The pathological interaction between diabetes and presymptomatic Alzheimer's disease

The amyloid cascade hypothesis: an updated critical review

Results from recent clinical trials of antibodies that target amyloid-β (Aβ) for Alzheimer's disease have created excitement and have been heralded as corroboration of the amyloid cascade hypothesis. However, while Aβ may contribute to disease, genetic, clinical, imaging and biochemical data suggest a more complex aetiology. Here we review the history and weaknesses of the amyloid cascade hypothesis in view of the new evidence obtained from clinical trials of anti-amyloid antibodies. These trials indicate that the treatments have either no or uncertain clinical effect on cognition. Despite the importance of amyloid in the definition of Alzheimer's disease, we argue that the data point to Aβ playing a minor aetiological role. We also discuss data suggesting that the concerted activity of many pathogenic factors contribute to Alzheimer's disease and propose that evolving multi-factor disease models will better underpin the search for more effective strategies to treat the disease.

Metallobiology and therapeutic chelation of biometals (copper, zinc and iron) in Alzheimer's disease: Limitations, and current and future perspectives

BACKGROUND

Alzheimer's disease (AD) is the most prevalent cause of cognitive impairment and dementia worldwide. The pathobiology of the disease has been studied in the form of several hypotheses, ranging from oxidative stress, amyloid-beta (Aβ) aggregation, accumulation of tau forming neurofibrillary tangles (NFT) through metal dysregulation and homeostasis, dysfunction of the cholinergic system, and to inflammatory and autophagic mechanism. However, none of these hypotheses has led to confirmed diagnostics or approved cure for the disease.

OBJECTIVE

This review is aimed as a basic and an encyclopedic short course into metals in AD and discusses the advances in chelation strategies and developments adopted in the treatment of the disease. Since there is accumulating evidence of the role of both biometal dyshomeostasis (iron (Fe), copper (Cu), and zinc (Zn)) and metal-amyloid interactions that lead to the pathogenesis of AD, this review focuses on unraveling therapeutic chelation strategies that have been considered in the treatment of the disease, aiming to sequester free and protein-bound metal ions and reducing cerebral metal burden. Promising compounds possessing chemically modified moieties evolving as multi-target ligands used as anti-AD drug candidates are also covered.

RESULTS AND CONCLUSION

Several multidirectional and multifaceted studies on metal chelation therapeutics show the need for improved synthesis, screening, and analysis of compounds to be able to effectively present chelating anti-AD drugs. Most drug candidates studied have limitations in their physicochemical properties; some enhance redistribution of metal ions, while others indirectly activate signaling pathways in AD. The metal chelation process in vivo still needs to be established and the design of potential anti-AD compounds that bi-functionally sequester metal ions as well as inhibit the Aβ aggregation by competing with the metal ions and reducing metal-induced oxidative damage and neurotoxicity may signal a bright end in chelation-based therapeutics of AD.

Diabetes and Alzheimer's Disease: Might Mitochondrial Dysfunction Help Deciphering the Common Path?

A growing number of clinical and epidemiological studies support the hypothesis of a tight correlation between type 2 diabetes mellitus (T2DM) and the development risk of Alzheimer's disease (AD). Indeed, the proposed definition of Alzheimer's disease as type 3 diabetes (T3D) underlines the key role played by deranged insulin signaling to accumulation of aggregated amyloid beta (Aβ) peptides in the senile plaques of the brain. Metabolic disturbances such as hyperglycemia, peripheral hyperinsulinemia, dysregulated lipid metabolism, and chronic inflammation associated with T2DM are responsible for an inefficient transport of insulin to the brain, producing a neuronal insulin resistance that triggers an enhanced production and deposition of Aβ and concomitantly contributes to impairment in the micro-tubule-associated protein Tau, leading to neural degeneration and cognitive decline. Furthermore, the reduced antioxidant capacity observed in T2DM patients, together with the impairment of cerebral glucose metabolism and the decreased performance of mitochondrial activity, suggests the existence of a relationship between oxidative damage, mitochondrial impairment, and cognitive dysfunction that could further reinforce the common pathophysiology of T2DM and AD. In this review, we discuss the molecular mechanisms by which insulin-signaling dysregulation in T2DM can contribute to the pathogenesis and progression of AD, deepening the analysis of complex mechanisms involved in reactive oxygen species (ROS) production under oxidative stress and their possible influence in AD and T2DM. In addition, the role of current therapies as tools for prevention or treatment of damage induced by oxidative stress in T2DM and AD will be debated.

A novel thiazolidinediones ATZD2 rescues memory deficits in a rat model of type 2 diabetes through antioxidant and antiinflammation

Type 2 diabetes (T2DM) has been associated with learning and memory impairment; however, drugs for diabetes could not prevent the development of cognitive decline in T2DM patients. In the present study, compounds derived from thiazolidinediones (TZD), a PPAR-γ agonist, were synthesized by conjuncting the alkyl-substituted benzimidazole group to TZD group (ATZDs). Based on the in vitro evaluation, the neuroprotection of ATZD2 was further investigated using a streptozotocin-induced T2DM rat model. Pharmacokinetic study showed that ATZD2 could pass the blood-brain barrier (BBB) while the rosiglitazone (RSG, the precursor compound of ATZD2) not. Administration of ATZD2 significantly promoted the survival rate and attenuated fasting blood glucose (FBG) levels as compared to RSG treatment in T2DM rats. Furthermore, ATZD2 treatment ameliorated the impairment of learning and memory by Morris water maze test. The beneficial effects of ATZD2 were associated with the down-regulation of hypoxia induced factor-1α, aldose reductase, and Bax expression which are related to T2DM pathology. ATZD2 treatment also attenuated the expression of inflammatory cytokines and restored the balance of redox in the diabetic hippocampus. These effects were more potent as compared with that of RSG at the same dose. The data indicate that ATZD2 may be a potent agent for the treatment of cognitive dysfunction in T2DM.

