Effect of intranasally administered insulin on cerebral blood flow and perfusion; a randomized experiment in young and older adults

Enhancing socio-communicative functions in an MCI patient with intra-nasal insulin: a case report

This report examines extended intra-nasal insulin treatment [INI] for an Insulin Resistant early Mild Cognitive Impairment [MCI] patient. Patient [EJ] also had medial temporal lobe [MTL] damage, poor short-term memory, significant irritability, and social and linguistic withdrawal at treatment start. Compared to baseline, nine months INI treatment increased grey matter volume, lowered beta-amyloid levels, and improved MCI and FAS scores. Patient also increased pragmatic capacities in social conversation and procedural memory. These findings align with results from prior clinical trials on INI and suggest that treatment can slow neurodegenerative disease progression in early MCI patients.

Putative Molecular Mechanisms Underpinning the Inverse Roles of Mitochondrial Respiration and Heme Function in Lung Cancer and Alzheimer's Disease

Mitochondria are the powerhouse of the cell. Mitochondria serve as the major source of oxidative stress. Impaired mitochondria produce less adenosine triphosphate (ATP) but generate more reactive oxygen species (ROS), which could be a major factor in the oxidative imbalance observed in Alzheimer's disease (AD). Well-balanced mitochondrial respiration is important for the proper functioning of cells and human health. Indeed, recent research has shown that elevated mitochondrial respiration underlies the development and therapy resistance of many types of cancer, whereas diminished mitochondrial respiration is linked to the pathogenesis of AD. Mitochondria govern several activities that are known to be changed in lung cancer, the largest cause of cancer-related mortality worldwide. Because of the significant dependence of lung cancer cells on mitochondrial respiration, numerous studies demonstrated that blocking mitochondrial activity is a potent strategy to treat lung cancer. Heme is a central factor in mitochondrial respiration/oxidative phosphorylation (OXPHOS), and its association with cancer is the subject of increased research in recent years. In neural cells, heme is a key component in mitochondrial respiration and the production of ATP. Here, we review the role of impaired heme metabolism in the etiology of AD. We discuss the numerous mitochondrial effects that may contribute to AD and cancer. In addition to emphasizing the significance of heme in the development of both AD and cancer, this review also identifies some possible biological connections between the development of the two diseases. This review explores shared biological mechanisms (Pin1, Wnt, and p53 signaling) in cancer and AD. In cancer, these mechanisms drive cell proliferation and tumorigenic functions, while in AD, they lead to cell death. Understanding these mechanisms may help advance treatments for both conditions. This review discusses precise information regarding common risk factors, such as aging, obesity, diabetes, and tobacco usage.

Effects of dietary soy content on cerebral artery function and behavior in ovariectomized female mice

As females age, they transition through menopause, experiencing a decrease in estrogen and an increase in cardiovascular and neurodegenerative disease risk. Most standard rodent chows contain phytoestrogen-rich soybean meal, which can mimic the effects of estrogen. Understanding the impact of this soybean meal on vascular outcomes is crucial to proper experimental design. Thus, this study aimed to compare the effects of standard and soy-free chows on cerebral artery endothelial function and cognitive function in ovariectomized mice. Young female C57Bl/6J mice (n = 43; ∼6 mo) were randomly assigned to three groups: sham, ovariectomy (OVX), or ovariectomy on a diet containing soy (OVX + Soy). In posterior cerebral arteries, the OVX mice had a 27% lower maximal response to insulin compared with the sham mice. The OVX + Soy mice had a 27% greater maximal vasodilation to insulin compared with the OVX mice and there were no differences in vasodilation between the OVX + Soy and sham groups. The group differences in vasodilation were mediated by differences in nitric oxide bioavailability. The OVX + Soy mice also had greater insulin receptor gene expression in cerebral arteries compared with the OVX mice. However, no differences in aortic or cerebral artery stiffness were observed between groups. Interestingly, the OVX + Soy group scored better on nesting behavior compared with both sham and OVX groups. In summary, we found that ovariectomy impairs insulin-mediated vasodilation in cerebral arteries, but a diet containing soy mitigates these effects. These findings highlight the importance of considering dietary soy when performing vascular and behavioral tests in mice, particularly in females.NEW & NOTEWORTHY To properly design experiments, we must consider how variables like diet impact our outcomes, particularly the effects of soy on females. We found that cerebral artery vasodilation in response to insulin was impaired in ovariectomized female mice compared with intact shams. However, ovariectomized mice fed a soy diet had a preserved cerebral artery insulin-mediated vasodilation. These results highlight that the effects of diet on vascular function may explain inconsistencies found between studies.

