Background— Long-term administration of statin therapy has been shown to reduce major coronary events and cardiac mortality within randomized clinical trials. In addition to lowering lipids, statins favorably affect platelet adhesion, thrombosis, endothelial function, inflammation, and plaque stability, which may potentially improve outcome after percutaneous coronary intervention (PCI). Therefore, we hypothesized that statin therapy has an early beneficial effect among patients undergoing PCI. Methods and Results— Each year from 1993 to 1999, we prospectively collected data among the first 1000 patients undergoing PCI. Patients who presented with acute or recent myocardial infarction or cardiogenic shock were excluded from the analysis. Baseline, procedural, and 6-month data of statin-treated and non–statin-treated patients were compared. Propensity score and multivariate survival analysis were used to adjust for heterogeneity between the two groups. Of 5052 patients who completed follow-up, 26.5% were t...

Early and Sustained Survival Benefit Associated With Statin Therapy at the Time of Percutaneous Coronary Intervention

Objective: To evaluate platelet function in sepsis. Data Sources: The MEDLINE database and bibliographies of selected articles. Data Synthesis: The common occurrence of thrombocytopenia in critically ill patients has been recognized for many years and is known to be associated with an increased mortality rate. Platelet function can be divided into four areas: activation, adhesion, aggregation, and secretion. Studies have found that activated platelets secrete key components of the coagulation and inflammatory cascades and are involved in the regulation of vascular tone. However, studies on platelet function in sepsis have been scarce, and their data are often conflicting. In sepsis, aggregation of circulating platelets seems to be reduced, yet platelet receptors are present in normal amounts. Conclusions: Platelets play a complex role in sepsis; they are able to modulate not only their own function but also that of cells around them. Further study is needed to better define the precise mechanisms and effects of platelet activation in sepsis and to determine the benefits and risks of inhibiting platelet function.

Platelet function in sepsis.

Cholesterol sulfate in human physiology: what's it all about?

In antiphospholipid syndrome (APS), antiphospholipid antibodies (aPL) binding to β2 glycoprotein I (β2GPI) induce endothelial cell–leukocyte adhesion and thrombus formation via unknown mechanisms. Here we show that in mice both of these processes are caused by the inhibition of eNOS. In studies of cultured human, bovine, and mouse endothelial cells, the promotion of monocyte adhesion by aPL entailed decreased bioavailable NO, and aPL fully antagonized eNOS activation by diverse agonists. Similarly, NO-dependent, acetylcholine-induced increases in carotid vascular conductance were impaired in aPL-treated mice. The inhibition of eNOS was caused by antibody recognition of domain I of β2GPI and β2GPI dimerization, and it was due to attenuated eNOS S1179 phosphorylation mediated by protein phosphatase 2A (PP2A). Furthermore, LDL receptor family member antagonism with receptor-associated protein (RAP) prevented aPL inhibition of eNOS in cell culture, and ApoER2–/– mice were protected from aPL inhibition of eNOS in vivo. Moreover, both aPL-induced increases in leukocyte–endothelial cell adhesion and thrombus formation were absent in eNOS–/– and in ApoER2–/– mice. Thus, aPL-induced leukocyte–endothelial cell adhesion and thrombosis are caused by eNOS antagonism, which is due to impaired S1179 phosphorylation mediated by β2GPI, apoER2, and PP2A. Our results suggest that novel therapies for APS can now be developed targeting these mechanisms.

