PubMed Health⌕ Search

Biomedical subjects

H Autrup

Publications and source records attributed to H Autrup.

At least 91 records · Page 5Linked to original sources
PubMed1985

Metabolism of benzo[a]pyrene by cultured rat and human buccal mucosa cells.

Primary cultures of epithelial and fibroblast cells derived from human oral mucosa were studied for the ability to activate a tobacco smoke carcinogen, benzo[a]pyrene (BP). The cells were exposed to benzo[a]pyrene for 18 h. The cell-free medium was extracted with ethylacetate/acetone, and high-pressure liquid chromatography analysis of this fraction revealed that BP tetrols and diols were the major metabolites formed by both epithelial and fibroblast cells. However, the epithelial cells had a much higher rate of biotransformation of BP as measured by binding to cellular DNA. The mean binding level to human buccal mucosal DNA was among the highest observed in stratified human epithelia. The major BP-DNA adduct was formed by the reaction of the 'bay-region' BP diolepoxide with the exocyclic 2-amino group in guanine. In contrast to human cells, BP phenols and BP 9,10-diol were the major metabolites produced by primary epithelial and fibroblast cells derived from rat buccal mucosa. The DNA binding levels of BP in the two rat cell types were identical, and the binding level was several-fold lower than in the human epithelial cells. When an established rat tongue epithelial cell line (RTE 2) was treated with polycyclic aromatic hydrocarbons--BP and 7,12-dimethylbenz[a]-anthracene--a slight toxic effect was observed. Our results indicate that primary cultures of oral mucosa are able to metabolize BP into its ultimate carcinogenic form at a rate similar to or higher than other potential target tissues for BP-induced carcinogenesis.

Animals↗
PubMed1985

Detection of 8,9-dihydro-(7'-guanyl)-9-hydroxyaflatoxin B1 in human urine.

A possible role of aflatoxin B1 (AFB) in the etiology of human liver cancer has been suggested from several epidemiological studies. This has been based upon the association between consumption of AFB-contaminated food and the liver cancer incidence in different parts of the world. To further establish the role of AFB as a major factor, we initiated a pilot study in three different districts of Kenya to determine the number of individuals exposed to significant amounts of AFB as measured by the urinary excretion of 8,9-dihydro-8-(7-guanyl)-9-hydroxyaflatoxin B1 (AFB-Gua), an adduct formed between the ultimate carcinogenic form of AFB and nucleic acids. This product has previously been detected in urine from rats treated with AFB. Urine collected at the outpatient clinics at the district hospitals were concentrated on C18 Sep-Pak columns and analyzed by high-pressure liquid chromatography under two different chromatographic conditions. The chemical identity of the samples showing a positive response in both chromatographic systems was verified by synchronous scanning fluorescence spectrophotometry. The highest number of individuals with detectable urinary AFB-Gua lived in either Murang'a district or the neighboring Meru and Embu districts. In Murang'a district a rate of 12% was observed in the January-March period, while only 1 of 32 patients (3%) had a detectable exposure in July-August.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Activation of chemical carcinogens by cultured human fetal liver, esophagus and stomach.

Cultured fetal human stomach, esophagus and liver activated benzo[a]pyrene (BP), aflatoxin B1 (AFB) and certain N-nitrosamines into metabolites that bound to cellular DNA. When the 3 organs were compared the highest level of activity was observed in the stomach. The interindividual variation was 10-fold and the amount of carcinogen-DNA adducts did not correlate with the sex or age of the fetus. The reaction products between BP or AFB and cellular DNA were investigated in liver explants. The carcinogen-DNA adduct patterns were identical to those observed in adult human tissues; BPDEI-Gua being the major adduct formed by BP and 2,3-dihydro-2-(7'-guanyl)-3-hydroxy-AFB by AFB. The results indicate that fetal organs can metabolize those oncogenic compounds at an early stage of the development, and that the metabolic pathways and DNA adducts are quite similar to those in experimental animals in which the compounds are carcinogenic.

Aflatoxin B1↗
PubMed1984

Prostaglandin H synthase-dependent co-oxygenation of (+/-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene in hamster trachea and human bronchus explants.

