The effects of KATP channel modulators on counterregulatory responses and cognitive function during acute controlled hypoglycaemia in healthy men: a pilot study

Glycaemic thresholds for counterregulatory hormone and symptom responses to hypoglycaemia in people with and without type 1 diabetes: a systematic review

AIM/HYPOTHESIS

The physiological counterregulatory response to hypoglycaemia is reported to be organised hierarchically, with hormone responses usually preceding symptomatic awareness and autonomic responses preceding neuroglycopenic responses. To compare thresholds for activation of these responses more accurately between people with or without type 1 diabetes, we performed a systematic review on stepped hyperinsulinaemic-hypoglycaemic glucose clamps.

METHODS

A literature search in PubMed and EMBASE was conducted. We included articles published between 1980 and 2018 involving hyperinsulinaemic stepped hypoglycaemic glucose clamps among people with or without type 1 diabetes. Key exclusion criteria were as follows: data were previously published; other patient population; a clamp not the primary intervention; and an inadequate clamp description. Glycaemic thresholds for counterregulatory hormone and/or symptom responses to hypoglycaemia were estimated and compared using generalised logrank test for interval-censored data, where the intervals were either extracted directly or calculated from the data provided by the study. A glycaemic threshold was defined as the glucose level at which the response exceeded the 95% CI of the mean baseline measurement or euglycaemic control clamp. Because of the use of interval-censored data, we described thresholds using median and IQR.

RESULTS

A total of 63 articles were included, whereof 37 papers included participants with type 1 diabetes (n=559; 67.4% male sex, aged 32.7±10.2 years, BMI 23.8±1.4 kg/m²) and 51 papers included participants without diabetes (n=733; 72.4% male sex, aged 31.1±9.2 years, BMI 23.6±1.1 kg/m²). Compared with non-diabetic control individuals, in people with type 1 diabetes, the median (IQR) glycaemic thresholds for adrenaline (3.8 [3.2-4.2] vs 3.4 [2.8-3.9 mmol/l]), noradrenaline (3.2 [3.2-3.7] vs 3.0 [2.8-3.1] mmol/l), cortisol (3.5 [3.2-4.2]) vs 2.8 [2.8-3.4] mmol/l) and growth hormone (3.8 [3.3-3.8] vs. 3.2 [3.0-3.3] mmol/l) all occurred at lower glucose levels in people with diabetes than in those without diabetes (all p≤0.01). Similarly, although both autonomic (median [IQR] 3.4 [3.4-3.4] vs 3.0 [2.8-3.4] mmol/l) and neuroglycopenic (median [IQR] 3.4 [2.8-N/A] vs 3.0 [3.0-3.1] mmol/l) symptom responses were elicited at lower glucose levels in people with type 1 diabetes, the thresholds for autonomic and neuroglycopenic symptoms did not differ for each individual subgroup.

CONCLUSIONS/INTERPRETATION

People with type 1 diabetes have glycaemic thresholds for counterregulatory hormone and symptom responses at lower glucose levels than people without diabetes. Autonomic and neuroglycopenic symptoms responses are generated at about similar levels of hypoglycaemia. There was a considerable variation in the methodology of the articles and the high insulin doses in most of the clamps may affect the counterregulatory responses.

FUNDING

This article has received funding from the Innovative Medicines Initiative 2 Joint Undertaking (JU) under grant agreement no. 777460.

REGISTRATION

This systematic review is registered in PROSPERO (CRD42019120083).

A Systematic Review of Neuroprotective Strategies in the Management of Hypoglycemia

Severe hypogylcemia has been found to induce cerebral damage. While a number of illnesses can lead to hypoglycemic episodes, antidiabetic medications prescribed for glycemic control are a common cause. Considering the rising prevalence of diabetes mellitus in the population, we investigated neuroprotective strategies during hypoglycemia in the form of a systematic review in adherence to the PRISMA statement. A review protocol was registered in the PROSPERO database. A systematic literature search of PubMed, Web of Science, and CENTRAL was performed in September 2018. Based on a predefined inclusion protocol, results were screened and evaluated by two researchers. Both animal experiments and human studies were included, and their risk of bias was assessed with SYRCLE’s and the Cochrane risk of bias tools, respectively. Of a total of 16,230 results, 145 were assessed in full-text form: 27 articles adhered to the inclusion criteria and were qualitatively analyzed. The retrieved neuroprotective strategies could be categorized into three subsets: (1) Energy substitution, (2) hypoglycemia unawareness, and (3) other neuroprotective strategies. While on a study level, the individual results appeared promising, more research is required to investigate not only specific neuroprotective strategies against hypoglycemic cerebral damage, but also its underlying pathophysiological mechanisms.

