Diabetes synergistically exacerbates poststroke dementia and tau abnormality in brain

Circulating non-esterified fatty acids, risk of dementia and cognitive decline: The cardiovascular health study and multi-ethnic study of atherosclerosis

Circulating non-esterified fatty acids (NEFAs) have toxic effects on a variety of organs central to cardiometabolic disease and can cross the blood-brain barrier. Whether NEFAs associate with cognitive decline or dementia remains unknown. Circulating total NEFA levels were measured in 3242 participants without dementia among older adults of the Cardiovascular Health Study (CHS) and related to adjudicated dementia over 6 years (n = 456 cases) and annually assessed cognitive decline. For confirmation, we related circulating NEFAs to cognition assessed 10 years later among 4361 participants in the Multi-Ethnic Study of Atherosclerosis (MESA). In CHS participants, each SD higher NEFA levels were associated with a hazard ratio (HR) for all-cause dementia of 1.11 (95 % CI: 1.01; 1.22). Baseline NEFA levels were also associated with more rapid decline in cognition over 6 years of follow-up. In MESA, circulating NEFA measurements were associated with lower cognitive scores measured 10 years later.'

The Promising Potency of Sodium-Glucose Cotransporter 2 Inhibitors in the Prevention of and as Treatment for Cognitive Impairment Among Type 2 Diabetes Patients

Type 2 diabetes mellitus (T2DM), accounting for the majority of diabetes mellitus prevalence, is associated with an increased risk of cognition decline and deterioration of cognition function in diabetic patients. The sodium-glucose cotransporter 2 (SGLT2), located in the renal proximal tubule, plays a role in urine glucose reabsorption. SGLT2 inhibitors (SGLT2i), have shown potential benefits beyond cardiac and renal improvement in preventing and treating cognitive impairment (CI), including mild cognitive impairment, Alzheimer's disease and vascular dementia in T2DM patients. Studies suggest that SGLT2i may ameliorate diabetic CI through metabolism pathways, inflammation, oxidative stress, neurotrophic factors and AChE inhibition. Clinical trials and meta-analyses have reported significant and insignificant results. Given their vascular effects, SGLT2i may offer unique protection against vascular CI. This review compiles mechanisms and clinical evidence, emphasizing the need for future analysis, evaluation, trials and meta-analyses to verify and recommend optimal SGLT2i selection and dosage for specific patients.

Insights into early pathogenesis of sporadic Alzheimer's disease: role of oxidative stress and loss of synaptic proteins

Oxidative stress, induced by impaired insulin signaling in the brain contributes to cognitive loss in sporadic Alzheimer's disease (sAD). This study evaluated early hippocampal oxidative stress, pre- and post-synaptic proteins in intraperitoneal (IP) and intracerebroventricular (ICV) streptozotocin (STZ) models of impaired insulin signaling. Adult male Wistar rats were injected with STZ, IP, or ICV, and sacrificed 1-, 3-, or 6-weeks post injection. Rat's cognitive behavior was assessed using Morris water maze (MWM) tests at weeks 3 and 6. Hippocampal synaptosomal fractions were examined for oxidative stress markers and presynaptic [synapsin I, synaptophysin, growth-associated protein-43 (GAP-43), synaptosomal-associated protein-25 (SNAP-25)] and postsynaptic [drebrin, synapse-associated protein-97 (SAP-97), postsynaptic density protein-95 (PSD-95)] proteins. IP-STZ and ICV-STZ treatment impaired rat's cognition, decreased the levels of reduced glutathione (GSH) and increased the levels of thiobarbituric acid reactive species (TBARS) in a time dependent manner. In addition, it reduced the expression of pre- and post-synaptic proteins in the hippocampus. The decline in cognition is significantly correlated with the reduction in synaptic proteins in the hippocampus. In conclusion, impaired insulin signaling in the brain is deleterious in causing early synaptosomal oxidative damage and synaptic loss that exacerbates with time and correlates with cognitive impairments. Our data implicates oxidative stress and synaptic protein loss as an early feature of sAD and provides insights into early biochemical and behavioral changes during disease progression.

Impaired Insulin Signaling Alters Mediators of Hippocampal Synaptic Dynamics/Plasticity: A Possible Mechanism of Hyperglycemia-Induced Cognitive Impairment

Alzheimer's disease (AD) is a neurological condition that affects the elderly and is characterized by progressive and irreversible neurodegeneration in the cerebral cortex [...].

