Acute glucagon induces postprandial peripheral insulin resistance

This study was supported by Fundacao para a Ciencia e Tecnologia (FCT) grant PIC/IC/82956/2007, PTDC/BIM-MET/0486/2012, PTDC/DTP-EPI/0207/2012 and by the Portuguese Diabetes Society (SPD). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Glucagon levels are often moderately elevated in diabetes. It is known that glucagon leads to a decrease in hepatic glutathione (GSH) synthesis that in turn is associated with decreased postprandial insulin sensitivity. Given that cAMP pathway controls GSH levels we tested whether insulin sensitivity decreases after intraportal (ipv) administration of a cAMP analog (DBcAMP), and investigated whether glucagon promotes insulin resistance through decreasing hepatic GSH levels. Insulin sensitivity was determined in fed male SpragueDawley rats using a modified euglycemic hyperinsulinemic clamp in the postprandial state upon ipv administration of DBcAMP as well as glucagon infusion. Glucagon effects on insulin sensitivity was assessed in the presence or absence of postprandial insulin sensitivity inhibition by administration of L-NMMA. Hepatic GSH and NO content and plasma levels of NO were measured after acute ipv glucagon infusion. Insulin sensitivity was assessed in the fed state and after ipv glucagon infusion in the presence of GSH-E. We founf that DBcAMP and glucagon produce a decrease of insulin sensitivity, in a dose-dependent manner. Glucagon-induced decrease of postprandial insulin sensitivity correlated with decreased hepatic GSH content and was restored by administration of GSH-E. Furthermore, inhibition of postprandial decrease of insulin sensitivity L-NMMA was not overcome by glucagon, but glucagon did not affect hepatic and plasma levels of NO. These results show that glucagon decreases postprandial insulin sensitivity through reducing hepatic GSH levels, an effect that is mimicked by increasing cAMP hepatic levels and requires physiological NO levels. These observations support the hypothesis that glucagon acts via adenylate cyclase to decrease hepatic GSH levels and induce insulin resistance. We suggest that the glucagon-cAMP-GSH axis is a potential therapeutic target to address insulin resistance in pathological conditions.publishersversionpublishe

Fast-to-fed shift in glucose homeostasis: clues to an earlier detection of human prediabetic states

FCM: UC Bioquímica I - PhD ThesisA acção da insulina está associada à libertação da substância hepática sensibilizadora da insulina (HISS), que aumenta o aporte de glucose periférico. No estado pós-prandial, a libertação da HISS é máxima, diminuindo com o período de jejum. O controlo prandial da acção da HISS é mediado pelo sistema parassimpático hepático/óxido nítrico (NO) e pelo glutationo (GSH) hepático. Os actuais métodos utilizados para avaliar a sensibilidade à insulina são realizados no estado de jejum. A presente dissertação destaca a hipótese de que o mecanismo dependente da HISS existe em humanos, e pode ser manipulado. Em humanos, uma robusta ferramenta para caracterizar a acção da insulina dependente da HISS, não só no estado de jejum, mas também após uma refeição, o teste rápido de sensibilidade à insulina (RIST), foi desenvolvido. O RIST pode ser realizado com reproductibilidade, e sem intra e intervariabilidade. A diminuição da sensibilidade à insulina observada no jejum é potenciada após uma refeição, e a administração de atropina, suprime este efeito. A inibição parcial da sensibilidade à insulina induzida pela refeição, é consistente com a hipótese de que um “sinal prandial” dependente do sistema parassimpático hepático é necessário para a libertação hepática da HISS. Quando voluntários magros e com excesso de peso foram submetidos a um período de 24h de jejum, a acção da insulina per se, foi similar em ambos os grupos estudados. Contudo, quando avaliados no estado pós-prandial, os resultados apresentados nesta dissertação mostraram que, a potenciação induzida pela refeição era inferior nos voluntários com excesso de peso, estando esta associada a uma alteração da componente da acção da insulina dependente da HISS. Estes resultados indicam a importância da avaliação da sensibilidade à insulina no estado pós-prandial, e sugerem também que este estado de pré-diabetes apenas pode ser detectado após a ingestão de uma refeição. Níveis elevados de glucagina estão associados à diabetes tipo 2. Sabendo que a glucagina leva a uma diminuição da síntese de GSH, e que o GSH é fundamental para a libertação da HISS, foi avaliado o efeito da glucagina na via da HISS. Em animais, tanto a administração de um análogo do cAMP, como de glucagina, produziram um decréscimo da sensibilidade à insulina, sendo este efeito dependente da dose. A resistência à insulina dependente da HISS observada aquando da administração de um inibidor do sintetase do NO, não se agravou com a posterior administração de glucagina. Estes resultados sugerem então que a glucagina induz um decréscimo da sensibilidade à insulina, sendo este dependente da via da HISS, e não por acção de outra via. Estas duas observações indicam que a glucagina, através da via de finalização do cAMP, leva à diminuição dos níveis hepáticos de GSH e, consequentemente, a uma alteração da via da HISS. Esta alteração poderá ser a responsável por um estado precoce de resistência à insulina

