Effects of insulinic therapy on cognitive impairment in patients with Alzheimer disease and diabetes mellitus type-2

Single nuclei transcriptomics in diabetic mice reveals altered brain hippocampal endothelial cell function, permeability, and behavior

Type 2 diabetes mellitus (T2DM) is a metabolic disorder with cerebrovascular and cardiovascular sequelae. Yet, a clear pattern of gene dysregulation by T2DM in dementia has yet to be defined. We used single nuclei RNA sequencing technology to profile the transcriptome of endothelial cells (EC) from anatomically defined hippocampus of db/db mice to identify differentially expressed (DE) genes, gene pathways and networks, predicted regulating transcription factors, and targets of DE long noncoding RNAs. We also applied gadolinium (Gd) enhanced magnetic resonance imaging (MRI) to assess blood brain barrier (BBB) permeability, and functionally assessed cognitive behavior. The murine gene expression profiles were then integrated with those of persons with Alzheimer's disease (AD) and vascular dementia (VaD). We reveal that the transcriptome of the diabetic hippocampal murine brain endothelium differs substantially from control wild types with molecular changes characterized by differential RNA coding and noncoding pathways enriched for EC signaling and for endothelial functions for neuroinflammation, endothelial barrier disruption, and neurodegeneration. Gd enhanced structural brain MRI linked endothelial molecular alterations to BBB dysfunction by neuroimaging. Integrated multiomics of hippocampal endothelial gene dysregulation associated with impairments in cognitive adaptive capacity. In addition, the diabetic transcriptome significantly and positively correlated with that of persons with AD and VaD. Taken together, our results from comprehensive, multilevel, integrated, single nuclei transcriptomics support the hypothesis of T2DM-mediated neuroinflammation and endothelial cell and barrier disruption as key mechanisms in cognitive decline in T2DM, thereby suggesting potential endothelial-specific molecular therapeutic targets.

Relationship between glycemic control and cognitive impairment: A systematic review and meta-analysis

Background

Diabetes mellitus, or hyperglycemia, is an independent risk factor for cognitive impairment. Here we systematically analyzed whether glycemic control could improve cognitive impairment in patients with diabetes mellitus (DM), hyperglycemia, or insulin resistance.

Methods

Three databases (PubMed, EMBASE, and Cochrane Library) and ClinicalTrials.gov were searched for randomized controlled trials analyzing the relationship between glycemic control and cognitive function assessments, published from database inception to June 2022. Patients in experimental groups were treated with antidiabetic drugs, while control groups were treated with a placebo or alternative antidiabetic drugs. Data analysis was conducted using RevMan 5.3 and StataSE-64, and standardized mean difference (SMD) and 95% confidence intervals (CIs) were calculated.

Results

Thirteen studies comprising 19,314 participants were included. Analysis revealed that glycemic control significantly attenuated the degree of decline in cognitive function assessment scores (SMD  =  0.15; 95% CI 0.05, 0.26; p  <  0.00001), and funnel plots confirmed no publication bias. Seven studies used Mini-Mental State Examination as the primary cognitive function assessment, showing that glycemic control significantly delayed the degree of decline in cognitive function assessment scores (SMD  =  0.18; 95% CI 0.03, 0.34; p  =  0.02). Similar results were seen in two studies using the Montreal Cognitive Assessment scale, but without significant difference (SMD  =  0.05; 95% CI-0.10, 0.21; p  =  0.51). One study using Auditory Word Learning Test (AVLT) showed that glycemic control significantly delayed the decline in cognitive function assessment scores (SMD  =  0.52; 95% CI 0.11,0.93; p  =  0.01), and another used Wechsler Memory Scale Revised, showing similar results (SMD  =  1.45; 95% CI 0.86, 2.04; p  <  0.00001). Likewise, a study that used Modified Mini-Mental State scale showed that glycemic control significantly delayed the decline in cognitive function assessment scores (SMD  =  -0.10; 95% CI-0.16, -0.03; p  =  0.005). Lastly, one study used AVLT subtests to show that glycemic control delayed the decline in cognitive function assessment scores, although not statistically significant (SMD  =  0.09; 95% CI-0.53, 0.71; p  =  0.78).

Conclusion

Glycemic control through antidiabetic treatment correlates with the improvement of cognitive impairment in patients with DM, hyperglycemia or insulin resistance. However, further studies are needed to validate the results of this study.

Systematic Review Registration

PROSPERO, identifier CRD42022342260.

Repositioning of antidiabetic drugs for Alzheimer's disease: possibility of Wnt signaling modulation by targeting LRP6 an in silico based study

Alzheimer disease (AD) is the most common, irreversible and progressive form of dementia for which the exact pathology and cause are still not clear. At present, we are only confined to symptomatic treatment, and the lack of disease-modifying therapeutics is worrisome. Alteration of Wnt signaling has been linked to metabolic diseases as well as AD. The crosstalk between Canonical Wnt signaling and insulin signaling pathway has been widely studied and accepted from several clinical and preclinical studies that have proven the beneficial effect of antidiabetic medications in the case of memory and cognition loss. This structure-based in silico study was focused on exploring the link between the currently available FDA approved antidiabetic drugs and the Wnt signaling pathway. The library of antidiabetics was obtained from drug bank and was screened for their binding affinity with protein (PDB ID: 3S2K) LRP6, a coreceptor of the Wnt signaling pathway using GLIDE module of Schrodinger. The top molecules, with higher docking score, binding energy and stable interactions, were subjected to energy-based calculation using MMGBSA, followed by a molecular dynamics-based simulation study. Drugs of class α-glucosidase inhibitors and peroxisome proliferator-activated receptors (PPARs) agonists were found to have a strong affinity towards LRP6 proteins, highlighting the possibility of the modulation of Wnt signaling by antidiabetics as one of the possible mechanisms for use in AD. However, further experimental based in vitro and in vivo studies are warranted for verification and support.Communicated by Ramaswamy H. Sarma.

Therapeutic Strategies for Tauopathies and Drug Repurposing as a Potential Approach

Tauopathies are neurodegenerative diseases characterized by the deposition of abnormal tau in the brain. To date, there are no disease-modifying therapies approved by the U.S. Food and Drug Administration (US FDA) for the treatment of tauopathies. In the past decades, extensive efforts have been provided to develop disease-modifying therapies to treat tauopathies. Specifically, exploring existing drugs with the intent of repurposing for the treatment of tauopathies affords a reasonable alternative to discover potent drugs for treating these formidable diseases. Drug repurposing will not only reduce formulation and development stage effort and cost but will also take a key advantage of the established toxicological studies, which is one of the main causes of clinical trial failure of new molecules. In this review, we provide an overview of the current treatment strategies for tauopathies and the recent progress in drug repurposing as an alternative approach to treat tauopathies.

Diabetes Treatment Is Associated With Better Cognitive Function: The Age Disparity

Background: Diabetes mellitus (DM) is a recognised risk factor for cognitive dysfunction. The purpose of this study was to explore the relationship between active treatment for DM and cognitive function in middle-aged (< 60 years) and older adults (≥60 years), respectively.

Methods: A total of 13,691 participants (58.55 ± 9.64 years, 47.40% of men) from the Chinese Health and Retirement Longitudinal Study (CHARLS) were included. The participants were classified into three groups according to whether or not they have diabetes and to their diabetes treatment status: diabetes-free, treated-diabetes and untreated-diabetes, in which the diabetes-free group was regarded as reference specially. Cognitive function was assessed by two interview-based measurements for mental intactness and episodic memory.

