N-acetylation pharmacogenetics.
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Acebutolol↗
Biomedical subjects
D W Hein
Publications and source records attributed to D W Hein.
Inheritance of liver N-acetyltransferase activity in the rapid and slow acetylator inbred hamster.
p-Aminobenzoic acid and p-aminosalicylic acid-N-acetyltransferase activities were determined in 105,000 X g liver cytosols from homozygous rapid acetylator (Bio. 4.24, Bio. 41.56 and Bio. 65.67) and homozygous slow acetylator (Bio. 1.5) inbred hamsters. Liver N-acetyltransferase activities were substantially higher in rapid as opposed to slow acetylator hamsters. Genetic crosses yielded F1 generation progeny with unimodal distributions of N-acetyltransferase activity intermediate between those of the rapid and slow acetylator parental strains, and F2 generation progeny with trimodal distributions (low/intermediate/high) of N-acetyltransferase activity not significantly different from a ratio of 1/2/1. Backcross matings yielded bimodal distributions of N-acetyltransferase activity in a ratio (intermediate/parental) not significantly different from 1/1. Each of these findings is consistent with simple autosomal Mendelian inheritance of two codominant alleles at a single gene locus.
4-Aminobenzoic Acid↗
Biochemical investigation of the basis for the genetic N-acetylation polymorphism in the inbred hamster.
Cytosolic acetyl coenzyme A-dependent N-acetyltransferase enzyme (E.C. 2.3.1.5) from inbred hamsters of each acetylator genotype was partially purified by ion-exchange chromatography. Two distinct N-acetyltransferase enzymes were identified; the first one exhibited a polymorphic expression across acetylator genotypes whereas the second exhibited a monomorphic expression. The monomorphic enzyme had consistently high isoniazid and procainamide N-acetyltransferase activity in homozygous rapid acetylator (Bio. 87.20), homozygous slow acetylator (Bio. 82.73/H), obligate heterozygous rapid acetylator F1 progeny and in each of the three acetylator genotypes of F2 progeny. In contrast, the polymorphic enzyme exhibited marked acetylator genotype-dependent N-acetyltransferase activity. High p-aminobenzoic acid N-acetyltransferase activity was exhibited in the homozygous rapid acetylator parental and F2 generation progeny, intermediate activity was exhibited in the heterozygous rapid acetylator F1 and F2 generation progeny and very low or nondetectable activity was exhibited in homozygous slow acetylator parental and F2 generation progeny. A similar gene dose-response relationship was exhibited by the polymorphic N-acetyltransferase enzyme toward isoniazid and procainamide. These results provide new insight into the biochemical basis for the substrate-dependent polymorphic and monomorphic expression of N-acetylation capacity in the inbred hamster.
4-Aminobenzoic Acid↗
Reinforcing and discriminative stimulus properties of mixed agonist-antagonist opioids.
Nine mixed agonist-antagonist opioids were evaluated in macaque monkeys for their ability to serve as positive reinforcers and for their discriminative stimulus similarity to etorphine and ethylketazocine. For tests of reinforcing properties, various doses of each drug were substituted for codeine under a fixed-ratio 30 time-out 600 sec schedule of i.v. delivery. Discriminative properties were assessed in separate groups of monkeys for which etorphine and saline, or ethylketazocine and saline, were established as discriminative stimuli for responses maintained under a fixed-ratio 20 schedule of food delivery. Two patterns of reinforcing and discriminative stimulus properties were observed. Buprenorphine, butorphanol, GPA 1657, nalbuphine, propiram and WY 16225 (dezocine) functioned as positive reinforcers and occasioned etorphine-appropriate but not ethylketazocine-appropriate responses. dl-Profadol also functioned as a positive reinforcer; its stereoisomers occasioned etorphine-appropriate but not, in general, ethylketazocine-appropriate responses. In contrast, levallorphan and oxilorphan did not function as positive reinforcers and occasioned ethylketazocine-appropriate but no more than 30% etorphine-appropriate responses. Under these experimental conditions, the reinforcing and discriminative stimulus profiles of the mixed agonist-antagonist opioids paralleled those of etorphine-like (mu) or ethylketazocine-like (kappa) opioid agonists.
