Brain glucose uptake and unawareness of hypoglycemia in patients with insulin-dependent diabetes mellitus

Frequency of Hypoglycemia Assessed by Continuous Glucose Monitoring in Advanced CKD

BACKGROUND

Hypoglycemia represents a risk for serious morbidity. We evaluated the prevalence and risk factors of hypoglycemia by continuous glucose monitoring (CGM) in patients with CKD with or without diabetes.

METHODS

In this cross-sectional study, outpatients with CKD stages G3-G5 (including hemodialysis) and type 2 diabetes without CKD were enrolled and underwent intermittently scanned CGM measurements for 7 days. The burden of CGM-measured hypoglycemia was assessed using the 7-day sum of area over the curve with glucose levels <70 mg/dl and the sum of time spent <54  mg/dl.

RESULTS

A total of 366 participants (148 participants with CKD and diabetes, 115 with CKD and without diabetes, and 103 without CKD and with diabetes) were included. Glucose levels of <54  mg/dl were observed in 41% of participants with CKD and diabetes, 48% of participants with CKD and without diabetes, and 14% of participants with diabetes and without CKD. However, only two participants reported hypoglycemic symptoms during CGM measurements, which were confirmed and documented by capillary blood glucose measurements. Between-group differences of 7-day area over the curve (<70 mg/dl) were as follows: hemodialysis group versus CKD stage G4 and G5 groups, -0.25 min·mg/dl per hour (95% confidence interval [CI], -6.40 to -0.59) P <0.001; CKD stage G4 and G5 groups versus CKD stage G3 group, -0.08 min·mg/dl per hour (95% CI, -0.0 to -0.50) P =0.15; and CKD stage G3 group versus diabetes without CKD group, -0.14 min·mg/dl per hour (95% CI, -0.0 to -0.20) P =0.01. In addition, the subgroup analysis of the diabetic or nondiabetic and at daytime or nighttime showed that the 7-day area over the curve (<70 mg/dl) and time spent (<54 mg/dl) was larger with worse kidney function.

CONCLUSIONS

The lowering level of kidney function was strongly associated with the burden of hypoglycemia in patients with CKD.

Chronic pancreatitis and nutritional support

Malnutrition in patients with chronic pancreatitis is common, but its evaluation is often missed in clinical practice. Pancreatic exocrine insufficiency is the single most important cause of malnutrition; therefore, it needs to be screened for and treated appropriately. Specific diet regimens in patients suffering from chronic pancreatitis are rarely reported in the literature. Patients suffering from chronic pancreatitis have a higher demand for energy but a lower caloric intake secondary to pancreatic exocrine insufficiency, combined with the malabsorption of liposoluble vitamin and micronutrients, which needs be corrected by appropriate dietary counselling. Diabetes is frequently observed in chronic pancreatitis and classified as type 3c, which is characterized by low levels of both serum insulin and glucagon; therefore, there is a tendency towards hypoglycaemia in patients treated with insulin. Diabetes contributes to malnutrition in chronic pancreatitis. Strategies to treat exocrine and endocrine insufficiency are important to achieve better control of the disease.

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.

An Overlapping Presentation of Hypoglycemia and Catatonia—A Case Report and Literature Review

Catatonia is a clinical syndrome characterized by a distinct constellation of psychomotor disturbances. It is known as a clinical manifestation of many medical and psychiatric conditions. Neuroglycopenia is a term that refers to a shortage of glucose in the brain resulting in the alteration of neuronal function. Catatonia has been observed in hypoglycemic states. We present a single case report of a 36-year-old male, with no known medical or psychiatric history, presenting with catatonia and hypoglycemia due to malnutrition. Catatonia and hypoglycemia may present similarly, and can present a challenge in differentiating the underlying etiology. It is unclear whether the hypoglycemia-catatonia overlap phenomenon is rare or rather underdiagnosed.

Reversibility of brain glucose kinetics in type 2 diabetes mellitus

AIMS/HYPOTHESIS

We have previously shown that individuals with uncontrolled type 2 diabetes have a blunted rise in brain glucose levels measured by ¹H magnetic resonance spectroscopy. Here, we investigate whether reductions in HbA_1c normalise intracerebral glucose levels.

METHODS

Eight individuals (two men, six women) with poorly controlled type 2 diabetes and mean ± SD age 44.8 ± 8.3 years, BMI 31.4 ± 6.1 kg/m² and HbA_1c 84.1 ± 16.2 mmol/mol (9.8 ± 1.4%) underwent ¹H MRS scanning at 4 Tesla during a hyperglycaemic clamp (~12.21 mmol/l) to measure changes in cerebral glucose at baseline and after a 12 week intervention that improved glycaemic control through the use of continuous glucose monitoring, diabetes regimen intensification and frequent visits to an endocrinologist and nutritionist.

RESULTS

Following the intervention, mean ± SD HbA_1c decreased by 24.3 ± 15.3 mmol/mol (2.1 ± 1.5%) (p=0.006), with minimal weight changes (p=0.242). Using a linear mixed-effects regression model to compare glucose time courses during the clamp pre and post intervention, the pre-intervention brain glucose level during the hyperglycaemic clamp was significantly lower than the post-intervention brain glucose (p<0.001) despite plasma glucose levels during the hyperglycaemic clamp being similar (p=0.266). Furthermore, the increases in brain glucose were correlated with the magnitude of improvement in HbA_1c (r = 0.71, p=0.048).

CONCLUSION/INTERPRETATION

These findings highlight the potential reversibility of cerebral glucose transport capacity and metabolism that can occur in individuals with type 2 diabetes following improvement of glycaemic control. Trial registration ClinicalTrials.gov NCT03469492.

Liver glycogen-induced enhancements in hypoglycemic counterregulation require neuroglucopenia

Iatrogenic hypoglycemia is a prominent barrier to achieving optimal glycemic control in patients with diabetes, in part due to dampened counterregulatory hormone responses. It has been demonstrated that elevated liver glycogen content can enhance these hormonal responses through signaling to the brain via afferent nerves, but the role that hypoglycemia in the brain plays in this liver glycogen effect remains unclear. During the first 4 h of each study, the liver glycogen content of dogs was increased by using an intraportal infusion of fructose to stimulate hepatic glucose uptake (HG; n = 13), or glycogen was maintained near fasting levels with a saline infusion (NG; n = 6). After a 2-h control period, during which the fructose/saline infusion was discontinued, insulin was infused intravenously for an additional 2 h to bring about systemic hypoglycemia in all animals, whereas brain euglycemia was maintained in a subset of the HG group by infusing glucose bilaterally into the carotid and vertebral arteries (HG-HeadEu; n = 7). Liver glycogen content was markedly elevated in the two HG groups (43 ± 4, 73 ± 3, and 75 ± 7 mg/g in NG, HG, and HG-HeadEu, respectively). During the hypoglycemic period, arterial plasma glucose levels were indistinguishable between groups (53 ± 2, 52 ± 1, and 51 ± 1 mg/dL, respectively), but jugular vein glucose levels were kept euglycemic (88 ± 5 mg/dL) only in the HG-HeadEu group. Glucagon and epinephrine responses to hypoglycemia were higher in HG compared with NG, whereas despite the increase in liver glycogen, neither increased above basal in HG-HeadEu. These data demonstrate that the enhanced counterregulatory hormone secretion that accompanies increased liver glycogen content requires hypoglycemia in the brain.NEW & NOTEWORTHY It is well known that iatrogenic hypoglycemia is a barrier to optimal glycemic regulation in patients with diabetes. Our data confirm that increasing liver glycogen content 75% above fasting levels enhances hormonal responses to insulin-induced hypoglycemia and demonstrate that this enhanced hormonal response does not occur in the absence of hypoglycemia in the brain. These data demonstrate that information from the liver regarding glycogen availability is integrated in the brain to optimize the counterregulatory response.

