Insulin-resistant Brain State Research Articles

Cognitive Dysfunction and Anxiety Resulting from Synaptic Downscaling, Hippocampal Atrophy, and Ventricular Enlargement with Intracerebroventricular Streptozotocin Injection in Male Wistar Rats.

Insulin-resistant brain state is proposed to be the early sign of Alzheimer's disease (AD), which can be studied in the intracerebroventricular streptozotocin (ICV-STZ) rodent model. ICV-STZ is reported to induce sporadic AD with the majority of the disease hallmarks as phenotype. On the other hand, available experimental evidence has used varying doses of STZ (< 1 to 3mg/kg) and studied its effect for different study durations, ranging from 14 to 270days. Though these studies suggest 3mg/kg of ICV-STZ to be the optimum dose for progressive pathogenesis, the reason for such is elusive.Here, we sought to investigate the mechanism of action of 3mg/kg ICV-STZ on cognitive and non-cognitive aspects at a follow-up interval of 2weeks for 2months. On the 60th day, we examined the layer thickness, cell density, ventricular volume, spine density, protein expression related to brain metabolism, and mitochondrial function by histological examination. The findings suggest a progressive loss of a spatial, episodic, and avoidance memory with an increase in anxiety in a span of 2months. Furthermore, hippocampal neurodegeneration, ventricular enlargement, diffused amyloid plaque deposition, loss of spine in the dentate gyrus, and imbalance in energy homeostasis were found on the 60th day post-injection. Interestingly, AD rats showed a uniform fraction of time spent in four quadrants of the water maze with a change in strategy when they were exposed to height. Our findings reveal that ICV-STZ injection at a dose of 3mg/kg can cause cognitive and neuropsychiatric abnormalities due to structural loss both at the neuronal as well as the synaptic level, which is tightly associated with the change in neuronal metabolism.

Failure of the Brain Glucagon-Like Peptide-1-Mediated Control of Intestinal Redox Homeostasis in a Rat Model of Sporadic Alzheimer's Disease.

The gastrointestinal system may be involved in the etiopathogenesis of the insulin-resistant brain state (IRBS) and Alzheimer’s disease (AD). Gastrointestinal hormone glucagon-like peptide-1 (GLP-1) is being explored as a potential therapy as activation of brain GLP-1 receptors (GLP-1R) exerts neuroprotection and controls peripheral metabolism. Intracerebroventricular administration of streptozotocin (STZ-icv) is used to model IRBS and GLP-1 dyshomeostasis seems to be involved in the development of neuropathological changes. The aim was to explore (i) gastrointestinal homeostasis in the STZ-icv model (ii) assess whether the brain GLP-1 is involved in the regulation of gastrointestinal redox homeostasis and (iii) analyze whether brain-gut GLP-1 axis is functional in the STZ-icv animals. Acute intracerebroventricular treatment with exendin-3(9-39)amide was used for pharmacological inhibition of brain GLP-1R in the control and STZ-icv rats, and oxidative stress was assessed in plasma, duodenum and ileum. Acute inhibition of brain GLP-1R increased plasma oxidative stress. TBARS were increased, and low molecular weight thiols (LMWT), protein sulfhydryls (SH), and superoxide dismutase (SOD) were decreased in the duodenum, but not in the ileum of the controls. In the STZ-icv, TBARS and CAT were increased, LMWT and SH were decreased at baseline, and no further increment of oxidative stress was observed upon central GLP-1R inhibition. The presented results indicate that (i) oxidative stress is increased in the duodenum of the STZ-icv rat model of AD, (ii) brain GLP-1R signaling is involved in systemic redox regulation, (iii) brain-gut GLP-1 axis regulates duodenal, but not ileal redox homeostasis, and iv) brain-gut GLP-1 axis is dysfunctional in the STZ-icv model.

Liraglutide Has Anti-Inflammatory and Anti-Amyloid Properties in Streptozotocin-Induced and 5xFAD Mouse Models of Alzheimer's Disease.

