Achim Peters

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.

Influence of Partial Sleep Deprivation on Energy Balance and Insulin Sensitivity in Healthy Women

Background: Voluntary sleep restriction is a lifestyle feature of modern societies that may contribute to obesity and diabetes. The aim of the study was to investigate the impact of partial sleep deprivation on the regulation of energy balance and insulin sensitivity. Subjects and Methods: In a controlled intervention, 14 healthy women (age 23–38 years, BMI 20.0–36.6 kg/m2) were investigated after 2 nights of >8 h sleep/night (T0), after 4 nights of consecutively increasing sleep curtailment (7 h sleep/ night, 6 h sleep/night, 6 h sleep/night and 4 h sleep/night; T1) and after 2 nights of sleep recovery (>8 h sleep/night; T2). Resting and total energy expenditure (REE, TEE), glucose-induced thermogenesis (GIT), physical activity, energy intake, glucose tolerance and endocrine parameters were assessed. Results: After a decrease in sleep du-ration, energy intake (+20%), body weight (+0.4 kg), leptin / fat mass (+29%), free triiodothyronine (+19%), free thyroxine (+10%) and GIT (+34%) significantly increased (all p < 0.05). Mean REE, physical activity, TEE, oral glucose tolerance, and ghrelin levels remained unchanged at T1. The effect of sleep loss on GIT, fT3 and fT4 levels was inversely related to fat mass. Conclusion: Short-term sleep deprivation increased energy intake and led to a net weight gain in women. The effect of sleep restriction on energy expenditure needs to be specifically addressed in future studies using reference methods for total energy expenditure.

How the Selfish Brain Organizes its Supply and Demand

During acute mental stress, the energy supply to the human brain increases by 12%. To determine how the brain controls this demand for energy, 40 healthy young men participated in two sessions (stress induced by the Trier Social Stress Test and non-stress intervention). Subjects were randomly assigned to four different experimental groups according to the energy provided during or after stress intervention (rich buffet, meager salad, dextrose-infusion and lactate-infusion). Blood samples were frequently taken and subjects rated their autonomic and neuroglycopenic symptoms by standard questionnaires. We found that stress increased carbohydrate intake from a rich buffet by 34 g (from 149 ± 13 g in the non-stress session to 183 ± 16 g in the stress session; P < 0.05). While these stress-extra carbohydrates increased blood glucose concentrations, they did not increase serum insulin concentrations. The ability to suppress insulin secretion was found to be linked to the sympatho-adrenal stress-response. Social stress increased concentrations of epinephrine 72% (18.3 ± 1.3 vs. 31.5 ± 5.8 pg/ml; P < 0.05), norepinephrine 148% (242.9 ± 22.9 vs. 601.1 ± 76.2 pg/ml; P < 0.01), ACTH 184% (14.0 ± 1.3 vs. 39.8 ± 7.7 pmol/l; P < 0.05), cortisol 131% (5.4 ± 0.5 vs. 12.4 ± 1.3 μg/dl; P < 0.01) and autonomic symptoms 137% (0.7 ± 0.3 vs. 1.7 ± 0.6; P < 0.05). Exogenous energy supply (regardless of its character, i.e., rich buffet or energy infusions) was shown to counteract a neuroglycopenic state that developed during stress. Exogenous energy did not dampen the sympatho-adrenal stress-responses. We conclude that the brain under stressful conditions demands for energy from the body by using a mechanism, which we refer to as “cerebral insulin suppression” and in so doing it can satisfy its excessive needs.

Defective Awakening Response to Nocturnal Hypoglycemia in Patients with Type 1 Diabetes Mellitus

