Protection of amyloid β protein (25–35)-induced neurotoxicity by methanol extract of Smilacis chinae rhizome in cultured rat cortical neurons

Abstract

Smilax has various pharmacological effects including antiinflammatory, anticancer and antioxidant activity. The present study aims to investigate the effect of the methanol extract of Smilacis chinae rhizome (SCR) from Smilax china L. (Liliaceae) on amyloid β protein (Aβ) (25–35), a synthetic 25–35 amyloid peptide, -induced neurotoxicity in cultured rat cerebral cortical neurons. Aβ (25–35) (10 μM) produced a reduction of cell viability, which was significantly reduced by (5 R,10 S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[ a, d]cyclohepten-5,10-imine (MK-801), an N-methyl- d-aspartate (NMDA) receptor antagonist, verapamil, an L-type Ca 2+ channel blocker, and N G -nitro- l-arginine methyl ester ( l-NAME), a nitric oxide synthase inhibitor. SCR, over a concentration range of 10–50 μg/ml, inhibited 10 μM Aβ (25–35)-induced neuronal cell death, which was measured by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. SCR (50 μg/ml) inhibited 10 μM Aβ (25–35)-induced elevation of cytosolic calcium concentration ([Ca 2+] c), which was measured by a fluorescent dye, Fluo-4 AM. Pretreatment of SCR (10 and 50 μg/ml) also inhibited glutamate release into medium induced by 10 μM Aβ (25–35), which was measured by HPLC, generation of reactive oxygen species and activation of caspase-3. These results suggest that SCR prevents Aβ (25–35)-induced neuronal cell damage in vitro.