Cerebrocortical beta activity in overweight humans responds to insulin detemir

The insulin resistant brain: impact on whole-body metabolism and body fat distribution

Insulin exerts its actions not only on peripheral organs but is also transported into the brain where it performs distinct functions in various brain regions. This review highlights recent advancements in our understanding of insulin's actions within the brain, with a specific emphasis on investigations in humans. It summarises current knowledge on the transport of insulin into the brain. Subsequently, it showcases robust evidence demonstrating the existence and physiological consequences of brain insulin action, while also introducing the presence of brain insulin resistance in humans. This pathophysiological condition goes along with an impaired acute modulation of peripheral metabolism in response to brain insulin action, particularly in the postprandial state. Furthermore, brain insulin resistance has been associated with long-term adiposity and an unfavourable adipose tissue distribution, thus implicating it in the pathogenesis of subgroups of obesity and (pre)diabetes that are characterised by distinct patterns of body fat distribution. Encouragingly, emerging evidence suggests that brain insulin resistance could represent a treatable entity, thereby opening up novel therapeutic avenues to improve systemic metabolism and enhance brain functions, including cognition. The review closes with an outlook towards prospective research directions aimed at further elucidating the clinical implications of brain insulin resistance. It emphasises the critical need to establish feasible diagnostic measures and effective therapeutic interventions.

Epigenetic Alterations in Alzheimer's Disease: Impact on Insulin Signaling and Advanced Drug Delivery Systems

Alzheimer's disease (AD) is a neurodegenerative condition that predominantly affects the hippocampus and the entorhinal complex, leading to memory lapse and cognitive impairment. This can have a negative impact on an individual's behavior, speech, and ability to navigate their surroundings. AD is one of the principal causes of dementia. One of the most accepted theories in AD, the amyloid β (Aβ) hypothesis, assumes that the buildup of the peptide Aβ is the root cause of AD. Impaired insulin signaling in the periphery and central nervous system has been considered to have an effect on the pathophysiology of AD. Further, researchers have shifted their focus to epigenetic mechanisms that are responsible for dysregulating major biochemical pathways and intracellular signaling processes responsible for directly or indirectly causing AD. The prime epigenetic mechanisms encompass DNA methylation, histone modifications, and non-coding RNA, and are majorly responsible for impairing insulin signaling both centrally and peripherally, thus leading to AD. In this review, we provide insights into the major epigenetic mechanisms involved in causing AD, such as DNA methylation and histone deacetylation. We decipher how the mechanisms alter peripheral insulin signaling and brain insulin signaling, leading to AD pathophysiology. In addition, this review also discusses the need for newer drug delivery systems for the targeted delivery of epigenetic drugs and explores targeted drug delivery systems such as nanoparticles, vesicular systems, networks, and other nano formulations in AD. Further, this review also sheds light on the future approaches used for epigenetic drug delivery.

Daily intranasal insulin at 40IU does not affect food intake and body composition: A placebo-controlled trial in older adults over a 24-week period with 24-weeks of follow-up

Centrally administered insulin stimulates the reward system to reduce appetite in response to food intake in animal studies. In humans, studies have shown conflicting results, with some studies suggesting that intranasal insulin (INI) in relatively high doses may decrease appetite, body fat, and weight in various populations. These hypotheses have not been tested in a large longitudinal placebo-controlled study. Participants in the Memory Advancement with Intranasal Insulin in Type 2 Diabetes (MemAID) trial were enrolled in this study. This study on energy homeostasis enrolled 89 participants who completed baseline and at least 1 intervention visit (42 women; age 65 ± 9 years; 46 INI, 38 with type 2 diabetes) and 76 completed treatment (16 women, age 64 ± 9; 38 INI, 34 with type 2 diabetes). The primary outcome was the INI effect on food intake. Secondary outcomes included the effect of INI on appetite and anthropometric measures, including body weight and body composition. In exploratory analyses, we tested the interaction of treatment with gender, body mass index (BMI), and diagnosis of type 2 diabetes. There was no INI effect on food intake or any of the secondary outcomes. INI also showed no differential effect on primary and secondary outcomes when considering gender, BMI, and type 2 diabetes. INI did not alter appetite or hunger nor cause weight loss when used at 40 I.U. intranasally daily for 24 weeks in older adults with and without type 2 diabetes.

Novel Noninvasive Approaches to the Treatment of Obesity: From Pharmacotherapy to Gene Therapy

Recent insights into the pathophysiologic underlying mechanisms of obesity have led to the discovery of several promising drug targets and novel therapeutic strategies to address the global obesity epidemic and its comorbidities. Current pharmacologic options for obesity management are largely limited in number and of modest efficacy/safety profile. Therefore, the need for safe and more efficacious new agents is urgent. Drugs that are currently under investigation modulate targets across a broad range of systems and tissues, including the central nervous system, gastrointestinal hormones, adipose tissue, kidney, liver, and skeletal muscle. Beyond pharmacotherapeutics, other potential antiobesity strategies are being explored, including novel drug delivery systems, vaccines, modulation of the gut microbiome, and gene therapy. The present review summarizes the pathophysiology of energy homeostasis and highlights pathways being explored in the effort to develop novel antiobesity medications and interventions but does not cover devices and bariatric methods. Emerging pharmacologic agents and alternative approaches targeting these pathways and relevant research in both animals and humans are presented in detail. Special emphasis is given to treatment options at the end of the development pipeline and closer to the clinic (ie, compounds that have a higher chance to be added to our therapeutic armamentarium in the near future). Ultimately, advancements in our understanding of the pathophysiology and interindividual variation of obesity may lead to multimodal and personalized approaches to obesity treatment that will result in safe, effective, and sustainable weight loss until the root causes of the problem are identified and addressed.

Polycystic ovary syndrome is linked with the fat mass obesity (FTO) gene variants rs17817449 and rs1421085 in western Saudi Arabia

Polycystic ovary syndrome (PCOS) is characterised by infertility, obesity, insulin resistance and clinical and/or biochemical signs of hyperandrogenism. Obesity is known to be correlated with PCOS causing ovulatory dysfunction and hormone imbalances. Moreover, fat mass and the obesity gene (FTO) were linked with obesity and PCOS. Therefore, it is of interest to determine the genotype and allele frequency for three FTO variants - rs17817449 (G/T), rs1421085 (C/T) and rs8050136 (A/C) -in western Saudi population. 95 PCOS patients and 94 controls were recruited for this study. The genetic variants were assayed using real-time polymerase chain reaction using TaqMan genotyping assays. The chi-squared test was applied to investigate the difference between single nucleotide polymorphisms on PCOS and control subjects, and binary logistic regression was used to determine the association of FTO variants with PCOS symptoms. Variants rs17817449 and rs1421085 were significantly linked with PCOS susceptibility in the study population. Rs17817449 and rs8050136 were significantly associated with hair loss in the PCOS group. Furthermore, rs1421085 and rs8050136 were associated with a high body mass index (BMI>30 kg/m2). Risk alleles in our population associated with hair loss and elevated BMI in women with PCOS were homozygous C for rs8050136. This data will help in defining the genetic predisposition of PCOS among women in western Saudi Arabia.

