Screening of Bioactive Phytochemicals in Some Indigenous Epiphytic Orchids of Bangladesh

Abstract

This investigation portrayed phytochemical screening, antioxidant, anti-inflammatory, antimicrobial, cytotoxic and analgesic activities of three medicinally important epiphytic orchids of Bangladesh, namely Rhynchostylis retusa (L.) Bl., Luisia zeylanica Lindl. and Papilionanthe teres (Roxb.) Schltr. The methanolic extracts of the leaves and roots of R. retusa and the leaves and stems of L. zeylanica and P. teres were used in the present investigation. Quantitative phytochemical screening revealed the presence of a number of bioactive phytochemicals, such as alkaloids, carbohydrates, flavonoids, glycosides, tannins, phenols, xanthoproteics, proteins, saponins, cardiac glycosides, coumarins, quinines, flavonols, steroids, terpenoids, phytosterols, phlobatannins etc. Antioxidant activity of the selected orchids showed significant DPPH free radical scavenging activity compared with that of ascorbic acid at 100 μg/ml. Excellent anti-inflammatory activity was also showed in these orchids, and the highest anti-inflammatory activity was recorded in P. teres (88.22%). Total phenol content was measured by using Folin-Ciocalteu reagent gallic acid was used as a reference standard. The maximum total phenol content was 205.33 mg/g GAE in L. zeylanica, and the minimum was 36.67 mg/g GAE in the roots of R. retusa. Antibacterial activity of methanolic extracts was tested against Bacillus subtilis, Staphylococcus aureus, Salmonella typhi, Pseudomonas aeruginosa and Escherichia coli. The maximum antibacterial activity was observed against Bacillus subtilis. The antifungal activity was also studied against Aspergillus niger and Fusarium oxysporum, and the highest antifungal activity was recorded against Aspergillus niger (70%) by P. teres. In brine shrimp lethality bioassay, encouraging cytotoxicity was observed after 24 h, and the maximum mortality of nauplii was recorded in L. zeylanica (LC50 value 77.175 μg/ml) as compared with anticancer drugs ‘vincristine sulphate’ (LC50 value 0.25 μg/ml). In analgesic assay, remarkable inhibitory effect was observed in acetic-acid-induced writhing test on mice by the extract of P. teres (86.19%). The percentage of paw licking inhibition was high in the late phase than in the early phase. The findings of the present investigation will facilitate the designing of new drugs to comate challenging diseases.