The enhancement of the neuroprotective properties of Silymarin and Silibinin by the addition of Phosphatidylcholine and various bioantioxidant vitamin E isomers against neurotoxin induced Parkinsonian symptoms in B-35 neuroblastoma cells in vitro
Parkinson's disease (PD) may be characterized, to some degree, by increases in oxidative stress and the subsequent loss of affected neurons. Silybum marianum, or milk thistle, consists primarily of silymarin, a polyphenolic flavonoid, and its major active compound silibinin, which have been shown to be strong antioxidants and hepatoprotective. Milk thistle extracts, when used in vitro, have protected hippocampal neurons against neurotoxic-induced stress. The neuroprotective behavior of silibinin may be through the amelioration of oxidative stress on memory impairment and cognitive deficits. One of the drawbacks of silymarin is its bioavailability; its poor absorption is due to the low level of hydrophobicity and its multiple-ringed structure, which impedes diffusion. To increase the bioavailability of silymarin, phytosomes can be formed, complexed with soy-derived phosphatidylcholine. Cotreatments with bioavailable lipophilic antioxidants, such as the Vitamin E species, may also aid silymarin in cell membrane stabilization. To test this, B35 neuroblastoma cells were pretreated in 96-well plates with each of the silymarin or bioantioxidant constituents for 24 hours before a potent dose of a neurotoxic insult, either MPP+ or 6-OHDA, in PD in vitro model. In posttreatment studies, cells were exposed to the insult first, followed by each potential neuroprotective agent, for 24 hours each. Cotreatments with each agent and the neurotoxic insults were performed to elucidate possible preconditioning or gene activation versus actual mechanisms of action. The MTT Assay determined the cell proliferation. Standard dose-response curves determined effective doses for silymarin at 10-3 to 10-4 mg/ml and for silibinin with phosphatidylcholine at 10-5 mg/ml, thus, complexed silibinin was more bioavailable. Delta tocotrienol outperformed alpha tocopherol under pretreatment conditions although the difference was not statistically significant. These results may indicate that silymarin, with phosphatidylcholine and alpha tocopherol or delta tocotrienol, has increased neuroprotective effect in PD models in vitro, and therefore may be useful in prevention or treatment of PD and other neurodegenerative diseases.