Nomenclature for N-acetyltransferases

A consolidated classification system is described for prokaryotic and eukaryotic N-acetyltransferases in accordance with the international rules for gene nomenclature. The root symbol (NAT) specifically identifies the genes that code for the N-acetyltransferases, and NAT* loci encoding proteins with similar function are distinguished by Arabic numerals. Allele characters, denoted by Arabic numbers or by a combination of Arabic numbers and uppercase Latin letters, are separated from gene loci by an asterisk, and the entire gene-allele symbols are italicized. Alleles at the different NAT* loci have been numbered chronologically irrespective of the species of origin. For designation of genotypes at a single NAT* locus, a slash serves to separate the alleles; in phenotype designations, which are not italicized, alleles are separated by a comma.

Metabolic activation and deactivation of arylamine carcinogens by recombinant human NAT1 and polymorphic NAT2 acetyltransferases

A genetic polymorphism at the NAT2 gene locus, encoding for polymorphic N-acetyltransferase (NAT2), segregates individuals into rapid, intermediate or slow acetylator phenotypes. Both rapid and slow acetylator phenotypes have been associated with increased incidence of cancer in certain target organs related to arylamine exposure, suggesting a role for acetylation in both the activation and deactivation of arylamine carcinogens. A second gene (NAT1) encodes for a different acetyltransferase isozyme (NAT1) that is not subject to the classical acetylation polymorphism. In order to assess the relative ability of NAT1 and NAT2 to activate and deactivate arylamine carcinogens, we tested the capacity of recombinant human NAT1 and NAT2, expressed in Escherichia coli XA90 strains DMG100 and DMG200 respectively, to catalyze the N-acetylation (deactivation) and O-acetylation (activation) of a variety of carbocyclic and heterocyclic arylamine carcinogens. Both NAT1 and NAT2 catalyzed the N-acetylation of each of the 17 arylamines tested. Rates of N-acetylation by NAT1 and NAT2 were considerably lower for heterocyclic arylamines such as 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), particularly those (e.g. IQ) with steric hindrance to the exocyclic amino group. For carbocyclic arylamines such as 4-aminobiphenyl and beta-naphthylamine, the apparent affinity was significantly (P < 0.05) higher for NAT2 than NAT1. NAT1/NAT2 activity ratios and clearance calculations suggest a significant role for the polymorphic NAT2 in the N-acetylation of carbocyclic arylamine carcinogens. Both NAT1 and NAT2 catalyzed acetyl coenzyme A-dependent O-acetylation of N-hydroxy-2-aminofluorene and N-hydroxy-4-aminobiphenyl to yield DNA adducts. NAT1 catalyzed paraoxon-resistant, intramolecular N,O-acetyltransferase-mediated activation of N-hydroxy-2-acetylaminofluorene and N-hydroxy-4-acetylaminobiphenyl at low rates; catalysis by NAT2 was not readily detectable in the presence of paraoxon. In summary these studies strongly suggest that the human acetylation polymorphism influences both the metabolic activation (O-acetylation) and deactivation (N-acetylation) of arylamine carcinogens via polymorphic expression of NAT2. These findings lend mechanistic support for human epidemiological studies suggesting associations between both rapid and slow acetylator phenotype and cancers related to arylamine exposure.

Clinical pharmacokinetics of isoniazid

The pharmacokinetics of isoniazid in man are described. Pronounced interindividual variation in circulating isoniazid concentration and clearance which occur after dosing with the drug are associated with hereditary differences in the acetylator status. The variations in rate of isoniazid inactivation and elimination in different (rapid and slow) acetylator phenotypes are primarily due to differences in the rate of acetylation of isoniazid by a genetically controlled polymorphic N-acetyltransferase in liver and small intestine. An appreciable 'first-pass' effect is observed following oral isoniazid administration, particularly in the rapid acetylator phenotype. Liver disease can cause a significant prolongation in the clearance of isoniazid; in the acutely ill patient, the prolongation correlates most closely with serum bilirubin elevation, although the degree of prolongation is less important than the intrinsic genetic difference between acetylator phenotypes. The effect of renal impairment on isoniazid excretion is relatively unimportant, even in slow acetylators. Methods for monitoring blood and urine concentrations of isoniazid and for acetylator phenotype determination which are convenient for the patient and clinician are available. Implications of phenotype differences in acetylator status for the optimal management of tuberculosis with isoniazid are considered. Attempts to devise new isoniazid formulations for this purpose are being evaluated.

