Regulatory effects of caffeic acid phenethyl ester on neuroinflammation in microglial cells

Caffeic acid phenethyl ester restores mitochondrial homeostasis against peritoneal fibrosis induced by peritoneal dialysis through the AMPK/SIRT1 pathway

Increasing evidence suggests that peritoneal fibrosis induced by peritoneal dialysis (PD) is linked to oxidative stress. However, there are currently no effective interventions for peritoneal fibrosis. In the present study, we explored whether adding caffeic acid phenethyl ester (CAPE) to peritoneal dialysis fluid (PDF) improved peritoneal fibrosis caused by PD and explored the molecular mechanism. We established a peritoneal fibrosis model in Sprague-Dawley rats through intraperitoneal injection of PDF and lipopolysaccharide (LPS). Rats in the PD group showed increased peritoneal thickness, submesothelial collagen deposition, and the expression of TGFβ1 and α-SMA. Adding CAPE to PDF significantly inhibited PD-induced submesothelial thickening, reduced TGFβ1 and α-SMA expression, alleviated peritoneal fibrosis, and improved the peritoneal ultrafiltration function. In vitro, peritoneal mesothelial cells (PMCs) treated with PDF showed inhibition of the AMPK/SIRT1 pathway, mitochondrial membrane potential depolarization, overproduction of mitochondrial reactive oxygen species (ROS), decreased ATP synthesis, and induction of mesothelial-mesenchymal transition (MMT). CAPE activated the AMPK/SIRT1 pathway, thereby inhibiting mitochondrial membrane potential depolarization, reducing mitochondrial ROS generation, and maintaining ATP synthesis. However, the beneficial effects of CAPE were counteracted by an AMPK inhibitor and siSIRT1. Our results suggest that CAPE maintains mitochondrial homeostasis by upregulating the AMPK/SIRT1 pathway, which alleviates oxidative stress and MMT, thereby mitigating the damage to the peritoneal structure and function caused by PD. These findings suggest that adding CAPE to PDF may prevent and treat peritoneal fibrosis.

Ramelteon protects against social defeat stress-associated abnormal behaviors

Psychological stress affects the neuroendocrine regulation, which modulates mental status and behaviors. Melatonin, a hormone synthesized primarily by the pineal gland, regulates many brain functions, including circadian rhythms, pain, sleep, and mood. Selective pharmacological melatonin agonist ramelteon has been clinically used to treat mood and sleep disorders. Posttraumatic stress disorder (PTSD) is a psychiatric condition associated with severe trauma; it is generally triggered by traumatic events, which lead to severe anxiety and uncontrollable trauma recall. We recently reported that repeated social defeat stress (RSDS) may induce robust anxiety-like behaviors and social avoidance in mice. In the present study, we investigated whether melatonin receptor activation by melatonin and ramelteon regulates RSDS-induced behavioral changes. Melatonin treatment improved social avoidance and anxiety-like behaviors in RSDS mice. Moreover, treatment of the non-selective MT1/MT2 receptor agonist, ramelteon, markedly ameliorated RSDS-induced social avoidance and anxiety-like behaviors. Moreover, activating melatonin receptors also balanced the expression of monoamine oxidases, glucocorticoid receptors, and endogenous antioxidants in the hippocampus. Taken together, our findings indicate that the activation of both melatonin and ramelteon regulates RSDS-induced anxiety-like behaviors and PTSD symptoms. The current study also showed that the regulatory effects of neuroendocrine mechanisms and cognitive behaviors on melatonin receptor activation in repeated social defeat stress.

The role of AMPKα subunit in Alzheimer's disease: In-depth analysis and future prospects

The AMP-activated protein kinase α (AMPKα) subunit is the catalytic subunit in the AMPK complex, playing a crucial role in AMPK activation. It has two isoforms: AMPKα1 and AMPKα2. Emerging evidence suggests that the AMPKα subunit exhibits subtype-specific effects in Alzheimer's disease (AD). This review discusses the role of the AMPKα subunit in the pathogenesis of AD, including its impact on β-amyloid (Aβ) pathology, Tau pathology, metabolic disorders, inflammation, mitochondrial dysfunction, inflammasome and pyroptosis. Additionally, it reviews the distinct roles of its isoforms, AMPKα1 and AMPKα2, in AD, which may provide more precise targets for future drug development in AD.

Caffeic acid and diabetic neuropathy: Investigating protective effects and insulin-like growth factor 1 (IGF-1)-related antioxidative and anti-inflammatory mechanisms in mice

Diabetic neuropathy (DN) represents a common and debilitating complication of diabetes, affecting a significant proportion of patients. Despite available treatments focusing on symptom management, there remains an unmet need for therapies that address the underlying pathophysiology. In pursuit of novel interventions, this study evaluated the therapeutic effects of caffeic acid-a natural phenolic compound prevalent in various foods-on diabetic neuropathy using a mouse model, particularly examining its interaction with the Insulin-like Growth Factor 1 (IGF-1) signaling pathway. Caffeic acid was administered orally at two dosages (5 mg/kg and 10 mg/kg), and a comprehensive set of outcomes including fasting blood glucose levels, body weight, sensory behavior, spinal cord oxidative stress markers, inflammatory cytokines, and components of the IGF-1 signaling cascade were assessed. Additionally, to determine the specific contribution of IGF-1 signaling to the observed benefits, IGF1R inhibitor Picropodophyllin (PPP) was co-administered with caffeic acid. Our results demonstrated that caffeic acid, at both dosages, effectively reduced hyperglycemia and alleviated sensory behavioral deficits in diabetic mice. This was accompanied by a marked decrease in oxidative stress markers and an increase in antioxidant enzyme activities within the spinal cord. Significantly lowered microglial activation and inflammatory cytokine expression highlighted the potent antioxidative and anti-inflammatory effects of caffeic acid. Moreover, increases in both serum and spinal levels of IGF-1, along with elevated phosphorylated IGF1R, implicated the IGF-1 signaling pathway as a mediator of caffeic acid's neuroprotective actions. The partial reversal of caffeic acid's benefits by PPP substantiated the pivotal engagement of IGF-1 signaling in mediating its effects. Our findings delineate the capability of caffeic acid to mitigate DN symptoms, particularly through reducing spinal oxidative stress and inflammation, and pinpoint the integral role of IGF-1 signaling in these protective mechanisms. The insights gleaned from this study not only position caffeic acid as a promising dietary adjunct for managing diabetic neuropathy but also highlight the therapeutic potential of targeting spinal IGF-1 signaling as part of a strategic treatment approach.

Plant-derived and dietary phenolic cinnamic acid derivatives: Anti-inflammatory properties

Cinnamic acids are aromatic acids primarily found in plants and plant-derived food. Phenolic cinnamic acids, with one or more hydroxyl groups in the aromatic ring, often contribute to the biological activities attributed to these compounds. The presence of hydroxyl groups and a carboxyl group makes cinnamic acids very hydrophilic, preventing them from crossing biological membranes and exerting their biological activities. To alleviate this condition, a panel of synthetic modifications have been made leading to a diverse set of phenolic cinnamic structures. In this review, an overview of the natural phenolic cinnamic acid derivatives and their plant sources (more than 200) is described. The synthetic approaches to obtain the referred derivatives (more than 200) namely esters and amides are reviewed. Further, their anti-inflammatory activity (more than 70 compounds) is scrutinized. Finally, future directions will be indicated to translate the research on phenolic cinnamic derivatives into potentially effective anti-inflammatory drugs.

Naturally occurring caffeic acid phenethyl ester from chestnut honey-based propolis and virtual screening towards DYRK1A

Neurodegenerative diseases (NDDs) are disorders with dysfunction and ongoing loss of neurons, glial cells and the neural networks in the brain and spinal cord. DYRK1A protein was reported to modulate to the cytoskeletal fraction in human and mouse brain, and the remaining protein is located in the cytosolic and nuclear fractions. Caffeic acid phenethyl ester (CAPE) is a natural derivative of caffeic acid and found in propolis, a bee product. In this study, we focused on isolation and characterisation of CAPE from chestnut honey-based propolis by HPLC-MS/MS technique and virtual screening of CAPE towards DYRK1A by molecular docking methods. Results revealed that CAPE might be a beneficial option to treat Alzheimer disease (AD) by suppressing DYRK1A protein.

Neuroprotective Effect of Lithospermum officinale Callus Extract on Inflamed Primary Microglial Cells

BACKGROUND

Plants that have therapeutic features for humans or animals are commonly referred to as "medicinal plants". They produce secondary metabolites with antioxidant, antimicrobial and/or anti-cancer effects. Lithospermum officinale, known as European stone seed, is a famous medicinal herb. However, due to the pyrrolizidine alkaloids (PzAl) in the root extract of L.officinal, there are therapeutic limitations to this herb.

