Influence on membrane-mediated cell activation by vesicles of silicone oil or perfluorohexyloctane.

PURPOSE: This study was conducted to investigate whether macrophage activation through cell membrane attachment might be supported by emulsified tamponade droplets of a certain vesicle size. It has been hypothesized that emulsification of vitreous tamponades might stimulate retinal membrane formation.
METHODS: In this laboratory investigation, similarly sized vesicles of silicone oil and the partially fluorinated alkane perfluorohexyloctane (F6H8) were produced by extrusion through polycarbonate membranes. Human neutrophils were obtained from blood donors. Human monocytes were negatively isolated from mononuclear cells by depletion of other cells. Cell activation status of phagocyting blood neutrophils was measured by a chemiluminescence assay. Fluorescent attached or internalized vesicles were monitored by fluorescent microscopy. The main outcome measures were the altered activation status of monocytes after vesicle incubation and the ability of human macrophages to attach and/or internalize vesicles in vitro.
RESULTS: Extruding silicone oil through a polycarbonate membrane resulted in the production of vesicles that remained stable for at least 2 days. F6H8 vesicles had to be stabilized with an emulsifier, in this case Pluronic PE6800 or Lipoid EPC. The mean vesicle diameter was similar with both components (F6H8: 13.08+/-2.95 microm, silicone oil: 10.05+/-4.6 microm). Neutrophil activation was not influenced by either emulsifier alone or by silicone oil vesicles without emulsifier. Stabilized F6H8 vesicles had a dose-dependent influence on blood neutrophil activation. Only silicone oil vesicles together with Lipoid EPC, not Pluronic PE6800, had a comparable influence on neutrophil activation. Neutrophil activation was influenced neither by 0.125% human serum albumin (HSA) alone nor by vesicles of F6H8 or silicone oil prepared with 0.125% HSA. Monocyte cell membrane attachment of silicone fluid was two times higher than that of F6H8 fluid. F6H8/Pluronic PE6800 vesicles enhanced this process 20-fold, whereas silicone oil vesicles did not enhance cell membrane attachment significantly.
CONCLUSIONS: These in vitro data do not support the hypothesis that emulsification of the tamponades silicone oil or F6H8 in the microenvironment of the eye might easily activate neutrophils or stimulate phagocytosis by monocytes. A prerequisite is the combination of a vesicle shape of the tamponades with specific stabilizing or modifying surfactants. Emulsified tamponades stabilized by artificial surfactants, but not by the naturally occurring protein HSA, favor cell activation by cell membrane attachment.