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Biomedical subjects

D Steinberg

Publications and source records attributed to D Steinberg.

At least 91 records · Page 5Linked to original sources
PubMed1996

Cloning and expression in Xenopus oocytes of a mouse homologue of the human acylcoenzyme A: cholesterol acyltransferase and its potential role in metabolism of oxidized LDL.

We used a Xenopus oocyte expression system to screen a mouse macrophage cDNA library for receptors for oxidized LDL (OxLDL). Injection of unfractionated mouse macrophage mRNA induced OxLDL binding activity on oocytes. An excess of acetylated LDL (AcLDL) inhibited the binding of OxLDL by only 30%, indicating the expression of OxLDL receptors distinct from the scavenger receptor (SRA). The library was screened and analyzed by competition binding using [125I]OxLDL and AcLDL, to avoid cloning of SRA. One of the purified clones encoded a peptide with 85% identity with human acyl-coenzyme A:cholesterol acyltransferase (ACAT). Injection of ACAT mRNA into oocytes induced specific binding of OxLDL. ACAT is expressed in mouse macrophages as a approximately 3.6 kB transcript and the expression is upregulated in human THP-1 cells treated with PMA.

Amino Acid Sequence↗
PubMed1996

Kinetic properties of glucosyltransferase adsorbed onto saliva-coated hydroxyapatite.

Results from previous studies have shown that several properties of glucosyltransferase (GTF) adsorbed onto saliva-coated hydroxyapatite beads differ from those of GTF in solution. For example: thermostability, pH-activity dependency, sensitivity to inhibitors. The aim of this study was to compare the kinetics of the adsorbed GTF with its kinetic properties in solution. Hydroxyapatite beads were coated with human parotid saliva (sHA). Following washes, cell-free GTF enzyme from Streptococcus sobrinus 6715 (S. sobrinus 6715) or Streptococcus mutans GS-5 (S. mutans GS-5) was adsorbed onto sHA. The GTF-coated sHA were then incubated with radiolabeled sucrose for intervals of 5-360 minutes and the amount of glucans synthesized in situ by the adsorbed GTF was determined and compared with that produced in solution. The adsorbed GTF (from S. sobrinus 6715) exhibited a sharp increase in glucan production within the first 5 minutes of incubation while surface-bound GTF of S. mutans GS-5 displayed an initial burst of activity within the first 15 minutes of incubation. During the next 6 hours (duration of experiment) the amount of glucan on the beads did not increase with either enzyme. In contrast, the kinetic profile of the two GTFs in solution demonstrated a linear increase in the amount of glucans formed, with no initial burst effect. The results indicate that the rapid formation of glucans by GTF adsorbed onto sHA could have implications for colonization by oral microorganisms on tooth surfaces. The accelerated synthesis of glucan on tooth surfaces may affect the microbiology of the dental plaque, and might also influence the movement of substances, such as acids and antiplaque agents, across the acquired pellicle and dental plaque.

Adsorption↗
PubMed1996

Oxidized low density lipoprotein--an extreme example of lipoprotein heterogeneity.

The intense interest in the possibility that oxidative modification of low density lipoprotein (LDL) plays an important role in atherogenesis has led to an explosion in the number of papers dealing one way or another with "oxidized LDL". A great deal has been learned about the biological properties of "oxidized LDL", the complex chemical processes accompanying oxidation and its pathogenetic role in experimental animal models. Yet the term itself--"oxidized LDL"--is woefully inadequate. In this short essay to honor the memory of my friend and colleague, Shlomo Eisenberg, I will attempt to indicate the questions that need to be asked; I do not provide the answers.

Arteriosclerosis↗
PubMed1996

Macrophage oxidative modification of low density lipoprotein occurs independently of its binding to the low density lipoprotein receptor.

