Chronic lipopolysaccharide exposure induces cognitive dysfunction without affecting BDNF expression in the rat hippocampus

Dietary menhaden fish oil supplementation suppresses lipopolysaccharide-induced neuroinflammation and cognitive impairment in diabetic rats

CONTEXT

Menhaden fish oil (FO) is widely recognized for inhibiting neuroinflammatory responses and preserving brain function. Nevertheless, the mechanisms of FO influencing brain cognitive function in diabetic states remain unclear.

OBJECTIVE

This study examines the potential role of FO in suppressing LPS-induced neuroinflammation and cognitive impairment in diabetic animals (DA).

MATERIALS AND METHODS

Thirty male Wistar rats were divided into 5 groups: i) DA received LPS induction (DA-LPS); ii) DA received LPS induction and 1 g/kg FO (DA-LPS-1FO); iii) DA received LPS induction and 3 g/kg FO (DA-LPS-3FO); iv) animals received normal saline and 3 g/kg FO (NS-3FO) and v) control animals received normal saline (CTRL). Y-maze test was used to measure cognitive performance, while brain samples were collected for inflammatory markers and morphological analysis.

RESULTS

DA received LPS induction, and 1 or 3 g/kg FO significantly inhibited hyperglycaemia and brain inflammation, as evidenced by lowered levels of pro-inflammatory mediators. Additionally, both DA-LPS-1FO and DA-LPS-3FO groups exhibited a notable reduction in neuronal damage and glial cell migration compared to the other groups. These results were correlated with the increasing number of entries and time spent in the novel arm of the Y-maze test.

DISCUSSION AND CONCLUSION

This study indicates that supplementation of menhaden FO inhibits the LPS signaling pathway and protects against neuroinflammation, consequently maintaining cognitive performance in diabetic animals. Thus, the current study suggested that fish oil may be effective as a supporting therapy option for diabetes to avoid diabetes-cognitive impairment.

Crosstalk between peripheral inflammation and brain: Focus on the responses of microglia and astrocytes to peripheral challenge

A growing body of evidence supports the link between peripheral inflammation and impairment of neurologic functions, including mood and cognitive abilities. The pathogenic event connecting peripheral inflammation and brain dysfunction is represented by neuroinflammation, a pathogenic phenomenon that provides an important contribution to neurodegeneration and cognitive decline also in Alzheimer's, Parkinson's, Huntington's diseases, as well as in Multiple Sclerosis. It is driven by resident brain immune cells, microglia and astrocytes, that acquire an activated phenotype in response to proinflammatory molecules moving from the periphery to the brain parenchyma. Although a huge progress has been made in clarifying cellular and molecular mechanisms bridging peripheral and central inflammation, a clear picture has not been achieved so far. Therefore, experimental models are of crucial relevance to clarify knowledge gaps in this regard. Many findings demonstrate that systemic inflammation induced by pathogen-associated molecular patterns, such as lipopolysaccharide (LPS), is able to trigger neuroinflammation. Therefore, LPS-administration is widely considered a useful tool to study this phenomenon. On this basis, the present review will focus on in vivo studies based on acute and subacute effects of systemic administration of LPS, with special attention on the state of art of microglia and astrocyte response to peripheral challenge.

Neuroprotective effect of human cord blood-derived extracellular vesicles by improved neuromuscular function and reduced gliosis in a rat model of Huntington's disease

Huntington's disease (HD) is a hereditary condition characterized by the gradual deterioration of nerve cells in the striatum. Recent scientific investigations have revealed the promising potential of Extracellular vesicles (EVs) as a therapy to mitigate inflammation and enhance motor function. This study aimed to examine the impact of administering EVs derived from human umbilical cord blood (HUCB) on the motor abilities and inflammation levels in a rat model of HD. After ultracentrifugation to prepare EVs from HUCB to determine the nature of the obtained contents, the expression of CD markers 81 and 9, the average size and also the morphology of its particles were investigated by DLS and Transmission electron microscopy (TEM). Then, in order to induce the HD model, 3-nitropropionic acid (3-NP) neurotoxin was injected intraperitoneal into the rats, after treatment by HUCB-EVs, rotarod, electromyogram (EMG) and the open field tests were performed on the rats. Finally, after rat sacrifice and the striatum was removed, Hematoxylin and eosin staining (H&E), stereology, immunohistochemistry, antioxidant tests, and western blot were performed. Our results showed that the contents of the HUCB-EVs express the CD9 and CD81 markers and have spherical shapes. In addition, the injection of HUCB-EVs improved motor and neuromuscular function, reduced gliosis, increased antioxidant activity and inflammatory factor, and partially prevented the decrease of neurons. The findings generally show that HUCB-EVs have neuroprotective effects and reduce neuroinflammation from the toxic effects of 3-NP, which can be beneficial for the recovery of HD.

Hibiscetin attenuates lipopolysaccharide-evoked memory impairment by inhibiting BDNF/caspase-3/NF-κB pathway in rodents

This study explores the neuroprotective potential of hibiscetin concerning memory deficits induced by lipopolysaccharide (LPS) injection in rats. The aim of this study is to evaluate the effect of hibiscetin against LPS-injected memory deficits in rats. The behavioral paradigms were conducted to access LPS-induced memory deficits. Various biochemical parameters such as acetyl-cholinesterase activity, choline-acetyltransferase, antioxidant (superoxide dismutase, glutathione transferase, catalase), oxidative stress (malonaldehyde), and nitric oxide levels were examined. Furthermore, neuroinflammatory parameters such as tumor necrosis factor-α, interleukin-1β (IL-1β), IL-6, and nuclear factor-kappa B expression and brain-derived neurotrophic factor as well as apoptosis marker i.e., caspase-3 were evaluated. The results demonstrated that the hibiscetin-treated group exhibited significant recovery in LPS-induced memory deficits in rats by using behavioral paradigms, biochemical parameters, antioxidant levels, oxidative stress, neuroinflammatory markers, and apoptosis markers. Recent research suggested that hibiscetin may serve as a promising neuroprotective agent in experimental animals and could offer an alternative in LPS-injected memory deficits in rodent models.

An updated overview on the relationship between human gut microbiome dysbiosis and psychiatric and psychological disorders

There is a lot of evidence establishing that nervous system development is related to the composition and functions of the gut microbiome. In addition, the central nervous system (CNS) controls the imbalance of the intestinal microbiota, constituting a bidirectional communication system. At present, various gut-brain crosstalk routes have been described, including immune, endocrine and neural circuits via the vagal pathway. Several empirical data have associated gut microbiota alterations (dysbiosis) with neuropsychiatric diseases, such as Alzheimer's disease, autism and Parkinson's disease, and with other psychological disorders, like anxiety and depression. Fecal microbiota transplantation (FMT) therapy has shown that the gut microbiota can transfer behavioral features to recipient animals, which provides strong evidence to establish a causal-effect relationship. Interventions, based on prebiotics, probiotics or synbiotics, have demonstrated an important influence of microbiota on neurological disorders by the synthesis of neuroactive compounds that interact with the nervous system and by the regulation of inflammatory and endocrine processes. Further research is needed to demonstrate the influence of gut microbiota dysbiosis on psychiatric and psychological disorders, and how microbiota-based interventions may be used as potential therapeutic tools.

The functional and structural changes in the hippocampus of COVID-19 patients

Since the hippocampus is predominantly susceptible to injuries caused by COVID-19, there are increasing data indicating the likelihood of post-infection memory loss and quickening neurodegenerative disorders, such as Alzheimer's disease. This is due to the fact that the hippocampus has imperative functions in spatial and episodic memory as well as learning. COVID-19 activates microglia in the hippocampus and induces a CNS cytokine storm, leading to loss of hippocampal neurogenesis. The functional and structural changes in the hippocampus of COVID-19 patients can explain neuronal degeneration and reduced neurogenesis in the human hippocampus. This will open a window to explain memory and cognitive dysfunctions in "long COVID" through the resultant loss of hippocampal neurogenesis.