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.

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.

Restoration of self-awareness of hypoglycemia in adults with long-standing type 1 diabetes: hyperinsulinemic-hypoglycemic clamp substudy results from the HypoCOMPaSS trial

OBJECTIVE

Impaired awareness of hypoglycemia (IAH) and defective counterregulation significantly increase severe hypoglycemia risk in type 1 diabetes (T1D). We evaluated restoration of IAH/defective counterregulation by a treatment strategy targeted at hypoglycemia avoidance in adults with T1D with IAH (Gold score ≥4) participating in the U.K.-based multicenter HypoCOMPaSS randomized controlled trial.

RESEARCH DESIGN AND METHODS

Eighteen subjects with T1D and IAH (mean ± SD age 50 ± 9 years, T1D duration 35 ± 10 years, HbA1c 8.1 ± 1.0% [65 ± 10.9 mmol/mol]) underwent stepped hyperinsulinemic-hypoglycemic clamp studies before and after a 6-month intervention. The intervention comprised the HypoCOMPaSS education tool in all and randomized allocation, in a 2 × 2 factorial study design, to multiple daily insulin analog injections or continuous subcutaneous insulin infusion therapy and conventional glucose monitoring or real-time continuous glucose monitoring. Symptoms, cognitive function, and counterregulatory hormones were measured at each glucose plateau (5.0, 3.8, 3.4, 2.8, and 2.4 mmol/L), with each step lasting 40 min with subjects kept blinded to their actual glucose value throughout clamp studies.

RESULTS

After intervention, glucose concentrations at which subjects first felt hypoglycemic increased (mean ± SE from 2.6 ± 0.1 to 3.1 ± 0.2 mmol/L, P = 0.02), and symptom and plasma metanephrine responses to hypoglycemia were higher (median area under curve for symptoms, 580 [interquartile range {IQR} 420-780] vs. 710 [460-1,260], P = 0.02; metanephrine, 2,412 [-3,026 to 7,279] vs. 5,180 [-771 to 11,513], P = 0.01). Glycemic threshold for deterioration of cognitive function measured by four-choice reaction time was unchanged, while the color-word Stroop test showed a degree of adaptation.

CONCLUSIONS

Even in long-standing T1D, IAH and defective counterregulation may be improved by a clinical strategy aimed at hypoglycemia avoidance.

The effects of acute hypoglycaemia on cognitive function in type 1 diabetes

Throughout life with type 1 diabetes mellitus people with the condition are exposed to multiple episodes of hypoglycaemia associated with insulin therapy. Hypoglycaemia affects several domains of cognitive function. Studies in non-diabetic adults and in people with type 1 diabetes have shown that almost all domains of cognitive function are impaired to some degree during acute hypoglycaemia, with complex tasks being more greatly affected.

The specific cognitive functions of attention and memory are both profoundly impaired during hypoglycaemia. These cognitive processes are fundamental to the performance of many day to day tasks. Their impairment disrupts everyday life and raises safety concerns for the pursuit of activities such as driving.

Mood and emotion are also negatively affected by hypoglycaemia, resulting in tense tiredness, while motivation is reduced, and anger may be generated in some individuals. Hypoglycaemia can cause embarrassing social situations, and may lead to chronic anxiety and depression in people with type 1 diabetes.

At present few therapeutic measures can modify or ameliorate the effects of hypoglycaemia on cognitive function, so instigation of measures to prevent exposure to hypoglycaemia is of major clinical importance, while preserving good glycaemic control.

Differential effects of insulin detemir and neutral protamine Hagedorn (NPH) insulin on hepatic glucose production and peripheral glucose uptake during hypoglycaemia in type 1 diabetes

AIMS/HYPOTHESIS

We compared the symptoms of hypoglycaemia induced by insulin detemir (NN304) (B29Lys(epsilon-tetradecanoyl),desB30 human insulin) and equally effective doses of neutral protamine Hagedorn (NPH) insulin in relation to possible differential effects on hepatic glucose production and peripheral glucose uptake.

