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

Lipoprotein(a) Lowering-From Lipoprotein Apheresis to Antisense Oligonucleotide Approach

It is well-known that elevated lipoprotein(a)—Lp(a)—levels are associated with a higher risk of cardiovascular (CV) mortality and all-cause mortality, although a standard pharmacotherapeutic approach is still undefined for patients with high CV risk dependent on hyperlipoproteinemia(a). Combined with high Lp(a) levels, familial hypercholesterolemia (FH) leads to a greater CVD risk. In suspected FH patients, the proportion of cases explained by a rise of Lp(a) levels ranges between 5% and 20%. In the absence of a specific pharmacological approach able to lower Lp(a) to the extent required to achieve CV benefits, the most effective strategy today is lipoprotein apheresis (LA). Although limited, a clear effect on Lp(a) is exerted by PCSK9 antagonists, with apparently different mechanisms when given with statins (raised catabolism) or as monotherapy (reduced production). In the era of RNA-based therapies, a new dawn is represented by the use of antisense oligonucleotides APO(a)L_rx, able to reduce Lp(a) from 35% to over 80%, with generally modest injection site reactions. The improved knowledge of Lp(a) atherogenicity and possible prevention will be of benefit for patients with residual CV risk remaining after the most effective available lipid-lowering agents.

The complexity of lipoprotein (a) lowering by PCSK9 monoclonal antibodies

Since 2012, clinical trials dedicated to proprotein convertase subtilisin kexin type 9 (PCSK9) inhibition with monoclonal antibodies (mAbs) have unambiguously demonstrated robust reductions not only in low-density lipoprotein (LDL) cholesterol (LDL-C) but also in lipoprotein (a) [Lp(a)] levels. The scientific literature published prior to those studies did not provide any evidence for a link between PCSK9 and Lp(a) metabolism. More recent investigations, either in vitro or in vivo, have attempted to unravel the mechanism(s) by which PCSK9 mAbs reduce circulating Lp(a) levels, with some showing a specific implication of the LDL receptor (LDLR) in Lp(a) clearance whereas others found no significant role for the LDLR in that process. This elusive pathway appears clearly distinct from that of the widely prescribed statins that also enhance LDLR function but do not lower circulating Lp (a) levels in humans. So how does PCSK9 inhibition with mAbs reduce Lp(a)? This still remains to be established.

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.

Structure, function, and genetics of lipoprotein (a)

Lipoprotein (a) [Lp(a)] has attracted the interest of researchers and physicians due to its intriguing properties, including an intragenic multiallelic copy number variation in the LPA gene and the strong association with coronary heart disease (CHD). This review summarizes present knowledge of the structure, function, and genetics of Lp(a) with emphasis on the molecular and population genetics of the Lp(a)/LPA trait, as well as aspects of genetic epidemiology. It highlights the role of genetics in establishing Lp(a) as a risk factor for CHD, but also discusses uncertainties, controversies, and lack of knowledge on several aspects of the genetic Lp(a) trait, not least its function.

Lipoprotein(a) catabolism is regulated by proprotein convertase subtilisin/kexin type 9 through the low density lipoprotein receptor

Elevated levels of lipoprotein(a) (Lp(a)) have been identified as an independent risk factor for coronary heart disease. Plasma Lp(a) levels are reduced by monoclonal antibodies targeting proprotein convertase subtilisin/kexin type 9 (PCSK9). However, the mechanism of Lp(a) catabolism in vivo and the role of PCSK9 in this process are unknown. We report that Lp(a) internalization by hepatic HepG2 cells and primary human fibroblasts was effectively reduced by PCSK9. Overexpression of the low density lipoprotein (LDL) receptor (LDLR) in HepG2 cells dramatically increased the internalization of Lp(a). Internalization of Lp(a) was markedly reduced following treatment of HepG2 cells with a function-blocking monoclonal antibody against the LDLR or the use of primary human fibroblasts from an individual with familial hypercholesterolemia; in both cases, Lp(a) internalization was not affected by PCSK9. Optimal Lp(a) internalization in both hepatic and primary human fibroblasts was dependent on the LDL rather than the apolipoprotein(a) component of Lp(a). Lp(a) internalization was also dependent on clathrin-coated pits, and Lp(a) was targeted for lysosomal and not proteasomal degradation. Our data provide strong evidence that the LDLR plays a role in Lp(a) catabolism and that this process can be modulated by PCSK9. These results provide a direct mechanism underlying the therapeutic potential of PCSK9 in effectively lowering Lp(a) levels.

