High levels of Lp(a) with a small apo(a) isoform are associated with coronary artery disease in African American and white men

Elevated levels of lipoprotein(a) [Lp(a)] and the presence of small isoforms of apolipoprotein(a) [apo(a)] have been associated with coronary artery disease (CAD) in whites but not in African Americans. Because of marked race/ethnicity differences in the distribution of Lp(a) levels across apo(a) sizes, we tested the hypothesis that apo(a) isoform size determines the association between Lp(a) and CAD. We related Lp(a) levels, apo(a) isoforms, and the levels of Lp(a) associated with different apo(a) isoforms to the presence of CAD (>/=50% stenosis) in 576 white and African American men and women. Only in white men were Lp(a) levels significantly higher among patients with CAD than in those without CAD (28.4 versus 16.5 mg/dL, respectively; P:=0.004), and only in this group was the presence of small apo(a) isoforms (<22 kringle 4 repeats) associated with CAD (P:=0.043). Elevated Lp(a) levels (>/=30 mg/dL) were found in 26% of whites and 68% of African Americans, and of those, 80% of whites but only 26% of African Americans had a small apo(a) isoform. Elevated Lp(a) levels with small apo(a) isoforms were significantly associated with CAD (P:<0.01) in African American and white men but not in women. This association remained significant after adjusting for age, diabetes mellitus, smoking, hypertension, HDL cholesterol, LDL cholesterol, and triglycerides. We conclude that elevated levels of Lp(a) with small apo(a) isoforms independently predict risk for CAD in African American and white men. Our study, by determining the predictive power of Lp(a) levels combined with apo(a) isoform size, provides an explanation for the apparent lack of association of either measure alone with CAD in African Americans. Furthermore, our results suggest that small apo(a) size confers atherogenicity to Lp(a).     

Lipoprotein(a) and atherosclerosis: New perspectives on the mechanism of action of an enigmatic lipoprotein

Although elevated plasma concentrations of lipoprotein(a) (Lp(a)) have been identified as a risk factor for coronary heart disease, the pathophysiologic and physiologic roles of Lp(a) continue to elude basic researchers and clinicians alike. Lp(a) is a challenging lipoprotein to study because it has a complex structure consisting of a low-density lipoprotein-like moiety to which is covalently attached the unique glycoprotein apolipoprotein(a) (apo(a)). Apo(a) contains multiply repeated kringle domains that are similar to a sequence found in the fibrinolytic proenzyme plasminogen; differing numbers of kringle sequences in apo(a) give rise to Lp(a) isoform size heterogeneity. In addition to elevated plasma concentrations of Lp(a), apo(a) isoform size has been identified as a risk factor for coronary heart disease, although studies addressing this relationship have been limited. The similarity of Lp(a) to low-density lipoprotein and plasminogen provides an enticing link between the processes of atherosclerosis and thrombosis, although a clear demonstration of this association in vivo has not been provided. Clearly, Lp(a) is a risk factor for both atherothrombotic and purely thrombotic events; a plethora of mechanisms to explain these clinical findings has been provided by both in vitro studies as well as animal models for Lp(a).     

Molecular analysis of apo(a) fragmentation in polygenic hypercholesterolemia: characterization of a new plasma fragment pattern

