Search PubMed⌕ Search

Biomedical subjects

W W Weber

Publications and source records attributed to W W Weber.

At least 73 records · Page 4Linked to original sources
PubMed1982

Biochemical characterization of genetically variant aromatic amine N-acetyltransferases in A/J and C57BL/6J mice.

Biochemical genetic studies to determine the molecular basis for the differences in N-acetylation between the A/J and C57BL/6J mouse strains were carried out. Purification of liver N-acetyltransferase from both strains showed that aminofluorene and p-aminobenzoic acid activities are not separable by protein purification techniques which exploit differences in charge and size. In addition, both aminofluorene and p-aminobenzoic acid N-acetyltransferase activities from the C57BL/6J mouse liver enzymes migrated as a single symmetrical protein band after polyacrylamide disc gel electrophoresis. For aminofluorene and p-aminobenzoic acid, the two mouse strains showed apparent Km differences which suggest a difference in a structural gene product, and at least may partially account for the observed differences in N-acetylation. N-Acetyltransferase activity of selected extrahepatic tissues showed that both small intestine and kidney reflect the animal's phenotype as determined by liver or blood N-acetyltransferase. Sex differences were apparent in this activity in C57BL/6J mouse kidney, with males exhibiting approximately 2.5-fold higher activity for aminofluorene and approximately 3-fold higher activity for p-aminobenzoic acid than did females.

4-Aminobenzoic Acid↗
PubMed1982

Relationship between the genetically determined acetylator phenotype and DNA damage induced by hydralazine and 2-aminofluorene in cultured rabbit hepatocytes.

The relationship between acetylation rates of rabbit hepatocytes and their susceptibility to genotoxicity by DNA-damaging chemicals that undergo N-acetylation was studied in primary cultures of hepatocytes from New Zealand White rabbits that have a genetically determined difference in acetylation rates. Hepatocytes from rapid and slow acetylator rabbits maintained in culture the difference in acetylation rates that existed in vivo, DNA repair, an index of DNA damage, was produced by hydralazine in hepatocytes from slow acetylator rabbits but not in those from rapid acetylators. In contrast to these results, hepatocytes from rapid acetylators were more sensitive than those from slow acetylators to toxicity from the carcinogen 2-aminofluorene and displayed greater amounts of DNA repair. The amount of DNA repair measured with either chemical was dose dependent. These phenotype-dependent differences in the genotoxicity of two DNA-damaging chemicals provide evidence for the role of the acetylation polymorphism as a factor in determining susceptibility to toxicity, and perhaps carcinogenicity, of these chemicals.

Acetylation↗
PubMed1982

Biochemical evidence for the coexistence of monomorphic and polymorphic N-acetyltransferase activities on a common protein in rabbit liver.

New Zealand White rabbits were classified as rapid or slow acetylators by measuring the N-acetylation half-life of i.v. administered sulfadiazine, by pedigree analysis and by determination of liver N-acetyltransferase (NAT) activity in vitro. Slow acetylator rabbits were found to have significantly lower levels of p-aminobenzoic acid NAT activity in vitro than did rapid acetylator rabbits, demonstrating genetic covariation of p-aminobenzoic acid (monomorphic) and isoniazid (polymorphic) NAT activity. Monomorphic and polymorphic NAT activities could not be separated by two extensive purification procedures involving sequential centrifugation, fractional precipitation with ammonium sulfate, ion-exchange chromatography on DEAE-cellulose, gel filtration on Sephadex or Sephacryl and isoelectric focusing or electrophoresis on polyacrylamide gels. In addition, indistinguishable heat inactivation patterns were demonstrated for the two NAT activities utilizing highly purified NAT preparations at two different temperatures. Each of these findings support the coexistence of monomorphic and polymorphic NAT activities on a common protein.

Acetylation↗
PubMed1982

A unique pharmacogenetic expression of the N-acetylation polymorphism in the inbred hamster.

