The presence of covalent DNA chemical addition products (adducts) in human term placentas was investigated by recently developed immunologic and 32P-postlabeling assays. DNA from placental specimens of smokers showed a small but not statistically significant increase in adduct levels when tested by antibodies to DNA modified with a benzo[a]pyrene dihydrodiol epoxide (BPDE-I), the ultimate carcinogenic derivative of benzo[a]pyrene. The postlabeling assay detected several modified nucleotides, one of which (adduct 1) strongly related to maternal smoking during pregnancy. This adduct was present in placental tissue from 16 of 17 smokers, but only 3 of 14 nonsmokers. Among smokers, levels of adduct 1 in general were only weakly related to questionnaire and biochemical measures of the intensity of smoking exposures, which suggests modulation by individual susceptibility factors. The adduct seemed to be derived from an aromatic carcinogen, but it may not result from several of the most intensely studied polycyclic aromatic hydrocarbons or aromatic amines in tobacco smoke. The data show the association of cigarette smoking with covalent damage to human DNA in vivo.

In animals and humans, estrogens are able to induce cancer in susceptible target organs, but the mechanism(s) of estrogen-induced carcinogenesis has not been elucidated. A well-known animal model is the development of renal carcinoma in estrogen-treated Syrian hamsters. Previous work demonstrated the presence of covalent DNA addition products (adducts) in premalignant kidneys of hamsters exposed to the synthetic estrogen, diethylstilbestrol, a known human carcinogen. In the present study, the natural hormone, 178-estradiol, and several synthetic steroid and stilbene estrogens were examined by a 32P-postlabeling assay for their capacity to cause covalent DNA alterations in hamster kidney. Chronic exposure to each of the estrogens tested led to the gradual formation of five chromatographically distinct unusual nucleotides specifically in kidney DNA. Irrespective of the estrogen used, chromatograms exhibited identical mobilities of each of these adducts in seven different systems on PEI-cellulose anionexchange TLC, in three different conditions on reversed-phase TLC, and in one system on silica gel partition TLC. Therefore, the DNA adducts observed did not contain moieties derived from the structurally diverse estrogens. It is concluded that each of the estrogens induced the binding of the same unknown endogenous compound (or compounds) to target tissue DNA. This novel property of estrogens is postulated to play a key role in hormone-induced malignancy.The formation of covalent DNA addition products (adducts) is generally accepted as a key feature of the initiation of carcinogenesis by "genotoxic" chemicals-chemicals that are able to damage genetic material (1, 2). Unless the modified DNA nucleotides are promptly repaired, miscoding may ensue upon DNA replication, leading to point mutations, activation of oncogenes, and chromosomal alterations (3). A number of short-term tests have been developed recently to detect genotoxic activity of chemicals (4-6). Also, DNA adduct formation has been shown in vivo in experimental animal test systems with many chemical carcinogens of diverse structure (1, 2, 7). However, a number of important carcinogens (8) exist that do not fit this description and therefore have been classified as nongenotoxic carcinogens (9). While their mechanism of action has not as yet been defined, some of them [such as estrogens (10-13) and the environmental pollutant 2, 3,7,8-tetrachlorodibenzo-p-dioxin (14, 15)] have been shown to promote transformation-i.e., they facilitate the expression of neoplastic properties of previously initiated susceptible cells. Estrogens were found to be negative in short-term assays for the induction of gene mutations, irrespective of whether this was measured in prokaryotic (16,17) or eukaryotic (18,39) A central question to be addressed in this context is whether or not estrogens, like the majority of chemical carcinogens, induce covalent DNA alterations in the target tissue of carcinogenesis in vivo. In the present study, experiments were carried out to searc...

Covalent DNA addition products (adducts) formed by the reaction of chemical carcinogens or their metabolites with DNA are critically involved in the initiation of chemical carcinogenesis and may serve as molecular markers and dosimeters for environmental carcinogen exposures. Using a highly sensitive 32P-postlabeling assay for DNA adduct analysis, we studied DNA damage elicited by cigarette smoke in tissues of smokers. A multitude of characteristic smoking-induced, presumably aromatic DNA adducts were found to occur in a dose- and time-dependent manner in the lung, bronchus, and larynx of smokers with cancer of these organs and to decline only slowly after cessation of smoking. Low levels of adducts appeared to persist for up to 14 years in the lungs of exsmokers with high previous exposures. These results corroborate data of epidemiological studies showing that the lung cancer risk and mortality of smokers increase with the intensity and duration of smoking and decline only slowly after cessation of smoking. Tissue distribution studies in autopsy samples revealed the presence of smoking-associated DNA lesions also in the kidney, bladder, esophagus, heart, ascending aorta, and liver. The most extensive DNA damage was found in lung and heart, i.e., 1 aromatic adduct in about 10(7) DNA nucleotides. Our results suggest that cigarette smoking-induced DNA adduct formation is causally related to cancer in the target organs.

No abstract