Intranasal LPS-mediated Parkinson's model challenges the pathogenesis of nasal cavity and environmental toxins

Infections in the Etiology of Parkinson's Disease and Synucleinopathies: A Renewed Perspective, Mechanistic Insights, and Therapeutic Implications

Increasing evidence suggests a potential role for infectious pathogens in the etiology of synucleinopathies, a group of age-related neurodegenerative disorders including Parkinson's disease (PD), multiple system atrophy and dementia with Lewy bodies. In this review, we discuss the link between infections and synucleinopathies from a historical perspective, present emerging evidence that supports this link, and address current research challenges with a focus on neuroinflammation. Infectious pathogens can elicit a neuroinflammatory response and modulate genetic risk in PD and related synucleinopathies. The mechanisms of how infections might be linked with synucleinopathies as well as the overlap between the immune cellular pathways affected by virulent pathogens and disease-related genetic risk factors are discussed. Here, an important role for α-synuclein in the immune response against infections is emerging. Critical methodological and knowledge gaps are addressed, and we provide new future perspectives on how to address these gaps. Understanding how infections and neuroinflammation influence synucleinopathies will be essential for the development of early diagnostic tools and novel therapies.

The Synergistic Effect Study of Lipopolysaccharide (LPS) and A53T-α-Synuclein: Intranasal LPS Exposure on the A53T-α-Synuclein Transgenic Mouse Model of Parkinson's Disease

Aging and interactions between genetic and environmental factors are believed to be involved the chronic development of Parkinson's disease (PD). Among PD patients, abnormally aggregated α-synuclein is a major component of the Lewy body. Generally, the intranasal route is believed to be a gate way to the brain, and it assists environmental neurotoxins in entering the brain and is related to anosmia during early PD. The current study applies the chronic intranasal application of lipopolysaccharides (LPS) in 4-, 8-, 12- and 16-month-old A53T-α-synuclein (A53T-α-Syn) transgenic C57BL/6 mice at 2-day intervals for a 2-month period, for evaluating the behavioral, pathological, and biochemical changes and microglial activation in these animals. According to our results, after intranasal administration of LPS, A53T-α-Syn mice showed severe progressive anosmia, hypokinesia, selective dopaminergic (DAergic) neuronal losses, decreased striatal dopamine (DA) level, and enhanced α-synuclein accumulation within the substantia nigra (SN) in an age-dependent way. In addition, we found obvious NF-кB activation, Nurr1 inhibition, IL-1β, and TNF-α generation within the microglia of the SN. Conversely, the wild-type (WT) mice showed mild, whereas A53T-α-Syn mice had moderate PD-like changes among the old mice. This study demonstrated the synergistic effect of intranasal LPS and α-synuclein burden on PD development. Its underlying mechanism may be associated with Nurr1 inhibition within microglia and the amplification of CNS neuroinflammation. The mice with multiple factors, including aging, neuroinflammation, and α-synuclein mutation, have played a significant role in enhancing our understanding of how inflammation and α-synuclein mutation contribute to the neurodegeneration observed in PD.

Crocin attenuates the lipopolysaccharide-induced neuroinflammation via expression of AIM2 and NLRP1 inflammasome in an experimental model of Parkinson's disease

The underlying mechanisms of inflammasome activation and the following dopaminergic neuron loss caused by chronic neuroinflammation remain entirely unclear. Therefore, this study aimed to investigate the impact of crocin on the inflammasome complex within an experimental model of Parkinson's disease (PD) using male Wistar rats. PD was induced by the stereotaxic injection of lipopolysaccharide (LPS), and crocin was intraperitoneally administrated one week before the lesion, and then treatment continued for 21 days. Open field (OF) and elevated plus maze tests were applied for behavioral assays. Furthermore, hematoxylin and eosin (H&E) and immunostaining were performed on whole brain tissue, while dissected substantia nigra (SN) was used for immunoblotting and real-time PCR to evaluate compartments involved in PD. The time spent in the center of test was diminished in the LPS group, while treatment with 30 mg/kg of crocin significantly increased it. H&E staining showed a significant increase in cell infiltration at the site of LPS injection, which was ameliorated upon crocin treatment. Notably, crocin-treated animals showed a reduced number of caspase-1 and IL-1β positive cells, whereas the number of positive cells was increased in the LPS group (P < 0.05). A significant decrease in tyrosine hydroxylase (TH) expression was also found in the LPS group, while crocin treatment significantly elevated its expression. IL-1β, IL-18, NLRP1, and AIM2 genes expression significantly increased in the LPS group. On the other hand, treatment with 30 mg/kg of crocin significantly downregulated the expression levels of these genes along with NLRP1 (P < 0.05). In summary, our findings suggest that crocin reduces neuroinflammation in PD by diminishing IL-1β and caspase-1 levels, potentially by inhibiting the expression of AIM2 and NLRP1 genes.

Do Bacterial Outer Membrane Vesicles Contribute to Chronic Inflammation in Parkinson's Disease?

Parkinson's disease (PD) is an increasingly common neurodegenerative disease. It has been suggested that the etiology of idiopathic PD is complex and multifactorial involving environmental contributions, such as viral or bacterial infections and microbial dysbiosis, in genetically predisposed individuals. With advances in our understanding of the gut-brain axis, there is increasing evidence that the intestinal microbiota and the mammalian immune system functionally interact. Recent findings suggest that a shift in the gut microbiome to a pro-inflammatory phenotype may play a role in PD onset and progression. While there are links between gut bacteria, inflammation, and PD, the bacterial products involved and how they traverse the gut lumen and distribute systemically to trigger inflammation are ill-defined. Mechanisms emerging in other research fields point to a role for small, inherently stable vesicles released by Gram-negative bacteria, called outer membrane vesicles in disease pathogenesis. These vesicles facilitate communication between bacteria and the host and can shuttle bacterial toxins and virulence factors around the body to elicit an immune response in local and distant organs. In this perspective article, we hypothesize a role for bacterial outer membrane vesicles in PD pathogenesis. We present evidence suggesting that these outer membrane vesicles specifically from Gram-negative bacteria could potentially contribute to PD by traversing the gut lumen to trigger local, systemic, and neuroinflammation. This perspective aims to facilitate a discussion on outer membrane vesicles in PD and encourage research in the area, with the goal of developing strategies for the prevention and treatment of the disease.

Regulatory Non-coding RNAs Involved in Oxidative Stress and Neuroinflammation: An Intriguing Crosstalk in Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the accumulation of α-synuclein and the degeneration of dopaminergic neurons in the substantia nigra. Although the molecular bases for PD development are not fully recognized, extensive evidence has suggested that the development of PD is strongly associated with neuroinflammation. It is noteworthy that while neuroinflammation might not be a primary factor in all patients with PD, it seems to be a driving force for disease progression, and therefore, exploring the role of pathways involved in neuroinflammation is of great importance. Besides, the importance of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and competing endogenous RNAs (ceRNAs), has been widely studied with a focus on the pathogenesis of PD. However, there is no comprehensive review regarding the role of neuroinflammation- related ncRNAs as prospective biomarkers and therapeutic targets involved in the pathogenesis of PD, even though the number of studies connecting ncRNAs to neuroinflammatory pathways and oxidative stress has markedly increased in the last few years. Hence, the present narrative review intended to describe the crosstalk between regulatory ncRNAs and neuroinflammatory targets with respect to PD to find and propose novel combining biomarkers or therapeutic targets in clinical settings.

