Transferred inter-cell ischemic preconditioning-induced neuroprotection may be mediated by adenosine A1 receptors

Ischemic preconditioning-induced neuroprotection is a well-known phenomenon. We hypothesize that this form of neuroprotection is transferable among the same type of cells. To test this hypothesis, human neuroblastoma SH-SY5Y cells were induced to become neuron-like cells. Primary rat cortical neuronal cultures were also used. These cells were subjected to various lengths of short oxygen-glucose deprivation (OGD, an in vitro simulation of ischemia) and then 1-h OGD. Some cells that were not exposed to a short episode of ischemia were incubated with culture medium from the cells that had 3- or 5-min OGD. Those cells were subjected to OGD for 1h at 1 or 24h after they were exposed to the medium. Cell injury was evaluated at 24h after the 1-h OGD by lactate dehydrogenase release assay. In another experiment, cells subjected to a 3-min OGD or exposed to the medium from cells that had a 3-min OGD were harvested at 30min after the OGD or the medium exposure for Western blotting of Akt, a prosurvival protein. Our study showed that a prior episode of ischemia lasting from 3 to 10min significantly reduced the 1-h OGD-induced cell injury. Medium from cells subjected to a 3-min OGD also induced acute and delayed phases of neuroprotection in OGD-naïve human neuron-like cells and primary rat cortical neuronal cultures. Cells subjected to a 3-min OGD or incubated with the medium from cells exposed to a 3-min OGD had increased phosphorylated/activated Akt. The increased phosphorylated Akt and neuroprotection induced by medium transferring were inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), an adenosine A1 receptor inhibitor. The 3-min OGD-induced neuroprotection was inhibited by LY294002, an Akt activation inhibitor. These results suggest that ischemic preconditioning-induced neuroprotection is transferable among the cells. Small molecules, such as adenosine, may mediate this effect.