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

Apheresis is a treatment option for patients with severe hypercholesterolemia and coronary artery disease. It is unknown whether such therapy changes kinetic parameters of lipoprotein metabolism, such as apolipoprotein B (apoB) secretion rates, conversion rates, and fractional catabolic rates (FCR). We studied the acute effect of apheresis on metabolic parameters of apoB in five patients with drug-resistant hyperlipoproteinemia, using endogenous labeling with D(3)-leucine, mass spectrometry, and multicompartmental modeling. Patients were studied prior to and immediately after apheresis therapy. The two tracer studies were modeled simultaneously, taking into account the non-steady-state concentrations of apoB. The low density lipoprotein (LDL)-apoB concentration was 120+/-32 mg dl(-1) prior to and 52+/-18 mg dl(-1) immediately after apheresis therapy. The metabolic studies indicate that no change in apoB secretion (13.9+/- 4.9 mg kg(-1) day(-1)) is required to fit the tracer and apoB mass data obtained before and after apheresis and that in four of the five patients the LDL-apoB FCR (0.21+/-0.02 day(-1)) was not altered after apheresis. In one subject the LDL-apoB FCR temporarily increased from 0.22 day(-1) to 0.35 day(-1) after apheresis. The conversion rate of very low density lipoprotein (VLDL)-apoB to LDL-apoB is temporarily decreased from 76 to 51% after apheresis and thus less LDL-apoB is produced after apheresis. We conclude that an acute reduction of LDL-apoB concentration does not affect apoB secretion or LDL-apoB FCR, but that apoB conversion to LDL is temporarily decreased. Thus, in most patients the decreased rate of delivery of neutral lipids or apoB to the liver does not result in an upregulation of LDL receptors or in decreased apoB secretion.     

Modification of coronary artery disease progression by cholesterol-lowering therapy: the angiographic studies

Large randomized placebo-controlled trials have demonstrated that cholesterol lowering with statin therapy reduces the incidence of adverse cardiac events. Smaller angiographic studies have shown that coronary artery disease progression can be slowed and, in some cases, reversed by cholesterol-lowering interventions. These anatomical changes, however, are small and occur too slowly to account for the early clinical benefit. Current evidence suggests that plaque stabilization is the most important mechanism, by which cholesterol-lowering therapy reduces both the incidence of adverse cardiac events and coronary artery disease progression.     

Advances in LDL-apheresis for the treatment of severe hypercholesterolemia

LDL-apheresis is an extracorporeal plasma-perfusion method that selectively removes apolipoprotein B-containing lipoproteins from the blood. It is indicated for patients with homozygous and drug-resistant heterozygous familial hypercholesterolemia. Clinical and angiographic regression of coronary artery disease has been demonstrated in patients treated with cholesterol-lowering programs that include LDL-apheresis.     

Cardiovascular disease with diabetes or the metabolic syndrome: should statins or fibrates be first line lipid therapy?

PURPOSE OF REVIEW: Subgroups with diabetes or with features of the metabolic syndrome have been increasingly highlighted in large clinical endpoint trials with lipid therapy. This review will focus on the results of trials with statins or fibrates and examine the strength of the evidence for major cardiovascular event reduction with each kind of therapy in these high-risk subgroups that typically have low-to-moderate levels of LDL cholesterol. RECENT FINDINGS: Of six statin trials in populations with moderately increased LDL cholesterol only one, the Heart Protection Study, has shown that statin therapy will significantly reduce the major coronary heart disease events of non-fatal myocardial infarction or coronary heart disease death in diabetes. None of these trials has shown that statins have a particular predilection for reducing cardiovascular events in individuals with higher levels of body weight or other features of the metabolic syndrome. There are far fewer trial data with fibrates than with statins. However, the Veterans Affairs High Density Lipoprotein Intervention Trial has shown that a fibrate can significantly reduce major cardiovascular events, most particularly coronary heart disease death, in those with diabetes as well as those without diabetes who have insulin resistance. Indeed, all fibrate trials show that this therapy appears to selectively benefit the individual with obesity and features of the metabolic syndrome. SUMMARY: Based principally on evidence from the Veterans Affairs High Density Lipoprotein Intervention Trial and the cumulative experience with statins, trial data would thus far suggest that the patient with a modest increase in LDL cholesterol who has diabetes or features of the metabolic syndrome might be likely to achieve more substantial cardiovascular benefit from fibrate than from statin therapy.     

