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W W Weber

Publications and source records attributed to W W Weber.

At least 19 recordsLinked to original sources
PubMed2001

The legacy of pharmacogenetics and potential applications.

Some 40 years of pharmacogenetic research indicates that knowledge of human genetic diversity is essential to a broader understanding of variation in human drug response, and suggests that drug therapy tailored to the genetic characteristics of the individual may be a realistic goal. Aided by new technologies, molecular studies of genetic polymorphisms of many human enzymes, receptors, and other proteins indicate that only a limited number of important protein variants account for the diversity in drug response, raising the prospect that these variants may be cataloged relatively soon for many human populations. The next great challenge of pharmacogenetics is to pin down the cellular location and effect of these variant proteins on the pathways and networks that govern individual variation in responses to drugs and other exogenous chemicals. In this paper, we will discuss some the current challenges to progress in pharmacogenetics and newer strategies that might be used to improve prospects of drug design and personalized therapy.

Animals↗
PubMed2001

Effect of pharmacogenetics on medicine.

Pharmacogenetics is moving rapidly to assemble a large set of polymorphisms that define the influence of genetic diversity on human drug response. Scientific and technological advances of the last 10 years have led to new approaches to the discovery of genetic drug susceptibility loci, the development of high-tech analytical strategies for drug susceptibility profiling, and a flood of new gene discoveries in the area of receptors and receptor polymorphisms. Extension and refinement of our knowledge of human genetic diversity is essential to the use of drugs in more of an individualized manner and to the discovery of better therapies, but knowledge of the functional consequences of this diversity, the next great challenge in pharmacogenetics, provides the best chance to profit from this diversity.

Drug Design↗
PubMed2001

Pharmacogenetic tactics and strategies: implications for paediatrics.

Genetic diversity exerts profound effects on variation in human drug response in adults, but comparatively little research that specifically relates to genetically abnormal responses in infancy and childhood has been reported. Specific genetic changes in human enzymes, receptors and other proteins that are implicated in drug response and their associated phenotypic correlates provide needed data for construction of profiles individualised to predict susceptibility to adverse drug reactions. If therapy adheres to such guidelines, failure to respond to drug therapy and drug toxicity among genetically susceptible persons can be greatly minimised or averted.

Forecasting↗
PubMed2000

Characterization of naturally occurring and recombinant human N-acetyltransferase variants encoded by NAT1.

The genotype at the NAT1* locus of an interethnic population of 38 unrelated subjects was determined by direct sequencing of 1.6-kb fragments amplified by PCR. The coding exon alone and together with the 3' noncoding exon of the wild-type (NAT1*4) and the three mutant alleles (NAT1*10, *11, and *16) detected was expressed in Escherichia coli and COS-1 cells, respectively, and the cytosolic fraction of mononuclear leukocytes from NAT1*4/*4 and NAT1*10/*10 homozygotes was also isolated. Recombinant and leukocyte cytosolic preparations were thoroughly characterized by N-acetylation activity with several NAT1-specific and -selective substrates, as well as by steady-state kinetics with varying amounts of the substrate (fixed acetyl CoA) and acetyl CoA (fixed substrate), thermodynamics, stability, and protein immunoreactivity with a polyclonal human anti-NAT1. The polyadenylation signal mutation in the 3' noncoding sequence of NAT1*10 affected none of the aforementioned parameters evaluated both with recombinant NAT1*10 and with the naturally occurring allele. Function was also unaffected by the coding and 3' noncoding exon mutations in NAT1*11. In contrast, the three extra adenosines located immediately after the sixth position of the polyadenylation signal in the 3' untranslated region of NAT1*16 ostensibly caused disruption of the predicted secondary structure of the pre-mRNA for NAT1 16, culminating in parallel 2-fold decreases in the amount and catalytic activity of NAT1 16 in COS-1 cell cytosol. This novel finding in N-acetylation pharmacogenetics clearly demonstrates a direct link between reduced catalytic activity and structural alteration in the 3' untranslated region of an NAT variant (NAT1*16) brought about by mutation.

