Chlorogenic Acid Prevents AMPA-Mediated Excitotoxicity in Optic Nerve Oligodendrocytes Through a PKC and Caspase-Dependent Pathways

Chlorogenic Acid: A Systematic Review on the Biological Functions, Mechanistic Actions, and Therapeutic Potentials

Chlorogenic acid (CGA) is a type of polyphenol compound found in rich concentrations in many plants such as green coffee beans. As an active natural substance, CGA exerts diverse therapeutic effects in response to a variety of pathological challenges, particularly conditions associated with chronic metabolic diseases and age-related disorders. It shows multidimensional functions, including neuroprotection for neurodegenerative disorders and diabetic peripheral neuropathy, anti-inflammation, anti-oxidation, anti-pathogens, mitigation of cardiovascular disorders, skin diseases, diabetes mellitus, liver and kidney injuries, and anti-tumor activities. Mechanistically, its integrative functions act through the modulation of anti-inflammation/oxidation and metabolic homeostasis. It can thwart inflammatory constituents at multiple levels such as curtailing NF-kB pathways to neutralize primitive inflammatory factors, hindering inflammatory propagation, and alleviating inflammation-related tissue injury. It concurrently raises pivotal antioxidants by activating the Nrf2 pathway, thus scavenging excessive cellular free radicals. It elevates AMPK pathways for the maintenance and restoration of metabolic homeostasis of glucose and lipids. Additionally, CGA shows functions of neuromodulation by targeting neuroreceptors and ion channels. In this review, we systematically recapitulate CGA's pharmacological activities, medicinal properties, and mechanistic actions as a potential therapeutic agent. Further studies for defining its specific targeting molecules, improving its bioavailability, and validating its clinical efficacy are required to corroborate the therapeutic effects of CGA.

Risk Assessment of Chlorogenic and Isochlorogenic Acids in Coffee By-Products

Chlorogenic and isochlorogenic acids are naturally occurring antioxidant dietary polyphenolic compounds found in high concentrations in plants, fruits, vegetables, coffee, and coffee by-products. The objective of this review was to assess the potential health risks associated with the oral consumption of coffee by-products containing chlorogenic and isochlorogenic acids, considering both acute and chronic exposure. An electronic literature search was conducted, revealing that 5-caffeoylquinic acid (5-CQA) and 3,5-dicaffeoylquinic acid (3,5-DCQA) are the major chlorogenic acids found in coffee by-products. Toxicological, pharmacokinetic, and clinical data from animal and human studies were available for the assessment, which indicated no significant evidence of toxic or adverse effects following acute oral exposure. The current state of knowledge suggests that long-term exposure to chlorogenic and isochlorogenic acids by daily consumption does not appear to pose a risk to human health when observed at doses within the normal range of dietary exposure. As a result, the intake of CQAs from coffee by-products can be considered reasonably safe.

Potential implications of polyphenolic compounds in neurodegenerative diseases

Neurodegenerative diseases are common chronic diseases related to progressive damage to the nervous system. Current neurodegenerative diseases present difficulties and despite extensive research efforts to develop new disease-modifying therapies, there is still no effective treatment for halting the neurodegenerative process. Polyphenols are biologically active organic compounds abundantly found in various plants. It has been reported that plant-derived dietary polyphenols may improve some disease states and promote health. Emerging pieces of evidence indicate that polyphenols are associated with neurodegenerative diseases. This review aims to overview the potential neuroprotective roles of polyphenols in most common neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, epilepsy, and ischemic stroke.

Impact of Calcium Influx on Endoplasmic Reticulum in Excitotoxic Neurons: Role of Chemical Chaperone 4-PBA