HMG-CoA reductase inhibitor augments the serum total cholesterol-lowering effect of human adipose tissue-derived multilineage progenitor cells in hyperlipidemic homozygous Watanabe rabbits

Familial hypercholesterolemia (FH) is an autosomal codominant disease characterized by high concentrations of proatherogenic lipoproteins secondary to deficiency in low-density lipoprotein (LDL) receptor. We reported recently the use of in situ stem cell therapy of human adipose tissue-derived multilineage progenitor cells (hADMPCs) in lowering serum total cholesterol in the homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits, an animal model of homozygous FH. Here we demonstrate that pravastatin, an HMG-CoA reductase inhibitor, augmented the cholesterol-lowering effect of transplanted hADMPCs and enhanced LDL clearance in homozygous WHHL rabbit. The results suggest the potential beneficial effects of in situ stem cell therapy in concert with appropriately selected pharmaceutical agents, in regenerative medicine.     

Statin therapy for prevention and treatment of acute and chronic cardiovascular disease: update on recent trials and metaanalyses

PURPOSE OF REVIEW: To summarize the evidence from recent clinical trials and metaanalyses on the efficacy of statin therapy to reduce death, myocardial infarction and stroke, and to review the effects of statins in patients with low LDL cholesterol, diabetes, end-stage renal disease, and acute coronary syndrome. RECENT FINDINGS: In large metaanalyses of randomized controlled trials relative risk reductions from statins compared with placebo for patients with manifest or with risk factors for coronary artery disease were 13% for overall mortality, 26% for fatal and nonfatal myocardial infarction, and 18% for fatal and nonfatal stroke. Evidence from large trials suggests that patients with type II diabetes compared with patients without diabetes have similar risk reductions from statins for cardiovascular events, but this benefit is not seen in patients with diabetes and end-stage renal disease. In patients with acute coronary syndrome, early treatment with high-dose atorvastatin reduces cardiovascular morbidity after the first 4 months following the event, but the impact on mortality endpoints remains less clear. Results from recent trials in patients with stable coronary artery disease or type II diabetes suggest that statins provide benefit at considerable low LDL cholesterol levels. Therefore, target values for LDL cholesterol of less than 1.8 mmol/l (<70 mg/dl) should be considered for all patients with coronary artery disease or equivalent coronary risk. SUMMARY: For patients at high risk of coronary artery disease there is growing evidence for the concept of 'the lower, the better' regarding LDL cholesterol levels. Ongoing trials are further investigating the safety of lower target values in patients at various risk of coronary artery disease.     

HELP LDL Apheresis Reduces Plasma Pentraxin 3 in Familial Hypercholesterolemia

Background

Pentraxin 3 (PTX3), a key component of the humoral arm of innate immunity, is secreted by vascular cells in response to injury, possibly aiming at tuning arterial activation associated with vascular damage. Severe hypercholesterolemia as in familial hypercholesterolemia (FH) promotes vascular inflammation and atherosclerosis; low-density lipoprotein (LDL) apheresis is currently the treatment of choice to reduce plasma lipids in FH. HELP LDL apheresis affects pro- and antiinflammatory biomarkers, however its effects on PTX3 levels are unknown. We assessed the impact of FH and of LDL removal by HELP apheresis on PTX3.

Methods

Plasma lipids, PTX3, and CRP were measured in 19 patients with FH undergoing chronic HELP LDL apheresis before and after treatment and in 20 control subjects. In the patients assessment of inflammation and oxidative stress markers included also plasma TNFα, fibrinogen and TBARS.

Results

At baseline, FH patients had higher (p = 0.0002) plasma PTX3 than matched control subjects. In FH PTX3 correlated positively (p≤0.05) with age, gender and CRP and negatively (p = 0.01) with HELP LDL apheresis vintage. The latter association was confirmed after correction for age, gender and CRP. HELP LDL apheresis acutely reduced (p≤0.04) plasma PTX3, CRP, fibrinogen, TBARS and lipids, but not TNFα. No association was observed between mean decrease in PTX3 and in LDL cholesterol. PTX3 paralleled lipids, oxidative stress and inflammation markers in time-course study.