Mitochondrial Perturbation in Alzheimer's Disease and Diabetes

Mitochondria are well-known cellular organelles that play a vital role in cellular bioenergetics, heme biosynthesis, thermogenesis, calcium homeostasis, lipid catabolism, and other metabolic activities. Given the extensive role of mitochondria in cell function, mitochondrial dysfunction plays a part in many diseases, including diabetes and Alzheimer's disease (AD). In most cases, there is overwhelming evidence that impaired mitochondrial function is a causative factor in these diseases. Studying mitochondrial function in diseased cells vs healthy cells may reveal the modified mechanisms and molecular components involved in specific disease states. In this chapter, we provide a concise overview of the major recent findings on mitochondrial abnormalities and their link to synaptic dysfunction relevant to neurodegeneration and cognitive decline in AD and diabetes. Our increased understanding of the role of mitochondrial perturbation indicates that the development of specific small molecules targeting aberrant mitochondrial function could provide therapeutic benefits for the brain in combating aging-related dementia and neurodegenerative diseases by powering up brain energy and improving synaptic function and transmission.

F1F0 ATP Synthase-Cyclophilin D Interaction Contributes to Diabetes-Induced Synaptic Dysfunction and Cognitive Decline

Mitochondrial abnormalities are well known to cause cognitive decline. However, the underlying molecular basis of mitochondria-associated neuronal and synaptic dysfunction in the diabetic brain remains unclear. Here, using a mitochondrial single-channel patch clamp and cyclophilin D (CypD)-deficient mice (Ppif -/-) with streptozotocin-induced diabetes, we observed an increase in the probability of Ca2+-induced mitochondrial permeability transition pore (mPTP) opening in brain mitochondria of diabetic mice, which was further confirmed by mitochondrial swelling and cytochrome c release induced by Ca2+ overload. Diabetes-induced elevation of CypD triggers enhancement of F1F0 ATP synthase-CypD interaction, which in turn leads to mPTP opening. Indeed, in patients with diabetes, brain cypD protein levels were increased. Notably, blockade of the F1F0 ATP synthase-CypD interaction by CypD ablation protected against diabetes-induced mPTP opening, ATP synthesis deficits, oxidative stress, and mitochondria dysfunction. Furthermore, the absence of CypD alleviated deficits in synaptic plasticity, learning, and memory in diabetic mice. Thus, blockade of ATP synthase interaction with CypD provides a promising new target for therapeutic intervention in diabetic encephalopathy.

Alzheimer's disease due to loss of function: A new synthesis of the available data

Alzheimer's Disease (AD) is a highly complex disease involving a broad range of clinical, cellular, and biochemical manifestations that are currently not understood in combination. This has led to many views of AD, e.g. the amyloid, tau, presenilin, oxidative stress, and metal hypotheses. The amyloid hypothesis has dominated the field with its assumption that buildup of pathogenic β-amyloid (Aβ) peptide causes disease. This paradigm has been criticized, yet most data suggest that Aβ plays a key role in the disease. Here, a new loss-of-function hypothesis is synthesized that accounts for the anomalies of the amyloid hypothesis, e.g. the curious pathogenicity of the Aβ42/Aβ40 ratio, the loss of Aβ caused by presenilin mutation, the mixed phenotypes of APP mutations, the poor clinical-biochemical correlations for genetic variant carriers, and the failure of Aβ reducing drugs. The amyloid-loss view accounts for recent findings on the structure and chemical features of Aβ variants and their coupling to human patient data. The lost normal function of APP/Aβ is argued to be metal transport across neuronal membranes, a view with no apparent anomalies and substantially more explanatory power than the gain-of-function amyloid hypothesis. In the loss-of-function scenario, the central event of Aβ aggregation is interpreted as a loss of soluble, functional monomer Aβ rather than toxic overload of oligomers. Accordingly, new research models and treatment strategies should focus on remediation of the functional amyloid balance, rather than strict containment of Aβ, which, for reasons rationalized in this review, has failed clinically.

Synergistic exacerbation of mitochondrial and synaptic dysfunction and resultant learning and memory deficit in a mouse model of diabetic Alzheimer's disease

Diabetes is considered to be a risk factor in Alzheimer's disease (AD) pathogenesis. Although recent evidence indicates that diabetes exaggerates pathologic features of AD, the underlying mechanisms are not well understood. To determine whether mitochondrial perturbation is associated with the contribution of diabetes to AD progression, we characterized mouse models of streptozotocin (STZ)-induced type 1 diabetes and transgenic AD mouse models with diabetes. Brains from mice with STZ-induced diabetes revealed a significant increase of cyclophilin D (CypD) expression, reduced respiratory function, and decreased hippocampal long-term potentiation (LTP); these animals had impaired spatial learning and memory. Hyperglycemia exacerbated the upregulation of CypD, mitochondrial defects, synaptic injury, and cognitive dysfunction in the brains of transgenic AD mice overexpressing amyloid-β as shown by decreased mitochondrial respiratory complex I and IV enzyme activity and greatly decreased mitochondrial respiratory rate. Concomitantly, hippocampal LTP reduction and spatial learning and memory decline, two early pathologic indicators of AD, were enhanced in the brains of diabetic AD mice. Our results suggest that the synergistic interaction between effects of diabetes and AD on mitochondria may be responsible for brain dysfunction that is in common in both diabetes and AD.