Acute and Chronic Lipopolysaccharide-Induced Stress Changes Expression of Proinflammatory Cytokine Genes in the Rat Brain Region-Specifically and Affects Learning and Memory

Goal of the current work was to conduct comparative analysis of the effects of acute and chronic lipopolysaccharide-induced stress on the behavior of rats in the Morris water maze test and on expression of mRNA of proinflammatory cytokines and BDNF in different brain structures. Relevance of this study is related to poor understanding of the effects of acute and chronic stress on manifestation of cognitive brain functions, as well as ambiguity of the literature data on the effects of both stresses on hypothalamic pituitary axis and expression of the proinflammatory cytokine genes. In the experiments with rats, acute lipopolysaccharide (LPS)-induced stress improved learning in the Morris water maze. For the period of learning, the rats under acute stress swam on average less distance to reach a hidden platform, spent less time in the peripheral zone of the pool (thigmotaxis), and had low speed compared to the control animals and to the group of rats under chronic LPS-induced stress. In the test without a platform in the pool there were no significant differences between the groups on the time spent in the platform quadrant and distance swum. Acute stress caused substantial increase of the TNF-α and IL-1β mRNA concentrations in the hippocampus and amygdala, but not in the frontal lobe in comparison with the control animals. Although chronic stress increased the levels of the TNF-α and IL-1β mRNA in the amygdala and hippocampus compared to the control groups, significance between the groups was only marginal and BDNF concentration did not differ from the control animals in any of the brain structures mentioned. Expression of the IL-6 mRNA only marginally increased in the amygdala of the animals under the acute LPS-induced stress and marginally decreased in the animals under chronic LPS stress in the hippocampus relative to the control groups. In total, the most pronounced molecular-biochemical changes occurred in the amygdala and hippocampus, where increase of the expression of the TNF-α and IL-1β interleukins mRNAs were observed in the animals under acute and chronic LPS-induced stress and no changes in the BDNF mRNA concentration were observed in the frontal lobe.

Cognitive- and memory-enhancing effects of Augmentin in Alzheimer’s rats through regulation of gene expression and neuronal cell apoptosis

Introduction: Alzheimer’s disease (AD) is the most common type of dementia among older persons. This study looked at how Augmentin affected behavior, gene expression, and apoptosis in rats in which AD had been induced by scopolamine.

Methods: The rats were divided into five groups: control, sham, memantine, Augmentin, and pre-Augmentin (the last group received Augmentin before scopolamine administration and was treated with memantine). A Morris water maze was utilized to measure spatial memory in the animals, and real-time quantitative reverse transcription PCR (qRT-PCR) and flow cytometry were employed to analyze gene expression and neuronal cell apoptosis, respectively.

Results: Memantine and Augmentin increased spatial memory in healthy rats. The use of scopolamine impaired spatial memory. Both Augmentin and memantine improved spatial memory in AD rats, particularly in the group that received memantine; however, the outcomes were more substantial when Augmentin was administered before scopolamine was given to induce AD. Furthermore, the expression of presenilin-2 (PSEN2) and inositol-trisphosphate 3-kinase B (ITPKB) increased, whereas the expression of DEAD-box helicase 5 (DDX5) fell in the AD-treated groups; however, the results were more substantial after combination therapy. According to flow cytometry studies, Augmentin pre-treatment reduced apoptosis in AD rats.

Discussion: The results showed that administering Augmentin to AD rats before memantine improved their spatial memory, reduced neuronal cell death, upregulated protective genes, and suppressed genes involved in AD pathogenesis.

Integrated metabolomics and transcriptomics reveal the neuroprotective effect of nervonic acid on LPS-induced AD model mice

Nervonic acid (NA) is one of the long-chain fatty acids with significant biological activity that has been widely studied in recent years. It is believed that NA may play a crucial role in the recovery of human cognitive disorders. Although many literatures have shown that NA has some neuroprotective effect in experimental animal models, the detailed neuroprotective mechanism of NA is still poorly understood. In this study, we applied behavioral, transcriptomic and metabolomic approaches to analyze the neuroprotective effect of NA and its molecular mechanism in AD (Alzheimer's disease) model mice. We demonstrated that NA improved motor skills and learning and memory abilities of mice at the behavioral level. To further understand the specific pathways involved in this protective effect, we applied the metabolomics and transcriptomics profilings and focused on the expression patterns of genes that NA might alter, particularly those related to the accumulation of metabolites in the brain. According to the results, pathways related to neuroinflammation were significantly increased in LPS (lipopolysaccharide)-induced AD mice compared with the normal control, and pathways related to neuronal growth and synaptic plasticity were significantly downregulated. When NA was used for protection, these signaling pathways induced by LPS were partially reversed. At the same time, compared with the AD model group, upregulation of arachidonic acid metabolism, purine metabolism, and primary bile acid biosynthesis and downregulation of amino acid metabolic pathways were particularly pronounced in the NA treatment group. We also verified the enzymes of some metabolic pathways were consistent with transcriptome result. In summary, our results show that NA can significantly ameliorate LPS-induced neuroinflammation and deterioration of learning and memory, and exerts a neuroprotective function through regulation of multiple gene transcription and metabolism pathways. In particular, the arachidonic acid metabolism which related to inflammation and the amino acids metabolism which related to the synthesis of neurotransmitters were most significant response to NA treatment. Our results provided the first preliminary evidences for molecular mechanism investigation of NA from a combined transcriptome and metabolome perspective.

Curcumin attenuates memory impairments and long-term potentiation deficits by damping hippocampal inflammatory cytokines in lipopolysaccharide-challenged rats

Neuroinflammation is a key pathological event triggering neurodegenerative process, resulting in neurologic sequelae. Curcumin (cur) has recently received increasing attention due to its anti-inflammatory properties. Therefore, we investigated the protective effects of curcumin on lipopolysaccharide (LPS)-induced memory impairments, long-term potentiation (LTP) deficits, hippocampal inflammatory cytokines, and neuronal loss in male rats. Rats were randomly divided into four groups as follows: (1) Vehicle; (2) cur; (3) LPS; and (4) cur/LPS. Following curcumin pretreatment (50 mg/kg, per oral via gavage, 14 consecutive days), animals received a single dose of LPS (1 mg/kg, intraperitoneally) or saline. Twenty-four hours after LPS/or saline administration, passive avoidance test (PAT), hippocampal LTP, inflammatory cytokines (TNFα, IL-1β), and neuronal loss were assessed in hippocampal tissue of rats. Our results indicated that pretreatment with curcumin in LPS-challenged rats attenuates memory impairment in PAT, which was accompanied by significant increase in the field excitatory post-synaptic potential (fEPSP) slope and population spike (PS) amplitude. Hence, pretreatment with curcumin in LPS-treated rats decreased hippocampal concentration of tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β), as well as reduced neuronal loss in the hippocampal tissue. This study provide evidence that pretreatment with curcumin attenuates LPS-induced memory impairment and LTP deficiency, which may be partly related to the amelioration of inflammatory cytokines and neuronal loss in the hippocampal tissue.

COVID-19 causes neuronal degeneration and reduces neurogenesis in human hippocampus

Recent investigations of COVID-19 have largely focused on the effects of this novel virus on the vital organs in order to efficiently assist individuals who have recovered from the disease. In the present study we used hippocampal tissue samples extracted from people who died after COVID-19. Utilizing histological techniques to analyze glial and neuronal cells we illuminated a massive degeneration of neuronal cells and changes in glial cells morphology in hippocampal samples. The results showed that in hippocampus of the studied brains there were morphological changes in pyramidal cells, an increase in apoptosis, a drop in neurogenesis, and change in spatial distribution of neurons in the pyramidal and granular layer. It was also demonstrated that COVID-19 alter the morphological characteristics and distribution of astrocyte and microglia cells. While the exact mechanism(s) by which the virus causes neuronal loss and morphology in the central nervous system (CNS) remains to be determined, it is necessary to monitor the effect of SARS-CoV-2 infection on CNS compartments like the hippocampus in future investigations. As a result of what happened in the hippocampus secondary to COVID-19, memory impairment may be a long-term neurological complication which can be a predisposing factor for neurodegenerative disorders through neuroinflammation and oxidative stress mechanisms.

Omarigliptin/galangin combination mitigates lipopolysaccharide-induced neuroinflammation in rats: Involvement of glucagon-like peptide-1, toll-like receptor-4, apoptosis and Akt/GSK-3β signaling

AIMS

The objectives of this work were to assess the possibility of administration of omarigliptin and/or galangin to combat lipopolysaccharide (LPS)-induced neuroinflammation in rats and to explore the possible mechanisms that might contribute to their actions.

MATERIALS AND METHODS

In a rat model of LPS-induced neuroinflammation, the changes in the behavioral tests, biochemical parameters, and the histopathological picture were assessed.

