(1/6753) Lipoprotein-associated phospholipase A2, platelet-activating factor acetylhydrolase, generates two bioactive products during the oxidation of low-density lipoprotein: use of a novel inhibitor.
A novel and potent azetidinone inhibitor of the lipoprotein-associated phospholipase A2 (Lp-PLA2), i.e. platelet-activating factor acetylhydrolase, is described for the first time. This inhibitor, SB-222657 (Ki=40+/-3 nM, kobs/[I]=6. 6x10(5) M-1.s-1), is inactive against paraoxonase, is a poor inhibitor of lecithin:cholesterol acyltransferase and has been used to investigate the role of Lp-PLA2 in the oxidative modification of lipoproteins. Although pretreatment with SB-222657 did not affect the kinetics of low-density lipoprotein (LDL) oxidation by Cu2+ or an azo free-radical generator as determined by assay of lipid hydroperoxides (LOOHs), conjugated dienes and thiobarbituric acid-reacting substances, in both cases it inhibited the elevation in lysophosphatidylcholine content. Moreover, the significantly increased monocyte chemoattractant activity found in a non-esterified fatty acid fraction from LDL oxidized by Cu2+ was also prevented by pretreatment with SB-222657, with an IC50 value of 5.0+/-0.4 nM. The less potent diastereoisomer of SB-222657, SB-223777 (Ki=6.3+/-0.5 microM, kobs/[I]=1.6x10(4) M-1.s-1), was found to be significantly less active in both assays. Thus, in addition to generating lysophosphatidylcholine, a known biologically active lipid, these results demonstrate that Lp-PLA2 is capable of generating oxidized non-esterified fatty acid moieties that are also bioactive. These findings are consistent with our proposal that Lp-PLA2 has a predominantly pro-inflammatory role in atherogenesis. Finally, similar studies have demonstrated that a different situation exists during the oxidation of high-density lipoprotein, with enzyme(s) other than Lp-PLA2 apparently being responsible for generating lysophosphatidylcholine. (+info)
(2/6753) Antiphospholipid, anti-beta 2-glycoprotein-I and anti-oxidized-low-density-lipoprotein antibodies in antiphospholipid syndrome.
Antiphospholipid antibodies (aPL), anti-beta 2-glycoprotein I (anti-beta 2-GPI) and anti-oxidized-low-density lipoprotein (LDL) antibodies are all implicated in the pathogenesis of antiphospholipid syndrome. To investigate whether different autoantibodies or combinations thereof produced distinct effects related to their antigenic specificities, we examined the frequencies of antiphospholipid syndrome (APS)-related features in the presence of different antibodies [aPL, beta 2-GPI, anti-oxidized low density lipoprotein (LDL)] in 125 patients with APS. Median follow-up was 72 months: 58 patients were diagnosed as primary APS and 67 as APS plus systemic lupus erythematosus (SLE). Anticardiolipin antibodies (aCL), anti-beta 2-GPI and anti-oxidized LDL antibodies were determined by ELISA; lupus anticoagulant (LA) by standard coagulometric methods. Univariate analysis showed that patients positive for anti-beta 2-GPI had a higher risk of recurrent thrombotic events (OR = 3.64, 95% CI, p = 0.01) and pregnancy loss (OR = 2.99, 95% CI, p = 0.004). Patients positive for anti-oxidized LDL antibodies had a 2.24-fold increase in the risk of arterial thrombosis (2.24, 95% CI, p = 0.03) and lower risk of thrombocytopenia (OR = 0.41 95% CI, p = 0.04). Patients positive for aCL antibodies had a higher risk of pregnancy loss (OR = 4.62 95% CI, p = 0.001). When these data were tested by multivariate logistic regression, the association between anti-beta 2-GPI and pregnancy loss and the negative association between anti-oxidized LDL antibodies and thrombocytopenia disappeared. (+info)
(3/6753) Suppression of atherosclerotic development in Watanabe heritable hyperlipidemic rabbits treated with an oral antiallergic drug, tranilast.
BACKGROUND: Inflammatory and immunological responses of vascular cells have been shown to play a significant role in the progression of atheromatous formation. Tranilast [N-(3,4-dimethoxycinnamoyl) anthranillic acid] inhibits release of cytokines and chemical mediators from various cells, including macrophages, leading to suppression of inflammatory and immunological responses. This study tested whether tranilast may suppress atheromatous formation in Watanabe heritable hyperlipidemic (WHHL) rabbits. METHODS AND RESULTS: WHHL rabbits (2 months old) were given either 300 mg x kg-1 x d-1 of tranilast (Tranilast, n=12) or vehicle (Control, n=13) PO for 6 months. Tranilast treatment was found to suppress the aortic area covered with plaque. Immunohistochemical analysis showed that there was no difference in the percentage of the RAM11-positive macrophage area and the frequency of CD5-positive cells (T cells) in intimal plaques between Tranilast and Control. Major histocompatibility complex (MHC) class II expression in macrophages and interleukin-2 (IL-2) receptor expression in T cells, as markers of the immunological activation in these cells, was suppressed in atheromatous plaque by tranilast treatment. Flow cytometry analysis of isolated human and rabbit peripheral blood mononuclear cells showed that an increase in expression both of MHC class II antigen on monocytes by incubation with interferon-gamma and of IL-2 receptor on T cells by IL-2 was suppressed by the combined incubation with tranilast. CONCLUSIONS: The results indicate that tranilast suppresses atherosclerotic development partly through direct inhibition of immunological activation of monocytes/macrophages and T cells in the atheromatous plaque. (+info)
(4/6753) Hypoalbuminemia increases lysophosphatidylcholine in low-density lipoprotein of normocholesterolemic subjects.
