LCAT Deficiency Research Articles

Disturbed apolipoprotein A-I-containing lipoproteins in fish-eye disease are improved by the lecithin:cholesterol acyltransferase produced by gene-transduced adipocytes in vitro

We report the in vitro efficacy of recombinant LCAT produced by lcat gene-transduced proliferative adipocytes (ccdPA/ lcat), which has been developed for enzyme replacement therapy. ApoA-I-specific immunodetection in combination with 1D and 2D gel electrophoreses showed that the disturbed high-density lipoprotein subpopulation profile was clearly ameliorated by the in vitro incubation with ccdPA/ lcat-derived recombinant LCAT. Thus, these results using ccdPA/ lcat strongly suggest the cell implantation could contribute the enzyme replacement for the patients with LCAT deficiency.

In Vivo Imaging of the Cornea in a Patient With Lecithin-Cholesterol Acyltransferase Deficiency

Cornea: October 2010 - Volume 29 - Issue 10 - p 1207 doi: 10.1097/ICO.0b013e3181d5291b

In Vivo Imaging of the Cornea in a Patient with Lecithin-Cholesterol Acyltransferase Deficiency

In Vivo Imaging of the Cornea in a Patient with Lecithin-Cholesterol Acyltransferase Deficiency

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.

家族性lecithin:cholesterol acyltransferase欠損症の一例

Lecithin: cholesterol acyltransferase (LCAT) is an enzyme that catalyzes the esterifying reaction of cholesterol in plasma high density lipoprotein (HDL). Deficiency of LCAT is a rare hereditary disease characterized by several clinical symptoms such as proteinuria, corneal opacity, and anemia due to a shortened life span of erythrocytes. In this communication, we report a case of 40 year-old female patient of LCAT deficiency. She visited a hospital for work-up of proteinuria, corneal opacity and anemia. Activity of her serum LCAT was found to be extremely low, and characteristic changes in plasma lipids due to deficiency of LCAT was observed: those were marked decreases in HDL-cholesterol, degree of esterification in serum cholesterol, and apoprotein A-I, A-II, B and C-II levels. The diagnosis of LCAT deficiency was finally made. We studied about histopathological changes in the patient's kidney, and erythrocyte membrane lipid composition and fluidity. Histopathological findings in renal biopsy were follows: a) Light microscopy showed spherical deposits stained with periodic acid-Schiff in mesangial matrix and adjacent capillary loops, and hyaline deposits in arterioles, b) Electron microscopy showed vacuoles in mesangial matrix and along the glomerular basement membranes. In erythrocyte membrane lipids, increase of cholesterol to phospholipid molar ratio was evident, being accompanied by changes in phospholipid fractions: increase of phosphatidylcholine, and decreases of phosphatidylethanolamine, sphingomyelin and lysophosphatidylcholine. In phospholipid acyl chains, increase of C18:2 and decreased of C18:1 were evident in the patient. Erythrocyte membrane fluidity was found to be decreased in the patient in a measurement by pyrene, probably being related to the changes in membrane lipid composition.(ABSTRACT TRUNCATED AT 250 WORDS)

An aid to the diagnosis of genetic disorders underlying adult-onset renal failure: a literature review

Several genetic disorders can present in adult patients with renal insufficiency. Genetic renal disease other than ADPKD accounts for ESRD in 3% of the adult Dutch population. Because of this low prevalence and their clinical heterogeneity most adult nephrologists are less familiar with these disorders. As a guideline to differential diagnosis, we provide an overview of the clinical manifestations and the pathogenesis of the main genetic disorders with chronic renal insufficiency surfacing in adulthood and add an algorithm plus 4 tables. We also indicate where molecular genetics nowadays can be of aid in the diagnostic process. The following disorders are discussed by mode of inheritance: 1) Autosomal dominant: autosomal dominant polycystic kidney disease, nephropathies associated with uromodulin (medullary cystic disease and familial juvenile hyperuricemic nephropathy), renal cysts and diabetes syndrome, nail-patella syndrome, glomerulopathy with fibronectin deposits. 2) Not autosomal dominant: Nephronophthisis, Fabry disease, primary oxalosis, Adenine Phosphoribosyl Transferase deficiency, Alport syndrome, Lecithin-cholesterol acyltransferase deficiency, adult-onset cystinosis.

