Mechanism Research Of Rosiglitazone For Anti-atherosclerosis And Significance Of ABCA1 Of Monocytes In Type 2 Diabetes Mellitus

Study BackgroundAtherosclerotic cardiovascular disease is the major cause of morbidity and mortality worldwide.Numerous epidemiological studies have established high-density lipoprotein cholesterol(HDL-C) and its major protein apolipoprotein A1 (apoA-1) are inversely associated with the risk of atherosclerotic vascular disease. One major mechanism by which HDL and apoA-1 protect against atherosclerosis is probably by promoting reverse cholesterol transport(RCT) from periphery to the liver, where it can be excreted from the body directly or indirectly after conversion into bile acids eventually.It is well known that RCT is a process of anti-atherosclerosis,and involves multiple steps,beginning with the cholesterol efflux of macrophages and the formation of HDL by ATP-binding cassette transporter A1(ABCA1).So,ABCA 1 has a significant relation with HDL and atherosclerosis.Overexpression of ABCA1 dramatically increases plasma HDL-C levels and inhibits atherosclerosis.Conversely, gene mutation or deletion of ABCA1 has little or no plasma HDL-C levels and markedly increases atherosclerosis.These data suggest that ABCA1expression promotes RCT. Recently,many studies have shown that rosiglitazone,a peroxisome proliferator-activated receptorγagonist,plays a role in anti-atherosclerosis not only in type 2 diabetes mellitus but also in nondiabetics.One important way is that rosiglitazone increases ABCA1 expression and plasma HDL-C levels.So,we suppose that one mechanism of rosiglitazone for anti-atherosclerosis is probably by promoting RCT,but it has never been proven.Here,process of RCT is indirectly reflected by cholesterol efflux rates from hepatic and extrahepatic cells determined through measuring release of radioactivity from[3H]-cholesterol prelabeled cells into medium by liquid scintillation counting and ABCA1 expression were evaluated by flow cytometry,we analyze the effect of ABCA1 in peritoneal macrophages, hepatocytes and adipocytes on RCT and explore the mechanism of rosiglitazone for anti-atherosclerosis.Atherosclerotic cardiovascular complications in type 2 diabetes arouse the interests of many scholars.It is easy to form atherosclerosis in type 2 diabetes attributable to the lipids metabolism with hyperglycemia.ABCA1 has a close correlation with lipids metabolism,and the effect on anti-atherosclerosis has been proved.But the research between ABCA1 and type 2 diabetes mellitus is little, thereby the change research in ABCA1 will provide a new direction in the mechanism of type 2 diabetes mellitus and atherosclerosis.ObjectivesThe aim of foundation research was to analyze the effect of ABCA1 expressions in monocytes/macrophages,hepatocytes and adipocytes on RCT and to research the mechanism of rosiglitazone for anti-atherosclerosis in atherosclerotic rabbits.In clinic, we analyze the change of ABCA1 of peripheral monocytes in patients with type 2 diabetes in order to illuminate the significance of ABCA1 in type 2 diabetes mellitus. MethodsIn foundation research,twenty-four rabbits were randomly divided into four groups:(1) control group(n=6):only high cholesterol diet for 6 weeks;(2) rosiglitazone group(n=6):the same cholesterol diet plus rosiglitazone(2mg/d) for 6 weeks;(3) rosiglitazone&simvastatin group(n=6):the same cholesterol diet plus rosiglitazone(2mg/d) and simvastatin(10mg/d) for 6 weeks;(4) glibenclamide group (n=6):the same cholesterol diet plus glibenclamide(2.5mg/d) for 6 weeks.ABCA1 expressions in peritoneal macrophages,hepatocytes and adipocytes were evaluated by flow cytometry and cholesterol effiux rates from them were determined through measuring release of radioactivity from[3H]-cholesterol prelabeled cells into medium by liquid scintillation spectrometry.Enzymatic and immune method were used to assay plasma lipids levels and cholesterol contents in liver,aorta and adipose tissues, and then,area of atherosclerotic plaque in aorta was calculated by professional image analysis software.In clinic research,the people blood sample(2ml) is obtained and divided into two groups(40 cases each):the type 2 diabetes group,the patients(21males, 33females,52.2±10.4years) were diagnosed type 2 diabetes mellitus in endocrinology branch of Nanfang Hospital but without the regular treatment by lipid-lowering