Results: Compared with the participants in the diabetes-free group, the older participants in the treated-diabetes group had better performance in terms of mental intactness (β = 0.37, 95% CI = 0.04–0.70). No significant association was observed in the middle-aged participants. In the subgroup analyses, the lower cognitive score was only observed in people without depression, who had never smoked and drunk, and with a normal weight (body mass index: 18.5–23.9 kg/m²).

Conclusion: The cognitive function of actively treated diabetic patients was better than that of patients without diabetes, but the improvement was significant only in elderly people. Depression, smoking, drinking, and an abnormal weight may attenuate this effect.

Comparison of cognitive status of diabetic and non-diabetic elderly in the last ten years in primary health care in Iran

Introduction. Cognitive disorders and chronic diseases such as diabetes are common problems of aging. The aim of this study was to determine and compare the cognitive status of diabetic and non-diabetic elderly in the past ten years in primary health care in Iran. Method: This cross-sectional study was performed on people aged 60 years and older in Kerman, Iran in 2020. In total, this study was performed on 200 patients (100 diabetic and 100 non-diabetic) meeting inclusion criteria. The Short Mental Status Questionnaire (MMSE) and The Informant Questionnaire for Cognitive Decline in the Elderly (IQCODE) were used to assess cognitive function. The validity and reliability of the questionnaires were confirmed in this study. Data were analyzed using Chi-square, T-test, and ANOVA analysis in SPSS 21 software. Results. The results showed that there was a statistically significant difference between diabetic and non-diabetic groups in the current cognitive status and cognitive status in the last ten years. The mean scores of cognitive function from the short mental status questionnaire in the diabetic group were lower than in the non-diabetic group (p = 0.001). The mean scores of the cognitive deficit screening questionnaire in diabetic elderly were higher than in non-diabetic elderly (p < 0.001). Conclusion. Based on the results of this study, health care providers and family physicians should focus on controlling diabetes and identifying any cognitive impairment in the early stages of comprehensive care of diabetic patients.

Role of ketone bodies in diabetes-induced dementia: sirtuins, insulin resistance, synaptic plasticity, mitochondrial dysfunction, and neurotransmitter

Patients with type 2 diabetes can have several neuropathologies, such as memory deficits. Recent studies have focused on the association between metabolic imbalance and neuropathological problems, and the associated molecular pathology. Diabetes triggers neuroinflammation, impaired synaptic plasticity, mitochondrial dysfunction, and insulin resistance in the brain. Glucose is a main energy substrate for neurons, but under certain conditions, such as fasting and starvation, ketone bodies can be used as an energy fuel for these cells. Recent evidence has shed new light on the role of ketone bodies in regulating several anti-inflammation cellular pathways and improving glucose metabolism, insulin action, and synaptic plasticity, thereby being neuroprotective. However, very high amount of ketone bodies can be toxic for the brain, such as in ketoacidosis, a dangerous complication that may occur in type 1 diabetes mellitus or alcoholism. Recent findings regarding the relationship between ketone bodies and neuropathogenesis in dementia are reviewed in this article. They suggest that the adequately low amount of ketone bodies can be a potential energy source for the treatment of diabetes-induced dementia neuropathology, considering the multifaceted effects of the ketone bodies in the central nervous system. This review can provide useful information for establishing the therapeutic guidelines of a ketogenic diet for diabetes-induced dementia.

Tonicity-responsive enhancer-binding protein promotes diabetic neuroinflammation and cognitive impairment via upregulation of lipocalin-2

Background

Diabetic individuals have increased circulating inflammatory mediators which are implicated as underlying causes of neuroinflammation and memory deficits. Tonicity-responsive enhancer-binding protein (TonEBP) promotes diabetic neuroinflammation. However, the precise role of TonEBP in the diabetic brain is not fully understood.

Methods

We employed a high-fat diet (HFD)-only fed mice or HFD/streptozotocin (STZ)-treated mice in our diabetic mouse models. Circulating TonEBP and lipocalin-2 (LCN2) levels were measured in type 2 diabetic subjects. TonEBP haploinsufficient mice were used to investigate the role of TonEBP in HFD/STZ-induced diabetic mice. In addition, RAW 264.7 macrophages were given a lipopolysaccharide (LPS)/high glucose (HG) treatment. Using a siRNA, we examined the effects of TonEBP knockdown on RAW264 cell’ medium/HG-treated mouse hippocampal HT22 cells.

Results

Circulating TonEBP and LCN2 levels were higher in experimental diabetic mice or type 2 diabetic patients with cognitive impairment. TonEBP haploinsufficiency ameliorated the diabetic phenotypes including adipose tissue macrophage infiltrations, neuroinflammation, blood–brain barrier leakage, and memory deficits. Systemic and hippocampal LCN2 proteins were reduced in diabetic mice by TonEBP haploinsufficiency. TonEBP (+ / −) mice had a reduction of hippocampal heme oxygenase-1 (HO-1) expression compared to diabetic wild-type mice. In particular, we found that TonEBP bound to the LCN2 promoter in the diabetic hippocampus, and this binding was abolished by TonEBP haploinsufficiency. Furthermore, TonEBP knockdown attenuated LCN2 expression in lipopolysaccharide/high glucose-treated mouse hippocampal HT22 cells.

Conclusions

These findings indicate that TonEBP may promote neuroinflammation and cognitive impairment via upregulation of LCN2 in diabetic mice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02331-8.

DL-3-n-butylphthalide ameliorates diabetes-associated cognitive decline by enhancing PI3K/Akt signaling and suppressing oxidative stress

DL-3-n-Butylphthalide (DL-NBP), a small molecular compound extracted from the seeds of Apium graveolens Linn (Chinese celery), has been shown to exert neuroprotective effects due to its anti-inflammatory, anti-oxidative and anti-apoptotic activities. DL-NBP not only protects against ischemic cerebral injury, but also ameliorates vascular cognitive impairment in dementia patients including AD and PD. In the current study, we investigated whether and how DL-NBP exerted a neuroprotective effect against diabetes-associated cognitive decline (DACD) in db/db mice, a model of type-2 diabetes. db/db mice were orally administered DL-NBP (20, 60, 120 mg· kg-1· d-1) for 8 weeks. Then the mice were subjected to behavioral test, their brain tissue was collected for morphological and biochemical analyses. We showed that oral administration of DL-NBP significantly ameliorated the cognitive decline with improved learning and memory function in Morris water maze testing. Furthermore, DL-NBP administration attenuated diabetes-induced morphological alterations and increased neuronal survival and restored the levels of synaptic protein PSD95, synaptophysin and synapsin-1 as well as dendritic density in the hippocampus, especially at a dose of 60 mg/kg. Moreover, we revealed that DL-NBP administration suppressed oxidative stress by upregulating Nrf2/HO-1 signaling, and increased brain-derived neurotrophic factor (BDNF) expression by activating PI3K/Akt/CREB signaling in the hippocampus. These beneficial effects of DL-NBP were observed in high glucose-treated PC12 cells. Our results suggest that DL-NBP may be a potential pharmacologic agent for the treatment of DACD.

Effects of compound K, a metabolite of ginsenosides, on memory and cognitive dysfunction in db/db mice involve the inhibition of ER stress and the NLRP3 inflammasome pathway

Accumulating clinical and epidemiological evidence indicates a close relationship between diabetes mellitus and dementia. The ginsenoside compound K (CK) has been reported to ameliorate diabetes mellitus and confer protection to the central nervous system. In this study, we investigated whether CK could improve memory impairment and cognitive dysfunction in diabetic db/db mice. Firstly, we found that CK treatments significantly improved behavioral impairment and cognitive dysfunction based on Morris water maze, Y-maze, and fear conditioning tests. Besides, CK decreased the fasting glucose level, increased lipid metabolism, and ameliorated glucose tolerance, insulin sensitivity, and dyslipidemia in diabetic db/db mice. In addition, CK treatments alleviated oxidative stress and inhibited the inflammatory response in hippocampal tissue. Further investigations showed that CK treatments inhibited the NLRP3 inflammasome pathway, as evidenced by the declined expression of TXNIP, NLRP3 inflammasomes, ASC, cleaved caspase-1, and mature IL-1β in hippocampal tissues. Moreover, CK treatments alleviated ER stress via down-regulating the level of BiP, CHOP, p-PERK, p-IRE1α and ATF6 in the hippocampus of db/db mice. These results suggest that CK improves memory and cognitive dysfunction, possibly by ameliorating glucose tolerance, insulin sensitivity, and dyslipidemia, suppressing oxidative stress and inflammatory response and modulating the NLRP3 inflammasome pathway and ER stress.

