Relation of serum lipoprotein(a) concentration and apolipoprotein(a) phenotype to coronary heart disease in patients with familial hypercholesterolemia

Reduction of lipoprotein(a) by LDL-apheresis using a dextran sulfate cellulose column in patients with familial hypercholesterolemia

Lipoprotein(a) (Lp(a)) was eliminated by LDL-apheresis using a dextran sulfate cellulose column in 3 homozygous and 10 heterozygous familial hypercholesterolemic patients. Immediately after LDL-apheresis by the LA-15 system (continuous LDL apheresis), there were significant reductions in Lp(a) concentrations (28.6 +/- 11.8 mg/dl (mean +/- S.E.) to 9.6 +/- 5.6 mg/dl (P < 0.01)), and in LDL-cholesterol concentrations (156 +/- 32 mg/dl to 48 +/- 18 mg/dl (P < 0.01)). Immediately following LDL-apheresis, Lp(a) and LDL-cholesterol were reduced by 67.4% +/- 11.6% and 68.3% +/- 11.8%, respectively. The removal of Lp(a) paralleled that of LDL-cholesterol. The reduced levels of Lp(a) nearly returned to baseline within 7 days. In 6 of the heterozygous FH patients the rates of recovery of LDL cholesterol and Lp(a) were calculated, according to Apstein's equation after discontinuing lipid altering drug treatment for 4 weeks. Mean constant k values of LDL cholesterol and Lp(a) were 0.354 (range: 0.136-0.752) and 0.427 (range 0.112-0.933), respectively. The average concentration during the 7 days following LDL-apheresis was calculated. Average reductions were 28% in LDL cholesterol and 18% in Lp(a). Pravastatin treatment, which continued for 4 weeks, significantly decreased LDL cholesterol (P < 0.01); however, before LDL-apheresis pravastatin treatment significantly increased Lp(a) levels (P < 0.05) in a small number (n = 6) of the FH patients, who had been regularly treated with LDL-apheresis. These results suggest that LDL-apheresis using the dextran sulfate cellulose column is an effective treatment to reduce levels of serum Lp(a) and LDL proportionally. This therapy may be of value in the prevention and regression of coronary artery disease in FH patients.

Effects of age, sex, and menopausal status on plasma lipoprotein(a) levels. The Framingham Offspring Study

BACKGROUND

Lipoprotein(a) [Lp(a)] is an atherogenic particle that structurally resembles a low density lipoprotein (LDL) particle but contains a molecule of apolipoprotein(a) attached to apolipoprotein B-100 by a disulfide bond. Because elevated plasma levels of Lp(a) have been shown to be an independent risk factor for coronary artery disease, it is important to define normal ranges for this lipoprotein.

METHODS AND RESULTS

We have measured Lp(a) in 1,284 men (mean age, 48 +/- 10 years) and 1,394 women (mean age, 48 +/- 10 years) free of cardiovascular and cerebrovascular disease and not on medications known to affect lipids who were seen at the third examination cycle of the Framingham Offspring Study. Plasma Lp(a) levels were measured by an enzyme-linked immunosorbent assay, which uses a "capture" monoclonal anti-apo(a) antibody that does not cross-react with plasminogen, and a polyclonal anti-apo(a) antibody conjugated to horseradish peroxidase. The assay was calibrated to total Lp(a) mass. The Lp(a) frequency distribution was highly skewed to the right, with 56% of the values in the 0-10-mg/dL range. Mean plasma Lp(a) concentrations were 14 +/- 17 mg/dL in men and 15 +/- 17 mg/dL in women. Values of more than 38 mg/dL were above the 90th percentile and values of more than 22 mg/dL were above the 75th percentile in both men and women.

CONCLUSIONS

We have determined mean Lp(a) levels for men and women participating in the Framingham Offspring Study. In this population, there was an inverse association between plasma levels of Lp(a) and triglycerides for both sexes (p < 0.006), but triglycerides accounted for only approximately 0.5% of the variation in Lp(a) levels. Associations of Lp(a) levels with total and LDL cholesterol levels were not significant after correction for the estimated contribution of Lp(a) cholesterol to total and LDL cholesterol. After controlling for age, Lp(a) values were 8% greater in postmenopausal women than in premenopausal women, but this difference was not statistically significant. Body mass index, alcohol consumption, cigarette smoking, use of beta-blockers or cholesterol-lowering medications, and use of drugs for the treatment of diabetes and hypertension were not correlated with Lp(a) levels.

