Macrophage-specific expression of group IIA sPLA2 results in accelerated atherogenesis by increasing oxidative stress

Sinapicacid Inhibits Group IIA Secretory Phospholipase A2 and Its Inflammatory Response in Mice

Human Group IIA secreted phospholipase A₂ (sPLA₂-IIA) enzyme plays a crucial role in several chronic inflammatory diseases such asasthma, atherosclerosis, gout, bronchitis, etc. Several studies showed that the antioxidants exert an anti-inflammatory function by inhibiting the sPLA₂-IIA enzyme. Hence, the present study evaluated an antioxidant molecule, sinapic acid, for sPLA₂-IIA inhibition as an anti-inflammatory function. Initially, the antioxidant efficacy of sinapic acid was evaluated, and it showed greater antioxidant potency. Further, sinapic acid inhibited 94.4 ± 4.83% of sPLA₂-IIA activity with an IC₅₀ value of 4.16 ± 0.13 µM. The mode of sPLA₂-IIA inhibition was examined by increasing the substrate concentration from 30 to 120nM and the calcium concentration from 2.5 to 15 mM, which did not change the level of inhibition. Further, sinapic acid altered the intrinsic fluorescence and distorted the far UltraViolet Circular Dichroism (UV-CD) spectra of the sPLA₂-IIA, indicating the direct enzyme-inhibitor interaction. Sinapic acid reduced the sPLA₂-IIA mediated hemolytic activity from 94 ± 2.19% to 12.35 ± 2.57% and mouse paw edema from 171.75 ± 2.2% to 114.8 ± 1.98%, demonstrating the anti-inflammatory efficiency of sinapic acid by in situ and in vivo methods, respectively. Finally, sinapic acid reduced the hemorrhagic effect of Vipera russelli venom hemorrhagic complex-I (VR-HC-I) as an anti-hemorrhagic function. Thus, the above experimental results revealed the sinapic acid potency to be an antioxidant, anti-inflammatory and anti-hemorrhagic molecule, and therefore, it appears to be a promising therapeutic agent.

On the present and future role of Lp-PLA2 in atherosclerosis-related cardiovascular risk prediction and management

Circulating concentration and activity of secretory phospholipase A₂ (sPLA₂) and lipoprotein-associated phospholipase A₂ (Lp-PLA₂) have been proven as biomarkers of increased risk of atherosclerosis-related cardiovascular disease (ASCVD). Lp-PLA₂ might be part of the atherosclerotic process and may contribute to plaque destabilisation through inflammatory activity within atherosclerotic lesions. However, all attempts to translate the inhibition of phospholipase into clinically beneficial ASCVD risk reduction, including in randomised studies, by either non-specific inhibition of sPLA₂ (by varespladib) or specific Lp-PLA₂ inhibition by darapladib, unexpectedly failed. This gives us a strong imperative to continue research aimed at a better understanding of how Lp-PLA₂ and sPLA₂ regulate vascular inflammation and atherosclerotic plaque development. From the clinical viewpoint there is a need to establish and validate the existing and emerging novel anti-inflammatory therapeutic strategies to fight against ASCVD development, by using potentially better animal models and differently designed clinical trials in humans.

Group IIA Secretory Phospholipase A2 Predicts Graft Failure and Mortality in Renal Transplant Recipients by Mediating Decreased Kidney Function

The acute phase protein group IIA secretory phospholipase A₂ (sPLA₂-IIA) has intrinsic proatherosclerotic properties. The present prospective cohort study investigated whether plasma sPLA₂-IIA associates with graft failure, cardiovascular, and all-cause mortality in renal transplant recipients (RTRs), patients with accelerated atherosclerosis formation both systemically and within the graft. In 511 RTRs from a single academic center with stable graft function >1 year, baseline plasma sPLA₂-IIA was determined by ELISA. Primary end points were death-censored graft failure and mortality (median follow-up, 7.0 years). Baseline sPLA₂-IIA was higher in RTRs than in healthy controls (median 384 ng/dL (range 86–6951) vs. 185 ng/dL (range 104–271), p < 0.001). Kaplan–Meier analysis demonstrated increased risk for graft failure (p = 0.002), as well as cardiovascular (p < 0.001) and all-cause mortality (p < 0.001), with increasing sPLA₂-IIA quartiles. Cox regression showed strong associations of sPLA₂-IIA with increased risks of graft failure (hazard ratio (HR) = 1.42 (1.11–1.83), p = 0.006), as well as cardiovascular (HR = 1.48 (1.18−1.85), p = 0.001) and all-cause mortality (HR = 1.39 (1.17−1.64), p < 0.001), dependent on parameters of kidney function. Renal function during follow-up declined faster in RTRs with higher baseline sPLA₂-IIA levels. In RTRs, sPLA₂-IIA is a significant predictive biomarker for chronic graft failure, as well as overall and cardiovascular disease mortality dependent on kidney function. This dependency is conceivably explained by sPLA₂-IIA impacting negatively on kidney function.

High density lipoprotein (HDL) particles from end-stage renal disease patients are defective in promoting reverse cholesterol transport

Atherosclerotic cardiovascular disease (CVD) represents the largest cause of mortality in end-stage renal disease (ESRD). CVD in ESRD is not explained by classical CVD risk factors such as HDL cholesterol mass levels making functional alterations of lipoproteins conceivable. HDL functions in atheroprotection by promoting reverse cholesterol transport (RCT), comprising cholesterol efflux from macrophage foam cells, uptake into hepatocytes and final excretion into the feces. ESRD-HDL (n = 15) were compared to healthy control HDL (n = 15) for their capacity to promote in vitro (i) cholesterol efflux from THP-1 macrophage foam cells and (ii) SR-BI-mediated selective uptake into ldla[SR-BI] cells as well as (iii) in vivo RCT. Compared with HDL from controls, ESRD-HDL displayed a significant reduction in mediating cholesterol efflux (p < 0.001) and SR-BI-mediated selective uptake (p < 0.01), two key steps in RCT. Consistently, also the in vivo capacity of ESRD-HDL to promote RCT when infused into wild-type mice was significantly impaired (p < 0.01). In vitro oxidation of HDL from healthy controls with hypochloric acid was able to fully mimic the impaired biological activities of ESRD-HDL. In conclusion, we demonstrate that HDL from ESRD patients is dysfunctional in key steps as well as overall RCT, likely due to oxidative modification.

Elevated Type II Secretory Phospholipase A2 Increases the Risk of Early Atherosclerosis in Patients with Newly Diagnosed Metabolic Syndrome

A critical association between type II secretory phospholipase A2 (sPLA2-IIa) and established atherosclerotic cardiovascular disease has been demonstrated. However, the contribution of sPLA2-IIa to early atherosclerosis remains unknown. This study investigated the association between early-stage atherosclerosis and sPLA2-IIa in metabolic syndrome (MetS) patients. One hundred and thirty-six MetS patients and 120 age- and gender-matched subjects without MetS were included. Serum sPLA2-IIa protein levels and activity were measured using commercial kits. Circulating endothelial activation molecules (vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), E-selectin, and P-selectin), and carotid intima-media thickness (cIMT), were measured as parameters of vascular endothelial dysfunction and early atherosclerosis. MetS patients exhibited significantly higher sPLA2-IIa protein and activity levels than the controls. Both correlated positively with fasting blood glucose and waist circumference in MetS patients. Additionally, MetS patients exhibited strikingly higher levels of endothelial activation molecules and increased cIMT than controls. These levels correlated positively with serum sPLA2-IIa protein levels and activity. Moreover, multivariate analysis showed that high sPLA2-IIa protein and activity levels were independent risk factors of early atherosclerosis in MetS patients. This study demonstrates an independent association between early-stage atherosclerosis and increased levels of sPLA2-IIa, implying that increased sPLA2-IIa may predict early-stage atherosclerosis in MetS patients.

