Pinocembrin protects rats against cerebral ischemic damage through soluble epoxide hydrolase and epoxyeicosatrienoic acids

Protective effect of pinocembrin from Penthorum chinense Pursh on hepatic ischemia reperfusion injury via regulating HMGB1/TLR4 signal pathway

Hepatic ischemia-reperfusion injury (HIRI) is of common occurrence during liver surgery and transplantation. Pinocembrin (PIN) is a kind of flavonoid monomer extracted from the local traditional Chinese medicine Penthorum chinense Pursh (P. chinense). However, the effect of PIN on HIRI has not determined. We investigated the protective effect and potential mechanism of PIN against HIRI. Model mice were subjected to partial liver ischemia for 60 min, experimental mice were pretreated with PIN orally for 7 days, and H₂ O₂ -induced oxidative damage model in AML12 hepatic cells was established in vitro. Histopathologic analysis and serum biochemical levels revealed that PIN had hepatoprotective activities against HIRI. The variation of GSH, SOD, MDA, and ROS levels indicated that PIN treatments attenuated oxidative stress in tissue. PIN pretreatment obviously ameliorated apoptosis, and restrained the expression of HMGB1 and TLR4 in vivo. In vitro, compared with H₂ O₂ group, the contents of ROS, mitochondrial membrane potential, apoptotic cells, and Bcl-2 protein were decreased, while the Bax protein expression was increased. Moreover, HMGB-1 small interfering RNA test and western blotting showed that PIN pretreatment reduced HMGB1 and TLR4 protein levels. In conclusion, PIN pretreatment effectively protected hepatocytes from HIRI and inhibited the HMGB1/TLR4 signaling pathway.

Neuroprotective Phytochemicals in Experimental Ischemic Stroke: Mechanisms and Potential Clinical Applications

Ischemic stroke is a challenging disease with high mortality and disability rates, causing a great economic and social burden worldwide. During ischemic stroke, ionic imbalance and excitotoxicity, oxidative stress, and inflammation are developed in a relatively certain order, which then activate the cell death pathways directly or indirectly via the promotion of organelle dysfunction. Neuroprotection, a therapy that is aimed at inhibiting this damaging cascade, is therefore an important therapeutic strategy for ischemic stroke. Notably, phytochemicals showed great neuroprotective potential in preclinical research via various strategies including modulation of calcium levels and antiexcitotoxicity, antioxidation, anti-inflammation and BBB protection, mitochondrial protection and antiapoptosis, autophagy/mitophagy regulation, and regulation of neurotrophin release. In this review, we summarize the research works that report the neuroprotective activity of phytochemicals in the past 10 years and discuss the neuroprotective mechanisms and potential clinical applications of 148 phytochemicals that belong to the categories of flavonoids, stilbenoids, other phenols, terpenoids, and alkaloids. Among them, scutellarin, pinocembrin, puerarin, hydroxysafflor yellow A, salvianolic acids, rosmarinic acid, borneol, bilobalide, ginkgolides, ginsenoside Rd, and vinpocetine show great potential in clinical ischemic stroke treatment. This review will serve as a powerful reference for the screening of phytochemicals with potential clinical applications in ischemic stroke or the synthesis of new neuroprotective agents that take phytochemicals as leading compounds.

Cytochrome P450 derived epoxidized fatty acids as a therapeutic tool against neuroinflammatory diseases

Cytochrome P450 (CYP) metabolism of arachidonic acid (ARA) produces epoxy fatty acids (EpFAs) such as epoxyeicosatrienoic acids (EETs) that are known to exert protective effects in inflammatory disorders. Endogenous EpFAs are further metabolized into corresponding diols by the soluble epoxide hydrolase (sEH). Through inhibition of sEH, many studies have demonstrated the cardioprotective and renoprotective effects of EpFAs; however, the role of sEH inhibition in modulating the pathogenesis of neuroinflammatory disorders is less well described. In this review, we discuss the current knowledge surrounding the effects of sEH inhibition and EpFA action in neuroinflammatory disorders such as Parkinson's Disease (PD), stroke, depression, epilepsy, and Alzheimer's Disease (AD), as well as the potential mechanisms that underlie the therapeutic effects of sEH inhibition.

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.

The Nrf2/HO-1 Axis as Targets for Flavanones: Neuroprotection by Pinocembrin, Naringenin, and Eriodictyol

Flavanones are a group of flavonoids that derive from their immediate chalcone precursors through the action of chalcone isomerase enzymes. The Aromatic A and B rings, C4-keto group, and the 15-carbon flavonoid skeleton are all evident in flavanones, but a notable absence of C2-C3 double bond and a lack of oxygenation at C-3 position of the C-ring makes them distinctively different from other groups such as flavonols (e.g., quercetin). On the basis of oxygenation level in the B ring, flavanones can vary from each other as exemplified by pinocembrin (no oxygenation), naringenin (4′-hydroxyl), or eriodictyol (3′,4′-dihydroxyl substitution). These groups are generally weaker free radical scavengers as compared to quercetin and derivatives though eriodictyol has a better free radical scavenging profile within the group due to the presence of the catechol functional moiety. In this communication, their antioxidant potential through the induction of antioxidant defenses is scrutinized. These compounds as exemplified by pinocembrin could induce the nuclear factor erythroid 2-related factor 2- (Nrf2-) heme oxygenase-1 (HO-1) axis leading to amelioration of oxidative stress in cellular and animal models. Their neuroprotective effect through such mechanism is discussed.

