Identification of type I diabetic patients at increased risk for hypoglycemia during intensive therapy

Hybrid Closed Loop in Adults With Type 1 Diabetes and Severely Impaired Hypoglycemia Awareness

BACKGROUND

Benefits of hybrid closed-loop (HCL) systems in a high-risk group with type 1 diabetes and impaired awareness of hypoglycemia (IAH) have not been well-explored.

METHODS

Adults with Edmonton HYPO scores ≥1047 were randomized to 26-weeks HCL (MiniMed™ 670G) vs standard therapy (multiple daily injections or insulin pump) without continuous glucose monitoring (CGM) (control). Primary outcome was percentage CGM time-in-range (TIR; 70-180 mg/dL) at 23 to 26 weeks post-randomization. Major secondary endpoints included magnitude of change in counter-regulatory hormones and autonomic symptom responses to hypoglycemia at 26-weeks post-randomization. A post hoc analysis evaluated glycemia risk index (GRI) comparing HCL with control groups at 26 weeks post-randomization.

RESULTS

Nine participants (median [interquartile range (IQR)] age 51 [41, 59] years; 44% male; enrolment HYPO score 1183 [1058, 1308]; Clarke score 6 [6, 6]; n = 5 [HCL]; n = 4 [control]) completed the study. Time-in-range was higher using HCL vs control (70% [68, 74%] vs 48% [44, 50%], P = .014). Time <70 mg/dL did not differ (HCL 3.8% [2.7, 3.9] vs control 6.5% [4.3, 8.6], P = .14) although hypoglycemia episode duration was shorter (30 vs 50 minutes, P < .001) with HCL. Glycemia risk index was lower with HCL vs control (38.1 [30.0, 39.2] vs 70.8 [58.5, 72.4], P = .014). Following 6 months of HCL use, greater dopamine (24.0 [12.3, 27.6] vs -18.5 [-36.5, -4.8], P = .014), and growth hormone (6.3 [4.6, 16.8] vs 0.5 [-0.8, 3.0], P = .050) responses to hypoglycemia were observed.

CONCLUSIONS

Six months of HCL use in high-risk adults with severe IAH increased glucose TIR and improved GRI without increased hypoglycemia, and partially restored counter-regulatory responses.

CLINICAL TRIAL REGISTRATION

ACTRN12617000520336.

Developing the UVA/Padova Type 1 Diabetes Simulator: Modeling, Validation, Refinements, and Utility

Arguably, diabetes mellitus is one of the best quantified human conditions. In the past 50 years, the metabolic monitoring technologies progressed from occasional assessment of average glycemia via HbA1c, through episodic blood glucose readings, to continuous glucose monitoring (CGM) producing data points every few minutes. The high-temporal resolution of CGM data enabled increasingly intensive treatments, from decision support assisting insulin injection or oral medication, to automated closed-loop control, known as the "artificial pancreas." Throughout this progress, mathematical models and computer simulation of the human metabolic system became indispensable for the technological progress of diabetes treatment, enabling every step, from assessment of insulin sensitivity via the now classic Minimal Model of Glucose Kinetics, to in silico trials replacing animal experiments, to automated insulin delivery algorithms. In this review, we follow these developments, beginning with the Minimal Model, which evolved through the years to become large and comprehensive and trigger a paradigm change in the design of diabetes optimization strategies: in 2007, we introduced a sophisticated model of glucose-insulin dynamics and a computer simulator equipped with a "population" of N = 300 in silico "subjects" with type 1 diabetes. In January 2008, in an unprecedented decision, the Food and Drug Administration (FDA) accepted this simulator as a substitute to animal trials for the pre-clinical testing of insulin treatment strategies. This opened the field for rapid and cost-effective development and pre-clinical testing of new treatment approaches, which continues today. Meanwhile, animal experiments for the purpose of designing new insulin treatment algorithms have been abandoned.

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.

Evaluation of Clinical Metrics for Identifying Defective Physiologic Responses to Hypoglycemia in Long-Standing Type 1 Diabetes

Repeated hypoglycemia exposure leads to impaired awareness of hypoglycemia (IAH) and the development of defective counterregulatory responses. To date, only pancreas or islet transplantation has demonstrated normalization of hypoglycemia awareness and the endogenous glucose production (EGP) response to defend against insulin-induced hypoglycemia in long-standing type 1 diabetes (T1D). This study aims to validate clinical metrics of IAH (Clarke score), hypoglycemia severity (HYPO score), glycemic lability (lability index), and continuous glucose monitoring (CGM) as predictors of absent autonomic symptom (AS) recognition and defective glucose counterregulation during insulin-induced hypoglycemia, thus enabling early identification of individuals with compromised physiologic defense against clinically significant hypoglycemia. Forty-three subjects with mean ± standard deviation age 43 ± 13 years and T1D duration 28 ± 13 years, including 32 with IAH and 11 with hypoglycemia awareness (Aware), and 12 nondiabetic control subjects, underwent single-blinded randomized-paired hyperinsulinemic-euglycemic and hypoglycemic clamp experiments. Receiver operating characteristic (ROC) curves and sensitivity analyses were performed to assess metric prediction of absent AS recognition and defective EGP responses to hypoglycemia. Clarke score and CGM measures of hypoglycemia exposure demonstrated good ability to predict absent AS recognition (area under the curve ≥0.80). A composite threshold of IAH-Clarke ≥4 with ROC curve-derived thresholds for CGM measures of hypoglycemia exposure showed high specificity and predictive value in identifying an absent AS response during the hypoglycemic clamp. Metrics demonstrated poor ability to predict defective glucose counterregulation by the EGP response, which was impaired even in the Aware group. Screening for IAH alongside assessment of CGM data can increase the specificity for identifying individuals with absent hypoglycemia symptom recognition who may benefit from further intervention.

Review: experimentally induced hypoglycemia-associated autonomic failure in humans: determinants, designs and drawbacks

Context

Iatrogenic hypoglycemia remains one of the leading hindrances of optimal glycemic management in insulin-treated diabetes. Recurring hypoglycemia leads to a condition of hypoglycemia-associated autonomic failure (HAAF). HAAF refers to a combination of (i) impaired hormonal counterregulatory responses and (ii) hypoglycemia unawareness to subsequent hypoglycemia, substantially increasing the risk of severe hypoglycemia. Several studies since the 1990s have experimentally induced HAAF, yielding variable results.

Objective

The aim of this review was to assess the varying designs, clinical outcomes, potential assets, and drawbacks related to these studies.

Method

A systemic literature search was conducted on PubMed and Embase in winter 2021 to include all human studies attempting to experimentally induce HAAF. In different combinations, the search terms used were “hypoglycemia-associated autonomic failure,” “HAAF,” “hypoglycemia,” “recurring,” “recurrent,” “repeated,” “consecutive,” and “unawareness,” yielding 1565 publications. Inclusion criteria were studies that had aimed at experimentally inducing HAAF and measuring outcomes of hormonal counterregulation and awareness of hypoglycemia.

