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In vivo metabolism of proapolipoprotein A-I in Tangier disease.

Tangier disease is a rare familial disorder characterized by extremely low levels of apolipoprotein A-I (apoA-I) and high density lipoproteins (HDL). In normal subjects, proapoA-I is secreted into plasma and converted to mature apoA-I by the cleavage of the amino-terminal six amino acids with the major isoprotein in plasma being mature apoA-I. In contrast, in Tangier disease there is a marked relative increase of proapoA-I as compared with mature apoA-I. ProapoA-I and mature apoA-I were isolated from normal and Tangier disease subjects, radio-labeled, and autologous apoA-I isoproteins injected into normal and Tangier subjects. The in vivo catabolism and conversion of proapoA-I and mature apoA-I in normal and Tangier disease subjects were quantitated. A comparison of the rate of catabolism of apoA-I isoproteins from plasma revealed a significantly faster rate of catabolism of both isoproteins of apoA-I in Tangier subjects when compared with normal subjects. The fractional conversion rate of proapoA-I to mature apoA-I was 3.9 d-1 in normal subjects and 3.6 d-1 in Tangier subjects. The results indicate that (a) apoA-I enters plasma as the pro isoprotein in both normal and Tangier subjects, (b) Tangier disease subjects have a normal fractional rate of conversion of proapoA-I to mature apoA-I, (c) proapoA-I is catabolized at the same rate as mature apoA-I in Tangier subjects, and (d) Tangier subjects catabolize both pro and mature apoA-I at a much greater rate than do normal subjects. Therefore, the relative increase in proapoA-I in Tangier disease is due to a marked decrease in mature apoA-I resulting from rapid catabolism of both pro- and mature apoA-I and not to defective conversion of proapoA-I to mature apoA-I.

Adult↗

[Tangier disease].

Tangier disease, a familial HDL-deficiency syndrome, was first reported by Fredrickson et al. in 1961. Since then, a great deal research on the mechanism of HDL-deficiency in this disease has been done from the prospective of lipoprotein compositions, in vivo HDL kinetics, cell and receptor interactions and genomic DNA analysis. These studies have found a relatively increased fractional catabolic rate of apo HDL with essentially no change in the synthesis of apo HDL. As yet, no structural defect has been found in the apo A-I gene. However, there have been reports of irregular lipid metabolism and of disorders in the Golgi apparatus and lysosome processing. Interestingly, the frequency of coronary heart disease is low in patients with Tangier disease. In this report, we describe the clinical and biochemical characteristics of Tangier disease and suggest some possible mechanisms for preventing coronary heart disease.

Apolipoproteins↗

Ocular complications of Tangier disease.

Tangier disease, or familial high-density lipoprotein deficiency, is an inherited disorder resulting in tissue deposition of excessive cholesterol esters. Although associated corneal clouding has been reported to produce little visual impairment, this patient with Tangier disease had corneal clouding, decreased corneal sensation, and cicatricial ectropion and experienced slowly progressive marked visual impairment. All ocular cases of Tangier disease are reviewed. Ectropion and incomplete eyelid closure may precede corneal clouding and should be recognized as signs associated with Tangier disease. The combination of exposure keratopathy and corneal infiltration can cause significant visual impairment.

Aged↗

Defective removal of cellular cholesterol and phospholipids by apolipoprotein A-I in Tangier Disease.

