Intranasal Insulin Administration Research Articles

Moderate aerobic training enhances the effectiveness of insulin therapy through hypothalamic IGF1 signaling in rat model of Alzheimer's disease

Alzheimer's disease (AD) is a neurological condition that is connected with a decline in a person's memory as well as their cognitive ability. One of the key topics of AD research has been the exploration of metabolic causes. We investigated the effects of treadmill exercise and intranasal insulin on learning and memory impairment and the expression of IGF1, BDNF, and GLUT4 in hypothalamus. The animals were put into 9 groups at random. In this study, we examined the impact of insulin on spatial memory in male Wistar rats and analyzed the effects of a 4-week pretreatment of moderate treadmill exercise and insulin on the mechanisms of improved hypothalamic glucose metabolism through changes in gene and protein expression of IGF1, BDNF, and GLUT4. We discovered that rat given Aβ25–35 had impaired spatial learning and memory, which was accompanied by higher levels of Aβ plaque burden in the hippocampus and lower levels of IGF1, BDNF, and GLUT4 mRNA and protein expression in the hypothalamus. Additionally, the administration of exercise training and intranasal insulin results in the enhancement of spatial learning and memory impairments, the reduction of plaque burden in the hippocampus, and the enhancement of the expression of IGF1, BDNF, and GLUT4 in the hypothalamus of rats that were treated with Aβ25–35. Our results show that the improvement of learning and spatial memory due to the improvement of metabolism and upregulation of the IGF1, BDNF, and GLUT4 pathways can be affected by pretreatment exercise and intranasal insulin.

Effect of acute intranasal insulin administration on muscle sympathetic nerve activity in healthy young adults.

Systemic insulin increases muscle sympathetic nerve activity (MSNA) via both central actions within the brainstem and peripheral activation of the arterial baroreflex. Augmented MSNA during hyperinsulinemia likely restrains peripheral vasodilation and contributes to the maintenance of blood pressure (BP). However, in the absence of insulin action within the peripheral vasculature, whether central insulin stimulation increases MSNA and influences peripheral hemodynamics in humans remains unknown. Herein, we hypothesized intranasal insulin administration would increase MSNA and BP in healthy young adults. Participants were assigned to time control [(TC), n=13 (5F/8M), 28±1 yrs] or 160 IU of intranasal insulin administered over five min [n=15 (5F/10M), 26±2 yrs]; five (1F/4M) participants completed both conditions. MSNA (fibular microneurography), BP (finger photoplethysmography), and leg blood flow (LBF, femoral Doppler ultrasound) were assessed at baseline, 15, and 30 minutes following insulin administration. Leg vascular conductance (LVC = [LBF ÷ mean BP] x 100) was calculated. Venous insulin and glucose concentrations remained unchanged throughout (p>0.05). Following intranasal insulin administration, MSNA (burst frequency; baseline = 100%; minute 15: 121±8%; minute 30: 118±6%; p=0.009, n=7) and mean BP (baseline = 100%; minute 15: 103±1%; minute 30: 102±1%; p=0.003) increased, while LVC decreased (baseline = 100%; minute 15: 93±3%; minute 30: 99±3%; p=0.03). In contrast, MSNA, mean BP, and LVC were unchanged in TC participants (p>0.05). We provide the first evidence that intranasal insulin administration in healthy young adults acutely increases MSNA and BP and decreases LVC. These results enhance mechanistic understanding of the sympathetic and peripheral hemodynamic response to insulin.

Impact of Peripheral Versus Central Insulin on Cerebrovascular Compliance in Healthy Young Adults

