The insulin-mediated modulation of visually evoked magnetic fields is reduced in obese subjects

Indigenous Medicinal Plants Used in the Management of Diabetes in Africa: 5 Years (2019-2024) in Perspective

(1) Background: The utilization of medicinal plants in the management of diabetes is of great importance to the health of the indigenous population on the African continent. The high cost of orthodox conventional medicines coupled with the perceived side effects encourages the high patronage of indigenous medicinal plants in the management of this metabolic disorder. We conducted a review on the indigenous African medicinal plants that could be useful in preclinical and clinical trials in the field of diabetes mellitus research. (2) Methods: Data were mined from research articles published and associated with the use of medicinal plants in the management of diabetes on the African continent (from January 2019 to March 2024). Literature from ethnobotanical studies on the African continent was searched from the Google Scholar, SCOPUS, Medline, Web of Science and PubMed databases. We employed the following keywords: "indigenous plants", "diabetes in Africa" and "antidiabetic effect of medicinal plants". (3) Results: A total of 52 medicinal plants belonging to 31 families were recorded in this study. Amaryllidaceae (14.28%), Fabaceae (9.52%) and Asteraceae (9.52%) were the most cited plant families. The frequently used indigenous medicinal plants on the African continent were Allium sativum L. (n = 6), Olea europaea L. (n = 6), Azadirachta indica A. Juss (n = 5), Allium cepa L. (n = 5) and Moringa oleifera Lam. (n = 5). The highly cited parts of the plant used in the management of diabetes were the leaves (45.55%), bark (14.44%) and bulbs (12.22%). The preferred methods of the preparation of herbal medicines were decoction (45.23%) and infusion (25%). Oral (52.32%) was the preferred route of the administration of herbal medicine on the African continent. (4) Conclusions: The data revealed some similarities in the way countries on the African continent manage diabetes. This interesting observation will assist in our quest towards obtaining a standardized protocol using indigenous medicinal plants to combat diseases on the African continent.

Spatiotemporal profile of altered neural reactivity to food images in obesity: Reward system is altered automatically and predicts efficacy of weight loss intervention

Introduction

Obesity presents a significant public health problem. Brain plays a central role in etiology and maintenance of obesity. Prior neuroimaging studies have found that individuals with obesity exhibit altered neural responses to images of food within the brain reward system and related brain networks. However, little is known about the dynamics of these neural responses or their relationship to later weight change. In particular, it is unknown if in obesity, the altered reward response to food images emerges early and automatically, or later, in the controlled stage of processing. It also remains unclear if the pretreatment reward system reactivity to food images is predictive of subsequent weight loss intervention outcome.

Methods

In this study, we presented high-calorie and low-calorie food, and nonfood images to individuals with obesity, who were then prescribed lifestyle changes, and matched normal-weight controls, and examined neural reactivity using magnetoencephalography (MEG). We performed whole-brain analysis to explore and characterize large-scale dynamics of brain systems affected in obesity, and tested two specific hypotheses: (1) in obese individuals, the altered reward system reactivity to food images occurs early and automatically, and (2) pretreatment reward system reactivity predicts the outcome of lifestyle weight loss intervention, with reduced activity associated with successful weight loss.

Results

We identified a distributed set of brain regions and their precise temporal dynamics that showed altered response patterns in obesity. Specifically, we found reduced neural reactivity to food images in brain networks of reward and cognitive control, and elevated reactivity in regions of attentional control and visual processing. The hypoactivity in reward system emerged early, in the automatic stage of processing (< 150 ms post-stimulus). Reduced reward and attention responsivity, and elevated neural cognitive control were predictive of weight loss after six months in treatment.

Discussion

In summary, we have identified, for the first time with high temporal resolution, the large-scale dynamics of brain reactivity to food images in obese versus normal-weight individuals, and have confirmed both our hypotheses. These findings have important implications for our understanding of neurocognition and eating behavior in obesity, and can facilitate development of novel integrated treatment strategies, including tailored cognitive-behavioral and pharmacological therapies.

The effect of intranasal insulin on appetite and mood in women with and without obesity: an experimental medicine study

BACKGROUND/OBJECTIVES

Intranasal (IN) administration of insulin decreases appetite in humans, but the underlying mechanisms are unclear, and it is unknown whether IN insulin affects the food intake of women with obesity.

SUBJECTS/METHODS

In a double-blind, placebo-controlled, crossover design, participants (35 lean women and 17 women with obesity) were randomized to receive 160 IU/1.6 mL of IN insulin or placebo in a counterbalanced order in the post prandial state. The effects of IN insulin on cookie intake, appetite, mood, food reward, cognition and neural activity were assessed.

RESULTS

IN insulin in the post prandial state reduced cookie intake, appetite and food reward relative to placebo and these effects were more pronounced for women with obesity compared with lean women. IN insulin also improved mood in women with obesity. In both BMI groups, IN insulin increased neural activity in the insula when viewing food pictures. IN insulin did not affect cognitive function.

CONCLUSIONS

These results suggest that IN insulin decreases palatable food intake when satiated by reducing food reward and that women with obesity may be more sensitive to this effect than lean women. Further investigation of the therapeutic potential of IN insulin for weight management in women with obesity is warranted.

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.

