Abstract:
Pigmentation, a process controlled by melanogenesis, plays a vital role in protecting the skin against
harmful ultraviolet rays. The level of protection is compromised in case of hypopigmentation.
This study aimed to evaluate an Aspalathus linearis extract, fractions and phytoconstituents, for
their efficacy on melanogenesis stimulation. Fifteen compounds were kinetically assessed against
tyrosinase; the rate-limiting enzyme of melanogenesis. Aspalathin and catechin significantly (p
value < 0.001) increased the enzymatic rate, showing 50% stimulatory effects at 119.70 ± 2.06 μg/
mL and 143.30 ± 2.74 μg/mL, respectively, by acting as subversive substrates. Five compounds
inhibited the enzyme’s activity, of which four exhibited competitive inhibition. To investigate the
molecular interactions between the compounds and the active site, molecular docking was done,
using tyrosinase (PBD: 2Y9X) and tyrosinase related protein 1 (PBD: 5M8P). All the compounds docked
successfully with acceptable docking scores. Further quantitative structure–activity relationship
analysis identified potential functional groups, linked to the specific activity. The crude extract,
its fractions, and compounds exhibited low antiproliferative activity with 50% cell viability at
concentrations higher than 100 μg/mL. Finally, both aspalathin and catechin exhibited a significant
increase (4.5%) in melanin production at 119.82 μg/mL and 76.92 μg/mL, respectively. This is the first
report of A. linearis’ compounds on skin re-pigmentation.
