| Abstract |
The anti-atherogenic role of high density lipoproteins (HDL) has been well established for many years. Low levels of HDL-cholesterol have been associated with an increased risk for coronary heart disease (CHD); nonetheless, recent studies have shown that the atheroprotective role of HDL is determined more by its quality rather than by its quantity. The current study tested the composition and the antioxidative/anti-inflammatory properties of HDL in humans aged <36 years old that have suffered a myocardial infarction (ΜI) and in age and sex-matched healthy controls, as well as in mouse models (apoA-I-/-, apoE-/-, SR-BI-/-). The ultimate goal is to correlate the composition and functions of HDL with the diagnosis and/or prognosis of CHD.
Measurement of HDL lipid levels showed a statistically significant decrease in HDL-total cholesterol (TC) and cholesterol ester/total cholesterol ratio (CE/TC) in patients with MI (n=13) compared with the control group (n=7) (40±9 vs. 54±13 mg/dl, p=0.014 and 0.65±0.10 vs. 0.86±0.08, p=0.0001, respectively). A statistically significant decrease was also observed in serum apoA-I levels between the patients and the healthy subjects (64±9 vs. 93±36.5 mg/dl, p=0.018, respectively). The HDL subpopulations analyzed by two-dimensional gel (2D) electrophoresis and the antioxidative/anti-inflammatory properties of HDL measured by a fluorometric assay in vitro were similar between the two groups. The activity of three proteins, CETP (cholesteryl ester transfer protein), LCAT (lecithin:cholesterol acyl transferase) and PON1 (paraoxonase 1), that are associated with HDL, was also measured. CETP transfers cholesterol esters from HDL to VLDL and LDL and triglycerides (TG) from VLDL to LDL and HDL, thus affecting the HDL composition and metabolism, and leading to the transfer of CE from HDL to the liver for clearance by the LDL-receptor. LCAT esterifies cholesterol on HDL and leads to the formation of mature spherical HDL particles, while decreased LCAT activity has been associated with increased risk of atherosclerosis. PON1 is an esterase, which hydrolyses oxidized phospholipids (PL) contributing to the antioxidative
properties of HDL. CETP and LCAT, but not PON1, activities of HDL were statistically significantly decreased in patients compared to the control group (6.55±1.69 vs. 9.07±2.26 pmol/μl/h, p=0.011, and 0.17±0.12 vs. 0.37±0.24 nmol/h, p=0.048, respectively). The decreased LCAT activity of HDL in patients can be associated with the decreased CE/TC ratio of patients’ HDL. The non-statistically significant difference in HDL-PON1 activity between patients and healthy subjects is in aggreement with the absence of any difference in the antioxidative/anti-inflammatory properties of HDL between these two groups.
Regarding the mouse models differences were observed in serum lipid levels and enzyme activities. ApoE-/- mice (n=9), which are considered one of the best models to study atherosclerosis, had statistically significantly increased serum TC, TG, and PL levels compared to the wild type (WT) C57BL/6J mice (n=10) (462±150 versus 182±38 mg/dl, p<0.0001, 111±30 versus 83±24 mg/dl, p=0.036 and 322±84 versus 193±51 mg/dl, p=0.0008, respectively), while the CE/TC ratio was significantly decreased in comparison with the control group (0.79±0.14 versus 0.91±0.06, p=0.025). LCAT activity in the serum of apoE-/- mice was also significantly decreased in comparison with the WT mice (0.10±0.016 versus 0.16±0.015 nmol CE/h, p=0.0004, n=5). SR-BI-/- mice (n=6), which are also models for atherosclerosis, had significantly increased serum PL levels compared to the WT mice (n=10) (250±27 versus 193±51 mg/dl, p=0.026). Serum TC and TG levels were also increased in this group of mice (241±103 versus 182±38 mg/dl and 130±92 versus 83±24 mg/dl, respectively), while the CE/TC ratio was significantly decreased (0.72±0.18 versus 0.91±0.06, p=0.008). Similarly, serum LCAT activity was significantly decreased in SR-BI-/- mice (n=4) compared to the WT mice (n=5) (0.07±0.003 versus 0.16±0.015 nmol CE/h, p=0.0004). Finally, in apoA-I-/- mice (n=2), which are deficient for apoA-I, the main apolipoprotein of HDL, serum TC, TG, PL levels, and CE/TC ratio were greatly decreased compared to the WT mice (n=10) (40±2 versus 182±38 mg/dl, 39±12 versus 83±24 mg/dl, 116±27 versus 193±51 mg/dl and 0.58±0.05 versus 0.91±0.06, respectively). Serum LCAT activity was also highly decreased in
apoA-I-/- mice (n=2) compared to the control mice (n=5) (0.03±0.018 versus 0.16±0.015 nmol CE/h). Serum PON1 activity was statistically significant decreased in apoE-/- (n=3) and SR-BI-/- (n=4) mice compared to the control mice (n=4) (294.2±57.4 vs. 402.7±28.2 U/lt, p=0.020 and 164.2±49.1 vs. 402.7±28.2 U/lt, p=0.0002, respectively). Serum PON1 activity was diminished in apoA-I-/- mice (n=2) compared to the control mice (n=4) (8.3±10.4 vs. 402.7±28.2 U/lt). In accordance to lower PON1 activity between the three mouse models and WT mice, HDL of all three mouse models was more pro-inflammatory than HDL of WT mice. Analysis of the HDL subpopulations by 2D gel electrophoresis showed that WT mice formed various HDL subpopulations mainly of α-electrophoretic mobility, which are enriched in apoA-I as expected. Similar analysis showed accumulation of preβ-HDL and α-HDL particles of fast electrophoretic mobility (small) in apoE-/- mice. SR-BI-/- mice formed α-HDL particles of fast electrophoretic mobility (small), that were enriched in apoA-I and α-HDL particles of slow electrophoretic mobility (large), that were enriched in apoE. ApoA-I-/- mice formed particles of slow electrophoretic mobility (large) enriched in apoE.
In conclusion, these findings show that there are differences in HDL lipids and apoA-I levels, and reduced LCAT and CETP activities of HDL between young patients who suffered an MI and the control group, which may affect the properties of HDL and may be related with increased risk for CHD. Prospective studies of larger groups of young patients with MI are needed to test whether the compositional abnormalities of HDL can be used as a biomarker for diagnosis and prognosis of MI in young adults. Regarding mouse models, there are also differences in HDL lipids levels and reduced LCAT and PON1 activities between apoA-I-/-, apoE-/- and SR-BI-/- mice and WT mice. Further studies of the same or other knock-out and transgenic mouse models in genes of the HDL pathway are necessary to find associations between these genes, HDL functions, low or high HDL syndromes or dyslipidemia, and atherosclerosis in mice. The ultimate goal is the recognition of similar phenotypes of HDL metabolism disturbances in humans and the identification of new markers for the diagnosis or prognosis of CHD.
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Σύσταση και ιδιότητες των λιποπρωτεϊνών υψηλής πυκνότητας (HDL) σε Έλληνες ασθενείς που υπέστησαν έμφραγμα του μυοκαρδίου σε ηλικία μικρότερη των 36 ετών και σε μοντέλα μυών
