Reduced PAF-acetylhydrolase activity associated with Lp(a) in patients with coronary artery disease

Lipoprotein(a), platelet function and cardiovascular disease

Lipoprotein(a) (Lp(a)) is associated with atherothrombosis through several mechanisms, including putative antifibrinolytic properties. However, genetic association studies have not demonstrated an association between high plasma levels of Lp(a) and the risk of venous thromboembolism, and studies in patients with highly elevated Lp(a) levels have shown that Lp(a) lowering does not modify the clotting properties of plasma ex vivo. Lp(a) can interact with several platelet receptors, providing biological plausibility for a pro-aggregatory effect. Observational clinical studies suggest that elevated plasma Lp(a) concentrations are associated with worse long-term outcomes in patients undergoing revascularization. Furthermore, in these patients, those with elevated plasma Lp(a) levels derive more benefit from prolonged dual antiplatelet therapy than those with normal Lp(a) levels. The ASPREE trial in healthy older individuals treated with aspirin showed a reduction in ischaemic events in those who had a single-nucleotide polymorphism in LPA that is associated with elevated Lp(a) levels in plasma, without an increase in bleeding events. In this Review, we re-examine the role of Lp(a) in the regulation of platelet function and suggest areas of research to define further the clinical relevance to cardiovascular disease of the observed associations between Lp(a) and platelet function.

Oxidized phospholipids and lipoprotein-associated phospholipase A2 (Lp-PLA2 ) in atherosclerotic cardiovascular disease: An update

Inflammation and oxidative stress conditions lead to a variety of oxidative modifications of lipoprotein phospholipids implicated in the occurrence and development of atherosclerotic lesions. Lipoprotein-associated phospholipase A2 (Lp-PLA₂ ) is established as an independent risk biomarker of atherosclerosis-related cardiovascular disease (ASCVD) and mediates vascular inflammation through the regulation of lipid metabolism in the blood and in atherosclerotic lesions. Lp-PLA₂ is associated with low- and high-density lipoproteins and Lipoprotein (a) in human plasma and specifically hydrolyzes oxidized phospholipids involved in oxidative stress modification. Several oxidized phospholipids (OxPLs) subspecies can be detoxified through enzymatic degradation by Lp-PLA₂ activation, forming lysophospholipids and oxidized non-esterified fatty acids (OxNEFAs). Lysophospholipids promote the expression of adhesion molecules, stimulate cytokines production (TNF-α, IL-6), and attract macrophages to the arterial intima. The present review article discusses new data on the functional roles of OxPLs and Lp-PLA₂ associated with lipoproteins.

Independent association of Lp(a) with platelet reactivity in subjects without statins or antiplatelet agents

The physiological effect of Lp(a) on platelet activity is unclear. Previous studies explored the relationship between Lp(a) and platelet aggregation in patients taking statins and antiplatelet agents, but few was conducted in individuals without the bias of those drugs that either influence Lp(a) or platelet activity. The aim of this study was to assess the relationship between Lp(a) levels and platelet aggregation in subjects not taking statins or antiplatelet drugs. A hospital-based cross-sectional study was conducted to investigate the independent contribution of Lp(a) to platelet activity by controlling the effects of potential confounding factors including lipoprotein-associated phospholipase A2 [Lp-PLA2]. Blood samples were collected from 92 subjects without statins or antiplatelet agents from the Second Xiangya Hospital. The univariate correlation analysis showed a significant correlation between AA-induced average aggregation rate [AAR] and ApoB (r = 0.324, P = 0.002), ApoA1 (r = 0.252, P = 0.015), Lp(a) (r = 0.370, P < 0.001), Lp-PLA2 (r = 0.233, P = 0.025) and platelet counts [PLT] (r = 0.389, P < 0.001). Multivariate regression analysis suggested that Lp(a) contributed independently to AA-induced average aggregation rate (β = 0.023, P = 0.027) after controlling for the effects of ApoB, Lp-PLA2 and platelet counts. Lp(a) is positively associated with platelet aggregation independent of Lp-PLA2, which may partly account for the atherothrombotic effect of Lp(a).