Objective: Vascular compliance is an essential component of cerebral blood flow regulation. Prior work has shown cerebral vasodilation (elicited by hypercapnia) reduces cerebrovascular compliance (Ci); however, this work has yet to be translated to other vasoactive compounds. Insulin has important vasodilatory effects in the peripheral circulation, but less is known about the role of insulin in cerebrovascular control. Herein, we hypothesized both peripheral (intravenous) and central (intranasal) insulin administration would increase indices of cerebral blood flow and reduce Ci in healthy young adults. Methods: Twenty-five healthy young adults (8 female; 26±7 yrs, 25±3 kg/m2) were assigned to two separate protocols (NCT05244694, NCT05153395). Middle cerebral artery blood velocity (MCAv, transcranial Doppler ultrasound) was measured at baseline and under two study conditions: 1) at the end of a 60 min hyperinsulinemic euglycemic infusion, and 2) 60 min following 160 IU of intranasal insulin. Indices of Ci were calculated using a modified Windkessel model applied to blood pressure (finger photoplethysmography) and corresponding MCAv waveforms collected over a 5-min period (10 waveforms) at baseline and during the aforementioned insulin conditions. Results: Blood glucose remained unchanged throughout both protocols (both p>0.05). MCAv was maintained over time under both insulin conditions (protocol 1: 60±13 to 62±17 cm/s, p=0.635; protocol 2: 58±9 to 53±14 cm/s, p=0.146). In contrast, Ci decreased (0.00028±0.00010 to 0.00021±0.00007 cm/s/mmHg, p=0.010) from baseline during peripheral (intravenous) insulin administration. No change in Ci (0.00049±0.00025 to 0.00040±0.00018 cm/s/mmHg, p=0.189) were observed following intranasal insulin administration. Conclusions: Contrary to our hypothesis, there was no effect of peripheral or central insulin administration on resting MCAv in healthy young adults. However, intravenous (but not intranasal) insulin reduced Ci by approximately 25% from baseline values. These findings advance our understanding of cerebrovascular control mechanisms during insulin exposure and provide the opportunity to extend this work to diseased states characterized by insulin resistance, including diabetes. CAFNR Joy of Discovery (JKL, JP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Muscle Sympathetic Action Potential Firing Patterns Following Intranasal Insulin Administration in Healthy Adults

Objective: Systemic insulin increases muscle sympathetic nervous system activity (MSNA) in healthy adults by augmenting firing frequency of medium-sized sympathetic action potentials (AP) and recruiting previously latent, larger axons. Whether these neural coding patterns are due to central or peripheral effects of insulin is unclear. We examined the impact of elevated central insulin on AP firing patterns in healthy adults. We hypothesized intranasal insulin administration, which increases central insulin levels, would increase MSNA via elevated firing frequency of APs and recruitment of previously latent, larger axons. Methods: Ten participants were assigned to time control [TC, n=6 (3M/3F)] or 160 IU of intranasal insulin [n=4 (3M/1F)] administered over 5 min. MSNA (fibular microneurography) was assessed at baseline and for 30 min following insulin administration. Sympathetic APs were identified using a matched mother wavelet and continuous wavelet transform. APs were divided into the proportion of those firing in small, medium, or large amplitude clusters. AP firing frequency, percent of APs firing within an MSNA burst (synchronous), and the probability of clusters firing more than once within an MSNA burst were identified. Data are reported as median (interquartile range). Results: MSNA burst frequency increased 15 min after intranasal insulin administration [24(20) to 31(23) bursts/min, p=0.03]. At this time, the percent of synchronous APs [72(27) to 90(24)%, p=0.02] and the probability of medium-sized AP clusters firing more than once within an MSNA burst [13(14) to 19(17)%, p=0.03] increased. No changes in MSNA burst frequency [23(14) to 25(13) bursts/min, p=0.27], percent of synchronous APs [74(15) to 75(34), p=0.48], nor firing probability of medium-sized AP clusters [6(12) to 8(7)%, p=0.97] occurred in TC. The total number of detected clusters did not change in either group (p>0.05). Conclusions: Intranasal insulin increases MSNA burst frequency due to a higher percent of synchronous APs, particularly medium-sized AP clusters; however, we did not observe recruitment of latent, larger axons. These exploratory data highlight potential differences in the sympathetic response to central versus peripheral insulin exposure in healthy adults. CAFNR Joy of Discovery (JKL, JP). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Intranasal Insulin Administration to Rats with Forebrain Ischemia and Reperfusion Injury Reduces Autophagy and Apoptosis Intensity in the Hippocampus and Frontal Cortex, a Possible Mechanism of Action

Intranasal Insulin Administration to Rats with Forebrain Ischemia and Reperfusion Injury Reduces Autophagy and Apoptosis Intensity in the Hippocampus and Frontal Cortex, a Possible Mechanism of Action

Effect of intranasal insulin administration on postoperative delirium prevention in elderly cardiac surgery patients: study protocol for a multicenter, double-blind, randomized, controlled trial

