Chemopreventive effect of syringic acid on 7,12-dimethylbenz(a)anthracene induced hamster buccal pouch carcinogenesis

Oral squamous cell carcinoma is most prevalent and refractory cancers worldwide. Recently, chemoprevention could be a promising approach in developing countries. The present study investigates the mechanism of syringic acid (SA), a phenolic constituent of plant Alpiniacalcarata Roscoe, and their leaves are used as traditional Indian Ayurveda medicines, mediated chemoprevention on 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch carcinogenesis (HBPC). Lipid peroxidation and antioxidants were measured in the plasma and buccal tissues in experimental hamsters. Modulating effect of SA on the expression pattern of PCNA, Cyclin D1, and mutant p53 markers was used for immunoexpression and western blotting analysis. In the present study, 100% tumor formation with marked abnormalities in the biochemical parameters of lipid peroxidation and antioxidants through up-regulation of molecular markers like PCNA, Cyclin D1, and mutant p53 was accompanied with tumor-bearing hamsters. Oral administration of SA at the doses of 50 and 100?mg/kg body weight (bw) to DMBA-treated hamsters significantly inhibited adverse changes in the biochemical parameters of the plasma and buccal mucosal tissues and also down-regulation of molecular marker expression (PCNA, Cyclin D1, and mutant p53). The present study thus suggests that SA has potent anti-lipid peroxidative, antioxidant, anti-cell proliferative, and apoptosis-inducing properties during DMBA-induced HBPC.     

Chemopreventive and antioxidant efficacy of (6)-paradol in 7,12-dimethylbenz(a)anthracene induced hamster buccal pouch carcinogenesis

The present study evaluated the chemopreventive potential of (6)-paradol, a pungent phenolic constituent of ginger, on 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. The mechanistic pathway for the chemopreventive potential of (6)-paradol was evaluated by measuring the status of tumor incidence, volume and burden as well as by analyzing the status of phase II detoxification agents, lipid peroxidation and antioxidants. Oral squamous cell carcinoma was induced in hamster buccal pouches by painting them with 0.5% DMBA in liquid paraffin three times a week for 14 weeks. We observed 100% tumor formation with marked biochemical abnormalities in tumor-bearing animals compared to control animals. Oral administration of 30 mg/kg b.w. (6)-paradol to DMBA-treated hamsters on alternate days from DMBA painting for 14 weeks, significantly reduced the formation of tumors and improved the status of detoxification agents, lipid peroxidation and antioxidants. Therefore, the present study suggests that (6)-paradol has potent chemopreventive, anti-lipid peroxidative and antioxidant potentials as well as a modulating effect on phase II detoxification enzyme and reduced glutathione (GSH) in DMBA-induced hamster buccal pouch carcinogenesis.     

Differences in benzo(a)pyrene metabolism between cultured human and murine bronchial cells after pre-treatment with benz(a)anthracene

Primary cultures of human and murine (strain C3Hz) bronchial epithelial cells were pretreated with benz(a)anthracene (BA) (10 microM). 16 h later the formation of phenolic as well as dihydrodiol metabolites of benzo(a)pyrene (BP) was measured. Whereas murine cultures showed enhanced metabolism towards both phenolic and dihydrodiol compounds, in the human cultures only phenolic BP-metabolites were increased. In view of their precursor role in the formation of biologically active diol-epoxides, formation of dihydrodiol-derivatives can be considered as a key factor in determining susceptibility to polycyclic aromatic hydrocarbon (PAH)-induced carcinogenesis. Therefore the observations of this study indicate that animal model systems for PAH carcinogenesis in man have to be selected on the basis of comparable metabolite patterns.     

