Intracerebroventricular streptozotocin impairs adult neurogenesis and cognitive functions via regulating neuroinflammation and insulin signaling in adult rats

Central Insulin-like Growth Factor-1 Treatment Enhances Working and Reference Memory by Reducing Neuroinflammation and Amyloid Beta Deposition in a Rat Model of Sporadic Alzheimer's Disease

Background/Objectives: Brain insulin resistance is a potential causal factor for dementia in Alzheimer's disease (AD). Insulin-like growth factor-1 (IGF-1), a neurotrophin, plays a key role in central insulin signaling and neuroprotection. Intracerebrovenitricular (ICV) administration of streptozotocin (STZ) disrupts insulin signal transduction, leading to brain insulin resistance, which may mimic the early pathophysiological changes in sporadic AD (sAD). In this study, we investigated whether restoring insulin signaling through ICV injection of IGF-1 could ameliorate spatial memory deficits during sAD progression in a rat model induced by ICV STZ injection. Methods: Male Wistar rats (n = 40) were subjected to double ICV injections of STZ (0.75 mg/kg/ventricle, days 2 and 4) and IGF-1 (1 μg/single injection, days 1 and 3), and placed at the Morris water maze (MWM) at baseline, 7, 45 and 90 days after injections. Reference (days 1-3 and day 4 MWM)) and working (days 5-8 MWM) memory, microglia activation (CD68+ cells), and amyloid β (Aβ) deposition (immunohistochemistry) were measured. Results: We found that ICVIGF-1 administration protected working memory demonstrated as (1) reduced latency to reach the platform, and reduced swimming distance in trials 3 (p < 0.05) and 4 (p < 0.01) on days 45 and 90 post-injection and (2) a short-term (up to 45 days post-injection) enhancement of reference memory, manifested by a reduction in swimming distance and latency (p < 0.05). Furthermore, IGF-1 treatment reduced neuroinflammation in CA2 (p < 0.05) and Aβ deposition in CA1(p < 0.01) of the hippocampus. Conclusions: Central IGF-1 attenuates spatial memory deficits in the ICVSTZ-induced sAD model by reducing neuroinflammation and Aβ accumulation in the hippocampus.

Insulin signaling disruption exacerbates memory impairment and seizure susceptibility in an epilepsy model with Alzheimer's disease-like pathology

Alzheimer's disease (AD) and epilepsy exhibit a complex bidirectional relationship. Curiously, diabetes as a comorbidity increases the risk of epilepsy among AD patients. Recently, we reported that the Wistar audiogenic rat (WAR) strain, a genetic model of epilepsy, displays a partial AD-like phenotype, including brain insulin resistance. We also assessed seizure susceptibility in an AD model created through intracerebroventricular injections of streptozotocin (icv-STZ), which induces AD features via brain insulin resistance. Our goal was to explore how disrupted brain insulin signaling influences AD-like features and seizure susceptibility in the WAR strain. Adult male WARs received a single intracerebroventricular injection of streptozotocin (icv-STZ) (1.5 mg/kg) or vehicle (saline). Two weeks post-injection, spatial memory was assessed using the Barnes Maze (BM) test. Three weeks later, the rats underwent an audiogenic kindling (AuK) protocol (20 acoustic stimuli, 2 per day) to evaluate seizure frequency and severity. Seizures were analyzed using the Categorized Severity Index and Racine's scale and Western blot analysis was performed on hippocampal tissue. Our findings revealed that icv-STZ significantly worsened memory performance, increased seizure frequency, and reduced seizure onset relative to vehicle. Furthermore, icv-STZ decreased Akt activation and increased Glycogen Synthase Kinase-3 (GSK3) phosphorylation, indicating disrupted insulin signaling. Notably, icv-STZ decreased tau phosphorylation without altering amyloid β precursor protein (AβPP) levels. In conclusion, a low-dose icv-STZ injection exacerbates memory deficits and seizure susceptibility in the WAR strain by disturbing downstream proteins involved in insulin signaling. This highlights the implications of brain insulin resistance in both AD and epilepsy.

Neuroprotective Effect of Chlorogenic Acid in an Animal Model of Sporadic Alzheimer's Disease Induced by Streptozotocin

Alzheimer's Disease is a degenerative neurological condition which leads to a decline in memory and cognitive function. Chlorogenic Acid (CGA) presents properties including neuroprotective, antioxidant and anti-inflammatory. The aim of this study was to examine the impact of CGA on cognitive impairments, neuroinflammation and neuronal damage in mice submitted to an experimental model of Sporadic Alzheimer Disease (SAD) induced by intracerebroventricular administration of streptozotocin (ICV-STZ). Male Swiss mice received bilateral ICV-STZ injections (3 mg/Kg) on days 1 and 3. The treatment with CGA (5 mg/Kg, orally) or vehicle (water, orally), was initiated and continued for 26 days, starting 2 h after the second induction procedure. At first, there was no change in serum glucose levels after SAD induction. ICV-STZ induces impairments in aversive, recognition, and spatial memory, while CGA treatment significantly alleviated these memory deficits. Furthermore, locomotor activity, working memory, and anxiety-related activities remained unaffected by the treatments. CGA treatment protects against ICV-STZ-induced increase in the nitrite/nitrate and TBARS levels. ICV-STZ induced a reduction in viable cells, depletion of BDNF, and triggered astrogliosis and microgliosis in the cortex and hippocampus. Treatment with CGA preserves viable cell count in the prefrontal cortex, CA1, and CA3 regions of the hippocampus. Additionally, it prevented BDNF depletion in the prefrontal cortex and hippocampus (CA1, CA3, and DG regions), and mitigated astrogliosis and microgliosis in the prefrontal cortex and hippocampus (CA1, CA3, and DG regions). These findings indicate the neuroprotective effects of CGA, underscoring their potential as therapeutic agents or adjuncts in the treatment of SAD.

Saroglitazar Enhances Memory Functions and Adult Neurogenesis via Up-Regulation of Wnt/β Catenin Signaling in the Rat Model of Dementia

Peroxisome proliferator-activated receptors (PPARs) have emerged as a promising target for the treatment of various neurodegenerative disorders. Studies have shown that both PPAR α & γ individually modulate various pathophysiological events like neuroinflammation and insulin resistance, which are known to variedly affect neurogenesis. Our study aimed to evaluate the effect of saroglitazar (SGZR), a dual PPAR agonist, on adult neurogenesis and spatial learning and memory, in intracerebroventricular streptozotocin (ICV STZ)-induced dementia in rats. We have found that SGZR at the dose of 4 mg/kg per oral showed significant improvement in learning and memory compared to ICV STZ-treated rats. A substantial increase in neurogenesis was observed in the subventricular zone (SVZ) and the dentate gyrus (DG), as indicated by an increase in the number of 5-bromo-2'-deoxyuridine (BrdU)+ cells, BrdU+ nestin+ cells, and doublecortin (DCX)+cells. Treatment with SGZR also decreased the active form of glycogen synthase kinase 3β (GSK3β) and hence enhanced the nuclear translocation of the β-catenin. Enhanced expression of Wnt transcription factors and target genes indicates that the up-regulation of Wnt signaling might be involved in the observed increase in neurogenesis. Hence, it can be concluded that the SGZR enhances memory functions and adult neurogenesis via the upregulation of Wnt β-catenin signaling in ICV STZ-treated rats.

MST1 selective inhibitor Xmu-mp-1 ameliorates neuropathological changes in a rat model of sporadic Alzheimer's Disease by modulating Hippo-Wnt signaling crosstalk

Alzheimer's disease (AD), the most prevalent form of dementia, is characterized by progressive cognitive impairment accompanied by aberrant neuronal apoptosis. Reports suggest that the pro-apoptotic mammalian set20-like kinase 1/2 (MST1/2) instigates neuronal apoptosis via activating the Hippo signaling pathway under various stress conditions, including AD. However, whether inhibiting MST1/2 has any therapeutic benefits in AD remains unknown. Thus, we tested the therapeutic effects of intervening MST1/2 activation via the pharmacological inhibitor Xmu-mp-1 in a sporadic AD rat model. Sporadic AD was established in adult rats by intracerebroventricular streptozotocin (ICV-STZ) injection (3 mg/kg body weight). Xmu-mp-1 (0.5 mg/kg/body weight) was administered once every 48 h for two weeks, and Donepezil (5 mg/kg body weight) was used as a reference standard drug. The therapeutic effects of Xmu-mp-1 on ICV-STZ rats were determined through various behavioral, biochemical, histopathological, and molecular tests. At the behavioral level, Xmu-mp-1 improved cognitive deficits in sporadic AD rats. Further, Xmu-mp-1 treatment reduced STZ-associated tau phosphorylation, amyloid-beta deposition, oxidative stress, neurotoxicity, neuroinflammation, synaptic dysfunction, neuronal apoptosis, and neurodegeneration. Mechanistically, Xmu-mp-1 exerted these neuroprotective actions by inactivating the Hippo signaling while potentiating the Wnt/β-Catenin signaling in the AD rats. Together, the results of the present study provide compelling support that Xmu-mp-1 negated the neuronal dysregulation in the rat model of sporadic AD. Therefore, inhibiting MST/Hippo signaling and modulating its crosstalk with the Wnt/β-Catenin pathway can be a promising alternative treatment strategy against AD pathology. This is the first study providing novel mechanistic insights into the therapeutic use of Xmu-mp-1 in sporadic AD.

Therapeutic Effects Of Combined and Chronic Treatment of Tat-GluA23y and D-Serine on Cognitive Dysfunction in Postmenopausal Rats

BACKGROUND

The incidence of Alzheimer's disease (AD) in female gender compared with male has been addressed as a health concern, particularly in menopausal age. We here hypothesized that co-administration of NMDARs agonist (D-serine) and AMPARs endocytosis inhibitor (Tat-GluA23y) might be a potential target for alleviating memory impairment in sporadic Alzheimer model of rats.

METHODS

Forty-eight female Wistar rats weighing 200-220 randomly divided into six groups. One month later, ovariectomized rats underwent stereotaxic surgery and were cannulated into the brain lateral ventricles. Streptozotocin was injected (3 mg/kg), then animals received the related treatments until the day 51, which experienced acquisition of spatial memory in Morris Water Maze test. Finally, the level of phosphorylated cAMP response element binding protein (CREB) in the hippocampus was measured by Western blotting.

