Discovery of soluble epoxide hydrolase inhibitors from natural products

Inhibition of soluble epoxide hydrolase by natural isothiocyanates

GOAL

The long-term goal of our research is to develop safe and effective soluble epoxide hydrolase (sEH) inhibitors. The objective of this study is to evaluate the potency and selectivity of six natural isothiocyanates (ITCs) as sEH inhibitors.

METHODS

Molecular docking was used to model likely interactions between the ligands and receptors. The sEH inhibitory activity was tested using a validated fluorescence-based assay and PHOME as a substrate. To evaluate their selectivity as sEH inhibitors, the inhibitory potential of the ITCs was determined on microsomal epoxide hydrolase (mEH) and cytochrome P450 (CYP) enzymes in human liver microsomes. Probe substrates such as styrene oxide (mEH substrate) and established substrates for CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 were used in this study. The metabolites of these substrates were analyzed using validated LC-MS/MS and HPLC-UV assays.

RESULTS

Molecular Docking revealed significant differences in binding site preference among the ITCs in silico and pointed to important interactions between the ligands and the catalytic residues of the sEH enzyme. In vitro, the ITCs showed varying degrees of sEH inhibition, but sulforaphane (SFN) and phenyl isothiocyanate (PITC) were the most potent inhibitors with IC50 values of 3.65 and 7.5 μM, respectively. mEH was not significantly inhibited by any of the ITCs. Erucin and iberin were the only ITCs that did not inhibit the activity of any of the tested CYP enzymes.

CONCLUSION

Our results demonstrate that natural ITCs have the potential to offer safe, selective, and potent sEH inhibition.

Inhibition of Soluble Epoxide Hydrolase by Cembranoid Diterpenes from Soft Coral Sinularia maxima: Enzyme Kinetics, Molecular Docking, and Molecular Dynamics

Soluble epoxide hydrolase (sEH) is essential for converting epoxy fatty acids, such as epoxyeicosatrienoic acids (EETs), into their dihydroxy forms. EETs play a crucial role in regulating blood pressure, mediating anti-inflammatory responses, and modulating pain, making sEH a key target for therapeutic interventions. Current research is increasingly focused on identifying sEH inhibitors from natural sources, particularly marine environments, which are rich in bioactive compounds due to their unique metabolic adaptations. In this study, the sEH inhibitory activities of ten cembranoid diterpenes (1-10) isolated from the soft coral Sinularia maxima were evaluated. Among them, compounds 3 and 9 exhibited considerable sEH inhibition, with IC50 values of 70.68 μM and 78.83 μM, respectively. Enzyme kinetics analysis revealed that these two active compounds inhibit sEH through a non-competitive mode. Additionally, in silico approaches, including molecular docking and molecular dynamics simulations, confirmed their stability and interactions with sEH, highlighting their potential as natural therapeutic agents for managing cardiovascular and inflammatory diseases.

Essential Oils of Laurus nobilis L.: From Chemical Analysis to In Silico Investigation of Anti-Inflammatory Activity by Soluble Epoxide Hydrolase (sEH) Inhibition

Laurus nobilis L. is commonly used in folk medicine in the form of infusion or decoction to treat gastrointestinal diseases and flatulence as a carminative, antiseptic, and anti-inflammatory agent. In this study, the essential oil (EO) composition of wild-grown L. nobilis L. leaves collected from seven different altitudinal locations in the Molise region and adjacent regions (Abruzzo and Campania) was investigated. EOs from the leaves were obtained by hydrodistillation and analyzed by GC-FID and GC/MS, and 78 compounds were identified. The major oil components were 1,8-cineol (43.52-31.31%), methyl-eugenol (14.96-4.07%), α-terpinyl acetate (13.00-8.51%), linalool (11.72-1.08%), sabinene (10.57-4.85%), α-pinene (7.41-3.61%), eugenol (4.12-1.97%), and terpinen-4-ol (2.33-1.25%). Chemometric techniques have been applied to compare the chemical composition. To shed light on the nutraceutical properties of the main hydrophobic secondary metabolites (≥1.0%) of laurel EOs, we assessed the in vitro antioxidant activities based on 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging activity and the reducing antioxidant power by using a ferric reducing power (FRAP) assay. Furthermore, we highlighted the anti-inflammatory effects of seven EOs able to interfere with the enzyme soluble epoxide hydrolase (sEH), a key enzyme in the arachidonic acid cascade, in concentrations ranging from 16.5 ± 4.3 to 8062.3 ± 580.9 mg/mL. Thanks to in silico studies, we investigated and rationalized the observed anti-inflammatory properties, ascribing the inhibitory activity toward the disclosed target to the most abundant volatile phytochemicals (≥1.0%) of seven EOs.

