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Biomedical subjects

M B Stemerman

Publications and source records attributed to M B Stemerman.

At least 37 records · Page 2Linked to original sources
PubMed1993

Inhibition of smooth muscle cell proliferation and DNA synthesis by Vasoprin--a biologic response modifier.

The effect of Vasoprin, a biologic response modifier (BRM), on smooth muscle cell DNA synthesis and intimal proliferation was studied. In this report, we have measured DNA specific activity (SA) and intimal thickening following balloon injury (balloon de-endothelialization (BDE)) after administration of Vasoprin. Various dose schedules were employed to assess Vasoprin's effect post BDE. Forty-eight hours following vascular injury (the peak of SMC DNA synthesis), Vasoprin administered at various treatment schedules showed between 54% and 72.6% +/- 9% (P < 0.0012) inhibition of DNA SA compared with vehicle controls. Vasoprin also diminished SMC intimal thickening following its administration. Seven days after vascular injury, at which time SMC neointimal proliferation reaches its peak, Vasoprin treated animals showed marked reduction in intimal thickening by 45.5% +/- 6.6% (P < 0.008), compared with the BDE rats receiving an agent vehicle as controls. The results of this report demonstrate that a biologic response modifier (Vasoprin) has a profound effect on SMC proliferation, and that the immune system may be a component in the progression of intimal thickening and hence vascular closure.

Animals↗
PubMed1993

Lipid fluidity modulates platelet aggregation and agglutination in vitro.

To determine the effect of altered membrane fluidity on platelet aggregation/agglutination, fresh, washed human platelets were treated with A2C, a cyclopropyl fatty acid ester which is known to enhance mobility of intrinsic membrane bilayer constituents and increase membrane fluidity. Fluorescence polarization studies demonstrated A2C incubation time- and concentration-dependent increases in platelet membrane fluidity (decreased fluorescence anisotropy). Preincubation with A2C was associated with diminished collagen, thrombin and ristocetin-induced platelet aggregation/agglutination. Aggregation/agglutination was diminished by 93 +/- 5% for collagen (0.2 mg/ml), 53 +/- 3% for thrombin (1.0 U/ml) and 85 +/- 9% for ristocetin (1.1 mg/ml). These data suggest that membrane fluidity is involved in the regulation of platelet function.

Agglutination↗
PubMed1993

Smooth muscle cell immediate-early gene and growth factor activation follows vascular injury. A putative in vivo mechanism for autocrine growth.

To understand the molecular events governing smooth muscle cell (SMC) proliferation in vivo, immediate-early gene (IEG) expression was assessed and related to growth factor ligand and receptor mRNA and SMC DNA synthesis after aortic injury. Balloon catheter injury evoked increases in SMC c-myc and thrombospondin (tsp) within 2 hours. The induction of these IEGs was followed by elevated transcripts to platelet-derived growth factor-A (PDGF-A), transforming growth factor-beta 1 (TGF-beta 1) and a basic fibroblast growth factor (bFGF) receptor. Whereas PDGF type-beta receptor mRNA was demonstrated in SMCs from control and balloon-injured aortas, no detectable signal was observed for the PDGF type-alpha receptor. To explore the potential linkage between IEG products and growth factor mRNA expression, cycloheximide was employed to block early protein synthesis after balloon injury. Induction of PDGF-A and TGF-beta 1 was attenuated by cycloheximide, but bFGF induction was unaffected. Moreover, cycloheximide superinduced IEGs and revealed PDGF-B transcripts, which were otherwise undetected. Seven days after aortic injury, a spontaneous increase in c-myc and tsp mRNA was noted. This IEG reactivation was followed 12 hours later by a twofold increase in SMC DNA synthesis. These findings corroborate an autocrine mode of SMC proliferation in vivo and suggest the IEG products may control such growth by stimulating growth factor genes.

3T3 Cells↗
PubMed1993

Localization of Fos and Jun proteins in rat aortic smooth muscle cells after vascular injury.

