Acute effects of low density lipoprotein apheresis on metabolic parameters of apolipoprotein B

Current Role of Lipoprotein Apheresis

Purpose of Review

Lipoprotein apheresis is a very efficient but time-consuming and expensive method of lowering levels of low-density lipoprotein cholesterol, lipoprotein(a)) and other apoB containing lipoproteins, including triglyceride-rich lipoproteins. First introduced almost 45 years ago, it has long been a therapy of “last resort” for dyslipidaemias that cannot otherwise be managed. In recent years new, very potent lipid-lowering drugs have been developed and the purpose of this review is to define the role of lipoprotein apheresis in the current setting.

Recent Findings

Lipoprotein apheresis still plays an important role in managing patients with homozygous FH and some patients with other forms of hypercholesterolaemia and cardiovascular disease. In particular, patients not achieving treatment goals despite modern lipid-lowering drugs, either because these are not tolerated or the response is insufficient. Recently, lipoprotein(a) has emerged as an important cardiovascular risk factor and lipoprotein apheresis has been used to decrease lipoprotein(a) concentrations in patients with marked elevations and cardiovascular disease. However, there is considerable heterogeneity concerning the recommendations by scientific bodies as to which patient groups should be treated with lipoprotein apheresis.

Summary

Lipoprotein apheresis remains an important tool for the management of patients with severe drug-resistant dyslipidaemias, especially those with homozygous FH.

Lipoprotein turnover and possible remnant accumulation in preeclampsia: insights from the Freiburg Preeclampsia H.E.L.P.-apheresis study

Background

Preeclampsia is a life-threatening disease in pregnancy, and its complex pathomechanisms are poorly understood. In preeclampsia, lipid metabolism is substantially altered. In late onset preeclampsia, remnant removal disease like lipoprotein profiles have been observed. Lipid apheresis is currently being explored as a possible therapeutic approach to prolong preeclamptic pregnancies. Here, apheresis-induced changes in serum lipid parameters are analyzed in detail and their implications for preeclamptic lipid metabolism are discussed.

Methods

In the Freiburg H.E.L.P.-Apheresis Study, 6 early onset preeclamptic patients underwent repeated apheresis treatments. Serum lipids pre- and post-apheresis and during lipid rebound were analyzed in depth via ultracentrifugation to yield lipoprotein subclasses.

Results

The net elimination of Apolipoprotein B and plasma lipids was lower than theoretically expected. Lipids returned to previous pre-apheresis levels before the next apheresis even though apheresis was repeated within 2.9 ± 1.2 days. Apparent fractional catabolic rates and synthetic rates were substantially elevated, with fractional catabolic rates for Apolipoprotein B / LDL-cholesterol being 0.7 ± 0.3 / 0.4 ± 0.2 [day^− 1] and synthetic rates being 26 ± 8 / 17 ± 8 [mg*kg^− 1*day^− 1]. The distribution of LDL-subclasses after apheresis shifted to larger buoyant LDL, while intermediate-density lipoprotein-levels remained unaffected, supporting the notion of an underlying remnant removal disorder in preeclampsia.

Conclusion

Lipid metabolism seems to be highly accelerated in preeclampsia, likely outbalancing remnant removal mechanisms. Since cholesterol-rich lipoprotein remnants are able to accumulate in the vessel wall, remnant lipoproteins may contribute to the severe endothelial dysfunction observed in preeclampsia.

Trial registration

ClinicalTrails.gov, NCT01967355.

Effect of mipomersen on LDL-cholesterol in patients with severe LDL-hypercholesterolaemia and atherosclerosis treated by lipoprotein apheresis (The MICA-Study)

BACKGROUND AND AIMS

In this study, we evaluated the effect of mipomersen in patients with severe LDL-hypercholesterolaemia and atherosclerosis, treated by lipid lowering drugs and regular lipoprotein apheresis.

METHODS

This prospective, randomized, controlled phase II single center trial enrolled 15 patients (9 males, 6 females; 59 ± 9 y, BMI 27 ± 4 kg/m²) with established atherosclerosis, LDL-cholesterol ≥130 mg/dL (3.4 mmol/L) despite maximal possible drug therapy, and fulfilling German criteria for regular lipoprotein apheresis. All patients were on stable lipid lowering drug therapy and regular apheresis for >3 months. Patients randomized to treatment (n = 11) self-injected mipomersen 200 mg sc weekly, at day 4 after apheresis, for 26 weeks. Patients randomized to control (n = 4) continued apheresis without injection. The primary endpoint was the change in pre-apheresis LDL-cholesterol.