RESULTS

Co-administration of D-serine and GluA23y significantly enhanced the acquisition and retrieval of impaired spatial memory in ovariectomized rats with AD (p < .001). Compared to Glu-A 23, D-serine caused more improvement in the mentioned parameters above, however, these values for both groups were still significantly different from the control group (P < .05).

CONCLUSION

Simultaneous treatment with D-serine and GluA23y synergistically improved STZ induced spatial memory impairment in OVX rat, probably partly via increase in phosphorylated CREB protein.

Effect of imipramine on memory, adult neurogenesis, neuroinflammation, and mitochondrial biogenesis in a rat model of alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline and memory loss. Imipramine, a tricyclic antidepressant, has potent anti-inflammatory and antioxidant properties in the central nervous system. The aim of this study was to investigate the neuroprotective effects of imipramine on streptozotocin (STZ)-induced memory impairment. Male Wistar rats received an intracerebroventricular injection of STZ (3 mg/kg, 3 μl/ventricle) using the stereotaxic apparatus. The Morris water maze and passive avoidance tests were used to evaluate cognitive functions. 24 h after the STZ injection, imipramine was administered intraperitoneally at doses of 10 or 20 mg/kg for 14 consecutive days. The mRNA and protein levels of neurotrophic factors (BDNF and GDNF) and pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α) were measured in the hippocampus using real-time PCR and ELISA techniques, respectively. In addition, real-time PCR was used to evaluate the mRNA levels of markers associated with neurogenesis (Nestin, DCX, and Ki67) and mitochondrial biogenesis (PGC-1α, NRF-1, and TFAM). The results showed that imipramine, especially at a dose of 20 mg/kg, effectively improved STZ-induced memory impairment. This improvement was associated with an increase in neurogenesis and neurotrophic factors and a decrease in neuroinflammation and mitochondrial biogenesis dysfunction. Based on these results, imipramine appears to be a promising therapeutic option for improving cognitive functions in neurodegenerative diseases such as AD.

Melatonin improves cognitive dysfunction and decreases gliosis in the streptozotocin-induced rat model of sporadic Alzheimer's disease

Introduction

Alzheimer's disease (AD) and other forms of dementia have a devastating effect on the community and healthcare system, as neurodegenerative diseases are causing disability and dependency in older population. Pharmacological treatment options are limited to symptomatic alleviation of cholinergic deficit and accelerated clearance of β-amyloid aggregates, but accessible disease-modifying interventions are needed especially in the early phase of AD. Melatonin was previously demonstrated to improve cognitive function in clinical setting and experimental studies also.

Methods

In this study, the influence of melatonin supplementation was studied on behavioral parameters and morphological aspects of the hippocampus and amygdala of rats. Streptozotocin (STZ) was injected intracerebroventricularly to induce AD-like symptoms in male adult Wistar rats (n = 18) which were compared to age-matched, sham-operated animals (n = 16). Melatonin was administered once daily in a dose of 20 mg/kg body weight by oral route. Behavioral analysis included open-field, novel object recognition, and radial-arm maze tests. TNF-α and MMP-9 levels were determined from blood samples to assess the anti-inflammatory and neuroprotective effects of melatonin. Immunohistological staining of brain sections was performed using anti-NeuN, anti-IBA-1, and anti-GFAP primary antibodies to evaluate the cellular reorganization of hippocampus.

Results and Discussion

The results show that after 40 days of treatment, melatonin improved the cognitive performance of STZ-induced rats and reduced the activation of microglia in both CA1 and CA3 regions of the hippocampus. STZ-injected animals had higher levels of GFAP-labeled astrocytes in the CA1 region, but melatonin treatment reduced this to that of the control group. In conclusion, melatonin may be a potential therapeutic option for treating AD-like cognitive decline and neuroinflammation.

The effect of intra-nasal co-treatment with insulin and growth factor-rich serum on behavioral defects, hippocampal oxidative-nitrosative stress, and histological changes induced by icv-STZ in a rat model

Impaired insulin and growth factor functions are thought to drive many alterations in neurodegenerative diseases like dementia and seem to contribute to oxidative stress and inflammatory responses. Recent studies revealed that nasal growth factor therapy could induce neuronal and oligodendroglia protection in rodent brain damage induction models. Impairment of several growth factors signaling was reported in neurodegenerative diseases. So, in the present study, we examined the effects of intranasal co-treatment of insulin and a pool of growth factor-rich serum (GFRS) which separated from activated platelets on memory, and behavioral defects induced by intracerebroventricular streptozotocin (icv-STZ) rat model also investigated changes in the hippocampal oxidative-nitrosative state and histology. We found that icv-STZ injection (3 mg/kg bilaterally) impairs spatial learning and memory in Morris Water Maze, leads to anxiogenic-like behavior in the open field arena, and induces oxidative-nitrosative stress, neuroinflammation, and neuronal/oligodendroglia death in the hippocampus. GFRS (1µl/kg, each other day, 9 doses) and regular insulin (4 U/40 µl, daily, 18 doses) treatments improved learning, memory, and anxiogenic behaviors. The present study showed that co-treatment (GFRS + insulin with respective dose) has more robust protection against hippocampal oxidative-nitrosative stress, neuroinflammation, and neuronal/oligodendroglia survival in comparison with the single therapy. Memory and behavioral improvements in the co-treatment of insulin and GFRS could be attributed to their effects on neuronal/oligodendroglia survival and reduction of neuroinflammation in the hippocampus.

Chitosan/PLA-loaded Magnesium oxide nanocomposite to attenuate oxidative stress, neuroinflammation and neurotoxicity in rat models of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by amyloid-beta (Aβ) aggregation, neuroinflammation, oxidative stress, and dysfunction in the mitochondria and cholinergic system. In this study, the synthesis of chitosan-polylactic acid-loaded magnesium oxide nanocomposite (CH/PLA/MgONCs) was examined using the green precipitation method. The synthesized CH/PLA/MgONCs were confirmed by using the UV-Vis spectrum, FT-IR, SEM-EDAX, and physical properties. The experiments were carried out using male Wistar rats by injecting streptozotocin (STZ) bilaterally into the brain's ventricles through the intracerebroventricular (ICV) route at a dose of 3 mg/kg. We also evaluated the effects of CH/PLA/MgONCs at doses of 10 mg/kg. To assess the cognitive dysfunction induced by ICV-STZ, we performed behavioral, biochemical, and histopathological analyses. In our study results, UV-Vis spectrum analysis of CH/PLA/MgONCs showed 285 nm, FT-IR analyses confirmed that the various functional groups were present, and SEM-EDAX analysis confirmed that a cauliflower-like spherical shape, Mg and O were present. Treatment with CH/PLA/MgONCs (10 mg/kg) showed a significant improvement in spatial and non-spatial memory functions. This was further supported by biochemical analysis showing improved antioxidant enzyme (GSH, SOD, CAT, and GPx activity) activities that significantly attenuated cholinergic activity and oxidative stress. In the CH/PLA/MgONCs-treated group, significant improvement was observed in the mitochondrial complex activity. ICV-STZ-induced neuroinflammation, as indicated by increased levels of TNF-α, IL-6, and CRP, was significantly reduced by CH/PLA/MgONCs treatment. Additionally, CH/PLA/MgONCs treated histological results showed improved healthy neuronal cells in the brain. Furthermore, in silico studies confirm that these molecules have good binding affinity and inhibit Aβ aggregation. In conclusion, CH/PLA/MgONCs treatment reversed AD pathology by improving memory and reducing oxidative stress, neuroinflammation, and mitochondrial dysfunction. These findings recommend that CH/PLA/MgONCs are possible therapeutic agents to treat AD.

Gelatin/polyethylene glycol-loaded magnesium hydroxide nanocomposite to attenuate acetylcholinesterase, neurotoxicity, and activation of GPR55 protein in rat models of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease marked by mitochondrial dysfunction, amyloid-β (Aβ) aggregation, and neuronal cell loss. G-protein-coupled receptor 55 (GPR55) has been used as a promising target for insulin receptors in diabetes therapy, but GPR55's role in AD is still unidentified. Gelatin (GE) and polyethylene glycol (PEG) polymeric hydrogels are commonly used in the drug delivery system. Therefore, the aim of the present study was the preparation of magnesium hydroxide nanocomposite using Clitoria ternatea (CT) flower extract, GE, and PEG (GE/PEG/Mg(OH)2NCs) by the green precipitation method. The synthesized GE/PEG/Mg(OH)2NCs were used to determine the effect of GPR55 activation of intracerebroventricular administration on streptozotocin (ICV-STC)-induced cholinergic dysfunction, oxidative stress, neuroinflammation, and cognitive deficits. The GE/PEG/Mg(OH)2NCs were administered following bilateral ICV-STC administration (3 mg/kg) in experimental rats. Neurobehavioral assessments were performed using a Morris water maze (MWM) and a passive avoidance test (PA). Cholinergic and antioxidant activity, oxidative stress, and mitochondrial complex activity were estimated in the cortex and hippocampus through biochemical analysis. Inflammatory markers (TNF-α, IL-6, and IL-1β) were determined using the ELISA method. Our study results demonstrated that the GE/PEG/Mg(OH)2NCs treatment significantly improved spatial and non-spatial memory functions in behavioral studies. Moreover, the treatment with GE/PEG/Mg(OH)2NCs group significantly attenuated cholinergic dysfunction, oxidative stress, and inflammatory markers, and also highly improved anti-oxidant activity (GSH, SOD, CAT, and GPx) in the cortex and hippocampus regions. The western blot results suggest the activation of the GPR55 protein expression through GE/PEG/Mg(OH)2NCs. The histopathological studies showed clear cytoplasm and healthy neurons, effectively promoting neuronal activity. Furthermore, the molecular docking results demonstrated the binding affinity and potential interactions of the compounds with the AChE enzyme. In conclusion, the GE/PEG/Mg(OH)2NCs treated groups showed reduced neurotoxicity and have the potential as a therapeutic agent to effectively target AD.