The availability of specific reagents to measure gene activity has provided important tools and potential new directions for the study of smooth muscle cell (SMC) proliferation in vivo. In this report, we have measured steady-state mRNA levels of several fos and jun family members in aortic tissue by Northern blotting after vascular injury. In addition, protein products of these genes were analyzed by immunocytochemistry. Within 15 minutes of balloon injury, mRNA levels of c-fos, fosB, c-jun, junB, and junD were elevated severalfold. In contrast, fos-related antigen (fra-1) mRNA showed a delayed onset of expression. The expression kinetics of these immediate early genes was similar to those in cultured cells stimulated to undergo proliferation by growth factors, suggesting that such SMC gene activation in vivo reflects permeation of blood-derived growth factors into the vessel wall or intravascular release of preformed growth factors. Translation of fos and jun genes into immunoreactive products was demonstrated 2 hours after balloon injury with antisera to Fos and Jun proteins. Treating rats with cycloheximide abolished this immunoreactivity. The distribution of Fos and Jun products was concentrated in SMC nuclei at the luminal border of the rat aorta. Such focal expression may have consequences for the initiation of SMC DNA synthesis and migration after vascular injury. Furthermore, the expression of Fos and Jun proteins in SMC after vascular balloon injury may be used as an index of SMC activation under a variety of experimental settings.

Animals↗
PubMed1992

Atherogenic levels of low-density lipoprotein increase endocytotic activity in cultured human endothelial cells.

Cultured human umbilical vein endothelial cells (EC) exposed to atherogenic low-density lipoprotein (LDL) levels for protracted periods demonstrated heightened endocytosis. Confluent EC were incubated with LDL 90 to 240 mg/dl cholesterol for 1 to 4 days and endocytosis was measured by 14C-sucrose uptake. Control EC and cells incubated with 90 mg/dl LDL cholesterol showed similar uptakes of 14C-sucrose during all measured time periods. In contrast, EC exposed to 240 mg/dl LDL cholesterol showed an increase in endocytosis beginning at 2 days, whereas 160 mg/dl LDL cholesterol promoted increased uptake by 4 days. The endocytotic activity of LDL-perturbed EC is reduced to levels seen in control cells by cytochalasin B, an actin polymerization inhibitor. This finding suggests a modulatory role for the cytoskeleton in endocytosis changes. Examination of LDL-perturbed EC cytoskeleton reveals structural remodeling resulting in a marked increase in stress fibers. Cytochalasin B exposure causes a loss of stress fibers with the formation of globular filamental aggregates. Such LDL-induced cellular functional changes may contribute mechanistically to endothelial dysfunction, which is widely held to be a major contributing factor in the pathogenesis of atherosclerosis.

Arteriosclerosis↗
PubMed1991

Effect of low-density lipoprotein on endothelial cell membrane fluidity and mononuclear cell attachment.

To determine the effects of prolonged low-density lipoprotein (LDL) exposure in vitro on cultured endothelial cell (EC) lipid dynamics and cellular function, human umbilical vein ECs were incubated in LDL concentrations [cholesterol (Chol) = 240 mg/dl] associated with the premature development of atherosclerosis. After 4 days of incubation, cells were examined for changes in cellular lipid composition and for membrane fluidity. Results indicate that LDL-EC have increased Chol content (control EC vs. LDL-EC = 22.4 +/- 5.26 vs. 38.9 +/- 0.24 nmol/10(6) cells, P less than 0.05) and cellular Chol-to-phospholipid ratio (0.61 +/- 0.10 vs. 1.21 +/- 0.10 mol/mol, P less than 0.05). Augmentation of EC Chol content was accompanied by a marked decrease in EC cellular membrane fluidity as assessed by fluorescence polarization (anisotropy, r values, 0.172 +/- 0.019 vs. 0.226 +/- 0.014, P less than 0.0001). LDL-induced changes in EC lipid dynamics were associated with enhanced EC binding of monocytes (P less than 0.05) and U937 cells (P less than 0.01). Both LDL-induced decreases in membrane fluidity and enhanced attachment of mononuclear cells were reversed to control levels following a 2-min incubation of LDL-EC with the membrane mobility agent, A2C. These data therefore suggest that LDL-induced modulations in lipid dynamics play an important role in perturbation of EC function.