How fisetin reduces the impact of age and disease on CNS function

It is becoming increasingly clear that neurological diseases are multi-factorial involving disruptions in multiple cellular systems. Thus, while each disease has its own initiating mechanisms and pathologies, certain common pathways appear to be involved in most, if not all, neurological diseases. Thus, it is unlikely that modulating only a single factor will be effective at either preventing disease development or slowing disease progression. A better approach is to identify small (< 900 daltons) molecules that have multiple biological activities relevant to the maintenance of brain function. We have identified an orally active, novel neuroprotective and cognition-enhancing molecule, the flavonoid fisetin. Fisetin not only has direct antioxidant activity but it can also increase the intracellular levels of glutathione, the major intracellular antioxidant. Fisetin can also activate key neurotrophic factor signaling pathways. In addition, it has anti-inflammatory activity and inhibits the activity of lipoxygenases, thereby reducing the production of pro-inflammatory eicosanoids and their by-products. This wide range of actions suggests that fisetin has the ability to reduce the impact of age-related neurological diseases on brain function.

Ameliorative effects of physcion 8-O-β-glucopyranoside isolated from Polygonum cuspidatum on learning and memory in dementia rats induced by Aβ1-40

CONTEXT

Polygonum cuspidatum Sieb. Et Zucc. (Polygonaceae) has been traditionally used in folk medicine to treat various diseases.

OBJECTIVE

This study investigates the ameliorative effects of physcion 8-O-β-glucopyranoside (PSG) isolated from P. cuspidatum on learning and memory in dementia rats induced by Aβ1-40.

MATERIALS AND METHODS

Dementia rats were prepared by intracerebroventricular injection of Aβ1-40. PSG (5, 10, 20, and 40 mg/kg/d, for 5 d) was administered orally. Ameliorative activity of PSG in dementia rats was evaluated by the Morris water maze (MWM) test, and its mechanisms were explored by evaluating AchE activity, levels of DA, NE, and 5-HT in hippocampus, and drebrin protein expressions in hippocampus.

RESULTS

Our results indicated that PSG (5, 10, 20, and 40 mg/kg/d) significantly inhibited the prolonged latency in dementia rats (p < 0.05), and inhibitory rates were 16.5, 22.7, 33.0, and 44.8% after 5 d of learning, indicating that PSG improves learning and memory of dementia rats. Furthermore, PSG significantly decreased AchE activity (10, 20, and 40 mg/kg/d; p < 0.05), increased 5-HT (20 and 40 mg/kg/d, p < 0.05), NE (10, 20, and 40 mg/kg/d; p < 0.05), and DA levels (5, 10, 20, and 40 mg/kg; p < 0.05) in the hippocampus. Additionally, PSG obviously decreased the Aβ contents in hippocampus (10, 20, and 40 mg/kg/d; p < 0.05), and up-regulated drebrin protein expressions (5, 10, 20, and 40 mg/kg/d; p < 0.05).

CONCLUSIONS

PSG can significantly enhance learning and memory in Aβ1-40-induced dementia rats, and the mechanisms may be related to increase levels of Ach, 5-HT, NE, and DA, decrease Aβ contents, and up-regulation of drebrin proteins in hippocampus.

At the interface of sensory and motor dysfunctions and Alzheimer's disease

Recent evidence indicates that sensory and motor changes may precede the cognitive symptoms of Alzheimer's disease (AD) by several years and may signify increased risk of developing AD. Traditionally, sensory and motor dysfunctions in aging and AD have been studied separately. To ascertain the evidence supporting the relationship between age-related changes in sensory and motor systems and the development of AD and to facilitate communication between several disciplines, the National Institute on Aging held an exploratory workshop titled "Sensory and Motor Dysfunctions in Aging and AD." The scientific sessions of the workshop focused on age-related and neuropathologic changes in the olfactory, visual, auditory, and motor systems, followed by extensive discussion and hypothesis generation related to the possible links among sensory, cognitive, and motor domains in aging and AD. Based on the data presented and discussed at this workshop, it is clear that sensory and motor regions of the central nervous system are affected by AD pathology and that interventions targeting amelioration of sensory-motor deficits in AD may enhance patient function as AD progresses.

Experimental induction of type 2 diabetes in aging-accelerated mice triggered Alzheimer-like pathology and memory deficits

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease constituting ~95% of late-onset non-familial/sporadic AD, and only ~5% accounting for early-onset familial AD. Availability of a pertinent model representing sporadic AD is essential for testing candidate therapies. Emerging evidence indicates a causal link between diabetes and AD. People with diabetes are >1.5-fold more likely to develop AD. Senescence-accelerated mouse model (SAMP8) of accelerated aging displays many features occurring early in AD. Given the role played by diabetes in the pre-disposition of AD, and the utility of SAMP8 non-transgenic mouse model of accelerated aging, we examined if high fat diet-induced experimental type 2 diabetes in SAMP8 mice will trigger pathological aging of the brain. Results showed that compared to non-diabetic SAMP8 mice, diabetic SAMP8 mice exhibited increased cerebral amyloid-β, dysregulated tau-phosphorylating glycogen synthase kinase 3β, reduced synaptophysin immunoreactivity, and displayed memory deficits, indicating Alzheimer-like changes. High fat diet-induced type 2 diabetic SAMP8 mice may represent the metabolic model of AD.