Animals↗
Relationship between N-acetylator phenotype and susceptibility toward hydrazine-induced lethal central nervous system toxicity in the rabbit.
Toxicity experiments carried out with rapid and slow acetylator rabbits showed that the slow acetylators exhibited greater susceptibility to lethal central nervous system actions of isoniazid and its metabolite, monoacetylhydrazine. Slow acetylator rabbits receiving a daily 30-mg/kg dose of isoniazid survived an average of 3.4 weeks, whereas rapid acetylators presented no signs of toxicity for the duration of the experiment (12 weeks). Concomitant administration of vitamin B6 (pyridoxine hydrochloride) raised the dose necessary for lethal convulsions by these agents in both rapid and slow acetylators. Inasmuch as isoniazid and other hydrazine drugs and foreign chemicals may produce a vitamin B6 deficiency in humans that can elicit seizures and lethal convulsions at high dose levels, these results suggest that the central nervous system toxicity produced by these agents might be more frequent and more severe in human slow acetylators.
Acetylation↗
Relationship of acetylator status to isoniazid toxicity, lupus erythematosus, and bladder cancer.
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Acetylation↗
Discriminative stimulus, antagonist, and rate-decreasing effects of cyclorphan: multiple modes of action.
This discriminative effects of cyclorphan were studied in pigeons trained to discriminate 0.32 mg/kg ethylketazocine, 1.8 mg/kg cyclazocine, or 32 mg/kg naltrexone from saline. A fourth group of pigeons was administered 100 mg/kg/day morphine and trained to discriminate 0.1 mg/kg naltrexone from saline. Cyclorphan produced dose-related ethylketazocine-appropriate responding that reached a maximum of 83% of the total session responses at 0.3 mg/kg. Higher cyclorphan doses produced less ethylketazocine-appropriate responding. IN pigeons trained to discriminate cyclazocine from saline, maximum drug-appropriate responding of greater than 90% occurred at 5.6-10.0 mg/kg cyclorphan. In narcotic-naive pigeons trained to discriminate 32 mg/kg naltrexone from saline, cyclorphan produced a maximum of less than 50% drug-appropriate responding. In contrast, in pigeons chronically administered morphine and trained to discriminate 0.1 mg/kg naltrexone from saline, 1.0 mg/kg cyclorphan resulted in 100% drug-appropriate responding. In pigeons responding under a multiple fixed-interval, fixed-ratio schedule of food delivery, cyclorphan produced a complete dose-related reversal of the rate-decreasing effects of 10 mg/kg morphine, the maximally effective antagonist doses being 1.0-3.2 mg/kg. Higher cyclorphan doses (10 mg/kg) resulted in response rate decreases that were not reversed by naloxone (1 mg/kg). Thus, cyclorphan has discriminative effects that are similar to those of both ethylketazocine and at 20 fold higher doses, cyclazocine. In addition, in morphine-treated pigeons, cyclorphan, across the same range of doses that produce ethylketazocine-appropriate responding, has discriminative effects that are similar to those of naltrexone, an effect that is probably related to the antagonist action of the drug.
Animals↗
Biochemical evidence for the coexistence of monomorphic and polymorphic N-acetyltransferase activities on a common protein in rabbit liver.
New Zealand White rabbits were classified as rapid or slow acetylators by measuring the N-acetylation half-life of i.v. administered sulfadiazine, by pedigree analysis and by determination of liver N-acetyltransferase (NAT) activity in vitro. Slow acetylator rabbits were found to have significantly lower levels of p-aminobenzoic acid NAT activity in vitro than did rapid acetylator rabbits, demonstrating genetic covariation of p-aminobenzoic acid (monomorphic) and isoniazid (polymorphic) NAT activity. Monomorphic and polymorphic NAT activities could not be separated by two extensive purification procedures involving sequential centrifugation, fractional precipitation with ammonium sulfate, ion-exchange chromatography on DEAE-cellulose, gel filtration on Sephadex or Sephacryl and isoelectric focusing or electrophoresis on polyacrylamide gels. In addition, indistinguishable heat inactivation patterns were demonstrated for the two NAT activities utilizing highly purified NAT preparations at two different temperatures. Each of these findings support the coexistence of monomorphic and polymorphic NAT activities on a common protein.
