Role of soluble epoxide hydrolase in age-related vascular cognitive decline

Targeting the soluble epoxide hydrolase pathway as a novel therapeutic approach for the treatment of pain

Chronic pain is a major burden and the complexities of chronic pain pathophysiology, including both peripheral and central sensitisation mechanisms, involves multiple cell types (neuronal, immune, neuroimmune, and vascular) which substantially complicates the development of new effective analgesic treatments. The epoxy fatty acids (EpFAs), including the epoxyeicosatrienoic acids (EETs), are derived from the metabolism of polyunsaturated fatty acids (PUFAs) via the cytochrome P450 enzymatic pathway and act to shut-down inflammatory signalling and provide analgesia. The EpFAs are rapidly metabolised by the enzyme soluble epoxide hydrolase (sEH) into their corresponding diol metabolites, which recent studies suggest are pro-inflammatory and pro-nociceptive. This review discusses clinical and mechanistic evidence for targeting the sEH pathway for the treatment of pain.

Overexpression of soluble epoxide hydrolase reduces post-ischemic recovery of cardiac contractile function

Cytochromes P450 can metabolize endogenous fatty acids, such as arachidonic acid, to bioactive lipids such as epoxyeicosatrienoic acids (EETs) that have beneficial effects. EETs protect hearts against ischemic damage, heart failure or fibrosis; however, their effects are limited by hydrolysis to less active dihydroxy oxylipins by soluble epoxide hydrolase (sEH), encoded by the epoxide hydrolase 2 gene (EPHX2, EC 3.3.2.10). Pharmacological inhibition or genetic disruption of sEH/EPHX2 have been widely studied for their impact on cardiovascular diseases. Less well studied is the role of increased EPHX2 expression, which occurs in a substantial human population that carries the EPHX2 K55R polymorphism or after induction by inflammatory stimuli. Herein, we developed a mouse model with cardiomyocyte-selective expression of human EPHX2 (Myh6-EPHX2) that has significantly increased total EPHX2 expression and activity. Myh6-EPHX2 hearts exhibit strong, cardiomyocyte-selective expression of EPHX2. EPHX2 mRNA, protein, and epoxide hydrolysis measurements suggest that Myh6-EPHX2 hearts have 12-fold increase in epoxide hydrolase activity relative to wild type (WT) hearts. This increased activity significantly decreased epoxide:diol ratios in vivo. Isolated, perfused Myh6-EPHX2 hearts were not significantly different from WT hearts in basal parameters of cardiac function; however, compared to WT hearts, Myh6-EPHX2 hearts demonstrated reduced recovery of heart contractile function after ischemia and reperfusion (I/R). This impaired recovery after I/R correlated with reduced activation of PI3K/AKT and GSK3β signaling pathways in Myh6-EPHX2 hearts compared to WT hearts. In summary, the Myh6-EPHX2 mouse line represents a novel model of cardiomyocyte-selective overexpression of EPHX2 that has detrimental effects on cardiac function.

Soluble epoxide hydrolase inhibition reverses cognitive dysfunction in a mouse model of metabolic syndrome by modulating inflammation

Midlife metabolic syndrome (MetS) is associated with cognitive impairment in late life. The mechanism of delayed MetS-related cognitive dysfunction (MetSCD) is not clear, but it has been linked to systemic inflammation and chronic cerebral microangiopathy. Currently there is no treatment for late life MetSCD other than early risk factor modification. We investigated the effect of soluble epoxide hydrolase (sEH) inhibitor 4-[[trans-4-[[(tricyclo[3.3.1.13,7]dec-1-ylamino)carbonyl]amino]cyclohexyl]oxy]-benzoic acid (t-AUCB) on cognitive performance, cerebral blood flow (CBF), and central and peripheral inflammation in the high-fat diet (HFD) model of MetS in mice. At 6 weeks of age, male mice were randomly assigned to receive either HFD or standard chow (STD) for 6 months. Mice received either t-AUCB or vehicle for 4 weeks. Cognitive performance was evaluated, followed by CBF measurement using magnetic resonance imaging (MRI). At the end of the study, blood was collected for measurement of eicosanoids and inflammatory cytokines. The brains were then analyzed by immunohistochemistry for glial activation markers. The HFD caused a significant impairment in novel object recognition. Treatment with t-AUCB increased plasma levels of 14,15-EET, prevented this cognitive impairment and modified hippocampal glial activation and plasma cytokine levels, without affecting CBF in mice on HFD. In conclusion, sEH inhibition for four weeks prevents cognitive deficits in mice on chronic HFD by modulating inflammatory processes without affecting CBF.

Systematic Review and Phenome-Wide Scans of Genetic Associations with Vascular Cognitive Impairment

Vascular cognitive impairment (VCI) is a heterogenous form of cognitive impairment that results from cerebrovascular disease. It is a result of both genetic and non-genetic factors. Although much research has been conducted on the genetic contributors to other forms of cognitive impairment (e.g. Alzheimer's disease), knowledge is lacking on the genetic factors associated with VCI. A better understanding of the genetics of VCI will be critical for prevention and treatment. To begin to fill this gap, the genetic contributors are reviewed with VCI from the literature. Phenome-wide scans of the identified genes are conducted and genetic variants identified in the review in large-scale resources displaying genetic variant-trait association information. Gene set are also carried out enrichment analysis using the genes identified from the review. Thirty one articles are identified meeting the search criteria and filters, from which 107 unique protein-coding genes are noted related to VCI. The phenome-wide scans and gene set enrichment analysis identify pathways associated with a diverse set of biological systems. This results indicate that genes with evidence of involvement in VCI are involved in a diverse set of biological functions. This information can facilitate downstream research to better dissect possible shared biological mechanisms for future therapies.

A clathrin mediated endocytosis scaffolding protein, Intersectin 1, changes in an isoform, brain region, and sex specific manner in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and is characterized by the accumulation of amyloid-beta (Aβ) plaques and neurofibrillary Tau tangles in the brain. We previously identified a set of candidate AD microRNAs (miRNAs) in human cerebrospinal fluid (CSF) and used a target prediction pipeline to identify mRNAs and pathways that could potentially be regulated by the miRNAs. Of these pathways, clathrin mediated endocytosis (CME) was selected for further investigation. CME is altered in multiple brain cell types in AD and is implicated in early cellular phenotypes such as enlarged early endosomes and pathogenic processing of Aβ. However, a comprehensive evaluation of major CME hub proteins in humans with AD across multiple brain regions is lacking. Thus, we used immunoblots to evaluate human post-mortem AD and control (CTL) frontal cortex (FC; AD n = 22, CTL n = 23) and hippocampus (HP; AD n = 34, CTL n = 22) for changes in Intersectin 1 (ITSN1), Phosphatidylinositol Binding Clathrin Assembly Protein gene (PICALM), Clathrin Light Chain (CLT), FCH and Mu Domain Containing Endocytic Adaptor 1 (FCHO1), Adaptor Related Protein Complex 2 (AP2) Subunit Alpha 1 (AP2A1), and Dynamin 2 (DNM2). Of these, we found that in AD, ITSN1-long (ITSN1-L) was decreased in the FC of males and HP of females, while ITSN1-short was increased in the HP of both males and females. We further evaluated ITSN1-L levels in cortex (CTX) and HP of the 5xFAD mouse model of Aβ pathology at different timepoints during aging and disease progression by immunoblot (n = 5-8 per group). At 3 months, female 5xFAD exhibited an increase of ITSN1-L in CTX but a decrease at 6 and 9 months. Additionally, immunofluorescent staining of 5xFAD primary HP neurons showed an increase of ITSN1-L in matured 5xFAD neurons at 21 and 28 days in vitro. Together, our studies show that in AD, isoforms of ITSN1 change in a brain region-and sex-dependent manner. Further, changes in ITSN1-L are transient with levels increasing during early Aβ accumulation and decreasing during later progression. These findings suggest that ITSN1 expression, and consequently CME activity, may change depending on the stage of disease progression.

