NDLI: Comparison of CYP2D6 Content and Metoprolol Oxidation Between Microsomes Isolated from Human Livers and Small Intestines

Content Provider	Springer Nature Link
Author	Madani, Soraya Paine, Mary F. Lewis, Lydia Thummel, Kenneth E. Shen, Danny D.
Copyright Year	1999
Abstract	Purpose. To assess the role of intestinal CYP2D6 in oral first-pass drug clearance by comparing the enzyme content and catalytic activity of a prototype CYP2D6 substrate, metoprolol, between microsomes prepared from human intestinal mucosa and from human livers. Methods. Microsomes were prepared from a panel of 31 human livers and 19 human intestinal jejunal mucosa. Microsomes were also obtained from the jejunum, duodenum and ileum of four other human intestines to assess regional distribution of intestinal CYP2D6. CYP2D6 content (pmole/mg microsomal protein) was determined by Western blot. CYP2D6 activity was measured by α-hydroxylation and O-demethylation of metoprolol. Results. Kinetic studies with microsomes from select livers (n = 6) and jejunal mucosa (n = 5) yielded K$_{M}$ estimates of 26 ± 9 μM and 44 ± 17 μM, respectively. The mean V$_{max}$ (per mg protein) for total formation of α-OH-M and ODM was 14-fold higher for the liver microsomes compared to the jejunal microsomes. Comparisons across intestinal regions showed that CYP2D6 protein content and catalytic activity were in the order of jejunum > duodenum > ileum. Excluding the poor metabolizer genotype donors, CYP2D6 content varied 13-and 100-fold across the panels of human livers (n = 31) and jejunal mucosa (n = 19), respectively. Metoprolol α-hydroxylation activity and CYP2D6 content were highly correlated in the liver microsomes (r = 0.84, p < 0.001) and jejunal microsomes (r = 0.75, p < 0.05). Using the well-stirred model, the mean microsomal intrinsic clearance (i.e., V$_{max}$/K$_{M}$) for the livers and jejunum were scaled to predict their respective in vivo organ intrinsic clearance and first-pass extraction ratio. Hepatic and intestinal first-pass extractions of metoprolol were predicted to be 48% and 0.85%, respectively. Conclusions. A much lower abundance and activity of CYP2D6 are present in human intestinal mucosa than in human liver. Intestinal mucosal metabolism contributes minimally to the first-pass effect of orally administered CYP2D6 substrates, unless they have exceptionally high microsomal intrinsic clearances and/or long residence time in the intestinal epithelium.
Starting Page	1199
Ending Page	1205
Page Count	7
File Format	PDF
ISSN	07248741
Journal	Pharmaceutical Research
Volume Number	16
Issue Number	8
e-ISSN	1573904X
Language	English
Publisher	Kluwer Academic Publishers-Plenum Publishers
Publisher Date	1999-01-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Pharmacology/Toxicology Pharmacy Biochemistry Medical Law Biomedical Engineering
Content Type	Text
Resource Type	Article
Subject	Organic Chemistry Pharmacology Molecular Medicine Pharmacology (medical) Biotechnology Pharmaceutical Science

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