Discovery of Soluble Epoxide Hydrolase Inhibitors from Chemical Synthesis and Natural Products

Soluble epoxide hydrolase (sEH) is an α/β hydrolase fold protein and widely distributed in numerous organs including the liver, kidney, and brain. The inhibition of sEH can effectively maintain endogenous epoxyeicosatrienoic acids (EETs) levels and reduce dihydroxyeicosatrienoic acids (DHETs) levels, resulting in therapeutic potentials for cardiovascular, central nervous system, and metabolic diseases. Therefore, since the beginning of this century, the development of sEH inhibitors is a hot research topic. A variety of potent sEH inhibitors have been developed by chemical synthesis or isolated from natural sources. In this review, we mainly summarized the interconnected aspects of sEH with cardiovascular, central nervous system, and metabolic diseases and then focus on representative inhibitors, which would provide some useful guidance for the future development of potential sEH inhibitors.

Small Molecule Soluble Epoxide Hydrolase Inhibitors in Multitarget and Combination Therapies for Inflammation and Cancer

The enzyme soluble epoxide hydrolase (sEH) plays a central role in metabolism of bioactive lipid signaling molecules. The substrate-specific hydrolase activity of sEH converts epoxyeicosatrienoic acids (EETs) to less bioactive dihydroxyeicosatrienoic acids. EETs exhibit anti-inflammatory, analgesic, antihypertensive, cardio-protective and organ-protective properties. Accordingly, sEH inhibition is a promising therapeutic strategy for addressing a variety of diseases. In this review, we describe small molecule architectures that have been commonly deployed as sEH inhibitors with respect to angiogenesis, inflammation and cancer. We juxtapose commonly used synthetic scaffolds and natural products within the paradigm of a multitarget approach for addressing inflammation and inflammation induced carcinogenesis. Structural insights from the inhibitor complexes and novel strategies for development of sEH-based multitarget inhibitors are also presented. While sEH inhibition is likely to suppress inflammation-induced carcinogenesis, it can also lead to enhanced angiogenesis via increased EET concentrations. In this regard, sEH inhibitors in combination chemotherapy are described. Urea and amide-based architectures feature prominently across multitarget inhibition and combination chemotherapy applications of sEH inhibitors.

Isolation of bioactive components with soluble epoxide hydrolase inhibitory activity from Stachys sieboldii MiQ. by ultrasonic-assisted extraction optimized using response surface methodology

Stachys sieboldii MiQ (SSM) is an important food and medicinal herb in Korea, used to improve memory of patients with senile dementia and cardiovascular diseases. However, little information on bioactive components from SSM or standardized extraction methods for these components is available. This study isolated and purified major components from SSM for the first time, and assessed their ability to inhibit soluble epoxide hydrolase (sEH). The results showed that acteoside is the most potent inhibitor of sEH, with an IC₅₀ of 33.5 ± 0.5 μM. Additional active components, including harpagide, tryptophan, and 8-acetate-harpagide, along with acteoside, were tentatively identified using high-performance liquid chromatography photodiode array tandem mass spectrometry (HPLC-PDA-MS/MS) and quantified using an ultraviolet detector at 210 nm. Further, an ultrasonic-assisted extraction technique for extraction of four bioactive compounds in SSM was developed and optimized using response surface methodology (RSM). The optimal extraction conditions were: extraction time, 30.46 minutes; extraction temperature, 67.95 °C, and methanol concentration 53.85%. The prediction model of RSM was validated with laboratory experiments. The similarity between predicted and actual values was 97.84%. The extraction method is thus a rapid, environment-friendly, energy-saving method can be applied to extract bioactive components from SSM in large quantities.

Natural soluble epoxide hydrolase inhibitors from Inula helenium and their interactions with soluble epoxide hydrolase

