Percutaneous coronary intervention results in acute increases in oxidized phospholipids and lipoprotein(a): short-term and long-term immunologic responses to oxidized low-density lipoprotein

BACKGROUND

This study was performed to assess whether oxidized low-density lipoprotein (OxLDL) levels are elevated after percutaneous coronary intervention (PCI).

METHODS AND RESULTS

Patients (n=141) with stable angina pectoris undergoing PCI had serial venous blood samples drawn before PCI, after PCI, and at 6 and 24 hours, 3 days, 1 week, and 1, 3, and 6 months. Plasma levels of OxLDL-E06, a measure of oxidized phospholipid (OxPL) content on apolipoprotein B-100 detected by antibody E06, lipoprotein(a) [Lp(a)], autoantibodies to malondialdehyde (MDA)-LDL and copper-oxidized LDL (Cu-OxLDL), and apolipoprotein B-100-immune complexes (apoB-IC) were measured. OxLDL-E06 and Lp(a) levels significantly increased immediately after PCI by 36% (P<0.0001) and 64% (P<0.0001), respectively, and returned to baseline by 6 hours. In vitro immunoprecipitation of Lp(a) from selected plasma samples showed that almost all of the OxPL detected by E06 was bound to Lp(a) at all time points, except in the post-PCI sample, suggesting independent release and subsequent reassociation of OxPL with Lp(a) by 6 hours. Strong correlations were noted between OxLDL-E06 and Lp(a) (r=0.68, P<0.0001). MDA-LDL and Cu-OxLDL autoantibodies decreased, whereas apoB-IC levels increased after PCI, but both returned to baseline by 6 hours. Subsequently, IgM autoantibodies increased and peaked at 1 month and then returned to baseline, whereas IgG autoantibodies increased steadily over 6 months.

CONCLUSIONS

PCI results in acute plasma increases of Lp(a) and OxPL and results in short-term and long-term immunologic responses to OxLDL. OxPL that are released or generated during PCI are transferred to Lp(a), suggesting that Lp(a) may contribute acutely to a protective innate immune response. In settings of enhanced oxidative stress and chronically elevated Lp(a) levels, the atherogenicity of Lp(a) may stem from its capacity as a carrier of proinflammatory oxidation byproducts.

Immunohistochemical detection of lipoprotein(a) in the wall of placental bed spiral arteries in normal and severe preeclamptic pregnancies

In normal pregnancy trophoblast invades the spiral arteries and produces the physiological fibrinoid degeneration of the vessel wall. In pre-eclampsia, physiological change is restricted and pathological change develops in the non-invaded arteries, including acute atherosis. This study was undertaken to determine if lipoprotein(a) [Lp(a)], which is associated with atherogenesis is present in the wall of spiral arteries that have undergone physiological and pathological change. One hundred and sixteen spiral arteries were examined from 18 normal and 24 severe pre-eclamptic pregnancies. Lp(a) was detected in all atherotic and necrotic lesions, in 57% of spiral arteries with medical disorganization or hyperplasia, and in 45% of those with physiological change. When Lp(a) was detected differences were found in the amount seen: it was most in atherosis, less in necrosis, less still in medical change, and least in physiological change. For the same vascular change generally more Lp(a) was detected in the pre-eclamptic group than in the normal group. The detection of Lp(a) helps to distinguish physiological fibrinoid from atherotic and necrotic fibrinoid. Many atherotic and necrotic areas initially overlooked using standard histology were highlighted using immunohistochemistry. Atherosis can develop in spiral arteries that have been invaded by trophoblast. In those with pre-eclampsia, atherosis was found in 56% of decidual but only in 8% of myometrial spiral arteries. Small areas of necrosis were common in physiologically changed arteries from normal pregnancies.

Native, oxidized lipoprotein(a) and lipoprotein(a) immune complex in patients with active and inactive rheumatoid arthritis: plasma concentrations and relationship to inflammation

BACKGROUND

Several studies suggest that lipoprotein (a) [Lp(a)] act as acute phase reactant and be associated with early atherosclerosis in rheumatoid arthritis (RA). Oxidized Lp(a) [ox-Lp(a)] and Lp(a) immune complex (IC) concentrations both increased in patients with coronary heart disease. We investigated Lp(a), ox-Lp(a) and Lp(a)-IC concentrations in RA patients and to explore the relationships with inflammatory disease activity markers.

METHODS

Plasma Lp(a), ox-Lp(a) and Lp(a)-IC concentrations, and inflammatory markers were analyzed in 54 patients with RA, including 23 active and 21 inactive RA, and 60 control subjects.