Cell Adhesion↗
PubMed1990

14, 15-Epoxyeicosatrienoic acid promotes endothelial cell dependent adhesion of human monocytic tumor U937 cells.

Arachidonic acid (AA) can be metabolized in endothelial cells (EC) to a series of epoxides via cytochrome P-450 epoxygenase with 14,15 epoxyeicosatrienoic acid (14,15-EET) as the major product. In this communication we report that 14,15-EET significantly enhances U937 cell attachment to EC with maximal cell attachment at 2.5 to 5 x 10(-7) M 14,15-EET. Thus, 14,15-EET may play a substantial role in inflammation and/or atherogenesis by inducing monocyte attachment to EC.

8,11,14-Eicosatrienoic Acid↗
PubMed1990

Bradykinin induces superoxide anion release from human endothelial cells.

The time-dependent release of superoxide anion (O2-) from bradykinin (Bk)-stimulated human umbilical vein endothelial cells (EC) was measured as the superoxide dismutase-inhibitable reduction of ferricytochrome C employing a novel application of microspectrophotometry. In the absence of Bk, O2- release by EC was not detectable. EC exposure to Bk (10(-6) to 10(-5) M) resulted in a rapid release of O2-. The release of O2- occurred within 5 minutes of exposure. O2- release was partially inhibited by indomethacin (63 +/- 6%), thus suggesting that arachidonic acid metabolism, through cyclooxygenase, contributes to EC O2- production. EC O2- release may be an important component in the pathophysiologic actions of Bk on vascular function.

Bradykinin↗
PubMed1990

Early proto-oncogene expression in rat aortic smooth muscle cells following endothelial removal.

To study the mechanism(s) of vascular smooth muscle cell proliferation in vivo, mRNA levels of c-fos, c-jun, and c-myc were determined by Northern blot analysis following vascular balloon de-endothelialization (BDE). Medial smooth muscle cells (SMC) were separated and studied by enzymatic digestion of the vessel wall. mRNA levels of c-fos and c-jun from aortic smooth muscle cells (SMC) were simultaneously induced within 30 minutes of BDE and declined to baseline by 1.5 hours, c-myc mRNA did not begin to increase until 1 hour after vascular injury. Levels of c-myc peaked at 2 hours and were sustained for an additional 4 hours before gradually declining. Smooth muscle cells derived from enzyme-treated control aortae that did not undergo BDE expressed c-fos and c-jun, but showed no evidence of c-myc message. In contrast, nonenzymatically treated, non-BDE whole aortae (containing both media and adventitia) demonstrated a prominent c-myc signal, but failed to express c-fos and c-jun. Corresponding examination of adventitia derived from enzyme-treated aortae showed this tissue to be a source of all three proto-oncogenes. The results of this study demonstrate the earliest in vivo molecular markers of vascular injury reported to date and implicate SMC proto-oncogene expression in the initiation of SMC proliferation. Furthermore these findings suggest two avenues for proto-oncogene induction, that are due to (1) vessel wall manipulation and (2) humoral stimulation.

Animals↗
PubMed1990

Atherogenic concentrations of low-density lipoprotein enhance endothelial cell generation of epoxyeicosatrienoic acid products.

