Soluble epoxide hydrolase inhibitory components from Rheum undulatum and in silico approach

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.

Insights into the inhibitory activities of neolignans and diarylnonanoid derivatives from nutmeg (Myristica fragrans Houtt.) seeds on soluble epoxide hydrolase using in vitro and in silico approaches

Two new neolignans, myrifralignans F-G (14 and 18), four new diarylnonanoid derivatives, myrifragranones A-D (21-24), and 18 known compounds were isolated and structurally elucidated from nutmeg (Myristica fragrans Houtt.) seeds. The absolute configurations of these secondary metabolites were determined using the electronic circular dichroism technique. The inhibitory potential of these isolated compounds on soluble epoxide hydrolase (sEH) was investigated for the first time. Among them, malabaricones B and C (19 and 20) and four new compounds 21-24 displayed inhibitory activities against sEH, with IC50 values ranging from 14.24 to 46.35 µM. Additionally, the binding mechanism, key binding interactions, stability, and dynamic behaviour of the active compounds with the sEH enzyme were analysed using in silico molecular docking and dynamics simulations. Our findings suggest that nutmeg could become a promising natural source for discovering and developing new sEH inhibitors.

A Review on Rhubarb-Derived Substances as Modulators of Cardiovascular Risk Factors—A Special Emphasis on Anti-Obesity Action

The currently available anti-obesity therapies encounter many associated risks and side effects often causing the ineffectiveness of treatment. Therefore, various plant-derived substances have been extensively studied as a promising support or even an alternative for existing anti-obesity therapies. This review is dealing with the anti-obesity potential of edible and ethnomedicinal rhubarb species and emerging possible role of the rhubarb-derived extracts or individual compounds in the prevention of obesity and perspectives for their use in an anti-obesity treatment. A special emphasis is put on the most popular edible specimens, i.e., Rheum rhabarbarum L. (garden rhubarb) and Rheum rhaponticum L. (rhapontic rhubarb, Siberian rhubarb); however, the anti-obesity potential of other rhubarb species (e.g., R. officinale, R. palmatum, and R. emodi) is presented as well. The significance of rhubarb-derived extracts and low-molecular specialized rhubarb metabolites of diversified chemical background, e.g., anthraquinones and stilbenes, as potential modulators of human metabolism is highlighted, including the context of cardiovascular disease prevention. The available reports present multiple encouraging rhubarb properties starting from the anti-lipidemic action of rhubarb fibre or its use as purgative medicines, through various actions of rhubarb-derived extracts and their individual compounds: inhibition of enzymes of cholesterol and lipid metabolism, targeting of key molecular regulators of adipogenesis, regulators of cell energy metabolism, the ability to inhibit pro-inflammatory signalling pathways and to regulate glucose and lipid homeostasis contributing to overall in vivo and clinical anti-obesity effects.

Design, synthesis and mechanistic study of novel diarylpyrazole derivatives as anti-inflammatory agents with reduced cardiovascular side effects

Novel diarylpyrazole (5a-d, 6a-e, 12, 13, 14, 15a-c and 11a-g) derivatives were designed, synthesized and evaluated for their dual COX-2/sEH inhibitory activities via recombinant enzyme assays to explore their anti-inflammatory activities and cardiovascular safety profiles. Comprehensively, the structures of the synthesized compounds were established via spectral and elemental analyses, followed by the assessment of both their in vitro COX inhibitory and in vivo anti-inflammatory activities. The most active compounds as COX inhibitors were further evaluated for their in vitro 5-LOX and sEH inhibitory activities, alongside with their in vivo analgesic and ulcerogenic effects. Compounds 6d and 11f showed excellent inhibitory activities against both COX-2 and sEH (COX-2 IC₅₀ = 0.043 and 0.048 µM; sEH IC₅₀ = 83.58 and 83.52 μM, respectively). Moreover, the compounds demonstrated promising results as anti-inflammatory and analgesic agents with considerable ED₅₀ values and gastric safety profiles. Remarkably, the most active COX inhibitors 6d and 11f possessed improved cardiovascular safety profiles, if compared to celecoxib, as shown by the laboratory evaluation of both essential cardiac biochemical parameters (troponin-1, prostacyclin, tumor necrosis factor-α, lactate dehydrogenase, reduced glutathione and creatine kinase-M) and histopathological studies. On the other hand, docking simulations confirmed that the newly synthesized compounds displayed sufficient structural features required for binding to the target COX-2 and sEH enzymes. Also, in silico ADME studies prediction and drug-like properties of the compounds revealed favorable oral bioavailability results. Collectively, the present work could be featured as a promising future approach towards novel selective COX-2 inhibitors with declined cardiovascular risks.