Results

The literature search yielded 27 eligible publications, of which 20 were successful in inducing HAAF while statistical significantly impairing both hormonal counterregulation and impairing awareness of hypoglycemia to subsequent hypoglycemia. Several factors were of significance as regards inducing HAAF: Foremost, the duration of antecedent hypoglycemia should be at least 90 minutes and blood glucose should be maintained below 3.4 mmol/L. Other important factors to consider are the type of participants, insulin dosage, and the risk of unintended hypoglycemia prior to the study.

Conclusion

Here we have outlined the most important factors to take into consideration when designing a study aimed at inducing HAAF, including to take into consideration other disease states susceptible to hypoglycemia, thus hopefully clarifying the field and allowing qualified studies in the future.

Insulin Granule-Loaded MicroPlates for Modulating Blood Glucose Levels in Type-1 Diabetes

Type-1 diabetes (T1DM) is a chronic metabolic disorder resulting from the autoimmune destruction of β cells. The current standard of care requires multiple, daily injections of insulin and accurate monitoring of blood glucose levels (BGLs); in some cases, this results in diminished patient compliance and increased risk of hypoglycemia. Herein, we engineered hierarchically structured particles comprising a poly(lactic-co-glycolic) acid (PLGA) prismatic matrix, with a 20 × 20 μm base, encapsulating 200 nm insulin granules. Five configurations of these insulin-microPlates (INS-μPLs) were realized with different heights (5, 10, and 20 μm) and PLGA contents (10, 40, and, 60 mg). After detailed physicochemical and biopharmacological characterizations, the tissue-compliant 10H INS-μPL, realized with 10 mg of PLGA, presented the most effective release profile with ∼50% of the loaded insulin delivered at 4 weeks. In diabetic mice, a single 10H INS-μPL intraperitoneal deposition reduced BGLs to that of healthy mice within 1 h post-implantation (167.4 ± 49.0 vs 140.0 ± 9.2 mg/dL, respectively) and supported normoglycemic conditions for about 2 weeks. Furthermore, following the glucose challenge, diabetic mice implanted with 10H INS-μPL successfully regained glycemic control with a significant reduction in AUC_0-120min (799.9 ± 134.83 vs 2234.60 ± 82.72 mg/dL) and increased insulin levels at 7 days post-implantation (1.14 ± 0.11 vs 0.38 ± 0.02 ng/mL), as compared to untreated diabetic mice. Collectively, these results demonstrate that INS-μPLs are a promising platform for the treatment of T1DM to be further optimized with the integration of smart glucose sensors.

Glucagon as a Therapeutic Approach to Severe Hypoglycemia: After 100 Years, Is It Still the Antidote of Insulin?

Hypoglycemia represents a dark and tormented side of diabetes mellitus therapy. Patients treated with insulin or drug inducing hypoglycemia, consider hypoglycemia as a harmful element, which leads to their resistance and lack of acceptance of the pathology and relative therapies. Severe hypoglycemia, in itself, is a risk for patients and relatives. The possibility to have novel strategies and scientific knowledge concerning hypoglycemia could represent an enormous benefit. Novel available glucagon formulations, even now, allow clinicians to deal with hypoglycemia differently with respect to past years. Novel scientific evidence leads to advances concerning physiopathological mechanisms that regulated glycemic homeostasis. In this review, we will try to show some of the important aspects of this field.

Sustained Impact of Real-time Continuous Glucose Monitoring in Adults With Type 1 Diabetes on Insulin Pump Therapy: Results After the 24-Month RESCUE Study

OBJECTIVE

In recent years, a growing number of people with type 1 diabetes gained access to real-time continuous glucose monitoring (rtCGM). Long-term benefits of rtCGM are unclear because of a lack of large studies of long duration. We evaluated whether real-world rtCGM use up to 24 months offered benefits, particularly in those living with impaired awareness of hypoglycemia (IAH).

RESEARCH DESIGN AND METHODS

This 24-month, prospective, observational cohort study followed 441 adults with insulin pumps receiving full reimbursement for rtCGM. Forty-two percent had IAH. The primary end point was evolution of HbA_1c, with secondary end points change in acute hypoglycemia complications, diabetes-related work absenteeism, and quality of life scores. Additionally, we evaluated whether people could achieve glycemic consensus targets during follow-up.

RESULTS

After 24 months, HbA_1c remained significantly lower compared with baseline (7.64% [60 mmol/mol] vs. 7.37% [57 mmol/mol], P < 0.0001). Sustained benefits were also observed for the score on the hypoglycemia fear survey and hypoglycemia-related acute complications irrespective of hypoglycemia awareness level. People with IAH had the strongest improvement, especially for severe hypoglycemia (862 events in the year before vs. 119 events per 100 patient-years in the 2nd year, P < 0.0001). Over 24 months, more people were able to meet hypoglycemia consensus targets at the expense of slightly fewer people achieving hyperglycemia consensus targets. Furthermore, the number of people with HbA_1c <7% (<53 mmol/mol) without severe hypoglycemia events more than doubled (11.0% vs. 25.4%, P < 0.0001).

CONCLUSIONS

Use of rtCGM led to sustained improvements in hypoglycemia-related glucose control over 24 months. Lower fear of hypoglycemia, fewer acute hypoglycemia-related events, and fewer diabetes-related days off from work were observed, particularly in those with IAH.

People with type 1 diabetes and impaired awareness of hypoglycaemia have a delayed reaction to performing a glucose scan during hypoglycaemia: a prospective observational study

AIMS

Considering that people with type 1 diabetes and impaired awareness of hypoglycaemia (IAH) have a delayed perception of hypoglycaemia, the question arises whether they perform scans later in case of hypoglycaemia than people without IAH. We assessed whether time to performing a scan after reaching hypoglycaemia while using a flash glucose monitoring (flash GM) system is different in people with IAH compared with people without IAH.

METHODS

Ninety-two people with type 1 diabetes [mean (± sd) age 42 ± 14 years, HbA1c 57 ± 9 mmol/mol] using a flash GM system for 3 months were included. Flash GM data were assessed for time until scan after reaching hypoglycaemia level 1 (< 3.9 mmol/l) and level 2 (< 3.0 mmol/l) and compared for type 1 diabetes with vs. without IAH via unpaired t-test/Mann-Whitney U test (P < 0.05).

RESULTS

Significant differences were found only for the delay between reaching hypoglycaemia and scan between people with and without IAH for Gold score [hypoglycaemia level 1: IAH 78 (51-105) min vs. without IAH 63 (42-89) min, P = 0.03; night-time hypoglycaemia level 2: IAH 140 (107-227) min vs. without IAH 96 (41-155) min, P = 0.004] and Pedersen-Bjergaard score [hypoglycaemia level 1: IAH 76 (52-97) min vs. without IAH 54 (38-71) min, P = 0.011; night-time hypoglycaemia level 1: IAH 132 (79-209) min vs. without IAH 89 (59-143) min, P = 0.011; night-time hypoglycaemia level 2: IAH 134 (66-212) min vs. without IAH 80 (37-131) min, P = 0.002). Data are shown as median (i.q.r.).

CONCLUSIONS

Time until scan after reaching hypoglycaemia might be an objective assessment tool for IAH, but needs to be investigated comprehensively in future studies.