Hypercholesterolemia is frequently associated with elevated Lp(a) levels, an independent risk factor for coronary, cerebrovascular, and peripheral vascular disease. A portion of apolipoprotein(a) [apo(a)] circulates as a series of fragments derived from the N-terminal region of apo(a). The relationship of elevated lipoprotein(a) [Lp(a)] levels to those of circulating apo(a) fragments in polygenic hypercholesterolemia is indeterminate. Therefore, plasma Lp(a) and plasma and urinary apo(a) fragment levels were measured by ELISA in 82 patients with polygenic type IIa hypercholesterolemia (low density lipoprotein cholesterol >/=4.13 mmol/L and triglycerides <2.24 mmol/L) and in 90 normolipidemic subjects. Lp(a) levels were significantly elevated in patients compared with control subjects (0.35+/-0.4 and 0.24+/-0.31 mg/mL, respectively; median 0.13 and 0.11 mg/mL, respectively; P=0.039), although apo(a) isoform distribution did not differ. Patients displayed significantly higher plasma and urinary apo(a) fragment levels than did control subjects (respective values were as follows: 4.97+/-5.51 and 2.15+/-2.57 [median 2.85 and 1.17] microg/mL in plasma, P<0.0001; 75+/-86 and 40+/-57 [median 38 and 17] ng/mg urinary creatinine in urine, P<0.0001). The ratio of plasma apo(a) fragments to Lp(a) levels was also significantly higher in patients than in control subjects (1.93+/-1.5% and 1.75+/-2.36%, respectively; P<0.0001). We conclude that increased plasma Lp(a) levels in polygenic hypercholesterolemia are associated with elevated circulating levels of apo(a) fragments but that this increase is not due to decreased renal clearance of apo(a) fragments. Furthermore, we identified a new pattern of apo(a) fragmentation characterized by the predominance of a fragment band whose size was related to that of the parent apo(a) isoform and that was superimposed on the series of fragments described previously by Mooser et al (J Clin Invest. 1996; 98:2414-2424). This new pattern was associated with small apo(a) isoforms and did not discriminate between hypercholesterolemic and normal subjects. However, this new apo(a) fragment pattern may constitute a novel marker for cardiovascular risk.     

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.     

Genetic basis and pathophysiological implications of high plasma Lp(a) levels.

Lipoprotein(a) or Lp(a) is a genetic variant of plasma low density lipoproteins (LDL) containing apoB100 covalently linked to apolipoprotein(a) or apo(a), the specific marker of Lp(a). Lp(a) is heterogeneous in size and density, accounting in part for the marked size polymorphism of apo(a), 300 to 800 kDa. The apo(a) size polymorphism is related to the different number of kringle repeats which are structurally similar although not identical to the kringle 4 of plasminogen. Recent studies on a genomic level have indicated that the apo(a) gene contains at least 19 different alleles varying in length between 48 and 190 kb, partially impacting on the plasma levels of Lp(a). High plasma levels of Lp(a) have been found to be associated with an increased prevalence of premature atherosclerotic cardiovascular disease by mechanism(s) yet to be established. Both atherogenic and thrombogenic potentials have been postulated and have been related to the LDL-like and plasminogen-like properties of Lp(a), respectively.     

Fish intake, independent of apo(a) size, accounts for lower plasma lipoprotein(a) levels in Bantu fishermen of Tanzania: The Lugalawa Study.

Plasma lipoprotein(a) [Lp(a)] levels are largely genetically determined by sequences linked to the gene encoding apolipoprotein(a) [apo(a)], the distinct protein component of Lp(a). Apo(a) is highly polymorphic in length due to variation in the numbers of a sequence encoding the apo(a) kringle 4 domain, and plasma levels of Lp(a) are inversely correlated with apo(a) size. In 2 racially homogeneous Bantu populations from Tanzania differing in their dietary habits, we found that median plasma levels of Lp(a) were 48% lower in those living on a fish diet than in those living on a vegetarian diet. Considering the relationship between apo(a) size and Lp(a) plasma concentration, we have extensively evaluated apo(a) isoform distribution in the 2 populations to determine the impact of apo(a) size in the determination of Lp(a) values. The majority of individuals (82% of the fishermen and 80% of the vegetarians) had 2 expressed apo(a) alleles. Additionally, the fishermen had a high frequency of large apo(a) isoforms, whereas a higher frequency of small isoforms was found in the vegetarians. When subjects from the 2 groups were matched for apo(a) phenotype, the median Lp(a) value was 40% lower in Bantus on the fish diet than in those on the vegetarian diet. A significant inverse relationship was also found between plasma n-3 polyunsaturated fatty acids and Lp(a) levels (r=-0.24, P=0.01). The results of this study are consistent with the concept that a diet rich in n-3 polyunsaturated fatty acids, and not genetic differences, is responsible for the lower plasma levels of Lp(a) in the fish-eating Bantus and strongly suggest that a sustained fish-based diet is able to lower plasma levels of Lp(a).     

Lipoprotein (a) levels and apolipoprotein (a) isoform size in patients with subclinical hypothyroidism: effect of treatment with levothyroxine.

