title: Genetic enhancement of microsomal epoxide hydrolase improves metabolic detoxification but impairs cerebral blood flow regulation.
abstract: Microsomal epoxide hydrolase (mEH) is a detoxifying enzyme for xenobiotic compounds. Enzymatic activity of mEH can be greatly increased by a point mutation, leading to an E404D amino acid exchange in its catalytic triad. Surprisingly, this variant is not found in any vertebrate species, despite the obvious advantage of accelerated detoxification. We hypothesized that this evolutionary avoidance is due to the fact that the mEH plays a dualistic role in detoxification and control of endogenous vascular signaling molecules. To test this, we generated mEH E404D mice and assessed them for detoxification capacity and vascular dynamics. In liver microsomes from these mice, turnover of the xenobiotic compound phenanthrene-9,10-oxide was four times faster compared to WT liver microsomes, confirming accelerated detoxification. mEH E404D animals also showed faster metabolization of a specific class of endogenous eicosanoids, arachidonic acid-derived epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs). Significantly higher DHETs/EETs ratios were found in mEH E404D liver, urine, plasma, brain and cerebral endothelial cells compared to WT controls, suggesting a broad impact of the mEH mutant on endogenous EETs metabolism. Because EETs are strong vasodilators in cerebral vasculature, hemodynamics were assessed in mEH E404D and WT cerebral cortex and hippocampus using cerebral blood volume (CBV)-based functional magnetic resonance imaging (fMRI). Basal CBV0levels were similar between mEH E404D and control mice in both brain areas. But vascular reactivity and vasodilation in response to the vasodilatory drug acetazolamide were reduced in mEH E404D forebrain compared to WT controls by factor 3 and 2.6, respectively. These results demonstrate a critical role for mEH E404D in vasodynamics and suggest that deregulation of endogenous signaling pathways is the undesirable gain of function associated with the E404D variant.
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
authors.forename: Anne
authors.initials: A
authors.lastname: Marowsky
authors.affiliation: Institute of Complex Systems (ICS-6), Research Center Julich, Wilhelm-Johnen-Straße, 52425, Julich, Germany.
authors.forename: Karen
authors.initials: K
authors.lastname: Haenel
authors.affiliation: Institute of Translational Immunology, University of Mainz, Obere Zahlbacherstrasse 63, 55131, Mainz, Germany.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Bockamp
authors.affiliation: Institute of Translational Immunology, University of Mainz, Obere Zahlbacherstrasse 63, 55131, Mainz, Germany.
authors.forename: Rosario
authors.initials: R
authors.lastname: Heck
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
authors.forename: Sibylle
authors.initials: S
authors.lastname: Rutishauser
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
authors.forename: Nandkishor
authors.initials: N
authors.lastname: Mule
authors.affiliation: Institute for Biomedical Engineering, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093, Zurich, Switzerland.
authors.forename: Diana
authors.initials: D
authors.lastname: Kindler
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.|Institute for Biomedical Engineering, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093, Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Rudin
authors.affiliation: Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland. arand@pharma.uzh.ch.
authors.forename: Michael
authors.initials: M
authors.lastname: Arand
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D020134:Catalytic Domain; D002540:Cerebral Cortex / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D002560:Cerebrovascular Circulation / Q000187:drug effects; D002561:Cerebrovascular Disorders / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D015777:Eicosanoids / Q000097:blood / Q000378:metabolism / Q000652:urine; D004851:Epoxide Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006624:Hippocampus / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008658:Inactivation, Metabolic; D051379:Mice; D008817:Mice, Mutant Strains; D008862:Microsomes, Liver / Q000201:enzymology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010616:Phenanthrenes / Q000378:metabolism; D017354:Point Mutation; D014655:Vascular Resistance / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology; D015262:Xenobiotics / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D015777:Eicosanoids; D010616:Phenanthrenes; D014665:Vasodilator Agents; D015262:Xenobiotics; C046665:9,10-epoxy-9,10-dihydrophenanthrene; D004851:Epoxide Hydrolases; C543485:EPHX1 protein, mouse
keywords: Eicosanoids; Enzymatic mechanism; Xenobiotic metabolism; fMRI
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