3' Untranslated Regions↗
PubMed2000

Tissue- and gender-specific expression of N-acetyltransferase 2 (Nat2*) during development of the outbred mouse strain CD-1.

The human N-acetyltransferase (Nat2) genetic polymorphisms have been modeled in mouse strains. We determined the phenotype and genotype of the N-acetyltransferase 2 (Nat2*) gene among outbred CD-1 mice and found a mixed population of heterozygous and rapid and slow homozygous genotypes. Phenotypes determined with p-aminobenzoic acid demonstrated complete concordance of slow and rapid genotype and phenotype. The kidney p-aminobenzoic acid/Nat2-acetylating activity of CD-1 female mice showed a 2.5-fold increase at 80 days of age compared with day 1, whereas males showed a 4.3-fold increase at 25 days and a 5.8-fold increase at 80 days. Immunoblot analysis revealed a 2-fold increase in male kidney Nat immunoreactive protein at 80 days of age, whereas no significant differences were detected in female mice. Likewise, the Nat2 mRNA levels determined by ribonuclease protection assay showed an increase in transcript levels in kidney of male mice during postnatal development, whereas they remained unchanged in females. Gender-associated differences of Nat2 activity, protein, and transcript levels were absent in liver. These observations suggest that the increase in Nat2 enzymatic activity in kidney is accomplished by an increase in transcript. We propose that the observed increase in Nat2 transcript expression in male mice may be a result of androgen regulation during development.

Aging↗
PubMed2000

Pharmacogenetics of the arylamine N-acetyltransferases: a symposium in honor of Wendell W. Weber.

This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics presented at the joint meeting of the American Society for Biochemistry and Molecular Biology and the American Society for Pharmacology and Experimental Therapeutics, June 4-8, Boston, Massachusetts. The presentations focused on the pharmacogenetics of the NAT1 and NAT2 arylamine N-acetyltransferases, including developmental regulation, structure-function relationships, and their possible role in susceptibility to breast, colon, and pancreatic cancers. The symposium honored Wendell W. Weber for over 35 years of leadership and scientific advancement in pharmacogenetics and was highlighted by his overview of the historical development of the field.

Animals↗
PubMed1999

Populations and genetic polymorphisms.

BACKGROUND: Population frequencies of many polymorphic genes of pharmacogenetic interest depend on race or ethnic specificity. Association of these genes with person-to-person differences in drug effectiveness (hypersensitivity or resistance) and drug toxicity may also depend on the racial or ethnic characteristics of a population. Information about ethnic specificity is an integral part of pharmacogenetics because it can suggest a starting point for further study of these traits, tailoring drug therapy to the individual patient, and rational development and clinical trials of new drugs. Ethnic specificities of several medically important metabolic traits serve to illustrate these ideas. Among the traits considered is primaquine sensitivity, a sex-linked trait attributed to glucose-6-phosphate dehydrogenase deficiency that mainly affects males among African, Mediterranean, and Oriental people. Additional examples include the remarkable sensitivity of the Japanese to alcohol (ethanol) compared with whites; the ethnic specificity of the cytochrome P-450 enzyme CYP2D6* (debrisoquine/sparteine) polymorphism that results in poor, extensive, and ultrarapid metabolizers of at least 30 drugs; the CYP2C19* (mephenytoin) polymorphism that accounts for variable metabolism of proguanil, omeprazole, and certain barbiturates; and the polymorphic (NAT2*) acetylation of hydrazine and aromatic amine drugs, such as isoniazid, hydralazine, and sulfasalazine.

Aryl Hydrocarbon Hydroxylases↗
PubMed1998

Substrate selectivity of mouse N-acetyltransferases 1, 2, and 3 expressed in COS-1 cells.