Overexpression of Human Soluble Epoxide Hydrolase Exacerbates Coronary Reactive Hyperemia Reduction in Angiotensin-II-Treated Mouse Hearts

ABSTRACT

Coronary reactive hyperemia (CRH) is impaired in cardiovascular diseases, and angiotensin-II (Ang-II) exacerbates it. However, it is unknown how Ang-II affects CRH in Tie2-sEH Tr (human-sEH-overexpressed) versus wild-type (WT) mice. sEH-overexpression resulted in CRH reduction in Tie2-sEH Tr versus WT. We hypothesized that Ang-II exacerbates CRH reduction in Tie2-sEH Tr versus WT. The Langendorff system measured coronary flow in Tie2-sEH Tr and WT. The hearts were exposed to 15-second ischemia, and CRH was assessed in 10 mice each. Repayment volume was reduced by 40.50% in WT treated with Ang-II versus WT (7.42 ± 0.8 to 4.49 ± 0.8 mL/g) and 48% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (5.18 ± 0.4 to 2.68 ± 0.3 mL/g). Ang-II decreased repayment duration by 50% in WT-treated with Ang-II versus WT (2.46 ± 0.5 to 1.24 ± 0.4 minutes) and 54% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (1.66 ± 0.4 to 0.76 ± 0.2 minutes). Peak repayment flow was reduced by 11.2% in WT treated with Ang-II versus WT (35.98 ± 0.7 to 32.11 ± 1.4 mL/g) and 4% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (32.18 ± 0.6 to 30.89 ± 1.5 mL/g). Furthermore, coronary flow was reduced by 43% in WT treated with Ang-II versus WT (14.2 ± 0.5 to 8.15 ± 0.8 mL/min/g) and 32% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (12.1 ± 0.8 to 8.3 ± 1.2 mL/min/g). Moreover, the Ang-II-AT 1 -receptor and CYP4A were increased in Tie2-sEHTr. Our results demonstrate that Ang-II exacerbates CRH reduction in Tie2-sEH Tr mice.

Sex-Specific Response of the Brain Free Oxylipin Profile to Soluble Epoxide Hydrolase Inhibition

Oxylipins are the oxidation products of polyunsaturated fatty acids and have been implicated in neurodegenerative disorders, including dementia. Soluble epoxide hydrolase (sEH) converts epoxy-fatty acids to their corresponding diols, is found in the brain, and its inhibition is a treatment target for dementia. In this study, male and female C57Bl/6J mice were treated with an sEH inhibitor (sEHI), trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB), for 12 weeks to comprehensively study the effect of sEH inhibition on the brain oxylipin profile, and modulation by sex. Ultra-high-performance liquid chromatography-tandem mass spectrometry was used to measure the profile of 53 free oxylipins in the brain. More oxylipins were modified by the inhibitor in males than in females (19 versus 3, respectively) and favored a more neuroprotective profile. Most were downstream of lipoxygenase and cytochrome p450 in males, and cyclooxygenase and lipoxygenase in females. The inhibitor-associated oxylipin changes were unrelated to serum insulin, glucose, cholesterol, or female estrous cycle. The inhibitor affected behavior and cognitive function as measured by open field and Y-maze tests in males, but not females. These findings are novel and important to our understanding of sexual dimorphism in the brain's response to sEHI and may help inform sex-specific treatment targets.

Wide-spread enhancer effect of SNP rs2279590 on regulating epoxide hydrolase-2 and protein tyrosine kinase 2-beta gene expression

Polymorphisms in the PTK2B-CLU locus have been associated with various neurodegenerative disorders including pseudoexfoliation glaucoma, Alzheimer's and Parkinson's. Many of these genomic variants are within enhancer elements and modulate genes associated with the disease pathogenesis. However, mechanisms by which they control the gene expression is unknown. Previously, we have shown that clusterin enhancer element surrounding rs2279590 intronic variant, a risk factor in the pathogenesis of pseudoexfoliation glaucoma modulates gene expression of clusterin (CLU), protein tyrosine kinase 2 beta (PTK2B) and epoxide hydrolase 2 (EPHX2). Here, we explored the mechanism by which rs2279590 enhancer regulates their gene expression through chromosome conformation capture assays. 3C assays revealed a strong enhancer-promoter chromatin interaction between rs2279590 enhancer and promoters of genes CLU, PTK2B and EPHX2 in the HEK293 wild type cells. Moreover, genomic knockout of rs2279590 element significantly decreases the chromatin-chromatin cross-linking frequency suggesting gene regulation at transcriptional level through formation of chromatin loop. In addition, molecular assays showed a significantly decreased expression of EPHX2 but not PTK2B at both mRNA and protein level in the lens capsule of pseudoexfoliation affected patients in comparison to control subjects implying a role of EPHX2 in the pathogenesis of pseudoexfoliation.

Soluble Epoxide Hydrolase Derived Linoleic Acid Oxylipins, Small Vessel Disease Markers, and Neurodegeneration in Stroke

Background Cerebral small vessel disease is associated with higher ratios of soluble-epoxide hydrolase derived linoleic acid diols (12,13-dihydroxyoctadecenoic acid [DiHOME] and 9,10-DiHOME) to their parent epoxides (12(13)-epoxyoctadecenoic acid [EpOME] and 9(10)-EpOME); however, the relationship has not yet been examined in stroke. Methods and Results Participants with mild to moderate small vessel stroke or large vessel stroke were selected based on clinical and imaging criteria. Metabolites were quantified by ultra-high-performance liquid chromatography-mass spectrometry. Volumes of stroke, lacunes, white matter hyperintensities, magnetic resonance imaging visible perivascular spaces, and free water diffusion were quantified from structural and diffusion magnetic resonance imaging (3 Tesla). Adjusted linear regression models were used for analysis. Compared with participants with large vessel stroke (n=30), participants with small vessel stroke (n=50) had a higher 12,13-DiHOME/12(13)-EpOME ratio (β=0.251, P=0.023). The 12,13-DiHOME/12(13)-EpOME ratio was associated with more lacunes (β=0.266, P=0.028) but not with large vessel stroke volumes. Ratios of 12,13-DiHOME/12(13)-EpOME and 9,10-DiHOME/9(10)-EpOME were associated with greater volumes of white matter hyperintensities (β=0.364, P<0.001; β=0.362, P<0.001) and white matter MRI-visible perivascular spaces (β=0.302, P=0.011; β=0.314, P=0.006). In small vessel stroke, the 12,13-DiHOME/12(13)-EpOME ratio was associated with higher white matter free water diffusion (β=0.439, P=0.016), which was specific to the temporal lobe in exploratory regional analyses. The 9,10-DiHOME/9(10)-EpOME ratio was associated with temporal lobe atrophy (β=-0.277, P=0.031). Conclusions Linoleic acid markers of cytochrome P450/soluble-epoxide hydrolase activity were associated with small versus large vessel stroke, with small vessel disease markers consistent with blood brain barrier and neurovascular-glial disruption, and temporal lobe atrophy. The findings may indicate a novel modifiable risk factor for small vessel disease and related neurodegeneration.

Association of Plasma Eicosanoid Levels With Immune, Viral, and Cognitive Outcomes in People With HIV

BACKGROUND AND OBJECTIVES

To determine whether plasma eicosanoid levels are associated with immune, viral, and cognitive outcomes in people with HIV (PWH).

METHODS

We measured 42 eicosanoids in a longitudinal study of 95 PWH and 25 demographically comparable uninfected participants. Routine clinical chemistry, virologic, immune markers, and a neuropsychological test battery assessing 7 cognitive domains were administered to all participants at 2 study visits over an average of 6.5 months.

RESULTS

Plasma eicosanoid concentrations were elevated in PWH (n = 95) compared with seronegative controls (n = 25) (100% prediction power at 5% false discovery rate [FDR], α = 0.0531) and were negatively associated with lower current and nadir CD4 lymphocyte counts. Higher levels of eicosanoids were associated with impairments in working memory, verbal fluency, and executive function. Higher plasma viral load was associated with elevated proinflammatory eicosanoids (24% prediction power at 5% FDR and 42.4% prediction power at 10% FDR, α = 0.10). Longitudinal analyses showed that eicosanoid levels were correlated with viral load and with plasma creatinine. Despite associations of eicosanoids with viral loads, elevated plasma eicosanoids were similar in virally suppressed and not fully suppressed PWH.

DISCUSSION

These data show that HIV infection is associated with a robust production of eicosanoids that are not substantially reduced by antiretroviral therapy (ART). The sustained elevation of these oxylipins in PWH despite ART may contribute to an accelerated aging phenotype that includes earlier than expected brain and peripheral organ damage.