Recent clinical and epidemiological studies support the contention that diabetes mellitus (DM) is a strong risk factor for the development of Alzheimer’s disease (AD). The use of insulin cell toxin, streptozotocin (STZ), when injected into the lateral ventricles, develops an insulin resistant brain state (IRBS) and represents a non-transgenic, or sporadic AD model (SAD), with several AD-like neuropathological features. The present study explored the effects of an anti-diabetic drug, liraglutide (LIR), in reversing major pathological hallmarks in the prodromal disease stage of both the 5xFAD transgenic and SAD mouse models of AD. Three-month-old 5xFAD and age-matched wild type mice were given a single intracerebroventricular (i.c.v) injection of STZ or vehicle (saline) and were subsequently treated with LIR, intraperitoneally (IP), once a day for 30 days. The extent of neurodegeneration, Aβ plaque load, and key proteins associated with the insulin signaling pathways were measured using Western blot and neuroinflammation (via immunohistological assays) in the cortical and hippocampal regions of the brain were assessed following a series of behavioral tests used to measure cognitive function after LIR or vehicle treatments. Our results indicated that STZ significantly increased neuroinflammation, Aβ plaque deposition and disrupted insulin signaling pathway, while 25 nmol/kg LIR, when injected IP, significantly decreased neuroinflammatory responses in both SAD and 5xFAD mice before significant cognitive changes were observed, suggesting LIR can reduce early neuropathology markers prior to the emergence of overt memory deficits. Our results indicate that LIR has neuroprotective effects and has the potential to serve as an anti-inflammatory and anti-amyloid prophylactic therapy in the prodromal stages of AD.

The Role of Neural Precursor Cell Expressed Developmentally Down-Regulated Protein 4.1- Mediated Insulin-Like Growth Factor-1R? Ubiquitination in the Pathogenesis of Alzheimer?s disease

To study the role of Neural precursor cell expressed developmentally down-regulated protein 4.1 on ubiquitination of central Insulin-like growth factor 1β pathway in Alzheimer’s Disease, and to clarify the molecular mechanism of Neural precursor cell expressed developmentally down-regulated protein 4.1 and Insulin-like growth factor 1β for central insulin signalling pathway damage. Mouse hippocampal neurons cells were isolated from Intracerebral haemorrhage mice. 30 μM or 300 μM S-Nitroso-l-cysteine were incubated with hippocampal neurons cells for 4 h. pCMV-Neural precursor cell expressed developmentally down-regulated protein 4.1 or siR- Neural precursor cell expressed developmentally down-regulated protein 4.1 were synthesized and transfected into S-Nitroso-l-cysteine treated hippocampal neurons cells. Cycloheximide and MG132 were incubated with hippocampal neuron cells after S-Nitroso-l-cysteine stimulation. Insulin resistant brain state model were constructed by streptozotocin injection. Western blot were used to test the expression of neural precursor cell expressed developmentally down-regulated protein 4.1, Insulin-like growth factor-1Rβ, Protein kinase B and p- Protein kinase B, Glycogen synthase kinase 3β and p- Glycogen synthase kinase 3β, Tau protein and p-Tau protein in vitro and in vivo. Coimmunoprecipitation were used to analyse Neural precursor cell expressed developmentally downregulated protein 4.1 and Insulin-like growth factor-1Rβ. Neural precursor cell expressed developmentally down-regulated protein 4.1 in the hippocampus of Tg2576 mice increased significantly compared to the control mice (p<0.05), while the expression of Insulin-like growth factor-1Rβ decreased significantly compared to the control mice (p<0.05). S-Nitroso-l-cysteine stimulated hippocampal neuron cells to increase the ubiquitination of Insulin-like growth factor-1Rβ (p<0.05) and decrease the expression of Insulin-like growth factor-1Rβ (p<0.05). Down-regulation of Neural precursor cell expressed developmentally downregulated protein 4.1 can decreased the ubiquitination of Insulin-like growth factor-1Rβ significantly (p<0.05), and rescued the S-Nitroso-l-cysteine inhibition effect on expression of Insulin-like growth factor-1Rβ. Over-expression Neural precursor cell expressed developmentally down-regulated protein 4.1 could increase the ubiquitination level of Insulin-like growth factor-1Rβ (p<0.05). MG132 and cyclohexide both can reverse the degradation of Insulin-like growth factor-1Rβ induced by S-Nitroso-l-cysteine. The phosphorylation degree of Protein kinase B and Glycogen synthase kinase 3β in neurons cells treated with S-Nitroso-l-cysteine decreased significantly (p<0.05), while Tau phosphorylation level in hippocampal neuron cells treated with Insulin-like growth factor-1 increased significantly (p<0.05). S-Nitroso-lcysteine can improve Tau protein phosphorylation (p<0.05) in neurons cells. C1060 site is necessary for its ubiquitination and degradation. Insulin-like growth factor-1Rβ were significantly lower (p<0.05) in the Streptozotocin model while Neural precursor cell expressed developmentally down-regulated protein 4.1 and Aβ were significantly higher (p<0.05) in the Streptozotocin model. p- Protein kinase B/Protein kinase B and p- Glycogen synthase kinase 3β/Glycogen synthase kinase 3β in the Streptozotocin dementia rats were significantly lower (p<0.05), and p-Tau/Tau were significantly increased (p<0.05). Abnormal increasing neural precursor cell expressed developmentally down-regulated protein 4.1 in brain injury tissue induced the rising ubiquitination of Insulin-like growth factor-1Rβ and rising of Aβ amount and Tau protein phosphorylation. C1060 site in Insulin-like growth factor-1Rβ was necessary for the Neural precursor cell expressed developmentally down-regulated protein 4.1 of ubiquitination and degradation of Insulin-like growth factor-1Rβ. In addition, Neural precursor cell expressed developmentally down- regulated protein 4.1 affects Insulin-like growth factor-1 signal pathway in brain, such as inhibiting Protein kinase B and Glycogen synthase kinase 3β phosphorylation, promoting Tau protein phosphorylation, and promoting β-amyloid secretions. The Role of Neural Precursor Cell Expressed Developmentally Down-Regulated Protein 4.1- Mediated Insulin-Like Growth Factor-1Rβ Ubiquitination in the Pathogenesis of Alzheimer’s disease

