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.

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.