The increased risk for ischemic heart disease (IHD) associated with subclinical hypothyroidism (SH) has been partly attributed to dyslipidemia. There is limited information on the effect of SH on lipoprotein (a) [Lp(a)], which is considered a significant predictor of IHD. Serum Lp(a) levels are predominantly regulated by apolipoprotein [apo(a)] gene polymorphisms. The aim of our study was to evaluate the Lp(a) levels and apo(a) phenotypes in patients with SH compared to healthy controls as well as the influence of levothyroxine substitution therapy on Lp(a) values in relation to the apo(a) isoform size. Lp(a) levels were measured in 69 patients with SH before and after restoration of a euthyroid state and in 83 age- and gender-matched healthy controls. Apo(a) isoform size was determined by sodium dodecyl sulfate (SDS) agarose gel electrophoresis followed by immunoblotting and development via chemiluminescence. Patients with SH exhibited increased Lp(a) levels compared to controls (median value 10.6 mg/dL vs. 6.0 mg/dL, p = 0.003]), but this was not because of differences in the frequencies of apo(a) phenotypes. There was no association between thyrotropin (TSH) and Lp(a) levels in patients with SH. In subjects with either low (LMW; 25 patients and 28 controls) or high (HMW; 44 patients and 55 controls) molecular weight apo(a) isoforms, Lp(a) concentrations were higher in patients than in the control group (median values 26.9 mg/dL vs. 21.8 mg/dL, p = 0.02 for LMW, and 6.0 mg/dL versus 3.3 mg/dL, p < 0.001 for HMW). Levothyroxine treatment resulted in an overall reduction of Lp(a) levels (10.6 mg/dL baseline vs. 8.9 mg/dL posttreatment, p = 0.008]). This effect was mainly evident in patients with LMW apo(a) isoforms associated with high baseline Lp(a) concentrations (median values 26.9 mg/dL vs. 23.2 mg/dL pretreatment and posttreatment, respectively; p = 0.03). In conclusion, even though a causal effect of thyroid dysfunction on Lp(a) was not clearly demonstrated in patients with SH, levothyroxine treatment is beneficial, especially in patients with increased baseline Lp(a) levels and LMW apo(a) isoforms.     

Corticotropin-induced reduction of plasma lipoprotein(a) concentrations in healthy individuals and hemodialysis patients: relation to apolipoprotein(a) size polymorphism

Lipoprotein(a) [Lp(a)], a strong independent cardiovascular risk factor, consists of the unique apolipoprotein(a) [apo(a)] covalently linked to a low-density lipoprotein particle. Apo(a) contains a widely differing number of the plasminogen-like kringle IV, a size polymorphism that is codominantly inherited. In addition to powerful genetic control, renal failure is known to influence the plasma Lp(a) concentration. There is still a lot to be learned about the mode and site of catabolism of Lp(a), and there is no readily applicable Lp(a)-lowering treatment available. Therefore, it was of interest to study further the Lp(a)-lowering effect of corticotropin (ACTH) that has been demonstrated in small studies. The main purpose of the present study was to investigate the influence of ACTH on different apo(a) isoforms. Short-term treatment with ACTH decreased the plasma Lp(a) concentration in all 26 study participants. The two study groups (12 healthy individuals and 14 hemodialysis patients) responded similarly, with a median decrease in plasma Lp(a) of 39% and 49%, respectively. In subjects with two clearly separable apo(a) bands, apo(a) phenotyping and densitometric scanning of the bands before and after treatment with ACTH revealed a change in the proportion of apo(a) isoforms, ie, a shift toward the isoform with lower molecular weight. This was observed in seven of nine investigated subjects (four of five healthy individuals and three of four hemodialysis patients).     

Does apolipoprotein(a) heterogeneity influence lipoprotein(a) effects on fibrinolysis?

