Regular ArticleMetabolism of Epoxyeicosatrienoic Acids by Cytosolic Epoxide Hydrolase: Substrate Structural Determinants of Asymmetric Catalysis
Abstract
The metabolism of cis-epoxyeicosatrienoic acids (EETs), methyl cis-epoxyeicosatrienoates, and cis-epoxyeicosanoic acids by cytosolic epoxide hydrolase was studied to identify substrate structural features important for stereoselective metabolism and chiral diol formation. 14(R), 15(S)-, 11(S),12(R)-, and 8(S),9(R)-EET, the predominant enantiomers present endogenously in rat organs, were metabolized at substantially higher rates than their antipodes. With the exception of 8(R),9(S)-EET (Km = 41 μM), differences in enantiomer hydration rates appear to be caused by Km-independent factors since the apparent Km values for the enantiomers of 14,15-, 11,12-, and 8(S),9(R)-EET were similar (between 3 and 5 μM). Chiral analysis of the diols resulting from enzymatic hydration of homochiral EETs showed that the regio and/or stereochemistry of water addition was EET regioisomer dependent. For the 11,12-EET enantiomers, water addition was nonregioselective; whereas, with both 8,9-EET antipodes water addition occurred predominantly at C9. Importantly, for 14,15-EET the regiochemistry of water addition was enantiomer-dependent. Only with 14(R),15(S)-EET did enzymatic hydration result in regiospecific addition at C15. Hence, enantioselective EET hydration is determined, principally, by enantiomer specific differences in rates of catalytic turnover and/or substrate binding parameters. On the other hand, the chirality of the diol products is determined by EET enantiomer-dependent differences in the regiochemistry of enzymatic oxirane cleavage and water addition. Esterification resulted in an overall reduction in the rates of epoxide hydration for all three EET-methyl esters (59, 89, and 68% of the EET rate for 8,9-, 11,12-, and 14,15-EET-methyl ester, respectively) and in the loss of regioselectivity during methyl 8(S),9(R)-EET oxirane cleavage. Catalytic EET hydrogenation reduced the rates of EET hydration (56, 45, and 23% of the EET rates for 8,9-, 11,12-, and 14,15-epoxyeicosanoic acids, respectively). Compared to 14,15-EET, enzyme catalyzed hydration of 14,15-epoxyeicosanoic acid was less regioselective and yielded products with a substantially lower chiral purity. Based on these data, as well as on the documentation of 14(R),15(R)-dihydroxyeicosatrienoic acid as an endogenous constituent of rat urine we concluded that: (1) cytosolic epoxide hydrolase plays a significant role in the regio- and stereoselective metabolism of endogenous EETs; (2) differences in the affinities and/or turnover rates of the enzyme for the individual EET antipodes may be responsible for enantioselective EET metabolism; and (3) for 14,15- and 8,9-EET, regioselective and/or enantioselective oxirane water addition is responsible for asymmetric diol formation. The protein spatial coordinates responsible for the asymmetry of EET hydration and diol formation must be circumscribed by a highly structured active site capable of recognizing, regio- and stereospecifically, overall substrate polarity, freedom of CC bond rotation, and/or protein-substrate π-π dipole interactions.
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Role of cytochrome P450-epoxygenase and soluble epoxide hydrolase in the regulation of vascular response
2023, Advances in PharmacologyThe role of cytochrome P450-epoxygenase has been seen in cardiovascular physiology and pathophysiology. The aberration in CYP450-epoxygenase genes occur due to genetic polymorphisms, aging, or environmental factors, that increase susceptibility to cardiovascular diseases (CVDs). The actual role played by the CYP450-epoxygenases is the metabolism of arachidonic acid (AA) and linoleic acid (LA) into epoxyeicosatrienoic acids (EETs) and epoxyoctadecaenoic acid (EpOMEs) metabolites (oxylipins) and others, which is involved in vasodilation and myocardial-protection. But the genetic polymorphisms in CYP450-epoxygenases lose their beneficial cardiovascular effects of oxylipins, and the soluble epoxide hydrolase (sEH) antagonizes beneficial oxylipins into diols. Like sEH converts EETs into dihydroxyeicosatrienoic acid (DHETs), EpOMEs into dihydroxyoctadecaenoic acid (DiHOMEs), and reverses its beneficial effects, and the sEH gene (Ephx2) polymorphisms cause the enzyme to become overactive and convert epoxy-fatty acids into diols, making them vulnerable to CVDs, including hypertension. Other, enzymes like ω-hydroxylases (CYP450-4A11 & CYP450-4F2)-derived oxylipins from AA, ω-terminal-hydroxyeicosatetraenoic acids (19-, 20-HETE), lipoxygenase-derived oxylipins, mid-chain hydroxyeicosatetraenoic acids (5-, 11-, 12-, 15-HETEs), and the cyclooxygenase-derived prostanoids (prostaglandins: PGD2, PGF2α; thromboxane: Txs, oxylipins) are involved in vasoconstriction, hypertension, inflammation, and cardiac toxicity. Also, there are significant interactions were seen between adenosine receptors [adenosine A2A receptor (A2AAR) and adenosine A1 receptor (A1AR)] with CYP450-epoxygenases, ω-hydroxylases, sEH, and their derived oxylipins in the regulation of the cardiovascular response. Moreover, polymorphisms exist in CYP450-epoxygenases, ω-hydroxylases, sEH, and the adenosine receptor genes in populations associated with CVDs. This chapter will discuss the role of oxylipins' interactions with adenosine receptors in cardiovascular function/dysfunction in mice and humans.
