Characterization of apo(a) polymorphism by a modified immunoblotting technique in an Italian population sample

Assessment of Apolipoprotein(a) Isoform Size Using Phenotypic and Genotypic Methods

Apolipoprotein(a) (apo(a)) is the protein component that defines lipoprotein(a) (Lp(a)) particles and is encoded by the LPA gene. The apo(a) is extremely heterogeneous in size due to the copy number variations in the kringle-IV type 2 (KIV2) domains. In this review, we aim to discuss the role of genetics in establishing Lp(a) as a risk factor for coronary heart disease (CHD) by examining a series of molecular biology techniques aimed at identifying the best strategy for a possible application in clinical research and practice, according to the current gold standard.

Association between Low-Molecular Weight Apolipoprotein(a) Isoforms and Obesity in Italian Women

OBJECTIVE

Low-molecular weight (MW) apolipoprotein(a) [apo(a)] isoforms are closely associated with an increased incidence of atherothrombotic disease, prevalence of which is higher in obese individuals, particularly in women. The hypothesis of this study was to assess whether there are differences in the distribution of apo(a) phenotypes between obese patients and healthy controls.

RESEARCH METHODS AND PROCEDURES

One hundred three obese Italian women (BMI > or = 30.0 kg/m2) were enrolled in the study, and apo(a) phenotyping was performed in all subjects. The prevalence of low-MW apo(a) isoforms, detected in plasma samples of our obese women, was compared with that found in a control group of 84 normal-weight, never-obese (BMI < 25.0 kg/m(2)), age-matched women.

RESULTS

The distribution of apo(a) isoforms in the population of obese women was significantly different from that found in normal-weight female subjects. In particular, the percentage of subjects in the obese group with at least one apo(a) isoform of low MW was significantly higher than that in the control group (51.4% vs. 32.1%, p = 0.0079).

DISCUSSION

Our results seem to suggest the possibility that small-sized apo(a) isoforms may be used together with other traditional risk factors to better assess the overall predisposition to atherothrombotic disease in obese women.

Evaluation of emerging biomarkers in cardiovascular risk stratification of hypertensive patients: a 2-year study

OBJECTIVE

To evaluate if there is a correlation between some new emerging biomarkers, such as lipoprotein(a) (Lp[a]), apo(a) isoform phenotyping, soluble advanced glycation end products (sRAGE), soluble CD40 ligand (sCD40L), serum myeloperoxidase (MPO), and cardiovascular risk stratification.

RESEARCH DESIGN AND METHODS

Three hundred patients were enrolled in this open-label, case-control design trial: 156 hypertensive patients and 144 healthy subjects as control group. Hypertensive patients were treated according to the latest ESH/ESC guidelines, until the desirable goal of systolic blood pressure (SBP)<140 mmHg, and diastolic blood pressure (DBP)<90 mmHg was reached. We evaluated at baseline and after 6, 12, 18, and 24 months: SBP, DBP, lipid profile, Lp(a), apo(a) isoform phenotyping, sRAGE, sCD40L, and MPO.

RESULTS

Hypertensive patients presented higher levels of blood pressure, Lp(a), sCD40L, and MPO and lower levels of sRAGE compared with controls. We observed a decrease of blood pressure, Lp(a), sCD40L, and MPO and an increase of sRAGE after anti-hypertensive treatment. Moreover we observed moderate, but statistically significant, correlations between blood pressure decrease and Lp(a), MPO, and sCD40L decrease and between blood pressure decrease and sRAGE increase. There was also a modest, positive correlation between low molecular weight apo(a) isoforms and hypertension. A limitation of this study is that we cannot exclude a role for lifestyle measures. Furthermore the studied markers seem to improve with blood pressure lowering treatment, but we do not have enough statistical power to definitely state which drug used has a specific action on the various variables measured.

CONCLUSION

Lp(a), sRAGE, MPO, sCD40L, and low molecular weight apo(a) isoforms are associated with hypertension and may represent an increased cardiovascular risk. Longer studies are needed to see if these parameters can be also used to predict specific complications linked to hypertension.

Different apoprotein(a) isoform proportions in serum and carotid plaque

INTRODUCTION

Cardio- and/or cerebro-vascular risk are associated with high lipoprotein (a) [Lp(a)] levels and low-molecular-weight (LMW) apo(a) isoforms. Aims of this study were to evaluate the deposition of apo(a) isoforms and apoprotein B (apo B) in atherosclerotic plaque from patients (males and females) who had carotid endarterectomy for severe stenosis, and to identify differences between patients classified by gender and divided according to the stability or instability of their plaques.

MATERIALS AND METHODS

We determined lipids, apo B and Lp(a) in serum and plaque extracts from 55 males and 25 females. Apo(a) was phenotyped and isoforms were classified by number of kringle IV (KIV) repeats.

RESULTS

Lp(a) levels were higher in female serum and plaque extracts than in male samples, while apo B levels were lower. More Lp(a) than apo B deposition was observed in plaque after normalization for serum levels. Thirty-one different apo(a) isoforms were detected in our patients, with a double band phenotype in 94% of cases. In both sexes, the low/high (L/H) molecular weight apo(a) isoform expression ratio was significantly higher in plaque than in serum. Females with unstable plaques had higher Lp(a) levels in both serum and tissue extracts, and fewer KIV repeats of the principal apo(a) isoform in the serum than the other female group or males.