Mixed nut consumption improves brain insulin sensitivity: a randomized, single-blinded, controlled, crossover trial in older adults with overweight or obesity

BACKGROUND

Improving brain insulin sensitivity, which can be assessed by measuring regional cerebral blood flow (CBF) responses to intranasal insulin, may prevent age-related metabolic and cognitive diseases.

OBJECTIVES

This study aimed to investigate longer-term effects of mixed nuts on brain insulin sensitivity in older individuals with overweight/obesity.

METHODS

In a randomized, single-blinded, controlled, crossover trial, 28 healthy adults (mean ± standard deviation: 65 ± 3 years; body mass index: 27.9 ± 2.3 kg/m2) received either daily 60-g mixed nuts (15 g of walnuts, pistachio, cashew, and hazelnuts) or no nuts (control) for 16 weeks, separated by an 8-week washout period. Throughout the study, participants were instructed to adhere to the Dutch food-based dietary guidelines. During follow-up, brain insulin action was assessed by quantifying acute effects of intranasal insulin on regional CBF using arterial spin labeling magnetic resonance imaging. Furthermore, effects on peripheral insulin sensitivity (oral glucose tolerance test), intrahepatic lipids, and cardiometabolic risk markers were assessed.

RESULTS

Body weight and composition did not change. Compared with control, mixed nut consumption improved regional brain insulin action in 5 clusters located in the left (difference in CBF responses to intranasal insulin: -4.5 ± 4.7 mL/100 g/min; P < 0.001; -4.6 ± 4.8 mL/100 g/min; P < 0.001; and -4.3 ± 3.6 mL/100 g/min; P = 0.007) and right occipital lobes (-4.3 ± 5.6 mL/100 g/min; and -3.9 ± 4.9 mL/100 g/min; P = 0.028). A fifth cluster was part of the left frontal lobe (-5.0 ± 4.6 mL/100 g/min; P < 0.001). Peripheral insulin sensitivity was not affected. Intrahepatic lipid content (-0.7%-point; 95% CI: -1.3%-point to -0.1%-point; P = 0.027), serum low-density lipoprotein cholesterol concentration (-0.24 mmol/L; 95% CI: -0.44 to -0.04 mmol/L; P = 0.019), and systolic blood pressure (-5 mm Hg; 95% CI: -8 to -1 mm Hg; P = 0.006) were lower after the mixed nut intervention.

CONCLUSIONS

Longer-term mixed nut consumption affected insulin action in brain regions involved in the modulation of metabolic and cognitive processes in older adults with overweight/obesity. Intrahepatic lipid content and different cardiometabolic risk markers also improved, but peripheral insulin sensitivity was not affected. This trial was registered at clinicaltrials.gov as NCT04210869.

The Upper Nasal Space: Option for Systemic Drug Delivery, Mucosal Vaccines and "Nose-to-Brain"

Sino-nasal disease is appropriately treated with topical treatment, where the nasal mucosa acts as a barrier to systemic absorption. Non-invasive nasal delivery of drugs has produced some small molecule products with good bioavailability. With the recent COVID pandemic and the need for nasal mucosal immunity becoming more appreciated, more interest has become focused on the nasal cavity for vaccine delivery. In parallel, it has been recognized that drug delivery to different parts of the nose can have different results and for "nose-to-brain" delivery, deposition on the olfactory epithelium of the upper nasal space is desirable. Here the non-motile cilia and reduced mucociliary clearance lead to longer residence time that permits enhanced absorption, either into the systemic circulation or directly into the CNS. Many of the developments in nasal delivery have been to add bioadhesives and absorption/permeation enhancers, creating more complicated formulations and development pathways, but other projects have shown that the delivery device itself may allow more differential targeting of the upper nasal space without these additions and that could allow faster and more efficient programs to bring a wider range of drugs-and vaccines-to market.