Combination Drug Therapy for the Management of Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of dementia worldwide. Even though the number of AD patients is rapidly growing, there is no effective treatment for this neurodegenerative disorder. At present, implementation of effective treatment approaches for AD is vital to meet clinical needs. In AD research, priorities concern the development of disease-modifying therapeutic agents to be used in the early phases of AD and the optimization of the symptomatic treatments predominantly dedicated to the more advanced AD stages. Until now, available therapeutic agents for AD treatment only provide symptomatic treatment. Since AD pathogenesis is multifactorial, use of a multimodal therapeutic intervention addressing several molecular targets of AD-related pathological processes seems to be the most practical approach to modify the course of AD progression. It has been demonstrated through numerous studies, that the clinical efficacy of combination therapy (CT) is higher than that of monotherapy. In case of AD, CT is more effective, mostly when started early, at slowing the rate of cognitive impairment. In this review, we have covered the major studies regarding CT to combat AD pathogenesis. Moreover, we have also highlighted the safety, tolerability, and efficacy of CT in the treatment of AD.

The Interplay between Diabetes and Alzheimer's Disease-In the Hunt for Biomarkers

The brain is an organ in which energy metabolism occurs most intensively and glucose is an essential and dominant energy substrate. There have been many studies in recent years suggesting a close relationship between type 2 diabetes mellitus (T2DM) and Alzheimer’s disease (AD) as they have many pathophysiological features in common. The condition of hyperglycemia exposes brain cells to the detrimental effects of glucose, increasing protein glycation and is the cause of different non-psychiatric complications. Numerous observational studies show that not only hyperglycemia but also blood glucose levels near lower fasting limits (72 to 99 mg/dL) increase the incidence of AD, regardless of whether T2DM will develop in the future. As the comorbidity of these diseases and earlier development of AD in T2DM sufferers exist, new AD biomarkers are being sought for etiopathogenetic changes associated with early neurodegenerative processes as a result of carbohydrate disorders. The S100B protein seem to be interesting in this respect as it may be a potential candidate, especially important in early diagnostics of these diseases, given that it plays a role in both carbohydrate metabolism disorders and neurodegenerative processes. It is therefore necessary to clarify the relationship between the concentration of the S100B protein and glucose and insulin levels. This paper draws attention to a valuable research objective that may in the future contribute to a better diagnosis of early neurodegenerative changes, in particular in subjects with T2DM and may be a good basis for planning experiments related to this issue as well as a more detailed explanation of the relationship between the neuropathological disturbances and changes of glucose and insulin concentrations in the brain.

Triad of impairment in older people with diabetes-reciprocal relations and clinical implications

Frailty is emerging as a new category complication of diabetes in older people. Clinically, frailty is still not well defined and mostly viewed as a decline in solely the physical domain. However, frailty is a multidimensional syndrome and the newly introduced concept of "triad of impairment" (physical, cognitive and emotional) may be a more representative of the broad nature of frailty. The components of the triad of impairment (TOI) commonly coexist and demonstrate a reciprocal relation. Diabetes in old age appears to increase the risk of the triad of impairment, which may eventually progress to disability. Therefore, older people with diabetes should be regularly assessed for the presence of these three key components. Adequate nutrition and regular resistance exercise training have been shown to have a positive impact on the long-term outcome in this population. However, the role of good glycaemic control and the use of current hypoglycaemic medications in reducing the incidence of this triad are less clear. Future research is needed to develop novel hypoglycaemic medications that not only focus on glycaemic control and cardiovascular safety but also on reducing the risk of the triad of impairment.

The effects of stress on cardiovascular disease and Alzheimer's disease: Physical exercise as a counteract measure

AD is a complicated multi-systemic neurological disorder that involves different biological pathways. Several risk factors have been identified, including chronic stress. Chronic stress produces an alteration in the activity of the hypothalamic pituitary adrenal (HPA) system, and the autonomic nervous system (ANS), which over time increase the risk of AD and also the incidence of cardiovascular disease (CVD) and risk factors, such as hypertension, obesity and type 2 diabetes, associated with cognitive impairment and AD. Considering the multi-factorial etiology of AD, understanding the complex interrelationships between different risk factors is of potential interest for designing adequate strategies for preventing, delaying the onset or slowing down the progression of this devastating disease. Thus, in this review we will explore the general mechanisms and evidence linking stress, cardiovascular disease and AD, and discuss the potential benefits of physical activity for AD by counteracting the negative effects of chronic stress, CVD and risk factors.

Amyloid beta and diabetic pathology cooperatively stimulate cytokine expression in an Alzheimer's mouse model

BACKGROUND

Diabetes is a risk factor for developing Alzheimer's disease (AD); however, the mechanism by which diabetes can promote AD pathology remains unknown. Diabetes results in diverse molecular changes in the brain, including dysregulation of glucose metabolism and loss of cerebrovascular homeostasis. Although these changes have been associated with increased Aβ pathology and increased expression of glial activation markers in APPswe/PS1dE9 (APP/PS1) mice, there has been limited characterization, to date, of the neuroinflammatory changes associated with diabetic conditions.

METHODS

To more fully elucidate neuroinflammatory changes associated with diabetes that may drive AD pathology, we combined the APP/PS1 mouse model with either high-fat diet (HFD, a model of pre-diabetes), the genetic db/db model of type 2 diabetes, or the streptozotocin (STZ) model of type 1 diabetes. We then used a multiplexed immunoassay to quantify cortical changes in cytokine proteins.

RESULTS

Our analysis revealed that pathology associated with either db/db, HFD, or STZ models yielded upregulation of a broad profile of cytokines, including chemokines (e.g., MIP-1α, MIP-1β, and MCP-1) and pro-inflammatory cytokines, including IL-1α, IFN-γ, and IL-3. Moreover, multivariate partial least squares regression analysis showed that combined diabetic-APP/PS1 models yielded cooperatively enhanced expression of the cytokine profile associated with each diabetic model alone. Finally, in APP/PS1xdb/db mice, we found that circulating levels of Aβ1-40, Aβ1-42, glucose, and insulin all correlated with cytokine expression in the brain, suggesting a strong relationship between peripheral changes and brain pathology.

CONCLUSIONS

Altogether, our multiplexed analysis of cytokines shows that Alzheimer's and diabetic pathologies cooperate to enhance profiles of cytokines reported to be involved in both diseases. Moreover, since many of the identified cytokines promote neuronal injury, Aβ and tau pathology, and breakdown of the blood-brain barrier, our data suggest that neuroinflammation may mediate the effects of diabetes on AD pathogenesis. Therefore, strategies targeting neuroinflammatory signaling, as well as metabolic control, may provide a promising strategy for intervening in the development of diabetes-associated AD.

A Different View to Older Diabetics: Management of Treatment According to Cognitive Functions

Background and aims. Diabetes Mellitus is a chronic systemic disease which has multiple complications and the presence of these complications affects the management of disease. It is also important to consider cognitive functions when managing the treatment of older diabetics. In this study, we aimed to make proposals for the appropriate drug choice to preserve cognitive functions in elderly diabetics.

