Preparation, characterization and in vitro evaluation of novel silymarin-loaded nanomicelles

Silymarin (SLM) is a mixture of flavonolignans extracted from fruits of Silybum marianum L. Gaertn. (Asteraceae). SLM has been used from the ancient times in the treatment of liver and gallbladder diseases and its efficacy in many pathologies is reported [ 1 ]. However, the low aqueous solubility and poor oral bioavailability limit its clinical use. To overcome these drawbacks, two novel nanomicellar formulations were developed. Polymeric nanomicelles made of Soluplus and mixed nanomicelles combining Soluplus with Vitamin E TPGS were obtained by the thin film method. The solubility of silymarin increased by ~ 6-fold when loaded into nanomicelles. Furthermore, both formulations were chemically and physically characterized in terms of average diameter, homogeneity, zeta potential, morphology, encapsulation efficiency, drug loading, critical micellar concentration and cloud point. Nanomicelles showed sizes of ~ 60 nm and polydispersity index 0.1. The encapsulation efficiency was 92% indicating the high affinity between silymarin and the core of the nanomicelles. The physical and chemical parameters of SLM-loaded formulations stored at room temperature and in refrigerated conditions were monitored over three months. Stability and release studies in media mimicking physiological conditions were conducted. A DPPH assay was performed to evaluate the antioxidant properties of SLM. Preliminary studies with artificial membranes indicated that nanomicelles increased the intestinal absorption of SLM. Subsequently, transport studies employing Caco-2 cells demonstrated that mixed nanomicelles statistically enhanced the permeability of SLM with respect to polymeric nanomicelles and unformulated extract. Finally, uptake studies indicated that both nanomicellar formulations entered into Caco-2 cells via energy-dependent mechanisms.