The EpiDerm Phototoxicity Test (EpiDerm H3D-PT)

Phototoxicity is defined as a toxic response from a substance applied to the body which is either elicited or increased (apparent at lower dose levels) after exposure to light, or that is induced by skin irradiation after systemic administration of a substance. Identification of the phototoxic potential of topically or systemically applied test chemicals is a crucial step in the safety assessment of cosmetic and pharmaceutical compounds absorbing UV and visible light. According to the European Medicines Agency and to the SCNFP all test chemicals absorbing significant amount of UV light should be investigated for their phototoxic potency. For ethical reasons, testing of unknown or newly synthesised test chemicals directly in human volunteers is impossible and testing of cosmetic compounds in animals is not an option in the EU. Therefore, before considering any human patch studies, all relevant available in vitro methods should be used for the complex evaluation of the toxicological profile of the compound. Knowledge about the phototoxic potency and skin penetration properties of the test compound are crucial steps in this procedure. The first step to determine the phototoxicity of UV absorbing compound is its evaluation in the validated 3T3 Neutral Red Uptake Phototoxicity Test (3T3 NRU PT) adopted as the OECD TG 432. In case of negative (non-phototoxic) result, due to high sensitivity of this in vitro method, the test chemical can be considered as ‘photo-safe’. However, if the result is positive, the test chemical should be further evaluated in a tiered testing strategy to avoid (1) false positive classification from the sensitive 3T3 NRU PT or (2) to determine safety margins for the test chemical use in a case of a true phototoxin (this consideration should be applicable only for pharmaceuticals where risk-benefit approach can be used). In vitro reconstituted human skin models are increasingly being investigated for their usability in hazard identification and safety testing, because their organotypic structure with a functional stratum corneum allows for assessment of bioavailability of topically applied test chemicals. An in vitro phototoxicity test using human reconstructed epidermis model EpiDerm™ (EpiDerm™ H3D–PT) has been developed and pre-validated almost 20 years ago. The EpiDerm™ H3D–PT assay is designed to detect the phototoxic potential and phototoxic potency of topically applied chemicals and formulations. Since the assay allows application of test materials to the air exposed surface (stratum corneum), it mimics the in vivo situation and thus may allow to predict phototoxic potency of test materials applied in usage concentrations. The test is based upon a comparison of the cytotoxicity of a chemical when tested with and without additional exposure to a non-toxic dose of UVA and visible light. Cytotoxicity is expressed as reduction of mitochondrial conversion of MTT to formazan, determined 1 day after chemical treatment and UVA exposure.

Phototoxicity, UV absorption, EpiDerm Phototoxicity Test (EpiDerm H3D-PT), International Council for Harmonisation (ICH), ICH S10 Guideline, solar simulator, EPI-200-PHO

Chlorpromazine, Promethazine, Bergamot oil, 5-Methoxypsoralen, 8-Methoxypsoralen, Anthracene, Acridine, Neutral red, Tetracycline, Rose Bengal, Ichthammol, Orange oil, Lemon oil, 5-Aminolevulinic acid, 7-Methylcoumarin, Amiodarone, Bithionol, Norfloxacin, Protoporphyrin IX, TetraChlorSalicylAnilide, Deterpenated Lemon, Litsea cubeba, Ichthyol pale, Bergamot oil, BM-DBM, Eusolex9020 (Avobenzone), PABA UV-filter, Benzophenone-3, Methoxycinnamate UV-filter, Mexoryl SX UV-filter, Penicillin G, Octyl salicylate, 4-Methylbenzylidene camphor, Octyl methoxycinnamate, Musk ambrette, 6-Methylcoumarin, Benzalkonium Chloride, DMSO, Ethanol, Eucalyptus oil, Hexachlorophene, l-Histidine, Sodium Dodecyl Sulfate (SDS), Sulisobenzone, Coumarin, Cinnamaldehyde, Titanium Dioxide nano-form: Eusolex T-2000, Titanium Dioxide nano-form: P25 AEROXID, Titanium Dioxide O2 nano-form: TIG-115