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K Gray

Publications and source records attributed to K Gray.

At least 55 records · Page 3Linked to original sources
PubMed1996

Characterization of chimeras between the ecotropic Moloney murine leukemia virus and the amphotropic 4070A envelope proteins.

A series of 22 chimeric envelope (env) genes were generated between the ecotropic Moloney murine leukemia virus and the amphotropic 4070A isolate. The chimeric envelopes were expressed within the complete, replication-competent provirus and tested for virus viability by transient expression assays. Eleven of the 22 viruses were viable. Five of these chimeric viruses showed an ecotropic host range, and six exhibited an amphotropic host range and viral interference. The host range determinants map to the first half of the surface (SU) protein. The N-terminal 72 amino acids of 4070A (42 of processed SU) are not required for amphotropic receptor usage. Ecotropic and amphotropic viruses differ in their ability to form large, multinucleated syncytia when cocultured with the rat XC cell line. Ecotropic murine leukemia virus forms large syncytia with XC cells, whereas no syncytia are reported for amphotropic virus. All chimeras which contained the N-terminal half of the ecotropic SU protein, encoding the receptor binding domain, formed the large multinucleated syncytia with XC cells.

3T3 Cells↗
PubMed1996

Altered expression of eukaryotic initiation factor 2B in skeletal muscle during sepsis.

Sepsis causes an inhibition of protein synthesis in skeletal muscles composed of fast-twitch fibers, in part, as a result of a decreased activity of the eukaryotic initiation factor 2B (eIF-2B). In the present study, we investigated the expression of two subunits of eIF-2B, i.e., the beta- and epsilon-subunits during sepsis. The expression of both beta- and epsilon-subunits of eIF-2B in gastrocnemius was decreased approximately 50% from control values during the first 5 days after induction of sepsis. The decreased expression of eIF-2B epsilon during sepsis correlated with similar reductions in eIF-2B epsilon mRNA. Restoration of protein synthesis (10 days postsurgery) was associated with a return of eIF-2B epsilon expression to values observed in control rats. Expression of eIF-2B epsilon was not altered in heart during sepsis or in gastrocnemius from nonseptic abscess animals. Amrinone, which ameliorated the inhibition of protein synthesis during sepsis, also prevented the fall in eIF-2B epsilon protein after 5 days of infection. The data provide evidence that expression of eIF-2B epsilon is markedly influenced in gastrocnemius during the course of the septic episode and support the concept that this change is a mechanism responsible for the inhibition of protein synthesis observed under this condition.

Amrinone↗
PubMed1996

Forearm training attenuates sympathetic responses to prolonged rhythmic forearm exercise.

We previously demonstrated that nonfatiguing rhythmic forearm exercise at 25% maximal voluntary contraction (12 2-s contractions/min) evokes sympathoexcitation without significant engagement of metabolite-sensitive muscle afferents (B.A. Batman, J.C. Hardy, U.A. Leuenberger, M.B. Smith, Q.X. Yang and L.I. Sinoway. J. Appl. Physiol. 76: 1077-1081, 1994). This is in contrast to the sympathetic nervous system responses observed during fatiguing static forearm exercise where metabolite-sensitive afferents are the key determinants of sympathetic activation. In this report we examined whether forearm exercise training would attenuate sympathetic nervous system responses to rhythmic forearm exercise. We measured heart rate, mean arterial blood pressure (MAP), muscle sympathetic nerve activity (microneurography), plasma norepinephrine (NE), and NE spillover and clearance (tritiated NE kinetics) during nonfatiguing rhythmic forearm exercise before and after a 4-wk unilateral forearm training paradigm. Training had no effect on forearm mass, maximal voluntary contraction, or heart rate but did attenuate the increase in MAP (increase in MAP: from 15.2 +/- 1.8 before training to 11.4 +/- 1.4 mmHg after training; P < 0.017), muscle sympathetic nerve activity (increase in bursts: from 10.8 +/- 1.4 before training to 6.2 +/- 1.1 bursts/min after training; P < 0.030), and the NE spillover (increases in arterial spillover: from 1.3 +/- 0.2 before training to 0.6 +/- 0.2 nmol.min-1.m-2 after training, P < 0.014; increase in venous spillover: from 2.0 +/- 0.6 before training to 1.0 +/- 0.5 nmol.min-1.m-2 after training, P < 0.037) seen in response to exercise performed by the trained forearm. Thus forearm training reduces sympathetic responses during a nonfatiguing rhythmic handgrip paradigm that does not engage muscle metaboreceptors. We speculate that this effect is due to a conditioning-induced reduction in mechanically sensitive muscle afferent discharge.