CONCLUSIONS

In both sexes, the same apo(a) isoforms are found in serum and atherosclerotic plaque, but in different proportions: in plaque, LMW apo(a) is almost always more strongly accumulated than HMW apo(a), irrespective of any combination of apo(a) isoforms in double band phenotypes or Lp(a) serum levels. Moreover, serum and tissue Lp(a) levels were higher in females than in males, and particularly in the group with unstable plaques.

The apolipoprotein(a) component of lipoprotein(a) mediates binding to laminin: contribution to selective retention of lipoprotein(a) in atherosclerotic lesions

Lipoprotein(a) [Lp(a)] entrapment by vascular extracellular matrix may be important in atherogenesis. We sought to determine whether laminin, a major component of the basal membrane, may contribute to Lp(a) retention in the arterial wall. First, immunohistochemistry experiments were performed to examine the relative distribution of Lp(a) and laminin in human carotid artery specimens. There was a high degree of co-localization of Lp(a) and laminin in atherosclerotic specimens, but not in non-atherosclerotic sections. We then studied the binding interaction between Lp(a) and laminin in vitro. ELISA experiments showed that native Lp(a) particles and 17K and 12K recombinant apolipoprotein(a) [r-apo(a)] variants interacted strongly with laminin whereas LDL, apoB-100, and the truncated KIV(6-P), KIV(8-P), and KIV(9-P) r-apo(a) variants did not. Overall, the ELISA data demonstrated that Lp(a) binding to laminin is mediated by apo(a) and a combination of the lysine analogue epsilon-aminocaproic acid and salt effectively decreases apo(a) binding to laminin. Secondary binding analyses with 125I-labeled r-apo(a) revealed equilibrium dissociation constants (K(d)) of 180 and 360 nM for the 17K and 12K variants binding to laminin, respectively. Such similar K(d) values between these two r-apo(a) variants suggest that isoform size does not appear to influence apo(a) binding to laminin. In summary, our data suggest that laminin may bind to apo(a) in the atherosclerotic intima, thus contributing to the selective retention of Lp(a) in this milieu.

Relation of apolipoprotein(a) size to alzheimer's disease and vascular dementia

Lipoprotein(a) [Lp(a)] level is a newly established vascular risk factor which has been suggested to play a role in dementia. However, the majority of Lp(a) cell-to-cell interactions are mediated by its specific apolipoprotein(a) [apo(a)] moiety. This suggests that the size polymorphism of apo(a) may be of importance in conveying the Lp(a)-related risk. Specifically, we postulated that variation in apo(a) isoform size may lead to increased risk of vascular dementia (VaD), Alzheimer's disease (AD), stroke, or all three of them. Under a case-control design we compared Lp(a) plasma levels and the distribution of apo(a) phenotypes in groups of subjects consisting of 50 VaD patients, 162 sporadic AD patients, 95 non-demented stroke patients (NDS), and 105 normal controls. The prevalence of small-sized apo(a) isoforms in the VaD group was significantly higher than that in the stroke and normal control groups, with an odds ratio of 5.29 (95% CI 2.24-12.49, p = 0.0001) for the development of VaD for individuals with at least one apo(a) isoform of low molecular weight (LMW). Furthermore, the possession of at least one small-sized apo(a) isoform significantly increased the risk of AD to 1.92 (95% CI 1.02-3.61, p = 0.0434). Our results demonstrate that possession of at least one LMW apo(a) isoform is significantly associated with dementia and specifically offer new evidence of a strong association between the lipoprotein system and post-stroke dementia.

Significance of apolipoprotein(a) phenotypes in acute coronary syndromes: relation with clinical presentation

BACKGROUND

High lipoprotein(a) [Lp(a)] levels and small-sized apolipoprotein(a) [apo(a)] phenotypes have been linked to acute coronary syndromes (ACS). We sought to determine whether Lp(a) concentrations and apo(a) phenotypes may be related to the clinical syndrome of presentation among ACS patients.

METHODS

Two hundred ten ACS patients and 105 controls were enrolled. One hundred thirteen patients presented with acute myocardial infarction (AMI) and 97 with unstable angina pectoris (UAP). Lp(a) concentrations were determined by ELISA and apo(a) isoforms were detected with a high-resolution immunoblotting method.

RESULTS

Lp(a) levels and the percentage of subjects with at least one small-sized apo(a) isoform were significantly higher both in AMI patients and in UAP subjects as compared with controls. Among ACS patients, the percentage of subjects with at least one small apo(a) phenotype was significantly higher in patients who presented with AMI than in those with UAP (p<0.001). Multivariate logistic regression analysis showed that the presence of at least one small-sized apo(a) isoform was associated with AMI as the patient's clinical syndrome of presentation (OR=2.51, 95% CI: 1.38-4.58, p<0.01).

CONCLUSIONS

Among ACS patients, apo(a) isoforms of low molecular weight were associated with AMI onset. High-resolution apo(a) phenotyping might be helpful to identify individuals at high risk for developing AMI.

Epidemiology, pathophysiology and therapeutic implications of lipoprotein(a) in kidney disease

Chronic kidney disease is associated with a tremendously increased risk for cardiovascular disease. Traditional risk factors for cardiovascular disease, however, show a diminished predictive power in these patients compared with the general population. This review provides an overview of lipoprotein(a), which is considered a nontraditional risk factor. The characteristic genetic and nongenetic changes of lipoprotein(a) in kidney disease are discussed and set into the context of risk prediction. In particular, genetically determined apolipoprotein(a) polymorphism is a powerful risk predictor for cardiovascular disease and total mortality in these patients. Finally, the limited interventional strategies available to lower lipoprotein(a) are considered.

