Intranasal insulin therapy for cognitive impairment and neurodegeneration: current state of the art

Association between triglyceride glucose index and cognitive decline: A meta-analysis

BACKGROUND

The triglyceride glucose (TyG) index, a novel surrogate indicator for insulin resistance (IR), is believed to be associated with various diseases. However, its connection with cognitive decline remains controversy.

METHODS

The PubMed, EMBASE, Cochrane Library, Web of Science, and Medline databases were systematically searched up to October 2023 to assess the association between the TyG index and the risk of cognitive decline. Effect estimates and 95 % confidence intervals (CIs) were calculated using a random-effects model.

RESULTS

Our review included 3 cohort studies and 9 case-control/cross-sectional studies with a total of 5,603,350 participants. In comparison to a low TyG index, a higher TyG index was connected to an elevated risk of cognitive decline (RR/HR = 1.14, 95 % CI [1.11, 1.17], P < 0.05; OR = 1.75, 95 % CI [1.34, 2.29], P < 0.05). Furthermore, the dose-response analysis from the case-control/cross-sectional studies revealed a 1.42 times higher risk of cognitive decline per 1 mg/dl increment of the TyG index (OR = 1.42, 95 % CI [1.19, 1.69], P < 0.05).

LIMITATIONS

The inclusion of observational studies in the meta-analysis demonstrated a lower hierarchy of evidence compared to randomized controlled trials. Moreover, we incorporated a restricted number of studies and identified significant heterogeneity among them, potentially attributed to the presence of numerous confounding variables.

CONCLUSION

TyG index is related to cognitive decline. In view of some of the limitations of this study, further research will be necessary to confirm this relationship.

Causal Association Between Type 2 Diabetes Mellitus and Alzheimer's Disease: A Two-Sample Mendelian Randomization Study

Background

There is now increasing evidence that type 2 diabetes mellitus (T2DM) is associated with Alzheimer's disease (AD). However, it is unclear whether the two are causally related.

Objective

To reveal the causal association between T2DM and AD, we performed a bidirectional Mendelian randomization (MR) analysis.

Methods

Genetic instrumental variables were systematically screened, and inverse-variance weighting, MR-Egger regression, weighted median, simple mode, and weighted mode were applied to assess the pathogenic associations between the two diseases, and sensitivity analyses were used to further validate the robustness of the results.

Results

The results of forward MR analysis with T2DM as the exposure were [OR = 0.998, 95% CI (0.975∼1.021), p = 0.857], and the results of reverse MR analysis with AD as the exposure were [OR = 0.966, 95% CI (0.934∼0.999), p = 0.043]. The results showed no significant association between T2DM and AD at the gene level (p < 0.025). Sensitivity analyses were consistent with the results of the main analysis, confirming the robustness of the study.

Conclusions

T2DM and AD may not be genetically causally associated.

Protective effect of intranasal insulin on postoperative cognitive dysfunction in elderly patients with metabolic syndrome undergoing noncardiac surgery: a randomized clinical trial

BACKGROUND

Insulin plays a crucial and multifactorial role in cognitive activity, with insulin resistance appearing in neurodegenerative and metabolic diseases. Insulin resistance contributes to the pathobiology of postoperative cognitive dysfunction (POCD) in experimental models, which can be rescued by intranasal insulin administration.

AIMS

To test the effect of intranasal insulin on the incidence of POCD in elderly patients with metabolic syndrome.

METHODS

The study was designed as a randomized, double-blind, placebo-controlled clinical trial. 116 elderly participants were randomly assigned to receive either 40 IU insulin (n = 58) or placebo (n = 58) for 7 days. The primary outcome was the incidence of POCD at 7 days and 3 months after surgery. Secondary outcomes included the degree of peripheral insulin resistance postoperatively, changes in peripheral inflammation levels and the safety of interventions.

RESULTS

The results showed that POCD occurred in the insulin group on the 7th postoperative day in 11 (20.8%) patients, which was fewer than the 23 (45.1%) patients in the placebo group (P = 0.008). The insulin group indicated better cognitive functional performance on language and memory test than the placebo group (P < 0.05). Mean peripheral plasma concentration of TNF-α (P < 0.05) and CRP (P < 0.001) in the insulin group was significantly declined compared with the placebo group on D3 and D7.

CONCLUSIONS

Intranasal insulin administration reduced the incidence of POCD and alleviated peripheral inflammatory levels in elderly patients with metabolic syndrome.

TRIAL REGISTRY

Chinese Clinical Trial Registry (ChiCTR1800015502).

Study on the Nasal Drug Delivery System of NMD Liposomes In Situ Thermosensitive Gel

Nimodipine (NMD) is a 1,4-dihydropyridine calcium antagonist that is effective in the prevention and treatment of cerebral arterial vasospasm and cerebral ischemic injury caused by subarachnoid hemorrhage. Since the drug itself is highly insoluble in water and has low oral bioavailability, while injectable formulations may cause pain and inflammation, the blood-brain barrier (BBB) prevents the effective delivery of therapeutic agents to the brain tissue. Therefore, in the present study, NMD liposomes were prepared by ethanol injection and innovatively lyophilised and loaded into temperature-sensitive in situ gels for intranasal administration as sprays to deliver drugs to brain tissues bypassing the blood-brain barrier. The optimal gel formulation was obtained by screening in which liposomes were divided into lecithin, cholesterol, and NMD in the ratio of 40:10: 1; Pluronic P407, Pluronic P188, Tween 80, polyvinyl ketone and ethyl nipagin in the ratio of (180:20:3:1:1); Pluronic P407, Pluronic P188, Tween 80, polyvinyl ketone, and ethyl nipagin in the ratio of (180:20:3:1:1). The prepared flow gel can form a solidified gel after a temperature of 31.07-32.07°C and a time of 58.51-59.89 s. Meanwhile, the NMD liposome gel formulation achieved sustained release over 56 h. The pharmacokinetic results of the developed NMD liposomal temperature-sensitive in situ gel and NMD temperature-sensitive in situ gel showed that liposomal nasal mucosal in situ gel is a more effective brain-targeted drug delivery system for NMD.

Mechanisms underlying HIV-associated cognitive impairment and emerging therapies for its management

People living with HIV are affected by the chronic consequences of neurocognitive impairment (NCI) despite antiretroviral therapies that suppress viral replication, improve health and extend life. Furthermore, viral suppression does not eliminate the virus, and remaining infected cells may continue to produce viral proteins that trigger neurodegeneration. Comorbidities such as diabetes mellitus are likely to contribute substantially to CNS injury in people living with HIV, and some components of antiretroviral therapy exert undesirable side effects on the nervous system. No treatment for HIV-associated NCI has been approved by the European Medicines Agency or the US Food and Drug Administration. Historically, roadblocks to developing effective treatments have included a limited understanding of the pathophysiology of HIV-associated NCI and heterogeneity in its clinical manifestations. This heterogeneity might reflect multiple underlying causes that differ among individuals, rather than a single unifying neuropathogenesis. Despite these complexities, accelerating discoveries in HIV neuropathogenesis are yielding potentially druggable targets, including excessive immune activation, metabolic alterations culminating in mitochondrial dysfunction, dysregulation of metal ion homeostasis and lysosomal function, and microbiome alterations. In addition to drug treatments, we also highlight the importance of non-pharmacological interventions. By revisiting mechanisms implicated in NCI and potential interventions addressing these mechanisms, we hope to supply reasons for optimism in people living with HIV affected by NCI and their care providers.

