Reproducibility over time of mephenytoin and debrisoquine hydroxylation phenotypes

Interethnic variation of CYP2C19 alleles, 'predicted' phenotypes and 'measured' metabolic phenotypes across world populations

The present study evaluates the worldwide frequency distribution of CYP2C19 alleles and CYP2C19 metabolic phenotypes ('predicted' from genotypes and 'measured' with a probe drug) among healthy volunteers from different ethnic groups and geographic regions, as well as the relationship between the 'predicted' and 'measured' CYP2C19 metabolic phenotypes. A total of 52 181 healthy volunteers were studied within 138 selected original research papers. CYP2C19*17 was 42- and 24-fold more frequent in Mediterranean-South Europeans and Middle Easterns than in East Asians (P<0.001, in both cases). Contrarily, CYP2C19*2 and CYP2C19*3 alleles were more frequent in East Asians (30.26% and 6.89%, respectively), and even a twofold higher frequency of these alleles was found in Native populations from Oceania (61.30% and 14.42%, respectively; P<0.001, in all cases), which may be a consequence of genetic drift process in the Pacific Islands. Regarding CYP2C19 metabolic phenotype, poor metabolizers (PMs) were more frequent among Asians than in Europeans, contrarily to the phenomenon reported for CYP2D6. A correlation has been found between the frequencies of CYP2C19 poor metabolism 'predicted' from CYP2C19 genotypes (gPMs) and the poor metabolic phenotype 'measured' with a probe drug (mPMs) when subjects are either classified by ethnicity (r=0.94, P<0.001) or geographic region (r=0.99, P=0.002). Nevertheless, further research is needed in African and Asian populations, which are under-represented, and additional CYP2C19 variants and the 'measured' phenotype should be studied.

Interethnic differences in drug metabolism: influence of genetic and environmental factors on debrisoquine hydroxylation phenotype

Genetic and environmental factors are determinants of the interindividual and interethnic variability in drug metabolism. The metabolism of several important drugs (e.g. haloperidol) cosegregates with that of debrisoquine. Thus, interethnic differences in debrisoquine hydroxylation polymorphism (CYP2D6) might be partly responsible for the variation in haloperidol disposition between races. The influence of tobacco, ethanol, caffeine, gender, and oral contraceptive use on the debrisoquine metabolic ratio (MR) has been analyzed in 633 Spanish healthy volunteers. MR was also determined in panels of healthy volunteers. 18 smokers were studied during a tobacco abstinence period, and 31 women three times during the same menstrual cycle. Among EMs, debrisoquine MR was significantly (P < 0.05) lower during smoking cessation (mean antilog +/- SD, 0.48 +/- 0.29) compared to a smoking period (0.61 +/- 0.23). During the lutheal phase of the menstrual cycle, debrisoquine MR was also significantly (P < 0.01) lower (0.33 +/- 0.41) compared to the ovulatory-phase (0.41 +/- 0.34) and the phase before ovulation (0.44 +/- 0.36). Among EMs, it is suggested that debrisoquine MR may be modified by tobacco smoking and sexual hormones. The clinical relevance of these findings remains unclear.

Comparison of popliteal lymph node responses in various strains of rats

Outbred (namely Wistar and Sprague-Dawley) and inbred (Wistar-Furth, Lewis, Fisher 344 and Brown-Norway) strains of rats were screened for their responses to reference compounds in the popliteal lymph node (PLN) assay. Streptozotocin and diphenylhydantoin gave positive responses as evidenced by increased weight and cellularity indices in all strains used whereas procainamide, isoniazid and barbital consistently gave negative responses. Although these findings overall are in agreement with previous investigations involving these compounds, the lack of marked interstrain differences in PLN responses argues against a strong immunogenetically controlled mechanism as could be assumed in presumably auto-immune reactions. The question is raised whether drug-induced side-effects predicted by the PLN assay are basically non-autoimmune as suggested by clinical and immunological findings in man.