Botanical Polyphenols Mitigate Microglial Activation and Microglia-Induced Neurotoxicity: Role of Cytosolic Phospholipase A2

Natural Immunomodulatory Agents as a Complementary Therapy for Poxviruses

Poxviruses target innate immunity mediators such as tumor necrosis factors, interleukins, interferons, complement, and chemokines. It also targets adaptive immunity such as CD4+ T cells, CD4+ T cells, and B cells. Emerging of the recent epidemic of monkeypox virus (MPXV), a zoonotic disease native to Central and Western Africa, besides the lack of permitted treatments for poxviruses infections, encouraged researchers to identify effective inhibitors to help in preventing and treating poxviruses infections. Natural bioactive components, particularly polyphenolics, are promising for creating powerful antioxidants, anti-inflammatory, immune-stimulating, and antiviral agents. As a result, they are potentially effective therapies for preventing and treating viral diseases, such as infections caused by poxviruses including the recent pandemic MPXV. Polyphenolics: rosmarinic acid, caffeic acid, resveratrol, quercitrin, myricitrin, gingerol, gallotannin, and propolis-benzofuran A, as well as isoquinoline alkaloids: galanthamine and thalimonine represent prospective antiviral agents against MPXV, they can inhibit MPXV and other poxviruses via targeting different viral elements including DNA Topoisomerase I (TOP1), Thymidine Kinase (TK), serine/threonine protein kinase (Ser/Thr kinase), and protein A48R. The bioactive extracts of different traditional plants including Guiera senegalensis, Larrea tridentata, Sarracenia purpurea, Kalanchoe pinnata (Lam.) Pers., Zingiber officinale Roscoe, Quercus infectoria, Rhus chinensis, Prunella vulgaris L., Salvia rosmarinus, and Origanum vulgare also can inhibit the growth of different poxviruses including MPXV, vaccinia virus (VACV), variola virus, buffalopox virus, fowlpox virus, and cowpox virus. There is an urgent need for additional molecular studies to identify and confirm the anti-poxviruses properties of various natural bioactive components, especially those that showed potent antiviral activity against other viruses.

Zingiberene, a non-zinc-binding class I HDAC inhibitor: A novel strategy for the management of neuropathic pain

BACKGROUND

Even though numerous Histone deacetylase inhibitors (HDACi) have been approved for the treatment of different types of cancer, and others are in clinical trials for the treatment of neurodegenerative diseases, the main problem related to the clinical use of available HDACi is their low isoform selectivity which causes undesirable effects and inevitably limits their therapeutic application. Previously, we demonstrated that a standardized Zingiber officinalis Roscoe rhizome extract (ZOE) reduced neuroinflammation through HDAC1 inhibition in a mice model of neuropathy, and this activity was related to terpenes fraction.

HYPOTHESIS/PURPOSE

The aim of this work was to identify the ZOE constituent responsible for the activity on HDAC1 and to study its possible application in trauma-induced neuropathic pain.

METHODS

The ability of ZOE and its terpenes fraction (ZTE) to inhibit HDAC and SIRT isoforms activity and protein expression was assessed in vitro. Then, a structure-based virtual screening approach was applied to predict which constituent could be responsible for the activity. In the next step, the activity of selected compound was tested in an in vitro model of neuroinflammation and in an in vivo model of peripheral neuropathy (SNI).

RESULTS

ZTE resulted to be more potent than ZOE on HDAC1, 2, and 6 isoforms, while ZOE was more active on HDAC8. Zingiberene (ZNG) was found to be the most promising HDAC1 inhibitor, with an IC₅₀ of 2.3 ± 0.1 µM. A non-zinc-binding mechanism of inhibition was proposed based on molecular docking. Moreover, the oral administration of ZNG reduced thermal hyperalgesia and mechanical allodynia in animals with neuropathy after 60 min from administration, and decreased HDAC-1 levels in the spinal cord microglia.

CONCLUSION

We found a new non-zinc-dependent inhibitor of HDAC class I, with a therapeutic application in trauma-related neuropathic pain forms in which microglia-spinal overexpression of HDAC1 occurs. The non-zinc-binding mechanism has the potential to reduce off target effects, leading to a higher selectivity and better safety profile, compared to other HDAC inhibitors.

