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Biomedical subjects

D Steinberg

Publications and source records attributed to D Steinberg.

At least 109 records · Page 6Linked to original sources
PubMed1995

Effect of the antioxidant N,N'-diphenyl 1,4-phenylenediamine (DPPD) on atherosclerosis in apoE-deficient mice.

Apolipoprotein (apo) E-deficient mice develop atherosclerotic lesions that contain epitopes formed during the oxidative modification of lipoproteins, and they demonstrate high titers of circulating autoantibodies against such epitopes, suggesting that this murine strain may provide a model to investigate the atherogenic mechanisms of oxidized lipoproteins (Palinski et al, Arterioscler Thromb. 1994; 14:605-616). To test the hypothesis that lipoprotein oxidation contributes to lesion formation in apoE-deficient mice, we studied the effect of the antioxidant N,N'-diphenyl 1,4-phenylenediamine (DPPD) in mice fed a high-fat diet containing 0.15% cholesterol. Animals were divided into two subgroups matched for sex and plasma cholesterol levels, and DPPD (0.5% wt/wt) was added to the diet of one subgroup. Throughout the 6 months of intervention, DPPD treatment had no significant effect on plasma cholesterol. Plasma levels of DPPD at the end of the experiment were 33.1 mumol/L. As judged by resistance to loss of polyunsaturated fatty acids, lipoproteins (d < 1.019 g/mL) from DPPD-treated animals showed greater resistance to copper-induced oxidation than lipoproteins from control animals. In addition, there was a greater than twofold prolongation of the lag time in the formation of conjugated dienes in the LDL and IDL fractions of DPPD-treated mice. Atherosclerosis was significantly reduced, by 36% in the DPPD-treated mice (14.0 +/- 4.53% of aortic surface area versus 21.9 +/- 11.6%; n = 32; P < .02). These results are consistent with the hypothesis that lipoprotein oxidation contributes to atherogenesis in apoE-deficient mice. However, further studies with other antioxidants are needed to validate this hypothesis.

Animals↗
PubMed1995

Mercury levels among dental personnel in Israel: a preliminary study.

Amalgam, the most prevalent dental restoration material used in dentistry, is potentially toxic because it contains mercury. Recent international publications confirm that mercury is potentially hazardous to dental personnel, who are exposed to mercury vapors both during their work at the office and from amalgam restorations in their own oral cavities. The purpose of our study was to compare urinary mercury levels of dental personnel with a control group, and to explore possible correlations between environmental factors in the dental office and the urinary level of the personnel. Our results indicate that the urinary mercury levels of the tested dental professionals were significantly higher than those of the control group (2.39 +/- 0.319 vs. 0.899 +/- 0.34 micrograms mercury/g creatinine). Of the dental personnel examined, 72% had detectable levels of urinary mercury, compared to 27% of the control group. Although mercury levels in all participants did not exceed the toxic limit, the above findings clearly point to the need for a continuation of this survey.

Adult↗
PubMed1995

Lipoperoxides in LDL incubated with fibroblasts that overexpress 15-lipoxygenase.

Oxidative modification of LDL plays an important role in early atherogenesis but the mechanisms, nonenzymatic and/or enzymatic, by which LDL is oxidized in vivo remain to be established. Several lines of evidence suggest that cellular 15-lipoxygenase (arachidonate 15-oxidoreductase, EC.1.13.11.13) (15-LO) may contribute to oxidative modification of LDL, including recent studies demonstrating that murine fibroblasts overexpressing 15-LO have an enhanced capacity to oxidize LDL in the medium. The present studies were undertaken to better understand the mechanisms by which cells expressing 15-LO bring about oxidative modification of LDL. LDL incubated 1-2 h with the 15-LO-enriched cells showed a much higher lipoperoxide (LOOH) content than did LDL incubated with control cells. By far the largest absolute increase occurred in cholesteryl ester hydroperoxide (CE-OOH), a much lesser increase in free fatty acid hydroperoxides (FFA-OOH), and only a very small increase in phospholipid hydroperoxides (PL-OOH). Addition of EDTA to the medium abolished these increases in LDL lipid hydroperoxides. Enrichment of LDL with probucol or vitamin E also prevented CE-OOH accumulation. Incubation of LDL with linoleic acid hydroperoxide in the absence of cells also caused a significant increase in CE-OOH and this was markedly inhibited by EDTA. These findings provide further evidence for the potential of 15-LO to participate in LDL oxidation by way of a mechanism involving introduction of LOOH into the LDL particle followed by metal-catalyzed propagation.