OBJECTIVE

This research was devoted to the evaluation of the anti-inflammatory capacity of methanolic extracts of L. officinale callus (LoE) (fresh cells) on rat microglial cells, the immune cells of the Central Nervous System, which play an essential role in the responses to neuroinflammation.

METHODS

Primary microglia were obtained from neonatal Wistar rats (1 to 3-days old), and then treated with various concentration of CfA and methanolic extracts of 17 and 31-day-old L. officinale callus before LPS-stimulation. In addition to HPLC analysis of the extracts, viability, nitric oxide production, and evaluation of pro-inflammatory genes and cytokines in the inflamed microglia were investigated by MTT, Griess methos, qrt-PCR, and ELISA.

RESULTS

Methanolic extract of the 17-day-old callus of L. officinale exhibited anti-inflammatory effects on LPS-stimulated microglial cells much higher than observed for CfA. The data were further supported by the decreased expression of Nos2, Tnf-α, and Cox-2 mRNA and the suppression of TNF-α and IL-1β release in the activated microglial cells pretreated with the effective dose of LoE (0.8 mg mL-1).

CONCLUSION

It was assumed that the better anti-neuroinflammatory performance of LoE than CfA in LPS-activated primary microglia could be a result of the synergism of the components of the extract and the lipophilic nature of RsA as the main phenolic acid of LoE. Considering that LoE shows a high antioxidant capacity and lacks PzAl, it is anticipated that LoE extract might be considered a reliable substitute to play a key role in the preparation of neuroprotective pharmaceutical formulas, which require in vivo research and further experiments.

Cornerstone Cellular Pathways for Metabolic Disorders and Diabetes Mellitus: Non-Coding RNAs, Wnt Signaling, and AMPK

Metabolic disorders and diabetes (DM) impact more than five hundred million individuals throughout the world and are insidious in onset, chronic in nature, and yield significant disability and death. Current therapies that address nutritional status, weight management, and pharmacological options may delay disability but cannot alter disease course or functional organ loss, such as dementia and degeneration of systemic bodily functions. Underlying these challenges are the onset of aging disorders associated with increased lifespan, telomere dysfunction, and oxidative stress generation that lead to multi-system dysfunction. These significant hurdles point to the urgent need to address underlying disease mechanisms with innovative applications. New treatment strategies involve non-coding RNA pathways with microRNAs (miRNAs) and circular ribonucleic acids (circRNAs), Wnt signaling, and Wnt1 inducible signaling pathway protein 1 (WISP1) that are dependent upon programmed cell death pathways, cellular metabolic pathways with AMP-activated protein kinase (AMPK) and nicotinamide, and growth factor applications. Non-coding RNAs, Wnt signaling, and AMPK are cornerstone mechanisms for overseeing complex metabolic pathways that offer innovative treatment avenues for metabolic disease and DM but will necessitate continued appreciation of the ability of each of these cellular mechanisms to independently and in unison influence clinical outcome.

The impact of aging and oxidative stress in metabolic and nervous system disorders: programmed cell death and molecular signal transduction crosstalk

Life expectancy is increasing throughout the world and coincides with a rise in non-communicable diseases (NCDs), especially for metabolic disease that includes diabetes mellitus (DM) and neurodegenerative disorders. The debilitating effects of metabolic disorders influence the entire body and significantly affect the nervous system impacting greater than one billion people with disability in the peripheral nervous system as well as with cognitive loss, now the seventh leading cause of death worldwide. Metabolic disorders, such as DM, and neurologic disease remain a significant challenge for the treatment and care of individuals since present therapies may limit symptoms but do not halt overall disease progression. These clinical challenges to address the interplay between metabolic and neurodegenerative disorders warrant innovative strategies that can focus upon the underlying mechanisms of aging-related disorders, oxidative stress, cell senescence, and cell death. Programmed cell death pathways that involve autophagy, apoptosis, ferroptosis, and pyroptosis can play a critical role in metabolic and neurodegenerative disorders and oversee processes that include insulin resistance, β-cell function, mitochondrial integrity, reactive oxygen species release, and inflammatory cell activation. The silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), AMP activated protein kinase (AMPK), and Wnt1 inducible signaling pathway protein 1 (WISP1) are novel targets that can oversee programmed cell death pathways tied to β-nicotinamide adenine dinucleotide (NAD+), nicotinamide, apolipoprotein E (APOE), severe acute respiratory syndrome (SARS-CoV-2) exposure with coronavirus disease 2019 (COVID-19), and trophic factors, such as erythropoietin (EPO). The pathways of programmed cell death, SIRT1, AMPK, and WISP1 offer exciting prospects for maintaining metabolic homeostasis and nervous system function that can be compromised during aging-related disorders and lead to cognitive impairment, but these pathways have dual roles in determining the ultimate fate of cells and organ systems that warrant thoughtful insight into complex autofeedback mechanisms.

Cellular Metabolism: A Fundamental Component of Degeneration in the Nervous System

It is estimated that, at minimum, 500 million individuals suffer from cellular metabolic dysfunction, such as diabetes mellitus (DM), throughout the world. Even more concerning is the knowledge that metabolic disease is intimately tied to neurodegenerative disorders, affecting both the central and peripheral nervous systems as well as leading to dementia, the seventh leading cause of death. New and innovative therapeutic strategies that address cellular metabolism, apoptosis, autophagy, and pyroptosis, the mechanistic target of rapamycin (mTOR), AMP activated protein kinase (AMPK), growth factor signaling with erythropoietin (EPO), and risk factors such as the apolipoprotein E (APOE-ε4) gene and coronavirus disease 2019 (COVID-19) can offer valuable insights for the clinical care and treatment of neurodegenerative disorders impacted by cellular metabolic disease. Critical insight into and modulation of these complex pathways are required since mTOR signaling pathways, such as AMPK activation, can improve memory retention in Alzheimer's disease (AD) and DM, promote healthy aging, facilitate clearance of β-amyloid (Aß) and tau in the brain, and control inflammation, but also may lead to cognitive loss and long-COVID syndrome through mechanisms that can include oxidative stress, mitochondrial dysfunction, cytokine release, and APOE-ε4 if pathways such as autophagy and other mechanisms of programmed cell death are left unchecked.

Caffeic Acid Phenethyl Ester Suppresses Oxidative Stress and Regulates M1/M2 Microglia Polarization via Sirt6/Nrf2 Pathway to Mitigate Cognitive Impairment in Aged Mice following Anesthesia and Surgery

Postoperative cognitive dysfunction (POCD) is a severe neurological complication after anesthesia and surgery. However, there is still a lack of effective clinical pharmacotherapy due to its unclear pathogenesis. Caffeic acid phenethyl ester (CAPE), which is obtained from honeybee propolis and medicinal plants, shows powerful antioxidant, anti-inflammatory, and immunomodulating properties. In this study, we aimed to evaluate whether CAPE mitigated cognitive impairment following anesthesia and surgery and its potential underlying mechanisms in aged mice. Here, isoflurane anesthesia and tibial fracture surgery were used as the POCD model, and H2O2-induced BV2 cells were established as the microglial oxidative stress model. We revealed that CAPE pretreatment suppressed oxidative stress and promoted the switch of microglia from the M1 to the M2 type in the hippocampus, thereby ameliorating cognitive impairment caused by anesthesia and surgery. Further investigation indicated that CAPE pretreatment upregulated hippocampal Sirt6/Nrf2 expression after anesthesia and surgery. Moreover, mechanistic studies in BV2 cells demonstrated that the potent effects of CAPE pretreatment on reducing ROS generation and promoting protective polarization were attenuated by a specific Sirt6 inhibitor, OSS_128167. In summary, our findings opened a promising avenue for POCD prevention through CAPE pretreatment that enhanced the Sirt6/Nrf2 pathway to suppress oxidative stress as well as favor microglia protective polarization.

Modulatory effect of caffeic acid in alleviating diabetes and associated complications

Diabetes mellitus (DM) is one of the most common metabolic disorders characterized by elevated blood glucose levels. Prolonged uncontrolled hyperglycemia often leads to multi-organ damage including diabetic neuropathy, nephropathy, retinopathy, cardiovascular disorders, and diabetic foot ulcers. Excess production of free radicals causing oxidative stress in tissues is often considered to be the primary cause of onset and progression of DM and associated complications. Natural polyphenols can be used to induce or inhibit the expression of antioxidant enzymes such as glutathione peroxidase, heme oxygenase-1, superoxide dismutase, and catalase that are essential in maintaining redox balance, and ameliorate oxidative stress. Caffeic acid (CA) is a polyphenolderived from hydroxycinnamic acid and possesses numerous physiological properties includ-ing antioxidant, anti-inflammatory, anti-atherosclerotic, immune-stimulatory, cardioprotective, antiproliferative, and hepatoprotective activities. CA acts as a regulatory compound affecting numerous biochemical pathways and multiple targets. These include various transcription factors such as nuclear factor-B, tumor necrosis factor-α, interleukin-6, cyclooxygenase-2, and nuclear factor erythroid 2-related factor 2. Therefore, this review summarizes the pharmacological properties, molecular mechanisms, and pharmacokinetic profile of CA in mitigating the adverse effects of DM and associated complications. The bioavailability, drug delivery, and clinical trials of CA have also been discussed.

