Attenuation of amydgala and frontal cortical responses to low blood glucose concentration in asymptomatic hypoglycemia in type 1 diabetes: a new player in hypoglycemia unawareness?

Recommendations for recognizing, risk stratifying, treating, and managing children and adolescents with hypoglycemia

There has been continuous progress in diabetes management over the last few decades, not least due to the widespread dissemination of continuous glucose monitoring (CGM) and automated insulin delivery systems. These technological advances have radically changed the daily lives of people living with diabetes, improving the quality of life of both children and their families. Despite this, hypoglycemia remains the primary side-effect of insulin therapy. Based on a systematic review of the available scientific evidence, this paper aims to provide evidence-based recommendations for recognizing, risk stratifying, treating, and managing patients with hypoglycemia. The objective of these recommendations is to unify the behavior of pediatric diabetologists with respect to the timely recognition and prevention of hypoglycemic episodes and the correct treatment of hypoglycemia, especially in patients using CGM or advanced hybrid closed-loop systems. All authors have long experience in the specialty and are members of the Italian Society of Pediatric Endocrinology and Diabetology. The goal of treating hypoglycemia is to raise blood glucose above 70 mg/dL (3.9 mmol/L) and to prevent further decreases. Oral glucose at a dose of 0.3 g/kg (0.1 g/kg for children using "smart pumps" or hybrid closed loop systems in automated mode) is the preferred treatment for the conscious individual with blood glucose <70 mg/dL (3.9 mmol/L), although any form of carbohydrate (e.g., sucrose, which consists of glucose and fructose, or honey, sugary soft drinks, or fruit juice) containing glucose may be used. Using automatic insulin delivery systems, the oral glucose dose can be decreased to 0.1 g/kg. Practical flow charts are included to aid clinical decision-making. Although representing the official position of the Italian Society of Pediatric Endocrinology and Diabetology (ISPED), these guidelines are applicable to the global audience and are especially pertinent in the era of CGM and other advanced technologies.

Kinetic Modeling of Brain [18-F]FDG Positron Emission Tomography Time Activity Curves with Input Function Recovery (IR) Method

Accurate positron emission tomography (PET) data quantification relies on high-quality input plasma curves, but venous blood sampling may yield poor-quality data, jeopardizing modeling outcomes. In this study, we aimed to recover sub-optimal input functions by using information from the tail (5th-100th min) of curves obtained through the frequent sampling protocol and an input recovery (IR) model trained with reference curves of optimal shape. Initially, we included 170 plasma input curves from eight published studies with clamp [18F]-fluorodeoxyglucose PET exams. Model validation involved 78 brain PET studies for which compartmental model (CM) analysis was feasible (reference (ref) + training sets). Recovered curves were compared with original curves using area under curve (AUC), max peak standardized uptake value (maxSUV). CM parameters (ref + training sets) and fractional uptake rate (FUR) (all sets) were computed. Original and recovered curves from the ref set had comparable AUC (d = 0.02, not significant (NS)), maxSUV (d = 0.05, NS) and comparable brain CM results (NS). Recovered curves from the training set were different from the original according to maxSUV (d = 3) and biologically plausible according to the max theoretical K1 (53//56). Brain CM results were different in the training set (p < 0.05 for all CM parameters and brain regions) but not in the ref set. FUR showed reductions similarly in the recovered curves of the training and test sets compared to the original curves (p < 0.05 for all regions for both sets). The IR method successfully recovered the plasma inputs of poor quality, rescuing cases otherwise excluded from the kinetic modeling results. The validation approach proved useful and can be applied to different tracers and metabolic conditions.

Effect of hypoglycemia on cognitive performance in older patients with diabetes: A meta-analysis

GOALS

The goal of this study was to use meta-analysis to compile information from various studies to investigate the existence and severity of cognitive impairment in elderly diabetes patients who have hypoglycemic episodes.

MATERIALS AND TECHNIQUES

For research studies on the relationship between hypoglycemia and cognitive decline or dementia in persons older than 45 years, we searched the PubMed, EMBASE, Cochrane Library, CNKI, WanFang, CBM and VIP databases for the period 1989 to 2022. We conducted random effects inverse variance on the meta-analysis and used the I2 statistic to assess heterogeneity.

RESULT

We selected 44 of the 518 studies we retrieved, 7 being appropriate for meta-analysis. Six thousand and forty-five individuals were involved in total. Both types of older diabetic patients with hypoglycemia performed considerably worse on tests of general intelligence than control participants (standardized mean difference, 0.58; 95% CI, 0.88-0.28). Also, elderly type-2 diabetes patients with hypoglycemic episodes had significantly worse memory performance (standardized mean difference, 0.19; 95% CI, 0.29-0.09). Additionally, we found that older type-2 diabetes patients with hypoglycemia had significantly poorer psychomotor function than those without hypoglycemia (standardized mean difference, 0.51; 95% CI, 0.38-0.63).

Impaired Awareness of Hypoglycemia in Type 1 Diabetes: A Report of An NIDDK Workshop in October 2021

Hypoglycemia remains a limiting factor in the optimal treatment of type 1 diabetes. Repeated episodes of hypoglycemia result in impaired awareness of subsequent hypoglycemic events, inducing a vicious feed-forward cycle and increasing the risk of morbidity and mortality. Why this occurs and how to manage the problem in clinical practice remain uncertain. To address the obstacles and barriers that have hindered progress in this clinically important area, the National Institute of Diabetes and Digestive and Kidney Diseases convened a workshop on 14-15 October 2021. This perspective offers a summary of this outstanding meeting, which brought clinical and basic scientists from the fields of diabetes, neuroscience, psychology, psychiatry, and imaging together, on how to best advance the field of impaired awareness of hypoglycemia and hypoglycemia in general in patients with diabetes.

Pathophysiology and management of hypoglycemia in diabetes

In the century since the discovery of insulin, diabetes has changed from an early death sentence to a manageable chronic disease. This change in longevity and duration of diabetes coupled with significant advances in therapeutic options for patients has fundamentally changed the landscape of diabetes management, particularly in patients with type 1 diabetes mellitus. However, hypoglycemia remains a major barrier to achieving optimal glycemic control. Current understanding of the mechanisms of hypoglycemia has expanded to include not only counter-regulatory hormonal responses but also direct changes in brain glucose, fuel sensing, and utilization, as well as changes in neural networks that modulate behavior, mood, and cognition. Different strategies to prevent and treat hypoglycemia have been developed, including educational strategies, new insulin formulations, delivery devices, novel technologies, and pharmacologic targets. This review article will discuss current literature contributing to our understanding of the myriad of factors that lead to the development of clinically meaningful hypoglycemia and review established and novel therapies for the prevention and treatment of hypoglycemia.

Altered functional connectivity during hypoglycaemia in type 1 diabetes

Behavioural responses to hypoglycaemia require coordinated recruitment of broadly distributed networks of interacting brain regions. We investigated hypoglycaemia-related changes in brain connectivity in people without diabetes (ND) and with type 1 diabetes with normal (NAH) or impaired (IAH) hypoglycaemia awareness. Two-step hyperinsulinaemic hypoglycaemic clamps were performed in 14 ND, 15 NAH and 22 IAH participants. BOLD timeseries were acquired at euglycaemia (5.0 mmol/L) and hypoglycaemia (2.6 mmol/L), with symptom and counter-regulatory hormone measurements. We investigated hypoglycaemia-related connectivity changes using established seed regions for the default mode (DMN), salience (SN) and central executive (CEN) networks and regions whose activity is modulated by hypoglycaemia: the thalamus and right inferior frontal gyrus (RIFG). Hypoglycaemia-induced changes in the DMN, SN and CEN were evident in NAH (all p < 0.05), with no changes in ND or IAH. However, in IAH there was a reduction in connectivity between regions within the RIFG (p = 0.001), not evident in the ND or NAH groups. We conclude that hypoglycaemia induces coordinated recruitment of the DMN and SN in diabetes with preserved hypoglycaemia awareness which is absent in IAH and ND. Changes in connectivity in the RIFG, a region associated with attentional modulation, may be key in impaired hypoglycaemia awareness.