The inhibition of soluble epoxide hydrolase (sEH) is regarded as a promising therapeutic approach to treat inflammation and its related disorders. In present work, we investigated inhibitory effects of forty-nine kinds of traditional Chinese medicines against sEH. Inula helenium showed significant inhibitory effect against sEH, and the extract of I. helenium were isolated to obtain eight compounds, including 4H-tomentosin (1), xanthalongin (2), and linoleic acid (3), 8-hydroxy-9-isobutyryloxy-10(2)-methylbutyrylthymol (4), dehydrocostus lactone (5), alantolactone (6), costunolide (7), and isoalantolactone (8). Among them, 4H-tomentosin (1), xanthalongin (2), and linoleic acid (3) showed significantly inhibitory activities on sEH with half maximal inhibitory concentration (IC50) from 5.88 ± 0.97 μM to 11.63 ± 0.58 μM. The inhibition kinetics suggested that 4H-tomentosin (1) and xanthalongin (2) were mixed-competitive type inhibitors with inhibition constant (Ki) values of 7.02 and 6.57 μM, respectively, and linoleic acid (3) was a competitive type inhibitor with a Ki values of 3.52 μM. The potential interactions of 4H-tomentosin (1), xanthalongin (2), and linoleic acid (3) with sEH were analyzed by molecular docking, which indicated that these bioactive compounds had interactions with key amino acid residues Tyr343, Ile363, Tyr383, and His524.

Role of Soluble Epoxide Hydrolase in Metabolism of PUFAs in Psychiatric and Neurological Disorders

Inflammation plays a key role in the pathogenesis of a number of psychiatric and neurological disorders. Soluble epoxide hydrolases (sEH), enzymes present in all living organisms, metabolize epoxy fatty acids (EpFAs) to corresponding 1,2-diols by the addition of a molecule of water. Accumulating evidence suggests that sEH in the metabolism of polyunsaturated fatty acids (PUFAs) plays a key role in inflammation. Preclinical studies demonstrated that protein expression of sEH in the prefrontal cortex, striatum, and hippocampus from mice with depression-like phenotype was higher than control mice. Furthermore, protein expression of sEH in the parietal cortex from patients with major depressive disorder was higher than controls. Interestingly, Ephx2 knock-out (KO) mice exhibit stress resilience after chronic social defeat stress. Furthermore, the sEH inhibitors have antidepressant effects in animal models of depression. In addition, pharmacological inhibition or gene KO of sEH protected against dopaminergic neurotoxicity in the striatum after repeated administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in an animal model of Parkinson’s disease (PD). Protein expression of sEH in the striatum from MPTP-treated mice was higher than control mice. A number of studies using postmortem brain samples showed that the deposition of protein aggregates of α-synuclein, termed Lewy bodies, is evident in multiple brain regions of patients from PD and dementia with Lewy bodies (DLB). Moreover, the expression of the sEH protein in the striatum from patients with DLB was significantly higher compared with controls. Interestingly, there was a positive correlation between sEH expression and the ratio of phosphorylated α-synuclein to α-synuclein in the striatum. In the review, the author discusses the role of sEH in the metabolism of PUFAs in inflammation-related psychiatric and neurological disorders.

Occurrence of urea-based soluble epoxide hydrolase inhibitors from the plants in the order Brassicales

Recently, dibenzylurea-based potent soluble epoxide hydrolase (sEH) inhibitors were identified in Pentadiplandra brazzeana, a plant in the order Brassicales. In an effort to generalize the concept, we hypothesized that plants that produce benzyl glucosinolates and corresponding isothiocyanates also produce these dibenzylurea derivatives. Our overall aim here was to examine the occurrence of urea derivatives in Brassicales, hoping to find biologically active urea derivatives from plants. First, plants in the order Brassicales were analyzed for the presence of 1, 3-dibenzylurea (compound 1), showing that three additional plants in the order Brassicales produce the urea derivatives. Based on the hypothesis, three dibenzylurea derivatives with sEH inhibitory activity were isolated from maca (Lepidium meyenii) roots. Topical application of one of the identified compounds (compound 3, human sEH IC₅₀ = 222 nM) effectively reduced pain in rat inflammatory pain model, and this compound was bioavailable after oral administration in mice. The biosynthetic pathway of these urea derivatives was investigated using papaya (Carica papaya) seed as a model system. Finally, a small collection of plants from the Brassicales order was grown, collected, extracted and screened for sEH inhibitory activity. Results show that several plants of the Brassicales order could be potential sources of urea-based sEH inhibitors.

Screening of soluble epoxide hydrolase inhibitory ingredients from traditional Chinese medicines for anti-inflammatory use

ETHNOPHARMACOLOGICAL RELEVANCE

Inhibition of soluble epoxide hydrolase (sEH) has been extensively reported to be anti-inflammatory in multiple animal models. Some anti-inflammatory traditional Chinese medicines (TCMs) and a few natural compounds were also found to be inhibitory to sEH in vitro.

AIM OF THE STUDY

To determine whether the active intergradient (AI) against sEH of anti-inflammatory TCMs in vitro is anti-inflammatory in vivo and the sEH inhibitory action of the AI contributes to its anti-inflammatory effect in vivo.