Plasma Epinephrine Contributes to the Development of Experimental Hypoglycemia-Associated Autonomic Failure

BACKGROUND

Recurrent hypoglycemia blunts counter-regulatory responses to subsequent hypoglycemic episodes, a syndrome known as hypoglycemia-associated autonomic failure (HAAF). Since adrenergic receptor blockade has been reported to prevent HAAF, we investigated whether the hypoglycemia-associated rise in plasma epinephrine contributes to pathophysiology and reported interindividual differences in susceptibility to HAAF.

METHODS

To assess the role of hypoglycemia-associated epinephrine responses in the susceptibility to HAAF, 24 adult nondiabetic subjects underwent two 2-hour hyperinsulinemic hypoglycemic clamp studies (nadir 54 mg/dL; 0-2 hours and 4-6 hours) on Day 1, followed by a third identical clamp on Day 2. We challenged an additional 7 subjects with two 2-hour infusions of epinephrine (0.03 μg/kg/min; 0-2 hours and 4-6 hours) vs saline on Day 1 followed by a 200-minute stepped hypoglycemic clamp (90, 80, 70, and 60 mg/dL) on Day 2.

RESULTS

Thirteen out of 24 subjects developed HAAF, defined by ≥20% reduction in average epinephrine levels during the final 30 minutes of the third compared with the first hypoglycemic episode (P < 0.001). Average epinephrine levels during the final 30 minutes of the first hypoglycemic episode were 2.3 times higher in subjects who developed HAAF compared with those who did not (P = 0.006).Compared to saline, epinephrine infusion on Day 1 reduced the epinephrine responses by 27% at the 70 and 60 mg/dL glucose steps combined (P = 0.04), with a parallel reduction in hypoglycemic symptoms (P = 0.03) on Day 2.

CONCLUSIONS

Increases in plasma epinephrine reproduce key features of HAAF in nondiabetic subjects. Marked interindividual variability in epinephrine responses to hypoglycemia may explain an individual's susceptibility to developing HAAF.

Hypoglycaemia and its management in primary care setting

Hypoglycaemia is common in patients with type 1 diabetes and type 2 diabetes and constitutes a major limiting factor in achieving glycaemic control among people with diabetes. While hypoglycaemia is defined as a blood glucose level under 70 mg/dL (3.9 mmol/L), symptoms may occur at higher blood glucose levels in individuals with poor glycaemic control. Severe hypoglycaemia is defined as an episode requiring the assistance of another person to actively administer carbohydrate, glucagon, or take other corrective actions to assure neurologic recovery. Hypoglycaemia is the most important safety outcome in clinical studies of glucose lowering agents. The American Diabetes Association Standards of Medical Care recommends that a management protocol for hypoglycaemia should be designed and implemented by every hospital, along with a clear prevention and treatment plan. A tailored approach, using clinical and pathophysiologic disease stratification, can help individualize glycaemic goals and promote new therapies to improve quality of life of patients. Data from recent large clinical trials reported low risk of hypoglycaemic events with the use of newer anti-diabetic drugs. Increased hypoglycaemia risk is observed with the use of insulin and/or sulphonylureas. Vulnerable patients with T2D at dual risk of severe hypoglycaemia and cardiovascular outcomes show features of "frailty." Many of such patients may be better treated by the use of GLP-1 receptor agonists or SGLT2 inhibitors rather than insulin. Continuous glucose monitoring (CGM) should be considered for all individuals with increased risk for hypoglycaemia, impaired hypoglycaemia awareness, frequent nocturnal hypoglycaemia and with history of severe hypoglycaemia. Patients with impaired awareness of hypoglycaemia benefit from real-time CGM. The diabetes educator is an invaluable resource and can devote the time needed to thoroughly educate the individual to reduce the risk of hypoglycaemia and integrate the information within the entire construct of diabetes self-management. Conversations about hypoglycaemia facilitated by a healthcare professional may reduce the burden and fear of hypoglycaemia among patients with diabetes and their family members. Optimizing insulin doses and carbohydrate intake, in addition to a short warm up before or after the physical activity sessions may help avoiding hypoglycaemia. Several therapeutic considerations are important to reduce hypoglycaemia risk during pregnancy including administration of rapid-acting insulin analogues rather than human insulin, pre-conception initiation of insulin analogues, and immediate postpartum insulin dose reduction.

Prevalence of severe hypoglycemia in a cohort of patients with type 1 diabetes

INTRODUCTION

Hypoglycemia is the major limiting factor in the glycemic management of type 1 diabetes. Severe hypoglycemia puts patients at risk of injury and death. Recurrent hypoglycemia leads to impaired awareness of hypoglycemia and this increases the risk of severe hypoglycemia. Recent studies have reported rates for severe hypoglycemia of 35% in type 1 diabetic patients.

OBJECTIVES

To assess the prevalence of severe hypoglycemia in type 1 diabetes mellitus patients and to evaluate the relationship between this and impaired awareness of hypoglycemia according to the Clarke test.

PATIENTS AND METHODS

The following data were collected from a cohort of type 1 diabetic patients: age, gender, duration of type 1 diabetes, treatment (multiple daily insulin injection or continuous subcutaneous insulin infusion), glycemia self-control, HbA1c, episodes of severe hypoglycemia and impaired awareness of hypoglycemia.

RESULTS

Of the participants, 39.8% had had at least one episode of severe hypoglycemia (in the previous 6 months), 11.4% with loss of consciousness (in the previous 12 months). According to the Clark test, 40.9% had impaired awareness of hypoglycemia. Older age and longer duration of diabetes were associated with a higher prevalence of severe hypoglycemia with unconsciousness; older age and a lower level of HbA1c were associated with impaired awareness of hypoglycemia.

CONCLUSIONS

Our study allows us to confirm the high rate of severe hypoglycemia and impaired awareness of hypoglycemia in patients with type 1 diabetes.

Glycemic Variability: Risk Factors, Assessment, and Control

Glycemic variability (GV) a well-established risk factor for hypoglycemia and a suspected risk factor for diabetes complications. GV is also a marker of the instability of a person's metabolic system, expressed as frequent high and low glucose excursions and overall volatile glycemic control. In this review, the author discusses topics related to the assessment, quantification, and optimal control of diabetes, including (1) the notion that optimal control of diabetes, that is, lowering of HbA1c-the commonly accepted gold-standard outcome-can be achieved only if accompanied by simultaneous reduction of GV; (2) assessment and visualization of the two principal dimensions of GV, amplitude and time, which is now possible via continuous glucose monitoring (CGM) and various metrics quantifying GV and the risks associated with hypo- and hyperglycemic excursions; and (3) the evolution of diabetes science and technology beyond quantifying GV and into the realm of GV control via pharmacological agents, for example, GLP-1 receptor agonists and DPP-4 inhibitors, which have pronounced variability-reducing effect, or real-time automated closed-loop systems commonly referred to as the "artificial pancreas." The author concludes that CGM allows close tracking over time, and therefore precise quantification, of glycemic variability in diabetes. The next step-optimal control of glucose fluctuations-is also taken by medications with pronounced GV-lowering effect primarily in type 2 diabetes, and by automated insulin delivery in type 1 diabetes. Contemporary CGM-based artificial pancreas systems use specific GV representations as input signals, and thus their main objective is to minimize GV and, from there, optimize glycemic control.