To investigate the effects of protracted low-density lipoprotein (LDL) exposure on endothelial cell (EC) epoxyeicosatrienoic acid (EET) generation, human umbilical vein ECs were incubated in atherogenic concentrations of LDL (240 mg cholesterol per deciliter) (LDL-EC). After 4 days' incubation with LDL, EC were stimulated with human thrombin in the presence of 1-[14C]-arachidonic acid. Substantially more EET products were generated by LDL-ECs than by cells not exposed to high levels of LDL (C-EC). Thrombin stimulation caused LDL-EC to produce five- to eightfold more in 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET, with 14,15-EET as the major product. This is the first demonstration, to date, that EETs can be induced in EC. Metapyrone (SKF-525A) markedly inhibited EC EET generation, indicating a role for the cytochrome P-450 enzyme system in human EC arachidonic acid metabolism. One EET product, 14,15-EET, has been found to be chemotactic and to promote adhesion of U937 cells, a human monocytic lymphoma cell line, to EC. Thus, protracted exposure to atherogenic LDL concentrations increases the generation of chemotactic and adhesion factors (ie, 14,15-EET) after thrombin stimulation, possibly through the cytochrome P-450 enzyme system.

8,11,14-Eicosatrienoic Acid↗
PubMed1989

Agonist-dependent generation of lipoxins from rat basophilic leukemia cell (RBL-1).

Incubation of RBL-1 cells in the presence of 15-HPETE and various agonists generated lipoxins and several isomers. Addition of either A23187, fMLP or PMA modulated the number of isomers and amount of lipoxins produced. Administration of A23187 yielded the largest amount of product (5.3 +/- 1.6 micrograms per 10(8) cells) and generated a total of six and three isomers of LXA4 and B4, respectively. This was 2-fold greater than fMLP, which produced a total of two isomers of LXA4 and LXB4. Addition of PMA generated only LXA4 (0.68 +/- 0.26 micrograms). This is similar to the control receiving only 15-HPETE. Biologically derived LXA4 (3 nM) isolated from RBL-1 incubations contracted a rat tail artery preparation to 12% of the maximum induced by phenylephrine (0.125 microM), whereas LXA4 standard (3 nM) elicited 17.6% of the maximum contraction. These results indicate that RBL-1 cells can utilize exogenous 15-HPETE to generate biologically active lipoxins. Further, the yield and isomers of lipoxins can be modified by different agonists.

Animals↗
PubMed1989

Low-density lipoprotein transport in blood vessel walls of squirrel monkeys.

Transmural accumulations of low-density lipoprotein (LDL) were examined in the blood vessel walls of four squirrel monkeys. Vascular wall concentrations of LDL were measured using quantitative autoradiography after 125I-labeled LDL circulation for 30 min. Profiles of relative tissue concentration from different sections in the same region were similar to each other, and there was little animal-to-animal variation. Concentrations were highest near the luminal endothelium, lower near the medial-adventitial border, and lowest within the media. Profiles from different regions fell into three groups: 1) aortic samples had steep intimal concentration gradients and near-zero media concentrations; 2) the iliac, femoral, popliteal, and common carotid arteries had higher intimal concentrations than group 1 but had similar concentrations deep within the media; and 3) the cerebral and coronary arteries, inferior vena cava, and pulmonary artery had intimal concentrations that were similar to group 2, but the concentrations deep within the media were greater than either groups 1 or 2. Arterial bifurcation profiles from the inner wall and the outer walls were similar to each other and to profiles from the upstream and downstream areas. Out of 280 total sites examined, 15 examples of profiles with substantially increased concentrations near the luminal endothelium were found scattered throughout the cardiovascular system, demonstrating that there are focal regions throughout the cardiovascular system which have greatly increased 125I-LDL transendothelial permeability.

Animals↗
PubMed1988

Low-density lipoprotein preparation by combined diafiltration and ultracentrifugation.

A method for isolating low-density lipoprotein by combining diafiltration and ultracentrifugation is described. Diafiltration separates plasma components by use of an ultrafiltration membrane that excludes particles of molecular weight greater than 300,000. The retentate is concentrated three- to fourfold by ultrafiltration, allowing large-scale preparation of low-density lipoprotein. Low-density lipoprotein prepared in this manner is similar in physical, chemical, and biologic properties to low-density lipoprotein isolated by sequential density ultracentrifugation alone. When low-density lipoprotein, prepared by either method, was added to human umbilical vein endothelial cell cultures, no cytotoxicity was observed. The techniques described reduce the demand on multiple rotors and ultracentrifuges for large-scale preparation of low-density lipoprotein suitable and often needed for tissue culture studies.

