Acute Effects of Oral Dehydroepiandrosterone on Counterregulatory Responses During Repeated Hypoglycemia in Healthy Humans

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.

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.

N-Hydroxyethyl-1-Deoxynojirimycin (Miglitol) Restores the Counterregulatory Response to Hypoglycemia Following Antecedent Hypoglycemia

Antecedent hypoglycemia suppresses the counterregulatory responses to subsequent hypoglycemic episodes, which can be prevented by normalizing portal-mesenteric vein (PMV) glycemia alone during the antecedent bout. Since the sodium-glucose transporter 3 receptor has been implicated in PMV glucosensing, we hypothesized that PMV infusion of the sodium-glucose cotransporter 3 receptor agonist N-hydroxyethyl-1-deoxynojirimycin (miglitol) would rescue the sympathoadrenal response to subsequent hypoglycemia. Rats underwent hyperinsulinemic-hypoglycemic clamps on 2 consecutive days without miglitol infusion (antecedent hypoglycemia without miglitol [HYPO]) or with miglitol infused upstream in the PMV, perfusing the glucosensors, or adjacent to the liver, bypassing PMV glucosensors, on day 1 or day 2. Control animals underwent day 1 euglycemic clamps, followed by hypoglycemic clamps on day 2. Peak epinephrine (EPI) responses for HYPO on day 2 were significantly blunted when compared with controls. Miglitol infusion on day 1 proved ineffective in restoring the EPI response following antecedent hypoglycemia, but day 2 miglitol infusion restored EPI responses to control levels. As norepinephrine and glucagon demonstrated similar responses, day 2 administration of miglitol effectively restored the counterregulatory response following antecedent hypoglycemia. In subsequent experiments, we demonstrate similar results with reduced miglitol infusion doses, approaching those currently prescribed for type 2 diabetes (correcting for rodent size), as well as the efficacy of oral miglitol administration in restoring the counterregulatory responses following antecedent hypoglycemia.

Short-time intensive insulin therapy upregulates 3 beta- and 17 beta-hydroxysteroid dehydrogenase levels in men with newly diagnosed T2DM

OBJECTIVE

Our previous study has found that short-term intensive insulin therapy in patients with newly diagnosed type 2 diabetes mellitus (T2DM) increased serum testosterone levels, but the underlying mechanisms remain unclear.

DESIGN AND METHODS

In this self-controlled study, 43 men with newly diagnosed drug naïve T2DM, aged 18-60 years, with HbA_{1c >}9.0% were treated with continuous subcutaneous insulin infusion (CSII) to normalize blood glucose within one week. Venous blood specimens were collected for measuring of serum total testosterone, dehydroepiandrosterone sulfate (DHEA-S), 3β- and 17β-hydroxysteroid dehydrogenase (3β- and 17β-HSD) concentrations before and after insulin therapy.

RESULTS

Testosterone increased from 13.0 (11.3, 14.6) nmol/L to 15.7 (13.9, 17.5) nmol/L after intensive insulin therapy (p<0.001), while the levels of DHEA-S decreased significantly after treatment (from 6.5 (5.7, 7.3) μmol/L to 6.0 (5.3, 6.7) μmol/L, p=0.001). The ratio of testosterone/DHEA-S increased significantly (2.4 (2.0, 2.8) vs. 3.1 (2.6, 3.7) nmol/μmol, p<0.001). After blood glucose normalization with the short-term CSII therapy, 3β-HSD increased from 11.0 (9.5, 12.5) pg/mL to 14.6 (13.5, 15.7) pg/mL, p=0.001, and 17β-HSD increased from 20.7 (16.3, 25.2) pg/mL to 28.2 (23.8, 32.5) pg/mL, p=0.009.

CONCLUSIONS

Blood glucose normalization via short-term intensive insulin therapy increases plasma total testosterone levels in men with newly diagnosed type 2 diabetes, associated with a decreased level of DHEA-S, probably because of the enhanced conversion from DHEA to testosterone catalyzed by 3β-HSD and 17β-HSD.

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.

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.

DHEA prevents ribavirin-induced anemia via inhibition of glucose-6-phosphate dehydrogenase

Ribavirin has been widely used for antiviral therapy. Unfortunately, ribavirin-induced anemia is often a cause of limiting or interrupting treatment. Our team has observed that dehydroepiandrosterone (DHEA) has a protective effect against in vitro and in vivo ribavirin-induced hemolysis. The aim of this study was to better understand this effect as well as the underlying mechanism(s). DHEA was able to reduce in vitro intraerythrocytic ATP depletion induced by ribavirin. Only 1% of ATP remained after incubation with ribavirin (2 mM) at 37 °C for 24 h vs. 37% if DHEA (200 μM) was added (p < 0.01). DHEA also helped erythrocytes conserve their size, with a shrinkage of only 10% vs 40% at 24 h with ribavirin alone (p < 0.01), and reduced phosphatidylserine exposure at the outer membrane, i.e. 27% vs 40% at 48 h, (p < 0.05). DHEA also inhibits ribavirin-induced hemolysis, i.e. 34% vs 46.5% at 72 h (p < 0.01). DHEA is an inhibitor of glucose-6-phosphate dehydrogenase (G6PD), a key enzyme in the hexose monophosphate shunt connected to the glycolytic pathway which is the only energy supplier of the red blood cell in the form of ATP. We have confirmed this inhibitory effect in the presence of ribavirin. All these observations suggest that ribavirin-induced hemolysis was initiated by ATP depletion, and that the inhibitory effect of DHEA on G6PD was able to rescue enough ATP to limit this hemolysis. This mechanism could be important for improving the therapeutic management of patients treated with ribavirin.