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Open access

Kim K B Clemmensen, Jonas S Quist, Dorte Vistisen, Daniel R Witte, Anna Jonsson, Oluf Pedersen, Torben Hansen, Jens J Holst, Torsten Lauritzen, Marit E Jørgensen, Signe Torekov, and Kristine Færch

Fasting duration has been associated with lower fasting blood glucose levels, but higher 2-h post-load levels, and research has indicated an adverse effect of ‘weekend behavior’ on human metabolism. We investigated associations of fasting duration and weekday of examination with glucose, insulin, glucagon and incretin responses to an oral glucose tolerance test (OGTT). This cross-sectional study is based on data from the ADDITION-PRO study, where 2082 individuals attended a health examination including an OGTT. Linear regression analysis was applied to study the associations of overnight fasting duration and day of the week with glucose, insulin, glucagon, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) responses to an OGTT. We found that a 1 h longer fasting duration was associated with 1.7% (95% CI: 0.8,2.5) higher 2-h glucose levels, as well as a 3.0% (95% CI: 1.3,4.7) higher GIP and 2.3% (95% CI: 0.3,4.4) higher GLP-1 response. Fasting insulin levels were 20.6% (95% CI: 11.2,30.7) higher on Mondays compared to the other weekdays, with similar fasting glucose levels (1.7%, 95% CI: 0.0,3.4). In this study, longer overnight fasting duration was associated with a worsening of glucose tolerance and increased incretin response to oral glucose. We found higher fasting insulin levels on Mondays compared to the other days of the week, potentially indicating a worsened glucose regulation after the weekend.

Open access

Doron Weinstein, Rive Sarfstein, Zvi Laron, and Haim Werner

Hyperinsulinemia is a major complication associated with the development of insulin resistance. In addition to its normal spectrum of metabolic effects, insulin can act as a growth factor and has the ability to promote mitogenic activity. Thus, hyperinsulinemia is regarded as a potentially important cancer risk factor among diabetic patients. However, the mechanisms of action of insulin in the specific context of prostate cancer (PCa) and, in particular, the specific receptor that mediates its actions have not been elucidated yet. The aims of this study were to investigate whether insulin can directly induce mitogenic activities in PCa-derived cell lines and to examine the mechanisms responsible for these actions. To this end, we used several PCa-derived cell lines, representing early and advanced stages of the disease. Our results indicated that insulin induces cell proliferation in a dose-dependent fashion in the LNCaP, C4-2, and P69 cell lines. We also demonstrated that insulin enabled LNCaP and C4-2 cells to progress through the cell cycle. Immunoprecipitation assays revealed that insulin activated the insulin receptor (INSR), but not the IGF1 receptor (IGF1R). In addition, INSR was able to compensate for and mediate IGF1 mitogenic signals following IGF1R inhibition. In conclusion, insulin exhibits direct mitogenic activities in PCa cells, which are mediated exclusively through the INSR. Further research is needed to fully dissect the molecular mechanisms underlying the biological actions of insulin in PCa.

Open access

Leanne Hodson and Fredrik Karpe

In health, the liver is metabolically flexible over the course of the day, as it undertakes a multitude of physiological processes including the regulation of intrahepatic and systemic glucose and lipid levels. The liver is the first organ to receive insulin and through a cascade of complex metabolic processes, insulin not only plays a key role in the intrahepatic regulation of glucose and lipid metabolism, but also in the regulation of systemic glucose and lipid concentrations. Thus, when intrahepatic insulin signalling becomes aberrant then this may lead to perturbations in intrahepatic metabolic processes that have the potential to impact on metabolic health. For example, obesity is associated with intrahepatic fat accumulation (known as nonalcoholic liver disease (NAFLD)) and hyperinsulinaemia, the latter as a result of insulin hypersecretion or impaired hepatic insulin extraction. Although insulin signalling directly alters intra- and extrahepatic metabolism, the regulation of hepatic glucose and fatty acid metabolism is also indirectly driven by substrate availability. Here we discuss the direct and indirect effects of insulin on intrahepatic processes such as the synthesis of fatty acids and peripherally regulating the flux of fatty acids to the liver; processes that may play a role in the development of insulin resistance and/or intrahepatocellular triacylglycerol (IHTAG) accumulation in humans.

