Changes in inflammatory processes associated with selective vulnerability following mild impairment of oxidative metabolism

Intestinal dysbiosis causes spatial memory impairment in alcohol-exposed male mice by inducing neuroinflammation

Alcohol abuse damages the brain and triggers cognitive impairment. Intestinal dysbiosis has recently been shown to be involved in psychiatric disorders, which suggests the possibility of intestine-to-brain interactions in the development of alcohol abuse. In this study, chronic intermittent alcohol exposure (CIAE) model was established in C57BL/6 male mice and the spatial memory were detected by Barnes maze (n = 16/group). The fecal microbiota and its metabolites were detected by 16S rDNA sequencing and non-target liquid chromatograph mass spectrometer (LC-MS) (n = 8/group). Effects of alcohol on intestinal barrier and blood-brain barrier (BBB) permeability were detected by Evens blue leakage assay (n = 4/group), and the activation state of microglia and TLR4 expression were conducted by immunofluorescence co-localization (n = 4/group). The morphological changes of microglia were analyzed with Image J Analyze Skeleton software, and the protein levels of TLR4 and inflammatory factors were detected by Western Blot (n = 8/group). Results indicated that alcohol alters the components of fecal microbiota and metabolites, and damages the intestinal barrier and BBB, leading to spatial memory impairment in mice. By giving mice specific prebiotics (n = 16/group), we pointed out that increased endotoxin coming from Gram negative bacteria such as lipopolysaccharides (LPS) cross the BBB to activate microglia and inflammatory pathways in the prefrontal cortical (PFC) and hippocampus (HIP), releasing inflammatory factors and resulting in neuroinflammation. Thus, the fecal microbiota seems to be a potential target in the management of alcoholic brain disease.

Exploring the Therapeutic Potential of Benfotiamine in a Sporadic Alzheimer's-Like Disease Rat Model: Insights into Insulin Signaling and Cognitive function

Alzheimer's disease (AD) is a complex neurodegenerative process, also considered a metabolic condition due to alterations in glucose metabolism and insulin signaling pathways in the brain, which share similarities with diabetes. This study aimed to investigate the therapeutic effects of benfotiamine (BFT), a vitamin B1 analog, in the early stages of the neurodegenerative process in a sporadic model of Alzheimer's-like disease induced by intracerebroventricular injection of streptozotocin (STZ). Supplementation with 150 mg/kg of BFT for 7 days reversed the cognitive impairment in short- and long-term memories caused by STZ in rodents. We attribute these effects to BFT's ability to modulate glucose transporters type 1 and 3 (GLUT1 and GLUT3) in the hippocampus, inhibit GSK3 activity in the hippocampus, and modulate the insulin signaling in the hippocampus and entorhinal cortex, as well as reduce the activation of apoptotic pathways (BAX) in the hippocampus. Therefore, BFT emerges as a promising and accessible intervention in the initial treatment of conditions similar to AD.

Stem Cell Therapy and Thiamine Deficiency-Induced Brain Damage

Wernicke's encephalopathy (WE) is a major central nervous system disorder resulting from thiamine deficiency (TD) in which a number of brain regions can develop serious damage including the thalamus and inferior colliculus. Despite decades of research into the pathophysiology of TD and potential therapeutic interventions, little progress has been made regarding effective treatment following the development of brain lesions and its associated cognitive issues. Recent developments in our understanding of stem cells suggest they are capable of repairing damage and improving function in different maladys. This article puts forward the case for the potential use of stem cell treatment as a therapeutic strategy in WE by first examining the effects of TD on brain functional integrity and its consequences. The second half of the paper will address the future benefits of treating TD with these cells by focusing on their nature and their potential to effectively treat neurodegenerative diseases that share some overlapping pathophysiological features with TD. At the same time, some of the obstacles these cells will have to overcome in order to become a viable therapeutic strategy for treating this potentially life-threatening illness in humans will be highlighted.

The importance of thiamine (vitamin B1) in humans

Thiamine (thiamin, B1) is a vitamin necessary for proper cell function. It exists in a free form as a thiamine, or as a mono-, di- or triphosphate. Thiamine plays a special role in the body as a coenzyme necessary for the metabolism of carbohydrates, fats and proteins. In addition, it participates in the cellular respiration and oxidation of fatty acids: in malnourished people, high doses of glucose result in acute thiamine deficiency. It also participates in energy production in the mitochondria and protein synthesis. In addition, it is also needed to ensure the proper functioning of the central and peripheral nervous system, where it is involved in neurotransmitter synthesis. Its deficiency leads to mitochondrial dysfunction, lactate and pyruvate accumulation, and consequently to focal thalamic degeneration, manifested as Wernicke's encephalopathy or Wernicke-Korsakoff syndrome. It can also lead to severe or even fatal neurologic and cardiovascular complications, including heart failure, neuropathy leading to ataxia and paralysis, confusion, or delirium. The most common risk factor for thiamine deficiency is alcohol abuse. This paper presents current knowledge of the biological functions of thiamine, its antioxidant properties, and the effects of its deficiency in the body.

The significance of glycolysis index and its correlations with immune infiltrates in Alzheimer’s disease

Alzheimer’s disease (AD) is a common neurodegenerative disorder without an effective treatment, and results in an increasingly serious health problem. However, its pathogenesis is complex and poorly understood. Nonetheless, the exact role of dysfunctional glucose metabolism in AD pathogenesis remains unclear. We screened 28 core glycolysis-related genes and introduced a novel metric, the glycolysis index, to estimate the activation of glycolysis. The glycolysis index was significantly lower in the AD group in four different brain regions (frontal cortex, FC; temporal cortex, TC; hippocampus, HP; and entorhinal cortex, EC) than that in the control group. Combined with differential expression and over-representation analyses, we determined the clinical and pathological relevance of glycolysis in AD. Subsequently, we investigated the role of glycolysis in the AD brain microenvironment. We developed a glycolysis-brain cell marker connection network, which revealed a close relationship between glycolysis and seven brain cell types, most of which presented abundant variants in AD. Using immunohistochemistry, we detected greater infiltrated microglia and higher expression of glycolysis-related microglia markers in the APP/PS1 AD model than that in the control group, consistent with our bioinformatic analysis results. Furthermore, the excellent predictive value of the glycolysis index has been verified in different populations. Overall, our present findings revealed the clinical and biological significance of glycolysis and the brain microenvironment in AD.

Single domain antibodies targeting pathological tau protein: Influence of four IgG subclasses on efficacy and toxicity

BACKGROUND

Eleven tau immunoglobulin G (IgG) antibodies have entered clinical trials to treat tauopathies, including Alzheimer's disease, but it is unclear which IgG subclass/subtype has the ideal efficacy and safety profile. Only two subtypes, with or without effector function, have been examined in the clinic and not for the same tau antibody. The few preclinical studies on this topic have only compared two subtypes of one antibody each and have yielded conflicting results.

METHODS

We selected two single domain antibodies (sdAbs) derived from a llama immunized with tau proteins and utilized them to generate an array of Fc-(sdAb)2 subclasses containing identical tau binding domains but differing Fc region. Unmodified sdAbs and their IgG subclasses were tested for efficacy in primary cultures and in vivo microdialysis using JNPL3 tauopathy mice.

FINDINGS

Unmodified sdAbs were non-toxic, blocked tau toxicity and promoted tau clearance. However, the efficacy/safety profile of their Fc-(sdAb)2 subclasses varied greatly within and between sdAbs. For one of them, all its subtypes were non-toxic, only those with effector function cleared tau, and were more effective in vivo than unmodified sdAb. For the other sdAb, all its subtypes were toxic in tauopathy cultures but not in wild-type cells, suggesting that bivalent binding of its tau epitope stabilizes a toxic conformation of tau, with major implications for tau pathogenesis. Likewise, its subclasses were less effective than the unmodified sdAb in clearing tau in vivo.

INTERPRETATION

These findings indicate that tau antibodies with effector function are safe and better at clearing pathological tau than effectorless antibodies, Furthermore, tau antibodies can provide a valuable insight into tau pathogenesis, and some may aggravate it.

FUNDING

Funding for these studies was provided by the National Institute of Health (R01 AG032611, R01 NS077239, RF1 NS120488, R21 AG 069475, R21 AG 058282, T32AG052909), and the NYU Alzheimer's Disease Center Pilot Grant Program (via P30 AG008051).

