Natural products have been a significant source of new drugs, especially in treating cancer, infectious diseases, hypertension, and neurological disorders. Although many natural metabolites have been screened and yielded pharmaceutically important drugs, many potential sources of natural product drug therapies still need to be investigated, including lichens. Lichens are symbiotic systems consisting of a filamentous fungus and a photosynthetic partner (an eukaryotic alga and/or cyanobacterium). Lichens produce an impressive variety of unique secondary compounds and have been used as ingredients in folk medicines for centuries. Demonstrated biological roles based on lichen chemistry include: antibiotics, anti-proliferative, antioxidants, anti-HIV, anti-cancer, immunomodulation, and anti-protozoans. Although North America is home to an impressive variety of lichen species, there is limited research to examine the biological potentials of these lichens. The core goal of this dissertation research has been to investigate some of the biological roles including, antibiotic, antioxidant, and anticancer potentials using lichen crude extracts and their metabolites collected from various locations in the United States. Antibiotic screening of crude extracts of 36 lichen species demonstrated inhibitory effects against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Methicillin-resistant S. aureus (MRSA). Generally, acetone extractions were found to be more effective than methanol extractions. It has also been shown that L. vulpina extract was bacteriocidal against MRSA with a relatively slow kill rate that disrupts cell membrane integrity and cell division as possible modes of action. Antioxidant screening of extracts from 11 lichen species, using the Oxygen Radical Absorbance Capacity (ORAC) assay, showed that lichen extracts inhibited the oxidative degradation of the fluorescent molecule (fluorescein-sodium salt) by the oxygen free radical initiator AAPH (2,2'-azobis(2-aminidopropane) dihydrochloride Acetone extracts as well as pure compounds from lichen species showed cytotoxic effects against Burkitt's lymphoma (Raji) cells and a colon cancer cell line (HT29 and SW620). They decreased proliferation, arrested cell cycle at various stages and force the cell to undergo apoptosis. The tested extracts or pure compounds were not toxic to normal cells. In colon cancer apoptosis took place independent of casapase-3. The results of this dissertation showed that lichen compounds merits for further investigation.



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Life Sciences; Biology



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lichen, antibacterial, anticancer, antioxidant, immunomodulation, secondary metabolites, mode of action, cell cycle, apoptosis, MTT, bacteriolysis, transmission electron microscopy



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