LPS induces mediators of neuroinflammation, cell proliferation, and GFAP expression in human astrocytoma cells U373MG: the anti-inflammatory and anti-proliferative effect of guggulipid

Meclizine moderates lipopolysaccharide-induced neuroinflammation in mice through the regulation of AKT/ NF-κβ/ERK/JNK signaling pathway

Neuroinflammation is identified as significant inflammatory reactions occurring in the central nervous system. Lipopolysaccharide (LPS) stimulates innate immune reactions and is used as an in vivo animal model for the investigation of inflammation. Meclizine (MCLZ) is a histamine antagonist with potential neuroprotective qualities. Forty adult male Swiss albino mice were divided into four groups (n = 10). Group 1 served as a control negative group. Groups 2-4 were injected with LPS (5 mg/kg; i.p). Group 2 served as LPS-control. Groups 3 & 4 were given MCLZ (12.5 & 25 mg/kg; p.o) respectively for 14 days. LPS administration resulted in significant neuroinflammation in mice as was revealed by significant inflammatory histopathological changes and positive immunohistochemical staining of glial fibrillary acidic proteins (GFAP) accompanied by significant elevations of brain tissue contents of interleukin-1-beta (IL-1β), tumor necrosis factor-alpha (TNF-α), nuclear factor kappa-beta (NF-κβ), protein kinase B (AKT), extracellular signal-regulated kinase (ERK) and C-Jun N-Terminal Kinases (JNK). MCLZ treatment significantly down-regulated all the aforementioned parameters in mice brains. Moreover, MCLZ treatment ameliorated the inflammatory histopathological changes and GFAP immunostaining in brain tissues. The current study identifies for the first time the protective anti-neuroinflammatory effects of MCLZ against LPS-induced neuroinflammation in mice. MCLZ protected against neuroinflammation via the amelioration of inflammatory histopathological changes as well as neuronal GFAP immunostaining and down-regulated the AKT/NF-κβ/ERK/JNK signaling pathway. MCLZ is anticipated as a potential protective candidate for the addition to the treatment protocol of neuroinflammation.

Dysregulation of inflammasome activation in glioma

Gliomas are the most common brain tumors characterized by complicated heterogeneity. The genetic, molecular, and histological pathology of gliomas is characterized by high neuro-inflammation. The inflammatory microenvironment in the central nervous system (CNS) has been closely linked with inflammasomes that control the inflammatory response and coordinate innate host defenses. Dysregulation of the inflammasome causes an abnormal inflammatory response, leading to carcinogenesis in glioma. Because of the clinical importance of the various physiological properties of the inflammasome in glioma, the inflammasome has been suggested as a promising treatment target for glioma management. Here, we summarize the current knowledge on the contribution of the inflammasomes in glioma and therapeutic insights. Video Abstract.

Gene Networks and Pathways Involved in LPS-Induced Proliferative Response of Bovine Endometrial Epithelial Cells

Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria involved in the pathogenic processes leading to mastitis and metritis in animals such as dairy cattle. LPS causes cell proliferation associated with endometrium inflammation. Former in vitro studies have demonstrated that LPS induces an intense stimulation of the proliferation of a pure population of bovine endometrial epithelial cells. In a follow-up transcriptomic study based on RNA-sequencing data obtained after 24 h exposure of primary bovine endometrial epithelial cells to 0, 2, and 8 μg/mL LPS, 752 and 727 differentially expressed genes (DEGs) were detected between the controls and LPS-treated samples that encode proteins known to be associated with either proliferation or apoptosis, respectively. The present bioinformatic analysis was performed to decipher the gene networks involved to obtain a deeper understanding of the mechanisms underlying the proliferative and apoptosis processes. Our findings have revealed 116 putative transcription factors (TFs) and the most significant number of interactions between these TFs and DEGs belong to NFKβ1, TP53, STAT1, and HIF1A. Moreover, our results provide novel insights into the early signaling and metabolic pathways in bovine endometrial epithelial cells associated with the innate immune response and cell proliferation to Escherichia coli-LPS infection. The results further indicated that LPS challenge elicited a strong transcriptomic response, leading to potent activation of pro-inflammatory pathways that are associated with a marked endometrial cancer, Toll-like receptor, NFKβ, AKT, apoptosis, and MAPK signaling pathways. This effect may provide a mechanistic explanation for the relationship between LPS and cell proliferation.