Animals↗
PubMed1994

Recognition of oxidatively damaged erythrocytes by a macrophage receptor with specificity for oxidized low density lipoprotein.

Macrophages specifically bind and internalize oxidatively modified low density lipoprotein (LDL) via the acetyl-LDL receptor and possibly one or more additional receptors jointly designated here as scavenger receptors. It is well accepted that these receptors are intimately involved in the formation of foam cells during atherogenesis. However, the normal physiological or pathophysiological role for these receptors has not been established. Oxidation of plasma membranes is a common accompaniment of cell damage and senescence. In particular, aged erythrocytes demonstrate peroxidation of their cell membrane lipids. In the present studies we show that oxidized human erythrocytes (treated with copper plus ascorbate or hydrogen peroxide) are bound and phagocytosed by mouse peritoneal macrophages in the absence of opsonizing antibodies. There was little or no binding of untreated erythrocytes. Oxidized LDL, but not acetylated or native LDL, inhibited this binding and uptake of oxidized erythrocytes. Inhibitors of scavenger receptor binding, including polyinosinic acid and fucoidin, also prevented binding of the oxidized red blood cells. We suggest that oxidative damage of erythrocytes results in the formation of lipid-protein conjugate(s) closely related to some of the conjugates found in oxidized LDL, making the oxidized erythrocyte a ligand for the macrophage scavenger receptors, apparently at a site distinct from that responsible for the binding of acetylated LDL. Oxidative modification of plasma membranes may represent a general mechanism that marks damaged cells for phagocytosis by macrophages.

Animals↗
PubMed1994

A sudden outbreak of illness suggestive of mass hysteria in schoolchildren.

OBJECTIVE: To clarify factors contributing to mass illness of sudden onset by studying an outbreak that was apparently triggered by a gaseous odor and that involved a rapid, extensive response by school and fire officials. SETTING: Urban elementary school. MAIN OUTCOME MEASURE: A standardized student questionnaire was designed to identify potential illness predictors. DESIGN: Four weeks following the outbreak, public health officials distributed the questionnaire to all students in regular classes in grades 3 through 6 (N = 319), representing 46% of the estimated 680 students present the day of the outbreak. RESULTS: Seventy-seven percent of the students who completed the questionnaire reported that they experienced physical symptoms during the epidemic. A stepwise regression analysis demonstrated several independent variables that predicted the severity of illness, including the intensity of the odor smelled during the outbreak (P < .0001), becoming sick after the fire trucks arrived (P < .0001), and believing in an environmental cause for the illness (P < .002). CONCLUSIONS: These results indicate that both psychological and environmental factors, real or perceived, may contribute to sudden-onset epidemics of hysteria. Moreover, the response intervention of officials may influence the extent of such outbreaks. Early recognition of psychological causes and dispersion of groups at risk could reduce morbidity and associated health care costs.

Child↗
PubMed1994

Prevention of thromboembolism in spinal cord injury: role of low molecular weight heparin.

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are major causes of morbidity and mortality in patients with acute spinal cord injury. Our preliminary studies indicated that low molecular weight heparin (LMWH) was significantly more effective than standard heparin in preventing these complications. We have now extended these studies by screening an additional 122 patients and treating 60 who met predefined criteria with LMWH in a dose of 3,500 anti-Xa U given subcutaneously once daily for 8 weeks. All patients were examined daily at bedside and had regularly scheduled venous ultrasonography; those with abnormalities had confirmatory venography and lung scans. Postmortem examinations were conducted in those who died. Forty completed the trial without incident, 6 had DVT (4 proximal and 2 distal), 1 had a fatal PE, 1 had postoperative bleeding requiring discontinuation of the LMWH, 10 were transferred or discharged, and 2 died of respiratory failure. The percentage of patients free of thrombosis or bleeding after 8 weeks of treatment was 85.9 +/- 5.0% standard error of mean (SEM). Thirty-three patients entered a follow-up observation period of 4 weeks without thromboprophylaxis; 2 weeks into this period 1 had a proximal DVT and 1 had a fatal PE; the course of the remainder was uneventful. We conclude that LMWH compares favorably with standard heparin in preventing venous thromboembolism, and is associated with significantly less bleeding. Eight weeks of prophylaxis seems adequate for most patients.

