70 Abstracts / Toxicology 226 (2006) 12–77 treated rats ((3) versus (4), P > 0.1, NS; (7) versus (8), P > 0.1, NS). We conclude that ethanol reduces UCP3 mRNA expression in skeletal muscle. These results contrast with other muscle diseases, which are characterized by up- regulation of UCP3. This effect of alcohol on UCP3 mRNA was prevented by  tocopherol suggesting that it may be a free radical-mediated phenomenon though more work is needed to investigate this. doi:10.1016/j.tox.2006.05.093 Photodegradation analysis as additional tool to verify phototoxicity Melanie Struwe, Markus Trunzer, Daniel Bauer, Michael Kiffe, Ulla Plappert-Helbig, Willi Suter Novartis Pharma AG, Exploratory Development, CH- 4002 Basel, Switzerland E-mail address: melanie.struwe@novartis.com (M. Struwe) Chemicals of different classes may lead to phototoxic effects by absorbing light energy within the sunlight range. This could be caused by several mechanisms such as formation of reactive intermediates, energy transfer to intracellular macromolecules or the generation of reac- tive oxygen species. Recently a photo-comet-assay in L5178Y mouse lymphoma cells was established, which allows the determination of photogenotoxicity and in parallel photocytotoxicity using Alamar Blue. Potential photodegradation was examined using LC/MS analysis techniques, in order to reveal mechanisms involved in between the absorption of the light energy and the result- ing biological effect. Using the alkaline comet-assay 10 well-known photosensitizers from different compound classes (chlorpromazine, 8-methoxypsoralen, ketoprofen, pro- mazine, dacarbacine, lomefloxacin, acridine, titan- dioxid, chlorhexidine, octylmethoxycinnamat) were tested. L5178Y suspension cells were incubated with the selected photosensitizer for 20 min and irradiated using simulated sunlight (290–800 nm) with an applied UV dose of about 600 mJ/cm 2 UV-A and 30 mJ/cm 2 UV-B. After a post-incubation of 10 min the alkaline comet- assay and Alamar Blue test (96 well plate format) were performed. A positive effect was defined as a tripling of the tail moment over the accompanying vehicle control. To exclude the influence of cytotoxicity on the comet- assay data, concentration with a relative viability >50% were considered. The results of our recently established test showed a good concordance with published data with regard to the classification of the chemicals as pho- togenotoxic and/or photocytotoxic. Of the above set, selected compounds were ana- lyzed for the presence of photodegradation products by spectrophotometry and LC/MS before and after irra- diation in PBS. In order to study photodegradation, irradiation was done in the range of 200–2000 mJ/cm 2 UV-A and 10–100 mJ/cm 2 UV-B, respectively. Regard- ing degradation rate and degradation products our data showed a good concordance to literature results, e.g. lomefloxacin degradated to approximately 20% of the starting concentration (1 mg/ml) at 2000 mJ/cm 2 UV-A and 100 mJ/cm 2 UV-B and four of five potential degra- dation products were detected. In addition, to the posi- tive phototoxicity in the photo-comet-assay, these pho- todegradation results provided further insight into the underlying mechanisms, which supports verification of phototoxicity.