Clone CYP2J2, a human P450 enzyme that is active in the metabolism of arachidonic acidto epoxyeicosatrienoic acids (EETs; Figure 1) and is abundant in heart (Wu et al., J. Biol. Chem., 1996(http://www.jbc.org/cgi/content/abstract/271/7/3460))
Figure 1: Metabolism of arachidonic acid by cytochromes P450
P450-derived eicosanoid effects on cardiovascular function
Subsequent studies demonstrated that EETs improved heart contractile function following ischemia (Wu et al., J. Biol. Chem., 1997 (http://www.jbc.org/cgi/content/abstract/272/19/12551); Seubert et al., Circ. Res., 2004(http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15256482&query_hl=116&itool=pubmed_docsum); Seubert et al., Circ. Res., 2006 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16857962&query_hl=65&itool=pubmed_docsum)), inhibited cardiac L-type calcium channels (Chen et al., Mol. Pharmacol., 1999 (http://molpharm.aspetjournals.org/cgi/content/abstract/55/2/288)), and activated ATP-sensitive potassium channels (Lu et al., J. Physiol., 2006 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16793897&query_hl=65&itool=pubmed_docsum); Figure 2). The group recently developed CYP2J2 transgenic mice that have improved post-ischemic cardiac function and represent the first in vivo animal model for evaluating P450 functions in heart (Seubert et al., Circ. Res., 2004 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15256482&query_hl=116&itool=pubmed_docsum)).
In collaboration with Harvard University’s James Liao, M.D., the group demonstrated that CYP2J2-derived eicosanoids decreased cytokine-induced endothelial adhesion molecule expression by a mechanism that involves inhibition of the transcription factor NF-kB (Node et al., Science, 1999 (http://www.sciencemag.org/cgi/content/abstract/285/5431/1276)). The group also showed that exposure of endothelial cells to hypoxia-reoxygenation decreased CYP2J2 expression and that maintenance of CYP2J2 protein levels attenuated hypoxia-reoxygenation-induced cell death (Yang et al., Mol. Pharmacol., 2001 (http://molpharm.aspetjournals.org/cgi/content/abstract/60/2/310)). Together, these studies demonstrate that CYP2J2 and its eicosanoid products play critical roles in cardiac myocyte and endothelial function and may be involved in limiting vascular inflammation and cardiac dysfunction following ischemia.
Figure 2: Effects of P450-derived eicosanoids in the cardiovascular system
P450-derived eicosanoid effects on renal function
Kidney studies have shown that P450-derived eicosanoids contribute substantially to integrated renal function (Figure 3). In 1999, the group cloned a new mouse P450, CYP2J5. CYP2J5 primarily expresses in the kidney, is active in the metabolism of arachidonic acid to EETs and localizes to proximal tubules and collecting ducts, sites where EETs affect renal fluid/electrolyte transport and mediate the actions of several hormones (Ma et al., J. Biol. Chem., 1999 (http://www.jbc.org/cgi/content/abstract/274/25/17777)). Interestingly, maximal CYP2J5 expression occurs during a critical time in postnatal renal development when abnormalities in renal function appear in animals that develop hypertension.
Figure 3: Effects of P450 epoxygenase metabolites in kidney
Further evidence to support the hypothesis that CYP2J products contribute to the development or maintenance of hypertension comes from two recent studies: one showing upregulation of a CYP2J immunoreactive protein and increased EET biosynthesis in kidneys of spontaneously hypertensive rats (Yu et al., Mol. Pharmacol., 2000) and another showing the chromosomal mapping of the Cyp2j cluster to an area that co-segregates with the hypertensive phenotype in Dahl salt-sensitive rats (Ma et al., Genomics, 1998(http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9570962&dopt=Abstract)). The newly developed Cyp2j5 knockout mice will be instrumental in evaluating the role of P450 in kidney function, renal eicosanoid metabolism and blood pressure regulation.
The group cloned and characterized the human CYP2J2 gene, and identified several functionally relevant CYP2J2 polymorphic variants (King et al., Mol. Pharmacol., 2002 (http://www.jbc.org/cgi/content/abstract/274/25/17777)). One of these variants associates with reduced CYP2J2 expression/activity and is present at higher frequency in patients with cardiovascular disease versus normals (Spiecker et al., Circulation, 2004 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15466638&query_hl=118&itool=pubmed_docsum)).
