Tyrosinase inhibitory activity of native plants from central Argentina: isolation of an active principle from Lithrea molleoides and its synergistic activity with commercial compounds.

CHIARI, M. E; PALACIOS S. M.; CARPINELLA M. C.*

Córdoba

Otro; 1° Reunión Internacional de Ciencias Farmacéuticas.; 2010

Introduction Tyrosinase (EC 1.14.18.1) is an enzyme capable of catalyzing melanin synthesis (1), a pigment produced by organisms in all kingdoms (2). In mammalian, melanin is responsible for protecting the skin against ultraviolet (UV)-induced damage and it is involved in dermatological disorders such as hiperpigmentation (3) and Parkinson’s disease (3,4). Tyrosinase is responsible for enzymatic browning of botanical or fishery products (5,6). In insects, tyrosinase is involved in sclerotization of cuticle, encapsulation and melanization of foreign organisms and wound healing (7). On the other hand, melanin reduces the susceptibility of melanized microbes to host defence (8). In this sense, tyrosinase inhibitors result in the best strategy for providing therapeutic or cosmetic agents (9), insecticides, antimicrobials or food additives. Numerous tyrosinase inhibitors have been described, however many of them show side effects (1,6,10-14). Plants are a vast source of compounds with different activities including tyrosinase inhibitors (15). According to previously described we have screened 91 extracts prepared from plants native to Argentina. From one of the most effective, Lithrea molleoides, an alkylresorcinol with high anti-tyrosinase effect was isolated. Materials and methods Plant material Extract from  L. molleoides was obtained by maceration with ethanol of crushed aerial plant material. Isolation of the tyrosinase inhibitor compound The extract from L. molleoides was disolved in ethanol and subjected to successive column and radial chromatographies. Finally one compound was isolated and identified as (Z,Z)-5-(trideca-4,7-dienyl)-resorcinol (16). Tyrosinase inhibitory assay Tyrosinase inhibitory activity was determined spectrophotometrically as described in Chiari et al. (16)  Mushroom tyrosinase dissolved in phosphate buffer was mixed with different concentrations of (Z,Z)-5-(trideca-4,7-dienyl)-resorcinol dissolved in ethanol or with ethanol as control. After incubation, L-tyrosine or L-DOPA was added and dopachrome formation was monitored in the reaction mixture.                 Synergistic activity assay Synergism among (Z,Z)-5-(trideca-4,7-dienyl)-resorcinol and kojic acid or hydroquinone was measured as explained above by adding to each well different combinations of mentioned compounds till reaching concentrations of each compound corresponding to 4, 8, 16 and 32 times below  its IC90. Results Tyrosinase inhibitory activity Compound IC50 (mg ml-1) a Monophenolase activity Diphenolase activity Lithrea molleoides 3.77 (2.40, 5.92) 79.44 (27.48, 229.67) (Z,Z)-5-(trideca-4,7-dienyl)-resorcinol 0.49 (0.22, 1.09) 14.94 (5.85, 38.09) Kojic acid 18.25 (9.37, 35.53) 2.64 (1.06, 6.57) Hydroquinone 1.55 (1.24, 1.92) 120.07 (30.63, 455.76) a values IC50 with 95% confidence limits (lower, upper)