Catechin and epicatechin from Smilacis chinae rhizome protect cultured rat cortical neurons against amyloid β protein (25-35)-induced neurotoxicity through inhibition of cytosolic calcium elevation

We previously reported that the Smilacis chinae rhizome inhibits amyloid beta protein (25-35) (A beta (25-35))-induced neurotoxicity in cultured rat cortical neurons. Here, we isolated catechin and epicatechin from S. chinae rhizome and also studied their neuroprotective effects on A beta (25-35)induced neurotoxicity in cultured rat cortical neurons. Catechin and epicatechin inhibited 10 mu M A beta (25-35)-induced neuronal cell death at a concentration of 10 mu M, which was measured by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. Catechin and epicatechin inhibited 10 mu M A beta (25-35)-induced elevation of cytosolic calcium concentration ([Ca2+](c)), which was measured by a fluorescent dye, Fluo-4 AM. Catechin and epicatechin also inhibited glutamate release into medium induced by 10 mu M A beta (25-35), which was measured by HPLC, generation of reactive oxygen species (ROS) and activation of caspase-3. These results suggest that catechin and epicatechin prevent A beta (25-35)-induced neuronal cell damage by interfering with the increase of [Ca2+](c), and then by inhibiting glutamate release, generation of ROS and caspase-3 activity. Furthermore, these effects of catechin and epicatechin may be associated with the neuroprotective effect of the S. chinae rhizome. (c) 2006 Elsevier Inc. All rights reserved.