Enhancing cancer immunotherapy via inhibition of soluble epoxide hydrolase.

Cancer therapy, including immunotherapy, is inherently limited by chronic inflammation-induced tumorigenesis and toxicity within the tumor microenvironment. Thus, stimulating the resolution of inflammation may enhance immunotherapy and improve the toxicity of immune checkpoint inhibition (ICI). As epoxy-fatty acids (EpFAs) are degraded by the enzyme soluble epoxide hydrolase (sEH), the inhibition of sEH increases endogenous EpFA levels to promote the resolution of cancer-associated inflammation. Here, we demonstrate that systemic treatment with ICI induces sEH expression in multiple murine cancer models. Dietary omega-3 polyunsaturated fatty acid supplementation and pharmacologic sEH inhibition, both alone and in combination, significantly enhance anti-tumor activity of ICI in these models. Notably, pharmacological abrogation of the sEH pathway alone or in combination with ICI counter-regulates an ICI-induced pro-inflammatory and pro-tumorigenic cytokine storm. Thus, modulating endogenous EpFA levels through dietary supplementation or sEH inhibition may represent a unique strategy to enhance the anti-tumor activity of paradigm cancer therapies.

Enhancement of the liver's neuroprotective role ameliorates traumatic brain injury pathology.

Traumatic brain injury (TBI) is a pervasive problem worldwide for which no effective treatment is currently available. Although most studies have focused on the pathology of the injured brain, we have noted that the liver plays an important role in TBI. Using two mouse models of TBI, we found that the enzymatic activity of hepatic soluble epoxide hydrolase (sEH) was rapidly decreased and then returned to normal levels following TBI, whereas such changes were not observed in the kidney, heart, spleen, or lung. Interestingly, genetic downregulation of hepatic Ephx2 (which encodes sEH) ameliorates TBI-induced neurological deficits and promotes neurological function recovery, whereas overexpression of hepatic sEH exacerbates TBI-associated neurological impairments. Furthermore, hepatic sEH ablation was found to promote the generation of A2 phenotype astrocytes and facilitate the production of various neuroprotective factors associated with astrocytes following TBI. We also observed an inverted V-shaped alteration in the plasma levels of four EET (epoxyeicosatrienoic acid) isoforms (5,6-, 8,9-,11,12-, and 14,15-EET) following TBI which were negatively correlated with hepatic sEH activity. However, hepatic sEH manipulation bidirectionally regulates the plasma levels of 14,15-EET, which rapidly crosses the blood-brain barrier. Additionally, we found that the application of 14,15-EET mimicked the neuroprotective effect of hepatic sEH ablation, while 14,15-epoxyeicosa-5(Z)-enoic acid blocked this effect, indicating that the increased plasma levels of 14,15-EET mediated the neuroprotective effect observed after hepatic sEH ablation. These results highlight the neuroprotective role of the liver in TBI and suggest that targeting hepatic EET signaling could represent a promising therapeutic strategy for treating TBI.

Robust ring-opening reaction via asymmetrically coordinated Fe single atoms scaffolded by spoke-like mesoporous carbon nanospheres.

The ability to construct metal single-atom catalysts (SACs) asymmetrically coordinated with organic heteroatoms represents an important endeavor toward developing high-performance catalysts over symmetrically coordinated counterparts. Moreover, it is of key importance in creating supporting matrix with porous architecture for situating SACs as it greatly impacts the mass diffusion and transport of electrolyte. Herein, we report the crafting of Fe single atoms with asymmetrically coordinated nitrogen (N) and phosphorus (P) atoms scaffolded by rationally designed mesoporous carbon nanospheres (MCNs) with spoke-like nanochannels for boosting ring-opening reaction of epoxide to produce an array of pharmacologically important ß-amino alcohols. Notably, interfacial defects in MCN derived from the use of sacrificial template create abundant unpaired electrons, thereby stably anchoring N and P atoms and in turn Fe atoms on MCN. Importantly, the introduction of P atom promotes the symmetry-breaking of common four N-coordinated Fe sites, resulting in the Fe-N3P sites on MCN (denoted Fe-N3P-MCN) with an asymmetric electronic configuration and thus superior catalytic capability. As such, the Fe-N3P-MCN catalysts manifest a high catalytic activity for ring-opening reaction of epoxide (97% yield) over the Fe-N3P docked on nonporous carbon surface (91%) as well as the sole Fe-N4 SACs grounded on the same MCN support (89%). Density functional theory calculations reveal that Fe-N3P SAC lowers the activation barrier for the C-O bond cleavage and the C-N bond formation, thus accelerating the ring-opening of epoxide. Our study provides fundamental and practical insights into developing advanced catalysts in a simple and controllable manner for multistep organic reactions.

