Intranasal insulin: from nose to brain

Insulin Delivery to the Brain via the Nasal Route: Unraveling the Potential for Alzheimer's Disease Therapy

This comprehensive review delves into the potential of intranasal insulin delivery for managing Alzheimer's Disease (AD) while exploring the connection between AD and diabetes mellitus (DM). Both conditions share features of insulin signalling dysregulation and oxidative stress that accelerate inflammatory response. Given the physiological barriers to brain drug delivery, including the blood-brain barrier, intranasal administration emerges as a non-invasive alternative. Notably, intranasal insulin has shown neuroprotective effects, impacting Aβ clearance, tau phosphorylation, and synaptic plasticity. In preclinical studies and clinical trials, intranasally administered insulin achieved rapid and extensive distribution throughout the brain, with optimal formulations exhibiting minimal systemic circulation. The detailed mechanism of insulin transport through the nose-to-brain pathway is elucidated in the review, emphasizing the role of olfactory and trigeminal nerves. Despite promising prospects, challenges in delivering protein drugs from the nasal cavity to the brain remain, including enzymes, tight junctions, mucociliary clearance, and precise drug deposition, which hinder its translation to clinical settings. The review encompasses a discussion of the strategies to enhance the intranasal delivery of therapeutic proteins, such as tight junction modulators, cell-penetrating peptides, and nano-drug carrier systems. Moreover, successful translation of nose-to-brain drug delivery necessitates a holistic understanding of drug transport mechanisms, brain anatomy, and nasal formulation optimization. To date, no intranasal insulin formulation has received regulatory approval for AD treatment. Future research should address challenges related to drug absorption, nasal deposition, and the long-term effects of intranasal insulin. In this context, the evaluation of administration devices for nose-to-brain drug delivery becomes crucial in ensuring precise drug deposition patterns and enhancing bioavailability.

Nose-to-brain delivery of nanotherapeutics: Transport mechanisms and applications

The blood-brain barrier presents a key limitation to the administration of therapeutic molecules for the treatment of brain disease. While drugs administered orally or intravenously must cross this barrier to reach brain targets, the unique anatomical structure of the olfactory system provides a route to deliver drugs directly to the brain. Entering the brain via receptor, carrier, and adsorption-mediated transcytosis in the nasal olfactory and trigeminal regions has the potential to increase drug delivery. In this review, we introduce the physiological and anatomical structures of the nasal cavity, and summarize the possible modes of transport and the relevant receptors and carriers in the nose-to-brain pathway. Additionally, we provide examples of nanotherapeutics developed for intranasal drug delivery to the brain. Further development of nanoparticles that can be applied to intranasal delivery systems promises to improve drug efficacy and reduce drug resistance and adverse effects by increasing molecular access to the brain. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

Distribution of insulin in primate brain following nose-to-brain transport

Introduction

Nose-to-brain (N2B) insulin delivery has potential for Alzheimer's disease (AD) therapy. However, clinical implementation has been challenging without methods to follow N2B delivery non-invasively. Positron emission tomography (PET) was applied to measure F-18-labeled insulin ([18F]FB-insulin) from intranasal dosing to brain uptake in non-human primates following N2B delivery.

Methods

[18F]FB-insulin was prepared by reacting A1,B29-di(tert-butyloxycarbonyl)insulin with [18F]-N-succinimidyl-4-fluorobenzoate. Three methods of N2B delivery for [18F]FB-insulin were compared - delivery as aerosol via tubing (rhesus macaque, n = 2), as aerosol via preplaced catheter (rhesus macaque, n = 3), and as solution via preplaced catheter (cynomolgus macaque, n = 3). Following dosing, dynamic PET imaging (120 min) quantified delivery efficiency to the nasal cavity and whole brain. Area under the time-activity curve was calculated for 46 regions of the cynomolgus macaque brain to determine regional [18F]FB-insulin levels.

Results

Liquid instillation of [18F]FB-insulin by catheter outperformed aerosol methods for delivery to the subject (39.89% injected dose vs 10.03% for aerosol via tubing, 0.17% for aerosol by catheter) and subsequently to brain (0.34% injected dose vs 0.00020% for aerosol via tubing, 0.05% for aerosol by catheter). [18F]FB-insulin was rapidly transferred across the cribriform plate to limbic and frontotemporal areas responsible for emotional and memory processing. [18F]FB-insulin half-life was longer in olfactory nerve projection sites with high insulin receptor density compared to the whole brain.

