Apolipoprotein (a) fragments in relation to human carotid plaque instability

Protein Corona Sensor Array Nanosystem for Detection of Coronary Artery Disease

Coronary artery disease (CAD) is the most common type of heart disease and represents the leading cause of death in both men and women worldwide. Early detection of CAD is crucial for decreasing mortality, prolonging survival, and improving patient quality of life. Herein, a non-invasive is described, nanoparticle-based diagnostic technology which takes advantages of proteomic changes in the nano-bio interface for CAD detection. Nanoparticles (NPs) exposed to biological fluids adsorb on their surface a layer of proteins, the "protein corona" (PC). Pathological changes that alter the plasma proteome can directly result in changes in the PC. By forming disease-specific PCs on six NPs with varying physicochemical properties, a PC-based sensor array is developed for detection of CAD using specific PC pattern recognition. While the PC of a single NP may not provide the required specificity, it is reasoned that multivariate PCs across NPs with different surface chemistries, can provide the desirable information to selectively discriminate the condition under investigation. The results suggest that such an approach can detect CAD with an accuracy of 92.84%, a sensitivity of 87.5%, and a specificity of 82.5%. These new findings demonstrate the potential of PC-based sensor array detection systems for clinical use.

Developing an SI-traceable Lp(a) reference measurement system: a pilgrimage to selective and accurate apo(a) quantification

In the past decade a remarkable rebirth of serum/plasma lipoprotein(a) (Lp(a)) as an independent risk factor of cardiovascular disease (CVD) occurred. Updated evidence for a causal continuous association in different ethnic groups between Lp(a) concentrations and cardiovascular outcomes has been published in the latest European Atherosclerosis Society (EAS) Lp(a) consensus statement. Interest in measuring Lp(a) at least once in a person's lifetime moreover originates from the development of promising new Lp(a) lowering drugs. Accurate and clinically effective Lp(a) tests are of key importance for the timely detection of high-risk individuals and for future evaluation of the therapeutic effects of Lp(a) lowering medication. To this end, it is necessary to improve the performance and standardization of existing Lp(a) tests, as is also noted in the Lp(a) consensus statement. Consequently, a state-of-the-art internationally endorsed reference measurement system (RMS) must be in place that allows for performance evaluation of Lp(a) field tests in order to certify their validity and accuracy. An ELISA-based RMS from Northwest Lipid Research Laboratory (University of Washington, Seattle, USA) has been available since the 1990s. A next-generation apo(a)/Lp(a) RMS is now being developed by a working group from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The envisioned apo(a) RMS is based on the direct measurement of selected proteotypic fragments generated after proteolytic digestion using quantitative protein mass spectrometry (MS). The choice for an MS-based RMS enables selective measurement of the proteotypic peptides and is by design apo(a) isoform insensitive. Clearly, the equimolar conversion of apo(a) into the surrogate peptide measurands is required to obtain accurate Lp(a) results. The completeness of proteolysis under reaction conditions from the candidate reference measurement procedure (RMP) has been demonstrated for the quantifying apo(a) peptides. Currently, the candidate apo(a) RMP is endorsed by the IFCC and recommendations for suitable secondary reference materials have been made in a recent commutability study paper. Ongoing efforts toward a complete apo(a) RMS that is listed by the Joint Committee on Traceability in Laboratory Medicine (JCTLM) are focused on the peptide-based calibration and the establishment of a network of calibration laboratories running the apo(a) RMS in a harmonized way. Once completed, it will be the holy grail for evaluation and certification of Lp(a) field methods.

Lipoprotein(a): A Genetically Determined, Causal, and Prevalent Risk Factor for Atherosclerotic Cardiovascular Disease: A Scientific Statement From the American Heart Association

High levels of lipoprotein(a) [Lp(a)], an apoB100-containing lipoprotein, are an independent and causal risk factor for atherosclerotic cardiovascular diseases through mechanisms associated with increased atherogenesis, inflammation, and thrombosis. Lp(a) is predominantly a monogenic cardiovascular risk determinant, with ≈70% to ≥90% of interindividual heterogeneity in levels being genetically determined. The 2 major protein components of Lp(a) particles are apoB100 and apolipoprotein(a). Lp(a) remains a risk factor for cardiovascular disease development even in the setting of effective reduction of plasma low-density lipoprotein cholesterol and apoB100. Despite its demonstrated contribution to atherosclerotic cardiovascular disease burden, we presently lack standardization and harmonization of assays, universal guidelines for diagnosing and providing risk assessment, and targeted treatments to lower Lp(a). There is a clinical need to understand the genetic and biological basis for variation in Lp(a) levels and its relationship to disease in different ancestry groups. This scientific statement capitalizes on the expertise of a diverse basic science and clinical workgroup to highlight the history, biology, pathophysiology, and emerging clinical evidence in the Lp(a) field. Herein, we address key knowledge gaps and future directions required to mitigate the atherosclerotic cardiovascular disease risk attributable to elevated Lp(a) levels.

