Effect of free fatty acids on insulin secretion, insulin sensitivity and incretin effect - a narrative review

ABSTRACT Deleterious effects of free fatty acids, FFAs, on insulin sensitivity are observed in vivo studies in humans. Mechanisms include impaired insulin signaling, oxidative stress, inflammation, and mitochondrial dysfunction, but the effects on insulin secretion are less well known. Our aim was to review the relationship of increased FFAs with insulin resistance, secretion and mainly with the incretin effect in humans. Narrative review. Increased endogenous or administered FFAs induce insulin resistance. FFAs effects on insulin secretion are debatable; inhibition and stimulation have been reported, depending on the type and duration of lipids exposition and the study subjects. Chronically elevated FFAs seem to decrease insulin biosynthesis, glucose-stimulated insulin secretion and β-cell glucose sensitivity. Lipids infusion decreases the response to incretins with unchanged incretin levels in volunteers with normal glucose tolerance. In contrast, FFAs reduction by acipimox did not restore the incretin effect in type-2 diabetes, probably due to the dysfunctional β-cell. Possible mechanisms of FFAs excess on incretin effect include reduction of the expression and levels of GLP-1 (glucagon like peptide-1) receptor, reduction of connexin-36 expression thus the coordinated secretory activity in response to GLP-1, and GIP (glucose-dependent insulinotropic polypeptide) receptors downregulation in islets cells. Increased circulating FFAs impair insulin sensitivity. Effects on insulin secretion are complex and controversial. Deleterious effects on the incretin-induced potentiation of insulin secretion were reported. More investigation is needed to better understand the extent and mechanisms of β-cell impairment and insulin resistance induced by increased FFAs and how to prevent them.

Factors Related to Blood Intact Incretin Levels in Patients with Type 2 Diabetes Mellitus

BACKGROUND: We performed this study to identify factors related to intact incretin levels in patients with type 2 diabetes mellitus (T2DM). METHODS: We cross-sectionally analyzed 336 patients with T2DM. Intact glucagon-like peptide 1 (iGLP-1) and intact glucose-dependent insulinotropic polypeptide (iGIP) levels were measured in a fasted state and 30 minutes after ingestion of a standard mixed meal. The differences between 30 and 0 minute iGLP-1 and iGIP levels were indicated as ΔiGLP-1 and ΔiGIP. RESULTS: In simple correlation analyses, fasting iGLP-1 was positively correlated with glucose, C-peptide, creatinine, and triglyceride levels, and negatively correlated with estimated glomerular filtration rate. ΔiGLP-1 was positively correlated only with ΔC-peptide levels. Fasting iGIP showed positive correlations with glycosylated hemoglobin (HbA1c) and fasting glucose levels, and negative correlations with ΔC-peptide levels. ΔiGIP was negatively correlated with diabetes duration and HbA1c levels, and positively correlated with Δglucose and ΔC-peptide levels. In multivariate analyses adjusting for age, sex, and covariates, fasting iGLP-1 levels were significantly related to fasting glucose levels, ΔiGLP-1 levels were positively related to ΔC-peptide levels, fasting iGIP levels were related to fasting C-peptide levels, and ΔiGIP levels were positively related to ΔC-peptide and Δglucose levels. CONCLUSION: Taken together, intact incretin levels are primarily related to C-peptide and glucose levels. This result suggests that glycemia and insulin secretion are the main factors associated with intact incretin levels in T2DM patients.

Calcium-sensing receptor-mediated L-tryptophan-induced secretion of cholecystokinin and glucose-dependent insulinotropic peptide in swine duodenum

This study aimed to elucidate the effect of tryptophan (Trp) on gut hormone secretion as well as the roles of the calcium-sensing receptor (CaSR) and its downstream signaling pathway in gut hormone secretion by assessing swine duodenal perfusion in vitro. Swine duodenum was perfused with Krebs-Henseleit buffer as a basal solution. Various concentrations (0, 10, and 20 mM) of Trp were applied to investigate its effect on gut hormone secretion. A CaSR antagonist was used to detect the involvement of CaSR and its signal molecules. The 20 mM Trp concentration promoted the secretion of cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP), elevated the mRNA level of CaSR, and upregulated the protein levels of CaSR, protein kinase C (PKC), and inositol trisphosphate receptor (IP3R). However, NPS 2143, an inhibitor of CaSR, attenuated the CCK and GIP release, reduced the mRNA level of CaSR, and decreased the protein levels of CaSR, PKC, and IP3R with 20 mM Trp perfusion. The results indicate that CCK and GIP secretion can be induced by Trp in swine duodenum in vitro, and the effect is mediated by CaSR and its downstream signal molecules PKC and IP3R.