Adult↗
PubMed1996

Aberrant crypts as a biomarker for colon cancer: evaluation of potential chemopreventive agents in the rat.

We assessed the effects of 41 potential chemopreventive agents in the F344 rat using the inhibition of carcinogen-induced aberrant crypt foci (ACF) in the colon as the measure of efficacy. ACF were induced by the carcinogen azoxymethane in F344 rats by two sequential weekly injections at a dose of 15 mg/kg. Two weeks after the last azoxymethane injection, animals were evaluated for the number of aberrant crypts detected in methylene blue-stained whole mounts of rat colon. The 41 agents were derived from a priority listing that was based on reports of chemopreventive activity in the literature and/or efficacy data from in vitro models of carcinogenesis. The list of agents included representative examples of phytochemicals, vitamins, minerals, inhibitors of proliferation, inducers of Phase 1 and Phase 2 metabolism systems, nonsteroidal anti-inflammatory agents, and differentiation agents. Eighteen agents were positive in the assay, significantly reducing the incidence of ACF at least in one of two doses tested. As a chemical class, the nonsteroidal anti-inflammatory drugs, which included ibuprofen, ketoprofen, piroxicam, and indomethacin, were most active; other less potent agents were arginine, butylated hydroxyanisole, curcumin, diallyl sulfide, difluoromethylornithine, 18 beta-glycyrrhetinic acid, indole-3-carbinol, oltipraz, purpurin, rutin, and the sodium salts of butyrate, selenite, and thiosulfate. Twenty-three agents did not inhibit ACF; included among these were several agents that promoted the development of ACF at one or both doses tested: benzyl isothiocyanate,calcium glucarate, catechin, dihydroepiandosterone, fluocinolone acetonide,folic acid, levamisole, 2-mercaptoethanesulfonic acid, nordihydroguiaretic acid, potassium glucarate, propyl gallate, beta-sitosterol, sodium cromolyn, sodium molybdate, and sulfasalazine. The aberrant crypt assay demonstrates reasonable specificity and sensitivity in predicting which agents are likely to prevent colon cancer.

Animals↗
PubMed1995

Modulation of skeletal muscle protein synthesis by amino acids and insulin during sepsis.

Effects of different concentrations of insulin and amino acids on protein synthesis in skeletal muscle of young, fed septic rats were determined in the perfused rat hindlimb. Rates of protein synthesis in gastrocnemius were measured by incorporation of [3H]-phenylalanine into protein. Perfusion of hindlimb muscles from young, fed control rats with medium containing either insulin and a complete mixture of amino acids at plasma concentration (1x) or a mixture of amino acids at 10-fold (10x) plasma concentration resulted in an approximately twofold stimulation of the rate of protein synthesis. The effect of amino acids on protein synthesis was partly accounted for by elevated concentrations of branched-chain amino acids ([BCAA] leucine, isoleucine, and valine). In young, fed septic rats, the rate of protein synthesis in muscle perfused with buffer containing the normal concentration of amino acids was reduced 40% as compared with control levels (P < .05). In contrast to controls, addition of insulin (1,000 microU/mL) did not augment protein synthesis in muscle from young, fed septic rats perfused with the complete mixture of amino acids. Addition of insulin 10,000 microU/mL stimulated protein synthesis approximately 80% in gastrocnemius of septic rats (P < .05). However, the rate of protein synthesis remained less than that observed in young, fed control rats at similar insulin concentrations. Perfusion with medium containing 10x plasma amino acids stimulated protein synthesis approximately fourfold in young, fed septic rats as compared with control animals. In contrast to controls, BCAA at 10x plasma concentration did not augment protein synthesis in young, fed septic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1995

Coordinate regulation by diethylstilbestrol of the platelet-derived growth factor-A (PDGF-A) and -B chains and the PDGF receptor alpha- and beta-subunits in the mouse uterus and vagina: potential mediators of estrogen action.

