Mitochondrial disturbances, excitotoxicity, neuroinflammation and kynurenines: novel therapeutic strategies for neurodegenerative disorders

Intranasal Delivery of Mitochondria Attenuates Brain Injury by AMPK and SIRT1/PGC-1α Pathways in a Murine Model of Photothrombotic Stroke

Ischemic stroke is one of the major causes of morbidity and mortality worldwide. Mitochondria play a vital role in the pathological processes of cerebral ischemic injury, but its transplantation and underlying mechanisms remain unclear. In the present study, we examined the effects of mitochondrial therapy on the modulation of AMPK and SIRT1/PGC-1α signaling pathway, oxidative stress, and NLRP3 inflammasome activation after photothrombotic ischemic stroke (pt-MCAO). The adult male mice were subjected to the pt-MCAO in which the proximal-middle cerebral artery was exposed with a 532-nm laser beam for 4 min by retro-orbital injection of a photosensitive dye (Rose Bengal: 15 mg/kg) before the laser light exposure and isolated mitochondria (100 μg protein) were administered intranasally at 30 min, 24 h, and 48 h following post-stroke. After 72 h, mice were tested for neurobehavioral outcomes and euthanized for infarct volume, brain edema, and molecular analysis. First, we found that mitochondria therapy significantly decreased brain infarct volume and brain edema, improved neurological dysfunction, attenuated ischemic stroke-induced oxidative stress, and neuroinflammation. Second, mitochondria treatment inhibited NLRP3 inflammasome activation. Finally, mitochondria therapy accelerated p-AMPKα(Thr172) and PGC-1α expression and resorted SIRT1 protein expression levels in pt-MCAO mice. In conclusion, our results demonstrate that mitochondria therapy exerts neuroprotective effects by inhibiting oxidative damage and inflammation, mainly dependent on the heightening activation of the AMPK and SIRT1/PGC-1α signaling pathway. Thus, intranasal delivery of mitochondria might be considered a new therapeutic strategy for ischemic stroke treatment.

Impact of NMDA receptors block versus GABA-A receptors modulation on synaptic plasticity and brain electrical activity in metabolic syndrome

PURPOSE

Metabolic syndrome (MetS) is a common disorder associated with disturbed neurotransmitter homeostasis. Memantine, an N-methyl-d-aspartate receptor (NMDAR) antagonist, was first used in Alzheimer's disease. Allopregnanolone (Allo), a potent positive allosteric modulator of the Gamma-Amino-Butyric Acid (GABA)-A receptors, decreases in neurodegenerative diseases. The study investigated the impact of Memantine versus Allo administration on the animal model of MetS to clarify whether the mechanism of abnormalities is related more to excitatory or inhibitory neurotransmitter dysfunction.

MATERIALS AND METHODS

Fifty-six male rats were allocated into 7 groups: 4 control groups, 1 MetS group, and 2 treated MetS groups. They underwent assessment of cognition-related behavior by open field and forced swimming tests, electroencephalogram (EEG) recording, serum markers confirming the establishment of MetS model and hippocampal Glial Fibrillary Acidic Protein (GFAP) and Brain-Derived Neurotrophic Factor (BDNF).

RESULTS

Allo improved anxiety-like behavior and decreased grooming frequency compared to Memantine. Both drugs increased GFAP and BDNF expression, improving synaptic plasticity and cognition-related behaviors. The therapeutic effect of Allo was more beneficial regarding lipid profile and anxiety. We reported progressive slowing of EEG waves in the MetS group with Memantine and Allo treatment with increased relative theta and decreased relative delta rhythms.

CONCLUSIONS

Both Allo and Memantine boosted the outcome parameters in the animal model of MetS. Allo markedly improved the anxiety-like behavior in the form of significantly decreased grooming frequency compared to the Memantine-treated groups. Both drugs were associated with increased hippocampal GFAP and BDNF expression, indicating an improvement in synaptic plasticity and so, cognition-related behaviors.

Calcium Modulating Effect of Polycyclic Cages: A Suitable Therapeutic Approach Against Excitotoxic-induced Neurodegeneration

Neurodegenerative disorders pose a significant challenge to global healthcare systems due to their progressive nature and the resulting loss of neuronal cells and functions. Excitotoxicity, characterized by calcium overload, plays a critical role in the pathophysiology of these disorders. In this review article, we explore the involvement of calcium dysregulation in neurodegeneration and neurodegenerative disorders. A promising therapeutic strategy to counter calcium dysregulation involves the use of calcium modulators, particularly polycyclic cage compounds. These compounds, structurally related to amantadine and memantine, exhibit neuroprotective properties by attenuating calcium influx into neuronal cells. Notably, the pentacycloundecylamine NGP1-01, a cage-like structure, has shown efficacy in inhibiting both N-methyl-D-aspartate (NMDA) receptors and voltage- gated calcium channels (VGCCs), making it a potential candidate for neuroprotection against excitotoxic-induced neurodegenerative disorders. The structure-activity relationship of polycyclic cage compounds is discussed in detail, highlighting their calcium-inhibitory activities. Various closed, open, and rearranged cage compounds have demonstrated inhibitory effects on calcium influx through NMDA receptors and VGCCs. Additionally, these compounds have exhibited neuroprotective properties, including free radical scavenging, attenuation of neurotoxicities, and reduction of neuroinflammation. Although the calcium modulatory activities of polycyclic cage compounds have been extensively studied, apart from amantadine and memantine, none have undergone clinical trials. Further in vitro and in vivo studies and subsequent clinical trials are required to establish the efficacy and safety of these compounds. The development of polycyclic cages as potential multifunctional agents for treating complex neurodegenerative diseases holds great promise.

