Genetics of the quantitative Lp(a) lipoprotein trait. II. Inheritance of Lp(a) glycoprotein phenotypes

Lipoprotein(a) Levels at Birth and in Early Childhood: The COMPARE Study

BACKGROUND AND OBJECTIVE

High lipoprotein(a) is a genetically determined causal risk factor for cardiovascular disease, and 20% of the adult population has high levels (ie, >42 mg/dL, >88 nmol/L). We investigated whether early life lipoprotein(a) levels measured in cord blood may serve as a proxy for neonatal venous blood levels, whether lipoprotein(a) birth levels (ie, cord or venous) predict levels later in life, and whether early life and parental levels correlate.

METHODS

The Compare study is a prospective cohort study of newborns (N = 450) from Copenhagen, Denmark, including blood sampling of parents. Plasma lipoprotein(a) was measured in cord blood (N = 402), neonatal venous blood (N = 356), and at 2 (N = 320) and 15 months follow-up (N = 148) of infants, and in parents (N = 705).

RESULTS

Mean lipoprotein(a) levels were 2.2 (95% CI, 1.9-2.5), 2.4 (2.0-2.7), 4.1 (3.4-4.9), and 14.6 (11.4-17.9) mg/dL in cord, neonatal venous, and 2- and 15-month venous samples, respectively. Lipoprotein(a) levels in cord blood correlated strongly with neonatal venous blood levels (R2 = 0.95, P < 0.001) and neonatal levels correlated moderately with 2- and 15-month levels (R2 = 0.68 and 0.67, both P < 0.001). Birth levels ≥ 90th percentile predicted lipoprotein(a) > 42 mg/dL at 15 months with positive predictive values of 89% and 85% for neonatal venous and cord blood. Neonatal and infant levels correlated weakly with parental levels, most pronounced at 15 months (R2 = 0.22, P < 0.001).

CONCLUSIONS

Lipoprotein(a) levels are low in early life, cord blood may serve as a proxy for neonatal venous blood, and birth levels ≥ 90th percentile can identify newborns at risk of developing high levels.

Elevated Lipoprotein(a): Background, Current Insights and Future Potential Therapies

Lipoprotein(a) forms a subfraction of the lipid profile and is characterized by the addition of apolipprotein(a) (apo(a)) to apoB100 derived particles. Its levels are mostly genetically determined inversely related to the number of protein domain (kringle) repeats in apo(a). In epidemiological studies, it shows consistent association with cardiovascular disease (CVD) and most recently with extent of aortic stenosis. Issues with standardizing the measurement of Lp(a) are being resolved and consensus statements favor its measurement in patients at high risk of, or with family histories of CVD events. Major lipid-lowering therapies such as statin, fibrates, and ezetimibe have little effect on Lp(a) levels. Therapies such as niacin or cholesterol ester transfer protein (CETP) inhibitors lower Lp(a) as well as reducing other lipid-related risk factors but have failed to clearly reduce CVD events. Proprotein convertase subtilisin kexin-9 (PCSK9) inhibitors reduce cholesterol and Lp(a) as well as reducing CVD events. New antisense therapies specifically targeting apo(a) and hence Lp(a) have greater and more specific effects and will help clarify the extent to which intervention in Lp(a) levels will reduce CVD events.

Performance evaluation of five lipoprotein(a) immunoassays on the Roche cobas c501 chemistry analyzer

Objectives

Measurement of lipoprotein(a) [Lp(a)] is used in risk assessment of atherosclerotic cardiovascular disease (ASCVD). The aim of the current study was to evaluate performance characteristic of five different Lp(a) assays using the cobas c501 (Roche Diagnostics) analyzer.

Design and methods

Lp(a) was measured using five Lp(a) assays (Diazyme, Kamiya, MedTest, Randox, and Roche) configured to mg/dL units. Assays from Diazyme and Kamiya were also configured using nmol/L units in separate experiments. Studies included sensitivity, imprecision, linearity, method comparison, and evaluation of healthy subjects. Imprecision (intra-day, 20 replicates; inter-day, duplicates twice daily for five days) and linearity were evaluated using patient pools. Linearity assessed a minimum of five patient splits spanning the analytical measurement range (AMR). Method comparison used 80 residual serum samples. Specimens from 120 self-reported healthy subjects (61 females / 59 males) were also tested. Method comparison for two assays in nmol/L units was conducted using 96 residual serum samples.

Results

Assay sensitivities met all manufacturer claims. Imprecision studies demonstrated %CVs ranging from 2.5 to 5.2% for the low pool (average concentration from 7.3 to 12.4 ​mg/dL); high pool %CVs ranged from 0.8 to 3.0% (average concentrations from 31.5–50.2 ​mg/dL). Linearity was confirmed for all assays. Variation in accuracy was observed when comparing results to an all method average. Lp(a) results were higher in females versus males in self-reported healthy subjects.

Conclusions

All assays performed according to manufacturer described performance characteristics, although differences were observed across Lp(a) assays tested when compared to an all method average.

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Five automated assays for Lp(a) measurement (mg/dL units) were compared.

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Differences in accuracy were observed across the methods investigated.

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Two assays were also compared using nmol/L units.

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More Lp(a) assay traceability to the international reference material is needed.