Voglibose attenuates cognitive impairment, Aβ aggregation, oxidative stress, and neuroinflammation in streptozotocin-induced Alzheimer's disease rat model

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease hallmarked by Amyloid-β (Aβ) aggregation, cognitive impairment, and neuronal and synaptic loss. In this study, AD was induced in male Wistar rats (n = 6) by the administration of intracerebroventricular-streptozotocin (ICV-STZ-3 mg/kg/day), and Voglibose (Vog) was administered at various doses (10, 25, and 50 mg/kg), while Galantamine (3 mg/kg) acted as a reference standard drug. Behavioral alterations in both spatial and non-spatial memory functions were evaluated in the experimental rats. At the end of the study, all experimental rats were sacrificed, and their brain parts, the cortex and hippocampus, were subjected to biochemical, western blot, and histopathological analysis. In our study results, the statistically significant dose-dependent results from the behavioral tests show the Voglibose-treated groups significantly improved (p < 0.0001) spatial and non-spatial memory functions when compared with ICV-STZ-treated group. Meanwhile, when compared with ICV-STZ-treated rats, treatment with Voglibose (10, 25, and 50 mg/kg) showed the activities of both acetylcholinesterase (AChE) and malondialdehyde (MDA) were significantly attenuated (p < 0.0001), while the operation of antioxidant enzymes was considerably enhanced (p < 0.0001). The molecular estimation showed that it significantly attenuates (p < 0.0001) the TNF-α, IL-1β, and CRP activity, and the western blot results demonstrate the significantly attenuated Aβ aggregation. The histopathological results showed that the Voglibose treatment had an effective improvement in clear cytoplasm and healthy neuronal cells. In conclusion, our results suggest that Voglibose has potent neuroprotective effects against the ICV-STZ-induced AD model. Furthermore, these results support the possibility of Voglibose as a therapeutic approach to improving cognitive function, suggesting that controlling Aβ aggregation might be a novel target for the development of AD.

Repurposing Diltiazem for Its Neuroprotective Anti-Dementia Role against Intra-Cerebroventricular Streptozotocin-Induced Sporadic Alzheimer's Disease-Type Rat Model

Alzheimer's disease (AD) is an age-related neuropsychiatric disorder and a common cause of progressive dementia. Diltiazem (DTZ), the non-dihydropyridine benzothiazepine class of calcium channel blocker (CCB), used clinically in angina and other cardiovascular disorders, has proven neurological benefits. In the present study, the neuroprotective anti-dementia effects of DTZ against intra-cerebroventricular-streptozotocin (ICV-STZ)-induced sporadic AD (SAD)-type rat model was investigated. ICV-STZ-induced cognitive impairments were measured via passive avoidance and Morris water maze tasks. Anti-oxidative enzyme status, pro-inflammatory markers, and amyloid-beta (Aβ) protein expression in rat brain tissues were measured using ELISA kits, Western blotting, and immunostaining techniques. The data revealed that ICV-STZ injection in rats significantly induced cognitive deficits and altered the levels of oxidative and pro-inflammatory markers (p < 0.05~p < 0.001). Treatment with DTZ (10 mg/kg, 20 mg/kg, and 40 mg/kg, p.o.) daily for twenty-one days, 1 h before a single ICV-STZ (3 mg/kg) injection, significantly improved cognitive impairments and ameliorated the ICV-STZ-induced altered nitrite, pro-inflammatory cytokines (TNF-α, and IL-1β) and anti-oxidative enzyme levels (superoxide dismutase, lipid peroxidation, and glutathione). Further, DTZ restored the increased Aβ protein expression in ICV-STZ-induced brain tissue. Considering the results obtained, DTZ might have a potential therapeutic role in treating and managing AD and related dementia pathologies due to its anti-dementia activity in SAD-type conditions in rats induced by ICV-STZ.

Melatonin reduces β-amyloid accumulation and improves short-term memory in streptozotocin-induced sporadic Alzheimer's disease model

Melatonin is a hormone secreted by the pineal gland, it can be associated with circadian rhythms, aging and neuroprotection. Melatonin levels are decreased in sporadic Alzheimer's disease (sAD) patients, which suggests a relationship between the melatonergic system and sAD. Melatonin may reduce inflammation, oxidative stress, TAU protein hyperphosphorylation, and the formation of β-amyloid (Aβ) aggregates. Therefore, the objective of this work was to investigate the impact of treatment with 10 mg/kg of melatonin (i.p) in the animal model of sAD induced by the intracerebroventricular (ICV) infusion of 3 mg/kg of streptozotocin (STZ). ICV-STZ causes changes in the brain of rats similar to those found in patients with sAD. These changes include; progressive memory decline, the formation of neurofibrillary tangles, senile plaques, disturbances in glucose metabolism, insulin resistance and even reactive astrogliosis characterized by the upregulation of glucose levels and glial fibrillary acidic protein (GFAP). The results show that ICV-STZ caused short-term spatial memory impairment in rats after 30 days of STZ infusion without locomotor impairment which was evaluated on day 27 post-injury. Furthermore, we observed that a prolonged 30-day treatment with melatonin can improve the cognitive impairment of animals in the Y-maze test, but not in the object location test. Finally, we demonstrated that animals receiving ICV-STZ have high levels of Aβ and GFAP in the hippocampus and that treatment with melatonin reduces Aβ levels but does not reduce GFAP levels, concluding that melatonin may be useful to control the progression of amyloid pathology in the brain.

Intranasal in situ gelling liquid crystal for delivery of resveratrol ameliorates memory and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is an illness that affects people aged 65 or older and affects around 6.5 million in the United States. Resveratrol is a chemical obtained from natural products and it exhibits biological activity based on inhibiting the formation, depolymerization of the amyloid, and decreasing neuroinflammation. Due to the insolubility of this compound; its incorporation in surfactant-based systems was proposed to design an intranasal formulation. A range of systems has been produced by mixing oleic acid, CETETH-20 and water. Polarised light microscopy (PLM), small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) confirm the initial liquid formulation (F) presented as microemulsion (ME). After dilution, the gelled systems were characterized as hexagonal mesophase and they showed feasibility proprieties. Pharmacological assays performed after intranasal administration showed the ability to improve learning and memory in animals, as well as remission of neuroinflammation via inhibition of interleukin.

Neuroprotective Role of DPP-4 Inhibitor Linagliptin Against Neurodegeneration, Neuronal Insulin Resistance and Neuroinflammation Induced by Intracerebroventricular Streptozotocin in Rat Model of Alzheimer's Disease

Alzheimer's disease (AD) is an age-related, multifactorial progressive neurodegenerative disorder manifested by cognitive impairment and neuronal death in the brain areas like hippocampus, yet the precise neuropathology of AD is still unclear. Continuous failure of various clinical trial studies demands the utmost need to explore more therapeutic targets against AD. Type 2 Diabetes Mellitus and neuronal insulin resistance due to serine phosphorylation of Insulin Receptor Substrate-1 at 307 exhibits correlation with AD. Dipeptidyl Peptidase-4 inhibitors (DPP-4i) have also indicated therapeutic effects in AD by increasing the level of Glucagon-like peptide-1 in the brain after crossing Blood Brain Barrier. The present study is hypothesized to examine Linagliptin, a DPP-4i in intracerebroventricular streptozotocin induced neurodegeneration, and neuroinflammation and hippocampal insulin resistance in rat model of AD. Following infusion on 1st and 3rd day, animals were treated orally with Linagliptin (0.513 mg/kg, 3 mg/kg, and 5 mg/kg) and donepezil (5 mg/kg) as a standard for 8 weeks. Neurobehavioral, biochemical and histopathological analysis was done at the end of treatment. Dose-dependently Linagliptin significantly reversed behavioral alterations done through locomotor activity (LA) and morris water maze (MWM) test. Moreover, Linagliptin augmented hippocampal GLP-1 and Akt-ser473 level and mitigated soluble Aβ (1-42), IRS-1 (s307), GSK-3β, TNF-α, IL-1β, IL-6, AchE and oxidative/nitrosative stress level. Histopathological analysis also exhibited neuroprotective and anti-amylodogenic effect in Hematoxylin and eosin and Congo red staining respectively. The findings of our study concludes remarkable dose-dependent therapeutic potential of Linagliptin against neuronal insulin resistance via IRS-1 and AD-related complication. Thus, demonstrates unique molecular mechanism that underlie AD.

Investigation Covering the Effect of Boron plus Taurine Application on Protein Carbonyl and Advanced Oxidation Protein Products Levels in Experimental Alzheimer Model

Alzheimer's disease (AD) is the most common form of dementia that occurs in the brain. This is a chronic neurodegenerative disease which is valid in 60-70% of all dementia patients. Boron, regarded as a potential antioxidant, has the effect of reducing oxidative stress. Taurine, as one of the thiol-containing amino acids, exists at different concentrations in both the neurons and glial cells of the central nervous system. It plays an important role in the protective and adjuvant therapies as an antioxidant due to its characteristics of maintaining the oxidant-antioxidant balance of the body as well as cell integrity and increasing body resistance. Based on this information, our objective was to reveal the effect of boron alone, taurine alone plus co-administration of taurine and boron application on brain tissue protein carbonyls (PC) and serum advanced oxidation protein products (AOPP) levels in the experimental Alzheimer's model. For this purpose, 5 groups were formed in our study which consisted of 30 Wistar albino male rats. The rats were given a single dose of STZ stereotaxically. At the end of this period, the rats were decapitated, plus their brain tissues and blood were removed. Our findings suggested that taurine alone and co-administration of boron and taurine had a decreasing effect on AOPP and PC levels of the experimental Alzheimer model of the rats.