Lecithin:cholesterol acyltransferase and vascular disease

Evaluation of: Calabresi L, Baldassarre D, Castelnuovo S et al.: Functional lecithin:cholesterol acyltransferase is not required for efficient atheroprotection in humans. Circulation 120, 628–635 (2009). Lecithin:cholesterol acyltransferase (LCAT) is an HDL-associated enzyme responsible for esterifying free cholesterol to cholesteryl ester within the plasma compartment. Mutations in the LCAT gene can cause LCAT deficiency, a very rare metabolic disorder associated with two hypoalphalipoproteinemia syndromes; familial LCAT deficiency, characterized by complete lack of enzyme activity, and fish-eye disease, with a partially defective enzyme. As LCAT deficiency causes hypoalphalipoproteinemia, carriers should be at increased risk of coronary artery disease because of defective reverse cholesterol transport; however, owing to the relatively small number of cases available, this hypothesis has not been confirmed. Calabresi et al. take advantage of the availability of 13 LCAT-deficient families to investigate t...

Point mutation (C to T) of the LCAT gene resulting in A140C substitution

Familial lecithin: cholesterol acyltransferase (LCAT) deficiency is an autosomal recessive disorder characterized by corneal opacity, hemolytic anemia, proteinuria, and a low serum level of high-density lipoprotein cholesterol (HDL-C). Also, LCAT activity is remarkably decreased or absent. A 57-year-old Japanese man presented with corneal opacity, proteinuria, and a very low serum level of HDL-C. His LCAT activity was too low to measure. From clinical observations and results of examinations, we suspected LCAT deficiency. We performed a kidney biopsy and gene analysis. Light microscopy revealed the vacuolation of glomerular capillary tufts. Electron microscopy revealed small deposits in the glomerular basement membrane (GBM), extracellular matrix, and vascular endothelial cells. We identified a homozygous C to T point mutation at nucleotide 501 (g.501 C>T) of exon 4 at codon 140, resulting in an arginine (Arg) to cysteine (Cys) amino acid substitution (A140C) in the patient. These findings were characteristic of LCAT deficiency, which was confirmed to be due to a mutation that has only been reported in Japan.

CETP IN RARE DYSLIPIDEMIAS

Objective: To determines CETP mass and activity in rare disorders of HDL metabolism. Methods: Patients: Fasting plasma samples were obtained from two individuals with TD and from patients with LCAT deficiency, analphalipoproteinemia, Hepatic lipase deficiency (HL), vasculitis, and hypoalphalipoprteinemia. Their clinical and laboratory findings have been previously reported. Assay: CETP activity was measured using commercial CETP Fluorescence kit (Roar Biomedical Inc., New York, NY). The kit includes donor (without apoA-I) and acceptor lipoprotein particles. Incubation of donor and acceptor with a CETP source results in the CETP mediated transfer of fluorescent neutral lipid from donor to acceptor, rate of which is determined by the increase in fluorescence intensity as the fluorescent neutral lipid is removed from the donor to the acceptor. The amount of fluorescent substrate transferred was expressed as pmoles of fluorescent substrate transferred within 3 hours. CETP concentration was measured by ELISA using specific rabbit antibody against human CETP. Results: While CETP mass correlated with serum HDL-C levels, the activity decreased in patients with LCAT deficiency, FED, HL deficiency and vascultis, but increased in TD. We speculate that the composition of HDL particles in these disorders differs and results in the different CE transfer rates. Conclusion: CETP mass correlates with the HDL-C concentration but the activity differ widely among the patients with rare disorders of HDL metabolism, probably due to the changes in HDL quality.

