Myriocin slows the progression of established atherosclerotic lesions in apolipoprotein E gene knockout mice

The serine palmitoyl transferase inhibitor myriocin potently suppresses the development of atherosclerosis in apolipoprotein E (apoE) gene knockout (apoE(-/-)) mice fed a high-fat diet. This is associated with reduced plasma sphingomyelin (SM) and glycosphingolipid levels. Furthermore, oral administration of myriocin decreases plasma cholesterol and triglyceride (TG) levels. Here, we aimed to determine whether myriocin could inhibit the progression (or stimulate the regression) of established atherosclerotic lesions and to examine potential changes in hepatic and plasma lipid concentrations. Adult apoE(-/-) mice were fed a high-fat diet for 30 days, and lesion formation was histologically confirmed. Replicate groups of mice were then transferred to either regular chow or chow containing myriocin (0.3 mg/kg/day) and maintained for a further 60 days. Myriocin significantly inhibited the progression of established atherosclerosis when combined lesion areas (aortic sinus, arch, and celiac branch point) were measured. Although the inhibition of lesion progression was observed mainly in the distal regions of the aorta, regression of lesion size was not detected. The inhibition of lesion progression was associated with reductions in hepatic and plasma SM, cholesterol, and TG levels and increased hepatic and plasma apoA-I levels, indicating that the modulation of pathways associated with several classes of atherogenic lipids may be involved.     

Monoclonal antibody LU-BCRU-G7 against a breast tumour-associated glycoprotein recognizes the disaccharide Gal{beta}1-3GlcNAc

The monoclonal antibody LU-BCRU-G7, that was generated by invitro immunization, shows clinical value as a prognostic markerin early stage breast carcinoma. It has now been characterizedwith regard to its binding epitope. Using a recently describedmethod based on the construction of N-substituted polyacrylamide(PAA) derivatives of carbohydrates (pseudopolysaccharides),the structure of the epitope for the monoclonal antibody LU-BCRU-G7has been determined. Competitive binding assays and inhibitoryenzyme-linked immunosorbent assays (ELISAs) using these pseudopolysaccharideshave shown the LU-BCRU-G7 epitope to be a disaccharide Galß1-3GlcNAc(Le^c; where Gal is D-galactose, Glc is D-glucose and GlcNAcis N-acetyl-D-glucosainine). Both galactose and N-acetyl glucosaminemoieties are essential for binding. Substitution on C-2 or C-3of the terminal galactose abolished binding, as did galactose-terminated oligosaccharides. The galactose moiety alone, asexpressed by the Galß-PAA conjugate, appeared to hea more important feature of the epitope than the GlcNAc-PAAconjugate, which failed to bind or inhibit the LU-BCRU-G7 antibody.In the N-acetyl glucosamine moiety, binding was decreased butnot eliminated by fucose substitution, as in Le^a, or changein configuration of C-4, as in Galß1-3GlcNAc. Omissionof the NAc group resulted in complete loss of activity. Thetetrasaccharide lacto-N-tetraose, although containing the terminalLe^c disaccharide, does not react with the antibody, suggestingconformational interference of the binding site. These findingsshow that the monoclonal antibody LU-BCRU-G7 recognizes a terminalisolactosamine fragment on a tumour-associated glycoprotein,which we have previously shown to be inversely related to survivalin breast cancer. breast cancer Galß1-3GlcNAc LU-BCRU-G7 monoclonal antibody pseudopolysaccharides     

High-sensitivity two-color detection of double-stranded DNA with a confocal fluorescence gel scanner using ethidium homodimer and thiazole orange.

Ethidium homodimer (EthD; lambda Fmax 620 nm) at EthD:DNA ratios up to 1 dye:4-5 bp forms stable fluorescent complexes with double-stranded DNA (dsDNA) which can be detected with high sensitivity using a confocal fluorescence gel scanner (Glazer, A.N., Peck, K. & Mathies, R.A. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 3851-3855). However, on incubation with unlabeled DNA partial migration of EthD takes place from its complex with dsDNA to the unlabeled DNA. It is shown here that this migration is dependent on the fractional occupancy of intercalating sites in the original dsDNA-EthD complex and that there is no detectable transfer from dsDNA-EthD complexes formed at 50 bp: 1 dye. The monointercalator thiazole orange (TO; lambda Fmax 530 nm) forms readily dissociable complexes with dsDNA with a large fluorescence enhancement on binding (Lee, L.G., Chen, C. & Liu, L.A. (1986) Cytometry 7, 508-517). However, a large molar excess of TO does not displace EthD from its complex with dsDNA. When TO and EthD are bound to the same dsDNA molecule, excitation of TO leads to efficient energy transfer from TO to EthD. This observation shows the practicability of 'sensitizing' EthD fluorescence with a second intercalating dye having a very high absorption coefficient and efficient energy transfer characteristics. Electrophoresis on agarose gels, with TO in the buffer, of preformed linearized M13mp18 DNA-EthD complex together with unlabeled linearized pBR322 permits sensitive fluorescence detection in the same lane of pBR322 DNA-TO complex at 530 nm and of M13mp18 DNA-EthD complex at 620 nm. These observations lay the groundwork for the use of stable DNA-dye intercalation complexes carrying hundreds of chromophores in two-color applications such as the physical mapping of chromosomes.     