PCSK9 is minimally associated with HDL but impairs the anti-atherosclerotic HDL effects on endothelial cell activation

Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) regulates the cell-surface localization of LDL receptors in hepatocytes and is associated with LDL and lipoprotein(a) [Lp(a)] uptake, reducing blood concentrations. However, the connection between PCSK9 and HDL is unclear. Here, we investigated the association of plasma PCSK9 with HDL subpopulations and examined the effects of PCSK9 on the atheroprotective function of HDL. We examined the association of PCSK9 with HDL in apoB-depleted plasma by ELISA, native PAGE, and immunoblotting. Our analyses showed that upon apoB-depletion, total circulating PCSK9 levels were 32% of those observed in normolipidemic plasma, and only 6% of PCSK9 in the apoB-depleted plasma, including both the mature and furin-cleaved forms, was associated with HDL. We also show human recombinant PCSK9 abolished the capacity of reconstituted HDL to reduce the formation of ROS in endothelial cells, while a PCSK9-blocking antibody enhanced the capacity of human HDL (in apoB-depleted plasma) to reduce ROS formation in endothelial cells and promote endothelial cell migration. Overall, our findings suggest that PCSK9 is only minimally associated with HDL particles, but PCSK9 in apoB-depleted plasma can affect the atheroprotective properties of HDL related to preservation of endothelial function. This study contributes to the elucidation of the pathophysiological role of plasma PCSK9 and highlights further the anti-atherosclerotic effect of PCSK9 inhibition.

Oxidized phospholipids and lipoprotein(a): An update

Over the past few years, there has been an undiminished interest in lipoprotein(a) [Lp(a)] and oxidized phospholipids (OxPLs), mainly carried on this lipoprotein. Elevated Lp(a) has been established as an independent causal risk factor for cardiovascular disease. OxPLs play an important role in atherosclerosis. The main questions that remain to be answered, however, is to what extent OxPLs contribute to the atherogenicity of Lp(a), what effect hypolipidaemic medications may have on their levels and the potential clinical benefit of their reduction. This narrative review aimed to summarize currently available data on OxPLs and cardiovascular risk, as well as the effect of established and emerging hypolipidaemic medications on Lp(a)-OxPLs.

Oxidized phospholipids and lipoprotein-associated phospholipase A2 as important determinants of Lp(a) functionality and pathophysiological role

Lipoprotein(a) [Lp(a)] is composed of a low density lipoprotein (LDL)-like particle to which apolipoprotein (a) [apo(a)] is linked by a single disulfide bridge. Lp(a) is considered a causal risk factor for ischemic cardiovascular disease (CVD) and calcific aortic valve stenosis (CAVS). The evidence for a causal role of Lp(a) in CVD and CAVS is based on data from large epidemiological databases, mendelian randomization studies, and genome-wide association studies. Despite the well-established role of Lp(a) as a causal risk factor for CVD and CAVS, the underlying mechanisms are not well understood. A key role in the Lp(a) functionality may be played by its oxidized phospholipids (OxPL) content. Importantly, most of circulating OxPL are associated with Lp(a); however, the underlying mechanisms leading to this preferential sequestration of OxPL on Lp(a) over the other lipoproteins, are mostly unknown. Several studies support the hypothesis that the risk of Lp(a) is primarily driven by its OxPL content. An important role in Lp(a) functionality may be played by the lipoprotein-associated phospholipase A₂ (Lp-PLA₂), an enzyme that catalyzes the degradation of OxPL and is bound to plasma lipoproteins including Lp(a). The present review article discusses new data on the pathophysiological role of Lp(a) and particularly focuses on the functional role of OxPL and Lp-PLA₂ associated with Lp(a).

Lipoprotein(a) in clinical practice: New perspectives from basic and translational science

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for coronary heart disease (CHD) and calcific aortic valve stenosis (CAVS). Genetic, epidemiological and in vitro data provide strong evidence for a pathogenic role for Lp(a) in the progression of atherothrombotic disease. Despite these advancements and a race to develop new Lp(a) lowering therapies, there are still many unanswered and emerging questions about the metabolism and pathophysiology of Lp(a). New studies have drawn attention to Lp(a) as a contributor to novel pathogenic processes, yet the mechanisms underlying the contribution of Lp(a) to CVD remain enigmatic. New therapeutics show promise in lowering plasma Lp(a) levels, although the complete mechanisms of Lp(a) lowering are not fully understood. Specific agents targeted to apolipoprotein(a) (apo(a)), namely antisense oligonucleotide therapy, demonstrate potential to decrease Lp(a) to levels below the 30-50 mg/dL (75-150 nmol/L) CVD risk threshold. This therapeutic approach should aid in assessing the benefit of lowering Lp(a) in a clinical setting.

