Stratum corneum lipid profile and maturation pattern of corneocytes in the outermost layer of fresh scars: the presence of immature corneocytes plays a much more important role in the barrier dysfunction than do changes in intercellular lipids

Background The functional characteristics of the stratum corneum (SC) of fresh scars as well as keloids and hypertrophic scars are characterized by elevated transepidermal water loss (TEWL) and increased SC hydration. Objectives To study the composition of the intercellular lipids and maturation properties of the cornified envelope (CE) of the SC, as these are the most important components for the SC barrier function in fresh scars. Methods SC lipids were extracted from the donor site for split-thickness skin grafting soon after re-epithelialization using a cup method, and were analysed with high-performance thin-layer chromatography. CEs, which were prepared from superficial layers of the SC, were double stained with Nile red and anti-involucrin. Results We found a significant decrease in the proportion of ceramide (CER) in the SC lipids of fresh scars. We also observed changes in the SC CER profile that consisted of an increase in CER 4 and CER 7 and a decrease in CER 3, without any significant change in the proportion of CER 1. These changes were insufficient to explain the remarkably high TEWL recorded in the early stage of fresh scars. In contrast, with double staining of CE with Nile red and anti-involucrin, we detected the presence of numerous immature and less hydrophobic corneocytes in the outermost layer of the SC of fresh scars. Scanning electron microscopy of such corneocytes revealed numerous fine wrinkles on their enlarged surface area. Most of all, we found a closely similar, time-dependent, exponential decrease in the ratio of immature corneocytes with a poorly hydrophobic CE and in the recorded TEWL values in fresh scars. There was a highly significant positive correlation between the proportion of immature corneocytes in the outermost layer of the SC and TEWL values. Conclusions These results suggest that the SC barrier dysfunction of the fresh scars is attributable to the presence of immature corneocytes with a less hydrophobic CE, rather than to the changes in SC lipid composition.