Exploring the role of polyphenols in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, inflammatory and autoimmune disorder which is mainly characterized by inflammation in joints, bone erosions and cartilaginous destruction that leads to joint dysfunction, deformation, and/or permanent functional impairment. The prevalence of RA is increasing, incurring a considerable burden on healthcare systems globally. The exact etiology of RA is unknown, with various pathways implicated in its pathophysiology. Non-steroidal anti-inflammatory drugs (NSAIDs) including celecoxib, diclofenac and ibuprofen, disease-modifying anti-rheumatic drugs (DMARD) including azathioprine, methotrexate and cyclosporine, biological agents including anakinra, infliximab, and rituximab and immunosuppressants are used for symptomatic relief in patients with RA, but these medications have severe adverse effects such as gastric ulcers, hypertension, hepatotoxicity and renal abnormalities which restrict their use in the treatment of RA; new RA treatments with minimal side-effects are urgently required. There is accumulating evidence that dietary polyphenols may show therapeutic efficacy in RA through their antioxidant, anti-inflammatory, apoptotic, and immunosuppressant activities and modulation of the tumor necrosis factor-α (TNF-α), interleukin (IL)-6, mitogen-activated protein kinase (MAPK), IL-1β, c-Jun N-terminal kinase (JNK), and nuclear factor κ light-chain-enhancer of activated B cell (NF-κB) pathways. While resveratrol, genistein, carnosol, epigallocatechin gallate, curcumin, kaempferol, and hydroxytyrosol have also been studied for the treatment of RA, the majority of data are derived from animal models. Here, we review the various pathways involved in the development of RA and the preclinical and clinical data supporting polyphenols as potential therapeutic agents in RA patients. Our review highlights that high-quality clinical studies are required to decisively establish the anti-rheumatic efficacy of polyphenolic compounds.

The Anti-Neuroinflammatory Role of Anthocyanins and Their Metabolites for the Prevention and Treatment of Brain Disorders

Anthocyanins are naturally occurring polyphenols commonly found in fruits and vegetables. Numerous studies have described that anthocyanin-rich foods may play a crucial role in the prevention and treatment of different pathological conditions, which have encouraged their consumption around the world. Anthocyanins exhibit a significant neuroprotective role, mainly due to their well-recognized antioxidant and anti-inflammatory properties. Neuroinflammation is an intricate process relevant in both homeostatic and pathological circumstances. Since the progression of several neurological disorders relies on neuroinflammatory process, targeting brain inflammation has been considered a promising strategy in those conditions. Recent data have shown the anti-neuroinflammatory abilities of many anthocyanins and of their metabolites in the onset and development of several neurological disorders. In this review, it will be discussed the importance and the applicability of these polyphenolic compounds as neuroprotective agents and it will be also scrutinized the molecular mechanisms underlying the modulation of neuroinflammation by these natural compounds in the context of several brain diseases.

Neuroinflammation in Alzheimer's Disease: Microglia, Molecular Participants and Therapeutic Choices

Alzheimer's disease is the world's most common dementing illness. It is pathologically characterized by β-amyloid accumulation, extracellular senile plaques and intracellular neurofibrillary tangles formation, and neuronal necrosis and apoptosis. Neuroinflammation has been widely recognized as a crucial process that participates in AD pathogenesis. In this review, we briefly summarized the involvement of microglia in the neuroinflammatory process of Alzheimer's disease. Its roles in the AD onset and progression are also discussed. Numerous molecules, including interleukins, tumor necrosis factor alpha, chemokines, inflammasomes, participate in the complex process of AD-related neuroinflammation and they are selectively discussed in this review. In the end of this paper from an inflammation- related perspective, we discussed some potential therapeutic choices.

Harpagophytum procumbens Extract Ameliorates Allodynia and Modulates Oxidative and Antioxidant Stress Pathways in a Rat Model of Spinal Cord Injury

Spinal cord injury (SCI) is a deliberating disorder with impairments in locomotor deficits and incapacitating sensory abnormalities. Harpagophytum procumbens (Hp) is a botanical widely used for treating inflammation and pain related to various inflammatory and musculoskeletal conditions. Using a modified rodent contusion model of SCI, we explored the effects of this botanical on locomotor function and responses to mechanical stimuli, and examined possible neurochemical changes associated with SCI-induced allodynia. Following spinal cord contusion at T10 level, Hp (300 mg/kg, p.o.) or vehicle (water) was administered daily starting 24 h post-surgery, and behavioral measurements made every-other day until sacrifice (Day 21). Hp treatment markedly ameliorated the contusion-induced decrease in locomotor function and increased sensitivity to mechanical stimuli. Determination of Iba1 expression in spinal cord tissues indicated microglial infiltration starting 3 days post-injury. SCI results in increased levels of 4-hydroxynonenal, an oxidative stress product and proalgesic, which was diminished at 7 days by treatment with Hp. SCI also enhanced antioxidant heme oxygenase-1 (HO-1) expression. Concurrent studies of cultured murine BV-2 microglial cells revealed that Hp suppressed oxidative/nitrosative stress and inflammatory responses, including production of nitric oxide and reactive oxygen species, phosphorylation of cytosolic phospholipases A₂, and upregulation of the antioxidative stress pathway involving the nuclear factor erythroid 2-related factor 2 and HO-1. These results support the use of Hp for management of allodynia by providing resilience against the neuroinflammation and pain associated with SCI and other neuropathological conditions.