Anti-obesity, antioxidant and in silico evaluation of Justicia carnea bioactive compounds as potential inhibitors of an enzyme linked with obesity: Insights from kinetics, semi-empirical quantum mechanics and molecular docking analysis

Obesity is a global health problem characterized by excessive fat deposition in adipose tissues and can be managed by targeting pancreatic lipase (PL) activity. In the present study, we investigated the in vitro antioxidant and anti-obesity potentials of methanolic leaf extract of Justicia carnea(MEJC) using lipase inhibition kinetics model. In silico evaluations of MEJC bioactive compounds as potential drug-like agents and inhibitors of PL were also investigated using SwissADME prediction tool, semi-empirical quantum mechanics(SQM), molecular electrostatic potential(MEP) and molecular docking analysis. Gas chromatography-mass spectrometry(GC-MS) revealed presence of campesterol, stigmasterol, beta-amyrin etc. MEJC scavenged reactive species and inhibited PL activity via a mixed inhibition pattern (K_i = 107.69 μg/mL; K_ii = 398.00 μg/mL) with IC₅₀ > orlistat's IC₅₀. Molecular docking of GC-MS identified compounds with porcine PL showed compounds 8,10,12 and 14 having high PL-binding affinity and similar binding pose with orlistat. Hydrophobic interactions and van der Waals forces were predominantly involved in the ligands' interactions with some key catalytic site amino acid residues (Ser-153,His-264). Compounds 10,12,13 and 14 indicated high drug-likeness, bioavailability, electronegativity, E_LUMO-E_HOMO energy gaps and MEP. Our findings show that MEJC is a rich natural source of antioxidant and anti-obesity agents which could be optimized for development of new anti-obesity drugs.

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.

N-Benzyl-linoleamide, a Constituent of Lepidium meyenii (Maca), Is an Orally Bioavailable Soluble Epoxide Hydrolase Inhibitor That Alleviates Inflammatory Pain

Lepidium meyenii (maca), a plant indigenous to the Peruvian Andes, recently has been utilized globally for claimed health or recreational benefits. The search for natural products that inhibit soluble epoxide hydrolase (sEH), with therapeutically relevant potencies and concentrations, led to the present study on bioactive amide secondary metabolites found in L. meyenii, the macamides. Based on known and suspected macamides, 19 possible macamides were synthesized and characterized. The majority of these amides displayed excellent inhibitory potency (IC50 ≈ 20-300 nM) toward the recombinant mouse, rat, and human sEH. Quantitative analysis of commercial maca products revealed that certain products contain known macamides (1-5, 8-12) at therapeutically relevant total concentrations (≥3.29 mg/g of root), while the inhibitory potency of L. meyenii extracts directly correlates with the sum of concentration/IC50 ratios of macamides present. Considering both its in vitro efficacy and high abundance in commercial products, N-benzyl-linoleamide (4) was identified as a particularly relevant macamide that can be utilized for in vivo studies. Following oral administration in the rat, compound 4 not only displayed acceptable pharmacokinetic characteristics but effectively reduced lipopolysaccharide-induced inflammatory pain. Inhibition of sEH by macamides provides a plausible biological mechanism of action to account for several beneficial effects previously observed with L. meyenii treatments.

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.