METHODS

After overnight intravenous infusion of soluble human insulin 18 participants with type 1 diabetes received subcutaneous injections of NPH insulin or insulin detemir (0.5 U/kg body weight) on separate occasions in random order. During the ensuing gradual development of hypoglycaemia cognitive function and levels of counter-regulatory hormones were measured and rates of endogenous glucose production and peripheral glucose uptake continuously evaluated using a primed constant infusion of [6,6-(2)H(2)]glucose. The study was terminated when plasma glucose concentration had fallen to 2.4 mmol/l or had reached a minimum at a higher concentration.

RESULTS

During the development of hypoglycaemia no difference between the two insulin preparations was observed in symptoms or hormonal responses. Significant differences were seen in rates of glucose flux. At and below plasma glucose concentrations of 3.5 mmol/l suppression of endogenous glucose production was greater with insulin detemir than with NPH insulin, whereas stimulation of peripheral glucose uptake was greater with NPH insulin than with insulin detemir.

CONCLUSIONS/INTERPRETATION

In participants with type 1 diabetes subcutaneously injected insulin detemir exhibits relative hepatoselectivity compared with NPH insulin, but symptoms of hypoglycaemia and hormonal counter-regulation are similar.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00760448.

Comparing hormonal and symptomatic responses to experimental hypoglycaemia in insulin- and sulphonylurea-treated Type 2 diabetes

AIMS

Patients with diabetes rely on symptoms to identify hypoglycaemia. Previous data suggest patients with Type 2 diabetes develop greater symptomatic and hormonal responses to hypoglycaemia at higher glucose concentrations than non-diabetic controls and these responses are lowered by insulin treatment. It is unclear if this is as a result of insulin therapy itself or improved glucose control. We compared physiological responses to hypoglycaemia in patients with Type 2 diabetes patients treated with sulphonylureas (SUs) or insulin (INS) with non-diabetic controls (CON).

METHODS

Stepped hyperinsulinaemic hypoglycaemic clamps were performed on 20 subjects with Type 2 diabetes, 10 SU-treated and 10 treated with twice-daily premixed insulin, and 10 age- and weight-matched non-diabetic controls. Diabetic subjects were matched for diabetes duration, glycated haemoglobin (HbA(1c)) and hypoglycaemia experience. We measured symptoms, counterregulatory hormones and cognitive function at glucose plateaux of 5, 4, 3.5, 3 and 2.5 mmol/l.

RESULTS

Symptomatic responses to hypoglycaemia occurred at higher blood glucose concentrations in SU-treated than INS-treated patients [3.5 (0.4) vs. 2.6 (0.5) mmol/l SU vs. INS; P = 0.001] or controls [SU vs. CON 3.5 (0.4) vs. 3.0 (0.6) mmol/l; P = 0.05]. They also had a greater increase in symptom scores at hypoglycaemia [13.6 (11.3) vs. 3.6 (6.1) vs. 5.1 (4.3) SU vs. INS vs. CON; P = 0.017]. There were no significant differences in counterregulatory hormone responses or impairment of cognitive function among groups.

CONCLUSIONS

Sulphonylurea-treated subjects are more symptomatic of hypoglycaemia at a higher glucose level than insulin-treated subjects. This may protect them from severe hypoglycaemia but hinder attainment of glycaemic goals.

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

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

Amplified hormonal counterregulatory responses to hypoglycemia in rats after systemic delivery of a SUR-1-selective K(+) channel opener?

OBJECTIVE

In glucose-sensing neurons, ATP-sensitive K(+) channels (K(ATP) channels) are thought to translate metabolic signals into an alteration in neuronal firing rates. Because these neurons express the Kir6.2/SUR-1 isoform of the K(ATP) channel, we sought to examine the therapeutic potential of the SUR-1-selective potassium channel opener (KCO), NN414, to amplify counterregulatory response to hypoglycemia.

