Enzyme-linked immunosorbent assay of lipoprotein(a) in serum and cord blood

The ins and outs of lipoprotein(a) assay methods

Pathophysiological, epidemiological and genetic studies convincingly showed lipoprotein(a) (Lp(a)) to be a causal mediator of atherosclerotic cardiovascular disease (ASCVD). This happens through a myriad of mechanisms including activation of innate immune cells, endothelial cells as well as platelets. Although these certainties whether or not Lp(a) is ready for prime-time clinical use remain debated. Thus, remit of the present review is to provide an overview of different methods that have been employed for the measurement of Lp(a). The methods include dynamic light scattering, multi-angle light scattering analysis, near-field imaging, sedimentation, gel filtration, and electron microscopy. The development of multiple Lp(a) detection methods is vital for improved prediction of ASCVD risk.

Plasma oxidized lipoprotein(a) and its immune complexes are present in newborns and children

BACKGROUND

Oxidized Lp(a) [ox-Lp(a)] has been reported to play more potent roles than native Lp(a) in atherosclerosis. We investigated the distribution characteristics of plasma ox-Lp(a) and Lp(a) immune complex [Lp(a)-IC] levels in newborns and children.

METHODS

Plasma ox-Lp(a) and Lp(a)-IC levels were measured in 747 children and 30 cord blood by ELISAs.

RESULTS

The mean levels of Lp(a), ox-Lp(a) and Lp(a)-IC were much lower in newborns than in children (P<0.001), and increased rapidly to that in children after birth. The distributions of Lp(a), ox-Lp(a) and Lp(a)-IC were skewed toward low values in children, no difference of their levels was found in each of the 13year groups. The levels of ox-Lp(a) correlated positively with total and LDL cholesterol, Lp(a) and Lp(a)-IC; Lp(a)-IC correlated positively with sex, total and LDL cholesterol, Lp(a) and ox-Lp(a), respectively. Multiple linear regression analysis showed Lp(a) and Lp(a)-IC accounted for 42% of the variation in ox-Lp(a) levels, and ox-Lp(a) accounted for 30% of that in Lp(a)-IC.

CONCLUSIONS

The fact that ox-Lp(a) and Lp(a)-IC are present in newborns and children suggests that oxidized lipoproteins play an initiating role in atherosclerotic process.

Lipoprotein (a) and Stroke

Background and Purpose— The relationship between elevated lipoprotein (a) levels[Lp(a)] and stroke is controversial. We systematically reviewed the literature to determine whether Lp(a) is a risk factor for stroke.

Methods— We searched MEDLINE (1966 to 2006), EMBASE (1974 to 2006), and Google scholar for articles on Lp(a) and cerebrovascular disease. From potentially relevant references retrieved, we excluded uncontrolled studies, studies of children with stroke, studies investigating carotid atherosclerosis, and studies lacking adequate data.

Results— Thirty-one studies comprising 56 010 subjects with >4609 stroke events met all inclusion criteria and were included in the meta-analysis. In case-control studies (n=23 with 2600 strokes) unadjusted mean Lp(a) was higher in stroke patients (standardized mean difference, 0.39; 95% CI, 0.23 to 0.54) and was more frequently abnormally elevated (OR, 2.39; 95% CI, 1.57 to 3.63). Sensitivity analysis and meta-regression did not find any influence of study design, measurement period of Lp(a) in relationship to stroke episode, subtype, age, and sex to explain the substantial heterogeneity between studies (I 2 =83.7%; P <0.001). There was no evidence of publication bias. In nested case-control studies (n=3 with 364 strokes) Lp(a) was not a risk factor for incident stroke (OR, 1.04; 95% CI, 0.6 to 1.8). In prospective cohort studies (n=5 with >1645 strokes), incident stroke was more frequent in patients in the highest tertile of Lp(a) distribution compared with the lowest tertile of Lp(a) (RR, 1.22; 95% CI, 1.04 to 1.43). There was no publication bias or heterogeneity in the prospective studies (I 2 =0.00%; P =0.67).

Conclusion— This meta-analysis suggests that elevated Lp(a) is a risk factor for incident stroke.

Cardiovascular risk factor profiles and endothelial function in coronary artery disease patients treated with statins

Although endothelial dysfunction is associated with cardiovascular risk factors and is improved by cholesterol-lowering therapy, the relationship between endothelial function and cardiovascular risk factor profiles has not been fully investigated in coronary artery disease patients who have been treated with statins. We investigated endothelial function in male hypercholesterolemic patients (n=53) who underwent statin therapy over 6 months in a cross-sectional study. Patients were classified into three groups based on the results of coronary angiography: a normal coronary artery group (n=15), an angina pectoris group (n=20) and a myocardial infarction group (n=18). Endothelial function was assessed by measuring flow-mediated dilatation after reactive hyperemia in the brachial artery, and serum lipid, lipoprotein (a), glucose and insulin levels were measured. Significant associations were observed between the status of coronary disease and systolic blood pressure, lipoprotein (a), glucose and insulin levels (p <0.05, respectively), and the levels of these risk factors in the myocardial infarction group were higher than those in the other groups. Flow-mediated dilatation was also associated with the status of coronary disease (p <0.05), and the myocardial infarction group showed the lowest levels of flow-mediated dilatation (p <0.05). Flow-mediated dilatation was negatively correlated with systolic and diastolic blood pressures, serum levels of lipoprotein (a), glucose and insulin, and the status of coronary disease. Stepwise multiple regression analysis also revealed that lipoprotein (a), diastolic blood pressure and the status of myocardial infarction were significantly correlated with impaired vasodilatation. Serum lipids, age and smoking habit were independent of flow-mediated dilatation. In conclusion, even after cholesterol-lowering treatment, male patients with myocardial infarction still had endothelial dysfunction, and higher levels of lipoprotein (a) may be associated with endothelial dysfunction in such patients.

Association Between Plasma Lipoprotein(a) Concentration and Restenosis After Stent Implantation

BACKGROUND

The plasma concentration of lipoprotein (a) [Lp(a)] is associated with atherosclerotic and thrombotic vascular diseases. The aim of the present study was to evaluate the association between plasma Lp(a) concentration and in-stent restenosis.

METHODS AND RESULTS

One hundred and 9 patients with successful elective coronary stent implantation underwent follow-up angiography at 24+/-6 weeks. Restenosis after stent implantation occurred in 38 patients. Univariate analysis showed that the reference diameter of the lesion was smaller in the restenosis group (2.93+/-0.29 mm) than in the no-restenosis group (3.21+/-0.43 mm) (p < 0.05). The lesion was longer in the restenosis group (14.2+/-5.3 mm) than in the no-restenosis group (11.6+/-4.9 mm) (p < 0.05). Plasma Lp(a) concentrations in the restenosis group (30.5+/-23.9 mg/dl) were higher than in the no-restenosis group (16.9+/-11.1 mg/dl) (p < 0.01). Other lipid concentrations were similar in both groups. Among the plasma Lp(a) concentrations, the rate of restenosis (71.4%) in the high Lp(a) group (> 40 mg/dl) (n = 14) was greater compared with the other groups: 33.3% in the intermediate Lp(a) group (10-40 mg/dl) (n = 54), and 24.4% in the low Lp(a) group (< 10 mg/dl) (n = 41) (p < 0.01). The late loss (0.57+/-0.53 mm) in the low Lp(a) group was significantly less than the other groups: 0.88+/-0.47 mm in the intermediate Lp(a) group, and 1.08+/-0.56 mm in the high Lp(a) group (p < 0.05). In a multivariate regression model, plasma Lp(a) concentration remained significant as an independent predictor of restenosis in patients undergoing stent implantation (p = 0.020 odds ratio (OR) 1.37 95%conficence interval (CI) 1.050-1.793), although the reference diameter (p = 0.025 OR 0.23 95%CI 0.061-0.830) and lesion length (p = 0.021 OR 1.12 95%CI 1.017-1.232) were related to stent restenosis.