Appraisal of definition of baseline length for somatosensory evoked magnetic fields

BACKGROUND

The baseline (BL) segment in the prestimulus period is generally assigned as a reference of evoked activities. However, an experimenter empirically defines its length in each condition. So far, the criterion for the length of a BL segment has not been established.

NEW METHOD

We evaluated the effect of the length of the BL segment by recording somatosensory evoked magnetic fields (SEFs) under fixed stimulus onset asynchrony (SOA). For the evaluation of the length of the BL segment in the prestimulus period, five proportions in relation to SOA were used as the BL segment. In addition, we adopted other two types of BL segment which were the single data point measured from the value of stimulus onset (BL0) and the mean value of the whole raw data throughout the recording (DC mean). We investigated the influence of the BL segments on SEFs by utilizing two indicators: normalized N20 m amplitudes and estimated locations of corresponding equivalent current dipoles (ECDs).

RESULTS

Both indicators did not show any significant differences, based on the factor of BL segments, in any SOA conditions.

COMPARISON WITH EXISTING METHOD

The BL0 had by far the largest variation in the ECD locations.Therefore, utilizing stimulus onset as the BL segment should be avoided. In addition, considering that other BL segments provided comparable values by the two indicators, the DC mean can reasonably be adopted.

CONCLUSIONS

We suggest that utilizing the DC mean could be employed as the BL segment.

Insulin on the brain: The role of central insulin signalling in energy and glucose homeostasis

Insulin signals to the brain where it coordinates multiple physiological processes underlying energy and glucose homeostasis. This review explores where and how insulin interacts within the brain parenchyma, how brain insulin signalling functions to coordinate energy and glucose homeostasis and how this contributes to the pathogenesis of metabolic disease.

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.

Insights into Manipulating Postprandial Energy Expenditure to Manage Weight Gain in Polycystic Ovary Syndrome

Women with polycystic ovary syndrome (PCOS) are more likely to be obese and have difficulty in losing weight. They demonstrate an obesity-independent deficit in adaptive energy expenditure. We used a clinically realistic preclinical model to investigate the molecular basis for the reduced postprandial thermogenesis (PPT) and develop a therapeutic strategy to normalize this deficit. Sheep exposed to increased androgens before birth develop the clinical features of PCOS. In adulthood they develop obesity and demonstrate an obesity-independent reduction in PPT. This is associated with reduced adipose tissue uncoupling protein expression and adipose tissue noradrenaline concentrations. These sheep are insulin resistant with reduced insulin signaling in the brain. Increasing brain insulin concentrations using intranasal insulin administration increased PPT in PCOS sheep without any effects on blood glucose concentrations. Intranasal insulin administration with food is a potential novel strategy to improve adaptive energy expenditure and normalize the responses to weight loss strategies in women with PCOS.

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Obesity can be prenatally programmed by androgens in an ovine model of PCOS

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This model has the same deficit in postprandial energy expenditure as women with PCOS

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Reduced adipose tissue thermogenesis links to lower central insulin signaling

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Therapeutic intranasal insulin raises postprandial energy expenditure in PCOS sheep

Brain insulin sensitivity is linked to adiposity and body fat distribution

Brain insulin action regulates eating behavior and energy fluxes throughout the body. However, numerous people are brain insulin resistant. How brain insulin responsiveness affects long-term weight and body fat composition in humans is still unknown. Here we show that high brain insulin sensitivity before lifestyle intervention associates with a more pronounced reduction in total and visceral fat during the program. High brain insulin sensitivity is also associated with less regain of fat mass during a nine year follow-up. Cross-sectionally, strong insulin responsiveness of the hypothalamus associates with less visceral fat, while subcutaneous fat is unrelated. Our results demonstrate that high brain insulin sensitivity is linked to weight loss during lifestyle intervention and associates with a favorable body fat distribution. Since visceral fat is strongly linked to diabetes, cardiovascular risk and cancer, these findings have implications beyond metabolic diseases and indicate the necessity of strategies to resolve brain insulin resistance.

Brain insulin action regulates eating behavior and whole-body energy fluxes, however the impact of brain insulin resistance on long-term weight and body fat composition is unknown. Here, the authors show that high brain insulin sensitivity is linked to weight loss during lifestyle intervention and associates with a favorable body fat distribution.

Insulin Action in the Hypothalamus Increases Second-Phase Insulin Secretion in Humans

BACKGROUND

Animal studies and initial correlative data in humans indicate that insulin action in the brain may affect pancreatic insulin secretion. An important brain region for this process is the hypothalamus, an area that can develop insulin resistance.

METHODS

Fifteen young, healthy men (27 ± 3 years) with a wide BMI spectrum (20-30 kg/m2) underwent 2 hyperglycemic clamps (target blood glucose: 10 mmol/L). In this double-blind study, subjects received 160 U of insulin or placebo as a nasal spray on 2 days in randomized order. On another day, insulin sensitivity of the hypothalamus was determined by functional magnetic resonance imaging.