RESULTS

Lp(a) and ox-Lp(a) concentrations in active RA were higher than those in both inactive RA and control; Lp(a)-IC concentrations in active RA were also higher than inactive RA, while no difference was found in Lp(a), ox-Lp(a) and Lp(a)-IC concentrations between inactive RA and control. Lp(a) concentrations were found positively correlated with ox-Lp(a) and Lp(a)-IC concentrations, respectively; ox-Lp(a) concentrations were also related with Lp(a)-IC. Lp(a), ox-Lp(a) and Lp(a)-IC were all found positively related with C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), respectively.

CONCLUSIONS

Native, oxidized Lp(a) and Lp(a)-IC concentrations increased in active RA patients. Inflammation may induce the changes of Lp(a), resulting in increased ox-Lp(a) and Lp(a)-IC, and may play an important role in atherosclerosis.

Lp(a) lipoprotein: an overview

The Lp(a) lipoprotein, a distinct class of serum lipoproteins, was detected in 1962. It consists of an LDL particle to which a long polypeptide chain is attached by a disulfide bridge. The level of Lp(a) lipoprotein is genetically determined. Single locus control was suggested already in the very first report, and this has been conclusively confirmed by the demonstration of absolute genetic linkage to the plasminogen gene, from which the LPA gene is likely to have evolved. The detection in 1974 of an association between Lp(a) lipoprotein and coronary heart disease has been confirmed in numerous studies. The Lp(a) lipoprotein may have atherogenic as well as thrombogenic properties and thus form the bridge between atherogenesis and thrombogenesis. Genes determining a moderate level of Lp(a) lipoprotein may be longevity genes, and it seems possible that Lp(a) lipoprotein, because of its affinity to vessel walls, may also influence placental function. Lp(a) lipoprotein measurements should be included in the diagnostic work-up of people with premature coronary heart disease or with such disease in close relatives.

Lp(a) particles mold fibrin-binding properties of apo(a) in size-dependent manner: a study with different-length recombinant apo(a), native Lp(a), and monoclonal antibody

OBJECTIVE

Small-sized apolipoprotein(a) [apo(a)] isoforms with high antifibrinolytic activity are frequently found in cardiovascular diseases, suggesting a role for apo(a) size in atherothrombosis. To test this hypothesis, we sought to characterize the lysine (fibrin)-binding function of isolated apo(a) of variable sizes.

METHODS AND RESULTS

Recombinant apo(a) [r-apo(a)] preparations consisting of 10 to 34 kringles and a monoclonal antibody that neutralizes the lysine-binding function were produced and used in parallel with lipoprotein(a) [Lp(a)] particles isolated from plasma in fibrin-binding studies. All r-apo(a) preparations displayed similar affinity and specificity for lysine residues on fibrin regardless of size (K(d) 3.6+/-0.3 nmol/L) and inhibited the binding of plasminogen with a similar intensity (IC50 16.8+/-5.4 nmol/L). In contrast, native Lp(a) particles displayed fibrin affinities that were in inverse relationship with the apo(a) kringle number. Thus, a 15-kringle apo(a) separated from Lp(a) and a 34-kringle r-apo(a) displayed an affinity for fibrin that was higher than that in the corresponding particles (K(d) 2.5 versus 10.5 nmol/L and K(d) 3.8 versus 541 nmol/L, respectively). However, fibrin-binding specificity of the r-apo(a) preparations and the Lp(a) particles was efficiently neutralized (IC50 0.07 and 4 nmol/L) by a monoclonal antibody directed against the lysine-binding function of kringle IV-10.

CONCLUSIONS

Our data indicate that fibrin binding is an intrinsic property of apo(a) modulated by the composite structure of the Lp(a) particle.

Autoantibodies against malondialdehyde-modified lipoprotein(a) in antiphospholipid syndrome

OBJECTIVE

To demonstrate the existence of antibodies that react against malondialdehyde (MDA)-modified lipoprotein(a) (MDA-Lp[a]), a molecule that exhibits behavioral similarities to MDA-modified low-density lipoprotein (MDA-LDL), and to assess the possible relationship of these antibodies (anti-MDA-Lp[a]) to anti-MDA-LDL antibodies (anti-MDA-LDL) in the antiphospholipid syndrome (APS).

METHODS

We studied 104 patients with APS (61 with primary APS and 43 with APS secondary to systemic lupus erythematosus) and 106 healthy controls. Anti-MDA-Lp(a) were measured by enzyme-linked immunosorbent assay (ELISA) using MDA-Lp(a) as antigen. Plasma levels of Lp(a) were determined. Anti-MDA-LDL, anticardiolipin antibodies (aCL), and anti-beta2-glycoprotein I antibodies (anti-beta2GPI) were also measured by ELISA. Inhibition assays were performed to determine the presence of cross-reactivity between anti-MDA-Lp(a) and anti-MDA-LDL.

