Disease and acetylation polymorphism

Isoniazid acetylation phenotypes in the Sudanese population; findings and implications

Background

Isoniazid (INH) is the mainstay antimicrobial in the treatment of tuberculosis (TB). It is acetlylated in the liver to acetyl-INH. However, there is variation in rate of acetylation of INH among TB patients (i.e. fast, intermediate or slow acetylators) which impacts on the treatment outcomes.

Aim

The isoniazid acetylation phenotypes in the expatriate Sudanese population were determined to provide future guidance since TB is prevalent in Sudan.

Methods

A community-based trial among Sudanese expatriates in Saudi Arabia was undertaken to identify INH-acetylation phenotypes. After overnight fasting, a single dose of 200 mg of INH was given to the volunteers. Three hours later, 5 ml of blood were drawn from each volunteer and prepared for High-Performance Liquid Chromatography (HPLC) analysis. The main outcomes were INH and Acetyl-INH concentrations in plasma and the subsequent Acetyl-INH/INH metabolic ratio (MR).

Results

The findings suggest that slow acetylation is highly prevalent among the study participants (n = 43; 84.31%). Moreover, there was no statistically significant correlation between age and the MR (r = −0.18, P = 0.20). Further, there was no significant association between gender and the MR (P = 0.124). Similarly, no significant association was found between smoking habits and MR (P = 0.24).

Conclusion

Isoniazid phenotyping suggests predominantly slow acetylation among the Sudanese in this sample. The study found no statistically significant associations between the MR and age or gender or smoking.

BIOTRANSFORMATION OF HYDRAZINE DERVATIVES IN THE MECHANISM OF TOXICITY

Hydrazine derivatives are environmental and food pollutants but are also important because of their use in medicine for the treatment of tuberculosis and cancer. However, hydrazines also pose significant health risks to humans as they are mutagenic and carcinogenic. This review examines various metabolic pathways (enzymatic and non-enzymatic) of hydrazines for the formation of reactive species that bind to cellular macromolecules and lead to cellular dysfunction. It is believed that this biotransformation is responsible for the pharmacology and pathophysiology of hydrazine derivatives.

Implications of gender differences for human health risk assessment and toxicology

This paper from The Human Health working group of SGOMSEC 16 examines a broad range of issues on gender effects in toxicology. Gender differences in toxicology begin at the gamete and embryo stage, continuing through development and maturation and into old age. Sex influences exposure, toxicokinetics, and toxicodynamics. The effects of sex have often been overlooked in both epidemiology and toxicology. In addition to the obvious modifying effects of the sex hormones and conditions affecting the male and female reproductive organs and sex roles, both genetic and hormonal effects influence many aspects of life and toxic responses. All aspects of toxicology should consider gender-balanced designs so that a more comprehensive understanding of differences and similarities can be obtained. Differential gene expression is a new frontier in toxicology. Risk assessment should account for gender and life cycle differences. The biological basis for altered sex ratios observed in several populations should be sought in animal models, and expanded to other compounds that might exert sex-selective effects. Wherever possible and feasible, toxicologic and environmental epidemiological studies should be designed and have sufficient statistical power to quantify differential gender-based exposures and outcomes.

Isoniazid acetylation phenotyping in Saudi Arabs

AIMS

The present study is designed to investigate the acetylator status in Saudi Arabs.

METHODS

Isoniazid (INH) acetylation phenotyping was studied in 136 Saudi Arabs in Riyadh, Saudi Arabia, using a single plasma sample taken 3 h post-INH oral dose of 200 mg. Metabolic ratio (MR) of plasma acetyl-INH (Ac-INH) to INH was used to determine the acetylation phenotype.

RESULTS

The MR had a bimodal distribution with an antimode of 1.0. The frequency distribution of slow acetylators (MR < 1.0) was 94.9% (n = 129). Using Hardy-Weinberg Law, the gene frequency (q) of the recessive allele determining slow acetylator phenotype was found to be 0.97.

CONCLUSION

INH phenotyping suggests a high frequency of slow acetylators among Saudi Arabs. There was no association between the MR of plasma Ac-INH/INH and age or gender.

A review and assessment of potential sources of ethnic differences in drug responsiveness

The International Conference on Harmonization (ICH) E5 guidelines were developed to provide a general framework for evaluating the potential impact of ethnic factors on the acceptability of foreign clinical data, with the underlying objective to facilitate global drug development and registration. It is well recognized that all drugs exhibit significant inter-subject variability in pharmacokinetics and pharmacologic response and that such differences vary considerably among individual drugs and depend on a variety of factors. One such potential factor involves ethnicity. The objective of the present work was to perform an extensive review of the world literature on ethnic differences in drug disposition and responsiveness to determine their general significance in relation to drug development and registration. A few examples of suspected ethnic differences in pharmacokinetics or pharmacodynamics were identified. The available literature, however, was found to be heterologous, including a variety of study designs and research methodologies, and most of the publications were on drugs that were approved a long time ago.