Deciphering the stereo-specific catalytic mechanisms of cis-epoxysuccinate hydrolases producing L(+)-tartaric acid.

Microbial epoxide hydrolases, cis-epoxysuccinate hydrolases (CESHs), have been utilized for commercial production of enantiomerically pure L(+)- and D(-)-tartaric acids for decades. However, the stereo-catalytic mechanism of CESH producing L(+)-tartaric acid (CESH[L]) remains unclear. Herein, the crystal structures of two CESH[L]s in ligand-free, product-complexed, and catalytic intermediate forms were determined. These structures revealed the unique specific binding mode for the mirror-symmetric substrate, an active catalytic triad consisting of Asp-His-Glu, and an arginine providing a proton to the oxirane oxygen to facilitate the epoxide ring-opening reaction, which has been pursued for decades. These results provide the structural basis for the rational engineering of these industrial biocatalysts.

Effects of sEH inhibition on the eicosanoid and cytokine storms in SARS-CoV-2-infected mice.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection involves an initial viral infection phase followed by a host-response phase that includes an eicosanoid and cytokine storm, lung inflammation and respiratory failure. While vaccination and early anti-viral therapies are effective in preventing or limiting the pathogenic host response, this latter phase is poorly understood with no highly effective treatment options. Inhibitors of soluble epoxide hydrolase (sEH) increase levels of anti-inflammatory molecules called epoxyeicosatrienoic acids (EETs). This study aimed to investigate the impact of sEH inhibition on the host response to SARS-CoV-2 infection in a mouse model with human angiotensin-converting enzyme 2 (ACE2) expression. Mice were infected with SARS-CoV-2 and treated with either vehicle or the sEH inhibitor 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU). At day 5 post-infection, SARS-CoV-2 induced weight loss, clinical signs, a cytokine storm, an eicosanoid storm, and severe lung inflammation with ~50% mortality on days 6-8 post-infection. SARS-CoV-2 infection induced lung expression of phospholipase A2 (PLA2), cyclooxygenase (COX) and lipoxygenase (LOX) pathway genes, while suppressing expression of most cytochrome P450 genes. Treatment with the sEH inhibitor TPPU delayed weight loss but did not alter clinical signs, lung cytokine expression or overall survival of infected mice. Interestingly, TPPU treatment significantly reversed the eicosanoid storm and attenuated viral-induced elevation of 39 fatty acids and oxylipins from COX, LOX and P450 pathways, which suggests the effects at the level of PLA2 activation. The suppression of the eicosanoid storm by TPPU without corresponding changes in lung cytokines, lung inflammation or mortality reveals a surprising dissociation between systemic oxylipin and cytokine signaling pathways during SARS-CoV-2 infection and suggests that the cytokine storm is primarily responsible for morbidity and mortality in this animal model.

Linoleic acid-derived diol 12,13-DiHOME enhances NLRP3 inflammasome activation in macrophages.

