Cloning and expression of cDNAs for polymorphic and monomorphic arylamine N-acetyltransferases from human liver

Luteolin-inhibited arylamine N-acetyltransferase activity and DNA-2-aminofluorene adduct in human and mouse leukemia cells

N-Acetyltransferase enzyme is an important enzyme in the first step of arylamine compounds metabolism. Luteolin has been shown to exit antibacterial and antineoplastic activity. The purpose of this present study is to evaluate the question of whether luteolin could affect arylamine N-acetyltransferase (NAT) activity and DNA-2-aminofluorene adduct formation in human (HL-60) and mouse (L1210) leukemia cells. By using HPLC, N-acetylation of 2-aminofluorene was determined. Luteolin displayed a dose-dependent inhibition to cytosolic NAT activity and intact human and mice leukemia cells. Time-course experiments showed that N-acetylation of 2-aminofluorene measured from intact human and mice leukemia cells were inhibited by luteolin for up to 24 hours. Using standard steady-state kinetic analysis, it was demonstrated that luteolin was a possible uncompetitive inhibitor to NAT activity in cytosols. The DNA-2-aminofluorene adduct formation in human and mouse leukemia cells were inhibited by luteolin. This report is the first demonstration to show that luteolin affects human and mice leukemia cells NAT activity and DNA-2-aminofluorene on adduct formation.

Inhibitory actions of luteolin on the growth and arylamine N-acetyltransferase activity in strains of Helicobacter pylori from ulcer patients

Helicobacter pylori is now recognized as an important cause of type B gastritis, which is strongly associated with gastric and duodenal ulcer disease. H. pylori may be a causative factor in patients with gastric cancer. The growth inhibition and N-acetylation of 2-Aminofluorene (AF) or P-aminobenzoic acid (PABA) by arylamine N-acetyltransferase (NAT) in H. pylori were inhibited by luteolin, a component in herbal medicine. The growth inhibition was based on the changes of optical density (OD) by using a spectrophotometer. The N-acetylation of AF or PABA by NAT from H. pylori were assayed by the amounts of acetylated and non-acetylated AF or PABA in cytosols and intact bacteria of H. pylori by using HPLC. An inhibition of growth on H. pylori demonstrated that luteolin elicited a dose-dependent growth inhibition in the H. pylori cultures. Cytosols and suspensions of H. pylori with or without specific concentrations of luteolin co-treatment showed different percentages of AF or PABA acetylation. The data indicated that there was decreased NAT activity associated with increased levels of luteolin in H. pylori cytosols and suspensions. Using standard steady-state kinetic analysis, it was demonstrated that luteolin was a possible uncompetitive inhibitor to NAT enzyme in H. pylori. This report is the first demonstration to show that luteolin can inhibit H. pylori growth and NAT activity.

Eubacterial arylamine N-acetyltransferases - identification and comparison of 18 members of the protein family with conserved active site cysteine, histidine and aspartate residues

Arylamine N-acetyltransferases (NATs) are enzymes involved in the detoxification of a range of arylamine and hydrazine-based xenobiotics. NATs have been implicated in the endogenous metabolism of p-aminobenzoyl glutamate in eukaryotes, although very little is known about the distribution and function of NAT in the prokaryotic kingdom. Using DNA library screening techniques and the analysis of data from whole-genome sequencing projects, we have identified 18 nat-like sequences from the Proteobacteria and Firmicutes. Recently, the three-dimensional structure of NAT derived from the bacterium Salmonella typhimurium (PDB accession code 1E2T) was resolved and revealed an active site catalytic triad composed of Cys(69)-His(107)-Asp(122). These residues have been shown to be conserved in all prokaryotic and eukaryotic NAT homologues together with three highly conserved regions which are found proximal to the active site triad. The characterization of prokaryotic NATs and NAT-like enzymes is reported. It is also predicted that prokaryotic NATs, based on gene cluster composition and distribution amongst genomes, participate in the metabolism of xenobiotics derived from decomposition of organic materials.

N-Acetyltransferase2 genotype correlated with isoniazid acetylation in Japanese tuberculous patients

Isoniazid (INH) is metabolized by polymorphic N-acetyltransferase2 (NAT2). In the present study, the relationship between the NAT2 genotype and the INH acetylator phenotype was examined in Japanese tuberculous patients and compared with healthy subjects. Subjects were classified according to the genotyping into NAT2*5B (allele4), NAT2*6A (allele3) and NAT2*7B (allele2), using the PCR-RFLP method. Twelve healthy subjects and 7 tuberculous patients participated in the INH acetylator phenotyping study, in which each subject was administered an oral dose of INH, followed by urine sampling for 24 h. Urinary concentrations of INH and N-acetylisoniazid (AcINH) were measured by the HPLC method. The urinary recoveries of INH (% of dose) in healthy subjects in relation to NAT2 genotyping were as follows: 6.4+/-2.2 in the homozygotes for the wild-type allele, 10.7+/-2.2 in the compound heterozygotes for the mutant allele, and 38.6+/-6.4 in the homozygotes for the mutant allele. In the patients study, the findings in the corresponding three groups were 4.0+/-1.7, 8.8 and 18.3+/-9.3. Although no significant difference was found because of the lower systemic exposure of INH in patients compared with healthy subjects, there were differences in the disposition kinetics of INH between subjects with and without mutations in the NAT2 gene, and these findings were observed not only in healthy subjects but also in patients who had comedicated drugs and hepatic dysfunctions. The findings indicated that the metabolism of INH by NAT2 is clearly impaired in subjects with mutations in the NAT2 gene, and thus genotyping for three NAT2 point mutations was adequate to predict the metabolism of INH in Japanese tuberculous patients as well as healthy subjects. This NAT2 genotyping could become a useful alternative to TDM for INH.

Arylamine N-acetyltransferases - of mice, men and microorganisms

Arylamine N-acetyltransferases (NATs) catalyse the transfer of an acetyl group from acetyl CoA to the terminal nitrogen of hydrazine and arylamine drugs and carcinogens. These enzymes are polymorphic and have an important place in the history of pharmacogenetics, being first identified as responsible for the polymorphic inactivation of the anti-tubercular drug isoniazid. NAT has recently been identified within Mycobacterium tuberculosis itself and is an important candidate for modulating the response of mycobacteria to isoniazid. The first three-dimensional structure of the unique NAT family shows the active-site cysteine to be aligned with conserved histidine and aspartate residues to form a catalytic triad, thus providing an activation mechanism for transfer of the acetyl group from acetyl CoA to cysteine. The unique fold could allow different members of the NAT family to play a variety of roles in endogenous and xenobiotic metabolism.