NO-Dependent Akt Inactivation by S-Nitrosylation as a Possible Mechanism of STZ-Induced Neuronal Insulin Resistance.

Sporadic Alzheimer's disease (sAD) is associated with energy metabolism deficiency and impairment of insulin receptor (IR) signaling in the brain. In this context, low doses of intracerebroventricular (icv) injection of streptozotocin (STZ) in rodents has been used as an experimental model of sAD which leads to an insulin-resistant brain state and neurodegeneration. However, the STZ effects on brain insulin signaling-related proteins it is not appropriately elucidated. The aim of this study was to evaluate the beginning and progression of alterations in the brain IR pathway of rats after 1, 3, 5, and 7 days of STZ injection and investigate intracellular signaling involved on STZ induced insulin resistance. We observed that STZ injection causes cognitive impairment in the animals, a temporal variation of the insulin signaling-related proteins and apoptosis cell death in the hippocampus. We also have shown that STZ causes insulin resistance and impairment on phosphoinositide 3-kinase (PI3K) activity in the Neuro-2a cells through protein kinase B (Akt) inactivation by S-nitrosylation, which could upregulate GSK3-β activity. STZ ability to cause an insulin-resistant neuron state involves NO production and ROS production which may play an important role in the mechanism linked to STZ-induced neurotoxicity. The icv injection of STZ model and STZ exposed Neuro-2a cells may be potential experimental models for assessing molecules related to the pathogenesis of sAD.

Intracerebroventricular streptozotocin induces impaired Barnes maze spatial memory and reduces astrocyte branching in the CA1 and CA3 hippocampal regions.

Sporadic Alzheimer's disease (SAD) is the most common form of dementia; therefore, there is an urgent need for a model that recapitulates the main pathologic hallmarks of this disease. The intracerebroventricular (icv) injection of streptozotocin (icv-STZ) in rats constitutes a promising model, and thus, icv-STZ rats develop insulin-resistant brain state and cognitive impairments. Even though a great piece of studies has hitherto described this system as a model for SAD, further behavioral and morphometric studies are still needed to fully characterize it. In this study, using Sprague Dawley rats, we evaluated short-term effects on behavior and hippocampus morphometry of the icv-STZ injection at two doses: 1 (STZ1) and 3mg/kg (STZ3). We found that, following icv-STZ injection, STZ3 animals, but not STZ1, exhibited impairments in spatial reference learning and memory (Barnes maze test) and in recognition memory (object recognition test). Furthermore, the results from behavioral and morpho-histochemical data are compatible. STZ3 rats displayed Stratum Radiatum volume reduction and a decreased NeuN immunoreactivity (neuron loss) in hippocampal CA1 region, together with an increased immunoreactivity for microglial (Iba1) and astroglial (GFAP) markers (neuroinflammation). Sholl analysis revealed the vulnerability of hippocampal astrocytes to STZ in CA1 and CA3. Thus, both doses induced a reduction in process length and in the number of main processes, accompanied by a frank decrease in branching complexity. The present study provides important knowledge of this AD rat model. Overall, we found that the only high STZ dose induced severe and acute neurodegenerative lesions, associated with an inflammation process.