Improving Effect of the Acute Administration of Dietary Fiber-Enriched Cereals on Blood Glucose Levels and Gut Hormone Secretion

Dietary fiber improves hyperglycemia in patients with type 2 diabetes through its physicochemical properties and possible modulation of gut hormone secretion, such as glucagon-like peptide 1 (GLP-1). We assessed the effect of dietary fiber-enriched cereal flakes (DC) on postprandial hyperglycemia and gut hormone secretion in patients with type 2 diabetes. Thirteen participants ate isocaloric meals based on either DC or conventional cereal flakes (CC) in a crossover design. DC or CC was provided for dinner, night snack on day 1 and breakfast on day 2, followed by a high-fat lunch. On day 2, the levels of plasma glucose, GLP-1, glucose-dependent insulinotropic polypeptide (GIP), and insulin were measured. Compared to CC, DC intake exhibited a lower post-breakfast 2-hours glucose level (198.5±12.8 vs. 245.9±15.2 mg/dL, P<0.05) and a lower incremental peak of glucose from baseline (101.8±9.1 vs. 140.3±14.3 mg/dL, P<0.001). The incremental area under the curve (iAUC) of glucose after breakfast was lower with DC than with CC (P<0.001). However, there were no differences in the plasma insulin, glucagon, GLP-1, and GIP levels. In conclusion, acute administration of DC attenuates postprandial hyperglycemia without any significant change in the representative glucose-regulating hormones in patients with type 2 diabetes (ClinicalTrials.gov. NCT 01997281).

Glucose-Dependent Insulinotropic Peptide Level Is Associated with the Development of Type 2 Diabetes Mellitus

BACKGROUND: Incretin hormone levels as a predictor of type 2 diabetes mellitus have not been fully investigated. Therefore, we measured incretin hormone levels to examine the relationship between circulating incretin hormones, diabetes, and future diabetes development in this study. METHODS: A nested case-control study was conducted in a Korean cohort. The study included the following two groups: the control group (n=149), the incident diabetes group (n=65). Fasting total glucagon-like peptide-1 (GLP-1) and total glucose-dependent insulinotropic peptide (GIP) levels were measured and compared between these groups. RESULTS: Fasting total GIP levels were higher in the incident diabetes group than in the control group (32.64±22.68 pmol/L vs. 25.54±18.37 pmol/L, P=0.034). There was no statistically significant difference in fasting total GLP-1 levels between groups (1.14±1.43 pmol/L vs. 1.39±2.13 pmol/L, P=0.199). In multivariate analysis, fasting total GIP levels were associated with an increased risk of diabetes (odds ratio, 1.005; P=0.012) independent of other risk factors. CONCLUSION: Fasting total GIP levels may be a risk factor for the development of type 2 diabetes mellitus. This association persisted even after adjusting for other metabolic parameters such as elevated fasting glucose, hemoglobin A1c, and obesity in the pre-diabetic period.

Correlation of Glypican-4 Level with Basal Active Glucagon-Like Peptide 1 Level in Patients with Type 2 Diabetes Mellitus