ACE2/ANG-(1-7)/Mas receptor axis activation prevents inflammation and improves cognitive functions in streptozotocin induced rat model of Alzheimer's disease-like phenotypes

Activation of the renin-angiotensin system (RAS), by Angiotensin converting enzyme/Angiotensin II/Angiotensin receptor-1 (ACE/Ang II/AT1 R) axis elicits amyloid deposition and cognitive impairment. Furthermore, ACE2 induced release of Ang-(1-7) binds with the Mas receptor and autoinhibits ACE/Ang II/AT1 axis activation. Inhibition of ACE by perindopril has been reported to improve memory in preclinical settings. However, the functional significance and mechanism by which ACE2/Mas receptor regulate cognitive functions and amyloid pathology is not known. The present study is aimed to determine the role of ACE2/Ang-(1-7)/Mas receptor axis in STZ induced rat model of Alzheimer's disease (AD). We have used pharmacological, biochemical and behavioural approaches to identify the role of ACE2/Ang-(1-7)/Mas receptor axis activation on AD-like pathology in both in vitro and invivo models. STZ treatment enhances ROS formation, inflammation markers and NFκB/p65 levels which are associated with reduced ACE2/Mas receptor levels, acetylcholine activity and mitochondrial membrane potential in N2A cells. DIZE mediated ACE2/Ang-(1-7)/Mas receptor axis activation resulted in reduced ROS generation, astrogliosis, NFκB level and inflammatory molecules and improved mitochondrial functions along with Ca²⁺ influx in STZ treated N2A cells. Interestingly, DIZE induced activation of ACE2/Mas receptor significantly restored acetylcholine levels and reduced amyloid-beta and phospho-tau deposition in cortex and hippocampus that resulted in improved cognitive function in STZ induced rat model of AD-like phenotypes. Our data indicate that ACE2/Mas receptor activation is sufficient to prevented cognitive impairment and progression of amyloid pathology in STZ induced rat model of AD-like phenotypes. These findings suggest the potential role of ACE2/Ang-(1-7)/Mas axis in AD pathophysiology by regulating inflammation cognitive functions.

Insight into the role of adult hippocampal neurogenesis in aging and Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and seriously affects the quality of life of the elderly. Neurodegeneration is closely related to hippocampal dysfunction in AD patients. The hippocampus is key to creating new memories and is also one of the first areas of the brain to deteriorate with age. Mammalian neurogenesis occurs mainly in the hippocampus. Recent studies have confirmed that neurogenesis in the hippocampus is sustainable but decreases with age, which seriously affects the learning and memory function of AD patients. At present, our understanding of neurogenesis is still relatively shallow, especially pertaining to the influence and role of neurogenesis during aging and cognitive deficits in AD patients. Interestingly, many recent studies have described the characteristics of neurogenesis in animal models. This article reviews the progress of neurogenesis research in the context of aging and AD to provide new insights into neurogenesis.

The Dialogue Between Neuroinflammation and Adult Neurogenesis: Mechanisms Involved and Alterations in Neurological Diseases

Adult neurogenesis occurs mainly in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles. Evidence supports the critical role of adult neurogenesis in various conditions, including cognitive dysfunction, Alzheimer's disease (AD), and Parkinson's disease (PD). Several factors can alter adult neurogenesis, including genetic, epigenetic, age, physical activity, diet, sleep status, sex hormones, and central nervous system (CNS) disorders, exerting either pro-neurogenic or anti-neurogenic effects. Compelling evidence suggests that any insult or injury to the CNS, such as traumatic brain injury (TBI), infectious diseases, or neurodegenerative disorders, can provoke an inflammatory response in the CNS. This inflammation could either promote or inhibit neurogenesis, depending on various factors, such as chronicity and severity of the inflammation and underlying neurological disorders. Notably, neuroinflammation, driven by different immune components such as activated glia, cytokines, chemokines, and reactive oxygen species, can regulate every step of adult neurogenesis, including cell proliferation, differentiation, migration, survival of newborn neurons, maturation, synaptogenesis, and neuritogenesis. Therefore, this review aims to present recent findings regarding the effects of various components of the immune system on adult neurogenesis and to provide a better understanding of the role of neuroinflammation and neurogenesis in the context of neurological disorders, including AD, PD, ischemic stroke (IS), seizure/epilepsy, TBI, sleep deprivation, cognitive impairment, and anxiety- and depressive-like behaviors. For each disorder, some of the most recent therapeutic candidates, such as curcumin, ginseng, astragaloside, boswellic acids, andrographolide, caffeine, royal jelly, estrogen, metformin, and minocycline, have been discussed based on the available preclinical and clinical evidence.

Dimethyl Fumarate Alleviates Adult Neurogenesis Disruption in Hippocampus and Olfactory Bulb and Spatial Cognitive Deficits Induced by Intracerebroventricular Streptozotocin Injection in Young and Aged Rats

The disorder of adult neurogenesis is considered an important mechanism underlying the learning and memory impairment observed in Alzheimer's disease (AD). The sporadic nonhereditary form of AD (sAD) affects over 95% of AD patients and is related to interactions between genetic and environmental factors. An intracerebroventricular injection of streptozotocin (STZ-ICV) is a representative and well-established method to induce sAD-like pathology. Dimethyl fumarate (DMF) has antioxidant and anti-inflammatory properties and is used for multiple sclerosis treatment. The present study determines whether a 26-day DMF therapy ameliorates the disruption of adult neurogenesis and BDNF-related neuroprotection in the hippocampus and olfactory bulb (OB) in an STZ-ICV rat model of sAD. Considering age as an important risk factor for developing AD, this study was performed using 3-month-old (the young group) and 22-month-old (the aged group) male Wistar rats. Spatial cognitive functions were evaluated with the Morris water maze task. Immunofluorescent labelling was used to assess the parameters of adult neurogenesis and BDNF-related neuroprotection in the hippocampus and OB. Our results showed that the STZ-ICV evoked spatial learning and memory impairment and disturbances in adult neurogenesis and BDNF expression in both examined brain structures. In the aged animals, the deficits were more severe. We found that the DMF treatment significantly alleviated STZ-ICV-induced behavioural and neuronal disorders in both age groups of the rats. Our findings suggest that DMF, due to its beneficial effect on the formation of new neurons and BDNF-related neuroprotection, may be considered as a promising new therapeutic agent in human sAD.

Protective effect of miR-34c antagomir against STZ-induced memory impairment by targeting mTOR and PSD-95 in the hippocampus of rats

After long times of ongoing research, still there is no appropriate cure for Alzheimer's disease (AD). Recently, epigenetic alterations, particularly miRNA, have gotten attention in AD research. Among various miRNA, miR-34c has been addressed to be elevated in the brain of AD patients, however, its exact role and downstream mechanisms have not been elucidated yet. This study aimed to investigate the therapeutic potential of miR-34c antagomir on cognitive dysfunction induced by streptozocin (STZ), considering postsynaptic density protein 95 (PSD-95) and mammalian target of rapamycin expression (mTOR). Forty rats were cannulated intraventricularly under deep anesthesia using stereotaxic apparatus and divided into five groups: saline + saline, STZ + saline, STZ + miR-34c antagomir, STZ + lipofectamine, and STZ + scrambled, and received the related treatments for two weeks. At the end of the treatments, spatial memory and locomotor activity were assessed by Morris water maze (MWM), and open fields, respectively. Finally, PSD-95 and mTOR levels were measured by quantitative real-time PCR (qPCR) and western blotting on hippocampal samples. Results showed that miR-34c antagomir markedly ameliorated spatial learning and memory deficits induced by STZ, and significantly enhanced PSD-95 and mTOR levels in the hippocampus. In conclusion, miR-34c antagomir may be considered as a promising novel therapeutic target for AD patients.

Examination of Longitudinal Alterations in Alzheimer’s Disease-Related Neurogenesis in an APP/PS1 Transgenic Mouse Model, and the Effects of P33, a Putative Neuroprotective Agent Thereon

Neurogenesis plays a crucial role in cognitive processes. During aging and in Alzheimer’s disease (AD), altered neurogenesis and neuroinflammation are evident both in C57BL/6J, APP_Swe/PS1_dE9 (Tg) mice and humans. AD pathology may slow down upon drug treatment, for example, in a previous study of our group P33, a putative neuroprotective agent was found to exert advantageous effects on the elevated levels of APP, Aβ, and neuroinflammation. In the present study, we aimed to examine longitudinal alterations in neurogenesis, neuroinflammation and AD pathology in a transgenic (Tg) mouse model, and assessed the putative beneficial effects of long-term P33 treatment on AD-specific neurological alterations. Hippocampal cell proliferation and differentiation were significantly reduced between 8 and 12 months of age. Regarding neuroinflammation, significantly elevated astrogliosis and microglial activation were observed in 6- to 7-month-old Tg animals. The amounts of the molecules involved in the amyloidogenic pathway were altered from 4 months of age in Tg animals. P33-treatment led to significantly increased neurogenesis in 9-month-old animals. Our data support the hypothesis that altered neurogenesis may be a consequence of AD pathology. Based on our findings in the transgenic animal model, early pharmacological treatment before the manifestation of AD symptoms might ameliorate neurological decline.

Prenatal Venlafaxine Exposure-Induced Neurocytoarchitectural and Neuroapoptotic Degeneration in Striatum and Hippocampus of Developing Fetal Brain, Manifesting Long-term Neurocognitive Impairments in Rat Offspring

Depression is a leading cause of disability which at its worst leads to suicide. Its treatment relies on psychotherapy in combination with certain antidepressants (AD_(s)) from various classes such as tricyclics, selective serotonin reuptake inhibitors, or serotonin and norepinephrine reuptake inhibitors (SNRIs). Among SNRIs, venlafaxine (VEN) is one such most commonly prescribed AD which is recently reported to be in the top 50 most prescribed drugs in the USA. Depression during pregnancy is a common condition, where prescribing an AD becomes necessary as untreated depression during pregnancy has its own complications for both mother and the child. This, probably, is why an incredible rise has been reported in prescribing ADs like VEN to pregnant women in the recent past, despite some studies, including the one from our own group, having reported the in-utero VEN-induced apoptotic neurodegeneration in the fetal neocortex and the consequent neurobehavioral anomalies in adulthood. However, there still exists a lack of insight into the effects of intrauterine exposures of VEN on other fetal brain regions like the hippocampus (HPC) and striatum (STR) and the consequent effects on their cognitive and emotional wellbeing in later life. Hence, this study has been conducted where pregnant Charles-Foster (CF) rats were oral gavaged with VEN (25, 40, and 50 mg/kg bw) from gestation day (GD) 05-19. On GD-19, half of the control and treated dams were euthanized to collect their fetuses. Fetal brains were dissected and processed for reactive oxygen species (ROS) estimation neurohistopathology and confocal microscopic studies. The remaining dams were allowed to deliver naturally, and litters were reared for up to 8 weeks then tested for their cognitive abilities by the Morris water maze test and for their emotionality by the Forced swimming test. Our results showed substantial neurocytoarchitectural deficits in both HPC and STR, along with enhanced ROS levels and apoptotic neurodegenerations. Furthermore, VEN-treated young rat offsprings displayed cognitive impairments and depressive behavior as the long-lasting impact of VEN in a dose-dependent manner. So it may be inferred that prenatal VEN-induced oxidative stress causes apoptotic neurodegeneration leading to neuronal loss in HPC and STR which consequently affects the development of the said brain areas resulting in impaired cognitive and emotional abilities of young adult offsprings. Therefore, extrapolating these findings in animal models, caution may be taken before prescribing VEN to pregnant women, especially during the sensitive phase of pregnancy.

