Mechanisms of amino acid-stimulated insulin secretion in congenital hyperinsulinism

The Regulation of Metabolic Homeostasis by Incretins and the Metabolic Hormones Produced by Pancreatic Islets

In healthy humans, the complex biochemical interplay between organs maintains metabolic homeostasis and pathological alterations in this process result in impaired metabolic homeostasis, causing metabolic diseases such as diabetes and obesity, which are major global healthcare burdens. The great advancements made during the last century in understanding both metabolic disease phenotypes and the regulation of metabolic homeostasis in healthy individuals have yielded new therapeutic options for diseases like type 2 diabetes (T2D). However, it is unlikely that highly desirable more efficacious treatments will be developed for metabolic disorders until the complex systemic regulation of metabolic homeostasis becomes more intricately understood. Hormones produced by pancreatic islet beta-cells (insulin) and alpha-cells (glucagon) are pivotal for maintaining metabolic homeostasis; the activity of insulin and glucagon are reciprocally correlated to achieve strict control of glucose levels (normoglycaemia). Metabolic hormones produced by other pancreatic islet cells and incretins produced by the gut are also crucial for maintaining metabolic homeostasis. Recent studies highlighted the incomplete understanding of metabolic hormonal synergism and, therefore, further elucidation of this will likely lead to more efficacious treatments for diseases such as T2D. The objective of this review is to summarise the systemic actions of the incretins and the metabolic hormones produced by the pancreatic islets and their interactions with their respective receptors.

The link between obesity and insulin resistance among children: Effects of key metabolites

BACKGROUND

Childhood obesity became a severe public health challenge, and insulin resistance (IR) was one of the common complications. Both obesity and IR were considered as the basis of metabolic disorders. However, it is unclear which common key metabolites are associated with childhood obesity and IR.

METHODS

The children were divided into normal weight and overweight/obese groups. Fasting blood glucose and fasting insulin were measured, and homeostasis model assessment of insulin resistance was calculated. Liquid chromatography-tandem mass spectrometry was applied for metabonomic analysis. Multiple linear regression analysis and correlation analysis explored the relationships between obesity, IR, and metabolites. Random forests were used to rank the importance of differential metabolites, and relative operating characteristic curves were used for prediction.

RESULTS

A total of 88 normal-weight children and 171 obese/overweight children participated in the study. There was a significant difference between the two groups in 30 metabolites. Childhood obesity was significantly associated with 10 amino acid metabolites and 20 fatty acid metabolites. There were 12 metabolites significantly correlated with IR. The ranking of metabolites in random forest showed that glutamine, tyrosine, and alanine were important in amino acids, and pyruvic-ox-2, ethylmalonic-2, and phenyllactic-2 were important in fatty acids. The area under the curve of body mass index standard deviation  score (BMI-SDS) combined with key amino acid metabolites and fatty acid metabolites for predicting IR was 80.0% and 76.6%, respectively.

CONCLUSIONS

There are common key metabolites related to IR and obese children, and these key metabolites combined with BMI-SDS could effectively predict the risk of IR.

Mitochondrial Dysfunction in Pancreatic Alpha and Beta Cells Associated with Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a complex multifactorial disease of epidemic proportions. It involves genetic and lifestyle factors that lead to dysregulations in hormone secretion and metabolic homeostasis. Accumulating evidence indicates that altered mitochondrial structure, function, and particularly bioenergetics of cells in different tissues have a central role in the pathogenesis of type 2 diabetes mellitus. In the present study, we explore how mitochondrial dysfunction impairs the coupling between metabolism and exocytosis in the pancreatic alpha and beta cells. We demonstrate that reduced mitochondrial ATP production is linked with the observed defects in insulin and glucagon secretion by utilizing computational modeling approach. Specifically, a 30-40% reduction in alpha cells' mitochondrial function leads to a pathological shift of glucagon secretion, characterized by oversecretion at high glucose concentrations and insufficient secretion in hypoglycemia. In beta cells, the impaired mitochondrial energy metabolism is accompanied by reduced insulin secretion at all glucose levels, but the differences, compared to a normal beta cell, are the most pronounced in hyperglycemia. These findings improve our understanding of metabolic pathways and mitochondrial bioenergetics in the pathology of type 2 diabetes mellitus and might help drive the development of innovative therapies to treat various metabolic diseases.

The Possibility of Suppression of Increased Postprandial Blood Glucose Levels by Gamma-Polyglutamic Acid-Rich Natto in the Early Phase after Eating: A Randomized Crossover Pilot Study

The natto containing high levels of gamma-polyglutamic acid (γ-PGA) was recently developed. We investigated the effect of γ-PGA-rich natto consumption on postprandial glycemic excursion in humans. A randomized crossover meal test study was performed on healthy volunteers aged 20-64 years using the following test meals: (1) white rice (WR), (2) low-γ-PGA natto meal (WR + low-γ-PGA natto), and (3) high-γ-PGA natto meal (WR + high-γ-PGA natto). Blood samples were obtained at each visit before and for 120 min after loading. The incremental area under the curve (IAUC) of blood glucose and insulin levels was calculated and compared among the test meals. The blood glucose's IAUC at 0-120 min, the primary endpoint, was 20.1% and 15.4% lower for the high- and low-γ-PGA natto meal than for the WR, with a significant difference only between the high-γ-PGA natto meal and WR (p < 0.05). The blood glucose's IAUC at 0-15, 0-30, and 0-45 min was lower for the high-γ-PGA natto meal than for the low-γ-PGA natto meal (all p < 0.05). The possibility that high-γ-PGA natto might suppress blood glucose elevations in the early phase after eating is indicated.

