Diabetes was induced by a single intraperitoneal injection of streptozotocin (Sigma, St. Louis, MO, USA) at a dose of 40 mg/kg [18 (link)19 (link)]. streptozotocin was freshly prepared in 10 mM citrate buffer (pH 4.6), and non-diabetic control animals were injected with citrate buffer only. Blood glucose concentrations were monitored using an Accu-ChekĀ® Active (Roche Diagnostics GmbH, Mannheim, Germany) glucose meter and diabetes mellitus was defined as hyperglycemic conditions with a glucose concentration exceeding 300 mg/dL. The body weight was decreased dose- and time dependent after streptozotocin injection [20 21 (link)].