Hot Spots for the Use of Intranasal Insulin: Cerebral Ischemia, Brain Injury, Diabetes Mellitus, Endocrine Disorders and Postoperative Delirium

A decrease in the activity of the insulin signaling system of the brain, due to both central insulin resistance and insulin deficiency, leads to neurodegeneration and impaired regulation of appetite, metabolism, endocrine functions. This is due to the neuroprotective properties of brain insulin and its leading role in maintaining glucose homeostasis in the brain, as well as in the regulation of the brain signaling network responsible for the functioning of the nervous, endocrine, and other systems. One of the approaches to restore the activity of the insulin system of the brain is the use of intranasally administered insulin (INI). Currently, INI is being considered as a promising drug to treat Alzheimer's disease and mild cognitive impairment. The clinical application of INI is being developed for the treatment of other neurodegenerative diseases and improve cognitive abilities in stress, overwork, and depression. At the same time, much attention has recently been paid to the prospects of using INI for the treatment of cerebral ischemia, traumatic brain injuries, and postoperative delirium (after anesthesia), as well as diabetes mellitus and its complications, including dysfunctions in the gonadal and thyroid axes. This review is devoted to the prospects and current trends in the use of INI for the treatment of these diseases, which, although differing in etiology and pathogenesis, are characterized by impaired insulin signaling in the brain.

Nose-to-Brain Delivery of Therapeutic Peptides as Nasal Aerosols

Central nervous system (CNS) disorders, such as psychiatric disorders, neurodegeneration, chronic pain, stroke, brain tumor, spinal cord injury, and many other CNS diseases, would hugely benefit from specific and potent peptide pharmaceuticals and their low inherent toxicity. The delivery of peptides to the brain is challenging due to their low metabolic stability, which decreases their duration of action, poor penetration of the blood-brain barrier (BBB), and their incompatibility with oral administration, typically resulting in the need for parenteral administration. These challenges limit peptides’ clinical application and explain the interest in alternative routes of peptide administration, particularly nose-to-brain (N-to-B) delivery, which allows protein and peptide drugs to reach the brain noninvasively. N-to-B delivery can be a convenient method for rapidly targeting the CNS, bypassing the BBB, and minimizing systemic exposure; the olfactory and trigeminal nerves provide a unique pathway to the brain and the external environment. This review highlights the intranasal delivery of drugs, focusing on peptide delivery, illustrating various clinical applications, nasal delivery devices, and the scope and limitations of this approach.

MemAID: Memory advancement with intranasal insulin vs. placebo in type 2 diabetes and control participants: a randomized clinical trial

BACKGROUND

This study aimed at assessing the long-term effects of intranasal insulin (INI) on cognition and gait in older people with and without type 2 diabetes mellitus (T2DM).

METHODS

Phase 2 randomized, double-blinded trial consisted of 24 week treatment with 40 IU of INI (Novolin® R, off-label use) or placebo (sterile saline) once daily and 24 week follow-up. Primary outcomes were cognition, normal (NW), and dual-task (DTW) walking speeds. Of 244 randomized, 223 completed baseline (51 DM-INI, 55 DM-Placebo, 58 Control-INI, 59 Control-Placebo; 109 female, 65.8 ± 9.1; 50-85 years old); 174 completed treatment (84 DM, 90 Controls); 156 completed follow-up (69 DM).

RESULTS

DM-INI had faster NW (~ 7 cm/s; p = 0.025) and DTW on-treatment (p = 0.007; p = 0.812 adjusted for baseline difference) than DM-Placebo. Control-INI had better executive functioning on-treatment (p = 0.008) and post-treatment (p = 0.007) and verbal memory post-treatment (p = 0.004) than Control-Placebo. DM-INI increased cerebral blood flow in medio-prefrontal cortex (p < 0.001) on MRI. Better vasoreactivity was associated with faster DTW (p < 0.008). In DM-INI, plasma insulin (p = 0.006) and HOMA-IR (p < 0.013) decreased post-treatment. Overall INI effect demonstrated faster walking (p = 0.002) and better executive function (p = 0.002) and verbal memory (p = 0.02) (combined DM-INI and Control-INI cohort, hemoglobin A1c-adjusted). INI was not associated with serious adverse events, hypoglycemic episodes, or weight gain.

CONCLUSION

There is evidence for positive INI effects on cognition and gait. INI-treated T2DM participants walked faster, showed increased cerebral blood flow and decreased plasma insulin, while controls improved executive functioning and verbal memory. The MemAID trial provides proof-of-concept for preliminary safety and efficacy and supports future evaluation of INI role to treat T2DM and age-related functional decline.