Placental arylamine N-acetyltransferase type 1: potential contributory source of urinary folate catabolite p-acetamidobenzoylglutamate during pregnancy

Human arylamine N-acetyltransferase type 1 (NAT1), better known as a drug-metabolising enzyme, has been proposed to acetylate the folate catabolite p-aminobenzoylglutamate (p-abaglu) to N-acetamidobenzoylglutamate (ap-abaglu) which is a major urinary folate catabolite. Using mass spectroscopic analysis, we demonstrate the formation of ap-abaglu by recombinant human NAT1 and human placental homogenates. Using density gradient centrifugation the placental enzymic activity which acetylates p-aba and the placental enzymic activity acetylating p-abaglu both have an S(20,w) value of 3.25 S. This is the expected value for a monomer of human NAT1 (33 kDa). The specific NAT1 inhibitor 5-iodosalicylate inhibits acetylation of both p-aba and p-abaglu catalysed by either recombinant human NAT1 or placental samples as the source of enzyme. These data demonstrate that NAT1 is the major placental enzyme involved in acetylating p-abaglu.

Effects of luteolin on arylamine N-acetyltransferase activity in rat blood and liver

In this study we investigated inhibition of Arylamine N-acetyltransferase (NAT) activity in rat blood and liver tissue cytosols by luteolin. Using high-performance liquid chromatography, NAT activity for acetylation of 2-aminofluorene and remaining unacetylated 2-aminofluorene were examined. The NAT activity in rat blood and liver tissue was inhibited by luteolin in a dose-dependent manner: higher concentrations of luteolin in the reaction resulted in greater inhibition of NAT activities in both examined tissues. The data also indicated that luteolin decreased apparent Km and Vmax of NAT enzymes from rat blood and liver tissue cytosols. This report is the first demonstration that luteolin can affect rat blood and liver tissue NAT activity.

Identification of specific histidine residues and the carboxyl terminus are essential for serotonin N-acetyltransferase enzymatic activity

Melatonin is synthesized in pinealocytes of the pineal gland and in photoreceptors of the retina. Synthesis rate from serotonin to melatonin is controlled by the rapid and dramatic enzymatic increase in darkness of serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AA-NAT, EC 2.3.1.87) and hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4). The primary structure of these critical indoleamine enzymes is now known and the regulation of the enzyme catalysis can be examined. As a first step, the conserved cysteine (C) and histidine (H) residues were targeted for site-directed mutagenesis as potential amino acid residues involved in the N-acetylation reaction of AA-NAT. Our studies concluded that among 6 histidine (H) to alanine (A) mutations, three residues (H110A, H118A, H120A) within the AA-NAT protein showed little or no enzymatic activity, whereas the others (H28A, H70A, H125A) retained enzymatic activity, compared to the unaltered AA-NAT protein. Cysteine to alanine mutations, C37A and C177A, had no significant effect on the AA-NAT enzymatic activity; however, C61A had a four-fold increase in K(m) for acetyl CoA and an altered sensitivity to the thiol modification chemical, N-ethylmaleimide (NEM), implying that C61 may participate in the acetyl CoA binding. Further studies examined the AA-NAT enzyme regulation of the highly conserved carboxyl terminus. When 12 terminal amino acid residues were deleted systematically from the carboxyl terminus of the 205 amino acid residue AA-NAT protein, enzyme activity was retained. However, further residue deletion resulted in enzyme activity plummeting, implicating that the essential information either for the correct structural folding into an active enzyme form or for enzyme stability is in the 193 residues. To test the relative importance of the AA-NAT carboxyl terminal region, a single leucine (L) was altered to alanine (A) or proline (P). Both mutants, either L193A or L193P, had a marked decrease in AA-NAT enzymatic activity and a decrease in thermal stability, suggesting the leucine, in addition to the cysteine and histidine residues, is involved in either enzyme catalysis or stability. In light of the recently reported three-dimensional structure of AA-NAT (17,18), the site-directed mutagenesis data demonstrate experimentally the importance of essential amino acid residues for acetyl CoA binding and AA-NAT activation.

Inhibition of N-acetyltransferase activity and DNA-2-aminofluorene adducts by glycyrrhizic acid in human colon tumour cells

Glycyrrhizic acid (GA) was tested for inhibition of arylamine N-acetyltransferase (NAT) activity in a human colon tumour (adenocarcinoma) cell line (colo 205). Two assay systems were performed, one with cellular cytosols (9000g supernatant), the other with intact colon tumour cell cultures. The NAT activity in a human colon tumour cell line was inhibited by GA in a dose-dependent manner in both types of systems examined. The data also indicated that GA decreased the apparent values of K(m) and V(max) of NAT enzymes from human colon tumour cells in both examined systems. The DNA-2-aminofluorene adduct formation in human colon tumour cells were inhibited by GA. This report is the first to demonstrate that GA does inhibit human colon tumour cell NAT activity and DNA adduct formation.

Immunohistochemical detection of carcinogen-DNA adducts in normal human prostate tissues transplanted into the subcutis of athymic nude mice: results with 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 3,2'-dimethyl-4-aminobiphenyl (DMAB) and relation to cytochrome P450s and N-acetyltransferase activity

Human prostate tissue transplanted into nude mice was examined immunohistochemically for DNA adducts formed after administration of 3,2'-dimethyl-4-aminobiphenyl (DMAB) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Positive staining for DMAB- or PhIP-DNA adducts was evident in 70-95% of both epithelial and stromal cells in human prostate xenografts. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed a normal human prostate epithelial cell line (PrEC) to express both cytochrome P450 1A2 (CYP1A2) and N-acetyltransferase 2 (NAT2) mRNA, while a normal human prostate fibroblast cell line (NHPF) expressed NAT2, but not CYP1A2 mRNA. In addition, NAT2 and to a lesser extent CYP1A2 mRNAs were also found in four cases of normal human prostate tissues. The results suggest that initial activation of chemicals by liver CYP1A2 and subsequent metabolism by prostate NAT2 is a major pathway of DNA adduct formation in human prostate cells. Thus, the data suggest that human prostate has the potential to be targeted by environmental carcinogens.

N-Acetyltransferase polymorphism and human cancer risk

Because of the important role ofN-acetyltransferase (NAT) enzymes in both metabolic activation and detoxification of certain precarcinogens, such as homo-and heterocyclic arylamines, extensive research in the past has focused on the relationship between the distribution of different variants of these enzymes and cancer susceptibility. In this context, we examined the relationship between the acetylator type of two NAT isozymes (NAT1 and NAT2) and cancer risk. It was shown that any independent overall association of those diseases with acetylation for eitherNATl orNAT2 is likely to be weak at most. Besides individual genetic profile, differences in the degree of exposure to environmental precarcinogens should also be considered. It was suggested that smoking and red meat intake were associated with bothNATl andNAT2 genotype in the carcinogenesis. A gene-gene interaction, even linkage betweenNATl andNAT2 may also exist.

