As the environment changes and the risk of sun damaged skin heightens, the phototoxic potential of pharmaceuticals, chemicals, cosmetics and consumer products is receiving increasing attention. Phototoxicity is a toxic reaction of a substance applied to the skin, which is elicited or increased after subsequent exposure to the light.
Drug-induced photosensitivity can be elicited by topical or systemic application of pharmaceuticals in combination with subsequent exposure to sunlight or artificial light. Since the photochemical reaction of drug molecules are a key trigger of phototoxic reactions, photochemical evaluations such as UV spectral analysis and reactive oxygen species (ROS) assay are carried out as photosafety assessment methods in pharmaceutical research to avoid adverse phototoxic events.
Despite years of use, animal-based phototoxicity studies have never been properly validated to determine their relevance to humans or even become a standardized test guideline. In fact, the only internationally accepted guideline for phototoxicity studies is the cell-based assays.
Creative Bioarray has developed and validated the 3T3 neutral red uptake photoxicity assay, erythrocyte hemolysis assay and a phototoxicity screening assay using 3D human epidermis model.
3T3 Neutral Red Uptake (NRU) Assay
The 3T3 neutral red uptake (NRU) assay evaluates phototoxicity by measuring the relative reduction in cell viability after exposure to the test article in the presence or absence of UV/VIS irradiation. Compounds that are phototoxic in vivo after systemic or topical application to the skin can be identified by this assay. The reliability and relevance of the 3T3 NRU assay have been evaluated and shown to be predictive compared to the acute phototoxic effects in animals and humans.
Erythrocyte Hemolysis Assay
Cellular membranes are susceptible to photochemically generated ROS and radicals. Erythrocyte damage caused by UVA and resultant hemolysis (photohemolysis) are used to assess the phototoxic potential of test articles. Sheep red blood cells (SRBC) were incubated with chemicals and irradiated with UVA. Following irradiation, SRBCs were incubated and measured with Drabkin’s reagent. The extent of phototoxicity was determined by the release of hemoglobin from SRBC.
In Vitro Human 3D Epidermis Model
3D reconstructed epidermis model, the test principle is similar to 3T3 NRU test, that is, to assess the differences of tissue viability in the presence and absence of UV/VIS irradiation. However, in 3D epidermis model, water-insoluble materials can be tested and a certain extent of metabolic capacity is retained in primary keratinocytes of the epidermal layer, and these cells may be applied to compounds that require metabolic activation.
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