Type 2 Diabetes and Alzheimer's Disease: The Emerging Role of Cellular Lipotoxicity

Type 2 diabetes (T2D) and Alzheimer's diseases (AD) represent major health issues that have reached alarming levels in the last decades. Although growing evidence demonstrates that AD is a significant comorbidity of T2D, and there is a ~1.4-2-fold increase in the risk of developing AD among T2D patients, the involvement of possible common triggers in the pathogenesis of these two diseases remains largely unknown. Of note, recent mechanistic insights suggest that lipotoxicity could represent the missing ring in the pathogenetic mechanisms linking T2D to AD. Indeed, obesity, which represents the main cause of lipotoxicity, has been recognized as a major risk factor for both pathological conditions. Lipotoxicity can lead to inflammation, insulin resistance, oxidative stress, ceramide and amyloid accumulation, endoplasmic reticulum stress, ferroptosis, and autophagy, which are shared biological events in the pathogenesis of T2D and AD. In the current review, we try to provide a critical and comprehensive view of the common molecular pathways activated by lipotoxicity in T2D and AD, attempting to summarize how these mechanisms can drive future research and open the way to new therapeutic perspectives.

Therapeutic approaches for improving cognitive function in the aging brain

The rapid aging of populations around the world has become an unprecedented challenge. Aging is associated with cognitive impairment, including dementia and mild cognitive impairment. Successful drug development for improving or maintaining cognition in the elderly is critically important. Although 4 drugs for improving cognition in Alzheimer's disease have been approved, a variety of potential drugs targeting age-related cognitive impairment are still in development. In addition, non-pharmacological interventions, including cognition-oriented treatments, non-invasive brain stimulation physical exercise, and lifestyle-related interventions, have also been suggested as cognitive enhancers in the last decade. In this paper, we reviewed the recent evidence of pharmacological and non-pharmacological interventions aimed at improving or maintaining cognition in the elderly.

Intranasal delivery of biotechnology-based therapeutics

Biotechnology-based therapeutics include a wide range of products, such as recombinant hormones, stem cells, therapeutic enzymes, monoclonal antibodies, genes, vaccines, among others. The administration of these macromolecules has been studied via various routes. The nasal route is one of the promising routes of administration for biotechnology products owing to its easy delivery, the rich vascularity of the nasal mucosa, high absorption and targeted action. Several preclinical studies have been reported for nasal delivery of these products and many are at the clinical stage. This review focuses on biotechnology-based therapeutics administered via the intranasal route for treating various diseases.

Falling Short: The Contribution of Central Insulin Receptors to Gait Dysregulation in Brain Aging

Insulin resistance, which manifests as a reduction of insulin receptor signaling, is known to correlate with pathological changes in peripheral tissues as well as in the brain. Central insulin resistance has been associated with impaired cognitive performance, decreased neuronal health, and reduced brain metabolism; however, the mechanisms underlying central insulin resistance and its impact on brain regions outside of those associated with cognition remain unclear. Falls are a leading cause of both fatal and non-fatal injuries in the older population. Despite this, there is a paucity of work focused on age-dependent alterations in brain regions associated with ambulatory control or potential therapeutic approaches to target these processes. Here, we discuss age-dependent alterations in central modalities that may contribute to gait dysregulation, summarize current data supporting the role of insulin signaling in the brain, and highlight key findings that suggest insulin receptor sensitivity may be preserved in the aged brain. Finally, we present novel results showing that administration of insulin to the somatosensory cortex of aged animals can alter neuronal communication, cerebral blood flow, and the motivation to ambulate, emphasizing the need for further investigations of intranasal insulin as a clinical management strategy in the older population.

Antidiabetic Drugs in the Treatment of Alzheimer's Disease

The public health burden of type 2 diabetes mellitus and Alzheimer's disease is steadily increasing worldwide, especially in the population of older adults. Epidemiological and clinical studies suggest a possible shared pathophysiology between the two diseases and an increased risk of AD in patients with type 2 diabetes mellitus. Therefore, in recent years, there has been a substantial interest in identifying the mechanisms of action of antidiabetic drugs and their potential use in Alzheimer's disease. Human studies in patients with mild cognitive impairment and Alzheimer's disease have shown that administration of some antidiabetic medications, such as intranasal insulin, metformin, incretins, and thiazolidinediones, can improve cognition and memory. This review aims to examine the latest evidence on antidiabetic medications as a potential candidate for the treatment of Alzheimer's disease.

The Potential Effect of Insulin on AChE and Its Interactions with Rivastigmine In Vitro

There is no definite cure for Alzheimer’s disease (AD) due to its multifactorial origin. Drugs that inhibit acetylcholinesterase (AChE), such as rivastigmine, are promising symptomatic treatments for AD. Emerging evidence suggests that insulin therapy can hinder several aspects of AD pathology. Insulin has been shown to modify the activity of AChE, but it is still unknown how insulin and AChE interact. Combination therapy, which targets several features of the disease based on existing medications, can provide a worthy therapy option for AD management. However, to date, no studies have examined the potential interaction of insulin with AChE and/or rivastigmine in vitro. In the present study, we employed the Response Surface Methodology (RSM) as an in vitro assessment to investigate the effect of insulin on both AChE activity and rivastigmine inhibitory action using a common spectrophotometric assay for cholinesterase activity, Ellman’s method. Our results showed that insulin, even at high concentrations, has an insignificant effect on both the activity of AChE and rivastigmine’s inhibitory action. The variance of our data is near zero, which means that the dispersion is negligible. However, to improve our understanding of the possible interaction of insulin and rivastigmine, or its target AChE, more in silico modelling and in vivo studies are needed.

Intranasal insulin for treatment of delirium in older hospitalised patients: study protocol for a randomised controlled trial

INTRODUCTION

Delirium is one of the most common conditions diagnosed in hospitalised older people and is associated with numerous adverse outcomes, yet there are no proven pharmacological treatments. Recent research has identified cerebral glucose hypometabolism as a pathophysiological mechanism offering a therapeutic target in delirium. Insulin, delivered via the intranasal route, acts directly on the central nervous system and has been shown to enhance cerebral metabolism and improve cognition in patients with mild cognitive impairment and dementia. This trial will determine whether intranasal insulin can reduce the duration of delirium in older hospitalised patients.

METHODS AND ANALYSIS

This is a prospective randomised, placebo-controlled, double-blind study with 6 months follow-up. One hundred patients aged 65 years or older presenting to hospital with delirium admitted under geriatric medicine will be recruited. Participants will be randomised to intranasal insulin detemir or placebo administered twice daily until delirium resolves, defined as Confusion Assessment Method (CAM) negative for 2 days, or discharge from hospital. The primary outcome measure will be duration of delirium using the CAM. Secondary outcome measures will include length of hospital stay, severity of delirium, adherence to treatment, hospital complications, new admission to nursing home, mortality, use of antipsychotic medications during hospital stay and cognitive and physical function at 6 months postdischarge.

ETHICS AND DISSEMINATION

This trial has been approved by the South Eastern Sydney Human Research and Ethics Committee. Dissemination plans include submission to a peer-reviewed journal for publication and presentation at scientific conferences.

TRIAL REGISTRATION NUMBER

ACTRN12618000318280.

Insulin Resistance Exacerbates Alzheimer Disease via Multiple Mechanisms

Alzheimer disease (AD) is a chronic neurodegenerative disease that accounts for 60–70% of dementia and is the sixth leading cause of death in the United States. The pathogenesis of this debilitating disorder is still not completely understood. New insights into the pathogenesis of AD are needed in order to develop novel pharmacologic approaches. In recent years, numerous studies have shown that insulin resistance plays a significant role in the development of AD. Over 80% of patients with AD have type II diabetes (T2DM) or abnormal serum glucose, suggesting that the pathogenic mechanisms of insulin resistance and AD likely overlap. Insulin resistance increases neuroinflammation, which promotes both amyloid β-protein deposition and aberrant tau phosphorylation. By increasing production of reactive oxygen species, insulin resistance triggers amyloid β-protein accumulation. Oxidative stress associated with insulin resistance also dysregulates glycogen synthase kinase 3-β (GSK-3β), which leads to increased tau phosphorylation. Both insulin and amyloid β-protein are metabolized by insulin degrading enzyme (IDE). Defects in this enzyme are the basis for a strong association between T2DM and AD. This review highlights multiple pathogenic mechanisms induced by insulin resistance that are implicated in AD. Several pharmacologic approaches to AD associated with insulin resistance are presented.

