J.J.L. Jacobs, C. Lehé, K.D.A. Cammans, P.K. Das, G.R. Elliott. Methyl Green-Pyronine Staining of Porcine Organotypic Skin Explant Cultures: An Alternative Model for Screening for Skin Irritants. ATLA (Alternatives To Laboratory Animals) 28: 279-92 (2000).

We describe a new alternative method for screening for irritants, using fresh intact porcine skin biopts. Test chemicals were applied to the epidermis of skin biopts which were then incubated for different times in tissue culture medium at 37o C and 5% carbon dioxide. A decrease in epidermal keratinocyte RNA, visualised in frozen sections using a modified methyl-green pyronine staining procedure, was used as a marker of irritancy. If a decrease in keratinocyte RNA was observed after a 4 hr incubation (strong irritant) the chemical had a MGP score of 3, after a 24 incubation (moderate irritant) the MGP score was 2 and after 48 hrs (weak irritant) the MGP score was 1. If no keratinocyte cytotoxicity was observed after a 48 hr incubation the chemical was classified as a non-irritant (MGP score 0). A minimum of 3 ears were used per chemical. The average MGP score was used to classify the chemical. Based on the MGP score for 20% sodium dodecyl sulphate (SDS), chemicals classified as strong or moderate irritants using the MGP test were grouped together as category R38 chemicals. Weak or non-irritants were none classified (NC). The MGP staining was able to correctly identified 23 of 25 skin irritants for which reference data were available.