Adult↗
PubMed1994

Rabbit and human atherosclerotic lesions contain IgG that recognizes epitopes of oxidized LDL.

Atherosclerotic lesions contain relatively large quantities of IgG. We have previously shown that both human and rabbit sera contain autoantibodies against epitopes of oxidized (Ox) low-density lipoprotein (LDL) and that LDL isolated from atherosclerotic lesions contains small amounts of tightly bound IgG. However, it is not known whether IgG isolated from atherosclerotic lesions recognizes epitopes present in native LDL or Ox-LDL. IgG was isolated from Watanabe heritable hyperlipidemic (WHHL) rabbit atherosclerotic lesions by sequential salt extractions, purified by fast protein liquid chromatography on protein G, and used in a solid-phase radioimmunoassay. IgG and immune complexes were also isolated from the saline extracts of human lesions by adsorption onto latex beads coated with anti-human IgG antibodies or protein A. IgG isolated from rabbit lesions showed significant titers against malondialdehyde (MDA)-modified LDL and LDL oxidized by copper ions for 4 and 18 hours but not against native LDL. On Western blots, lesion IgG stained MDA-LDL and fragments of Ox-LDL. Western blots of immune complexes isolated from human lesions revealed the presence in the isolated complexes of both apoprotein B and apoprotein B fragments, which reacted with antibodies to MDA-lysine. Furthermore, rabbit lesion IgG immunostained epitopes of Ox-LDL present in human atherosclerotic lesions. Immunostains obtained with rabbit lesion IgG were similar to those obtained with a monoclonal antibody specific for MDA-lysine. The results show that human and rabbit atherosclerotic lesions contain IgG that recognizes epitopes characteristic of Ox-LDL. These data suggest that immunologic processes may be an important component of the atherogenic process.

Adult↗
PubMed1994

ApoE-deficient mice are a model of lipoprotein oxidation in atherogenesis. Demonstration of oxidation-specific epitopes in lesions and high titers of autoantibodies to malondialdehyde-lysine in serum.

Apolipoprotein (apo) E-deficient transgenic mice develop marked hyperlipidemia and progressive atherosclerotic lesions. To explore whether oxidative modification of lipoproteins is involved in atherogenesis in this murine model, we performed extensive immunocytochemical studies. Atherosclerotic lesions ranging from early fatty streaks to very advanced plaques were examined from the aortic valve region and the thoracic and abdominal aorta. Using guinea pig antisera against malondialdehyde (MDA)-lysine and 4-hydroxynonenal-lysine, two epitopes generated during the oxidative modification of low-density lipoprotein (LDL), we demonstrated the presence of these "oxidation-specific epitopes" in atherosclerotic lesions. In early lesions, oxidation-specific epitopes were found predominantly in macrophage-rich areas, whereas diffuse extracellular staining predominated in necrotic areas of advanced lesions. We have previously shown that autoantibodies against MDA-lysine are present in the circulation of humans and rabbits and that the immunoglobulin fraction extracted from their lesions contains autoantibodies against several "oxidation-specific" epitopes. Sera from apoE-deficient mice also contained circulating autoantibodies to MDA-lysine, and both early and advanced lesions were rich in murine immunoglobulins. Titers of serum autoantibodies were significantly higher in apoE-deficient mice than in C57BL/6 mice. Autoantibodies in murine plasma recognized MDA-lysine epitopes in atherosclerotic lesions of rabbits, and the immunostaining was competitively inhibited by excess human MDA-LDL. Similar findings were obtained by competitive radioimmunoassay. Finally, a morphometric technique was developed and tested in these mice that allows a quantitative assessment of aortic atherosclerosis. These findings suggest that in apoE-deficient mice, lipoprotein oxidation is involved in atherogenesis and that these transgenic mice constitute an appropriate model with which to study the antiatherogenic effect of antioxidant intervention.

Animals↗
PubMed1994

Inhibition of hypercholesterolemia-induced atherosclerosis in the nonhuman primate by probucol. I. Is the extent of atherosclerosis related to resistance of LDL to oxidation?