Crosstalk between adenosine receptors and CYP450-derived oxylipins in the modulation of cardiovascular, including coronary reactive hyperemic response
2022, Pharmacology and TherapeuticsAdenosine is a ubiquitous endogenous nucleoside or autacoid that affects the cardiovascular system through the activation of four G-protein coupled receptors: adenosine A1 receptor (A1AR), adenosine A2A receptor (A2AAR), adenosine A2B receptor (A2BAR), and adenosine A3 receptor (A3AR). With the rapid generation of this nucleoside from cellular metabolism and the widespread distribution of its four G-protein coupled receptors in almost all organs and tissues of the body, this autacoid induces multiple physiological as well as pathological effects, not only regulating the cardiovascular system but also the central nervous system, peripheral vascular system, and immune system. Mounting evidence shows the role of CYP450-enzymes in cardiovascular physiology and pathology, and the genetic polymorphisms in CYP450s can increase susceptibility to cardiovascular diseases (CVDs). One of the most important physiological roles of CYP450-epoxygenases (CYP450-2C & CYP2J2) is the metabolism of arachidonic acid (AA) and linoleic acid (LA) into epoxyeicosatrienoic acids (EETs) and epoxyoctadecaenoic acid (EpOMEs) which generally involve in vasodilation. Like an increase in coronary reactive hyperemia (CRH), an increase in anti-inflammation, and cardioprotective effects. Moreover, the genetic polymorphisms in CYP450-epoxygenases will change the beneficial cardiovascular effects of metabolites or oxylipins into detrimental effects. The soluble epoxide hydrolase (sEH) is another crucial enzyme ubiquitously expressed in all living organisms and almost all organs and tissues. However, in contrast to CYP450-epoxygenases, sEH converts EETs into dihydroxyeicosatrienoic acid (DHETs), EpOMEs into dihydroxyoctadecaenoic acid (DiHOMEs), and others and reverses the beneficial effects of epoxy-fatty acids leading to vasoconstriction, reducing CRH, increase in pro-inflammation, increase in pro-thrombotic and become less cardioprotective. Therefore, polymorphisms in the sEH gene (Ephx2) cause the enzyme to become overactive, making it more vulnerable to CVDs, including hypertension. Besides the sEH, ω-hydroxylases (CYP450-4A11 & CYP450-4F2) derived metabolites from AA, ω terminal-hydroxyeicosatetraenoic acids (19-, 20-HETE), lipoxygenase-derived mid-chain hydroxyeicosatetraenoic acids (5-, 11-, 12-, 15-HETEs), and the cyclooxygenase-derived prostanoids (prostaglandins: PGD2, PGF2α; thromboxane: Txs, oxylipins) are involved in vasoconstriction, hypertension, reduction in CRH, pro-inflammation and cardiac toxicity. Interestingly, the interactions of adenosine receptors (A2AAR, A1AR) with CYP450-epoxygenases, ω-hydroxylases, sEH, and their derived metabolites or oxygenated polyunsaturated fatty acids (PUFAs or oxylipins) is shown in the regulation of the cardiovascular functions. In addition, much evidence demonstrates polymorphisms in CYP450-epoxygenases, ω-hydroxylases, and sEH genes (Ephx2) and adenosine receptor genes (ADORA1 & ADORA2) in the human population with the susceptibility to CVDs, including hypertension. CVDs are the number one cause of death globally, coronary artery disease (CAD) was the leading cause of death in the US in 2019, and hypertension is one of the most potent causes of CVDs. This review summarizes the articles related to the crosstalk between adenosine receptors and CYP450-derived oxylipins in vascular, including the CRH response in regular salt-diet fed and high salt-diet fed mice with the correlation of heart perfusate/plasma oxylipins. By using A2AAR−/−, A1AR−/−, eNOS−/−, sEH−/− or Ephx2−/−, vascular sEH-overexpressed (Tie2-sEH Tr), vascular CYP2J2-overexpressed (Tie2-CYP2J2 Tr), and wild-type (WT) mice. This review article also summarizes the role of pro-and anti-inflammatory oxylipins in cardiovascular function/dysfunction in mice and humans. Therefore, more studies are needed better to understand the crosstalk between the adenosine receptors and eicosanoids to develop diagnostic and therapeutic tools by using plasma oxylipins profiles in CVDs, including hypertensive cases in the future.