N-acetyltransferase 2 genetic polymorphism: effects of carcinogen and haplotype on urinary bladder cancer risk

A role for the N-acetyltransferase 2 (NAT2) genetic polymorphism in cancer risk has been the subject of numerous studies. Although comprehensive reviews of the NAT2 acetylation polymorphism have been published elsewhere, the objective of this paper is to briefly highlight some important features of the NAT2 acetylation polymorphism that are not universally accepted to better understand the role of NAT2 polymorphism in carcinogenic risk assessment. NAT2 slow acetylator phenotype(s) infer a consistent and robust increase in urinary bladder cancer risk following exposures to aromatic amine carcinogens. However, identification of specific carcinogens is important as the effect of NAT2 polymorphism on urinary bladder cancer differs dramatically between monoarylamines and diarylamines. Misclassifications of carcinogen exposure and NAT2 genotype/phenotype confound evidence for a real biological effect. Functional understanding of the effects of NAT2 genetic polymorphisms on metabolism and genotoxicity, tissue-specific expression and the elucidation of the molecular mechanisms responsible are critical for the interpretation of previous and future human molecular epidemiology investigations into the role of NAT2 polymorphism on cancer risk. Although associations have been reported for various cancers, this paper focuses on urinary bladder cancer, a cancer in which a role for NAT2 polymorphism was first proposed and for which evidence is accumulating that the effect is biologically significant with important public health implications.

A review of sutures and suturing techniques

The ideal suture is strong, handles easily, and forms secure knots. It causes minimal tissue inflammation and does not promote infection. It stretches and accommodates wound edema. Although no single suture possesses all of these features, proper selection of sutures helps achieve better results in skin surgery. Proper suturing technique is essential for obtaining good cosmetic results and avoiding scarring and poor wound healing. Techniques that must be mastered include good eversion of skin edges, avoiding suture marks, maintaining uniform tensile strength along the skin edges, and precise approximation along skin edges.

A role for bioactivation and covalent binding within epidermal keratinocytes in sulfonamide-induced cutaneous drug reactions

Cutaneous reactions are the most common manifestation of delayed-type hypersensitivity caused by sulfamethoxazole and dapsone. In light of the recognized metabolic and immunologic activity of the skin, we investigated the potential role of normal human epidermal keratinocytes in the development of these reactions. Adult and neonatal normal human epidermal keratinocytes metabolized sulfamethoxazole and dapsone to N-4-hydroxylamine and N-acetyl derivatives in a time-dependent manner. The latter was catalyzed by N-acetyltransferase 1 alone as normal human epidermal keratinocytes did not express mRNA for N-acetyltransferase 2. Investigation of metabolism-dependent toxicity of sulfamethoxazole and dapsone, and subsequent incubation of normal human epidermal keratinocytes with the respective hydroxylamine metabolites, demonstrated that these cells were resistant to the cytotoxic effects of sulfamethoxazole hydroxylamine but not dapsone hydroxylamine. With prior depletion of glutathione, however, normal human epidermal keratinocytes became susceptible to the toxicity of sulfamethoxazole hydroxylamine. Covalent adduct formation by sulfamethoxazole hydroxylamine was detected in normal human epidermal keratinocytes, even in the absence of cell death, and was increased with glutathione depletion. Major protein targets of sulfamethoxazole hydroxylamine were observed in the region of 160, 125, 95, and 57 kDa. Dapsone hydroxylamine also caused covalent adduct formation in normal human epidermal keratinocytes. Together, these observations provide a basis for our hypothesis that normal human epidermal keratinocytes are involved in the initiation and propagation of a cutaneous hypersensitivity response to these drugs.