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.

Nasal insulin administration does not affect hepatic glucose production at systemic fasting insulin levels

AIMS

To evaluate the effects of brain insulin on endogenous glucose production in fasting humans, with a focus on hepatic glucose release by performing a randomized, placebo-controlled, blinded, crossover experiment.

MATERIALS AND METHODS

On two separate days, ² H₂ -glucose was infused to nine healthy lean men, and blood was sampled from the hepatic vein and a radial artery. On day 1, participants received 160 U human insulin through nasal spray, and on day 2 they received placebo spray, together with an intravenous insulin bolus to mimic spillover of nasal insulin to the circulation. Hepatic glucose fluxes and endogenous glucose production were calculated.

RESULTS

Plasma insulin concentrations were similar on the two study days, and no differences in whole-body endogenous glucose production or hepato-splanchnic glucose turnover were detected.

CONCLUSIONS

Nasal administration of insulin does not influence whole-body or hepatic glucose production in fasting humans. By contrast, pharmacological delivery of insulin to the brain might modulate insulin effectiveness in glucose-producing tissue when circulating insulin levels are elevated; therefore, the metabolic consequences of brain insulin action appear to be dependent on metabolic prandial status.

Oral Glucose Tolerance is Associated with Neuroelectric Indices of Attention Among Adults with Overweight and Obesity

OBJECTIVE

This study aimed to elucidate the relationship between glucose levels and insulin resistance and sensitivity obtained from oral glucose tolerance tests and neurophysiological indices of attention among adults with overweight and obesity.

METHODS

Forty adults with overweight or obesity (BMI ≥ 25 kg/m² ) underwent dual-energy x-ray absorptiometry to assess visceral adipose tissue. Repeated venous blood samples were collected during an oral glucose tolerance test to measure insulin resistance (homeostatic model assessment of insulin resistance) and indices of insulin sensitivity (Matsuda index and Stumvoll metabolic clearance rate). Attention was assessed using event-related brain potentials recorded during a visual oddball task. Amplitude and latency of the P3 wave form in a central-parietal region of interest were used to index attentional resource allocation and information processing speed.

RESULTS

Following adjustment for visceral adipose tissue, reduced values of Matsuda index and Stumvoll metabolic clearance rate (indicating poor insulin sensitivity) were correlated with longer peak latency, whereas insulin area under the curve was positively related to peak latency, indicating slower information processing. Individuals with decreased insulin sensitivity (Matsuda index < 4.3) had significantly longer P3 latencies compared with individuals with normal insulin sensitivity.

CONCLUSIONS

Higher fasting glucose, but not homeostatic model assessment of insulin resistance, and reduced indices of glucose sensivity are associated with decrements in attention characterized by slower reaction time and slower information processing speed among adults with overweight and obesity.

Insulin Regulates GABAA Receptor-Mediated Tonic Currents in the Prefrontal Cortex

Recent studies, have shown that insulin increases extrasynaptic GABA_A receptor-mediated currents in the hippocampus, causing alterations of neuronal excitability. The prefrontal cortex (PFC) is another brain area which is involved in cognition functions and expresses insulin receptors. Here, we used electrophysiological, molecular, and immunocytochemical techniques to examine the effect of insulin on the extrasynaptic GABA_A receptor-mediated tonic currents in brain slices. We found that insulin (20–500 nM) increases GABA_A-mediated tonic currents. Our results suggest that insulin promotes the trafficking of extrasynaptic GABA_A receptors from the cytoplasm to the cell membrane. Western blot analysis and immunocytochemistry showed that PFC extrasynaptic GABA_A receptors contain α-5 and δ subunits. Insulin effect on tonic currents decreased the firing rate and neuronal excitability in layer 5–6 PFC cells. These effects of insulin were dependent on the activation of the PI3K enzyme, a key mediator of the insulin response within the brain. Taken together, these results suggest that insulin modulation of the GABA_A-mediated tonic currents can modify the activity of neural circuits within the PFC. These actions could help to explain the alterations of cognitive processes associated with changes in insulin signaling.

Effects of Regular and Long-Acting Insulin on Cognition and Alzheimer's Disease Biomarkers: A Pilot Clinical Trial

Background: Long acting insulin detemir administered intranasally for three weeks enhanced memory for adults with Alzheimer’s disease dementia (AD) or amnestic mild cognitive impairment (MCI). The investigation of longer-term administration is necessary to determine whether benefits persist, whether they are similar to benefits provided by regular insulin, and whether either form of insulin therapy affects AD biomarkers.

Objective: The present study aimed to determine whether four months of treatment with intranasal insulin detemir or regular insulin improves cognition, daily functioning, and AD biomarkers for adults with MCI or AD.

Methods: This randomized, double-blind, placebo-controlled trial included an intent-to-treat sample consisting of 36 adults diagnosed with MCI or mild to moderate AD. Participants received placebo (n = 12), 40 IU of insulin detemir (n = 12), or 40 IU of regular insulin (n = 12) daily for four months, administered with a nasal delivery device. A cognitive battery was administered at baseline and after two and four months of treatment. MRI was administered for all participants and lumbar puncture for a subset (n = 20) at baseline and four months. The primary outcome was change from baseline to four months on a memory composite (sum of Z scores for delayed list and story recall). Secondary outcomes included: global cognition (Alzheimer’s Disease Assessment Scale-Cognition), daily functioning (Dementia Severity Rating Scale), MRI volume changes in AD-related regions of interest, and cerebrospinal fluid AD markers.

Results: The regular insulin treated group had better memory after two and four months compared with placebo (p < 0.03). No significant effects were observed for the detemir-assigned group compared with the placebo group, or for daily functioning for either group. Regular insulin treatment was associated with preserved volume on MRI. Regular insulin treatment was also associated with reduction in the tau-P181/Aβ₄₂ ratio.

Conclusion: Future research is warranted to examine the mechanistic basis of treatment differences, and to further assess the efficacy and safety of intranasal insulin.