Apolipoprotein(a) polymorphism predicts the increase of Lp(a) by pravastatin in patients with familial hypercholesterolaemia treated with bile acid sequestration

HMG-CoA reductase inhibitors effectively reduce the concentration of low density lipoproteins (LDL) in plasma. Lipoprotein(a) [Lp(a)] may be as atherogenic as LDL. A few studies, only one of which was placebo controlled, suggest that the HMG CoA reductase inhibitors either do not affect Lp(a) or they increase Lp(a). The response of Lp(a) to HMG-CoA reductase inhibition has not been related to apolipoprotein(a) phenotypes in previous studies. We conducted a double-blind, placebo controlled study of pravastatin in 51 patients with familial hypercholesterolemia (FH) (n = 43) or probable FH (n = 8). All patients had LDL-cholesterol concentration above 4.1 mmol l-1 despite treatment with diet and bile acid sequestration. In patients assigned to pravastatin (n = 34), the mean concentrations of total cholesterol and LDL cholesterol fell significantly (P < 0.01) when compared to placebo. Lp(a) increased (P < 0.01) from a mean (+/- SD) of 33.6 +/- 40.8 mg dl-1 to 41.1 +/- 46.1 mg dl-1 on pravastatin but was unchanged during placebo treatment. The percentage increase in Lp(a) was the same in patients with different apo(a) phenotypes, and hence the absolute increase in Lp(a) was greatest in patients with the low molecular weight apo(a) phenotypes.

Lipoprotein (a) as an independent risk factor for myocardial infarction in patients with common hypercholesterolaemia

AIMS

To examine whether lipoprotein (a) (Lp(a)) increases the risk of myocardial infarction (MI) in patients with common hypercholesterolaemia.

METHODS

15 middle aged men with common hypercholesterolaemia (mean serum low density lipoprotein (LDL) cholesterol 4.94 mmol/l, SD 1.0) and a history of MI were selected consecutively from referrals to a lipid clinic. A control group that had not sustained an MI and with similar age, sex, cigarette smoking and blood pressure characteristics was also selected from the same clinic. Serum cholesterol, triglyceride, LDL cholesterol, high density lipoprotein cholesterol, apolipoproteins AI and B and Lp(a) were measured in both groups. Lp(a) was assayed by immunoturbidity.

RESULTS

The serum concentration of Lp(a) was significantly higher in patients with MI (geometric mean 0.64 (95% confidence interval 0.36 to 1.14) v 0.30 (0.21 to 0.42) g/l, p = 0.02), but there were no significant differences in other variables. Stepwise logistic regression analysis showed that Lp(a) was the only significant predictor of MI (p < 0.02). The odds ratio of MI (adjusted for age, smoking, blood pressure and apolipoprotein B) for an Lp(a) of > 0.57 g/l was 16.5, 95% confidence interval 2.3 to 125.4 (p = 0.001).

CONCLUSION

In middle aged men with common hypercholesterolaemia the serum concentration of Lp(a) is a powerful and independent risk factor for MI. Lp(a) should probably be routinely measured in all patients referred to a lipid clinic.

Determination of lipoprotein(a): enzyme immunoassay and immunoradiometric assay compared

Lipoprotein(a) (Lp(a)) concentration in plasma is a strong independent risk factor for pre-mature atherosclerosis. Lp(a) closely resembles LDL. Its protein moiety contains apolipoprotein (apo) B-100 and apo(a). Two enzyme immunoassays (EIAs) for Lp(a) have been developed. In both, polyclonal antibodies for apo(a) are used as capturing antibodies. In the first, Lp(a) is detected with anti-apo(a) (apo(a)-EIA). In the second, detection is carried out with anti-apo B (Lp(a):B-EIA). Neither plasminogen nor LDL cross-reacted in the assays. Lp(a) was also measured using a commercial sandwich immunoradiometric assay (IRMA). This assay uses two monoclonal antibodies for apo(a). One of them, the solid phase antibody, cross-reacted with plasminogen. However, at physiological plasminogen concentrations there was no competition for solid phase binding sites. A quantity of plasma samples (201) were assayed for Lp(a) with the three methods. The best correlation was obtained between the IRMA and the Lp(a):B-EIA (r = 0.909). Correlations between the apo(a)-EIA and the IRMA or the Lp(a):B-EIA were 0.763 and 0.695, respectively. As compared to the EIAs, the IRMA overestimated Lp(a) by about 30%. It is concluded that both the Lp(a):B-EIA and the IRMA reflect the concentration of Lp(a) particles in plasma. In contrast, the apo(a)-EIA measures apo(a) antigen and may therefore be susceptible to the size polymorphism of apo(a).

Antioxidants and lipid metabolism. Implications for the present and direction for the future

Numerous angiographic trials have demonstrated that the atherosclerotic process can be modified through reductions in levels of low-density lipoprotein (LDL) cholesterol. Recent research has focused on other potential modalities by which atheroroma development might be inhibited. These newer strategies include reduction of the oxidative potential of LDL particles through modification of dietary fat intake; prevention of LDL oxidation through the use of antioxidants; and inhibition of monocyte and macrophage function by omega-3 fatty acids and leukotriene-1 antagonists. Inhibition of acyl-coenzyme A:cholesterol acyltransferase (ACAT) may block intestinal cholesterol absorption and reduce synthesis of very-low-density lipoprotein (VLDL), while simultaneously enriching high-density lipoprotein (HDL) cholesterol. Modification of cholesterol ester transfer protein may be associated with improved reverse cholesterol transport or enlarged HDL particles. In the future, a wide variety of therapeutic modalities may be available for use alone or in combination to reverse atherosclerosis or prevent its progression.

