Oxidative modification of low density lipoprotein induced byhyperhomocysteinaemia following application of methionine

AIM:To observe the oxidative modification of low density lipoprotein iinduced by hyper homocysteinaemia following application of methionine. RESULTS:Following application of methionine, the levels of hyperhomocysteine, ox-LDL and TBARS in group M and group M+Ch were significntly higher than those of group C and group Ch (P＜0.01). The oxidative modification of low density lipoprotein induced by homocysteine in vitro were significantly increased with the concentrations of LDL and homocysteine (P＜0.01).     

IGF-1R,p-ERK is involved in LDLs-induced mouse peritoneal macrophage survival

AIM: To study the effects of low density lipoproteins (LDLs) on insulin-like growth factor-1 receptor (IGF-1R), phosphorylated extracellular signal-regulated kinase (p-ERK), Bcl-2 and Bax protein expression in mouse peritoneal macrophages (MPMs). METHODS: Using the methods of immunocytochemistry and Western blotting, the expression of IGF-1R, p-ERK, Bcl-2 and Bax protein in MPMs treated with LDLs, anti-IGF-1R antibody (α-IR-3) or ERK inhibitor (PD98059) were detected. RESULTS: oxLDL significantly increased the IGF-1R protein expression in a dose and time-dependent manner. P-ERK protein expression induced by oxLDL peaked at 5 min. Moreover, oxLDL could induced ERK translocation from cytoplasm to nuclear. When given α-IR-3, p-ERK protein expression was significantly inhibited, and ERK translocation disappeared. oxLDL increased Bcl-2 protein expression and reduced Bax expression in a dose and time-dependent manner. When given PD98059, Bcl-2 and Bax protein expression induced by oxLDL altered significantly. Native LDL had no significant effect on the expression of these four proteins. CONCLUSIONS: oxLDL may promote cultured MPMs survival at least by enhancing IGF-1R expression and ERK phosphorylation, and there may be many pathways involved in MPMs survival induced by oxLDL, Whereas native LDL had no effects on culture MPMs.     

Mast cells change cellular cholesterol content and inhibit cholesterol efflux from THP-1 macrophage-derived foam cells

AIM:Mast cells (MC) are present in the arterial intima,the site of atherogenesis. The present studies explore the effect of MC on cholesterol content,distribution and efflux in THP-1 macrophage-derived foam cells (THP-1FCs）. METHODS:THP-1FCs were incubated with high-density lipoproteins 3 (HDL₃) in the absence or presence of mast cell granules (MCGs) harvested from compound 48/80-stimulated rat peritoneal MC. The intracellular cholesterol level,cholesterol effluxing capacity,ATP-binding cassette transporter A1(ABCA1) mRNA and HDL₃ treated with MCGs were detected to characterize the role of MC on intracellular cholesterol. RESULTS:MCGs had high levels of cellular total cholesterol(TC),free cholesterol(FC) but not esterifed cholesterol(EC) compared to control group where the TC concentrations ranged from 527.3 mg/g to 917.9 mg/g cellular protein with EC accounting for 7.6% of the cholesterol. Cholesterol efflux was 14% less in MCGs group compared to control group. ABCA1 mRNA expression in MCG-treated THP-1FCs remained unchanged in 20 hours. In contrast,treatment of HDL₃ with MCGs resulted in rapid degradation of the main HDL₃ apoliproteins,apoA-Ⅰ. SDS-PAGE revealed that a minor polypeptide band with about 26 kD molecular mass appeared below the apoA-Ⅰband. Densitometric analysis of the gel demonstrated that ≈ 28% of apoA-Ⅰhad been degraded by the MCGs. CONCLUSION:These results indicate that MC decreases cholesterol efflux,increases cellular accumulation in TC and FC by depleting HDL₃ and apoA-Ⅰ,but not by inhibiting ABCA1 mRNA expression.     

