Abnormality of water barrier function in psoriasis. Role of ceramide fractions

In psoriasis the formation of the cornified layer is deranged and water flux is reportedly increased. We investigated three different forms of psoriasis: transepidermal water loss was measured on uninvolved skin and psoriatic plaques; lipids from plaques were extracted; and ceramide distribution in scale vs normal stratum corneum was compared. Moreover, the lipid biochemical results were compared with transepidermal water loss rates in the same lesions. To assess potential alteration in ceramide distribution, lipids from both psoriatic scale and normal stratum corneum were extracted by the Bligh-Dyer method, separated on high performance thin layer chromatography plates, and quantified by computerized densitometry. Water flux was measured as transepidermal water loss using an evaporimeter; results between uninvolved and involved psoriatic skin and age-matched control skin were statistically evaluated.

In comparison with normal stratum corneum, psoriatic plaque ceramides showed a different distribution; in particular, ceramide 1 was significantly decreased. The increased transepidermal water loss values of psoriatic plaques vs control skin and between psoriatic involved vs uninvolved skin were significant.

Our findings indicate that in psoriasis the altered ceramide distribution can be linked specifically to the defect in keratinocyte differentiation; the defect in skin barrier function may be attributed largely or in part to ceramide 1 reduction.