Two human acetyl-CoA:arylamine N-acetyltransferases (NAT1 and NAT2) have been identified. Therapeutic and carcinogenic agents that are substrates for these isoenzymes (including isoniazid, sulfamethazine, p-aminobenzoic acid, 5-aminosalicyclic acid, and 2-aminofluorene) have been used to evaluate the role of the N-acetylation polymorphisms of NAT1 and NAT2 in the treatment of disease and differential risk of various cancers among individuals of differing acetylator phenotypes. The mouse is frequently used as a model of the human acetylator polymorphism. As three Nat isoenzymes have been identified in mouse, it is necessary to determine the selectivity of mouse Nats toward common NAT substrates. In the present study, Nat1*, Nat2*8, and Nat3* were expressed in COS-1 cells, and their substrate selectivity was evaluated with various substrates. Under the conditions used, mouse Nat2 had 20-, 2.4-, and 5.4-fold higher catalytic activity for p-aminobenzoic acid, 5-aminosalicylic acid, and 2-aminofluorene, respectively, than Nat1. Isoniazid N-acetylation was catalyzed only by mouse Nat1. For the substrates tested in this study, mouse Nat3 exhibited activity only toward 5-aminosalicylic acid and only at 1/20 the activity shown by Nat2. In addition, p-aminobenzoylglutamate, the first endogenous NAT substrate identified, was selective for mouse Nat2. These results further support the functional analogy of mouse Nat2 and human NAT1.

4-Aminobenzoic Acid↗
PubMed1998

Characterization of a hormone response element in the mouse N-acetyltransferase 2 (Nat2*) promoter.

Multiple variant alleles of the human arylamine N-acetyltransferase genes, NAT1* and NAT2*, alter the capacity of individuals to metabolize arylamines by N-acetylation. Although biochemical and genetic studies have improved our understanding of the molecular basis of the acetylation polymorphism in humans and other mammals, regulation of NAT* gene expression is not understood. In the present study, a segment of the 5'-untranslated region of mouse Nat2* was sequenced and characterized. Primer extension analysis and RNase protection assays exposed multiple transcription initiation sites located 112 to 151 bases upstream of the translational start site. Computer sequence analysis revealed a promoter-like region located within the region 530 bases upstream of the translational start site consisting of TATA boxes, upstream promoter elements such as a CAAT box and Sp1 binding site, regulatory elements such as a palindromic hormone response element (HRE), and enhancer regions such as an AP-1 transcription factor binding site. Transient expression of CAT reporter constructs of the mouse Nat2*-palindromic HRE demonstrated positive regulation of the HSV-thymidine kinase 1 (tk1) promoter and induced the expression of chloramphenicol acetyltransferase (CAT). This induction was initiated by the addition of hormones such as 5alpha-dihydrotestosterone (DHT) or dexamethasone and was entirely dependent on the presence of androgen or glucocorticoid receptors, respectively. Together with recent discoveries regarding the effects of testosterone on the expression of Nat2* in mouse kidney during development, the findings reported in this article suggest that the HRE found in the promoter region of Nat2* is a potential candidate for the mediation of androgenic regulation of Nat2* in mouse kidney.

Animals↗
PubMed1997

Kinetics of arylamine N-acetyltransferase in tissues from human breast cancer.

N-Acetyltransferase activity and Michaelis-Menten kinetic constants were determined in cancerous and non-cancerous breast tissues from 30 female patients with breast cancer. The results derived from tissue cytosol showed that 12 rapid, ten intermediate and eight slow acetylators based on p-aminobenzoic acid and 2-aminofluorene for substrates. The mean apparent Km values for the monomorphic substrate p-aminobenzoic acid and polymorphic substrate 2-aminofluorene were: 55.0 +/- 18.7, 114.0 +/- 30.0, and 137.0 +/- 37.2 microM; and 62.5 +/- 23.7, 166.0 +/- 67.0, and 239.0 +/- 76.6 microM for the slow, intermediate, and rapid enzymes, respectively. Compared to the enzymes from slow acetylators, the rapid acetylators exhibited mean apparent Vmax values eight- and ten-fold greater for p-aminobenzoic acid and 2-aminofluorene, respectively. A similar trend was obtained from the blood cytosols of cancerous patients and healthy volunteers. N-Acetyltransferase activity of breast cancerous and non-cancerous tissues were 1.5- and 2.2-fold different between rapid and slow acetylator with p-aminobenzoic acid and 2-aminofluorene as substrates, respectively. In breast cancerous tissues, 75% and 70% of the cytosolic N-acetyltransferase activity were inhibited under 2 mM of tamoxifen as substrates of 2-aminofluorene and p-aminobenzoic acid, respectively. Similar results were also found in non-cancerous tissues and blood samples from breast cancer patients and healthy volunteers. The effect of 1 mM tamoxifen on the N-acetyltransferase activity from breast cancerous tissues with positive estrogen receptor was 1.6-fold higher than that of negative estrogen receptor. This is the first demonstration to show that anti-estrogen drug can affect N-acetyltransferase activity in breast cancerous tissues. Therefore, this finding may provide a clue to the use of tamoxifen in prevention of human breast cancer.