MATERIALS AND METHODS

In vitro inhibition assay of the sEH was conducted for the methanol and ethanol extracts of 27 anti-inflammatory TCMs. Two potent extracts were subject to further separation guided by bioassay to afford promising AI against sEH in vitro [Fr.5 of the crude ethanol extract of Rhizoma coptidis (FFCERC)]. Finally, the in vivo anti-inflammatory effect and sEH inhibitory potency of FFCERC was evaluated in a lipopolysacchride (LPS)-challenged murine model of acute systemic inflammation. The inflammatory status was characterized by the inflammatory cytokines TNF-α and interleukin-6 (IL-6) and sEH inhibitory function was evaluated by the plasma levels of epoxyeicosantrienoic acids (EETs) and dihydroxyeicosatrienoic acids (DHETs), which are the sEH mediated substrates and products, respectively.

RESULTS

At the concentration of 25µg/mL, the crude ethanol extracts of 6 TCMs including Herba Asari, Radix Polygalae, Fructus Amomi, Radix Astragali, Radix Scutellariae, and Rhizoma Coptidis were potent against sEH. The crude extracts of Herba Asari and Rhizoma Coptidis were selected for further separation to afford FFCERC as the most promising AI for in vivo evaluation. Oral administration of FFCERC attenuated the significant increase in TNF-α and IL-6 caused by LPS challenge in a dose-dependent manner. In parallel, oral administration of FFCERC shifted the changes in plasma levels of EETs and DHETs caused by LPS-challenge like a synthetic sEH inhibitor.

CONCLUSIONS

A sEH inhibitory AI from Rhizoma Coptidis is anti-inflammatory and the inhibition of sEH contributes to this biological effect, indicating that sEH may be at least one of multiple therapeutic targets for relevant TCMs.

Identification, characterization, kinetics, and molecular docking of flavonoid constituents from Archidendron clypearia (Jack.) Nielsen leaves and twigs

In our search for natural soluble epoxide hydrolase (sEH) inhibitors from plants, we found that the methanolic extract of the leaves and twigs of Archidendron clypearia (Jack.) Nielsen (Fabaceae) significantly inhibits sEH in vitro. In a phytochemical investigation of the water layer of A. clypearia, we isolated two new chalcones, clypesides A-B (1-2), 13 flavonoid derivatives (3-15) and established their structures based on an extensive 1D and 2D NMR, CD data, and MS analysis. All of the flavonoid derivatives inhibited sEH enzymatic activity in a dose-dependent manner, with IC50 values ranging from 10.0±0.4 to 30.1±2.1μM. A kinetic analysis of compounds 4, 8-10, 12, 13, and 15 revealed that the compounds 8-10 were non-competitive, 4, 13, and 15 were mixed-type, and 12 was competitive inhibitors. Additionally, molecular docking increased our understanding of their receptor-ligand binding. These results demonstrated that flavonoid derivatives from A. clypearia are potential sEH inhibitors.

Discovery of enantioselectivity of urea inhibitors of soluble epoxide hydrolase

Soluble epoxide hydrolase (sEH) hydrolyzes epoxyeicosatrienoic acids (EETs) in the metabolic pathway of arachidonic acid and has been considered as an important therapeutic target for chronic diseases such as hypertension, diabetes and inflammation. Although many urea derivatives are known as sEH inhibitors, the enantioselectivity of the inhibitors is not highlighted in spite of the stereoselective hydrolysis of EETs by sEH. In an effort to explore the importance of enantioselectivity in the urea scaffold, a series of enantiomers with the stereocenter adjacent to the urea nitrogen atom were prepared. The selectivity of enantiomers of 1-(α-alkyl-α-phenylmethyl)-3-(3-phenylpropyl)ureas showed wide range differences up to 125 fold with the low IC50 value up to 13 nM. The S-configuration with planar phenyl and small alkyl groups at α-position is crucial for the activity and selectivity. However, restriction of the free rotation of two α-groups with indan-1-yl or 1,2,3,4-tetrahydronaphthalen-1-yl moiety abolishes the selectivity between the enantiomers, despite the increase in activity up to 13 nM. The hydrophilic group like sulfonamido group at para position of 3-phenylpropyl motif of 1-(α-alkyl-α-phenylmethyl-3-(3-phenylpropyl)urea improves the activity as well as enantiomeric selectivity. All these ureas are proved to be specific inhibitor of sEH without inhibition against mEH.

