Soluble Epoxide Hydrolase Inhibition for Ocular Diseases: Vision for the Future

Targeted lipidomics uncovers oxylipin perturbations and potential circulation biomarkers in Bietti's crystalline dystrophy

PURPOSE

Abnormalities in lipid metabolism have been proposed in Bietti's crystalline dystrophy (BCD). We aim to characterize the lipid profiles in a case-control study.

METHODS

All participants were genetically confirmed by CYP4V2 gene sequencing and underwent chorioretinopathy evaluation by calculating the percentages of AF atrophy (PAFA). Fasting blood samples of BCD patients and controls were collected, and plasma was analyzed for routine lipid profiles. Targeted lipidomic evaluation includes long chain polyunsaturated fatty acids (LCPUFA) and associated eicosanoid metabolites.

RESULTS

Routine lipids profiles showed elevated plasma levels of triglyceride (P = 0.043) and low-density lipoprotein cholesterol (P = 0.024) in BCD patients. Lipidomic analysis showed significantly decreased levels of ω-3 LCPUFA including docosahexaenoic acid (DHA, 22:6, P = 0.00068) and eicosapentaenoic acid (EPA, 20:5, P = 0.0016), as well as ω-6 LCPUFA arachidonic acid (ARA, 20:4, P < 0.0001) in BCD patients. Eicosanoid metabolites, either derived from ω-3 and/ or ω-6 LCPUFAs via cyclooxygenase (COX) or lipoxygenase (LOX) pathways, including 5-HEPE, 12-HEPE, 13-HDHA, 15-HETE, 12-HETE, 5-HETE, 6k-PGF1a, PGE2, PGJ2, and TXB2, exhibited significant differences (P < 0.0001) between BCD patients and controls. Genotypes of CYP4V2, specifically the biallelic null mutations, were observed to correlate with more remarkably reduced levels of oxylipins, involving major LOX pathway metabolites including 5-HETE, 5-HEPE, 12-HEPE and LTB4.

CONCLUSIONS

BCD patients demonstrated significant decreases in plasma levels of ω-3 and ω-6 LCPUFA (DHA, EPA, and ARA), as well as their downstream metabolites via the COX and LOX pathways, suggesting that these might be implicated in BCD pathogenesis and could serve as biomarkers and therapeutic targets of the disease.

KEY MESSAGES

What is known BCD is a vision-threatening hereditary disease the causative gene of which is CYP4V2. Abnormalities in lipid metabolism have been proposed and demonstrated previously in BCD studies. The detailed pathogenesis remains unclear and controversial. What is new We observed prominent lipidomic alterations in the circulation when compared with age, gender, and bodymass index (BMI)-matched healthy controls. BCD patients demonstrated significant decreases in plasma levels of ω-3 and ω-6 LCPUFA (DHA, EPA, and ARA). Remarkable changes were observed in the downstream metabolites of the LCPUFA via the COX and LOX pathways. Genotypes of CYP4V2, specifically the biallelic null mutations, were observed to correlate with more remarkably reduced levels of oxylipins, involving major LOX pathway metabolites.

Effects of age on lacrimal gland bioactive lipids

PURPOSE

Polyunsaturated fatty acids (PUFA) are a source of bioactive lipids regulating inflammation and its resolution.

METHODS

Changes in PUFA metabolism were compared between lacrimal glands (LGs) from young and aged C57BL/6 J mice using a targeted lipidomics assay, as was the gene expression of enzymes involved in the metabolism of these lipids.

RESULTS

Global reduction in PUFAs and their metabolites was observed in aged LGs compared to young controls, averaging between 25 and 66 % across all analytes. ꞷ-6 arachidonic acid (AA) metabolites were all reduced in aged LGs, where the changes in prostaglandin E2 (PGE2) and lipoxin A4 (LXA4) were statistically significant. Several other 5-lipoxygenase (5-LOX) mediated metabolites were significantly reduced in the aged LGs, including D-series resolvins (e.g., RvD4, RvD5, and RvD6). Along with the RvDs, several ꞷ-3 docosahexaenoic acid (DHA) metabolites such as 14-HDHA, neuroprotectin D1 (NPD1), Maresin 2 (MaR2), and MaR 1 metabolite (22-COOH-MaR1) were significantly reduced in aged LGs. Similarly, ꞷ-3 eicosapentaenoic acid (EPA) and its metabolites were significantly reduced in aged LGs, where the most significantly reduced was 18-HEPE. Using metabolite ratios (product:precursor) for specific metabolic conversions as surrogate enzymatic measures, reduced 12-LOX activity was identified in aged LGs.