12,13-dihydroxy-9z-octadecenoic acid (12,13-DiHOME) is a linoleic acid diol derived from cytochrome P-450 (CYP) epoxygenase and epoxide hydrolase (EH) metabolism. 12,13-DiHOME is associated with inflammation and mitochondrial damage in the innate immune response, but how 12,13-DiHOME contributes to these effects is unclear. We hypothesized that 12,13-DiHOME enhances macrophage inflammation through effects on NOD-like receptor protein 3 (NLRP3) inflammasome activation. To test this hypothesis, we utilized human monocytic THP1 cells differentiated into macrophage-like cells with phorbol myristate acetate (PMA). 12,13-DiHOME present during lipopolysaccharide (LPS)-priming of THP1 macrophages exacerbated nigericin-induced NLRP3 inflammasome activation. Using high-resolution respirometry, we observed that priming with LPS+12,13-DiHOME altered mitochondrial respiratory function. Mitophagy, measured using mito-Keima, was also modulated by 12,13-DiHOME present during priming. These mitochondrial effects were associated with increased sensitivity to nigericin-induced mitochondrial depolarization and reactive oxygen species production in LPS+12,13-DiHOME-primed macrophages. Nigericin-induced mitochondrial damage and NLRP3 inflammasome activation in LPS+12,13-DiHOME-primed macrophages were ablated by the mitochondrial calcium uniporter (MCU) inhibitor, Ru265. 12,13-DiHOME present during LPS-priming also enhanced nigericin-induced NLRP3 inflammasome activation in primary murine bone marrow-derived macrophages. In summary, these data demonstrate a pro-inflammatory role for 12,13-DiHOME by enhancing NLRP3 inflammasome activation in macrophages.

Epoxyeicosatrienoic Acids Prevent Cardiac Dysfunction in Viral Myocarditis via Interferon Type I Signaling.

Myocarditis is a challenging inflammatory disease of the heart, and better understanding of its pathogenesis is needed to develop specific drug therapies. Epoxyeicosatrienoic acids (EETs), active molecules synthesized by CYP (cytochrome P450) enzymes from arachidonic acids and hydrolyzed to less active dihydroxyeicosatrienoic acids by sEH (soluble epoxide hydrolase), have been attributed anti-inflammatory activity. Here, we investigated whether EETs have immunomodulatory activity and exert protective effects on coxsackie B3 virus-induced myocarditis. Viral infection altered eicosanoid epoxide and diol levels in both patients with myocarditis and in the murine heart and correlated with the increased expression and activity of sEH after coxsackie B3 virus infection. Administration of a sEH inhibitor prevented coxsackie B3 virus-induced cardiac dysfunction and inflammatory infiltration. Importantly, EET/sEH inhibitor treatment attenuated viral infection or improved viral resistance by activating type I IFN (interferon) signaling. At the molecular level, EETs enhanced the interaction between GSK3ß (glycogen synthase kinase-3 beta) and TBK1 (TANK-binding kinase 1) to promote IFN-ß production. Our findings revealed that EETs and sEH inhibitors prevent the progress of coxsackie B3 virus-induced myocarditis, particularly by promoting viral resistance by increasing IFN production.

sEH-derived metabolites of linoleic acid drive pathologic inflammation while impairing key innate immune cell function in burn injury.

Fatty acid composition in the Western diet has shifted from saturated to polyunsaturated fatty acids (PUFAs), and specifically to linoleic acid (LA, 18:2), which has gradually increased in the diet over the past 50 y to become the most abundant dietary fatty acid in human adipose tissue. PUFA-derived oxylipins regulate a variety of biological functions. The cytochrome P450 (CYP450)­formed epoxy fatty acid metabolites of LA (EpOMEs) are hydrolyzed by the soluble epoxide hydrolase enzyme (sEH) to dihydroxyoctadecenoic acids (DiHOMEs). DiHOMEs are considered cardioprotective at low concentrations but at higher levels have been implicated as vascular permeability and cytotoxic agents and are associated with acute respiratory distress syndrome in severe COVID-19 patients. High EpOME levels have also correlated with sepsis-related fatalities; however, those studies failed to monitor DiHOME levels. Considering the overlap of burn pathophysiology with these pathologies, the role of DiHOMEs in the immune response to burn injury was investigated. 12,13-DiHOME was found to facilitate the maturation and activation of stimulated neutrophils, while impeding monocyte and macrophage functionality and cytokine generation. In addition, DiHOME serum concentrations were significantly elevated in burn-injured mice and these increases were ablated by administration of 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), a sEH inhibitor. TPPU also reduced necrosis of innate and adaptive immune cells in burned mice, in a dose-dependent manner. The findings suggest DiHOMEs are a key driver of immune cell dysfunction in severe burn injury through hyperinflammatory neutrophilic and impaired monocytic actions, and inhibition of sEH might be a promising therapeutic strategy to mitigate deleterious outcomes in burn patients.