High plasma levels of lipoprotein(a) [Lp(a)] are considered to be an independent risk factor for premature cardiovascular disease and are inversely associated with apolipoprotein(a) [apo(a)] isoform sizes. The contribution of apo(a) polymorphism to the inhibition of fibrinolysis, a mechanism that may favor thrombus development, was therefore evaluated by measuring the ability of Lp(a) particles of distinct apo(a) isoform content to compete with plasminogen for fibrin binding during plasminogen activation by fibrin-bound tissue-type plasminogen activator. The rate of plasmin generation was most efficiently inhibited by an isoform with a molecular weight (M(r)) of approximately 540 Kd. An isoform with M(r) approximately 590 Kd produced a less pronounced effect, whereas the isoform with M(r) approximately 610 Kd failed to inhibit plasminogen activation. These effects were directly proportional to the amount of Lp(a) bound to the carboxy-terminal lysine residues of degraded fibrin. The relative affinity of the binding (kd range, 16 to 180 nmol/L) reflected the ability of individual Lp(a) isoforms to inhibit the binding of plasminogen (kd, 600 nmol/L). The question of the influence of kringle sequence variability on the binding to fibrin was not addressed by the present work. These data suggest that apo(a) isoform types with high affinity for fibrin may influence the ability of Lp(a) to interfere with fibrinolysis and contribute thereby to the association of elevated levels of Lp(a) with atherosclerotic and thrombotic risks.     

A critical evaluation of the role of Lp(a) in cardiovascular disease: can Lp(a) be useful in risk assessment?

Lp(a) is a structurally complex particle which resembles LDL, but which also contains the distinctive glycoprotein apo(a). Apo(a) is characterized by a variable number of repeated kringle domains, which gives rise to differently-sized Lp(a) isoforms in the population. Although epidemiological studies indicate that elevated Lp(a) concentration and/or small apo(a) isoform sizes increase the risk of coronary heart disease (CHD), a causal role for Lp(a) in CHD remains unproven. This is largely due to the difficulty in establishing a relevant animal model to probe Lp(a) function, and the lack of intervention studies in which Lp(a) concentrations are lowered and outcomes followed. The accumulation of apo(a)/Lp(a) in arterial lesions has provided the rationale for numerous in vitro studies aimed at dissecting its function in this milieu. These studies have resulted in the proposal of numerous proatherogenic, prothrombotic and antifibrinolytic roles for both native and modified apo(a)/Lp(a). Although characterization of Lp(a) in the general population is not presently justified, Lp(a) analysis in patients at risk for CHD may be warranted.     

Lipoprotein Lp(a) in homozygous familial hypercholesterolemia: density profile, particle heterogeneity and apolipoprotein(a) phenotype.

Homozygous familial hypercholesterolemia (FH) is a genetic disorder featuring a functional defect in cellular LDL receptors, marked elevation in circulating LDL concentrations, and premature atherosclerosis. The potential atherogenic role of apo B-containing lipoproteins other than LDL in this disease is indeterminate. We describe the quantitative and qualitative characteristics of Lp(a) as a function of apo(a) phenotype in a group of eight, unrelated homozygous FH patients. Plasma Lp(a) levels were significantly elevated (2.5-fold; mean 50 +/- 32 mg/dl) as compared to those in healthy subjects. The S2 isoform of apo(a) occurred most frequently (6 of eight patients); the rare B isoform presented in three patients. Plasma Lp(a) levels in homozygous FH did not correspond to those predicted by apo(a) phenotype. Analyses of the density distribution of Lp(a) and of Lp(a) particle size and heterogeneity as a function of density did not reveal any anomalies characteristic of homozygous FH. However, comparison of the hydrated density of Lp(a) particles as a function of apo(a) isoform content revealed a clear influence of isoform on this parameter; thus, in a B/S2 heterozygous patient, the density distribution of Lp(a) fractions containing isoform B alone, B and S2, and S2 alone, demonstrated that the apparent molecular weight of apo(a) plays a determining role in controlling the hydrated density and size of the resulting Lp(a) particle. Indeed, patients expressing the high molecular weight, S2 isoform uniformly displayed a dense form of Lp(a) (hydrated density approximately 1.055 g/ml). In subjects presenting two apo(a) isoforms, each isoform resided on distinct lipoprotein particles; in such cases, the plasma levels of the denser isoform predominated, suggesting differences in rates of formation, or rates of tissular catabolism, or in the plasma stability of the particles, or a combination of these mechanisms. Considered together, our data may be interpreted to suggest that the elevated circulating levels of Lp(a) in homozygous FH patients may reflect either an increased biosynthesis, or diminished catabolism via the cellular LDL receptor pathway, or a combination of both.     

