Oxidative DNA Damage Induced by Carcinogenic Dinitropyrenes in the Presence of P450 Reductase

Effect of docosahexaenoic acid as a chemopreventive agent on experimentally induced hamster buccal pouch carcinogenesis

PURPOSE

The current study was directed to investigate the effectiveness of docosahexaenoic acid (DHA) as a chemopreventive agent on experimentally induced hamster buccal pouch (HBP) carcinogenesis.

MATERIAL AND METHODS

In this study we used 40 Syrian male hamsters, five weeks old, were divided into 4 groups (GI, GII, GIII, and GIV) of 10 animals in each as follows, GI: Topical application of liquid paraffin alone (thrice a week for 14 weeks), GII: Topical application of 7, 12 dimethyl benz[a]anthracene (DMBA) alone (0.5% in liquid paraffin, thrice a week for 14 weeks), GIII: Topical application of DMBA (0.5% in liquid paraffin, thrice a week for 14 weeks) + Oral administration of DHA (125 mg/kg b.w. in 1 ml distilled water by oral gavage, thrice a week for 14 weeks on alternative days of DMBA application), GIV: Oral administration of DHA alone (125 mg/kg b.w. in 1 ml distilled water by oral gavage, thrice a week for 14 weeks).

RESULTS

Gross observations and histopathological findings revealed that, in GI: normal stratified squamous epithelium, in GII: well and moderately differentiated squamous cell carcinoma (SCC), in GIII: variable results ranges from hyperkeratosis, hyperkeratosis and focal hyperplasia, mild dysplasia, and well differentiated SCC with superficial invasion of tumor cells not extended to deeper areas, while in GIV: normal similar to GI. Immunohistochemical results indicated that oral DHA treatment to DMBA treated hamsters restored the normal expression of bcl-2.

CONCLUSION

Our results indicated that DHA has the potential to be a dietary chemopreventive agent due to its capacity to improve carcinogen detoxification and to block/suppress the initiation and promotion stages of experimentally produced HBP carcinogenesis.

Anti-cancer effects of 3,5-dimethylaminophenol in A549 lung cancer cells

Exposure to 3,5-dimethylaminophenol (3,5-DMAP), the metabolite of the 3-5-dimethylaniline, was shown to cause high levels of oxidative stress in different cells. The aim of the present work was to observe whether this metabolite can lead to cytotoxicity, oxidative stress, DNA damage and cell cycle changes in non-small cell lung cancer A549 cells. 3,5-DMAP caused a dose-dependent increase in cytotoxicity, generation of superoxide (O₂^-.), inductions in the enzyme activities orchestrating cellular antioxidant balance, increases in lipid peroxidation as well as DNA damage. However, 3,5-DMAP showed significantly lower cytotoxicity towards human lung fibroblast (HLF) cells. 3,5-DMAP also led to molecular events, like inducing apoptotic markers (ie. p53, Bad, Bax and cytochrome c); decreasing anti-apoptotic proteins (Bcl-2) and alterations in cell cycle. Our findings indicate that the cytotoxicity caused by this particular alkylaniline metabolite led to initiation of caspase 3-mediated apoptosis. Furthermore, 3,5-DMAP attenuated carcinogenic properties like migration capacity of A549 cells and eventually inhibited growth of A549 cells in an in vivo mouse model. Tumor sections showed that 3,5-DMAP down-regulated c-Myc expression but up-regulated p53 and cytochrome c, all of which might result in tumor growth arrest. Co-treatment with N-acetylcysteine provided reductions in cytotoxicity and positively modulated genetic events induced by 3,5-DMAP in A549 cells. In conclusion, our findings demonstrate 3,5-DMAP may be a potential anti-cancer drug in cancer, due to its self redox cycling properties.