Kurarinone alleviated Parkinson's disease via stabilization of epoxyeicosatrienoic acids in animal model.

Parkinson's disease (PD) is one of the most common neurodegenerative disorders and is characterized by loss of dopaminergic neurons in the substantia nigra (SN), causing bradykinesia and rest tremors. Although the molecular mechanism of PD is still not fully understood, neuroinflammation has a key role in the damage of dopaminergic neurons. Herein, we found that kurarinone, a unique natural product from Sophora flavescens, alleviated the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced behavioral deficits and dopaminergic neurotoxicity, including the losses of neurotransmitters and tyrosine hydroxylase (TH)-positive cells (SN and striatum [STR]). Furthermore, kurarinone attenuated the MPTP-mediated neuroinflammation via suppressing the activation of microglia involved in the nuclear factor kappa B signaling pathway. The proteomics result of the solvent-induced protein precipitation and thermal proteome profiling suggest that the soluble epoxide hydrolase (sEH) enzyme, which is associated with the neuroinflammation of PD, is a promising target of kurarinone. This is supported by the increase of plasma epoxyeicosatrienoic acids (sEH substrates) and the decrease of dihydroxyeicosatrienoic acids (sEH products), and the results of in vitro inhibition kinetics, surface plasmon resonance, and cocrystallization of kurarinone with sEH revealed that this natural compound is an uncompetitive inhibitor. In addition, sEH knockout (KO) attenuated the progression of PD, and sEH KO plus kurarinone did not further reduce the protection of PD in MPTP-induced PD mice. These findings suggest that kurarinone could be a potential natural candidate for the treatment of PD, possibly through sEH inhibition.

Disruption of Ephx2 in cardiomyocytes but not endothelial cells improves functional recovery after ischemia-reperfusion in isolated mouse hearts.

Cytochromes P450 metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs) which have numerous effects. After cardiac ischemia, EET-induced coronary vasodilation increases delivery of oxygen/nutrients to the myocardium, and EET-induced signaling protects cardiomyocytes against postischemic mitochondrial damage. Soluble epoxide hydrolase 2 (EPHX2) diminishes the benefits of EETs through hydrolysis to less active dihydroxyeicosatrienoic acids. EPHX2 inhibition or genetic disruption improves recovery of cardiac function after ischemia. Immunohistochemical staining revealed EPHX2 expression in cardiomyocytes and some endothelial cells but little expression in cardiac smooth muscle cells or fibroblasts. To determine specific roles of EPHX2 in cardiac cell types, we generated mice with cell-specific disruption of Ephx2 in endothelial cells (Ephx2fx/fx/Tek-cre) or cardiomyocytes (Ephx2fx/fx/Myh6-cre) to compare to global Ephx2-deficient mice (global Ephx2-/-) and WT (Ephx2fx/fx) mice in expression, EET hydrolase activity, and heart function studies. Most cardiac EPHX2 expression and activity is in cardiomyocytes with substantially less activity in endothelial cells. Ephx2fx/fx/Tek-cre hearts have similar EPHX2 expression, hydrolase activity, and postischemic cardiac function as control Ephx2fx/fx hearts. However, Ephx2fx/fx/Myh6-cre hearts were similar to global Ephx2-/- hearts with significantly diminished EPHX2 expression, decreased hydrolase activity, and enhanced postischemic cardiac function compared to Ephx2fx/fx hearts. During reperfusion, Ephx2fx/fx/Myh6-cre hearts displayed increased ERK activation compared to Ephx2fx/fx hearts, which could be reversed by EEZE treatment. EPHX2 did not regulate coronary vasodilation in this model. We conclude that EPHX2 is primarily expressed in cardiomyocytes where it regulates EET hydrolysis and postischemic cardiac function, whereas endothelial EPHX2 does not play a significant role in these processes.