RESULTS

Of the patients randomized to mipomersen, 3 discontinued the drug early (<12 weeks therapy) for side effects. For these, another 3 were recruited and randomized. Further, 4 patients discontinued mipomersen between 12 and 26 weeks for side effects (moderate to severe injection site reactions n = 3 and elevated liver enzymes n = 1). In those treated for >12 weeks, mipomersen reduced pre-apheresis LDL-cholesterol significantly by 22.6 ± 17.0%, from a baseline of 4.8 ± 1.2 mmol/L to 3.7 ± 0.9 mmol/L, while there was no significant change in the control group (+1.6 ± 9.3%), with the difference between the groups being significant (p=0.006). Mipomersen also decreased pre-apheresis lipoprotein(a) (Lp(a)) concentration from a median baseline of 40.2mg/dL (32.5,71) by 15% (-19.4,3.6) though without significance (p=0.3).

CONCLUSIONS

Mipomersen reduces LDL-cholesterol (significantly) and Lp(a) (non-significantly) in patients on maximal lipid-lowering drug therapy and regular apheresis, but is often associated with side effects.

The potential of mipomersen, an ApoB synthesis inhibitor, to reduce necessity for LDL-apheresis in patients with heterozygous familial hypercholesterolemia and coronary artery disease

INTRODUCTION

LDL-apheresis is a treatment option for familial hypercholesterolemia (FH) with country-specific thresholds for LDL-cholesterol (LDL-C) for initiation. Apheresis also reduces lipoprotein(a) [Lp(a)] and may be used to lower Lp(a) in high-risk patients. Mipomersen, an apolipoproteinB-synthesis-inhibitor, reduces LDL-C and Lp(a). We hypothesized that mipomersen may prevent the necessity for apheresis by reducing the both below thresholds.

METHODS

Data from a study in 123 patients with heterozygous FH and coronary artery disease on maximally tolerated lipid-lowering therapy were used to evaluate in what percentage adding mipomersen resulted in lipid-levels below apheresis-thresholds. Different thresholds were tested: LDL-C ≥ 2.59 mmol/l, ≥ 3.36 mmol/l, ≥ 4.14 mmol/l, Lp(a) ≥ 60 mg/dl.

RESULTS

Mipomersen decreased LDL-C by 28% (baseline 153 mg/dl), Lp(a) by 21% (baseline 45 mg/dl) (placebo no effect). Mipomersen reduced the percentage of patients with LDL-C ≥ 4.14 mmol/l from 39 to 2%, with LDL ≥ 3.36 mmol/l from 62 to 16%, with LDL ≥ 2.59 mmol/l from 98 to 54%, and with Lp(a) ≥ 60 mg/dl from 39 to 23%.

SUMMARY

When added to maximally tolerated lipid-lowering therapy, mipomersen may reduce the necessity for apheresis in many of these patients. In Germany, the threshold for apheresis for LDL typically is 2.59 mmol/l, for Lp(a) 60 mg/dl. Almost 50% of the patients could avoid apheresis with the addition of mipomersen. Further studies are warranted to evaluate whether patients who qualify for apheresis could be adequately controlled with mipomersen.

