Montelukast treatment protects nigral dopaminergic neurons against microglial activation in the 6-hydroxydopamine mouse model of Parkinson's disease

Leukotriene signaling in neurodegeneration: implications for treatment strategies

Leukotrienes (LTs) are a group of substances that cause inflammation. They are produced by the enzyme 5-lipoxygenase (5-LOX) from arachidonic acid. Cysteinyl LTs are a group of lipid molecules that have a prominent role in inflammatory signaling in the allergic diseases. Although they are traditionally known for their role in allergic disease, current advancements in bio-medical research have shed light on the involvement of these inflammatory mediators in diseases such as in the inflammation related to central nervous system (CNS) disorders. Among the CNS diseases, LTs, along with 5-LOX and their receptors, have been shown to be associated with multiple sclerosis (MS), Alzheimer's disease (AD), and Parkinson's disease (PD). Through a comprehensive review of current research and experimentation, this investigation provides an insight on the biosynthesis, receptors, and biological effects of LTs in the body. Furthermore, implications of leukotriene signaling in CNS and its intricate role in neurodegeneration are also studied. Through the revelation of these insights, our aim is to establish a foundation for the development of enhanced and focused therapeutic approaches in the continuous endeavor to combat neurodegeneration. Furthermore, the pharmacological inhibition of leukotriene signaling with selective inhibitors offers promising prospects for future interventions and treatments for neurodegenerative diseases.

Neuromodulatory effects of leukotriene receptor antagonists: A comprehensive review

Cysteinyl leukotrienes (CysLTs) are central to the pathophysiology of asthma and various inflammatory disorders. Leukotriene receptor antagonists (LTRAs) effectively treat respiratory conditions by targeting cysteinyl leukotriene receptors, CysLT1 and CysLT2 subtypes. This review explores the multifaceted effects of LTs, extending beyond bronchoconstriction. CysLT receptors are not only present in the respiratory system but are also crucial in neuronal signaling pathways. LTRAs modulate these receptors, influencing downstream signaling, calcium levels, inflammation, and oxidative stress (OS) within neurons hinting at broader implications. Recent studies identify novel molecular targets, sparking interest in repurposing LTRAs for therapeutic use. Clinical trials are investigating their potential in neuroinflammation control, particularly in Alzheimer's disease (AD) and Parkinson's diseases (PD). However, montelukast, a long-standing LTRA since 1998, raises concerns due to neuropsychiatric adverse drug reactions (ADRs). Despite widespread use, understanding montelukast's metabolism and underlying ADR mechanisms remains limited. This review comprehensively examines LTRAs' diverse biological effects, emphasizing non-bronchoconstrictive activities. It also analyses plausible mechanisms behind LTRAs' neuronal effects, offering insights into their potential as neurodegenerative disease modulators. The aim is to inform clinicians, researchers, and pharmaceutical developers about LTRAs' expanding roles, particularly in neuroinflammation control and their promising repurposing for neurodegenerative disease management.

Montelukast improves disease outcome in SOD1G93A female mice by counteracting oligodendrocyte dysfunction and aberrant glial reactivity

BACKGROUND AND PURPOSE

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive motor neuron (MN) loss and consequent muscle atrophy, for which no effective therapies are available. Recent findings reveal that disease progression is fuelled by early aberrant neuroinflammation and the loss of oligodendrocytes with neuroprotective and remyelinating properties. On this basis, pharmacological interventions capable of restoring a pro-regenerative local milieu and re-establish proper oligodendrocyte functions may be beneficial.

EXPERIMENTAL APPROACH

Here, we evaluated the in vivo therapeutic effects of montelukast (MTK), an antagonist of the oligodendroglial G protein-coupled receptor 17 (GPR17) and of cysteinyl-leukotriene receptor 1 (CysLT1R) receptors on microglia and astrocytes, in the SOD1G93A ALS mouse model. We chronically treated SOD1G93A mice with MTK, starting from the early symptomatic disease stage. Disease progression was assessed by behavioural and immunohistochemical approaches.

KEY RESULTS

Oral MTK treatment significantly extended survival probability, delayed body weight loss and ameliorated motor functionalityonly in female SOD1G93A mice. Noteworthy, MTK significantly restored oligodendrocyte maturation and induced significant changes in the reactive phenotype and morphological features of microglia/macrophages and astrocytes in the spinal cord of female SOD1G93A mice, suggesting enhanced pro-regenerative functions. Importantly, concomitant MN preservation has been detected after MTK administration. No beneficial effects were observed in male mice, highlighting a sex-based difference in the protective activity of MTK.

CONCLUSIONS AND IMPLICATIONS

Our results provide the first preclinical evidence indicating that repurposing of MTK, a safe and marketed anti-asthmatic drug, may be a promising sex-specific strategy for personalized ALS treatment.

