Isolation of proanthocyanidins from Pinus thunbergii needles and tyrosinase inhibition activity

Abstract

In the present work, we investigated the anti-tyrosinase activity, mechanism and antioxidant activity of proanthocyanidins (PAs) isolated from Pinus thunbergii needles. The results showed that PAs mainly consisted of catechin/epicatechin and had a strong inhibitory effect on the monophenolase and diphenolase activity of tyrosinase. PAs could reduce the steady state activity of tyrosinase monophenolase while prolonging the reaction delay time in a dose-dependent manner. The inhibitory effect of PAs on tyrosinase diphenolase was reversible, with the IC50 value of 37.64 μg/mL. The inhibition kinetic analysis by Lineweaver-Burk plots showed that PAs were a mixed-type inhibitor of tyrosinase diphenolase, with inhibition constants KI and KIS of 29.92 μg/mL and 128.27 μg/mL, respectively. Further, determination of the metal chelating ability, scanning study, fluorescence quenching, and DOPA (dihydroxyphenylalanine) oxidation were used to study the potential inhibition mechanism of PAs on tyrosinase. The results confirmed that PAs could chelate with copper ions in the active site of tyrosinase to inhibit tyrosinase activity. Moreover, ABTS [2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)] and FRAP (ferric reducing antioxidant power) assay showed good antioxidant capacity of PAs. This study revealed the possibility of Pinus thunbergii needle PAs as a new tyrosinase inhibitor in the fields of food, medicine, and cosmetics industries.