Alzheimer’s disease (AD), a progressive neurodegenerative disorder that deprives the patient of memory, is associated mainly with extracellular senile plaque induced by the accumulation of amyloid β protein (Aβ). Silybum marianum (Asteraceae; SM) is a medicinal plant that has long been used in traditional medicine as a hepatoprotective remedy owing to its antioxidant and anti-inflammatory activities. The present study examined the methanol extract of the aerial parts of SM for neuroprotection against Aβ (25-35)-induced neuronal death in cultured rat cortical neurons to investigate a possible therapeutic role of SM in AD. The primary cortical neuron cultures were prepared using embryonic day 15 to 16 SD rat fetuses. Cultured cortical neurons exposed to 10 μM Aβ (25-35) for 36 h underwent neuronal cell death. At 10 and 50 μg/mL, SM prevented Aβ (25-35)-induced neuronal cell death and apoptosis in cultured cortical neurons. Furthermore, SM inhibited the Aβ (25-35)-induced decrease in anti-apoptotic protein, Bcl-2, and the increase in the proapoptotic proteins, Bax and active caspase-3. Cultured cortical neurons exposed to 1 mM N-methyl-D-aspartate (NMDA) for 14 h induced neuronal cell death. SM (10 and 50 μg/mL) prevented NMDA-induced neuronal cell death. These results suggest that SM inhibited Aβ (25-35)-induced neuronal apoptotic death via inhibition of NMDA receptor activation and that SM has a possible therapeutic role in preventing the progression of neurodegeneration in AD.

Introduction
 Materials and Methods
  Plant materials and extraction and reagents
  Experimental animals
  Induction of neurotoxicity and analysis of neuronalviability in primary cultures of rat cerebral corticalneurons
  Western blotting
  Statistical analysis
 Results
  Protective effect of SM against Aβ (25-35)-inducedneuronal cell death
  Inhibitory effect of SM on Aβ-induced change ofapoptosis-associated proteins
  Protective effect of SM against NMDA-inducedneuronal cell death
 Discussion
 References

• Hae Min Lee(College of Veterinary Medicine and Veterinary Medical Center, Chungbuk National University, Cheongju 28644, Korea)
• Ji Yeon Jang(College of Veterinary Medicine and Veterinary Medical Center, Chungbuk National University, Cheongju 28644, Korea)
• Yeon Hee Seong(College of Veterinary Medicine and Veterinary Medical Center, Chungbuk National University, Cheongju 28644, Korea) Corresponding author