Knockout of cytochrome P450 3A yields new mouse models for understanding xenobiotic metabolism

Abstract

Cytochrome P450 3A (CYP3A) enzymes constitute an important detoxification system that contributes to primary metabolism of more than half of all prescribed medications. To investigate the physiological and pharmacological roles of CYP3A, we generated Cyp3a-knockout (Cyp3a -/-) mice lacking all functional Cyp3a genes. Cyp3a -/-mice were viable, fertile, and without marked physiological abnormalities. However, these mice exhibited severely impaired detoxification capacity when exposed to the chemotherapeutic agent docetaxel, displaying higher exposure levels in response to both oral and intravenous administration. These mice also demonstrated increased sensitivity to docetaxel toxicity, suggesting a primary role for Cyp3a in xenobiotic detoxification. To determine the relative importance of intestinal versus hepatic Cyp3a in first-pass metabolism, we generated transgenic Cyp3a -/-mice expressing human CYP3A4 in either the intestine or the liver. Expression of CYP3A4 in the intestine dramatically decreased absorption of docetaxel into the bloodstream, while hepatic expression aided systemic docetaxel clearance. These results suggest that CYP3A expression determines impairment of drug absorption and efficient systemic clearance in a tissue-specific manner. The genetic models used in this study provide powerful tools to further study CYP3A-mediated xenobiotic metabolism, as well as interactions between CYP3A and other detoxification systems.

Metabolite Kinetics: The Segregated Flow Model for Intestinal and Whole Body Physiologically Based Pharmacokinetic Modeling to Describe Intestinal and Hepatic Glucuronidation of Morphine in Rats In Vivo

“…In contrast, physiologically based pharmacokinetic (PBPK) models address events of sequential elimination and include transmembrane barriers Pang, 1986, 1993;Pang, 2003;Pang et al, 2009;Chow and Pang, 2013) and transporters (Sun et al, 2006. The intestine, richly endowed with enzymes and transporters (van Herwaarden et al, 2007;Zhang et al, 2007Zhang et al, , 2009Liu et al, 2010), strongly affects firstpass metabolism and controls the flow of substrate to the liver (Pang and Chow, 2012). Intestinally formed metabolites may undergo immediate sequential metabolism or excretion (Pang and Gillette, 1979).…”

Pregnane X receptor‐ and CYP3A4‐humanized mouse models and their applications

“…A Cyp3a-null mouse model was generated by a heroic effort through deletion of the complete mouse Cyp3a cluster, including the catalytically active Cyp3a13, Cyp3a57 and Cyp3a59 enzymes (van Herwaarden et al, 2007). Surprisingly, there were no marked developmental or physiological abnormalities, thus revealing that these genes are dispensable in mice in the absence of dietary or chemical stress.…”

“…Docetaxel, a derivative of paclitaxel and an advanced chemotherapeutic drug, exhibits 18-fold and sevenfold higher area under the curve (AUC) after oral or intravenous administration of drug to Cyp3a-null mice compared with wild-type mice (van Herwaarden et al, 2007). In contrast, CYP3A4-humanized mice rapidly metabolize docetaxel as revealed by reduced AUC compared with wild-type mice.…”

“…In contrast to the previous whole body hPXR model, expression of human PXR in this mouse line is under the control of the native mouse Pxr promoter (Scheer et al, 2008). All hPXR mice show a normal phenotype, except for the Alb-VP-PXR mice that exhibited growth retardation, hepatomegaly and histological liver toxicity.A Cyp3a-null mouse model was generated by a heroic effort through deletion of the complete mouse Cyp3a cluster, including the catalytically active Cyp3a13, Cyp3a57 and Cyp3a59 enzymes (van Herwaarden et al, 2007). Surprisingly, there were no marked developmental or physiological abnormalities, thus revealing that these genes are dispensable in mice in the absence of dietary or chemical stress.…”

Methemoglobinemia Induced by 1,2-Dichloro-4-nitrobenzene in Mice with a Disrupted Glutathione S-Transferase Mu 1 Gene

“…In phase I enzymes, Cyp1a1, Cyp1a2, Cyp1b1, and Cyp2e1 knockout (null) mice were produced, and many studies were performed to examine in vivo metabolism, toxicity, and carcinogenesis (Gonzalez and Kimura, 2003). In addition, knockout mice of the Cyp3a family were recently produced and applied to the generation of CYP3A4 humanized mice to predict in vivo human metabolism (van Herwaarden et al, 2007). In phase II enzymes, toxicological approaches using knockout mice are very limited, although six lines of knockout mice for cytosolic GSTs have been established so far.…”