Inhibition of Xanthine oxidase by 1-O-methyl chrysophanol, a hydroxyanthraquinone isolated from Amycolatopsis thermoflava ICTA 103

Hyperuricemia caused by elevated levels of serum uric acid is responsible for implication of gout and other associated disorders that influence the human health. So far, Xanthine oxidase (XO) inhibitors are the choice of first line drugs for the treatment of hyperuricemia. The objective of the present study was to isolate a potent XO inhibitor from the actinobacteria and to evaluate its inhibitory mechanism. Initially, XO was isolated from bovine milk using standard protocol and enzyme kinetics were evaluated. Thereafter, culture filtrates of actinobacteria ( Amycolatopsis thermoflava ICTA 103), Streptomyces luteireticuli ICTA 16, Streptomyces kurssanovii ICTA165 and Amycolatopsis lurida ICTA 194) were screened for XO inhibition using in vitro qualitative NBT plate assay followed by extraction and purification of potent inhibitor 1- O -methyl chrysophanol (OMC), from the culture filtrate of Amycolatopsis thermoflava ICTA 103, which belongs to hydroxy anthraquinones (HAQ) family. Further, in silico molecular model building was performed to study the binding affinity of OMC towards XO followed by quantitative in vitro spectroscopic assays. The molecular building study explored the mechanistic view of binding interaction between inhibitor & enzyme and the results were corroborates with the in vitro kinetic study. The in vitro results revealed the significant enzyme inhibition potential of OMC with an IC50 and K i value of 24.8 ± 0.072 µM & 2.218 ± 0.3068 µM respectively. These results are comparable to standard allopurinol, however, more significant than its structural analog, chrysophanol. The kinetic analysis revealed that OMC is a reversible slow binding inhibitor and the Lineweaver - Burkplot analysis showed mixed type inhibition of OMC against XO. These results are in agreement with chrysophanol. Findings of this study proposed a new derivative of HAQ in the pipeline of hyperuricemia therapeutic drug candidates. ### Competing Interest Statement The authors have declared no competing interest.