HDL function is impaired in acute myocardial infarction independent of plasma HDL cholesterol levels

BACKGROUND

High-density lipoproteins (HDLs) protect against the development of atherosclerotic cardiovascular disease. HDL function represents an emerging concept in cardiovascular research.

OBJECTIVE

This study investigated the association between HDL functionality and acute myocardial infarction (MI) independent of HDL-cholesterol plasma levels.

METHODS

Participants (non-ST-segment elevation MI, non-STEMI, n = 41; STEMI, n = 37; non-MI patients, n = 33) from a prospective follow-up study enrolling patients with acute chest pain were matched for age and plasma HDL cholesterol. The in vitro capacity of HDL to (1) mediate cholesterol efflux from macrophage foam cells, (2) prevent low-density lipoprotein oxidation, and (3) inhibit TNF-α-induced vascular adhesion molecule-1 expression in endothelial cells was determined.

RESULTS

STEMI-HDL displayed reduced cholesterol efflux (P < .001) and anti-inflammatory functionality (P = .001), whereas the antioxidative properties were unaltered. Cholesterol efflux correlated with the anti-inflammatory HDL activity (P < .001). Not C-reactive protein levels, a marker of systemic inflammation, but specifically plasma myeloperoxidase levels were independently associated with impaired HDL function (efflux: P = .022; anti-inflammation: P < .001). Subjects in the higher risk quartile of efflux (odds ratio [OR], 5.66; 95% confidence interval [CI], 1.26-25.00; P = .024) as well as anti-inflammatory functionality of HDL (OR, 5.53; 95% CI, 1.83-16.73; P = .002) had a higher OR for MI vs those in the three lower risk quartiles combined.

CONCLUSION

Independent of plasma HDL cholesterol levels, 2 of 3 antiatherogenic HDL functionalities tested were significantly impaired in STEMI patients, namely cholesterol efflux and anti-inflammatory properties. Increased myeloperoxidase levels might represent a major contributing mechanism for decreased HDL functionality in MI patients.

The 763C>G Polymorphism of The Secretory PLA2IIa Gene Is Associated with Endometriosis in Iranian Women

Background

Endometriosis is a chronic gynecological disease resulting from complex interactions between genetic, hormonal, environmental and oxidative stress and intrinsic inflammatory components. The aim of this study was to investigate the potential association of the 763C>G polymorphism in the secretory phospholipase A2 group IIa gene (PLA2G2A) with the risk of endometriosis in Iranian women.

Materials and Methods

Ninety seven patients with endometriosis along with 107 women who were negative for endometriosis after laparoscopy and laparatomy, and served as the control group, were enrolled for this cross-sectional study. Samples were genotyped using the polymerase chain reaction-restriction fragment length polymorphism method.

Results

Multivariate analysis was used to examine the association between the risk of endometriosis and the 763C>G polymorphism of PLA2G2A. Genotype distributions of PLA2G2A were significantly different between patients and the controls (p<0.001, OR=0.22, 95% CI=0.21-0.39). Correlation analysis showed that there was a significant association between the normal homozygous genotype and susceptibility to endometriosis (p<0.001).

Conclusion

The present study suggests that the 763C>G polymorphism of PLA2G2A plays an important role as an independent factor in the risk of endometriosis in Iranian women.

Simvastatin and bezafibrate increase cholesterol efflux in men with type 2 diabetes

BACKGROUND

The importance of functional properties of high-density lipoproteins (HDL) for atheroprotection is increasingly recognized. We determined the impact of lipid-lowering therapy on 3 key HDL functionalities in Type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

A placebo-controlled, randomized cross-over study (three 8-week treatment periods with simvastatin (40 mg daily), bezafibrate (400 mg daily), alone and in combination) was carried out in 14 men with T2DM. Cholesterol efflux was determined using human THP-1 monocyte-derived macrophages, HDL antioxidative capacity was measured as inhibition of low-density lipoprotein oxidation in vitro, and HDL anti-inflammatory capacity was assessed as suppression of thrombin-induced monocyte chemotactic protein 1 expression in human umbilical vein endothelial cells. Pre-β-HDL was assayed using crossed immunoelectrophoresis.

RESULTS

While cholesterol efflux increased in response to simvastatin, bezafibrate and combination treatment (+12 to +23%; anova, P = 0.001), HDL antioxidative capacity (P = 0.23) and HDL anti-inflammatory capacity (P = 0.15) did not change significantly. Averaged changes in cellular cholesterol efflux during active treatment were correlated positively with changes in HDL cholesterol, apoA-I and pre-β-HDL (P < 0.05 to P < 0.001). There were no inter-relationships between changes in the three HDL functionalities during treatment (P > 0.10). Changes in HDL antioxidative capacity and anti-inflammatory capacity were also unrelated to changes in HDL cholesterol and apoA-I, while changes in HDL antioxidative capacity were related inversely to pre-β-HDL (P < 0.05).

CONCLUSION

Simvastatin and bezafibrate increase cholesterol efflux, parallel to HDL cholesterol and apoA-I responses. The antioxidative and anti-inflammatory properties of HDL are not to an important extent affected by these therapeutic interventions.

Secretory phospholipase A(2)-IIA and cardiovascular disease: a mendelian randomization study

OBJECTIVES

This study sought to investigate the role of secretory phospholipase A2 (sPLA2)-IIA in cardiovascular disease.

BACKGROUND

Higher circulating levels of sPLA2-IIA mass or sPLA2 enzyme activity have been associated with increased risk of cardiovascular events. However, it is not clear if this association is causal. A recent phase III clinical trial of an sPLA2 inhibitor (varespladib) was stopped prematurely for lack of efficacy.

METHODS

We conducted a Mendelian randomization meta-analysis of 19 general population studies (8,021 incident, 7,513 prevalent major vascular events [MVE] in 74,683 individuals) and 10 acute coronary syndrome (ACS) cohorts (2,520 recurrent MVE in 18,355 individuals) using rs11573156, a variant in PLA2G2A encoding the sPLA2-IIA isoenzyme, as an instrumental variable.

RESULTS

PLA2G2A rs11573156 C allele associated with lower circulating sPLA2-IIA mass (38% to 44%) and sPLA2 enzyme activity (3% to 23%) per C allele. The odds ratio (OR) for MVE per rs11573156 C allele was 1.02 (95% confidence interval [CI]: 0.98 to 1.06) in general populations and 0.96 (95% CI: 0.90 to 1.03) in ACS cohorts. In the general population studies, the OR derived from the genetic instrumental variable analysis for MVE for a 1-log unit lower sPLA2-IIA mass was 1.04 (95% CI: 0.96 to 1.13), and differed from the non-genetic observational estimate (OR: 0.69; 95% CI: 0.61 to 0.79). In the ACS cohorts, both the genetic instrumental variable and observational ORs showed a null association with MVE. Instrumental variable analysis failed to show associations between sPLA2 enzyme activity and MVE.

CONCLUSIONS

Reducing sPLA2-IIA mass is unlikely to be a useful therapeutic goal for preventing cardiovascular events.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Expression of type IIA secretory phospholipase A2 inhibits cholesteryl ester transfer protein activity in transgenic mice

OBJECTIVE

High circulating levels of group IIA secretory phospholipase A2 (sPLA2-IIA) activity and mass are independent cardiovascular risk factors. Therefore, inhibition of sPLA2-IIA may be a target for the treatment of atherosclerotic cardiovascular disease. The present study evaluated the effects of sPLA2-IIA inhibition with varespladib acid in a novel mouse model, human apolipoprotein B (apoB)/human cholesteryl ester transfer protein (CETP)/human sPLA2-IIA triple transgenic mice (TTT) fed a Western-type diet.