Open access

Caio Jordão Teixeira, Junia Carolina Santos-Silva, Dailson Nogueira de Souza, Alex Rafacho, Gabriel Forato Anhe, and Silvana Bordin

Pancreatic islets from pregnant rats develop a transitory increase in the pancreatic β-cell proliferation rate and mass. Increased apoptosis during early lactation contributes to the rapid reversal of those morphological changes. Exposure to synthetic glucocorticoids during pregnancy has been previously reported to impair insulin secretion, but its impacts on pancreatic islet morphological changes during pregnancy and lactation have not been described. To address this issue, we assessed the morphological and molecular characteristics of pancreatic islets from rats that underwent undisturbed pregnancy (CTL) or were treated with dexamethasone between the 14th and 19th days of pregnancy (DEX). Pancreatic islets were analyzed on the 20th day of pregnancy (P20) and on the 3rd, 8th, 14th and 21st days of lactation (L3, L8, L14 and L21, respectively). Pancreatic islets from CTL rats exhibited transitory increases in cellular proliferation and pancreatic β-cell mass at P20, which were reversed at L3, when a transitory increase in apoptosis was observed. This was followed by the appearance of morphological features of pancreatic islet neogenesis at L8. Islets from DEX rats did not demonstrate an increase in apoptosis at L3, which coincided with an increase in the expression of M2 macrophage markers relative to M1 macrophage and T lymphocyte markers. Islets from DEX rats also did not exhibit the morphological characteristics of pancreatic islet neogenesis at L8. Our data demonstrate that maternal pancreatic islets undergo a renewal process during lactation that is impaired by exposure to DEX during pregnancy.

Open access

Yuka Goto, Yoshie Otsuka, Kenji Ashida, Ayako Nagayama, Nao Hasuzawa, Shimpei Iwata, Kento Hara, Munehisa Tsuruta, Nobuhiko Wada, Seiichi Motomura, Yuji Tajiri, and Masatoshi Nomura

Background and Aims:

It is currently unclear whether sodium–glucose co-transporter 2 (SGLT2) inhibitor administration can improve the insulin sensitivity as well as rapidly reduce plasma glucose concentrations in humans during the early phase of treatment initiation. This study aimed to investigate the effect of SGLT2 inhibitor on insulin sensitivity in the early phase of treatment initiation.

Methods and Results

This single-center, open label, and single-arm prospective study recruited 20 patients (14 men) with type 2 diabetes mellitus (T2DM). We examined the patients’ metabolic parameters before and 1 week after SGLT2 inhibitor (10 mg/day of empagliflozin) administration. The glucose infusion rate (GIR) was evaluated using the euglycemic hyperinsulinemic glucose clamp technique. Changes in laboratory and anthropometric parameters before and after SGLT2 inhibitor administration were analyzed according to the change in the GIR. The BMI, body fat amount, skeletal muscle amount, systolic blood pressure, and triglyceride level significantly decreased along with the treatment, while urinary glucose level and log GIR value significantly increased. Notably, changes in the GIR after SGLT2 inhibitor administration, which indicated improvement in peripheral insulin sensitivity, were negatively correlated with T2DM duration and positively with reduction in fluctuation of daily plasma glucose profiles before and after treatment.

Conclusion

SGLT2 inhibitor improved insulin sensitivity in the skeletal muscle independent of anthropometric changes. Patients with short duration of T2DM and insulin resistance can be good candidates for short-term SGLT2 inhibitor administration to improve insulin sensitivity in the skeletal muscle.

Open access

Amalie R Lanng, Lærke S Gasbjerg, Natasha C Bergmann, Sigrid Bergmann, Mads M Helsted, Matthew P Gillum, Bolette Hartmann, Jens J Holst, Tina Vilsbøll, and Filip K Knop

Background

Ingestion of the calorically dense compound alcohol may cause metabolic disturbances including hypoglycaemia, hepatic steatosis and insulin resistance, but the underlying mechanisms are uncertain. The gastrointestinal tract is well recognised as a major influencer on glucose, protein and lipid metabolism, but its role in alcohol metabolism remains unclear.