Midline Thalamic Damage Associated with Alcohol-Use Disorders: Disruption of Distinct Thalamocortical Pathways and Function

The thalamus, a significant part of the diencephalon, is a symmetrical and bilateral central brain structure. The thalamus is subdivided into three major groups of nuclei based on their function: sensorimotor nuclei (or principal/relay nuclei), limbic nuclei and nuclei bridging these two domains. Anatomically, nuclei within the thalamus are described by their location, such as anterior, medial, lateral, ventral, and posterior. In this review, we summarize the role of medial and midline thalamus in cognition, ranging from learning and memory to flexible adaptation. We focus on the discoveries in animal models of alcohol-related brain damage, which identify the loss of neurons in the medial and midline thalamus as drivers of cognitive dysfunction associated with alcohol use disorders. Models of developmental ethanol exposure and models of adult alcohol-related brain damage and are compared and contrasted, and it was revealed that there are similar (anterior thalamus) and different (intralaminar [adult exposure] versus ventral midline [developmental exposure]) thalamic pathology, as well as disruptions of thalamo-hippocampal and thalamo-cortical circuits. The final part of the review summarizes approaches to recover alcohol-related brain damage and cognitive and behavioral outcomes. These approaches include pharmacological, nutritional and behavioral interventions that demonstrated the potential to mitigate alcohol-related damage. In summary, the medial/midline thalamus is a significant contributor to cognition function, which is also sensitive to alcohol-related brain damage across the life span, and plays a role in alcohol-related cognitive dysfunction.

Supplemental thiamine as a practical, potential way to prevent Alzheimer's disease from commencing

It is better to attempt stopping Alzheimer's disease (AD) before it starts than trying to cure it after it has developed. A cerebral scan showing deposition of either amyloid or tau identifies those elderly persons whose cognition is currently normal but who are at risk of subsequent cognitive loss that may develop into AD. Synaptic hypometabolism is usually present in such at-risk persons. Although inadequate adenosine triphosphate (ATP) may cause synaptic hypometabolism, that may not be the entire cause because, in fact, measurements in some of the at-risk persons have shown normal ATP levels. Thiamine deficiency is often seen in elderly, ambulatory persons in whom thiamine levels correlate with Mini-Mental State Examination scores. Thiamine deficiency has many consequences including hypometabolism, mitochondrial depression, oxidative stress, lactic acidosis and cerebral acidosis, amyloid deposition, tau deposition, synaptic dysfunction and abnormal neuro-transmission, astrocyte function, and blood brain barrier integrity, all of which are features of AD. Although the clinical benefits of administering supplementary thiamine to patients with AD or mild cognitive impairment have been mixed, it is more likely to succeed at preventing the onset of cognitive loss if administered at an earlier time, when the number of aberrant biochemical pathways is far fewer. Providing a thiamine supplement to elderly persons who still have normal cognition but who have deposition of either amyloid or tau, may prevent subsequent cognitive loss and eventual dementia. A clinical trial is needed to validate that possibility.

Neuroprotective Effects of Thiamine and Precursors with Higher Bioavailability: Focus on Benfotiamine and Dibenzoylthiamine

Thiamine (vitamin B1) is essential for brain function because of the coenzyme role of thiamine diphosphate (ThDP) in glucose and energy metabolism. In order to compensate thiamine deficiency, several thiamine precursors with higher bioavailability were developed since the 1950s. Among these, the thioester benfotiamine (BFT) has been extensively studied and has beneficial effects both in rodent models of neurodegeneration and in human clinical studies. BFT has antioxidant and anti-inflammatory properties that seem to be mediated by a mechanism independent of the coenzyme function of ThDP. BFT has no adverse effects and improves cognitive outcome in patients with mild Alzheimer’s disease (AD). Recent in vitro studies show that another thiamine thioester, dibenzoylthiamine (DBT) is even more efficient that BFT, especially with respect to its anti-inflammatory potency. Thiamine thioesters have pleiotropic properties linked to an increase in circulating thiamine concentrations and possibly in hitherto unidentified metabolites in particular open thiazole ring derivatives. The identification of the active neuroprotective derivatives and the clarification of their mechanism of action open extremely promising perspectives in the field of neurodegenerative, neurodevelopmental and psychiatric conditions.

Preliminary Evidence for a Relationship between Elevated Plasma TNFα and Smaller Subcortical White Matter Volume in HCV Infection Irrespective of HIV or AUD Comorbidity

Classical inflammation in response to bacterial, parasitic, or viral infections such as HIV includes local recruitment of neutrophils and macrophages and the production of proinflammatory cytokines and chemokines. Proposed biomarkers of organ integrity in Alcohol Use Disorders (AUD) include elevations in peripheral plasma levels of proinflammatory proteins. In testing this proposal, previous work included a group of human immunodeficiency virus (HIV)-infected individuals as positive controls and identified elevations in the soluble proteins TNFα and IP10; these cytokines were only elevated in AUD individuals seropositive for hepatitis C infection (HCV). The current observational, cross-sectional study evaluated whether higher levels of these proinflammatory cytokines would be associated with compromised brain integrity. Soluble protein levels were quantified in 86 healthy controls, 132 individuals with AUD, 54 individuals seropositive for HIV, and 49 individuals with AUD and HIV. Among the patient groups, HCV was present in 24 of the individuals with AUD, 13 individuals with HIV, and 20 of the individuals in the comorbid AUD and HIV group. Soluble protein levels were correlated to regional brain volumes as quantified with structural magnetic resonance imaging (MRI). In addition to higher levels of TNFα and IP10 in the 2 HIV groups and the HCV-seropositive AUD group, this study identified lower levels of IL1β in the 3 patient groups relative to the control group. Only TNFα, however, showed a relationship with brain integrity: in HCV or HIV infection, higher peripheral levels of TNFα correlated with smaller subcortical white matter volume. These preliminary results highlight the privileged status of TNFα on brain integrity in the context of infection.

Region-selective permeability of the blood-brain barrier to α-aminoisobutyric acid during thiamine deficiency and following its reversal

Thiamine deficiency (TD) results in focal lesions in several regions of the rat brain including the thalamus and inferior colliculus. Since alterations in blood-brain barrier (BBB) integrity may play a role in this damage, we have examined the influence of TD on the unidirectional blood-to-brain transfer constant (K_i) of the low molecular weight species α-aminoisobutyric acid (AIB) in vulnerable and non-vulnerable brain regions at different stages during progression of the disorder, and following its reversal with thiamine. Analysis of the regional distribution of K_i values showed early (day 10) increased transfer of [¹⁴C]-AIB across the BBB in the vulnerable medial thalamus as well as the non-vulnerable caudate and hippocampus. At the acute symptomatic stage (day 14), more widespread BBB permeability changes were detected in most areas including the lateral thalamus, inferior colliculus, and non-vulnerable cerebellum and pons. Twenty-four hours following thiamine replenishment, a heterogeneous pattern of increased BBB permeability was observed in which many structures maintained increased uptake of [¹⁴C]-AIB. No increase in the [³H]-dextran space, a marker of intravascular volume, was detected in brain regions during the progress of TD, suggesting that BBB permeability to this large tracer was unaffected. These results indicate that BBB opening i) occurs early during TD, ii) is not restricted to vulnerable areas of the brain, iii) is progressive, iv) persists for at least 24 h following treatment with thiamine, and v) is likely selective in nature, depending on the molecular species being transported.

Dynamics of Internalization and Intracellular Interaction of Tau Antibodies and Human Pathological Tau Protein in a Human Neuron-Like Model

We and others have shown in various in vivo, ex vivo and cell culture models that several tau antibodies interact with pathological tau within neurons. To further clarify this interaction in a dynamic human model, we differentiated SH-SY5Y cells with retinoic acid and BDNF to create a neuron-like model. Therein, tau antibodies were primarily taken up by receptor-mediated endocytosis, and prevented toxicity of human brain-derived paired helical filament-enriched tau (PHF). Subsequently, we monitored in real-time the interaction of antibodies and PHF within endocytic cellular compartments. Cells were pre-treated with fluorescently-tagged PHF and then incubated with tau antibodies, 4E6, 6B2, or non-specific isotype control IgG1 labeled with a pH sensitive dye. The uptake and binding of the efficacious antibody, 4E6, to PHF occurred mainly within the soma, whereas the ineffective antibody, 6B2, and ineffective control IgG1, were visualized via the processes and showed limited colocalization with PHF within this period. In summary, we have developed a neuron-like model that clarifies the early intracellular dynamics of the interaction of tau antibodies with pathological tau, and identifies features associated with efficacy. Since the model is entirely human, it is suitable to verify the therapeutic potential of humanized antibodies prior to extensive clinical trials.

Anti-inflammatory and antioxidative effects of thiamin supplements in patients with gestational diabetes mellitus

OBJECTIVE

The aim of this study was to evaluate the effects of thiamin supplementation on biomarkers of inflammation and oxidative stress in patients with gestational diabetes mellitus (GDM).

METHODS

This randomized, double-blind, placebo-controlled trial was conducted among 60 patients with GDM. Patients were randomly allocated into two groups to receive either 100 mg/day thiamin supplements (n = 30) or placebo (n = 30) for 6 weeks.