GPR39 Deficiency Impairs Memory and Alters Oxylipins and Inflammatory Cytokines Without Affecting Cerebral Blood Flow in a High-Fat Diet Mouse Model of Cognitive Impairment

Vascular cognitive impairment (VCI) is the second most common cause of dementia. There is no treatment for VCI, in part due to a lack of understanding of the underlying mechanisms. The G-protein coupled receptor 39 (GPR39) is regulated by arachidonic acid (AA)-derived oxylipins that have been implicated in VCI. Furthermore, GPR39 is increased in microglia of post mortem human brains with VCI. Carriers of homozygous GPR39 SNPs have a higher burden of white matter hyperintensity, an MRI marker of VCI. We tested the hypothesis that GPR39 plays a protective role against high-fat diet (HFD)-induced cognitive impairment, in part mediated via oxylipins actions on cerebral blood flow (CBF) and neuroinflammation. Homozygous (KO) and heterozygous (Het) GPR39 knockout mice and wild-type (WT) littermates with and without HFD for 8 months were tested for cognitive performance using the novel object recognition (NOR) and the Morris water maze (MWM) tests, followed by CBF measurements using MRI. Brain tissue and plasma oxylipins were quantified with high-performance liquid chromatography coupled to mass spectrometry. Cytokines and chemokines were measured using a multiplex assay. KO mice, regardless of diet, swam further away from platform location in the MWM compared to WT and Het mice. In the NOR test, there were no effects of genotype or diet. Brain and plasma AA-derived oxylipins formed by 11- and 15-lipoxygenase (LOX), cyclooxygenase (COX) and non-enzymatically were increased by HFD and GPR39 deletion. Interleukin-10 (IL-10) was lower in KO mice on HFD than standard diet (STD), whereas IL-4, interferon γ-induced protein-10 (IP-10) and monocyte chemotactic protein-3 (MCP-3) were altered by diet in both WT and KO, but were not affected by genotype. Resting CBF was reduced in WT and KO mice on HFD, with no change in vasoreactivity. The deletion of GPR39 did not change CBF compared to WT mice on either STD or HFD. We conclude that GPR39 plays a role in spatial memory retention and protects against HFD-induced cognitive impairment in part by modulating inflammation and AA-derived oxylipins. The results indicate that GPR39 and oxylipin pathways play a role and may serve as therapeutic targets in VCI.

Age-dependent cognitive impairment, hydrocephalus and leukocyte infiltration in transgenic mice with endothelial expression of human EPHX2

Soluble epoxide hydrolase (sEH) is upregulated in microvascular endothelium of human brain with vascular cognitive impairment (VCI). Transgenic endothelial expression of human sEH in mice (Tie2hsEH) induces endothelial dysfunction (ED), a pathogenetic mechanism of VCI. We sought to determine if endothelial upregulation of sEH is sufficient to cause cognitive impairment, and if cognitive impairment due to chronic hypoperfusion induced by unilateral common carotid artery occlusion (CCAO) is exacerbated in Tie2hsEH mice. Behavioral performance was assessed by the open field, rotarod, novel object, Morris water maze and fear conditioning tests. Cerebral blood flow and brain morphology were evaluated by MRI, and inflammatory changes investigated using immunohistochemistry and flow cytometry. We demonstrate that transgenic endothelial expression of sEH is sufficient to induce cognitive impairment, associated with leukocyte infiltration, brain atrophy and accelerated, age-dependent ventriculomegaly, identifying ED and sEH upregulation as potential underlying mechanisms and therapeutic targets for VCI.

Soluble Epoxide Hydrolase and Diabetes Complications

Type 2 diabetes mellitus (T2DM) can result in microvascular complications such as neuropathy, retinopathy, nephropathy, and cerebral small vessel disease, and contribute to macrovascular complications, such as heart failure, peripheral arterial disease, and large vessel stroke. T2DM also increases the risks of depression and dementia for reasons that remain largely unclear. Perturbations in the cytochrome P450-soluble epoxide hydrolase (CYP-sEH) pathway have been implicated in each of these diabetes complications. Here we review evidence from the clinical and animal literature suggesting the involvement of the CYP-sEH pathway in T2DM complications across organ systems, and highlight possible mechanisms (e.g., inflammation, fibrosis, mitochondrial function, endoplasmic reticulum stress, the unfolded protein response and autophagy) that may be relevant to the therapeutic potential of the pathway. These mechanisms may be broadly relevant to understanding, preventing and treating microvascular complications affecting the brain and other organ systems in T2DM.

Inflammatory markers in type 2 diabetes with vs. without cognitive impairment; a systematic review and meta-analysis

People with type 2 diabetes mellitus (T2DM) are at increased risk of mild cognitive impairment and dementia. Systemic inflammation has been proposed as a common risk factor. This study aimed to summarize the clinical data pertaining to peripheral blood inflammatory markers. We identified original peer-reviewed articles reporting blood inflammatory marker concentrations in groups of people with a T2DM diagnosis who have cognitive impairment (CI; including mild cognitive impairment, Alzheimer's disease, vascular cognitive impairment) vs. normal cognition (NC). Between-group standardized mean differences (SMD) were summarized in random effects meta-analyses. From 2108 records, data were combined quantitatively from 40 studies. Concentrations of interleukin-6 (IL-6; N_CI/N_NC = 934/3154, SMD 0.74 95% confidence interval [0.07, 1.42], Z₅ = 2.15, p = 0.03; I² = 98.08%), C-reactive protein (CRP; N_CI/N_NC = 1610/4363, SMD 0.80 [0.50, 1.11], Z₁₄ = 5.25, p < 0.01; I² = 94.59%), soluble vascular cell adhesion molecule-1 (sVCAM-1; N_CI/N_NC = 104/1063, SMD 1.64 95% confidence interval [0.21, 3.07], Z₂ = 2.25, p = 0.02; I² = 95.19%), and advanced glycation end products (AGEs; N_CI/N_NC = 227/317, SMD 0.84 95% confidence interval [0.41, 1.27], Z₂ = 3.82, p < 0.01; I² = 81.07%) were higher among CI groups compared to NC. Brain derived neurotropic factor (BDNF) concentrations were significantly lower in CI compared to NC (N_CI/N_NC = 848/2063, SMD -0.67 95% confidence interval [-0.99, -0.35], Z₃ = -4.09, p < 0.01; I² = 89.20%). Cognitive impairment among people with T2DM was associated with systemic inflammation and lower BDNF concentrations. These inflammatory characteristics support an increased inflammatory-vascular interaction associated with cognitive impairment in T2DM. PROSPERO (CRD42020188625).

Epoxyeicosatrienoic acids and soluble epoxide hydrolase in physiology and diseases of the central nervous system

Epoxyeicosatrienoic acids (EETs) are fatty acid signaling molecules synthesized by cytochrome P450 epoxygenases from arachidonic acid. The biological activity of EETs is terminated when being metabolized by soluble epoxide hydrolase (sEH), a process that serves as a key regulator of tissue EETs levels. EETs act through several signaling pathways to mediate various beneficial effects, including anti-inflammation, anti-apoptosis, and anti-oxidation with relieve of endoplasmic reticulum stress, thereby sEH has become a potential therapeutic target in cardiovascular disease and cancer therapy. Enzymes for EET biosynthesis and metabolism are both widely detected in both neuron and glial cells in the central nervous system (CNS). Recent studies discovered that astrocyte-derived EETs not only mediate neurovascular coupling and neuronal excitability by maintaining glutamate homeostasis but also glia-dependent neuroprotection. Genetic ablation as well as pharmacologic inhibition of sEH has greatly helped to elucidate the physiologic actions of EETs, and maintaining or elevating brain EETs level has been demonstrated beneficial effects in CNS disease models. Here, we review the literature regarding the studies on the bioactivity of EETs and their metabolic enzyme sEH with special attention paid to their action mechanisms in the CNS, including their modulation of neuronal activity, attenuation of neuroinflammation, regulation of cerebral blood flow, and improvement of neuronal and glial cells survival. We further reviewed the recent advance on the potential application of sEH inhibition for treating cerebrovascular disease, epilepsy, and pain disorder.