Cholesterol: the good, the bad, and the ugly - therapeutic targets for the treatment of dyslipidemia

Maintaining cholesterol and triglyceride (TG) levels within healthy limits is critical for decreasing the risk of heart disease. Dyslipidemia refers to the abnormal levels of lipids in the blood, including low high-density lipoprotein cholesterol (HDL-C), also known as good cholesterol, high low-density lipoprotein cholesterol (LDL-C), also known as bad cholesterol, and/or high TG levels that contribute to the development and progression of atherosclerosis. In this article we reviewed some of the current therapeutic targets for the treatment of dyslipidemia, with a primary focus on endothelial lipase and lecithin cholesterol acyl transferase for raising HDL-C, and the proprotein convertase subtilisin-like kexin type 9 (PCSK9), microsomal triglyceride transfer protein, and the messenger RNA of apolipoprotein B for lowering LDL-C. In addition, we reviewed the role of apolipoprotein AI (apoAI) in raising HDL-C, where we discuss three apoAI-based drugs under development. These are its mutated dimer (apoAI-Milano), a complex with phospholipids, and a mimetic peptide. Atherosclerosis, mainly because of dyslipidemia, is a leading cause of cardiovascular disease. Regarding the title of this article, the 'good' refers to HDL-C, the 'bad' refers to LDL-C, and the 'ugly' refers to atherosclerosis.

Lipoprotein(a): a promising marker for residual cardiovascular risk assessment

Atherosclerotic cardiovascular diseases (CVD) are still the leading cause of morbidity and mortality worldwide, although optimal medical therapy has been prescribed for primary and secondary preventions. Residual cardiovascular risk for some population groups is still considerably high although target low density lipoprotein-cholesterol (LDL-C) level has been achieved. During the past few decades, compelling pieces of evidence from clinical trials and meta-analyses consistently illustrate that lipoprotein(a) (Lp(a)) is a significant risk factor for atherosclerosis and CVD due to its proatherogenic and prothrombotic features. However, the lack of effective medication for Lp(a) reduction significantly hampers randomized, prospective, and controlled trials conducting. Based on previous findings, for patients with LDL-C in normal range, Lp(a) may be a useful marker for identifying and evaluating the residual cardiovascular risk, and aggressively lowering LDL-C level than current guidelines' recommendation may be reasonable for patients with particularly high Lp(a) level.

The elevation of apoB in hypercholesterolemic patients is primarily attributed to the relative increase of apoB/Lp-PLA₂

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is a risk factor of cardiovascular disease. Plasma Lp-PLA₂ is mainly associated with apolipoprotein (apo)B-containing lipoproteins, primarily with low density lipoproteins (LDLs). Importantly, only a proportion of circulating lipoproteins contain Lp-PLA₂. We determined the plasma levels of Lp-PLA₂-bound apoB (apoB/Lp-PLA₂) in patients with primary hypercholesterolemia. The effect of simvastatin therapy was also addressed. The plasma apoB/Lp-PLA₂ concentration in 50 normolipidemic controls and 53 patients with primary hypercholesterolemia at baseline and at 3 months posttreatment with simvastatin (40 mg/day) was determined by an enzyme-linked immunosorbent assay. The concentration of the apoB-containing lipoproteins that do not bind Lp-PLA₂ [apoB/Lp-PLA₂⁻] was calculated by subtracting the apoB/Lp-PLA₂ from total apoB. The apoB/Lp-PLA₂ levels were 3.6-fold higher, while apoB/Lp-PLA₂⁻ were 1.3-fold higher in patients compared with controls. After 3 months of simvastatin treatment apoB/Lp-PLA₂ and apoB/Lp-PLA₂⁻ levels were reduced by 52% and 33%, respectively. The elevation in apoB-containing lipoproteins in hypercholesterolemic patients is mainly attributed to the relative increase in the proatherogenic apoB/Lp-PLA₂, while simvastatin reduces these particles to a higher extent compared with apoB/Lp-PLA₂⁻. Considering that Lp-PLA₂ is proatherogenic, the predominance of apoB/Lp-PLA₂ particles in hypercholesterolemic patients may contribute to their higher atherogenicity and incidence of cardiovascular disease.