What Can Inflammation Tell Us about Therapeutic Strategies for Parkinson's Disease?

Parkinson's disease (PD) is a common neurodegenerative disorder with a complicated etiology and pathogenesis. α-Synuclein aggregation, dopaminergic (DA) neuron loss, mitochondrial injury, oxidative stress, and inflammation are involved in the process of PD. Neuroinflammation has been recognized as a key element in the initiation and progression of PD. In this review, we summarize the inflammatory response and pathogenic mechanisms of PD. Additionally, we describe the potential anti-inflammatory therapies, including nod-like receptor pyrin domain containing protein 3 (NLRP3) inflammasome inhibition, nuclear factor κB (NF-κB) inhibition, microglia inhibition, astrocyte inhibition, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibition, the peroxisome proliferator-activated receptor γ (PPARγ) agonist, targeting the mitogen-activated protein kinase (MAPK) pathway, targeting the adenosine monophosphate-activated protein kinase (AMPK)-dependent pathway, targeting α-synuclein, targeting miRNA, acupuncture, and exercise. The review focuses on inflammation and will help in designing new prevention strategies for PD.

Clinical Trial Highlights: Anti-Inflammatory and Immunomodulatory Agents

 Inflammation and immune dysregulation have been linked to the pathogenesis and progression of Parkinson's disease (PD), and represent an attractive target for therapeutic intervention, given the potential for repurposing of existing anti-inflammatory and immunomodulatory agents. Despite the fact that initial studies of drugs with secondary anti-inflammatory effects did not yield positive results, agents specifically targeting immune and inflammatory pathways may hold more promise. This article will briefly review the evidence base for targeting the immune system and neuroinflammation in PD, and discuss in detail the recently completed and currently active trials of primary anti-inflammatory/immunomodulatory drugs in PD.

3-N-butylphthalide attenuates neuroinflammation in rotenone-induced Parkinson's disease models via the cGAS-STING pathway

Neuroinflammation is crucial in the onset and progression of dopaminergic neuron loss in Parkinson's disease (PD). We aimed to determine whether 3-N-Butylphthalide (NBP) can protect against PD by inhibiting the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway and the inflammatory response of microglia. MitoSOX/MitoTracker/Hoechst staining was used to detect the levels of mitochondrial reactive oxygen species (ROS) in BV2 cells. Quantitative Real-Time Polymerase Chain Reaction was used to measure the levels of free cytoplasmic mitochondrial DNA (mtDNA) in BV2 cells and mouse brain tissues. Behavioral impairments were assessed using rotarod, T-maze, and balance beam tests. Dopaminergic neurons and microglia were observed using immunohistochemical staining. Expression levels of cGAS, STING, nuclear factor kappa-B (NfκB), phospho- NfκB (p-NfκB), inhibitor of NfκBα (IκBα), and phospho-IκBα (p-IκBα) proteins in the substantia nigra and striatum were detected using Western Blot. NBP decreased mitochondrial ROS levels in rotenone-treated BV2 cells. NBP alleviated behavioral impairments and protected against rotenone-induced microgliosis and damage to dopaminergic neurons in the substantia nigra and striatum of rotenone-induced PD mice. NBP decreased rotenone-induced mtDNA leakage and mitigated neuroinflammation by inhibiting cGAS-STING pathway activation. NBP exhibited a protective effect in rotenone-induced PD models by significantly inhibiting the cGAS-STING pathway. Moreover, NBP can alleviate neuroinflammation, and is a potential therapeutic drug for alleviating clinical symptoms and delaying the progression of PD. This study provided insights for the potential role of NBP in PD therapy, potentially mitigating neurodegeneration, and consequently improving the quality of life and lifespan of patients with PD. The limitations are that we have not confirmed the exact mechanism by which NBP decreases mtDNA leakage, and this study was unable to observe the actual clinical therapeutic effect, so further cohort studies are required for validation.

Montelukast Ameliorates Scopolamine-induced Alzheimer's Disease: Role on Cholinergic Neurotransmission, Antioxidant Defence System, Neuroinflammation and Expression of BDNF

BACKGROUND

Alzheimer's disease (AD) is an overwhelming neurodegenerative disease with progressive loss of memory. AD is characterized by the deposition of the senile plaques mainly composed of β-amyloid (Aβ) fragment, BDNF decline, Cholinergic system overactivity and neuroinflammation. Montelukast (MTK), a leukotriene receptor antagonist, showed astounding neuroprotective effects in a variety of neurodegenerative disorders.

OBJECTIVE

This study aims to investigate the ameliorative effects of Montelukast in the scopolamineinduced Alzheimer's disease (AD) model in rats and evaluate its activity against neuroinflammation.