Inhibition of Soluble Epoxide Hydrolase Is Protective against the Multiomic Effects of a High Glycemic Diet on Brain Microvascular Inflammation and Cognitive Dysfunction

Diet is a modifiable risk factor for cardiovascular disease (CVD) and dementia, yet relatively little is known about the effect of a high glycemic diet (HGD) on the brain’s microvasculature. The objective of our study was to determine the molecular effects of an HGD on hippocampal microvessels and cognitive function and determine if a soluble epoxide hydrolase (sEH) inhibitor (sEHI), known to be vasculoprotective and anti-inflammatory, modulates these effects. Wild type male mice were fed a low glycemic diet (LGD, 12% sucrose/weight) or an HGD (34% sucrose/weight) with/without the sEHI, trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB), for 12 weeks. Brain hippocampal microvascular gene expression was assessed by microarray and data analyzed using a multi-omic approach for differential expression of protein and non-protein-coding genes, gene networks, functional pathways, and transcription factors. Global hippocampal microvascular gene expression was fundamentally different for mice fed the HGD vs. the LGD. The HGD response was characterized by differential expression of 608 genes involved in cell signaling, neurodegeneration, metabolism, and cell adhesion/inflammation/oxidation effects reversible by t-AUCB and hence sEH inhibitor correlated with protection against Alzheimer’s dementia. Ours is the first study to demonstrate that high dietary glycemia contributes to brain hippocampal microvascular inflammation through sEH.

GPR39 localization in the aging human brain and correlation of expression and polymorphism with vascular cognitive impairment

INTRODUCTION

The pathogenesis of vascular cognitive impairment (VCI) is not fully understood. GPR39, an orphan G-protein coupled receptor, is implicated in neurological disorders but its role in VCI is unknown.

METHODS

We performed GPR39 immunohistochemical analysis in post mortem brain samples from mild cognitive impairment (MCI) and control subjects. DNA was analyzed for GPR39 single nucleotide polymorphisms (SNPs), and correlated with white matter hyperintensity (WMH) burden on pre mortem magnetic resonance imaging.

RESULTS

GPR39 is expressed in aged human dorsolateral prefrontal cortex, localized to microglia and peri-capillary cells resembling pericytes. GPR39-capillary colocalization, and density of GPR39-expressing microglia was increased in aged brains compared to young. SNP distribution was equivalent between groups; however, homozygous SNP carriers were present only in the MCI group, and had higher WMH volume than wild-type or heterozygous SNP carriers.

DISCUSSION

GPR39 may play a role in aging-related VCI, and may serve as a therapeutic target and biomarker for the risk of developing VCI.

Association of plasma and CSF cytochrome P450, soluble epoxide hydrolase, and ethanolamide metabolism with Alzheimer's disease

BACKGROUND

Alzheimer's disease, cardiovascular disease, and other cardiometabolic disorders may share inflammatory origins. Lipid mediators, including oxylipins, endocannabinoids, bile acids, and steroids, regulate inflammation, energy metabolism, and cell proliferation with well-established involvement in cardiometabolic diseases. However, their role in Alzheimer's disease is poorly understood. Here, we describe the analysis of plasma and cerebrospinal fluid lipid mediators in a case-control comparison of ~150 individuals with Alzheimer's disease and ~135 healthy controls, to investigate this knowledge gap.

METHODS

Lipid mediators were measured using targeted quantitative mass spectrometry. Data were analyzed using the analysis of covariates, adjusting for sex, age, and ethnicity. Partial least square discriminant analysis identified plasma and cerebrospinal fluid lipid mediator discriminates of Alzheimer's disease. Alzheimer's disease predictive models were constructed using machine learning combined with stepwise logistic regression.

RESULTS

In both plasma and cerebrospinal fluid, individuals with Alzheimer's disease had elevated cytochrome P450/soluble epoxide hydrolase pathway components and decreased fatty acid ethanolamides compared to healthy controls. Circulating metabolites of soluble epoxide hydrolase and ethanolamides provide Alzheimer's disease predictors with areas under receiver operator characteristic curves ranging from 0.82 to 0.92 for cerebrospinal fluid and plasma metabolites, respectively.

CONCLUSIONS

Previous studies report Alzheimer's disease-associated soluble epoxide hydrolase upregulation in the brain and that endocannabinoid metabolism provides an adaptive response to neuroinflammation. This study supports the involvement of P450-dependent and endocannabinoid metabolism in Alzheimer's disease. The results further suggest that combined pharmacological intervention targeting both metabolic pathways may have therapeutic benefits for Alzheimer's disease.

Vascular contributions to cognitive impairment and dementia: the emerging role of 20-HETE

The accumulation of extracellular amyloid-β (Aβ) and intracellular hyperphosphorylated τ proteins in the brain are the hallmarks of Alzheimer's disease (AD). Much of the research into the pathogenesis of AD has focused on the amyloid or τ hypothesis. These hypotheses propose that Aβ or τ aggregation is the inciting event in AD that leads to downstream neurodegeneration, inflammation, brain atrophy and cognitive impairment. Multiple drugs have been developed and are effective in preventing the accumulation and/or clearing of Aβ or τ proteins. However, clinical trials examining these therapeutic agents have failed to show efficacy in preventing or slowing the progression of the disease. Thus, there is a need for fresh perspectives and the evaluation of alternative therapeutic targets in this field. Epidemiology studies have revealed significant overlap between cardiovascular and cerebrovascular risk factors such as hypertension, diabetes, atherosclerosis and stroke to the development of cognitive impairment. This strong correlation has given birth to a renewed focus on vascular contributions to AD and related dementias. However, few genes and mechanisms have been identified. 20-Hydroxyeicosatetraenoic acid (20-HETE) is a potent vasoconstrictor that plays a complex role in hypertension, autoregulation of cerebral blood flow and blood-brain barrier (BBB) integrity. Multiple human genome-wide association studies have linked mutations in the cytochrome P450 (CYP) 4A (CYP4A) genes that produce 20-HETE to hypertension and stroke. Most recently, genetic variants in the enzymes that produce 20-HETE have also been linked to AD in human population studies. This review examines the emerging role of 20-HETE in AD and related dementias.

Biomarkers Related to Endothelial Dysfunction and Vascular Cognitive Impairment: A Systematic Review

INTRODUCTION

The damage in the endothelium and the neurovascular unit appears to play a key role in the pathogenesis of vascular cognitive impairment (VCI). Although there have been many advances in understanding the physiopathology of this disease, several questions remain unanswered. The association with other degenerative diseases and the heterogeneity of its clinical spectrum establish a diagnostic problem, compromising a better comprehension of the pathology and halting the development of effective treatments. The investigation of biomarkers is an important movement to the development of novel explicative models and treatment targets involved in VCI.

METHODS

We searched MEDLINE considering the original research based on VCI biomarkers in the past 20 years, following prespecified selection criteria, data extraction, and qualitative synthesis.

RESULTS

We reviewed 42 articles: 16 investigated plasma markers, 17 analyzed neuropathological markers, 4 studied CSF markers, 4 evaluated neuroimaging markers (ultrasound and MRI), and 1 used peripheral Doppler perfusion imaging.

CONCLUSIONS

The biomarkers in these studies suggest an intrinsic relationship between endothelial dysfunction and VCI. Nonetheless, there is still a need for identification of a distinctive set of markers that can integrate the clinical approach of VCI, improve diagnostic accuracy, and support the discovery of alternative therapies.

Regulation of cardiovascular biology by microsomal epoxide hydrolase

Microsomal epoxide hydrolase/epoxide hydrolase 1 (mEH/EPHX1) works in conjunction with cytochromes P450 to metabolize a variety of compounds, including xenobiotics, pharmaceuticals and endogenous lipids. mEH has been most widely studied for its role in metabolism of xenobiotic and pharmaceutical compounds where it converts hydrophobic and reactive epoxides to hydrophilic diols that are more readily excreted. Inhibition or genetic disruption of mEH can be deleterious in the face of many industrial, environmental or pharmaceutical exposures and EPHX1 polymorphisms are associated with the development of exposure-related cancers. The role of mEH in endogenous epoxy-fatty acid (EpFA) metabolism has been less well studied. In vitro, mEH metabolizes most EpFAs at a far slower rate than soluble epoxide hydrolase (sEH) and has thus been generally considered to exert a minor role in EpFA metabolism in vivo. Indeed, sEH inhibitors or sEH-deficiency increase EpFA levels and are protective in animal models of cardiovascular disease. Recently, however, mEH was found to have a previously unrecognized and substantial role in EpFA metabolism in vivo. While few studies have examined the role of mEH in cardiovascular homeostasis, there is now substantial evidence that mEH can regulate cardiovascular function through regulation of EpFA metabolism. The discovery of a prominent role for mEH in epoxyeicosatrienoic acid (EET) metabolism, in particular, suggests that additional studies on the role of mEH in cardiovascular biology are warranted.