S-nitrosoglutathione reverts dietary sucrose-induced insulin resistance

The liver is a fundamental organ to ensure whole-body homeostasis, allowing for a proper increase in insulin sensitivity from the fast to the postprandial status. Hepatic regulation of glucose metabolism is crucial and has been shown to be modulated by glutathione (GSH) and nitric oxide (NO). However, knowledge of the metabolic action of GSH and NO in glucose homeostasis remains incomplete. The current study was designed to test the hypothesis that treatment with S-nitrosoglutathione is sufficient to revert insulin resistance induced by a high-sucrose diet. Male Wistar rats were divided in a control or high-sucrose group. Insulin sensitivity was determined: (i) in the fast state; (ii) after a standardized test meal; (iii) after GSH + NO; and after (iv) S-nitrosoglutathione (GSNO) administration. The fasting glucose level was not different between the control and high-sucrose group. In the liver, the high-sucrose model shows increased NO and unchanged GSH levels. In control animals, insulin sensitivity increased after a meal or administration of GSH+NO/GSNO, but this was abrogated by sucrose feeding. GSNO was able to revert insulin resistance induced by sucrose feeding, in a dose-dependent manner, suggesting that they have an insulin-sensitizing effect in vivo. These effects are associated with an increased insulin receptor and Akt phosphorylation in muscle cells. Our findings demonstrate that GSNO promotes insulin sensitivity in a sucrose-induced insulin-resistant animal model and further implicates that this antioxidant molecule may act as a potential pharmacological tool for the treatment of insulin resistance in obesity and type 2 diabetes.publishersversionpublishe

Effects of CPAP on nitrate and norepinephrine levels in severe and mild-moderate sleep apnea

Background: Reduced plasma nitrate (NOx) levels and increased urinary norepinephrine (U-NE) levels have been described in severe obstructive sleep apnea (OSA), and are reverted by continuous positive airway pressure (CPAP). The effect of CPAP on these biomarkers in mild-moderate OSA is not well understood. The aim of this study was to compare NOx and U-NE levels and blood pressure (BP) between male patients with mild-moderate and severe OSA and determine the impact of 1 month of CPAP therapy on these parameters. Methods: We undertook a prospective study of 67 consecutive OSA patients (36 mild-moderate, 31 severe). Measurements of plasma NOx at 11 pm, 4 am and 7 am, 24-h U-NE and ambulatory BP were obtained at baseline and after 1 month of CPAP. Results: At baseline, NOx levels showed a significant decrease during the night in both groups (p < 0.001). U-NE level and BP were significantly higher in the severe OSA group. After 1 month of CPAP, there was a significant increase in NOx levels and a reduction in U-NE level and BP only in patients with severe OSA. Conclusions: One month of CPAP results in significant improvements in NOx levels, 24-h U-NE level and BP in patients with severe OSA, but not in patients with mild-moderate OSA.publishersversionpublishe