Pharmacogenomics: the future of drug therapy

Pharmacogenomics aims to optimize patient management by customizing and synthesizing drugs based on genetic variations in drug response. Polymorphisms affecting metabolism, receptors, and absorption can influence drug sensitivity, toxicity, and dosing. The Human Genome Project, DNA chips, and bioinformatics advance the practice of this field by, respectively, identifying polymorphisms related to drug response, determining an individual's profile of polymorphisms, and integrating data to facilitate clinical decision making. Potential benefits of pharmacogenomics include increasing efficacy and preventing adverse drug reactions, thus improving patient care and decreasing costs. These factors imply that a thorough understanding of the principles and applications of pharmacogenomics will be an indispensable part of the future of drug therapy in clinical medicine.

Pharmacogenomics in cardiovascular diseases

Considerable heterogeneity exists in the way individuals respond to medications, in terms of both efficacy and safety. Inherited differences in the absorption, metabolism, excretion, and target for drug therapy have important effects on drug efficacy and safety. Pharmacogenomics aims to discover new therapeutic targets and understand genetic polymorphisms that determine the safety and efficacy of medications. The goal of pharmaco-genomics is customization of drug therapy with administration of a medication in an optimum dose that will be safe and effective with reduction in morbidity and mortality.

Pharmacogenomics: a clinician's primer on emerging technologies for improved patient care

Pharmacogenomics is a term recently coined to embody the concept of individualized and rational drug selection based on the genotype of a particular patient. Customization of drug therapy offers the potential for optimal safety and efficacy in an individual patient. Such a process contrasts current prescribing practices, which use medications shown to be safe and effective in patient populations or based on anecdotal experiences. Within patient populations, medications vary in their efficacy among individual patients. More importantly, a medication that is safe and effective in one patient may be ineffective or even harmful in another. Underlying many of these phenotypic differences are genotypic variants (polymorphisms) of key enzymes and proteins that affect the safety and efficacy of a drug in an individual patient. An understanding of these polymorphisms has the potential to enhance patient care by allowing physicians to customize the selection of medication to meet individual patient needs. Pharmacogenomics may also lead to improved compliance and shorter time to optimal disease management, thereby reducing morbidity and mortality. Significant cost savings could result from reductions in polypharmacy as well as from fewer physician encounters and hospitalizations for exacerbations of underlying illness and because of adverse drug reactions.

Quantitation of three-month intraindividual variability and influence of sex and menstrual cycle phase on CYP1A2, N-acetyltransferase-2, and xanthine oxidase activity determined with caffeine phenotyping

OBJECTIVE

To evaluate intraindividual variability and the effects of sex and menstrual cycle phase on the activity of cytochrome P450 1A2 (CYP1A2), N-acetyltransferase 2 (NAT2), and xanthine oxidase.

METHODS

Ten white men were given 2 mg/kg caffeine orally every 14 days for 3 months. The same dosage of caffeine was given to 10 premenopausal white women during the midfollicular and midluteal phases of three complete menstrual cycles. Phenotype was determined with urinary caffeine metabolite ratios.

RESULTS

For CYP1A2, mean metabolic ratio (+/- SD) was 5.97 +/- 2.78 during the midfollicular phase and 5.32 +/- 1.99 during the midluteal phase (p = 0.2). For extensive and poor metabolizer of NAT2. Mean midfollicular phase metabolite ratios were 0.71 +/- 0.060 and 0.37 +/- 0.030, and mean midluteal phase metabolite ratios were 0.69 +/- 0.076 and 0.39 +/- 0.053 (p = 0.9). For xanthine oxidase, mean midfollicular phase metabolite ratio was 0.63 +/- 0.06 and mean midluteal phase metabolite ratio was 0.63 +/- 0.05 (p = 0.3). Among the men, mean CYP1A2, NAT2 rapid and slow acetylator, and xanthine oxidase indices were 9.42 +/- 10.18, 0.66 +/- 0.021, 0.31 +/- 0.056, and 0.64 +/- 0.03. There were no differences in metabolite ratios between men and women for CYP1A2, NAT2 extensive metabolizers, or xanthine oxidase. A statistically significant sex difference was found for poor metabolizers of NAT2 (p < 0.05). Median coefficients of variation for CYP1A2, NAT2 extensive and poor metabolizers, and xanthine oxidase ratios were 16.8% (range, 4.5% to 49.3%), 2.9% (range, 2.2% to 4.7%), 13.4% (range, 7.5% to 27.2%), and 4.5% (range, 2.3% to 13.0%).

CONCLUSION

Stratification by menstrual cycle phase or sex need not be performed for pharmacokinetic or clinical investigations of substrates for CYP1A2, NAT2, or xanthine oxidase in which the subject are adults.