CONCLUSIONS

Plasma Lp(a) concentration is an independent predictor of stent restenosis.

Serum high-density lipoprotein-cholesterol levels modify the association between plasma levels of oxidatively modified low-density lipoprotein and coronary artery disease in men

We investigated the association among plasma levels of oxidatively modified low-density lipoprotein (Ox-LDL), high-density lipoprotein-cholesterol (HDL-C), and the prevalence of coronary artery disease (CAD) in a case-control study. Cases (n = 183, male [M]/female [F]:138/45, age: 64.9 +/- 10.6 years) were defined as patients with angiographically proven coronary atherosclerosis (>/=50% stenosis) and controls were subjects with normal coronary arteries (n = 74, M/F:36/38, age: 57.6 +/- 14.4 years). Plasma Ox-LDL levels were measured by a sensitive detection method using the monoclonal antibody DLH3. In women, both Ox-LDL and lipid variables were similar between cases and controls. In men, cases had significantly lower (P <.05) levels of HDL-C (39.1 +/- 10.3 v 42.8 +/- 10.9 mg/dL) and apolipoprotein (apo) A-I than controls, while the difference in Ox-LDL between cases and controls was not significant (1.05 +/- 0.79 and 0.83 +/- 0.65 ng/10 microg LDL protein, respectively). However, HDL-C levels interacted with the association between Ox-LDL levels and CAD in males: increased Ox-LDL levels were significantly associated with CAD after controlling for age when HDL-C levels were high, but were not associated with CAD when HDL-C levels were low, as assessed by a multiple logistic regression analysis. In addition, the combination of HDL-C and Ox-LDL levels was a better indicator for CAD in males than HDL-C levels alone (-2 log likelihood, 24.1 v 19.4) after controlling for age and conventional risk factors of CAD, while Ox-LDL levels were not significantly associated with CAD. HDL-C levels interact with the association between plasma Ox-LDL levels and CAD in men, and increased Ox-LDL levels are an indicator of CAD in male subjects with high HDL-C levels.

The associations among thoracic aortic atherosclerosis, coronary atherosclerosis and the function of high density lipoprotein

We sought to determine the associations among thoracic aortic atherosclerosis, coronary atherosclerosis and the function of high density lipoprotein (HDL) in a case-control study. The function of HDL can be assessed by the fractional esterification rate of cholesterol in low density lipoprotein (LDL)- and very low density lipoprotein (VLDL)-depleted plasma (FER(HDL)), which reflects a balance of cholesterol uptake by HDL and cholesterol ester (CE) transport in the reverse cholesterol transport (RCT) system in humans. Cases (n=51, age: 64.3+/-8.0 years) and controls (n=51, age: 58.7+/-13.1 years) were defined as subjects with/without angiographically proven coronary artery disease (CAD), respectively and examined for thoracic aortic atherosclerosis (TAA) by transesophageal echocardiography. The severity of TAA was determined by the ratio of average sclerotic areas (ASA) and average sclerotic lengths (ASL). The cases had significantly (P<0.05) higher values of ASA (0.22+/-0.18 vs. 0.10+/-0.11), ASL (0.82+/-0.56 vs. 0.48+/-0.45), ASA/ASL ratio (0.23+/-0.08 vs. 0.17+/-0.09) and FER(HDL) (10.3+/-3.8 vs. 8.3+/-3.5% per hour) and lower HDL-C and apolipoprotein A-I levels than the controls. A receiver operating characteristic (ROC) curve analysis showed that ASA/ASL and FER(HDL) had moderate discriminating ability for CAD and the diagnostic accuracy of ASA/ASL was better than that of FER(HDL) (area under ROC curve: 0.703 and 0.656, respectively). Multivariate logistic regression analysis indicated that ASA/ASL and FER(HDL) were independent indicators for CAD [odds ratio (95% CI): 7.5 (2.4-27), P<0.01 and 4.0 (1.2-15), P<0.05] after adjusting for age, gender and other conventional risk factors, and that a high FER(HDL) value greatly increased the relative risk of CAD associated with a high ASA/ASL. The function of HDL, as assessed by FER(HDL), enhances the ability of TAA to predict CAD.

The significance of atherogenic indices in patients on hemodialysis

Atherosclerotic diseases (ASD) are the major cause of mortality and morbidity in patients on hemodialysis (HD). To evaluate the significance and usefulness of atherogenic indices, we examined lipoprotein(a) (Lp(a)), remnant-like particles cholesterol (RLP.C), homocysteine (Hcy), cardiac troponin T (TnT), and ankle-arm blood pressure index (AABI) in 114 patients on HD (male 79, female 35; age 62.1 +/- 1.3 years). As a result, serum cardiac TnT and AABI levels in patients with diabetes mellitus (DM) (n = 33) were significantly higher than those in patients without DM (n = 81). In patients with cerebrovascular diseases (CVD), serum levels of both RLP.C and Hcy, and AABI levels were significantly higher than those in patients without CVD. In patients with coronary artery diseases (CAD), serum cardiac TnT and AABI levels were significantly higher than those in patients without CAD. In patients with peripheral vascular diseases (PVD), serum levels of both Hcy and cardiac TnT were significantly higher than those in patients without PVD. Multiple regression analysis did show that the presence of DM, serum Hcy levels and age were independent factors as- sociated with ASD: ASD = -0.348 + 0.426 x DM (scored: 0, absence; 1, presence) + 0.005 x Hcy (nmol/ml) + 0. 010 x Age (years) (p < 0.001). In conclusion, the presence of DM and advanced age are major determinants for atherosclerosis. In addition, serum Hcy levels are independent risk factors for atherosclerosis irrespective of the absence of DM.

