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 β protein (25–35) (Aβ (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 Aβ (25–35)-induced neurotoxicity in cultured rat cortical neurons. Catechin and epicatechin inhibited 10 μM Aβ (25–35)-induced neuronal cell death at a concentration of 10 μM, 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 μM Aβ (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 μM Aβ (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 Aβ (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.