Lentiviral-mediated RNA interference of lipoprotein-associated phospholipase A2 ameliorates inflammation and atherosclerosis in apolipoprotein E-deficient mice

Lipoprotein associated phospholipase A2 (Lp-PLA2) overexpression is implicated in athero-sclerosis. In the present study, we evaluated the effects of lentiviral-mediated RNA interference (RNAi) of Lp-PLA2 on inflammation and atherosclerosis in apolipoprotein E-deficient mice. Apolipoprotein E-deficient mice were randomly allocated to control and experimental groups, and constrictive collars were used to induce plaque formation. Eight weeks after surgery, the lentiviral-mediated RNAi construct was used to silence expression of Lp-PLA2. Control and experimental lentivirus was transfected directly into carotid plaques or administered systemically. Tissues were collected for analysis 7 weeks after transfection. Inflammatory gene expression in the plasma and atherosclerotic lesions was then determined at the mRNA and protein levels. We observed no differences in body weight and plasma lipid levels at the end of the investigation. However, the expression levels of Lp-PLA2 and pro-inflammatory cytokines were significantly reduced in the RNAi groups, compared to the controls, whereas the plasma concentration of anti-inflammatory cytokines was markedly increased. Moreover, our results demonstrated a significant reduction in plaque area and lipid content, as well as a rise in collagen content following RNAi treatment. Importantly, when comparing the two methods of viral delivery, we found that transluminal local transfection exhibited enhanced improvement of plaque stability as compared to systemic administration. Inhibition of Lp-PLA2 by lentiviral-mediated RNAi ameliorates inflammation and atherosclerosis in apolipoprotein E-deficient mice. In addition, transluminal local delivery of Lp-PLA2 shRNA is superior to systemic administration for stabilizing atherosclerotic plaques.

Regression of atherosclerosis in apolipoprotein E-deficient mice by lentivirus-mediated gene silencing of lipoprotein-associated phospholipase A2

Overexpression of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is implicated in atherosclerosis. We tested the hypothesis that lentivirus-mediated Lp-PLA(2) silencing could inhibit atherosclerosis in apolipoprotein E-deficient mice. Sixty eight apolipoprotein E-deficient mice were fed a high-fat diet and a constrictive collar was placed around the left carotid artery to induce plaque formation. The mice were randomly divided into control, negative control (NC) and RNA interference (RNAi) groups. Lp-PLA(2) RNAi or scrambled NC lentivirus viral suspensions were constructed and transfected into the carotid plaques 8 weeks after surgery; the control group was administered saline. The carotid plaques were assessed 7 weeks later using hematoxylin and eosin, Masson's trichrome and oil red O staining; plasma and lesion inflammatory gene expression were examined using ELISAs and real-time PCR. Seven weeks after transfection, the serum concentration and plaque mRNA expression of Lp-PLA(2) was significantly lower in the RNAi group, and lead to reduced local and systemic inflammatory gene expression. Lp-PLA(2) RNAi also ameliorated plaque progression, reduced the plaque lipid content and increased the plaque collagen content. The effects of Lp-PLA(2) RNAi were independent of serum lipoprotein levels, as the triglyceride and total cholesterol levels of the control, NC and RNAi groups were not significantly different. These findings support the hypothesis that lentivirus-mediated Lp-PLA(2) gene silencing has therapeutic potential to inhibit atherosclerosis and increase plaque stability, without altering the plasma lipoprotein profile.