Potential Use of Agave Genus in Neuroinflammation Management

Agavaceae contains about 480 species, commonly used in the production of alcoholic beverages such as tequila and mezcal, making it a resource of economic and cultural importance. Uses of this plant rely mainly on the stem; other components such as the leaves are discarded, generating agro-industrial waste, despite being a source of bioactive and nutraceutical products. Reports show anti-inflammatory and anti-neuroinflammatory effects of these species, with flavonoids and saponins being mainly responsible. Neuroinflammation is a brain process that plays a key role in the pathogenesis of various neurodegenerative disorders and its effects contribute greatly to mortality and morbidity worldwide. This can be triggered by mechanisms such as glial reactions that lead to the release of inflammatory and oxidative molecules, causing damage to the CNS. Treatments do not cure chronic disease associated with inflammation; they only slow its progression, producing side effects that affect quality of life. Plant-based therapy is promising for treating these diseases. Pharmacological activities have been described for the Agavaceae family; however, their role in neuroinflammation has not been fully investigated, and represents an important target for study. This review synthesizes the existing literature on the biologically active compounds of Agave species that are related in some way to inflammation, which will allow us to propose a line of research with this genus on the forefront to orient experimental designs for treating neuroinflammation and associated diseases.

Eosinophils Restrict Diesel Exhaust Particles Induced Cell Proliferation of Lung Epithelial A549 Cells, Vial Interleukin-13 Mediated Mechanisms: Implications for Tissue Remodelling And Fibrosis

BACKGROUND

Diesel exhaust particulates (DEPs) affect lung physiology and cause serious damage to the lungs. A number of studies demonstrated that, eosinophils play a very important role in the development of tissue remodelling and fibrosis of lungs. However, the exact mechanism of pathogenesis of tissue remodelling and fibrosis is not known.

METHODS

Both in vitro and in vivo models were used in the study. HL-60 and A549 cells were used in the study. Balb/C mice of 8 to 12 weeks old were used for in vivo study. Cell viability by MTT assay, RNA isolation by tri reagent was accomplished. mRNA expression of inflammatory genes were accomplished by real time PCR or qPCR. Immunohistochemistry was done to asses the localization and expressions of proteins. One way ANOVA followed by post hoc test were done for the statistical analysis. Graph-Pad Prism software was used for statistical analysis.

RESULTS

We for the first time demonstrate that, Interleukin-13 plays a very important role in the development of tissue remodelling and fibrosis. We report that, diesel exhaust particles significantly induce eosinophils cell proliferation and interleukin-13 release in in vitro culture conditions. Supernatant collected from DEP-induced eosinophils cells significantly restrict cell proliferation of epithelial cells in response to exposure of diesel exhast particles. Furthermore, purified interleukin-13 decreases the proliferation of A549 cells, highliting the involvement of IL-13 in tissue remodeling. Notably, Etoricoxib (selective COX-2 inhibitor) did not inhibit DEP-triggered release of interleukin-13, suggesting another cell signalling pathway. The in vivo exposer of DEP to the lungs of mice, resulted in high level of eosinophils degranulation as depicted by the EPX-1 immunostaining and altered level of mRNA expressions of inflammatory genes. We also found that, a-SMA, fibroblast specific protein (FSP-1) has been changed in response to DEP in the mice lungs along with the mediators of inflammation.

CONCLUSION

Altogether, we elucidated, the mechanistic role of eosinophils and IL-13 in the DEP-triggered proliferation of lungs cells thus providing an inside in the pathophysiology of tissue remodelling and fibrosis of lungs.