Pinocembrin Protects from AGE-Induced Cytotoxicity and Inhibits Non-Enzymatic Glycation in Human Insulin

Advanced glycation end products (AGEs) are the end products of the glycation reaction and have a great importance in clinical science for their association with oxidative stress and inflammation, which play a major role in most chronic diseases, such as cardiovascular disease, neurodegenerative diseases, and diabetes. Their pathogenic effects are generally induced by the interaction between AGEs and the receptor for advanced glycation end product (RAGE) on the cell surface, which triggers reactive oxygen species production, nuclear factor kB (NF-kB) activation, and inflammation. Pinocembrin, the most abundant flavonoid in propolis, has been recently proven to interfere with RAGE activation in Aβ–RAGE-induced toxicity. In the present study, we investigated the ability of pinocembrin to interfere with RAGE signaling pathways activated by AGEs. Interestingly, pinocembrin was able to inhibit oxidative stress and NF-kB activation in cells exposed to AGEs. In addition, it was able to block caspase 3/7 and 9 activation, thus suggesting an active role of this molecule in counteracting AGE–RAGE-induced toxicity mediated by NF-kB signaling pathways. The ability of pinocembrin to affect the glycation reaction has been also tested. Our data suggest that pinocembrin might be a promising molecule in protecting from AGE-mediated pathogenesis.

Genetic Deletion of Soluble Epoxide Hydroxylase Causes Anxiety-Like Behaviors in Mice

Soluble epoxide hydrolase (sEH), an enzyme with COOH-terminal hydrolase and NH₂-terminal lipid phosphatase activities, is expressed in regions of the brain such as the cortex, white matter, hippocampus, substantia nigra, and striatum. sEH is involved in the regulation of cerebrovascular and neuronal function upon pathological insults. However, the physiological significance of sEH and its underlying mechanism in modulating brain function are not fully understood. In this study, we investigated the role of sEH in anxiety and potential underlying mechanisms in mice. Western blot for protein phosphorylation and expression was performed. Immunohistochemical analyses and Nissl and Golgi staining were performed for histological examination. Mouse behaviors were evaluated by open field activity, elevated plus maze, classical fear conditioning, social preference test, and Morris water maze. Our results demonstrated that the expression of sEH was upregulated during postnatal development in wild-type (WT) mice. Genetic deletion of sEH (sEH^-/-) in mice resulted in anxiety-like behavior and disrupted social preference. Increased olfactory bulb (OB) size and altered integrity of neurites were observed in sEH^-/- mice. In addition, ablation of sEH in mice decreased protein expression of tyrosine hydroxylase and reduced dopamine production in the brain. Moreover, the level of phosphorylated calmodulin kinase II (CaMKII) and glycogen synthase kinase 3 α/β (GSK3α/β) was higher in sEH^-/- mice than in WT mice. Collectively, these findings suggest that sEH is a key player in neurite outgrowth of neurons, OB development in the brain, and the development of anxiety-like behavior, by regulating the CaMKII-GSK3α/β signaling pathway.

Pinocembrin protects hemorrhagic brain primarily by inhibiting toll-like receptor 4 and reducing M1 phenotype microglia

Neuroinflammation is a major contributor to intracerebral hemorrhage (ICH) progression, but no drug is currently available to reduce this response and protect against ICH-induced injury. Recently, the natural product pinocembrin has been shown to ameliorate neuroinflammation and is undergoing a phase II clinical trial for ischemic stroke treatment. In this study, we examined the efficacy of pinocembrin in an ICH model, and further examined its effect on microglial activation and polarization. In vivo, pinocembrin dose-dependently reduced lesion volume by ∼47.5% and reduced neurologic deficits of mice at 72h after collagenase-induced ICH. The optimal dose of pinocembrin (5mg/kg) suppressed microglial activation as evidenced by decreases in CD68-positive microglia and reduced proinflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. Pinocembrin also reduced the number of classically activated M1-like microglia without affecting M2-like microglia in the perilesional region. Additionally, pinocembrin decreased the expression of toll-like receptor (TLR)4 and its downstream target proteins TRIF and MyD88. The protection by pinocembrin was lost in microglia-depleted mice and in TLR4^lps-del mice, and pinocembrin failed to decrease the number of M1-like microglia in TLR4^lps-del mice. In lipopolysaccharide-stimulated BV-2 cells or primary microglia, pinocembrin decreased M1-related cytokines and markers (IL-1β, IL-6, TNF-α, and iNOS), NF-κB activation, and TLR4 expression, but it did not interfere with TLR4/MyD88 and TLR4/TRIF interactions or affect microglial phagocytosis of red blood cells. Inhibition of the TLR4 signaling pathway and reduction in M1-like microglial polarization might be the major mechanism by which pinocembrin protects hemorrhagic brain. With anti-inflammatory properties, pinocembrin could be a promising new drug candidate for treating ICH and other acute brain injuries.

The Natural Flavonoid Pinocembrin: Molecular Targets and Potential Therapeutic Applications

Pinocembrin is a natural flavonoid compound extracted from honey, propolis, ginger roots, wild marjoram, and other plants. In preclinical studies, it has shown anti-inflammatory and neuroprotective effects as well as the ability to reduce reactive oxygen species, protect the blood-brain barrier, modulate mitochondrial function, and regulate apoptosis. Considering these pharmaceutical characteristics, pinocembrin has potential as a drug to treat ischemic stroke and other clinical conditions. In this review, we summarize its pharmacologic characteristics and discuss its mechanisms of action and potential therapeutic applications.