Apolipoprotein E phenotypes in familial hypercholesterolaemia: importance for expression of disease and response to therapy

To study the possible importance of variation at the apolipoprotein (apo) E gene locus for the clinical expression of heterozygous familial hypercholesterolaemia (FH), we determined apo E phenotype and serum lipoprotein pattern in 120 patients with FH. The allele frequency of the patients studies were: epsilon 2 0.033, epsilon 3 0.733, and epsilon 4 0.233. There was no influence of apo E phenotype on the serum concentrations of total. VLDL, LDL or HDL cholesterol, triglycerides, or of apo AI, B or (a). Serum concentrations of apo E were significantly higher in patients with the apo E 3/3 phenotype compared to those with apo E 4/3 or 4/4, and the highest concentrations were found in patients carrying the epsilon 2-allele. The cholesterol-lowering response to therapy with cholestyramine or pravastatin was not related to apo E phenotype. It is concluded that variation at the apo E gene locus is not of major importance for the expression of heterozygous FH.

Cardiovascular risk factors in non-insulin-dependent diabetic subjects with microalbuminuria

In subjects with insulin-dependent diabetes mellitus, microalbuminuria has been associated with increased triglyceride and lipoprotein (a) (Lp[a]) concentrations and increased blood pressure. However, few studies have examined whether this association is present in subjects with non-insulin-dependent diabetes mellitus (NIDDM). We measured lipids, lipoproteins, Lp(a), blood pressure, and albumin excretion in 234 subjects with NIDDM from the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Seventy-two subjects had microalbuminuria (> or = 30 mg/dl). These subjects had increased systolic and diastolic blood pressures and higher fasting glucose concentrations relative to subjects without microalbuminuria. However, there were no significant differences between subjects with and without microalbuminuria with respect to lipids, lipoproteins, Lp(a), self-reported myocardial infarction, obesity, or body fat distribution. Subjects with diabetic retinopathy had increased microalbuminuria. In multivariate analysis both glycemia and blood pressure continued to be significantly related to the presence of microalbuminuria. We conclude that NIDDM subjects with microalbuminuria have elevated blood pressure and more severe glycemia but do not have a significantly more atherogenic pattern of lipids, lipoproteins, or Lp(a) than subjects without microalbuminuria.

Glutamine/histidine polymorphism in apo A-IV affects plasma concentrations of lipoprotein(a) and fibrin split products in coronary heart disease patients

A glutamine/histidine polymorphism at residue 360 in apolipoprotein (apo) A-IV that generates two electrophoretically detectable isoforms, apo A-IV-1 and apo A-IV-2, affects the plasma concentration of lipoprotein(a) (Lp[a]) in a healthy population. To verify this unexpected association we analyzed the effect of the apo A-IV polymorphism on Lp(a) serum concentrations in 275 male coronary heart disease patients. Allele frequencies of apo A-IV-1 and apo A-IV-2 were 0.917 and 0.083, respectively. In addition, apo A-IV-1/2 heterozygotes showed a 30% lower geometric mean concentration of Lp(a) than apo A-IV-1/1 homozygotes in this study. The relative frequency of Lp(a) concentrations > 20 mg/dl was significantly increased by a factor of 2.25 in apo A-IV-1/1 homozygotes. Other lipid parameters were not significantly affected by this apo A-IV polymorphism. Because of the relations between Lp(a) and the fibrinolytic system, we also analyzed the effect of the apo A-IV polymorphism on hemostatic variables. Apo A-IV-1/2 heterozygosity was associated with a 70% higher geometric mean plasma concentration of D-dimer, i.e., proteolytic fragments of cross-linked fibrin. Plasma concentrations of prothrombin fragments F1 + F2, fibrinogen, plasminogen, and plasminogen activator inhibitor-1 were unaffected. In conclusion, our results indicate a hitherto unappreciated role of the apo A-IV gene or a closely linked locus for the regulation of Lp(a) metabolism and hemostasis and also possibly for atherosclerosis and thrombosis.

Variation in lipoprotein(a) concentrations among individuals with the same apolipoprotein (a) isoform is determined by the rate of lipoprotein(a) production

Lipoprotein(a) [Lp(a)] is an atherogenic lipoprotein which is similar in structure to, but metabolically distinct from, LDL. Factors regulating plasma concentrations of Lp(a) are poorly understood. Apo(a), the protein that distinguishes Lp(a) from LDL, is highly polymorphic, and apo(a) size is inversely correlated with plasma Lp(a) level. Even within the same apo(a) isoform class, however, plasma Lp(a) concentrations vary widely. A series of in vivo kinetic studies were performed using purified radiolabeled Lp(a) in individuals with the same apo(a) isoform but different Lp(a) levels. In a group of seven subjects with a single S4-apo(a) isoform and Lp(a) levels ranging from 1 to 13.2 mg/dl, the fractional catabolic rate (FCR) of 131I-labeled S2-Lp(a) (mean 0.328 day-1) was not correlated with the plasma Lp(a) level (r = -0.346, P = 0.45). In two S4-apo(a) subjects with a 10-fold difference in Lp(a) level, the FCR's of 125I-labeled S4-Lp(a) were very similar in both subjects and not substantially different from the FCRs of 131I-S2-Lp(a) in the same subjects. In four subjects with a single S2-apo(a) isoform and Lp(a) levels ranging from 9.4 to 91 mg/dl, Lp(a) concentration was highly correlated with Lp(a) production rate (r = 0.993, P = 0.007), but poorly correlated with Lp(a) FCR (mean 0.304 day-1). Analysis of Lp(a) kinetic parameters in all 11 subjects revealed no significant correlation of Lp(a) level with Lp(a) FCR (r = -0.53, P = 0.09) and a strong correlation with Lp(a) production rate (r = 0.99, P < 0.0001). We conclude that the substantial variation in Lp(a) levels among individuals with the same apo(a) phenotype is caused primarily by differences in Lp(a) production rate.

