Endothelial glycosaminoglycans in inflammation

Capillary leak and intravascular thrombosis are serious consequences of endotoxaemia and are indicative of a generalised alteration in the homeostatic properties of the vascular endothelium. The sulphated glycosaminoglycans (GAGs), heparan, dermatan and chondroitin sulphate, are important constituents of the endothelium and are thought to play a pivotal role in regulating vascular permeability, haemostasis, cellular traffic and cellular proliferation. Changes in endothelial GAGs as a result of the inflammatory process may therefore underlie some of the pathological events associated with gram negative sepsis. This thesis is primarily concerned with exploring the potential role of endothelial glycosaminoglycans in inflammation and sepsis. In order to study the role of GAGs in inflammation, methods were developed to isolate and characterise both cell associated and supernatant GAGs from cultured human umbilical endothelial cells (HUVEC). A novel method of visualising endothelial GAGs was also developed to explore the location and distribution of endothelial anions in both unstimulated and cytokine treated cultures. Unstimulated endothelial cells were found to release heparan, dermatan and chondroitin sulphate into the tissue culture medium, while only heparan and dermatan sulphate were found to be associated with cultured cells. To investigate the metabolism of sulphated GAGs in HUVECs exposed to inflammatory stimuli, cultures were treated with interleukin 1 (IL1), tumour necrosis factor alpha (TNF), interferon gamma (IFN), lipopolyssacharide (LPS) and neutrophils. IL1 and TNF caused a significant reduction in cell associated GAGs as a result of increased GAG release and decreased GAG synthesis. The combination of neutrophils and either IL1, TNF or LPS caused an even greater reduction in cell associated GAGs. All of these results were supported by histochemical analysis of endothelial cell associated GAGs and indicated that visualisation of GAGs may be a sensitive marker of endothelial injury. To define the conditions which were most likely to cause HUVEC damage, simultaneous measurements of neutrophil adhesion molecule expression, HUVEC GAGs and cellular fibronectin (FN) were recorded following treatment with LPS and or formyl - Methionine - Leucine - Phenylalanine (fMLP). Maximal loss of GAGs and FN occurred when both endothelial cells and neutrophils were maximally stimulated. Neutrophil activation alone however, was insufficient to cause widespread loss of these endothelial components. The results presented in this thesis indicate that endothelial glycosaminoglycans are significantly modulated by a number of physiological inflammatory stimuli. Endothelial GAGs may be important in relation to the pathophysiology of inflammation and sepsis.