Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Rao, S.
Impact of Lysophosphatidylcholines and Endothelial Lipase-modified HDL on vascular reactivity
[ Dissertation ] Medical University of Graz; 2013. pp. 104
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- Autor*innen der Med Uni Graz:
- Rao Shailaja Prabhakar
- Betreuer*innen:
- Frank Sasa
- Kratky Dagmar
- Marsche Gunther
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- Abstract:
- CHAPTER I Previously we identified palmitoyl-, oleoyl-, linoleoyl-, and arachidonoyl-lysophosphatidylcholine (LPC 16:0, 18:1, 18:2 and 20:4) as the most prominent LPC species generated by endothelial lipase (EL). In the present study, we examined the impact of those LPC on acetylcholine (ACh)- induced vascular relaxation. All tested LPC attenuated ACh-induced relaxation, measured ex vivo, using mouse aortic rings and wire myography. The rank order of potency was as follows: 18:2.20:4.16:0.18:1. The attenuating effect of LPC 16:0 on relaxation was augmented by indomethacin-mediated cyclooxygenase (COX)-inhibition and CAY10441, a prostacyclin (PGI2)- receptor (IP) antagonist. Relaxation attenuated by LPC 20:4 and 18:2 was improved by indomethacin and SQ29548, a thromboxane A2 (TXA2)- receptor antagonist. The effect of LPC 20:4 could also be improved by TXA2- and PGI2-synthase inhibitors. As determined by EIA assays, the tested LPC promoted secretion of PGI2, TXA2, PGF2a, and PGE2, however, with markedly different potencies. LPC 16:0 was the most potent inducer of superoxide anion production by mouse aortic rings, followed by LPC 18:2, 20:4 and 18:1, respectively. The strong antioxidant tempol recovered relaxation impairment caused by LPC 18:2, 18:1 and 20:4, but not by LPC 16:0. The tested LPC attenuate ACh-induced relaxation through induction of proconstricting prostanoids and superoxide anions. The potency of attenuating relaxation and the relative contribution of underlying mechanisms are strongly related to LPC acyl- chain length and degree of saturation. CHAPTER II In the second part we studied the impact of EL on HDL composition and function. Inflammation causes dramatic changes in HDL composition and function, which can turn HDL profile from anti-atherogenic to pro-atherogenic in nature. Considering capacity of EL to provoke structural and compositional alterations in HDL, we hypothesize that EL induced alterations of the lipid and protein composition of HDL might yield dysfunctional HDL, with dramatically impaired endothelial function. We observed that aortas of EL overexpressing mice were unable to relax as efficiently to ACh as compared to their LacZ controls. HDL isolated from EL-overexpressing mice (EL-HDL) upon adenoviral injection exhibited, compared with LacZ-HDL, markedly decreased relative PL-, moderately increased triglyceride (TG)-, slightly decreased total cholesterol (TC)- and slightly increased protein content. As revealed by mass spectrometry various phosphatidylcholine and lysophosphatidylcholine species were markedly decreased in EL- compared with LacZ-HDL. The LC-MS/MS analysis/spectral counting, Western blotting and arylesterase activity measurements revealed decreased apoM and PON1 in EL-HDL. As found by non-denaturing gradient gel electrophoresis (GGE) EL-HDL was slightly smaller in size than LacZ-HDL. Most importantly, wire myography measurements using mouse aortic rings precontracted with norepinephrine (NE) revealed markedly diminished vasorelaxing capacity of EL- compared with LacZ-HDL. Incubation of human HDL with EL-overexpressing HepG2 cells for 16 h resulted in similar alterations in lipid and protein composition in human EL-HDL as found for mouse EL-HDL. However, in contrast to mouse EL-HDL, human EL-HDL was profoundly smaller in size compared with LacZ-HDL, as found by non-denaturing GGE. Most importantly, vasorelaxing capacity of human EL-HDL was markedly decreased when compared with human LacZ-HDL. Based on these results we concluded that EL-modification of human and mouse HDL markedly diminishes vasorelaxing capacity of HDL, most likely due to EL-mediated alterations in lipid and protein composition of HDL.