Intranasal metformin treatment ameliorates cognitive functions via insulin signaling pathway in ICV-STZ-induced mice model of Alzheimer's disease

AIMS

The relationship between type 2 diabetes and Alzheimer's disease (AD) provides evidence that insulin and insulin sensitizers may be beneficial for the treatment of AD. The present study investigated the effect and mechanism of action of intranasal metformin treatment on impaired cognitive functions in an experimental mice model of AD.

MAIN METHODS

Intracerebroventricularly (ICV) streptozotocin (STZ)-injected mice were treated with intranasal or oral metformin for 4 weeks. Learning and memory functions were evaluated using Morris water maze. Metformin and Aβ42 concentrations were determined by liquid chromatography tandem mass spectrometry and ELISA respectively. The expressions of insulin receptor, Akt and their phosphorylated forms were determined in the hippocampi and cerebral cortices of mice.

KEY FINDINGS

ICV-STZ-induced AD mice displayed impaired learning and memory functions which were improved by metformin treatment. ICV-STZ injection or intranasal/oral metformin treatments had no effect on blood glucose concentrations. Intranasal treatment yielded higher concentration of metformin in the hippocampus and lower in the plasma compared to oral treatment. ICV-STZ injection and metformin treatments did not change amyloid β-42 concentration in the hippocampus of mice. In hippocampal and cortical tissues of ICV-STZ-induced AD mice, insulin receptor (IR) and Akt expressions were unchanged, while phosphorylated insulin receptor (pIR) and pAkt expressions decreased compared to control. Metformin treatments did not change IR and Akt expressions but increased pIR and pAkt expressions.

SIGNIFICANCE

The present study showed for the first time that intranasal metformin treatment improved the impaired cognitive functions through increasing insulin sensitivity in ICV-STZ-induced mice model of AD.

Effect of Letrozole on hippocampal Let-7 microRNAs and their correlation with working memory and phosphorylated Tau protein in an Alzheimer's disease-like rat model

Background

Let-7 microRNAs (miRNAs) may contribute to neurodegeneration, including Alzheimer's disease (AD), but, they were not investigated in Streptozotocin (STZ)-induced AD. Letrozole increases the expression of Let-7 in cell lines, with conflicting evidence regarding its effects on memory. This study examined Let-7 miRNAs in STZ-induced AD, their correlation with memory and hyperphosphorylated Tau (p-Tau) and the effects of Letrozole on them.

Methods

Seven groups of adult Sprague Dawley rats were used: Negative control, Letrozole, Letrozole Vehicle, STZ (with AD induced by intracerebroventricular injection of STZ in artificial cerebrospinal fluid (aCSF)), CSF Control, STZ + Letrozole (STZ-L), and CSF + Letrozole Vehicle. Alternation percentage in T-maze was used as a measure of working memory. Let-7a, b and e and p-Tau levels in the hippocampus were estimated using quantitative real-time reverse transcription–polymerase chain reaction (qRT–PCR) and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

Significant decreases in alternation percentage and increase in p-Tau concentration were found in the STZ, Letrozole and STZ-L groups. Expression levels of all studied microRNAs were significantly elevated in the Letrozole and the STZ-L groups, with no difference between the two, suggesting that this elevation might be linked to Letrozole administration. Negative correlations were found between alternation percentage and the levels of all studied microRNAs, while positive ones were found between p-Tau concentration and the levels of studied microRNAs.

Conclusions

This study shows changes in the expression of Let-7a, b and e miRNAs in association with Letrozole administration, and correlations between the expression of the studied Let-7 miRNAs and both the status of working memory and the hippocampal p-Tau levels. These findings might support the theory suggesting that Letrozole aggravates pre-existing lesions. They also add to the possibility of Let-7’s neurotoxicity.

Effect of the MAGL/FAAH Dual Inhibitor JZL-195 on Streptozotocin-Induced Alzheimer's Disease-like Sporadic Dementia in Mice with an Emphasis on Aβ, HSP-70, Neuroinflammation, and Oxidative Stress

Alzheimer's disease is identified by pathological hallmarks such as intracellular neurofibrillary tangles (NFTs) and extracellular amyloid β plaques. Several hypotheses exist to define the neurodegeneration including microglial activation associated with neuroinflammatory processes. Recently, pharmacological inhibition of endocannabinoid (eCB)-degrading enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), is being investigated to modulate the pathology of Alzheimer's disease. While MAGL inhibitors upregulate 2-acyl glycerol (2-AG) levels and reduce neuroinflammation, FAAH inhibitors elevate anandamide (AEA) levels and prevent the degradation of HSP-70, thereby preventing the phosphorylation of tau protein and formation of NFTs in neural cells. We investigated the possible neuroprotective potential of the dual MAGL/FAAH inhibitor JZL-195 (20 mg/kg) against ICV-STZ-induced sporadic Alzheimer's disease (SAD) in Swiss albino mice using donepezil (5 mg/kg) as the standard. The protective effects of JZL-195 were observed by the reversal of altered levels of Aβ1-42, HSP-70, neuroinflammatory cytokines, and oxidative stress markers. However, JZL-195 expressed no cognitive improvement when assessed by spontaneous alternation behavior and Morris water maze tests and no effects on the AChE enzyme level in the hippocampal tissues of mice. Therefore, the findings of the present study indicate that although JZL-195 exhibited no improvement in cognitive deficits associated with sporadic Alzheimer's disease, it displayed significant reversal of the biochemical anomalies, thereby suggesting its therapeutic potential against the sporadic Alzheimer's disease model.

Roflumilast Reduces Pathological Symptoms of Sporadic Alzheimer's Disease in Rats Produced by Intracerebroventricular Streptozotocin by Inhibiting NF-κB/BACE-1 Mediated Aβ Production in the Hippocampus and Activating the cAMP/BDNF Signalling Pathway

Alzheimer's disease (AD) is a neurological disease that gradually causes memory loss and cognitive impairment. The intracellular secondary messenger cyclic nucleotide cAMP helps in memory acquisition and consolidation. In several models of AD, increasing their levels using phosphodiesterase (PDE) inhibitors improved cognitive performance and prevent memory loss. Thus, the current investigation was undertaken to investigate the therapeutic potential of the PDE-4 inhibitor roflumilast (RFM) against intracerebroventricular (ICV) streptozotocin (STZ)-induced sporadic AD in rats. STZ (3 mg/kg) was given to rats via the ICV route on the stereotaxic apparatus, followed by RFM (0.51 mg/kg/oral) treatment for 15 days, and donepezil (5 mg/kg/oral) was employed as a reference standard drug. Subsequently, we observed that RFM dramatically increased rats learning and memory capacities as measured by the Morris water maze and a novel object recognition task. RFM enhanced the levels of cAMP and brain-derived neurotrophic factors (BDNFs) while decreasing the expression of nuclear factor kappa B (NF-κB) and glial fibrillary acidic protein (GFAP) in the hippocampus of ICV-STZ-infused rats. RFM was found to significantly reduce ICV-STZ-induced neuroinflammation, amyloidogenesis, oxidative stress cholinergic impairments, GSK-3β, and phosphorylated tau levels in the rat hippocampus. Supporting these, histopathological study using Cresyl violet and Congo red demonstrated that RFM reduced neuronal alterations and Aβ deposition in the hippocampus of AD rats. These findings suggest that RFM could be a promising candidate for the management of AD by inhibiting NF-κB/BACE-1 mediated Aβ production in the hippocampus and activating the cAMP/BDNF signalling pathway.

Self-Fluorescent Lone Tryptophan Nanoparticles as Theranostic Agents Against Alzheimer's Disease

Aggregation of β-amyloid (Aβ42) peptide in the neural extracellular space leads to cellular dysfunction, resulting in Alzheimer's disease (AD). The hydrophobic core of the amyloidogenic Aβ42 peptide contains aromatic residues that play an important role in the self-assembly and subsequent aggregation of the peptide. Hence, targeting these hydrophobic core residues by potent low molecular agents can be a promising therapeutic approach toward AD. In the current work, we have developed self-fluorescent solo tryptophan nanoparticles (TNPs) as nanotheranostic systems against AD. We demonstrated that TNPs could significantly inhibit as well as disrupt the fibrils formed by both Aβ42 peptide and another reductionist approach-based amyloid model dipeptide, phenylalanine-phenylalanine (FF). More importantly, these nanostructures were nontoxic to neural cells and could protect the neurons from Aβ42 peptide and FF aggregate-induced cytotoxicity. In addition, efficacy studies performed in animal model further revealed that the TNPs could rescue spatial and learning memory in intracerebroventricular streptozotocin-administration-induced AD phenotype in rats. Moreover, our pharmacokinetics study further established the BBB permeability and brain delivery potency of TNPs. The inherent excellent fluorescent properties of these nanoparticles could be exploited further to use them as imaging modalities for tagging and detecting FF and Aβ42 peptide fibrils. Overall, our results clearly illustrated that the solo TNPs could serve as promising nanotheranostic agents for AD therapy.

Exosomes derived from bone-marrow mesenchymal stem cells alleviate cognitive decline in AD-like mice by improving BDNF-related neuropathology

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive decline in cognitive ability. Exosomes derived from bone-marrow mesenchymal stem cells (BMSC-exos) are extracellular vesicles that can execute the function of bone-marrow mesenchymal stem cells (BMSCs). Given the versatile therapeutic potential of BMSC and BMSC-exos, especially their neuroprotective effect, the aim of this study was to investigate the potential effect of BMSC-exos on AD-like behavioral dysfunction in mice and explore the possible molecular mechanism.

