Highly selective N-glucuronidation of four piperazine-containing drugs by UDP-glucuronosyltransferase 2B10

ABSTRACT

Background: N-glucuronidation is known to be an important metabolic pathway for detoxification and elimination of drugs containing aromatic amines. However, the metabolic pathways for piperazine-containing drugs are not fully established.

Methods: N-glucuronidation potential of four piperazine-containing drugs, namely two antihistamines (i.e. cyclizine and chlorcyclizine) and two tetracyclic antidepressants (i.e. mirtazapine and mianserin), was determined by using expressed UDP-glucuronosyltransferase (UGT) enzymes and liver microsomes from both human and animals.

Results: Among 13 expressed UGT enzymes, only UGT1A4 and UGT2B10 showed conjugating activities toward these four drugs. Reaction phenotyping, chemical inhibition, and activity correlation analysis revealed that UGT2B10 was a high-affinity enzyme and mainly responsible for hepatic N-glucuronidation of all drugs except mianserin. Both UGT1A4 and UGT2B10 were important contributors to mianserin N-glucuronidation. Moreover, significant species differences were observed in N-glucuronidation of all test drugs. In particular, liver microsomes from four experimental animals (i.e. mouse, rat, dog, and monkey) showed none or negligible activity in catalyzing N-glucuronidation of four drugs.

Conclusions: UGT2B10 plays a critical role in N-glucuronidation of piperazine-containing drugs. Also, conventional experimental animals might be inappropriate models for studying human N-glucuronidation.

Abbreviations: CL_int: intrinsic clearance; CL_max: maximal clearance; HLM: human liver microsomes; K_m: Michaelis–Menten constant; K_i: substrate inhibition constant; MS: mass spectroscopy; NNAL: 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol; QTOF: Quadrupole time-of-flight; S₅₀: the substrate concentration resulting in 50% of V_max; UDP-GlcA: uridine diphosphoglucuronic acid; UGT: UDP-glucuronosyltransferase; UPLC: ultra performance liquid chromatography; V_max: maximal velocity.

KEYWORDS:

• N-glucuronidation
• UGT2B10
• antihistamines
• tetracyclic antidepressants
• species differences

Additional information

Funding

This work was supported by the China Postdoctoral Science Foundation [grant number 2017M622835], [grant number 2018T110900]; the Medical Scientific Research Foundation of Guangdong Province, China [grant number A2016350]; the National Natural Science Foundation of China [grant number 81503341], [grant number 81573488], [grant number 81722049]; The PhD Start-up Fund of Natural Science Foundation of Guangdong Province [grant number 2015A030310339]; and the Program for Pearl River New Stars of Science and Technology in Guangzhou [grant number 201610010143].