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

Lipoprotein (a): a Unique Independent Risk Factor for Coronary Artery Disease

The current epidemic affecting Indians is coronary artery disease (CAD), and is currently one of the most common causes of mortality and morbidity in developed and developing countries. The higher rate of CAD in Indians, as compared to people of other ethnic origin, may indicate a possible genetic susceptibility. Hence, Lp(a), an independent genetic risk marker for atherosclerosis and cardiovascular disease assumes great importance. Lp(a), an atherogenic lipoprotein, contains a cholesterol rich LDL particle, one molecule of apolipoprotein B-100 and a unique protein, apolipoprotein (a) which distinguishes it from LDL. Apo(a) is highly polymorphic and an inverse relationship between Lp(a) concentration and apo(a) isoform size has been observed. This is genetically controlled suggesting a functional diversity among the apo(a) isoforms. The LPA gene codes for apo(a) whose genetic heterogeneity is due to variations in its number of kringles. The exact pathogenic mechanism of Lp(a) is still not completely elucidated, but the structural homology of Lp(a) with LDL and plasmin is possibly responsible for its acting as a link between atherosclerosis and thrombosis. Upper limits of normal Lp(a) levels have not been defined for the Indian population. A cut off limit of 20 mg/dL has been suggested while for the Caucasian population it is 30 mg/dL. Though a variety of assays are available for its measurement, standardization of the analytical method is highly complicated as a majority of the methods are affected by the heterogeneity in apo(a) size. No therapeutic drug selectively targets Lp(a) but recently, new modifiers of apo(a) synthesis are being considered.

Lipoprotein(a): resurrected by genetics

Plasma lipoprotein(a) [Lp(a)] is a quantitative genetic trait with a very broad and skewed distribution, which is largely controlled by genetic variants at the LPA locus on chromosome 6q27. Based on genetic evidence provided by studies conducted over the last two decades, Lp(a) is currently considered to be the strongest genetic risk factor for coronary heart disease (CHD). The copy number variation of kringle IV in the LPA gene has been strongly associated with both Lp(a) levels in plasma and risk of CHD, thereby fulfilling the main criterion for causality in a Mendelian randomization approach. Alleles with a low kringle IV copy number that together have a population frequency of 25-35% are associated with a doubling of the relative risk for outcomes, which is exceptional in the field of complex genetic phenotypes. The recently identified binding of oxidized phospholipids to Lp(a) is considered as one of the possible mechanisms that may explain the pathogenicity of Lp(a). Drugs that have been shown to lower Lp(a) have pleiotropic effects on other CHD risk factors, and an improvement of cardiovascular endpoints is up to now lacking. However, it has been established in a proof of principle study that lowering of very high Lp(a) by apheresis in high-risk patients with already maximally reduced low-density lipoprotein cholesterol levels can dramatically reduce major coronary events.

Nicotinic acid inhibits hepatic APOA gene expression: studies in humans and in transgenic mice

Elevated plasma lipoprotein(a) (LPA) levels are recognized as an independent risk factor for cardiovascular diseases. Our knowledge on LPA metabolism is incomplete, which makes it difficult to develop LPA-lowering medications. Nicotinic acid (NA) is the main drug recommended for the treatment of patients with increased plasma LPA concentrations. The mechanism of NA in lowering LPA is virtually unknown. To study this mechanism, we treated transgenic (tg) APOA mice with NA and measured plasma APOA and hepatic mRNA levels. In addition, mouse and human primary hepatocytes were incubated with NA, and the expression of APOA was followed. Feeding 1% NA reduced plasma APOA and hepatic expression of APOA in tg-APOA mice. Experiments with cultured human and mouse primary hepatocytes in addition to reporter assays performed in HepG2 cells revealed that NA suppresses APOA transcription. The region between -1446 and -857 of the human APOA promoter harboring several cAMP response element binding sites conferred the negative effect of NA. In accordance, cAMP stimulated APOA transcription, and NA reduced hepatic cAMP levels. It is suggested that cAMP signaling might be involved in reducing APOA transcription, which leads to the lowering of plasma LPA.

Report of the National Heart, Lung, and Blood Institute Workshop on Lipoprotein(a) and Cardiovascular Disease: Recent Advances and Future Directions

It has been estimated that ∼37% of the US population judged to be at high risk for developing coronary artery disease (CAD), based on the National Cholesterol Education Program guidelines, have increased plasma lipoprotein(a) [Lp(a)], whereas Lp(a) is increased in only 14% of those judged to be at low risk. Therefore, the importance of establishing a better understanding of the relative contribution of Lp(a) to the risk burden for CAD and other forms of vascular disease, as well as the underlying mechanisms, is clearly evident. However, the structural complexity and size heterogeneity of Lp(a) have hindered the development of immunoassays to accurately measure Lp(a) concentrations in plasma. The large intermethod variation in Lp(a) values has made it difficult to compare data from different clinical studies and to achieve a uniform interpretation of clinical data. A workshop was recently convened by the National Heart, Lung, and Blood Institute (NHLBI) to evaluate our current understanding of Lp(a) as a risk factor for atherosclerotic disorders; to determine how future studies could be designed to more clearly define the extent to which, and mechanisms by which, Lp(a) participates in these processes; and to present the results of the NHLBI-supported program for the evaluation and standardization of Lp(a) immunoassays. This report includes the most recent data presented by the workshop participants and the resulting practical and research recommendations.

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.

The association of serum lipoprotein(a) levels, apolipoprotein(a) size and (TTTTA)(n) polymorphism with coronary heart disease

BACKGROUND

The association between lipoprotein(a) levels, apolipoprotein(a) size and the (TTTTA)(n) polymorphism which is located in the 5' non-coding region of the apo(a) gene was studied in 263 patients with severe coronary heart disease and 97 healthy subjects.

METHODS

Lp(a) levels were measured by ELISA, apo(a) isoform size was determined by SDS-agarose gel electrophoresis, and analysis of the (TTTTA)(n) was carried out by PCR. For statistical calculation, both groups were divided into low (at least one apo(a) isoform with < or = 22 Kringle IV) and high (both isoforms with >22 KIV) apo(a) isoform sizes, and into low number (<10 in both alleles) and high number of (> or =10 at least one allele) TTTTA repeats.

