Stealth Liposomes Encapsulating a Potent ACAT1/SOAT1 Inhibitor F12511: Pharmacokinetic, Biodistribution, and Toxicity Studies in Wild-Type Mice and Efficacy Studies in Triple Transgenic Alzheimer's Disease Mice

Cholesterol is essential for cellular function and is stored as cholesteryl esters (CEs). CEs biosynthesis is catalyzed by the enzymes acyl-CoA:cholesterol acyltransferase 1 and 2 (ACAT1 and ACAT2), with ACAT1 being the primary isoenzyme in most cells in humans. In Alzheimer's Disease, CEs accumulate in vulnerable brain regions. Therefore, ACATs may be promising targets for treating AD. F12511 is a high-affinity ACAT1 inhibitor that has passed phase 1 safety tests for antiatherosclerosis. Previously, we developed a nanoparticle system to encapsulate a large concentration of F12511 into a stealth liposome (DSPE-PEG2000 with phosphatidylcholine). Here, we injected the nanoparticle encapsulated F12511 (nanoparticle F) intravenously (IV) in wild-type mice and performed an HPLC/MS/MS analysis and ACAT enzyme activity measurement. The results demonstrated that F12511 was present within the mouse brain after a single IV but did not overaccumulate in the brain or other tissues after repeated IVs. A histological examination showed that F12511 did not cause overt neurological or systemic toxicity. We then showed that a 2-week IV delivery of nanoparticle F to aging 3xTg AD mice ameliorated amyloidopathy, reduced hyperphosphorylated tau and nonphosphorylated tau, and reduced neuroinflammation. This work lays the foundation for nanoparticle F to be used as a possible therapy for AD and other neurodegenerative diseases.

Acute ACAT1/SOAT1 Blockade Increases MAM Cholesterol and Strengthens ER-Mitochondria Connectivity

Cholesterol is a key component of all mammalian cell membranes. Disruptions in cholesterol metabolism have been observed in the context of various diseases, including neurodegenerative disorders such as Alzheimer's disease (AD). The genetic and pharmacological blockade of acyl-CoA:cholesterol acyltransferase 1/sterol O-acyltransferase 1 (ACAT1/SOAT1), a cholesterol storage enzyme found on the endoplasmic reticulum (ER) and enriched at the mitochondria-associated ER membrane (MAM), has been shown to reduce amyloid pathology and rescue cognitive deficits in mouse models of AD. Additionally, blocking ACAT1/SOAT1 activity stimulates autophagy and lysosomal biogenesis; however, the exact molecular connection between the ACAT1/SOAT1 blockade and these observed benefits remain unknown. Here, using biochemical fractionation techniques, we observe cholesterol accumulation at the MAM which leads to ACAT1/SOAT1 enrichment in this domain. MAM proteomics data suggests that ACAT1/SOAT1 inhibition strengthens the ER-mitochondria connection. Confocal and electron microscopy confirms that ACAT1/SOAT1 inhibition increases the number of ER-mitochondria contact sites and strengthens this connection by shortening the distance between these two organelles. This work demonstrates how directly manipulating local cholesterol levels at the MAM can alter inter-organellar contact sites and suggests that cholesterol buildup at the MAM is the impetus behind the therapeutic benefits of ACAT1/SOAT1 inhibition.

Blocking cholesterol storage to treat Alzheimer's disease

Cholesterol serves as an essential lipid molecule in various membrane organelles of mammalian cells. The metabolites of cholesterol also play important functions. Acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT1), also named as sterol O-acyltransferase 1, is a membrane-bound enzyme residing at the endoplasmic reticulum (ER). It converts cholesterol to cholesteryl esters (CEs) for storage, and is expressed in all cells. CEs cannot partition in membranes; they can only coalesce as cytosolic lipid droplets. Excess CEs are found in the vulnerable region of the brains of patients with late-onset Alzheimer's disease (AD), and in cell and mouse models for AD. Reducing CE contents by genetic inactivation of ACAT1, or by pharmacological inhibition of ACAT is shown to reduce amyloidopathy and other hallmarks for AD. To account for the various beneficial actions of the ACAT1 blockade (A1B), a working hypothesis is proposed here: the increase in CE contents observed in the AD brain is caused by damages of cholesterol-rich lipid rafts that are known to occur in neurons affected by AD. These damages cause cholesterol to release from lipid rafts and move to the ER where it will be converted to CEs by ACAT1. In addition, the increase in CE contents may also be caused by overloading with cholesterol-rich substances, or through activation of ACAT1 gene expression by various proinflammatory agents. Both scenarios may occur in microglia of the chronically inflamed brain. A1B ameliorates AD by diverting the cholesterol pool destined for CE biosynthesis such that it can be utilized more efficiently to repair membrane damage in various organelles, and to exert regulatory actions more effectively to defend against AD. To test the validity of the A1B hypothesis in cell culture and in vivo, the current status of various anti-ACAT1 agents that could be further developed is briefly discussed.

The epigenetic drug 5-azacytidine interferes with cholesterol and lipid metabolism

DNA methylation and histone acetylation inhibitors are widely used to study the role of epigenetic marks in the regulation of gene expression. In addition, several of these molecules are being tested in clinical trials or already in use in the clinic. Antimetabolites, such as the DNA-hypomethylating agent 5-azacytidine (5-AzaC), have been shown to lower malignant progression to acute myeloid leukemia and to prolong survival in patients with myelodysplastic syndromes. Here we examined the effects of DNA methylation inhibitors on the expression of lipid biosynthetic and uptake genes. Our data demonstrate that, independently of DNA methylation, 5-AzaC selectively and very potently reduces expression of key genes involved in cholesterol and lipid metabolism (e.g. PCSK9, HMGCR, and FASN) in all tested cell lines and in vivo in mouse liver. Treatment with 5-AzaC disturbed subcellular cholesterol homeostasis, thereby impeding activation of sterol regulatory element-binding proteins (key regulators of lipid metabolism). Through inhibition of UMP synthase, 5-AzaC also strongly induced expression of 1-acylglycerol-3-phosphate O-acyltransferase 9 (AGPAT9) and promoted triacylglycerol synthesis and cytosolic lipid droplet formation. Remarkably, complete reversal was obtained by the co-addition of either UMP or cytidine. Therefore, this study provides the first evidence that inhibition of the de novo pyrimidine synthesis by 5-AzaC disturbs cholesterol and lipid homeostasis, probably through the glycerolipid biosynthesis pathway, which may contribute mechanistically to its beneficial cytostatic properties.