Exposure to High-Dose Diesel Exhaust Particles Induces Intracellular Oxidative Stress and Causes Endothelial Apoptosis in Cultured In Vitro Capillary Tube Cells

Previous studies suggest a direct correlation between exposure to diesel exhaust particles (DEP) and the onset of vascular permeability, presumably through the disruption of the adherens junctions. This would lead to deleterious effects on vasculature, such as acute myocardial infarction and atherosclerosis. Although the mechanism remains unclear, we demonstrate DEP-induced mitochondrial reactive oxygen species generation, which may be a central cause of the above vascular disorders. In vitro capillary-like HUVEC tube cells are used in this study and show that acute DEP exposure stimulates ATP depletion, followed by depolarization of their actin cytoskeleton, which sequentially inhibits PI3K/Akt activity and induces endothelial apoptosis. These events are accompanied by induction of p53/Mdm2 feedback regulation at 10 µg/mL DEP and produce 20 % cell apoptosis. Nevertheless, 100 µg/mL DEP augments tube cell apoptosis up to 70 % but disrupts the p53 negative regulator Mdm2. Addition of N-acetylcysteine provides substantial protection against the cytotoxic effects of DEP. In summary, exposure to a low dose of DEP actin triggers cytoskeleton depolarization, reduces PI3K/Akt activity, and induces a p53/Mdm2 feedback loop, and a high dose causes apoptosis by depleting Mdm2.

Enicostemma littorale prevents tumor formation in 7,12-dimethylbenz(a)anthracene-induced hamster buccal pouch carcinogenesis

Oral cancer is one of the most common malignancies worldwide, and India has recorded the highest annual incidence of oral cancer in comparison with other countries. Altered lipid peroxidation and antioxidant status along with defect in detoxification cascade have been implicated in the pathogenesis of several cancers including oral cancer. The aim of this study was to investigate the chemopreventive potential of ethanolic extract of Enicostemma littorale leaves (ElELet) in 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. Oral tumor was developed in the buccal pouches of male golden Syrian hamsters by painting with 0.5% DMBA three times a week for 14 weeks. We observed 100% tumor formation with increase in tumor volume and tumor burden in the hamsters treated with DMBA alone. Imbalance in phase I (cytochrome P450 and cytochrome b5) and phase II (glutathione reductase, glutathione- S-transferase, glutathione, and Deoxythymidine-diaphorase (DT)-diaphorase) detoxification agents and lipid peroxidation by-products (thiobarbituric acid reactive substances) and antioxidant (superoxide dismutase, catalase, glutathione peroxidase, and vitamins E and C) status was noticed in hamsters treated with DMBA alone. Oral administration of ElELet at a dose of 250 mg/kg body weight to hamsters treated with DMBA significantly prevented both precancerous and cancerous lesions in the oral cavity. ElELet modulated the status of phase I and II detoxification agents and antioxidants in favor of the suppression of oral carcinogenesis. This study thus suggests that E. littorale might have inhibited the oral carcinogenesis in DMBA-treated hamsters through its antioxidant potential. The present findings are also substantiated by histological studies during DMBA-induced oral carcinogenesis.

Nitroaromatic compounds: Environmental toxicity, carcinogenicity, mutagenicity, therapy and mechanism

Vehicle pollution is an increasing problem in the industrial world. Aromatic nitro compounds comprise a significant portion of the threat. In this review, the class includes nitro derivatives of benzene, biphenyls, naphthalenes, benzanthrone and polycyclic aromatic hydrocarbons, plus nitroheteroaromatic compounds. The numerous toxic manifestations are discussed. An appreciable number of drugs incorporate the nitroaromatic structure. The mechanistic aspects of both toxicity and therapy are addressed in the context of a unifying mechanism involving electron transfer, reactive oxygen species, oxidative stress and antioxidants.

Contributions of human enzymes in carcinogen metabolism

Considerable support exists for the roles of metabolism in modulating the carcinogenic properties of chemicals. In particular, many of these compounds are pro-carcinogens that require activation to electrophilic forms to exert genotoxic effects. We systematically analyzed the existing literature on the metabolism of carcinogens by human enzymes, which has been developed largely in the past 25 years. The metabolism and especially bioactivation of carcinogens are dominated by cytochrome P450 enzymes (66% of bioactivations). Within this group, six P450s--1A1, 1A2, 1B1, 2A6, 2E1, and 3A4--accounted for 77% of the P450 activation reactions. The roles of these P450s can be compared with those estimated for drug metabolism and should be considered in issues involving enzyme induction, chemoprevention, molecular epidemiology, interindividual variations, and risk assessment.