Conclusion

FH is associated with increased plasma PTX3, which is acutely reduced by HELP LDL apheresis independently of LDL cholesterol, as reflected by the lack of association between change in PTX3 and in LDL levels. These results, together with the finding of a negative relationship between PTX3 and duration of treatment suggest that HELP LDL apheresis may influence both acutely and chronically cardiovascular outcomes in FH by modulating PTX3.     

LDL apheresis as an alternate method for plasma LPS purification in healthy volunteers and dyslipidemic and septic patients

Lipopolysaccharide (LPS) is a key player for innate immunity activation. It is therefore a prime target for sepsis treatment, as antibiotics are not sufficient to improve outcome during septic shock. An extracorporeal removal method by polymyxin (PMX) B direct hemoperfusion (PMX-DHP) is used in Japan, but recent trials failed to show a significant lowering of circulating LPS levels after PMX-DHP therapy. PMX-DHP has a direct effect on LPS molecules. However, LPS is not present in a free form in the circulation, as it is mainly carried by lipoproteins, including LDLs. Lipoproteins are critical for physiological LPS clearance, as LPSs are carried by LDLs to the liver for elimination. We hypothesized that LDL apheresis could be an alternate method for LPS removal. First, we demonstrated in vitro that LDL apheresis microbeads are almost as efficient as PMX beads to reduce LPS concentration in LPS-spiked human plasma, whereas it is not active in PBS. We found that PMX was also adsorbing lipoproteins, although less specifically. Then, we found that endogenous LPS of patients treated by LDL apheresis for familial hypercholesterolemia is also removed during their LDL apheresis sessions, with both electrostatic-based devices and filtration devices. Finally, LPS circulating in the plasma of septic shock and severe sepsis patients with gram-negative bacteremia was also removed in vitro by LDL adsorption. Overall, these results underline the importance of lipoproteins for LPS clearance, making them a prime target to study and treat endotoxemia-related conditions.     

National cholesterol education program keeps a priority on lifestyle modification to decrease cardiovascular disease risk.

The National Cholesterol Education Program's updated third Adult Treatment Panel report on clinical guidelines for cholesterol testing and management adds to the base of knowledge provided by two previous Adult Treatment Panel reports. Similar to the other reports, it has distinctive features and goals that are in accord with the most currently available clinical trial evidence. The major new feature of the third report is a focus on primary prevention of coronary heart disease in persons with multiple coronary heart disease risk factors. The guidelines provide the rationale for intensive cholesterol-lowering therapy in clinical management, and they provide detailed information to help inform clinical judgment for implementation of both medical nutrition management (therapeutic lifestyle changes) and drug therapy for treatment of high blood cholesterol.     

Dietary cholesterol and atherosclerosis

The perceived relationship between dietary cholesterol, plasma cholesterol and atherosclerosis is based on three lines of evidence: animal feeding studies, epidemiological surveys, and clinical trials. Over the past quarter century studies investigating the relationship between dietary cholesterol and atherosclerosis have raised questions regarding the contribution of dietary cholesterol to heart disease risk and the validity of dietary cholesterol restrictions based on these lines of evidence. Animal feeding studies have shown that for most species large doses of cholesterol are necessary to induce hypercholesterolemia and atherosclerosis, while for other species even small cholesterol intakes induce hypercholesterolemia. The species-to-species variability in the plasma cholesterol response to dietary cholesterol, and the distinctly different plasma lipoprotein profiles of most animal models make extrapolation of the data from animal feeding studies to human health extremely complicated and difficult to interpret. Epidemiological surveys often report positive relationships between cholesterol intakes and cardiovascular disease based on simple regression analyses; however, when multiple regression analyses account for the colinearity of dietary cholesterol and saturated fat calories, there is a null relationship between dietary cholesterol and coronary heart disease morbidity and mortality. An additional complication of epidemiological survey data is that dietary patterns high in animal products are often low in grains, fruits and vegetables which can contribute to increased risk of atherosclerosis. Clinical feeding studies show that a 100 mg/day change in dietary cholesterol will on average change the plasma total cholesterol level by 2.2-2.5 mg/dl, with a 1.9 mg/dl change in low density lipoprotein (LDL) cholesterol and a 0.4 mg/dl change in high density lipoprotein (HDL) cholesterol. Data indicate that dietary cholesterol has little effect on the plasma LDL:HDL ratio. Analysis of the available epidemiological and clinical data indicates that for the general population, dietary cholesterol makes no significant contribution to atherosclerosis and risk of cardiovascular disease.     