The role of prostaglandin H synthase (PHS) in the metabolism of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol) has been examined in short-term explant cultures of hamster and human tracheobronchial tissues. Labeled BP-7,8-diol was incubated with the explants in the presence and absence of the PHS substrate arachidonic acid (20:4) and the PHS inhibitor indomethacin. The addition of 10 microM to 200 microM 20:4 to incubations of hamster trachea with 5 microM BP-7,8-diol caused significant increases in the formation of 7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[ a]pyrene (anti-BPDE). These increases were not seen when 1 microM or 20 microM BP-7,8-diol was employed. The stimulation of anti-BPDE formation was observed after incubations of from 1 to 48 h. This stimulation was inhibited to the basal level by 20 microM indomethacin, supporting the role of PHS in the response. No effect of 20:4 was seen on the uptake of BP-7,8-diol by the tracheas or on the formation of water-soluble metabolites. Significant increases in covalent binding of BP-7,8-diol metabolites to DNA of the tracheal epithelium were also elicited by the addition of 20:4, however these increases were not well correlated quantitatively with the increases in anti-BPDE formation. H.p.l.c. profiles of deoxynucleoside adducts from basal and 20:4-stimulated incubations were qualitatively identical. Far greater variability of metabolism was seen in human bronchus explants, but 20:4-dependent increases in anti-BPDE formation could be demonstrated in those tissues as well. Inhibition of this stimulation by indomethacin was either absent or incomplete. This variation in the effect of indomethacin was explained by the examination of the products of 20:4 metabolism by the two tissues. Hamster trachea produced almost exclusively PHS metabolites whereas human bronchus yielded predominantly products of lipoxygenases, enzymes insensitive to indomethacin. In conclusion, this study indicates that co-oxygenation of chemical carcinogens can occur in hamster and human tracheobronchial tissues. The concentration-dependence observed with BP-7,8-diol, however, suggests that this pathway is of minor importance in the activation of BP in these tissues.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1984

Interindividual variation in carcinogen metabolism, DNA damage and DNA repair.

A number of laboratory approaches are currently available to measure interindividual variation in carcinogen metabolism, amounts of carcinogen-DNA adducts and DNA repair capacity. Wide interindividual variations have been found among strains of experimental inbred animals and among individuals in outbred populations, including humans. The quantitative relationships, if any, between these parameters and the human cancer risk will be determined by biochemical and molecular epidemiological studies, of high and low cancer risk populations and of cancer-prone families.

Animals↗
PubMed1983

High-frequency transfection and cytopathology of the hepatitis B virus core antigen gene in human cells.

A protoplast fusion method was developed to stably transfect human cells with pSV2-derived plasmids at frequencies greater than 10(-3). This procedure made it possible to test the biological effect of a hepatitis B virus (HBV) gene independent of the viral structures required for infection. A pSV2gpt+ plasmid constructed to carry a subgenomic fragment of HBV that contained the core antigen gene (HBc gene) was transfected into human cells. A human epithelial cell line was stably transfected with the HBc+ gene by selecting recipient cells for expression of guanine phosphoribosyl transferase expression. With this gpt+/HBc+ cell line it was shown that growth in serum-free medium or treatment with 5'-azacytidine stimulates the production of the HBV core antigen. A hepatocellular carcinoma carrying the entire HBV genome was stimulated to produce the HBc gene product in response to the same factors that stimulated HBcAg production in the gpt+/HBc+ cell line constructed by transfection. The temporal relation between the cytopathologic response and HBc gene expression was similar for both cell types, indicating a primary role for HBc gene expression in the cytopathology of HBV-infected human liver.

Azacitidine↗
PubMed1983

Formaldehyde damage to DNA and inhibition of DNA repair in human bronchial cells.

Cultured bronchial epithelial and fibroblastic cells from humans were used to study DNA damage and toxicity caused by formaldehyde. Formaldehyde caused the formation of cross-links between DNA and proteins, caused single-strand breaks in DNA, and inhibited the resealing of single-strand breaks produced by ionizing radiation. Formaldehyde also inhibited the unscheduled DNA synthesis that occurs after exposure of cells to ultraviolet irradiation or to benzo[a]pyrene diolexpoxide but at doses substantially higher than those required to inhibit the resealing of x-ray-induced single-strand breaks. Therefore, formaldehyde could exert its mutagenic and carcinogenic effects by both damaging DNA and inhibiting DNA repair.

Bronchi↗
PubMed1983

Detection of putative adduct with fluorescence characteristics identical to 2,3-dihydro-2-(7'-guanyl)-3-hydroxyaflatoxin B1 in human urine collected in Murang'a district, Kenya.

Food samples collected in Murang'a district, Kenya are known to be contaminated with a mycotoxin, aflatoxin B1 (AFB), and a positive correlation exists between the dietary intake of AFB and the incidence of liver cancer. When urine samples collected in this district were analyzed for the presence of 2,3-dihydro-2-(7'-guanyl)-3-hydroxyaflatoxin B1 (AFB-GuaI) by h.p.l.c., 6 of 81 samples had a detectable level of a compound whose fluorescence spectrum was identical to chemically synthesized AFB-GuaI as confirmed by photoncounting fluorescence spectrophotometry. These results are an indication of interaction between the ultimate carcinogenic form of AFB and cellular nucleic acids in vivo and further support the hypothesis that AFB may play an important role in the etiology of human liver cancer.

Aflatoxin B1↗
PubMed1983

Metabolism of benzo(a)pyrene and 1-naphthol in cultured human tumorous and nontumorous colon.

