Hyperglycemia in rodent models of type 2 diabetes requires insulin-resistant alpha cells. Proc Natl Acad Sci U S A. 2014;111:13217-13222. [PMID: 25157166 DOI: 10.1073/pnas.1409638111]

Hyperglucagonemia and glucagon hypersecretion in early type 2 diabetes result from multifaceted dysregulation of pancreatic mouse α-cells

Hyperglucagonemia has been implicated in the pathogenesis of type 2 diabetes (T2D). In contrast to β-cells, studies on the function of the pancreatic α-cell in T2D are scarce. Consequently, the processes underlying hyperglucagonemia and α-cell dysfunction are largely unknown, limiting the appropriate design of specific pharmacological and therapeutic strategies. In the current study, we aimed to analyze the alterations of the pancreatic α-cell and its glucagon responses in diabetic db/db mice at early stages of the disease. In this context of glucose intolerance, hyperinsulinemia, and β-cell dysfunction, hyperglucagonemia was only present at fed conditions and was associated with insulin resistance. Yet, we found that the glucagon-to-insulin ratio in db/db mice did not change with fed or fasted states, further supporting that the metabolic regulation of glucagon release was impaired. Pancreatic β-cell dysfunction in db/db mice was manifested by increased basal secretion from isolated islets along with reduced insulin content. In contrast, α-cells from diabetic animals presented upregulated secretion and islet content of glucagon compared with controls. Electrophysiological analysis of dispersed α-cells revealed that altered secretion was not the result of impaired exocytosis. Instead, we found defective regulation of Ca2+ signaling by glucose. Besides these functional alterations, we also observed augmented α-cell mass in diabetic mice, which was accompanied by disrupted islet cytoarchitecture as well as increased α-cell size and number, without pieces of evidence of upregulated proliferation. Overall, these findings indicate that hyperglucagonemia in early T2D results from multifaceted α-cell deregulation in mice.

Abnormal glucagon secretion contributes to a longitudinal decline in glucose tolerance

CONTEXT

Defects in insulin secretion and action contribute to the progression of prediabetes to diabetes. However, the contribution of α-cell dysfunction to this process has been unclear.

OBJECTIVE

Understand the relative contributions of α-cell and β-cell dysfunction to declining glucose tolerance.

DESIGN

Longitudinal, community-based observational study.

SETTING

Clinical Research Unit at an Academic Medical Center.

PATIENTS/PARTICIPANTS

We studied 96 subjects without diabetes (55 ± 1 years; BMI 27.7 ± 0.4 Kg/M2) on 2 occasions, 3 years apart using an oral 75g glucose challenge. Indices for insulin secretion and action were estimated using the oral minimal model. Glucagon secretion rate (GSR) was estimated by deconvolution from peripheral glucagon concentrations.

INTERVENTION

This was an observational study.

MAIN OUTCOME MEASURE

Glucose tolerance status (categorical variable) and then symmetrical percent change in peak and 120-minute glucose (post-OGTT) concentrations (continuous variables).

RESULTS

32 subjects progressed from normal to Impaired Glucose Tolerance (IGT) or from IGT to type 2 diabetes. Disposition Index (DI) declined in the progressors (568±98 vs. 403±65 10-4 dl/kg/min per μU/ml, baseline vs. 3-years p=0.04). α-cell suppression by glucose (δGSR/δglucose) did not change in the non-progressors (1.5±0.1 vs. 1.3±0.1 nmol/min/L, p=0.37) but decreased (1.0±0.2 vs. 0.8±0.2 nmol/min/L, p<0.01) in those who progressed. Analysis of the entire cohort showed that DI and δGSR/δglucose were independently and inversely correlated with an increase in glycemic excursion.

CONCLUSIONS

These data show that α-cell dysfunction accompanies a decline in β-cell function as IGT or overt type 2 diabetes develops.

ZBED3 exacerbates hyperglycemia by promoting hepatic gluconeogenesis through CREB signaling

BACKGROUND

Elevated hepatic glucose production (HGP) is a prominent manifestation of impaired hepatic glucose metabolism in individuals with diabetes. Increased hepatic gluconeogenesis plays a pivotal role in the dysregulation of hepatic glucose metabolism and contributes significantly to fasting hyperglycemia in diabetes. Previous studies have identified zinc-finger BED domain-containing 3 (ZBED3) as a risk gene for type 2 diabetes (T2DM), and its single nucleotide polymorphism (SNPs) is closely associated with the fasting blood glucose level, suggesting a potential correlation between ZBED3 and the onset of diabetes. This study primarily explores the effect of ZBED3 on hepatic gluconeogenesis and analyzes the relevant signaling pathways that regulate hepatic gluconeogenesis.

METHODS

The expression level of ZBED3 was assessed in the liver of insulin-resistant (IR)-related disease. RNA-seq and bioinformatics analyses were employed to examine the ZBED3-related pathway that modulated HGP. To investigate the role of ZBED3 in hepatic gluconeogenesis, the expression of ZBED3 was manipulated by upregulation or silencing using adeno-associated virus (AAV) in mouse primary hepatocytes (MPHs) and HHL-5 cells. In vivo, hepatocyte-specific ZBED3 knockout mice were generated. Moreover, AAV8 was employed to achieve hepatocyte-specific overexpression and knockdown of ZBED3 in C57BL/6 and db/db mice. Immunoprecipitation and mass spectrometry (IP-MS) analyses were employed to identify proteins that interacted with ZBED3. Co-immunoprecipitation (co-IP), glutathione S-transferase (GST) - pulldown, and dual-luciferase reporter assays were conducted to further elucidate the underlying mechanism of ZBED3 in regulating hepatic gluconeogenesis.

RESULTS

The expression of ZBED3 in the liver of IR-related disease models was found to be increased. Under the stimulation of glucagon, ZBED3 promoted the expression of hepatic gluconeogenesis-related genes PGC1A, PCK1, G6PC, thereby increasing HGP. Consistently, the rate of hepatic gluconeogenesis was found to be elevated in mice with hepatocyte-specific overexpression of ZBED3 and decreased in those with ZBED3 knockout. Additionally, the knockdown of ZBED3 in the liver of db/db mice resulted in a reduction in hepatic gluconeogenesis. Moreover, the study revealed that ZBED3 facilitated the nuclear translocation of protein arginine methyltransferases 5 (PRMT5) to influence the regulation of PRMT5-mediated symmetrical dimethylation of arginine (s-DMA) of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), which in turn affects the phosphorylation of CREB and ultimately promotes HGP.

CONCLUSIONS

This study indicates that ZBED3 promotes hepatic gluconeogenesis and serves as a critical regulator of the progression of diabetes.

The role of GABA in type 1 diabetes

Gamma aminobutyric acid (GABA) is synthesized from glutamate by glutamic decarboxylase (GAD). The entero-pancreatic biology of GABA, which is produced by pancreatic islets, GAD-expressing microbiota, enteric immune cells, or ingested through diet, supports an essential physiologic role of GABA in the health and disease. Outside the central nervous system (CNS), GABA is uniquely concentrated in pancreatic β-cells. They express GAD65, which is a type 1 diabetes (T1D) autoantigen. Glutamate constitutes 10% of the amino acids in dietary protein and is preeminently concentrated in human milk. GABA is enriched in many foods, such as tomato and fermented cheese, and is an over-the-counter supplement. Selected microbiota in the midgut have the enzymatic capacity to produce GABA. Intestinal microbiota interact with gut-associated lymphoid tissue to maintain host defenses and immune tolerance, which are implicated in autoimmune disease. Although GABA is a widely known inhibitory neurotransmitter, oral GABA does not cross the blood brain barrier. Three diabetes-related therapeutic actions are ascribed to GABA, namely, increasing pancreatic β-cell content, attenuating excess glucagon and tamping down T-cell immune destruction. These salutary actions have been observed in numerous rodent diabetes models that usually employed high or near-continuous GABA doses. Clinical studies, to date, have identified positive effects of oral GABA on peripheral blood mononuclear cell cytokine release and plasma glucagon. Going forward, it is reassuring that oral GABA therapy has been well-tolerated and devoid of serious adverse effects.

