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

The role of gastric emptying in glucose homeostasis and defense against hypoglycemia: Innocent bystander or partner in crime?

Maintenance of plasma glucose (PG) homeostasis is due to a complex network system. Even a minor fall in PG activates multiple neuroendocrine actions promoting hormonal, metabolic and behavioral responses, which prevent and ultimately recover hypoglycemia, primarily neuroglycopenia. Among these responses, gastric emptying (GE) plays an important role by coordinated mechanisms which regulate transit and absorption of nutrients through the small intestine. A bidirectional relationship between GE and glycemia has been established: GE may explain the up to 30-40 % variance in glycemic response following a carbohydrate-rich meal. In addition, acute and chronic hyperglycemia induce deceleration of GE after meals. Hypoglycemia accelerates GE, but its role in counterregulation has been poorly investigated. The role of GE as a counterregulatory mechanism has been confirmed in pathophysiological conditions, such as gastroparesis or following recurrent hypoglycemia. Therefore, it could represent an "ancestral" mechanism, highly conservative and effective in all individuals, conditions and clinical contexts. Recent guidelines recommend GLP-1 receptor agonists (GLP-1RAs) either as the first injectable therapy for type 2 diabetes mellitus or in combination with insulin. Considering the potential impact on GE, it would be important to study subjects on GLP-1 RAs during hypoglycemia, to establish whether a possible deceleration of GE impairs glucose counterregulation.

Effects of Hypoglycemia on Cardiovascular Function in Patients with Diabetes

Hypoglycemia is common in patients with type 1 and type 2 diabetes (T1D, T2D), treated with insulin or sulfonylureas, and has multiple short- and long-term clinical implications. Whether acute or recurrent, hypoglycemia significantly affects the cardiovascular system with the potential to cause cardiovascular dysfunction. Several pathophysiological mechanisms have been proposed linking hypoglycemia to increased cardiovascular risk, including hemodynamic changes, myocardial ischemia, abnormal cardiac repolarization, cardiac arrhythmias, prothrombotic and proinflammatory effects, and induction of oxidative stress. Hypoglycemia-induced changes can promote the development of endothelial dysfunction, which is an early marker of atherosclerosis. Although data from clinical trials and real-world studies suggest an association between hypoglycemia and cardiovascular events in patients with diabetes, it remains uncertain whether this association is causal. New therapeutic agents for patients with T2D do not cause hypoglycemia and have cardioprotective benefits, whereas increasing the use of new technologies, such as continuous glucose monitoring devices and insulin pumps, has the potential to reduce hypoglycemia and its adverse cardiovascular outcomes in patients with T1D.

Severe hypoglycemia and risk of hospitalization for heart failure in adults with diabetes treated with oral medications with or without insulin: A population-based study

AIMS

We aimed to determine if severe hypoglycemia (SH) independently increases the risk of hospitalization for heart failure (hHF) in type 2 diabetes, regardless of the prevalent or incident cardiovascular disease (CVD).

METHODS

This was a nationwide population-based propensity score-matched study using Korean National Health Insurance Service data (2002-2018). The hazards of hHF were compared in individuals who experienced SH (n = 8,965) and 1:3 matched controls, among adults with diabetes using oral anti-diabetes medications (OADs) with or without insulin and without previous hHF at baseline.

RESULTS

During 236,417 person-years, 1,189 cases of hHF occurred. The hazard of hHF was higher in individuals with SH compared to matched controls (adjusted hazard ratio [aHR] 1.503, 95 % confidence interval [CI] 1.324-1.707). The increase in aHR remained significant when excluding participants with prevalent or incident major adverse cardiovascular events (MACE; aHR 1.352, 95 % CI 1.228-1.622) and any CVD (aHR 1.342, 95 % CI 1.025-1.756). Two or more SH events were associated with further increase in hHF risk.