Receptor for Advanced Glycation End Product, Organ Crosstalk, and Pathomechanism Targets for Comprehensive Molecular Therapeutics in Diabetic Ischemic Stroke

Diabetes mellitus, a well-established risk factor for stroke, is related to higher mortality and poorer outcomes following the stroke event. Advanced glycation end products(AGEs), their receptors RAGEs, other ligands, and several other processes contribute to the cerebrovascular pathomechanism interaction in the diabetes-ischemic stroke combination. Critical reappraisal of molecular targets and therapeutic agents to mitigate them is required to identify key elements for therapeutic interventions that may improve patient outcomes. This scoping review maps evidence on the key roles of AGEs, RAGEs, other ligands such as Leukotriene B4 (LTB4), High-mobility group box 1 (HMGB1) nuclear protein, brain-kidney-muscle crosstalk, alternate pathomechanisms in neurodegeneration, and cognitive decline related to diabetic ischemic stroke. RAGE, HMGB1, nitric oxide, and polyamine mechanisms are important therapeutic targets, inflicting common consequences of neuroinflammation and oxidative stress. Experimental findings on a number of existing-emerging therapeutic agents and natural compounds against key targets are promising. The lack of large clinical trials with adequate follow-up periods is a gap that requires addressing to validate the emerging therapeutic agents. Five therapeutic components, which include agents to mitigate the AGE-RAGE axis, improved biomarkers for risk stratification, better renal dysfunction management, adjunctive anti-inflammatory-antioxidant therapies, and innovative neuromuscular stimulation for rehabilitation, are identified. A comprehensive therapeutic strategy that features all the identified components is needed for outcome improvement in diabetic stroke patients.

Association between diabetes mellitus and post-stroke cognitive impairment

Stroke survivors suffer from various physical, emotional, and cognitive impairments. These changes are dynamic and depend on multiple factors, including underlying diseases, baseline brain function and pathology, the site of the stroke and the post-stroke inflammation, neurogenesis as well as the subsequent remodeling of the neuro-network. First we review the structural and pathological changes of the brain in stroke survivors with diabetes mellitus, which may lead to post-stroke cognitive dysfunction. Second, we provide evidence of hyperglycemia, diabetes mellitus, hypoglycemia, and their relationship with post-stroke cognitive impairment (PSCI) and post-stroke dementia (PSD). In addition to conventional biomarkers, such as HbA1c, we also provide other novel tools to predict PSCI/PSD, such as glycemic variability, receptor for advanced glycation end products, and gut microbiota. Finally, we attempt to provide some modifying methods for glycemic control, focusing on the prevention of PSCI/PSD.

Rodent Models of Post-Stroke Dementia

Post-stroke cognitive impairment is one of the most common complications in stroke survivors. Concomitant vascular risk factors, including aging, diabetes mellitus, hypertension, dyslipidemia, or underlying pathologic conditions, such as chronic cerebral hypoperfusion, white matter hyperintensities, or Alzheimer’s disease pathology, can predispose patients to develop post-stroke dementia (PSD). Given the various clinical conditions associated with PSD, a single animal model for PSD is not possible. Animal models of PSD that consider these diverse clinical situations have not been well-studied. In this literature review, diverse rodent models that simulate the various clinical conditions of PSD have been evaluated. Heterogeneous rodent models of PSD are classified into the following categories: surgical technique, special structure, and comorbid condition. The characteristics of individual models and their clinical significance are discussed in detail. Diverse rodent models mimicking the specific pathomechanisms of PSD could provide effective animal platforms for future studies investigating the characteristics and pathophysiology of PSD.

Neurodegeneration and Vascular Burden on Cognition After Midlife: A Plasma and Neuroimaging Biomarker Study

Background and Objectives: Neurodegeneration and vascular burden are the two most common causes of post-stroke cognitive impairment. However, the interrelationship between the plasma beta-amyloid (Aβ) and tau protein, cortical atrophy and brain amyloid accumulation on PET imaging in stroke patients is undetermined. We aimed to explore: (1) the relationships of cortical thickness and amyloid burden on PET with plasma Aβ40, Aβ42, tau protein and their composite scores in stroke patients; and (2) the associations of post-stroke cognitive presentations with these plasma and neuroimaging biomarkers.

Methods: The prospective project recruited first-ever ischemic stroke patients around 3 months after stroke onset. The plasma Aβ40, Aβ42, and total tau protein were measured with the immunomagnetic reduction method. Cortical thickness was evaluated on MRI, and cortical amyloid plaque deposition was evaluated by ¹⁸F-florbetapir PET. Cognition was evaluated with Mini-Mental State Examination (MMSE), Geriatric Depression Scale (GDS), Dementia Rating Scale-2 (DRS-2).

Results: The study recruited 24 stroke patients and 13 normal controls. The plasma tau and tau*Aβ42 levels were correlated with mean cortical thickness after age adjustment. The Aβ42/Aβ40 ratio was correlated with global cortical ¹⁸F-florbetapir uptake value. The DRS-2 and GDS scores were associated with mean cortical thickness and plasma biomarkers, including Aβ42/Aβ40, tau, tau*Aβ42, tau/Aβ42, and tau/Aβ40 levels, in stroke patients.

Conclusion: Plasma Aβ, tau, and their composite scores were associated with cognitive performance 3 months after stroke, and these plasma biomarkers were correlated with corresponding imaging biomarkers of neurodegeneration. Further longitudinal studies with a larger sample size are warranted to replicate the study results.