Discussion

The catheter-based liquid delivery approach combined with PET imaging successfully tracked the fate of N2B [18F]FB-insulin and is thought to be broadly applicable for assessments of other therapeutic agents. This method can be rapidly applied in humans to advance clinical evaluation of N2B insulin as an AD therapeutic.

Highlights for

[18F]FB-insulin passage across the cribriform plate was detected by PET.Intranasal [18F]FB-insulin reached the brain within 13 min.[18F]FB-insulin activity was highest in emotional and memory processing regions.Aerosol delivery was less efficient than liquid instillation by preplaced catheter.Insulin delivery to the cribriform plate was critical for arrival in the brain.

Transnasal-brain delivery of nanomedicines for neurodegenerative diseases

Neurodegenerative diseases (NDs) have become a serious global health problem as the population ages. Traditionally, treatment strategies for NDs have included oral and intravenous administration; however, the blood–brain barrier (BBB) can prevent drugs from reaching the brain, rendering the treatment incomplete and the effect unsatisfactory. Additionally, the prolonged or excessive use of drugs that can cross the BBB can damage liver and kidney function. Recent studies have shown that nose-to-brain drug delivery can noninvasively bypass the BBB, allowing drugs to enter the brain through the olfactory or trigeminal nerve pathways; additionally, nanoparticle carriers can enhance drug delivery. This review introduces drug carrier nanoparticles for nose-to-brain delivery systems, compares the advantages and disadvantages of different nanoparticles, and discusses the factors influencing nose-to-brain nanomedicine delivery and enhancement strategies. We also summarize nose-to-brain delivery and nanomedicines for treating NDs, the current challenges of this approach, and the future promise of nanomedicine-based ND treatment.

Protective Effect of Insulin in Mouse Nasal Mucus Against Olfactory Epithelium Injury

Insulin is present in nasal mucus and plays an important role in the survival and activity of individual olfactory sensory neurons (OSNs) via insulin receptor-mediated signaling. However, it is unclear whether insulin acts prophylactically against olfactotoxic drug-induced olfactory epithelium (OE) injury, and whether the degree of damage is affected by the concentration of insulin in the nasal mucus. The apoptosis-inducing drug methimazole was administered to the nasal mucus of diabetic and normal mice along with different concentrations of insulin. Immunohistochemical analysis was used to assess the relationship between damage to the OE and the mucus insulin concentration and the protective effect of insulin administration against eosinophilic cationic protein (ECP)-induced OE injury. Diabetic mice had lower concentrations of insulin in their nasal mucus than normal mice (diabetic vs. normal mice, p < 0.001). Methimazole administration reduced the number of OSNs in normal mice and had a more marked effect in diabetic mice. However, unilateral insulin administration prevented the methimazole-induced reduction in the number of OSNs on the ipsilateral side but not on the contralateral side (OSNs; Insulin vs. contralateral side, p < 0.001). Furthermore, intranasal ECP administration damaged the OE by inducing apoptosis (OSNs; ECP vs. contralateral side, p < 0.001), but this damage was largely prevented by insulin administration (OSNs; Insulin + ECP vs. contralateral side, p = 0.36), which maintained the number of mature OSNs. The severity of methimazole-induced damage to the OE is related to the insulin concentration in the nasal mucus (Correlation between the insulin concentration in nasal mucus and the numbers of OSNs, R² = 0.91, p < 0.001), which may imply that nasal insulin protects OSNs and that insulin administration might lead to the development of new therapeutic agents for ECP-induced OE injury.

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.

A Comprehensive Review of Intranasal Insulin and Its Effect on the Cognitive Function of Diabetics

Diabetes mellitus continues to be a disease that affects a good percentage of our population. The majority affected need insulin on a day-to-day basis. Before the invention of the first manufactured insulin in 1978, dealing with diabetes took a significant toll on patient's lives. As technology and human innovation prevail, significant advancements have taken place in managing this chronic disease. Patients have an option to decide their mode of insulin delivery. Intranasal insulin, one such form, has a rapid mode of action while effectively controlling postprandial hyperglycemia. It has also been proven to reduce hypoglycemia and insulin resistance problems, which seem to be the main adverse effects of using conventional insulin regularly. However, due to the large dosages needed and high incurring costs, Intranasal Insulin is currently being used as adjunctive therapy along with conventional insulin.  We conducted a literature search in PubMed indexed journals using the medical terms "Intranasal insulin," "diabetes," and "cognitive impairment" to provide an overview of the mechanism of action of Intranasal Insulin, its distinctive cognitive benefits, and how it can be compared to the standard parenteral insulin therapy. One unique feature of intranasal insulin is its ability to directly affect the central nervous system, bypassing the blood-brain barrier. Not only does this help in reducing the peripheral side effects of insulin, but it has also proven to play a role in improving the cognitive function of diabetics, especially those who have Alzheimer's or mild cognitive impairment, as decreased levels of insulin in the brain has been shown to impact cognitive function negatively. However, it does come with its limitations of poor absorption through the nasal mucosa due to mucociliary clearance and proteolytic enzymes, our body's natural defence mechanisms. This review focuses on the efficacy of intranasal insulin, its potential benefits, limitations, and role in cognitive improvement in people with diabetes with pre-existing cognitive impairment.