drugs,and the control group,the patients(22males,18females, 49.8±12.5years) visited in orthopedic spine branch of Nanfang Hospital and excluded hyperlipidemia.Above two groups,hypertension,CAD,Serious liver and kidney dysfunction and tumor were all excluded.There was no difference in age and gender of the two groups.And then,monocytes of the blood was extracted and ABCA1 expression in monocytes before and after stimulation of the oxidized low density lipoprotein was detected with flow cytometer in type 2 diabetes group and the control group.Plasma lipids levels in the different group and concentrations of fasting plasma glucose and glycosylated hemoglobin in type 2 diabetes group were assayed and the correlation of ABCA1expression in type 2 diabetes group with age,blood lipids and glycometabolism was analyzed.Results1.Foundation research1) There were no significant differences in body weight among the four groups at the baseline.After 6 weeks of experiment,all atherosclerotic models of rabbit were created successfully,and there was no difference in body weight among the four groups.2) Compared with control group,in rosiglitazone group,ABCA1 expressions in peripheral mononuclear cells,peritoneal macrophages,adipocytes and hepatocytes; [~3H]cholesterol efflux rates in peritoneal macrophages,adipocytes and hepatocytes, and serum levels of HDL-Cand apoA-1 were all increased,while contents of cholesterol in aorta,adipose and liver tissues and area of atherosclerosis in aorta were all decreased,and there was no difference in NHDL-C level.3) The effects of rosiglitazone&simvastatin group were similar with rosiglitazone group,however,in difference,the serum NHDL-C level was decreased in rosiglitazone&simvastatin group as compared with control group.Compared with rosiglitazone group,in rosiglitazone&simvastatin group,ABCA1 expressions in peripheral mononuclear cells,peritoneal macrophages,adipocytes and hepatocytes, [~3H]cholesterol efflux rates in peritoneal macrophages,adipocytes and hepatocytes, and serum levels of HDL-C and apoA-1 were all higher,while contents of cholesterol in aorta,adipose and liver tissues and area of atheroscler osis in aorta were all lower.4) Compared with control group,in glibenclamide group,ABCA1 expressions in peripheral mononuclear cells,peritoneal macrophages,adipocytes and hepatocytes, [~3H]cholesterol efflux rates in peritoneal macrophages,adipocytes and hepatocytes, and serum levels of HDL-C and apoA-1 were all decreased,while contents of cholesterol in aorta,adipose and liver tissues and area of atherosclerosis in aorta were all increased,and there was no difference in NHDL-C level.5) In all experimental animals,cholesterol contents in aorta,adipose and liver tissues respectively had a negative correlation with[3H]cholesterol efflux rates from peritoneal macrophages,adipocytes and hepatocytes which were positively associated with ABCA1 expressions in them severally.ABCA1 expression in monocytes respectively had a positive correlation with[3H]cholesterol efflux rates from peritoneal macrophages,hepatocytes and adipocytes.2.Clinical research1) Compared with control group,type 2 diabetes enhanced the plasma levels of TG and NHDL-C which are pro-atherosclerosis,and reduced the serum apoA-1 and HDL-C levels which are anti-atherosclerosis.2) Type 2 diabetes group up-regulate the ABCA1 as compared with control group,while the change(stimulated expression / initial expression) of ABCA1 after stimulated by oxidized low density lipoprotein was significantly greater in type 2 diabetes group than in control group.But the ultimate expression of ABCA1 in type 2 diabetes group was still smaller than in the control group.3) In type 2 diabetes group,the ABCA1 had no correlation with age,fasting plasma glucose(FPG),and HbA1C.But the change of ABCA1 was positive correlation with plasma high density lipoprotein cholesterol level.Conclusions1.Expressions of ABCA1 in monocytes/macrophages,hepatocytes and adipocytes are positive regulators of RCT.2.Rosiglitazone promotes RCT by up-regulating ABCA1 expressions in monocytes/macrophages,hepatocytes and adipocytes to repress atherosclerosis.3.ABCA1expression in monocytes is a credible index which reflects RCT indirectly.4.Patients with type 2 diabetes already have the injuried lipids spectrum and RCT,thus forming the foundation of pro-atherosclerosis and coronary heart disease.