Naltrexone for treatment of impaired awareness of hypoglycemia in type 1 diabetes: A randomized clinical trial

Effects of Intranasal Naloxone on Hypoglycemia-Associated Autonomic Failure (HAAF) in Susceptible Individuals

CONTEXT

Hypoglycemia-associated autonomic failure (HAAF), defined as blunting of counter-regulatory hormone and symptom responses to recurrent hypoglycemia, remains a therapeutic challenge in diabetes treatment. The opioid system may play a role in HAAF pathogenesis since activation of opioid receptors induces HAAF. Blockade of opioid receptors with intravenous naloxone ameliorates HAAF experimentally, yet is not feasible therapeutically.

OBJECTIVE

To investigate the effects of opioid receptor blockade with intranasal naloxone on experimentally-induced HAAF.

DESIGN

Randomized, double-blinded, placebo-controlled crossover study.

SETTING

Academic research center.

PARTICIPANTS

Healthy non-diabetic volunteers.

INTERVENTIONS

Paired two-day studies, 5-10 weeks apart, each consisting of three consecutive hypoglycemic episodes (hyperinsulinemic hypoglycemic clamps, glucose nadir: 54 mg/dL): two on day 1 with administration of intranasal naloxone vs. placebo, followed by the third episode on day 2.

MAIN OUTCOME MEASURES

Differences in counter-regulatory hormones responses and hypoglycemia symptoms between first and third hypoglycemic episodes in naloxone vs. placebo studies.

RESULTS

Out of 17 participants, 9 developed HAAF, confirming variable inter-individual susceptibility. Among participants susceptible to HAAF, naloxone maintained some hormonal and symptomatic responses to hypoglycemia and prevented the associated requirement for increased glucose infusion. Unexpectedly, naloxone reduced plasma epinephrine and growth hormone responses to the first hypoglycemic episode but prevented further reduction with subsequent hypoglycemia.

CONCLUSIONS

This is the first study to report that intranasal naloxone, a widely used opioid receptor antagonist, may ameliorate some features of HAAF. Further investigation is warranted into mechanisms of variable inter-individual susceptibility to HAAF and the effects of intranasal naloxone in people with diabetes at risk for HAAF.

Experimental pharmacological approaches to reverse impaired awareness of hypoglycemia-a review

The colossal global burden of diabetes management is compounded by the serious complication of hypoglycemia. Protective physiologic hormonal and neurogenic counterregulatory responses to hypoglycemia are essential to preserve glucose homeostasis and avert serious morbidity. With recurrent exposure to hypoglycemic episodes over time, these counterregulatory responses to hypoglycemia can diminish, resulting in an impaired awareness of hypoglycemia (IAH). IAH is characterized by sudden neuroglycopenia rather than preceding cautionary autonomic symptoms. IAH increases the risk of subsequent sudden and severe hypoglycemic episodes in patients with diabetes. The postulated causative mechanisms behind IAH are complex and varied. It is therefore challenging to identify a single effective therapeutic strategy. In this review, we closely examine the efficacy and feasibility of a myriad of pharmaceutical interventions in preventing and treating IAH as described in clinical and preclinical studies. Pharmaceutical agents outlined include N-acetyl cysteine, GABA A receptor blockers, opioid receptor antagonists, AMP activated protein kinase agonists, potassium channel openers, dehydroepiandrosterone, metoclopramide, antiadrenergic agents, antidiabetic agents and glucagon.