Matherial and methods. A total of 270 older diabetic patients were reviewed. Possible risk factors of cognitive impairment were investigated. Correlation analysis was performed between MMSE and GDS, age, HbA1c, duration of diabetes.

Results. Sulfonylurea (adj. OR: 2.33, %95 CI: 1.11-4.90) and insulin treatment (adj. OR: 3.79, %95 CI: 1.56-9.21) were found associated with increased risk of cognitive impairment. In addition, there was a negative correlation between MMSE and GDS (r: -.129, p<0.05).

Conclusion. We suggest that insulin and sulfonylureas should be used with caution in those with cognitive impairment.

Drug interactions with dementia-related pathophysiological pathways worsen or prevent dementia

Many risk factors are known to induce or precipitate dementia. Drugs acting via different mechanisms can modulate cognitive performance and exert either beneficial or deleterious effects on cognition through functional or neuropathological mechanisms. This review discusses the association between several classes of drugs and cognitive impairment and dementia risk. These drugs can be divided into drugs targeting CNS disorders (e.g., anticholinergic drugs, antiepileptics, antipsychotics, benzodiazepines, and opioids) and drugs targeting non‐CNS disorders (e.g., antidiabetics, antihypertensives, proton pump inhibitors, and statins). Furthermore, we sought to highlight the pharmacological mechanisms underlying their possible detrimental or beneficial effects on cognition. Anticholinergic and antiepileptic drugs were excluded from this review because their effects on cognition are well known. Studies investigating benzodiazepines have revealed an increased risk of dementia. Conclusions on dementia risk or cognitive impairment regarding opioids and antipsychotic drugs are difficult to draw. These different classes appear to impair cognition not by a single clear mechanism of action specific to each class but by several relatively interdependent and interconnected mechanisms (e.g., impaired neurotransmission, neuroinflammation, neuronal death, oxidative stress, or interactions with dementia‐related pathways). The dementia risk initially associated with the use of proton pump inhibitors might have been overestimated. In contrast, statins, antihypertensive medications, and antidiabetics could potentially decrease the risk of dementia and cognitive impairment by acting in ways opposite to the mechanisms cited above.

Linked Articles

This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc

L-3-n-butylphthalide attenuates cognitive deficits in db/db diabetic mice

Numerous epidemiological studies have shown that diabetes mellitus (DM) is associated with dementia and cognition decline. However, there is currently no effective treatment for diabetes-induced cognitive dysfunction. The neuroprotective effect of L-3-n-butylphthalide (L-NBP) has been demonstrated in vascular dementia animal models. The purpose of this study was to determine whether L-NBP can ameliorate cognitive deficits in db/db mice, a model of obesity and type 2 diabetes. The mice were administered with vehicle or L-NBP (120 mg/kg) by gavage daily for 6 weeks. Then, Morris water maze tasks were performed, and hippocampal LTP was recorded in vivo. Next, the synaptic structure of the CA1 hippocampus region was investigated via electron microscopy. Finally, the expression levels of MDA, SOD, 8-OHdG, and NADPH oxidase subunits gp91 and p67, as well as the expression of NF-κB p65, TNF-α, IL-1β and caspase-3 were measured by Western blot, RT-PCR and ELISA. Treatment with L-NBP significantly attenuated the learning and memory deficits in db/db mice. Concomitantly, L-NBP also increased hippocampus synaptic plasticity, characterized by an enhanced in vivo LTP, and suppressed oxidative stress, as indicated by increased SOD activity and decreased MDA, 8-OHdG, and NADPH oxidase subunits p67 and gp91. L-NBP also significantly decreased NF-κB p65, TNF-α, IL-1βand caspase-3 levels in the hippocampus. L-NBP significantly ameliorated cognitive decline in type 2 diabetic mice, and this effect was accompanied by an improvement in hippocampal plasticity and an amelioration of oxidative stress, inflammation and apoptosis cascades. Thus, L-NBP may be a promising therapeutic agent against DM-mediated cognitive dysfunction.

Impact of pharmacological treatment of diabetes mellitus on dementia risk: systematic review and meta-analysis

BACKGROUND

The association between diabetes mellitus (DM) treatment and dementia is not well understood.

OBJECTIVE

To investigate the association between treatment of diabetes, hypoglycemia, and dementia risk.

RESEARCH DESIGN AND METHODS

We performed a systematic review and meta-analysis of pharmacological treatment of diabetes and incident or progressive cognitive impairment. We searched Ovid MEDLINE, Embase, Cochrane Central Registry of Controlled Trials, and PsychINFO from inception to 18 October 2017. We included cross-sectional, case-control, cohort, and randomized controlled studies. The study was registered with PROSPERO (ID CRD42017077953).

RESULTS

We included 37 studies into our systematic review and 13 into our meta-analysis. Ten studies investigated any antidiabetic treatment compared with no treatment or as add-on therapy to prior care. Treatment with an antidiabetic agent, in general, was not associated with incident dementia (risk ratio (RR) 1.01; 95% CI 0.93 to 1.10). However, we found differential effects across drug classes, with a signal of harm associated with insulin therapy (RR 1.21; 95% CI 1.06 to 1.39), but potentially protective effects with thiazolidinedione exposure (RR 0.71; 95% CI 0.55 to 0.93). Severe hypoglycemic episodes were associated with a nearly twofold increased likelihood of incident dementia (RR 1.77; 95% CI 1.35 to 2.33). Most studies did not account for DM duration or severity.

CONCLUSIONS AND LIMITATIONS

The association between treatment for diabetes and dementia is differential according to drug class, which is potentially mediated by hypoglycemic risk. Not accounting for DM duration and/or severity is a major limitation in the available evidence base.

Impact of glycemic status on longitudinal cognitive performance in men with and without HIV infection

OBJECTIVES

To determine the relationship between glycemic status and cognitive performance in men living with HIV (MLWH) and without HIV infection.

DESIGN

A prospective HIV/AIDS cohort study in four US cities between 1999 and 2016.

METHODS

Glycemic status was categorized as normal glucose, impaired fasting glucose, controlled diabetes mellitus and uncontrolled diabetes mellitus at each semiannual visit. Cognitive performance was evaluated using nine neuropsychological tests which measure attention, constructional ability, verbal learning, executive functioning, memory and psychomotor speed. Linear mixed models were used to assess the association between glycemic status and cognition.

RESULTS

Overall, 900 MLWH and 1149 men without HIV were included. MLWH had significantly more person-visits with impaired fasting glucose (52.1 vs. 47.9%) and controlled diabetes mellitus (58.2 vs. 41.8%) than men without HIV (P < 0.05). Compared with men with normal glucose, men with diabetes mellitus had significantly poorer performance on psychomotor speed, executive function and verbal learning (all P < 0.05). There was no difference in cognition by HIV serostatus. The largest effect was observed in individuals with uncontrolled diabetes mellitus throughout the study period, equivalent to 16.5 and 13.4 years of aging on psychomotor speed and executive function, respectively, the effect of which remained significant after adjusting for HIV-related risk factors. Lower CD4+ nadir was also associated with worse cognitive performance.

CONCLUSION

Abnormalities in glucose metabolism were more common among MLWH than men without HIV and were related to impaired cognitive performance. Metabolic status, along with advanced age and previous immunosuppression, may be important predictors of cognition in the modern antiretroviral therapy era.

