lipoprotein-X Research Articles

SAT-086 A Rare Case of Cholestatic Liver Disease Causing Markedly Elevated LDL Successfully Managed with Plasmapheresis and Ursodeoxycholic Acid

Background Hypercholesterolemia (HC) in cholestatic liver disease commonly involves a high lipoprotein-X (LpX) and low LDL receptors. No evidence has been found to suggest the association of LpX with an increased risk of cardiovascular disease (CVD). Hence, lipid lowering therapy is unnecessary as HC improves with treatment of cholestasis, but plasmapheresis should be considered in markedly elevated LDL values given the uncertainty of short term complications. Clinical Case A 47-year-old man with HTN, DMT2, nephrotic syndrome secondary to DM glomerulosclerosis and CKD stage 3 was admitted for an NSTEMI and acute heart failure due to non-ischemic cardiomyopathy. On exam he had jaundice and hepatomegaly without xanthelasma or tendon xanthomas. Laboratory evaluation revealed elevated HDL 200 [35-75 mg/dl], LDL 2,182 [0-130 mg/dl] and triglyceride 326 [30-150 mg/dl] although his lipid panel four months ago was normal. He had no family history of HC or premature CAD. Interestingly, two months prior the patient was seen in GI clinic due to jaundice, pruritus, acholia and coluria. Work-up showed cholestasis with total bilirubin 5.2 [0.1-1.2 mg/dl], AST 148 [0-40 U/L], ALT 112 [5-25 U/L], alkaline phosphatase 1,874 [20-120 U/L] and GGT 2,307 [3-60 U/L]. Further evaluation was unrevealing with negative viral hepatitis serologies, antinuclear antibodies, anti-smooth muscle antibody, anti-mitochondrial antibody, ceruloplasmin, α-1antitrypsin. He underwent liver biopsy which demonstrated cholestatic hepatitis with advanced biliary fibrosis, lymphocytic cholangitis and perivenular infiltrate thought secondary to an atypical autoimmune cholangiopathy. Due to concern for hyperviscosity and potential CVD complications, two sessions of plasma exchange were performed with a rapid lowering of LDL to 661 mg/dL. He was given a dose of evolocumab and discharged on ursodeoxycholic acid with improvement in liver function and normalization of lipid panel within three weeks. His HC was presumed mainly from atypical autoimmune cholangiopathy. LpX was unlikely since his Apolipoprotein B was elevated at 239 [RR 52-109 mg/dl]. Once his liver function normalized, he was started on high intensity statin and ezetimibe due to an elevated CVD risk with a low ApoA 30 mg/dL [RR 94-176]. Conclusion This is a rare case of cholestatic liver disease causing markedly elevated LDL, successfully managed with plasma exchange and ursodeoxycholic acid with subsequent resolution of LDL abnormality.

Controversy over the atherogenicity of lipoprotein-X.

Lipoprotein-X (Lp-X) is an abnormal lipoprotein containing abundant free cholesterol and phospholipids, as well as some apolipoprotein E (apoE). Serum Lp-X increases in patients with cholestasis and lecithin-cholesterol acyltransferase deficiency, as well as in those receiving intravenous lipid emulsion. Lp-X is often associated with skin xanthomas in cholestatic patients. However, earlier studies showed that Lp-X is not taken up by murine macrophages, but exerts antiatherogenic actions. In this review, we discuss the heterogeneity of Lp-X and its potential atherogenicity. Mass spectrometry revealed that Lp-X of cholestatic patients is similar in lipid composition to low-density lipoprotein (LDL) and high-density lipoprotein, but not to bile acids, suggesting that Lp-X is synthesized in the liver. Palmar xanthomas appear in patients with cholestasis, but regress over months after improvement of hypercholesterolemia. Lp-X isolated from cholestatic patients is rich in apoE, and causes more lipid accumulation than oxidized LDL and acetyl LDL in human monocyte-derived macrophages. Lp-X is heterogeneous in apoE content. Lp-X is taken up in cholestatic patients by apoE-recognizing lipoprotein receptors. Further research is warranted to fully understand the atherogenicity of Lp-X and the clinical significance of elevated Lp-X concentrations, particularly in cholestatic patients.