4-Aminobenzoic Acid↗
PubMed1997

Induction of human prostaglandin endoperoxide H synthase-2 (PHS-2) mRNA by TCDD.

Numerous transcription response elements (e.g. AP-1, AP-2, GRE, CREB, as well as DRE) have been identified in the transcription regulation region of the PHS-2 gene in both mouse and human. The discovery of a DRE in the region raised the possibility that PHS-2 could be induced by TCDD, a dioxin compound. The time course and dose dependence of TCDD induction of PHS-2 mRNA expression were observed in HUVEC, primary human epithelial cells. In the observed time range (0-24 hours) the steady-state mRNA expression levels of PHS-2, as well as of mRNA for CYP1A1, increased with time at a TCDD dose of 20 nM. At the 24 hour time point, TCDD-treated cells displayed significant dose-dependent elevation of PHS-2 over the range of 0-40 nM TCDD. The increases in PHS-2 mRNA in both the time course and dose dependence experiments were consistent with that of CYP1A1. In contrast, mRNA for PHS-1, the constitutively expressed isoform of PHS, did not show significant changes under the conditions tested. These results are the first to indicate that TCDD can elevate PHS-2 mRNA level in a time and dose dependent manner. Further work needs to be done to learn the molecular mechanism of activation of PHS-2 by TCDD and the relation of TCDD action with other regulatory factors in the control of PHS-2 expression.

Cells, Cultured↗
PubMed1996

Evidence for arylamine N-acetyltransferase in the nematode Anisakis simplex.

N-Acetyltransferase activities with p-aminobenzoic acid and 2-aminofluorene were determined in Anisakis simplex, a nematode found in the intestine of the salt water fish Trichiurus lepturus. The N-acetyltransferase activity was determined using an acetyl CoA recycling assay and high pressure liquid chromatography. The N-acetyltransferase activity from a number of Anisakis simplex whole tissue homogenizations was found to be 2.89 +/- 0.52 nmol/min per mg for 2-aminofluorene and 2.54 +/- 0.45 nmol/min per mg for p-aminobenzoic acid. The K(m) and Vmax values obtained were 1.06 +/- 0.69 mM and 9.34 +/- 1.94 nmol/min per mg for 2-aminofluorene, and 2.25 +/- 0.10 mM and 14.44 +/- 0.7 nmol/min per mg for p-aminobenzoic acid. The optimal pH value for the enzyme activity was pH 8.0 for both substrates tested. The optimal temperature for enzyme activity was 37 degrees C for both substrates. The N-acetyltransferase activity was inhibited by iodoacetamide: at 0.25 mM iodoacetamide, activity was reduced 50% and 1.0 mM iodoacetamide inhibits activity more than 90%. Among a series of divalent cations and salts, Cu2+ and Zn2+ were demonstrated to be the most potent inhibitors. This is the first demonstration of acetyl CoA/arylamine N-acetyltransferase activity in a nematode and extends the number of phyla in which this activity has been found.

4-Aminobenzoic Acid↗
PubMed1996

Ahr locus phenotype in congenic mice influences hepatic and pulmonary DNA adduct levels of 2-amino-3-methylimidazo[4,5-f]quinoline in the absence of cytochrome P450 induction.