Vascular dysfunction associated with type 2 diabetes and Alzheimer's disease: a potential etiological linkage

The endothelium performs a crucial role in maintaining vascular integrity leading to whole organ metabolic homeostasis. Endothelial dysfunction represents a key etiological factor leading to moderate to severe vasculopathies observed in both Type 2 diabetic and Alzheimer’s Disease (AD) patients. Accordingly, evidence-based epidemiological factors support a compelling hypothesis stating that metabolic rundown encountered in Type 2 diabetes engenders severe cerebral vascular insufficiencies that are causally linked to long term neural degenerative processes in AD. Of mechanistic importance, Type 2 diabetes engenders an immunologically mediated chronic pro-inflammatory state involving interactive deleterious effects of leukocyte-derived cytokines and endothelial-derived chemotactic agents leading to vascular and whole organ dysfunction. The long term negative consequences of vascular pro-inflammatory processes on the integrity of CNS basal forebrain neuronal populations mediating complex cognitive functions establish a striking temporal comorbidity of AD with Type 2 diabetes. Extensive biomedical evidence supports the pivotal multi-functional role of constitutive nitric oxide (NO) production and release as a critical vasodilatory, anti-inflammatory, and anti-oxidant, mechanism within the vascular endothelium. Within this context, we currently review the functional contributions of dysregulated endothelial NO expression to the etiology and persistence of Type 2 diabetes-related and co morbid AD-related vasculopathies. Additionally, we provide up-to-date perspectives on critical areas of AD research with special reference to common NO-related etiological factors linking Type 2 diabetes to the pathogenesis of AD.

Increased tau phosphorylation and impaired brain insulin/IGF signaling in mice fed a high fat/high cholesterol diet

Previous studies demonstrated that a high fat/high cholesterol (HFC) diet results in a loss of working memory in mice correlated with neuroinflammatory changes and increased AβPP processing (Thirumangalakudi et al. (2008) J Neurochem 106, 475-485). To further explore the nature of the molecular correlates of cognitive impairment, in this study, we examined changes in tau phosphorylation, insulin/IGF-1 signaling (IIS) including GSK3, and levels of specific synaptic proteins. Immunoblot analysis of hippocampal tissue from C57BL/6 mice fed HFC for 2 months with anti-phospho-tau (i.e., PHF1 and phospho-Thr-231 tau) antibodies demonstrated the presence of hyperphosphorylated tau. The tau phosphorylation correlated with activated GSK3, a prominent tau kinase normally kept inactive under the control of IIS. That IIS itself was impaired due to the hyperlipidemic diet was confirmed by a down-regulation of insulin receptor substrate-1 and phospho-Akt levels. Although no significant changes in the levels of the pre-synaptic protein (i.e., synaptophysin) in response to HFC were apparent in immunoblot analysis, there was a clear down-regulation of the post-synaptic protein, PSD95, and drebrin, a dendritic spine-specific protein, indicative of altered synaptic plasticity. The results, in concert with previous findings with the same model, suggest that high dietary fat/cholesterol elicits brain insulin resistance and altered IIS leading to Alzheimer's disease-like cognitive impairment in 'normal' mice.

Streptozotocin-induced diabetes increases amyloid plaque deposition in AD transgenic mice through modulating AGEs/RAGE/NF-κB pathway

BACKGROUND

An increasing number of studies have demonstrated of that diabetes mellitus (DM) is associated with an increased prevalence of Alzheimer disease (AD), the underlying mechanisms are still obscure.

METHODS

We developed a streptozotocin (STZ)-induced diabetic AD transgenic mouse model and evaluated the effect of hyperglycemia on senile plaque formation.

RESULTS

Our data showed that administration of STZ increased the level of blood glucose and increased the advanced glycation end products (AGEs) in brain tissue, and further enhanced the expression levels of the receptor for AGEs (RAGE) and the nuclear factor-kappa B (NF-κB) in the brain, and accelerated the senile plaque formation in the transgenic mice. Our results showed that STZ-induced insulin-deficient hyperglycemia caused the pathophysiology of AD in APP/PS1 transgenic mice by modulating the AGEs/RAGE/NF-κB pathway.

CONCLUSIONS

Our study suggests that there is a close linkage of DM and cerebral amyloidosis in the pathogenesis of AD.

Food for thought: the role of appetitive peptides in age-related cognitive decline

Through their well described actions in the hypothalamus, appetitive peptides such as insulin, orexin and leptin are recognized as important regulators of food intake, body weight and body composition. Beyond these metabolic activities, these peptides also are critically involved in a wide variety of activities ranging from modulation of immune and neuroendocrine function to addictive behaviors and reproduction. The neurological activities of insulin, orexin and leptin also include facilitation of hippocampal synaptic plasticity and enhancement of cognitive performance. While patients with metabolic disorders such as obesity and diabetes have greater risk of developing cognitive deficits, dementia and Alzheimer's disease (AD), the underlying mechanisms that are responsible for, or contribute to, age-related cognitive decline are poorly understood. In view of the importance of these peptides in metabolic disorders, it is not surprising that there is a greater focus on their potential role in cognitive deficits associated with aging. The goal of this review is to describe the evidence from clinical and pre-clinical studies implicating insulin, orexin and leptin in the etiology and progression of age-related cognitive decline. Collectively, these studies support the hypothesis that leptin and insulin resistance, concepts normally associated with the hypothalamus, are also applicable to the hippocampus.