The Effects of Incensole Acetate on Neuro-inflammation, Brain-Derived Neurotrophic Factor and Memory Impairment Induced by Lipopolysaccharide in Rats

Incensole acetate (IA) is a major component of Boswellia serrata resin that has been shown to have anti-inflammatory, anti-oxidant and neuroprotective properties. The present study determined the effect of IA on lipopolysaccharide (LPS)-induced memory impairment, and hippocampal cytokines and oxidative stress indicators level. We used 32 Wistar rats (220-250 g weight) randomly divided into four groups. The control group, which only received the saline-diluted DMSO (vehicle); LPS group which received LPS and was treated with the vehicle; and two IA-treated groups which received 2.5 or 5 mg/ kg IA before LPS injection. Morris water maze (MWM) and passive avoidance (PA) tests were performed. Finally, the brains were removed and were used to assess cytokines levels and oxidative stress status. Compared to the LPS group, IA administration reduced the time spent and path traveled to reach the hidden platform during 5 days of learning in MWM while increased the time spent in the target quadrant in the probe test. Moreover, IA increased latency while decreased entry number and time spent in the dark chamber of PA test compared to the LPS group. Additionally, pre-treatment with IA attenuated interleukin(IL)-6, tumor necrosis alpha (TNF-α), glial fibrillary acidic protein (GFAP), malondialdehyde (MDA) and nitric oxide (NO) metabolites levels while increased those of IL-10, total thiol, superoxide dismutase (SOD), catalase (CAT) and brain-derived neurotrophic factor (BDNF). Our results indicated that IA improved LPS-induced learning and memory impairments. The observed effects seem to be mediated via a protective activity against neuro-inflammation and brain tissue oxidative damage and through improving BDNF.

Matrix metalloproteinases in the pathogenesis of dengue viral disease: Involvement of immune system and newer therapeutic strategies

Globally, the burden due to dengue infection is increasing with a recent estimate of 96 million progressing to the disease every year. Dengue pathogenesis and the factors influencing it are not completely known. It is now widely speculated that there is an important role of matrix metalloproteinases (MMPs) in the initiation and progression of dengue pathogenesis; however, their exact roles are not fully understood. Overactivation of matrix metalloproteinases may contribute to the severity of dengue pathogenesis. Cytokines and various other mediators of inflammation interact with the vascular endothelium and matrix metalloproteinases may be one of the components among them. Extensive plasma leakage into tissue spaces may result in a shock. It is evident in the literature that MMP2 and MMP9 increase in dengue patients is correlated with the severity of the disease; however, the underlying mechanism is still unknown. Activation of innate cells and adaptive immune cells which include, B and T cells, macrophages or monocytes and dendritic cells also contribute to the dengue pathology. Newer therapeutic strategies include microRNAs, such as miR-134 (targets MMP3 and MMP1) and MicroRNA-320d, (targets MMP/TIMP proteolytic system). The use of antibodies-based therapeutics like (Andecaliximab; anti-matrix metalloproteinase-9 antibody) is also suggested against MMPs in dengue. In this review, we summarize some recent developments associated with the involvement of immune cells and their mediators associated with the matrix metalloproteinases mediated dengue pathogenesis. We highlight that, there is still very little knowledge about the MMPs in dengue pathogenesis which needs attention and extensive investigations.

Lipopolysaccharide-Induced Matrix Metalloproteinase-9 Expression Associated with Cell Migration in Rat Brain Astrocytes