The effects of estrogen on the reproductive tract involve cell proliferation, migration, and differentiation, which need to be well coordinated. Polypeptide growth factors are believed to play a vital role in a number of these cellular processes. Among the growth factors now documented to be associated with estrogen action are epidermal growth factor, transforming growth factor-alpha (TGF alpha), transforming growth factor-beta 1 (TGF beta 1), TGF beta 2, TGF beta 3, and insulin-like growth factor-I (IGF-I). Platelet-derived growth factors (PDGFs) are also potent mitogens, which consist of two peptide chains, denoted A and B, that dimerize to isoforms (PDGF-AA, -AB, and -BB) which differ in their functional properties, secretory behavior, receptor binding, and physiological effects. To study the role of the PDGF-A and -B chains and the PDGF receptor subunits, alpha and beta, during estrogen action in the mouse reproductive tract, time-dependent changes in the expression of these genes were examined by Northern and in situ RNA analyses and by immunohistochemistry after a single treatment of immature CD-1 (17- to 19-day-old) mice with the synthetic estrogen, diethylstilbestrol (DES). Our results demonstrate estrogen modulation of the expression of messenger RNA (mRNA) and protein for the PDGF ligands and receptors in both the uterus and vagina of the mouse. Northern and in situ RNA analyses demonstrate time-dependent estrogen induction of the mRNA levels for these genes in both tissues within 3 h after treatment. However, distinctive mRNA expression profiles for the PDGF ligand and receptor genes are exhibited by the uterus and vagina in response to DES, especially in that the induction of transcripts for PDGF-A and both receptor subunits is more transient in the vagina than in the uterus. Steroid specificity studies demonstrate predominant estrogen-specific regulation of mRNA induction for these genes. Analysis of cell-specific RNA expression by in situ hybridization reveals prominent induction of transcripts for the PDGF chains and receptor subunits in the uterine and vaginal epithelium after estrogen treatment, although enhanced expression of mRNA is also noted in the stroma, particularly for the PDGF receptor subunit genes. Cellular localization of the PDGF ligand and receptor protein molecules by immunohistochemistry detected significant immunostaining for all of these proteins in both the uterus and vagina of control animals. After DES treatment, the uterus exhibits a significant decrease in the level of PDGF ligand and receptor proteins immunostained within 6 h, whereas less dramatic effects ar observed in the vagina.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Construction of Syrian hamster lines congenic at the polymorphic acetyltransferase locus (NAT2): acetylator genotype-dependent N- and O-acetylation of arylamine carcinogens.

Congenic Bio. 1.5/H-NAT2 Syrian hamster lines were constructed by introducing the NAT2r gene from MHA/SsLak inbred hamsters into a background BIO 1.5 Syrian inbred hamster line. Genetic identity of the Bio. 1.5/H-NAT2 congenic lines and nonidentity with the previously constructed Bio. 82.73/H-Pat congenic lines were determined by "DNA fingerprints" of genomic DNA derived from the different hamster lines. The N-acetylation capacity of the Bio. 1.5/H-NAT2 congenic hamster lines was clearly NAT2-dependent both in vivo and in vitro, with highest levels expressed in Bio. 1.5/H-NAT2r homozygous rapid acetylators, intermediate levels in Bio. 1.5/H-NAT2r/NAT2s heterozygous acetylators, and lowest levels in Bio. 1.5/H-NAT2s homozygous slow acetylators. The NAT2-dependent expression of N-acetyltransferase activity was evident toward p-aminobenzoic acid, 4-aminophenol, 2-aminofluorene, 4-aminobiphenyl, beta-naphthylamine, and 3,2'-dimethyl-4-amino-biphenyl in liver, kidney, colon, lung, and urinary bladder cytosols. The polymorphic acetyltransferase (NAT2) and the monomorphic acetyltransferase (NAT1) were isolated from hepatic cytosols and tested separately for their ability to catalyze arylamine N-acetyltransferase and N-hydroxyarylamine O-acetyltransferase activities. Both arylamine N-acetylation and N-hydroxyarylamine O-acetylation were clearly acetylator genotype-dependent when catalyzed by NAT2, and both were clearly acetylator genotype-independent when catalyzed by NAT1. NAT2/NAT1 activity ratios varied with the particular arylamine substrate acetylated. These studies show an important role for NAT2 acetylator genotype in Syrian hamster carcinogenic arylamine metabolism and confirm its role in the metabolic activation of N-hydroxyarylamines. The Bio. 1.5/H-NAT2 congenic lines provide a new model for investigating the precise role of the NAT2 gene locus in arylamine metabolism and toxicity.