Current and future therapies to treat impaired awareness of hypoglycemia

In order to achieve optimal glycemic control, intensive insulin regimes are needed for individuals with Type 1 Diabetes (T1D) and insulin-dependent Type 2 Diabetes (T2D). Unfortunately, intensive glycemic control often results in insulin-induced hypoglycemia. Moreover, recurrent episodes of hypoglycemia result in both the loss of the characteristic warning symptoms associated with hypoglycemia and an attenuated counterregulatory hormone responses. The blunting of warning symptoms is known as impaired awareness of hypoglycemia (IAH). Together, IAH and the loss of the hormonal response is termed hypoglycemia associated autonomic failure (HAAF). IAH is prevalent in up to 25% in people with T1D and up to 10% in people with T2D. IAH and HAAF increase the risk of severe hypoglycemia 6-fold and 25-fold, respectively. To reduce this risk for severe hypoglycemia, multiple different therapeutic approaches are being explored that could improve awareness of hypoglycemia. Current therapies to improve awareness of hypoglycemia include patient education and psychoeducation, the use of novel glycemic control technology, pancreas/islet transplantation, and drug therapy. This review examines both existing therapies and potential therapies that are in pre-clinical testing. Novel treatments that improve awareness of hypoglycemia, via improving the counterregulatory hormone responses or improving hypoglycemic symptom recognition, would also shed light on the possible neurological mechanisms that lead to the development of IAH. To reduce the risk of severe hypoglycemia in people with diabetes, elucidating the mechanism behind IAH, as well as developing targeted therapies is currently an unmet need for those that suffer from IAH.

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.

A New Analysis Tool for Continuous Glucose Monitor Data

BACKGROUND

With the development of continuous glucose monitoring systems (CGMS), detailed glycemic data are now available for analysis. Yet analysis of this data-rich information can be formidable. The power of CGMS-derived data lies in its characterization of glycemic variability. In contrast, many standard glycemic measures like hemoglobin A1c (HbA1c) and self-monitored blood glucose inadequately describe glycemic variability and run the risk of bias toward overreporting hyperglycemia. Methods that adjust for this bias are often overlooked in clinical research due to difficulty of computation and lack of accessible analysis tools.

METHODS

In response, we have developed a new R package rGV, which calculates a suite of 16 glycemic variability metrics when provided a single individual's CGM data. rGV is versatile and robust; it is capable of handling data of many formats from many sensor types. We also created a companion R Shiny web app that provides these glycemic variability analysis tools without prior knowledge of R coding. We analyzed the statistical reliability of all the glycemic variability metrics included in rGV and illustrate the clinical utility of rGV by analyzing CGM data from three studies.

RESULTS

In subjects without diabetes, greater glycemic variability was associated with higher HbA1c values. In patients with type 2 diabetes mellitus (T2DM), we found that high glucose is the primary driver of glycemic variability. In patients with type 1 diabetes (T1DM), we found that naltrexone use may potentially reduce glycemic variability.

CONCLUSIONS

We present a new R package and accompanying web app to facilitate quick and easy computation of a suite of glycemic variability metrics.

Impact of Hybrid Closed Loop Therapy on Hypoglycemia Awareness in Individuals with Type 1 Diabetes and Impaired Hypoglycemia Awareness

Objective: This study evaluated the efficacy of using a hybrid closed loop (HCL) system in restoring hypoglycemia awareness in individuals with impaired awareness of hypoglycemia (IAH). Research Design and Methods: Participants with IAH (Gold score ≥4) were recruited into a randomized crossover pilot study. They participated in two 8-week periods using a HCL system (Medtronic 670G™) (intervention) and standard insulin pump therapy (control). Hyperinsulinemic hypoglycemic clamp studies were undertaken at baseline and at the end of each study period for the evaluation of the counter-regulatory hormonal and symptomatic responses to hypoglycemia. Results: Seventeen participants (mean age [standard deviation] 35.8 years [11.2 years]) were included in the study. Peak epinephrine levels (median, interquartile range [IQR]) in response to hypoglycemia were similar postintervention and control periods; 234.7 pmol/L (109.2; 938.9) versus 188.3 pmol/L (133.7; 402.9), P = 0.233. However, both peak adrenergic and neuroglycopenic symptom scores were higher after intervention; 5.0 (4.5; 9.0) versus 4.0 (4.0; 5.5), P = 0.009, and 8.5 (6.0; 15.0) versus 6.5 (6.0; 7.0) P = 0.014, respectively. Self-reported hypoglycemia awareness improved: median (IQR) Gold score was 4.0 (3.0; 5.5) versus 5.5 (4.5; 6.0); intervention versus control, P = 0.033. Time spent <3.9 and <3.0 mmol/L was lower in the intervention group than in control, P = 0.002. Other patient-reported outcomes (hypoglycemia fear and diabetes treatment satisfaction) did not change. Conclusions: A short-term use of a HCL system failed to demonstrate an improvement in counter-regulatory hormonal responses. However, higher hypoglycemia symptom scores during controlled hypoglycemia, better self-reported hypoglycemia awareness, and less time spent in hypoglycemia suggest the potential benefits of a HCL system in people with IAH. Trial Registration: anzctr.org.au Identifier: ACTRN12616000909426.

