Comparison of chemical structures and cytoprotection abilities between direct and indirect antioxidants

Abstract

To study structural and biological relationships in antioxidants, the cytoprotection, cytotoxicity, and Keap1–Nrf2 pathway activation potentials of nine natural antioxidants were compared. Sulforaphane, quercetin, isoliquiritigenin, curcumin, lycopene, and 3,5-dihydroxy-4-methoxybenzyl alcohol (DHMBA) activated the Keap1-Nrf2 pathway, whereas chlorogenic acid, gallic acid, rosmarinic acid, and cyanidin-3-O-glucoside did not. Hence, the former group was considered indirect antioxidants, and the latter direct antioxidants. Except for DHMBA and sulforaphane, the indirect antioxidants exhibited higher logP values and cytoprotectiveness, albeit with higher cytotoxicities, compared to the direct antioxidants. Exceptionally, DHMBA and sulforaphane showed lower logP values and higher cytoprotectiveness without cytotoxicity, indicating that indirect antioxidants might be more beneficial than direct antioxidants for cytoprotection, although caution towards cytotoxicity should be exercised regarding those with high logP values. In this regard, indirect antioxidants with low logP values like DHMBA and sulforaphane might serve as promising ingredients in functional foods.