Abstract 556: Lipoprotein Remodeling and Cholesterol Exchange Monitored Using Fluorescent Lipids and Proteins

We developed a sensitive and robust in vitro method to monitor lipoprotein cholesterol and protein exchange and lipoprotein remodeling, using non-exchangeable fluorescent phosphatidylethanolamine (PE) as a lipoprotein marker. We applied this method to monitor the exchange of unesterified cholesterol (FC) and apoA-I among isolated human lipoproteins and synthetic lipoprotein-X (LpX). Fluorescent FC, but not PE, rapidly equilibrated between VLDL and HDL, and transferred almost entirely from VLDL or HDL to LDL. Fluorescent apoA-I bound specifically to HDL and remodeled fluorescent PE and FC-labeled LpX into a new lipoprotein particle that contained both fluorescent lipids and apoA-I. LpX-derived fluorescent PE incorporated into plasma HDL only. The incorporation of LpX-derived fluorescent FC into plasma lipoproteins was similar to fluorescent FC alone, consistent with remodeling of LpX to HDL with concomitant exchange of FC between lipoproteins. LPL remodeled fluorescent PE and FC-tagged VLDL into a new particle containing both fluorescent lipids and apoA-I. We also developed a model system to study lipid transfer in vitro and in vivo by depositing lipids on calcium silicate hydrate crystals to form dense lipid coated donor particles that are readily separated from acceptor membranes and can be used as a surrogate for cell-dependent cholesterol efflux. These methodologies can readily be applied to study the other members of the vast lipoprotein proteome and the wide variety of remodeling events involved in lipoprotein-mediated lipid homeostasis in health and disease.

Lipoprotein X in autoimmune liver disease causing interference in routine and specialist biochemical investigations

AbstractPrimary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are chronic, immune-mediated diseases which may be associated with the presence of lipoprotein X (LpX). This is an abnormal lipoprotein resulting in marked elevation of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) concentration. LpX is rich in free cholesterol (FC) and phospholipids (PL) and low in esterified cholesterol (CE). We describe two cases with florid lipid stigmata and presence of LpX. A patient with PBC presented with itching and palmar xanthomata. TC = 55.5 mmol/L, direct LDL-C = 14.9 mmol/L, high-density lipoprotein cholesterol (HDL-C) = 0.5 mmol and triglycerides (TG) = 11.3 mmol/L. Lipoprotein electrophoresis (LPE) showed the presence of LpX. An apolipoprotein E (Apo E) phenotype and genotype reported E2E3 and E3E3 isoforms, respectively. A patient with PSC presented with itchy eruptive xanthomata. TC = 22.8 mmol/L, calculated LDL-C = 21.7 mmol/L, HDL-C = 0.2 mmol/L and TG = 1.6 mmol/L...

Lipoprotein-X in cholestatic patients causes xanthomas and promotes foam cell formation in human macrophages

Lipoprotein-X (Lp-X) is an abnormal phospholipid-rich lipoprotein found in patients with cholestatic liver disease. Some patients exhibit skin xanthomas and severe hyperlipidemia. We investigated whether Lp-X induces foam cell formation in human-derived macrophages. To compare the atherogenic properties of Lp-X and modified LDL, we isolated Lp-X from 2 patients who had drug-induced cholestasis and xanthoma striata in the interphalangeal folds. We prepared oxidized LDL and acetylated LDL from healthy volunteers for the positive control experiments. When human monocyte-derived macrophages were incubated with these lipoproteins, the isolated Lp-X induced more prominent lipid accumulation than oxidized LDL or acetylated LDL. One case underwent liver biopsy, with the bile ducts showing marked damage, fulfilling the criteria for vanishing bile duct syndrome. The other case was clinically diagnosed as drug-induced hypersensitivity syndrome. In both cases, Lp-X levels decreased markedly and the xanthomas disappeared completely after the improvement of cholestasis. This study indicates that Lp-X induces foam cell formation in human-derived macrophages. Our findings strongly suggest that persistently elevated Lp-X may cause xanthomas.