BackgroundPostoperative delirium (POD) is a complication after surgery which leads to worse outcomes. The frequency of this syndrome is increasing as more elderly patients undergo major surgery. The frequency is around 10–25% but reaches as high as 50% for cardiac surgery. Although intranasal insulin (INI) administration of up to 160 units in patients with cognitive dysfunction and delirium has been shown to improve memory function and brain metabolism without complications such as hypoglycemia, it remains unknown whether INI prevents POD after cardiac surgeryMethodsA multicenter, double-blind, randomized, controlled trial will be conducted at University of Tsukuba Hospital and Tsukuba Medical Center Hospital, Japan, from July 1, 2023, to December 31, 2025. A total of 110 elderly patients (65 years old or older) undergoing cardiac surgery requiring cardiopulmonary bypass will be enrolled and randomly allocated to intranasal insulin or intranasal saline groups. The primary outcome is the incidence of POD within 7 days after surgery. Secondary outcomes include days and times of delirium, screening tests of cognitive function, pain scores, duration of postoperative tracheal intubation, and length of ICU stay.DiscussionThe present objective is to assess whether 80 IU INI administration during surgery prevents POD after cardiac surgery. The results may provide strategic choices to prevent POD in patients with cardiac surgery requiring cardiopulmonary bypass.Trial registrationThe trial was registered with the Japan Registry for Clinical Trials with identifier jRCTs031230047 on April 21, 2023.

Safety of intranasal insulin administration in patients undergoing cardiovascular surgery: An open-label, nonrandomized, dose-escalation study

ObjectiveThis study aimed to determine the maximum safe dose of intranasal insulin administration during cardiac surgery. MethodsThis open-label, Phase 1, single-center, dose-escalation clinical trial recruited patients scheduled to undergo elective cardiac surgery or major vascular surgery requiring cardiopulmonary bypass between February and September 2021. They were grouped into 5 dose-escalation cohorts and administered 0, 40, 80, 160, and 240 IU insulin (n = 6 in each group) via a metered nasal dispenser after the induction of general anesthesia. Blood samples were collected at 10-minute intervals for the first 60 minutes and at 30-minute intervals thereafter. Hypoglycemia was defined as a blood glucose level <70 mg/dL. Patient recruitment was terminated after hypoglycemia was observed in 2 patients in any of the groups. ResultsIn total, 27 of 29 enrolled patients were administered intranasal insulin or saline. Hypoglycemia was not observed after the administration of intranasal insulin in the 0, 40, 80, or 160 IU groups; however, it was observed in 2 of 3 patients in the 240 IU group. The serum insulin concentration was elevated in the 160-IU group, but the C-peptide concentration was not elevated in any of the groups. ConclusionsThe administration of up to 160 IU intranasal insulin did not induce clinically significant hypoglycemia. However, 160 IU intranasal insulin should be administered cautiously because insulin can enter the systemic circulation in a dose-dependent manner.

Effect of intra‐nasal insulin therapy on food intake among African American adults: the FIINAAL study

AbstractBackgroundIntranasal insulin is a promising treatment for cognitive decline in Alzheimer’s Disease (AD) and mild cognitive impairment (MCI). However, intranasal insulin has been shown to promote weight loss, leading to concerns about decreased appetite, decreased food intake, and unintentional weight loss as negative side effects among metabolic and ingestive behavior effects of intranasal insulin sprays among AD and MCI patients. But, side effects related to food intake and appetite are not well studied, particularly among African American adults who are under‐represented in AD research.Method39 middle‐aged, cognitively normal, community‐dwelling African American adults (Table 1) were enrolled in the Food Intake and Intranasal Insulin in African American Adults (FIINAAL) study assessing effects of intranasal insulin on acute food intake and appetite ratings. This double‐blind, placebo‐controlled, randomized crossover study compared a single intranasal dose of 10 IUs of Novologã insulin, delivered with the Kurveã device, to an intranasal placebo. Participants ate a eucaloric, macronutrient‐balanced lead‐in diet for three days prior to each dose. The dose was administered in the morning following an overnight fast. An ad libitum test lunch followed the dose and participants rated their appetite immediately before and after each dose, and after the meal. Mixed effects linear model t‐tests were used to compare differences in food intake and appetite ratings between insulin and placebo conditions.ResultThere were no significant differences in test lunch energy (calories) or macronutrient intake between insulin and placebo conditions. However, fullness ratings increased significantly more after receiving a dose of insulin than after a dose of placebo (Figure 1). In addition, desire to consume sweet and fatty foods decreased significantly more after insulin than after placebo (Figure 2).ConclusionIn middle aged African American adults, acute intranasal insulin administration was associated with a reduced desire to eat palatable foods and with increased feelings of fullness, but not with reduced food intake at a test meal. Because reduced appetite appears to be an acute side effect of intranasal insulin administration, future work should study whether chronic intranasal insulin administration results in reduced appetite and, consequently, reduced food intake and body weight over time.