KEY FINDINGS

Administration of either omarigliptin or galangin to LPS-injected rats was able to significantly improve the behavioral changes with restoration of the oxidant/antioxidant balance, decrement of toll-like receptor-4 levels, and amelioration of the neuroinflammation associated with inhibition of apoptosis and restoration of glucagon-like peptide-1 levels in the cerebral tissues. In addition, omarigliptin and/or galangin significantly reduced the levels of phospho-Akt and glycogen synthase kinase 3 beta (GSK-3β) and significantly increased the expression of beclin-1 in the cerebral tissues compared versus the group treated with LPS alone. As a result, these changes were positively reflected on the histopathological and the electron microscopic picture of the cerebral tissues. These beneficial effects were maximally evidenced in rats treated with omarigliptin/galangin combination relative to the use of either omarigliptin or galangin alone.

SIGNIFICANCE

Omarigliptin/galangin combination might be proposed as a promising therapeutic line for mitigation of the pathophysiologic events of LPS-induced neuroinflammation.

Effect of forced treadmill exercise on stimulation of BDNF expression, depression symptoms, tactile memory and working memory in LPS-treated rats

Neuroinflammation has been implicated in cognitive dysfunction and the occurrence of depression in neurodegenerative diseases. Brain-derived neurotrophic factor (BDNF) is believed to be involved with the benefits of exercise training in boosting memory and learning processes and antidepressant therapies. This study aimed to investigate the effect of forced treadmill exercise on hippocampal BDNF expression levels, depression symptoms, tactile memory and working memory in lipopolysaccharide (LPS)-treated rats. For this purpose, 40 male Wistar rats received 0.25 mg/kg of LPS or saline intraperitoneally for 9 consecutive days before exercise. They again received a single injection of 0.5 mg/kg of LPS or saline on days 20 and 41 after exercise. Exercise groups had to run on a motorized treadmill 5 days a week for 8 weeks. Following the last exercise training session, forced swim test (FST), Y maze and novel object recognition (NOR) task were performed. Finally, the hippocampus of rats was removed and used for determination of BDNF expression levels by real-time polymerase chain reaction (real-time PCR). The data showed that LPS decreased BDNF expression levels, Y maze score, and recognition index in NOR and increased immobility time in FST (p < 0.05). In contrast, forced treadmill exercise increased BDNF expression levels and improved the percentage of spontaneous alternation, recognition index, and immobility time in LPS-treated rats (p < 0.05). There was a significant correlation between BDNF expression levels with immobility time and recognition index (p < 0.05) but not with the percentage of spontaneous alternation (p > 0.05). The findings suggest that forced treadmill exercise may protect the brain of LPS-treated rats by improving the symptoms of depression and cognitive function through its effect on BDNF expression levels.

Amyloid beta acts synergistically as a pro-inflammatory cytokine

The amyloid beta (Aβ) peptide is believed to play a central role in Alzheimer's disease (AD), the most common age-related neurodegenerative disorder. However, the natural, evolutionarily selected functions of Aβ are incompletely understood. Here, we report that nanomolar concentrations of Aβ act synergistically with known cytokines to promote pro-inflammatory activation in primary human astrocytes (a cell type increasingly implicated in brain aging and AD). Using transcriptomics (RNA-seq), we show that Aβ can directly substitute for the complement component C1q in a cytokine cocktail previously shown to induce astrocyte immune activation. Furthermore, we show that astrocytes synergistically activated by Aβ have a transcriptional signature similar to neurotoxic "A1" astrocytes known to accumulate with age and in AD. Interestingly, we find that this biological action of Aβ at low concentrations is distinct from the transcriptome changes induced by the high/supraphysiological doses of Aβ often used in in vitro studies. Collectively, our results suggest an important, cytokine-like function for Aβ and a novel mechanism by which it may directly contribute to the neuroinflammation associated with brain aging and AD.

Hydrogen sulfide and mesenchymal stem cells-extracted microvesicles attenuate LPS-induced Alzheimer's disease

Both hydrogen sulfide (H2 S) and mesenchymal stem cells (MSCs) extracted microvesicles (MVs) are potent anti-inflammatory molecules. They play an essential role in lowering the production of tumor necrosis factor-alpha (TNF-α). The latter could strongly stimulate MiR-155 that contributes to neurodegeneration and Alzheimer's disease (AD). miR-155 could repress the expression of inositol 5-phosphatase-1 (SHIP-1) leading eventually to activation of Akt kinase and neurofibrillary development in AD. The current study was conducted to evaluate the role of miR-155 in a rat model of lipopolysaccharide (LPS)-induced AD and to investigate the effect of using MVs and H2 S that were given either separately or combined in regulating pro-inflammatory signaling. Thirty female Wistar albino rats aged 6 months to 1 year were equally divided into five groups; control group, LPS-induced AD group, LPS + MVs group, LPS + NaHS group, and LPS + MVs and NaHS group. The increased miR-155 level was associated with decreased SHIP-1 level and positively correlated with TNF-α. In addition, treatment with MVs and/or NaHS resulted in attenuation of inflammation, decreasing miR-155, pAkt levels, and downregulation of apoptosis along with improvement of the hippocampal and cortical histopathological alterations. LPS enhanced production of malondialdehyde (MDA) and reduced glutathione (GSH) levels indicating oxidative stress-induced neural damage, whereas MVs and NaHS could mitigate oxidative damage and accelerate antioxidant capacity via increasing catalase enzyme. In conclusion, downregulation of TNF-α, miR-155, and pAkt and increased SHIP-1 could improve the neuro-inflammatory state and cognitive function of LPS-induced Alzheimer's disease.

Role of microbes in the pathogenesis of neuropsychiatric disorders

Microbes inhabit different anatomical sites of the human body including oral cavity, gut, and skin. A growing literature highlights how microbiome variation is associated with human health and disease. There is strong evidence of bidirectional communication between gut and brain mediated by neurotransmitters and microbial metabolites. Here, we review the potential involvement of microbes residing in the gut and in other body sites in the pathogenesis of eight neuropsychiatric disorders, discussing findings from animal and human studies. The data reported provide a comprehensive overview of the current state of the microbiome research in neuropsychiatry, including hypotheses about the mechanisms underlying the associations reported and the translational potential of probiotics and prebiotics.

A Review of the Brain-Gut-Microbiome Axis and the Potential Role of Microbiota in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative process characterized by loss of neurons in the hippocampus and cerebral cortex, leading to progressive cognitive decline. Pathologically, the hallmark of AD is accumulation of "senile" plaques composed of amyloid-β (Aβ) protein surrounding neurons in affected regions. Despite extensive research into AD pathogenesis and therapeutic targets, there remains no breakthroughs in its management. In recent years, there has been a spark of interest in the connection between the brain and gastrointestinal tract, referred to as the brain-gut axis, and its potential implications for both metabolic and neurologic disease. Moreover, the gastrointestinal flora, referred to as the microbiome, appears to exert significant influence over the brain-gut axis. With the need for expanded horizons in understanding and treating AD, many have turned to the brain-gut-microbiome axis for answers. Here we provide a review of the brain-gut-microbiome axis and discuss the evidence supporting alterations of the axis in the pathogenesis of AD. Specifically, we highlight the role for the microbiome in disruption of Aβ metabolism/clearance, increased permeability of the blood-brain barrier and modulation of the neuroinflammatory response, and inhibition of hippocampal neurogenesis. The majority of the above described findings are the result of excellent, albeit basic and pre-clinical studies. Therefore, we conclude with a brief description of documented clinical support for brain-gut-microbiome axis alteration in AD, including potential microbiome-based therapeutics for AD. Collectively, these findings suggest that the brain-gut-microbiome axis may be a "lost link" in understanding and treating AD and call for future work.

Reversal of lipopolysaccharide-induced learning and memory deficits by agmatine in mice

MATERIALS AND METHODS

Learning and memory functions in animals were evaluated by using Novel object recognition (NOR) and Morris water maze (MWM) tests. Following 7 days of LPS administration, animals were subjected to NOR test on Day-8 and MWM test on Days-9 to 13 for the assessment of recognition and spatial learning and memory, respectively.

RESULTS

LPS administration produced significant deficits in recognition and spatial memory in mice after seven days of LPS administration. In LPS pre-treated mice, agmatine treatment on Day-8 resulted in the increased exploration to the novel object. Agmatine treatment (Day 8-12) in mice showed reduction in the escape latency and time spent in the target quadrant (probe trial) in the MWM test. However, co-administration of agmatine with LPS in mice for 7 days showed higher discrimination index in NOR test on Day-8. This co-administration also decreased escape latency and time spent in the target quadrant in MWM test on Days 9-13 as compared to LPS control group.