The oxidative modification of low density lipoproteins (LDL) by arterial wall cells is thought to contribute to atherogenesis. Monocyte/macrophages, among other arterial wall cells, oxidatively modify LDL to a form that is recognized by scavenger/oxidized LDL receptors. It has recently been suggested that LDL binding to the LDL receptor (B/E receptor) is essential for macrophage-mediated oxidation of LDL. In the present study, we compared the ability of resident peritoneal macrophages from LDL-R-deficient (LDLR-/-) mice to oxidize LDL with that of resident peritoneal macrophages from C57B6 mice. The LDLR-/- macrophages oxidized LDL at least as rapidly as did the C57B6 macrophages both in F-10 medium and in Dulbecco's modified Eagle's medium supplemented with 1 microM copper (DMEM-Cu2+). Studies were also conducted to examine the effect of preincubation of LDLR-/- and C57B6 macrophages with 10% lipoprotein-deficient serum (LPDS), which up-regulates LDL receptors, or with acetylated LDL (Ac-LDL), which increases cellular cholesterol and down-regulates LDL receptors. Preincubation with 10% LPDS had no significant effect on subsequent LDL oxidation by either type of cells in F10 medium, but the C57B6 cells did show a small (18%) but significant increase in LDL oxidation in DMEM-Cu2+. Preincubation with 50 micrograms/ml Ac-LDL in F10 medium had no effect on LDL oxidation by either LDLR-/- or C57B6 macrophages. Preincubation with 100 micrograms/ml Ac-LDL had no effect on subsequent LDL oxidation by C57B6 cells but, unexpectedly, caused a modest (26%) fall in LDL oxidation by the receptor-negative cells. Using DMEM-Cu2+ medium, preincubation with Ac-LDL reduced LDL oxidation substantially (50-66%) but the effect was just as great in LDL-R negative cells (59-66%) as in C57B6 cells (50-58%), suggesting that the effect is not due to changes in LDL receptor density. It may be related somehow to the Ac-LDL-induced increase in cell cholesterol content. The data demonstrate that the absence of LDL receptors does not reduce the ability of macrophages to oxidize LDL and that LDL binding to LDL receptors is not an essential requirement for macrophage oxidation of LDL.

Animals↗
PubMed1996

Antibacterial effect of propolis and honey on oral bacteria.

PURPOSE: To investigate the antibacterial properties of propolis and honey against oral bacteria in vitro and in vivo. MATERIALS AND METHODS: In vitro study: The antibacterial effects of propolis and honey on oral streptococci were determined using the broth method. Clinical study: The short-term antibacterial effect of propolis solution and honey on salivary total bacteria and Streptococcus mutans was tested in 10 volunteers. RESULTS: Propolis demonstrated an antibacterial effect both in vitro on isolated oral streptococci and in the clinical study on salivary bacterial counts. Honey induced bacteria growth at low concentrations, while at high concentrations honey had an inhibitory effect on bacterial growth in vitro. Salivary counts of total bacteria and Streptococcus mutans were lower for 1 hour after application of honey. The antibacterial effect of the honey tested may be attributed to its osmolarity effect.

Adult↗
PubMed1995

The 94- to 97-kDa mouse macrophage membrane protein that recognizes oxidized low density lipoprotein and phosphatidylserine-rich liposomes is identical to macrosialin, the mouse homologue of human CD68.

We have previously reported the partial purification of a 94- to 97-kDa plasma membrane protein from mouse peritoneal macrophages that binds oxidatively modified low density lipoprotein (OxLDL) and phosphatidylserine-rich liposomes. We have now identified that protein as macrosialin, a previously cloned macrophage-restricted membrane protein in the lysosomal-associated membrane protein family (mouse homologue of human CD68). Early in the course of purification of the 94- to 97-kDa protein, a new OxLDL-binding band at 190-200 kDa appeared and copurified with the 94- to 97-kDa protein. The HPLC pattern of tryptic peptides from this higher molecular mass ligand-binding band closely matched that derived from the 94- to 97-kDa band. Specifically, the same three macrosialin-derived tryptic peptides (9, 9, and 15 residues) were present in the purified 94- to 97-kDa band and in the 190- to 200-kDa band and antisera raised against peptide sequences in macrosialin recognized both bands. An antiserum against macrosialin precipitated most of the 94- to 97-kDa OxLDL-binding material. We conclude that the binding of OxLDL to mouse macrophage membranes is in part attributable to macrosialin. Our previous studies show that OxLDL competes with oxidized red blood cells and with apoptotic thymocytes for binding to mouse peritoneal macrophages. Whether macrosialin plays a role in recognition of OxLDL and oxidatively damaged cells by intact macrophages remains uncertain.