Apolipoprotein(a) null phenotype is related to a delayed age at onset of Alzheimer's disease

Apolipoprotein(a) [apo(a)] is a highly polymorphic glycoprotein which has been suggested to play a role in Alzheimer's disease (AD). Plasma lipoprotein(a) [Lp(a)] levels and the differential expression of apo(a) isoforms were analyzed in 73 sporadic AD patients compared with 73 age- and gender-matched healthy controls. The distribution of apo(a) isoforms and Lp(a) concentrations were similar in the two groups. However, we observed that AD patients with no apo(a) isoform from immunoblots (subjects with the 'null phenotype') had a mean age at onset of 76.8+/-8.8 versus 66.9+/-9.6 years of those who expressed at least one apo(a) band (P = 0.010). Multivariate analysis showed that this effect was independent of apolipoproteinE epsilon4 allele. We conclude that the expression of at least one apo(a) isoform may interact with other pathogenic mechanisms involved in controlling the age at onset of AD.

Lipoprotein(a)-associated atherothrombotic risk in hemodialysis patients

BACKGROUND

Hemodialysis patients show a considerably higher risk of atherothrombotic disease than the general population. We investigated both lipoprotein(a) [Lp(a)] plasma levels and apolipoprotein(a) [apo(a)] phenotypes in relation to occurrence of atherothrombotic events in hemodialysis patients compared with subjects showing a normal kidney function.

METHODS

Lp(a) levels and apo(a) isoforms were determined in 118 hemodialysis patients, including 59 with prior atherothrombotic events, and in 182 subjects with normal creatinine clearance, including 82 who experienced a prior atherothrombotic event.

RESULTS

Lp(a) levels in hemodialysis patients (median; 20 mg/dl) were higher (p < 0.01) than in age- and sex-matched subjects with normal renal function without a history of atherothrombosis (11.3 mg/dl). Among hemodialysis patients, median Lp(a) levels were higher in subjects with than in those without prior atherothrombosis (34 vs. 15 mg/dl, p < 0.05). In hemodialysis patients and in subjects without nephropathy, the percentage of low-molecular-weight apo(a) phenotypes were significantly higher in patients with than in those without a history of prior atherothrombotic events (56.9% vs. 33.9%, p < 0.05; 62.2% vs. 25%, p < 0.00001,respectively). Stepwise regression analysis indicated that the presence of at least one apo(a) isoform of low molecular weight was an independent predictor of atherothrombosis in hemodialysis patients (p < 0.05).

CONCLUSIONS

Elevated Lp(a) plasma levels appear to be associated with atherothrombosis, independent of their origin due to genetic factors or related to the impaired kidney function. Low-molecular-weight apo(a) isoforms are reliable genetic markers of atherothrombosis both in patients with impaired kidney function and in subjects without nephropathy.

Relationship between apolipoprotein(a) size polymorphism and coronary heart disease in overweight subjects

BACKGROUND

Overweight is associated with an increased cardiovascular risk which is only partially explained by conventional risk factors. The objective of this study was to evaluate lipoprotein(a) [Lp(a)] plasma levels and apolipoprotein(a) [apo(a)] phenotypes in relation to coronary heart disease (CHD) in overweight subjects.

METHODS

A total of 275 overweight (BMI > or = 27 kg/m2) subjects, of which 155 had experienced a CHD event, 337 normal weight subjects with prior CHD and 103 CHD-free normal weight subjects were enrolled in the study. Lp(a) levels were determined by an ELISA technique and apo(a) isoforms were detected by a high-resolution immunoblotting method.

RESULTS

Lp(a) levels were similar in the three study groups. Overweight subjects with CHD had Lp(a) concentrations significantly higher than those without [median (interquartile range): 20 (5-50.3) versus 12.6 (2.6-38.6) mg/dl, P < 0.05]. Furthermore, overweight subjects with CHD showed a higher prevalence of low molecular weight apo(a) isoforms than those without (55.5% versus 40.8%, P < 0.05) and with respect to the control group (55.5% versus 39.8%, P < 0.05). Stepwise regression analysis showed that apo(a) phenotypes, but not Lp(a) levels, entered the model as significant independent predictors of CHD in overweight subjects.

CONCLUSIONS

Our data indicate that small-sized apo(a) isoforms are associated with CHD in overweight subjects. The characterization of apo(a) phenotypes might serve as a reliable biomarker to better assess the overall CHD risk of each subject with elevated BMI, leading to more intensive treatment of modifiable cardiovascular risk factors.

Association between small apolipoprotein(a) isoforms and frontotemporal dementia in humans

Apolipoprotein(a) [apo(a)] is a genetically polymorphic glycoprotein that has several similarities to apolipoprotein E. However, its role as a risk factor for frontotemporal dementia (FTD) remains to be elucidated. We therefore investigated the effect of an apo(a) polymorphism on the incidence of FTD in a sample of Caucasian Italian patients. From the entire group of FTD patients (n=54), 55.6% of the subjects had at least one apo(a) low molecular weight (MW) isoform, compared to 29.9% of non-demented controls (n=77). The difference between the two groups was statistically significant (odds ratio 2.93, 95% confidence interval 1.42-6.06, P=0.003). The FTD group was further divided into sporadic (n=26) and familial (n=28) cases. Even after such dichotomization, both sporadic and familial FTD patients showed a significantly higher prevalence of low MW apo(a) isoforms than the cognitively healthy controls (P=0.011 and P=0.025, respectively). Our data suggest a role of apo(a) phenotypes of low MW in mediating susceptibility to FTD.

