Photoprotecting action and phytochemical analysis of a multiple radical scavenger lipophilic fraction obtained from the leaf of the seagrass Thalassia testudinum

The apolar fraction F1 of Thalassia testudinum was chemically characterized by gas chromatography-mass spectrometry, which led to the identification of 43 metabolites, all of them reported for the first time in the genus Thalassia. More than 80% of the F1 composition was constituted by aromatic metabolites including the major components 1,1-bis(p-tolyl)ethane (6.0%), 4,4′-diisopropylbiphenyl (4.8%) and a 1,1-bis(p-tolyl)ethane isomer (4.7%). This lipophilic fraction was assayed for its antioxidant effects and skin protective action. In vitro assays showed that F1 strongly scavenged DPPH* (IC ₅₀ 312.0 ± 8.0 μg mL ^-1), hydroxyl (IC ₅₀ 23.8 ± 0.5 μg mL ^-1) and peroxyl radical (IC ₅₀ 6.6 ± 0.3 μg mL ^-1), as well as superoxide anion (IC ₅₀ 50.0 ± 0.7 μg mL ^-1). Also, F1 markedly inhibited the spontaneous lipid peroxidation (LPO) in brain homogenates (IC ₅₀ 93.0 ± 6.0 μg mL ^-1) and the LPS-stimulated nitrite generation on RAW624.7 macrophages (58.6 ± 3.2%, 400 μg mL ^-1). In agreement with these findings, its topical application at 250 and 500 μg cm ^-2 strikingly reduced skin damage on mice exposed to acute UVB radiation by 45% and 70%, respectively and significantly attenuated the LPO developed following the first 48 h after acute exposure to UVB irradiation, as manifested by the decreased malondialdehide level and by the increased of reduced gluthatione content. Our results suggest that F1 may contribute to skin repair by attenuating oxidative stress due to its antioxidant activity. The lipophilic fraction F1 obtained from Thalassia testudinum mainly composed of benzene derivatives, strongly scavenged DPPHE*, HOE*, RO ₂E* and O ₂E* ^-; markedly inhibited the spontaneous lipid peroxidation in brain homogenates and the LPS-stimulated nitrite generation on RAW624.7 macrophages. In agreement with these findings, its topical application strikingly reduced skin damage on mice exposed to acute UVB radiation and significantly attenuated the lipid peroxidation in vivo after acute exposure to UVB irradiation. This suggests that the antioxidant activity of F1 partially accounted for its skin protective action.