Defining the role of lipoprotein apheresis in the management of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal co-dominant disorder characterized by a marked elevation of serum low-density lipoprotein (LDL) cholesterol (LDL-C) concentration, which in turn is associated with a greatly increased risk of premature cardiovascular disease. International consensus recommends the use of statins as the first line of treatment for patients with this condition. However, homozygote FH patients with persistently elevated LDL-C levels are usually resistant to multiple-drug therapy. Fortunately, LDL apheresis (or simply 'lipoprotein apheresis') provides a treatment option for patients who are refractory or intolerant to lipid-lowering medications, or if there is progressive cardiovascular disease despite maximal drug therapy. Lipoprotein apheresis is an extracorporeal LDL-C-lowering treatment similar in concept to renal dialysis. There are now five main methods for extracorporeal lipoprotein apheresis in use, namely dextran sulfate adsorption (DSA), heparin extracorporeal LDL precipitation (HELP), polyacrylate full blood adsorption (PFBA or DALI® system) using hemoperfusion, immunoadsorption, and filtration plasmapheresis. Lipoprotein apheresis has been shown to be successful in reducing LDL-C levels, as well as levels of lipoprotein(a) [Lp(a)], a prothrombotic proatherogenic lipoprotein. In contrast, however, lipoprotein apheresis seems to have a smaller effect in preventing atherosclerosis progression, thus suggesting that a major component of the reduction in cardiovascular events may be mediated by mitigating Lp(a) levels. Side effects are infrequent and mild, and have mainly consisted of lightheadedness, nausea, vomiting, and hypotension. As these are often bradykinin-mediated and associated with concomitant ACE inhibitor use, angiotensin type 2 receptor antagonists should be used instead of ACE inhibitors with DALI and PFBA. Nevertheless, there is scope for wider application of lipoprotein apheresis. The high cost and invasive nature of lipoprotein apheresis limits uptake; however, it is an important treatment modality that should be considered in carefully selected patients. National and international registries compiling outcome data for lipoprotein apheresis need to be established to help expand the evidence base regarding its effectiveness.

Thematic review series: patient-oriented research. What we have learned about VLDL and LDL metabolism from human kinetics studies

Lipoprotein metabolism is the result of a complex network of many individual components. Abnormal lipoprotein concentrations can result from changes in the production, conversion, or catabolism of lipoprotein particles. Studies in hypolipoproteinemia and hyperlipoproteinemia have elucidated the processes that control VLDL secretion as well as VLDL and LDL catabolism. Here, we review the current knowledge regarding apolipoprotein B (apoB) metabolism, focusing on selected clinically relevant conditions. In hypobetalipoproteinemia attributable to truncations in apoB, the rate of secretion is closely linked to the length of apoB. On the other hand, in patients with the metabolic syndrome, it appears that substrate, in the form of free fatty acids, coupled to the state of insulin resistance can induce hypersecretion of VLDL-apoB. Studies in patients with familial hypercholesterolemia, familial defective apoB, and mutant forms of proprotein convertase subtilisin/kexin type 9 show that mutations in the LDL receptor, the ligand for the receptor, or an intracellular chaperone for the receptor are the most important determinants in regulating LDL catabolism. This review also demonstrates the variance of results within similar, or even the same, phenotypic conditions. This underscores the sensitivity of metabolic studies to methodological aspects and thus the importance of the inclusion of adequate controls in studies.

In-vivo metabolism of VLDL-apolipoprotein-B, -CIII and -E in normolipidemic subjects

BACKGROUND AND AIM

ApoE and apoC-III are important components of lipoprotein metabolism. While the function of both apoproteins is relatively well understood, little is known about the in vivo metabolism of these proteins, partly because of the lack of a standardized method to isolate these apoproteins in large sample numbers.

METHODS AND RESULTS

We developed a new reverse phase HPLC method (acetonitril/phosphate gradient; Aquapore RP-300, 7 microm, 220 x 4.6 mm) to isolate a number of different apoproteins, including apoC-III and apoE from VLDL. This method was then used in a study which aimed at determining VLDL-apoE-3 and VLDL-apoC-III metabolism. In addition VLDL-apoB and LDL-apoB metabolism was determined. Endogenous labeling with d(3)-leucine, mass spectrometry and multicompartmental modeling was used in 6 normolipidemic healthy male subjects. Tracer/tracee ratios of free plasma leucine, VLDL-apoE, -apoC-III, -apoB, and LDL-apoB leucine were determined over 60 h following a bolus of d(3)-leucine (5 mg kg(-1)). In all subjects sufficient apoC-III could be isolated by reverse phase HPLC to derive metabolic parameters, while apoE metabolic parameters could only be determined if apoE plasma concentration was 0.75 mg dl(-1) or higher. Compared to VLDL-apoB (FCR 10.4 +/- 3.3 d(-1), production 17.8 +/- 4.5 mg kg(-1) d(-1)), VLDL-apoE-3 (FCR 1.03 +/- 0.11 d(-1), production 0.50 +/- 0.29 mg kg(-1) d(-1)) and VLDL-apoC-III (FCR 1.67 +/- 1.22 d(-1), production 0.44 +/- 0.24 mg kg(-1) d(-1)) parameters were much lower. This indicates that apoE-3 and apoC-III recirculate in plasma and that only a small fraction of apoE and apoC-III on VLDL is newly synthesized.