Drug acetylation in liver disease

N-Acetylation is a phase II conjugation reaction mediated in humans by the polymorphic N-acetyltransferase 2 (NAT2) and N-acetyltransferase 1 (NAT1). Acetylation of some drugs may be modestly decreased in patients with chronic liver disease, whereas acute liver injury has no effect on drug acetylation. For NAT2 substrates, the impairment in acetylation capacity seems to be phenotype-specific, with a more prominent effect being exerted in rapid than slow acetylators. Thus, in the presence of significant hepatic dysfunction, the activity of NAT2 may not exhibit its usual bimodal distribution, and hence phenotypic assignment may not be reliable. Furthermore, it remains to be evaluated whether the precautions advised for slow acetylators when treated with drugs metabolised by NAT2 apply to all patients (regardless of phenotype) with liver cirrhosis.

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.

N-acetyltransferase 2 polymorphism in patients infected with human immunodeficiency virus

OBJECTIVES

To evaluate the prevalence of slow acetylation of hepatic N-acetyltransferase 2 (NAT2) in patients with different stages of human immunodeficiency virus (HIV) infection, to assess the relationship between acetylation capacity and the degree of immunosuppression, and to study the concordance between NAT2 phenotype and genotype.

METHODS

This prospective study in a consecutive sample of HIV-infected patients was performed in the outpatient department of a university hospital that provides primary and tertiary care. The NAT2 genotype was assessed by polymerase chain reaction and restriction fragment length polymorphism, the NAT2 phenotype was determined by caffeine test (urinary metabolic ratio of the caffeine metabolites 5-acetylamino-6-formylamino-3-methyluracil and 1-methylxanthine).

RESULTS

Fifty patients with Centers for Disease Control HIV infection stages A (10 patients), B (20 patients), and C (20 patients) were included in the study after each gave informed consent. According to genotyping and phenotyping, 32 (64%) patients were slow acetylators, with a concordance of the two methods of 96%. The overall distribution was similar to distributions reported in other white populations. The slow acetylator phenotype was found in seven, 16, and nine patients with stage A, B, and C, respectively. Eight of the 10 patients with previous adverse reactions to sulfonamides had slow acetylator phenotypes. Acetylation capacity was independent of CD4 cell counts.

CONCLUSIONS

This study revealed an excellent agreement between genotypes and phenotypes of NAT2 in patients with HIV infection. There was no increase in prevalence of slow acetylation in patients with advanced stages of the disease. This apparent discrepancy to an earlier study may be the result of differences in co-medication of the patients studied and may point to the relevance of drug interactions in the treatment of patients with HIV infection.

Polymorphic acetylation: lack of influence of rheumatic disease activity and concomitant drug administration

Acetylation polymorphisms have been linked with a tendency to develop rheumatic diseases. We investigated the effect of changes in the disease activity of patients with rheumatoid arthritis (RA) during disease-modifying antirheumatic drug (DMARD) treatment, and on the capacity of these patients to acetylate the sulphonamide sulphadimidine. Fifty-four patients with RA treated with gold, sulphasalazine or D-penicillamine, 12 patients with AS and 16 patients with non-inflammatory arthritis (NI) were investigated over a 24-week period. The capacity of these individuals to acetylate sulphadimidine was determined at baseline and after 12 and 24 weeks. Although there was a tendency for sulphadimidine acetylation to increase in patients with RA from a median of 84.5% [interquartile range (IQR) 77.0-95.0%] at baseline to 90.5% (IQR 77.5-96.0%) at week 24, this failed to reach statistical significance. In contrast, the trend in patients with AS or NI was towards a decrease in acetylation. There was no correlation between changes in disease activity and sulphadimidine acetylation during DMARD intervention.

Racial variation in the O-acetylation phenotype of human colonic mucosa

O-acetylated and non-O-acetylated sialoglycoproteins can be distinguished by the mPAS (mild periodic acid-Schiff) histochemical technique. Individual adults show one of three different patterns of staining of large intestinal mucosa: uniformly mPAS-positive, uniformly mPAS-negative, or mPAS-negative with scattered mPAS-positive crypts. To test our hypothesis that these variations are the result of a single autosomal gene (oat) polymorphism, we have studied the frequency of the three patterns of staining in a total of 435 adult colon specimens from six geographically separate populations: British, South African blacks, Icelanders, Japanese, Hong Kong Chinese, and Bahrainis. The distribution of the three types of staining fell into two groups. In Japanese and Chinese, uniformly mPAS-positive cases were much more frequent than uniformly mPAS-negative cases; this distribution differed significantly (chi 2, P < 0.001) from that in non-Sino-Japanese, where the uniformly mPAS-positive phenotype was much less frequently found than the uniformly mPAS-negative phenotype. In neither of the groups did the frequency of the three phenotypes differ significantly from that predicted for a single gene polymorphism by the Hardy-Weinberg law. The variation in staining patterns between populations is consistent with variation in frequency of a single polymorphic autosomal gene (oat) controlling O-acetylation of sialic acid, probably by an O-acetyl transferase enzyme. Loss of function mutation in the high acetylator gene (oata) in a colonic crypt stem cell in heterozygous individuals would account for the scattered discordant crypts. Gene frequencies for a variety of enzymes differ between the Sino-Japanese and non-Sino-Japanese races.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative activation of proguanil and dapsone acetylation in Thai soldiers

