Protective Effect of Apelin-13 on Kidney and Platelet Functions in Adenine-Induced Chronic Renal Failure in Rats

Abstract
Background: Apelin and angiotensin I receptor-related protein J receptor (APJ) were found to be expressed in the kidney. Also, in cases of Chronic Renal Failure (CRF), platelet function was found to be affected. Apelin-13 treatment effect on both kidney and platelet functions in cases of CRF was not fully understood.
Aim of Study: To investigate the possible protective effect of apelin-13 on kidney and platelet function in adenine-induced CRF in rats.
Material and Methods: Rats were divided into three groups of eight rats each as follow: Intact control group received a standard diet for 28 days, adenine treated group received a standard diet added to it adenine (0.75% w/w) for 28 days, and adenine + apelin treated group received a standard diet added to it adenine as in the adenine treated group with a concomitant treatment with apelin-13 for 28 days. Apelin-13 was dissolved in saline immediately before use and was given at a dose of 5μg/kg body weight/day subcutaneously. 24-hour urine samples were collected, and 24-hour water intake was estimated on the 28th day of the study, while each rat was kept in a separate metabolic cage. The collected urine samples were measured for volume, total protein, and creatinine levels. After 28 days from the start of the experimental period, rats were fasted overnight, and their blood pressure was measured using the Power Lab. Blood samples were collected and a part of it was placed in heparinized tubes to investigate platelet indices and another part of blood was kept in non-heparinized tubes which were left to clot for 30min at room temperature. Clotted blood was centrifuged at 3000rpm for 15min. The supernatant serum was pipetted off using fine tipped automatic pipettes and stored at –20ºC until assayed.
Results: Treatment with adenine (0.75%, w/w) for 28 days caused a significant decrease (p<0.001) in Body Mass Index (BMI) and a significant increase (p<0.001) of the relative kidney weight when compared with that of the control group. On concomitant treatment with apelin-13 and adenine significantly mitigated (p<0.001) the adenine-induced reduction in BMI and the increase in relative kidney weight. Water intake and urine output of adenine treated rats were signifi-cantly higher (p<0.001) than that in control rats, while, simultaneous treatment with adenine and apelin-13 signifi-cantly decreased (p<0.001) both in comparison to adenine treated group. Also, in comparison with control group, the serum levels of creatinine, uric acid and urea were enhanced significantly (p<0.001) in adenine treated group, indicating that adenine-induced CRF model has been successfully estab-lished in this experiment. However, these enhancements were significantly decreased (p<0.001) by concomitant treatment with apelin-13. On the other hand, there was a significant decrease (p<0.001) in the creatinine clearance in adenine treated group in comparison to the control one, however, simultaneous treatment with adenine and apelin-13 signifi-cantly deteriorated this effect. Also, in this study, comparing to those of normal group, the Superoxide Dismutase (SOD) and Glutathione Reductase (GR) levels in adenine treated group were significantly decreased (p<0.001) while, Malonal-dehyde (MDA) was significantly increased (p<0.001). The alteration of SOD, GR and MDA serum levels was remarkably reversed by concomitant treatment with apelin-13. A significant increase (p<0.001) in platelet count, Mean Platelet Volume (MPV), Platelet Distribution Width (PDW) and plateletcrit, but a significant decline (p<0.001) in bleeding time in adenine treated group in comparison to the control one. These changes were significantly reversed (p<0.001) by the concomitant treatment with adenine and apelin-13 in comparison to the adenine treated group.
Conclusion: Apelin-13 treatment improved both kidney and platelet functions, and may give a promising strategy for slowing the progression of CRF and its complications.