Quantitative analysis of inulin distribution in the brain focused on nose-to-brain route via olfactory epithelium by reverse esophageal cannulation

This study aimed to determine the effect of intranasal dosing speed and administrating volume of nose-to-brain delivery on candidates for peptide drugs (molecular weight ca. 1-10 kDa). Using inulin as the model molecule of a peptide drug, intranasal administration by cannulation from the airway side through the esophagus was tested in mice. This was done to determine the quantitative distribution levels of the drug in the brain and cerebral spinal fluid (CSF). Distribution levels were increased with slower and constant speed (5 μL/min), with higher dosing volume equivalent to nasal volume per body weight in mice (25 μL), and were recorded 0.27% injected dose per gram of tissue (ID/g) in the brain, and 0.24% injected dose per milliliter (ID/mL) in the CSF at 60 min. Then, brain distribution resulting from reverse cannulation was two times more than that of the typical intranasal administration method using a micropipette. In addition, the percentage of inulin estimated to reach the brain via direct transport (%DTP) during reverse cannulation was estimated to be 93%, suggesting that ~95% of the total dose was transferred directly to the brain via the olfactory mucosa. These results show that distribution of the peptide drug in the brain was increased through constant administration at a slow and constant speed.

Zone-specific damage of the olfactory epithelium under protein restriction

Oxidative stress causes tissue damage, affecting age-related pathologies. Protein restriction (PR) provides a powerful intervention strategy for reducing oxidative stress, which may have a positive effect on individual organs. However, it is unknown whether PR intervention influences the olfactory system. Here, we investigated how 10 months of PR could affect the cell dynamics of the olfactory epithelium (OE) in mice. We found that PR reduced age-related loss of outer hair cells in the cochlea, providing preventive effects against age-related hearing loss. In contrast, PR resulted in reduced mature olfactory sensory neurons (OSNs), increased proliferative basal cells, and increased apoptotic OSNs in zone 1 (the only area containing neurons expressing NQO1 [quinone dehydrogenase 1]) of the OE in comparison with animals given a control diet. Substantial oxidative stress occurred in NQO1-positive cells and induced apoptotic OSNs in zone 1. These results indicate that in contrast to the positive effect on the auditory system, PR induces oxidative stress and structurally and functionally negative effects on OSNs in zone 1, which is probably involved in the bioactivation of NQO1.

Insulin Resistance Is Associated with Reduced Food Odor Sensitivity across a Wide Range of Body Weights

The worldwide obesity epidemic is a major health problem driven by the modern food environment. Recently, it has been shown that smell perception plays a key role in eating behavior and is altered in obesity. However, the underlying mechanisms of this phenomenon are not well understood yet. Since the olfactory system is closely linked to the endocrine system, we hypothesized that hormonal shifts in obesity might explain this relationship. In a within-subject, repeated-measures design, we investigated sensitivity to a food and a non-food odor in the hungry and sated state in 75 young healthy (26 normal weight, 25 overweight, and 24 obese) participants (37 women). To determine metabolic health status and hormonal reactivity in response to food intake, we assessed pre- and postprandial levels of insulin, leptin, glucose, and ghrelin. Odor sensitivity did not directly depend on body weight status/body mass index (BMI) or hunger state. However, we could establish a strong negative mediating effect of insulin resistance on the relationship between BMI/waist-hip ratio and olfactory sensitivity for the food odor. These findings indicate an impact of metabolic health status on sensitivity to food odors. Our results contribute to a better understanding of the mechanisms behind altered smell perception in obesity.