Alzheimer amyloid-β- peptide disrupts membrane localization of glucose transporter 1 in astrocytes: implications for glucose levels in brain and blood

Alzheimer’s disease (AD) is associated with disturbances in blood glucose regulation, and type-2 diabetes elevates the risk for dementia. A role for amyloid-β peptide (Aβ) in linking these age-related conditions has been proposed, tested primarily in transgenic mouse lines that overexpress mutated amyloid precursor protein (APP). Because APP has its own impacts on glucose regulation, we examined the BRI-Aβ42 line (“Aβ₄₂-tg”), which produces extracellular Aβ_1–42 in the CNS without elevation of APP. We also looked for interactions with diet-induced obesity (DIO) resulting from a high-fat, high-sucrose (“western”) diet. Aβ₄₂-tg mice were impaired in both spatial memory and glucose tolerance. Although DIO induced insulin resistance, Aβ_1–42 accumulation did not, and the impacts of DIO and Aβ on glucose tolerance were merely additive. Aβ₄₂-tg mice exhibited no significant differences from wild-type in insulin production, body weight, lipidemia, appetite, physical activity, respiratory quotient, an-/orexigenic factors, or inflammatory factors. These negative findings suggested that the phenotype in these mice arose from perturbation of glucose excursion in an insulin-independent tissue. To wit, cerebral cortex of Aβ₄₂-tg mice had reduced glucose utilization, similar to human patients with AD. This was associated with insufficient trafficking of glucose transporter 1 to the plasma membrane in parenchymal brain cells, a finding also documented in human AD tissue. Together, the lower cerebral metabolic rate of glucose and diminished function of parenchymal glucose transporter 1 indicate that aberrant regulation of blood glucose in AD likely reflects a central phenomenon, resulting from the effects of Aβ on cerebral parenchyma, rather than a generalized disruption of hypothalamic or peripheral endocrinology. The involvement of a specific glucose transporter in this deficit provides a new target for the design of AD therapies.

Risk factors and nomogram for diabetes mellitus in idiopathic chronic pancreatitis

BACKGROUND AND AIM

Diabetes mellitus (DM) is a common complication of idiopathic chronic pancreatitis (ICP), which impairs the quality of life for patients. This study aimed to identify risk factors and develop nomogram for DM in ICP to help early diagnosis.

METHODS

Idiopathic chronic pancreatitis patients admitted to our center from January 2000 to December 2013 were included. Cumulative rates of DM were calculated by Kaplan-Meier method. Patients were randomly assigned, in a 2:1 ratio, to the training and validation cohort. Based on training cohort, risk factors for DM were identified through Cox proportional hazards regression model, and nomogram was developed. Internal and external validations were performed based on the training and validation cohort, respectively.

RESULTS

Totally, 1633 patients with ICP were finally enrolled. The median follow-up duration was 9.8 years. DM was found in 26.3% (430/1633) of patients after the onset of CP. Adult at onset of ICP, biliary stricture at/before diagnosis of CP, steatorrhea at/before diagnosis of CP, and complex pathologic changes in main pancreatic duct were identified risk factors for DM development. The nomogram achieved good concordance indexes in the training and validation cohorts, respectively, with well-fitted calibration curves.

CONCLUSIONS

Risk factors were identified, and nomogram was developed to determine the risk of DM in ICP patients. Patients with one or more of the risk factors including adult at onset of ICP, biliary stricture at/before diagnosis of CP, steatorrhea at/before diagnosis of CP, and complex pathologic changes in main pancreatic duct have higher incidence of DM.

Hippocampal Neurochemical Profile and Glucose Transport Kinetics in Patients With Type 1 Diabetes

CONTEXT

Longstanding type 1 diabetes (T1D) may lead to alterations in hippocampal neurochemical profile. Upregulation of hippocampal glucose transport as a result of recurrent exposure to hypoglycemia may preserve cognitive function during future hypoglycemia in subjects with T1D and impaired awareness of hypoglycemia (IAH). The effect of T1D on hippocampal neurochemical profile and glucose transport is unknown.

OBJECTIVE

To test the hypothesis that hippocampal neurochemical composition is altered in T1D and glucose transport is upregulated in T1D with IAH.

DESIGN AND PARTICIPANTS

Hippocampal neurochemical profile was measured with single-voxel magnetic resonance spectroscopy at 3T during euglycemia in 18 healthy controls (HC), 10 T1D with IAH, and 12 T1D with normal awareness to hypoglycemia (NAH). Additionally, 12 HC, 8 T1D-IAH, and 6 T1D-NAH were scanned during hyperglycemia to assess hippocampal glucose transport with metabolic modeling.

SETTING

University medical center.

MAIN OUTCOME MEASURES

Concentrations of hippocampal neurochemicals measured during euglycemia and ratios of maximal transport rate to cerebral metabolic rate of glucose (Tmax/CMRGlc), derived from magnetic resonance spectroscopy-measured hippocampal glucose as a function of plasma glucose.

RESULTS

Comparison of hippocampal neurochemical profile revealed no group differences (HC, T1D, T1D-IAH, and T1D-NAH). The ratio Tmax/CMRGlc was not significantly different between the groups, T1D-IAH (1.58 ± 0.09) and HC (1.65 ± 0.07, P = 0.54), between T1D-NAH (1.50 ± 0.09) and HC (P = 0.19), and between T1D-IAH and T1D-NAH (P = 0.53).

CONCLUSIONS

Subjects with T1D with sufficient exposure to recurrent hypoglycemia to create IAH did not have alteration of Tmax/CMRglc or neurochemical profile compared with participants with T1D-NAH or HC.

Differential Resting State Connectivity Responses to Glycemic State in Type 1 Diabetes

CONTEXT

Individuals with type 1 diabetes mellitus (T1DM) have alterations in brain activity that have been postulated to contribute to the adverse neurocognitive consequences of T1DM; however, the impact of T1DM and hypoglycemic unawareness on the brain's resting state activity remains unclear.

OBJECTIVE

To determine whether individuals with T1DM and hypoglycemia unawareness (T1DM-Unaware) had changes in the brain resting state functional connectivity compared to healthy controls (HC) and those with T1DM and hypoglycemia awareness (T1DM-Aware).

DESIGN

Observational study.

SETTING

Academic medical center.

PARTICIPANTS

27 individuals with T1DM and 12 HC volunteers participated in the study.