RESULTS

Lp(a) levels were higher (P=0.007), apo(a) isoforms size < or =22 KIV and TTTTA repeats > or = 10 were more frequent (P=0.007 and 0.01) in cases than in controls. Lp(a) levels were found to be increased with low apo(a) weight in both groups (both P<0.0001). In multivariate logistic regression analysis, only the Lp(a) levels (P=0.005) and (TTTTA)(n) polymorphism (P=0.002) were found to be significantly associated with CHD.

CONCLUSION

Nevertheless, these results indicate that in CHD patients the (TTTTA)(n) polymorphism has an effect on Lp(a) levels which is independent of the apo(a) size.

[Phenotypic expression of Lp(a) in Spanish children and adolescents]

BACKGROUND

To know the distribution of phenotypes Lp(a) in an young population.

METHODS

Lipoprotein levels, lipoprotein(a), apolipoproteins and the Lp(a) phenotypes were determined in 105 children, selected according to their cholesterol concentrations.

RESULTS

The Lp(a) concentrations were significantly higher in group with low molecular weight respect to group with high molecular weight. The most frequent isoform was S3.

CONCLUSIONS

The Lp(a) concentrations correlate inversely with the molecular weight of Apo(a) isoforms.

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.

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.

Enhanced macrophage uptake of lipoprotein(a) after Ca2+-induced aggregate-formation

We tested the hypothesis that aggregated lipoprotein(a) [Lp(a)] is avidly taken up by macrophages. Lp(a) was isolated by sequential centrifugations and gel chromatography from a patient with high plasma levels of Lp(a) who was being treated with low density lipoprotein (LDL)-apheresis. Aggregated Lp(a) was prepared by mixing native Lp(a) with 2.5 mmol/L CaCl2, and 54% of the 125I-Lp(a) aggregated after interacting with CaCl2. The binding and degradation of aggregated Lp(a) in macrophages were 4.6- and 4.7-fold higher than those of native Lp(a), respectively. An excess amount of LDL did not inhibit either increase. Cholesterol esterification in macrophages was markedly stimulated by aggregated Lp(a), and macrophages were transformed into foam cells. Cytochalasin B, a phagocytosis inhibitor, strongly inhibited the degradation and cholesterol esterification (78 and 83%, respectively). These findings suggested that aggregation may be partially involved in Lp(a) accumulation, thereby contributing to the acceleration of atherosclerosis.

Lipoprotein (a) phenotype distribution in a population of bypass patients and its influence on lipoprotein (a) concentration

A case control study was undertaken to compare the distribution of apolipoprotein (a) phenotypes in patients suffering from atherosclerosis and undergoing coronary bypass surgery with the distribution observed in adequately selected controls. Cases differed from controls for triglycerides (1.90 +/- 0.88 mmol l-1 and 1.16 +/- 0.79 mmol l-1, P < 0.0001, respectively), HDL cholesterol (1.15 +/- 0.34 mmol l-1 and 1.69 +/- 0.42 mmol l-1, P < 0.0001, respectively), apolipoprotein AI (1.31 +/- 0.24 g l-1 and 1.70 +/- 0.29 g l-1, P < 0.0001, respectively) and lipoprotein a (Lp(a)) (0.32 +/- 0.30 g l-1 and 0.19 +/- 0.20 g l-1, P < 0.0001, respectively). The apolipoprotein (a) phenotypes were distributed differently in cases and controls (chi 2 = 25.26, P < 0.0001) with a lower percentage of isoforms of larger size and a higher percentage of isoforms of smaller size in patients. The Lp(a) concentration remained significantly higher in patients than in controls for most of the phenotypes, suggesting that both a high Lp(a) concentration and a different apolipoprotein (a) size distribution could be involved in the development of atherosclerosis in this population. In addition, patients exhibiting the highest Lp(a) concentrations had higher levels of LDL cholesterol and apolipoprotein B than patients exhibiting the lowest Lp(a) concentrations. This feature was not observed in controls. By contrast, controls with the highest Lp(a) concentration had significantly higher triglyceride levels than controls with the lowest Lp(a) concentration. This feature was not observed in patients. Our results indicate that patients undergoing bypass surgery have higher Lp(a) concentrations than controls, this increase being not completely explained by the difference in apolipoprotein (a) phenotype distribution. The high Lp(a) concentration seems to be associated with different lipid profiles in patients than in controls.

Lipoprotein(a) in Korean children and a history of coronary or cerebral vascular events in their older family members

The purpose of this study was to determine the relationships between serum apolipoprotein concentration and family history of coronary or cerebral events in schoolchildren. In 269 primary schoolchildren aged 6-11 years (145 boys and 124 girls) we measured the blood concentrations of total cholesterol, apolipoproteins B and A-1, and lipoprotein(a), and questioned their parents about coronary or cerebral vascular events. Serum concentrations of apo B, A-1 and Lp(a) significantly increased with age. In children with serum cholesterol concentration > 5.18 mmol/L the concentrations of apo B, A-1, Lp(a) and apo B/apo A-1 ratio were significantly higher. The concentrations of total cholesterol, apo B, Lp(a), and apo B/apo A-1 ratio in the obese group (body weight 20% above the median body weight for age and height) differed significantly from those in the non-obese group. Serum concentrations of Lp(a) in the children who had positive family histories of coronary or cerebral events (geometric mean = 0.174 x/divided by 0.036g/L) and was significantly higher than that in the children with negative history (geometric mean = 0.086 x/divided by 0.36g/L). Family history was an independent and major contributor to high Lp(a). In evaluating children's lipid profiles, measurement of Lp(a) may help to identify children and their families at increased risk and this may facilitate the targeting of preventive measures.

Lipoprotein(a) in cirrhosis. A new index of liver functions?