Soluble epoxide hydrolase inhibition improves cognitive function and parenchymal artery dilation in a hypertensive model of chronic cerebral hypoperfusion

OBJECTIVE

Parenchymal arterioles (PAs) regulate perfusion of the cerebral microcirculation, and impaired PA endothelium-dependent dilation occurs in dementia models mimicking chronic cerebral hypoperfusion (CCH). Epoxyeicosatrienoic acids (EETs) are vasodilators; their actions are potentiated by soluble epoxide hydrolase (sEH) inhibition. We hypothesized that chronic sEH inhibition with trifluoromethoxyphenyl-3 (1-propionylpiperidin-4-yl) urea (TPPU) would prevent cognitive dysfunction and improve PA dilation in a hypertensive CCH model.

METHODS

Bilateral carotid artery stenosis (BCAS) was used to induce CCH in twenty-week-old male stroke-prone spontaneously hypertensive rats (SHSRP) that were treated with vehicle or TPPU for 8 weeks. Cognitive function was assessed by novel object recognition. PA dilation and structure were assessed by pressure myography, and mRNA expression in brain tissue was assessed by qRT-PCR.

RESULTS

TPPU did not enhance resting cerebral perfusion, but prevented CCH-induced memory deficits. TPPU improved PA endothelium-dependent dilation but reduced the sensitivity of PAs to a nitric oxide donor. TPPU treatment had no effect on PA structure or biomechanical properties. TPPU treatment increased brain mRNA expression of brain derived neurotrophic factor, doublecortin, tumor necrosis factor-alpha, sEH, and superoxide dismutase 3, CONCLUSIONS: These data suggest that sEH inhibitors may be viable treatments for cognitive impairments associated with hypertension and CCH.

PET imaging of soluble epoxide hydrolase in non-human primate brain with [18F]FNDP

Purpose

Soluble epoxide hydrolase (sEH) is a promising candidate positron emission tomography (PET) imaging biomarker altered in various disorders, including vascular cognitive impairment (VCI), Alzheimer’s disease (AD), Parkinson’s disease (PD), stroke, and depression, known to regulate levels of epoxyeicosatrienoic acids (EETs) and play an important role in neurovascular coupling. [¹⁸F]FNDP, a PET radiotracer for imaging sEH, was evaluated through quantitative PET imaging in the baboon brain, radiometabolite analysis, and radiation dosimetry estimate.

Methods

Baboon [¹⁸F]FNDP dynamic PET studies were performed at baseline and with blocking doses of the selective sEH inhibitor AR-9281 to evaluate sEH binding specificity. Radiometabolites of [¹⁸F]FNDP in mice and baboons were measured by high-performance liquid chromatography. Regional brain distribution volume (V_T) of [¹⁸F]FNDP was computed from PET using radiometabolite-corrected arterial input functions. Full body distribution of [¹⁸F]FNDP was studied in CD-1 mice, and the human effective dose was estimated using OLINDA/EXM software.

Results

[¹⁸F]FNDP exhibited high and rapid brain uptake in baboons. AR-9281 blocked [¹⁸F]FNDP uptake dose-dependently with a baseline V_T of 10.9 ± 2.4 mL/mL and a high-dose blocking V_T of 1.0 ± 0.09 mL/mL, indicating substantial binding specificity (91.70 ± 1.74%). The V_ND was estimated as 0.865 ± 0.066 mL/mL. The estimated occupancy values of AR-9281 were 99.2 ± 1.1% for 1 mg/kg, 88.6 ± 1.3% for 0.1 mg/kg, and 33.8 ± 3.8% for 0.02 mg/kg. Murine biodistribution of [¹⁸F]FNDP enabled an effective dose estimate for humans (0.032 mSv/MBq). [¹⁸F]FNDP forms hydrophilic radiometabolites in murine and non-human primate plasma. However, only minute amounts of the radiometabolites entered the animal brain (< 2% in mice).

Conclusions

[¹⁸F]FNDP is a highly sEH-specific radiotracer that is suitable for quantitative PET imaging in the baboon brain. [¹⁸F]FNDP holds promise for translation to human subjects.

Soluble Epoxide Hydrolase Inhibition to Face Neuroinflammation in Parkinson's Disease: A New Therapeutic Strategy

Neuroinflammation is a crucial process associated with the pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD). Several pieces of evidence suggest an active role of lipid mediators, especially epoxy-fatty acids (EpFAs), in the genesis and control of neuroinflammation; 14,15-epoxyeicosatrienoic acid (14,15-EET) is one of the most commonly studied EpFAs, with anti-inflammatory properties. Soluble epoxide hydrolase (sEH) is implicated in the hydrolysis of 14,15-EET to its corresponding diol, which lacks anti-inflammatory properties. Preventing EET degradation thus increases its concentration in the brain through sEH inhibition, which represents a novel pharmacological approach to foster the reduction of neuroinflammation and by end neurodegeneration. Recently, it has been shown that sEH levels increase in brains of PD patients. Moreover, the pharmacological inhibition of the hydrolase domain of the enzyme or the use of sEH knockout mice reduced the deleterious effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. This paper overviews the knowledge of sEH and EETs in PD and the importance of blocking its hydrolytic activity, degrading EETs in PD physiopathology. We focus on imperative neuroinflammation participation in the neurodegenerative process in PD and the putative therapeutic role for sEH inhibitors. In this review, we also describe highlights in the general knowledge of the role of sEH in the central nervous system (CNS) and its participation in neurodegeneration. We conclude that sEH is one of the most promising therapeutic strategies for PD and other neurodegenerative diseases with chronic inflammation process, providing new insights into the crucial role of sEH in PD pathophysiology as well as a singular opportunity for drug development.

A single meal has the potential to alter brain oxylipin content

Our objective was to determine whether consumption of a single meal has the potential to alter brain oxylipin content. We examined the cerebrum of mice fed a single high-fat/high-sucrose Western meal or a low-fat/low-sucrose control meal, as well as fasted mice. We found no changes in fatty acid composition of cerebrum across the groups. The cerebral oxylipin profile of mice fed a Western meal is distinct from the profile of mice fed a low-fat/low-sucrose meal. Cerebral gene expression of cyclooxygenase 1, cyclooxygenase 2, and epoxide hydrolase 1 were elevated in Western meal-fed mice compared to low-fat/low-sucrose meal-fed mice. Mice that consumed either meal had lower gene expression of cytochrome P450, family 2, subfamily j, polypeptide 12 than fasted mice. Our data in this hypothesis-generating study indicates that the composition of a single meal has the potential to alter brain oxylipins and the gene expression of the enzymes responsible for their production.

Epoxy Fatty Acids Are Promising Targets for Treatment of Pain, Cardiovascular Disease and Other Indications Characterized by Mitochondrial Dysfunction, Endoplasmic Stress and Inflammation

Bioactive lipid mediators resulting from the metabolism of polyunsaturated fatty acids (PUFA) are controlled by many pathways that regulate the levels of these mediators and maintain homeostasis to prevent disease. PUFA metabolism is driven primarily through three pathways. Two pathways, the cyclooxygenase (COX) and lipoxygenase (LO) enzymatic pathways, form metabolites that are mostly inflammatory, while the third route of metabolism results from the oxidation by the cytochrome P450 enzymes to form hydroxylated PUFA and epoxide metabolites. These epoxygenated fatty acids (EpFA) demonstrate largely anti-inflammatory and beneficial properties, in contrast to the other metabolites formed from the degradation of PUFA. Dysregulation of these systems often leads to chronic disease. Pharmaceutical targets of disease focus on preventing the formation of inflammatory metabolites from the COX and LO pathways, while maintaining the EpFA and increasing their concentration in the body is seen as beneficial to treating and preventing disease. The soluble epoxide hydrolase (sEH) is the major route of metabolism of EpFA. Inhibiting its activity increases concentrations of beneficial EpFA, and often disease states correlate to mutations in the sEH enzyme that increase its activity and decrease the concentrations of EpFA in the body. Recent approaches to increasing EpFA include synthetic mimics that replicate biological activity of EpFA while preventing their metabolism, while other approaches focus on developing small molecule inhibitors to the sEH. Increasing EpFA concentrations in the body has demonstrated multiple beneficial effects in treating many diseases, including inflammatory and painful conditions, cardiovascular disease, neurological and disease of the central nervous system. Demonstration of efficacy in so many disease states can be explained by the fundamental mechanism that EpFA have of maintaining healthy microvasculature and preventing mitochondrial and endoplasmic reticulum stress. While there are no FDA approved methods that target the sEH or other enzymes responsible for metabolizing EpFA, current clinical efforts to test for efficacy by increasing EpFA that include inhibiting the sEH or administration of EpFA mimics that block metabolism are in progress.

