Neuroinflammation is a key player in Parkinson's disease and a prime target for therapy

Cellular and molecular mediators of neuroinflammation in the pathogenesis of Parkinson's disease

Neuroinflammation is a host-defense mechanism associated with restoration of normal structure and function of the brain and neutralization of an insult. Increasing neuropathological and biochemical evidence from the brains of individuals with Parkinson's disease (PD) provides strong evidence for activation of neuroinflammatory pathways. Microglia, the resident innate immune cells, may play a major role in the inflammatory process of the diseased brain of patients with PD. Although microglia forms the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly affect neurons by releasing various molecular mediators such as inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β), nitric oxide, prostaglandin E2, and reactive oxygen and nitrogen species. Moreover, recent studies have reported that activated microglia phagocytose not only damaged cell debris but also intact neighboring cells. This phenomenon further supports their active participation in self-enduring neuronal damage cycles. As the relationship between PD and neuroinflammation is being studied, there is a realization that both cellular and molecular mediators are most likely assisting pathological processes leading to disease progression. Here, we discuss mediators of neuroinflammation, which are known activators released from damaged parenchyma of the brain and result in neuronal degeneration in patients with PD.

NADPH oxidase and aging drive microglial activation, oxidative stress, and dopaminergic neurodegeneration following systemic LPS administration

Parkinson's disease is characterized by a progressive degeneration of substantia nigra (SN) dopaminergic neurons with age. We previously found that a single systemic lipopolysaccharide (LPS, 5 mg/kg, i.p.) injection caused a slow progressive loss of tyrosine hydroxylase immunoreactive (TH+IR) neurons in SN associated with increasing motor dysfunction. In this study, we investigated the role of NADPH oxidase (NOX) in inflammation-mediated SN neurotoxicity. A comparison of control (NOX2(+/+) ) mice with NOX subunit gp91(phox) -deficient (NOX2(-/-) ) mice 10 months after LPS administration (5 mg/kg, i.p.) resulted in a 39% (P < 0.01) loss of TH+IR neurons in NOX2(+/+) mice, whereas NOX2(-/-) mice did not show a significant decrease. Microglia (Iba1+IR) showed morphological activation in NOX2(+/+) mice, but not in NOX2(-/-) mice at 1 hr. Treatment of NOX2(+/+) mice with LPS resulted in a 12-fold increase in NOX2 mRNA in midbrain and 5.5-6.5-fold increases in NOX2 protein (+IR) in SN compared with the saline controls. Brain reactive oxygen species (ROS), determined using diphenyliodonium histochemistry, was increased by LPS in SN between 1 hr and 20 months. Diphenyliodonium (DPI), an NOX inhibitor, blocked LPS-induced activation of microglia and production of ROS, TNFα, IL-1β, and MCP-1. Although LPS increased microglial activation and ROS at all ages studied, saline control NOX2(+/+) mice showed age-related increases in microglial activation, NOX, and ROS levels at 12 and 22 months of age. Together, these results suggest that NOX contributes to persistent microglial activation, ROS production, and dopaminergic neurodegeneration that persist and continue to increase with age.

Effects of Hominis placenta on LPS-induced cell toxicity in BV2 microglial cells

ETHNOPHARMACOLOGICAL RELEVANCE

Hominis placenta (HP) dried placenta extracted from pregnant women after delivery has been widely used to treat chronic inflammatory diseases. HP has been reported to be effective to alleviate the arthritic symptoms by modulating the expression of inflammatory factors in adjuvant-induced arthritis rats. However, the mechanism of action of HP is unknown. Neuroinflammation has been implicated in the pathogenesis of several neurodegenerative disease, including Alzheimer's disease (AD), Parkinson's disease (PD) and amyotropic lateral sclerosis (ALS). Activated microglia produce large amounts of toxic soluble factors, which can be responsible for the neurodegenerative disease. Chronic microglial activation leads to neuroinflammation, which contributes to neuronal dysfunction, injury and loss in these diseases. Lipopolysaccharide (LPS) is widely used for neuroinflammation caused by microglial activation of immune cells in the central nervous system (CNS) and subsequent release of inflammatory or neurotoxic factors. In the present study, we investigated the effects and signaling pathway of HP in the LPS induced BV2 microglial cells.

MATERIALS AND METHOD

BV2 microglial cells were pretreated with 50 μM HP for 2h prior to 2 μg/ml LPS for 15 min. Cell viability was determined by MTT assay. The level of protein expression was analyzed by western blot. Immunofluorescence was performed with an anti-COX2 antibody in BV2 cells.

RESULTS

HP decreased LPS-induced microglial cell death by 24% and inhibited LPS-induced activation of c-Jun N-terminal kinase (JNK) by 23% and p42/44MAP kinase (ERK) by 34% treatment of LPS. In addition, HP attenuated LPS-induced pro-inflammatory proteins such as iNOS and COX2 in microglial cells 34% and 28% respectively.

CONCLUSIONS

Our data shows that HP has a protective role against LPS stimulation through inhibition of MAPK signaling and suppression of inflammation caused by neurotoxin including LPS. These findings suggest that HP could be a potential therapeutic agent of neurodegenerative diseases which accompanied with microglial activation.

Alterations in TH- and ChAT-immunoreactive neurons in the DMV and gastric dysmotility in an LPS-induced PD rat model

To study movement disorder in Parkinson's disease (PD), an animal model of PD can be created by injecting lipopolysaccharide (LPS) into the substantia nigra of rats. In addition to body movement disorders, patients with PD often experience gastrointestinal (GI) dysfunction, such as gastroparesis. However, the underlying mechanism of these disorders remains unclear. The dorsal motor nucleus of vagus (DMV) is a well-known visceral nucleus that regulates GI function. The present study investigated alterations in DMV neurons and gastric motility in rats with LPS-induced PD (LPS-PD rats). Gastric motility was recorded using a strain gauge force transducer in vivo. The distributions of tyrosine hydroxylase (TH)- and choline acetyltransferase (ChAT)-positive neurons in the DMV were determined using immunofluorescence and confocal laser microscopy. Our results indicated that in LPS-PD rats, the number of neurons in the substantia nigra, including neurons with TH immunoreactivity, was markedly reduced, although glial cell proliferation was clearly observed. However, enhanced TH immunoreactivity and decreased ChAT immunoreactivity were found in the DMV. Furthermore, weakened gastric motility was recorded in anesthetized LPS-PD rats. In conclusion, rats with LPS-induced PD exhibited gastric dysmotility with an alteration in DMV neurons. This PD model may be used to study autonomic nervous system disorders that are often observed in patients with early-stage PD.

Neuroprotective and behavioural assessments of an imidazolium compound (DBZIM) in a rat model of Parkinson's disease induced by 6-OHDA

The neuroprotective effect of DBZIM, a novel imidazolium compound, has previously been documented to slow down neurodegeneration in a mouse model of Parkinson's disease. In this study, we conducted behavioural studies and further investigated the neuroprotection in a rat Parkinsonian model induced by 6-hydroxydopamine (6-OHDA). DBZIM was found to significantly reduce the 6-OHDA-induced asymmetrical rotation and preferential usage of contralateral forelimbs. Furthermore, the degeneration of tyrosine hydroxylase immunopositive (TH+) dopaminergic neurones in the substantia nigra par compacta (SNc) was illustrated by immunohistochemistry. The significant loss of TH+ neurones by 6-OHDA administration was ameliorated by three different doses of DBZIM treatment in a bell-shape manner. Such neuroprotection was also observed in the 6-OHDA-lesioned striata. High-performance liquid chromatography (HPLC) analysis of the striatal tissues revealed that DBZIM beneficially maintained the dopamine level by slowing down its metabolism. In addition, DBZIM attenuated the activation of astrocytes and microglia. This suggests that anti-inflammation may be an additional mechanism underlying the DBZIM-mediated neuroprotection. These findings warrant further investigation of DBZIM as a promising and potent agent for the future treatment of Parkinson's disease.