Functional characterization of human N-acetyltransferase 2 (NAT2) single nucleotide polymorphisms

N-Acetyltransferase 2 (NAT2) catalyses the activation and/or deactivation of a variety of aromatic amine drugs and carcinogens. Polymorphisms in the N-acetyltransferase 2 (NAT2) gene have been associated with a variety of drug-induced toxicities, as well as cancer in various tissues. Eleven single nucleotide polymorphisms (SNPs) have been identified in the NAT2 coding region, but the specific effects of each of these SNPs on expression of NAT2 protein and N-acetyltransferase enzymatic activity are poorly understood. To investigate the functional consequences of SNPs in the NAT2 coding region, reference NAT2*4 and NAT2 variant alleles possessing one of the 11 SNPs in the NAT2 coding region were cloned and expressed in yeast (Schizosaccharomyces pombe). Reductions in catalytic activity for the N-acetylation of a sulfonamide drug (sulfamethazine) and an aromatic amine carcinogen (2-aminofluorene) were observed for NAT2 variants possessing G191A (R64Q), T341C (I114T), A434C (E145P), G590A (R197Q), A845C (K282T) or G857A (G286T). Reductions in expression of NAT2 immunoreactive protein were observed for NAT2 variants possessing T341C, A434C or G590A. Reductions in protein stability were noted for NAT2 variants possessing G191A, A845C, G857A or, to some extent, G590A. No significant differences in mRNA expression or transformation efficiency were observed among any of the NAT2 alleles. These results suggest two mechanisms for slow acetylator phenotype(s) and more clearly define the effects of individual SNPs on human NAT2 expression, stability and catalytic activity.

GSTM1 null and NAT2 slow acetylation genotypes, smoking intensity and bladder cancer risk: results from the New England bladder cancer study and NAT2 meta-analysis

Associations between bladder cancer risk and NAT2 and GSTM1 polymorphisms have emerged as some of the most consistent findings in the genetic epidemiology of common metabolic polymorphisms and cancer, but their interaction with tobacco use, intensity and duration remain unclear. In a New England population-based case-control study of urothelial carcinoma, we collected mouthwash samples from 1088 of 1171 cases (92.9%) and 1282 of 1418 controls (91.2%) for genotype analysis of GSTM1, GSTT1 and NAT2 polymorphisms. Odds ratios and 95% confidence intervals of bladder cancer among New England Bladder Cancer Study subjects with one or two inactive GSTM1 alleles (i.e. the 'null' genotype) were 1.26 (0.85-1.88) and 1.54 (1.05-2.25), respectively (P-trend = 0.008), compared with those with two active copies. GSTT1 inactive alleles were not associated with risk. NAT2 slow acetylation status was not associated with risk among never (1.04; 0.71-1.51), former (0.95; 0.75-1.20) or current smokers (1.33; 0.91-1.95); however, a relationship emerged when smoking intensity was evaluated. Among slow acetylators who ever smoked at least 40 cigarettes/day, risk was elevated among ever (1.82; 1.14-2.91, P-interaction = 0.07) and current heavy smokers (3.16; 1.22-8.19, P-interaction = 0.03) compared with rapid acetylators in each category; but was not observed at lower intensities. In contrast, the effect of GSTM1-null genotype was not greater among smokers, regardless of intensity. Meta-analysis of the NAT2 associations with bladder cancer showed a highly significant relationship. Findings from this large USA population-based study provided evidence that the NAT2 slow acetylation genotype interacts with tobacco smoking as a function of exposure intensity.