Salt-sensitive hypertension in GR mutant rats is associated with altered plasma polyunsaturated fatty acid levels and aortic vascular reactivity.

In humans, glucocorticoid resistance is attributed to mutations in the glucocorticoid receptor (GR). Most of these mutations result in decreased ligand binding, transactivation, and/or translocation, albeit with normal protein abundances. However, there is no clear genotype‒phenotype relationship between the severity or age at disease presentation and the degree of functional loss of the receptor. Previously, we documented that a GR+/- rat line developed clinical features of glucocorticoid resistance, namely, hypercortisolemia, adrenal hyperplasia, and salt-sensitive hypertension. In this study, we analyzed the GR+/em4 rat model heterozygously mutant for the deletion of exon 3, which encompasses the second zinc finger, including the domains of DNA binding, dimerization, and nuclear localization signals. On a standard diet, mutant rats exhibited a trend toward increased corticosterone levels and a normal systolic blood pressure and heart rate but presented with adrenal hyperplasia. They exhibited increased adrenal soluble epoxide hydroxylase (sEH), favoring an increase in less active polyunsaturated fatty acids. Indeed, a significant increase in nonactive omega-3 and omega-6 polyunsaturated fatty acids, such as 5(6)-DiHETrE or 9(10)-DiHOME, was observed with advanced age (10 versus 5 weeks old) and following a switch to a high-salt diet accompanied by salt-sensitive hypertension. In thoracic aortas, a reduced soluble epoxide hydrolase (sEH) protein abundance resulted in altered vascular reactivity upon a standard diet, which was blunted upon a high-salt diet. In conclusion, mutations in the GR affecting the ligand-binding domain as well as the dimerization domain resulted in deregulated GR signaling, favoring salt-sensitive hypertension in the absence of obvious mineralocorticoid excess.

Arachidonic acid metabolism regulates the development of retinopathy of prematurity among preterm infants.

Extremely preterm infants are at risk of developing retinopathy of prematurity (ROP), characterized by neovascularization and neuroinflammation leading to blindness. Polyunsaturated fatty acid (PUFA) supplementation is recommended in preterm infants to lower the risk of ROP, however, with no significant improvement in visual acuity. Reasonably, this could be as a result of the non-consideration of PUFA metabolizing enzymes. We hypothesize that abnormal metabolism of the arachidonic acid (AA) pathway may contribute to severe stages of ROP. The present study investigated the AA-metabolizing enzymes in ROP pathogenesis by a targeted gene expression analysis of blood (severe ROP = 70, No/Mild = 56), placenta (preterm placenta = 6, full term placenta = 3), and human primary retinal cell cultures and further confirmed at the protein level by performing IHC in sections of ROP retina. The lipid metabolites were identified by LC-MS in the vitreous humor (VH; severe ROP = 15, control = 15). Prostaglandins D2 (p = 0.02), leukotrienes B5 (p = 0.0001), 11,12-epoxyeicosatrienoic acid (p = 0.01), and lipid-metabolizing enzymes of the AA pathway such as CYP1B1, CYP2C8, COX2, and ALOX15 were significantly upregulated while EPHX2 was significantly (0.04) downregulated in ROP cases. Genes involved in hypoxic stress, angiogenesis, and apoptosis showed increased expression in ROP. An increase in the metabolic intermediates generated from the AA metabolism pathway further confirmed the role of these enzymes in ROP, while metabolites for EPHX2 activity were low in abundance. Inflammatory lipid intermediates were higher compared to anti-inflammatory lipids in VH and showed an association with enzyme activity. Both the placenta of preterm infants who developed ROP and hypoxic retinal cultures showed a reduced expression of EPHX2. These findings suggested a strong involvement of EPHX2 in regulating retinal neovascularization and inflammation. The study results underscore the role of arachidonic acid metabolism in the development of ROP and as a potential target for preventing vision loss among preterm-born infants.