The potent food mutagen/carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) undergoes metabolic N-hydroxylation by cytochromes P450, including cytochrome P450 1A2, followed by generation of an unstable ester catalyzed by acetyltransferases; promutagenic DNA adducts result. Genetic polymorphisms in these enzymes have been implicated in human cancer risk related to arylamine exposure. We investigated the effects of Ahr locus and acetylator polymorphisms on 32P-postlabeled IQ/DNA adducts in lungs and livers of female C57BL/6 mice congenic for slow acetylation and/or Ahr-nonresponsiveness; some groups were pretreated with beta-naphthoflavone (beta NF), a cytochrome P450 1A inducer. Total adducts in lung were doubled by beta NF pretreatment in Ahr-responsive mice only and consisted of < or = 30% adduct 2 and < or = 60% adduct 3. In contrast, in Ahr-nonresponsive mice, adducts 2 and 3 were each < or= 7% of the total. Livers of noninduced Ahr-responsive mice formed 6-18-fold more adducts than those of nonresponsive mice. This striking difference was not due to altered levels of cyp1a-2, as indicated by specific enzyme assays and immunoblotting, and was not accompanied by a comparable increase in the ability of liver preparations to activate IQ to a mutagen in the Ames test. Pretreatment of responsive mice with beta NF to induce cyp1a-1 and cyp1a-2 led to a reduction in liver adduct levels. Acetylation phenotype also had a significant effect in Ahr-responsive mice, with 3-fold more adducts in slow than in rapid acetylators. These results indicate that in uninduced mice, the normal Ah receptor facilitates formation of IQ/DNA adducts in liver and alters the profile of adducts in lung, via an unknown mechanism, whereas the Ah receptor-dependent enzyme induction reduces adducts in liver, probably due to increased detoxification, but increases them in lung.

Acetylation↗
PubMed1996

Kinetics of acetyl coenzyme A:arylamine N-acetyltransferase from rapid and slow acetylator frog tissues.

N-acetyltransferase (NAT) activity was determined in 100 frog (Rana tigrina) livers using 2-aminofluorene and p-aminobenzoic acid as substrates. Overall, the liver NAT activity of the 50 females was higher than the liver NAT activity of the 50 males. The activities (mean +/- SD) of NAT from the bladder, blood, colon, and liver of males was 0.30 +/- 0.11, 0.05 +/- 0.03, 0.09 +/- 0.05, and 0.93 +/- 0.56 nmol/min/mg protein for the acetylation of aminofluorene and 0.29 +/- 0.06, 0.36 +/- 0.04, 0.26 +/- 0.02, and 0.32 +/- 0.14 nmol/min/mg protein for the acetylation of p-aminobenzoic acid. In the bladder, blood, colon, and liver from female frogs, the activities obtained were 1.00 +/- 0.41, 0.52 +/- 0.07, 0.08 +/- 0.05, and 1.27 +/- 0.49 nmol/min/mg protein for aminofluorene and 0.34 +/- 0.12, 0.36 +/- 0.04, 0.34 +/- 0.07, and 0.48 +/- 0.21 nmol/min/mg protein for p-aminobenzoic acid. Kinetic constants for arylamine NAT activity in the blood, liver, bladder, and colon from frogs with rapid, intermediate, and slow acetylator activities were determined. KM and Vmax values for aminofluorene were 2- to 6-fold higher for liver than for the other tissues. KM and Vmax values for p-aminobenzoic acid showed a smaller variation among the tissues examined, with values obtained for the liver and bladder being somewhat higher than the values for the blood and colon. An apparent KM difference for aminofluorene was found in the liver from frogs with high and low acetylator activity. Based on the aminofluorene NAT activity of liver, there seems to be a polymorphism in NAT activity with 4 rapid, 21 intermediate, and 75 slow acetylators among the 100 frogs assayed. Distribution of acetylator phenotypes was similar among the 50 males and 50 females in this study. This is the first demonstration of acetyl coenzyme A:arylamine NAT activity in an amphibian and could lead to the development of a frog model for monitoring the effect of pollution of wetland environments on native species.