Small molecules targeting selective PCK1 and PGC-1α lysine acetylation cause anti-diabetic action through increased lactate oxidation

Small molecules selectively inducing peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1α acetylation and inhibiting glucagon-dependent gluconeogenesis causing anti-diabetic effects have been identified. However, how these small molecules selectively suppress the conversion of gluconeogenic metabolites into glucose without interfering with lipogenesis is unknown. Here, we show that a small molecule SR18292 inhibits hepatic glucose production by increasing lactate and glucose oxidation. SR18292 increases phosphoenolpyruvate carboxykinase 1 (PCK1) acetylation, which reverses its gluconeogenic reaction and favors oxaloacetate (OAA) synthesis from phosphoenolpyruvate. PCK1 reverse catalytic reaction induced by SR18292 supplies OAA to tricarboxylic acid (TCA) cycle and is required for increasing glucose and lactate oxidation and suppressing gluconeogenesis. Acetylation mimetic mutant PCK1 K91Q favors anaplerotic reaction and mimics the metabolic effects of SR18292 in hepatocytes. Liver-specific expression of PCK1 K91Q mutant ameliorates hyperglycemia in obese mice. Thus, SR18292 blocks gluconeogenesis by enhancing gluconeogenic substrate oxidation through PCK1 lysine acetylation, supporting the anti-diabetic effects of these small molecules.

Defining the activity of pro-reparative extracellular vesicles in wound healing based on miRNA payloads and cell type-specific lineage mapping

Small extracellular vesicles (EVs) are released by cells and deliver biologically active payloads to coordinate the response of multiple cell types in cutaneous wound healing. Here we used a cutaneous injury model as a donor of pro-reparative EVs to treat recipient diabetic obese mice, a model of impaired wound healing. We established a functional screen for microRNAs (miRNAs) that increased the pro-reparative activity of EVs and identified a down-regulation of miR-425-5p in EVs in vivo and in vitro associated with the regulation of adiponectin. We tested a cell type-specific reporter of a tetraspanin CD9 fusion with GFP to lineage map the release of EVs from macrophages in the wound bed, based on the expression of miR-425-5p in macrophage-derived EVs and the abundance of macrophages in EV donor sites. Analysis of different promoters demonstrated that EV release under the control of a macrophage-specific promoter was most abundant and that these EVs were internalized by dermal fibroblasts. These findings suggested that pro-reparative EVs deliver miRNAs, such as miR-425-5p, that stimulate the expression of adiponectin that has insulin-sensitizing properties. We propose that EVs promote intercellular signaling between cell layers in the skin to resolve inflammation, induce proliferation of basal keratinocytes, and accelerate wound closure.

(-)-Gallocatechin Gallate Mitigates Metabolic Syndrome-Associated Diabetic Nephropathy in db/db Mice

Metabolic syndrome (MetS) significantly predisposes individuals to diabetes and is a prognostic factor for the progression of diabetic nephropathy (DN). This study aimed to evaluate the efficacy of (-)-gallocatechin gallate (GCG) in alleviating signs of MetS-associated DN in db/db mice. We administered GCG and monitored its effects on several metabolic parameters, including food and water intake, urinary output, blood glucose levels, glucose and insulin homeostasis, lipid profiles, blood pressure, and renal function biomarkers. The main findings indicated that GCG intervention led to marked improvements in these metabolic indicators and renal function, signifying its potential in managing MetS and DN. Furthermore, transcriptome analysis revealed substantial modifications in gene expression, notably the downregulation of pro-inflammatory genes such as S100a8, S100a9, Cd44, Socs3, Mmp3, Mmp9, Nlrp3, IL-1β, Osm, Ptgs2, and Lcn2 and the upregulation of the anti-oxidative gene Gstm3. These genetic alterations suggest significant effects on pathways related to inflammation and oxidative stress. In conclusion, GCG demonstrates therapeutic efficacy for MetS-associated DN, mitigating metabolic disturbances and enhancing renal health by modulating inflammatory and oxidative responses.

Induction of diabetes by Tacrolimus in a phenotypic model of obesity and metabolic syndrome

Introduction

The pathogenesis of Post-Transplant Diabetes Mellitus (PTDM) is complex and multifactorial and it resembles that of Type-2 Diabetes Mellitus (T2DM). One risk factor specific to PTDM differentiates both entities: the use of immunosuppressive therapy. Specifically, Tacrolimus interacts with obesity and insulin resistance (IR) in accelerating the onset of PTDM. In a genotypic model of IR, the obese Zucker rats, Tacrolimus is highly diabetogenic by promoting the same changes in beta-cell already modified by IR. Nevertheless, genotypic animal models have their limitations and may not resemble the real pathophysiology of diabetes. In this study, we have evaluated the interaction between beta-cell damage and Tacrolimus in a non-genotypic animal model of obesity and metabolic syndrome.

Methods

Sprague Dawley rats were fed a high-fat enriched diet during 45 days to induce obesity and metabolic dysregulation. On top of this established obesity, the administration of Tacrolimus (1mg/kg/day) during 15 days induced severe hyperglycaemia and changes in morphological and structural characteristics of the pancreas.

Results

Obese animals administered with Tacrolimus showed increased size of islets of Langerhans and reduced beta-cell proliferation without changes in apoptosis. There were also changes in beta-cell nuclear factors such as a decrease in nuclear expression of MafA and a nuclear overexpression of FoxO1A, PDX-1 and NeuroD1. These animals also showed increased levels of pancreatic insulin and glucagon.

Discussion

This model could be evidence of the relationship between the T2DM and PTDM physiopathology and, eventually, the model may be instrumental to study the pathogenesis of T2DM.

Diabetic sensory neuropathy and insulin resistance are induced by loss of UCHL1 in Drosophila

Diabetic sensory neuropathy (DSN) is one of the most common complications of type 2 diabetes (T2D), however the molecular mechanistic association between T2D and DSN remains elusive. Here we identify ubiquitin C-terminal hydrolase L1 (UCHL1), a deubiquitinase highly expressed in neurons, as a key molecule underlying T2D and DSN. Genetic ablation of UCHL1 leads to neuronal insulin resistance and T2D-related symptoms in Drosophila. Furthermore, loss of UCHL1 induces DSN-like phenotypes, including numbness to external noxious stimuli and axonal degeneration of sensory neurons in flies' legs. Conversely, UCHL1 overexpression improves DSN-like defects of T2D model flies. UCHL1 governs insulin signaling by deubiquitinating insulin receptor substrate 1 (IRS1) and antagonizes an E3 ligase of IRS1, Cullin 1 (CUL1). Consistent with these results, genetic and pharmacological suppression of CUL1 activity rescues T2D- and DSN-associated phenotypes. Therefore, our findings suggest a complete set of genetic factors explaining T2D and DSN, together with potential remedies for the diseases.

Not the second fiddle: α cell development, identity, and function in health and diabetes

Historic and emerging studies provide evidence for the deterioration of pancreatic α cell function and identity in diabetes mellitus. Increased access to human tissue and the availability of more sophisticated molecular technologies have identified key insights into how α cell function and identity are preserved in healthy conditions and how they become dysfunctional in response to stress. These studies have revealed evidence of impaired glucagon secretion, shifts in α cell electrophysiology, changes in α cell mass, dysregulation of α cell transcription, and α-to-β cell conversion prior to and during diabetes. In this review, we outline the current state of research on α cell identity in health and disease. Evidence in model organisms and humans suggests that in addition to β cell dysfunction, diabetes is associated with a fundamental dysregulation of α cell identity. Importantly, epigenetic studies have revealed that α cells retain more poised and open chromatin at key cell-specific and diabetes-dysregulated genes, supporting the model that the inherent epigenetic plasticity of α cells makes them susceptible to the transcriptional changes that potentiate the loss of identity and function seen in diabetes. Thus, additional research into the maintenance of α cell identity and function is critical to fully understanding diabetes. Furthermore, these studies suggest α cells could represent an alternative source of new β cells for diabetes treatment.

Glucagon in type 2 diabetes: Friend or foe?