Plasma Lp(a), apolipoprotein(a) isoforms and acute myocardial infarction in men and women: a case-control study in the Jerusalem population

The relationship of Lp(a) with manifestations of coronary heart disease (CHD) has not been studied extensively in women. There is little information as to the association of the unique Lp(a) apolipoprotein moiety (apo(a)) with CHD in either men or women. We therefore assessed the association of the apo(a) polymorphism and of Lp(a) with first acute myocardial infarction (MI) in a population-based case-control study in Jewish residents of Jerusalem between the ages of 25 and 64. The patients consisted of 238 men and 47 women hospitalized for a first acute MI in the 4 hospitals of Jerusalem serving the population (70% response rate among all first MI patients). The control subjects comprised 318 men and 159 women sampled from the national population registry and who were free of CHD (75% response). Lp(a) and apo(a) were measured in plasma stored at -20 degrees C for 6-24 months. Among men, plasma Lp(a) concentrations were higher in cases than controls in both univariate and multivariate analyses. The elevated risk was limited to the upper fifth of the Lp(a) distribution (unadjusted odds ratio = 1.65, P < 0.01 vs. the lower four quintiles, multivariable odds ratio = 1.82, P < 0.01). Among women, Lp(a) was not elevated in acute MI patients. Apo(a) isoforms with a B, S1 or S2 band (associated with higher Lp(a) values and having lower molecular weights) were more prevalent in female MI cases than controls (unadjusted odds ratio = 2.5, P = 0.016). This association could not be attributed to the higher Lp(a) concentrations associated with these isoforms and was not seen in men. In conclusion, our study points to an association of the apo(a) isoforms with acute MI in women, not evident in this population sample in men. Previously described associations of elevated Lp(a) with acute MI were confirmed in men but not in women. While the role of chance and inadequate statistical power cannot be excluded, the suggestion of a sex difference in the strength of these associations deserves further investigation, as does the question of whether apo(a) phenotype contributes to risk independently of Lp(a) level.

A cross-sectional evaluation of cardiovascular risk factors in coronary heart disease associated with type 1 (insulin-dependent) diabetes mellitus

The contribution from lipoproteins, blood pressure, albuminuria and demographic variables to coronary heart disease in 90 adult subjects with and 172 without Type 1 diabetes mellitus was examined in order to investigate whether risk factors were of equivalent importance in diabetic and non-diabetic coronary heart disease. Coronary heart disease (CHD) was present in roughly 25% of subjects in each group. In Type 1 diabetes those with CHD had significantly higher levels of systolic blood pressure, albumin excretion, serum creatinine, triglycerides, VLDL cholesterol and C-peptide, and reductions in serum concentrations of HDL and HDL2 cholesterol, in comparison to those without. However, the prevalence of smokers, and concentrations of Lp(a), ApoB and fibrinogen were comparable. Blood pressure and HDL cholesterol were higher in the CHD group with Type 1 diabetes in comparison to the nondiabetic group with CHD, although LDL concentrations and the prevalence of Lp(a) concentrations > 200 mg/l were lower. Logistic regression analysis revealed the strongest independent predictors of CHD in Type 1 diabetes were serum triglycerides, systolic blood pressure, age, serum LDL cholesterol, and the daily insulin dosage, whereas in the non-diabetic control group HDL2 cholesterol, Lp(a), ApoA1 and ApoB, total serum cholesterol and body mass index were additional predictors. CHD in Type 1 diabetes appears to be most closely associated with increasing age and levels of blood pressure and total serum lipids. Apolipoproteins and albuminuria did not seem to be important independent predictors of CHD in Type 1 diabetes, whereas the former were more clearly associated with CHD in non-diabetic controls.

Plasma lipoprotein (a) protein concentration and coronary artery disease in black patients compared with white patients

PURPOSE

This study examines the relation between lipoprotein (a) protein levels and other lipid parameters and coronary artery disease in white and black patients.

PATIENTS AND METHODS

Plasma lipoprotein (a) protein levels were measured prior to coronary angiography in a population of 127 white and 111 black patients. Each angiogram was given a total coronary artery disease score based on the number and severity of atherosclerotic coronary lesions.