CHARACTERIZATION OF A NEW LCAT MUTATION CAUSING FAMILIAL LCAT DEFICIENCY (FLD) AND THE ROLE OF APOE AS A MODIFIER GENE OF THE FLD PHENOTYPE

Introduction: LCAT (lecithin:cholesterol acyltransferase ) is an enzyme which plays an essential role in cholesterol esterification and reverse cholesterol transport. Familial LCAT deficiency (FLD) is a disease characterized by a defect in LCAT resulting in extremely low HDL-C, premature corneal opacities, anemia as well as proteinuria and renal failure. Method: We have identified two brothers presenting characteristics of familial LCAT deficiency. We sequenced the LCAT gene, measured the lipid profile as well as the LCAT activity in 15 members of this kindred. We also characterized the plasma lipoproteins by agarose gel electrophoresis and size exclusion chromatography and sequenced several candidate genes related to dysbetalipoproteinemia in this family. Results: We have identified the first French Canadian kindred with familial LCAT deficiency. Two brothers affected by FLD, were homozygous for a novel LCAT mutation. This c.102delG mutation occurs at the codon for His35 causing a frameshift that stops transcription at codon 61 abolishing LCAT enzymatic activity both in vivo and in vitro. It has a dramatic effect on the lipoprotein profile, with an important reduction of HDL-C in both heterozygotes (22%) and homozygotes (88%) and a significant decrease in LDL-C in heterozygotes (35%) as well as homozygotes (58%). Furthermore, the lipoprotein profile differed markedly between the two affected brothers who had different APOE genotypes. We propose that APOE could be an important modifier gene explaining heterogeneity in lipoprotein profiles observed among FLD patients. Our results suggest that a LCAT-/- genotype associated with an APOE ?2 allele could be a novel mechanism leading to dysbetalipoproteinemia.

Report and Abstracts of the Joint Annual Congress of the AMBQ-CAMB 2009

The second joint congress of l’Association des Médicins Biochimistes du Québec (AMBQ) and the Canadian Association of Medical Biochemists (CAMB) was held this year from October 7 to 9 in Montreal. The setting was the picturesque Hôtel Place d’Armes, which is situated in the historic Old Montreal district. There were over 60 attendees comprising both Specialists and Medical residents-in-training and representing the breadth of Canada from the Atlantic to the Pacific. The scientific committee composed of Dr. Jean. Dubé (Centre Hospitalier U. de Sherbrooke), Dr. Bernard Fruteau-de-Laclos (Centre Hospitalier AUQ), Dr. Élaine Letendre (Centre Hospitalier U. de Montreal), Dr. Bassam A. Nassar (Capital Health) and Dr. Claude Petitclerc (CHUM) arranged a series of informative and interesting scientific sessions. Day 1 saw a training session for the medical residents conducted by Dr. Yves Giguère (Centre Hospitalier de l’U. Laval) on Prenatal Screening. A meeting of the specialty committee of the Royal College for Medical Biochemistry followed this. A major topic of this meeting was the re-alignment of the training requirements. Day 2 began with the business meeting of the AMBQ. The scientific sessions began later that day with a session on “Pharmacotoxicology and the Role of the Laboratory” chaired by Drs. Andre Mattman (B.C. Children & Women’s Health Centre) and Bassam A. Nassar. The first speaker, Dr. Margaret Thompson (Hospital for Sick Children), in her talk “Clinical Toxicology – for the Laboratory” reviewed the role of the Ontario Poison Centre, which may serve as a model for the rest of the country. This was followed by Dr. Zulfikarali Verjee (HSC), who is clearly a master of the subject, with his talk, “Challenges in Urine Drug Screens: Ongoing Issues”. The morning session ended with Dr. Andre Mattman’s presentation “Heavy Metal Toxins – How and Why to Test in the Clinical Laboratory”. Day 3 moderated by Dr. Élaine Letendre (CHUM) focused on risk factors for cardiovascular disease. The first speaker in the morning was Dr. Jacques Genest Jr. (McGill University Health Centre) who reviewed the new Canadian guidelines for the diagnosis and treatment of dyslipidemias. He described in detail the thinking behind the new guidelines. This was followed by a presentation by Dr. Allan Jaffe (Mayo Clinic) who gave the audience a most authoritative description of the soon to be introduced fourth generation high sensitivity assays for troponins. These assays will have a marked impact on the assessment of cardiac damage perhaps even more so than the original introduction of the troponins. The afternoon featured three speakers discussing the pro and cons of high-sensitivity C-reactive protein for the assessment of cardiovascular disease. Dr. Jean Grégoire (Institut de cardiologie de Montréal) presented the pro side of the debate reviewing in particular the recent Jupiter trial. Dr. James Brophy (MUHC) presented the con side of the debate in a most entertaining manner. He even had the audience performing stretching exercises! It was left to Dr. Jean Bergeron (CHUL) to provide a balanced view of the two preceding speakers. The last day, Day 4, was primarily dedicated to oral and poster presentations by the residents. A jury consisting of Drs. Jean Dubé (CHUS), Yves Guigère (CHUL), and Joël Girouard (CHUL) had the “difficult” task of awarding prizes to the best oral and to the best poster presentations. The winners this year were Dr. Alexis Blaass (U. de Montréal) for the oral presentation entitled “Characterization of a new LCAT mutation causing familial LCAT deficiency (FLD) and the role of APOE as a modifier gene of the FLD phenotype” and Dr. Adell Elsharif (McMaster U.) for the poster presentation entitled “Method Validation Study to Evaluate the Analytical Performance of the STAT–SITE Meter for the Measurement of Serum Beta-Hydroxybutyrate”. The scientific portion of the conference ended with a most comprehensive presentation on smoking cessation, both clinical approaches and therapeutics by Dr. Joanne Provencher (Hôpital Laval). Dr. Provencher reminded us that smoking cessation by an individual could be achieved with the correct support. The day and the congress ended with a business meeting of the CAMB chaired by the out going president, Dr. Bassam A. Nassar. A new executive was elected: Dr. Elizabeth MacNamara (SMBD-Jewish General Hospital, president), Dr. Yves Guigère (CHUL, vice-president), Dr. Andrew Don-Wauchope (McMaster U. Health Sciences Centre, secretary-treasurer), Dr. Andre Mattman (BCCWHC, councilor), Dr. Brian M. Gilfix (MUHC, councilor), Dr. John Heathcote (Vancouver, councilor), and Dr. Datlily Ooi (Children’s Hospital of Eastern Ontario, councilor), We all look forward to next year’s combined meeting which is again slated to take place in Montreal in October.