RTN3 - ASC interaction: The potential mechanism behind diabetes-induced cortical neuritic dystrophy

Recent studies have found that people with diabetes are more vulnerable to cognitive dysfunction, particularly Alzheimer's disease (AD). Previous studies revealed that Reticulon 3 (RTN3) oligomers could induce cortical neuritic dystrophy (CND) in the brains of diabetic rats. However, it is not clear how diabetes induces RTN3 aggregation. In this study, we examined in vivo and in vitro diabetes models to explore the underlying effects of RTN3-mediated neurite dystrophy. The results showed that the binding ability of ASC and RTN3 was significantly increased during diabetes- or high glucose-induced neuritic dystrophy, and ASC siRNA or an anti-inflammatory drug (CP 424174) could inhibit neuritic dystrophy in vitro. These results suggest that the ASC and RTN3 interaction is involved in diabetes-induced CND, and anti-inflammatory therapy might be an effective way to prevent and inhibit diabetes-induced CND.

Blood-brain barrier dysfunction in ischemic stroke and diabetes: the underlying link, mechanisms and future possible therapeutic targets

Ischemic stroke caused by occlusion of cerebral artery is responsible for the majority of stroke that increases the morbidity and mortality worldwide. Diabetes mellitus (DM) is a crucial risk factor for ischemic stroke. Prolonged DM causes various microvascular and macrovascular changes, and blood-brain barrier (BBB) permeability that facilitates inflammatory response following stroke. In the acute phase following stroke, BBB disruption has been considered the initial step that induces neurological deficit and functional disabilities. Stroke outcomes are significantly worse among DM. In this article, we review stroke with diabetes-induce BBB damage, as well as underlying mechanism and possible therapeutic targets for stroke with diabetes.

Effects of Aerobic Exercise on Tau and Related Proteins in Rats with Photochemically-Induced Infarction

BACKGROUND

Recent evidence indicates brain ischemia is associated with accumulations of abnormal tau and related proteins. However, the effects of aerobic training on these proteins have not been evaluated.

OBJECTIVE

We aimed to evaluate the effect of aerobic exercise on the phosphorylation and acetylation of tau and on the expressions of tau related proteins in a rat stroke model and to compare the effects of aerobic exercise with those observed in our previous study on task specific training (TST).

METHODS

Twenty-four Sprague- Dawley rats with photothrombotic cortical infarction were used in the current study. The rehabilitation group (RG) received treadmill training 40 min/day for 28 days, whereas the sedentary group (SG) did not receive any type of training. Functional tests such as the single pellet reaching task, rotarod, and radial arm maze tests were performed weekly for 4 weeks post-infarction.

RESULTS

Levels of p-taus396 and p-AMPK were found to be lower in ipsilateral cortices in the RG than in the SG (p < 0.05). Levels of p-taus262, Ac-tau, p-GSK3βS9, p-Akt, p-Sin1, and p-P70-S6K were significantly lower in ipsilateral than in contralateral cortices in the RG (p < 0.05). Aerobic training also improved motor, balance, and memory functions.

CONCLUSION

Aerobic training inhibited the phosphorylation and acetylation of tau and modulated the expressions of tau related proteins after stroke by modifying the p70-S6K pathway and p-AMPK. By comparison with our previous study on the effects of TST, we have evidence to suggest that TST and aerobic exercise differ, although both types of rehabilitation inhibit tau phosphorylation and acetylation.

A pilot of the feasibility and usefulness of an aged obese model for use in stroke research

Background: Animal models of stroke have been criticised as having poor predictive validity, lacking risk factors prevalent in an aging population. This pilot study examined the development of comorbidities in a combined aged and high-fat diet model, and then examined the feasibility of modelling stroke in such rats. Methods: Twelve-month old male Wistar-Han rats (n=15) were fed a 60% fat diet for 8 months during which monthly serial blood samples were taken to assess the development of metabolic syndrome and pro-inflammatory markers. Following this, to pilot the suitability of these rats for undergoing surgical models of stroke, they underwent 30min of middle cerebral artery occlusion (MCAO) alongside younger controls fed a standard diet (n=10). Survival, weight and functional outcome were monitored, and blood vessels and tissues collected for analysis. Results: A high fat diet in aged rats led to substantial obesity. These rats did not develop type 2 diabetes or hypertension. There was thickening of the thoracic arterial wall and vacuole formation in the liver; but of the cytokines examined changes were not seen. MCAO surgery and behavioural assessment was possible in this model (with some caveats discussed in manuscript). Conclusions: This study shows MCAO is possible in aged, obese rats. However, this model is not ideal for recapitulating the complex comorbidities commonly seen in stroke patients.