Lipoprotein(a), apolipoprotein(a) polymorphism and restenosis after intracoronary stent placement in Type 2 diabetic patients

The relationship between lipoprotein(a) [Lp(a)] and restenosis after intracoronary stent implantation has never been analysed in diabetic patients. The aim of the present prospective study was to evaluate whether Lp(a) levels and apolipoprotein(a) [apo(a)] phenotypes are predictors of restenosis after elective stent implantation in Type 2 diabetic patients with de novo lesions of coronary arteries. We recruited 102 Type 2 diabetic patients with a new lesion successfully treated with elective placement of one or two Palmaz-Schatz stents. Follow-up angiography was scheduled at 6 months or earlier if clinically indicated. Seven patients were lost to the follow up. Among 95 patients enrolled, restenosis was present in 37 (38.9%) and absent in 58 (61.1%). The restenosis group showed Lp(a) levels higher than the nonrestenosis group (25.1+/-14.4 vs. 21.3+/-14.6 mg/dl), but the difference was not significant. The restenosis group had a percentage of subjects with at least one apo(a) isoform of low molecular weight (MW) significantly greater than the nonrestenosis group (75.7% vs. 55.1%; P<.05). A multiple logistic regression analysis showed that presence of multivessel disease (risk relative [RR]: 5.83; 95% confidence interval [CI]: 1.21-28.15; P<.05) was the only predictor of restenosis after stent placement in diabetic patients. Lp(a) and apo(a) polymorphisms did not enter the model as predictive variables. Our study shows that the presence of multivessel disease is a predictor of restenosis after intracoronary stent implantation in diabetic patients. On the contrary, Lp(a) and apo(a) polymorphisms do not appear to be reliable markers of restenosis in patients with Type 2 diabetes mellitus.

Differential apolipoprotein(a) isoform expression in heterozygosity is an independent contributor to lipoprotein(a) levels variability

BACKGROUND AND METHODS

Lipoprotein(a) [Lp(a)] levels represent an independent risk factor for cardio- and cerebrovascular diseases. Since lipoprotein(a) levels show a wide variability even in subjects with similar apolipoprotein(a) isoforms, we investigated the contribution of apolipoprotein(a) heterozygosity to lipoprotein(a) variance. Lipoprotein(a) levels, apolipoprotein(a) isoforms identification and expression, and the correlation with other lipo-apolipoprotein parameters have been investigated in 628 subjects >18 years of age.

RESULTS

In our study, 246 subjects were found heterozygous for apolipoprotein(a) isoforms. Lipoprotein(a) levels were higher in females. About 40% of the subjects expressed the larger isoform more intensely than the dominant isoform. Lipoprotein(a) was correlated with apolipoprotein(a) dominant isoform size, HDL-cholesterol and smaller apolipoprotein(a) isoform expression rate. Lipoprotein(a) was independently correlated with the smaller apolipoprotein(a) isoform, with its expression rate and with LDL-cholesterol. The inclusion of the smaller apolipoprotein(a) expression rate in a multiple regression model explained at least an additional 4% of the lipoprotein(a) variance after correction for apolipoprotein(a) size.

CONCLUSIONS

The smaller isoforms are not always effectively dominant in heterozygosis since 40% of the subjects expressed more the larger isoform. The individual variability of apolipoprotein(a) isoform expression in heterozygosis could explain part of the lipoprotein(a) levels variability.

Restenosis after intracoronary stent placement: can apolipoprotein(a) polymorphism play a role?

BACKGROUND

The relationship between lipoprotein(a) and restenosis after intracoronary stent implantation has been analysed by two specific studies, but the role of apoliprotein(a) polymorphism was not considered. The aim of the present prospective study was to evaluate whether lipoprotein(a) levels and apolipoprotein(a) phenotypes are predictors of restenosis after elective stent implantation in patients with de novo lesions of coronary arteries.

METHODS

We recruited 182 patients with a new lesion successfully treated with elective placement of one or two Palmaz-Schatz stents. Follow-up angiography was scheduled at 6 months or earlier if clinically indicated. Nine patients were lost to the follow up. Among 173 patients enrolled, restenosis was present in 52 (30.0%) and absent in 121 (70.0%).

RESULTS

Lipoprotein(a) levels were higher in the restenosis than in the nonrestenosis group (29.5+/-17.2 versus 27.4+/-20.2 mg/dl), even if the difference did not attain statistical significance (P=0.067). The restenosis group had a percentage of subjects with at least one apolipoprotein(a) isoform of low molecular weight significantly greater than the nonrestenosis group (82.7 versus 66.9%; P=0.035). A multiple logistic regression analysis showed that multiple stenting (RR: 4.01; CI 95%: 1.65-13.91; P=0.004), presence of diabetes (RR: 3.96; CI 95%: 1.67-9.37; P=0.002) and presence of multivessel disease (RR: 2.71; CI 95%: 1.19-6.16; P=0.017) were predictors of restenosis after stent placement. Lipoprotein(a) and apolipoprotein(a) polymorphism did not enter the model as predictive variables.