The prevalence of putative poor metaboliser (PM) phenotypes of proguanil oxidation in Caucasian populations is 3-10%. The PM frequency in Oriental populations is unknown. In this study the plasma metabolic ratios of proguanil and dapsone to their principal metabolites cycloguanil and monoacetyldapsone were determined in Thai soldiers receiving antifolate drug combinations for malaria prophylaxis. The distribution ratio of proguanil to cycloguanil (PROG/CYC) was highly skewed with no evidence of bimodality. Assuming subjects with a PROG/CYC ratio greater than 10 are PMs from studies in Caucasians, the incidence of PMs in the soldiers would be 18% (30 of 170). The mean PROG/CYC ratio for PMs in the Thai soldiers was 31.2 +/- 28.9 (n = 30) compared with 25.5 +/- 2.5 (n = 3) in a study of Caucasians. The corresponding values for putative EMs were 5.4 +/- 2.1 (n = 140) and 2.4 +/- 0.2 (n = 134). Similar to other Oriental populations, Thais were found to be predominantly (76%, 173 of 228) rapid acetylators of dapsone.

HLA and disease

Many human diseases are associated with HLA class I, class II and class III antigens. It appears that the class III antigen disease associations can be explained by a direct defect operating at the level of either the class III gene or its gene product. The mechanism underlying class I and class II antigen disease associations is at present unknown. In this review we have considered thirty diseases which have been ranked according to their relative risk as defined by the frequency of a given HLA antigen in patient and control populations. The chronic inflammatory disorder, ankylosing spondylitis and its association with HLA B27 has been used as a model to study the HLA linked diseases. We have suggested that the disease may be caused by the Gram-negative microorganism Klebsiella which has antigenic similarity to HLA B27. It is proposed that some antibodies made against Klebsiella bind to HLA B27, thereby acting as autoantibodies leading to the pathological sequelae of chronic inflammatory arthritis. This is the crosstolerance hypothesis or molecular mimicry model and it has been compared to the receptor model. It is further suggested that the crosstolerance hypothesis can be utilised as a general theory to explain the association of other diseases with the class I and class II antigens, and offer a possible explanation for the polymorphism of HLA.

Genetic polymorphisms of drug metabolism

The molecular mechanisms of 3 genetic polymorphisms of drug metabolism have been studied at the level of enzyme activity, enzyme protein and RNA/DNA. As regards debrisoquine/sparteine polymorphism, cytochrome P-450IID6 was absent in livers of poor metabolizers; aberrant splicing of premRNA of P-450IID6 may be responsible for this. Moreover, 3 mutant alleles of the P-450IID6 locus on chromosome 22 associated with the poor metabolizer phenotype were identified by Southern analysis of leucocyte DNA. The presence of 2 identified mutant alleles allowed the prediction of the phenotype in approximately 25% of poor metabolizers. The additional gene-inactivating mutations which are operative in the remainder of poor metabolizers are now being studied. Regarding mephenytoin polymorphism, although the deficient reaction, S-mephenytoin 4'-hydroxylation, has been well defined in human liver microsomes, the mechanism of this polymorphism remains unclear. All antibodies prepared to date against cytochrome P-450 fractions with this activity recognize several structurally similar enzymes and several cDNAs related to these enzymes have been isolated and expressed in heterologous systems. However, which isozyme is affected by this polymorphism is not known. As regards N-acetylation polymorphism, N-acetyltransferases have been purified from human liver, specific antibodies prepared; it was observed that immunoreactive N-acetyltransferase is decreased or undetectable in liver of "slow acetylators". Two genes that encode functional N-acetyltransferase were characterized. The product of one of these genes has identical activity and characteristics as the polymorphic liver enzyme. Cloned DNA from rapid and slow acetylator individuals has been analyzed to identify the structural or regulatory defect that causes deficient N-acetyltransferase.

N-acetylation in healthy and diseased children

Acetylation capacity was examined in three groups of Czech children by measuring the plasma and urine concentrations of sulphamethazine and its acetylated metabolite 6 h after an oral test dose of 20 mg/kg sulphamethazine. Amongst 82 healthy children aged 4-15 y there were 32 (39%) fast acetylators; there was no significant difference between the number of boys and girls, or between children over or less than 6 years of age. In 41 patients aged 3-15 y with phenylketonuria, the acetylation indices showed a significantly higher proportion of fast acetylators - 24 (58.5%) using plasma measurements and 29 (70.7%) using urine data. In them the ratio between slow and fast acetylators was inverted compared to normal children. The preponderance of fast acetylators was greater in boys than in girls and in children over 6 years of age. An increased acetylation capacity in patients with phenylketonuria was apparent even in individuals classified as slow acetylators, because in them the plasma concentration of the acetylated metabolite was higher than in control acetylators. Amongst 48 young patients (5-15 y) with insulin-dependent diabetes there were 19 (39.6%) fast and 29 (60.4%) slow acetylators, which corresponded well to the phenotype distribution in control children. This did not support the suggested association between the fast acetylator phenotype and Type I diabetes.

