Low concentrations of silibinin and choline-calixarene or INU-C8-PEG carriers assembling silibinin promote antioxidant and antiapoptotic effects in neuronal and retinal epithelial cells.

Silibinin (SLB), the main component of silymarin (Silybum Marianum), is a flavonoid known for its multiple biological activities. In cancer model, SLB shows antioxidant, anti-inflammatory, anti-cancer and anti-angiogenic activities, and appears to yield neuroprotection in neurodegenerative models. In this study, our first objective was to investigate the effects of SLB in cellular models for oxidative stress mimicking a common pathological mechanism to neurodegenerative diseases, including retinal diseases such as age-related macular degeneration (AMD) and diabetic retinopathy. Three different cell culture types were used: the retinoic acid (RA)-differentiated SY5Y cells as a neuron-like cell model, the human corneal epithelial cells (HCEC) as an in vitro ocular disease model and the human retinal pigment epithelial cells (ARPE19) as a typical model for AMD studies. Undifferentiated SY5Y human neuroblastoma was used as a positive control of anti-cancer SLB effects. As a second objective, due to the hydrophobic nature of SLB decreasing its bioavailability, two nanocarriers, the choline-calix[4]arene derivative (CALIX) and the polymeric micelles, INU-C8-PEG, both loaded with SLB, were designed to improve its delivery to the retina. Their biological activity was tested on ARPE19 cells, being these cells with its tight junctions a blood-retinal-barrier model for drug permeation studies. Our results show toxic effects of high SLB concentrations (10-100?M) on neuroblastoma cells, but lack of toxicity and prevention of oxidative stress-induced cell death in RA-differentiated SY5Y, HCEC and ARPE19 cells using low concentrations of SLB (0.01-1?M). Analyses of SLB-loaded CALIX or INU-C8-PEG in ARPE19 cells insulted with H2O2 or FeSO4 and assessed for viability and apoptotic protein expression reveal a good correspondence between free and SLB-loaded carriers in promoting cell survival. In conclusion, we demonstrate that SLB anti-cancer and protective effects depend on its concentrations, and CALIX and INU-C8-PEG2000 are promising carriers for SLB delivery and potential therapy for retinopathies.