Cuidados de enfermería para la persona adulta, diabética con hipoglucemia: revisión integrativa

Introducción: La hipoglucemia es la complicación más frecuente del tratamiento con insulina en adultos. Los eventos de hipoglucemia severa se asocian con complicaciones a corto, mediano y largo plazo en  pacientes con diabetes ellmitus. Una de las estrategias para reducir  la frecuencia de hipoglucemia son las intervenciones de enfermería y  aunque hay pocos estudios que las enuncian de manera explícita, se ha publicado respecto a las necesidades de dichos pacientes, que permiten determinar características definitorias de  diagnósticos enfermeros y a partir de ellos establecer metas e intervenciones enfermeras, para el cuidado de dichos pacientes.  Objetivo: identificar los cuidados de enfermería para prevenir y controlar los eventos de hipoglucemia en pacientes adultos diagnosticados con diabetes mellitus. Metodología: revisión integrativa, se realizó en seis fases: planteamiento de la pregunta PICO; búsqueda en bases de datos y metabuscadores; lectura crítica; análisis, clasificación, validación por nivel de evidencia y grado de recomendación, y presentación de la información. Resultados: la revisión reportó cinco categorías: factores de riesgo y protectores, miedo a la hipoglucemia, atención brindada al paciente, disminución de la hipoglucemia y descripción del impacto de la hipoglucemia en los pacientes. Conclusiones: a partir de las necesidades reportadas en las 5 categorías de los resultados se determinaron características definitorias y factores relacionados que permitieron formular diagnósticos de enfermería y determinar como principales intervenciones: enseñanza del proceso de enfermedad, medicamentos prescritos, entrenamiento de asertividad, manejo de la hipoglicemia, nutricional y de la medicación, mejorar el afrontamiento, enseñanza individual, facilitar el aprendizaje y potenciación de la disposición de aprendizaje.

Infusion of N-acetyl cysteine during hypoglycaemia in humans does not preserve the counterregulatory response to subsequent hypoglycaemia

AIM

Administration of N-acetyl cysteine (NAC) during hypoglycaemia will preserve the counterregulatory response to subsequent hypoglycaemia in healthy humans.

METHODS

This was a randomized double-blind cross over study where humans were given either a 60-minute infusion of NAC (150 mg/kg) followed by a 4-hour infusion of NAC (50 mg/kg) or saline starting 30 minutes before the initiation of a 2-hour hypoglycaemic (HG) clamp at 8 am. After rest at euglycaemia for ~2 hours, subjects were exposed to a 2nd HG clamp at 2 pm and discharged home in euglycaemia. They returned the following day for a 3rd HG clamp at 8 am.

RESULTS

Twenty-two subjects were enrolled. Eighteen subjects completed the entire protocol. The epinephrine response during clamp 3 (171 ± 247 pg/mL) following clamp 1 NAC infusion was lower than the response during the clamp 1 NAC infusion (538 ± 392 pg/mL) (clamp 3 to clamp 1 NAC: P = .0013). The symptom response during clamp 3 (7 ± 5) following clamp 1 NAC infusion was lower than the response during the clamp 1 NAC infusion (16 ± 10) (clamp 3 to clamp 1 NAC: P = .0003). Nine subjects experienced rash, pruritus or nausea during NAC infusion.