The Gut Microbiota Links Dietary Polyphenols With Management of Psychiatric Mood Disorders

The pathophysiology of depression is multifactorial yet generally aggravated by stress and its associated physiological consequences. To effectively treat these diverse risk factors, a broad acting strategy is required and is has been suggested that gut-brain-axis signaling may play a pinnacle role in promoting resilience to several of these stress-induced changes including pathogenic load, inflammation, HPA-axis activation, oxidative stress and neurotransmitter imbalances. The gut microbiota also manages the bioaccessibility of phenolic metabolites from dietary polyphenols whose multiple beneficial properties have known therapeutic efficacy against depression. Although several potential therapeutic mechanisms of dietary polyphenols toward establishing cognitive resilience to neuropsychiatric disorders have been established, only a handful of studies have systematically identified how the interaction of the gut microbiota with dietary polyphenols can synergistically alleviate the biological signatures of depression. The current review investigates several of these potential mechanisms and how synbiotics, that combine probiotics with dietary polyphenols, may provide a novel therapeutic strategy for depression. In particular, synbiotics have the potential to alleviate neuroinflammation by modulating microglial and inflammasome activation, reduce oxidative stress and balance serotonin metabolism therefore simultaneously targeting several of the major pathological risk factors of depression. Overall, synbiotics may act as a novel therapeutic paradigm for neuropsychiatric disorders and further understanding the fundamental mechanisms of gut-brain-axis signaling will allow full utilization of the gut microbiota's as a therapeutic tool.

Polyphenols in the treatment of autoimmune diseases

In addition to protecting body from infections and diseases, the immune system produces auto-antibodies that can cause complex autoimmune disorders, such as Type I diabetes, primary biliary cirrhosis, rheumatoid arthritis, and multiple sclerosis, to name a few. In such cases, the immune system fails to recognize between foreign agents and its own body cells. Different factors, such as genetic factors (CD25, STAT4), epigenetic factors (DNA methylation, histone modifications) and environmental factors (xenobiotics, drugs, hormones) trigger autoimmunity. Glucocorticoids, non-steroidal anti-inflammatory drugs (NSAIDs), immunosuppressive and biological agents are currently used to manage autoimmune diseases of different origins. However, complete cure remains elusive. Many dietary and natural products including polyphenols have been widely studied as possible alternative treatment strategies for the management of autoimmune disorders. Polyphenols possess a wide-range of pharmacological and therapeutic properties, including antioxidant and anti-inflammatory activities. As immunomodulatory agents, polyphenols are emerging pharmaceutical tools for management of various autoimmune disorders including vitiligo, ulcerative colitis and multiple sclerosis (MS). Polyphenols activate intracellular pathways such as arachidonic acid dependent pathway, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway, mitogen-activated protein kinases (MAPKs) pathway, phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway and epigenetic modulation, which regulate the host's immune response. This timely review discusses putative points of action of polyphenols in autoimmune diseases, characterizing their efficacy and safety as therapeutic agents in managing autoimmune disorders.

Small-molecule inhibitors as potential therapeutics and as tools to understand the role of phospholipases A2

Phospholipase A2 (PLA2) enzymes are involved in various inflammatory pathological conditions including arthritis, cardiovascular and autoimmune diseases. The regulation of their catalytic activity is of high importance and a great effort has been devoted in developing synthetic inhibitors. We summarize the most important small-molecule synthetic PLA2 inhibitors developed to target each one of the four major types of human PLA2 (cytosolic cPLA2, calcium-independent iPLA2, secreted sPLA2, and lipoprotein-associated LpPLA2). We discuss recent applications of inhibitors to understand the role of each PLA2 type and their therapeutic potential. Potent and selective PLA2 inhibitors have been developed. Although some of them have been evaluated in clinical trials, none reached the market yet. Apart from their importance as potential medicinal agents, PLA2 inhibitors are excellent tools to unveil the role that each PLA2 type plays in cells and in vivo. Modern medicinal chemistry approaches are expected to generate improved PLA2 inhibitors as new agents to treat inflammatory diseases.