CONCLUSION

SH was associated with increased risks of hHF among adults with diabetes using OAD with or without insulin. The increased risk was attenuated but remained significant in those without prevalent or incident MACE or CVDs.

Insulin: evolution of insulin formulations and their application in clinical practice over 100 years

The first preparation of insulin extracted from a pancreas and made suitable for use in humans after purification was achieved 100 years ago in Toronto, an epoch-making achievement, which has ultimately provided a life-giving treatment for millions of people worldwide. The earliest animal-derived formulations were short-acting and contained many impurities that caused adverse reactions, thereby limiting their therapeutic potential. However, since then, insulin production and purification improved with enhanced technologies, along with a full understanding of the insulin molecule structure. The availability of radio-immunoassays contributed to the unravelling of the physiology of glucose homeostasis, ultimately leading to the adoption of rational models of insulin replacement. The introduction of recombinant DNA technologies has since resulted in the era of both rapid- and long-acting human insulin analogues administered via the subcutaneous route which better mimic the physiology of insulin secretion, leading to the modern basal-bolus regimen. These advances, in combination with improved education and technologies for glucose monitoring, enable people with diabetes to better meet individual glycaemic goals with a lower risk of hypoglycaemia. While the prevalence of diabetes continues to rise globally, it is important to recognise the scientific endeavour that has led to insulin remaining the cornerstone of diabetes management, on the centenary of its first successful use in humans.

Severe Hypoglycemia and Incident Heart Failure Among Adults With Type 2 Diabetes

CONTEXT

The association of severe hypoglycemia on the incidence of heart failure (HF) is unclear.

OBJECTIVE

We evaluated the association of severe hypoglycemia with incident HF among individuals with type 2 diabetes.

METHODS

We included participants with type 2 diabetes from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) study. Severe hypoglycemia episodes were assessed during the initial 24 months following randomization and defined using 2 methods: (1) symptomatic, severe hypoglycemic event requiring medical assistance (first definition); or (2) requiring any assistance (second definition). Participants without HF at baseline and during the first 24 months of the study were prospectively followed for incident HF hospitalization. Multivariable Cox regression was used to generate adjusted hazard ratios (HR) for the association of severe hypoglycemia and incident HF.

RESULTS

Among 9208 participants (mean age 63 years, 38% female, 62% White), 365 had ≥ 1 episode of severe hypoglycemic. Over a median follow-up duration of 3 years, there were 249 incident HF events. After multivariable adjustment for relevant confounders, participants with severe hypoglycemia requiring medical assistance had a 68% higher relative risk of incident HF (HR 1.68; 95% CI, 1.06-2.66), as compared with individuals who never experienced any episode of hypoglycemia. Severe hypoglycemia requiring any assistance was also associated with a 49% higher relative risk of HF (HR 1.49; 95% CI, 1.01-2.21).

CONCLUSION

In a large cohort of adults with type 2 diabetes, severe hypoglycemia was independently associated with greater risk of incident HF.

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.

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.

A Case of Hypoglycemia Associated With the Ketogenic Diet and Alcohol Use

The ketogenic diet, which has become an increasingly popular diet, severely restricts carbohydrate intake to shunt metabolism towards fatty acid oxidation and production of ketones as a fuel source. There have been many studies illustrating the positive effects of a ketogenic diet in weight loss and other benefits; however, the long-term effects and potential adverse events of a ketogenic diet have not been well studied or documented in literature. There are a few case reports of ketogenic diet resulting in hypoglycemia. We report a case of hypoglycemia with a blood glucose of 39 mg/dL and ketosis in a 69-year-old woman who strictly followed a ketogenic diet for nearly one year. She presented with malaise, sugar cravings, and mental fogginess, and after intake of alcoholic beverages, was admitted to the hospital with hypoglycemia. She had elevated beta-hydroxybutyrate, and low insulin and C-peptide, all consistent with a starvation ketosis. This case illustrates that adherence to a ketogenic diet for a prolonged period of time, in combination with alcohol intake, can disrupt normal glucose homeostatic mechanisms and result in a significant degree of hypoglycemia. This pattern of hypoglycemia may not present with classic symptoms, most likely partly due to effects of the ketogenic diet on brain function. This case provides insight that supports the need to counsel patients about alcohol intake while on the ketogenic diet. More information is needed on long-term complications of the ketogenic diet on glucose homeostasis in the body as well as in the brain.