RESULTS

Thiamin supplementation significantly decreased serum high-sensitivity C-reactive protein (hs-CRP) (β - 0.98 mg/L; 95% CI, -1.54, -0.42; p = .001) and plasma malondialdehyde (MDA) levels (β - 0.86 µmol/L; 95% CI, -1.15, -0.57; p < .001) when compared with the placebo. In addition, thiamin supplementation downregulated gene expression of tumor necrosis factor-alpha (TNF-α) (p = .002) in peripheral blood mononuclear cells of patients with GDM. Thiamin supplementation did not affect other biomarkers of inflammation and oxidative stress.

CONCLUSION

Overall, thiamin supplementation for 6 weeks to patients with GDM significantly reduced hs-CRP and MDA levels, and gene expression of TNF-α, but did not affect other biomarkers of inflammation and oxidative stress.

CLINICAL TRIAL REGISTRATION NUMBER

Clinical Trials.govIdentifier no. http://www.irct.ir: IRCT20170513033941N58.

Enterohemorrhagic Escherichia coli infection inhibits colonic thiamin pyrophosphate uptake via transcriptional mechanism

Colonocytes possess a specific carrier-mediated uptake process for the microbiota-generated thiamin (vitamin B1) pyrophosphate (TPP) that involves the TPP transporter (TPPT; product of the SLC44A4 gene). Little is known about the effect of exogenous factors (including enteric pathogens) on the colonic TPP uptake process. Our aim in this study was to investigate the effect of Enterohemorrhagic Escherichia coli (EHEC) infection on colonic uptake of TPP. We used human-derived colonic epithelial NCM460 cells and mice in our investigation. The results showed that infecting NCM460 cells with live EHEC (but not with heat-killed EHEC, EHEC culture supernatant, or with non-pathogenic E. Coli) to lead to a significant inhibition in carrier-mediated TPP uptake, as well as in level of expression of the TPPT protein and mRNA. Similarly, infecting mice with EHEC led to a significant inhibition in colonic TPP uptake and in level of expression of TPPT protein and mRNA. The inhibitory effect of EHEC on TPP uptake by NCM460 was found to be associated with reduction in the rate of transcription of the SLC44A4 gene as indicated by the significant reduction in the activity of the SLC44A4 promoter transfected into EHEC infected cells. The latter was also associated with a marked reduction in the level of expression of the transcription factors CREB-1 and ELF3, which are known to drive the activity of the SLC44A4 promoter. Finally, blocking the ERK1/2 and NF-kB signaling pathways in NCM460 cells significantly reversed the level of EHEC inhibition in TPP uptake and TPPT expression. Collectively, these findings show, for the first time, that EHEC infection significantly inhibit colonic uptake of TPP, and that this effect appears to be exerted at the level of SLC44A4 transcription and involves the ERK1/2 and NF-kB signaling pathways.

A Pivotal Role for Thiamine Deficiency in the Expression of Neuroinflammation Markers in Models of Alcohol-Related Brain Damage

BACKGROUND

Alcohol-related brain damage (ARBD) is associated with neurotoxic effects of heavy alcohol use and nutritional deficiency, in particular thiamine deficiency (TD), both of which induce inflammatory responses in brain. Although neuroinflammation is a critical factor in the induction of ARBD, few studies have addressed the specific contribution(s) of ethanol (EtOH) versus TD.

METHODS

Adult rats were randomly divided into 6 conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH for 6 months; CET with injections of thiamine (CET + T); severe pyrithiamine-induced TD (PTD); moderate PTD; moderate PTD during CET; and pair-fed controls. After the treatments, the rats were split into 3 recovery phase time points: the last day of treatment (time point 1), acute recovery (time point 2: 24 hours posttreatment), and delayed recovery (time point 3: 3 weeks posttreatment). At these time points, vulnerable brain regions (thalamus, hippocampus, frontal cortex) were collected and changes in neuroimmune markers were assessed using a combination of reverse transcription polymerase chain reaction and protein analysis.

RESULTS

CET led to minor fluctuations in neuroimmune genes, regardless of the structure being examined. In contrast, PTD treatment led to a profound increase in neuroimmune genes and proteins within the thalamus. Cytokine changes in the thalamus ranged in magnitude from moderate (3-fold and 4-fold increase in interleukin-1β [IL-1β] and IκBα) to severe (8-fold and 26-fold increase in tumor necrosis factor-α and IL-6, respectively). Though a similar pattern was observed in the hippocampus and frontal cortex, overall fold increases were moderate relative to the thalamus. Importantly, neuroimmune gene induction varied significantly as a function of severity of TD, and most genes displayed a gradual recovery across time.

CONCLUSIONS

These data suggest an overt brain inflammatory response by TD and a subtle change by CET alone. Also, the prominent role of TD in the immune-related signaling pathways leads to unique regional and temporal profiles of induction of neuroimmune genes.

Melatonin Administration Methods for Research in Mammals and Birds

Endocrine research in animals often entails exogenous hormone administration. Special issues arise when developing administration protocols for hormones with circadian and seasonal periodicity. This article reviews various methods for the exogenous administration of hormones with such periodicities by focusing on melatonin. We discuss that methodological variations across studies can affect experimental results. Melatonin administration techniques used in vertebrates includes infusion pumps, beeswax pellets, oral administration, injections, SILASTIC capsules, osmotic pumps, transdermal delivery, beads, and sponges.

Molecular mechanisms involved in the adaptive regulation of the colonic thiamin pyrophosphate uptake process

A considerable amount of the thiamin generated by gut microbiota exists in the form of thiamin pyrophosphate (TPP). We have previously shown that human colonocytes possess an efficient carrier-mediated uptake process for TPP that involves the SLC44A4 system and this uptake process is adaptively regulated by prevailing extracellular TPP level. Little is known about the molecular mechanisms that mediate this adaptive regulation. We addressed this issue using human-derived colonic epithelial NCM460 cells and mouse colonoids as models. Maintaining NCM460 cells in the presence of a high level of TPP (1 mM) for short (2 days)- and long-term (9 days) periods was found to lead to a significant reduction in [³H] TPP uptake compared with cells maintained in its absence. Short-term exposure showed no changes in level of expression of SLC44A4 protein in total cell homogenate (although there was a decreased expression in the membrane fraction), mRNA, and promoter activity. However, a significant reduction in the level of expression of the SLC44A4 protein, mRNA, and promoter activity was observed upon long-term maintenance with the substrate. Similar changes in Slc44a4 mRNA expression were observed when mouse colonoids were maintained with TPP for short- and long-term periods. Expression of the transcription factors ELF3 and CREB-1 (which drive the SLC44A4 promoter) following long-term exposure was unchanged, but their binding affinity to the promoter was decreased and specific histone modifications were also observed. These studies demonstrate that, depending on the period of exposure, different mechanisms are involved in the adaptive regulation of colonic TPP uptake by extracellular substrate level.

Affinity of Tau antibodies for solubilized pathological Tau species but not their immunogen or insoluble Tau aggregates predicts in vivo and ex vivo efficacy

Background

A few tau immunotherapies are now in clinical trials with several more likely to be initiated in the near future. A priori, it can be anticipated that an antibody which broadly recognizes various pathological tau aggregates with high affinity would have the ideal therapeutic properties. Tau antibodies 4E6 and 6B2, raised against the same epitope region but of varying specificity and affinity, were tested for acutely improving cognition and reducing tau pathology in transgenic tauopathy mice and neuronal cultures.

Results

Surprisingly, we here show that one antibody, 4E6, which has low affinity for most forms of tau acutely improved cognition and reduced soluble phospho-tau, whereas another antibody, 6B2, which has high affinity for various tau species was ineffective. Concurrently, we confirmed and clarified these efficacy differences in an ex vivo model of tauopathy. Alzheimer’s paired helical filaments (PHF) were toxic to the neurons and increased tau levels in remaining neurons. Both toxicity and tau seeding were prevented by 4E6 but not by 6B2. Furthermore, 4E6 reduced PHF spreading between neurons. Interestingly, 4E6’s efficacy relates to its high affinity binding to solubilized PHF, whereas the ineffective 6B2 binds mainly to aggregated PHF. Blocking 4E6's uptake into neurons prevented its protective effects if the antibody was administered after PHF had been internalized. When 4E6 and PHF were administered at the same time, the antibody was protective extracellularly.

Conclusions

Overall, these findings indicate that high antibody affinity for solubilized PHF predicts efficacy, and that acute antibody-mediated improvement in cognition relates to clearance of soluble phospho-tau. Importantly, both intra- and extracellular clearance pathways are in play. Together, these results have major implications for understanding the pathogenesis of tauopathies and for development of immunotherapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0126-z) contains supplementary material, which is available to authorized users.