Monitoring the Neurotransmitter Response to Glycemic Changes Using an Advanced Magnetic Resonance Spectroscopy Protocol at 7T

The primary excitatory and inhibitory neurotransmitters glutamate (Glu) and gamma-aminobutyric acid (GABA) are thought to be involved in the response of the brain to changes in glycemia. Therefore, their reliable measurement is critical for understanding the dynamics of these responses. The concentrations of Glu and GABA, as well as glucose (Glc) in brain tissue, can be measured in vivo using proton (¹H) magnetic resonance spectroscopy (MRS). Advanced MRS methodology at ultrahigh field allows reliable monitoring of these metabolites under changing metabolic states. However, the long acquisition times needed for these experiments while maintaining blood Glc levels at predetermined targets present many challenges. We present an advanced MRS acquisition protocol that combines commercial 7T hardware (Siemens Scanner and Nova Medical head coil), BaTiO₃ dielectric padding, optical motion tracking, and dynamic frequency and B₀ shim updates to ensure the acquisition of reproducibly high-quality data. Data were acquired with a semi-LASER sequence [repetition time/echo time (TR/TE) = 5,000/26 ms] from volumes of interest (VOIs) in the prefrontal cortex (PFC) and hypothalamus (HTL). Five healthy volunteers were scanned to evaluate the effect of the BaTiO₃ pads on B 1 + distribution. Use of BaTiO₃ padding resulted in a 60% gain in signal-to-noise ratio in the PFC VOI over the acquisition without the pad. The protocol was tested in six patients with type 1 diabetes during a clamp study where euglycemic (~100 mg/dL) and hypoglycemic (~50 mg/dL) blood Glc levels were maintained in the scanner. The new protocol allowed retention of all HTL data compared with our prior experience of having to exclude approximately half of the HTL data in similar clamp experiments in the 7T scanner due to subject motion. The advanced MRS protocol showed excellent data quality (reliable quantification of 11-12 metabolites) and stability (p > 0.05 for both signal-to-noise ratio and water linewidths) between euglycemia and hypoglycemia. Decreased brain Glc levels under hypoglycemia were reliably detected in both VOIs. In addition, mean Glu level trended lower at hypoglycemia than euglycemia for both VOIs, consistent with prior observations in the occipital cortex. This protocol will allow robust mechanistic investigations of the primary neurotransmitters, Glu and GABA, under changing glycemic conditions.

Effects of Gastric Bypass Surgery on the Brain: Simultaneous Assessment of Glucose Uptake, Blood Flow, Neural Activity, and Cognitive Function During Normo- and Hypoglycemia

While Roux-en-Y gastric bypass (RYGB) surgery in obese individuals typically improves glycemic control and prevents diabetes, it also frequently causes asymptomatic hypoglycemia. Previous work showed attenuated counterregulatory responses following RYGB. The underlying mechanisms as well as the clinical consequences are unclear. In this study, 11 subjects without diabetes with severe obesity were investigated pre- and post-RYGB during hyperinsulinemic normo-hypoglycemic clamps. Assessments were made of hormones, cognitive function, cerebral blood flow by arterial spin labeling, brain glucose metabolism by ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography, and activation of brain networks by functional MRI. Post- versus presurgery, we found a general increase of cerebral blood flow but a decrease of total brain FDG uptake during normoglycemia. During hypoglycemia, there was a marked increase in total brain FDG uptake, and this was similar for post- and presurgery, whereas hypothalamic FDG uptake was reduced during hypoglycemia. During hypoglycemia, attenuated responses of counterregulatory hormones and improvements in cognitive function were seen postsurgery. In early hypoglycemia, there was increased activation post- versus presurgery of neural networks in brain regions implicated in glucose regulation, such as the thalamus and hypothalamus. The results suggest adaptive responses of the brain that contribute to lowering of glycemia following RYGB, and the underlying mechanisms should be further elucidated.

Effects of continuous glucose monitor-recorded nocturnal hypoglycaemia on quality of life and mood during daily life in type 1 diabetes

AIMS/HYPOTHESIS

The aim of this work was to assess the effect of spontaneous nocturnal hypoglycaemia on quality of life and mood during subsequent days in type 1 diabetes.

METHODS

A total of 153 people with type 1 diabetes participated in 6 days of blinded continuous glucose monitoring while documenting hypoglycaemic symptoms, quality of life and mood, daily. Hypoglycaemia was defined by interstitial glucose ≤3.9 mmol/l (IG_3.9) and ≤ 3.0 mmol/l (IG_3.0) for ≥15 min and was classified as asymptomatic if no hypoglycaemic symptoms were reported.

RESULTS

Self-estimated quality of life assessed by the EQ-5D VAS (but not by the WHO Well-Being Index) was higher the day after asymptomatic (but not after symptomatic) hypoglycaemic nights, as compared with non-hypoglycaemic nights (IG_3.9, p = 0.021; IG_3.0, p = 0.048). The effect increased with lower glucose nadir and longer duration of nocturnal hypoglycaemia (IG_3.9, p = 0.03). The finding was confined to participants with impaired hypoglycaemia awareness. There was no effect of nocturnal hypoglycaemia on mood or self-estimated effectiveness at work the following day.

CONCLUSIONS/INTERPRETATION

Individuals with type 1 diabetes and impaired hypoglycaemia awareness reported higher quality of life on days preceded by nights with asymptomatic (but not symptomatic) hypoglycaemia. The effect was amplified by lower glucose nadir and longer duration of the episodes and may help explain resistance to implementation of interventions to reduce hypoglycaemia in many people with impaired hypoglycaemia awareness.

Increased cerebral FDG-PET uptake in type 1 diabetes patients with impaired awareness of hypoglycaemia

Approximately 20% of type 1 diabetes (T1D) patients have an impaired awareness of hypoglyceamia (IAH). IAH represents a risk factor for severe and recurrent hypoglycaemic events, which can lead to brain damage. Because no effective treatments are currently available to prevent IAH in this population, characterising the set of brain alterations associated with IAH may reveal novel preclinical diagnostic or therapeutic strategies. Using state-of-the art neuroimaging techniques, we compared ¹⁸ F-fluorodeoxyglucose-positron emission tomography (FDG-PET) uptake at rest between 10 T1D patients with IAH and nine patients with normal awareness of hypoglycaemia (NAH). T1D-IAH patients showed a pattern of increased FDG-PET uptake with respect to NAH patients (P < .05 corrected). Topographically, glucose metabolism was increased in the frontal and precuneus regions. Importantly, within the IAH group, this abnormal hypermetabolism correlated with IAH severity. This hypermetabolic state appeared to be unrelated to compensatory mechanisms as a result of reduced grey matter density or a neuroinflammatory state. We observed an abnormal increase in FDG-uptake in T1D patients with IAH in brain regions strongly related to cognition. Because this hypermetabolic state correlated with IAH severity, its biological characterisation could reveal new preventive or therapeutic strategies. A possible mechanism could be that glucose transport is increased in hypoglycaemia unawareness to compensate for recurrent hypoglycaemia, although this need to be confirmed in further research.