Over the last few years, lipoprotein(a) [Lp(a)] levels have been investigated because clinical studies have related it to increased cardiovascular and cerebrovascular risk. Although it is known that serum Lp(a) concentrations are controlled genetically, little is known about its metabolism. We studied changes in the lipid profile and Lp(a) values in 57 patients (34 males and 23 females) affected by cirrhosis of the liver subdivided into Child's classes in order to assess whether this lipoprotein is sensitive to reduced liver protein synthesis. The patients presented with low total cholesterol, normal HDL-cholesterol (HDL-c), LDL-cholesterol (LDL-c), triglycerides, apoprotein A1 (Apo-A1) and apoprotein B100 (Apo-B100) concentrations, while Lp(a) concentrations seemed elevated. Grouping the patients into Child's classes revealed that all the lipid parameters investigated reduced as the disease progressed. Lp(a) reduced significantly between Child's Classes I and II and seems to be correlated with the severity of cirrhosis and the clinical worsening of the patients' conditions. These findings suggest that Lp(a) is not only an index of atherosclerosis risk, but also plays a role in monitoring liver functions.

Levels of lipoprotein(a) and plasma lipids in Spanish children aged from 4 to 18 years

Increased plasma lipoprotein(a)-Lp(a)-levels are linked to a high risk of cardiovascular disease unrelated to other lipoproteins. It seems that Lp(a) values in childhood remain unaltered up to adulthood. In a randomly chosen population of 1970 children, aged from 4 to 18 years and living in a Spanish community, the following serum parameters were studied: total cholesterol, total triglycerides, Lp(a), high-density lipoprotein cholesterol and low-density lipoprotein cholesterol. Mean Lp(a) serum values were 15.0 +/- 14.7 mg dl-1. No differences were seen between either sex in the first years of childhood. Of the studied children, 15.1% presented Lp(a) concentrations above 30 mg dl-1. A correlation between Lp(a) and total cholesterol concentrations, which disappeared when low-density lipoprotein cholesterol concentrations were corrected according to cholesterol present in Lp(a), was observed.

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.

Reduction of lipoprotein(a) following treatment with lovastatin in patients with unremitting nephrotic syndrome

Pharmocologic treatment of the hyperlipidemia associated with the nephrotic syndrome with lovastatin has been previously shown to be safe and effective. However, there is no information on the effect of lovastatin treatment on plasma lipoprotein(a) [Lp(a)] levels in patients with the nephrotic syndrome. We administered lovastatin (40 to 80 mg/day) to 20 adult patients with unremitting nephrotic syndrome for 8 weeks to assess its effect on plasma Lp(a) and other plasma lipid concentrations. Apoprotein(a) (apo(a)) phenotype was determined in all patients. Patients were grouped according to their plasma Lp(a) levels. Those with elevated plasma Lp(a) (> or = 30 mg/dL) were placed in group I and those with normal Lp(a) levels (< 30 mg/dL) were placed in group II. Mean total cholesterol and LDL cholesterol were similarly and significantly reduced in groups I and II (-35.9% and -43.3%, P < 0.0005, P < 0.0005 group I, and -31.0% and -42.0%, P < 0.02, P < 0.03 group II, respectively). The median reduction in plasma Lp(a) was -32% (P < 0.003) in nephrotic patients in group I, whereas the median decline in plasma Lp(a) levels in nephrotic patients in group II was only -8.0% (P = 0.052). The overall frequency of the high molecular weight (M(r)) apo(a) phenotype S4 was 70% in nephrotic patients. There was no correlation between plasma Lp(a) and apo(a) phenotype. Treatment with lovastatin results in a favorable response in terms of total and low-density lipoprotein cholesterol lowering in patients with the nephrotic syndrome; however, plasma Lp(a) levels are uniformly and significantly reduced only in nephrotic patients with elevated baseline plasma Lp(a) concentrations. There was no correlation between plasma Lp(a) concentration and other lipid and biochemical parameters.

High lipoprotein(a) levels with predominance of high molecular weight apo(a) isoforms in patients with pulmonary embolism

Lipoprotein(a) (Lp(a)) may interact with the cellular components and protein co-factors of fibrinolysis. To evaluate the effect of Lp(a) in thromboembolic diseases of the venous system, we measured serum levels and the isoform distribution of apo(a) in 25 patients with pulmonary embolism (18 men, 7 women, aged 21-77 years). The control group was adjusted for sex and age (P = 0.189). Serum Lp(a) concentration was significantly higher in the study group (median: 9.3 vs. 4.3 mg dL-1). As the distribution of high and low molecular weight subtypes of apo(a) did not show any differences (P = 0.127) between the two groups, the elevated Lp(a) levels in patients with pulmonary embolism could not be attributed to the investigated kringle-4 polymorphism of the apo(a) gene and therefore other genetic or non-genetic implications are indicated.

Antifibrinolytic effect of recombinant apolipoprotein(a) in vitro is primarily due to attenuation of tPA-mediated Glu-plasminogen activation

The effect of a 17-kringle form of recombinant apo(a) [r-apo(a)] on in vitro fibrin clot lysis was studied. In these assays, fibrin clots were formed in the wells of microtiter plates, and lysis of the clots was monitored by measurement of the turbidity at 405 nm. The results indicate that r-apo(a) produces a dose-dependent antifibrinolytic effect in clots formed using either purified components or barium-adsorbed plasma. This effect was found to be independent of clot structure, since lysis of clots formed using both high and low concentrations of thrombin was prolonged by r-apo(a) to the same extent. The two components of the antifibrinolytic effect of r-apo(a) were determined to be (i) attenuation of tPA-mediated plasminogen activation (the major component) and (ii) inhibition of plasmin degradation of fibrin, although r-apo(a) did not directly attenuate plasmin activity, as measured by S-2251 hydrolysis. r-Apo(a) interfered most substantially with tPA-mediated activation of Glu-plasminogen and less substantially with tPA-mediated Lys-plasminogen activation and urokinase-mediated activation of plasminogen. In summary, we have demonstrated that apo(a) is able to attenuate fibrin clot lysis in vitro, primarily as a consequence of the interference by apo(a) with tPA-mediated Glu-plasminogen activation. These studies illuminate possible mechanisms by which Lp(a) may contribute to the development of vascular disease in vivo.