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.     

High levels of inflammatory biomarkers are associated with increased allele-specific apolipoprotein(a) levels in African-Americans

BACKGROUND: A role of inflammation for cardiovascular disease (CVD) is established. Lipoprotein(a) [Lp(a)] is an independent CVD risk factor where plasma levels are determined by the apolipoprotein(a) [apo(a)] gene, which contains inflammatory response elements. DESIGN: We investigated the effect of inflammation on allele-specific apo(a) levels in African-Americans and Caucasians. We determined Lp(a) levels, apo(a) sizes, allele-specific apo(a) levels, fibrinogen and C-reactive protein (CRP) levels in 167 African-Americans and 259 Caucasians. RESULTS: Lp(a) levels were increased among African-Americans with higher vs. lower levels of CRP [<3 vs. > or =3 mg/liter (143 vs. 108 nmol/liter), P = 0.009] or fibrinogen (<340 vs. > or =340 mg/liter, P = 0.002). We next analyzed allele-specific apo(a) levels for different apo(a) sizes. No differences in allele-specific apo(a) levels across CRP or fibrinogen groups were seen among African-Americans or Caucasians for small apo(a) sizes (<22 kringle 4 repeats). Allele-specific apo(a) levels for medium apo(a) sizes (22-30 kringle 4 repeats) were significantly higher among African-Americans, with high levels of CRP or fibrinogen compared with those with low levels (88 vs. 67 nmol/liter, P = 0.014, and 91 vs. 59 nmol/liter, P < 0.0001, respectively). No difference was found for Caucasians. CONCLUSIONS: Increased levels of CRP or fibrinogen are associated with higher allele-specific medium-sized apo(a) levels in African-Americans but not in Caucasians. These findings indicate that proinflammatory conditions result in a selective increase in medium-sized apo(a) levels in African-Americans and suggest that inflammation-associated events may contribute to the interethnic difference in Lp(a) levels between African-Americans and Caucasians.     

Polymorphism in apolipoprotein(a) kringle IV 37 (Met/Thr): Frequency in a London population and its association with coronary artery disease

Background: A raised concentration of lipoprotein(a) [Lp(a)] in human plasma has been considered as a risk factor for coronary artery disease (CAD). Apolipoprotein(a) and plasminogen genes are exceptionally similar to a variable number of plasminogen-like kringle IV repeats in the apo(a) gene. Polymorphisms have been previously identified in the apolipoprotein(a) kringle IV 37. Hypothesis: In order to determine the frequency of the apolipoprotein(a) kringle IV 37 Met⁶⁶→Thr polymorphism in a London-based population and to assess the relationship of this polymorphism with CAD in Caucasian patients, we geno-typed two groups of people of different ethnic origin (Caucasian and Afro-Caribbean) for the mutation using standard polymerase chain reaction (PCR) techniques. Methods: The first group consisted of 182 unrelated Caucasian patients (107 men and 75 women, mean age 59.7 ± 10.2 years) recruited at St. George's Hospital. They were defined as patients with 0, 1 or ≥ 2 vessel disease patients depending on the degree of stenosis in none, one, or several major epicardial arteries. The second group comprised 64 unrelated patients of Afro-Caribbean origin attending a hypertension clinic at St. George's Hospital. Results: It was shown that the prevalence of the Met⁶⁶→Thr mutation is markedly higher in Caucasians than in Afro-Caribbeans and that this mutation is not associated with either Lp(a) levels or severity of CAD.     

