Bilirubin-Encapsulated Albumin Nanoparticle as a Therapeutic ROS Scavenger

Abstract

Bilirubin (BR) is a bile pigment and the end-product of heme catabolism which occurs abundantly in the blood plasma. Bilirubin is an endogenous antioxidant capable of scavenging different reactive oxygen species (ROS) and free radicals, thereby playing a role in protecting the cells and tissues from oxidative damage. Indeed, numerous experimental studies proved the potential of bilirubin for antioxidant, anti-inflammatory, and anticancer activities. However, its low water-solubility, toxicity on normal cells, rapid clearance, and high sensitivity to oxygen restrict further clinical developments, requiring an appropriate drug carrier capable of stably encapsulating and delivering a defined dosage to the site of action. Albumin is the most abundant protein in blood with a long circulatory half-life due to its size and FcRn binding property. Albumin has the capability to bind nutrients, metabolites, metals, and drugs, lending itself to a promising carrier that can affect the pharmacokinetics of the payload. Moreover, albumin is localized explicitly to tumors or inflamed tissues in either an active or a passive manner. Recently, serum albumin nanoparticles, i.e., BSA-NPs, have been used for delivering various types of therapeutic agents encapsulated inside or modified on the surface. This study explored how to synthesize and characterize albumin nanoparticles encapsulating hydrophobic bilirubin by the desolvation method. In addition, we measured its ROS scavenging, biocompatibility, and toxicity on cancerous cells. Using this method, albumin nanoparticles encapsulating bilirubin (BSA-BR-NPS) with a sTable size around 164 nm and a spherical morphology obtained with a high yield of around 70%. The entrapment efficiency (EE) was around 66%, and the drug loading (DL) was around 11%. The BSA-BR-NPs could scavenge more than 90% of the free radicals in radical scavenging measurement. The in vitro cellular assay of nanoparticles on different normal cells showed low toxicity on normal cells, which approved its biocompatibility. On the other hand, the BSA-BR-NPs had significant toxicity on cancerous cells. These results demonstrated that BSA-BR-NPS improved and optimized therapeutic efficiency of BR by addressing its limitations.