Alpha-synuclein induces lysosomal rupture and cathepsin dependent reactive oxygen species following endocytosis

α-synuclein dysregulation is a critical aspect of Parkinson's disease pathology. Recent studies have observed that α-synuclein aggregates are cytotoxic to cells in culture and that this toxicity can be spread between cells. However, the molecular mechanisms governing this cytotoxicity and spread are poorly characterized. Recent studies of viruses and bacteria, which achieve their cytoplasmic entry by rupturing intracellular vesicles, have utilized the redistribution of galectin proteins as a tool to measure vesicle rupture by these organisms. Using this approach, we demonstrate that α-synuclein aggregates can induce the rupture of lysosomes following their endocytosis in neuronal cell lines. This rupture can be induced by the addition of α-synuclein aggregates directly into cells as well as by cell-to-cell transfer of α-synuclein. We also observe that lysosomal rupture by α-synuclein induces a cathepsin B dependent increase in reactive oxygen species (ROS) in target cells. Finally, we observe that α-synuclein aggregates can induce inflammasome activation in THP-1 cells. Lysosomal rupture is known to induce mitochondrial dysfunction and inflammation, both of which are well established aspects of Parkinson's disease, thus connecting these aspects of Parkinson's disease to the propagation of α-synuclein pathology in cells.

Head injury and risk of Parkinson disease: a systematic review and meta-analysis

Head trauma has been implicated in the etiopathogenesis of Parkinson's disease (PD). We performed a meta-analysis to investigate the association between head trauma and the risk of developing PD. We included observational studies if they (1) clearly defined PD, (2) defined head trauma leading to concussion, and (3) presented odds ratios (ORs) and 95% confidence intervals (CIs) or provided data to compute these statistics. Random effect model was used to estimate the pooled, adjusted OR. Heterogeneity between studies was evaluated with the Q test and the I(2) statistic. We conducted a sensitivity analysis to assess the influence of each study and repeated the analysis by excluding the studies with the largest weights. We used funnel plot to assess the presence of publication bias. After reviewing more than 636 article titles, 34 articles were selected for full review. In total, 22 studies (19 case-control studies, 2 nested case-control studies, and 1 cohort study) were included in the meta-analysis. The pooled OR for the association of PD and head trauma was 1.57 (95% CI, 1.35-1.83). The results of our meta-analysis indicate that a history of head trauma that results in concussion is associated with a higher risk of developing PD. © 2013 Movement Disorder Society.

Inflammatory cells and cytokines in the olfactory bulb of a rat model of neuroinflammation; insights into neurodegeneration?

This study examined inflammatory cell and cytokine production in brain tissue from a lipopolysaccharide (LPS)-treated rat model that mimics many of the neuropathologic changes associated with neurodegenerative diseases We also monitored the appearance of a glial cell line-derived neurotrophic factor (GDNF) and circulating nitric oxide (NO) levels, as well as an immune system-associated cells in a selected area of the brain, the olfactory lobe. The studies were based on the hypothesis that LPS treatment stimulates temporal changes within the brain and that these responses include immune cell recruitment, increased tissue levels of immune modulating cytokines and NO, as well as greater glial cell activation resulting in increased production of GDNF. As previously reported by other investigators, our animal model of systemic LPS treatment leads to an increase in the concentrations of circulating cytokines, including TNF-α, IL-Iβ, and IL-6, with a maximum response 6 h post LPS administration. Concomitant with cytokine elevations, circulating NO levels were elevated for several hours post LPS administration. The brain content of the GDNF was also elevated over a similar time frame. Lymphocytes, neutrophils, macrophages, plasma cells, and cytokines were all seen in various areas of LPS-treated brains, often around blood vessels associated with the meninges, with these localizations possibly indicating involvement of both the blood-brain and blood-cerebral spinal fluid barriers in these inflammatory episodes. Our results suggest an involvement of both the peripheral and the central nervous system immune components in response to inflammation and inflammatory episodes. This leads us to propose that inflammation initiates an immune response by activating both microglia and astrocytes and that the presence of continuing and increasing proinflammatory mechanisms results in a situation, where cellular protective mechanisms are overcome and the more susceptible cells enter into cell death pathways, initiating a train of events that is a major part of neurodegeneration.

The role of glia in α-synucleinopathies

α-Synuclein (AS)-positive inclusions are the pathological hallmark of Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA), all belonging to the category of α-synucleinopathies. α-Synucleinopathies represent progressive neurodegenerative disorders characterised by increasing incidences in the population over the age of 65. The relevance of glial reactivity and dysfunction in α-synucleinopathies is highlighted by numerous experimental evidences. Glial AS inclusion pathology is prominent in oligodendroglia of MSA (glial cytoplasmic inclusions) and is a common finding in astroglial cells of PD and DLB, resulting in specific dysfunctional responses. Involvement of AS-dependent astroglial and microglial activation in neurodegenerative mechanisms, and therefore in disease initiation and progression, has been suggested. The aim of this review is to summarise and discuss the multifaceted responses of glial cells in α-synucleinopathies. The beneficial, as well as detrimental, effects of glial cells on neuronal viability are taken into consideration to draw an integrated picture of glial roles in α-synucleinopathies. Furthermore, an overview on therapeutic approaches outlines the difficulties of translating promising experimental studies into successful clinical trials targeting candidate glial pathomechanisms.

Role of oxidative stress in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder associated with a selective loss of the dopamine(DA)rgic neurons in the substantia nigra pars compacta and the degeneration of projecting nerve fibers in the striatum. Because there is currently no therapy that delays the neurodegenerative process, modification of the disease course by neuroprotective therapy is an important unmet clinical need. Toward this end, understanding cellular mechanisms that render the nigral neurons particularly vulnerable have been a subject of intensive research. Increasing evidence suggests that oxidative stress plays a major role. The metabolism of DA itself contributes to oxidative stress, resulting in modification of intracellular macromolecules whose functions are important for cell survival. Mitochondrial dysfunction and the consequent increase in reactive oxygen species also trigger a sequence of events that leads to cell demise. In addition, activated microglia produce nitric oxide and superoxide during neuroinflammatory responses, and this is aggravated by the molecules released by damaged DAergic neurons such as α-synuclein, neuromelanin and matrix metalloproteinase-3. Ways to reduce oxidative stress therefore can provide a therapeutic strategy. NAD(P)H:quinone reductase (NQO1) and other antioxidant enzymes, whose gene expression are commonly under the regulation of the transcription factor Nrf2, can serve as target proteins utilized toward development of disease-modifying therapy for PD.

Argininosuccinate synthase as a novel biomarker for inflammatory conditions

Argininosuccinate synthase (ASS) plays an important role in regulating metabolic functions in mammals. We previously reported that hepatic ASS is released into circulation at very high concentrations in response to endotoxin and acute liver injury. We propose that ASS may serve as a novel biomarker for various inflammatory conditions. Our data showed that ASS accumulated in serum and urine of septic, obese or tumor mice in a condition-dependent fashion. Moreover, ASS significantly increased in urine within the first week after tumor cell implantation in mice which subsequently develop tumors. These results suggest that ASS is a novel biomarker increased upon diverse inflammatory conditions.

Fucoidan protects against lipopolysaccharide-induced rat neuronal damage and inhibits the production of proinflammatory mediators in primary microglia

BACKGROUND

Fucoidan, a sulfated polysaccharide extracted from brown algae, possesses potent antiinflammatory effects.

AIMS

To examine the effect of fucoidan treatment on inflammation-mediated dopaminergic neuronal damage and its potential mechanisms.

METHODS

Microglial activation and injury of dopaminergic neurons were induced by intranigral injection of lipopolysaccharide (LPS), and the effects of fucoidan treatment on animal behavior, microglial activation and survival ratio of dopaminergic neurons were investigated. We further observed the efficacy of fucoidan on tumor necrosis factor-alpha (TNF-α) and the production of reactive oxygen species (ROS) in LPS-activated primary microglia.

RESULTS

Fucoidan significantly improved the behavioral manifestation, prevented the loss of dopaminergic neurons and inhibited the deleterious activation of microglia in the substantia nigra pars compacta of LPS-treated rats. Further in vitro experiments indicated that the excessive production of TNF-α and ROS in LPS-induced primary microglia were significantly inhibited by fucoidan administration.

CONCLUSION

This is the first study to demonstrate that fucoidan possesses neuroprotective effects on injured dopaminergic neurons in a LPS-induced animal model of Parkinson's disease. The mechanisms underlying these effects may include its potent down-regulation of intracellular ROS and subsequent proinflammatory cytokine release in LPS-activated microglia.