The cytosolic adaptor AP-1A is essential for the trafficking and function of Niemann-Pick type C proteins

Niemann-Pick type C (NPC) disease is a fatal neurodegenerative disorder characterized by over-accumulation of low-density lipoprotein-derived cholesterol and glycosphingolipids in late endosomes/lysosomes (LE/L) throughout the body. Human mutations in either NPC1 or NPC2 genes have been directly associated with impaired cholesterol efflux from LE/L. Independent from its role in cholesterol homeostasis and its NPC2 partner, NPC1 was unexpectedly identified as a critical player controlling intracellular entry of filoviruses such as Ebola. In this study, a yeast three-hybrid system revealed that the NPC1 cytoplasmic tail directly interacts with the clathrin adaptor protein AP-1 via its acidic/di-leucine motif. Consequently, a nonfunctional AP-1A cytosolic complex resulted in a typical NPC-like phenotype mainly due to a direct impairment of NPC1 trafficking to LE/L and a partial secretion of NPC2. Furthermore, the mislocalization of NPC1 was not due to cholesterol accumulation in LE/L, as it was not rescued upon treatment with Mβ-cyclodextrin, which almost completely eliminated intracellular free cholesterol. Our cumulative data demonstrate that the cytosolic clathrin adaptor AP-1A is essential for the lysosomal targeting and function of NPC1 and NPC2.

The structure of acyl coenzyme A-cholesterol acyltransferase and its potential relevance to atherosclerosis

Acyl coenzyme A-cholesterol acyltransferase (ACAT) catalyzes the formation of intracellular cholesterol esters. It is present in a variety of tissues and is believed to play significant roles in cholesterol homeostasis. Under pathologic conditions, accumulation of the ACAT reaction product as cytoplasmic cholesterol ester lipid droplets within macrophages and smooth muscle cells is a characteristic feature of early lesions of human atherosclerotic plaques. ACAT is a membrane protein located in the endoplasmic reticulum. Its activity is susceptible to inactivation by detergents, and it has never been purified to homogeneity; no antibodies directed against it have been reported. Through a somatic cell and molecular genetic approach, we have recently succeeded in molecular cloning and functional expression of a human macrophage ACAT cDNA. This cDNA contains an open reading frame of 1650 base pairs encoding an integral membrane protein of 550 amino acids. Protein homology analysis shows that the predicted protein sequence shares short regions of homology with other enzymes involved in the catalysis of acyl adenylate formation with subsequent acyl thioester formation and acyl transfer. The ACAT cDNA will enable the investigation of ACAT biochemistry and molecular biology. It will speed up the design of specific ACAT inhibitors as drugs that may provide more effective therapeutic treatment or prevention of atherosclerosis. In addition, studies on the physiologic roles of ACAT in various tissues can now be undertaken through transgenic animal research.

Occurrence and Molecular Characterization of Three Pineapple Mealybug Wilt-Associated Viruses in Pineapple in Taiwan

Pineapple (Ananas comosus) is one of the major fruit crops in Taiwan, accounting for 275 million U.S. dollars in 2006, following betel nut and citrus production in crop value. Tainung No. 17 is the most important cultivar, accounting for more than 70% of pineapples planted. Mealybug wilt of pineapple (MWP) is one of the most destructive diseases of pineapple. Pineapple mealybug wilt-associated virus-1 (PMWaV-1), PMWaV-2, and PMWaV-3 were identified as three distinct species in Ampelovirus from diseased Hawaiian pineapple (1,2). In November of 2007, pineapples (cv. Tainung No. 17) planted in Pingtung County of southern Taiwan showed symptoms similar to MWP. Mealybugs (Dysmicoccus brevipes) were also found. Three primer pairs, 225/226, 223/224, and 263/264 described previously specific for the HSP70h genes of PMWaV-1 (1), -2, and -3 (2), respectively, were used to detect the presence of these three viruses by reverse transcription (RT)-PCR. Expected DNA fragments of 590, 610, and 499 nt were obtained from the total RNA isolated from the leaves of diseased pineapples with primer pairs 225/226, 223/224, and 263/264, respectively. The RT-PCR amplified fragments were cloned, sequenced, and analyzed. The 590-nt fragment (Accession No. EU769113) shared 91.6 to 99.5% nucleotide and 96.8 to 99.5% amino acid identity to those of five isolates of PMWaV-1 available in the GenBank; one each from Hawaii (Accession No. AF414119) and Thailand (Accession No. EF620774) and three from Australia (Accession Nos. EF488752, EF467923, and EF467925). The 610-nt fragment (Accession No. EU769115) showed 98.7 and 99.7% nucleotide and 98% and 100% amino acid identity to those of PMWaV-2 from Hawaii (Accession No. AF283103) and Thailand (Accession No. EU016675), respectively. The 499-nt fragment (Accession No. FJ209047) shared 86.8 to 99.0% nucleotide and 94.0 to 100.0% amino acid identity to those of five PMWaV-3 isolates available in the GenBank; one from Hawaii (Accession No. DQ399259) and four from Australia (Accession Nos. EF467918, EF467919, EF488754, and EF488755). Using primer pairs FJ08-1 (5'-ATGGCTGATTCGAGC)/FJ08-2 (5'-TTATTTGCGTCCACC), FJ08-7 (5'-AGTGAGATTGATCGT)/FJ08-8 (5'-TGCAGGTATCCGCTG), and FJ08-35 (5'-AACGACCGAACTCGC)/FJ08-36 (5'-ATACTACAGATATTG) specific to the coat protein (CP) genes of PMWaV-1, -2, and -3, respectively, expected DNA fragments of 774, 909, and 789 nt were amplified by RT-PCR. The 774-nt CP gene of PMWaV-1 (Accession No. EU769114) shared 99% nucleotide and 98.4% amino acid identity to those of Hawaiian isolate (Accession No. AF414119). The 909-nt CP gene of PMWaV-2 (Accession No. EU769116) shared 99.0 and 99.1% nucleotide identity with isolates from Hawaii (Accession No. AF283103) and Cuba (Accession No. DQ225114), respectively, and 99.3% amino acid identity with both. The 789-nt CP gene of PMWaV-3 (Accession No. FJ209048) shared 99.1% nucleotide and 98.1% amino acid identity to those of the Hawaiian isolate (Accession No. DQ399259). One to two viruses among PMWaV-1, -2, and -3 were detected in all 40 samples collected from diseased pineapples. To our knowledge, this is the first report to identify three PMWaVs in the most important and widely planted pineapple cultivar in Taiwan, Tainung No. 17, by molecular characterization of the HSP70h and CP genes. References: (1) D. M. Sether et al. Plant Dis. 85:856, 2001. (2) D. M. Sether et al. Plant Dis. 89:450, 2005.