Lipoprotein(a) and long-term recurrent infarction after an episode of ST-segment elevation acute myocardial infarction

BACKGROUND

In established ischemic heart disease, the relationship between lipoprotein(a) and new cardiovascular events showed contradictory results. Our aim was to assess the relationship between lipoprotein(a) and very long-term recurrent myocardial infarction (MI) after an index episode of ST-segment elevation acute myocardial infarction (STEMI).

METHODS

We included 435 consecutive STEMI patients discharged from October 2000 to June 2003 in a single teaching center. The relationship between lipoprotein(a) at discharge and recurrent MI was evaluated through negative binomial regression and Cox regression analysis.

RESULTS

The mean age was 65 years (55-74 years), 25.5% were women, 34.7% were diabetic, and 66% had a MI of anterior location. Fibrinolysis, rescue, or primary angioplasty was performed in 215 (49.4%), 19 (4.4%), and 18 (4.1%) patients, respectively. The median lipoprotein(a) was 30.4 mg/dL (12-59.4 mg/dL). After a median follow-up of 9.6 years (4.1-15 years), 180 (41.4%) deaths and 187 MI in 133 (30.6%) patients were recorded. After a multivariate adjustment, the risk gradient of lipoprotein(a) showed a neutral effect along most of the continuum and only extreme higher values identified those at higher risk of recurrent MI (P = 0.020). Those with lipoprotein(a) values >95th percentile (≥135 mg/dL) showed a higher risk of recurrent MI (incidence rate ratio, 2.34; 95% confidence interval, 1.37-4.02; P = 0.002). Lipoprotein(a) was not related to the risk of mortality (P = 0.245).

CONCLUSIONS

After an episode of STEMI, only extreme high values of lipoprotein(a) were associated with an increased risk of long-term recurrent MI.

Potent reduction of plasma lipoprotein (a) with an antisense oligonucleotide in human subjects does not affect ex vivo fibrinolysis

It is postulated that lipoprotein (a) [Lp(a)] inhibits fibrinolysis, but this hypothesis has not been tested in humans due to the lack of specific Lp(a) lowering agents. Patients with elevated Lp(a) were randomized to antisense oligonucleotide [IONIS-APO(a)_Rx] directed to apo(a) (n = 7) or placebo (n = 10). Ex vivo plasma lysis times and antigen concentrations of plasminogen, factor XI, plasminogen activator inhibitor 1, thrombin activatable fibrinolysis inhibitor, and fibrinogen at baseline, day 85/92/99 (peak drug effect), and day 190 (3 months off drug) were measured. The mean ± SD baseline Lp(a) levels were 477.3 ± 55.9 nmol/l in IONIS-APO(a)_Rx and 362.1 ± 89.9 nmol/l in placebo. The mean± SD percentage change in Lp(a) for IONIS-APO(a)_Rx was -69.3 ± 12.2% versus -5.4 ± 6.9% placebo (P < 0.0010) at day 85/92/99 and -15.6 ± 8.9% versus 3.2 ± 12.2% (P = 0.003) at day 190. Clot lysis times and coagulation/fibrinolysis-related biomarkers showed no significant differences between IONIS-APO(a)_Rx and placebo at all time points. Clot lysis times were not affected by exogenously added Lp(a) at concentrations up to 200 nmol/l to plasma with very low (12.5 nmol/l) Lp(a) levels, whereas recombinant apo(a) had a potent antifibrinolytic effect. In conclusion, potent reductions of Lp(a) in patients with highly elevated Lp(a) levels do not affect ex vivo measures of fibrinolysis; the relevance of any putative antifibrinolytic effects of Lp(a) in vivo needs further study.