The oxidative metabolism of benzo(a)pyrene and the conjugative metabolism of 1-naphthol by explant cultures of normal human colon and colonic tumor tissue, obtained at surgery, have been studied. After 24 hr in culture, the explants were exposed to either [1-14C]-1-naphthol (20 to 100 microM) or [3H]-benzo(a) pyrene (1.5 microM) for a further 1.5 to 24 hr. Both normal-appearing tissue and tumor tissue metabolized benzo(a)pyrene to a wide variety of organic solvent-soluble metabolites, including monohydroxybenzo(a)pyrenes, dihydrodiols, and tetrols. 1-Naphthol was metabolized by cultured human colonic mucosa and tumor tissue to both its glucuronic acid and sulfate ester conjugates. In the normal tissues, with naphthol (20 microM), sulfate ester conjugation predominated. However, with the tumor tissue, sulfate ester conjugation decreased; thus, the percentage of glucuronic acid conjugates, expressed as a percentage of total metabolites formed, was increased significantly compared to normal tissue. The relationship, if any, of these changes to neoplastic transformation is unclear. The technique of explant culture described in this study may be of use for the study of other facets of the pathobiology of solid tumors.

Adenocarcinoma↗
PubMed1983

Methylated DNA adducts in the large intestine of ICR/Ha and C57BL/Ha mice given 1,2-dimethylhydrazine.

The site-specific incidence of 1,2-dimethylhydrazine (DMH)-induced neoplastic changes in intestinal segments of ICR/Ha mice correlates with the persistence of O6-methylguanine (O6MGua) after a single carcinogen injection. Six hours after the injection, the amount of O6MGua in four anatomic (proximal to distal) segments was 16.0, 20.8, 37.5, and 52.8 mumol/mol guanine, respectively. Correlation between the incidence of neoplasms and the amount of alkylation was also observed 14, 40, and 96 hours after DMH treatment. Similar levels of O6MGua were found in the corresponding colon segments of C57BL/Ha mice. After repeated treatment (5 wk) with unlabeled DMH, the amount of O6MGua still correlated with the incidence of neoplasms in ICR/Ha mice. However, in each strain the level of O6MGua was significantly lower in pretreated mice than in mice without DMH pretreatment. Furthermore, the amount of adducts in DNA isolated from different crypt depths showed that within a few hours of the DMH injection the amount of adducts was independent of DNA synthetic activity. Although ICR/Ha and C57BL/Ha mice have different susceptibility to DMH-induced colon cancer, this interstrain difference is not reflected in the amounts or persistence of the miscoding base O6MGua.

1,2-Dimethylhydrazine↗
PubMed1982

Differences in metabolism of chemical carcinogens in cultured human epithelial tissues and cells.

The metabolism of chemical carcinogens has been studied in cultured human bronchus, colon, duodenum, pancreatic duct, and esophagus. Metabolite patterns and carcinogen-DNA adducts are generally qualitatively similar among animal species, individuals within a species, and tissues within an individual. However, wide quantitative differences are observed between individuals in outbred animal species, including humans. These interindividual differences in amounts of carcinogen-DNA adducts and in activities of enzymes that are important in the metabolism of chemical carcinogens are similar in magnitude (10-to 150-fold) to those observed in pharmacogenetic studies of drug metabolism. The role of these differences as risk factors in human cancer is being investigated.

Aryl Hydrocarbon Hydroxylases↗
PubMed1982

Comparison of benzo(a)pyrene metabolism in bronchus, esophagus, colon, and duodenum from the same individual.

The metabolism of benzo(a)pyrene has been investigated in cultured normal human bronchus, colon, duodenum, and esophagus obtained from the same patient. The highest total metabolism was found in bronchus and duodenum, while the highest mean binding level was observed in the bronchus followed, in order, by the esophagus, duodenum, and transverse colon. A 30-fold interindividual variation in the binding level was found in each of the four organs studied, and a positive correlation between the binding levels in bronchus, colon, and duodenum was found. In human bronchus, a positive correlation was found between level of binding of benzo(a)pyrene to DNA and the amount of both benzo(a)pyrene 7,8-diol and the combined group of 3-hydroxybenzo(a)pyrene, benzo(a)pyrene 9,10-diol, and water-soluble metabolites. A significantly higher relative amount of benzo(a)pyrene tetrols and benzo(a)pyrene 9,10-diol was formed by human bronchus compared to the gastrointestinal tissues, while a higher level of benzo(a)pyrene phenols was formed by the latter. The relative distribution of benzo(a)pyrene-DNA adducts was similar in all four organs, the major DNA adduct being formed by trans-addition of anti-7,8-dihydroxy-9,10-epoxide-7,8,9,10-tetrahydrobenzo(a)pyrene to the 2-amino group at guanine. These results indicate that the metabolism of benzo(a)pyrene by at least four different organs is qualitatively similar but that quantitative differences exist.