Antioxidant and inflammatory aspects of lipoprotein-associated phospholipase A₂ (Lp-PLA₂): a review

The association of cardiovascular events with Lp-PLA₂ has been studied continuously today. The enzyme has been strongly associated with several cardiovascular risk markers and events. Its discovery was directly related to the hydrolysis of the platelet-activating factor and oxidized phospholipids, which are considered protective functions. However, the hydrolysis of bioactive lipids generates lysophospholipids, compounds that have a pro-inflammatory function. Therefore, the evaluation of the distribution of Lp-PLA₂ in the lipid fractions emphasized the dual role of the enzyme in the inflammatory process, since the HDL-Lp-PLA₂ enzyme contributes to the reduction of atherosclerosis, while LDL-Lp-PLA₂ stimulates this process. Recently, it has been verified that diet components and drugs can influence the enzyme activity and concentration. Thus, the effects of these treatments on Lp-PLA₂ may represent a new kind of prevention of cardiovascular disease. Therefore, the association of the enzyme with the traditional assessment of cardiovascular risk may help to predict more accurately these diseases.

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.

Biology of platelet-activating factor acetylhydrolase (PAF-AH, lipoprotein associated phospholipase A2)

INTRODUCTION

This article is focused on platelet-activating factor acetylhydrolase (PAF-AH), a lipoprotein bound, calcium-independent phospholipase A(2) activity also referred to as lipoprotein-associated phospholipase A(2) or PLA(2)G7. PAF-AH catalyzes the removal of the acyl group at the sn-2 position of PAF and truncated phospholipids generated in settings of inflammation and oxidant stress.

DISCUSSION

Here, I discuss current knowledge related to the structural features of this enzyme, including the molecular basis for association with lipoproteins and susceptibility to oxidative inactivation. The circulating form of PAF-AH is constitutively active and its expression is upregulated by mediators of inflammation at the transcriptional level. This mechanism is likely responsible for the observed up-regulation of PAF-AH during atherosclerosis and suggests that increased expression of this enzyme is a physiological response to inflammatory stimuli. Administration of recombinant forms of PAF-AH attenuate inflammation in a variety of experimental models. Conversely, genetic deficiency of PAF-AH in defined human populations increases the severity of atherosclerosis and other syndromes. Recent advances pointing to an interplay among oxidized phospholipid substrates, Lp(a), and PAF-AH could hold the key to a number of unanswered questions.

The role of oxidized phospholipids in mediating lipoprotein(a) atherogenicity

PURPOSE OF REVIEW

To review emerging data on the relationship between lipoprotein(a) and oxidized phospholipids.

RECENT FINDINGS

We have recently proposed that a unique physiological role of lipoprotein(a) may be to bind and transport proinflammatory oxidized phospholipids and that this interaction may mediate a common biological influence on cardiovascular disease. In a large series of clinical studies performed to date, a very strong correlation was found between plasma levels of lipoprotein(a) and the content of oxidized phospholipids on apolipoprotein B-100 particles (OxPL/apoB), measured by monoclonal antibody E06, which binds the phosphocholine head group of oxidized phospholipids but not native phospholipids. The correlation of OxPL/apoB to lipoprotein(a) is very strong in individuals with small apolipoprotein(a) isoforms (r = approximately 0.95) and modest in individuals with large isoforms (r = approximately 0.60). In-vitro studies have demonstrated that the vast majority of oxidized phospholipids detected by E06 are bound to lipoprotein(a) in human plasma. A similarly strong association with oxidized phospholipids was also documented in transgenic mice overexpressing lipoprotein(a), even in mice not fed atherogenic diets or with overt atherosclerosis.

SUMMARY

A better understanding of the ability of human lipoprotein(a) to bind oxidized phospholipids may allow clinically important insights into the role of oxidized phospholipids and lipoprotein(a) in human atherogenesis and cardiovascular disease and may provide novel diagnostic tools and therapeutic interventions aimed at measuring and treating elevated levels of OxPL/apoB and lipoprotein(a).