A method for genotyping murine arylamine N-acetyltransferase type 2 (NAT2): a gene expressed in preimplantation embryonic stem cells encoding an enzyme acetylating the folate catabolite p-aminobenzoylglutamate

Mice have three arylamine N-acetyltransferase (NAT) isoenzymes (NAT1, NAT2, and NAT3) of which NAT2 is known to be polymorphic. Humans have two polymorphic isoenzymes, NAT1 and NAT2. The isoenzymes mouse NAT1 and human NAT2 are expressed predominantly in the liver and intestine and are involved in drug and xenobiotic metabolism. Mouse NAT2 and human NAT1 have a widespread tissue distribution and the folate catabolite p-aminobenzoylglutamate (pAB-Glu) has been proposed as a candidate endogenous substrate. All mice have detectable NAT2 activity, although inbred mouse strains have either a fast or slow acetylator phenotype conferred by the presence of either NAT2*8 (fast) or NAT2*9 (slow) alleles at the NAT2 locus. In this report, we describe a simple method for distinguishing these murine alleles by polymerase chain reaction followed by restriction fragment length polymorphism analysis. We compared the tissue distribution of the acetylation activity found in both fast (C57BL/6J) and slow (A/J) acetylating strains of mice using pAB-Glu and p-aminobenzoic acid as probe substrates. It has previously been demonstrated that murine NAT2 is expressed in the neural tube prior to closure (Stanley L, Copp A, Rolls S, Smelt V, Perry VH and Sim E, Teratology 58: 174-182, 1998). We demonstrate here that murine NAT2 is expressed in preimplantation embryonic stem cells. Murine NAT2 is likely to be expressed prior to neurulation and this may be important in view of the protective role of folate in neural tube development.

Effects of berberine on arylamine N-acetyltransferase activity in human colon tumor cells

Berberine was used to determine loss of viable cells and inhibition of arylamine Nacetyltransferase (NAT) activity in a human colon tumor (adenocarcinoma) cell line. The viable cells were determined by trypan blue exclusion under a light microscope. The NAT activity was measured by high performance liquid chromatography for the amounts of N-acetyl-2-aminofluorene (AAF), N-acetyl-p-aminobenzoic acid (N-Ac-PABA), and the remaining 2-aminofluorene (AF) and p-aminobenzoic acid (PABA). The viability and NAT activity in a human colon tumor cell line was inhibited by berberine in a dose-dependent manner, i.e., the higher the concentration of berberine, the higher the inhibition of NAT activity and cell death. The NAT activities measured in the intact human colon tumor cells were decreased over 50% by AAF and NAc-PABA production from acetylation of AF and PABA. The apparent values of Kmoff and Vmax of NAT from colon tumor cells were also inhibited by berberine in cytosols and in intact cells. This report is the first to show that berberine did affect human colon tumor cell NAT activity.

Paeonol promotion of DNA adduct formation and arylamines N-acetyltransferase activity in human colon tumour cells

Paeonol was used to determine any effects on the N-acetyltransferase (NAT) activity in human colon tumour cells as measured by HPLC exhibited for the amounts of N-acetyl-2-aminofluorene (AAF) and N-acetyl-p-aminobenzoic acid (N-Ac-PABA) and remaining 2-aminofluorene (AF) and p-aminobenzoic acid (PABA). The NAT activity in the human colon tumour intact cells and cytosols was promoted by paeonol in a dose-dependent manner, that is, the higher the concentrations of paeonol, the higher the promotion of NAT activity. The apparent Vmax values from NAT of human colon tumour cells were also promoted by paeonol in cytosols and in intact cells. The data also demonstrated that co-treatment with paeonol in the media an increase in AF-DNA adduct formation was seen in the human colon tumour cells. This report is the first demonstration to show paeonol did promote human colon tumour cell NAT activity and AF-DNA adduct formation.

Cloning and characterization of arylamine N-acetyltransferase genes from Mycobacterium smegmatis and Mycobacterium tuberculosis: increased expression results in isoniazid resistance

Arylamine N-acetyltransferases (NATs) are found in many eukaryotic organisms, including humans, and have previously been identified in the prokaryote Salmonella typhimurium. NATs from many sources acetylate the antitubercular drug isoniazid and so inactivate it. nat genes were cloned from Mycobacterium smegmatis and Mycobacterium tuberculosis, and expressed in Escherichia coli and M. smegmatis. The induced M. smegmatis NAT catalyzes the acetylation of isoniazid. A monospecific antiserum raised against pure NAT from S. typhimurium recognizes NAT from M. smegmatis and cross-reacts with recombinant NAT from M. tuberculosis. Overexpression of mycobacterial nat genes in E. coli results in predominantly insoluble recombinant protein; however, with M. smegmatis as the host using the vector pACE-1, NAT proteins from M. tuberculosis and M. smegmatis are soluble. M. smegmatis transformants induced to express the M. tuberculosis nat gene in culture demonstrated a threefold higher resistance to isoniazid. We propose that NAT in mycobacteria could have a role in acetylating, and hence inactivating, isoniazid.

Genetic polymorphisms of human N-acetyltransferase, cytochrome P450, glutathione-S-transferase, and epoxide hydrolase enzymes: relevance to xenobiotic metabolism and toxicity

In this review, an overview is presented of the current knowledge of genetic polymorphisms of four of the most important enzyme families involved in the metabolism of xenobiotics, that is, the N-acetyltransferase (NAT), cytochrome P450 (P450), glutathione-S-transferase (GST), and microsomal epoxide hydrolase (mEH) enzymes. The emphasis is on two main topics, the molecular genetics of the polymorphisms and the consequences for xenobiotic metabolism and toxicity. Studies are described in which wild-type and mutant alleles of biotransformation enzymes have been expressed in heterologous systems to study the molecular genetics and the metabolism and pharmacological or toxicological effects of xenobiotics. Furthermore, studies are described that have investigated the effects of genetic polymorphisms of biotransformation enzymes on the metabolism of drugs in humans and on the metabolism of genotoxic compounds in vivo as well. The effects of the polymorphisms are highly dependent on the enzyme systems involved and the compounds being metabolized. Several polymorphisms are described that also clearly influence the metabolism and effects of drugs and toxic compounds, in vivo in humans. Future perspectives in studies on genetic polymorphisms of biotransformation enzymes are also discussed. It is concluded that genetic polymorphisms of biotransformation enzymes are in a number of cases a major factor involved in the interindividual variability in xenobiotic metabolism and toxicity. This may lead to interindividual variability in efficacy of drugs and disease susceptibility.

Effects of garlic compounds diallyl sulfide and diallyl disulfide on arylamine N-acetyltransferase activity in strains of Helicobacter pylori from peptic ulcer patients

Arylamine N-acctyltransferase (NAT) activities with p-aminobenzoic acid (PABA) and 2-aminofluorene (2-AF) were determined in the bacterium Helicobacter pylori collected from peptic ulcer patients. Two assay systems were performed, one with cellular cytosols, the other with intact cell suspensions. Cytosols or suspensions of H. pylori with or without specific concentrations of diallyl sulfide (DAS) or diallyl disulfide (DADS) co-treatment showed different percentages of 2-AF and PABA acetylation. The data indicated that there was decreased NAT activity associated with increased levels of DAS or DADS in H. pylori cytosols and suspensions. Viability studies on H. pylori demonstrated that DAS or DADS elicited dose-dependent bactericide affects on H. pylori cultures. The data also indicated that DAS and DADS decreased the apparent values of K(m) and Vmax of NAT enzyme from H. pylori in both systems examined. This report is the first demonstration that garlic components can affect H. pylori growth and NAT activity.