BACKGROUND: A phospholipid, lysophosphatidylcholine (LPC), is the major determinant of the atherosclerotic properties of oxidized low-density lipoprotein (LDL). Under normal circumstances most LPC is bound to albumin. We hypothesized that lipoprotein LPC concentrations are increased in hypoalbuminemic patients with the nephrotic syndrome, irrespective of their lipid levels. To test this hypothesis, we selected nephrotic and control subjects with matched LDL cholesterol levels. METHODS: Lipoproteins and the albumin-rich lipoprotein-deficient fractions were separated by ultracentrifugation and their phospholipid composition was analyzed by thin-layer chromatography. RESULTS: Nephrotic subjects (albumin 23 +/- 2 g/liter and LDL cholesterol 3.1 +/- 0.2 mmol/liter) had a LDL LPC concentration that was increased (P < 0.05) to 66 +/- 7 vs. 35 +/- 6 micromol/liter in matched controls (albumin 42 +/- 5 g/liter and LDL cholesterol 3.1 +/- 0.2 mmol/liter). LPC in very low-density lipoprotein plus intermediate-density lipoprotein (VLDL + IDL) in these subjects was also increased to 33 +/- 7 vs. 9 +/- 2 micromol/liter in controls (P < 0.05). Conversely, LPC was decreased to 19 +/- 4 micromol/liter in the albumin-containing fraction of these hypoalbuminemic patients, as compared to 46 +/- 10 micromol/liter in the controls (P < 0.05). LPC was also low (14 +/- 4 micromol/liter) in the albumin-containing fraction of hypoalbuminemic, hypocholesterolemic patients with nonrenal diseases. In hyperlipidemic nephrotic subjects (albumin 21 +/- 2 g/liter and LDL cholesterol 5.7 +/- 0.5 mmol/liter) the LPC levels in LDL and VLDL + IDL were further increased, to 95 +/- 20 and 56 +/- 23 micromol/liter, respectively (P < 0.05). CONCLUSION: These findings suggest that in the presence of hypoalbuminemia in combination with proteinuria, LPC shifts from albumin to VLDL, IDL and LDL. This effect is independent of hyperlipidemia. Increased LPC in lipoproteins may be an important factor in the disproportionate increase in cardiovascular disease in nephrotic patients with hypoalbuminemia. (+info)
(5/6753) Liver-specific inactivation of the abetalipoproteinemia gene completely abrogates very low density lipoprotein/low density lipoprotein production in a viable conditional knockout mouse.
Conventional knockout of the microsomal triglyceride transfer protein large subunit (lMTP) gene is embryonic lethal in the homozygous state in mice. We have produced a conditional lMTP knockout mouse by inserting loxP sequences flanking exons 5 and 6 by gene targeting. Homozygous floxed mice were born live with normal plasma lipids. Intravenous injection of an adenovirus harboring Cre recombinase (AdCre1) produced deletion of exons 5 and 6 and disappearance of lMTP mRNA and immunoreactive protein in a liver-specific manner. There was also disappearance of plasma apolipoprotein (apo) B-100 and marked reduction in apoB-48 levels. Wild-type mice showed no response, and heterozygous mice, an intermediate response, to AdCre1. Wild-type mice doubled their plasma cholesterol level following a high cholesterol diet. This hypercholesterolemia was abolished in AdCre1-treated lMTP-/- mice, the result of a complete absence of very low/intermediate/low density lipoproteins and a slight reduction in high density lipoprotein. Heterozygous mice showed an intermediate lipoprotein phenotype. The rate of accumulation of plasma triglyceride following Triton WR1339 treatment in lMTP-/- mice was <10% that in wild-type animals, indicating a failure of triglyceride-rich lipoprotein production. Pulse-chase experiments using hepatocytes isolated from wild-type and lMTP-/- mice revealed a failure of apoB secretion in lMTP-/- animals. Therefore, the liver-specific inactivation of the lMTP gene completely abrogates apoB-100 and very low/intermediate/low density lipoprotein production. These conditional knockout mice are a useful in vivo model for studying the role of MTP in apoB biosynthesis and the biogenesis of apoB-containing lipoproteins. (+info)
(6/6753) Platelet high affinity low density lipoprotein binding and import of lipoprotein derived phospholipids.