Nutrition education in portuguese medical students: impact on the attitudes and knowledge

Nutrition has been underrepresented in the curriculum of many medical schools and therefore physicians do not feel adequately prepared to provide dietary counselling. The aim of the present study is to determine the impact of a Nutrition and Metabolism curricular unit on nutrition attitudes, knowledge and confidence on future clinical practice of medical students.info:eu-repo/semantics/publishedVersio

From old indexes to new technologies

Funding Information: This work was supported by FEDER, Portugal2020, and co‐financed by Lisboa2020 and Alentejo2020 (ALT20‐03‐0247‐FEDER‐113469 and LISBOA‐01‐0247‐FEDER‐113469), ‘Fundação para a Ciência e a Tecnologia’—FCT iNOVA4Health (UIDB/Multi/04462/2020), European Commission Marie Skłodowska‐Curie Action H2020 (mtFOIE GRAS, grant agreement n. 734719) and the Sociedade Portuguesa de Diabetologia. Publisher Copyright: © 2022 The Authors. European Journal of Clinical Investigation published by John Wiley & Sons Ltd on behalf of Stichting European Society for Clinical Investigation Journal Foundation.Background: Diabetes is a heterogeneous and multifactorial disease. However, glycemia and glycated hemoglobin have been the focus of diabetes diagnosis and management for the last decades. As diabetes management goes far beyond glucose control, it has become clear that assessment of other biochemical parameters gives a much wider view of the metabolic state of each individual, enabling a precision medicine approach. Methods: In this review, we summarize and discuss indexes that have been used in epidemiological studies and in the clinical practice. Results: Indexes of insulin secretion, sensitivity/resistance and metabolism have been developed and validated over the years to account also with insulin, C-peptide, triglycerides or even anthropometric measures. Nevertheless, each one has their own objective and consequently, advantages and disadvantages for specific cases. Thus, we discuss how new technologies, namely new sensors but also new softwares/applications, can improve the diagnosis and management of diabetes, both for healthcare professionals but also for caretakers and, importantly, to promote the empowerment of people living with diabetes. Conclusions: In long-term, the solution for a better diabetes management would be a platform that allows to integrate all sorts of relevant information for the person with diabetes and for the healthcare practitioners, namely glucose, insulin and C-peptide or, in case of need, other parameters/indexes at home, sometimes more than once a day. This solution would allow a better and simpler disease management, more adequate therapeutics thereby improving patients' quality of life and reducing associated costs.publishersversionepub_ahead_of_prin

Loss of postprandial insulin clearance control by Insulin-degrading enzyme drives dysmetabolism traits

Systemic insulin availability is determined by a balance between beta-cell secretion capacity and insulin clearance (IC). Insulin-degrading enzyme (IDE) is involved in the intracellular mechanisms underlying IC. The liver is a major player in IC control yet the role of hepatic IDE in glucose and lipid homeostasis remains unexplored. We hypothesized that IDE governs postprandial IC and hepatic IDE dysfunction amplifies dysmetabolic responses and prediabetes traits such as hepatic steatosis. In a European/Portuguese population-based cohort, IDE SNPs were strongly associated with postprandial IC in normoglycemic men but to a considerably lesser extent in women or in subjects with prediabetes. Liver-specific knockout-mice (LS-IDE KO) under normal chow diet (NCD), showed reduced postprandial IC with glucose intolerance and under high fat diet (HFD) were more susceptible to hepatic steatosis than control mice. This suggests that regulation of IC by IDE contributes to liver metabolic resilience. In agreement, LS-IDE KO hepatocytes revealed reduction of Glut2 expression levels with consequent impairment of glucose uptake and upregulation of CD36, a major hepatic free fatty acid transporter. Together these findings provide strong evidence that dysfunctional IC due to abnormal IDE regulation directly impairs postprandial hepatic glucose disposal and increases susceptibility to dysmetabolic conditions in the setting of Western diet/lifestyle.publishe