RESULTS

White and black patients exhibited no differences in total plasma cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides. Black patients had higher lipoprotein (a) protein levels than white patients (8.6 versus 4.0 mg/dL; p < 0.0001). The extent and severity of coronary artery disease was the same in white and black patients. White and black patients with coronary artery disease had higher lipoprotein (a) levels than patients without coronary lesions (4.37 versus 1.99 mg/dL, p = 0.027 for white; 9.23 versus 6.87 mg/dL, p = 0.072 for black). In both groups of patients, there was a weak but significant positive correlation between lipoprotein (a) protein levels and coronary artery disease score.

CONCLUSION

Lipoprotein (a) is higher in patients with coronary artery disease. Black patients have higher plasma lipoprotein (a) protein levels than white patients and a comparable degree of coronary artery disease. It follows that the cardiovascular pathogenicity of lipoprotein (a) is not significantly greater in black patients despite higher lipoprotein (a) levels.

Probucol protects lipoprotein (a) against oxidative modification

Probucol, which decreases cholesterol levels and has antioxidant properties, was administered orally to patients with familial combined hyperlipidemia and high plasma lipoprotein(a) [Lp(a)] levels. The drug had no effect on Lp(a) concentrations after 4 weeks, but was found to be distributed in both Lp(a) and low-density lipoprotein (LDL). Before treatment, in each case LDL and Lp(a) isolated from the same individual were readily oxidized by copper, resulting in increased electrophoretic mobility and enhanced uptake and degradation by macrophages of both lipoproteins. After probucol treatment, both lipoproteins acquired resistance to in vitro oxidation by copper. Furthermore, probucol prevented their enhanced uptake and degradation by the macrophages. It is surmised that oxidized Lp(a) may carry an atherogenic potential that could be opposed by probucol administration.

Homocysteine and other sulfhydryl compounds enhance the binding of lipoprotein(a) to fibrin: a potential biochemical link between thrombosis, atherogenesis, and sulfhydryl compound metabolism

We have previously shown that lipoprotein(a) [Lp(a)], an atherogenic lipoprotein that contains apolipoprotein(a), which shares partial structural homology to plasminogen, binds to a plasmin-modified fibrin surface, and we have postulated that this interaction may be atherogenic. Moderate elevations in blood homocysteine, a relatively common condition, predispose to premature atherosclerosis. The reasons for this are not established. We now report that homocysteine, at concentrations as low as 8 microM, significantly increases the affinity of Lp(a) for fibrin. Homocysteine induces a 20-fold increase in the affinity between Lp(a) and plasmin-treated fibrin and a 4-fold increase with unmodified fibrin. Lp(a) binding is inhibited by epsilon-aminocaproic acid, indicating lysine binding site specificity. Homocysteine does not enhance the binding of Lp(a) to other surface-bound proteins. Cysteine, glutathione, and N-acetylcysteine also increase the affinity between Lp(a) and fibrin. Homocysteine does not affect the binding of low density lipoprotein or plasminogen to fibrin, nor does it alter the gel-filtration elution pattern of Lp(a). Immunoblot analysis documents the fact that homocysteine partially reduces Lp(a). These results suggest that homocysteine alters the intact Lp(a) particle so as to increase the reactivity of the plasminogen-like apolipoprotein(a) portion of the molecule. The observation that sulfhydryl amino acids increase Lp(a) binding to fibrin suggests a biochemical relationship between sulfhydryl compound metabolism, thrombosis, and atherogenesis.

Serum Lp(a) as a discriminant marker of early atherosclerotic plaque at three extracoronary sites in hypercholesterolemic men. The PCVMETRA Group

To investigate the role of lipoprotein (a) (Lp[a]) as an atherogenic condition related to hypercholesterolemia, we studied the serum concentration of Lp(a) as measured by immunonephelometry in relation to the presence of asymptomatic echographic plaques in the peripheral arteries of 103 untreated hypercholesterolemic, normotensive, middle-aged men. Plaque was found at carotid, aortic, and femoral sites in 36%, 51%, and 53% of subjects, respectively. The Lp(a) level was higher in the group with carotid plaques than in the group without (0.29 +/- 0.20 versus 0.17 +/- 0.14 g/l, p < 0.01), not significantly higher in the group with aortics plaque than in the group without (0.24 +/- 0.19 versus 0.19 +/- 0.16 g/l), and not different between groups with and without femoral plaques (0.21 +/- 0.18 versus 0.22 +/- 0.17 g/l). A logistic regression analysis confirmed that Lp(a) was associated with carotid plaques (p = 0.004), independent of other risk factors. However, in patients with low density lipoprotein cholesterol values above the group median value (4.7 mmol/l), Lp(a) was associated not only with carotid plaques (p < 0.01) but also with aortic plaques (p < 0.05), as well as with the number of diseased sites (p = 0.02). In contrast, in patients with low density lipoprotein cholesterol levels below or equal to 4.7 mmol/l, Lp(a) only remained associated with carotid plaques (p < 0.05). Thus, in symptom-free, hypercholesterolemic men, early atherosclerosis was influenced by serum Lp(a), particularly in the carotid arteries, as well as by the presence of a higher level of low density lipoprotein cholesterol.