Targeting impaired nutrient sensing with repurposed therapeutics to prevent or treat age-related cognitive decline and dementia: A systematic review

BACKGROUND

Dementia is a debilitating syndrome that significantly impacts individuals over the age of 65 years. There are currently no disease-modifying treatments for dementia. Impairment of nutrient sensing pathways has been implicated in the pathogenesis of dementia, and may offer a novel treatment approach for dementia.

AIMS

This systematic review collates all available evidence for Food and Drug Administration (FDA)-approved therapeutics that modify nutrient sensing in the context of preventing cognitive decline or improving cognition in ageing, mild cognitive impairment (MCI), and dementia populations.

METHODS

PubMed, Embase and Web of Science databases were searched using key search terms focusing on available therapeutics such as 'metformin', 'GLP1', 'insulin' and the dementias including 'Alzheimer's disease' and 'Parkinson's disease'. Articles were screened using Covidence systematic review software (Veritas Health Innovation, Melbourne, Australia). The risk of bias was assessed using the Cochrane Risk of Bias tool v 2.0 for human studies and SYRCLE's risk of bias tool for animal studies.

RESULTS

Out of 2619 articles, 114 were included describing 31 different 'modulation of nutrient sensing pathway' therapeutics, 13 of which specifically were utilized in human interventional trials for normal ageing or dementia. Growth hormone secretagogues improved cognitive outcomes in human mild cognitive impairment, and potentially normal ageing populations. In animals, all investigated therapeutic classes exhibited some cognitive benefits in dementia models. While the risk of bias was relatively low in human studies, this risk in animal studies was largely unclear.

CONCLUSIONS

Modulation of nutrient sensing pathway therapeutics, particularly growth hormone secretagogues, have the potential to improve cognitive outcomes. Overall, there is a clear lack of translation from animal models to human populations.

Insulin injections inhibits PTZ-induced mitochondrial dysfunction, oxidative stress and neurological deficits via the SIRT1/PGC-1α/SIRT3 pathway

With an associated 20% death risk, epilepsy mainly involves seizures of an unpredictable and recurrent nature. This study was designed to evaluate the neuroprotective effects and underlying mechanisms of insulin on mitochondrial disruption, oxidative stress, cell apoptosis and neurological deficits after epilepsy seizures. Mice were exposed to repetitive injections of pentylenetetrazol at a dose of 37 mg per kg. The influence of insulin was assessed by many biochemical assays, histopathological studies and neurobehavioral experiments. The administration of insulin was proven to increase the latency of seizures while also decreasing their intensity. It also caused a reversal of mitochondrial dysfunction and ameliorated oxidative stress. Additionally, insulin pretreatment upregulated Bcl-2, downregulated Bax, and then played a neuroprotective role against hippocampal neuron apoptosis. Furthermore, when insulin was administered, SIRT1/PGC-1α/SIRT3 signals were activated, possibly due to the fact that insulin's neuroprotective and anti-mitochondrial damage characteristics added to its observed antiepileptic functions. Finally, insulin treatment is thus extremely valuable for effecting improvements in neurological functions, as has been estimated in a series of functional tests. In conclude, the results of this study consequently demonstrate insulin to have significant potential for future application in epilepsy management.

Diabetes-Alzheimer's Disease Link: Targeting Mitochondrial Dysfunction and Redox Imbalance

Significance: It is of common sense that the world population is aging and life expectancy is increasing. However, as the population ages, there is also an exponential risk to live into the ages where the brain-related frailties and neurodegenerative diseases develop. Hand in hand with those events, the world is witnessing a major upsurge in diabetes diagnostics. Remarkably, all of this seems to be narrowly related, and clinical and research communities highlight for the upcoming threat that it will represent for the present and future generations. Recent Advances: It is of utmost importance to clarify the influence of diabetes-related metabolic features on brain health and the mechanisms underlying the increased likelihood of developing neurodegenerative diseases, in particular Alzheimer's disease. Thereupon, a wealth of evidence suggests that mitochondria and associated oxidative stress are at the root of the link between diabetes and co-occurring disorders in the brain. Critical Issues: The scientific community has been challenged with constant failures of clinical trials raising major issues in the advance of the therapeutic field to fight chronic diseases epidemics. Thus, a change of paradigms is urgently needed. Future Directions: It has become urgent to identify new and solid candidates able to clinically reproduce the positive outcomes obtained in preclinical studies. On this basis, strategies settled to counteract diabetes-induced neurodegeneration encompassing mitochondrial dysfunction, redox status imbalance, and/or insulin dysregulation seem worth to follow. Hopefully, ongoing innovative research based on reliable experimental tools will soon bring the desired answers allowing pharmaceutical industry to apply such knowledge to human medicine.

Biomaterials in treatment of Alzheimer's disease

Alzheimer's disease (AD) is a non-recoverable progressive neurodegenerative disorder most prevalent but not limited to the old age population. After all the scientific efforts, there are still many unmet criteria and loopholes in available treatment and diagnostic strategies, limiting their efficacy. The poor drug efficacy is attributed to various biological hurdles, including blood-brain barrier (BBB) and peripheral side effects as most prominent ones and the lack of promising carriers to precisely deliver the drug to the brain by conserving its therapeutic potency. The increasing disease prevalence and unavailability of effective therapy calls for developing a more innovative, convenient and affordable way to treat AD. To fulfill such need, researchers explored various biomaterials to develop potential vectors or other forms to target the bioactives in the brain by preserving their inherent properties, improving the existing lacuna like poor solubility, permeability and bioavailability etc. and minimize the side effect. The unique characteristic properties of biomaterials are used to develop different drug carriers, surface modifying target active ligands, functional carriers, drug conjugate, biosensing probe, diagnostic tool and many more. The nanoparticulate system and other colloidal carriers like hydrogel and biodegradable scaffold can effectively target the drug moieties to the brain. Also, the use of different target-acting ligands and stimuli-responsive carriers assures the site-specificity and controlled release at the desired site by interaction with receptors and various exo- and endogenous stimuli. This review article has highlighted the application of biomaterials for targeting the drug to the brain and as promising diagnostic tools to detect the markers for better AD management. The work particularly focuses on the use of biomaterials as smart drug carriers including pH, thermo, photo, electro and magnetically triggered system; novel drug carriers for brain targeting including polymeric carriers (polymeric nanoparticle, dendrimer and polymeric micelle); lipid carrier (liposome, nanoemulsion, NLC and SLN); inorganic nanoparticles (quantum dots, gold nanoparticles etc.); and other drug vectors (hydrogel, biodegradable scaffold, and carbon nanotube) in treatment of AD. It also highlighted the application of some novel carrier systems and biomaterials as biosensor and other diagnostic tools for early and precise AD diagnosis.

The insulin resistance by triglyceride glucose index and risk for dementia: population-based study

Background

Insulin resistance is suggested to have negative effects on cognition; however, results from large population studies are lacking. In this study, the potential relationships between the triglyceride glucose (TyG) index, a simple surrogate marker of insulin resistance, and dementia were evaluated using a large-scale population dataset.

Methods

This was a retrospective, observational, cohort study using data from the National Health Information Database from 2009 to 2015 and included 5,586,048 participants 40 years age or older. The TyG index was used as a measure of insulin resistance, and participants were divided into quartiles based on TyG index. The incidence of dementia was assessed using hazard ratios (HRs) estimated with Cox proportional hazard modeling.

Results

During a median follow-up of 7.21 years, dementia was diagnosed in 142,714 (2.55%) participants. Alzheimer’s disease (AD) and vascular dementia (VD) were diagnosed in 74.3% and 12.5% of the participants. Multivariate-adjusted HRs for patients in the TyG index 4th quartile were higher for dementia (HRs = 1.14; 95% confidence interval [CI] 1.12–1.16), AD (HRs = 1.12; 95% CI 1.09–1.14), and VD (HRs = 1.18; 95% CI 1.12–1.23) compared with the 1st quartile of TyG index; however, this had a small effect size (Cohen’s d = 0.10, 0.08, and 0.13, respectively). These effects were independent of age, sex, smoking status, physical activity, body mass index, systolic blood pressure, and total cholesterol.