Lipoprotein oxidation is believed to play an important role in atherogenesis. To investigate whether inhibition of oxidation of low density lipoprotein (LDL) would alter atherogenesis in the nonhuman primate, we administered probucol, a potent antioxidant, to Macaca nemestrina fed a high-fat, high-cholesterol diet. Probucol was administered to half of the 16 monkeys 14 wk after starting the hypercholesterolemic diet, and was given daily until they were sacrificed after 11 mos. To evaluate the antioxidant effect of probucol, the resistance of isolated plasma LDL to in vitro oxidation was evaluated. Probucol significantly increased the resistance of LDL to oxidative modification, as shown by an increase in the lag time required for conjugated diene formation. Lesions in the probucol-treated animals appeared less mature, and increased accumulation of lipid was observed in smooth muscle cells. Comparison of all control and probucol-treated monkeys demonstrated that intimal lesion areas in the thoracic aortas of the probucol-treated monkeys were reduced by 43% (P < 0.0001), but no significant difference in lesion area was found in the abdominal aortas or in the iliac arteries. However, the lag phase of conjugated diene formation was not prolonged in 2 of the 8 probucol-treated animals. A plot of intimal lesion size versus lag phase of all 16 animals showed a trend that lesion size was inversely related to oxidation resistance for all anatomic sites. The strong inverse relationship between intimal lesion size and resistance of LDL to oxidation supports a role for lipoprotein oxidation in the development and progression of lesions of atherosclerosis. The possibility that some of the effect is due to other biological properties of probucol cannot be ruled out.

Animals↗
PubMed1994

A comparison of the antiatherogenic effects of probucol and of a structural analogue of probucol in low density lipoprotein receptor-deficient rabbits.

The efficacies of probucol and a close structural analogue as antioxidants in the prevention of atherogenesis in LDL receptor-deficient rabbits were compared. The antioxidant potency of the analogue in vitro was equal to that of probucol. Its biological availability was much greater: almost comparable concentrations in total plasma were achieved by feeding 1% probucol (wt/wt) and 0.05% analogue (wt/wt). Total plasma concentrations were comparable, but the concentration of probucol within the LDL fraction was about twice that of the analogue. Probucol slowed lesion progression by almost 50%, confirming earlier reports; the analogue, however, showed no detectable inhibitory effect on atherogenesis. Resistance of LDL to oxidation was measured at the end of the study by incubating it with Cu2+ and measuring the rate of diene conjugation. Probucol prolonged diene conjugation lag time from the control value of 130 min to values > 1,000 min. The analogue approximately tripled the lag time (mean, 410 min) and yet failed to slow the atherogenic process. The results suggest that LDL resistance to oxidation must reach some threshold level before there is significant protection against atherogenesis. However, probucol has additional biological effects, possibly not shared by the analogue, that could contribute to its antiatherogenic potential.

Animals↗
PubMed1994

P-selectin mediates the interaction of circulating leukocytes with platelets and microvascular endothelium in response to oxidized lipoprotein in vivo.

BACKGROUND: Oxidized low density lipoprotein (oxLDL) has been demonstrated to stimulate leukocyte/endothelium interaction, an early feature of atherogenesis. Using the skinfold chamber model for intravital microscopy in hamsters and mice, we have shown that oxLDL-induced leukocyte adhesion to microvascular endothelium shares many characteristics with leukocyte adhesion during inflammation and ischemia/reperfusion, including the involvement of beta 2 integrin adhesion molecules. In light of the two-step model of leukocyte adhesion, we have examined the contribution of P-selectin to oxLDL-induced leukocyte/endothelium interaction. P-selectin is an inducible adhesion molecule on platelets and endothelium, mediating the initial steps of leukocyte margination and rolling along the endothelial lining, as well as of aggregate formation between platelets and leukocytes. EXPERIMENTAL DESIGN: For our studies, we used the dorsal skinfold chamber model for intravital fluorescence microscopy on awake Syrian golden hamsters. Hamsters were treated 10 minutes before oxLDL-injection (oxidized by Cu2+, 4 mg/kg body weight, intravenously) with blocking antibodies to P-selectin (2 mg/kg body weight intravenously, N = 7). RESULTS: In seven control animals (pretreated with an irrelevant IgG antibody), oxLDL injection elicited leukocyte rolling and adhesion on both venular and arteriolar endothelium, and also the formation of aggregates tumbling down the microvessels and firmly adhering to the microvascular endothelium. The aggregates consisted of leukocytes and activated, dendritic platelets, as assessed by scanning electron microscopy of the buffy coat isolated by density gradient centrifugation of whole blood taken from hamsters 15 minutes after injection of oxLDL. Leukocyte adhesion to venular and arteriolar endothelium, as well as the formation of leukocyte/platelet aggregates were significantly reduced by pretreatment of the animals with anti-P-selectin antibodies. CONCLUSIONS: These data emphasize the similarities between leukocyte adhesion in response to oxLDL and in other pathophysiologic conditions, identifying P-selectin as a crucial player in the interaction between leukocytes and microvascular endothelium as well as in the formation of circulating leukocyte/platelet aggregates.