A Century of Diabetes Technology: Signals, Models, and Artificial Pancreas Control

Arguably, diabetes mellitus is one of the best-quantified human conditions: elaborate in silico models describe the action of the human metabolic system; real-time signals such as continuous glucose monitoring are readily available; insulin delivery is being automated; and control algorithms are capable of optimizing blood glucose fluctuation in patients' natural environments. The transition of the artificial pancreas (AP) to everyday clinical use is happening now, and is contingent upon seamless concerted work of devices encompassing the patient in a digital treatment ecosystem. This review recounts briefly the story of diabetes technology, which began a century ago with the discovery of insulin, progressed through glucose monitoring and subcutaneous insulin delivery, and is now rapidly advancing towards fully automated clinically viable AP systems.

Diabetes Technology: Monitoring, Analytics, and Optimal Control

Over the past 50 years, the diabetes technology field progressed remarkably through self-monitoring of blood glucose (SMBG), continuous subcutaneous insulin infusion (CSII), risk and variability analysis, mathematical models and computer simulation of the human metabolic system, real-time continuous glucose monitoring (CGM), and control algorithms driving closed-loop control systems known as the "artificial pancreas" (AP). This review follows these developments, beginning with an overview of the functioning of the human metabolic system in health and in diabetes and of its detailed quantitative network modeling. The review continues with a brief account of the first AP studies that used intravenous glucose monitoring and insulin infusion, and with notes about CSII and CGM-the technologies that made possible the development of contemporary AP systems. In conclusion, engineering lessons learned from AP research, and the clinical need for AP systems to prove their safety and efficacy in large-scale clinical trials, are outlined.

Utilizing the Ambulatory Glucose Profile to Standardize and Implement Continuous Glucose Monitoring in Clinical Practice

Use of continuous glucose monitoring (CGM) is recognized as a valuable component of diabetes self-management and is increasingly considered a standard of care for individuals with diabetes who are treated with intensive insulin therapy. As the clinical use of CGM technology expands, consistent and standardized glycemic metrics and glucose profile visualization have become increasingly important. A common set of CGM metrics has been proposed by an international expert panel in 2017, including standard definitions of time in ranges, glucose variability, and adequacy of data collection. We describe the core CGM metrics, as well as the standardized glucose profile format consolidating 2 weeks of CGM measurements, referred to as the ambulatory glucose profile (AGP), which was also recommended by the CGM expert panel. We present an updated AGP report featuring the core CGM metrics and a visualization of glucose patterns that need clinical attention. New tools for use by clinicians and patients to interpret AGP data are reviewed. Strategies based on the authors' experience in implementing CGM technology across the clinical care spectrum are highlighted.

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.

Automated closed-loop control of diabetes: the artificial pancreas

The incidence of Diabetes Mellitus is on the rise worldwide, which exerts enormous health toll on the population and enormous pressure on the healthcare systems. Now, almost hundred years after the discovery of insulin in 1921, the optimization problem of diabetes is well formulated as maintenance of strict glycemic control without increasing the risk for hypoglycemia. External insulin administration is mandatory for people with type 1 diabetes; various medications, as well as basal and prandial insulin, are included in the daily treatment of type 2 diabetes. This review follows the development of the Diabetes Technology field which, since the 1970s, progressed remarkably through continuous subcutaneous insulin infusion (CSII), mathematical models and computer simulation of the human metabolic system, real-time continuous glucose monitoring (CGM), and control algorithms driving closed-loop control systems known as the "artificial pancreas" (AP). All of these developments included significant engineering advances and substantial bioelectronics progress in the sensing of blood glucose levels, insulin delivery, and control design. The key technologies that enabled contemporary AP systems are CSII and CGM, both of which became available and sufficiently portable in the beginning of this century. This powered the quest for wearable home-use AP, which is now under way with prototypes tested in outpatient studies during the past 6 years. Pivotal trials of new AP technologies are ongoing, and the first hybrid closed-loop system has been approved by the FDA for clinical use. Thus, the closed-loop AP is well on its way to become the digital-age treatment of diabetes.

Prevention and Management of Severe Hypoglycemia and Hypoglycemia Unawareness: Incorporating Sensor Technology

PURPOSE OF REVIEW

In addition to assisting in achieving improved glucose control, continuous glucose monitoring (CGM) sensor technology may also aid in detection and prevention of hypoglycemia. In this paper, we report on the current scientific evidence on the effectiveness of this technology in the prevention of severe hypoglycemia and hypoglycemia unawareness.

RECENT FINDINGS

Recent studies have found that the integration of CGM with continuous subcutaneous insulin infusion (CSII) therapy, a system known as sensor-augmented pump (SAP) therapy, very significantly reduces the occurrence of these conditions by providing real-time glucose readings/trends and automatically suspending insulin infusion when glucose is low (LGS) or, even, before glucose is low but is predicted to soon be low (PLGS). Initial data indicate that even for patients with type 1 diabetes treated with multiple daily injections, real-time CGM alone has been found to reduce both severe hypoglycemia and hypoglycemia unawareness. Closed loop systems (artificial pancreas) comprised of CGM and CSII without patient intervention to adjust basal insulin, which automatically reduce, increase, and suspend insulin delivery, represent a potential new option that is moving toward becoming a reality in the near future. Sensor technology promises to continue to improve patients' lives not only by attaining glycemic control but also by reducing hypoglycemia, a goal best achieved in conjunction with structured individualized patient education.

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.

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).

Interdisciplinary approach to compensation of hypoglycemia in diabetic patients with chronic heart failure

Diabetes mellitus is a chronic disease requiring lifelong control with hypoglycemic agents that must demonstrate excellent efficacy and safety profiles. In patients taking glucose-lowering drugs, hypoglycemia is a common cause of death associated with arrhythmias, increased thrombus formation, and specific effects of catecholamines due to sympathoadrenal activation. Focus is now shifting from merely glycemic control to multifactorial approach. In the context of individual drugs and classes, this article reviews interdisciplinary strategies evaluating metabolic effects of drugs for treatment of chronic heart failure (CHF) which can mask characteristic hypoglycemia symptoms. Hypoglycemia unawareness and cardiac autonomic neuropathy are discussed. Data suggesting that hypoglycemia modulates immune response are reviewed. The potential role of gut microbiota in improving health of patients with diabetes and CHF is emphasized. Reports stating that nondiabetic CHF patients can have life-threatening hypoglycemia associated with imbalance of thyroid hormones are discussed. Regular glycemic control based on HbA1c measurements and adequate pharmacotherapy remain the priorities in diabetes management. New antihyperglycemic drugs with safer profiles should be preferred in vulnerable CHF patients. Multidrug interactions must be considered. Emerging therapies with reduced hypoglycemia risk, telemedicine, sensor technologies, and genetic testing predicting hypoglycemia risk may help solving the challenges of hypoglycemia in CHF patients with diabetes. Interdisciplinary work may involve cardiologists, diabetologists/endocrinologists, immunologists, gastroenterologists, microbiologists, nutritionists, imaging specialists, geneticists, telemedicine experts, and other relevant specialists. This review emphasizes that systematic knowledge on pathophysiology of hypoglycemia in diabetic patients with CHF is largely lacking and the gaps in our understanding require further discoveries.