The Metabolic Basis for Nervous System Dysfunction in Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease

Disorders of metabolism affect multiple systems throughout the body but may have the greatest impact on both central and peripheral nervous systems. Currently available treatments and behavior changes for disorders that include diabetes mellitus (DM) and nervous system diseases are limited and cannot reverse the disease burden. Greater access to healthcare and a longer lifespan have led to an increased prevalence of metabolic and neurodegenerative disorders. In light of these challenges, innovative studies into the underlying disease pathways offer new treatment perspectives for Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease. Metabolic disorders are intimately tied to neurodegenerative diseases and can lead to debilitating outcomes, such as multi-nervous system disease, susceptibility to viral pathogens, and long-term cognitive disability. Novel strategies that can robustly address metabolic disease and neurodegenerative disorders involve a careful consideration of cellular metabolism, programmed cell death pathways, the mechanistic target of rapamycin (mTOR) and its associated pathways of mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP-activated protein kinase (AMPK), growth factor signaling, and underlying risk factors such as the apolipoprotein E (APOE-ε4) gene. Yet, these complex pathways necessitate comprehensive understanding to achieve clinical outcomes that target disease susceptibility, onset, and progression.

Role of Zerumbone, a Phytochemical Sesquiterpenoid from Zingiber zerumbet Smith, in Maintaining Macrophage Polarization and Redox Homeostasis

Macrophages and microglia are highly versatile cells that can be polarized into M1 and M2 phenotypes in response to diverse environmental stimuli, thus exhibiting different biological functions. In the central nervous system, activated resident macrophages and microglial cells trigger the production of proinflammatory mediators that contribute to neurodegenerative diseases and psychiatric disorders. Therefore, modulating the activation of macrophages and microglia by optimizing the inflammatory environment is beneficial for disease management. Several naturally occurring compounds have been reported to have anti-inflammatory and neuroprotective properties. Zerumbone is a phytochemical sesquiterpenoid and also a cyclic ketone isolated from Zingiber zerumbet Smith. In this study, we found that zerumbone effectively reduced the expression of lipocalin-2 in macrophages and microglial cell lines. Lipocalin-2, also known as neutrophil gelatinase-associated lipocalin (NGAL), has been characterized as an adipokine/cytokine implicated in inflammation. Moreover, supplement with zerumbone inhibited reactive oxygen species production. Phagocytic activity was decreased following the zerumbone supplement. In addition, the zerumbone supplement remarkably reduced the production of M1-polarization-associated chemokines CXC10 and CCL-2, as well as M1-polarization-associated cytokines interleukin (IL)-6, IL-1β, and tumor necrosis factor-α. Furthermore, the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 and the production of NO were attenuated in macrophages and microglial cells supplemented with zerumbone. Notably, we discovered that zerumbone effectively promoted the production of the endogenous antioxidants heme oxygenase-1, glutamate-cysteine ligase modifier subunit, glutamate-cysteine ligase catalytic subunit, and NAD(P)H quinone oxidoreductase-1 and remarkably enhanced IL-10, a marker of M2 macrophage polarization. Endogenous antioxidant production and M2 macrophage polarization were increased through activation of the AMPK/Akt and Akt/GSK3 signaling pathways. In summary, this study demonstrated the protective role of zerumbone in maintaining M1 and M2 polarization homeostasis by decreasing inflammatory responses and enhancing the production of endogenous antioxidants in both macrophages and microglia cells. This study suggests that zerumbone can be used as a potential therapeutic drug for the supplement of neuroinflammatory diseases.

5'AMP-activated protein kinase: an emerging target of phytochemicals to treat chronic inflammatory diseases

Inflammation is a defensive response of the organism to traumatic, infectious, toxic, ischemic, and autoimmune injury. Inflammatory mediators are released to effectively eliminate the inflammatory trigger and restore homeostasis. However, failure of these processes can lead to chronic inflammatory conditions and diseases such as inflammatory bowel diseases, rheumatoid arthritis, inflammatory lung diseases, atherosclerosis, and neurodegenerative diseases. The cure of chronic inflammatory diseases remains challenging as current therapies have various limitations, such as pronounced side effects, progressive loss of efficacy, and high cost especially for biologics. In this context, phytochemicals (such as alkaloids, flavonoids, lignans, phenolic acids, saponins, terpenoids, and other classes) are considered as an interesting alternative approach. Among the numerous targets of phytochemicals, AMP-activated protein kinase (AMPK) can be considered as an interesting target in the context of inflammation. AMPK regulates inflammatory response by inhibiting inflammatory pathways (NF-κB, JAK/STAT, and MAPK) and regulating several other processes of the inflammatory response (oxidative stress, autophagy, and apoptosis). In this review, we summarize and discuss the studies focusing on phytochemicals that showed beneficial effects by blocking different inflammatory pathways implicating AMPK activation in chronic inflammatory disease models. We also highlight elements to consider when investigating AMPK in the context of phytochemicals.

Caffeic acid phenethyl ester ameliorates imidacloprid-induced acute toxicity in the rat cerebral cortex

This study aimed to investigate the role of caffeic acid phenethyl ester (CAPE), a compound found in propolis, on imidacloprid (IMI), a nicotinic acetylcholine receptor agonist that causes cerebral toxicity. 60 adult rats were randomly divided into five groups: control, IMI (100 mg/kg), and IMI+CAPE (1, 5, 10 mg/kg). Cerebral cortex tissue was examined histopathologically, biochemically, spectrophotometrically and immunohistochemically. The results showed that IMI caused toxicity in the cerebral cortex. However, CAPE (5 and 10 mg/kg) attenuated the deteriorated histopathological score and normalized the apoptotic markers (Bax and Caspase-3). Additionally, CAPE dose-dependently normalized the levels of TNF-α, dopamin, GFAP and NGF, and at the highest dose (10 mg/kg) also normalized the balance of oxidative parameters (MDA, SOD, CAT, and GSH). In conclusion, the antioxidant, anti-inflammatory, and anti-apoptotic effects of CAPE may be a promising treatment for acute IMI-induced cerebral cortex toxicity.

Hybrid molecules based on caffeic acid as potential therapeutics: A focused review

Caffeic acid-based compounds possess a high degree of structural diversity and show a variety of pharmacological properties, providing a useful framework for the discovery of new therapeutic agents. They are well-known analogues of antioxidants found in many natural products and synthetic compounds. The present review surveys the recent developments in structure-activity relationships (SAR) and mechanism of action (MOA) of various caffeic acid-containing compounds that play important roles in the design and synthesis of new bioactive molecules with antioxidant, antidiabetic, antiviral, antibacterial, anticancer, anti-inflammatory, and other properties. This review should provide inspiration to scientists in the research fields of organic synthesis and medicinal chemistry related to the development of new antioxidants with versatile therapeutic potential.

Caffeic Acid Phenethyl Ester (CAPE) Improves Boar Sperm Quality and Antioxidant Capacity in Liquid Preservation (17°C) Linked to AMPK Activity Maintenance

Liquid preservation of boar sperm is crucial for artificial insemination application in pig production. However, time-dependent oxidative damage to sperm is one of the major challenges during the liquid preservation period. Caffeic acid phenethyl ester (CAPE) possesses excellent antioxidant properties and has potential therapeutic use in reproductive organ injury linked to oxidative stress. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) involves in modulating the cellular redox state and exerts a beneficial effect on sperm preservation. In the present study, we firstly assessed different concentrations of CAPE that affect sperm quality during liquid storage to determine the appropriate addition. To further investigate whether CAPE exerts protective effects on boar sperm through modulation of AMPK activity, sperm quality parameters, antioxidant capacity, and marker protein expressions were evaluated under co-incubation with H₂O₂. The results showed that sperm treated with 210 μmol/L CAPE exhibited the highest motion parameters (total motility and progressive motility) and best functional integrity (mitochondrial activity, plasma membrane integrity, and acrosomal integrity). Even in the presence of H₂O₂, the addition of 210 μmol/L CAPE not only significantly improved sperm quality parameters, but also elevated CAT, SOD, and GSH-Px activities to enhance sperm antioxidant capacity. In addition, we found that CAPE could affect the protein activities of AMPK, phospho-AMPK α (p-AMPK), SOD, and Caspase-3 regardless of whether H₂O₂ is present or not. Our findings suggested that CAPE has potential application in liquid preservation of boar sperm and preliminary indicated that CAPE-induced improvement of sperm quality and antioxidant capacity should be mediated through conservation of AMPK activity. Further studies are required to illustrate the specific mechanism by which CAPE attenuates oxidative stress-mediated damages dependent on AMPK activity.