Animals↗
PubMed1993

Peroxidase-dependent metal-independent oxidation of low density lipoprotein in vitro: a model for in vivo oxidation?

Oxidative modification of low density lipoprotein is believed to be an important pathway by which the lipoprotein becomes atherogenic. The in vitro systems for oxidative modification of low density lipoprotein thus far described all appear to depend upon the presence in the medium of free transition metal ions (copper or iron). In vivo, on the other hand, these metals are present almost exclusively in tightly complexed forms that do not catalyze oxidative modification. The present studies describe oxidation of low density lipoprotein in a simple system that does not depend upon the presence of added free metal ions. It requires the presence of horseradish peroxidase and either hydrogen peroxide or lipid hydroperoxides.

Free Radicals↗
PubMed1993

Effects of oleate-rich and linoleate-rich diets on the susceptibility of low density lipoprotein to oxidative modification in mildly hypercholesterolemic subjects.

We report the results of feeding oleate- or linoleate-enriched diets for 8 wk to mildly hypercholesterolemic subjects and the resulting alterations in composition and functional properties of their plasma LDL and HDL. LDL isolated from subjects on oleate-enriched diets was less susceptible to copper-mediated oxidation, as measured by conjugated diene and lipid peroxide formation, and less susceptible to LDL-protein modification, as evidenced by reduced LDL macrophage degradation after copper- or endothelial cell-induced oxidation. For all subjects, the percentage of 18:2 in LDL correlated strongly with the extent of conjugated diene formation (r = 0.89, P < 0.01) and macrophage degradation (r = 0.71, P < 0.01). Oxidation of LDL led to initial rapid depletion of unsaturated fatty acids in phospholipids followed by extensive loss of unsaturated fatty acids in cholesteryl esters and triglycerides. Changes in HDL fatty acid composition also occurred. However, HDL from both dietary groups retained its ability to inhibit oxidative modification of LDL. This study demonstrates that alterations in dietary fatty acid composition can effectively alter the fatty acid distribution of LDL and HDL in hypercholesterolemic subjects and that susceptibility to LDL oxidation is altered by these changes. Substitution of monounsaturated (rather than polyunsaturated) fatty acids for saturated fatty acids in the diet might be preferable for the prevention of atherosclerosis.

Adult↗
PubMed1993

Oxidatively modified low density lipoprotein is a chemoattractant for human T lymphocytes.

Oxidatively modified low density lipoprotein (Ox-LDL) is a known chemoattractant for monocytes. Here we demonstrate, using a modified Boyden chamber assay, that human peripheral blood T lymphocytes, but not B lymphocytes, also respond chemotactically to Ox-LDL, showing a threefold increase over control and an optimum response at 10 micrograms/ml. Copper and endothelial cell-oxidized LDL and beta-VLDL were used and gave similar results. The activity was not chemokinetic and native LDL possessed no chemoattractant activity. The chemoattractant activity was found to reside in the lipid fraction of Ox-LDL. Lysophosphatidylcholine is a major phospholipid component of Ox-LDL and is known to be chemotactic for monocytes. We show that lysophosphatidylcholine is also chemotactic for T lymphocytes with a maximal fourfold increase at 10 microM. Nonmetabolizable analogues of lysophosphatidylcholine had no such chemotactic effect. Thus, Ox-LDL, by virtue of its lysophosphatidylcholine content, may contribute to the recruitment of both T lymphocytes and monocytes into developing atherosclerotic lesions.

Animals↗