In vivo bioluminescence imaging and histopathopathologic analysis reveal distinct roles for resident and recruited immune effector cells in defense against invasive aspergillosis

Background

Invasive aspergillosis (IA) is a major cause of infectious morbidity and mortality in immune compromised patients. Studies on the pathogenesis of IA have been limited by the difficulty to monitor disease progression in real-time. For real-time monitoring of the infection, we recently engineered a bioluminescent A. fumigatus strain.

Results

In this study, we demonstrate that bioluminescence imaging can track the progression of IA at different anatomic locations in a murine model of disease that recapitulates the natural route of infection. To define the temporal and functional requirements of distinct innate immune cellular subsets in host defense against respiratory A. fumigatus infection, we examined the development and progression of IA using bioluminescence imaging and histopathologic analysis in mice with four different types of pharmacologic or numeric defects in innate immune function that target resident and recruited phagocyte subsets. While bioluminescence imaging can track the progression and location of invasive disease in vivo, signals can be attenuated by severe inflammation and associated tissue hypoxia. However, especially under non-inflammatory conditions, such as cyclophosphamide treatment, an increasing bioluminescence signal reflects the increasing biomass of alive fungal cells.

Conclusions

Imaging studies allowed an in vivo correlation between the onset, peak, and kinetics of hyphal tissue invasion from the lung under conditions of functional or numeric inactivation of phagocytes and sheds light on the germination speed of conidia under the different immunosuppression regimens. Conditions of high inflammation -either mediated by neutrophil influx under corticosteroid treatment or by monocytes recruited during antibody-mediated depletion of neutrophils- were associated with rapid conidial germination and caused an early rise in bioluminescence post-infection. In contrast, 80% alveolar macrophage depletion failed to trigger a bioluminescent signal, consistent with the notion that neutrophil recruitment is essential for early host defense, while alveolar macrophage depletion can be functionally compensated.

In vitro synthesis of 1,N6-etheno-2'-deoxyadenosine and 1,N2-etheno-2'-deoxyguanosine by 2,4-dinitrophenol and 1,3-dinitropyrene in presence of a bacterial nitroreductase

The formation of covalent nitro-PAH DNA adducts and nitro-PAH mediated oxidative lesions are two possible mechanisms for the initiation of nitro-PAH carcinogenesis. Sixty-minute incubation of 1,3-dinitropyrene (100 microM) or 1,4-dinitrophenol (100 microM) with a mixture of 150 microM NADH, 0.5 units of E. coli nitroreductase, 100 microM linoleic acid, 0.5 mM ferrous iron, and 100 microM 2'-deoxyadenosine (2'-dA) or 100 microM 2'-deoxyguanosine (2'-dG) were analyzed by liquid chromatography multistage mass spectrometry. Mixtures of 1,N(6)-etheno-2'-deoxyadenosine (epsilondA) plus 4-oxo-2-nonenal (4-ONE) and 1,N(2)-etheno-2'-deoxyguanosine (epsilondG) plus 4-ONE could be detected from 2'-dA and 2'-dG, respectively. Addition of 2% propanol inhibited the formation of etheno adducts. Analyses of disappearance kinetics of dA and dG showed that dG was more rapidly eliminated than does dA (t[1/2] = 23.3 min and 98.3 min for dG and dA, respectively). Curves of formation kinetics revealed that the peak of epsilondG was at 55.6 min while that of epsilondA was at 186.9 min. These peaks represented 1.43% and 1.25% of the original dG and dA, respectively. In both cases, the peaks were followed by rapid degradations of etheno adducts. The results, obtained in this system, do not allow any extrapolation to realistic cellular responses; nevertheless, these data questioned the validity of the use of unsubstituted etheno adducts as reliable oxidative stress and nitro-PAH exposure biomarkers.