Tangier disease is a rare genetic disorder characterized by extremely low plasma levels of HDL and apo A-I, deposition of cholesteryl esters in tissues, and a high prevalence of cardiovascular disease. We examined the possibility that HDL apolipoprotein-mediated removal of cellular lipids may be defective in Tangier disease. With fibroblasts from normal subjects, purified apo A-I cleared cells of cholesteryl esters, depleted cellular free cholesterol pools available for esterification, and stimulated efflux of radiolabeled cholesterol, phosphatidylcholine, and sphingomyelin. With fibroblasts from two unrelated Tangier patients, however, apo A-I had little or no effect on any of these lipid transport processes. Intact HDL also was unable to clear cholesteryl esters from Tangier cells even though it promoted radiolabeled cholesterol efflux to levels 50-70% normal. Passive desorption of radiolabeled cholesterol or phospholipids into medium containing albumin or trypsinized HDL was normal for Tangier cells. Binding studies showed that the interaction of apo A-I with high-affinity binding sites on Tangier fibroblasts was abnormal. These results indicate that apo A-I has an impaired ability to remove cholesterol and phospholipid from Tangier fibroblasts, possibly because of a defective interaction of apo A-I with cell-surface binding sites. Failure of apo A-I to acquire cellular lipids may account for the rapid catabolism of nascent HDL particles and the low plasma HDL levels in Tangier disease.

Apolipoprotein A-I↗

A novel nonsense mutation in the ABC1 gene causes a severe syringomyelia-like phenotype of Tangier disease.

Tangier disease is a rare autosomal recessive disorder caused by mutations in the recently identified ATP-binding cassette transporter 1 gene (ABC1). A typical clinical manifestation of Tangier disease is peripheral neuropathy. Former studies differentiated between two manifestations: the more frequent mono- or polyneuropathic form and a syringomyelia-like type. It is unknown whether specific mutations in the ABC1 gene or a particular genetic background are responsible for either of these forms. A family is presented comprising a case with a severe syringomyelia-like phenotype of Tangier disease and absence of cardiovascular disease. Sequencing analysis of the ABC1 gene was performed. A new homozygous C-->T transition in exon 18 was found in the index patient. This mutation results in a stop codon at position 909 (R909X) leading to premature termination of translation. Her clinically asymptomatic daughters, her sister and one of her nieces were heterozygous. Sural nerve biopsies were studied in the index patient at the age of 45 and 54 years; both revealed a severe neuropathy, characterized by a subtotal and finally complete loss of nerve fibres. The entire loss of Schwann cells resulted in an extraordinary form of endoneurial sclerosis. Only rare capillaries, lipid-laden macrophages and fibroblasts had survived in the endoneurium. This case appears to be unique in respect to the underlying novel mutation in the ABC1 gene and its association with complete endoneurial sclerosis of all fascicles in the sural nerve and absence of cardiovascular disease.

ATP Binding Cassette Transporter 1↗

Different substrate specificities of plasma lecithin: cholesterol acyl transferase in fish eye disease and Tangier disease.

Esterification of plasma free cholesterol is mediated by lecithin:cholesterol acyl transferase (LCAT). The free cholesterol of plasma high density lipoproteins (HDL) is considered to be the preferred substrate for LCAT. It therefore appeared as a paradox that plasma cholesterol esterification, both in vivo and in vitro, is normal in fish eye disease and Tangier disease, two familial conditions with extremely low plasma HDL levels. Fish eye disease plasma, however, was shown to have LCAT activity primarily acting on combined very low (VLDL) and low (LDL) density lipoproteins, denominated beta-LCAT, while it lacked LCAT activity esterifying HDL cholesterol (alpha-LCAT). Here we show that Tangier plasma, in contrast, has both alpha- and beta-LCAT. Thus, in both fish eye and Tangier diseases it is beta-LCAT that explains the apparent normal plasma cholesterol esterification. We also show that Tangier plasma, having alpha-LCAT activity, normalizes the low cholesteryl ester content as well as the abnormally small size of fish eye disease HDL particles during incubation.

Cholesterol↗

Subpopulations of high density lipoproteins in homozygous and heterozygous Tangier disease.