BACKGROUND: Previous studies have reported that glypican-4 (GPC4) regulates insulin signaling by interacting with insulin receptor and through adipocyte differentiation. However, GPC4 has not been studied with regard to its effects on clinical factors in patients with type 2 diabetes mellitus (T2DM). We aimed to identify factors associated with GPC4 level in T2DM. METHODS: Between January 2010 and December 2013, we selected 152 subjects with T2DM and collected serum and plasma into tubes pretreated with aprotinin and dipeptidyl peptidase-4 inhibitor to preserve active gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1). GPC4, active GLP-1, active GIP, and other factors were measured in these plasma samples. We performed a linear regression analysis to identify factors associated with GPC4 level. RESULTS: The subjects had a mean age of 58.1 years, were mildly obese (mean body mass index [BMI], 26.1 kg/m2), had T2DM of long-duration (mean, 101.3 months), glycated hemoglobin 7.5%, low insulin secretion, and low insulin resistance (mean homeostatic model assessment of insulin resistance [HOMA-IR], 1.2). Their mean GPC4 was 2.0±0.2 ng/mL. In multivariate analysis, GPC4 was independently associated with age (β=0.224, P=0.009), and levels of active GLP-1 (β=0.171, P=0.049) and aspartate aminotransferase (AST; β=–0.176, P=0.043) after being adjusted for other clinical factors. CONCLUSION: GPC4 was independently associated with age, active GLP-1, and AST in T2DM patients, but was not associated with HOMA-IR and BMI, which are well known factors related to GPC4. Further study is needed to identify the mechanisms of the association between GPC4 and basal active GLP-1 levels.

Novel Molecules Regulating Energy Homeostasis: Physiology and Regulation by Macronutrient Intake and Weight Loss

Excess energy intake, without a compensatory increase of energy expenditure, leads to obesity. Several molecules are involved in energy homeostasis regulation and new ones are being discovered constantly. Appetite regulating hormones such as ghrelin, peptide tyrosine-tyrosine and amylin or incretins such as the gastric inhibitory polypeptide have been studied extensively while other molecules such as fibroblast growth factor 21, chemerin, irisin, secreted frizzle-related protein-4, total bile acids, and heme oxygenase-1 have been linked to energy homeostasis regulation more recently and the specific role of each one of them has not been fully elucidated. This mini review focuses on the above mentioned molecules and discusses them in relation to their regulation by the macronutrient composition of the diet as well as diet-induced weight loss.

Clinical observation on the combined therapy of sitagliptin with insulin for patients with brittle diabetes / 中南大学学报(医学版)

OBJECTIVE@#To observe the clinical efficacy of sitagliptin plus insulin on patients with brittle diabetes and to determine the effect of the combined therapy on glucagon secretion.
@*METHODS@#This randomized, double-blinded and placebo-controlled trial included 30 patients with brittle diabetes. Participants were randomly assigned (1:1) to receive the treatment of either sitagliptin plus insulin or placebo plus insulin for 12 weeks. The blood glucose, hemoglobin A1c, insulin dose, C-peptide, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and other parameters were determined.
@*RESULTS@#After 12 weeks of treatment, blood glucose was controlled better by sitagliptin plus insulin (P<0.01). The patients had significantly lower glucose variability indices, lower daily insulin requirement and hemoglobin A1c in the group of sitagliptin plus insulin (P<0.01). After steamed bun test, past-meal GLP-1 levels at 30 min were higher (P<0.01) while GIP levels were lower (P<0.01), with glucagon suppression in the sitagliptin plus insulin group. No significant change was observed at any time point in placebo plus insulin group.
@*CONCLUSION@#Sitagliptin significantly decreases blood glucose level and blood glucose fluctuation, which may contribute to the ability of sitagliptin in decreasing glucagon secretion.

The effects of gastric bypass procedures on blood glucose, gastric inhibitory polypeptide and glucagon-like peptide-1 of normal glucose tolerance dogs / 中华外科杂志