Conclusion

In this large population study, TyG index was associated with an increased risk of dementia, including AD and VD, that was independent of traditional cardiovascular risk factors, although the effect size of the TyG index was small.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-020-00758-4.

Dysregulation of Insulin-Linked Metabolic Pathways in Alzheimer's Disease: Co-Factor Role of Apolipoprotein E ɛ4

BACKGROUND

Brain insulin resistance and deficiency are well-recognized abnormalities in Alzheimer's disease (AD) and likely mediators of impaired energy metabolism. Since apolipoprotein E (APOE) is a major risk factor for late-onset AD, it was of interest to examine its potential contribution to altered insulin-linked signaling networks in the brain.

OBJECTIVE

The main goal was to evaluate the independent and interactive contributions of AD severity and APOE ɛ4 dose on brain expression of insulin-related polypeptides and inflammatory mediators of metabolic dysfunction.

METHODS

Postmortem fresh frozen frontal lobe tissue from banked cases with known APOE genotypes and different AD Braak stages were used to measure insulin network polypeptide immunoreactivity with a commercial multiplex enzyme-linked immunosorbent assay (ELISA).

RESULTS

Significant AD Braak stage and APOE genotype-related abnormalities in insulin, C-peptide, gastric inhibitory polypeptide (GIP), glucaton-like peptide-1 (GLP-1), leptin, ghrelin, glucagon, resistin, and plasminogen activator inhibitor-1 (PAI-1) were detected. The main factors inhibiting polypeptide expression and promoting neuro-inflammatory responses included AD Braak stage and APOE ɛ4/ɛ4 rather than ɛ3/ɛ4.

CONCLUSION

This study demonstrates an expanded role for impaired expression of insulin-related network polypeptides as well as neuroinflammatory mediators of brain insulin resistance in AD pathogenesis and progression. In addition, the findings show that APOE has independent and additive effects on these aberrations in brain polypeptide expression, but the impact is decidedly greater for APOE ɛ4/ɛ4 than ɛ3/ɛ4.

Association of Low-Density Lipoprotein Receptor-Related Protein 1 and Its rs1799986 Polymorphism With Mild Cognitive Impairment in Chinese Patients With Type 2 Diabetes

Background

Low-density lipoprotein receptor-related protein 1 (LRP1) is involved in cerebral glucose metabolism and amyloid-β clearance. This study aimed to investigate the pathogenetic roles of LRP1 and its rs1799986 polymorphism in mild cognitive impairment (MCI) among patients with type 2 diabetes mellitus (T2DM).

Methods

A total of 166 Chinese patients with T2DM were enrolled and divided into two groups according to Montreal Cognitive Assessment (MoCA) scores. Neuropsychological tests were performed. Soluble LRP1 (sLRP1) levels were assessed using enzyme-linked immunosorbent assay, and the genotype of LRP1 rs1799986 was detected using the Sequenom method.

Results

Diabetic patients with MCI (n = 60) exhibited significantly lower plasma sLRP1 levels (p = 0.033) and worse glucose control (p = 0.009) than the healthy cognition controls (n = 106). Multivariate regression analysis revealed plasma sLRP1 levels [odds ratio (OR) = 0.971, p = 0.005] and HbA1c (OR = 1.298, p = 0.003) as a risk factor for MCI in diabetic patients, in addition to insulin use and hypertension. However, there was no association between plasma sLRP1 levels and HbA1c. After adjusting for age, sex, and education level, plasma sLRP1 levels in the MCI group were negatively correlated with Stroop Color Word Test B number (r = −0.335, p = 0.011), which represents selective attention, cognitive flexibility, and processing speed. Additionally, patients with T2DM carrying the T allele of LRP1 rs1799986 showed higher Auditory Verbal Learning Test (AVLT) delayed recall scores (p = 0.025).

Conclusion

Decreased plasma sLRP1 levels are associated with MCI, particularly with attention dysfunction, in patients with T2DM. Moreover, the T allele of LRP1 rs1799986 may decrease susceptibility to MCI. Further studies with large cohorts should be designed to elucidate the roles of LRP1 in hyperglycemia-induced cognitive decline.

Elevating Insulin Signaling Using a Constitutively Active Insulin Receptor Increases Glucose Metabolism and Expression of GLUT3 in Hippocampal Neurons

Insulin signaling is an integral component of healthy brain function, with evidence of positive insulin-mediated alterations in synaptic integrity, cerebral blood flow, inflammation, and memory. However, the specific pathways targeted by this peptide remain unclear. Previously, our lab used a molecular approach to characterize the impact of insulin signaling on voltage-gated calcium channels and has also shown that acute insulin administration reduces calcium-induced calcium release in hippocampal neurons. Here, we explore the relationship between insulin receptor signaling and glucose metabolism using similar methods. Mixed, primary hippocampal cultures were infected with either a control lentivirus or one containing a constitutively active human insulin receptor (IRβ). 2-NBDG imaging was used to obtain indirect measures of glucose uptake and utilization. Other outcome measures include Western immunoblots of GLUT3 and GLUT4 on total membrane and cytosolic subcellular fractions. Glucose imaging data indicate that neurons expressing IRβ show significant elevations in uptake and rates of utilization compared to controls. As expected, astrocytes did not respond to the IRβ treatment. Quantification of Western immunoblots show that IRβ is associated with significant elevations in GLUT3 expression, particularly in the total membrane subcellular fraction, but did not alter GLUT4 expression in either fraction. Our work suggests that insulin plays a significant role in mediating neuronal glucose metabolism, potentially through an upregulation in the expression of GLUT3. This provides further evidence for a potential therapeutic mechanism underlying the beneficial impact of intranasal insulin in the clinic.

Intranasal Insulin Treatment Attenuates Metabolic Distress and Early Brain Injury After Subarachnoid Hemorrhage in Mice

BACKGROUND

Intranasal administration of insulin to the brain bypasses the blood brain barrier (BBB) and can increase cerebral glucose uptake and prevent energy failure. Intranasal insulin treatment has shown neuroprotective effects in multiple central nervous system (CNS) lesions, but the effects of intranasal insulin on the metabolic and pathological process of subarachnoid hemorrhage (SAH) are not clear. This study is designed to explore the effects of intranasal insulin treatment on metabolic distress and early brain injury (EBI) after experimental SAH.

METHODS

SAH model was built by endovascular filament perforation method in adult male C57BL/6J mice, and then, insulin was administrated via intranasal route at 0, 24, and 48 h post-SAH. EBI was assessed according to the neurological performance, BBB damage, brain edema, neuroinflammatory reaction, and neuronal apoptosis at each time point. To evaluate metabolic conditions, microdialysis was used to continuously monitor the real-time levels of glucose, pyruvate, and lactate in interstitial fluid (ISF) in living animals. The mRNA and protein expression of glucose transporter-1 and 3 (GLUT-1 and -3) were also tested by RT-PCR and Western blot in brain after SAH.

RESULTS

Compared to vehicle, intranasal insulin treatment promoted the relative mRNA and protein levels of GLUT-1 in SAH brain (0.98 ± 0.020 vs 0.33 ± 0.016 at 24 h, 0.91 ± 0.25 vs 0.21 ± 0.013 at 48 h and 0.94 ± 0.025 vs 0.28 ± 0.015 at 72 h in mRNA/0.96 ± 0.023 vs 0.36 ± 0.015 at 24 h, 0.91 ± 0.022 vs 0.22 ± 0.011 at 48 h and 0.95 ± 0.024 vs 0.27 ± 0.014 at 72 h in protein, n = 8/Group, p < 0.001). Similar results were also observed in GLUT-3. Intranasal insulin reduced the lactate/pyruvate ratio (LPR) and increased ISF glucose level. It also improved neurological dysfunction, BBB damage, and brain edema and attenuated the levels of pro-inflammatory cytokines as well as neuronal apoptosis after SAH.