Diabetes, stroke, and neuroresilience: looking beyond hyperglycemia

Ischemic stroke is a leading cause of morbidity and mortality among type 2 diabetic patients. Preclinical and translational studies have identified critical pathophysiological mediators of stroke risk, recurrence, and poor outcome in diabetic patients, including endothelial dysfunction and inflammation. Most clinical trials of diabetes and stroke have focused on treating hyperglycemia alone. Pioglitazone has shown promise in secondary stroke prevention for insulin-resistant patients; however, its use is not yet widespread. Additional research into clinical therapies directed at diabetic pathophysiological processes to prevent stroke and improve outcome for diabetic stroke survivors is necessary. Resilience is the process of active adaptation to a stressor. In patients with diabetes, stroke recovery is impaired by insulin resistance, endothelial dysfunction, and inflammation, which impair key neuroresilience pathways maintaining cerebrovascular integrity, resolving poststroke inflammation, stimulating neural plasticity, and preventing neurodegeneration. Our review summarizes the underpinnings of stroke risk in diabetes, the clinical consequences of stroke in diabetic patients, and proposes hypotheses and new avenues of research for therapeutics to stimulate neuroresilience pathways and improve stroke outcome in diabetic patients.

Association of diabetes with stroke and post-stroke dementia: A population-based cohort study

INTRODUCTION

The impact of prediabetes and diabetes on stroke and the development of dementia after a stroke remain unclear.

METHODS

A total of 2655 dementia-free participants (including a stroke-free cohort and a prevalent stroke cohort) were followed-up for 12 years. Dementia and post-stroke dementia were determined by clinical examinations and national registry data. Diabetes was ascertained via medical examination, medication use, medical records, or glycated hemoglobin (HbA1c) ≥6.5%. Prediabetes was defined as HbA1c ≥5.7% in diabetes-free participants.

RESULTS

In the stroke-free cohort, 236 participants developed ischemic stroke, and 47 developed post-stroke dementia. Diabetes was associated with ischemic stroke (hazard ratio [HR] 1.76, 95% confidence interval [CI] 1.16 to 2.67) and post-stroke dementia (HR 2.56, 95% CI 1.04 to 6.25). In the prevalent stroke cohort, diabetes was also related to dementia risk. Prediabetes was not significantly related to stroke or post-stroke dementia.

DISCUSSION

Diabetes, but not prediabetes, is associated with an increased risk of ischemic stroke and post-stroke dementia.

Cerebellar Insulin/IGF-1 signaling in diabetic rats: Effects of exercise training

The Diabetes Mellitus (DM) is a chronic disease associated with loss of brain regions such as the cerebellum, increasing the risk of developing neurodegenerative diseases such as Parkinson's disease (PD). In the brain of diabetic and PD organisms the insulin/IGF-1 signaling is altered. Exercise training is an effective intervention for the prevention of neurodegerative diseases since it release neurotrophic factors and regulating insulin/IGF-1 signaling in the brain. This study aimed to evaluate the proteins involved in the insulin/IGF-1 pathway in the cerebellum of diabetic rats subjected to exercise training protocol. Wistar rats were distributed in four groups: sedentary control (SC), trained control (TC), sedentary diabetic (SD) and trained diabetic (TD). Diabetes was induced by Alloxan (ALX) (32mg/kgb.w.). The training program consisted in swimming 5days/week, 1h/day, during 6 weeks, supporting an overload corresponding to 90% of the anaerobic threshold. At the end, cerebellum was extracted to determinate the protein expression of GSK-3β, IRβ and IGF-1R and the phosphorylation of β-amyloid, Tau, ERK1+ERK2 by Western Blot analysis. All dependent variables were analyzed by one-way analysis of variance with significance level of 5%. Diabetes causes hyperglycemia in both diabetic groups; however, in TD, there was a reduction in hyperglycemia compared to SD. Diabetes increased Tau and β-amyloid phosphorylation in both SD and TD groups. Furthermore, aerobic exercise increased ERK1+ERK2 expression in TC. The data showed that in cerebellum of diabetic rats induced by alloxan there are some proteins expression like Parkinson cerebellum increased, and the exercise training was not able to modulate the expression of these proteins.

Illuminating the Effects of Stroke on the Diabetic Brain: Insights From Imaging Neural and Vascular Networks in Experimental Animal Models

Type 1 diabetes is known to cause circulatory problems in the eyes, heart, and limbs, and the brain is no exception. Because of the insidious effects of diabetes on brain circulation, patients with diabetes are two to four times more likely to have an ischemic stroke and are less likely to regain functions that are lost. To provide a more mechanistic understanding of this clinically significant problem, imaging studies have focused on how stroke affects neural and vascular networks in experimental models of type 1 diabetes. The emerging picture is that diabetes leads to maladaptive changes in the cerebrovascular system that ultimately limit neuronal rewiring and recovery of functions after stroke. At the cellular and systems level, diabetes is associated with abnormal cerebral blood flow in surviving brain regions and greater disruption of the blood-brain barrier. The abnormal vascular responses to stroke can be partly attributed to aberrant vascular endothelial growth factor (VEGF) signaling because genetic or pharmacological inhibition of VEGF signaling can mitigate vascular dysfunction and improve stroke recovery in diabetic animals. These experimental studies offer new insights and strategies for optimizing stroke recovery in diabetic populations.

Diabetes Worsens Ischemia-Reperfusion Brain Injury in Rats Through GSK-3β

Background:

Diabetes aggravates brain injury after cerebral ischemia/reperfusion (I/R).

