Differential effect of phosphodiesterase 4 inhibitors on the proliferation of human peripheral blood mononuclear cells from normals and subjects with atopic dermatitis

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Abstract
1. The aims of this study were to compare the effects of selective inhibitors of the type 3, type 4 and type 5 phosphodiesterase (PDE) isoenzymes on the phytohaemagglutinin (PHA)-stimulated proliferation of human peripheral blood mononuclear cells (HPBM) from normals and subjects with atopic dermatitis (AD). 2. Mononuclear cells were isolated from peripheral venous blood of normals and subjects with AD. A concentration-response curve was carried out with PHA (0.5-5 micrograms ml-1) and a concentration which produced a submaximal stimulation of proliferation (2 micrograms ml-1) was selected for further experiments. HPBM (10(5) cells per well) were stimulated with PHA (2 micrograms ml-1) in the absence or presence of PDE inhibitor (0.01 microM-10 microM) and 24 h later [3H]-thymidine (0.1 microCi per well) was added. Cells were incubated for an additional 24 h period and [3H]-thymidine incorporation measured. 3. The type 4 PDE inhibitors (rolipram, RO 20-1724 and denbufylline) produced a concentration-related inhibition of proliferation of HPBM from normal and AD subjects. The IC50 for rolipram was significantly (P < 0.05) lower in HPBM from AD patients 0.28 microM (95% confidence limits (CL): 0.158-0.499, n = 5) vs normal subjects 2.6 microM (95% CL: 0.867-7.05, n = 5, P < 0.05) as were the IC50 values for denbufylline: 0.26 microM (95% CL: 0.152-0.440, n = 5) vs 1.84 microM (95% CL: 0.467-7.23, n = 5, P < 0.05) respectively and RO 20-1724: 1.49 microM (95% CL: 0.61 microM-3.64 microM) vs 6.46 microM (95% CL: 2.03 microM-20.46 microM), respectively. 4. The mixed type 3/4 inhibitors (zardaverine and benzafentrine) produced a concentration-related inhibition of proliferation of HPBM from normal and AD subjects. The IC50 value for zardaverine in HPBM from normal subjects: 1.8 microM (95% CL: 0.43 microM-7.85 microM, n = 4) was similar to that in AD subjects: 1.03 microM (95% CL: 0.48 microM-2.28 microM) as was the IC50 value for benzafentrine in normal 3.8 microM (95% CL: 2.45 microM-5.9 microM) and atopic 5.5 microM (95% CL: 3.84 microM-7.78 microM) HPBM. The type 5 PDE inhibitor, zaprinast was ineffective at inhibiting the proliferation of normal HPBM. The type 3 PDE inhibitor, siguazodan only inhibited [3H]-thymidine incorporation at a concentration of 10 microM. 5. These results show that combined inhibition of the type 3 and 4 PDE isoenzymes in HPBM from normal subjects has a greater antiproliferative effect than inhibition of the type 4 isoenzyme alone. In addition these data indicate that the proliferative response of HPBM from AD subjects is more sensitive to PDE 4 inhibition than the proliferation of HPBM from normals.