RESULTS

Glucose levels were comparable on both study days. In the whole group, C-peptide levels were not significantly different between conditions. Though, there was a significant interaction between insulin sensitivity of the hypothalamus × nasal spray × time on C-peptide levels (p = 10-6). The group was therefore divided according to median hypothalamic insulin sensitivity. C-peptide concentrations were higher after intranasal insulin compared to placebo spray in the group with a strong hypothalamic insulin response (p < 0.0001, β = 6.00 ± 1.24) and lower in the brain insulin-resistant group (p = 0.005, β = -2.68 ± 0.95). Neither somatostatin nor glucagon kinetics was altered by the nasal spray.

CONCLUSIONS

In participants with high hypothalamic insulin sensitivity, insulin action in the brain enhanced second-phase insulin secretion from pancreatic beta cells. This reaction could, for example, contribute to late postprandial glucose regulation by suppressing hepatic glucose production by portal venous insulin.

Programming of central and peripheral insulin resistance by low birthweight and postnatal catch-up growth in male mice

AIMS

Intra-uterine growth restriction (IUGR) followed by accelerated postnatal growth is associated with an increased risk of obesity and type 2 diabetes. We aimed to determine central and peripheral insulin sensitivity in mice that underwent IUGR followed by postnatal catch-up growth and investigate potential molecular mechanisms underpinning their physiology.

METHODS

We used a C57BL/6J mouse model of maternal diet-induced IUGR (maternal diet, 8% protein) followed by cross-fostering to a normal nutrition dam (maternal diet, 20% protein) and litter size manipulation to cause accelerated postnatal catch-up growth. We performed intracerebroventricular insulin injection and hyperinsulinaemic-euglycaemic clamp studies to examine the effect of this early nutritional manipulation on central and peripheral insulin resistance. Furthermore, we performed quantitative real-time PCR and western blotting to examine the expression of key insulin-signalling components in discrete regions of the hypothalamus.

RESULTS

IUGR followed by accelerated postnatal growth caused impaired glucose tolerance and peripheral insulin resistance. In addition, these 'recuperated' animals were resistant to the anorectic effects of central insulin administration. This central insulin resistance was associated with reduced protein levels of the p110β subunit of phosphoinositide 3-kinase (PI3K) and increased serine phosphorylation of IRS-1 in the arcuate nucleus (ARC) of the hypothalamus. Expression of the gene encoding protein tyrosine phosphatase 1B (PTP1B; Ptpn1) was also increased specifically in this region of the hypothalamus.

CONCLUSIONS/INTERPRETATION

Mice that undergo IUGR followed by catch-up growth display peripheral and central insulin resistance in adulthood. Recuperated offspring show changes in expression/phosphorylation of components of the insulin signalling pathway in the ARC. These defects may contribute to the resistance to the anorectic effects of central insulin, as well as the impaired glucose homeostasis seen in these animals.

Traumatic Brain Injury: At the Crossroads of Neuropathology and Common Metabolic Endocrinopathies

Building on the seminal work by Geoffrey Harris in the 1970s, the neuroendocrinology field, having undergone spectacular growth, has endeavored to understand the mechanisms of hormonal connectivity between the brain and the rest of the body. Given the fundamental role of the brain in the orchestration of endocrine processes through interactions among neurohormones, it is thus not surprising that the structural and/or functional alterations following traumatic brain injury (TBI) can lead to endocrine changes affecting the whole organism. Taking into account that systemic hormones also act on the brain, modifying its structure and biochemistry, and can acutely and chronically affect several neurophysiological endpoints, the question is to what extent preexisting endocrine dysfunction may set the stage for an adverse outcome after TBI. In this review, we provide an overview of some aspects of three common metabolic endocrinopathies, e.g., diabetes mellitus, obesity, and thyroid dysfunction, and how these could be triggered by TBI. In addition, we discuss how the complex endocrine networks are woven into the responses to sudden changes after TBI, as well as some of the potential mechanisms that, separately or synergistically, can influence outcomes after TBI.

An insulin resistance associated neural correlate of impulsivity in type 2 diabetes mellitus

Central insulin resistance (IR) influences striatal dopamine (DA) tone, an important determinant of behavioral self-regulation. We hypothesized that an association exists between the degree of peripheral IR and impulse control, mediated by the impact of IR on brain circuits controlling the speed of executing “go” and/or “stop” responses. We measured brain activation and associated performance on a stop signal task (SST) in obese adults with type 2 diabetes (age, 48.1 ± 6.9 yrs (mean ± SD); BMI, 36.5 ± 4.0 kg/m²; HOMA-IR, 7.2 ± 4.1; 12 male, 18 female). Increasing IR, but not BMI, was a predictor of shorter critical stop signal delay (cSSD), a measure of the time window during which a go response can be successfully countermanded (R² = 0.12). This decline was explained by an IR-associated increase in go speed (R² = 0.13) with little impact of IR or BMI on stop speed. Greater striatal fMRI activation contrast in stop error (SE) compared with stop success (SS) trials (CON_SE>SS) was a significant predictor of faster go speeds (R² = 0.33, p = 0.002), and was itself predicted by greater IR (CON_SE>SS vs HOMA-IR: R² = 0.10, p = 0.04). Furthermore, this impact of IR on striatal activation was a significant mediator of the faster go speeds and greater impulsivity observed with greater IR. These findings suggest a neural mechanism by which IR may increase impulsivity and degrade behavioral self-regulation.