Arteriosclerosis↗
PubMed1988

Perturbation of cultured human endothelial cells by atherogenic levels of low density lipoprotein.

Cultured human umbilical vein endothelial cells (EC) exposed to atherogenic levels of low density lipoprotein (LDL) for protracted periods demonstrated no measurable evidence of overt cytotoxicity, but were perturbed as indicated by an increase in prostacyclin (PGI2) production. Confluent EC were incubated with high LDL concentrations (240 or 330 mg/dl cholesterol) for 1 to 12 days. LDL was added to culture media containing 25% human lipoprotein-deficient serum to determine the effects of LDL independent of other lipoproteins. LDL did not injure EC as assessed by cell count, vital dye exclusion, 51chromium release, and lactate dehydrogenase release. Although high concentrations of LDL did not cause EC cytotoxicity, such LDL concentrations did results in increased PGI2 generation. PGI2 accumulation in postincubation media was increased two-to-fivefold in otherwise unstimulated cells as measured by radioimmunoassay of the stable PGI2 breakdown product, 6-keto-PGF1-alpha. This elevation persisted for the entire 12-day exposure to high LDL concentrations. These results indicate that prolonged exposure to atherogenic concentrations of LDL does not effect EC viability, but does cause an endothelial perturbation as demonstrated by an increased PGI2 production.

Arteriosclerosis↗
PubMed1988

Reversible changes in stress fiber expression and cell shape in regenerating rat and rabbit aortic endothelium.

The influence of intimal de-endothelialization on stress fiber expression in regenerating rat and rabbit aortic endothelium was studied using immunofluorescence microscopy. Rat thoracic and abdominal aortae were balloon de-endothelialized, and endothelial cell shape and stress fiber expression was studied in both uninjured and de-endothelialized animals. In control animals, the majority of thoracic endothelial cells did not contain stress fibers while the majority of abdominal endothelial cells did. One week after injury, all the endothelial cells distal to the regenerating edge contained very prominent stress fibers. In areas directly adjacent to the still de-endothelialized surface, the endothelial cells had an intense, diffuse cytoplasmic staining without stress fibers. Regenerating endothelium also had a substantially higher length-to-width ratio, but smaller cell areas. Six weeks after injury, the endothelium had completely regenerated, and stress fibers were lost from the majority of the thoracic endothelial cells. Changes in abdominal aorta stress fiber expression were not as marked. In the rabbit, all the control thoracic endothelial cells had stress fibers; however, cells at the leading edge of a narrow region of de-endothelialization had few stress fibers. The results suggest that stress fibers do not play a primary role in cellular migration in situ. The transient increase in stress fiber expression in the rat may result from a temporary demand for greater adhesive capabilities until the subendothelial extracellular matrix is remodeled.

Animals↗
PubMed1987

Endothelial cell perturbation and low-density lipoprotein. Quantitative autoradiography.

The focal entry and accumulation of LDL within the arterial wall of the normal animal may represent an early stage in the development of the atherosclerotic plaque. Concentrations of LDL 10 to 100 times normal medial concentrations might be difficult to clear from the arterial wall, permitting accumulation of lipid. Elevated LDL concentrations, in proximity to smooth muscle cells, appear to stimulate SMC proliferation. High LDL concentrations might also enhance mononuclear cell adhesion to endothelium. Since LDL has a high affinity for heparin and heparin for growth factors, LDL accumulation may be a mechanism for the concentration of such materials in the intima. The observation of markedly enhanced macromolecular permeability foci could be related to several potential mechanisms of initiation of atherosclerosis. This observation is of particular note when the focal occurrence of atherosclerosis is considered. Although atherosclerosis is seen as a generalized thickening of the intima, it is the focal narrowing of the lumen that is often responsible for the stenosis which produces symptoms such as angina or myocardial infarction.

Animals↗