Chemopreventive effects of Lawsonia Inermis L. (Henna) leaf powder and its pigment artifact, lawsone on skin carcinogenesis in mice
The medicinal plant Lawsonia inermis L, commonly known as 'henna' and lawsone (2-hydroxy-1,4-naphthoquinone), the red-orange pigment artifact formed during the extraction or preparation of the dye from henna leaves, were evaluated for chemopreventive effects against skin carcinogenesis in three mouse models. In the two-stage mouse skin carcinogenesis model using UV-B radiation for initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) for tumor promotion, oral feeding of henna leaf powder (0.0025%) in drinking water ad libitum decreased tumor incidence by 66% and multiplicity by 40%. Similarly, in the above mouse model, orally fed lawsone (0.0025%) decreased tumor incidence by 72% and multiplicity by 50%. The tumor inhibitory trend continued throughout the 20-week test period. Similar antitumor activities were observed when henna leaf powder (0.5mg/ml) was applied topically on the back skin in the UV-B initiated, TPA promoted and peroxynitrite initiated, TPA promoted mouse skin carcinogenesis models. Topically applied lawsone (0.015mg/ml) also exhibited similar protection against tumor formation in the 7,12-dimtehylbenz(a)anthracene induced and TPA promoted skin cancer in mice. Also, there was a delay of 1 to 2 weeks in tumor appearance in both henna leaf powder and lawsone treated groups in all three test models. This study ascertains the skin cancer chemopreventive activity of henna leaf powder and lawsone when administered by either oral or topical routes. Further, the results suggest that lawsone, the pigment artifact is primarily responsible for the observed chemopreventive effect of henna leaf powder in the mouse skin carcinogenesis models used.