APPROACH AND RESULTS

sPLA2-IIA expression increased atherosclerotic lesion formation in TTT compared with human apoB/human CETP double transgenic mice (P<0.01). Varespladib acid effectively inhibited plasma sPLA2-IIA activity. Surprisingly, however, administration of varespladib acid to TTT had no impact on atherosclerosis, which could be attributed to a proatherogenic plasma lipoprotein profile that appears in response to sPLA2-IIA inhibition because of increased plasma CETP activity. In the TTT model, sPLA2-IIA decreased CETP activity by reducing the acceptor properties of sPLA2-IIA-modified very low-density lipoproteins specifically because of a significantly lower apoE content. Increasing very low-density lipoprotein-apoE content by means of adenovirus-mediated gene transfer in sPLA2-IIA transgenic mice restored the acceptor properties for CETP.

CONCLUSIONS

These data show that in a humanized triple transgenic mouse model with hypercholesterolemia, sPLA2-IIA inhibition increases CETP activity via increasing the very low-density lipoprotein-apoE content, resulting in a proatherogenic lipoprotein profile.

Low normal free T4 confers decreased high-density lipoprotein antioxidative functionality in the context of hyperglycaemia

OBJECTIVES

Low normal thyroid function may promote the development of atherosclerotic cardiovascular disease by thus far poorly defined mechanisms. We tested the impact of thyroid function on HDL antioxidative capacity, a metric of its antiatherogenic functionality, in euthyroid subjects with varying degrees of glucose tolerance.

DESIGN AND SUBJECTS

Seventy subjects with Type 2 diabetes mellitus (T2DM), 37 subjects with impaired fasting glucose (IFG) and 31 subjects with normal fasting glucose (NFG) (revised NCEP-ATPIII criteria) participated in a cross-sectional study.

MEASUREMENTS

HDL antioxidative capacity (standardized for HDL cholesterol) was measured as the percentage inhibition of low-density lipoprotein oxidation in vitro.

RESULTS

TSH, free T4 and HDL antioxidative capacity were not different among NFG, IFG and T2DM subjects (P > 0·25 for each). HDL antioxidative capacity was correlated positively with free T4 (r = 0·320, P = 0·007), and negatively with plasma glucose (r = -0·394, P < 0·001) in T2DM only. Taking account of age and sex, the relationship of HDL antioxidative functionality with free T4 was modified by glucose tolerance status (P = 0·040 and P = 0·008 for interactions of IFG and T2DM with free T4 respectively). Prevailing plasma glucose also interacted positively with free T4 on HDL antioxidative capacity (P = 0·054).

CONCLUSIONS

In the context of chronic hyperglycaemia, low free T4 within the euthyroid range confers diminished HDL antioxidative capacity, a pathophysiologically relevant metric of HDL functionality.

rHDL administration increases reverse cholesterol transport in mice, but is not additive on top of ezetimibe or cholestyramine treatment

OBJECTIVE

Promoting reverse cholesterol transport (RCT) is a major atheroprotective property of HDL. The present study explored the effect of stimulating the first step of RCT (cholesterol efflux from macrophages) alone or in combination with stimulating the last step of RCT (fecal sterol excretion).

METHODS AND RESULTS

Reconstituted HDL (rHDL) was injected into wild-type mice either with or without administration of the cholesterol absorption inhibitor ezetimibe or the bile acid sequestrant cholestyramine. Single dose administration of rHDL (100 mg apoA-I/kg) resulted in an early (4 h) increase in plasma free cholesterol levels (p < 0.001), without affecting hepatic cholesterol levels or fecal mass sterol excretion. rHDL injection also increased [(3)H]cholesterol appearance in plasma at an early time-point (4 h) after intraperitoneal administration of [(3)H]cholesterol-labeled mouse macrophage foam cells and fecal radioactivity excretion indicating completed RCT was increased by 26% (p < 0.05). Ezetimibe treatment inhibited intestinal cholesterol absorption by 74% (p < 0.01), but also the bile acid sequestrant cholestyramine decreased cholesterol absorption significantly (24%, p < 0.01). Consequently, ezetimibe increased RCT 2.1-fold (p < 0.001) primarily within fecal neutral sterols, while cholestyramine increased RCT by 3.6-fold (p < 0.001), primarily within bile acids (p < 0.001), but also within neutral sterols (p < 0.001). However, no additive effects of both intestinal sterol uptake inhibitors were observed on top of rHDL administration.

CONCLUSION

These data demonstrate that increasing the first step of RCT by rHDL administration results in transient cholesterol mobilization from macrophages to plasma. This effect is not further enhanced by stimulating the last step of RCT, fecal sterol excretion.

The inverse relation of HDL anti-oxidative functionality with serum amyloid a is lost in metabolic syndrome subjects

OBJECTIVE

Anti-oxidative properties of high density lipoproteins (HDL) are relevant for atheroprotection. HDL carry serum amyloid A (SAA), which may impair HDL functionality. We questioned whether HDL anti-oxidative capacity is determined by SAA.

DESIGN AND METHODS

Relationships of HDL anti-oxidative capacity (% inhibition of low density lipoprotein oxidation in vitro) with SAA were determined in 54 non-diabetic subjects without metabolic syndrome (MetS) and 68 subjects with MetS (including 51 subjects with Type 2 diabetes mellitus).

RESULTS

SAA levels were higher in MetS subjects, coinciding higher high sensitive C-reactive protein (hs-CRP) and lower HDL cholesterol and apolipoprotein (apo) A-I levels (P<0.001 for all). HDL anti-oxidative capacity was not different between subjects with and without MetS (P=0.76), but the HDL anti-oxidation index (HDL anti-oxidative capacity multiplied by individual HDL cholesterol concentrations), as a measure of global anti-oxidative functionality of HDL, was lower in Mets subjects (P<0.001). HDL anti-oxidative capacity was correlated inversely with SAA levels in subjects without MetS (r=-0.286, P=0.036). Notably, this relationship was independent of HDL cholesterol or apoA-I (P<0.05 for both). In contrast, no relation of HDL anti-oxidative capacity with SAA was observed in MetS subjects (r=0.032, P=0.80). The relationship of SAA with HDL anti-oxidative capacity was different in subjects with MetS compared to subjects without MetS (P=0.039 for the interaction between the presence of MetS and SAA on HDL anti-oxidative capacity) taking age and diabetes status into account.

CONCLUSION

Higher SAA levels may impair HDL anti-oxidative functionality. The relationship of this physiologically relevant HDL functionality measure with circulating SAA levels is apparently disturbed in metabolic syndrome.

Preparation and activity analysis of recombinant human high-density lipoprotein

Population studies have consistently shown a highly inverse correlation between plasma concentration of high-density lipoprotein and the risk of atherosclerotic cardiovascular disease in humans. High-density lipoprotein (HDL) as a therapeutic target is an intense area of ongoing investigation. Aiming to solve the shortcomings of native HDL application, we prepared recombinant human HDL (rhHDL) that contains a similar composition and has similar functions with native HDL. Six kinds of recombinant human apolipoproteins (rhapo)-rhapoA-I, rhapoA-II, rhapoA-IV, rhapoC-I, rhapoC-II, and rhapoE-were expressed in Pichia pastoris and purified with chromatography. By the facilitation of cholate, six kinds of rhapo penetrated among the phosphatidylcholine acyl chains. After purification by density-gradient centrifugation, rhHDL was acquired. Based on morphological observation, we confirmed that the micellar complexes of rhapo with phosphatidylcholine and cholesterol were prepared. We carried on comparative studies in vitro and in vivo between native HDL and rhHDL. Cellular cholesterol efflux assays showed that rhHDL could promote the efflux of excess cholesterol from macrophages. Furthermore, rhHDL has similar effects with native HDL on the blood lipid metabolism in hyperlipidemic mice. In conclusion, rhHDL has similar effects on antiatherosclerosis with native HDL through reverse cholesterol transport, antioxidative, and antithrombotic properties. It could be used as a therapeutic HDL-replacement agent.