Lp(a)/apo(a) modulate MMP-9 activation and neutrophil cytokines in vivo in inflammation to regulate leukocyte recruitment

Lipoprotein(a) [Lp(a)] is an independent risk factor for cardiovascular diseases, but the mechanism is unclear. The pathogenic risk of Lp(a) is associated with elevated plasma concentration, small isoforms of apolipoprotein [apo(a)], the unique apolipoprotein of Lp(a), and a mimic of plasminogen. Inflammation is associated with both the initiation and recovery of cardiovascular diseases, and plasminogen plays an important role in leukocyte recruitment. Because Lp(a)/apo(a) is expressed only in primates, transgenic mice were generated, apo(a)tg and Lp(a)tg mice, to determine whether Lp(a)/apo(a) modifies plasminogen-dependent leukocyte recruitment or whether apo(a) has an independent role in vivo. Plasminogen activation was markedly reduced in apo(a)tg and Lp(a)tg mice in both peritonitis and vascular injury inflammatory models, and was sufficient to reduce matrix metalloproteinase-9 activation and macrophage recruitment. Furthermore, neutrophil recruitment and the neutrophil cytokines, CXCL1/CXCL2, were suppressed in apo(a)tg mice in the abdominal aortic aneurysm model. Reconstitution of CXCL1 or CXCL2 restored neutrophil recruitment in apo(a)tg mice. Apo(a) in the plasminogen-deficient background and Lp(a)tg mice were resistant to inhibition of macrophage recruitment that was associated with an increased accumulation of apo(a) in the intimal layer of the vessel wall. These data indicate that, in inflammation, Lp(a)/apo(a) suppresses neutrophil recruitment by plasminogen-independent cytokine inhibition, and Lp(a)/apo(a) inhibits plasminogen activation and regulates matrix metalloproteinase-9 activation and macrophage recruitment.

Lipoprotein(a) metabolism: potential sites for therapeutic targets

Lipoprotein(a) [Lp(a)] resembles low-density lipoprotein (LDL), with an LDL lipid core and apolipoprotein B (apoB), but contains a unique apolipoprotein, apo(a). Elevated Lp(a) is an independent risk factor for coronary and peripheral vascular diseases. The size and concentration of plasma Lp(a) are related to the synthetic rate, not the catabolic rate, and are highly variable with small isoforms associated with high concentrations and pathogenic risk. Apo(a) is synthesized in the liver, although assembly of apo(a) and LDL may occur in the hepatocytes or plasma. While the uptake and clearance site of Lp(a) is poorly delineated, the kidney is the site of apo(a) fragment excretion. The structure of apo(a) has high homology to plasminogen, the zymogen for plasmin and the primary clot lysis enzyme. Apo(a) interferes with plasminogen binding to C-terminal lysines of cell surface and extracellular matrix proteins. Lp(a) and apo(a) inhibit fibrinolysis and accumulate in the vascular wall in atherosclerotic lesions. The pathogenic role of Lp(a) is not known. Small isoforms and high concentrations of Lp(a) are found in healthy octogenarians that suggest Lp(a) may also have a physiological role. Studies of Lp(a) function have been limited since it is not found in commonly studied small mammals. An important aspect of Lp(a) metabolism is the modification of circulating Lp(a), which has the potential to alter the functions of Lp(a). There are no therapeutic drugs that selectively target elevated Lp(a), but a number of possible agents are being considered. Recently, new modifiers of apo(a) synthesis have been identified. This review reports the regulation of Lp(a) metabolism and potential sites for therapeutic targets.

A physiological function for apolipoprotein(a): a natural regulator of the inflammatory response

Structural similarities between apolipoprotein(a) (apo(a)), the unique apoprotein of lipoprotein(a), and plasminogen, the zymogen of plasmin, can interfere with functions of plasmin (ogen) in vitro. The purpose of this study was to evaluate the role of apo(a) in inflammation in vivo using apo(a) transgenic mice and to determine if effects are plasminogen-dependent using backgrounds that are either plasminogen-replete or plasminogen-deficient. After administration of peritoneal inflammatory stimuli, thioglycollate, bioimplants or lipopolysaccharide, the number of responding peritoneal neutrophils and macrophages were quantified. Apo(a), in either wild-type or plasminogen deficient backgrounds, inhibited neutrophil recruitment but had no effect on plasminogen-dependent macrophage recruitment. Macrophage-inflammatory protein-2, a neutrophil chemokine, was reduced in apo(a) mice, and injection of this chemokine prior to thioglycollate restored neutrophil recruitment in apo(a) transgenic mice. In the lipopolysaccharide model, mice with apo(a), unlike mice without apo(a), did not increase neutrophil recruitment in response to the stimulus. In the bioimplant model, neutrophil recruitment and neutrophil cytokines were reduced in apo(a)tg mice but only in a plasminogen-deficient background. These results indicate for the first time that apo(a), independent of plasminogen interaction, inhibits neutrophil recruitment in vivo in diverse peritoneal inflammatory models. Hence, apo(a) may function as a cell specific suppressor of the inflammatory response.