Objective

To examine the effects of oral and intravenous alcohol, respectively, on plasma concentrations of several gluco-regulatory hormones including serum/plasma insulin, C-peptide, glucagon, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1) and fibroblast growth factor 21 (FGF21).

Design and methods

In a double-blinded, randomised, crossover design, we subjected 12 healthy men to intragastric ethanol infusion (IGEI) and an isoethanolaemic intravenous ethanol infusion (IVEI) (0.7 g alcohol per kg body weight), respectively, on two separate experimental days.

Results

Isoethanolaemia during the two alcohol administration forms was obtained (P = 0.38). During both interventions, plasma glucose peaked after ~30 min and thereafter fell below baseline concentrations. GIP and GLP-1 concentrations were unaffected by the two interventions. Insulin concentrations were unaffected by IGEI but decreased during IVEI. C-peptide, insulin secretion rate and glucagon concentrations were lowered similarly during IGEI and IVEI. FGF21 concentrations increased dramatically (nine-fold) and similarly during IGEI and IVEI.

Conclusions

Alcohol does not seem to affect the secretion of incretin hormones but decreased insulin and glucagon secretion independently of gut-derived factors. IGEI as well as IVEI potently stimulate FGF21 secretion indicating a gut-independent effect of alcohol on FGF21 secretion in humans.

Open access

L Ahlkvist, K Brown, and B Ahrén

We previously demonstrated that the overall incretin effect and the β-cell responsiveness to glucagon-like peptide-1 (GLP1) are increased in insulin-resistant mice and may contribute to the upregulated β-cell function. Now we examined whether this could, first, be explained by increased islet GLP1 receptor (GLP1R) protein levels and, secondly, be leveraged by G-protein-coupled receptor 119 (GPR119) activation, which stimulates GLP1 secretion. Female C57BL/6J mice, fed a control (CD, 10% fat) or high-fat (HFD, 60% fat) diet for 8 weeks, were anesthetized and orally given a GPR119 receptor agonist (GSK706A; 10 mg/kg) or vehicle, followed after 10 min with gavage with a liquid mixed meal (0.285 kcal). Blood was sampled for determination of glucose, insulin, intact GLP1, and glucagon, and islets were isolated for studies on insulin and glucagon secretion and GLP1R protein levels. In HFD vs CD mice, GPR119 activation augmented the meal-induced increase in the release of both GLP1 (AUCGLP1 81±9.6 vs 37±6.9 pM×min, P=0.002) and insulin (AUCINS 253±29 vs 112±19 nM×min, P<0.001). GPR119 activation also significantly increased glucagon levels in both groups (P<0.01) with, however, no difference between the groups. By contrast, GPR119 activation did not affect islet hormone secretion from isolated islets. Glucose elimination after meal ingestion was significantly increased by GPR119 activation in HFD mice (0.57±0.04 vs 0.43±0.03% per min, P=0.014) but not in control mice. Islet GLP1R protein levels was higher in HFD vs CD mice (0.8±0.1 vs 0.5±0.1, P=0.035). In conclusion, insulin-resistant mice display increased islet GLP1R protein levels and augmented meal-induced GLP1 and insulin responses to GPR119 activation, which results in increased glucose elimination. We suggest that the increased islet GLP1R protein levels together with the increased GLP1 release may contribute to the upregulated β-cell function in insulin resistance.