Tangier disease (TD) is characterized by severe high-density lipoproteins (HDL) deficiency, hypercatabolism of HDL constituents, impaired cellular cholesterol efflux, and mutations in the gene of ATP-binding cassette 1 (ABC-1). In the present study, we determined plasma lipid and apolipoprotein levels, and HDL subpopulations, in 110 subjects from a large TD kindred in which the proband was homozygous for an A-->C missense mutation at nucleotide 5338 of the ABC-1 transcript. In the proband HDL-C, apoA-I, and apoA-II concentrations were 2, 1, and 2 mg/dl, respectively, apoA-I was present only in prebeta(1), while apoA-II was found free of apoA-I in two distinct alpha mobility subpopulations with different sizes. The smaller size particles contained only apoA-II while the larger one contained apoA-II and apo(a). Relative to unaffected male relatives (n=30), male heterozygotes (n=21) had significant reductions (P<0.001) in plasma HDL-C (-45%), apoA-I (-34%), apoA-II (-59%), apoA-IV (-40%), Lp(a) (-62%), and apoB (-55%) concentrations, and a significant increase (P<0.05, +33%) in plasma apoC-III levels. Female heterozygotes (n=11) similarly had significant reductions (P<0.001) in the concentrations of plasma HDL-C (-42%), apoA-I (-27%), apoA-II (-52%), Lp(a) (-27%), and (P<0.01) apoA-IV (-28%), apoB (-13%), and a significant increase (P<0.05) in plasma apoE levels (+29%) as compared to unaffected female relatives (n=41). Large size HDL subpopulations, especially the two LpA-I particles: alpha(1) and prealpha(1) were dramatically reduced in both male and female heterozygotes relative to their unaffected family members. Since apoA-II decreased more than apoA-I in both male and female heterozygotes, the ratios of apoA-I/apoA-II were significantly (P<0.01) increased. The prevalence of CHD was 60% higher in the 32 heterozygotes than in the 71 unaffected relatives even though the latter group was on average 7 years older. We conclude that TD homozygotes have only prebeta(1) apoA-I-containing HDL subpopulations, while heterozygotes have HDL that is selectively depleted in the large alpha(1), prealpha(1), and alpha(2), prealpha(2) subpopulations, resulting in HDL particles that are small in size, poor in cholesterol, but relatively enriched in apoA-I compared to those of their unaffected relatives. These abnormalities appear to result in a higher risk of CHD in heterozygotes than in unaffected controls.

Adult↗

The gene encoding ATP-binding cassette transporter 1 is mutated in Tangier disease.

Tangier disease (TD) is an autosomal recessive disorder of lipid metabolism. It is characterized by absence of plasma high-density lipoprotein (HDL) and deposition of cholesteryl esters in the reticulo-endothelial system with splenomegaly and enlargement of tonsils and lymph nodes. Although low HDL cholesterol is associated with an increased risk for coronary artery disease, this condition is not consistently found in TD pedigrees. Metabolic studies in TD patients have revealed a rapid catabolism of HDL and its precursors. In contrast to normal mononuclear phagocytes (MNP), MNP from TD individuals degrade internalized HDL in unusual lysosomes, indicating a defect in cellular lipid metabolism. HDL-mediated cholesterol efflux and intracellular lipid trafficking and turnover are abnormal in TD fibroblasts, which have a reduced in vitro growth rate. The TD locus has been mapped to chromosome 9q31. Here we present evidence that TD is caused by mutations in ABC1, encoding a member of the ATP-binding cassette (ABC) transporter family, located on chromosome 9q22-31. We have analysed five kindreds with TD and identified seven different mutations, including three that are expected to impair the function of the gene product. The identification of ABC1 as the TD locus has implications for the understanding of cellular HDL metabolism and reverse cholesterol transport, and its association with premature cardiovascular disease.

ATP Binding Cassette Transporter 1↗

Double deletions and missense mutations in the first nucleotide-binding fold of the ATP-binding cassette transporter A1 ( ABCA1) gene in Japanese patients with Tangier disease.