Effects of a new low dose soy protein/?-sitosterol association on plasma lipid levels and oxidation

BACKGROUND

High doses of soy protein are able to decrease plasma cholesterolemia significantly, but they unbalance daily protein intake and strongly modify nutritional habits in patients.

AIM OF THE STUDY

To evaluate the antihypercholesterolemic efficacy of a low dose soy protein product with added beta-sitosterol (rapport = 4:1) in 36 moderately hypercholesterolemic subjects.

METHODS

The study was divided into 3 separate periods of 40 days each: a stabilization diet period, followed by a treatment period during which all subjects took 10 g of the test product once daily and, finally, a wash out period. The following parameters were monitored: weight, dietary habits, plasma lipid levels, glycemia, uric acid, fibrinogenemia and antibodies against oxidized LDL (ox-LDL Ab).

RESULTS

From the end of the stabilization diet period to the end of the supplementation with the soy protein product with added beta-sitosterol we observed a 19.64 +/- 20.32 mg/dL, 8.47 +/- 54.61 mg/dL, 1.69 +/- 10.92 mg/dL, and 7.06 +/- 16.66 mg/dL mean +/- SD decrease respectively in LDL-C (p < 0.001), TG (p = 0.358), VLDLs (p = 0.358) and apoB (p = 0.016) levels, associated with a 1.31 +/- 8.08 mg/dL and 1.03 +/- 19.09 mg/dL mean increase respectively in HDLC (p = 0.251) and apoAI (p = 0.749) plasma concentrations. The dietary supplementation did not influence Lp(a) (p = 0.984) and ox-LDL Ab (p = 0.953) plasma levels. A statistically significant correlation was observed for LDL-C plasma levels, between the end of the stabilization diet period and the end of the period of supplementation with soy proteins with added beta-sitosterols (p < 0.001).

CONCLUSION

Although further long-term clinical studies are necessary before claims can be made regarding the therapeutic effects of the tested formulation, the preliminary findings regarding its efficacy and safety as an antihypercholesterolemic agent are encouraging.

Family history of early cardiovascular disease in children with moderate to severe hypercholesterolemia: relationship to lipoprotein (a) and low-density lipoprotein cholesterol levels

Lipoprotein (a) (Lp(a)) is an established cardiovascular risk factor in adults. We sought to evaluate whether raised Lp(a) levels were predictive of a family history of early cardiovascular disease (CVD) in children already at increased risk for premature atherosclerosis because of elevated low-density lipoprotein (LDL) cholesterol levels. Lp(a) and serum lipid levels were measured in 69 children and offspring with established moderate to severe hypercholesterolemia (serum cholesterol > 170 mg/dL) who were aged 10.7 +/- 4.3 years (range 1.5 to 21 years) and had been referred to a pediatric lipid center. The children represented families with a positive (n = 27) or negative (n = 42) history for premature CVD (<55 years of age in parent or grandparent). In all children, Lp(a) levels ranged from 1 to 140 mg/dL, with a median of 29 mg/dL. Mean total cholesterol, LDL cholesterol, and high-density lipoprotein (HDL) cholesterol levels were 234 mg/dL, 166 mg/dL, and 45 mg/dL, respectively. There was no difference in median Lp(a) levels between the children with a positive family history and those with a negative family history (29.9 mg/dL vs 29.0 mg/dL, respectively). In contrast, children with a positive family history showed significantly higher LDL cholesterol levels (186 +/- 61 mg/dL vs 153 +/- 52 mg/dL, P = .02). Thus, in this group of hypercholesterolemic children, LDL cholesterol but not Lp(a) levels were associated with a family history of premature CVD. Further studies are needed to identify additional specific risk factors associated with the development of CVD in this population.