How Does Exercise Reduce the Rate of Age-Associated Cognitive Decline? A Review of Potential Mechanisms

The rate of age-associated cognitive decline varies considerably between individuals. It is important, both on a societal and individual level, to investigate factors that underlie these differences in order to identify those which might realistically slow cognitive decline. Physical activity is one such factor with substantial support in the literature. Regular exercise can positively influence cognitive ability, reduce the rate of cognitive aging, and even reduce the risk of Alzheimer's disease (AD) and other dementias. However, while there is substantial evidence in the extant literature for the effect of exercise on cognition, the processes that mediate this relationship are less clear. This review examines cardiovascular health, production of brain derived neurotrophic factor (BDNF), insulin sensitivity, stress, and inflammation as potential pathways, via which exercise may maintain or improve cognitive functioning, and may be particularly pertinent in the context of the aging brain. A greater understanding of these mechanisms and their potential relationships with exercise and cognition will be invaluable in providing biomarkers for investigating the efficacy of differing exercise regimes on cognitive outcomes.

Central effects of insulin detemir on feeding, body weight, and metabolism in rats

Insulin detemir (DET) is a basal insulin analog that, in contrast to other long-acting forms of insulin, has significant weight-gain-sparing effects in diabetic patients. We hypothesized that this effect of DET may be due to its enhanced catabolic action in the central nervous system. We investigated the long-term effects of single third ventricular (3V) microinjections of equimolar doses of DET and regular insulin in normal male rats on feeding, body weight, energy expenditure (EE), and respiratory quotient (RQ). Also, in acute testing, we assessed the ability of lower doses of DET to alter feeding, EE, and RQ when microinjected directly into the paraventricular nucleus (PVN). The anabolic peptide ghrelin served as a positive control in acute testing. 3V administration of both DET (0.5-2.0 mU) and regular insulin (2.0-8.0 mU) significantly reduced feeding and body weight over 48 and 120 h, respectively, with DET yielding greater inhibitory effects. DET also stimulated greater elevations of EE and reductions of RQ over 72 and 48 h postinjection, respectively. In acute (4 h) testing, microinjections of DET (0.5 mU) into the PVN reduced feeding, increased EE, and reduced RQ, while ghrelin (100 pmol) had the opposite effects. When administered sequentially into the PVN, DET (0.25 and 0.5 mU) reversed ghrelin-induced feeding, EE, and RQ effects. These data support the notion that the weight-sparing effect of DET is at least in part based on its central catabolic action and that enhanced EE and reduced RQ may participate in this effect.

Hypothalamic and Striatal Insulin Action Suppresses Endogenous Glucose Production and May Stimulate Glucose Uptake During Hyperinsulinemia in Lean but Not in Overweight Men

Intranasal spray application facilitates insulin delivery to the human brain. Although brain insulin modulates peripheral metabolism, the mechanisms involved remain elusive. Twenty-one men underwent two hyperinsulinemic-euglycemic clamps with d-[6,6-²H₂]glucose infusion to measure endogenous glucose production and glucose disappearance. On two separate days, participants received intranasal insulin or placebo. Insulin spillover into circulation after intranasal insulin application was mimicked by an intravenous insulin bolus on placebo day. On a different day, brain insulin sensitivity was assessed by functional MRI. Glucose infusion rates (GIRs) had to be increased more after nasal insulin than after placebo to maintain euglycemia in lean but not in overweight people. The increase in GIRs was associated with regional brain insulin action in hypothalamus and striatum. Suppression of endogenous glucose production by circulating insulin was more pronounced after administration of nasal insulin than after placebo. Furthermore, glucose uptake into tissue tended to be higher after nasal insulin application. No such effects were detected in overweight participants. By increasing insulin-mediated suppression of endogenous glucose production and stimulating peripheral glucose uptake, brain insulin may improve glucose metabolism during systemic hyperinsulinemia. Obese people appear to lack these mechanisms. Therefore, brain insulin resistance in obesity may have unfavorable consequences for whole-body glucose homeostasis.

Deciphering Brain Insulin Receptor and Insulin-Like Growth Factor 1 Receptor Signalling

Insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1R) are highly conserved receptor tyrosine kinases that share signalling proteins and are ubiquitously expressed in the brain. Central application of insulin or IGF1 exerts several similar physiological outcomes, varying in strength, whereas disruption of the corresponding receptors in the brain leads to remarkably different effects on brain size and physiology, thus highlighting the unique effects of the corresponding hormone receptors. Central insulin/IGF1 resistance impacts upon various levels of the IR/IGF1R signalling pathways and is a feature of the metabolic syndrome and neurodegenerative diseases such as Alzheimer's disease. The intricacy of brain insulin and IGF1 signalling represents a challenge for the identification of specific IR and IGF1R signalling differences in pathophysiological conditions. The present perspective sheds light on signalling differences and methodologies for specifically deciphering brain IR and IGF1R signalling.

Sustained Treatment with Insulin Detemir in Mice Alters Brain Activity and Locomotion

Aims

Recent studies have identified unique brain effects of insulin detemir (Levemir^®). Due to its pharmacologic properties, insulin detemir may reach higher concentrations in the brain than regular insulin. This might explain the observed increased brain stimulation after acute insulin detemir application but it remained unclear whether chronic insulin detemir treatment causes alterations in brain activity as a consequence of overstimulation.

Methods

In mice, we examined insulin detemir’s prolonged brain exposure by continuous subcutaneous (s.c.) application using either micro-osmotic pumps or daily s.c. injections and performed continuous radiotelemetric electrocorticography and locomotion recordings.

Results

Acute intracerebroventricular injection of insulin detemir activated cortical and locomotor activity significantly more than regular insulin in equimolar doses (0.94 and 5.63 mU in total), suggesting an enhanced acute impact on brain networks. However, given continuously s.c., insulin detemir significantly reduced cortical activity (theta: 21.3±6.1% vs. 73.0±8.1%, P<0.001) and failed to maintain locomotion, while regular insulin resulted in an increase of both parameters.

Conclusions

The data suggest that permanently-increased insulin detemir levels in the brain convert its hyperstimulatory effects and finally mediate impairments in brain activity and locomotion. This observation might be considered when human studies with insulin detemir are designed to target the brain in order to optimize treatment regimens.

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.

Weight-sparing effect of insulin detemir: a consequence of central nervous system-mediated reduced energy intake?

Insulin therapy is often associated with adverse weight gain. This is attributable, at least in part, to changes in energy balance and insulin's anabolic effects. Adverse weight gain increases the risk of poor macrovascular outcomes in people with diabetes and should therefore be mitigated if possible. Clinical studies have shown that insulin detemir, a basal insulin analogue, exerts a unique weight-sparing effect compared with other basal insulins. To understand this property, several hypotheses have been proposed. These explore the interplay of efferent and afferent signals between the muscles, brain, liver, renal and adipose tissues in response to insulin detemir and comparator basal insulins. The following models have been proposed: insulin detemir may reduce food intake through direct or indirect effects on the central nervous system (CNS); it may have favourable actions on hepatic glucose metabolism through a selective effect on the liver, or it may influence fluid homeostasis through renal effects. Studies have consistently shown that insulin detemir reduces energy intake, and moreover, it is clear that this shift in energy balance is not a consequence of reduced hypoglycaemia. CNS effects may be mediated by direct action, by indirect stimulation by peripheral mediators and/or via a more physiological counter-regulatory response to insulin through restoration of the hepatic-peripheral insulin gradient. Although the precise mechanism remains unclear, it is likely that the weight-sparing effect of insulin detemir can be explained by a combination of mechanisms. The evidence for each hypothesis is considered in this review.