Lobeline: A multifunctional alkaloid modulates cholinergic and glutamatergic activities

Developing drugs for Alzheimer's disease (AD) is an extremely challenging task due to its devastating pathology. Previous studies have indicated that natural compounds play a crucial role as lead molecules in the development of drugs. Even though, there are remarkable technological advancements in the isolation and synthesis of natural compounds, the targets for many of them are still unknown. In the present study, lobeline, a piperidine alkaloid has been identified as a cholinesterase inhibitor through chemical similarity assisted target fishing method. The structural similarities between lobeline and donepezil, a known acetylcholinesterase (AChE) inhibitor encouraged us to hypothesize that lobeline may also exhibit AChE inhibitory properties. It was further confirmed by in silico, in vitro and biophysical studies that lobeline could inhibit cholinesterase. The binding profiles indicated that lobeline has a higher affinity for AChE than BChE. Since excitotoxicity is one of the major pathological events associated with AD progression, we also investigated the neuroprotective potential of lobeline against glutamate mediated excitotoxicity in rat primary cortical neurons. The cell based NMDA receptor (NMDAR) assay with lobeline suggested that neuroprotective potential of lobeline is mediated through the blockade of NMDAR activity.

A Vegetarian Diet Significantly Changes Plasma Kynurenine Concentrations

Tryptophan is an essential amino acid and a precursor of a number of physiologically important metabolites, including serotonin, melatonin, tryptamine, and kynurenines. We assessed tryptophan, kynurenines, and vitamin B2 and B6, as well as biomarkers of liver function and inflammation, in a group of 158 female omnivores and vegetarians aged 18-40 years. The majority of women were omnivores, and 22% were vegetarians. Vegetarians had 25% lower serum ALT, significantly higher pyridoxal concentrations, and significantly lower plasma concentrations of most kynurenines, varying from 8% lower concentrations of median plasma kynurenine to 42% lower concentrations of plasma xanthurenic acid, compared to omnivores. No significant differences were observed in vitamin B2 status or in inflammation markers, C-reactive protein and neopterin between the groups. Vegetarians had lower levels of several plasma kynurenines compared to omnivores. The reason for this is unknown; however, lower ALT concentrations, suggesting a better liver status, and a more favourable vitamin B6 status might be contributing factors.

Targeted Metabolomics Shows That the Level of Glutamine, Kynurenine, Acyl-Carnitines and Lysophosphatidylcholines Is Significantly Increased in the Aqueous Humor of Glaucoma Patients

The composition of the aqueous humor of patients with glaucoma is relevant to understand the underlying causes of the pathology. Information on the concentration of metabolites and small molecules in the aqueous humor of healthy subjects is limited. Among the causes of the limitations is the lack of healthy controls since, until recently, they were not surgically intervened; therefore, the aqueous humor of patients operated for cataract was used as a reference. Sixteen aqueous humor samples from healthy subjects undergoing refractive surgery and eight samples from glaucoma patients were used to assess the concentration of 188 compounds using chromatography and mass spectrometry. The concentration of 80 of the 188 was found to be reliable, allowing comparison of data from the two groups (glaucoma and control). The pattern found in the controls is similar to, but not the same as, that reported using samples from “controls” undergoing cataract surgery. Comparing data from glaucoma patients and healthy subjects, 57 of the 80 compounds were significantly (p < 0.05) altered in the aqueous humor. Kynurenine and glutamine, but not glutamate, were significantly increased in the glaucoma samples. Furthermore, 10 compounds were selected considering a statistical score of p < 0.0001 and the degree of change of more than double or less than half. The level of C10 (decanoyl)-carnitine decreased, while the concentration of spermidine and various acyl-carnitines and lysophosphatidylcholines increased in glaucoma. Principal component analysis showed complete segregation of controls and cases using the data for the 10 selected compounds. The receiver operating characteristic curve these 10 compounds and for glutamine allowed finding cut-off values and significant sensitivity and specificity scores. The concentration of small metabolites in the aqueous humor of glaucoma patients is altered even when they take medication and are well controlled. The imbalance affects membrane components, especially those of the mitochondria, suggesting that mitochondrial abnormalities are a cause or consequence of glaucoma. The increase in glutamine in glaucoma is also relevant because it could be a means of keeping the concentration of glutamate under control, thus avoiding its potential to induce the death of neurons and retinal cells. Equally notable was the increase in kynurenine, which is essential in the metabolism of nicotine adenine dinucleotides.

Using Noninvasive Electrophysiology to Determine Time Windows of Neuroprotection in Optic Neuropathies

The goal of neuroprotection in optic neuropathies is to prevent loss of retinal ganglion cells (RGCs) and spare their function. The ideal time window for initiating neuroprotective treatments should be the preclinical period at which RGCs start losing their functional integrity before dying. Noninvasive electrophysiological tests such as the Pattern Electroretinogram (PERG) can assess the ability of RGCs to generate electrical signals under a protracted degenerative process in both clinical conditions and experimental models, which may have both diagnostic and prognostic values and provide the rationale for early treatment. The PERG can be used to longitudinally monitor the acute and chronic effects of neuroprotective treatments. User-friendly versions of the PERG technology are now commercially available for both clinical and experimental use.

The effect of sodium channels on neurological/neuronal disorders: A systematic review

Neurological and neuronal disorders are associated with structural, biochemical, or electrical abnormalities in the nervous system. Many neurological diseases have not yet been discovered. Interventions used for the treatment of these disorders include avoidance measures, lifestyle changes, physiotherapy, neurorehabilitation, pain management, medication, and surgery. In the sodium channelopathies, alterations in the structure, expression, and function of voltage-gated sodium channels (VGSCs) are considered as the causes of neurological and neuronal diseases. Online databases, including Scopus, Science Direct, Google Scholar, and PubMed were assessed for studies published between 1977 and 2020 using the keywords of review, sodium channels blocker, neurological diseases, and neuronal diseases. VGSCs consist of one α subunit and two β subunits. These subunits are known to regulate the gating kinetics, functional characteristics, and localization of the ion channel. These channels are involved in cell migration, cellular connections, neuronal pathfinding, and neurite outgrowth. Through the VGSC, the action potential is triggered and propagated in the neurons. Action potentials are physiological functions and passage of impermeable ions. The electrophysiological properties of these channels and their relationship with neurological and neuronal disorders have been identified. Subunit mutations are involved in the development of diseases, such as epilepsy, multiple sclerosis, autism, and Alzheimer's disease. Accordingly, we conducted a review of the link between VGSCs and neurological and neuronal diseases. Also, novel therapeutic targets were introduced for future drug discoveries.