Metrics for glycaemic control - from HbA1c to continuous glucose monitoring

As intensive treatment to lower levels of HbA_1c characteristically results in an increased risk of hypoglycaemia, patients with diabetes mellitus face a life-long optimization problem to reduce average levels of glycaemia and postprandial hyperglycaemia while simultaneously avoiding hypoglycaemia. This optimization can only be achieved in the context of lowering glucose variability. In this Review, I discuss topics that are related to the assessment, quantification and optimal control of glucose fluctuations in diabetes mellitus. I focus on markers of average glycaemia and the utility and/or shortcomings of HbA_1c as a 'gold-standard' metric of glycaemic control; the notion that glucose variability is characterized by two principal dimensions, amplitude and time; measures of glucose variability that are based on either self-monitoring of blood glucose data or continuous glucose monitoring (CGM); and the control of average glycaemia and glucose variability through the use of pharmacological agents or closed-loop control systems commonly referred to as the 'artificial pancreas'. I conclude that HbA_1c and the various available metrics of glucose variability reflect the management of diabetes mellitus on different timescales, ranging from months (for HbA_1c) to minutes (for CGM). Comprehensive assessment of the dynamics of glycaemic fluctuations is therefore crucial for providing accurate and complete information to the patient, physician, automated decision-support or artificial-pancreas system.

Sex Differences and Role of Estradiol in Hypoglycemia-Associated Counter-Regulation

Vital nerve cell functions, including maintenance of transmembrane voltage and information transfer, occur at high energy expense. Inadequate provision of the obligate metabolic fuel glucose exposes neurons to risk of dysfunction or injury. Clinical hypoglycemia rarely occurs in nondiabetic individuals but is an unfortunate regular occurrence in patients with type 1 or advanced insulin-treated type 2 diabetes mellitus. Requisite strict glycemic control, involving treatment with insulin, sulfonylureas, or glinides, can cause frequent episodes of iatrogenic hypoglycemia due to defective counter-regulation, including reduced glycemic thresholds and diminished magnitude of motor responses. Multiple components of the body's far-reaching energy balance regulatory network, including the hindbrain dorsal vagal complex, provide dynamic readout of cellular energetic disequilibrium, signals that are utilized by the hypothalamus to shape counterregulatory autonomic, neuroendocrine, and behavioral outflow toward restoration of glucostasis. The ovarian steroid hormone 17β-estradiol acts on central substrates to preserve nerve cell energy stability brain-wide, thereby providing neuroprotection against bio-energetic insults such as neurodegenerative diseases and acute brain ischemia. The current review highlights recent evidence implicating estrogen in gluco-regulation in females by control of hindbrain metabolic sensor screening and signaling of hypoglycemia-associated neuro-energetic instability. It is anticipated that new understanding of the mechanistic basis of how estradiol influences metabolic sensory input from this critical brain locus to discrete downstream regulatory network substrates will likely reveal viable new molecular targets for therapeutic simulation of hormone actions that promote positive neuronal metabolic state during acute and recurring hypoglycemia.

Diabetic autonomic neuropathy

Diabetes mellitus is the commonest cause of an autonomic neuropathy in the developed world. Diabetic autonomic neuropathy causes a constellation of symptoms and signs affecting cardiovascular, urogenital, gastrointestinal, pupillomotor, thermoregulatory, and sudomotor systems. Several discrete syndromes associated with diabetes cause autonomic dysfunction. The most prevalent of these are: generalized diabetic autonomic neuropathy, autonomic neuropathy associated with the prediabetic state, treatment-induced painful and autonomic neuropathy, and transient hypoglycemia-associated autonomic neuropathy. These autonomic manifestations of diabetes are responsible for the most troublesome and disabling features of diabetic peripheral neuropathy and result in a significant proportion of the mortality and morbidity associated with the disease.

Hypoglycemia in the Critically Ill Patient

Hypoglycemia is diagnosed convincingly when typical symptoms are associated with a low plasma glucose concentration and are relieved by glucose administration. It requires urgent treatment (usually with intravenous glucose in the hospital setting), diagnostic explanation, and long-term prevention. The latter is based upon an understanding of the pathogenesis of hypoglycemia in the affected patient. Postabsorptive (fasting) hypoglycemia is often caused by drugs (especially insulin, a sulfonylurea, or alcohol); it can also result from endogenous hyperinsulinism (insulinoma, autoimmune hypoglycemia), a non-β-cell tumor, hormonal deficiencies, or a variety of clinical syndromes including sepsis, cardiac, renal, and hepatic failure, and even inanition per se. Hypoglycemia is a treatable cause of acute morbidity. It is sometimes a cause of chronic morbidity and even mortality that could have been prevented.

Managing hypoglycaemia

Intensive glycaemic control reduces the diabetic microvascular disease burden but iatrogenic hypoglycaemia is a major barrier preventing tight glycaemic control because of the limitations of subcutaneous insulin preparations and insulin secretagogues. Severe hypoglycaemia is uncommon early in the disease as robust physiological defences, particularly glucagon and adrenaline release, limit falls in blood glucose whilst associated autonomic symptoms drive patients to take action by ingesting oral carbohydrate. With increasing diabetes duration, glucagon release is progressively impaired and sympatho-adrenal responses are activated at lower glucose levels. Repeated hypoglycaemic episodes contribute to impaired defences, increasing the risk of severe hypoglycaemia in a vicious downward spiral. Managing hypoglycaemia requires a systematic clinical approach with structured insulin self-management training and support of experienced diabetes educators. Judicious use of technologies includes insulin analogues, insulin pump therapy, continuous glucose monitoring, and in a few cases islet cell transplantation. Some individuals require specialist psychological support.

Glucose Variability: Timing, Risk Analysis, and Relationship to Hypoglycemia in Diabetes

Glucose control, glucose variability (GV), and risk for hypoglycemia are intimately related, and it is now evident that GV is important in both the physiology and pathophysiology of diabetes. However, its quantitative assessment is complex because blood glucose (BG) fluctuations are characterized by both amplitude and timing. Additional numerical complications arise from the asymmetry of the BG scale. In this Perspective, we focus on the acute manifestations of GV, particularly on hypoglycemia, and review measures assessing the amplitude of GV from routine self-monitored BG data, as well as its timing from continuous glucose monitoring (CGM) data. With availability of CGM, the latter is not only possible but also a requirement-we can now assess rapid glucose fluctuations in real time and relate their speed and magnitude to clinically relevant outcomes. Our primary message is that diabetes control is all about optimization and balance between two key markers-frequency of hypoglycemia and HbA1c reflecting average BG and primarily driven by the extent of hyperglycemia. GV is a primary barrier to this optimization, including to automated technologies such as the "artificial pancreas." Thus, it is time to standardize GV measurement and thereby streamline the assessment of its two most important components-amplitude and timing.

