Third ventricular plasma-cell lesion with delayed intraventricular transudation of contrast medium.

We report a patient presenting with hydrocephalus secondary to a posterior third ventricular plasma-cell lesion which exhibited delayed transudation of contrast medium into the adjacent aqueduct and fourth ventricle.

LDL receptor-related protein mediates cell-surface clustering and hepatic sequestration of chylomicron remnants in LDLR-deficient mice.

It has been proposed that in the liver, chylomicron remnants (lipoproteins carrying dietary lipid) may be sequestered before being internalized by hepatocytes. To study this, chylomicron remnants labeled with a fluorescent dye were perfused into isolated livers of LDL receptor-deficient (LDLR-deficient) mice (Ldlr(-/-)) and examined by confocal microscopy. In contrast to livers from normal mice, there was clustering of the chylomicron remnants on the cell surface in the space of DISSE: These remnant clusters colocalized with clusters of LDLR-related protein (LRP) and could be eliminated by low concentrations of receptor-associated protein, an inhibitor of LRP. When competed with ligands of heparan sulfate proteoglycans (HSPGs), the remnant clusters still appeared but were fewer in number, although syndecans (membrane HSPGs) colocalized with the remnant clusters. This suggests that the clustering of remnants is not dependent on syndecans but that the syndecans may modify the binding of remnants. These results establish that sequestration is a novel process, the clustering of remnants in the space of DISSE: The clustering involves remnants binding to the LRP, and this may be stabilized by binding with syndecans, eventually followed by endocytosis.

Postprandial lipoproteins and atherosclerosis.

During the postprandial state, dietary lipid is transported from the intestine to peripheral tissues by plasma lipoproteins called chylomicrons. In the capillary beds of peripheral tissues, chylomicron triglycerides are lipolyzed by the enzyme, lipoprotein lipase, allowing the delivery of free fatty acids to the cells. As a result, this produces a new particle of smaller size and enriched with cholesteryl ester referred to as chylomicron remnants. These particles are rapidly removed from the blood primarily by the liver. The liver has a complex chylomicron remnant removal system which is comprised of a combination of different mechanisms that include the low-density-lipoprotein receptor (LDLR) and the LDLR-related-protein (LRP). Furthermore, it has been suggested that there is a sequestration component whereby chylomicron remnants bind to heparan sulfate proteoglycans (HSPG) and/or hepatic lipase; this is then followed by transport to one or both of the above receptors for hepatic uptake. Over the years, a major concern has arisen about the association of chylomicron remnants and coronary heart disease (CHD) in man. Slow removal of chylomicron remnants, as reflected by a prolonged postprandial state, is now commonly observed in patients with CHD and those that have abnormal lipid disorders such as hypertriglyceridemia, familial hypercholesterolemia, familial combined hyperlipidemia and non-insulin-dependent-diabetes-mellitus. The present review will focus on (a) the details of the metabolic pathway (exogenous pathway) that describes the two-step processing of postprandial lipoproteins, (b) the role of the liver, the receptors, and the importance of efficient removal of chylomicron remnants from the blood circulation, and (c) the potential atherogenic effects of chylomicron remnants on the arterial wall.

Rapid initial removal of chylomicron remnants by the mouse liver does not require hepatically localized apolipoprotein E.

Apolipoprotein E (apoE) is a ligand for the low density lipoprotein receptor (LDLR) and the low density lipoprotein receptor-related protein (LRP). The aim of the present study was to clarify the role of hepatically localized apoE in the rapid initial removal of chylomicron remnants by using the isolated perfused liver. Radiolabeled chylomicron remnants were perfused in a single nonrecirculating pass into the livers of C57BL/6J (wild-type) mice, apoE-knockout mice, and apoE/LDLR-knockout mice for a period of 20 min. Aliquots of the perfusate leaving the liver were collected at regular intervals and the rate of removal of radioactivity was determined. At a trace concentration of chylomicron remnants (0.05 microgram of protein per ml), wild-type mouse livers removed at a steady state of 50-55% of total chylomicron remnants perfused per pass; livers from apoE-knockout mice had the same capacity as wild-type mouse livers. When the concentration of remnants was increased to 12 microgram of protein per ml, a level at which it has been shown that LDL receptor and LRP are near saturation, the capacity of the wild-type mouse livers to remove chylomicron remnants was decreased to 10-25% per pass, confirming that the removal mechanisms were nearing saturation. However, instead of finding a greater reduction in the removal rates or impairment in chylomicron remnant removal, livers from apoE-knockout mice were just as efficient as those from wild-type mice in removing remnants. Livers of mice that lacked both apoE and the LDLR also had a similar rate of removal at relatively low remnant concentrations (0.05-0.5 microgram/ml), but had reduced capacity in removing remnants at a relatively high concentration (4-12 microgram/ml) of chylomicron remnants ( approximately 20% per pass). The rate of removal at these concentrations, however, was similar to that attributed to the LRP in previous studies. Chylomicron remnants, whose apolipoproteins were disrupted by trypsinization, were removed at a normal rate by wild-type mouse livers but there was almost no removal by apoE-knockout mouse livers. At higher concentrations, however, the removal of apolipoprotein-disrupted chylomicron remnants was decreased. Our present findings do not support the hypothesis that hepatically localized apoE is a critical factor in the rapid initial removal of chylomicron remnants by either of the major pathways but do suggest that hepatically localized apoE can be added to lipoproteins to accelerate their uptake, although this process may have a limited capacity to compensate for apoE deficiency on lipoproteins.

