Cigarette smoke and monocytes : a dangerous relationship for the endothelium?

Cigarette smoke induces vascular endothelial cell (EC) dysfunctions, a key event in the development of atherosclerosis. Circulating monocytes (HM) participate in the atherogenic process by adhering to a damaged endothelium and migrating into the intima where they differentiate to macrophages and contribute to plaque growth. We recently demonstrated that cigarette smoke condensate (CSC) induces HM to release chemotactic factors, with consequent recruitment and transmigration of inflammatory cells through EC. In order to further evaluate how CSC might affect HM/EC interaction, we analyzed the effect of CSC (30 g/ml) alone and/or of conditioned medium (CM) from HM previously incubated with (CM/CSC) or without CSC. The incubation with CSC, CM or CM/CSC did not affect EC vitality, as shown by the MTT assay. In contrast, CSC cooperated with TNFalfa in inducing the expression of matrix metalloproteinase-1 and -9 in EC, but it did not affect the expression of adhesion molecules VCAM-1 and ICAM-1. CSC, CM and CM/CSC reduced HM rolling on TNFalfa-activated EC assessed by time-lapse video microscopy. Then, we used the iCELLigence System to acquire quantitative information about the biological status of EC, including cell number, adhesion, viability, and morphology. Only the addition of CM/CSC to confluent EC monolayer dramatically modified the pattern of the electric flow, suggesting modifications in EC morphology. Indeed, an altered actin cytoskeleton organization was observed by immunofluorescence studies performed with FITC-conjugated phalloidin. In particular, CM/CSC caused the shrinking of the EC cytoplasm by about 50% (p<0.01 vs CSC or CM). In contrast, EC morphology was not affected by exposure to CM or CSC. In conclusion, cigarette smoke condensate, at nontoxic concentration, induces HM to secrete some soluble factors able to affect EC morphology, with a consequent negative impact on EC permeability thus facilitating HM transmigration through the EC monolayer.