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.

Regulation of Pain Perception by Microbiota in Parkinson Disease

Pain perception involves current stimulation in peripheral nociceptive nerves and the subsequent stimulation of postsynaptic excitatory neurons in the spinal cord. Importantly, in chronic pain, the neural activity of both peripheral nociceptors and postsynaptic neurons in the central nervous system is influenced by several inflammatory mediators produced by the immune system. Growing evidence has indicated that the commensal microbiota plays an active role in regulating pain perception by either acting directly on nociceptors or indirectly through the modulation of the inflammatory activity on immune cells. This symbiotic relationship is mediated by soluble bacterial mediators or intrinsic structural components of bacteria that act on eukaryotic cells, including neurons, microglia, astrocytes, macrophages, T cells, enterochromaffin cells, and enteric glial cells. The molecular mechanisms involve bacterial molecules that act directly on neurons, affecting their excitability, or indirectly on non-neuronal cells, inducing changes in the production of proinflammatory or anti-inflammatory mediators. Importantly, Parkinson disease, a neurodegenerative and inflammatory disorder that affects mainly the dopaminergic neurons implicated in the control of voluntary movements, involves not only a motor decline but also nonmotor symptomatology, including chronic pain. Of note, several recent studies have shown that Parkinson disease involves a dysbiosis in the composition of the gut microbiota. In this review, we first summarize, integrate, and classify the molecular mechanisms implicated in the microbiota-mediated regulation of chronic pain. Second, we analyze the changes on the commensal microbiota associated to Parkinson disease and propose how these changes affect the development of chronic pain in this pathology. SIGNIFICANCE STATEMENT: The microbiota regulates chronic pain through the action of bacterial signals into two main locations: the peripheral nociceptors and the postsynaptic excitatory neurons in the spinal cord. The dysbiosis associated to Parkinson disease reveals increased representation of commensals that potentially exacerbate chronic pain and reduced levels of bacteria with beneficial effects on pain. This review encourages further research to better understand the signals involved in bacteria-bacteria and bacteria-host communication to get the clues for the development of probiotics with therapeutic potential.

Aging, Parkinson's Disease, and Models: What Are the Challenges?

Parkinson's disease (PD) is a chronic, neurodegenerative condition characterized by motor symptoms such as bradykinesia, rigidity, and tremor, alongside multiple nonmotor symptoms. The appearance of motor symptoms is linked to progressive dopaminergic neuron loss within the substantia nigra. PD incidence increases sharply with age, suggesting a strong association between mechanisms driving biological aging and the development and progression of PD. However, the role of aging in the pathogenesis of PD remains understudied. Numerous models of PD, including cell models, toxin-induced models, and genetic models in rodents and nonhuman primates (NHPs), reproduce different aspects of PD, but preclinical studies of PD rarely incorporate age as a factor. Studies using patient neurons derived from stem cells via reprogramming methods retain some aging features, but their characterization, particularly of aging markers and reproducibility of neuron type, is suboptimal. Investigation of age-related changes in PD using animal models indicates an association, but this is likely in conjunction with other disease drivers. The biggest barrier to drawing firm conclusions is that each model lacks full characterization and appropriate time-course assessments. There is a need to systematically investigate whether aging increases the susceptibility of mouse, rat, and NHP models to develop PD and understand the role of cell models. We propose that a significant investment in time and resources, together with the coordination and sharing of resources, knowledge, and data, is required to accelerate progress in understanding the role of biological aging in PD development and improve the reliability of models to test interventions.

Lambda-cyhalothrin enhances inflammation in nigrostriatal region in rats: Regulatory role of NF-κβ and JAK-STAT signaling

The risk to develop neurobehavioural abnormalities in humans on exposure to lambda-cyhalothrin (LCT) - a type II synthetic pyrethroid has enhanced significantly due to its extensive uses in agriculture, homes, veterinary practices and public health programs. Earlier, we found that the brain dopaminergic system is vulnerable to LCT and affects motor functions in rats. In continuation to this, the present study is focused to unravel the role of neuroinflammation in LCT-induced neurotoxicity in substantia nigra and corpus striatum in rats. Increase in the mRNA expression of proinflammatory cytokines (TNF- α, IL-1β, IL-6) and iNOS whereas decrease in anti-inflammatory cytokine (IL-10) was distinct both in substantia nigra and corpus striatum of rats treated with LCT (0.5, 1.0, 3.0 mg/kg body weight, p.o, for 45 days) as compared to control rats. Further, LCT-treated rats exhibited increased levels of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1), the glial marker proteins both in substantia nigra and corpus striatum as compared to controls. Exposure of rats to LCT also caused alterations in the levels of heat shock protein 60 (HSP60) and mRNA expression of toll-like receptors (TLR2 and TLR4) in the substantia nigra and corpus striatum. An increase in the phosphorylation of key proteins involved in NF-kβ (P65, Iκβ, IKKα, IKKβ) and JAK/STAT (STAT1, STAT3) signaling and alteration in the protein levels of JAK1 and JAK2 was prominent in LCT-treated rats. Histological studies revealed damage of dopaminergic neurons and reactive gliosis as evidenced by the presence of darkly stained pyknotic neurons and decrease in Nissl substance and an increase in infiltration of immune cells both in substantia nigra and corpus striatum of LCT-treated rats. Presence of reactive microglia and astrocytes in LCT-treated rats was also distinct in ultrastructural studies. The results exhibit that LCT may damage dopaminergic neurons in the substantia nigra and corpus striatum by inducing inflammation as a result of stimulation of neuroglial cells involving activation of NF-κβ and JAK/STAT signaling.

Detection of β-N-methylamino-l-alanine in postmortem olfactory bulbs of Alzheimer's disease patients using UHPLC-MS/MS: An autopsy case-series study

Introduction

Cyanobacterial blooms produce toxins that may become aerosolized, increasing health risks through inhalation exposures. Health related effects on the lower respiratory tract caused by these toxins are becoming better understood. However, nasal exposures to cyanotoxins remain understudied, especially for those with neurotoxic potential. Here, we present a case series study evaluating exposure to β-N-methylamino-l-alanine (BMAA), a cyanobacterial toxin linked to neurodegenerative disease, in postmortem olfactory tissues of individuals with varying stages of Alzheimer's disease (AD).

Methods

Olfactory bulb (Ob) tissues were collected during autopsies performed between 2014 and 2017 from six South Florida brain donors (ages 47-78) with residences less than 140 m from a freshwater body. A triple quadrupole tandem mass spectrometry (UHPLC-MS/MS) method validated according to peer AOAC International guidelines was used to detect BMAA and two BMAA isomers: 2,4-diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl)glycine (AEG). Quantitative PCR was performed on the contralateral Ob to evaluate the relative expression of genes related to proinflammatory cytokines (IL-6 & IL-18), apoptotic pathways (CASP1 & BCL2), and mitochondrial stress (IRF1 & PINK1). Immunohistochemistry was also performed on the adjacent olfactory tract (Ot) to evaluate co-occurring neuropathology with BMAA tissue concentration.