Elements in the C terminus of apolipoprotein [a] responsible for the binding to the tenth type III module of human fibronectin

In previous studies, we showed that the C-terminal domain, F2, but not the N-terminal domain, F1, is responsible for the binding of apolipoprotein [a] (apo[a]) to human fibronectin (Fn). To pursue those observations, we prepared, by both elastase digestion and recombinant technology, subsets of F2 of a different length containing either kringle (K) V or the protease domain (PD). We also studied rhesus monkey apo[a], which is known to contain PD but not KV. In the case of Fn, we used both an intact product and its tenth type III module (10FN-III) expressed in Escherichia coli. The binding studies carried out on microtiter plates showed that the affinity of F2 for immobilized 10FN-III was approximately 6-fold higher than that for Fn (dissociation constants = 1.75 +/- 0.31 nM and 10.25 +/- 1.62 nM, respectively). The binding was also exhibited by rhesus apo[a] and by an F2 subset containing the PD linked to an upstream microdomain comprising KIV-8 to KIV-10 and KV, inactive by itself. Competition experiments on microtiter plates showed that both Fn and 10FN-III, when in solution, are incompetent to bind F2. Together, our results indicate that F2 binds to immobilized 10FN-III more efficiently than whole Fn and that the binding can be sustained by truncated forms of F2 that contain the catalytically inactive PD linked to an upstream four K microdomain.

Apo(a) promotes thrombosis in a vascular injury model by a mechanism independent of plasminogen

OBJECTIVE

Structural similarity between apolipoprotein(a) [apo(a)], the unique apoprotein of lipoprotein(a), and plasminogen (Plg), the zymogen for plasmin, results in inhibition of functions of Plg by apo(a) in vitro. The objective of this study was to evaluate the interaction of Plg and apo(a) in vivo.

METHODS AND RESULTS

Vascular injury was induced in the carotid artery with a perivascular cuff in: (i) wild-type (WT); (ii) Plg deficient (Plg-/-); (iii) apo(a) (6 KIV construct) transgenic [apo(a)tg]; and (iv) apo(a) transgenic and Plg deficient [apo(a):Plg-/-] mice. At 10 days after cuff placement, the media and adventitia area were increased in the injured carotids compared with the uninjured carotids, and collagen deposition was greater in apo(a)tg, Plg-/- and apo(a):Plg-/- mice compared with WT mice. The incidence of a thrombus was greater (P < 0.05) in apo(a):Plg-/- mice (83%) than WT (20%), Plg-/- (12%), and apo(a)tg mice (9%). In the thrombi from apo(a)tg and apo(a):Plg-/- mice, P-selectin and von Willebrand factor immunostaining, indicating a platelet-rich thrombi, was greater than in WT and Plg-/- mice. The presence of fibrin(ogen) in the thrombi was greater in Plg-/- and apo(a):Plg-/- mice than apo(a)tg and WT mice. Of the four genotypes, only the apo(a):Plg-/- mice had both increased platelet and increased fibrin(ogen) deposition.

CONCLUSIONS

The major finding of this study is the high incidence of thrombosis after vascular injury in apo(a)transgenic mice in a Plg deficient background, providing strong evidence for a prothrombotic role of apo(a) independent of Plg in vivo.

An Apolipoprotein(a) Peptide Delays Chylomicron Remnant Clearance and Increases Plasma Remnant Lipoproteins and Atherosclerosis In Vivo

Objective— Humans with high expression of apolipoprotein(a) [apo(a)] and high plasma levels of lipoprotein(a) [Lp(a)] are at increased risk for atherosclerosis, but the mechanism is not known. We have previously shown that the KIV 5–8 domain of apo(a) has unique cell-surface binding properties, and naturally occurring fragments of apo(a) encompassing this domain are thought to be atherogenic in humans. To investigate the effect of KIV 5–8 on lipoprotein metabolism and atherosclerosis in vivo, we created several independent lines of liver-targeted KIV 5–8 transgenic mice.