<p><b>OBJECTIVE</b>To observe postoperative glucose tolerance, gastric inhibitory polypeptide (GIP) , and glucogan-like peptide-1 (GLP-1) in normal glucose level dogs after undergoing gastric bypass procedures, and to explore the mechanism of gastric bypass procedures to treat type 2 diabetes.</p><p><b>METHODS</b>The 6 dogs with normal glucose tolerance had undergone gastric bypass procedures, and measure preoperative and postoperative oral and intravenous glucose tolerance (at time points 1, 2, and 4 weeks) through changes in blood glucose, insulin, gastric inhibitory polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and measure preoperative and postoperative week 4 pancreatic tissue morphology.</p><p><b>RESULTS</b>Second weeks after operation, the fasting blood sugar was (3.58 ± 0.33) mmol/L, and significantly lower than preoperative (t = 3.571, P < 0.05). The GLP-1 level before oral glucose tolerance test (OGTT) and 30 minutes after OGTT were (0.90 ± 0.21) and (0.91 ± 0.19) pmol/L respectively, and significantly higher than preoperative (t value were -3.660 and -2.971, P < 0.05). GLP-1 levels began to decrease in the second week after surgery. After 4 weeks, the index recovered to the preoperative level. Four weeks after surgery when compared with preoperative, islet morphology, islet number (6.8 ± 0.8 and 7.1 ± 0.8 respectively) and islet cells (16.7 ± 2.5 and 16.3 ± 3.1 respectively) did not change significantly (P > 0.05).</p><p><b>CONCLUSION</b>Gastric bypass procedures could be briefly affect normal glucose tolerance in dogs' blood glucose, insulin and diabetes-related gastrointestinal hormones.</p>

Effect of different dietary loads on glucose-dependent insulinotropic polypeptide in subjects with normal glucose tolerance / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the secretion patterns of glucose-dependent insulinotropic polypeptide (GIP) after different dietary loads in subjects with normal glucose tolerance (NGT) and their relation to insulin secretion and plasma glucose levels.</p><p><b>METHODS</b>Fourteen subjects with normal glucose tolerance underwent 75 g glucose tolerance test(OGTT) followed by mixed meal tolerance test(MMT) one week later. Blood glucose, insulin, and GIP were measured in the fasting state and at 0, 15, 30, 60, 90 and 120 min after glucose load or mixed meal load.</p><p><b>RESULTS</b>The first peak value of GIP after glucose load occurred at 15 min (45.09∓4.67 pmol/L). After a brief decline, GIP continued to increase till reaching 59.66∓11.73 pmol/L at 120 min after the load. After the mixed meal load, GIP secretion presented with two peaks: the first peak appeared at 15 min (71.69∓14.19 pmol/L) with a level significantly higher than that at 15 min following glucose load (P<0.05), and the second occurred at 90 min (55.35∓13.19 pmol/L). The area under curve of GIP showed no significant difference between the two loads (P>0.05). Compared with glucose load, mixed meal load resulted in an increase of the first GIP peak and an earlier insulin peak (30 min vs 60 min), but a significant decrease of blood glucose at 15 min (P<0.05).</p><p><b>CONCLUSION</b>Compared with glucose load, mixed meal (containing fat) can strongly stimulate GIP release and cause earlier occurrence of the insulin peak, which might be an important reason for the lower blood glucose after mixed meal.</p>

The Role of the Sweet Taste Receptor in Enteroendocrine Cells and Pancreatic beta-Cells

The sweet taste receptor is expressed in taste cells located in taste buds of the tongue. This receptor senses sweet substances in the oral cavity, activates taste cells, and transmits the taste signals to adjacent neurons. The sweet taste receptor is a heterodimer of two G protein-coupled receptors, T1R2 and T1R3. Recent studies have shown that this receptor is also expressed in the extragustatory system, including the gastrointestinal tract, pancreatic beta-cells, and glucose-responsive neurons in the brain. In the intestine, the sweet taste receptor regulates secretion of incretin hormones and glucose uptake from the lumen. In beta-cells, activation of the sweet taste receptor leads to stimulation of insulin secretion. Collectively, the sweet taste receptor plays an important role in recognition and metabolism of energy sources in the body.

Glucose-dependent insulinotropic peptide in Type 2 diabetes after gastric bypass surgery / 中南大学学报(医学版)

Glucose-dependent insulinotropic peptide (GIP), the incretins, is synthesized and released from the duodenum and proximal jejunum. Continual high-fat diet powerfully stimulated GIP secretion, leading to obesity and harmful lipid deposition in islet cells and peripheral tissues, and giving rise to insulin resistance and major disturbances in the secretion of insulin. We can improve Type 2 diabetes by compromising GIP action. The exclusion of proximal small intestine and reduction of GIP secretion may be the important reasons for Type 2 diabetes after gastric bypass surgery.