Associations among serum lipoprotein(a) levels, apolipoprotein(a) phenotypes, and myocardial infarction in patients with extremely low and high levels of serum lipoprotein(a)

A high serum lipoprotein(a) [Lp(a)] level, which is genetically determined by apolipoprotein(a) [apo(a)] size polymorphism, is an independent risk factor for coronary atherosclerosis. However, the associations among Lp(a) levels, apo(a) phenotypes, and myocardial infarction (MI) have not been studied. Patients with MI (cases, n = 101, M/F: 86/15, age: 62+/-10y) and control subjects (n = 92, M/F: 53/39, age: 58+/-14y) were classified into quintile groups (Groups I to V) according to Lp(a) levels. Apo(a) isoform phenotyping was performed by a sensitive, high-resolution technique using sodium dodecyl sulfate-agarose/gradient polyacrylamide gel electrophoresis (3-6%), which identified 26 different apo(a) phenotypes, including a null type. Groups with higher Lp(a) levels (Groups II, III, and V) had higher percentages of MI patients than that with the lowest Lp(a) levels (Group I) (54%, 56%, or 75% vs. 32%, p<0.05). Groups with different Lp(a) levels had different frequency distributions of apo(a) isoprotein phenotypes: Groups II, III, IV, and V, which had increasing Lp(a) levels, had increasingly higher percentages of smaller isoforms (A1-A4, A5-A9) and decreasingly lower percentages of large isoforms (A10-A20, A21-A25) compared to Group I. An apparent inverse relationship existed between Lp(a) and the apo(a) phenotype. Subjects with the highest Lp(a) levels (Group V) had significantly (p<0.05) higher serum levels of total cholesterol, apo B, and Lp(a). Patients with MI and the controls had different distributions of apo(a) phenotypes: i.e., more small isoforms and more large size isoforms, respectively (A1-A4/A5-A9/A10-A20/A21-A25: 35.7%/27.7%/20.8%/15.8% and 22.8%/23.9%/29.4%/23.9%, respectively). Lp(a) (parameter estimate +/- standard error: 0.70+/-0.20, Wald chi2 = 12.4, p = 0.0004), apo(a) phenotype (-0.43+/-0.15, Wald chi2 = 8.17, p = 0.004), High-density lipoprotein-cholesterol, apo A-I, and apo B were significantly associated with MI after adjusting for age, gender, and conventional risk factors, as assessed by a univariate logistic regression analysis. The association between Lp(a) and MI was independent of the apo(a) phenotype, but the association between the apo(a) phenotype and MI was not independent of Lp(a), as assessed by a multivariate logistic regression analysis. This association was not influenced by other MI- or Lp(a)-related lipid variables. These results suggest that apo(a) phenotype contributes to, but does not completely explain, the increased Lp(a) levels in MI. A stepwise logistic regression analysis with and without Lp(a) in the model identified Lp(a) and the apo(a) phenotype as significant predictors for MI, respectively.

Quantity and function of high density lipoprotein as an indicator of coronary atherosclerosis

OBJECTIVES

To examine the association between the fractional esterification rate of cholesterol (C) in low density lipoprotein- and very low density lipoprotein-depleted plasma (FER(HDL)) and coronary artery disease (CAD) and the influence of serum HDL-C levels.

BACKGROUND

The function of HDL in reverse cholesterol transport is involved in the antiatherogenic action of HDL, and FER(HDL) is a newly established quantitative measure of HDL function in vivo.

METHODS

Cases (n = 185, F/M: 43/142) and controls (n = 74, F/M:27/47) were defined as subjects with/without angiographically proven CAD, respectively.

RESULTS

The cases had significantly (p < 0.05) higher FER(HDL) values (13.2+/-0.3 %/h vs. 12.1+/-0.5 %/h) and lower HDL-C levels (39.0+/-1.0 mg/dL vs. 46.8+/-1.4 mg/dL) than the controls. The associations of FER(HDL) and HDL-C with CAD were linear and significant (p < 0.05). Multiple logistic regression analysis indicated that the association of FER(HDL) with CAD varied with the HDL-C level: significant for the low HDL-C tertile (chi-square = 6.20, p < 0.05) but not significant for the middle and high HDL-C tertiles (chi-square = 0.08 and 0.03, n.s.). The risk of CAD, relative to that in patients with low FER(HDL) and high HDL-C, was higher in patients with low FER(HDL) and low HDL-C (odds ratio [95% confidence interval]: 2.37 [1.12-4.97], p < 0.05) and was highest in patients with high FER(HDL) and low HDL-C (3.85 [1.84-8.06], p < 0.01).

CONCLUSIONS

The functional assay of HDL (FER(HDL)) is an independent risk factor for CAD. The combination of FER(HDL) and HDL-C could be a potent indicator for CAD, and may reflect a potential mechanism of atherosclerosis.

Stimulatory effects of lipoprotein(a) and low-density lipoprotein on human umbilical vein endothelial cell migration and proliferation are partially mediated by fibroblast growth factor-2

We previously reported a transient increase in plasma lipoprotein(a) (Lp(a)) concentrations following acute myocardial infarction and surgical operations, and demonstrated Lp(a) accumulation in healing tissues. In the present study, the stimulatory effect of Lp(a) on migration and proliferation of human umbilical vein endothelial cells (HUVEC) was assessed by quantitative assay methods and compared it with that of LDL. Lp(a) stimulated both migration and proliferation of HUVEC in a dose-dependent manner and the stimulatory activities for migration and proliferation were two times higher than those of LDL in terms of moles of apoB. In addition, this stimulatory activity of Lp(a) was not affected by the difference of Lp(a) phenotype. Although each neutralizing antibody to hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF) and interleukin-1beta (IL-1beta) had no further effect on migration and proliferation of HUVEC treated with Lp(a), only antibody to fibroblast growth factor-2 (FGF-2) partially suppressed them. Moreover, pertussis toxin, which inhibits FGF-2-stimulated endothelial cell movement, also partially suppressed Lp(a)-induced HUVEC migration. FGF-2 concentrations in the medium of HUVEC treated with Lp(a) were constant in spite of the increase in FGF-2 mRNA levels in HUVEC. Taken together, it is suggest that Lp(a) stimulates HUVEC migration and proliferation, which is mediated, at least in part, by FGF-2 and may promote the angiogenesis during wound healing.

Immunolocalization of lipoprotein(a) in wounded tissues

Fifty samples from inflamed tissues were examined by immunohistochemical techniques, using antibodies against apo(a), apo B, plasminogen, fibrinogen, proliferating cell nuclear antigen (PCNA), and various components of extracellular matrix. The immunohistochemical features of granulation tissues were characterized by different stages of wound healing. In the first stage, immunoreactivities for anti-apo(a) and anti-apo B were weak and focal, whereas those for anti-plasminogen and anti-fibrinogen were strong and were widespread on the tissue surface. In the second stage, granulation tissues were covered with loose fibrous connective tissue, designated as a "fibrous cap." In this stage, markedly positive staining for lipoprotein(a) [Lp(a)] was observed closer to the surface of the fibrous cap than plasminogen, suggesting that Lp(a) may prevent external fibrinolysis. Lp(a) was also found in endothelial cells and the extracellular space of small vessels underlying the fibrous cap. In the last stage of healing, apo(a) and apo B were not detectable in completely organized tissues. These findings suggest that Lp(a) plays a role in the wound healing.

