Constantinos C. Tellis

The role of lipoprotein-associated phospholipase A2 in atherosclerosis may depend on its lipoprotein carrier in plasma.

Platelet-activating factor (PAF) acetylhydrolase exhibits a Ca(2+)-independent phospholipase A2 activity and degrades PAFas well as oxidized phospholipids (oxPL). Such phospholipids are accumulated in the artery wall and may play key roles in vascular inflammation and atherosclerosis. PAF-acetylhydrolase in plasma is complexed to lipoproteins; thus it is also referred to as lipoprotein-associated phospholipase A2 (Lp-PLA2). Lp-PLA2 is primarily associated with low-density lipoprotein (LDL), whereas a small proportion of circulating enzyme activity is also associated with high-density lipoprotein (HDL). The majority of the LDL-associated Lp-PLA2 (LDL-Lp-PLA2) activity is bound to atherogenic small-dense LDL particles and it is a potential marker of these particles in plasma. The distribution of Lp-PLA2 between LDL and HDL is altered in various types of dyslipidemias. It can be also influenced by the presence of lipoprotein (a) [Lp(a)] when plasma levels of this lipoprotein exceed 30 mg/dl. Several lines of evidence suggest that the role of plasma Lp-PLA2 in atherosclerosis may depend on the type of lipoprotein particle with which this enzyme is associated. In this regard, data from large Caucasian population studies have shown an independent association between the plasma Lp-PLA2 levels (which are mainly influenced by the levels of LDL-Lp-PLA2) and the risk of future cardiovascular events. On the contrary, several lines of evidence suggest that HDL-associated Lp-PLA2 may substantially contribute to the HDL antiatherogenic activities. Recent studies have provided evidence that oxPL are preferentially sequestered on Lp(a) thus subjected to degradation by the Lp(a)-associated Lp-PLA2. These data suggest that Lp(a) may be a potential scavenger of oxPL and provide new insights into the functional role of Lp(a) and the Lp(a)-associated Lp-PLA2 in normal physiology as well as in inflammation and atherosclerosis. The present review is focused on recent advances concerning the Lp-PLA2 structural characteristics, the molecular basis of the enzyme association with distinct lipoprotein subspecies, as well as the potential role of Lp-PLA2 associated with different lipoprotein classes in atherosclerosis and cardiovascular disease.

Lipoprotein-Associated Phospholipase A2 Bound on High-Density Lipoprotein Is Associated With Lower Risk for Cardiac Death in Stable Coronary Artery Disease Patients : A 3-Year Follow-Up

OBJECTIVES The aim of this study was to examine the prognostic value of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) associated with high-density lipoprotein (HDL) (HDL-Lp-PLA(2)) in patients with stable coronary artery disease (CAD). BACKGROUND Lp-PLA(2) is a novel risk factor for cardiovascular disease. It has been postulated that the role of Lp-PLA(2) in atherosclerosis may depend on the type of lipoprotein with which it is associated. METHODS Total plasma Lp-PLA(2) and HDL-Lp-PLA(2) mass and activity, lipids, and C-reactive protein were measured in 524 consecutive patients with stable CAD who were followed for a median of 34 months. The primary endpoint was cardiac death, and the secondary endpoint was hospitalization for acute coronary syndromes, myocardial revascularization, arrhythmic event, or stroke. RESULTS Follow-up data were obtained from 477 patients. One hundred twenty-three patients (25.8%) presented with cardiovascular events (24 cardiac deaths, 47 acute coronary syndromes, 28 revascularizations, 22 arrhythmic events, and 2 strokes). Total plasma Lp-PLA(2) mass and activity were predictors of cardiac death (hazard ratio [HR]: 1.013; 95% confidence interval [CI]: 1.005 to 1.021; p = 0.002; and HR: 1.040; 95% CI: 1.005 to 1.076; p = 0.025, respectively) after adjustment for traditional risk factors for CAD. In contrast, HDL-Lp-PLA(2) mass and activity were associated with lower risk for cardiac death (HR: 0.972; 95% CI: 0.952 to 0.993; p = 0.010; and HR: 0.689; 95% CI: 0.496 to 0.957; p = 0.026, respectively) after adjustment for traditional risk factors for CAD. CONCLUSIONS Total plasma Lp-PLA(2) is a predictor of cardiac death, while HDL-Lp-PLA(2) is associated with lower risk for cardiac death in patients with stable CAD, independently of other traditional cardiovascular risk factors.

