Manglicolous lichen Parmotrema tinctorum (Despr. ex Nyl.) Hale: Isolation, characterization and biological evaluation

Abstract

The chemical examination of the ethanolic extract of manglicolous lichen Parmotrema tinctorum (Pt-Et) has resulted in isolation of six known metabolites, i.e., methyl-β-orcinolcarboxylate (1), isolecanoric acid (2), methyl-2,6-dihydroxy-4-methylbenzoate (3), haematommic acid (4), ethyl haematommate (5), and atranorin (6). All the isolates 1-6 and Pt-Et have been screened against DPPH and superoxide free radicals, six different cancer cell lines (MDA-MB-231, SW620, HeLa, FADU, A549, SKOV3) and one normal human cell line (NHME). Compound 3 exhibits prominent inhibition of superoxide free radical, which appears to be better than that of the standard (ascorbic acid) with an IC₅₀ value of 26.0 µg/mL. From the SRB assay results, it is observed that the better IC₅₀ values have been obtained from 4 and 5 on HeLa, FADU, and A549, respectively. In addition, all the tested samples show low cell lysis on NHME, which indicates low toxicity. Consequently, the outcomes revealed that P. tinctorum could be a new source to treat oxidative stress and cancer. This work is the first report of antioxidant and cytotoxicity studies on the isolated metabolites 1-6.