Abstract
Targeting of drug nanocarriers (NCs) to intercellular adhesion molecule‐1 (ICAM‐1), an endothelial‐surface protein overexpressed in many pathologies, has shown promise for therapeutic delivery into and across this lining. However, due to the role of ICAM‐1 in inflammation, the effects of targeting this receptor need investigation. Since ICAM‐1 binding by natural ligands (leukocyte integrins) results in release of the “soluble ICAM‐1” ectodomain (sICAM‐1), an inflammatory regulator, we investigated the influence of targeting ICAM‐1 with NCs on this process. For this, sICAM‐1 was measured by ELISA from cell‐medium supernatants, after incubation of endothelial cell (EC) monolayers in the absence versus presence of anti‐ICAM NCs. In the absence of NCs, ECs released sICAM‐1 when treated with a pro‐inflammatory cytokine. This was reduced by inhibiting matrix metalloproteinases MMP‐9 or MMP‐2, yet inhibiting both did not render additive effects. Release of sICAM‐1 mainly occurred at the basolateral versus apical side, and both MMP‐9 and MMP‐2 influenced apical release, while basolateral release depended on MMP‐9. Interestingly, anti‐ICAM NCs reduced sICAM‐1 to a greater extent than MMP inhibition, both at the apical and basolateral sides. This effect was enhanced with time, although NCs had been removed after binding to cells, ruling out a “trapping” effect of NCs. Instead, inhibiting anti‐ICAM NC endocytosis counteracted their inhibition on sICAM‐1 release. Hence, anti‐ICAM NCs inhibited sICAM‐1 release by mobilizing ICAM‐1 from the cell‐surface into intracellular vesicles. Since elevated levels of sICAM‐1 associate with numerous diseases, this effect represents a secondary benefit of using ICAM‐1‐targeted NCs for drug delivery.
Highlights
Being at the interface between the circulation and subjacent tissues, vascular endothelial cells (ECs) contribute to important physiological functions, including transport of metabolites and signaling molecules that communicate between these two compartments, regulation of vascular tone, hemostatic function, inflammatory response, and so on.[1]
Since intercellular adhesion molecule-1 (ICAM-1) binding by natural ligands results in release of the “soluble ICAM-1” ectodomain, an inflammatory regulator, we investigated the influence of targeting ICAM-1 with NCs on this process
Given that elevated soluble ICAM-1” ectodomain (sICAM-1) is considered a pathological marker implicated in the development of numerous pathologies,[6,22] attenuation of its release may benefit these conditions
Summary
Being at the interface between the circulation and subjacent tissues, vascular endothelial cells (ECs) contribute to important physiological functions, including transport of metabolites and signaling molecules that communicate between these two compartments, regulation of vascular tone, hemostatic function, inflammatory response, and so on.[1] As such, ECs are important targets for therapeutic intervention An illustration of this relevance is the fact that numerous drug delivery strategies are being explored to target pharmaceuticals to the endothelium, either for endothelialsurface release into the circulation, uptake into ECs to treat endothelial maladies, or transport across this lining to access subjacent tissues.[2,3]. By contributing to the adhesion of leukocytes to the endothelium, their extravasation into sites of disease and other associated signaling cascades, endothelial CAMs play an important role in the inflammatory processes that underlie most maladies.[4,5] An example is that of intercellular adhesion molecule-1 (ICAM-1), an immunoglobulin(Ig)-like transmembrane glycoprotein overexpressed on the endothelial lumen during many pathological states.[5,6,7] Given these properties, targeting endothelial ICAM-1 has been studied for both diagnostic and therapeutic applications.[8,9,10,11,12,13,14]
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