Phenolic Acids and Prevention of Cognitive Decline: Polyphenols with a Neuroprotective Role in Cognitive Disorders and Alzheimer's Disease

Cognitive impairment, also known as cognitive decline, can occur gradually or suddenly and can be temporary or more permanent. It represents an increasingly important public health problem and can depend on normal aging or be linked to different neurodegenerative disorders, including Alzheimer's disease (AD). It is now well-established that lifestyle factors including dietary patterns play an important role in healthy aging as well as in the prevention of cognitive decline in later life. Among the natural compounds, dietary polyphenols including phenolic acids have been recently the focus of major attention, with their supplementation being associated with better cognitive status and prevention of cognitive decline. Despite their therapeutic potential, human studies investigating the relation between phenolic acids intake and cognitive outcomes are rather scarce. In this review, we provide preclinical evidence that different dietary polyphenols such as rosmarinic acid, ellagic acid, and cinnamic aldehyde can exert neuroprotective and pro-cognitive activities through different molecular mechanisms including the modulation of pro-oxidant and antioxidant machinery as well as inflammatory status. Future and more numerous in vivo studies are needed to strengthen the promising results obtained at the preclinical level. Despite the excellent pharmacokinetic properties of phenolic acids, which are able to be accumulated in the brain at pharmacologically relevant levels, future studies should also identify which among the different metabolites produced as a consequence of phenolic acids' consumption may be responsible for the potential neuroprotective effects of this subgroup of polyphenols.

Phenolic Acids and Prevention of Cognitive Decline: Polyphenols with a Neuroprotective Role in Cognitive Disorders and Alzheimer's Disease

Cognitive impairment, also known as cognitive decline, can occur gradually or suddenly and can be temporary or more permanent. It represents an increasingly important public health problem and can depend on normal aging or be linked to different neurodegenerative disorders, including Alzheimer's disease (AD). It is now well-established that lifestyle factors including dietary patterns play an important role in healthy aging as well as in the prevention of cognitive decline in later life. Among the natural compounds, dietary polyphenols including phenolic acids have been recently the focus of major attention, with their supplementation being associated with better cognitive status and prevention of cognitive decline. Despite their therapeutic potential, human studies investigating the relation between phenolic acids intake and cognitive outcomes are rather scarce. In this review, we provide preclinical evidence that different dietary polyphenols such as rosmarinic acid, ellagic acid, and cinnamic aldehyde can exert neuroprotective and pro-cognitive activities through different molecular mechanisms including the modulation of pro-oxidant and antioxidant machinery as well as inflammatory status. Future and more numerous in vivo studies are needed to strengthen the promising results obtained at the preclinical level. Despite the excellent pharmacokinetic properties of phenolic acids, which are able to be accumulated in the brain at pharmacologically relevant levels, future studies should also identify which among the different metabolites produced as a consequence of phenolic acids' consumption may be responsible for the potential neuroprotective effects of this subgroup of polyphenols.

Protection against Amyloid-β Oligomer Neurotoxicity by Small Molecules with Antioxidative Properties: Potential for the Prevention of Alzheimer’s Disease Dementia

Soluble oligomeric assemblies of amyloid β-protein (Aβ), called Aβ oligomers (AβOs), have been recognized as primary pathogenetic factors in the molecular pathology of Alzheimer’s disease (AD). AβOs exert neurotoxicity and synaptotoxicity and play a critical role in the pathological progression of AD by aggravating oxidative and synaptic disturbances and tau abnormalities. As such, they are important therapeutic targets. From a therapeutic standpoint, it is not only important to clear AβOs or prevent their formation, it is also beneficial to reduce their neurotoxicity. In this regard, recent studies have reported that small molecules, most with antioxidative properties, show promise as therapeutic agents for reducing the neurotoxicity of AβOs. In this mini-review, we briefly review the significance of AβOs and oxidative stress in AD and summarize studies on small molecules with AβO-neurotoxicity-reducing effects. We also discuss mechanisms underlying the effects of these compounds against AβO neurotoxicity as well as their potential as drug candidates for the prevention and treatment of AD.

Regulatory Effects of Quercetin on M1/M2 Macrophage Polarization and Oxidative/Antioxidative Balance

Macrophage polarization plays essential and diverse roles in most diseases, such as atherosclerosis, adipose tissue inflammation, and insulin resistance. Homeostasis dysfunction in M1/M2 macrophage polarization causes pathological conditions and inflammation. Neuroinflammation is characterized by microglial activation and the concomitant production of pro-inflammatory cytokines, leading to numerous neurodegenerative diseases and psychiatric disorders. Decreased neuroinflammation can be obtained by using natural compounds, including flavonoids, which are known to ameliorate inflammatory responses. Among flavonoids, quercetin possesses multiple pharmacological applications and regulates several biological activities. In the present study, we found that quercetin effectively inhibited the expression of lipocalin-2 in both macrophages and microglial cells stimulated by lipopolysaccharides (LPS). The production of nitric oxide (NO) and expression levels of the pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, were also attenuated by quercetin treatment. Our results also showed that quercetin significantly reduced the expression levels of the M1 markers, such as interleukin (IL)-6, tumor necrosis factor (TNF)-α, and IL-1β, in the macrophages and microglia. The M1 polarization-associated chemokines, C–C motif chemokine ligand (CCL)-2 and C-X-C motif chemokine ligand (CXCL)-10, were also effectively reduced by the quercetin treatment. In addition, quercetin markedly reduced the production of various reactive oxygen species (ROS) in the microglia. The microglial phagocytic ability induced by the LPS was also effectively reduced by the quercetin treatment. Importantly, the quercetin increased the expression levels of the M2 marker, IL-10, and the endogenous antioxidants, heme oxygenase (HO)-1, glutamate-cysteine ligase catalytic subunit (GCLC), glutamate-cysteine ligase modifier subunit (GCLM), and NAD(P)H quinone oxidoreductase-1 (NQO1). The enhancement of the M2 markers and endogenous antioxidants by quercetin was activated by the AMP-activated protein kinase (AMPK) and Akt signaling pathways. Together, our study reported that the quercetin inhibited the effects of M1 polarization, including neuroinflammatory responses, ROS production, and phagocytosis. Moreover, the quercetin enhanced the M2 macrophage polarization and endogenous antioxidant expression in both macrophages and microglia. Our findings provide valuable information that quercetin may act as a potential drug for the treatment of diseases related to inflammatory disorders in the central nervous system.

Fenofibrate inhibits hypoxia-inducible factor-1 alpha and carbonic anhydrase expression through activation of AMP-activated protein kinase/HO-1/Sirt1 pathway in glioblastoma cells

Cancer and its associated conditions have significant impacts on public health at many levels worldwide, and cancer is the leading cause of death among adults. Peroxisome proliferator-activated receptor α (PPARα)-specific agonists, fibrates, have been approved by the Food and Drug Administration for managing hyperlipidemia. PPARα-specific agonists exert anti-cancer effects in many human cancer types, including glioblastoma (GBM). Recently, we have reported that the hypoxic state in GBM stabilizes hypoxia-inducible factor-1 alpha (HIF-1α), thus contributing to tumor escape from immune surveillance by activating the expression of the pH-regulating protein carbonic anhydrase IX (CA9). In this study, we aimed to study the regulatory effects of the PPARα agonist fibrate on the regulation of HIF-1α expression and its downstream target protein in GBM. Our findings showed that fenofibrate is the high potency compound among the various fibrates that inhibit hypoxia-induced HIF-1α and CA9 expression in GBM. Moreover, fenofibrate-inhibited HIF-1α expression is mediated by HO-1 activation in GBM cells through the AMP-activated protein kinase (AMPK) pathway. In addition, fenofibrate-enhanced HO-1 upregulation activates SIRT1 and leads to subsequent accumulation of SIRT1 in the nucleus, which further promotes HIF-1α deacetylation and inhibits CA9 expression. Using a protein synthesis inhibitor, cycloheximide, we also observed that fenofibrate inhibited HIF-1α protein synthesis. In addition, the administration of the proteasome inhibitor MG132 showed that fenofibrate promoted HIF-1α protein degradation in GBM. Hence, our results indicate that fenofibrate is a useful anti-GBM agent that modulates hypoxia-induced HIF-1α expression through multiple cellular pathways.

Caffeic acid phenethyl ester inhibits the growth of bladder carcinoma cells by upregulating growth differentiation factor 15

BACKGROUND

Caffeic acid phenethyl ester (CAPE), a bioactive component of propolis, has beneficial effects on cancer prevention. Growth differentiation factor 15 (GDF15) is an antitumor gene of bladder cancer. Therefore, this study investigated the anti-cancer effect of CAPE on bladder carcinoma cells and related mechanisms.