New views and possibilities of antidiabetic drugs in treating and/or preventing mild cognitive impairment and Alzheimer's Disease

Mounting evidence suggests that diabetes mellitus (DM) is associated with mild cognitive impairment (MCI), vascular dementia and Alzheimer's disease (AD). Biological, clinical and epidemiological data support a close link between DM and AD. Increasingly, studies have found that several antidiabetic agents can promote neurogenesis, and clinically ameliorate cognitive and memory impairments in different clinical settings. Data has shown that these antidiabetic drugs positively affect mitochondrial and synaptic function, neuroinflammation, and brain metabolism. Evidence to date strongly suggests that these antidiabetic drugs could be developed as disease-modifying therapies for MCI and AD in patients with and without diabetes.

Disturbed sleep and diabetes: A potential nexus of dementia risk

Type 2 diabetes (T2D) and sleep disturbance (e.g., insomnia, sleep-disordered breathing) are prevalent conditions among older adults that are associated with cognitive decline and dementia, including Alzheimer's disease (AD). Importantly, disturbed sleep is associated with alterations in insulin sensitivity and glucose metabolism, and may increase the risk of T2D, and T2D-related complications (e.g., pain, nocturia) can negatively affect sleep. Despite these associations, little is known about how interactions between T2D and sleep disturbance might alter cognitive trajectories or the pathological changes that underlie dementia. Here, we review links among T2D, sleep disturbance, cognitive decline and dementia-including preclinical and clinical AD-and identify gaps in the literature, that if addressed, could have significant implications for the prevention of poor cognitive outcomes.

An Update on Type 2 Diabetes Mellitus as a Risk Factor for Dementia

With the rapidly expanding evidence on brain structural and functional changes in type 2 diabetes mellitus (T2DM) patients, there is an increasing need to update our understanding on how T2DM associates with dementia as well as the underlying pathophysiological mechanisms. A literature search of T2DM and dementia or cognition impairments was carried out in electronic databases Medline, EMBASE, and Google Scholar. In this review, the chosen evidence was limited to human subject studies only, and data on either type 1 diabetes mellitus (T1DM) or non-classified diabetes were excluded. T2DM is a risk factor for both vascular dementia (VaD) and Alzheimer's disease (AD), although AD pathological marker studies have not provided sufficient evidence. T2DM interacts additively or synergistically with many factors, including old age, hypertension, total cholesterol, and APOEɛ4 carrier status for impaired cognition functions seen in patients with T2DM. In addition, comorbid T2DM can worsen the clinical presentations of patients with either AD or VaD. In summary, T2DM increases the risk for AD through different mechanisms for VaD although some mechanisms may overlap. Tau-related neurofibrillary tangles instead of amyloid-β plaques are more likely to be the pathological biomarkers for T2DM-related dementia. Degeneration of neurons in the brain, impaired regional blood supply/metabolism, and genetic predisposition are all involved in T2DM-associated dementia or cognitive impairments.

Antidiabetic Polypill Improves Central Pathology and Cognitive Impairment in a Mixed Model of Alzheimer's Disease and Type 2 Diabetes

Type 2 diabetes (T2D) is an important risk factor to suffer dementia, being Alzheimer's disease (AD) as the most common form. Both AD and T2D are closely related to aging and with a growing elderly population it might be of relevance to explore new therapeutic approaches that may slow or prevent central complications associated with metabolic disorders. Therefore, we propose the use of the antidiabetic polypill (PP), a pharmacological cocktail, commonly used by T2D patients that include metformin, aspirin, simvastatin, and an angiotensin-converting enzyme inhibitor. In order to test the effects of PP at the central level, we have long-term treated a new mixed model of AD-T2D, the APP/PS1xdb/db mouse. We have analyzed AD pathological features and the underlying specific characteristics that relate AD and T2D. As expected, metabolic alterations were ameliorated after PP treatment in diabetic mice, supporting a role for PP in maintaining pancreatic activity. At central level, PP reduced T2D-associated brain atrophy, showing both neuronal and synaptic preservation. Tau and amyloid pathologies were also reduced after PP treatment. Furthermore, we observed a reduction of spontaneous central bleeding and inflammation after PP treatment in diabetic mice. As consequence, learning and memory processes were improved after PP treatment in AD, T2D, and AD-T2D mice. Our data provide the basis to further analyze the role of PP, as an alternative or adjuvant, to slow down or delay the central complications associated with T2D and AD.

Insulin signaling: An opportunistic target to minify the risk of Alzheimer's disease

Alzheimer's disease (AD) is progressive neurodegenerative disorder characterized by accumulation of senile plaques, neurofibrillary tangles (NFT) and neurodegeneration. The diabetes mellitus (DM) is one of the risk factors for AD pathogenesis by impairment in insulin signaling and glucose metabolism in central as well as peripheral system. Insulin resistance, impaired glucose and lipid metabolism are leading to the Aβ (Aβ) aggregation, Tau phosphorylation, mitochondrial dysfunction, oxidative stress, protein misfolding, memory impairment and also mark over Aβ transport through central to peripheral and vice versa. Several pathways, like enzymatic degradation of Aβ, forkhead box protein O1 (FOXO) signaling, insulin signaling shared common pathological mechanism for both AD and DM. Recent evidence showed that hyperinsulinemia and hyperglycemia affect the onset and progression of AD differently. Some researchers have suggested that hyperglycemia influences vascular tone, while hyperinsulinemia may underlie mitochondrial deficit. The objective of this review is to determine whether existing evidence supports the concept that impairment in insulin signaling and glucose metabolism play an important role in pathogenesis of AD. In the first part of this review, we tried to explain the interconnecting link between AD and DM, whereas the second part includes more information on insulin resistance and its involvement in AD pathogenesis. In the final part of this review, we have focused more toward the AD treatment by targeting insulin signaling like anti-diabetic, antioxidant, nutraceuticals and dietary supplements. To date, more researches should be done in this field in order to explore the pathways in insulin signaling, which might ameliorate the treatment options and reduce the risk of AD due to DM.

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.

Cognitive impairment is correlated with insulin resistance degree: the "PA-NICO-study"

Several epidemiological studies have shown that Diabetes Mellitus (DM) or Insulin Resistance (IR) increases the risk of dementia. Besides, some authors suggested that poor glucose control to be associated with worse cognitive function. We aimed to assess cognitive functions and IR-degree over time in diabetic. We also evaluated whether a greater magnitude of cognitive decline could be related with their IR degree. We enrolled 335 diabetic patients and 142 non-diabetic subjects; participants were subdivided into three groups in accordance with their IRdegree assessed by Homa-Index (HI): Normal-HI (non-diabetic NHI < 2,6), Moderate-HI (MHI > 2,6 < 10) and High-HI (HHI > 10). Metabolic status and a comprehensive neuropsycological test battery (MMSE, ADAS-Cog, ACDS-ADL) were assessed at baseline and every 12-months during the follow-up (6,8 years). At the end of the study, the average MMSE decreased significantly in patients of HHI group (P = .001) compared to baseline. MMSE scores were also reduced both in MHI group and in controls, but the difference between two groups was not significant. In HHI group, similar effects were observed for the ADAS-Cog score compared to baseline (P = 0.001); instead, when ACDS-ADL was evaluated, no differences was observed among the three groups. These results remained unchanged also after adjustment for confounding variables (i.e. APOε-status, sex, BMI, education level, heart diseases and HbA1c). We suggest that higher IR-degree is associated with greater cognitive decline in diabetic patients; so we hypothesize that IR degree, more than IR status itself, could be related to the severity of cognitive impairment.