Imaging the brain to assess brain insulin action

AbstractBackgroundEver since the brain was identified as an insulin‐sensitive organ, it was quickly appreciated that insulin action in the brain affects cognitive and metabolic processes [1]. Epidemiological evidence suggests a strong link between reduced peripheral insulin sensitivity and age‐related neurodegenerative processes, including Alzheimer’s disease (AD) [2].MethodCharacterization of brain insulin resistance in humans is challenging and relies on different neuroimaging methods in combination with insulin stimulation techniques. In my talk, I will focus on the administration of intranasal insulin, which has been established over the last decades to disentangle peripheral from brain insulin effects [1]. In combination with functional neuroimaging, I will show recent data on the quantification of brain insulin sensitivity non‐invasively in humans of different age and weight groups [3].ResultWe could show that intranasal insulin can affect region‐specific activity and functional connectivity of the human brain. These diverse central insulin responses largely depend on its action in the hypothalamus, amygdala, hippocampus, striatum and parts of the insula and prefrontal cortex and influences a variety of metabolic and cognitive processes [3]. Specifically, I will show that disrupted brain insulin action can result in increased accumulation of visceral fat and altered reward learning in persons at high risk to develop T2D [4], but also in healthy individuals after overconsumption of high caloric foods (unpublished). Moreover, I will show that the effect of intranasal insulin in the hippocampus decreases with age in women but not men and that brain insulin responsivity is affected by the menstrual cycle (unpublished). Moreover, just recently, we could link enhanced brain insulin action in the mesocorticolimbic circuitry with improved cognitive and metabolic functions [5].ConclusionAs brain insulin acts on striatal dopamine function and hippocampal plasticity, enhancing brain insulin action could lead to new treatment options in diabetes and aging‐associated diseases.

Elevated Insulin Levels Engage the Salience Network during Multisensory Perception

Introduction: Brain insulin reactivity has been reported in connection with systematic energy metabolism, enhancement in cognition, olfactory sensitivity, and neuroendocrine circuits. High receptor densities exist in regions important for sensory processing. The main aim of the study was to examine whether intranasal insulin would modulate the activity of areas in charge of olfactory-visual integration. Methods: As approach, a placebo-controlled double-blind within crossover design was chosen. The experiments were conducted in a research unit of a university hospital. On separate mornings, twenty-six healthy normal-weight males aged between 19 and 31 years received either 40 IU intranasal insulin or placebo vehicle. Subsequently, they underwent 65 min of functional magnetic resonance imaging whilst performing an odor identification task. Functional brain activations of olfactory, visual, and multisensory integration as well as insulin versus placebo were assessed. Regarding the odor identification task, reaction time, accuracy, pleasantness, and intensity measurements were taken to examine the role of integration and treatment. Blood samples were drawn to control for peripheral hormone concentrations. Results: Intranasal insulin administration during olfactory-visual stimulation revealed strong bilateral engagement of frontoinsular cortices, anterior cingulate, prefrontal cortex, mediodorsal thalamus, striatal, and hippocampal regions (p ≤ 0.001 familywise error [FWE] corrected). In addition, the integration contrast showed increased activity in left intraparietal sulcus, left inferior frontal gyrus, left superior frontal gyrus, and left middle frontal gyrus (p ≤ 0.013 FWE corrected). Conclusions: Intranasal insulin application in lean men led to enhanced activation in multisensory olfactory-visual integration sites and salience hubs which indicates stimuli valuation modulation. This effect can serve as a basis for understanding the connection of intracerebral insulin and olfactory-visual processing.

Intranasal insulin for COVID-19-related smell loss.