Inhibition of Tryptophan Catabolism Is Associated With Neuroprotection During Zika Virus Infection

Zika virus (ZIKV) is an arbovirus belonging to Flaviviridae family that emerged as a global health threat due to its association with microcephaly and other severe neurological complications, including Guillain-Barré Syndrome (GBS) and Congenital Zika Syndrome (CZS). ZIKV disease has been linked to neuroinflammation and neuronal cell death. Neurodegenerative processes may be exacerbated by metabolites produced by the kynurenine pathway, an important pathway for the degradation of tryptophan, which induces neuronal dysfunction due to enhanced excitotoxicity. Here, we exploited the hypothesis that ZIKV-induced neurodegeneration can be rescued by blocking a target enzyme of the kynurenine pathway, the Indoleamine 2,3-dioxygenase (IDO-1). RT-PCR analysis showed increased levels of IDO-1 RNA expression in undifferentiated primary neurons isolated from wild type (WT) mice infected by ZIKV ex vivo, as well as in the brain of ZIKV-infected A129 mice. Pharmacological inhibition of IDO-1 enzyme with 1-methyl-D-tryptophan (1-MT), in both in vitro and in vivo systems, led to significant reduction of ZIKV-induced neuronal death without interfering with the ability of ZIKV to replicate in those cells. Furthermore, in vivo analyses using both genetically modified mice (IDO^-/- mice) and A129 mice treated with 1-MT resulted in reduced microgliosis, astrogliosis and Caspase-3 positive cells in the brain of ZIKV-infected A129 mice. Interestingly, increased levels of CCL5 and CXCL-1 chemokines were found in the brain of 1-MT treated-mice. Together, our data indicate that IDO-1 blockade provides a neuroprotective effect against ZIKV-induced neurodegeneration, and this is amenable to inhibition by pharmacological treatment.

Ethanol Extract of Maclura tricuspidata Fruit Protects SH-SY5Y Neuroblastoma Cells against H2O2-Induced Oxidative Damage via Inhibiting MAPK and NF-κB Signaling

Free radical generation and oxidative stress push forward an immense influence on the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. Maclura tricuspidata fruit (MT) contains many biologically active substances, including compounds with antioxidant properties. The current study aimed to investigate the neuroprotective effects of MT fruit on hydrogen peroxide (H₂O₂)-induced neurotoxicity in SH-SY5Y cells. SH-SY5Y cells were pretreated with MT, and cell damage was induced by H₂O₂. First, the chemical composition and free radical scavenging properties of MT were analyzed. MT attenuated oxidative stress-induced damage in cells based on the assessment of cell viability. The H₂O₂-induced toxicity caused by ROS production and lactate dehydrogenase (LDH) release was ameliorated by MT pretreatment. MT also promoted an increase in the expression of genes encoding the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). MT pretreatment was associated with an increase in the expression of neuronal genes downregulated by H₂O₂. Mechanistically, MT dramatically suppressed H₂O₂-induced Bcl-2 downregulation, Bax upregulation, apoptotic factor caspase-3 activation, Mitogen-activated protein kinase (MAPK) (JNK, ERK, and p38), and Nuclear factor-κB (NF-κB) activation, thereby preventing H₂O₂-induced neurotoxicity. These results indicate that MT has protective effects against H₂O₂-induced oxidative damage in SH-SY5Y cells and can be used to prevent and protect against neurodegeneration.

Neuroinflammation and the Kynurenine Pathway in CNS Disease: Molecular Mechanisms and Therapeutic Implications

Diseases of the central nervous system (CNS) remain a significant health, social and economic problem around the globe. The development of therapeutic strategies for CNS conditions has suffered due to a poor understanding of the underlying pathologies that manifest them. Understanding common etiological origins at the cellular and molecular level is essential to enhance the development of efficacious and targeted treatment options. Over the years, neuroinflammation has been posited as a common link between multiple neurological, neurodegenerative and neuropsychiatric disorders. Processes that precipitate neuroinflammatory conditions including genetics, infections, physical injury and psychosocial factors, like stress and trauma, closely link dysregulation in kynurenine pathway (KP) of tryptophan metabolism as a possible pathophysiological factor that 'fuel the fire' in CNS diseases. In this study, we aim to review emerging evidence that provide mechanistic insights between different CNS disorders, neuroinflammation and the KP. We provide a thorough overview of the different branches of the KP pertinent to CNS disease pathology that have therapeutic implications for the development of selected and efficacious treatment strategies.

Kynurenine induces an age-related phenotype in bone marrow stromal cells

Advanced age is one of the important contributing factors for musculoskeletal deterioration. Although the exact mechanism behind this degeneration is unknown, it has been previously established that nutritional signaling plays a vital role in musculoskeletal pathophysiology. Our group established the vital role of the essential amino acid, tryptophan, in aging musculoskeletal health. With advanced age, inflammatory factors activate indoleamine 2,3-dioxygenase (IDO1) and accumulate excessive intermediate tryptophan metabolites such as Kynurenine (KYN). With age, Kynurenine accumulates and suppresses osteogenic differentiation, impairs autophagy, promotes early senescence, and alters cellular bioenergetics of bone marrow stem cells. Recent studies have shown that Kynurenine negatively impacts bone marrow stromal cells (BMSCs) and, consequently, promotes bone loss. Overall, understanding the mechanism behind BMSCs losing their ability for osteogenic differentiation can provide insight into the prevention of osteoporosis and the development of targeted therapies. Therefore, in this article, we review Kynurenine and how it plays a vital role in BMSC dysfunction and bone loss with age.

