Werner Kern

Sniffing neuropeptides: a transnasal approach to the human brain

Neuropeptides act as neuronal messengers in the brain, influencing many neurobehavioral functions. Their experimental and therapeutic use in humans has been hampered because, when administered systemically, these compounds do not readily pass the blood–brain barrier, and they evoke potent hormone-like side effects when circulating in the blood. We administered three peptides, melanocortin(4–10) (MSH/ACTH(4–10)), vasopressin and insulin, intranasally and found that they achieved direct access to the cerebrospinal fluid (CSF) within 30 minutes, bypassing the bloodstream.

Intranasal insulin improves memory in humans.

Previous studies have suggested an acutely improving effect of insulin on memory function. To study changes in memory associated with a prolonged increase in brain insulin activity in humans, here we used the intranasal route of insulin administration known to provide direct access of the substance to the cerebrospinal fluid compartment. Based on previous results indicating a prevalence of insulin receptors in limbic and hippocampal regions as well as improvements in memory with systemic insulin administration, we expected that intranasal administration of insulin improves primarily hippocampus dependent declaration memory function. Also, improvements in mood were expected. We investigated the effects of 8 weeks of intranasal administration of insulin (human regular insulin 4 x 40 IU/d) on declarative memory (immediate and delayed recall of word lists), attention (Stroop test), and mood in 38 healthy subjects (24 males) in a double blind, between-subject comparison. Blood glucose and plasma insulin levels did not differ between the placebo and insulin conditions. Delayed recall of words significantly improved after 8 weeks of intranasal insulin administration (words recalled, Placebo 2.92 +/- 1.00, Insulin 6.20 +/- 1.03, p < 0.05). Moreover, subjects after insulin reported signs of enhanced mood, such as reduced anger (p < 0.02) and enhanced self-confidence (p < 0.03). Results indicate a direct action of prolonged intranasal administration of insulin on brain functions, improving memory and mood in the absence of systemic side effects. These findings could be of relevance for the treatment of patients with memory disorders like in Alzheimers disease.

Improving Influence of Insulin on Cognitive Functions in Humans

Insulin receptors have been identified in limbic brain structures, but their functional relevance is still unclear. In order to characterize some of their effects, we evaluated auditory evoked brain potentials (AEP) in a vigilance task, behavioral measures of memory (recall of words) and selective attention (Stroop test) during infusion of insulin. The hormone was infused at two different rates (1.5 mU/kg × min, ‘low insulin’, and 15 mU/kg × min, ‘high insulin’), inducing respectively serum levels of 543 ± 34 and 24,029 ± 1,595 pmol/l. This experimental design allowed to compare cognitive parameters under two conditions presenting markedly different insulin levels, but with minimal incidence on blood glucose concentrations since these were kept constant by glucose infusion. A ‘no insulin treatment’ group was not included in order to avoid leaving patients infused with glucose without insulin treatment. Measures were taken during a baseline phase preceding insulin infusion and every 90 min during the 360 min of insulin infusion. Compared with ‘low insulin’, ‘high insulin’ induced a slow negative potential shift in the AEP over the frontal cortex (average amplitude, high insulin: 0.27 ± 0.48 µV; low insulin: 1.87 ± 0.48 µV, p < 0.005), which was paralleled by enhanced memory performance (words recalled, high insulin: 22.04 ± 0.93; low insulin: 19.29 ± 0.92, p < 0.05). Also, during ‘high insulin’ subjects displayed enhanced performance on the Stroop test (p < 0.05) and expressed less difficulty in thinking than during ‘low insulin’ (p < 0.03). Results indicate an improving effect of insulin on cognitive function, and may provide a frame for further investigations of neurobehavioral effects of insulin in patients with lowered or enhanced brain insulin, i.e., patients with Alzheimer’s disease or diabetes mellitus.