Genetic analysis of Bemisia (Hemiptera: Aleyrodidae) populations by isoelectric focusing electrophoresis.

Twenty-one whitefly populations in the genus Bemisia were evaluated for genetic variation at 3 allozyme loci. Nine of the 22 populations that exhibited polymorphic loci were subjected to allozyme analysis using a minimum of 10 enzymes, representing 10 to 14 distinct loci. Among those nine variants examined, calculated genetic distances ranged between 0.03 and 0.52, with three main groups emerging from the analysis. One group comprised two closely related Western Hemisphere variants of B. tabaci: type A from California, United States and a geographically proximal population from Culiacan, Mexico. A second cluster contained five collections previously identified as B. tabaci type B and Bemisia argentifolii, while a third group contained a single population from Benin, Africa. The latter two groups were grouped separately from New World populations and are thought to have a recent origin in the Eastern Hemisphere.

The nuclear matrix protein CDP represses hepatic transcription of the human cholesterol-7alpha hydroxylase gene.

To date, the molecular mechanisms that govern hepatic-specific transcription of the human cholesterol 7alpha-hydroxylase (CYP7A1) gene are poorly understood. We recently reported that the region extending from -1888 to +46, which includes the promoter, is not capable of conferring expression to human CYP7A1 promoter lacZ transgenes in the livers of mice, but that expression is observed with transgenes containing the entire structural gene. To locate liver-specific elements in other segments of the human gene, DNase I hypersensitivity studies were performed with transcriptionally active, liver-derived HepG2 cells and with transcriptionally inactive HeLa cells. Three DNase I hypersensitivity sites were detected within the first intron of the human CYP7A1 gene, but only in HepG2 cells. Transient transfection experiments with HepG2 cells revealed a transcriptional repressor within intron 1. Five binding sites for the CAAT displacement protein (CDP) were detected within intron 1. Since CDP is a nuclear matrix protein, two methods were employed to localize nuclear matrix attachment sites within intron 1 of the human CYP7A1 gene. A matrix attachment site was found throughout the entirety of intron 1. Gel retardation experiments and cell transfection studies provided evidence for the repression mechanism. Repression is achieved by displacement by CDP of two hepatic activators, namely HNF-1alpha and C/EBPalpha, that bind to three different sites within intron 1. Additionally, CDP represses transactivation mediated by these two activators.

Expression of the human cholesterol 7alpha-hydroxylase gene in transgenic mice.

We have generated transgenic mice expressing human CYP7A1 transgenes. Only 1.5 kilobases (kb) of 5' upstream sequence and 6.5 kb of 3' sequence were sufficient for hepatic transcription of the transgenes. However, the 5' end segment alone was not sufficient to direct liver expression, suggesting that additional hepatic regulatory elements reside in the 3' extension or within introns. The level of expression of these transgenes was low in comparison to the levels of the endogenous mouse CYP7A1 mRNA. To generate mice expressing higher levels of CYP7A1 mRNA, we injected a large human genomic PAC clone, extending up to -105 kb 5' of the structural gene and about 50 kb 3' of the gene. These transgenic mice expressed CYP7A1 mRNA at higher levels, suggesting that additional hepatic regulatory elements are found either 5' of -1520 or beyond 6.5 kb 3' of the gene.

Evaluation of the components of the chylomicron remnant removal mechanism by use of the isolated perfused mouse liver.