Comparison of the effect of simvastatin versus simvastatin/ezetimibe versus rosuvastatin on markers of inflammation and oxidative stress in subjects with hypercholesterolemia

OBJECTIVES Statins may exhibit anti-inflammatory and antioxidant effects. Whether different statins at equivalent doses or the combination of low-dose statin with ezetimibe have comparable anti-inflammatory and antioxidant effects is unknown. The aim of this study was to compare the effects of simvastatin, simvastatin/ezetimibe or rosuvastatin at equivalent low-density lipoprotein cholesterol lowering doses on inflammation and oxidative stress indices in subjects with hypercholesterolemia. METHODS This was a pre-specified analysis of a prospective, randomized, open-label, blinded endpoint (PROBE) study. We enrolled one hundred and fifty three (n = 153) hypercholesterolemic subjects who were randomized to receive simvastatin 40 mg or simvastatin/ezetimibe 10/10 mg or rosuvastatin 10 mg daily. Plasma 8-Epi prostaglandin F2 alpha (8-epiPGF2a), oxidized LDL (oxLDL) and lipoprotein-associated phospholipase A2 (Lp-PLA2) activity and mass were measured at baseline and following 12 weeks of treatment. RESULTS A significant reduction in plasma 8-isoprostane and oxLDL levels was observed in all treatment groups [by 10%, 8% and 6% (p < 0.05 compared with baseline) and 41%, 40% and 39% (p < 0.001 compared with baseline) in simvastatin, simvastatin/ezetimibe and rosuvastatin groups, respectively]. In all treatment groups a significant reduction in total plasma Lp-PLA2 activity and mass was observed (by 36%, 31% and 38% and 36%, 32% and 32% for simvastatin, simvastatin/ezetimibe and rosuvastatin, respectively, p < 0.001 compared with baseline). No intergroup differences were observed. CONCLUSIONS Simvastatin 40 mg, simvastatin/ezetimibe 10/10 mg and rosuvastatin 10 mg significantly reduced 8-epiPGF2a, oxLDL and Lp-PLA2 activity and mass to a similar extent.

Effect of simvastatin or its combination with ezetimibe on Toll-like receptor expression and lipopolysaccharide - induced cytokine production in monocytes of hypercholesterolemic patients.

OBJECTIVES Toll-like receptors (TLRs) are key players in the innate immune system. Recently, a pivotal role of TLR2 and TLR4 has been recognized in atherogenesis. We investigated the effect of simvastatin monotherapy or its combination with ezetimibe on TLR2 and TLR4 membrane expression and on lipopolysaccharide (LPS)-induced interleukin-1β (IL-1β) and interleukin-6 (IL-6) production in peripheral blood monocytes of patients with primary hypercholesterolemia. METHODS This was a prospective, randomized, open-label, blinded endpoint study. After a 3-month period of lifestyle changes patients (n = 60) (mean age 55 ± 13) with LDL-cholesterol levels above those recommended by the NCEP ATP III, were randomly allocated to open-label simvastatin 40 mg (n = 30) or simvastatin/ezetimibe 10/10 mg (n = 30) daily. Both groups were similar with regard to demographics, risk factors, medications and baseline lipid values. TLR2 and TLR4 membrane expression in monocytes, LPS-induced intracellular production of IL-1β and IL-6 were assessed by flow cytometry at baseline and 3 months post-treatment in both patient groups, as well as in 30 age- and sex-matched normolipidemic controls. RESULTS Hypercholesterolemic patients exhibited higher TLR2 and TLR4 membrane expression compared with controls (p < 0.02). LPS induced a significant increase in the intracellular levels of IL-1β and IL-6 in all groups however both patient groups exhibited significantly lower levels compared with controls. Three months of treatment with either simvastatin or its combination with ezetimibe resulted in a significant reduction of TLR2 and TLR4 expression (p < 0.01 compared with baseline values) with no intergroup differences. Furthermore, in both groups the post-treatment values of LPS-induced IL-1β and IL-6 production were significantly lower compared with baseline (p < 0.05 for all comparisons). CONCLUSIONS A high simvastatin dose or the combination of a low-dose simvastatin with ezetimibe reduce to a similar extent TLR2, TLR4 membrane expression and LPS-induced IL-6 and IL-1β production in monocytes of hypercholesterolemic patients. The pathophysiological significance of these effects regarding atherosclerosis, reserves further investigation.

Smoking induces lipoprotein-associated phospholipase A2 in cardiovascular disease free adults: The ATTICA Study