Sleep disruption alters nocturnal ACTH and cortisol secretory patterns

Recent studies have provided evidence that nocturnal cortisol secretion is coupled to ultradian rhythms of sleep. The present study was designed to specify how exogenous and sleep-related endogenous factors influence nocturnal adrenocorticotropin (ACTH) and cortisol secretion. We compared the influences of (1) temporary sleep deprivation, (2) arousals continuously induced during sleep and, (3) undisturbed sleep (baseline) on pituitary-adrenocortical activity in 10 healthy men. Sleep deprivation (DS) and continuous arousals during sleep (AS) were introduced at the beginning of the second rapid eye movement (REM) sleep period which is an epoch close to the first significant nocturnal rise in plasma cortisol. Compared with the baseline nights, plasma cortisol significantly increased immediately after continuous arousals were started or the subject was awakened and remained awake. Despite this exogenously provoked first cortisol peak, average cortisol release during DS and AS was no higher than during undisturbed sleep. The arousal-induced cortisol burst was followed by a temporary inhibition of cortisol secretion, suggesting that once the subject is aroused (i.e., in stage 1 sleep or awake), the hypothalamus-pituitary-adrenal (HPA) system becomes highly sensitive to negative feedback inhibition. Spontaneously occurring endogenous cortisol peaks of comparable size during undisturbed sleep did not exhibit such a temporary inhibition of cortisol secretion. We hypothesize that sleep attenuates negative feedback inhibition within the HPA system, whereas wakefulness (or stage 1 sleep) reflects increased feedback sensitivity of this system.

Differential Sensitivity of Men and Women to Anorexigenic and Memory-Improving Effects of Intranasal Insulin

CONTEXT Brain insulin is critically involved in the regulation of body weight and memory processing. Long-term administration of intranasal insulin reduces body weight in men, but not in women, while improving hippocampus-dependent memory processing in both genders. OBJECTIVES Our objectives were to assess the effects of a single dose of intranasal insulin on food intake and memory function in men and women, and to determine any gender differences. METHODS A total of 32 healthy, normal-weight subjects (14 men, 18 women) were intranasally administered 160 IU regular human insulin or vehicle before performing a hippocampus-dependent two-dimensional-object location task, a working memory task (digit span), and a hippocampus-independent mirror tracing task. Subsequently, food intake from an ad libitum breakfast buffet was measured. RESULTS Insulin treatment decreased food intake in men but not in women (difference to placebo condition, men: -192.57 +/- 78.48 kcal, P < 0.03; women: 18.54 +/- 42.89 kcal, P > 0.67). In contrast, hippocampus-dependent memory and working memory were improved in women (P < 0.03, P < 0.05, respectively), whereas men did not benefit from acute insulin treatment (P > 0.17, P > 0.20). Performance on the hippocampus-independent mirror tracing task was not affected by insulin in women or men. CONCLUSIONS In accordance with animal data, results indicate that men are more sensitive than women to the acute anorexigenic effect of central nervous insulin signaling, whereas insulins beneficial effect on hippocampus-dependent memory functions is more pronounced in women. Our findings provide support for the notion of a fundamental gender difference in central nervous insulin signaling that pertains to the regulation of energy homeostasis and memory functions.

Intranasal insulin improves memory in humans: superiority of insulin aspart.

There is compelling evidence that intranasal administration of regular human insulin (RH-I) improves memory in humans. Owing to the reduced tendency of its molecules to form hexamers, the rapid-acting insulin analog insulin aspart (ASP-I) is more rapidly absorbed than RH-I after subcutaneous administration. Since after intranasal insulin administration, ASP-I may also be expected to access the brain, we examined whether intranasal ASP-I has stronger beneficial effects on declarative memory than RH-I in humans. Acute (40 IU) and long-term (4 × 40 IU/day over 8 weeks) effects of intranasally administered ASP-I, RH-I, and placebo on declarative memory (word lists) were assessed in 36 healthy men in a between-subject design. Plasma insulin and glucose levels were not affected. After 8 weeks of treatment, however, word list recall was improved compared to placebo in both the ASP-I (p<0.01) and the RH-I groups (p<0.05). ASP-I-treated subjects performed even better than those of the RH-I-treated group (p<0.05). Our results indicate that insulin-induced memory improvement can be enhanced by using ASP-I. This finding may be especially relevant for a potential clinical administration of intranasal insulin in the treatment of memory disorders like Alzheimers disease.

Identification of Nesfatin-1 in Human and Murine Adipose Tissue: A Novel Depot-Specific Adipokine with Increased Levels in Obesity