Neurological outcomes of antidiabetic therapy: What the neurologist should know

Considering the causative or contributory effects of diabetes mellitus on common neurological diseases such as polyneuropathy, stroke and dementia, modern antidiabetic drugs may be expected to reduce incidence or progression of these conditions. Nevertheless, most observed benefits have been small, except in the context of therapy for diabetes mellitus type I and new-onset polyneuropathy. Recently, semaglutide, a GLP-1 analog, has been shown to significantly reduce stroke incidence in a randomized controlled trial. Beneficial effects of antidiabetic drugs on stroke severity or outcome have been controversial, though. The level of risk conferred by diabetes mellitus, the complex pathophysiology of neurological diseases, issues of trial design, side-effects of antidiabetic drugs as well as co-medication might be interacting factors that determine the performance of antidiabetic therapy with respect to neurological outcomes. It might be speculated that early treatment of prediabetes might prevent cerebral arteriosclerosis, cognitive decline or polyneuropathy more effectively, but this remains to be demonstrated.

Insulin-Like Growth Factor-1 but Not Insulin Predicts Cognitive Decline in Huntington's Disease

Background

Huntington's disease (HD) is one of several neurodegenerative disorders that have been associated with metabolic alterations. Changes in Insulin Growth Factor 1 (IGF-1) and/or insulin input to the brain may underlie or contribute to the progress of neurodegenerative processes. Here, we investigated the association over time between changes in plasma levels of IGF-1 and insulin and the cognitive decline in HD patients.

Methods

We conducted a multicentric cohort study in 156 patients with genetically documented HD aged from 22 to 80 years. Among them, 146 patients were assessed at least twice with a follow-up of 3.5 ± 1.8 years. We assessed their cognitive decline using the Unified Huntington’s Disease Rating Scale, and their IGF-1 and insulin plasmatic levels, at baseline and once a year during the follow-up. Associations were evaluated using a mixed-effect linear model.

Results

In the cross-sectional analysis at baseline, higher levels of IGF-1 and insulin were associated with lower cognitive scores and thus with a higher degree of cognitive impairment. In the longitudinal analysis, the decrease of all cognitive scores, except the Stroop interference, was associated with the IGF-1 level over time but not of insulin.

Conclusions

IGF-1 levels, unlike insulin, predict the decline of cognitive function in HD.

Potential effects of current drug therapies on cognitive impairment in patients with type 2 diabetes

Type 2 diabetes mellitus is a complex metabolic disease that can cause serious damage to various organs. Among the best-known complications, an important role is played by cognitive impairment. Impairment of cognitive functioning has been reported both in type 1 and 2 diabetes mellitus. While this comorbidity has long been known, no major advances have been achieved in clinical research; it is clear that appropriate control of blood glucose levels represents the best current (although unsatisfactory) approach in the prevention of cognitive impairment. We have focused our attention on the possible effect on the brain of antidiabetic drugs, despite their effects on blood glucose levels, giving a brief rationale on the mechanisms (e.g. GLP-1, BDNF, ghrelin) that might be involved. Indeed, GLP-1 agonists are currently clinically studied in other neurodegenerative diseases (i.e. Parkinson's and Alzheimer's disease); furthermore, also other antidiabetic drugs have proven efficacy in preclinical studies. Overall, promising results are already available and finding new intervention strategies represents a current need in this field of research.

Increased insulin-like growth factor-1 levels in cerebrospinal fluid of advanced subacute sclerosing panencephalitis patients

PURPOSE

Subacute sclerosing panencephalitis (SSPE) is a progressive, lethal disease. Brain histopathology in certain SSPE patients shows, neurofibrillary tangles composed of abnormally phosphorylated, microtubule-associated protein tau (PHF-tau). Because the, phosphorylation of tau is inhibited by insulin and insulin-like growth factor-1 (IGF-1), we investigated cerebrospinal fluid (CSF) insulin and IGF-1 levels in SSPE patients.

METHODS AND RESULTS

In this study CSF IGF-1 and insulin levels of 45 SSPE and 25 age-matched control patients were investigated. CSF IGF-1 levels were significantly higher in SSPE patients at stage 4, compared to other stages (p 0.05). CSF insulin and IGF-1 levels were both positively correlated with serum measles IgG.

CONCLUSIONS

The correlation between CSF insulin and IGF-1 levels and serum measles virus IgG titer may be the result of, insulin activating IGF-1 receptors, and consequently, IGF-1 stimulating, plasma cells and enhancing IgG production. Increased IGF-1 may also, inhibit the phosphorylation of tau. Further studies examining the, correlation between IGF-1, insulin, tau, and PHF-tau levels in the same, patients may clarify any possible pathogenetic relation between these, pathways.

Reestablishment of the hyperglycemia to the normal levels seems not to be essential to the anxiolytic-like effect induced by insulin

Diabetes is a chronic metabolic disease accompanied by several comorbidities, including neuropsychiatric conditions. Since the hyperglycemia appears to be the primary factor involved in diabetic conditions, we examined the effect of insulin treatment in diabetic rats on behavioral responses related to anxiety and aversive memory extinction. For this, normoglycemic (NGL) or streptozotocin-diabetic (DBT) rats were submitted to the elevated T maze (ETM) and the contextual conditioned fear (CCF) tests. Therefore, animals were subjected to the prolonged treatment with insulin (6 IU/day, s.c.) to investigate the effect of the treatment on distinct behaviors. When anxiety-like responses such as the inhibitory avoidance (IA) on the ETM and the time of freezing in the first session of the CCF test were evaluated, our data showed a more pronounced anxiogenic-like behavior in DBT animals when compared to NGL ones. In addition, an increased freezing time was observed in DBT animals exposed to the CCF test (sessions 2 and 3) when compared to the NGL group, suggestive of an impairment in the extinction of aversive memory. Insulin treatment induced an anxiolytic-like effect when IA and freezing time (session 1) was evaluated, but did not alter the impaired extinction of aversive memory (sessions 2 and 3). To better understand the involvement of a rigorous control of glycaemia, we also investigated the effect of a lower dose of insulin (3 IU/day, s.c.), unable to reestablish the hyperglycemia to the normal levels, on the same behavioral parameters. Our data show that independent of the dose of insulin, the same effects were observed when animals were evaluated in the ETM and CCF tests. However, only the highest dose of insulin was able to reduce the hyperglycemia to the normal levels. To conclude, our data suggest that a severe glycemic control by insulin treatment seems to be important, but not essential in improving diabetes-induced anxiety.

Long-term central pathology and cognitive impairment are exacerbated in a mixed model of Alzheimer's disease and type 2 diabetes

Type 2 diabetes (T2D) is a well-characterized risk factor for Alzheimer's disease (AD), the most common cause of dementia. Since both, T2D and dementia are closely related to aging and they chronically coexist in elderly patients, it is of particular relevance to know whether long-term evolution of T2D and dementia interfere with each other years after the onset of the diseases. In order to elucidate this interaction, we have characterized a mixed model of T2D and AD, the APP/PS1xdb/db mouse, at 36 weeks of age, when both diseases have long coexisted and evolved. In aged APP/PS1xdb/db mice we observed dysfunctional metabolic control, when compared with diabetic mice alone, suggesting that AD may also contribute to T2D pathology in the long-term. Learning and memory were severely impaired in APP/PS1xdb/db mice, accompanied by reduced cortical size, neuronal branching simplification and reduction of dendritic spine density. Increased tau phosphorylation was also observed in old APP/PS1xdb/db mice. A shift in amyloid-β (Aβ) pathology was detected, and while insoluble Aβ was reduced, more toxic soluble species were favoured. Microglia burden was significantly increased in the proximity of senile plaques and an overall increase of spontaneous haemorrhages was also observed in APP/PS1xdb/db mice, suggesting a possible disruption of the blood brain barrier in the mixed model. It is therefore feasible that strict metabolic control may slow or delay central complications when T2D and dementia coexist in the long term.