RESULTS

Anti-MDA-Lp(a) were detected in 38 of 104 patients (37%) but in only 6 of 106 controls (6%) (chi2 = 28, P<0.0001). Levels of anti-MDA-Lp(a) were also higher in patients than in controls (P<0.0001). Titers of these antibodies did not correlate with plasma levels of Lp(a). The presence of anti-MDA-Lp(a) was significantly associated with that of anti-MDA-LDL (chi2 = 22.09, P<0.0001). There was a strong correlation between the titers of anti-MDA-Lp(a) and anti-MDA-LDL (r = 0.59, P<0.0001), and inhibition assays showed significant cross-reactivity between the 2 populations of antibodies. Anticardiolipin antibodies and anti-beta2GPI were present in sera from 67 patients (64%) and 48 patients (46%), respectively. No correlation was found between the titer of anti-MDA-Lp(a) and titers of either aCL or anti-beta2GPI.

CONCLUSION

We report for the first time the existence of autoantibodies against MDA-Lp(a). The presence of antibodies reacting not only against MDA-LDL but also against MDA-Lp(a) supports the hypothesis of a role for oxidative phenomena in the pathogenesis of APS and atherosclerosis.

Lipoprotein(a) oxidation and autoantibodies: a new path in atherothrombosis

Lipoprotein(a) (Lp(a)) is considered a vascular pathogen of outstanding importance. High plasma levels of this lipoprotein are associated with premature arterial disease; however, the mechanisms involved have not been clarified. The atherosclerotic process is increasingly regarded as a chronic inflammatory reaction in the arterial wall where oxidation-mediated endothelial injury involving modified forms of low-density lipoprotein (LDL) seems to be a key event. Autoimmune pathways are involved in the progression of atherosclerosis and humoral response to oxidatively modified LDL can be considered among these pathways. A number of factors can be encountered in the pathogenesis of the accelerated arterial disease seen in patients with antiphospholipid (Hughes) syndrome (APS) and systemic lupus erythematosus (SLE). Among these, high levels of Lp(a) have been described in both and increasing evidence indicates that patients with antiphospholipid antibodies (aPL) are under oxidative stress. Recent studies suggest that the so-called 'oxidation theory of atherosclerosis' may also be applied to Lp(a). This fact makes this lipoprotein potentially suitable as a target of the immune system and antibodies reacting against oxidatively-modified Lp(a) by malondialdehyde have been recently described in APS and SLE. It is therefore likely that an immune response to the oxidized moiety of Lp(a) might be influential in the pathogenicity of this lipoprotein and, subsequently, of atherosclerosis.

Detection of IgG-bound lipoprotein(a) immune complexes in patients with coronary heart disease

BACKGROUND

LDL-immune complexes (IC) have a powerful pathogenic role for inducing foam cell formation in vitro more efficiently than any other known mechanism. Studies have also shown that plasma LDL-IC concentration is a powerful marker for the development of atherosclerosis. The structure, fatty acid composition and antioxidant concentrations of Lp(a) and LDL are quite similar. The same oxidation pattern has also been described for both lipoproteins. Modified forms of Lp(a), some resembling oxidized Lp(a), have been identified in human atheromatous lesions. The existence of autoantibodies against MDA-Lp(a) in vivo is also presented. Therefore, we suppose that Lp(a) might trigger an immune response leading to the production of autoantibodies and subsequently to the formation of immune complexes. This study examined the existence of IgG-bound Lp(a)-IC and investigated its value as a risk factor for the development of atherosclerosis.

METHODS

We developed two "sandwich" ELISAs for measuring plasma Lp(a)-IC and LDL-IC concentrations, using anti-human IgG(Fab) as the capture antibody, and quantitating with monoclonal anti-apo(a) or anti-apoB enzyme conjugate. Their concentrations were studied in 160 patients with coronary heart disease (CHD) and 290 control subjects.

RESULTS

Plasma TC, LDL-C, TG and apoB concentrations in CHD patients were all significantly increased, whereas HDL-C and apoAI concentrations were decreased. The Lp(a) concentrations in the patients with CHD were also significantly different from those of control (262.4+/-220.0 vs. 211.3+/-199.4 mg/l, P<0.005). Plasma Lp(a)-IC (2.24+/-1.71 vs. 1.62+/-1.50 AU, P<0.0001) and LDL-IC (2.77+/-1.29 vs. 1.40+/-0.92 AU, P<0.0001) concentrations in patients with CHD were both significantly higher than those of control. The relationships between Lp(a)-IC, LDL-IC concentrations and other lipid traits in all the studied subjects (n=450) were carried out. LDL-IC concentrations were positively correlated with LDL-C, apoB, TC, TG and Lp(a) concentrations, while negatively correlated with HDL-C and apoAI concentrations, respectively. Similarly, Lp(a)-IC concentrations were positively correlated with Lp(a), LDL-C, apoB and TC concentrations, while negatively correlated with HDL-C and apoAI concentrations, respectively. Furthermore, a significantly positive relation between LDL-IC and Lp(a)-IC concentrations was also found (r=0.313, P<0.0001).

