Existing lightening agents such as kojic acid and hydroquinine acid have limitations, according to the authors.
High toxicity, low stability and poor skin penetration means formulators are searching for alternatives, explained the researchers led by F Sharififar from the Kerman University of Medical Sciences, Kerman.
Published online in the International Journal of Cosmetic Science, the study focused on five plants traditionally used in Iran for skin lightening but found extracts from the fruits of the Q. infectoria and T. chebula to be the most effective.
They were found to have good tyrosinase inhibiting properties, the enzyme involved in the synthesis of melanin, as well as strong antioxidant properties, according to the study.
The extracts’ tyrosinase inhibiting activity was tested on mushroom tyrosinase and compared to that of kojic acid.
At 62.5 micro grams per millilitre the tyrosine inhibition of Q infectoria was similar to that of kojic acid (approximately 40 per cent). At increasing concentrations up to 1000 micro grams per millilitre the extract performed at similar levels to kojic acid, except for a small drop in efficacy at a concentration of 500 micrograms.
The efficacy of T. chebula also went up with concentration but peaked at a concentration of 250 micrograms per millilitre. Concentrations above this point saw a drop in activity, according to the study.
High concentrations of gallic acid and ellagic acid in the extracts could explain their activity, explained the scientists, as flavonoid derivatives such as these are known to bind to copper ions in the active sites of tyrosinase enzyme thereby inhibiting its action.
The team also looked at the antioxidant properties of the extracts as reactive oxygen species are thought to play a role in melanin production by melanocytes.
According to the study, the antioxidant power of the Q. infectoria and T. chebula was significantly higher than the other extracts tested.
The team claims this is the first study to characterise the skin lightening potential of these plants, but states further research is needed to investigate the cytotoxicity of the extracts before moving onto in vivo tests.
Source: International Journal of Cosmetic Science
2009, 1-7, doi 10.1111/j.1468-2494.2009.00503.x
An evaluation of extracts of five traditional medicinal plants from Iran on the inhibition of mushroom tyrosinase activity and scavenging of free radicals
P. Khazaeli, R. Goldoozian, F Sharififar