Effect of mininally modified low density lipoprotein on the adhesive function of vascular endothelial cell and its mechanism

AIM: To observe the effect of MM-LDL (minimally modified LDL) on the interaction between human umbilical vein endothelial cell (HUVEC) and U937 monocyte-like cell line and the exporession of vascular cell adhesion-1 (VCAM-1), intercellular adhesion molecule-1(ICAM-1), P-selectin.METHODS:The adhesive percentage between HUVEC treated with MM-LDL and U937 was determined by counting and the expression of VCAM-1, ICAM-1, P-selectin were examined by ELISA. RESULTS: Treatment of HUVEC with MM-LDL (75 mg/L) for 4 hours significantly increased adhesion of U937 to HUVEC ( P <0.01) and did not induce the surface expression of VCAM-1, ICAM-1, P-selectin . Recombination tumor necrosis factor-alpha (rTNF_α) 5.0 μg/L, as a positive control, induced the expression of these adhesion molecules ( P <0.05). Prolonged (18 h) exposure to MM-LDL resulted in the expression of P-selectin, but not VCAM-1.CONCLUSION: the adhesion of monocytes to endothelial cells induced by MM-LDL is not mediated by VCAM-1, ICAM-1. P-selectin induction may be partly involved in the process.     

Effect of 17β-estradiol on the levels of plasma oxidized low density lipoprotein in ovariectomized rabbits

AIM: To observe the changes of plasma oxidized low density lipoprotein(oxLDL) levels of ovariectomized cholesterol-fed rabbits with or without 17β-estradiol(E₂) replacement therapy.METHODS: All rabbits were ovariectomized and fed standard chow supplemented with 1.5% cholesterol for 14 weeks. Two weeks after operation, the rabbits were randomly assigned to four groups. Three groups were treated with E₂ 1 mg, 2 mg, 4 mg respectively, the other group served as control. Serum superoxide dismutase (SOD) levels and plasma oxLDL levels were measured at 0, 3, 8, 12 weeks after hormone replacement therapy. The aortic atherosclerotic lesion areas were determined by computer. RESULTS: We found that there were striking increase of serum SOD levels ( P<0.05 ) and significant decrease in both the plasma oxLDL levels and the aortic atherosclerotic lesion areas ( P<0.01 respectively). Moreover, a positive correlation was found between plasma oxLDL levels and the areas of atherosclerotic plaque in all rabbits. CONCLUSIONS: Estrogen attenuates atherogenesis in cholesterol-fed ovariectomized rabbits. And this beneficial effect of E₂ may be duo to its lowering of plasma oxLDL level.     

Dual roles of oxidized LDL in modulating expression of inflammatory molecules in HUVECs

AIM:To determine the role of LOX-1/PPAR pathway in regulating expression of adhesion molecules elicited by oxidizing low density lipoprotein(Ox-LDL) through Lectin-like oxidized low-density lipoprotein receptor-1(LOX-1) in human umbilical vein endothelial cells(HUVECs). METHODS:HUVECs were incubated with Ox-LDL,poly(I),carrageenan or 15-deoxy-△12,14-prostaglanding J2 (15d-PGJ₂ ). PPAR mRNA and protein were examined by real time RT-PCR and Western blotting. ICAM-1 and E-selectin were detected by RT-PCR and Western blotting respectively. RESULTS:Ox-LDL increased PPAR expression in HUVECs,which was inhibited by pretreatment of HUVECs with LOX-1 blockers. Preincubation of HUVECs with 15d-PGJ₂ attenuated the expression of intercellular adhesion molecule-1(ICAM-1) and E-selectin in response to Ox-LDL. Upregulation of ICAM-1 and E-selectin mediated by Ox-LDL were suppressed more significantly by the combination of 15d-PGJ₂ and polyinosonic acid as compared to either 15d-PGJ₂ or polyinosonic acid alone. CONCLUSION:The results indicate that Ox-LDL exerts a biphasic effects on inflammatory response. It evokes harmful effects by inflammatory injury on one side and protective effects by triggering the LOX-1/ PPAR signaling pathway on the other hand.     

Endothelial lipase and atherosclerosis

Endothelial lipase (EL),a newly described member of the triglyceride lipase gene family,displays a previously phospholipase A1 activity,remodels high density lipoprotein (HDL) particle and reduced plasma HDL-cholesterol levels and the ability to joint to scavenger receptor class B type 1 (SR-B1).Furthermore,EL also increases cellular apolipoprotein B-containing lipoprotein uptake,monocyte adhesion and infiltration into the tissues.Recently,some studies showed that the vascular atherosclerotic lesions were markedly attenuated in EL deficient mice compared with control,suggesting that EL may play a significant role in the formation of atherosclerotic lesions.