Results

BMAA was detected in the Ob of all cases at a median concentration of 30.4 ng/g (Range <LLOQ - 488.4 ng/g). Structural isomers were also detected with median concentrations of 28.8 ng/g (AEG) and 103.6 ng/g (2,4-DAB). In addition, we found that cases with BMAA tissue concentrations above the <LLOQ also displayed increased expression of IL-6 (3.3-fold), CASP1 (1.7-fold), and IRF1 (1.6-fold). Reactive microglial, astrogliosis, myelinopathy, and neuronopathy of axonal processes in the Ot were also observed in cases with higher BMAA tissue concentrations.

Conclusion

Our study demonstrates that the cyanobacterial toxin BMAA can be detected in the olfactory pathway, a window to the brain, and its presence may increase the occurrence of proinflammatory cytokines, reactive glia, and toxicity to axonal processes. Further studies will be needed to evaluate BMAA's toxicity via this route of exposure and factors that increase susceptibility.

Gut microbiome and Parkinson's disease: Perspective on pathogenesis and treatment

BACKGROUND

Parkinson's disease (PD) is a disease of ⍺-synuclein aggregation-mediated dopaminergic neuronal loss in the substantia nigra pars compacta, which leads to motor and non-motor symptoms. Through the last two decades of research, there has been growing consensus that inflammation-mediated oxidative stress, mitochondrial dysfunction, and cytokine-induced toxicity are mainly involved in neuronal damage and loss associated with PD. However, it remains unclear how these mechanisms relate to sporadic PD, a more common form of PD. Both enteric and central nervous systems have been implicated in the pathogenesis of sporadic PD, thus highlighting the crosstalk between the gut and brain.

AIM

of Review: In this review, we summarize how alterations in the gut microbiome can affect PD pathogenesis. We highlight various mechanisms increasing/decreasing the risk of PD development. Based on the previous supporting evidence, we suggest how early interventions could protect against PD development and how controlling specific factors, including our diet, could modify our perspective on disease mechanisms and therapeutics. We explain the strong relationship between the gut microbiota and the brain in PD subjects, by delineating the multiple mechanisms involved inneuroinflammation and oxidative stress. We conclude that the neurodetrimental effects of western diet (WD) and the neuroprotective effects of Mediterranean diets should be further exploredin humans through clinical trials. Key Scientific Concepts of Review: Alterations in the gut microbiome and associated metabolites may contribute to pathogenesis in PD. In some studies, probiotics have been shown to exert anti-oxidative effects in PD via improved mitochondrial dynamics and homeostasis, thus reducing PD-related consequences. However, there is a significant unmet need for randomized clinical trials to investigate the effectiveness of microbial products, probiotic-based supplementation, and dietary intervention in reversing gut microbial dysbiosis in PD.

Lipopolysaccharide mouse models for Parkinson's disease research: a critical appraisal

Parkinson's disease, the most common movement disorder, has a strong neuroinflammatory aspect. This is evident by increased pro-inflammatory cytokines in the serum, and the presence of activated microglial cells, and inflammatory cytokines in the substantia nigra of post-mortem brains as well as cerebrospinal fluid of Parkinson's disease patients. The central and peripheral neuroinflammatory aspects of Parkinson's disease can be investigated in vivo via administration of the inflammagen lipopolysaccharide, a component of the cell wall of gram-negative bacteria. In this mini-review, we will critically evaluate different routes of lipopolysaccharide administration (including intranasal systemic and stereotasic), their relevance to clinical Parkinson's disease as well as the recent findings in lipopolysaccharide mouse models. We will also share our own experiences with systemic and intrastriatal lipopolysaccharide models in C57BL/6 mice and will discuss the usefulness of lipopolysaccharide mouse models for future research in the field.

Infection, Learning, and Memory: Focus on Immune Activation and Aversive Conditioning

Here we review the effects of immune activation primarily via lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, on hippocampal and non-hippocampal-dependent learning and memory. Rodent studies have found that LPS alters both the acquisition and consolidation of aversive learning and memory, such as those evoking evolutionarily adaptive responses like fear and disgust. The inhibitory effects of LPS on the acquisition and consolidation of contextual fear memory are discussed. LPS-induced alterations in the acquisition of taste and place-related conditioned disgust memory within bottle preference tasks and taste reactivity tests (taste-related), in addition to conditioned context avoidance tasks and the anticipatory nausea paradigm (place-related), are highlighted. Further, conditioned disgust memory consolidation may also be influenced by LPS-induced effects. Growing evidence suggests a central role of immune activation, especially pro-inflammatory cytokine activity, in eliciting the effects described here. Understanding how infection-induced immune activation alters learning and memory is increasingly important as bacterial and viral infections are found to present a risk of learning and memory impairment.

Inflammatory Animal Models of Parkinson’s Disease

Accumulating evidence suggests that microglia and peripheral immune cells may play determinant roles in the pathogenesis of Parkinson’s disease (PD). Consequently, there is a need to take advantage of immune-related models of PD to study the potential contribution of microglia and peripheral immune cells to the degeneration of the nigrostriatal system and help develop potential therapies for PD. In this review, we have summarised the main PD immune models. From a historical perspective, we highlight first the main features of intranigral injections of different pro-inflammogens, including lipopolysaccharide (LPS), thrombin, neuromelanin, etc. The use of adenoviral vectors to promote microglia-specific overexpression of different molecules in the ventral mesencephalon, including α-synuclein, IL-1β, and TNF, are also presented and briefly discussed. Finally, we summarise different models associated with peripheral inflammation whose contribution to the pathogenesis of neurodegenerative diseases is now an outstanding question. Illustrative examples included systemic LPS administration and dextran sulfate sodium-induced colitis in rodents.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

Changes in activity of µ- and m-calpains and signs of neuroinflammation in the hippocampus and striatum of rats after single intraperitoneal injection of subseptic dose of endotoxin

Some mechanisms of neuronal degeneration in endotoxinemia are already well described, but need to be detailed. In this study, we tested the effect of a single intraperitoneal injection of a LPS sub-septic dose (1 mg/kg of animal weight) on calpain activity in the striatum and hippocampus. We showed, that in the hippocampus the day after LPS administration an increase in production of IL-1β and TNF-α mRNA, followed by elevated mRNA expression and activity of µ- and m-calpains without signs of microglia activation is observed. In striatal cells, the day after LPS injection an increase in expression of IL-1β, TNF-α, IBA-1, m-calpain and calpastatin mRNA is revealed, which only intensifies over time. The elicited changes are accompanied by a decrease in motor behavior, which can be considered as a sign of sickness behavior. In the hippocampus, 180 days after LPS administration expression of TNF-α, content and activity of µ-calpain are increased. In the striatum, elevation in expression of TNF-α, IBA-1, µ- and m-calpain mRNA, with hyperactivation of only m-calpain, is observed. Significantly reduced motor activity can be a consequence of LPS-induced neuronal death. A long-lasting endotoxin activates microglia that damage neurons via proinflammation cytokines and calpain hyperactivation. The endotoxin hypothesis of neurodegeneration is unproven, but if correct, then neurodegeneration may be reduced by decreasing endotoxin-induced neuroinflammation and m-calpain hyperactivation. Therefore, the drugs, that decrease endotoxin-induced neuroinflammation and differently inhibit µ- or m-calpain, can be used to prevent or reduce the severity of neurodegeneration.

