Obtenção de extratos padronizados em ácido clorogênico, rutina e isoquercitrina a partir das folhas de Morus nigra L. : inibição de tirosinase e citotoxicidade

Abstract

Melanogenesis is a process responsible for melanin production, which is stored in melanocytes containing tyrosinase. This enzyme is responsible for skin hyperpigmentation due to the overproduction of melanin. Inhibition of this enzyme is a target in the cosmetics industry, since it controls undesirable skin conditions. Plant species of the Morus genus are known for the beneficial uses offered in different parts of the plant, including tyrosinase inhibition. Thus, this project aimed to study the inhibitory activity of tyrosinase by extracts from Morus nigra leaves, as well as the characterization of the chromatographic profile of its extract and viability of incorporation in cosmetics from their cytotoxicity, in order to become a new therapeutic option from a natural source. M. nigra leaves were collected, pulverized, equally divided into five batches and the standardized extract was obtained by passive maceration. There was no significant difference between batches for total solids content, yield and moisture content, which shows good reproducibility of the extraction process also demonstrated by TLC chromatographic profile. Tyrosinase enzymatic activity was determined for each batch, providing the percentage of enzyme inhibition and IC 50 values obtained by constructing dose-response curves and compared with kojic acid, a well-known tyrosinase inhibitor. High inhibition of tyrosinase activity was observed (above 90 % at 15,625 g/mL) and IC 50 values ranging from 5.00 g/mL ± 0.23 to 8.49 g/mL ± 0.59, comparable to kojic acid (3.37 g/mL ± 0.65). According to ICH and Anvisa guidelines, the chromatographic method employed using High Profile Liquid Chromatography (HPLC) was validated. HPLC analysis revealed the presence of chlorogenic acid, rutin and its major compound, isoquercitrin. Thus, M. nigra leaf extract was standardized using these polyphenols as markers. Cytotoxicity was assessed by MTT assay on murine melanomas (B16F10), human keratinocytes (HaCat) and mouse fibroblasts (L-929). Cytotoxicity was not observed to the cell lines in tyrosinase IC 50 values. This study demonstrated the potential of M. nigra extract as a promising whitening agent of natural source against skin hyperpigmentation.