CONCLUSIONS

The intranasal insulin treatment protects brain from EBI possibly via improving metabolic distress after SAH.

Electroacupuncture improves cognitive deficits and insulin resistance in an OLETF rat model of Al/D-gal induced aging model via the PI3K/Akt signaling pathway

To investigate the effect of electroacupuncture (EA) on cognitive function and insulin resistance (IR) in an Al/D-gal-induced aging model for Alzheimer's disease (AD) using Ostuka Long-Evans Tokushima Fatty (OLETF) rats. The Al/D-gal-OLETF rats for AD were randomly divided into the EA and non-EA groups. Cognitive function was assessed using the Morris water maze (MWM). The morphology of the hippocampal neurons was observed using hematoxylin & eosin (H&E) staining. Aβ and total Tau in the hippocampus and cerebrospinal fluid (CSF) were detected using western blotting (WB) and enzyme-linked immunosorbent assay (ELISA). Fasting blood glucose (FPG) was determined using the glucose oxidase method. Plasma fasting insulin (FINS), serum C-peptide (C-P), and CSF insulin were detected using ELISA. The expression of the genes and proteins in the PI3K signaling pathway was detected using quantitative real-time PCR and WB. After EA intervention, the hippocampal Aβ and total Tau protein levels, body weight, FPG, FINS, and C-P were significantly decreased. The MWM showed that the percentage of time in the target quadrant of the EA group was elevated in the probe test. The protein levels of p-IRS1, p-IRS2, IDE, and p-GSK3β were significantly increased, while p-PI3K-p85α and p-Akt were decreased. In conclusion, EA improves cognitive function and insulin resistance in rat models of AD. The PI3K/Akt signaling pathway is involved in those changes.

Insulin mediated novel therapies for the treatment of Alzheimer's disease

Alzheimer's disease, a progressive neurodegenerative disorder, is one of the leading causes of death in the USA, along with cancer and cardiac disorders. AD is characterized by various neurological factors like amyloid plaques, tau hyperphosphorylation, mitochondrial dysfunction, acetylcholine deficiency, etc. Together, impaired insulin signaling in the brain is also observed as essential factor to be considered in AD pathophysiology. Hence, currently researchers focused on studying the effect of brain insulin metabolism and relation of diabetes with AD. Based on the investigations, AD is also considered as type 3 or brain diabetes. Besides the traditional view of correlating AD with aging, a better understanding of various pathological factors and effects of other physical ailments is necessary to develop a promising therapeutic approach. There is a vast scope of studying the relation of systemic insulin level, insulin signaling, its neuroprotective potency and effect of diabetes on AD progression. The present work describes worldwide status of AD and its relation with diabetes mellitus and insulin metabolism; pathophysiology of AD; different metabolic pathways associating insulin metabolism with AD; insulin receptor and signaling in the brain; glucose metabolism; insulin resistance; and various preclinical and clinical studies reported insulin-based therapies to treat AD via systemic route and through direct intranasal delivery to the brain.

Intranasal insulin treatment modulates the neurotropic, inflammatory, and oxidant mechanisms in the cortex and hippocampus in a low-grade inflammation model

The inflammatory process plays a critical role in the development of neurodegenerative diseases. Insulin is used in preclinical and clinical studies of neurological disorders. Its intranasal (IN) administration directly in the brain allows for its peripheral metabolic effects to be avoided. Swiss male mice were injected with lipopolysaccharide (LPS) (0.1 mg/kg) to induce low-grade inflammation. IN insulin treatment was initiated 4 h later at a dose of 1.7 IU once daily for 5 days. LPS induced cognitive deficits, which the IN insulin treatment reversed. LPS significantly decreased, whereas IN insulin significantly increased the levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor-β in the cortex. In the hippocampus, IN insulin significantly decreased the BDNF level. LPS significantly increased the interleukin (IL)-6 levels in the cortex, while IN Insulin significantly decreased its levels in the hippocampus. The tumor necrosis factor-α levels were significantly decreased by IN insulin both in the cortex and hippocampus. Moreover, IN insulin significantly increased the IL-10 levels in the cortex. The levels of oxidative and nitrosative stress were significantly higher in the LPS-treated mice; however, IN insulin had a modulatory effect on both. LPS significantly increased the antioxidant enzyme activity both in the cortex and hippocampus, whereas IN insulin significantly increased the activity of both superoxide dismutase and catalase in the hippocampus and that of catalase in the cortex. The hydrogen peroxide levels revealed that LPS significantly affected the electron transport chain. Therefore, IN insulin could be useful in the treatment of neuroinflammatory diseases.

Liposomal Formulations for Nose-to-Brain Delivery: Recent Advances and Future Perspectives

Restricted drug entry to the brain that is closely associated with the existence of the blood brain barrier (BBB) has limited the accessibility of most potential active therapeutic compounds to the brain from the systemic circulation. Recently, evidences for the presence of direct nose-to-brain drug transport pathways have been accumulated by several studies and an intranasal drug administration route has gained attention as a promising way for providing direct access to the brain without the needs to cross to the BBB. Studies aiming for developing nanoparticles as an intranasal drug carrier have shown considerable promise in overcoming the challenges of intranasal drug delivery route. This review gives a comprehensive overview of works having investigated liposomes as a potential vehicle to deliver drugs to the brain through nose-to-brain route while considering the excellent biocompatibility and high potential of liposomes for clinical development. Herein, studies are reviewed with special emphasis on the impact of formulation factors, such as liposome composition and surface modification of liposomes with targeting moieties, in addition to intranasal environmental factors that may affect the extent/site of absorption of intranasally administered, liposome-encapsulated drugs.

[Diabetes mellitus and cognitive impairment]

The review discusses literature data and the results of our own studies on the effect of diabetes on cognitive functions and cerebrovascular pathology, as well as possible ptogenetic mechanisms for the implementation of this effect. The results of studies on the effects of antidiabetic drugs on cognitive function are presented.

Oridonin prevents insulin resistance-mediated cognitive disorder through PTEN/Akt pathway and autophagy in minimal hepatic encephalopathy

Minimal hepatic encephalopathy (MHE) was characterized for cognitive dysfunction. Insulin resistance (IR) has been identified to be correlated with the pathogenesis of MHE. Oridonin (Ori) is an active terpenoid, which has been reported to rescue synaptic loss and restore insulin sensitivity. In this study, we found that intraperitoneal injection of Ori rescued IR, reduced the autophagosome formation and synaptic loss and improved cognitive dysfunction in MHE rats. Moreover, in insulin‐resistant PC12 cells and N2a cells, we found that Ori blocked IR‐induced synaptic deficits via the down‐regulation of PTEN, the phosphorylation of Akt and the inhibition of autophagy. Taken together, these results suggested that Ori displays therapeutic efficacy towards memory deficits via improvement of IR in MHE and represents a novel bioactive therapeutic agent for treating MHE.

Altered expression of insulin-degrading enzyme and regulator of calcineurin in the rat intracerebral streptozotocin model and human apolipoprotein E-ε4-associated Alzheimer's disease

INTRODUCTION

This study assesses insulin-degrading enzyme (IDE) and regulator of calcineurin 1 (RCAN1) as potential mediators of brain insulin deficiency and neurodegeneration in experimental and human Alzheimer's disease (AD).

METHODS

Temporal lobes from Long Evans rats treated with intracerebral streptozotocin or vehicle and postmortem frontal lobes from humans with normal aging AD (Braak 0-2), moderate (Braak 3-4) AD, or advanced (Braak 5-6) AD were used to measure IDE and RCAN mRNA and protein.

RESULTS

Intracerebral streptozotocin significantly increased IDE and RCAN mRNA and protein. In humans with apolipoprotein E (ApoE) ε3/ε4 or ε4/ε4 and AD, IDE was elevated at Braak 3-4, but at Braak 5-6, IDE expression was significantly reduced. RCAN1 mRNA was similarly reduced in ApoE ε4+ patients with moderate or severe AD, whereas RCAN1 protein declined with the severity of AD and ApoE ε4 dose.