Philip E. Cryer, MD: Seminal Contributions to the Understanding of Hypoglycemia and Glucose Counterregulation and the Discovery of HAAF (Cryer Syndrome)

Optimized glycemic control prevents and slows the progression of long-term complications in patients with type 1 and type 2 diabetes. In healthy individuals, a decrease in plasma glucose below the physiological range triggers defensive counterregulatory responses that restore euglycemia. Many individuals with diabetes harbor defects in their defenses against hypoglycemia, making iatrogenic hypoglycemia the Achilles heel of glycemic control. This Profile in Progress focuses on the seminal contributions of Philip E. Cryer, MD, to our understanding of hypoglycemia and glucose counterregulation, particularly his discovery of the syndrome of hypoglycemia-associated autonomic failure (HAAF).

Effects of sitagliptin on counter-regulatory and incretin hormones during acute hypoglycaemia in patients with type 1 diabetes: a randomized double-blind placebo-controlled crossover study

AIMS

To assess whether the dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin affects glucagon and other counter-regulatory hormone responses to hypoglycaemia in patients with type 1 diabetes.

METHODS

We conducted a single-centre, randomized, double-blind, placebo-controlled, three-period crossover study. We studied 16 male patients with type 1 diabetes aged 18-52 years, with a diabetes duration of 5-20 years and intact hypoglycaemia awareness. Participants received sitagliptin (100 mg/day) or placebo for 6 weeks and attended the hospital for three acute hypoglycaemia studies (at baseline, after sitagliptin treatment and after placebo). The primary outcome was differences between the three hypoglycaemia study days with respect to plasma glucagon responses from the initialization phase of the hypoglycaemia intervention to 40 min after onset of the autonomic reaction.

RESULTS

Sitagliptin treatment significantly increased active levels of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1. No significant differences were observed for glucagon or adrenergic counter-regulatory responses during the three hypoglycaemia studies. Growth hormone concentration at 40 min after occurrence of autonomic reaction was significantly lower after sitagliptin treatment [median (IQR) 23 (0.2-211.0) mEq/l] compared with placebo [median (IQR) 90 (8.8-180) mEq/l; p = 0.008].

CONCLUSIONS

Sitagliptin does not affect glucagon or adrenergic counter-regulatory responses in patients with type 1 diabetes, but attenuates the growth hormone response during late hypoglycaemia.

Diazoxide improves hormonal counterregulatory responses to acute hypoglycemia in long-standing type 1 diabetes

Individuals with long-standing type 1 diabetes (T1D) are at increased risk of severe hypoglycemia secondary to impairments in normal glucose counterregulatory responses (CRRs). Strategies to prevent hypoglycemia are often ineffective, highlighting the need for novel therapies. ATP-sensitive potassium (KATP) channels within the hypothalamus are thought to be integral to hypoglycemia detection and initiation of CRRs; however, to date this has not been confirmed in human subjects. In this study, we examined whether the KATP channel-activator diazoxide was able to amplify the CRR to hypoglycemia in T1D subjects with long-duration diabetes. A randomized, double-blind, placebo-controlled cross-over trial using a stepped hyperinsulinemic hypoglycemia clamp was performed in 12 T1D subjects with prior ingestion of diazoxide (7 mg/kg) or placebo. Diazoxide resulted in a 37% increase in plasma levels of epinephrine and a 44% increase in plasma norepinephrine during hypoglycemia compared with placebo. In addition, a subgroup analysis revealed that the response to oral diazoxide was blunted in participants with E23K polymorphism in the KATP channel. This study has therefore shown for the first time the potential utility of KATP channel activators to improve CRRs to hypoglycemia in individuals with T1D and, moreover, that it may be possible to stratify therapeutic approaches by genotype.

Causative anti-diabetic drugs and the underlying clinical factors for hypoglycemia in patients with diabetes

Recent clinical trials indicated that the intensive glycemic control do not reduce cardiovascular disease mortality among diabetic patients, challenging a significance of the strict glycemic control in diabetes management. Furthermore, retrospective analysis of the Action to Control Cardiovascular Risk in Diabetes study demonstrated a significant association between hypoglycemia and mortality. Here, we systematically reviewed the drug-induced hypoglycemia, and also the underlying clinical factors for hypoglycemia in patients with diabetes. The sulfonylurea use is significantly associated with severe hypoglycemia in patients with type 2 diabetes. The use of biguanide (approximately 45%-76%) and thiazolidinediones (approximately 15%-34%) are also highly associated with the development of severe hypoglycemia. In patients treated with insulin, the intensified insulin therapy is more frequently associated with severe hypoglycemia than the conventional insulin therapy and continuous subcutaneous insulin infusion. Among the underlying clinical factors for development of severe hypoglycemia, low socioeconomic status, aging, longer duration of diabetes, high HbA1c and low body mass index, comorbidities are precipitating factors for severe hypoglycemia. Poor cognitive and mental functions are also associated with severe hypoglycemia.

Hypoglycaemia in diabetes mellitus: epidemiology and clinical implications

Hypoglycaemia is a frequent adverse effect of treatment of diabetes mellitus with insulin and sulphonylureas. Fear of hypoglycaemia alters self-management of diabetes mellitus and prevents optimal glycaemic control. Mild (self-treated) and severe (requiring help) hypoglycaemia episodes are more common in type 1 diabetes mellitus but people with insulin-treated type 2 diabetes mellitus are also exposed to frequent hypoglycaemic events, many of which occur during sleep. Hypoglycaemia can disrupt many everyday activities such as driving, work performance and leisure pursuits. In addition to accidents and physical injury, the morbidity of hypoglycaemia involves the cardiovascular and central nervous systems. Whereas coma and seizures are well-recognized neurological sequelae of hypoglycaemia, much interest is currently focused on the potential for hypoglycaemia to cause dangerous and life-threatening cardiac complications, such as arrhythmias and myocardial ischaemia, and whether recurrent severe hypoglycaemia can cause permanent cognitive impairment or promote cognitive decline and accelerate the onset of dementia in middle-aged and elderly people with diabetes mellitus. Prevention of hypoglycaemia is an important part of diabetes mellitus management and strategies include patient education, glucose monitoring, appropriate adjustment of diet and medications in relation to everyday circumstances including physical exercise, and the application of new technologies such as real-time continuous glucose monitoring, modified insulin pumps and the artificial pancreas.

Blunted glucagon but not epinephrine responses to hypoglycemia occurs in youth with less than 1 yr duration of type 1 diabetes mellitus

CONTEXT

Glycemic control is limited by the barrier of hypoglycemia. Recurrent hypoglycemia impairs counterregulatory (CR) hormone responses to subsequent hypoglycemia.

OBJECTIVE

To determine the glucagon and epinephrine responses to insulin-induced hypoglycemia in adolescents with recent-onset type 1 diabetes mellitus (T1DM).

METHODS

We assessed the CR responses to hypoglycemia by performing a hyperinsulinemic (2.0 mU/kg/min), euglycemic (BG 90 mg/dL; 5.0 mmol/L)-hypoglycemic (BG 55 mg/dL; 3.0 mmol/L) clamp in 25 recent-onset (<1 yr duration) patients 9-18 yr old (mean ± SD: 13.4 ± 2.7) with T1DM and 16 non-diabetic controls 19-25 yr old (mean ± SD 23.3 ± 1.8). Twenty of the T1DM subjects were retested 1-yr (53 ± 3 wk) later.

