Diazoxide-mediated insulin suppression in obese men: a dose-response study

Liver insulinization as a driver of triglyceride dysmetabolism

Metabolic dysfunction-associated fatty liver disease (MAFLD) is an increasingly prevalent fellow traveller with the insulin resistance that underlies type 2 diabetes mellitus. However, the mechanistic connection between MAFLD and impaired insulin action remains unclear. In this Perspective, we review data from humans to elucidate insulin's aetiological role in MAFLD. We focus particularly on the relative preservation of insulin's stimulation of triglyceride (TG) biosynthesis despite its waning ability to curb hepatic glucose production (HGP). To explain this apparent 'selective insulin resistance', we propose that hepatocellular processes that lead to TG accumulation require less insulin signal transduction, or 'insulinization,' than do those that regulate HGP. As such, mounting hyperinsulinaemia that barely compensates for aberrant HGP in insulin-resistant states more than suffices to maintain hepatic TG biosynthesis. Thus, even modestly elevated or context-inappropriate insulin levels, when sustained day and night within a heavily pro-lipogenic metabolic milieu, may translate into substantial cumulative TG biosynthesis in the insulin-resistant state.

Driver versus navigator causation in biology: the case of insulin and fasting glucose

BACKGROUND

In biomedicine, inferring causal relation from experimental intervention or perturbation is believed to be a more reliable approach than inferring causation from cross-sectional correlation. However, we point out here that even in interventional inference there are logical traps. In homeostatic systems, causality in a steady state can be qualitatively different from that in a perturbed state. On a broader scale there is a need to differentiate driver causality from navigator causality. A driver is essential for reaching a destination but may not have any role in deciding the destination. A navigator on the other hand has a role in deciding the destination and the path but may not be able to drive the system to the destination. The failure to differentiate between types of causalities is likely to have resulted into many misinterpretations in physiology and biomedicine.

METHODS

We illustrate this by critically re-examining a specific case of the causal role of insulin in glucose homeostasis using five different approaches (1) Systematic review of tissue specific insulin receptor knock-outs, (2) Systematic review of insulin suppression and insulin enhancement experiments, (3) Differentiating steady state and post-meal state glucose levels in streptozotocin treated rats in primary experiments, (4) Mathematical and theoretical considerations and (5) Glucose-insulin relationship in human epidemiological data.

RESULTS

All the approaches converge on the inference that although insulin action hastens the return to a steady state after a glucose load, there is no evidence that insulin action determines the steady state level of glucose. Insulin, unlike the popular belief in medicine, appears to be a driver but not a navigator for steady state glucose level. It is quite likely therefore that the current line of clinical action in the field of type 2 diabetes has limited success largely because it is based on a misinterpretation of glucose-insulin relationship. The insulin-glucose example suggests that we may have to carefully re-examine causal inferences from perturbation experiments and set up revised norms for experimental design for causal inference.

Identification, pathophysiology, and clinical implications of primary insulin hypersecretion in nondiabetic adults and adolescents

BACKGROUND

Excessive insulin secretion may lead to glucose dysregulation. Our aim was to identify primary (independent of insulin resistance) insulin hypersecretion in subjects with normal glucose tolerance and its role in the progression of dysglycemia.

METHODS

In 1,168 adults, insulin secretion rate (ISR) and β cell function were estimated by C-peptide modeling during an oral glucose tolerance test (OGTT) and an i.v. glucose tolerance test. Whole-body insulin sensitivity was measured by a hyperinsulinemic-euglycemic clamp. After regressing ISR on insulin sensitivity, subjects in the upper tertile of the distribution of residuals were defined as primary hypersecretors. This approach was applied to a biethnic cohort of 182 obese adolescents, who received an OGTT, a hyperglycemic, and a euglycemic clamp.

RESULTS

Adult hypersecretors showed older age, more familial diabetes, sedentary lifestyle, increased fat mass, and worse lipid profile compared with the rest of the cohort, despite virtually identical BMI and insulin sensitivity. Insulin secretion was increased by 53% due to enhanced (+23%) β cell glucose sensitivity. Despite the resulting hyperinsulinemia, glucose tolerance was worse in hypersecretors among both adults and adolescents, coupled with higher indices of liver insulin resistance and increased availability of gluconeogenic substrates. At the 3-year follow-up, adult hypersecretors had increased incidence of impaired glucose tolerance/type 2 diabetes.