Partial blockage of sterol biosynthesis with a squalene synthase inhibitor in early postnatal Niemann-Pick type C npcnih null mice brains reduces neuronal cholesterol accumulation, abrogates astrogliosis, but may inhibit myelin maturation

Niemann-Pick C disease (NPC) is a fatal, neurovisceral genetic disorder. Cell culture studies showed that NPC1 or NPC2 mutations cause malfunctions in cellular cholesterol trafficking and lead to accumulation of cholesterol and other lipids in the late endo/lysosomes. Previous work showed that neuronal cholesterol accumulation occurs in the brains of young postnatal NPC1-/- mice. Here, to evaluate the potential of partial blockage of cholesterol biosynthesis as a therapy for the NPC disease, we first developed a simple method to monitor the relative rates of lipid biosynthesis in mice brains. We next administered squalene synthase inhibitor (SSI) CP-340868 to young mice. The results show that treating 8-day-old NPC1-/- mice with CP-340868 for 6 days significantly inhibits cholesterol biosynthesis in the mice brains. It reduces neuronal cholesterol accumulation, reduces GM3 ganglioside accumulation, and diminishes astrogliosis in the brain. These results suggest that neuronal cholesterol accumulation contributes to early pathogenesis in the NPC1-/- mice brains. The SSI treatment also reduced brain galactolipid content, suggesting that blocking endogenous cholesterol synthesis in the young mice brains may disrupt the normal myelin maturation processes. The methods described in the current work have general applicability for lipid metabolism studies in mice brains in various pathophysiological conditions.

Waveguide couplers with new power splitting ratios made possible by cascading of short multimode interference sections

We show that it is possible to obtain 2 x 2 waveguide couplers with new power splitting ratios for cross coupling of 7%, 64%, 80% and 93% by cascading two short MMI sections. These couplers have simple geometry and low loss. They offer valuable new possibilities for designing waveguide power taps, high-Q ring resonators, ladder-structure optical filters, and loop-mirror partial reflectors.

Second-trimester diagnosis of limb-body wall complex with literature review of pathogenesis

Three fetuses having limb-body wall complex (LBWC) with craniofacial defects and 9 fetuses having LBWC without craniofacial defects were diagnosed and delivered in the second trimester at Mackay Memorial Hospital during the period January 1990 - May 2006. Cases of LBWC with craniofacial defects showed severe anomalies of the upper limbs, craniofacial defects, constrictive amniotic bands and cranioplacental attachment, whereas, cases of LBWC without craniofacial defects presented major anomalies of the lower limbs, abnormal genitalia, anal atresia, renal defects, abdominoplacental attachment and umbilical cord abnormalities. The perinatal findings of LBWC with or without craniofacial defects were compared and the pathogenesis was discussed.

Adenovirus expressing an NPC1-GFP fusion gene corrects neuronal and nonneuronal defects associated with Niemann pick type C disease

Niemann Pick type C (NPC) disease is an autosomal recessive disorder characterized by abnormal cholesterol metabolism and accumulation in lysosomal and endosomal compartments. Although peripheral organs are affected, the progressive neurodegeneration in the brain is typically most deleterious, leading to dystonia, ataxia, seizures, and premature death. Although the two genes underlying this disorder in humans and mouse models of the disease have been identified (NPC1 in 95% and NPC2/HE1 in 5% of human cases), their cellular roles have not Been fully defined, and there is currently no effective treatment for this disorder. To help address these issues, we constructed a recombinant adenovirus, Ad(NPC1-GFP), which contains a cDNA encoding a mouse NPC1 protein with a green fluorescent protein (GFP) fused to its C-terminus. Fluorescence microscopy and cholesterol trafficking assays demonstrate that the GFP-tagged NPC1 protein is functional and detectable in cells from different species (hamster, mouse, human) and of different types (ovary-derived cells, fibroblasts, astrocytes, neurons from peripheral and central nervous systems) in vitro. Combined with results from time-lapse microscopy and in vivo brain injections, our findings suggest that this adenovirus offers advantages for expressing NPC1 and analyzing its cellular localization, movement, functional properties, and beneficial effects in vitro and in vivo.

Enhancement of human ACAT1 gene expression to promote the macrophage-derived foam cell formation by dexamethasone

In macrophages, the accumulation of cholesteryl esters synthesized by the activated acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT1) results in the foam cell formation, a hallmark of early atherosclerotic lesions. In this study, with the treatment of a glucocorticoid hormone dexamethasone (Dex), lipid staining results clearly showed the large accumulation of lipid droplets containing cholesteryl esters in THP-1-derived macrophages exposed to lower concentration of the oxidized low-density lipoprotein (ox-LDL). More notably, when treated together with specific anti-ACAT inhibitors, the abundant cholesteryl ester accumulation was markedly diminished in THP-1-derived macrophages, confirming that ACAT is the key enzyme responsible for intracellular cholesteryl ester synthesis. RT-PCR and Western blot results indicated that Dex caused up-regulation of human ACAT1 expression at both the mRNA and protein levels in THP-1 and THP-1-derived macrophages. The luciferase activity assay demonstrated that Dex could enhance the activity of human ACAT1 gene P1 promoter, a major factor leading to the ACAT1 activation, in a cell-specific manner. Further experimental evidences showed that a glucocorticoid response element (GRE) located within human ACAT1 gene P1 promoter to response to the elevation of human ACAT1 gene expression by Dex could be functionally bound with glucocorticoid receptor (GR) proteins. These data supported the hypothesis that the clinical treatment with Dex, which increased the incidence of atherosclerosis, may in part due to enhancing the ACAT1 expression to promote the accumulation of cholesteryl esters during the macrophage-derived foam cell formation, an early stage of atherosclerosis.

Plasma membrane cholesterol: a possible barrier to intracellular oxygen in normal and mutant CHO cells defective in cholesterol metabolism

The effect of the cholesterol content of the plasma membrane on the intracellular concentration of oxygen in Chinese hamster ovary (CHO) cells and their mutants was investigated by EPR oximetry. Total and free cholesterol content was significantly higher in 25 RA CHO cells as compared to wild-type and M 19 CHO cells, with most of the free cholesterol in normal and mutant CHO cells located in the plasma membrane. The plasma membrane cholesterol content also was altered by various biochemical means, and the effect on the oxygen gradient was studied. Comparing the three cell lines, the gradient was larger with increased content of cholesterol in the plasma cell membrane. This result also is supported by an additional increase in the oxygen gradients with the incorporation of additional cholesterol in the plasma membrane and a decrease in the oxygen gradient when the cholesterol was depleted from the plasma membrane. The results indicate that the concentration of cholesterol in the plasma membrane can be an important factor for the magnitude of the oxygen gradient observed across the cell membrane.