[The Parkinson puzzle]

Parkinson's disease is one of the most frequent progressive degenerative disorders with unknown origin of the nervous system. The commutation of the disease on Guam led to the discovery of a neurotoxin which was also found in other continents. This neurotoxin was identified in the common cyanobacteria (blue-green algae). Early clinical observations suggested some loose correlations with gastric and duodenal ulcer and Parkinson's disease, while recent studies revealed a toxin, almost identical to that found in cyanobacteria in one strain of Helicobacter pylori, which proved to cause Parkinson like symptoms in animals. Therefore, it cannot be ruled out that there is a slowly progressive poisoning in Parkinson's disease. The disease specific alpha-sinuclein inclusions can be found in nerve cells of the intestinal mucosa far before the appearance of clinical symptoms indicating that the disease may start in the intestines. These results are strengthened by the results of Borody's fecal transplants, after which in Parkinson patients showed a symptomatic improvement. Based on these observations the Parkinson puzzle is getting complete. Although these observations are not evidence based, they may indicate a new way for basic clinical research, as well as a new way of thinking for clinicians. These new observations in psycho-neuro-immunology strengthen the fact that immunological factors may also play a critical factor facilitating local cell necrosis which may be influenced easily.

Neonatal systemic exposure to lipopolysaccharide enhances susceptibility of nigrostriatal dopaminergic neurons to rotenone neurotoxicity in later life

Brain inflammation via intracerebral injection with lipopolysaccharide (LPS) in early life has been shown to increase risks for the development of neurodegenerative disorders in adult rats. To determine if neonatal systemic LPS exposure has the same effects on enhancement of adult dopaminergic neuron susceptibility to rotenone neurotoxicity as centrally injected LPS does, LPS (2 μg/g body weight) was administered intraperitoneally into postnatal day 5 (P5) rats and when grown to P70, rats were challenged with rotenone, a commonly used pesticide, through subcutaneous minipump infusion at a dose of 1.25 mg/kg/day for 14 days. Systemically administered LPS can penetrate into the neonatal rat brain and cause acute and chronic brain inflammation, as evidenced by persistent increases in IL-1β levels, cyclooxygenase-2 expression and microglial activation in the substantia nigra (SN) of P70 rats. Neonatal LPS exposure resulted in suppression of tyrosine hydroxylase (TH) expression, but not actual death of dopaminergic neurons in the SN, as indicated by the reduced number of TH+ cells and unchanged total number of neurons (NeuN+) in the SN. Neonatal LPS exposure also caused motor function deficits, which were spontaneously recoverable by P70. A small dose of rotenone at P70 induced loss of dopaminergic neurons, as indicated by reduced numbers of both TH+ and NeuN+ cells in the SN, and Parkinson's disease (PD)-like motor impairment in P98 rats that had experienced neonatal LPS exposure, but not in those without the LPS exposure. These results indicate that although neonatal systemic LPS exposure may not necessarily lead to death of dopaminergic neurons in the SN, such an exposure could cause persistent functional alterations in the dopaminergic system and indirectly predispose the nigrostriatal system in the adult brain to be damaged by environmental toxins at an ordinarily nontoxic or subtoxic dose and develop PD-like pathological features and motor dysfunction.

Targeting estrogen receptor β in microglia and T cells to treat experimental autoimmune encephalomyelitis

A therapeutic goal in the treatment of certain CNS diseases, including multiple sclerosis, amyotrophic lateral sclerosis, and Parkinson disease, is to down-regulate inflammatory pathways. Inflammatory molecules produced by microglia are responsible for removal of damaged neurons, but can cause collateral damage to normal neurons located close to defective neurons. Although estrogen can inactivate microglia and inhibit the recruitment of T cells and macrophages into the CNS, there is controversy regarding which of the two estrogen receptors (ERs), ERα or ERβ, mediates the beneficial effects in microglia. In this study, we found that ERβ, but not ERα, is expressed in microglia. Using the experimental autoimmune encephalomyelitis (EAE) model in SJL/J mice, we evaluated the benefit of an ERβ agonist as a modulator of neuroinflammation. Treatment of EAE mice with LY3201, a selective ERβ agonist provided by Eli Lilly, resulted in marked reduction of activated microglia in the spinal cord. LY3201 down-regulated the nuclear transcription factor NF-κB, as well as the NF-κB-induced gene inducible nitric oxide synthase in microglia and CD3(+) T cells. In addition, LY3201 inhibited T-cell reactivity through regulation of indoleamine-2,3-dioxygenase. In the EAE model, treatment with LY3201 decreased mortality in the first 2 wk after disease onset, and also reduced the severity of symptoms in mice surviving for 4 wk. Our data show that ERβ-selective agonists, by modulating the immune system in both microglia and T cells, offer promise as a useful class of drugs for treating degenerative diseases of the CNS.

Anti-inflammatory mechanism of exogenous C2 ceramide in lipopolysaccharide-stimulated microglia

Ceramide is a major molecule among the sphingolipid metabolites which are produced in the brain and other organs and act as intracellular second messengers. Although a variety of physiological roles of ceramide have been reported in the periphery and central nervous systems, the role of ceramide in microglial activation has not been clearly demonstrated. In the present study, we examined the effects of exogenous cell permeable short chain ceramides on microglial activation in vitro and in vivo. We found that C2, C6, and C8 ceramide and C8 ceramide-1-phosphate inhibited iNOS and proinflammatory cytokines in lipopolysaccharide (LPS)-stimulated BV2 microglial cells and rat primary microglia. In addition, the administration of C2 ceramide suppressed microglial activation in the brains of LPS-exposed mice. By HPLC and LC/MS/MS analyses, we found that C2 ceramide on its own, rather than its modified form (i.e. ceramide-1-phosphate or long chain ceramides), mainly work by penetrating into microglial cells. Further mechanistic studies by using the most effective C2 ceramide among the short chain ceramides tested, revealed that C2 ceramide exerts anti-inflammatory effects via inhibition of the ROS, MAPKs, PI3K/Akt, and Jak/STAT pathways with upregulation of PKA and hemeoxygenase-1 expressions. Interestingly, we found that C2 ceramide inhibits TLR4 signaling by interfering with LPS and TLR4 interactions. Therefore, our data collectively suggests the therapeutic potential of short chain ceramides such as C2 for neuroinflammatory disorders such as Alzheimer's disease and Parkinson's disease.

Anti-inflammatory role of the isoflavone diadzein in lipopolysaccharide-stimulated microglia: implications for Parkinson's disease

Microglial activation and subsequent release of toxic pro-inflammatory factors are believed to play an important role in neuronal cell death associated with Parkinson's disease (PD). Compounds that inhibit microglia activation and suppress pro-inflammatory factor release have been reported to have neuroprotective effects in animal models of PD. In this study, we tested whether diadzein, a natural isoflavone found in soybean, attenuated lipopolysaccharide (LPS)-induced release of inflammatory mediators in BV-2, a murine microglial cell line. Diadzein pretreatment was found to significantly suppress the production of the pro-inflammatory factors nitric oxide and IL-6 as well as their mRNA expression in conjunction with reductions in ROS production, p38 MAPK phosphorylation, and NF-κB activation. Furthermore, transfer of conditioned media (CM) from BV-2 cells pretreated with diadzein resulted in a significantly reduction in dopaminergic neurotoxicity compared with CM from microglia stimulated with LPS alone. Together, our results suggest that diadzein's neuroprotective properties may be due to its ability to dampen induction of microglial activation and the subsequent release of soluble pro-inflammatory factors. This appears to be via inhibition of oxidative induction of the p38 MAP kinase-NFκB pathway, resulting in reduced expression of pro-inflammatory genes and release of their corresponding gene products.

Brain insulin dysregulation: implication for neurological and neuropsychiatric disorders

Arduous efforts have been made in the last three decades to elucidate the role of insulin in the brain. A growing number of evidences show that insulin is involved in several physiological function of the brain such as food intake and weight control, reproduction, learning and memory, neuromodulation and neuroprotection. In addition, it is now clear that insulin and insulin disturbances particularly diabetes mellitus may contribute or in some cases play the main role in development and progression of neurodegenerative and neuropsychiatric disorders. Focusing on the molecular mechanisms, this review summarizes the recent findings on the involvement of insulin dysfunction in neurological disorders like Alzheimer's disease, Parkinson's disease and Huntington's disease and also mental disorders like depression and psychosis sharing features of neuroinflammation and neurodegeneration.