Hyperglucagonemia is one of the 'ominous' eight factors underlying the pathogenesis of type 2 diabetes (T2D). Glucagon is a peptide hormone involved in maintaining glucose homoeostasis by increasing hepatic glucose output to counterbalance insulin action. Long neglected, the introduction of dual and triple agonists exploiting glucagon signalling pathways has rekindled the interest in this hormone beyond its classic effect on glycaemia. Glucagon can promote weight loss by regulating food intake, energy expenditure, and brown and white adipose tissue functions through mechanisms still to be fully elucidated, thus its role in T2D pathogenesis should be further investigated. Moreover, the role of glucagon in the development of T2D micro- and macro-vascular complications is elusive. Mounting evidence suggests its beneficial effect in non-alcoholic fatty liver disease, while few studies postulated its favourable role in peripheral neuropathy and retinopathy. Contrarily, glucagon receptor agonism might induce renal changes resembling diabetic nephropathy, and data concerning glucagon actions on the cardiovascular system are conflicting. This review aims to summarise the available findings on the role of glucagon in the pathogenesis of T2D and its complications. Further experimental and clinical data are warranted to better understand the implications of glucagon signalling modulation with new antidiabetic drugs.

A randomized trial of oral gamma aminobutyric acid (GABA) or the combination of GABA with glutamic acid decarboxylase (GAD) on pancreatic islet endocrine function in children with newly diagnosed type 1 diabetes

Gamma aminobutyric acid(GABA) is synthesized by glutamate decarboxylase(GAD) in β-cells. Regarding Type 1 diabetes(T1D), animal/islet-cell studies found that GABA promotes insulin secretion, inhibits α-cell glucagon and dampens immune inflammation, while GAD immunization may also preserve β-cells. We evaluated the safety and efficacy of oral GABA alone, or combination GABA with GAD, on the preservation of residual insulin secretion in recent-onset T1D. Herein we report a single-center, double-blind, one-year, randomized trial in 97 children conducted March 2015 to June 2019(NCT02002130). Using a 2:1 treatment:placebo ratio, interventions included oral GABA twice-daily(n = 41), or oral GABA plus two-doses GAD-alum(n = 25), versus placebo(n = 31). The primary outcome, preservation of fasting/meal-stimulated c-peptide, was not attained. Of the secondary outcomes, the combination GABA/GAD reduced fasting and meal-stimulated serum glucagon, while the safety/tolerability of GABA was confirmed. There were no clinically significant differences in glycemic control or diabetes antibody titers. Given the low GABA dose for this pediatric trial, future investigations using higher-dose or long-acting GABA formulations, either alone or with GAD-alum, could be considered, although GABA alone or in combination with GAD-alum did nor preserve beta-cell function in this trial.

Small Hepatitis B Virus Surface Antigen Promotes Hepatic Gluconeogenesis via Enhancing Glucagon/cAMP/Protein Kinase A/CREB Signaling

Hepatitis B virus (HBV) is a major risk factor for serious liver diseases. The liver plays a unique role in controlling carbohydrate metabolism to maintain the glucose level within the normal range. Chronic HBV infection has been reported to associate with a high prevalence of diabetes. However, the detailed molecular mechanism underlying the potential association remains largely unknown. Here, we report that liver-targeted delivery of small HBV surface antigen (SHBs), the most abundant viral protein of HBV, could elevate blood glucose levels and impair glucose and insulin tolerance in mice by promoting hepatic gluconeogenesis. Hepatocytes with SHB expression also exhibited increased glucose production and expression of gluconeogenic genes glucose-6-phosphatase (G6pc) and phosphoenolpyruvate carboxykinase (PEPCK) in response to glucagon stimulation. Mechanistically, SHBs increased cellular levels of cyclic AMP (cAMP) and consequently activated protein kinase A (PKA) and its downstream effector cAMP-responsive element binding protein (CREB). SHBs-induced activation of CREB enhanced transcripts of gluconeogenic genes, thus promoting hepatic gluconeogenesis. The elevated cAMP level resulted from increased transcription activity and expression of adenylyl cyclase 1 (AC1) by SHBs through a binary E-box factor binding site (BEF). Taken together, we unveiled a novel pathogenic role and mechanism of SHBs in hepatic gluconeogenesis, and these results might highlight a potential target for preventive and therapeutic intervention in the development and progression of HBV-associated diabetes. IMPORTANCE Chronic HBV infection causes progressive liver damage and is found to be a risk factor for diabetes. However, the mechanism in the regulation of glucose metabolism by HBV remains to be established. In the current study, we demonstrate for the first time that the small hepatitis B virus surface antigen (SHBs) of HBV elevates AC1 transcription and expression to activate cAMP/PKA/CREB signaling and subsequently induces the expression of gluconeogenic genes and promotes hepatic gluconeogenesis both in vivo and in vitro. This study provides a direct link between HBV infection and diabetes and implicates that SHBs may represent a potential target for the treatment of HBV-induced metabolic disorders.

The impact of macronutrient composition on metabolic regulation: An Islet-Centric view

AIM

The influence of dietary carbohydrates and fats on weight gain is inconclusively understood. We studied the acute impact of these nutrients on the overall metabolic state utilizing the insulin:glucagon ratio (IGR).

METHODS

Following in vitro glucose and palmitate treatment, insulin and glucagon secretion from islets isolated from C57Bl/6J mice was measured. Our human in vivo study included 21 normoglycaemia (mean age 51.9 ± 16.5 years, BMI 23.9 ± 3.5 kg/m² , and HbA1c 36.9 ± 3.3 mmol/mol) and 20 type 2 diabetes (T2D) diagnosed individuals (duration 12 ± 7 years, mean age 63.6 ± 4.5 years, BMI 29.1 ± 2.4 kg/m² , and HbA1c 52.3 ± 9.5 mmol/mol). Individuals consumed a carbohydrate-rich or fat-rich meal (600 kcal) in a cross-over design. Plasma insulin and glucagon levels were measured at -30, -5, and 0 min, and every 30 min until 240 min after meal ingestion.

RESULTS

The IGR measured from mouse islets was determined solely by glucose levels. The palmitate-stimulated hormone secretion was largely glucose independent in the analysed mouse islets. The acute meal tolerance test demonstrated that insulin and glucagon secretion is dependent on glycaemic status and meal composition, whereas the IGR was dependent upon meal composition. The relative reduction in IGR elicited by the fat-rich meal was more pronounced in obese individuals. This effect was blunted in T2D individuals with elevated HbA1c levels.

CONCLUSION

The metabolic state in normoglycaemic individuals and T2D-diagnosed individuals is regulated by glucose. We demonstrate that consumption of a low carbohydrate diet, eliciting a catabolic state, may be beneficial for weight loss, particularly in obese individuals.

Glucagon receptor signaling at white adipose tissue does not regulate lipolysis

Although the physiological role of glucagon receptor signaling in the liver is well defined, the impact of glucagon receptor (Gcgr) signaling on white adipose tissue (WAT) continues to be debated. Although numerous studies propose that glucagon stimulates WAT lipolysis, we lack evidence that physiological concentrations of glucagon regulate WAT lipolysis. In turn, we performed studies in both wild-type and WAT Gcgr knockout mice to determine if glucagon regulates lipolysis at WAT in the mouse. We assessed the effects of fasting and acute exogenous glucagon administration in wild-type C57BL/6J and Gcgr^Adipocyte+/+ versus Gcgr^Adipocyte-/- mice. Using an ex vivo lipolysis protocol, we further examined the direct effects of glucagon on physiologically (fasted) and pharmacologically stimulated lipolysis. We found that adipocyte Gcgr expression did not affect fasting-induced lipolysis or hepatic lipid accumulation in lean or diet-induced obese (DIO) mice. Acute glucagon administration did not affect serum nonesterified fatty acids (NEFA), leptin, or adiponectin concentration, but did increase serum glucose and FGF21, regardless of genotype. Glucagon did not affect ex vivo lipolysis in explants from either Gcgr^Adipocyte+/+ or Gcgr^Adipocyte-/- mice. Gcgr expression did not affect fasting-induced or isoproterenol-stimulated lipolysis from WAT explants. Moreover, glucagon receptor signaling at WAT did not affect body weight or glucose homeostasis in lean or DIO mice. Our studies have established that physiological levels of glucagon do not regulate WAT lipolysis, either directly or indirectly. Given that glucagon receptor agonism can improve dyslipidemia and decrease hepatic lipid accumulation, it is critical to understand the tissue-specific effects of glucagon receptor action. Unlike the crucial role of hepatic glucagon receptor signaling in maintaining glucose and lipid homeostasis, we observed no metabolic consequence of WAT glucagon receptor deletion.NEW & NOTEWORTHY It has been postulated that glucagon stimulates lipolysis and fatty acid release from white adipose tissue. We observed no metabolic effects of eliminating or activating glucagon receptor signaling at white adipose tissue.

