Three-dimensional analyses of individual corneocytes with atomic force microscope: morphological changes related to age, location and to the pathologic skin conditions.

Background/aims: The past morphological studies on individual corneocytes have so far mainly focused on their two-dimensional characteristics, particularly on their projected area, which have been widely employed for the estimation of the turnover rate of the stratum corneum because of the practical use. However, sometimes a poor correlation has been reported between the projected area of corneocytes and actually measured turnover time of the stratum corneum. The objective of the present study is to perform detailed three-dimensional measurements of individual corneocytes with atomic force microscope. Through analyses of the obtained data, we tried to find morphological parameters that reflect more closely the differentiation process of the corneocytes in the stratum corneum than the frequently used two-dimensional projected area. Methods: We measured such morphological parameters as the volume, average thickness and real surface area of individual corneocytes isolated from the covered skin (the flexor surface of the upper arm) and the exposed skin (the cheek) of 12 healthy individuals belonging to different age brackets, in addition to their projected area. We further introduced a new parameter, a flatness index calculated by dividing the projected area of corneocytes by their thickness. Similarly, we measured corneocytes obtained from eight patients with atopic dermatitis (AD) and psoriatic patients. Results: Obtained results showed that most of these morphological parameters varied greatly depending upon the anatomical location and age of the subjects. Needless to say great differences were found between healthy skin and lesional skin of atopic dermatitis or psoriasis. However, the volume and thickness of corneocytes collected from the same location of normal skin of the covered area (upper arm) with tape-strippings were noted to decrease as they differentiated in the stratum corneum, showing an increase in their surface area and projected area with a resultant increase in the flatness index. Moreover, the corneocyte collected from the lesional skin of AD or psoriasis showed a great decrease in flatness index, reflecting their poor differentiation in the stratum corneum due to its enhanced turnover rate. Most of all, we found a poor correlation between the projected area and the various three-dimensional morphologic parameters of the corneocytes, indicating that the projected area does not reflect the volume or thickness of corneocytes that are also greatly influenced by the differentiation process of corneocytes in the stratum corneum. Conclusions: To estimate the differentiation speed of the corneocytes, we suggest using their flatness index rather than the two-dimensional cell surface area, because the former is a concept that takes into account the three-dimensional characteristics of corneocytes.