CONCLUSIONS

We report the existence of Lp(a)-IC in both the plasma of patients with CHD and control subjects. Lp(a)-IC concentration increases in the CHD patients.

Beta2 glycoprotein I containing immune-complexes in lupus patients: association with thrombocytopenia and lipoprotein (a) levels

In this study we determined the prevalence and clinical associations of immune-complexes-containing beta-2-glycoprotein I (beta2GPI) in randomly selected SLE patients. We studied 38 consecutive SLE patients attending the Rheumatology Unit. Previous arterial or venous-thrombosis were documented by the appropriate diagnostic test. Lipid profile including total cholesterol, LDL, VLDL, HDL and Lp(a) levels were determined from the sera of the fasting patients. Antibodies to cardiolipin, oxidized LDL and beta2GPI were detected employing ELISA. Beta2GPI containing IgG immune-complexes were assayed by using a dot-blot assay. Fourteen SLE patients (36.8%) were found to be positive for the presence of IgG anti-beta2GPI antibodies. Ten of the SLE patients (26.3%) were found to have high levels of beta2GPI containing immune-complexes. There was a positive correlation between beta2GPI-IC levels and the occurrence of thrombocytopenia in the patients (P < 0.05). Furthermore, patients with SLE and venous thrombosis had higher levels of beta2GPI-IC when compared with thrombosis-free patients or with healthy controls (P < 0.05). Patients with higher Lp(a) levels (> 50 mg/dl) possessed higher levels of beta2GPI-IC as compared with patients with lower Lp(a) concentration (< 20 mg/dl) (P < 0.05). These results suggest that IC-containing beta2GPI can help in defining a subpopulation of SLE patients with increased risk of thrombocytopenia and further aid in resolving mechanisms of immune-mediated tissue damage.

Standardization of Lp(a) measurements

Two direct binding ELISAs were developed in our laboratory for measuring Lp(a) in human plasma. The first ELISA was performed by using a monoclonal antibody to apo(a) bound to the solid phase and a second monoclonal antibody to apo(a) as detecting antibody. The second ELISA was performed by using the same monoclonal antibody bound to the solid phase and an anti-apo B polyclonal antibody as detecting antibody. The immunoreactivity of Lp(a) particles of different size, isolated from subjects with F, B or S2 isoform, were evaluated by the two ELISA methods. Superimposable standard curves were obtained by the three Lp(a) preparations when using the apo(a) detection system, but the Lp(a) containing the largest apo(a) isoform S2 had a significantly reduced slope by the apo B detection method. Lp(a) concentration was determined in plasma samples by the two ELISA methods. When Lp(a) with apo(a) isoform S2 was used to calibrate the assays, similar Lp(a) values were obtained by the two different detecting systems on samples from subjects with isoforms S2, S3 or S4, while values in the samples with B and S1 isoforms were significantly higher. When Lp(a) with isoform B was used as calibrator, comparable Lp(a) values were obtained by the two methods on samples with B isoform, while the values were lower in the samples with the higher molecular weight isoforms when measured by the apo B detection method. A pilot study was conducted to evaluate Lp(a) values obtained by different methods calibrated with a common fresh-frozen serum with a defined apo(a) isoform.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of new enzyme-linked immunosorbent assay for oxidized lipoprotein(a) by using purified human oxidized lipoprotein(a) autoantibodies as capture antibody

BACKGROUND

Oxidized Lp(a) [ox-Lp(a)] has been reported to play more potent role than native Lp(a) in atherosclerosis. Ox-Lp(a), autoantibodies, and Lp(a) immune complexes have all been detected in vivo. Thus, the isolation of its autoantibodies and the investigation of ox-Lp(a) may provide a new means to explore the exact pathogenic role of ox-Lp(a). We isolated and identified human autoantibodies against ox-Lp(a) and developed a new ELISA for ox-Lp(a) by using autoantibodies as capture antibody.

METHODS

Ox-Lp(a) autoantibodies were isolated and identified from healthy subjects by affinity chromatography. 2 "sandwich" ELISAs were developed for measuring ox-Lp(a) level, using autoantibodies against ox-Lp(a) or rabbit antiserum against ox-LDL as the capture antibody and quantitating with monoclonal anti-apo(a) enzyme conjugate, respectively. Ox-Lp(a) levels were studied by both the ELISAs in 100 patients with coronary heart disease (CHD) and 100 control subjects.

RESULTS

The isolated ox-Lp(a) autoantibodies reacted with both apo(a) and apoB epitopes of Ox-Lp(a). Compared to control, plasma ox-Lp(a) levels in patients with CHD were significantly increased (ELISA using human autoantibodies: 24.3+/-33.4 vs. 8.4+/-9.3 microg/ml, P<0.0001; ELISA using antibodies against ox-LDL: 13.0+/-13.8 vs. 7.3+/-9.7 microg/ml, P<0.0001, respectively). Furthermore, a significantly positive relationship between ox-Lp(a) levels detected by 2 ELISAs was also found (R=0.78, P<0.0001).

