Eulophia nuda, is a highly medicinal orchid with strong antioxidant and anticancer potentials in traditional systems of medicine. But few reports are available on scientific validation. The aim of the study was to investigate phytochemical constituents, antioxidant and cytotoxic efficacies of extracts of Eulophia nuda, and the underlying mechanisms-of-action via up-regulation of nuclear transcription factor-erythroid-2 related factor (Nrf2) and hemeoxygenase-1 (HO-1) pathways.
Petroleum ether (PEE), ethyl acetate (EAE), methanol (ME) and aqueous methanol (AqME) extracts of shade dried tubers were obtained and were concentrated in vacuo. Total phenols, flavonoids, condensed tannins, ascorbic acid and carotenoids were estimated from the extracts using standard methods. Antioxidant activities of extracts were determined by total antioxidant, FRAP, ABTS, DPPH, OH, H2O2, NO, O2·- radical scavenging assays. Cytotoxicity of EAE and ME were assessed against MCF7 cells in vitro. LC-ESI/MS profiling of EAE was carried out. Quantitative Real-Time (qRT) PCR was used for expression analysis of Nrf2 and HO1 genes in EAE-treated MCF7 cells.
In vitro models confirmed strong dose-dependent antioxidant and free-radical scavenging potencies of E. nuda tuber extracts. Overall antioxidant efficacies were in the order EAE>ME>AqME>PEE. EAE showed striking cytotoxicity followed by ME (0.86% and 5.17% cell survival at 1000 µg ml-1, respectively). LC-ESI/MS profiling of most potent extract EAE revealed 37 identified compounds including catechin, taxifolin, tocopherol, trigallic acid and chlorogenic acid, all known for their strong antioxidant/anticancer properties. Expression levels of Nrf2 and HO1 genes were up-regulated in MCF7 cells beyond 50 µg ml-1 extract concentration with >2-fold increase at 200 µg ml-1 EAE.
The data demonstrated that E. nuda extracts possess strong free radical scavenging and antioxidant efficacies and the mechanism of action may be via inducing Nrf2 and HO-1.