A novel function of lipoprotein [a] as a preferential carrier of oxidized phospholipids in human plasma

Oxidized phospholipids (OxPLs) on apolipoprotein B-100 (apoB-100) particles are strongly associated with lipoprotein [a] (Lp[a]). In this study, we evaluated whether Lp[a] is preferentially the carrier of OxPL in human plasma. The content of OxPL on apoB-100 particles was measured with monoclonal antibody E06, which recognizes the phosphocholine (PC) headgroup of oxidized but not native phospholipids. To assess whether OxPLs were preferentially bound by Lp[a] as opposed to other lipoproteins, immunoprecipitation and ultracentrifugation experiments, in vitro transfer studies, and chemiluminescent ELISAs were performed. Immunoprecipitation of Lp[a] from human plasma with an apolipoprotein [a] (apo[a])-specific antibody demonstrated that more than 85% of E06 reactivity (i.e., OxPL) coimmunoprecipitated with Lp[a]. Ultracentrifugation experiments showed that nearly all OxPLs were found in fractions containing apo[a], as opposed to other apolipoproteins. In vitro transfer studies showed that oxidized LDL preferentially donates OxPLs to Lp[a], as opposed to LDL, in a time- and temperature-dependent manner, even in aqueous buffer. Approximately 50% of E06 immunoreactivity could be extracted from isolated Lp[a] following exposure of plasma to various lipid solvents. These data demonstrate that Lp[a] is the preferential carrier of PC-containing OxPL in human plasma. This unique property of Lp[a] suggests novel insights into its physiological function and mechanisms of atherogenicity.

Lymphocytic hypophysitis

BACKGROUND

Lymphocytic hypophysitis is a disorder of the pituitary gland that presents as a sellar mass lesion and/or hypopituitarism. It causes pituicyte destruction and hypopituitarism and is speculated to have an autoimmune basis.

DIAGNOSIS

Lymphocytic hypophysitis should be considered in the differential diagnosis of pituitary masses and/or hypopituitarism in females who are pregnant or in the early postpartum period, especially in cases associated with other autoimmune diseases or unusual patterns of hormone deficiencies. A definitive diagnosis requires tissue biopsy. A presumptive clinical diagnosis can be made based on a history of gestational or postpartum hypopituitarism, a contrast-enhancing sellar mass with imaging features characteristic of lymphocytic hypophysitis, a pattern of pituitary hormone deficiency with early loss of adrenocorticotrophic hormone and thyroid-stimulating hormone unlike that typically found with macroadenomas, relatively rapid development of hypopituitarism and a degree of pituitary failure disproportionate to the size of the mass. Symptoms resulting from partial or panhypopituitarism occur in approximately 80% of cases and multiple deficiencies are found in approximately 75% of cases.

MANAGEMENT

Appropriate management remains controversial. Corticosteroid therapy has been advocated as a means of attenuating inflammation, but given the uncertainty of its efficacy and the known adverse effects, such therapy does not seem justified for most patients. The optimal surgical strategy involves partial resection of the mass to decompress the surrounding structures. All patients with lymphocytic hypophysitis require appropriate replacement therapy for deficient hormones. Long-term follow-up is mandatory to monitor for the development of other hormonal deficits.

New Insights Into the Role of Lipoprotein(a)-Associated Lipoprotein-Associated Phospholipase A 2 in Atherosclerosis and Cardiovascular Disease

Lipoprotein(a) [Lp(a)] plays an important role in atherosclerosis. The biological effects of Lp(a) have been attributed either to apolipoprotein(a) or to its low-density lipoprotein-like particle. Lp(a) contains platelet-activating factor acetylhydrolase, an enzyme that exhibits a Ca 2+ -independent phospholipase A 2 activity and is complexed to lipoproteins in plasma; thus, it is also referred to as lipoprotein-associated phospholipase A 2 . Substrates for lipoprotein-associated phospholipase A 2 include phospholipids containing oxidatively fragmented residues at the sn-2 position (oxidized phospholipids; OxPLs). OxPLs may play important roles in vascular inflammation and atherosclerosis. Plasma levels of OxPLs present on apolipoprotein B-100 particles (OxPL/apolipoprotein B) are correlated with coronary artery, carotid, and peripheral arterial disease. Furthermore, OxPL/apolipoprotein B levels in plasma are strongly correlated with Lp(a) levels, are preferentially sequestered on Lp(a), and thus are potentially subjected to degradation by the Lp(a)-associated lipoprotein-associated phospholipase A 2 . The present review article focuses specifically on the characteristics of the lipoprotein-associated phospholipase A 2 associated with Lp(a) and discusses the possible role of this enzyme in view of emerging data showing that OxPLs in plasma are preferentially sequestered on Lp(a) and may significantly contribute to the increased atherogenicity of this lipoprotein.