Streptozotocin Impairs Proliferation and Differentiation of Adult Hippocampal Neural Stem Cells in Vitro-Correlation With Alterations in the Expression of Proteins Associated With the Insulin System.

Rats intracerebroventricularily (icv) treated with streptozotocin (STZ), shown to generate an insulin resistant brain state, were used as an animal model for the sporadic form of Alzheimer’s disease (sAD). Previously, we showed in an in vivo study that 3 months after STZ icv treatment hippocampal adult neurogenesis (AN) is impaired. In the present study, we examined the effects of STZ on isolated adult hippocampal neural stem cells (NSCs) using an in vitro approach. We revealed that 2.5 mM STZ inhibits the proliferation of NSCs as indicated by reduced number and size of neurospheres as well as by less BrdU-immunoreactive NSCs. Double immunofluorescence stainings of NSCs already being triggered to start with their differentiation showed that STZ primarily impairs the generation of new neurons, but not of astrocytes. For revealing mechanisms possibly involved in mediating STZ effects we analyzed expression levels of insulin/glucose system-related molecules such as the glucose transporter (GLUT) 1 and 3, the insulin receptor (IR) and the insulin-like growth factor (IGF) 1 receptor. Applying quantitative Real time-PCR (qRT-PCR) and immunofluorescence stainings we showed that STZ exerts its strongest effects on GLUT3 expression, as GLUT3 mRNA levels were found to be reduced in NSCs, and less GLUT3-immunoreactive NSCs as well as differentiating cells were detected after STZ treatment. These findings suggest that cultured NSCs are a good model for developing new strategies to treat nerve cell loss in AD and other degenerative disorders.

Alzheimer's disease and metabolic syndrome: A link from oxidative stress and inflammation to neurodegeneration.

Alzheimer's disease (AD) is the most common cause of dementia and one of the most important causes of morbidity and mortality among the aging population. AD diagnosis is made post-mortem, and the two pathologic hallmarks, particularly evident in the end stages of the illness, are amyloid plaques and neurofibrillary tangles. Currently, there is no curative treatment for AD. Additionally, there is a strong relation between oxidative stress, metabolic syndrome, and AD. The high levels of circulating lipids and glucose imbalances amplify lipid peroxidation that gradually diminishes the antioxidant systems, causing high levels of oxidative metabolism that affects cell structure, leading to neuronal damage. Accumulating evidence suggests that AD is closely related to a dysfunction of both insulin signaling and glucose metabolism in the brain, leading to an insulin-resistant brain state. Four drugs are currently used for this pathology: Three FDA-approved cholinesterase inhibitors and one NMDA receptor antagonist. However, wide varieties of antioxidants are promissory to delay or prevent the symptoms of AD and may help in treating the disease. Therefore, therapeutic efforts to achieve attenuation of oxidative stress could be beneficial in AD treatment, attenuating Aβ-induced neurotoxicity and improve neurological outcomes in AD. The term inflammaging characterizes a widely accepted paradigm that aging is accompanied by a low-grade chronic up-regulation of certain pro-inflammatory responses in the absence of overt infection, and is a highly significant risk factor for both morbidity and mortality in the elderly.

The diabetic brain and cognition.

The prevalence of both Alzheimer's disease (AD) and vascular dementia (VaD) is increasing with the aging of the population. Studies from the last several years have shown that people with diabetes have an increased risk for dementia and cognitive impairment. Therefore, the authors of this consensus review tried to elaborate on the role of diabetes, especially diabetes type 2 (T2DM) in both AD and VaD. Based on the clinical and experimental work of scientists from 18 countries participating in the International Congress on Vascular Disorders and on literature search using PUBMED, it can be concluded that T2DM is a risk factor for both, AD and VaD, based on a pathology of glucose utilization. This pathology is the consequence of a disturbance of insulin-related mechanisms leading to brain insulin resistance. Although the underlying pathological mechanisms for AD and VaD are different in many aspects, the contribution of T2DM and insulin resistant brain state (IRBS) to cerebrovascular disturbances in both disorders cannot be neglected. Therefore, early diagnosis of metabolic parameters including those relevant for T2DM is required. Moreover, it is possible that therapeutic options utilized today for diabetes treatment may also have an effect on the risk for dementia. T2DM/IRBS contribute to pathological processes in AD and VaD.