Quercetin Potentiates Docosahexaenoic Acid to Suppress Lipopolysaccharide-induced Oxidative/Inflammatory Responses, Alter Lipid Peroxidation Products, and Enhance the Adaptive Stress Pathways in BV-2 Microglial Cells

High levels of docosahexaenoic acid (DHA) in the phospholipids of mammalian brain have generated increasing interest in the search for its role in regulating brain functions. Recent studies have provided evidence for enhanced protective effects when DHA is administered in combination with phytochemicals, such as quercetin. DHA and quercetin can individually suppress lipopolysaccharide (LPS)–induced oxidative/inflammatory responses and enhance the antioxidative stress pathway involving nuclear factor erythroid-2 related factor 2 (Nrf2). However, studies with BV-2 microglial cells indicated rather high concentrations of DHA (IC₅₀ in the range of 60–80 µM) were needed to produce protective effects. To determine whether quercetin combined with DHA can lower the levels of DHA needed to produce protective effects in these cells is the goal for this study. Results showed that low concentrations of quercetin (2.5 µM), in combination with DHA (10 µM), could more effectively enhance the expression of Nrf2 and heme oxygenase 1 (HO-1), and suppress LPS–induced nitric oxide, tumor necrosis factor-α, phospho-cytosolic phospholipase A₂, reactive oxygen species, and 4-hydroxynonenal, as compared to the same levels of DHA or quercetin alone. These results provide evidence for the beneficial effects of quercetin in combination with DHA, and further suggest their potential as nutraceuticals for improving health.

Activation of microglia synergistically enhances neurodegeneration caused by MPP+ in human SH-SY5Y cells

While MPP⁺ may not directly activate microglia, the initial neuronal damage inflicted by the toxin may trigger microglia, possibly leading to synergistic pro-apoptotic interaction between neuro-inflammation and toxin-induced neurotoxicity, which may further aggravate neurodegeneration. However, what molecular targets are synergistically up or downregulated during this interaction is not well understood. Here, we addressed this by co-culturing fully differentiated human SH-SY5Y cells treated with parkinsonian toxin 1-Methyl-4-phenylpyridinium (MPP⁺), with endotoxin-activated microglial cell line EOC 20 to determine how this interaction affects pro-apoptotic (p38, JNK, and bax:bcl2 ratios) and pro-survival (NF-κB, MEK1) signaling at both mRNA and protein levels. Concurrent MPP⁺ and endotoxin-treatment aggravated a decrease in SH-SY5Y cell viability and caused strong synergistic increases in the bax:bcl2 ratio, but also NF-κB and JNK signaling. These effects were attenuated by microglia inhibitor minocycline. Altogether, these data provide further molecular insights into the important role or even conditional requirement of microglia activation in the progressive neurodegenerative nature of PD.

N-acetylcysteine targets 5 lipoxygenase-derived, toxic lipids and can synergize with prostaglandin E2 to inhibit ferroptosis and improve outcomes following hemorrhagic stroke in mice

Objectives

N‐acetylcysteine (NAC) is a clinically approved thiol‐containing redox modulatory compound currently in trials for many neurological and psychiatric disorders. Although generically labeled as an “antioxidant,” poor understanding of its site(s) of action is a barrier to its use in neurological practice. Here, we examined the efficacy and mechanism of action of NAC in rodent models of hemorrhagic stroke.

Methods

Hemin was used to model ferroptosis and hemorrhagic stroke in cultured neurons. Striatal infusion of collagenase was used to model intracerebral hemorrhage (ICH) in mice and rats. Chemical biology, targeted lipidomics, arachidonate 5‐lipoxygenase (ALOX5) knockout mice, and viral‐gene transfer were used to gain insight into the pharmacological targets and mechanism of action of NAC.

Results

NAC prevented hemin‐induced ferroptosis by neutralizing toxic lipids generated by arachidonate‐dependent ALOX5 activity. NAC efficacy required increases in glutathione and is correlated with suppression of reactive lipids by glutathione‐dependent enzymes such as glutathione S‐transferase. Accordingly, its protective effects were mimicked by chemical or molecular lipid peroxidation inhibitors. NAC delivered postinjury reduced neuronal death and improved functional recovery at least 7 days following ICH in mice and can synergize with clinically approved prostaglandin E₂ (PGE₂).

