Abstract:
Skin hyper-pigmentation is a condition initiated by the overproduction of melanin existing in
the melanocytes. Melanin pigment is responsible for the colour of skin in humans. It is
formed through a series of oxidative reactions involving the amino acid tyrosine in the
presence of the key enzyme tyrosinase. In continuation with our efforts to identify tyrosinase
inhibitors from plants sources, the methanol extract from leaf, bark and fruit of Ceratonia
siliqua were screened for tyrosinase inhibition and diphenolase activity. The bark extract
exhibited significant inhibition on mushroom tyrosinase using L-tyrosine as a substrate and
showed diphenolase activity. The extract further significantly inhibited tyrosinase mRNA
levels in B16-F10 mouse melanocytes. Bioassay-guided fractionation led to the isolation of
six compounds. Compounds (-)-epicatechin-3-O-gallate, 1,2,3,6-tetra-O-galloyl-ß-D-glucose
and Gallocatechin-3-O-gallate showed tyrosinase inhibitions with the IC50 values of 27.52,
83.30 and 28.30 μg/mL, respectively. These compounds also exhibited L-DOPA activities
with IC50 values of >200, 150 and 200 μg/mL, respectively. A clinical study was conducted
using 20 volunteers in a patch testing trial for irritancy potential and skin depigmentation.
The clinical results showed the sample to be non-irritant with irritancy potential of -34.21 and
depigmentation trial showed an improvement in the even skin tone of UV induced
pigmentation at 3% after 28 days of application.