Rat brain glucose transporter-2, insulin receptor and glial expression are acute targets of intracerebroventricular streptozotocin: risk factors for sporadic Alzheimer's disease?

Accumulated evidence suggests that the insulin-resistant brain state and cerebral glucose hypometabolism might be the cause, rather than the consequence, of the neurodegeneration found in a sporadic Alzheimer's disease (sAD). We have explored whether the insulin receptor (IR) and the glucose transporter-2 (GLUT2), used here as their markers, are the early targets of intracerebroventricularly (icv) administered streptozotocin (STZ) in an STZ-icv rat model of sAD, and whether their changes are associated with the STZ-induced neuroinflammation. The expression of IR, GLUT2 and glial fibrillary acidic protein (GFAP) was measured by immunofluorescence and western blot analysis in the parietal (PC) and the temporal (TC) cortex, in the hippocampus (HPC) and the hypothalamus. One hour after the STZ-icv administration (1.5mg/kg), the GFAP immunoreactivity was significantly increased in all four regions, thus indicating the wide spread neuroinflammation, pronounced in the PC and the HPC. Changes in the GLUT2 (increment) and the IR (decrement) expression were mild in the areas close to the site of the STZ injection/release but pronounced in the ependymal lining cells of the third ventricle, thus indicating the possible metabolic implications. These results, together with the finding of the GLUT2-IR co-expression, and also the neuronal IR expression in PC, TC and HPC, indicate that the cerebral GLUT2 and IR should be further explored as the possible sAD etiopathogenic factors. It should be further clarified whether their alterations are the effect of a direct STZ-icv toxicity or they are triggered in a response to STZ-icv induced neuroinflammation.

Long-Term Effects of Intracerebroventricular Streptozotocin Treatment on Adult Neurogenesis in the Rat Hippocampus.

Altered adult hippocampal neurogenesis (AN) plays a role in the etiopathology of Alzheimer's disease (AD), a disorder characterized by a progressive loss of memory and spatial orientation impairment. Diabetes is shown to be one risk factor for the development of the sporadic form of AD (sAD), which affects >95% of AD patients. Streptozotocin intracerebroventricularily (STZ icv) treated rats, which develop an insulin-resistant brain state and learning and memory deficits preceding amyloid beta and tau pathology, may act as an appropriate animal model for sAD. The goal of our quantitative immunohistochemistry study was to compare short-term (1 month) and long-term (3 months) effects of STZ icv treatment on different AN stages. Applying MCM2 antibodies we quantified cell (e.g. stem cell) proliferation, by the use of NeuroD and DCX antibodies we analyzed immature neurons. BrdU incorporation with approximately 27 days of survival before sacrifice allowed us to quantify and identify surviving newborn cells. Performing co-localization studies with antibodies detecting BrdU and cell-type specific markers we could confirm that STZ treatment does not affect the differentiation fate of newly generated cells. Whereas STZ icv treatment does not seem to considerably influence cell proliferation over a shortterm period (1 month), in the long-term (3 months) it significantly decreased generation of immature and mature neurons. This reduction seen after 3 months was specific for the septal hippocampus, discussed to be important for spatial learning. Moreover, AN changes display the same timeline as the development of amyloid beta pathology in this animal model of sAD.

Effect of acute lipopolysaccharide-induced inflammation in intracerebroventricular-streptozotocin injected rats

Lipopolysaccharide (LPS) is often used to investigate the exacerbatory effects of an immune-related challenge in transgenic models of various neurodegenerative diseases. However, the effects of this inflammatory challenge in an insulin resistant brain state, as seen in diabetes mellitus, a major risk factor for both vascular dementia (VaD) and Alzheimer's disease (AD), is not as well characterized. We investigated the effects of an LPS-induced inflammatory challenge on behavioral and biological parameters following intracerebroventricular (ICV) injection of streptozotocin (STZ) in male Sprague–Dawley rats. Subjects received a one-time bilateral ICV infusion of STZ (25 mg/mL, 8 μL per ventricle) or ACSF. One week following ICV infusions, LPS (1 mg/mL, i.p.) or saline was administered to activate the immune system. Behavioral testing began on the 22nd day following STZ-ICV infusion, utilizing the open field and Morris water maze (MWM) tasks. Proteins related to immune function, learning and memory, synaptic plasticity, and key histopathological markers observed in VaD and AD were evaluated. The addition of an LPS-induced immune challenge partially attenuated spatial learning and memory deficits in the MWM in STZ-ICV injected animals. Additionally, LPS administration to STZ-treated animals partially mitigated alterations observed in several protein levels in STZ-ICV alone, including NR2A, GABAB1, and β-amyloid oligomers. These results suggest that an acute LPS-inflammatory response has a modest protective effect against some of the spatial learning and memory deficits and protein alterations associated with STZ-ICV induction of an insulin resistant brain state.