Obesity in Aging Exacerbates Neuroinflammation, Dysregulating Synaptic Function-Related Genes and Altering Eicosanoid Synthesis in the Mouse Hippocampus: Potential Role in Impaired Synaptic Plasticity and Cognitive Decline

There is strong evidence that obesity has deleterious effects on cognitive function of older adults. Previous preclinical studies demonstrate that obesity in aging is associated with a heightened state of systemic inflammation, which exacerbates blood-brain barrier disruption, promoting neuroinflammation and oxidative stress. To test the hypothesis that synergistic effects of obesity and aging on inflammatory processes exert deleterious effects on hippocampal function, young and aged C57BL/6 mice were rendered obese by chronic feeding of a high-fat diet followed by assessment of learning and memory function, measurement of hippocampal long-term potentiation (LTP), assessment of changes in hippocampal expression of genes relevant for synaptic function and determination of synaptic density. Because there is increasing evidence that altered production of lipid mediators modulate LTP, neuroinflammation and neurovascular coupling responses, the effects of obesity on hippocampal levels of relevant eicosanoid mediators were also assessed. We found that aging exacerbates obesity-induced microglia activation, which is associated with deficits in hippocampal-dependent learning and memory tests, impaired LTP, decreased synaptic density, and dysregulation of genes involved in regulation of synaptic plasticity. Obesity in aging also resulted in an altered hippocampal eicosanoid profile, including decreases in vasodilator and pro-LTP epoxy-eicosatrienoic acids (EETs). Collectively, our results taken together with previous findings suggest that obesity in aging promotes hippocampal inflammation, which in turn may contribute to synaptic dysfunction and cognitive impairment.

Genetic deletion of soluble epoxide hydrolase delays the progression of Alzheimer's disease

Background

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme with COOH-terminal hydrolase and NH2-terminal lipid phosphatase activities. It is expressed in various cell types in the brain and is involved in the pathogenesis of inflammatory and neurodegenerative diseases. Alzheimer’s disease (AD) is a progressive neuroinflammatory and neurodegenerative disease. However, the pathological significance of sEH and underlying molecular mechanism in AD remain unclear.

Methods

To examine the role of sEH in pathogenesis of AD, we used wild-type (WT) mice, soluble epoxide hydrolase deficient (sEH^−/−) and two mouse models of AD, including amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (APP/PS1 Tg) and APP/PS1 Tg/sEH^−/− mice. Western blotting analysis and immunohistochemistry assay were performed to evaluate the protein expression. Locomotion, nesting building ability, Y-maze, and Morris water maze tests were conducted to study mouse behavior. The levels of interleukin (IL)-1β, IL-4, IL-6, and IL-10 and the activities of NF-κB and nuclear factor of activated T cells (NFAT) were measured by commercial assay kits. The quantitative protein level profiling in the brain lysate was analyzed using LC-MS/MS approaches.

Results

We demonstrated that the level of sEH was increased in the brain and predominantly appeared in hippocampal astrocytes of APP/PS1 Tg mice. Genetic ablation of sEH in APP/PS1 Tg mice delayed the progression of AD as evidenced by the alleviation in behavior outcomes and Aβ plaque deposition. In addition, loss of the function of sEH in APP/PS1 Tg mice increased astrogliosis and the production of astrocyte-derived anti-inflammatory cytokines including IL-1β, IL-4, and IL-10, as well as the activity of NF-kB and NFAT. Moreover, analysis of gene ontology in the AD brain revealed that important signaling pathways and processes related to AD pathogenesis such as translational regulation, oxidative stress, cytoskeleton reorganization, and small GTPase signal transduction were altered in APP/PS1 Tg/sEH^−/− mice compared with APP/PS1 Tg mice.

Conclusion

Our results suggest that sEH is a crucial regulator in the progression of AD and might be a potential therapeutic target for the treatment of AD.

Targeted Assessment of Enlargement of the Perivascular Space in Alzheimer's Disease and Vascular Dementia Subtypes Implicates Astroglial Involvement Specific to Alzheimer's Disease

Waste clearance from the brain parenchyma occurs along perivascular pathways. Enlargement of the perivascular space (ePVS) is associated with pathologic features of Alzheimer's disease (AD), although the mechanisms and implications of this dilation are unclear. Fluid exchange along the cerebral vasculature is dependent on the perivascular astrocytic water channel aquaporin-4 (AQP4) and loss of perivascular AQP4 localization is found in AD. We directly measured ePVS in postmortem samples of pathologically characterized tissue from participants who were cognitively intact or had AD or mixed dementia (vascular lesions with AD). We found that both AD and mixed dementia groups had significantly increased ePVS compared to cognitively intact subjects. In addition, we found increased global AQP4 expression of the AD group over both control and mixed dementia groups and a qualitative reduction in perivascular localization of AQP4 in the AD group. Among these cases, increasing ePVS burden was associated with the presence of tau and amyloid-β pathology. These findings are consistent with the existing evidence of ePVS in AD and provide novel information regarding differences in AD and vascular dementia and the potential role of astroglial pathology in ePVS.

L-arginine supplementation and thromboxane synthase inhibition increases cerebral blood flow in experimental cerebral malaria

Cerebral malaria pathogenesis involves vascular dysfunction with low nitric oxide (NO) bioavailability, vasoconstriction and impaired vasodilation, leading to ischemia, tissue hypoxia and ultimately death. Cerebral blood flow (CBF) involves NO and other pathways, including arachidonic acid (AA)-derived metabolites. Here we show that mice with experimental cerebral malaria (ECM) by P. berghei ANKA showed marked decreases in CBF (as assessed by laser speckle contrast imaging - LSCI) and that administration of L-arginine supplementation (50 mg/kg) and/or of the thromboxane synthase inhibitor Ozagrel (100 mg/kg) induced immediate increases in CBF. L-arginine in combination with artesunate (32 mg/kg) induced immediate reversal of brain ischemia in the short-term (1 hour), but the effect subsided after 3 and 6 hours. Neither L-arginine nor Ozagrel reversed blood brain barrier breakdown. Mice with ECM showed brain levels of selected AA-derived metabolites with a vasoconstrictor profile, with increased levels of 8-isoprostanes, 20-HETE and 14,15-DHET, whereas mice infected with a non-ECM-inducing strain of P. berghei (NK65) showed a vasodilator profile, with normal levels of 20-HETE and 14,15-DHET and increased levels of PGE2. L-arginine is capable of partially reversing cerebral ischemia and AA metabolites may play a role in the cerebrovascular dysfunction in ECM.