Quantitative (hyposmia and anosmia) and qualitative (phantosmia and parosmia) olfactory disorders are common consequences of COVID-19 infection found in more than 38% of patients even months after resolution of acute disease. SARS-CoV-2 has tropism for angiotensin-converting enzyme 2 (ACE2) in the respiratory system, suggesting that it is the mechanism of damage to the olfactory neuroepithelium and of involvement at the central nervous system. The olfactory bulb is the organ with the highest insulin uptake in the central nervous system. Insulin increases the production of Growth Factors (GF); therefore, in this study, the administration of intranasal insulin is proposed as a viable treatment for olfactory disturbances. The aim of this study was to obtain improvement in olfaction after 4 weeks of intranasal insulin administration in a group of patients presenting chronic olfactory disturbances secondary to COVID-19 infection, quantified using the Threshold, Discrimination, and Identification (TDI) score based on the Sniffin Sticks®. Experimental, longitudinal, prolective and prospective study of patients with a previous diagnosis of COVID-19 in the last 3-18months and who persisted with anosmia or hyposmia. The sample size was calculated with "satulator". The intervention was performed from January to May 2022. Throughout four appointments, a baseline olfactory measurement was obtained using the TDI score based on the Sniffin Sticks® test. In the first three appointments, Gelfoam® cottonoids soaked in 40IU of NPH insulin were placed on the nasal roof of each nostril for 15min. Descriptive statistics, student's paired t test and a multiple linear regression were utilized to ascertain statistical significance of the outcome on the TDI score obtained on the fourth and final appointment. 27 patients were included in the study. Table 1 summarizes the sample characteristics. The results exhibit that 93% of the sample had an improvement. The initial mean TDI score was 67% (63-71) compared to the final mean of 83% (80-86, p < 0.01). TDI subsection analysis is shown in Table 2. There was no significant difference in pre-intervention and post-intervention glucose measurements after the intranasal insulin administration. The administration of intranasal insulin has promising results, pointing towards an alternative of treatment for chronic olfactory disturbances secondary to neuroepithelial damage caused by upper respiratory tract infections. Furthermore, this is the first study to use a three-point assessment of olfaction in post-COVID-19 patients, while using the Sniffin Sticks® TDI score adapted to Latin Spanish.

Intranasal Insulin Treatment Partially Corrects the Altered Gene Expression Profile in the Hippocampus of Developing Rats with Perinatal Iron Deficiency.

Perinatal iron deficiency (FeD) targets the hippocampus and leads to long-term cognitive deficits. Intranasal insulin administration improves cognitive deficits in adult humans with Alzheimer's disease and type 2 diabetes and could provide benefits in FeD-induced hippocampal dysfunction. Assess intranasal insulin administration on the hippocampal transcriptome in a developing rat model of perinatal FeD. Perinatal FeD was induced using low-iron diet from gestational day 3 until postnatal day (P) 7, followed by an iron sufficient (FeS) diet through P21. Intranasal insulin was administered at a dose of 0.3 IU, twice daily from P8 to P21. Hippocampi were removed on P21 from FeS control, FeD control, FeS insulin, and FeD insulin groups. Total RNA was isolated and profiled using next-generation sequencing. Gene expression profiles were characterized using custom workflows and expression patterns examined using Ingenuity Pathways Analysis (n = 7-9 per group). Select RNAseq results were confirmed via qPCR. Transcriptomic profiling revealed that mitochondrial biogenesis and flux, oxidative phosphorylation, quantity of neurons, CREB signaling in neurons, and RICTOR-based mTOR signaling were disrupted with FeD and positively affected by intranasal insulin treatment with the most benefit observed in the FeD insulin group. Both perinatal FeD and intranasal insulin administration altered gene expression profile in the developing hippocampus. Intranasal insulin treatment reversed the adverse effects of FeD on many molecular pathways and could be explored as an adjunct therapy in perinatal FeD.

Intranasal insulin - effects on the sense of smell.