Is the Brain a Key Player in Glucose Regulation and Development of Type 2 Diabetes?

Ever since Claude Bernards discovery in the mid 19th-century that a lesion in the floor of the third ventricle in dogs led to altered systemic glucose levels, a role of the CNS in whole-body glucose regulation has been acknowledged. However, this finding was later overshadowed by the isolation of pancreatic hormones in the 20th century. Since then, the understanding of glucose homeostasis and pathology has primarily evolved around peripheral mechanism. Due to scientific advances over these last few decades, however, increasing attention has been given to the possibility of the brain as a key player in glucose regulation and the pathogenesis of metabolic disorders such as type 2 diabetes. Studies of animals have enabled detailed neuroanatomical mapping of CNS structures involved in glucose regulation and key neuronal circuits and intracellular pathways have been identified. Furthermore, the development of neuroimaging techniques has provided methods to measure changes of activity in specific CNS regions upon diverse metabolic challenges in humans. In this narrative review, we discuss the available evidence on the topic. We conclude that there is much evidence in favor of active CNS involvement in glucose homeostasis but the relative importance of central vs. peripheral mechanisms remains to be elucidated. An increased understanding of this field may lead to new CNS-focusing pharmacologic strategies in the treatment of type 2 diabetes.

Hypoglycemia unawareness in type 1 diabetes suppresses brain responses to hypoglycemia

BACKGROUND

Among nondiabetic individuals, mild glucose decrements alter brain activity in regions linked to reward, motivation, and executive control. Whether these effects differ in type 1 diabetes mellitus (T1DM) patients with and without hypoglycemia awareness remains unclear.

METHODS

Forty-two individuals (13 healthy control [HC] subjects, 16 T1DM individuals with hypoglycemia awareness [T1DM-Aware], and 13 T1DM individuals with hypoglycemia unawareness [T1DM-Unaware]) underwent blood oxygen level-dependent functional MRI brain imaging during a 2-step hyperinsulinemic euglycemic (90 mg/dl)-hypoglycemic (60 mg/dl) clamp for assessment of neural responses to mild hypoglycemia.

RESULTS

Mild hypoglycemia in HC subjects altered activity in the caudate, insula, prefrontal cortex, and angular gyrus, whereas T1DM-Aware subjects showed no caudate and insula changes, but showed altered activation patterns in the prefrontal cortex and angular gyrus. Most strikingly, in direct contrast to HC and T1DM-Aware subjects, T1DM-Unaware subjects failed to show any hypoglycemia-induced changes in brain activity. These findings were also associated with blunted hormonal counterregulatory responses and hypoglycemia symptom scores during mild hypoglycemia.

CONCLUSION

In T1DM, and in particular T1DM-Unaware patients, there is a progressive blunting of brain responses in cortico-striatal and fronto-parietal neurocircuits in response to mild-moderate hypoglycemia. These findings have implications for understanding why individuals with impaired hypoglycemia awareness fail to respond appropriately to falling blood glucose levels.

FUNDING

This study was supported in part by NIH grants R01DK020495, P30 DK045735, K23DK109284, K08AA023545. The Yale Center for Clinical Investigation is supported by an NIH Clinical Translational Science Award (UL1 RR024139).

Evaluating the relationships of hypoglycaemia and HbA1c with screening-detected diabetes distress in type 1 diabetes

AIMS

To explore the relationship between diabetes distress, glucose control and awareness of hypoglycaemia in adults with type 1 diabetes.

METHODS

We performed a cross-sectional study using data collected from 280 consecutive type 1 diabetes patients who used a routine clinic consultation tool that recorded HbA1c, hypoglycaemia awareness (measured using the Gold score) and diabetes distress (measured using the Diabetes Distress Scale 2 [DDS2]). We assessed correlations between DDS2 and HbA1c and DDS2 and Gold score and performed an ordinal regression analysis to identify factors contributing to distress.

RESULTS

Diabetes distress was significantly correlated with HbA1c (r = .319, P < .001) and Gold score (r = .258, P < .001) independently and with synergistic effect. Female gender was also associated with diabetes distress, while age, BMI, duration of diabetes, severity of complications and use of CSII pumps were not. Occurrence of severe hypoglycaemia (SH) episodes increased with Gold score in a linear manner throughout the scale.

CONCLUSIONS

This study has identified new evidence of a significant, independent relationship between diabetes distress measured by the DDS2 and reduced awareness of hypoglycaemia in people with type 1 diabetes. It also demonstrates that diabetes distress is significantly associated with HbA1c and female gender independently. The DDS2 identifies distress associated with both hypo- and hyperglycaemia and can be a useful creening tool. Additionally, the occurrence of SH increases with increasing Gold score.

Cognitive, neurophysiologic and metabolic sequelae of previous hypoglycemic coma revealed by hyperinsulinemic-hypoglycemic clamp in type 1 diabetic patients

To examine the relationship between electroencephalographic (EEG) activity and hypoglycemia unawareness, we investigated early parameters of vigilance and awareness of various symptom categories in response to hypoglycemia in intensively treated type 1 diabetic (T1DM) patients with different degrees of hypoglycemia unawareness. Hypoglycemia was induced with a hyperinsulinemic-hypoglycemic clamp in six T1DM patients with a history of hypoglycemia unawareness previous severe hypoglycemic coma (SH) and in six T1DM patients without (C) history of hypoglycemia unawareness previous severe hypoglycemic coma. Cognitive function tests (four choice reaction time), counterregulatory responses (adrenaline), and symptomatic responses were evaluated at euglycemia (90 mg/dl) and during step-wise plasma glucose reduction (68, 58 and 49 mg/dl). EEG activity was recorded continuously throughout the study and analyzed by spectral analysis. Cognitive function deteriorated significantly at a glucose threshold of 55 ± 1 mg/dl in both groups (p = ns) during hypoglycemia, while the glucose threshold for autonomic symptoms was significantly lower in SH patients than in C patients (49 ± 1 vs. 54 ± 1 mg/dl, p < 0.05, respectively). In SH patients, eye-closed resting EEG showed a correlation between the mean dominance frequency and plasma glucose (r = 0.62, p < 0.001). Theta relative power increased during controlled hypoglycemia compared to euglycemia (21.6 ± 6 vs. 15.5 ± 3% Hz p < 0.05) and was higher than in the C group (21.6 ± 6 vs. 13.8 ± 3%, p < 0.03). The cognitive task beta activity was lower in the SH group than in the C group (14.8 ± 3 Hz, vs. 22.6 ± 4 vs. p < 0.03). Controlled hypoglycemia elicits cognitive dysfunction in both C and SH patients; however, significant EEG alterations during hypoglycemia were detected mainly in patients with a history of hypoglycemia unawareness and previous severe hypoglycemic coma. These data suggest that prior episodes of hypoglycemic coma modulate brain electric activity.

Hypothalamic Glucose Transport in Humans During Experimentally Induced Hypoglycemia-Associated Autonomic Failure

CONTEXT

Upregulated brain glucose transport in response to recurrent hypoglycemia may contribute to the development of hypoglycemia-associated autonomic failure (HAAF) and impaired awareness of hypoglycemia. Whether recurrent hypoglycemia alters glucose transport in the hypothalamus is unknown.