Insulin Detemir Is Transported From Blood to Cerebrospinal Fluid and Has Prolonged Central Anorectic Action Relative to NPH Insulin

Insulin detemir (DET) reduces glycemia comparably to other long-acting insulin formulations but causes less weight gain. Insulin signaling in the brain is catabolic, reducing food intake. We hypothesized that DET reduces weight gain, relative to other insulins, owing to increased transport into the central nervous system and/or increased catabolic action within the brain. Transport of DET and NPH insulin into the cerebrospinal fluid (CSF) was compared over several hours and after the administration of different doses peripherally in rats. DET and NPH had comparable saturable, receptor-mediated transport into the CSF. CSF insulin remained elevated significantly longer after intraperitoneal DET than after NPH. When administered acutely into the 3rd cerebral ventricle, both DET and NPH insulin reduced food intake and body weight at 24 h, and both food intake and body weight remained lower after DET than after NPH after 48 h. In direct comparison with another long-acting insulin, insulin glargine (GLAR), DET led to more prolonged increases in CSF insulin despite a shorter plasma half-life in both rats and mice. Additionally, peripheral DET administration reduced weight gain and increased CSF insulin compared with saline or GLAR in mice. Overall, these data support the hypothesis that DET has distinct effects on energy balance through enhanced and prolonged centrally mediated reduction of food intake.

Selective insulin resistance in homeostatic and cognitive control brain areas in overweight and obese adults

OBJECTIVE

Impaired brain insulin action has been linked to obesity, type 2 diabetes, and neurodegenerative diseases. To date, the central nervous effects of insulin in obese humans still remain ill defined, and no study thus far has evaluated the specific brain areas affected by insulin resistance.

RESEARCH DESIGN AND METHODS

In 25 healthy lean and 23 overweight/obese participants, we performed magnetic resonance imaging to measure cerebral blood flow (CBF) before and 15 and 30 min after application of intranasal insulin or placebo. Additionally, participants explicitly rated pictures of high-caloric savory and sweet food 60 min after the spray for wanting and liking.

RESULTS

In response to insulin compared with placebo, we found a significant CBF decrease in the hypothalamus in both lean and overweight/obese participants. The magnitude of this response correlated with visceral adipose tissue independent of other fat compartments. Furthermore, we observed a differential response in the lean compared with the overweight/obese group in the prefrontal cortex, resulting in an insulin-induced CBF reduction in lean participants only. This prefrontal cortex response significantly correlated with peripheral insulin sensitivity and eating behavior measures such as disinhibition and food craving. Behaviorally, we were able to observe a significant reduction for the wanting of sweet foods after insulin application in lean men only.

CONCLUSIONS

Brain insulin action was selectively impaired in the prefrontal cortex in overweight and obese adults and in the hypothalamus in participants with high visceral adipose tissue, potentially promoting an altered homeostatic set point and reduced inhibitory control contributing to overeating behavior.

Weight-neutral effect of once-daily insulin detemir in Chinese type 2 diabetes patients: subgroup analysis of the SOLVE study

BACKGROUND

The present subanalysis of the Study of Once Daily Levemir (SOLVE) study was to evaluate the safety and efficacy of once-daily insulin detemir as add-on to oral antidiabetic drugs (OADs) in Chinese type 2 diabetes patients according to body mass index in a real-life setting.

METHODS

In all, 3272 eligible patients who were treated with diet, exercise, and one or more OAD were prescribed once-daily insulin detemir by their physician according to routine clinical practice and were followed-up for 24 weeks. The incidence of serious adverse reactions (SADRs), including major hypoglycemia, was the primary endpoint. Subanalyses were performed on patients in the following BMI groups: normal weight (BMI < 25 kg/m2); overweight (25 ≤ BMI < 30 kg/m2); and obese (BMI ≥ 30 kg/m2).

RESULTS

No SADRs were reported during the study. Significant improvements in glycemic levels were observed in all subgroups. For normal weight, overweight, and obese patients, the mean change in HbA1c (%/[mmol/mol]) was -1.26/-14, -1.09/-12, and -1.06/-12, respectively. The mean change in fasting plasma glucose in normal weight, overweight, and obese patients was -2.77, -2.57, and -2.71 mmol/L, respectively. Slight weight gain (0.25 kg), slight weight loss (-0.36 kg), and weight loss (-1.32 kg) were observed in the normal weight, overweight, and obese patients, respectively (P < 0.001). Linear regression analysis revealed a negative relationship between weight change and baseline BMI (slope = -0.16; P < 0.001).

CONCLUSIONS

Once-daily insulin detemir as add-on to OADs in Chinese patients with type 2 diabetes showed effective glycemic control and a low risk of hypoglycemia. Weight-neutral effects were observed in different BMI subgroups.

GLP-1 and exendin-4 transiently enhance GABAA receptor-mediated synaptic and tonic currents in rat hippocampal CA3 pyramidal neurons

Glucagon-like peptide-1 (GLP-1) is a hormone that stimulates insulin secretion. Receptors for GLP-1 are also found in the brain, including the hippocampus, the center for memory and learning. Diabetes is a risk factor for decreased memory functions. We studied effects of GLP-1 and exendin-4, a GLP-1 receptor agonist, on γ-aminobutyric acid (GABA) signaling in hippocampal CA3 pyramidal neurons. GABA is the main inhibitory neurotransmitter and decreases neuronal excitability. GLP-1 (0.01-1 nmol/L) transiently enhanced synaptic and tonic currents, and the effects were blocked by exendin (9-39). Ten pmol/L GLP-1 increased both the spontaneous inhibitory postsynaptic current (sIPSC) amplitudes and frequency by a factor of  1.8. In 0.1, 1 nmol/L GLP-1 or 10, 50, or 100 nmol/L exendin-4, only the sIPSC frequency increased. The tonic current was enhanced by 0.01-1 nmol/L GLP-1 and by 0.5-100 nmol/L exendin-4. When action potentials were inhibited by tetrodotoxin (TTX), inhibitory postsynaptic currents decreased and currents were no longer potentiated by GLP-1 or exendin-4. In contrast, although the tonic current decreased in TTX, it was still enhanced by GLP-1 or exendin-4. The results demonstrate GLP-1 receptor regulation of hippocampal function and are consistent with GLP-1 receptor agonists enhancing GABAA signaling by pre- and postsynaptic mechanisms.