Acetylation↗
PubMed1994

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.

Acetylation↗
PubMed1994

Accuracy of dose calculation methods for retracted tissue compensators.

Uncertainties arise in dose calculations involving retracted tissue compensators due to the effects of the compensator upon the scatter component of the dose. Many commercial treatment-planning systems cannot allow directly for the presence of a compensator in isodose calculation or else use simple 2D methods. We present data to test calculation accuracy for a wax compensation system by comparing retraction factors measured along central-axis and off-axis raylines for a variety of compensator shapes, with those derived using effective attenuation coefficient and 3D analytical calculations. The accuracy of using measured uniform-thickness retraction factors for non-uniform shapes and the dose uniformity achievable using a simple compensation system are also discussed. We conclude that the accuracy of simple calculation methods is shape dependent and that calculation errors and dose variations can exceed +/-5% where missing-tissue thickness variations are large. The analytical method is shown to give good agreement with experiment and indicates that it should be possible to adapt algorithms that calculate scatter from the patient for use with compensators.

Algorithms↗
PubMed1994

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)

Acetyl Coenzyme A↗
PubMed1994

Interleukin-1 receptor antagonist prevents sepsis-induced inhibition of protein synthesis.

To understand the role of interleukin-1 (IL-1) as a mediator of the sepsis-induced skeletal muscle catabolism, we investigated the effects of a specific IL-1 receptor antagonist (IL-1ra) on skeletal muscle protein metabolism in a rodent model of chronic abdominal sepsis. A constant infusion of IL-1ra (2 mg.kg-1.h-1) or saline was begun immediately after the induction of sepsis and continued for 5 days. The effect of IL-1ra on protein metabolism was examined in individual muscles (gastrocnemius, soleus, heart) containing different fiber types. Infusion of IL-1ra in control animals did not alter protein metabolism in any of the muscles examined. Muscle weight, protein content, and the rate of protein synthesis in gastrocnemius were reduced by sepsis, whereas none of these parameters were affected in soleus or heart. Infusion of IL-1ra prevented the sepsis-induced loss of muscle protein and inhibition of protein synthesis in gastrocnemius but was without effect in soleus or heart. IL-1ra infusion restored translational efficiency in the gastrocnemius of septic rats and was without effect on the RNA content. These results provide evidence for a role of IL-1 as a mediator of the sepsis-induced abnormalities in skeletal muscle protein metabolism.

Abdomen↗
PubMed1994

Role of diprotonated phosphate in evoking muscle reflex responses in cats and humans.

Lactic acid and H+ evoke muscle reflexes that raise sympathetic nerve activity. Whether these substances are direct afferent stimulants or markers for the acidification of other substances is unknown. Diprotonated phosphate (H2PO4-), a possible mediator of fatigue, increases as the cell acidifies and phosphate is produced. Its role in evoking muscle reflexes is unknown. We used 31P-nuclear magnetic resonance to measure forearm muscle H+ and H2PO4- and microneurography to measure muscle sympathetic nerve activity (MSNA, peroneal nerve) during a handgrip protocol designed to dissociate H+ from H2PO4-. Ischemic handgrip (50% maximal voluntary contraction x 2 min) was followed by a 1-min rest period during which the muscle was freely perfused. This was followed by a second bout of ischemic handgrip and a 5-min recovery. In seven of eight subjects, MSNA correlated with H2PO4-, whereas it correlated with pH in only one subject. To determine whether muscle reflex responses are evoked by H+, lactic acid, monoprotonated phosphate (HPO4(2-), or H2PO4-, we injected H+, lactate, H2PO4- [all 50 mM in 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffered to pH 6], and HPO4(2-) (50 mM, pH 7.5 in 10 mM HEPES) into the arterial supply of the triceps surae of the cat (n = 9) as we measured mean arterial blood pressure (MAP). H2PO4- increased MAP more than HPO4(2-), H+, or lactate (27.1 +/- 3.7 vs. 5.0 +/- 1.3, 4.6 +/- 3.1, and 7.7 +/- 3.2 rise in mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Sympathetic and blood pressure responses to voluntary apnea are augmented by hypoxemia.