The synthesis of a novel thio-linked disaccharide of chondroitin as a potential inhibitor of polysaccharide lyases

A thio-linked disaccharide based on the structure of the glycosaminoglycan chondroitin was synthesized as a potential inhibitor of chondroitin AC lyase from Flavobacterium heparinum for structural analysis of the active site. Instead it was found to be a slow substrate, thereby demonstrating that lyases, in contrast to glycosidases, can cleave thioglycoside links between sugars.     

N-terminal tagging of human P2X7 receptor disturbs calcium influx and dye uptake

The P2X7 receptor is a frequently studied member of the purinergic receptor family signalling via channel opening and membrane pore formation. Fluorescent imaging is an important molecular method for studying cellular receptor expression and localization. Fusion of receptors to fluorescent proteins might cause major functional changes and requires careful functional evaluation such as has been done for the rat P2X7 receptor. This study examines fusion constructs of the human P2X7 receptor. We assessed surface expression, channel opening with calcium influx, and pore formation using YO-PRO-1 dye uptake in response to BzATP stimulation in transfected cells. We found that tagging at the N-terminal of the human P2X7 receptor with the enhanced green fluorescent protein (eGFP) disturbed channel opening and pore formation despite intact surface expression. A triple hemagglutinin (3HA) fused to the N-terminal also disrupted pore formation but not channel opening showing that even a small tag alters the normal function of the receptor. Together, this suggests that in contrast to what has been observed for the rat P2X7 receptor, the human P2X7 receptor contains N-terminal motifs important for signalling that prevent the construction of a functionally active fusion protein.     

A light and electron microscopic procedure for sequential double antigen localization using diaminobenzidine and benzidine dihydrochloride

Very few double-antigen staining methods are available that are applicable to both light and electron microscopy. The objective of this study was to develop for localization of two neural antigens simultaneously a procedure which would be sensitive, simple to perform, offer permanent reaction products, and permit correlated light and ultrastructural analysis. The method employs sequential immunoperoxidase staining without antibody elution, in which the first sequence of antibodies is visualized with 3,3'-diaminobenzidine (DAB) and the second with benzidine dihydrochloride (BDHC). The DAB reaction product (brown and diffuse) was easily distinguishable from the BDHC deposit (blue, granular, and more electron-dense) by both light and electron microscopy. The procedure was used to simultaneously localize choline acetyltransferase-and either substance P or tyrosine hydroxylase in rat brain at both light and ultrastructural levels. Control experiments demonstrated the absence of both color mixing and antibody crossreactions, even when both primary antibodies were from the same species. This study demonstrates the usefulness of BDHC as a chromogen for immunoperoxidase staining either alone or in combination with DAB, and describes a double method which should have wide applicability for detailed studies of most pairs of antigens at both light and ultrastructural levels.     

Lipid transfers between reconstituted high density lipoprotein complexes and low density lipoproteins: effects of plasma protein factors

In this study we examined the transfer of lipids between reconstituted high density lipoprotein discs (r-HDL) and human low density lipoproteins (LDL) in the presence and absence of lecithin:cholesterol acyltransferase (LCAT) or of plasma phospholipid transfer protein (PLTP). We found that spontaneous transfer of phospholipids from r-HDL to LDL occurred by an apparent first order reaction with a half-time of 5.8 to 6.9 hr depending on the phospholipid. During the time of incubation of r-HDL with LDL (from 0 to 25 hr), the phospholipid content of r-HDL decreased more than 30%, the free cholesterol content increased 2.5-fold, and low levels of cholesteryl esters appeared in r-HDL. These compositional changes gave rise to small discoidal particles with a limiting diameter of 77 A and two molecules of apoA-I per particle. When LCAT was included in the reaction mixture, the r-HDL lost even more phospholipid, lost some free cholesterol, and gained cholesteryl esters relative to the apolipoprotein content, due to the enzymatic reaction. The products of the LCAT reaction had a diameter of 93 A and three, rather than two, apoA-I molecules per particle. Inclusion of PLTP into the reaction mixture accelerated the transfer of phospholipids (half-time of 1.7 hr) and the formation of the 77 A product. In addition to these compositional and morphological changes, which may be important in the interconversions of native HDL subspecies, the prolonged incubations revealed some slow reactions, such as the esterification of LDL cholesterol by LCAT, a background formation of cholesteryl esters in r-HDL, and an apparent hydrolysis of cholesteryl esters in LDL in the presence of r-HDL.     