CONCLUSION

In this study, global reduction of PUFAs and their metabolites was found in the LGs of aged female C57BL/6 J compared to young controls. A consistent reduction was observed across all detected lipid analytes except for ꞷ-3 docosapentaenoic acid (DPA) and its special pro-resolving mediator (SPM) metabolites in aged mice, suggesting an increased risk for LG inflammation.

Beyond VEGF: Targeting Inflammation and Other Pathways for Treatment of Retinal Disease

Neovascular eye diseases include conditions such as retinopathy of prematurity, proliferative diabetic retinopathy, and neovascular age-related macular degeneration. Together, they are a major cause of vision loss and blindness worldwide. The current therapeutic mainstay for these diseases is intravitreal injections of biologics targeting vascular endothelial growth factor (VEGF) signaling. Lack of universal response to these anti-VEGF agents coupled with the challenging delivery method underscore a need for new therapeutic targets and agents. In particular, proteins that mediate both inflammatory and proangiogenic signaling are appealing targets for new therapeutic development. Here, we review agents currently in clinical trials and highlight some promising targets in preclinical and early clinical development, focusing on the redox-regulatory transcriptional activator APE1/Ref-1, the bioactive lipid modulator soluble epoxide hydrolase, the transcription factor RUNX1, and others. Small molecules targeting each of these proteins show promise for blocking neovascularization and inflammation. The affected signaling pathways illustrate the potential of new antiangiogenic strategies for posterior ocular disease. SIGNIFICANCE STATEMENT: Discovery and therapeutic targeting of new angiogenesis mediators is necessary to improve treatment of blinding eye diseases like retinopathy of prematurity, diabetic retinopathy, and neovascular age-related macular degeneration. Novel targets undergoing evaluation and drug discovery work include proteins important for both angiogenesis and inflammation signaling, including APE1/Ref-1, soluble epoxide hydrolase, RUNX1, and others.

Decreased Expression of Soluble Epoxide Hydrolase Suppresses Murine Choroidal Neovascularization

Neovascular or "wet" age-related macular degeneration (nAMD) is a leading cause of blindness among older adults. Choroidal neovascularization (CNV) is a major pathological feature of nAMD, in which abnormal new blood vessel growth from the choroid leads to irreversible vision loss. There is a critical need to develop novel therapeutic strategies to address limitations of the current anti-vascular endothelial growth factor biologics. Previously, we identified soluble epoxide hydrolase (sEH) as a possible therapeutic target for CNV through a forward chemical genetic approach. The purpose of this study was to validate sEH as a target by examining retinal expression of sEH protein and mRNA by immunohistochemistry and RNAscope in situ hybridization, respectively, and to assess the efficacy of an adeno-associated virus (AAV) vector designed to knock down the sEH gene, Ephx2, in the murine laser-induced (L-) CNV model. nAMD patient postmortem eye tissue and murine L-CNV showed overexpression of sEH in photoreceptors and retinal pigment epithelial cells. Ephx2 knockdown significantly reduced CNV and normalized mRNA expression levels of CNV-related inflammatory markers. Thus, this study further establishes sEH as a promising therapeutic target against CNV associated with nAMD.

Cytochrome P450-derived fatty acid epoxides and diols in angiogenesis and stem cell biology

Cytochrome P450 (CYP) enzymes are frequently referred to as the third pathway for the metabolism of arachidonic acid. While it is true that these enzymes generate arachidonic acid epoxides i.e. the epoxyeicosatrienoic acids (EETs), they are able to accept a wealth of ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) to generate a large range of regio- and stereo-isomers with distinct biochemical properties and physiological actions. Probably the best studied are the EETs which have well documented effects on vascular reactivity and angiogenesis. CYP enzymes can also participate in crosstalk with other PUFA pathways and metabolize prostaglandin G₂ and H₂, which are the precursors of effector prostaglandins, to affect macrophage function and lymphangiogenesis. The activity of the PUFA epoxides is thought to be kept in check by the activity of epoxide hydrolases. However, rather than being inactive, the diols generated have been shown to regulate neutrophil activation, stem and progenitor cell proliferation and Notch signaling in addition to acting as exercise-induced lipokines. Excessive production of PUFA diols has also been implicated in pathologies such as severe respiratory distress syndromes, including COVID-19, and diabetic retinopathy. This review highlights some of the recent findings related to this pathway that affect angiogenesis and stem cell biology.