Oscillations of arterial pressure during sleep are the hemodynamic hallmark of the sleep apnea syndrome. The mechanism of these transient pressure elevations is incompletely understood. To investigate the role of the arterial chemoreflex in the neurocirculatory responses to apnea, we measured mean arterial pressure (MAP; Finapres) and muscle sympathetic nerve activity (MSNA; peroneal microneurography) during voluntary end-expiratory apnea during exposure to room air, 10.5% O2 in N2 (hypoxemia), and 100% O2 (hyperoxia) in 11 healthy men. While the men breathed spontaneously, MSNA (in bursts/min) rose during hypoxemia and decreased during hyperoxia and MAP remained unchanged. During room air exposure, apnea led to a rise of 94 +/- 54% in MSNA total amplitude and a rise of 6.5 +/- 2.1 mmHg in MAP. MSNA and MAP increased by 616 +/- 158% and 10.8 +/- 2.4 mmHg, respectively, during hypoxemic apnea of equal duration (time-matched responses) and by 98 +/- 41% and 4.9 +/- 2.0 mmHg, respectively, during hyperoxic apnea (P < 0.05 for hypoxemic vs. hyperoxic apnea for both). Thus, in awake healthy humans, activation of the arterial chemoreflex by hypoxemia appears to contribute importantly to the sympathetic and blood pressure responses to apnea.

Administration, Inhalation↗
PubMed1994

The Neuropsychiatric Inventory: comprehensive assessment of psychopathology in dementia.

We developed a new instrument, the Neuropsychiatric Inventory (NPI), to assess 10 behavioral disturbances occurring in dementia patients: delusions, hallucinations, dysphoria, anxiety, agitation/aggression, euphoria, disinhibition, irritability/lability, apathy, and aberrant motor activity. The NPI uses a screening strategy to minimize administration time, examining and scoring only those behavioral domains with positive responses to screening questions. Both the frequency and the severity of each behavior are determined. Information for the NPI is obtained from a caregiver familiar with the patient's behavior. Studies reported here demonstrate the content and concurrent validity as well as between-rater, test-retest, and internal consistency reliability; the instrument is both valid and reliable. The NPI has the advantages of evaluating a wider range of psychopathology than existing instruments, soliciting information that may distinguish among different etiologies of dementia, differentiating between severity and frequency of behavioral changes, and minimizing administration time.

Aged↗
PubMed1994

Evaluation of photoaffinity labeled sites of bacteriorhodopsin using molecular modeling.

Three successful photoaffinity labeling experiments of bacteriorhodopsin (bR) have been reported that used photoactivatible analogs of retinal to label the retinal binding site of the protein. Using molecular modeling techniques, the information about the retinal binding site derived from these studies is compared to the retinal binding site as defined by Henderson et al. (1990) using electron diffraction data. This comparison suggests some limitations to the use of photoaffinity labeling experiments for the determination of high resolution structural information.

Affinity Labels↗
PubMed1993

Metabolic activation of N-hydroxy-2-aminofluorene and N-hydroxy-2-acetylaminofluorene by monomorphic N-acetyltransferase (NAT1) and polymorphic N-acetyltransferase (NAT2) in colon cytosols of Syrian hamsters congenic at the NAT2 locus.