Phospholipase A(2) enzymes in metabolic and cardiovascular diseases

PURPOSE OF REVIEW

The phospholipase A2 (PLA2) family of proteins includes lipolytic enzymes that liberate the sn-2 fatty acyl chains from phospholipids to yield nonesterified fatty acids and lysophospholipids. The purpose of this review is to discuss recent findings showing distinct roles of several of these PLA2 enzymes in inflammatory metabolic diseases such as diabetes and atherosclerosis.

RECENT FINDINGS

The group 1B PLA2 digestion of phospholipids in the intestinal lumen facilitates postprandial lysophospholipid absorption, which suppresses hepatic fatty acid oxidation leading to increased VLDL synthesis, decreased glucose tolerance, and promotion of tissue lipid deposition to accentuate diet-induced hyperlipidemia, diabetes, and obesity. Other secretory PLA2s promote inflammatory metabolic diseases by generating bioactive lipid metabolites to induce inflammatory cytokine production, whereas the major intracellular PLA2s, cPLA2α, and iPLA2, generate arachidonic acid and lysophosphatic acid in response to extracellular stimuli to activate leukocyte chemotactic response.

SUMMARY

Each member of the PLA2 family of enzymes serves a distinct role in generating active lipid metabolites that promote inflammatory metabolic diseases including atherosclerosis, hyperlipidemia, obesity, and diabetes. The development of specific drugs that target one or more of these PLA2 enzymes may be novel strategies for treatment of these chronic inflammatory metabolic disorders.

Increased LCAT activity and hyperglycaemia decrease the antioxidative functionality of HDL

BACKGROUND

Type 2 diabetes mellitus increases the risk of atherosclerotic cardiovascular disease. Antioxidative properties of high density lipoprotein (HDL) are important for atheroprotection. This study investigated whether the antioxidative functionality of HDL is altered in type 2 diabetes mellitus and aimed to identify potential determinants of this parameter.

MATERIALS AND METHODS

In a cross-sectional study, we investigated 74 patients with type 2 diabetes and 75 control subjects. Antioxidative properties of HDL were measured and expressed as either (i) HDL antioxidative capacity or (ii) HDL antioxidation index after multiplying HDL antioxidative capacity results with individual plasma HDL cholesterol concentrations. Lecithin:cholesterol acyltransferase (LCAT) and paraoxonase-1 (PON-1) activities were determined.

RESULTS

HDL antioxidative capacity was similar in patients with diabetes and controls, while the HDL antioxidation index was decreased in patients with diabetes (P = 0.005) owing to lower plasma HDL cholesterol (P < 0.001). LCAT activity was higher and PON-1 activity lower in type 2 diabetes mellitus (each P < 0.001). In the combined subjects, HDL antioxidative capacity was inversely related to LCAT activity (P < 0.01). The HDL antioxidation index correlated negatively with blood glucose (P < 0.001), HbA1c and LCAT activity (each P < 0.01), and positively with PON-1 activity (P < 0.01). Multiple linear regression analysis demonstrated that high LCAT activity was associated with both decreased HDL antioxidation capacity (P < 0.05) and index (P < 0.001) independent of diabetes status, glycaemic control and PON-1.

CONCLUSIONS

Overall, the antioxidative functionality of HDL is impaired in type 2 diabetes mellitus mostly because of lower HDL cholesterol. Hyperglycaemia, increased LCAT activity and lower PON-1 activity likely contribute to impaired antioxidative functionality of HDL.

Pancreatic β-cell function relates positively to HDL functionality in well-controlled type 2 diabetes mellitus

BACKGROUND

High density lipoproteins (HDLs) have been implicated in glucose homeostasis. Among subjects with normal fasting glucose (NFG), impaired fasting glucose (IFG) and Type 2 diabetes mellitus (T2DM) we tested whether pancreatic β-cell function relates to HDL functionality, as determined by HDL anti-oxidative capacity and cellular cholesterol efflux to plasma.

SUBJECTS AND METHODS

HDL anti-oxidative capacity (inhibition of LDL oxidation in vitro), cellular cholesterol efflux (the ability of plasma to stimulate cholesterol efflux out of cultured fibroblasts obtained from a single human donor), glucose and insulin were determined in fasting plasma samples from 37 subjects with NFG, 36 with IFG and 22 with T2DM (no glucose lowering drug or insulin treatment; HbA1c 6.0±1.0%). Homeostasis model assessment was used to estimate pancreatic β-cell function (HOMA-β) and insulin resistance (HOMAir).

RESULTS

HOMA-β was lowest, whereas HOMAir was highest in T2DM (P<0.01 and P<0.001 vs. NFG). HDL anti-oxidative capacity and cellular cholesterol efflux did not differ significantly according to glucose tolerance category. In univariate analysis and after controlling for HOMAir both HDL anti-oxidative capacity (P<0.05) and cellular cholesterol efflux (P<0.01) were positively correlated with HOMA-β in T2DM, but not in NFG and IFG. In age-, sex- and HOMAir-adjusted analyses, T2DM status interacted positively with HDL anti-oxidative capacity (P=0.001) and cellular cholesterol efflux (P=0.042) on HOMA-β. HbA1c interacted similarly with HDL functionality measures on HOMA-β.

CONCLUSIONS

Pancreatic β-cell function relates to pathophysiologically relevant measures of HDL function in T2DM, but not in NFG and IFG. Better HDL functionality may contribute to maintenance of β-cell function in subjects with well-controlled T2DM.

ApoE promotes hepatic selective uptake but not RCT due to increased ABCA1-mediated cholesterol efflux to plasma

ApoE plays an important role in lipoprotein metabolism. This study investigated the effects of adenovirus-mediated human apoE overexpression (AdhApoE3) on sterol metabolism and in vivo reverse cholesterol transport (RCT). In wild-type mice, AdhApoE3 resulted in decreased HDL cholesterol levels and a shift toward larger HDL in plasma, whereas hepatic cholesterol content increased (P < 0.05). These effects were dependent on scavenger receptor class B type I (SR-BI) as confirmed using SR-BI-deficient mice. Kinetic studies demonstrated increased plasma HDL cholesteryl ester catabolic rates (P < 0.05) and higher hepatic selective uptake of HDL cholesteryl esters in AdhApoE3-injected wild-type mice (P < 0.01). However, biliary and fecal sterol output as well as in vivo macrophage-to-feces RCT studied with (3)H-cholesterol-loaded mouse macrophage foam cells remained unchanged upon human apoE overexpression. Similar results were obtained using hApoE3 overexpression in human CETP transgenic mice. However, blocking ABCA1-mediated cholesterol efflux from hepatocytes in AdhApoE3-injected mice using probucol increased biliary cholesterol secretion (P < 0.05), fecal neutral sterol excretion (P < 0.05), and in vivo RCT (P < 0.01), specifically within neutral sterols. These combined data demonstrate that systemic apoE overexpression increases i) SR-BI-mediated selective uptake into the liver and ii) ABCA1-mediated efflux of RCT-relevant cholesterol from hepatocytes back to the plasma compartment, thereby resulting in unchanged fecal mass sterol excretion and overall in vivo RCT.