Insulin is secreted upon glucose stimulation by both gastrointestinal enteroendocrine K-cells and L-cells engineered with the preproinsulin gene

Transgenic mice carrying the human insulin gene driven by the K-cell glucose-dependent insulinotropic peptide (GIP) promoter secrete insulin and display normal glucose tolerance tests after their pancreatic p-cells have been destroyed. Establishing the existence of other types of cells that can process and secrete transgenic insulin would help the development of new gene therapy strategies to treat patients with diabetes mellitus. It is noted that in addition to GIP secreting K-cells, the glucagon-like peptide 1 (GLP-1) generating L-cells share/ many similarities to pancreatic p-cells, including the peptidases required for proinsulin processing, hormone storage and a glucose-stimulated hormone secretion mechanism. In the present study, we demonstrate that not only K-cells, but also L-cells engineered with the human preproinsulin gene are able to synthesize, store and, upon glucose stimulation, release mature insulin. When the mouse enteroendocrine STC-1 cell line was transfected with the human preproinsulin gene, driven either by the K-cell specific GIP promoter or by the constitutive cytomegalovirus (CMV) promoter, human insulin co-localizes in vesicles that contain GIP (GIP or CMV promoter) or GLP-1 (CMV promoter). Exposure to glucose of engineered STC-1 cells led to a marked insulin secretion, which was 7-fold greater when the insulin gene was driven by the CMV promoter (expressed both in K-cells and L-cells) than when it was driven by the GIP promoter (expressed only in K-cells). Thus, besides pancreatic p-cells, both gastrointestinal enteroendocrine K-cells and L-cells can be selected as the target cell in a gene therapy strategy to treat patients with type 1 diabetes mellitus.

Incretinas, Incretinomiméticos, Inhibidores de DPP IV: 1er parte / Incretins, Incretinmimetics, Inhibitors

En los últimos años se reconoce un nuevo mecanismo involucrado en la fisiopatología de la Diabetes Mellitus tipo 2: el déficit de producción y/o acción de las incretinas. Las incretinas son enterohormonas que estimulan la secreción de insulina en respuesta a la ingesta de nutrientes. Glucagon like péptido-1 (GLP1) y Polipéptido insulinotrópico glucosa dependiente (GIP) son las principales incretinas descubiertas hasta hoy. Ambas presentan también efecto trófico sobre las células beta de los islotes pancreáticos. GLP-1 presenta otras acciones como son la inhibición de la secreción de glucagón, enlentecimiento del vaciamiento gástrico e inhibición del apetito. Ambas incretinas son rápidamente clivadas por la enzima dipeptidil peptidasa 4 (DPP-4). Nuevas drogas como los incretinomiméticos, análogos y los inhibidores de DPP-4 se presentan como una terapéutica prometedora para los pacientes con diabetes tipo 2.

Two main patophysiological mechanisms are currently involved in Type 2 Diabetes (T2DM), insulin resistance and impairment of beta cell function. However in the last years a new mechanism was reported: a significant decrease in incretins production and or action. Incretins are gut hormones whose main action is stimulating insulin secretion in response to nutrients. The more known incretins are glucagon like peptide-1 (GLP-1) and Gastric insulinothropic peptide (GIP). GLP-1 and GIP not only increase insulin secretion, nor decrease glucagon secretion, slow gastric emptying and reduce apetite generating weight lose. Both incretins are rapidly clived by the enzyme dipeptidil peptidase 4 (DPP4). In order to emulate incretins action, several drugs where developed: agonists of GLP-1 receptors, GLP-1 mimetics, and inhibitors of the DPP4. All of them seems to became a very promise tool for the treatment of T2DM.

