Seasonal variation in stratum corneum (SC) biophysical and biological characteristics has been described previously. In particular, the winter season has been shown to affect more severely the properties of facial skin compared with forearm skin. Moreover, when compromised, such as in dry skin conditions, facial SC has been shown to contain increased inflammatory cytokines and proteases. Nevertheless, there have been no comparative studies of the activities and depth activity of several proteases in the SC on different body sites and at different times of the year. In this study, we examined the distribution of key serine protease activities (kallikrein 5, kallikrein 7, urokinase, plasmin and a tryptase-like enzyme) in different layers of the SC on the cheek and the forearm by analysis of consecutive tape strippings of healthy Caucasian subjects during winter and summer. The protein content of the tape strippings was quantified by absorption measurements with a recently developed and novel infrared densitometer SquameScan(TM) 850A while the SC enzyme activities were determined using fluorogenic peptide substrates. Transepidermal water loss (TEWL), skin pH and skin hydration were higher on the cheek than on the forearm. In the same way, the activity of the inflammatory-related proteases plasmin, urokinase and tryptase was approximately five to eight times and the activity of the desquamatory-related proteases kallikrein 5 and kallikrein 7 approximately two to four times higher on the cheek than on the forearm. There were no gender-related differences in these enzyme activities except for the increased kallikrein 7 in the forearm skin of the female subjects in winter. Reduced kallikrein 5 was associated with increased SC cohesion, as judged by increased protein removal, in forearm skin in the winter months of the year although the skin was clinically normal. It can be concluded that (i) protected skin areas show lower TEWL, skin pH and skin hydration and less protease activities than skin areas that are exposed to the environment, possibly indicating subclinical inflammation on these body sites, (ii) in normal healthy forearm skin, the outer SC exhibits greater serine protease activity than its deeper layers, (iii) compared with the forearm, urokinase- and plasmin-like activities are elevated on SC strippings from the cheek, confirming activation of the plasminogen cascade, and (iv) tryptase-like activity in the SC is also elevated in samples from the cheek, possibly indicating involvement of mast cells in these barrier-compromised body sites or the synthesis of a novel tryptase-like enzyme by keratinocytes. Although elevation of the activities of urokinase, plasmin, kallikrein 5, kallikrein 7 and now a tryptase-like enzyme was observed on SC derived from skin of clinically normal cheeks, we anticipate even higher activities in skin conditions where the epidermal barrier is further impaired.
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