METHODS

BMSC-exos were extracted from the supernatant of cultured mouse BMSCs, which were isolated from the femur and tibia of adult C57BL/6 mice, purified and sorted via flow cytometry, and cultured in vitro. BMSC-exos were identified via transmission electron microscopy, and typical marker proteins of exosomes were also detected via Western blot. A sporadic AD mouse model was established by intracerebroventricular injection of streptozotocin (STZ). Six weeks later, BMSC-exos were administered via lateral ventricle injection or caudal vein injection lasting five consecutive days, and the control mice were intracerebroventricularly administered an equal volume of solvent. Behavioral performance was observed via the open field test (OFT), elevated plus maze test (EPM), novel object recognition test (NOR), Y maze test (Y-maze), and tail suspension test (TST). The mRNA and protein expression levels of IL-1β, IL-6, and TNF-α in the hippocampus were measured via quantitative polymerase chain reaction (qPCR) and Western blot, respectively. Moreover, the protein expression of Aβ1-42, BACE, IL-1β, IL-6, TNF-α, GFAP, p-Tau (Ser396), Tau5, synaptotagmin-1 (Syt-1), synapsin-1, and brain-derived neurotrophic factor (BDNF) in the hippocampus was detected using Western blot, and the expression of GFAP, IBA1, Aβ1-42 and DCX in the hippocampus was measured via immunofluorescence staining.

RESULTS

Lateral ventricle administration, but not caudal vein injection of BMSC-exos improved AD-like behaviors in the STZ-injected mouse model, as indicated by the increased number of rearing, increased frequency to the central area, and increased duration and distance traveled in the central area in the OFT, and improved preference index of the novel object in the NOR. Moreover, the hyperactivation of microglia and astrocytes in the hippocampus of the model mice was inhibited after treatment with BMSC-exos via lateral ventricle administration, accompanied by the reduced expression of IL-1β, IL-6, TNF-α, Aβ1-42, and p-Tau and upregulated protein expression of synapse-related proteins and BDNF. Furthermore, the results of the Pearson test showed that the preference index of the novel object in the NOR was positively correlated with the hippocampal expression of BDNF, but negatively correlated with the expression of GFAP, IBA1, and IL-1β. Apart from a positive correlation between the hippocampal expression of BDNF and Syt-1, BDNF abundance was found to be negatively correlated with markers of glial activation and the expression of the inflammatory cytokines, Aβ1-42, and p-Tau, which are characteristic neuropathological features of AD.

CONCLUSIONS

Lateral ventricle administration, but not caudal vein injection of BMSC-exos, can improve AD-like behavioral performance in STZ-injected mice, the mechanism of which might be involved in the regulation of glial activation and its associated neuroinflammation and BDNF-related neuropathological changes in the hippocampus.

Dimethyl Fumarate as the Peripheral Blood Inflammatory Mediators Inhibitor in Prevention of Streptozotocin-Induced Neuroinflammation in Aged Rats

Purpose

Intracerebroventricular-(ICV)-streptozotocin-(STZ)-induced neuroinflammation is a model of Alzheimer’s disease (AD) compatible with the inflammation hypothesis of ageing (“inflammaging” state). Previously, we observed age-dependent (young vs aged) dimethyl fumarate (DMF)-induced anti-inflammatory and neuroprotective effects in the brain along with improvement in cognitive functions in rats with the ICV-STZ-induced model of AD. To evaluate whether DMF reduces neuroinflammation based on the peripheral inflammatory response inhibition, we determined peripheral inflammatory mediators in young and aged rats with the ICV-STZ-induced AD pathology following DMF therapy.

Materials and Methods

Young (4-month-old) and aged (22-month-old) rats were fed with 0.4% DMF rat chow for 21 consecutive days after ICV-STZ (3 mg/ventricle) injections. After behavioral testing, blood and spleens were collected to determine the numbers of leukocytes (WBC), lymphocytes and their subpopulations, haematological parameters, the concanavalin (Con)-A-induced production and plasma concentration of interferon (IFN)-γ, interleukin (IL)-6, IL-10 and corticosterone (COR).

Results

Age-dependent anti-inflammatory effect of the DMF treatment in rats with ICV-STZ injections manifested as decreased peripheral WBC and lymphocyte numbers, including TCD3⁺CD4⁺CD8⁻, TCD3⁺CD4⁻CD8⁺, B (CD45RA⁺) and NK (161a⁺), in aged rats. Furthermore, DMF lowered the blood and spleen lymphocyte production of pro-inflammatory IFN-γ and IL-6 in young and aged rats, whereas it enhanced the plasma level of anti-inflammatory IL-10 and lymphocyte’s ability to produce it in aged rats only. In parallel to changes in peripheral WBC numbers in the model of AD, DMF decreased the red blood cell number, haemoglobin concentration, haematocrit and mean platelet volume in aged, but not young, rats. In contrast to controls, DMF did not influence the COR response in STZ groups.

Conclusion

Besides preventing neuroinflammation, DMF acts on the pro-/anti-inflammatory balance in the periphery and causes an anti-inflammatory shift in T lymphocytes which could contribute to DMF’s therapeutic effects in the ICV-STZ-induced model of AD, in particular, in aged rats.

Quercetin Exhibits α7nAChR/Nrf2/HO-1-Mediated Neuroprotection Against STZ-Induced Mitochondrial Toxicity and Cognitive Impairments in Experimental Rodents

The objective of the present study was to investigate the α7nAChR-mediated Nrf2-dependant protective activity against streptozotocin (STZ)-induced brain mitochondrial toxicity in Alzheimer's disease (AD)-like rats. STZ (3 mg/kg) was injected through an intracerebroventricular route to induce AD-like dementia. Repeated Quercetin (50 mg/kg, i.p.) administration attenuated cognitive impairments in the STZ-challenged animals during Morris water-maze and Y-maze tests. Quercetin significantly mitigated the STZ-induced increase in cholinergic dysfunction, such as the increase in acetylcholinesterase activity, decrease in acetylcholine level, and activity of choline acetyltransferase, and increase in amyloid-beta aggregation and mitochondrial toxicity in respect of mitochondrial bioenergetics, integrity, and oxidative stress in memory-challenged rat hippocampus, prefrontal cortex and, amygdala. Further, Quercetin significantly attenuated STZ-induced reduction in the α7nAChRs and HO-1 expression levels in the selected rat brain regions. On the contrary, trigonelline (10 mg/kg, i.p.) and methyllycaconitine (2 mg/kg; i.p.) abolished the neuroprotective effects of Quercetin against STZ-induced behavioral, molecular, and biochemical alterations in the AD-like animals. Hence, Quercetin exhibits α7nAChR/Nrf2/HO-1-mediated neuroprotection against STZ-challenged AD-like animals. Thus, Quercetin could be considered as a potential therapeutic option in the management of AD.

Toxic Effect of Streptozotocin on Cultured Mouse Hippocampal Neurons

In primary dissociated hippocampal cell cultures from 18-day-old mouse embryos, streptozotocin in concentrations of 2-5 mM produced a dose-dependent cytotoxic effect on day 3 in vitro, whereas on day 11 of culturing, the neurons were resistant to streptozotocin. The neurons in the 3-day cultures were functionally immature, which was seen from their weak spontaneous bioelectric activity in the form of rare single action potentials; by day 11 of culturing, the neurons reached a high level of differentiation and their functional properties acquired a character of network burst activity. Thus, streptozotocin had the most pronounced cytotoxic effect on immature hippocampal neurons in vitro.

Role of protein tyrosine phosphatase 1B inhibitor in central insulin resistance and associated cognitive deficits

BACKGROUND

Protein tyrosine phosphatase 1B (PTP1B) inhibitors are potential candidates for the treatment of peripheral insulin resistance and diabetes mellitus. Similar to peripheral action within the brain also, PTP1B activation impairs insulin signaling pathways. Activation of PTP1B in brain also accentuates neuroinflammation, oxidative stress and decreases neurotrophic factors in various brain dysfunctions including cognitive decline.

OBJECTIVES

The main objective of our study was to elucidate the role of alendronate, a potent PTP1B inhibitor (blood brain barrier crossing bisphosphonate) in central insulin resistance and associated memory deficits.

METHODOLOGY

To induce central insulin resistance, streptozotocin (3 mg/kg) intracerebroventricular (ICV) was administered in two alternate days (1^st and 3^rd). After 21 days, memory was assessed via using the passive avoidance and Morris water maze paradigm. At the end of behavioral studies, animals were sacrificed to assess a variety of biochemical and molecular parameters in the hippocampus and cerebral cortex region of the brain. Treatment drug alendronate (3 mg/kg/day, p.o) and standard drug donepezil (3 mg/kg/i.p.) were administered from the 3^rd day of STZ administration till the end of the study. Inhibition of PTP1B activates phosphoinsotide-3 kinase (PI3 K) (down-stream regulator of insulin signaling pathway).Thus, to illuminate the mechanism of action of alendronate, PI3 K inhibitor, wortmannin was administered in presence of alendronate in one group.

RESULTS

Administration of alendronate to ICV streprozotocin treated rats resulted in modulation of the insulin signaling pathway and associated behavioral, biochemical and molecular changes in central insulin resistance. However, the protective effect of alendronate was entirely vanished when it was administered in the presence of wortmannin.

CONCLUSION

Alendronate can be an important treatment strategy in central insulin signaling pathway dysfunction and associated cognitive deficits. Protective effect of alendronate is via modulation of PI3-K/Akt signaling pathway.

