Use of caffeine metabolism for phenotyping human FMO activity and genotyping of FMO gene polymorphism

초록

It is known that the major form of flavin-containing monooxygenases (FMOs) present in adult huamn liver is FMO3. After finding that production of theophylline (TP) and theobromine (TB) from caffeine (CA) is catalyzed primarily by hepatic FMO (BBRC, 235:685-688), we have attempted to phenotype human with respect to their FMO activity in vivo by adminostering coffee(100mg CA). 1hr urine samples between 4 and 5hr were collected from 83 healthy Korean volunteers and their urinary CA metabolites were analyzed. The ratio of urinary(TB+TP)/(CA) was used as an indes of FMO activity. Upon identifying the volunteers with high and low FMO activities, we have sequenced their FMO3 genes in full (9 exons and junction sequences between introns and exons) from their genomic DNA obtained from peripheral blood. Comparing the wequences of FMO3 gene in subjects with high and low activities, we found 6 point mutation sites on exon sequences. In most subjects with low activity, we foung point mutations on Lys→Glu158(AAG→GAG) and/or Glu→Glu308(GAG→GGG) in exons 4 and 7, respectively, using the restriction enzymes Hinf I (for exon 4) and Dra II (for exon 7). A stop codon (Gly148→STOP; GGA→TGA) was found in a subject with extremely low FMO activity. Also heterozygotes with mutations on either one of the above two mutation sites showed low FMO activity. These subjects may have defective metabolism for many clinically used drugs and dietary plant alkaloids which are metabolized by FMO.