N-acetylation phenotyping with sulphadimidine in a Turkish population

The distribution of acetylator phenotypes was studied in 244 unrelated Turkish subjects. Sulphadimidine and its acetylated metabolite were measured in 6 h plasma and 0-6 h urine samples after an oral dose of 10 mg/kg. Subjects with 37.5% or less acetylsulphadimidine in plasma were regarded as slow acetylators and the others as rapid acetylators. The mean plasma concentration of acetylsulphadimidine was about 2.5-times lower in slow acetylators. Urinary excretion of total sulphadimidine (free + acetylated) was also significantly lower in slow acetylators compared to rapid acetylators. The frequency of slow acetylators was 60.7% in the population (95% confidence interval 54.3% to 66.8%). Sulphadimidine acetylation showed no variation due to sex, age, body weight or pre-existing disease.

Genetically determined N-acetylation and oxidation capacities in Japanese patients with non-occupational urinary bladder cancer

Genetically determined polymorphisms of N-acetylation and oxidative capacity have been studied using dapsone and metoprolol in 51 Japanese patients with spontaneous bladder cancer and 203 healthy control subjects. The results for N-acetylation pharmacogenetics were against the initial expectation that there would be a preponderance of slow acetylators in the cancer group, as 3 such patients (5.9%) were found as compared to 13 (6.4%) in the healthy group. There was no poor metabolizer (PM) of metoprolol in the cancer group, whereas in the healthy group one (0.5%) was a PM. There were no significant differences between the groups in the frequency of slow acetylator and poor oxidiser phenotypes, or in the frequency distribution profiles of acetylation (monoacetyldapsone/dapsone) and oxidative metabolic ratio (log metoprolol/alpha-hydroxymetoprolol). The results indicate that neither N-acetylation nor the debrisoquine/sparteine-type oxidative phenotype and/or capacity represent a genetic predisposition to spontaneous bladder carcinogenesis in Japanese patients. In the normal Japanese population there is a great predominance of rapid acetylators and extensive oxidisers.

Complement system protein C4 and susceptibility to hydralazine-induced systemic lupus erythematosus

21 patients with systemic lupus erythematosus induced by long-term treatment with hydralazine were investigated to see whether susceptibility to this syndrome was associated with deficiency of the classical pathway complement protein, C4. 16 of 21 (76%) patients had one or more C4 null (ie, non-productive) alleles compared with 35 of 82 normal subjects (43%). This difference was significant. The HLA-DR4 antigen, known to be in linkage disequilibrium with the C4B null allele, was also significantly more frequent in the patients (14 of 21 patients compared with 31 of 81 normal subjects). Susceptibility to hydralazine-induced lupus, as in idiopathic systemic lupus erythematosus, may depend partly upon genetically determined C4 levels.

Racial differences in drug response. Altered sensitivity to and clearance of propranolol in men of Chinese descent as compared with American whites

To determine whether the pharmacokinetics and pharmacodynamics of beta-blockade differ among racial groups, we gave 10 men of Chinese descent and 10 American white men 10, 20, 40, and 80 mg of propranolol every eight hours; the dosages were given in random order, and each dose was given for one day. The degree of beta-blockade was measured as the reduction in the heart rate and blood pressure in the supine and upright positions and during treadmill exercise testing. The Chinese subjects had at least a twofold greater sensitivity to the beta-blocking effects of propranolol than the white subjects, as indicated by the mean (+/- SEM) plasma concentrations producing a 20 percent reduction in the heart rate in both the supine position (197 +/- 31 vs. 536 +/- 58 nmol per liter; P less than 0.05) and the upright position (131 +/- 27 vs. 343 +/- 39 nmol per liter; P less than 0.05) and after exercise testing (96 +/- 12 vs. 185 +/- 23 nmol per liter; P less than 0.05). In addition, the Chinese subjects had much greater sensitivity to the hypotensive effects of propranolol, as shown by the concentrations that reduced blood pressure by 10 percent in the supine position (73 +/- 5 vs. 748 +/- 7 nmol per liter; P less than 0.01) and in the upright position (89 +/- 5 vs. 401 +/- 6 nmol per liter; P less than 0.01). No difference in beta-receptor density or affinity of lymphocytes was found between the groups. The Chinese group had a 45 percent higher free fraction of propranolol in plasma, which may have contributed to the increased drug effect but cannot explain it entirely. This group metabolized propranolol more rapidly than the white group, which resulted in a 76 percent higher clearance of an oral dose (3740 +/- 737 vs. 2125 +/- 214 ml per minute; P less than 0.05) because of increased metabolism through multiple metabolic pathways. We conclude that Chinese men have greater sensitivity than white men to the effects of propranolol on heart rate and blood pressure. Decreased protein binding may be responsible in part, but most of the effect remains to be explained.