Preventive effects of probucol on restenosis after percutaneous transluminal coronary angioplasty

This protocol was performed to elucidate the preventive effects of probucol on restenosis after percutaneous transluminal coronary angioplasty (PTCA). A total of 118 patients with 134 vessels undergoing successful PTCA was randomly and prospectively assigned to the probucol group (group P) or the control group (group C). The subjects consisted of 91 men and 27 women, with a mean age of 63.4 +/- 2.3 years. Sixty-six vessels of 59 patients in group P and 68 vessels of 59 patients in group C were evaluated by coronary angiography at 3 months after PTCA. Probucol (0.5 mg/day) was administered between >7 days before PTCA and 3 months after PTCA. The serum total cholesterol (TC) level and the formula low-density lipoprotein cholesterol (formula LDL-C) in group P decreased from 203.8 +/- 43.1 to 169.6 +/- 39.4 mg/dl and from 131.4 +/- 0.7 to 108.7 +/- 2.5 mg/dl, whereas in group C, the levels decreased only from 202.3 +/- 32.1 to 194.2 +/- 29.8 mg/dl and from 129.2 +/- 38.1 to 124.3 +/- 31.7 mg/dl, respectively. The restenosis rate was significantly lower in group P (19.7%; 13 of 66 vessels) than in group C (39.7%; 27 of 68 vessels; p < 0.05). In group P, the probucol blood concentration was significantly higher in the subjects without restenosis (31 +/- 9 microg/ml) than in those with restenosis (18 +/- 8 microg/ml; p < 0.01), but the serum TC and formula LDL-C levels were not significantly different between these two groups. In summary, long-term administration of probucol significantly reduces the incidence of restenosis after PTCA. it was suggested that the mechanism of this preventive effect was not reducing the serum TC or formula LDL-C levels, but rather an inhibitory action on smooth muscle cell proliferation.

Evaluation of the coagulation and fibrinolytic systems in men with intermittent claudication

The authors evaluated elements of the coagulation and fibrinolytic systems in 18 male patients with intermittent claudication vs 19 men matched for risk factors who served as controls. Prothrombin time and activated partial thromboplastin time did not significantly differ in the patients and the controls. The plasminogen level in the two groups was not significantly different. The level of lipoprotein(a) was significantly higher in the patients than in the controls. The levels of antigen and the activity of protein C did not differ significantly between the two groups. The thrombomodulin level was significantly higher in the patients than in the controls. There were no significant differences between the two groups in the levels of alpha 2-macroglobulin, C1-inactivator, or antithrombin III. The levels of fibrinogen and alpha 1-antitrypsin were significantly higher in the patients vs the controls. Significantly lower levels of alpha 2-plasmin inhibitor and higher levels of alpha 2-plasmin inhibitor/plasmin complex and thrombin/antithrombin III complex were found in the patients vs the controls. These findings suggest that the levels of thrombin/antithrombin III complex, alpha 2-plasmin inhibitor/plasmin complex, and thrombomodulin may perhaps serve as indicators for injury to the peripheral endothelium and that the coagulation and fibrinolytic systems may be activated in patients with intermittent claudication.

The long-term effect of eicosapentaenoic acid on serum levels of lipoprotein (a) and lipids in patients with vascular disease

The effects of eicosapentaenoic acid (EPA) on serum lipoprotein (a) (Lp(a)) and other lipid levels in patients with vascular disease were examined. The serum levels of Lp(a), total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL) were measured in 24 patients with vascular disease. An elevated serum Lp(a) level (39 +/- 22 mg/dl) was noted in 9 patients, elevated total cholesterol level (263 +/- 31 mg/dl) in 12 patients, elevated triglyceride level (240 +/- 98 mg/dl) in 10 patients and elevated LDL level (651 +/- 88 mg/dl) in 6 patients before administration of EPA. EPA (1,800 mg/day) was given to these patients for long periods ranging from 6 to 24 months. The serum levels of Lp(a), TC, TG and LDL were lowered significantly (p < 0.05) after EPA administration for 12 and 18 months, for 6, 12, 18 and 24 months, for 18 months and for 12 and 18 months, respectively. These findings indicated that long-term administration of EPA may lower Lp(a) and serum lipids, which is beneficial for patients with various arterial diseases in terms of preventing progression of the disease.

Serum lipoprotein(a) concentrations and apolipoprotein(a) phenotypes in the families of NIDDM patients

We studied the quantitative and qualitative characteristics of lipoprotein(a) [Lp(a)] as a function of apolipoprotein(a) [apo(a)] phenotype in 87 members (42 males, 45 females) of 20 diabetic families, 26 of whom were diagnosed with non-insulin-dependent diabetes mellitus (NIDDM) with moderate glycaemic control (HbA1c 7.1 +/- 1.2%). Apo(a) phenotyping was performed by a sensitive, high-resolution technique using SDS-agarose/gradient PAGE (3-6%). To date, 26 different apo(a) phenotypes, including a null type, have been identified. Serum Lp(a) levels of NIDDM patients and non-diabetic members of the same family who had the same apo(a) phenotypes were compared, while case control subjects were chosen from high-Lp(a) non-diabetic and low-Lp(a) nondiabetic groups with the same apo(a) phenotypes in the same family. Serum Lp(a) levels were significantly higher in NIDDM patients than in non-diabetic subjects (39.8 +/- 33.3 vs 22.3 +/- 19.5 mg/dl, p < 0.05). The difference in the mean Lp(a) level between the diabetic and non-diabetic groups was significantly (p < 0.05) greater than that between the high-Lp(a) non-diabetic and low-Lp(a) non-diabetic groups. An analysis of covariance and a least square means comparison indicated that the regression line between serum Lp(a) levels [log Lp(a)] and apo(a) phenotypes in the diabetic patient group was significantly (p < 0.01) elevated for each apo(a) phenotype, compared to the regression line of the control group. These data together with our previous findings that serum Lp(a) levels are genetically controlled by apo(a) phenotypes, suggest that Lp(a) levels in diabetic patients are not regulated by smaller apo(a) isoforms, and that serum Lp(a) levels are greater in diabetic patients than in non-diabetic family members, even when they share the same apo(a) phenotypes.

A new case of apoA-I deficiency showing codon 8 nonsense mutation of the apoA-I gene without evidence of coronary heart disease

We report a 39-year-old Japanese man with HDL and apoA-I deficiency as well as data from members of his family. Corneal opacity and a stomatocyte were found but not tonsillar hypertrophy, xanthomas, or splenomegaly. His serum HDL cholesterol, apoA-I, apoA-II, and LDL cholesterol levels were t mg/dL, < 3 mg/dL, 6 mg/dL, and 175 mg/dL, respectively. Plasma triglyceride, phospholipid, apoB, apoC-III, and apoE levels were all within normal limits. Lecithin:cholesterol acyltransferase activity was half of normal, while lipoprotein lipase and hepatic triglyceride lipase activities were within normal limits. ApoA-I deficiency was confirmed by combined isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by an immunoblotting method. We surveyed the apoA-I gene of the patient and five of his family members by direct sequencing after amplification by polymerase chain reaction and found a codon 8 nonsense mutation (TGG --> TAG, Trp --> stop) in exon 3 of the apoA-I gene. The results of a pedigree analysis by DNA sequencing and restricted fragment length polymorphism (Sty I) were consistent with an autosomal codominant trait. Coronary angiography was performed to evaluate coronary atherosclerosis, but no significant luminal narrowing was detected. An intracoronary ultrasound study showed mild intimal hyperplasia in segment 6. In summary, this is a case of apoA-I deficiency without evidence of coronary heart disease.