Patient preferences in retinal drug delivery

Retinal vascular diseases (RVDs) are often treated with intravitreally (IVT) injected drugs, with relatively low patient compliance and potential risks. Ongoing research explores alternative RVD treatments, including eye drops and oral tablets. This study surveyed RVD patients treated with IVT injections to establish factors influencing low compliance rates while gauging treatment delivery method preferences. Demographics, perspectives, and treatment preferences were collected via IRB-approved, self-administered survey sent to Glick Eye Institute patients treated via IVT injections. Demographics, diagnoses, and treatments were ascertained from respondents’ medical records. Gender, age, and number of IVT injections received were used as stratifications. Five-level Likert-style scales and t-tests evaluated responses and stratification comparisons. The most common diagnoses in the respondent population (n = 54; response rate = 5%) were age-related macular degeneration, macular edema, and diabetic retinopathy. Respondents had varying levels of education, income, and age. Most (83%) admitted feeling anxious prior to their first IVT injection, but 80% reported willingness to receive IVT injections indefinitely, with a preference for ophthalmologist visits every 1–3 months. Eye drops would be preferred over IVT injections by 76% of respondents, while 65% preferred oral tablets, due to several perceived negative factors of IVT injections and positive factors for eye drops. Stratified groups did not differ in responses to survey questions. RVD patients will accept IVT injections for vision preservation, but alternative delivery methods like eye drops or oral tablets would be preferred. Thus, development of eye drop and oral therapeutics for RVD treatment is further emphasized by these findings.

Targeted Lipidomic Analysis of Aqueous Humor Reveals Signaling Lipid-Mediated Pathways in Primary Open-Angle Glaucoma

Simple Summary

Analysis of the eye liquids collected from a cohort of primary open-angle glaucoma patients identified signaling lipids, the pattern of which suggests a role of arachidonic acid/platelet activating-factor (PAF)-dependent pathways and oxidative stress in the pathogenesis of the disease and provides novel targets for its diagnostics and treatment.

Abstract

Primary open-angle glaucoma (POAG) is characterized by degeneration of retinal ganglion cells associated with an increase in intraocular pressure (IOP) due to hindered aqueous humor (AH) drainage through the trabecular meshwork and uveoscleral pathway. Polyunsaturated fatty acids and oxylipins are signaling lipids regulating neuroinflammation, neuronal survival and AH outflow. Among them, prostaglandins have been previously implicated in glaucoma and employed for its treatment. This study addressed the role of signaling lipids in glaucoma by determining their changes in AH accompanying IOP growth and progression of the disease. Eye liquids were collected from patients with POAG of different stages and cataract patients without glaucoma. Lipids were identified and quantified by UPLC-MS/MS. The compounds discriminating glaucoma groups were recognized using ANCOVA and PLS-DA statistic approaches and their biosynthetic pathways were predicted by bioinformatics. Among 22 signaling lipids identified in AH, stage/IOP-dependent alterations in glaucoma were provided by a small set of mediators, including 12,13-DiHOME, 9- and 13-HODE/KODE, arachidonic acid and lyso-PAF. These observations correlated with the expression of cytochromes P450 (CYPs) and phospholipases A2 in the ocular tissues. Interestingly, tear fluid exhibited similar lipidomic alterations in POAG. Overall, POAG may involve arachidonic acid/PAF-dependent pathways and oxidative stress as evidenced from an increase in its markers, KODEs and 12,13-DiHOME. The latter is a product of CYPs, one of which, CYP1B1, is known as POAG and primary congenital glaucoma-associated gene. These data provide novel targets for glaucoma treatment. Oxylipin content of tear fluid may have diagnostic value in POAG.

Computational insights into the known inhibitors of human soluble epoxide hydrolase

Human soluble epoxide hydrolase (hsEH) is involved in the hydrolysis of epoxyeicosatrienoic acids (EETs), which have potent anti-inflammatory properties. Given that EET conversion generates nonbioactive molecules, inhibition of this enzyme would be beneficial. Past decades of work on hsEH inhibitors resulted in numerous potential compounds, of which a hundred hsEH-ligand complexes were crystallized and deposited in the Protein Data Bank (PDB). We analyzed all deposited hsEH-ligand complexes to gain insight into the binding of inhibitors and to provide feedback on the future drug design processes. We also reviewed computationally driven strategies that were used to propose novel hsEH inhibitors.

