Inhibition of melanogenesis and antioxidant properties of Magnolia grandiflora L. flower extract

Abstract

Background: Magnolia grandiflora L. flower is wildly used in Asian as a traditional herbal medication. The purpose of the study was to investigate the antimelanogenic and antioxidant properties of Magnolia grandiflora L. flower extract. In the study, the inhibitory effects of M. grandiflora L. flower extract on mushroom tyrosinase, B16F10 intracellular tyrosinase activity and melanin content were determined spectrophotometrically. Meanwhile, the antioxidative capacity of the flower extract was also investigated.

Results: Our results revealed that M. grandiflora L. flower extract inhibit mushroom tyrosinase activity (IC(50) = 11.1%; v/v), the flower extract also effectively suppressed intracellular tyrosinase activity (IC(50) = 13.6%; v/v) and decreased the amount of melanin (IC(50) = 25.6%; v/v) in a dose-dependent manner in B16F10 cells. Protein expression level of tyrosinase and tyrosinase-related protein 1 (TRP-1) were also decreased by the flower extract. Additionally, antioxidant capacities such as ABTS(+) free radical scavenging activity, reducing capacity and total phenolic content of the flower extract were increased in a dose-dependent pattern.

Conclusions: Our results concluded that M. grandiflora L. flower extract decreased the expression of tyrosinase and TRP-1, and then inhibited melanogenesis in B16F10 cells. The flower extract also show antioxidant capacities and depleted cellular reactive oxygen species (ROS). Hence, M. grandiflora L. flower extract could be applied as a type of dermatological whitening agent in skin care products.

Figure 1

Effect of M. grandiflora L. flower extract on B16F10 cell viability. Cells were treated with various concentration of flower extract (10, 12.5, 15, 17.5, 20%; v/v) for 24 h and the cell viability was measured by MTT assay. Results are expressed as percentage of cell viability relative to control. Data are presented as mean ± S.D. Values are significantly different by comparison with control. ** p < 0.01.

Figure 2

Inhibitory effect of M. grandiflora L. flower extract on mushroom tyrosinase activity, B16F10 melanin content and intracellular tyrosinase actvity. (A) Different concentrations of the flower extract (10, 15, 20%; v/v) or kojic acid (200 μM) was incubated with the same units of mushroom tyrosinase. Following incubation, the amount of dopachrome produced was determined at 490 nm spectrophotometrically. (B) & (C) B16F10 melanoma cells were stimulated with α-MSH (100 nM) for 24 h, and then the melanin content or intracellular tyrosinase activity were measured after treatment with various concentrations of the flower extract (final concentration 10, 15, 20%; v/v) or arbutin (2.0 mM) for another 24 h. Results are represented as percentages of control, and data are presented as mean ± S.D. for three separate experiments. Values are significantly different by comparison with control. *** p < 0.001.

Figure 3

Effect of M. grandiflora L. flower extract on melanogenesis-related proteins expression. (A) B16F10 cells were cultured with α-MSH (100 nM) for 24 h and then treated with various concentration of the flower extract (10, 15, 20%; v/v) or kojic acid (200 μM) for another 24 hr. Then the content of cellular MITF, tyrosinase, TRP-1 and TRP-2 proteins were analyzed by western blotting assay. (B) The relative amounts of MITF, tyrosinase, TRP-1 and TRP-2 compared to total GAPDH were calculated and analyzed by Multi Gauge 3.0 software and the values represented the mean of triplicate experiments ± S.D.

Figure 4

Antioxidant activities of M. grandiflora L. flower extract. (A) ABTS⁺ radical scavenging capacity assay. The flower extract (10, 15, 20%; v/v), vitamin C (50 μM), vitamin E (50 μM) or BHA (0.1 mg/ml) were incubated with ABTS⁺ solution, respectively. (B) Determination of total phenolic content. Different concentrations of the M. grandiflora flower extract (10, 15, 20%; v/v) and gallic acid (2 μg/ml) were used in the assay. (C) Reducing capacity assay. Different concentrations of the flower extract (10, 15, 20%; v/v) or BHA (0.05 mg/ml) were used in the test. (D) Determination of ROS content in B16F10 cells. Cells were treated with various concentrations of the flower extract (10, 15, 20%; v/v) or Trolox (2.0 mM) for 24 h and then the ROS content was measured by the DCF-DA assay. Results are represented as percentages of control, and the data are mean ± S.D. for three separate experiments. Values are significantly different by comparison with control. *** p < 0.001.