DISCUSSION

The findings suggest that IDE and RCAN1 differentially modulate brain insulin signaling in relation to AD severity and ApoE genotype.

Early-Stage Alzheimer's Disease Is Associated with Simultaneous Systemic and Central Nervous System Dysregulation of Insulin-Linked Metabolic Pathways

BACKGROUND

Brain insulin resistance is a well-recognized abnormality in Alzheimer's disease (AD) and the likely mediator of impaired glucose utilization that emerges early and progresses with disease severity. Moreover, the rates of mild cognitive impairment (MCI) or AD are significantly greater in people with diabetes mellitus or obesity.

OBJECTIVE

This study was designed to determine whether systemic and central nervous system (CNS) insulin resistant disease states emerge together and thus may be integrally related.

METHODS

Insulin-related molecules were measured in paired human serum and cerebrospinal fluid (CSF) samples from 19 with MCI or early AD, and 21 controls using a multiplex ELISA platform.

RESULTS

In MCI/AD, both the CSF and serum samples had significantly elevated mean levels of C-peptide and an incretin, and reduced expression of Visfatin, whereas only CSF showed significant reductions in insulin and leptin and only serum had increased glucagon, PAI-1, and ghrelin. Although the overall CSF and serum responses reflected insulin resistance together with insulin deficiency, the specific alterations measured in CSF and serum were different.

CONCLUSION

In MCI and early-stage AD, CNS and systemic insulin-related metabolic dysfunctions, including insulin resistance, occur simultaneously, suggesting that they are integrally related and possibly mediated similar pathogenic factors.

Broadening the definition of brain insulin resistance in aging and Alzheimer's disease

It has been >20 years since studies first revealed that the brain is insulin sensitive, highlighted by the expression of insulin receptors in neurons and glia, the presence of circulating brain insulin, and even localized insulin production. Following these discoveries, evidence of decreased brain insulin receptor number and function was reported in both clinical samples and animal models of aging and Alzheimer's disease, setting the stage for the hypothesis that neuronal insulin resistance may underlie memory loss in these conditions. The development of therapeutic insulin delivery to the brain using intranasal insulin administration has been shown to improve aspects of memory or learning in both humans and animal models. However, whether this approach functions by compensating for poorly signaling insulin receptors, for reduced insulin levels in the brain, or for reduced trafficking of insulin into the brain remains unclear. Direct measures of insulin's impact on cellular physiology and metabolism in the brain have been sparse in models of Alzheimer's disease, and even fewer studies have analyzed these processes in the aged brain. Nevertheless, recent evidence supports the role of brain insulin as a mediator of glucose metabolism through several means, including altering glucose transporters. Here, we provide a review of contemporary literature on brain insulin resistance, highlight the rationale for improving memory function using intranasal insulin, and describe initial results from experiments using a molecular approach to more directly measure the impact of insulin receptor activation and signaling on glucose uptake in neurons.

The Full Spectrum of Alzheimer's Disease Is Rooted in Metabolic Derangements That Drive Type 3 Diabetes

The standard practice in neuropathology is to diagnose Alzheimer's disease (AD) based on the distribution and abundance of neurofibrillary tangles and Aβ deposits. However, other significant abnormalities including neuroinflammation, gliosis, white matter degeneration, non-Aβ microvascular disease, and insulin-related metabolic dysfunction require further study to understand how they could be targeted to more effectively remediate AD. This review addresses non-Aβ and non-pTau AD-associated pathologies, highlighting their major features, roles in neurodegeneration, and etiopathic links to deficits in brain insulin and insulin-like growth factor signaling and cognitive impairment. The discussion delineates why AD with its most characteristic clinical and pathological phenotypic profiles should be regarded as a brain form of diabetes, i.e., type 3 diabetes, and entertains the hypothesis that type 3 diabetes is just one of the categories of insulin resistance diseases that can occur independently or overlap with one or more of the others, including type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease.

Possible Clues for Brain Energy Translation via Endolysosomal Trafficking of APP-CTFs in Alzheimer's Disease

Vascular dysfunctions, hypometabolism, and insulin resistance are high and early risk factors for Alzheimer's disease (AD), a leading neurological disease associated with memory decline and cognitive dysfunctions. Early defects in glucose transporters and glycolysis occur during the course of AD progression. Hypometabolism begins well before the onset of early AD symptoms; this timing implicates the vulnerability of hypometabolic brain regions to beta-secretase 1 (BACE-1) upregulation, oxidative stress, inflammation, synaptic failure, and cell death. Despite the fact that ketone bodies, astrocyte-neuron lactate shuttle, pentose phosphate pathway (PPP), and glycogenolysis compensate to provide energy to the starving AD brain, a considerable energy crisis still persists and increases during disease progression. Studies that track brain energy metabolism in humans, animal models of AD, and in vitro studies reveal striking upregulation of beta-amyloid precursor protein (β-APP) and carboxy-terminal fragments (CTFs). Currently, the precise role of CTFs is unclear, but evidence supports increased endosomal-lysosomal trafficking of β-APP and CTFs through autophagy through a vague mechanism. While intracellular accumulation of Aβ is attributed as both the cause and consequence of a defective endolysosomal-autophagic system, much remains to be explored about the other β-APP cleavage products. Many recent works report altered amino acid catabolism and expression of several urea cycle enzymes in AD brains, but the precise cause for this dysregulation is not fully explained. In this paper, we try to connect the role of CTFs in the energy translation process in AD brain based on recent findings.

Comparative efficacy and acceptability of antidiabetic agents for Alzheimer's disease and mild cognitive impairment: A systematic review and network meta-analysis

This study (registered with PROSPERO, CRD42018085967) compares the efficacy (i.e. pro-cognitive effects) and acceptability of antidiabetic agents for Alzheimer's disease (AD) and mild cognitive impairment (MCI). Cochrane Library (CENTRAL), PubMed/MEDLINE, EMBASE and PsycINFO were searched from inception to January 15, 2018 for randomized controlled trials comparing antidiabetic agents with placebo and/or another active antidiabetic agent for the treatment of AD or MCI. Nineteen eligible studies (n = 4855) evaluating the effects of 6 different antidiabetic drugs (i.e. intranasal insulin, pioglitazone, rosiglitazone, metformin, sitagliptin and liraglutide) were included. The results of 29 pairwise comparisons indicated that cognition was significantly improved in subjects treated with antidiabetic agents compared with placebo. Pioglitazone 15 to 30 mg demonstrated the greatest efficacy compared to placebo in network meta-analysis. No significant differences in acceptability were identified when comparing agents with each other and with placebo. The current findings indicate a pro-cognitive class effect of antidiabetic agents in AD/MCI. Other antidiabetic agents should also be investigated in future studies.

Streptozotocin-induced β-cell damage, high fat diet, and metformin administration regulate Hes3 expression in the adult mouse brain

Diabetes mellitus is a group of disorders characterized by prolonged high levels of circulating blood glucose. Type 1 diabetes is caused by decreased insulin production in the pancreas whereas type 2 diabetes may develop due to obesity and lack of exercise; it begins with insulin resistance whereby cells fail to respond properly to insulin and it may also progress to decreased insulin levels. The brain is an important target for insulin, and there is great interest in understanding how diabetes affects the brain. In addition to the direct effects of insulin on the brain, diabetes may also impact the brain through modulation of the inflammatory system. Here we investigate how perturbation of circulating insulin levels affects the expression of Hes3, a transcription factor expressed in neural stem and progenitor cells that is involved in tissue regeneration. Our data show that streptozotocin-induced β-cell damage, high fat diet, as well as metformin, a common type 2 diabetes medication, regulate Hes3 levels in the brain. This work suggests that Hes3 is a valuable biomarker helping to monitor the state of endogenous neural stem and progenitor cells in the context of diabetes mellitus.

