Naturally occurring cationic proteins secreted by human granulocytes have pro-inflammatory effects including induction of increased vascular permeability and oedema, which are likely to be mediated by damage to vascular endothelium. Synthetic cationic polyamino acids have been shown to exert similar inflammatory effects in vivo. We have therefore used a range of synthetic polycationic amino acids to investigate the characteristics required to cause endothelial cell damage, assessed by in vitro inhibition of leucine incorporation into macromolecules by human umbilical vein endothelial cells (HUVEC) in culture. Exposure of HUVEC to 20 nM-2 microM cationic polypeptides of similar Mr(av) (approximately 40,000) in the presence of 20% serum produced a dose-dependent inhibition of [3H]leucine incorporation by polymers of ornithine, arginine or lysine. Similar results were obtained using [3H]thymidine. Neutral or anionic polypeptides of similar Mr were without effect. The molar potency of polylysines increased over the range Mr 40,000-120,000, while polylysines of Mr(av) less than 25,000 had no effect. In the absence of serum, inhibition occurred more rapidly and at lower doses. Inhibition of leucine and thymidine incorporation was time-dependent, e.g. exposure to 800 nM-polylysine, Mr(av) 90,000, led to progressively increasing inhibition that was complete after 24 h exposure, and was irreversible. The effects of polycations could not be blocked by pretreatment of the cells with polyanions. Precoating of the culture surface with polylysines had no effect on leucine incorporation by HUVEC or their subsequent response to polylysines in solution. Exposure to the peptide Arg-Gly-Asp-Ser inhibited incorporation by 30% but did not increase susceptibility to polylysine.(ABSTRACT TRUNCATED AT 250 WORDS)

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