IDO-1 inhibition protects against neuroinflammation, oxidative stress and mitochondrial dysfunction in 6-OHDA induced murine model of Parkinson's disease

Parkinson's disease (PD), a common neurodegenerative motor disorder characterized by striatal dopaminergic neuronal loss and localized neuroinflammation in the midbrain region. Activation of microglia is associated with various inflammatory mediators and Kynurenine pathway (KP) being one of the major regulator of immune response, is involved in the neuroinflammatory and neurotoxic cascade in PD. In the current study, 1-Methyltryptophan (1-MT), an Indolamine-2,3-dioxygenase-1 (IDO-1) inhibitor was tested at different doses (2.5 mg/kg, 5 mg/kg and 10 mg/kg) for its effect on behavioral parameters, oxidative stress, neuroinflammation, apoptosis, mitochondrial dysfunction, neurotransmitter levels, biochemical and behavioral alterations in unilateral 6-OHDA (3 μg/μL) murine model of PD. The results showed improved locomotion in open field test and motor coordination in rota-rod, reduced oxidative stress, neuroinflammatory markers (TNF-α, IFN-γ, IL-6), mitochondrial dysfunction and neuronal apoptosis (caspase-3). Also, restoration of neurotransmitter levels (dopamine and homovanillic acid) in the striatum and increased striatal BDNF levels were observed. Overall findings suggest that 1-MT could be a potential candidate for further studies to explore its possibility as an alternative in the pharmacotherapy of PD.

Treatment of neuropsychiatric systemic lupus erythematosus: clinical challenges and future perspectives

Introduction: Neuropsychiatric (NP) involvement represents an emerging frontier in systemic lupus erythematosus (SLE), posing significant challenges due to its clinical diversity and obscure pathophysiology. The authors herein discuss selected aspects in the management of NPSLE based on existing literature and our experience, aiming to facilitate routine medical care.Areas covered: Research related to diagnosis, neuroimaging, treatment and outcome is discussed, focusing on data published in PubMed during the last 5 years. Selected translational studies of clinical relevance are included.Expert opinion: Identification of NPSLE patients who may benefit from appropriate treatment can be facilitated by attribution algorithms. Immunosuppressants are typically indicated in recurrent seizures, optic neuritis, myelopathy, psychosis and peripheral nerve disease, although a low threshold is recommended for cerebrovascular disease and other NP manifestations, especially when SLE is active. With the exception of stroke with positive antiphospholipid antibodies, anti-coagulation is rarely indicated in other syndromes. Refractory NPSLE can be treated with rituximab, whereas the role of other biologics remains unknown. Advances in the fields of biomarkers, neuroimaging for brain structural, perfusion or functional abnormalities, and design of novel compounds targeting not only systemic autoimmunity but also inflammatory and regenerative pathways within the nervous system, hold promise for optimizing NPSLE management.

4-Oxatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione Derivatives as NMDA Receptor- and VGCC Blockers with Neuroprotective Potential

The impact of excitotoxicity mediated by N-methyl-D-aspartate (NMDA) receptor overactivation and voltage gated calcium channel (VGCC) depolarization is prominent among the postulated processes involved in the development of neurodegenerative disorders. NGP1-01, a polycyclic amine, has been shown to be neuroprotective through modulation of the NMDA receptor and VGCC, and attenuation of MPP+-induced neurotoxicity. Recently, we reported on the calcium modulating effects of tricycloundecene derivatives, structurally similar to NGP1-01, on the NMDA receptor and VGCC of synaptoneurosomes. In the present study, we investigated novel 4-oxatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione derivatives for their cytotoxicity, neuroprotective effects via attenuation of MPP+-induced neurotoxicity and calcium influx inhibition abilities through the NMDA receptor and VGCC using neuroblastoma SH-SY5Y cells. All compounds, in general, showed low or no toxicity against neuroblastoma cells at 10-50 µM concentrations. At 10 µM, all compounds significantly attenuated MPP+-induced neurotoxicity as evident by the enhancement in cell viability between 23.05 ± 3.45% to 53.56 ± 9.29%. In comparison to known active compounds, the derivatives demonstrated mono or dual calcium modulating effect on the NMDA receptor and/or VGCC. Molecular docking studies using the NMDA receptor protein structure indicated that the compounds are able to bind in a comparable manner to the crystallographic pose of MK-801 inside the NMDA ion channel. The biological characteristics, together with results from in silico studies, suggest that these compounds could act as neuroprotective agents for the purpose of halting or slowing down the degenerative processes in neuronal cells.

Neuroprotection in Parkinson's disease: facts and hopes

Parkinson’s disease (PD) is the second most common neurodegenerative disease worldwide. Behind the symptoms there is a complex pathological mechanism which leads to a dopaminergic cell loss in the substantia nigra pars compacta. Despite the strong efforts, curative treatment has not been found yet. To prevent a further cell death, numerous molecules were tested in terms of neuroprotection in preclinical (in vitro, in vivo) and in clinical studies as well. The aim of this review article is to summarize our knowledge about the extensively tested neuroprotective agents (Search period: 1991–2019). We detail the underlying pathological mechanism and summarize the most important results of the completed animal and clinical trials. Although many positive results have been reported in the literature, there is still no evidence that any of them should be used in clinical practice (Cochrane analysis was performed). Therefore, further studies are needed to better understand the pathomechanism of PD and to find the optimal neuroprotective agent(s).

Neuroprotective effects of anthocyanins and its major component cyanidin-3-O-glucoside (C3G) in the central nervous system: An outlined review

Anthocyanins, a class of water soluble flavonoids extracted from plants like berries and soybean seed, have been shown to display obvious anti-oxidative, anti-inflammatory, and anti-apoptotic activities. They are recommended as a supplementation for prevention and/or treatment of disorders ranging from cardiovascular disease, metabolic syndrome, and cancer. In the central nervous system (CNS), anthocyanins and its major component cyanidin-3-O-glucoside (C3G) have been reported to produce preventive and/or therapeutic activities in a wide range of disorders, such as cerebral ischemia, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and glioblastoma. Both anthocyanins and C3G can also affect some important processes in aging, including neuronal apoptosis and death as well as learning and memory impairment. Further, the anthocyanins and C3G have been shown to prevent neuro-toxicities induced by different toxic factors, such as lipopolysaccharide, hydrogen peroxide, ethanol, kainic acid, acrolein, glutamate, and scopolamine. Mechanistic studies have shown that inhibition of oxidative stress and neuroinflammation are two critical mechanisms by which anthocyanins and C3G produce protective effects in CNS disorder prevention and/or treatment. Other mechanisms, including suppression of c-Jun N-terminal kinase (JNK) activation, amelioration of cellular degeneration, activation of the brain-derived neurotrophic factor (BDNF) signaling, and restoration of Ca²⁺ and Zn²⁺ homeostasis, may also mediate the neuroprotective effects of anthocyanins and C3G. In this review, we summarize the pharmacological effects of anthocyanins and C3G in CNS disorders as well as their possible mechanisms, aiming to get a clear insight into the role of anthocyanins in the CNS.

