Acetylation and oxidation phenotypes in malignant lymphoma

N-acetyltransferase: the practical consequences of polymorphic activity in man

Over the years, numerous studies have supported the premise that individuals possessing the "slow acetylator" phenotype are more at risk from developing drug side-effects. Most prominent amongst these reports are those concerned with hepatotoxicity and peripheral neuropathy following treatment with isoniazid, lupus-like symptoms during procainamide therapy and experiencing hypersensitivity reactions to the various sulphonamide derivatives. Similarly, "slow acetylators" undergoing heavy exposure to arylamines and related carcinogens are more likely to develop bladder cancer. Contrariwise, there appears a slight risk of "rapid acetylators" developing pancreatic tumours.Other therapeutic agents for which polymorphic N-acetylation plays a minor role in their metabolism have been investigated but any impact of this metabolic difference on clinical efficacy or associated toxicity is still under question. In the search for clues as to the underlying aetiology, patient groups with many disease states have been examined for association with differences in N-acetylation and the majority have provided data that could be interpreted as equivocal. Studies have given contradictory, often opposing, results, calculated risk factors that are (perhaps) just significant but certainly not high, and patients within the cohorts who are always exceptions. Undoubtedly, other as yet unappreciated factors are at play.

Hair dye use, genetic variation in N-acetyltransferase 1 (NAT1) and 2 (NAT2), and risk of non-Hodgkin lymphoma

BACKGROUND

Several previous studies have found non-Hodgkin lymphoma (NHL) risk to be associated with hair dye use, particularly use of permanent, dark colors and use before 1980, when hair dye formulations changed.

METHODS

We examined NHL risk in relation to reported hair dye use among 1,321 cases and 1,057 controls from a US population-based multi-center study. DNA was extracted from blood or buccal cells to identify genetic variation in N-acetyltransferase 1 (NAT1) and 2 (NAT2), which encode enzymes that metabolize aromatic amine compounds found in hair dyes.

RESULTS

Among women, 509 cases and 413 controls reported hair dye use [odds ratio (OR) = 1.2; 95% confidence interval (95% CI) = 0.9, 1.6]. Risk estimates were higher for use before 1980 than for use in 1980 or later, particularly for use of permanent, intense tone (black, dark brown, dark blonde) products (<1980-OR = 1.6; 95% CI 0.9, 2.7; >or=1980-OR = 0.6; 95% CI 0.4, 1.1). Risk estimates were increased for women who used permanent, intense tone products before 1980 if they had the rapid/intermediate NAT2 phenotype (OR = 3.3; 95% CI 1.3, 8.6) or the NAT1 10 allele (OR = 2.5; 95% CI 0.9, 7.6), but not if they were slow NAT2 acetylators (OR = 1.5; 95% CI 0.6, 3.6) or had no copies of the NAT1 10 allele (OR = 1.5; 95% CI 0.7, 3.3). NHL risk was not increased among women who began hair dye use after 1980 or among men.

CONCLUSION

Our results support previous research demonstrating elevated NHL risk among women who used dark color or intense tone permanent hair dyes before 1980. We present the first evidence suggesting that this risk may differ by genetic variation in NAT1 and NAT2.

Bioinformatics Research on Inter-racial Difference in Drug Metabolism I. Analysis on Frequencies of Mutant Alleles and Poor Metabolizers on CYP2D6 and CYP2C19

The enzyme activities of CYP2D6 and CYP2C19 show a genetic polymorphism, and the frequency of poor metabolizers (PMs) on these enzymes depends on races. In the present study, the frequencies of mutant alleles and PMs in each race were analyzed based on information from published studies, considering the genetic polymorphisms of CYP2D6 and CYP2C19 as the causal factors of racial and inter-individual differences in pharmacokinetics. As a result, it was shown that there were racial differences in the frequencies of each mutant allele and PMs. The frequencies of PMs on CYP2D6 are 1.9% of Asians and 7.7% of Caucasians, and those of PMs on CYP2C19 are 15.8% of Asians and 2.2% of Caucasians. Based on the results, it was suggested that there would be racial differences in the frequencies of PM subjects whose blood concentrations might be higher for drugs metabolized by these enzymes. Additionally, it was suggested that enzyme activities would vary according to the number of functional alleles even in subjects judged to be extensive metabolizers (EMs). In the bridging study, genetic information regarding CYP2D6 and CYP2C19 of the subjects will help extrapolate foreign clinical data to a domestic population.

Cancer risk related to genetic polymorphisms in carcinogen metabolism and DNA repair

Chemical carcinogenesis involves metabolism in the body of the carcinogen to the ultimate carcinogen and its interaction with DNA. There is considerable interindividual variation in the metabolic ability to activate as well as detoxify the carcinogens and in the ability to repair the carcinogen-DNA adducts. In many cases such differences occur as genetic polymorphisms and form the basis for variation in susceptibility to carcinogens and thereby to cancer risk. The activation mechanism is particularly related to the cytochromes P-450 (CYPs), and four of these are known to activate carcinogens: CYP1A1, CYP1A2, CYP2E1, and CYP3A4. Increased cancer risk has been related to polymorphisms in the CYPs and other activating enzymes. The DNA repair mechanisms show considerable complexity, and deficient repair mechanisms in certain human disorders are clearly related to increased cancer risk. Yet, there is no unambiguous epidemiological evidence available for cancer risk among individuals in general. In vivo methods have to be refined and developed for use in epidemiological studies.

The Role of Pharmacogenetics in Cancer Chemotherapy and the Development of Malignancy

The role of pharmacogenetics in the area of cancer chemotherapy and the development of malignancy has not been well defined. Only four chemotherapeutic agents have been evaluated for toxicity or clinical response based on genetic differences in metabolism. These include 5-fluorouracil, 6-mercaptopurine, amonafide, and cyclophosphamide. Severe toxicity of 5-fluorouracil and amonafide due to individual differences in drug metabolism has been reported in the literature. Tumor response in leukemic children may be associated with genetic differences in metabolism of 6-mercaptorpurine. The development of malignancy may be secondary to an individual's ability to detoxify carcinogens found in the environment. For example, the incidence of bladder cancer appears higher in subjects who have occupational exposure to aromatic amines and the slow acetylator phenotype. Some evidence also exists that smokers who are very extensive metabolizers of debrisoquin may be more prone to developing lung cancer. Strong evidence for an association between other cancer types and pharmacogenetics requires more study.

Drug oxidation and N-acetylation in rats pretreated with subtoxic doses of streptolysin O

SLO in sublytic doses (100 HU/kg body wt) depressed the hepatic microsomal cytochrome P450 and aminopyrine-N-demethylase but increased significantly the cytosolic N-acetyltransferase after acute and subacute (5 days) pretreatment of male Wistar rats. Aniline hydroxylase was reduced after acute and unchanged after subacute pretreatment. The effects of SLO on the oxidative enzymes and drug N-acetylation might have been caused by the membranal and immunological properties of the toxin.

Oxidative polymorphism of debrisoquine is not related to human colo-rectal cancer

The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio greater than 12.6, were classified as poor metabolisers of DBQ (n.s.). No difference was found in the distribution of the frequencies of the MR of DBQ between patients and controls. It is concluded that polymorphic oxidation of DBQ is not related to the risk of developing colo-rectal cancer in human beings.

Acetylator genotype and arylamine-induced carcinogenesis

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