Effects of insulin detemir and NPH insulin on body weight and appetite-regulating brain regions in human type 1 diabetes: a randomized controlled trial

Studies in rodents have demonstrated that insulin in the central nervous system induces satiety. In humans, these effects are less well established. Insulin detemir is a basal insulin analog that causes less weight gain than other basal insulin formulations, including the current standard intermediate-long acting Neutral Protamine Hagedorn (NPH) insulin. Due to its structural modifications, which render the molecule more lipophilic, it was proposed that insulin detemir enters the brain more readily than other insulins. The aim of this study was to investigate whether insulin detemir treatment differentially modifies brain activation in response to food stimuli as compared to NPH insulin. In addition, cerebral spinal fluid (CSF) insulin levels were measured after both treatments. Brain responses to viewing food and non-food pictures were measured using functional Magnetic Resonance Imaging in 32 type 1 diabetic patients, after each of two 12-week treatment periods with insulin detemir and NPH insulin, respectively, both combined with prandial insulin aspart. CSF insulin levels were determined in a subgroup. Insulin detemir decreased body weight by 0.8 kg and NPH insulin increased weight by 0.5 kg (p = 0.02 for difference), while both treatments resulted in similar glycemic control. After treatment with insulin detemir, as compared to NPH insulin, brain activation was significantly lower in bilateral insula in response to visual food stimuli, compared to NPH (p = 0.02 for right and p = 0.05 for left insula). Also, CSF insulin levels were higher compared to those with NPH insulin treatment (p = 0.003). Our findings support the hypothesis that in type 1 diabetic patients, the weight sparing effect of insulin detemir may be mediated by its enhanced action on the central nervous system, resulting in blunted activation in bilateral insula, an appetite-regulating brain region, in response to food stimuli.

Trial Registration

ClinicalTrials.gov NCT00626080.

Cerebral blood flow and glucose metabolism in appetite-related brain regions in type 1 diabetic patients after treatment with insulin detemir and NPH insulin: a randomized controlled crossover trial

OBJECTIVE

To test the hypothesis that insulin detemir, which is associated with less weight gain than other basal insulin formulations, exerts its weight-modulating effects by acting on brain regions involved in appetite regulation, as represented by altered cerebral blood flow (CBF) or cerebral glucose metabolism (CMRglu).

RESEARCH DESIGN AND METHODS

Twenty-eight male type 1 diabetic patients (age 36.9 ± 9.7 years, BMI 24.9 ± 2.7 kg/m(2), A1C 7.5 ± 0.6%) successfully completed a randomized crossover study, consisting of two periods of 12-week treatment with either insulin detemir or NPH insulin, both in combination with prandial insulin aspart. After each treatment period, patients underwent positron emission tomography scans to measure regional CBF and CMRglu.

RESULTS

After 12 weeks, A1C, daily insulin doses, fasting insulin, and blood glucose levels were similar between treatments. Insulin detemir resulted in body weight loss, whereas NPH insulin induced weight gain (between-treatment difference 1.3 kg; P = 0.02). After treatment with insulin detemir relative to NPH insulin, CBF was higher in brain regions involved in appetite regulation, whereas no significant difference in CMRglu was observed.

CONCLUSIONS

Treatment with insulin detemir versus NPH insulin resulted in weight loss, paralleled by increased CBF in appetite-related brain regions in the resting state, in men with well-controlled type 1 diabetes. These findings lend support to the hypothesis that a differential effect on the brain may contribute to the consistently observed weight-sparing effect of insulin detemir.

Insulin detemir: a review of its use in the management of diabetes mellitus

Insulin detemir (Levemir®) is a long-acting insulin analogue indicated for use as basal insulin therapy in patients with type 1 or 2 diabetes mellitus. The protracted action of insulin detemir is explained by increased self-association and reversible binding to albumin, which slows its systemic absorption from the injection site. In glucose-clamp studies, less within-patient variability in glucose-lowering effect was seen with insulin detemir than with neutral protamine Hagedorn (NPH) insulin or insulin glargine in patients with type 1 or 2 diabetes. The beneficial effect of insulin detemir on glycaemic control was shown in numerous randomized, open-label, multicentre trials, including when used as basal-bolus therapy in patients with type 1 or 2 diabetes and as basal therapy in addition to oral antidiabetic drugs in insulin-naive patients with type 2 diabetes. In terms of glycosylated haemoglobin (HbA(1c)).[primary endpoint in most trials], insulin detemir was generally at least as effective as NPH insulin, insulin glargine or insulin lispro protamine suspension in patients with type 1 or 2 diabetes, and at least as effective as biphasic insulin aspart in patients with type 2 diabetes. Less within-patient variability in blood glucose was also generally seen with insulin detemir than with NPH insulin in patients with type 1 or 2 diabetes. Significantly less weight gain was generally seen with insulin detemir than with NPH insulin in patients with type 1 diabetes or with insulin detemir than with NPH insulin, insulin glargine, insulin lispro protamine suspension or biphasic insulin aspart (in one study) in patients with type 2 diabetes (i.e. insulin detemir generally had a weight-sparing effect). The addition of insulin detemir to liraglutide plus metformin improved glycaemic control in insulin-naive patients with type 2 diabetes and inadequate glycaemic control, although a significantly greater reduction in bodyweight was seen in patients receiving liraglutide plus metformin than in those receiving add-on therapy with insulin detemir. Results of two trials in patients aged 2-16 or 6-17 years (and a subgroup analysis in children aged 2-5 years) indicate that a basal-bolus insulin regimen incorporating insulin detemir appears to be a suitable option for use in paediatric patients with type 1 diabetes. Less within-patient variation in self-measured fasting plasma glucose was seen with insulin detemir than with NPH insulin in one of the studies. Insulin detemir was noninferior to NPH insulin in pregnant women with type 1 diabetes in terms of the HbA(1c) value achieved at 36 gestational weeks. In addition, maternal and neonatal outcomes with insulin detemir were similar to those seen with NPH insulin. Subcutaneous insulin detemir was generally well tolerated in the treatment of patients with type 1 or 2 diabetes, including in paediatric patients and pregnant women with type 1 diabetes. The majority of adverse events, including serious adverse events, reported in insulin detemir recipients were not considered to be related to the study drug. Insulin detemir was generally associated with a significantly lower risk of nocturnal hypoglycaemia than NPH insulin in patients with type 1 or 2 diabetes, particularly nocturnal minor hypoglycaemia. In conclusion, insulin detemir is a useful option for use as basal insulin therapy in patients with type 1 or 2 diabetes.