METHODS

The expressions of GDF15, N-myc downstream-regulated gene 1 (NDRG1), and maspin, and the activations of ERK, JNK, p38, and AMPKα1/2 in human bladder cells after gene transfection or knockdown were determined by immunoblot, RT-qPCR, and reporter assays. The assays of 5-ethynyl-2'-deoxyuridine (EdU), CyQUANT cell proliferation, and Matrigel invasion, and the xenograft animal study were used to assess the cell proliferation, invasion, and tumorigenesis.

RESULTS

GDF15 expression in epithelial cells was negatively correlated with neoplasia in vitro. Also, GDF15 exhibits in bladder fibroblasts and smooth muscle cells. CAPE-induced expressions of NDRG1 and maspin decreased cell proliferation and invasion of bladder carcinoma cells in a GDF15-dependent manner in vitro. The xenograft animal study suggesting CAPE attenuated tumor growth in vivo. CAPE increased phosphorylation of ERK, JNK, p38, and AMPKα1/2 to modulate the GDF15 expressions. Pretreatments with ERK, JNK, or p38 inhibitors partially inhibited the CAPE effects on the inductions of GDF15, NDRG1, or maspin. Knockdown of AMPKα1/2 attenuated the CAPE-induced GDF15 expression and cell proliferation in bladder carcinoma cells.

CONCLUSIONS

Our findings indicate that CAPE is a promising agent for anti-tumor growth in human bladder carcinoma cells via the upregulation of GDF15.

A Novel Synthetic Precursor of Styryl Sulfone Neuroprotective Agents Inhibits Neuroinflammatory Responses and Oxidative Stress Damage through the P38 Signaling Pathway in the Cell and Animal Model of Parkinson's Disease

A novel class of styryl sulfones were designed and synthesized as CAPE derivatives by our work team, which showed a multi-target neuroprotective effect, including antioxidative and anti-neuroinflammatory properties. However, the underlying mechanisms remain unclear. In the present study, the anti-Parkinson’s disease (PD) activity of 10 novel styryl sulfone compounds was screened by the cell viability test and the NO inhibition test in vitro. It was found that 4d exhibited the highest activity against PD among them. In a MPTP-induced mouse model of PD, the biological activity of 4d was validated through suppressing dopamine neurotoxicity, microglial activation, and astrocytes activation. With compound 4d, we conducted the mechanistic studies about anti-inflammatory responses through inhibition of p38 phosphorylation to protect dopaminergic neurons, and antioxidant effects through promoting nuclear factor erythroid 2-related factor 2 (Nrf2). The results revealed that 4d could significantly inhibit 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenylpyridinium (MPTP/MPP⁺)-induced p38 mitogen-activated protein kinase (MAPK) activation in both in vitro and in vivo PD models, thus inhibiting the NF-κB-mediated neuroinflammation-related apoptosis pathway. Simultaneously, it could promote Nrf2 nuclear transfer, and upregulate the expression of antioxidant phase II detoxification enzymes HO-1 and GCLC, and then reduce oxidative damage.

Recent progresses in the pharmacological activities of caffeic acid phenethyl ester

The past decades have seen a growing interest in natural products. Caffeic acid phenethyl ester (CAPE), a flavonoid isolated from honeybee propolis, has shown multiple pharmacological potentials, including anti-cancer, anti-inflammatory, antioxidant, antibacterial, antifungal, and protective effects on nervous systems and multiple organs, since it was found as a potent nuclear factor κB (NF-κB) inhibitor. This review summarizes the advances in these beneficial effects of CAPE, as well as the underlying mechanisms, and proposes that CAPE offers an opportunity for developing therapeutics in multiple diseases. However, clinical trials on CAPE are necessary and encouraged to obtain certain clinically relevant conclusions.

Efficacy of Caffeic Acid on Diabetes and Its Complications in the Mouse

Diabetic dyslipidemia and hyperglycemia contribute to excessive reactive oxygen species (ROS) production, leading to deleterious complications, such as nephropathy, atherosclerosis and cardiac dysfunction, and target major organs in the body. The aim of this study was to investigate the effect of caffeic acid (CA) on mouse weight and survival, serum level of fasting blood glucose (FBG), serum lipid parameters and atherogenic indices, oxidative damage in blood, liver and kidney tissue, pathophysiological changes and their function markers in healthy and alloxan-induced type 1 diabetic mice. Diabetes was induced in mice with a single intravenous injection of alloxan (75 mg kg⁻¹). Two days later, CA (50 mg kg⁻¹) was given intraperitoneally for seven days in diabetic mice. Diabetes affected glucose level, lipid profile, hematological and biochemical parameters, induced DNA damage and apoptotic/necrotic death in whole blood cells, liver and kidney, leading to weight loss and a decreased lifespan. CA treatment of diabetic mice revealed a protective effect on the liver and kidney, hypoglycemic and hypolipidemic properties and high protection against atherogenic outcomes. The obtained results suggest that CA is a safe and potent agent against diabetes that acts as an effective antioxidant in reducing serum glucose, lipid profile and atherogenic indices, leading to increased lifespan in mice.

Propolis Extract and Its Bioactive Compounds-From Traditional to Modern Extraction Technologies

Propolis is a honeybee product known for its antioxidant, anti-inflammatory, anticancer, and antimicrobial effects. It is rich in bioactive molecules whose content varies depending on the botanical and geographical origin of propolis. These bioactive molecules have been studied individually and as a part of propolis extracts, as they can be used as representative markers for propolis standardization. Here, we compare the pharmacological effects of representative polyphenols and whole propolis extracts. Based on the literature data, polyphenols and extracts act by suppressing similar targets, from pro-inflammatory TNF/NF-κB to the pro-proliferative MAPK/ERK pathway. In addition, they activate similar antioxidant mechanisms of action, like Nrf2-ARE intracellular antioxidant pathway, and they all have antimicrobial activity. These similarities do not imply that we should attribute the action of propolis solely to the most representative compounds. Moreover, its pharmacological effects will depend on the efficacy of these compounds’ extraction. Thus, we also give an overview of different propolis extraction technologies, from traditional to modern ones, which are environmentally friendlier. These technologies belong to an open research area that needs further effective solutions in terms of well-standardized liquid and solid extracts, which would be reliable in their pharmacological effects, environmentally friendly, and sustainable for production.

The taste of neuroinflammation: Molecular mechanisms linking taste sensing to neuroinflammatory responses

Evidence indicates a critical role of neuroinflammatory response as an underlying pathophysiological process in several central nervous system disorders, including neurodegenerative diseases. However, the molecular mechanisms that trigger neuroinflammatory processes are not fully known. The discovery of bitter taste receptors in regions other than the oral cavity substantially increased research interests on their functional roles in extra-oral tissues. It is now widely accepted that bitter taste receptors, for instance, in the respiratory, intestinal, reproductive and urinary tracts, are crucial not only for sensing poisonous substances, but also, act as immune sentinels, mobilizing defense mechanisms against pathogenic aggression. The relatively recent discovery of bitter taste receptors in the brain has intensified research investigation on the functional implication of cerebral bitter taste receptor expression. Very recent data suggest that responses of bitter taste receptors to neurotoxins and microbial molecules, under normal condition, are necessary to prevent neuroinflammatory reactions. Furthermore, emerging data have revealed that downregulation of key components of the taste receptor signaling cascade leads to increased oxidative stress and inflammasome signaling in neurons that ultimately culminate in neuroinflammation. Nevertheless, the mechanisms that link taste receptor mediated surveillance of the extracellular milieu to neuroinflammatory responses are not completely understood. This review integrates new data on the molecular mechanisms that link bitter taste receptor sensing to neuroinflammatory responses. The role of bitter taste receptor-mediated sensing of toxigenic substances in brain disorders is also discussed. The therapeutic significance of targeting these receptors for potential treatment of neurodegenerative diseases is also highlighted.

Natural antioxidants for neuroinflammatory disorders and possible involvement of Nrf2 pathway: A review

The transcription factor Nrf2 (nuclear factor-erythroid 2 p45-related factor 2) play a crucial role in cellular redox and metabolic system. Activation of Nrf2 may be an effective therapeutic approach for neuroinflammatory disorders, through activation of antioxidant defences system, lower the inflammation, line up the mitochondrial function, and balancing of protein homeostasis. Various recent studies revealed that many of active substance obtained from plants have been found to activate the Nrf2 and to exert neuroprotective effects in various experimental models, raising the possibility that activation of Nrf2 may be an effective therapeutic approaches for neuroinflammatory disorders. The objective of this review was to evaluate the neuroprotective property of natural substance against neuroinflammatory disorders by reviewing the studies done till today. The outcomes of various in vitro and in vivo examinations have shown that natural compounds producing neuroprotective effects in neuronal system via activation of Nrf2. Herein, we also reviewed the studies to understand the role of Nrf2 for curing CNS disorders. Here we can conclude, herbal/natural moieties having potency to fight and prevent from neuroinflammatory disorders due to their abilities to activate Nrf2 pathway.