Objective:

To investigate whether limb I/R causes cerebral injury in a rat diabetes model and whether glycogen synthase kinase-3β (GSK-3β) is involved.

Methods:

Male adult Sprague-Dawley rats were assigned into streptozotocin-induced diabetes (n = 30; blood glucose ≥16.7 mmol/L) or control (n = 20) groups, further subdivided into diabetes I/R (3-hour femoral artery/vein clamping), diabetes-I/R + TDZD-8 (I/R plus GSK-3β inhibitor), diabetes-sham, control-sham and control-I/R groups (n = 10 each). Cortical and hippocampal morphology (hematoxylin/eosin); hippocampal CA1 apoptosis (TUNEL assay); cleaved caspase-3 (apoptosis), and Iba1 (microglial activation) protein expression (immunohistochemistry); phosphorylated/total GSK-3β and nuclear factor-κB (NF-κB) protein levels (Western blotting); and serum and brain tissue tumor necrosis factor (TNF)-α levels (enzyme-linked immunosorbent assay) were analyzed.

Results:

The diabetes-I/R group showed greater cortical and hippocampal injury, apoptosis, cleaved caspase-3 expression and Iba1 expression than the control-I/R group; TDZD-8 reduced injury/apoptosis and cleaved caspase-3/Iba1 expressions. The diabetes-I/R group had lower p-GSK-3β and p-NF-κBp65 expression than the control-I/R group (P < 0.05); TDZD-8 increased p-GSK-3β expression but decreased p-NF-κBp65 expression (P < 0.05). The diabetes-I/R group showed higher elevation of serum and brain tissue TNF-α than the control-I/R group (P < 0.05); TDZD-8 reduced TNF-α production.

Conclusions:

Diabetes exacerbates limb I/R-induced cerebral damage and activates NF-κB and GSK-3β.

Neuroinflammation is not a Prerequisite for Diabetes-induced Tau Phosphorylation

Abnormal phosphorylation and aggregation of tau is a key hallmark of Alzheimer's disease (AD). AD is a multifactorial neurodegenerative disorder for which Diabetes Mellitus (DM) is a risk factor. In animal models for DM, the phosphorylation and aggregation of tau is induced or exacerbated, however the underlying mechanism is unknown. In addition to the metabolic dysfunction, DM is characterized by chronic low-grade inflammation. This was reported to be associated with a neuroinflammatory response in the hypothalamus of DM animal models. Neuroinflammation is also implicated in the development and progression of AD. It is unknown whether DM also induces neuroinflammation in brain areas affected in AD, the cortex and hippocampus. Here we investigated whether neuroinflammation could be the mechanistic trigger to induce tau phosphorylation in the brain of DM animals. Two distinct diabetic animal models were used; rats on free-choice high-fat high-sugar (fcHFHS) diet that are insulin resistant and streptozotocin-treated rats that are insulin deficient. The streptozotocin-treated animals demonstrated increased tau phosphorylation in the brain as expected, whereas the fcHFHS diet fed animals did not. Remarkably, neither of the diabetic animal models showed reactive microglia or increased GFAP and COX-2 levels in the cortex or hippocampus. From this, we conclude: 1. DM does not induce neuroinflammation in brain regions affected in AD, and 2. Neuroinflammation is not a prerequisite for tau phosphorylation. Neuroinflammation is therefore not the mechanism that explains the close connection between DM and AD.

Xanthoceraside attenuates tau hyperphosphorylation and cognitive deficits in intracerebroventricular-streptozotocin injected rats

RATIONALE

Xanthoceraside, a novel triterpenoid saponin extracted from the fruit husks of Xanthoceras sorbifolia Bunge, reverses cognitive deficits in intracerebroventricular injection of Aβ25-35 or Aβ1-42 mice. However, whether xanthoceraside has a positive effect on hyperphosphorylated tau protein remains unclear.

OBJECTIVES

We investigated the effects of xanthoceraside on behavioural impairments induced by intracerebroventricular injection of streptozotocin (STZ) in rats and its potential mechanisms.

MATERIALS AND METHODS

The rats were administered with xanthoceraside (0.06, 0.12 or 0.24 mg/kg) or vehicle once daily after STZ intracerebroventricular injections. The Y-maze test and novel object recognition test were performed 21 and 22 days after the second STZ injection, respectively. The levels of hyperphosphorylated tau, phosphatidylinositol-3-kinase (PI3K)/serine/threonine protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), protein phosphatase 1 (PP-1) and protein phosphatase 2A (PP-2A) were also tested by Western blot.

RESULTS

Xanthoceraside treatment significantly attenuated learning and memory impairments and reduced the level of STZ-induced hyperphosphorylated tau protein. Xanthoceraside also enhanced PP-2A and PP-1 expressions, increased PI3K (p85) and Akt (Ser473) phosphorylation and decreased GSK-3β (tyr216) phosphorylation.

CONCLUSIONS

Xanthoceraside has protective effect against learning and memory impairments and inhibits tau hyperphosphorylation in the hippocampus, possibly through the inhibition of the PI3K/Akt-dependent GSK-3β signalling pathway and an enhancement of phosphatases activity.