Neuroinflammation is a landmark of neuroinflammatory and neurodegenerative diseases. Matrix metalloproteinase (MMP)-9, one member of MMPs, has been shown to contribute to the pathology of these brain diseases. Several experimental models have demonstrated that lipopolysaccharide (LPS) exerts a pathological role through Toll-like receptors (TLRs) in neuroinflammation and neurodegeneration. However, the mechanisms underlying LPS-induced MMP-9 expression in rat brain astrocytes (RBA-1) are not completely understood. Here, we applied pharmacological inhibitors and siRNA transfection to assess the levels of MMP-9 protein, mRNA, and promoter activity, as well as protein kinase phosphorylation in RBA-1 cells triggered by LPS. We found that LPS-induced expression of pro-form MMP-9 and cell migration were mediated through TLR4, proto-oncogene tyrosine-protein kinase (c-Src), proline-rich tyrosine kinase 2 (Pyk2), platelet-derived growth factor receptor (PDGFR), phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), p38 mitogen-activated protein kinase (MAPK), and Jun amino-terminal kinase (JNK)1/2 signaling molecules in RBA-1 cells. In addition, LPS-stimulated binding of c-Jun to the MMP-9 promoter was confirmed by chromatin immunoprecipitation (ChIP) assay, which was blocked by pretreatment with c-Src inhibitor II, PF431396, AG1296, LY294002, Akt inhibitor VIII, p38 MAP kinase inhibitor VIII, SP600125, and tanshinone IIA. These results suggest that in RBA-1 cells, LPS activates a TLR4/c-Src/Pyk2/PDGFR/PI3K/Akt/p38 MAPK and JNK1/2 pathway, which in turn triggers activator protein 1 (AP-1) activation and ultimately induces MMP-9 expression and cell migration.

Active Fraction Combination from Liuwei Dihuang Decoction (LW-AFC) Alleviated the LPS-Induced Long-Term Potentiation Impairment and Glial Cells Activation in Hippocampus of Mice by Modulating Immune Responses

Neuroinflammation is known as a typical feature associated with many neurodegenerative diseases including Alzheimer's disease (AD) and impairs the synaptic plasticity of the hippocampus. LW-AFC is an active fraction combination being extracted from Liuwei Dihuang decoction, a classic traditional Chinese medicine prescription. This study aimed to investigate the effects of LW-AFC on synaptic plasticity in mice with lipopolysaccharide (LPS) treatment. The results showed that the administration of LPS caused fever and long-term potentiation (LTP) impairment in mice. The pretreatment with LW-AFC had an antipyretic effect on fever and improved the impaired LTP induced by LPS, alleviated the microglia and astrocytes activation in the hippocampus, regulated the abnormal T-lymphocyte subpopulation in the spleen and blood caused by LPS, and reduced the aberrant secretion of cytokines in the brain and plasma. The compounds paeoniflorin, morroniside, and loganic acid in LW-AFC regulated the TNF-α secretion in non-LPS- and LPS-stimulated BV-2 cells. These data suggest that LW-AFC improves the LPS-induced impairment of LTP and alleviates the activation of glial cells in the hippocampus, which might be associated with modulating immune responses.

Neuromodulatory Activity of Dietary Phenolics Derived from Corchorus olitorius L

Dietary phenolics are known for their potent antioxidant and anti-inflammatory activities, making them promising candidates for protection against neuroinflammation and neurodegeneration. Hydroalcohol extract of Egyptian species of Corchorus olitorius L. (Co) leaves was investigated for its neuroprotective effects in a lipopolysaccharide-induced neuroinflammatory mouse model. Twenty five metabolites were characterized from the bioactive extract using high-performance liquid chromatography HPLC/PDA/HRESI/MSⁿ , revealing 1,5-dicaffeoylquinic acid (Co11) as one of the major constituents (5.7%), which was isolated and its identity was confirmed by spectral data as first report. Co significantly protected microglia against H₂ O₂ -induced cytotoxicity and immunohistochemistry showed reduced expression of the astrocytic marker, glial fibrillary acidic protein, and the inflammatory marker, cyclooxygenase-2. These findings correlated with significant improvement of cognitive functions and reduction of LPS-induced neurodegeneration in Co-treated mice as revealed by histopathology. The current study shows promising effects of Co in limiting neurodegeneration and cognitive impairment caused by neuroinflammation and glial cell activation. PRACTICAL APPLICATION: Information presented here shed light on the promising effects of Corchorus olitorius (Co) for the modulation of neuroinflammatory pathways improving the neuroinflammation-related neurodegeneration and cognitive decline. This makes Co a promising candidate as a nutraceutical supplement to be used against neuroinflammation-related disorders.