Innovation in the Treatment of Uremia: Proceedings from the Cleveland Clinic Workshop: Causes of Dysregulation of Lipid Metabolism in Chronic Renal Failure

End-stage renal disease (ESRD) is associated with accelerated atherosclerosis and premature death from cardiovascular disease. These events are driven by oxidative stress inflammation and lipid disorders. ESRD-induced lipid abnormalities primarily stem from dysregulation of high-density lipoprotein (HDL), triglyceride-rich lipoprotein metabolism, and oxidative modification of lipoproteins. In this context, production and plasma concentration of Apo-I and Apo-II are reduced, HDL maturation is impaired, HDL composition is altered, HDL antioxidant and anti-inflammatory functions are depressed, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentration is elevated in ESRD. The associated defect in HDL maturation is largely caused by acquired lecithin-cholesterol acyltransferase deficiency while its triglyceride enrichment is due to hepatic lipase deficiency. Hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are mediated by down-regulation of lipoprotein lipase, hepatic lipase, very low-density lipoprotein (VLDL) receptor, and LDL receptor-related protein, relative reduction in ApoC-II/ApoC-III ratio, up-regulation of acyl-CoA cholesterol acyltransferase, and elevated plasma level of cholesterol ester-poor prebeta HDL. Impaired clearance and accumulation of oxidation-prone VLDL and chylomicron remnants and abnormal LDL composition in the face of oxidative stress and inflammation favors their uptake by macrophages and resident cells in the artery wall. The effect of heightened influx of lipids is compounded by impaired HDL-mediated reverse cholesterol transport leading to foam cell formation which is the central event in atherosclerosis plaque formation and subsequent plaque rupture, thrombosis, and tissue damage.