Non-cognitive symptoms and related conditions in the Alzheimer's disease: a literature review

The Alzheimer's disease is considered a progressive cognitive disorder; however, several non-cognitive symptoms accompany all stages of the disease, appearing at times before the cognitive symptoms become manifest. This article reviews the literature on non-cognitive symptoms normally related to the Alzheimer's disease, including gait and balance dysfunction, olfactory dysfunction, diabetes, pain, and psychiatric symptoms.

Glycogen synthase kinase-3 inhibition prevents learning deficits in diabetic mice

There is an increasing awareness that diabetes has an impact on the central nervous system, with reports of impaired learning, memory, and mental flexibility being more common in diabetic subjects than in the general population. Insulin-deficient diabetic mice also display learning deficits associated with defective insulin-signaling in the brain and increased activity of GSK3. In the present study, AR-A014418, a GSK3β inhibitor, and TX14(A), a neurotrophic factor with GSK3 inhibitory properties, were tested against the development of learning deficits in mice with insulin-deficient diabetes. Treatments were started at onset of diabetes and continued for 10 weeks. Treatment with AR-A014418 or TX14(A) prevented the development of learning deficits, assessed by the Barnes maze, but only AR-A014418 prevented memory deficits, as assessed by the object recognition test. Diabetes-induced increased levels of amyloid β protein and phosphorylated tau were not significantly affected by the treatments. However, the diabetes-induced decrease in synaptophysin, a presynaptic protein marker of hippocampal plasticity, was partially prevented by both treatments. These results suggest a role for GSK3 and/or reduced neurotrophic support in the development of cognitive deficits in diabetic mice that are associated with synaptic damage.

Diabetes exacerbates amyloid and neurovascular pathology in aging-accelerated mice

Mounting evidence supports a link between diabetes, cognitive dysfunction, and aging. However, the physiological mechanisms by which diabetes impacts brain function and cognition are not fully understood. To determine how diabetes contributes to cognitive dysfunction and age-associated pathology, we used streptozotocin to induce type 1 diabetes (T1D) in senescence-accelerated prone 8 (SAMP8) and senescence-resistant 1 (SAMR1) mice. Contextual fear conditioning demonstrated that T1D resulted in the development of cognitive deficits in SAMR1 mice similar to those seen in age-matched, nondiabetic SAMP8 mice. No further cognitive deficits were observed when the SAMP8 mice were made diabetic. T1D dramatically increased Aβ and glial fibrillary acidic protein immunoreactivity in the hippocampus of SAMP8 mice and to a lesser extent in age-matched SAMR1 mice. Further analysis revealed aggregated Aβ within astrocyte processes surrounding vessels. Western blot analyses from T1D SAMP8 mice showed elevated amyloid precursor protein processing and protein glycation along with increased inflammation. T1D elevated tau phosphorylation in the SAMR1 mice but did not further increase it in the SAMP8 mice where it was already significantly higher. These data suggest that aberrant glucose metabolism potentiates the aging phenotype in old mice and contributes to early stage central nervous system pathology in younger animals.

Calorie restriction reduces the influence of glucoregulatory dysfunction on regional brain volume in aged rhesus monkeys

Insulin signaling dysregulation is related to neural atrophy in hippocampus and other areas affected by neurovascular and neurodegenerative disorders. It is not known if long-term calorie restriction (CR) can ameliorate this relationship through improved insulin signaling or if such an effect might influence task learning and performance. To model this hypothesis, magnetic resonance imaging was conducted on 27 CR and 17 control rhesus monkeys aged 19-31 years from a longitudinal study. Voxel-based regression analyses were used to associate insulin sensitivity with brain volume and microstructure cross-sectionally. Monkey motor assessment panel (mMAP) performance was used as a measure of task performance. CR improved glucoregulation parameters and related indices. Higher insulin sensitivity predicted more gray matter in parietal and frontal cortices across groups. An insulin sensitivity × dietary condition interaction indicated that CR animals had more gray matter in hippocampus and other areas per unit increase relative to controls, suggesting a beneficial effect. Finally, bilateral hippocampal volume adjusted by insulin sensitivity, but not volume itself, was significantly associated with mMAP learning and performance. These results suggest that CR improves glucose regulation and may positively influence specific brain regions and at least motor task performance. Additional studies are warranted to validate these relationships.

Davunetide (NAP) as a preventative treatment for central nervous system complications in a diabetes rat model

AIMS

Central nervous system complications including cognitive impairment are an early manifestation of diabetes mellitus, also evident in animal models. NAP (generic name, davunetide), a neuroprotective peptide was tested here for its ability to prevent diabetes-related brain pathologies in the streptozotocin injected diabetes rat model.

METHODS

Diabetes was induced by an intraperitoneal streptozotocin injection (55 mg/kg). Intranasal NAP or vehicle was administered daily starting on the day following streptozotocin injection. Cognitive assessment was performed 12 weeks after diabetes induction, using the Morris water maze paradigm. Brain structural integrity was assessed on the 15th week of diabetes by magnetic resonance T2 scan. Characterization of cellular populations, apoptosis and synaptic density was performed 16 weeks after diabetes induction, using immunohistochemical markers and quantified in the prefrontal cortex, the cerebral cortex and the hippocampus of both hemispheres.