Lipoprotein (a) concentrations in patients with various dyslipidaemias

Although the genetic background is the most important determinant of lipoprotein (a) (Lp(a)) concentration other factors, such as coexistent dyslipidaemia, could modify its levels. We undertook the present study to examine the serum Lp(a) concentration in various dyslipidaemias and to reveal any correlation of serum Lp(a) concentration with the other lipid parameters in a large group of dyslipidaemic Greek patients. A total of 242 patients followed as outpatients in our lipid clinic were studied. The patients were stratified into four main groups. Patients with cholesterol levels greater than 5.17 mmol/L but normal triglycerides were regarded as hypercholesterolaemic (n=85), patients with triglycerides greater than 2.25 mmol/L but normal cholesterol levels as hypertriglyceridaemic (n=51), patients with both increased cholesterol and triglyceride levels as having mixed hyperlipidaemia (n=62), and finally patients with decreased (<0.90 mmol/L) high-density lipoprotein (HDL) cholesterol but normal cholesterol and triglyceride levels as having primary hypoalphalipoproteinaemia (n=44). Hypercholesterolaemic patients exhibited the highest serum Lp(a) levels, while hypertriglyceridaemic patients exhibited the lowest. Patients with mixed hyperlipidaemia had intermediate serum Lp(a) concentration, which was significantly higher than that of hypertriglyceridaemic patients but significantly lower than that of hypercholesterolaemic patients. Interestingly, patients with low serum HDL-cholesterol levels presented with low serum Lp(a) concentration similar to that of hypertriglyceridaemic patients. In hypercholesterolaemic patients no correlation was found between serum total and low-density lipoprotein (LDL) cholesterol nor apolipoprotein B (apoB) levels and Lp(a) concentration. On the contrary, in hypertriglyceridaemic patients an inverse correlation was observed between serum triglycerides and Lp(a) concentration. After dividing the hypertriglyceridaemic patients into one group with elevated (>1.3 g/L) serum apoB levels (n=32) and another group with normal apoB levels (n=19), we found that the median serum Lp(a) concentration was three times higher in hyperapoB patients compared to patients with normal apoB levels. We conclude that serum Lp(a) levels are different in various types of primary hyperlipidaemia and are modulated according to the type of lipid elevation.

Arthritis in a patient with homozygous familial hypercholesterolemia

Familial hypercholesterolemia is a disorder of lipoprotein metabolism characterized by elevated cholesterol, low-density lipoprotein cholesterol, xanthomas and early onset atherosclerosis. Tendinitis and arthritis have been reported in patients with familial hypercholesterolemia. A report is presented of a 9-year-old girl with an acute arthritic attack who was diagnosed as homozygote familial hypercholesterolemia with hypercholesterolemic arthritis.

Sib-pair analysis detects elevated Lp(a) levels and large variation of Lp(a) concentration in subjects with familial defective ApoB

Whether or not Lp(a) plasma levels are affected by the apoB R3500Q mutation, which causes Familial Defective apoB (FDB), is still a matter of debate. We have analyzed 300 family members of 13 unrelated Dutch index patients for the apoB mutation and the apolipoprotein(a) [apo(a)] genotype. Total cholesterol, LDL-cholesterol, and lipoprotein(a) [Lp(a)] concentrations were determined in 85 FDB heterozygotes and 106 non-FDB relatives. Mean LDL levels were significantly elevated in FDB subjects compared to non-FDB relatives (P < 0.001). Median Lp(a) levels were not different between FDB subjects and their non-FDB relatives. In contrast, sib-pair analysis demonstrated a significant effect of the FDB status on Lp(a) levels. In sib pairs identical by descent for apo(a) alleles but discordant for the FDB mutation (n = 11) each sib with FDB had a higher Lp(a) level than the corresponding non-FDB sib. Further, all possible sib pairs (n = 105) were grouped into three categories according to the absence/presence of the apoB R3500Q mutation in one or both subjects of a sib pair. The variability of differences in Lp(a) levels within the sib pairs increased with the number (0, 1, and 2) of FDB subjects present in the sib pair. This suggests that the FDB status increases Lp(a) level and variability, and that apoB may be a variability gene for Lp(a) levels in plasma.

Correlation of toddlers' serum lipoprotein(a) concentration with parental values and grandparents' coronary heart disease: the STRIP baby study

The correlation between lipoprotein(a) (Lp(a)) concentrations in children aged 7-24 months and their family members was determined and the association between the Lp(a) values of the children and a family history of coronary heart disease (CHD) was assessed. The Lp(a) values of the children correlated strongly with midparent Lp(a) values as early as at 7 months of age (r = 0.54 to 0.59, p < 0.0001). This correlation was stronger than the correlation of serum total cholesterol and total cholesterol corrected for Lp(a)-cholesterol between children and parents. None of the parents had CHD. The median Lp(a) concentration of the parents with a family history of CHD was significantly higher than that of parents with no such history (111 vs 87 mg/1, p = 0.024). However, the children's Lp(a) levels were not associated with CHD in their grandparents. The genetic dependence of the Lp(a) concentration is already evident in infancy. The Lp(a) concentration in young parents, but not in their 24-month-old children, is associated with CHD in grandparents. This may be explained by a dilution of the genetic influence on Lp(a) over two generations.