PKR downregulation prevents neurodegeneration and β-amyloid production in a thiamine-deficient model

Brain thiamine homeostasis has an important role in energy metabolism and displays reduced activity in Alzheimer's disease (AD). Thiamine deficiency (TD) induces regionally specific neuronal death in the animal and human brains associated with a mild chronic impairment of oxidative metabolism. These features make the TD model amenable to investigate the cellular mechanisms of neurodegeneration. Once activated by various cellular stresses, including oxidative stress, PKR acts as a pro-apoptotic kinase and negatively controls the protein translation leading to an increase of BACE1 translation. In this study, we used a mouse TD model to assess the involvement of PKR in neuronal death and the molecular mechanisms of AD. Our results showed that the TD model activates the PKR-eIF2α pathway, increases the BACE1 expression levels of Aβ in specific thalamus nuclei and induces motor deficits and neurodegeneration. These effects are reversed by PKR downregulation (using a specific inhibitor or in PKR knockout mice).

Associations between in vivo neuroimaging and postmortem brain cytokine markers in a rodent model of Wernicke's encephalopathy

Thiamine (vitamin B1) deficiency, associated with a variety of conditions, including chronic alcoholism and bariatric surgery for morbid obesity, can result in the neurological disorder Wernicke's encephalopathy (WE). Recent work building upon early observations in animal models of thiamine deficiency has demonstrated an inflammatory component to the neuropathology observed in thiamine deficiency. The present, multilevel study including in vivo magnetic resonance imaging (MRI) and spectroscopy (MRS) and postmortem quantification of chemokine and cytokine proteins sought to determine whether a combination of these in vivo neuroimaging tools could be used to characterize an in vivo MR signature for neuroinflammation. Thiamine deficiency for 12days was used to model neuroinflammation; glucose loading in thiamine deficiency was used to accelerate neurodegeneration. Among 38 animals with regional brain tissue assayed postmortem for cytokine/chemokine protein levels, three groups of rats (controls+glucose, n=6; pyrithiamine+saline, n=5; pyrithiamine+glucose, n=13) underwent MRI/MRS at baseline (time 1), after 12days of treatment (time 2), and 3h after challenge (glucose or saline, time 3). In the thalamus of glucose-challenged, thiamine deficient animals, correlations between in vivo measures of pathology (lower levels of N-acetyle aspartate and higher levels of lactate) and postmortem levels of monocyte chemotactic protein-1 (MCP-1, also known as chemokine ligand 2, CCL2) support a role for this chemokine in thiamine deficiency-related neurodegeneration, but do not provide a unique in vivo signature for neuroinflammation.

miR-21 improves the neurological outcome after traumatic brain injury in rats

The expression levels of microRNAs (miRNAs) including miR-21, have been reported to change in response to traumatic brain injury (TBI), suggesting that they may influence the pathophysiological process in brain injury. To analyze the potential effect of miR-21 on neurological function after TBI, we employed the fluid percussion injury rat model and manipulated the expression level of miR-21 in brain using intracerebroventricular infusion of miR-21 agomir or antagomir. We found that upregulation of miR-21 level in brain conferred a better neurological outcome after TBI by improving long-term neurological function, alleviating brain edema and decreasing lesion volume. To further investigate the mechanism underlying this protective effect, we evaluated the impact of miR-21 on apoptosis and angiogenesis in brain after TBI. We found that miR-21 inhibited apoptosis and promoted angiogenesis through regulating the expression of apoptosis- and angiogenesis-related molecules. In addition, the expression of PTEN, a miR-21 target gene, was inhibited and Akt signaling was activated in the procedure. Taken together, these data indicate that miR-21 could be a potential therapeutic target for interventions after TBI.

In vitro immune functions in thiamine-replete and -depleted lake trout (Salvelinus namaycush)

In this study we examined the impacts of in vivo thiamine deficiency on lake trout leukocyte function measured in vitro. When compared outside the context of individual-specific thiamine concentrations no significant differences were observed in leukocyte bactericidal activity or in concanavalin A (Con A), and phytohemagglutinin-P (PHA-P) stimulated leukocyte proliferation. Placing immune functions into context with the ratio of in vivo liver thiamine monophosphate (TMP--biologically inactive form) to thiamine pyrophosphate (TPP--biologically active form) proved to be the best indicator of thiamine depletion impacts as determined using regression modeling. These observed relationships indicated differential effects on the immune measures with bactericidal activity exhibiting an inverse relationship with TMP to TPP ratios, Con A stimulated mitogenesis exhibiting a positive relationship with TMP to TPP ratios and PHA-P stimulated mitogenesis exhibiting no significant relationships. In addition, these relationships showed considerable complexity which included the consistent observation of a thiamine-replete subgroup with characteristics similar to those seen in the leukocytes from thiamine-depleted fish. When considered together, our observations indicate that lake trout leukocytes experience cell-type specific impacts as well as an altered physiologic environment when confronted with a thiamine-limited state.

Thiamine deficiency results in release of soluble factors that disrupt mitochondrial membrane potential and downregulate the glutamate transporter splice-variant GLT-1b in cultured astrocytes

Loss of astrocytic glutamate transporters is a major feature of both thiamine deficiency (TD) and Wernicke's encephalopathy. However, the underlying basis of this process is not well understood. In the present study we have investigated the possibility of release of astrocytic soluble factors that might be involved in the regulation of the glutamate transporter GLT-1b in these cells. Treatment of naïve astrocytes with conditioned media from astrocytes exposed to TD conditions resulted in a progressive decrease in glutamate uptake over 24 h. Immunoblotting and flow cytometry measurements indicated this was accompanied by a 20-40% loss of GLT-1b. Astrocytes exposed to either TD or TD conditioned media showed increased disruption of mitochondrial membrane potential compared to control cells, and treatment of astrocytes with TD resulted in an increase in the pro-inflammatory cytokine TNF-α and elevated levels of phospho-IκB fragment, indicative of increased activation of NF-κB. Inhibition of TNF-α activity with the use of a neutralizing antibody blocked the increased NF-κB activation, while inhibition of NF-κB ameliorated the decrease in GLT-1b and reversed the decrease in glutamate uptake occurring with TD treatment. Together, these findings indicate that astrocytes exposed to TD conditions show responses suggesting that soluble factors released by these cells under conditions of TD play a regulatory role in terms of glutamate transport function and mitochondrial integrity.

A rat model for chronic spinal nerve root compression

OBJECTIVES

The pathophysiology of radiculopathy associated with lumbar spinal stenosis and lumbar disc herniation is incompletely understood. The goal of the present study was to establish a chronic spinal nerve root compression model that can mimic lumbar disc herniation or spinal stenosis using silicone tube compression. We also try to link the pathology changes of damaged nerve root with the reaction of microglia in spinal cord in same rat at different time points.

METHODS

Thirty rats were used in this study. The L5 nerve roots (dorsal and ventral) were exposed by hemilaminectomy; the diameter of the L5 nerve root was measured at the 2 mm proximal from the dorsal root ganglia. The dorsal and ventral nerve roots of L5 were compressed using a silicone tube, and the sham group was only exposed dorsal and ventral roots of L5. Five rats from the sham group were perfused at 8 days after surgery, and 25 rats from the model groups were perfused at 3, 8, 12, 45 days, and 5 months after surgery, each model group was composed of 5 rats according to the time point. The L5 spinal cord segments and nerve root that compressed by silicone tube were harvested from the same rat. Microglia and neuron in the spinal cord were stained by immunohistochemistry, and the nerve root was shown by electron microscope.

RESULTS

In sham-operated rat, the arrangement of axon and myelin sheath is normal, the ventral root is mainly composed of large axon (>6 μm) and it is composed of 46.3 % of all the axons of the ventral root; the average myelin thickness of large axon is 1.86 μm; the dorsal root is mainly composed of medium (2-3.9 or 4-5.9 μm) axons and they are composed of 79.1 % of all the axons of the dorsal root; the average myelin thickness of this category is 0.94 or 1.55 μm. The average myelin thickness of large axon in ventral root reduced to 0.97 and 1.19 μm from more than 1.86 μm after compression for 3 and 8 days separately. Most of myelin sheath disappeared after 12 days of compression; the myelin sheath was partly restored at 45 days after compression which the myelin sheath thickness of large axons in ventral root was 0.47 μm. The medium category in dorsal root reduced to 0.59 or 0.72 μm from 0.94 μm, and 1.55 μm after compression for 3 days (p < 0.05 to p < 0.0001). The medium category axon in dorsal root is also 0.47 μm after compression for 45 days (p ≤ 0.0001). The myelin sheath was almost totally restored at the 5 months of compression; the myelin sheath thickness returned to normal and the axons were intact in structure under EM. The number of Iba1-positive microglia increased by 18.69, 40.44, and 18.49 % after compression for 3, 8, and 12 days separately in the ipsilateral dorsal horn and 21.26, 32.15, 22.87 % in ventral horns, and the activation of microglia was also prominent in contralateral sides of the dorsal and ventral horn at 8 days time point. The microglia cell reconverted to resting status after compression for 45 days or 5 months.