Acute inorganic nitrate intake increases regional insulin action in the brain: Results of a double-blind, randomized, controlled cross-over trial with abdominally obese men

AIMS

Improving brain insulin sensitivity may be a promising approach in the prevention and treatment of metabolic and cognitive diseases. Our aim was to investigate acute effects of inorganic nitrate on regional cerebral blood flow (CBF) responses to intranasal insulin in abdominally obese men.

METHODS

Eighteen apparently healthy men, aged 18-60 years and with a waist circumference ≥ 102 cm, participated in a randomized, double-blind, placebo-controlled cross-over trial. The study consisted of two test days separated by at least one week. Men received in random order a drink providing 10 mmol (i.e., 625 mg nitrate) potassium nitrate or an isomolar placebo drink with potassium chloride. Brain insulin action was assessed 120-150 min after the drinks by quantifying acute effects of nasal insulin on regional CBF using arterial spin labeling Magnetic Resonance Imaging. Glucose and insulin concentrations were measured at regular intervals, while blood pressure was determined fasted and at 240 min.

RESULTS

Inorganic nitrate intake increased regional insulin action in five brain clusters. The two largest clusters were located in the right temporal lobe (ΔCBF: 7.0 ± 3.8 mL/100 g/min, volume: 5296 mm³, P < 0.001; and ΔCBF: 6.5 ± 4.3 mL/100 g/min, volume: 3592 mm³, P < 0.001), while two other cortical clusters were part of the right frontal (ΔCBF: 9.0 ± 6.0 mL/100 g/min, volume: 1096 mm³, P = 0.007) and the left parietal lobe (ΔCBF: 6.1 ± 4.3 mL/100 g/min, volume: 1024 mm³, P = 0.012). One subcortical cluster was located in the striatum (ΔCBF: 5.9 ± 3.2 mL/100 g/min, volume: 1792 mm³, P < 0.001). No effects of nitrate were observed on CBF before administration. Following nitrate intake, circulating nitrate plus nitrite concentrations increased over time (P = 0.003), but insulin and glucose concentrations and blood pressure did not change.

CONCLUSION

Acute inorganic nitrate intake may improve regional brain insulin action in abdominally obese men. These regions are involved in the regulation of different metabolic and cognitive processes. The trial was registered on January 6th, 2021 at ClinicalTrials.gov as NCT04700241.

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.

Repeated Preoperative Intranasal Administration of Insulin Decreases the Incidence of Postoperative Delirium in Elderly Patients Undergoing Laparoscopic Radical Gastrointestinal Surgery: A Randomized, Placebo-Controlled, Double-Blinded Clinical Study

STUDY OBJECTIVES

This study aimed to investigate the effects of repeated preoperative intranasal administration of insulin on the incidence of postoperative delirium (POD) and the levels of serum pro-inflammatory markers in elderly patients undergoing laparoscopic radical gastrointestinal surgery.

DESIGN

Prospective, randomized, double-blinded, placebo-controlled clinical study.

SETTING

General Hospital of Western Theater Command from August 2019 to December 2019.

PATIENTS

Ninety elderly patients underwent laparoscopic radical gastrointestinal tumor resections under general anesthesia.

INTERVENTIONS

Patients were randomly divided into a control group (0.5 mL saline administered intranasally) or an insulin group (20 U/0.5 mL insulin administered intranasally) for 2 days prior to surgery, with 45 patients in each group.

MEASUREMENTS

The incidence of delirium was measured at postoperative day 1 (T2), day 3 (T3), and day 5 (T4) using the Confusion Assessment Method for the intensive care unit (CAM-ICU). Plasma levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α were measured at T0 (before insulin or saline administration), T1 (at the end of surgery), T2, T3, and T4 by enzyme-linked immunosorbent assay.

