Structural and functional response of the isolated toad skin to mucosal lithium

Effects of lithium carbonate (Li2CO3) on in-vitro-cultured normal human skin explants

The early morphological changes induced by lithium carbonate, a well-known psoriasis-provoking drug, were studied on cultured skin. Normal human skin from patients undergoing mastectomy was cultured in the presence of 3 mM, 6 mM and 10 mM of Li2CO3 for 4 days. The morphological changes were then evaluated by three observers in a blind manner and their reports were matched and collated. The cultured skin in the presence of Li2CO3 showed cell crowding of keratinocytes in the lower part of the epidermis, indicating epidermal hyperplasia. Another striking finding was intercellular oedema and vacuolar alteration with formation of small cavities in the upper dermis. There was no evidence of parakeratosis or any other histological characteristic of psoriasis, except hyperproliferation of the epidermis. Based on our knowledge of mechanisms of lithium action, we proposed two competitive explanations for its action on the epidermis: i) that lithium acts directly on dividing cells of the epidermis; and ii) that it acts indirectly by altering epidermal barrier function. Although we lack definite proof, we suggest that the observed morphological changes, in particular the non-specific stimulus to epidermal proliferation, are the primary events which initiate the process that will ultimately lead to the development of psoriasis in a predisposed patient.