Type I diabetes mellitus decreases in vivo macrophage-to-feces reverse cholesterol transport despite increased biliary sterol secretion in mice

Type I diabetes mellitus (T1DM) increases atherosclerotic cardiovascular disease; however, the underlying pathophysiology is still incompletely understood. We investigated whether experimental T1DM impacts HDL-mediated reverse cholesterol transport (RCT). C57BL/6J mice with alloxan-induced T1DM had higher plasma cholesterol levels (P < 0.05), particularly within HDL, and increased hepatic cholesterol content (P < 0.001). T1DM resulted in increased bile flow (2.1-fold; P < 0.05) and biliary secretion of bile acids (BA, 10.5-fold; P < 0.001), phospholipids (4.5-fold; P < 0.001), and cholesterol (5.5-fold; P < 0.05). Hepatic cholesterol synthesis was unaltered, whereas BA synthesis was increased in T1DM (P < 0.001). Mass fecal BA output was significantly higher in T1DM mice (1.5-fold; P < 0.05), fecal neutral sterol excretion did not change due to increased intestinal cholesterol absorption (2.1-fold; P < 0.05). Overall in vivo macrophage-to-feces RCT, using [(3)H]cholesterol-loaded primary mouse macrophage foam cells, was 20% lower in T1DM (P < 0.05), mainly due to reduced tracer excretion within BA (P < 0.05). In vitro experiments revealed unchanged cholesterol efflux toward T1DM HDL, whereas scavenger receptor class BI-mediated selective uptake from T1DM HDL was lower in vitro and in vivo (HDL kinetic experiments) (P < 0.05), conceivably due to increased glycation of HDL-associated proteins (+65%, P < 0.01). In summary, despite higher mass biliary sterol secretion T1DM impairs macrophage-to-feces RCT, mainly by decreasing hepatic selective uptake, a mechanism conceivably contributing to increased cardiovascular disease in T1DM.

Type II secretory phospholipase A2 and prognosis in patients with stable coronary heart disease: mendelian randomization study

Background

Serum type II secretory phospholipase A₂ (sPLA₂-IIa) has been found to be predictive of adverse outcomes in patients with stable coronary heart disease. Compounds targeting sPLA₂-IIa are already under development. This study investigated if an association of sPLA₂-IIa with secondary cardiovascular disease (CVD) events may be of causal nature or mainly a matter of confounding by correlated cardiovascular risk markers.

Methodology/Principal Findings

Eight-year follow-up data of a prospective cohort study (KAROLA) of patients who underwent in-patient rehabilitation after an acute cardiovascular event were analysed. Associations of polymorphisms (SNP) in the sPLA₂-IIa-coding gene PLA2G2A with serum sPLA₂-IIa and secondary fatal or non-fatal CVD events were examined by multiple regression. Hazard ratios (HR) were compared with those expected if the association between sPLA₂-IIa and CVD were causal. The strongest determinants of sPLA₂-IIa (rs4744 and rs10732279) were associated with an increase of serum concentrations by 81% and 73% per variant allele. HRs (95% confidence intervals) estimating the associations of the SNPs with secondary CVD events were increased, but not statistically significant (1.16 [0.89–1.51] and 1.18 [0.91–1.52] per variant allele, respectively). However, these estimates were very similar to those expected when assuming causality (1.18 and 1.17), based on an association of natural log-transformed sPLA₂-IIa concentration with secondary events with HR = 1.33 per unit.

Conclusion

The present findings regarding genetic polymorphisms, determination of serum sPLA₂-IIa, and prognosis in CVD patients are consistent with a genuine causal relationship and thus might point to a valid drug target for prevention of secondary CVD events.

Skin autofluorescence is inversely related to HDL anti-oxidative capacity in type 2 diabetes mellitus

OBJECTIVE

High density lipoprotein (HDL) particles protect apolipoprotein B-containing lipoproteins from oxidative modification. An impaired anti-oxidative functionality of HDL in type 2 diabetes mellitus (T2DM) may contribute to enhanced formation of oxidative stress products, such as Advanced Glycation Endproducts (AGEs). We tested whether in T2DM the HDL anti-oxidative capacity is related to the accumulation of AGEs in the skin.

METHODS

Skin autofluorescence (AF), a non-invasive read-out for AGEs, and HDL anti-oxidative capacity, i.e. the ability of HDL to protect against LDL oxidation in vitro, were assessed in 67 non-smoking T2DM patients without complications (median age: 60 (53-65), 60% males, 6.5 (5.2-8.5) years of diabetes duration).

RESULTS

In univariate analysis, skin AF correlated inversely with HDL anti-oxidative capacity (r=-0.305, P<0.02), but not with HDL cholesterol or apolipoprotein A-I. HDL anti-oxidative capacity correlated inversely with glucose, HbA(1c), triglycerides, and insulin resistance (homeostasis model assessment) (P<0.05 to P ≤ 0.001). Multiple linear regression showed that skin AF remained inversely related to HDL anti-oxidative capacity (partial r=-0.314, P=0.015) taking account of age, plasma glucose, non-HDL cholesterol, triglycerides, HOMA(ir), and CRP.

CONCLUSION

These findings suggest that skin AF is inversely related to the HDL anti-oxidative capacity rather than to the HDL cholesterol concentration in T2DM. Impaired anti-oxidative functionality of HDL could contribute to tissue accumulation of AGEs.

Overexpression of apolipoprotein O does not impact on plasma HDL levels or functionality in human apolipoprotein A-I transgenic mice

Apolipoprotein (apo) O is a newly discovered apolipoprotein preferentially contained within HDL; however, currently, no data are available on the (patho)physiological effects of apoO. Therefore, the present study assessed the impact of apoO overexpression on (i) plasma lipids and lipoproteins as well as on (ii) HDL functionality. Human apoO was overexpressed by means of recombinant adenovirus (AdhapoO) in human apoA-I transgenic mice, a humanized mouse model of HDL metabolism. AdhapoO substantially increased apoO in plasma and within HDL. However, plasma triglycerides, phospholipids, total cholesterol and HDL cholesterol did not change. HDL size distribution, lipid composition and the apoA-I and the apoO distribution over the different HDL fractions separated by FPLC remained unaltered. Furthermore, enrichment of HDL with apoO did not impact on HDL functionality assessed in four independent ways, namely (i) stimulation of cholesterol efflux from macrophage foam cells, (ii) protection against LDL oxidation, (iii) anti-inflammatory activity on endothelial cells, and (iv) induction of vasodilation in isolated aortic rings ex vivo as a measure of stimulating vascular NO production. These results demonstrate that although overexpression of apoO results in a substantial enrichment of HDL particles with this novel apolipoprotein, apoO does not impact the plasma lipoprotein profile or HDL functionality.

A bifunctional role for group IIA secreted phospholipase A2 in human rheumatoid fibroblast-like synoviocyte arachidonic acid metabolism

Human group IIA-secreted phospholipase A(2) (sPLA(2)-IIA) is an important regulator of cytokine-mediated inflammatory responses in both in vitro and in vivo models of rheumatoid arthritis (RA). However, treatment of RA patients with sPLA(2)-IIA inhibitors shows only transient benefit. Using an activity-impaired sPLA(2)-IIA mutant protein (H48Q), we show that up-regulation of TNF-dependent PGE(2) production and cyclooxygenase-2 (COX-2) induction by exogenous sPLA(2)-IIA in RA fibroblast-like synoviocytes (FLSs) is independent of its enzyme function. Selective cytosolic phospholipase A(2)-α (cPLA(2)-α) inhibitors abrogate TNF/sPLA(2)-IIA-mediated PGE(2) production without affecting COX-2 levels, indicating arachidonic acid (AA) flux to COX-2 occurs exclusively through TNF-mediated activation of cPLA(2)-α. Nonetheless, exogenous sPLA(2)-IIA, but not H48Q, stimulates both AA mobilization from FLSs and microparticle-derived AA release that is not used for COX-2-dependent PGE(2) production. sPLA(2)-IIA-mediated AA production is inhibited by pharmacological blockade of sPLA(2)-IIA but not cPLA(2)-α. Exogenous H48Q alone, like sPLA(2)-IIA, increases COX-2 protein levels without inducing PGE(2) production. Unlike TNF, sPLA(2)-IIA alone does not rapidly mobilize NF-κB or activate phosphorylation of p38 MAPK, two key regulators of COX-2 protein expression, but does activate the ERK1/2 pathway. Thus, sPLA(2)-IIA regulates AA flux through the cPLA(2)-α/COX-2 pathway in RA FLSs by up-regulating steady state levels of these biosynthetic enzymes through an indirect mechanism, rather than direct provision of substrate to the pathway. Inhibitors that have been optimized for their potency in enzyme activity inhibition alone may not adequately block the activity-independent function of sPLA(2)-IIA.