Permeability changes and effect of chemotherapy in brain adjacent to tumor in an experimental model of metastatic brain tumor from breast cancer

Background

Brain tumor vasculature can be significantly compromised and leakier than that of normal brain blood vessels. Little is known if there are vascular permeability alterations in the brain adjacent to tumor (BAT). Changes in BAT permeability may also lead to increased drug permeation in the BAT, which may exert toxicity on cells of the central nervous system. Herein, we studied permeation changes in BAT using quantitative fluorescent microscopy and autoradiography, while the effect of chemotherapy within the BAT region was determined by staining for activated astrocytes.

Methods

Human metastatic breast cancer cells (MDA-MB-231Br) were injected into left ventricle of female NuNu mice. Metastases were allowed to grow for 28 days, after which animals were injected fluorescent tracers Texas Red (625 Da) or Texas Red dextran (3 kDa) or a chemotherapeutic agent ¹⁴C-paclitaxel. The accumulation of tracers and ¹⁴C-paclitaxel in BAT were determined by using quantitative fluorescent microscopy and autoradiography respectively. The effect of chemotherapy in BAT was determined by staining for activated astrocytes.

Results

The mean permeability of texas Red (625 Da) within BAT region increased 1.0 to 2.5-fold when compared to normal brain, whereas, Texas Red dextran (3 kDa) demonstrated mean permeability increase ranging from 1.0 to 1.8-fold compared to normal brain. The K_in values in the BAT for both Texas Red (625 Da) and Texas Red dextran (3 kDa) were found to be 4.32 ± 0.2 × 10⁵ mL/s/g and 1.6 ± 1.4 × 10⁵ mL/s/g respectively and found to be significantly higher than the normal brain. We also found that there is significant increase in accumulation of ¹⁴C-Paclitaxel in BAT compared to the normal brain. We also observed animals treated with chemotherapy (paclitaxel (10 mg/kg), erubilin (1.5 mg/kg) and docetaxel (10 mg/kg)) showed activated astrocytes in BAT.

Conclusions

Our data showed increased permeation of fluorescent tracers and ¹⁴C-paclitaxel in the BAT. This increased permeation lead to elevated levels of activated astrocytes in BAT region in the animals treated with chemotherapy.

Recent advances in the mechanisms of neuroinflammation and their roles in neurodegeneration

Neuroinflammation is associated with the pathogenesis of many neurological disorders including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington disease. Current studies in this area have advanced the mechanism of neuroinflammation and its role in neurodegeneration. Studies from epidemiologic, clinical and animal models also contributed in the various new mechanisms of neuroinflammation. In this line, activation of monocytes is an important emerging mechanism that has a, profound role in neuroinflammation and neurodegeneration. Ion channels, matrix metalloproteases and microRNAs are also found to be the key players in the pathogenesis of neuroinflammation. In particular, microRNA-32 regulates microglia-mediated neuroinflammation and thus neurodegeneration. Notably, some important studies describe the role of Th17 cells in neuroinflammation, but, very little knowledge is available about their mechanism of action. Particularly, the role of autophagy gets emphasized, which plays a very critical role in protein aggregation and neurodegeneration. In this review, we highlight and discuss the mechanisms of these mediators of inflammation by which they contribute to the disease progression. In conclusion, we focus on the various newer molecular mechanisms that are associated with the basic understanding of neuroinflammation in neurodegeneration.

In vitro evaluation of the synergistic antioxidant and anti-inflammatory activities of the combined extracts from Malaysian Ganoderma lucidum and Egyptian Chlorella vulgaris

Background

Since oxidative stress and inflammation are two linked factors in the pathogenesis of several human diseases. Thus identification of effective treatment is of great importance. Edible mushroom and microalgae are rich in the effective antioxidant phytochemicals. Hence, their beneficial effects on oxidative stress-associated inflammation are extremely required to be investigated.