In Vivo Imaging of the Cornea in a Patient with Lecithin-Cholesterol Acyltransferase Deficiency

To report high-resolution, in vivo imaging of the cornea in a patient with lecithin-cholesterol acyltransferase (LCAT) deficiency. A 60-year-old Ecuadorian woman with bilateral corneal opacities and confirmed LCAT deficiency was imaged with Fourier domain optical coherence tomography (FD-OCT) and noncontact Rostock confocal laser scanning microscopy. The FD-OCT revealed a thinned epithelium, homogeneous hyperreflective stroma, and focal disruptions of Bowman's layer. Focal areas of hyperreflectivity with multiple dark striae and reduced and irregular keratocytes were seen throughout the stroma by noncontact Rostock module. The corneal endothelium was normal. New anterior segment in vivo imaging technology permits high-resolutional visualization and monitoring of corneal pathology.

Cholesterol homeostasis in ABCA1/LCAT double-deficient mouse

We examined cholesterol homeostasis in mice with the two major cholesterol transport pathways for catabolism interrupted by disrupting abca1, lcat, or both. Plasma HDL markedly decreased in these genotype but LDL/VLDL decreased only in the double deficiency. Fractional catabolic rate of HDL increased in the order of wild type < abca1(−/−) = lcat(−/−) < abca1(−/−)lcat(−/−). Cholesterol accumulated in the liver by disrupting either gene and more by the double disruption. HDL biogenesis by primary-cultured hepatocytes was negligible in the abca1 deficiency and substantially reduced in the lcat deficiency. Secretion of LDL/VLDL was also decreased in these cells but to a less extent. Cholesterol content in the hepatocytes was in a reciprocal order to lipoprotein generation. Expression of hepatic mRNA of the sterol-related genes reflected the cellular cholesterol increase, such as decrease in SREBP2 and HMG-CoA reductase and increase in apoA-I, apoE, and ABCG1. Cholesterol decreased in the steroidogenic organs by disruption of either gene resulting from low-plasma HDL. Cholesterol in other peripheral tissues generally decreased under normal chow feeding, and interestingly, it was recovered by high-cholesterol feeding, including the cholesterol content in the brain. No apparent vascular lipid deposition was observed in any genotype. Deletion of the two major factors in “reverse cholesterol transport” may not directly result in severe cholesterol transport stagnation in the body of mouse. Other compensatory pathways may back up cholesterol transport among the organs and tissues even when these pathways are impaired.

Functional Lecithin: Cholesterol Acyltransferase Is Not Required for Efficient Atheroprotection in Humans

Background— Mutations in the LCAT gene cause lecithin:cholesterol acyltransferase (LCAT) deficiency, a very rare metabolic disorder with 2 hypoalphalipoproteinemia syndromes: classic familial LCAT deficiency (Online Mendelian Inheritance in Man No. 245900), characterized by complete lack of enzyme activity, and fish-eye disease (Online Mendelian Inheritance in Man No. 136120), with a partially defective enzyme. Theoretically, hypoalphalipoproteinemia cases with LCAT deficiency should be at increased cardiovascular risk because of high-density lipoprotein deficiency and defective reverse cholesterol transport. Methods and Results— The extent of preclinical atherosclerosis was assessed in 40 carriers of LCAT gene mutations from 13 Italian families and 80 healthy controls by measuring carotid intima-media thickness (IMT). The average and maximum IMT values in the carriers were 0.07 and 0.21 mm smaller than in controls ( P =0.0003 and P =0.0027), respectively. Moreover, the inheritance of a mutated LCAT genotype had a remarkable gene-dose–dependent effect in reducing carotid IMT ( P =0.0003 for average IMT; P =0.001 for maximum IMT). Finally, no significant difference in carotid IMT was found between carriers of LCAT gene mutations that cause total or partial LCAT deficiency (ie, familial LCAT deficiency or fish-eye disease). Conclusions— Genetically determined low LCAT activity in Italian families is not associated with enhanced preclinical atherosclerosis despite low high-density lipoprotein cholesterol levels. This finding challenges the notion that LCAT is required for effective atheroprotection and suggests that elevating LCAT expression or activity is not a promising therapeutic strategy to reduce cardiovascular risk.