Apolipoprotein (a) phenotypes and lipoprotein (a) concentrations in patients with type III hyperlipoproteinaemia

Abstract. Objectives . The familial lipoprotein disorder type III hyperlipoproteinaemia (HLP) carries a marked increase in the risk of accelerated and premature atherosclerosis, but there is considerable variation amongst affected individuals in their susceptibility to cardiovascular disease (CVD). Therefore, it was the aim of our study to investigate the possible influence of lipoprotein (a) [Lp(a)] in the pathogenesis of type III HLP. Design . Apolipoprotein (a) [apo(a)] phenotypes and Lp(a) concentrations were determined in patients with the disease and in an appropriate control group. Setting . University out-patient lipid disorder clinic. Subjects . Seventy-six apoE-2 homozygous patients with type III HLP and 76 normolipidaemic and healthy age- and sex-matched controls. Main outcome measures . The frequencies of different apo(a) phenotypes and their correlations with Lp(a) serum concentrations were determined in patients and controls. Results . Lp(a) concentrations were not significantly different in type III HLP patients (14.1±19.1 mg dl^-1) as compared with the controls (13.3±16.2 mg dl^-1; P = 0.549, NS). In addition, there was no significant difference in apo(a) phenotype frequencies amongst both groups (0.2 > P > 0.1). Conclusions . We conclude that the apo(a) polymorphism does not participate (to a significant extent) in the phenotypical expression of type III HLP.     

Analyses of serum lipoprotein(a) and the relation to phenotypes and genotypes of apolipoprotein(a) in type 2 diabetic patients with retinopathy.

To elucidate the association of lipoprotein(a) (Lp(a)) with diabetic retinopathy (DR), we studied the serum Lp(a) concentrations (n = 412), apolipoprotein(a) (apo(a)) phenotypes expressed by the number of kringle 4 (K4) repeats (n = 150), apo(a) gene genotypes (n = 161) of type 2 diabetes with or without DR. The 5'-untranslated region of apo(a) gene was classified into seven haplotypes (A to G) and 18 genotypes by PCR-RFLP at three distinct sites. The serum Lp(a) concentrations were significantly higher in diabetic patients than in normal controls. Furthermore, the patients with DR, especially proliferative retinopathy showed higher serum Lp(a) concentrations than those without DR. Although a negative correlation was found between the serum Lp(a) concentrations and the number of K4 repeats in total diabetic patients, no difference was seen in the distribution of the number of K4 repeats between those with and without DR. In the same apo(a) phenotypes, the patients with DR had higher Lp(a) concentrations than those without DR. Among the genotypes, type CC showed significantly higher serum Lp(a) concentrations than the other genotypes. However, there was no difference in the ratios of the type CC between the patients with and without DR. In conclusion, other factors than phenotypes and genotypes in the 5'-untranslated region of apo(a) may be responsible for the elevation of serum Lp(a) in diabetic patients with retinopathy.     

Sequence polymorphisms in the apolipoprotein(a) gene and their association with lipoprotein(a) levels and myocardial infarction. The ECTIM Study.

Lp(a) concentrations are largely determined by apo(a) isoform size, but several studies have shown that apo(a) isoforms could not entirely explain the increase of Lp(a) levels observed in patients with coronary heart disease (CHD). Since up to 90% of the variance in Lp(a) levels has been suggested to be attributable to the apo(a) locus, the hypothesis that polymorphisms of the apo(a) gene other than size could contribute to the increase of Lp(a) levels in CHD patients must be considered. This hypothesis was tested in the ECTIM Study comparing 594 patients with myocardial infarction and 682 control subjects in Northern Ireland and France. In addition to apo(a) phenotyping, five previously described polymorphisms of the apo(a) gene were genotyped: a (TTTTA)n repeat at position -1400 from the ATG, a G/A at -914, a C/T at -49, a G/A at -21 and a Met/Thr affecting amino acid 4168. As reported earlier [Parra HJ, Evans AE, Cambou JP, Amouyel P, Bingham A, McMaster D, Schaffer P, Douste-Blazy P, Luc G, Richard JL, Ducimetiere P, Fruchart JC, Cambien F. A case-control study of lipoprotein particles in two populations at contrasting risk for coronary heart disease. The ECTIM study. Arterioscler Thromb 1992; 12:701-707], mean Lp(a) levels were higher in cases than in controls (20.7 vs 14.6 mg/dl in Belfast, 17.2 vs 8.9 mg/dl in France, P < 0.001 for case-control and population differences). In the present study, mean apo(a) isoform size differed significantly between cases and controls (25.7 vs 26.6 kr in Belfast, 25.9 vs 27.4 kr in France, P < 0.001 for case-control and P = 0.13 for population difference). After adjustment for apo(a) isoforms, Lp(a) levels remained significantly higher in cases than in controls (difference, 4.6 mg/dl; P < 0.001). Genotype and allele frequencies did not differ significantly between cases and controls for any of the five polymorphisms studied. The five polymorphisms were in strong linkage disequilibrium and had a combined heterozygosity of 0.83. In multivariate regression analysis adjusted for apo(a) isoforms, only the (TTTTA)n polymorphism was significantly associated with Lp(a) levels; it explained 4.5% of Lp(a) variability in cases and 3.1% in controls. The Lp(a) case/control difference was not reduced after taking into account the (TTTTA)n effect. We conclude that the increase of Lp(a) levels observed in MI cases, and which was not directly attributable to apo(a) size variation, was not related to the five polymorphisms of the apo(a) gene considered.     

