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K W Bock

Publications and source records attributed to K W Bock.

At least 73 records · Page 4Linked to original sources
PubMed1991

Genomic alterations of the c-myc protooncogene in relation to the overexpression of c-erbB2 and Ki-67 in human breast and cervix carcinomas.

Genomic alterations of c-myc (amplification, rearrangements and hypomethylation) were investigated in 30 breast carcinomas and 20 cervix carcinomas. In breast carcinomas c-myc alterations were compared with overexpression of the c-erbB2 protooncogene and the proliferation marker Ki-67. Alterations of c-myc were found in 50% of the breast carcinomas and in 25% of the cervix carcinomas. In 23% of the breast carcinomas c-erbB2 overexpression was associated with c-myc alterations. In 17% of the cases there was overexpression of c-erbB2 without detectable alterations of c-myc. Hence, in 67% of breast cancers alterations of c-myc and/or c-erbB2 have been found, while in 81% of the samples Ki-67 expression was increased. The results suggest that the study of c-myc alterations provides an important complement to that of other prognostic indicators of breast cancer such as c-erbB2 expression.

Adult↗
PubMed1991

Assessment of biological activities of mixtures of polychlorinated dibenzo-p-dioxins: comparison between defined mixtures and their constituents.

As a first step to assess biological activities of complex mixtures of polychlorinated dibenzo-p-dioxins (PCDDs), induction of 7-ethoxyresorufin O-deethylase (EROD) by defined mixtures and their constituents has been analysed in vitro. Two cell systems have been compared: primary hepatocyte cultures and hepatoma H4IIE cells. EC50 values of PCDDs were compared with that of the most potent compound, 2,3,7,8-Cl4DD (2,3,7,8-tetrachlorodibenzo-p-dioxin) and expressed as 2,3,7,8-Cl4DD equivalents (TEs). TEs for three defined mixtures containing up to 49 PCDDs could be predicted from the sum of TEs for the 2,3,7,8-substituted congeners. Efficacies (maximal enzyme induction) of less potent PCDDs (1,2,3,4-Cl4DD, Cl8DD and of a mixture containing 86% Cl8DD and of benz(a)anthracene were lower in hepatocytes (by 33%) and in H4IIE cells (by 50%). The results suggest that biological activities of complex PCDD mixtures are largely due to additive effects of their 2,3,7,8-substituted constituents.

Animals↗
PubMed1991

The UDP glucuronosyltransferase gene superfamily: suggested nomenclature based on evolutionary divergence.

A nomenclature system for the UDP glucuronosyltransferase superfamily is proposed, based on divergent evolution of the genes. A total of 26 distinct cDNAs in five mammalian species have been sequenced to date. Comparison of the deduced amino acid sequences leads to the definition of two families and a total of three subfamilies. For naming each gene, we propose that the root symbol UGT for human (Ugt for mouse), representing "UDP glucuronosyltransferase," be followed by an Arabic number denoting the family, a letter designating the subfamily, and an Arabic numeral representing the individual gene within the family or subfamily (hyphen before the Arabic number for mouse), e.g., human UGT2B1 and murine Ugt2b-1. Whereas the gene and cDNA should be italicized, the corresponding transcript, protein, and enzyme activity should not be written with lowercase letters or in italics, e.g., human or murine UGT2B1. Recent experimental evidence suggests that several exons of the UGT1 gene might be shared, indicating that distinct UGT1 transcripts and proteins may arise via alternative splicing; the gene and gene product of alternative splicing will be designated with an asterisk, e.g., UGT1*6 and UGT1*6, respectively. When an orthologous gene between species cannot be identified with certainty, as occurs in the UGT2B subfamily, we recommend sequential naming of the genes chronologically as they become characterized. We suggest that the human nomenclature system be used for species other than the mouse. We anticipate that this UGT gene nomenclature system will require updating on a regular basis.

Animals↗
PubMed1991

Immunochemical localization and functional characterization of cytochrome P450IIE1 in rat hepatocyte foci and nodules.

