The Effects Of Probucol On Function Of HDL And Its Potential Anti-atherosclerosis Mechanisms In Atherosclerotic Rabbits

Study BackgroundAtherosclerosis (AS) is the most common diseases in the cardio-cerebral vascular system, which is harmful to human health seriously. Numerous epidemiological studies have established high-density lipoprotein cholesterol (HDL-C) is inversely associated with the risk of atherosclerotic cardiovascular disease. However, some scholars found that a number of paradox patients did not benefit when increasing HDL-C level of medication, but some drugs of decreasing of HDL-C levels were able to inhibit the progressment of AS. The puzzling phenomenon tells us: HDL-C level really do not represent HDL function, HDL function may be more important than its concentration. High density lipoprotein (HDL) always has considered a protective factor to AS. HDL has anti- atherosclerosis property through playing a role in the reverse cholesterol transport (RCT). RCT is the process that cholesterol in extrahepatic tissues is returned to liver for excretion as bile. HDL in this process plays the role of porters, and ATP binding cassette transporter Al (ABCA1) and SR-BI (scavenger receptor class B typeⅠ) are the key genes in RCT, RCT is the key pathway of cholesterol excretion and one of the important mechanisms of anti-atheroselerosis.ABCA1 and SR-BI play an important role in mediating cellular cholesterol efflux. ABCA1 is a cAMP-induced apolipoprotein receptor, which can make use of ATP involved in cholesterol and phospholipid transport from cells to HDL with the blood circulation to the liver for metabolism. SR-BI is another receptor protein, which also can mediated cholesterol efflux and has function of causing a two-way transfer cholesterol(can mediate the liver selective uptake cholesterol ester, but also mediated cholesterol efflux of peripheral cells such as macrophages).Probucol is a special of lipid-lowering drugs which significantly lower HDL-C, while it still has an obvious anti-atherosclerotic effect. Some studies have suggested an important mechanism for promoting RCT in vivo, but the exact mechanisms remain unclear. Previous studies reported that probucol promoted cholesterol metabolism primarily through regulating SR-BI expression and function, but some studies show that there was no significant relationship between them. In addition, the role of ABCA1 in the mechanism against AS of probucol currently was disputed. Some studies have found that probucol could cause changes in HDL subclasses, but the mechanism remains unknown.ObjectivesWe observe ABCA1, SR-BI expression and [3H] cholesterol efflux rates of peritoneal macrophages, hepatic cells and HDL subclasses in atherosclerotic rabbit treated by probucol, and analysis of influence of probucol on these indicators in the AS state, so as to explore the mechanism of probucol against AS.MethodsEighteen rabbits were randomly divided into three groups:(1) control group (n=6):only normal diet for 12weeks; (2) atherosclerosis(AS) group:maintained cholesterol diet of 12 weeks; (3) probucol group:the same cholesterol diet plus probucol (400mg/ (kg·d) for 12 weeks. The expressions of ABCA1 and SR-BI in peritoneal macrophages and hepatocytes were evaluated by flow cytometry and cholesterol efflux rates from them were determined through measuring release of radioactivity from [3H]cholesterol in prelabeled cells into medium by liquid scintillation spectrometry. The concentrations of HDL2 and HDL3 by precipitation methods. The aorta was excised for investigating the histological characteristics at the end of 12 weeks after the confirmation of the death of the rabbits.Results1) There were no significant differences in TC, LDL-C, HDL-C, NHDL-C among the four groups at the baseline. After 12 weeks of experiment, compared with control group, the levels of serum total cholesterol (TC) (23.25±3.30 vs1.79±0.21, P <0.001), low-density lipoprotein cholesterol (LDL-C) (18.09±4.04 vs 1.09±0.23, P <0.001), high density lipoprotein cholesterol (HDL-C) (1.11±0.09 vs 0.45±0.12, P <0.001) and non-high-density lipoprotein cholesterol (NHDL-C) (1.58±0.25 vs 1.02±0.15, P<0.001) in AS group were significantly increased. compared with AS group, the levels of serum total cholesterol (TC) (16.70±0.70 vs 23.25±3.30, P< 0.001), low-density lipoprotein cholesterol (LDL-C) (13.79±2.01 vs 18.09±4.04, P< 0.05), high density lipoprotein cholesterol (HDL-C) (0.51±0.06 vs 1.11±0.09, P< 0.001) and non-high-density lipoprotein cholesterol (NHDL-C) (16.19±0.64 vs 22.15±3.22, P<0.001) in probucol group were significantly reduced and there was no difference in TG level (1.60±0.17 vs 1.58±0.25 P>0.05.2) The protein expression levels of ABCA1 (P<0.05), the protein expressi on of SR-BI (P< 0.001) and the [3H] cholesterol efflux rates (P<0.001)in per itoneal macrophages and hepatocytes were all increased in probucol group com pared with that in AS group.3) Compared with AS group, probucol reduced plasma HDL2/HDL (0.24±0.02 vs 0.33±0.03, P<0.05) and compared with control group, the level of plasma HDL2 /HDL in AS group was reduced (0.33±0.03 vs 0.40±0.03, P<0.05).4) Compared with AS group, probucol reduced aortic IMT significantly (239.83±50.51 vs 527.41±85.16, P< 0.001), and compared with control group, the aortic IMT in AS group was increased(527.41±85.16 vs 203.20±30.61, P<0.001). Conclusions1. Probucol reduces plasma TC, LDL-C, HDL-C levels.2. Probucol had effect of improving function of HDL through up-regulates ABCA1 and SR-BI expression and cholesterol efflux rates in peritoneal macrophages and hepatocytes, and so improve reverse cholesterol transport (RCT) of atherosclerotic rabbits.3. Probucol reduce HDL-C, but it through make change in HDL subclasses, that promote more cholesterol efflux from extrahepatic cells, thereby accelerating the process of RCT in vivo4. HDL-C level do not really represent HDL function, HDL function may be more important than its concentration.