors. Such environmental factors are well defined for smoking-induced lung cancer; however, the roles of specific genes have still to be elucidated. Glutathione transferase pi (GSTP) catalyzes the detoxification of electrophilic diol epoxides produced by the metabolism of polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BaP), a common constituent of tobacco smoke. Activity-altering polymorphisms in Gstp have therefore been speculated to be potential risk modifiers in lung cancer development. To clearly establish a role for GSTP in lung tumorigenesis, we investigated whether deletion of the murine Gstp genes (Gstp1 and Gstp2) alters susceptibility to chemically induced lung tumors following exposure to BaP, 3-methylcholanthrene (3-MC), and urethane. Gstp-null mice were found to have substantially increased numbers of adenomas relative to wild-type mice following exposure to all three compounds (8.3-, 4.3-, and 8.7-fold increase for BaP, 3-MC, and urethane, respectively). In Gstp-null mice, the capacity of pulmonary cytosol to catalyze conjugation of the BaP diol epoxide was significantly reduced. Concomitant with this, a significant increase in the level of BaP DNA adducts was measured in the lungs of null animals; however, no increase in DNA adducts was measured in the case of 3-MC exposure, suggesting that an alternative protective pathway exists. Indeed, significant differences in pulmonary gene expression profiles were also noted between wild-type and null mice. This is the first report to establish a clear correlation between Gstp status and lung cancer in vivo.

Mechanism of carcinogenesis induced by a veterinary antimicrobial drug, nitrofurazone, via oxidative DNA damage and cell proliferation

Nitrofurazone, a veterinary antimicrobial drug, causes mammary and ovarian tumors in animals. We investigated the mechanisms of carcinogenesis by nitrofurazone. Nitrofurazone significantly stimulated the proliferation of estrogen-dependent MCF-7 cells. Nitrofurazone caused Cu(II)-mediated damage to 32P-5'-end-labeled DNA fragments obtained from human genes only when cytochrome P450 reductase was added. DNA damage was inhibited by catalase and bathocuproine. DNA damage was preferably induced at the 5'-ACG-3' sequence, a hotspot of the p53 gene. These findings suggest that nitrofurazone metabolites are involved in tumor initiation through oxidative DNA damage and nitrofurazone itself enhances cell proliferation, leading to promotion and/or progression in carcinogenesis.

Mechanism of metal-mediated DNA damage induced by a metabolite of carcinogenic acetamide

Acetamide is carcinogenic in rats and mice. To clarify the mechanism of carcinogenesis by acetamide, we investigated DNA damage by and acetamide metabolite, acetohydroxamic acid (AHA), using 32P-5'-end-labeled DNA fragments. AHA treated with amidase induced DNA damage in the presence of Cu(II) and displayed a similar DNA cleavage pattern of hydroxylamine. DNA damage was inhibited by both catalase and bathocuproine, suggesting that H2O2 and Cu(I) are involved. Carboxy-PTIO, a specific scavenger of nitric oxide (NO), partially inhibited DNA damage. The amount of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) by amidase-treated AHA was similar to that by hydroxylamine. ESR spectrometry revealed that amidase-treated AHA as well as hydroxylamine generated NO in the presence of Cu(II). From these results, it has been suggested that AHA might be converted into hydroxylamine by amidase. These results suggest that metal-mediated DNA damage mediated by amidase-catalyzed hydroxylamine generation plays an important role in the carcinogenicity of acetamide.

Oxidation of N-hydroxyguanidines by copper(II): model systems for elucidating the physiological chemistry of the nitric oxide biosynthetic intermediate N-hydroxyl-L-arginine

The redox chemistry of models of N-hydroxy-L-arginine, the biosynthetic intermediate in the synthesis of NO by the family of nitric oxide synthase enzymes, has been explored experimentally and theoretically. The oxidation of N-hydroxyguanidine model compounds by Cu(II) was studied as a means of establishing possible metabolic fates and intermediates of this important functional group. These studies indicate than an iminoxyl intermediate is formed and may be an important biological species generated from N-hydroxyguanidines including N-hydroxy-L-arginine.

Oxidative DNA damage induced by photodegradation products of 3(')-azido-3(')-deoxythymidine

3(')-Azido-3(')-deoxythymidine (AZT) is carcinogenic to experimental animals and can cause the formation of 8-oxo-7,8-dihydro-2(')-deoxyguanosine (8-oxodG) in humans and animals. To clarify the mechanism of carcinogenesis by AZT, we investigated DNA damage induced by its photodegradation products, using 32P-5(')-end-labeled DNA fragments obtained from human genes. Following exposure to UVB, AZT induced DNA damage in the presence of Cu(II). Catalase inhibited DNA damage, indicating the involvement of H(2)O(2). UVB-exposed AZT plus Cu(II) induced 8-oxodG formation in a dose-dependent manner. Mass spectrum of UVB-exposed AZT demonstrated the generation of a hydroxylamine derivative. The colorimetric determination suggested that AZT was converted into the hydroxylamine derivative depending on UVB doses. UVB-exposed AZT induced double base damage at the 5(')-ACG-3(') sequence, complementary to a hot spot of the p53 gene. The basic compound, hydroxylamine, showed similar site specificity. The hydroxylamine derivative produced by photodegradation and/or possible metabolism of AZT induces oxidative DNA damage, which may participate in carcinogenesis.

Urease enhances the formation of iron nitrosyl hemoglobin in the presence of hydroxyurea

Although it has been shown that hydroxyurea (HU) therapy produces measurable amounts of nitric oxide (NO) metabolites, including iron nitrosyl hemoglobin (HbNO) in patients with sickle cell disease, the in vivo mechanism for formation of these is not known. Much in vitro data and some in vivo data indicates that HU is the NO donor, but other studies suggest a role for nitric oxide synthase (NOS). In this study, we confirm that the NO-forming reactions of HU with hemoglobin (Hb) or other blood constituents is too slow to account for NO production measured in vivo. We hypothesize that, in vivo, HU is partially metabolized to hydroxylamine (HA), which quickly reacts with Hb to form methemoglobin (metHb) and HbNO. We show that addition of urease, which converts HU to HA, to a mixture of blood and HU, greatly enhances HbNO formation.