P450IIE1 was studied in rat hepatocyte foci and nodules from male Wistar rats, treated for 7 weeks with N-nitroso-morpholine (20, 40 and 80 mg/ml of drinking water). Livers were examined after 15, 23 and 31 weeks. Using specific anti-P450IIE1 IgG, different phenotypes of P450IIE1-altered foci were observed: (i) positive foci, predominant at early times and at the two lower dosages, (ii) negative foci and (iii) mixed-type foci consisting of P450IIE1-positive and -negative hepatocytes which were preponderant at 31 weeks. Immunoblotting of microsomes from livers containing foci and nodules obtained at week 31 of the experiment revealed a decrease in P450IIE1 level, which was correlated to decreased high affinity dimethylnitrosamine demethylase activity. The results suggest phenotypic heterogeneity of P450IIE1-altered foci with predominantly negative foci at later stages.

Animals↗
PubMed1991

Roles of UDP-glucuronosyltransferases in chemical carcinogenesis.

UDP-glucuronosyltransferases (UGT) play a major role in the elimination of nucleophilic metabolites of carcinogens, such as phenols and quinols of polycyclic aromatic hydrocarbons. In this way they prevent their further oxidation to electrophiles, which may react with DNA, RNA, and protein. They also inactivate carcinogenic, N-oxidized metabolites of aromatic amines. Furthermore, glucuronides may be stable transport forms of proximate carcinogens excreted via the biliary or urinary tract, thereby liberating the ultimate carcinogen at the target of carcinogenicity. Isozymes of the UGT enzyme superfamily that control the glucuronidation of metabolites of aromatic hydrocarbons and of N-oxidized aromatic amines have been identified in rats and humans. Phenol UGT appears to be coinduced with other drug-metabolizing enzymes via the Ah or dioxin receptor. This isozyme probably controls various proximate carcinogens and contributes to the persistently altered enzyme pattern, leading to the "toxin-resistance phenotype" at cancer prestages. Knowledge about UGTs in different species, their regulation, and their tissue distribution will improve the risk assessment of carcinogens.

Animals↗
PubMed1990

Persistently increased expression of a 3-methylcholanthrene-inducible phenol uridine diphosphate-glucuronosyltransferase in rat hepatocyte nodules and hepatocellular carcinomas.

Increased UDP-glucuronosyltransferase in rat hepatocyte nodules and hepatocellular carcinomas produced by feeding 2-acetylaminofluorene or N-nitrosomorpholine was studied using isozyme-selective substrates, antibodies, and DNA probes. UDP-glucuronosyltransferase (UDP-GT) activities toward 4-methylumbelliferone, 1-naphthol, and benzo[a]pyrene-3,6-quinol were reversibly increased by short term feeding of 2-acetylaminofluorene but were persistently increased in hepatocyte nodules and differentiated hepatocellular carcinomas. Immunoblot analysis revealed that short term feeding of 2-acetylaminofluorene increased a Mr 55,000 polypeptide corresponding to the previously characterized UDP-GTI or phenol UDP-GT. However, in some hepatocyte nodules and hepatocellular carcinomas either the Mr 55,000 or a new Mr 53,000 polypeptide was preferentially increased, suggesting heterogeneous UDP-GT forms in liver nodules and carcinomas. Northern blot hybridization with a synthetic DNA probe to phenol UDP-GT demonstrated increased levels of mRNA in liver nodules. The results suggest persistently increased expression of at least two phenol UDP-GT enzyme forms in hepatocyte nodules, which may contribute to the toxin-resistance phenotype frequently observed at cancer prestages.

2-Acetylaminofluorene↗
PubMed1990

Zinc increases EGF-stimulated DNA synthesis in primary mouse hepatocytes. Studies in tumor promoter-treated cell cultures.

To investigate factors influencing cell proliferation, cells are often cultured in serum-free medium. In the present study it is shown that addition of zinc chloride (40 microM) to primary mouse hepatocytes, cultured in Dulbecco's minimal essential medium, markedly enhanced growth factor (EGF)-stimulated [3H]thymidine incorporation into DNA. Treatment of cell cultures with phenobarbital or 3,4,3',4'-tetrachlorobiphenyl (enzyme inducers and tumor promoters in vivo) or with 12-O-tetradecanoylphorbol-13-acetate (the classical skin tumor promoter) further increased EGF-stimulated DNA synthesis. The results emphasize the need to adequately substitute zinc in serum-free cultured cells.

Animals↗
PubMed1990

Detection of genomic alterations in carcinogen-induced mouse liver tumors by DNA fingerprint analysis.