Time-resolved immunofluorometric assay for the quantification of lipoprotein(a) in serum

Although two recent studies have failed to reveal lipoprotein(a) (LP(a)) serum concentrations > 300 mg/l to be an independent risk factor for early onset of atherosclerosis, Lp(a) serum concentrations are frequently measured to evaluate the additional risk of coronary heart disease. We describe a time-resolved immunofluorometric assay (TRIFMA) for quantifying Lp(a) levels in humans serum using commercially available reagents, which is rapid, robust and simple to perform. The two-site immunometric assay was based on microtitre plates as solid phase coated with a polycloncal anti Lp(a) antibody. The liquid-phase antibody was labelled with biotin and detected by europium labelled streptavidin in the DELFIA 1232 fluorometer. The measuring range was 2-1600 mg/l. The intra-assay imprecision was < 7% (CV), the inter-assay imprecision < 12% (CV). No interference was detected with plasminogen concentration up to 2.2 g/l. There was an acceptable correlation with a commercially available enzyme immunoassay (r = 0.95) and with electroimmunodiffusion (r = 0.85) on 100 routine serum samples measured. The assay appeared to detect different Lp(a) isoforms as dilution curves were parallel for B/F, S2 and S4 isoforms.

Measurement of Lp(a) with a two-step monoclonal competitive sandwich ELISA method

OBJECTIVE

To evaluate the results of Lipoprotein (a)[Lp(a)] measurements by a competitive two-step monoclonal enzyme-linked immuno sorbent assay method comparing them with those by a conventional ELISA.

METHODS

Serum having various isoforms of Lp(a) and purified Lp(a) were assayed using the method described here and commercially available kits. The reference range was determined with the use of 324 normal subjects by means of calculation from Lp(a) results of logarithmic transformation.

RESULTS

Our method takes advantage of a competitive reaction between fixed antibody and free antibody to Lp(a), having the detection range up to 1000 mg/L with the lowest detection limit of 2 mg/L. The anti-Lp(a) monoclonal antibody employed in the assay system reacts uniformly with all phenotypes of Lp(a) but showing very low cross-reactivity for plasminogen and LDL. Within-run and between-run precisions were excellent, giving CVs of 2.9 and 4.0% with mean values of 145 and 635 mg/L, respectively. In comparison of the results by our method with those by a polyclonal method (Biopool) or a monoclonal antibody method (Terumo), they correlated well; Y (our method) = 0.99 x (polyclonal method, Biopool) - 1.9, r = 0.994 (n = 60), and Y = 0.94 X(monoclonal method, Terumo) -9.8, r = 0.97 (n = 60), respectively. The reference range was 105.9 +/- 25.4 mg/L, the difference between the sexes was not significant.

CONCLUSION

Our method has proven highly accurate and specific. It is applicable with auto analyzer because it does not require such a pre-dilution step as is necessary for Lp(a) determination by conventional ELISA assay. Accordingly, we can conclude that our test method is workable for both clinical laboratories and mass screening.

Comparison of a new immunoturbidometric assay of human serum lipoprotein (a) to the ELISA and the IRMA methods

In the present work we have tested a new immunoturbidometric (IT) lipoprotein(a) (Lp(a)) assay and compared it with two other Lp(a) assay systems (IRMA and ELISA) commonly used in clinical chemistry laboratories. In addition, we have examined the effects of long-term storage and plasminogen on the results of Lp(a). Intra-assay and inter-assay coefficients of variation of the IT method were from 1.6 to 5.5% and from 2.8 to 10.7% depending on the concentration of Lp(a). The correlations between methods were 0.957 (IRMA vs. IT), 0.969 (IRMA vs. ELISA) and 0.956 (IT vs. ELISA) and the regression curves were IRMA = 1.07*IT + 11, IRMA = 1.84*ELISA + 2 and IT = 1.62*ELISA + 17, respectively. Storage of the samples for 5 years at -70 degrees C did not affect serum Lp(a) levels. There was a slight increasing effect of high concentrations of plasminogen on the Lp(a) results, but on physiological serum levels of plasminogen the effect was not significant. We conclude that the IT method provides a simple way to screen serum Lp(a) levels.

Increased concentrations of serum Lp(a) lipoprotein in patients with primary gout

OBJECTIVES

To investigate if serum Lp(a) lipoprotein (Lp(a)), a risk factor for atherosclerotic diseases, increases in patients with gout, who frequently also have atherosclerotic disease.

METHODS

Fasting blood samples were taken for measurement of Lp(a) and other variables in 175 male patients with primary gout. Serum concentrations of Lp(a) were measured by enzyme linked immunosorbent assay. The median value and frequency distribution of Lp(a) in gout patients were compared with those in 172 control male subjects. In addition, we examined the effect of niceritorol on serum Lp(a) values in gout patients in whom the Lp(a) concentration was greater than 20 mg/dl.

RESULTS

Serum Lp(a) was significantly higher in patients with gout than control subjects (median 15.5 mg/dl upsilon 8.6 mg/dl; p < 0.01). The frequency distribution of Lp(a) in gout was significantly shifted towards greater concentrations compared with control, although skewed distribution was noted in both groups. Serum Lp(a) concentration was not related to age, body mass index, alcohol intake, creatinine, fasting blood sugar or uric acid in patients with gout. Niceritorol decreased the serum concentrations of Lp(a) in gout.

CONCLUSIONS

These observations suggest that serum Lp(a) concentrations are increased in patients with gout and may play a role as one of the risk factors for atherosclerotic diseases in gout. Niceritorol seems effective in decreasing high levels of Lp(a) in patients with gout without detrimental influence on serum uric acid concentration.

Prevention of restenosis after percutaneous transluminal coronary angioplasty by reducing lipoprotein (a) levels with low-density lipoprotein apheresis. Low-Density Lipoprotein Apheresis Angioplasty Restenosis Trial (L-ART) Group

This study was designed to test the hypothesis that high plasma lipoprotein (a) (Lp[a]) levels are associated with an increase incidence of restenosis after angioplasty. Elective transluminal coronary angioplasty was performed in 66 patients (58 men and 8 women) aged 57 +/- 9 years (mean +/- SD). Two days before and 5 days after angioplasty, all patients underwent low-density lipoprotein (LDL) apheresis with a dextran sulfate cellulose column as an Lp(a) absorbent; 39 patients also received 10 mg of pravastatin and 1,500 mg of niacin daily. Restenosis was defined as a recurrent luminal stenosis of > or = 50% in a previously dilated segment. Median Lp(a) levels were reduced from 23.3 mg/dl before apheresis to 10.9 mg/dl after apheresis (p < 0.0001). Angiography performed 2 to 9 months after angioplasty revealed restenosis in at least 1 site in 38% of the 137 control patients and in 32% of the 66 patients who underwent apheresis. Restenosis also occurred in 37% of the patients who underwent apheresis alone and in 28% of the patients who also received pravastatin and niacin in combination with LDL apheresis. The restenosis rate was 21% in the 42 patients whose Lp(a) levels were significantly reduced > or = 50%, and in 50% of the 24 patients whose Lp(a) levels were significantly reduced < 50% (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Fully mechanized latex immunoassay for serum lipoprotein(a)

We have developed a fully automated system to quantify lipoprotein(a) (Lp(a)) in human serum, based on the latex-enhanced turbidimetric immunoassay by application of the Immuno Chemistry Analyzer 501X. This assay was carried out with undiluted serum and was able to detect at Lp(a) levels higher than 4.0 mg/l. When judged to be out of range of the calibration (> 600 mg/l), the sample was automatically re-tested after automatic 10-fold dilution. Within-run C.V.s ranged from 1.9 to 2.1% and between-run C.V.s from 2.7 to 3.9%. Results by the present method were in good agreement with those by the in-house ELISA (r = 0.978) and the commercial ELISA (r = 0.990). The distribution of Lp(a) levels in sera from 508 healthy donors was highly skewed; the mean and median were 158 mg/l and 105 mg/l, respectively.