Insulin action in the brain: Roles in energy and glucose homeostasis

A growing body of evidence from research in rodents and humans has identified insulin as an important neuoregulatory peptide in the brain, where it coordinates diverse aspects of energy balance and peripheral glucose homeostasis. This review discusses where and how insulin interacts within the brain and evaluates the physiological and pathophysiological consequences of central insulin signalling in metabolism, obesity and type 2 diabetes.

Brain Insulin Resistance at the Crossroads of Metabolic and Cognitive Disorders in Humans

Ever since the brain was identified as an insulin-sensitive organ, evidence has rapidly accumulated that insulin action in the brain produces multiple behavioral and metabolic effects, influencing eating behavior, peripheral metabolism, and cognition. Disturbances in brain insulin action can be observed in obesity and type 2 diabetes (T2D), as well as in aging and dementia. Decreases in insulin sensitivity of central nervous pathways, i.e., brain insulin resistance, may therefore constitute a joint pathological feature of metabolic and cognitive dysfunctions. Modern neuroimaging methods have provided new means of probing brain insulin action, revealing the influence of insulin on both global and regional brain function. In this review, we highlight recent findings on brain insulin action in humans and its impact on metabolism and cognition. Furthermore, we elaborate on the most prominent factors associated with brain insulin resistance, i.e., obesity, T2D, genes, maternal metabolism, normal aging, inflammation, and dementia, and on their roles regarding causes and consequences of brain insulin resistance. We also describe the beneficial effects of enhanced brain insulin signaling on human eating behavior and cognition and discuss potential applications in the treatment of metabolic and cognitive disorders.

Impaired insulin action in the human brain: causes and metabolic consequences

Over the past few years, evidence has accumulated that the human brain is an insulin-sensitive organ. Insulin regulates activity in a limited number of specific brain areas that are important for memory, reward, eating behaviour and the regulation of whole-body metabolism. Accordingly, insulin in the brain modulates cognition, food intake and body weight as well as whole-body glucose, energy and lipid metabolism. However, brain imaging studies have revealed that not everybody responds equally to insulin and that a substantial number of people are brain insulin resistant. In this Review, we provide an overview of the effects of insulin in the brain in humans and the relevance of the effects for physiology. We present emerging evidence for insulin resistance of the human brain. Factors associated with brain insulin resistance such as obesity and increasing age, as well as possible pathogenic factors such as visceral fat, saturated fatty acids, alterations at the blood-brain barrier and certain genetic polymorphisms, are reviewed. In particular, the metabolic consequences of brain insulin resistance are discussed and possible future approaches to overcome brain insulin resistance and thereby prevent or treat obesity and type 2 diabetes mellitus are outlined.

Brain-based etiology of weight regulation

Caloric intake and energy balance are highly regulated to maintain metabolic homeostasis and weight. However, hedonic-motivated food intake, in particular consumption of highly rewarding foods, may act to override hemostatic signaling and contribute to overconsumption, weight gain, and obesity. Here, we review human neuroimaging literature that has delivered valuable insight into the neural correlates of hedonic-motivated ingestive behavior, weight gain, weight loss, and metabolic status. Our primary focus is the brain regions that are thought to encode aspects of food hedonics, gustatory and somatosensory processing, and executive functioning. Further, we discuss the variability of regional brain response as a function of obesity, weight gain, behavioral and surgical weight loss, as well as in type 2 diabetes.

Insulin action in the human brain: evidence from neuroimaging studies

Thus far, little is known about the action of insulin in the human brain. Nonetheless, recent advances in modern neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) or magnetoencephalography (MEG), have made it possible to investigate the action of insulin in the brain in humans, providing new insights into the pathogenesis of brain insulin resistance and obesity. Using MEG, the clinical relevance of the action of insulin in the brain was first identified, linking cerebral insulin resistance with peripheral insulin resistance, genetic predisposition and weight loss success in obese adults. Although MEG is a suitable tool for measuring brain activity mainly in cortical areas, fMRI provides high spatial resolution for cortical as well as subcortical regions. Thus, the action of insulin can be detected within all eating behaviour relevant regions, which include regions deeply located within the brain, such as the hypothalamus, midbrain and brainstem, as well as regions within the striatum. In this review, we outline recent advances in the field of neuroimaging aiming to investigate the action of insulin in the human brain using different routes of insulin administration. fMRI studies have shown a significant insulin-induced attenuation predominantly in the occipital and prefrontal cortical regions and the hypothalamus, successfully localising insulin-sensitive brain regions in healthy, mostly normal-weight individuals. However, further studies are needed to localise brain areas affected by insulin resistance in obese individuals, which is an important prerequisite for selectively targeting brain insulin resistance in obesity.

The brain response to peripheral insulin declines with age: a contribution of the blood-brain barrier?

Objectives

It is a matter of debate whether impaired insulin action originates from a defect at the neural level or impaired transport of the hormone into the brain. In this study, we aimed to investigate the effect of aging on insulin concentrations in the periphery and the central nervous system as well as its impact on insulin-dependent brain activity.

Methods

Insulin, glucose and albumin concentrations were determined in 160 paired human serum and cerebrospinal fluid (CSF) samples. Additionally, insulin was applied in young and aged mice by subcutaneous injection or intracerebroventricularly to circumvent the blood-brain barrier. Insulin action and cortical activity were assessed by Western blotting and electrocorticography radiotelemetric measurements.

