Response of mononuclear leukocyte cyclic adenosine monophosphate-phosphodiesterase activity to treatment with topical fluorinated steroid ointment in atopic dermatitis

Abstract

Our studies of mononuclear leukocyte peripheral blood homogenates demonstrate significantly increased cyclic adenosine monophosphate-specific phosphodiesterase activity in patients with atopic dermatitis who were untreated for 1 week, compared with normal adult nonatopic control subjects. Phosphodiesterase activity is not related to the extent or activity of the patient's disease or the presence or absence of allergic respiratory disease. Enzyme kinetic studies showed a triphasic plot in normal mononuclear leukocytes but a biphasic plot in atopic dermatitis. This may be interpreted as an absence of an enzyme with a low (0.080) Michaelis Menton constant (Km) in atopic dermatitis samples. One week of therapy with a topical fluorinated steroid ointment caused a significant reduction in disease activity. Although a slight reduction in mean total phosphodiesterase activity occurred, it did not reach statistical significance. One week's treatment, however, caused the abnormal biphasic kinetic plot to revert to a triphasic plot with return of the low Km enzyme form in those patients who showed a fall in phosphodiesterase activity. This finding suggests that the elevated phosphodiesterase activity in atopic dermatitis may be responsive in a limited degree to topical steroid therapy.