CONCLUSION

Results implies the protective and curative effects of agmatine against LPS-induced loss of memory functions in experimental animals.HighlightsSubchronic but not acute lipopolysaccharides induce memory deficitsLipopolysaccharides impairs recognition and spatial memory in mice.Agmatine prevents lipopolysaccharides-induced loss of memory.Agmatine reverses deficits in learning and memory by lipopolysaccharides.

Effects of crocin on spatial or aversive learning and memory impairments induced by lipopolysaccharide in rats

OBJECTIVE

Neuroinflammation and oxidative stress play essential roles in the pathogenesis and progression of neurodegenerative diseases, such as Alzheimer's disease. Crocin, main active constituent of Crocus sativus L. (saffron), possesses anti-inflammatory, anti-apoptotic and anti-oxidative capacity. The aim of the present study was to investigate the neuroprotective effect of crocin on lipopolysaccharide (LPS)-induced learning and memory deficits and neuroinflammation in rats.

MATERIALS AND METHODS

The animals were randomly classified into four groups, including control, LPS, crocin 50 and crocin 100. The rats were treated with either crocin (50 and 100 mg/kg) or saline for a week. Later, LPS (1 mg/kg, i.p.) or saline was administered, and treatments with crocin or saline were continued for 3 more weeks. The behavioral tasks for spatial and aversive memories were performed by the Morris water maze and passive avoidance tasks from post-injection days 18 to 24. Furthermore, the levels of interleukine-1β, lipid peroxidation and total thiol were assayed in the hippocampus and cerebral cortex.

RESULTS

Our results demonstrated that treatment of LPS-treated rats with crocin decreased the escape latency in the Morris water maze and increased the time spent in the target quadrant in the probe trial. Moreover, crocin increased step-through latency in the passive avoidance test. However, there was no significant difference in the oxidative and neuroinflammatory responses among the experimental groups.

CONCLUSION

Pretreatment with crocin attenuates spatial or aversive learning and memory deficits in LPS-treated rats.

Diet, Microbiota and Brain Health: Unraveling the Network Intersecting Metabolism and Neurodegeneration

Increasing evidence gives support for the idea that extra-neuronal factors may affect brain physiology and its predisposition to neurodegenerative diseases. Epidemiological and experimental studies show that nutrition and metabolic disorders such as obesity and type 2 diabetes increase the risk of Alzheimer's and Parkinson's diseases after midlife, while the relationship with amyotrophic lateral sclerosis is uncertain, but suggests a protective effect of features of metabolic syndrome. The microbiota has recently emerged as a novel factor engaging strong interactions with neurons and glia, deeply affecting their function and behavior in these diseases. In particular, recent evidence suggested that gut microbes are involved in the seeding of prion-like proteins and their spreading to the central nervous system. Here, we present a comprehensive review of the impact of metabolism, diet and microbiota in neurodegeneration, by affecting simultaneously several aspects of health regarding energy metabolism, immune system and neuronal function. Advancing technologies may allow researchers in the future to improve investigations in these fields, allowing the buildup of population-based preventive interventions and development of targeted therapeutics to halt progressive neurologic disability.

Ellagic Acid Inhibits Neuroinflammation and Cognitive Impairment Induced by Lipopolysaccharides

Neuroinflammation is a predisposing factor for the development of cognitive impairment and dementia. Among the new molecules that are currently being studied, ellagic acid (EA) has stood out for its neuroprotective properties. The present study investigated the effects of ellagic acid in the object recognition test, oxidative stress, cholinergic neurotransmission, glial cell expression, and phosphorylated Tau protein expression. For this, 32 male Wistar rats received an intraperitoneal (IP) application of lipopolysaccharides (LPS) at a dose of 250 µg/kg or 0.9% saline solution (SAL) for 8 days. Two hours after the IP injections, the animals received 100 mg/kg of EA or SAL via intragastric gavage. Behavioral parameters (open field test and object recognition) were performed on days 5, 6, and 7 of the experimental periods. The results showed that the treatment with EA in the LPS group was able to inhibit cognitive impairment, modulate the immune system response by significantly reducing glial cell expression, attenuating phosphorylated Tau and oxidative damage with consequent improvement in the antioxidant system, as well as preventing the increase of acetylcholinesterase activity. Thus, the neuroprotective effects of EA and its therapeutic potential in cognitive disorders secondary to neuroinflammation were demonstrated.

Tualang Honey and its Methanolic Fraction Improve LPS-induced Learning and Memory Impairment in Male Rats: Comparison with Memantine

Background:

Tualang honey (TH) has been shown to exert beneficial effects on learning and memory function in various animal models. However, its learning and memory effects in lipopolysaccharide (LPS) rat model have not been elucidated.

Objective:

The present study aimed to investigate the cognitive-enhancing effects of TH and its methanolic fraction in comparison to the clinically approved N-methyl-D-aspartate (NMDA) receptor antagonist (memantine) using LPS rat model.

Methods:

A total of ninety male Sprague Dawley rats were divided into 5 groups: (i) control, (ii) untreated LPS (iii) LPS treated with 200 mg/kg TH, (iv) LPS treated with 150 mg/kg methanol fraction of TH (MTH) and (v) LPS treated with 10 mg/kg memantine. All treatments were administered intraperitoneally once daily for 14 days. Morris water maze (MWM) and novel object recognition (NOR) tests were performed to assess spatial and recognition memory function.

Results:

The present study confirmed that LPS significantly impairs spatial and recognition memory and alone treatment with TH or MTH improved spatial and recognition memory comparable to memantine.

Conclusion:

Both TH and its methanolic fraction improved spatial and recognition memory of LPS rat model comparable to memantine. Thus, TH and its methanolic fraction have potential preventivetherapeutic effects for neurodegenerative diseases involving neuroinflammation.

Effect of Systemic Inflammation on Rat Attentional Function and Neuroinflammation: Possible Protective Role for Food Restriction

Background: Aging is characterized by subtle cognitive decline, which correlates with increased peripheral inflammation. Acute activation of the peripheral immune system, via lipopolysaccharide (LPS) injection, elicits deficits in hippocampal-dependent spatial memory. Little is known concerning the effect of chronic inflammation on prefrontal cortex (PFC)-dependent vigilance. We examined the impact of repeated LPS injections in young and middle-age rats on the 5-choice serial reaction time task (5-CSRTT), expecting repeated LPS treatment to induce attentional deficits with greater disruption in middle-age. Methods: Male Fischer-344 rats, 4- and 12-months-old, were food restricted and trained on the 5-CSRTT. Once rats reached criterion, they were injected with LPS (1 mg/kg, i.p.) weekly for 4 weeks and testing started 48 h after each injection. To examine the possibility that mild food restriction inherent to the behavioral task influenced inflammation markers, a second group of food-restricted or ad-lib-fed rats was assessed for cytokine changes 48 h after one injection. Results: Performing LPS-treated rats exhibited a sickness response, manifesting as reduced initiated and completed trials during the first week but recovered by the second week of testing. After the first week, LPS-treated rats continued to exhibit longer response latencies, despite no change in food retrieval latency, suggestive of LPS-induced cognitive slowing. Similarly, LPS-induced impairment of attention was observed as increased omissions with heightened cognitive demand and increased age. Repeated LPS-treatment increased the level of PFC IL-1α, and PFC IL-6 was marginally higher in middle-age rats. No effect of age or treatment was observed for plasma cytokines in performing rats. Histological examination of microglia indicated increased colocalization of Iba1+ and CD68+ cells from middle-age relative to young rats. Examination of food restriction demonstrated an attenuation of age- and LPS-related increases in plasma cytokine levels. Conclusions: Systemic inflammation, induced through LPS treatment, impaired attentional function, which was independent of sickness and exacerbated by increased cognitive demand and increased age. Additional studies revealed that food restriction, associated with the task, attenuated markers of neuroinflammation and plasma cytokines. The results emphasize the need for improved methods for modeling low-level chronic systemic inflammation to effectively examine its impact on attention during aging.