Oxidized Phospholipids, Lipoprotein(a), Lipoprotein-Associated Phospholipase A2 Activity, and 10-Year Cardiovascular Outcomes

BACKGROUND

Oxidized phospholipids (OxPL) circulate on apolipoprotein B-100 particles (OxPL/apoB), and primarily on Lp(a) lipoprotein (a) [Lp(a)]. The relationship of OxPL/apoB levels to future cardiovascular events is not known.

METHODS AND RESULTS

The Bruneck study is a prospective population-based survey of 40- to 79-year-old men and women recruited in 1990. Plasma levels of OxPL/apoB and lipoprotein (a) [Lp(a)] were measured in 765 subjects in 1995 and incident cardiovascular disease (CVD), defined as cardiovascular death, myocardial infarction, stroke, and transient ischemic attack, was assessed from 1995 to 2005. During the follow-up period, 82 subjects developed CVD. In multivariable analysis, which included traditional risk factors, high sensitivity C-reactive protein (hsCRP), and lipoprotein-associated phospholipase A2 (Lp-PLA2) activity, subjects in the highest tertile of OxPL/apoB had a significantly higher risk of cardiovascular events than those in the lowest tertile (hazard ratio[95% CI] 2.4[1.3 to 4.3], P=0.004). The strength of the association between OxPL/apoB and CVD risk was amplified with increasing Lp-PLA2 activity (P=0.018 for interaction). Moreover, OxPL/apoB levels predicted future cardiovascular events beyond the information provided by the Framingham Risk Score (FRS). The effects of OxPL/apoB and Lp(a) were not independent of each other but they were independent of all other measured risk factors.

CONCLUSIONS

This study demonstrates that OxPL/apoB levels predict 10-year CVD event rates independently of traditional risk factors, hsCRP, and FRS. Increasing Lp-PLA2 activity further amplifies the risk of CVD mediated by OxPL/apoB.

Plasma markers of endothelial dysfunction in type 2 diabetics

BACKGROUND

Type 2 diabetes, or non-insulin-dependent diabetes mellitus, represents an independent risk factor for cardiovascular diseases (CVD), being characterized by a continuous low-grade inflammation and endothelial activation state. Atherosclerotic lesions occur in diabetic patients at an earlier age with severe clinical manifestations and poor outcome. Our objective was to investigate the correlation between lipoprotein-associated phospholipase A2 (PLA2-LDL), myeloperoxidase (MPO), and paraoxonase (PON), enzymes implicated in the evolution of endothelial dysfunction associated with type 2 diabetes.

METHODS

One hundred diabetic patients [50 without documented coronary artery disease (group 1) and 50 with CVD (group 2)] and 46 healthy controls were investigated for PLA2-LDL, MPO, and PON activities.

RESULTS

PLA2-LDL activity was significantly higher in group 2 than in group 1 and among controls. PON activity was lower in group 1 than in controls, reaching the lowest level in group 2. MPO activity was higher in type 2 diabetics than among controls, with similar values in groups 1 and 2.

CONCLUSIONS

The evaluation of PLA2-LDL, MPO, and PON activities may improve early diagnosis of CVD in asymptomatic patients with type 2 diabetes and can help to evaluate accelerated atherosclerosis and microvascular disease.

Lipoprotein(a) as a cardiovascular risk factor

Evidence for the role of lipoprotein(a) (Lp[a]) in atherosclerosis and thrombosis has considerably increased over the past few years. Therefore, Lp(a) is currently classified as an emerging lipid risk factor for cardiovascular disease. High Lp(a) plasma levels carried in particles with small-sized apolipoprotein(a) isoforms are associated with preclinical vascular changes, cardiovascular disease and the mode of presentation of coronary artery disease (acute coronary syndromes). However, randomized clinical trials with an emphasis on agents that specifically lower plasma Lp(a) do not exist. At present, screening for increases in Lp(a) in the general population is not recommended. The measurement of Lp(a) may be of value in individuals with an increased risk of cardiovascular disease, particularly in patients with high low-density lipoprotein cholesterol plasma levels, since a high Lp(a) concentration in such subjects further increases the risk of coronary heart disease.