RESULTS

At the initial and 1-yr studies, peak glucagon (pGON) and incremental glucagon (ΔGON) during hypoglycemia were lower in the T1DM subjects [median pGON = 47 pg/mL (quartiles: 34, 72), ΔGON = 16 (4, 27) initially and pGON = 50 pg/mL (42, 70), ΔGON = 12 (9, 19) at 1-yr] than in controls [pGON = 93 pg/mL (60, 111); ΔGON = 38 pg/mL (19, 66), p = 0.01 and p = 0.004 for ΔGON at initial and 1-yr study, respectively]. In contrast, peak epinephrine (pEPI) and incremental epinephrine (ΔEPI) levels were similar in the T1DM (pEPI = 356 pg/mL (174, 797) and ΔEPI = 322 pg/mL (143, 781) initially and pEPI = 469 pg/mL (305, 595) and ΔEPI = 440 pg/mL (285, 574) at 1 yr) and in controls (pEPI = 383 pg/mL (329, 493) and ΔEPI = 336 pg/mL (298, 471) p = 0.97 and 0.21 for ΔEPI at initial and 1-yr study, respectively).

CONCLUSIONS

Even within the first year of T1DM, glucagon responses to hypoglycemia are blunted but epinephrine responses are not, suggesting that the mechanisms involved in the loss of these hormonal responses, which are key components in pathophysiology of hypoglycemia-associated autonomic failure, are different.

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.

Neuronal damage and cognitive impairment associated with hypoglycemia: An integrated view

The aim of the present review is to offer a current perspective about the consequences of hypoglycemia and its impact on the diabetic disorder due to the increasing incidence of diabetes around the world. The main consequence of insulin treatment in type 1 diabetic patients is the occurrence of repetitive periods of hypoglycemia and even episodes of severe hypoglycemia leading to coma. In the latter, selective neuronal death is observed in brain vulnerable regions both in humans and animal models, such as the cortex and the hippocampus. Cognitive damage subsequent to hypoglycemic coma has been associated with neuronal death in the hippocampus. The mechanisms implicated in selective damage are not completely understood but many factors have been identified including excitotoxicity, oxidative stress, zinc release, PARP-1 activation and mitochondrial dysfunction. Importantly, the diabetic condition aggravates neuronal damage and cognitive failure induced by hypoglycemia. In the absence of coma prolonged and severe hypoglycemia leads to increased oxidative stress and discrete neuronal death mainly in the cerebral cortex. The mechanisms responsible for cell damage in this condition are still unknown. Recurrent moderate hypoglycemia is far more common in diabetic patients than severe hypoglycemia and currently important efforts are being done in order to elucidate the relationship between cognitive deficits and recurrent hypoglycemia in diabetics. Human studies suggest impaired performance mainly in memory and attention tasks in healthy and diabetic individuals under the hypoglycemic condition. Only scarce neuronal death has been observed under moderate repetitive hypoglycemia but studies suggest that impaired hippocampal synaptic function might be one of the causes of cognitive failure. Recent studies have also implicated altered mitochondrial function and mitochondrial oxidative stress.

Lack of association between residual insulin production and glucagon response to hypoglycemia in youth with short duration of type 1 diabetes

OBJECTIVE

To examine the loss of glucagon response to hypoglycemia and its relationship with residual β-cell function early in the course of type 1 diabetes (T1D) in youth.

RESEARCH DESIGN AND METHODS

Twenty-one youth with T1D duration <1 year (ages 8-18 years, T1D duration 6-52 weeks) underwent mixed-meal tolerance tests (MMTTs) to assess residual β-cell function and hypoglycemic clamps to assess glucagon responses to hypoglycemia. Glucagon responses to hypoglycemia in T1D subjects were compared with those in 12 nondiabetic young adults (ages 19-25 years).

RESULTS

Peak MMTT-stimulated C-peptide levels (range 0.12-1.43) were ≥ 0.2 nmol/L in all but one T1D subject. As expected, the median of glucagon responses to hypoglycemia in the T1D subjects (18 pg/mL [interquartile range 7-32]) was significantly reduced compared with the responses in nondiabetic control subjects (38 pg/mL [19-66], P = 0.02). However, there was no correlation between the incremental increase in plasma glucagon during the hypoglycemic clamp and the incremental increase and peak plasma C-peptide level during the MMTT. Similarly, the seven T1D subjects who failed to achieve an increase in glucagon ≥ 12 pg/mL (i.e., 3 SD above baseline values) had C-peptide response ≥ 0.2 nmol/L (0.54-1.12), and the one T1D subject with peak stimulated <0.2 nmol/L had a 14 pg/mL increase in plasma glucagon in response to hypoglycemia.

CONCLUSIONS

Impaired plasma glucagon responses to hypoglycemia are evident in youth with T1D during the first year of the disease. Moreover, defective and absent glucagon responses to hypoglycemia were observed in patients who retained clinically important residual endogenous β-cell function.

Hypoglycemia and diabetes: a report of a workgroup of the American Diabetes Association and the Endocrine Society

OBJECTIVE

To review the evidence about the impact of hypoglycemia on patients with diabetes that has become available since the past reviews of this subject by the American Diabetes Association and The Endocrine Society and to provide guidance about how this new information should be incorporated into clinical practice.

PARTICIPANTS

Five members of the American Diabetes Association and five members of The Endocrine Society with expertise in different aspects of hypoglycemia were invited by the Chair, who is a member of both, to participate in a planning conference call and a 2-day meeting that was also attended by staff from both organizations. Subsequent communications took place via e-mail and phone calls. The writing group consisted of those invitees who participated in the writing of the manuscript. The workgroup meeting was supported by educational grants to the American Diabetes Association from Lilly USA, LLC and Novo Nordisk and sponsorship to the American Diabetes Association from Sanofi. The sponsors had no input into the development of or content of the report.

EVIDENCE

The writing group considered data from recent clinical trials and other studies to update the prior workgroup report. Unpublished data were not used. Expert opinion was used to develop some conclusions.

CONSENSUS PROCESS

Consensus was achieved by group discussion during conference calls and face-to-face meetings, as well as by iterative revisions of the written document. The document was reviewed and approved by the American Diabetes Association's Professional Practice Committee in October 2012 and approved by the Executive Committee of the Board of Directors in November 2012 and was reviewed and approved by The Endocrine Society's Clinical Affairs Core Committee in October 2012 and by Council in November 2012.

CONCLUSIONS

The workgroup reconfirmed the previous definitions of hypoglycemia in diabetes, reviewed the implications of hypoglycemia on both short- and long-term outcomes, considered the implications of hypoglycemia on treatment outcomes, presented strategies to prevent hypoglycemia, and identified knowledge gaps that should be addressed by future research. In addition, tools for patients to report hypoglycemia at each visit and for clinicians to document counseling are provided.

Hypoglycemia and diabetes: a report of a workgroup of the American Diabetes Association and the Endocrine Society

OBJECTIVE

To review the evidence about the impact of hypoglycemia on patients with diabetes that has become available since the past reviews of this subject by the American Diabetes Association and The Endocrine Society and to provide guidance about how this new information should be incorporated into clinical practice.

