Phytochemical Analysis, Antioxidant, Antimicrobial, and Cytotoxic Activity of Different Extracts of Xanthoparmelia stenophylla Lichen from Stara Planina, Serbia

Abstract

The aim of this study was to identify some of the secondary metabolites present in acetonic, methanolic, and hexanic extracts of lichen Xanthoparmelia stenophylla and to examine their antioxidant, antimicrobial, and cytotoxic activity. Compounds of the depsid structure of lecanoric acid, obtusic acid, and atranorin as well as usnic acid with a dibenzofuran structure were identified in the extracts by HPLC. The acetone extract was shown to have the highest total phenolic (167.03 ± 1.12 mg GAE/g) and total flavonoid content (178.84 ± 0.93 mg QE/g) as well as the best antioxidant activity (DPPH IC50 = 81.22 ± 0.54). However, the antimicrobial and antibiofilm tests showed the best activity of hexanic extract, especially against strains of B. cereus, B. subtilis, and S. aureus (MIC < 0.08, and 0.3125 mg/mL, respectively). Additionally, by using the MTT method, the acetonic extract was reported to exhibit a strong cytotoxic effect on the HeLa and HCT-116 cell lines, especially after 72 h (IC50 = 21.17 ± 1.85 and IC50 = 21.48 ± 3.55, respectively). The promising antioxidant, antimicrobial, and cytotoxic effects of Xanthoparmelia stenophylla extracts shown in the current study should be further investigated in vivo and under clinical conditions.

Keywords: DPPH; biological activities; ethnopharmacology; flavonoid content; pharmaceutical potential; phenolic content; usnic acid.

Figure 1

HPLC chromatograms of acetonic, methanolic, and hexanic extracts of lichen Xanthoparmelia stenophylla and the isolated compound usnic acid obtained at 254 nm. 1—Lecanoric acid; 2—obtusic acid; 3—usnic acid; 4—atranorin. (A) Chromatogram of Xanthoparmelia stenophylla acetonic extract obtained at 254 nm; (B) chromatogram of Xanthoparmelia stenophylla methanolic extract obtained at 254 nm; (C) chromatogram of Xanthoparmelia stenophylla hexanic extract obtained at 254 nm; (D) chromatogram of usnic acid obtained at 254 nm.

Figure 2

Chemical structures of compounds identified in the Xanthoparmelia stenophylla extracts: (A) lecanoric acid; (B) obtusic acid; (C) usnic acid; (D) atranorin.

Figure 3

The impact of the tested extracts and usnic acid on the metabolic activity of P. aeruginosa biofilm.

Figure 4

The impact of the tested extracts and usnic acid on the metabolic activity of S. aureus ATCC 6538 biofilm.