Abstract 230: Lipoprotein X Causes Renal Disease in LCAT Deficiency

Familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is characterized by low HDL, accumulation of an abnormal cholesterol-rich multilamellar particle called lipoprotein-X (LpX) in plasma, and renal disease. The aim of our study was to determine if LpX is nephrotoxic and to gain insight into the pathogenesis of FLD renal disease. We administered a synthetic LpX, nearly identical to endogenous LpX in its physical, and chemical properties, to wild-type and Lcat -/- mice. Our in vitro and in vivo studies demonstrated an apoA-I and LCAT-dependent pathway for LpX conversion to HDL-like particles, which likely mediates normal plasma clearance of LpX. Plasma clearance of exogenous LpX was markedly delayed in Lcat -/- mice, which have low HDL but only minimal amounts of endogenous LpX and do not spontaneously develop renal disease. Chronically administered exogenous LpX deposited in all renal glomerular cellular and matrical compartments of Lcat -/- mice, and induced proteinuria and nephrotoxic gene changes, as well as all of the hallmarks of FLD renal disease as assessed by histological, TEM, and SEM analyses. Extensive in vivo EM studies revealed LpX uptake by macropinocytosis into mouse glomerular endothelial cells, podocytes, and mesangial cells and delivery to lysosomes, where it was degraded. Endocytosed LpX appeared to be degraded by both human podocyte and mesangial cell lysosomal PLA 2 and induced podocyte secretion of pro-inflammatory IL-6 in vitro and renal Cxl10 expression in Lcat -/- mice. In conclusion, LpX is a nephrotoxic particle that in the absence of LCAT induces all of the histological and functional hallmarks of FLD and hence may serve as a biomarker for monitoring recombinant LCAT therapy. In addition, our studies suggest that LpX-induced loss of endothelial barrier function and release of cytokines by renal glomerular cells likely plays a role in the initiation and progression of FLD nephrosis.

Lipid profiling of lipoprotein X: Implications for dyslipidemia in cholestasis

Lipoprotein X (Lp-X) is an abnormal lipoprotein that may typically be formed in intra- and extrahepatic cholestasis and potentially interfere with lipid analysis in the routine lab.To gain insight into lipid class and species composition, Lp-X, LDL and HDL from cholestatic and control serum samples were subjected to mass spectrometric analysis including phospholipids (PL), sphingolipids, free cholesterol (FC), cholesteryl esters (CE) and bile acids.Our analysis of Lp-X revealed a content of 46% FC, 49% PL with 34% phosphatidylcholine (PC) as main PL component. The lipid species pattern of Lp-X showed remarkable high fractions of mono-unsaturated species including PC 32:1 and PC 34:1 and phosphatidylethanolamine (PE) 32:1 and 34:1. LDL and HDL lipid composition in the same specimens strongly reflected the lipid composition of Lp-X with increased PC 32:1, PC 34:1, PE 32:1, PE 34:1 and FC accompanied by decreased CE compared to controls.Comparison of Lp-X and biliary lipid composition clearly indicates that Lp-X does not originate from a sole release of bile lipids. Moreover, these data present evidence for increased hepatic fatty acid and PL synthesis which may represent a reaction to high hepatic FC level observed during cholestasis.

Lipoprotein X Causes Renal Disease in LCAT Deficiency.