Nesfatin-1 is a recently identified anorexigenic peptide derived from its precursor protein, nonesterified fatty acid/nucleobindin 2 (NUCB2). Although the hypothalamus is pivotal for the maintenance of energy homeostasis, adipose tissue plays an important role in the integration of metabolic activity and energy balance by communicating with peripheral organs and the brain via adipokines. Currently no data exist on nesfatin-1 expression, regulation, and secretion in adipose tissue. We therefore investigated NUCB2/nesfatin-1 gene and protein expression in human and murine adipose tissue depots. Additionally, the effects of insulin, dexamethasone, and inflammatory cytokines and the impact of food deprivation and obesity on nesfatin-1 expression were studied by quantitative RT-PCR and Western blotting. We present data showing NUCB2 mRNA (P < 0.001), nesfatin-1 intracellular protein (P < 0.001), and secretion (P < 0.01) were significantly higher in sc adipose tissue compared with other depots. Also, nesfatin-1 protein expression was significantly increased in high-fat-fed mice (P < 0.01) and reduced under food deprivation (P < 0.01) compared with controls. Stimulation of sc adipose tissue explants with inflammatory cytokines (TNFalpha and IL-6), insulin, and dexamethasone resulted in a marked increase in intracellular nesfatin-1 levels. Furthermore, we present evidence that the secretion of nesfatin-1 into the culture media was dramatically increased during the differentiation of 3T3-L1 preadipocytes into adipocytes (P < 0.001) and after treatments with TNF-alpha, IL-6, insulin, and dexamethasone (P < 0.01). In addition, circulating nesfatin-1 levels were higher in high-fat-fed mice (P < 0.05) and showed positive correlation with body mass index in human. We report that nesfatin-1 is a novel depot specific adipokine preferentially produced by sc tissue, with obesity- and food deprivation-regulated expression.

Obese men respond to cognitive but not to catabolic brain insulin signaling.

Context and objective:Insulin acts in the brain to reduce food intake and body weight and is considered a major adiposity signal in energy homeostasis. In normal-weight men, intranasal insulin administration reduces body fat and improves declarative memory. The present experiments aimed to generalize these findings to obese patients, with a view to evaluate the therapeutic potential of the compound.Design, subjects and measurements:Insulin and placebo, respectively, were intranasally administered four times a day (amounting to 160 IU day−1) over 8 weeks to two groups of 15 obese men each.Results:Contrasting with the catabolic effects in normal-weight men, insulin treatment did not induce any significant reduction of body weight (P>0.50) and body fat (P>0.44) in the obese subjects. However, in accordance with the effects in normal-weight men, declarative memory and mood were improved (P<0.05) and hypothalamic–pituitary–adrenal axis activity as assessed by circulating ACTH (P<0.01) and cortisol levels (P<0.04) was reduced.Conclusions:Our results indicate that in obese men, intranasal insulin is functionally active in the central nervous system but fails to affect the neuronal networks critically involved in body weight regulation. We conclude that obesity in men is associated with central nervous resistance to the adiposity signal insulin. This defect likely contributes to the persistence of obesity in spite of elevated levels of circulating insulin in obese patients.

Costs of managing severe hypoglycaemia in three European countries

Abstract Objectives: To assess the costs of severe hypoglycaemic events (SHEs) in diabetes patients in Germany, Spain and the UK. Methods: Healthcare resource use was measured by surveying 639 patients aged ≥16 years, receiving insulin for type 1 (n=319) or type 2 diabetes (n=320), who experienced ≥1 SHE in the preceding year. Patients were grouped by location of SHE treatment: group 1, community (family/domestic); group 2, community (healthcare professional); group 3, hospital. Costs were calculated from published unit costs applied to estimated resource use. Costs per SHE were derived from patient numbers per subgroup. Weighted average costs were derived using a prevalence database. Results: Hospital treatment was a major cost in all countries. In Germany and Spain, costs per SHE for type 1 patients differed from those for type 2 patients in each group. Average SHE treatment costs were higher for patients with type 2 diabetes (Germany, €533; Spain, €691; UK, €537) than type 1 diabetes patients (€441, €577 and €236, respectively). Telephone calls, visits to doctors, blood glucose monitoring and patient education contributed substantially to costs for non-hospitalised patients. Conclusions: Treatment of SHEs adds significantly to healthcare costs. Average costs were lower for type 1 than for insulin-treated type 2 diabetes, in all three countries.

Intranasal Insulin to Improve Memory Function in Humans

Background: Compelling evidence indicates that central nervous insulin enhances learning and memory and in particular benefits hippocampus-dependent (i.e., declarative) memory. Intranasal administration of insulin provides an effective way of delivering the compound to the central nervous system, bypassing the blood-brain barrier and avoiding systemic side effects. Methods: Here we review a series of recent studies on the effects of intranasally administered insulin on memory functions in humans. In accordance with the beneficial effects of intravenously administered insulin on hippocampus-dependent declarative memory observed in hyperinsulinemic-euglycemic clamp studies, intranasal insulin administration similarly improves this type of memory, but in the absence of adverse peripheral side effects. Result andConclusion: Considering that cerebrospinal fluid insulin levels are reduced in patients suffering from Alzheimer’s disease, these results may be of considerable relevance for future clinical applications of insulin in the treatment of memory disorders.