High rate of hypoglycemia in 6770 type 2 diabetes patients with comorbid dementia: A multicenter cohort study on 215,932 patients from the German/Austrian diabetes registry

AIMS

Dementia and type 2 diabetes (T2D) are two major phenomena in older people. To compare anti-hyperglycemic therapy and diabetes-related comorbidities between elderly T2D patients with or without comorbid dementia.

METHODS

215,932 type 2 diabetes patients aged ≥ 40 years (median [Q1;Q3]: 70.4 [61.2;77.7] years) from the standardized, multicenter German/Austrian diabetes patient registry, DPV, were studied. To identify patients with comorbid dementia, the registry was searched by ICD-10 codes, DSM-IV/-5 codes, respective search terms and/or disease-specific medication. For group comparisons, multiple hierarchic regression modeling with adjustments for age, sex, and duration of diabetes was applied.

RESULTS

3.1% (n=6770; 57% females) of the eligible T2D patients had clinically recognized comorbid dementia. After adjustment for demographics, severe hypoglycemia (insulin group: 14.8 ± 0.6 vs. 10.4 ± 0.2 events per 100 patient-years, p<0.001), hypoglycemia with coma (insulin group: 7.6 ± 0.4 vs. 3.9 ± 0.1 events per 100 patient-years, p<0.001), depression (9.9 vs. 4.7%, p<0.001), hypertension (74.7 vs. 72.2%, p<0.001), stroke (25.3 vs. 6.5%, p<0.001), diabetic foot syndrome (6.0 vs. 5.2%, p=0.004), and microalbuminuria (34.7 vs. 32.2%, p<0.001) were more common in dementia patients compared to T2D without dementia. Moreover, patients with dementia received insulin therapy more frequently (59.3 vs. 54.7%, p<0.001), but metabolic control (7.7 ± 0.1 vs. 7.7 ± 0.1%) was comparable to T2D without dementia.

CONCLUSIONS

In T2D with dementia, higher rates of hypoglycemia and other diabetes-related comorbidities were observed. Hence, the risks of a glucocentric and intense diabetes management with insulin and a focus on tight glycemic control without considering other factors may outweigh the benefits in elderly T2D patients with comorbid dementia.

Central vascular disease and exacerbated pathology in a mixed model of type 2 diabetes and Alzheimer's disease

Aging remains the main risk factor to suffer Alzheimer's disease (AD), though epidemiological studies also support that type 2 diabetes (T2D) is a major contributor. In order to explore the close relationship between both pathologies we have developed an animal model presenting both AD and T2D, by crossing APP/PS1 mice (AD model) with db/db mice (T2D model). We traced metabolic and cognitive evolution before T2D or AD pathology is present (4 weeks of age), when T2D has debuted but no senile plaques are present (14 weeks of age) and when both pathologies are well established (26 weeks of age). APP/PS1xdb/db mice showed an age-dependent synergistic effect between T2D and AD. Significant brain atrophy and tau pathology were detected in the cortex by 14 weeks, that spread to the hippocampus by 26 weeks of age. Severe cognitive impairment was also detected as soon as at 14 weeks of age. Interestingly, in APP/PS1xdb/db mice we observed a shift in Aβ soluble/insoluble levels, and whereas more toxic soluble species were favoured, senile plaques (SP) were reduced. An overall increase of microglia activation was observed in APP/PS1xdb/db mice. We also found exacerbated hemorrhagic burden in APP/PS1xdbd/db mice, suggesting that blood brain barrier alterations may be responsible for the early pathological features observed. Moreover, metabolic parameters can predict many of these alterations, supporting a role for T2D in AD pathology. This new model provides a relevant tool to further explore the relationship between T2D, AD and vascular implications, offering the possibility to assess therapeutic approaches, that by improving T2D metabolic control could delay or prevent AD pathology.

Clinical Characteristics for the Relationship between Type-2 Diabetes Mellitus and Cognitive Impairment: A Cross-Sectional Study

We explored the potential differences in cognitive status, lipid and glucose metabolism, ApoEε4 alleles and imaging between diabetic and non-diabetic subjects. 83 subjects with normal cognitive function and 114 mild cognitive impaired patients were divided into four groups by history of diabetes. General demographics was collected from all participants followed by MRI scan, biochemical examinations and a series of neuropsychological tests. Student's t test, multiple regressions and one-way ANOVA were applied to investigate the differences between groups. Comparing diabetic patients with non-diabetic subjects in the mild cognitive impaired group, we found several decreased items in recall of three words in MMSE (p=0.020), AVLT and SCWT (p<0.050). The multiple linear regression revealed that two-hour glucose level (B= -0.255, p<0.001) and fasting C-peptide (B= -0.466, p=0.001) had negative effects on the score of MMSE. In addition, diabetic patients treated with insulin and other diabetes medication performed better in part of the AVLT (p<0.050) compared to patients with insulin treatment or oral antidiabetic medication only. Patients with metformin medication had a better memory outcome compared to patients with sulphonylurea medication in the AVLT long delay free recall (p =0.010). These findings show that patients of mild cognitive impairment with diabetes mellitus have a worse outcome in attention, information processing speed and memory compared to non-diabetic patients. Higher two-hour glucose level and C-peptide level may be risk factors for severe cognitive impairment in type-2 diabetes mellitus patients. The results of this study also suggest that medication may have effects on cognitive function.

Increased Spontaneous Central Bleeding and Cognition Impairment in APP/PS1 Mice with Poorly Controlled Diabetes Mellitus

Alzheimer’s disease (AD) and vascular dementia (VaD) are the most common causes of dementia, and borderlines are blurred in many cases. Aging remains the main risk factor to suffer dementia; however, epidemiological studies reveal that diabetes may also predispose to suffer AD. In order to further study this relationship, we have induced hypoinsulinemic diabetes to APPswe/PS1dE9 (APP/PS1) mice, a classical model of AD. APP/PS1 mice received streptozotocin (STZ) ip at 18 weeks of age, when AD pathology is not yet established in this animal model. Cognition was evaluated at 26 weeks of age in the Morris water maze and the new object discrimination tests. We observed that STZ-induced episodic and working memory impairment was significantly worsened in APP/PS1 mice. Postmortem assessment included brain atrophy, amyloid-beta and tau pathology, spontaneous bleeding, and increased central inflammation. Interestingly, in APP/PS1-STZ diabetic mice, we detected a shift in Aβ soluble/insoluble levels, towards more toxic soluble species. Phospho-tau levels were also increased in APP/PS1-STZ mice, accompanied by an exacerbated inflammatory process, both in the close proximity to senile plaque (SP) and in SP-free areas. The presence of hemorrhages was significantly higher in APP/PS1-STZ mice, and although pericytes and endothelium were only partially affected, it remains possible that blood-brain barrier alterations underlie observed pathological features. Our data support the implication of the diabetic process in AD and VaD, and it is feasible that improving metabolic control could delay observed central pathology.

Glucose regulation, cognition, and brain MRI in type 2 diabetes: a systematic review

Type 2 diabetes is associated with cognitive dysfunction and structural brain changes. Abnormalities in glucose regulation are involved in several complications related to type 2 diabetes, but their role in these cerebral complications is unclear. We systematically reviewed studies of the association between glucose regulation (glycaemia, hypoglycaemic events, insulin concentration, insulin resistance, and glucose-lowering treatment) and cognitive function and brain abnormalities on MRI in people with type 2 diabetes. The 86 papers included showed that glycaemia, particularly high HbA1c concentration and glucose variability, are negatively associated with cognitive function in people with type 2 diabetes without dementia. However, the strength of this association is weak, and HbA1c generally accounted for less than 10% of the variance in cognition. Importantly, few studies have measured long-term cerebral outcomes, such as dementia and structural brain changes on MRI, and the effect of glucose-lowering treatment on these outcomes. More randomised controlled trials are needed to establish the effect of glucose-lowering treatment on long-term cognitive function in people with type 2 diabetes.