Activation of heterocyclic amines by combinations of prostaglandin H synthase-1 and -2 with N-acetyltransferase 1 and 2

Cooking of meats produces several heterocyclic amines which are mutagenic and potentially carcinogenic. We found that metabolic activation of one of these heterocyclic amines, the quinoline derivative 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), can be catalyzed by prostaglandin H synthase (PHS) as well as by CYP1A2. N-Acetyltransferase (NAT) increased IQ-DNA adduct formation by either of these pathways. In sonicate from transiently transfected COS cells, NAT1 increased CYP1A2 catalyzed adduct formation 4-fold while NAT2 increased adduct formation 12-fold. Both expressed human and purified ovine PHS-1 and PHS-2 catalyzed IQ-DNA adduct formation. The presence of NAT1 and NAT2 increased PHS-1 catalyzed adduct formation 2.5- and 4-fold, respectively. PHS-2 catalyzed IQ adduct formation was also enhanced by either NAT. The pyridine derivative, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, also produced by protein pyrolysis, did not form detectable DNA adducts during incubation with PHS. These results indicate that IQ is a substrate for both PHS-1 and PHS-2 and that NAT increases the ability of the resulting IQ metabolites to cause DNA damage. PHS activity, constitutive and induced, as well as NAT polymorphisms should be considered as factors in environmental carcinogenesis.

A novel amplicon at 8p22-23 results in overexpression of cathepsin B in esophageal adenocarcinoma

Cathepsin B (CTSB) is overexpressed in tumors of the lung, prostate, colon, breast, and stomach. However, evidence of primary genomic alterations in the CTSB gene during tumor initiation or progression has been lacking. We have found a novel amplicon at 8p22-23 that results in CTSB overexpression in esophageal adenocarcinoma. Amplified genomic NotI-HinfI fragments were identified by two-dimensional DNA electrophoresis. Two amplified fragments (D4 and D5) were cloned and yielded unique sequences. Using bacterial artificial chromosome clones containing either D4 or D5, fluorescent in situ hybridization defined a single region of amplification involving chromosome bands 8p22-23. We investigated the candidate cancer-related gene CTSB, and potential coamplified genes from this region including farnesyl-diphosphate farnesyltransferase (FDFT1), arylamine N-acetyltransferase (NAT-1), lipoprotein lipase (LPL), and an uncharacterized expressed sequence tag (D8S503). Southern blot analysis of 66 esophageal adenocarcinomas demonstrated only CTSB and FDFT1 were consistently amplified in eight (12.1%) of the tumors. Neither NAT-1 nor LPL were amplified. Northern blot analysis showed overexpression of CTSB and FDFT1 mRNA in all six of the amplified esophageal adenocarcinomas analyzed. CTSB mRNA overexpression also was present in two of six nonamplified tumors analyzed. However, FDFT1 mRNA overexpression without amplification was not observed. Western blot analysis confirmed CTSB protein overexpression in tumor specimens with CTSB mRNA overexpression compared with either normal controls or tumors without mRNA overexpression. Abundant extracellular expression of CTSB protein was found in 29 of 40 (72. 5%) of esophageal adenocarcinoma specimens by using immunohistochemical analysis. The finding of an amplicon at 8p22-23 resulting in CTSB gene amplification and overexpression supports an important role for CTSB in esophageal adenocarcinoma and possibly in other tumors.

Placental expression of arylamine N-acetyltransferases: evidence for linkage disequilibrium between NAT1*10 and NAT2*4 alleles of the two human arylamine N-acetyltransferase loci NAT1 and NAT2

The study of placental xenobiotic metabolism is important for the determination of foetal exposure to environmental chemicals as placental metabolism influences the nature of chemicals reaching the foetus from its mother's blood. Arylamine N-acetyltransferases are drug metabolizing enzymes which N-acetylate hydrazines and arylamines, including carcinogenic arylamines and sulphonamide drugs. The two human arylamine N-acetyltransferase isoenzymes, NAT1 and NAT2, are encoded at multi-allelic loci. Here, we have determined N-acetyltransferase (NAT) activity in term placentas from normal, uncomplicated pregnancies. Both NAT1 and NAT2 enzyme activities were detectable. Placental NAT1 activity was at least 1000 fold greater than NAT2 activity. There was a 6 fold inter-placental variation in NAT1 activity. Mean placental NAT1 specific activity was 1.42 nmoles para-aminobenzoic acid N-acetylated.min-1.mg protein-1, which is comparable to NAT1 specific activities which have been measured in adult tissues. The NAT1, but not the NAT2, protein was detectable in placentas by Western blotting. Maternal and foetal NAT genotypes were determined from placenta, using placental blood clots and cord blood respectively, allowing NAT haplotype determination. There appeared to be linkage disequilbrium between NAT1* and NAT2* alleles such that the combination NAT1*10/NAT2*4 was found 3.5 times more frequently than would be expected.

Pharmacogenetics and cancer chemotherapy

Cancer chemotherapy is limited by significant inter-individual variations in responses and toxicities. Such variations are often due to genetic alterations in drug metabolising enzymes (pharmacokinetic polymorphisms) or receptor expression (pharmacodynamic polymorphisms). Pharmacogenetic screening prior to anticancer drug administration may lead to identification of specific populations predisposed to drug toxicity or poor drug responses. The role of polymorphisms in specific enzymes, such as thiopurine S-methyltransferases (TPMT), dihydropyrimidine dehydrogenase (DPD), aldehyde dehydrogenases (ALDH), glutathione S-transferases (GST), uridine diphosphate glucuronosyl-transferases (UGTs) and cytochrome P450 (CYP 450) enzymes in cancer therapy are discussed in this review.

Effects of the garlic components diallyl sulfide and diallyl disulfide on arylamine N-acetyltransferase activity in human colon tumour cells

Diallyl sulfide (DAS) and diallyl disulfide (DADS), major components of garlic, were used to determine inhibition of arylamine N-acetyltransferase (NAT) activity in a human colon tumour (adenocarcinoma) cell line. Two assay systems were performed, one with cellular cytosols (9000g supernatant), the other with intact bacterial cell suspensions. The NAT activity in a human colon tumour cell line was inhibited by DAS and DADS in a dose-dependent manner in both system: that is, the greater the concentration of DAS and DADS in the reaction, the greater the inhibition of NAT activities in both systems. The data also indicated that DAS and DADS decrease the apparent values of Km and Vmax of NAT enzymes from human colon tumour cells in both systems examined. This is the first report to demonstrate that garlic components do affect human colon tumour cell NAT activity.

Inhibitory actions of glycyrrhizic acid on arylamine N-acetyltransferase activity in strains of Helicobacter pylori from peptic ulcer patients

Arylamine N-acetyltransferase (NAT) activities with 2-aminofluorene (2-AF) and p-aminobenzoic acid (PABA) as substrates were determined in Helicobacter pylori, collected from patients with peptic ulcers. The NAT activity was determined using an acetyl CoA recycling assay and high pressure liquid chromatography. Inhibition of growth studies from H. pylori demonstrated that glycyrrhizic acid elicited dose-dependent bactericidal effect in H. pylori cultures, i.e.; the greater the concentration of glycyrrhizic acid, the greater the inhibition of growth of H. pylori. Cytosols or suspensions of H. pylori with and without selected concentrations of glycyrrhizic acid co-treatment showed different percentages of 2-AF and PABA acetylation. The data indicated that there was decreased NAT activity associated with increased glycyrrhizic acid in H. pylori cytosols and intact cells. For the cytosol and intact bacteria examinations, the apparent values of Km and Vmax were decreased after co-treated with 80 M glycyrrhizic acid. This report is the first demonstration of glycyrrhizic acid inhibition of arylamine NAT activity and glycyrrhizic acid inhibition of growth in the bacterium H. pylori.