RESULTS

Impaired spatial memory of the diabetic rats was observed in the water maze by attenuated learning curve and worsened performance in the probe memory test. NAP treatment significantly improved both measurements. T2 magnetic resonance imaging revealed atrophy in the prefrontal cortex of the diabetes rat group, which was prevented by NAP treatment. Immunohistochemical analysis showed that NAP treatment protected against major loss of the synaptic marker synaptophysin and astrocytic apoptosis, resulting from streptozotocin treatment.

CONCLUSIONS

Our results show for the first time protective effects for NAP (davuentide) in a diabetes rat model at the behavioral and structural levels against one of the most severe complications of diabetes.

Fisetin lowers methylglyoxal dependent protein glycation and limits the complications of diabetes

The elevated glycation of macromolecules by the reactive dicarbonyl and α-oxoaldehyde methylglyoxal (MG) has been associated with diabetes and its complications. We have identified a rare flavone, fisetin, which increases the level and activity of glyoxalase 1, the enzyme required for the removal of MG, as well as the synthesis of its essential co-factor, glutathione. It is shown that fisetin reduces two major complications of diabetes in Akita mice, a model of type 1 diabetes. Although fisetin had no effect on the elevation of blood sugar, it reduced kidney hypertrophy and albuminuria and maintained normal levels of locomotion in the open field test. This correlated with a reduction in proteins glycated by MG in the blood, kidney and brain of fisetin-treated animals along with an increase in glyoxalase 1 enzyme activity and an elevation in the expression of the rate-limiting enzyme for the synthesis of glutathione, a co-factor for glyoxalase 1. The expression of the receptor for advanced glycation end products (RAGE), serum amyloid A and serum C-reactive protein, markers of protein oxidation, glycation and inflammation, were also increased in diabetic Akita mice and reduced by fisetin. It is concluded that fisetin lowers the elevation of MG-protein glycation that is associated with diabetes and ameliorates multiple complications of the disease. Therefore, fisetin or a synthetic derivative may have potential therapeutic use for the treatment of diabetic complications.

Astrocytic gap junctional communication is reduced in amyloid-β-treated cultured astrocytes, but not in Alzheimer's disease transgenic mice

Alzheimer's disease is characterized by accumulation of amyloid deposits in brain, progressive cognitive deficits and reduced glucose utilization. Many consequences of the disease are attributed to neuronal dysfunction, but roles of astrocytes in its pathogenesis are not well understood. Astrocytes are extensively coupled via gap junctions, and abnormal trafficking of metabolites and signalling molecules within astrocytic syncytia could alter functional interactions among cells comprising the neurovascular unit. To evaluate the influence of amyloid-beta on astrocyte gap junctional communication, cultured astrocytes were treated with monomerized amyloid-β(1-40) (1 μmol/l) for intervals ranging from 2 h to 5 days, and the areas labelled by test compounds were determined by impaling a single astrocyte with a micropipette and diffusion of material into coupled cells. Amyloid-β-treated astrocytes had rapid, sustained 50-70% reductions in the area labelled by Lucifer Yellow, anionic Alexa Fluor® dyes and energy-related compounds, 6-NBDG (a fluorescent glucose analogue), NADH and NADPH. Amyloid-β treatment also caused a transient increase in oxidative stress. In striking contrast with these results, spreading of Lucifer Yellow within astrocytic networks in brain slices from three regions of 8.5-14-month-old control and transgenic Alzheimer's model mice was variable, labelling 10-2000 cells; there were no statistically significant differences in the number of dye-labelled cells among the groups or with age. Thus amyloid-induced dysfunction of gap junctional communication in cultured astrocytes does not reflect the maintenance of dye transfer through astrocytic syncytial networks in transgenic mice; the pathophysiology of Alzheimer's disease is not appropriately represented by the cell culture system.

Hyperglycaemia and diabetes impair gap junctional communication among astrocytes

Sensory and cognitive impairments have been documented in diabetic humans and animals, but the pathophysiology of diabetes in the central nervous system is poorly understood. Because a high glucose level disrupts gap junctional communication in various cell types and astrocytes are extensively coupled by gap junctions to form large syncytia, the influence of experimental diabetes on gap junction channel-mediated dye transfer was assessed in astrocytes in tissue culture and in brain slices from diabetic rats. Astrocytes grown in 15–25 mmol/l glucose had a slow-onset, poorly reversible decrement in gap junctional communication compared with those grown in 5.5 mmol/l glucose. Astrocytes in brain slices from adult STZ (streptozotocin)-treated rats at 20–24 weeks after the onset of diabetes also exhibited reduced dye transfer. In cultured astrocytes grown in high glucose, increased oxidative stress preceded the decrement in dye transfer by several days, and gap junctional impairment was prevented, but not rescued, after its manifestation by compounds that can block or reduce oxidative stress. In sharp contrast with these findings, chaperone molecules known to facilitate protein folding could prevent and rescue gap junctional impairment, even in the presence of elevated glucose level and oxidative stress. Immunostaining of Cx (connexin) 43 and 30, but not Cx26, was altered by growth in high glucose. Disruption of astrocytic trafficking of metabolites and signalling molecules may alter interactions among astrocytes, neurons and endothelial cells and contribute to changes in brain function in diabetes. Involvement of the microvasculature may contribute to diabetic complications in the brain, the cardiovascular system and other organs.

