ABSTRACT
ObjectiveTo observe the pharmacodynamic effects of Cinnamomi Cortex on the incretin effect in the rat model of diabetes mellites （DM） induced by streptozotocin （STZ） and explore the underlying mechanism from glucagon-like peptide-1 （GLP-1） and dipeptidyl peptidase-4 （DPP-4）. MethodForty SD rats were randomly assigned into blank， model， sitagliptin （0.1 g·kg-1）， and low- and high-dose Cinnamomi Cortex （0.45 and 0.9 g·kg-1， respectively） groups. The DM rat model was established by a high-fat diet combined with intraperitoneal injection of 40 mg·kg-1 STZ in other groups except the blank group. The intervention lasted for 8 weeks. The status， body weight， water intake， food intake， and fasting blood glucose （FBG） of the rats were observed and determined. Hematoxylin-eosin staining was employed to reveal the pathological changes of the pancreas， and immunohistochemistry to detect the expression of glucagon in the pancreas. Biochemical assay was employed to measure the serum levels of lipid metabolism indexes such as total cholesterol （TC）， triglyceride （TG）， low-density lipoprotein （LDL）， and high-density lipoprotein （HDL）. Enzyme-linked immunosorbent assay was employed to determine the levels of glycosylated hemoglobin， insulin， glucagon， GLP-1， and glucose-dependent insulinotropic polypeptide （GIP） in rat serum， and Western blot to determine the protein levels of GLP-1 and DPP-4 in the pancreas. ResultAfter 8 weeks of intervention， the model group showed higher body weight， FBG， TC， TG， LDL， glycosylated hemoglobin， glucagon， insulin， and insulin resistance index and lower HDL， GLP-1， and GIP than the blank group （P<0.05， P<0.01）. The Cinnamomi Cortex groups showed lower body weight， FBG， TC， TG， LDL， glycosylated hemoglobin， glucagon， insulin， and insulin resistance index and higher HDL， GLP-1， and GIP than the model group （P<0.05， P<0.01）. The Cinnamomi Cortex groups showed recovered morphology of islet cells and no nucleus aggregation. Compared with the model group， the Cinnamomi Cortex groups showed declined levels of glucagon in the center of islet cells. Compared with the blank group， the model group showed up-regulated protein level of DPP-4 and down-regulated protein level of GLP-1 （P<0.01）. Compared with the model group， the high-dose Cinnamomi Cortex groups showed down-regulated protein level of DPP-4 and up-regulated protein level of GLP-1 （P<0.05）. ConclusionCinnamomi Cortex may reduce blood glucose and improve incretin effect to lower the blood glucose level by regulating DPP-4 and GLP-1 in DM rats.
ABSTRACT
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.
Subject(s)
Humans , Insulin Resistance , Diabetes Mellitus, Type 2 , Diabetes Mellitus, Type 2/drug therapy , Blood Glucose , Gastric Inhibitory Polypeptide/metabolism , Incretins , Fatty Acids, Nonesterified , Insulin Secretion , Insulin/metabolismABSTRACT
La diabetes mellitus tipo 2 es una enfermedad metabólica crónica, frecuente y progresiva, responsable del 90% de los casos de diabetes a nivel mundial. Aproximadamente el 60% de los individuos que padecen este desorden no alcanzan niveles óptimos de hemoglobina glicosilada, a pesar de la disponibilidad de numerosas alternativas terapéuticas. Los dos objetivos más importantes a cumplir en el manejo actual de la diabetes tipo 2 son la capacidad de los agentes antidiabéticos de exhibir eficacia prolongada y la capacidad de preservar la función de las células beta pancreáticas. El efecto incretina se encuentra reducido en pacientes con diabetes tipo 2. Exenatida pertenece a un nuevo grupo de drogas antidiabéticas que mejoran el control de la glucemia en estos pacientes a través de mecanismos fisiológicos glucorregulatorios que mejoran el efecto incretina. Los ensayos clínicos fase III con exenatida demostraron una reducción media de aproximadamente el 1% en los valores de hemoglobina glicosilada. Los datos a largo plazo de estudios de extensión no controlados indican una mejoría sostenida en los niveles de hemoglobina glicosilada y una reducción progresiva del peso luego de 3 años de tratamiento con esta droga. La droga es generalmente bien tolerada y los efectos adversos más frecuentes son los gastrointestinales, con una intensidad leve a moderada. El objetivo de esta revisión es analizar la evidencia publicada hasta la fecha sobre la eficacia y tolerabilidad del tratamiento con exenatida y su rol en el tratamiento de la diabetes tipo 2.
Type 2 diabetes mellitus is a common, chronic and progressive metabolic disorder, which accounts for 90% of diabetes cases worldwide. Approximately 60% of individuals with the disease do not achieve target glycosylated hemoglobin levels, despite the availability of many antidiabetic agents. The two most important needs in the present management of diabetes are the ability of antidiabetic agents to exhibit prolonged efficacy in reducing hyperglycemia and to preserve beta-cell function. The incretin effect appears to be reduced in patients with type 2 diabetes. Exenatide is the first in a novel class of antidiabetic drugs that improves glycemic control in patients with type 2 diabetes through several physiological glucoregulatory mechanisms which improve the incretin effect. Overall, mean glycosylated hemoglobin (HbA1c) reductions achieved in the exenatide phase III clinical trials were in the order of 1%. Long-term data from the uncontrolled open-label extension studies indicate that adjunctive exenatide therapy leads to sustained improvements in HbA1c and progressive weight loss for at least 3 years. The drug is generally well tolerated. The most common adverse events were gastrointestinal in nature and mild to moderate in severity. The objective of this review is to discuss the available published evidence on exenatide therapeutic efficacy and tolerability, and the role of this new drug in the treatment of type 2 diabetes.