Patterns of postmeal insulin secretion in individuals with sulfonylurea-treated KCNJ11 neonatal diabetes show predominance of non-KATP-channel pathways

OBJECTIVE

Insulin secretion in sulfonylurea-treated KCNJ11 permanent neonatal diabetes mellitus (PNDM) is thought to be mediated predominantly through amplifying non-K_ATP-channel pathways such as incretins. Affected individuals report symptoms of postprandial hypoglycemia after eating protein/fat-rich foods. We aimed to assess the physiological response to carbohydrate and protein/fat in people with sulfonylurea-treated KCNJ11 PNDM.

RESEARCH DESIGN AND METHODS

5 adults with sulfonylurea-treated KCNJ11 PNDM and five age, sex and body mass index-matched controls without diabetes had a high-carbohydrate and high-protein/fat meal on two separate mornings. Insulin(i) and glucose(g) were measured at baseline then regularly over 4 hours after the meal. Total area under the curve (tAUC) for insulin and glucose was calculated over 4 hours and compared between meals in controls and KCNJ11 cases.

RESULTS

In controls, glucose values after carbohydrate and protein/fat were similar (median glucose tAUC_0-4h21.4 vs 19.7 mmol/L, p=0.08). In KCNJ11 cases glucose levels were higher after carbohydrate than after protein/fat (median glucose tAUC_0-4h58.1 vs 31.3 mmol/L, p=0.04). These different glycemic responses reflected different patterns of insulin secretion: in controls, insulin secretion was greatly increased after carbohydrate versus protein/fat (median insulin tAUC_0-4h727 vs 335 pmol/L, p=0.04), but in KCNJ11 cases insulin secretion was similar after carbohydrate and protein/fat (median insulin tAUC_0-4h327 vs 378 pmol/L, p=0.50).

CONCLUSIONS

Individuals with sulfonylurea-treated KCNJ11 PNDM produce similar levels of insulin in response to both carbohydrate and protein/fat meals despite carbohydrate resulting in much higher glucose levels and protein/fat resulting in relatively low glucose levels. This suggests in an inability to modulate insulin secretion in response to glucose levels, consistent with a dependence on non-K_ATP pathways for insulin secretion.

TRIAL REGISTRATION NUMBER

NCT02921906.

Direct Sensing of Nutrients via a LAT1-like Transporter in Drosophila Insulin-Producing Cells

Dietary leucine has been suspected to play an important role in insulin release, a hormone that controls satiety and metabolism. The mechanism by which insulin-producing cells (IPCs) sense leucine and regulate insulin secretion is still poorly understood. In Drosophila, insulin-like peptides (DILP2 and DILP5) are produced by brain IPCs and are released in the hemolymph after leucine ingestion. Using Ca²⁺-imaging and ex vivo cultured larval brains, we demonstrate that IPCs can directly sense extracellular leucine levels via minidiscs (MND), a leucine transporter. MND knockdown in IPCs abolished leucine-dependent changes, including loss of DILP2 and DILP5 in IPC bodies, consistent with the idea that MND is necessary for leucine-dependent DILP release. This, in turn, leads to a strong increase in hemolymph sugar levels and reduced growth. GDH knockdown in IPCs also reduced leucine-dependent DILP release, suggesting that nutrient sensing is coupled to the glutamate dehydrogenase pathway.

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IPCs directly sense extracellular leucine levels via minidiscs (MND)

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MND knockdown in IPCs abolishes loss of DILP2 and DILP5

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This leads to a strong increase in hemolymph sugar levels and reduces growth

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GDH knockdown in IPCs reduces leucine-dependent DILP release

Macronutrient Composition and Management of Non-Insulin-Dependent Diabetes Mellitus (NIDDM): A New Paradigm for Individualized Nutritional Therapy in Diabetes Patients

Medical nutrition therapy constitutes an important lifestyle intervention in diabetes management. Several nutrition patterns have been effective in improving diabetes control, but there has been a debate about the optimal macronutrient composition in diabetes meal planning. For many years, the recommended diets for persons with and without diabetes were similar, i.e. heart-healthy and low in fat. For almost three decades, carbohydrates have been lauded, lipids demonized, and proteins considered of little importance. However, in the past few years, this concept has been questioned and reassessed. Modern nutritional recommendations for people with diabetes are headed towards individualization, but lack specific guidelines. Nutritional algorithms may help nutritionists in diabetes meal planning. This review aims to discuss: 1) the effects of the three major macronutrients (carbohydrates, proteins, and lipids) on glucose levels, 2) current recommendations for macronutrient intake for people with diabetes, and 3) specific parameters that need to be taken into consideration when determining the macronutrient composition for a person with diabetes, for example body mass index, degree of insulin resistance, HbA1c value, and lipid profile (especially triglycerides and HDL cholesterol). These aspects are analyzed in the context of the results of recent studies, especially randomized controlled trials (RCTs). Finally, we introduce an individualized nutritional concept that proposes carbohydrate over lipid restriction, substitution of SFAs with MUFAs and PUFAs, and adequate intake of dietary fiber, which are key factors in optimizing diabetes management.

