ABSTRACT
Diabetes mellitus aggrevates and worsens the brain damage caused by global or focal
cerebral ischemia. The purpose of our study was to explore what is the underlying
mechanism of the exaggerated brain damage caused by diabetic ischemia. In our
experiments we investigated whether there is a difference in the activation of the
mitochondria-dependent apoptotic pathway after ischemic injury in diabetic rats
compared to non-diabetic animals. In further experiments we examined whether
increased free radical production and activation of astrocytes contribute to the
exaggerated brain damage after diabetic ischemia compared to non-diabetic ischemia.
Finally, we investigated the heat shock protein expression and synthesis in
hyperglycemic ischemia. Early activation of apoptotic cell death pathway in diabetic
animals was observed. The results show that the production of free radicals such as
superoxide anion, nitric oxide and peroxynitrite are stimulated in neurons after diabetic
ischemic injury. In astrocytes only nitric oxide production was enhanced. These data
suggest that diabetic ischemia increases peroxynitrite production in neurons by
enhancing the formation of superoxide since peroxynitrite is derived from the reaction
of NO and superoxide. As a reaction to the increased stress caused by hyperglycemia
enhanced the heat shock protein expression and synthesis in neuronal cells. Finally, we
detected reactive astrogliosis in both ischemic groups, although in the diabetic animals
damage of astrocytes was observed early after the ischemic injury. These results draw
attention to the enhanced intracellular events leading to cell damage may further limit
the time-window of the effective therapy, if the patient suffer from diabetes mellitus.