Neonatal lipopolysaccharide exposure induces long-lasting learning impairment, less anxiety-like response and hippocampal injury in adult rats

Infection during early neonatal period has been shown to cause lasting neurological disabilities and is associated with the subsequent impairment in development of learning and memory ability and anxiety-related behavior in adults. We have previously reported that neonatal lipopolysaccharide (LPS) exposure resulted in cognitive deficits in juvenile rats (P21); thus, the goal of the present study was to determine whether neonatal LPS exposure has long-lasting effects in adult rats. After an LPS (1mg/kg) intracerebral (i.c.) injection in postnatal day 5 (P5) Sprague-Dawley female rat pups, neurobehavioral tests were carried out on P21 and P22, P49 and P50 or P70 and P71 and brain injury was examined at 66days after LPS injection (P71). Our data indicate that neonatal LPS exposure resulted in learning deficits in the passive avoidance task, less anxiety-like (anxiolytic-like) responses in the elevated plus-maze task, reductions in the hippocampal volume and the number of neuron-specific nuclear protein (NeuN)+ cells, as well as axonal injury in the CA1 region of the middle dorsal hippocampus in P71 rats. Neonatal LPS exposure also resulted in sustained inflammatory responses in the P71 rat hippocampus, as indicated by an increased number of activated microglia and elevation of interleukin-1β content in the rat hippocampus. This study reveals that neonatal LPS exposure causes persistent injuries to the hippocampus and results in long-lasting learning disabilities, and these effects are related to the chronic inflammation in the rat hippocampus.

Parasite-induced alterations of sensorimotor pathways in gammarids: collateral damage of neuroinflammation?

Some larval helminths alter the behavior of their intermediate hosts in ways that favor the predation of infected hosts, thus enhancing trophic transmission. Gammarids (Crustacea: Amphipoda) offer unique advantages for the study of the proximate factors mediating parasite-induced behavioral changes. Indeed, amphipods infected by distantly related worms (acanthocephalans, cestodes and trematodes) encysted in different microhabitats within their hosts (hemocoel, brain) present comparable, chronic, behavioral pathologies. In order to evaluate the potential connection between behavioral disturbances and immune responses in parasitized gammarids, this Review surveys the literature bearing on sensorimotor pathway dysfunctions in infected hosts, on the involvement of the neuromodulator serotonin in altered responses to environmental stimuli, and on systemic and neural innate immunity in arthropods. Hemocyte concentration and phenoloxidase activity associated with melanotic encapsulation are depressed in acanthocephalan-manipulated gammarids. However, other components of the arsenal deployed by crustaceans against pathogens have not yet been investigated in helminth-infected gammarids. Members of the Toll family of receptors, cytokines such as tumor necrosis factors (TNFs), and the free radical nitric oxide are all implicated in neuroimmune responses in crustaceans. Across animal phyla, these molecules and their neuroinflammatory signaling pathways are touted for their dual beneficial and deleterious properties. Thus, it is argued that neuroinflammation might mediate the biochemical events upstream of the serotonergic dysfunction observed in manipulated gammarids – a parsimonious hypothesis that could explain the common behavioral pathology induced by distantly related parasites, both hemocoelian and cerebral.

Inflammation and white matter degeneration persist for years after a single traumatic brain injury

A single traumatic brain injury is associated with an increased risk of dementia and, in a proportion of patients surviving a year or more from injury, the development of hallmark Alzheimer's disease-like pathologies. However, the pathological processes linking traumatic brain injury and neurodegenerative disease remain poorly understood. Growing evidence supports a role for neuroinflammation in the development of Alzheimer's disease. In contrast, little is known about the neuroinflammatory response to brain injury and, in particular, its temporal dynamics and any potential role in neurodegeneration. Cases of traumatic brain injury with survivals ranging from 10 h to 47 years post injury (n = 52) and age-matched, uninjured control subjects (n = 44) were selected from the Glasgow Traumatic Brain Injury archive. From these, sections of the corpus callosum and adjacent parasaggital cortex were examined for microglial density and morphology, and for indices of white matter pathology and integrity. With survival of ≥3 months from injury, cases with traumatic brain injury frequently displayed extensive, densely packed, reactive microglia (CR3/43- and/or CD68-immunoreactive), a pathology not seen in control subjects or acutely injured cases. Of particular note, these reactive microglia were present in 28% of cases with survival of >1 year and up to 18 years post-trauma. In cases displaying this inflammatory pathology, evidence of ongoing white matter degradation could also be observed. Moreover, there was a 25% reduction in the corpus callosum thickness with survival >1 year post-injury. These data present striking evidence of persistent inflammation and ongoing white matter degeneration for many years after just a single traumatic brain injury in humans. Future studies to determine whether inflammation occurs in response to or, conversely, promotes white matter degeneration will be important. These findings may provide parallels for studying neurodegenerative disease, with traumatic brain injury patients serving as a model for longitudinal investigations, in particular with a view to identifying potential therapeutic interventions.

The role of oxidative stress in Parkinson's disease

Oxidative stress plays an important role in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Disruptions in the physiologic maintenance of the redox potential in neurons interfere with several biological processes, ultimately leading to cell death. Evidence has been developed for oxidative and nitrative damage to key cellular components in the PD substantia nigra. A number of sources and mechanisms for the generation of reactive oxygen species (ROS) are recognized including the metabolism of dopamine itself, mitochondrial dysfunction, iron, neuroinflammatory cells, calcium, and aging. PD causing gene products including DJ-1, PINK1, parkin, alpha-synuclein and LRRK2 also impact in complex ways mitochondrial function leading to exacerbation of ROS generation and susceptibility to oxidative stress. Additionally, cellular homeostatic processes including the ubiquitin-proteasome system and mitophagy are impacted by oxidative stress. It is apparent that the interplay between these various mechanisms contributes to neurodegeneration in PD as a feed forward scenario where primary insults lead to oxidative stress, which damages key cellular pathogenetic proteins that in turn cause more ROS production. Animal models of PD have yielded some insights into the molecular pathways of neuronal degeneration and highlighted previously unknown mechanisms by which oxidative stress contributes to PD. However, therapeutic attempts to target the general state of oxidative stress in clinical trials have failed to demonstrate an impact on disease progression. Recent knowledge gained about the specific mechanisms related to PD gene products that modulate ROS production and the response of neurons to stress may provide targeted new approaches towards neuroprotection.

Acacetin protects dopaminergic cells against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neuroinflammation in vitro and in vivo

Acacetin (5,7-dihydroxy-4'-methoxyflavone), a constituent of flavone naturally present in plants, has anti-cancer and anti-inflammatory activities. Neuroinflammation is thought to be one of the major pathological mechanisms responsible for Parkinson's disease (PD), and has been a primary target in the development of treatment for PD. In the present study, we evaluated the neuroprotective effect of acacetin in PD induced by 1-methyl-4-phenylpyridine (MPP+)/or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and examined the related pathways in vitro and in vivo. In primary mesencephalic culture, acacetin protected dopaminergic (DA) cells and inhibited production of inflammatory factors such as nitric oxide, prostaglandin E2, and tumor necrosis factor-α against MPP+-induced toxicity in a dose-dependent manner. Then, we confirmed the effect of acacetin (10 mg/kg/d for 3 d, per os (p.o.)) in a mouse model of PD induced by MPTP (30 mg/kg/d for 5 d, intraperitoneally (i.p.)). In the behavioral test (pole test), the acacetin-treated mice showed decreased time of turning and locomotor activity, which were longer in MPTP-only treated mice. In addition, the acacetin-treated group inhibited degeneration of DA neurons and depletion of dopamine level induced by MPTP toxicity in the substantia nigra and striatum of the brain. Moreover, the acacetin-treated group inhibited microglia activation, accompanied by production of inducible nitric oxide synthases and cyclooxygenase-2. These results suggest that acacetin can protect DA neurons against the neurotoxicity involved in PD via its anti-inflammatory action.