CONCLUSION

The chronic spinal nerve root compression with silicone tube produces a recoverable damage to nerve root, which produces recoverable microglial activation in the spinal cord. These results demonstrated that the chronic spinal nerve root compression with silicone tube could mimic the pathological changes of lumbar spinal stenosis or lumbar disc herniation.

Decoding Alzheimer's disease from perturbed cerebral glucose metabolism: implications for diagnostic and therapeutic strategies

Alzheimer's disease (AD) is an age-related devastating neurodegenerative disorder, which severely impacts on the global economic development and healthcare system. Though AD has been studied for more than 100 years since 1906, the exact cause(s) and pathogenic mechanism(s) remain to be clarified. Also, the efficient disease-modifying treatment and ideal diagnostic method for AD are unavailable. Perturbed cerebral glucose metabolism, an invariant pathophysiological feature of AD, may be a critical contributor to the pathogenesis of this disease. In this review, we firstly discussed the features of cerebral glucose metabolism in physiological and pathological conditions. Then, we further reviewed the contribution of glucose transportation abnormality and intracellular glucose catabolism dysfunction in AD pathophysiology, and proposed a hypothesis that multiple pathogenic cascades induced by impaired cerebral glucose metabolism could result in neuronal degeneration and consequently cognitive deficits in AD patients. Among these pathogenic processes, altered functional status of thiamine metabolism and brain insulin resistance are highly emphasized and characterized as major pathogenic mechanisms. Finally, considering the fact that AD patients exhibit cerebral glucose hypometabolism possibly due to impairments of insulin signaling and altered thiamine metabolism, we also discuss some potential possibilities to uncover diagnostic biomarkers for AD from abnormal glucose metabolism and to develop drugs targeting at repairing insulin signaling impairment and correcting thiamine metabolism abnormality. We conclude that glucose metabolism abnormality plays a critical role in AD pathophysiological alterations through the induction of multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, and so forth. To clarify the causes, pathogeneses and consequences of cerebral hypometabolism in AD will help break the bottleneck of current AD study in finding ideal diagnostic biomarker and disease-modifying therapy.

Autophagy alleviates neurodegeneration caused by mild impairment of oxidative metabolism

Thiamine deficiency (TD) causes mild impairment of oxidative metabolism and region-selective neuronal loss in the brain, which may be mediated by neuronal oxidative stress, endoplasmic reticulum (ER) stress, and neuroinflammation. TD-induced brain damage is used to model neurodegenerative disorders, and the mechanism for the neuronal death is still unclear. We hypothesized that autophagy might be activated in the TD brain and play a protective role in TD-induced neuronal death. Our results demonstrated that TD induced the accumulation of autophagosomes in thalamic neurons measured by transmission electron microscopy, and the up-regulation of autophagic markers LC3-II, Atg5, and Beclin1 as measured with western blotting. TD also increased the expression of autophagic markers and induced LC3 puncta in SH-SY5Y neuroblastoma cells. TD-induced expression of autophagic markers was reversed once thiamine was re-administered. Both inhibition of autophagy by wortmannin and Beclin1 siRNA potentiated TD-induced death of SH-SY5Y cells. In contrast, activation of autophagy by rapamycin alleviated cell death induced by TD. Intraperitoneal injection of rapamycin stimulated neuronal autophagy and attenuated TD-induced neuronal death and microglia activation in the submedial thalamus nucleus (SmTN). TD inhibited the phosphorylation of p70S6 kinase, suggesting mTOR/p70S6 kinase pathway was involved in the TD-induced autophagy. These results suggest that autophagy is neuroprotective in response to TD-induced neuronal death in the central nervous system. This opens a potential therapeutic avenue for neurodegenerative diseases caused by mild impairment of oxidative metabolism. Autophagy is neuroprotective in response to thiamine deficiency (TD)-induced neuronal death. TD caused neuronal damage and induced the formation of autophagosome, and increased the expression of autophagy-related proteins. Autophagy sequestered damaged and dysfunctional organelles/protein, and transported them to lysosomes for degradation/recycling. This process provided nutrients for injured neurons. Wortmannin and knockdown of Beclin1 inhibited autophagy, and exacerbated TD-induced cell death, while activation of autophagy by rapamycin offered protection against TD neurotoxicity.

The impact of oxidative stress in thiamine deficiency: a multifactorial targeting issue

Thiamine (vitamin B1) deficiency, the underlying cause of Wernicke-Korsakoff syndrome, is associated with the development of focal neuronal loss in vulnerable areas of the brain. Although the actual mechanism(s) that lead to the selective histological lesions characteristic of this disorder remain unresolved, oxidative stress has been shown to play a major role in its pathophysiology. In this review, the multifactorial influence of oxidative stress on a variety of processes known to take part in the development of structural lesions in TD including excitotoxicity, neuroinflammation, blood-brain barrier integrity, mitochondrial integrity, apoptosis, nucleic acid function, and neural stem cells will be discussed, and therapeutic strategies undertaken for treating neurodegeneration examined which may have an impact on the future treatment of this important vitamin deficiency.

Influence of the core circadian gene "Clock" on obesity and leptin resistance in mice

Alterations in metabolism could be due to cell-autonomous effects associated with altered expression of Clock in central nervous system feeding centers and/or peripheral tissues involved in metabolism. Clock mutant mice are hyperphagic and obese, which indicates that Clock is related to obesity. In the present study, we used intracerebroventricular injection of recombinant adenoviral vector harboring Clock genes to explore the role of Clock on diet induced obesity and the mechanisms involved in leptin resistance and leptin signaling in mice. The results demonstrated that expression of Clock in the arcuate nucleus of diet induced obesity mice was down-regulated. The recombinant adenoviral vector harboring Clock genes could reduce obesity indexes of diet induced obesity mice including body weight, BMI and total fat mass, attenuate hyperleptinemia, increase leptin sensitivity and decrease accumulated suppressor of cytokine signaling-3 in the arcuate nucleus. These results indicate that Clock plays an important role on obesity, which may be involved in leptin resistance and regulation of suppressor of cytokine signaling-3 in arcuate nucleus.

Mitochondrial dysfunction and oxidative stress activate inflammasomes: impact on the aging process and age-related diseases

Oxidative stress and low-grade inflammation are the hallmarks of the aging process and are even more enhanced in many age-related degenerative diseases. Mitochondrial dysfunction and oxidative stress can provoke and potentiate inflammatory responses, but the mechanism has remained elusive. Recent studies indicate that oxidative stress can induce the assembly of multiprotein inflammatory complexes called the inflammasomes. Nod-like receptor protein 3 (NLRP3) is the major immune sensor for cellular stress signals, e.g., reactive oxygen species, ceramides, and cathepsin B. NLRP3 activation triggers the caspase-1-mediated maturation of the precursors of IL-1β and IL-18 cytokines. During aging, the autophagic clearance of mitochondria declines and dysfunctional mitochondria provoke chronic oxidative stress, which disturbs the cellular redox balance. Moreover, increased NF-κB signaling observed during aging could potentiate the expression of NLRP3 and cytokine proforms enhancing the priming of NLRP3 inflammasomes. Recent studies have demonstrated that NLRP3 activation is associated with several age-related diseases, e.g., the metabolic syndrome. We will review here the emerging field of inflammasomes in the appearance of the proinflammatory phenotype during the aging process and in age-related diseases.

Selective loss of AMPA receptors at corticothalamic synapses in the epileptic stargazer mouse

Absence seizures are common in the stargazer mutant mouse. The mutation underlying the epileptic phenotype in stargazers is a defect in the gene encoding the normal expression of the protein stargazin. Stargazin is involved in the membrane trafficking and synaptic targeting of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) at excitatory glutamatergic synapses. Thus, the genetic defect in the stargazer results in a loss of AMPARs and consequently, excitation at glutamatergic synapses. Absence seizures are known to arise in thalamocortical networks. In the present study we show for the first time, using Western blot analysis and quantitative immunogold cytochemistry, that in the epileptic stargazer mouse, there is a global loss of AMPAR protein in nucleus reticularis (RTN) and a selective loss of AMPARs at corticothalamic synapses in inhibitory neurons of the RTN thalamus. In contrast, there is no significant loss of AMPARs at corticothalamic synapses in excitatory relay neurons in the thalamic ventral posterior (VP) region. The findings of this study thus provide cellular and molecular evidence for a selective regional loss of synaptic AMPAR within the RTN that could account for the loss of function at these inhibitory neuron synapses, which has previously been reported from electrophysiological studies. The specific loss of AMPARs at RTN but not relay synapses in the thalamus of the stargazer, could contribute to the absence epilepsy phenotype by altering thalamocortical network oscillations. This is supported by recent evidence that loss of glutamate receptor subunit 4 (GluA4) (the predominant AMPAR-subtype in the thalamus), also leads to a specific reduction in strength in the cortico-RTN pathway and enhanced thalamocortical oscillations, in the Gria4(-/-) model of absence epilepsy. Thus further study of thalamic changes in these models could be important for future development of drugs targeted to absence epilepsy.