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Antiphospholipid antibodies promote leukocyte-endothelial cell adhesion and thrombosis in mice by antagonizing eNOS via β2GPI and apoER2

Background— Lysophosphatidic acid (LPA) is a platelet-activating component of mildly oxidized LDL (mox-LDL) and lipids isolated from human atherosclerotic plaques. Specific antagonists of platelet LPA receptors could be useful inhibitors of thrombus formation in patients with cardiovascular disease. Methods and Results— Short-chain analogs of phosphatidic acid (PA) were examined for their effect on two initial platelet responses, platelet shape change and Ca2+ mobilization. Dioctylglycerol pyrophosphate [DGPP(8:0)] and dioctylphosphatidic acid [PA(8:0)], recently described selective antagonists of the LPA1 and LPA3 receptors, inhibited platelet activation evoked by LPA but not by other platelet stimuli. DGPP(8:0) was more potent than PA(8:0). DGPP(8:0) also inhibited platelet shape change induced by mox-LDL and lipid extracts from human atherosclerotic plaques. Notably, we demonstrate for the first time that the lipid-rich core isolated from soft plaques was able to directly induce shape change. This effe...

Subtype-Selective Antagonists of Lysophosphatidic Acid Receptors Inhibit Platelet Activation Triggered by the Lipid Core of Atherosclerotic Plaques

Background—Cholesterol 3-sulfate is present on a variety of cells and in human LDL, and it has been found inatherosclerotic lesions of human aorta. Its precise biological role has not yet been described.Methods and Results—In this study, we investigated the interaction of platelets with cholesterol sulfate. Platelets adheredin a concentration-dependent and saturable manner to cholesterol sulfate but did not adhere to cholesterol, cholesterolacetate, estrone sulfate, or dehydroepiandrosterone sulfate, suggesting that the specificity of this interaction isdetermined not only by the cholesterol moiety but also by the sulfate group. This adhesion did not increase after plateletactivation, and it was not cation-dependent. Soluble cholesterol sulfate inhibited adhesion in a concentration-dependentmanner. However, antibodies against glycoprotein Ib, glycoprotein IIb/IIIa, CD36, P-selectin, von Willebrand factor, orthrombospondin had no significant effect on platelet adhesion to cholesterol sulfate. Perfusion of whole blood in aparallel-plate flow chamber resulted in the rapid and progressive adhesion of platelets to cholesterol sulfate but not tocholesterol acetate or estrone sulfate.Conclusions—Cholesterol sulfate supports platelet adhesion and may be one of the factors determining the prothromboticpotential of atherosclerotic lesions. (Circulation. 2001;103:2032-2034.)Key Words: atherosclerosis n thrombosis n cell adhesion molecules

Cholesterol sulfate: a new adhesive molecule for platelets.

β2-Glycoprotein I, an anionic phospholipid-binding 50-kDa plasma protein, circulates in the plasma at a concentration of 30–200 μg/ml. Its physiological role remains uncertain, but an important clue to this role is suggested by the finding that antibodies to this protein are frequently found in patients with antiphospholipid antibodies and thrombosis. β2-Glycoprotein I belongs to the complement control protein (CCP) superfamily with five CCP domains. The fifth CCP domain of β2-glycoprotein I has a unique structure and contains a stretch of positively charged amino acids that mediates the binding to phospholipids. This interaction may mediate the clearance of anionic phospholipid-containing surfaces from the circulation. Mutations in this domain affect its binding to phospholipids. We have identified a patient with primary antiphospholipid syndrome who is a compound heterozygous for two mutations in the fifth CCP. One mutation is located in exon 7 (codon 306), and the second mutation is in exon 8 (codon 316). The mutant β2-glycoprotein I was present in normal quantities in his plasma but did not bind to cardiolipin. He had recurrent deep vein thrombosis and pulmonary embolism at age 28 and a thrombotic stroke at age 35, with no other identifiable risk factor for a hypercoagulable state. This report offers some insight into the mechanism of formation of antiphospholipid antibodies and suggests the possible role of the deficiency of β2-glycoprotein I in the pathogenesis of thrombosis. Am. J. Hematol. 65:160–165, 2000. © 2000 Wiley-Liss, Inc.