Human familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is characterized by low HDL, accumulation of an abnormal cholesterol-rich multilamellar particle called lipoprotein-X (LpX) in plasma, and renal disease. The aim of our study was to determine if LpX is nephrotoxic and to gain insight into the pathogenesis of FLD renal disease. We administered a synthetic LpX, nearly identical to endogenous LpX in its physical, chemical and biologic characteristics, to wild-type and Lcat-/- mice. Our in vitro and in vivo studies demonstrated an apoA-I and LCAT-dependent pathway for LpX conversion to HDL-like particles, which likely mediates normal plasma clearance of LpX. Plasma clearance of exogenous LpX was markedly delayed in Lcat-/- mice, which have low HDL, but only minimal amounts of endogenous LpX and do not spontaneously develop renal disease. Chronically administered exogenous LpX deposited in all renal glomerular cellular and matrical compartments of Lcat-/- mice, and induced proteinuria and nephrotoxic gene changes, as well as all of the hallmarks of FLD renal disease as assessed by histological, TEM, and SEM analyses. Extensive in vivo EM studies revealed LpX uptake by macropinocytosis into mouse glomerular endothelial cells, podocytes, and mesangial cells and delivery to lysosomes where it was degraded. Endocytosed LpX appeared to be degraded by both human podocyte and mesangial cell lysosomal PLA2 and induced podocyte secretion of pro-inflammatory IL-6 in vitro and renal Cxl10 expression in Lcat-/- mice. In conclusion, LpX is a nephrotoxic particle that in the absence of Lcat induces all of the histological and functional hallmarks of FLD and hence may serve as a biomarker for monitoring recombinant LCAT therapy. In addition, our studies suggest that LpX-induced loss of endothelial barrier function and release of cytokines by renal glomerular cells likely plays a role in the initiation and progression of FLD nephrosis.

Lipoprotein-X in a Patient with Lymphoplasmacytic Sclerosing Cholangitis: An Unusual Cause of Secondary Hypercholesterolemia

This paper presents an interesting case study of lymphoplasmacytic sclerosing cholangitis and a superb review of lipoprotein-X (Lp-X) with very high levels of total cholesterol and low-density lipoprotein (LDL) cholesterol by gel electrophoresis, and mild elevations in triglycerides, having resulted in the use of a statin (1). Fortunately, the patient had a low-normal apolipoprotein B (apoB), a more sensitive measure of atherogenic lipoprotein particles, questioning whether such statin treatment was necessary. As reviewed by the authors, this elevated measure of total cholesterol in a patient with marked cholestasis is measuring the cholesterol in both LDL and Lp-X. Lp-X is found clinically in adults with obstructive liver disease, whether intra- or extrahepatic. Phospholipids, which have no apoB, are excreted in the bile, and when there is cholestasis, they increase in the serum. Lp-X has more apolipoproteins A1, C, and E, more albumin in its core, and in the large case study cohorts cited in this article, have not been found to be atherogenic. This was also found in one of the original reports of 18 women with increased total cholesterol in primary biliary cirrhosis and illustrates the increasing phospholipid content and decreasing cholesterol ester/free cholesterol found in Lp-X (2). Because Lp-X has less apo B, it is less readily removed by the hepatic LDL receptor in the liver, with more removal through the reticuloendothelial system of the liver and spleen. In this case, a direct measure of LDL cholesterol was also very low, helping in

Cholesterol metabolism in cholestatic liver disease and liver transplantation: From molecular mechanisms to clinical implications

The aim of this review is to enlighten the critical roles that the liver plays in cholesterol metabolism. Liver transplantation can serve as gene therapy or a source of gene transmission in certain conditions that affect cholesterol metabolism, such as low-density-lipoprotein (LDL) receptor gene mutations that are associated with familial hypercholesterolemia. On the other hand, cholestatic liver disease often alters cholesterol metabolism. Cholestasis can lead to formation of lipoprotein X (Lp-X), which is frequently mistaken for LDL on routine clinical tests. In contrast to LDL, Lp-X is non-atherogenic, and failure to differentiate between the two can interfere with cardiovascular risk assessment, potentially leading to prescription of futile lipid-lowering therapy. Statins do not effectively lower Lp-X levels, and cholestasis may lead to accumulation of toxic levels of statins. Moreover, severe cholestasis results in poor micellar formation, which reduces cholesterol absorption, potentially impairing the cholesterol-lowering effect of ezetimibe. Apolipoprotein B-100 measurement can help distinguish between atherogenic and non-atherogenic hypercholesterolemia. Furthermore, routine serum cholesterol measurements alone cannot reflect cholesterol absorption and synthesis. Measurements of serum non-cholesterol sterol biomarkers - such as cholesterol precursor sterols, plant sterols, and cholestanol - may help with the comprehensive assessment of cholesterol metabolism. An adequate cholesterol supply is essential for liver-regenerative capacity. Low preoperative and perioperative serum cholesterol levels seem to predict mortality in liver cirrhosis and after liver transplantation. Thus, accurate lipid profile evaluation is highly important in liver disease and after liver transplantation.