Treatment of refractory familial hypercholesterolemia by low-density lipoprotein apheresis using an automated dextran sulfate cellulose adsorption system. The Liposorber Study Group

A subgroup of patients with familial hypercholesterolemia (FH) respond inadequately to standard diet and drug therapy, and are therefore at high risk for the premature development or progression of coronary artery disease. This study evaluated low-density lipoprotein (LDL) cholesterol and lipoprotein (a) removal in a multicenter, controlled trial with a new LDL apheresis procedure (Liposorber LA-15 System). The study comprised patients with FH who had not responded adequately to diet and maximal drug therapy. There were 54 patients with heterozygous FH (45 randomized to treatment and 9 control subjects) and 10 with homozygous FH (all of whom received LDL apheresis). The study included three 6-week treatment phases and a 4-week rebound phase. Treatments were administered at 7- to 14-day intervals. Mean acute reductions in LDL cholesterol were 76% in heterozygous FH patients and 81% in homozygous ones. Time-averaged levels of LDL cholesterol were reduced 41% (243 to 143 mg/dl) in heterozygous FH patients and 53% (447 to 210 mg/dl) in homozygous ones. The substantial acute reduction of lipoprotein (a) (means: 65%, heterozygous FH; 68%, homozygous FH) has not been reported with other therapies. The Liposorber LA-15 System represents an important therapeutic option in FH patients who respond inadequately to diet and drug therapy.

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.

The effect of alcohol withdrawal on serum concentrations of Lp(a), apolipoproteins A-1 and B, and lipids

Moderate alcohol consumption is associated with a decreased risk of coronary artery disease. The mechanism of the putative protective effect of alcohol intake, however, remains elusive. Recent studies suggest that a ratio of apolipoprotein A-I/apolipoprotein B and Lp(a) are better indicators of the risk of atherosclerosis than total cholesterol and high density lipoprotein cholesterol. To assess the effect of alcohol on these analytes, we determined the concentration of Lp(a), apolipoprotein A-I, apolipoprotein B, total cholesterol, and high-density lipoprotein cholesterol, and calculated low-density lipoprotein cholesterol in serum of 12 patients meeting DSM-III-R criteria for alcohol dependence at the time of admission for treatment of alcohol withdrawal (before). The analyses were repeated after 4 weeks of supervised abstinence on a locked research unit (after). With abstinence, there was a significant increase in the concentration of Lp(a), the atherogenic index and the ratio of low-density to high-density lipoprotein cholesterol but a significant decrease in total cholesterol, high-density lipoprotein cholesterol, apolipoprotein A-I, and the apolipoprotein A-I/B ratio. Apolipoprotein B and low-density lipoprotein cholesterol showed no significant changes before and after alcohol abstinence. Thus, decreased Lp(a) and increased high-density lipoprotein cholesterol and apolipoprotein A-I may be factors mediating the putative protective effect of alcohol in coronary artery disease.

Molecular genetics of familial hypercholesterolaemia: common and rare mutations of the low density lipoprotein receptor gene

Mutations of the low density lipoprotein (LDL) receptor gene give rise to familial hypercholesterolaemia (FH), one of the most common single-gene diseases in the world. Approximately 150 different LDL receptor gene mutations have been reported until now and the list seems to be continuously growing. Although hampering molecular genetic diagnosis of FH, this wide variability at the DNA level provides a useful tool to population genetics and may ultimately lead to better understanding of the variation in disease manifestations from family to family. The Finns are among the few populations in which one or two mutant LDL receptor genes explain the majority of FH cases. Either of the two 'Finnish-type' LDL receptor gene deletions, FH-Helsinki or FH-North Karelia, is present in more than 60% of the Finnish FH patients; there are no reports on their existence in other ethnic groups. Assays for these mutations were shown to markedly complement clinical diagnosis of FH in Finland.

Lipoprotein [Lp(a)] and peripheral vascular disease

Lipoprotein(a) [Lp(a)], which combines structural elements of the lipid and fibrinolytic systems, is a major independent risk factor for the development of coronary heart disease. Eighty-four consecutive patients with peripheral vascular disease (of whom 42 had concomitant ischaemic heart disease) and 43 healthy controls were enrolled in a case-control study. We found that the mean Lp(a) concentration in male patients with peripheral vascular disease (PVD) was almost threefold higher than that of controls, while in female patients the Lp(a) concentration was more than twice that of controls. This marked difference was borne out in patients with and without concomitant ischaemic heart disease (IHD). A multivariate logistic regression analysis indicated that Lp(a) is independently associated with PVD when adjusted for age and sex (odds ratio per 100 mg l-1 increase in Lp(a) = 1.35; P < 0.01). A similar association is observed for patients with concomitant IHD (odds ratio per 100 mg l-1 increase in Lp(a) = 1.65; P < 0.01).