METHODS

Thirty rats were split into five groups: Control group (1 mL/kg normal saline, i.p.), Montelukast perse (10 mg/kg, i.p.), Disease group treated with Scopolamine (3 mg/kg, i.p.), Donepezil group (3 mg/kg, i.p.), Montelukast treatment group (10 mg/kg, i.p.) and behavioural and biochemical tests were carried out to assess the neuro protective effect.

RESULTS

Scopolamine treatment led to a significant reduction in learning and memory and an elevation in cholinesterase levels when compared with the control group (p < 0.01). Additionally, elevated oxidative stress and Amyloid-β levels were associated with enhanced neuroinflammation (p < 0.05, p < 0.01). Furthermore, the decline in neurotrophic factor BDNF is also observed when compared with the normal control group (p < 0.01). Montelukast pre-treatment significantly attenuated learning and memory impairment and cholinesterase levels. Besides, Montelukast and standard drug donepezil administration significantly suppressed the oxidative stress markers (p < 0.01), Amyloid-β levels, neuroinflammatory mediators (p < 0.05) and caused a significant increase in BDNF levels (p < 0.05).

CONCLUSION

Montelukast bestowed ameliorative effects in scopolamine-induced AD animal models as per the previous studies via attenuation of memory impairment, cholinesterase neurotransmission, oxidative stress, Amyloid-β levels, neuroinflammatory mediators and enhanced BDNF levels.

Multidirectional associations between the gut microbiota and Parkinson's disease, updated information from the perspectives of humoral pathway, cellular immune pathway and neuronal pathway

The human gastrointestinal tract is inhabited by a diverse range of microorganisms, collectively known as the gut microbiota, which form a vast and complex ecosystem. It has been reported that the microbiota-gut-brain axis plays a crucial role in regulating host neuroprotective function. Studies have shown that patients with Parkinson's disease (PD) have dysbiosis of the gut microbiota, and experiments involving germ-free mice and fecal microbiota transplantation from PD patients have revealed the pathogenic role of the gut microbiota in PD. Interventions targeting the gut microbiota in PD, including the use of prebiotics, probiotics, and fecal microbiota transplantation, have also shown efficacy in treating PD. However, the causal relationship between the gut microbiota and Parkinson's disease remains intricate. This study reviewed the association between the microbiota-gut-brain axis and PD from the perspectives of humoral pathway, cellular immune pathway and neuronal pathway. We found that the interactions among gut microbiota and PD are very complex, which should be "multidirectional", rather than conventionally regarded "bidirectional". To realize application of the gut microbiota-related mechanisms in the clinical setting, we propose several problems which should be addressed in the future study.

β2-Adrenoreceptor Agonists, Montelukast, and Parkinson Disease Risk

OBJECTIVE

This study was undertaken to examine the association between montelukast use, β2-adrenoreceptor (β2AR) agonist use, and later Parkinson disease (PD).

METHODS

We ascertained use of β2AR agonists (430,885 individuals) and montelukast (23,315 individuals) from July 1, 2005 to June 30, 2007, and followed 5,186,886 PD-free individuals from July 1, 2007 to December 31, 2013 for incident PD diagnosis. We estimated hazard ratios and 95% confidence intervals using Cox regressions.

RESULTS

We observed 16,383 PD cases during on average 6.1 years of follow-up. Overall, use of β2AR agonists and montelukast were not related to PD incidence. A 38% lower PD incidence was noted among high-dose montelukast users when restricted to PD registered as the primary diagnosis.

INTERPRETATION

Overall, our data do not support inverse associations between β2AR agonists, montelukast, and PD. The prospect of lower PD incidence with high-dose montelukast exposure warrants further investigation, especially with adjustment for high-quality data on smoking. ANN NEUROL 2023;93:1023-1028.

Exploring the neuroprotective effects of montelukast on brain inflammation and metabolism in a rat model of quinolinic acid-induced striatal neurotoxicity

BACKGROUND

One intrastriatal administration of quinolinic acid (QA) in rats induces a lesion with features resembling those observed in Huntington's disease. Our aim is to evaluate the effects of the cysteinyl leukotriene receptor antagonist montelukast (MLK), which exhibited neuroprotection in different preclinical models of neurodegeneration, on QA-induced neuroinflammation and regional metabolic functions.

