Objective: To evaluate the polygenic regulated caffeine metabolism in a group of 67 patients with a documented primary biliary cirrhosis (PBC) classified according to the histologic stage proposed by Scheuer.
Methods: Over a 14-year period, drug liver metabolism, using caffeine as a probe drug, has been systematically carried out in addition to the usual clinical, histological and biochemical investigations performed in patients with PBC. The "Caffeine test" consisted of a 200 mg caffeine oral intake. Urines were collected over 24 hours: caffeine (137X), 1-7-dimethylxanthine (17X), 1-3-dimethylxanthine (13X), 1-3-dimethylurate (13U), 3-7-dimethylxanthine (37X), 1-7-dimethylurate (17U), 1-methylxanthine (1X), 1-methylurate (1U), 7-methylxanthine (7X), 3-methylxanthine (3X), and 5-acetylamino-6-formylamino-3-methyluracyl (AFMU) were analyzed by high performance liquid chromatography (HPLC). Total and individual metabolite urinary elimination rates were expressed in micromol/24 hours. Enzyme activities were evaluated from the following urinary metabolite ratios: (AFMU+1U+1X)/17U for CYP1A2, 17U/17X for CYP2A6, AFMU/(AFMU+U+ 1X) for NAT-2, 1U/1X for XO.
Results: Compared to healthy subjects, patients with PBC presented a reduced metabolism of caffeine due to a decreased CYP1A2 activity, all the more important since the patients had an advanced histological stage. This picture was nearly identical to the observed picture in chronic liver diseases from various origins. PBC affected the various metabolic pathways of caffeine in a differential manner. CYP1A2 activity was decreased but XO and mainly CYP2A6 activities were increased as shown by the raised urinary ratio 17U/total metabolite elimination. In contrast to the described loss of bimodality of the NAT-2 index distribution in patients with alcoholic cirrhosis, we found a clear-cut, bimodal distribution in patients with PBC, without a high incidence of slow acetylator status.
Conclusion: Metabolism of caffeine is strongly and differentially disturbed in patients with PBC and apparently not exactly in the same way as that in alcoholic cirrhosis which is more often taken as an index of chronic liver disease. This suggests the need for caution with medicines whose metabolism is under polygenic regulation. Because of the relationships between caffeine metabolism modifications and histological stages, the caffeine test might be used along with the usual tests to safely follow-up the evolution of the disease.