INTERVENTION

All participants underwent blood oxygenation level dependent (BOLD) resting state functional magnetic brain imaging during a 2-step hyperinsulinemic euglycemic (90 mg/dL)-hypoglycemic (60 mg/dL) clamp.

OUTCOME

Changes in resting state functional connectivity.

RESULTS

Using 2 separate methods of functional connectivity analysis, we identified distinct differences in the resting state brain responses to mild hypoglycemia between HC, T1DM-Aware, and T1DM-Unaware participants, particularly in the angular gyrus, an integral component of the default mode network (DMN). Furthermore, changes in angular gyrus connectivity also correlated with greater symptoms of hypoglycemia (r = 0.461, P = 0.003) as well as higher scores of perceived stress (r = 0.531, P = 0.016).

CONCLUSION

These findings provide evidence that individuals with T1DM have changes in the brain's resting state connectivity patterns, which may be further associated with differences in awareness to hypoglycemia. These changes in connectivity may be associated with alterations in functional outcomes among individuals with T1DM.

Central Mechanisms of Glucose Sensing and Counterregulation in Defense of Hypoglycemia

Glucose homeostasis requires an organism to rapidly respond to changes in plasma glucose concentrations. Iatrogenic hypoglycemia as a result of treatment with insulin or sulfonylureas is the most common cause of hypoglycemia in humans and is generally only seen in patients with diabetes who take these medications. The first response to a fall in glucose is the detection of impending hypoglycemia by hypoglycemia-detecting sensors, including glucose-sensing neurons in the hypothalamus and other regions. This detection is then linked to a series of neural and hormonal responses that serve to prevent the fall in blood glucose and restore euglycemia. In this review, we discuss the current state of knowledge about central glucose sensing and how detection of a fall in glucose leads to the stimulation of counterregulatory hormone and behavior responses. We also review how diabetes and recurrent hypoglycemia impact glucose sensing and counterregulation, leading to development of impaired awareness of hypoglycemia in diabetes.

Recurrent glucose deprivation leads to the preferential use of lactate by neurons in the ventromedial hypothalamus

Increased GABAergic output in the ventromedial hypothalamus (VMH) contributes to counterregulatory failure in recurrently hypoglycemic (RH) rats, and lactate, an alternate fuel source in the brain, contributes to this phenomenon. The current study assessed whether recurring bouts of glucose deprivation enhanced neuronal lactate uptake and, if so, whether this influenced γ-aminobutyric acid (GABA) output and the counterregulatory responses. Glucose deprivation was induced using 5-thioglucose (5TG). Control rats received an infusion of artificial extracellular fluid. These groups were compared with RH animals. Subsequently, the rats underwent a hypoglycemic clamp with microdialysis. To test whether 5TG affected neuronal lactate utilization, a subgroup of 5TG-treated rats was microinjected with a lactate transporter inhibitor [cyano-4-hydroxycinnamate (4CIN)] just before the start of the clamp. Both RH and 5TG raised VMH GABA levels, and this was associated with impaired counterregulatory responses. 4CIN reduced VMH GABA levels and restored the hormone responses in the 5TG group. We then evaluated [¹⁴C]lactate uptake in hypothalamic neuronal cultures. Recurring exposure to low glucose increased monocarboxylate transporter-2 mRNA expression and augmented lactate uptake. Taken together, our data suggest that glucose deprivation, per se, enhances lactate utilization in hypothalamic neurons, and this may contribute to suppression of the counterregulatory responses to hypoglycemia.

Glycemic Variability and Brain Glucose Levels in Type 1 Diabetes

The impact of glycemic variability on brain glucose transport kinetics among individuals with type 1 diabetes mellitus (T1DM) remains unclear. Fourteen individuals with T1DM (age 35 ± 4 years; BMI 26.0 ± 1.4 kg/m²; HbA_1c 7.6 ± 0.3) and nine healthy control participants (age 32 ± 4; BMI 23.1 ± 0.8; HbA_1c 5.0 ± 0.1) wore a continuous glucose monitor (Dexcom) to measure hypoglycemia, hyperglycemia, and glycemic variability for 5 days followed by ¹H MRS scanning in the occipital lobe to measure the change in intracerebral glucose levels during a 2-h glucose clamp (target glucose concentration 220 mg/dL). Hyperglycemic clamps were also performed in a rat model of T1DM to assess regional differences in brain glucose transport and metabolism. Despite a similar change in plasma glucose levels during the hyperglycemic clamp, individuals with T1DM had significantly smaller increments in intracerebral glucose levels (P = 0.0002). Moreover, among individuals with T1DM, the change in brain glucose correlated positively with the lability index (r = 0.67, P = 0.006). Consistent with findings in humans, streptozotocin-treated rats had lower brain glucose levels in the cortex, hippocampus, and striatum compared with control rats. These findings that glycemic variability is associated with brain glucose levels highlight the need for future studies to investigate the impact of glycemic variability on brain glucose kinetics.

Impact of Hypoglycemia on Brain Metabolism During Diabetes

Diabetes is a metabolic disease afflicting millions of people worldwide. A substantial fraction of world's total healthcare expenditure is spent on treating diabetes. Hypoglycemia is a serious consequence of anti-diabetic drug therapy, because it induces metabolic alterations in the brain. Metabolic alterations are one of the central mechanisms mediating hypoglycemia-related functional changes in the brain. Acute, chronic, and/or recurrent hypoglycemia modulate multiple metabolic pathways, and exposure to hypoglycemia increases consumption of alternate respiratory substrates such as ketone bodies, glycogen, and monocarboxylates in the brain. The aim of this review is to discuss hypoglycemia-induced metabolic alterations in the brain in glucose counterregulation, uptake, utilization and metabolism, cellular respiration, amino acid and lipid metabolism, and the significance of other sources of energy. The present review summarizes information on hypoglycemia-induced metabolic changes in the brain of diabetic and non-diabetic subjects and the manner in which they may affect brain function.

The impact of hypoglycaemia awareness status on regional brain responses to acute hypoglycaemia in men with type 1 diabetes

AIMS/HYPOTHESIS

Impaired awareness of hypoglycaemia (IAH) in type 1 diabetes increases the risk of severe hypoglycaemia sixfold and can be resistant to intervention. We explored the impact of IAH on central responses to hypoglycaemia to investigate the mechanisms underlying barriers to therapeutic intervention.

METHODS

We conducted [¹⁵O]water positron emission tomography studies of regional brain perfusion during euglycaemia (target 5 mmol/l), hypoglycaemia (achieved level, 2.4 mmol/l) and recovery (target 5 mmol/l) in 17 men with type 1 diabetes: eight with IAH, and nine with intact hypoglycaemia awareness (HA).