Endoplasmic reticulum stress-mediated hippocampal neuron apoptosis involved in diabetic cognitive impairment

Poor management of DM causes cognitive impairment while the mechanism is still unconfirmed. The aim of the present study was to investigate the activation of C/EBP Homology Protein (CHOP), the prominent mediator of the endoplasmic reticulum (ER) stress-induced apoptosis under hyperglycemia. We employed streptozotocin- (STZ-) induced diabetic rats to explore the ability of learning and memory by the Morris water maze test. The ultrastructure of hippocampus in diabetic rats and cultured neurons in high glucose medium were observed by transmission electron microscopy and scanning electron microscopy. TUNEL staining was also performed to assess apoptotic cells while the expression of CHOP was assayed by immunohistochemistry and Western blot assay in these hippocampal neurons. Six weeks after diabetes induction, the escape latency increased and the average frequency in finding the platform decreased in diabetic rats (P < 0.05). The morphology of neuron and synaptic structure was impaired; the number of TUNEL-positive cells and the expression of CHOP in hippocampus of diabetic rats and high glucose medium cultured neurons were markedly altered (P < 0.05). The present results suggested that the CHOP-dependent endoplasmic reticulum (ER) stress-mediated apoptosis may be involved in hyperglycemia-induced hippocampal synapses and neurons impairment and promote the diabetic cognitive impairment.

Diabetes-induced central neuritic dystrophy and cognitive deficits are associated with the formation of oligomeric reticulon-3 via oxidative stress

Diabetes is a high risk factor to dementia. To investigate the molecular mechanism of diabetic dementia, we induced type 2 diabetes in rats and examined potential changes in their cognitive functions and the neural morphology of the brains. We found that the diabetic rats with an impairment of spatial learning and memory showed the occurrence of RTN3-immunoreactive dystrophic neurites in the cortex. Biochemical examinations revealed the increase of a high molecular weight form of RTN3 (HW-RTN3) in diabetic brains. The corresponding decrease of monomeric RTN3 was correlated with the reduction of its inhibitory effects on the activity of β-secretase (BACE1), a key enzyme for generation of β-amyloid peptides. The results from immunoprecipitation combined with protein carbonyl detection showed that carbonylated RTN3 was significantly higher in cortical tissues of diabetic rats compared with control rats, indicating that diabetes-induced oxidative stress led to RTN3 oxidative damage. In neuroblastoma SH-SY5Y cells, high glucose and/or H2O2 treatment significantly increased the amounts of carbonylated proteins and HW-RTN3, whereas monomeric RTN3 was reduced. Hence, we conclude that diabetes-induced cognitive deficits and central neuritic dystrophy are correlated with the formation of aggregated RTN3 via oxidative stress. We provided the first evidence that oxidative damage caused the formation of toxic RTN3 aggregates, which participated in the pathogenesis of central neuritic dystrophy in diabetic brain. Present findings may offer a new therapeutic strategy to prevent or reduce diabetic dementia.

Method parameters' impact on mortality and variability in rat stroke experiments: a meta-analysis

Background

Even though more than 600 stroke treatments have been shown effective in preclinical studies, clinically proven treatment alternatives for cerebral infarction remain scarce. Amongst the reasons for the discrepancy may be methodological shortcomings, such as high mortality and outcome variability, in the preclinical studies. A common approach in animal stroke experiments is that A) focal cerebral ischemia is inflicted, B) some type of treatment is administered and C) the infarct sizes are assessed. However, within this paradigm, the researcher has to make numerous methodological decisions, including choosing rat strain and type of surgical procedure. Even though a few studies have attempted to address the questions experimentally, a lack of consensus regarding the optimal methodology remains.

Methods

We therefore meta-analyzed data from 502 control groups described in 346 articles to find out how rat strain, procedure for causing focal cerebral ischemia and the type of filament coating affected mortality and infarct size variability.

Results

The Wistar strain and intraluminal filament procedure using a silicone coated filament was found optimal in lowering infarct size variability. The direct and endothelin methods rendered lower mortality rate, whereas the embolus method increased it compared to the filament method.

Conclusions

The current article provides means for researchers to adjust their middle cerebral artery occlusion (MCAo) protocols to minimize infarct size variability and mortality.

Participation of antioxidant and cholinergic system in protective effect of naringenin against type-2 diabetes-induced memory dysfunction in rats

Naringenin is a flavone flavonoid possessing antidiabetic, antioxidant and memory improving effects. Therefore, we studied the influence of naringenin against type-2 diabetes-induced memory dysfunction in rats. Type-2 diabetes was induced by high-fat diet and high-fat emulsion for two weeks and a low dose of streptozotocin (35 mg/kg). The memory deficit was assessed by using a novel object recognition paradigm. The changes in oxidative markers and cholinesterase (ChE) levels were evaluated in the hippocampal region. After confirmation of diabetes, naringenin (50mg/kg) treatment was given to animals as a preventive and in another set of experiments naringenin (25 and 50mg/kg) or pioglitazone (5mg/kg) or donepezil (3mg/kg) treatments were started after long-standing diabetes (4 weeks after confirmation). Both the treatment schedules show significant protection and improvement in cognitive behavior against diabetes-induced memory dysfunction and biochemical changes. Also, treatment with pioglitazone and donepezil improved memory performance in rats. Naringenin was found to decrease oxidative stress by depleting elevated lipid peroxide and nitric oxide and elevating reduced glutathione levels. Cholinergic function was improved by naringenin through the inhibition of elevated ChE activity. In conclusion, the present study suggests that naringenin acts as an antioxidant and ChE inhibitor against type-2 diabetes-induced memory dysfunction.

