Hormetic and UV-protective effects of azulene-related compounds

We have previously reported a possible anti-inflammatory activity of azulene-, tropolone- and azulenequinone-related compounds. To further pursue the newly discovered biological activity of these compounds, five compounds that inhibited nitric oxide production by activated macrophages were investigated for their possible hormetic and anti-radiation effects. Viable cell number of human oral normal cells (gingival fibroblast, pulp cell and periodontal ligament fibroblast) and three oral squamous cell carcinoma cell lines on treatment with various concentrations of each azulene-related compound was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Apoptosis induction was monitored by caspase-3 activation and DNA fragmentation. Among five compounds, only benzo[b]cyclohepta[e][1,4]thiazine slightly stimulated the growth of all three normal cell types, but not tumor cell lines, at concentrations slightly higher than cytotoxic concentrations. Using a newly established evaluation system for UV-induced cellular damage, we found that this compound slightly but significantly protected the cells from UV-induced cellular injury, and its effect was synergistically enhanced by sodium ascorbate. These data suggest the possible application of benzo[b]cyclohepta[e][1,4]thiazine in UV protection therapy.