Evidence for a cholesterol-lowering gene in a French-Canadian kindred with familial hypercholesterolemia

We describe a four-generation kindred with familial hypercholesterolemia (FH) in which two of the eight heterozygotes for a 5-kb deletion (exons 2 and 3) in the low density lipoprotein (LDL) receptor gene were found to have normal LDL-cholesterol levels. In our search for a gene responsible for the cholesterol-lowering effect in this family, we have studied variation in the genes encoding the LDL receptor, apolipoprotein (apo) B, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, apoAI-CIII-AIV, and lipoprotein lipase. The analysis showed that it was unlikely that variation in any of these genes was responsible for the cholesterol-lowering effect. Expression of the LDL receptor, as assessed in vitro with measurements of activity and mRNA levels, was similar in normo and hyperlipidemic subjects carrying the deletion. Analysis of the apo E isoforms revealed that most of the e2 allele carriers in this family, including the two normolipidemic 5-kb deletion carriers, were found to have LDL-cholesterol levels substantially lower than subjects with the other apo E isoforms. Thus, this kindred provides evidence for the existence of a gene or genes, including the apo e2 allele, with profound effects on LDL-cholesterol levels.C. S. and M. G. contributed equally to this work.     

Hepatocyte-directed gene transfer in vivo leads to transient improvement of hypercholesterolemia in low density lipoprotein receptor-deficient rabbits.

Familial hypercholesterolemia is an inherited disease in humans, caused by a deficiency of low density lipoprotein (LDL) receptors, that we have used as a model for developing liver-directed gene therapies. Our strategy is to reconstitute hepatic LDL receptor expression in vivo by administering a DNA-protein complex that is capable of targeting the delivery of functional LDL receptor genes to hepatocytes. Infusion of this DNA-protein complex into the peripheral circulation of a rabbit animal model for familial hypercholesterolemia resulted in hepatocyte-specific gene transfer and a temporary amelioration of hypercholesterolemia. This noninvasive approach to gene therapy should have applications in the treatment of a wide spectrum of human diseases.     

PCSK9 function and physiology

PCSK9 has exploded onto center stage plasma cholesterol metabolism, raising hopes for a new strategy to treat hypercholesterolemia. PCSK9 in a plasma protein that triggers increased degradation of the LDL receptor. Gain-of-function mutations in PCSK9 reduce LDL receptor levels in the liver, resulting in high levels of LDL cholesterol in the plasma and increased susceptibility to coronary heart disease. Loss-of-function mutations lead to higher levels of the LDL receptor, lower LDL cholesterol levels and protection from coronary heart disease. Two papers in this issue of the Journal of Lipid Research exemplify the rapid pace of progress in understanding PCSK9 molecular interactions and physiology. Dr. Shilpa Pandit and coworkers from Merck Research Laboratories describe the functional basis for the hypercholesterolemia associated with gain-of-function missense mutations in PCSK9. Dr. Jay Horton's group at UT Southwestern describe the kinetics and metabolism of PCSK9 and the impact of PCSK9 on LDL receptors in the liver and adrenal gland.     

Influence of LDL apheresis on LDL subtypes in patients with coronary heart disease and severe hyperlipoproteinemia

Epidemiologic studies and in vitro experiments indicate that low density lipoprotein (LDL) subtypes differ concerning their atherogenic potential. Small, dense LDL are more atherogenic than large, buoyant LDL. LDL apheresis is a potent therapeutic modality to lower elevated LDL-cholesterol. It is unknown whether such therapy induces a shift in the LDL subtype distribution. In this study we evaluated the influence of LDL apheresis on the LDL subtype distribution in patients with CHD and familial hypercholesterolemia (FH, n = 22), combined hyperlipidemia (CHLP, n = 6), or Lp[a]-hyperlipoproteinemia (Lp[a]-HLP, n = 4) regularly treated by LDL apheresis (immunoadsorption (n = 14), HELP apheresis (n = 8), dextran sulfate adsorption (n = 7), cascade filtration (n = 3)). On the basis of 6 LDL subfractions (d 1.020;-1.057 g/mL) isolated by density gradient ultracentrifugation the LDL-density profile was determined in each patient before and after apheresis. There was a relative increase of LDL-subfractions 1, 2, and 3 (P < 0.01, P < 0. 05, and P < 0.01, respectively) and a concomitant decrease of LDL subfractions 5 and 6 (P < 0.05) after apheresis. Subgroup analysis indicates that the degree of the small, dense LDL reduction was much more prominent in patients with CHLP compared to patients with FH or Lp[a]-HLP, whereas the type of apheresis technique had no effect. The extent of small, dense LDL reduction correlated with the preapheresis concentrations of small, dense LDL and triglycerides but not with the extent of triglyceride reduction.We conclude that LDL apheresis not only decreases LDL mass, but also improves LDL-density profile, particularly in patients with CHLP.     