Methods

This study evaluated the functional constituents, antioxidant and anti-inflammatory activities of Malaysian Ganoderma lucidum aqueous extract (GLE) and Egyptian Chlorella vulgaris ethanolic extract (CVE). Also, the synergistic, addictive or antagonistic activities of the combination between the two extracts (GLE-CVE) were studied. Expression of inducible nitric oxide synthase, cyclooxygenase-2, and nuclear factor-kappa B, as well as levels of nitric oxide, tumor necrosis factor (TNF)-α, lipid peroxidation, reduced glutathione and antioxidant enzymes were determined using in vitro model of lipopolysaccharide-stimulated white blood cells.

TLR4 interaction with LPS in glioma CD133+ cancer stem cells induces cell proliferation, resistance to chemotherapy and evasion from cytotoxic T lymphocyte-induced cytolysis

Despite advances in treatment modalities, 5-year survival among glioma patients remains poor. Glioma cancer stem cells (CSCs) exhibit high tumorigenic activity and are associated with resistance to treatment and tumor recurrence. Because overexpression of toll-like receptor 4 (TLR4) correlated with cancer development, we investigated LPS-induced TLR4 signaling in glioma CD133-positive (CD133+) CSCs. The proliferation of CD133+ CSCs isolated from CSCs derived from the U251 and SF295 glioma cell lines and from human glioma samples was upregulated on a time- and concentration-dependent basis by LPS stimulation, with increases in CD133, NANOG, and NESTIN mRNA and protein levels. Also elevated was cytokine expression, which was coupled to phosphorylation of mitogen-activated protein kinase, and activation of cyclins and cyclin-dependent kinase complexes. TLR4 knockdown reduced LPS-induced CD133+ CSC proliferation, whereas Adriamycin-induced CD133+ CSC apoptosis was moderately inhibited by treatment with LPS, implying a protective effect of LPS. The capacity of glioma CD133+ CSC-reactive cytotoxic T lymphocyte to selectively kill CD133+ CSCs was reduced by LPS, and this effect was not apparent after TLR4 knockdown in CD133+ CSCs. These data suggest TLR4 signaling is a factor in CD133+ CSC immune evasion, and thus disruption of TLR4 signaling is a potential therapeutic strategy in glioma.

Mouse Model of Neurological Complications Resulting from Encephalitic Alphavirus Infection

Long-term neurological complications, termed sequelae, can result from viral encephalitis, which are not well understood. In human survivors, alphavirus encephalitis can cause severe neurobehavioral changes, in the most extreme cases, a schizophrenic-like syndrome. In the present study, we aimed to adapt an animal model of alphavirus infection survival to study the development of these long-term neurological complications. Upon low-dose infection of wild-type C57B/6 mice, asymptomatic and symptomatic groups were established and compared to mock-infected mice to measure general health and baseline neurological function, including the acoustic startle response and prepulse inhibition paradigm. Prepulse inhibition is a robust operational measure of sensorimotor gating, a fundamental form of information processing. Deficits in prepulse inhibition manifest as the inability to filter out extraneous sensory stimuli. Sensory gating is disrupted in schizophrenia and other mental disorders, as well as neurodegenerative diseases. Symptomatic mice developed deficits in prepulse inhibition that lasted through 6 months post infection; these deficits were absent in asymptomatic or mock-infected groups. Accompanying prepulse inhibition deficits, symptomatic animals exhibited thalamus damage as visualized with H&E staining, as well as increased GFAP expression in the posterior complex of the thalamus and dentate gyrus of the hippocampus. These histological changes and increased GFAP expression were absent in the asymptomatic and mock-infected animals, indicating that glial scarring could have contributed to the prepulse inhibition phenotype observed in the symptomatic animals. This model provides a tool to test mechanisms of and treatments for the neurological sequelae of viral encephalitis and begins to delineate potential explanations for the development of such sequelae post infection.