Intranasal Insulin Enhances Intracerebroventricular Streptozotocin-Induced Decrease in Olfactory Discriminative Learning via Upregulation of Subventricular Zone-Olfactory Bulb Neurogenesis in the Rat Model

Olfactory perception and learning play a vital role in the animal's entire life for habituation and survival. Insulin and insulin receptor signaling is well known to modulate the olfactory function and is also involved in the regulation of neurogenesis. A very high density of insulin receptors is present in the olfactory bulb (OB), the brain area involved in the olfactory function, where active adult neurogenesis also takes place. Hence, our study was aimed to explore the effect of intranasal insulin treatment and the involvement of the subventricular zone-olfactory bulb (SVZ-OB) neurogenesis on olfactory discriminative learning and memory in intracerebroventricular streptozotocin (ICV STZ) rat model. Our findings revealed that intranasal insulin treatment significantly increased ICV STZ-induced decrease in the olfactory discriminative learning. No significant change was observed in the post-treatment olfactory memory upon ICV STZ and intranasal insulin treatment. ICV STZ also caused a substantial decline in the SVZ-OB neurogenesis, as indicated by the reduction in the number of 5-bromo-2'-deoxyuridine (BrdU+) cells, BrdU+ Nestin+ cells, and Doublecortin (DCX+) cells, which was reversed by intranasal insulin treatment. Intranasal insulin treatment also increased the number of immature neurons reaching the olfactory bulb (OB) as indicated by an increase in the DCX expression in the OB as compared to the ICV STZ administered group. ICV STZ administration also resulted in the modulation of the expression of the genes regulating postnatal SVZ-OB neurogenesis like Mammalian achaete scute homolog 1 (Mash 1), Neurogenin 2 (Ngn 2), Neuronal differentiation 1 (Neuro D1), and T box brain protein 2 (Tbr 2). Intranasal insulin treatment reverted these changes in gene expression, which might be responsible for the observed increase in the SVZ-OB neurogenesis and hence the olfactory discriminative learning.

Protriptyline improves spatial memory and reduces oxidative damage by regulating NFκB-BDNF/CREB signaling axis in streptozotocin-induced rat model of Alzheimer's disease

Antidepressants are well known to exert their role via upregulation of brain derived neurotrophic factor (BDNF). BDNF has been reported to exerts its neuroprotective effect in rodent and primate models as well as in patients of Alzheimer's disease (AD). The aim of our study was to evaluate the effect of protriptyline (PRT), a tricyclic antidepressant, in streptozotocin (STZ)- induced rat model of AD. Total 10 µl of STZ was injected into each ventricle (1 mg/kg). PRT (10 mg/kg, i.p.) treatment was started 3-day post STZ administration and continued till 21 days. We found that STZ treatment significantly increased pTau, Aβ42 and BACE-1 expression, oxidative stress and neurodegeneration in hippocampus and cortex of adult rats. STZ induced impairment in spatial learning and retention memory was associated with increased NFκB and reduced CREB and BDNF expression in cortex and hippocampus. Interestingly, PRT treatment significantly reduced pTau, Aβ42 and BACE-1 levels, neurodegeneration, oxidative stress and glial activation, contributing to the improved spatial learning and retention memory in STZ treated rats. Moreover, PRT treatment significantly improved p-ERK/ERK ratio and enhanced BDNF and CREB levels by reducing NFκB and GFAP expression in STZ treated rats. Our data suggest that impaired NFκB and CREB signaling potentially contribute in AD pathogenesis by elevating oxidative stress and neuroinflammation mediated neurodegeneration. Our study has established protriptyline as a multi target molecule in pre-clinical model of AD and further investigations on PRT like molecules could pave way for further development of effective new treatments in neurodegenerative disorders.

Impaired Learning and Memory Ability Induced by a Bilaterally Hippocampal Injection of Streptozotocin in Mice: Involved With the Adaptive Changes of Synaptic Plasticity

Background: Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive cognitive decline, psychiatric symptoms and behavioral disorders, resulting in disability, and loss of self-sufficiency. Objective: To establish an AD-like mice model, investigate the behavioral performance, and explore the potential mechanism. Methods: Streptozotocin (STZ, 3 mg/kg) was microinjected bilaterally into the dorsal hippocampus of C57BL/6 mice, and the behavioral performance was observed. The serum concentrations of insulin and nesfatin-1 were measured by ELISA, and the activation of hippocampal microglia and astrocytes was assessed by immunohistochemistry. The protein expression of several molecular associated with the regulation of synaptic plasticity in the hippocampus and the pre-frontal cortex (PFC) was detected via western blotting. Results: The STZ-microinjected model mice showed a slower bodyweight gain and higher serum concentration of insulin and nesfatin-1. Although there was no significant difference between groups with regard to the ability of balance and motor coordination, the model mice presented a decline of spontaneous movement and exploratory behavior, together with an impairment of learning and memory ability. Increased activated microglia was aggregated in the hippocampal dentate gyrus of model mice, together with an increase abundance of Aβ_1-42 and Tau in the hippocampus and PFC. Moreover, the protein expression of NMDAR2A, NMDAR2B, SynGAP, PSD95, BDNF, and p-β-catenin/β-catenin were remarkably decreased in the hippocampus and the PFC of model mice, and the expression of p-GSK-3β (ser9)/GSK-3β were reduced in the hippocampus. Conclusion: A bilateral hippocampal microinjection of STZ could induce not only AD-like behavioral performance in mice, but also adaptive changes of synaptic plasticity against neuroinflammatory and endocrinal injuries. The underlying mechanisms might be associated with the imbalanced expression of the key proteins of Wnt signaling pathway in the hippocampus and the PFC.

Molecular mechanisms of altered adult hippocampal neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia globally. AD is a progressive neurodegenerative disorder, eventually manifesting as severe cognitive impairment. Adult hippocampal neurogenesis (AHN) occurs throughout adulthood and plays an important role in hippocampus-dependent learning and memory. The stages of AHN, predominantly comprising the proliferation, differentiation, survival, and maturation of newborn neurons, are affected to varying degrees in AD. However, the exact molecular mechanisms remain to be elucidated. Recent evidence suggests that the molecules involved in AD pathology contribute to the compromised AHN in AD. Notably, various interventions may have common signaling pathways that, once identified, could be harnessed to enhance adult neurogenesis. This in turn could putatively rescue cognitive deficits associated with impaired neurogenesis as observed in animal models of AD. In this manuscript, we review the current knowledge concerning AHN under normal physiological and AD pathological conditions and highlight the possible role of specific molecules in AHN alteration in AD. In addition, we summarize in vivo experiments with emphasis on the effect of the activation of certain key signalings on AHN in AD rodent models. We propose that these signaling targets and corresponding interventions should be considered when developing novel therapies for AD.

Additional methodological considerations regarding optimization of the dose of intracerebroventricular streptozotocin A response to: "Optimization of intracerebroventricular streptozotocin dose for the induction of neuroinflammation and memory impairments in rats" by Ghosh et al., Metab Brain Dis 2020 July 21

A recent article by Ghosh et al. entitled "Optimization of intracerebroventricular streptozotocin dose for the induction of neuroinflammation and memory impairments in rats" provides an important new set of information on neuroinflammation and cognitive deficit in a rat model of sporadic Alzheimer's disease (sAD) based on intracerebroventricular administration of streptozotocin (STZ-icv) in Charles-Foster rats in the early post-treatment period of 21 days. This comment is supposed to supplement the aforementioned manuscript by providing additional perspective on important factors that should be taken into account in the process of optimization of the streptozotocin (STZ) dose for intracerebroventricular treatment, and provides a brief overview of possible sources of variation of experimental results reported by different groups working with STZ-icv rodent models.

Memantine treatment exerts an antidepressant-like effect by preventing hippocampal mitochondrial dysfunction and memory impairment via upregulation of CREB/BDNF signaling in the rat model of chronic unpredictable stress-induced depression

Mitochondrial and cognitive dysfunctions have long been associated with major depressive disorders (MDDs). Studies have shown that Memantine, an N-methyl-D-aspartate (NMDA) receptor antagonist, possesses an antidepressant-like effect. Hence, the NMDA receptor can be a better therapeutic target for MDD. Therefore, the present study was designed to study the impact of Memantine on mitochondrial functional status and depression-like symptoms in the chronic unpredictable stress (CUS) model of depression. CUS for 28 days resulted in depression-like symptoms (as indicated by increased immobility time in the forced swim test) and a decline in the spatial learning and retention memory in the Morris water maze (MWM) test, which was prevented by Memantine (10 mg/kg/day) treatment. We observed elevated plasma corticosterone (CORT) levels, microdialysates glutamate concentration, and synaptosomal calcium (Ca2+) ion levels after 28 days of CUS. Memantine treatment prevented only increased plasma CORT and synaptosomal Ca2+ ion levels. Memantine treatment also restored CUS induced increase in oxidative stress parameters [increased neuronal nitric oxide synthase (nNOS) expression, nitric oxide (NO) levels, lipid peroxidation (LPO) and superoxide dismutase (SOD) activity], decrease in mitochondrial electron transport chain (ETC) enzymes activity and mitochondrial membrane potential (MMP). CUS also reduced the expression of cell survival genes, cyclic-AMP response element-binding protein (CREB), and brain-derived nerve growth factor (BDNF), which was reversed by treatment with Memantine. CUS, however, caused a non-significant decrease in the hippocampal adenosine triphosphate (ATP) levels and a non-significant increase in the expression of pro-apoptotic genes, Caspase 3, and the number of TUNEL positive cells, indicating that hippocampal mitochondrial dysfunction caused due to CUS was not severe enough to affect overall energy production, mitochondrial integrity, and cellular apoptosis status. Thus, Memantine treatment exerts an antidepressant-like effect by preventing CUS induced excitotoxicity, oxidative stress, and enhancing CUS induced decrease in mitochondrial functioning and expression of cell survival genes via upregulation of stress-responsive CREB/BDNF signaling.

Exosomes from human umbilical cord Mesenchymal stem cells attenuates stress-induced hippocampal dysfunctions

Human Mesenchymal Stem Cells (MSCs) especially human umbilical cord MSCs is the novel regenerative cell resource for regenerative therapy. However, the biological underpinning of MSCs in neuroprotections requires deep understanding. Exosomes is an important biological factor due to its multiple types of contents with various biological function. In current study, we collected the exosome from umbilical cord mesenchymal stem cells (hUC-MSCs) and tested the neuroprotective effects to brain stress. Proteomic analysis indicates significant enriched protein components display the functions in metabolic regulation. We then injected the exosome (MSC-Ex) to adult mice by i.v injection. On physiological level, treatment of MSC-Ex increased the adiponectin level in peripheral central nervous system (CNS). Moreover, MSC-Ex significantly accelerated the differentiation of adult neural stem cells but did not benefit the related cognitive behavior. We then created acute brain disorder model with STZ intra-hippocampal injection. Compared with STZ group, treatment of MSC-Ex improved cognitive function. Moreover, MSC-Ex promotes hippocampal neurogenesis that was suppressed by STZ injection. In conclusion, hUC-MSCs derived exosome would exert the neural regenerative effects associating with its metabolism regulatory capacity.