Treatment of Type 1 Diabetes through Genetically Engineered K-cell Transplantation in a Mouse Model / 당뇨병

BACKGROUND: K-cells function as targets for insulin gene therapy. In a previous study, we constructed EBV-based plasmids expressing rat preproinsulin controlled by glucose-dependent insulinotropic polypeptide promoters. In the present study, we attempted to correct hyperglycemia in vivo using genetically engineered K-cells in a mouse model of type 1 diabetes. METHODS: K-cells expressing insulin were transplanted under the kidney capsules of STZ-induced diabetic mice. The blood glucose levels and body weights of the experimental animals were measured daily. After four weeks, the mice were injected intra-peritoneally with 2 g/kg glucose following a 6 hr fast. Blood glucose levels were measured immediately following glucose injections. All animals were sacrificed at the end of the glucose tolerance study, and pancreas and graft-bearing kidney tissue samples were stained with antibodies against insulin, glucagon, and C-peptide. RESULTS: The body weights of K-cell-transplanted diabetic mice increased after transplantation, whereas those of untreated diabetic control mice continued to decline. The blood glucose levels of K-cell-transplanted diabetic mice decreased gradually during the two weeks following transplantation. After intra-peritoneal injection of glucose into K-cell-transplanted diabetic mice, blood glucose levels increased at 30 minutes, and were restored to the normal range between 60 and 90 minutes, while untreated control diabetic mice continued to experience hyperglycemia. Kidney capsules containing transplanted K-cells were removed, and sections were stained with anti-insulin antibodies. We detected insulin-positive cells in the kidney capsules of K-cell-transplanted diabetic mice, but not in untreated control mice. CONCLUSION: We detected glucose-dependent insulin secretion in genetically engineered K-cells in a mouse model of type 1 diabetes. Our results suggest that genetically modified insulin producing K-cells may act as surrogate beta-cells to effectively treat type 1 diabetes.

Gastrin, secretin, GIP and VIP alter levels of IL-2 and IFN-gamma in human peripheral blood mononuclear cells under various culture conditions

Gastrointestinal hormones have traditionally been viewed as mere regulators of gut movement and secretions, but, it is becoming increasingly apparent that other body systems may be affected by these hormones. Secretion of gut hormones is influenced by the type of food we take. Therefore, the more we know about the effects of gut hormones on the various body tissues, the more we know about the different mechanisms by which our diets affect our health. This in vitro study aimed to explore the effects of physiologically-relevant concentrations of four gut hormones on the production of IL-2 and IFN-gamma by human peripheral blood mononuclear cells and how culture conditions may modif_ those effects. Peripheral blood mononuclear cells were separated by density gradient centrifugation from the blood of 15 adults. Cells were cultured with/without PHA and treated with four concentrations of gastrin, secretin, GIP and VIP. IL-2 and IFN-gamma in culture supernatants were assayed by ELISA. Gastrin, secretin, GIP and VIP increased IL-2 and TFN-gamma levels under some culture conditions and depressed lL-2 under other conditions. An increase was oflen observed under culture conditions in which the cytokine production was not initially high. Repeated administration of the hormone was also more likely to result in a stimulatory effect. Physiologically-relevant concentrations of gastrin, secretin, GIP and VIP are potential immunomodulators as they have shown their ability to alter the production of IL-2 and/or IFN-gamma under various culture conditions

Perfil de expressão de genes modulados pela amilina em ilhotas pancreáticas de rato / Gene expression profile of genes modulated by amylin in rat pancreatic islets

O Diabetes Mellitus tipo 2 (DM 2) é uma doença crônica na qual os pacientes apresentam capacidade secretória de insulina inadequada para suplantar a resistência insulínica concomitante e, como resultado, advém a hiperglicemia. Os mecanismos que explicam a diminuição da secreção insulínica não são completamente conhecidos e acredita-se que o depósito de amilina, um achado histopatológico freqüente nesses pacientes, esteja envolvido. A amilina humana é uma proteína co-secretada com a insulina capaz de se agregar e se depositar nas ilhotas pancreáticas. Ainda não está totalmente estabelecido se a toxicidade da amilina humana é mediada pelas fibrilas maduras, conforme demonstrado em trabalhos mais antigos, ou por oligômeros de tamanho intermediário, como tem sido aventado nos trabalhos mais recentes. O objetivo deste estudo foi avaliar o perfil de genes modulados por oligômeros, bem como por fibrilas maduras de amilina, em ilhotas pancreáticas de rato. As ilhotas foram isoladas a partir de ratos Wistar, mantidas em cultura por 24 horas e a seguir tratadas com 10 M de oligômeros ou de fibrilas maduras de amilina por 24 horas adicionais em concentração fisiológica ou suprafisiológica de glicose. O RNA total foi extraído e utilizado para análise da expressão gênica por microarranjos de DNA. O conteúdo de RNA de alguns genes modulados nas condições experimentais estudadas também foi avaliado por RT-qPCR, a fim de validar os resultados obtidos pela análise de microarranjos. A análise das vias significativamente afetadas pelas preparações de amilina demonstrou que, em ilhotas mantidas em concentração fisiológica de glicose, os oligômeros de amilina modularam, entre outros, processos relacionados à Resposta ao Estresse e à Apoptose, processos não modulados pelas fibrilas maduras de amilina. Em concentração suprafisiológica de glicose, o tratamento com oligômeros de amilina deixou de modular as vias relacionadas a Estresse e Apoptose, surgindo como moduladas...