Acetylator phenotype and congenital malformations

The hypothesis has been tested that an unusual maternal acetylator phenotype can predispose to congenital malformations in the fetus. The acetylator phenotype of normal caucasian control women and of mothers of malformed children was established by measuring urinary sulphadimidine and its acetylated metabolite. A further control group was the fathers of the malformed newborn. The malformations studied were facial-cleft, spina-bifida and congenital heart disease. The acetylator phenotype was shown not be modified by pregnancy. 49 of 100 (49%) control women were rapid acetylators. Amongst the 108 mothers of malformed babies, 56 (52.8%) were slow acetylators and 52 (47.2%) were fast acetylators, 42 out of 83 (50.5%) of the fathers of malformed were slow acetylators and 41 (49.5%) were fast acetylators. Thus, the acetylator phenotype of the mothers of malformed children is no different from the acetylator phenotype of controls.

Acetylator polymorphism in Parkinson's disease

Acetylator phenotype has been determined using sulphamethazine in 100 patients with Parkinson's disease and in 93 age-matched normal control subjects. Sixty-nine patients and 54 control subjects were classified as slow acetylators (NS). No relation was found among acetylator polymorphism and age at onset or clinical stage of disease. Amongst slow acetylators, the percentage of acetylated sulphamethazine in plasma was significantly lower in patients than in controls. Despite this finding, the results do not support any relationship between acetylator polymorphism and the risk of developing Parkinson's disease.

N-acetylation polymorphism of dapsone in a Japanese population

1. The N-acetylation of dapsone (DDS) was studied in 182 unrelated healthy Japanese subjects. The frequency of slow acetylators determined using the plasma monoacetyldapsone (MADDS) to DDS ratio (MADDS/DDS, slow acetylators less than 0.30 and rapid acetylators greater than 0.35) at 3 h after an oral dose of DDS (100 mg) was 6.6% (12 of the 182 subjects) with a 95% confidence interval of 3.8 to 11.2%. 2. The frequency distribution histogram of the plasma MADDS/DDS ratio showed an apparent trimodal pattern. However, the numbers of heterozygous (n = 105) and homozygous rapid acetylators (n = 65) derived from the observed data did not agree with those predicted for the respective rapid acetylators (n = 70, and n = 100) by applying the Hardy-Weinberg Law, when the suggested antimode of 0.85 discriminating these two rapid acetylators was employed. 3. The incidence of slow acetylators was unexpectedly lower in the males (1.4%, 1 of the 69 subjects, with a 95% confidence interval of 0.2 to 7.7%) compared with the incidence in the females (9.7%, 11 of the 113 subjects, with a 95% confidence interval of 5.5 to 16.6%). The difference reached a marginally significant level (Fisher's exact probability test, P = 0.02). 4. The mean plasma concentration of MADDS was significantly (P less than 0.001) lower in the slow compared to the rapid acetylators and there was a highly significant correlation (rs = 0.757, P less than 0.001) between plasma MADDS levels and MADDS/DDS ratios. 5. Slow acetylators showed a significantly (P less than 0.001) lower urinary MADDS/DDS ratio and excreted less (P less than 0.001) MADDS than rapid acetylators.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotoxicity of antituberculous drugs in a patient without active tuberculosis

A 56-year old patient presented 3 months after initiation of an antituberculous regimen with Isoniacid (INH, 5 mg/kg daily), Ethambutol (20 mg/kg daily) and Rifampicin (675 mg daily) a mild sensory polyneuropathy and a bilateral retrobulbar neuritis which progressed to a severe optic atrophy. Multiple hyperintense foci were detected with NMR-imaging in the cerebral white matter suggestive of demyelination. INH and Ethambutol are known for their neurotoxic effects but suggestion was made that neurologic signs may not be due to drug neurotoxicity but could be induced by immunological processes initiated by the tubercle bacillus. In the reported patient the suspected tuberculosis of the urogenital tract was never proved histologically. Most likely his neurological symptoms were therefore cause by the administration of INH and Ethambutol. Patients with a low serum zinc level and a slow acetylation of INH are reported to be at special risk; both factors were present in our patient.

N-acetylation phenotyping with dapsone in a mainland Chinese population

1 The N-acetylation of dapsone (DDS) was studied in 108 unrelated Chinese subjects residing in the mainland of China. 2 The frequency of slow acetylators determined using the plasma monoacetyldapsone to DDS ratio (MADDS/DDS, slow acetylators less than 0.30 and rapid acetylators greater than 0.35) at 3 h after an oral dose of DDS (100 mg) was 13.0% (14 of the 108 subjects) with a 95% confidence interval of 7.9 to 20.6%. 3 The mean plasma concentration of MADDS was about three times lower in the slow than in the rapid acetylators and there was a highly significant correlation (rs = 0.886, P less than 0.001) between plasma MADDS concentration and acetylation ratio. 4 Urinary acetylation ratios (MADDS/DDS) and cumulative urinary excretion of MADDS were significantly (P less than 0.001) lower in slow acetylators compared with rapid acetylators. In addition, there was a significant relationship (rs = 0.510 to 0.718, P less than 0.001) between plasma and urinary acetylation ratios. However, the distribution of the urinary acetylation ratio was not bimodal. 5 The urinary acetylation ratio after an oral dose of DDS is not a discriminative index for determining acetylation phenotype.