Acetylation↗
A unique pharmacogenetic expression of the N-acetylation polymorphism in the inbred hamster.
Liver N-acetyltransferase (NAT) preparations (105,000 x g cytosol) were obtained from both sexes of 26 strains of inbred hamsters. Liver NAT activity levels were determined for six arylamine substrates; isoniazid, p-aminobenzoic acid (PABA), p-aminosalicylic acid (PAS), sulfamethazine (SMZ), procainamide and 2-aminofluorene. The N-acetylation of isoniazid, SMZ, procainamide and 2-aminofluorene exhibited a monomorphic expression in the hamster as the genetic variation in NAT activity levels between hamster strains was only about 2-fold for each substrate. In contrast, the N-acetylation of PABA and PAS showed a polymorphic expression in the hamster. Two inbred hamster lines (Bio 1.5 and Bio 82.73) had over 400-fold lower PABA NAT and over 20-fold lower PAS NAT activity levels than did the other inbred strains. In addition, the genetically determined N-acetylation differences between the rapid and slow acetylator hamster strains were also demonstrated in vivo for PABA but not for SMZ. Comparison of Michaelis-Menten kinetic constants of PABA NAT activity in a rapid and slow acetylator strain showed a 20-fold lower Km in the rapid acetylator strain suggesting an intrinsic structural difference in rapid and slow acetylator hamster liver NAT. Thus, the pharmacogenetic expression of the N-acetylation polymorphism is quite unique in the inbred hamster, in that PABA and PAS are genetically polymorphic substrates, whereas isoniazid, SMZ, procainamide and 2-aminofluorene are monomorphic, in direct contrast to man and rabbit.
Acetylation↗
Identification of genetically homozygous rapid and slow acetylators of drugs and environmental carcinogens among established inbred rabbit strains.
Liver and gut mucosa N-acetyltransferase (NAT) cytosol (105,000 x g) was prepared from selected lines of New Zealand White rapid and slow acetylator rabbits bred and housed at the University of Michigan, and from inbred and partially inbred rabbits obtained from The Jackson Laboratory. Liver NAT activity was determined with p-aminobenzoic acid, p-aminosalicyclic acid, procainamide, sulfamethazine, isoniazid and 2-aminofluorene as substrates. Gut mucosal NAT activity was determined with 2-aminofluorene. A gene dose-response relationship was observed for both liver NAT and gut mucosa NAT with all substrates tested. Highest levels were always observed in homozygous rapid acetylator inbred strains (B/J, III/J, IIIC/J, III/DwJ, IIIEP/J and IIIVO/J), lower levels in obligate heterozygous rapid acetylator rabbits and lowest levels in homozygous slow acetylator inbred (ACEP/J, III/cdJ, IIIVO/ahJ, and IIIVO/vptJ) and outbred rabbits. The differences in magnitude of liver NAT activity level between acetylator genotypes was dependent on the substrate employed, progressively increasing in the following order: p-aminobenzoic acid, p-aminosalicyclic acid, procainamide, sulfamethazine, isoniazid, 2-aminofluorene. The determination of kinetic constants for liver p-aminosalicyclic acid NAT activity indicated a 2-fold difference in apparent Vmax between rapid acetylator genotypes and a 30-fold difference between rapid and slow acetylator phenotypes. In addition, the apparent Km for p-aminosalicyclic acid was significantly lower in the slow acetylators than in the rapid acetylators.
Acetylation↗
Association of arylhydroxamic acid N,O-acyltransferase and genetically polymorphic N-acetyltransferase in established inbred rabbit strains.