Alzheimer's Disease: Recent Concepts on the Relation of Mitochondrial Disturbances, Excitotoxicity, Neuroinflammation, and Kynurenines

The pathomechanism of Alzheimer's disease (AD) certainly involves mitochondrial disturbances, glutamate excitotoxicity, and neuroinflammation. The three main aspects of mitochondrial dysfunction in AD, i.e., the defects in dynamics, altered bioenergetics, and the deficient transport, act synergistically. In addition, glutamatergic neurotransmission is affected in several ways. The balance between synaptic and extrasynaptic glutamatergic transmission is shifted toward the extrasynaptic site contributing to glutamate excitotoxicity, a phenomenon augmented by increased glutamate release and decreased glutamate uptake. Neuroinflammation in AD is predominantly linked to central players of the innate immune system, with central nervous system (CNS)-resident microglia, astroglia, and perivascular macrophages having been implicated at the cellular level. Several abnormalities have been described regarding the activation of certain steps of the kynurenine (KYN) pathway of tryptophan metabolism in AD. First of all, the activation of indolamine 2,3-dioxygenase, the first and rate-limiting step of the pathway, is well-demonstrated. 3-Hydroxy-L-KYN and its metabolite, 3-hydroxy-anthranilic acid have pro-oxidant, antioxidant, and potent immunomodulatory features, giving relevance to their alterations in AD. Another metabolite, quinolinic acid, has been demonstrated to be neurotoxic, promoting glutamate excitotoxicity, reactive oxygen species production, lipid peroxidation, and microglial neuroinflammation, and its abundant presence in AD pathologies has been demonstrated. Finally, the neuroprotective metabolite, kynurenic acid, has been associated with antagonistic effects at glutamate receptors, free radical scavenging, and immunomodulation, giving rise to potential therapeutic implications. This review presents the multiple connections of KYN pathway-related alterations to three main domains of AD pathomechanism, such as mitochondrial dysfunction, excitotoxicity, and neuroinflammation, implicating possible therapeutic options.

Amphiphilic Nanocarrier Systems for Curcumin Delivery in Neurodegenerative Disorders

Neurodegenerative diseases have become a major challenge for public health because of their incurable status. Soft nanotechnology provides potential for slowing down the progression of neurodegenerative disorders by using innovative formulations of neuroprotective antioxidants like curcumin, resveratrol, vitamin E, rosmarinic acid, 7,8-dihydroxyflavone, coenzyme Q10, and fish oil. Curcumin is a natural, liposoluble compound, which is of considerable interest for nanomedicine development in combination therapies. The neuroprotective effects of combination treatments can involve restorative mechanisms against oxidative stress, mitochondrial dysfunction, inflammation, and protein aggregation. Despite the anti-amyloid and anti-tau potential of curcumin and its neurogenesis-stimulating properties, the utilization of this antioxidant as a drug in neuroregenerative therapies has huge limitations due to its poor water solubility, physico-chemical instability, and low oral bioavailability. We highlight the developments of soft lipid- and polymer-based delivery carriers of curcumin, which help improve the drug solubility and stability. We specifically focus on amphiphilic liquid crystalline nanocarriers (cubosome, hexosome, spongosome, and liposome particles) for the encapsulation of curcumin with the purpose of halting the progressive neuronal loss in Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis (ALS).

Amelioration of oxidative stress in differentiated neuronal cells by rutin regulated by a concentration switch

Increasing studies have implicated superfluous production of reactive oxygen species (ROS) as a significant factor in the progress of neurodegenerative disorders ranging from ischemic stroke to amyotrophic lateral sclerosis. The possible mechanisms relating to oxidative stress and neurodegeneration are yet to be thoroughly understood. Rutin, a flavonoid, has been well documented for its beneficial and pharmacological activities against diverse targets. However, the mechanism involved in the beneficial effects of rutin against neurodegeneration still remains unclear. Our study investigates the concentration switch effects of rutin on differentiated human neuroblastoma cells (IMR32) in vitro to unveil the possible mechanism of its action. IMR32 cells were differentiated using retinoic acid and challenged with different doses of rutin for 24 h duration to study the influence of ROS on differentiated neuronal cells and ROS-mediated apoptosis. The study showed that the high (100 μM) and low (100 nM and 10μM) rutin concentrations significantly avert ROS generation by two different mechanisms, by enhancing apoptosis through the modulation of levels of Bcl2, Caspase-3, survivin and its antioxidant activity via stress-related proteins, JNK and p38 MAPK. Our study suggests that rutin is a multi-targeted therapeutic and preventive agent that may act as an adjuvant complementary therapeutic molecule to treat oxidative stress-mediated neurodegeneration.