Management of lipoprotein X and its complications in a patient with primary sclerosing cholangitis.

Lipoprotein X (LpX) is an abnormal lipoprotein found in conditions such as lecithin:cholesterol acyltransferase deficiency and cholestatic states (e.g., primary biliary cirrhosis and primary sclerosing cholangitis). Management of severe hypercholesterolemia due to LpX with drugs and physical removal methods is not well established in the literature. A case is discussed of a 51-year-old woman who presented with multiple electrolyte abnormalities, xanthomas and neuropathy found to be secondary to LpX in the setting of primary sclerosing cholangitis. This case highlights that oral medications, including statins, may be insufficient to normalize lipid levels or improve clinical symptoms of LpX and presents therapeutic plasma exchange as a safe and effective therapeutic option to treat the morbid sequela of LpX hyperlipidemia.

Differences in reaction specificity toward lipoprotein X and abnormal LDL among 6 homogeneous assays for LDL-cholesterol

BackgroundWe investigated the reaction specificity toward cholesterol in lipoprotein X (Lp-X) and abnormal LDL among 6 homogeneous assays for low-density lipoprotein cholesterol (LDL-C) based on different measurement principles. MethodsThe homogeneous LDL-C assays used were based on the liquid selective detergent, selective solubilization, elimination, enzyme-selective protection, calixarene complex, and phosphate complex inhibition methods. The fraction with a density of 1.006–1.063kg/l was isolated from cholestatic sera, and the reactivity of cholesterol in the lipoprotein fractions by gel filtration for each homogeneous LDL-C assay was determined. ResultsThe liquid selective detergent and elimination methods showed increased cholesterol reactivity in the Lp-X fraction in a concentration-dependent manner, while the selective solubilization and phosphate complex inhibition methods were less reactive toward Lp-X cholesterol. Meanwhile, the homogeneous LDL-C assays showed decreased reactivity against cholesterol in abnormal LDL, with increased ratios of phospholipids and triglycerides against cholesterol. ConclusionThe homogeneous LDL-C assays showed differential reactivity toward Lp-X and abnormal LDL. Our findings enable accurate interpretation of the LDL-C values in these homogeneous assays, and suggest that these methods should be improved to distinguish between normal LDL and abnormal LDL or Lp-X.

The X of dyslipemias

Patients with cholestatic diseases can present secondary hypercholesterolemia, as a result of the accumulation of lipoprotein X (Lp-X); an abnormal LDL form, considered as the biochemical parameter more sensitive and specific for the diagnosis of cholestasis intra or extrahepatic cholestasis. The aim of this clinical communication is to illustrate this association. A 54-year-old male with severe cholestatic liver disease which in turn presents a progressive total cholesterol rise and LDL with presence of lipoprotein X. Total and LDL cholesterol were down to normal, also coinciding with the improvement of cholestatic liver disease conferring cardiovascular protection pattern.