Functional Lecithin: Cholesterol Acyltransferase Is Not Required for Efficient Atheroprotection in Humans

Mutations in the LCAT gene cause lecithin:cholesterol acyltransferase (LCAT) deficiency, a very rare metabolic disorder with 2 hypoalphalipoproteinemia syndromes: classic familial LCAT deficiency (Online Mendelian Inheritance in Man No. 245900), characterized by complete lack of enzyme activity, and fish-eye disease (Online Mendelian Inheritance in Man No. 136120), with a partially defective enzyme. Theoretically, hypoalphalipoproteinemia cases with LCAT deficiency should be at increased cardiovascular risk because of high-density lipoprotein deficiency and defective reverse cholesterol transport. The extent of preclinical atherosclerosis was assessed in 40 carriers of LCAT gene mutations from 13 Italian families and 80 healthy controls by measuring carotid intima-media thickness (IMT). The average and maximum IMT values in the carriers were 0.07 and 0.21 mm smaller than in controls (P=0.0003 and P=0.0027), respectively. Moreover, the inheritance of a mutated LCAT genotype had a remarkable gene-dose-dependent effect in reducing carotid IMT (P=0.0003 for average IMT; P=0.001 for maximum IMT). Finally, no significant difference in carotid IMT was found between carriers of LCAT gene mutations that cause total or partial LCAT deficiency (ie, familial LCAT deficiency or fish-eye disease). Genetically determined low LCAT activity in Italian families is not associated with enhanced preclinical atherosclerosis despite low high-density lipoprotein cholesterol levels. This finding challenges the notion that LCAT is required for effective atheroprotection and suggests that elevating LCAT expression or activity is not a promising therapeutic strategy to reduce cardiovascular risk.

Splenomegaly with sea-blue histiocytosis, dyslipidemia, and nephropathy in a patient with lecithin-cholesterol acyltransferase deficiency: a clinicopathologic correlation

A 31-year–old man with no significant medical history presented with a 5-day history of progressive left upper quadrant abdominal pain. Physical examination revealed a tender guarded abdomen, no icterus, and bilateral corneal “arcus senilis”–like changes. Laboratory workup showed a mild normocytic, normochromic anemia; and target cells were seen in the peripheral blood smear. Serum was turbid; and the lipid profile showed elevated total cholesterol, low high-density lipoprotein cholesterol, and elevated triglycerides. Urinalysis revealed nephrotic range proteinuria with microhematuria. An abdominal computed tomographic scan demonstrated a homogeneously enlarged spleen. The patient was discharged after symptomatic treatment to be followed as an ambulatory patient. Several days later, he returned with severe left upper quadrant pain and was admitted to the surgical service for further evaluation. A splenectomy was performed for a suspected splenic lymphoma. Upon gross examination, spleen was moderately enlarged, weighing 780 g. Sectioning revealed a beefy red cut surface without gross lesions. Wright-Giemsa–stained touch imprints showed many sea-blue histiocytes. A renal biopsy was also performed, demonstrating focal segmental glomerular sclerosis and mesangial expansion with extramembranous and intramembranous deposition of lipids. In the absence of hematologic malignancy and in light of the abnormal lipid profile, a disorder of lipid metabolism was suspected. Histologic and ultrastructural findings in the kidney and spleen raised the likelihood of lecithin-cholesterol acyltransferase (LCAT) deficiency, which was confirmed by the markedly decreased serum LCAT activity and serum LCAT mass. We describe a case with the triad of splenomegaly with sea-blue histiocytes, nephropathy, and dyslipidemia in a patient with LCAT deficiency.