Interpretation

NAC is a promising, protective therapy for ICH, which acted to inhibit toxic arachidonic acid products of nuclear ALOX5 that synergized with exogenously delivered protective PGE₂ in vitro and in vivo. The findings provide novel insight into a target for NAC, beyond the generic characterization as an antioxidant, resulting in neuroprotection and offer a feasible combinatorial strategy to optimize efficacy and safety in dosing of NAC for treatment of neurological disorders involving ferroptosis such as ICH. Ann Neurol 2018;84:854–872

Unveiling anti-oxidative and anti-inflammatory effects of docosahexaenoic acid and its lipid peroxidation product on lipopolysaccharide-stimulated BV-2 microglial cells

BACKGROUND

Phospholipids in the central nervous system are enriched in n-3 and n-6 polyunsaturated fatty acids (PUFA), especially docosahexaenoic acid (DHA) and arachidonic acid (ARA). These PUFA can undergo enzymatic reactions to produce lipid mediators, as well as reaction with oxygen free radicals to produce 4-hydroxyhexenal (4-HHE) from DHA and 4-hydroxynonenal (4-HNE) from ARA. Recent studies demonstrated pleiotropic properties of these peroxidation products through interaction with oxidative and anti-oxidant response pathways. In this study, BV-2 microglial cells were used to investigate ability for DHA, 4-HHE, and 4-HNE to stimulate the anti-oxidant stress responses involving the nuclear factor erythroid-2-related factor 2 (Nrf2) pathway and synthesis of heme oxygenase (HO-1), as well as to mitigate lipopolysaccharide (LPS)-induced nitric oxide (NO), reactive oxygen species (ROS), and cytosolic phospholipase A₂ (cPLA₂). In addition, LC-MS/MS analysis was carried out to examine effects of exogenous DHA and LPS stimulation on endogenous 4-HHE and 4-HNE levels in BV-2 microglial cells.

METHODS

Effects of DHA, 4-HHE, and 4-HNE on LPS-induced NO production was determined using the Griess reagent. LPS-induced ROS production was measured using CM-H₂DCFDA. Western blots were used to analyze expression of p-cPLA₂, Nrf2, and HO-1. Cell viability and cytotoxicity were measured using the WST-1 assay, and cell protein concentrations were measured using the BCA protein assay kit. An ultra-high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was used to determine levels of free 4-HHE and 4-HNE in cells.

RESULTS

DHA (12.5-100 μM), 4-HHE (1.25-10 μM), and 4-HNE (1.25-10 μM) dose dependently suppressed LPS-induced production of NO, ROS, and as p-cPLA₂ in BV-2 microglial cells. With the same concentrations, these compounds could enhance Nrf2 and HO-1 expression in these cells. Based on the estimated IC₅₀ values, 4-HHE and 4-HNE were five- to tenfold more potent than DHA in inhibiting LPS-induced NO, ROS, and p-cPLA₂. LC-MS/MS analysis indicated ability for DHA (10-50 μM) to increase levels of 4-HHE and attenuate levels of 4-HNE in BV-2 microglial cells. Stimulation of cells with LPS caused an increase in 4-HNE which could be abrogated by cPLA₂ inhibitor. In contrast, bromoenol lactone (BEL), a specific inhibitor for the Ca²⁺-independent phospholipase A₂ (iPLA₂), could only partially suppress levels of 4-HHE induced by DHA or DHA + LPS.

CONCLUSIONS

This study demonstrated the ability of DHA and its lipid peroxidation products, namely, 4-HHE and 4-HNE at 1.25-10 μM, to enhance Nrf2/HO-1 and mitigate LPS-induced NO, ROS, and p-cPLA₂ in BV-2 microglial cells. In addition, LC-MS/MS analysis of the levels of 4-HHE and 4-HNE in microglial cells demonstrates that increases in production of 4-HHE from DHA and 4-HNE from LPS are mediated by different mechanisms.

Therapeutic effects of diosgenin in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease of the central nervous system. Currently, there is no drug available to cure this kind of disease. Diosgenin is a plant-derived steroid saponin. A previous study in our lab revealed that diosgenin can promote oligodendrocyte progenitor cell differentiation and accelerate remyelination. In the present study, we found that diosgenin dose-dependently alleviated the progression of experimental autoimmune encephalomyelitis with reduced central nervous system inflammation and demyelination. We also found that diosgenin treatment can significantly inhibit the activation of microglia and macrophages, suppress CD4+ T cell proliferation and hinder Th1/Th17 cell differentiation. Therefore, we suggested that diosgenin may be a potential therapeutic drug for inflammatory demyelinating diseases, such as MS.