Lipoprotein X: clinical implications

In this issue of the journal, Stepien et al. describe a case of serum lipoprotein X (Lp-X) in a patient with cholestasis and severe hyperlipidaemia. This abnormal lipoprotein is rich in phospholipid and unesterified cholesterol. The main protein component is albumin within the core and apolipoprotein C upon the surface. Unlike low-density lipoprotein (LDL), Lp-X does not contain apolipoprotein B nor is it removed by the LDL receptor, but Lp-X is cleared by the reticuloendothelial system and the kidneys. Lp-X is about 50 nm in diameter and its major component bile acid is lithocholic. Early studies reported the presence of Lp-X in the serum of patients with cholestasis. The failure of Lp-X to exert feedback inhibition on cholesterol synthesis may contribute to the mechanism of hypercholesterolaemia in obstructive jaundice. However, the presence of serum Lp-X does not facilitate the distinction between intrahepatic and extrahepatic cholestasis. Bile lipoprotein is a precursor of Lp-X and in cholestasis this refluxes into the plasma pool and binds to albumin to form Lp-X. Serum Lp-X usually disappears soon after the cholestasis is relieved. The ratio of plasma bile salts to albumin is important for the integrity of Lp-X and it is catabolized by the action of phospholipase which helps convert lecithin into lysolecithin. In graft versus host disease involving the liver and with cholestasis plasma Lp-X can result in severe hypercholesterolaemia, xanthelasma and cholesteroloma. Lp-X can also be found in cholestasis of pregnancy and primary biliary cirrhosis (PBC). The case presented by Stepien et al. confirms these earlier observations of raised serum Lp-X in cholestasis. Increased serum cholesterol concentrations occur in PBC and this is largely due to the presence of Lp-X, although it is debatable whether this confers increased cardiovascular risk. Indeed, Lp-X may not be atherogenic and data suggest it may have antioxidant LDL activity. Additionally, Lp-X is not significantly taken up by macrophages but is taken up by hepatocytes. Sometimes severe and prolonged cholestasis can result in very high serum Lp-X concentrations resulting in severe hypercholesterolaemia and tendon xanthomata. Complete regression of these xanthomata has been described by treatment with apheresis, which the authors stated should be considered possible first-choice treatment for patients with massive Lp-X accumulation due to cholestasis. Statin therapy may be ineffective in lowering Lp-X. Lecithin-cholesterol acyltransferase (LCAT) is an enzyme responsible for cholesterol esterification in plasma. Lp-X is found in LCAT deficiency which is characterized by low concentrations of high-density lipoprotein (HDL) as well as anaemia, corneal opacities, proteinuria and chronic kidney disease. The Lp-X found in LCAT deficiency may contribute to the renal disease observed in this condition by stimulating monocyte renal infiltration. Proteoglycans have an important role in regulating the uptake of Lp-X into kidney mesangial cells and this mechanism is independent of the scavenger receptor. Guerin et al. reported that in LCAT deficiency the presence of Lp-X is correlated with a progressive change in renal function. In addition to cholestasis and LCAT deficiency, Lp-X may also be found in the plasma after intravenous infusion of Intralipid emulsion such as occurs with total parenteral nutrition. Intralipid administration can elicit an increase in serum total cholesterol (mainly unesterified), phospholipid and LDL. The Lp-X associated with Intralipid infusion seems to occur when phospholipid clearance is exceeded, resulting in phospholipid accumulation with unesterified cholesterol. Pseudohyponatraemia has also been described in some patients with severe hypercholesterolaemia secondary to raised Lp-X. Thus the presence of Lp-X should be considered in pseudohyponatraemia associated with cholestasis. Sivakumar et al. described not only pseudohyponatraemia, but also pseudohypokalaemia and pseudohypochloridaemia in the presence of high concentrations of Lp-X. Various researchers have also found assay bias for serum LDL-cholesterol in the presence of Lp-X. This is an important practical point when it comes to interpreting LDL cholesterol results in severely cholestatic serum samples. Lp-X possesses strong aggregatory properties and can bind to alkaline phosphatase (ALP) producing a Lp-X-ALP complex. This complex may be found in cholestasis; typically that evoked by hepatic malignancy. The Lp-X-ALP complex is also associated with the presence of high-molecular mass ALP and the liver isoenzyme of ALP. Brocklehurst et al. described a stationary band of ALP using starch gel electrophoresis of serum samples from patients with biliary obstruction which was thought to be due to ALP binding to Lp-X. The strong aggregating ability of Lp-X may be important as it can bind and remove free cholesterol from the circulation. There are various assays available for measuring serum Lp-X. Agarose gel electrophoresis utilizes the cathodal

