Antioxidant properties of probucol released from mesoporous silica

Antioxidants play a vital role in scavenging reactive oxygen species (ROS) produced by the reduction of molecular oxygen from various cellular mechanisms. Under oxidative stress, an increase in the levels of ROS overwhelms the antioxidant response, causing oxidative damage to biological molecules, and leading to the development of various diseases. Drug compounds with potent antioxidant properties are typically poorly water soluble and highly hydrophobic. An extreme case is Probucol (PB), a potent antioxidant with reported water solubility of 5 ng/ml, and oral bioavailiability of < 10%. In this study, PB was loaded in mesoporous silica at various drug loadings to understand the changes to the physical properties of the loaded drug, and it's in vitro drug release. Further in vitro studies were conducted in endothelial and microglia cell models to compare the free radical scavening efficiency of ascorbic acid, PB, and PB release from mesoporous silica particles. Out of the three different mesostructured particles studied, the maximum loading of PB was achieved for large pore mesoporous particles (SBA-15) at 50 wt% drug loading, before complete pore filling was observed. For all materials, loadings above complete pore filling resulted in the recrystallization of PB on the external surface. In vitro drug release measurements showed a rapid dissolution rate at low drug loadings compared to a bimodal release profile of amorphous and crystalline drug at higher drug loadings. PB loaded in mesoporous particle was shown to enhance the antioxidant response to extracellular ROS in the endothelial cell line model, and to intracellular ROS in the microglia cell model. Our results indicate that the antioxidant properties of PB can be significantly improved by using mesoporous silica as a delivery vehicle.