Caffeine phenotyping of cytochrome P4501A2, N-acetyltransferase, and xanthine oxidase in patients with familial adenomatous polyposis.

Patients with familial adenomatous polyposis (FAP) and age and sex matched controls were tested for cytochrome P4501A2 (CYP1A2), N-acetyltransferase, and xanthine oxidase activities using caffeine urinary metabolites as a discriminator. FAP patients showed significant underactivity of N-acetyltransferase (which inactivates some carcinogens) and significant overactivity of CYP1A2 (which activates some carcinogens). Xanthine oxidase activity, which can generate free radicals and cause cellular damage, was significantly increased in the FAP patients. All but one of the FAP patients had undergone colectomy. A separate group of six patients was therefore assessed before and at an average time of eight weeks after colectomy. No effect on enzyme activity was seen. The differences in enzyme activities detected in this study could produce an excess of active carcinogenic metabolites in the bile of FAP patients and contribute to the high risk for intestinal cancer in FAP.