CONCLUSION

We isolated human autoantibodies against ox-Lp(a), which can recognize both apo(a) and apoB epitopes of ox-Lp(a). The developed ELISA for ox-Lp(a) by using human auoantibodies may more accurately reflect the state of Lp(a) oxidation in vivo. Ox-Lp(a) levels increase in patients with CHD.

Development of antibody against epitope of lipoprotein(a) modified by oxidation: evaluation of new enzyme-linked immunosorbent assay for oxidized lipoprotein(a)

BACKGROUND

Recently, the biological effects of oxidized lipoprotein(a) [Lp(a)] have been reported to be more potent than Lp(a), the arteriosclerosis-relevant lipoprotein. Thus, investigations with oxidized Lp(a) are expected to provide viewpoints different from the conventional ones based on Lp(a).

METHODS AND RESULTS

An anti-Lp(a) monoclonal antibody (161E2) was produced against synthetic peptide antigen (Arg-Asn-Pro-Asp-Val-Ala-Pro). This epitope was characterized as having various properties because its external exposure was induced as a result of oxidative modification. Using 161E2 antibody, we developed a new enzyme-linked immunosorbent assay to measure Lp(a) modified by oxidative stress. The present data demonstrated that oxidized Lp(a) that contains the epitope of 161E2 antibody was present in the serum of humans. Therefore, we used this new enzyme-linked immunosorbent assay to evaluate the role of oxidized Lp(a) in patients with hypertension, which induces oxidative stress. Interestingly, hypertensive patients with complications showed a significantly higher level of oxidized Lp(a) in serum than did normotensive subjects (P:<0.01), whereas there was no significant difference in native Lp(a) between normotensive and hypertensive subjects. Importantly, positive immunostaining with 161E2 monoclonal antibody was found in the human arteriosclerotic tissue.

CONCLUSIONS

We developed a new antibody against an epitope in Lp(a) as a result of oxidation treatment but not in native Lp(a). The present data demonstrated in vivo the presence of oxidized Lp(a) in the atherosclerotic tissue and its elevation in hypertensive patients. The presence of oxidized Lp(a) may be important in understanding the role of Lp(a) in cardiovascular disease.

A comparison of Lp(a) levels in fresh and frozen plasma using ELISAs with either anti-apo(a) or anti-apoB reporting antibodies

Sandwich ELISAs with an anti-apo(a) trapping antibody and either an anti-apolipoprotein B or anti-apolipoprotein(a) reporting antibody, were used to measure the concentrations of Lp(a) in 230 plasma samples that were either freshly drawn or stored at -20 degrees C for 4-6 weeks. The assays produced significantly different results for the fresh and frozen samples, however, the magnitudes of these differences were small, about 8% higher for the frozen samples, and independent of total cholesterol, HDL cholesterol, triglyceride, apolipoprotein B or Lp(a) concentration or assay configuration. A similar difference was seen for a freshly drawn plasma sample assayed at the time as the fresh and frozen samples, indicating the differences were due to inherent differences in the assays at the times the assays were performed. The assay configuration was an important factor in determining the Lp(a) concentrations for identically treated samples. ELISAs using the apoB reporting antibody yielded concentrations that were significantly less than those determined by ELISAs using the anti-apo(a) reporting antibody. The assay differences did not correlate with total cholesterol, HDL cholesterol, triglyceride, or apoB concentration. However, the magnitude of the difference did correlate well with Lp(a) amount. Low Lp(a) concentrations produced greater assay differences than high Lp(a) concentrations.

A new Lp(a) assay that is unaffected by apo(a) size polymorphism

We developed sandwich ELISA methods in which anti-apo(a) kringle 4 type 5 through protease (K4 x 5-Pro) domain monoclonal antibody (clone: 203E2) is employed in each instance as the capture antibody and one of the three species of monoclonal antibody [Mab] (clones: 108B8, 202A9, 2B3) is used as the labeled antibody. Using serum containing apo(a) with 34 repeats of kringle 4 as the calibrator, a commercial kit using anti-Lp(a) polyclonal antibody (Pab) or anti-apo(a) Mab overestimated the Lp(a) concentration in samples containing apo(a) with more than 34 repeats of kringle 4 and underestimated the Lp(a) concentration in samples containing apo(a) with fewer than 34 repeats of kringle 4. Moreover, it was demonstrated that the ratios of commercial kit values to anti-apo(a) K4 x 5-Pro Mab-based method values increased as the size of apo(a) increased. The ratios of apo(a) K5 x Pro Mab-based method values to anti-apo(a) K4 x 5-Pro Mab-based method values, however, remained almost constant regardless of the size polymorphism. Thus, we suggest that apo(a) size heterogeneity can significantly affect Lp(a) measurement in the Lp(a) assay using anti-Lp(a) Pab. The novel Lp(a) assay method, using only anti-apo(a) K4 x 5-Pro Mab, is not subject to this phenomenon.