Molecular genetics of human polymorphic N-acetyltransferase: enzymatic analysis of 15 recombinant wild-type, mutant, and chimeric NAT2 allozymes

Human polymorphic N-acetyltransferase (NAT2) catalyzes the N-acetylation of arylamine drugs and carcinogens. Human acetylator phenotype is regulated at the NAT2 locus and has been associated with differential risk to certain drug toxicities or cancer. We examined arylamine substrate and acetyl coenzyme A cofactor affinities, and the N-acetyltransferase catalytic activities of the wild-type and 14 different mutant or chimeric human NAT2 alleles expressed in an Escherichia coli JM105 expression system. NAT2 alleles contained nucleic acid substitutions at positions 191(G-->A; Arg64-->Gln), 282(C-->T; silent), 341(T-->C; Ile114-->Thr), 481(C-->T; silent), 590(G-->A; Arg197-->Gln), 803(A-->G; Lys268-->Arg), 857(G-->A; Gly286-->Glu) and various combinations (282/590; 282/803; 282/857; 341/481; 341/803; 341/481/803; 481/803) of the 870 base pair NAT2 coding region. Expression of all 15 NAT2 alleles produced immunoreactive NAT2 protein with N-acetylation activity. NAT2 proteins encoded by alleles with nucleic acid substitutions at positions 191, 341, 590, 282/590, 341/481, 341/803, and 341/481/803 exhibited arylamine N-acetyltransferase maximum velocities significantly (P < 0.001) lower than the wildtype NAT2. Thus, nucleic acid substitutions at positions 191, 341, and 590 either alone or in combination with other silent or conservative amino acid substitutions were sufficient to result in NAT2 proteins with significant reductions in N-acetylation activities. The recombinant NAT2 proteins also showed relative differences in intrinsic stability following incubation at 37 degrees C and 50 degrees C. NAT2 encoded by alleles with nucleotide substitutions at positions 191 and 857 were particularly unstable relative to the wild type.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic activation of aromatic and heterocyclic N-hydroxyarylamines by wild-type and mutant recombinant human NAT1 and NAT2 acetyltransferases

Recombinant human NAT1 and polymorphic NAT2 wild-type and mutant N-acetyltransferases (encoded by NAT2 alleles with mutations at 282/857, 191, 282/590, 341/803, 341/481/803, and 341/481) were expressed in Escherichia coli strains XA90 and/or JM105, and tested for their capacity to catalyze the metabolic activation (via O-acetylation) of the N-hydroxy (N-OH) derivatives of 2-aminofluorene (AF), and the heterocyclic arylamine mutagens 2-amino-3-methylimidazo [4,5-f]quinoline (IQ), 2-amino-3,4-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Both NAT1 and NAT2 (including all mutant human NAT2s tested) catalyzed the metabolic activation of each of the N-hydroxyarylamines to products that bound to DNA. Metabolic activation of N-OH-AF was greater than that of the heterocyclic N-hydroxyarylamines. The relative capacity of NAT1 versus NAT2 to catalyze activation varied with N-hydroxyarylamine substrate. N-OH-MeIQx and N-OH-PhIP exhibited a relative specificity for NAT2. These results provide mechanistic support for a role of the genetic acetylation polymorphism in the metabolic activation of heterocyclic amine mutagens and carcinogens.

Acetylator genotype and arylamine-induced carcinogenesis

A diverse array of arylamine chemicals derived from industry, diet, cigarette smoke and other environmental sources are carcinogenic. These chemicals require metabolic activation by host enzymes to chemically reactive electrophiles to initiate the carcinogenic response. Genetic regulation of activation and/or deactivation pathways are thought to account in large measure for corresponding differences in tumor incidence from these chemicals between tissues, between species, or between individuals within a species. Various acetyltransfer reactions are involved in arylamine metabolism and much has been learned regarding their enzymology, genetic regulation, and toxicological significance. The small amount of human data are supported by systematic investigations carried out in animal models characterized with respect to the acetylation polymorphism. Enzymological and genetic investigations suggest that common enzymes encoded by the acetyltransferase gene carry out a diverse set of acetyltransferase reactions. Thus, the acetylation polymorphism can influence both activation and deactivation pathways in arylamine metabolism. Of particular significance recently have been reports documenting the O-acetylation of N-hydroxyarylamine carcinogens and its genetic coregulation with the well-characterized arylamine N-acetylation polymorphism. The toxicological consequences of this polymorphic pathway have yet to be fully explored. Epidemiological investigations show associations between acetylator phenotype and the incidence and/or severity of tumors in the urinary bladder, colon and larynx. Associations between acetylator phenotype and breast cancer are more equivocal and require further study. The divergent influence of acetylator phenotype on the incidence of tumors in different organ sites suggests an important role for extrahepatic acetyltransferases, and further characterization of them in human and animal tissues is needed. The advent of newer methodologies to monitor chemical exposures and to measure acetylator phenotype (rapid, intermediate and slow) using less invasive and more standardized protocols should soon result in a much more definitive understanding regarding the role of acetylator status in arylamine-induced carcinogenesis.

