In vitro and in silico study of Piper nigrum on cyclooxygenase-2, inducible nitric oxide synthase and antioxidant enzymes

Abstract

The antioxidant potential of the polyphenolic fruit extract of Piper nigrum (Piperaceae), a well known medicinal plant was evaluated. This evaluation was carried out via a reducing power assay; 1,1-diphenyl-2-picrylhydrazyl (DPPH), nitric oxide and superoxide radical assays; and a hydrogen peroxide scavenging assay under in vitro conditions and compared with that of the standard reference compound, ascorbic acid. Moreover the phytochemical characterization of the extract was also measured by determining total phenolic, flavonoid and tannin contents and ascorbic acid content. The polyphenolic extract of P. nigrum fruits (PNE) showed significant and concentration-dependent free radical scavenging of DPPH, nitric oxide, superoxide and hydrogen peroxide radicals with inhibition percentages ranging between 71% and 158%, when compared to the standard compound ascorbic acid (140–201%). In addition to this, the extract had effective reducing power. Total phenolic content was found to be highly correlated with scavenging potential of different reactive oxygen and nitrogen species (r=0.897–0.958). In silico methods were also applied to elaborate the possibility of the interaction of bioactive compounds reported to be present in PNE with molecular antioxidant targets. The compounds showed high binding efficiencies towards catalase, superoxide dismutase, glutathione peroxidase, glutathione-S-transferase, glutathione reductase, cyclooxygenase-2 and inducible nitric oxide synthase. These results enabled us to conclude that P. nigrum fruits can be a potential source of natural antioxidants to be used therapeutically.