Insulin sensitivity of the human brain

The brain is an insulin sensitive organ and insulin signaling is important to regulate feeding behavior, body weight, and cognitive processes. Insulin resistance in peripheral tissues is a hallmark in the development of type 2 diabetes mellitus (T2DM), yet the finding of insulin resistance in the brain is relatively novel. Studies in humans revealed that environmental factors like obesity, age, and the genetic background have an impact on central insulin sensitivity. According to the physiological effects of insulin in the brain, disturbances of this signaling chain lead to an impairment of cognitive functions and a deterioration of eating behavior with a potential role in the pathogenesis of obesity and T2DM. First attempts to treat insulin resistance not only in peripheral tissues but also in the CNS have therefore come on its way: Cerebral insulin resistance can at least partially be overcome by intranasal treatment with insulin or by commercial insulins that exhibit specific effects in the brain due to their pharmacokinetic properties. Despite the advances towards a better understanding of insulin function in the human brain in the last years, achieving a more profound knowledge of mechanisms behind central insulin function and identifying further strategies to overcome insulin resistance must be a main goal of future research.

Insulin detemir attenuates food intake, body weight gain and fat mass gain in diet-induced obese Sprague-Dawley rats

OBJECTIVE

Initiation and intensification of insulin therapy commonly causes weight gain, a barrier to therapy. A contrasting body of evidence indicates that insulin functions as an adiposity negative feedback signal and reduces food intake, weight gain and adiposity via action in the central nervous system. Basal insulin analogs, detemir (Det) and glargine (Glar), have been associated with less hypoglycemia compared with neutral protamine hagedorn insulin, and Det with less weight gain, especially in patients with higher body mass index (BMI). We sought to determine whether insulin therapy per se causes body weight and fat mass gain when delivered via a clinically relevant subcutaneous (SC) route in the absence of hypoglycemia and glycosuria in non-diabetic lean and diet-induced obese rats.

MATERIALS AND METHODS

Rats were exposed to either a low-fat diet (LFD; 13.5% fat) or high-fat diet (HFD; 60% fat), and received Det (0.5 U kg(-1)), Glar (0.2 U kg(-1)) or vehicle (Veh) SC once daily for 4 weeks. These dosages of insulin were equipotent in rats with respect to blood-glucose concentration and did not induce hypoglycemia.

RESULTS

As predicted by current models of energy homeostasis, neither insulin Det nor Glar therapy affected food intake and weight gain in LFD rats. Det treatment significantly attenuated food intake, body weight gain and fat mass gain relative to the Glar and Veh in high-fat fed animals, mirroring observations in humans.

CONCLUSIONS

That neither insulin group gained excess weight, suggests weight gain with SC basal insulin therapy may not be inevitable. Our data further suggest that Det possesses a unique property to attenuate the development of obesity associated with a HFD.

The obese brain: association of body mass index and insulin sensitivity with resting state network functional connectivity

Obesity is a key risk factor for the development of insulin resistance, Type 2 diabetes and associated diseases; thus, it has become a major public health concern. In this context, a detailed understanding of brain networks regulating food intake, including hormonal modulation, is crucial. At present, little is known about potential alterations of cerebral networks regulating ingestive behavior. We used "resting state" functional magnetic resonance imaging to investigate the functional connectivity integrity of resting state networks (RSNs) related to food intake in lean and obese subjects using independent component analysis. Our results showed altered functional connectivity strength in obese compared to lean subjects in the default mode network (DMN) and temporal lobe network. In the DMN, obese subjects showed in the precuneus bilaterally increased and in the right anterior cingulate decreased functional connectivity strength. Furthermore, in the temporal lobe network, obese subjects showed decreased functional connectivity strength in the left insular cortex. The functional connectivity magnitude significantly correlated with body mass index (BMI). Two further RSNs, including brain regions associated with food and reward processing, did not show BMI, but insulin associated functional connectivity strength. Here, the left orbitofrontal cortex and right putamen functional connectivity strength was positively correlated with fasting insulin levels and negatively correlated with insulin sensitivity index. Taken together, these results complement and expand previous functional neuroimaging findings by demonstrating that obesity and insulin levels influence brain function during rest in networks supporting reward and food regulation.

Insulin reduces neuronal excitability by turning on GABA(A) channels that generate tonic current

Insulin signaling to the brain is important not only for metabolic homeostasis but also for higher brain functions such as cognition. GABA (γ-aminobutyric acid) decreases neuronal excitability by activating GABA_A channels that generate phasic and tonic currents. The level of tonic inhibition in neurons varies. In the hippocampus, interneurons and dentate gyrus granule cells normally have significant tonic currents under basal conditions in contrast to the CA1 pyramidal neurons where it is minimal. Here we show in acute rat hippocamal slices that insulin (1 nM) “turns on” new extrasynaptic GABA_A channels in CA1 pyramidal neurons resulting in decreased frequency of action potential firing. The channels are activated by more than million times lower GABA concentrations than synaptic channels, generate tonic currents and show outward rectification. The single-channel current amplitude is related to the GABA concentration resulting in a single-channel GABA affinity (EC₅₀) in intact CA1 neurons of 17 pM with the maximal current amplitude reached with 1 nM GABA. They are inhibited by GABA_A antagonists but have novel pharmacology as the benzodiazepine flumazenil and zolpidem are inverse agonists. The results show that tonic rather than synaptic conductances regulate basal neuronal excitability when significant tonic conductance is expressed and demonstrate an unexpected hormonal control of the inhibitory channel subtypes and excitability of hippocampal neurons. The insulin-induced new channels provide a specific target for rescuing cognition in health and disease.

Insulin detemir is not transported across the blood-brain barrier

Insulin detemir has a different profile of action on the central nervous system (CNS) than human insulin. It has been hypothesized that this is caused by an altered ability of insulin detemir to cross the blood-brain barrier (BBB). Here, we measured the permeability of the BBB to insulin detemir. We labeled insulin detemir with radioactive iodine (I-Det) and examined its ability to cross the BBB of the mouse. Permeation was assessed after intravenous injection and by brain perfusion in the presence or absence of excess insulin detemir. The ability of insulin detemir to inhibit human insulin transport across the BBB was also assessed. I-Det did not cross the BBB either after intravenous injection or when studied by brain perfusion, a method which removes or reduces the influence of circulating proteins. Unlabeled detemir was about 10 times less potent than human insulin at inhibiting the transport of radioactive human insulin across the BBB. The altered CNS profile of insulin detemir may be caused by its poor access to CNS receptors and by a block of human insulin from crossing the BBB.