Immunoturbidimetric determination of lipoprotein(a): improvement in the measurement of turbid and triglyceride-rich samples

Immunoturbidimetry (IT), a widely used method in clinical chemical laboratories, was checked for its suitability for lipoprotein(a) (Lp(a)) quantification. When the conventional sample diluents were used, turbidimetry gave false results particularly with frozen or lipemic sera which correlated poorly with electroimmunodiffusion (EID). L-Proline which is known to dissociate Lp(a) from other apo B-containing lipoproteins improved the results considerably. One hundred frozen sera were investigated in IT with and without the addition of L-proline to the sample diluent. EID served as a comparison method. In a method comparison (IT vs. EID) linear regression analysis improved from r = 0.793: y = 0.89x - 9.4 (without L-proline) to r = 0.949: y = 0.98x + 4.8 (with L-proline). The improvement of the correlation of the two methods was most pronounced in sera with triglyceride values exceeding 5.5 mmol/l. The IT assay described here was linear between 50 and 1100 mg/l. Total imprecision (coefficient of variation) was below 10%. The assay was not affected by the addition of LDL or plasminogen to the samples. The Lp(a) concentration of the calibrator, i.e. a secondary standard serum, was compared with that of a purified primary Lp(a) standard which consisted of a mixture of four apo(a) isoforms. Total Lp(a) mass (lipids, protein, carbohydrates) was determined chemically and was compared with the Lp(a) mass determined immunochemically by IT and EID. Recovery of the purified Lp(a) was 106% (range 90-116%) in IT and 102% (range 91-115%) in EID. Dose response curves from pure single isoforms (S1 and S4), calibrator and serum samples were parallel. We consider IT to be a simple and rapid method for Lp(a) quantification which is not biased by different apo(a) isoforms.

High plasma levels of apo(a) fragments in Caucasians and African-Americans with end-stage renal disease: implications for plasma Lp(a) assay

Apolipoprotein(a) [apo(a)] is a plasma glycoprotein that is highly polymorphic in size due to differences in the number of a tandemly arrayed cysteine-rich repeat called kringle (K)4 at its N-terminus. Most plasma apo(a) is covalently attached to apolipoprotein B-100 and circulates as part of lipoprotein(a) [Lp(a)]. A fraction of apo(a) circulates free of lipoproteins. Almost all of the free apo(a) consists of fragments containing variable numbers of K4 repeats derived from the N-terminal region. Previously we provided evidence suggesting that the apo(a) fragments present in human plasma are the source of the apo(a) fragments in human urine. If this were the case, it would be expected that plasma levels of fragments would be higher in subjects with end-stage renal disease (ESRD). In this paper we quantified the levels of apo(a) fragments and plasma Lp(a) in 26 Caucasian and 26 African-American subjects with ESRD and 52 healthy subjects matched for race, sex and the size of the apo(a) isoforms. The plasma levels of apo(a) fragments and Lp(a) were both higher in the ESRD subjects. In addition, the ratio of apo(a) fragments to total immunodetectable apo(a) was increased in ESRD. To determine how much the increase in the apo(a) fragments contributed to the increase in plasma Lp(a) in ESRD, the plasma Lp(a) levels were measured employing two different anti-apo(a) enzyme-linked immunoabsorption assays (ELISA). One assay detected both free and bound apo(a), whereas the other assay detected only bound apo(a). Although the plasma levels of apo(a) in the ESRD subjects tended to be higher using the assay that detected both fragments and full-length apo(a), the increase was modest. Thus, although a greater proportion of the apo(a) in ESRD plasma circulates as fragments, most of the elevation in plasma levels of Lp(a) associated with renal insufficiency is due to an increase in intact Lp(a).

In vivo glucosylated LpA-I subfraction. Evidence for structural and functional alterations

This study compared the structural and functional properties of glucosylated and non-glucosylated LpA-I particle subfractions (GLpA-I and NGLpA-I, respectively) isolated from patients with poorly controlled type 1 (insulin-dependent) diabetes. Compared with NGLpA-I, GLpA-I showed an enrichment in triglycerides (P < .05) and a depletion in phospholipid (P < .05) content. Moreover, the triglycerides-to-cholesteryl esters ratio was increased (P < .05), suggesting an increased cholesteryl ester transfer protein activity and a possible transport defect that accelerates atherogenesis. The surface-to-core constituents ratio, an indirect estimate of particles size, is lower in GLpA-I (P < .01) than in NGLpA-I, correlating well with a larger median size (P < .05) as seen by electron microscopy. The apolipoprotein (apo) A-I conformation was evaluated through determination of the immunological accessibility of three different domains defining specific epitopes for anti-apo A-I monoclonal antibodies. We observed a marked decreased accessibility for two of these regions, which interestingly have already been implicated in the interaction with cells. Cell culture data suggest that nonenzymatic glycosylation occurring on apo A-I can modify lipoprotein function, since it results in a decreased binding of GLpA-I to HeLa cells and impaired cholesterol efflux from Fu5AH rat hepatoma cells.