Type 2 Diabetes Mellitus (T2DM) and Carbohydrate Metabolism in Relation to T2DM from Endocrinology, Neurophysiology, Molecular Biology, and Biochemistry Perspectives

Type 2 diabetes mellitus (T2DM) is a severe disease caused by metabolic disorders, particularly carbohydrate metabolism disorders. The disease is a fatal global trouble characterised by high prevalence rates, causing death, blindness, kidney failure, myocardial infarction, amputation of lower limps, and stroke. Biochemical metabolic pathways like glycolysis, gluconeogenesis, glycogenesis, and glycogenolysis are critical pathways that regulate blood glucose levels with the glucokinase (GK) enzyme playing a central role in glucose homeostasis. Any factor that perturbs the aforementioned biochemical pathways is detrimental. Endocrinological, neurophysiological, and molecular biological pathways that are linked to carbohydrate metabolism should be studied, grasped, and manipulated in order to alleviate T2DM global chaos. The challenge, howbeit, is that, since the body is an integration of systems that complement one another, studying one “isolated” system is not very useful. This paper serves to discuss endocrinology, neurophysiology, and molecular biology pathways that are involved in carbohydrate metabolism in relation to T2DM.

Pro-α-cell-derived β-cells contribute to β-cell neogenesis induced by antagonistic glucagon receptor antibody in type 2 diabetic mice

The deficiency of pancreatic β-cells is the key pathogenesis of diabetes, while glucagon-secreting α-cells are another player in the development of diabetes. Here, we aimed to investigate the effects of glucagon receptor (GCGR) antagonism on β-cell neogenesis in type 2 diabetic (T2D) mice and explore the origins of the neogenic β-cells. We showed that GCGR monoclonal antibody (mAb) elevated plasma insulin level and increased β-cell mass in T2D mice. By using α-cell lineage-tracing (glucagon-cre-β-gal) mice and inducible Ngn3⁺ pancreatic endocrine progenitor lineage-tracing (Ngn3-CreERT2-tdTomato) mice, we found that GCGR mAb treatment promoted α-cell regression to progenitors, and induced Ngn3⁺ progenitor reactivation and differentiation toward β-cells. Besides, GCGR mAb upregulated the expression levels of β-cell regeneration-associated genes and promoted insulin secretion in primary mouse islets, indicative of a direct effect on β-cell identity. Our findings suggest that GCGR antagonism not only increases insulin secretion but also promotes pro-α-cell-derived β-cell neogenesis in T2D mice.

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Blockage of α-cell-derived glucagon promotes β-cell regeneration in situ in type 2 diabetic (T2D) mice

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Glucagon receptor (GCGR) mAb induces the trans-differentiation of α-cells to β-cells

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GCGR mAb promotes α-cell regression to pancreatic endocrine progenitors

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GCGR mAb induces Ngn3⁺ progenitor reactivation and differentiation toward β-cells

Modeling the Amino Acid Effect on Glucagon Secretion from Pancreatic Alpha Cells

Type 2 Diabetes Mellitus (T2DM) is a burdensome problem in modern society, and intensive research is focused on better understanding the underlying cellular mechanisms of hormone secretion for blood glucose regulation. T2DM is a bi-hormonal disease, and in addition to 100 years of increasing knowledge about the importance of insulin, the second hormone glucagon, secreted by pancreatic alpha cells, is becoming increasingly important. We have developed a mathematical model for glucagon secretion that incorporates all major metabolic processes of glucose, fatty acids, and glutamine as the most abundant postprandial amino acid in blood. In addition, we consider cAMP signaling in alpha cells. The model predictions quantitatively estimate the relative importance of specific metabolic and signaling pathways and particularly emphasize the important role of glutamine in promoting glucagon secretion, which is in good agreement with known experimental data.

Organophosphate pesticides and new-onset diabetes mellitus: From molecular mechanisms to a possible therapeutic perspective

Organophosphate is a commonly used pesticide in the agricultural sector. The main action of organophosphate focuses on acetylcholinesterase inhibition, and it therefore contributes to acute cholinergic crisis, intermediate syndrome and delayed neurotoxicity. From sporadic case series to epidemiologic studies, organophosphate has been linked to hyperglycemia and the occurrence of new-onset diabetes mellitus. Organophosphate-mediated direct damage to pancreatic beta cells, insulin resistance related to systemic inflammation and excessive hepatic gluconeogenesis and polymorphisms of the enzyme governing organophosphate elimination are all possible contributors to the development of new-onset diabetes mellitus. To date, a preventive strategy for organophosphate-mediated new-onset diabetes mellitus is still lacking. However, lowering reactive oxygen species levels may be a practical method to reduce the risk of developing hyperglycemia.

Central regulation of glucose metabolism in an insulin-dependent and -independent manner

The central nervous system (CNS) contributes significantly to glucose homeostasis. The available evidence indicates that insulin directly acts on the CNS, in particular the hypothalamus, to regulate hepatic glucose production, thereby controlling whole-body glucose metabolism. Additionally, insulin also acts on the brain to regulate food intake and fat metabolism, which may indirectly regulate glucose metabolism. Studies conducted over the last decade have found that the CNS can regulate glucose metabolism in an insulin-independent manner. Enhancement of central leptin signalling reverses hyperglycaemia in insulin-deficient rodents. Here, I review the mechanisms by which central insulin and leptin actions regulate glucose metabolism. Although clinical studies have shown that insulin treatment is currently indispensable for managing diabetes, unravelling the neuronal mechanisms underlying the central regulation of glucose metabolism will pave the way for the design of novel therapeutic drugs for diabetes.

Interplay Between Systemic Metabolic Cues and Autonomic Output: Connecting Cardiometabolic Function and Parasympathetic Circuits

There is consensus that the heart is innervated by both the parasympathetic and sympathetic nervous system. However, the role of the parasympathetic nervous system in controlling cardiac function has received significantly less attention than the sympathetic nervous system. New neuromodulatory strategies have renewed interest in the potential of parasympathetic (or vagal) motor output to treat cardiovascular disease and poor cardiac function. This renewed interest emphasizes a critical need to better understand how vagal motor output is generated and regulated. With clear clinical links between cardiovascular and metabolic diseases, addressing this gap in knowledge is undeniably critical to our understanding of the interaction between metabolic cues and vagal motor output, notwithstanding the classical role of the parasympathetic nervous system in regulating gastrointestinal function and energy homeostasis. For this reason, this review focuses on the central, vagal circuits involved in sensing metabolic state(s) and enacting vagal motor output to influence cardiac function. It will review our current understanding of brainstem vagal circuits and their unique position to integrate metabolic signaling into cardiac activity. This will include an overview of not only how metabolic cues alter vagal brainstem circuits, but also how vagal motor output might influence overall systemic concentrations of metabolic cues known to act on the cardiac tissue. Overall, this review proposes that the vagal brainstem circuits provide an integrative network capable of regulating and responding to metabolic cues to control cardiac function.

Glucagon Resistance and Decreased Susceptibility to Diabetes in a Model of Chronic Hyperglucagonemia

Elevation of glucagon levels and increase in α-cell mass are associated with states of hyperglycemia in diabetes. Our previous studies have highlighted the role of nutrient signaling via mTOR complex 1 (mTORC1) regulation that controls glucagon secretion and α-cell mass. In the current studies we investigated the effects of activation of nutrient signaling by conditional deletion of the mTORC1 inhibitor, TSC2, in α-cells (αTSC2^KO). We showed that activation of mTORC1 signaling is sufficient to induce chronic hyperglucagonemia as a result of α-cell proliferation, cell size, and mass expansion. Hyperglucagonemia in αTSC2^KO was associated with an increase in glucagon content and enhanced glucagon secretion. This model allowed us to identify the effects of chronic hyperglucagonemia on glucose homeostasis by inducing insulin secretion and resistance to glucagon in the liver. Liver glucagon resistance in αTSC2^KO mice was characterized by reduced expression of the glucagon receptor (GCGR), PEPCK, and genes involved in amino acid metabolism and urea production. Glucagon resistance in αTSC2^KO mice was associated with improved glucose levels in streptozotocin-induced β-cell destruction and high-fat diet-induced glucose intolerance. These studies demonstrate that chronic hyperglucagonemia can improve glucose homeostasis by inducing glucagon resistance in the liver.