OBJECTIVE

To test the hypothesis that hypothalamic glucose transport will increase in healthy volunteers preconditioned with recurrent hypoglycemia to induce HAAF.

SETTING

University medical center.

DESIGN AND PARTICIPANTS

Thirteen healthy subjects underwent paired euglycemic and hypoglycemic preconditioning studies separated by at least 1 month. Following preconditioning, hypothalamic glucose transport was measured by magnetic resonance spectroscopy (MRS) in the afternoon on day 2 of each preconditioning protocol.

OUTCOME MEASURE

The ratio of maximal transport rate to cerebral metabolic rate of glucose (Tmax/CMRglc), obtained from MRS-measured glucose in the hypothalamus as a function of plasma glucose.

RESULTS

HAAF was successfully induced based on lower epinephrine, glucagon, and cortisol during the third vs first hypoglycemic preconditioning clamp (P ≤ 0.01). Hypothalamic glucose transport was not different following recurrent euglycemia vs hypoglycemia (Tmax/CMRglc 1.62 ± 0.09 after euglycemia preconditioning and 1.75 ± 0.14 after hypoglycemia preconditioning; P was not significant). Hypothalamic glucose concentrations measured by MRS were not different following the two preconditioning protocols.

CONCLUSIONS

Glucose transport kinetics in the hypothalamus of healthy humans with experimentally induced HAAF were not different from those measured without HAAF. Future studies of patients with diabetes and impaired awareness of hypoglycemia will be necessary to determine if the existence of the diabetes state is required for this adaptation to hypoglycemia to occur.

Adrenaline release evokes hyperpnoea and an increase in ventilatory CO2 sensitivity during hypoglycaemia: a role for the carotid body

KEY POINTS

Hypoglycaemia is counteracted by release of hormones and an increase in ventilation and CO2 sensitivity to restore blood glucose levels and prevent a fall in blood pH. The full counter-regulatory response and an appropriate increase in ventilation is dependent on carotid body stimulation. We show that the hypoglycaemia-induced increase in ventilation and CO2 sensitivity is abolished by preventing adrenaline release or blocking its receptors. Physiological levels of adrenaline mimicked the effect of hypoglycaemia on ventilation and CO2 sensitivity. These results suggest that adrenaline, rather than low glucose, is an adequate stimulus for the carotid body-mediated changes in ventilation and CO2 sensitivity during hypoglycaemia to prevent a serious acidosis in poorly controlled diabetes.

ABSTRACT

Hypoglycaemia in vivo induces a counter-regulatory response that involves the release of hormones to restore blood glucose levels. Concomitantly, hypoglycaemia evokes a carotid body-mediated hyperpnoea that maintains arterial CO2 levels and prevents respiratory acidosis in the face of increased metabolism. It is unclear whether the carotid body is directly stimulated by low glucose or by a counter-regulatory hormone such as adrenaline. Minute ventilation was recorded during infusion of insulin-induced hypoglycaemia (8-17 mIU kg(-1)  min(-1) ) in Alfaxan-anaesthetised male Wistar rats. Hypoglycaemia significantly augmented minute ventilation (123 ± 4 to 143 ± 7 ml min(-1) ) and CO2 sensitivity (3.3 ± 0.3 to 4.4 ± 0.4 ml min(-1)  mmHg(-1) ). These effects were abolished by either β-adrenoreceptor blockade with propranolol or adrenalectomy. In this hypermetabolic, hypoglycaemic state, propranolol stimulated a rise in P aC O2, suggestive of a ventilation-metabolism mismatch. Infusion of adrenaline (1 μg kg(-1)  min(-1) ) increased minute ventilation (145 ± 4 to 173 ± 5 ml min(-1) ) without altering P aC O2 or pH and enhanced ventilatory CO2 sensitivity (3.4 ± 0.4 to 5.1 ± 0.8 ml min(-1)  mmHg(-1) ). These effects were attenuated by either resection of the carotid sinus nerve or propranolol. Physiological concentrations of adrenaline increased the CO2 sensitivity of freshly dissociated carotid body type I cells in vitro. These findings suggest that adrenaline release can account for the ventilatory hyperpnoea observed during hypoglycaemia by an augmented carotid body and whole body ventilatory CO2 sensitivity.

Brain glucose metabolism during hypoglycemia in type 1 diabetes: insights from functional and metabolic neuroimaging studies

Hypoglycemia is the most frequent complication of insulin therapy in patients with type 1 diabetes. Since the brain is reliant on circulating glucose as its main source of energy, hypoglycemia poses a threat for normal brain function. Paradoxically, although hypoglycemia commonly induces immediate decline in cognitive function, long-lasting changes in brain structure and cognitive function are uncommon in patients with type 1 diabetes. In fact, recurrent hypoglycemia initiates a process of habituation that suppresses hormonal responses to and impairs awareness of subsequent hypoglycemia, which has been attributed to adaptations in the brain. These observations sparked great scientific interest into the brain's handling of glucose during (recurrent) hypoglycemia. Various neuroimaging techniques have been employed to study brain (glucose) metabolism, including PET, fMRI, MRS and ASL. This review discusses what is currently known about cerebral metabolism during hypoglycemia, and how findings obtained by functional and metabolic neuroimaging techniques contributed to this knowledge.

A qualitative evaluation of DAFNE-HART: A psychoeducational programme to restore hypoglycaemia awareness

AIMS

Impaired awareness of hypoglycaemia (IAH) in people with type 1 diabetes is a dangerous condition that is associated with a six-fold greater risk of severe hypoglycaemia than for people with awareness. A new psychoeducational programme, DAFNE-HART, has been specifically designed to address persistent IAH. The initial pilot showed promising outcomes including fewer hypoglycaemic episodes and improved hypoglycaemia awareness. This aim of this paper is to report the development and qualitative evaluation of DAFNE-HART from participant interviews.

METHODS

DAFNE-HART incorporates diabetes education with two psychological approaches that have demonstrated efficacy in long-term health conditions: motivational interviewing and cognitive behaviour therapy. The course, delivered across two UK locations included both group and individual support over a 6-week period facilitated by DAFNE educators, trained and supervised by a clinical psychologist. Semi-structured interviews were conducted with 19 participants immediately after their courses and the interviews were analysed using grounded theory.

RESULTS

Five main themes emerged which describe the behavioural changes people made to their diabetes management, the development of new attitudes and beliefs, their experiences of regaining hypoglycaemia cues, reactions to the course format and the significance of the relationship with their care provider. Participants provide insights into how the course changed their view of IAH and led to practical changes in minimising hypoglycaemia.

CONCLUSIONS

Integration of psychological techniques into diabetes education can address the cognitive and motivational barriers to restoring awareness and optimal diabetes management. It is suggested that further research is needed to evaluate this programme in a larger sample, over a longer time frame.