Three-generation reproductive toxicity study of dietary bisphenol A in CD Sprague-Dawley rats

Bisphenol A (BPA) was evaluated at concentrations of 0, 0.015, 0.3, 4.5, 75, 750, and 7500 ppm ( approximately 0.001, 0.02, 0.3, 5, 50, and 500 mg/kg/day of BPA) administered in the diet ad libitum to 30 CD((R)) Sprague-Dawley rats/sex/dose for 3 offspring generations, 1 litter/generation, through F3 adults. Adult systemic toxicity at 750 and 7500 ppm in all generations included: reduced body weights and body weight gains, reduced absolute and increased relative weanling and adult organ weights (liver, kidneys, adrenals, spleen, pituitary, and brain), and female slight/mild renal and hepatic pathology at 7500 ppm. Reproductive organ histopathology and function were unaffected. Ovarian weights as well as total pups and live pups/litter on postnatal day (PND) 0 were decreased at 7500 ppm, which exceeded the adult maximum tolerated dose (MTD). Mating, fertility, gestational indices; ovarian primordial follicle counts; estrous cyclicity; precoital interval; gestational length; offspring sex ratios; postnatal survival; nipple/areolae retention in preweanling males; epididymal sperm number, motility, morphology; daily sperm production (DSP), and efficiency of DSP were all unaffected. At 7500 ppm, vaginal patency (VP) and preputial separation (PPS) were delayed in F1, F2, and F3 offspring, associated with reduced body weights. Anogenital distance (AGD) on PND 0 was unaffected for F2 and F3 males and F3 females (F2 female AGD was increased at some doses, not at 7500 ppm, and was considered not biologically or toxicologically relevant). Adult systemic no observed adverse effect level (NOAEL) = 75 ppm (5 mg/kg/day); reproductive and postnatal NOAELs = 750 ppm (50 mg/kg/day). There were no treatment-related effects in the low-dose region (0.001-5 mg/kg/day) on any parameters and no evidence of nonmonotonic dose-response curves across generations for either sex. BPA should not be considered a selective reproductive toxicant, based on the results of this study.

Mutations in the midway gene disrupt a Drosophila acyl coenzyme A: diacylglycerol acyltransferase

During Drosophila oogenesis, defective or unwanted egg chambers are eliminated during mid-oogenesis by programmed cell death. In addition, final cytoplasm transport from nurse cells to the oocyte depends upon apoptosis of the nurse cells. To study the regulation of germline apoptosis, we analyzed the midway mutant, in which egg chambers undergo premature nurse cell death and degeneration. The midway gene encodes a protein similar to mammalian acyl coenzyme A: diacylglycerol acyltransferase (DGAT), which converts diacylglycerol (DAG) into triacylglycerol (TAG). midway mutant egg chambers contain severely reduced levels of neutral lipids in the germline. Expression of midway in insect cells results in high levels of DGAT activity in vitro. These results show that midway encodes a functional DGAT and that changes in acylglycerol lipid metabolism disrupt normal egg chamber development in Drosophila.

Cloning and functional expression of the mucrosobin protein, a beta-fibrinogenase of Trimeresurus mucrosquamatus (Taiwan Habu)

A venom-specific cDNA encoding for a thrombin-like enzyme designated as mucrosobin has been cloned and sequenced from the cDNA library of the venomous gland of Trimeresurus mucrosquamatus. The full-length cDNA of mucrosobin was assembled by oligonucleotide screening and 5'-rapid amplification of cDNA ends. The amino acid sequence deduced from the cDNA consists of 257 amino acid residues with a putative signal peptide of 24 residues. It is highly homologous to the other thrombin-like enzymes (batroxobin, mucofirase, and calobin), suggesting that it is a serine proteinase with a conserved catalytic triad of His(41), Asp(84) and Ser(179) in the deduced form of mucrosobin protein. Northern blot analysis revealed that the mucrosobin gene encodes an mRNA of 1.5 kb and suggested a tissue-specific expression in the venomous gland. In an effort to study the biological property of mocrosobin, we have expressed the 28-kDa protein as inclusion bodies in Escherichia coli. For analyzing enzymatic activity, the inclusion bodies were solubilized and the recombinant protein was refolded with a two-step dialysis protocol. The refolded recombinant protein exhibited a specific beta-fibrinogenolytic activity. This study offers a possibility of using genetic engineering to acquire a functional snake venom protein with therapeutic potential.

Catalysis of ACAT may be completed within the plane of the membrane: a working hypothesis

Two ACAT sharing protein sequence homology near their C termini have been identified. Both proteins may span the endoplasmic reticulum (ER) membrane several times. There is good evidence implicating the role of ACAT1 in macrophage foam cell formation, and ACAT2 in intestinal cholesterol absorption. On the other hand, the functional roles of ACAT1 and ACAT2 in the VLDL or chylomicron assembly process are less clear. It is possible that both enzymes are able to form lipid droplets (which are present in the cytoplasm), and participate in lipoprotein assembly (which occurs in the ER lumen). To link the site of ACAT catalysis with its function, we propose that part of the ACAT catalytic site may reside within the lipid bilayer, allowing catalysis to be completed within the plane of the membrane. Cholesteryl esters (CE) produced in situ may burst into cytoplasmic lipid droplets, carrying phospholipid monolayers as their outer coats. In cells engaged in lipoprotein assembly and secretion, CE in the bilayer may be recognized by the specific protein microsomal triacylglycerol transfer protein (MTP), reaching out from the lumenal side of the membrane. MTP then lipidates the growing apolipoprotein B (apoB) chain with CE and TG during the early stages of apoB lipoprotein assembly.

Stepwise logistic regression analysis of tumor contour features for breast ultrasound diagnosis

To assist the ultrasound (US) differential diagnosis of solid breast tumors by using stepwise logistic regression (SLR) analysis of tumor contour features, we retrospectively reviewed 111 medical records of digitized US images of breast pathologies. They were pathologically proved benign breast tumors from 40 patients (i.e., 40 fibroadenomas) and malignant breast tumors from 71 patients (i.e., 71 infiltrative ductal carcinomas). Radiologists, before analysis by the computer-aided diagnosis (CAD) system, segmented the tumors manually. The contour features were calculated by measuring the radial length of tumor boundaries. The features selection process was accomplished using a stepwise analysis procedure. Then, an SLR model with contour features was used to classify tumors as benign or malignant. In this experiment, cases were sampled with "leave-one-out" test methods to evaluate the SLR performance using a receiver operating characteristic (ROC) curve. The accuracy of our SLR model with contour features for classifying malignancies was 91.0% (101 of 111 tumors), the sensitivity was 97.2% (69 of 71), the specificity was 80.0% (32 of 40), the positive predictive value was 89.6% (69 of 77), and the negative predictive value was 94.1% (32 of 34). The CAD system using SLR can differentiate solid breast nodules with relatively high accuracy and its high negative predictive value could potentially help inexperienced operators to avoid misdiagnoses. Because the SLR model is trainable, it could be optimized if a larger set of tumor images were supplied.

Acyl-coenzyme A: cholesterol acyltransferase modulates the generation of the amyloid beta-peptide

The pathogenic event common to all forms of Alzheimer's disease is the abnormal accumulation of the amyloid beta-peptide (Abeta). Here we provide strong evidence that intracellular cholesterol compartmentation modulates the generation of Abeta. Using genetic, biochemical and metabolic approaches, we found that cholesteryl-ester levels are directly correlated with Abeta production. Acyl-coenzyme A:cholesterol acyltransferase (ACAT), the enzyme that catalyses the formation of cholesteryl esters, modulates the generation of Abeta through the tight control of the equilibrium between free cholesterol and cholesteryl esters. We also show that pharmacological inhibitors of ACAT, developed for the treatment of atherosclerosis, are potent modulators of Abeta generation, indicating their potential for use in the treatment of Alzheimer's disease.

