Detection of CYP2C9*5 in a white Brazilian subject

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates. In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry. The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Mapping genes that predict treatment outcome in admixed populations

There is great interest in characterizing the genetic architecture underlying drug response. For many drugs, gene-based dosing models explain a considerable amount of the overall variation in treatment outcome. As such, prescription drug labels are increasingly being modified to contain pharmacogenetic information. Genetic data must, however, be interpreted within the context of relevant clinical covariates. Even the most predictive models improve with the addition of data related to biogeographical ancestry. The current review explores analytical strategies that leverage population structure to more fully characterize genetic determinants of outcome in large clinical practice-based cohorts. The success of this approach will depend upon several key factors: (1) the availability of outcome data from groups of admixed individuals (that is, populations recombined over multiple generations), (2) a measurable difference in treatment outcome (that is, efficacy and toxicity end points), and (3) a measurable difference in allele frequency between the ancestral populations.

CYP2C9, CYP2C19 and CYP2D6 allele frequencies in the Ashkenazi Jewish population

OBJECTIVE

To determine and compare the cytochrome P450 (CYP)2C9, CYP2C19 and CYP2D6 allele and genotype frequencies in the Ashkenazi Jewish (AJ) population with other populations.

METHODS

CYP2C9, CYP2C19 and CYP2D6 genotypes were determined in 250 anonymous, unrelated, healthy AJ individuals from the greater New York (USA) metropolitan area. Genotyping was performed using the Tag-Ittrade mark Mutation Detection system and the recently redefined CYP2D6*41A allele was identified by a restriction fragment length polymorphism assay.

RESULTS

Among the 250 AJ individuals, the CYP2C9*1, *2, *3 and *5 allele frequencies were 0.772, 0.140, 0.086 and 0.002, respectively, and the genotypes were distributed into extensive- (60.8%), intermediate- (32.8%) and poor- (6.4%) metabolizer phenotypes. The CYP2C19*1, *2 and *4 allele frequencies were 0.830, 0.152 and 0.018, respectively, and the genotypes were distributed into extensive (69.2%), intermediate (27.6%) and poor (3.2%) metabolizers. The most common CYP2D6 alleles identified were *1, *2A, *4 and *41A, and their frequencies were 0.286 0.152 0.226 and 0.140, respectively. The CYP2D6 genotypes were distributed into ultrarapid- (8.8%), extensive- (70.0%), intermediate- (16.0%) and poor- (5.2%) metabolizer phenotypes.

CONCLUSION

Although the CYP2C9 allele and genotype frequencies in the AJ subjects were similar to those in other North American Caucasian populations, genotyping the CYP2C19*4 and CYP2D6*41A alleles in the AJ population resulted in the clinically relevant reclassification of the predicted metabolizer phenotypes. Inclusion of CYP2C19*4 reclassified individuals from either extensive- or intermediate- to the intermediate- or poor-metabolizer phenotypes, respectively. Inclusion of the redefined CYP2D6*41A allele increased the ultrarapid-, intermediate- and poor-metabolizer phenotype combined frequencies to 30%, indicating that approximately one in three AJ individuals may benefit from genotype-based drug selection and dosage. In addition, the ultrarapid CYP2D6 genotype frequency in the AJ population (8.8%) was approximately twofold higher than that in other North American Caucasians.

Impact of population admixture on the distribution of the CYP3A5*3 polymorphism

Objective: To compare the effectiveness of self-identified ethnic/color and marker-based biogeographical ancestry classifications in genotyping the CYP3A5*3 polymorphism in the Brazilian population. Methods: Individual DNA from 308 healthy Brazilians, self-identified as white, intermediate and black was genotyped for the CYP3A5*3 polymorphism and for a set of insertion–deletion polymorphisms, validated as ancestry informative markers (AIMs). The Structure software was used to analyze the AIMs data and to obtain estimates of the African component of ancestry (ACA). Nonlinear logistic regression modeling was developed to describe the association between the CYP3A5*3 polymorphism and the individual ACA values. Results: The CYP3A5*3 allele and genotype distribution differed significantly across the self-reported 'color’ groups (p < 0.0001, Fisher exact test), with a trend for decreasing frequency of both the CYP3A5*3 allele and the *3/*3 genotype from white to intermediate to black individuals (p < 0.0001, χ2 test for trend in proportions). When the population sample was proportioned in quartiles according to the individual ACA values, the frequency of the CYP3A5*3 allele and the *3/*3 genotype declined progressively from the lowest (<0.25 ACA) to the highest (>0.75 ACA) quartile. Nonlinear logistic regression showed that the odds of having the CYP3A5*3 allele decreases monotonically (p < 0.0001, Wald statistics) with the increase of the ACA, throughout the ACA range (0.15–0.93) observed in the overall population sample. Conclusion: Interethnic admixture is a source of cryptic population structure that may lead to spurious genotype–phenotype associations in pharmacogenetic/-genomic studies. Logistic regression modeling of CYP3A5*3 polymorphism shows that admixture must be dealt with as a continuous variable, rather than proportioned in arbitrary subcategories for the convenience of data quantification and analysis.

Fast RPLC-UV method on short sub-two microns particles packed column for the assay of tenoxicam in plasma samples

An extraction-less sample preparation technique followed by a RPLC-UV method on sub-two microns particles packed short column were used for the assay of tenoxicam in plasma samples. Protein precipitation was made by means of trichloroacetic acid addition. Supernatant was injected to the chromatographic column without any further pH adjustment. The mobile phase consisted in a mixture of acetonitrile and aqueous 0.1% phosphoric acid, at 2 mL/min flow rate and gradient elution. The Zorbax SB-C18 column (50 mm length, 4.6 mm internal diameter and 1.8 microm particle size) was thermostated at 60 degrees C. The mobile phase gradient composition program allowed separation of tenoxicam and piroxicam (internal standard), column clean-up and re-equilibration within 4 min. UV detection was achieved at 368+/-10 nm. The method is characterized by a low limit of quantitation of 25 ng/mL for tenoxicam, with a linearity interval up to 5500 ng/mL. The use of a low volume detection cell and detector high frequency data acquisition rate produced high precision and accuracy through a whole bioequivalence study of tenoxicam in two commercially available tablet formulations, after a single oral administration dose. Full method validation is presented. The high throughput characteristic of the proposed method allowed full validation and bioanalytical study completion within a 96 h period.