Inhibitory Effect of Memantine on Streptozotocin-Induced Insulin Receptor Dysfunction, Neuroinflammation, Amyloidogenesis, and Neurotrophic Factor Decline in Astrocytes

Our earlier studies showed that insulin receptor (IR) dysfunction along with neuroinflammation and amyloidogenesis played a major role in streptozotocin (STZ)-induced toxicity in astrocytes. N-methyl-D-aspartate (NMDA) receptor antagonist-memantine shows beneficial effects in Alzheimer's disease (AD) pathology. However, the protective molecular and cellular mechanism of memantine in astrocytes is not properly understood. Therefore, the present study was undertaken to investigate the effect of memantine on insulin receptors, neurotrophic factors, neuroinflammation, and amyloidogenesis in STZ-treated astrocytes. STZ (100 μM) treatment for 24 h in astrocytes resulted significant decrease in brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and insulin-degrading enzyme (IDE) expression in astrocytes. Treatment with memantine (1-10 μM) improved STZ-induced neurotrophic factor decline (BDNF, GDNF) along with IR dysfunction as evidenced by a significant increase in IR protein expression, phosphorylation of IRS-1, Akt, and GSK-3 α/β in astrocytes. Further, memantine attenuated STZ-induced amyloid precursor protein (APP), β-site APP-cleaving enzyme-1 and amyloid-β_1-42 expression and restored IDE expression in astrocytes. In addition, memantine also displays protective effects against STZ-induced astrocyte activation showed by reduction of inflammatory markers, nuclear factor kappa-B translocation, glial fibrillary acidic protein, cyclooxygenase-2, tumor necrosis factor-α level, and oxidative-nitrostative stress. The results suggest that besides the NMDA receptor antagonisic activity, effect on astroglial IR and neurotrophic factor may also be an important factor in the beneficial effect of memantine in AD pathology. Graphical Abstract Novel neuroprotective mechanisms of memenatine in streptozotocin-induced toxicity in astrocytes.

Protection of streptozotocin induced insulin receptor dysfunction, neuroinflammation and amyloidogenesis in astrocytes by insulin

Impaired insulin signaling, amyloid pathology and neuroinflammation are closely associated with neurodegenerative disorder like Alzheimer's disease (AD). Our earlier studies showed that intracerebroventricular streptozotocin (STZ) induces insulin receptor (IR) signaling defect in the hippocampus, which is associated with memory impairment in rats. Astrocytes are the most abundant cells in the brain and play a major role in neuroinflammation. However, involvement of astrocytes in STZ induced IR dysfunction has not received much attention. Therefore, the present study was planned to explore the effect of STZ on IR signaling, proinflammatory markers and amyloidogenesis in rat astrocytoma cell line, (C6). STZ (100 μM) treatment in astrocytes (n = 3) for 24 h, resulted significant decrease in IR mRNA and protein expression, phosphorylation of IRS-1, Akt, GSK-3α and GSK-3β (p < 0.01). Further STZ induced amyloidogenic protein expression as evidenced by the increase in APP, BACE-1 and Aβ1-42 expression (p < 0.05) in astrocytes. STZ also significantly induced astrocytes activation as evidenced by increased expression of GFAP and p-P38 MAPK (p < 0.05). STZ treatment caused enhanced translocation of p65 NF-kB, triggered over expression of TNF-α, IL-1β, COX-2, oxidative/nitrosative stress and caspase activation (p < 0.05) in astrocytes. Insulin (25-100 nM) pretreatment (n = 3) significantly prevented changes in IR signaling, amyloidogenic protein expression and levels of proinflammatory markers (p < 0.05) in STZ treated astroglial cells. In the present study, the protective effect of insulin suggests that, IR dysfunction along with amyloidogenesis and neuroinflammation may have played a major role in STZ induced toxicity in astrocytes which are relevant to AD pathology.