Diosgenin Prevents Microglial Activation and Protects Dopaminergic Neurons from Lipopolysaccharide-Induced Neural Damage In Vitro and In Vivo

Background: The prevention of age-related neurodegenerative disorders is an important issue in an aging society. Microglia-mediated neuroinflammation resulting in dopaminergic neuron loss may lead to the pathogenesis of Parkinson’s disease (PD). Lipopolysaccharide (LPS), an endotoxin, induces neuroinflammatory microglial activation, contributing to dopaminergic neuron damage. Diosgenin is a phytosteroid sapogenin with a wide spectrum of pharmacological activities, e.g., anti-inflammatory activity. However, the preventive effect of diosgenin on neuroinflammation is not clear. Thus, in this study, we further investigated the neuroprotective effect of diosgenin on LPS-induced neural damage in vitro and in vivo. Methods: For in vitro experiments, primary mesencephalic neuron-glia cultures and primary microglia cultures isolated from Sprague–Dawley rats were used. Cells were pretreated with diosgenin and then stimulated with LPS. The expression of proinflammatory cytokines or tyrosine hydroxylase (TH) in the cells was analyzed. In vivo, rats were fed a diet containing 0.1% (w/w) diosgenin for 4 weeks before being administered a unilateral substantia nigra (SN) injection of LPS. Four weeks after the LPS injection, the rats were assessed for lesion severity using the amphetamine-induced rotation test and TH immunohistochemistry. Results: Diosgenin pretreatment prevented LPS-induced neurite shortening in TH-positive neurons in mesencephalic neuron-glia cultures. In addition, pretreatment of primary microglia with diosgenin significantly reduced tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) expression. Moreover, diosgenin pretreatment significantly suppressed LPS-induced extracellular signal-regulated kinase (ERK) activation. In vivo, the intranigral injection of LPS in rats fed a diosgenin-containing diet significantly improved motor dysfunction and reduced TH expression in SN. Conclusion: These results support the effectiveness of diosgenin in protecting dopaminergic neurons from LPS-induced neuroinflammation.

Differential seeding and propagating efficiency of α-synuclein strains generated in different conditions

Background

Accumulation of alpha-synuclein (α-syn) is a main pathological hallmark of Parkinson’s and related diseases, which are collectively known as synucleinopathies. Growing evidence has supported that the same protein can induce remarkably distinct pathological progresses and disease phenotypes, suggesting the existence of strain difference among α-syn fibrils. Previous studies have shown that α-syn pathology can propagate from the peripheral nervous system (PNS) to the central nervous system (CNS) in a “prion-like” manner. However, the difference of the propagation potency from the periphery to CNS among different α-syn strains remains unknown and the effect of different generation processes of these strains on the potency of seeding and propagation remains to be revealed in more detail.

Methods

Three strains of preformed α-syn fibrils (PFFs) were generated in different buffer conditions which varied in pH and ionic concentrations. The α-syn PFFs were intramuscularly (IM) injected into a novel bacterial artificial chromosome (BAC) transgenic mouse line that expresses wild-type human α-syn, and the efficiency of seeding and propagation of these PFFs from the PNS to the CNS was evaluated.

Results

The three strains of α-syn PFFs triggered distinct propagation patterns. The fibrils generated in mildly acidic buffer led to the most severe α-syn pathology, degeneration of motor neurons and microgliosis in the spinal cord.

Conclusions

The different α-syn conformers generated in different conditions exhibited strain-specific pathology and propagation patterns from the periphery to the CNS, which further supports the view that α-syn strains may be responsible for the heterogeneity of pathological features and disease progresses among synucleinopathies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00242-5.

The efficacy of systemic administration of lipopolysaccharide in modelling pre-motor Parkinson's disease in C57BL/6 mice

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterised by the loss of dopaminergic neurons in the substantia nigra. Mounting evidence indicates a crucial role of inflammation and concomitant oxidative stress in the disease progression. Therefore, the aim of this study was to investigate the ability of systemically administered lipopolysaccharide (LPS) to induce motor and non-motor symptoms of PD, inflammation, oxidative stress and major neuropathological hallmarks of the disease in regions postulated to be affected, including the olfactory bulb, hippocampus, midbrain and cerebellum. Twenty-one male C57BL/6 mice, approximately 20 weeks old, received a dose of 0.3 mg/kg/day of LPS systemically on 4 consecutive days and behavioural testing was conducted on days 14-18 post-treatment, followed by tissue collection. Systemically administered LPS increased latency time in the buried food seeking test (indicative of olfactory impairment), and decreased time spent in central zone of the open field (anxiety-like behaviour). However, there was no change in latency time in the rotarod test or the expression of tyrosine hydroxylase (TH) in the midbrain. Systemically administered LPS induced increased glial markers GFAP and Iba-1 and oxidative stress marker 3-nitrotyrosine (3-NT) in the olfactory bulb, hippocampus, midbrain and cerebellum, and there were region specific changes in the expression of NFκB, IL-1β, α-synuclein, TH and BDNF proteins. The model could be useful to further elucidate early non-motor aspects of PD and the possible mechanisms contributing to the non-motor deficits.

The intestinal luminal sources of α-synuclein: a gastroenterologist perspective

Parkinson's disease is characterized by nonmotor/motor dysfunction, midbrain dopaminergic neuronal death, and α-synuclein (aSN) deposits. The current hypothesis is that aSN accumulates in the enteric nervous system to reach the brain. However, invertebrate, vertebrate, and nutritional sources of aSN reach the luminal compartment. Submitted to local amyloidogenic forces, the oligomerized proteins' cargo can be sensed and sampled by a specialized mucosal cell to be transmitted to the adjacent enteric nervous system, starting their upward journey to the brain. The present narrative review extends the current mucosal origin of Parkinson's disease, presenting the possibility that the disease starts in the intestinal lumen. If substantiated, eliminating the nutritional sources of aSN (eg, applying a vegetarian diet) might revolutionize the currently used dopaminergic pharmacologic therapy.

Natural Molecules and Neuroprotection: Kynurenic Acid, Pantethine and α-Lipoic Acid

The incidence of neurodegenerative diseases has increased greatly worldwide due to the rise in life expectancy. In spite of notable development in the understanding of these disorders, there has been limited success in the development of neuroprotective agents that can slow the progression of the disease and prevent neuronal death. Some natural products and molecules are very promising neuroprotective agents because of their structural diversity and wide variety of biological activities. In addition to their neuroprotective effect, they are known for their antioxidant, anti-inflammatory and antiapoptotic effects and often serve as a starting point for drug discovery. In this review, the following natural molecules are discussed: firstly, kynurenic acid, the main neuroprotective agent formed via the kynurenine pathway of tryptophan metabolism, as it is known mainly for its role in glutamate excitotoxicity, secondly, the dietary supplement pantethine, that is many sided, well tolerated and safe, and the third molecule, α-lipoic acid is a universal antioxidant. As a conclusion, because of their beneficial properties, these molecules are potential candidates for neuroprotective therapies suitable in managing neurodegenerative diseases.

Lipopolysaccharide animal models of Parkinson's disease: Recent progress and relevance to clinical disease

Parkinson's disease (PD) is one of the most common neurodegenerative movement disorders which is characterised neuropathologically by progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the presence of Lewy bodies (made predominately of α-synuclein) in the surviving neurons. Animal models of PD have improved our understanding of the disease and have played a critical role in the development of neuroprotective agents. Neuroinflammation has been strongly implicated in the pathogenesis of PD, and recent studies have used lipopolysaccharide (LPS), a component of gram-negative bacteria and a potent activator of microglia cells, to mimic the inflammatory events in clinical PD. Modulating the inflammatory response could ameliorate PD associated complications and thus, it is essential to understand the extent to which LPS models reflect human PD. This review will outline the routes of administration of LPS such as stereotaxic, systemic and intranasal, their ability to recapitulate neuropathological markers of PD, and mechanisms of LPS induced toxicity. We will also discuss the ability of the models to replicate motor symptoms and non-motor symptoms of PD such as gastrointestinal dysfunction, olfactory dysfunction, anxiety, depression and cognitive dysfunction.