Variability in drug metabolism: importance of genetic constitution

In man wide variability exists in the rate of metabolism of drugs and among factors which contribute to this phenomenon genetic constitution is of major importance. The metabolism of a number of drugs is subject to polymorphism and the frequency distribution of particular pharmacokinetic parameters shows bimodality, with poor (PM) and extensive metabolizers (EM). Acetylation of a number of drugs is known to be polymorphic and the incidence of poor metabolizers varies markedly among different populations. Debrisoquine and sparteine are frequently applied model substrates for the characterization of a polymorphism in oxidative metabolism. Polymorphic drug oxidation may have important clinical implications, because when standard dosage regimens are applied plasma concentrations will reach far above the maximum acceptable in poor metabolizers and consequently side effects may arise. Regarding the multiplicity of the drug oxidizing enzyme system (cytochrome P-450) it could be of interest to combine model substrates in a cocktail to be able to characterize human subjects simultaneously for a number of independent polymorphisms.

The polymorphic metabolism of dextromethorphan

The ability of healthy male volunteers to metabolize a 30-mg oral dose of dextromethorphan (DM) was studied in 252 Americans. Two blood samples were collected at four and 24 hours after administration of the dose. The resulting plasma was analyzed for unchanged DM. The volunteers were classified as slow, intermediate, or fast metabolizers on the basis of plasma concentrations of DM. Further differentiation of slow and intermediate metabolizers was achieved by comparing the two-point estimates of elimination-rate constants. In the population studied, 84.3% were fast DM metabolizers, 6.8% were intermediate metabolizers, and 8.8% were slow metabolizers. Previous reports have related the slow DM metabolizers to slow debrisoquin metabolizers, but no such correlations have been achieved with intermediate DM metabolizers. These intermediate DM metabolizers may suggest a new polymorphism not related to debrisoquin or may suggest that "debrisoquin gene" regulation is more complex than originally suggested.

Acetylator phenotypes in rheumatoid arthritis patients with or without adverse drug reactions to sodium-aurothiomalate or d-penicillamine

The acetylator phenotype was determined in 59 patients with classical, seropositive and erosive rheumatoid arthritis (RA) treated with sodium-aurothiomalate or d-penicillamine. Patients with adverse drug reactions (ADR) leading to drug withdrawal (n = 29) were compared with a group of patients without ADR (n = 30). The frequency of slow acetylators was significantly (p less than 0.05) increased in all RA patients, irrespective of the presence of ADR, particularly in the male patients, compared with a control population. No association was found between acetylator phenotype and clinical data or secondary Sjögrens's syndrome (SS).

The effect of glucose on acetylation status

Forty-nine healthy volunteers (47 male, 2 female) had their sulphadimidine acetylator status determined on a control day and on a second occasion when they were given an oral glucose load. They were classified as fast and slow acetylators using the standard urine method and as fast, slow and intermediate acetylators using calculated metabolic and total body clearances. Twenty-seven (55%) were slow acetylators and this proportion was not altered by glucose loading either with or before sulphadimidine ingestion. On the control day, five (10%) were fast and 17 (35%) were intermediate acetylators but these sub-groups were not clearly distinguishable from each other when glucose was given. The glucose load did not cause any individual to change from slow to fast categories. Two type 2 (insulin independent) diabetics also showed no difference in acetylator status when studied with widely different blood glucose concentrations. We conclude that glucose can induce minor increases in sulphadimidine clearance but is unlikely to alter phenotypic acetylation status. Previous observations of an increased incidence of fast acetylators in diabetics may therefore indicate a genetic marker.

The effects of a new phthalazine derivative (MDL 899) on human lymphocyte functions

MDL-899 is new phthalazine derivative which has been developed as a substitute for hydralazine, which has several undesirable effects, in the treatment of hypertension. The effects of MDL-899 on human lymphocyte functions are analyzed. This drug inhibited in a dose-related fashion the blastogenesis of lymphocytes upon PHA and Con A activation and down-regulated the activation of allogeneic mixed lymphocyte reactions (MLR). On the contrary the drug enhanced the activation of autologous MLR of non T/T type. This effect was five times higher on cells which carried the HLA DR 4 phenotype. The above reported observations suggest that MDL-899, as well as hydralazine, affects the in vitro responsiveness of human lymphocytes mostly in subjects with HLA-DR 4 phenotype. Whether the impact of MDL-899 on immune function gives rise to a lupus like syndrome is not known. For this reason further studies are warranted to assess its long-term in vivo effects.