MAIN RESULTS

Compared with the control group, the insulin group demonstrated a decreased POD incidence (12.5% vs. 47.5%, p = 0.001) within 5 days after surgery. The incidence of POD was significantly lower in the Ins group than in the Con group at T2 (12.5% vs. 32.5%, p = 0.032) and at T3 (2.5% vs. 20%, p = 0.034). The incidence of POD decreased in both groups over time and was similar at T4 (0% vs 10%, p = 0.116). Compared with the baseline value at T0, serum TNF-α, IL-6 and IL-1β concentrations increased significantly at T1-4 (p <0.05). Compared with the control group at the same time point, the expression levels of TNF-α, IL-6 and IL-1β in group I at T2 and T3 were significantly reduced (p <0.05). The incidence rates of adverse events were similar in the two groups.

CONCLUSIONS

Repeated preoperative intranasal administration of insulin prevented the occurrence of delirium after laparoscopic radical gastrointestinal surgery in elderly patients and reduced TNF-α, IL-1β, and IL-6 levels.

Metabolic determinants of Alzheimer's disease: A focus on thermoregulation

Alzheimer's disease (AD) is a complex age-related neurodegenerative disease, associated with central and peripheral metabolic anomalies, such as impaired glucose utilization and insulin resistance. These observations led to a considerable interest not only in lifestyle-related interventions, but also in repurposing insulin and other anti-diabetic drugs to prevent or treat dementia. Body temperature is the oldest known metabolic readout and mechanisms underlying its maintenance fail in the elderly, when the incidence of AD rises. This raises the possibility that an age-associated thermoregulatory deficit contributes to energy failure underlying AD pathogenesis. Brown adipose tissue (BAT) plays a central role in thermogenesis and maintenance of body temperature. In recent years, the modulation of BAT activity has been increasingly demonstrated to regulate energy expenditure, insulin sensitivity and glucose utilization, which could also provide benefits for AD. Here, we review the evidence linking thermoregulation, BAT and insulin-related metabolic defects with AD, and we propose mechanisms through which correcting thermoregulatory impairments could slow the progression and delay the onset of AD.

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.

Brain insulin signalling in metabolic homeostasis and disease

Insulin signalling in the central nervous system regulates energy homeostasis by controlling metabolism in several organs and by coordinating organ crosstalk. Studies performed in rodents, non-human primates and humans over more than five decades using intracerebroventricular, direct hypothalamic or intranasal application of insulin provide evidence that brain insulin action might reduce food intake and, more importantly, regulates energy homeostasis by orchestrating nutrient partitioning. This Review discusses the metabolic pathways that are under the control of brain insulin action and explains how brain insulin resistance contributes to metabolic disease in obesity, the metabolic syndrome and type 2 diabetes mellitus.

Insulin action in the brain regulates both central and peripheral functions

The brain has been traditionally thought to be insensitive to insulin, primarily because insulin does not stimulate glucose uptake/metabolism in the brain (as it does in classic insulin-sensitive tissues such as muscle, liver, and fat). However, over the past 20 years, research in this field has identified unique actions of insulin in the brain. There is accumulating evidence that insulin crosses into the brain and regulates central nervous system functions such as feeding, depression, and cognitive behavior. In addition, insulin acts in the brain to regulate systemic functions such as hepatic glucose production, lipolysis, lipogenesis, reproductive competence, and the sympathoadrenal response to hypoglycemia. Decrements in brain insulin action (or brain insulin resistance) can be observed in obesity, type 2 diabetes (T2DM), aging, and Alzheimer's disease (AD), indicating a possible link between metabolic and cognitive health. Here, we describe recent findings on the pleiotropic actions of insulin in the brain and highlight the precise sites, specific neuronal population, and roles for supportive astrocytic cells through which insulin acts in the brain. In addition, we also discuss how boosting brain insulin action could be a therapeutic option for people at an increased risk of developing metabolic and cognitive diseases such as AD and T2DM. Overall, this perspective article serves to highlight some of these key scientific findings, identify unresolved issues, and indicate future directions of research in this field that would serve to improve the lives of people with metabolic and cognitive dysfunctions.

Cerebral perfusion alterations in type 2 diabetes mellitus - a systematic review

Type 2 diabetes mellitus (T2DM) is related to abnormal brain structure and function, increasing the risk of cognitive impairment and dementia. We systematically reviewed the published literature focusing on cerebral perfusion in patients with T2DM. Although no significant difference was found in global cerebral blood flow (CBF) between the T2DM group and the healthy control group, the regional cerebral perfusion in T2DM was significantly reduced in multiple locations, including the occipital lobe, domains involved in the default mode network and the cerebellum. The decline in regional CBF was associated with a wide range of cognitive disorders in T2DM, including learning, memory, attention, and executive processing, as well as visual function. In addition, diabetes-related biochemical indicators, such as glycated hemoglobin and insulin resistance, were negatively correlated with regional CBF. In general, these functional perfusion imaging studies indicate that decreased CBF in T2DM may be a potential cause of cognitive impairment.

