Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
El-Gamal, D.
Cyanate is a novel inducer of endothelial dysfunction: A potential link between inflammation, smoking and uremia
[ Dissertation ] Medical University of Graz; 2012. pp. 105
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- Autor*innen der Med Uni Graz:
- El-Gamal Dalia
- Betreuer*innen:
- Heinemann Akos
- Marsche Gunther
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- Abstract:
- Many studies have evaluated the impact of protein carbamylation on structure and/or function of proteins, enzymes and hormones. Irreversible carbamylation of proteins by the reactive electrophile ¿cyanate¿ has been demonstrated to predict cardiovascular risk and is thought to promote vascular dysfunction; however, the underlying mechanisms remain unclear. Endogenous sources of cyanate include the slow breakdown of urea in vivo and myeloperoxidase-catalyzed oxidation of thiocyanate. Exogenous sources of cyanate also exist as it was shown that humans are significantly exposed to cyanate, a major constituent of smoke, generated when coal, fuel, biomass, or tobacco is burned. Although humans are exposed to considerable amounts of cyanate, very little is known about its impact on human health. In particular, the effect of cyanate on the endothelium, regulator of vascular homeostasis, has not been investigated yet. has not been investigated yet. In the first part of this thesis, we show that cyanate induces the expression of inflammatory mediators in human coronary artery endothelial cells (HCAEC). Cyanate induced a significant increase in ICAM-1 expression depending on activation of p38 MAPK and NF-¿B signaling pathways. Cyanate-activated endothelial cells displayed enhanced neutrophil adhesion which was reversed upon NF-¿B inhibition. Additionally, cyanate promoted the release of inflammatory chemokines in cultured endothelial cells. Mice receiving cyanate in drinking water exhibited marked endothelial ICAM-1 expression in the aorta as evident by immunohistochemical staining. In addition, elevated plasma levels of carbamyllysine (a marker for cyanate exposure which reflects the extent of plasma protein carbamylation), was observed. In patients with renal disease, a significant correlation between plasma carbamyllysine levels and soluble ICAM-1 was observed. In the second part of this work, prompted by the recent finding that smoke serves as an efficient and direct route for isocyanic acid/cyanate delivery, we focused on exploring the effect(s) resulting from chronic cyanate inhalation. Smokers are particularly exposed to significant levels of isocyanic acid/cyanate resulting from not only pyrolysis of tobacco itself but also urea a major tobacco additive. In mice, chronic cyanate inhalation induced significant plasma protein carbamylation, corresponding to levels previously observed in humans with cardiovascular disease. Notably, cyanate treatment markedly attenuated arterial vasorelaxation of aortic rings in response to acetylcholine. Moreover, total endothelial nitric oxide synthase (eNOS), phospho-eNOS (S1177) and levels of the active dimeric form were significantly reduced in aortic tissue of cyanate-treated mice, which was accompanied by a marked decrease in nitric oxide production. Resembling our findings in mice, cyanate treatment of HCAEC decreased eNOS protein expression, whereas eNOS protein expression was not altered when low molecular weight substances (i.e. cyanate) were removed from cell culture medium, ruling out a role of carbamylated proteins in modulating eNOS. We show for the first time that cyanate inhalation disrupts endothelial function by altering eNOS activity. This data suggest that cyanate, a potentially harmful constituent in smoke, induces endothelial dysfunction, and may hence contribute towards increased cardiovascular risk of smokers. The findings of this current work denote cyanate as a potential inducer of endothelial dysfunction, thereby linking inflammation, smoking, and uremia.