Critical appraisal of the safety and efficacy of insulin detemir in glycemic control and cardiovascular risk management in diabetics

Insulin detemir is an analog of human insulin designed to provide a long duration of basal insulin action. This is achieved by protracted absorption from the injection depot, which results in part from increased self-association of insulin detemir molecules and in part from reversible albumin binding. Subsequent albumin binding in the circulation is thought to buffer changes in the effects at target tissues that could otherwise arise from variability in absorption rate. In consequence, insulin detemir has shown a less variable pharmacodynamic profile than alternative basal insulins; this manifests as more consistent temporal glucose reduction profiles in repeat-clamp studies. In clinical trials, insulin detemir has been characterized by consistent risk reductions in hypoglycemia, as well as reduced weight gain in comparison with other basal insulins. Given some recent associations that have been made in prospective and epidemiologic studies between glucose variability and/or hypoglycemia and increased cardiovascular risk, and the long-known association between excess weight and cardiovascular risk, it is possible that the clinical profile of insulin detemir may carry prognostic value with regard to cardiovascular safety, although this is yet to be substantiated. There have also been some concerns raised recently over the use of insulin analogs and cancer risk, but available clinical data and the receptor interaction profile of insulin detemir suggest no excess in risk in comparison with human insulin therapy. Optimal approaches for the clinical use of insulin detemir have been emerging through an increasing clinical study base, and the analog is becoming established as a potentially valuable therapy option.

An update on the treatment of type 1 and type 2 diabetes mellitus: focus on insulin detemir, a long-acting human insulin analog

Basal insulin analogs are used to minimize unpredictable processes of NPH insulin. Modification of the human insulin molecule results in a slower distribution to peripheral target tissues, a longer duration of action with stable concentrations and thus a lower rate of hypoglycemia. Insulin detemir is a basal insulin analog that provides effective therapeutic options for patients with type 1 and type 2 diabetes. For glycemic control, no significant differences were found in HbA_1c levels compared with NPH and insulin glargine. It is comparable with insulin glargine in significantly reducing rates of all types of hypoglycemia. Clinical studies have demonstrated that detemir is responsible for significantly lower within-subject variability and no or less weight gain than NPH insulin and glargine. Recent pharmacodynamic studies have shown that detemir can be used once daily in many patients with diabetes. Together with patient-friendly injection devices and dose adjustments, it provides a treatment option with the potential to lower the key barriers of adherence to insulin therapy in type 2 diabetes. Recent guidelines for treatment of type 2 diabetes suggest starting intensive therapy of hyperglycemia at an early stage of diabetes and recommend therapeutic options that provide the possibility of reaching HbA_1c goals individually, with a low risk of hypoglycemia or other adverse effects of treatment. The properties of insulin detemir match these requirements.

Euglycemic infusion of insulin detemir compared with human insulin appears to increase direct current brain potential response and reduces food intake while inducing similar systemic effects

OBJECTIVE

In the treatment of diabetic patients, the long-acting insulin analog insulin detemir is less prone to induce weight gain than other insulin formulations. Assuming that because of its pharmacologic properties, detemir displays stronger central nervous anorexigenic efficacy than human insulin, we compared acute effects of human insulin and detemir on electroencephalography (EEG) measures and food intake.

RESEARCH DESIGN AND METHODS

Frontocortical EEG direct current (DC) potentials were recorded in 15 healthy men during two hyperinsulinemic-euglycemic clamps that included an insulin bolus injection (human insulin, 17.75 mU/kg body wt; detemir, 90 mU/kg body wt) followed by a steady 90-min infusion (1.0 vs. 2.0 mU x kg(-1) x min(-1)). A higher dosage was chosen for detemir to compensate for its delay in impact relative to human insulin and to elicit similar systemic effects. At 20 min after infusion, subjects were allowed to eat ad libitum from a test buffet.

RESULTS

Mean glucose infusions to maintain euglycemia (P > 0.93) and blood glucose concentrations (P > 0.34) did not differ between conditions. Detemir infusion induced a negative DC-potential shift, averaging -372.2 microV from 21 to 90 min that was not observed during human insulin infusion (146.5 microV, P = 0.02). Detemir, in comparison with human insulin, reduced subsequent food intake by 303 kcal (1,257 vs. 1,560, P < 0.04).

CONCLUSIONS

While inducing comparable peripheral effects, detemir exerts stronger acute effects on brain functions than human insulin and triggers a relative decrease in food consumption, suggesting an enhanced anorexigenic impact of detemir compared with human insulin on central nervous networks that control nutrient uptake.

Insulin detemir: A historical perspective on a modern basal insulin analogue

Insulin detemir provides prolonged, reproducible blood glucose reduction through a mechanism unique among basal insulins. It was originally studied clinically in predominantly basal + bolus regimens and found to be associated with a low risk of hypoglycaemia compared to insulin NPH, and reduced weight gain compared to other basal insulins. Insulin detemir has been increasingly studied in basal-only insulin regimens in type 2 diabetes, in which an understanding of how to optimize its use has been built incrementally. Glycaemic control and limitation of weight gain tend to be maximized by once-daily (evening) dosing, earlier initiation and careful titration to appropriate fasting glucose targets.

Central nervous insulin resistance: a promising target in the treatment of metabolic and cognitive disorders?

Research on functions and signalling pathways of insulin has traditionally focused on peripheral tissues such as muscle, fat and liver, while the brain was commonly believed to be insensitive to the effects of this hormone secreted by pancreatic beta cells. However, since the discovery some 30 years ago that insulin receptors are ubiquitously found in the central nervous system, an ever-growing research effort has conclusively shown that circulating insulin accesses the brain, which itself does not synthesise insulin, and exerts pivotal functions in central nervous networks. As an adiposity signal reflecting the amount of body fat, insulin provides direct negative feedback to hypothalamic nuclei that control whole-body energy and glucose homeostasis. Moreover, insulin affects distinct cognitive processes, e.g. by triggering the formation of psychological memory contents. Accordingly, metabolic and cognitive disorders such as obesity, type 2 diabetes mellitus and Alzheimer's disease are associated with resistance of central nervous structures to the effects of insulin, which may derive from genetic polymorphisms as well as from long-term exposure to excess amounts of circulating insulin due to peripheral insulin resistance. Thus, overcoming central nervous insulin resistance, e.g. by pharmacological interventions, appears to be an attractive strategy in the treatment and prevention of these disorders. Enhancement of central nervous insulin signalling by administration of intranasal insulin, insulin analogues and insulin sensitisers in basic research approaches has yielded encouraging results that bode well for the successful translation of these effects into future clinical practice.

Insulin detemir causes increased symptom awareness during hypoglycaemia compared to human insulin

AIM

The long-acting insulin analogue detemir (Levemir) has structural and physicochemical properties which differ from human insulin. The aim of the present study was to test whether this leads to altered hormone and symptom response during hypoglycaemia.