Amino Acid Sequence↗
PubMed1995

Clinical trials of antioxidants in atherosclerosis: are we doing the right thing?

The hypothesis that oxidative modification of low density lipoprotein contributes to the progression of atherosclerosis is supported by an impressive body of in-vitro findings and by persuasive results in animal models of atherosclerosis. The hypothesis was originally proposed specifically to account for foam cell formation but oxidation of LDL has now been shown to confer on it a long list of new biological properties any one of which could in principle enhance its atherogenicity. The relative importance of these altered biological properties in vivo remains uncertain. Whatever the precise mechanisms, we know that antioxidants can slow the atherogenic process in several experimental models, including LDL-receptor-deficient rabbits, cholesterol-fed rabbits, and cholesterol-fed non-human primates. Of 18 published studies, 13 have given strongly positive results, the rate of progression of lesions being reduced by 50-80%; 2 have yielded marginally positive results; and 3 have been negative (see ref 3 for references). Furthermore, the fact that four different antioxidant compounds have been used--probucol, butylated hydroxytoluene, N,N'-diphenyl-phenylenediamine, and vitamin E--supports the conclusion that they are working via the property they all share, namely, their antioxidant potential.

Animals↗
PubMed1995

Enhanced levels of lipoperoxides in low density lipoprotein incubated with murine fibroblast expressing high levels of human 15-lipoxygenase.

There is strong experimental evidence that oxidized low density lipoprotein (Ox-LDL) plays an important role in atherosclerosis. However, the mechanisms by which Ox-LDL is formed in vivo are unknown. To test whether 15-lipoxygenase (15-LO) could play a role in oxidation of LDL by cells, we expressed 15-LO activity in murine fibroblasts, which do not normally have 15-LO activity, and tested their ability to modify LDL. Using a retroviral vector, we prepared fibroblasts that expressed 2- to 20-fold more 15-LO activity than control fibroblasts infected with a vector containing beta-galactosidase (lacZ). Compared with LDL incubated with lacZ cells, LDL incubated with 15-LO-containing cells were enriched with lipid hydroperoxides. When these LDL samples were subsequently subjected to oxidative stress, they were more susceptible to further oxidative modification, as judged by increased conjugated diene formation and by increased ability to compete with 125I-Ox-LDL for uptake by macrophages. These findings establish that cellular 15-LO can contribute to oxidative modification of LDL, but the quantitative significance of these findings to the in vivo oxidation of LDL remains to be established.

Animals↗
PubMed1995

A macrophage receptor for oxidized low density lipoprotein distinct from the receptor for acetyl low density lipoprotein: partial purification and role in recognition of oxidatively damaged cells.

The binding and uptake of oxidatively modified low density lipoprotein (OxLDL) by mouse peritoneal macrophages occurs, in part, via the well characterized acetyl LDL receptor. However, several lines of evidence indicate that as much as 30-70% of the uptake can occur via a distinct receptor that recognizes OxLDL with a higher affinity than it recognizes acetyl LDL. We describe the partial purification and characterization of a 94- to 97-kDa plasma membrane protein from mouse peritoneal macrophages that specifically binds OxLDL. This receptor is shown to be distinct from the acetyl LDL receptor as well as from two other macrophage proteins that also bind OxLDL--the Fc gamma RII receptor and CD36. We suggest that this OxLDL-binding membrane protein participates in uptake of OxLDL by murine macrophages and also represents a receptor responsible for macrophage binding and phagocytosis of oxidatively damaged cells.

Animals↗
PubMed1995

Recognition of oxidatively damaged and apoptotic cells by an oxidized low density lipoprotein receptor on mouse peritoneal macrophages: role of membrane phosphatidylserine.