Lipoprotein (a) levels, apolipoprotein (a) phenotypes and thyroid autoimmunity

It has been reported that euthyroid normolipidemic males and postmenopausal females exhibit significantly higher serum lipoprotein (a) (Lp(a)) levels compared with age- and sex-matched normolipidemic controls. However, it is well known that there is an inverse correlation between Lp(a) concentration and apolipoprotein (a) (apo(a)) isoform size. Thus, it is imperative to exclude differences in apo(a) isoform frequencies between subjects with or without thyroid autoimmunity in order to verify if there is an association between thyroid autoimmunity and increased Lp(a) concentration. To exclude such an effect of different apo(a) isoform frequencies, we determined apo(a) phenotypes in 22 patients (9 males and 13 postmenopausal females) with thyroid autoimmunity and in 64 (29 males and 35 females) age- and sex-matched individuals without thyroid autoimmunity (control group). There were no significant differences in the values of lipid parameters between the two groups, including Lp(a). We did not detect any significant differences in the apo(a) phenotype frequencies between the two groups. Additionally, in neither of the subgroups formed according to the presence of low molecular vs high molecular weight apo(a) isoforms were there any significant differences in median serum Lp(a) levels between patients with and without thyroid autoimmunity. Thus, our results contradict the previously reported association between thyroid autoimmunity and Lp(a) concentrations.     

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)     

Serum lipoprotein(a) concentrations and apolipoprotein(a) isoforms: association with the severity of clinical presentation in patients with coronary heart disease.

OBJECTIVE: The aim of this study was to investigate the possible associations between lipoprotein(a) [Lp(a)] concentrations or apolipoprotein(a) isoforms and the mode of clinical presentation of coronary heart disease (CHD) (acute thrombotic event or not). METHODS: A total of 131 CHD patients and 71 age- and gender-matched individuals without known CAD (free of symptoms of heart disease) were enrolled in the study. CHD patients were classified into patients with a history of an acute coronary syndrome (ACS, n=94) and patients with stable angina (SA, n=37). Lp(a) levels were measured with an ELISA method, whereas apolipoprotein(a) isoform analysis was performed (in all patients and 33 controls) by electrophoresis in 1.5% SDS-agarose gels followed by immunoblotting. Isoform size was expressed as the number of kringle 4 (K4) repeats. RESULTS: ACS patients had higher Lp(a) plasma levels 121.9 (0.8-84.1) mg/dl] and a greater proportion of elevated (> or = 30 mg/dl) Lp(a) concentrations (25.5%) compared with SA patients [9.2 (0.8-50.5) mg/dl, P < 0.01 and 10.8%, P < 0.05] and controls [8.0 (0.8-55.0) mg/dl, P < 0.01 and 11.2%, P < 0.05], while there were no differences between SA patients and controls. The median apolipoprotein(a)-isoform size was 26 K4. In 17 (10%) patients we could not detect any apolipoprotein(a) isoform bands by immunoblotting. ACS patients had a higher proportion of isoforms < 26 K4 (low molecular weight) than SA patients (56/85 vs. 12/33, P < 0.005) and controls (10/29, P < 0.005). CONCLUSIONS: CAD patients with a history of ACS have higher Lp(a) plasma levels and a significantly higher proportion of low molecular weight apolipoprotein(a) isoforms compared with patients with SA or to controls.