The report describes a method for the assay of five enzymatic activities involved in establishing the stratum corneum permeability barrier: β-glucocerebrosidase, acid phosphatase, phospholipase A₂ (PLA₂) and two serine proteases: chymotrypsin and its activator in the stratum corneum, trypsin. The specific activities of these different enzymes have been determined along with their pH profiles and sensivities to specific inhibitors. It can be noted that only two presented a pH optimum similar to the pH of the stratum corneum. This could suggest that their activities are regulated by local variations in pH. The method was applied to a pathological situation, that of a non-eczematous dry atopic dermatitis. Atopic skin had significantly reduced trypsin activity, increased acid phosphatase and no change in the activities of three other studied enzymes. Understanding these activities can provide a tool for the characterization of skin pathologies and for the development of a certain number of applications in cosmetology and therapeutics.

Phospholipases A2 (PLA2) 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 PLA2 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-bromophenacyl bromide, and resistance to a trifluoromethyl ketone derivative of arachidonic acid, AACOCF3, a specific inhibitor of cytosolic PLA2), this enzyme was characterized as a secretory PLA2 (sPLA2). Immunohistochemistry revealed strong labelling of type I pancreatic sPLA2 at the stratum corneum-stratum granulosum junction, type II sPLA2 being undetectable. An increase in PLA2 activity in tape-stripped material from the deepest level of the stratum corneum was correlated with partial morphological disappearance of type I sPLA2 immunolabelling. Our data thus provide the first convincing evidence that pancreatic sPLA2 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 PLA2 activity in easily available tape strippings should allow further clinical studies aimed to explore possible PLA2 abnormalities in various dermatoses.

Skin surface enzyme activities were found to be significantly different in healthy and in skin with atopic dermatitis and, following appropriate treatment, a close correlation was observed between the clinical staging of the atopic dermatitis and the levels of the assayed marker enzymes. Samples were taken, by stripping with simple adhesive tapes, from a group of subjects on cure in a spa. The corneocytes were recovered from the first layers of the stratum corneum. Aqueous extracts of the strips were tested for their activity on chromophoric substrates which allow fluorescence spectrometry to be used to assay the trypsin-like, acid-phosphatase-like and phospholipase-A2-like activities. We show that the restoration of return to activities close to those of healthy subjects is related to the general condition of the patients, who showed a clearly improved SCORAD. Recovery of the trypsin-like activity and attenuation of the phospholipase-like activity, paralleled the regression of the dermatitis as assessed by a decrease in clinically evaluated parameters of xerosis and inflammation.