RESEARCH DESIGN AND METHODS

In vivo dose-response studies with NN414 delivered intravenously to normal Sprague-Dawley rats before the induction of controlled hypoglycemia were performed. Based on these studies, the potential for NN414 to restore counterregulatory responses in chronically cannulated nondiabetic and diabetic BB rats was explored using the in vivo hyperinsulinemic-hypoglycemic clamp technique.

RESULTS

NN414 delivered systemically amplified epinephrine responses during acute hypoglycemia and showed a persisting effect to amplify the epinephrine response when given 24 h before the hypoglycemic study. Local delivery of a potassium-channel blocker to the ventromedial hypothalamus reversed the effects of systemic NN414. In addition, NN414 amplified the epinephrine response to hypoglycemia in both nondiabetic and diabetic BB rats with defective hormonal counterregulation.

CONCLUSIONS

These studies demonstrate in a variety of rodent models that systemic delivery of Kir6.2/SUR-1-selective KCOs enhance the glucose counterregulatory response to insulin-induced hypoglycemia. Future studies in human subjects are now required to determine their potential as a therapy for hypoglycemia-associated autonomic failure in type 1 diabetes.

Effects of glimepiride and glyburide on glucose counterregulation and recovery from hypoglycemia

Severe hypoglycemia, the most serious side effect of sulfonylurea therapy, has been reported to occur more frequently with glyburide than glimepiride. The present studies were undertaken to test the hypothesis that a differential effect on glucagon secretion may be involved. We performed hyperinsulinemic hypoglycemic (approximately 2.5 mmol/L) clamps in 16 healthy volunteers who received in randomized order placebo, glyburide (10 mg), and glimepiride (4 mg) just before beginning the insulin infusion and measured plasma glucagon, insulin, C-peptide, glucagon, epinephrine, cortisol, and growth hormone levels during the clamp and during a 3-hour recovery period after discontinuation of the insulin infusion. Neither sulfonylurea altered glucagon responses or those of other counterregulatory hormones (except cortisol) during the clamp. However, glyburide delayed plasma glucose recovery from hypoglycemia (plasma glucose at end of recovery period: control, 4.9 +/- 0.2 mmol/L; glyburide, 3.7 +/- 0.2 mmol/L; P = .0001; glimepiride, 4.5 +/- 0.2 mmol/L; P = .08). Despite lower plasma glucose levels, glyburide stimulated insulin secretion during this period (0.89 +/- 0.13 vs 1.47 +/- 0.15 pmol x kg(-1) x min(-1), control vs glyburide; P = .001), whereas glimepiride did not (P = .08). Short-term administration of glyburide or glimepiride did not alter glucagon responses during hypoglycemia. In contrast, during recovery from hypoglycemia, glyburide but not glimepiride inappropriately stimulates insulin secretion at low plasma glucose levels. This differential effect on insulin secretion may be an important factor in explaining why glyburide causes severe hypoglycemia more frequently than glimepiride.

Hypoglycaemia and cognitive function

Acute hypoglycaemia impairs cerebral function, and available data indicate that cognitive performance becomes impaired at a blood glucose level of 2.6-3.0 mmol/l in healthy subjects. Methodological problems limit comparisons between studies, but in general complex tasks are more sensitive to hypoglycaemia than simple tasks, and some cognitive abilities are completely abolished. The onset of hypoglycaemic cognitive dysfunction is immediate, but recovery may be considerably delayed. There is persuasive evidence of adaptation to hypoglycaemia, partly due to increased brain glucose uptake capacity, although other mechanisms may exist. Patients who are exposed to chronic or recurrent hypoglycaemia become remarkably tolerant to the state, but this is insufficient to prevent severe hypoglycaemia with neuroglycopenic decompensation, probably because symptomatic and counterregulatory responses adapt even more. During experimental hypoglycaemia, administration of non-glucose cerebral fuels preserves cognitive function. However, little progress has been made as yet towards protecting cognitive function during hypoglycaemia in clinical practice. The chronic effects of recurrent hypoglycaemia remain contentious. There are numerous case reports of hypoglycaemic brain damage and of cognitive deterioration attributed to repeated severe hypoglycaemia. The major prospective studies, including the Diabetes Control and Complications Trial, did not report cognitive declines in intensively treated patients, but had unrepresentative study populations and may have been too short to detect such effects. Structural and functional brain changes are not only associated with recurrent severe hypoglycaemia, but also with hyperglycaemia and early disease onset and may in part be due to hyperglycaemic microvascular disease. Children may be more prone to acute metabolic insults, and there is evidence of developmental disadvantage associated with hypoglycaemic episodes.