Rg1 improves LPS-induced Parkinsonian symptoms in mice via inhibition of NF-κB signaling and modulation of M1/M2 polarization

Ginsenoside Rg1 is one of the most active ingredients in ginseng, which has been reported to protect dopaminergic neurons and improve behavioral defects in MPTP model, 6-OHDA model and rotenone model. However, it is unclear whether Rg1 exerted neuroprotection in LPS-induced sub-acute PD model. In this study, we investigated the neuroprotective effect of Rg1 in the sub-acute PD mouse model and explored the related mechanisms. Rg1 (10, 20, 40 mg·kg^-1·d^-1) was orally administered to mice for 18 days. A sub-acute PD model was established in the mice through LPS microinjection into the substantia nigra (SN) from D8 to D13. We found that Rg1 administration dose-dependently inhibited LPS-induced damage of dopaminergic neurons and activation of glial cells in the substantia nigra pars compacta (SNpc). The neuroprotective effects of Rg1 were associated with the reduction of pro-inflammatory cytokines and the improvement of anti-inflammatory cytokines and neurotrophin in the midbrain. Rg1 shifted the polarization of microglia towards the M2 phenotype from M1, evidenced by decreased M1 markers (inducible NO synthase, CD16, etc.) and increased M2 markers (arginase 1 (Arg1), CD206, etc) in the midbrain. Furthermore, Rg1 administration markedly inhibited nuclear translocation of NF-κB in midbrain microglia. In conclusion, Rg1 protects PD mice induced by continuous LPS injection by inhibiting the nuclear entry of NF-κB and regulating the polarization balance of microglia, shedding new light on a disease-modifying therapy of PD.

Neuroprotection of Rotenone-Induced Parkinsonism by Ursolic Acid in PD Mouse Model

BACKGROUND

Parkinson's Disease (PD) is characterized by both motor and non-motor symptoms. The presynaptic neuronal protein, α-Synuclein, plays a pivotal role in PD pathogenesis and is associated with both genetic and sporadic origin of the disease. Ursolic Acid (UA) is a well-known bioactive compound found in various medicinal plants, widely studied for its anti-inflammatory and antioxidant activities.

OBJECTIVE

In this research article, the neuroprotective potential of UA has been further explored in the Rotenone-induced mouse model of PD.

METHODS

To investigate our hypothesis, we have divided mice into 4 different groups, control, drug only control, Rotenone-intoxicated group, and Rotenone-intoxicated mice treated with UA. After the completion of dosing, behavioral parameters were estimated. Then mice from each group were sacrificed and the brains were isolated. Further, the biochemical tests were assayed to check the balance between the oxidative stress and endogenous anti-oxidants; and TH (Tyrosine Hydroxylase), α-Synuclein, Akt (Serine-threonine protein kinase), ERK (Extracellular signal-regulated kinase) and inflammatory parameters like Nuclear Factor-κB (NF-κB) and Tumor Necrosis Factor- α (TNF-α) were assessed using Immunohistochemistry (IHC). Western blotting was also done to check the expressions of TH and α-Synuclein. Moreover, the expression levels of PD related genes like α-Synuclein, β-Synuclein, Interleukin-1β (IL-1β), and Interleukin-10 (IL-10) were assessed by using Real-time PCR.

RESULTS

The results obtained in our study suggested that UA significantly reduced the overexpression of α-Synuclein and regulated the phosphorylation of survival-related kinases (Akt and ERK) apart from alleviating the behavioral abnormalities and protecting the dopaminergic neurons from oxidative stress and neuroinflammation.

CONCLUSION

Thus, our study shows the neuroprotective potential of UA, which can further be explored for possible clinical intervention.

Altered Gut Microbiome in Parkinson's Disease and the Influence of Lipopolysaccharide in a Human α-Synuclein Over-Expressing Mouse Model

The interaction between the gut microbiota and alpha-synuclein (αSyn) aggregation in Parkinson’s disease (PD) is receiving increasing attention. The objective of this study was to investigate gut microbiota, and effects of an inflammatory lipopolysaccharide (LPS) trigger in a human αSyn over-expressing mouse model of PD (Thy1-αSyn). Stool samples from patients with confirmed PD and Thy1-αSyn mice were analyzed using 16S ribosomal RNA sequencing. Compared to healthy controls, the relative abundance of mucin-degrading Verrucomicrobiae and LPS-producing Gammaproteobacteria were greater in PD patients. In mice, the abundance of Gammaproteobacteria was negligible in both Thy1-αSyn and wild-type (WT) animals, while Verrucomicrobiae were reduced in Thy1-αSyn mice. The effect of LPS on intestinal barrier function was investigated in vitro using intestinal epithelial (IEC-6) cells, and in vivo via administration of LPS in drinking water to Thy1-αSyn mice. Acute exposure to LPS in vitro resulted in a reduction and altered distribution of the tight junction markers ZO-1 and e-Cadherin around the cell membrane in IEC-6 cells, as shown by immunohistochemistry. LPS administration in Thy1-αSyn mice resulted in the emergence of early motor manifestations at 10 weeks, compared to untreated mice who were still asymptomatic at this age. This study reaffirms that an altered microbiome exists in patients with PD, and supports the notion of a proinflammatory gut microbiome environment as a trigger for PD pathogenesis.

Nutritional Modulation of Immune and Central Nervous System Homeostasis: The Role of Diet in Development of Neuroinflammation and Neurological Disease

The gut-microbiome-brain axis is now recognized as an essential part in the regulation of systemic metabolism and homeostasis. Accumulating evidence has demonstrated that dietary patterns can influence the development of metabolic alterations and inflammation through the effects of nutrients on a multitude of variables, including microbiome composition, release of microbial products, gastrointestinal signaling molecules, and neurotransmitters. These signaling molecules are, in turn, implicated in the regulation of the immune system, either promoting or inhibiting the production of pro-inflammatory cytokines and the expansion of specific leukocyte subpopulations, such as Th17 and Treg cells, which are relevant in the development of neuroinflammatory and neurodegenerative conditions. Metabolic diseases, like obesity and type 2 diabetes mellitus, are related to inadequate dietary patterns and promote variations in the aforementioned signaling pathways in patients with these conditions, which have been linked to alterations in neurological functions and mental health. Thus, maintenance of adequate dietary patterns should be an essential component of any strategy aiming to prevent neurological pathologies derived from systemic metabolic alterations. The present review summarizes current knowledge on the role of nutrition in the modulation of the immune system and its impact in the development of neuroinflammation and neurological disease.

Occupational exposures and parkinsonism among Shanghai women textile workers

BACKGROUND

Endotoxin, a contaminant of cotton dust, is an experimental model for parkinsonism (PS).