CONCLUSION

We found no difference in the hormone and symptom response to experimental hypoglycaemia measured in subjects who were administered NAC as opposed to saline the day before. This observation suggests that further development of NAC as a therapy for impaired awareness of hypoglycaemia in patients with diabetes may be unwarranted.

Hypoglycemia-associated autonomic failure, counterregulatory responses, and therapeutic options in type 1 diabetes

Hypoglycemia remains a major barrier to the achievement of target levels of glycemic control for most individuals with insulin-dependent type 1 diabetes (T1D). Both the loss of β cells and an accompanying defect in the α cell response to hypoglycemia predispose patients with T1D to the development of low blood glucose. Increased glucose variability, exposure to hypoglycemia, and impaired awareness of hypoglycemia all contribute to increased risk of experiencing severe hypoglycemia, which is explained by progressive impairment in epinephrine secretion and autonomic symptom generation in response to hypoglycemia leading to defective glucose counterregulation and hypoglycemia unawareness that characterize hypoglycemia-associated autonomic failure (HAAF). Interruption of HAAF requires interfering with the mechanisms of brain adaptation to low blood glucose that affect central glucose sensing and the autonomic response to hypoglycemia, or avoidance of hypoglycemia that may allow for eventual recovery of counterregulatory and autonomic symptom responses. Strategies for hypoglycemia avoidance that include continuous glucose monitoring may reduce, but do not eliminate, clinically significant hypoglycemia, with ongoing counterregulatory defects and impaired awareness of hypoglycemia. Complete avoidance of hypoglycemia can be achieved following pancreatic islet transplantation and allows for the restoration of counterregulatory and autonomic symptom responses that evidences the potential for reversing HAAF in T1D.

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.

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'.

Potential approaches to prevent hypoglycemia-associated autonomic failure

Clear health benefits are associated with intensive glucose control in type 1 diabetes mellitus (T1DM). However, maintaining near-normal glycemia remains an elusive goal for many patients, in large part owing to the risk of severe hypoglycemia. In fact, recurrent episodes of hypoglycemia lead to 'hypoglycemia-associated autonomic failure' (HAAF), characterized by defective counter-regulatory responses to hypoglycemia. Extensive studies to understand the mechanisms underlying HAAF have revealed multiple potential etiologies, suggesting various approaches to prevent the development of HAAF. In this review, we present an overview of the literature focused on pharmacological approaches that may prevent the development of HAAF. The purported underlying mechanisms of HAAF include: 1) central mechanisms (opioid receptors, ATP-sensitive K+(KATP) channels, adrenergic receptors, serotonin selective receptor inhibitors, γ-aminobuyric acid receptors, N-methyl D-aspartate receptors); 2) hormones (cortisol, estrogen, dehydroepiandrosterone (DHEA) or DHEA sulfate, glucagon-like peptide-1) and 3) nutrients (fructose, free fatty acids, ketones), all of which have been studied vis-à-vis their ability to impact the development of HAAF. A careful review of the current literature reveals many promising therapeutic approaches to treat or reduce this important limitation to optimal glycemic control.

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.

Type 1 Diabetes and Impaired Awareness of Hypoglycemia Are Associated with Reduced Brain Gray Matter Volumes