The relationship between the energetic efficiency in different micro-organisms and the rate and type of metabolite overproduced

Summary Data regarding the degree of energy conservation as determined by the and the highest rates of metabolite production reported for various micro-organisms have been collated and analysed. The results have indicated that the highest rates of metabolite production occur in micro-organisms possessing low efficiencies of energy conservation. Moreover, in the case of exopolysaccharide production the oxidation state of the polymer is inversely related to the value of the producing organism. In general, the rate of ATP turnover associated with exopolysaccharide production or the potential rate associated with over-production of other metabolites is inversely related to the value of the producing organism. Analysis of current production rates for a range of metabolites suggests that there is scope for major improvements of existing processes by careful selection of appropriate micro-organisms.     

A Balanced Tissue Composition Reveals New Metabolic and Gene Expression Markers in Prostate Cancer

Molecular analysis of patient tissue samples is essential to characterize the in vivo variability in human cancers which are not accessible in cell-lines or animal models. This applies particularly to studies of tumor metabolism. The challenge is, however, the complex mixture of various tissue types within each sample, such as benign epithelium, stroma and cancer tissue, which can introduce systematic biases when cancers are compared to normal samples. In this study we apply a simple strategy to remove such biases using sample selections where the average content of stroma tissue is balanced between the sample groups. The strategy is applied to a prostate cancer patient cohort where data from MR spectroscopy and gene expression have been collected from and integrated on the exact same tissue samples. We reveal in vivo changes in cancer-relevant metabolic pathways which are otherwise hidden in the data due to tissue confounding. In particular, lowered levels of putrescine are connected to increased expression of SRM, reduced levels of citrate are attributed to upregulation of genes promoting fatty acid synthesis, and increased succinate levels coincide with reduced expression of SUCLA2 and SDHD. In addition, the strategy also highlights important metabolic differences between the stroma, epithelium and prostate cancer. These results show that important in vivo metabolic features of cancer can be revealed from patient data only if the heterogeneous tissue composition is properly accounted for in the analysis.     

Loss of ABCA8B decreases myelination by reducing oligodendrocyte precursor cells in mice

The myelin sheath, which is wrapped around axons, is a lipid-enriched structure produced by mature oligodendrocytes. Disruption of the myelin sheath is observed in several neurological diseases, such as multiple sclerosis. A crucial component of myelin is sphingomyelin, levels of which can be increased by ABCA8, a member of the ATP-binding cassette transporter family. ABCA8 is highly expressed in the cerebellum, specifically in oligodendroglia. However, whether ABCA8 plays a role in myelination and mechanisms that would underlie this role remain unknown. Here, we found that the absence of Abca8b, a mouse ortholog of ABCA8, led to decreased numbers of cerebellar oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes in mice. We show that in oligodendrocytes, ABCA8 interacts with chondroitin sulfate proteoglycan 4 (CSPG4), a molecule essential for OPC proliferation, migration, and myelination. In the absence of Abca8b, localization of CSPG4 to the plasma membrane was decreased, contributing to reduced cerebellar CSPG4 expression. Cerebellar CSPG4+ OPCs were also diminished, leading to decreased mature myelinating oligodendrocyte numbers and cerebellar myelination levels in Abca8b^?/? mice. In addition, electron microscopy analyses showed that the number of nonmyelinated cerebellar axons was increased, whereas cerebellar myelin thickness (g-ratio), myelin sheath periodicity, and axonal diameter were all decreased, indicative of disordered myelin ultrastructure. In line with disrupted cerebellar myelination, Abca8b^?/? mice showed lower cerebellar conduction velocity and disturbed locomotion. In summary, ABCA8 modulates cerebellar myelination, in part through functional regulation of the ABCA8-interacting protein CSPG4. Our findings suggest that ABCA8 disruption may contribute to the pathophysiology of myelin disorders.