Results

In humans, CSF glucose and insulin concentrations were tightly correlated with the respective serum/plasma concentrations. The CSF/serum ratio for insulin was reduced in older subjects while the CSF/serum ratio for albumin increased with age like for most other proteins. Western blot analysis in murine whole brain lysates revealed impaired phosphorylation of AKT (P-AKT) in aged mice following peripheral insulin stimulation whereas P-AKT was comparable to levels in young mice after intracerebroventricular insulin application. As readout for insulin action in the brain, insulin-mediated cortical brain activity instantly increased in young mice subcutaneously injected with insulin but was significantly reduced and delayed in aged mice during the treatment period. When insulin was applied intracerebroventricularly into aged animals, brain activity was readily improved.

Conclusions

This study discloses age-dependent changes in insulin CSF/serum ratios in humans. In the elderly, cerebral insulin resistance might be partially attributed to an impaired transport of insulin into the central nervous system.

Intranasal Neuropeptide Administration To Target the Human Brain in Health and Disease

Central nervous system control of metabolic function relies on the input of endocrine messengers from the periphery, including the pancreatic hormone insulin and the adipokine leptin. This concept primarily derives from experiments in animals where substances can be directly applied to the brain. A feasible approach to study the impact of peptidergic messengers on brain function in humans is the intranasal (IN) route of administration, which bypasses the blood-brain barrier and delivers neuropeptides to the brain compartment, but induces considerably less, if any, peripheral uptake than other administration modes. Experimental IN insulin administration has been extensively used to delineate the role of brain insulin signaling in the control of energy homeostasis, but also cognitive function in healthy humans. Clinical pilot studies have found beneficial effects of IN insulin in patients with memory deficits, suggesting that the IN delivery of this and other peptides bears some promise for new, selectively brain-targeted pharmaceutical approaches in the treatment of metabolic and cognitive disorders. More recently, experiments relying on the IN delivery of the hypothalamic hormone oxytocin, which is primarily known for its involvement in psychosocial processes, have provided evidence that oxytocin influences metabolic control in humans. The IN administration of leptin has been successfully tested in animal models but remains to be investigated in the human setting. We briefly summarize the literature on the IN administration of insulin, leptin, and oxytocin, with a particular focus on metabolic effects, and address limitations and perspectives of IN neuropeptide administration.

[Targeting the brain through the nose. Effects of intranasally administered insulin]

The assumption that the human brain is an insulin-independent organ was disproved with the discovery of insulin receptors in the central nervous system in the year 1978. Evidence has been provided for a high density of insulin receptors in brain regions responsible for cognitive memory processes (hippocampus) and for the regulation of appetite (hypothalamus). Accordingly, in animal studies an increased insulin level in the central nervous system leads to an improvement of hippocampal memory function and a decrease of food intake. Similar results were obtained in humans using the method of intranasal administration of insulin. Intranasal insulin reaches the brain and the cerebrospinal fluid via the olfactory epithelium and olfactory nerve fiber bundles leading through the lamina cribrosa to the olfactory bulb. Thus, this method renders the investigation of specific insulin effects in humans possible. The therapeutic potential of an intranasal insulin administration for the treatment of diseases for which an imbalance of the central nervous insulin metabolism is discussed (e.g. Alzheimer's disease, diabetes mellitus and obesity) can only be estimated with the help of further clinical studies.

Polymorphism rs3123554 in CNR2 reveals gender-specific effects on body weight and affects loss of body weight and cerebral insulin action

OBJECTIVE

The cannabinoid-receptor system is involved in the regulation of food intake. Here, we test whether single nucleotide polymorphisms (SNPs) in CNR2, encoding the cannabinoid-receptor 2, are associated with weight in a cross-sectional cohort. Furthermore, we wanted to investigate if the identified hits influence weight loss during lifestyle intervention; and study a potential involvement of cerebral insulin action.

METHODS

2006 subjects at increased risk for type 2 diabetes mellitus were genotyped for 5 tagging SNPs in the CNR2 locus. All subjects underwent a 75-g OGTT. 345 subjects participated in a lifestyle intervention (TUebingen Lifestyle Intervention Programme). Cerebrocortical insulin sensitivity was measured by magnetoencephalography after intranasal insulin application in 43 subjects.

RESULTS

In the cross-sectional cohort, the minor allele of rs3123554 was associated with lower BMI (Padd = 0.01, Prec = 0.004), and this was attributable to its effect in women only. Interestingly, during lifestyle intervention, carriers of the same allele lost less body weight (Padd = 0.03, Prec = 0.008). Moreover, carriers of this minor allele showed lower cerebral insulin sensitivity (Prec = 0.0402).

CONCLUSIONS

The minor allele of rs3123554 is associated cross-sectionally with lower body weight, whereas during intervention the same allele led to less reduction of body weight. Reduced cerebral insulin sensitivity in carriers of this allele might contribute to these disadvantageous effects during lifestyle intervention.