Type 2 diabetes mellitus is a chronic disease in which there is inability of pancreatic cells to secrete sufficient insulin to overcome the insulin resistance in the peripheral tissues with resultant hyperglycemia. Mechanisms leading to diminished insulin secretion are not completely known and the amyloid deposit, a frequent histopathological finding in patients with type 2 diabetes, is believed to be involved. Human amylin, a protein co-secreted with insulin, is capable of aggregating and forming deposits in the pancreatic islets. It is not fully established whether amylin cytotoxicity is mediated by mature amylin fibrils or by soluble oligomers. The objective of this study was to evaluate the gene profiling modulated by oligomers as well as by mature amylin fibrils in rat pancreatic islets. The islets were isolated from Wistar rats, maintained in culture for 24 hours and then treated with 10 M of oligomers or mature amylin fibrils for additional 24 hour in physiologic and supraphysiologic glucose concentrations. Total RNA was extracted and used for gene expression analysis by microarray. RNA content of some modulated genes was evaluated by RT-qPCR in order to validate the results obtained from the microarray analysis. The analysis of the pathways significantly affected by the two amylin preparations demonstrated that, in islets maintained in physiological glucose concentration, amylin oligomers modulated, among others, processes related to Response to stress and to Apoptosis, which were not modulated by mature amylin fibrils. In supraphysiological glucose concentration, treatment with oligomers did not modulate the pathways related to Stress and Apoptosis, which were replaced by processes related to Endocytosis regulation and Nitric oxide biosynthesis. RT-qPCR results suggested that only amylin oligomers modulate genes related to apoptosis (Anxa1, Rab5a) and oxidative stress (Nos2 e Xdh), which is in agreement with studies indicating a role...

Estudo da expressão dos receptores do peptídeo insulinotrópico dependente de glicose (GIPR) e do hormônio luteinizante (LHCGR) em tumores e hiperplasias do córtex adrenal / Expression study of glucose-dependent insulinotropic peptide receptor (GIPR) and luteinizing hormone receptor (LHCGR) in adrenocortical tumors and hyperplasia

O objetivo deste estudo foi quantificar por PCR em tempo real a expressão dos genes dos receptores do peptídeo insulinotrópico dependente de glicose (GIPR) e do hormônio luteinizante (LHCGR) em tumores e hiperplasias adrenocorticais (hiperplasia adrenal macronodular independente de ACTH; doença nodular adrenocortical pigmentosa primária e aumento da adrenal associado à neoplasia endócrina múltipla tipo 1). O nível de expressão do GIPR foi mais elevado nos tumores malignos que nos benignos em pacientes adultos e pediátricos, enquanto o nível de expressão do LHCGR foi extremamente baixo nos tumores malignos em pacientes adultos. Não se observou diferença no nível de expressão de ambos os receptores nas diferentes formas de hiperplasia.

The aim of this study was to quantify by real-time PCR the gene expression of glucose-dependent insulinotropic peptide receptor (GIPR) and luteinizing hormone receptor (LHCGR) in adrenocortical tumors and hyperplasia (ACTH-independent macronodular adrenal hyperplasia, primary pigmented nodular adrenocortical disease and adrenal enlargement associated with multiple endocrine neoplasia type 1. The GIPR expression level was more elevated in the malignant tumors that in the benign ones, of both adult and pediatric patients, whereas the level of LHCGR expression was extremely low in malignant tumors of adult patients. No difference in the expression level of these receptors was observed in the different forms of adrenocortical hyperplasia.