Effects of varespladib methyl on biomarkers and major cardiovascular events in acute coronary syndrome patients

OBJECTIVES

The purpose of this study was to investigate the effects of varespladib on cardiovascular biomarkers in acute coronary syndrome patients.

BACKGROUND

Secretory phospholipase A(2) (sPLA(2)) represents a family of proatherogenic enzymes that hydrolyze lipoprotein phospholipids, increasing their affinity for intimal proteoglycans; contribute to cholesterol loading of macrophages by nonscavenger receptor mediated pathways; and activate inflammatory pathways. In prospective studies, high sPLA(2)-IIA levels predicted major adverse cardiovascular events in acute coronary syndrome (ACS) and stable coronary heart disease patients.

METHODS

This randomized, double-blind, prospective controlled clinical trial (phase 2B) was designed to investigate the effects of sPLA(2) inhibition with varespladib 500 mg daily versus placebo as adjunctive therapy to atorvastatin 80 mg daily on biomarkers (low-density lipoprotein cholesterol [LDL-C], high-sensitivity C-reactive protein [hsCRP], and sPLA(2)-IIA levels), major adverse cardiovascular events (unstable angina, myocardial infarction, death), and safety. In all, 625 ACS subjects were randomized within 96 h of the index event and treated for a minimum of 6 months.

RESULTS

After 8 weeks (primary efficacy end point), varespladib/atorvastatin reduced mean LDL-C levels from baseline by 49.6% compared with 43.4% with placebo/atorvastatin (p = 0.002). Respective 8-week median reductions in sPLA(2)-IIA levels were 82.4% and 15.6% (p < 0.0001), and hsCRP levels were lowered by 75.0% and 71.0% (p = 0.097). At 24 weeks, respective reductions with varespladib and placebo were as follows: LDL-C 43.5% versus 37.6% (p < 0.05), hsCRP 79.8% versus 77.0% (p = 0.02), and sPLA(2)-IIA 78.5% versus 6.4% (p < 0.0001). Major adverse cardiovascular events were not different from placebo 6 months post-randomization (7.3% varespladib vs. 7.7% placebo). No treatment differences in elevated liver function studies on >1 occasion were observed.

CONCLUSIONS

Varespladib therapy effectively reduced LDL-C and inflammatory biomarkers in ACS patients treated with conventional therapy including atorvastatin 80 mg daily. There were no treatment differences in clinical cardiovascular events. (FRANCIS [Fewer Recurrent Acute Coronary Events With Near-Term Cardiovascular Inflammation Suppression]-ACS Trial: A Study of the Safety and Efficacy of A 002 in Subjects With Acute Coronary Syndromes; NCT00743925).

Voluntary exercise increases cholesterol efflux but not macrophage reverse cholesterol transport in vivo in mice

Physical exercise beneficially impacts on the plasma lipoprotein profile as well as on the incidence of cardiovascular events and is therefore recommended in primary and secondary prevention strategies against atherosclerotic cardiovascular disease. However, the underlying mechanisms of the protective effect of exercise remain largely unknown. Therefore, the present study tested the hypothesis that voluntary exercise in mice impacts on cholesterol efflux and in vivo reverse cholesterol transport (RCT). After two weeks of voluntary wheel running (average 10.1 ± 1.4 km/day) plasma triglycerides were lower (p < 0.05), while otherwise lipid and lipoprotein levels did not change. Macrophage cholesterol efflux towards plasma was significantly increased in running (n = 8) compared to sedentary (n = 6) mice (14.93 ± 1.40 vs. 12.33 ± 2.60%, p < 0.05). In addition, fecal excretion of bile acids (3.86 ± 0.50 vs. 2.90 ± 0.51 nmol/d, p = 0.001) and neutral sterols (2.75 ± 0.43 vs. 1.94 ± 0.22 nmol/d, p < 0.01) was significantly higher in running mice. However, RCT from macrophages to feces remained essentially unchanged in running mice compared with sedentary controls (bile acids: 3.2 ± 1.0 vs. 2.9 ± 1.1 % of injected dose, n.s.; neutral sterols: 1.4 ± 0.7 vs. 1.1 ± 0.5 % injected dose, n.s.). Judged by the plasma lathosterol to cholesterol ratio, endogenous cholesterol synthesis was increased in exercising mice (0.15 ± 0.03 vs. 0.11 ± 0.02, p < 0.05), while the hepatic mRNA expression of key transporters for biliary cholesterol (Abcg5/g8, Sr-bI) as well as bile acid (Abcb11) and phospholipd (Abcb4) excretion did not change. These data indicate that the beneficial effects of exercise on cardiovascular health include increased cholesterol efflux, but do not extend to other components of RCT. The increased fecal cholesterol excretion observed in running mice is likely explained by higher endogenous cholesterol synthesis, however, it does not reflect increased RCT in the face of unchanged expression of key transporters for biliary sterol secretion.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

Myeloperoxidase and serum amyloid A contribute to impaired in vivo reverse cholesterol transport during the acute phase response but not group IIA secretory phospholipase A(2)

Atherosclerosis is linked to inflammation. HDL protects against atherosclerotic cardiovascular disease, mainly by mediating cholesterol efflux and reverse cholesterol transport (RCT). The present study aimed to test the impact of acute inflammation as well as selected acute phase proteins on RCT with a macrophage-to-feces in vivo RCT assay using intraperitoneal administration of [(3)H]cholesterol-labeled macrophage foam cells. In patients with acute sepsis, cholesterol efflux toward plasma and HDL were significantly decreased (P < 0.001). In mice, acute inflammation (75 microg/mouse lipopolysaccharide) decreased [(3)H]cholesterol appearance in plasma (P < 0.05) and tracer excretion into feces both within bile acids (-84%) and neutral sterols (-79%, each P < 0.001). In the absence of systemic inflammation, overexpression of serum amyloid A (SAA, adenovirus) reduced overall RCT (P < 0.05), whereas secretory phospholipase A(2) (sPLA(2), transgenic mice) had no effect. Myeloperoxidase injection reduced tracer appearance in plasma (P < 0.05) as well as RCT (-36%, P < 0.05). Hepatic expression of bile acid synthesis genes (P < 0.01) and transporters mediating biliary sterol excretion (P < 0.01) was decreased by inflammation. In conclusion, our data demonstrate that acute inflammation impairs cholesterol efflux in patients and macrophage-to-feces RCT in vivo in mice. Myeloperoxidase and SAA contribute to a certain extent to reduced RCT during inflammation but not sPLA(2). However, reduced bile acid formation and decreased biliary sterol excretion might represent major contributing factors to decreased RCT in inflammation.

