Epidermal activity of NAD-dependent isocitrate dehydrogenase in psoriasis during treatment with dithranol

The activity of ICDH(NAD) was measured in subcorneal and basal epidermal layers in 8 patients with psoriasis and in 7 healthy controls treated once a day with 0.15% dithranol in white petrolatum for 2 weeks. Skin biopsies were taken before and on days 2, 6, and 14 of the treatment. Lowry's microtechniques were used in conjunction with a bioluminescent system (bacterial luciferase) for enzymatic assays. The enzymic activity could be related to the type of keratinization present in the stratum corneum overlying the epidermal areas under study. In orthokeratotic areas from the controls, in noninvolved, and in treated involved skin the activity was low. In parakeratotic areas, as found in treated noninvolved and in involved psoriatic skin, the enzymic activity was increased to a level at least twice that found in orthokeratosis. Since ICDH(NAD) activity reflects an aspect of mitochondrial function, the results suggest that mitochondrial activity may be important in control of keratinization.