Glucose-induced inhibition of the appetitive brain response to visual food cues in polycystic ovary syndrome patients

We postulate that insulin regulation of food intake is compromised when insulin resistance is present. In order to investigate the effect of insulin sensitivity on appetitive brain responses, we conducted functional magnetic resonance imaging studies in a group of women diagnosed with polycystic ovary syndrome (PCOS) in which insulin sensitivity ranged from normal to resistant. Subjects (n=19) were imaged while viewing pictures of high calorie (HC) foods and low calorie (LC) foods after ingesting either 75 g glucose or an equivalent volume of water. The insulin sensitive group showed reduced blood oxygen level dependent (BOLD) signal in response to food pictures following glucose ingestion in numerous corticolimbic brain regions, whereas the insulin resistant group did not. There was a significant interaction between insulin sensitivity (sensitive vs resistant) and condition (water vs glucose). The largest clusters identified included the left insula, bilateral limbic/parahippocampal gyrus/culmen/midbrain, bilateral limbic lobe/precuneus, and left superior/mid temporal gyrus/parietal for HC and LC stimuli combined, the left parahippocampal gyrus/fusiform/pulvinar/midbrain for HC pictures, and the left superior/mid temporal gyrus/parietal and middle/inferior frontal gyrus/orbitofrontal cortex for LC pictures. Furthermore, BOLD signal in the anterior cingulate, medial frontal gyrus, posterior cingulate/precuneus, and parietal cortex during a glucose challenge correlated negatively with insulin sensitivity. We conclude the PCOS women with insulin resistance have an impaired brain response to a glucose challenge. The inability of postprandial hyperinsulinemia to inhibit brain responsiveness to food cues in insulin resistant subjects may lead to greater non-homeostatic eating.

Variation in the obesity risk gene FTO determines the postprandial cerebral processing of food stimuli in the prefrontal cortex

Variation in FTO is the strongest genetic determinant of body weight and has recently been linked with impaired neural processing of food stimuli. However, whether this brain-expressed gene affects neuronal processing of food-related stimuli after ingestion is still poorly understood. In this study, twenty-four participants were examined before, 30 and 120 min after ingesting 75 g of glucose solution or water on two separate days. Functional magnetic resonance imaging (fMRI) during visual food presentation was performed. All participants were genotyped for FTO SNP rs8050136. We detected significant differences between FTO genotypes in the prefrontal cortex 30 min post-glucose load in BOLD-response to food pictures (p=0.0017), while no differences were detected in response to water ingestion or 120 min post-glucose load. Since the prefrontal cortex plays a major role in the inhibitory control of eating, we propose that reduced postprandial activity in FTO risk allele carriers contributes to overeating and obesity.

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.

Binge drinking induces whole-body insulin resistance by impairing hypothalamic insulin action

Individuals with a history of binge drinking have an increased risk of developing the metabolic syndrome and type 2 diabetes. Whether binge drinking impairs glucose homeostasis and insulin action is unknown. To test this, we treated Sprague-Dawley rats daily with alcohol (3 g/kg) for three consecutive days to simulate human binge drinking and found that these rats developed and exhibited insulin resistance even after blood alcohol concentrations had become undetectable. The animals were resistant to insulin for up to 54 hours after the last dose of ethanol, chiefly a result of impaired hepatic and adipose tissue insulin action. Because insulin regulates hepatic glucose production and white adipose tissue lipolysis, in part through signaling in the central nervous system, we tested whether binge drinking impaired brain control of nutrient partitioning. Rats that had consumed alcohol exhibited impaired hypothalamic insulin action, defined as the ability of insulin infused into the mediobasal hypothalamus to suppress hepatic glucose production and white adipose tissue lipolysis. Insulin signaling in the hypothalamus, as assessed by insulin receptor and AKT phosphorylation, decreased after binge drinking. Quantitative polymerase chain reaction showed increased hypothalamic inflammation and expression of protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin signaling. Intracerebroventricular infusion of CPT-157633, a small-molecule inhibitor of PTP1B, prevented binge drinking-induced glucose intolerance. These results show that, in rats, binge drinking induces systemic insulin resistance by impairing hypothalamic insulin action and that this effect can be prevented by inhibition of brain PTP1B.

Immediate neural responses of appetitive motives and its relationship with hedonic appetite and body weight as revealed by magnetoencephalography

Background

We aimed to determine the brain areas related to food motivation and to examine individual variability using magnetoencephalography (MEG) during a fasted state. Correlation analysis was performed between MEG responses and the subscale and aggregated scores of the Power of Food Scale (PFS) and body mass index (BMI).

Material/Methods

Eight healthy, right-handed males [age, 29.0±10.4 years; BMI, 22.7±2.4 kg/m² (mean ±SD)] were enrolled. The MEG experiment consisted of 2 food sessions and 2 control sessions in an alternating and counterbalanced order. During the MEG recordings, participants viewed a set of food pictures (food session) or mosaic pictures (control session) projected on a screen.

Results

When participants viewed pictures of food items, we were able to estimate equivalent current dipoles (ECDs) in the insular cortex in all participants peaked approximately 300 ms after the onset of each picture presentation. When they viewed mosaic pictures, 1 of 8 participants exhibited corresponding ECDs. Of note, significant correlations were observed between the intensities of the MEG responses and the subscale scores of Factor 1 (food available) (r=0.846, P=0.008) and those of Factor 2 (food present) (r=0.875, P=0.004), the aggregated scores of PFS (r=0.820, P=0.013), and BMI (r=0.898, P=0.002).

