Preventive effects of Dendrobium hybrid extract on free radical activity and melanoma cell proliferation by inducing apoptotic gene expression.

Dendrobium species are used in folk medicines due to their medicinal properties by acting as antioxidants and anticancer agents. Derived from parent plants used in dermatological treatments and cosmetics, Dendrobium Pearl Vera hybrid (DH) was extracted and investigated for its inhibitory effects on free radicals and skin cancer cell proliferation. Based on colorimetric spectrophotometry, the propanolic extract (DH-P) from the whole plant contained flavonoids, phenolics and alkaloids at 80.11±0.69, 50.51±0.44 and 38.75±1.77 µg/g fresh weight, respectively. Using high-resolution mass spectrometry, eight compounds involved in skin protection were annotated: Fuanosine, L-glutamine, threonic acid, quercetagetin, shikimic acid, mannose, p-coumaric acid and L-malic acid. DH-P scavenged free radicals in a concentration-dependent manner and inhibited the activity of collagenase and hyaluronidase, but not in a concentration-dependent manner. Treatment using DH-P for 96 h significantly decreased the proliferation of SK-MEL-28 melanoma cells in a dose-dependent manner, with a half-maximal inhibitory concentration of 20.23±1.04 µg/ml. Thus, DH-P at 20 µg/ml was used in further studies. Cell migration was not inhibited by DH-P. However, DH-P may induce SK-MEL-28 cell death through apoptosis, as nuclear condensation and fragmentation was observed after 48 h DH-P treatment. Gene expression analysis was performed to evaluate key signaling molecules involved in cell apoptosis, such as bax, bcl-2, cytochrome c, caspases (cas)-3 and -9 and p53. The expression levels of cas-3 and cas-9, executors in the apoptosis pathway, were significantly upregulated in the SK-MEL-28 cells treated with DH-P for 48 h, further confirming that cell death may occur through an apoptosis mechanism.