Immunohistochemical expression of proinflammatory cytokines IL-1β, IL-6, TNF-α and involvement of COX-2, quantitatively confirmed by Western blot analysis, in Wernicke's encephalopathy

Selective cerebral vulnerability is a major consequence of Wernicke's encephalopathy (WE), in which focal areas of the brain exhibit symmetrical profound neuronal loss and accompanying gliosis, occurring most frequently in diencephalic regions such as the thalamus and the mammillary bodies. Many processes have been proposed to explain the selective cerebral vulnerability and the focal neuronal cell death in Wernicke's encephalopathy. There are several mechanisms which are common to the pathophysiology of encephalopathies caused by thiamine deficiency (TD). Recently, emphasis is being placed on deficit in mitochondrial oxidative metabolism, oxidative/nitrosative stress, and the release of proinflammatory cytokines such as IL-1β, IL-6, and tumor necrosis factor-α (TNF-α). Cyclooxygenase-2 (COX-2) plays major roles in regulating brain damage and inflammation. Here we present two fatal cases of non-alcohol associated WE. The immunohistochemical study revealed increased proinflammatory cytokine immunoreactivity in the neurons of the mammillary bodies and medial thalamus, and in the periaqueductal regions, compared with basal constitutive levels of expression in the frontal cortex. Positive (WE cases) and negative (immediate trauma deaths) case-controls were used to confirm the results. TD induced IL-1β proteins weakly, while moderate increase was observed for TNF-α and IL-6. Immunofluorescence analysis by confocal microscopy confirmed the staining results for immunoreactivity in WE brains. Further, the induction of proinflammatory cytokine protein expression levels was quantified by Western blot analysis.

Measurement of serum, liver, and brain cytokine induction, thiamine levels, and hepatopathology in rats exposed to a 4-day alcohol binge protocol

BACKGROUND

 In rodent and human studies, ethanol (EtOH) exposure is associated with elevated brain levels of the magnetic resonance spectroscopy (MRS) signal representing choline-containing compounds (Cho). One interpretation of elevated brain Cho is that it is a marker of neuroinflammation, and some evidence suggests that EtOH exposure promotes neuroinflammation. This study aimed to determine whether binge EtOH exposure (intragastric 3 g/kg 25% EtOH every 8 hours for 4 days) would induce the expression of certain cytokines in blood, liver, or brain, thereby supporting the neuroinflammation hypothesis of elevated Cho.

METHODS

Ten of 18 wild-type male Wistar rats (~322 g at baseline) were exposed to EtOH and attained average blood alcohol levels of ~315 mg/dl across 4 days. Blood for cytokine immunoassays was collected at baseline, after 5 doses of EtOH (binge), and immediately preceding euthanasia either 4 or 24 hours after the last dose of EtOH. Blood was additionally assayed for the levels of thiamine and liver enzymes; liver histopathology was performed postmortem; and tissue from liver and 6 brain regions was assayed for the potential induction of 7 cytokines.

RESULTS

There were no group effects on the levels of thiamine or its phosphate derivatives, thiamine monophosphate or thiamine diphosphate. ANOVAs of liver enzyme levels indicated that only alkaline phosphatase (ALP) levels were higher in the EtOH group than in control group at binge; ALP elevations, however, are difficult to explain in the absence of changes in the levels of additional liver enzymes. Postmortem liver pathology provided evidence for minimal microvesicular lipidosis and portocentric fibrosis in the EtOH group. Group effects on the levels of the measured cytokines in the blood (TNF-α, IFN-γ, IL-1β, IL-4, IL-5, IL-13, and GRO/CXCL1) were not significant. Similarly, postmortem evaluation of liver cytokines did not reveal group effects. Postmortem evaluation of the 7 cytokines in 6 brain regions (anterior cerebellar vermis, cingulate cortex, frontal cortex, hippocampus, hypothalamus, striatum) also failed to identify group effects.

CONCLUSIONS

A single 4-day bout of binge EtOH exposure alone was insufficient to induce the expression of 7 cytokines in blood, liver, or 6 brain regions of wild-type Wistar rats. Alternative interpretations for elevations in brain Cho in response to a 4-day binge EtOH treatment are therefore necessary and may include induction of cytokines not measured herein or other noninflammatory mechanisms.

Interactions between chemokine and mu-opioid receptors: anatomical findings and electrophysiological studies in the rat periaqueductal grey

Opioids have immunomodulatory functions and may alter susceptibility to immune disorders. Behavioral studies also indicate that chemokines, molecules expressed by immune cells, block opioid-induced analgesia in the periaqueductal grey (PAG). Bi-directional heterologous desensitization of opioid and chemokine receptors has been described in cell systems. We report the anatomical and functional interactions of chemokine receptors with the mu-opioid receptor (MOR) in the rat brain. The chemokine receptors, CXCR4 and CX3CR1, as well as their chemokine substrates, CXCL12 and CX3CL1, are widely expressed in the central nervous system (CNS). Immunohistochemical techniques were utilized to investigate MOR-CXCR4 and MOR-CX3CR1 receptor colocalization in multiple brain areas. Our results demonstrate co-expression of these receptors on individual neurons in several regions including cingulate cortex, hippocampus, and PAG, suggesting functional receptor interactions. Whole-cell patch-clamp recordings of PAG neurons in a rat brain slice preparation were used to examine morphine or chemokine (CXCL12, CX3CL1) effects alone, or in combination on neuronal membrane properties. Morphine (10 μM) hyperpolarized and reduced input resistance of PAG neurons. CXCL12 and CX3CL1 (10 nM) had no impact on either parameter. In the presence of CXCL12, morphine's electrophysiological effects were blocked in all neurons examined, whereas with CX3CL1, morphine's effects were blocked in 57% of neurons studied. The data provide electrophysiological evidence for MOR-CXCR4 and MOR-CX3CR1 heterologous desensitization in the PAG at the single-cell level. These interactions may contribute to the limited utility of opioid analgesics for inflammatory pain treatment and supports chemokines as neuromodulators.

Neuronal MCP-1 mediates microglia recruitment and neurodegeneration induced by the mild impairment of oxidative metabolism

Chemokines are implicated in the neuroinflammation of several chronic neurodegenerative disorders. However, the precise role of chemokines in neurodegeneration is unknown. Thiamine deficiency (TD) causes abnormal oxidative metabolism in the brain as well as a well-defined microglia activation and neurodegeneration in the submedial thalamus nucleus (SmTN), which are common features of neurodegenerative diseases. We evaluated the role of chemokines in neurodegeneration and the underlying mechanism in a TD model. Among the chemokines examined, TD selectively induced neuronal expression of monocyte chemoattractant protein-1 (MCP-1) in the SmTN prior to microglia activation and neurodegeneration. The conditioned medium collected from TD-induced neurons caused microglia activation. With a neuron/microglia co-culture system, we showed that MCP-1-induced neurotoxicity required the presence of microglia, and exogenous MCP-1 was able to activate microglia and stimulated microglia to produce cytokines. A MCP-1 neutralizing antibody inhibited MCP-1-induced microglia activation and neuronal death in culture and in the thalamus. MCP-1 knockout mice were resistant to TD-induced neuronal death in SmTN. TD selectively induced the accumulation of reactive oxygen species in neurons, and antioxidants blocked TD-induced MCP-1 expression. Together, our results indicated an induction of neuronal MCP-1 during mild impairment of oxidative metabolism caused by microglia recruitment/activation, which exacerbated neurodegeneration.

Microglial activation is a major contributor to neurologic dysfunction in thiamine deficiency

In Wernicke's encephalopathy and thiamine deficiency (TD), the cause of this brain disorder, development of inflammation is an important aspect of the disease process. How this pathological mechanism relates to the neurologic impairment associated with TD, however, remains unclear. A key feature of the inflammatory process is the activation of microglia. In the present study, we evaluated the role of microglial activation in the pathophysiology of TD by examining the relationship between levels of CD11b/c and CD68, two proteins associated with microglial activation, and neurological dysfunction under conditions of TD. Rats with TD showed large increases in expression of both CD11b/c and CD68 in the vulnerable thalamus and inferior colliculus, with no change in mRNA levels in the relatively non-vulnerable frontal cortex. These alterations in CD11b/c and CD68 expression were reflected in dramatic upregulation of both proteins by immunoblotting and immunohistochemical methods. Co-treatment of rats with TD and the anti-inflammatory drug minocycline prevented microglial activation, and onset of neurological changes, including loss of righting reflex, was delayed by approximately 39h, compared to animals with TD alone. In addition, co-treatment of rats with TD and N-acetylcysteine prevented the increase in CD11b/c and CD68, but did not alter the onset of neurological impairment. These results suggest that microglial activation plays a role in the development of neurological impairment in TD and possibly Wernicke's encephalopathy, and that while development of oxidative stress may be involved in microglial activation, the basis of this neurologic dysfunction is likely to be multifactorial in nature.