Novel human N-acetyltransferase 2 alleles that differ in mechanism for slow acetylator phenotype

Three novel human NAT2 alleles (NAT2*5D, NAT2*6D, and NAT2*14G) were identified and characterized in a yeast expression system. The common rapid (NAT2*4) and slow (NAT2*5B) acetylator human NAT2 alleles were also characterized for comparison. The novel recombinant NAT2 allozymes catalyzed both N- and O-acetyltransferase activities at levels comparable with NAT2 5B and significantly below NAT2 4, suggesting that they confer slow acetylation phenotype. In order to investigate the molecular mechanism of slow acetylation in the novel NAT2 alleles, we assessed mRNA and protein expression levels and protein stability. No differences were observed in NAT2 mRNA expression among the novel alleles, NAT2*4 and NAT2*5B. However NAT2 5B and NAT2 5D, but not NAT2 6D and NAT2 14G protein expression were significantly lower than NAT2 4. In contrast, NAT2 6D was slightly (3.4-fold) and NAT2 14G was substantially (29-fold) less stable than NAT2 4. These results suggest that the 341T --> C (Ile(114) --> Thr) common to the NAT2*5 cluster is sufficient for reduction in NAT2 protein expression, but that mechanisms for slow acetylator phenotype differ for NAT2 alleles that do not contain 341T --> C, such as the NAT2*6 and NAT2*14 clusters. Different mechanisms for slow acetylator phenotype in humans are consistent with multiple slow acetylator phenotypes.

Functional characterization of nucleotide polymorphisms in the coding region of N-acetyltransferase 1

N-acetyltransferase 1 (NAT1) catalyses the activation and/or deactivation of aromatic and heterocyclic amine carcinogens. A genetic polymorphism in NAT1 is associated with an increased risk of various cancers and drug toxicities, but epidemiological investigations are severely compromised by a poor understanding of the relationship between NAT1 genotype and phenotype. Human reference NAT1*4 and 12 known human NAT1 allelic variants possessing nucleotide polymorphisms in the NAT1 coding region were cloned and expressed in yeast (Schizosaccharomyces pombe). Large reductions in N- and O-acetyltransferase catalytic activities were observed for recombinant NAT1 allozymes encoded by NAT1*14B, NAT1*15, NAT1*17, NAT1*19 and NAT1*22. Each of these alleles exhibited NAT1 protein expression levels below the limit of detection as measured by Western blot. No differences between high and low activity NAT1 alleles were observed in relative mRNA expression or relative transformation efficiency. The recombinant NAT1 17 and NAT1 22 allozymes showed reduced intrinsic stability when compared with NAT1 4. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) N-acetylation was not catalysed by any of the NAT1 allozymes. Large differences in the metabolic activation via O-acetylation of 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP) were noted for NAT1 allelic variants. The results of these studies suggest an important role for the NAT1 genetic polymorphism in metabolism of aromatic and heterocyclic amine carcinogens. Furthermore, these results suggest that low NAT1 phenotype results from NAT1 allelic variants that encode reduced expression of NAT1 and/or less-stable NAT1 protein.