Existence of hepatitis C virus in Culex quinquefasciatus after ingestion of infected blood: experimental approach to evaluating transmission by mosquitoes

We used PCR to detect hepatitis C virus (HCV) RNA among supernatants of ground Culex quinquefasciatus mosquitoes that (i) had been fed HCV-positive blood, (ii) had been intrathoracically inoculated with HCV-positive blood, or (iii) were from homes of hepatitis C patients. HCV RNA was detectable under all three conditions, but it did not replicate in mosquitoes and was not detectably transmitted during feeding.

Synthetic peptide-based vaccine and diagnostic system for effective control of FMD

We have designed synthetic peptides corresponding to two different regions of the genome of foot-and-mouth disease virus (FMDV) that are effective as (a) a vaccine or (b) a diagnostic reagent which differentiates convalescent from vaccinated animals, respectively. The peptide vaccine is based on a sequence from the prominent G-H loop of VP1, one of the four capsid proteins. The sequence was optimized by the inclusion of a cyclic constraint and adjoining sequences, and broader immunogenicity was obtained by the incorporation of consensus residues at hypervariable positions. The peptide also included a promiscuous T-helper epitope for effective immunogenicity in outbred populations of large animals.The diagnostic reagent, a peptide based on non-structural (NS) protein 3B, is used in immuno-assays for the detection of antibodies. Antibodies to this NS protein are present in the sera of infected animals but not in the sera of vaccinated animals. The VP1 peptide can be used in complementary immuno-assays for confirmation of NS test results and to monitor for vaccination. This system for differential diagnosis is important to establish the disease-free status of a country.

Prenatal diagnosis of partial monosomy 18p(18p11.2-->pter) and trisomy 21q(21q22.3-->qter) with alobar holoprosencephaly and premaxillary agenesis

A prenatal diagnosis of partial monosomy 18p(18p11.2-->pter) and trisomy 21q(21q22.3-->qter) in a fetus with alobar holoprosencephaly (HPE) and premaxillary agenesis (PMA) but without the classical Down syndrome phenotype is reported. A 27-year-old primigravida woman was referred for genetic counselling at 21 weeks' gestation due to sonographic findings of craniofacial abnormalities. Level II ultrasonograms manifested alobar HPE and median orofacial cleft. Cytogenetic analysis and fluorescence in situ hybridization (FISH) on cells obtained from amniocentesis revealed partial monosomy 18p and a cryptic duplication of 21q,46,XY,der(18)t(18;21)(p11.2;q22.3), resulting from a maternal t(18;21) reciprocal translocation. The breakpoints were ascertained by molecular genetic analysis. The pregnancy was terminated. Autopsy showed alobar HPE with PMA, pituitary dysplasia, clinodactyly and classical 18p deletion phenotype but without the presence of major typical phenotypic features of Down syndrome. The phenotype of this antenatally diagnosed case is compared with those observed in six previously reported cases with monosomy 18p due to 18;21 translocation. The present study is the first report of concomitant deletion of HPE critical region of chromosome 18p11.3 and cryptic duplication of a small segment of distal chromosome 21q22.3 outside Down syndrome critical region. The present study shows that cytogenetic analyses are important in detecting chromosomal aberrations in pregnancies with prenatally detected craniofacial abnormalities, and adjunctive molecular investigations are useful in elucidating the genetic pathogenesis of dysmorphism.

Synergistic transcriptional activation of human Acyl-coenzyme A: cholesterol acyltransterase-1 gene by interferon-gamma and all-trans-retinoic acid THP-1 cells

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme involved in cellular cholesterol homeostasis and in atherosclerotic foam cell formation. Human ACAT-1 gene contains two promoters (P1 and P7), each located in a different chromosome (1 and 7) (Li, B. L., Li, X. L., Duan, Z. J., Lee, O., Lin, S., Ma, Z. M., Chang, C. C., Yang, X. Y., Park, J. P., Mohandas, T. K., Noll, W., Chan, L., and Chang, T. Y. (1999) J. Biol Chem. 274, 11060-11071). Interferon-gamma (IFN-gamma), a cytokine that exerts many pro-atherosclerotic effects in vivo, causes up-regulation of ACAT-1 mRNA in human blood monocyte-derived macrophages and macrophage-like cells but not in other cell types. To examine the molecular nature of this observation, we identified within the ACAT-1 P1 promoter a 159-base pair core region. This region contains 4 Sp1 elements and an IFN-gamma activated sequence (GAS) that overlaps with the second Sp1 element. In the monocytic cell line THP-1 cell, the combination of IFN-gamma and all-trans-retinoic acid (a known differentiation agent) enhances the ACAT-1 P1 promoter but not the P7 promoter. Additional experiments showed that all-trans-retinoic acid causes large induction of the transcription factor STAT1, while IFN-gamma causes activation of STAT1 such that it binds to the GAS/Sp1 site in the ACAT-1 P1 promoter. Our work provides a molecular mechanism to account for the effect of IFN-gamma in causing transcriptional activation of ACAT-1 in macrophage-like cells.

Recombinant expression and characterization of the Candida rugosa lip4 lipase in Pichia pastoris: comparison of glycosylation, activity, and stability

Although Candida rugosa utilizes a nonuniversal serine codon (CUG) for leucine, it is possible to express lipase genes (LIP) in heterologous systems. After replacing the 19 CUG codons in LIP4 with serine codons by site-directed mutagenesis, a recombinant LIP4 was functionally overexpressed in Pichia pastoris in this study. This recombinant glycosylated lipase was secreted into the culture medium with a high purity of 100 mg/liter in a culture broth. Purified recombinant LIP4 had a molecular mass of 60 kDa, showing a range similar to that of lipase in a commercial preparation. Since LIP4 has only a glycosylation site at position Asn-351, this position may also be the major glycosylation site in C. rugosa lipases. Although the thermal stability of recombinant LIP4 significantly increased from 52 to 58 degrees C after glycosylation, there were no significant differences in the catalytic properties of recombinant glycosylated lipase from P. pastoris and the unglycosylated one from Escherichia coil. These two recombinant LIP4s showed higher esterase activities toward long-chain ester (C16 and C18) and exhibited higher lipase activities toward unsaturated and long-chain lipids. In addition, LIP4 does not show interfacial activation as compared with LIP1 toward lipid substrates of tributyrin and triolein. These observations demonstrated that LIP4 shows distinguished catalytic activities with LIP1 in spite of their high sequence homology.