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

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

Plasma lipoprotein(a) concentration in familial hypercholesterolemic patients without coronary artery disease

Familial Hypercholesterolemia (FH) is a condition characterized by markedly elevated blood cholesterol, low-density lipoproteins (LDL), and apolipoprotein B-100 (apo B). The molecular basis of this monogenic disease is the defective functioning of the cellular receptor for LDL that recognizes apo B. Lipoprotein(a) [Lp(a)] is a circulating lipoprotein that is structurally related to LDL, as it also contains apo B. To assess the impact of the LDL receptor deficiency on the plasma Lp(a) concentration, we measured Lp(a) in 28 FH patients and in 31 unaffected relatives. Because elevation of Lp(a) concentration in plasma of patients with coronary artery disease (CAD) appears to occur independently from plasma cholesterol levels, to avoid potentially confounding problems, members of the families chosen had no history for the disease. Whereas apo B clearly showed a bimodality of distribution by being significantly higher in the FH patients (166 +/- 38 mg/dL) than in the unaffected relatives (92 +/- 18 mg/dL), Lp(a) concentration did not differ in the two groups of patients (30 +/- 24 mg/dL in the FH patients v 31 +/- 23 in the normolipidemic relatives). Similar results were obtained when only siblings were further considered. We conclude that although Lp(a) is closely related to LDL structurally, its level in plasma is not significantly affected by the LDL receptor activity.

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.

Lipoprotein(a). Link between structure and pathology

It is now established that high plasma levels of lipoprotein(a) are associated with an increased risk of atherosclerotic cardiovascular disease. However, the mechanisms underlying this increased risk have not been elucidated. Lipoprotein(a) represents a class of lipoprotein particles having a cholesteryl ester-rich low-density lipoprotein (LDL)-like structure with a protein moiety represented by apolipoprotein B100 covalently linked to apolipoprotein(a), the specific marker of lipoprotein(a). Lipoprotein(a) particles with a triglyceride-rich core have also been described. Apolipoprotein(a) is a glycoprotein containing about 30% carbohydrates by weight, with a polypeptide chain highly polymorphic in size (300-700 kDa) and structurally similar to plasminogen. There appears to be a relation between apolipoprotein(a) size and lipoprotein(a) species. From a number of studies, it is becoming apparent that lipoprotein(a) can transverse the endothelium and accumulate in the arterial initima either extra- or intracellularly. Immunochemical evidence has also indicated that apolipoprotein(a) in the artery wall is colocalized with fibrin(ogen), suggesting that this complexation may have an atherogenic potential by promoting the transformation of resident macrophages into foam cells. This might also occur by the chemical modification of lipoprotein(a) by the action of either oxygen-free radicals, malondialdehyde, or interactions with matrix components. These findings invite the speculation that much of the apolipoprotein B detected in atherosclerotic lesions is contributed by lipoprotein(a). The role that lipoprotein(a) size and density heterogeneity and apolipoprotein(a) polymorphism might play in the intima accumulation of apolipoprotein B is not established.

Lipoprotein(a) levels in chronic renal disease states, dialysis and transplantation

Lipoprotein(a) is an independent risk factor for cardiovascular disease. Lipoprotein(a) levels were measured in 196 patients (103 Male [M]: 93 Female [F]) with chronic renal diseases and in 116 controls. Median levels of Lipoprotein(a) [Lp(a)] were found to be significantly elevated in patients with untreated chronic renal disease (285,285 mg/L; M,F; range 30-1675 mg/L) and in those treated with continuous ambulatory peritoneal dialysis (320, 603; M,F; range 50-1450) compared with controls (70,51; M,F; range 1-750; p less than 0.01 Males, p less than 0.001 Females). Lp(a) levels in patients treated by haemodialysis (133,35; M,F; range 5-685) and renal transplantation (100,95; M,F; range 10-1700) were not significantly different from controls. Lipoprotein(a) levels correlated inversely with serum albumin in the combined dialysis group (r = -0.34, p less than 0.001), and with urinary protein loss in the combined transplant and chronic renal diseases groups (r = 0.29, p less than 0.01). This correlation of Lp(a) with protein metabolism suggests a similarity with changes in other apolipoprotein-B containing lipoproteins in nephrosis. These findings may be relevant to the increased risk of atherosclerosis in patients with chronic renal disease and to their optimum mode of renal replacement therapy.

Lovastatin alters blood rheology in primary hyperlipoproteinemia: dependence on lipoprotein(a)?

As part of a randomized, single-blind, comparative study evaluating the efficacy of lovastatin and bezafibrate retard in the treatment of primary hypercholesterolemia, hemorheologic parameters (whole blood viscosity, hematocrit, plasma viscosity, red blood cell aggregation and deformability, and fibrinogen) were studied in 35 patients. Whole blood viscosity and plasma viscosity improved significantly after 3 months of treatment with lovastatin, whereas other hemorheologic variables remained unchanged. Stratifying 24 patients by their lipoprotein Lp(a) levels showed that in those with low Lp(a) (less than or equal to 25 mg/dL) high-density lipoprotein cholesterol increased and red blood cell aggregation as well as deformability decreased considerably, whereas in the group with high Lp(a) levels (greater than 25 mg/dL), the opposite behavior was observed. Treatment of primary hypercholesterolemia with lovastatin may not only reduce the risk for atherosclerotic complications by its pronounced decrease of low-density lipoprotein cholesterol, but also may favorably alter blood rheology, and may decrease insudation of plasmatic components into the arterial wall and improve tissue perfusion, in particular on the microcirculatory level. The possible relevance of Lp(a) levels for the hemorheologic effects of lovastatin remains to be elucidated.