Watermaze performance after middle cerebral artery occlusion in the rat: the role of sensorimotor versus memory impairments

In rodent stroke models, investigation of deficits in spatial memory using the Morris watermaze may be confounded by coexisting sensory or motor impairments. To target memory specifically, we devised a watermaze protocol to minimize the impact of sensory and motor impairments in female Lister-hooded rats exposed to proximal electrocoagulation of the middle cerebral artery (MCAO). Rats were trained in a reference-memory task comprising 4 trials/day; trial 1 being a probe trial (platform absent for the first 60 seconds). Training ended once animals reached a strict criterion based on the probe-trial performance. Memory retention was tested 1, 7, and 28 days later. The MCAO did not affect the number of days to reach criterion during acquisition or the time spent in target quadrant during retention testing, compared with sham or unoperated rats. However, MCAO rats showed slightly poorer accuracy in crossing the platform location and increased thigmotactic swimming compared with controls. Our results show that spatial memory deficits are minimal in this rodent stroke model, and suggest that previously published watermaze impairments are attributable to sensory and motor deficits but not memory deficits. We recommend using probe trials and training to a predetermined performance criterion in future studies assessing watermaze memory deficits in rodent stroke models.

Agmatine, an endogenous ligand of imidazoline receptor protects against memory impairment and biochemical alterations in streptozotocin-induced diabetic rats

Agmatine, a polycationic amine synthesized via decarboxylation of l-arginine by arginine decarboxylase is reported to exhibit anti-hyperglycemic, antioxidant and memory enhancing effects. Therefore, we tested its influence against cognitive dysfunction in streptozotocin-induced diabetic rats using Morris water maze and object recognition paradigm. Lipid peroxidation and glutathione levels as parameters of oxidative stress and choline esterase (ChE) activity as a marker of cholinergic function were assessed in the cerebral cortex and hippocampus. Thirty days after diabetes induction rats showed a severe deficit in learning and memory associated with increased lipid peroxidation, decreased reduced glutathione, and elevated ChE activity. In contrast, chronic treatment with agmatine (5-10mg/kg, i.p. for 30 days) improved cognitive performance, lowered hyperglycemia, oxidative stress, and ChE activity in diabetic rats. Further, memory improving effects of agmatine were independent of adrenal I(2) imidazoline receptors. In a separate set, agmatine treatment for an initial 15 days after diabetes confirmation also significantly reduced memory impairment during training trials after 30 days of diabetes confirmation. Moreover, treatment during training trials (30 days after diabetes) also significantly reduced memory impairment in diabetic rats. In conclusion, the present study demonstrates that treatment with agmatine prevents changes in oxidative stress and ChE activity, and probably consequent memory impairment in diabetic rats.

3-Bromo-7-nitroindazole attenuates brain ischemic injury in diabetic stroke via inhibition of endoplasmic reticulum stress pathway involving CHOP

AIMS

The role of nitric oxide (NO) and endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of cerebral ischemic/reperfusion (I/R) injury and diabetes. The aim of the study was to investigate the neuroprotective potential of 3-bromo-7-nitroindazole (3-BNI), a potent and selective neuronal nitric oxide synthase (nNOS) inhibitor against ER stress and focal cerebral I/R injury associated with comorbid type 2 diabetes in-vivo.

MAIN METHODS

Type 2 diabetes was induced by feeding high-fat diet and streptozotocin (35 mg/kg) treatment in rats. Focal cerebral ischemia was induced by 2h middle cerebral artery occlusion (MCAO) followed by 22 h of reperfusion. Immunohistochemistry and western blotting methods were employed for the detection and expression of ER stress/apoptosis markers [78 kDa glucose regulated protein (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP)]. TUNEL assay for DNA fragmentation was also performed.

KEY FINDINGS

The diabetic rats subjected to cerebral I/R had prominent neurological damage and functional deficits compared with sham-operated rats. Massive DNA fragmentation was observed in ischemic penumbral region of diabetic brains. Concomitantly, the enhanced immunoreactivity and expression of ER stress/apoptosis markers were noticed. 3-BNI (30 mg/kg, i.p.) treatment significantly inhibited the cerebral infarct, edema volume and improved functional recovery of neurological deficits. The neuroprotection was further evident by lesser DNA fragmentation with a concomitant reduction of GRP78 and CHOP.