Memantine and Ibuprofen pretreatment exerts anti-inflammatory effect against streptozotocin-induced astroglial inflammation via modulation of NMDA receptor-associated downstream calcium ion signaling

We had previously reported that neuroinflammation and memory impairment associated with intracerebroventricular streptozotocin (ICV STZ) injection in rats was due to glial activation and modulation of the N-methyl-D-aspartate (NMDA) receptor function. However, the exact role of the NMDA receptor and the molecules associated with downstream calcium ion signaling in STZ-induced astroglial activation is not known. Thus, in the present study, Memantine (an NMDA receptor antagonist) and Ibuprofen (an anti-inflammatory drug) were used as the pharmacological tool to investigate the molecular mechanisms involved in STZ-induced astroglial inflammation. We have studied the effect of STZ (100 μM) treatment for 24 h on NMDA receptor subunits (NR1, NR2A, and NR2B) expression and its associated calcium ion regulated molecules calcium/calmodulin-dependent protein kinase II subunit α (CaMKIIα), cyclic AMP-response element-binding (CREB) protein, Calpain, and Caspase 3. We have found a significant increase in the expression of NR1, NR2B, Calpain, and Caspase 3 expression, whereas a decrease in the level of NR2A, CaMKIIα, and CREB protein expression after 24 h of STZ treatment. These results indicate that STZ altered the NMDA receptor subunit expression and its downstream calcium (Ca²⁺) ion signaling molecules. We have also found that both Memantine (5 µM) and Ibuprofen (200 μM) significantly prevented the STZ-induced change in CaMKIIα, CREB, Calpain, and Caspase 3 expressions in C6 astrocytoma cells. Interestingly, only Memantine (and not Ibuprofen) was able to prevent the changes in NMDA receptor subunit expression in STZ-treated astrocytoma cells. STZ treatment also increased the level of glial fibrillary acidic protein (GFAP), tumor necrosis factor-alpha (TNF-α), inducible nitric oxide synthase (iNOS), and decreased the level of interleukin-10 (IL-10), indicating inflammatory condition, which was restored by both Memantine and Ibuprofen. These results suggest that both Memantine and Ibuprofen exert anti-inflammatory effect against STZ-induced astroglial activation and neuroinflammation via modulation of NMDA receptor-associated downstream calcium signaling cascade. However, only Memantine (not Ibuprofen) was able to revert STZ-induced changes in NMDA receptor subunit expression.

Fluorescent Dopamine-Tryptophan Nanocomposites as Dual-Imaging and Antiaggregation Agents: New Generation of Amyloid Theranostics with Trimeric Effects

The aggregation of neurotoxic amyloid-β (Aβ) polypeptides into aberrant extracellular senile plaques is the major neuropathological hallmark of Alzheimer's disease (AD). Inhibiting aggregation of these peptides to control the progression of this deadly disease can serve as a viable therapeutic option. In the current work, inherently fluorescent theranostic dopamine-tryptophan nanocomposites (DTNPs) were developed and investigated for their amyloid inhibition propensity along with their ability to act as a cellular bioimaging agent in neuronal cells. The antiaggregation potency of the nanocomposites was further investigated against an in vitro established reductionist amyloid aggregation model consisting of a mere dipeptide, phenylalanine-phenylalanine (FF). As opposed to large peptide/protein-derived robust and high-molecular-weight amyloid aggregation models of Alzheimer's disease, our dipeptide-based amyloid model provides an edge over others in terms of the ease of handling, synthesis, and cost-effectiveness. Results demonstrated positive antiaggregation behavior of the DTNPs toward both FF-derived amyloid fibrils and preformed Aβ-peptide fibers by means of electron microscopic and circular dichroism-based studies. Our results further pointed toward the neuroprotective effects of the DTNPs in neuroblastoma cells against FF amyloid fibril-induced toxicity and also that they significantly suppressed the accumulation of Aβ42 oligomers in both cortex and hippocampus regions and improved cognitive impairment in an intracerebroventricular streptozotocin (ICV-STZ)-induced animal model of dementia. Besides, DTNPs also exhibited excellent fluorescent properties and light up the cytoplasm of neuroblastoma cells when being coincubated with cells, confirming their ability to serve as an intracellular bioimaging agent. Overall, these results signify the potency of the DTNPs as promising multifunctional theranostic agents for treating AD.

Oral benfotiamine reverts cognitive deficit and increase thiamine diphosphate levels in the brain of a rat model of neurodegeneration

It is well known that patients with Alzheimer's disease (AD) have imbalances in blood thiamine concentrations and lower activity of thiamine-dependent enzymes. Benfotiamine, a more bioavailable thiamine analog, has been proposed as an alternative to counteract these changes related to thiamine metabolism. Thus, our study aimed to analyze the effects of benfotiamine supplementation on brain thiamine absorption, as well as on parameters related to neuronal energy metabolism and disease progression in an experimental model of sporadic AD induced by intracerebroventricular injection of streptozotocin (STZ) in rats. The supplementation with 150 mg/kg of benfotiamine for 30 days increased the concentrations of thiamine diphosphate in the hippocampus and entorhinal cortex. This led to an improvement in mitochondria enzymes and insulin signaling pathway, with inactivation of GSK3α/β and ERK1/2, which are two tau-kinases related to the progression of AD, which could decrease tau hyperphosphorylation and apoptosis signaling. Besides, we observed an increased amount of Glun2b subunit of NMDA receptors, decreased inflammation, and improvement of cognitive deficit. Together, these results suggest that benfotiamine could be a potential therapeutic approach in the treatment of sporadic AD.

Central cholinergic function and metabolic changes in streptozotocin-induced rat brain injury

As glucose hypometabolism in the brain is an early sign of Alzheimer´s dementia (AD), the diabetogenic drug streptozotocin (STZ) has been used to induce Alzheimer-like pathology in rat brain by intracereboventricular injection (icv-STZ). However, many details of the pathological mechanism of STZ in this AD model remain unclear. Here, we report metabolic and cholinergic effects of icv-STZ using microdialysis in freely moving animals. We found that icv-STZ at a dose of 3 mg/kg (2 × 1.5 mg/kg) causes overt toxicity reflected in body weight loss. Three weeks after STZ administration, histological examination revealed a high number of glial fibrillary acidic protein reactive cells in the hippocampus, accompanied by Fluoro-Jade C-positive cells in the CA1 region. Glucose and lactate levels in microdialysates were unchanged, but mitochondrial respiration measured ex vivo was reduced by 9%-15%. High-affinity choline uptake, choline acetyltransferase, and acetylcholine esterase (AChE) activities in the hippocampus were reduced by 16%, 28%, and 30%, respectively. Importantly, extracellular acetylcholine (ACh) levels in the hippocampus were unchanged and responded to behavioral and pharmacological challenges. In comparison, extracellular ACh levels and cholinergic parameters in the striatum were unchanged or slightly increased. We conclude that the icv-STZ model poorly reflects central cholinergic dysfunction, an important characteristic of dementia. The icv-STZ model may be more aptly described as an animal model of hippocampal gliosis.

Sex-specific metabolic alterations in the type 1 diabetic brain of mice revealed by an integrated method of metabolomics and mixed-model

Type 1 diabetes (T1D) can cause brain region-specific metabolic disorders, but whether gender influences T1D-related brain metabolic changes is rarely reported. Therefore, here we examined metabolic changes in six different brain regions of male and female mice under normal and T1D conditions using an integrated method of NMR-based metabolomics and linear mixed-model, and aimed to explore sex-specific metabolic changes from normal to T1D. The results demonstrate that metabolic differences occurred in all brain regions between two genders, while the hippocampal metabolism is more likely to be affected by T1D. At the 4th week after streptozotocin treatment, brain metabolic disorders mainly occurred in the cortex and hippocampus in female T1D mice, but the striatum and hippocampus in male T1D mice. In addition, anaerobic glycolysis was significantly altered in male mice, mainly in the striatum, midbrain, hypothalamus and hippocampus, but not in female mice. We also found that female mice exhibited a hypometabolism status relative to male mice from normal to T1D. Collectively, this study suggests that T1D affected brain region-specific metabolic alterations in a sex-specific manner, and may provide a metabolic view on diabetic brain diseases between genders.

Neurogenesis and brain aging

Human aging affects the entire organism, but aging of the brain must undoubtedly be different from that of all other organs, as neurons are highly differentiated postmitotic cells, for the majority of which the lifespan in the postnatal period is equal to the lifespan of the entire organism. In this work, we examine the distinctive features of brain aging and neurogenesis during normal aging, pathological aging (Alzheimer's disease), and accelerated aging (Hutchinson-Gilford progeria syndrome and Werner syndrome).

Effect of amyloid toxicity or chronic cerebral hypoperfusion on brain insulin resistance in a rat model with intracerebroventricular streptozotocin

Sporadic Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder affected by amyloid and vascular pathogenesis. Brain insulin resistance (BIR) has been suggested as one of the pathomechanisms of sporadic AD. We investigated how the amyloid and vascular pathogenesis of AD interacts with BIR. We examined experimental groups mimicking amyloid pathogenesis following intracerebroventriculr (icv) injection of amyloid β or vascular pathogenesis following permanent ligation of the bilateral common carotid arteries in Wistar rats that had undergone icv injection of streptozotocin. Behavioral tests and pathologic studies were performed. Cognitive impairments were induced by BIR superimposed by amyloid or vascular pathogenesis. Neuroinflammation in the white matter and hippocampus was aggravated by an interaction between BIR and vascular pathogenesis. Amyloid-associated pathology in the white matter was enhanced by BIR and vascular pathogenesis. Tau-associated pathology in the hippocampus was altered by BIR in a relation with amyloid or vascular pathogenesis. Our study may provide useful experimental insights based on an integrated approach to the influence of amyloid and vascular pathogenesis on BIR, permitting better understanding of the heterogeneous pathogenesis of sporadic AD. Pathologic responses in sporadic AD may differ depending on amyloid and vascular pathogenesis and may sometimes be synergistically aggravated when combined with BIR.