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.

Familial hypercholesterolaemia and LDL receptor mutations

Inherited defects in the gene for the low density lipoprotein (LDL)-receptor give rise to familial hypercholesterolaemia (FH), a disorder in which defective catabolism of LDL causes a marked increase in its concentration in plasma. As a result, there is excessive deposition of cholesterol in the arterial wall leading to accelerated atherosclerosis and premature coronary heart disease in most patients, although there are differences in its severity. Many different mutations have been found in the LDL receptor genes of FH patients, and although this heterogeneity has provided information about the relationship between structure and function in different domains of the protein, it makes simple DNA-based diagnosis of the disease impossible. When sufficient groups of patients with defined mutations are available it will be possible to determine the relative importance of any particular mutation compared with other genetic or environmental factors in relation to the severity of their symptoms or their response to treatment.

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

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

Normolipaemic plane xanthomas: an association with increased vascular permeability and serum lipoprotein(a) concentration

We present a normolipaemic young man with extensive facial plane xanthomas and xanthelasmas with a high level of lipoprotein(a) and possibly increased vascular permeability. These associations are of potential importance in understanding the pathogenesis of xanthoma formation and in the identification of patients at risk from coronary atherosclerosis.

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.

Automated measurement of lipoprotein(a) by immunoturbidimetric analysis

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

Lack of change of lipoprotein (a) concentration with improved glycemic control in subjects with type II diabetes

Recently, lipoprotein (a) [Lp(a)] has been identified as a major risk factor for coronary heart disease. No data are available on the effect of improved metabolic control on plasma Lp(a) concentrations in subjects with type II diabetes mellitus, a group at high risk for coronary heart disease. We examined the effects of improved metabolic control on plasma lipid and lipoproteins and Lp(a) concentrations in 12 subjects before and after 21 days of tight metabolic control. Glycosylated hemoglobin declined from 8.9% to 6.9% (P less than .002). Lp(a) increased slightly from 21.4 to 25.8 mg/dL (P = .119) with improved metabolic control. There were no significant differences in total, low-density, or high-density cholesterol values, although the decline in triglyceride concentrations was statistically significant. The distribution of apolipoprotein (a) [apo (a)] isoforms in subjects with type II diabetes mellitus was not unusual and the apo (a) isoform patterns did not change with improved metabolic control. Although the number of subjects was small, there was no decline in Lp(a) concentrations with improved control and thus the effect of glycemic control on Lp(a) concentrations may be much smaller in type II than in type I diabetes. These results suggest that diabetic subjects with elevated Lp(a) concentrations should have intensive management of conventional cardiovascular risk factors such as high-density lipoprotein cholesterol (HDLC), low-density lipoprotein cholesterol (LDLC), and blood pressure.

Lack of association between lipoprotein (a) concentrations and coronary heart disease mortality in diabetes: the Wisconsin Epidemiologic Study of Diabetic Retinopathy

Recently, considerable data have suggested that lipoprotein (a) [Lp(a)] is a strong independent risk factor for coronary heart disease. Since Lp(a) is increased in both insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM), this study examined the relationship of Lp(a) concentrations to coronary heart disease (CHD) mortality in the 4-year follow-up of the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR). Twenty-four older-onset subjects and 11 younger-onset subjects who died of CHD (cases) before the age of 70 were matched by age, gender, and type of diabetes to subjects who remained alive (controls). The distribution and mean levels of Lp(a) in the cases and controls were very similar, suggesting a lack of association between Lp(a) concentrations and CHD mortality. Although the number of subjects was small, caution should be used in extrapolating results on Lp(a) relationships in nondiabetic subjects to diabetic subjects.

Laboratory facilities for investigating lipid disorders in the United Kingdom: results of the British Hyperlipidaemia Association survey

AIMS

To determine the availability of facilities for the investigation of hyperlipidaemia in the United Kingdom.

METHODS

A questionnaire was sent to all health districts in the United Kingdom.

RESULTS

The response rate was 81%. All laboratories used enzymatic techniques to measure serum triglyceride and cholesterol concentrations, although there were differences in standardisation procedures. Reference ranges for serum lipids were quoted by 58% of laboratories while 50% quoted "desirable limits". Almost half specified that fasting blood samples were required. High density lipoprotein cholesterol concentrations were estimated by 75% and apolipoproteins AI and B by 14% of laboratories; there were differences in specimen type and considerable diversity in procedures used for measurement.

CONCLUSIONS

Many laboratories were unaware of current recommendations for screening for hypercholesterolaemia in the community. The present survey indicated an urgent need for the introduction of better reference methods, standardisation, and quality assurance procedures before apolipoproteins become a routine part of coronary heart disease risk assessment.