Mechanisms of hypoglycemia unawareness and implications in diabetic patients

Hypoglycemia unawareness (HU) is defined at the onset of neuroglycopenia before the appearance of autonomic warning symptoms. It is a major limitation to achieving tight diabetes and reduced quality of life. HU occurs in approximately 40% of people with type 1 diabetes mellitus (T1DM) and with less frequency in T2DM. Though the aetiology of HU is multifactorial, possible mechanisms include chronic exposure to low blood glucose, antecedent hypoglycaemia, recurrent severe hypoglycaemia and the failure of counter-regulatory hormones. Clinically it manifests as the inability to recognise impeding hypoglycaemia by symptoms, but the mechanisms and mediators remain largely unknown. Prevention and management of HU is complex, and can only be achieved by a multifactorial intervention of clinical care and structured patient education by the diabetes team. Less know regarding the impact of medications on the development or recognition of this condition in patients with diabetes. Several medications are thought to worsen or promote HU, whereas others may have an attenuating effect on the problem. This article reviews recent advances in how the brain senses and responds to hypoglycaemia, novel mechanisms by which people with insulin-treated diabetes develop HU and impaired counter-regulatory responses. The consequences that HU has on the person with diabetes and their family are also described. Finally, it examines the evidence for prevention and treatment of HU, and summarizes the effects of medications that may influence it.

Recurrent Hypoglycemia Increases Anxiety and Amygdala Norepinephrine Release During Subsequent Hypoglycemia

Recurrent hypoglycemia (RH) is a common and debilitating side effect of therapy in patients with both type 1 and, increasingly, type 2 diabetes. Previous studies in rats have shown marked effects of RH on subsequent hippocampal behavioral, metabolic, and synaptic processes. In addition to impaired memory, patients experiencing RH report alterations in cognitive processes that include mood and anxiety, suggesting that RH may also affect amygdala function. We tested the impact of RH on amygdala function using an elevated plus-maze test of anxiety together with in vivo amygdala microdialysis for norepinephrine (NEp), a widely used marker of basolateral amygdala cognitive processes. In contrast to findings in the hippocampus and prefrontal cortex, neither RH nor acute hypoglycemia alone significantly affected plus-maze performance or NEp release. However, animals tested when hypoglycemic who had previously experienced RH had elevated amygdala NEp during plus-maze testing, accompanied by increased anxiety (i.e., less time spent in the open arms of the plus-maze). The results show that RH has widespread effects on subsequent brain function, which vary by neural system.

Central nervous system PET-CT imaging reveals regional impairments in pediatric patients with Wolfram syndrome

Wolfram syndrome (WFS) is inherited as an autosomal recessive disease with main clinical features of diabetes mellitus, optic atrophy, diabetes insipidus and deafness. However, various neurological defects may also be detected. The aim of this study was to evaluate aspects of brain structure and function using PET-CT (positron emission tomography and computed tomography) and MRI (magnetic resonance imaging) in pediatric patients with WFS. Regional changes in brain glucose metabolism were measured using standardized uptake values (SUVs) based on images of (18F) fluorodeoxyglucose (FDG) uptake in 7 WFS patients aged 10.1-16.0 years (mean 12.9±2.4) and in 20 healthy children aged 3-17.9 years (mean 12.8±4.1). In all patients the diagnosis of WFS was confirmed by DNA sequencing of the WFS1 gene. Hierarchical clustering showed remarkable similarities of glucose uptake patterns among WFS patients and their differences from the control group. SUV data were subsequently standardized for age groups <13 years old and>13 years old to account for developmental differences. Reduced SUVs in WFS patients as compared to the control group for the bilateral brain regions such as occipital lobe (-1.24±1.20 vs. -0.13±1.05; p = 0.028) and cerebellum (-1.11±0.69 vs. -0.204±1.00; p = 0.036) were observed and the same tendency for cingulate (-1.13±1.05 vs. -0.15±1.12; p = 0.056), temporal lobe (-1.10±0.98 vs. -0.15±1.10; p = 0.057), parietal lobe (-1.06±1.20 vs. -0.08±1.08; p = 0.058), central region (-1.01±1.04 vs. -0.09±1.06; p = 0.060), basal ganglia (-1.05±0.74 vs. -0.20±1.07; p = 0.066) and mesial temporal lobe (-1.06±0.82 vs. -0.26±1.08; p = 0.087) was also noticed. After adjusting for multiple hypothesis testing, the differences in glucose uptake were non-significant. For the first time, regional differences in brain glucose metabolism among patients with WFS were shown using PET-CT imaging.

Improving management of type 1 diabetes in the UK: the Dose Adjustment For Normal Eating (DAFNE) programme as a research test-bed. A mixed-method analysis of the barriers to and facilitators of successful diabetes self-management, a health economic analysis, a cluster randomised controlled trial of different models of delivery of an educational intervention and the potential of insulin pumps and additional educator input to improve outcomes

Background

Many adults with type 1 diabetes cannot self-manage their diabetes effectively and die prematurely with diabetic complications as a result of poor glucose control. Following the positive results obtained from a randomised controlled trial (RCT) by the Dose Adjustment For Normal Eating (DAFNE) group, published in 2002, structured training is recommended for all adults with type 1 diabetes in the UK.

Aim

With evidence that blood glucose control is not always improved or sustained, we sought to determine factors explaining why some patients benefit from training more than other patients, identifying barriers to successful self-management, while developing other models to make skills training more accessible and effective.

Findings

We confirmed that glycaemic outcomes are not always improved or sustained when the DAFNE programme is delivered routinely, although improvements in psychosocial outcomes are maintained. DAFNE courses and follow-up support is needed to help participants instil and habituate key self-management practices such as regular diary/record keeping. DAFNE graduates need structured professional support following training. This is currently either unavailable or provided ad hoc without a supporting evidence base. Demographic and psychosocial characteristics had minimal explanatory power in predicting glycaemic control but good explanatory power in predicting diabetes-specific quality of life over the following year. We developed a DAFNE course delivered for 1 day per week over 5 weeks. There were no major differences in outcomes between this and a standard 1-week DAFNE course; in both arms of a RCT, glycaemic control improved by less than in the original DAFNE trial. We piloted a course delivering both the DAFNE programme and pump training. The pilot demonstrated the feasibility of a full multicentre RCT and resulted in us obtaining subsequent Health Technology Assessment programme funding. In collaboration with the National Institute for Health Research (NIHR) Diabetes Research Programme at King’s College Hospital (RG-PG-0606-1142), London, an intervention for patients with hypoglycaemic problems, DAFNE HART (Dose Adjustment for Normal Eating Hypoglycaemia Awareness Restoration Training), improved impaired hypoglycaemia awareness and is worthy of a formal trial. The health economic work developed a new type 1 diabetes model and confirmed that the DAFNE programme is cost-effective compared with no structured education; indeed, it is cost-saving in the majority of our analyses despite limited glycated haemoglobin benefit. Users made important contributions but this could have been maximised by involving them with grant writing, delaying training until the group was established and funding users’ time off work to maximise attendance. Collecting routine clinical data to conduct continuing evaluated roll-out is possible but to do this effectively requires additional administrator support and/or routine electronic data capture.

Conclusions

We propose that, in future work, we should modify the current DAFNE curricula to incorporate emerging understanding of behaviour change principles to instil and habituate key self-management behaviours that include key DAFNE competencies. An assessment of numeracy, critical for insulin dose adjustment, may help to determine whether or not additional input/support is required both before and after training. Models of structured support involving professionals should be developed and evaluated, incorporating technological interventions to help overcome the barriers identified above and enable participants to build effective self-management behaviours into their everyday lives.

Trial registration

ClinicalTrials.gov NCT01069393.

Funding

The NIHR Programme Grants for Applied Research programme.

Cognitive, behavioural and psychological barriers to the prevention of severe hypoglycaemia: A qualitative study of adults with type 1 diabetes

OBJECTIVES

Severe hypoglycaemia affects approximately one in three people with type 1 diabetes and is the most serious side effect of insulin therapy. Our aim was to explore individualistic drivers of severe hypoglycaemia events.