Impact of LDL apheresis on atheroprotective reverse cholesterol transport pathway in familial hypercholesterolemia

In familial hypercholesterolemia (FH), low HDL cholesterol (HDL-C) levels are associated with functional alterations of HDL particles that reduce their capacity to mediate the reverse cholesterol transport (RCT) pathway. The objective of this study was to evaluate the consequences of LDL apheresis on the efficacy of the RCT pathway in FH patients. LDL apheresis markedly reduced abnormal accelerated cholesteryl ester transfer protein (CETP)-mediated cholesteryl ester (CE) transfer from HDL to LDL, thus reducing their CE content. Equally, we observed a major decrease (-53%; P < 0.0001) in pre-β1-HDL levels. The capacity of whole plasma to mediate free cholesterol efflux from human macrophages was reduced (-15%; P < 0.02) following LDL apheresis. Such reduction resulted from a marked decrease in the ABCA1-dependent efflux (-71%; P < 0.0001) in the scavenger receptor class B type I-dependent efflux (-21%; P < 0.0001) and in the ABCG1-dependent pathway (-15%; P < 0.04). However, HDL particles isolated from FH patients before and after LDL apheresis displayed a similar capacity to mediate cellular free cholesterol efflux or to deliver CE to hepatic cells. We demonstrate that rapid removal of circulating lipoprotein particles by LDL apheresis transitorily reduces RCT. However, LDL apheresis is without impact on the intrinsic ability of HDL particles to promote either cellular free cholesterol efflux from macrophages or to deliver CE to hepatic cells.     

Regulation of cholesterol metabolism by dietary plant sterols

Renewal has occurred in the use of plant sterols for the treatment of hypercholesterolemias. A novel development was to convert plant sterols to corresponding stanols and esterify them to fat soluble form. In contrast to the crystalline plant sterols or stanols, plant stanol esters can be easily consumed during normal food intake in soluble form in different fat-containing food constituents when they have a potent cholesterol-lowering effect, shown in normo- and hypercholesterolemic men and women without or with coronary heart disease, children and diabetes. Cholesterol lowering is approximately 10% for total and 15% for LDL cholesterol, with the respective values for stanol ester margarine (2-3 g/day stanols) being 15% and 20%. Stanol esters reduce cholesterol absorption efficiency by up to 65%, increase cholesterol elimination in feces as cholesterol itself, usually not as bile acids, and stimulate cholesterol synthesis. Serum beta-carotene level is lowered, but no fat malabsorption or lowering of serum fat soluble vitamins have been observed. In contrast to plant sterols, stanols and their esters are minimally absorbed and they reduce serum plant sterol concentrations, also preventing statin-induced increase of plant sterols. Stanol ester margarine has been included in dietary treatment of hypercholesterolemia followed by the addition of drug treatment in resistant cases.     