RESULTS

Hypoglycaemia with HA was associated with increased activation in brain regions including the thalamus, insula, globus pallidus (GP), anterior cingulate cortex (ACC), orbital cortex, dorsolateral frontal (DLF) cortex, angular gyrus and amygdala; deactivation occurred in the temporal and parahippocampal regions. IAH was associated with reduced catecholamine and symptom responses to hypoglycaemia vs HA (incremental AUC: autonomic scores, 26.2 ± 35.5 vs 422.7 ± 237.1; neuroglycopenic scores, 34.8 ± 88.8 vs 478.9 ± 311.1; both p < 0.002). There were subtle differences (p < 0.005, k ≥ 50 voxels) in brain activation at hypoglycaemia, including early differences in the right central operculum, bilateral medial orbital (MO) cortex, and left posterior DLF cortex, with additional differences in the ACC, right GP and post- and pre-central gyri in established hypoglycaemia, and lack of deactivation in temporal regions in established hypoglycaemia.

CONCLUSIONS/INTERPRETATION

Differences in activation in the post- and pre-central gyri may be expected in people with reduced subjective responses to hypoglycaemia. Alterations in the activity of regions involved in the drive to eat (operculum), emotional salience (MO cortex), aversion (GP) and recall (temporal) suggest differences in the perceived importance and urgency of responses to hypoglycaemia in IAH compared with HA, which may be key to the persistence of the condition.

Impaired hypoglycaemia awareness in type 1 diabetes: lessons from the lab

Hypoglycaemia remains the most common metabolic adverse effect of insulin and sulfonylurea therapy in diabetes. Repeated exposure to hypoglycaemia leads to a change in the symptom complex that characterises hypoglycaemia, culminating in a clinical phenomenon referred to as impaired awareness of hypoglycaemia (IAH). IAH effects approximately 20-25% of people with type 1 diabetes and increases the risk of severe hypoglycaemia. This review focuses on the mechanisms that are responsible for the much higher frequency of hypoglycaemia in people with diabetes compared with those without, and subsequently how repeated exposure to hypoglycaemia leads to the development of IAH. The mechanisms that result in IAH development are incompletely understood and likely to reflect changes in multiple aspects of the counterregulatory response to hypoglycaemia, from adaptations within glucose and non-glucose-sensing cells to changes in the integrative networks that govern glucose homeostasis. Finally, we propose that the general process that incorporates many of these changes and results in IAH following recurrent hypoglycaemia is a form of adaptive memory called 'habituation'.

Acidosis mediates recurrent hypoglycemia-induced increase in ischemic brain injury in treated diabetic rats

OBJECTIVES

Cerebral ischemia is a serious possible manifestation of diabetic vascular disease. Recurrent hypoglycemia (RH) enhances ischemic brain injury in insulin-treated diabetic (ITD) rats. In the present study, we determined the role of ischemic acidosis in enhanced ischemic brain damage in RH-exposed ITD rats.

METHODS

Diabetic rats were treated with insulin and mild/moderate RH was induced for 5 days. Three sets of experiments were performed. The first set evaluated the effects of RH exposure on global cerebral ischemia-induced acidosis in ITD rats. The second set evaluated the effect of an alkalizing agent (Tris-(hydroxymethyl)-aminomethane: THAM) on ischemic acidosis-induced brain injury in RH-exposed ITD rats. The third experiment evaluated the effect of the glucose transporter (GLUT) inhibitor on ischemic acidosis-induced brain injury in RH-exposed ITD rats. Hippocampal pH and lactate were measured during ischemia and early reperfusion for all three experiments. Neuronal survival in Cornu Ammonis 1 (CA1) hippocampus served as a measure of ischemic brain injury.

FINDINGS

Prior RH exposure increases lactate concentration and decreases pH during ischemia and early reperfusion when compared to controls. THAM and GLUT inhibitor treatments attenuated RH-induced increase in ischemic acidosis. GLUT inhibitor treatment reduced the RH-induced increase in lactate levels. Both THAM and GLUT inhibitor treatments significantly decreased ischemic damage in RH-exposed ITD rats.

CONCLUSIONS

Ischemia causes increased acidosis in RH-exposed ITD rats via a GLUT-sensitive mechanism. Exploring downstream pathways may help understand mechanisms by which prior exposure to RH increases cerebral ischemic damage.

Antecedent Hypoglycemia Does Not Attenuate the Acceleration of Gastric Emptying by Hypoglycemia

Context

Acute hypoglycemia accelerates gastric emptying and increases cardiac contractility. However, antecedent hypoglycemia attenuates counterregulatory hormonal responses to subsequent hypoglycemia.

Objective

To determine the effect of antecedent hypoglycemia on gastric and cardiac responses to subsequent hypoglycemia in health.

Design

A prospective, single-blind, randomized, crossover study (performed at the Royal Adelaide Hospital, Adelaide, South Australia, Australia).

Patients

Ten healthy young men 18 to 35 years of age were studied for 36 hours on two occasions.

Interventions

Participants were randomly assigned to either antecedent hypoglycemia [three 45-minute periods of strict hypoglycemia (2.8 mmol/L] or control [three 45-minute periods of strict euglycemia (6 mmol/L)] during the initial 12-hour period. Participants were monitored overnight, and the following morning blood glucose was clamped at 2.8 mmol/L for 60 minutes and then at 6 mmol/L for 120 minutes. At least 6 weeks later participants returned for the alternative intervention. Gastric emptying and cardiac fractional shortening were measured with scintigraphy and two-dimensional echocardiography, respectively, on the morning of all 4 study days.

Results

A single, acute episode of hypoglycemia accelerated gastric emptying (P = 0.01) and augmented fractional shortening (P < 0.01). Gastric emptying was unaffected by antecedent hypoglycemia (P = 0.74) whereas fractional shortening showed a trend to attenuation (P = 0.06). The adrenaline response was diminished (P < 0.05) by antecedent hypoglycemia.

Conclusions

In health, the acceleration of gastric emptying during hypoglycemia is unaffected by antecedent hypoglycemia, whereas the increase in cardiac contractility may be attenuated.

Opioid Receptor Activation Impairs Hypoglycemic Counterregulation in Humans

Although intensive glycemic control improves outcomes in type 1 diabetes mellitus (T1DM), iatrogenic hypoglycemia limits its attainment. Recurrent and/or antecedent hypoglycemia causes blunting of protective counterregulatory responses, known as hypoglycemia-associated autonomic failure (HAAF). To determine whether and how opioid receptor activation induces HAAF in humans, 12 healthy subjects without diabetes (7 men, age 32.3 ± 2.2 years, BMI 25.1 ± 1.0 kg/m²) participated in two study protocols in random order over two consecutive days. On day 1, subjects received two 120-min infusions of either saline or morphine (0.1 μg/kg/min), separated by a 120-min break (all euglycemic). On day 2, subjects underwent stepped hypoglycemic clamps (nadir 60 mg/dL) with evaluation of counterregulatory hormonal responses, endogenous glucose production (EGP, using 6,6-D2-glucose), and hypoglycemic symptoms. Morphine induced an ∼30% reduction in plasma epinephrine response together with reduced EGP and hypoglycemia-associated symptoms on day 2. Therefore, we report the first studies in humans demonstrating that pharmacologic opioid receptor activation induces some of the clinical and biochemical features of HAAF, thus elucidating the individual roles of various receptors involved in HAAF's development and suggesting novel pharmacologic approaches for safer intensive glycemic control in T1DM.

