Role of simvastatin and insulin in memory protection in a rat model of diabetes mellitus and dementia

Abstract Objectives The memory protective role of simvastatin and/or insulin, in a rat model of diabetes mellitus (DM) and dementia was examined. Methods DM was induced by an intraperitoneal injection of streptozotocin. Diabetic rats were divided into untreated; insulin treated; simvastatin treated with 10 and 20 mg/kg/day; and combined insulin plus simvastatin treatment in the previous doses. Treatment started after blood glucose elevation and persisted for 6 weeks. Morris water maze and Y maze tests were held to detect behavioral changes. Serum glucose, cholesterol and insulin levels, the hippocampi insulin, amyloid beta (As) 1–42 and oxidative stress markers were measured. Results Insulin increased the time spent in the target quadrant in the Morris water maze test and the percentage of alternations in the Y maze test, despite the mild improvements in brain parameters demonstrated by amyloid beta 1–42, malondialdehyde and reduced glutathione levels; while simvastatin in both doses improved brain parameters with no positive impact on behavioral tests. Insulin combined with simvastatin 20 mg/kg/day was effective in enhancing the behavioral tests and the measured brain parameters. Conclusions Treatment with insulin and simvastatin could provide a promising memory protective effect in diabetics.