Impact of geographical distribution on polyphenol compostion, antioxidant, antimicrobial and cytotoxic potential of Rhynchostylis retusa (L.) Blume roots

Introduction

Rhynchostylis retusa (L.) Blume lies in the heart of majestic Himalayan mountains and is well-documented in Traditional System of Medicine. R. retusa roots are used to treat rheumatic disease, asthma, tuberculosis, epilepsy, kidney, and menstrual disorders. Besides earlier reports, current study was focused to investigate locational variations of polyphenols, antioxidant, antimicrobial and cytotoxicity activities of R. retusa roots.

Method

R. retusa roots of four locations of Himachal Pradesh, India were used in the current study. The targeted polyphenols were determined using UPLC-PDA while total phenolic and total flavonoid contents were by spectroscopic method. The antioxidant activity was assessed by DPPH ֹ and ABTS ֗⁺ assays. Antimicrobial activity was performed against gram-positive (Bacillus subtilis and Staphylococcus aureus) and gram-negative bacteria (Salmonella typhimurium and Escherichia coli) while cytotoxicity activity was against HT29 cancer cell line.

Result

In present study, 50 % ethanol revealed higher yield in Kangra region (1375 m; 32.1109° N, 76.5363° E) sample followed by water and ethanol. Among all extracts, gallic acid and protocatechuic acid were most abundant phenolic acids. The highest TPC and TFC were found in the ethanol extract of Bilaspur (680 m; 31.33°N 76.75°E) sample (155.58±6.92 mg GAE/g and 262.25±8.32 mg RE/g) and Kangra (135.64±4.36 mg GAE/g and 281.75±4.38 mg RE/g) regions, respectively. The ethanol extract from Hamirpur (790 m 31.6862° N, 76.5213° E), exhibited highest antioxidant activity (IC₅₀ 33.31±0.72 µg/mL and 12.45±0.68 µg/mL), in DPPH ֹ and ABTS ֗⁺ assays, respectively. The ethanol extract from Bilaspur (5 mm and 3 mm ZOI for B. subtilis and S. aureus), Kangra (4 mm and 2.5 mm for B. subtilis and S. aureus), and Hamirpur showed most potent antimicrobial activity. Whereas, Mandi (760 m; 31.7087° N, 76.9320° E) samples showed least potential as compared to other targeted locations. Further, ethanol extracts of all locations were found most effective in terms of their cytotoxic activity against HT29 cancer cell lines.

Conclusion

Current investigations illuminate ethanol's pivotal role in extracting polyphenols and unleashing the pharmacological potential of R. retusa root extract. Thus, ethanol may be considered as a suitable solvent to extract, fractionate and isolate the bioactive compounds for health perspectives. Findings also suggested that Kangra region (1375 m; 32.1109° N, 76.5363° E) sample has highest potential and can be focused for further study.