Catalysis of the cysteine conjugation and protein binding of acetaminophen by microsomes from a human lymphoblast line transfected with the cDNAs of various forms of human cytochrome P450

Title

Catalysis of the cysteine conjugation and protein binding of acetaminophen by microsomes from a human lymphoblast line transfected with the cDNAs of various forms of human cytochrome P450

Creator

Zhou L X; Erickson R R; Hardwick J P; Park S S; Wrighton S A; Holtzman J L

Publisher

Journal of Pharmacology and Experimental Therapeutics

Date

1997
1997-05

Description

We have previously found that for acetaminophen kinetic differences exist between the hepatic microsomal catalyzed protein binding and cysteine conjugation. We have also observed that the protein binding of acetaminophen is only to intralumenal proteins. Together these data suggested that two pools of the reactive metabolite, N-acetyl-p-benzoquinone imine (NABQI), are formed during the oxidative metabolism of acetaminophen: one on the cytosolic surface and the other within the lumen of the microsomes. This would indicate that some of forms of cytochrome P450 (CYP) catalyzing NABQI formation have their active site on the cytosolic surface and others on the lumenal surface. We have examined this question by comparing the rates of cysteine conjugation and protein binding of acetaminophen by microsomes from lymphoblasts tranfected with the cDNAs for human CYPs. We found that CYP2D6 catalyzed only cysteine conjugation; CYP1A2 and 3A4 catalyzed only protein binding; CYP2E1 catalyzed both; and CYP1A1, CYP2A6 and CYP2B6 catalyzed neither. These data suggest that CYP2D6 has its active site only on the cytosolic surface; CYP1A2 and CYP3A4 only on the lumenal surface; and CYP2E1 has catalytic sites on both the lumenal and cytosolic surfaces of the membrane. In mouse studies we have found that ethanol administration increased acetaminophen protein binding by 265% but cysteine conjugation by only 61%. CYP2E1 and CYP2B increased, whereas CYP3A decreased and the others did not change. These data suggest that in control mice CYP2E1 catalyzes the bulk of protein binding, whereas CYP2D catalyzes slightly more cysteine conjugation than does CYP2E1.

Subject

activation; ethanol; hepatic microsomes; hepatocytes; inhibitors; monoclonal-antibodies; oxidation; para-benzoquinone imine; Pharmacology & Pharmacy; rat-liver; reactive metabolite formation

Identifier

n/a

Format

Journal Article

URL Address

n/a

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Rights

Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).

Pages

785-790

Issue

2

Volume

281

Citation

Zhou L X; Erickson R R; Hardwick J P; Park S S; Wrighton S A; Holtzman J L, “Catalysis of the cysteine conjugation and protein binding of acetaminophen by microsomes from a human lymphoblast line transfected with the cDNAs of various forms of human cytochrome P450,” NEOMED Bibliography Database, accessed November 27, 2021, https://neomed.omeka.net/items/show/8382.

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