METHODS

In-depth semi-structured interviews were conducted with a purposive sample of 17 adults with type 1 diabetes and a history of recurrent severe hypoglycaemia, to elicit experiences of hypoglycaemia (symptoms/awareness, progression from mild to severe and strategies for prevention/treatment). Interviews were analysed using an adapted grounded theory approach.

RESULTS

Three main themes emerged: hypoglycaemia-induced cognitive impairment, behavioural factors and psychological factors. Despite experiencing early hypoglycaemic symptoms, individuals often delayed intervention due to impaired/distracted attention, inaccurate risk assessment, embarrassment, worry about rebound hyperglycaemia or unavailability of preferred glucose source. Delay coupled with use of a slow-acting glucose source compromised prevention of severe hypoglycaemia.

CONCLUSION

Our qualitative data highlight the multifaceted, idiosyncratic nature of severe hypoglycaemia and confirm that individuals with a history of recurrent severe hypoglycaemia may have specific thought and behaviour risk profiles. Individualised prevention plans are required, emphasising both the need to attend actively to mild hypoglycaemic symptoms and to intervene promptly with an appropriate, patient-preferred glucose source to prevent progression to severe hypoglycaemia.

Banting memorial lecture 2013. A life in balance: wandering the pathways of control

‘To keep in equilibrium’, one of the Oxford English Dictionary’s many definitions of balance, is a desirable target for anylife, but has special meaning for the life of a person with diabetes. Achieving balance—between hypo- and hyperglycaemia; between energy intake and energy consumption; between insulin action and insulin secretion; between attention to diabetes and attention to everything else—remains challenging, but progress has been made over the last three decades, both in our understanding of how nature achieves balance and in the tools we have to try to reproduce the actions of nature in disease states. In particular, the role of the brain in controlling diabetes, from glucose sensing to decision making, has been investigated. Physiological and neuro-imaging studies are finally being translated into patient benefit, with the aim of improving, as Dr Banting put it, the provision of ‘energy for the economic burdens of life’.

Severe hypoglycaemia in type 1 diabetes mellitus: underlying drivers and potential strategies for successful prevention

Hypoglycaemia remains an over-riding factor limiting optimal glycaemic control in type 1 diabetes. Severe hypoglycaemia is prevalent in almost half of those with long-duration diabetes and is one of the most feared diabetes-related complications. In this review, we present an overview of the increasing body of literature seeking to elucidate the underlying pathophysiology of severe hypoglycaemia and the limited evidence behind the strategies employed to prevent episodes. Drivers of severe hypoglycaemia including impaired counter-regulation, hypoglycaemia-associated autonomic failure, psychosocial and behavioural factors and neuroimaging correlates are discussed. Treatment strategies encompassing structured education, insulin analogue regimens, continuous subcutaneous insulin infusion pumps, continuous glucose sensing and beta-cell replacement therapies have been employed, yet there is little randomized controlled trial evidence demonstrating effectiveness of new technologies in reducing severe hypoglycaemia. Optimally designed interventional trials evaluating these existing technologies and using modern methods of teaching patients flexible insulin use within structured education programmes with the specific goal of preventing severe hypoglycaemia are required. Individuals at high risk need to be monitored with meticulous collection of data on awareness, as well as frequency and severity of all hypoglycaemic episodes.

A psychoeducational program to restore hypoglycemia awareness: the DAFNE-HART pilot study

OBJECTIVE

To develop and pilot a novel intervention addressing motivational and cognitive barriers to avoiding hypoglycemia in people with type 1 diabetes and persistent impaired awareness of hypoglycemia (IAH) despite training in flexible insulin therapy.

RESEARCH DESIGN AND METHODS

A 6-week intervention using motivational interviewing and cognitive behavioral techniques was designed. Diabetes educators were trained and supported in its delivery to 23 people with IAH (Gold score ≥4).

RESULTS

Twelve months postcourse, hypoglycemia awareness had improved (P < 0.001). Median (range) rates of severe hypoglycemia (SH) fell from 3 (0-104) to 0 (0-3) per person per year (P < 0.0001) and moderate from 14 (0-100) to 0 (0-18) per person per 6 weeks (P < 0.001). Worry and behavior around hyperglycemia improved. HbA1c was unchanged.

CONCLUSIONS

A pilot intervention targeting motivation and cognitions around hypoglycemia engaged patients with resistant IAH and recurrent SH and was associated with significant improvement, supporting the hypothesis that these factors underpin problematic hypoglycemia.

Experiences, views, and support needs of family members of people with hypoglycemia unawareness: interview study

OBJECTIVE Hypoglycemia unawareness (HU) affects ~25% of people with type 1 diabetes. People with HU are often reliant on family to detect hypoglycemia and treat severe episodes. We explored the impact of HU on family members' lives, their involvement in preventing and managing hypoglycemia, and their information and support needs. RESEARCH DESIGN AND METHODS This study employed an exploratory, qualitative design comprising in-depth interviews with 24 adult family members of persons with type 1 diabetes and HU. RESULTS Family members described restricting their lives so that they could help the person with HU detect and treat hypoglycemia. Some described being very physically afraid of their partner/relative when they had a hypoglycemic episode due to their aggressive and argumentative behavior and personality changes; this could also make treatment administration difficult. Family members also reported feeling anxious and worried about the safety of the person with HU, particularly when they were left unsupervised. These concerns were often precipitated by traumatic events, such as discovering the person with HU in a coma. Family members could neglect their own health and well-being to care for the person with HU and resentment could build up over time. Family members highlighted extensive, unmet needs for information and emotional support; however, some struggled to recognize and accept their own need for help. CONCLUSIONS Our findings reveal a caregiver group currently "in the shadow of the patient" and in urgent need of information and emotional support. Raising awareness among health care professionals is essential, and developing proactive support for family should be considered.

Defective counterregulation and hypoglycemia unawareness in diabetes: mechanisms and emerging treatments

For people with diabetes, hypoglycemia remains the limiting factor in achieving glycemic control. This article reviews recent advances in how the brain senses and responds to hypoglycemia. Novel mechanisms by which individuals with insulin-treated diabetes develop hypoglycemia unawareness and impaired counterregulatory responses are outlined. Prevention strategies for reducing the incidence of hypoglycemia are discussed.

Hypoglycemia-induced increases in thalamic cerebral blood flow are blunted in subjects with type 1 diabetes and hypoglycemia unawareness

The thalamus has been found to be activated during the early phase of moderate hypoglycemia. Here, we tested the hypothesis that this region is less activated during hypoglycemia in subjects with type 1 diabetes (T1DM) and hypoglycemia unawareness relative to controls. Twelve controls (5 F/7 M, age 40 ± 14 years, body mass index 24.2 ± 2.7 kg/m(2)) and eleven patients (7 F/4 M, age 39 ± 13 years, body mass index 26.5 ± 4.4 kg/m(2)) with well-controlled T1DM (A1c 6.8 ± 0.4%) underwent a two-step hyperinsulinemic (2.0 mU/kg per minute) clamp. Cerebral blood flow (CBF) weighted images were acquired using arterial spin labeling to monitor cerebral activation in the midbrain regions. Blood glucose was first held at 95 mg/dL and then allowed to decrease to 50 mg/dL. The CBF image acquisition during euglycemia and hypoglycemia began within a few minutes of when the target blood glucose values were reached. Hypoglycemia unaware T1DM subjects displayed blunting of the physiologic CBF increase that occurs in the thalamus of healthy individuals during the early phase of moderate hypoglycemia. A positive correlation was observed between thalamic response and epinephrine response to hypoglycemia, suggesting that this region may be involved in the coordination of the counter regulatory response to hypoglycemia.

