N1-glucosides as urinary metabolites of sulphadimidine, sulphamerazine and sulphamethoxazole

Metabolic Profile of FYX-051 (4-(5-Pyridin-4-yl-1H-[1,2,4]triazol-3-yl)pyridine-2-carbonitrile) in the Rat, Dog, Monkey, and Human: Identification of N-Glucuronides and N-Glucosides

FYX-051, 4-(5-pyridin-4-yl-1H-[1,2,4]triazol-3-yl)pyridine-2-carbonitrile, is a novel xanthine oxidoreductase inhibitor that can be used for the treatment of gout and hyperuricemia. We examined the metabolism of FYX-051 in rats, dogs, monkeys, and human volunteers after the p.o. administration of this inhibitor. The main metabolites in urine were pyridine N-oxide in rats, triazole N-glucoside in dogs, and triazole N-glucuronide in monkeys and humans, respectively. Furthermore, N-glucuronidation and N-glucosidation were characterized by two types of conjugation: triazole N(1)- and N(2)-glucuronidation and N(1)- and N(2)-glucosidation, respectively. N(1)- and N(2)-glucuronidation was observed in each species, whereas N(1)- and N(2)-glucosidation was mainly observed in dogs. With regard to the position of conjugation, N(1)-conjugation was predominant; this resulted in a considerably higher amount of N(1)-conjugate in each species than N(2)-conjugate. The present results indicate that the conjugation reaction observed in FYX-051 metabolism is unique, i.e., N-glucuronidation and N-glucosidation occur at the same position of the triazole ring, resulting in the generation of four different conjugates in mammals. In addition, a urinary profile of FYX-051 metabolites in monkeys and humans was relatively similar; triazole N-glucuronides were mainly excreted in urine.

Uridine diphosphate sugar-selective conjugation of an aldose reductase inhibitor (AS-3201) by UDP-glucuronosyltransferase 2B subfamily in human liver microsomes

N-Glucosidation is known as a major metabolic reaction for barbiturates in humans. However, the enzyme(s) involved in this N-glucosidation has not been clarified yet. Thus, to clarify the enzyme(s) involved in the N-glucosidation in human liver microsomes, we investigated the N-glucosyltransferase activity in recombinant UDP-glucuronosyltransferases (UGTs) using AS-3201, an aldose reductase inhibitor, as a substrate. AS-3201 was found to be biotransformed to both N-glucoside and N-glucuronide in human liver microsomes. The N-glucosyltransferase activities were detectable with multiple UGT isoforms (UGT1A1, UGT1A3, UGT1A4, UGT2B4, UGT2B7, and UGT2B15). In contrast, the N-glucuronyltransferase activities for the same substrate were seen with UGT1A (UGT1A1, UGT1A3, UGT1A4, and UGT1A9) but not UGT2B isoforms. We then determined the relative activity factor of each recombinant UGT and estimated the contribution of each UGT isoform to the N-glucosidation in human liver microsomes. The results showed that UGT2B isoforms mainly contribute to AS-3201 N-glucosidation in human liver microsomes. In addition, the activity of AS-3201 N-glucosyltransferase significantly correlated with that of amobarbital N-glucosyltransferase in microsomes from sixteen human livers (r=0.964, P<0.01), indicating that UGT2B isoforms were also involved in the barbiturate N-glucosidation in humans. The findings of this study clearly show that UGT2B specifically utilizes UDP-glucose but not UDP-glucuronic acid as a sugar donor for the conjugation of AS-3201 in human liver microsomes.