METHODS

We investigated associations between exposures to endotoxin, solvents, magnetic fields, and night shift work, and neurologist-determined PS among Shanghai women textile workers, including 537 retired cotton factory workers ages ≥50 years and an age-matched reference group of 286 retired textile workers not exposed to cotton dust. Repeat exams were conducted 2.5 years after enrollment among 467 cotton workers and 229 reference workers.

RESULTS

We identified 39 prevalent PS cases and 784 non-cases. No consistent or statistically significant associations were observed for endotoxin, solvents, magnetic fields, or shift work with PS risk, severity, or progression.

CONCLUSIONS

Despite the null findings, additional studies of endotoxin exposure and risk of PS in other well-characterized occupational cohorts are warranted in view of toxicological evidence that endotoxin is a pathogenic agent and its widespread occurrence in multiple industries worldwide.

The Synergy of Aging and LPS Exposure in a Mouse Model of Parkinson's Disease

Aging is an inevitable physiological challenge occurring in organisms over time, and is also the most important risk factor of neurodegenerative diseases. In this study, we observed cellular and molecular changes of different age mice and LPS-induced Parkinson disease (PD) model. The results showed that behavioral performance and dopaminergic (DA) neurons were declined, accompanied by increased expression of pro-inflammatory factors (TLR2, p-NF-kB-p65, IL-1β and TNF-α), as well as pro-oxidative stress factor gp91phox in aged mice compared with young mice. Aging exaggerated inflammatory M1 microglia, and destroyed the balance between oxidation and anti-oxidation. The intranasal LPS instillation induced PD model in both young and aged mice. The poor behavioral performance and the loss of DA neurons as well as TLR2, p-NF-kB-p65, IL-1β, TNF-α, iNOS and gp91phox were further aggravated in LPS-aged mice. Interestingly, the expression of Nrf2 and HO-1 was up-regulated by LPS only in young LPS-PD mice, but not in aged mice. The results indicate that the synergy of aging process and LPS exposure may prominently aggravate the DA neurons loss caused by more serious neuroinflammation and oxidative stress in the brain.

Bioconversion of Tyrosine and Tryptophan Derived Biogenic Amines by Neuropathogenic Bacteria

The biochemical potential of pathogenic bacteria may cause alteration in the neurophysiological environment; consequently, neuroendocrine and immune responses of the host are modulated by endogenously produced metabolic products of neuropathogenic bacteria. The present study was designed to detect the derived biogenic amines in spent culture media of Bacillus cereus (Bc), Clostridium tetani (Ct), Listeria monocytogenes (Lm), and Neisseria meningitidis (Nm). Overnight grown culture in different culture media i.e., Nutrient broth (NB), Luria basal broth (LB), Brain Heart Infusion broth (BHI), and human serum supplemented RPMI 1640 medium (RPMI) were used to prepare filter-sterilized, cell-free cultural broths (SCFBs) and subjected to high performance liquid chromatography with electrochemical detection (HPLC-EC) along with the control SCFBs. Comparative analysis of biogenic amines in neuropathogenic bacterial SCFBs with their respective control (SCFB) revealed the complete degradation of dopamine (DA) into its metabolic products by Bc, Ct, and Nm, whereas Lm showed negligible degradation of DA. A relatively high concentration of 5-hydroxyindol acetic acid (5HIAA) by Bc in NB and LB indicated the tryptophan metabolism by the serotonin (5HT) pathway. Our study suggests that microbial endocrinology could help unravel new perspectives to the progression of infectious diseases.

Protective effects of fisetin and other berry flavonoids in Parkinson's disease

Parkinson's disease (PD) is an age-associated degenerative disease of the midbrain that results from the loss of dopaminergic neurons in the substantia nigra. It initially presents as a movement disorder with cognitive and other behavioral problems appearing later in the progression of the disease. Current therapies for PD only delay the onset or reduce the motor symptoms. There are no treatments to stop the nerve cell death or to cure the disease. It is becoming increasingly clear that neurological diseases such as PD are multi-factorial involving disruptions in multiple cellular systems. Thus, it is unlikely that modulating only a single factor will be effective at either preventing disease development or slowing disease progression. A better approach is to identify small molecules that have multiple biological activities relevant to the maintenance of brain function. Flavonoids are polyphenolic compounds that are widely distributed in fruits and vegetables and therefore regularly consumed in the human diet. While flavonoids were historically characterized on the basis of their antioxidant and free radical scavenging effects, more recent studies have shown that flavonoids have a wide range of activities that could make them particularly effective as agents for the treatment of PD. In this article, the multiple physiological benefits of flavonoids in the context of PD are first reviewed. Then, the evidence for the beneficial effects of the flavonol fisetin in models of PD are discussed. These results, coupled with the known actions of fisetin, suggest that it could reduce the impact of PD on brain function.

Lipopolysaccharide-Induced Striatal Nitrosative Stress and Impaired Social Recognition Memory Are Not Magnified by Paraquat Coexposure

Systemic inflammation triggered by lipopolysaccharide (LPS) administration disrupts blood-brain barrier (BBB) homeostasis in animal models. This event leads to increased susceptibility of several encephalic structures to potential neurotoxicants present in the bloodstream. In this study, we investigated the effects of alternate intraperitoneal injections of LPS on BBB permeability, social recognition memory and biochemical parameters in the striatum 24 h and 60 days after treatments. In addition, we investigated whether the exposure to a moderate neurotoxic dose of the herbicide paraquat could potentiate LPS-induced neurotoxicity. LPS administration caused a transient disruption of BBB integrity, evidenced by increased levels of exogenously administered sodium fluorescein in the striatum. Also, LPS exposure caused delayed impairment in social recognition memory (evaluated at day 38 after treatments) and increase in the striatal levels of 3-nitrotyrosine. These events were observed in the absence of significant changes in motor coordination and in the levels of tyrosine hydroxylase (TH) in the striatum and substantia nigra. PQ exposure, which caused a long-lasting decrease of striatal mitochondrial complex I activity, did not modify LPS-induced behavioral and striatal biochemical changes. The results indicate that systemic administration of LPS causes delayed social recognition memory deficit and striatal nitrosative stress in adult mice and that the coexposure to a moderately toxic dose of PQ did not magnify these events. In addition, PQ-induced inhibition of striatal mitochondrial complex I was also not magnified by LPS exposure, indicating the absence of synergic neurotoxic effects of LPS and PQ in this experimental model.

An adverse outcome pathway for parkinsonian motor deficits associated with mitochondrial complex I inhibition

Epidemiological studies have observed an association between pesticide exposure and the development of Parkinson's disease, but have not established causality. The concept of an adverse outcome pathway (AOP) has been developed as a framework for the organization of available information linking the modulation of a molecular target [molecular initiating event (MIE)], via a sequence of essential biological key events (KEs), with an adverse outcome (AO). Here, we present an AOP covering the toxicological pathways that link the binding of an inhibitor to mitochondrial complex I (i.e., the MIE) with the onset of parkinsonian motor deficits (i.e., the AO). This AOP was developed according to the Organisation for Economic Co-operation and Development guidelines and uploaded to the AOP database. The KEs linking complex I inhibition to parkinsonian motor deficits are mitochondrial dysfunction, impaired proteostasis, neuroinflammation, and the degeneration of dopaminergic neurons of the substantia nigra. These KEs, by convention, were linearly organized. However, there was also evidence of additional feed-forward connections and shortcuts between the KEs, possibly depending on the intensity of the insult and the model system applied. The present AOP demonstrates mechanistic plausibility for epidemiological observations on a relationship between pesticide exposure and an elevated risk for Parkinson's disease development.

