Effects of acetylsalicylic acid administration on liver CYP1A, UGT and antioxidant enzymes in a rat model of dimethylbenzanthracene (DMBA)-induced mammary carcinogenesis.

Introduction There are growing evidences that support the regular use of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) as effective chemopreventive agents for breast cancer (1). A recent study showed that dietary acetylsalicylic (ASA) and salicylic acid (SA) both inhibited the formation of dimethylbenzanthracene (DMBA)-induced rat mammary tumours, suggesting as a possible mechanism of salicylate chemopreventive action the concomitant inhibition of tumour angiogenesis (2). To exert its carcinogenic effect, DMBA undergoes bioactivation, which requires oxidation to DMBA-3,4-diol-1,2-epoxide by hepatic and extrahepatic phase I enzymes, especially cytochrome P450 (CYP)1A (3). Cancer chemopreventive agents can modulate both phase I and phase II enzymes involved in the bioactivation or detoxification of carcinogens, respectively, and antioxidant enzymes as well. In view of the acknowledged importance of the liver in DMBA activation and detoxification, the aim of this work was to investigate the effect of a pre-treatment with ASA on the activity and expression of CYP1A, on CYP-mediated oxidative metabolism of DMBA itself, and on selected conjugative and antioxidant enzymes. Materials and methods Seventy-two 45 day-old female Sprague-Dawley rats were randomly divided into 4 groups (n=18 each) and treated per os as follows: control (olive oil); ASA (50 mg/ml saline/rat for 21 days); DMBA (10 mg/ml olive oil/rat at days 7, 14, and 21); DMBA+ASA (treated according to DMBA and ASA treatment schedule). Six animals from each group were sacrificed 24 hr after each DMBA administration (days 8, 15 and 22 of the experiment) and the hepatic subfractions were isolated by differential ultracentrifugation. CYP1A1-related O-dealkylation of either ethoxy- or methoxyresorufin, CYP1A1/2 apoprotein levels, and the extent of the in vitro metabolism of 3HDMBA were measured by published procedures (4,5). The assayed phase II and antioxidant enzyme activities included 1-naphthol-uridindiphosphoglucuronyl-transferase (UGT), glutathione S-transferase (GST) accepting 1-chloro-2,4-dinitrobenzene, 3,4-dichloronitrobenzene or ethacrynic acid as substrates, and DT-diaphorase (6); reduced glutathione content (GSH) was also determined (6). Data (means ±SEM) were expressed as percentage of control values and subjected to statistical evaluation by means of ANOVA followed by Student-Newman-Keul’s test. Results At the different time points, DMBA significantly increased CYP1A content and functions (up to 10-fold), as well as the extent of its own metabolism. These effects, however, were not consistently affected by ASA administration. Conversely, ASA was able to considerably enhance the DMBA-mediated time-dependent increase in both GSH level and DT-diaphorase activity, reaching the statistical significance 24 h after the second and the third-, or the third administration of the carcinogen, respectively (Fig. 1). Discussion and Conclusion Previous experiments demonstrated that ASA was able to reduce the amount of DMBA-DNA adduct formation in both the human mammary carcinoma cell line MCF-7 and mammary cells derived from DMBA-induced rat mammary tumours (7). The present data suggest that ASA could also exert its beneficial effect on DMBA-induced mammary carcinogenesis by modulation of liver antioxidant defence systems rather than by decreasing the expression of bioactivating enzymes. It is proposed that the increased GSH content and DT-diaphorase activity may eventually lower the amount of the ultimate carcinogen that can react with critical target sites of the mammary gland. This, however, does not exclude the possibility of an interference of ASA on DMBA activation and detoxification in the same orga