Immunoquantification of lipoprotein(a): comparison of nephelometry with electroimmunodiffusion

A new fully automated nephelometric immunoassay for lipoprotein(a) quantification in human serum was evaluated using the Behring Nephelometer Analyzer. The assay exhibited a good linearity in the concentration range of 110-1,770 mg/l; at higher concentrations, samples were automatically diluted by a factor of 4. The method is simple, robust, and shows an excellent stability of the calibration curve over several weeks. Intra-assay and day-to-day coefficients of variation were 2% and 4.5%, respectively. The method correlated well with electroimmunodiffusion (r = 0.977; n = 123; P = 0.0001). Unspecific turbidity as expressed by an elevated blank value occurred in 3% of all freshly measured samples (n = 392). Storage of the samples for 1 week at 4 degrees C had no significant influence on the results. Frozen sera, on the other hand, cannot be assayed by this method. We believe that this assay is well suited for use in clinical routine work.

Diagnostic value of immune cholesterol as a marker for atherosclerosis

BACKGROUND

The serum of patients with coronary atherosclerosis contains circulating immune complexes including low-density lipoproteins (LDLs). We have developed a technique for the evaluation of LDL content in circulating immune complexes by measuring total cholesterol levels in polyethylene glycol precipitates (immune cholesterol). In the present study, the value of immune cholesterol in the diagnosis of atherosclerosis was compared with that of other laboratory parameters, such as total cholesterol levels, triglycerides, LDL cholesterol, high-density lipoprotein cholesterol, lipoprotein(a), and apolipoproteins B and A-1.

METHODS

Immune cholesterol and the other parameters were determined in blood samples from 200 patients with documented coronary and extracoronary atherosclerosis. Coronary atherosclerosis was assessed by coronary angiography; stenoses in the aortic arch and branches and in lower-limb arteries were evaluated by angiography and ultrasonography.

RESULTS

Only immune cholesterol and the ratio of apolipoprotein B to apolipoprotein A-1 correlated significantly with the severity of coronary atherosclerosis. The accuracy of the diagnosis of coronary atherosclerosis by immune cholesterol was 78%, considerably higher than that of other laboratory parameters. Use of a combined parameter consisting of immune cholesterol, LDL cholesterol, and the patient's age increased the diagnostic accuracy to 81%. A high level of immune cholesterol is characteristic not only of coronary atherosclerosis but also of extracoronary atherosclerosis. The sensitivity, specificity and accuracy of the diagnosis of extracoronary atherosclerosis were even higher than those for coronary atherosclerosis.

CONCLUSION

Immune cholesterol may be employed as a novel marker in the diagnosis of advanced atherosclerosis.

Lipoprotein(a) immunoassays: comparison of a semi-quantitative latex method and two monoclonal enzyme immunoassays

Lipoprotein(a) is considered an independent risk factor for atherosclerosis. A variety of analytical methods have been proposed for lipoprotein(a) measurement, the majority of which require dedicated instruments and are costly to perform, particularly when the aim is to screen for high lipoprotein(a) concentrations in large populations. We evaluated the sensitivity and specificity of a newly developed semi-quantitative latex method to assess its suitability for identifying subjects with high lipoprotein(a) levels. Based on clinical data, a sensitivity limit of 20 mg/dl of total lipoprotein(a) particle was selected for the latex method. Results obtained by the latex method on 204 subjects were compared with two enzyme immunoassays using two anti-apo(a) monoclonal antibodies with different specificities. In one assay, the detecting monoclonal antibody (MAb a-5) is directed against an epitope present in a variable number depending on the apo(a) size isoforms in lipoprotein(a), while the other assay the detecting monoclonal antibody (MAb a-40) is directed against an epitope present only once in lipoprotein(a) particles, irrespective of their apo(a) size. Both the latex method and the MAb a-5 assay demonstrated a 100% sensitivity, in that no false-negative results were found using the MAb a-40 assay as the gold standard. Eleven subjects (5.4%) were misclassified as false positive by MAb a-5 assay and 23 (11.3%) were misclassified by the latex method. Based on its 100% sensitivity and 89% specificity, we conclude that the lipoprotein(a) latex method is a cost-effective rapid approach for screening large populations.