Regeneration during Obesity: An Impaired Homeostasis

Simple Summary

Regeneration represents the biological processes that allow cells and tissues to renew and develop. During obesity, a variety of changes and reactions are seen. This includes inflammation and metabolic disorders. These obesity-induced changes do impact the regeneration processes. Such impacts that obesity has on regeneration would affect tissues and organs development and would also have consequences on the outcomes of therapies that depend on cells regeneration (such as burns, radiotherapy and leukemia) given to patients suffering from obesity. Therefore, a particular attention should be given to patients suffering from obesity in biological, therapeutic and clinical contexts that depend on regeneration ability.

Abstract

Obesity is a health problem that, in addition to the known morbidities, induces the generation of a biological environment with negative impacts on regeneration. Indeed, factors like DNA damages, oxidative stress and inflammation would impair the stem cell functions, in addition to some metabolic and development patterns. At the cellular and tissulaire levels, this has consequences on growth, renewal and restoration which results into an impaired regeneration. This impaired homeostasis concerns also key metabolic tissues including muscles and liver which would worsen the energy balance outcome towards further development of obesity. Such impacts of obesity on regeneration shows the need of a specific care given to obese patients recovering from diseases or conditions requiring regeneration such as burns, radiotherapy and leukemia. On the other hand, since stem cells are suggested to manage obesity, this impaired regeneration homeostasis needs to be considered towards more optimized stem cells-based obesity therapies within the context of precision medicine.

Identification of Candidate Genes and Pathways Associated with Obesity-Related Traits in Canines via Gene-Set Enrichment and Pathway-Based GWAS Analysis

The present study aimed to identify causative loci and genes enriched in pathways associated with canine obesity using a genome-wide association study (GWAS). The GWAS was first performed to identify candidate single-nucleotide polymorphisms (SNPs) associated with obesity and obesity-related traits including body weight and blood sugar in 18 different breeds of 153 dogs. A total of 10 and 2 SNPs were found to be significantly (p < 3.74 × 10^-7) associated with body weight and blood sugar, respectively. None of the SNPs were identified to be significantly associated with obesity trait. We subsequently followed up the GWAS analysis with gene-set enrichment and pathway analyses. A gene-set with 1057, 1409, and 1243 SNPs annotated to 449, 933 and 820 genes for obesity, body weight, and blood sugar, respectively was created by sub-setting the GWAS result at a threshold of p < 0.01 for the gene-set enrichment analysis. In total, 84 GO and 21 KEGG pathways for obesity, 114 GO and 44 KEGG pathways for blood sugar, 120 GO and 24 KEGG pathways for body weight were found to be enriched. Among the pathways and GO terms, we highlighted five enriched pathways (Wnt signaling pathway, adherens junction, pathways in cancer, axon guidance, and insulin secretion) and seven GO terms (fat cell differentiation, calcium ion binding, cytoplasm, nucleus, phospholipid transport, central nervous system development, and cell surface) that were found to be shared among all the traits. Our data provide insights into the genes and pathways associated with obesity and obesity-related traits.

Altered glucose metabolism and insulin resistance in cancer-induced cachexia: a sweet poison

Cancer cachexia is a wasting disorder characterised by specific skeletal muscle and adipose tissue loss. Cancer cachexia is also driven by inflammation, altered metabolic changes such as increased energy expenditure, elevated plasma glucose, insulin resistance and excess catabolism. In cachexia, host-tumor interaction causes release of the lactate and inflammatory cytokines. Lactate released by tumor cells takes part in hepatic glucose production with the help of gluconeogenic enzymes. Thus, Cori cycle between organs and cancerous cells contributes to increased glucose production and energy expenditure. A high amount of blood glucose leads to increased production of insulin. Overproduction of insulin causes inactivation of PI3K/Akt/m-TOR pathway and finally results in insulin resistance. Insulin is involved in maintaining the vitality of organs and regulate the metabolism of glucose, protein and lipids. Insulin insensitivity decreases the uptake of glucose in the organs and results in loss of skeletal muscles and adipose tissues. However, looking into the complexity of this metabolic syndrome, it is impossible to rely on a single variable to treat patients having cancer cachexia. Hence, it becomes greater a challenge to produce a clinically effective treatment for this metabolic syndrome. Thus, the present paper aims to provide an understanding of pathogenesis and mechanism underlining the altered glucose metabolism and insulin resistance and its contribution to the progression of skeletal muscle wasting and lipolysis, providing future direction of research to develop new pharmacological treatment in cancer cachexia.

Direct Effects of D-Chiro-Inositol on Insulin Signaling and Glucagon Secretion of Pancreatic Alpha Cells

The insulin resistance state of pancreatic α-cells seems to be related to glucagon hypersecretion in type 2 diabetes. Treatment that can improve the insulin sensitivity of α-cells could control glucagon levels in patients with diabetes mellitus. The aim of this study was to investigate the preventive role of D-chiro-inositol (DCI), which has insulin receptor-sensitizer effects on insulin signaling pathways and glucagon secretion in pancreatic α-TC1 clone 6 cells. Cells were chronically treated with palmitate to induce insulin resistance in the presence/absence of DCI. DCI treatment improved the insulin signaling pathway and restored insulin-mediated glucagon suppression in α-TC1-6 cells exposed to palmitate. These results indicate that DCI treatment prevents the insulin resistance of α-TC1-6 cells chronically exposed to palmitate. Our data provide evidence that DCI could be useful to improve the insulin sensitivity of pancreatic α-cells in diabetes treatment.

Fasting glucagon concentrations are associated with longitudinal decline of β-cell function in non-diabetic humans

PURPOSE

Abnormal glucagon concentrations are a feature of prediabetes but it is uncertain if α-cell dysfunction contributes to a longitudinal decline in β-cell function. We therefore sought to determine if a decline in β-cell function is associated with a higher nadir glucagon in the postprandial period or with higher fasting glucagon.

METHODS

This was a longitudinal study in which 73 non-diabetic subjects were studied on 2 occasions 6.6 ± 0.3 years apart using a 2-hour, 7-sample oral glucose tolerance test. Disposition Index (DI) was calculated using the oral minimal model applied to the measurements of glucose, insulin, C-peptide concentrations during the studies. We subsequently examined the relationship of glucagon concentrations at baseline with change in DI (used as a measure of β-cell function) after adjusting for changes in weight and the baseline value of DI.

RESULTS

After adjusting for covariates, nadir postprandial glucagon concentrations were not associated with changes in β-cell function as quantified by DI. On the other hand, fasting glucagon concentrations during the baseline study were inversely correlated with longitudinal changes in DI.

CONCLUSIONS

Defects in α-cell function, manifest as elevated fasting glucagon, are associated with a subsequent decline in β-cell function. It remains to be ascertained if abnormal α-cell function contributes directly to loss of β-cell secretory capacity in the pathogenesis of type 2 diabetes.

Glucagon receptor antagonist upregulates circulating GLP-1 level by promoting intestinal L-cell proliferation and GLP-1 production in type 2 diabetes

OBJECTIVE

Glucagon receptor (GCGR) blockage improves glycemic control and increases circulating glucagon-like peptide-1 (GLP-1) level in diabetic animals and humans. The elevated GLP-1 has been reported to be involved in the hypoglycemic effect of GCGR blockage. However, the source of this elevation remains to be clarified.

RESEARCH DESIGN AND METHODS

REMD 2.59, a human GCGR monoclonal antibody (mAb), was administrated for 12 weeks in db/db mice and high-fat diet+streptozotocin (HFD/STZ)-induced type 2 diabetic (T2D) mice. Blood glucose, glucose tolerance and plasma GLP-1 were evaluated during the treatment. The gut length, epithelial area, and L-cell number and proliferation were detected after the mice were sacrificed. Cell proliferation and GLP-1 production were measured in mouse L-cell line GLUTag cells, and primary mouse and human enterocytes. Moreover, GLP-1 receptor (GLP-1R) antagonist or protein kinase A (PKA) inhibitor was used in GLUTag cells to determine the involved signaling pathways.