Blunted rise in brain glucose levels during hyperglycemia in adults with obesity and T2DM

In rodent models, obesity and hyperglycemia alter cerebral glucose metabolism and glucose transport into the brain, resulting in disordered cerebral function as well as inappropriate responses to homeostatic and hedonic inputs. Whether similar findings are seen in the human brain remains unclear. In this study, 25 participants (9 healthy participants; 10 obese nondiabetic participants; and 6 poorly controlled, insulin- and metformin-treated type 2 diabetes mellitus (T2DM) participants) underwent 1H magnetic resonance spectroscopy scanning in the occipital lobe to measure the change in intracerebral glucose levels during a 2-hour hyperglycemic clamp (glucose ~220 mg/dl). The change in intracerebral glucose was significantly different across groups after controlling for age and sex, despite similar plasma glucose levels at baseline and during hyperglycemia. Compared with lean participants, brain glucose increments were lower in participants with obesity and T2DM. Furthermore, the change in brain glucose correlated inversely with plasma free fatty acid (FFA) levels during hyperglycemia. These data suggest that obesity and poorly controlled T2DM progressively diminish brain glucose responses to hyperglycemia, which has important implications for understanding not only the altered feeding behavior, but also the adverse neurocognitive consequences associated with obesity and T2DM.

Cerebral glycogen in humans following acute and recurrent hypoglycemia: Implications on a role in hypoglycemia unawareness

Supercompensated brain glycogen levels may contribute to the development of hypoglycemia-associated autonomic failure (HAAF) following recurrent hypoglycemia (RH) by providing energy for the brain during subsequent periods of hypoglycemia. To assess the role of glycogen supercompensation in the generation of HAAF, we estimated the level of brain glycogen following RH and acute hypoglycemia (AH). After undergoing 3 hyperinsulinemic, euglycemic and 3 hyperinsulinemic, hypoglycemic clamps (RH) on separate occasions at least 1 month apart, five healthy volunteers received [1-¹³C]glucose intravenously over 80+ h while maintaining euglycemia. ¹³C-glycogen levels in the occipital lobe were measured by ¹³C magnetic resonance spectroscopy at ∼8, 20, 32, 44, 56, 68 and 80 h at 4 T and glycogen levels estimated by fitting the data with a biophysical model that takes into account the tiered glycogen structure. Similarly, prior ¹³C-glycogen data obtained following a single hypoglycemic episode (AH) were fitted with the same model. Glycogen levels did not significantly increase after RH relative to after euglycemia, while they increased by ∼16% after AH relative to after euglycemia. These data suggest that glycogen supercompensation may be blunted with repeated hypoglycemic episodes. A causal relationship between glycogen supercompensation and generation of HAAF remains to be established.

Cerebral blood flow response to hypoglycemia is altered in patients with type 1 diabetes and impaired awareness of hypoglycemia

It is unclear whether cerebral blood flow responses to hypoglycemia are altered in people with type 1 diabetes and impaired awareness of hypoglycemia. The aim of this study was to investigate the effect of hypoglycemia on both global and regional cerebral blood flow in type 1 diabetes patients with impaired awareness of hypoglycemia, type 1 diabetes patients with normal awareness of hypoglycemia and healthy controls ( n = 7 per group). The subjects underwent a hyperinsulinemic euglycemic-hypoglycemic glucose clamp in a 3 T MR system. Global and regional changes in cerebral blood flow were determined by arterial spin labeling magnetic resonance imaging, at the end of both glycemic phases. Hypoglycemia generated typical symptoms in patients with type 1 diabetes and normal awareness of hypoglycemia and healthy controls, but not in patients with impaired awareness of hypoglycemia. Conversely, hypoglycemia increased global cerebral blood flow in patients with impaired awareness of hypoglycemia, which was not observed in the other two groups. Regionally, hypoglycemia caused a redistribution of cerebral blood flow towards the thalamus of both patients with normal awareness of hypoglycemia and healthy controls, consistent with activation of brain regions associated with the autonomic response to hypoglycemia. No such redistribution was found in the patients with impaired awareness of hypoglycemia. An increase in global cerebral blood flow may enhance nutrient supply to the brain, hence suppressing symptomatic awareness of hypoglycemia. Altogether these results suggest that changes in cerebral blood flow during hypoglycemia contribute to impaired awareness of hypoglycemia.

Insulin deficiency results in reversible protein kinase A activation and tau phosphorylation

Alzheimer's disease (AD) is a highly prevalent multifactorial disease for which Diabetes Mellitus (DM) is a risk factor. Abnormal phosphorylation and aggregation of tau is a key hallmark of AD. In animal models, DM induces or exacerbates the phosphorylation of tau, suggesting that DM may influence the risk at AD by directly facilitating tau pathology. Previously we reported that tau phosphorylation induced in response to metabolic stress is reversible. Since identification and understanding of early players in tau pathology is pivotal for therapeutic intervention, we here investigated the mechanism underlying tau phosphorylation in the diabetic brain and its potential for reversibility. To model DM we used streptozotocin-treatment to induce insulin deficiency in rats. Insulin depletion leads to increased tau phosphorylation in the brain and we investigated the activation status of known tau kinases and phosphatases in this model. We identified protein kinase A (PKA) as a tau kinase activated by DM in the brain. The potential relevance of this signaling pathway to AD pathogenesis is indicated by the increased level of active PKA in temporal cortex of early stage AD patients. Our data indicate that activation of PKA and tau phosphorylation are associated with insulin deficiency per se, rather than the downstream energy deprivation. In vitro studies confirm that insulin deficiency results in PKA activation and tau phosphorylation. Strikingly, both active PKA and induced tau phosphorylation are reversed upon insulin treatment in the steptozotocin animal model. Our data identify insulin deficiency as a direct trigger that induces the activity of the tau kinase PKA and results in tau phosphorylation. The reversibility upon insulin treatment underscores the potential of insulin as an early disease-modifying intervention in AD and other tauopathies.

Reduction in N-methyl-D-aspartate Receptor-mediated Cell Death in Hippocampal Neurons by Glucose Reduction Preconditioning

BACKGROUND

Repeated episodes of reduced glucose availability can precondition the brain against damage caused by severe hypoglycemia. Because N-methyl-D-aspartate (NMDA) receptor activation may contribute to neuronal loss in the hippocampus following glucose deprivation, we tested the hypothesis that preconditioning with reduced glucose decreased NMDA receptor-mediated cell death in hippocampal neurons.

METHODS

Hippocampal slice cultures from 7-day old rats were used to study glucose reduction preconditioning and N-methyl-D-aspartate receptor (NMDAR)-mediated cell death. Preconditioning involved reductions in glucose to the following levels: 0.1 mM, 0.5, or 1.0 mM for 30 minutes, 60 minutes, or 90 minutes on 3 consecutive days. Cell death following 1-hour total glucose deprivation was measured with a vital dye technique (SYTOX fluorescence). As an index of NMDAR activity, cell death following application of 1 mM NMDA, was also measured.