CONCLUSION

Primary insulin hypersecretion, independent of insulin resistance, is associated with a worse clinical and metabolic phenotype in adults and adolescents and predicts deterioration of glucose control over time.

FUNDING

The relationship between insulin sensitivity and cardiovascular disease (RISC) Study was partly supported by EU grant QLG1-CT-2001-01252.

High-Dose, Diazoxide-Mediated Insulin Suppression Boosts Weight Loss Induced by Lifestyle Intervention

CONTEXT

Obesity-related hyperinsulinism may impede lifestyle-initiated weight loss.

OBJECTIVE

Proof-of-concept study to investigate the amplifying effects of diazoxide (DZX)-mediated insulin suppression on lifestyle-induced weight loss in nondiabetic, hyperinsulinemic, obese men.

DESIGN

Twelve-month study comprising an initial 6-month, double-blind trial, followed by a partially de-blinded 6-month extension in men with obesity with a body mass index of 30 to 37.5 kg/m2 and a fasting serum C-peptide level >1.00 nM. Patients were randomized into three treatment groups: DZX + placebo (DZX + PL), DZX + metformin (DZX + MTF), and double PL (PL + PL).

RESULTS

At 6 months, DZX treatment was associated with a 6.1-kg PL-subtracted decline in fat mass (FM), and at 12 months, FM had decreased by a total of 15.7 ± 2.5 kg. Twelve months of DZX treatment was also associated with a significant decline in systolic (-6.6%) and diastolic (-8.6%) blood pressure and low-density lipoprotein-cholesterol (-18%) and triglycerides (-43%) and a 39% rise in high-density lipoprotein-cholesterol. These effects were achieved at the cost of a small rise in fasting glucose (95% CI: 0.2 to 1.0 mM) and hemoglobin A1c (95% CI: -0.08% to 0.44%). There were no differences between DZX monotherapy and the combination of DZX + MTF.

CONCLUSION

High-dose DZX treatment of 1 year resulted in a substantial decrease in FM, blood pressure, and lipid levels at the cost of a small rise in blood glucose levels.

Interventions for the Treatment of Craniopharyngioma-Related Hypothalamic Obesity: A Systematic Review

OBJECTIVE

Craniopharyngiomas (CPs) and their treatment are associated with hypothalamic damage that causes hypothalamic obesity (HO) in 30%-70% of cases. Thus, there is ongoing research regarding tangible solutions for HO, because these patients have unrelenting resistance to basic weight-loss interventions. This review aims to summarize the interventions that are used to treat CP-related HO (CP-HO), including pharmacotherapy and bariatric surgery.

METHODS

The Cochrane Library, EMBASE, and PubMed databases were searched up to June 2017 for relevant reports. Two reviewers conducted independent evaluations of the studies identified.

RESULTS

Eighteen articles were included in the systematic review, with 3 reports describing pharmacotherapy in randomized controlled trials and 15 reports describing bariatric surgery. Although several studies described effective interventions for treating CP-HO, the evidence base was limited by its low quality and our inability to perform a meta-analysis, which was related to a lack of adequate or integrated data.

CONCLUSIONS

Octreotide appears to be a preferred treatment for patients with CP-HO, based on limited data. Gastric bypass surgery may also be suitable for select patients with CP-HO, based on a review of various procedures in this setting. Microsurgical preservation of the hypothalamic structures is mandatory to decrease CP-HO-related morbidity and mortality. Further studies with adequate analytical power and sufficient follow-up are needed to identify effective strategies for CP-HO treatment.

Effects of Diazoxide-Mediated Insulin Suppression on Glucose and Lipid Metabolism in Nondiabetic Obese Men

CONTEXT

It has been suggested that stimulation of lipolysis by diazoxide (DZX)-mediated insulin suppression may be useful in treating obesity. However, the optimal dose to promote lipolysis without causing hyperglycemia is unknown.

OBJECTIVE

To assess the effects of DZX in nondiabetic obese men on lipid and glucose metabolism.

DESIGN

Double-blind, placebo (PL)-controlled, 6-month trial in men with a body mass index of 30 to 37.5 kg/m2 treated with a combination of caloric restriction, a standardized exercise program, and DZX or PL dose escalation.