Tangier disease (TD) is a rare autosomal recessive disease characterized by plasma high-density lipoprotein deficiency caused by an ATP-binding cassette transporter A1 ( ABCA1) gene mutation. We describe three different mutations in Japanese patients with TD. The first patient was homozygous for double deletions of 1221 bp between intron 12 and 14 and 19.9 kb between intron 16 and 31. The breakpoint sequence analyses suggest that it is a simultaneous event caused by double-loop formation through multiple Alu. The second patient was homozygous for a novel mutation of A3198C in exon 19, resulting in Asn935His. The third patient was homozygous for A3199G of exon 19 that leads to Asn935Ser, which is the same mutation found in German and Spanish families. Both Asn mutations involved Walker A motif of the first nucleotide-binding fold.

ATP Binding Cassette Transporter 1↗

Cholesterol and apolipoprotein B metabolism in Tangier disease.

Tangier disease (TD), caused by mutations in the gene encoding ATP-binding cassette 1 (ABCA1), is a rare genetic disorder in which homozygotes have a marked deficiency of high density lipoproteins (HDL), as well as concentrations of low density lipoproteins (LDL) that are typically 40% of normal. Although it is well known that the reduced levels of HDL in TD are due to hypercatabolism, the mechanism responsible for the low LDL levels has not been defined. Recently, it has been reported that intestinal cholesterol absorption is altered in ABCA1 deficient mice, suggesting that aberrant cholesterol metabolism may contribute to the LDL reductions in TD. In order to explore this possibility, as well as to define the role that ABCA1 plays in the metabolism of apolipoprotein (apoB)-containing lipoproteins, we determined the kinetics of apoB-100 within lipoproteins, and cholesterol absorption, biosynthesis, and turnover, in a compound heterozygote for TD. The levels of HDL cholesterol, LDL cholesterol and LDL apoB-100 in this subject were 7, 27 and 69% of normal, respectively, the latter of which was due to a two-fold increase in LDL catabolism (0.54 vs. 0.26+/-0.07 poolsday(-1)) relative to controls (n=11). NMR analysis of plasma lipoproteins revealed that 91% of the LDL cholesterol in the TD subject was contained within small, dense LDL, as compared with only 20% for controls (n=70). Cholesterol absorption was 97% of the value for controls (n=15) in the TD subject, at 45%, with cholesterol synthesis and turnover increased modestly by 17 and 25%, respectively. Our data are consistent with the concept that the reductions of LDL observed in TD are due to enhanced catabolism, secondary to changes in LDL composition and size, with neither cholesterol absorption nor metabolism significantly influenced by mutations in ABCA1.

ATP Binding Cassette Transporter 1↗

Confocal microscopy and corneal sensitivity in a patient with corneal manifestations of Tangier disease.

PURPOSE: Tangier disease is an autosomal recessive disorder in which cholesterol-rich lipids are deposited at various tissues of the body including the cornea. In this case report, the corneal changes in a patient with Tangier disease are described. METHODS: A 72-year-old patient who was diagnosed with Tangier disease 25 years before received a complete eye examination including confocal microscopy and Cochet-Bonnet esthesiometry. RESULTS: Slit-lamp biomicroscopy and confocal microscopy showed bilateral corneal opacifications caused by lipid accumulation. Confocal microscopy showed that pathologic changes in the cornea in Tangier disease are limited to the stroma. Neither a reduced corneal sensation nor lid abnormalities as previously described in Tangier disease were found. CONCLUSION: Confocal microscopy helps to identify corneal changes in the stroma caused by Tangier disease easily missed in a slit-lamp examination. The ocular manifestations of Tangier disease do not necessarily include a reduced corneal sensitivity and lid abnormalities.

Aged↗

Human ATP-binding cassette transporter 1 (ABC1): genomic organization and identification of the genetic defect in the original Tangier disease kindred.