RESULTS

A preconditioning protocol of 30 minutes of 0.1 mM glucose per day for 3 days reduced cell death following 1-hour total glucose by 65% to 70%, depending on cellular region. No reduction in NMDAR-mediated cell death was seen following any of the preconditioning treatments. However, when NMDAR-mediated cell death was assessed following preconditioning combined with subsequent total glucose deprivation, cell death was reduced in the cultures that had been preconditioned with 0.1 mM glucose for 30 minutes×3 days.

CONCLUSIONS

We found that that glucose reduction preconditioning protects hippocampal neurons against severe glucose deprivation-induced neuronal damage. This preconditioning was not associated with reductions in NMDAR-mediated cell death except when the preconditioning was combined with an additional exposure to a period of total glucose deprivation.

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.

Insulin glargine 300 U/mL in the management of diabetes: clinical utility and patient perspectives

There is ongoing interest in optimizing basal insulin treatment by developing insulins with a flat pharmacological profile, a long duration of action (typically beyond 24 hours) and minimum day-to-day variation. Glargine-300 is a modified form of the long-acting insulin analog glargine in that it has been concentrated at 300 units/mL rather than the conventional 100 units/mL. Glargine-300 has a longer duration of action and a flatter pharmacological profile than original glargine-100. This property allows for more flexibility around the timing of administration, when injected once per day. Open-label studies in patients with diabetes have shown that treatment with glargine-300 achieves comparable glycemic control compared to treatment with glargine-100, albeit with consistently higher insulin requirements. These studies also showed that treatment with glargine-300 was associated with lower risks of nocturnal hypoglycemia in patients with type 2 diabetes, particularly those already on insulin, whereas data are mixed in insulin-naïve patients with type 2 diabetes or in patients with type 1 diabetes. Treatment with glargine-300 did not appear to affect the risk of overall hypoglycemia, whereas studies lacked sufficient power to investigate the effect on the risk of severe hypoglycemia. Future studies need to establish the role of glargine-300 in the treatment of diabetes alongside the other new long-acting insulin analog, insulin degludec, which was recently introduced to the market.

Cardiovascular Disease Predicts Severe Hypoglycemia in Patients with Type 2 Diabetes

BACKGROUND

To investigate whether a history of prior cardiovascular disease (CVD) is associated with severe hypoglycemia (SH) in patients with type 2 diabetes.

METHODS

We conducted a prospective cohort study from January 2001 to December 2012 with a median follow-up time of 9.5 years (5,814 person-years). Patients aged 25 to 75 years with type 2 diabetes and without chronic kidney disease were enrolled (n=894), and 624 patients completed follow-up. SH was defined as hypoglycemic episodes requiring hospitalization or medical care in an emergency department. We used the Cox proportional hazards regression analysis to test associations between SH episodes and potential explanatory variables.

RESULTS

Among the 624 participants who completed follow-up, 60 patients (9.6%) had previous CVD. Compared to patients without CVD, patients with previous CVD were older, had a longer duration of diabetes and hypertension, received more insulin, and had more diabetic microvascular complications at baseline. During follow-up, 62 patients (9.9%) experienced at least one SH episode (incidence of 1.33 per 100 patient-years). The development of SH was associated with a history of CVD (hazard ratio, 1.99; 95% confidence interval, 1.07 to 3.72; P=0.031) after adjusting for sex, age, diabetic duration, hypertension, hemoglobin A1c levels, diabetic complications, cardiovascular autonomic neuropathy, and insulin use.

CONCLUSION

A history of CVD was an independent risk factor for the development of SH in patients with type 2 diabetes mellitus. For patients with CVD, modulation of glycemic targets and diabetic education for the prevention of hypoglycemia should be implemented.

Predictors for Mild and Severe Hypoglycemia in Insulin-Treated Japanese Diabetic Patients

The objective of this study was to explore predictors, including social factors, lifestyle factors, and factors relevant to glycemic control and treatment, for mild and severe hypoglycemia in insulin-treated Japanese diabetic patients. This study included 123 insulin-treated diabetic patients who were referred to the diabetes clinic between January and July 2013 at Shiga University of Medical Science Hospital. After a survey examining the various factors, patients were followed for 6 months. During the follow-up period, blood glucose was self-monitored. Mild hypoglycemia was defined as blood glucose level 50–69 mg/dl, and severe hypoglycemia was defined as blood glucose level ≤49 mg/dl. Multinomial logistic regression was used to estimate the adjusted odds ratio (OR) and 95% confidence interval (CI) of each factor for mild and severe hypoglycemia. During the 6-month follow-up period, 41 (33.3%) patients experienced mild hypoglycemia, and 20 (16.3%) experienced severe hypoglycemia. In multivariable-adjusted analyses, assistance from family members at the time of the insulin injection [presence/absence, OR (95% CI): 0.39 (0.16–0.97)] and drinking [current drinker/non- and ex-drinker, OR (95% CI): 4.89 (1.68–14.25)] affected mild hypoglycemia. Assistance from family members at the time of insulin injection [presence/absence, OR (95% CI): 0.19 (0.05–0.75)] and intensive insulin therapy [yes/no, OR (95% CI): 3.61 (1.06–12.26)] affected severe hypoglycemia. In conclusion, our findings suggest that not only a factor relevant to glycemic control and treatment (intensive insulin therapy) but also a social factor (assistance from family members) and a lifestyle factor (current drinking) were predictors for mild or severe hypoglycemia in Japanese insulin-treated diabetic patients.

Evaluation of blood glucose fluctuation in Japanese patients with type 1 diabetes mellitus by self-monitoring of blood glucose and continuous glucose monitoring

AIMS

Accurate assessment of blood glucose fluctuation is essential for managing blood glucose control while avoiding hypoglycemia in patients with diabetes mellitus. In this study, blood glucose was measured by continuous glucose monitoring (CGM) in patients with type 1 diabetes mellitus (T1DM) whom self-monitoring of blood glucose (SMBG) was carried out three or more times per day, and evaluation was performed using blood glucose fluctuation parameters obtained by CGM and SMBG.

METHODS

Twenty-nine insulin-depleted patients with T1DM were enrolled. Their blood glucose fluctuations were measured at the same time by SMBG and CGM, and the correlations were evaluated.

RESULTS

Correlations were found between the following values obtained by SMBG and CGM: mean and standard deviation of blood glucose levels, average daily risk range, Morbus value and high-blood-glucose index. The hypoglycemia duration and the nocturnal hypoglycemia duration showed no correlation with any of the blood glucose fluctuation parameters obtained by SMBG.

CONCLUSIONS

The findings suggest that routine SMBG and glycated hemoglobin (HbA1c) measurement are sufficient for evaluation of hyperglycemia in T1DM. On the other hand, blood glucose fluctuation parameters obtained by SMBG and HbA1c have been shown to have no correlations with either hypoglycemia duration or nocturnal hypoglycemia duration.

