Evaluation of a general toxicity study incorporating phototoxicity assessments in Sprague-Dawley rats

In Silico Phototoxicity Prediction of Drugs and Chemicals by using Derek Nexus and QSAR Toolbox

Phototoxicity testing is crucial for evaluating the potential harmful effects of pharmaceuticals and chemicals on human skin when exposed to sunlight. Traditional in vivo models involving mice, rats, guinea pigs, as well as in vitro assays such as the 3T3 Neutral Red Uptake phototoxicity assay and methods based on the use of reconstructed human epidermis, have been established for phototoxicity testing. While these approaches are extremely valuable, they are costly in terms of both time and resources. Consequently, in silico approaches based on the use of predictive software tools can offer more rapid and cost-effective phototoxicity screening solutions. With this goal in mind, the current study evaluated two in silico tools - Derek Nexus 6.1.0/Derek Knowledge Base 2020 1.0 (Lhasa Limited, UK) and the QSAR Toolbox (v 4.5) developed by the Organisation for Economic Co-operation and Development (OECD) - for their capacity to predict the phototoxicity of several substances from diverse classes. Derek Nexus and the QSAR Toolbox were both found to be very useful for predicting the phototoxicity of drugs and other chemicals. Derek Nexus predicted phototoxicity of the compounds, with a sensitivity of 63%, specificity of 93%, Positive Predictive Values of 90% and Negative Predictive Value of 69%, overall accuracy of 77% and balanced accuracy of 78%. The QSAR Toolbox achieved sensitivity of 73%, specificity of 85%, Positive Predictive Value of 85% and Negative Predictive Value of 74%, overall accuracy of 79% and balanced accuracy of 79%. The results show that Derek Nexus and the QSAR Toolbox can be usefully incorporated in the workflow of phototoxicity testing for pharmaceuticals and chemicals.

Assessment of phototoxicity in pigmented Long-Evans rat: sparfloxacin and 8-methoxypsoralen

The aim of the present work was to evaluate the effects of photo-activated toxicity induced after administration of two known melanin-binding phototoxic compounds, sparfloxacin (SPX) and 8-methoxypsoralen (8-MOP), followed or not by UVA/Vis exposure, in pigmented rats (Long Evans: LE) and albino rats (Sprague Dawley: SD). Groups of three rats were treated with SPX or 8-MOP by oral gavage for six consecutive days. Irradiated animals were submitted to a UVA/Vis light dose standardized to 10 J/cm² UVA daily. Clinical signs, cutaneous reactions and body weight were monitored throughout the study period. Ear biopsy weight, lymph node weight and lymph node cell count were determined at necropsy. Ophthalmologic examinations were performed before the first treatment and on the day of sacrifice. Microscopic examinations were performed on skin biopsies and eyes. Phototoxicity was demonstrated for both SPX and 8-MOP in the pigmented and albino strains, in terms of auricular irritation, lymph node weight and proliferation index, cutaneous reactions and ocular histopathology. LE rats were less sensitive than SD rats, especially at the ocular level, supporting the notion that pigmentation may provide protection against photo-activation. The pigmented rat may be a more relevant model than the albino rat for human safety evaluation.