Secretory phospholipase A2, group IIA is a novel serum amyloid A target gene: activation of smooth muscle cell expression by an interleukin-1 receptor-independent mechanism

Atherosclerosis is a multifactorial vascular disease characterized by formation of inflammatory lesions. Elevated circulating acute phase proteins indicate disease risk. Serum amyloid A (SAA) is one such marker but its function remains unclear. To determine the role of SAA on aortic smooth muscle cell gene expression, a preliminary screen of a number of genes was performed and a strong up-regulation of expression of secretory phospholipase A(2), group IIA (sPLA(2)) was identified. The SAA-induced increase in sPLA(2) was validated by real time PCR, Western blot analysis, and enzyme activity assays. Demonstrating that SAA increased expression of sPLA(2) heteronuclear RNA and that inhibiting transcription eliminated the effect of SAA on sPLA(2) mRNA suggested that the increase was transcriptional. Transient transfections and electrophoretic mobility shift assays identified CAAT enhancer-binding protein (C/EBP) and nuclear factor kappaB (NFkappaB) as key regulatory sites mediating the induction of sPLA(2). Moreover, SAA activated the inhibitor of NF-kappaB kinase (IKK) in cultured smooth muscle cells. Previous reports showed that interleukin (IL)-1beta up-regulates Pla2g2a gene transcription via C/EBPbeta and NFkappaB. Interestingly, SAA activated smooth muscle cell IL-1beta mRNA expression, however, blocking IL-1 receptors had no effect on SAA-mediated activation of sPLA(2) expression. Thus, the observed changes in sPLA(2) expression were not secondary to SAA-induced IL-1 receptor activation. The association of SAA with high density lipoprotein abrogated the SAA-induced increase in sPLA(2) expression. These data suggest that during atherogenesis, SAA can amplify the involvement of smooth muscle cells in vascular inflammation and that this can lead to deposition of sPLA(2) and subsequent local changes in lipid homeostasis.

Increased type IIA secretory phospholipase A(2) expression contributes to oxidative stress in end-stage renal disease

End-stage renal disease (ESRD) patients exhibit increased in vivo oxidative stress conceivably contributing to cardiovascular mortality. The type IIA secretory phospholipase A(2) (sPLA(2)) has proatherogenic activity. We explored the hypothesis that sPLA(2) contributes to oxidative stress generation and endothelial dysfunction in ESRD patients and transgenic (tg) mice. Patients with ESRD had increased in vivo oxidative stress as assessed by plasma isoprostane levels (p < 0.001). Active sPLA(2) in plasma was substantially increased compared with healthy controls (1,156 +/- 65 versus 184 +/- 5 ng/dL, p < 0.001) and correlated with plasma isoprostanes (r = 0.61, p < 0.001). Correspondingly, human sPLA(2) tg mice display increased generation of reactive oxygen species within aortic vascular smooth muscle cells, leading to severe endothelial dysfunction (maximal vasodilation in response to 10 micromol/L acetylcholine, sPLA(2) 36 +/- 8%, controls 80 +/- 2% of phenylephrine-induced vasoconstriction). Increased vascular oxidative stress in sPLA(2) tg mice is dependent on the induction of vascular cyclooxygenase (COX)2 expression. Conversely, ESRD patients show increased formation of COX2-derived prostaglandins (p < 0.05) correlated with plasma sPLA(2) (r = 0.71, p < 0.05). Our data indicate that increased expression of sPLA(2) might represent a novel causative risk factor contributing to the increased cardiovascular disease morbidity and mortality in ESRD.

Neuroprotective effects of a nanocrystal formulation of sPLA(2) inhibitor PX-18 in cerebral ischemia/reperfusion in gerbils

The group IIA secretory phospholipase A2 (sPLA(2)-IIA) has been studied extensively because of its involvement in inflammatory processes. Up-regulation of this enzyme has been shown in a number of neurodegenerative diseases including cerebral ischemia and Alzheimer's disease. PX-18 is a selective sPLA(2) inhibitor effective in reducing tissue damage resulting from myocardial infarction. However, its use as a neuroprotective agent has been hampered due to its low solubility. In this study, we test the possible neuroprotective effects of PX-18 formulated as a suspension of nanocrystals. Transient global cerebral ischemia was induced in gerbils by occlusion of both common carotid arteries for 5 min. Four days after ischemia/reperfusion (I/R), extensive delayed neuronal death, DNA damage, and increases in reactive astrocytes and microglial cells were observed in the hippocampal CA1 region. PX-18 nanocrystals (30 and 60 mg/kg body wt) and vehicle controls were injected i.p. immediately after I/R. PX-18 nanocrystal injection significantly reduced delayed neuronal death, DNA damage, as well as glial cell activation. These findings demonstrated the effective neuroprotection of PX-18 in the form of nanocrystal against I/R-induced neuronal damage. The results also suggest that nanocrystals hold promise as an effective strategy for the delivery of compounds with poor solubility that would otherwise be precluded from preclinical development.

Involvement of oxidative pathways in cytokine-induced secretory phospholipase A2-IIA in astrocytes

Recent studies have suggested the involvement of secretory phospholipase A2-IIA (sPLA2-IIA) in neuroinflammatory diseases. Although sPLA2-IIA is transcriptionally induced through the NF-kappaB pathway by pro-inflammatory cytokines, whether this induction pathway is affected by other intracellular signaling pathways has not been investigated in detail. In this study, we demonstrated the induction of sPLA2-IIA mRNA and protein expression in astrocytes by cytokines and detected the protein in the culture medium after stimulation. We further investigated the effects of oxidative pathways and botanical antioxidants on the induction pathway and observed that IL-1beta-induced sPLA2-IIA mRNA expression in astrocytes is dependent on ERK1/2 and PI-3 kinase, but not p38 MAPK. In addition to apocynin, a known NADPH oxidase inhibitor, botanical antioxidants, such as resveratrol and epigallocatechin gallate, also inhibited IL-1beta-induced sPLA2-IIA mRNA expression. These compounds also suppressed IL-1beta-induced ERK1/2 activation and translocation of the NADPH oxidase subunit p67 phox from cytosol to membrane fraction. Taken together, these results support the involvement of reactive oxygen species from NADPH oxidase in cytokine induction of sPLA2-IIA in astrocytes and promote the use of botanical antioxidants as protective agents for inhibition of inflammatory responses in these cells.

The synergistic inhibition of atherogenesis in apoE-/- mice between pravastatin and the sPLA2 inhibitor varespladib (A-002)

Secretory phospholipase A2 (sPLA2) activity promotes foam cell formation, increases proinflammatory bioactive lipid levels, decreases HDL levels, increases atherosclerosis in transgenic mice, and is an independent marker of cardiovascular disease. The effects of the sPLA2 inhibitor A-002 (varespladib) and pravastatin as monotherapies and in combination on atherosclerosis, lipids, and paraoxonase (PON) activity in apoE(-/-) mice were investigated. Male apoE(-/-) mice were placed on a 12-week high-fat diet supplemented with A-002 alone or combined with pravastatin. Atherosclerotic lesions were examined for size and composition using en face analysis, Movat staining, anti-CD68, and anti-alpha actin antibodies. Plasma lipids and PON activity were measured. A-002 decreased atherosclerotic lesion area by approximately 75% while increasing fibrous cap size by over 200%. HDL levels increased 40% and plasma PON activity increased 80%. Pravastatin monotherapy had no effect on lesion size but when combined with A-002, decreased lesion area 50% and total cholesterol levels 18% more than A-002 alone. A-002, a sPLA2 inhibitor, acts synergistically with pravastatin to decrease atherosclerosis, possibly through decreased levels of systemic inflammation or decreased lipid levels. A-002 treatment also resulted in a profound increase in plasma PON activity and significantly larger fibrous caps, suggesting the formation of more stable plaque architecture.

The secretory phospholipase A2 group IIA: a missing link between inflammation, activated renin-angiotensin system, and atherogenesis?

Inflammation, lipid peroxidation and chronic activation of the rennin – angiotensin system (RAS) are hallmarks of the development of atherosclerosis. Recent studies have suggested the involvement of the pro-inflammatory secretory phospholipase A₂ (sPLA₂)-IIA in atherogenesis. This enzyme is produced by different cell types through stimulation by pro-inflammatory cytokines. It is detectable in the intima and in media smooth muscle cells, not only in atherosclerotic lesions but also in the very early stages of atherogenesis. sPLA₂-IIA can hydrolyse the phospholipid monolayers of low density lipoproteins (LDL). Such modified LDL show increased affinity to proteoglycans. The modified particles have a greater tendency to aggregate and an enhanced ability to insert cholesterol into cells. This modification may promote macrophage LDL uptake leading to the formation of foam cells. Furthermore, sPLA₂-IIA is not only a mediator for localized inflammation but may be also used as an independent predictor of adverse outcomes in patients with stable coronary artery disease or acute coronary syndromes. An interaction between activated RAS and phospholipases has been indicated by observations showing that inhibitors of sPLA₂ decrease angiotensin (Ang) II-induced macrophage lipid peroxidation. Meanwhile, various interactions between Ang II and oxLDL have been demonstrated suggesting a central role of sPLA₂-IIA in these processes and offering a possible target for treatment. The role of sPLA₂-IIA in the perpetuation of atherosclerosis appears to be the missing link between inflammation, activated RAS and lipidperoxidation.

