Kristina Pechandova

Aim: CYP2C8 represents 7% of the hepatic cytochrome system and metabolizes around 5% of drugs in phase I processes. It also plays a significant role in metabolism of endogenous compounds. More than 20 single-nucleotide polymorphisms (SNPs) have been noted, mainly in exons 3, 5, and 8. The most studied SNPs may lead to decreased enzyme activity and may have impact on drug metabolism. Variant alleles are called CYP2C8*2 (I269F), CYP2C8*3 (R139K, K399R), and CYP2C8*4 (I264M). Our aim was to investigate the frequency of major functional SNPs among the Czech population. Material and methods: DNA was isolated from whole blood of 161 healthy, young, and unrelated subjects (94 men and 67 women, aged from 23 to 28 years). The genotypes of polymorphic positions CYP2C8*2 , CYP2C8*3 (G416A, A1196G), and CYP2C8*4 were determined by polymerase chain reaction-restriction fragment length polymorphism. Results and conclusion: Observed allele frequencies were 10.9%, 5.9%, and 0.3% for the alleles CYP2C8*3 , CYP2C8*4 , and CYP2C8*2 , respectively. Both CYP2C8*3 (G416A, A1196G) alleles have been found in complete linkage disequilibrium. The allele distribution complies well with Hardy-Weinberg equilibrium. Allele frequencies of functionally important CYP2C8 variants in the Czech population are similar to that of other Caucasian populations.

Polymorphisms in drug metabolizing enzymes are considered as a major factor influencing the incidence of adverse drug reactions or failure of pharmacotherapy. Our aim was to compare the distribution of functional polymorphisms in the genes CYP2D6 and CYP2C19 between healthy control group and of patients reffered to our department due to adverse drug reactions or insufficient efficacy of a treatment. The group of patients comprised of 60 subjects, 218 healthy unrelated subjects were included in the cotrol group. In both groups genotypes of CYP2D6 and CYP2C19 were analyzed. There were significantly fewer extensive metabolizers of CYP2D6 in the patient group comparison with healthy control subjects (25.0% vs. 49.8%) while the proportion of intermediate metabolizers was significantly higher than in helthy population (58.3% vs. 38.5%). We also observed more poor metabolizers than in control group (13.3% vs. 6.8%), but the difference did not reach level of statistical significance probably due to low number of subjects. The distribution of either ultrarapid metabolizers of CYP2D6 or deficient alleles of CYP2C19 was similar in both groups. Clinically apparent alteration of drug effects are often caused by partial or complete deficit of CYP2D6 activity. Our results confirm the importance of CYP2D6 polymorphisms on the efficycy and safety of pharmacotherapy.

There exists a marked inter-individual variability of P-glycoprotein expression and activity, which can be of clinical importance due to the large number of drugs that are substrates for the transporter. Previously identified polymorphisms in the MDR1 gene belong to important factors causing this phenomenon. Our aim was to investigate the frequency of major functional SNPs of the MDR1 gene coding for P-glycoprotein in the Czech population. DNA was isolated from whole blood of 189 healthy, young and unrelated subjects (99 females and 90 males, aged from 23 to 28 years). The genotypes of polymorphic positions C3435T, G2677T/A, C1236T and T-76A were determined by PCR-RFLP. Observed allelic frequencies were 56.5%, 46.0%, 0.53%, 44.5% and 37.6% for the alleles 3435T, 2677T, 2677A, 1236T and -76A, respectively. We have found 64 subjects homozygous for 3435T, 42 for 2677T, 40 for 1236T and 31 for -76A alleles. The allelic distribution complies well with Hardy-Weinberg equilibrium. Allelic frequencies of functionally important MDR1 variants are in the Czech population similar to that of other Caucasian populations.

The majority of human P450 dependent drug metabolism is carried out by polymorphic enzymes which can alter plasma concentration of the pharmacological active substance followed by an enhanced or suppressed pharmacological effect. The response of individual patients to drugs can be affected by variations in DNA sequence mainly by single nucleotide polymorphisms (SNPs). Knowledge of functionally important SNPs prior to the drug administrations may assist in the development of individualized pharmacotherapy avoiding unexpected drug responses, such as harmful adverse drug reactions or treatment failures. This review discusses both the basic characteristics of the major polymorphic cytochrome P450 enzymes and examines the pharmacogenetic methods employed to estimate metabolic status. We will focus mainly on the basic principles of genotyping assays involving molecular biology tools.