Streptozotocin produces oxidative stress, inflammation and decreases BDNF concentrations to induce apoptosis of RIN5F cells and type 2 diabetes mellitus in Wistar rats

Background: Neurodegenerative disorders, such as deficits in learning, memory and cognition and Alzheimer's disease are associated with diabetes mellitus. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor and is known to possess anti-obesity, anti-diabetic actions and is believed to have a role in memory and Alzheimer's disease. Objective: To investigate whether STZ can reduce BDNF production by rat insulinoma (RIN5F) cells in vitro and decrease BDNF levels in the pancreas, liver and brain in vivo. Methods: Streptozotocin (STZ)-induced cytotoxicity to RIN5F cells in vitro and type 2 DM in Wistar rats was employed in the present study. Cell viability, activities of various anti-oxidants and secretion of BDNF by RIN5F cells in vitro were measured using MIT assay, biochemical methods and ELISA respectively. In STZ-induced type 2 DM rats: plasma glucose, interleukin-6 and tumor necrosis factor-alpha levels and BDNF protein expression in the pancreas, liver and brain tissues were measured. In addition, neuronal count and morphology in the hippocampus and hypothalamus areas was assessed. Results: STZ-induced suppression of RIN5F cell viability was abrogated by BDNF. STZ suppressed BDNF secretion by RIN5F cells in vitro. STZ-induced type 2 DM rats showed hyperglycemia, enhanced plasma IL-6 and TNF-alpha levels and reduced plasma and pancreas, liver and brain tissues (P < 0.001) and increased oxidative stress compared to untreated control. Hypothalamic and hippocampal neuron in STZ-treated animals showed a decrease in the number of neurons and morphological changes suggesting of STZ cytotoxicity. Conclusions: The results of the present study suggest that STZ is not only cytotoxic to pancreatic beta cells but also to hypothalamic and hippocampal neurons by inducing oxidative stress. STZ ability to suppress BDNF production by pancreas, liver and brain tissues suggests that impaired memory, learning, and cognitive dysfunction seen in diabetes mellitus could be due to BDNF deficiency. (C) 2017 Elsevier Inc. All rights reserved.