Acetyl Coenzyme A↗
PubMed1995

Activation of 2-aminofluorene by prostaglandin endoperoxide H synthase-2.

Prostaglandin endoperoxide H synthase is the key enzyme in the conversion of arachidonic acid to tissue prostanoids. Two isoforms of prostaglandin endoperoxide H synthase have been identified: PHS-1 is constitutively expressed in most tissues under normal physiological conditions and PHS-2 is expressed in response to inflammatory agents, tumor promotors, and other agents related to mitogenesis. Previous work demonstrated that PHS-1 can activate arylamine carcinogens. We report here that PHS-2 can also activate an arylamine carcinogen to form DNA adducts. This is shown by: (1) use of purified ovine PHS-2 to form DNA adducts; (2) increased DNA adduct formation, PHS-2 mRNA, and PHS-2 protein after treatment of HUVEC cells with the PHS-2 inducer PMA; and (3) transient expression of PHS-2 cDNA in COS-1 cells gave rise to both elevations of PHS-2 enzyme protein and DNA adduct formation. Finally, two PHS inhibitors, aspirin and indomethacin, showed significant inhibition of PHS-2-mediated DNA adduct formation.

Animals↗
PubMed1995

DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in colon, bladder, and kidney of congenic mice differing in Ah responsiveness and N-acetyltransferase genotype.

Heterocyclic amines, suspected as cancer initiators, require metabolic activation to exert genotoxicity. The food carcinogen 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ) undergoes activation via N-hydroxylation by cytochrome P450 1A2, followed by O-esterification by N-acetyltransferase. We examined the effects of the Ah locus and acetylator polymorphisms (implicated in human colon and bladder cancer risk) on levels of 32P-postlabeled IQ-DNA adducts in C57BL/6 mice congenic for slow acetylation and/or Ah nonresponsiveness. Some were pretreated with beta-naphthoflavone (beta NF), an inducer of cytochromes P450 1A. Guanine adducts were detected in all organs, the predominant one corresponding to N2-(deoxyguanosine-8-yl)-IQ. In the kidney, beta NF pretreatment reduced total adducts by 50% in Ah-responsive animals (P = 0.021); the Ah or acetylator phenotype did not otherwise affect total adducts. In the colon of Ah-nonresponsive animals, rapid acetylators had 3-fold more adducts than slow acetylators (P = 0.0001, vehicle-pretreated; P = 0.0031, beta NF-pretreated). In Ah-responsive mice of either acetylator phenotype, beta NF pretreatment reduced total adducts in the colon by 70% (P = 0.0003). A significant interaction of phenotypes occurred in the bladder; beta NF-pretreatment caused a 2.5-fold increase in adducts but only in the Ah-responsive, rapid acetylator mice. In sum, these polymorphisms influenced the level of IQ-DNA adducts in the kidney, urinary bladder, and colon in complex ways.

Acetylation↗
PubMed1995

Influence of heredity on human sensitivity to environmental chemicals.

Hereditary peculiarities in individual responses to environmental chemicals are a common occurrence in human populations. Genetic variation in glutathione S-transferase, CYP1A2, N-acetyltransferase, and paraoxonase exemplify the relationship of metabolic variation to individual susceptibility to cancer and other toxicants of environmental origin. Heritable receptor protein variants, a subset of proteins of enormous pharmacogenetic potential that have not thus far been extensively explored from the pharmacogenetic standpoint, are also considered. Examples of interest that are considered include receptor variants associated with retinoic acid resistance in acute promyelocytic leukemia, with paradoxical responses to antiandrogens in prostate cancer, and with retinitis pigmentosa. Additional heritable protein variants of pharmacogenetic interest that result in antibiotic-induced deafness, glucocorticoid-remediable aldosteronism and hypertension, the long-QT syndrome, and beryllium-induced lung disease are also discussed. These traits demonstrate how knowledge of the molecular basis and mechanism of the variant response may contribute to its prevention in sensitive persons as well as to improved therapy for genetically conditioned disorders that arise from environmental chemicals.

Carcinogens, Environmental↗