RESULTS

Treatment with the GCGR mAb lowered blood glucose level, improved glucose tolerance and elevated plasma GLP-1 level in both db/db and HFD/STZ-induced T2D mice. Besides, the treatment promoted L-cell proliferation and LK-cell expansion, and increased the gut length, epithelial area and L-cell number in these two T2D mice. Similarly, our in vitro study showed that the GCGR mAb promoted L-cell proliferation and increased GLP-1 production in GLUTag cells, and primary mouse and human enterocytes. Furthermore, either GLP-1R antagonist or PKA inhibitor diminished the effects of GCGR mAb on L-cell proliferation and GLP-1 production.

CONCLUSIONS

The elevated circulating GLP-1 level by GCGR mAb is mainly due to intestinal L-cell proliferation and GLP-1 production, which may be mediated via GLP-1R/PKA signaling pathways. Therefore, GCGR mAb represents a promising strategy to improve glycemic control and restore the impaired GLP-1 production in T2D.

Postprandial Lipemia Modulates Pancreatic Alpha-Cell Function in the Prediction of Type 2 Diabetes Development: The CORDIOPREV Study

Diabetes (T2DM) is a major global health issue, and developing new approaches to its prevention is of paramount importance. We hypothesized that abnormalities in lipid metabolism are involved in alpha-cell deregulation. We therefore studied the metabolic factors underlying alpha-cell dysfunction in T2DM progression after a dietary intervention (Mediterranean and low-fat). Additionally, we evaluated whether postprandial glucagon levels may be considered as a predictive factor of T2DM in cardiovascular patients. Non-T2DM participants from the CORDIOPREV study were categorized by tertiles of the area under the curve (AUC) for triacylglycerols and also by tertiles of AUC for glucagon. Our results showed that patients with higher triacylglycerols levels presented elevated postprandial glucagon (P = 0.009). Moreover, we observed higher risk of T2DM (hazard ratio: 2.65; 95% confidence interval: 1.56-4.53) in subjects with elevated glucagon. In conclusion, high postprandial lipemia may induce alpha-cell dysfunction in cardiovascular patients. Our results also showed that postprandial glucagon levels could be used to predict T2DM development.

Pancreatic α-cells - The unsung heroes in islet function

The pancreatic islets of Langerhans consist of several hormone-secreting cell types important for blood glucose control. The insulin secreting β-cells are the best studied of these cell types, but less is known about the glucagon secreting α-cells. The α-cells secrete glucagon as a response to low blood glucose. The major function of glucagon is to release glucose from the glycogen stores in the liver. In both type 1 and type 2 diabetes, glucagon secretion is dysregulated further exaggerating the hyperglycaemia, and in type 1 diabetes α-cells fail to counter regulate hypoglycaemia. Although glucagon has been recognized for almost 100 years, the understanding of how glucagon secretion is regulated and how glucagon act within the islet is far from complete. However, α-cell research has taken off lately which is promising for future knowledge. In this review we aim to highlight α-cell regulation and glucagon secretion with a special focus on recent discoveries from human islets. We will present some novel aspects of glucagon function and effects of selected glucose lowering agents on glucagon secretion.

The Role of α-Cells in Islet Function and Glucose Homeostasis in Health and Type 2 Diabetes

Pancreatic α-cells are the major source of glucagon, a hormone that counteracts the hypoglycemic action of insulin and strongly contributes to the correction of acute hypoglycemia. The mechanisms by which glucose controls glucagon secretion are hotly debated, and it is still unclear to what extent this control results from a direct action of glucose on α-cells or is indirectly mediated by β- and/or δ-cells. Besides its hyperglycemic action, glucagon has many other effects, in particular on lipid and amino acid metabolism. Counterintuitively, glucagon seems also required for an optimal insulin secretion in response to glucose by acting on its cognate receptor and, even more importantly, on GLP-1 receptors. Patients with diabetes mellitus display two main alterations of glucagon secretion: a relative hyperglucagonemia that aggravates hyperglycemia, and an impaired glucagon response to hypoglycemia. Under metabolic stress states, such as diabetes, pancreatic α-cells also secrete GLP-1, a glucose-lowering hormone, whereas the gut can produce glucagon. The contribution of extrapancreatic glucagon to the abnormal glucose homeostasis is unclear. Here, I review the possible mechanisms of control of glucagon secretion and the role of α-cells on islet function in healthy state. I discuss the possible causes of the abnormal glucagonemia in diabetes, with particular emphasis on type 2 diabetes, and I briefly comment the current antidiabetic therapies affecting α-cells.

RFRP-3, the Mammalian Ortholog of GnIH, Is a Novel Modulator Involved in Food Intake and Glucose Homeostasis

RF amide-related peptide 3 (RFRP-3) is a reproductive inhibitor and an endogenous orexigenic neuropeptide that may be involved in energy homeostasis. In this study, we evaluated the effect of acute or chronic RFRP-3 treatment (administered via intraperitoneal injection) on the food intake, meal microstructure and weight of rats, as well as the mechanism through which RFRP-3 is involved in glucose metabolism in the pancreas and glucose disposal tissues of rat in vivo. Our results showed that the intraperitoneal administration of RFRP-3 to rats resulted in marked body mass increased, hyperphagia, hyperlipidemia, hyperglycemia, glucose intolerance, hypoinsulinism, hyperglucagon, and insulin resistance, as well as significant increases in the size of pancreatic islets and the inflammatory reaction. Thus, we strongly assert that RFRP-3 as a novel neuroendocrine regulator involved in blood glucose homeostasis.

Obesity dysregulates fasting-induced changes in glucagon secretion

Hyperglucagonemia, a hallmark in obesity and insulin resistance promotes hepatic glucose output, exacerbating hyperglycemia and thus predisposing to the development type 2 diabetes. As such, glucagon signaling is a key target for new therapeutics to manage insulin resistance. We evaluated glucagon homeostasis in lean and obese mice and people. In lean mice, fasting for 24 h caused a rise in glucagon. In contrast, a decrease in serum glucagon compared to baseline was observed in diet-induced obese mice between 8 and 24 h of fasting. Fasting decreased serum insulin in both lean and obese mice. Accordingly, the glucagon:insulin ratio was unaffected by fasting in obese mice but increased in lean mice. Re-feeding (2 h) restored hyperglucagonemia in obese mice. Pancreatic perfusion studies confirm that fasting (16 h) decreases pancreatic glucagon secretion in obese mice. Consistent with our findings in the mouse, a mixed meal increased serum glucagon and insulin concentrations in obese humans, both of which decreased with time after a meal. Consequently, fasting and re-feeding less robustly affected glucagon:insulin ratios in obese compared to lean participants. The glucoregulatory disturbance in obesity may be driven by inappropriate regulation of glucagon by fasting and a static glucagon:insulin ratio.

Cell Autonomous Dysfunction and Insulin Resistance in Pancreatic α Cells

To date, type 2 diabetes is considered to be a "bi-hormonal disorder" rather than an "insulin-centric disorder," suggesting that glucagon is as important as insulin. Although glucagon increases hepatic glucose production and blood glucose levels, paradoxical glucagon hypersecretion is observed in diabetes. Recently, insulin resistance in pancreatic α cells has been proposed to be associated with glucagon dysregulation. Moreover, cell autonomous dysfunction of α cells is involved in the etiology of diabetes. In this review, we summarize the current knowledge about the physiological and pathological roles of glucagon.

Glucagon Receptor Antagonism Improves Glucose Metabolism and Cardiac Function by Promoting AMP-Mediated Protein Kinase in Diabetic Mice

The antidiabetic potential of glucagon receptor antagonism presents an opportunity for use in an insulin-centric clinical environment. To investigate the metabolic effects of glucagon receptor antagonism in type 2 diabetes, we treated Lepr^db/db and Lep^ob/ob mice with REMD 2.59, a human monoclonal antibody and competitive antagonist of the glucagon receptor. As expected, REMD 2.59 suppresses hepatic glucose production and improves glycemia. Surprisingly, it also enhances insulin action in both liver and skeletal muscle, coinciding with an increase in AMP-activated protein kinase (AMPK)-mediated lipid oxidation. Furthermore, weekly REMD 2.59 treatment over a period of months protects against diabetic cardiomyopathy. These functional improvements are not derived simply from correcting the systemic milieu; nondiabetic mice with cardiac-specific overexpression of lipoprotein lipase also show improvements in contractile function after REMD 2.59 treatment. These observations suggest that hyperglucagonemia enables lipotoxic conditions, allowing the development of insulin resistance and cardiac dysfunction during disease progression.

