N-acetylation phenotyping with sulphadimidine in a Turkish population

Estimating N-acetyltransferase metabolic activity and pharmacokinetic parameters of isoniazid from genotypes in Chinese subjects

BACKGROUND

To establish quantitative relationship between metabolic activity of N-acetyltransferase (NAT2) and single nucleotide polymorphisms (SNPs), and estimate pharmacokinetic parameters of isoniazid (INH) on the basis of NAT2 alleles in Chinese subjects.

METHODS

Concentrations of INH and acetylisoniazid in plasma of 24 subjects were measured 0-14 h after oral administration of INH. Pharmacokinetic parameters were simulated. NAT2 alleles were determined by a reversed dot blot method. Correlation between various NAT2 SNPs and metabolic ratio (MR) or INH pharmacokinetic parameters was studied by multiple linear regression analysis.

RESULTS

There was quantitative relationship between various NAT2 alleles and MR of sulphadimidine (r(2)=0.836, P<0.0001). The pharmacokinetic parameters such as k, C(max), AUC, Cl of INH and C(max), AUC of AcINH can be calculated by NAT2 variant patterns. There was good correlation between observed and calculated data (r(2)>0.75, P<0.0001) except for C(max) of INH (r(2)=0.35, P=0.021). The 95% confidence intervals for prediction error ranged from -3.3%-5.6% for k to -10.5%-37.0% for C(max) of INH.

CONCLUSION

NAT2 genotypes can be used to predict pharmacokinetic parameters of INH. It may be useful in the rational use of INH.

Deciphering the ancient and complex evolutionary history of human arylamine N-acetyltransferase genes

The human N-acetyltransferase genes NAT1 and NAT2 encode two phase-II enzymes that metabolize various drugs and carcinogens. Functional variability at these genes has been associated with adverse drug reactions and cancer susceptibility. Mutations in NAT2 leading to the so-called slow-acetylation phenotype reach high frequencies worldwide, which questions the significance of altered acetylation in human adaptation. To investigate the role of population history and natural selection in shaping NATs variation, we characterized genetic diversity through the resequencing and genotyping of NAT1, NAT2, and the pseudogene NATP in a collection of 13 different populations with distinct ethnic backgrounds and demographic pasts. This combined study design allowed us to define a detailed map of linkage disequilibrium of the NATs region as well as to perform a number of sequence-based neutrality tests and the long-range haplotype (LRH) test. Our data revealed distinctive patterns of variability for the two genes: the reduced diversity observed at NAT1 is consistent with the action of purifying selection, whereas NAT2 functional variation contributes to high levels of diversity. In addition, the LRH test identified a particular NAT2 haplotype (NAT2*5B) under recent positive selection in western/central Eurasians. This haplotype harbors the mutation 341T-->C and encodes the "slowest-acetylator" NAT2 enzyme, suggesting a general selective advantage for the slow-acetylator phenotype. Interestingly, the NAT2*5B haplotype, which seems to have conferred a selective advantage during the past approximately 6,500 years, exhibits today the strongest association with susceptibility to bladder cancer and adverse drug reactions. On the whole, the patterns observed for NAT2 well illustrate how geographically and temporally fluctuating xenobiotic environments may have influenced not only our genome variability but also our present-day susceptibility to disease.

Potential chemoprotective effects of the coffee components kahweol and cafestol palmitates via modification of hepatic N-acetyltransferase and glutathione S-transferase activities

Coffee drinking has been associated with reduced incidence of colorectal cancer, possibly via chemoprotection/modification of the metabolism of dietary heterocyclic amine carcinogens such as 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine (PhIP) by kahweol and cafestol palmitates (K/C), two components of unfiltered coffee. Using the PhIP-exposed male Fisher F344 rat as a model, K/C have been shown to reduce colonic PhIP-DNA adducts by > 50%. We have used the male F344 rat to investigate the effects of dietary K/C (0.02-0.2% as a 1:1 mixture) on the metabolism of PhIP by N-acetyltransferase- (NAT), sulfotransferase- (SULT), and glutathione-dependent pathways. K/C decreased hepatic NAT-dependent PhIP activation by up to 80% in a dose-dependent manner. Conversely, hepatic glutathione S-transferase (GST) activity/expression increased, e.g., 3-4 fold toward 1-chloro-2,4-dinitrobenzene (total activity), up to 23-fold toward 4-vinylpyridine (rGSTP1), and approximately 7-fold for rGSTA2 protein. These effects had fully developed after 5 days of the test diet and persisted for at least 5 days after withdrawal of K/C. Hepatic glutathione increased two- to threefold and this increase was more short-lived than other changes. K/C did not modify hepatic SULT activity or colon NAT and GST activities. Benzylisothiocyanate and black tea, which have also been shown to reduce the formation of PhIP-DNA adducts in this model, had little effect on hepatic NAT, SULT, GST, or GSH. In primary culture of rat hepatocytes, both kahweol and cafestol palmitates reduced NAT activity by 80%. In summary, the unique potential of K/C to convert rapid acetylators to a slow acetylator phenotype, accompanied by GST induction, might contribute to chemoprevention against cancers associated with heterocyclic amines.