Characterization of Cerebral Damage in a Monkey Model of Alzheimer's Disease Induced by Intracerebroventricular Injection of Streptozotocin.

In line with recent findings showing Alzheimer's disease (AD) as an insulin-resistant brain state, a non-transgenic animal model with intracerebroventricular streptozotocin (icv-STZ) administration has been proposed as a representative experimental model of AD. Although icv-STZ rodent models of AD have been increasingly researched, studies in non-human primate models are very limited. In this study, we aimed to characterize the cerebral damage caused by icv-STZ in non-human primates; to achieve this, three cynomolgus monkeys (Macaca fascicularis) were administered four dosages of STZ (2 mg/kg) dissolved in artificial cerebrospinal fluid and another three controls were injected with only artificial cerebrospinal fluid at the cerebellomedullary cistern. In vivo neuroimaging was performed with clinical 3.0 T MRI, followed by quantitative analysis with FSL for evaluation of structural changes of the brain. Immunohistochemistry was performed to evaluate cerebral histopathology. We showed that icv-STZ caused severe ventricular enlargement and parenchymal atrophy, accompanying amyloid-β deposition, hippocampal cell loss, tauopathy, ependymal cell loss, astrogliosis, and microglial activation, which are observed in human aged or AD brain. The findings suggest that the icv-STZ monkey model would be a valuable resource to study the mechanisms and consequences of a variety of cerebral pathologies including major pathological hallmarks of AD. Furthermore, the study of icv-STZ monkeys could contribute to the development of treatments for age- or AD-associated cerebral changes.

Staging of cognitive deficits and neuropathological and ultrastructural changes in streptozotocin-induced rat model of Alzheimer's disease.

Sporadic Alzheimer's disease (sAD) is the most common form of dementia. Rats injected intracerebroventricularly with streptozotocin (STZ-icv) develop insulin-resistant brain state and represent a non-transgenic sAD model with a number of AD-like cognitive and neurochemical features. We explored cognitive, structural and ultrastructural changes in the brain of the STZ-icv rat model over a course of 9 months. Cognitive functions were measured in the STZ-icv- (0.3, 1 and 3 mg/kg) and age-matched control rats by passive avoidance test. Structural changes were assessed by Nissl and Bielschowsky silver staining. Immunohistochemistry and electron microscopy analysis were used to detect amyloid β- (Aβ(1-42)) and hyperphosphorylated tau (AT8) accumulation and ultrastructural changes in the brain. Memory decline was time- (≤3 months/acute, ≥3 months/progressive) and STZ-icv dose-dependent. Morphological changes were manifested as thinning of parietal cortex (≥1 month) and corpus callosum (9 months), and were more pronounced in the 3 mg/kg STZ group. Early neurofibrillary changes (AT8) were detected from 1 month onward in the neocortex, and progressed after 3 months to the hippocampus. Intracellular Aβ(1-42) accumulation was found in the neocortex at 3 months following STZ-icv treatment, while diffuse Aβ(1-42)-positive plaque-like formations were found after 6 months in the neocortex and hippocampus. Ultrastructural changes revealed enlargement of Golgi apparatus, pyknotic nuclei, and time-dependent increase in lysosome size, number, and density. Our data provide a staging of cognitive, structural/ultrastructural, and neuropathological markers in the STZ-icv rat model that in many aspects seems to be generally comparable to stages seen in human sAD.

Molecular and biochemical trajectories from diabetes to Alzheimer's disease: A critical appraisal.

Diabetes mellitus (DM), a metabolic disorder is a major orchestra influencing brain and behavioral responses via direct or indirect mechanisms. Many lines of evidence suggest that diabetic patients apparently face severe brain complications, but the story is far from being fully understood. Type 2 diabetes, an ever increasing epidemic and its chronic brain complications are implicated in the development of Alzheimer's disease (AD). Evidences from clinical and experimental studies suggest that insulin draws a clear trajectory from the peripheral system to the central nervous system. This review is a spot light on striking pathological, biochemical, molecular and behavioral commonalities of AD and DM. Incidence of cognitive decline in diabetic patients and diabetic symptoms in AD patients has brought the concept of brain diabetes to attention. Brain diabetes reflects insulin resistant brain state with oxidative stress, cognitive impairment, activation of various inflammatory cascade and mitochondrial vulnerability as a shared footprint of AD and DM. It has become extremely important for the investigators to understand the patho-physiology of brain complications in diabetes and put intensive pursuits for therapeutic interventions. Although, decades of research have yielded a range of molecules with potential beneficial effects, but they are yet to meet the expectations.