Propolis in Metabolic Syndrome and Its Associated Chronic Diseases: A Narrative Review

Propolis is a resinous product collected by bees from plants to protect and maintain the homeostasis of their hives. Propolis has been used therapeutically by humans for centuries. This review article attempts to analyze the potential use of propolis in metabolic syndrome (MetS) and its associated chronic diseases. MetS and its chronic diseases were shown to be involved in at least seven out of the top 10 causes of death in 2019. Patients with MetS are also at a heightened risk of severe morbidity and mortality in the present COVID-19 pandemic. Propolis with its antioxidant and anti-inflammatory properties is potentially useful in ameliorating the symptoms of MetS and its associated chronic diseases. The aim of this article is to provide a comprehensive review on propolis and its therapeutic benefit in MetS and its chronic diseases, with an emphasis on in vitro and in vivo studies, as well as human clinical trials. Moreover, the molecular and biochemical mechanisms of action of propolis are also discussed. Propolis inhibits the development and manifestation of MetS and its chronic diseases by inhibiting of the expression and interaction of advanced glycation end products (AGEs) and their receptors (RAGEs), inhibiting pro-inflammatory signaling cascades, and promoting the cellular antioxidant systems.

CAPE and Neuroprotection: A Review

Propolis, a product of the honey bee, has been used in traditional medicine for many years. A hydrophobic bioactive polyphenolic ester, caffeic acid phenethyl ester (CAPE), is one of the most extensively investigated active components of propolis. Several studies have indicated that CAPE has a broad spectrum of pharmacological activities as anti-oxidant, anti-inflammatory, anti-viral, anti-fungal, anti-proliferative, and anti-neoplastic properties. This review largely describes CAPE neuroprotective effects in many different conditions and summarizes its molecular mechanisms of action. CAPE was found to have a neuroprotective effect on different neurodegenerative disorders. At the basis of these effects, CAPE has the ability to protect neurons from several underlying causes of various human neurologic diseases, such as oxidative stress, apoptosis dysregulation, and brain inflammation. CAPE can also protect the nervous system from some diseases which negatively affect it, such as diabetes, septic shock, and hepatic encephalopathy, while numerous studies have demonstrated the neuroprotective effects of CAPE against adverse reactions induced by different neurotoxic substances. The potential role of CAPE in protecting the central nervous system (CNS) from secondary injury following various CNS ischemic conditions and CAPE anti-cancer activity in CNS is also reviewed. The structure–activity relationship of CAPE synthetic derivatives is discussed as well.

Propolis: A useful agent on psychiatric and neurological disorders? A focus on CAPE and pinocembrin components

Propolis consists of a honeybee product, with a complex mix of substances that have been widely used in traditional medicine. Among several compounds present in propolis, caffeic acid phenethyl ester (CAPE), and pinocembrin emerge as two principal bioactive compounds, with benefits in a variety of body systems. In addition to its well-explored pharmacological properties, neuropharmacological activities have been poorly discussed. In an unprecedented way, the present review addresses the current finding on the promising therapeutic purposes of propolis, focusing on CAPE and pinocembrin, highlighting its use on neurological disturbance, as cerebral ischemia, neuroinflammation, convulsion, and cognitive impairment, as well as psychiatric disorders, such as anxiety and depression. In addition, we provide a critical analysis, discussion, and systematization of the molecular mechanisms which underlie these central nervous system effects. We hypothesize that the pleiotropic action of CAPE and pinocembrin, per se or associated with other substances present in propolis may result in the therapeutic activities reported. Inhibition of the pro-inflammatory cascade, antioxidant activity, and positive neurotrophic modulatory effects consist of the main molecular targets attributed to CAPE and pinocembrin in health benefits.

Caffeic Acid Phenethyl Ester Protects against Experimental Autoimmune Encephalomyelitis by Regulating T Cell Activities

Multiple sclerosis (MS) is an autoimmune inflammatory disease of the central nervous system (CNS) characterized by progressive demyelination and disabling outcomes. CD4⁺ T cells are the most critical driving factor of relapsing MS, but little improvement has been noted upon deletion of the whole T cell population. Caffeic acid phenethyl ester (CAPE), one of the main active compounds of propolis, exhibits potent antitumour, anti-inflammatory, and antioxidant properties by suppressing nuclear factor-κB (NF-κB) transactivation. To investigate the therapeutic potential of CAPE in MS, we studied the effects of CAPE on cytokine levels, T cells, and NF-κB activities and in an experimental MS animal model. The results showed that cerebrospinal fluid (CSF) from patients with relapsing MS is characterized by increased levels of proinflammatory cytokines/chemokines that preferentially skew towards T helper 1 (Th1) cytokines. In vitro studies demonstrated that CAPE not only inhibited T cell proliferation and activation but also effectively modulated T cell subsets. Under both Th0- and Th1-polarizing conditions, the proportion of CD4⁺IFN-γ⁺ cells was downregulated, while CD4⁺Foxp3⁺ cells were increased. Moreover, nuclear translocation of NF-κB p65 was inhibited by CAPE. In a murine experimental autoimmune encephalomyelitis model, prophylactic treatment with CAPE significantly decreased the disease incidence and severity. Compared to the vehicle group, mice pretreated with CAPE showed diminished inflammatory cell infiltration, microglia/macrophage activation, and demyelination injury. Additionally, CAPE pretreatment reduced the level of Th1 cells in both spleen and the CNS and increased regulatory T cells (Tregs) in the CNS. In conclusion, our results highlight the potential merit of CAPE in suppressing T cell activity mainly through targeting the pathogenic Th1 lineage, which may be beneficial for MS treatment.

SIRT1 activation by minocycline on regulation of microglial polarization homeostasis

Sirtuin 1 (SIRT1) has been reported to be involved in the mechanisms underlying longevity and has also been indicated as a valuable regulator of age-related neurological disorders. Some natural products increase SIRT1 activity and stimulate deacetylation of various proteins. In the present study, SIRT1 overexpression by genetic modification or treatment with SIRT1 activators significantly inhibited the secretion of nitric oxide and expression of inducible nitric oxide synthase, cyclooxygenase 2, and proinflammatory mediator-interleukin 1β-in microglia. SIRT1 activation also decreased the levels of K379 acetyl-p53 and the protein inhibitor of activated Stat 1 expression in microglial cells. In addition, it dramatically promoted M2 polarization of microglia, which enhanced cell motility and altered phagocytic ability. We also used minocycline, a well-known inhibitor of microglial activation, to study the mechanism of SIRT1 signaling. Minocycline treatment decreased neuroinflammatory responses and promoted M2 polarization of microglia. It also reduced the acetyl-p53 level in the brain tissues in an inflammatory mouse model. Our findings demonstrated that SIRT1 participates in the maintenance of microglial polarization homeostasis and that minocycline exerts regulatory effects on SIRT1 activation. Therefore, our results indicate that SIRT1 activation may be a useful therapeutic target for the treatment of neuroinflammation-associated disorders.

Circulating metabolomics profiling reveals novel pathways associated with cognitive decline in patients with hypertension

Background:

Hypertension is a significant risk factor for cardiovascular disease, and it is associated with dementia, including Alzheimer’s disease (AD). Although it may be correlated with AD in terms of symptoms, the link between hypertension and AD pathological biomarkers, and the potential underlying mechanism of hypertension with cognitive decline, are still not well understood.

Methods:

The Mini-Mental State Examination (MMSE) scores were used to evaluate cognitive function. Enzyme-linked immunosorbent assays were used to examine plasma amyloid-beta (Aβ)₄₀, Aβ₄₂, and tau concentration in hypertensive patients. Metabolomics and metagenomics were performed to identify the significantly changed circulating metabolites and microbiota between healthy individuals and hypertensive patients. Pearson’s correlation was used to examine the association between cognitive indicators and differential metabolites.

Results:

We found significantly decreased MMSE scores, elevated plasma Aβ₄₀, and decreased Aβ₄₂/Aβ₄₀ ratio in hypertensive patients, which are critically associated with AD pathology. Based on metabolomics, we found that significantly altered metabolites in the plasma of hypertensive patients were enriched in the benzoate degradation and phenylpropanoid biosynthesis pathways, and they were also correlated with changes in MMSE scores and Aβ₄₂/Aβ₄₀ ratio. In addition, metabolomics signaling pathway analysis suggested that microbial metabolism was altered in hypertensive patients. We also identified altered blood microbiota in hypertensive patients compared with the controls.

Conclusions:

Our study provides a novel metabolic and microbial mechanism, which may underlie the cognitive impairment in hypertensive patients.