Comparative Proteomics Analysis of the Postmitochondrial Supernatant Fraction of Human Lens-Free Whole Eye and Liver

The increasing incidence of ocular diseases has accelerated research into therapeutic interventions needed for the eye. Ocular enzymes play important roles in the metabolism of drugs and endobiotics. Various ocular drugs are designed as prodrugs that are activated by ocular enzymes. Moreover, ocular enzymes have been implicated in the bioactivation of drugs to their toxic metabolites. The key purpose of this study was to compare global proteomes of the pooled samples of the eye (n = 11) and the liver (n = 50) with a detailed analysis of the abundance of enzymes involved in the metabolism of xenobiotics and endobiotics. We used the postmitochondrial supernatant fraction (S9 fraction) of the lens-free whole eye homogenate as a model to allow accurate comparison with the liver S9 fraction. A total of 269 proteins (including 23 metabolic enzymes) were detected exclusively in the pooled eye S9 against 648 proteins in the liver S9 (including 174 metabolic enzymes), whereas 424 proteins (including 94 metabolic enzymes) were detected in both the organs. The major hepatic cytochrome P450 and UDP-glucuronosyltransferases enzymes were not detected, but aldehyde dehydrogenases and glutathione transferases were the predominant proteins in the eye. The comparative qualitative and quantitative proteomics data in the eye versus liver is expected to help in explaining differential metabolic and physiologic activities in the eye. SIGNIFICANCE STATEMENT: Information on the enzymes involved in xenobiotic and endobiotic metabolism in the human eye in relation to the liver is scarcely available. The study employed global proteomic analysis to compare the proteomes of the lens-free whole eye and the liver with a detailed analysis of the enzymes involved in xenobiotic and endobiotic metabolism. These data will help in better understanding of the ocular metabolism and activation of drugs and endobiotics.

Plasma amino acids and oxylipins as potential multi-biomarkers for predicting diabetic macular edema

To investigate the pathophysiologic characteristics of diabetic complications, we identified differences in plasma metabolites in subjects with type 2 diabetes (T2DM) with or without diabetic macular edema (DME) and a disease duration > 15 years. An cohort of older T2DM patients with prolonged disease duration was established, and clinical information and biospecimens were collected following the guidelines of the National Biobank of Korea. DME phenotypes were identified by ophthalmologic specialists. For metabolomics studies, propensity matched case and control samples were selected. To discover multi-biomarkers in plasma, non-targeted metabolite profiling and oxylipin profiling in the discovery cohort were validated in an extended cohort. From metabolomic studies, 5 amino acids (asparagine, aspartic acid, glutamic acid, cysteine, and lysine), 2 organic compounds (citric acid and uric acid) and 4 oxylipins (12-oxoETE, 15-oxoETE, 9-oxoODE, 20-carboxy leukotriene B4) were identified as candidate multi-biomarkers which can guide DME diagnosis among non-DME subjects. Receiver operating characteristic curves revealed high diagnostic value of the combined 5 amino acids and 2 organic compounds (AUC = 0.918), and of the 4 combined oxylipins (AUC = 0.957). Our study suggests that multi-biomarkers may be useful for predicting DME in older T2DM patients.

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.

Pharmacological Potential of Small Molecules for Treating Corneal Neovascularization

Under healthy conditions, the cornea is an avascular structure which allows for transparency and optimal visual acuity. Its avascular nature is maintained by a balance of proangiogenic and antiangiogenic factors. An imbalance of these factors can result in abnormal blood vessel proliferation into the cornea. This corneal neovascularization (CoNV) can stem from a variety of insults including hypoxia and ocular surface inflammation caused by trauma, infection, chemical burns, and immunological diseases. CoNV threatens corneal transparency, resulting in permanent vision loss. Mainstay treatments of CoNV have partial efficacy and associated side effects, revealing the need for novel treatments. Numerous natural products and synthetic small molecules have shown potential in preclinical studies in vivo as antiangiogenic therapies for CoNV. Such small molecules include synthetic inhibitors of the vascular endothelial growth factor (VEGF) receptor and other tyrosine kinases, plus repurposed antimicrobials, as well as natural source-derived flavonoid and non-flavonoid phytochemicals, immunosuppressants, vitamins, and histone deacetylase inhibitors. They induce antiangiogenic and anti-inflammatory effects through inhibition of VEGF, NF-κB, and other growth factor receptor pathways. Here, we review the potential of small molecules, both synthetics and natural products, targeting these and other molecular mechanisms, as antiangiogenic agents in the treatment of CoNV.