Impairment of the insulinotropic effect of gastric inhibitory polypeptide [GIP] in obese and diabetic rats is related to the down-regulation of its pancreatic receptors

The association of obesity with type 2 diabetes has been recognized for years. Insulin resistance induced by obesity increases the chances of developing diabetes mellitus in which insulin release is markedly reduced. In type 2 diabetes, there is a possibility that an important part of the impaired insulin secretion is due to loss of the insulinotropic effect of the gastric inhibitory polypeptide [GIP] hormone. The aim of this study was to detect changes that occur in the pancreatic GIP receptor expression and in GIP secretion in obese and type 2 diabetic rats in response to oral glucose administration and its relation to glucose and insulin plasma levels during oral glucose tolerance test [OGTT]. Three groups of rats [n=10/ group] were included in this study: A control group receiving standard chow for 10 weeks, an obese group, in which obesity was induced by feeding rats standard chow with the addition of 32% of the caloric intake as fat for 10 weeks and a type 2 diabetic group, receiving the standard chow with the addition of fructose as 66% of the caloric intake for 10 weeks. Parameters measured in all groups included: Obesity index, systolic blood pressure, serum triglycerides as well as plasma glucose, insulin and GIP levels at 0, 5, 10, 20, 60, 90 and 120min. of an OGTT and pancreatic islets GIP receptors gene expression [GIP-Rs] using PCR method. At the end of 10 weeks, the obese and diabetic groups both had significantly increased fasting plasma glucose levels and insulin resistance indices [HOMA-IR], in addition to significantly higher blood pressure and serum triglycerides levels compared to the control group, indicating the presence of insulin resistance. In addition, the obese group had a significantly increased obesity index and fasting GIP level compared to the control and diabetic groups. During the first 20min. following oral glucose intake, both the obese and the diabetic rats had a significant increase in the glucose excursion compared to that of the control group, with a more significant increase in the diabetic group compared to the obese group. Both the obese and diabetic groups had a significant decrease of early-insulin secretion compared to control, with a more significant decrease in the diabetic group compared to the obese group. During the first 20min. of the OGTT, there was also a significant increase in the incremental change of GIP from 0 to 20min [GIP delta 0-20] in the obese group [60.1 +/- 6.66pmol/L] compared to that of the control [33.96 +/- 4.69pmol/L] and the diabetic [29.34 +/- 2.62pmol/L] groups, which were not significantly different from each other. However, there was a significant decrease of GIP-Rs expression in both the obese [88.07 +/- 10.36 micro g/ml] and the diabetic [87.51 +/- 4.72 micro g/ml] groups compared to the control group [120.35 +/- 8.06 micro g/ml], indicating that the loss of the GIP insulinotropic effect in obese and diabetic rats during the first 20min. of OGTT was due to a reduction in pancreatic GIP-Rs. During the next 20 to 120min. following oral glucose load, plasma GIP was decreasing in all groups, however, the obese group had a significantly increased plasma glucose level compared to the control group and a significant hyperinsulinemia compared to the other two groups. Such hyperinsulinemia in the presence of a decreasing GIP secretion and reduced GIP-Rs indicates the possibility of up-regulation of another compensatory mechanism to overcome the GIP-Rs defect. Moreover, the diabetic group had a significantly increased plasma glucose level compared to that of the other two groups and its plasma insulin level was significantly lower than that of the control group until the 90min. interval and thereafter it showed a non-significant difference with that of the control group. This study revealed that both obese and diabetic rats had an impaired insulinotropic effect of GIP in response to oral glucose administration during OGTT due to impaired gene expression of its pancreatic receptors and not due to impaired secretion. Also there was an associated compensatory hyperinsulinemia in obese rats during the second hour of the OGTT, which may lead to exhaustion of B-cells on the long run, increasing the incidence of diabetes mellitus. Therefore GIP-Rs could be a potential target to prevent transition of obesity to diabetes and to improve insulin secretion in type 2 diabetes mellitus