In this study, we retrospectively analyzed the anatomical MRI data acquired from 52 subjects with type 1 diabetes (26M/26F, 36 ± 11 years old, A1C = 7.2 ± 0.9%) and 50 age, sex and BMI frequency-matched non-diabetic controls (25M/25F, 36 ± 14 years old). The T1D group was further sub-divided based on whether subjects had normal, impaired, or indeterminate awareness of hypoglycemia (n = 31, 20, and 1, respectively). Our goals were to test whether the gray matter (GM) volumes of selected brain regions were associated with diabetes status as well as with the status of hypoglycemia awareness. T1D subjects were found to have slightly smaller volume of the whole cortex as compared to controls (-2.7%, p = 0.016), with the most affected brain region being the frontal lobe (-3.6%, p = 0.024). Similar differences of even larger magnitude were observed among the T1D subjects based on their hypoglycemia awareness status. Indeed, compared to the patients with normal awareness of hypoglycemia, patients with impaired awareness had smaller volume of the whole cortex (-7.9%, p = 0.0009), and in particular of the frontal lobe (-9.1%, p = 0.006), parietal lobe (-8.0%, p = 0.015) and temporal lobe (-8.2%, p = 0.009). Such differences were very similar to those observed between patients with impaired awareness and controls (-7.6%, p = 0.0002 in whole cortex, -9.1%, p = 0.0003 in frontal lobe, -7.8%, p = 0.002 in parietal lobe, and -6.4%, p = 0.019 in temporal lobe). On the other hand, patients with normal awareness did not present significant volume differences compared to controls. No group-differences were observed in the occipital lobe or in the anterior cingulate, posterior cingulate, hippocampus, and thalamus. We conclude that diabetes status is associated with a small but statistically significant reduction of the whole cortex volume, mainly in the frontal lobe. The most prominent structural effects occurred in patients with impaired awareness of hypoglycemia (IAH) as compared to those with normal awareness, perhaps due to the long-term exposure to recurrent episodes of hypoglycemia. Future studies aimed at quantifying relationships of structural outcomes with functional outcomes, with cognitive performance, as well as with parameters describing glucose variability and severity of hypoglycemia episodes, will be necessary to further understand the impact of T1D on the brain.

Evaluation of the counter-regulatory responses to hypoglycaemia in patients with type 1 diabetes during opiate receptor blockade with naltrexone

AIMS

Hypoglycaemia is the major limiting factor in achieving optimal glycaemic control in people with type 1 diabetes (T1DM), especially intensively treated patients with impaired glucose counter-regulation during hypoglycaemia. Naloxone, an opiate receptor blocker, has been reported to enhance the acute counter-regulatory response to hypoglycaemia when administered intravenously in humans. The current study was undertaken to investigate the oral formulation of the long-acting opiate antagonist, naltrexone, and determine if it could have a similar effect, and thus might be useful therapeutically in treatment of T1DM patients with a high risk of hypoglycaemia.

MATERIALS AND METHODS

We performed a randomized, placebo-controlled, double-blinded, cross-over study in which 9 intensively treated subjects with T1DM underwent a 2-step euglycaemic-hypoglycaemic-hyperinsulinaemic clamp on 2 separate occasions. At 12 hours and at 1 hour before the clamp study, participants received 100 mg of naltrexone or placebo orally. Counter-regulatory hormonal responses were assessed at baseline and during each step of the hyperinsulinaemic-clamp.

RESULTS

Glucose and insulin levels did not differ significantly between the naltrexone and placebo visits; nor did the glucose infusion rates required to keep glucose levels at target. During hypoglycaemia, naltrexone, in comparison with the placebo group, induced an increase in epinephrine levels ( P  = .05). However, no statistically significant differences in glucagon, cortisol and growth hormone responses were observed.

CONCLUSION

In contrast to the intravenous opiate receptor blocker naloxone, overnight administration of the oral long-acting opiate receptor blocker, naltrexone, at a clinically used dose, had a limited effect on the counter-regulatory response to hypoglycaemia in intensively treated subjects with T1DM.

Management of Hypoglycemia in Children and Adolescents with Type 1 Diabetes Mellitus

Hypoglycemia and fear of hypoglycemia limit appropriate glycemic control in many children and adolescents with type 1 diabetes. Traditional approaches to the prevention of hypoglycemia including patient education about modifiable risk factors for hypoglycemia (changes in insulin, diet, and exercise) and frequency of self glucose monitoring remain important for hypoglycemia prevention. Continuous glucose monitoring systems with or without a partial closed-loop control of insulin infusion have been very useful in the prevention of hypoglycemia. Oral carbohydrate and parenteral glucagon continue to be the mainstays of hypoglycemia treatment. In the future, we can look forward to regulatory approval of closed-loop insulin delivery and glucose monitoring systems to facilitate euglycemia, as well as glucagon administered by the intranasal route to treat hypoglycemia.