REVISTA ARGENTINA DE ENDOCRINOLOGÍA Y METABOLISMO
González, C.D.1; Santoro, S.G.2; Sinay, I. 3
El propósito de este trabajo es revisar las estrategias farmacológicas específicamente destinadas a disminuir la insulinorresistencia. Se plantean cuatro objetivos, siendo el primero la inhibición de la producción hepática de glucosa. Aquí se incluye a la metformina, biguanida que reduce la gluconeogénesis desde lactato y aumenta la actividad de la AMPK (enzima que estimula la oxidación de ácidos grasos no esterificados y disminuye la gluconeogénesis y síntesis de colesterol). También se encuentran el BAY-27-9955 y NNC-25-2504L (antagonistas del glucagon), y los inhibidores de la glucógeno fosforilasa hepática, glucógeno sintasa-kinasa-3, piruvatodeshidrogensa- kinasa, fructosa-1,6-difosfatasa y glucosa-6-fosfatasa. Los insulinosensibilizadores, segundo objetivo, incluyen a tiazolidinodionas (agonistas PPARg) que aumentan la exposición de GLUT 4, lipogénesis y disminuyen la gluconeogénesis; y a drogas en desarrollo: nuevos agonistas PPAR, activadores RxR, agonistas b3 e inhibidores de la PTB-1B. El tercer objetivo son los modificadores del metabolismo lipídico, y contiene a los inhibidores de la 11b-HSD1. Los activadores del receptor insulínico, dependientes e independientes de insulina, constituyen el cuarto objetivo. La importancia del desarrollo de nuevos fármacos radica en que el control de la insulinorresistencia retrasaría la aparición de diabetes 2, e implicaría un menor riesgo cardiovascular
Insulin-resistance is the pathophysiological expression of the metabolic syndrome. Therefore, it is intimately related to obesity, hypertension, diabetes and hyperlipidemia. The aim of this article is to review the pharmacological strategies specifically assigned to lower insulin-resistance, and to describe a number of projects in this area which might achieve certain success in the future. According to Laborde and Manchem 3 the following pharmacological aims can be considered: hepatic glucose production inhibitors, insulin-sensitizers, lipid metabolism modifiers, and insulin receptor activators, among others. In the first group biguanides, glucagon receptor acantagonists, and inhibitors of glycogen synthase-kinase, hepatic glycogen-phosphorilase, pyruvate-dehydrogenase- kinase, fructose 1,6-biphosphatase and glucose–6-phosphate are included. Metformin, a biguanide, lowers with a intermediate efficacy the hepatic output of glucose. As regards its mechanism of action, it inhibits the complex I of the respiratory chain, consequently stimulating pyruvate kinase and inhibiting pyruvate-carboxilase, therefore glyconeogenesis from lactate is reduced 4-5. It also stimulates AMPK which enhances non sterified fatty acid oxidation, and lowers hepatic glucose and cholesterol production 7. In addition, it has effects on certain factors associated to macrovascular disease (lowers PAI-1, factor VII, fibrinogen and platelet adhesion) and an anti-inflammatory activity 7. There are two non peptidic molecules, BAY-27-9955 12 and NNC-25-250413, capable of antagonize the effects of glucagon in the hepatic production of glucose. With reference to the inhibition of glycogen synthase kinase 3, there are six families of agents in early development 14, as well as the other groups of inhibitors of the hepatic production of glucose. Among the insulin-sensitizers, thiazolidinediones, PPARg agonists, are well known for lowering insulin-resistance by raising the expression of GLUT 4, enhancing lipogenesis, reducing non sterified fatty acids and the use of glucose by the muscle, lowering hepatic glyconeogenesis and stimulating hepatic glucose intake. Furthermore they produce a down regulation of TNFa, interleukine 6 and resistin (apparently linked to the development of insulin-resistance) 16. An anti-inflammatory, anti-atherogenic as well as an anti-hypertensive effect have been reported 17-18. In addition, table 1 shows diverse PPAR agonists in development. Moreover, there are some agents capable of activating the RxR receptor, which is a protein that after linking PPARg stimulates the transcription of certain molecules related to glucose metabolism 21. Another target related to insulin-sensibilization is the stimulation of b3 adrenergic receptor. However, there are two main problems related to their use in humans: lack of enough specificity and biodisponibility. Table 2 shows the state of these projects 20. Another possibility is the inhibition of PTB-B1, an enzyme that ends insulin intracellular signal. Table 3 shows the projects in this area 20. The third group, lipid modifiers, is referred mainly to inhibitors of 11b-HSD 1, an enzyme that catalyzes the conversion of cortisone to cortisol. Among them, thiazolidinediones, BVT-2733 and carbenexolone analogs can be considered 25-26. Finally, insulin receptor activators can be subdivided in those independent of insulin (L-783281, which do not need insulin for their activity) and dependent of insulin (TLK-16998) 3. Concluding: as insulin-resistance precedes type 2 diabetes mellitus, and is probably an independent risk factor for cardiovascular disease 28, the development of specific drugs for its treatment acquires major importance for the prevention and management of those entities 27.