Tyrosinase inhibitory effects and inhibition mechanisms of nobiletin and hesperidin from citrus peel crude extracts

Abstract

The inhibitory effects of nobiletin and hesperidin from citrus peel crude extracts on tyrosinase diphenolase activity are evaluated. IC₅₀ of nobiletin and hesperidin is 1.49 mM and 16.08 mM, respectively and their inhibition mechanism is competitive type with K_i = 2.82 mM and noncompetitive with K_i = 9.16 mM, respectively. Crude extracts from citrus peel (C. unshiu Marc.) were extracted with 95% ethanol and fractionated by petroleum ether (PCPE). The ethanol phase (ECPE) was further desorbed from macroporous adsorption resin (FGRE). Their IC₅₀ values were 8.09 mg/mL, 7.53 mg/mL and 4.80 mg/mL, respectively. Their inhibition on melanogenesis in B16 mouse melanoma cells was also evaluated. FGRE showed a significant inhibition (42.5% at 31.25 μg/mL, p < 0.01) while hesperidin showed almost no inhibition. Nobiletin and PCPE give efficacious antiproliferation effects on B16 mouse melanoma cell with IC₅₀ values 88.6 μM and 62.96 μg/mL, respectively, by the MTT test. Hesperidin and other crude extracts showed very low cytotoxity to the B16 cell.

Keywords::

• Citrus unshiu
• Marc
• nobiletin
• hesperidin
• B16 mouse melanoma
• crude extract
• tyrosinase inhibitor
• melanin
• traditional Chinese medicine
• SAR

Acknowledgements

We sincerely thank Mr Falin Wen for his generous help in cultivar authentication, Ms Lei Jiang for her kind guidance on cell culture and all the colleagues such as Yongzhi Zhang, Baosong Teng, Zhaogui Chen, Zhiyong Liu for their helpful support in the laboratory.