Evaluating the SERCA2 and VEGF mRNAs as Potential Molecular Biomarkers of the Onset and Progression in Huntington's Disease

Abnormalities of intracellular Ca²⁺ homeostasis and signalling as well as the down-regulation of neurotrophic factors in several areas of the central nervous system and in peripheral tissues are hallmarks of Huntington’s disease (HD). As there is no therapy for this hereditary, neurodegenerative fatal disease, further effort should be made to slow the progression of neurodegeneration in patients through the definition of early therapeutic interventions. For this purpose, molecular biomarker(s) for monitoring disease onset and/or progression and response to treatment need to be identified. In the attempt to contribute to the research of peripheral candidate biomarkers in HD, we adopted a multiplex real-time PCR approach to analyse the mRNA level of targeted genes involved in the control of cellular calcium homeostasis and in neuroprotection. For this purpose we recruited a total of 110 subjects possessing the HD mutation at different clinical stages of the disease and 54 sex- and age-matched controls. This study provides evidence of reduced transcript levels of sarco-endoplasmic reticulum-associated ATP2A2 calcium pump (SERCA2) and vascular endothelial growth factor (VEGF) in peripheral blood mononuclear cells (PBMCs) of manifest and pre-manifest HD subjects. Our results provide a potentially new candidate molecular biomarker for monitoring the progression of this disease and contribute to understanding some early events that might have a role in triggering cellular dysfunctions in HD.

Diabetes after pancreatic surgery: novel issues

In the developed world, pancreatic surgery is becoming more common, with an increasing number of patients developing diabetes because of either partial or total pancreatectomy, with a significant impact on quality of life and survival. Although these patients are expected to consume increasing health care resources in the near future, many aspects of diabetes after pancreatectomy are still not well defined. The treatment of diabetes in these patients takes advantage of the therapies used in type 1 and 2 diabetes; however, no specific guidelines for its management, both immediately after pancreatic surgery or in the long term, have been developed. In this article, on the basis of both the literature and our clinical experience, we address the open issues and discuss the most appropriate therapeutic options for patients with diabetes after pancreatectomy.

Effect of acute hyperinsulinemia on brain metabolism evaluated by 1H MR spectroscopy--a pilot study

To determine whether acutely-induced supraphysiological hyperinsulinemia influences brain metabolism in patients with type 1 diabetes (D) and healthy controls (C) as detected by MR Spectroscopy. Group D consisted of 4 patients with the average duration of diabetes for 7 years. They were matched according to age, sex and BMI to 4 healthy controls. 1H MR Spectroscopy was performed with a 1.5 Tesla. Spectra were obtained from parietooccipital white matter repeatedly during a 3-h hyperinsulinemic euglycemic clamp with 2 mU.kg(-1).min(-1). In group D, significantly lower basal concentrations of N-acetylaspartate (p=0.02), choline (p=0.03), creatine (p=0.002) and inositol (p=0.007) were detected compared to C. After the induction of hyperinsulinemia, concentrations of choline, creatine, GABA, inositol, lactate, NAA and composite signal glutamate + glutamine (Glx) stayed stable. The detection of glucose signal is less realiable at 1.5 Tesla but we registered the alteration in glucose concentration (p=0.003) in the whole group. Originally sightly elevated glucose concentration in D decreased on the contrary to the increase of originally lower glucose level in C. In conclusions, brain metabolism was altered in D. Short term supraphysiological euglycemic hyperinsulinemia induced changes in the concentration of brain glucose in both C and D.

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’.

Hypoglycemia

Hypoglycemia remains a common problem for patients with diabetes and is associated with substantial morbidity and mortality. This article summarizes our current knowledge of the epidemiology, pathogenesis, risk factors, and complications of hypoglycemia in patients with diabetes and discusses prevention and treatment strategies.

Increased brain transport and metabolism of acetate in hypoglycemia unawareness

CONTEXT

Intensive insulin therapy reduces the risk for long-term complications in patients with type 1 diabetes mellitus (T1DM) but increases the risk for hypoglycemia-associated autonomic failure (HAAF), a syndrome that includes hypoglycemia unawareness and defective glucose counterregulation (reduced epinephrine and glucagon responses to hypoglycemia).

OBJECTIVE

The objective of the study was to address mechanisms underlying HAAF, we investigated whether nonglucose fuels such as acetate, a monocarboxylic acid (MCA), can support cerebral energetics during hypoglycemia in T1DM individuals with hypoglycemia unawareness.

DESIGN

Magnetic resonance spectroscopy was used to measure brain transport and metabolism of [2-(13)C]acetate under hypoglycemic conditions.

SETTING

The study was conducted at the Yale Center for Clinical Investigation Hospital Research Unit, Yale Magnetic Resonance Research Center.

PATIENTS AND OTHER PARTICIPANTS

T1DM participants with moderate to severe hypoglycemia unawareness (n = 7), T1DM controls without hypoglycemia unawareness (n = 5), and healthy nondiabetic controls (n = 10) participated in the study.

MAIN OUTCOME MEASURE(S)

Brain acetate concentrations, (13)C percent enrichment of glutamine and glutamate, and absolute rates of acetate metabolism were measured.

RESULTS

Absolute rates of acetate metabolism in the cerebral cortex were 1.5-fold higher among T1DM/unaware participants compared with both control groups during hypoglycemia (P = .001). Epinephrine levels of T1DM/unaware subjects were significantly lower than both control groups (P < .05). Epinephrine levels were inversely correlated with levels of cerebral acetate use across the entire study population (P < .01), suggesting a relationship between up-regulated brain MCA use and HAAF.

CONCLUSION

Increased MCA transport and metabolism among T1DM individuals with hypoglycemia unawareness may be a mechanism to supply the brain with nonglucose fuels during episodes of acute hypoglycemia and may contribute to the syndrome of hypoglycemia unawareness, independent of diabetes.

Increased brain lactate concentrations without increased lactate oxidation during hypoglycemia in type 1 diabetic individuals

Previous studies have reported that brain metabolism of acetate is increased more than twofold during hypoglycemia in type 1 diabetic (T1D) subjects with hypoglycemia unawareness. These data support the hypothesis that upregulation of blood-brain barrier monocarboxylic acid (MCA) transport may contribute to the maintenance of brain energetics during hypoglycemia in subjects with hypoglycemia unawareness. Plasma lactate concentrations are ∼10-fold higher than acetate concentrations, making lactate the most likely alternative MCA as brain fuel. We therefore examined transport of [3-(13)C]lactate across the blood-brain barrier and its metabolism in the brains of T1D patients and nondiabetic control subjects during a hypoglycemic clamp using (13)C magnetic resonance spectroscopy. Brain lactate concentrations were more than fivefold higher (P < 0.05) during hypoglycemia in the T1D subjects compared with the control subjects. Surprisingly, we observed no increase in the oxidation of blood-borne lactate in the T1D subjects, as reflected by similar (13)C fractional enrichments in brain glutamate and glutamine. Taken together, these data suggest that in addition to increased MCA transport at the blood-brain barrier, there may be additional metabolic adaptations that contribute to hypoglycemia unawareness in patients with T1D.