CONCLUSIONS

Our study confirms that multiple stenting, diabetes and multivessel disease are powerful predictors of restenosis after intracoronary stent implantation. On the contrary, lipoprotein(a) and apolipoprotein(a) polymorphism do not appear to be reliable markers of restenosis in patients with stent implantation.

Silent coronary artery disease in type 2 diabetes mellitus: the role of Lipoprotein(a), homocysteine and apo(a) polymorphism

BACKGROUND

There is little data on the relationship between novel cardiovascular risk factors and silent coronary artery disease (CAD) in diabetic patients. We investigated whether Lipoprotein(a), homocysteine and apolipoprotein(a) polymorphism are associated with angiographically assessed asymptomatic coronary artery disease (CAD) in diabetic patients.

METHODS

1,971 type 2 diabetic patients without clinical signs of cardiovascular diseases and with a negative history of CAD were consecutively evaluated. Among them, 179 patients showed electrocardiographic abnormalities suggestive of ischemia or previous asymptomatic myocardial infarction. These 179 patients were subjected to a non-invasive test for CAD (ECG stress testing and/or scintigraphy). Among patients with a highly positive stress testing (n = 19) or a positive scintigraphy (n = 74), 75 showed an angiographically documented CAD (CAD group). Seventy-five patients without CAD (NO CAD group) were matched by age, sex and duration of diabetes to CAD patients. In NO CAD patients an exercise ECG test, a 48-hour ambulatory ECG and a stress echocardiogram were negative for CAD.

RESULTS

Lipoprotein(a) levels (22.0 +/- 18.9 versus 16.0 +/- 19.4 mg/dl; p < 0.05), homocysteine levels (13.6 +/- 6.6 versus 11.4 +/- 4.9 mmol/l; p < 0.05) and the percentage of subjects with at least one small apolipoprotein(a) isoform (70.7% versus 29.3%; p < 0.0001) were higher in CAD than NO CAD group. Logistic regression analysis showed that apolipoprotein(a) polymorphism (OR:8.65; 95%CI:3.05-24.55), microalbuminuria (OR:6.16; 95%CI:2.21-17.18), smoking (OR:2.53; 95%CI:1.05-6.08), HDL (OR:3.16; 95%CI:1.28-7.81), homocysteine (OR:2.25; 95%CI:1.14-4.43) and Lipoprotein(a) (OR:2.62; 95%CI:1.01-6.79) were independent predictors of asymptomatic CAD.

CONCLUSIONS

The present investigation shows an independent association of Lipoprotein(a), homocysteine and apo(a) polymorphism with silent CAD. Other studies are needed to establish whether these parameters are suitable for CAD screening in diabetic patients.

Assessment of asymptomatic coronary artery disease in apparently uncomplicated type 2 diabetic patients: a role for lipoprotein(a) and apolipoprotein(a) polymorphism

OBJECTIVE

In patients with uncomplicated diabetes, there is low probability of finding significant coronary artery disease (CAD) by noninvasive tests. Therefore, screening for its presence is not justified, and it is important to find reliable predictors of silent CAD to identify patients with uncomplicated diabetes for further screening. The relationship between lipoprotein(a) [Lp(a)], apolipoprotein(a) [apo(a)] polymorphism, and silent CAD has never been studied. We investigated the association of Lp(a) and apo(a) polymorphism with angiographically documented asymptomatic CAD in type 2 diabetic patients without evident complications.

RESEARCH DESIGN AND METHODS

A total of 1,323 diabetic patients without any clinical and electrocardiographic evidence of CAD were evaluated. Of 121 patients with highly positive results of exercise electrocardiography (ECG) (n = 30) or positive results on exercise thallium scintigraphy (n = 91), 103 subjects showed angiographically documented CAD (CAD group). Of 1,106 patients with negative results on exercise ECG, 103 subjects without CAD (NO CAD group) were selected and matched by age, gender, and duration of diabetes to patients in the CAD group. In patients in the NO CAD group, results of exercise ECG, 48-h ambulatory ECG, and stress echocardiography were negative for CAD.

RESULTS

The CAD group had higher Lp(a) levels (21.7 +/- 17.7 vs. 15.2 +/- 19.0 mg/dl; P = 0.0093) than the NO CAD group, and a percentage of subjects had at least one small apo(a) isoform (68.9 vs. 29.1%; P = 0.0000) higher than the NO CAD group. Logistic regression analysis showed that apo(a) phenotypes (odds ratio [OR] 8.13, 95% CI 3.65-21.23), microalbuminuria (5.38, 2.44-11.88), smoking (2.72, 1.31-5.64), and Lp(a) levels (2.41, 1.15-5.03) were predictors of asymptomatic CAD.

CONCLUSIONS

Our investigation reports the first evidence of an independent association of Lp(a) and apo(a) polymorphism with asymptomatic CAD. This suggests that Lp(a) levels and apo(a) phenotypes could be used together with other risk factors as markers of asymptomatic CAD in patients with diabetes.

