Modulation of cell adhesion molecule expression and function on human lung microvascular endothelial cells by inhibition of phosphodiesterases 3 and 4

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Abstract
Expression of cell adhesion molecules (CAM) on the lung microvascular endothelium is believed to play a key role in the recruitment of leukocytes in pulmonary inflammation. Moreover, regulation of CAM expression may be an important mechanism through which this inflammation may be controlled. Experimental evidence has suggested that combined phosphodiesterase (PDE) 3 and 4 inhibitors increase cyclic AMP levels within cells greater than inhibition of either isoenzyme alone. In the present study we assessed the effect of combinations of rolipram (PDE4 inhibitor), ORG 9935 (PDE3 inhibitor) and salbutamol (β‐agonist) on CAM expression and neutrophil or eosinophil adhesion to human lung microvascular endothelial cells (HLMVEC). Tumour necrosis factor‐α (TNF‐α)‐induced intercellular adhesion molecule (ICAM)‐1, vascular cell adhesion molecule (VCAM)‐1 and E‐selectin expression were measured on HLMVEC monolayers at 6 h by a specific ELISA technique in the presence of different combinations of medium, rolipram, ORG 9935 and salbutamol. Rolipram in combination with salbutamol, but neither agent alone, inhibited TNF‐α‐induced E‐selectin expression, whilst ICAM‐1 and VCAM‐1 expression were not affected. ORG 9935 had no significant effect on CAM expression alone. However, in combination with rolipram a syngergistic inhibition of VCAM‐1 and E‐selectin, but not ICAM‐1, expression was observed. No further inhibition was seen in the additional presence of salbutamol. Neutrophil adhesion to TNF‐α‐stimulated (6 h) HLMVEC was mainly E‐selectin dependent in this model, as ENA2 an anti‐E‐selectin monoclonal antibody (mAb) abrogated neutrophil adhesion. Eosinophil adhesion was E‐selectin‐, ICAM‐1‐ and VCAM‐1‐dependent, as assessed by the inhibitory activity of ENA2 and the ability of a mAb to the ICAM‐1 ligand, CD18, and a mAb to the VCAM‐1 ligand, VLA4, to attenuate adhesion. Rolipram in the presence of salbutamol or ORG 9935 significantly inhibited neutrophil adherence to TNF‐α‐stimulated HLMVEC. Eosinophil adherence to monolayers was inhibited only when HLMVEC were activated in the presence of rolipram and ORG 9935. Collectively, the findings presented in this manuscript suggest that inhibition of PDE4 with appropriate activation of adenylate cyclase is sufficient to inhibit induction of E‐selectin expression on HLMVEC to a level that has functional consequences for neutrophil adhesion. In contrast, combined inhibition of PDE3 and 4 isoenzymes is necessary to inhibit VCAM‐1 and to have inhibitory effects on eosinophil adhesion to activated HLMVEC. Upregulation of ICAM‐1 expression on HLMVEC does not appear to be modulated by PDE3 and 4 inhibition. These data may have implications for the use of selective PDE4 inhibitors in lung inflammation.