Activation of microglia and astrocytes: a roadway to neuroinflammation and Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that is of high importance to the neuroscience world, yet the complex pathogenicity is not fully understood. Inflammation is usually observed in AD and could implicate both beneficial or detrimental effects depending on the severity of the disease. During initial AD pathology, microglia and astrocyte activation is beneficial since they are involved in amyloid-beta clearance. However, with the progression of the disease, activated microglia elicit detrimental effects by the overexpression of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) bringing forth neurodegeneration in the surrounding brain regions. This results in decline in Aβ clearance by microglia; Aβ accumulation thus increases in the brain resulting in neuroinflammation. Thus, Aβ accumulation is the effect of increased release of pro-inflammatory molecules. Reactive astrocytes acquire gain of toxic function and exhibits neurotoxic effects with loss of neurotrophic functions. Astrocyte dysfunctioning results in increased release of cytokines and inflammatory mediators, neurodegeneration, decreased glutamate uptake, loss of neuronal synapses, and ultimately cognitive deficits in AD. We discuss the role of intracellular signaling pathways in the inflammatory responses produced by astrocytes and microglial activation, including the glycogen synthase kinase-3β, nuclear factor kappa B cascade, mitogen-activated protein kinase pathways and c-Jun N-terminal kinase. In this review, we describe the role of neuroinflammation in the chronicity of AD pathogenesis and an overview of the recent research towards the development of new therapies to treat this disorder.

Berberine ameliorates lipopolysaccharide-induced learning and memory deficit in the rat: insights into underlying molecular mechanisms

Systemic lipopolysaccharide (LPS) triggers neuroinflammation with consequent development of behavioral and cognitive deficits. Neuroinflammation plays a crucial role in the pathogenesis of neurodegenerative disorders including Alzheimer's disease (AD). Berberine is an isoquinoline alkaloid in Berberis genus with antioxidant and anti-inflammatory property and protective effects in neurodegenerative disorders. In this research, beneficial effect of this alkaloid against LPS-induced cognitive decline was assessed in the adult male rats. LPS was intraperitoneally administered at a dose of 1 mg/kg to induce neuroinflammation and berberine was given via gavage at doses of 10 or 50 mg/kg, one h after LPS, for 7 days. Treatment of LPS group with berberine at a dose of 50 mg/kg (but not at a dose of 10 mg/kg) improved spatial recognition memory in Y maze, performance in novel object recognition task (NORT), and prevented learning and memory dysfunction in passive avoidance tasks. Furthermore, berberine lowered hippocampal activity of acetylcholinesterase (AChE), malondialdehyde (MDA), protein carbonyl, activity of caspase 3, and DNA fragmentation and improved antioxidant capacity through enhancing glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase, and glutathione (GSH). Besides, berberine attenuated inflammation-related indices, as was evident by lower levels of nuclear factor-kappa B (NF-κB), toll-like receptor 4 (TLR4), tumor necrosis factor α (TNFα), and interleukin 6 (IL-6). Berberine also appropriately restored hippocampal 3-nitrotyrosine (3-NT), cyclooxygenase 2 (Cox 2), glial fibrillary acidic protein (GFAP), sirtuin 1, and mitogen-activated protein kinase (p38 MAPK) with no significant alteration of brain-derived neurotrophic factor (BDNF). In summary, berberine could partially ameliorate LPS-induced cognitive deficits via partial suppression of apoptotic cascade, neuroinflammation, oxido-nitrosative stress, AChE, MAPK, and restoration of sirtuin 1.

Mahdy E, R. Youness E, Shafee N, S.S. Mowafy M, M. Mabrouk M. Effect of Co Enzyme Q10 Alone or in Combination with Vitamin C on Lipopolysaccharide-Induced Brain Injury in Rats

Our was to determine the impact of CoenzymeQ10 (Co Q10) and vitamin C alone or in combination on oxidative stress in brain tissue of rats during endotoxemia induced by single intraperitoneal dose of Lipopolysaccharide (LPS), 500µg/kg. Both CoQ10&vitamin C were given orally to rats with doses (200&100 mg/kg) respectively for 7successive days prior induction of endotoxemia .LPS injected, with Co Q10 with doses (100 &200 mg/kg) &vit. C (50&100 mg/kg).In addition CoQ10 and vitamin C together in doses (100&50 mg/kg) & (200&100 mg/kg) respectively were added to LPS-treated rats. Then euthanized 4 hours later. Histopathological assessment of brain tissue was done. Results: LPS injection induced oxidative stress in brain tissue, resulting in marked increase in malondiadehyde (MDA), nitrite (NO) and Amyloid beta (Aβ), while decreasing reduced glutathione (GSH), paraoxonase-1 (PON1) and brain derived neurotrophic factor (BDNF).CoQ10 and vit.C administration with doses(200&100 mg/ kg) before endotoxemia result in reduction of brain MDA, NO and Aβ, while increasing levels of GSH, PON1 and BDNF compared to controls. The addition of both Co Q10 &vit.C to LPS- treated rats lead to decrease of brain NO, MDA and Aβ, also increase of GSH, PON1 and BDNF. This effect was more obviouswith high doses, this due to the ameliorating effect of both CoQ10 and vit.C on oxidative stress of brain tissue during endotoxemia.This consisted with the histopathological results. Conclusion: this work focuses on the possible role of CoQ10 &vit.C as antioxidants in protecting brain tissue.

Sulforaphane Alleviates Lipopolysaccharide-induced Spatial Learning and Memory Dysfunction in Mice: The Role of BDNF-mTOR Signaling Pathway

Peripheral immune activation could cause neuroinflammation, leading to a series of central nervous system (CNS) disorders, such as spatial learning and memory dysfunction. However, its pathogenic mechanism and therapeutic strategies are not yet determined. The present study aimed to investigate the therapeutic effects of sulforaphane (SFN) on lipopolysaccharide (LPS)-induced spatial learning and memory dysfunction, and tried to elucidate its relationship with the role of hippocampal brain-derived neurotrophic factor (BDNF)-mammalian target of rapamycin (mTOR) signaling pathway. Intraperitoneal injection of LPS for consecutive 7 days to mice caused abnormal behaviors in Morris water maze test (MWMT), while systemic administration of SFN notably reversed the abnormal behaviors. In addition, hippocampal levels of inflammatory cytokines, synaptic proteins, BDNF-tropomyosin receptor kinase B (TrkB) and mTOR signaling pathways were altered in the processes of LPS-induced cognitive dysfunction and SFN's therapeutic effects. Furthermore, we found that ANA-12 (a TrkB inhibitor) or rapamycin (a mTOR inhibitor) could block the beneficial effects of SFN on LPS-induced cognitive dysfunction, and that hippocampal levels of synaptic proteins, BDNF-TrkB and mTOR signaling pathways were also notably changed. In conclusion, the results of the present study suggest that SFN could elicit improving effects on LPS-induced spatial learning and memory dysfunction, which is likely related to the regulation of hippocampal BDNF-mTOR signaling pathway.

Anthocyanins Improve Hippocampus-Dependent Memory Function and Prevent Neurodegeneration via JNK/Akt/GSK3β Signaling in LPS-Treated Adult Mice

Microglia plays a critical role in the brain and protects neuronal cells from toxins. However, over-activation of microglia leads to deleterious effects. Lipopolysaccharide (LPS) has been reported to affect neuronal cells via activation of microglia as well as directly to initiate neuroinflammation. In the present study, we evaluated the anti-inflammatory and anti-oxidative effect of anthocyanins against LPS-induced neurotoxicity in an animal model and in cell cultures. Intraperitoneal injections of LPS (250 μg/kg/day for 1 week) induce ROS production and promote neuroinflammation and neurodegeneration which ultimately leads to memory impairment. However, anthocyanins treatment at a dose of 24 mg/kg/day for 2 weeks (1 week before and 1 week co-treated with LPS) prevented ROS production, inhibited neuroinflammation and neurodegeneration, and improved memory functions in LPS-treated mice. Both histological and immunoblot analysis indicated that anthocyanins reversed the activation of JNK, prevented neuroinflammation by lowering the levels of inflammatory markers (p-NF-kB, TNF-α, and IL-1β), and reduced neuronal apoptosis by reducing the expression of Bax, cytochrome c, cleaved caspase-3, and cleaved PARP-1, while increasing the level of survival proteins p-Akt, p-GSK3β, and anti-apoptotic Bcl-2 protein. Anthocyanins treatment increased the levels of memory-related pre- and post-synaptic proteins and improved the hippocampus-dependent memory in the LPS-treated mice. Overall, this data suggested that consumption of naturally derived anti-oxidant agent such as anthocyanins ameliorated several pathological events in the LPS-treated animal model and we believe that anthocyanins would be a safe therapeutic agent for slowing the inflammation-induced neurodegeneration in the brain against several diseases such as Alzheimer's disease and Parkinson's disease.