Heterozygous apolipoprotein (a) status and protein expression as a risk factor for premature coronary heart disease

Exactly how apolipoprotein a [APO(a)] isoform size affects the degree of cardiovascular risk associated with high lipoprotein a [LP(a)] levels is not fully understood. Using a sodium dodecyl sulfate-agarose APO(a) & LP(a) phenotyping method, we assessed the role of APO(a) size heterogeneity according to the number of kringle 4 repeats and the differential APO(a) protein expression in 91 male Spanish patients with premature coronary heart disease (CHD) compared with 99 healthy Spanish men. CHD patients had significantly increased median plasma LP(a) levels (0.31 g/L) and a higher percentage of subjects with LP(a) levels of 0.30 g/L or greater (51%) than controls (0.15 g/L and 23%, respectively). Patients with the double-band phenotype had significantly higher plasma LP(a) levels (median 0.37 g/L) compared with those expressing a single-band phenotype (median 0.20 g/L; P =.018) and with their corresponding controls (median 0.15 g/L; P <.001). The double-band phenotype and LP(a) values of 0.30 g/L or greater had a significant association with CHD (odds ratio [OR] 6.47, 95% confidence interval [CI] 2.51-16.7), stronger than that observed for the entire group (OR 4.19, 95% CI 1.97-8.90). The adjusted OR for the APO(a) protein pattern that equally expressed both isoforms indicates an independent association with premature CHD (OR 3.33; 95% CI 1.08-10.3). These results suggest that APO(a) phenotyping might be used in subjects with hyperlipoproteinemia a as a powerful marker to assess the risk of premature CHD because heterozygous status, mainly when both isoforms are equally expressed, is associated with higher cardiovascular risk.

Association of lipoprotein(a) levels and apolipoprotein(a) phenotypes with coronary artery disease in Type 2 diabetic patients and in non-diabetic subjects

AIMS

We investigated whether in Type 2 diabetic patients lipoprotein(a) (Lp(a)) levels and apolipoprotein(a) (apo(a)) polymorphism are associated with angiographically documented coronary artery disease (CAD). We also examined whether there are differences in the distributions of Lp(a) levels and apo(a) phenotypes between CAD patients with and without diabetes.

METHODS

A hundred and seven diabetic patients with CAD, 274 diabetic patients without CAD, 201 non-diabetic patients with CAD, and 358 controls were enrolled.

RESULTS

Diabetic patients with CAD showed Lp(a) levels (21.2 +/- 17.7 vs. 15.1 +/- 17.8 mg/dl; P = 0.0018) and a percentage of subjects with at least one apo(a) isoform of low molecular weight (MW) (67.2% vs. 27.7%; P = 0.0000) significantly greater than diabetic patients without CAD. Multivariate analysis showed that in diabetic patients Lp(a) levels and apo(a) phenotypes were significantly associated with CAD; odds ratios (ORs) of high Lp(a) levels for CAD were 2.17 (1.28-3.66), while ORs of the presence of at least one apo(a) isoform of low MW were 5.35 (3.30-8.60). Lp(a) levels (30.2 +/- 23.7 vs. 21.2 +/- 17.7 mg/dl; P = 0.0005) and the percentage of subjects with at least one apo(a) isoform of low MW (87.0% vs. 67.2%; P = 0.0001) were significantly higher in CAD patients without than in those with diabetes.

CONCLUSIONS

Our data suggest that Lp(a) levels and apo(a) phenotypes are independently associated with CAD in Type 2 diabetic patients; thus both these parameters may be helpful in selecting diabetic subjects at high genetic cardiovascular risk. However, Lp(a) levels and apo(a) polymorphism seem to be cardiovascular risk factors less important in diabetic than in non-diabetic subjects. Diabet. Med. 18, 589-594 (2001)

Relationship between lipoprotein(a) phenotypes and plaminogen activator inhibitor type 1 in diabetic patients

It has been demonstrated in vitro that lipoprotein(a) [Lp(a)] increases the endothelial synthesis of plasminogen activator inhibitor 1 (PAI-1). However, this effect in vivo is controversial, and the possible relationship between PAI-1 and Lp(a) phenotypes has not been evaluated. The aim of the study was to determine the influence of Lp(a) and its phenotypes on PAI-1 serum concentrations in diabetic patients. For this purpose we include 75 Caucasian diabetic patients (34 consecutive type I and 41 consecutive type II) without late diabetic complications. Lp(a) and PAI-1 were assessed by ELISA. Lp(a) phenotypes were determined by SDS-PAGE followed by immunoblotting, and grouped according to size in small (F,B,S1,S2), big (S3,S4), and null. A linear correlation between Lp(a) and PAI-1 was not observed either as a whole or when type I and type II diabetic patients were analyzed separately. However, significant differences were detected in PAI-1 levels when Lp(a) phenotypes were considered (small: 42.1+/-31.8 ng/mL; big: 37.2+/-26.1 ng/mL; null: 14.4+/-14.4; p< 0.05). The significant differences were due to the low PAI-1 concentrations observed in patients with null phenotype. Our results suggest that fibrinolytic activity might be preserved in diabetic patients with null Lp(a) phenotype. Furthermore, it could be speculated that diabetic patients with null phenotype should be considered at low risk to develop cardiovascular disease.

Are lipid-dependent indicators of cardiovascular risk affected by renal transplantation?