Tetra-aryl cyclobutane and stilbenes from the rhizomes of Rheum undulatum and their α-glucosidase inhibitory activity: Biological evaluation, kinetic analysis, and molecular docking simulation

One achiral tetra-aryl cyclobutane [rheundulin A (1)] and three stilbene glycosides [rheundulins B-D (2-4)] were isolated from the methanol extract of Rheum undulatum L., along with eight known compounds (5-12). Structural determination of the new compounds (1-4) was accomplished using comprehensive spectroscopic methods. Compound 1 represents the first example of a dimeric stilbene linked via a cyclobutane ring from the Rheum genus. All isolates were screened for their inhibition against α-glucosidase. Among them, stilbene derivatives (5 and 6) showed strong inhibitory effects on α-glucosidase with IC₅₀ values of 0.5 and 15.4 µM, respectively, which were significantly higher than that of the positive control, acarbose (IC₅₀ = 126.8 µM). Rheundulin A (1) showed moderate α-glucosidase inhibition with an IC₅₀ value of 80.1 µM. In addition, kinetic analysis and molecular docking simulation of the most active compound (5) with α-glucosidase were performed for the first time. Kinetic studies revealed that compound 5 competitively inhibited the active site of α-glucosidase (K_i = 0.40 µM), while 6 had a mixed-type inhibitory effect against α-glucosidase (K_i = 15.34 µM). Molecular docking simulations of 5 and 6 demonstrated negative-binding energies, indicating high proximity to the active site and tight binding to α-glucosidase enzyme.

Kushenol A and 8-prenylkaempferol, tyrosinase inhibitors, derived from Sophora flavescens

Tyrosinase is known for an enzyme that plays a key role in producing the initial precursor of melanin biosynthesis. Inhibition of the catalytic reaction of this enzyme led to some advantage such as skin-whitening and anti-insect agents. To find a natural compound with inhibitory activity towards tyrosinase, the five flavonoids of kushenol A (1), 8-prenylkaempferol (2), kushenol C (3), formononetin (4) and 8-prenylnaringenin (5) were isolated by column chromatography from a 95% methanol extract of Sophora flavescens. The ability of these flavonoids to block the conversion of L-tyrosine to L-DOPA by tyrosinase was tested in vitro. Compounds 1 and 2 exhibited potent inhibitory activity, with IC50 values less than 10 µM. Furthermore, enzyme kinetics and molecular docking analysis revealed the formation of a binary encounter complex between compounds 1–4 and the enzyme. Also, all of the isolated compounds (1–5) were confirmed to possess antioxidant activity.

Tyrosinase inhibitory components from the seeds of Cassia tora

Ten compounds (1-10) isolated from the seeds of Cassia tora were evaluated for tyrosinase inhibition. Compounds 3, 4, and 7 inhibited tyrosinase enzymatic activity in a dose-dependent manner, with IC₅₀ values of 3.0 ± 0.8, 7.0 ± 0.4, and 9.2 ± 3.4 μM, respectively. Kinetic analyses revealed a mechanism consistent with competitive inhibition. In silico molecular docking showed that compounds 3 and 4 docked in the active site of tyrosinase, whereas 7 interacted with Ala246 and Val248 at outside of the active site, and His244 and Glu256 at inside. Additionally, compounds 3, 4, and 7 suppressed melanogenesis in α-MSH-treated B16F10 melanoma cells at a concentration of 10 μM.

Soluble Epoxide Hydrolase Inhibitory Activity of Components Isolated from Apios americana Medik

A new compound 1, 5-methoxy-2,5,7,4′-tetrahydroxy-coumaronochromone, along with seven known compounds (2–8), were isolated from Apios americana using open column chromatography. Their structures were established based on an analysis of 1D and 2D NMR, and MS spectra. Among these, two compounds 1 and 2 showed inhibitory activity on soluble epoxide hydrolase (sEH) at a concentration below 50 μM. The respective competitive (1) and mixed (2) inhibitors were revealed to have K_i values of 21.0 ± 0.8 and 14.5 ± 1.5 μM, based on the Dixon plot. The potential inhibitor (2) was visually presented in a predicted binding pose in the receptor by molecular docking. Additionally, molecular dynamics were performed for a detailed understanding of their complex by Gromacs 4.6.5 package.