Conclusions

We demonstrated the involvement of the immediate neural responses of the insular cortex in individual differences in appetitive motivation. The signal intensities of the insular cortex were associated with self-awareness of appetitive motive.

Differential effect of glucose ingestion on the neural processing of food stimuli in lean and overweight adults

Eating behavior is crucial in the development of obesity and Type 2 diabetes. To further investigate its regulation, we studied the effects of glucose versus water ingestion on the neural processing of visual high and low caloric food cues in 12 lean and 12 overweight subjects by functional magnetic resonance imaging. We found body weight to substantially impact the brain's response to visual food cues after glucose versus water ingestion. Specifically, there was a significant interaction between body weight, condition (water versus glucose), and caloric content of food cues. Although overweight subjects showed a generalized reduced response to food objects in the fusiform gyrus and precuneus, the lean group showed a differential pattern to high versus low caloric foods depending on glucose versus water ingestion. Furthermore, we observed plasma insulin and glucose associated effects. The hypothalamic response to high caloric food cues negatively correlated with changes in blood glucose 30 min after glucose ingestion, while especially brain regions in the prefrontal cortex showed a significant negative relationship with increases in plasma insulin 120 min after glucose ingestion. We conclude that the postprandial neural processing of food cues is highly influenced by body weight especially in visual areas, potentially altering visual attention to food. Furthermore, our results underline that insulin markedly influences prefrontal activity to high caloric food cues after a meal, indicating that postprandial hormones may be potential players in modulating executive control.

Metabolic neuroimaging of the brain in diabetes mellitus and hypoglycaemia

Functional neuroimaging techniques can be used to study changes in regional brain activation, using changes in surrogate markers such as regional cerebral perfusion and rates of glucose uptake or metabolism. These approaches are shedding new light on two major health problems: the increasing burden of type 2 diabetes mellitus (T2DM), which is driven by the rising prevalence of insulin resistance and obesity; and recurrent intractable problematic hypoglycaemia, which is driven by the cognitive impairment that can occur in association with iatrogenic hypoglycaemic episodes. Some patients with diabetes mellitus lose awareness of being hypoglycaemic, which puts them at risk of severe hypoglycaemia as they are unlikely to take action to prevent the condition worsening. Involvement of corticolimbic brain and centres serving higher executive functions as well as the hypothalamus has been demonstrated in both situations and has implications for therapy. This Review describes the relevant principles of functional neuroimaging techniques and presents data supporting the notion that the dysregulation of central pathways involved in metabolic regulation, reward and appetite could contribute to problematic hypoglycaemia during therapy for diabetes mellitus and to insulin-resistant obesity and T2DM. Understanding these dysregulations could enable the development of novel clinical interventions.

Monounsaturated fatty acids prevent the aversive effects of obesity on locomotion, brain activity, and sleep behavior

Fat and physical inactivity are the most evident factors in the pathogenesis of obesity, and fat quality seems to play a crucial role for measures of glucose homeostasis. However, the impact of dietary fat quality on brain function, behavior, and sleep is basically unknown. In this study, mice were fed a diet supplemented with either monounsaturated fatty acids (MUFAs) or saturated fatty acids (SFAs) and their impact on glucose homeostasis, locomotion, brain activity, and sleep behavior was evaluated. MUFAs and SFAs led to a significant increase in fat mass but only feeding of SFAs was accompanied by glucose intolerance in mice. Radiotelemetry revealed a significant decrease in cortical activity in SFA-mice whereas MUFAs even improved activity. SFAs decreased wakefulness and increased non-rapid eye movement sleep. An intracerebroventricular application of insulin promoted locomotor activity in MUFA-fed mice, whereas SFA-mice were resistant. In humans, SFA-enriched diet led to a decrease in hippocampal and cortical activity determined by functional magnetic resonance imaging techniques. Together, dietary intake of MUFAs promoted insulin action in the brain with its beneficial effects for cortical activity, locomotion, and sleep, whereas a comparable intake of SFAs acted as a negative modulator of brain activity in mice and humans.

Nasal insulin changes peripheral insulin sensitivity simultaneously with altered activity in homeostatic and reward-related human brain regions

AIMS/HYPOTHESIS

Impaired insulin sensitivity is a major factor leading to type 2 diabetes. Animal studies suggest that the brain is involved in the regulation of insulin sensitivity. We investigated whether insulin action in the human brain regulates peripheral insulin sensitivity and examined which brain areas are involved.

METHODS

Insulin and placebo were given intranasally. Plasma glucose, insulin and C-peptide were measured in 103 participants at 0, 30 and 60 min. A subgroup (n = 12) was also studied with functional MRI, and blood sampling at 0, 30 and 120 min. For each time-point, the HOMA of insulin resistance (HOMA-IR) was calculated as an inverse estimate of peripheral insulin sensitivity.

RESULTS

Plasma insulin increased and subsequently decreased. This excursion was accompanied by slightly decreased plasma glucose, resulting in an initially increased HOMA-IR. At 1 h after insulin spray, the HOMA-IR subsequently decreased and remained lower up to 120 min. An increase in hypothalamic activity was observed, which correlated with the increased HOMA-IR at 30 min post-spray. Activity in the putamen, right insula and orbitofrontal cortex correlated with the decreased HOMA-IR at 120 min post-spray.

