HUMAN URINARY-EXCRETION OF SULFAMATE AND GLUCURONIDE CONJUGATES OF 2-AMINO-3,8-DIMETHYLIMIDAZO[4,5-F]QUINOXALINE (MELQX)

The contribution of Phase II conjugation reactions to human dispositio n of 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline (MelQx) was invest igated by analysis of urine for MelQx and its sulfamate and glucuronid e metabolites. Subjects consumed pan-fried fish, beef, or bacon and co llected 0-12 and 12-24-h postconsumption urine samples. MelQx content of the samples was determined both with and without acid treatment tha t quantitatively hydrolyzes the Phase II conjugates. The amount of unc onjugated MelQx in the urine of seven subjects ranged between 2 and 36 ng in the first 12-h sample and was undetectable in the second. Hydro lysis increased the MelQx content 3-13-fold in the urine of six subjec ts, while the urine of one subject showed no significant change. Uncon jugated MelQx excreted in urine was found to range between 0.5 and 4.7 % of the ingested dose. In acid-treated urine the amount of MelQx was found to range between 1 and 14% of the ingested dose. A method for is olating the acid-labile conjugates in urine was developed, which inclu ded the following steps: acetone/methanol precipitation; solid-phase e xtraction; ion exchange fractionation, normal phase aminopropyl fracti onation, and reverse phase high pressure liquid chromatography separat ion of the metabolites. Acidic hydrolysis of the fractions obtained in the last step, followed by gas chromatography-mass spectrometry analy sis of the MelQx produced, was used to confirm the presence of the sul famate and the glucuronide metabolites in human urine. The results pro vide evidence that glucuronidation and amine sulfamation are significa nt pathways of detoxification of MelQx in humans. In addition, the inc reased amount of MelQx released after acid hydrolysis facilitates the quantitative analysis of urinary MelQx.