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Genetic polymorphisms of CYP3A4: CYP3A418 allele is found in five healthy Malaysian subjects

https://doi.org/10.1016/j.cca.2007.05.004Get rights and content

Abstract

Background

Cytochrome P450 3A4 (CYP3A4) is the major cytochrome involved in metabolizing of > 60% of all drugs used in humans. A number of allelic variations in CYP3A4 gene are known to affect catalytic activity including CYP3A44, CYP3A45 and CYP3A418. We investigated the frequencies of CYP3A44, CYP3A45 and CYP3A418 alleles in a Malaysian population. This will impact treatment of patients receiving drugs metabolized by these alleles.

Methods

The study was conducted in 121 healthy Malaysian volunteers. DNA was extracted from leucocytes and the 3 alleles were determined by PCR–RFLP. The PCR product was later digested with restriction enzymes BstMA I, BshV I and Hpa II.

Results

No mutations were detected for CYP3A44 and CYP3A45 alleles. The frequency of the CYP3A418 allele in the Malaysian population is 2.1%. All 5 subjects with CYP3A418 mutations were found to be heterozygous.

Conclusion

The present study describes polymorphisms of CYP3A4 among Malaysian subjects. Clinical relevance of these genetic variants in these healthy volunteers is under investigation.

Introduction

Interindividual variation in drug metabolism is caused by many factors including environmental factors, concurrent drug therapy as well as genetic factors. Much of this variation, however, has shown to be caused by genetic polymorphisms of the human cytochrome P450 enzymes (CYP) [1]. CYP is the most important enzymatic system involved in drug metabolism. It is also involved in the metabolisms of a large number of certain endogenous compounds such as steroids, prostaglandins, thromboxanes, fatty acid derivatives and retinoic acid derivatives [2]. Approximately 65% of current drugs used are metabolized by CYP enzymes and half of them are mediated by the CYP3A subfamily [3]. The CYP3A subfamily consists of 4 members: CYP3A4, CYP3A5, CYP3A7 and CYP3A47 [4]. The CYP3A subfamily represents about 30% of the total CYP in the human liver [5].

CYP3A4 is involved in the metabolism of > 60% of all drugs used in humans [6], [7]. It is found in the human livers and intestines [8]. It plays important roles in the metabolism of a wide variety of drugs such as antidiabetics, antiarrhythmics, antihistamines and synthetic estrogens [9]. Variant CYP3A4 alleles in the population may contribute to interindividual variability in CYP3A4 activity. Detecting genetic polymorphisms may therefore help to predict an individual's ability to respond to certain drugs. Among Asian subjects, a number of allelic variations in CYP3A4 gene are known to affect catalytic activity including CYP3A44, CYP3A45 and CYP3A418 [10], [11], [12], [13], [14].

The CYP3A44 allele has A13989G change leading to Ile118Val substitution in exon 5 [10]. The CYP3A45 variant allele has a C to G point mutation in exon 7 causing amino acid change where Pro is substituted with Arg at site 218 [10]. CYP3A418 is a variant allele in exon 10 involving T to C transition that changes Leu to Pro at site 293 [11]. Table 1 summarizes the sequences and effect of mutations in these variant alleles. These polymorphisms may have important clinical implications in individuals for carrying these variants. This will also impact treatment of patients receiving drugs metabolized by these alleles. Dai et al. [12] for example indicated that CYP3A418 showed significantly a higher turnover number for both testosterone and insecticide chlorpyrifos in vitro.

To date, allelic frequencies and genotypes of CYP3A44, CYP3A45 and CYP3A418 have been reported among the Chinese [10], [11], [12], Korean [13], Japanese [14] and Caucasian [12] populations but none has been reported for the Malaysian population, so far. Therefore, the aim of this study is to investigate the allelic distribution of these three alleles in the Malaysian population by using a polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) method.

Section snippets

Subjects

One hundred and twenty-one healthy volunteers were recruited, consisting of 61 men and 60 women. These were students and staff of Universiti Sains Malaysia, Health Campus, Kelantan, Malaysia. Subjects were informed about the experimental procedures and study aim before giving written informed consents. They were ascertained to be healthy from the medical history, physical examination and routine laboratory tests. All subjects ageing between 18 and 50 years with a normal body mass index (BMI)

Results and discussions

In all reactions, correct lengths of expected PCR products were obtained. In the PCR–RFLP analyses, the restriction enzymes used in the present study was found to have worked successfully as depicted in Fig. 1, Fig. 3. The restriction enzyme used for CYP3A45 genotyping (BshV I) was further confirmed to be correct by digestion of λ DNA for 1 h at 37 °C (result not shown). PCR–RFLP is one of the most reliable methods used for recognition of genetic mutations. The method is based on a specific

Acknowledgements

This study was financially supported by Universiti Sains Malaysia short-term grant (grant no. 304/PPSP/6131450). The author was supported by Universiti Sains Malaysia Academic Staff Training Scheme. We would like to thank Dr. Imran Ahmad (Department of Family Medicine) for his cooperation in collecting the blood samples.

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