Liver N-acetyltransferase (NAT) preparations (105,000 x g cytosol) were obtained from both sexes of 26 strains of inbred hamsters. Liver NAT activity levels were determined for six arylamine substrates; isoniazid, p-aminobenzoic acid (PABA), p-aminosalicylic acid (PAS), sulfamethazine (SMZ), procainamide and 2-aminofluorene. The N-acetylation of isoniazid, SMZ, procainamide and 2-aminofluorene exhibited a monomorphic expression in the hamster as the genetic variation in NAT activity levels between hamster strains was only about 2-fold for each substrate. In contrast, the N-acetylation of PABA and PAS showed a polymorphic expression in the hamster. Two inbred hamster lines (Bio 1.5 and Bio 82.73) had over 400-fold lower PABA NAT and over 20-fold lower PAS NAT activity levels than did the other inbred strains. In addition, the genetically determined N-acetylation differences between the rapid and slow acetylator hamster strains were also demonstrated in vivo for PABA but not for SMZ. Comparison of Michaelis-Menten kinetic constants of PABA NAT activity in a rapid and slow acetylator strain showed a 20-fold lower Km in the rapid acetylator strain suggesting an intrinsic structural difference in rapid and slow acetylator hamster liver NAT. Thus, the pharmacogenetic expression of the N-acetylation polymorphism is quite unique in the inbred hamster, in that PABA and PAS are genetically polymorphic substrates, whereas isoniazid, SMZ, procainamide and 2-aminofluorene are monomorphic, in direct contrast to man and rabbit.

Acetylation↗
PubMed1982

Identification of genetically homozygous rapid and slow acetylators of drugs and environmental carcinogens among established inbred rabbit strains.

Liver and gut mucosa N-acetyltransferase (NAT) cytosol (105,000 x g) was prepared from selected lines of New Zealand White rapid and slow acetylator rabbits bred and housed at the University of Michigan, and from inbred and partially inbred rabbits obtained from The Jackson Laboratory. Liver NAT activity was determined with p-aminobenzoic acid, p-aminosalicyclic acid, procainamide, sulfamethazine, isoniazid and 2-aminofluorene as substrates. Gut mucosal NAT activity was determined with 2-aminofluorene. A gene dose-response relationship was observed for both liver NAT and gut mucosa NAT with all substrates tested. Highest levels were always observed in homozygous rapid acetylator inbred strains (B/J, III/J, IIIC/J, III/DwJ, IIIEP/J and IIIVO/J), lower levels in obligate heterozygous rapid acetylator rabbits and lowest levels in homozygous slow acetylator inbred (ACEP/J, III/cdJ, IIIVO/ahJ, and IIIVO/vptJ) and outbred rabbits. The differences in magnitude of liver NAT activity level between acetylator genotypes was dependent on the substrate employed, progressively increasing in the following order: p-aminobenzoic acid, p-aminosalicyclic acid, procainamide, sulfamethazine, isoniazid, 2-aminofluorene. The determination of kinetic constants for liver p-aminosalicyclic acid NAT activity indicated a 2-fold difference in apparent Vmax between rapid acetylator genotypes and a 30-fold difference between rapid and slow acetylator phenotypes. In addition, the apparent Km for p-aminosalicyclic acid was significantly lower in the slow acetylators than in the rapid acetylators.

Acetylation↗
PubMed1982

Association of arylhydroxamic acid N,O-acyltransferase and genetically polymorphic N-acetyltransferase in established inbred rabbit strains.

Partially purified liver preparations from 17 inbred and partially inbred rabbit strains were assayed for polymorphic N-acetyltransferase (NAT) and arylhydroxamic acid N,O-acyltransferase (AHAT) activities. The AC/J, AX/J, B/J, WH/J, X/J, Y-l/J, III/J, IIIC/J, III/DwJ, IIIEP/J and IIIVO/J inbred strains were identified as rapid acetylators and had high AHAT activity. The ACEP/J, AXBU/J, OS/J, III/cdJ, IIIVO/ahJ and IIIVO/vptJ strains were identified as slow acetylators and had low AHAT activity. These findings provide added evidence for the hypothesis that polymorphic NAT and AHAT activities are properties of the same enzyme. Additional studies in five of the rapid acetylator strains showed that they had significantly higher levels of liver NAT activity towards other arylamine acetylator predictor drugs and carcinogens than did obligate heterozygous (Rr) rapid acetylators from our rabbit colony. This indicates that the inbred animals are homozygous (RR) rapid acetylators and that there is a gene-dose response difference between the two rapid acetylator genotypes. Availability of established inbred and partially inbred strains shown to possess both acetylator phenotypes enhances the opportunity for using the rabbit as a genetic model for evaluating the role of the isoniazid acetylator polymorphism as a host factor in arylamine-related carcinogenesis.

