Abstract
Twenty-seven flavonoids isolated from Dalbergia parviflora with vast structural diversity were screened for inhibitory activity against mushroom and murine tyrosinases using l-DOPA as the substrate. Among the flavonoids tested, only four—khrinone (5), cajanin (9), (3RS)-3′-hydroxy-8-methoxy vestitol (21), and (6aR,11aR)-3,8-dihydroxy-9-methoxy pterocarpan (27)—reacted with mushroom tyrosinase, with IC50 values of 54.0, 67.9, 67.8, and 16.7 μM, respectively, and only compound 27 showed inhibitory activity against murine tyrosinase. With cell-based assays, only compounds 9 and 27 effectively inhibited melanogenesis in B16-F10 melanoma cells (by 34% and 59%, respectively), at a concentration of 15 μM, without being significantly toxic to the cells. However, the crude extract of D. parviflora and some of the flavonoid constituents appeared to increase melanin production in B16-F10 cells, suggesting that there are flavonoids with both inhibitory and stimulatory melanogenesis in the crude extract. Studies on the correlation between the enzyme-based and cell-based assays showed that only the flavonoids with IC50 values below 50 μM against mushroom tyrosinase could inhibit the mammalian tyrosinase, and thus, reduce melanogenesis in B16-F10. Flavonoids with the IC50 values greater than 50 μM, on the other hand, could not inhibit the mammalian tyrosinase, and had either no effect or enhancement of melanogenesis. In conclusion, the tyrosinase enzyme from mushroom is not as selective as the one from mammalian source for the enzyme-based melanogenesis inhibitory screening, and the mammalian cell-based assay appears to be a more reliable model for screening than the enzyme-based one.
Highlights
Tyrosinase (EC 1.14.18.1) is the key enzyme involved in melanin biosynthesis in living organisms
We suggest that, in flavonoids, anti-tyrosinase activity against mushroom would only appear in parallel with mammalian tyrosinase activity and melanogenesis inhibition when the enzyme inhibition activity in mushroom tyrosinase is greater than 60% at a concentration of 200 μM or an IC50 lower than 50 μM
The test samples, L-DOPA, and tyrosinase enzyme solutions were dissolved in 50% (v/v) dimethyl sulfoxide (DMSO) and 20 mM phosphate buffer solution (PBS) of pH 6.8, respectively
Summary
Tyrosinase (EC 1.14.18.1) is the key enzyme involved in melanin biosynthesis in living organisms. Subsequently, L-DOPA to DOPA quinone, in the initial steps in melanogenesis, a process which is Mushroom tyrosinase widely used as afoods, substitute for mammalian mainly responsible for darkhas skinbeen color. Several the inhibitory activity of mushroom tyrosinase by flavonoids and the actual inhibitory effect of plant flavonoids have been reported to have varying degrees of inhibitory activity towards melanin formation in mammalian cells. AndWe identified, have reported, previously, the isolation and structure of estrogenic-like compounds from the and six including 22 isoflavones, 12 isoflavanones, 10 isoflavans, six flavonones, four flavanonols, heartwood of Dalbergia parviflora, a Thai folk medicine traditionally used as a blood tonic and pterocarpans [10,11]. Thecrude structural diversity flavonoidsprepared has provided good source for the studying the parviflora werebetween tested enzymatic for their ability to inhibit mushroom and murine tyrosinases using L-DOPA as correlation assay and cell-based assays. The overall melanin production in B16-F10 melanoma cells were studied to observe the correlation between the results of the enzyme-based and cell-based assays
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