Biological activities of select North American lichens

Abstract

The search for novel, pharmacologically significant compounds is a perpetual quest on which biologists, chemists, and bioinformaticians incessantly embark. The sources of these compounds are often of natural origin, making bioprospecting an enticing area of research. One such source of these natural compounds are lichens, which can produce a plethora of bioactive compounds. Historically, lichens have been held as medicine in traditional healing, while in modern times, research has begun to lend validity to these claims. The aim of this thesis was to extract, separate, identify, and evaluate the anti-cancer and antibiotic activity of numerous bioactive compounds and extracts from North American lichens. Antibacterial efficacy was analyzed via resazurin reduction assay, while anticancer ability was evaluated using the MTT assay and propidium iodide flow cytometry. The lichens studied include Xanthoparmelia mexicana, Lobothallia alphoplaca, and Umbilicaria muhlenbergii. Results from the crude acetone maceration extracts of the lichen showed promise of antibacterial activity against gram-positive bacteria (Xanthoparmelia mexicana, MIC of 41.9 μg mL-1 and 20.9 μg mL-1 against E. faecalis and S. aureus, respectively) while other crude extracts showed promising anticancer activity (Lobothallia alphoplaca, IC50 of 87.0 μg mL-1 against MCF-7 cells, MTT assay). Furthermore, Umbilicaria muhlenbergii showed bioactive prowess against both gram-positive bacteria and cancerous cells, with an MIC of 22.5 μg mL-1 against S. aureus and an IC50 of 13.3 μg mL-1 against MCF-7 cells. Due to it’s marked bioactivity, Umbilicaria muhlenbergii crude extract was further separated with silica gel 60 column chromatography, where multiple fractions were found to be bioactive against select bacteria and MCF-7 cells. Two of these silica gel 60 fractions were then further separated with Sephadex LH-20, yielding multiple fractions which exhibited bioactivity against select bacteria, in addition to anti-cancer abilities and cell-cycle arrest abilities. Further studies will need to be undertaken to fully identify compounds from and evaluate the bioactivity of the lichen extracts investigated.