Intranasal insulin (IN) administration is a promising way to deliver the peptide to the central nervous system (CNS), bypassing the blood-brain-barrier and gastrointestinal absorption inhibition. IN receptors are localized in the olfactory mucosa and the brain, mainly in the olfactory bulb, hypothalamus, hippocampus, amygdala, cerebral cortex, and cerebellum. The pleiotropic mechanism of insulin action is characterized by its anti-inflammatory properties, antithrombotic, vasodilatory, and antiapoptotic effects. It prevents energy failure and has regenerative properties, affects neuro-regeneration and counteracts insulin resistance. Hence, insulin has been suggested for various pathological states including neurocognitive disorders, obesity, and as a therapeutic option for smell loss. A sharply increased prevalence of olfactory dysfunction was observed due to the COVID-19 pandemic. The pandemic also emphasized the lack of therapeutic options for smell loss. Intranasal insulin administration has therefore been suggested to serve as potential treatment, influencing the regenerative capacities of the olfactory mucosa. This narrative review summarizes current knowledge on possible effects of intranasal insulin on the sense of smell.

Comparative Therapeutic Effect of Single/Combined Administration of Saxagliptin, Metformin and Intranasal Insulin on Dexamethasone Induced Insulin Resistance in Albino Wistar Rat Model.

Glucocorticoids have therapeutic benefits in the management of several inflammatory and immunological disorders. Despite these medicinal effects, they have the drawback of causing metabolic disorders such as hyperglycemia, insulin resistance etc., which is known to be a key indicator of metabolic syndrome. Metabolic syndrome is a major predisposing factor to type 2 diabetes mellitus and cardiomyopathy. This study was designed to compare and evaluate the effects of saxagliptin, metformin and intranasal insulin (when used singly or in combination) on dexamethasone induced insulin resistance. Fifty-six female rats were randomly assigned into eight groups. Group 1 represented the control; Group 2 was administered with dexamethasone (1mg/kg) (untreated); Group 3 received dexamethasone + intranasal insulin (2IU); Group 4 received dexamethasone + intranasal insulin + metformin (40mg/kg); Group 5; received dexamethasone + intranasal + saxagliptin (8mg/kg); Group 6 received dexamethasone + metformin (40mg/kg); Group 7 received dexamethasone + saxagliptin (8mg/kg); Group 8 received dexamethasone + saxagliptin(8mg/kg) + metformin(40mg/kg). Treatments were given for one week. At the end of the study, blood samples were collected for biochemical assays and pancreas excised for histological examination. Dexamethasone (1mg/kg) induced hyperglycemia, hyperinsulinemia, dyslipidemia, impaired glucose tolerance and disrupted the structural integrity of the pancreas. Treatment with saxagliptin, metformin and their combination significantly decreased blood glucose level, decreased LDL Level and improved glucose tolerance. The selected hypoglycemic agents used in present study ameliorate the dexamethasone induced hyperglycemia and insulin resistance of which the combination of metformin with saxagliptin showed greater efficacy.

1534-P: Nasal-Insulin–Induced Change of Functional MRI Signal at the Level of Hypothalamic Nuclei in the Patients with Type 2 Diabetes Mellitus