The apolipoprotein(a) gene is regulated by sex hormones and acute-phase inducers in YAC transgenic mice

High plasma concentrations of apolipoprotein (a) (apo(a)) have been implicated as a major independent risk factor for atherosclerosis in humans. Apo(a) is a large, evolutionarily new gene (present primarily in primates) for which considerable controversy exists concerning the factors that regulate its expression. To investigate the in vivo regulation of apo(a), we have created several lines of YAC transgenic mice containing a 110-kb human apo(a) gene surrounded by greater than 60 kb of 5' and 3' flanking DNA. Studies in humans have suggested that acute-phase inducers increase and sex steroids decrease apo(a) concentrations, but these results are controversial. Analysis of the YAC transgenic mice conclusively supports the hypothesized role of sex steroids and refutes the suggested role of acute-phase inducers in regulating the apo(a) gene.

Lipoprotein(a) in type 1 diabetic patients with renal disease

Lp(a) was measured in 64 normoalbuminuric, 52 microalbuminuric, and 37 proteinuric Type 1 diabetic patients and 54 healthy subjects. Microalbuminuric and proteinuric Type 1 diabetic patients had higher median Lp(a) values (133 (16-1932) and 169 (17-1149) mg l-1) than patients with normal AER (73 (15-1078) mg l-1; p = 0.048 and p = 0.027). Lp(a) in healthy subjects (110 (15-1630)mg l-1) did not differ from the diabetic subgroups. The frequency of Lp(a) values in the upper quarter of the normal distribution was similar in the diabetic groups and did not differ between diabetic and control subjects. The cumulative distribution of Lp(a) was similar in all groups. Lp(a) concentrations were not related to AER, age, gender, duration of diabetes, body mass index, glycaemic control, serum creatinine, free insulin or systolic blood pressure. Cholesterol, LDL-cholesterol, triglycerides, and apo B were higher in microalbuminuric and proteinuric than in normoalbuminuric Type 1 diabetic patients. Lp(a) was independently related to diastolic blood pressure, fibrinogen, and macroangiopathy. In conclusion, median Lp(a) concentrations tend to be higher in Type 1 diabetic patients with early and established renal disease, although the differences are small and the overlap between groups large. Lp(a) is related to diastolic blood pressure and fibrinogen, and this association of powerful risk factors suggests that Lp(a) may play a role in the pathogenesis of cardiovascular disease in Type 1 diabetic patients with proteinuria. Whether Lp(a) is an independent determinant of increased cardiovascular risk in these patients needs to be elucidated by prospective studies.

Lp(a) concentration and apo(a) isoform size. Relation to the presence of coronary artery disease in familial hypercholesterolemia

We studied the relation between the concentration of lipoprotein(a) [Lp(a)] in plasma, apolipoprotein (a) [apo(a)] phenotype, and the clinical expression of coronary artery disease (CAD) in a previously described cohort of patients with familial hypercholesterolemia (FH) and an appropriate population of control subjects. The plasma concentration of Lp(a) was markedly skewed in both the FH and control populations; however, the distribution was less skewed in FH (50% greater than 300 mg/L) compared with control subjects (27% greater than 300 mg/L). Patients with FH had significantly higher median and mean log Lp(a) levels compared with control subjects. There was no difference in the level of Lp(a) between men and women in both the control and FH groups. Frequency distribution analysis of the major apo(a) isoform size for each subject showed that, in contrast to the near-normal distribution seen in control subjects, two major subpopulations were apparent in the FH cohort, based on apo(a) isoform size > 700 kD or < or = 700 kD. There was no correlation between Lp(a) plasma concentration and apo(a) isoform size in either population. FH subjects with smaller apo(a) isoforms were more likely to have a history of signs of, or symptoms of CAD than those with larger isoforms. These data illustrate that on the basis of Lp(a) plasma concentration alone, there is no significant difference between FH patients with and without signs or symptoms of CAD. In the control population the smaller apo(a) isoforms were associated with higher Lp(a) levels, whereas in the FH population both small and large apo(a) isoforms were associated with higher Lp(a) levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the structure and function of the apolipoprotein(a) gene

Lp(a) is an LDL-like lipoprotein that is a major inherited risk factor for atherosclerosis. It is distinguished from Lp(a) by the addition of apolipoprotein(a). The gene structure of apolipoprotein(a) is homologous to plasminogen, and competition with plasminogen activity may account for some of the pathophysiology associated with Lp(a). Six highly related genes have now been identified, and at least four are found in close proximity in overlapping genomic clones. Studies have begun on the regulation of apolipoprotein (a) gene expression, and the human apolipoprotein(a) gene has been inserted into transgenic mice, where it leads to the development of arterial lesions.

Lipoprotein(a) concentrations and phenotypes in controls and patients with hypercholesterolemia or hypertriglyceridemia

Lipoprotein(a) [Lp(a)] concentrations are known to be stable under various dietary and drug regimens. Little is known about the influence of hyperlipoproteinemia on Lp(a) levels. Therefore, we investigated Lp(a) concentrations and apolipoprotein(a) [apo(a)] polymorphism in 147 patients with hypertriglyceridemia and in 93 patients with hypercholesterolemia and compared them with 404 subjects without hyperlipoproteinemia (controls). Despite a similar apo(a) isoform and phenotype distribution, Lp(a) concentrations differed significantly (P < .0001) between the three groups. The median Lp(a) level in control subjects was 17 mg/dL (mean, 38 mg/dL), compared with 38 mg/dL (mean, 56 mg/dL) in patients with hypercholesterolemia and 9 mg/dL (mean, 21 mg/dL) in those with hypertriglyceridemia. These differences persisted after exclusion of 61 subjects with coronary heart disease. The inverse correlation between the molecular weight of the apo(a) isoforms and the Lp(a) concentration was preserved within each group (P < .001), but for every molecular weight range studied the level of Lp(a) was always higher in patients with hypercholesterolemia and always lower in those with hypertriglyceridemia than in controls. We conclude that hypertriglyceridemia or hypercholesterolemia have profound--but divergent--influences on the concentration of Lp(a).