Excessive activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propoinic acid (AMPA) receptors instigates excitotoxicity via enhanced calcium influx in the neurons thus inciting deleterious consequences. Additionally, Endoplasmic Reticulum (ER) is pivotal in maintaining the intracellular calcium balance. Considering this, studying the aftermath of enhanced calcium uptake by neurons and its effect on ER environment can assist in delineating the pathophysiological events incurred by excitotoxicty. The current study was premeditated to decipher the role of ER pertaining to calcium homeostasis in AMPA-induced excitotoxicity. The findings showed, increased intracellular calcium levels (measured by flowcytometry and spectroflourimeter using Fura 2AM) in AMPA excitotoxic animals (male Sprague dawely rats) (intra-hippocampal injection of 10 mM AMPA). Further, ER resident proteins like calnexin, PDI and ERp72 were found to be upregulated, which further modulated the functioning of ER membrane calcium channels viz. IP3R, RyR, and SERCA pump. Altered calcium homeostasis further led to ER stress and deranged the protein folding capacity of ER post AMPA toxicity, which was ascertained by unfolded protein response (UPR) pathway markers such as IRE1α, eIF2α, and ATF6α. Chemical chaperone, 4-phenybutric acid (4-PBA), ameliorated the protein folding capacity and subsequent UPR markers. In addition, modulation of calcium channels and calcium regulating machinery of ER post 4-PBA administration restored the calcium homeostasis. Therefore the study reinforces the significance of ER stress, a debilitating outcome of impaired calcium homeostasis, under AMPA-induced excitotoxicity. Also, employing chaperone-based therapeutic approach to curb ER stress can restore the calcium imbalance in the neuropathological diseases.

Mechanistic Insight on Autophagy Modulated Molecular Pathways in Cerebral Ischemic Injury: From Preclinical to Clinical Perspective

Cerebral ischemia is one of the most devastating brain injuries and a primary cause of acquired and persistent disability worldwide. Despite ongoing therapeutic interventions at both the experimental and clinical levels, options for stroke-related brain injury are still limited. Several evidence suggests that autophagy is triggered in response to cerebral ischemia, therefore targeting autophagy-related signaling pathways can provide a new direction for the therapeutic implications in the ischemic injury. Autophagy is a highly conserved lysosomal-dependent pathway that degrades and recycles damaged or non-essential cellular components to maintain neuronal homeostasis. But, whether autophagy activation promotes cell survival against ischemic injury or, on the contrary, causes neuronal death is still under debate. We performed an extensive literature search from PubMed, Bentham and Elsevier for various aspects related to molecular mechanisms and pathobiology involved in autophagy and several pre-clinical studies justifiable further in the clinical trials. Autophagy modulates various downstream molecular cascades, i.e., mTOR, NF-κB, HIF-1, PPAR-γ, MAPK, UPR, and ROS pathways in cerebral ischemic injury. In this review, the various approaches and their implementation in the translational research in ischemic injury into practices has been covered. It will assist researchers in finding a way to cross the unbridgeable chasm between the pre-clinical and clinical studies.

Chlorogenic Acid Decreases Glutamate Release from Rat Cortical Nerve Terminals by P/Q-Type Ca2+ Channel Suppression: A Possible Neuroprotective Mechanism

The glutamatergic neurotransmitter system has received substantial attention in research on the pathophysiology and treatment of neurological disorders. The study investigated the effect of the polyphenolic compound chlorogenic acid (CGA) on glutamate release in rat cerebrocortical nerve terminals (synaptosomes). CGA inhibited 4-aminopyridine (4-AP)-induced glutamate release from synaptosomes. This inhibition was prevented in the absence of extracellular Ca²⁺ and was associated with the inhibition of 4-AP-induced elevation of Ca²⁺ but was not attributed to changes in synaptosomal membrane potential. In line with evidence observed through molecular docking, CGA did not inhibit glutamate release in the presence of P/Q-type Ca²⁺ channel inhibitors; therefore, CGA-induced inhibition of glutamate release may be mediated by P/Q-type Ca²⁺ channels. CGA-induced inhibition of glutamate release was also diminished by the calmodulin and Ca²⁺/calmodilin-dependent kinase II (CaMKII) inhibitors, and CGA reduced the phosphorylation of CaMKII and its substrate, synapsin I. Furthermore, pretreatment with intraperitoneal CGA injection attenuated the glutamate increment and neuronal damage in the rat cortex that were induced by kainic acid administration. These results indicate that CGA inhibits glutamate release from cortical synaptosomes by suppressing P/Q-type Ca²⁺ channels and CaMKII/synapsin I pathways, thereby preventing excitotoxic damage to cortical neurons.

