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

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 dermatitits (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 mu g ml(-1)) and a concentration which produced a submaximal stimulation of proliferation (2 mu g ml(-1)) was selected for further experiments. HPBM (10(5) cells per well) were stimulated with PHA (2 mu g ml(-1)) in the absence or presence of PDE inhibitor (0.01 mu M-10 mu M) and 24 h later [H-3]-thymidine (0.1 mu Ci per well) was added. Cells were incubated for an additional 24 h period and [H-3]-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 mu M (95% confidence limits (CL): 0.158-0.499, n=5) vs normal subjects 2.6 mu M (95% CL: 0.867- 7.05, n=5, P<0.05) as were the IC50 values for denbufylline: 0.26 mu M (95% CL: 0.152-0.440, n=5) vs 1.84 mu M (95% CL: 0.467-7.23, n=5, P<0.05) respectively and RO 20-1724: 1.49 mu M (95% CL: 0.61 mu M-3.64 mu M) vs 6.46 mu M (95% CL: 2.03 mu M-20.46 mu M), 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 mu M (95% CL: 0.43 mu M-7.85 mu M, n=4) was similar to that in AD subjects: 1.03 mu M (95% CL: 0.48 mu M-2.28 mu M) as was the IC50 value for benzafentrine in normal 3.8 mu M (95% CL: 2.45 mu M-5.9 mu M) and atopic 5.5 mu M (95% CL: 3.84 mu M-7.78 mu M) HPBM. The type 5 PDE inhibitor, zaprinast was ineffective at inhibiting the proliferation of normal HPBM. The type 3 PDE inhibitor, siguazodan only inhibited [H-3]-thymidine incorporation at a concentration of 10 mu M. 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.