Biology of secretory phospholipase A2

Introduction

The secretory phospholipase A₂ (sPLA₂) family provides a seemingly endless array of potential biological functions that is only beginning to be appreciated. In humans, this family comprises 9 different members that vary in their tissue distribution, hydrolytic activity, and phospholipid substrate specificity. Through their lipase activity, these enzymes trigger various cell-signaling events to regulate cellular functions, directly kill bacteria, or modulate inflammatory responses. In addition, some sPLA₂’s are high affinity ligands for cellular receptors.

Objective

This review merely scratches the surface of some of the actions of sPLA₂s in innate immunity, inflammation, and atherosclerosis. The goal is to provide an overview of recent findings involving sPLA₂s and to point to potential pathophysiologic mechanisms that may become targets for therapy.

Role of secretory phospholipases in atherogenesis

Elevated circulating levels of secretory phospholipase A(2) (sPLA(2)) are associated with atherosclerotic cardiovascular disease. sPLA(2) can contribute to atherogenesis by hydrolyzing phospholipids of circulating lipoproteins and lipoproteins entrapped in the arterial wall and/or in cells that reside in the intima and that participate in the inflammatory response to lipoprotein deposition. This article reviews differences and similarities between sPLA(2)-IIA, sPLA(2)-V, and sPLA(2)-X, all of which are members of this family of enzymes with reported potential proatherogenic features. Published data suggest that each of the enzymes has a distinct profile characterized by differences in tissue expression and localization, capacity to act on phospholipids of cell membranes and lipoproteins, and their interaction with arterial proteoglycans. In addition, the article discusses results from the authors' laboratory showing that diet-induced or gene-induced hyperlipidemia in mice enhances the expression of sPLA(2)-V in different tissues, but not sPLA(2)-IIA. Such differences indicate that these enzymes may have different roles in atherosclerotic cardiovascular disease through their distinct profiles.

Macrophage secretory phospholipase A2 group X enhances anti-inflammatory responses, promotes lipid accumulation, and contributes to aberrant lung pathology

Secreted phospholipase A2 group X (sPLA(2)-X) is one of the most potent enzymes of the phospholipase A(2) lipolytic enzyme superfamily. Its high catalytic activity toward phosphatidylcholine (PC), the major phospholipid of cell membranes and low-density lipoproteins (LDL), has implicated sPLA(2)-X in chronic inflammatory conditions such as atherogenesis. We studied the role of sPLA(2)-X enzyme activity in vitro and in vivo, by generating sPLA(2)-X-overexpressing macrophages and transgenic macrophage-specific sPLA(2)-X mice. Our results show that sPLA(2)-X expression inhibits macrophage activation and inflammatory responses upon stimulation, characterized by reduced cell adhesion and nitric oxide production, a decrease in tumor necrosis factor (TNF), and an increase in interleukin (IL)-10. These effects were mediated by an increase in IL-6, and enhanced production of prostaglandin E(2) (PGE(2)) and 15-deoxy-Delta12,14-prostaglandin J(2) (PGJ(2)). Moreover, we found that overexpression of active sPLA(2)-X in macrophages strongly increases foam cell formation upon incubation with native LDL but also oxidized LDL (oxLDL), which is mediated by enhanced expression of scavenger receptor CD36. Transgenic sPLA(2)-X mice died neonatally because of severe lung pathology characterized by interstitial pneumonia with massive granulocyte and surfactant-laden macrophage infiltration. We conclude that overexpression of the active sPLA(2)-X enzyme results in enhanced foam cell formation but reduced activation and inflammatory responses in macrophages in vitro. Interestingly, enhanced sPLA(2)-X activity in macrophages in vivo leads to fatal pulmonary defects, suggesting a crucial role for sPLA(2)-X in inflammatory lung disease.

Plasma adhesion and inflammation markers: asymmetrical dimethyl-L-arginine and secretory phospholipase A2 concentrations before and after laparoscopic gastric banding in morbidly obese patients

BACKGROUND

The aim of this study was to examine the relationship between subclinical inflammation and weight loss by laparoscopic adjustable gastric banding (LAGB).

METHODS

Plasma concentrations of intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), sensitive C-Reactive Protein (sCRP), asymmetrical dimethyl-L-arginine (ADMA), Secretory Phospholipase A2 (sPLA2), and metabolic markers, such as homeostatic model assessment insulin resistance (HOMA-IR) and body mass index (BMI) were determined in morbidly obese patients (n=18, BMI 48.6 +/- 1.7 kg/m2) at baseline and 1 month after operations. Baseline levels in patients were also compared with age-matched controls (n=20, BMI 21.3 +/- 1.8 kg/m2). Plasma ICAM-1, VCAM, sCRP and ADMA, and sPLA2 concentrations were determined by enzyme-linked immunoassay methods and colorimetric method, respectively.

RESULTS

Plasma sCRP, ICAM-1, ADMA and sPLA2 concentrations and HOMA-IR were significantly higher in morbidly obese patients than in controls (for each, P<0.01). Plasma VCAM-1 concentration was not changed in obese patients. HOMA-IR was significantly correlated with ICAM-1, ADMA and sPLA2 in the obese group at baseline (for each, P<0.01). There was a significant correlation between plasma sCRP and plasma glucose, VCAM-1, ICAM-1, ADMA and sPLA2 concentrations (for each, P<0.01). 1 month after LAGB, mean body weight loss was 13.2 +/- 6.3 kg, and plasma sCRP and ADMA concentrations and HOMA-IR and BMI were significantly decreased (for each, P<0.01). However, these levels cannot be decreased to the levels of the controls.

CONCLUSION

Obesity and insulin resistance appear to be associated with low-grade inflammation and endothelial dysfunction. Insulin resistance and endothelial dysfunction were improved by weight loss after LAGB.

Group V Secretory Phospholipase A2Promotes Atherosclerosis

OBJECTIVE

Group V secretory phospholipase A2 (GV sPLA2) has been detected in both human and mouse atherosclerotic lesions. This enzyme has potent hydrolytic activity towards phosphatidylcholine-containing substrates, including lipoprotein particles. Numerous studies in vitro indicate that hydrolysis of high density lipoproteins (HDL) and low density lipoproteins (LDL) by GV sPLA2 leads to the formation of atherogenic particles and potentially proinflammatory lipid mediators. However, there is no direct evidence that this enzyme promotes atherogenic processes in vivo.

METHODS AND RESULTS

We performed gain-of-function and loss-of-function studies to investigate the role of GV sPLA2 in atherogenesis in LDL receptor-deficient mice. Compared with control mice, animals overexpressing GV sPLA2 by retrovirus-mediated gene transfer had a 2.7 fold increase in lesion area in the ascending region of the aortic root. Increased atherosclerosis was associated with an increase in lesional collagen deposition in the same region. Mice deficient in bone marrow-derived GV sPLA2 had a 36% reduction in atherosclerosis in the aortic arch/thoracic aorta.

CONCLUSIONS

Our data in mouse models provide the first in vivo evidence that GV sPLA2 contributes to atherosclerotic processes, and draw attention to this enzyme as an attractive target for the treatment of atherosclerotic disease.