Acetylator phenotype in relation to age and gender in the Baltimore Longitudinal Study of Aging

This study investigated in healthy Caucasians the possible occurrence of age and gender-associated differences in NAT2 acetylator phenotype. Acetylator phenotype was determined after a single oral dose of 100 mg dapsone during testing of oral glucose tolerance in 510 Caucasian volunteers aged from 19 to 93 years, 339 men and 171 women, from the Baltimore Longitudinal Study of Aging. Participants were classified as slow or rapid acetylators according to the ratio of monoacetyldapsone to dapsone concentration in plasma. The ratio dividing the two groups, 0.30, was chosen after inspection of a probit plot and histogram of the monoacetyldapsone/dapsone ratios. Fifty-one percent of the participants were slow acetylators and 49% were rapid acetylators. Because there was no significant difference between the sexes in the monoacetyl-dapsone/dapsone ratios, all 510 participants were pooled into a single group for further analysis. In the combined analysis, there was a small decline in the prevalence of the slow acetylator phenotype with age, but this age effect accounted for less than 1% of the total variance in the monoacetyldapsone/dapsone ratio (r2 = 0.009). Also, it was shown in a group of 20 participants that administration of glucose with dapsone does not influence the determination of acetylator phenotype. In a large healthy Caucasian. American population, there was no biologically important effect of age or sex on the distribution of NAT2 acetylator phenotype.

Acetylation phenotypes and biological variation in a French Caucasian population

Factors affecting the caffeine acetylation phenotype were investigated in a French Caucasian population of 150 unrelated supposedly healthy subjects, aged 18 to 63 years. This population, including 75 men and 75 women, was used to determine whether the acetylation polymorphism is related to environmental influences such as smoking habits, intake of alcohol, use of oral contraceptives, use of certain drugs. The acetylation phenotype was assessed from the molar ratio of two caffeine metabolites: 5-acetylamino-6-formylamino-3-methyluracil/1-methylxanthine. For values less than 0.85, the subjects were classified as poor acetylators (frequency, mean +/- SD: 61.3 +/- 7.9%) in this study. Dose recoveries of 5-acetylamino-6-formylamino-3-methyluracil (mean +/- SD) were 1.26 +/- 0.85% and 3.58 +/- 1.64% in slow and rapid acetylators, respectively. The recovery (mean +/- SD) of 1-methylxanthine in the 3 hour-urine was 2.86 +/- 1.51% in slow acetylators and 2.36 +/- 1.27% in rapid acetylators. The mean value (and SD) of the molar ratio was 0.437 (0.177) and 1.669 (0.651) for slow and rapid acetylators. Three other metabolite ratios can also provide an acetylation index: 5-acetylamino-6-formylamino-3-methyluracil/5-acetylamino-6-formylamino-3 - methyluracil + 1-methylxanthine + 1-methyluric acid; 5-acetylamino-6-formylamino-3-methyluracil/1-methylxanthine + 1-methyluric acid + 1,7-dimethyluric acid; and 5-acetylamino-6-formylamino-3-methyluracil/1-methylxanthine + 1-methyluric acid + 1,7-dimethyluric acid + 1,7-dimethylxanthine with a bimodal distribution for the former and a trimodal distribution for the two latter ratios, both showing about 95% concordance with the 5-acetylamino-6-formylamino-3-methyluracil/1-methylxanthine ratio. Age did not influence the excretion of caffeine and its five major metabolites. A marked influence of sex was observed only on the unchanged caffeine excretion, and the effect was greater in slow acetylators than in rapid acetylators. The 5-acetylamino-6-formylamino-3-methyluracil excretion was about three times higher in rapid acetylators than in slow acetylators in both sexes.

Metabolic phenotypes and colorectal neoplasia

It now appears likely that the development of colonic adenomas and carcinomas involves a series of steps in which environmental or endogenous carcinogens induce or promote neoplasia through the accumulation of multiple, specific genetic mutations. Genetic predisposition to this process may take the form of inherited defects in control of cellular proliferation as in familial polyposis coli, or genetically determined polymorphism which affects enzyme activities relevant to the production or detoxication of carcinogens. Genetic effects may also influence levels of hormones and/or their target cell receptors which regulate the metabolic and proliferative activity of colonocytes. This review highlights data suggesting a role for polymorphism associated with xenobiotic acetylation, hydroxylation, and conjugation with glutathione in the metabolism of potential carcinogens, as well as for dehydroepiandrosterone in the metabolic control of cell proliferation. The study of genetically determined polymorphism in colorectal cancer may provide new insights into the epidemiology of cancer and result in new methods for the detection of higher risk groups.