Lecithin: Cholesterol Acyltransferase Expression Has Minimal Effects on Macrophage Reverse Cholesterol Transport In Vivo

Lecithin:cholesterol acyltransferase (LCAT) catalyzes the formation of plasma cholesteryl ester, plays a key role in high-density lipoprotein metabolism, and has been believed to be critical in the process of reverse cholesterol transport (RCT). The role of LCAT in RCT from macrophages was quantified with a validated assay involving intraperitoneal injection in mice of (3)H-cholesterol-labeled J774 macrophages and monitoring the appearance of tracer in plasma, liver, bile, and feces. Human LCAT overexpression in human apolipoprotein A-I transgenic mice substantially increased plasma high-density lipoprotein cholesterol levels but surprisingly did not increase macrophage RCT. Even in the setting of coexpression of scavenger receptor BI or cholesteryl ester transfer protein, both of which promoted the transfer of LCAT-derived high-density lipoprotein cholesterol ester to the liver, LCAT overexpression still had no effect on RCT. Serum from LCAT-overexpressing mice had reduced ability to promote cholesterol efflux from macrophages ex vivo via ABCA1. To determine the effect of LCAT deficiency on macrophage RCT, LCAT(-/-) and LCAT(+/-) mice were compared with wild-type mice. Despite extremely low plasma levels of high-density lipoprotein cholesterol, LCAT-deficient mice had only a 50% reduction in RCT. LCAT(+/-) mice had normal RCT despite a significant reduction in high-density lipoprotein cholesterol. Serum from LCAT-deficient mice had increased ability to promote ABCA1-mediated cholesterol efflux from macrophages ex vivo. These results demonstrate that LCAT overexpression does not promote an increased rate of macrophage RCT. Although LCAT activity does become rate limiting in the context of complete LCAT deficiency, RCT is reduced by only 50% even in the absence of LCAT. These data suggest that macrophage RCT may not be as dependent on LCAT activity as has previously been believed.

Characterization of a new LCAT mutation causing familial LCAT deficiency (FLD) and the role of APOE as a modifier gene of the FLD phenotype

Familial LCAT deficiency (FLD) is a disease characterized by a defect in the enzyme lecithin:cholesterol acyltransferase (LCAT) resulting in low HDL-C, premature corneal opacities, anemia as well as proteinuria and renal failure. We have identified the first French Canadian kindred with familial LCAT deficiency. Two brothers, presenting classical signs of FLD, were shown to be homozygous for a novel LCAT mutation. This c.102delG mutation occurs at the codon for His35 and causes a frameshift that stops transcription at codon 61 abolishing LCAT enzymatic activity both in vivo and in vitro. It has a dramatic effect on the lipoprotein profile, with an important reduction of HDL-C in both heterozygotes (22%) and homozygotes (88%) and a significant decrease in LDL-C in heterozygotes (35%) as well as homozygotes (58%). Furthermore, the lipoprotein profile differs markedly between the two affected brothers who had different APOE genotypes. We propose that APOE could be an important modifier gene explaining heterogeneity in lipoprotein profiles observed among FLD patients. Our results suggest that a LCAT−/− genotype associated with an APOE ɛ2 allele could be a novel mechanism leading to dysbetalipoproteinemia.

LCAT synthesized by primary astrocytes esterifies cholesterol on glia-derived lipoproteins

Lipid trafficking in the brain is essential for the maintenance and repair of neuronal membranes, especially after neurotoxic insults. However, brain lipid metabolism is not completely understood. In plasma, LCAT catalyses the esterification of free cholesterol on circulating lipoproteins, a key step in the maturation of HDL. Brain lipoproteins are apolipoprotein E (apoE)-containing, HDL-like particles secreted initially as lipid-poor discs by glial cells. LCAT is synthesized within the brain, suggesting that it may play a key role in the maturation of these lipoproteins. Here we demonstrate that astrocytes are the primary producers of brain LCAT. This LCAT esterifies free cholesterol on nascent apoE-containing lipopoproteins secreted from glia. ApoE is the major LCAT activator in glia-conditioned media (GCM), and both the cholesterol transporter ABCA1 and apoE are required to generate glial LCAT substrate particles. LCAT deficiency leads to the appearance of abnormal approximately 8 nm particles in GCM, and exogenous LCAT restores the lipoprotein particle distribution to the wild-type (WT) pattern. In vivo, complete LCAT deficiency results in a dramatic increase in apoE-HDL and reduced apolipoprotein A-I (apoA-I)-HDL in murine cerebrospinal fluid (CSF). These data show that brain LCAT esterifies cholesterol on glial-derived apoE-lipoproteins, and influences CSF apoE and apoA-I levels.