High allele frequency of apolipoprotein(a) phenotype LpS4 is associated with low serum Lp(a) concentrations in Koreans

We determined apo(a) phenotypes using SDS-PAGE followed by immunoblotting in samples from a control group of 179 and from 68 Korean patients with coronary artery disease (CAD). The CAD group showed significantly higher Lp(a) levels than the control group, which might be partially attributable to the differences in apo(a) phenotype frequencies although it was not statistically significant, and was partially attributable to the significant difference in Lp(a) levels of S2 or null phenotypes between the two groups. The apo(a) allele frequencies between ethnic groups already reported (Austrians, American blacks, Japanese, and Koreans), were compared by the Chi-square test. In the Korean population, the apo(a) allele frequencies demonstrated a high frequency of the LpS4 allele associated with a low Lp(a) concentration. This result suggests that the concentration and allele frequency of Lp(a) might be one of the factors in explaining the low incidence of CAD in the Korean population.

Frequent occurrence of familial aggregations of high lipoprotein(a) levels associated with small apolipoprotein(a) isoforms

School-age children with high lipoprotein(a) [Lp(a)] levels were screened and family studies were conducted to examine the relationship between high Lp(a) levels and apolipoprotein(a) [apo(a)] isoforms in families. All the probands from 17 families had one of the A2 to A12 apo(a) isoforms, which are the smaller apo(a) isoforms of the 25 different isoforms thus far detected. The ratio of subjects with high plasma Lp(a) levels was 0.47 among the first-degree relatives. All 15 relatives with high plasma Lp(a) levels shared one of the small apo(a) isoforms with the proband in each family, while 16 of 17 relatives with normal Lp(a) levels did not. These data indicate the frequent occurrence of familial aggregations of high Lp(a) levels associated with one of the small apo(a) isoforms.

High degree of genetic polymorphism in apolipoprotein(a) associated with plasma lipoprotein(a) levels in Japanese and Chinese populations

We have developed a sensitive, high-resolutin method for the analysis of the apolipoprotein(a) [apo(a)] isoforms using sodium dodecyl sulfate (SDS)-agarose/gradient polyacrylamide gel electrophoresis. In an analysis of the genetic polymorphism of apo(a) isoforms and their relationship with plasma lipoprotein(a) [Lp(a)] levels in Japanese and Chinese, this method identified 25 different apo(a) isoforms and detected one or two apo(a) isoforms in more than 99.5% of the individuals tested. The apparent molecular weights of the apo(a) isoforms ranged from 370 kDa to 950 kDa, and 22 of the 25 different apo(a) isoforms had a higher molecular weight than of apo B-100. Studies on Japanese families confirmed the autosomal codominant segregation of apo(a) isoforms and the existence of a null allele at the apo(a) locus. The observed frequency distribution of apo(a) isoform phenotypes fit the expectations of the Hardy-Weinberg equilibrium in both the Japanese and Chinese populations. Our data indicate the existence of at least 26 alleles, including a null allele, at the apo(a) locus. The frequency distribution patterns of the apo(a) isoform alleles in Japanese and Chinese were similar to each other and also similar to that of apo(a) gene sizes reported in Caucasian American individuals. The average heterozygosity at the apo(a) locus was 92% in Japanese and 93% in Chinese. A highly significant inverse correlation was observed between plasma Lp(a) levels and the size of apo(a) isoforms in both the Japanese (r = 0.677, P = 0.0001) and the Chinese (r = -0.703, P = 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

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

Apo(a), the specific lipoprotein(a) (Lp(a)) apolipoprotein, is characterized by different isoforms (from 6 to 11 on SDS-PAGE) encoded by a system of autosomal codominant alleles. Electrophoresis on agarose gel displays a better resolving power than SDS-PAGE (a larger number of apo(a) isoforms is detected). The aim of this work was to set up a simple technique that uses a capillary blotting apparatus and a polyvinylidene difluoride membrane for protein transfer. We tested an Italian population sample of 202 healthy subjects (123 men and 79 women) and we detected 22 apo(a) isoforms varying from 280 to 775 kDa. In our sample, 135 subjects (66.5%) had a single-band phenotype, 64 (31.7%) had a double-band phenotype and 3 subjects (1.5%) had no detectable bands ('null' phenotype). This simple and reproducible technique could be applied in the genetic screening of apo(a) polymorphisms and for clinical investigations of the risk of developing cardiovascular diseases.

Plasma triglycerides and lipoprotein(a): inverse relationship in a hyperlipidemic Italian population

The relationship between plasma lipoprotein(a) (Lp(a)) levels and other clinical/biochemical variables was investigated in 1200 consecutive hyperlipidemic patients. Plasma Lp(a) concentrations were measured by a sandwich-ELISA method, while the patients were either on diet or diet plus lipid-lowering drugs; 38% of them had a plasma Lp(a) level > 30 mg/dl. The median plasma Lp(a) concentration and the frequency of Lp(a) > 30 mg/dl were significantly lower in individuals with severe hypertriglyceridemia vs. hypercholesterolemics (HC) or mixed hyperlipidemics (M-HLP), but similar to normolipidemic healthy controls. Patients with isolated moderate hypertriglyceridemia had Lp(a) levels intermediate between HC and M-HLP subjects. The in vitro addition of triglyceride-rich lipoproteins to normotriglyceridemic plasma did not affect the Lp(a) measurement. Plasma Lp(a) concentrations in the whole hyperlipidemic population correlated negatively with triglycerides and positively with total cholesterol, HDL-cholesterol and age, being unrelated to either body mass index or lipid-lowering treatment. In HC patients, the presence of tendon xanthomas was associated with twofold higher Lp(a) levels. These findings argue for a regulatory role of triglycerides on plasma Lp(a) levels in hyperlipidemic patients.