Laparoscopic Sleeve Gastrectomy Outcomes in Patients with Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common disease among the bariatric population. However, there are limited data regarding the impact of laparoscopic sleeve gastrectomy (SG) on these patients. The study was conducted at University Hospital, United States. The purpose of this study was to examine per cent excess body weight loss (%EWL) and diabetes control in patients who have PCOS compared with those without PCOS. A total of 550 female patients underwent SG between December 2011 and October 2016. Retrospective analysis was completed to include follow-up data at 1, 3, 6, and 12 months and yearly after that. Outcomes measured were %EWL and hemoglobin A1c (HgbA1c). The mean and median follow-up for the entire cohort was 21 and 15 months, respectively. Seventy-eight per cent of patients completed at least 12 months of follow-up for %EWL, although only 21 per cent had similar follow-up for HgbA1c. PCOS patients had similar age (36.3 vs 36.2 years, P = 0.90), preoperative BMI (47.2 vs 47.2, P = 0.99), preoperative HgbA1c (6% vs 5.8%, P = 0.31), conversion rate to gastric bypass, and other associated comorbidities compared with non-PCOS comparisons. There was no difference in %EWL at 12-month (49.7% vs 53.1%, P = 0.53) or 24-month (43% vs 49.8%, P = 0.46) postoperative intervals. There was no difference in absolute change of HgbA1c at 12 months (-0.47% vs -0.67%, P = 0.39). SG has equivalent short-term results in %EWL and reduction in HgbA1c for patients who have PCOS and those who do not.

Targeting hepatic glucokinase to treat diabetes with TTP399, a hepatoselective glucokinase activator

The therapeutic success of interventions targeting glucokinase (GK) activation for the treatment of type 2 diabetes has been limited by hypoglycemia, steatohepatitis, and loss of efficacy over time. The clinical characteristics of patients with GK-activating mutations or GK regulatory protein (GKRP) loss-of-function mutations suggest that a hepatoselective GK activator (GKA) that does not activate GK in β cells or affect the GK-GKRP interaction may reduce hyperglycemia in patients with type 2 diabetes while limiting hypoglycemia and liver-associated adverse effects. Here, we review the rationale for TTP399, an oral hepatoselective GKA, and its progression from preclinical to clinical development, with an emphasis on the results of a randomized, double-blind, placebo- and active-controlled phase 2 study of TTP399 in patients with type 2 diabetes. In this 6-month study, TTP399 (800 mg/day) was associated with a clinically significant and sustained reduction in glycated hemoglobin, with a placebo-subtracted least squares mean HbA1c change from baseline of −0.9% (P < 0.01). Compared to placebo, TTP399 (800 mg/day) also increased high-density lipoprotein cholesterol (3.2 mg/dl; P < 0.05), decreased fasting plasma glucagon (−20 pg/ml; P < 0.05), and decreased weight in patients weighing ≥100 kg (−3.4 kg; P < 0.05). TTP399 did not cause hypoglycemia, had no detrimental effect on plasma lipids or liver enzymes, and did not increase blood pressure, highlighting the importance of tissue selectivity and preservation of physiological regulation when targeting key metabolic regulators such as GK.

Disruption of the hippocampal and hypothalamic blood-brain barrier in a diet-induced obese model of type II diabetes: prevention and treatment by the mitochondrial carbonic anhydrase inhibitor, topiramate

BACKGROUND

Type II diabetes is a vascular risk factor for cognitive impairment and increased risk of dementia. Disruption of the blood-retinal barrier (BRB) and blood-brain barrier (BBB) are hallmarks of subsequent retinal edema and central nervous system dysfunction. However, the mechanisms by which diet or metabolic syndrome induces dysfunction are not understood. A proposed mechanism is an increase in reactive oxygen species (ROS) and oxidative stress. Inhibition of mitochondrial carbonic anhydrase (mCA) decreases ROS and oxidative stress. In this study, topiramate, a mCA inhibitor, was examined for its ability to protect the BRB and BBB in diet-induced obese type II diabetic mice.

METHODS

BBB and BRB permeability were assessed using 14C-sucrose and 99mTc-albumin in CD-1 mice fed a low-fat (control) or a high-fat diet. Topiramate administration was compared to saline controls in both preventative and efficacy arms examining BRB and BBB disruption. Body weight and blood glucose were measured weekly and body composition was assessed using EchoMRI. Metabolic activity was measured using a comprehensive laboratory animal monitoring system. Brain tissues collected from the mice were assessed for changes in oxidative stress and tight junction proteins.

RESULTS

High-fat feeding caused increased entry of 14C-sucrose and 99mTc-albumin into the brains of diet-induced obese type II diabetic mice. Increased permeability to 14C-sucrose was observed in the hypothalamus and hippocampus, and attenuated by topiramate treatment, while increased permeability to 99mTc-albumin occurred in the whole brain and was also attenuated by topiramate. Treatment with topiramate decreased measures of oxidative stress and increased expression of the tight junction proteins ZO-1 and claudin-12. In the retina, we observed increased entry of 99mTc-albumin simultaneously with increased entry into the whole brain during the preventative arm. This occurred prior to increased entry to the retina for 14C-sucrose which occurred during the efficacy arm. Treatment with topiramate had no effect on the retina.

CONCLUSIONS

Blood-brain barrier and blood-retinal barrier dysfunction were examined in a mouse model of diet-induced obese type II diabetes. These studies demonstrate that there are spatial and temporal differences in 14C-sucrose and 99mTc-albumin permeability in the brain and retina of diet-induced obese type II diabetic mice. Topiramate, a mitochondrial carbonic anhydrase inhibitor, is efficacious at both preventing and treating BBB disruption in this diet-induced obese type II diabetic mouse model.

The α-cell in diabetes mellitus

Findings from the past 10 years have placed the glucagon-secreting pancreatic α-cell centre stage in the development of diabetes mellitus, a disease affecting almost one in every ten adults worldwide. Glucagon secretion is reduced in patients with type 1 diabetes mellitus, increasing the risk of insulin-induced hypoglycaemia, but is enhanced in type 2 diabetes mellitus, exacerbating the effects of diminished insulin release and action on blood levels of glucose. A better understanding of the mechanisms underlying these changes is therefore an important goal. RNA sequencing reveals that, despite their opposing roles in the control of blood levels of glucose, α-cells and β-cells have remarkably similar patterns of gene expression. This similarity might explain the fairly facile interconversion between these cells and the ability of the α-cell compartment to serve as a source of new β-cells in models of extreme β-cell loss that mimic type 1 diabetes mellitus. Emerging data suggest that GABA might facilitate this interconversion, whereas the amino acid glutamine serves as a liver-derived factor to promote α-cell replication and maintenance of α-cell mass. Here, we survey these developments and their therapeutic implications for patients with diabetes mellitus.

Pancreatic islet-autonomous insulin and smoothened-mediated signalling modulate identity changes of glucagon+ α-cells

The mechanisms that restrict regeneration and maintain cell identity following injury are poorly characterized in higher vertebrates. Following β-cell loss, 1-2% of the glucagon-producing α-cells spontaneously engage in insulin production in mice. Here we explore the mechanisms inhibiting α-cell plasticity. We show that adaptive α-cell identity changes are constrained by intra-islet insulin- and Smoothened-mediated signalling, among others. The combination of β-cell loss or insulin-signalling inhibition, with Smoothened inactivation in α- or δ-cells, stimulates insulin production in more α-cells. These findings suggest that the removal of constitutive 'brake signals' is crucial to neutralize the refractoriness to adaptive cell-fate changes. It appears that the maintenance of cell identity is an active process mediated by repressive signals, which are released by neighbouring cells and curb an intrinsic trend of differentiated cells to change.