Hyperlipoproteinemia has been reported to frequently occur in kidney transplanted patients, thus possibly explaining, at least in part, the increased incidence of cardiovascular disease in this population. To evaluate the impact of renal transplantation (Tx), and related immunosuppressive therapy, on plasma lipoprotein and Lp(a) profile, we selected a cohort of kidney transplanted patients (36 M/14 F; age 33.8 + 12.0 yr, range 13-62) lacking significant causes of hyperlipidemia. All patients received a triple immunosuppressive regimen and showed a stable renal function after Tx (plasma creatinine: 1.36 +/- 0.35 mg/dL). One year after Tx, we found a significant increase of total cholesterol (TC), LDL, HDL, ApoB and ApoA-I (p < 0.005), while plasma triglyceride levels remained unmodified. Lp(a) plasma levels after Tx were within the normal range and displayed a significant inverse relationship with apo(a) size. Noteworthy, LDL/HDL ratio and ApoB/ ApoA-I ratio in kidney transplanted patients were almost superimposable with those of normal controls. Specifically, LDL/HDL ratio significantly decreased in 64% of patients after Tx, due to a prevalent increase of HDL, and was associated with a moderate amelioration of plasma TG. In a multiple linear regression model, post-Tx HDL level was significantly related to recipient's age, gender, BMI and cyclosporine (CyA) trough levels (Adj-R2 = 0.35, p = 0.0002), with gender and CyA trough levels being the better predictors of HDL. In conclusion, immunosuppressive regimens, in themselves, do not appear to significantly increase the atherogenic risk related to lipoproteins. Rather, other factors can affect the lipoprotein profile and its vascular effects in renal transplant recipients.

Contribution of apolipoprotein(a) size, pentanucleotide TTTTA repeat and C/T(+93) polymorphisms of the apo(a) gene to regulation of lipoprotein(a) plasma levels in a population of young European Caucasians

Several studies indicate that the inter-individual variation in plasma concentrations of lipoprotein(a) (Lp(a)) is mainly under genetic control. To define the effect of three DNA polymorphisms on apolipoprotein(a) (apo(a)) expression, we have determined plasma Lp(a) concentrations, apo(a) isoform size, KpnI allele size, the TTTTA pentanucleotide repeat number in the 5' control region of the apo(a) gene and the +93 C/T polymorphism in a European Caucasian population. The simultaneous determination of the kringle 4 (K4) number by genotyping and by phenotyping revealed that the size distribution of non-expressed apo(a) alleles was markedly skewed towards alleles with greater than 25 K4 repeats. This is consistent with the inverse relationship frequently described between the kringle 4 number and the plasma Lp(a) level. Apportioning the Lp(a) concentration from the surface of the peaks on apo(a) phenotyping blots, we have observed that the Lp(a) plasma concentration associated with alleles having more than 25 K4 units does not exceed 400 mg/l, whereas the range of Lp(a) concentrations associated with smaller alleles was broad, from 0 to more than 1000 mg/l. It can thus be concluded that the number of K4 repeats is the main determinant of Lp(a) concentration when this number is more than 25, whereas other polymorphisms may be involved in the alleles with fewer than 26 K4. Analyses of the TTTTA repeat number and of the +93 C/T polymorphism were performed in subjects with KpnI alleles of the same length: low Lp(a) concentrations were shown to be preferentially associated with the presence of apo(a) alleles with more than eight pentanucleotide repeats while no association was revealed between Lp(a) plasma levels and the C/T polymorphism. These results demonstrate that the (TTTTA)(n) polymorphism affects the Lp(a) expression independently of apo(a) size polymorphism.

Differential expression of double-band apolipoprotein(a) phenotypes in healthy Spanish subjects detected by SDS-agarose immunoblotting

A sodium dodecyl sulphate-agarose apolipoprotein(a) [apo(a)] phenotyping method was set up to attain accurate scanning densitometry of proteins. Serum samples from 99 healthy Spanish men were analysed and twenty-five different apo(a) isoforms (12 to 37 kringle 4 repeats) were detected. Double-band phenotypes accounted for 39.4% (n = 39) and three different patterns of protein expression were identified: pattern A (20.5% of double-band phenotyped samples) predominantly expressed the highest molecular weight isoform; pattern B (53.9%) mainly the lowest molecular weight isoform, and pattern AB (25.6%), expressed both isoforms equally. A significant linear association between expression pattern and lipoprotein(a) [Lp(a)] concentration > or = 0.30 g/l was observed. Single-band phenotyped samples (n = 60) were stratified according to apo(a) kringle 4 repeat categories and showed that 90% of isoforms < 20 K4 repeats had high Lp(a) concentrations (> or = 0.30 g/l), whereas isoforms with 20 to 24 or more than 24 kringle 4 repeats had Lp(a) concentrations > or = 0.30 g/l in 47% and 14%, respectively. A logistic regression model was fitted to test the association between apo(a) size, expression pattern and Lp(a) concentration. In this model, apo(a) isoform < 25 kringle 4 repeats was significantly associated with serum Lp(a) concentration > or = 0.30 g/l in both single and double-band phenotyped samples (odds ratio = 8.9, p < 0.001). In the latter, a differential expression pattern with respect to smaller size isoforms (pattern AB vs A) was significantly associated with Lp(a) concentration > or = 0.30 g/l (odds ratio = 17.97, P = 0.045). Heterogeneity in protein apo(a) size expressed according to kringle 4 repeat number could be categorized in heterozygous phenotypes as three patterns. When small-sized isoform was expressed (pattern B) or both isoforms were equally expressed (pattern AB), the probability of having Lp(a) > or = 0.30 g/l is higher.