IDO chronic immune activation and tryptophan metabolic pathway: A potential pathophysiological link between depression and obesity

Obesity and depression are among the most pressing health problems in the contemporary world. Obesity and depression share a bidirectional relationship, whereby each condition increases the risk of the other. By inference, shared pathways may underpin the comorbidity between obesity and depression. Activation of cell-mediated immunity (CMI) is a key factor in the pathophysiology of depression. CMI cytokines, including IFN-γ, TNFα and IL-1β, induce the catabolism of tryptophan (TRY) by stimulating indoleamine 2,3-dioxygenase (IDO) resulting in the synthesis of kynurenine (KYN) and other tryptophan catabolites (TRYCATs). In the CNS, TRYCATs have been related to oxidative damage, inflammation, mitochondrial dysfunction, cytotoxicity, excitotoxicity, neurotoxicity and lowered neuroplasticity. The pathophysiology of obesity is also associated with a state of aberrant inflammation that activates aryl hydrocarbon receptor (AHR), a pathway involved in the detection of intracellular or environmental changes as well as with increases in the production of TRYCATs, being KYN an agonists of AHR. Both AHR and TRYCATS are involved in obesity and related metabolic disorders. These changes in the TRYCAT pathway may contribute to the onset of neuropsychiatric symptoms in obesity. This paper reviews the role of immune activation, IDO stimulation and increased TRYCAT production in the pathophysiology of depression and obesity. Here we suggest that increased synthesis of detrimental TRYCATs is implicated in comorbid obesity and depression and is a new drug target to treat both diseases.

A noradrenergic lesion aggravates the effects of systemic inflammation on the hippocampus of aged rats

Neuroinflammation is potentiated by early degeneration of the locus coeruleus noradrenergic pathway (LC-NE) commonly seen in aging-related neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. In animal models, lipopolysaccharide (LPS) induces strong peripheral immune responses that can cause cognitive changes secondary to neuroinflammation. The influence of the peripheral immune response on cognition might be exacerbated by LC-NE degeneration, but this has not been well characterized previously. In this study, we investigated how systemic inflammation affects neuroinflammation and cognition in aged rats that have had either normal or damaged LC-NE transmitter systems. Rats were first exposed to the selective noradrenergic (NE) neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) to induce degeneration of central NE pathways. Two weeks later, the rats received a low dose of LPS. This resulted in 3 treatment groups (Control, LPS-, and DSP4+LPS-treated rats) studied at 4 hours (short-term subgroup) and 7 days (long-term subgroup) following the LPS injection. DSP4+LPS-treated rats exhibited increased serum levels of several pro-inflammatory cytokines, increased astroglial and microglial activation in the hippocampus, and poorer performance in the novel object recognition task (NORT) compared to controls and LPS-treated rats. Additionally, serum and brain tissue levels of brain-derived neurotrophic factor (BDNF) were modulated over time in the DSP4+LPS group compared to the other two groups. Specifically, DSP4+LPS-treated rats in the short-term subgroup had lower hippocampal BDNF levels (~25%) than controls and LPS-treated rats, which negatively correlated with hippocampal astrogliosis and positively correlated with hippocampal IL-1β levels. Serum and hippocampal BDNF levels in the DSP4+LPS-treated rats in the long-term subgroup returned to levels similar to the control group. These results show that systemic inflammation in LC-NE-lesioned aged rats promotes an exacerbated systemic and central inflammatory response compared to LC-NE-intact rats and alters BDNF levels, indicating the important role of this neurotransmitter system in response to neuroinflammation.

Antarctic Krill Oil Diet Protects against Lipopolysaccharide-Induced Oxidative Stress, Neuroinflammation and Cognitive Impairment

Oxidative stress and neuroinflammation are implicated in the development and pathogenesis of Alzheimer’s disease (AD). Here, we investigated the anti-inflammatory and antioxidative effects of krill oil. Oil from Euphausia superba (Antarctic krill), an Antarctic marine species, is rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We examined whether krill oil diet (80 mg/kg/day for one month) prevents amyloidogenesis and cognitive impairment induced by intraperitoneal lipopolysaccharide (LPS) (250 µg/kg, seven times daily) injections in AD mice model and found that krill oil treatment inhibited the LPS-induced memory loss. We also found that krill oil treatment inhibited the LPS-induced expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) and decreased reactive oxygen species (ROS) and malondialdehyde levels. Krill oil also suppresses IκB degradation as well as p50 and p65 translocation into the nuclei of LPS-injected mice brain cells. In association with the inhibitory effect on neuroinflammation and oxidative stress, krill oil suppressed amyloid beta (1–42) peptide generation by the down-regulating APP and BACE1 expression in vivo. We found that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (50 and 100 µM) dose-dependently decreased LPS-induced nitric oxide and ROS generation, and COX-2 and iNOS expression as well as nuclear factor-κB activity in cultured microglial BV-2 cells. These results suggest that krill oil ameliorated impairment via anti-inflammatory, antioxidative, and anti-amyloidogenic mechanisms.

Microbiome-Derived Lipopolysaccharide Enriched in the Perinuclear Region of Alzheimer's Disease Brain

Abundant clinical, epidemiological, imaging, genetic, molecular, and pathophysiological data together indicate that there occur an unusual inflammatory reaction and a disruption of the innate-immune signaling system in Alzheimer’s disease (AD) brain. Despite many years of intense study, the origin and molecular mechanics of these AD-relevant pathogenic signals are still not well understood. Here, we provide evidence that an intensely pro-inflammatory bacterial lipopolysaccharide (LPS), part of a complex mixture of pro-inflammatory neurotoxins arising from abundant Gram-negative bacilli of the human gastrointestinal (GI) tract, are abundant in AD-affected brain neocortex and hippocampus. For the first time, we provide evidence that LPS immunohistochemical signals appear to aggregate in clumps in the parenchyma in control brains, and in AD, about 75% of anti-LPS signals were clustered around the periphery of DAPI-stained nuclei. As LPS is an abundant secretory product of Gram-negative bacilli resident in the human GI-tract, these observations suggest (i) that a major source of pro-inflammatory signals in AD brain may originate from internally derived noxious exudates of the GI-tract microbiome; (ii) that due to aging, vascular deficits or degenerative disease these neurotoxic molecules may “leak” into the systemic circulation, cerebral vasculature, and on into the brain; and (iii) that this internal source of microbiome-derived neurotoxins may play a particularly strong role in shaping the human immune system and contributing to neural degeneration, particularly in the aging CNS. This “Perspectives” paper will further highlight some very recent developments that implicate GI-tract microbiome-derived LPS as an important contributor to inflammatory-neurodegeneration in the AD brain.

Lipopolysaccharide-induced memory impairment in rats: a model of Alzheimer's disease

Alzheimer's disease (AD) is a primary cause of dementia in the middle-aged and elderly worldwide. Animal models for AD are widely used to study the disease mechanisms as well as to test potential therapeutic agents for disease modification. Among the non-genetically manipulated neuroinflammation models for AD, lipopolysaccharide (LPS)-induced animal model is commonly used. This review paper aims to discuss the possible factors that influence rats' response following LPS injection. Factors such as dose of LPS, route of administration, nature and duration of exposure as well as age and gender of animal used should be taken into account when designing a study using LPS-induced memory impairment as model for AD.

Environmental Enrichment Improves Spatial Learning and Memory in Vascular Dementia Rats with Activation of Wnt/β-Catenin Signal Pathway

Background

Environmental enrichment (EE) has a beneficial effect on some neuropsychiatric disorders. In this study, we aimed to investigate whether environmental enrichment could improve the spatial learning and memory in rats with vascular dementia (VaD) and the mechanism underpinning it.

Material/Methods

Bilateral common carotid occlusion (2-vessel occlusion [2VO]) was used to develop the animal model of vascular dementia. Adult male Sprague-Dawley (SD) rats were used in the experiment and were randomly divided into 4 groups: sham group, 2VO group, sham+EE group, and 2VO+EE group (n=19/group). The 2VO group and 2VO+EE group underwent bilateral common carotid occlusion. Two different housing conditions were used in this experiment: standard environment (SE) and enriched environment (EE). Rats in the sham group and 2VO group were put into SE cages for 4 weeks, while rats in the sham+EE group and 2VO+EE group were put in EE cages for 4 weeks. The Morris water maze and Y-maze were used to assess spatial learning and memory. Apoptosis was detected by TUNEL. The damage of neurons in the hippocampus was assessed by Nissl staining. The level of wnt pathway proteins were detected by Western blot.