OBJECTIVES We studied the association of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) mass and activity with various lifestyle, clinical and biochemical characteristics in cardiovascular disease (CVD) free adults. BACKGROUND Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is a novel biomarker of inflammation and risk for CVD. The Lp-PLA(2) mass and activity are primarily influenced by the plasma levels of low-density lipoprotein (LDL), however the influence of various lifestyle characteristics on Lp-PLA(2) have not been adequately studied. METHODS AND RESULTS In a random sub-sample of 186 subjects, 64 men (52+/-13 years) and 122 women (48+/-13 years) from the ATTICA Study (Greece), Lp-PLA(2) activity and mass in total plasma as well as the enzyme activity and mass associated with high-density lipoprotein (HDL-Lp-PLA(2)) were determined using established methods. Several socio-demographic, lifestyle, clinical and biochemical parameters were assessed in all participants. Multiple linear regression analysis revealed that among the lifestyle characteristics, total plasma Lp-PLA(2) activity and mass were positively and independently associated with current smoking (p=0.02 and p=0.05, respectively), as well as with exposure to second-hand smoke (p=0.02 and p=0.01, respectively). Furthermore, HDL-Lp-PLA(2) activity and mass were inversely and independently associated with current smoking (p=0.04 and p=0.09, respectively). CONCLUSIONS Smoking is associated with and might even induce an increase in proatherogenic total plasma Lp-PLA(2), but attenuates antiatherogenic HDL-Lp-PLA(2). These results further support the role of smoking as an important avoidable cause of CVD.

Lipoprotein-associated phospholipase A2 and arterial stiffness evaluation in patients with inflammatory bowel diseases

BACKGROUND AND AIMS The association between inflammatory bowel diseases (IBD) and cardiovascular disease (CVD) remains equivocal. Arterial stiffness, as assessed by pulse wave velocity (PWV), and lipoprotein-associated phospholipase A2 (Lp-PLA2) are surrogates of CVD risk. AIM The aim of this study was to assess carotid-femoral PWV and Lp-PLA2 in patients with IBD without history of CVD. METHODS Established CVD risk factors, IBD characteristics, PWV and Lp-PLA2 activity were assessed in 44 patients with IBD, 29 with Crohns disease (CD) and 15 with ulcerative colitis (UC), and 44 matched controls. RESULTS IBD patients had lower total and low density lipoprotein cholesterol (LDL-C) levels. There was no difference in PWV between patients and controls (6.8 vs. 6.4m/s), but patients with CD had higher PWV compared to those with UC (7 vs. 6.3m/s; p=0.044), and to controls. Smoking rates were significantly higher among CD patients. Factors associated with PWV were age, mean arterial pressure and smoking. Lp-PLA2 activity was significantly lower in patients with IBD (46.8 vs. 53.9 nmol/mL/min; p=0.011). There was no difference in Lp-PLA2 between CD and UC patients. LDL-C was the only significant predictor of Lp-PLA2. CONCLUSIONS Our study showed lower Lp-PLA2 activity in patients with IBD compared with controls, reflecting lower LDL-C in the former. There was no difference in PWV between the two groups. Arterial stiffness was higher in patients with CD, which is likely related to higher smoking rates. These findings challenge a possible association between IBD and CVD, but further studies are required.

Pathophysiological role and clinical significance of lipoprotein-associated phospholipase A₂ (Lp-PLA₂) bound to LDL and HDL.

Lipoprotein-associated phospholipase A2 (Lp-PLA2), also named as platelet-activating factor (PAF)-acetylhydrolase, exhibits a Ca2+-independent phospholipase A2 activity and catalyzes the hydrolysis of the ester bond at the sn-2 position of PAF and oxidized phospholipids (oxPL). These phospholipids are formed under oxidative and inflammatory conditions, and may play important roles in atherogenesis. The vast majority of plasma Lp-PLA2 mass binds to low-density lipoprotein (LDL) while a smaller amount is associated with high-density lipoprotein (HDL). Lp-PLA2 is also bound to lipoprotein (a) [Lp(a)], very low-density lipoprotein (VLDL) and remnant lipoproteins. Several lines of evidence suggest that the role of plasma Lp-PLA2 in atherosclerosis may depend on the type of lipoprotein particle with which this enzyme is associated. Data from large Caucasian population studies have supported plasma Lp-PLA2 (primarily LDL-associated Lp-PLA2) as a cardiovascular risk marker independent of, and additive to, traditional risk factors. On the contrary, the HDL-associated Lp-PLA2 may express antiatherogenic activities and is also independently associated with lower risk for cardiac death. The present review presents data on the biochemical and enzymatic properties of Lp-PLA2 as well as its structural characteristics that determine the association with LDL and HDL. We also critically discuss the possible pathophysiological and clinical significance of the Lp- PLA2 distribution between LDL and HDL in human plasma, in view of the results of prospective epidemiologic studies on the association of Lp-PLA2 with future cardiovascular events as well the recent studies that evaluate the possible effectiveness of specific Lp-PLA2 inhibitors in reducing residual cardiovascular risk.

