The impact of chemical structure on redox behavior and biological activity of hydroxybenzoic acids.

Hydroxybenzoic acids (HBAs) are dietary phenolics with recognized antioxidant potential, yet the links between their chemical structure and biological activity remain unclear. Four HBAs - gallic (GA), gentisic (GE), protocatechuic (PR), and vanillic (VA) acids - were compared. Antioxidant efficiency correlated with hydroxyl density, with GA showing the highest activity and VA the weakest. In the Cellular Antioxidant Activity assay, GA again exhibited the strongest effect, whereas PR, GE, and VA showed lower activities, reflecting differences in bioavailability. GA reduced the viability of both HT29 (cancer) and CCD841 (normal) colon cells in a dose- and time-dependent manner, while GE, PR, and VA were largely non-toxic up to 1 mM. PR and VA significantly reduced hydrogen peroxide-induced DNA damage, whereas GA and GE did not. Overall, these findings highlight the importance of evaluating phenolics using complementary chemical and biological assays to better assess their role in cellular redox homeostasis.