Soluble Epoxide Hydrolase Inhibitory Activity of Selaginellin Derivatives from Selaginella tamariscina

Selaginellin derivatives 1–3 isolated from Selaginellatamariscina were evaluated for their inhibition of soluble epoxide hydrolase (sEH) to demonstrate their potential for the treatment of cardiovascular disease. All selaginellin derivatives (1–3) inhibited sEH enzymatic activity and PHOME hydrolysis, in a dose-dependent manner, with IC₅₀ values of 3.1 ± 0.1, 8.2 ± 2.2, and 4.2 ± 0.2 μM, respectively. We further determined that the derivatives function as non-competitive inhibitors. Moreover, the predicted that binding sites and interaction between 1–3 and sEH were solved by docking simulations. According to quantitative analysis, 1–3 were confirmed to have high content in the roots of S. tamariscina; among them, selaginellin 3 exhibited the highest content of 189.3 ± 0.0 μg/g.

In vitro inhibitory effects of ethanol extract of Danshen (Salvia miltiorrhiza) and its components on the catalytic activity of soluble epoxide hydrolase

BACKGROUND

Soluble epoxide hydrolase (sEH) has been demonstrated to be a key enzyme involved in the pathologic development of several cardiovascular diseases and inflammation, and inhibition of sEH is therefore very helpful or crucial for the treatment of ischemia-reperfusion injury, cardiac hypertrophy, hypertension and inflammation. Danshen, the dried root of Salvia miltiorrhiza (Fam. Labiatae), has been used for the treatment of cardiovascular and cerebrovascular diseases in China and other countries for hundreds of years. Recent studies indicated that Danshen and its preparations also have potential for the management of inflammation. However, little information is available about the possibility of Danshen and its components on sEH inhibition.

PURPOSE AND METHODS

Danshen extracts and its constituents were tested for sEH inhibition using its physiological substrate, 8,9-EET, based on a LC-MS/MS assay in this study.

RESULTS

Among the tested 15 compounds, tanshinone IIA and cryptotanshinone were found to be the potent (Ki = 0.87 μM) and medium (Ki = 6.7 μM) mixed-type inhibitors of sEH, respectively. Salvianolic acid C (Ki = 8.6 μM) was proved to be a moderate noncompetitive sEH inhibitor. In consistent with the inhibition results of the pure compounds, the 75% ethanol extract of Danshen (EE, IC50 = 86.5 μg/ml) which contained more tanshinone IIA and cryptotanshinone exhibited more potent inhibition on sEH than the water extract (WE, IC50 > 200 μg/ml) or 1 M NaHCO3 (BE, IC50 > 200 μg/ml) extract.

CONCLUSION

These data indicated that using the ethanol fraction of Danshen and increasing the amounts of tanshinone IIA, cryptotanshinone and salvianolic acid C, especially the contents of tanshinone IIA in Danshen extract or preparations to enhance the inhibitory effects on sEH might be efficient ways to improve its cardiovascular protective and anti-inflammatory effects, and that herbal medicines could be an untapped reservoir for sEH-inhibition agents and developing sEH inhibitors from the cardiovascular protective and anti-inflammatory herbs is a promising approach.

Potent natural soluble epoxide hydrolase inhibitors from Pentadiplandra brazzeana baillon: synthesis, quantification, and measurement of biological activities in vitro and in vivo

We describe here three urea-based soluble epoxide hydrolase (sEH) inhibitors from the root of the plant Pentadiplandra brazzeana. The concentration of these ureas in the root was quantified by LC-MS/MS, showing that 1, 3-bis (4-methoxybenzyl) urea (MMU) is the most abundant (42.3 μg/g dry root weight). All of the ureas were chemically synthesized, and their inhibitory activity toward recombinant human and recombinant rat sEH was measured. The most potent compound, MMU, showed an IC₅₀ of 92 nM via fluorescent assay and a Ki of 54 nM via radioactivity-based assay on human sEH. MMU effectively reduced inflammatory pain in a rat nociceptive pain assay. These compounds are among the most potent sEH inhibitors derived from natural sources. Moreover, inhibition of sEH by these compounds may mechanistically explain some of the therapeutic effects of P. brazzeana.

Soluble epoxide hydrolase inhibitory activity of phenolic components from the rhizomes and roots of Gentiana scabra

Two new (1 and 2) and seven known phenolic compounds were isolated from a methanol extract of the rhizomes and roots of Gentiana scabra. Their structures were identified by spectroscopic analysis and comparing with reported values. The inhibitory effects of each compound on soluble epoxide hydrolase (sEH) were evaluated. Among them, compounds 2, 6, and 9 potently inhibited sEH activity.