Modulation of inflammatory cytokines and mitogen-activated protein kinases by acetate in primary astrocytes

Acetate supplementation attenuates neuroglia activation in a rat model of neuroinflammation by a mechanism associated with an increase in brain acetyl-CoA, an alteration in histone acetylation, and reduction of interleukin (IL)-1β expression. We propose that reduced astroglial activation occurs by disrupting astrocyte-derived inflammatory signaling and cytokine release. Using primary astroglial cultures, we found that LPS (0-25 ng/ml, 4 h) increased tumor necrosis factor (TNF-α) and IL-1β in a concentration-dependent manner, which was reduced by treatment with sodium acetate (12 mM). LPS did not alter H3K9 acetylation or IL-6 levels, whereas acetate treatment increased H3K9 acetylation by 2-fold and decreased basal levels of IL-6 by 2-fold. Acetate treatment attenuated the LPS-induced increase in TNF-α mRNA, but did not reverse the mRNA levels of other pro-inflammatory cytokines. By contrast, LPS decreased TGF-β1 and IL-4 protein and TGF-β1 mRNA, all of which was reversed with acetate treatment. Further, we found that acetate treatment completely reversed LPS-induced phosphorylation of MAPK p38 and decreased basal levels of phosphorylated extracellular signal-regulated kinases1/2 (ERK1/2) by 2-fold. Acetate treatment also reversed LPS-elevated NF-κB p65, CCAAT/enhancer-binding protein beta protein levels, and reduced basal levels of phosphorylated NF-κB p65 at serine 536. These results suggest that acetate treatment has a net anti-inflammatory effect in LPS-stimulated astrocytes that is largely associated with a disruption in MAPK and NF-κB signaling.

Protective Roles for Potassium SK/K(Ca)2 Channels in Microglia and Neurons

New concepts on potassium channel function in neuroinflammation suggest that they regulate mechanisms of microglial activation, including intracellular calcium homeostasis, morphological alterations, pro-inflammatory cytokine release, antigen presentation, and phagocytosis. Although little is known about voltage independent potassium channels in microglia, special attention emerges on small (SK/KCNN1-3/K(Ca)2) and intermediate (IK/KCNN4/K(Ca)3.1)-conductance calcium-activated potassium channels as regulators of microglial activation in the field of research on neuroinflammation and neurodegeneration. In particular, recent findings suggested that SK/K(Ca)2 channels, by regulating calcium homeostasis, may elicit a dual mechanism of action with protective properties in neurons and inhibition of inflammatory responses in microglia. Thus, modulating SK/K(Ca)2 channels and calcium signaling may provide novel therapeutic strategies in neurological disorders, where neuronal cell death and inflammatory responses concomitantly contribute to disease progression. Here, we review the particular role of SK/K(Ca)2 channels for [Ca(2+)](i) regulation in microglia and neurons, and we discuss the potential impact for further experimental approaches addressing novel therapeutic strategies in neurological diseases, where neuronal cell death and neuroinflammatory processes are prominent.

Anti-inflammatory properties rather than anti-oxidant capability is the major mechanism of neuroprotection by sodium salicylate in a chronic rotenone model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder manifesting in motor, cognitive and behavioral anomalies. Loss of dopaminergic neurons in the substantia nigra region of the brain is the hallmark feature of PD, which is attributed to oxidative and inflammatory stress besides other diverse factors and hence drugs targeting these pathways hold promise as neuro-therapeutics. The anti-oxidative as well as anti-inflammatory properties of sodium salicylate (SS), suggest its neuroprotective potentials in PD. Since PD is a progressive neurodegenerative disorder, the mechanistic basis for utilizing SS as a neuroprotectant in PD could be better understood in the chronic models. The present study utilizes a rotenone-based model of PD to evaluate the neuro-modulatory efficacy of SS. Subcutaneous injection of rotenone (2mg/kg body weight) was given to male SD rats every day, for a period of 5 weeks, which developed all the essential features of PD in these animals. Simultaneously, another group was injected SS intraperitoneally at the dose of 100mg/kg body weight, in addition to the rotenone. In the animals receiving rotenone+SS, significant improvement was observed in the various characteristic hallmarks of PD such as dopamine and tyrosine hydroxylase levels as well as the motor dysfunction symptoms. It attenuated the reactive oxygen species levels significantly but failed to reduce the levels of protein carbonylation and lipid peroxidation. However, SS effectively abridged the levels of inflammatory mediators like cyclooxygenase-2 (COX-2), nuclear factor kappa B and inducible nitric oxide synthase. Correspondingly, a significant decrease in the levels of pro-inflammatory cytokines interleukin-6, interleukin-1β and tumor necrosis factor-α was also observed following SS co-treatment. Thus, neuroprotective efficacy of SS in this chronic model of PD can be largely attributed to its anti-inflammatory effects rather than its free radical-scavenging properties.

Acetate reduces microglia inflammatory signaling in vitro

Acetate supplementation increases brain acetyl-CoA and histone acetylation and reduces lipopolysaccharide (LPS)-induced neuroglial activation and interleukin (IL)-1β expression in vivo. To determine how acetate imparts these properties, we tested the hypothesis that acetate metabolism reduces inflammatory signaling in microglia. To test this, we measured the effect acetate treatment had on cytokine expression, mitogen-activated protein kinase (MAPK) signaling, histone H3 at lysine 9 acetylation, and alterations of nuclear factor-kappa B (NF-κB) in primary and BV-2 cultured microglia. We found that treatment induced H3K9 hyperacetylation and reversed LPS-induced H3K9 hypoacetylation similar to that found in vivo. LPS also increased IL-1β, IL-6, and tumor necrosis factor-alpha (TNF-α) mRNA and protein, whereas treatment returned the protein to control levels and only partially attenuated IL-6 mRNA. In contrast, treatment increased mRNA levels of transforming growth factor-β1 (TGF-β1) and both IL-4 mRNA and protein. LPS increased p38 MAPK and JNK phosphorylation at 4 and 2-4 h, respectively, whereas treatment reduced p38 MAPK and JNK phosphorylation only at 2 h. In addition, treatment reversed the LPS-induced elevation of NF-κB p65 protein and phosphorylation at serine 468 and induced acetylation at lysine 310. These data suggest that acetate metabolism reduces inflammatory signaling and alters histone and non-histone protein acetylation.

Leukocyte recruitment in the brain in sepsis: involvement of the annexin 1-FPR2/ALX anti-inflammatory system

Unregulated inflammation underlies many diseases, including sepsis. Much interest lies in targeting anti-inflammatory mechanisms to develop new treatments. One such target is the anti-inflammatory protein annexin A1 (AnxA1) and its receptor, FPR2/ALX. Using intravital videomicroscopy, we investigated the role of AnxA1 and FPR2/ALX in a murine model of endotoxin-induced cerebral inflammation [intraperitoneal injection of lipopolysaccharide (LPS)]. An inflammatory response was confirmed by elevations in proinflammatory serum cytokines, increased cerebrovascular permeability, elevation in brain myeloperoxidase, and increased leukocyte rolling and adhesion in cerebral venules of wild-type (WT) mice, which were further exacerbated in AnxA1-null mice. mRNA expression of TLR2, TLR4, MyD-88, and Ly96 was also assessed. The AnxA1-mimetic peptide, AnxA1(Ac2-26) (100 μg/mouse, ∼33 μmol) mitigated LPS-induced leukocyte adhesion in WT and AnxA1-null animals without affecting leukocyte rolling, in comparison to saline control. AnxA1(Ac2-26) effects were attenuated by Boc2 (pan-FPR antagonist, 10 μg/mouse, ∼12 nmol), and by minocycline (2.25 mg/mouse, ∼6.3 nmol). The nonselective Fpr agonists, fMLP (6 μg/mouse, ∼17 nmol) and AnxA1(Ac2-26), and the Fpr2-selective agonist ATLa (5 μg/mouse, ∼11 nmol) were without effect in Fpr2/3(-/-) mice. In summary, our novel results demonstrate that the AnxA1/FPR2 system has an important role in effecting the resolution of cerebral inflammation in sepsis and may, therefore, provide a novel therapeutic target.

Rifampicin and Parkinson's disease

Rifampicin is a macrocyclic antibiotic used extensively for the treatment of Mycobacterium tuberculosis and other mycobacterial infections. Recently, it was discovered that rifampicin exhibits neuroprotective effects. It has been shown to protect PC12 cells against MPP(+)-induced apoptosis and inhibit the expression of α-synuclein multimers. In in vitro studies, rifampicin pretreatment protects PC12 cells against rotenone-induced cell death. Qualitative and quantitative analyses uncover that rifampicin significantly suppresses rotenone-induced apoptosis by ameliorating mitochondrial oxidative stress. It reduces microglial inflammation and improves neuron survival. Our results indicate that rifampicin is cytoprotective under a variety of experimental conditions, and suggest that it may be useful in PD therapeutics. It is the aim of this paper to review the experimental neuroprotection data reported using rifampicin with a focus on the molecular and cellular mechanisms of cytoprotective effect in in vitro models of PD.