Lipoprotein(a) and ischemic cerebrovascular disease in young adults

BACKGROUND AND PURPOSE

Serum lipoprotein(a) level is genetically determined and remains almost constant throughout life. Based on this property, we investigated the serum lipoprotein(a) levels of ischemic stroke patients in the chronic stage (mean period after stroke, 27 months) and its relation to the types of ischemic stroke.

METHODS

We measured serum lipoprotein(a) levels in 101 patients with chronic ischemic stroke and 37 normal control subjects, taking the clinical profiles into consideration.

RESULTS

Lipoprotein(a) levels in patients with atherothrombotic stroke were 28.0 +/- 19.6 mg/dL (mean +/- SD), which were significantly (P < .01) higher than those in patients with lacunar stroke and in normal control subjects (16.4 +/- 13.5 and 11.7 +/- 10.5 mg/dL, respectively). The lipoprotein(a) levels in patients with atherothrombotic stroke were significantly higher in the subgroup who were a younger age at onset: onset before age 50 years, 35.3 +/- 20.5; onset at age 50 to 59, 35.4 +/- 21.7; onset at age 60 to 69, 17.0 +/- 12.8; and onset at age 70 or older, 16.3 +/- 6.8 mg/dL (P < .01 for onset before age 50 versus 60 to 69 years or 70 years or older; P < .01 for onset at 50 to 59 years versus 60 to 69 years or 70 years or older). Serum lipoprotein(a) was significantly increased (40.2 +/- 20.1 mg/dL) in young adults with atherothrombotic stroke (onset at younger than age 45 years) compared with that in patients older than 45 years (P < .01).

CONCLUSIONS

We conclude that lipoprotein(a) is a genetic, independent, and critical risk factor for ischemic stroke, especially in young adults.

Serum insulin level versus blood pressure: a cross-sectional, case-controlled study in non-obese, middle-aged Japanese subjects with normal glucose tolerance

To assess the relationship between blood pressure (BP) and serum insulin level in non-obese (body mass index (BMI) < or = 27 kg m-2), middle-aged (40-64 years of age) Japanese subjects with normal glucose tolerance, a three-phase study protocol was designed. First, the responses of plasma glucose and serum insulin to an oral glucose load were compared between 40 patients with untreated essential hypertension and 40 age-, sex- and BMI-matched normotensive control subjects. Second, the glucose and insulin responses to an i.v. glucose load were evaluated in 7 non-obese hypertensive, 7 non-obese normotensive and 7 obese hypertensive subjects. Third, BP and serum lipid profile were compared between 21 hyperinsulinaemic (serum insulin level (while fasting, after glucose loading, or both) > 2 SDs higher than the mean) and 21 age-, sex- and BMI-matched normoinsulinaemic subjects (serum insulin level within 1 SD of the mean). The glucose and insulin responses to the oral glucose load were comparable between the hypertensive and normotensive groups. Similarly, the glucose and insulin responses to the i.v. glucose load were comparable between the non-obese hypertensive and normotensive groups, whereas the mean AUCinsulin in the obese hypertensive group was significantly greater (p < 0.01) than that in either of the non-obese groups. The respective mean values for systolic and diastolic BPs did not differ between the hyperinsulinaemic and normoinsulinaemic groups. The mean serum triglyceride and HDL cholesterol concentrations were significantly higher (p < 0.01) and lower (p < 0.05), respectively, in the hyperinsuslinaemic than in the normoinsulinaemic group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of LDL-apheresis in preventing restenosis after percutaneous transluminal coronary angioplasty (PTCA): LDL-apheresis angioplasty restenosis trial (L-ART)

To investigate the efficacy of reducing plasma lipoprotein(a) (Lp(a)) as well as low density lipoprotein cholesterol (LDL-C) levels on the prevention of restenosis after PTCA, LDL-apheresis was attempted on a total of 54 patients at six institutions. LDL-apheresis using a dextran sulfate cellulose column has been proven to be an effective method for reducing both plasma Lp(a) and LDL-C levels. As a subgroup (apheresis-drug combined group), 29 of the 54 patients were given Pravastatin (HMG CoA reductase inhibitor) and Niceritrol (Nicotinic Acid) in addition to LDL-apheresis to maintain low plasma levels of both Lp(a) and LDL-C through the follow-up period of 5 months after PTCA. Patients whose plasma Lp(a) levels were reduced by more than 50% showed a lower restenosis rate than those whose plasma Lp(a) levels were reduced by less than 50% (21.2% vs. 52.4%, P = 0.0179), especially in patients with high plasma Lp(a) levels above 30 mg/dl where a much lower restenosis rate (15.0%) was observed. Furthermore, in the apheresis-drug combined group, the restenosis rate was 11.8% regardless of baseline plasma Lp(a) levels, including even those below 30 mg/dl. In conclusion, in patients with high plasma Lp(a) levels, a greater than 50% reduction in Lp(a) levels by LDL-apheresis is effective in preventing restenosis after PTCA. If the plasma Lp(a) reduction rate is greater than 50%, LDL-apheresis combined with lipid-lowering drugs such as niceritrol and pravastatin seems to be more effective, even in patients with low plasma Lp(a) levels.

Lp(a): an acute-phase reactant?

The present study was designed to confirm the transient increases of plasma Lp(a) levels as an acute-phase reactant and to clarify the significance of these increases with the use of patients with acute myocardial infarction and patients subjected to surgical operations. Although interleukin 6, C-reactive protein and alpha 1 antitrypsin reached the maximal levels 1-2 days, 3 days and 4-5 days, respectively, after the episodes, the peak time of Lp(a) levels was delayed some extent in both patient groups. Studying the transient increases of Lp(a) levels as a function of apo(a) isoforms analyzed by density-gradient ultracentrifugation and SDS-PAGE, the higher-density Lp(a) particles preferentially containing high-molecular-weight apo(a) isoforms increased more than the lower-density Lp(a) particles containing low-molecular-weight apo(a) after the episodes. The immunohistochemical findings suggest that Lp(a) may play an important role as an acute-phase reactant in the repair of tissue injury, especially in the process of angiogenesis.

