Identification of pancreatic type I secreted phospholipase A2 in human epidermis and its determination by tape stripping

Phospholipases A(2) (PLA(2)) catalyse the release of fatty acids from the sn-2 position of phospholipids and have been suggested to play a key part in permeability barrier homeostasis, Using a sensitive and versatile fluorometric method, significant PLA(2) activity has been detected in both human skin homogenates and tape strippings of stratum corneum. Based on various properties (resistance to heat and sulphuric acid treatment, neutral optimal pH, absolute requirement for millimolar calcium concentrations, inhibition by dithiothreitol and p-bromnphenacyl bromide, and resistance to a trifluoromethyl ketone derivative of arachidonic acid, AACOCF3, a specific inhibitor of cytosolic PLA(2)), this enzyme was characterized as a secretory PLA(2) (sPLA(2)), Immunohistochemistry revealed strong labelling of type I pancreatic sPLA(2) at the stratum corneum-stratum granulosum junction, type II sPLA(2) being undetectable, An increase in PLA(2) activity in tape-stripped material from the deepest level of the stratum corneum was correlated with partial morphological disappearance of type I sPLA(2) immunolabelling. Our data thus provide the first convincing evidence that pancreatic sPLA(2) is significantly expressed in human epidermis, where it might participate in the accumulation of free fatty acids contributing to the permeability barrier. In addition, our method for determining PLA(2) activity in easily available tape strippings should allow further clinical studies aimed to explore possible PLA(2) abnormalities in various dermatoses.