Results

Compared with the 2VO group, the rats in the 2VO+EE group had better behavioral performance, fewer apoptotic neurons, and more surviving neurons. Western blot analysis showed that the levels of wnt pathway proteins were higher in 2VO+EE rats than in the 2VO group.

Conclusions

Environmental enrichment can improve the spatial learning and memory in rats with vascular dementia, and the mechanism may be related to activation of the wnt/β-catenin signal pathway.

Tocilizumab's effect on cognitive deficits induced by intracerebroventricular administration of streptozotocin in Alzheimer's model

Neuroinflammation plays pivotal roles in the pathogenesis of Alzheimer's disease (AD). IL-6 is pleiotropic cytokine which plays significant pathological role in inflammatory diseases and causes prolonged inflammation. Additionally, IL-6 activates microglia cells and enhances the accumulation of amyloid-β peptides. Moreover, IL-6 signal transduction is mediated by membrane-bound and soluble IL-6 receptors. Tocilizumab which is a humanized anti-human IL-6 receptor (IL-6R) monoclonal antibody binds to both of these receptors and inhibits IL-6 signaling by this route. The objective was to investigate tocilizumab's potential effects in the treatment of AD. Male Sprague-Dawley rats were divided into three groups: sham (control), streptozotocin (STZ), and tocilizumab-STZ. We used a single dose of intracerebroventricular (ICV) tocilizumab, beginning 1 h prior to injection of STZ for 3 weeks. The rats in STZ and tocilizumab-STZ groups were given ICV-STZ (3 mg/kg). Behavioral parameters were evaluated on days 17-20 and the rats were sacrificed on day-21 to examine histopathological changes. STZ injection caused significant decrease in the mean escape latency in passive avoidance and also declined the performance improvement in Morris water maze tests. Tocilizumab-STZ group significantly improved learning and spatial memory functions by increasing RLT in the passive avoidance and by shortening escape latency in reaching the platform in the Morris water maze. Histopathological changes were examined using hematoxylin and eosin and immunohistochemical (IHC) stainings. IHC analysis revealed that while protein expressions of amyloid-ß (3.5 ± 0.2) and IL-6 (2.9 ± 0.4) showed intense immune-positivity in STZ group, amyloid-ß (1.3 ± 0.1) and IL-6 (1.5 ± 0.2) immunoreactivities were substantially decreased in tocilizumab treatment group. We conclude that tocilizumab treatment attenuated significantly STZ-induced cognitive impairment and histopathological changes. Further studies would be desirable to investigate clinically relevant protective effects of tocilizumab in AD.

Fundamental role of pan-inflammation and oxidative-nitrosative pathways in neuropathogenesis of Alzheimer's disease in focal cerebral ischemic rats

Alzheimer's disease (AD) is a chronic progressive neurodegenerative condition of the brain, and it is the most common cause of dementia. Several neurobiological etiologies of AD are described in the literature. These include vascular, infectious, toxic, nutritional, metabolic, and inflammatory. However, these heterogeneous etiologies have a common denominator - viz. Inflammation and oxidative stress. Lipopolysaccharide (LPS) elevates the synthesis of proinflammatory cytokines and chemokines; chronically, together they trigger various pathological responses in the periphery and the CNS including dysfunctional memory consolidation and memory decline. Aging - the main risk factor for AD is inherently associated with inflammation. There are several age-related comorbidities that are also associated with inflammation and oxidative stress. Such co-prevailing aggravating factors, therefore, persist against a background of underlying aging-related pathology. They may converge, and their synergistic propagation may modify the disease course. A critical balance exists between homeostasis/repair and inflammatory factors; chronic, unrelenting inflammatory milieu succeeds in promoting a neuroinflammatory and neurodegenerative outcome. Extensive evidence is available that CNS inflammation is associated with neurodegeneration. LPS, proinflammatory cytokines, several mediators secreted by microglia, and oxidative-nitrosative stress in concert play a pivotal role in triggering neuroinflammatory processes and neurodegeneration. The persistent uncontrolled activity of the above factors can potentiate cognitive decline in tandem enhancing vulnerability to AD. Despite significant progress during the past twenty years, the prevention and treatment of AD have been tantalizingly elusive. Current studies strongly suggest that amelioration/prevention of the deleterious effects of inflammation may prove beneficial in preventing AD onset and retarding cognitive dysfunction in aging and AD. A concerted multi-focal therapeutic effort around the inflammation-oxidative-nitrosative stress paradigm may be crucial in preventing and treating AD. This paper informs on such relevant polypharmacy approach.

Effects of melatonin on cognitive impairment and hippocampal neuronal damage in a rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH), which induces oxidative stress and inflammation in the brain, has previously been associated with cognitive impairment and neuronal cell damage. Melatonin is a well-known free radical scavenger and antioxidant; therefore, the present study investigated the protective effects of melatonin against CCH-induced cognitive impairment and neuronal cell death in a CCH rat model, which was generated via permanent bilateral common carotid artery occlusion (2VO). The rats in the 2VO group exhibited markedly increased escape latencies in a Morris water maze test, as compared with the rats in the sham group. In addition, increased neuronal cell damage was detected in the hippocampal CA1 region of the 2VO rats, as compared with the rats in the sham group. Treatment of the 2VO rats with melatonin significantly reduced the escape latency and neuronal cell damage, and was associated with reduced levels of malondialdehyde, microglial activation, and tumor necrosis factor-α and interleukin-1β in the ischemic hippocampus. The results of the present study suggest that melatonin may attenuate CCH-induced cognitive impairment and hippocampal neuronal cell damage by decreasing oxidative stress, microglial activation and the production of pro-inflammatory cytokines in the ischemic hippocampus.

Fundamental role of pan-inflammation and oxidative-nitrosative pathways in neuropathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a chronic progressive neurodegenerative condition of the brain, and it is the most common cause of dementia. Several neurobiological etiologies of AD are described in the literature. These include vascular, infectious, toxic, nutritional, metabolic, and inflammatory. However, these heterogeneous etiologies have a common denominator - viz. Inflammation and oxidative stress. Lipopolysaccharide (LPS) elevates the synthesis of proinflammatory cytokines and chemokines; chronically, together they trigger various pathological responses in the periphery and the CNS including dysfunctional memory consolidation and memory decline. Aging - the main risk factor for AD is inherently associated with inflammation. There are several age-related comorbidities that are also associated with inflammation and oxidative stress. Such co-prevailing aggravating factors, therefore, persist against a background of underlying aging-related pathology. They may converge, and their synergistic propagation may modify the disease course. A critical balance exists between homeostasis/repair and inflammatory factors; chronic, unrelenting inflammatory milieu succeeds in promoting a neuroinflammatory and neurodegenerative outcome. Extensive evidence is available that CNS inflammation is associated with neurodegeneration. LPS, proinflammatory cytokines, several mediators secreted by microglia, and oxidative-nitrosative stress in concert play a pivotal role in triggering neuroinflammatory processes and neurodegeneration. The persistent uncontrolled activity of the above factors can potentiate cognitive decline in tandem enhancing vulnerability to AD. Despite significant progress during the past twenty years, the prevention and treatment of AD have been tantalizingly elusive. Current studies strongly suggest that amelioration/prevention of the deleterious effects of inflammation may prove beneficial in preventing AD onset and retarding cognitive dysfunction in aging and AD. A concerted multi-focal therapeutic effort around the inflammation-oxidative-nitrosative stress paradigm may be crucial in preventing and treating AD. This paper informs on such relevant polypharmacy approach.

Tumor necrosis factor alpha and its receptors in behaviour and neurobiology of adult mice, in the absence of an immune challenge

Tumor necrosis factor alpha (TNF-α) is a vital component of the immune system and CNS. We previously showed that 3-month-old TNF-α and TNF-α receptor knockout mice had impaired cognition, whilst at 12-months-old mice had better cognition. To extend these findings on possible age-dependent TNF-α effects in the brain, we investigated the behaviour of 6-month-old TNF-α knockout mice and their neurobiological correlates. 6-month-old TNF(-/-), TNF-R1(-/-) and TNF-R2(-/-) mice were compared to age-matched WT mice and tested for various behaviours. ELISA hippocampal levels of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) and qPCR mRNA levels of Tnfa, Tnfr1, Tnfr2, Il10 and Il1β were measured. TNF-R1(-/-) and TNF(-/-) mice were found to have lesser exploratory behaviour than WT mice, while TNF-R1(-/-) mice displayed better memory than WT and TNF-R2(-/-) mice. Both TNF(-/-) and TNF-R2(-/-) mice exhibited significantly lower immobility on the depression test than WT mice. Additionally, TNF(-/-) mice expressed significantly lower levels of BDNF than WT mice in the hippocampus while TNF-R1(-/-) mice displayed significantly lower BDNF levels compared to both WT and TNF-R2(-/-) mice. TNF-R2(-/-) mice also displayed significantly higher levels of NGF compared to TNF-R1(-/-) mice. These results illustrate that TNF-α and its receptors mediate several behavioural phenotypes. Finally, BDNF and NGF levels appear to be regulated by TNF-α and its receptors even under immunologically unchallenged conditions.