Neuromodulation and neuroprotective effects of chlorogenic acids in excitatory synapses of mouse hippocampal slices

The increased healthspan afforded by coffee intake provides novel opportunities to identify new therapeutic strategies. Caffeine has been proposed to afford benefits through adenosine A2A receptors, which can control synaptic dysfunction underlying some brain disease. However, decaffeinated coffee and other main components of coffee such as chlorogenic acids, also attenuate brain dysfunction, although it is unknown if they control synaptic function. We now used electrophysiological recordings in mouse hippocampal slices to test if realistic concentrations of chlorogenic acids directly affect synaptic transmission and plasticity. 3-(3,4-dihydroxycinnamoyl)quinic acid (CA, 1-10 μM) and 5-O-(trans-3,4-dihydroxycinnamoyl)-D-quinic acid (NCA, 1-10 μM) were devoid of effect on synaptic transmission, paired-pulse facilitation or long-term potentiation (LTP) and long-term depression (LTD) in Schaffer collaterals-CA1 pyramidal synapses. However, CA and NCA increased the recovery of synaptic transmission upon re-oxygenation following 7 min of oxygen/glucose deprivation, an in vitro ischemia model. Also, CA and NCA attenuated the shift of LTD into LTP observed in hippocampal slices from animals with hippocampal-dependent memory deterioration after exposure to β-amyloid 1-42 (2 nmol, icv), in the context of Alzheimer's disease. These findings show that chlorogenic acids do not directly affect synaptic transmission and plasticity but can indirectly affect other cellular targets to correct synaptic dysfunction. Unraveling the molecular mechanisms of action of chlorogenic acids will allow the design of hitherto unrecognized novel neuroprotective strategies.

Neuroprotective Effects of Coffee Bioactive Compounds: A Review

Coffee is one of the most widely consumed beverages worldwide. It is usually identified as a stimulant because of a high content of caffeine. However, caffeine is not the only coffee bioactive component. The coffee beverage is in fact a mixture of a number of bioactive compounds such as polyphenols, especially chlorogenic acids (in green beans) and caffeic acid (in roasted coffee beans), alkaloids (caffeine and trigonelline), and the diterpenes (cafestol and kahweol). Extensive research shows that coffee consumption appears to have beneficial effects on human health. Regular coffee intake may protect from many chronic disorders, including cardiovascular disease, type 2 diabetes, obesity, and some types of cancer. Importantly, coffee consumption seems to be also correlated with a decreased risk of developing some neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, and dementia. Regular coffee intake may also reduce the risk of stroke. The mechanism underlying these effects is, however, still poorly understood. This review summarizes the current knowledge on the neuroprotective potential of the main bioactive coffee components, i.e., caffeine, chlorogenic acid, caffeic acid, trigonelline, kahweol, and cafestol. Data from both in vitro and in vivo preclinical experiments, including their potential therapeutic applications, are reviewed and discussed. Epidemiological studies and clinical reports on this matter are also described. Moreover, potential molecular mechanism(s) by which coffee bioactive components may provide neuroprotection are reviewed.

Glia and Neural Stem and Progenitor Cells of the Healthy and Ischemic Brain: The Workplace for the Wnt Signaling Pathway

Wnt signaling plays an important role in the self-renewal, fate-commitment and survival of the neural stem/progenitor cells (NS/PCs) of the adult central nervous system (CNS). Ischemic stroke impairs the proper functioning of the CNS and, therefore, active Wnt signaling may prevent, ameliorate, or even reverse the negative effects of ischemic brain injury. In this review, we provide the current knowledge of Wnt signaling in the adult CNS, its status in diverse cell types, and the Wnt pathway’s impact on the properties of NS/PCs and glial cells in the context of ischemic injury. Finally, we summarize promising strategies that might be considered for stroke therapy, and we outline possible future directions of the field.

Chlorogenic Acid Alleviates Aβ25-35-Induced Autophagy and Cognitive Impairment via the mTOR/TFEB Signaling Pathway

Purpose

Chlorogenic acid (CGA), a phenolic acid isolated from fruits and vegetables, has been established to have neuroprotective properties in relation to Alzheimer's disease (AD). However, the precise mechanism by which CGA prevents cognitive deficits in AD has not been well studied. This study aimed to explore the potential molecular mechanism of CGA action using an Aβ_25-35-induced SH-SY5Y neuron injury and cogxnitive deficits model in APP/PS1 mice.