In addition to the CYP2J work, Zeldin’s group has cloned and characterized CYP2C8, the major human liver P450 arachidonic acid epoxygenase (Zeldin et al., Arch. Biochem. Biophys., 1995 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7574697&dopt=Abstract); Zeldin et al., Arch. Biochem. Biophys., 1996 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8651708&dopt=Abstract)) and characterized several mouse CYP2C isoforms (Luo et al., Arch. Biochem. Biophys., 1998 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9721182&dopt=Abstract); Tsao et al., Mol. Pharmacol., 2000 (http://molpharm.aspetjournals.org/cgi/content/abstract/58/2/279); Tsao et al., J. Pharmacol. Exp. Therap., 2001 (http://jpet.aspetjournals.org/cgi/content/abstract/299/1/39); DeLozier et al., J. Pharmacol. Exp. Therap., 2004 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15084647&query_hl=121&itool=pubmed_docsum);Wang et al., Mol. Pharmacol., 2004 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15102943&query_hl=125&itool=pubmed_docsum) ).
The group has also identified two new P450 subfamilies, the CYP2Ns and the CYP2Ps, which relate phylogenetically to the CYP2Js. CYP2Ns and the CYP2Ps are abundant in extrahepatic tissues and are active in the metabolism of arachidonic acid to EETs (Oleksiak et al., J. Biol. Chem., 2000 (http://www.jbc.org/cgi/content/abstract/275/4/2312); Oleksiak et al.; Oleksiak et al., Arch. Biochem. Biophys., 2003 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=12623071&query_hl=128&itool=pubmed_docsum)).
The group was also the first to document a role for soluble epoxide hydrolase (EPHX2, sEH) in the regio- and stereoselective metabolism of EETs to dihydroxyeicosatrienoic acids (DHETs) and to show that DHETs were endogenous constituents of liver and lung (Zeldin et al., J. Biol. Chem., 1993 (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8454612&dopt=Abstract); Zeldin et al., Arch. Biochem. Biophys., 1995 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7840649&dopt=Abstract); Zeldin et al., Arch. Biochem. Biophys., 1996 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8651708&dopt=Abstract); Zeldin et al., J. Clin. Invest., 1995 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7738183&dopt=Abstract)). In collaboration with Deanna Kroetz, Ph.D. of the University of California, San Francisco, the group’s data showed that sEH regulates EET hydrolysis and blood pressure in spontaneously hypertensive rats (Yu et al., Circ. Res., 2000 (http://circres.ahajournals.org/cgi/content/abstract/87/11/992)). More recently, Zeldin’s group identified several functionally relevant EPHX2 polymorphic variants (Przybyla-Zawislak et al., Mol. Pharmacol., 2003 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=12869654&query_hl=130&itool=pubmed_docsum)) and demonstrated that one of these variants associates with cardiovascular disease and stroke in humans (Fornage et al., Hum. Mol. Genetics, 2005 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=pubmed&term=the+soluble+epoxide+hydrolase+gene+harbors+sequence+variation+associated+with+susceptibility+to+and+protection+from+incident+ischemic+stroke&tool=fuzzy&ot=The+Soluble+Epoxide+Hydrolase+Gene+Harbors+Sequence+Variation+Associatred+with+Susceptibility+to+and+Protection+from+Incident+Ischemic+Stroke); Lee et al., Hum. Mol. Genetics, 2006 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16595607&query_hl=41&itool=pubmed_docsum)).
Summary
Zeldin's research has led to a better understanding of the role of cytochromes P450 in the metabolism of arachidonic acid to compounds which modulate fundamental biological processes in extrahepatic tissues, especially the heart, kidney and vasculature. The opportunities for translational research in this area include development of novel therapeutics for blood pressure control, vascular inflammation, atherosclerosis and ischemic heart disease. The identification of individuals who are at increased risk for these disorders due to P450 or sEH genetic variation may also lead to new approaches to disease prevention.
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