Acetyltransferases↗
PubMed1981

Pharmacokinetic studies on the drug-related lupus syndrome. Differences in antinuclear antibody development and drug-induced DNA damage in rapid and slow acetylator animal models.

Pharmacogenetic study of an inbred mouse model system derived from A/J (slow acetylator) and C57BL/6J (rapid acetylator) parental strains shows that spontaneous occurrence of antinuclear antibodies is associated with the slow acetylator phenotype although the development of spontaneous and procainamide-induced antinuclear antibodies is a dissociable process. In another study using primary cultures of intact hepatocytes obtained from slow and rapid acetylator rabbits, observations indicate that the amount of DNA damage induced by exposure to hydrazine and arylamine containing foreign compounds depends on the concentration of the foreign compound used as well as on the acetylator phenotype. Exposure to hydralazine induced greater DNA damage in slow acetylator hepatocytes whereas exposure to the arylamine carcinogen, 2-aminofluorene, induced greater DNA damage in rapid acetylator hepatocytes.

Acetylation↗
PubMed1981

An enzyme marker to ensure reliable determinations of human isoniazid acetylator phenotype in vitro.

Human liver N-acetyltransferase (NAT) activity undergoes rapid inactivation after death. Thus, in vitro determination of acetylator phenotype in liver autopsies may be unreliable. In the present investigation, the relative stabilities of monomorphic and polymorphic NAT activity were compared in situ in human and rabbit liver of rapid and slow acetylator phenotype. In both phenotypes, the monomorphic NAT activity was considerably less stable than the polymorphic, enabling it to be utilized as an enzyme marker to assure reliable in vitro phenotype classification.

4-Aminobenzoic Acid↗
PubMed1981

Formation, metabolic activation by N, O-acyltransfer, and hydrolysis of N-acyl-N-arylamine derivatives.

Amines and hydroxylamines can be produced from N-substituted aryl compounds by many organisms. Both functional groups can by N-acetylated enzymatically be preparations from the tissues of most mammalian species. The N-acylated products are subject to further metabolism including oxidation, hydrolysis, conjugation, or, with arylhydroxamic acids, N-O-acyltransfer. These reactions are of concern because they lead to changes in the levels of compounds that can alter tissue macromolecules. Select N-hydroxyarylamines and N-acyloxyarylamines can react with nucleic acid, and the hydroxylamines are mutagenic in bacterial systems. Thus the relative rates of these biochemical reactions within an organism may determine whether exposure to an arylamine will cause an adverse biologic effect. The ability of an arylamine to induce tumors reflects the composite effects of genetic determinants (i.e., species, strain, sex, and organ) as well as exposure to xenobiotic compounds because these factors modulate the metabolic pathways crucial to the carcinogenic process. The extreme genetic differences in the levels of the enzymes involved in the metabolism of N-acyl derivatives of arylamines in man and experimental animals offers an experimental approach that may aid in elucidating the mechanisms by which these compounds induce cancer.

Acetyltransferases↗
PubMed1980

Evidence that arylhydroxamic acid N,O-acyltransferase and the genetically polymorphic N-acetyltransferase are properties of the same enzyme in rabbit liver.

Arylhydroxamic acid N,O-acyltransferase and Co-ASAc-dependent N-acetyltransferase activities were measured simultaneously in liver cytosols from rabbits of known acetylator phenotype. Both activities were high in rapid acetylator rabbits and low in slow acetylator rabbits indicating that these two acetyl transfer steps in the metabolic activation of certain arylamines are under common genetic control in this species. The two enzyme activities could not be resolved by sequential centrifugation, fractional precipitation with ammonium sulfate, ion exchange chromatograhy on DEAE-cellulose, gel filtration on Sephacryl, and electrophoresis on polyacrylamide gels. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis of extracts of disc gel electrophoretic slices showed that a single symmetrical protein band with a molecular weight of 33,000 was associated with both activities. The results obtained strongly suggest that the CoASAc-dependent N-acetyltransferase reaction and the intramolecular N,O-acetyl transfer by arylhydroxamic acid N,O-acyltransferase are properties of the same enzyme.