CONCLUSIONS

We conclude that HPLC methodology can be used to isolate VLDL-apoC-III and apoE for metabolic studies and that the metabolic fate of apoC-III and apoE is different from that of apoB because both apoproteins recycle through the VLDL fraction.

In vivo metabolism of LDL subfractions in patients with heterozygous FH on statin therapy

LDL can be subfractionated into buoyant (1.020-1.029 g/ml(-1)), intermediate (1.030-1.040 g/ml(-1)), and dense (1.041-1.066 g/ml(-1)) LDLs. We studied the rebound of these LDL-subfractions after LDL apheresis in seven patients with heterozygous familial hypercholesterolemia (FH) regularly treated by apheresis (58 +/- 9 years, LDL-cholesterol = 342 +/- 87 mg/dl(-1), triglycerides = 109 +/- 39 mg/dl(-1)) and high-dose statins. Apolipoprotein B (apoB) concentrations were measured in LDL subfractions immediately after and on days 1, 2, 3, 5, and 7 after apheresis. Compartmental models were developed to test three hypotheses: 1) that dense LDLs are derived from the delipidation of buoyant and intermediate LDLs (model A); 2) that dense LDLs are generated directly from LDL-precursors (model B); or 3) that a model combining both pathways (model C) is necessary to describe the metabolism of dense LDLs. In all models, it was assumed that apoB production and fractional catabolic rate (FCR) did not change with apheresis. Apheresis decreased buoyant, intermediate, and dense LDL-apoB by 60 +/- 12%, 67 +/- 5%, and 69 +/- 11%, respectively. Models B and C, but not model A, described the rebound data. The model with the greatest biological plausibility (model C) was used to estimate metabolic parameters. FCR was 1.05 +/- 0.86 d(-1), 0.48 +/- 0.11 d(-1), and 0.69 +/- 0.24 d(-1) for buoyant, intermediate, and dense LDLs, respectively. Dense LDL production was 17.3 +/- 0.2 mg/kg(-1)/d(-1), 58% of which was derived directly from LDL precursors (VLDL, IDL, or direct secretion), while 42% was derived from buoyant and intermediate LDLs. Thus, our data indicate that in statin-treated patients with heterozygous FH dense LDLs originate from two sources. Whether this is also valid in other metabolic situations (with predominant small, dense LDLs) remains to be determined.

LDL apheresis

Low density lipoprotein (LDL) apheresis provides a safe and effective means of treating patients with homozygous familial hypercholesterolaemia (FH). It also has a role in preventing the progression of coronary artery disease in heterozygotes and others with severe dyslipidaemia who are refractory to or intolerant of high doses of lipid-lowering drugs. Established methods involve either adsorption of apolipoprotein B-containing lipoproteins by affinity columns containing anti-apolipoprotein B antibodies or dextran sulphate, or their precipitation at low pH by heparin, in each instance after first separating plasma from blood cells with a cell separator. The most recently developed method enables lipoproteins to be adsorbed directly from whole blood, using polyacrylate columns. All 4 methods have proved to be similarly efficient when used weekly or biweekly to lower LDL cholesterol and Lp(a) without unduly reducing HDL cholesterol. Economic constraints restrict the use of LDL apheresis to the treatment of potentially fatal disorders such as FH, where there is clear evidence of benefit compared with conventional therapy. Widening the indications to include the treatment of other dyslipidaemic disorders such as steroid-resistant nephrotic syndrome, post-transplant donor vessel disease, stroke and prevention of re-stenosis after coronary angioplasty requires evidence from controlled trials that is currently lacking.

Apolipoprotein B metabolism: tracer kinetics, models, and metabolic studies

The study of apolipoprotein (apo) B metabolism is central to our understanding of lipoprotein metabolism. However, the assembly and secretion of apoB-containing lipoproteins is a complex process. Specialized techniques, developed and applied to in vitro and in vivo studies of apoB metabolism, have provided insights into the mechanisms involved in the regulation of this process. Moreover, these studies have important implications for understanding both the pathophysiology as well as the therapeutic options for the dyslipidemias. The purpose of this review is to examine the role of apoB in lipoprotein metabolism and to explore the applications of kinetic analysis and multicompartmental modeling to the study of apoB metabolism. New developments and significant advances over the last decade are discussed.