Plasma levels of lipoprotein-associated phospholipase A2 are increased in patients with β-thalassemia

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an independent cardiovascular risk factor. We investigated the plasma levels of Lp-PLA2 activity and mass as a function of plasma lipid levels, LDL subclass profile, and oxidative stress in patients with β-thalassemia. Thirty-five patients with β-thalassemia major (β-TM) and 25 patients with β-thalassemia intermedia (β-TI) participated in the study. Lp-PLA2 activity and mass were measured in total plasma, in apolipoprotein (apo)B-depleted plasma (HDL-Lp-PLA2), and in LDL subclasses. Lp-PLA2 activity produced and secreted from peripheral blood monocytes in culture was also determined. Patients with β-thalassemia are characterized by a predominance of small-dense LDL particles, increased oxidative stress, and very high plasma levels of Lp-PLA2 mass and activity, despite low LDL-cholesterol levels. A significant positive correlation between plasma Lp-PLA2 activity or mass and 8-isoprostane (8-epiPGF2a) and ferritin levels as well as intima-media thickness (IMT) values was observed. An increase in secreted and cell-associated Lp-PLA2 activity from monocytes in culture was observed in both patient groups. The HDL-Lp-PLA2 activity and mass as well as the ratio of HDL-Lp-PLA2/plasma Lp-PLA2 were significantly higher in both patient groups compared with the control group. In conclusion, patients with β-thalassemia exhibit high plasma Lp-PLA2 levels, attributed to increased enzyme secretion from monocytes/macrophages and to the predominance of sdLDL particles in plasma. Plasma Lp-PLA2 is correlated with carotid IMT, suggesting that this enzyme may be implicated in premature carotid atherosclerosis observed in β-thalassemia.

Plasma triglyceride levels and body mass index values are the most important determinants of preβ-1 HDL concentrations in patients with various types of primary dyslipidemia

OBJECTIVE Experimental studies have shown that the prebeta-1 subclass of high-density lipoprotein particles (prebeta-1 HDL) may play an important role in the reverse cholesterol transport pathway as the initial acceptors of cellular cholesterol. The aim of the present study was the direct comparison of prebeta-1 HDL values in individuals with various types of primary dyslipidemias. METHODS Four hundred and eighty-six unrelated individuals were included in the study. According to their lipid values study participants were subdivided into four groups: control group (n=206), type IIA dyslipidemia group (n=148), type IIB dyslipidemia group (n=49) and type IV dyslipidemia group (n=83). RESULTS All dyslipidemic patients displayed higher concentrations of prebeta-1 HDL compared to control individuals. However, patients with dyslipidemias characterized by an abnormal catabolism of triglyceride-rich lipoproteins (such as dyslipidemias of type IIB and IV) tend to have higher prebeta-1 HDL values compared to patients with hypercholesterolemia, and this increase is proportional to the degree of hypertriglyceridemia. In addition, patients with metabolic syndrome exhibited significantly higher levels of prebeta-1 HDL compared to individuals that do not fulfill the criteria for the diagnosis of this syndrome. Multiple regression analysis revealed that serum triglyceride concentrations and body mass index (BMI) values were the most important determinants of prebeta-1 HDL levels in our population. CONCLUSION All dyslipidemic patients exhibit increased prebeta-1 HDL concentrations as compared to normolipidemic individuals. Whether this increase represents a defensive mechanism against atherosclerosis or it is indicative of impaired maturation of HDL particles and thus of a defective reverse cholesterol transport mechanism remains to be established.

High density lipoprotein is positively correlated with the changes in circulating total adiponectin and high molecular weight adiponectin during dietary and fenofibrate treatment.

OBJECTIVEThe investigation of the relationship between high density lipoprotein (HDL) and adiponectin.DESIGNThirty-seven obese or overweight [body mass index ≥27 Kg/m2], hypertriglyceridemic patients underwent one of the following interventions for 3 months: 1) Low-calorie diet (n=19), 2) Low-calorie diet plus fenofibrate (n=18).RESULTSCirculating total adiponectin did not change significantly in the low-calorie diet group. However, in the subgroup of patients whose high density lipoprotein cholesterol (HDL-C) decreased over the first month of diet, a statistically significant reduction of the circulating total adiponectin was observed (p=0.010), while in the subgroup of patients whose HDL-C increased over the latter 2 months of the diet, an increase in circulating total adiponectin over the 2 months was found (p=0.043). The percentage change of HDL-C over the first month of diet was positively correlated with the percentage change of circulating total adiponectin (r=0.579, p=0.019). The percentage change of HDL-C over the 3 months of diet was positively correlated with the percentage changes of circulating total adiponectin (r=0.527, p=0.030) and high molecular weight (HMW) adiponectin (r=0.524, p=0.031). The change in circulating total adiponectin over the first month of diet was positively correlated with the HDL-C at 1 month (r=0.606, p=0.013). The change in HMW adiponectin over the 3 months of diet was positively correlated with the HDL-C at 3 months (r=0.602, p=0.011). The percentage change of circulating HMW adiponectin over the first month of fenofibrate treatment was positively correlated with the percentage change of HDL-C (r=0.594, p=0.012).CONCLUSIONSHDL is positively correlated with the changes in circulating adiponectin during dietary and fenofibrate treatment.