Caffeic acid phenethyl ester reversed cadmium-induced cell death in hippocampus and cortex and subsequent cognitive disorders in mice: Involvements of AMPK/SIRT1 pathway and amyloid-tau-neuroinflammation axis

Exposure to nonbiodegradable cadmium (Cd) causes many health problems including the damage to the nervous system. This study aimed to increase knowledge about its neurotoxic effects and the neuroprotective potential of caffeic acid phenethyl ester (CAPE, a polyphenol abundant in honeybee propolis). In mice, CAPE (10 μmol/kg/day body weight) attenuated significantly learning and memory deficits induced by CdCl₂ (1.5 mg/kg/day body weight). For the CdCl₂-treated mice, CAPE increased crossing number in open field test, decreased the alternation in Y-maze test, and increased the latency time and error number in step down test. CAPE also inhibited CdCl₂-initiated Aβ accumulation and activation of pro-inflammatory factors and microglia in the brains. Therefore, CAPE could be a food-derived neuroprotective agent against Cd-induced neurotoxicity and neurodegenerative disorders, through attenuating neuronal apoptosis and neuroinflammation via the AMPK/SIRT1 pathway and amyloid-tau-neuroinflammation axis.

Naturally Derived Heme-Oxygenase 1 Inducers and Their Therapeutic Application to Immune-Mediated Diseases

Heme oxygenase (HO) is the primary antioxidant enzyme involved in heme group degradation. A variety of stimuli triggers the expression of the inducible HO-1 isoform, which is modulated by its substrate and cellular stressors. A major anti-inflammatory role has been assigned to the HO-1 activity. Therefore, in recent years HO-1 induction has been employed as an approach to treating several disorders displaying some immune alterations components, such as exacerbated inflammation or self-reactivity. Many natural compounds have shown to be effective inductors of HO-1 without cytotoxic effects; among them, most are chemicals present in plants used as food, flavoring, and medicine. Here we discuss some naturally derived compounds involved in HO-1 induction, their impact in the immune response modulation, and the beneficial effect in diverse autoimmune disorders. We conclude that the use of some compounds from natural sources able to induce HO-1 is an attractive lifestyle toward promoting human health. This review opens a new outlook on the investigation of naturally derived HO-1 inducers, mainly concerning autoimmunity.

Cognitive impairment with diabetes mellitus and metabolic disease: innovative insights with the mechanistic target of rapamycin and circadian clock gene pathways

Introduction: Dementia is the 7th leading cause of death that imposes a significant financial and service burden on the global population. Presently, only symptomatic care exists for cognitive loss, such as Alzheimer's disease.Areas covered: Given the advancing age of the global population, it becomes imperative to develop innovative therapeutic strategies for cognitive loss. New studies provide insight to the association of cognitive loss with metabolic disorders, such as diabetes mellitus.Expert opinion: Diabetes mellitus is increasing in incidence throughout the world and affects 350 million individuals. Treatment strategies identifying novel pathways that oversee metabolic and neurodegenerative disorders offer exciting prospects to treat dementia. The mechanistic target of rapamycin (mTOR) and circadian clock gene pathways that include AMP activated protein kinase (AMPK), Wnt1 inducible signaling pathway protein 1 (WISP1), erythropoietin (EPO), and silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1) provide novel strategies to treat cognitive loss that has its basis in metabolic cellular dysfunction. However, these pathways are complex and require precise regulation to maximize treatment efficacy and minimize any potential clinical disability. Further investigations hold great promise to treat both the onset and progression of cognitive loss that is associated with metabolic disease.

The tiliroside derivative, 3-O-[(E)-(2-oxo-4-(p-tolyl) but-3-en-1-yl] kaempferol produced inhibition of neuroinflammation and activation of AMPK and Nrf2/HO-1 pathways in BV-2 microglia

Neuroinflammation is now widely accepted as an important pathophysiological mechanism in neurodegenerative disorders, thus providing a critical target for novel compounds. In this study, 3-O-[(E)-(2-oxo-4-(p-tolyl)but-3-en-1-yl] kaempferol (OTBK) prevented the production of pro-inflammatory mediators TNFα, IL-6, PGE₂ and nitrite from BV-2 microglia activated with LPS and IFNγ. These effects were accompanied by reduction in the levels of pro-inflammatory proteins COX-2 and iNOS. Involvement of NF-κB in the anti-inflammatory activity of OTBK was evaluated in experiments showing that the compound prevented phosphorylation, nuclear accumulation and DNA binding of p65 sub-unit induced by stimulation of BV-2 microglia with LPS and IFNγ. Exposure of mouse hippocampal HT22 neurons to conditioned media from LPS + IFNγ-stimulated BV-2 cells resulted in reduced cell viability and generation of cellular reactive oxygen species. Interestingly, conditioned media from LPS/IFNγ-stimulated BV-2 cells which were treated with OTBK did not induce neuronal damage or oxidative stress. OTBK was shown to increase protein levels of phospho-AMPKα, Nrf2 and HO-1 in BV-2 microglia. It was further revealed that OTBK treatment increased Nrf2 DNA binding in BV-2 microglia. The actions of the compound on AMPKα and Nrf2 were shown to contribute to its anti-inflammatory activity as demonstrated by diminished activity in the presence of the AMPK antagonist dorsomorphin and Nrf2 inhibitor trigonelline. These results suggest that OTBK inhibits neuroinflammation through mechanisms that may involve activation of AMPKα and Nrf2 in BV-2 microglia.

Natural products as a potential modulator of microglial polarization in neurodegenerative diseases

Neurodegenerative diseases (NDs) are characterized by the progressive loss of structure and function of neurons most common in elderly population, mainly including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). Neuroinflammation caused by microglia as the resident macrophages of the central nervous system (CNS) plays a contributory role in the onset and progression of NDs. Activated microglia, as in macrophages, to be heterogeneous, can polarize into M1 (pro-inflammatory) and M2 (anti-inflammatory) functional phenotypes. The former elaborate pro-inflammatory mediators promoting neuroinflammation and neuronal damage. In contrast, the latter generate anti-inflammatory mediators and neurotrophins that inhibit neuroinflammation and promote neuronal healing. Consistently, the regulation of microglial polarization from M1 to M2 phenotype appears as an outstanding therapeutic and preventive approach for NDs treatment. Although non-steroidal anti-inflammatory drugs (NSAIDs) currently used to alleviate M1 microglia-associated neuroinflammation responsible for the development of NDs, these drugs have different degrees of adverse effects and limited efficacy. As the advantages of novel structure, multi-target, high efficiency and low toxicity, natural products as the modulators of microglial polarization have attracted considerable concerns in the therapeutic areas of NDs. In this review, we mainly summarized the therapeutic potential of natural products and their various molecular mechanisms for NDs treatment through modulating microglial polarization. The aim of the current review is expected to be useful to develop innovative modulators of microglial polarization from natural products for the amelioration and treatment of NDs.

Caffeic Acid Phenethyl Ester (CAPE) Protects PC12 Cells Against Cisplatin-Induced Neurotoxicity by Activating the AMPK/SIRT1, MAPK/Erk, and PI3k/Akt Signaling Pathways

Peripheral sensory neuropathy (PSN) is a well-known side effect of cisplatin characterized by axonal damage. In the early stage of neurotoxicity, cisplatin affects proteins that modulate neurite outgrowth and neuroplasticity, without inducing mitochondrial damage or apoptosis. There are no preventive therapies for cisplatin-induced peripheral neuropathy; therefore, measures to improve axonal growth and connectivity would be beneficial. Caffeic acid phenethyl ester (CAPE) is a bioactive component of propolis with neurotrophic and neuroprotective activities. We have recently showed that CAPE protects against cisplatin-induced neurotoxicity by activating NGF high-affinity receptors (trkA) and inducing neuroplasticity. We have now assessed other potential early targets of cisplatin and additional mechanisms involved in the neuroprotection of CAPE. Cisplatin reduced axonal cytoskeletal proteins (F-actin and β-III-tubulin) without inducing oxidative damage in PC12 cells. It also reduced energy-related proteins (AMPK α, p-AMPK α, and SIRT1) and glucose uptake. At this stage of neurotoxicity, glutamate excitotoxicity is not involved in the toxicity of cisplatin. CAPE attenuated the downregulation of the cytoskeleton and energy-related markers as well as SIRT1 and phosphorylated AMPK α. Moreover, the neuroprotective mechanism of CAPE also involves the activation of the neurotrophic signaling pathways MAPK/Erk and PI3k/Akt. The PI3K/Akt pathway is involved in the upregulation of SIRT1 induced by CAPE, but not in the upregulation of cytoskeletal proteins. Altogether, these findings suggest that the neuroprotective effect of CAPE against cisplatin-induced neurotoxicity involves both (a) a neurotrophic mechanism that mimics the mechanism triggered by the NGF itself and (b) a non-neurotrophic mechanism that upregulates the cytoskeletal proteins.