Hyperinsulinemic Hypoglycemia in Infancy: Current Concepts in Diagnosis and Management

PURPOSE

Molecular basis of various forms of hyperinsulinemic hypoglycemia, involving defects in key genes regulating insulin secretion, are being increasingly reported. However, the management of medically unresponsive hyperinsulinism still remains a challenge as current facilities for genetic diagnosis and appropriate imaging are limited only to very few centers in the world. We aim to provide an overview of spectrum of clinical presentation, diagnosis and management of hyperinsulinism.

METHODS

We searched the Cochrane library, MEDLINE and EMBASE databases, and reference lists of identified studies.

CONCLUSION

Analysis of blood samples, collected at the time of hypoglycemic episodes, for intermediary metabolites and hormones is critical for diagnosis and treatment. Increased awareness among clinicians about infants at-risk of hypoglycemia, and recent advances in genetic diagnosis have made remarkable contribution to the diagnosis and management of hyperinsulinism. Newer drugs like lanreotide a long acting somatostatin analogue and sirolimus (mammalian target of rapamycin (mTOR) inhibitor) appears promising as patients with diffuse disease can be treated successfully without subtotal pancreatectomy, minimizing the long-term sequelae of diabetes and pancreatic insufficiency. Newer insights in understanding the molecular and histological basis and improvements in imaging and surgical techniques will modify the approach to patients with congenital hyperinsulinism.

Plasma insulin levels are regulated by release, rather than transcription or translation, in barfin flounder, Verasper moseri

We evaluated whether transcription or translation of the preproinsulin gene or insulin release into plasma is the primary regulator of plasma insulin level in barfin flounder. Three experimental groups were used: one tested 2h after feeding (Fed), one tested after fasting for 5 days (Fasted), and one tested 2 h after feeding following 5 days of fasting (Refed). No significant differences in insulin transcription, insulin concentrations in the principal islets (PI), or plasma total insulin-like growth factor-I (IGF-I) levels were observed between the three groups. In contrast, plasma insulin level in the Fasted group was significantly lower (P<0.002) than that in the other groups. These results suggest that insulin release is the primary regulator of plasma insulin level and is more sensitive to short-term changes in nutritional conditions than IGF-I level. Furthermore, we estimated the capacity for insulin release. Based on various individual measures, the average insulin stored in the PI was 82.8 μg/kg body weight (BW), and the maximum plasma content of insulin was estimated to be <1.7 μg/kg BW. The half-life of plasma insulin in diabetogenic chemically (alloxan) treated flounder injected with insulin was estimated to be 2.79 h, which is much longer than that in mammals, assuming a two-compartment model for the β phase. These results suggest that the capacity for insulin release in fish is ensured by at least two systems, such as the ability to store excess insulin in Brockman bodies, and enhanced efficiency of insulin storage by elongating its half-life.

Molecular mechanisms of protein induced hyperinsulinaemic hypoglycaemia

The interplay between glucose metabolism and that of the two other primary nutrient classes, amino acids and fatty acids is critical for regulated insulin secretion. Mitochondrial metabolism of glucose, amino acid and fatty acids generates metabolic coupling factors (such as ATP, NADPH, glutamate, long chain acyl-CoA and diacylglycerol) which trigger insulin secretion. The observation of protein induced hypoglycaemia in patients with mutations in GLUD1 gene, encoding the enzyme glutamate dehydrogenase (GDH) and HADH gene, encoding for the enzyme short-chain 3-hydroxyacyl-CoA dehydrogenase has provided new mechanistic insights into the regulation of insulin secretion by amino acid and fatty acid metabolism. Metabolic signals arising from amino acid and fatty acid metabolism converge on the enzyme GDH which integrates both signals from both pathways and controls insulin secretion. Hence GDH seems to play a pivotal role in regulating both amino acid and fatty acid metabolism.

Pediatric hypoglycemia

Hypoglycemia in the pediatric population is a common finding important to recognize and manage to prevent brain injury. Recent advances in molecular genetics have provided new insight into its biochemical and physiologic basis and have led to more appropriate and specific treatment. Although a major cause of brain injury in pediatrics, the ability to predict the long-term outcome in these patients remains difficult. Identification of these at-risk individuals is important. The physiologic adaptations associated with transition from fetal to neonatal life are now better understood thus allowing for improved surveillance and management. Despite these advances, analytical limitations of point-of-care testing instruments at low glucose concentration continue to persist, This review aims to address these questions and provide an overview of pediatric hypoglycemia and the molecular pathways involved.