Acetylator genotype is regulated at the polymorphic acetyltransferase (NAT2) gene locus in humans and other mammals such as Syrian hamsters. Human slow acetylator phenotypes have been associated with increased incidences of urinary bladder cancers, whereas rapid acetylators have been associated with increased incidences of colorectal cancers. The genetic predisposition of rapid acetylators to colorectal cancers suggests localized metabolic activation of arylamine carcinogen metabolites by polymorphic N-acetyltransferase (NAT2) in colon tissues. We tested this hypothesis in Bio. 82.73/H Syrian hamster lines which are congenic at the NAT2 gene locus. Congenic Bio. 82.73/H Syrian hamsters expressed acetylator genotype-dependent N-acetyltransferase activity in colon cytosols toward arylamine carcinogens such as 2-aminofluorene and 4-aminobiphenyl. Partial purification of the hamster colon cytosol by anion exchange chromatography identified two N-acetyltransferase isozymes analogous to those previously described in liver and urinary bladder. One of the isozymes (NAT2) exhibited acetylator genotype-dependent expression for the N-acetylation of each arylamine tested: p-aminophenol; 2-aminofluorene; 4-aminobiphenyl; 3,2'-dimethyl-4-aminobiphenyl; and 2-amino-dipyrido[1,2-a:3',2'd]imidazole as well as for the metabolic activation (via O-acetylation) of N-hydroxy-2-aminofluorene to form DNA adducts. Although NAT2 catalyzed the metabolic activation of N-hydroxy-2-acetyl-aminofluorene to DNA adducts, the rates were lower, were paraoxon-sensitive, and did not reflect acetylator genotype. A second isozyme (NAT1) also catalyzed the N-acetylation of each arylamine as well as the metabolic activation of N-hydroxy-2-aminofluorene and N-hydroxy-2-acetylaminofluorene to DNA adducts at rates that were independent of acetylator genotype. Metabolic activation of N-hydroxy-2-aminofluorene catalyzed by both NAT1 and NAT2 was resistant to 100 microM paraoxon, an inhibitor of microsomal deacetylases. Metabolic activation of N-hydroxy-2-acetylaminofluorene by NAT1 and NAT2 was partially sensitive to 100 microM paraoxon. Michaelis-Menten kinetic constants were determined for the colon NAT1 and NAT2 isozymes and compared to previous determinations for liver NAT1 and NAT2. For each of the arylamines tested, both apparent Km and apparent Vmax were higher for NAT2 than NAT1. In rapid acetylator hamster colon, NAT2/NAT1 activity ratios were 18 and 13 for the N-acetylation of 2-aminofluorene and 4-aminobiphenyl and 28 for the O-acetylation of N-hydroxy-2-aminofluorene. These results strongly support the role of the polymorphic NAT2 gene locus in the local metabolic activation of N-hydroxyarylamine carcinogens in colon and provide mechanistic support for human epidemiological studies suggesting a predisposition of rapid acetylators to colorectal cancer.

Acetylation↗
PubMed1993

Human acetylator genotype: relationship to colorectal cancer incidence and arylamine N-acetyltransferase expression in colon cytosol.

Polymorphic expression of arylamine N-acetyltransferase (EC 2.3.1.5) may be a differential risk factor in metabolic activation of arylamine carcinogens and susceptibility to cancers related to arylamine exposures. Human epidemiological studies suggest that rapid acetylator phenotype may be associated with higher incidences of colorectal cancer. We used restriction fragment length polymorphism analysis to determine acetylator genotypes of 44 subjects with colorectal cancer and 28 non-cancer subjects of similar ethnic background (i.e., approximately 25% Black and 75% White). The polymorphic N-acetyltransferase gene (NAT2) was amplified by the polymerase chain reaction from DNA templates derived from human colons of colorectal and non-cancer subjects. No significant differences in NAT2 allelic frequencies (i.e., WT, M1, M2, M3 alleles) or in acetylator genotypes were found between the colorectal cancer and non-cancer groups. No significant differences in NAT2 allelic frequencies were observed between Whites and Blacks or between males and females. Cytosolic preparations from the human colons were tested for expression of arylamine N-acetyltransferase activity. Although N-acetyltransferase activity was expressed for each of the arylamines tested (i. e., p-aminobenzoic acid, 4-aminobiphenyl, 2-aminofluorene, beta-naphthylamine), no correlation was observed between acetylator genotype and expression of human colon arylamine N-acetyltransferase activity. Similarly, no correlation was observed between subject age and expression of human colon arylamine N-acetyltransferase activity. These results suggest that arylamine N-acetyltransferase activity expressed in human colon is catalyzed predominantly by NAT1, an arylamine N-acetyltransferase that is not regulated by NAT2 acetylator genotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylation↗