Lipopolysaccharide-initiated persistent rhinitis causes gliosis and synaptic loss in the olfactory bulb

The olfactory mucosa (OM) is exposed to environmental agents and therefore vulnerable to inflammation. To examine the effects of environmental toxin-initiated OM inflammation on the olfactory bulb (OB), we induced persistent rhinitis in mice and analyzed the spatial and temporal patterns of histopathological changes in the OM and OB. Mice received unilateral intranasal administration of lipopolysaccharide (LPS) or saline three times per week, and were immunohistologically analyzed at 1, 3, 7, 14 and 21 days after the first administration. LPS administration induced an inflammatory response in the OM, including the infiltration of Ly-6G-, CD11b-, Iba-1- and CD3-positive cells, the production of interleukin-1β by CD11b- and Iba-1-positive cells, and loss of olfactory sensory neurons (OSNs). In the OB, we observed activation of microglia and astrocytes and decreased expression of tyrosine hydroxylase in periglomerular cells, vesicular glutamate transporter 1, a presynaptic protein, in mitral and tufted projection neurons, and 5T4 in granule cells. Thus, the OM inflammation exerted a detrimental effect, not only on OSNs, but also on OB neurons, which might lead to neurodegeneration.

Parkinson's disease: Microglial/macrophage-induced immunoexcitotoxicity as a central mechanism of neurodegeneration

Parkinson's disease is one of the several neurodegenerative disorders that affects aging individuals, with approximately 1% of those over the age of 60 years developing the disorder in their lifetime. The disease has the characteristics of a progressive disorder in most people, with a common pattern of pathological change occurring in the nervous system that extends beyond the classical striatal degeneration of dopaminergic neurons. Earlier studies concluded that the disease was a disorder of alpha-synuclein, with the formation of aggregates of abnormal alpha-synuclein being characteristic. More recent studies have concluded that inflammation plays a central role in the disorder and that the characteristic findings can be accounted for by either mutation or oxidative damage to alpha-synuclein, with resulting immune reactions from surrounding microglia, astrocytes, and macrophages. What has been all but ignored in most of these studies is the role played by excitotoxicity and that the two processes are intimately linked, with inflammation triggered cell signaling enhancing the excitotoxic cascade. Further, there is growing evidence that it is the excitotoxic reactions that actually cause the neurodegeneration. I have coined the name immunoexcitotoxicity to describe this link between inflammation and excitotoxicity. It appears that the two processes are rarely, if ever, separated in neurodegenerative diseases.

The underlying mechanism of prodromal PD: insights from the parasympathetic nervous system and the olfactory system

Neurodegeneration of Parkinson's disease (PD) starts in an insidious manner, 30-50% of dopaminergic neurons have been lost in the substantia nigra before clinical diagnosis. Prodromal stage of the disease, during which the disease pathology has started but is insufficient to result in clinical manifestations, offers a valuable window for disease-modifying therapies. The most focused underlying mechanisms linking the pathological pattern and clinical characteristics of prodromal PD are the prion hypothesis of alpha-synuclein and the selective vulnerability of neurons. In this review, we consider the two potential portals, the vagus nerve and the olfactory bulb, through which abnormal alpha-synuclein can access the brain. We review the clinical, pathological and neuroimaging evidence of the parasympathetic nervous system and the olfactory system in the neurodegenerative process and using the two systems as models to discuss the internal homogeneity and heterogeneity of the prodromal stage of PD, including both the clustering and subtyping of symptoms and signs. Finally, we offer some suggestions on future directions for imaging studies in prodromal Parkinson's disease.

Environmental Toxicants-Induced Immune Responses in the Olfactory Mucosa

Olfactory sensory neurons (OSNs) are the receptor cells for the sense of smell. Although cell bodies are located in the olfactory mucosa (OM) of the nasal cavity, OSN axons directly project to the olfactory bulb (OB) that is a component of the central nervous system (CNS). Because of this direct and short connection from this peripheral tissue to the CNS, the olfactory system has attracted attention as a port-of-entry for environmental toxicants that may cause neurological dysfunction. Selected viruses can enter the OB via the OM and directly affect the CNS. On the other hand, environmental toxicants may induce inflammatory responses in the OM, including infiltration of immune cells and production of inflammatory cytokines. In addition, these inflammatory responses cause the loss of OSNs that are then replaced with newly generated OSNs that re-connect to the OB after inflammation has subsided. It is now known that immune cells and cytokines in the OM play important roles in both degeneration and regeneration of OSNs. Thus, the olfactory system is a unique neuroimmune interface where interaction between nervous and immune systems in the periphery significantly affects the structure, neuronal circuitry, and immunological status of the CNS. The mechanisms by which immune cells regulate OSN loss and the generation of new OSNs are, however, largely unknown. To help develop a better understanding of the mechanisms involved, we have provided a review of key research that has investigated how the immune response in the OM affects the pathophysiology of OSNs.

On the translocation of bacteria and their lipopolysaccharides between blood and peripheral locations in chronic, inflammatory diseases: the central roles of LPS and LPS-induced cell death

We have recently highlighted (and added to) the considerable evidence that blood can contain dormant bacteria. By definition, such bacteria may be resuscitated (and thus proliferate). This may occur under conditions that lead to or exacerbate chronic, inflammatory diseases that are normally considered to lack a microbial component. Bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, are well known as potent inflammatory agents, but should normally be cleared. Thus, their continuing production and replenishment from dormant bacterial reservoirs provides an easy explanation for the continuing, low-grade inflammation (and inflammatory cytokine production) that is characteristic of many such diseases. Although experimental conditions and determinants have varied considerably between investigators, we summarise the evidence that in a great many circumstances LPS can play a central role in all of these processes, including in particular cell death processes that permit translocation between the gut, blood and other tissues. Such localised cell death processes might also contribute strongly to the specific diseases of interest. The bacterial requirement for free iron explains the strong co-existence in these diseases of iron dysregulation, LPS production, and inflammation. Overall this analysis provides an integrative picture, with significant predictive power, that is able to link these processes via the centrality of a dormant blood microbiome that can resuscitate and shed cell wall components.

Exposure to bacterial endotoxin generates a distinct strain of α-synuclein fibril

A single amyloidogenic protein is implicated in multiple neurological diseases and capable of generating a number of aggregate "strains" with distinct structures. Among the amyloidogenic proteins, α-synuclein generates multiple patterns of proteinopathies in a group of diseases, such as Parkinson disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). However, the link between specific conformations and distinct pathologies, the key concept of the strain hypothesis, remains elusive. Here we show that in the presence of bacterial endotoxin, lipopolysaccharide (LPS), α-synuclein generated a self-renewable, structurally distinct fibril strain that consistently induced specific patterns of synucleinopathies in mice. These results suggest that amyloid fibrils with self-renewable structures cause distinct types of proteinopathies despite the identical primary structure and that exposure to exogenous pathogens may contribute to the diversity of synucleinopathies.

