Читать книгу pH of the Skin: Issues and Challenges - Группа авторов - Страница 57

The acidity of the skin surface is also involved in the regulation of the corneocyte desquamation, namely SC integrity and cohesion. The main enzymes regulating the integrity/cohesion, kallikrein 5 (previously named SC trypsin-like enzyme) and kallikrein 7 (previously named SC chymotrypsin-like enzyme) exhibit normal-to-alkaline pH optima [29, 30]. A superbase-induced elevation in SC pH in a rodent model resulted in a reversible increase of the activity of these 2 key enzymes [31]. Moreover, the increase of kallikrein 5 and 7 induced the degradation of desmoglein 1 and a reduction of the corneodesmosome-density, thus stimulating the process of desquamation [31]. Acidification of skin surface results in a normalization of lipid processing and inhibition of the degradation of corneodesmosomes [32].

The acidic buffer system of the SC is essential for modulating the non-specific antimicrobial protection as part of the regulation of the innate immunity [33]. Elevation of skin surface pH values is beneficial for growing pathogens on the skin surface, such as Staphylococcus aureus and Candida albicans, while normal flora predominantly grows in an acidic environment [7, 34]. The absence of an acidic SC at birth has been associated with an increased risk of bacterial and yeast infections in neonates [35] and more pronounced in pre-term infants [36]. The clinical importance of these findings is reflected in the pathophysiology of diaper dermatitis during infancy. The incomplete acidification of the SC, together with the ammonia-induced alkalization activates stool enzymes (trypsin, lipases), causing irritation and further perturbation of the skin barrier and subsequently an induction of an inflammatory cascade.