Nine-month follow-up of the insulin receptor signalling cascade in the brain of streptozotocin rat model of sporadic Alzheimer's disease.

Sporadic Alzheimer disease (sAD) is associated with impairment of insulin receptor (IR) signalling in the brain. Rats used to model sAD develop insulin-resistant brain state following intracerebroventricular treatment with a betacytotoxic drug streptozotocin (STZ-icv). Brain IR signalling has been explored usually at only one time point in periods ≤3 months after the STZ-icv administration. We have investigated insulin signalling in the rat hippocampus at five time points in periods ≤9 months after STZ-icv treatment. Male Wistar rats were given vehicle (control)- or STZ (3 mg/kg)-icv injection and killed 0.5, 1, 3, 6 and 9 months afterwards. Insulin-1 (Ins-1), IR, phospho- and total (p/t)-glycogen synthase kinase 3-β (GSK-3β), p/t-tau and insulin degrading enzyme (IDE) mRNA and/or protein were measured. Acute upregulation of tau and IR mRNA (p < 0.05) was followed by a pronounced downregulation of Ins-1, IR and IDE mRNA (p < 0.05) in the course of time. Acute decrement in p/t-tau and p/t-GSK-3β ratios (p < 0.05) was followed by increment in both ratios (3-6 months, p < 0.05) after which p/t-tau ratio demonstrated a steep rise and p/t-GSK-3β ratio a steep fall up to 9 months (p < 0.05). Acute decline in IDE and IR expression (p < 0.05) was followed by a slow progression of the former and a slow recovery of the latter in 3-9 months. Results indicate a biphasic pattern in time dependency of onset and progression of changes in brain insulin signalling of STZ-icv model (partly reversible acute toxicity and chronic AD-like changes) which should be considered when using this model as a tool in translational sAD research.

In vitro streptozotocin model for modeling Alzheimer-like changes: effect on amyloid precursor protein secretases and glycogen synthase kinase-3.

There is accumulating evidence for a pathogenetic link between sporadic Alzheimer's disease (AD) and diabetes mellitus (DM). At subdiabetogenic doses, the cerebral administration of the diabetogenic substance streptozotocin (STZ) induces an insulin-resistant brain state (IRBS). The aim of the present pilot study was to investigate the effect of STZ on Alzheimer-like characteristics such as amyloid precursor protein (APP) cleavage secretases, betaA4 fragment, and glycogen synthase kinase (GSK) in vitro. Different STZ concentrations (0-5 mM) and incubation intervals (0-48 h) were tested to find appropriate cell culture conditions for further biochemical analyses in human neuroblastoma cells (SK-N-MC). Lactate dehydrogenase (LDH) was measured spectrophotometrically. Intracellular ATP was determined using bioluminescent luciferase assay. Secretase activity (alpha, beta, and gamma) was measured by employing commercial fluorometric secretase activity assay kits, betaA4 fragment by immunoprecipitation. Glycogen synthase kinase-3alpha/beta (total and phospho-GSK) content was assayed by ELISA technique. In vitro STZ administration (1 mM) induced a significant reduction in intracellular ATP concentration without pronounced cell death after 24 and 48 h as measured by LDH. Under these experimental conditions, a significant increase in beta-secretase and a significant drop in alpha-secretase were obtained, whereas gamma-secretase was not changed significantly. Simultaneously, the betaA4 concentration was increased by about threefold. Furthermore, STZ significantly increased total GSK and markedly decreased phospho-GSK. A direct link between STZ, intracellular ATP deficit, and Alzheimer-related enzymes was shown in this in vitro pilot study. Thus, these results support the hypothesis that sporadic AD is being recognized as an IRBS, which can be modulated by in vitro STZ model. Continuing investigations relating pathogenetic mechanisms and AD-like hallmarks are necessary to modulate different cascades of the IRBS using in vitro models.