Therapeutic Advantages of Dual Targeting of PPAR-δ and PPAR-γ in an Experimental Model of Sporadic Alzheimer's Disease

Background:

Alzheimer’s disease (AD) is associated with progressive impairments in brain responsiveness to insulin and insulin-like growth factor (IGF). Although deficiencies in brain insulin and IGF could be ameliorated with trophic factors such as insulin, impairments in receptor expression, binding, and tyrosine kinase activation require alternative strategies. Peroxisome proliferator-activated receptor (PPAR) agonists target genes downstream of insulin/IGF stimulation. Furthermore, their anti-oxidant and anti-inflammatory effects address other pathologies contributing to neurodegeneration.

Objectives:

The goal of this research was to examine effects of dual delivery of L165, 041 (PPAR-δ) and F-L-Leu (PPAR-γ) agonists for remediating in the early stages of neurodegeneration.

Model:

Experiments were conducted using frontal lobe slice cultures from an intracerebral Streptozotocin (i.c. STZ) rat model of AD.

Results:

PPAR-δ+ PPAR-γ agonist treatments increased indices of neuronal and myelin maturation, and mitochondrial proliferation and function, and decreased neuroinflammation, AβPP-Aβ, neurotoxicity, ubiquitin, and nitrosative stress, but failed to restore choline acetyl transferase expression and adversely increased HNE(lipid peroxidation) and acetylcholinesterase, which would have further increased stress and reduced cholinergic function in the STZ brain cultures.

Conclusion:

PPAR-δ + PPAR-γ agonist treatments have substantial positive early therapeutic targeting effects on AD-associated molecular and biochemical brain pathologies. However, additional or alternative strategies may be needed to optimize disease remediation during the initial phases of treatment.

Nose-to-brain delivery of insulin enhanced by a nanogel carrier

Recent evidences suggest that insulin delivery to the brain can be an important pharmacological therapy for some neurodegenerative pathologies, including Alzheimer disease (AD). Due to the presence of the Blood Brain Barrier, a suitable carrier and an appropriate route of administration are required to increase the efficacy and safety of the treatment. Here, poly(N-vinyl pyrrolidone)-based nanogels (NG), synthetized by e-beam irradiation, alone and with covalently attached insulin (NG-In) were characterized for biocompatibility and brain delivery features in a mouse model. Preliminarily, the biodistribution of the "empty" nanocarrier after intraperitoneal (i.p.) injection was investigated by using a fluorescent-labeled NG. By fluorescence spectroscopy, SEM and dynamic light scattering analyses we established that urine clearance occurs in 24h. Histological liver and kidneys inspections indicated that no morphological alterations of tissues occurred and no immunological response was activated after NG injection. Furthermore, after administration of the insulin-conjugated nanogels (NG-In) through the intranasal route (i.n.) no alteration or immunogenic response of the nasal mucosa was observed, suggesting that the formulation is well tolerated in mouse. Moreover, an enhancement of NG-In delivery to the different brain areas and of its biological activity, measured as Akt activation levels, with reference to free insulin administration was demonstrated. Taken together, these results indicate that the synthesized NG-In enhances brain insulin delivery upon i.n. administration and strongly encourage its further evaluation as therapeutic agent against some neurodegenerative diseases.

Nose-to-brain peptide delivery - The potential of nanotechnology

Nose-to-brain (N-to-B) delivery offers to protein and peptide drugs the possibility to reach the brain in a non-invasive way. This article is a comprehensive review of the state-of-the-art of this emerging peptide delivery route, as well as of the challenges associated to it. Emphasis is given on the potential of nanosized drug delivery carriers to enhance the direct N-to-B transport of protein or peptide drugs. In particular, polymer- and lipid- based nanocarriers are comparatively analyzed in terms of the influence of their physicochemical characteristics and composition on their in vivo fate and efficacy. The use of biorecognitive ligands and permeation enhancers in order to enhance their brain targeting efficiency is also discussed. The article concludes highlighting the early stage of this research field and its still unveiled potential. The final message is that more explicatory PK/PD studies are required in order to achieve the translation from preclinical to the clinical development phase.

Novel calcium-related targets of insulin in hippocampal neurons

Both insulin signaling disruption and Ca²⁺ dysregulation are closely related to memory loss during aging and increase the vulnerability to Alzheimer's disease (AD). In hippocampal neurons, aging-related changes in calcium regulatory pathways have been shown to lead to higher intracellular calcium levels and an increase in the Ca²⁺-dependent afterhyperpolarization (AHP), which is associated with cognitive decline. Recent studies suggest that insulin reduces the Ca²⁺-dependent AHP. Given the sensitivity of neurons to insulin and evidence that brain insulin signaling is reduced with age, insulin-mediated alterations in calcium homeostasis may underlie the beneficial actions of insulin in the brain. Indeed, increasing insulin signaling in the brain via intranasal delivery has yielded promising results such as improving memory in both clinical and animal studies. However, while several mechanisms have been proposed, few have focused on regulation on intracellular Ca²⁺. In the present study, we further examined the effects of acute insulin on calcium pathways in primary hippocampal neurons in culture. Using the whole-cell patch-clamp technique, we found that acute insulin delivery reduced voltage-gated calcium currents. Fura-2 imaging was used to also address acute insulin effects on spontaneous and depolarization-mediated Ca²⁺ transients. Results indicate that insulin reduced Ca²⁺ transients, which appears to have involved a reduction in ryanodine receptor function. Together, these results suggest insulin regulates pathways that control intracellular Ca²⁺ which may reduce the AHP and improve memory. This may be one mechanism contributing to improved memory recall in response to intranasal insulin therapy in the clinic.

A comprehensive screening platform for aerosolizable protein formulations for intranasal and pulmonary drug delivery

Aerosolized administration of biopharmaceuticals to the airways is a promising route for nasal and pulmonary drug delivery, but - in contrast to small molecules - little is known about the effects of aerosolization on safety and efficacy of biopharmaceuticals. Proteins are sensitive against aerosolization-associated shear stress. Tailored formulations can shield proteins and enhance permeation, but formulation development requires extensive screening approaches. Thus, the aim of this study was to develop a cell-based in vitro technology platform that includes screening of protein quality after aerosolization and transepithelial permeation. For efficient screening, a previously published aerosolization-surrogate assay was used in a design of experiments approach to screen suitable formulations for an IgG and its antigen-binding fragment (Fab) as exemplary biopharmaceuticals. Efficient, dose-controlled aerosol-cell delivery was performed with the ALICE-CLOUD system containing RPMI 2650 epithelial cells at the air-liquid interface. We could demonstrate that our technology platform allows for rapid and efficient screening of formulations consisting of different excipients (here: arginine, cyclodextrin, polysorbate, sorbitol, and trehalose) to minimize aerosolization-induced protein aggregation and maximize permeation through an in vitro epithelial cell barrier. Formulations reduced aggregation of native Fab and IgG relative to vehicle up to 50% and enhanced transepithelial permeation rate up to 2.8-fold.

Intranasal delivery of N-terminal modified leptin-pluronic conjugate for treatment of obesity

Leptin is an adipocyte-secreted hormone that is delivered via a specific transport system across the blood-brain barrier (BBB) to the brain where it acts on the hypothalamus receptors to control appetite and thermogenesis. Peripheral resistance to leptin due to its impaired brain delivery prevents therapeutic use of leptin in overweight and moderately obese patients. To address this problem, we modified the N-terminal amine of leptin with Pluronic P85 (LepNP85) and administered this conjugate intranasally using the nose-to-brain (INB) route to bypass the BBB. We compared this conjugate with the native leptin, the N-terminal leptin conjugate with poly(ethylene glycol) (LepNPEG5K), and two conjugates of leptin with Pluronic P85 attached randomly to the lysine amino groups of the hormone. Compared to the random conjugates of leptin with P85, LepNP85 has shown higher affinity upon binding with the leptin receptor, and similarly to native hormone activated hypothalamus receptors after direct injection into brain. After INB delivery, LepNP85 conjugate was transported to the brain and accumulated in the hypothalamus and hippocampus to a greater extent than the native leptin and LepNPEG5K and activated leptin receptors in hypothalamus at lower dose than native leptin. Our work suggests that LepNP85 can access the brain directly after INB delivery and confirms our hypothesis that the improvement in brain accumulation of this conjugate is due to its enhanced brain absorption. In conclusion, the LepNP85 with optimized conjugation chemistry is a promising candidate for treatment of obesity.