Tailoring Formulations for Intranasal Nose-to-Brain Delivery: A Review on Architecture, Physico-Chemical Characteristics and Mucociliary Clearance of the Nasal Olfactory Mucosa

The blood-brain barrier and the blood-cerebrospinal fluid barrier are major obstacles in central nervous system (CNS) drug delivery, since they block most molecules from entering the brain. Alternative drug delivery routes like intraparenchymal or intrathecal are invasive methods with a remaining risk of infections. In contrast, nose-to-brain delivery is a minimally invasive drug administration pathway, which bypasses the blood-brain barrier as the drug is directed from the nasal cavity to the brain. In particular, the skull base located at the roof of the nasal cavity is in close vicinity to the CNS. This area is covered with olfactory mucosa. To design and tailor suitable formulations for nose-to-brain drug delivery, the architecture, structure and physico-chemical characteristics of the mucosa are important criteria. Hence, here we review the state-of-the-art knowledge about the characteristics of the nasal and, in particular, the olfactory mucosa needed for a rational design of intranasal formulations and dosage forms. Also, the information is suitable for the development of systemic or local intranasal drug delivery as well as for intranasal vaccinations.

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.

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.

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

INTRODUCTION

Growing evidence supports the concept that insulin resistance plays an important role in the pathogenesis of cognitive impairment and neurodegeneration, including in Alzheimer's disease (AD). The metabolic hypothesis has led to the development and utilization of insulin- and insulin agonist-based treatments. Therapeutic challenges faced include the ability to provide effective treatments that do not require repeated injections and also the ability to minimize the potentially hazardous off-target effects.

AREAS COVERED

This review covers the role of intranasal insulin therapy for cognitive impairment and neurodegeneration, particularly AD. The literature reviewed focuses on data published within the past 5 years as this field is evolving rapidly. The review provides evidence that brain insulin resistance is an important and early abnormality in AD, and that increasing brain supply and utilization of insulin improves cognition and memory. Emphasis was placed on discussing outcomes of clinical trials and interpreting discordant results to clarify the benefits and limitations of intranasal insulin therapy.

EXPERT OPINION

Intranasal insulin therapy can efficiently and directly target the brain to support energy metabolism, myelin maintenance, cell survival and neuronal plasticity, which begin to fail in the early stages of neurodegeneration. Efforts must continue toward increasing the safety, efficacy and specificity of intranasal insulin therapy.

Further experimentation of inhaled; LANTUS, ACTRAPID and HUMULIN with todays' production systems

BACKGROUND

Several aerosol production systems have been used for aerosol insulin production. However; since the first studies several new models of jet-nebulizers and ultrasound nebulizers have been introduced in the market.

MATERIALS AND METHODS

Three different models of jet-nebulizers (different brands, same properties) and three different ultrasound nebulizers (different brands, same properties). Six residual cups (2 small ≤ 6 ml and 3 large ≤ 8 ml) were used for the jet-nebulizers. The ultrasound nebulizers were used with their facemasks or with their inlets which were included in the purchase package.

RESULTS

Ultrasound nebulizers; LANTUS produces by far the lowest mean droplets (2.44) half the size of the other two drugs (4.43=4.97). GIMA nebulizer is the most efficient producing one third of the droplet size of SHIMED and one second of EASYNEB (2.06<3.15<6.62). Finally, the 4 ml loading concentration is more suitable for supporting the production of smaller droplets (3.65<4.24). Drugs and nebulizers act interactively yielding very large droplets when ACTRAPID and HUMULIN are administered in joint with SHIMED nebulizer (9.59=7.72). Jet-nebulizers; HUMULIN again is the least preferred insulin since it hardly reaches the low but equal performance of others at the loading level of 6 ml. Residual cups E and B produce uniquely lower mean droplets at loading level 6.

CONCLUSIONS

Ultrasound nebulizers; the best suggested combination should be LANTUS insulin, GIMA nebulizer administered at loading dose of 4 ml jet-nebulizers. A global review can give the best combination: the lowest mean droplets are produced when the drugs LANTUS (mostly) and ACTRAPID are administered, applying the SUNMIST nebulizer in concert with residual cup B at loading levels of 6 ml.

Therapeutic potential of conopeptides

Conopeptides from the venoms of marine snails have attracted much interest as leads in drug design. Currently, one drug, Prialt(®), is on the market as a treatment for chronic neuropathic pain. Conopeptides target a range of ion channels, receptors and transporters, and are typically small, relatively stable peptides that are generally amenable to production using solid-phase peptide synthesis. With only a small fraction of the predicted diversity of conopeptides examined so far, these peptides represent an exciting and largely untapped resource for drug discovery. Recent efforts at chemically re-engineering conopeptides to improve their biopharmaceutical properties promise to accelerate the translation of these fascinating marine peptides to the clinic.