Plasma epoxyeicosatrienoic acids and diabetes-related cardiovascular disease: The cardiovascular health study
2022, eBioMedicineEpoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid that may impact atherosclerosis, and animal experimental studies suggest EETs protect cardiac function. Plasma EETs are mostly esterified to phospholipids and part of an active pool. To address the limited information about EETs and CVD in humans, we conducted a prospective study of total plasma EETs (free + esterified) and diabetes-related CVD in the Cardiovascular Health Study (CHS).
We measured 4 EET species and their metabolites, dihydroxyepoxyeicosatrienoic acids (DHETs), in plasma samples from 892 CHS participants with type 2 diabetes. We determined the association of EETs and DHETs with incident myocardial infarction (MI) and ischemic stroke using Cox regression.
During follow-up (median 7.5 years), we identified 150 MI and 134 ischemic strokes. In primary, multivariable analyses, elevated levels of each EET species were associated with non-significant lower risk of incident MI (for example, hazard ratio for 1 SD higher 14,15-EET: 0.86, 95% CI: 0.72–1.02; p=0.08). The EETs-MI associations became significant in analyses further adjusted for DHETs (hazard ratio for 1 SD higher 14,15-EET adjusted for 14,15-DHET: 0.76, 95% CI: 0.63–0.91; p=0.004). Elevated EET levels were associated with higher risk of ischemic stroke in primary but not secondary analyses. Three DHET species were associated with higher risk of ischemic stroke in all analyses.
Findings from this prospective study complement the extensive studies in animal models showing EETs protect cardiac function and provide new information in humans. Replication is needed to confirm the associations.
US National Institutes of Health.
Epoxyeicosatrienoic acid: A potential therapeutic target of heart failure with preserved ejection fraction
2022, Biomedicine and PharmacotherapyCitation Excerpt :These epoxygenase are abundantly expressed in human tissues [7]. EETs once generated, they would be quickly metabolized, mainly by sEH, to their corresponding less-active DHETs [24]. In parallel, AA can also be metabolized by the COX or LOX pathways into prostanoids and leukotrienes (Fig. 1) [25].
Heart failure with preserved ejection fraction (HFpEF) reduces the quality of life, costs substantial medical resources, and has a high mortality. However, we lack an effective therapy for HFpEF due to our limited knowledge of its mechanism. Therefore, it is crucial to explore novel therapeutics, such as those with endogenous protective roles, and seek new targeted therapies. Epoxyeicosatrienoic acids (EETs) are endogenous bioactive metabolites of arachidonic acids produced by cytochrome P450 (CYP) epoxygenases. EETs can function as endogenous cardioprotective factors with potent inhibitory roles in inflammation, endothelial dysfunction, cardiac remodeling, and fibrosis, which are the fundamental mechanisms of HFpEF. This suggests that EETs have the potential function to protect against HFpEF. Therefore, we present an overview of the ever-expanding world of EETs and how they might help alleviate the pathophysiology underlying HFpEF to provide new insights for research in this field.
Structure-function relationship between soluble epoxide hydrolases structure and their tunnel network
2022, Computational and Structural Biotechnology JournalEnzymes with buried active sites maintain their catalytic function via a single tunnel or tunnel network. In this study we analyzed the functionality of soluble epoxide hydrolases (sEHs) tunnel network, by comparing the overall enzyme structure with the tunnel’s shape and size. sEHs were divided into three groups based on their structure and the tunnel usage. The obtained results were compared with known substrate preferences of the studied enzymes, as well as reported in our other work evolutionary analyses data. The tunnel network architecture corresponded well with the evolutionary lineage of the source organism and large differences between enzymes were observed from long fragments insertions. This strategy can be used during protein re-engineering process for large changes introduction, whereas tunnel modification can be applied for fine-tuning of enzyme.
Plasma epoxyeicosatrienoic acids and dihydroxyeicosatrieonic acids, insulin, glucose and risk of diabetes: The strong heart study
2021, EBioMedicineEpoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid with multiple biological functions. Rodent experiments suggest EETs play a role in insulin sensitivity and diabetes, but evidence in humans is limited. To address this knowledge gap, we conducted a case-cohort study in the Strong Heart Family Study, a prospective cohort among American Indians.
We measured 4 EET species and 4 species of corresponding downstream metabolites, dihydroxyeicosatrieonic acids (DHETs), in plasma samples from 1161 participants, including 310 with type 2 diabetes. We estimated the associations of total (esterified and free) EETs and DHETs with incident diabetes risk, adjusting for known risk factors. We also examined cross-sectional associations with plasma fasting insulin and glucose in the case-cohort and in 271 participants without diabetes from the older Strong Heart Study cohort, and meta-analyzed the results from the 2 cohorts.
We observed no significant association of total EET or DHET levels with incident diabetes. In addition, plasma EETs were not associated with plasma insulin or plasma glucose. However, higher plasma 14,15-DHET was associated with lower plasma insulin and lower plasma glucose.
In this first prospective study of EETs and diabetes, we found no evidence for a role of total plasma EETs in diabetes. The novel associations of 14,15-DHET with insulin and glucose warrant replication and exploration of possible mechanisms.
US National Institutes of Health