Postprandial hypoglycaemia after Roux-en-Y gastric bypass in individuals with type 2 diabetes

AIMS/HYPOTHESIS

Postprandial hypoglycaemia (PPHG) is a complication of Roux-en-Y gastric bypass (RYGB) surgery in normoglycaemic individuals. In type 2 diabetes, RYGB improves glucose metabolism, but whether this improvement is related to the later development of PPHG is not known. We investigated the presence and mechanisms of PPHG in individuals with type 2 diabetes undergoing RYGB.

METHODS

A total of 35 obese individuals with type 2 diabetes underwent an OGTT before and 24 months after surgery. PPHG was defined as a plasma glucose level of ≤3.3 mmol/l when not taking glucose-lowering agents. Insulin sensitivity was assessed by oral glucose insulin sensitivity index and beta-cell function by mathematical modelling of the plasma glucose, insulin and C-peptide concentrations.

RESULTS

After surgery, PPHG occurred in 11 of 35 individuals who underwent RYGB. Before surgery, BMI was lower, glycaemic control less good and time of glucose peak earlier in the PPHG vs No PPHG group, and the duration of diabetes was shorter with PPHG (all p ≤ 0.05). In addition, insulin sensitivity was greater in the PPHG than No PPHG group (p = 0.03). After surgery, BMI and fasting glucose and insulin levels decreased similarly in the two groups; insulin secretion during the first hour of the OGTT increased more in the PPHG than No PPHG group (p = 0.04). Beta-cell glucose sensitivity increased more in individuals with PPHG than those without (p = 0.002). Over the same time interval, the glucagon-like peptide 1 (GLP-1) response was lower in individuals with PPHG before surgery (p = 0.05), and increased more after surgery. At 2 h after glucose ingestion in the OGTT, postsurgery plasma glucagon level was significantly lower in the PPHG than No PPHG group.

CONCLUSIONS/INTERPRETATION

In morbidly obese individuals with type 2 diabetes, spontaneous PPHG may occur after bariatric surgery independently of a remission of diabetes. Before surgery, individuals had a shorter duration and were more insulin sensitive. Two years after surgery, these individuals developed greater beta-cell glucose sensitivity, and showed greater insulin and GLP-1 release early in the OGTT.

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.

Risk of recurrent severe hypoglycemia remains associated with a past history of severe hypoglycemia up to 4 years: Results from a large prospective contemporary pediatric cohort of the DPV initiative

OBJECTIVES

In a contemporary cohort of youth with type 1 diabetes, we examined the interval between episodes of severe hypoglycemia (SH) as a risk factor for recurrent SH or hypoglycemic coma (HC).

METHODS

This was a large longitudinal observational study. Using the DPV Diabetes Prospective follow-up data, we analyzed frequency and timing of recurrent SH (defined as requiring assistance from another person) and HC (loss of consciousness or seizures) in 14 177 youths with type 1 diabetes aged <20 years and at least 5 years of follow-up.

RESULTS

Among 14 177 patients with type 1 diabetes, 72% (90%) had no, 14% (6.8%) had 1 and 14% (3.2%) >1 SH (HC). SH or HC in the last year of observation was highest with SH in the previous year (odds ratio [OR] 4.7 [CI 4.0-5.5]/4.6 [CI 3.6-6.0]), but remained elevated even 4 years after an episode (OR 2.0 [CI 1.6-2.7]/2.2 [CI 1.5-3.1]). The proportion of patients who experienced SH or HC during the last year of observation was highest with SH/HC recorded during the previous year (23% for SH and 13% for HC) and lowest in those with no event (4.6% for SH and 2% for HC) in the initial 4 years of observation.