Methods and Results— The transgenic mice have plasma apo(a) peptide concentrations that are similar to Lp(a) concentrations in humans at risk for coronary artery disease. Remarkably, the transgenic mice had a 2- to 4-fold increase in cholesterol-rich remnant lipoproteins (RLPs) when fed a cholesterol-rich diet, and a 5- to 20-fold increase in atherosclerosis lesion area in the aortic root. Using an in vivo clearance study, we found only slight differences in the triglyceride and apolipoprotein B secretion rates between the 2 groups of mice, suggesting an RLP clearance defect. Using an isolated perfused mouse liver system, we showed that transgenic livers had a slower rate of RLP removal, which was retarded further when KIV 5–8 , full-length apo(a), or Lp(a) were added to the perfusate. An apo(a) peptide that does not interact with cells, K(IV 2 ) 3 , did not retard RLP removal, and low-density lipoprotein (LDL) had a much smaller effect than Lp(a).

Conclusions— We propose that high levels of apo(a)/Lp(a), perhaps acting via a specific cell-surface binding domain, inhibit hepatic clearance of remnants, leading to high plasma levels of RLPs and markedly enhanced atherosclerosis. We speculate that the KIV 5–8 region of apo(a) competes with one or more receptors for remnant clearance in the liver and that this process may represent one mechanism accounting for increased atherosclerosis in humans with high secretion levels of apo(a).

Evidence for a Proinflammatory and Proteolytic Environment in Plaques From Endarterectomy Segments of Human Carotid Arteries

Objectives Based on previous observations on apolipoprotein(a), apo(a), in human unstable carotid plaques, we explored whether in the inflammatory environment of human atheroma, proteolytic events affect other hepatic and topically generated proteins in relation to the issue of plaque stability.

Methods and Results Forty unstable and 24 stable plaques from endarterectomy segments of affected human carotid arteries were extracted with buffered saline (PBS) and then 6 mol/L guanidine-hydrochloride (GdHCl) to identify loosely and tightly bound products, respectively. The extracts were studied before and after ultracentrifugation at d 1.21 g/mL. In the extracts, the concentrations of interleukin (IL)-6, −8, and −18 were significantly higher in the unstable plaques and correlated to those of MMP-2 and MMP-9. By Western blots, both apoB and apo(a) were highly fragmented and mostly present in the d 1.21 bottom that also contained fragments of apoE (10 and 22 kDa), decorin, biglycan, and versican. Fragmentation was higher in the unstable plaques. In baseline plasmas, concentrations of lipids, lipoproteins, and ILs did not differ between patients with unstable and stable plaques.

Conclusions In unstable and to a lesser extent in stable plaques, there is a proinflammatory and proteolytic microenvironment with the generation of fragments with potential pathobiological significance that requires investigation.

In situ zymography: a molecular pathology technique to localize endogenous protease activity in tissue sections

Proteases play important roles in modulating a wide range of cellular functions, in the regulation of biologic processes, and in the pathogenesis of various diseases. Several molecular techniques are available to identify and characterize proteases in cells and tissues. Most of these techniques do not provide information on the activity of proteases in tissues. In situ zymography (ISZ) is a relatively low-cost technique that uses specific protease substrates to detect and localize specific protease activities in tissue sections. Used in combination with other techniques, ISZ provides data that further our understanding of the role of specific proteases in various pathologic and physiologic conditions. This review describes the general principle of ISZ and highlights the past and future applications of this technique in molecular pathology.

Apolipoprotein(A) expression in intracranial aneurysms

OBJECTIVE

Elevated serum levels of lipoprotein(a), a risk factor for atherosclerosis (AS), are also associated with the presence of asymptomatic intracranial aneurysms. AS is present in some aneurysms, but its contribution to aneurysm formation and growth is unclear. Apolipoprotein(a) [apo(a)], the active moiety of lipoprotein(a), is present in atherosclerotic circle of Willis vessels but not in normal circle of Willis vessels. We wished to determine whether apo(a) is present in intracranial aneurysms independently of AS.