Lp(a) levels and atherosclerotic vascular disease in a sample of patients with familial hypercholesterolemia sharing the same gene defect

There is considerable variation in the severity of cardiovascular disease among patients with familial hypercholesterolemia (FH). Some reports have suggested that plasma lipoprotein(a) [Lp(a)] levels may explain such variation and that FH subjects deficient in LDL receptors, especially those with coronary heart disease, tend to have elevated Lp(a) levels. We have investigated the possible role of the LDL receptor in determining plasma Lp(a) levels in genetically homogeneous FH population and the contribution of Lp(a) to cardiovascular risk. A total of 98 FH subjects and 66 healthy first- and second-degree relatives from 30 families with FH due to the French-Canadian > 10-kilobase deletion of the LDL receptor gene were studied. A reference group of 392 normolipidemic French-Canadian participants in a Heart Health Survey was used for comparison. FH subjects were subdivided into subsets of 63 individuals free from atherosclerotic vascular disease (AVD) and 35 individuals with AVD. A complete cardiovascular evaluation was performed, and plasma lipid, lipoprotein, and Lp(a) levels were measured in all subjects in the absence of medication. Apolipoprotein (a) [apo(a)] phenotype was determined in 112 of FH and non-FH subjects. The log-transformed values for plasma Lp(a) were not significantly different among the three groups: 0.98 +/- 0.54 (mean +/- SD) in FH subjects with AVD, 0.89 +/- 0.51 in FH subjects without AVD, and 0.82 +/- 0.64 in their relatives. The distribution of the apo(a) phenotypes did not differ between the FH and non-FH groups. Comparison of two age- and sex-matched subgroups of FH subjects, with and without AVD, failed to show any differences in Lp(a) level. However, mean Lp(a) log values in the reference group (n = 392) were significantly lower than values obtained for the total FH group (0.79 +/- 0.57 versus 0.92 +/- 0.52, respectively; P < .05) but were not different from those of the unaffected family members. Thus, in our sample, the LDL receptor appears not to influence plasma Lp(a) levels; rather, these levels reflect shared apo(a) genes. The cardiovascular risk in this group of subjects with FH was related to age, male sex, total and LDL cholesterol, and higher apoB but not Lp(a) levels.

Transfer of lipoprotein(a) and LDL into aortic intima in normal and in cholesterol-fed rabbits

To study the relative atherogenic potential of lipoprotein(a) [Lp(a)], the transfer of Lp(a) and LDL into the arterial wall was compared in normal rabbits, cholesterol-fed rabbits, and normal rabbits in which the plasma concentration of Lp(a) before injection of labeled lipoproteins was increased by an intravenous mass injection of 45 mg Lp(a). Aorta was removed either 60 minutes or 180 minutes after intravenous injection of a mixed preparation of human 125I-Lp(a) and 131I-LDL; intimal clearance was calculated as radioactivity in aortic intima/inner media divided by the average concentration of the appropriate radioactivity in plasma and by the length of the exposure time. The intimal clearance of labeled Lp(a) and LDL in the aortic arch after 60 minutes of exposure was 87 +/- 9 and 47 +/- 7 nL.cm-2.h-1 (n = 9) in normal rabbits and 82 +/- 14 and 62 +/- 10 nL.cm-2.h-1 (n = 10) in cholesterol-fed rabbits; after 180 minutes of exposure, the intimal clearance of labeled Lp(a) and LDL was 62 +/- 14 and 84 +/- 21 nL.cm-2.h-1 (n = 6) and 30 +/- 6 and 47 +/- 12 nL.cm-2.h-1 (n = 4) in cholesterol-fed and Lp(a)-injected rabbits, respectively. Linear regression analysis showed positive associations between intimal clearance of the two lipoproteins in all four groups of rabbits in the aortic arch, the thoracic aorta, and the abdominal aorta. Aortic immunoreactivity of human apolipoprotein(a) was detected in the intima in association with fatty streak lesions, predominantly within the cytoplasm of foam cells. These results suggest that Lp(a) is transferred into the aortic intima by a mechanism similar to that for LDL and that Lp(a) can be taken up by intimal foam cells; however, Lp(a) and LDL may be metabolized differently upon entrance into the arterial wall.