Anomalous lipoprotein-X in type 2 diabetes mellitus

Type 2 diabetes mellitus (DM2) is the most common form of diabetes characterized by the disturbances of carbohydrate, protein, and lipid metabolism including dyslipidemia and elevation of the low-density lipoprotein (LDLP) levels. Lipoprotein-X (LP-X) represents an anomalous subclass of LDLP a distinctive feature of which is the high content of phospholipids and non-esterified cholesterol coupled with the low level of cholesterol ethers, triglycerides, and proteins. LP-X was detected in the blood of the patients with various diseases of the liver and biliary ducts associated with cholestasis. The results of our previous investigations suggest the presence of LP-X in the blood of the patients with familial Mediterranean fever and ischemic stroke complicated by concomitant diabetes mellitus. The objective of the present work was to elucidate whether LP-X actually occurs in the blood of the patients presenting with type 2 diabetes mellitus. We used the method of polyanionic precipitation of LDLP preliminarily separated by agar gel electrophoresis. The study has demonstrated for the first time the presence of LP-X in the blood of the patients with type 2 diabetes mellitus. Its possible pathogenetic role and mechanisms of LP-X generation in DM2 are discussed.

Multiple lipoprotein and electrolyte laboratory artifacts caused by lipoprotein X in obstructive biliary cholestasis secondary to pancreatic cancer

Lipoprotein X (Lp-X) is an abnormal lipoprotein which may form in patients with intra- and extra-hepatic cholestasis. The presence of very high levels of Lp-X has been shown to be a rare cause of pseudohyponatremia. We present a patient with severe obstructive cholestasis secondary to pancreatic cancer leading to very high Lp-X concentrations resulting in pseudohyponatremia, pseudohypokalemia, pseudohypochloremia and interference with the selective micellary solubilization direct low density lipoprotein cholesterol assay. These spurious laboratory anomalies impeded the initial clinical management of the patient including the attempted correction of the electrolyte abnormalities. After relief of obstruction following biliary stent placement, the patient's lipid levels normalized. Clinicians must be wary of laboratory artifacts and remember to correlate the laboratory values with the clinical presentation of the patient. Assays employing direct ion-selective electrodes such as those in blood gas analyzers are not subject to the interference of high concentrations of lipids or proteins, and maybe useful in situations where such interference is suspected. Furthermore the Vertical Auto Profile (VAP®) ultracentrifugation assay may be useful to detect lipoprotein X and low density lipoprotein cholesterol levels when the selective micellary solubilization technique fails to detect or quantify these lipid moieties.

Effect of Recombinant Human Lecithin Cholesterol Acyltransferase Infusion on Lipoprotein Metabolism in Mice

Lecithin cholesterol acyl transferase (LCAT) deficiency is associated with low high-density lipoprotein (HDL) and the presence of an abnormal lipoprotein called lipoprotein X (Lp-X) that contributes to end-stage renal disease. We examined the possibility of using LCAT an as enzyme replacement therapy agent by testing the infusion of human recombinant (r)LCAT into several mouse models of LCAT deficiency. Infusion of plasma from human LCAT transgenic mice into LCAT-knockout (KO) mice rapidly increased HDL-cholesterol (C) and lowered cholesterol in fractions containing very-low-density lipoprotein (VLDL) and Lp-X. rLCAT was produced in a stably transfected human embryonic kidney 293f cell line and purified to homogeneity, with a specific activity of 1850 nmol/mg/h. Infusion of rLCAT intravenously, subcutaneously, or intramuscularly into human apoA-I transgenic mice showed a nearly identical effect in increasing HDL-C approximately 2-fold. When rLCAT was intravenously injected into LCAT-KO mice, it showed a similar effect as plasma from human LCAT transgenic mice in correcting the abnormal lipoprotein profile, but it had a considerably shorter half-life of approximately 1.23 ± 0.63 versus 8.29 ± 1.82 h for the plasma infusion. rLCAT intravenously injected in LCAT-KO mice crossed with human apolipoprotein (apo)A-I transgenic mice had a half-life of 7.39 ± 2.1 h and increased HDL-C more than 8-fold. rLCAT treatment of LCAT-KO mice was found to increase cholesterol efflux to HDL isolated from mice when added to cells transfected with either ATP-binding cassette (ABC) transporter A1 or ABCG1. In summary, rLCAT treatment rapidly restored the normal lipoprotein phenotype in LCAT-KO mice and increased cholesterol efflux, suggesting the possibility of using rLCAT as an enzyme replacement therapy agent for LCAT deficiency.