Diabetes and dementia

s the population ages, attention has focused on the rise in the number of people suffering from dementia. Even the Prime Minister has taken on the Dementia Challenge and promised to double the money spent on research into dementia over the next 10 years. 1 Dementia is a feared condition and can have an overwhelming impact on the affected person as well as on family and carers. In contrast, the diagnosis of type 2 diabetes may be accepted with relative equanimity, causing more concern about change of lifestyle than alarm at the associated health risks. UK prevalences of dementia and diabetes are 800 000 and 3 million respectively, but the dominance of diabetes in older people means the risk of developing both conditions is significant. Interestingly, while the number of people with diabetes increases inexorably, there is good evidence that the frequency of dementia is plateauing, so that ‘later-born populations have a lower risk of prevalent dementia than those born earlier in the past century.’ 2 A leader in Practical Diabetes in April 2013 3 highlighted the shared pathogenesis between type 2 diabetes and dementia, raising the possibility that an insulin-sensitising agent might be useful in treating the insulin-resistant brain state seen in Alzheimer’s disease. In this article we discuss the interaction between diabetes and dementia and the role of education in helping people to care for these twin disorders.

Geniposide Ameliorates Learning Memory Deficits, Reduces Tau Phosphorylation and Decreases Apoptosis via GSK3β Pathway in Streptozotocin‐Induced Alzheimer Rat Model

Intracerebral-ventricular (ICV) injection of streptozotocin (STZ) induces an insulin-resistant brain state that may underlie the neural pathogenesis of sporadic Alzheimer disease (AD). Our previous work showed that prior ICV treatment of glucagon-like peptide-1 (GLP-1) could prevent STZ-induced learning memory impairment and tau hyperphosphorylation in the rat brain. The Chinese herbal medicine geniposide is known to relieve symptoms of type 2 diabetes. Because geniposide is thought to act as a GLP-1 receptor agonist, we investigated the potential therapeutic effect of geniposide on STZ-induced AD model in rats. Our result showed that a single injection of geniposide (50 μM, 10 μL) to the lateral ventricle prevented STZ-induced spatial learning deficit by about 40% and reduced tau phosphorylation by about 30% with Morris water maze test and quantitative immunohistochemical analysis, respectively. It has been known that tau protein can be phosphorylated by glycogen synthase kinase-3 (GSK3) and STZ can increase the activity of GSK3β. Our result with Western blot analysis showed that central administration of geniposide resulted in an elevated expression of GSK3β(pS-9) but suppressed GSK3β(pY-216) indicating that geniposide reduced STZ-induced GSK3β hyperactivity. In addition, ultrastructure analysis showed that geniposide averted STZ-induced neural pathology, including paired helical filament (PHF)-like structures, accumulation of vesicles in synaptic terminal, abnormalities of endoplasmic reticulum (ER) and early stage of apoptosis. In summary, our study suggests that the water soluble and orally active monomer of Chinese herbal medicine geniposide may serve as a novel therapeutic agent for the treatment of sporadic AD.

Mitochondrial Abnormalities in a Streptozotocin-Induced Rat Model of Sporadic Alzheimer&amp;apos;s Disease

This study aimed to show that the rat model of sporadic Alzheimer's disease (sAD) generated by the intracerebroventricular (icv) injection of a sub-diabetogenic dose of streptozotocin (icvSTZ) is characterized by brain mitochondrial abnormalities. Three-month-old male Wistar rats were investigated 5 weeks after a single bilateral icv injection of STZ (3 mg/ Kg) or vehicle. icvSTZ administration induced a decrease in brain weight and cognitive decline, without affecting blood glucose levels. icvSTZ administration also resulted in a significant increase in hippocampal amyloid beta peptide 1-42 (Aβ(1-42)) levels as well as in cortical and hippocampal hyperphosphorylated tau protein levels. Brain mitochondria from icvSTZ rats revealed deficits in their function, as shown by a decrease in mitochondrial transmembrane potential, repolarization level, ATP content, respiratory state 3, respiratory control ratio and ADP/O index and an increase in lag phase of repolarization. Mitochondria from icvSTZ rats also displayed a decrease in pyruvate and α-ketoglutarate dehydrogenases and cytochrome c oxidase activities and an increase in the susceptibility to calcium-induced mitochondrial permeability transition. An increase in hydrogen peroxide and lipid peroxidation levels and a reduction in glutathione content were also observed in mitochondria from icvSTZ rats. These results demonstrate that the insulin-resistant brain state that characterizes this rat model of sAD is accompanied by the occurrence of mitochondrial abnormalities reinforcing the validity of this animal model to study sAD pathogenesis and potential therapies.