Role of soluble epoxide hydrolase in pain and depression comorbidity.

The coexistence of chronic pain and depression in clinical practice places a substantial social burden and profoundly impacts in patients. Although a clear correlation exists, the underlying mechanism of comorbidity between chronic pain and depression remains elusive. Research conducted in recent decades has uncovered that soluble epoxide hydrolase, a pivotal enzyme in the metabolism of polyunsaturated fatty acids, plays a crucial role in inflammation. Interestingly, this enzyme is intricately linked to the development of both pain and depression. With this understanding, this review aims to summarize the roles of soluble epoxide hydrolase in pain, depression, and their comorbidity. Simultaneously, we will also explore the underlying mechanisms, providing guidance for future research and drug development.

Cardioprotective response and senescence in aged sEH null female mice exposed to LPS.

Deterioration of physiological systems, like the cardiovascular system, occurs progressively with age impacting an individual's health and increasing susceptibility to injury and disease. Cellular senescence has an underlying role in age-related alterations and can be triggered by natural aging or prematurely by stressors such as the bacterial toxin lipopolysaccharide (LPS). The metabolism of polyunsaturated fatty acids by CYP450 enzymes produces numerous bioactive lipid mediators that can be further metabolized by soluble epoxide hydrolase (sEH) into diol metabolites, often with reduced biological effects. In our study, we observed age-related cardiac differences in female mice, where young mice demonstrated resistance to LPS injury, and genetic deletion or pharmacological inhibition of sEH using trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid attenuated LPS-induced cardiac dysfunction in aged female mice. Bulk RNA-sequencing analyses revealed transcriptomics differences in aged female hearts. The confirmatory analysis demonstrated changes to inflammatory and senescence gene markers such as Il-6, Mcp1, Il-1ß, Nlrp3, p21, p16, SA-ß-gal, and Gdf15 were attenuated in the hearts of aged female mice where sEH was deleted or inhibited. Collectively, these findings highlight the role of sEH in modulating the aging process of the heart, whereby targeting sEH is cardioprotective.NEW & NOTEWORTHY Soluble epoxide hydrolase (sEH) is an essential enzyme for converting epoxy fatty acids to their less bioactive diols. Our study suggests deletion or inhibition of sEH impacts the aging process in the hearts of female mice resulting in cardioprotection. Data indicate targeting sEH limits inflammation, preserves mitochondria, and alters cellular senescence in the aged female heart.

Crystal structure of an antibody specifically recognizing 3,4-methyl enedioxy methamphetamine through the epoxide moiety.

3,4-methylenedioxymethamphetamine (MDMA) or publicly known as "ecstasy" is a drug abuse substance. Since antibodies that detect MDMA typically also recognize its chemical analogue, methamphetamine (METH), we identified antibodies specifically recognizing MDMA, but not METH, named 1bB11 and 1bF12, using phage display. The crystal structure of 1bB11 in complex with MDMA was determined at 3.2 Å resolution. Key interactions were found between the epoxide moiety of MDMA and S34 and Y36 of the light chain. Additional interaction with E33 of the heavy chain contributes to anchoring MDMA. Mutagenesis-based biochemical analysis confirmed the importance of these residues in MDMA binding. Comparing the structure of 1bB11 to a scFv6H4, which binds both METH and MDMA, revealed opposite binding orientations. Taken together, our data provides a structural framework for selective binding to MDMA by the 1bB11 antibody, paving a way to develop a highly specific antibody for diagnosis.

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.

Structure of epoxide hydrolase 2 from Mangifera indica throws light on the substrate specificity determinants of plant epoxide hydrolases.