Apolipoprotein(a) phenotypes and serum lipoprotein(a) levels in maintenance hemodialysis patients with/without diabetes mellitus

We studied the quantitative and qualitative characteristics of lipoprotein(a) [Lp(a)] as a function of apolipoprotein(a) [apo(a)] phenotypes in 152 patients (123 males, 29 females) undergoing maintenance hemodialysis (HD) with or without diabetes mellitus (DM), in 101 patients with diabetes mellitus without hemodialysis (58 males, 43 females), and in 421 normal controls (333 males, 88 females). Serum Lp(a) levels were significantly (P < 0.01) higher in patients than in controls (26.2 +/- 18.3 mg/dl in HD with DM, 26.4 +/- 22.0 mg/dl in HD without DM, 27.1 +/- 27.3 mg/dl in DM without HD, and 14.9 +/- 13.7 mg/dl in controls, respectively). Apo(a) phenotyping was performed by a sensitive, high resolution technique using SDS-agarose/gradient (3 to 6%) PAGE. In normal controls, the molecular weights of apo(a) isoforms were inversely correlated with plasma Lp(a) levels, and the same tendency was found in patients who were undergoing hemodialysis and/or who had diabetes mellitus. We assumed the differences in apo(a) phenotypes detectable with our method reflected consecutive differences in molecular weights of apo(a). The results of an analysis of covariance and a least square means comparison indicated that the regression lines between serum Lp(a) levels [log Lp(a)] and apo(a) phenotypes in patient groups were significantly (P < 0.01) elevated for every apo(a) phenotype, as compared to the regression line of the control group. Even after the low molecular weight apo(a) phenotypes (A1-A8) were omitted, the same tendency was observed. However, no differences were observed between the patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined therapy with probucol and pravastatin in hypercholesterolaemia. One year follow-up study

The effect of co-administration of low doses of pravastatin to hypercholesterolaemic patients already receiving long-term probucol treatment (mean 500-1,000 mg/day for 350 days) were investigated. Pravastatin 5 mg/day (Group 1; 12 m, 13 f; mean age 59.1 y) or 10 mg/day (Group 2; 8 m, 11 f; mean age 60.8 y) was administered, and blood was taken after 0, 3, 6, and 12 months. Both groups showed a significant reduction in serum total cholesterol (TC), phospholipid (PL), low density lipoprotein-cholesterol (LDL-C), LDL-triglyceride (TG), LDL-PL, apolipoprotein (apo) B, and apo E after the combined therapy. These levels were reduced more in Group 2 than in Group 1 subjects. In Group 2, significant falls in serum TG and apo CII were also observed. The changes in TC, PL, LDL-C, apo B, apo CII and apo E were dependent upon the dose of pravastatin, as assessed by two-way analysis of variance. Serum high density lipoprotein (HDL)3-C, apo AI and apo AII were slightly but significantly increased in both groups after 12 months of combined therapy, but the increase was not sufficient to reverse the probucol-induced lowering of the HDL level. We conclude that combined therapy resulted in a significant reduction in atherogenic lipoproteins and apolipoproteins, and an increasing dose of pravastatin (5 mg to 10 mg daily) made the lipid lowering effect more prominent. The reduction in serum HDL-C due to long-term probucol administration was not reversed by the addition of pravastatin.

Studies on apolipoprotein(a) phenotypes. Part 1. Phenotype frequencies in a healthy Japanese population

The frequency distribution for serum lipoprotein(a) (Lp(a)) concentrations in healthy Japanese was highly skewed, with a mean +/- S.D. of 14.6 +/- 13.6 mg/dl and a median of 11.0 mg/dl. The present study provides the first evidence on the frequencies of Lp(a) phenotypes and alleles in healthy Japanese subjects. There was a strong inverse relationship between the apparent molecular weights of apo(a) isoforms and plasma Lp(a) concentrations, as reported previously. However, because of the considerable overlap between the Lp(a) concentrations of the different phenotypes, it was impossible to predict Lp(a) concentration from Lp(a) phenotypes, or vice versa. The present results suggest that the distribution of Lp(a) concentrations, mean and median values and Lp(a) phenotype and allele frequencies in healthy Japanese are not significantly different from the results for Europeans, whereas they are significantly different from other Asian populations, i.e. Chinese, Indians and Malaysians.

Studies on apolipoprotein(a) phenotypes. Part 2. Phenotype frequencies and Lp(a) concentrations in different phenotypes in patients with angiographically defined coronary artery diseases

In the present paper, we have evaluated serum Lp(a) concentrations, the frequencies of Lp(a) phenotypes and alleles and the association between the Lp(a) phenotypes and serum Lp(a) levels in 470 patients with angiographically defined coronary artery disease (CAD). Serum Lp(a) concentrations were significantly increased in proportion to the number of diseased vessels in the CAD patients. The frequencies of Lp(a) phenotypes in the CAD patients were significantly different from those in healthy subjects. In particular, the frequency of double-band phenotypes was higher in the CAD group. The frequencies of Lp(a) alleles in the CAD patients, however, were not significantly different from those in the healthy subjects. There was a strong inverse relationship between the apparent molecular weights of apo(a) isoforms and serum Lp(a) concentrations. Lp(a) levels in the CAD patients were higher than those in the healthy subjects with the same phenotype. The present results suggest that it is important to consider some posttranslational or environmental modifications and other factors, in addition to the genetic factor, when assessing contributions to plasma Lp(a) levels.

Optimization and characterization of capture ELISA methodology for Lp(a) lipoprotein quantification

In order to better characterize and optimize a typical capture ELISA system for Lp(a) lipoprotein, we have analysed kinetic details of the reaction. Plate coating with polyclonal antibody, recognition of captured analyte with monoclonal antibody, and detection of monoclonal antibody with alkaline phosphatase-labeled antiglobulin were essentially complete after one hour, probably being driven forward by a relative excess of reagent. However, complete capture of the Lp(a) analyte required about 6 h at low input concentrations. Shorter time periods for capture might therefore result in decreased sensitivity and reproducibility. Deviations from linearity in the assay dose response were associated with incomplete capture of Lp(a) and significant depletion of the monoclonal recognition antibody. With the final reaction conditions described, no significant differences in immunochemical reactivity between samples were found by analysis of dose response slopes. Finally, interferences from plasminogen, -20 degrees C storage, anticoagulants, LDL, haemolysis, and bilirubin were minimal.

Vascular risk factors in Japanese non-insulin-dependent diabetic patients with microalbuminuria

To determine if non-insulin-dependent diabetes mellitus (NIDDM) patients with microalbuminuria would have augmented vascular risk factors, we studied the relationships between blood pressure, serum lipids, plasma fibrinogen, and uric acid concentrations and plasma lipoprotein (a) level in 25 Japanese NIDDM patients with microalbuminuria [albumin excretion rate (AER) 20-200 micrograms/min] and 25 individually pair-matched NIDDM patients with normal urinary albumin excretion (AER less than 20 micrograms/min), matched for age, sex, body mass index, treatment and HbAlc level. Microalbuminuric patients had significantly higher systolic blood pressure (p less than 0.05) and plasma fibrinogen level (p less than 0.05) and lower high-density lipoprotein (HDL) cholesterol concentration (p less than 0.05) as compared with those in normoalbuminuric patients, respectively, while there were no differences in serum triglycerides and uric acid levels between the two groups. Plasma lipoprotein (a) level, assessed in 15 microalbuminuric and 15 normoalbuminuric patients, was comparable in the two groups. The results suggest that some of the vascular risk factors are already present in microalbuminuric NIDDM patients when compared with normoalbuminuric patients.

