In silico docking studies and in vitro xanthine oxidase inhibitory activity of commercially available terpenoids

Objective Xanthine oxidase is a highly versatile enzyme that is widely distributed among different species. The hydroxylation of purines is catalysed by xanthine oxidase and especially the conversion of xanthine to uric acid. Xanthine oxidase inhibitors are much useful, since they possess lesser side effects compared to uricosuric and anti-inflammatory agents. The present study deals with in silico and in vitro xanthine oxidase inhibitory analysis of commercially available terpenoids (bisabolol, 2-caryophyllene, limonene, and ±- terpinene). Methods Molecular docking studies were performed using AutoDock 4.2 and in vitro xanthine oxidase inhibitory activity was carried out using xanthine as the substrate. In addition, enzyme kinetics was performed using Lineweaver Burkplot analysis. Allopurinol, a known xanthine oxidase inhibitor was used as the standard. Results The results revealed that bisabolol exhibited a lowest binding energy value of about -7.33 kcal/mol. All other compounds showed binding energy values ranging between -7.33 to -5.87 kcal/mol which was less than the standard (-4.78 kcal/mol). In the xanthine oxidase assay, IC50 value of bisabolol was found to be 34.70 μg/ml, whereas that of allopurinol was 8.48 μg/ml. All the remaining compounds exhibited IC50 values ranging between 34.70 to 68.45 μg/ml. In the enzyme kinetic studies, bisabolol, 2-caryophyllene showed non competitive and Limonene, ±- terpinene and allopurinol showed competitive type of enzyme inhibition. Conclusion It can be concluded that terpenoids could be a promising remedy for the treatment of gout and related inflammatory disorders. Further in vivo studies are required to develop potential compounds with lesser side effects.