The isolated perfused mouse liver was utilized to evaluate the relative contribution of various molecules believed to participate in the removal of chylomicron remnants by the liver. Sixty percent of asialofetuin was removed from the perfusate per pass; bovine serum albumin was not removed. Normal mouse livers removed chylomicron remnants more efficiently (40-50%/pass) than nascent chylomicrons (10-20%/pass). The fractional removal rate of remnants decreased as their concentration in the perfusate increased demonstrating saturability. Remnant removal by livers of low density lipoprotein receptor-deficient (LDLRD) mice paralleled that of normal mice at low remnant concentrations (0.05, 0.2 microg protein/ml); as concentration increased (4-16 microg protein/ml), removal by LDLRD livers was reduced. About 50% of the capacity to remove remnants was due to the LDL receptor. The role of the LDLR-related protein (LRP) was estimated using the receptor-associated protein (RAP). Four microg/ml of RAP inhibited only LRP; it reduced the removal of remnants by 30-40% in normal livers. When RAP was included in the perfusate of LDLRD livers, remnant removal persisted but was diminished, particularly late in the perfusion; the capacity was approximately 30% of controls. The present study has established that there is more than one mechanism operating for the removal of chylomicron remnants by the liver, provides estimates of the concentration of each to the removal of remnants, and indicates a method for further studies. It is concluded that in normal livers, the LDL receptor has the greatest capacity for removing chylomicron remnants. The LRP contributes to the process as well and a third component, perhaps "sequestration," accounts for up to 30% of the capacity for the initial removal of chylomicron remnants.

Modulation of monocyte chemokine production and nuclear factor kappa B activity by oxidants.

Reactive oxygen species can directly damage tissue. In this setting, amplification of tissue damage also occurs through infiltration of inflammatory cells either acutely or chronically. Several recent studies suggest that reactive oxygen species stimulate production of certain chemokines, which are potent chemoattractants for inflammatory cells. In the present study, we examined whether oxidants, generated by the combination of xanthine and xanthine oxidase (X/XO), alter chemokine production by monocytes and U937 cells. Our findings demonstrate that X/XO stimulates monocytes, but not U937 cells, to produce increased amounts of interleukin-8 (IL-8) and monocyte chemoattractant protein. This effect is attenuated by pretreatment with dimethylsulfoxide (DMSO), a scavenger of hydroxyl radicals, but is not affected by superoxide dismutase or catalase. In contrast, X/XO-induced cytotoxicity, evidenced by lactate dehydrogenase release, is mediated primarily by hydrogen peroxide, as catalase reverses this effect. Finally, exposure to X/XO causes an increase in nuclear factor kappa B (NF-kappaB), and this effect is attenuated by DMSO. These studies suggest that reactive oxygen species can induce production of molecules that amplify inflammation through attraction of inflammatory cells. It appears the hydroxyl radical is the principal oxidant species involved in stimulation of chemokine production.

Hepatocyte nuclear factor 1 binds to and transactivates the human but not the rat CYP7A1 promoter.

Cholesterol 7alpha-hydroxylase (CYP7A1), a liver-specific enzyme, catalyzes the rate-limiting step in the degradation pathway of cholesterol to bile acids, and thus plays a key role in cholesterol homeostasis. To elucidate the mechanisms that control hepatic expression of the human CYP7A1 gene, we are studying the promoter region. Initially, we observed that up to 40% of the overall transcriptional activity of the promoter in HepG2 cells was associated with DNA sequences from -65 to -1 of the human gene. Within this region, a binding site for the liver-enriched transcription factor HNF-1 (-56 to -49) has been identified. Binding of HNF-1 to this site leads to transcriptional activation of the human promoter. The corresponding segment from the rat CYP7A1 gene does not bind HNF-1; instead, it is bound by the orphan receptors ARP-1 (COUP-TFII) and LXRalpha, that are implicated in dietary regulation.

Cloning of a unique lipase from endothelial cells extends the lipase gene family.

A new lipoprotein lipase-like gene has been cloned from endothelial cells through a subtraction methodology aimed at characterizing genes that are expressed with in vitro differentiation of this cell type. The conceptual endothelial cell-derived lipase protein contains 500 amino acids, including an 18-amino acid hydrophobic signal sequence, and is 44% identical to lipoprotein lipase and 41% identical to hepatic lipase. Comparison of primary sequence to that of lipoprotein and hepatic lipase reveals conservation of the serine, aspartic acid, and histidine catalytic residues as well as the 10 cysteine residues involved in disulfide bond formation. Expression was identified in cultured human umbilical vein endothelial cells, human coronary artery endothelial cells, and murine endothelial-like yolk sac cells by Northern blot. In addition, Northern blot and in situ hybridization analysis revealed expression of the endothelial-derived lipase in placenta, liver, lung, ovary, thyroid gland, and testis. A c-Myc-tagged protein secreted from transfected COS7 cells had phospholipase A1 activity but no triglyceride lipase activity. Its tissue-restricted pattern of expression and its ability to be expressed by endothelial cells, suggests that endothelial cell-derived lipase may have unique functions in lipoprotein metabolism and in vascular disease.