Docosahexaenoic Acid Increases the Potency of Soluble Epoxide Hydrolase Inhibitor in Alleviating Streptozotocin-Induced Alzheimer's Disease-Like Complications of Diabetes

Diabetes is a risk factor for Alzheimer's disease and it is associated with significant memory loss. In the present study, we hypothesized that the soluble epoxide hydrolase (sEH) inhibitor N-[1-(1-oxopropyl)-4-piperidinyl]-N'-[4-(trifluoromethoxy)phenyl)-urea (also known as TPPU) could alleviate diabetes-aggravated Alzheimer's disease-like symptoms by improving memory and cognition, and reducing the oxidative stress and inflammation associated with this condition. Also, we evaluated the effect of edaravone, an antioxidant on diabetes-induced Alzheimer's-like complications and the additive effect of docosahexaenoic acid (DHA) on the efficacy of TPPU. Diabetes was induced in male Sprague-Dawley rats by intraperitoneally administering streptozotocin (STZ). Six weeks after induction of diabetes, animals were either treated with vehicle, edaravone (3 or 10 mg/kg), TPPU (1 mg/kg) or TPPU (1 mg/kg) + DHA (100 mg/kg) for 2 weeks. The results demonstrate that the treatments increased the memory response of diabetic rats, in comparison to untreated diabetic rats. Indeed, DHA + TPPU were more effective than TPPU alone in reducing the symptoms monitored. All drug treatments reduced oxidative stress and minimized inflammation in the brain of diabetic rats. Expression of the amyloid precursor protein (APP) was increased in the brain of diabetic rats. Treatment with edaravone (10 mg/kg), TPPU or TPPU + DHA minimized the level of APP. The activity of acetylcholinesterase (AChE) which metabolizes acetylcholine was increased in the brain of diabetic rats. All the treatments except edaravone (3 mg/kg) were effective in decreasing the activity of AChE and TPPU + DHA was more efficacious than TPPU alone. Intriguingly, the histological changes in hippocampus after treatment with TPPU + DHA showed significant protection of neurons against STZ-induced neuronal damage. Overall, we found that DHA improved the efficacy of TPPU in increasing neuronal survival and memory, decreasing oxidative stress and inflammation possibly by stabilizing anti-inflammatory and neuroprotective epoxides of DHA. In the future, further evaluating the detailed mechanisms of action of sEH inhibitor and DHA could help to develop a strategy for the management of Alzheimer's-like complications in diabetes.

Role of epoxy-fatty acids and epoxide hydrolases in the pathology of neuro-inflammation

Neuroinflammation is a physiologic response aimed at protecting the central nervous system during injury. However, unresolved and chronic neuroinflammation can lead to long term damage and eventually neurologic disease including Parkinson's disease, Alzheimer's disease and dementia. Recently, enhancing the concentration of epoxyeicosatrienoic acids (EETs) through blocking their hydrolytic degradation by soluble epoxide hydrolase (sEH) has been applied towards reducing the long-term damage associated with central neurologic insults. Evidence suggests this protective effect is mediated, at least in part, through polarization of microglia to an anti-inflammatory phenotype that blocks the inflammatory actions of prostaglandins and promotes wound repair. This mini-review overviews the epidemiologic basis for using sEH inhibition towards neuroinflammatory disease and pharmacologic studies testing sEH inhibition in several neurologic diseases. Additionally, the combination of sEH inhibition with other eicosanoid signaling pathways is considered as an enhanced approach for developing potent neuroprotectants.

Humble beginnings with big goals: Small molecule soluble epoxide hydrolase inhibitors for treating CNS disorders

Soluble epoxide hydrolase (sEH) degrades epoxides of fatty acids including epoxyeicosatrienoic acid isomers (EETs), which are produced as metabolites of the cytochrome P450 branch of the arachidonic acid pathway. EETs exert a variety of largely beneficial effects in the context of inflammation and vascular regulation. sEH inhibition is shown to be therapeutic in several cardiovascular and renal disorders, as well as in peripheral analgesia, via the increased availability of anti-inflammatory EETs. The success of sEH inhibitors in peripheral systems suggests their potential in targeting inflammation in the central nervous system (CNS) disorders. Here, we describe the current roles of sEH in the pathology and treatment of CNS disorders such as stroke, traumatic brain injury, Parkinson's disease, epilepsy, cognitive impairment, dementia and depression. In view of the robust anti-inflammatory effects of stem cells, we also outlined the potency of stem cell treatment and sEH inhibitors as a combination therapy for these CNS disorders. This review highlights the gaps in current knowledge about the pathologic and therapeutic roles of sEH in CNS disorders, which should guide future basic science research towards translational and clinical applications of sEH inhibitors for treatment of neurological diseases.

Omega-6 oxylipins generated by soluble epoxide hydrolase are associated with knee osteoarthritis

Omega-6 FAs are inflammatory mediators that are increased in joints with osteoarthritis (OA), but their association with OA progression is not yet well defined. To investigate the relationship between omega-6 FAs and knee OA, we measured with LC-MS the levels of 22 omega-6 lipids (arachidonic acid, linoleic acid, and 20 oxylipins) in synovial fluid (SF) from 112 knees of 102 individuals (58 with knee OA; 44 controls). We hypothesized that oxylipin metabolites would increase in OA knee SF and with radiographically progressive disease. We validated results by comparing samples from affected and unaffected knees in 10 individuals with unilateral OA. In adjusted analysis, SF levels of three omega-6 oxylipins [prostaglandin D2, 11,12-dihydroxyeicosatrienoic acid (DHET), and 14,15-DHET] were associated with OA. Of these, 11,12-DHET and 14,15-DHET were higher in affected versus unaffected knees of people with unilateral disease (P < 0.014 and P < 0.003, respectively). Levels of these and 8,9-DHET were also associated with radiographic progression over 3.3 years in 87 individuals. Circulating levels of all three were associated with gene variants at the soluble epoxide hydrolase enzyme. Lipidomic profiling in SF identified an additional inflammatory pathway associated with knee OA and radiographic progression.

An optimized radiosynthesis of [18 F]FNDP, a positron emission tomography radiotracer for imaging soluble epoxide hydrolase (sEH)

In this concise practitioner protocol, the radiochemical synthesis of [¹⁸ F]FNDP suitable for human positron emission tomography studies is described and the results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice requirements.

P450 Eicosanoids and Reactive Oxygen Species Interplay in Brain Injury and Neuroprotection

Significance: Eicosanoids are endogenous lipid mediators that play important roles in brain function and disease. Acute brain injury such as that which occurs in stroke and traumatic brain injury increases the formation of eicosanoids, which, in turn, exacerbate or diminish injury. In chronic neurodegenerative diseases such as Alzheimer's disease and vascular dementia (VD), eicosanoid synthetic and metabolizing enzymes are altered, disrupting the balance between neuroprotective and neurotoxic eicosanoids. Recent Advances: Human and experimental studies have established the opposing roles of hydroxy- and epoxyeicosanoids and their potential utility as diagnostic biomarkers and therapeutic targets in neural injury. Critical Issues: A gap in knowledge remains in understanding the cellular and molecular mechanisms underlying the neurovascular actions of specific eicosanoids, such as specific isomers of epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic acids (HETEs). Future Directions: EETs and HETEs exert their actions on brain cells by targeting multiple mechanisms, which include surface G-protein coupled receptors. The identification of high-affinity receptors for EETs and HETEs and their cellular localization in the brain will be a breakthrough in our understanding of these eicosanoids as mediators of cell-cell communications and contributors to brain development, function, and disease. Antioxid. Redox Signal. 28, 987-1007.

Metabolic/inflammatory/vascular comorbidity in psychiatric disorders; soluble epoxide hydrolase (sEH) as a possible new target

The common and severe psychiatric disorders, including major depressive disorder (MDD) and bipolar disorder (BD), are associated with inflammation, oxidative stress and changes in peripheral and brain lipid metabolism. Those pathways are implicated in the premature development of vascular and metabolic comorbidities, which account for considerable morbidity and mortality, including increased dementia risk. During endoplasmic reticulum stress, the soluble epoxide hydrolase (sEH) enzyme converts anti-inflammatory fatty acid epoxides generated by cytochrome p450 enzymes into their corresponding and generally less anti-inflammatory, or even pro-inflammatory, diols, slowing the resolution of inflammation. The sEH enzyme and its oxylipin products are elevated post-mortem in MDD, BD and schizophrenia. Preliminary clinical data suggest that oxylipins increase with symptoms in seasonal MDD and anorexia nervosa, requiring confirmation in larger studies and other cohorts. In rats, a soluble sEH inhibitor mitigated the development of depressive-like behaviors. We discuss sEH inhibitors under development for cardiovascular diseases, post-ischemic brain injury, neuropathic pain and diabetes, suggesting new possibilities to address the mood and cognitive symptoms of psychiatric disorders, and their most common comorbidities.

