Effects of dithranol on neutrophil superoxide generation in patients with psoriasis

The effect of dithranol on superoxide generation in vivo has not been studied previously. Neutrophils produce large amounts of superoxide following stimulation by phorbol 12-myristate-13-acetate (PMA). We studied the effect of dithranol on PMA-activated superoxide generation by isolated neutrophils from normal subjects, and measured whole blood luminescence in response to PMA, using samples from 13 psoriatic patients before and during dithranol treatment. Oxidized dithranol had no effect on the PMA-stimulated superoxide generation in neutrophils, but there was a modest dose-related increase in superoxide generation by neutrophils exposed to dithranol before activation. Similar results were found with neutrophils obtained from the 13 psoriasis patients. Three of these patients suffered a dithranol burn and developed a neutrophilia, with a marked increase in stimulated superoxide generating ability. Our findings suggest that dithranol treatment of a psoriasis plaque is associated with a decrease in oxygen radical generating capacity in vivo. However, where inflammation of perilesional and uninvolved skin occurs, neutrophils appear to become semi-activated or primed.