Hypothalamic insulin signalling as a nexus regulating mood and metabolism

Insulin has long been known as a metabolic hormone critical in the treatment of diabetes for its peripheral effects on blood glucose. However, in the last 50 years, insulin has entered the realm of neuroendocrinology and many studies have described its function on insulin receptors in the brain in relation to both metabolic and mood disorders. Indeed, rodent models of impaired insulin signalling show signs of dysregulated energy and glucose homeostasis, as well as anxiety-like and depressive behaviours. Importantly, many metabolic diseases such as obesity and diabetes increase the risk of developing mood disorders; however, the brain mechanisms underlying the connection between metabolism and mood remain unresolved. We present the current literature on the importance of the insulin receptor with respect to regulating glucose and energy homeostasis and mood-related behaviours. Specifically, we hypothesise that the insulin receptor in the hypothalamus, classically known as the homeostatic centre of the brain, plays a causal role in linking metabolic and behavioural effects of insulin signalling. In this review, we discuss insulin signalling in the hypothalamus as a critical point of neural integration controlling metabolism and mood.

Long-Term Intranasal Insulin Aspart: A Profile of Gene Expression, Memory, and Insulin Receptors in Aged F344 Rats

Intranasal insulin is a safe and effective method for ameliorating memory deficits associated with pathological brain aging. However, the impact of different formulations and the duration of treatment on insulin's efficacy and the cellular processes targeted by the treatment remain unclear. Here, we tested whether intranasal insulin aspart, a short-acting insulin formulation, could alleviate memory decline associated with aging and whether long-term treatment affected regulation of insulin receptors and other potential targets. Outcome variables included measures of spatial learning and memory, autoradiography and immunohistochemistry of the insulin receptor, and hippocampal microarray analyses. Aged Fischer 344 rats receiving long-term (3 months) intranasal insulin did not show significant memory enhancement on the Morris water maze task. Autoradiography results showed that long-term treatment reduced insulin binding in the thalamus but not the hippocampus. Results from hippocampal immunofluorescence revealed age-related decreases in insulin immunoreactivity that were partially offset by intranasal administration. Microarray analyses highlighted numerous insulin-sensitive genes, suggesting insulin aspart was able to enter the brain and alter hippocampal RNA expression patterns including those associated with tumor suppression. Our work provides insights into potential mechanisms of intranasal insulin and insulin resistance, and highlights the importance of treatment duration and the brain regions targeted.

Intranasal insulin administration decreases cerebral blood flow in cortico-limbic regions: A neuropharmacological imaging study in normal and overweight males

AIM

To assess and compare the effects of 160 IU intranasal insulin (IN-INS) administration on regional cerebral blood flow (rCBF) in healthy male individuals with normal weight and overweight phenotypes.

METHODS

Thirty young male participants (mean age 25.9 years) were recruited and stratified into two cohorts based on body mass index: normal weight (18.5-24.9 kg/m² ) and overweight (25.0-29.9 kg/m² ). On separate mornings participants received 160 IU of IN-INS using an intranasal protocol and intranasal placebo as part of a double-blind crossover design. Thirty minutes following administration rCBF data were collected using a magnetic resonance imaging method called pseudocontinuous arterial spin labelling. Blood samples were collected to assess insulin sensitivity and changes over time in peripheral glucose, insulin and C-peptide.

RESULTS

Insulin sensitivity did not significantly differ between groups. Compared with placebo, IN-INS administration reduced rCBF in parts of the hippocampus, insula, putamen, parahippocampal gyrus and fusiform gyrus in the overweight group. No effect was seen in the normal weight group. Insula rCBF was greater in the overweight group versus normal weight only under placebo conditions. Peripheral glucose and insulin levels were not affected by IN-INS. C-peptide levels in the normal weight group decreased significantly over time following IN-INS administration but not placebo.

CONCLUSION

Insulin-induced changes within key regions of the brain involved in gustation, memory and reward were observed in overweight healthy male individuals. Following placebo administration, differences in gustatory rCBF were observed between overweight and normal weight healthy individuals.