Loss of astrocytic glutamate transporters in Wernicke encephalopathy

Wernicke encephalopathy (WE), a neurological disorder caused by thiamine deficiency (TD), is characterized by structural damage in brain regions that include the thalamus and cerebral cortex. The basis for these lesions is unclear, but may involve a disturbance of glutamatergic neurotransmission. We have therefore investigated levels of the astrocytic glutamate transporters EAAT1 and EAAT2 in order to evaluate their role in the pathophysiology of this disorder. Histological assessment of the frontal cortex revealed a significant loss of neurons in neuropathologically confirmed cases of WE compared with age-matched controls, concomitant with decreases in alpha-internexin and synaptophysin protein content of 67 and 52% by immunoblotting. EAAT2 levels were diminished by 71% in WE, with levels of EAAT1 also reduced by 62%. Loss of both transporter sites was confirmed by immunohistochemical methods. Development of TD in rats caused a profound loss of EAAT1 and EAAT2 in the thalamus accompanied by decreases in other astrocyte-specific proteins. Treatment of TD rats with N-acetylcysteine prevented the downregulation of EAAT2 in the medial thalamus, and ameliorated the loss of several other astrocyte proteins, concomitant with increased neuronal survival. Our results suggest that (1) loss of EAAT1 and EAAT2 glutamate transporters is associated with structural damage to the frontal cortex in patients with WE, (2) oxidative stress plays an important role in this process, and (3) TD has a profound effect on the functional integrity of astrocytes. Based on these findings, we recommend that early treatment using a combination of thiamine AND antioxidant approaches should be an important consideration in cases of WE.

Neurodegeneration in thiamine deficient rats-A longitudinal MRI study

Selective neurodegeneration accompanied by mitochondrial dysfunction characterizes neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Thiamine deficiency (TD) in rats is a model for the study of cellular and molecular mechanisms that lead to selective neuronal loss caused by chronic oxidative deficits. Neurodegeneration in TD-rats develops over a period of 12 to 14 days and can be partially reversed by thiamine administration. The aim of this study was to characterize the in-vivo progression of neurodegeneration and the neuronal rescue processes in TD using T(2) magnetic resonance mapping and diffusion tensor imaging (DTI). Each rat was scanned prior to TD induction (day 0), before the appearance of neurological symptoms (day 10), during the symptomatic stage (days 12 and 14) and during the recuperation period (days 31 and 87). Time-dependent lesions were revealed mainly in the thalamus and the inferior colliculi. Early decrease in the fractional anisotropy (FA) was found on day 10 in the inferior colliculi and to a lesser degree in the thalamus, while the earliest detectable changes in the T(2) parameter occurred only on day 12. FA values in the thalamus remained significantly low after thiamine restoration, suggesting irreversible disarrangement and replacement of neuronal structures. While T(2) values in the frontal cortex demonstrated no lesions, FA values significantly increased on days 14 and 31. An enlargement of the lateral ventricles was observed and persevered during the recovery period. This longitudinal MRI study demonstrated that in TD MRI can detect neurodegeneration and neuronal recovery. DTI is more sensitive than T(2) mapping in the early detection of TD lesions.

Fractalkine/CX3CL1 enhances GABA synaptic activity at serotonin neurons in the rat dorsal raphe nucleus

Serotonin (5-hydroxytryptamine; 5-HT) has an important role in mood regulation, and its dysfunction in the central nervous system (CNS) is associated with depression. Reports of mood and immune disorder co-morbidities indicate that immune-5-HT interactions may mediate depression present in immune compromised disease states including HIV/AIDS, multiple sclerosis, and Parkinson's disease. Chemokines, immune proteins that induce chemotaxis and cellular adhesion, and their G-protein coupled receptors distribute throughout the CNS, regulate neuronal patterning, and mediate neuropathology. The purpose of this study is to investigate the neuroanatomical and neurophysiological relationship between the chemokine fractalkine/CX3CL1 and its receptor CX3CR1 with 5-HT neurons in the rat midbrain raphe nuclei (RN). Immunohistochemistry was used to examine the colocalization of CX3CL1 or CX3CR1 with 5-HT in the RN, and whole-cell patch-clamp recordings in rat brain slices were used to determine the functional impact of CX3CL1 on 5-HT dorsal raphe nucleus (DRN) neurons. Greater than 70% of 5-HT neurons colocalize with CX3CL1 and CX3CR1 in the RN. CX3CL1 localizes as discrete puncta throughout the cytoplasm, whereas CX3CR1 concentrates to the perinuclear region of 5-HT neurons and exhibits microglial expression. CX3CL1 and CX3CR1 also colocalize with one another on individual RN cells. Electrophysiology studies indicate a CX3CL1-mediated enhancement of spontaneous inhibitory postsynaptic current (sIPSC) amplitude and dose-dependent increase of evoked IPSC (eIPSC) amplitude without affecting eIPSC paired-pulse ratio, a finding observed selectively in 5-HT neurons. CX3CL1's effect on eIPSC amplitude is blocked by pretreatment with an anti-CX3CL1 neutralizing antibody. Thus, CX3CL1 enhances postsynaptic GABA receptor number or sensitivity on 5-HT DRN neurons under conditions of both spontaneous and synaptically-evoked GABA release. CX3CL1 may indirectly inhibit 5-HT neurotransmission by increasing the sensitivity of 5-HT DRN neurons to GABA inputs. Therapies targeting CX3CL1 may treat serotonin related mood disorders, including depression experienced by patients with compromised immune systems.

Astrocytes are a major target in thiamine deficiency and Wernicke's encephalopathy

Thiamine deficiency (TD) is the underlying cause, and an established model, of Wernicke's encephalopathy (WE). Although the neurologic dysfunction and brain damage that results from TD has been well-described, the precise mechanisms that lead to the selective histological lesions characteristic of this disorder remain a mystery. Over the course of many years, various processes have been proposed that could lead to focal neuronal cell death in this disorder. But despite a concerted effort to relate these processes to a clear sequelae of events culminating in development of the focal neuropathology, little success has resulted. In recent years, however, a role for astrocytes in the pathophysiology of TD has been emerging. Here, alterations in glutamate uptake, and levels of the astrocytic glutamate transporters EAAT1 and EAAT2 in TD and WE, are discussed in terms of an excitotoxic event, along with the GABA transporter subtype GAT-3, and changes in other astrocytic proteins including GFAP and glutamine synthetase. Lactic acidosis, changes in the water channel protein AQP-4 and brain edema are also a focus of attention in relation to astrocyte dysfunction, while involvement of oxidative stress and inflammatory processes, along with white matter injury in terms of excitotoxicity are other key issues considered. In summary, a new appraisal of the extent of involvement of astrocytes in TD and WE is presented, with the evidence suggesting these cells represent a major target for damage during the disease process.

Oxidant-induced changes in mitochondria and calcium dynamics in the pathophysiology of Alzheimer's disease

Considerable data support the hypothesis that mitochondrial abnormalities link gene defects and/or environmental insults to the neurodegenerative process. The interaction of oxidants with calcium and the mitochondrial enzymes of the tricarboxylic acid cycle are central to that relationship. Abnormalities that were discovered in brains or fibroblasts from patients with Alzheimer's disease (AD) have been modeled in vitro and in vivo to assess their pathophysiological importance and to determine how they might be reversed. The conclusions are consistent with the hypothesis that the AD-related abnormalities result from oxidative stress. The selection of compounds for reversal is complex because the actions of the relevant compounds vary under different conditions, such as cell redox states and acute versus chronic changes. However, the models that have been developed are useful for testing the effectiveness of the potential medications. The results suggest that the reversal of mitochondrial deficits and a reduction in oxidative stress will reduce clinical and pathological changes and benefit patients.

Dietary supplementation with resveratrol reduces plaque pathology in a transgenic model of Alzheimer's disease

Resveratrol, a polyphenol found in red wine, peanuts, soy beans, and pomegranates, possesses a wide range of biological effects. Since resveratrol's properties seem ideal for treating neurodegenerative diseases, its ability to diminish amyloid plaques was tested. Mice were fed clinically feasible dosages of resveratrol for forty-five days. Neither resveratrol nor its conjugated metabolites were detectable in brain. Nevertheless, resveratrol diminished plaque formation in a region specific manner. The largest reductions in the percent area occupied by plaques were observed in medial cortex (-48%), striatum (-89%) and hypothalamus (-90%). The changes occurred without detectable activation of SIRT-1 or alterations in APP processing. However, brain glutathione declined 21% and brain cysteine increased 54%. The increased cysteine and decreased glutathione may be linked to the diminished plaque formation. This study supports the concept that onset of neurodegenerative disease may be delayed or mitigated with use of dietary chemo-preventive agents that protect against beta-amyloid plaque formation and oxidative stress.