RESULTS

The mean maximal tolerated dose of DZX was 422 ± 44 mg/d (range, 200 to 700 mg/d). Dose-limiting events were edema (n = 11), hyperglycemia (n = 6), and nausea (n = 2). After dose reduction to a level free of clinical side effects, DZX treatment was associated with a markedly greater decrease in fasting insulin levels than PL (-72.3 ± 3.5% vs -23.0 ± 12.6%; P < 0.001) and a significant improvement of blood pressure and plasma lipid levels. The decline in insulin levels occurred at the cost of a small increase in plasma glucose (0.6 ± 0.2 mmol/L vs -0.1 ± 0.1 mmol/L; P = 0.04) and hemoglobin A1C (0.2 ± 0.1% vs 0.0 ± 0.1%; P = 0.17).

CONCLUSION

In nondiabetic obese men, insulin levels can be reduced up to 70% without major metabolic side effects. The marked intersubject variation in maximal tolerated dose indicates that DZX dose titration needs to be individualized.

Bi-stability in type 2 diabetes mellitus multi-organ signalling network

Type 2 diabetes mellitus (T2DM) is believed to be irreversible although no component of the pathophysiology is irreversible. We show here with a network model that the apparent irreversibility is contributed by the structure of the network of inter-organ signalling. A network model comprising all known inter-organ signals in T2DM showed bi-stability with one insulin sensitive and one insulin resistant attractor. The bi-stability was made robust by multiple positive feedback loops suggesting an evolved allostatic system rather than a homeostatic system. In the absence of the complete network, impaired insulin signalling alone failed to give a stable insulin resistant or hyperglycemic state. The model made a number of correlational predictions many of which were validated by empirical data. The current treatment practice targeting obesity, insulin resistance, beta cell function and normalization of plasma glucose failed to reverse T2DM in the model. However certain behavioural and neuro-endocrine interventions ensured a reversal. These results suggest novel prevention and treatment approaches which need to be tested empirically.

Social behavioural epistemology and the scientific community

The progress of science is influenced substantially by social behaviour of and social interactions within the scientific community. Similar to innovations in primate groups, the social acceptance of an innovation depends not only upon the relevance of the innovation but also on the social dominance and connectedness of the innovator. There are a number of parallels between many well-known phenomena in behavioural evolution and various behavioural traits observed in the scientific community. It would be useful, therefore, to use principles of behavioural evolution as hypotheses to study the social behaviour of the scientific community. I argue in this paper that a systematic study of social behavioural epistemology is likely to boost the progress of science by addressing several prevalent biases and other problems in scientific communication and by facilitating appropriate acceptance/rejection of novel concepts.

The Classically Cardioprotective Agent Diazoxide Elicits Arrhythmias in Type 2 Diabetes Mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is associated with an enhanced propensity for ventricular tachyarrhythmias (VTs) under conditions of metabolic demand. Activation of mitochondrial adenosine triphosphate-sensitive potassium (KATP) channels by low-dose diazoxide (DZX) improves hypoglycemia-related complications, metabolic function, and triglyceride and free fatty acid levels and reverses weight gain in T2DM.

OBJECTIVES

In this study, we hypothesized that DZX prevents ischemia-mediated arrhythmias in T2DM via its putative cardioprotective and antidiabetic property.

METHODS

Zucker obese diabetic fatty (ZO) rats (n = 43) with T2DM were studied. Controls consisted of Zucker lean (ZL; n = 13) and normal Sprague-Dawley (SprD; n = 30) rats. High-resolution optical action potential mapping was performed before and during challenge with no-flow ischemia for 12 min.

RESULTS

Electrophysiological properties were relatively stable in T2DM hearts at baseline. In contrast, ischemia uncovered major differences between groups, because action potential duration (APD) in T2DM failed to undergo progressive adaptation to ischemic challenge. DZX promoted the incidence of arrhythmias, because all DZX-treated T2DM hearts exhibited ischemia-induced VTs that persisted on reperfusion. In contrast, untreated T2DM and controls did not exhibit VT during ischemia. Unlike DZX, pinacidil promoted ischemia-mediated arrhythmias in both control and T2DM hearts. Rapid and spatially heterogeneous shortening of APD preceded the onset of arrhythmias in T2DM. DZX-mediated proarrhythmia in T2DM was not related to changes in the messenger ribonucleic acid expression of Kir6.1, Kir6.2, SUR1A, SUR1B, SUR2A, SUR2B, or ROMK (renal outer medullary potassium channel).