Characterization by yeast artificial chromosome cloning of the linked apolipoprotein(a) and plasminogen genes and identification of the apolipoprotein(a) 5' flanking region

The apoprotein(a) [apo(a)] gene encodes a protein component of the circulating lipoprotein(a) [Lp(a)]. The apo(a) gene is highly homologous to the plasminogen gene. It encodes one of the most polymorphic human proteins, due to variability in the number of repetitions of structures called kringles. In addition, Lp(a) levels vary among individuals by more than two orders of magnitude, the high levels being highly correlated with predisposition to early atherosclerotic disease. To better understand the genetics and function of the apo(a) gene, we have cloned in yeast artificial chromosome vectors DNA fragments comprising the linked apo(a) and plasminogen genes and other members of the plasminogen family. By a combination of pulsed-field gel electrophoresis and genome walking experiments, we have identified the 5' portion and flanking regions of the apo(a) gene.

Changes in Lp(a) lipoprotein levels during the treatment of hypercholesterolaemia with simvastatin

Thirty-six patients with total serum cholesterol levels above 6.5 mmol/l and Lipoprotein(a) levels above 100 mg.l-1 were evaluated in a 24 week double-blind, placebo controlled, cross-over study to assess the possible changes in Lp(a) during treatment with the HMG CoA reductase inhibitor simvastatin. The median plasma Lp(a) increased from 359 to 464 mg.l-1 during simvastin treatment as compared to placebo (not significant). Individual changes in Lp(a) varied. In a multivariate linear regression analysis the individual change in Lp(a) was correlated with the baseline Lp(a) (r = 0.64), the change in serum triglycerides (r = 0.48) and the baseline apolipoprotein B (r = 0.36). Differences between the Lp(a) phenotypes may explain some of the varied Lp(a) responses. It appears that the effect of simvastatin on the Lp(a) level in individuals is usually insignificant, but in patients with a high Lp(a) simvastatin may further increase it.

Significant association between low-molecular-weight apolipoprotein(a) isoforms and intermittent claudication

The role of lipoprotein(a) (Lp[a]) and apolipoprotein(a) (apo[a]) isoforms in symptomatic peripheral atherosclerosis was studied in 100 randomly selected middle-aged (45-69 years) men with intermittent claudication (IC) and 100 randomly selected healthy control (C) subjects. IC and C subjects were matched pairwise for sex, age, and smoking habits. Plasma Lp(a) concentrations were significantly higher in IC subjects, with a median value of 20.12 mg/dl, compared with 11.11 mg/dl in C subjects (p less than 0.0009). The elevated Lp(a) concentration was to a great extent due to a significant difference in the frequency distribution of apo(a) isoforms between IC and C subjects (p less than 0.029). Low-molecular-weight apo(a) isoforms were more prevalent in IC than C subjects. Also, IC subjects with apo(a) S2 and S3 phenotypes had higher Lp(a) concentrations than control subjects with the same phenotypes: S2:60.70 mg/dl (IC) and 48.69 mg/dl (C), p less than 0.038; and S3: 30.18 mg/dl (IC) and 12.01 mg/dl (C), p less than 0.042, so other still-unknown factors, genetic or nongenetic, may be important. Stepwise logistic regression analysis demonstrated that Lp(a) concentration contributed significantly (p less than 0.0002) to IC, independent of age, smoking, hypertension, diabetes mellitus, plasma total cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, apo B, and plasma total triglycerides. Apo(a) isoforms grouped according to molecular weight were also independent of the above risk factors associated (p = 0.016) with the occurrence of IC because of their low-molecular-weight but were not independent of Lp(a) concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein(a) gene accounts for greater than 90% of the variation in plasma lipoprotein(a) concentrations

Plasma lipoprotein(a) [Lp(a)], a low density lipoprotein particle with an attached apolipoprotein(a) [apo(a)], varies widely in concentration between individuals. These concentration differences are heritable and inversely related to the number of kringle 4 repeats in the apo(a) gene. To define the genetic determinants of plasma Lp(a) levels, plasma Lp(a) concentrations and apo(a) genotypes were examined in 48 nuclear Caucasian families. Apo(a) genotypes were determined using a newly developed pulsed-field gel electrophoresis method which distinguished 19 different genotypes at the apo(a) locus. The apo(a) gene itself was found to account for virtually all the genetic variability in plasma Lp(a) levels. This conclusion was reached by analyzing plasma Lp(a) levels in siblings who shared zero, one, or two apo(a) genes that were identical by descent (ibd). Siblings with both apo(a) alleles ibd (n = 72) have strikingly similar plasma Lp(a) levels (r = 0.95), whereas those who shared no apo(a) alleles (n = 52), had dissimilar concentrations (r = -0.23). The apo(a) gene was estimated to be responsible for 91% of the variance of plasma Lp(a) concentration. The number of kringle 4 repeats in the apo(a) gene accounted for 69% of the variation, and yet to be defined cis-acting sequences at the apo(a) locus accounted for the remaining 22% of the inter-individual variation in plasma Lp(a) levels. During the course of these studies we observed the de novo generation of a new apo(a) allele, an event that occurred once in 376 meioses.

