Antioxidative and cardiovascular-protective activities of metabolite usnic acid and psoromic acid produced by lichen species Usnea complanata under submerged fermentation

Context: Lichens have been used for various purposes such as dyes, perfumes and remedies in folk medicine indicating the pharmaceutical potential of lichens.

Objective: lichen growth in nature is very slow. To overcome this major drawback, we standardized the culture media to culture the lichen Usnea complanata (Müll.Arg.) Motyka (Parmeliaceae) for (1) in vitro synthesis of natural lichen substances, and (2) determination of antioxidative and cardiovascular-protective activity of usnic acid and psoromic acid.

Materials and methods: lichen U. complanata has been cultured in fermentor under submerged condition. Antioxidative and cardiovascular-protective activity of the extract and the purified lichen substances usnic and psoromic acid have been determined.

Results: Except methanol, all other extracts exhibited antioxidative action in terms of free radical scavenging activity (FRSA) with a half-inhibiting concentration (IC₅₀) value of 22.86 to 25.0 µg/mL, nitric oxide radical scavenging activity (NORSA) 141.3 to 149.1 µg/mL and for lipid peroxidation inhibition (LPI) 125 to 157.9 µg/mL. Usnic acid or psoromic acid showed antioxidative action with IC₅₀ values ranging from 0.174 to 0.271 mg/mL. Methanol and ethyl acetate extract showed hydroxy-3-methyl-glutaryl-CoA reductase (HMGR) inhibition of 65.18 to 74.81%. Only 43.47% inhibition of angiotensin converting Enzyme (ACE) was shown by methanol extract. Usnic acid showed noncompetitive type of HMGR inhibition and uncompetitive type of ACE inhibition. Psoromic acid exhibited competitive type of HMGR inhibition and mixed type of ACE inhibition.

Discussion: U. complanata showed both cardiovascular-protective and antioxidant properties. The lichen species U. complanata may be a natural bioresource for possible pharmaceutical applications.