Dietary selenium reduces the formation of aberrant crypts in rats administered 3,2'-dimethyl-4-aminobiphenyl

Human epidemiologic studies suggest that low selenium status is associated with increased cancer risk and that selenium supplementation is associated with reduction in the incidence of several cancers, including colorectal cancer. Aromatic and heterocyclic amine carcinogens are thought to be important in the etiology of human colorectal cancer, but no information is available on the effects of selenium on aromatic amine-induced colon cancer. In order to investigate this effect, aberrant crypt foci (ACF), the putative preneoplastic lesions of colon cancer in humans and rodents, were used as a biomarker to test the hypothesis that selenium supplementation can reduce aromatic amine-induced colon carcinogenesis. Male weanling F344 inbred rats were fed a basal torula yeast selenium-deficient diet supplemented with 0, 0.1, or 2. 0 mg selenium/kg diet as selenite, selenate, or selenomethionine (SeMet). Animals were fed the diets for 4 weeks and then administered 1 sc injection/week for 2 weeks of 3, 2'-dimethyl-4-aminobiphenyl (DMABP; 100 mg/kg) or vehicle (peanut oil). At 12 weeks, the rats were euthanized and the colon and rectum were removed, opened longitudinally, and fixed in 70% ethanol. Glutathione peroxidase activities in erythrocytes and liver cytosol and selenium concentrations in the colon/rectum and kidney increased significantly (p < 0.05) and in a dose-dependent manner with each of the three selenium diets. No ACF were identified in vehicle-treated rats. In DMABP-treated rats, ACF frequencies decreased significantly (p < 0.05) in groups supplemented with 0.1 or 2.0 mg selenium/kg diet as selenite and selenate but not SeMet. There were no significant differences in ACF and aberrant crypts between rats fed 0.1 vs 2.0 mg selenium/kg diet. These results suggest that dietary selenium, depending on chemical form, can reduce aromatic amine-induced colon carcinogenesis.

N-Acetyltransferase genetics and their role in predisposition to aromatic and heterocyclic amine-induced carcinogenesis

N-Acetyltransferases (EC 2.3.1.5) are important in both the activation and deactivation of aromatic and heterocyclic amine carcinogens. Two N-acetyltransferase isozymes (NAT1 and NAT2) encoded by NAT1 and NAT2, respectively, have been identified. Both NAT1 and NAT2 exhibit genetic polymorphisms, and recent investigations have increased our understanding of the relationship between genotype and phenotype. Several studies have shown a role for NAT1 and NAT2 acetylation polymorphisms in cancer risk in human populations, but the findings have been inconsistent. These findings may relate to variability in carcinogen exposures and to differences in acetylator genotype/phenotype determinations.

Rodent models of the human acetylation polymorphism: comparisons of recombinant acetyltransferases

The acetylation polymorphism is associated with differential susceptibility to drug toxicity and cancers related to aromatic and heterocyclic amine exposures. N-Acetylation is catalyzed by two cytosolic N-acetyltransferases (NAT1 and NAT2) which detoxify many carcinogenic aromatic amines. NAT1 and NAT2 also activate (via O-acetylation) the N-hydroxy metabolites of aromatic and heterocyclic amine carcinogens to electrophilic intermediates which form DNA adducts and initiate cancer. The classical N-acetylation polymorphism is regulated at the NAT2 locus, which segregates individuals into rapid, intermediate, and slow acetylator phenotypes. Some human epidemiological studies associate slow acetylator and rapid acetylator phenotypes with increased susceptibility to urinary bladder and colorectal cancers, respectively. The acetylation polymorphism has been characterized in three rodent species (mouse, Syrian hamster, and rat) to test associations between NAT2 acetylator phenotype and susceptibility to aromatic and heterocyclic amine-induced cancers in various tumor target organs. NAT1 and NAT2 from rapid and slow acetylator mouse, Syrian hamster, and rat each have been cloned and sequenced. Recombinant NAT1 and NAT2 enzymes enzymes encoded by these genes have been characterized with respect to their catalytic activities for both activation (O-acetylation) and deactivation (N-acetylation) of aromatic and heterocyclic amine carcinogens. The acetylation polymorphisms in mouse, Syrian hamster, and rat are herein reviewed and compared as models of the human acetylation polymorphism.