Tangier disease is characterized by low serum high density lipoproteins and a biochemical defect in the cellular efflux of lipids to high density lipoproteins. ABC1, a member of the ATP-binding cassette family, recently has been identified as the defective gene in Tangier disease. We report here the organization of the human ABC1 gene and the identification of a mutation in the ABC1 gene from the original Tangier disease kindred. The organization of the human ABC1 gene is similar to that of the mouse ABC1 gene and other related ABC genes. The ABC1 gene contains 49 exons that range in size from 33 to 249 bp and is over 70 kb in length. Sequence analysis of the ABC1 gene revealed that the proband for Tangier disease was homozygous for a deletion of nucleotides 3283 and 3284 (TC) in exon 22. The deletion results in a frameshift mutation and a premature stop codon starting at nucleotide 3375. The product is predicted to encode a nonfunctional protein of 1,084 aa, which is approximately half the size of the full-length ABC1 protein. The loss of a Mnl1 restriction site, which results from the deletion, was used to establish the genotype of the rest of the kindred. In summary, we report on the genomic organization of the human ABC1 gene and identify a frameshift mutation in the ABC1 gene of the index case of Tangier disease. These results will be useful in the future characterization of the structure and function of the ABC1 gene and the analysis of additional ABC1 mutations in patients with Tangier disease.

ATP Binding Cassette Transporter 1↗

Novel approaches to treating cardiovascular disease: lessons from Tangier disease.

Atherosclerotic cardiovascular disease (CVD) remains the leading cause of morbidity and mortality in Western societies. Although cholesterol is a major CVD risk factor, therapeutic interventions to lower plasma cholesterol levels have had limited success in reducing coronary events. Thus, novel approaches are needed to reduce or eliminate CVD. A potential therapeutic target is a newly discovered ATP binding cassette transporter called ABCA1, a cell membrane protein that is the gateway for secretion of excess cholesterol from macrophages into the high density lipoprotein (HDL) metabolic pathway. Mutations in ABCA1 cause Tangier disease, a severe HDL deficiency syndrome characterised by accumulation of cholesterol in tissue macrophages and prevalent atherosclerosis. Studies of Tangier disease heterozygotes revealed that the relative activity of ABCA1 determines plasma HDL levels and susceptibility to CVD. Drugs that induce ABCA1 in mice increase clearance of cholesterol from tissues and inhibit intestinal absorption of dietary cholesterol. Thus, ABCA1-stimulating drugs have the potential to both mobilise cholesterol from atherosclerotic lesions and eliminate cholesterol from the body. By reducing plaque formation and rupture independently of the atherogenic factors involved, these drugs would be powerful agents for treating CVD.

Animals↗

The high density lipoprotein- and apolipoprotein A-I-induced mobilization of cellular cholesterol is impaired in fibroblasts from Tangier disease subjects.

Tangier disease (also known as familial HDL-deficiency) is characterized by very low high density lipoprotein (HDL) plasma levels, splenomegaly, and massive cholesteryl ester accumulation in the cytoplasm of various cell types. Since this phenotype may in part be caused by a defect in the pathway mediating cholesterol efflux from peripheral cells, we investigated the HDL3-mediated mobilization of cholesterol synthesized de novo from [14C]-mevalonolactone in cultivated fibroblasts from two patients with Tangier disease. Our results indicate that the HDL3-induced translocation of [14C]-cholesterol from intracellular pools to the plasma membrane and its subsequent secretion into the extracellular medium was approximately 50% less in the cells from the patients than in controls. The same result was also obtained with artificial apolipoprotein A-I-containing phospholipid vesicles. By contrast, no significant difference in HDL3-induced cholesterol efflux was observed when plasma membrane was labeled with exogenous [14C]-cholesterol. We conclude that inefficient cholesterol efflux in Tangier disease is primarily caused by impaired HDL3-induced activation of cholesterol translocation from intracellular pools to the plasma membrane.

1,2-Dipalmitoylphosphatidylcholine↗

Postprandial hypertriglyceridaemia in patients with Tangier disease.