Genetically determined variability in acetylation and oxidation. Therapeutic implications

The clinical significance of two separate genetic polymorphisms which alter drug metabolism, acetylation and oxidation is discussed, and methods of phenotyping for both acetylator and polymorphic oxidation status are reviewed. Particular reference is made to the dapsone method, which provides a simple means of distinguishing fast and slow - and possibly intermediate - acetylators, and to the sparteine method which allows a clear separation of oxidation phenotypes. Although acetylation polymorphism has been known for some time, definite indications for phenotyping are few. It is doubtful whether acetylator phenotype makes a significant difference to the outcome in most isoniazid treatment regimens, and peripheral neuropathy from isoniazid in slow acetylators is easily overcome by pyridoxine administration. However, in comparison with rapid acetylators, slow acetylators receiving isoniazid have an increased susceptibility to phenytoin toxicity, and perhaps also to carbamazepine toxicity. It is also possible that rapid acetylators receiving isoniazid attain higher serum fluoride concentrations from enflurane and similar anaesthetics than do similarly treated slow acetylators. Thus, when drug interactions of these types are suspected, phenotyping for acetylator status may be advisable. If routine monitoring of serum procainamide and N-acetylprocainamide concentrations is practised, phenotyping of subjects prior to therapy with these agents should not be necessary. Although acetylator phenotype influences serum concentrations of hydralazine, when this drug is given in combination with other drugs acetylator phenotype has not been shown to influence the therapeutic response. Slow acetylator phenotype along with female gender and the presence of HLA-DR antigens appear to be risk factors in the development of hydralazine-induced systemic lupus erythematosus (SLE). Determination of acetylator phenotype may therefore help determine susceptibility to this adverse reaction. In the case of sulphasalazine, adult slow acetylators require a lower daily dose of the drug than fast acetylators in order to maintain ulcerative colitis in remission without significant side effects. It is therefore advisable to determine acetylator phenotype prior to sulphasalazine therapy. Work on the association of acetylation polymorphism with various disease states is also reviewed. It is possible that a higher incidence of bladder cancer is associated with slow acetylation phenotype - especially in individuals exposed to high levels of arylamines. The question as to whether idiopathic SLE is more common in slow acetylators remains unresolved. There appears to be no difference between fa

Liquid chromatographic analysis of sulfaquinoxaline and its application to pharmacokinetic studies in rabbits

A specific, sensitive high-performance liquid chromatographic method is described for sulfaquinoxaline (I) and its major metabolite, the N4-acetyl metabolite (II), in biological fluids. Detection limits for I and II were 0.25 and 0.50 micrograms/mL in plasma and 0.10 and 0.20 micrograms/mL in urine, respectively. The pharmacokinetics of sulfaquinoxaline and its metabolite were studied in New Zealand White rabbits after individual doses of 50 mg/kg of sulfaquinoxaline and its metabolite were administered intravenously. Mean (+/- SD) plasma half-lives were 12.7 (8.0) h for sulfaquinoxaline and 15.4 (3.5) h for the metabolite. After administration of the N-acetyl metabolite sulfaquinoxaline appeared in the plasma and urine indicating that deacetylation had occurred. The repercussions of this observation are briefly discussed with respect to two rabbits in which plasma analyses and complete urine collections were made. As sulfaquinoxaline is administered prophylactically to rabbits by some breeders, it is recommended that investigators allow a washout period of about one week after receipt of the animals.

A rapid method for determination of acetylation phenotype using dapsone

A rapid, simple one-stage protein precipitation method for the estimation of plasma dapsone (DDS) and monoacetyldapsone (MADDS) concentration by high-pressure liquid chromatography (h.p.l.c.) is described. Its performance in the assignment of acetylator phenotype was compared with a reference h.p.l.c. method utilising an extraction procedure and internal standard. The rapid h.p.l.c. technique combined with measurement of the plasma MADDS/DDS ratio is, in our opinion, the method of choice for the determination of the acetylator phenotype in population studies.

Aromatic amines and the pathogenesis of lupus erythematosus

The acetylation pathway of drug metabolism is the pathway by which aromatic amines and hydrazines are metabolized. Hydralazine and procainamide are aromatic amines or hydrazines that are metabolized by this pathway. Persons who are genetically slow acetylators are predisposed to development of lupus from these two drugs, suggesting that the free amine or hydrazine moiety is the inciting agent. When acetylprocainamide was given as an antiarrhythmic drug to patients with procainamide-induced lupus, the disease went into remission, indicating that the free amine group on procainamide had induced the disease. The genetic acetylator phenotypes of persons with idiopathic lupus were studied, and an excess of genetic slow acetylators was observed. This suggests amines or hydrazines induce some cases of this disease. One patient was identified with a lupus-like illness due to occupational exposure to hydrazine itself.