Genotyping of the polymorphic N-acetyltransferase (NAT2) and loss of heterozygosity in bladder cancer patients

Acetylation is one of the major routes in metabolism and detoxification of a large number of drugs, chemicals and carcinogens. Slow acetylators are said to be more susceptible to developing bladder cancer and because of investigations about tumor risk based on phenotyping procedures, it was our aim to study the distribution of allelic constellations of the N-acetyltransferase (NAT2) by genotyping patients with bladder cancer. We analysed NAT2 gene of blood and tumor DNA from 60 patients with primary bladder cancer and DNA of blood samples from 154 healthy individuals. Using ASO-PCR/RFLP techniques we identified 70% of patients with bladder cancer (n = 42) to be slow acetylators while genotyping of controls resulted in 61% with slow acetylators (n = 94). In addition, dividing bladder cancer patients in males and females the genotype NAT2*5B/NAT2*6A occured with much higher frequencies in males (OR = 4, 95%); CI = 1.8-8.9). Furthermore, investigating bladder cancer tissues we could detect loss of heterozygosity (LOH) in slow and rapid acetylator genotypes. In eleven out of 60 tumor samples (18.3%) we observed allelic loss at the NAT2 locus while in control DNA of blood from the same patients both alleles were still detectable.

Acetylation of arylamines by the placenta

The N-acetylation of arylamines and hydrazines used as drugs may alter their pharmacological or toxicological activity. Arylamine N-acetyltransferase (NATs) are involved in drug metabolism, as they catalyse the N-acetylation of arylamine and mono-substituted hydrazine substrates. Placental metabolism regulates the nature of the chemicals which reach the developing fetus. The study of drug metabolism during pregnancy is important in determining the effect on the fetus of drugs administered to the mother and the maternal drug dose required, important if the treatment is to be effective. There are two forms of NAT in humans, NAT1 and NAT2, which are encoded at multi-allelic loci. There is inter-individual variation in both NAT1 and NAT2 activity, which has implications in drug dosage. Using a combination of enzyme activity measurements and Western blotting, this study has characterised the arylamine N-acetylation capabilities of placenta and cord blood. NAT1 activity in placenta and cord blood demonstrated inter-individual variation and the variation was in the range expected for adult NAT1 activity. The genotypes of both NAT1* and NAT2* were determined using DNA prepared using placental blood clots (maternal DNA) and cord blood (fetal DNA). The results indicate that placental NAT activity is an important factor when considering N-acetylation during pregnancy.

Cytosolic arylamine N-acetyltransferase (NAT) deficiency in the dog and other canids due to an absence of NAT genes

The purpose of this study was to determine the molecular basis in the dog for an unusual and absolute deficiency in the activity of cytosolic N-acetyltransferase (NAT), an enzyme important for the metabolism of arylamine and hydrazine compounds. NAT activity towards two NAT substrates, p-aminobenzoic acid and sulfamethazine, was undetectable in dog liver cytosol, despite substrate concentrations ranging from 10 microM to 4 mM and a wide range of incubation times. Similarly, no protein immunoreactive to NAT antibody was evident on western blot analysis of canine liver cytosol. Southern blot analysis of genomic DNA from a total of twenty-five purebred and mixed bred dogs, and eight wild canids, probed with a full-length human NAT2 cDNA, suggested an absence of NAT sequences in all canids. Polymerase chain reaction amplification of genomic DNA using degenerate primers designed to mammalian NAT1 and NAT2 consensus sequences generated products of the expected size in human, mouse, rabbit, and cat DNA, but no NAT products in any dog or wild canids. These results support the conclusion that cytosolic NAT deficiency in the domestic dog is due to a complete absence of NAT genes, and that this defect is shared by other canids.

Interpatient variability: genetic predisposition and other genetic factors

Polymorphisms and other genetic factors related to enzymes metabolizing drugs and xenobiotic chemicals are well known. This article focuses on selected molecular mechanisms and introduces some of the clinical implications arising from genetically determined interpatient variability or expression in some of these enzymes. Selected are the polymorphic enzymes of cytochromes P-450 (CYP) as examples of phase I enzymes and methyl transferases, n-acetyl transferases, and glutathione-s-transferases as examples of phase II enzymes. The polymorphism surrounding arylhydrocarbon hydroxylase induction is briefly described. Phase I enzymatic reactions are predominantly oxidative, whereas phase II reactions often couple with the byproducts of phase I. Overall, in poor metabolizers, whether phase I or phase II, there is limited metabolism in most patients unless another major metabolic pathway involving other enzymes exists. Drug metabolism also depends on whether the parent compound is a prodrug that forms an active metabolite, and poor metabolizers under this condition will form only trace amounts of an active compound. Therefore, the clinical significance of genetic polymorphisms and other genetic factors may be related to substrate, metabolite, or the major elimination pathway.

Acetyl CoA:arylamine N-acetyltransferase activity in rat hepatocytes cultured on different extracellular matrices

N-Acetyltransferase (NAT) activity towards p-aminobenzoic acid and sulfamethazine was examined in primary cultures of rat hepatocytes cultured on three extracellular matrices (ECM)-type I collagen, thermally denatured type I collagen, and Matrigel((R)). Whereas protein and DNA content declined markedly during the first 24 hr of culture, p-acetylamidobenzoate (AcPABA) and N-acetylsulfamethazine (AcSMZ) formation were readily detectable on all three ECM for the 6-day culture period. Protein and DNA content, as well as NAT activities, were higher on Matrigel than on either of the other two ECM. Additional studies were conducted to confirm the expression of both enzymes during the culture period. The ratio of AcPABA to AcSMZ formation remained relatively stable throughout the 6-day culture period, suggesting that both enzymes continued to be expressed throughout the study period. Further studies in cells cultured on Matrigel revealed that AcPABA formation exhibited a time-dependent decline when cytosol from cultured cells was incubated at 50 degrees C, whereas AcSMZ formation proved to be thermostable. Moreover, methotrexate substantially inhibited AcPABA formation, but had only modest effects on AcSMZ. These studies support the conclusion that AcPABA and AcSMZ are predominantly formed by way of different enzymes throughout the culture period. These findings are supported by the observation that NAT1 and NAT2 mRNA were detectable on all days examined. These data indicate that primary cultures of rat hepatocytes should prove useful in probing the regulation of NAT and its role in toxicity.