METHODS

The right and left striatum of Sprague Dawley and athymic nude rats were injected with QA and vehicle (VEH), respectively. Starting from the day before QA injection, animals were treated with 1 or 10 mg/kg of MLK or VEH for 14 days. At 14 and 30 days post-lesion, animals were monitored with magnetic resonance imaging (MRI) and positron emission tomography (PET) using [18F]-VC701, a translocator protein (TSPO)-specific radiotracer. Striatal neuroinflammatory response was measured post-mortem in rats treated with 1 mg/kg of MLK by immunofluorescence. Rats treated with 10 mg/kg of MLK also underwent a [18F]-FDG PET study at baseline and 4 months after lesion. [18F]-FDG PET data were then used to assess metabolic connectivity between brain regions by applying a covariance analysis method.

RESULTS

MLK treatment was not able to reduce the QA-induced increase in striatal TSPO PET signal and MRI lesion volume, where we only detected a trend towards reduction in animals treated with 10 mg/kg of MLK. Post-mortem immunofluorescence analysis revealed that MLK attenuated the increase in striatal markers of astrogliosis and activated microglia in the lesioned hemisphere. We also found a significant increase in a marker of anti-inflammatory activity (MannR) and a trend towards reduction in a marker of pro-inflammatory activity (iNOS) in the lesioned striatum of MLK-compared to VEH-treated rats. [18F]-FDG uptake was significantly reduced in the striatum and ipsilesional cortical regions of VEH-treated rats at 4 months after lesion. MLK administration preserved glucose metabolism in these cortical regions, but not in the striatum. Finally, MLK was able to counteract changes in metabolic connectivity and measures of network topology induced by QA, in both lesioned and non-lesioned hemispheres.

CONCLUSIONS

Overall, MLK treatment produced a significant neuroprotective effect by reducing neuroinflammation assessed by immunofluorescence and preserving regional brain metabolism and metabolic connectivity from QA-induced neurotoxicity in cortical and subcortical regions.

Neuroinflammation in Parkinson"s Disease and its Treatment Opportunities

Parkinson’s disease (PD) is a complex, chronic, and progressive neurodegenerative disease that is characterized by irreversible dopaminergic neuronal loss in the substantia nigra. Alpha-synuclein is normally a synaptic protein that plays a key role in PD due to pathological accumulation as oligomers or fibrils. Clustered alpha-synuclein binds to the Toll-like receptors and activates the microglia, which initiates a process that continues with pro-inflammatory cytokine production and secretion. Pro-inflammatory cytokine overproduction and secretion induce cell death and accelerate PD progression. Microglia are found in a resting state in physiological conditions. Microglia became activated by stimulating Toll-like receptors on it under pathological conditions, such as alpha-synuclein aggregation, environmental toxins, or oxidative stress. The interaction between Toll-like receptors and its downstream pathway triggers an activation series, leads to nuclear factor-kappa B activation, initiates the inflammasome formation, and increases cytokine levels. This consecutive inflammatory process leads to dopaminergic cell damage and cell death. Microglia become overactive in response to chronic inflammation, which is observed in PD and causes excessive cytotoxic factor production, such as reactive oxidase, nitric oxide, and tumor necrosis factor-alpha. This inflammatory process contributes to the exacerbation of pathology by triggering neuronal damage or death. Current treatments, such as dopaminergic agonists, anticholinergics, or monoamine oxidase inhibitors alleviate PD symptoms, but they can not stop the disease progression. Finding a radical treatment option or stopping the progression is essential when considering that PD is the second most reported neurodegenerative disorder. Many cytokines are released during inflammation, and they can start the phagocytic process, which caused the degradation of infected cells along with healthy ones. Therefore, targeting the pathological mechanisms, such as microglial activation, mitochondrial dysfunction, and oxidative stress, that should be involved in the treatment program is important. Neuroinflammation is one of the key factors involved in PD pathogenesis as well as alpha-synuclein accumulation, synaptic dysfunction, or dopaminergic neuronal loss, especially in the substantia nigra. Therefore, evaluating the therapeutic efficiency of the mechanisms is important, such as microglial activation and nuclear factor-kappa B pathway or inflammasome formation inhibition, and cytokine release interruption against neuroinflammation may create new treatment possibilities for PD. This study examined the pathological relation between PD and neuroinflammation, and targeting neuroinflammation as an opportunity for PD treatments, such as Toll-like receptor antagonists, NOD-like receptor family pyrin domain containing-3 inflammasome inhibitors, cytokine inhibitors, peroxisome proliferator-activated receptor-γ agonists, reactive oxygen species inhibitors, and nonsteroidal anti-inflammatory drugs.