Background Nocturnal hypoglycemia frequently occurs in patients with type 1 diabetes mellitus (T1DM). It can be fatal and is believed to promote the development of the hypoglycemia-unawareness syndrome. Whether hypoglycemia normally provokes awakening from sleep in individuals who do not have diabetes, and whether this awakening response is impaired in T1DM patients, is unknown. Methods and Findings We tested two groups of 16 T1DM patients and 16 healthy control participants, respectively, with comparable distributions of gender, age, and body mass index. In one night, a linear fall in plasma glucose to nadir levels of 2.2 mmol/l was induced by infusing insulin over a 1-h period starting as soon as polysomnographic recordings indicated that stage 2 sleep had been reached. In another night (control), euglycemia was maintained. Only one of the 16 T1DM patients, as compared to ten healthy control participants, awakened upon hypoglycemia (p = 0.001). In the control nights, none of the study participants in either of the two groups awakened during the corresponding time. Awakening during hypoglycemia was associated with increased hormonal counterregulation. In all the study participants (from both groups) who woke up, and in five of the study participants who did not awaken (three T1DM patients and two healthy control participants), plasma epinephrine concentration increased with hypoglycemia by at least 100% (p < 0.001). A temporal pattern was revealed such that increases in epinephrine in all participants who awakened started always before polysomnographic signs of wakefulness (mean ± standard error of the mean: 7.5 ± 1.6 min). Conclusions A fall in plasma glucose to 2.2 mmol/l provokes an awakening response in most healthy control participants, but this response is impaired in T1DM patients. The counterregulatory increase in plasma epinephrine that we observed to precede awakening suggests that awakening forms part of a central nervous system response launched in parallel with hormonal counterregulation. Failure to awaken increases the risk for T1DM patients to suffer prolonged and potentially fatal hypoglycemia.

Chronic fentanyl application induces adrenocortical insufficiency

We report a case of a 64‐year‐old man with secondary adrenocortical insufficiency who has been on a chronic transdermal fentanyl treatment because of sciatic pain syndrome. Shortly before admission to our hospital, the patient had discontinued his hydrocortisone medication. Adrenal crisis was assumed and during therapy with hydrocortisone infusion, the patient recovered. We suspected an opiate‐induced suppression of the hypothalamus‐pituitary‐adrenal (HPA) axis. Therefore, we gradually reduced the opiate dosage. After 1 week, HPA axis function was markedly improved. We conclude that opiate medication may inhibit – in a life‐threatening way – the organisms ability to respond to physical, emotional or metabolic stressors.

Evidence for a relationship between VEGF and BMI independent of insulin sensitivity by glucose clamp procedure in a homogenous group healthy young men.

Background This is the first study to experimentally explore the direct relationship between circulating VEGF levels and body mass index (BMI) as well as to unravel the role of insulin sensitivity in this context under standardized glucose clamp conditions as the methodical gold-standard. In order to control for known influencing factors such as gender, medication, and arterial hypertension, we examined a highly homogeneous group of young male subjects. Moreover, to encompass also subjects beyond the normal BMI range, low weight and obese participants were additionally included and stress hormones as a main regulator of VEGF were assessed. Methodology/Principal Findings Under euglycemic clamp conditions, VEGF was measured in 15 normal weight (BMI 20–25 kg/m2), 15 low weight (BMI<20 kg/m2), and 15 obese (BMI>30 kg/m2) male subjects aged 18–30 years and the insulin sensitivity index (ISI) was calculated. Since stress axis activation promotes VEGF secretion, concentrations of ACTH, cortisol, and catecholamines were monitored. Despite of comparable ACTH (P = 0.145), cortisol (P = 0.840), and norepinephrine (P = 0.065) levels, VEGF concentrations differed significantly between BMI-groups (P = 0.008) with higher concentrations in obese subjects as compared to normal weight (P = 0.061) and low weight subjects (P = 0.002). Pearsons correlation analysis revealed a positive relationship between BMI and VEGF levels (r = 0.407; P = 0.010) but no correlation of VEGF with ISI (r = 0.224; P = 0.175). Conclusions/Significance Our data demonstrate a positive correlation between concentrations of circulating VEGF levels and BMI in healthy male subjects under highly controlled conditions. This relationship which is apparently disconnected from insulin sensitivity may be part of some pathogenetic mechanisms underlying obesity and type 2 diabetes.

Build-ups in the supply chain of the brain: on the neuroenergetic cause of obesity and type 2 diabetes mellitus.

Obesity and type 2 diabetes have become the major health problems in many industrialized countries. A few theoretical frameworks have been set up to derive the possible determinative cause of obesity. One concept views that food availability determines food intake, i.e. that obesity is the result of an external energy “push” into the body. Another one views that the energy milieu within the human organism determines food intake, i.e. that obesity is due to an excessive “pull” from inside the organism. Here we present the unconventional concept that a healthy organism is maintained by a “competent brain-pull” which serves systemic homeostasis, and that the underlying cause of obesity is “incompetent brain-pull”, i.e. that the brain is unable to properly demand glucose from the body. We describe the energy fluxes from the environment, through the body, towards the brain with a mathematical “supply chain” model and test whether its predictions fit medical and experimental data sets from our and other research groups. In this way, we show data-based support of our hypothesis, which states that under conditions of food abundance incompetent brain-pull will lead to build-ups in the supply chain culminating in obesity and type 2 diabetes. In the same way, we demonstrate support of the related hypothesis, which states that under conditions of food deprivation a competent brain-pull mechanism is indispensable for the continuance of the brain´s high energy level. In conclusion, we took the viewpoint of integrative physiology and provided evidence for the necessity of brain-pull mechanisms for the benefit of health. Along these lines, our work supports recent molecular findings from the field of neuroenergetics and continues the work on the “Selfish Brain” theory dealing with the maintenance of the cerebral and peripheral energy homeostasis.