Loss of the decrement in intraislet insulin plausibly explains loss of the glucagon response to hypoglycemia in insulin-deficient diabetes: documentation of the intraislet insulin hypothesis in humans

The intraislet insulin hypothesis for the signaling of the glucagon secretory response to hypoglycemia states that a decrease in arterial glucose --> a decrease in beta-cell insulin secretion --> a decrease in tonic alpha-cell inhibition by insulin --> an increase in alpha-cell glucagon secretion. To test this hypothesis in humans, a hyperinsulinemic- euglycemic ( approximately 5.0 mmol/l [90 mg/dl] x 2 h) and then a hypoglycemic ( approximately 3.0 mmol/l [55 mg/dl] x 2 h) clamp was performed in 14 healthy young adults on two occasions, once with oral administration of the ATP-sensitive potassium channel agonist diazoxide to selectively suppress baseline insulin secretion and once with the administration of a placebo. The decrement in plasma C-peptide during the induction of hypoglycemia was reduced by approximately 50% in the diazoxide clamps (from 0.3 +/- 0.0 to 0.1 +/- 0.0 nmol/l [0.8 +/- 0.1 to 0.4 +/- 0.1 ng/ml]) compared with the placebo clamps (from 0.4 +/- 0.0 to 0.1 +/- 0.0 nmol/l [1.2 +/- 0.1 to 0.4 +/- 0.1 ng/ml]) (P = 0.0015). This reduction of the decrement in intraislet insulin during induction of hypoglycemia caused an approximately 50% reduction (P = 0.0010) of the increase in plasma glucagon in the diazoxide clamps (from 29 +/- 3 to 35 +/- 2 pmol/l [102 +/- 9 to 123 +/- 8 pg/ml]) compared with the placebo clamps (from 28 +/- 2 to 43 +/- 5 pmol/l [98 +/- 7 to 151 +/- 16 pg/ml]). Baseline glucagon levels, the glucagon response to intravenous arginine, and the autonomic (adrenomedullary, sympathetic neural, and parasympathetic neural) responses to hypoglycemia were not altered by diazoxide. These data indicate that a decrease in intraislet insulin is a signal for the glucagon secretory response to hypoglycemia in healthy humans. The absence of that signal plausibly explains the loss of the glucagon response to falling plasma glucose concentrations, a key feature of the pathogenesis of iatrogenic hypoglycemia, in insulin-deficient (type 1 and advanced type 2) diabetes.

Hypothalamic ATP-sensitive K + channels play a key role in sensing hypoglycemia and triggering counterregulatory epinephrine and glucagon responses

It has been postulated that specialized glucose-sensing neurons in the ventromedial hypothalamus (VMH) are able to detect falling blood glucose and trigger the release of counterregulatory hormones during hypoglycemia. The molecular mechanisms used by glucose-sensing neurons are uncertain but may involve cell surface ATP-sensitive K(+) channels (K(ATP) channels) analogous to those of the pancreatic beta-cell. We examined whether the delivery of sulfonylureas directly into the brain to close K(ATP) channels would modulate counterregulatory hormone responses to either brain glucopenia (using intracerebroventricular 5-thioglucose) or systemic hypoglycemia in awake chronically catheterized rats. The closure of brain K(ATP) channels by global intracerebroventricular perfusion of sulfonylurea (120 ng/min glibenclamide or 2.7 microg/min tolbutamide) suppressed counterregulatory (epinephrine and glucagon) responses to brain glucopenia and/or systemic hypoglycemia (2.8 mmol/l glucose clamp). Local VMH microinjection of a small dose of glibenclamide (0.1% of the intracerebroventricular dose) also suppressed hormonal responses to systemic hypoglycemia. We conclude that hypothalamic K(ATP) channel activity plays an important role in modulating the hormonal counterregulatory responses triggered by decreases in blood glucose. Our data suggest that closing of K(ATP) channels in the VMH (much like the beta-cell) impairs defense mechanisms against glucose deprivation and therefore could contribute to defects in glucose counterregulation.