Prediabetes blunts DPP4 genetic control of postprandial glycaemia and insulin secretion

Funding Information: The PREVADIAB-2 study was supported by a grant from the Portuguese Directorate General of Health. This work was financed by Fundação para a Ciência e Tecnologia (reference number PTDC/BIM/MET/4265/2014), by iNOVA4Health UIDB/Multi/04462/2020 and by ONEIDA (project E-411021.01, Lisboa-01-0145-FEDER-016417, co-funded by FEEI [Fundos Europeus Estruturais e de Investimento] from Programa Operacional Regional Lisboa 2020. We also acknowledge the research infrastructure CONGENTO (project LISBOA-01-0145-FEDER-022170), co-financed by Lisboa Regional Operational Programme (Lisboa 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund and the Foundation for Science and Technology (Portugal).Aims/hypothesis: Imbalances in glucose metabolism are hallmarks of clinically silent prediabetes (defined as impaired fasting glucose and/or impaired glucose tolerance) representing dysmetabolism trajectories leading to type 2 diabetes. CD26/dipeptidyl peptidase 4 (DPP4) is a clinically proven molecular target of diabetes-controlling drugs but the DPP4 gene control of dysglycaemia is not proven. Methods: We dissected the genetic control of post-OGTT and insulin release responses by the DPP4 gene in a Portuguese population-based cohort of mainly European ancestry that comprised individuals with normoglycaemia and prediabetes, and in mouse experimental models of Dpp4 deficiency and hyperenergetic diet. Results: In individuals with normoglycaemia, DPP4 single-nucleotide variants governed glycaemic excursions (rs4664446, p=1.63x10−7) and C-peptide release responses (rs2300757, p=6.86x10−5) upon OGTT. Association with blood glucose levels was stronger at 30 min OGTT, but a higher association with the genetic control of insulin secretion was detected in later phases of the post-OGTT response, suggesting that the DPP4 gene directly senses glucose challenges. Accordingly, in mice fed a normal chow diet but not a high-fat diet, we found that, under OGTT, expression of Dpp4 is strongly downregulated at 30 min in the mouse liver. Strikingly, no genetic association was found in prediabetic individuals, indicating that post-OGTT control by DPP4 is abrogated in prediabetes. Furthermore, Dpp4 KO mice provided concordant evidence that Dpp4 modulates post-OGTT C-peptide release in normoglycaemic but not dysmetabolic states. Conclusions/interpretation: These results showed the DPP4 gene as a strong determinant of post-OGTT levels via glucose-sensing mechanisms that are abrogated in prediabetes. We propose that impairments in DPP4 control of post-OGTT insulin responses are part of molecular mechanisms underlying early metabolic disturbances associated with type 2 diabetes. Graphical abstract: [Figure not available: see fulltext.]publishersversionepub_ahead_of_prin

Effect of DBcAMP on insulin sensitivity.

<p>Insulin sensitivity decreases after DBcAMP 0.01, 0.1 and 1mg/kg ipv infusion. Results are means±SEM. Paired t-test. ** = p<0.01, * = p<0.05.</p

DBcAMP and glucagon produces a decrease of peripheral insulin sensitivity.

<p>The cAMP analog and glucagon promote an increase in hepatic cAMP levels that are related to the decrease of hepatic GSH synthesis, leading to an impairment of peripheral postprandial insulin sensitivity. On the other hand, in the presence of increased GSH levels the glucagon is abrogated and peripheral insulin sensitivity is restored. DBcAMP: N6,2‟-O-dibutyryladenosine 3‟,5‟-cyclicmonophosphate; cAMP: 3‟,5‟-cyclic adenosine 5‟-monophosphate; GSH:gluthatione.</p