Zinc Supplementation Does Not Affect Glucagon Response to Intravenous Glucose and Insulin Infusion in Patients with Well-Controlled Type 2 Diabetes

Glucagon dysregulation is an essential component in the pathophysiology of type 2 diabetes. Studies in vitro and in animal models have shown that zinc co-secreted with insulin suppresses glucagon secretion. Zinc supplementation improves blood glucose control in patients with type 2 diabetes, although there is little information about how zinc supplementation may affect glucagon secretion. The objective of this study was to evaluate the effect of 1-year zinc supplementation on fasting plasma glucagon concentration and in response to intravenous glucose and insulin infusion in patients with type 2 diabetes. A cross-sectional study was performed after 1-year of intervention with 30 mg/day zinc supplementation or a placebo on 28 patients with type 2 diabetes. Demographic, anthropometric, and biochemical parameters were determined. Fasting plasma glucagon and in response to intravenous glucose and insulin infusion were evaluated. Patients of both placebo and supplemented groups presented a well control of diabetes, with mean values of fasting blood glucose and glycated hemoglobin within the therapeutic goals established by ADA. No significant differences were observed in plasma glucagon concentration, glucagon/glucose ratio or glucagon/insulin ratio fasting, after glucose or after insulin infusions between placebo and supplemented groups. No significant effects of glucose or insulin infusions were observed on plasma glucagon concentration. One-year zinc supplementation did not affect fasting plasma glucagon nor response to intravenous glucose or insulin infusion in well-controlled type 2 diabetes patients with an adequate zinc status.

Disrupted sphingolipid metabolism following acute clozapine and olanzapine administration

Background

Second generation antipsychotics (SGAs) induce glucometabolic side-effects, such as hyperglycemia and insulin resistance, which pose a therapeutic challenge for mental illness. Sphingolipids play a role in glycaemic balance and insulin resistance. Endoplasmic reticulum (ER) stress contributes to impaired insulin signalling and whole-body glucose intolerance. Diabetogenic SGA effects on ER stress and sphingolipids, such as ceramide and sphingomyelin, in peripheral metabolic tissues are unknown. This study aimed to investigate the acute effects of clozapine and olanzapine on ceramide and sphingomyelin levels, and protein expression of key enzymes involved in lipid and glucose metabolism, in the liver and skeletal muscle.

Methods

Female rats were administered olanzapine (1 mg/kg), clozapine (12 mg/kg), or vehicle (control) and euthanized 1-h later. Ceramide and sphingomyelin levels were examined using electrospray ionization (ESI) mass spectrometry. Expression of lipid enzymes (ceramide synthase 2 (CerS2), elongation of very long-chain fatty acid 1 (ELOVL1), fatty acid synthase (FAS) and acetyl CoA carboxylase 1 (ACC1)), ER stress markers (inositol-requiring enzyme 1 (IRE1) and eukaryotic initiation factor (eIF2α) were also examined.

Results

Clozapine caused robust reductions in hepatic ceramide and sphingolipid levels (p < 0.0001), upregulated CerS2 (p < 0.05) and ELOVL1 (+ 37%) and induced significant hyperglycemia (vs controls). In contrast, olanzapine increased hepatic sphingomyelin levels (p < 0.05 vs controls). SGAs did not alter sphingolipid levels in the muscle. Clozapine increased (+ 52.5%) hepatic eIF2α phosphorylation, demonstrating evidence of activation of the PERK/eIF2α ER stress axis. Hepatic IRE1, FAS and ACC1 were unaltered.

Conclusions

This study provides the first evidence that diabetogenic SGAs disrupt hepatic sphingolipid homeostasis within 1-h of administration. Sphingolipids may be key candidates in the mechanisms underlying the diabetes side-effects of SGAs; however, further research is required.

Niclosamide ethanolamine improves diabetes and diabetic kidney disease in mice

Diabetes and its renal complications are major medical challenges worldwide. There are no effective drugs currently available for treating diabetes and diabetic kidney disease (DKD), especially in type 1 diabetes (T1D). Evidence has suggested that niclosamide ethanolamine salt (NEN) could improve diabetic symptoms in mice of type 2 diabetes (T2D). However, its role in T1D and DKD has not been studied to date. Here we report that NEN could protect against diabetes in streptozotocin (STZ) induced T1D mice. It increased serum insulin levels, corrected the unbalanced ratio of α-cells to β-cells, and induced islet morphologic changes under diabetic conditions. In addition, NEN could impede the progression of DKD in T1D. Specifically, it reduced urinary albumin levels, NAG, NGAL and TGF-β1 excretion, ameliorated renal hypertrophy, alleviated podocyte dysfunction, and suppressed the renal cortical activation of mTOR/4E-BP1 signaling pathway. Moreover, it is hepatoprotective and does not exhibit heart toxicity. Therefore, these findings open up a completely novel therapy for diabetes and DKD.

The Role of Glucagon in the Pathophysiology and Treatment of Type 2 Diabetes

Type 2 diabetes is a disease involving both inadequate insulin levels and increased glucagon levels. While glucagon and insulin work together to achieve optimal plasma glucose concentrations in healthy individuals, the usual regulatory balance between these 2 critical pancreatic hormones is awry in patients with diabetes. Although clinical discussion often focuses on the role of insulin, glucagon is equally important in understanding type 2 diabetes. Furthermore, an awareness of the role of glucagon is essential to appreciate differences in the mechanisms of action of various classes of glucose-lowering therapies. Newer drug classes such as dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 receptor agonists improve glycemic control, in part, by affecting glucagon levels. This review provides an overview of the effect of glucose-lowering therapies on glucagon on the basis of an extensive PubMed literature search to identify clinical studies of glucose-lowering therapies in type 2 diabetes that included assessment of glucagon. Clinical practice currently benefits from available therapies that impact the glucagon regulatory pathway. As clinicians look to the future, improved treatment strategies are likely to emerge that will either use currently available therapies whose mechanisms of action complement each other or take advantage of new therapies based on an improved understanding of glucagon pathophysiology.

Dietary Supplement of Large Yellow Tea Ameliorates Metabolic Syndrome and Attenuates Hepatic Steatosis in db/db Mice

Yellow tea has been widely recognized for its health benefits. However, its effects and mechanism are largely unknown. The current study investigated the mechanism of dietary supplements of large yellow tea and its effects on metabolic syndrome and the hepatic steatosis in male db/db mice. Our data showed that dietary supplements of large yellow tea and water extract significantly reduced water intake and food consumption, lowered the serum total and low-density lipoprotein cholesterol and triglyceride levels, and significantly reduced blood glucose level and increased glucose tolerance in db/db mice when compared to untreated db/db mice. In addition, the dietary supplement of large yellow tea prevented the fatty liver formation and restored the normal hepatic structure of db/db mice. Furthermore, the dietary supplement of large yellow tea obviously reduced the lipid synthesis related to gene fatty acid synthase, the sterol regulatory element-binding transcription factor 1 and acetyl-CoA carboxylase α, as well as fatty acid synthase and sterol response element-binding protein 1 expression, while the lipid catabolic genes were not altered in the liver of db/db mice. This study substantiated that the dietary supplement of large yellow tea has potential as a food additive for ameliorating type 2 diabetes-associated symptoms.

Impaired Insulin Action Is Associated With Increased Glucagon Concentrations in Nondiabetic Humans

Context

Abnormal glucagon concentrations contribute to hyperglycemia, but the mechanisms of α-cell dysfunction in prediabetes are unclear.

Objective

We sought to determine the relative contributions of insulin secretion and action to α-cell dysfunction in nondiabetic participants across the spectrum of glucose tolerance.

Design

This was a cross-sectional study. A subset of participants (n = 120) was studied in the presence and absence of free fatty acid (FFA) elevation, achieved by infusion of Intralipid (Baxter Healthcare, Deerfield, IL) plus heparin, to cause insulin resistance.

Setting

An inpatient clinical research unit at an academic medical center.

Participants

A total of 310 nondiabetic persons participated in this study.

Interventions

Participants underwent a seven-sample oral glucose tolerance test. Subsequently, 120 participants were studied on two occasions. On one day, infusion of Intralipid plus heparin raised FFA. On the other day, participants received glycerol as a control.

Main Outcome Measure(s)

We examined the relationship of glucagon concentration with indices of insulin action after adjusting for the effects of age, sex, and weight. Subsequently, we sought to determine whether an acute decrease in insulin action, produced by FFA elevation, altered glucagon concentrations in nondiabetic participants.

Results

Fasting glucagon concentrations correlated positively with fasting insulin and C-peptide concentrations and inversely with insulin action. Fasting glucagon was not associated with any index of β-cell function in response to an oral challenge. As expected, FFA elevation decreased insulin action and also raised glucagon concentrations.

Conclusions

In nondiabetic participants, glucagon secretion was altered by changes in insulin action.