Acetyltransferases↗
PubMed1980

N-acetylation of drugs. Observations on the properties of partially purified N-acetyltransferase from peripheral blood of rabbit.

A method is described for the partial purification of N-acetyltransferase (EC 2.3.1.5) from peripheral blood of rabbit. This enzyme purified from both rapid- and slow-ioniazid-acetylator phenotype rabbits was examined with regard to stability, substrate specificity, cation effect, rate of inactivation, temperature and pH optimum. Data show that in the biochemical characteristics examined the enzyme is independent of acetylator phenotype. The possible significance of these findings to the evolutionary origin of drug-acetylating enzymes in rabbit blood and liver is discussed.

Acetylation↗
PubMed1980

Characterization of human lymphocyte N-acetyltransferase and its relationship to the isoniazid acetylator polymorphism.

Characterization of human lymphocyte N-acetyltransferase (NAT) for specific activity, substrate specificity, inhibition, pH optimum, apparent Km kinetic mechanism, trypsin stability, freezing stability, and heat stability was carried out in rapid and slow isoniazid (INH) acetylators. There is a statistically significant difference in the heat stability of lymphocyte NAT from rapid and slow INH phenotypes. The lymphocyte enzyme from rapid INH acetylators is less heat stable than the lymphocyte enzyme from slow INH acetylators. This is an indication of a structural, possibly polymorphic, difference in lymphocyte NAT from the two acetylator phenotypes.

Acetylation↗
PubMed1980

Inheritance of acetylator phenotype in mice.

The inheritance of two acetylator traits in a new mouse model of the human isoniazid acetylator polymorphism has been characterized. A/J mice have little or no blood p-aminobenzoic acid N-acetyltransferase activity and can excrete a low ratio of acetylsulfamethazine to sulfamethazine in urine. C57BL/6J mice have considerable blood p-aminobenzoic acid N-acetyltransferase activity and can excrete a high ratio of acetylsulfamethazine to sulfamethazine in urine. The expression of the blood p-aminobenzoic acid acetylation trait in F1, F2 and backcross progeny from A/J and C57BL/6J matings is consistent with simple Mendelian inheritance of two codominant alleles. Inheritance of in vivo acetylation rate, as measured by urinary ratio of acetylsulfamethazine to sulfamethazine, is independent of the blood acetylator polymorphism and is probably governed by simple Mendelian inheritance with incomplete dominance of low urinary ratio over high. Incomplete dominance appears to be limited to animals bearing one or two genes for rapid acetylation of p-aminobenzoic acid by blood hemolysates.

4-Aminobenzoic Acid↗
PubMed1980

Antinuclear antibodies related to acetylator phenotype in mice.

A/J mice are proposed as a model of the human lupus diathesis since we previously determined that they express a slow acetyltor phenotype while others showed them to have a predisposition to develop spontaneous and drug-induced antinuclear antibodies. A/J mice were mated with C57BL/6J mice, a rapid acetylator phenotype which is relatively resistant to spontaneous and drug-induced antinuclear antibodies, to assess the importance of slow acetylator status as a component of the lupus diathesis. Procainamide, a potent inducer of antinuclear antibodies, was acetylated to a lesser degree by A/J mice than by C57BL/6J mice. This difference, detectable by in vitro assay but not by urinary levels of acetylated drug, represents a genetic polymorphism which can be detected in F2 and backcross progency of these two strains. We confirmed that A/J mice have a higher incidence of spontaneous antinuclear antibodies than C57BL/6J mice and that in A/J mice these antibodies can be induced by oral procainamide (6 g/l of drinking water for 37 weeks); procainamide tended to suppress antinuclear antibody formation in C57BL/6J mice, however. Rapid and slow acetylators among F2 and backcross populations were identified by a test for N-acetyltransferase activity in blood hemolysates. These two groups together with their respective rapid and slow acetylator parents were compared in respect to incidence of antinuclear antibodies. Slow acetylator phenotypes among F2 and backcross mice were predisposed to high titers of antinuclear antibodies like the slow acetyltor A/J strain. However, long-term exposure to procainamide suppressed antinuclear antibody formation as was found in the rapid acetylator C57BL/6J strain. Thus, the ability to N-acetylate procainamide is not the sole factor controlling the ability of this drug to induce antinuclear antibodies.

Acetylation↗