Early behavioral and metabolomic change after mild to moderate traumatic brain injury in the developing brain

Pathophysiology of developmental traumatic brain injury (TBI) is unique due to intrinsic differences in the developing brain. Energy metabolic studies of the brain during early development (P13 to P30) have indicated acute oxidative energy metabolic decreases below 24 h after TBI, which generally recovered by 48 h. However, marked neurodegeneration and altered neural functional connectivity have been observed at later stages into adolescence. As secondary neurodegeneration is most prominent during the first week after TBI in the rat model, we hypothesized that the subacute TBI-metabolome may contain predictive markers of neurodegeneration. Sham and TBI metabolomes were examined at 72 h after a mild to moderate intensity TBI in male Sprague-Dawley rats aged P31. Sensorimotor behavior was assessed at 24, 48 and 72 h after injury, followed by 72-hour postmortem brain removal for metabolomics using Liquid Chromatography/Mass Spectrometry (LC-MS) measurement. Broad TBI-induced metabolomic shifts occurred with relatively higher intensity in the injury-lateralized (ipsilateral) hemisphere. Intensity of metabolomic perturbation correlated with the extent of sensorimotor behavioral deficit. N-acetyl-aspartate (NAA) levels at 72 h after TBI, predicted the extent of neurodegeneration assessed histochemically 7-days post TBI. Results from the multivariate untargeted approach clearly distinguished metabolomic shifts induced by TBI. Several pathways including amino acid, fatty acid and energy metabolism continued to be affected at 72 h after TBI, whose collective effects may determine the overall pathological response after TBI in early development including neurodegeneration.

An Expanded Neuroimmunomodulation Axis: sCD83-Indoleamine 2,3-Dioxygenase-Kynurenine Pathway and Updates of Kynurenine Pathway in Neurologic Diseases

Many neurologic diseases are related to autoimmune dysfunction and a variety of molecules or reaction pathways are involved in the regulation of immune function of the nervous system. Soluble CD83 (sCD83) is the soluble form of CD83, a specific marker of mature dendritic cell, which has recently been shown to have an immunomodulatory effect. Indoleamine 2,3-dioxygenase (IDO; corresponding enzyme intrahepatic, tryptophan 2,3-dioxygenase, TDO), a rate-limiting enzyme of extrahepatic tryptophan kynurenine pathway (KP) participates in the immunoregulation through a variety of mechanisms solely or with the synergy of sCD83, and the imbalances of metabolites of KP were associated with immune dysfunction. With the complement of sCD83 to IDO-KP, a previously known immunomodulatory axis, this review focused on an expanded neuroimmunomodulation axis: sCD83-IDO-KP and its involvement in nervous system diseases.

Neuroprotective Effects of Guanosine Administration on In Vivo Cortical Focal Ischemia in Female and Male Wistar Rats

Guanosine (GUO) has neuroprotective effects in experimental models of brain diseases involving glutamatergic excitotoxicity in male animals; however, its effects in female animals are poorly understood. Thus, we investigated the influence of gender and GUO treatment in adult male and female Wistar rats submitted to focal permanent cerebral ischemia in the motor cortex brain. Female rats were subdivided into non-estrogenic and estrogenic phase groups by estrous cycle verification. Immediately after surgeries, the ischemic animals were treated with GUO or a saline solution. Open field and elevated plus maze tasks were conducted with ischemic and naïve animals. Cylinder task, immunohistochemistry and infarct volume analyses were conducted only with ischemic animals. Female GUO groups achieved a full recovery of the forelimb symmetry at 28-35 days after the insult, while male GUO groups only partially recovered at 42 days, in the final evaluation. The ischemic insult affected long-term memory habituation to novelty only in female groups. Anxiety-like behavior, astrocyte morphology and infarct volume were not affected. Regardless the estrous cycle, the ischemic injury affected differently female and male animals. Thus, this study points that GUO is a potential neuroprotective compound in experimental stroke and that more studies, considering the estrous cycle, with both genders are recommended in future investigation concerning brain diseases.

Gender-Specific Degeneration of Dementia-Related Subcortical Structures Throughout the Lifespan

Age-related changes in brain structure are a question of interest to a broad field of research. Structural decline has been consistently, but not unambiguously, linked to functional consequences, including cognitive impairment and dementia. One of the areas considered of crucial importance throughout this process is the medial temporal lobe, and primarily the hippocampal region. Gender also has a considerable effect on volume deterioration of subcortical grey matter (GM) structures, such as the hippocampus. The influence of age×gender interaction on disproportionate GM volume changes might be mediated by hormonal effects on the brain. Hippocampal volume loss appears to become accelerated in the postmenopausal period. This decline might have significant influences on neuroplasticity in the CA1 region of the hippocampus highly vulnerable to pathological influences. Additionally, menopause has been associated with critical pathobiochemical changes involved in neurodegeneration. The micro- and macrostructural alterations and consequent functional deterioration of critical hippocampal regions might result in clinical cognitive impairment-especially if there already is a decline in the cognitive reserve capacity. Several lines of potential vulnerability factors appear to interact in the menopausal period eventually leading to cognitive decline, mild cognitive impairment, or Alzheimer's disease. This focused review aims to delineate the influence of unmodifiable risk factors of neurodegenerative processes, i.e., age and gender, on critical subcortical GM structures in the light of brain derived estrogen effects. The menopausal period appears to be of key importance for the risk of cognitive decline representing a time of special vulnerability for molecular, structural, and functional influences and offering only a narrow window for potential protective effects.

Neuroprotective effects of honokiol: from chemistry to medicine

The incidence of neurological disorders is growing in developed countries together with increased lifespan. Nowadays, there are still no effective treatments for neurodegenerative pathologies, which make necessary to search for new therapeutic agents. Natural products, most of them used in traditional medicine, are considered promising alternatives for the treatment of neurodegenerative diseases. Honokiol is a natural bioactive phenylpropanoid compound, belonging to the class of neolignan, found in notable amounts in the bark of Magnolia tree, and has been reported to exert diverse pharmacological properties including neuroprotective activities. Honokiol can permeate the blood brain barrier and the blood-cerebrospinal fluid to increase its bioavailability in neurological tissues. Diverse studies have provided evidence on the neuroprotective effect of honokiol in the central nervous system, due to its potent antioxidant activity, and amelioration of the excitotoxicity mainly related to the blockade of glutamate receptors and reduction in neuroinflammation. In addition, recent studies suggest that honokiol can attenuate neurotoxicity exerted by abnormally aggregated Aβ in Alzheimer's disease. The present work summarizes what is currently known concerning the neuroprotective effects of honokiol and its potential molecular mechanisms of action, which make it considered as a promising agent in the treatment and management of neurodegenerative diseases. © 2017 BioFactors, 43(6):760-769, 2017.