Oxidative stress in genetic mouse models of Parkinson's disease

There is extensive evidence in Parkinson's disease of a link between oxidative stress and some of the monogenically inherited Parkinson's disease-associated genes. This paper focuses on the importance of this link and potential impact on neuronal function. Basic mechanisms of oxidative stress, the cellular antioxidant machinery, and the main sources of cellular oxidative stress are reviewed. Moreover, attention is given to the complex interaction between oxidative stress and other prominent pathogenic pathways in Parkinson's disease, such as mitochondrial dysfunction and neuroinflammation. Furthermore, an overview of the existing genetic mouse models of Parkinson's disease is given and the evidence of oxidative stress in these models highlighted. Taken into consideration the importance of ageing and environmental factors as a risk for developing Parkinson's disease, gene-environment interactions in genetically engineered mouse models of Parkinson's disease are also discussed, highlighting the role of oxidative damage in the interplay between genetic makeup, environmental stress, and ageing in Parkinson's disease.

Quercetin and sesamin protect dopaminergic cells from MPP+-induced neuroinflammation in a microglial (N9)-neuronal (PC12) coculture system

A growing body of evidence indicates that the majority of Parkinson's disease (PD) cases are associated with microglia activation with resultant elevation of various inflammatory mediators and neuroinflammation. In this study, we investigated the effects of 2 natural molecules, quercetin and sesamin, on neuroinflammation induced by the Parkinsonian toxin 1-methyl-4-phenylpyridinium (MPP⁺) in a glial-neuronal system. We first established that quercetin and sesamin defend microglial cells against MPP⁺-induced increases in the mRNA or protein levels of 3 pro-inflammatory cytokines (interleukin-6, IL-1β and tumor necrosis factor-alpha), as revealed by real time-quantitative polymerase chain reaction and enzyme-linked immunoabsorbent assay, respectively. Quercetin and sesamin also decrease MPP⁺-induced oxidative stress in microglial cells by reducing inducible nitric oxide synthase protein expression as well as mitochondrial superoxide radicals. We then measured neuronal cell death and apoptosis after MPP⁺ activation of microglia, in a microglial (N9)-neuronal (PC12) coculture system. Our results revealed that quercetin and sesamin rescued neuronal PC12 cells from apoptotic death induced by MPP⁺ activation of microglial cells. Altogether, our data demonstrate that the phytoestrogen quercetin and the lignan sesamin diminish MPP⁺-evoked microglial activation and suggest that both these molecules may be regarded as potent, natural, anti-inflammatory compounds.

Astrocyte-specific IKK2 activation in mice is sufficient to induce neuroinflammation but does not increase susceptibility to MPTP

A key regulator of inflammatory gene expression is the transcription factor NF-κB that is controlled by the IκB proteins. We used a transgenic mouse model expressing a constitutively active IκB-kinase-2 (IKK2-CA) in astrocytes under control of the human glial fibrillary acidic protein promotor (IKK2-mice) to investigate neuroinflammation, proinflammatory cytokine expression, microglial activation and a potential enhanced susceptibility to the neurotoxin MPTP (4×10 mg/kg). Readouts included the determination of cytokines, striatal dopamine (DA), nigral tyrosine hydroxylase (TH) positive neurons, microglial activation and motor activity. IKK2-CA expression in astrocytes conditionally induced by the tet-off system resulted in a widespread neuroinflammation indicated by the increased expression of inflammatory cytokines and the presence of activated microglia and astrogliosis. Additionally, striatal DA concentrations but not nigral TH-positive neurons were reduced in IKK2-mice by 20%. Motor activity of IKK2-mice was not affected. Surprisingly, there was a similar reduction in striatal DA concentrations and the number of nigral TH-positive neurons in IKK2 and control mice after MPTP treatment. In conclusion, although naïve IKK2-mice showed reduced striatal DA concentrations and an increase in inflammatory markers in the brain, a higher susceptibility to MPTP was not observed. This finding argues against a prominent role of astrocyte specific, IKK2-mediated neuroinflammation in MPTP-induced neurodegeneration.

Emerging roles of microglial activation and non-motor symptoms in Parkinson's disease

Recent data has indicated that the traditional view of Parkinson's disease (PD) as an isolated disorder of the nigrostriatal dopaminergic system alone is an oversimplification of its complex symptomatology. Aside from classical motor deficits, various non-motor symptoms including autonomic dysfunction, sensory and cognitive impairments as well as neuropsychiatric alterations and sleep disturbances are common in PD. Some of these non-motor symptoms can even antedate the motor problems. Many of them are associated with extranigral neuropathological changes, such as extensive α-synuclein pathology and also neuroinflammatory responses in specific brain regions, i.e. microglial activation, which has been implicated in several aspects of PD pathogenesis and progression. However, microglia do not represent a uniform population, but comprise a diverse group of cells with brain region-specific phenotypes that can exert beneficial or detrimental effects, depending on the local phenotype and context. Understanding how microglia can be neuroprotective in one brain region, while promoting neurotoxicity in another, will improve our understanding of the role of microglia in neurodegeneration in general, and of their role in PD pathology in particular. Since neuroinflammatory responses are in principle modifiable, such approaches could help to identify new targets or adjunctive therapies for the full spectrum of PD-related symptoms.

Role of prostaglandins in neuroinflammatory and neurodegenerative diseases

Increasing data demonstrates that inflammation participates in the pathophysiology of neurodegenerative diseases. Among the different inflammatory mediators involved, prostaglandins play an important role. The effects induced by prostaglandins might be mediated by activation of their known receptors or by nonclassical mechanisms. In the present paper, we discuss the evidences that link prostaglandins, as well as the enzymes that produce them, to some neurological diseases.

Brain transcriptomic profiling in idiopathic and LRRK2-associated Parkinson's disease

LRRK2 mutations are the most common genetic cause of Parkinson's disease (PD). We performed a whole-genome RNA profiling of locus coeruleus post-mortem tissue, a histopathologically affected brain tissue in PD, from idiopathic PD (IPD) and LRRK2-associated PD patients. The differentially expressed genes found in IPD and LRRK2-associated PD are involved in the gene ontology terms of synaptic transmission and neuron projection. In addition, differentially expressed genes in the IPD group are associated with immune system related pathways. Specifically, the study performed highlights the presence of differential expression of genes located in the chromosome 6p21.3 belonging to the class II HLA. Our findings support the hypothesis of a potential role of neuroinflammation and the involvement of the HLA genetic area in IPD pathogenesis. Future studies are necessary to shed light on the relation of immune system related pathways in the etiopathogenesis of PD.

Inhibition of 26S protease regulatory subunit 7 (MSS1) suppresses neuroinflammation

Recently, researchers have focused on immunosuppression induced by rifampicin. Our previous investigation found that rifampicin was neuroprotective by inhibiting the production of pro-inflammatory mediators, thereby suppressing microglial activation. In this study, using 2-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS), we discovered that 26S protease regulatory subunit 7 (MSS1) was decreased in rifampicin-treated microglia. Western blot analysis verified the downregulation of MSS1 expression by rifampicin. As it is indicated that the modulation of the ubiquitin-26S proteasome system (UPS) with proteasome inhibitors is efficacious for the treatment of neuro-inflammatory disorders, we next hypothesized that silencing MSS1 gene expression might inhibit microglial inflammation. Using RNA interference (RNAi), we showed significant reduction of IkBα degradation and NF-kB activation. The production of lipopolysaccharides-induced pro-inflammatory mediators such as inducible nitric oxide synthase (iNOS), nitric oxide, cyclooxygenase-2, and prostaglandin E₂ were also reduced by MSS1 gene knockdown. Taken together, our findings suggested that rifampicin inhibited microglial inflammation by suppressing MSS1 protein production. Silencing MSS1 gene expression decreased neuroinflammation. We concluded that MSS1 inhibition, in addition to anti-inflammatory rifampicin, might represent a novel mechanism for the treatment of neuroinflammatory disorders.