Knowledge-Based Compact Disease Models: A Rapid Path from High-Throughput Data to Understanding Causative Mechanisms for a Complex Disease

High-throughput profiling of human tissues typically yields the gene lists composed of a variety of more or less relevant molecular entities. These lists are riddle by false positive observations that often obstruct generation of mechanistic hypothesis that may explain complex phenotype. From general probabilistic considerations, the gene lists enriched by the mechanistically relevant targets can be far more useful for subsequent experimental design or data interpretation. Using Alzheimer's disease as example, the candidate gene lists were processed into different tiers of evidence consistency established by enrichment analysis across subdatasets collected within the same experiment and across different experiments and platforms. The cutoffs were established empirically through ontological and semantic enrichment; resultant shortened gene list was reexpanded by Ingenuity Pathway Assistant tool. The resulting subnetworks provided the basis for generating mechanistic hypotheses that were partially validated by mined experimental evidence. This approach differs from previous consistency-based studies in that the cutoff on the Receiver Operating Characteristic of the true-false separation process is optimized by flexible selection of the consistency building procedure. The resultant Compact Disease Models (CDM) composed of the gene list distilled by this analytic technique and its network-based representation allowed us to highlight possible role of the protein traffic vesicles in the pathogenesis of Alzheimer's. Considering the distances and complexity of protein trafficking in neurons, it is plausible to hypothesize that spontaneous protein misfolding along with a shortage of growth stimulation may provide a shortcut to neurodegeneration. Several potentially overlapping scenarios of early-stage Alzheimer pathogenesis are discussed, with an emphasis on the protective effects of Angiotensin receptor 1 (AT-1) mediated antihypertensive response on cytoskeleton remodeling, along with neuronal activation of oncogenes, luteinizing hormone signaling and insulin-related growth regulation, forming a pleiotropic model of its early stages. Compact Disease Model generation is a flexible approach for high-throughput data analysis that allows extraction of meaningful, mechanism-centered gene sets compatible with instant translation of the results into testable hypotheses.

Insulin Resistance and Neurodegeneration: Progress Towards the Development of New Therapeutics for Alzheimer's Disease

Alzheimer's disease (AD) should be regarded as a degenerative metabolic disease caused by brain insulin resistance and deficiency, and overlapping with the molecular, biochemical, pathophysiological, and metabolic dysfunctions in diabetes mellitus, non-alcoholic fatty liver disease, and metabolic syndrome. Although most of the diagnostic and therapeutic approaches over the past several decades have focused on amyloid-beta (Aβ42) and aberrantly phosphorylated tau, which could be caused by consequences of brain insulin resistance, the broader array of pathologies including white matter atrophy with loss of myelinated fibrils and leukoaraiosis, non-Aβ42 microvascular disease, dysregulated lipid metabolism, mitochondrial dysfunction, astrocytic gliosis, neuro-inflammation, and loss of synapses vis-à-vis growth of dystrophic neurites, is not readily accounted for by Aβ42 accumulations, but could be explained by dysregulated insulin/IGF-1 signaling with attendant impairments in signal transduction and gene expression. This review covers the diverse range of brain abnormalities in AD and discusses how insulins, incretins, and insulin sensitizers could be utilized to treat at different stages of neurodegeneration.

Linking mitochondrial dysfunction, metabolic syndrome and stress signaling in Neurodegeneration

Mounting evidence suggests a link between metabolic syndrome (MetS) such as diabetes, obesity, non-alcoholic fatty liver disease in the progression of Alzheimer's disease (AD), Parkinson's disease (PD) and other neurodegenerative diseases (NDDs). For instance, accumulated Aβ oligomer is enhancing neuronal Ca²⁺ release and neural NO where increased NO level in the brain through post translational modification is modulating the level of insulin production. It has been further confirmed that irrespective of origin; brain insulin resistance triggers a cascade of the neurodegeneration phenomenon which can be aggravated by free reactive oxygen species burden, ER stress, metabolic dysfunction, neuorinflammation, reduced cell survival and altered lipid metabolism. Moreover, several studies confirmed that MetS and diabetic sharing common mechanisms in the progression of AD and NDDs where mitochondrial dynamics playing a critical role. Any mutation in mitochondrial DNA, exposure of environmental toxin, high-calorie intake, homeostasis imbalance, glucolipotoxicity is causative factors for mitochondrial dysfunction. These cumulative pleiotropic burdens in mitochondria leads to insulin resistance, increased ROS production; enhanced stress-related enzymes that is directly linked MetS and diabetes in neurodegeneration. Since, the linkup mechanism between mitochondrial dysfunction and disease phenomenon of both MetS and NDDs is quite intriguing, therefore, it is pertinent for the researchers to identify and implement the therapeutic interventions for targeting MetS and NDDs. Herein, we elucidated the pertinent role of MetS induced mitochondrial dysfunction in neurons and their consequences in NDDs. Further, therapeutic potential of well-known biomolecules and chaperones to target altered mitochondria has been comprehensively documented. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Impact of Single or Repeated Dose Intranasal Zinc-free Insulin in Young and Aged F344 Rats on Cognition, Signaling, and Brain Metabolism

Novel therapies have turned to delivering compounds to the brain using nasal sprays, bypassing the blood brain barrier, and enriching treatment options for brain aging and/or Alzheimer's disease. We conducted a series of in vivo experiments to test the impact of intranasal Apidra, a zinc-free insulin formulation, on the brain of young and aged F344 rats. Both single acute and repeated daily doses were compared to test the hypothesis that insulin could improve memory recall in aged memory-deficient animals. We quantified insulin signaling in different brain regions and at different times following delivery. We measured cerebral blood flow (CBF) using MRI and also characterized several brain metabolite levels using MR spectroscopy. We show that neither acute nor chronic Apidra improved memory or recall in young or aged animals. Within 2 hours of a single dose, increased insulin signaling was seen in ventral areas of the aged brains only. Although chronic Apidra was able to offset reduced CBF with aging, it also caused significant reductions in markers of neuronal integrity. Our data suggest that this zinc-free insulin formulation may actually hasten cognitive decline with age when used chronically.

Obesity Reduces Cognitive and Motor Functions across the Lifespan

Due to a sedentary lifestyle, more and more people are becoming obese nowadays. In addition to health-related problems, obesity can also impair cognition and motor performance. Previous results have shown that obesity mainly affects cognition and motor behaviors through altering brain functions and musculoskeletal system, respectively. Many factors, such as insulin/leptin dysregulation and inflammation, mediate the effect of obesity and cognition and motor behaviors. Substantial evidence has suggested exercise to be an effective way to improve obesity and related cognitive and motor dysfunctions. This paper aims to discuss the association of obesity with cognition and motor behaviors and its underlying mechanisms. Following this, mechanisms of exercise to improve obesity-related dysfunctions are described. Finally, implications and future research direction are raised.

Brain signaling systems in the Type 2 diabetes and metabolic syndrome: promising target to treat and prevent these diseases

The changes in the brain signaling systems play an important role in etiology and pathogenesis of Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), being a possible cause of these diseases. Therefore, their restoration at the early stages of T2DM and MS can be regarded as a promising way to treat and prevent these diseases and their complications. The data on the functional state of the brain signaling systems regulated by insulin, IGF-1, leptin, dopamine, serotonin, melanocortins and glucagon-like peptide-1, in T2DM and MS, are analyzed. The pharmacological approaches to restoration of these systems and improvement of insulin sensitivity, energy expenditure, lipid metabolism, and to prevent diabetic complications are discussed.