Epoxide hydrolases (EHs) are a group of ubiquitous enzymes that catalyze hydrolysis of chemically reactive epoxides to yield corresponding dihydrodiols. Despite extensive studies on EHs from different clades, generic rules governing their substrate specificity determinants have remained elusive. Here, we present structural, biochemical and molecular dynamics simulation studies on MiEH2, a plant epoxide hydrolase from Mangifera indica. Comparative structure-function analysis of nine homologs of MiEH2, which include a few AlphaFold structural models, show that the two conserved tyrosines (MiEH2Y152 and MiEH2Y232) from the lid domain dissect substrate binding tunnel into two halves, forming substrate-binding-pocket one (BP1) and two (BP2). This compartmentalization offers diverse binding modes to their substrates, as exemplified by the binding of smaller aromatic substrates, such as styrene oxide (SO). Docking and molecular dynamics simulations reveal that the linear epoxy fatty acid substrates predominantly occupy BP1, while the aromatic substrates can bind to either BP1 or BP2. Furthermore, SO preferentially binds to BP2, by stacking against catalytically important histidine (MiEH2H297) with the conserved lid tyrosines engaging its epoxide oxygen. Residue (MiEH2L263) next to the catalytic aspartate (MiEH2D262) modulates substrate binding modes. Thus, the divergent binding modes correlate with the differential affinities of the EHs for their substrates. Furthermore, long-range dynamical coupling between the lid and core domains critically influences substrate enantioselectivity in plant EHs.

Epoxide-Mediated Trans-Thioglycosylation and Application to the Synthesis of Oligosaccharides Related to the Capsular Polysaccharides of C. jejuni HS:4.

The enzyme-resistant thioglycosides are highly valuable immunogens because of their enhanced metabolic stability. We report the first synthesis of a family of thiooligosaccharides related to the capsular polysaccharides (CPS) of Campylobacter jejuni HS:4 for potential use in conjugate vaccines. The native CPS structures of the pathogen consist of a challenging repeating disaccharide formed with ß(1→4)-linked 6-deoxy-ß-D-ido-heptopyranoside and N-acetyl-D-glucosamine; the rare 6-deoxy-ido-heptopyranosyl backbone and ß-anomeric configuration of the former monosaccharide makes the synthesis of this family of antigens very challenging. So far, no synthesis of the thioanalogs of the CPS antigens have been reported. The unprecedented synthesis presented in this work is built on an elegant approach by using ß-glycosylthiolate as a glycosyl donor to open the 2,3-epoxide functionality of pre-designed 6-deoxy-ß-D-talo-heptopyranosides. Our results illustrated that this key trans-thioglycosylation can be designed in a modular and regio and stereo-selective manner. Built on the success of this novel approach, we succeeded the synthesis of a family of thiooligosaccharides including a thiohexasaccharide which is considered to be the desired antigen length and complexity for immunizations. We also report the first direct conversion of base-stable but acid-labile 2-trimethylsilylethyl glycosides to glycosyl-1-thioacetates in a one-pot manner.

Catalytic Epoxidation of Carbonyl Compounds via Carbonyl Ylides: from Racemic to Enantioselective.

Transition metal-catalyzed epoxidation of carbonyl compounds through carbonyl ylides represents a highly effective method for synthesizing a diverse range of valuable epoxides. This review offers an in-depth overview of the latest developments in inter- and intramolecular epoxidation reactions involving metal carbenes and carbonyl compounds, encompassing both racemic to enantioselective transformations. These catalytic epoxidations are reviewed by highlighting their product selectivity, diversity and applicability, and the related mechanistic rationale is showcased where possible.

Review on Catalytic Meinwald Rearrangement of Epoxides.

The past few decades have witnessed tremendous development within epoxides. Among the many known reactions involving epoxide, Meinwald rearrangements represent one of the most important and attractive approaches, which can transform epoxides into versatile carbonyl compounds. Given the high efficiency of this protocol, substantial efforts have been made by researchers by utilizing multiple catalyst systems. This review provides an overview of recent advances in the Meinwald rearrangement (from 2014 onward), along with detailed discussions on mechanistic insights. This review aims to highlight the importance and value of these methodologies, thereby promoting further investigation and application.