Automated measurement of lipoprotein(a) by immunoturbidimetric analysis

Immunoturbidimetric analysis of lipoprotein(a) in plasma or serum was developed for use on the Roche COBAS FARA II and COBAS MIRA clinical chemistry analyzers. The components of the assay are: (1) buffer consisting of 2.25% polyethylene glycol in phosphate-buffered saline, 0.2% gelatin, and a surfactant; (2) fractionated goat anti-human lipoprotein(a) IgG; (3) five standards with lipoprotein(a) concentrations ranging from 0.05 to 1.0 g/l; (4) two controls with concentrations of approximately 0.2 and 0.5 g/l. The analyzer delivers sample and buffer, incubates the reaction mixture at 37 degrees C for 5 min, delivers neat lipoprotein(a) antibody, and incubates for an additional 10 min. The lipoprotein(a) concentration of samples is calculated by the COBAS DENS (Data Evaluation for Non-linear Standard Curves) option by fitting the standard curve values to a four-parameter logit-log curve model. Total imprecision results (CV%) for the FARA II and MIRA were under 11% (NCCLS protocol EP5-T). The assay is linear beyond the highest calibrator to 2.6 g/l. No interference was observed for plasminogen up to 2.3 g/l, apolipoprotein B up to 4.36 g/l, hemoglobin up to 10 g/l, bilirubin up to 4.0 g/l, and triglycerides up to 4.36 g/l. Comparison with a double monoclonal ELISA used at the Northwest Lipid Research Laboratories yielded: R = 0.970, slope = 1.013, and y-intercept = 0.00009 (n = 37). Comparison with a commercially available ELISA kit for lipoprotein(a) yielded: r = 0.987, slope = 1.243, and y-intercept = 0.024 (n = 40). This assay provides rapid, accurate, and precise screening of lipoprotein(a) in serum or plasma.

A competitive ELISA for lipoprotein(a)

A competitive ELISA for lipoprotein(a) (Lp(a)) is described. The method uses a commercially available polyclonal anti-Lp(a) antibody and an IgG biotinstreptavidin-horseradish peroxidase detection system. The method is simple and robust with an assay sensitivity of 0.7 ng/well (1.4 micrograms/l). The antibody cross-reactivity was 0.14% against LDL and 0.70% against plasminogen. The coefficients of variation obtained with control sera of 266 and 552 mg/l were: 5.0% and 4.6% (n = 6), respectively for the intraassay; and 10.8% and 9.5% (n = 16), respectively for the interassay. The method showed an excellent correlation with a commercial immunoradiometric assay (IRMA), y (ELISA) = 0.94x (IRMA) - 8, (r = 0.98). A recovery study in which a 200 mg/L standard and four plasma samples were diluted with different proportions of a low plasma sample, gave linear relationships and also confirmed the specificity of the antibody.

Lipoprotein(a) profiles and evolution in newborns

Plasma Lp(a) concentrations in newborns were quantified by a specific and sensitive ELISA assay and their evolution was followed between birth and 6 months. The influence of the diet on Lp(a) levels was also investigated. Moreover, the high sensitivity of the assay enabled the localisation of the Lp(a) fraction in the lipoprotein profile obtained after plasma separation by gel chromatography. Lp(a) levels are low at birth and rise significantly between 0 and 7 days post partum; in this newborn population, a continuous rise of the mean Lp(a) levels was observed until 180 days, in contrast with the apo B concentration that plateaus after 7 days. An early screening enabled the detection of newborns with elevated Lp(a) levels compared to the mean value of their age group. A further follow-up of some cases at 16 months confirmed the high Lp(a) levels measured in the infants and at least one of the parents. The investigation of the lipoprotein profiles as a function of the age of the newborn enabled an estimation of the size and distribution of the Lp(a) lipoprotein in four infants. At birth, Lp(a) particles were larger than LDL and tend to become more heterogeneous with increasing age of the newborn. We could not observe any statistically significant influence of the nutritional factors on the plasma Lp(a) concentrations at any age.

Reduction of serum lipoprotein(a) levels in hyperlipidaemic patients with alpha-tocopheryl nicotinate

The effect of low dose (600 mg/day) alpha-tocopheryl nicotinate on serum lipoprotein(a) (Lp(a] concentration was studied in 28 hyperlipidaemic patients. Serum lipids, lipoproteins and apolipoproteins, except for Lp(a), tended to increase after treatment. In particular, the changes in HDL-cholesterol and apo C-II levels were statistically significant. On the other hand, serum Lp(a) levels in all patients decreased significantly after 2 months of treatment. Furthermore, no difference between before and after treatment was observed in the group with initial Lp(a) levels less than 18 mg/dl, whereas Lp(a) concentrations decreased significantly after treatment in the group with levels greater than or equal to 18 mg/dl. The effects of probucol and alpha-tocopheryl nicotinate on serum Lp(a), total cholesterol and HDL-cholesterol were entirely different. Possible mechanisms of alpha-tocopheryl nicotinate on serum Lp(a) and lipoprotein metabolism are discussed.

Immunochemical determination of lipoprotein Lp(a): comparison of Laurell electrophoresis and ELISA

The lipoprotein Lp(a) concentrations in serum from 520 persons (317 men and 203 women) were measured by two different Laurell electrophoresis assays (one in house and one commercial) and by an ELISA technique, using polyclonal antibodies from two different animal species. The following results were obtained. 1. The two Laurell techniques gave similar results. The mean values of all three methods were comparable, whereas median values obtained by ELISA were markedly lower (0.85, 0.97 and 0.057 g/l for the two Laurell assays and the ELISA, respectively). 2. All three methods correlated very well with a correlation coefficient of greater than 0.95. 3. Women had significantly higher values than men (p less than 0.01). It was concluded that Lp(a) serum concentrations in the 'pathological range' could be measured with high enough precision by Laurell electrophoresis and by ELISA using polyclonal antibodies from different animal species.

Transient changes of serum lipoprotein(a) as an acute phase protein

Serum lipoprotein(a) (Lp(a)) was serially determined after acute attacks of myocardial infarction and after surgical operations. Acute phase proteins, such as C-reactive protein, alpha 1-acid glycoprotein, alpha 1-antitrypsin and haptoglobin, increased rapidly and markedly after the episodes. Initial values of serum Lp(a) concentrations were almost the same in both groups. Increases in serum Lp(a) levels were also observed during the first few days, with a return to the initial levels after more than 1 month. The periods for reaching maximal levels of acute phase proteins were similar in both groups of patients. On the contrary, the period required for Lp(a) to reach the maximal level in the myocardial infarction group was significantly longer than in the post-operative group. The present study suggests that Lp(a) has the characteristics of an acute phase reactant and may play an important role in recovery from tissue damage.

Lipoprotein(a) in nonhuman primates. Presence and characteristics of Lp(a) immunoreactive materials using anti-human Lp(a) serum

Lipoprotein(a) (Lp(a] immunoreactive materials were examined in serum samples from 77 nonhuman primates of 24 species by Ouchterlony's double diffusion procedure and an enzyme-linked immunosorbent assay (ELISA) using rabbit antisera to human Lp(a). The precipitates obtained with sera from orang-utan and chimpanzee formed reactions of complete identity with the Lp(a) precipitate with human serum. When sera from Old World monkeys and human subjects were tested in wells next to each other, spurs developed between the 2 precipitates, indicating that Lp(a)-like lipoproteins in Old World monkeys have partial identity with human Lp(a). Lp(a) immunoreactive materials were identified in association with lipids by means of fat staining of the precipitates. On the other hand, reactants which could be precipitated with anti-human Lp(a) sera were not detectable in prosimians and New World monkeys. These results suggest that serum Lp(a)-like lipoprotein is phylogenetically acquired in Old World monkeys. However, the possibility that the structures of serum Lp(a)-like lipoproteins in prosimians and New World monkeys are too different to react with anti-human Lp(a) sera cannot be ruled out.