Roles of acyl-coenzyme A:cholesterol acyltransferase-1 and -2

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that produces cholesteryl esters in various tissues. In mammals, two ACAT genes (ACAT1 and ACAT2) have been identified. Together, these two enzymes are involved in storing cholesteryl esters as lipid droplets, in macrophage foam-cell formation, in absorbing dietary cholesterol, and in supplying cholesteryl esters as part of the core lipid for lipoprotein synthesis and assembly. The key difference in tissue distribution of ACAT1 and ACAT2 between humans, mice and monkeys is that, in adult human liver (including hepatocytes and bile duct cells), the major enzyme is ACAT1, rather than ACAT2. There is compelling evidence implicating a role for ACAT1 in macrophage foam-cell formation, and for ACAT2 in intestinal cholesterol absorption. However, further studies at the biochemical and cell biological levels are needed in order to clarify the functional roles of ACAT1 and ACAT2 in the VLDL or chylomicron synthesis/assembly process.

Prenatal diagnosis of de novo distal 11q deletion associated with sonographic findings of unilateral duplex renal system, pyelectasis and orofacial clefts

In utero diagnosis of de novo distal 11q deletion associated with renal and orofacial malformations has not been previously described. We present a 35-year-old pregnant woman with prenatal sonographic findings of a unilateral duplex renal system, pyelectasis and orofacial clefts at 20 weeks' gestation. Both genetic amniocentesis and postnatal cytogenetic analysis revealed de novo 46,XX,del(11)(q23). After birth, the fetus manifested a dysmorphic phenotype correlated with del(11q) syndrome. Genetic marker analysis showed a paternally derived distal deletion of chromosome 11q and a breakpoint centromeric to D11S1341. The present case represents the earliest prenatal diagnosis of a duplex renal system, pyelectasis and an additional feature of orofacial clefts associated with distal 11q deletion. Prenatal sonographic detection of a duplex renal system, pyelectasis and orofacial clefts should warrant a careful assessment of fetal anatomy and prompt cytogenetic analysis looking for chromosomal aberrations.

Organization of human ACAT-2 gene and its cell-type-specific promoter activity

Acyl-CoA:cholesterol acyltransferase (ACAT) plays important roles in cellular cholesterol homeostasis. Two ACAT genes exist in mammals. We report here the genomic organization of human ACAT-2 gene and analysis of its promoter activity in various cell lines. The human ACAT-2 gene spans over 18 kb and contains 15 exons. Three transcription start sites and one poly(A) site are identified by the 5'/3'-RACE. In addition, the human ACAT-2 gene is linked to the insulin-like growth factor binding protein 6 (IGFBP-6) gene in a head-to-tail manner with a small intergenic region of about 1.2 kb. The 5'-flanking region of human ACAT-2 gene contains many potential cis-acting elements for multiple transcriptional regulatory factors but lacks TATA and CCAAT boxes. Using promoter-luciferase reporter assays, we demonstrate the transcriptional activity of ACAT-2 gene promoter is high in Caco-2 cells, especially after these cells become postconfluent and behave as intestinal enterocytes.

Accumulation and aggregation of amyloid beta-protein in late endosomes of Niemann-pick type C cells

There is growing evidence suggesting that cholesterol metabolism is linked to susceptibility to Alzheimer's disease by influencing amyloid beta-protein (Abeta) metabolism. However, the precise cellular linkage sites between cholesterol and Abeta have not yet been clarified. To address this issue, we investigated Niemann-Pick type C (NPC) model cells and NPC mutant cells, which showed aberrant cholesterol trafficking. We observed a remarkable Abeta accumulation in late endosomes of both NPC model cells and mutant cells where cholesterol accumulates and a significant accumulation in the NPC mouse brain. This Abeta accumulation was independent of its constitutive secretion and production through an endocytic pathway. In addition, it is characterized by a marked predominance of Abeta42 and insolubility in SDS, suggesting the presence of aggregated Abeta in late endosomes. Most importantly, Abeta accumulation is coupled with the cholesterol levels in late endosomes. Thus, late endosomes of NPC cells are a novel pool of aggregated Abeta42 as well as cholesterol, suggesting a direct interaction between aggregated Abeta and cholesterol.

Prenatal diagnosis and genetic analysis of type I and type II thanatophoric dysplasia

Thanatophoric dysplasia (TD) is one of the most common neonatal lethal skeletal dysplasias. Prenatal sonographic and molecular genetic diagnoses of three cases of TD type I (TD1) and one case of TD type II (TD2) are presented here. Two fetuses of TD1 were characterized by polyhydramnios, macrocephaly, short limbs, a narrow thoracic cage and curved short femora, but without a cloverleaf skull at 27 and 31 weeks' gestation, respectively. The third fetus with TD1 was, however, not associated with macrocephaly, polyhydramnios, chest narrowing and severe femoral bowing on prenatal ultrasound at 18 weeks' gestation. The TD2 fetus was characterized by polyhydramnios, short limbs, a narrow thoracic cage, straight short femora, hydrocephalus and a cloverleaf skull at 24 weeks' gestation. Three-dimensional ultrasound was able to enhance the visualization of thickened, redundant skin folds and craniofacial and limb deformities associated with TD. Molecular analysis of the fibroblast growth factor receptor 3 (FGFR3) gene by restriction enzyme digestion analysis and direct sequencing using cultured amniotic fluid cells or cord blood cells revealed a missense mutation of 742C-->T (Arg248Cys) in all cases with TD1 and a missense mutation of 1948A-->G (Lys650Glu) in the case with TD2. The present report shows that adjunctive applications of molecular genetic analysis of the FGFR3 gene and three-dimensional ultrasound are useful for prenatal diagnosis of TD.

Induction of acyl-coenzyme A:cholesterol acyltransferase-1 by 1,25-dihydroxyvitamin D(3) or 9-cis-retinoic acid in undifferentiated THP-1 cells

We have previously shown that acyl-coenzyme A: cholesterol acyltransferase-1 (ACAT-1) protein content increases significantly during the human monocyte-macrophage differentiation process. To gain further insight, we used undifferentiated human monocytic THP-1 cells as a model system with which to examine whether ACAT-1 mRNA and protein content can be increased by treating cells with 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] or with 9-cis-retinoic acid (9-cis-RA), two agents known to upregulate the expression of various genes during the monocyte-macrophage differentiation process. Immunoblot analysis with anti-human ACAT-1 antibodies revealed that ACAT-1 protein was increased by 2.6-fold, using 1,25-(OH)(2)D(3) at a physiological concentration (100 pM). ACAT-1 protein was also increased when using 9-cis-RA, but only at relatively high concentrations (0.1;-1 microM). Northern blot analysis revealed that among the four ACAT-1 mRNA transcripts (2.8, 3.6, 4.2, and 7.0 kb) examined, only the 2.8- and 3.6-kb transcripts were selectively increased. On the basis of enzyme assays in vitro, ACAT activity was increased 3.0-fold by using 100 nM 1,25-(OH)(2)D(3), and 1.8-fold by using 1 microM 9-cis-RA. Together, our results suggest that 1,25-(OH)(3) participates in ACAT-1 gene expression during the monocyte-macrophage differentiation process.