DNA fingerprint analysis was used to study structural abnormalities in the genome of mouse liver tumor cells. Liver tumors were induced in three strains of mice, namely C57BL/6J, C3H/He and B6C3F1, by a single injection of 20 micrograms/g body wt. diethylnitrosamine on day 15 after birth. DNA from liver tumors was digested with Hinfl restriction enzyme and hybridized on Southern blots with wild-type bacteriophage M13 DNA as probe. The resulting fingerprints of tumor DNA were compared with those of DNA from normal liver tissue. Genomic aberrations were detected in two out of 68 tumors analyzed, one stemming from a C57BL/6J and the other from a C3H/He mouse.

Animals↗
PubMed1990

Paracetamol test: modification by renal function, urine flow and pH.

Factors which might affect paracetamol disposition have been studied in a heterogenous group of patients in need of mild analgesia in an intensive care unit. Following oral administration of 1 g of paracetamol, plasma and urinary concentrations of the parent compound and metabolites were assessed by HPLC. The renal clearance of paracetamol was significantly correlated with urine flow (r = 0.84) and creatinine clearance (r = 0.77), but not with urine pH. Metabolite output was diminished in patients with reduced renal function. Despite the heterogeneity of patients and the diversity of drug treatment, the urine to plasma paracetamol concentration ratio appeared remarkably constant in patients with normal renal function (9.8 +/- 2.7). It is concluded that the metabolite to paracetamol ratio may only be regarded as a measure of the drug metabolizing capacity in subjects with normal renal function, if factors influencing urine volume and paracetamol absorption are standardized.

Acetaminophen↗
PubMed1990

Induction of drug-metabolizing enzymes by xenobiotics.

1. Isozymes of the cytochromes P-450, UDP-glucuronosyl transferases (UDPGT) and glutathione S-transferases appear to be differentially inducible by prototype inducers, such as 3-methylcholanthrene (MC), phenobarbital, pregnenolone 16 alpha-carbonitrile and clofibrate. 2. Mechanisms of induction include both transcriptional and post-transcriptional control. MC-type inducers (representing a large number of planar polycyclic aromatics, beta-naphthoflavone and polyhalogenated aromatics) bind with high affinity to the Ah receptor which controls gene expression similar to steroid hormone receptors. The Ah receptor controls the expression of several drug metabolizing enzymes. For example, both cytochrome P450 IA1 and UDPGT-1 appear to be co-induced by inducers with widely differing potencies, such as 2,3,7,8-tetrachloro-dibenzo-p-dioxin, 1,2,3,7,8-pentachloro-dibenzo-p-dioxin and benz(a)anthracene. Much less is known about the mechanism of action of other inducer prototypes. 3. Induction and co-induction of drug-metabolizing enzymes are generally considered as adaptive responses leading to more efficient elimination and detoxication of xenobiotics such as benzo(a)pyrene. For example, when the mutagenicity of benzo(a)pyrene and benzo(a)pyrene-3,6-quinone was studied in the Ames test, glucuronidation or glutathione conjugation (concomitant with cytochrome P-450-dependent reactions) markedly decreased their mutagenicity. The protective effect was more pronounced with the homogenate S9 fraction of MC-treated rats. However, at 'non-physiological' levels of exposure enzyme induction may lead to increased toxic risk.

Animals↗
PubMed1989

Tumor-promoting activity and cytotoxicity of 3,4,3',4'-tetrachlorobiphenyl on N-nitrosomorpholine-induced murine liver foci.

Effects of 3,4,3',4'-tetrachlorobiphenyl (TCB) on glucose-6-phosphatase (G6Pase)-altered hepatic foci of N-nitrosomorpholine (NNM)-treated B6C3F1 mice were investigated. TCB was chosen as a selective 3-methylcholanthrene-type inducer and tumor promoter. To initiate hepatocarcinogenesis, mice were treated with NNM (160 mg/l, in drinking water for 7 weeks), as in previous studies with the rat model. After a treatment-free interval of 22 weeks, TCB was administered (5 x 50 mg/kg, every 3 days), and liver foci were analysed 10 weeks after the start of TCB treatment. Unexpectedly, the number of G6Pase-negative and -positive foci per liver was markedly diminished following TCB treatment (to 32% and 57%, respectively). On the other hand, the mean volume of the remaining G6Pase-altered foci was enhanced, owing to an increase in the percentage of foci of large size (greater than 0.5 mm2). Throughout the experimental period of 39 weeks prolonged liver injury due to NNM and TCB treatment was demonstrated by histology and by elevated serum levels of glutamate-oxaloacetate transaminase. The results suggest that (in contrast to the rat system) TCB exhibited opposing effects on liver foci in the mouse model: (a) moderate tumor-promoting effects and (b) cytotoxic effects in NNM-injured liver, leading to decreased numbers of liver foci.

