Abstract
Melanogenesis is a process responsible for melanin production, which is stored in melanocytes containing tyrosinase. Inhibition of this enzyme is a target in the cosmetics industry, since it controls undesirable skin conditions such as hyperpigmentation due to the overproduction of melanin. Species of the Morus genus are known for the beneficial uses offered in different parts of its plants, 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 its chromatographic profile and 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. Tyrosinase enzymatic activity was determined for each batch, providing the percentage of enzyme inhibition and IC50 values obtained by constructing dose-response curves and compared to kojic acid, a well-known tyrosinase inhibitor. High inhibition of tyrosinase activity was observed (above 90% at 15.625 μg/mL). The obtained IC50 values ranged from 5.00 μg/mL ± 0.23 to 8.49 μg/mL ± 0.59 and were compared to kojic acid (3.37 μg/mL ± 0.65). High Performance Liquid Chromatography analysis revealed the presence of chlorogenic acid, rutin and, its major compound, isoquercitrin. The chromatographic method employed was validated according to ICH guidelines and the extract was standardized using these polyphenols as markers. Cytotoxicity, assessed by MTT assay, was not observed on murine melanomas, human keratinocytes and mouse fibroblasts in tyrosinase IC50 values. This study demonstrated the potential of M. nigra leaf extract as a promising whitening agent of natural source against skin hyperpigmentation.
Highlights
Melanin is one of the most widely distributed pigments found in bacteria, fungi, plants and animals [1]
A sample from batch 3 was discarded due to contamination during the drying period, the yield could not be calculated for this batch
The results show no significant difference between batches for total solids content and humidity content in analysis by ANOVA (p
Summary
Melanin is one of the most widely distributed pigments found in bacteria, fungi, plants and animals [1]. Melanogenesis is initiated with tyrosine oxidation catalyzed by tyrosinase to dopaquinone, which is converted to dopa and dopachrome through auto-oxidation. Dopa is the substrate of tyrosinase and oxidized to dopaquinone again by the enzyme. The reaction products from dopachrome, dihydroxyindole (DHI) and dihydroxyindole-2-carboxylic acid (DHICA), suffer oxidation to form the brown-to-black eumelanin. In the presence of cysteine or glutathione, dopaquinone is converted to cysteinyldopa or glutathionyldopa subsequently forming the yellow-to-reddish-brown pheomelanin [2, 3]. There are two groups of pigmentary disorders: the abnormal presence of exogenous or endogenous pigments in the skin and disorders of the quantitative and qualitative distribution of normal pigment, which includes hyperpigmentation and hypopigmentation [5]. Sometimes seen during pregnancy, and postinflammatory hyperpigmentation of the skin [7]
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