The role of glucose transporters in brain disease: diabetes and Alzheimer’s Disease

The occurrence of altered brain glucose metabolism has long been suggested in both diabetes and Alzheimer’s diseases. However, the preceding mechanism to altered glucose metabolism has not been well understood. Glucose enters the brain via glucose transporters primarily present at the blood-brain barrier. Any changes in glucose transporter function and expression dramatically affects brain glucose homeostasis and function. In the brains of both diabetic and Alzheimer’s disease patients, changes in glucose transporter function and expression have been observed, but a possible link between the altered glucose transporter function and disease progress is missing. Future recognition of the role of new glucose transporter isoforms in the brain may provide a better understanding of brain glucose metabolism in normal and disease states. Elucidation of clinical pathological mechanisms related to glucose transport and metabolism may provide common links to the etiology of these two diseases. Considering these facts, in this review we provide a current understanding of the vital roles of a variety of glucose transporters in the normal, diabetic and Alzheimer’s disease brain.

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.

Insulin therapy and hypoglycemia

Hypoglycemia is the most important and common side effect of insulin therapy. It is also the rate limiting factor in safely achieving excellent glycemic control. A three-fold increased risk of severe hypoglycemia occurs in both type 1 and type 2 diabetes with tight glucose control. This dictates a need to individualize therapy and glycemia goals to minimize this risk. Several ways to reduce hypoglycemia risk are recognized and discussed. They include frequent monitoring of blood sugars with home blood glucose tests and sometimes continuous glucose monitoring (CGM) in order to identify hypoglycemia particularly in hypoglycemia unawareness. Considerations include prompt measured hypoglycemia treatment, attempts to reduce glycemic variability, balancing basal and meal insulin therapy, a pattern therapy approach and use of a physiological mimicry with insulin analogues in a flexible manner. Methods to achieve adequate control while focusing on minimizing the risk of hypoglycemia are delineated in this article.

Brain activation during working memory is altered in patients with type 1 diabetes during hypoglycemia

OBJECTIVE

To investigate the effects of acute hypoglycemia on working memory and brain function in patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging during euglycemic (5.0 mmol/L) and hypoglycemic (2.8 mmol/L) hyperinsulinemic clamps, we compared brain activation response to a working-memory task (WMT) in type 1 diabetic subjects (n = 16) with that in age-matched nondiabetic control subjects (n = 16). Behavioral performance was assessed by percent correct responses.

RESULTS

During euglycemia, the WMT activated the bilateral frontal and parietal cortices, insula, thalamus, and cerebellum in both groups. During hypoglycemia, activation decreased in both groups but remained 80% larger in type 1 diabetic versus control subjects (P < 0.05). In type 1 diabetic subjects, higher HbA(1c) was associated with lower activation in the right parahippocampal gyrus and amygdala (R(2) = 0.45, P < 0.002). Deactivation of the default-mode network (DMN) also was seen in both groups during euglycemia. However, during hypoglycemia, type 1 diabetic patients deactivated the DMN 70% less than control subjects (P < 0.05). Behavioral performance did not differ between glycemic conditions or groups.

CONCLUSIONS

BOLD activation was increased and deactivation was decreased in type 1 diabetic versus control subjects during hypoglycemia. This higher level of brain activation required by type 1 diabetic subjects to attain the same level of cognitive performance as control subjects suggests reduced cerebral efficiency in type 1 diabetes.

Diffusion-weighted imaging of hyperacute cerebral hypoglycemia

BACKGROUND AND PURPOSE

Cerebral hypoglycemia can result in reversible metabolic brain insults and can be associated with impaired diffusion disturbances. Our aim was to evaluate possible changes in DWI of the human brain during hyperacute short-term severe hypoglycemia.

MATERIALS AND METHODS

Ten individuals scheduled for a clinical IST were examined with DWI while the test was performed. Venous blood glucose was continuously measured, and sequential DWI sequences were performed without interruption. Hypoglycemia was terminated with intravenous glucose administration when glucose levels were at ≤2.0 mmol/L.

RESULTS

Blood glucose levels were lowered to a mean nadir of 1.75 ± 0.38 mmol/L. No alterations of cerebral diffusion could be observed in any individuals on DWI.

CONCLUSIONS

Hyperacute short-term severe hypoglycemia does not induce visible changes in DWI of the human brain.

Recurrent hypoglycemia increases hypothalamic glucose phosphorylation activity in rats

The mechanisms underpinning impaired defensive counterregulatory responses to hypoglycemia that develop in some people with diabetes who suffer recurrent episodes of hypoglycemia are unknown. Previous work examining whether this is a consequence of increased glucose delivery to the hypothalamus, postulated to be the major hypoglycemia-sensing region, has been inconclusive. Here, we hypothesized instead that increased hypothalamic glucose phosphorylation, the first committed intracellular step in glucose metabolism, might develop following exposure to hypoglycemia. We anticipated that this adaptation might tend to preserve glucose flux during hypoglycemia, thus reducing detection of a falling glucose. We first validated a model of recurrent hypoglycemia in chronically catheterized (right jugular vein) rats receiving daily injections of insulin. We confirmed that this model of recurrent insulin-induced hypoglycemia results in impaired counterregulation, with responses of the key counterregulatory hormone, epinephrine, being suppressed significantly and progressively from the first day to the fourth day of insulin-induced hypoglycemia. In another cohort, we investigated the changes in brain glucose phosphorylation activity over 4 days of recurrent insulin-induced hypoglycemia. In keeping with our hypothesis, we found that recurrent hypoglycemia markedly and significantly increased hypothalamic glucose phosphorylation activity in a day-dependent fashion, with day 4 values 2.8 ± 0.6-fold higher than day 1 (P < .05), whereas there was no change in glucose phosphorylation activity in brain stem and frontal cortex. These findings suggest that the hypothalamus may adapt to recurrent hypoglycemia by increasing glucose phosphorylation; and we speculate that this metabolic adaptation may contribute, at least partly, to hypoglycemia-induced counterregulatory failure.

Development of fluorescent glucose bioprobes and their application on real-time and quantitative monitoring of glucose uptake in living cells

We developed a novel fluorescent glucose bioprobe, GB2-Cy3, for the real-time and quantitative monitoring of glucose uptake in living cells. We synthesized a series of fluorescent glucose analogues by adding Cy3 fluorophores to the α-anomeric position of D-glucose through various linkers. Systematic and quantitative analysis of these Cy3-labeled glucose analogues revealed that GB2-Cy3 was the ideal fluorescent glucose bioprobe. The cellular uptake of this probe competed with the cellular uptake of D-glucose in the media and was mediated by a glucose-specific transport system, and not by passive diffusion. Flow cytometry and fluorescence microscopy analyses revealed that GB2-Cy3 is ten times more sensitive than 2-NBDG, a leading fluorescent glucose bioprobe. GB2-Cy3 can also be utilized for the quantitative flow cytometry monitoring of glucose uptake in metabolically active C2C12 myocytes under various treatment conditions. As opposed to a glucose uptake assay performed by using radioisotope-labeled deoxy-D-glucose and a scintillation counter, GB2-Cy3 allows the real-time monitoring of glucose uptake in living cells under various experimental conditions by using fluorescence microscopy or confocal laser scanning microscopy (CLSM). Therefore, we believe that GB2-Cy3 can be utilized in high-content screening (HCS) for the discovery of novel therapeutic agents and for making significant advances in biomedical studies and diagnosis of various diseases, especially metabolic diseases.

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.