Partially purified liver preparations from 17 inbred and partially inbred rabbit strains were assayed for polymorphic N-acetyltransferase (NAT) and arylhydroxamic acid N,O-acyltransferase (AHAT) activities. The AC/J, AX/J, B/J, WH/J, X/J, Y-l/J, III/J, IIIC/J, III/DwJ, IIIEP/J and IIIVO/J inbred strains were identified as rapid acetylators and had high AHAT activity. The ACEP/J, AXBU/J, OS/J, III/cdJ, IIIVO/ahJ and IIIVO/vptJ strains were identified as slow acetylators and had low AHAT activity. These findings provide added evidence for the hypothesis that polymorphic NAT and AHAT activities are properties of the same enzyme. Additional studies in five of the rapid acetylator strains showed that they had significantly higher levels of liver NAT activity towards other arylamine acetylator predictor drugs and carcinogens than did obligate heterozygous (Rr) rapid acetylators from our rabbit colony. This indicates that the inbred animals are homozygous (RR) rapid acetylators and that there is a gene-dose response difference between the two rapid acetylator genotypes. Availability of established inbred and partially inbred strains shown to possess both acetylator phenotypes enhances the opportunity for using the rabbit as a genetic model for evaluating the role of the isoniazid acetylator polymorphism as a host factor in arylamine-related carcinogenesis.
Acetyltransferases↗
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.
Animals↗
An enzyme marker to ensure reliable determinations of human isoniazid acetylator phenotype in vitro.
Human liver N-acetyltransferase (NAT) activity undergoes rapid inactivation after death. Thus, in vitro determination of acetylator phenotype in liver autopsies may be unreliable. In the present investigation, the relative stabilities of monomorphic and polymorphic NAT activity were compared in situ in human and rabbit liver of rapid and slow acetylator phenotype. In both phenotypes, the monomorphic NAT activity was considerably less stable than the polymorphic, enabling it to be utilized as an enzyme marker to assure reliable in vitro phenotype classification.
4-Aminobenzoic Acid↗
Pharmacological analysis of the discriminative stimulus characteristics of ethylketazocine in the rhesus monkey.
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Animals↗
Narcotic discrimination in pigeons.
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Animals↗
Narcotic drug discriminations by rhesus monkeys and pigeons.
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Animals↗
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.
Acetylation↗
Acetylator phenotype-dependent and -independent expression of arylamine N-acetyltransferase isozymes in rapid and slow acetylator inbred rat liver.
Although mouse, hamster, and rabbit models of the human N-acetylation polymorphism have been identified and characterized, many investigations of arylamine toxicity and carcinogenicity are carried out in the rat, particularly the Fischer 344 (F-344) inbred rat. We partially characterized a new rat model of the N-acetylation polymorphism by determining expression of arylamine N-acetyltransferase activities in liver cytosols derived from adult male inbred F-344, WKY, and their F1 hybrid rat strains. Levels of N-acetyltransferase activity differed significantly between the strains for many arylamine substrates, with highest levels in F-344, lowest levels in WKY, and intermediate levels in F1 hybrids of these two parental strains. However, for some other arylamine substrates, levels of N-acetyltransferase activity did not differ significantly between the rat strains. Partial purification of rat liver cytosols from the three strains resulted in identification of two N-acetyltransferase isozymes. The levels of N-acetyltransferase activity of one isozyme differed significantly between strains analogous to the pattern observed in crude cytosol. In contrast, the levels of N-acetyltransferase activity of the second isozyme did not differ between the strains. Based upon these results, the F-344 inbred strain is designated a rapid acetylator phenotype, the WKY inbred strain is designated a slow acetylator phenotype, and F1 hybrids of the two parental strains are designated intermediate acetylator phenotype. The identification of acetylator phenotype-dependent and -independent hepatic N-acetyltransferase isozymes in the inbred rat mimics the biochemical basis for acetylator phenotype-dependent and -independent expressions of N-acetylation in humans and other mammalian species.
Acetylation↗