Anti-UV Activity of Lignin–Carbohydrate Complex and Related Compounds

Background: We recently reported that an alkaline extract of the leaves of Sasa senanensis Rehder (SE) and Lentinus edodes mycelia extract (LEM), exhibiting lignin−carbohydrate complex (LCC)-like activity, protected cells from UV-induced injury (referred to as anti-UV activity). We investigated whether LCC is the major active components responsible for anti-UV activity. Materials and Methods: Human oral squamous cell carcinoma HSC-2 cells were exposed to short UV irradiation in phosphate-buffered saline, containing different concentrations of LCC. After culturing for 48 h in fresh culture medium, the viable cell number was determined by the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) method. From the dose-response curve, the 50% cytotoxic concentration (CC 50 ) and the concentration that increased the viability of the UV-irradiated cells to 50% of the control value (EC 50 ) were determined. The selectivity index (SI) was determined by the following equation: SI=CC 50 /EC 50 . Results: LCCs (Fr. VI) of pine cones and seed shell, and sulfated LCC exhibited relatively high anti-UV activity (SI=7.1-38), compared with that of SE and LEM. LCCs with lower lignin content (Fr. VII) exhibited anti-UV activity, approximately one half that of Fr. VI. However, polysaccharides (laminarin, pullulan, dextran) introduced with dimethylaminoethyl- or sulfate groups with different substitution ratios were totally inactive (SI<1). The introduction of a sulfate group to LCC did not enhance the anti-UV activity of LCC. Sodium ascorbate and vanillin were the most active (SI=65), whereas gallic acid (SI=5), epigallocatechin gallate (SI=2.6), ar- trumeron (SI<1), and turmeric extract (SI<1) were much less active. Conclusion: The prominent anti-UV activity of SE and LEM seems to be generated by LCCs present in the extract. Ultraviolet rays (UV) are invisible electromagnetic waves