MODULATION OF CELL-ADHESION MOLECULE EXPRESSION AND FUNCTION ON HUMANLUNG MICROVASCULAR ENDOTHELIAL-CELLS BY INHIBITION OF PHOSPHODIESTERASE-3 AND PHOSPHODISETERASE-4

1 Expression of cell adhesion molecules (CAM) on the lung microvascula r endothelium is believed to play a key role in the recruitment of leu kocytes in pulmonary inflammation. Moreover, regulation of CAM express ion may be an important mechanism through which this inflammation may be controlled. Experimental evidence has suggested that combined phosp hodiesterase (PDE) 3 and 4 inhibitors increase cyclic AMP levels withi n cells greater than inhibition of either isoenzyme alone. In the pres ent study we assessed the effect of combinations of rolipram (PDE4 inh ibitor), ORG 9935 (PDE3 inhibitor) and salbutamol (beta-agonist) on CA M expression and neutrophil or eosinophil adhesion to human lung micro vascular endothelial cells (HLMVEC). 2 Tumour necrosis factor-alpha (T NF-alpha)-induced intercellular adhesion molecule (ICAM)-1, vascular c ell adhesion molecule (VCAM)-1 and E-selectin expression were measured on HLMVEC monolayers at 6 h by a specific ELISA technique in the pres ence of different combinations of medium, rolipram, ORG 9935 and salbu tamol. 3 Rolipram in combination with salbutamol, but neither agent al one, inhibited TNF-alpha-induced E-selectin expression, whilst ICAM-1 and VCAM-1 expression were not affected. ORG 9935 had no significant e ffect on CAM expression alone. However, in combination with rolipram a syngergistic inhibition of VCAM-1 and E-selectin, but not ICAM-1, exp ression was observed. No further inhibition was seen in the additional presence of salbutamol. 4 Neutrophil adhesion to TNF-alpha-stimulated (6 h) HLMVEC was mainly E-selectin dependent in this model, as ENA(2) an anti-E-selectin monoclonal antibody (mAb) abrogated neutrophil adh esion. Eosinophil adhesion was E-selectin-, ICAM-1- and VCAM-1-depende nt, as assessed by the inhibitory activity of ENA(2) and the ability o f a mAb to the ICAM-1 ligand, CD18, and a mAb to the VCAM-1 ligand, VL A(4), to attenuate adhesion. 5 Rolipram in the presence of salbutamol or ORG 9935 significantly inhibited neutrophil adherence to TNF-alpha- stimulated HLMVEC. Eosinophil adherence to monolayers was inhibited on ly when HLMVEC were activated in the presence of rolipram and ORG 9935 . 6 Collectively, the findings presented in this manuscript suggest th at 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 adhesi on to activated HLMVEC. Upregulation of ICAM-1 expression on HLMVEC do es not appear to be modulated by PDE3 and 4 inhibition. These data may have implications for the use of selective PDE4 inhibitors in lung in flammation.