Metabolic neuroimaging of the brain in diabetes mellitus and hypoglycaemia

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

Recurrent hypoglycemia is associated with loss of activation in rat brain cingulate cortex

A subset of people with diabetes fail to mount defensive counterregulatory responses (CRR) to hypoglycemia. Although the mechanisms by which this occurs remain unclear, recurrent exposure to hypoglycemia may be an important etiological factor. We hypothesized that loss of CRR to recurrent exposure to hypoglycemia represents a type of stress desensitization, in which limbic brain circuitry involved in modulating stress responses might be implicated. Here, we compared activation of limbic brain regions associated with stress desensitization during acute hypoglycemia (AH) and recurrent hypoglycemia (RH). Healthy Sprague Dawley rats were exposed to either acute or recurrent 3-d hypoglycemia. We also examined whether changes in neuronal activation were caused directly by the CRR itself by infusing epinephrine, glucagon, and corticosterone without hypoglycemia. AH increased neuronal activity as quantified by c-fos immunoreactivity (FOS-IR) in the cingulate cortex and associated ectorhinal and perirhinal cortices but not in an adjacent control area (primary somatosensory cortex). FOS-IR was not observed after hormone infusion, suggesting that AH-associated activation was caused by hypoglycemia rather than by CRR. Importantly, AH FOS-IR activation was significantly blunted in rats exposed to RH. In conclusion, analogous with other models of stress habituation, activation in the cingulate cortex and associated brain areas is lost with exposure to RH. Our data support the hypothesis that limbic brain areas may be associated with the loss of CRR to RH in diabetes.

Patient experience of hypoglycaemia unawareness in Type 1 diabetes: are patients appropriately concerned?

OBJECTIVE

Risk of severe hypoglycaemia is increased by absence of subjective awareness of hypoglycaemia and reduced by avoidance of minor hypoglycaemia. For many, problems persist despite educational strategies that work for others. We explored psychological factors that might inhibit the efforts of an individual in hypoglycaemia avoidance.

METHODS

People with Type 1 diabetes and hypoglycaemia unawareness gave semi-structured interviews exploring their perceptions and experiences of their condition. Identified factors were grouped into categories and analysed to establish links and form a grounded theory in a constant comparative analysis. A questionnaire was devised from the qualitative analysis to identify patients with problematic beliefs about their hypoglycaemia.

RESULTS

Saturation (no new themes emerging) was reached with 17 patients. Responses fell into two groups: high concern and low concern regarding hypoglycaemia unawareness. Those in the first group described severe hypoglycaemia as aversive and wanted to regain awareness. The second group included three patients in whom unawareness was not associated with severe hypoglycaemia, nevertheless unhelpful attitudes which inhibited hypoglycaemia avoidance were expressed. Responses from this group fell into categories: (1) normalizing the presence of unawareness; (2) underestimating its consequences; (3) wanting to avoiding the 'sick role'; and (4) overestimating the consequences of hyperglycaemia.

CONCLUSIONS

A qualitative analysis of patient interviews identified deficits in education, technology and motivation in hypoglycaemia unawareness. Interventions can therefore be tailored to target underlying problems that prevent individual patients from regaining awareness. A brief assessment tool was devised to categorize patients' hypoglycaemia unawareness accordingly. Psychological interventions should be developed to address the problems of 'low concern' regarding hypoglycaemia unawareness.

Simultaneous measurement of glucose transport and utilization in the human brain

Glucose is the primary fuel for brain function, and determining the kinetics of cerebral glucose transport and utilization is critical for quantifying cerebral energy metabolism. The kinetic parameters of cerebral glucose transport, K(M)(t) and V(max)(t), in humans have so far been obtained by measuring steady-state brain glucose levels by proton ((1)H) NMR as a function of plasma glucose levels and fitting steady-state models to these data. Extraction of the kinetic parameters for cerebral glucose transport necessitated assuming a constant cerebral metabolic rate of glucose (CMR(glc)) obtained from other tracer studies, such as (13)C NMR. Here we present new methodology to simultaneously obtain kinetic parameters for glucose transport and utilization in the human brain by fitting both dynamic and steady-state (1)H NMR data with a reversible, non-steady-state Michaelis-Menten model. Dynamic data were obtained by measuring brain and plasma glucose time courses during glucose infusions to raise and maintain plasma concentration at ∼17 mmol/l for ∼2 h in five healthy volunteers. Steady-state brain vs. plasma glucose concentrations were taken from literature and the steady-state portions of data from the five volunteers. In addition to providing simultaneous measurements of glucose transport and utilization and obviating assumptions for constant CMR(glc), this methodology does not necessitate infusions of expensive or radioactive tracers. Using this new methodology, we found that the maximum transport capacity for glucose through the blood-brain barrier was nearly twofold higher than maximum cerebral glucose utilization. The glucose transport and utilization parameters were consistent with previously published values for human brain.

Adrenergic mediation of hypoglycemia-associated autonomic failure

OBJECTIVE

We tested the hypothesis that adrenergic activation, cholinergic activation, or both, mediate the effect of recent antecedent hypoglycemia to reduce the sympathoadrenal response to subsequent hypoglycemia, the key feature of hypoglycemia-associated autonomic failure in diabetes, in humans.

RESEARCH DESIGN AND METHODS

Seventeen healthy adults were studied on 2 consecutive days on three occasions. Day 1 involved hyperinsulinemic euglycemic (90 mg/dL × 1 h), then hypoglycemic (54 mg/dL × 2 h) clamps, in the morning and afternoon on all three occasions with 1) saline infusion, 2) adrenergic blockade with the nonselective α-adrenergic and β-adrenergic antagonists phentolamine and propranolol, or 3) adrenergic blockade plus cholinergic blockade with the muscarinic cholinergic antagonist atropine in random sequence. Day 2 involved similar morning euglycemic and hypoglycemic clamps, with saline infusion, on all three occasions.

RESULTS

Compared with the responses to hypoglycemia during saline infusion on day 1, the plasma epinephrine and norepinephrine responses to hypoglycemia were reduced on day 2 (351 ± 13 vs. 214 ± 22 pg/mL for epinephrine and 252 ± 4 vs. 226 ± 7 pg/mL for norepinephrine during the last hour; both P < 0.0001). However, the plasma epinephrine and norepinephrine responses to hypoglycemia were not reduced on day 2 when adrenergic or adrenergic plus cholinergic blockade was produced during hypoglycemia on day 1.

CONCLUSIONS

Adrenergic blockade prevents the effect of hypoglycemia to reduce the plasma catecholamine responses to subsequent hypoglycemia. Thus, adrenergic activation mediates the effect of recent antecedent hypoglycemia to reduce the sympathoadrenal response to subsequent hypoglycemia, the key feature of hypoglycemia-associated autonomic failure in diabetes, in humans.

Neuroendocrine responses to hypoglycemia

The counterregulatory response to hypoglycemia is a complex and well-coordinated process. As blood glucose concentration declines, peripheral and central glucose sensors relay this information to central integrative centers to coordinate neuroendocrine, autonomic, and behavioral responses and avert the progression of hypoglycemia. Diabetes, both type 1 and type 2, can perturb these counterregulatory responses. Moreover, defective counterregulation in the setting of diabetes can progress to hypoglycemia unawareness. While the mechanisms that underlie the development of hypoglycemia unawareness are not completely known, possible causes include altered sensing of hypoglycemia by the brain and/or impaired coordination of responses to hypoglycemia. Further study is needed to better understand the intricacies of the counterregulatory response and the mechanisms contributing to the development of hypoglycemia unawareness.