Exploring the potential of natural and synthetic neuroprotective steroids against neurodegenerative disorders: A literature review

Neurodegeneration is a complex process, which leads to progressive brain damage due to loss of neurons. Despite exhaustive research, the cause of neuronal loss in various degenerative disorders is not entirely understood. Neuroprotective steroids constitute an important line of attack, which could play a major role against the common mechanisms associated with various neurodegenerative disorders like Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Natural endogenous steroids induce the neuroprotection by protecting the nerve cells from neuronal injury through multiple mechanisms, therefore the structural modifications of the endogenous steroids could be helpful in the generation of new therapeutically useful neuroprotective agents. The review article will keep the readers apprised of the detailed description of natural as well as synthetic neuroprotective steroids from the medicinal chemistry point of view, which would be helpful in drug discovery efforts aimed toward neurodegenerative diseases.

The establishment of tocopherol reference intervals for Hungarian adult population using a validated HPLC method

Evidence suggests that decreased α-tocopherol (the most biologically active substance in the vitamin E group) level can cause neurological symptoms, most likely ataxia. The aim of the current study was to first provide reference intervals for serum tocopherols in the adult Hungarian population with appropriate sample size, recruiting healthy control subjects and neurological patients suffering from conditions without symptoms of ataxia, myopathy or cognitive deficiency. A validated HPLC method applying a diode array detector and rac-tocol as internal standard was utilized for that purpose. Furthermore, serum cholesterol levels were determined as well for data normalization. The calculated 2.5-97.5% reference intervals for α-, β/γ- and δ-tocopherols were 24.62-54.67, 0.81-3.69 and 0.29-1.07 μm, respectively, whereas the tocopherol/cholesterol ratios were 5.11-11.27, 0.14-0.72 and 0.06-0.22 μmol/mmol, respectively. The establishment of these reference intervals may improve the diagnostic accuracy of tocopherol measurements in certain neurological conditions with decreased tocopherol levels. Moreover, the current study draws special attention to the possible pitfalls in the complex process of the determination of reference intervals as well, including the selection of study population, the application of internal standard and method validation and the calculation of tocopherol/cholesterol ratios.

Memantine and Kynurenic Acid: Current Neuropharmacological Aspects

Glutamatergic neurotransmission, of special importance in the human brain, is implicated in key brain functions such as synaptic plasticity and memory. The excessive activation of N-methyl- D-aspartate (NMDA) receptors may result in excitotoxic neuronal damage; this process has been implicated in the pathomechanism of different neurodegenerative disorders, such as Alzheimer’s disease (AD). Memantine is an uncompetitive antagonist of NMDA receptors with a favorable pharmacokinetic profile, and is therefore clinically well tolerated. Memantine is approved for the treatment of AD, but may additionally be beneficial for other dementia forms and pain conditions. Kynurenic acid (KYNA) is an endogenous antagonist of NMDA receptors which has been demonstrated under experimental conditions to be neuroprotective. The development of a well-tolerated NMDA antagonist may offer a novel therapeutic option for the treatment of neurodegenerative disease and pain syndromes. KYNA may be a valuable candidate for future drug development.

Expression of brain-derived neurotrophic factor in astrocytes - Beneficial effects of glatiramer acetate in the R6/2 and YAC128 mouse models of Huntington's disease

Glatiramer acetate (GA) is a FDA-approved drug which is licensed for the treatment of relapsing-remitting multiple sclerosis and which may exert neuroprotective effects via brain-derived neurotrophic factor (BDNF). In this study, we investigate effects of GA on BDNF expression especially in astrocytes in vitro and in vivo in brains of R6/2 and YAC128 transgenic mouse models of Huntington's disease (HD) where a pathogenic role of astroglial cells has recently been shown. We show that GA increases the expression of functionally active BDNF in astrocyte culture and in astrocytes of GA treated HD mice. In the brains of these mice, GA decreases neurodegeneration and restores BDNF levels. The beneficial effect of GA in R6/2 mice also comprises reduced weight loss and prolonged life span and, for both models, also improved motor performance. Further studies with this safe and effective drug in HD are warranted.

Early expression of the receptor for advanced glycation end products in a toxic model produced by 6-hydroxydopamine in the rat striatum

The receptor for advanced glycation end products (RAGE) is commonly involved in different neurodegenerative and inflammatory disorders. The cellular signaling associated to RAGE activation may occur upon binding to different ligands. In this study we investigated whether the toxic model produced by 6-hydroxydopamine (6-OHDA) in rats comprises early noxious responses related to RAGE-mediated signaling cascades. In order to explore a possible interaction between 6-OHDA and RAGE, affinity parameters of RAGE with 6-OHDA were estimated by different means. The possible binding sites of 6-OHDA with the VC1 homodimer for both rat and human RAGE were also modeled. Our results show that the striatal infusion of 6-OHDA recruits RAGE upregulation, as evidenced by an early expression of the receptor. 6-OHDA was also found to bind the VC1 homodimer, although its affinity was moderate when compared to other ligands. This work contributes to the understanding of the role of RAGE activation for 6-OHDA-induced neurotoxicity.

Neuroprotection as a Potential Therapeutic Perspective in Neurodegenerative Diseases: Focus on Antiepileptic Drugs

Neuroprotection is conceived as one of the potential tool to prevent or slow neuronal death and hence a therapeutic hope to treat neurodegenerative diseases, like Parkinson's and Alzheimer's diseases. Increase of oxidative stress, mitochondrial dysfunction, excitotoxicity, inflammatory changes, iron accumulation, and protein aggregation have been identified as main causes of neuronal death and adopted as targets to test experimentally the putative neuroprotective effects of various classes of drugs. Among these agents, antiepileptic drugs (AEDs), both the old and the newer generations, have shown to exert protective effects in different experimental models. Their mechanism of action is mediated mainly by modulating the activity of sodium, calcium and potassium channels as well as the glutamatergic and GABAergic (gamma-aminobutyric acid) synapses. Neurological pathologies in which a neuroprotective action of AEDs has been demonstrated in specific experimental models include: cerebral ischemia, Parkinson's disease, and Alzheimer's disease. Although the whole of experimental data indicating that neuroprotection can be achieved is remarkable and encouraging, no firm data have been produced in humans so far and, at the present time, neuroprotection still remains a challenge for the future.