Insulin resistance in the hypothalamus is related to both increased appetite and systemic metabolic deterioration and may be an essential cause of metabolic diseases. In human studies, hypothalamic activity after intranasal insulin administration (INIA) has been measured by functional MRI (fMRI). However, to date, the resolution of fMRI has not been high enough to assess which neuronal nuclei in the hypothalamus are responsible for insulin. The purpose of this study was to investigate whether we can assess hypothalamic reaction after INIA at the nuclear level using high-resolution fMRI and if so, to examine its association with clinical parameters. Here, we studied 20 men with type 2 diabetes (T2DM) and 20 non-obese men without diabetes (CON). All subjects underwent fMRI with INIA (160 IU human insulin). The average of the cleaned blood oxygenation level-dependent (BOLD) signal from -15 min to 0 min was used as the baseline value in each subject. The signal change compared to the baseline value was calculated at every 5 min after INIA. The mean ages of subjects were both around 50 years and HbA1c levels were 6.88±1.13% in T2DM and 5.24±0.25% in CON (p&amp;lt;0.001). There were significant differences in the BOLD signal changes after INIA in the posterior nucleus (PH) at 5 min and posterior lateral hypothalamic area (LHAp) at 5 and 10 min between T2DM and CON. In other hypothalamic nuclei, there were no significant differences between T2DM and CON in the rate of change of the BOLD signal up to 30 min after INIA. Multiple regression analysis revealed that fasting plasma glucose (FPG) was a significant independent variable for activity change of the PH at 5 min and LHAp at 5 and 10 min, while BMI and HOMA-IR were not. In summary, we successfully detected nasal-insulin-induced change of fMRI signal at the level of hypothalamic nuclei. We found the differences in neural activity in the PH and LHAp early after INIA between those with and without diabetes, which were associated with FPG. Disclosure M.Kiya: None. Y.Tamura: None. H.Kaga: None. N.Ito: None. T.Tajima: None. H.Naito: None. M.Sato: None. S.Kadowaki: None. S.Kakehi: None. H.Watada: Research Support; Boehringer Ingelheim Japan, Inc., Mitsubishi Tanabe Pharma Corporation, LifeScan Diabetes Institute, Eli Lilly Japan K.K., Sun Pharmaceutical Industries Ltd., Teijin Pharma Limited, Taisho Pharmaceutical Holdings Co., Ltd., Ono Pharmaceutical Co., Ltd., Kowa Company, Ltd., Merck Sharp &amp; Dohme Corp., Sanwa Kagaku Kenkyusho, Speaker's Bureau; Mitsubishi Tanabe Pharma Corporation, Taiho Pharmaceutical Co. Ltd., Novo Nordisk, Abbott Japan Co., Ltd., Astellas Pharma Inc., Merck Sharp &amp; Dohme Corp., Kissei Pharmaceutical Co., Ltd., AstraZeneca, Ono Pharmaceutical Co., Ltd., Boehringer Ingelheim Japan, Inc., Sanofi, Sun Pharmaceutical Industries Ltd., Eli Lilly Japan K.K. Funding Japan Society for the Promotion of Science (21H03380, 22K17835); Ministry of Education, Culture, Sports, Science and Technology of Japan; Suzuken Memorial Foundation

Intranasal insulin therapy in the treatment of alzheimer’s disease – A narrative review

The administration of intranasal insulin improves symptoms related to Alzheimer’s disease. The research was conducted through a hypothesis-based review, such as, PubMed, DynaMed, and EBSCOhost. The articles published between 2011 and 2020 were included. The studies included randomized controlled trials and cohort studies. The study populations included participants associated with cognitive-related conditions. The group of humans and animal models were also considered. All ten articles showed how the administration of intranasal insulin can improve the symptoms related to Alzheimer’s disease. However, these findings varied on the level of dose used, the duration of the treatment and the type of insulin formulations used. Future studies can consider to provide a more homogenous group of study population, cognitive-related activities to observe, and duration of the administration in order to provide a more credible result.

Brain insulin responsiveness is linked to age and peripheral insulin sensitivity.

Insulin action in the brain influences cognitive processes, peripheral metabolism and eating behaviour. However, the influence of age and peripheral insulin sensitivity on brain insulin action remains unclear. We used intranasal administration of insulin and functional magnetic resonance imaging in a randomized, placebo-controlled within-subject design in 110 participants (54 women, body mass index 18-49 kg/m2 , age 21-74 years). Cerebral blood flow was measured before and after nasal spray application to assess brain insulin action. Peripheral insulin sensitivity was assessed by a five-point oral glucose tolerance test. Linear regressions were used to investigate associations between age and peripheral insulin sensitivity with brain insulin action in predefined region of interests (i.e. insulin-sensitive brain regions). We found significant negative associations between age and insulin action in the hippocampus (β = -0.215; p = .017) and caudate nucleus (β = -0.184; p = .047); and between peripheral insulin sensitivity and insulin action in the amygdala (β = -0.190, p = .023). Insulin action in the insular cortex showed an interaction effect between age and peripheral insulin sensitivity (β = -0.219 p = .005). Furthermore, women showed the strongest negative association between age and hippocampal insulin action, while men showed the strongest associations with peripheral insulin sensitivity and age in reward-related brain regions. We could show a region-specific relationship between brain insulin responsiveness, age and peripheral insulin sensitivity. Our findings underline the need to study brain insulin action in both men and women and further substantiate that brain insulin sensitivity is a possible link between systemic metabolism and neurocognitive functions.

From Determining Brain Insulin Resistance in a Sporadic Alzheimer's Disease Model to Exploring the Region-Dependent Effect of Intranasal Insulin.