Soluble epoxide hydrolase as a therapeutic target for pain, inflammatory and neurodegenerative diseases

Eicosanoids are biologically active lipid signaling molecules derived from polyunsaturated fatty acids. Many of the actions of eicosanoid metabolites formed by cyclooxygenase and lipoxygenase enzymes have been characterized, however, the epoxy-fatty acids (EpFAs) formed by cytochrome P450 enzymes are newly described by comparison. The EpFA metabolites modulate a diverse set of physiologic functions that include inflammation and nociception among others. Regulation of EpFAs occurs primarily via release, biosynthesis and enzymatic transformation by the soluble epoxide hydrolase (sEH). Targeting sEH with small molecule inhibitors has enabled observation of the biological activity of the EpFAs in vivo in animal models, greatly contributing to the overall understanding of their role in the inflammatory response. Their role in modulating inflammation has been demonstrated in disease models including cardiovascular pathology and inflammatory pain, but extends to neuroinflammation and neuroinflammatory disease. Moreover, while EpFAs demonstrate activity against inflammatory pain, interestingly, this action extends to blocking chronic neuropathic pain as well. This review outlines the role of modulating sEH and the biological action of EpFAs in models of pain and inflammatory diseases.

Cytochrome P450 eicosanoids in cerebrovascular function and disease

Cytochrome P450 eicosanoids play important roles in brain function and disease through their complementary actions on cell-cell communications within the neurovascular unit (NVU) and mechanisms of brain injury. Epoxy- and hydroxyeicosanoids, respectively formed by cytochrome P450 epoxygenases and ω-hydroxylases, play opposing roles in cerebrovascular function and in pathological processes underlying neural injury, including ischemia, neuroinflammation and oxidative injury. P450 eicosanoids also contribute to cerebrovascular disease risk factors, including hypertension and diabetes. We summarize studies investigating the roles P450 eicosanoids in cerebrovascular physiology and disease to highlight the existing balance between these important lipid signaling molecules, as well as their roles in maintaining neurovascular homeostasis and in acute and chronic neurovascular and neurodegenerative disorders.

PET imaging of the neurovascular interface in cerebrovascular disease

Cerebrovascular disease encompasses a range of pathologies that affect different components of the cerebral vasculature and brain parenchyma. Large artery atherosclerosis, acute cerebral ischaemia, and intracerebral small vessel disease all demonstrate altered metabolic processes that are key to their pathogenesis. Although structural imaging techniques such as MRI are the mainstay of clinical care and research in cerebrovascular disease, they have limited ability to detect these pathophysiological processes in vivo. By contrast, PET can detect and quantify metabolic processes that are relevant to each facet of cerebrovascular disease. Information obtained from PET studies has helped to shape the understanding of key concepts in cerebrovascular medicine, including vulnerable atherosclerotic plaque, salvageable ischaemic penumbra, neuroinflammation and selective neuronal loss after ischaemic insult. PET has also helped to elucidate the relationships between chronic hypoxia, neuroinflammation, and amyloid-β deposition in cerebral small vessel disease. This Review describes how PET-based imaging of metabolic processes at the neurovascular interface has contributed to our understanding of cerebrovascular disease.

Modulation of innate immunity of patients with Alzheimer's disease by omega-3 fatty acids

The innate immune system of patients with Alzheimer's disease and mild cognitive impairment (MCI) is deregulated with highly increased or decreased transcription of inflammatory genes and consistently depressed phagocytosis of amyloid-β_1-42 (Aβ) by monocytes and macrophages. Current immune therapies target single mechanisms in the adaptive immune system but not innate immunity. Here, we summarize recent advances in therapy by ω-3, ω-6, and epoxy fatty acids; specialized proresolving mediators; and vitamin D₃ that have proven immune effects and emerging cognitive effects in patients with MCI. The hypothesis of this approach is that macrophages of normal participants, but not those of patients with Alzheimer's disease and MCI, possess effective phagocytosis for Aβ and protect homeostasis of the brain and, furthermore, that defective MCI macrophages recover phagocytic function via ω-3. Recent studies of fish-derived ω-3 supplementation in patients with MCI have shown polarization of Apoε3/ε3 patients' macrophages to an intermediate M1-M2 phenotype that is optimal for Aβ phagocytosis and the stabilization of cognitive decline. Therefore, accumulating preclinical and preliminary clinical evidence indicates that ω-3 supplementation should be tested in a randomized controlled clinical trial and that the analysis should involve the apolipoprotein E genotype and intervening conditions during trial.-Fiala, M., Kooij, G., Wagner, K., Hammock, B., Pellegrini, M. Modulation of innate immunity of patients with Alzheimer's disease by omega-3 fatty acids.

Functional vascular contributions to cognitive impairment and dementia: mechanisms and consequences of cerebral autoregulatory dysfunction, endothelial impairment, and neurovascular uncoupling in aging

Increasing evidence from epidemiological, clinical and experimental studies indicate that age-related cerebromicrovascular dysfunction and microcirculatory damage play critical roles in the pathogenesis of many types of dementia in the elderly, including Alzheimer's disease. Understanding and targeting the age-related pathophysiological mechanisms that underlie vascular contributions to cognitive impairment and dementia (VCID) are expected to have a major role in preserving brain health in older individuals. Maintenance of cerebral perfusion, protecting the microcirculation from high pressure-induced damage and moment-to-moment adjustment of regional oxygen and nutrient supply to changes in demand are prerequisites for the prevention of cerebral ischemia and neuronal dysfunction. This overview discusses age-related alterations in three main regulatory paradigms involved in the regulation of cerebral blood flow (CBF): cerebral autoregulation/myogenic constriction, endothelium-dependent vasomotor function, and neurovascular coupling responses responsible for functional hyperemia. The pathophysiological consequences of cerebral microvascular dysregulation in aging are explored, including blood-brain barrier disruption, neuroinflammation, exacerbation of neurodegeneration, development of cerebral microhemorrhages, microvascular rarefaction, and ischemic neuronal dysfunction and damage. Due to the widespread attention that VCID has captured in recent years, the evidence for the causal role of cerebral microvascular dysregulation in cognitive decline is critically examined.

18F-FNDP for PET Imaging of Soluble Epoxide Hydrolase

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme located within cytosol and peroxisomes that converts epoxides to the corresponding diols and hydrolyzes phosphate monoesters. It serves to inactivate epoxyeicosatrienoic acids (EETs), which are generated in the brain to couple neuronal activity and cerebral blood flow in normal and pathologic states. Altered regulation of sEH was observed previously in various neuropathologic disorders including vascular dementia and stroke. Inhibitors of sEH are pursued as agents to mitigate neuronal damage after stroke. We developed N-(3,3-diphenylpropyl)-6-¹⁸F-fluoronicotinamide (¹⁸F-FNDP), which proved highly specific for imaging of sEH in the mouse and nonhuman primate brain with PET.

METHODS

¹⁸F-FNDP was synthesized from the corresponding bromo precursor. sEH inhibitory activity of ¹⁸F-FNDP was measured using an sEH inhibitor screening assay kit. Biodistribution was undertaken in CD-1 mice. Binding specificity was assayed in CD-1 and sEH knock-out mice and Papio anubis (baboon) through pretreatment with an sEH inhibitor to block sEH binding. Dynamic PET imaging with arterial blood sampling was performed in 3 baboons, with regional tracer binding quantified using distribution volume. The metabolism of ¹⁸F-FNDP in baboons was assessed using high-performance liquid chromatography.

RESULTS

¹⁸F-FNDP (inhibition binding affinity constant, 1.73 nM) was prepared in 1 step in a radiochemical yield of 14% ± 7%, specific radioactivity in the range of 888-3,774 GBq/μmol, and a radiochemical purity greater than 99% using an automatic radiosynthesis module. The time of preparation was about 75 min. In CD-1 mice, regional uptake followed the pattern of striatum > cortex > hippocampus > cerebellum, consistent with the known brain distribution of sEH, with 5.2% injected dose per gram of tissue at peak uptake. Blockade of 80%-90% was demonstrated in all brain regions. Minimal radiotracer uptake was present in sEH knock-out mice. PET baboon brain distribution paralleled that seen in mouse, with a marked blockade (95%) noted in all regions indicating sEH-mediated uptake of ¹⁸F-FNDP. Two hydrophilic metabolites were identified, with 20% parent compound present at 90 min after injection in baboon plasma.

CONCLUSION

¹⁸F-FNDP can be synthesized in suitable radiochemical yield and high specific radioactivity and purity. In vivo imaging experiments demonstrated that ¹⁸F-FNDP targeted sEH in murine and nonhuman primate brain specifically. ¹⁸F-FNDP is a promising PET radiotracer likely to be useful for understanding the role of sEH in a variety of conditions affecting the central nervous system.