Molecular Control of Systemic Bile Acid Homeostasis by the Liver Glucocorticoid Receptor

Systemic bile acid (BA) homeostasis is a critical determinant of dietary fat digestion, enterohepatic function, and postprandial thermogenesis. However, major checkpoints for the dynamics and the molecular regulation of BA homeostasis remain unknown. Here we show that hypothalamic-pituitary-adrenal (HPA) axis impairment in humans and liver-specific deficiency of the glucocorticoid receptor (GR) in mice disrupts the normal changes in systemic BA distribution during the fasted-to-fed transition. Fasted mice with hepatocyte-specific GR knockdown had smaller gallbladder BA content and were more susceptible to developing cholesterol gallstones when fed a cholesterol-rich diet. Hepatic GR deficiency impaired liver BA uptake/transport via lower expression of the major hepatocyte basolateral BA transporter, Na(+)-taurocholate transport protein (Ntcp/Slc10a1), which affected dietary fat absorption and brown adipose tissue activation. Our results demonstrate a role of the HPA axis in the endocrine regulation of BA homeostasis through the liver GR control of enterohepatic BA recycling.

The selfish brain: Competition for energy resources.

Obesity and type 2 diabetes have become the major health problems in many industrialized countries. Here, I present the unconventional concept that a healthy organism maintains its systemic homeostasis by a “competent brain‐pull”, i.e., the brains ability to properly demand glucose from the body, and that the underlying cause of obesity is “incompetent brain‐pull.” I describe the energy fluxes from the environment, through the body, toward the brain as the final consumer in a “supply chain” model. There is data‐based support for the hypothesis, which states that under conditions of food abundance incompetent brain‐pull will lead to build ups in the supply chain culminating in obesity and type 2 diabetes. There is also support for the related hypothesis, which states that under conditions of food deprivation, a competent brain‐pull mechanism is indispensable for the continuation of the brains high energy level. To experimentally determine how the competent brain‐pull functions to demand for cerebral energy, healthy young men undergoing psychosocial stress were studied. It was found that the brain under stressful conditions demands for energy from the body by using a brain‐pull mechanism, which is referred to as “cerebral insulin suppression” and in so doing it can satisfy its excessive needs during stress. This article gives an overview about the recent work on the “Selfish Brain” theory dealing with the maintenance of the cerebral and peripheral energy homeostasis. Am. J. Hum. Biol., 2011.

Hyperinsulinemia causes activation of the hypothalamus-pituitary-adrenal axis in humans

OBJECTIVE: Hyperactivity of the hypothalamus-pituitary-adrenal (HPA) axis is frequently found in hyperinsulinemic subjects, such as patients with diabetes or abdominal obesity. Here, the question has been posed as to whether hyperinsulinemia increases HPA secretory activity.METHODS: We performed paired—euglycemic and stepwise hypoglycemic (76–66–56–46 mg/dl)—clamp experiments in two groups (each of 15 healthy men) at different insulin infusions rates, ie, 1.5 mU/min/kg (low-insulin condition) and 15.0 mU/min/kg (high-insulin condition).RESULTS: During the euglycemic clamp, the high rate insulin infusion increased plasma ACTH levels, whereas plasma ACTH levels remained essentially unchanged during the low-insulin condition (condition by time interaction, P=0.008). Likewise, serum cortisol levels were higher during the high- vs low-insulin condition (condition by time interaction, P=0.004). During the hypoglycemic clamp, plasma ACTH levels did not differ between the low- vs high-insulin condition, while serum cortisol levels were higher during the high- vs low-insulin condition at the beginning of the clamp (plasma glucose ∼76 mg/dl; P=0.032).CONCLUSION: Data indicate that hyperinsulinemia acutely increases HPA secretory activity in healthy men. This finding appears to be relevant to the pathogenesis of many clinical abnormalities associated which diabetes and abdominal adiposity, often referred to as the metabolic syndrome.