Role of the enterohepatic circulation of bile salts in lipoprotein metabolism.

The enterohepatic circulation of bile salts and cholesterol plays a central role in maintaining whole body cholesterol homeostasis. Hepatic lipoprotein metabolism is reviewed and the role of disturbances in bile salt metabolism in the pathogenesis of dyslipidemias is discussed. Further, the manipulation of bile salt metabolism to treat dyslipidemia is reviewed.

Multiple processes are involved in the uptake of chylomicron remnants by mouse peritoneal macrophages.

The processes responsible for the uptake of chylomicron remnants by macrophages were investigated using freshly isolated cells from low density lipoprotein (LDL) receptor, very low density lipoprotein (VLDL) receptor and apolipoprotein E knockout mice. In peritoneal macrophages from normal mice, the metabolism of chylomicron remnants was inhibited 40% by anti-LDL receptor antibody and 60% by a high concentration of receptor-associated protein (RAP). Together they reduced the amount processed by 70%. Digestion of cell proteoglycans decreased remnant degradation by 20% while the addition of acetyl-LDL had no effect. When LDL receptors were absent, the absolute rates of metabolism were less than that of normal cells and were not inhibited by the anti-LDL receptor antibody; the rates, however, were reduced to less than half by RAP. These suggest that the LDL receptor-related protein (LRP) or another LDL receptor family member(s) contributes to chylomicron remnant uptake and becomes the major mechanism of uptake when LDL receptors are absent. In contrast, the VLDL receptor was not involved as its absence did not affect chylomicron remnant metabolism. Similarly, the absence of apoE production did not affect the amount of remnant uptake; however, the proportion that was sensitive to RAP was eliminated. The level of LRP expression was not altered in these cells whereas there was a decrease in LDL receptors. This suggests that the apoE content of chylomicron remnants is sufficient for its recognition by LDL receptors but additional apoE is required for its uptake by the LRP and that there is an up-regulation of a non-LDL receptor family mechanism in apoE deficiency. Together these studies suggest that even in the absence of LDL receptors or apoE secretion, chylomicron remnants could contribute to lipid accumulation in the artery wall during atherogenesis.

Accelerated lipoprotein uptake by transplantable hepatomas that express hepatic lipase.

To test the hypothesis that hepatic lipase plays a key role in lipoprotein removal in vivo, a novel system was used. Hepatoma cells (HTC 7288c) were transfected with a cDNA encoding hepatic lipase in culture and grown as solid tumors in vivo. In culture, transfected cells degraded chylomicron remnants and low density lipoprotein (LDL) somewhat more efficiently than untransfected cells. Tumors from the transplanted cells produced hepatic lipase localized to the surface of tumors from transfected cells but not tumors from non-transfected cells, grown in the same rat. The tumors from transfected cells removed, per gm of tissue, 34% (P < 0.001) more 125I-labeled LDL than tumors from non-transfected cells in the same animal. The uptake of chylomicron remnants (by tumors from transfected cells) was also modestly enhanced (15 +/- 6%, P < 0.005). There were no differences in the uptake of 125I-labeled albumin or 125I-labeled asialoglycoprotein. Compared to the liver, the untransfected tumors took up 12%, and the transfected tumors took up about 18% as much LDL per gram of tissue. The uptake of chylomicron remnants compared to liver was far lower. Both types of tumors had about twice as much LDL receptor related protein as the liver. Wild-type tumors had the highest level of LDL receptor, twice hepatic lipase-secreting tumors, and six times that of the liver. Using the novel approach of transfecting transplantable tumor cells with hepatic lipase, the ability of hepatic lipase to facilitate the removal of apoB-containing lipoproteins was demonstrated. The liver still removes low density lipoprotein and especially chylomicron remnants more rapidly than the tumors, suggesting factors in addition to hepatic lipase and LDL receptor level play a major role in hepatic lipoprotein removal.

Interaction between ApoB and hepatic lipase mediates the uptake of ApoB-containing lipoproteins.