Genotyping of N-acetylation polymorphism and correlation with procainamide metabolism

We studied the genotypes of polymorphic N-acetyltransferase (NAT2) in 145 Japanese subjects by the polymerase chain reaction-restriction fragment length polymorphism method. The rapid-type NAT2*4 was expressed at a higher frequency (68.6%) than the slow-type genes with specific point mutations (NAT2*6A, 19.3%; NAT2*7B, 9.7%; NAT2*5B, 2.4%). The frequency of NAT2* genotypes consisted of 44% of a homozygote of NAT2*4, 49% of a heterozygote of NAT2*4 and mutant genes, and 7% of a combination of mutant genes. The metabolic activity for procainamide to N-acetylprocainamide was measured in 11 healthy subjects whose genotype had been determined. Although the acetylation activity substantially varied interindividually, the variability was considerably reduced after classification according to the genotype. The N-acetylprocainamide/procainamide ratio in urinary excretion was 0.60 +/- 0.17 (mean +/- SD) for those with NAT2*4/*4, 0.37 +/- 0.06 for NAT2*4/*6A, 0.40 +/- 0.03 for NAT2*4/*7B, and 0.17 for NAT2*6A/*7B. The results indicated that the NAT2* genotype correlates with acetylation of procainamide.

Genetic polymorphisms in human drug-metabolizing enzymes: potential uses of reverse genetics to identify genes of toxicological relevance

The human mind was engaged with fundamental questions on the nature of heredity long before the study of genetics became a scientific discipline. Many traits, such as height, eye color, blood pressure, or cancer susceptibility, have been known to run in families, although the genes or combination of genes that underlie these observable characteristics remain unknown in most cases. Differences in susceptibility to environmental agents in humans are likewise determined by variations in genetic background--genetic polymorphisms. In this article, we review the current status of studies on human polymorphisms in drug-metabolizing enzymes and discuss various approaches to the analysis of genetic polymorphisms. We expect that in the near future, novel methods in genetic analysis of human populations will be likely to play a key role in the identification of genes of toxicological relevance.

Purification and characterization of arylalkylamine N-acetyltransferase from cockroach testicular organs

Arylalkylamine N-acetyltransferase (NAT; EC2.3.1.87) catalyzes N-acetylation of various arylalkylamines using acetyl-CoA as a donor substrate. A type of NAT was purified 2700-fold from 451 pairs of cockroach testicular organs consisting of testis and its accessory gland. The NAT activity was recovered as a single peak on any column chromatography examined, suggesting that the testicular organ contained only one form of NAT. Five steps of successive column chromatographies gave a single protein band on SDS-polyacrylamide gel electrophoresis with estimated molecular mass of 28 kDa. The molecular mass of the native enzyme was also determined to be approximately 30 kDa by molecular sieve chromatography, indicating that the enzyme is a monomer protein. The enzyme acted on various arylalkylamines such as tryptamine, serotonin, dopamine, octopamine, norepinephrine, tyramine and methoxytryptamine, with K(m) values ranging from 20 to 50 microM. The optimum pH for these substrates was around 6.0. Internal amino acid sequences derived from two proteolytic fragments of the enzyme were determined as Leu-Leu-Gly-Glu-Asn-Gly-Asp-Glu and Phe-Phe-Phe-Leu-Glu-Glu-Pro-Leu-Asn-Ile-Ser-Leu-Gln, both of which exhibited significant homology to the C-terminal sequence of known vertebrate NATs; however, homology was less than 45%. These results suggest that a unique NAT is present in the cockroach testicular organ at high levels, and likely plays a role in the regulation of testicular function.

A fragment consisting of the first 204 amino-terminal amino acids of human arylamine N-acetyltransferase one (NAT1) and the first transacetylation step of catalysis

Human arylamine N-acetyltransferase 1 (NAT1) has 290 amino acids and acetylates arylamines from acetyl coenzyme A. The acetyl group forms a thiolester with Cys 68 in the enzyme, and the acetyl group is then transferred to the arylamine. When NAT1 is expressed using the pGEX vector, the glutathione S-transferase (GST)-NAT1 fusion protein catalyses the acetylation of the NAT1 substrate p-aminobenzoic acid from acetyl CoA. Neither GST alone, nor a fusion protein of GST with the N-terminal 204 amino acids of NAT, catalyses the acetylation of p-aminobenzoic acid from acetyl CoA. Using [3H]acetyl CoA as substrate, it is shown that the full-length NAT1 and the N-terminal 204 amino acids of NAT1 each form an acetylated intermediate on reaction with acetyl CoA.

Molecular mechanisms of genetic polymorphisms of drug metabolism

One of the major causes of interindividual variation of drug effects is genetic variation of drug metabolism. Genetic polymorphisms of drug-metabolizing enzymes give rise to distinct subgroups in the population that differ in their ability to perform certain drug biotransformation reactions. Polymorphisms are generated by mutations in the genes for these enzymes, which cause decreased, increased, or absent enzyme expression or activity by multiple molecular mechanisms. Moreover, the variant alleles exist in the population at relatively high frequency. Genetic polymorphisms have been described for most drug metabolizing enzymes. The molecular mechanisms of three polymorphisms are reviewed here. The acetylation polymorphism concerns the metabolism of a variety of arylamine and hydrazine drugs, as well as carcinogens by the cytosolic N-acetyltransferase NAT2. Seven mutations of the NAT2 gene that occur singly or in combination define numerous alleles associated with decreased function. The debrisoquine-sparteine polymorphism of drug oxidation affects the metabolism of more than 40 drugs. The poor metabolizer phenotype is caused by several "loss of function" alleles of the cytochrome P450 CYP2D6 gene. On the other hand, "ultrarapid" metabolizers are caused by duplication or amplification of an active CYP2D6 gene. Intermediate metabolizers are often heterozygotes or carry alleles with mutations that decrease enzyme activity only moderately. The mephenytoin polymorphism affects the metabolism of mephenytoin and several other drugs. Two mutant alleles of CYP2C19 have so far been identified to cause this polymorphism. These polymorphisms show recessive transmission of the poor or slow metabolizer phenotype, i.e. two mutant alleles define the genotype in these individuals. Simple DNA tests based on the primary mutations have been developed to predict the phenotype. Analysis of allele frequencies in different populations revealed major differences, thereby tracing the molecular history and evolution of these polymorphisms.