Inhibition of Rho-kinase by Fasudil protects dopamine neurons and attenuates inflammatory response in an intranasal lipopolysaccharide-mediated Parkinson's model

Microglia activation and inflammatory factors in brain microenvironment are associated with degeneration of neurons in the substantia nigra (SN) of Parkinson's disease (PD) patients and various PD models. There is increasing evidence that the Rho/ROCK (Rho kinase) signalling pathway may play a critical role in the inflammatory response, and ROCK inhibitor has been reported to have neuroprotective effects. In this study, we examined the neuroprotective potential and possible mechanism of ROCK inhibitor Fasudil in an intranasal lipopolysaccharide (LPS)-induced PD model. ROCK was activated with LPS stimulation and inhibited by Fasudil treatment in this PD model. Behavioural tests demonstrated a clear improvement in motor performance after Fasudil treatment. Furthermore, Fasudil resulted in a significant attenuation of dopamine cell loss, α-synuclein accumulation and inflammatory response with the reversion of inflammatory M1 to anti-inflammatory M2 microglia, decreased NF-кB activation, and IL-12 and TNF-α generation in the SN and olfactory bulb in this model. This study establishes a role for Fasudil in protecting against LPS-mediated dopamine degeneration and provides a therapeutic strategy for the treatment of PD.

The prion hypothesis of Parkinson's disease

The discovery of alpha-synuclein's prion-like behaviors in mammals, as well as a non-Mendelian type of inheritance, has led to a new concept in biology, the "prion hypothesis" of Parkinson's disease. The misfolding and aggregation of alpha-synuclein (α-syn) within the nervous system occur in many neurodegenerative diseases including Parkinson's disease (PD), Lewy body dementia (LBD), and multiple system atrophy (MSA). The molecular basis of synucleinopathies appears to be tightly coupled to α-syn's conformational conversion and fibril formation. The pathological form of α-syn consists of oligomers and fibrils with rich in β-sheets. The conversion of its α-helical structure to the β-sheet rich fibril is a defining pathologic feature of α-syn. These kinds of disorders have been classified as protein misfolding diseases or proteopathies which share key biophysical and biochemical characteristics with prion diseases. In this review, we highlight α-syn's prion-like activities in PD and PD models, describe the idea of a prion-like mechanism contributing to PD pathology, and discuss several key molecules that can modulate the α-syn accumulation and propagation.

Lipoic acid protects dopaminergic neurons in LPS-induced Parkinson's disease model

Parkinson's disease (PD) is a chronic neurodegenerative disease of the central nervous system (CNS), characterized by a loss of dopaminergic neurons, which is thought to be caused by both genetic and environmental factors. Recent findings suggest that neuroinflammation may be a pathogenic factor in the onset and progression of sporadic PD. Here we explore the potential therapeutic effect of lipoic acid (LA) on a lipolysaccharide (LPS)-induced inflammatory PD model. Our results for the first time showed that LA administration improved motor dysfunction, protected dopaminergic neurons loss, and decreased α-synuclein accumulation in the substantia nigra (SN) area of brain. Further, LA inhibited the activation of nuclear factor-κB (NF-κB) and expression of pro-inflammatory molecules in M1 microglia. Taken together, these results suggest that LA may exert a profound neuroprotective effect and is thus a promising anti-neuroinflammatory and anti-oxidative agent for halting the progression of PD. Interventions aimed at either blocking microglia-derived inflammatory mediators or modulating the polarization of microglia may be potentially useful therapies that are worth further investigation.

Characterization of the lipopolysaccharide induced model of Parkinson's disease: Role of oxidative stress and neuroinflammation

INTRODUCTION

Primary pathology underlying Parkinson's disease (PD) is the loss of dopaminergic neurons in the substantia nigra (SN). A variety of genetic and environmental factors underlie this loss of dopaminergic neurons. However, recent studies have highlighted the role of elevated oxidative stress and the pro-inflammatory responses contributing to or exacerbating the nigrostriatal degeneration.

METHODS

With the establishment of neuroinflammation as an important process involved in the PD pathogenesis, in the present study this pathogenic feature was replicated in animals using lipopolysaccharide (LPS) (5 ug/5 ul PBS) infused stereotaxically into the SN of rats.

RESULTS

LPS injected into the SN successfully replicated the pathogenic features of PD in rats as it elicited an inflammatory response via action of microglia. LPS infusion resulted in glial cell activation as depicted from immunohistochemistry (IHC) analysis of GFAP and Iba-1. Also, a significant increase in the mRNA expression of proinflammatory cytokines, i.e. TNF-α and IL-1β, was observed after 7 days of LPS infusion whereas the alterations in the oxidative stress markers, i.e ROS, lipid peroxidation, NO formation, NADPH oxidase activity, glutathione system, SOD and catalase, became highly significant after 14 days of infusion. As a consequence, after 21 days of LPS infusion we observed activation of apoptotic pathway indicated by increased expression of caspases 3 and caspase 9. This was followed by a significant decline in the expression of tyrosine hyroxylase (TH) as revealed by IHC. Further, there was a marked decrease in the level of dopamine and its metabolites enough for the production of behavioral abnormality in rats.

CONCLUSION

Hence, the present study provides extensive characterization of LPS induced model of PD. Study also confirms the co-existence and complex interplay between inflammation and oxidative stress contributing equally to the dopaminergic neuronal degeneration process in PD.

Parkinson's disease and enhanced inflammatory response

Parkinson's disease (PD) is the first and second most prevalent motor and neurodegenerative disease, respectively. The clinical symptoms of PD result from a loss of midbrain dopaminergic (DA) neurons. However, the molecular cause of DA neuron loss remains elusive. Mounting evidence implicates enhanced inflammatory response in the development and progression of PD pathology. This review examines current research connecting PD and inflammatory response.

Heterogeneous induction of microglia M2a phenotype by central administration of interleukin-4

BACKGROUND

Acquisition of the M1 or M2 phenotypes by microglia has been shown to occur during the development of pathological conditions, with M1 activation being widely involved in neurotoxicity in relation with the anatomical localization and the reactivity of subtypes of microglia cells. On the contrary, little is known on the ability of microglia to undergo M2 polarization by interleukin-4 (IL4), the typical M2a polarization signal for peripheral macrophages.

METHODS

Recombinant mouse IL4 was injected in the third cerebral ventricle of mice to induce brain alternative polarization. The mRNA levels of Fizz1, Arg1, and Ym1 genes, known to be up-regulated by IL4 in peripheral macrophages, together with additional polarization markers, were evaluated in the striatum and frontal cortex at different time intervals after central administration of IL4; in parallel, M2a protein expression was evaluated in tissue extracts and at the cellular level.

RESULTS

Our results show that the potency and temporal profile of IL4-mediated M2a gene induction vary depending on the gene analyzed and according to the specific brain area analyzed, with the striatum showing a reduced M2a response compared with the frontal cortex, as further substantiated by assays of polarization protein levels. Of notice, Fizz1 mRNA induction reached 100-fold level, underscoring the potency of this specific IL4 signaling pathway in the brain. In addition, immunochemistry assays demonstrated the localization of the M2 response specifically to microglia cells and, more interestingly, the existence of a subpopulation of microglia cells amenable to undergoing M2a polarization in the healthy mouse brain.

CONCLUSIONS

These results show that the responsiveness of brain macrophages to centrally administered IL4 may vary depending on the gene and brain area analyzed, and that M2a polarization can be ascribed to a subpopulation of IL4-responsive microglia cells. The biochemical pathways that enable microglia to undergo M2a activation represent key aspects for understanding the physiopathology of neuroinflammation and for developing novel therapeutic and diagnostic agents.