Leukotrienes vs. Montelukast—Activity, Metabolism, and Toxicity Hints for Repurposing

Increasing environmental distress is associated with a growing asthma incidence; no treatments are available but montelukast (MTK)—an antagonist of the cysteinyl leukotrienes receptor 1—is widely used in the management of symptoms among adults and children. Recently, new molecular targets have been identified and MTK has been proposed for repurposing in other therapeutic applications, with several ongoing clinical trials. The proposed applications include neuroinflammation control, which could be explored in some neurodegenerative disorders, such as Alzheimer’s and Parkinson’s diseases (AD and PD). However, this drug has been associated with an increasing number of reported neuropsychiatric adverse drug reactions (ADRs). Besides, and despite being on the market since 1998, MTK metabolism is still poorly understood and the mechanisms underlying neuropsychiatric ADRs remain unknown. We review the role of MTK as a modulator of leukotriene pathways and systematize the current knowledge about MTK metabolism. Known toxic effects of MTK are discussed, and repurposing applications are presented comprehensively, with a focus on AD and PD.

Brain-Specific Increase in Leukotriene Signaling Accompanies Chronic Neuroinflammation and Cognitive Impairment in a Model of Gulf War Illness

Persistent cognitive impairment is a primary central nervous system-related symptom in veterans afflicted with chronic Gulf War Illness (GWI). Previous studies in a rat model have revealed that cognitive dysfunction in chronic GWI is associated with neuroinflammation, typified by astrocyte hypertrophy, activated microglia, and enhanced proinflammatory cytokine levels. Studies in a mouse model of GWI have also shown upregulation of several phospholipids that serve as reservoirs of arachidonic acid, a precursor of leukotrienes (LTs). However, it is unknown whether altered LT signaling is a component of chronic neuroinflammatory conditions in GWI. Therefore, this study investigated changes in LT signaling in the brain of rats displaying significant cognitive impairments six months after exposure to GWI-related chemicals and moderate stress. The concentration of cysteinyl LTs (CysLTs), LTB4, and 5-Lipoxygenase (5-LOX), the synthesizing enzyme of LTs, were evaluated. CysLT and LTB4 concentrations were elevated in the hippocampus and the cerebral cortex, along with enhanced 5-LOX expression in neurons and microglia. Such changes were also associated with increased proinflammatory cytokine levels in the hippocampus and the cerebral cortex. Enhanced CysLT and LTB4 levels in the brain could also be gleaned from their concentrations in brain-derived extracellular vesicles in the circulating blood. The circulating blood in GWI rats displayed elevated proinflammatory cytokines with no alterations in CysLT and LTB4 concentrations. The results provide new evidence that a brain-specific increase in LT signaling is another adverse alteration that potentially contributes to the maintenance of chronic neuroinflammation in GWI. Therefore, drugs capable of modulating LT signaling may reduce neuroinflammation and improve cognitive function in GWI. Additional findings demonstrate that altered LT levels in the brain could be tracked efficiently by analyzing brain-derived EVs in the circulating blood.

Leukotriene Signaling as a Target in α-Synucleinopathies

Parkinson’s disease (PD) and dementia with Lewy bodies (DLB) are two common types of α-synucleinopathies and represent a high unmet medical need. Despite diverging clinical manifestations, both neurodegenerative diseases share several facets of their complex pathophysiology. Apart from α-synuclein aggregation, an impairment of mitochondrial functions, defective protein clearance systems and excessive inflammatory responses are consistently observed in the brains of PD as well as DLB patients. Leukotrienes are lipid mediators of inflammatory signaling traditionally known for their role in asthma. However, recent research advances highlight a possible contribution of leukotrienes, along with their rate-limiting synthesis enzyme 5-lipoxygenase, in the pathogenesis of central nervous system disorders. This review provides an overview of in vitro as well as in vivo studies, in summary suggesting that dysregulated leukotriene signaling is involved in the pathological processes underlying PD and DLB. In addition, we discuss how the leukotriene signaling pathway could serve as a future drug target for the therapy of PD and DLB.

Neuroimaging and biomarker evidence of neurodegeneration in asthma

BACKGROUND

Epidemiologic studies have shown that Alzheimer's disease (AD) and related dementias (ADRD) are seen more frequently with asthma, especially with greater asthma severity or exacerbation frequency.

OBJECTIVE

To examine the changes in brain structure that may underlie this phenomenon, we examined diffusion-weighted magnetic resonance imaging (dMRI) and blood-based biomarkers of AD (phosphorylated tau 181, p-Tau181), neurodegeneration (neurofilament light chain, NfL), and glial activation (glial fibrillary acidic protein, GFAP).

METHODS

dMRI data were obtained in 111 individuals with asthma, ranging in disease severity from mild to severe, and 135 healthy controls. Regression analyses were used to test the relationships between asthma severity and neuroimaging measures, as well as AD pathology, neurodegeneration, and glial activation, indexed by plasma p-Tau181, NfL, and GFAP, respectively. Additional relationships were tested with cognitive function.