CONCLUSIONS/INTERPRETATION

Central insulin action in specific brain areas, including the hypothalamus, may time-dependently regulate peripheral insulin sensitivity. This introduces a potential novel mechanism for the regulation of peripheral insulin sensitivity and underlines the importance of cerebral insulin action for the whole organism.

Fat intake modulates cerebral blood flow in homeostatic and gustatory brain areas in humans

BACKGROUND

The hypothalamus is the central homeostatic control region of the brain and, therefore, highly influenced by nutrients such as glucose and fat. Immediate and prolonged homeostatic effects of glucose ingestion have been well characterized. However, studies that used stimulation with fat have mainly investigated immediate perceptional processes. Besides homeostatic processes, the gustatory cortex, including parts of the insular cortex, is crucial for the processing of food items.

OBJECTIVE

The aim of this study was to investigate the effect of high- compared with low-fat meals on the hypothalamus and the insular cortex.

DESIGN

Eleven healthy men participated in a single-blinded, functional MRI study of high- and low-fat meals on 2 measurement days. Cerebral blood flow (CBF) was measured before and 30 and 120 min after intake of high- and low-fat yogurts. Hunger was rated and blood samples were taken before each CBF measurement.

RESULTS

High-fat yogurt induced a pronounced decrease in CBF in the hypothalamus, and the corresponding CBF change correlated positively with the insulin change. Furthermore, insular activity increased after 120 min in the low-fat condition only. The CBF change in both regions correlated positively in the high-fat condition.

CONCLUSIONS

The decrease in hypothalamic activity and the interaction with the insular cortex elicited by fat may contribute to an efficient energy homeostasis. Therefore, fat might be a modulator of homeostatic and gustatory brain regions and their interaction. This trial was registered at clinicaltrials.gov as NCT01516021.

Postprandial administration of intranasal insulin intensifies satiety and reduces intake of palatable snacks in women

The role of brain insulin signaling in the control of food intake in humans has not been thoroughly defined. We hypothesized that the hormone contributes to the postprandial regulation of appetite for palatable food, and assessed the effects on appetite and snack intake of postprandial versus fasted intranasal insulin administration to the brain in healthy women. Two groups of subjects were intranasally administered 160 IU insulin or vehicle after lunch. Two hours later, consumption of cookies of varying palatability was measured under the pretext of a taste test. In a control study, the effects of intranasal insulin administered to fasted female subjects were assessed. Compared with placebo, insulin administration in the postprandial but not in the fasted state decreased appetite as well as intake and rated palatability of chocolate chip cookies (the most palatable snack offered). In both experiments, intranasal insulin induced a slight decrease in plasma glucose but did not affect serum insulin concentrations. Data indicate that brain insulin acts as a relevant satiety signal during the postprandial period, in particular reducing the intake of highly palatable food, and impacts peripheral glucose homeostasis. Postprandial intranasal insulin administration might be useful in curtailing overconsumption of snacks with accentuated rewarding value.

Intranasal administration of insulin to the brain impacts cognitive function and peripheral metabolism

In recent years, the central nervous system (CNS) has emerged as a principal site of insulin action. This notion is supported by studies in animals relying on intracerebroventricular insulin infusion and by experiments in humans that make use of the intranasal pathway of insulin administration to the brain. Employing neurobehavioural and metabolic measurements as well as functional imaging techniques, these studies have provided insight into a broad range of central and peripheral effects of brain insulin. The present review focuses on CNS effects of insulin administered via the intranasal route on cognition, in particular memory function, and whole-body energy homeostasis including glucose metabolism. Furthermore, evidence is reviewed that suggests a pathophysiological role of impaired brain insulin signaling in obesity and type 2 diabetes, which are hallmarked by peripheral and possibly central nervous insulin resistance, as well as in conditions such as Alzheimer's disease where CNS insulin resistance might contribute to cognitive dysfunction.

Toll-like receptors 2 and 4 impair insulin-mediated brain activity by interleukin-6 and osteopontin and alter sleep architecture

Impaired insulin action in the brain represents an early step in the progression toward type 2 diabetes, and elevated levels of saturated free fatty acids are known to impair insulin action in prediabetic subjects. One potential mediator that links fatty acids to inflammation and insulin resistance is the Toll-like receptor (TLR) family. Therefore, C3H/HeJ/TLR2-KO (TLR2/4-deficient) mice were fed a high-fat diet (HFD), and insulin action in the brain as well as cortical and locomotor activity was analyzed by using telemetric implants. TLR2/4-deficient mice were protected from HFD-induced glucose intolerance and insulin resistance in the brain and displayed an improvement in cortical and locomotor activity that was not observed in C3H/HeJ mice. Sleep recordings revealed a 42% increase in rapid eye movement sleep in the deficient mice during daytime, and these mice spent 41% more time awake during the night period. Treatment of control mice with a neutralizing IL-6 antibody improved insulin action in the brain as well as cortical activity and diminished osteopontin protein to levels of the TLR2/4-deficient mice. Together, our data suggest that the lack of functional TLR2/4 protects mice from a fat-mediated impairment in insulin action, brain activity, locomotion, and sleep architecture by an IL-6/osteopontin-dependent mechanism.