Determination of acetylation genotypes using metabolites of caffeine and para aminobenzoic acid

• Main Author: Thompson, Linda K.
• Format: Others
• Published: DigitalCommons@Robert W. Woodruff Library, Atlanta University Center 1987
• Subjects: Biology
• Online Access: http://digitalcommons.auctr.edu/dissertations/1629; http://digitalcommons.auctr.edu/cgi/viewcontent.cgi?article=3047&context=dissertations

A large number of drugs and procedures are used to assess acetylator status in humans. However, these methods using test drugs such as isoniazid and sulfamethazine are relatively invasive. Recently, Grant and co-workers (Br. J. Clin. Pharmacol. 17: 459, 1984) developed a less-invasive method that uses caffeine as a test drug for determination of human acetylator phenotype. We sought to confirm the utility of this test using genetically defined inbred Syrian hamsters; homozygous rapid (RR) acetylator (Bio. 87.20), homozygous slow (rr) acetylator (Bio. 82.73/H) and heterozygous rapid (Rr) acetylator (Bio. 87.20 x Bio. 82:73/H Fl) progeny. Each animal was injected with 20 mg/kg of caffeine i.p. and urine was collected at 6 and 24 hours following diuretic (furosemide) priming. The urinary excretion ratio of two caffeine metabolites, 5-acetylamino-6-formylamino-3-methyluracil (AFMU) and 1-methylxanthine (IX) exhibited a trimodal distribution corresponding to acetylator genotype (rr, Rr, RR). Para-aminobenzoic acid (PABA) is a substrate which readily distinguishes the three acetylator acetylator genotypes in hamsters. Consequently, we monitored the PABA to acetyl-PABA ratios excreted in the same hamsters to aid in the verification of acetylator genotypes. Acetylator genotype as assigned by the PABA: acetyl-PABA ratio was completely concordant with acetylator genotype as assigned by the AFMU:1X ratio. Since recent evidence has suggested that cimetidine inhibits the microsomal metabolism of caffeine (Br. J. Clin. Pharmacol. 12: 155, 1981), we also investigated the actions of cimetidine on the caffeine test in the inbred hamster. A decrease in the AFMU:1X metabolic ratio was observed after pre-treatment with increasing concentrations of cimetidine. However, non-overlapping acetylator genotype dependent differences were still observed. These results support the validity of the caffeine test and suggest that the trimodal distribution of AFMl:lX reported in human population reflect acetylator genotype.