Peripheral soluble epoxide hydrolase inhibition reduces hypernociception and inflammation in albumin-induced arthritis in temporomandibular joint of rats

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the synovial tissue, joint dysfunction, and damage. Epoxyeicosatrienoic acids (EETs) are endogenous anti-inflammatory compounds, which are quickly converted by the soluble epoxide hydrolase (sEH) enzyme into a less active form with decreased biological effects. The inhibition of the sEH enzyme has been used as a strategy to lower nociception and inflammation. The goal of this study was to investigate whether the peripheral treatment with the sEH enzyme inhibitor 1- trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU) could prevent the hypernociception and inflammation in the albumin-induced arthritis model in rats' temporomandibular joint (TMJ). After the induction of experimental arthritis, animals were assessed for nociceptive behavior test, leukocyte infiltration counts and histologic analysis, ELISA to quantify several cytokines and Western blotting. The peripheral pretreatment with TPPU inhibited the arthritis-induced TMJ hypernociception and leukocyte migration. Moreover, the local concentrations of proinflammatory cytokines were diminished by TPPU, while the anti-inflammatory cytokine interleukin-10 was up-regulated in the TMJ tissue. Finally, TPPU significantly decreased protein expression of iNOS, while did not alter the expression of MRC1. This study provides evidence that the peripheral administration of TPPU reduces hypernociception and inflammation in TMJ experimental arthritis.

Ribonuclease attenuates retinal ischemia reperfusion injury through inhibition of inflammatory response and apoptosis in mice

The present study was aimed to reveal the function of extracellular RNAs (exRNAs) in retinal ischemia reperfusion (I/R) injury, and evaluate whether RNase administration can effectivelyreduce I/Rinjury. A retinal I/R injury C57BL/6J wild-type mice model was established by elevating intraocular pressure for 1 h. All mice received 3 doses of RNase or the same dose of normal saline at different time points. After 7 days of reperfusion, retinal damage was quantified by counting retinal ganglion cells and measuring retinal layer thickness. The apoptotic retinal cells were detected by the TUNEL experiment, and the expressions of caspase-3, proinflammatory cytokines in retinal tissues, and glial fibrillary acidic protein (GFAP) protein and mRNA were detected to determine the underlying mechanism. It was found that RNase administration (1) reduced the significant loss of retinal morphology caused by I/R injury; (2) down-regulated the expression of NF-κBp65, IL-6 and GFAP relative to the I/R mice; (3) decreased the apoptosis of retinal cells and the levels of caspase-3; (4) attenuated exRNAs levels in retinal tissues on day 7 after retinal I/R. In short, increased exRNAs may contribute to retinal I/R damages in mice, and RNase therapy can effectively attenuate retinal damage by reducing inflammatory response and apoptosis.

Soluble epoxide hydrolase inhibitor, TPPU, increases regulatory T cells pathway in an arthritis model

Epoxyeicosatrienoic acids (EET) and related epoxy fatty acids (EpFA) are endogenous anti‐inflammatory compounds, which are converted by the soluble epoxide hydrolase (sEH) to dihydroxylethersatrienoic acids (DHETs) with lessened biological effects. Inhibition of sEH is used as a strategy to increase EET levels leading to lower inflammation. Rheumatoid arthritis is a chronic autoimmune disease that leads to destruction of joint tissues. This pathogenesis involves a complex interplay between the immune system, and environmental factors. Here, we investigate the effects of inhibiting sEH with 1‐trifluoromethoxyphenyl‐3‐(1‐propionylpiperidin‐4‐yl) urea (TPPU) on a collagen‐induced arthritis model. The treatment with TPPU ameliorates hyperalgesia, edema, and decreases the expression of important pro‐inflammatory cytokines of Th1 and Th17 profiles, while increasing Treg cells. Considering the challenges to control RA, this study provides robust data supporting that inhibition of the sEH is a promising target to treat arthritis.