Hepatic lipase (HL) on the surface of hepatocytes and endothelial cells lining hepatic sinusoids, the adrenal glands, and the ovary hydrolyzes triglycerides and phospholipids of circulating lipoproteins. Its expression significantly enhances low density lipoprotein (LDL) uptake via the LDL receptor pathway. A specific interaction between LPL, a homologous molecule to HL, and apoB has been described (Choi, S. Y., Sivaram, P., Walker, D. E., Curtiss, L. K., Gretch, D. G., Sturley, S. L., Attie, A. D., Deckelbaum, R. J., and Goldberg, I. J. (1995) J. Biol. Chem. 270, 8081-8086). The present studies tested the hypothesis that HL enhances the uptake of lipoproteins by a specific interaction of HL with apoB. On a ligand blot, HL bound to apoB26, 48, and 100 but not to apoE or apoAI. HL binding to LDL in a plate assay with LDL-coated plates was significantly greater than to bovine serum albumin-coated plates. Neither heat denatured HL nor bacterial fusion protein of HL bound to LDL in the plate assays. 125I-LDL bound to HL-saturated heparin-agarose gel with a Kd of 52 nM, and somewhat surprisingly, this binding was not inhibited by excess LPL. In cell culture experiments HL enhanced the uptake of 125I-LDL at both 4 and 37 degreesC. The enhanced binding and uptake of LDL was significantly inhibited by monoclonal anti-apoB antibodies. In contrast to LPL, both amino- and carboxyl-terminal antibodies blocked the apoB interaction with HL to the same extent. Thus, we conclude that there is a unique interaction between HL and apoB that facilitates the uptake of apoB-containing lipoproteins by cells where HL is present.

Improved method for the on-line metal chelate affinity chromatography-high-performance liquid chromatographic determination of tetracycline antibiotics in animal products.

An improved on-line metal chelate affinity chromatography-high-performance liquid chromatography (MCAC-HPLC) method for the determination of tetracycline antibiotics in animal tissues and egg has been developed. Extraction was carried out with ethyl acetate. The extract was then evaporated to dryness and reconstituted in methanol prior to on-line MCAC clean-up and HPLC-UV determination. Recoveries of tetracycline, oxytetracycline, demeclocycline and chlortetracycline in the range 42% to 101% were obtained from egg, poultry, fish and venison tissues spiked at 25 micrograms kg-1. Limits of detection less than 10 microgram kg-1 were estimated for all four analytes. This method has higher throughput, higher recovery and lower limits of detection than a previously reported on-line MCAC-HPLC method which involved aqueous extraction and solid-phase extraction clean-up.

Determination of 19-nortestosterone and trenbolone in animal tissues by high-performance liquid chromatography with immunoaffinity clean-up.

A method for the simultaneous determination of residues of 17 beta-trenbolone and 17 beta, 19-nortestosterone and their epimers in animal tissues is described, involving immunoaffinity chromatography clean-up and high-performance liquid chromatography with dual-wavelength UV detection. The method has been validated at 2 micrograms/kg in pig and cattle liver and corned beef with recoveries of 41% upwards. The method has been applied to the determination of incurred residues of 19-nortestosterone and trenbolone. Various alternative extraction steps for incurred trenbolone have been investigated, including direct extraction, protease digestion, heating and ultrasonic probe treatment. Glucuronidase digestion has been shown to be the most effective method for this analyte.

Aspects of extraction, spiking and distribution in the determination of incurred residues of chloramphenicol in animal tissues.

Studies of distribution, extraction procedures and spiking protocols in the determination of incurred chloramphenicol residues in animal tissues have been carried out. An extraction procedure involving glucuronidase enzyme digestion was found to extract 10 times more incurred chloramphenicol from pig kidney than direct extraction without digestion. However, neither protease digestion nor ultrasonic probe treatment resulted in improved chloramphenicol extraction. Chloramphenicol was found to be inhomogeneously distributed within kidney from a treated pig. Highest concentrations were detected in the renal medulla. Muscle tissues from the same animal were found to contain a lower concentration of chloramphenicol residues, but no chloramphenicol residues were detectable in the liver. Chloramphenicol recovery from spiked pig liver was found to be lower than that from kidney, but was improved by the addition of piperonyl butoxide before extraction. This additive had no effect on recovery from spiked pig or cattle kidney. The implications of these results for regulatory surveillance of animal tissue for chloramphenicol residues are discussed.

Effects of extraction and spiking procedures on the determination of incurred residues of oxytetracycline in cattle kidney.

The effects of different extraction and spiking procedures on the determination of incurred oxytetracycline residues in animal tissues have been investigated. The extraction procedures investigated--direct aqueous or organic solvent extraction, enzymic digestion or sonication--all gave similar results for incurred oxytetracycline concentration in cattle kidney after correction for spike recovery. There was therefore no evidence for binding or conjugation of oxytetracycline in this tissue. Highest recovery from spiked tissue was obtained using ethyl acetate as extractant. The effects of spiking procedure (spike contact time, spike solvent and tissue state) on recovery from spiked cattle kidney were also small, indicating that added oxytetracycline spike does not interact with the tissue.