Metabolic and structural role of thiamine in nervous tissues

In the literature, previous descriptions of the role of thiamine (B1 vitamin) focused mostly on its biochemical functions as a coenzyme precursor of some key enzymes of the carbohydrate metabolism. This report reviews recent developments on the metabolic and structural role of thiamine, e.g., the coenzyme and noncoenzyme functions of the vitamin. Taking into account analysis of our experimental data relating to the effects of thiamine deficiency on developing central nervous system (CNS) and data available in literature, we seek to establish a clear difference between the metabolic and structural role of thiamine. Our experimental data indicate that the specific and nonspecific effects express two diametrically diverse functions of thiamine in development: the nonspecific effects show up the metabolic consequences of thiamine deficiency resulting in apoptosis and severe cellular deficit; inversely, the specific effects announced the structural consequences of thiamine deficiency, described as cellular membrane damage, irregular and ectopic cells. The review highlights the existence of noncoenzyme functions of this vitamin through its interactions with biological membranes.

Thiamine deficiency induces oxidative stress and exacerbates the plaque pathology in Alzheimer's mouse model

Mitochondrial dysfunction, oxidative stress and reductions in thiamine-dependent enzymes have been implicated in multiple neurological disorders including Alzheimer's disease (AD). Experimental thiamine deficiency (TD) is an established model for reducing the activities of thiamine-dependent enzymes in brain. TD diminishes thiamine-dependent enzymes throughout the brain, but produces a time-dependent selective neuronal loss, glial activation, inflammation, abnormalities in oxidative metabolism and clusters of degenerating neurites in only specific thalamic regions. The present studies tested how TD alters brain pathology in Tg19959 transgenic mice over expressing a double mutant form of the amyloid precursor protein (APP). TD exacerbated amyloid plaque pathology in transgenic mice and enlarged the area occupied by plaques in cortex, hippocampus and thalamus by 50%, 200% and 200%, respectively. TD increased Abeta(1-42) levels by about three fold, beta-CTF (C99) levels by 33% and beta-secretase (BACE1) protein levels by 43%. TD-induced inflammation in areas of plaque formation. Thus, the induction of mild impairment of oxidative metabolism, oxidative stress and inflammation induced by TD alters metabolism of APP and/or Abeta and promotes accumulation of plaques independent of neuron loss or neuritic clusters.

Translocation of amyloid precursor protein C-terminal fragment(s) to the nucleus precedes neuronal death due to thiamine deficiency-induced mild impairment of oxidative metabolism

Thiamine deficiency (TD) is a model of neurodegeneration induced by mild impairment of oxidative metabolism. TD produces time-dependent glial activation, inflammation, oxidative stress, altered metabolism of amyloid precursor protein (APP), exacerbation of plaque formation from APP, and finally, selective neuron death in specific brain regions. The sub-medial thalamic nucleus (SmTN) is the most sensitive region to TD. Alteration in APP metabolism and nuclear translocation of carboxy-terminal fragments (CTF) of APP has been implicated in neuron death in other models of neurodegeneration. These experiments tested whether TD causes translocation of CTF into the nucleus of neurons in the SmTN that are destined to die after 9 days of TD by examining overlapping immunoreactivity (IR) of antibody APP 369 with either Alz90, 6E10 or 4G8 epitopes in the nuclei of the neurons in the SmTN. TD caused the accumulation of the CTF of APP in nuclei of SmTN neurons within 3 days of TD. These changes did not occur in the cortex which is spared in TD. Western blot analysis of nuclear fractions revealed a significant (61%; P < 0.026) increase in CTF 12 levels in TD SmTN (2.08 +/- 0.56) compared to control SmTN (1.29 +/- 0.41). Although TD increased CTF 15 levels in TD SmTN (1.95 +/- 0.73) compared to control SmTN (0.62 +/- 0.52) by 214%; P < 0.665 and decreased the full-length holo-APP levels in TD SmTN (0.32 +/- 0.30) compared to control SmTN (0.47 +/- 0.18) by 34%; P < 0.753, the differences were statistically insignificant. TD did not alter CTF 15 or CTF 12 levels in cortex. These findings demonstrate that changes in APP metabolism occur in early stages of TD, and they may play an important role in TD-induced selective neuronal loss.

Oxidative stress and transcriptional regulation in Alzheimer disease

Alzheimer disease (AD) is defined by progressive impairments in memory and cognition and by the presence of extracellular neuritic plaques and intracellular neurofibrillary tangles. However, oxidative stress and impaired mitochondrial function always accompany AD. Mitochondria are a major site of production of free radicals [ie, reactive oxygen species (ROS)] and primary targets of ROS. ROS are cytotoxic, and evidence of ROS-induced damage to cell membranes, proteins, and DNA in AD is overwhelming. Nevertheless, therapies based on antioxidants have been disappointing. Thus, alternative strategies are necessary. ROS also act as signaling molecules including for transcription. Thus, chronic exposure to ROS in AD could activate cascades of genes. Although initially protective, prolonged activation may be damaging. Thus, therapeutic approaches based on modulation of these gene cascades may lead to effective therapies. Genes involved in several pathways including antioxidant defense, detoxification, inflammation, etc, are induced in response to oxidative stress and in AD. However, genes that are associated with energy metabolism, which is necessary for normal brain function, are mostly down-regulated. Redox-sensitive transcription factors such as activator protein-1, nuclear factor-kappaB, specificity protein-1, and hypoxia-inducible factor are important in redox-dependent gene regulation. Peroxisome proliferators-activated receptor-gamma coactivator (PGC-1alpha) is a coactivator of several transcription factors and is a potent stimulator of mitochondrial biogenesis and respiration. Down-regulated expression of PGC-1alpha has been implicated in Huntington disease and in several Huntington disease animal models. PGC-1alpha role in regulation of ROS metabolism makes it a potential candidate player between ROS, mitochondria, and neurodegenerative diseases. This review summarizes the current progress on how oxidative stress regulates the expression of genes that might contribute to AD pathophysiology and the implications of the transcriptional modifications for AD. Finally, potential therapeutic strategies based on the updated understandings of redox state-dependent gene regulation in AD are proposed to overcome the lack of efficacy of antioxidant therapies.

Responses of the mitochondrial alpha-ketoglutarate dehydrogenase complex to thiamine deficiency may contribute to regional selective vulnerability

Thiamine-dependent enzymes are diminished in multiple neurodegenerative diseases. Thiamine deficiency (TD) reduces the activity of thiamine dependent-enzymes [e.g., the alpha-ketoglutarate dehydrogenase complex (KGDHC)], induces regional selective neurodegeneration and serves as a model of a mild impairment of oxidative metabolism. The current experiments tested whether changes in KGDHC protein subunits (E1k, E2k and E3) or activity or message levels underlie the selective loss of neurons in particular brain regions. Thus, TD-induced changes in these variables in the brain region most vulnerable to TD [the sub-medial thalamic nucleus (SmTN)] were compared to those in a region that is relatively resistant to TD (cortex) at stages of TD when the neuron loss in SmTN is not present, minimal or severe. Impaired motor performance on rotarod was apparent by 8 days of TD (-32%) and was severe by 10 days of TD (-97%). At TD10, the overall KGDHC activity measured by an in situ histochemical staining method declined 52% in SmTN but only 20% in cortex. Reductions in the E2k and E3 mRNA in SmTN occurred as early as TD6 (-28 and -18%, respectively) and were more severe by TD10 (-61 and -66%, respectively). On the other hand, the level of E1k mRNA did not decline in SmTN until TD10 (-48%). In contrast, TD did not alter mRNA levels of the subunits in cortex at late stages. Western blots and immunocytochemistry revealed different aspects of the changes in protein levels. In SmTN, the immunoreactivity of E1k and E3 by Western blotting increased 34 and 40%, respectively, only at TD8. In cortex, the immunoreactivity of the three subunits was not altered. Immunocytochemical staining of brain sections from TD10 mice indicated a reduction in the immunoreactivity of all subunits in SmTN, but not in cortex. These findings demonstrate that the response of the KGDHC activity, mRNA and immunoreactivity of E1k, E2k and E3 to TD is region and time dependent. Loss of KGDHC activity in cortex is likely related to post-translational modification rather than a loss of protein, whereas in SmTN transcriptional and post-translational modifications may account for diminished KGDHC activity. Moreover, the earlier detection in TD induced-changes of the transcripts of KGDHC indicates that transcriptional modification of the two subunits (E2k and E3) of KGDHC may be one of the early events in the cascade leading to selective neuronal death.