We recently reported that oxidized low density lipoprotein (OxLDL), but not acetyl LDL (AcLDL), inhibited the binding and phagocytosis of nonopsonized, oxidatively damaged red blood cells (OxRBCs) by mouse peritoneal macrophages, implying the involvement of a "scavenger receptor" other than the AcLDL receptor. Numerous studies establish that loss of plasma membrane phospholipid asymmetry, which increases phosphatidylserine expression on the outer leaflet of the membrane, can play a key role in macrophage recognition of damaged and apoptotic cells. We report here that this recognition is in part attributable to the same mouse macrophage receptor that recognizes OxLDL. As described in an accompanying paper, this is a plasma membrane protein of 94-97 kDa. Phosphatidylserine liposomes show strong ligand binding to the same 94- to 97-kDa protein and this binding is inhibited by OxLDL but not by AcLDL. Inhibition of the RBC membrane phospholipid translocase by incubation with sodium vanadate caused a progressive increase in the appearance of phosphatidylserine on the cell surface and a parallel increase in the binding of these RBCs to macrophages, binding that was inhibited by OxLDL. Finally, OxLDL also inhibited the binding of sickled RBCs and apoptotic thymocytes to mouse macrophages. However, the latter was incomplete (approximately 50%), suggesting that other receptors are also involved. We suggest that the OxLDL receptor plays a significant role in recognition of damaged and apoptotic cells.

Animals↗
PubMed1995

Asymmetry of finger temperature and early behavior.

Measures of the temperature of the fingertips of eighty-three 4-year-old children revealed an unexpected asymmetry in which the index finger of the left hand but the ring finger of the right hand were the coolest digits. In addition, a subset of 20 children who had the coolest right compared with the left ring finger were more fearful to unfamiliar events and also had a cooler right than left forehead at 21 months of age.

Arousal↗
PubMed1995

Adsorption of human salivary proteins to titanium powder. I. Adsorption of human salivary albumin.

Titanium (Ti) is among the most widely used implant materials in dentistry today. The success of Ti implants is associated with their interactions with the surrounding tissues and biological fluids. In the present study, the adsorption of salivary proteins to Ti and the effect of calcium (Ca) on this process were investigated. Untreated and Ca-treated Ti powders were suspended in human clarified whole saliva. After incubation, the supernatant fluid was collected for protein analysis. The powders were then washed and resuspended in EDTA to desorb proteins from Ti surfaces. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Bradford protein assay were conducted to determine the concentration and type of proteins that adsorbed onto Ti surfaces. The presence of Ca ions enhanced the adsorption of salivary proteins to Ti. A 66 kDa protein, identified by immunoblotting as albumin, was found as the main adsorbed salivary protein. Adsorption of albumin to Ti pretreated with Ca was significantly greater than to native Ti. The Ca-dependent adsorption process was reversed by EDTA. The data suggest that salivary albumin is one of the main constituents of a salivary biofilm formed on Ti dental implants and its adsorption to Ti surfaces is Ca-dependent. The presence of albumin on Ti dental implants may affect plaque accumulation on the implants and the biocompatibility of Ti implants.

Adsorption↗
PubMed1995

Adsorption of salivary proteins onto prosthetic titanium components.

In vivo adsorption of salivary proteins onto prosthetic titanium components was analyzed after exposure of titanium abutments to the oral environment for a period of 2 to 6 weeks. Gel electrophoresis and Western immunoblotting were used to separate and identify the proteins, which were mainly alpha-amylase and serum albumin. Selective adsorption of proteins enables attachment of specific oral bacteria and thus may alter the composition of the dental plaque formed on titanium surfaces.

Adsorption↗
PubMed1995

Long-term course of obsessive-compulsive disorder treated in adolescence.

OBJECTIVE: To investigate the long-term course of obsessive-compulsive disorder treated in adolescence. METHOD: Fifteen young adults treated for the disorder in adolescence, mainly through not only by behavior therapy and family therapy, were followed up between 9 and 14 years later. RESULTS: Data were collected on 14 of the cases (93%, N = 15) from various sources including interview in person in 6 cases. Of the 14 cases, 6 were found to satisfy DSM-III-R criteria for obsessive-compulsive disorder at long-term follow-up, while 8 were not. These recovered participants were not currently taking medication, and long-lasting recovery was associated with good social adjustment. Chronic course was not attributable to lack of subsequent treatment. CONCLUSIONS: The recovery rate of 57% (N = 14) is similar to those found in other recent studies of outcome following vigorous treatment in adolescence. The findings are over the longest follow-up period so far reported for obsessive-compulsive disorder treated in adolescence. Positive response to treatment in adolescence can be followed by relapse after longer periods than have usually been studied.

Adjustment Disorders↗