Adenoma, Bile Duct↗
PubMed1989

Heterogeneous alterations of UDP-glucuronosyltransferases in mouse hepatic foci.

UDP-glucuronosyltransferase (UDPGT) was studied immunohistochemically in hepatic foci and nodules of N-nitrosomorpholine-treated mice. Serial sections were stained for glucose-6-phosphatase (G6Pase). It was found that a high percentage of G6Pase-negative liver foci and nodules were also UDPGT-negative (34%). In addition, G6Pase-negative foci without altered UDPGT phenotype (30%) and UDPGT-negative foci without altered G6Pase phenotype (8%) were detected. G6Pase-positive foci were also present (24%). Interestingly, most G6Pase-positive foci were UDPGT-positive (16%). Some G6Pase-positive lesions without altered UDPGT phenotype were also found (8%). The major phenotype observed in rat hepatocarcinogenesis models (UDPGT-positive/G6Pase-negative foci) was not detectable in the mouse model. These results demonstrate heterogeneous alterations of UDPGTs in mouse hepatic foci. They furthermore suggest marked differences between the mouse and the rat in the regulation of UDPGTs in similarly induced rat hepatic foci.

Animals↗
PubMed1988

Properties of a 3-methylcholanthrene-inducible phenol UDP-glucuronosyltransferase from rat liver.

Functional and molecular probes are described which are useful to identify a 3-methylcholanthrene-inducible phenol UDP-glucuronosyltransferase (GTMC) from rat liver. Two different procedures for isolation of GTMC were compared, method 1 utilizing DEAE-Sepharose chromatography or method 2, chromatofocusing. Method 2 appeared to be superior in separating different isoenzymes. Subsequently the enzyme was purified by affinity chromatography on UDP-hexanolamine Sepharose. With both methods a protein was purified with a subunit Mr of 55,000, catalyzing glucuronidation of a variety of planar phenols and, in particular, of benzo(a)pyrene-3,6-quinol to its mono- and diglucuronide. Antibodies to GTMC recognized a polypeptide with a subunit Mr of 55,000 as the major 3-methylcholanthrene-inducible isoenzyme in rat liver microsomes. The described functional and molecular probes may help to differentiate GTMC from similar isoenzymes conjugating planar phenols and to elucidate its regulation and biological function.

Animals↗
PubMed1988

Altered growth control of rat hepatocytes after treatment with 3,4,3',4'-tetrachlorobiphenyl in vivo and in vitro.

Alterations of hepatocyte growth control by inducers of drug-metabolizing enzymes were investigated using 3,4,3',4'-tetrachlorobiphenyl (TCB) as the inducing agent. TCB was chosen as a selective 3-methylcholanthrene-type inducer and liver tumor promoter which probably exerts its biological actions through binding to the aryl hydrocarbon (Ah) receptor. In vivo treatment of rats with TCB (200 mg/kg) markedly stimulated growth of enzyme altered liver foci and [3H]-thymidine incorporation into nuclear DNA. Hepatocyte cultures from TCB-treated rats were more sensitive to exogenous growth factors such as EGF than those from untreated controls. In vitro TCB exposure of hepatocyte cultures also altered hepatocyte growth control in a dose-dependent manner and induced drug-metabolizing enzymes. TCB treatment in vivo enhanced EGF-stimulated autophosphorylation of the EGF receptor in liver plasma membranes. The results suggest that altered growth control is due to a direct effect of TCB on hepatocytes. The proposed model may be useful to elucidate a possible linkage between the functional stress imposed on hepatocytes by sustained overexpression of an adaptive program and modulation of hepatocyte growth control.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1987

Differential induction of human liver UDP-glucuronosyltransferase activities by phenobarbital-type inducers.