Methods

Three-month-old male APP/PS1 double transgenic mice and a human neuroblastoma cell line (SH-SY5Y) were used to assess the effects of CGA on AD in vivo and in vitro, respectively. Cognitive function in mice was measured using a Morris water maze (MWM) test. Hematoxylin and eosin, monodansylcadaverine fluorescence, LysoTracker Red (LTR), and immunofluorescence staining were used to evaluate the morphological changes in vivo and in vitro. The protein expressions of autophagy markers (LC3B-II/LC3B-I, p62/SQSTM, beclin1 and Atg5) and lysosomal-function-related markers (cathepsin D, mTOR, p-mTOR P70S6K, p-p70s6k and TFEB) were analyzed with Western blot analyses.

Results

CGA treatment significantly improved spatial memory, relieved neuron damage, and inhibited autophagy in APP/PS1 mice (P<0.05). Moreover, CGA notably suppressed autophagosome production and enhanced autophagy flux in SH-SY5Y cells induced by Aβ_25-35 (P<0.05). Further analysis showed that CGA markedly promoted lysosomal activity, and this was accompanied by upregulated cathepsin D protein expression, which was induced by the mTOR/TFEB signaling pathway in APP/PS1 mice and Aβ_25-35-exposed SH-SY5Y cells (P<0.05).

Conclusion

CGA treatment restored autophagic flux in the brain and alleviated cognitive impairments in APP/PS1 mice via enhanced activation of the mTOR/TFEB signaling pathway.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Brazilian Green Propolis Rescues Oxidative Stress-Induced Mislocalization of Claudin-1 in Human Keratinocyte-Derived HaCaT Cells

Claudin-1 (CLDN1) is expressed in the tight junction (TJ) of the skin granular layer and acts as a physiological barrier for the paracellular transport of ions and nonionic molecules. Ultraviolet (UV) and oxidative stress may disrupt the TJ barrier, but the mechanism of and protective agents against this effect have not been clarified. We found that UVB and hydrogen peroxide (H₂O₂) caused the internalization of CLDN1 and increased the paracellular permeability of lucifer yellow, a fluorescent marker, in human keratinocyte-derived HaCaT cells. Therefore, the mechanism of mislocalization of CLDN1 and the protective effect of an ethanol extract of Brazilian green propolis (EBGP) were investigated. The UVB- and H₂O₂-induced decreases in CLDN1 localization were rescued by EBGP. H₂O₂ decreased the phosphorylation level of CLDN1, which was also rescued by EBGP. Wild-type CLDN1 was distributed in the cytosol after treatment with H₂O₂, whereas T191E, its H₂O₂-insensitive phosphorylation-mimicking mutant, was localized at the TJ. Both protein kinase C activator and protein phosphatase 2A inhibitor rescued the H₂O₂-induced decrease in CLDN1 localization. The tight junctional localization of CLDN1 and paracellular permeability showed a negative correlation. Our results indicate that UVB and H₂O₂ could induce the elevation of paracellular permeability mediated by the dephosphorylation and mislocalization of CLDN1 in HaCaT cells, which was rescued by EBGP. EBGP and its components may be useful in preventing the destruction of the TJ barrier through UV and oxidative stress.

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

Glia form a central component of the nervous system whose varied activities sustain an environment that is optimised for healthy development and neuronal function. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA)-type glutamate receptors (AMPAR) are a central mediator of glutamatergic excitatory synaptic transmission, yet they are also expressed in a wide range of glial cells where they influence a variety of important cellular functions. AMPAR enable glial cells to sense the activity of neighbouring axons and synapses, and as such many aspects of glial cell development and function are influenced by the activity of neural circuits. However, these AMPAR also render glia sensitive to elevations of the extracellular concentration of glutamate, which are associated with a broad range of pathological conditions. Excessive activation of AMPAR under these conditions may induce excitotoxic injury in glial cells, and trigger pathophysiological responses threatening other neural cells and amplifying ongoing disease processes. The aim of this review is to gather information on AMPAR function from across the broad diversity of glial cells, identify their contribution to pathophysiological processes, and highlight new areas of research whose progress may increase our understanding of nervous system dysfunction and disease.