HPLC analysis for amobarbital N-glycosides in urine

A study was undertaken to determine if humans excrete both amobarbital N-glucuronides and N-glucosides in urine after an oral dose of amobarbital. Amobarbital N-glucuronides were synthesized and characterized. A reverse phase LC method using post-column pH adjustment and UV detection at 240 nm was developed and used for the quantification of the amobarbital N-glucosides and N-glucuronides in human urine. Amobarbital was administered orally to seven male subjects and the total urine was collected for a period of 48-53 h after dosing. After filtration, the urine was injected directly onto the HPLC column to analyze for the presence of metabolites. The previously identified (5S)-amobarbital N-glucoside was detected in all seven subjects. The (5R)-amobarbital N-glucoside was detected at lower concentrations in only four of the subjects. At the levels at which amobarbital N-glucosides were detected, there was no evidence for the formation and excretion of the amobarbital N-glucuronides. Amobarbital N-glucuronidation is not a quantitatively significant pathway for the biodisposition of amobarbital in humans.

High-performance liquid chromatographic method for the routine determination of sulphadimidine, its hydroxy metabolites and N4-acetylsulphadimidine in body fluids and cell culture media

A simple high-performance liquid chromatographic method is presented for the determination of trace amounts of sulphadimidine (SDD), its hydroxylated metabolites and N4-acetyl-SDD in blood plasma, urine, hepatocyte culture media and microsomal incubations. The synthesis of 5-hydroxy-SDD and an improved method for the isolation of 4-methylhydroxy-SDD from urine are described and their respective specific absorption coefficients at 265 nm are calculated by on-line radiochemical and ultraviolet detection. The limit of detection of the analytical method is 0.05 micrograms/ml for SDD and its hydroxy metabolites and 0.2 micrograms/ml for N4-acetyl-SDD. Linear calibration graphs for SDD and its metabolites were constructed from 0.2 to 50 micrograms/ml. The method has been applied to biotransformation studies in vivo and in vitro.

Barbital N-glucoside is not detected as a urinary excretion product of barbital in humans

A study was undertaken to determine if humans excreted barbital N-glucoside as a urinary metabolite following oral administration of barbital. A liquid chromatography method using gradient elution was developed for detecting and quantifying barbital N-glucoside and barbital in urine. Following a single oral dose of barbital to male caucasian and oriental subjects that had previously been shown to excrete amobarbital and phenobarbital N-glucosides, no barbital N-glucoside conjugate was observed in the urine. This result indicates that N-glucosylation of barbiturates is not a general pathway for the biodisposition of barbiturates in man.

Pharmacokinetics, N1-glucuronidation and N4-acetylation of sulfadimethoxine in man

Sulfadimethoxine is metabolized by O-dealkylation, N4-acetylation and N1-glucuronidation. In man, only N1-glucuronidation and N4-acetylation takes place, leading to the final double conjugate N4-acetylsulfadimethoxine-N1-glucuronide. The N1-glucuronides are directly measured by high pressure liquid chromatography. When N4-acetylsulfadimethoxine is administered as parent drug, 30% of the dose is N1-glucuronidated and excreted. Fast acetylators show a shorter half-life for sulfadimethoxine than slow acetylators (27.8 +/- 4.2 h versus 36.3 +/- 5.4 h; P = 0.013), similarly the half-life of the N4-acetyl conjugate is also shorter in fast acetylators (41.3 +/- 5.2 h versus 53.5 +/- 8.5 h, P = 0.036). No measurable plasma concentrations of the N1-glucuronides from sulfadimethoxine are found in plasma. N1-glucuronidation results in a 75% decrease in protein binding of sulfadimethoxine. N4-acetylsulfadimethoxine and its N1-glucuronide showed the same high protein binding of 99%. Approximately 50-60% of the oral dose of sulfadimethoxine is excreted in the urine, leaving 40-50% for excretion into bile and faeces.

Drug glucosidation

A number of studies have shown that drug glucosidation occurs in vertebrates. This review summarizes information on the chemical, physical and biological properties of eleven drug glucosides. Three out of two hundred individuals exhibited a complete lack of amobarbital-N-glucoside formation. The data from a pair of identical twins who were deficient in this metabolic pathway suggested the presence of a recessive trait controlled by a single pair of autosomal genes which regulate N-glucoside formation. In addition, average values seemed to be subject to interethnic variation.