(1) UDP-glucuronosyltransferase (UDP-GT) activities and their inducibility were investigated in human liver microsomes from a "liver bank". (2) UDP-GT activities were differentially induced in liver microsomes from patients treated with the phenobarbital-type inducers phenytoin or pentobarbital. UDP-GT activity towards bilirubin was induced 3-fold. Enzyme activities towards paracetamol, benzo(a)pyrene-3,6-quinol, 4-methylumbelliferone and 1-naphthol were moderately induced and to similar extents (2-fold). In contrast, morphine and 4-hydroxybiphenyl glucuronidation were not significantly affected. Cytochrome P-450 dependent 7-ethoxycoumarin O-deethylase was increased 5-fold. (3) A human hepatoma cell line (Hep G2) was studied to obtain information on the inducibility of human UDP-GT activities by 3-methylcholanthrene-type inducers. UDP-GT activities towards benzo(a)pyrene-3,6-quinol and 1-naphthol were moderately but significantly induced by 3-methylcholanthrene-treatment of the cells (2-fold), whereas 7-ethoxyresorufin O-deethylase and 7-ethoxycoumarin O-deethylase were increased over 100- and 10-fold, respectively. (4) The results suggest the existence of differentially inducible UDP-GT isoenzymes in human liver. The findings may be useful as a guide to characterize human liver UDP-GT isoenzymes.

Acetaminophen↗
PubMed1987

Species differences of glucuronidation and sulfation in relation to hepatocarcinogenesis.

The role of glucuronidation and sulfation in the control of proximal and ultimate carcinogens is briefly reviewed. In accordance with the adopted practice of tumor risk assessment, data from two rodent species (rat, mouse) and man have been compared. Sulfate esters have been established as ultimate carcinogens in 2-acetylaminofluorene, safrole and estragole induced hepatocarcinogenesis. In interspecies comparisons the tumor incidence paralleled sulfotransferase activity (Miller and Miller 1981). Glucuronides are often stable transport forms of carcinogens and in this way determine their organ specificity, for example in 2-naphthylamine-induced bladder carcinogenesis and in colon carcinogenesis produced by 2',3-dimethyl-4-aminobiphenyl. In contrast to sulfotransferase activity certain UDP-glucuronyltransferase activities are differentially inducible by xenobiotics. A 3-methylcholanthrene-inducible phenol-glucuronyltransferase (GT1), present in rat, mouse and man, appears to be part of an adaptive program to detoxify aromatic hydrocarbons. After initiation of hepatocarcinogenesis permanent alterations of these enzymes occur; GT1 is markedly increased whereas sulfotransferase is decreased. Together with changes of other drug metabolizing enzymes these alterations often lead to toxin-resistance of initiated hepatocytes. This phenomenon may facilitate selective growth of initiated hepatocytes and may enhance the probability of multiple hits in their genome.

Animals↗
PubMed1987

The role of conjugation reactions in detoxication.

The role of conjugating enzymes is best understood by looking at the interaction between phase I (mostly cytochromes P-450) and phase II (conjugation) enzymes of drug metabolism. A balance between phase I and II enzymes of detoxication largely determines the disposition to drug toxicity. Reactive electrophilic metabolites, generated by phase I enzymes, are often controlled by GSH-transferases, whereas nucleophilic metabolites such as phenols are controlled by UDP-glucuronosyltransferases (GT) and sulfotransferases. It is more and more recognized that the control of the more stable and more abundant nucleophiles is as important as the control of electrophiles, since the former can be readily converted to electrophiles. For example, phenols and quinols can undergo quinone/quinol redox-cycles with the generation of reactive oxygen species. In the case of benzo(a)pyrene-3,6-quinol toxicity can be prevented by glucuronidation. Conjugating enzymes consist of families of isoenzymes with distinct but overlapping substrate specificity. Rather than dealing with individual isoenzymes, adaptive programs are emphasized by which gene expression of a battery of phase I and II enzymes is turned on by certain types of inducing agents. Mechanistically best known is the program turned on by 3-methylcholanthrene-type inducers which includes enhanced synthesis of certain isoenzymes of cytochrome P-450, GT and probably GSH-transferase. The program may adapt the organism to efficiently detoxify and eliminate aromatic compounds such as benzo(a)pyrene. Evidence is presented that this program exists in both rodents and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