Antioxidant and Photoprotective Metabolites of Bunodophoron melanocarpum , A Lichen from the Andean Páramo

Background: Oxidative stress caused by exposure to ultraviolet radiation has been associated with dermal problems, including skin cancer. In this study, we determined the photoprotective and antioxidant activity of isolated metabolites from the lichen Bunodophoron melanocarpum (Sphaerophoraceae) to find new sunscreens prototypes.

Methods: The constituents of B. melanocarpum were isolated by phytochemical methods and their structures were determined by spectroscopy (IR, 1D and 2D NMR). Antioxidant activity was measured by scavenging DPPH free radicals (EC50), ferric reducing power (FRP), and inhibition of lipid peroxidation (% ILP). The photoprotective capacity against ultraviolet(UVA and UVB) radiations was determined in vitro by calculating their sun protection factor(SPF), critical wavelength and UVA ratio and these values were compared against commercial sunscreens. The lipophilicity and possible skin penetration to the lipid-rich stratum corneum of the isolates, was determined by calculating their octanol/water partition coefficients (Log P) and Gibbs free energy of transfer (ΔtG0 ).

Results: Sphaerophorin (1), everninic acid (2), sphaerophorol carboxylic acid (3) and friedelin(4) were isolated from B. melanocarpum. Orsellinic acid-type compounds 1 and 3 are dual agents with antioxidant capacity as free radical scavengers (EC50= 0.0857 and 0.1828 mol compound /mol DPPH•, respectively) and photoprotective properties particularly against UVB radiation(SPF 25.78 ± 0.53 and 22.00 ± 1.03, respectively). In addition, they had lipophilicity (Log P 7.07 ±0.64 and 4.03 ± 0.32, respectively) and ΔtG0 (-40.32 ± 3.67 and -22.97 ± 1.82 kJmol-1, respectively)suitable to act on the skin.

Conclusion: Sphaerophorin (1) and sphaerophorol carboxylic acid (3) are dual agents with antioxidant and UVB photoprotective properties and are also lipophilic substances that spontaneously would diffuse across the skin.