METHODS

With a purified anti-apo(a) monoclonal antibody, aneurysms (n = 25) and feeding vessels (n = 23) were examined for apo(a) expression by immunohistochemical analysis. Circle of Willis arteries with and without AS (n = 19), cavernous angiomas (n = 5), and arteriovenous malformations (n = 6) acted as control samples.

RESULTS

AS was present in 32% of aneurysms, and all of those aneurysms demonstrated mural immunopositivity for apo(a). However, aneurysms devoid of AS also demonstrated apo(a) immunopositivity. Apo(a) was demonstrated in 86% of available feeding vessels. Apo(a) deposition was not observed in cavernous angiomas but was present in arteriovenous malformations. Eleven Circle of Willis arteries (57.9%) were devoid of AS and demonstrated no apo(a) immunostaining, whereas the eight (42.1%) with AS were immunopositive for apo(a).

CONCLUSION

Apo(a) expression in intracranial aneurysms may occur independently of AS. Apo(a) in feeding vessels suggests a possible role for apo(a) in early events leading to aneurysm formation. Multilayered transmural apo(a) deposition in established aneurysms suggests apo(a) involvement in aneurysm growth, possibly via cycles of injury and repair. The absence of apo(a) in cavernous angiomas suggests that such injury might be pressure-mediated.

Lipoprotein(a) and the atherothrombotic process: mechanistic insights and clinical implications

Although many epidemiologic studies have pointed at an association between plasma levels of lipoprotein(a) (Lp(a)) and cardiovascular risk, the data obtained have been conflicting because of a number of factors, particularly those dealing with plasma storage, lack of assay standardization, population sample size, age, gender, ethnic variations, and variable disease endpoints. Moreover, the attention has been primarily focused on whole Lp(a), with relatively less emphasis on its constituent apolipoprotein(a) and on the apolipoprotein B100-containing lipoprotein, mainly low-density lipoprotein (LDL), to which apolipoprotein(a) is linked. According to recent studies, small-size apolipoprotein(a) isoforms may represent a cardiovascular risk factor either by themselves or synergistically with plasma Lp(a) concentration. Moreover, the density properties of the LDL moiety may have an impact on Lp(a) pathogenicity. It has also become apparent that Lp(a) can be modified by oxidative events and by the action of lipolytic and proteolytic enzymes with the generation of products that exhibit atherothrombogenic potential. The role of the O-glycans linked to the inter-kringle linkers of apolipoprotein(a) is also emerging. This information is raising the awareness of the pleiotropic functions of Lp(a) and is opening new vistas on pathogenetic mechanisms whose knowledge is essential for developing rational therapies against this complex cardiovascular pathogen.

Lipoprotein(a): an emerging cardiovascular risk factor

Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.

Stimulation of interleukin-8 production in human THP-1 macrophages by apolipoprotein(a). Evidence for a critical involvement of elements in its C-terminal domain

In the vessel wall, macrophages are among the cells that upon activation contribute to the atherosclerotic process. Low density lipoproteins (LDL) can mediate this activation but only after enzymatic or oxidative modification. Lipoprotein(a) (Lp(a)) is an LDL variant that has been shown to have an atherogenic potential by no clearly established mechanisms. In the present study we examined whether native Lp(a) can activate macrophages and, if so, identify the structural elements involved in this action. For this purpose, we utilized human THP-1 macrophages, prepared by treating THP-1 monocytes with phorbol ester, and we exposed them to Lp(a) and its two derivatives, apo(a)-free LDL (Lp(a-)) and free apo(a). We also studied apo(a) fragments, F1 (N terminus) and F2 (C terminus) and subfragments thereof, obtained by leukocyte elastase digestion. By Northern blot analyses, Lp(a), but not Lp(a-), caused up to a 12-fold increase in interleukin 8 (IL-8) mRNA as compared with untreated cells. Free apo(a) also induced the production of IL-8 mRNA; however, the effect was 3-4-fold higher than that of Lp(a). The increase in mRNA was associated with the accumulation of IL-8 protein in the culture medium. F1 had only a minimal effect, whereas F2 was 1.5-2-fold more potent than apo(a), an activity mostly contained in the Kringle V-protease region. A monoclonal antibody specific for Kringle V inhibited the apo(a)-mediated effect on IL-8. We conclude that Lp(a) via elements contained in the C-terminal domain of apo(a) causes in THP-1 macrophages an increased production of IL-8, a chemokine with pro-inflammatory properties, an event that may be relevant to the process of atherosclerosis.