Analysis of lorazepam and its 30-glucuronide in human urine by capillary electrophoresis: evidence for the formation of two distinct diastereoisomeric glucuronides

Baldacci, Andrea; Thormann, Wolfgang (2006). Analysis of lorazepam and its 30-glucuronide in human urine by capillary electrophoresis: evidence for the formation of two distinct diastereoisomeric glucuronides. Journal of separation science, 29(1), pp. 153-63. Weinheim: Wiley-VCH 10.1002/jssc.200500268

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Lorazepam (LOR) is a 3-hydroxy-1,4-benzodiazepine that is chiral and undergoes enantiomerization at room temperature. In humans, about 75% of the administered dose of LOR is excreted in the urine as its 30-glucuronide. CE-MS with negative ESI was used to confirm the presence of LOR-30-glucuronide in urines that stemmed from a healthy individual who ingested 1 or 2 mg LOR, whereas free LOR could be detected in extracts prepared from enzymatically hydrolyzed urines. As the 30-glucuronidation reaction occurs at the chiral center of the molecule, two diastereoisomers can theoretically be formed, molecules that can no longer interconvert. The stereoselective formation of LOR glucuronides in humans and in vitro was investigated. MEKC analysis of extracts of the nonhydrolyzed urines suggested the presence of the two different LOR glucuronides in the urine. The formation of the same two diastereoisomers was also observed in vitro employing incubations of LOR with human liver microsomes in the presence of uridine 5'-diphospho-glucuronic acid as coenzyme. The absence of other coenzymes excluded the formation of phase I or other phase II metabolites of LOR. Both results revealed a stereoselectivity, one diastereoisomer being formed in a higher amount than the other. After enzymatic hydrolysis using beta-glucuronidase, these peaks could not be detected any more. Instead, LOR was monitored. Analysis of the extracts prepared from enzymatically hydrolyzed urines by MEKC in the presence of 2-hydroxypropyl-beta-CD revealed the enantiomerization process of LOR (observation of two peaks of equal magnitude connected with a plateau zone). The data presented provide for the first time the evidence of the stereoselectivity of the LOR glucuronidation in humans.

Item Type:

Journal Article (Original Article)

Division/Institute:

04 Faculty of Medicine > Service Sector > Institute of Clinical Pharmacology and Visceral Research (discontinued)

UniBE Contributor:

Thormann, Wolfgang

ISSN:

1615-9306

ISBN:

16485721

Publisher:

Wiley-VCH

Language:

English

Submitter:

Factscience Import

Date Deposited:

04 Oct 2013 14:45

Last Modified:

06 Dec 2013 13:41

Publisher DOI:

10.1002/jssc.200500268

PubMed ID:

16485721

Web of Science ID:

000235291100018

URI:

https://boris.unibe.ch/id/eprint/18576 (FactScience: 768)

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