Pharmacotherapeutic properties of Strelitzia nicolai aril extract containing bilirubin

The surprising discovery of an animal pigment bilirubin found in the plant Strelitzia nicolai, has led us to investigate the biological properties of bilirubin in human physiology. Classically, it is a well-known toxic metabolite in the degradation of hemoglobin, however at slightly elevated levels could be beneficial. Reports suggest that bilirubin could be involved in scavenging of reactive oxygen species (ROS), anti-inflammatory actions and cellular signaling. This study aimed to investigate the possible therapeutic effects of the seed aril extract of S. nicolai and bilirubin. High Performance Liquid Chromatography (HPLC) and Attenuated Total reflectance-Fourier transform Infrared (ATR-FTIR) analysis were used to confirm the organic functional groups present in the aril extracts. Subsequently, the antioxidant potential was established using the hydrogen peroxide and nitric oxide scavenging activity. In vitro anti-bacterial, anti-inflammatory, anti-hypertensive and glucose metabolism assays were conducted. This was also supplemented by in silico binding affinity of bilirubin to the metabolic enzymes. The antioxidant activity of the aril extract using the nitric oxide inhibition showed increased activity when compared with the bilirubin isolate. Conversely, the bilirubin isolate proved to be a potent hydrogen peroxide inhibitor. The S. nicolai aril extract showed greater glucose metabolising potential over bilirubin. Both the bilirubin and aril extract did not possess any antibacterial activity. This study reveals new insights into the presence of the only animal pigment found in the plant species and the potential advantages of bilirubin found in a plant. This study proposes that the constricted view of bilirubin as a toxic compound needs to be revisited. Furthermore, this extract containing bilirubin might be a suitable candidate for the therapeutic intervention for oxidative stress related diseases.