Effect of statins in stroke prevention

PURPOSE OF REVIEW: This paper reviews recent studies into the outcomes of clinical trials in which statin therapy has been used in the prevention and treatment of strokes. RECENT DEVELOPMENTS: Epidemiologic studies found no or little association between blood cholesterol levels and stroke. Randomized trials have confirmed that LDL lowering decreased the risk of stroke, in diabetic or hypertensive patients with 'normal' LDL cholesterol at baseline, and in patients with coronary artery disease, with respectively 48, 27 and 25% reduction in stroke incidence. A meta-analysis of trials showed that the greater the LDL cholesterol reduction, the greater the intima-media thickness and stroke risk reductions. Even if statins also have 'pleiotropic' effects, their main action seems to be through LDL reduction. The Heart Protection Study only included strokes that occurred 4.6 years before--a time when the stroke event rate is low and the cardiac event rate is high, and so may not have had the power to find a true effect of LDL cholesterol lowering in preventing recurrent stroke. The Stroke Prevention by Aggressive Reduction in Cholesterol Levels (SPARCL) trial may give a definite answer because SPARCL investigators included 4732 patients with brain infarction or transient ischemic attacks and no history of myocardial infarction within 6 months of their stroke event, at a time when the expected stroke rate is very high and the myocardial infarction rate is very low. The results should be announced by mid-2006. SUMMARY: The positive effect of statins on stroke observed in trials of patients with coronary heart disease depended mainly on between-group LDL reduction, but other mechanisms could be involved. Though effective in prevention of major coronary events after a first stroke, statins have not yet been proven effective in prevention of recurrent stroke.     

A cholesterol-lowering gene maps to chromosome 13q

A cholesterol-lowering gene has been postulated from familial hypercholesterolemia (FH) families having heterozygous persons with normal LDL levels and homozygous individuals with LDL levels similar to those in persons with heterozygous FH. We studied such a family with FH that also had members without FH and with lower-than-normal LDL levels. We performed linkage analyses and identified a locus at 13q, defined by markers D13S156 and D13S158. FASTLINK and GENEHUNTER yielded LOD scores >5 and >4, respectively, whereas an affected-sib-pair analysis gave a peak multipoint LOD score of 4.8, corresponding to a P value of 1.26x10-6. A multipoint quantitative-trait-locus (QTL) linkage analysis with maximum-likelihood binomial QTL verified this locus as a QTL for LDL levels. To test the relevance of this QTL in an independent normal population, we studied MZ and DZ twin subjects. An MZ-DZ comparison confirmed genetic variance with regard to lipid concentrations. We then performed an identity-by-descent linkage analysis on the DZ twins, with markers at the 13q locus. We found strong evidence for linkage at this locus with LDL (P<.0002), HDL (P<.004), total cholesterol (P<.0002), and body-mass index (P<.0001). These data provide support for the existence of a new gene influencing lipid concentrations in humans.     

Molecular biology of PCSK9: its role in LDL metabolism

Proprotein convertase subtilisin-like kexin type 9 (PCSK9) is a newly discovered serine protease that destroys low density lipoprotein (LDL) receptors in liver and thereby controls the level of LDL in plasma. Mutations that increase PCSK9 activity cause hypercholesterolemia and coronary heart disease (CHD); mutations that inactivate PCSK9 have the opposite effect, lowering LDL levels and reducing CHD. Although the mechanism of PCSK9 action is not yet clear, the protease provides a new therapeutic target to lower plasma levels of LDL and prevent CHD.     

Proprotein convertase subtilisin kexin 9: the third locus implicated in autosomal dominant hypercholesterolemia

PURPOSE OF REVIEW: Autosomal dominant hypercholesterolemia is a genetic disease in which patients have elevated LDL cholesterol levels and premature atherosclerosis. Mutations in the LDL receptor and its ligand apolipoprotein B are causative for autosomal dominant hypercholesterolemia, and the study of this pathway has been crucial to understanding LDL metabolism and receptor-mediated endocytosis in general. Recently, families were identified with a clinical diagnosis of autosomal dominant hypercholesterolemia, but without linkage to the LDL receptor or apolipoprotein B genes. Identification and study of the causative genes in these families should provide additional insights into LDL metabolism. RECENT FINDINGS: Recent microarray studies and database searches identified a novel member of the proprotein convertase family called proprotein convertase subtilisin kexin 9 (PCSK9). A role for PCSK9 in cholesterol metabolism was proposed from the expression studies and confirmed by the discovery that PCSK9 missense mutations were associated with a form of autosomal dominant hypercholesterolemia, Hchola3. The cellular role for PCSK9 and the mechanism behind its mutations are under study, and a role for PCSK9 in regulating LDL receptor protein levels has been demonstrated. SUMMARY: PCSK9 is the third locus implicated in autosomal dominant hypercholesterolemia (Hchola3), and it appears to play an important role in cellular cholesterol metabolism. Understanding the function of PCSK9 will be important for broadening our knowledge of LDL metabolism and may aid in the development of novel hypocholesterolemic agents.