Electron Transport Disturbances and Neurodegeneration: From Albert Szent-Györgyi's Concept (Szeged) till Novel Approaches to Boost Mitochondrial Bioenergetics

Impaired function of certain mitochondrial respiratory complexes has long been linked to the pathogenesis of chronic neurodegenerative disorders such as Parkinson's and Huntington's diseases. Furthermore, genetic alterations of mitochondrial genome or nuclear genes encoding proteins playing essential roles in maintaining proper mitochondrial function can lead to the development of severe systemic diseases associated with neurodegeneration and vacuolar myelinopathy. At present, all of these diseases lack effective disease modifying therapy. Following a brief commemoration of Professor Albert Szent-Györgyi, a Nobel Prize laureate who pioneered in the field of cellular respiration, antioxidant processes, and the roles of free radicals in health and disease, the present paper overviews the current knowledge on the involvement of mitochondrial dysfunction in central nervous system diseases associated with neurodegeneration including Parkinson's and Huntington's disease as well as mitochondrial encephalopathies. The review puts special focus on the involvement and the potential therapeutic relevance of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α), a nuclear-encoded master regulator of mitochondrial biogenesis and antioxidant responses in these disorders, the transcriptional activation of which may hold novel therapeutic value as a more system-based approach aiming to restore mitochondrial functions in neurodegenerative processes.

Carbon nanotubes and graphene as emerging candidates in neuroregeneration and neurodrug delivery

Neuroregeneration is the regrowth or repair of nervous tissues, cells, or cell products involved in neurodegeneration and inflammatory diseases of the nervous system like Alzheimer’s disease and Parkinson’s disease. Nowadays, application of nanotechnology is commonly used in developing nanomedicines to advance pharmacokinetics and drug delivery exclusively for central nervous system pathologies. In addition, nanomedical advances are leading to therapies that disrupt disarranged protein aggregation in the central nervous system, deliver functional neuroprotective growth factors, and change the oxidative stress and excitotoxicity of affected neural tissues to regenerate the damaged neurons. Carbon nanotubes and graphene are allotropes of carbon that have been exploited by researchers because of their excellent physical properties and their ability to interface with neurons and neuronal circuits. This review describes the role of carbon nanotubes and graphene in neuroregeneration. In the future, it is hoped that the benefits of nanotechnologies will outweigh their risks, and that the next decade will present huge scope for developing and delivering technologies in the field of neuroscience.

Ischemic preconditioning protects neurons from damage and maintains the immunoreactivity of kynurenic acid in the gerbil hippocampal CA1 region following transient cerebral ischemia

Pyramidal neurons in region I of hippocampus proper (CA1) are particularly vulnerable to excitotoxic processes following transient forebrain ischemia. Kynurenic acid (KYNA) is a small molecule derived from tryptophan when this amino acid is metabolized through the kynurenine pathway. In the present study, we examined the effects of ischemic preconditioning (IPC) on the immunoreactivity and protein levels of KYNA following 5 min of transient forebrain ischemia in gerbils. The animals were randomly assigned to 4 groups (sham-operated group, ischemia-operated group, IPC + sham-operated group and IPC + ischemia-operated group). IPC was induced by subjecting the gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated group, we observed a significant loss of pyramidal neurons in the CA1 stratum pyramidale (SP) at 5 days post-ischemia; however, in the IPC + ischemia-operated group, the pyramidal neurons were well protected. KYNA immunoreactivity in the SP of the ischemia-operated group was significantly altered following ischemia-reperfusion and was very low 5 days following ischemia-reperfusion. In the IPC + ischemia-operated group, however, KYNA immunoreactivity was constitutively detected in the SP of the CA1 region after the ischemic insult. We also found that the alteration pattern of the KYNA protein level in the CA1 region following ischemia was generally similar to the immunohistochemical changes observed. In brief, our findings demonstrated that IPC maintained and even increased KYNA immunoreactivity in the SP of the CA1 region following ischemia-reperfusion. The data from the present study thus indicate that the enhancement of KYNA expression by IPC may be necessary for neuronal survival following transient ischemic injury.

Signaling pathways leading to ischemic mitochondrial neuroprotection

There is extensive evidence that ischemic/reperfusion mediated mitochondrial dysfunction is a major contributor to ischemic damage. However data also indicates that mild ischemic stress induces mitochondrial dependent activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sub-injurious ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Current research demonstrates that mitochondria are not only the inducers of but are also an important target of ischemic preconditioning mediated protection. Numerous proteins and signaling pathways are activated by ischemic preconditioning which protect the mitochondria against ischemic damage. In this review we examine some of the proteins activated by ischemic precondition which counteracts the deleterious effects of ischemia/reperfusion thereby maintaining normal mitochondrial activity and lead to ischemic tolerance.

Modeling the interaction between quinolinate and the receptor for advanced glycation end products (RAGE): relevance for early neuropathological processes

The receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor involved in neurodegenerative and inflammatory disorders. RAGE induces cellular signaling upon binding to a variety of ligands. Evidence suggests that RAGE up-regulation is involved in quinolinate (QUIN)-induced toxicity. We investigated the QUIN-induced toxic events associated with early noxious responses, which might be linked to signaling cascades leading to cell death. The extent of early cellular damage caused by this receptor in the rat striatum was characterized by image processing methods. To document the direct interaction between QUIN and RAGE, we determined the binding constant (Kb) of RAGE (VC1 domain) with QUIN through a fluorescence assay. We modeled possible binding sites of QUIN to the VC1 domain for both rat and human RAGE. QUIN was found to bind at multiple sites to the VC1 dimer, each leading to particular mechanistic scenarios for the signaling evoked by QUIN binding, some of which directly alter RAGE oligomerization. This work contributes to the understanding of the phenomenon of RAGE-QUIN recognition, leading to the modulation of RAGE function.