The GRK2 Overexpression Is a Primary Hallmark of Mitochondrial Lesions during Early Alzheimer Disease

Increasing evidence points to vascular damage as an early contributor to the development of two leading causes of age-associated dementia, namely Alzheimer disease (AD) and AD-like pathology such as stroke. This review focuses on the role of G protein-coupled receptor kinases (GRKs) as they relate to dementia and how the cardio and cerebrovasculature is involved in AD pathogenesis. The exploration of GRKs in AD pathogenesis may help bridge gaps in our understanding of the heart-brain connection in relation to neurovisceral damage and vascular complications of AD. The a priori basis for this inquiry stems from the fact that kinases of this family regulate numerous receptor functions in the brain, myocardium and elsewhere. The aim of this review is to discuss the finding of GRK2 overexpression in the context of early AD pathogenesis. Also, we consider the consequences for this overexpression as a loss of G-protein coupled receptor (GPCR) regulation, as well as suggest a potential role for GPCRs and GRKs in a unifying theory of AD pathogenesis through the cerebrovasculature. Finally, we synthesize this newer information in an attempt to put it into context with GRKs as regulators of cellular function, which makes these proteins potential diagnostic and therapeutic targets for future pharmacological intervention.

Biana: a software framework for compiling biological interactions and analyzing networks

Background

The analysis and usage of biological data is hindered by the spread of information across multiple repositories and the difficulties posed by different nomenclature systems and storage formats. In particular, there is an important need for data unification in the study and use of protein-protein interactions. Without good integration strategies, it is difficult to analyze the whole set of available data and its properties.

Results

We introduce BIANA (Biologic Interactions and Network Analysis), a tool for biological information integration and network management. BIANA is a Python framework designed to achieve two major goals: i) the integration of multiple sources of biological information, including biological entities and their relationships, and ii) the management of biological information as a network where entities are nodes and relationships are edges. Moreover, BIANA uses properties of proteins and genes to infer latent biomolecular relationships by transferring edges to entities sharing similar properties. BIANA is also provided as a plugin for Cytoscape, which allows users to visualize and interactively manage the data. A web interface to BIANA providing basic functionalities is also available. The software can be downloaded under GNU GPL license from http://sbi.imim.es/web/BIANA.php.

Conclusions

BIANA's approach to data unification solves many of the nomenclature issues common to systems dealing with biological data. BIANA can easily be extended to handle new specific data repositories and new specific data types. The unification protocol allows BIANA to be a flexible tool suitable for different user requirements: non-expert users can use a suggested unification protocol while expert users can define their own specific unification rules.

Type 1 diabetes exaggerates features of Alzheimer's disease in APP transgenic mice

A number of studies suggest an association between Alzheimer's disease (AD) and diabetes: AD patients show impaired insulin function, whereas cognitive deficits and increased risk of developing AD occur in diabetic patients. The reasons for the increased risk are not known. Recent studies of disturbances in the insulin-signaling pathway have revealed new perspectives on the links between AD and Type 1 diabetes with a particular focus on glycogen synthase-kinase-3 (GSK3). We have therefore characterized a mouse model of combined insulin-deficient diabetes and AD and find that diabetes exaggerated defects in the brain of APP transgenic mice. Mice with combined APP overexpression and diabetes showed a decreased insulin receptor activity and an increased GSK3beta activity. Concomitantly, tau phosphorylation and number of Abeta plaques, the two pathologic hallmarks of AD, were increased in the brain of diabetic-APP transgenic mice. Our results indicate that the pathologic features of AD are exaggerated in the brain of APP transgenic mice that have concurrent insulin-deficient diabetes, and underscore a possible mechanism of brain dysfunction common to AD and diabetes.

Exercise and cognitive function: a hypothesis for the association of type II diabetes mellitus and Alzheimer's disease from an evolutionary perspective

The association of type II diabetes mellitus (DM2) with Alzheimer's disease (AD) has received considerable attention in recent years. In the present paper, a hypothesis for this association from an evolutionary perspective, with emphasis on the close interplay between exercise and cognitive function, will be advanced in order to provide a biological rationale for the notion that the fundamental metabolic features of DM2 act in the brain over a protracted time span to induce the neuropathological characteristics of Alzheimer's disease thereby producing cognitive impairment. It is hoped that this hypothesis puts the association of DM2 and AD on firm conceptual grounds from a biological perspective and offers directions for further research.

Therapies for hyperglycaemia-induced diabetic complications: from animal models to clinical trials

Diabetic complications — the long-term damage to various organ systems — are a great cause of mortality and morbidity in both type 1 and type 2 diabetes. There are currently few therapeutic options to prevent or ameliorate these complications.

High blood glucose levels and the subsequent metabolic consequences of hyperglycaemia are widely considered the primary event that initiates diabetic complications, although there is accumulating evidence that impaired insulin signalling arising from insulin deficiency and insulin resistance may also have a pathogenic role.

Vascular dysfunction is a prominent complication of diabetes that is widely held to underlie damage to organ systems such as the macrovasculature, kidneys, eyes and nerves. Other consequences of diabetes, such as dyslipidaemia and hypertension, are key modifiers of vascular injury and act as accelerators of diabetic complications.

Numerous pathogenic mechanisms, including increased polyol pathway flux and mitochondrial activity, activation of protein kinase C and NADPH oxidase and signalling through the receptor for advanced glycation end products (RAGE) pathway, seem to form a central pathogenic axis that is common to most, if not all, of the complications of diabetes. These disorders all promote excess production of pro-oxidative molecules. Organ-specific mechanisms, such as diminished growth factor support and repair pathway activation, must also be considered.