Attenuation of Salmonella enterica Serovar Typhimurium by altering biological functions of murein lipoprotein and lipopolysaccharide

We constructed Salmonella enterica serovar Typhimurium double-knockout mutants in which either the lipoprotein A (lppA) or the lipoprotein B (lppB) gene was deleted from an msbB-negative background strain by marker exchange mutagenesis. These mutants were highly attenuated when tested with in vitro and in vivo models of Salmonella pathogenesis.

A sandwich ELISA based on anti-apo(a) and anti-apo B monoclonal antibodies for lipoprotein(a) measurement

Lipoprotein(a) (Lp(a)) is one of the most important independent risk factors for the prediction of premature atherosclerosis. Lp(a) is a low-density lipoprotein (LDL)-like particle which contains a glycoprotein (apoprotein(a)) disulfide linked to apo B-100. We describe a sandwich ELISA based on an anti-apo(a) monoclonal antibody (MAb) and an anti-apo B MAb for the quantitative determination of Lp(a) in human serum. The assay is sensitive, precise and specific. Samples with different apo(a) isoforms had a linear response in a range of 3-70 mg/dl of Lp(a). Correlations between the ELISA and a commercial ELISA, an immunoradiometric assay and electroimmunodiffusion were 0.92, 0.96 and 0.98, respectively. The frequency distribution of Lp(a) concentration in blood donors showed the skew toward the right reported in other populations. Patients with angiographically assessed coronary atherosclerosis had three times higher levels of Lp(a) than those with no signs of coronary atherosclerosis.

A particle concentration fluorescence immunoassay for Lp(a)

The quantitation of Lp(a) by immunoassay presents a major technical problem, because the molecular mass of the (a) protein of Lp(a) can vary between 419,000 and 838,000 Da (Gaubatz et al. (1990) J. Lipid Res. 31, 603-612), and this variability is determined by at least 24 alleles of the (a) gene. In an attempt to overcome this problem, we have developed an assay that is independent of variation of the size of (a). The assay utilizes a mixture of monoclonal antibodies to (a) which do not react to plasminogen or to apolipoprotein (apo) B. These antibodies are bound to inert microscopic beads to capture the Lp(a) particles. Subsequently, a fluorescein-labeled monoclonal antibody to apo B is used for detection and quantitation. The assay is done with special microtiter plates containing filters so that the particles can be thoroughly washed after capture on the microbeads. Because Lp(a) particles contain only one apo B particle and the molecular weight of apo B is constant, the assay is not affected by variation in the size of apo(a). By binding the mixture of monoclonal antibodies to inert beads, it is possible to greatly increase the amount of antibody bound to an exposed surface and thus increase the sensitivity of the assay. A mixture of monoclonal antibodies can be used to increase the affinity of the capture step of the assay. The assay can be completed in 4 h and has a wide working range.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological variation of lipoprotein(a) in a diabetic population. Analysis of the causes and clinical implications

The aims of the present study were to evaluate the biological variability of lipoprotein(a) (Lp(a)) in diabetic patients and to investigate the biological sources of this variability. Lp(a) was measured by ELISA in four serum specimens collected in 3-month intervals from 70 patients. The other parameters analyzed were: total cholesterol, high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), triglycerides, glucose, HbA and albumin excretion rate. The overall biological within-subject variance (CVb) was 31.7%, and it was inversely correlated with Lp(a) serum levels. According to the initial ranges of Lp(a) serum levels (< 15, 15-30 and > 30 mg/dl) the CVb were 42.3%, 24.1% and 23.7%, respectively. In multivariate analysis the total intra-individual coefficient of variation (CVt) of triglycerides and the CVt of the albumin excretion rate (AER) were independently associated with the CVb of Lp(a) (R2 = 0.54). The intra-individual biological variation of Lp(a) produced a misclassification of 20% of diabetic patients for cardiovascular risk attributable to this lipoprotein. In conclusion, the higher biological variability of Lp(a) observed in diabetic patients suggests that a single determination could be inaccurate to assess the cardiovascular risk associated with this lipoprotein, at least in those patients in whom serum levels are near the cut-off considered as risk for cardiovascular disease (> 30 mg/dl). Finally, triglycerides and AER are the main factors influencing Lp(a) serum levels in the diabetic population.

Measurement of serum Lp(a) by COBAS MIRA using a latex immunoturbidimetric assay kit

We had an opportunity to test a reagent kit for serum lipoprotein (a) [Lp(a)] assay, which was based on the latex immunoturbidimetric assay method, and applied it to COBAS MIRA (Roche). Reproducibility of the assay procedure was 0.92-4.0% CV of three samples which contained 12.58-60.4 mg/dl of Lp(a). Minimum detectable concentration was 1.5-2.0 mg/dl. It was confirmed that interference of co-existing substances, i.e. hemoglobin, bilirubin, and intralipid, was negligible. No cross reactivity was seen with plasminogen. Correlation with a ELISA method was excellent. Frequency distribution of Lp(a) in healthy Japanese was similar to that found in white population.