Modifiers of endogenous nitrosamine synthesis and metabolism

Modulation of cigarette smoke-related end-points in mutagenesis and carcinogenesis

The epidemic of lung cancer and the increase of other tumours and chronic degenerative diseases associated with tobacco smoking have represented one of the most dramatic catastrophes of the 20th century. The control of this plague is one of the major challenges of preventive medicine for the next decades. The imperative goal is to refrain from smoking. However, chemoprevention by dietary and/or pharmacological agents provides a complementary strategy, which can be targeted not only to current smokers but also to former smokers and passive smokers. This article summarises the results of studies performed in our laboratories during the last 10 years, and provides new data generated in vitro, in experimental animals and in humans. We compared the ability of 63 putative chemopreventive agents to inhibit the bacterial mutagenicity of mainstream cigarette smoke. Modulation by ethanol and the mechanisms involved were also investigated both in vitro and in vivo. Several studies evaluated the effects of dietary chemopreventive agents towards smoke-related intermediate biomarkers in various cells, tissues and organs of rodents. The investigated end-points included metabolic parameters, adducts to haemoglobin, bulky adducts to nuclear DNA, oxidative DNA damage, adducts to mitochondrial DNA, apoptosis, cytogenetic damage in alveolar macrophages, bone marrow and peripheral blood erytrocytes, proliferation markers, and histopathological alterations. The agents tested in vivo included N-acetyl-L-cysteine, 1,2-dithiole-3-thione, oltipraz, phenethyl isothiocyanate, 5,6-benzoflavone, and sulindac. We started applying multigene expression analysis to chemoprevention research, and postulated that an optimal agent should not excessively alter per se the physiological background of gene expression but should be able to attenuate the alterations produced by cigarette smoke or other carcinogens. We are working to develop an animal model for the induction of lung tumours following exposure to cigarette smoke. The most encouraging results were so far obtained in models using A/J mice and Swiss albino mice. The same smoke-related biomarkers used in animal studies can conveniently be applied to human chemoprevention studies. We participated in trials evaluating the effects of N-acetyl-L-cysteine and oltipraz in smokers from Italy, The Netherlands, and the People's Republic of China. We are trying to develop a pharmacogenomic approach, e.g. based on genetic metabolic polymorphisms, aimed at predicting not only the risk of developing cancer but also the individual responsiveness to chemopreventive agents.

DNA alterations in rat organs after chronic exposure to cigarette smoke and/or ethanol ingestion

In spite of the epidemiological evidence supporting a synergism between alcohol consumption and cigarette smoking in the pathogenesis of cancers of the aerodigestive tract, there is a paucity of experimental studies evaluating the effects of these agents under well-controlled conditions and exploring the mechanisms involved. We exposed groups of female BD6 rats, aged 8 months, to ethanol (5% in drinking water for 8 consecutive months) and/or whole-body to mainstream cigarette smoke (1 h/day, 5 days/week for 8 months). DNA was purified from different organs and analyzed for the presence of DNA-protein crosslinks and 32P-postlabeled DNA adducts after butanol enrichment. No significant increase of DNA-protein crosslinks, compared to untreated controls, was induced by any treatment in liver, lung, or heart. 'Spontaneous' nucleotidic modifications were detected by 32P-postlabeling in organs of untreated rats, with the highest levels occurring in the heart. Ingestion of ethanol did not affect DNA adduct levels in any of the organs examined: esophagus, liver, lung, and heart. Exposure to cigarette smoke induced formation of DNA adducts in the lung and heart, but not in the esophagus or liver. The combined ingestion of ethanol resulted in a significant formation of smoke-related DNA adducts in the esophagus and in their further, dramatic increase in the heart. It thus appears that ethanol consumption increases the bioavailability of DNA binding smoke components in the upper digestive tract and favors their systemic distribution. The mechanisms responsible for the interaction between ethanol and smoke and for the selective localization of DNA alterations in different organs are discussed. Formation of DNA adducts in the organs examined may be relevant in the pathogenesis of lung and esophageal cancers as well as in the pathogenesis of other types of chronic degenerative diseases, such as chronic obstructive pulmonary diseases and cardiomyopathies.

Modulation of cyclophosphamide mutagenicity by vitamin C in the in vivo rodent micronucleus assay

The modulatory effect of vitamin C (Vit C) on the mutagenic effect of the antineoplastic drug cyclophosphamide (CP) was assessed in the in vivo micronucleus test in Swiss mice. Simultaneous oral administration of Vit C with i.p. administration of CP was found to decrease the frequency of micronucleated polychromatic erythrocytes elevated by CP. Vit C exhibited a significant antimutagenic effect over a wide dose range (1.56-200 mg/kg). The dose-response relationship was highly significant. These results demonstrated the ability of the in vivo micronucleus test to detect in vivo modulation of CP mutagenicity by Vit C. Our earlier results and those from other laboratories also indicate that this model system is suitable for primary in vivo screening of modulation of mutagenesis.

Soybean and ascorbate feeding in experimental carcinogenesis: immunological studies

Soybean and/or sodium ascorbate have been demonstrated to have protective effects against carcinogenicity of the nitrosamine precursors dibutylamine and sodium nitrite in rats. Some immunological aspects of the cellular and humoral compartments of the immune system were investigated in this experimental model. The parameters chosen for the study were the lymphocyte transformation test, migration inhibition test, the demonstration of Fc and Fc plus complement receptors on the lymphocyte surface (EA and EAC rosette-forming test), and the determination of total serum proteins and their fractions. The results indicated that dibutylnitrosamine can be formed in vivo from its precursors dibutylamine and sodium nitrite, and that it affects the immune system of rats which showed an immunosuppressed state present as depressed cellular and humoral immunity. The protective role of soybean and/or ascorbate against carcinogenicity of dibutylamine and sodium nitrite was demonstrated by the absence of tumor formation. These agents were found to be capable of increasing the defense mechanism of rats by enhancing both cellular and humoral immunity in the presence of the carcinogenic nitrosamine precursors dibutylamine and sodium nitrite.