PARTICIPANTS

Five members of the American Diabetes Association and five members of The Endocrine Society with expertise in different aspects of hypoglycemia were invited by the Chair, who is a member of both, to participate in a planning conference call and a 2-day meeting that was also attended by staff from both organizations. Subsequent communications took place via e-mail and phone calls. The writing group consisted of those invitees who participated in the writing of the manuscript. The workgroup meeting was supported by educational grants to the American Diabetes Association from Lilly USA, LLC and Novo Nordisk and sponsorship to the American Diabetes Association from Sanofi. The sponsors had no input into the development of or content of the report.

EVIDENCE

The writing group considered data from recent clinical trials and other studies to update the prior workgroup report. Unpublished data were not used. Expert opinion was used to develop some conclusions.

CONSENSUS PROCESS

Consensus was achieved by group discussion during conference calls and face-to-face meetings, as well as by iterative revisions of the written document. The document was reviewed and approved by the American Diabetes Association's Professional Practice Committee in October 2012 and approved by the Executive Committee of the Board of Directors in November 2012 and was reviewed and approved by The Endocrine Society's Clinical Affairs Core Committee in October 2012 and by Council in November 2012.

CONCLUSIONS

The workgroup reconfirmed the previous definitions of hypoglycemia in diabetes, reviewed the implications of hypoglycemia on both short- and long-term outcomes, considered the implications of hypoglycemia on treatment outcomes, presented strategies to prevent hypoglycemia, and identified knowledge gaps that should be addressed by future research. In addition, tools for patients to report hypoglycemia at each visit and for clinicians to document counseling are provided.

Comparison of regional cerebral blood flow responses to hypoglycemia using pulsed arterial spin labeling and positron emission tomography

Different brain regions sense and modulate the counterregulatory responses that can occur in response to declining plasma glucose levels. The aim of this study was to determine if changes in regional cerebral blood flow (rCBF) during hypoglycemia relative to euglycemia are similar for two imaging modalities–pulsed arterial spin labeling magnetic resonance imaging (PASL-MRI) and positron emission tomography (PET). Nine healthy non-diabetic participants underwent a hyperinsulinemic euglycemic (92±3 mg/dL) – hypoglycemic (53±1 mg/dL) clamp. Counterregulatory hormone levels were collected at each of these glycemic levels and rCBF measurements within the previously described network of hypoglycemia-responsive regions (thalamus, medial prefrontal cortex and globus pallidum) were obtained using PASL-MRI and [¹⁵O] water PET. In response to hypoglycemia, rCBF was significantly increased in the thalamus, medial prefrontal cortex, and globus pallidum compared to euglycemia for both PASL-MRI and PET methodologies. Both imaging techniques found similar increases in rCBF in the thalamus, medial prefrontal cortex, and globus pallidum in response to hypoglycemia. These brain regions may be involved in the physiologic and symptom responses to hypoglycemia. Compared to PET, PASL-MRI may provide a less invasive, less expensive method for assessing changes in rCBF during hypoglycemia without radiation exposure.

Hypoglycemia-associated autonomic failure in diabetes

The concept of hypoglycemia-associated autonomic failure (HAAF) in diabetes posits that recent antecedent hypoglycemia, as well as sleep or prior exercise, causes both defective glucose counterregulation (by attenuating the adrenomedullary epinephrine response, in the setting of absent insulin and glucagon responses) and hypoglycemia unawareness (by attenuating the sympathoadrenal, largely the sympathetic neural, response) and thus a vicious cycle of recurrent hypoglycemia. Albeit with different time courses, the pathophysiology of defense against hypoglycemia - no decrease in therapeutic insulin, no increase in glucagon and an attenuated increase in sympathoadrenal activity - is the same in type 1 diabetes and advanced type 2 diabetes. Hypoglycemia unawareness is reversible by 2-3 weeks of scrupulous avoidance of hypoglycemia in most affected patients. The pathophysiology of HAAF in diabetes explains why the incidence of hypoglycemia increases as patients approach the absolute endogenous insulin deficient end of the disease, provides a comprehensive set of risk factors including those indicative of HAAF, and leads logically to the practice of hypoglycemia risk factor reduction. Because of the risk of hypoglycemic mortality, presumably from cardiac arrhythmias, glycemic goals in diabetes should be individualized, based in part on the risk of hypoglycemia. By practicing hypoglycemia risk reduction - addressing the issue, applying the principles of aggressive glycemic therapy and considering both the conventional risk factors and those indicative of HAAF - it is possible to both improve glycemic control and reduce the risk of hypoglycemia in many patients with diabetes.

Diabetes technology: markers, monitoring, assessment, and control of blood glucose fluctuations in diabetes

People with diabetes face a life-long optimization problem: to maintain strict glycemic control without increasing their risk for hypoglycemia. Since the discovery of insulin in 1921, the external regulation of diabetes by engineering means has became a hallmark of this optimization. Diabetes technology has progressed remarkably over the past 50 years-a progress that includes the development of markers for diabetes control, sophisticated monitoring techniques, mathematical models, assessment procedures, and control algorithms. Continuous glucose monitoring (CGM) was introduced in 1999 and has evolved from means for retroactive review of blood glucose profiles to versatile reliable devices, which monitor the course of glucose fluctuations in real time and provide interactive feedback to the patient. Technology integrating CGM with insulin pumps is now available, opening the field for automated closed-loop control, known as the artificial pancreas. Following a number of in-clinic trials, the quest for a wearable ambulatory artificial pancreas is under way, with a first prototype tested in outpatient setting during the past year. This paper discusses key milestones of diabetes technology development, focusing on the progress in the past 10 years and on the artificial pancreas-still not a cure, but arguably the most promising treatment of diabetes to date.

Glucagon secretion and signaling in the development of diabetes

Normal release of glucagon from pancreatic islet α-cells promotes glucose mobilization, which counteracts the hypoglycemic actions of insulin, thereby ensuring glucose homeostasis. In treatment of diabetes aimed at rigorously reducing hyperglycemia to avoid chronic complications, the resulting hypoglycemia triggering glucagon release from α-cells is frequently impaired, with ensuing hypoglycemic complications. This review integrates the physiology of glucagon secretion regulating glucose homeostasis in vivo to single α-cell signaling, and how both become perturbed in diabetes. α-cells within the social milieu of the islet micro-organ are regulated not only by intrinsic signaling events but also by paracrine regulation, particularly by adjacent insulin-secreting β-cells and somatostatin-secreting δ-cells. We discuss the intrinsic α-cell signaling events, including glucose sensing and ion channel regulation leading to glucagon secretion. We then discuss the complex crosstalk between the islet cells and the breakdown of this crosstalk in diabetes contributing to the dysregulated glucagon secretion. Whereas, there are many secretory products released by β- and δ-cells that become deficient or excess in diabetes, we discuss the major ones, including the better known insulin and lesser known somatostatin, which act as putative paracrine on/off switches that very finely regulate α-cell secretory responses in health and diabetes. Of note in several type 1 diabetes (T1D) rodent models, blockade of excess somatostatin actions on α-cell could normalize glucagon secretion sufficient to attain normoglycemia in response to hypoglycemic assaults. There has been slow progress in fully elucidating the pathophysiology of the α-cell in diabetes because of the small number of α-cells within an islet and the islet mass becomes severely reduced and inflamed in diabetes. These limitations are just now being surmounted by new approaches.