Primary antiphospholipid antibody syndrome with mutations in the phospholipid binding domain of β2-glycoprotein I

Background Sulfatides are sulfated glycosphingolipids expressed on the surface of erythrocytes, leukocytes, and platelets. Sulfatides interact with several cell adhesion molecules involved in hemostasis. Beta2-glycoprotein I is an anionic phospholipid-binding plasma protein, and the phospholipid-bound form is the target for most anti-phospholipid antibodies that are associated with recurrent thrombosis, miscarriages, and neurological symptoms. In this study, we examined whether beta2-glycoprotein I forms a complex with sulfatides and thereby becomes a target for anti-phospholipid antibodies. Methods and results Beta2-glycoprotein I binds to surface-bound sulfatides but not to other glycolipids, such as ceramide, cerebrosides, sphingomyelin, or ganglioside. At a sulfatide coating density of 1 microg/well, beta2-glycoprotein I reaches half-maximal binding at 2.5 microg/mL, and the binding is saturated at 10 microg/mL. The binding of beta2-glycoprotein I also depends on the coating density of sulfatides in the well. At a constant beta2-glycoprotein I concentration of 5 microg/mL, maximal binding of beta2-glycoprotein I is observed at a coating density of 1 mug/well. The serum from 14 patients with anti-cardiolipin antibodies, a subset of anti-phospholipid antibodies, bound to sulfatide-bound beta2-glycoprotein I and previous absorption on cardiolipin-coated surfaces decreased the immunoreactivity toward sulfatide-beta2-glycoprotein I complex by >50% in 12 of 14 patients. Furthermore, immunoaffinity-purified anti-cardiolipin antibodies from 4 of 5 patients reacted with sulfatide-bound beta2-glycoprotein I. Conclusions These results show that not only anionic phospholipids, as commonly known, but also sulfatides are targets for most anti-phospholipid antibodies. We therefore postulate that interactions of these antibodies with sulfatides may contribute to some of the clinical symptoms of the anti-phospholipid antibody syndrome.

Sulfatides Targets for Anti-Phospholipid Antibodies

h2-glycoprotein I is a phospholipid-binding protein of 326 amino acids and is found in plasma at a concentration off200 Ag/ml. It has a sequence of positively charged amino acids located at the carboxy terminus that mediates anionic phospholipid binding. Two polymorphisms (306Cys !Gly and 316Trp !Ser) located at the phospholipid-binding site have been described. Homozygous state for either mutation and a compound heterozygous state show no phospholipid binding. Interestingly, heterozygotes for either 306Cys !Gly or 316Trp !Ser mutation have normal cardiolipin binding suggesting that h2-glycoprotein I may circulate as a multimeric structure where wild-type subunits compensate the defective binding of the mutant ones. We investigated the effect of these mutations on quaternary structure of h2glycoprotein I and phospholipid binding. As previously reported, under native conditions, h2-glycoprotein I shows an apparent molecular weight of f320 kDa and it can be dissociated into subunits of lower molecular weight by boiling in 6 M urea. We show that the multimeric structure is not affected by the presence of mutations in the phospholipid-binding domain. h2-glycoprotein I induces aggregation of anionic phospholipid vesicles suggesting again a multivalent interaction where at least two binding sites are required to bridge adjacent vesicles. h2glycoprotein I-induced aggregation does not cause vesicle fusion or damage as demonstrated by fluorescence resonance energy transfer (FRET) or encapsulated calcein release. In conclusion, the normal cardiolipin binding in heterozygous state for mutations at phospholipidbinding domain may be due to the multimeric structure of h2-glycoprotein I. D 2002 Published by Elsevier Science Ltd.

Perumal Thiagarajan

Papers

Cholesterol sulfate: a new adhesive molecule for platelets.

Primary antiphospholipid antibody syndrome with mutations in the phospholipid binding domain of β2-glycoprotein I

Sulfatides Targets for Anti-Phospholipid Antibodies

Regular Article Polymorphisms h2-glycoprotein I: phospholipid binding and multimeric structure