1. ^*Dermatology and ,
2. ^†Medical Services (Metabolism), VA Medical Center, University of California, San Francisco, California, USA
3. ^‡Departments of Dermatology and Toxicology, Vrije Universiteit Brussel, Brussels, Belgium

Correspondence: Barbara E. Brown, Dermatology Service (190), VA Medical Center, 4510 Clement Street, San Francisco, CA 94121, USA. Email: kimbro46@aol.com

Received 5 March 2003; Revised 2 April 2005; Accepted 6 April 2005.

Abstract

We showed recently that short-term increases in stratum corneum (SC) pH are accompanied by minor alterations in permeability barrier homeostasis and SC integrity/cohesion. Since prolonged SC neutralization more closely mirrors clinical situations (i.e., neonatal skin, occupational dermatitis conditions), we assessed here whether sustained elevations of SC pH by long-term application of 1,1,3,3-tetramethylguanidine superbase provoke profound alterations in SC function. Sustained SC neutralization altered not only barrier recovery kinetics but also basal permeability barrier function. These abnormalities were attributable to a decrease in -glucocerebrosidase (-GlcCer'ase) and acidic sphingomyelinase (aSMase) catalytic activity and enzyme degradation consequent to a pH-induced sustained serine protease (SP) activity. The role of SP in this process was shown by the normalization of enzyme activities/content by co-applied SP inhibitors (SPI). To address whether lipid-processing enzymes are potential substrates for the stratum corneum chymotryptic enzyme (SCCE), protein extracts from human SC were treated for 2 h at 37°C with recombinant active SCCE at pH 7.2. Recombinant SCCE induced a significant decrease in the immunoblotting of both -GlcCer'ase or aSMase compared with control experiments performed in the absence of the active SCCE. Finally, with sustained SC neutralization, SC integrity/cohesion deteriorated, attributable to SP-mediated degradation of corneodesmosomes (CD) as well as CD constituent proteins, desmoglein 1. These abnormalities were again reversed by co-applied SPI. In conclusion, prolonged SC neutralization provokes profound abnormalities in SC function, due to pH-induced high SP activity that, in turn, degrades lipid processing enzymes and CD proteins.