BACKGROUND: Tangier disease (TD) is the phenotypic expression of rare familial syndromes with mutations in the ABCA1 transporter. TD results in extremely low high density lipoprotein (HDL) cholesterol and reduced low density lipoprotein cholesterol, with normal or mildly increased fasting triglyceride (TG) concentrations. Although there is a close relation between HDL cholesterol values and atherogenesis, the risk of coronary artery disease is variable in TD. Raised fasting or postprandial TG values frequently accompany low HDL cholesterol and can add to the risk of a vascular event. AIMS: To investigate the postprandial TG response in TD. PATIENTS AND METHODS: Five patients (three homozygotes (HTD) and two heterozygotes (hTD)) from one family were studied. One was defined by DNA analysis as homozygous for a new mutation (C2033A) resulting in truncation of the ABCA1 protein. Their TG concentrations were measured before and four, six, and eight hours after a standardised fat load and compared with a control group. RESULTS: Two patients with HTD had high fasting TG concentrations. The third patient with HTD, the two with hTD, and the control group had TG concentrations within the reference range. The patients with HTD had increased postprandial peak TG values when compared with those with hTD and controls. CONCLUSION: Patients with HTD, with or without fasting hypertriglyceridaemia, may have an increased TG response to a fatty meal. The small number of patients does not allow definitive conclusions to be made. However, postprandial hypertriglyceridaemia could be a reason why some patients with TD develop premature atherosclerosis.

Adult↗

Novel mutations in the gene encoding ATP-binding cassette 1 in four tangier disease kindreds.

Tangier disease (TD) is an autosomal co-dominant disorder in which homozygotes have a marked deficiency of high density lipoprotein (HDL) cholesterol and, in some cases, peripheral neuropathy and premature coronary heart disease (CHD). Homozygotes are further characterized by cholesteryl ester deposition in various tissues throughout the body, most notably in those of the reticuloendothelial system. Several studies have demonstrated that the excess lipid deposition in TD is due to defective apolipoprotein-mediated efflux of cellular cholesterol and phospholipids. Although much progress has been made in our understanding of the metabolic basis of TD, the precise molecular defect had remained elusive until very recently. By positional cloning methods, we: 1) confirm the assignment of TD to chromosome 9q31, 2) provide evidence that human ATP-binding cassette-1 (hABC-1) maps to a 250 kb region on 9q31, and 3) describe novel deletion, insertion, and missense mutations in the gene encoding hABC-1 in four unrelated TD kindreds. These results establish a causal role for mutations in hABC-1 in TD and indicate that this transporter has a critical function in the regulation of intracellular lipid trafficking that dramatically affects plasma HDL cholesterol levels.

ATP-Binding Cassette Transporters↗

Accumulation of cardiolipin and lysocardiolipin in fibroblasts from Tangier disease subjects.

Tangier disease (TD) is an inherited disorder of lipid metabolism characterized by very low high density lipoprotein (HDL) plasma levels, cellular cholesteryl ester accumulation and reduced cholesterol excretion in response to HDL apolipoproteins. Molecular defects in the ATP binding cassette transporter 1 (ABCA1) have recently been identified as the cause of TD. ABCA1 plays a key role in the translocation of cholesterol across the plasma membrane, and defective ABCA1 causes cholesterol storage in TD cells. Not only cholesterol efflux, but also phospholipid efflux was shown to be impaired in TD cells. By use of thin layer chromatography, high performance liquid chromatography and time-of-flight secondary ion mass spectrometry, we characterized the cellular phospholipid content in fibroblasts from three homozygous TD patients. The cellular content of the major phospholipids was not found to be significantly altered in TD fibroblasts. However, the two phospholipids cardiolipin and lysocardiolipin, which make up minute amounts in normal cells, were at least 3-5-fold enriched in fibroblasts from TD subjects. A structurally closely related phospholipid (lysobisphosphatidic acid) has recently been shown to be enriched in Niemann-Pick type C, another lipid storage disorder. Altogether these data may indicate that the role of these phospholipids is a regulatory one rather than that of a bulk mediator of cholesterol solubilization in sterol trafficking and efflux.

ATP Binding Cassette Transporter 1↗