CONCLUSIONS

Even 4 years after an episode of SH/HC, risk for SH/HC remains higher compared to children who never experienced SH/HC. Clinicians should continue to regularly track hypoglycemia history at every visit, adjust diabetes education and therapy in order to avoid recurrences.

Risk of Severe Hypoglycemia in Type 1 Diabetes Over 30 Years of Follow-up in the DCCT/EDIC Study

OBJECTIVE

During the Diabetes Control and Complications Trial (DCCT), intensive diabetes therapy achieving a mean HbA_1c of ∼7% was associated with a threefold increase in the rate of severe hypoglycemia (defined as requiring assistance) compared with conventional diabetes therapy with a mean HbA_1c of 9% (61.2 vs. 18.7 per 100 patient-years). After ∼30 years of follow-up, we investigated the rates of severe hypoglycemia in the DCCT/Epidemiology of Diabetes Inverventions and Complications (EDIC) cohort.

RESEARCH DESIGN AND METHODS

Rates of severe hypoglycemia were reported quarterly during DCCT and annually during EDIC (i.e., patient recall of episodes in the preceding 3 months). Risk factors influencing the rate of severe hypoglycemia over time were investigated.

RESULTS

One-half of the DCCT/EDIC cohort reported episodes of severe hypoglycemia. During EDIC, rates of severe hypoglycemia fell in the former DCCT intensive treatment group but rose in the former conventional treatment group, resulting in similar rates (36.6 vs. 40.8 episodes per 100 patient-years, respectively) with a relative risk of 1.12 (95% CI 0.91-1.37). A preceding episode of severe hypoglycemia was the most powerful predictor of subsequent episodes. Entry into the DCCT study as an adolescent was associated with an increased risk of severe hypoglycemia, whereas insulin pump use was associated with a lower risk. Severe hypoglycemia rates increased with lower HbA_1c similarly among participants in both treatment groups.

CONCLUSIONS

Rates of severe hypoglycemia have equilibrated over time between the two DCCT/EDIC treatment groups in association with advancing duration of diabetes and similar HbA_1c levels. Severe hypoglycemia persists and remains a challenge for patients with type 1 diabetes across their life span.

Comparison of Pulse Rate Variability and Heart Rate Variability for Hypoglycemia Syndrome

BACKGROUND

Heart rate variability (HRV) is a signal obtained from RR intervals of electrocardiography (ECG) signals to evaluate the balance between the sympathetic nervous system and the parasympathetic nervous system; not only HRV but also pulse rate variability (PRV) extracted from finger pulse plethysmography (PPG) can reflect irregularities that may occur in heart rate and control procedures.

OBJECTIVES

The purpose of this study is to compare the HRV and PRV during hypoglycemia in order to evaluate the features that computed from PRV that can be used in detection of hypoglycemia.

METHODS

To this end, PRV and HRV of 10 patients who required testing with insulin-induced hypoglycemia (IIHT) in Clinics of Endocrinology and Metabolism Diseases of Bezm-i Alem University (Istanbul, Turkey), were obtained. The recordings were done at three stages: prior to IIHT, during the IIHT, and after the IIHT. We used Bland-Altman analysis for comparing the parameters and to evaluate the correlation between HRV and PRV if exists.

RESULTS

Significant correlation (r > 0.90, p < 0.05) and close agreement were found between HRV and PRV for mean intervals, the root-mean square of the difference of successive intervals, standard deviation of successive intervals and the ratio of the low-to-high frequency power.

CONCLUSIONS

In conclusion, all the features computed from PRV and HRV have close agreement and correlation according to Bland-Altman analyses' results and features computed from PRV can be used in detection of hypoglycemia.