N-acetyltransferases: pharmacogenetics and clinical consequences of polymorphic drug metabolism

Since the discovery of polymorphic N-acetylation of drugs nearly 40 years ago, great progress has been made in understanding the molecular genetics of acetylation as well as the clinical consequences of being a rapid or slow acetylator. Inborn errors (several different alleles) at the NAT2 locus are responsible for the traditional acetylator polymorphism. Studies have revealed variant alleles at the NAT1 locus as well. The consequences of pharmacogenetic variation in these enzymes include (i) altered kinetics of specific drug substrates; (ii) drug-drug interactions resulting from altered kinetics; (iii) idiosyncratic adverse drug reactions. The latter have been extensively investigated for the arylamine-containing sulfonamide antimicrobial drugs. Individual differences in multiple metabolic pathways can increase the likelihood of covalent binding of reactive metabolites of the drugs to cell macromolecules with resultant cytotoxicity and immune response to neoantigens. This can result clinically in an idiosyncratic hypersensitivity reaction, manifested by fever, skin rash, and variable toxicity to organs including liver, bone marrow, kidney, lung, heart, and thyroid. Slow acetylation by NAT2 is a risk factor for such reactions to sulfonamides. Given the incidence of these severe adverse drug reactions (much less than 1/1000), slow acetylation cannot be the sole mechanism of predisposition in the population. Differences in rates of production of hydroxylamine metabolites of the drugs by cytochrome P450 (CYP2C9), myeloperoxidase, and thyroid, roxidase, along with an inherited abnormality in detoxification of the hydroxylamines are critically important in determining individual differences in adverse reaction risk. Both NATs, particularly NAT1, also can further metabolize hydroxylamine metabolites to N-acetoxy derivatives. Intensive investigation of patients with these rare adverse reactions using a variety of tools from in vitro cell toxicity assays through molecular genetic analysis will help elucidate mechanisms of predisposition and ultimately lead to diagnostic tools to characterize individual risk and prevent idiosyncratic drug toxicity.

Determination and allelic allocation of seven nucleotide transitions within the arylamine N-acetyltransferase gene in the Polish population

The frequency of various genotypes of arylamine N-acetyltransferase (NAT2) was investigated in 248 Polish unrelated children. Allele-specific polymerase chain reaction (PCR) was applied for mutation at 341 nucleotide (nt) of NAT2 coding sequence and PCR/restriction fragment length polymorphism for the other mutations. Genotypes coded for slow acetylation in 62.9% (56.6% to 68.9%). The frequency of specific NAT2 alleles was *4 (wild-type), 22.0%; *5A (341C, 481T), 5.2%; *5B (341C, 481T, 803G), 33.1%; *5C (341C, 803G), 6.0%; *6A (282T, 590A), 30.0%; *7B (282T, 857A), 3.4%; and *12A (803G), 0.2%. No mutations were found at 191, 434, and 845 nt. By a molecular-genetic procedure, genotypes *4/*6A were confirmed not to mask *6B/*13 (590A/282T). *6B and *13 were absent in a composite sample representative of 826 alleles (95% confidence limits, 0% to 0.45%). Five cases of genotype-phenotype discrepancy were sequenced and their mutation allocation confirmed; 21 further genotypes were confirmed by sequencing. This first evaluation of NAT2 genes among a Slavic population should provide a basis for clinical and epidemiologic investigations of NAT2 in the Polish population.

The effect of acetylation and deacetylation on the disposition of dapsone and monoacetyl dapsone hydroxylamines in human erythrocytes in-vitro

The fates of both dapsone and monoacetyl hydroxylamine have been studied in terms of acetylation and deacetylation within the human erythrocyte in-vitro. A comparison between the two metabolites showed equipotency in methaemoglobin generation at 15 min, although the monoacetyl derivative was the more rapid haemoglobin oxidizer. Within the erythrocytes, both dapsone and monoacetyl hydroxylamines were found to undergo acetylation, deacetylation and diacetylation. Of the inhibitors of acetylation studied, folate caused an increase in methaemoglobin formation associated with both metabolites, which led to a rise in both acetylated and non-acetylated amine formation. Amethopterin was associated with a rise in hydroxylamine mediated methaemoglobin formation which coincided with a fall in acetylated products. It is possible that the hydroxylamines undergo erythrocytic processes of acetylation and deacetylation before methaemoglobin-mediated reduction to their respective amines.

Demonstration of slow acetylator genotype of N-acetyltransferase in isoniazid neuropathy using an archival hematoxylin and eosin section of a sural nerve biopsy specimen

The genotype for N-acetyltransferase was analyzed in five Japanese patients with isoniazid neuropathy by using the allele specific polymerase chain reaction for a single slice of the 30-year-old paraffin-embedded and hematoxylin-eosin stained sural nerve biopsy specimens. We found slow acetylator genotypes for N-acetyltransferase in all isoniazid neuropathy patients. This result confirmed that patients with the slow acetylator genotype tend to develop neuropathy after administration of isoniazid.

Xenogenetics in multifactorial disease susceptibility

Susceptibility to multifactorial disease includes both genetic and environmental components. These two aspects of susceptibility are interlinked through genetic control of an individual's response to the environment. As a first step in identifying disease susceptibility genes that influence the response of an individual to foreign compounds (xenobiotics), it is necessary to study disorders in which there is an identified environmental trigger. Establishing a DNA resource from individuals with known environmental exposure ('a xenogenetic register') for diseases with an established environmental aetiology is an essential step in beginning to understand how environmental factors contribute to the susceptibility to polygenic diseases. A complementary approach to identification of environmental factors is suggested using a comparison of genetically homogeneous subdivisions of individuals with polygenic diseases where there is no clue to the environmental trigger.

Evidence for the lack of hepatic N-acetyltransferase in suncus (Suncus murinus)

The abilities of liver cytosol fractions from the suncus and Sprague-Dawley (SD) rats to N-acetylate aniline, p-aminobenzoic acid, p-aminosalicylic acid and 2-aminofluorene (AF) were compared. The cytosol from rats N-acetylated these substrates at efficient rates, whereas the cytosol from the suncus did not N-acetylate these substrates at detectable rates. When AF was given to the suncus, 2-acetylaminofluorene (AAF), a metabolite of AF formed by N-acetyltransferase (NAT), was not detectable in serum, whereas the metabolite was seen clearly in rats. Northern blot and Southern blot analyses, using cDNAs coding for human NATs as probes, indicated that not only the transcripts but also the genes of the enzymes were undetectable in suncus. These results suggest that the suncus is among the few species known to lack NATs.

Simultaneous expression of human CYP3A7 and N-acetyltransferase in Chinese hamster CHL cells results in high cytotoxicity for carcinogenic heterocyclic amines

To investigate whether several food-derived heterocyclic amines are activated to genotoxic products in human fetal livers, cell lines stably expressing CYP3A7, a human fetus-specific form of cytochrome P450, NADPH-cytochrome P450 reductase, and human monomorphic or polymorphic N-acetyltransferase (NAT1 or NAT2) were established. The expression of CYP3A7 mRNAs and proteins was determined by RNA blot and immunoblot analyses, respectively. The introduction of CYP3A7 cDNA to CR-68 cells which had been transfected with guinea pig NADPH-cytochrome P450 reductase, NAT1, or NAT2 cDNA resulted in increased sensitivity of the cells to aflatoxin B1 compared to parental cells. The cytotoxicity assay for 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) showed that 7P-145 cells, which expressed the reductase, CYP3A7, and NAT2, were approximately 4-, 30-, and 14-fold more sensitive to respective IQ, MeIQ, and MeIQx than parental CR-68 cells. There were no clear differences in sensitivity to these compounds among CHL, CR-68, and the cells which expressed the reductase and CYP3A7 (7R-54), the reductase and NAT1 (CNM-4), the reductase and NAT2 (CNP-40), and the reductase, NAT1, and CYP3A7 (7M-124). From these results, it was suggested that both CYP3A7 and polymorphic NAT2 are required for mutagenic activation of several heterocyclic amines in human fetal livers.