CONCLUSIONS

Ischemia uncovers a paradoxical resistance of T2DM hearts to APD adaptation. DZX reverses this property, resulting in rapid and heterogeneous APD shortening. This promotes reentrant VT during ischemia. DZX should be avoided in diabetic patients at risk of ischemic events.

Weight loss in obese men by caloric restriction and high-dose diazoxide-mediated insulin suppression

OBJECTIVE

To examine the concept whether high-dose diazoxide (DZX)-mediated insulin suppression, in combination with moderate caloric restriction and increased physical activity, can establish a weight loss of at least 15% in obese hyperinsulinaemic men.

DESIGN

Open, uncontrolled, 6-month pilot study. Energy intake was reduced by 30%, and walking for at least 30 min a day was strongly recommended. DZX treatment was started at 50 mg t.i.d. and increased by 50 mg per dose every 4 weeks to a maximum of 300 mg t.i.d., unless hyperglycaemia or other side-effects occurred.

SUBJECTS AND METHODS

Eighteen obese hyperinsulinaemic men with a body mass index of 30-35 kg/m(2). Measurements included body weight, body composition, blood pressure, glycaemic control, insulin response, adiponectin and serum lipids.

RESULTS

Body weight decreased by 9.4 kg (95% CI: 5.6-13.2 kg, p < 0.001), waist circumference reduced by 9.2 cm (95% CI: 5.3-12.9 cm, p < 0.001) and total body fat mass decreased by 23.3% (95% CI: 13.7-32.9%, p < 0.001), without a concomitant change in soft tissue lean body mass or bone mass. Fat loss was inversely related to fasting insulin levels achieved at 6 months (r = -0.76, p < 0.002). Diastolic blood pressure decreased by 10.9 mmHg (95% CI: 6.5-15.4 mmHg, p < 0.002). Fasting and postmeal peak insulin levels were reduced by about 65% (p < 0.001) and decreased to the normal range for non-obese men. Fasting and postmeal peak glucose levels increased by 0.8 +/- 0.3 mmol/l (p = 0.01) and 1.4 +/- 0.7 mmol/l (p = 0.06) respectively. Haemoglobin A1c rose by 0.5% to 5.9 +/- 0.2%.

CONCLUSION

High-dose DZX-mediated insulin suppression, in combination with moderate caloric restriction and lifestyle advice, is associated with a clinically relevant degree of weight reduction. A more extensive exploration is warranted to optimize this mode of treatment and to further clarify its risks and benefits.

No effect of inhibition of insulin secretion by diazoxide on weight loss in hyperinsulinaemic obese subjects during an 8-week weight-loss diet

AIM

Obesity is positively associated with hyperinsulinaemia, and it has been suggested that hyperinsulinaemia may contribute to maintain the obese state in insulin-resistant obese individuals. The aim of the present study was to investigate the effect of inhibition of insulin secretion by diazoxide on weight loss in obese, normoglycaemic (fasting plasma glucose of > or =6.1 mmol/l), hyperinsulinaemic (fasting plasma insulin of > or =100 pmol/l) adults during a 2.5 MJ/day energy-deficient diet.

METHODS

In an 8-week, double-blind, placebo-controlled parallel design, 35 overweight and obese subjects (age: 23-54 years, body mass index: 27-66 kg/m(2)) were randomized either to 2 mg/kg/day (maximum 200 mg/day) of oral diazoxide or to placebo. Body composition and resting energy expenditure (REE) were measured before and after the intervention. Blood samples, and appetite sensations by visual analogue scales, were collected during fasting, during an oral glucose tolerance test (OGTT) and 4 h postprandially after a test meal. Subsequently, an ad libitum meal was given.

RESULTS

Thirty-one subjects completed the protocol. Eight weeks of diazoxide decreased incremental area under the response curve (iAUC) for insulin (iAUC(insulin)) and for C-peptide (iAUC(C-peptide)) and increased iAUC for glucose (iAUC(glucose)) during the OGTT and the test meal compared with the use of placebo (p < 0.003). No differences in changes between the groups in body weight, body fat, REE or appetite were observed during the 8-week trial.

CONCLUSION

These findings do not suggest that hyperinsulinaemia per se contributes to maintenance of the obese state, and insulin secretion inhibition seems not a promising drug target.