RESULTS

Asthma participants had widespread and large-magnitude differences in several dMRI metrics, which were indicative of neuroinflammation and neurodegeneration, and which were robustly associated with GFAP and, to a lesser extent, NfL. The AD biomarker p-Tau181 was only minimally associated with neuroimaging outcomes. Further, asthma severity was associated with deleterious changes in neuroimaging outcomes, which in turn were associated with slower processing speed, a test of cognitive performance.

CONCLUSIONS

Asthma, particularly when severe, is associated with characteristics of neuroinflammation and neurodegeneration, and may be a potential risk factor for neural injury and cognitive dysfunction. There is a need to determine how asthma may affect brain health and whether treatment directed toward characteristics of asthma associated with these risks can mitigate these effects.

Elucidating the Neuroprotective Role of PPARs in Parkinson's Disease: A Neoteric and Prospective Target

One of the utmost frequently emerging neurodegenerative diseases, Parkinson's disease (PD) must be comprehended through the forfeit of dopamine (DA)-generating nerve cells in the substantia nigra pars compacta (SN-PC). The etiology and pathogenesis underlying the emergence of PD is still obscure. However, expanding corroboration encourages the involvement of genetic and environmental factors in the etiology of PD. The destruction of numerous cellular components, namely oxidative stress, ubiquitin-proteasome system (UPS) dysfunction, autophagy-lysosome system dysfunction, neuroinflammation and programmed cell death, and mitochondrial dysfunction partake in the pathogenesis of PD. Present-day pharmacotherapy can alleviate the manifestations, but no therapy has been demonstrated to cease disease progression. Peroxisome proliferator-activated receptors (PPARs) are ligand-directed transcription factors pertaining to the class of nuclear hormone receptors (NHR), and are implicated in the modulation of mitochondrial operation, inflammation, wound healing, redox equilibrium, and metabolism of blood sugar and lipids. Numerous PPAR agonists have been recognized to safeguard nerve cells from oxidative destruction, inflammation, and programmed cell death in PD and other neurodegenerative diseases. Additionally, various investigations suggest that regular administration of PPAR-activating non-steroidal anti-inflammatory drugs (NSAIDs) (ibuprofen, indomethacin), and leukotriene receptor antagonists (montelukast) were related to the de-escalated evolution of neurodegenerative diseases. The present review elucidates the emerging evidence enlightening the neuroprotective outcomes of PPAR agonists in in vivo and in vitro models experiencing PD. Existing articles up to the present were procured through PubMed, MEDLINE, etc., utilizing specific keywords spotlighted in this review. Furthermore, the authors aim to provide insight into the neuroprotective actions of PPAR agonists by outlining the pharmacological mechanism. As a conclusion, PPAR agonists exhibit neuroprotection through modulating the expression of a group of genes implicated in cellular survival pathways, and may be a propitious target in the therapy of incapacitating neurodegenerative diseases like PD.

Potential Effects of Leukotriene Receptor Antagonist Montelukast in Treatment of Neuroinflammation in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder where misfolded alpha-synuclein-enriched aggregates called Lewy bodies are central in pathogenesis. No neuroprotective or disease-modifying treatments are currently available. Parkinson’s disease is considered a multifactorial disease and evidence from multiple patient studies and animal models has shown a significant immune component during the course of the disease, highlighting immunomodulation as a potential treatment strategy. The immune changes occur centrally, involving microglia and astrocytes but also peripherally with changes to the innate and adaptive immune system. Here, we review current understanding of different components of the PD immune response with a particular emphasis on the leukotriene pathway. We will also describe evidence of montelukast, a leukotriene receptor antagonist, as a possible anti-inflammatory treatment for PD.

The Leukotriene Receptor Antagonist Montelukast Attenuates Neuroinflammation and Affects Cognition in Transgenic 5xFAD Mice

Alzheimer's disease (AD) is the most common form of dementia. In particular, neuroinflammation, mediated by microglia cells but also through CD8+ T-cells, actively contributes to disease pathology. Leukotrienes are involved in neuroinflammation and in the pathological hallmarks of AD. In consequence, leukotriene signaling-more specifically, the leukotriene receptors-has been recognized as a potential drug target to ameliorate AD pathology. Here, we analyzed the effects of the leukotriene receptor antagonist montelukast (MTK) on hippocampal gene expression in 5xFAD mice, a commonly used transgenic AD mouse model. We identified glial activation and neuroinflammation as the main pathways modulated by MTK. The treatment increased the number of Tmem119+ microglia and downregulated genes related to AD-associated microglia and to lipid droplet-accumulating microglia, suggesting that the MTK treatment targets and modulates microglia phenotypes in the disease model compared to the vehicle. MTK treatment further reduced infiltration of CD8+T-cells into the brain parenchyma. Finally, MTK treatment resulted in improved cognitive functions. In summary, we provide a proof of concept for MTK to be a potential drug candidate for AD and provide novel modes of action via modulation of microglia and CD8+ T-cells. Of note, 5xFAD females showed a more severe pathology, and in consequence, MTK treatment had a more pronounced effect in the females compared to the males. The effects on neuroinflammation, i.e., microglia and CD8+ T-cells, as well as the effects on cognitive outcome, were dose-dependent, therefore arguing for the use of higher doses of MTK in AD clinical trials compared to the approved asthma dose.