Olfaction under metabolic influences

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

Airway delivery of peptides and proteins using nanoparticles

Delivery of peptides and proteins via the airways is one of the most exciting potential applications of nanomedicine. These macromolecules could be used for many therapeutic applications, however due to their poor stability in physiological medium and difficulties in delivering them across biological barriers, they are very difficult to use in therapy. Nanoparticulate drug delivery systems have emerged as one of the most promising technologies to overcome these limitations, owing mainly to their proven capacity to cross biological barriers and to enter cells in high yields, thus improving delivery of macromolecules. In this review, we summarize the current advances in nanoparticle designed for transmucosal delivery of peptides and proteins. Challenges that must be overcome in order to derive clinical benefits are also discussed.

Peptide therapeutics: it's all in the delivery

Recent work has demonstrated that the route of administration affects the pharmacokinetics and biological activity of peptides. For example, the physiological profile of insulin consists of basal and prandial components with a small-scale oscillatory element. Insulin is used more efficiently when the pharmacokinetic profile mimics features of physiological release. Noninvasive administration of insulin by oral, transdermal, nasal and pulmonary routes resembles the relatively sharp peak and short duration of exposure of prandial release. The route of administration per se, can affect the response by avoiding first-pass metabolism or perhaps altering the timing in which the peptide reaches different sets of receptors. GLP-I delivered by injection and inhalation produces different side effect profiles. Nonclinical studies on two potential treatments for obesity, oxyntomodulin and PYY 3-36, are also presented to illustrate the relationship between exposure and effect as functions of route of administration.

Enhancement of nose-to-brain delivery of basic fibroblast growth factor for improving rat memory impairments induced by co-injection of β-amyloid and ibotenic acid into the bilateral hippocampus

Basic fibroblast growth factor (bFGF) delivery to the brain of animals appears to be an emerging potential therapeutic approach to neurodegenerative diseases, such as Alzheimer's disease (AD). The intranasal route of administration could provide an alternative to intracerebroventricular infusion. A nasal spray of bFGF had been developed previously and the objective of the present study was to investigate whether bFGF nasal spray could enhance brain uptake of bFGF and ameliorate memory impairment induced by co-injection of β-amyloid(25-35) and ibotenic acid into bilateral hippocampus of rats. The results of brain uptake study showed that the AUC(0-12h) of bFGF nasal spray in olfactory bulb, cerebrum, cerebellum and hippocampus was respectively 2.47, 2.38, 2.56 and 2.19 times that of intravenous bFGF solution, and 1.11, 1.95, 1.40 and 1.93 times that of intranasal bFGF solution, indicating that intranasal administration of bFGF nasal spray was an effective means of delivering bFGF to the brain, especially to cerebrum and hippocampus. In Morris water maze tasks, intravenous administration of bFGF solution at high dose (40 μg/kg) showed little improvement on spatial memory impairment. In contrast, bFGF solution of the same dose following intranasal administration could significantly ameliorate spatial memory impairment. bFGF nasal spray obviously improved spatial memory impairment even at a dose half (20 μg/kg) of bFGF solution, recovered their acetylcholinesterase and choline acetyltransferase activity to the sham control level, and alleviated neuronal degeneration in rat hippocampus, indicating neuroprotective effects on the central nerve system. In a word, bFGF nasal spray may be a new formulation of great potential for treating AD.

Insulin but not leptin protects olfactory mucosa from apoptosis

The mammalian olfactory mucosa (OM) is continually renewed throughout life. Owing to their position in the nasal cavity, OM cells are exposed to multiple insults, including high levels of odourants that can induce their death. OM regeneration is therefore essential to maintain olfactory function, and requires the tight control of both cell death and proliferation. Apoptosis has been implicated in OM cell death. Olfaction is one of the senses involved in food intake and depends on individual nutritional status. We have previously reported the influence of hormones related to nutritional status on odour perception and have shown that the OM is a target of insulin and leptin, two hormones known for their anti-apoptotic properties. In the present study, we investigated the potential anti-apoptotic effect of these metabolic hormones on OM cells. Both Odora cells (an olfactive cell line) and OM cells treated with etoposide, a p53 activity inducer, exhibited mitochondrial-dependent apoptosis that was inhibited by the pan-caspase inhibitor zVAD-fmk. Insulin, but not leptin, impaired this apoptotic effect. Insulin addition to the culture medium reduced p53 phosphorylation, caspase-3 and caspase-9 cleavage, and caspase-3 enzymatic activity induced by etoposide. The apoptotic wave observed in the OM after interruption of the neuronal connections between the OM and the olfactory bulb by bulbectomy was impaired by intranasal insulin treatment. These findings suggest that insulin may be involved in OM cellular dynamics, through endocrine and/or paracrine-autocrine effects of circulating or local insulin, respectively.