The binding of low density lipoprotein (LDL) to the platelet cell membrane could facilitate the transfer of phospholipids from LDL to the platelets. A polyclonal antibody against the platelet glycoproteins IIb/IIIa inhibited the high affinity binding of 125I-LDL by up to 80%. The transfer of pyrene (py)-labeled sphingomyelin (SM), phosphatidylcholine and phosphatidylethanolamine from LDL to the platelets was unaffected by the antibody. The lectin wheat germ agglutinin (WGA) reduced the binding of 125I-LDL to the platelets by approximately 80%. In contrast, the lectin stimulated the transfer of SM from LDL into the platelets by about three-fold. WGA also specifically augmented the transfer of py-SM between lipid vesicles and the platelets, the stimulation being abolished in the presence of N-acetylglucosamine. Dextran sulfate (DS) increased the specific binding of 125I-LDL to the platelets by up to 2.8-fold. On the other hand, the import of LDL-derived py-phospholipids was unaffected by DS. Together, the results indicate that the phospholipid transfer from LDL to the platelets is independent of the high affinity LDL binding to the platelets and is specifically stimulated by WGA. Thus, the interactions of platelets with LDL phospholipids differ markedly from those with the apoprotein components of the lipoproteins. (+info)
(7/6753) Oxidized low-density lipoprotein regulates matrix metalloproteinase-9 and its tissue inhibitor in human monocyte-derived macrophages.
BACKGROUND: Macrophages in human atherosclerotic plaques produce a family of matrix metalloproteinases (MMPs), which may influence vascular remodeling and plaque disruption. Because oxidized LDL (ox-LDL) is implicated in many proatherogenic events, we hypothesized that ox-LDL would regulate expression of MMP-9 and tissue inhibitor of metalloproteinase-1 (TIMP-1) in monocyte-derived macrophages. MWRHOSA AND RESULTS: Mononuclear cells were isolated from normal human subjects with Ficoll-Paque density gradient centrifugation, and adherent cells were allowed to differentiate into macrophages during 7 days of culture in plastic dishes. On day 7, by use of serum-free medium, the macrophages were incubated with various concentrations of native LDL (n-LDL) and copper-oxidized LDL. Exposure to ox-LDL (10 to 50 microg/mL) increased MMP-9 mRNA expression as analyzed by Northern blot, protein expression as measured by ELISA and Western blot, and gelatinolytic activity as determined by zymography. The increase in MMP-9 expression was associated with increased nuclear binding of transcription factor NF-kappaB and AP-1 complex on electromobility shift assay. In contrast, ox-LDL (10 to 50 microg/mL) decreased TIMP-1 expression. Ox-LDL-induced increase in MMP-9 expression was abrogated by HDL (100 microg/mL). n-LDL had no significant effect on MMP-9 or TIMP-1 expression. CONCLUSIONS: These data demonstrate that unlike n-LDL, ox-LDL upregulates MMP-9 expression while reducing TIMP-1 expression in monocyte-derived macrophages. Furthermore, HDL abrogates ox-LDL-induced MMP-9 expression. Thus, ox-LDL may contribute to macrophage-mediated matrix breakdown in the atherosclerotic plaques, thereby predisposing them to plaque disruption and/or vascular remodeling. (+info)
(8/6753) Antibodies against phospholipids and oxidized LDL in alcoholic patients.
Antiphospholipid antibodies (APA) are a generic term describing antibodies that recognize various phospholipids. Hepatocyte damage is a cardinal event in the course of alcoholic liver injury and autoantibodies against phospholipids could play an important role in this process. APA in alcoholic patients seem to reflect membrane lesions, impairment of immunological reactivity, liver disease progression and they correlate significantly with disease severity. LDL oxidation is supposed to be one of the most important pathogenic mechanisms of atherosclerosis and antibodies against oxidized low-density lipoprotein (oxLDL) are some kind of an epiphenomenon of this process. The scope of our study was to determine some autoantibodies (IgG-oxLDL and antiphospholipid antibodies) and their possible changes in alcoholic patients. We studied IgG-oxLDL and four APA - anticardiolipin antibodies (ACA), antiphosphatidylserine antibodies (APSA) antiphosphatidylethanolamine antibodies (APE) and antiphosphatidylcholine antibodies (APCA) in 35 alcoholic patients with mildly affected liver function at the beginning of the abuse treatment. The control group consisted of 60 healthy blood donors. In the studied group, we obtained positive results concerning total ACA in 17.1 % of alcoholic patients (8.3 % in the control group), 11.4 % IgG-ACA (6.7 %), 8.6 % IgM-ACA (3.3 %), 14.3 % total APE (6.7 %), 14.3 % total APCA (8.3 %) and 20 % total APSA (8.3 % in the control group). The IgG-oxLDL (406.4+/-52.5 vs 499.9+/-52.5 mU/ml) was not affected in alcoholic patients. We conclude that the autoantibodies against oxLDL are present in sera of alcoholics and healthy blood donors. Based on our results which revealed a wide range of IgG-oxLDL titres in the healthy population, this parameter does not appear to be very promising for the evaluation of the risk of atherosclerosis. Alcoholics with only mild affection of liver functions did not exhibit a significantly higher prevalence of all studied antiphospholipid antibodies (ACA, APSA, APE, APCA) which could lead to membrane lesions in these patients. (+info)