Open access

Selina Mäkinen, Yen H Nguyen, Paulina Skrobuk, and Heikki A Koistinen

Saturated fatty acids are implicated in the development of insulin resistance, whereas unsaturated fatty acids may have a protective effect on metabolism. We tested in primary human myotubes if insulin resistance induced by saturated fatty acid palmitate can be ameliorated by concomitant exposure to unsaturated fatty acid oleate. Primary human myotubes were pretreated with palmitate, oleate or their combination for 12 h. Glucose uptake was determined by intracellular accumulation of [3H]-2-deoxy-d-glucose, insulin signalling and activation of endoplasmic reticulum (ER) stress by Western blotting, and mitochondrial reactive oxygen species (ROS) production by fluorescent dye MitoSOX. Exposure of primary human myotubes to palmitate impaired insulin-stimulated Akt-Ser473, AS160 and GSK-3β phosphorylation, induced ER stress signalling target PERK and stress kinase JNK 54 kDa isoform. These effects were virtually abolished by concomitant exposure of palmitate-treated myotubes to oleate. However, an exposure to palmitate, oleate or their combination reduced insulin-stimulated glucose uptake. This was associated with increased mitochondrial ROS production in palmitate-treated myotubes co-incubated with oleate, and was alleviated by antioxidants MitoTempo and Tempol. Thus, metabolic and intracellular signalling events diverge in myotubes treated with palmitate and oleate. Exposure of human myotubes to excess fatty acids increases ROS production and induces insulin resistance.

Open access

Riying Liang, Meijun Wang, Chang Fu, Hua Liang, Hongrong Deng, Ying Tan, Fen Xu, and Mengyin Cai

Background:

Obesity is associated with the development and progression of chronic kidney disease. Emerging evidence suggests that glucagon-like peptide-1 receptor agonist could reduce renal damage and albuminuria. Sirtuin 1 (SIRT1) was considered as a crucial regulator in metabolism-related kidney disease. Herein, the role of SIRT1 in liraglutide-ameliorated high-fat diet (HFD)-induced kidney injury was illustrated.

Methods:

Male C57BL/6 mice were fed HFD for 20 weeks to induce kidney injury that was then treated with liraglutide for 8 weeks to estimate its protective effect on the kidney. Also, the mechanism of the drug in SV40 MES 13 (SV40) mouse mesangial cells was elucidated.

Results:

Liraglutide treatment ameliorated HFD-induced metabolic disorders, including hyperglycemia, increasing body weight, and insulin resistance. In addition, kidney weight, urine albumin-to-creatinine, and kidney morphological changes such as vacuolated tubules, glomerulomegaly, thickened glomerular basement membrane, and tubulointerstitial fibrosis were also significantly ameliorated. Furthermore, apoptotic cells and apoptosis markers were downregulated in the kidney of liraglutide-treated mice. In addition, the expression of SIRT1 protein was upregulated, whereas thioredoxin-interacting protein (TXNIP), which serves as a mediator of oxidative stress and apoptosis in metabolism disease, was downregulated by liraglutide. In SV40 cells, the effect of liraglutide on reversing the upregulation of cleaved caspase-3 induced by high glucose (30 mM) was hampered when SIRT1 was knocked down; also, the downregulation of TXNIP by liraglutide was blocked.

Conclusions:

Liraglutide might have a beneficial effect on metabolism-related kidney damage by inhibiting apoptosis via activation of SIRT1 and suppression of TXNIP pathway.

Open access

Jukka Koffert, Henri Honka, Jarmo Teuho, Saila Kauhanen, Saija Hurme, Riitta Parkkola, Vesa Oikonen, Andrea Mari, Andreas Lindqvist, Nils Wierup, Leif Groop, and Pirjo Nuutila

Objective

Meal ingestion is followed by a redistribution of blood flow (BF) within the splanchnic region contributing to nutrient absorption, insulin secretion and glucose disposal, but factors regulating this phenomenon in humans are poorly known. The aim of the present study was to evaluate the organ-specific changes in BF during a mixed-meal and incretin infusions.

Design

A non-randomized intervention study of 10 healthy adults to study splanchnic BF regulation was performed.

Methods

Effects of glucose-dependent insulinotrophic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) infusions and mixed-meal were tested in 10 healthy, glucose tolerant subjects using PET-MRI multimodal imaging technology. Intestinal and pancreatic BF and blood volume (BV) were measured with 15O-water and 15O-carbon monoxide, respectively.

Results

Ingestion of a mixed-meal led to an increase in pancreatic and jejunal BF, whereas duodenal BF was unchanged. Infusion of GIP and GLP-1 reduced BF in the pancreas. However, GIP infusion doubled blood flow in the jejunum with no effect of GLP-1.

Conclusion

Together, our data suggest that meal ingestion leads to increases in pancreatic BF accompanied by a GIP-mediated increase in jejunal but not duodenal blood flow.