Acetylator phenotype and genotype in patients infected with HIV: discordance between methods for phenotype determination and genotype

The acetylator phenotype and genotype of AIDS patients, with and without an acute illness, was compared with that of healthy control subjects (30 per group). Two probe drugs, caffeine and dapsone, were used to determine the phenotype in the acutely ill cohort. Polymerase chain reaction amplification and restriction fragment length polymorphism analysis served to distinguish between the 26 known NAT2 alleles and the 21 most common NAT1 alleles. The distribution (%) of slow:rapid acetylator phenotype seen among acutely ill AIDS patients differed with the probe substrate used: 70:30 with caffeine versus 53:47 with dapsone. Phenotype assignment differed considerably between the two methods and there were numerous discrepancies between phenotype and genotype. The NAT2 genotype distribution was 45:55 slow:rapid. Control subjects, phenotyped only with caffeine, were 67:33 slow:rapid versus 60:40 genotypically. Stable AIDS patients, phenotyped only with dapsone, were 55:45 slow:rapid versus 46:54 genotypically. Following resolution of their acute infections, 12 of the acutely ill subjects were rephenotyped with dapsone. Phenotype assignment remained unchanged in all cases. The distribution of NAT1 alleles was similar in all three groups. It is evident from the amount of discordance between caffeine phenotype and dapsone phenotype or genotype that caution should be exercised in the use of caffeine as a probe for NAT2 in acutely ill patients. It is also clear that meaningful study of the acetylation polymorphism requires both phenotypic and genotypic data.

Glutathione S-transferase genotypes and stomach cancer in a population-based case-control study in Warsaw, Poland

Glutathione S-transferases are important in the detoxification of a wide range of human carcinogens. Previous studies have shown inconsistent associations between the GSTT1 and GSTM1 null genotypes and stomach cancer risk. We investigated the relationship between these and related genotypes and stomach cancer risk in a population-based case-control study in Warsaw, Poland, where stomach cancer incidence and mortality rates are among the highest in Europe. DNA from blood samples was available for 304 stomach cancer patients and 427 control subjects. We observed a 1.48-fold increased risk for stomach cancer (95% confidence interval 0.97-2.25) in patients with the GSTT1 null genotype but no evidence of increased risk associated with the GSTM1, GSTM3 or GSTP1 genotypes. Furthermore, the stomach cancer risk associated with the GSTT1 null genotype varied by age at diagnosis, with odds ratios of 3.85, 1.91, 1.78 and 0.59 for those diagnosed at ages less than 50, 50-59, 60-69 and 70 years or older, respectively (P trend = 0.01). This was due to a shift in the GSTT1 genotype distribution across age groups among stomach cancer patients only. These results suggest that the GSTT1 null genotype may be associated with increased risk of stomach cancer.

Determination of human NAT2 acetylator genotype by restriction fragment-length polymorphism and allele-specific amplification

The human N-acetylation polymorphism, encoded by the NAT2 gene locus, has been associated with higher incidence and/or severity to the adverse effects of therapeutic drugs, and to the carcinogenic actions of environmental and occupational chemicals. In this paper, we describe an efficient method of restriction fragment-length polymorphism and allele-specific amplification analysis which distinguishes between each of 15 (NAT2*4, *5A, *5B, *5C, *6A, *6B, *7A, *7B, *12A, *12B, *13, *14A, *14B, *17, *18) NAT2 alleles that have been identified in human populations. The method should have broad applicability to improvement of drug therapy and to molecular epidemiology investigations of genetic predisposition to cancer and other diseases.