Non-Invasive Strategies for Nose-to-Brain Drug Delivery

Intranasal drug administration is a promising method for delivering drugs directly to the brain. Animal studies have described pathways and potential brain targets, but nose-to-brain delivery and treatment efficacy in humans remains debated. We describe the proposed pathways and barriers for nose-to-brain drug delivery in humans, drug properties that influence central nervous system delivery, clinically tested methods to enhance absorption, and the devices used in clinical trials. This review compiles the available evidence for nose-to-brain drug delivery in humans and summarizes the factors involved in nose-to-brain drug delivery.

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.

ApoE and cerebral insulin: Trafficking, receptors, and resistance

Central nervous system (CNS) insulin resistance is associated with Alzheimer's disease (AD). In addition, the apolipoprotein E4 (apoE4) isoform is a risk factor for AD. The connection between these two factors in relation to AD is being actively explored. We summarize this literature with a focus on the transport of insulin and apoE across the blood-brain barrier (BBB) and into the CNS, the impact of apoE and insulin on the BBB, and the interactions between apoE, insulin, and the insulin receptor once present in the CNS. We highlight how CNS insulin resistance is apparent in AD and potential ways to overcome this resistance by repurposing currently approved drugs, with apoE genotype taken into consideration as the treatment response following most interventions is apoE isoform-dependent. This review is part of a special issue focusing on apoE in AD and neurodegeneration.

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.

Safety of intranasal human insulin: A review

AIMS

To conduct a review in order to assess the safety of intranasal human insulin in clinical studies as well as the temporal stability of nasal insulin sprays.

MATERIAL AND METHODS

An electronic search was performed using MEDLINE. We selected original research on intranasal human insulin without further additives in humans. The studies included could be of any design as long as they used human intranasal insulin as their study product. All outcomes and adverse side effects were extracted.

RESULTS

A total of 38 studies in 1092 individuals receiving acute human intranasal insulin treatment and 18 studies in 832 individuals receiving human intranasal insulin treatment lasting between 21 days and 9.7 years were identified. No cases of symptomatic hypoglycaemia or severe adverse events (AEs) were reported. Transient local side effects in the nasal area were frequently experienced after intranasal insulin and placebo spray, while other AEs were less commonly reported. There were no reports of participants being excluded as a result of AEs. No instances of temporal stability of nasal insulin were reported in the literature. Tests on insulin that had been repacked into spray flasks showed that it had a chemical stability of up to 57 days.

CONCLUSIONS

Our retrospective review of published studies on intranasal insulin did not reveal any safety concerns; however, there were insufficient data to ensure the long-term safety of this method of chronic insulin administration. Improved insulin preparations that cause less nasal irritation would be desirable for future treatment.

Expression of a Constitutively Active Human Insulin Receptor in Hippocampal Neurons Does Not Alter VGCC Currents

Memory and cognitive decline are the product of numerous physiological changes within the aging brain. Multiple theories have focused on the oxidative, calcium, cholinergic, vascular, and inflammation hypotheses of brain aging, with recent evidence suggesting that reductions in insulin signaling may also contribute. Specifically, a reduction in insulin receptor density and mRNA levels has been implicated, however, overcoming these changes remains a challenge. While increasing insulin receptor occupation has been successful in offsetting cognitive decline, alternative molecular approaches should be considered as they could bypass the need for brain insulin delivery. Moreover, this approach may be favorable to test the impact of continued insulin receptor signaling on neuronal function. Here we used hippocampal cultures infected with lentivirus with or without IRβ, a constitutively active, truncated form of the human insulin receptor, to characterize the impact continued insulin receptor signaling on voltage-gated calcium channels. Infected cultures were harvested between DIV 13 and 17 (48 h after infection) for Western blot analysis on pAKT and AKT. These results were complemented with whole-cell patch-clamp recordings of individual pyramidal neurons starting 96 h post-infection. Results indicate that while a significant increase in neuronal pAKT/AKT ratio was seen at the time point tested, effects on voltage-gated calcium channels were not detected. These results suggest that there is a significant difference between constitutively active insulin receptors and the actions of insulin on an intact receptor, highlighting potential alternate mechanisms of neuronal insulin resistance and mode of activation.