Azelaic acid vs. placebo: effects on normal human keratinocytes and melanocytes. Electron microscopic evaluation after long-term application in vivo

The effects of topically applied 20% azelaic acid (AA) on normal human epidermis were investigated vs. placebo in a double blind study by electron microscopy in 15 volunteers. After 3 months of local application twice daily, the pattern of epidermal keratinization was found altered in skin treated with AA. In particular, the number and thickness of tonofilament bundles and the number of keratohyaline granules seemed decreased; the remaining granules were smaller, occasionally showing irregular electron densities. The perinuclear endoplasmic reticulum and the cytoplasmic cisternae were enlarged and swollen mitochondria were regularly observed in most malpighian keratinocytes. Thorough quantitative evaluation of the number and distribution of melanocytes by a MOP-videoplan computer system showed no differences between verum and placebo sites, although, the mean number of melanocytes had increased in both, as compared to the untreated controls taken before onset of therapy. No significant qualitative changes of the normal melanocytes were found. These findings indicate that azelaic acid may influence the differentiation of normal human keratinocytes by reducing the synthesis of keratin precursors and may, therefore, act as a mild antikeratinizing agent, whereas, the pigmentary system in normal human epidermis does not show any specific change after 3 months of treatment with AA.

Initial hyperproliferation and incomplete terminal differentiation of cultured human keratinocytes from lesional and uninvolved psoriatic skin

Human epidermal keratinocytes (KCs) were isolated from lesional and from uninvolved skin of 8 patients with chronic plaque-like psoriasis and from the normal skin of 8 healthy volunteers. Primary KC cultures, grown on 3T3 cell feeder layers, were examined over a period of 4 weeks and their plating efficiency, colony growth area, DNA synthesis and ultrastructural cell differentiation were evaluated. Psoriatic KCs formed colonies one day earlier than non-psoriatic controls and proliferated faster during the first 2 weeks, as assessed by the mean colony growth area and 3H-thymidine incorporation. After 4 weeks, however, no significant differences were observed between the in vitro proliferation parameters of normal and psoriatic KCs. At the ultrastructural level, cultures of lesional psoriatic KCs consisted of more cell layers with adherent transitional cells and incomplete formation of cornified envelopes, even after 4 weeks, while KCs from uninvolved psoriatic skin were characterized by a transient delay of in vitro maturation. These results indicate that the characteristic hyperproliferation of psoriatic KCs may only be maintained over a short period of primary culture, whereas defective terminal differentiation of lesional psoriatic KCs was maintained throughout the culture period.