Purification of recombinant human N-acetyltransferase type 1 (NAT1) expressed in E. coli and characterization of its potential role in folate metabolism

Human arylamine N-acetyltransferase type 1 (NAT1) has been cloned from human genomic DNA, into the vector pET(5a) and expressed in Escherichia coli. The recombinant protein has been purified to apparent homogeneity using anion exchange chromatography. The arylamine acceptor specificity, and the effect of potential NAT1 inhibitors has been investigated using purified recombinant protein. The Km of the recombinant NAT1 protein for the substrates para-aminobenzoate (p-aba) and 4-aminosalicylate are 14.3 and 11.8 microM, respectively. Folate and amethopterin were found to be potent competitive inhibitors of p-aba acetylation, with Ki values of 13.3 and 9.5 microM, respectively. The pteroate moiety of folate, in contrast is a poor inhibitor, with 100 microM pteroate inhibiting only 40% of NAT1 activity. A catabolite of folate para-aminobenzoly-L-glutamate has also been shown to be a NAT1 substrate with a Km value of 263 microM.

Pineal gene expression: dawn in a dark matter

The mammalian pineal gland serves as a neuroendocrine interface to convert environmental lighting conditions into a humoral message, the nocturnally elevated synthesis of melatonin. Regulation and fine tuning of the circadian melatonin production in response to external cues requires complex interactions of transsynaptic signalling. These requirements are fulfilled by a high degree of plasticity on all levels between receptor activation and cellular response. Many receptors on pinealocytic membranes and enzymes involved in melatonin synthesis are linked to the second messenger cAMP. Crosstalk between second and third messengers converges in the pineal gland--as in other tissues--eventually on a modulated activity of transcription factors. Of fundamental importance for genes involved in the transsynaptic signalling to create a circadian profile in melatonin synthesis is the cAMP-inducible promoter element, the CRE (cAMP responsive element). Indeed, the CRE is shared by many pineal genes that are of physiological importance. Recently, the deciphering of molecular determinants regulating expression of cAMP-inducible genes in the mammalian pineal gland, like NAT, c-jun, or the beta-adrenergic receptor suggests a modulation in their transcription by a dual regulatory mechanism: posttranslational activation of the early third messenger CREB (cAMP responsive element binding protein) stimulates, cis-acting cAMP-induced transcriptional upregulation of the late third messenger ICER (inducible cAMP early repressor) inhibits genes with a CRE.

Differential characteristics and regulation of arylamine and arylalkylamine N-acetyltransferases in the frog retina (Rana perezi)

Arylamine N-acetyltransferase activity (A-NAT: E.C.2.3.1.5) from Rana perezi retina was studied using p-phenetidine as specific substrate. Enzyme characteristics and regulation were compared with respect to the arylalkylamine N-acetyltransferase (AA-NAT: E.C.2.3.1.87) from the same tissue. A-NAT activity is distributed in both neural retina and choroid-pigmented epithelium complex, showing a 10-fold higher specific activity in neural retina. In contrast, AA-NAT activity is restricted to neural retina. Subcellular localization in neural retina indicated that both enzymatic activities are in the supernatant fraction (39,000 g, 20 min). p-Phenetidine acetylation was linear as a function of the neural retina amount in the assay (1/16 to 1 retina), and it is insensitive to phosphate buffer pH in the range 6.5-8.4. A-NAT kinetic showed a hyperbolic shape for both cosubstrates. Kinetic constants were KM = 11.2 microM, Vmax = 0.49 nmol/h/mg prot. for p-phenetidine (50 microM acetyl-CoA), and KM = 113.4 microM, Vmax = 3.1 nmol/h/mg prot. for acetyl-CoA (5 mM p-phenetidine). The additivity test for both enzymatic activities in retina homogenates demonstrated that both acceptor amines do not compete for the catalytic sites. Serotonin addition in the assay modifies differentially the kinetic characteristics of both enzymes. Serotonin acted as a strong mixed inhibitor, mainly competitive in nature (competitive Ki = 18.1 microM; non-competitive Ki = 1.9 mM) for AA-NAT. However, it acted as a weak inhibitor with respect to A-NAT, mainly non-competitive, (competitive Ki = 5.7 mM; non-competitive Ki = 8.7 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Complementary DNAs for two arylamine N-acetyltransferases with identical 5' non-coding regions from rat pineal gland

A cDNA library was constructed from the pineal gland of rats injected with isoproterenol and screened with 32P-labeled cDNAs encoding arylamine N-acetyltransferases from rabbit and human liver. Two types of cDNAs for arylamine N-acetyltransferases (A-type and B-type) were isolated. Expression of the cDNAs in Chinese hamster ovary cells indicated that A-type N-acetyltransferase acetylates both arylamines and arylalkylamines, while the B-type enzyme acetylates only arylamines. Therefore, neither the A-type nor the B-type of enzyme seems to be the arylalkylamine N-acetyltransferase involved in melatonin synthesis in the pineal gland. Nucleotide sequence analysis revealed that both A-type and B-type cDNAs code for 290 amino acids, and that they showed 82.8% similarity in the coding region. However, the nucleotide sequence in the 5' non-coding region was identical in the A-type and B-type cDNAs. In addition, the 5' non-coding region contained another possible open reading frame for 79 amino acids. Data base research revealed that the complementary sequence of the 5' non-coding region has high similarity with the coding regions of cDNAs for high-mobility-group proteins (HMG) 1 and 2, which are thought to regulate mRNA transcription.

The N-acetyltransferase (NAT) gene: an early risk marker for diabetic nephropathy in Japanese type 2 diabetic patients?

A point mutation in the N-acetyltransferase gene (NAT2) leads to the recessive trait for the slow acetylator phenotype, which is suggested to be associated with microalbuminuria in Type 1 diabetic patients. Our study was designed to elucidate whether the NAT2 gene polymorphism would be a marker for diabetic nephropathy. The genotype distribution was studied in Japanese Type 2 diabetic patients with established nephropathy (n = 43), with microalbuminuria (n = 24), with normoalbuminuria (n = 18), non-diabetic patients with kidney disease (n = 62), and healthy control subjects (n = 51). The different alleles of the NAT2 gene were identified by restriction fragment length polymorphism analysis: the gene was amplified from genomic DNA (obtained from blood) and digested with restriction enzymes. The genotype was classified by the specific pattern of each allele (M1, M2, M3) in the agarose electrophoresis and ethdium bromide fluorescence. Alleles M1, M2, and M3 of NAT2 gene were found in 42.4% of all subjects (40.0% in all diabetic patients and 44.2% in all non-diabetic controls). The prevalence of the genotype, encoding the slow acetylator phenotype, was 7.0% in diabetic patients with established diabetic nephropathy, 20.8% in microalbuminuric diabetic patients, 0% in normoalbuminuric diabetic patients, 6.5% in non-diabetic patients with kidney disease, and 7.8% in healthy control subjects. The differences in the prevalence were non-significant. The results suggest that the N-acetyltransferase gene polymorphism may not be a genetic risk marker for diabetic nephropathy in Japanese Type 2 diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)