METHODS

12 healthy subjects [6f/6m, age 32 +/- 6 years (mean +/- s.d.), body mass index (BMI) 24.2 +/- 2.5 kg/m(2)] underwent a 200-min stepwise hypoglycaemic clamp (45 min steps of 4.4, 3.7, 3.0 and 2.3 mmol/l) with either detemir or human insulin in random order. A bolus of detemir (660 mU/kg) or human insulin (60 mU/kg) was given before insulin was infused at a rate of 5 (detemir) or 2 (human insulin) mU/kg/min. Blood was drawn and a semi-quantitative symptom questionnaire was administered before and after each plateau of the hypoglycaemic clamp. Cognitive function was assessed during each step.

RESULTS

Blood glucose levels and glucose infusion rates were comparable with detemir and human insulin. The total symptom score was higher with detemir during the 3 and 2.3 mmol glucose step compared to human insulin (p = 0.048). Especially sweating was increased with detemir (p = 0.02) with an earlier and faster increase during the clamp (interaction insulin x time: p = 0.04). No significant differences between detemir and human insulin in cortisol, norepinephrine, epinephrine, glucagon, growth hormone, lactate or free fatty acid (FFA) levels during hypoglycaemia were observed, and there were no significant differences in cognitive function tests.

CONCLUSIONS

Insulin detemir increased symptom awareness during hypoglycaemia compared to human insulin in healthy individuals, whereas counter-regulatory hormone response and cognitive function were unaltered.

Insulin-mediated cortical activity in the slow frequency range is diminished in obese mice and promotes physical inactivity

AIMS/HYPOTHESIS

There is evidence from mouse models and humans that alterations in insulin action in the brain are accompanied by an obese phenotype; however, the impact of insulin with regard to behavioural aspects such as locomotion is unknown.

METHODS

To address insulin action in the brain with regard to cortical activity in distinct frequency bands and the behavioural consequences, the insulin signalling pathway was followed from the receptor to electrical activity and locomotion. Western blot analysis, electrocorticograms with intracerebroventricular (i.c.v.) application of insulin, and measurements of locomotor activity were performed in lean and obese, as well as Toll-like receptor (TLR) 2/4-deficient, mice.

RESULTS

We show that insulin application i.c.v. into lean mice was accompanied by a profound increase in cortical activity in the slow frequency range, while diet-induced obese mice displayed insulin resistance. In parallel, insulin administered i.c.v. increased locomotor activity in lean mice, whereas a phosphatidylinositol-3 (PI3) kinase inhibitor or obesity abolished insulin-mediated locomotion. A potential candidate that links insulin signalling to locomotion is the Kv1.3 channel that is activated by PI3-kinase. Pharmacological inhibition of Kv1.3 channels that bypassed insulin receptor activation promoted activity. Moreover, mice deficient in TLR2/4-dependent signalling displayed an increase in cortical activity in the slow frequency range that was correlated with improved spontaneous and insulin-mediated locomotor activity.

CONCLUSIONS/INTERPRETATION

Our data provide functional evidence for a direct effect of insulin on brain activation patterns in the slow frequency bands and locomotor activity in lean mice, while in obese mice, insulin-mediated locomotion is blunted and further aggravates physical inactivity.

Evaluation of the lack of anorectic effect of intracerebroventricular insulin in rats

Insulin detemir is a novel human insulin analog that does not show the usual propensity for weight gain in diabetic patients. We speculated that this beneficial effect could be due to insulin detemir exerting stronger anorectic effects within the brain than other insulins. To study the central effects of regular human insulin and insulin detemir on food intake, the present study was undertaken. We used acute intracerebroventricular insulin injections to compare food intake and body weight in rats fed ad libitum. Contrary to previously published data, we found that neither regular human insulin (8 or 32 mU) nor insulin detemir (1,290 pmol) reduced food intake in this model. Melanotan-II was also injected intracerebroventricularly as a positive control, and significantly reduced food intake and body weight, suggesting that our intracerebroventricular model is able to show anorectic effects. A series of experiments was therefore conducted in which different set-ups were tested to investigate which factors would be required to produce the reported anorectic effect of intracerebroventricular insulin. Although we varied rat strain, stereotactic coordinates, formulations of insulin and vehicle, dose, volume, and time of injection, the anorectic effect of intracerebroventricular insulin could not be replicated. Therefore, we suggest that acute intracerebroventricularly injected insulin does not robustly inhibit food intake in rats. Based on our results, the acute intracerebroventricular injection procedure may not be a preferred method for studying the central anorectic effects of insulin in rats. Instead, administrations over time or locally in hypothalamic nuclei might be recommended.

Increased resting-state functional connectivity in obese adolescents; a magnetoencephalographic pilot study

BACKGROUND

Obesity is not only associated with metabolic abnormalities, but also with cognitive dysfunction and changes in the central nervous system. The present pilot study was carried out to investigate functional connectivity in obese and non-obese adolescents using magnetoencephalography (MEG).

METHODOLOGY/PRINCIPAL FINDINGS

Magnetoencephalographic recordings were performed in 11 obese (mean BMI 38.8+/-4.6 kg/m(2)) and 8 lean (mean BMI 21.0+/-1.5 kg/m(2)) female adolescents (age 12-19 years) during an eyes-closed resting-state condition. From these recordings, the synchronization likelihood (SL), a common method that estimates both linear and non-linear interdependencies between MEG signals, was calculated within and between brain regions, and within standard frequency bands (delta, theta, alpha1, alpha2, beta and gamma). The obese adolescents had increased synchronization in delta (0.5-4 Hz) and beta (13-30 Hz) frequency bands compared to lean controls (P(delta total) = 0.001; P(beta total) = 0.002).

CONCLUSIONS/SIGNIFICANCE

This study identified increased resting-state functional connectivity in severe obese adolescents. Considering the importance of functional coupling between brain areas for cognitive functioning, the present findings strengthen the hypothesis that obesity may have a major impact on human brain function. The cause of the observed excessive synchronization is unknown, but might be related to disturbed motivational pathways, the recently demonstrated increase in white matter volume in obese subjects or altered metabolic processes like hyperinsulinemia. The question arises whether the changes in brain structure and communication are a dynamic process due to weight gain and whether these effects are reversible or not.

Insulin analogues: action profiles beyond glycaemic control

A variety of studies have documented significant improvements in the treatment of type 1 and 2 diabetes after the introduction of artificial insulins. This review gives an overview of insulin analogues which are currently approved for therapeutical use. Clinical data regarding the efficiency to control blood glucose level as well as improving HbA1c level in comparison to conventional insulin preparations in type 1 and 2 diabetic patients are summarized. Furthermore, special features of insulin analogues regarding their signalling properties are discussed with focus on the proliferative effects of insulin glargine as well as some recent data of insulin detemir.