A possible novel anti-inflammatory mechanism for the pharmacological prolyl hydroxylase inhibitor 3,4-dihydroxybenzoate: implications for use as a therapeutic for Parkinson's disease

Parkinson's disease (PD) is an age-related neurodegenerative disorder characterized in part by the preferential loss of nigrostriatal dopaminergic neurons. Although the precise etiology of PD is unknown, accumulating evidence suggests that PD involves microglial activation that exerts neurotoxic effects through production of proinflammatory cytokines and increased oxidative and nitrosative stress. Thus, controlling microglial activation has been suggested as a therapeutic target for combating PD. Previously we demonstrated that pharmacological inhibition of a class of enzymes known as prolyl hydroxylases via 3,4-dihydroxybenzoate administration protected against MPTP-induced neurotoxicity, however the exact mechanisms involved were not elucidated. Here we show that this may be due to DHB's ability to inhibit microglial activation. DHB significantly attenuated LPS-mediated induction of nitric oxide synthase and pro-inflammatory cytokines in murine BV2 microglial cells in vitro in conjunction with reduced ROS production and activation of NFκB and MAPK pathways possibly due to up-regulation of HO-1 levels. HO-1 inhibition partially abrogates LPS-mediated NFκB activity and subsequent NO induction. In vivo, DHB pre-treatment suppresses microglial activation elicited by MPTP treatment. Our results suggest that DHB's neuroprotective properties could be due to its ability to dampen induction of microglial activation via induction of HO-1.

Artemisinin attenuates lipopolysaccharide-stimulated proinflammatory responses by inhibiting NF-κB pathway in microglia cells

Microglial activation plays an important role in neuroinflammation, which contributes to neuronal damage, and inhibition of microglial activation may have therapeutic benefits that could alleviate the progression of neurodegeneration. Recent studies have indicated that the antimalarial agent artemisinin has the ability to inhibit NF-κB activation. In this study, the inhibitory effects of artemisinin on the production of proinflammatory mediators were investigated in lipopolysaccharide (LPS)-stimulated primary microglia. Our results show that artemisinin significantly inhibited LPS-induced production of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1) and nitric oxide (NO). Artemisinin significantly decreased both the mRNA and the protein levels of these pro-inflammatory cytokines and inducible nitric oxide synthase (iNOS) and increased the protein levels of IκB-α, which forms a cytoplasmic inactive complex with the p65-p50 heterodimeric complex. Artemisinin treatment significantly inhibited basal and LPS-induced migration of BV-2 microglia. Electrophoretic mobility shift assays revealed increased NF-κB binding activity in LPS-stimulated primary microglia, and this increase could be prevented by artemisinin. The inhibitory effects of artemisinin on LPS-stimulated microglia were blocked after IκB-α was silenced with IκB-α siRNA. Our results suggest that artemisinin is able to inhibit neuroinflammation by interfering with NF-κB signaling. The data provide direct evidence of the potential application of artemisinin for the treatment of neuroinflammatory diseases.

Clozapine protects dopaminergic neurons from inflammation-induced damage by inhibiting microglial overactivation

Increasing evidence suggests a possible involvement of neuroinflammation in some psychiatric disorders, and also pharmacological reports indicate that anti-inflammatory effects are associated with therapeutic actions of psychoactive drugs, such as anti-depressants and antipsychotics. The purpose of this study was to explore whether clozapine, a widely used antipsychotic drugs, displays anti-inflammatory and neuroprotective effects. Using primary cortical and mesencephalic neuron-glia cultures, we found that clozapine was protective against inflammation-related neurodegeneration induced by lipopolysaccharide (LPS). Pretreatment of cortical or mesencephalic neuron-glia cultures with clozapine (0.1 or 1 μM) for 24 h attenuated LPS-induced neurotoxicity. Clozapine also protected neurons against 1-methyl-4-phenylpyridinium(+) (MPP(+))-induced neurotoxicity, but only in cultures containing microglia, indicating an indispensable role of microglia in clozapine-afforded neuroprotection. Further observation revealed attenuated LPS-induced microglial activation in primary neuron-glia cultures and in HAPI microglial cell line with clozapine pretreatment. Clozapine ameliorated the production of microglia-derived superoxide and intracellular reactive oxygen species (ROS), as well as the production of nitric oxide and TNF-α following LPS. In addition, the protective effect of clozapine was not observed in neuron-glia cultures from mice lacking functional NADPH oxidase (PHOX), a key enzyme for superoxide production in immune cells. Further mechanistic studies demonstrated that clozapine pretreatment inhibited LPS-induced translocation of cytosolic subunit p47(phox) to the membrane in microglia, which was most likely through inhibiting the phosphoinositide 3-kinase (PI3K) pathway. Taken together, this study demonstrates that clozapine exerts neuroprotective effect via the attenuation of microglia activation through inhibition of PHOX-generated ROS production and suggests potential use of antipsychotic drugs for neuroprotection.

Lipopolysaccharide induces paired immunoglobulin-like receptor B (PirB) expression, synaptic alteration, and learning-memory deficit in rats

Some typical immune proteins are expressed in the nervous system, among which the paired-immunoglobulin-like receptor B (PirB) is a receptor for major histocompatibility complex class I antigen (MHC-I), but may play a physiological role in the brain for neuronal circuitry stability by inhibiting synaptic plasticity. Chronic neuroinflammation is common to many neurodegenerative diseases and is often associated with neuronal/synaptic damage and dysfunction. Here we examined the expression of PirB in the rat brain following intracerebral application of lipopolysaccharide (LPS), which has been shown to induce proinflammatory changes and cognitive deficits in rodents. One month after unilateral intrahippocampal LPS injection (10 μg in 4 μl phosphate-buffered saline, PBS), increased protein levels and immunoreactivity of PirB were detected in the ipsilateral hippocampal formation and cortex of the experimental group relative to vehicle (PBS) control. The increased PirB labeling was localized to astrocytes and neurons. Reduced synaptophysin protein levels and immunoreactivity were also found in the ipsilateral hippocampal formation and cortex in LPS-treated rats relative to controls. Morris water maze tests indicated that hippocampus-dependent spatial learning and memory were impaired in LPS-treated animals. Our findings add new experimental data for an upregulation of immune proteins in neuronal and glial cells in the brain in a model of endotoxin-induced neuroinflammation, synaptic alteration, and cognitive decline. The results suggest that PirB modulation may be involved in the pathological process under neurodegenerative conditions.

Health implications of engineered nanomaterials

With the development of nanotechnology, a growing number of people are expected to be exposed to its products, the engineered nanomaterials (ENMs). Some physico-chemical properties of ENMs, linked to their size in the nanoscale (1-100 nm), make them potentially more reactive, and therefore raise concern about possible adverse effects in humans. In this article, I discuss human diseases which may be predicted after exposure to ENMs, and how their pathogenetic mechanisms may be linked to exposure; in this regard, special emphasis has been given to the triad of oxidative stress/inflammation/genotoxicity and to the interaction of ENMs/proteins in different biological compartments. The analysis of possible adverse effects has been made on an organ-by-organ basis, starting from the skin, respiratory system and gastrointestinal tract. These sites are in fact not only those exposed to the highest amounts of ENMs, but are also the portals of entry to internal organs for possible systemic effects. Although the list and the relevance of possible human disorders linked to ENM exposure are at least as impressive as that of their direct or indirect beneficial effects for human health, we must be clear that ENM-linked diseases belong to the realm of possible risk (i.e. cannot be excluded, but are unlikely), whereas ENMs with proven beneficial effects are on the market. Therefore, the mandatory awareness about possible adverse effects of ENMs should in no way be interpreted as a motivation to disregard the great opportunity represented by nanotechnology.

Contributions of central and systemic inflammation to the pathophysiology of Parkinson's disease

Idiopathic Parkinson's disease (PD) represents a complex interaction between the inherent vulnerability of the nigrostriatal dopaminergic system, a possible genetic predisposition, and exposure to environmental toxins including inflammatory triggers. Evidence now suggests that chronic neuroinflammation is consistently associated with the pathophysiology of PD. Activation of microglia and increased levels of pro-inflammatory mediators such as TNF-α, IL-1β and IL-6, reactive oxygen species and eicosanoids has been reported after post-mortem analysis of the substantia nigra from PD patients and in animal models of PD. It is hypothesised that chronically activated microglia secrete high levels of pro-inflammatory mediators which damage neurons and further activate microglia, resulting in a feed forward cycle promoting further inflammation and neurodegeneration. Moreover, nigrostriatal dopaminergic neurons are more vulnerable to pro-inflammatory and oxidative mediators than other cell types because of their low intracellular glutathione concentration. Systemic inflammation has also been suggested to contribute to neurodegeneration in PD, as lymphocyte infiltration has been observed in brains of PD patients and in animal models of PD, substantiating the current theory of a fundamental role of inflammation in neurodegeneration. We will examine the current evidence in the literature which offers insight into the premise that both central and systemic inflammation may contribute to neurodegeneration in PD. We will discuss the emerging possibility of the use of diagnostic tools such as imaging technologies for PD patients. Finally, we will present the immunomodulatory therapeutic strategies that are now under investigation and in clinical trials as potential neuroprotective drugs for PD.