Estrogenic status modulates the effect of soy on hepatic responses to 7,12-dimethylbenz(a)anthracene (DMBA)

We examined the influence of estradiol (E2) status and soy protein isolate (SPI) intake on the hepatic responses altered by 7,12-dimethylbenz(a)anthracene (DMBA, a polycyclic aromatic hydrocarbon [PAH]). Sprague-Dawley rats were ovariectomized (OVX) at PND50 and infused with E2 or vehicle for 14 d and gavaged with 50 mg/kg DMBA or vehicle 24 h before sacrifice at PND64. Rats were fed an AIN-93G diet made with SPI or casein as sole protein source throughout the study. Basal AhR protein levels were reduced (P < 0.05) by SPI feeding irrespective of the E2 status. However, DMBA increased (P < 0.05) AhR-induced CYP1A1 gene expression in OVX, SPI-fed rats, but reduced (P < 0.05) CYP1A1 in OVX + E2, SPI-fed rats. Chromatin-immunoprecipitation demonstrated lower (P < 0.05) DMBA-mediated recruitment of estrogen receptor alpha to the CYP1A1 promoter by SPI feeding in the presence of E2, suggesting an estrogen-like action of SPI on DMBA-mediated signaling in the absence of E2. Further, microarray analysis (Rat 230-2.0 Affymetrix-GeneChip™) revealed 231 genes common to SPI + DMBA and SPI + E2 + DMBA (normalized to E2) treatments. AhR-activated genes (CYP1A1, CYP1A2, and NQO1) were down-regulated by SPI + E2 + DMBA compared to SPI + DMBA. Unique interactions among SPI, DMBA and E2 altered the expression profile of 316 genes, not observed by either treatment alone. Our data suggest that although E2 status does not effect soy-mediated AhR degradation, it modulates the effects of soy on many genes, including CYP1A1.     

Comparative kinetics of oral benz(a)anthracene, chrysene and triphenylene in rats: study with hydrocarbon mixtures

Distribution and elimination of benz(a)anthracene (B(a)A) was compared in blood, liver, brain, parametrial adipose and mammary tissue of young female rats after oral administration of the polycyclic aromatic hydrocarbons (PAH) singly or in equimolar mixtures with chrysene (Ch) or triphenylene (Tr). The relative availability of B(a)A in tissues was not influenced by Ch or Tr in the mixture. However, the presence of B(a)A halved the relative availability of Tr and raised that of Ch. The relative availability of the three isomers decreased in the order Tr greater than B(a)A greater than Ch; this may be correlated to their solubility in water.     

Role of mammary epithelial and stromal P450 enzymes in the clearance and metabolic activation of 7,12-dimethylbenz(a)anthracene in mice

Microsomal cytochrome P450 (P450) enzymes, which are important in the metabolism of carcinogens, are expressed in both epithelial and stromal cells in the mammary gland. The aim of this study was to investigate the roles of mammary epithelial P450 enzymes in the bioactivation and disposition of 7,12-dimethylbenz(a)anthracene (DMBA), a breast carcinogen, in the mammary gland. A new mouse model (named MEpi-Cpr-null) was produced, wherein P450 activities in the mammary epithelial cells are suppressed through tissue-specific deletion of the gene for P450 reductase (Cpr), an enzyme required for the activities of all microsomal P450 enzymes. Comparisons between wild-type and MEpi-Cpr-null mice showed that the tissue-specific deletion of Cpr in the mammary epithelial cells was accompanied by significant increases in the levels of DMBA and DMBA-DNA adduct in the mammary gland following a single intraperitoneal injection of DMBA at 50mg/kg. Immunohistochemical and immunoblot analysis further revealed greater induction of CYP1B1 expression by the DMBA treatment in the mammary stroma of the MEpi-Cpr-null mice than in that of the WT mice. These findings not only demonstrate that the epithelial P450 enzymes play important roles in the clearance of DMBA, but also suggest that P450 enzymes in both mammary epithelial and stromal cells contribute to carcinogen-mediated DNA damage.     

