Phenotype-genotype analysis of CYP1A2 in Japanese patients receiving oral theophylline therapy.

OBJECTIVE

To clarify the association between the cytochrome P450 (CYP) 1A2 genotype with the CYP1A2 phenotype and to search for the CYP1A2*1K haplotype, which has been shown to decrease CYP1A2 inducibility and/or other functional polymorphisms in Japanese.

METHODS

Two polymorphisms, CYP1A21C and CYP1A21F, were genotyped in 126 patients receiving oral slow-release theophylline (TP) therapy and in 224 healthy volunteers. The CYP1A2 phenotype was assessed by the plasma [1-methyluric acid (1U)+3-methylxanthine (3X)]/TP ratio in the patients. The volunteers were given 150 mg caffeine, and the urine [1X+1U+5-acetylamino-6-amino-3-methyluracil (AAMU)]/17U ratio was used for CYP1A2 phenotyping. CYP1A2 intron 1 and six exons (exon 2-exon 7) were sequenced in the patients whose (1U+3X)/TP ratios were below the mean-2SD of those of all patients, and intron 1 was also sequenced in an additional 20 healthy volunteers exhibiting putative low CYP1A2 activities.

RESULTS

The individual (1U+3X)/TP ratios ranged from 0.007 to 0.21 (a 30-fold difference) in the patients, and the (1X+1U+AAMU)/17U ratios ranged from 1.6 to 112 (a 70-fold difference) in the healthy volunteers. The CYP1A2 activities were not significantly influenced by CYP1A21C or CYP1A21F. We found no functional polymorphisms by a sequencing analysis.

CONCLUSION

These results suggest that the CYP1A21C and CYP1A21F genotypes are not crucial factors for the variability of CYP1A2 activity and that the CYP1A2*1K haplotype is either nil or only shows a very low frequency in Japanese.