Montelukast alleviates inflammation in experimental autoimmune encephalomyelitis by altering Th17 differentiation in a mouse model

Montelukast is a leukotriene receptor antagonist that is known to prevent allergic rhinitis and asthma. Blocking the Cysteinyl leukotriene receptor (CysLTR1), one of the primary receptors of leukotrienes, has been demonstrated to be efficacious in ameliorating experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), through disrupting chemotaxis of infiltrating T cells. However, the role of CysLTR1 in the pathogenesis of MS is not well understood. Here, we show that MS patients had higher expression of CysLTR1 in the circulation and central nervous system (CNS). The majority of CD4⁺ T cells expressed CysLTR1 in MS lesions. Among T-cell subsets, Th17 cells had the highest expression of CysLTR1, and blocking CysLTR1 signalling abrogated their development in vitro. Inhibition of CysLTR1 by montelukast suppressed EAE development in both a prophylactic and therapeutic manner and inhibited myelin loss in EAE mice. Similarly, the in vivo results showed that montelukast inhibited Th17 response in EAE mice and that Th17 cells treated with montelukast had reduced encephalitogenic in adoptive EAE. Our findings strongly suggest that targeting Th17 response by inhibiting CysLTR1 signalling could be a promising therapeutic strategy for the treatment of MS and CNS inflammatory diseases.

Doxycycline inhibits α-synuclein-associated pathologies in vitro and in vivo

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are neurodegenerative disorders characterized by the misfolding and aggregation of alpha-synuclein (aSyn). Doxycycline, a tetracyclic antibiotic shows neuroprotective effects, initially proposed to be due to its anti-inflammatory properties. More recently, an additional mechanism by which doxycycline may exert its neuroprotective effects has been proposed as it has been shown that it inhibits amyloid aggregation. Here, we studied the effects of doxycycline on aSyn aggregation in vivo, in vitro and in a cell free system using real-time quaking induced conversion (RT-QuiC). Using H4, SH-SY5Y and HEK293 cells, we found that doxycycline decreases the number and size of aSyn aggregates in cells. In addition, doxycycline inhibits the aggregation and seeding of recombinant aSyn, and attenuates the production of mitochondrial-derived reactive oxygen species. Finally, we found that doxycycline induces a cellular redistribution of aggregates in a C.elegans animal model of PD, an effect that is associated with a recovery of dopaminergic function. In summary, we provide strong evidence that doxycycline treatment may be an effective strategy against synucleinopathies.

The Leukotriene Receptor Antagonist Montelukast Reduces Alpha-Synuclein Load and Restores Memory in an Animal Model of Dementia with Lewy Bodies

Dementia with Lewy bodies (DLB) represents a huge medical need as it accounts for up to 30% of all dementia cases, and there is no cure available. The underyling spectrum of pathology is complex and creates a challenge for targeted molecular therapies. We here tested the hypothesis that leukotrienes are involved in the pathology of DLB and that blocking leukotrienes through Montelukast, a leukotriene receptor antagonist and approved anti-asthmatic drug, might alleviate pathology and restore cognitive functions. Expression of 5-lipoxygenase, the rate-limiting enzyme for leukotriene production, was indeed elevated in brains with DLB. Treatment of cognitively deficient human alpha-synuclein overexpressing transgenic mice with Montelukast restored memory. Montelukast treatment resulted in modulation of beclin-1 expression, a marker for autophagy, and in a reduction in the human alpha-synulcein load in the transgenic mice. Reducing the protein aggregation load in neurodegenerative diseases might be a novel model of action of Montelukast. Moreover, this work presents leukotriene signaling as a potential drug target for DLB and shows that Montelukast might be a promising drug candidate for future DLB therapy development.