The medial amygdalar nucleus: a novel glucose-sensing region that modulates the counterregulatory response to hypoglycemia

OBJECTIVE

To determine whether the medial amygdalar nucleus (MAN) represents a novel brain glucose-sensing region involved in the detection of hypoglycemia and generation of a counterregulatory hormone response.

RESEARCH DESIGN AND METHODS

Fura-2 calcium imaging was used to assess glucose responsivity in neurons isolated from the MAN and single-cell real-time reverse transcription PCR used to examine gene expression within glucose-responsive neurons. In vivo studies with local MAN perfusion of the glucoprivic agent, 2-deoxyglucose (2-DG), under normal and hypoglycemic conditions and also after MAN lesioning with ibotenic acid, were used to examine the functional role of MAN glucose sensors. In addition, retrograde neuronal tracer studies were used to examine reciprocal pathways between the MAN and the ventromedial hypothalamus (VMH).

RESULTS

The MAN contains a population of glucose-sensing neurons (13.5%), which express glucokinase, and the selective urocortin 3 (UCN3) receptor CRH-R2, but not UCN3 itself. Lesioning the MAN suppressed, whereas 2-DG infusion amplified, the counterregulatory response to hyperinsulinemic hypoglycemia in vivo. However, 2-DG infusion to the MAN or VMH under normoglycemic conditions had no systemic effect. The VMH is innervated by UCN3 neurons that arise mainly from the MAN, and ∼1/3 of MAN UCN3 neurons are active during mild hypoglycemia.

CONCLUSIONS

The MAN represents a novel limbic glucose-sensing region that contains characteristic glucokinase-expressing glucose-sensing neurons that respond directly to manipulations of glucose availability both in vitro and in vivo. Moreover, UCN3 neurons may provide feedback inhibitory regulation of the counterregulatory response through actions within the VMH and the MAN.

Type 1 diabetes is associated with alexithymia in nondepressed, non-mentally ill diabetic patients: a case-control study

OBJECTIVE

Alexithymia refers to difficulty in identifying and expressing emotions, and it is a characteristic common to several psychiatric and medical conditions, including autoimmune disorders. Type 1 diabetes (T1D) is an autoimmune disorder with increased psychiatric comorbidity. Previously reported associations between alexithymia and T1D may have been confounded by the presence of depression. The central aim of this study was to examine alexithymia levels in psychiatrically uncomplicated T1D outpatients with that of nondiabetic controls.

METHODS

Ninety-six T1D patients without any DSM-IV Axis I diagnoses and 105 age- and sex-matched healthy controls entered the study. Alexithymia and depressive symptoms were assessed with the Toronto Alexithymia Scale (TAS-20) and the Beck Depression Inventory (BDI-21), respectively. Multivariate regression models were used to evaluate the association of alexithymia with the presence of diabetes, duration of diabetes, diabetes control, parameters of treatment intensification, and diabetic complications.

RESULTS

T1D was positively associated with the TAS-20 "identifying feelings" (beta coefficient=2.64, P=.003) and "externally oriented thinking" (beta coefficient=1.73, P=.011) subscales. The prevalence of overall alexithymia (TAS-20 total score, > or =60) was 22.2% in T1D patients and 7.6% in the controls (OR, 4.6; 95% CI, 1.7-12.8). TAS-20 scores were positively associated with diabetes duration and negatively with treatment intensification parameters.

CONCLUSIONS

Alexithymia is higher in psychiatrically uncomplicated T1D patients than in healthy controls even after adjustment for confounding depressive symptoms; it is greater with longer diabetes duration and is associated with some reduced parameters of treatment intensification but not with worse outcome in terms of glycemic control or somatic complications.

Hypoglycemia unawareness is associated with reduced adherence to therapeutic decisions in patients with type 1 diabetes: evidence from a clinical audit

OBJECTIVE

Hypoglycemia unawareness increases severe hypoglycemia risk. Hypoglycemia avoidance restores awareness, but it is difficult to sustain. We compared adherence to treatment changes by awareness status.

RESEARCH DESIGN AND METHODS

Case notes of 90 type 1 diabetic patients were analyzed retrospectively, identifying awareness status and insulin regimens over four visits. The proportion of patients adhering to advice and percent advice taken were calculated.

RESULTS

A total of 31 patients with hypoglycemia awareness and 19 patients with hypoglycemia unawareness were identified, with insulin regimens available in 23 and 13, respectively. Patients with hypoglycemia unawareness were older (P = 0.001) and had longer diabetes duration (P = 0.002) and lower A1C (P = 0.007). More patients with hypoglycemia unawareness reported severe hypoglycemia (P = 0.002) and fewer were adherent (53.8 vs. 87.0%, P = 0.046), with lower adherence scores (42.5 +/- 24.7 vs. 75.3 +/- 27.5%, P = 0.001).

CONCLUSIONS

Reduced adherence to changes in insulin regimen in hypoglycemia unawareness is compatible with habituation to hypoglycemic stress. Therapies aimed at reversing repetitive harmful behaviors may be useful to restore hypoglycemia awareness and protection from severe hypoglycemia.

Mechanisms of the blunting of the sympatho-adrenal response: a theory

Development of therapeutic measures to reduce the risk of potentially fatal episodes of hypoglycaemia and thus to achieve the full benefits of intensive insulin therapy in diabetic patients requires a complete understanding of the multi-factorial mechanisms for repeated hypoglycaemia-induced blunting of the sympatho-adrenal response (BSAR). After critical analysis of the hypotheses, this review paper suggests a heuristic theory. This theory suggests two mechanisms for the BSAR, each involving a critical role for the central brain noradrenergic system. Furthermore, this theory also suggests that the lateral hypothalamus (LH) plays an important role in this phenomenon. Within the framework of this theory, explanations for 1) sexual dimorphism in the adrenomedullary response (AR), 2) dissociation in the blunting of the AR and the sympathetic response (SR) and 3) antecedent exercise-induced blunting of the AR are provided. In addition, habituation of orexin-A neurons is suggested to cause defective awakening. Moreover, potential therapeutics measures have been also suggested that will reduce or prevent severe episodes of hypoglycaemia.

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.

[Hypoglycemia as a limiting factor in the management of type 1 diabetes]

Type 1 diabetic patients frequently present hypoglycemic episodes during their insulinotherapy, which, besides the discomfort and constrains does not allow the ideal glycemic control. Further, hypoglycemic events lead to the deficiency of the counter-regulation mechanisms in the subsequent episode, with a decrease in the release of epinephrine and the symptoms of warming, with great risk of severe hypoglycemia. The occurrence of hypoglycemia during some risky activities, specially driving, could result in accidents with the patient and /or third parts including property damage, stressing here the need to advise diabetics against having the necessary caution while driving. Generally the connective recovery is total after correcting a hypoglycemic coma. However when these episodes are repetitive, particularly in children, they could result in definitive cognitive disturbances. Hypoglycemic events without a warning signal (hypoglycemic unawareness) are difficult to reverse, thus it is necessary to prevent their occurrence, adjusting the treatment with glycemic targets, using continuous glucose monitoring at home and teaching them how to have an early recognition of hypoglycemia.