Time-dependent acetylsalicylic acid effects on liver CYP1A and antioxidant enzymes in a rat model of 7,12-dimethylbenzanthracene (DMBA)-induced mammary carcinogenesis

7,12-Dimethylbenzanthracene (DMBA) is an abundant environmental contaminant, which undergoes bioactivation, primarily by the CYP1 family, both in liver and extra-hepatic tissues. Dietary acetylsalicylic acid (ASA) has been recently reported to inhibit DMBA-mediated mammary tumour formation in rats. Chemopreventive substances may reduce the risk of developing cancer by decreasing metabolic enzymes responsible for generating reactive species (phase I enzymes) and/or increasing phase II enzymes that can deactivate radicals and electrophiles. To test these hypotheses, Sprague-Dawley female rats were orally administered ASA as lysine acetylsalicylate (50mg per capita/day for 21 days in water), DMBA (10mg per capita in olive oil on day 7, 14, and 21), ASA and DMBA in combination, and vehicles only, respectively. Six rats for each group were sacrificed on day 8, 15, and 22. The DMBA-mediated increase in hepatic CYP1A expression and related activities was not significantly affected by ASA, which, conversely, enhanced in a time-dependent manner the liver reduced glutathione content (up to 52%) and the activity of NAD(P)H-quinone oxidoreductase (up to 34%) in DMBA-treated rats. It is proposed that the positive modulation of the hepatic antioxidant systems by ASA may play a role in the chemoprevention of mammary tumourigenesis induced by DMBA in the female rat.     

Effects of red mold dioscorea on oral carcinogenesis in DMBA-induced hamster animal model

Monascus-fermented products offer valuable therapeutic benefits and have been extensively used for centuries in East Asia. Dioscorea has been proved to have anti-cancer effect. The aim of this study is to investigate the anti-tumor ability of the ethanol extract of red mold dioscorea (RMDE) on 7,12-dimethyl-1,2-benz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. We induced oral squamous cell carcinoma (OSCC) in the buccal pouch of male Syrian golden hamsters by painting with 0.5% DMBA three times a week for 14 weeks. From 9 to 14 weeks, a dose of 50, 100, and 200 mg RMDE per kg body weight were painting with the hamsters for 6 weeks on days alternate to the DMBA application. The results demonstrated that RMDE decreased nitric oxide (NO), reactive oxygen species (ROS), and prostaglandin E₂ (PGE₂) overexpression in hamster buccal pouches in the DMBA treatment group and increased p53, serum tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) to significantly stimulate caspase-8 and -3 activities, indicating that RMDE reduced oxidative damage causing by DMBA and induced apoptosis in oral cancer cells. Therefore, RMDE may have therapeutic potentials against OSCC.     

Induction of CYP1A1 and CYP1B1 by benzo(k)fluoranthene and benzo(a)pyrene in T-47D human breast cancer cells: roles of PAH interactions and PAH metabolites

The interactions of polycyclic aromatic hydrocarbons (PAH) and cytochromes P450 (CYP) are complex; PAHs are enzyme inducers, substrates, and inhibitors. In T-47D breast cancer cells, exposure to 0.1 to 1 microM benzo(k)fluoranthene (BKF) induced CYP1A1/1B1-catalyzed 17beta-estradiol (E(2)) metabolism, whereas BKF levels greater than 1 muM inhibited E(2) metabolism. Time course studies showed that induction of CYP1-catalyzed E(2) metabolism persisted after the disappearance of BKF or co-exposed benzo(a)pyrene, suggesting that BKF metabolites retaining Ah receptor agonist activity were responsible for prolonged CYP1 induction. BKF metabolites were shown, through the use of ethoxyresorufin O-deethylase and CYP1A1-promoter-luciferase reporter assays to induce CYP1A1/1B1 in T-47D cells. Metabolites formed by oxidation at the C-2/C-3 region of BKF had potencies for CYP1 induction exceeding those of BKF, whereas C-8/C-9 oxidative metabolites were somewhat less potent than BKF. The activities of expressed human CYP1A1 and 1B1 with BKF as substrate were investigated by use of HPLC with fluorescence detection, and by GC/MS. The results showed that both enzymes efficiently catalyzed the formation of 3-, 8-, and 9-OHBKF from BKF. These studies indicate that the inductive effects of PAH metabolites as potent CYP1 inducers are likely to be additional important factors in PAH-CYP interactions that affect metabolism and bioactivation of other PAHs, ultimately modulating PAH toxicity and carcinogenicity.