In vitro cytotoxicity of montelukast in HAPI and SH-SY5Y cells

Montelukast is a cysteinyl leukotriene (CysLT) receptor antagonist with efficacy against a variety of diseases, including asthma and inflammation-related conditions. However, various neuropsychiatric events (NEs) suspected to be related to montelukast have been reported recently, with limited understanding on their association and underlying mechanisms. This study aimed to investigate whether montelukast can induce neuroinflammation and neurotoxicity in microglial HAPI cells and neural SH-SY5Y cells. The present study also compared the effects of montelukast with a 5-lipoxygenase inhibitor (zileuton) and a cyclooxygenase-2 inhibitor (celecoxib) to better understand modulation of related pathways. HAPI or SH-SY5Y cells were treated with the indicated drugs (3.125 μM-100 μM) for 24 h to investigate drug-induced neuroinflammation and neurotoxicity. Montelukast induced cytotoxicity in HAPI cells (50-100 μM), accompanied with caspase-3/7 activation, prostaglandin E₂ (PGE₂) release, and reactive oxygen species (ROS) production. Whilst both montelukast and zileuton down-regulated CysLT release in HAPI cells, zileuton did not significantly affect cell viability or inflammatory and oxidative factors. Celecoxib decreased HAPI cell viability (6.25-100 μM), accompanied with increasing caspase-3/7 activation and ROS production, but in contrast to montelukast increased CysLT release and decreased PGE₂ production. Similar to observations in HAPI cells, both montelukast and celecoxib (50-100 μM) but not zileuton produced toxicity in SH-SY5Y neuroblastoma cells. Similarly, CM from HAPI cells treated with either montelukast or zileuton produced toxicity in SH-SY5Y cells. The results of the current study show the capability of montelukast to directly induce toxicity and inflammation in HAPI cells, possibly through the involvement of PGE₂ and ROS, and toxicity in undifferentiated SH-SY5Y neuroblastoma cells. The current study highlights the importance of consideration between benefit and risk of montelukast usage and provides references for future investigation on decreasing montelukast-related NEs.

Modulation of neuroinflammation by cysteinyl leukotriene 1 and 2 receptors: implications for cerebral ischemia and neurodegenerative diseases

Neuroinflammation is a complex biological process and has been known to play an important role in age-related cerebrovascular and neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease, and Parkinson's disease. Cysteinyl leukotrienes (CysLTs) are potent inflammatory lipid mediators that exhibit actions mainly through activating type 1 and type 2 CysLT receptors (CysLT1 and CysLT2). Accumulating evidence shows that CysLT1 and CysLT2 are activated at different stages of pathological process in various cell types in the brain such as vascular endothelial cells, astrocytes, microglia, and neurons in response to insults. However, the precise roles and mechanisms of CysLT1 and CysLT2 in regulating the pathogenesis of cerebral ischemia, Alzheimer's disease, and Parkinson's disease are not fully understood. In this article, we focus on current advances that link activation of CysLT1 and CysLT2 to the pathological process during brain ischemia and neurodegeneration and discuss mechanisms by which CysLT1 and CysLT2 mediate inflammatory process and brain injury. Multitarget anti-inflammatory potentials of CysLT1 and CysLT2 antagonism for neuroinflammation and brain injury will also be reviewed.

Montelukast attenuates rotenone-induced microglial activation/p38 MAPK expression in rats: Possible role of its antioxidant, anti-inflammatory and antiapoptotic effects

Montelukast (MK),a cysteinyl leukotriene (CysLT1) receptor antagonist, latterly exhibited a remarkable neuroprotective activity in various neurodegenerative disorders. This study aims to elucidate the neuroprotective effect of MK in rotenone-induced Parkinson's disease(PD) model in rats. Ninety six male rats were split into four groups: vehicle control (0.2 ml/kg/48 h, sc), MK (10 mg/kg/day, ip), rotenone (1.5 mg/kg/48 h, sc.) and rotenone pretreated with MK. Rotenone treatment led to significant reduction in motor functioning and elevation in oxidative stress markers. Additionally, upregulation of p38 mitogen-activated protein kinase (p38 MAPK) and CysLT1 receptor expressions were anchored with enhanced striatal microglial activation generating a severe neuro-inflammatory milieu. Furthermore, an augmentation in p53 expression and cleaved caspases-3 activity increased apoptotic neurodegeneration synchronized with reduction of striatal tyrosine hydroxylase (TH) content. Changes in neuronal morphology was also noted. MK administration significantly mitigated motor impairment and rise in oxidative stress mediators. As well, the anti-inflammatory activity of MK was manifested by hindering the principal controller of inflammatory pathway, nuclear factor-kappa B, followed by its downstream pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-1 beta), by attenuating striatal microglial activation and hampering the expression of both p38 MAPK and CysLT1. Moreover, MK revealed a decline in p53 expression with its downstream cleaved caspases-3 which resulted in preservation of striatal TH terminals as verified by increased striatal TH content and improvement in the histopathological changes incited by rotenone. In conclusion, MK endowed neuroprotective effects in rotenone-induced PD animal model via attenuation of microglial cell activation and p38 MAPK expression.