SIGNIFICANCE

The study demonstrates the neuroprotective potential of 3-BNI in diabetic stroke model which may be partly due to inhibition of ER stress pathway involving CHOP.

Sodium phenylbutyrate ameliorates focal cerebral ischemic/reperfusion injury associated with comorbid type 2 diabetes by reducing endoplasmic reticulum stress and DNA fragmentation

Endoplasmic reticulum (ER) stress has been postulated to play a crucial role in the pathophysiology of cerebral ischemic/reperfusion (I/R) injury and diabetes. Diabetes is a major risk factor and also common amongst the people who suffer from stroke. In this study, we have investigated the neuroprotective potential of sodium 4-phenylbutyrate (SPB; 30-300mg/kg), a chemical chaperone by targeting ER stress in a rat model of transient focal cerebral ischemia associated with comorbid type 2 diabetes. Intraperitoneal treatment with SPB (100 and 300mg/kg) significantly ameliorated brain I/R damage as evidenced by reduction in cerebral infarct and edema volume. It also significantly improved the functional recovery of various neurobehavioral impairments (neurological deficit score, grip strength and rota rod) evoked by I/R compared with vehicle-treatment. Further, SPB (100mg/kg) significantly reduced the DNA fragmentation as shown by prominent reduction in terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive cells. This effect was observed concomitantly with significant attenuation in upregulation of 78kDa glucose regulated protein (GRP78), CCAAT/enhancer binding protein homologous protein or growth arrest DNA damage-inducible gene 153 (CHOP/GADD153) and activation of caspase-12, specific markers of ER stress/apoptosis. The neuroprotection observed with SPB was independent of its effect on cerebral blood flow and blood glucose. In conclusion, this study demonstrates the neuroprotective effect of SPB owing to amelioration of ER stress and DNA fragmentation. It also suggest that targeting ER stress might offer a promising therapeutic approach and benefits against ischemic stroke associated with comorbid type 2 diabetes.

Attenuation of vascular dementia by sodium butyrate in streptozotocin diabetic rats

RATIONALE

Vascular dementia is the second leading cause of dementia, which is strongly associated with diabetes. Diabetes and dementia have become a major public health concern worldwide. At this point of time, it is very important to find the possible pharmacological agents which may be useful in management and therapy of dementia including Alzheimer's disease, vascular dementia, etc.

OBJECTIVES

To investigate the effect of sodium butyrate on streptozotocin (STZ) diabetes induced vascular dementia in rats.

METHODS

Diabetes and subsequent endothelial dysfunction and dementia were induced in rats by administration of single dose of STZ. Drug treatment was started after 1 month of STZ administration and treatment was continued until the end of the study. Morris water maze (MWM) test was employed for testing learning and memory. Endothelial function was measured on isolated aortic rings using student physiograph. Serum glucose, body weight, serum nitrite/nitrate, aortic superoxide anion generation, brain thiobarbituric acid reactive species (TBARS), reduced glutathione (GSH) levels, and acetylcholinesterase activity were also tested.

RESULTS

STZ treatment produced endothelial dysfunction, impairment of learning and memory, reduction in body weight and serum nitrite/nitrate, and increase in serum glucose, aortic and brain oxidative stress (increased superoxide anion, TBARS, and decreased GSH levels), and brain acetylcholinesterase activity. Treatment of sodium butyrate attenuated diabetes induced impairment of learning, memory, endothelial function, and various biochemical parameters.

CONCLUSIONS

Sodium butyrate may be considered as potential pharmacological agent for the management of diabetes induced vascular dementia.

Cortical neurons develop insulin resistance and blunted Akt signaling: a potential mechanism contributing to enhanced ischemic injury in diabetes

Patients with diabetes are at higher risk of stroke and experience increased morbidity and mortality after stroke. We hypothesized that cortical neurons develop insulin resistance, which decreases neuroprotection via circulating insulin and insulin-like growth factor-I (IGF-I). Acute insulin treatment of primary embryonic cortical neurons activated insulin signaling including phosphorylation of the insulin receptor, extracellular signal-regulated kinase (ERK), Akt, p70S6K, and glycogen synthase kinase-3β (GSK-3β). To mimic insulin resistance, cortical neurons were chronically treated with 25 mM glucose, 0.2 mM palmitic acid (PA), or 20 nM insulin before acute exposure to 20 nM insulin. Cortical neurons pretreated with insulin, but not glucose or PA, exhibited blunted phosphorylation of Akt, p70S6K, and GSK-3β with no change detected in ERK. Inhibition of the phosphatidylinositol 3-kinase (PI3-K) pathway during insulin pretreatment restored acute insulin-mediated Akt phosphorylation. Cortical neurons in adult BKS-db/db mice exhibited higher basal Akt phosphorylation than BKS-db(+) mice and did not respond to insulin. Our results indicate that prolonged hyperinsulinemia leads to insulin resistance in cortical neurons. Decreased sensitivity to neuroprotective ligands may explain the increased neuronal damage reported in both experimental models of diabetes and diabetic patients after ischemia-reperfusion injury.