Abstract
Calcineurin (CN) is a Ca(2+)/calmodulin-dependent protein phosphatase expressed at high levels in brain. Many findings have shown that calcineurin plays an important role in tau hyperphosphorylation, which is one of the neuropathologic features in the brains of Alzheimer's disease (AD). Based on the molecular screening model using p-nitrophenyl phosphate (p-NPP) as a substrate for preliminary screening and (32)P-labeled 19-residue phosphopeptide as a specific substrate for final determination, we found that the total ginsenoside extracts from stems and leaves of Panax ginseng (GSL) could enhance the phosphatase activity of purified CN. In the human neuroblastoma cells SY5Y, inhibition of CN by cyclosporine A (CsA) could induce hyperphosphorylation of tau at multiple sites, accompanied with oxidative stress. Pretreatment of the cells with GSL prior to CsA exposure could alleviate CsA-induced CN inhibition and tau hyperphosphorylation to some degree. Further oxidative parameters demonstrated that GSL caused increased SOD activity and content of SH significantly. It is speculated that GSL weakens CsA-induced CN inhibition through the antioxidant mechanisms. Although our results indicate that GSL may have neuroprotective effects on some characteristic features of AD, the chemical compositions of GSL and their potential for affecting the disease mechanism need to be further studied.