Deferoxamine attenuates lipopolysaccharide-induced neuroinflammation and memory impairment in mice

Background

Neuroinflammation often results in enduring cognitive impairment and is a risk factor for postoperative cognitive dysfunction. There are currently no effective treatments for infection-induced cognitive impairment. Previous studies have shown that the iron chelator deferoxamine (DFO) can increase the resistance of neurons to injury and disease by stimulating adaptive cellular stress responses. However, the impact of DFO on the cognitive sequelae of neuroinflammation is unknown.

Methods

A mouse model of lipopolysaccharide (LPS)-induced cognitive impairment was established to evaluate the neuroprotective effects of DFO against LPS-induced memory deficits and neuroinflammation. Adult C57BL/6 mice were treated with 0.5 μg of DFO 3 days prior to intracerebroventricular microinjection of 2 μg of LPS. Cognitive function was assessed using a Morris water maze from post-injection days 1 to 3. Animal behavioral tests, as well as pathological and biochemical assays were performed to evaluate the LPS-induced hippocampal damage and the neuroprotective effect of DFO.

Results

Treatment of mice with LPS resulted in deficits in cognitive performance in the Morris water maze without changing locomotor activity, which were ameliorated by pretreatment with DFO. DFO prevented LPS-induced microglial activation and elevations of IL-1β and TNF-α levels in the hippocampus. Moreover, DFO attenuated elevated expression of caspase-3, modulated GSK3β activity, and prevented LPS-induced increases of MDA and SOD levels in the hippocampus. DFO also significantly blocked LPS-induced iron accumulation and altered expression of proteins related to iron metabolism in the hippocampus.

Conclusions

Our results suggest that DFO may possess a neuroprotective effect against LPS-induced neuroinflammation and cognitive deficits via mechanisms involving maintenance of less brain iron, prevention of neuroinflammation, and alleviation of oxidative stress and apoptosis.

3-methyladenine, an autophagic inhibitor, attenuates therapeutic effects of sirolimus on scopolamine-induced cognitive dysfunction in a rat model

Previous studies have demonstrated that sirolimus has therapeutic effects for Alzheimer's disease which characterized by cognitive dysfunction. However, its underlying mechanisms have not been fully elucidated. In the present study, we aimed to investigate the mechanisms of therapeutic effects of sirolimus for cognitive dysfunction rat model which induced by chronic administration of scopolamine. Forty Wistar rats were randomly divided into 4 groups (n=10 each): saline group and scopolamine group, sirolimus plus scopolamine group and 3-methyladenine pretreatment group. Morris water maze test was applied to measure the cognitive function of rat. After behavioral test, rats were sacrificed and prefrontal cortex and hippocampus were harvested for measuring amyloid-β (Aβ), Beclin-1 and mammalian target of rapamycin (mTOR). Compared with saline group, scopolamine administered significantly decreased the cognitive performance of rats during the Morris water maze test and changed Aβ, Beclin-1 and mTOR levels in rat prefrontal cortex and hippocampus (P<0.05); In addition, rats in sirolimus plus scopolamine group significantly reversed scopolamine-induced effects (P<0.05). Most importantly, 3-methyladenine abrogated the effects of sirolimus on scopolamine-induced cognitive dysfunction (P<0.05). In conclusion, the mechanism of sirolimus exerting therapeutic effects for scopolamine-induced cognitive dysfunction is likely related to the activation of autophagy.

Effect of intravenous infusion of dobutamine hydrochloride on the development of early postoperative cognitive dysfunction in elderly patients via inhibiting the release of tumor necrosis factor-α

To investigate the effects of dobutamine hydrochloride on early postoperative cognitive dysfunction (POCD) and plasma tumor necrosis factor (TNF)-α concentration in patients undergoing hip arthroplasty, 124 patients undergoing unilateral total hip arthroplasty, aged 70-92 years old, were randomly assigned to four groups (n=31) as follows: a control group of patients receiving only saline (intravenous infusion, i.v.); and groups receiving 2, 4, or 6μgkg(-1)min(-1) (i.v.) of dobutamine hydrochloride. Cognitive functions were assessed on the day before surgery (T1), and the 1st day (T2), 3rd day (T3), and 7th day (T4) postsurgery using the Mini Mental State Examination (MMSE). The plasma TNF-α protein level was determined 10min before anesthesia (Ta), and 10min (Tb), 30min (Tc), and 60min (Td) after anesthesia by an enzyme-linked immunosorbent assay. Cognitive disorder was observed within the first 3 days after hip arthroplastic surgery, and it had recovered 7 days after the operation in the control group of patients. Administration of 2 or 4μgkg(-1)min(-1) dobutamine hydrochloride was able to reverse the early POCD. Simultaneously, an increase of plasma TNF-α levels 30min after anesthesia was observed (41.34±9.61 vs. 27.75±5.45), which was significantly suppressed by the administration of low-dose dobutamine hydrochloride (29.23±7.32 vs. 41.34±9.61) but not by high-dose dobutamine hydrochloride (45.9±12.11 vs. 41.34±9.61). Together, our data indicated that the plasma concentration of TNFα was engaged in the effect of dobutamine hydrochloride on POCD.

Spatial learning in the Morris water maze in mice genetically different in the predisposition to catalepsy: the effect of intraventricular treatment with brain-derived neurotrophic factor

Hereditary catalepsy in mice is accompanied with volume reduction of some brain structures and high vulnerability to inflammatory agents. Here an association between hereditary catalepsy and spatial learning deficit in the Morris water maze (MWM) in adult mouse males of catalepsy-resistant AKR, catalepsy-prone CBA and AKR.CBA-D13Mit76 (D13) strains was studied. Recombinant D13 strain was created by means of the transfer of the CBA-derived allele of the major gene of catalepsy to the AKR genome. D13 mice showed a low MWM performance in the acquisition test and high expression of the gene coding proinflammatory interleukin-6 (Il-6) in the hippocampus and cortex compared with mice of the parental AKR and CBA strains. An acute ivc administration of 300 ng of brain derived neurotrophic factor (BDNF) normalized the performance in the MWM, but did not decrease the high Il-6 gene expression in the brain of D13 mice. These results indicated a possible association between the hereditary catalepsy, MWM performance, BDNF and level of Il-6 mRNA in the brain, although the relation between these characteristics seems to be more complex. D13 recombinant mice with deficit of spatial learning is a promising model for study of the genetic and molecular mechanisms of learning disorders as well as for screening potential cognitive enhancers.

Isoflurane anesthesia aggravates cognitive impairment in streptozotocin-induced diabetic rats

Several lines of evidence demonstrate that isoflurane anesthesia would be a great risk factor for the patients undergoing surgeries to suffer from postoperative cognitive dysfunction (POCD). Additionally, diabetes is also an important pathogenic factor for the emergence of cognitive dysfunction. If patient is suffering from diabetes, the incidence of cognitive dysfunction greatly increased. We therefore aimed to investigate the effects of isoflurane anesthesia on cognitive dysfunction in a diabetic rat model induced by a single injection of streptozotocin (STZ). Wistar rats received 2 h of 2% isoflurane or oxygen exposure 1 month after a single intraperitoneal injection of 60 mg/kg of STZ or the vehicle. The results showed that isoflurane anesthesia significantly aggravates STZ-induced an increase of the latency to the platform and a decrease of the proportion of time spent in the target quadrant of rats in Morris water maze test. In addition to the expression of amyloid-β (Aβ), superoxide dismutase (SOD), malonyldialdehyde (MDA), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), isoflurane anesthesia significantly increased as compared with a single injection of STZ. However, isoflurane anesthesia had no effect on the blood glucose and leptin. In conclusion, our results suggested that isoflurane anesthesia aggravating cognitive impairment induced by STZ is probably related to the activation of oxidative stress and inflammatory response in rat hippocampus.