Melatonin decreases M1 polarization via attenuating mitochondrial oxidative damage depending on UCP2 pathway in prorenin-treated microglia

Accumulating evidence suggests that neuroinflammation and oxidative stress in cardiovascular center contribute to the pathological processes underlying hypertension. Microglia activation triggers the inflammation and oxidative stress. Melatonin is a documented potent anti-inflammatory regent and antioxidant, the underlying roles of melatonin in regulating microglia activation via mitochondria remain unclear. In present study, we investigated the protective role of melatonin in decreasing M1 phenotype switching via attenuating mitochondrial oxidative damage in dependence on uncoupling protein 2 (UCP2) pathway in microglia. Prorenin (20 nmol/L; 24 hr) was used to induce inflammation in cultured microglia. Mitochondrial morphology was detected by transmission electron microscope. The reactive oxygen species (ROS) production by using DCFH-DA fluorescence imaging and mitochondrial membrane potential (MMP, ΔΨm) was evaluated by JC-1 staining. The indicator of the redox status as the ratio of the amount of total NADP+ to total NADPH, and the expression of 6 subunits of NADPH oxidase is measured. The pro-inflammatory cytokines releasing was measured by qPCR. UCP2 and activated AMPKα (p-AMPKα) expression were examined by immunoblot. Melatonin (100 μM) markedly alleviated the M1 microglia phenotype shifting and abnormal mitochondria morphology. Melatonin attenuated prorenin-induced ΔΨm increasing and ROS overproduction. Melatonin decreased the redox ratio (NADP+/NADPH) and the p47phox and gp91phox subunits of NADPH oxidase expression in prorenin-treated microglia. These effects were reversed in the presence of UCP2 siRNA. Our results suggested that the protective effect of melatonin against prorenin-induced M1 phenotype switching via attenuating mitochondrial oxidative damage depending on UCP2 upregulation in prorenin-treated microglia.

Caffeic acid phenethyl ester attenuates neuropathic pain by suppressing the p38/NF-κB signal pathway in microglia

Background

Management of neuropathic pain is still a clinical challenge. Evidence has accumulated indicating that propolis is effective in attenuating neuropathic pain; however, the mechanism is not fully understood. Our present study investigated the effects and the possible mechanism of caffeic acid phenethyl ester (CAPE), the main ingredient of propolis, in improving neuropathic pain via its inhibition on p38/NF-κB signal pathway in microglia.

Materials and methods

Chronic constriction injury (CCI) mice model and the microglial cell line BV-2 were used to investigate the effects and the mechanism of CAPE. Cell signaling was measured by real-time PCR, Western blotting and immunofluorescence assay.

Results

CAPE relieved neuropathic pain behaviors induced by CCI in mice. CAPE also inhibited CCI-induced activation of microglia. Furthermore, CAPE suppressed the phosphorylation of p38 mitogen-activated protein kinase, inhibited the translocation of NF-κB and decreased the expression of proinflammatory cytokines tumor necrosis factor-α, IL-1β and IL-6.

Conclusion

CAPE was found to be an effective and safe drug candidate for alleviating neuropathic pain by its powerful inhibition on the P38/NF-κB signal pathway.

Connection between Systemic Inflammation and Neuroinflammation Underlies Neuroprotective Mechanism of Several Phytochemicals in Neurodegenerative Diseases

Oxidative damage, mitochondrial dysfunction, and neuroinflammation are strongly implicated in the pathogenesis of neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD), and a substantial portion of elderly population at risk of these diseases requires nutritional intervention to benefit health due to lack of clinically relevant drugs. To this end, anti-inflammatory mechanisms of several phytochemicals such as curcumin, resveratrol, propolis, polyunsaturated fatty acids (PUFAs), and ginsenosides have been extensively studied. However, correlation of the phytochemicals with neuroinflammation or brain nutrition is not fully considered, especially in their therapeutic mechanism for neuronal damage or dysfunction. In this article, we review the advance in antioxidative and anti-inflammatory effects of phytochemicals and discuss the potential communication with brain microenvironment by improved gastrointestinal function, enhanced systemic immunity, and neuroprotective outcomes. These data show that phytochemicals may modulate and suppress neuroinflammation of the brain by several approaches: (1) reducing systemic inflammation and infiltration via the blood-brain barrier (BBB), (2) direct permeation into the brain parenchyma leading to neuroprotection, (3) enhancing integrity of disrupted BBB, and (4) vagal reflex-mediated nutrition and protection by gastrointestinal function signaling to the brain. Therefore, many phytochemicals have multiple potential neuroprotective approaches contributing to therapeutic benefit for pathogenesis of neurodegenerative diseases, and development of strategies for preventing these diseases represents a considerable public health concern and socioeconomic burden.

Neuroprotective Effect of Caffeic Acid Phenethyl Ester in A Mouse Model of Alzheimer's Disease Involves Nrf2/HO-1 Pathway

Alzheimer's disease (AD) is a progressive pathology, where dementia symptoms gradually worsen over a number of years. The hallmarks of AD, such as amyloid β-peptide (Aβ) in senile plaque and neurofibrillary tangles, are strongly intertwined with oxidative stress, which is considered one of the common effectors of the cascade of degenerative events. The endogenous nuclear factor erythroid 2-related factor 2 (Nrf2) is the "master regulator" of the antioxidant response and it is known as an indicator and regulator of oxidative stress. The present study aimed to determine the potential neuroprotective activity of caffeic acid phenethyl ester (CAPE), a polyphenolic compound abundant in honeybee, against the neurotoxicity of Aβ_1-42 oligomers (AβO) in mice. An intracerebroventricular (i.c.v.) injection of AβO into the mouse brain triggered increased reactive oxygen species levels, neurodegeneration, neuroinflammation, and memory impairment. In contrast, the intraperitoneal administration of CAPE (10 mg/kg) after i.c.v. AβO-injection counteracted oxidative stress accompanied by an induction of Nrf2 and heme oxygenase-1 via the modulation of glycogen synthase kinase 3β in the hippocampus of mice. Additionally, CAPE treatment decreased AβO-induced neuronal apoptosis and neuroinflammation, and improved learning and memory, protecting mice against the decline in spatial cognition. Our findings demonstrate that CAPE could potentially be considered as a promising neuroprotective agent against progressive neurodegenerative diseases such as AD.

Combined treatment with GSNO and CAPE accelerates functional recovery via additive antioxidant activities in a mouse model of TBI

Traumatic brain injury (TBI) is the major cause of physical disability and emotional vulnerability. Treatment of TBI is lacking due to its multimechanistic etiology, including derailed mitochondrial and cellular energy metabolism. Previous studies from our laboratory show that an endogenous nitric oxide (NO) metabolite S-nitrosoglutathione (GSNO) provides neuroprotection and improves neurobehavioral function via anti-inflammatory and anti-neurodegenerative mechanisms. To accelerate the rate and enhance the degree of recovery, we investigated combining GSNO with caffeic acid phenethyl ester (CAPE), a potent antioxidant compound, using a male mouse model of TBI, controlled cortical impact in mice. The combination therapy accelerated improvement of cognitive and depressive-like behavior compared with GSNO or CAPE monotherapy. Separately, both GSNO and CAPE improved mitochondrial integrity/function and decreased oxidative damage; however, the combination therapy had greater effects on Drp1 and MnSOD. Additionally, while CAPE alone activated AMPK, this activation was heightened in combination with GSNO. CAPE treatment of normal animals also significantly increased the expression levels of pAMPK, pACC (activation of AMPK substrate ACC), and pLKB1 (activation of upstream to AMPK kinase LKB1), indicating that CAPE activates AMPK via LKB1. These results show that while GSNO and CAPE provide neuroprotection and improve functional recovery separately, the combination treatment invokes greater recovery by significantly improving mitochondrial functions and activating the AMPK enzyme. Both GSNO and CAPE are in human consumption without any known adverse effects; therefore, a combination therapy-based multimechanistic approach is worthy of investigation in human TBI.

AMP-activated protein kinase-dependent induction of autophagy by erythropoietin protects against spinal cord injury in rats

AIMS

Autophagy has been regarded as a promising therapeutic target for spinal cord injury (SCI). Erythropoietin (EPO) has been demonstrated to exhibit neuroprotective effects in the central nervous system (CNS); however, the molecular mechanisms of its protection against SCI remain unknown. This study aims to investigate whether the neuroprotective effects of EPO on SCI are mediated by autophagy via AMP-activated protein kinase (AMPK) signaling pathways.

METHODS

Functional assessment and Nissl staining were used to investigate the effects of EPO on SCI. Expressions of proteins were detected by Western blot and immunohistochemistry.

RESULTS

Treatment with EPO significantly reduced the loss of motor neurons and improved the functional recovery following SCI. Erythropoietin significantly enhanced the SCI-induced autophagy through activating AMPK and inactivating mTOR signaling. The inhibitor of AMPK, compound C, could block the EPO-induced autophagy and beneficial action on SCI, whereas the activator of AMPK, metformin, could mimic the effects of EPO. In the in vitro studies, EPO enhanced the hypoxia-induced autophagy in an AMPK-dependent manner.

CONCLUSIONS

The AMPK-dependent induction of autophagy contributes to the neuroprotection of EPO on SCI.