Role of plasma and liver cholesterol- and lipoprotein-metabolism determinants in LpX formation in the mouse

Cholestasis is characterized by hypercholesterolemia and the appearance of an abnormal lipoprotein, lipoprotein X (LpX), in plasma. The mechanisms responsible for this cholestatic plasma lipid phenotype are not fully understood. We used ATP-binding cassette A1 (ABCA1)(−/−) and scavenger receptor class B type I (SR-BI)(−/−) mice to test the hypothesis that hepatic sinusoidal cholesterol transporters contribute to LpX formation and hypercholesterolemia during cholestasis. Bile-duct ligation (BDL) of both ABCA1(−/−) and SR-BI(−/−) mice, as well as their respective controls, induced a dramatic increase in plasma cholesterol and phospholipid concentrations. Plasma fractionation revealed the presence of LpX in plasma of cholestatic mice, irrespective of their genetic background. We observed that the presence of HDL before cholestasis, a decrease in the activity of LCAT, and an increase in VLDL synthesis were not required for hypercholesterolemia and lipoprotein modifications induced by obstructive cholestasis in mice. In addition, murine cholestasis resulted in increased hepatic cholesterol synthesis that may contribute to the higher plasma free cholesterol levels found during the early hours after BDL. Together these findings indicate that hypercholesterolemia and LpX formation associated with obstructive cholestasis are correlated with an increase in hepatic cholesterol synthesis and are independent of plasma HDL levels, LCAT activity, VLDL synthesis, and ABCA1 and SR-BI expression.

Human Lecithin:Cholesterol Acyltransferase Deficiency

Lecithin:cholesterol acyltransferase deficiency (LCAT-def) is characterized by low levels of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) and the accumulation of lipoprotein-X (LpX). Despite the low HDL, atherosclerosis is uncommon in LCAT-def. The decreased LDL would be a possible explanation but the underlying mechanism is not clear. In addition, the mechanism(s) for LpX accumulation is not known. The aim of the present study is to elucidate the mechanism(s) responsible for the low LDL and determine the plasma kinetics of LpX in LCAT-def. We conducted a radiotracer study in LCAT-def (n=2) and normal controls (n=10) and a stable isotope study in one patient and other controls (n=7). LCAT-def LDL was catabolized faster than control LDL in the control subjects as well as in LCAT-def patients. Control LDL was catabolized faster in LCAT-def patients than the controls. The production rate of LDL apolipoprotein B-100 was normal in LCAT-def. The increased LDL apoB-100 catabolism was confirmed by a stable isotope study. LpX was catabolized more slowly in LCAT-def. The decreased LDL in LCAT-def is attributable to an increased catabolism caused by a rapid catabolism of abnormal LDL and an upregulation of LDL receptor pathway. The decreased catabolism of LpX contributes to its accumulation in LCAT-def.

Pseudohyponatraemia in a patient with obstructive jaundice

Introduction Pseudohyponatraemia is uncommonly associated with severe hypercholesterolaemia. Severe hypercholesterolaemia encountered in obstructive jaundice due to an abnormal lipoprotein, lipoprotein X (LpX), may result in pseudohyponatraemia. Case report We report a case of falsely low sodium measurements in a patient with severe hypercholesterolaemia due to obstructive liver disease. The pathophysiology, complications and analytical effects of LpX are briefly discussed. Conclusion The possibility of pseudohyponatraemia should be considered in severely hypercholesterolaemic samples.