The Antioxidant and Membrane Activities of the Benzotropalone Pigment Purpurogallin

Abstract

Abstract—The phenolic compound purpurogallin (PPG) is found in oak nutgalls and is a red pigment with a benzotropolone ring structure. PPG shows pronounced cytoprotective and anti-inflammatory activities. PPG might be effective in preventing and treating diverse systemic inflammatory diseases, affecting functional activities of various cell metabolic and signaling pathways that are associated with inflammation. A study was made to compare the antioxidant (free radical) properties for PPG, dihydroquercetin (DHQ), ascorbic acid, and trolox using two test systems, hemoglobin (Hb)–H₂O₂–luminol (LM) and 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AAPH)–LM. PPG was additionally tested for its effect on the permeability of flat lipid bilayer membranes (LBMs). Moderate antioxidant activity was observed for PPG in the Hb–H₂O₂–LM system; its neutralizing potential towards hydroxyl and superoxide anions was comparable with that of ascorbic acid. The compounds were ranked according to the efficiency of their antioxidant activity in the system: DHQ > trolox > ascorbic acid > PPG. Interestingly, when the AAPH–LM system was used to test antioxidant activity, PPG did not show neutralizing activity towards peroxyl radicals formed in the system. PPG did not significantly change the permeability of flat LBMs in a dose range of 1.5–30 μM, suggesting lack of a primary membrane effect. Putative mechanisms and characteristics of cytoprotective, antioxidant, and anti-inflammatory activities of PPG are discussed.