The role of α-synuclein in neurodegeneration — An update

Genetic, neuropathological and biochemical evidence implicates α-synuclein, a 140 amino acid presynaptic neuronal protein, in the pathogenesis of Parkinson’s disease and other neurodegenerative disorders. The aggregated protein inclusions mainly containing aberrant α-synuclein are widely accepted as morphological hallmarks of α-synucleinopathies, but their composition and location vary between disorders along with neuronal networks affected. α-Synuclein exists physiologically in both soluble and membran-bound states, in unstructured and α-helical conformations, respectively, while posttranslational modifications due to proteostatic deficits are involved in β-pleated aggregation resulting in formation of typical inclusions. The physiological function of α-synuclein and its role linked to neurodegeneration, however, are incompletely understood. Soluble oligomeric, not fully fibrillar α-synuclein is thought to be neurotoxic, main targets might be the synapse, axons and glia. The effects of aberrant α-synuclein include alterations of calcium homeostasis, mitochondrial dysfunction, oxidative and nitric injuries, cytoskeletal effects, and neuroinflammation. Proteasomal dysfunction might be a common mechanism in the pathogenesis of neuronal degeneration in α-synucleinopathies. However, how α-synuclein induces neurodegeneration remains elusive as its physiological function. Genome wide association studies demonstrated the important role for genetic variants of the SNCA gene encoding α-synuclein in the etiology of Parkinson’s disease, possibly through effects on oxidation, mitochondria, autophagy, and lysosomal function. The neuropathology of synucleinopathies and the role of α-synuclein as a potential biomarker are briefly summarized. Although animal models provided new insights into the pathogenesis of Parkinson disease and multiple system atrophy, most of them do not adequately reproduce the cardinal features of these disorders. Emerging evidence, in addition to synergistic interactions of α-synuclein with various pathogenic proteins, suggests that prionlike induction and seeding of α-synuclein could lead to the spread of the pathology and disease progression. Intervention in the early aggregation pathway, aberrant cellular effects, or secretion of α-synuclein might be targets for neuroprotection and disease-modifying therapy.

NOP Receptor Ligands as Potential Agents for Inflammatory and Autoimmune Diseases

Nociceptin/orphanin FQ (N/OFQ) is a seventeen-amino acid peptide that is the endogenous ligand of a G-protein-coupled receptor (NOP). Various immune cells express the precursor protein and secrete N/OFQ as well as display binding sites for this peptide. The functional capacity of NOP receptor was demonstrated in vitro and in vivo studies by the ability of N/OFQ to induce chemotaxis of immune cells, to regulate the expression of cytokines and other inflammatory mediators, and to control cellular and humoral immunity. In this context, N/OFQ could modulate the outcome of some inflammatory diseases, such as sepsis and autoimmune pathologies by mechanisms not clearly elucidated yet. In fact, human body fluid revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's diagnose. Preclinical studies pointed to the blockade of NOP receptor signaling as successful in treating these experimental conditions. Further preclinical and clinical studies are required to investigate the potential of NOP ligands in treating inflammatory diseases.

Neuropathology of sporadic Parkinson's disease: evaluation and changes of concepts

Parkinson's disease (PD), one of the most frequent neurodegenerative disorders, is no longer considered a complex motor disorder characterized by extrapyramidal symptoms, but a progressive multisystem or-more correctly-multiorgan disease with variegated neurological and nonmotor deficiencies. It is morphologically featured not only by the degeneration of the dopaminergic nigrostriatal system, responsible for the core motor deficits, but by multifocal involvement of the central, peripheral and autonomic nervous system and other organs associated with widespread occurrence of Lewy bodies and dystrophic Lewy neurites. This results from deposition of abnormal α-synuclein (αSyn), the major protein marker of PD, and other synucleinopathies. Recent research has improved both the clinical and neuropathological diagnostic criteria of PD; it has further provided insights into the development and staging of αSyn and Lewy pathologies and has been useful in understanding the pathogenesis of PD. However, many challenges remain, for example, the role of Lewy bodies and the neurobiology of axons in the course of neurodegeneration, the relation between αSyn, Lewy pathology, and clinical deficits, as well as the interaction between αSyn and other pathologic proteins. Although genetic and experimental models have contributed to exploring the causes, pathomechanisms, and treatment options of PD, there is still a lack of an optimal animal model, and the etiology of this devastating disease is far from being elucidated.

Achieving stable human stem cell engraftment and survival in the CNS: is the future of regenerative medicine immunodeficient?

There is potential for a variety of stem cell populations to mediate repair in the diseased or injured CNS; in some cases, this theoretical possibility has already transitioned to clinical safety testing. However, careful consideration of preclinical animal models is essential to provide an appropriate assessment of stem cell safety and efficacy, as well as the basic biological mechanisms of stem cell action. This article examines the lessons learned from early tissue, organ and hematopoietic grafting, the early assumptions of the stem cell and CNS fields with regard to immunoprivilege, and the history of success in stem cell transplantation into the CNS. Finally, we discuss strategies in the selection of animal models to maximize the predictive validity of preclinical safety and efficacy studies.

Stress, depression and Parkinson's disease

In this review, we focus on the relationship among Parkinson's disease (PD), stress and depression. Parkinson's disease patients have a high risk of developing depression, and it is possible that stress contributes to the development of both pathologies. Stress dysfunction may have a role in the etiology of preclinical non-motor symptoms of PD (such as depression) and, later in the course of the disease, may worsen motor symptoms. However, relatively few studies have examined stress or depression and the injured nigrostriatal system. This review discusses the effects of stress on neurodegeneration and depression, and their association with the symptoms and progression of PD.

Generation of reactive oxygen species in 1-methyl-4-phenylpyridinium (MPP+) treated dopaminergic neurons occurs as an NADPH oxidase-dependent two-wave cascade

BACKGROUND

Reactive oxygen species (ROS), superoxide and hydrogen peroxide (H2O2), are necessary for appropriate responses to immune challenges. In the brain, excess superoxide production predicts neuronal cell loss, suggesting that Parkinson's disease (PD) with its wholesale death of dopaminergic neurons in substantia nigra pars compacta (nigra) may be a case in point. Although microglial NADPH oxidase-produced superoxide contributes to dopaminergic neuron death in an MPTP mouse model of PD, this is secondary to an initial die off of such neurons, suggesting that the initial MPTP-induced death of neurons may be via activation of NADPH oxidase in neurons themselves, thus providing an early therapeutic target.

METHODS

NADPH oxidase subunits were visualized in adult mouse nigra neurons and in N27 rat dopaminergic cells by immunofluorescence. NADPH oxidase subunits in N27 cell cultures were detected by immunoblots and RT-PCR. Superoxide was measured by flow cytometric detection of H2O2-induced carboxy-H2-DCFDA fluorescence. Cells were treated with MPP+ (MPTP metabolite) following siRNA silencing of the Nox2-stabilizing subunit p22phox, or simultaneously with NADPH oxidase pharmacological inhibitors or with losartan to antagonize angiotensin II type 1 receptor-induced NADPH oxidase activation.

RESULTS

Nigral dopaminergic neurons in situ expressed three subunits necessary for NADPH oxidase activation, and these as well as several other NADPH oxidase subunits and their encoding mRNAs were detected in unstimulated N27 cells. Overnight MPP+ treatment of N27 cells induced Nox2 protein and superoxide generation, which was counteracted by NADPH oxidase inhibitors, by siRNA silencing of p22phox, or losartan. A two-wave ROS cascade was identified: 1) as a first wave, mitochondrial H2O2 production was first noted at three hours of MPP+ treatment; and 2) as a second wave, H2O2 levels were further increased by 24 hours. This second wave was eliminated by pharmacological inhibitors and a blocker of protein synthesis.

CONCLUSIONS

A two-wave cascade of ROS production is active in nigral dopaminergic neurons in response to neurotoxicity-induced superoxide. Our findings allow us to conclude that superoxide generated by NADPH oxidase present in nigral neurons contributes to the loss of such neurons in PD. Losartan suppression of nigral-cell superoxide production suggests that angiotensin receptor blockers have potential as PD preventatives.