Effects of azelaic acid on sebaceous gland, sebum excretion rate and keratinization pattern in human skin. An in vivo and in vitro study.

The effects of azelaic acid (AZA) on the epidermis of 47 individuals (12 with normal skin, 15 with seborrheic skin and 20 suffering from acne) and on in vitro cultured keratinocytes are reported. Topical application of a 20% AZA cream significantly improved the lesions of acne patients, but failed to induce clinically detectable changes in normal or seborrheic epidermis. Complementary investigations clearly showed that AZA treatment failed to induce specific changes in sebum composition, excretion rate, or in the size of sebaceous glands, but modified epidermal keratinization. Keratohyalin granules and tonofilament bundles were reduced in size and number, mitochondria were swollen and the rough endoplasmic reticulum of malpighian keratinocytes enlarged. The infundibular epidermis of acne individuals showed marked reduction of the horny layer thickness, widening of the horny cell cytoplasm, transitional corneal cells, normalization of filaggrin distribution, and the comedo contained few bacteria and spores. In vitro, AZA exerted marked time- and dose-dependent antiproliferative cytostatic effects on cultured keratinocytes, with a 50% inhibitory dose of 20 mM, decreased some keratinocyte proteins (highly soluble fractions S2, keratohyalin macroaggregate R2, and non-cross-linked fibrous protein S4) and a 95 kD and a 35 kD protein of the cytosolic fraction. Mitochondria were frequently damaged and the rough endoplasmic reticulum enlarged. Our results indicate that AZA is an antikeratinizing agent, displaying antiproliferative cytostatic effects on keratinocytes and modulating the early and terminal phases of epidermal differentiation.