Few animal models of diabetic complications faithfully reflect the advanced stages of organ pathology seen in humans. Current models can be viewed as potentially illustrating early biochemical and functional disorders of diabetes that ultimately lead to advanced pathology. New animal models are being developed using both a reductionist approach for examining specific gene products of interest and also by combining diverse molecular and physiological risk factors.

Control of blood glucose levels and lipids remains the most meaningful approach for preventing diabetic complications. This strategy is likely to be complemented by a diverse range of more focused therapeutics that have emerged from mechanistic studies in animal models and which are currently in clinical development. Some of these, such as those targeting cardiovascular disease, have the potential to affect several diabetic complications, whereas others focus on intervening in organ-specific pathogenic mechanisms. It is probable that combination therapies aimed at the hyperglycaemia-driven pathogenic axis and also at organ-specific disorders will provide the most effective approach to treating the diverse complications of diabetes.

Long-term diabetes increases the likelihood of developing complications such as macrovascular disease, nephropathy, retinopathy and neuropathy. This Review highlights the range of pathologies that are precipitated by hyperglycaemia and discusses recent developments in preclinical and clinical research for each of these complications.

Long-term diabetes increases the likelihood of developing secondary damage to numerous systems, and these complications represent a substantial cause of morbidity and mortality. Establishing the causes of diabetes remains the key step towards eradicating the disease, but the prevention and amelioration of diabetic complications is equally important for the millions of individuals who already have the disease or are likely to develop it before prophylaxis or a cure become routinely available. In this Review, we focus on four common complications of diabetes, discuss the range of pathologies that are precipitated by hyperglycaemia and highlight emerging targets for therapeutic intervention.

Human cerebral neuropathology of Type 2 diabetes mellitus

The cerebral neuropathology of Type 2 diabetes (CNDM2) has not been positively defined. This review includes a description of CNDM2 research from before the 'Pubmed Era'. Recent neuroimaging studies have focused on cerebrovascular and white matter pathology. These and prior studies about cerebrovascular histopathology in diabetes are reviewed. Evidence is also described for and against the link between CNDM2 and Alzheimer's disease pathogenesis. To study this matter directly, we evaluated data from University of Kentucky Alzheimer's Disease Center (UK ADC) patients recruited while non-demented and followed longitudinally. Of patients who had come to autopsy (N = 234), 139 met inclusion criteria. These patients provided the basis for comparing the prevalence of pathological and clinical indices between well-characterized cases with (N = 50) or without (N = 89) the premortem diagnosis of diabetes. In diabetics, cerebrovascular pathology was more frequent and Alzheimer-type pathology was less frequent than in non-diabetics. Finally, a series of photomicrographs demonstrates histopathological features (including clinical-radiographical correlation) observed in brains of persons that died after a history of diabetes. These preliminary, correlative, and descriptive studies may help develop new hypotheses about CNDM2. We conclude that more work should be performed on human material in the context of CNDM2.

Beta amyloid and hyperphosphorylated tau deposits in the pancreas in type 2 diabetes

Strong epidemiologic evidence suggests an association between Alzheimer disease (AD) and type 2 diabetes. To determine if amyloid beta (Abeta) and hyperphosphorylated tau occurs in type 2 diabetes, pancreas tissues from 21 autopsy cases (10 type 2 diabetes and 11 controls) were analyzed. APP and tau mRNAs were identified in human pancreas and in cultured insulinoma beta cells (INS-1) by RT-PCR. Prominent APP and tau bands were detected by Western blotting in pancreatic extracts. Aggregated Abeta, hyperphosphorylated tau, ubiquitin, apolipoprotein E, apolipoprotein(a), IB1/JIP-1 and JNK1 were detected in Langerhans islets in type 2 diabetic patients. Abeta was co-localized with amylin in islet amyloid deposits. In situ beta sheet formation of islet amyloid deposits was shown by infrared microspectroscopy (SIRMS). LPS increased APP in non-neuronal cells as well. We conclude that Abeta deposits and hyperphosphorylated tau are also associated with type 2 diabetes, highlighting common pathogenetic features in neurodegenerative disorders, including AD and type 2 diabetes and suggesting that Abeta deposits and hyperphosphorylated tau may also occur in other organs than the brain.

Diet-induced metabolic disturbances as modulators of brain homeostasis

A number of metabolic disturbances occur in response to the consumption of a high fat western diet. Such metabolic disturbances can include the progressive development of hyperglycemia, hyperinsulemia, obesity, metabolic syndrome, and diabetes. Cumulatively, diet-induced disturbances in metabolism are known to promote increased morbidity and negatively impact life expectancy through a variety of mechanisms. While the impact of metabolic disturbances on the hepatic, endocrine, and cardiovascular systems is well established there remains a noticeable void in understanding the basis by which the central nervous system (CNS) becomes altered in response to diet-induced metabolic dysfunction. In particular, it remains to be fully elucidated which established features of diet-induced pathogenesis (observed in non-CNS tissues) are recapitulated in the brain, and identification as to whether the observed changes in the brain are a direct or indirect effect of peripheral metabolic disturbances. This review will focus on each of these key issues and identify some critical experimental questions which remain to be elucidated experimentally, as well as provide an outline of our current understanding for how diet-induced alterations in metabolism may impact the brain during aging and age-related diseases of the nervous system.