Thermal degradation, kinetic analysis, and apoptosis induction in human melanoma for oleanolic and ursolic acids

Abstract

This study deals with the comparative analysis of thermal degradation (including kinetic study) in dynamic air atmosphere, for two similar-structured triterpenoid acids—ursolic (URS) and oleanolic (OLE) acids. As kinetic methods, two integral methods (Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa) and one differential method (Friedman) were used. The “in-depth” kinetic analysis was completed by applying the nonparametric kinetics (NPK) method, which confirmed the multiprocess degradation suggested by isoconversional methods (the observed variation in Ea vs. conversion degree). The NPK method revealed that ursolic acid is degraded solely by two parallel chemical processes, while in the case of oleanolic acid, the processes are accompanied by physical ones. The physicochemical investigation was completed with a bioactivity evaluation regarding the apoptotic process caused by the two compounds in A2058 human melanoma cell line. It was found that the similar-structured triterpenoids possess different biological effects, OLE being antiapoptotic, while URS being strong apoptotic.