Adolescent↗
PubMed1982

Metabolism of N-nitrosamines by cultured human and rat esophagus.

The metabolism of several N-nitrosamines (N-nitrosodimethylamine, N-nitrosoethylmethylamine, N-nitrosodiethylamine, N-nitrosobenzylmethylamine, and N-nitrosopyrrolidine) in cultured human and rat esophagus has been investigated by measuring (a) CO2, (b) metabolites with an oxo group, and (c) metabolites bound to DNA. Both acyclic and cyclic N-nitrosamines were metabolized by rat esophagus. The highest level of metabolite binding was seen with N-nitrosobenzylmethylamine, an organotrophic carcinogen for the rat esophagus. The binding level was about 100-fold higher than in human esophagus. This compound methylated rat esophageal DNA at positions 7 and O6 of guanine. The level of benzylation in rat was one-tenth of the level of methylation. Formation of benzaldehyde exceeded that of formaldehyde plus CO2 by a factor of six, indicating that the methylene group was preferentially oxidized. N-Nitrosoethylmethylamine, another unsymmetrical N-nitrosamine, was preferentially oxidized by rat esophagus in the ethyl group, as shown by higher formation of CO2 and acetaldehyde from the compound labeled in the ethyl group. The highest binding level to DNA from this compound was observed with the methyl group. No binding was detected to human esophagus. N-Nitrosopyrrolidine was oxidized by both rat and human esophagus in the alpha position, as measured by the formation of 2,4-dinitrophenylhydrazone derivative of 4-hydroxybutanal. Binding of metabolites of N-nitrosopyrrolidine to DNA was detected only in rat esophagus. As measured by the formation of both CO2 and formaldehyde, N-nitrosodimethylamine was metabolized by both human and rat esophagus. While most of the radioactivity associated with DNA was found to be incorporated into guanine and adenine, methylation of the guanine positions 7 and O6 was detected by chromatography of the hydrolyzed rat DNA. The results indicate significant quantitative and perhaps qualitative differences between cultured rat and human esophagus in their ability to activate N-nitrosamines, although unknown physiological differences after culture may contribute to this difference.

Alkylation↗
PubMed1982

Detection of metabolites of N-nitrosopyrrolidine and N-nitrosoethylmethylamine in cultures of human bladder epithelial cells of normal origin.

Cultured human bladder epithelial cells of normal origin are capable of metabolizing N-nitrosamines. Cultures from three different cell lines were incubated with NPYR and NEMA in order to investigate the formation of volatile N-nitrosamines. Seven volatile compounds with positive TEA response, including NDMA and NEMA, were detected in the culture media incubated with NPYR. The identity of NEMA, which was the main component of this group of metabolites, was confirmed by mass spectrometry. Culture media incubated with NEMA showed formation of NDMA. In four of five incubation experiments with NPYR, NHPYR was detected as a metabolite. The formation of metabolites containing the N-nitroso group presumably occurs via a beta-hydroxylation pathway.

Cells, Cultured↗
PubMed1982

Studies of host factors in carcinogenesis using cultured human tissues and cells.

Recent progress in the development of conditions for culturing epithelial tissues and cells from adult humans has provided cancer researchers with an opportunity to investigate directly the various facets of carcinogenesis in human cells. Studies of activation and deactivation of several classes of chemical carcinogens have revealed that the metabolic pathways and the predominant adducts formed with DNA are generally similar in humans and experimental animals. Wide quantitative interindividual differences are found in humans and other outbred animal species. When the metabolic capabilities of specimens from different levels of biological organization are compared, the profile of benzo[a]pyrene metabolites is similar in cultured tissues and cells, but subcellular fractions, e.g., microsomes, produce a qualitatively and quantitatively aberrant pattern. To test the interactive effects of cell types in the metabolic activation of carcinogens and to assess further interindividual differences among people, human tissue- and cell-mediated mutagenesis assays have been developed. The fact that terminally differentiated cells such as pulmonary alveolar macrophages can activate benzo[a]pyrene and mediate an increase in frequencies of mutations and sister chromatid exchanges in cocultivated 'detector' cell populations, i.e., Chinese hamster V79 cells, suggests that non-target cells of chemical carcinogens may play an important role in the activation of environmental carcinogens. Malignant transformation of human epithelial and fibroblastic cells in vitro has been accomplished by several research groups. Asbestos, a cocarcinogenic agent in bronchogenic carcinogenesis, has been found to induce polyploid epithelial lesions with atypical cells in human bronchial explants. Carcinogenesis studies using cultured human tissues and cells are providing new insights into the mechanisms of carcinogenesis and are useful in identifying host factors that influence individual risk to environmental carcinogens.

Biotransformation↗