Treatment of vascular risk factors in patients with a diagnosis of Alzheimer's disease: a systematic review

BACKGROUND

Increasing evidence suggests vascular risk factors (VRF) play a role in the pathogenesis of Alzheimer's disease (AD). Epidemiological studies have found associations between VRF and risk of AD. Treating VRF in patients with AD offers a potential treatment option but ineffective treatments should be avoided in this group who are frequently on multiple medications and in whom compliance may be challenging.

METHODS

Studies containing information on the treatment of VRF in patients with a diagnosis of AD were identified using a defined search strategy. Randomised controlled trials and observational studies were included.

RESULTS

The pre-specified search strategy retrieved 11,992 abstract articles, and 25 papers including those identified on review of reference lists and reviews met the inclusion criteria. Of these, 11 were randomised controlled trials (RCTs) and 14 observational studies. Observational studies suggested that a VRF package and treatment of hypertension and statin therapy may be associated with improved outcome but these studies suffered from potential bias. The few RCTs performed were mostly small with short duration follow-up, and do not provide clear evidence either way.

CONCLUSIONS

Observational data raises the possibility that treating VRF could alter the rate of decline in AD. However RCT data are not yet available to support this hypothesis and to alter clinical practice. RCTs in larger numbers of individuals with longer follow-up, ideally in the early stages of AD, are required to address this potentially important treatment question.

Garlic extract attenuates brain mitochondrial dysfunction and cognitive deficit in obese-insulin resistant rats

Oxidative stress in the obese-insulin resistant condition has been shown to affect cognitive as well as brain mitochondrial functions. Garlic extract has exerted a potent antioxidant effect. However, the effects of garlic extract on the brain of obese-insulin resistant rats have never been investigated. We hypothesized that garlic extract improves cognitive function and brain mitochondrial function in obese-insulin resistant rats induced by long-term high-fat diet (HFD) consumption. Male Wistar rats were fed either normal diet or HFD for 16 weeks (n = 24/group). At week 12, rats in each dietary group received either vehicle or garlic extract (250 and 500 mg·kg(-1)·day(-1)) for 28 days. Learning and memory behaviors, metabolic parameters, and brain mitochondrial function were determined at the end of treatment. HFD led to increased body weight, visceral fat, plasma insulin, cholesterol, and malondialdehyde (MDA) levels, indicating the development of insulin resistance. Furthermore, HFD rats had cognitive deficit and brain mitochondrial dysfunction. HFD rats treated with both doses of garlic extract had decreased body weight, visceral fat, plasma cholesterol, and MDA levels. Garlic extract also improved cognitive function and brain mitochondrial function, which were impaired in obese-insulin resistant rats caused by HFD consumption.

Does insulin therapy for type 1 diabetes mellitus protect against Alzheimer's disease?

Alzheimer's disease is the most common cause of dementia in the United States. A better understanding of the disease's underlying pathways may provide novel treatment and/or prevention strategies for this progressive chronic neurodegenerative disorder. In recent years, there has been a growing interest in the possible links between insulin and Alzheimer's disease. Insulin-induced hypoglycemia causes adaptive changes in the brain, including an improved ability to use alternative fuels. Insulin has been shown to facilitate reduction of intracellular amyloid plaque and downregulation of amyloid-β-derived diffusible ligand-binding sites. Insulin also promotes tau hypophosphorylation, which stabilizes microtubules and promotes tubulin polymerization. Excess exogenous insulin may also play a role in overcoming the decreased utilization and transport of glucose in patients with Alzheimer's disease. Intranasal insulin therapy may have beneficial effects on cognition and function in patients with Alzheimer's disease, as well as having only minor adverse effects, and this route of administration been the focus in clinical trials. These data support the mechanistic pathways that might link excess exogenous insulin administered to patients with type 1 diabetes mellitus to possible protection from Alzheimer's disease and provide a rationale for using insulin to prevent the disease in high-risk patients.

Insulin reverses anxiety-like behavior evoked by streptozotocin-induced diabetes in mice

Clinical and preclinical data suggest that diabetes is often associated with anxiety. Insulin, a peptide hormone has been reported to have key functions in the brain and in alleviating several psychological impairments, occur as a consequence of diabetes. However, its effects in diabetes-induced anxiety are scanty. The present study examined whether; insulin can reverse the anxiety-like behavior in streptozotocin (STZ)-induced diabetes in mice. After 8-weeks of diabetes induced by STZ (200 mg/kg, intraperitoneally (i.p.)), mice were given insulin (1-2 IU/kg/day, i.p.)/ diazepam (1 mg/kg/day, i.p.)/ vehicle for 14 days and evaluated for behavioral effects in three validated models of anxiety viz. elevated plus maze (EPM), light-dark (L/D) and hole board (HB) tests. STZ-induced diabetic mice elicited significant behavioral effects which include, decreased percentage open arm entries and time in EPM, reduced latency and time spent in light chamber in L/D, decreased number of head dips, squares crossed and rearings in HB tests respectively. Insulin treatment attenuated the behavioral effects evoked by STZ-induced diabetes in mice as indicated by increased open arms activity in EPM, decreased aversion in light chamber during L/D test and increased exploratory behavior in HB test. In conclusion, this study revealed that insulin can reverse anxiety-like behavior in STZ-induced diabetes in mice.

Central proliferation and neurogenesis is impaired in type 2 diabetes and prediabetes animal models

Type 2 diabetes (T2D) is an important risk factor to suffer dementia, including Alzheimer’s disease (AD), and some neuropathological features observed in dementia could be mediated by T2D metabolic alterations. Since brain atrophy and impaired neurogenesis have been observed both T2D and AD we analyzed central nervous system (CNS) morphological alterations in the db/db mice (leptin receptor KO mice), as a model of long-term insulin resistance and T2D, and in C57Bl6 mice fed with high fat diet (HFD), as a model of diet induced insulin resistance and prediabetes. Db/db mice showed an age-dependent cortical and hippocampal atrophy, whereas in HFD mice cortex and hippocampus were preserved. We also detected increased neurogenesis and cell proliferation rates in young db/db mice when compared with control littermates. Our study shows that metabolic parameters serve as predictors of both atrophy and altered proliferation and neurogenesis in the CNS. Moreover in the cortex, atrophy, cell proliferation and neurogenesis were significantly correlated. Our data suggest that T2D may underline some of the pathological features observed in the dementia process. They also support that blood glucose control in elderly patients could help to slow down dementia evolution and maybe, improve its prognosis.

Plasma prion protein concentration and progression of Alzheimer disease

BACKGROUND/OBJECTIVE

Recently, PrP(c) has been linked to AD pathogenesis. Second, a relation of PrP(c) plasma levels with cognitive status and decline of healthy elderly subjects has been reported. Therefore, we hypothesized baseline plasma levels of PrP(c) to be associated with AD progression in cognitive and functional domains.

MATERIALS AND METHODS

AD patients (n = 84) were included into an observational study at time of diagnosis. Baseline plasma PrP(c) levels were determined. Decline was assessed annually (mean follow-up time 3 years) with the aid of different standardized tests (MMSE, iADL, bADL, GDS, UPDRSIII). Multiple regression analyses were used to uncover potential associations between decline and PrP(c) levels.

RESULTS

No association of PrP(c) and decline could be established. Presence of diabetes mellitus was linked to slower deterioration. Intake of neuroleptic drugs or memantine was associated with faster progression.

CONCLUSION

Plasma PrP(c) at baseline could not be shown to be related to AD progression in this study. An interesting association of diabetes mellitus and decline warrants further investigation.