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.

Excessive uptake of atherogenic lipoproteins such as modified lowdensity lipoprotein complexes by vascular macrophages leads to foam cell formation, a critical step in atherogenesis. Cholesterol efflux mediated by high-density lipoproteins (HDL) constitutes a protective mechanism against macrophage lipid overloading. The molecular mechanisms underlying this reverse cholesterol transport process are currently not fully understood. To identify effector proteins that are involved in macrophage lipid uptake and release, we searched for genes that are regulated during lipid influx and efflux in human macrophages using a differential display approach. We report here that the ATP-binding cassette (ABC) transporter ABCG1 (ABC8) is induced in monocyte-derived macrophages during cholesterol influx mediated by acetylated low-density lipoprotein. Conversely, lipid efflux in cholesterol-laden macrophages, mediated by the cholesterol acceptor HDL 3, suppresses the expression of ABCG1. Immunocytochemical and flow cytometric analyses revealed that ABCG1 is expressed on the cell surface and in intracellular compartments of cholesterol-laden macrophages. Inhibition of ABCG1 protein expression using an antisense strategy resulted in reduced HDL 3-dependent efflux of cholesterol and choline-phospholipids. In a comprehensive analysis of the expression and regulation of all currently known human ABC transporters, we identified an additional set of ABC genes whose expression is regulated by cholesterol uptake or HDL 3-mediated lipid release, suggesting a potential function for these transporters in macrophage lipid homeostasis. Our results demonstrating a regulator function for ABCG1 in cholesterol and phospholipid transport define a biologic activity for ABC transporters in macrophages.

Mutations in the gene encoding ATP-binding cassette transporter 1 ( ABC1) have been reported in Tangier disease (TD), an autosomal recessive disorder that is characterized by almost complete absence of plasma high-density lipoprotein (HDL), deposition of cholesteryl esters in the reticulo-endothelial system (RES) and aberrant cellular lipid trafficking. We demonstrate here that mice with a targeted inactivation of Abc1 display morphologic abnormalities and perturbations in their lipoprotein metabolism concordant with TD. ABC1 is expressed on the plasma membrane and the Golgi complex, mediates apo-AI associated export of cholesterol and phospholipids from the cell, and is regulated by cholesterol flux. Structural and functional abnormalities in caveolar processing and the trans-Golgi secretory pathway of cells lacking functional ABC1 indicate that lipid export processes involving vesicular budding between the Golgi and the plasma membrane are severely disturbed.

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Recent data indicate that ceramide (Cer) and lysophosphatidylcholine (LPC) regulate immune cell functions. Since these bioactive lipids are generated in blood plasma by inflammatory lipases, we hypothesized that they may be involved in the process of acute systemic sepsis. In order to provide support for this hypothesis, we analyzed the plasma levels of Cer and LPC by quantitative tandem mass spectrometry in 102 sepsis patients starting with the day at which the sepsis criteria were fulfilled for the first time, as well as on day 4 and day 11. The values were compared with 56 healthy controls and correlated with sepsisrelated mortality within 30 days of study entry. Most Cer species were increased in sepsis patients, while all LPC species were markedly decreased. In addition, we determined the molar ratios with their precursor molecules sphingomyelin (SPM) and phosphatidylcholine (PC), which reflect the enzymatic reactions responsible for their formation. Species-specific as well as total Cer-SPM ratios were increased, whereas LPC-PC ratios were decreased in sepsis patients. The increased Cer-SPM ratios as well as the decreased LPC-PC ratios showed a strong predictive power for sepsis-related mortality. Together with existing data from in vitro experiments and animal models, the results provide the first ex vivo indication for the role of Cer and lysophospholipids in systemic inflammation in humans.

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The fatty acid transport protein family is a group of evolutionarily conserved proteins that are involved in the cellular uptake and metabolism of long and very long chain fatty acids. However, little is known about their respective physiological roles. To analyze the functional significance of fatty acid transport protein 4 (Fatp4, Slc27a4), we generated mice with a targeted disruption of the Fatp4 gene. Fatp4-null mice displayed features of a neonatally lethal restrictive dermopathy. Their skin was characterized by hyperproliferative hyperkeratosis with a disturbed epidermal barrier, a flat dermal–epidermal junction, a reduced number of pilo-sebaceous structures, and a compact dermis. The rigid skin consistency resulted in an altered body shape with facial dysmorphia, generalized joint flexion contractures, and impaired movement including suckling and breathing deficiencies. Lipid analysis demonstrated a disturbed fatty acid composition of epidermal ceramides, in particular a decrease in the C26:0 and C26:0-OH fatty acid substitutes. These findings reveal a previously unknown, essential function of Fatp4 in the formation of the epidermal barrier.

Abstract. Prevention of contrast agent-induced nephropathy is of crucial importance for a number of diagnostic studies. N-Acetylcysteine (NAC) was recently reported to decrease serum creatinine levels in this setting, and its administration before radiocontrast medium administration has been widely recommended. The objective of this prospective study was to investigate whether there are effects of NAC on serum creatinine levels that are independent of alterations in GFR. Volunteers with normal renal function who did not receive radiocontrast medium were studied. Fifty healthy volunteers completed the study protocol. NAC was administered orally at a dose of 600 mg every 12 h, for a total of four doses. Surrogate markers of renal function, such as serum creatinine, urea, albumin, and cystatin C levels, were measured and estimated GFR (eGFR) was assessed immediately before the administration of NAC and 4 and 48 h after the last dose. There was a significant decrease in the mean serum creatinine concentration (P Ͻ 0.05) and a significant increase in the eGFR (P Ͻ 0.02) 4 h after the last dose of NAC. The cystatin C concentrations did not change significantly. In several studies, a protective effect of NAC on renal function after radiocontrast medium administration has been postulated. This is the first study to demonstrate an effect of NAC on creatinine levels and eGFR, surrogate markers of renal injury, without any effect on cystatin C levels. Before renoprotective effects of NAC against contrast agent-induced nephropathy are considered, the direct effects of NAC on creatinine levels, urea levels, and eGFR should be assessed.Nephropathy and subsequent renal failure constitute a major concern when radiocontrast agents are administered to patients. With the use of radiocontrast agents in more then 10 million procedures annually in the United States, an incidence of radiocontrast agent-induced nephropathy of 0.5%, and mortality rates reported to be as high as 34% among those patients (1,2), the occurrence and prevention of adverse events have substantial medical and economic effects. Hydration of the patient and administration of N-acetylcysteine (NAC) are currently recommended to prevent renal injury (3). In studies to establish the protective effects of any given regimen, serum creatinine levels serve as a surrogate marker of GFR and changes are thought to reflect renal injury. However, any changes in serum creatinine levels that are not based on corresponding alterations of GFR should raise significant concerns regarding application of the model.A recent study suggested additive protective properties of NAC used in conjunction with hydration. Interestingly, that advantage was based on a decrease in serum creatinine concentrations among patients exposed to contrast agent plus NAC, whereas unchanged serum creatinine concentrations were observed after radiocontrast agent exposure among patients without NAC (3). This decrease in serum creatinine concentrations might reflect either an increase in creatinine excretion or...