Introduction
Phytochemical studies on Argentinean species of Dalea genus1,2 carried out by our group have provided new structures like prenylated flavonoids, with several biological activity, such as antioxidants3, antimicrobials4-6, tyrosinase inhibitors, among others2. The promising results motivate the studies of another species of this genus.
In the present work different extracts (hexane, benzene, ethyl acetate and ethanol) of Dalea pazensis Rusby roots were obtained in order to evaluate their inhibitory activity on the tyrosinase enzyme.
Additionally, a phytochemical screening of the most active extracts was performed in order to determine the chemical family compounds.
Tyrosinase acts as a rate-limiting enzyme in melanin biosynthesis. Therefore, tyrosinase inhibitors are important substances to treat abnormal pigmentation disorders, such as melasma, age spot and sites of actinic damage, arising from accumulation of an excessive level of epidermal pigmentation7, 8.
D. pazensis is a Bolivian species collected in Yotala, locality close to
Materials and methods
Preparation of extracts: From 35 g of roots of D. pazensis four extracts with solvents of increasing polarity were obtained using a soxhlet extractor: hexane (0.41 g), benzene (0.51 g), ethyl acetate (0.53 g) and ethanol (1.06 g).
Tyrosinase inhibitory activity: It was carried out according to the method of Rahman et al.9 adapted to the following working conditions, tyrosinase (250 U/mL), L-tyrosine (1, 7 mM) was used as substrate, Kojic acid was used as reference inhibitor, the appearance of dopacromo was measured spectrophotometrically at 475nm. The inhibition of the samples was expressed as percentage of inhibition and calculated using the following equation9:
A475nm (control)
Statistics
Results were expressed as the measured ± SD of three independent experiments.
Results and discussion
The benzene extract showed the most inhibitory effect on tyrosinase enzyme, with 95.93±0.82 % at a concentration of 1 µg/mL. At the same concentration, the ethyl acetate, ethanol, and hexane extracts produced an inhibition of 64.59±2.19, 34.90±5.33, and 27.46±0.26 %, respectively. All the four extracts were subjected to the Shinoda test, giving positive results which were more intense in the most active extracts, thus indicating the presence of flavonoid compounds.
Conclusion
In similar previous studies carried out with D. boliviana (species collected in Argentina), the most active extract, showed a similar inhibition of the enzyme tyrosinase at a concentration tenfold higher than that found in the present study (89. 02±1. 45% for ethyl acetate extract at a concentration of 10 µg/mL)2. From D. boliviana prenyl flavonoid derivates with an important anti-tyrosinase activity were obtained. For this reason, it is interesting to deep the studies initiated on D. pazensis in order to determine the chemical structures responsible for the inhibitory effect of the extracts on tyrosinase enzyme.
References
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