Apolipoprotein(a) phenotypes as genetic markers of coronary atherosclerosis severity

We investigated Lp(a) levels and apo(a) polymorphism in relation to the severity of coronary artery disease, expressed both by the number of coronary arteries stenosed and three different coronary scoring systems. In a sample of 267 patients with coronary artery disease, a Mono-, Bi- or Multi-vessel coronary stenosis was documented by angiography. Twenty-five apo(a) isoforms were detected by a high resolution phenotyping method. Lp(a) levels did not show any differences among subgroups of patients. Both the percentage of apo(a) isoforms of low molecular weight (<655 kDa) (P=0.00015) and the percentage of subjects with at least one apo(a) isoform of low molecular weight (P=0.00027) were significantly correlated with increasing number of coronary vessels stenosed. In multivariate analysis, only apo(a) isoforms of low molecular weight were predictors of coronary atherosclerosis severity, when we used as the dependent variable both the '1-2-multi-vessels' categorization (P=0.000067) and the Gensini (P=0.008767), or Green Lane (P= 0.000001) or Dahlen (P=0.000102) coronary scoring system. Our data show that apo(a) isoforms of low molecular weight are associated with a greater severity of coronary atherosclerosis. If these data are confirmed by prospective studies, apo(a) phenotypes might be used as genetic markers of a greater severity of coronary atherosclerotic lesions.

Evaluation of the genotyping and phenotyping approaches in the investigation of apolipoprotein (a) size polymorphism

Apoprotein (a) size polymorphism was evaluated at the genotypic and phenotypic level in 110 individuals. Both methods were well correlated with respect to size (r = 0.971), providing that the protein size was expressed as a number of kringle 4 repeats. Despite the fact that the immunoblotting method used was sensitive enough to detect less than 1 ng of lipoprotein (a), 62 samples had single-band phenotypes and one sample had no detectable band, whereas only seven samples had single-band genotypes. The mean size of the alleles coding for the undetected isoforms was significantly larger (141 kb) than for the detected isoforms (123 kb), corroborating the earlier finding of an inverse relationship between the size and the plasma expression level of apoprotein (a). Furthermore, increasing detectability was achieved by loading the gel with different amounts of plasma for each sample. Our results indicate that genotyping is more resolving and more sensitive, but requires a more specialized technology. Phenotyping was carried out using commercially available reagents.

Association of lipoprotein(a) levels and apolipoprotein(a) phenotypes with coronary heart disease in patients with essential hypertension

BACKGROUND

Besides hypertension, several cardiovascular risk factors can play a role in the development of coronary heart disease (CHD) in hypertensive patients. Lipoprotein(a) [Lp(a)] is an important and independent cardiovascular risk factor, but its role in the development of CHD in hypertensives has not been studied.

OBJECTIVE

To investigate whether or not Lp(a) levels and isoforms of apolipoprotein(a) [apo(a)] are predictors of CHD in patients with essential hypertension.

METHODS

Lp(a) levels and apo(a) polymorphism were evaluated in 249 patients with essential hypertension, in 142 non-hypertensive patients with CHD and in 264 healthy controls.

RESULTS

Hypertensives with CHD (n = 61) had Lp(a) levels [19 (range 0.5-73.5) versus 7 mg/dl (range 0-83.5), P < 0.001] and a percentage of apo(a) isoforms of low (< 655 kDa) relative molecular mass (RMM, 59.2 versus 25.9%, P < 0.001) higher than did those without CHD (n = 188). Moreover, there were more subjects with at least one apo(a) isoform of low RMM in the subgroup of patients with CHD than there were in that of those without CHD (80.3 versus 30.8%, P< 0.001). Lp(a) levels and apo(a) polymorphism did not differ significantly between hypertensive and non-hypertensive patients with CHD. Stepwise regression analysis indicated that high Lp(a) levels (P= 0.002073) and particularly the presence of at least one apo(a) isoform of low RMM (P < 0.000001) are strong predictors of CHD in hypertensive patients.

CONCLUSIONS

Our data show that high Lp(a) levels and the presence of at least one apo(a) isoform of low RMM are strong and independent genetic risk factors for CHD in hypertensive patients. These findings suggest that Lp(a) and apo(a) isoforms should be assessed together with other cardiovascular risk factors to establish the overall CHD risk status of each hypertensive patient

A quantitative immunoassay for the lysine-binding function of lipoprotein(a). Application to recombinant apo(a) and lipoprotein(a) in plasma

Apo(a), the unique apoprotein of lipoprotein(a) (Lp[a]), can express lysine-binding sites(s) (LBS). However, the LBS activity of Lp(a) is variable, and this heterogeneity may influence its pathogenetic properties. An LBS-Lp(a) immunoassay has been developed to quantitatively assess the LBS function of Lp(a). Lp(a) within a sample is captured with an immobilized monoclonal antibody specific for apo(a), and the captured Lp(a) is reacted with an antibody specific for functional LBS. The binding of this LBS-specific antibody is then quantified by using an alkaline phosphatase-conjugated disclosing antibody. The critical LBS-specific antibody was raised to kringle 4 of plasminogen. When applied to plasma samples, the LBS activity of Lp(a) ranged from 0% to 100% of an isolated reference Lp(a); the signal corresponded to the percent retention of Lp(a) on a lysine-Sepharose but did not correlate well with total Lp(a) levels in plasma. Mutation of residues in the putative LBS in the carboxy-terminal kringle 4 repeat (K4-37) in an eight-kringle apo(a) construct resulted in marked but not complete loss of activity in the LBS-Lp(a) immunoassay. These data suggest that this kringle is the major but not the sole source of LBS activity in apo(a). The LBS-Lp(a) immunoassay should prove to be a useful tool in establishing the role of the LBS in the pathogenicity of Lp(a).