Cloning, sequencing, and recombinant expression of NAT1, NAT2, and NAT3 derived from the C3H/HeJ (rapid) and A/HeJ (slow) acetylator inbred mouse: functional characterization of the activation and deactivation of aromatic amine carcinogens

An acetylator polymorphism has been described in the mouse and the inbred strains C3H/HeJ and A/HeJ constitute rapid and slow acetylators, respectively. The NAT1, NAT2, and NAT3 genes from C3H/HeJ and A/HeJ acetylator inbred mouse strains were amplified using the polymerase chain reaction, cloned into the plasmid vector pUC19, and sequenced. They were then subcloned into the prokaryotic expression vector pKK223-3 and expressed in Escherichia coli strain JM105. The 870-bp nucleotide coding region of NAT1 and NAT3 did not differ between the rapid and slow acetylator mouse strains, or from that of previously published mouse NAT1 and NAT3 sequences. However, NAT2 did differ between the rapid and slow acetylator strains with an A296 T transition which causes a (Asn99-->Ile) substitution in the deduced amino acid sequence. Recombinant NAT1, NAT2, and NAT3 proteins catalyzed N-, O-, and N,O-acetyltransferase activities. NAT3 catalyzed aromatic amine N-acetyltransferase activities at very low rates, which confirms a previous study. Apparent K(m) and Vmax kinetic constants for N-acetylation were 5- to 10-fold lower for recombinant mouse NAT1 than NAT2. Intrinsic clearances for recombinant mouse NAT1- and NAT2-catalyzed N-acetylation of aromatic amine carcinogens were comparable. Both recombinant mouse NAT1 and NAT2 catalyzed the metabolic activation of N-hydroxyarylamine (O-acetylation) and N-hydroxyarylamide (N,O-acetylation) carcinogens. Recombinant mouse NAT3 catalyzed N,O-acetylation at very low rates, while O-acetylation was undetectable. No difference was observed between rapid and slow acetylator recombinant NAT2 proteins to activate aromatic amines by O- or N,O-acetylation, in substrate specificity, expression of immunoreactive protein, electrophoretic mobility, or N-acetyltransferase Michaelis-Menten kinetic constants. However, the slow acetylator recombinant NAT2 protein was over 10-fold less stable than rapid acetylator recombinant NAT2. These studies demonstrate metabolic activation and deactivation by recombinant mouse NAT1, NAT2, and NAT3 proteins and confirm and extend previous studies on the molecular basis for the acetylation polymorphism in the mouse.

Similarity of the discriminative stimulus effects of ketamine, cyclazocine, and dextrorphan in the pigeon

Separate groups of pigeons were trained to discriminate the IM injection of ketamine, cyclazocine, or dextrorphan from saline. Each of the training drugs and phencyclidine produced dose-related, drug-appropriate responding in each group of birds. In contrast, ethylketazocine and nalorphine generally produced responding appropriate for saline. These results indicate that common elements of discriminable effects exist among ketamine, cyclazocine, and dextrorphan, structurally dissimilar compounds that are generally considered to belong to distinct pharmacological classes.

Identification of a novel allele at the human NAT1 acetyltransferase locus

Humans possess two N-acetyltransferase isozymes (NAT1 and NAT2). We cloned and sequenced a novel NAT1 allele (Genbank HSU 80835) that contained nucleotide substitutions at -344 (C-->T), -40 (A-->T), 445 [G-->A(Val-->Ile)], 459 [G-->A(silent)], 640 [T-->G(Ser-->Ala)], a 9 base pair deletion between nucleotides 1065 and 1090, and 1095 (C-->A). The novel NAT1 allele which we have designated NAT1*17 is similar to NAT1*11 except for a G445A substitution (Val149-->Ile) in the NAT1 coding region. The G445A (Val149-->Ile) substitution yielded no significant changes in levels of immunoreactivity, as detected by Western blot, nor in intrinsic stability of the recombinant N-acetyltransferase protein. However, the G445A (Val149-->Ile) substitution yielded expression of recombinant NAT1 protein that catalyzed the N-acetylation of aromatic amines and the O- and N,O-acetylation of their N-hydroxylated metabolites at rates up to 2-fold higher than wild-type recombinant human NAT1.