Metabolites with antioxidant and photo-protective properties from Usnea roccellina Motyka, a lichen from Colombian Andes

Abstract

The antioxidant and photo-protective efficacy of the extract and isolated compounds from the lichen Usnea rocellina Motyka were evaluated. The antioxidant activity was determined by scavenging the DPPH radicals and ferric reducing power. The photo-protective property of extracts and isolated compound against ultraviolet A (UVA) and B (UVB) radiations was measured in vitro by calculation of their sun protection factor (SPF), critical wavelength and UVA ratio comparing to commercialised sunscreens (avobenzone and benzophenone-3). 3-methoxycarbonyl-2-hydroxy-6-methoxy-4-methylbenzoic acid (1), reported here for the first time, along with (+)-(9b-R)-usnic acid (2) and decarboxythamnolic acid (3) were isolated. The structure of the isolated compounds was characterized by interpreting their spectroscopic (NMR, IR, UV), and spectrometric data. The findings of this study demonstrated that the compound 3 is a better antioxidant compared to other isolated compound and extract, and was similar to standard (BHT and ascorbic acid) ascorbic acid. On the other hand, 1 showed to be an UVB absorbing with a moderate in vitro SPF whereas 2 and 3 showed broad UVB and UVA absorbing properties. The possible skin penetration, determined by calculating octanol/water partition coefficients allowed to confirm this property in 2 and 3. These results suggest 3 as a dual agent with antioxidant and broad spectrum absorbing properties therefore it is able to prevent oxidative skin damage caused by solar radiation.

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

“…EBm was less potent than positive controls (BHT and AA) to act as free radical scavenger but, it was more potent than other lichen extracts that have been a source of potent antioxidants. 15,23,24 To our knowledge, everninic acid (2), sphaerophorol carboxylic acid (3) and friedelin (4) are reported here for the first time for this species along with sphaerophorin (1) reported previously. 12 The orsellinic acid-type isolated compounds 1, 2 and 3 were better free radical scavengers than EBm; therefore, they can be considered as its active constituents.…”

“…The potency (EC 50 ) of the extract of B. melanocarpum (EBm) and compounds 1 to 4 as free radical scavengers was determined at 25.0 °C using 1,1-diphenyl-2-picrylhydrazyl (DPPH • ) as free radical according to Brand-Williams et al 14 methodology and some modifications as indicated by Rojas et al 15 Butylated hydroxytoluene (BHT) and ascorbic acid (AA) were the positive controls. EtOH solutions of DPPH • and extract or compounds were mixed in different ratios and their initial absorbance and its decrease was recorded (λ 515 nm, every 15 min) until a steady state was reached.…”

“…It is defined as the amount of sample (extract, compound or positive control) necessary to decrease the initial DPPH • concentration by 50 % and it was expressed as mol of compound / mol of DPPH • or mg of sample / mg of DPPH • . 14,15 Reactivity of lichen compounds as free radical scavengers The reactivity of 1 to 4 as free radical scavengers was determined at 25.0 °C by a kinetic study calculating the second-order rate constants (k 2 , M -1 ×s -1 ) for the reaction between each compound (AH) and DPPH • in a ratio 8:1 to 24:1 [AH] 0 /[DPPH • ] 0 . 15 Under the condition [DPPH • ] 0 <<[AH] 0 , the decrease of [DPPH • ] followed a pseudo-firstorder kinetics according to:…”

“…The ferric reducing power (FRP) of EBm and 1 to 4 was determined according to Oyaizu 16 as is described by Rojas et al 15 The capability of antioxidants to reduce ferric (Fe 3+ ) to ferrous (Fe 2+ ) ions was measured through the formation of Perl's Prussian blue complex. Samples and positive control (BHT) solutions (50 -500 ppm) were prepared in EtOH.…”

“…1) that have been a source of potent antioxidants. 15,23,24 Sphaerophorin (1), everninic (2) and sphaerophorol carboxylic (3) acids (EC 50 = 0.0905, 0.0953 and 0.1169 mg compound / mg DPPH•, respectively) were more active than the extract, whereas the triterpene friedelin (4) was inactive (EC 50 = 3.4013 mg compound / mg DPPH•) as free radical scavenger.…”