The low density lipoprotein receptor is not required for normal catabolism of Lp(a) in humans

Lipoprotein(a) [Lp(a)] is an atherogenic lipoprotein which is similar in structure to low density lipoproteins (LDL). The role of the LDL receptor in the catabolism of Lp(a) has been controversial. We therefore investigated the in vivo catabolism of Lp(a) and LDL in five unrelated patients with homozygous familial hypercholesterolemia (FH) who have little or no LDL receptor activity. Purified 125I-Lp(a) and 131I-LDL were simultaneously injected into the homozygous FH patients, their heterozygous FH parents when available, and control subjects. The disappearance of plasma radioactivity was followed over time. As expected, the fractional catabolic rates (FCR) of 131I-LDL were markedly decreased in the homozygous FH patients (mean LDL FCR 0.190 d-1) and somewhat decreased in the heterozygous FH parents (mean LDL FCR 0.294 d-1) compared with controls (mean LDL FCR 0.401 d-1). In contrast, the catabolism of 125I-Lp(a) was not significantly different in the homozygous FH patients (mean FCR 0.251 d-1), heterozygous FH parents (mean FCR 0.254 d-1), and control subjects (mean FCR 0.287 d-1). In summary, absence of a functional LDL receptor does not result in delayed catabolism of Lp(a), indicating that the LDL receptor is not a physiologically important route of Lp(a) catabolism in humans.

Apolipoprotein(a) phenotypes and lipoprotein(a) concentrations in patients with hyperthyroidism

Lipoprotein(a) [Lp(a)] is a low-density lipoprotein (LDL) particle in which apolipoprotein B-100 (apoB) is attached to a glycoprotein called apolipoprotein(a) [apo(a)]. Apo(a) has several genetically determined phenotypes differing in molecular weight, to which Lp(a) concentrations in plasma are inversely correlated. High plasma levels of Lp(a) are associated with atherosclerotic diseases. It is therefore of interest to study whether factors other than the apo(a) gene locus are involved in the regulation of Lp(a) concentrations. We measured plasma concentrations of Lp(a) and other lipoproteins and determined apo(a) phenotypes in 31 patients with hyperthyroidism, before and after the patients had become euthyroid by treatment. The mean concentration of LDL cholesterol rose from 2.67 to 3.88 mmol/l (P < 0.01), apoB rose from 0.79 to 1.03 g/l (P < 0.01), and the median Lp(a) concentration increased from 9.74 to 18.97 mg/dl (P < 0.01) on treatment. Lp(a) concentrations were inversely associated to the size of the apo(a) molecule both before (P < 0.01) and after treatment (P < 0.01). The increase in Lp(a) was significant in patients with high molecular weight apo(a) phenotypes (n = 9; P < 0.01) and in patients with low molecular weight apo(a) phenotypes (n = 16; P < 0.01), but not in those with apo(a) "null types" (n = 6; P = 0.5). The low levels LDL cholesterol and apoB in untreated hyperthyroidism may result from increased LDL receptor activity. The increase in Lp(a) levels were not correlated with the increase in LDL cholesterol or apoB.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Apolipoprotein E polymorphism and heterozygous familial hypercholesterolemia. Sex-specific effects

The impact of apolipoprotein (apo) E polymorphism on interindividual variation in plasma lipid, lipoprotein, and apolipoprotein levels was studied in a sample of familial hypercholesterolemic (FH) patients (147 women, 116 men) with the same mutation, a > 10-kilobase deletion of the low-density lipoprotein (LDL) receptor gene. Each trait was adjusted for concomitants (age, age squared, height, weight, weight squared) for each sex separately before the apoE genotypic effects were estimated. The relative contribution of concomitants to sample variability was found to be very different in women and in men. Allelic variation in the apoE gene was shown to explain a statistically significant portion of the variability in adjusted lipid traits. Moreover, the contribution of apoE polymorphism was different between sexes. In women, there was significant variability (P < .01) among apoE genotypes for total cholesterol, LDL cholesterol, and total and LDL apoB. In men, significant variability (P < .01) was observed among apoE genotypes in very-low-density lipoprotein (VLDL) cholesterol and triglyceride levels. Women with the epsilon 3/2 genotype had significantly lower means for total cholesterol, LDL cholesterol, and LDL apoB than women with the epsilon 3/3 genotype (P < .05). In men, the mean VLDL cholesterol was significantly higher for the epsilon 2/2 genotype and was significantly lower for the epsilon 4/2 genotype than the mean for the epsilon 3/3 genotype (P < .05). Overall, the greatest influence was associated with the epsilon 2 allele, and the LDL cholesterol-lowering effect of this allele was present only in FH women. No statistically significant apoE effect was shown on lipoprotein(a) levels in either sex.(ABSTRACT TRUNCATED AT 250 WORDS)

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).