A case-control study of lipoprotein particles in two populations at contrasting risk for coronary heart disease. The ECTIM Study

The incidence of coronary heart disease (CHD) in middle-aged men is more than three times higher in Northern Ireland than in France. The ECTIM study, which is based on WHO MONICA centers in Belfast (Northern Ireland), Strasbourg (eastern France), Toulouse (southwestern France), and Lille (northern France), has been established to investigate this striking difference. Male patients aged 25-64 years with myocardial infarction (MI) and control subjects sampled from the general population were recruited in the four centers. Hypolipidemic drug treatment was much more frequent in France than in Belfast. "Hypercholesterolemia" defined by the presence of hypolipidemic drug treatment or a low density liproprotein cholesterol level greater than 200 mg/dl was more frequent in cases than in controls in both countries but was similar in both control groups. An in-depth study of lipid variables, including measurements of cholesterol fractions, triglycerides, apolipoproteins (apo), and lipoprotein particles (Lp), was performed in nonhypercholesterolemic subjects. In Northern Ireland and France, patients in comparison with controls had lower levels of high density lipoprotein cholesterol, apo A-I, apo A-II, Lp A-I, and Lp A-II:A-I and higher levels of Lp E:B and Lp(a):B. The levels of triglycerides, very low density lipoprotein cholesterol, apo B, and Lp C-III:B were higher in cases than in controls only in Belfast. In control subjects, the mean levels of cholesterol fractions and apolipoproteins were similar in Northern Ireland and France; however, the level of Lp A-I was lower and the levels of Lp E:B and Lp(a):B were higher in Northern Ireland than in France.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of serum Lp (a) levels. Opposite effects after estrogen treatment and orchidectomy in males with prostatic carcinoma

Serum concentrations of lipoprotein (a) [Lp (a)] were determined in two groups of elderly males suffering from prostatic carcinoma, who were randomized to treatment with estrogen (n = 15) or orchidectomy (n = 16). Estrogen was given as oral ethinylestradiol, 150 micrograms daily, combined with intramuscular polyestradiol phosphate, 80 mg/mo. The baseline levels were similar in both groups, but 6 mo after initiation of therapy, serum Lp (a) levels were decreased approximately 50% in the estrogen-treated group (P less than 0.001) in contrast to a 20% increase (P less than 0.01) in the orchidectomized group. Concomitantly, LDL cholesterol decreased by 30% and HDL cholesterol increased by almost 60% in the estrogen-treated patients. There was no relationship between the change in LDL cholesterol and Lp (a) reduction. In conclusion, Lp (a) levels in males were found to drastically decrease upon estrogen treatment and to increase after orchidectomy, suggesting that sex hormones, and particularly estrogens, exert a regulatory role on the serum Lp (a) level in man.

Lipoprotein(a) and acute-phase proteins in acute myocardial infarction

Lipoprotein(a) (Lp(a)) and the acute-phase proteins, orosomucoid, haptoglobin and alpha 1-antitrypsin, were studied in 32 patients with acute myocardial infarction. Samples were taken at admission and, after fasting overnight, on the following 6 days. In a subgroup of 21 patients total serum cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides were also estimated. In a linear regression model a significant relation between the relative values of Lp(a) and the time in days was obtained (p = 0.001). Compared with the acute-phase proteins, however, Lp(a) showed a weak increase and the individual responses were very variable. There were no correlations between the individual changes in Lp(a) and the changes in the acute-phase proteins, but Lp(a) changes correlated significantly with the changes in total cholesterol and low-density lipoprotein (LDL) cholesterol. It is suggested that the Lp(a) reaction in myocardial infarction is linked to the reaction of the lipoproteins. There may also be several clinical conditions, including different medications, which influence the Lp(a) level.

Apolipoprotein (a) alleles determine lipoprotein (a) particle density and concentration in plasma

The distribution of Lp(a) lipoprotein (Lp[a]) and genetic apolipoprotein(a) (apo[a]) isoforms in plasma samples from 29 healthy normolipidemic subjects of known apo(a) phenotype was evaluated by density gradient ultracentrifugation. The density of Lp(a) was directly related to the size of the apo(a) isoform, ranging from 1.043 g/ml for the LpF phenotype to 1.114 g/ml for the LpS4 phenotype. Heterozygotes had two distinct Lp(a) particles, each containing one of the respective isoforms in plasma. In each heterozygote, the concentration of the lighter Lp(a) species was higher than that of the denser Lp(a) population. These data suggest that apo(a) alleles determine the density and the metabolism and thereby also the concentrations of Lp(a) particles in plasma.

Apolipoprotein(a) phenotypes, Lp(a) concentration and plasma lipid levels in relation to coronary heart disease in a Chinese population: evidence for the role of the apo(a) gene in coronary heart disease

Elevated lipoprotein(a) (Lp[a]) concentrations are associated with premature coronary heart disease (CHD). In the general population, Lp(a) levels are largely determined by alleles at the hypervariable apolipoprotein(a) (apo[a]) gene locus, but other genetic and environmental factors also affect plasma Lp(a) levels. In addition, Lp(a) has been hypothesized to be an acute phase protein. It is therefore unclear whether the association of Lp(a) concentrations with CHD is primary in nature. We have analyzed apo(a) phenotypes, Lp(a) levels, total cholesterol, and HDL-cholesterol in patients with CHD, and in controls from the general population. Both samples were Chinese individuals residing in Singapore. Lp(a) concentrations were significantly higher in the patients than in the population (mean 20.7 +/- 23.9 mg/dl vs 8.9 +/- 12.9 mg/dl). Apo(a) isoforms associated with high Lp(a) levels (B, S1, S2) were significantly more frequent in the CHD patients than in the population sample (15.9% vs 8.5%, P less than 0.01). Higher Lp(a) concentrations in the patients were in part explained by this difference in apo(a) allele frequencies. Results from stepwise logistic regression analysis indicate that apo(a) type was a significant predictor of CHD, independent of total cholesterol and HDL cholesterol, but not independent of Lp(a) levels. The data demonstrate that alleles at the apo(a) locus determine the risk for CHD through their effects on Lp(a) levels, and firmly establish the role of Lp(a) as a primary genetic risk factor for CHD.