Isolation of an IgG anti-B from a human Fab-phage display library

BACKGROUND

ABO incompatibility is a common cause for mild hemolysis in the newborn, ranging from 1 in 30 to 1 in 150 births. Fortunately, hemolysis requiring transfusion is rare and restricted to blood group O mothers, because blood group A and B individuals make poor IgG anti-B and anti-A responses. No human IgG ABO antibody sequences have been reported, in part because of the difficulty in obtaining human IgG hybridomas. Phage-display technology may be able to circumvent these difficulties, but its application to carbohydrate antigens is poorly studied.

STUDY DESIGN AND METHODS

A human IgG1 phage-display Fab library was constructed from splenocytes derived from a nonhyperimmunized blood group O person, and panned against group B RBCs.

RESULTS

After five rounds of panning, essentially all phage bound to group B RBCs. Nucleotide sequence analysis of a single monoclonal IgG1lambda phage, FB5.7, revealed a highly mutated VH4 family heavy chain, and a nearly germline VL7 family lambda light chain. The Fab agglutinated group B, but not group A, random-donor RBCs. However, group B ELISA reactivity could be inhibited by soluble B-trisaccharide, soluble A-trisaccharide, galactose, and N-acetyl galactosamine. Similarly, galactose and N-acetyl galactosamine were able to inhibit group B RBC agglutination.

CONCLUSION

FB5.7 is the first human IgG ABO MoAb described. Alhough it behaves serologically like a group B-specific antibody, it demonstrates interaction with both the A and B epitopes. Phage-display technology can be used to better define the relationship between antibody genotype and phenotype in anti-carbohydrate responses in nonhyperimmunized hosts, and thus to improve our understanding of the composition of the antibody repertoire.

Fate of endogenously synthesized cholesterol in Niemann-Pick type C1 cells

Mammalian cells obtain cholesterol via two pathways: endogenous synthesis in the endoplasmic reticulum and exogenous sources mainly through the low density lipoprotein (LDL) receptor pathway. We performed pulse-chase experiments to monitor the fate of endogenously synthesized cholesterol and showed that, after reaching the plasma membrane from the endoplasmic reticulum, the newly synthesized cholesterol eventually accumulates in an internal compartment in Niemann-Pick type C1 (NPC1) cells. Thus, the ultimate fate of endogenously synthesized cholesterol in NPC1 cells is the same as LDL-derived cholesterol. However, the time required for endogenous cholesterol to accumulate internally is much slower than LDL-derived cholesterol. Different pathways thus govern the post-plasma membrane trafficking of endogenous cholesterol and LDL-derived cholesterol to the internal compartment. Results using the inhibitor N-butyldeoxynojirimycin, which depletes cellular complex glycosphingolipids, demonstrates that the cholesterol trafficking defect in NPC1 cells is not caused by ganglioside accumulation. The ultimate cause of death in NPC disease is progressive neurological deterioration in the central nervous system, where the major source of cholesterol is derived from endogenous synthesis. Our current study provides a plausible link between defects in intracellular trafficking of endogenous cholesterol and the etiology of Niemann-Pick type C disease.

Recombinant expression of the Candida rugosa lip4 lipase in Escherichia coli

It is difficult to express recombinant Candida rugosa lipases (CRLs) in heterologous systems, since C. rugosa utilizes a nonuniversal serine codon CUG for leucine. In this study, recombinant LIP4 in which all 19 CUG codons had been converted to a universal serine codon was overexpressed in Escherichia coli BL21(DE3). The recombinant LIP4 was found mainly in the inclusion bodies and showed a low catalytic activity. To increase the amount of soluble form and activity of recombinant LIP4, the DNA was fused to the gene for thioredoxin (TrxFus-LIP4) and then expressed in E. coli strain AD494(DE3). This strategy promotes the formation of disulfide bonds in the cytosol and yields enzymatically active forms of LIP4. The purified recombinant TrxFus-LIP4 and LIP4 expressed in AD494(DE3) had the same catalytic profiles. In addition, recombinant LIP4 had higher esterase activities toward long-chain ester and lower lipase activities toward tributyrin, triolein, and olive oil. This system for the expression of fungal lipase in E. coli strain AD494(DE3) is reliable and may produce enzymatically active forms of recombinant lipase without an in vitro refolding procedure.

Towards a quantitative model of immunogenicity: counting pathways in sequence space

One of the fundamental aims of structural biology is the identification of high-affinity ligands for arbitrary receptors. The maturation of the antibody repertoire elegantly and robustly solves this problem through an evolutionary mechanism comprising repeated cycles of mutation and preferential replication. To understand better the limitations and biases of this process, we developed an interpretation of antibody maturation within the framework of sequence space and fitness landscapes. Several well-described phenomena can be directly derived from this framework, and new predictions can be made. Ultimately, this reconceptualization of the clonal selection process suggests a quantitative, testable model of immunogenicity.

Immunological quantitation and localization of ACAT-1 and ACAT-2 in human liver and small intestine

By using specific anti-ACAT-1 antibodies in immunodepletion studies, we previously found that ACAT-1, a 50-kDa protein, plays a major catalytic role in the adult human liver, adrenal glands, macrophages, and kidneys but not in the intestine. Acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity in the intestine may be largely derived from a different ACAT protein. To test this hypothesis, we produced specific polyclonal anti-ACAT-2 antibodies that quantitatively immunodepleted human ACAT-2, a 46-kDa protein expressed in Chinese hamster ovary cells. In hepatocyte-like HepG2 cells, ACAT-1 comprises 85-90% of the total ACAT activity, with the remainder attributed to ACAT-2. In adult intestines, most of the ACAT activity can be immunodepleted by anti-ACAT-2. ACAT-1 and ACAT-2 do not form hetero-oligomeric complexes. In differentiating intestinal enterocyte-like Caco-2 cells, ACAT-2 protein content increases by 5-10-fold in 6 days, whereas ACAT-1 protein content remains relatively constant. In the small intestine, ACAT-2 is concentrated at the apices of the villi, whereas ACAT-1 is uniformly distributed along the villus-crypt axis. In the human liver, ACAT-1 is present in both fetal and adult hepatocytes. In contrast, ACAT-2 is evident in fetal but not adult hepatocytes. Our results collectively suggest that in humans, ACAT-2 performs significant catalytic roles in the fetal liver and in intestinal enterocytes.

