The roles of CYP450 epoxygenases and metabolites, epoxyeicosatrienoic acids, in cardiovascular and malignant diseases

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Abstract

Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid to biologically active eicosanoids. The primary epoxidation products are four regioisomers of cis-epoxyeicosatrienoic acid (EET): 5,6-, 8,9-, 11,12-, and 14,15-EET. CYP2J2, CYP2C8, and CYP2C9 are the predominant epoxygenase isoforms involved in EET formation. CYP2J and CYP2C gene families in humans are abundantly expressed in the endothelium, myocardium, and kidney. The cardiovascular effects of CYP epoxygenases and EETs range from vasodilation, anti-hypertension, pro-angiogenesis, anti-atherosclerosis, and anti-inflammation to anti-injury caused by ischemia-reperfusion. Using transgenic animals for in vivo analyses of CYP epoxygenases revealed comprehensive and marked cardiovascular protective effects. In contrast, CYP epoxygenases and their metabolites, EETs, are upregulated in human tumors and promote tumor progression and metastasis. These biological effects result from the anti-apoptosis, pro-mitogenesis, and anti-migration roles of CYP epoxygenases and EETs at the cellular level. Importantly, soluble epoxide hydrolase (sEH) inhibitors are anti-hypertensive and anti-inflammatory and, therefore, protect the heart from damage, whereas the terfenadine-related, specific inhibitors of CYP2J2 exhibit strong anti-tumor activity in vitro and in vivo. Thus, CYP2J2 and arachidonic acid-derived metabolites likely play important roles in regulating cardiovascular functions and malignancy under physiological and/or pathological conditions. Moreover, although challenges remain to improving the drug-like properties of sEH inhibitors and identifying efficient ways to deliver sEH inhibitors, sEH will likely become an important therapeutic target for cardiovascular diseases. In addition, CYP2J2 may be a therapeutic target for treating human cancers and leukemia.

Introduction

It is well established that arachidonic acid (AA) is converted to eicosanoid mediators by the cyclooxygenase, lipoxygenase, and cytochrome P450 (CYP) monooxygenase pathways [1]. The CYP pathway produces two types of eicosanoid products: epoxyeicosatrienoic acids (EETs), formed by CYP epoxygenases, and hydroxyeicosatetraenoic acids (HETEs), formed by CYP oxidases dependent on NADPH [2] (Fig. 1).

EETs are synthesized predominantly by the epoxygenases of the CYP2 family, including the 2C and 2J classes, although some other mammalian CYP isoforms have been reported to generate EETs (e.g., CYP1A, CYP2B, and CYP2D) [3]. To date, CYP2C8 and CYP2C9 genes in the 2C family and the CYP2J2 gene in the 2J family have been cloned and characterized in humans [4]. CYP2C and CYP2J are mainly expressed in epithelial cells, endothelial cells, smooth muscle cells, cardiomyocytes, autonomic ganglion cells, and islet cells in the heart, vessel, kidney, lung, and pancreas [5], [6], [7], [8], [9], [10], [11], [12]. Specifically, CYP2C8 is expressed mainly in the endothelium, CYP2C9 is expressed mainly in the kidney, and CYP2J2 is expressed mainly in the endothelium and myocardiocytes.

CYP2C isoforms are mainly responsible for EET biosynthesis in human liver and kidney, whereas CYP2J is the major enzyme for EET biosynthesis in heart and endothelial cells in rats and humans [9], [13]. These enzymes are localized in the endoplasmic reticulum and use AA hydrolyzed from phospholipids as a substrate when Ca2+-dependent type IV phospholipase A2 is activated and translocated from the cytosol to intracellular membranes [14], [15]. These CYP epoxygenases add an epoxide group to one of the four double bonds of AA and form four regioisomeric EETs: 5,6-, 8,9-, 11,12-, and 14,15-EET. Studies with purified CYP epoxygenases indicate that, although each enzyme is able to convert AA to all four EET regioisomers, the main products in many cases are 11,12- and 14,15-EET [16]. EETs are further converted to more stable and less bioactive metabolites, dihydroxyeicosatrienoic acids (DHETs) [17], which are easily measured in biological samples such as urine and plasma, as well as in tissues [18], [19].

Accumulating evidence indicates that EETs exhibit important, but diverse, physiological and pathophysiological roles. Over the past 2 decades, it has become increasingly evident that EETs exert many protective effects on the cardiovascular system. Recent observations revealed that forced expression of CYP2J2 and elevated levels of EETs promote tumor malignancy, including proliferation and metastasis in vivo and in vitro, but the selective inhibition of CYP2J2 attenuates these effects [19], [20], [21]. This review article highlights the progress made on determining the roles of CYP epoxygenases and their metabolites (EETs) in cardiovascular and malignant diseases. It also discusses the therapeutic potential of CYP epoxygenases and EETs, as well as the existing challenges to applying them clinically.

Section snippets

Molecular and cellular mechanisms of EETs

The molecular and cellular mechanisms through which EETs regulate various biological functions have been intensively investigated. The current understanding is that EETs may exert different biological effects via different mechanisms in different tissues and cells.

Vascular effect of EETs: vasodilation

Physiological roles of CYP epoxygenase activity in vessels are substantially EET-mediated by hyperpolarization and other mechanisms. Four regioisoforms of EETs have important vasodilator properties independent of nitric oxide (NO) and prostacyclin (PGI2) in coronary artery and peripheral vascular beds.

EETs and Tumors

The pathological consequences of cancer are related mainly to uncontrolled tumor growth and metastasis, both of which are a consequence of abnormal tumor cell proliferation, adhesion, invasion, and migration. Although angiogenesis is pivotal in the processes of wound healing and tissue regeneration, it is also implicated in the pathological growth of neoplastic tumors.

CYP epoxygenases and their derived eicosanoids promote endothelial cell proliferation, migration, and angiogenesis, as described

Summary

Rapid progress has been made in evaluating the roles of CYP epoxygenase and its metabolites, EETs, in the initiation and development of human diseases, especially cardiovascular, inflammatory, and neurological diseases. Although it remains unclear whether these effects are mediated via binding to a putative EET cell-surface and/or intracellular receptor, the collective preclinical evidence has demonstrated that potentiation of the CYP epoxygenase pathway elicits protection against various

Acknowledgments

This work was supported by funds from National Natural Science Foundation of China grants (Nos. 30930039, 30971247 and 30971248) and National Basic Research Program of China (No. 2007CB512004).

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