Interaction of LDL and Lp[a] with human skin fibroblasts

We have studied the interaction of LDL and Lp[a] with fibroblasts. Our studies suggest that Lp[a] does not effectively compete with LDL for binding to the LDL receptor, and does not efficiently suppress the activity of the intracellular enzyme HMG-CoA reductase. However, Lp[a-], formed by reduction of the disulfide bond between apo[a] and apoB, behaves much like homologous LDL, whether or not apo[a] is removed from the mixture, and in spite of the fact that one or more apoB disulfides may also have been cleaved. In our studies we also noted that Lp[a] often enhanced binding of 125I-LDL by fibroblasts. Further investigation has suggested that this interaction is time-dependent. Experiments in receptor-negative fibroblasts indicate that the enhancement is not related to the presence of the LDL receptor; however, it is inhibited by the removal of calcium from the medium. The presence of sialic acid at millimolar concentrations in the medium inhibits much of the Lp[a]-enhanced binding of 125I-LDL to the cells. These studies suggest that Lp[] may in some way enhance LDL binding to cells, perhaps via interaction with cell surface glycosaminoglycans or proteoglycans or with collagen.

The relation of LDL receptor activity to lipoprotein(a) plasma concentration in patients without coronary artery disease

Elevation of blood cholesterol, low-density lipoproteins (LDL) and apolipoprotein B (apoB) are hallmarks of familial hypercholesterolemia (FH), a genetic condition caused by the defective functioning of the cellular receptor for apoB-100 in LDL. ApoB-100 is also present in lipoprotein(a) (Lp(a)). In this lipoprotein, apoB-100 is linked to a plasminogen-like protein called apo(a). By direct comparison of the Lp(a) and apoB plasma concentrations in 28 affected and 31 unaffected members of seven families carrying the FH trait and without history of coronary artery disease, we reached the conclusion that LDL receptor activity is not a major determinant of the Lp(a) plasma levels in these subjects. This suggests that the molecular determinants for catabolism of Lp(a) are not the same as those for LDL. Consistent with this view is our observation that the turnover rate of Lp(a) and of LDL apoB, calculated from their rate of reappearance in plasma following Lp(a)/LDL apheresis, differ greatly.

Serum lipoprotein(a) levels differ in different phenotypes of primary hyperlipoproteinemia

Previous studies have indicated that serum lipoprotein(a) [Lp(a)] levels are mostly under genetic control. We have attempted to determine whether serum Lp(a) levels differ in different phenotypes of primary hyperlipoproteinemia (HL). A total of 129 subjects with HL (three with type I, 43 with familial hypercholesterolemia [FH], 17 with type IIa [non-FH], 11 with type IIb, six with type III [E2/2], 44 with type IV, and five with type V) and 18 normolipidemic controls were included in the study. Thirty-two FH subjects were being treated with hypolipidemic agents, but none of the other subjects were receiving any medication. Fasting blood samples were collected for determination of both serum lipid and Lp(a) levels. Lp(a) level was measured by enzyme-linked immunosorbent assay. The 18 controls had serum Lp(a) concentrations of 18.0 +/- 14.5 mg/dL (mean +/- SD), and four of them had high serum Lp(a) levels (> or = 25 mg/dL). Serum Lp(a) concentrations in FH subjects tended to be higher than in the controls (30.5 +/- 25.0 mg/dL), and the incidence of high Lp(a) levels in FH subjects was significantly higher than in the controls (51% v 22%, P < .01). There was no difference between serum Lp(a) levels of FH subjects depending on whether they were receiving medication. In contrast, most of the subjects with selective hypertriglyceridemia had very low serum Lp(a) levels (1.5 +/- 0.7, 8.1 +/- 8.3, and 3.5 +/- 5.3 mg/dL in type I, IV, and V, respectively; P < .01 v controls).(ABSTRACT TRUNCATED AT 250 WORDS)