Embryonic striatal neurons from niemann-pick type C mice exhibit defects in cholesterol metabolism and neurotrophin responsiveness

Niemann-Pick type C (NP-C) disease is a progressive and fatal neuropathological disorder previously characterized by abnormal cholesterol metabolism in peripheral tissues. Although a defective gene has been identified in both humans and the npc(nih) mouse model of NP-C disease, how this leads to abnormal neuronal function is unclear. Here we show that whereas embryonic striatal neurons from npc(nih) mice can take up low density lipoprotein-derived cholesterol, its subsequent hydrolysis and esterification are significantly reduced. Given the importance of cholesterol to a variety of signal transduction mechanisms, we assessed the effect of this abnormality on the ability of these neurons to respond to brain-derived neurotrophic factor (BDNF). In contrast to its effects on wild type neurons, BDNF failed to induce autophosphorylation of the TrkB receptor and to increase neurite outgrowth in npc(nih) neurons, despite expression of TrkB on the cell surface. The results suggest that abnormal cholesterol metabolism occurs in neurons in the brain during NP-C disease, even at embryonic stages of development prior to the onset of phenotypic symptoms. Moreover, this defect is associated with a lack of TrkB function and BDNF responsiveness, which may contribute to the loss of neuronal function observed in NP-C disease.

Role of Niemann-Pick type C1 protein in intracellular trafficking of low density lipoprotein-derived cholesterol

Niemann-Pick type C (NPC) is a disease that affects intracellular cholesterol-trafficking pathways. By cloning the hamster ortholog of NPC1, we identified the molecular lesions in two independently isolated Chinese hamster ovary cell mutants, CT60 and CT43. Both mutants lead to premature translational terminations of the NPC1 protein. Transfecting hamster NPC1 cDNA complemented the defects of the mutants. Investigation of the CT mutants, their parental cells, and an NPC1-stable transfectant allow us to present evidence that NPC1 is involved in a post-plasma membrane cholesterol-trafficking pathway. We found that the initial movement of low density lipoprotein (LDL)-derived cholesterol to the plasma membrane (PM) did not require NPC1. After reaching the PM and subsequent internalization, however, cholesterol trafficking back to the PM did involve NPC1. Both LDL-derived cholesterol and cholesterol originating from the PM accumulated in a dense, intracellular compartment in the CT mutants. Cholesterol movement from this compartment to the PM or endoplasmic reticulum was defective in the CT mutants. Our results functionally distinguish the dense, intracellular compartment from the early endocytic hydrolytic organelle and imply that NPC1 is involved in sorting cholesterol from the intracellular compartment back to the PM or to the endoplasmic reticulum.

Localization of human acyl-coenzyme A: cholesterol acyltransferase-1 (ACAT-1) in macrophages and in various tissues

To investigate the distribution of acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) in various human tissues, we examined tissues of autopsy cases immunohistochemically. ACAT-1 was demonstrated in macrophages, antigen-presenting cells, steroid hormone-producing cells, neurons, cardiomyocytes, smooth muscle cells, mesothelial cells, epithelial cells of the urinary tracts, thyroid follicles, renal tubules, pituitary, prostatic, and bronchial glands, alveolar and intestinal epithelial cells, pancreatic acinar cells, and hepatocytes. These findings showed that ACAT-1 is present in a variety of human tissues examined. The immunoreactivities are particularly prominent in the macrophages, steroid hormone-producing cells, followed by hepatocytes, and intestinal epithelia. In cultured human macrophages, immunoelectron microscopy revealed that ACAT-1 was located mainly in the tubular rough endoplasmic reticulum; immunoblot analysis showed that the ACAT-1 protein content did not change with or without cholesterol loading; however, on cholesterol loading, about 30 to 40% of the total immunoreactivity appeared in small-sized vesicles. These vesicles were also enriched in 78-kd glucose-regulated protein (GRP 78), a specific marker for the endoplasmic reticulum. Immunofluorescent microscopy demonstrated extensive colocalization of ACAT-1 and GRP 78 signals in both the tubular and vesicular endoplasmic reticulum before and after cholesterol loading. These results raise the possibility that foam cell formation may activate an endoplasmic reticulum vesiculation process, producing vesicles enriched in the ACAT-1 protein.

Emission characteristics of VOCs from athletic tracks

Dynamic and flow-through flux chambers are convenient tools for field measurements of gas or VOC emission flux from solid surfaces in the field. This study was undertaken to collect on site and quantify the emissions of volatile organic compounds (VOCs) released from athletic running tracks. Three typical types of tracks, one synthetic rubber and two tracks (types I and II) consisting mainly of polyurethane, were studied. They were all installed with adhesives and backings, both of which contributed significant amount of VOCs. VOCs released from the track surface were collected with a flux chamber and subsequently analyzed by a gas chromatograph/mass spectrometer (GC/MS). Also, for each track and at each selected time the emission flux and mass emission were measured on site under outdoor conditions over a period of 40 min. GC/MS analyses show that the VOCs emitted include 2-methyl furan, butanal, methyl ethyl ketone, benzene, heptane, methyl isobutyl ketone, toluene+octane, hexanal, nonane+ethylbenzene, xylenes+styrene, propyl benzene, decane, 1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, 1,2, 3-trimethyl benzene and undecane. Of these, hexanal was the common and principal compound for all three types of tracks. 2-Methyl furan and methyl isobutyl ketone were the characteristic compounds for the synthetic rubber and the type II of polyurethane tracks, respectively. In the field studies, no unique compounds were found in the type I of polyurethane tracks. For each of these three types of tracks the total-VOCs emission flux was correlated to the track age and track surface temperature. The results of multiple regression analysis showed good correlation. The type II polyurethane track had the highest decay rate, while the synthetic rubber track had the lowest decay rate. Two years after the track installation, the VOC concentrations measured at 1.5 m above the track, the breathing height of school children, were not significantly higher than the background levels.

Human acyl-CoA:cholesterol acyltransferase-1 is a homotetrameric enzyme in intact cells and in vitro

Acyl-CoA:cholesterol acyltransferase (ACAT) is a key enzyme in cellular cholesterol homeostasis and in atherosclerosis. ACAT-1 may function as an allosteric enzyme. We took a multifaceted approach to investigate the subunit composition of ACAT-1. When ACAT-1 with two different tags were co-expressed in the same Chinese hamster ovary cells, antibody specific to one tag caused co-immunoprecipitation of both types of ACAT-1 proteins. Radioimmunoprecipitations of cells expressing the untagged ACAT-1 or the 6-histidine-tagged ACAT-1 yielded a single radiolabeled band of predicted size on SDS-polyacrylamide gel electrophoresis. These results show that ACAT-1 exists as homo-oligomers in intact Chinese hamster ovary cells. We solubilized HisACAT-1 with the detergent deoxycholate or CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonic acid), performed gel filtration chromatography and sucrose density gradient centrifugations in H(2)O and D(2)O, and determined the Stokes radii and sedimentation coefficients of the HisACAT1-detergent complexes. The estimated molecular mass of HisACAT-1 is 263 kDa, which is 4 times that of the HisACAT-1 monomer (69 kDa). Finally, cross-linking experiments in intact cells and in vitro show that the increase in cross-linker concentrations causes an increase in size of the HisACAT-1-positive signals, forming material(s) 4 times the size of the monomer, supporting the conclusion that ACAT-1 is a homotetrameric enzyme.