Impaired response to insulin has been linked to many neurodegenerative disorders like Alzheimer's disease (AD). Animal model of sporadic AD has been developed by intracerebroventricular (icv) administration of streptozotocin (STZ), which given peripherally causes insulin resistance. Difficulty in demonstrating insulin resistance in this model led to our aim: to determine brain regional and peripheral response after intranasal (IN) administration of insulin in control and STZ-icv rats, by exploring peripheral and central metabolic parameters. One month after STZ-icv or vehicle-icv administration to 3-month-old male Wistar rats, cognitive status was determined after which rats received 2IU of fast-acting insulin aspart intranasally (CTR + INS; STZ + INS) or saline only (CTR and STZ). Rats were sacrificed 2h after administration and metabolic and glutamatergic parameters were measured in plasma, CSF, and the brain. Insulin and STZ increased amyloid-β concentration in plasma (CTR + INS and STZ vs CTR), while there was no effect on glucose and insulin plasma and CSF levels. INS normalized the levels of c-fos in temporal cortex of STZ + INS vs STZ (co-localized with neurons), while hypothalamic c-fos was found co-localized with the microglial marker. STZ and insulin brain region specifically altered the levels and activity of proteins involved in cell metabolism and glutamate signaling. Central changes found after INS in STZ-icv rats suggest hippocampal and cortical insulin sensitivity. Altered hypothalamic metabolic parameters of STZ-icv rats were not normalized by INS, indicating possible hypothalamic insulin insensitivity. Brain insulin sensitivity depends on the affected brain region and presence of metabolic dysfunction induced by STZ-icv administration.

Investigating the effects of antipsychotics on brain insulin action: Study protocol for a multi-modality magnetic resonance imaging (MRI) study in healthy controls.

Antipsychotics (APs) are the cornerstone of treatment for schizophrenia (SCZ) but are unfortunately associated with serious metabolic adverse effects including weight gain and type 2 diabetes. The pathophysiology of AP-induced metabolic dysfunction is largely undetermined. Brain insulin resistance has been posited to be at the cross-roads of many cognitive and metabolic disorders, and disruption of central insulin action has emerged as a possible explanatory mechanism underlying AP induced metabolic dysfunction. Previous studies suggest that change in neuroimaging-based parameters with intranasal insulin administration can be leveraged to investigate brain insulin resistance. In this proof-of-concept study, we will utilize neural signatures of insulin action in the brain to examine if APs disrupt brain insulin signaling. It is hypothesized that: 1) intranasal insulin (INI), but not intranasal placebo (INP), will change cerebral blood flow and resting state connectivity, as well as increase glutamate levels in the striatum and dorsolateral prefrontal cortex; 2) oral olanzapine (OLA), but not oral placebo (PL), will inhibit the effect of INI on these parameters. Thirty-two healthy volunteers will undergo a single blind, cross-over design, wherein all participants receive the following four treatment combinations, 2-6 weeks apart, in a random sequence: INP + PL, INP + OLA, INI + PL, and INI + OLA. Participants will undergo an MRI-based assay of brain insulin resistance 15 minutes after administering 160 IU INI or INP. The scanning protocol includes resting and task-based functional MRI, arterial spin labelling, and proton magnetic resonance spectroscopy. Demonstrating that OLA can acutely induce brain insulin resistance is clinically relevant to metabolic health in SCZ. Evidence of brain insulin resistance induced by acute AP dosing can inform the early use of adjunctive insulin sensitizers for the treatment of metabolic comorbidities associated with AP treatment in severe mental illness. Trial registration ClinicalTrials.gov Registration: NCT03741478.

The Role of Insulin Signaling in Hippocampal-Related Diseases: A Focus on Alzheimer's Disease.

Alzheimer's disease (AD) is a global concern and has become a major public health event affecting human health. Insulin is a metabolic hormone secreted mainly by the peripheral tissue pancreas. In recent years, more and more evidence has proved that insulin regulates various functions of the brain. The hippocampus, one of the earliest brain regions affected by AD, is widely distributed with insulin receptors. Studies have shown that type 2 diabetes mellitus, characterized by insulin resistance, is closely related to AD, which has drawn extensive attention to the relationship between hippocampal insulin signaling and AD. Therefore, we provide an overview of intranasal insulin administration on memory and its underlying mechanism. We also highlight the molecular link between hippocampal insulin resistance and AD and provide a theoretical basis for finding new therapeutic targets for AD in clinical practice.