IS APELIN A PROMISING TARGET IN DIABETES MELLITUS OF RATS: TYPE I VS. TYPE II?

Abstract

Background: Apelin is a novel adipokine identified as an endogenous ligand of receptor APJ. Apelin and its receptor APJ are expressed in a wide variety of tissues including heart, brain, kidneys and lungs. Apelin in human physiology acts as a regulating peptide of cardiovascular, hypothalamus-hypophysis, metabolic, gastrointestinal and immune systems.
Objective: The present study was carried out to assess the value of apelin in management of type II vs. type I diabetes mellitus in rats.
Design: A total number of 60 healthy adult male albino rats were used. Rats were divided into 2 groups: group I (n=40) Streptozotocin induced diabetic group; model of type I diabetes and group II (n=20) high fat diet induced obesity and diabetic group; model of type II diabetes. Group I was subdivided into 4 equal subgroups (saline treated control, an insulin treated, an apelin treated and an apelin and insulin treated subgroups), while group II was further subdivided into 2 equal subgroups (a saline treated control and an apelin treated groups). In all groups the body weight, nose to anus length were measured, and these data were used to calculate the body mass index (BMI). In addition, serum glucose, insulin, triglycerides, total cholesterol, LDL and HDL cholesterol were estimated and used to calculate the homeostasis model assessment as a measure of insulin resistance (HOMA-IR) and the homeostasis model assessment as a measure of β cell function (HOMA-β).
Results: This study revealed that an intraperitoneal injection of apelin induced insignificant changes in most of parameters measured in animals of group I when compared with insulin treated subgroup. On the other hand, animals of group II showed a significant decrease in serum levels of glucose and insulin when compared with saline treated controls with resulting a significant decrease in HOMA-IR and a significant increase in HOMA- β. Furthermore, apelin injection induced a significant increase in serum triglyceride, total cholesterol and LDL cholesterol levels and insignificant changes in HDL cholesterol levels in group II rats.
Conclusion: In models of type II diabetes, apelin significantly induced amelioration of serum glucose level and enhance insulin sensitivity that was denoted by a significant reduction in HOMA-IR, this was not the case in rats of type I diabetes, so it is promising therapeutic target in management of obesity induced type II diabetes rather than type I.
Key words: Apelin, type II diabetes, high fat diet (HFD), Streptozotocin induced diabetes, HOMA-IR, HOMA-β, obesity.