Medizinische Universität Graz - Research portal
Selected Publication:
Holzer, M.
HDL composition and function in atherosclerosis and chronic kidney diseases
[ Dissertation ] Medical University of Graz, 2011. pp. 125
[OPEN ACCESS]
FullText
- Authors Med Uni Graz:
- Holzer Michael
- Advisor:
- Marsche Gunther
- Altmetrics:
- Abstract:
- Epidemiological studies have shown that HDL-cholesterol levels are inversely correlated with the risk for cardiovascular diseases (CVD). HDL is thought to protect against atherosclerosis by mediating reverse cholesterol transport and potentially through anti-oxidative and anti-inflammatory activities. It recently emerged that HDL can loose its anti-atherogenic functions and may even become pro-atherogenic. The mechanisms underlying this transformation are not well understood. Within the first project, we investigated whether HDL is post-translational modified by cyanate in atherosclerotic lesions. Proteins are carbamylated through cyanate (OCN¿), a reactive electrophile that irreversibly transforms lysine to homocitrulline (also known as carbamyllysine). Cyanate is formed from thiocyanate via myeloperoxidase (MPO) or by decomposition of urea. MPO can binds to HDL within human atherosclerotic lesions and might therefore act in closest proximity to HDL. We established a state of the art method to quantitatively assess homocitrulline and 3-chlorotyrosine (a specific MPO oxidation marker) via liquid chromatography tandem mass spectrometry. The mass spectrometry analysis revealed that carbamylation through OCN¿ is a major modification of HDL in atherosclerotic lesions, which was more than 20-fold higher than the MPO oxidation product 3-chlorotyrosine. The comparison with total lesion protein and lesion derived low-density lipoprotein (LDL) indicates that HDL is a specific target for carbamylation. We translated the mass spectrometry result to functional experiments and revealed that protein carbamylation alters HDL structure and function. Carbamylation increased binding affinity of HDL to its physiological receptor scavenger receptor B-I (SR-BI), shifting the balance between SR-BI mediated cholesterol efflux and uptake towards cholesterol uptake, thereby causing intracellular cholesterol accumulation. In addition, our studies provide convincing evidence that the anti-oxidative capacity of HDL is reduced upon carbamylation. Moreover, the activity of the HDL-associated anti-inflammatory enzyme paraoxonase 1 was strongly reduced, whereas lipoprotein-associated phospholipase A2 activity increased. In summary, the present results provide evidence that protein carbamylation is an important modulator of HDL functions in atherosclerotic lesions, thereby rendering HDL dysfunctional. In the second part, we investigated the effect of advanced renal disease on HDL composition and function. Functional impairment of HDL during renal disease may contribute to the excess cardiovascular mortality in these patients. The data available regarding the impact of advanced renal disease on HDL composition and functionality are limited. In particular, the effect of renal disease on the first step of reverse cholesterol transport, the efflux of cellular cholesterol from macrophages to HDL, has not been determined yet We used mass spectrometry and biochemical analyses to show that HDL isolated from patients on maintenance hemodialysis (HD) has a considerable altered protein and lipid composition. Our studies revealed a significant increase in serum amyloid A1, albumin, lipoprotein-associated phospholipase A2 and apoC-III content of HD-HDL, whereas apoA-I and apoA-II levels were decreased. Proteomic alterations were accompanied by a decreased phospholipid and increased triglyceride and lyso-phospholipid content of HDL. In regard to function, HDL from hemodialysis patients was less potent in promoting cholesterol efflux from lipid-laden macroph ...