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Biomedical subjects

G M Chisolm

Publications and source records attributed to G M Chisolm.

At least 73 records · Page 4Linked to original sources
PubMed1985

Monocytes and neutrophils oxidize low density lipoprotein making it cytotoxic.

Free radicals are believed to be involved in leukocyte induced tissue injury. The present studies were performed to determine whether low density lipoprotein (LDL) might serve as a mediator of tissue injury after leukocyte induced free radical oxidation of LDL. Our results show that incubation of LDL with monocytes or polymorphonuclear leukocytes (PMN) leads to oxidation of the lipoprotein rendering it toxic to proliferating fibroblasts. Monocyte activation enhances these effects. Butylated hydroxytoluene (BHT), vitamin E (vit E) and glutathione (GSH) virtually prevent the oxidation of LDL and the formation of cytotoxic LDL, indicating that these alterations are mediated by leukocyte-derived free radicals. This is the first demonstration that short-lived free radicals emanating from phagocytic cells could mediate cell injury through the action of a stable cytotoxin formed by the oxidation of LDL. The fact that lipoproteins can transfer a cytotoxic effect from leukocytes to proliferating cells reveals a pathway for cell destruction which may have implications in atherosclerotic plaque progression, macrophage mediated toxicity to tumor cells and tissue injury by inflammatory processes.

Cells, Cultured↗
PubMed1983

The effect of ionophore A23187 on albumin internalization in cultured human umbilical vein endothelial cells.

The effects of calcium and the calcium ionophore A23187 on endocytosis were studied in cultured human umbilical vein endothelial cells using iodinated human albumin to measure bulk phase endocytosis. In the absence of the ionophore, varying the levels of extracellular calcium did not affect endocytosis. In the presence of 10 microM A23187, the endocytic clearance of albumin decreased approx. 50% when exposed to physiological concentrations of extracellular calcium, but increased approx. 50% at lower calcium concentrations. Since the ionophore is known to alter cellular calcium levels, these results are compatible with a role for intracellular calcium in the modulation of endothelial cell endocytosis.

Calcimycin↗
PubMed1983

Transmural [125I]albumin concentration in the rabbit aorta during acute hypoxia.

We have quantified the concentration profile of 125I-labeled rabbit albumin in the avascular intima and media of the rabbit descending thoracic aorta following intravenous injection under control and acute hypoxic conditions in vivo. Our purpose was to determine if alterations occurred in the transmural concentration profiles which could be attributed to hypoxia-induced changes in the permeability of the intimal endothelium to plasma-borne macromolecules. The profiles were obtained with frozen serial sections of the aorta from experiments of 30 min duration. Acute hypoxia was induced by addition of nitrogen to the breathing mixture. The hypoxia resulted in arterial pO2 values of 23--32 mm Hg while the arterial pO2 in the control animals ranged from 80 to 88 mm Hg. All animals were under sodium pentobarbital anesthesia. The results revealed no detectable changes in the concentration profile in the inner media accompanying hypoxia. However, increases in the label concentration in the outer media of the hypoxic animals suggested either dilation or increased permeability of the adventitial blood vessels.

Animals↗
PubMed1983

Reendothelialization and maintenance of endothelial integrity in longitudinal denuded tracks in the thoracic aorta of rats.

Endothelial repair was studied during, and up to 26 weeks following reendothelialization of longitudinal tracks denuded of endothelium. Deendothelialized tracks were produced on the ventral aspect of the thoracic aortas of rats. A standardized denudation procedure was used in conjunction with continuous intravenous infusion of [3H]thymidine to obtain quantitative evaluations of replication, migration, and cell density. The method of denudation was relatively gentle, selective, and reproducible. Reendothelialization was completed in less than 66 h. During reendothelialization, cell migration and replication proceeded simultaneously until confluence was reached. Following confluence, as migration ceased, cell density returned toward control levels. It continued to rise, associated with continued, though attenuated, nuclear incorporation of [3H]thymidine, until it reached 1 1/2 - 2 1/2 times that of adjacent uninjured control endothelium. The boundaries, or margins, of the tracks were well demarcated as judged by the pattern of labeled cells within and unlabeled cells adjacent to reendothelialized tracks. Widths of deendothelialized and reendotheliazed tracks were similar. Thus, endothelial cells in uninjured regions surrounding denuded tracks were not observed to contribute to reendothelialization by proliferation. During reendothelialization, unlabeled cells were observed within reendothelializing tracks. Thus, some cells migrated relatively long distances (0.3-0.4 mm) before either replicating or sloughing from the luminal surface. Endothelial cell density within reendothelialized tracks remained elevated at 12 and 26 weeks following denudation. At 12 weeks there was little intermingling of cells inside tracks (labeled during reendothelialization) with unlabeled cells in adjacent uninjured areas. At 26 weeks, after a terminal 12-day continuous labeling period in previously unlabeled animals, replication of cells inside tracks was far less than that in adjacent uninjured endothelium. Thus, the newly regenerated cell population in tracks remained synchronously quiescent and physically segregated for long periods of time, despite normally occurring hemodynamic and remodeling factors which might be expected to favor continuous cell turnover and migration. Our findings relating to endothelial cell migration and replication during reendothelialization vary somewhat from those reported using other methods of deendothelialization.

Animals↗
PubMed1983

Low density lipoprotein cytotoxicity induced by free radical peroxidation of lipid.

Low density lipoprotein (LDL) has been reported to be injurious or toxic to cells in vitro. This injurious effect is, in some instances, due to oxidation of the lipid moiety of the lipoprotein. The objectives of this study were to determine if the oxidation rendering the lipoprotein toxic to human skin fibroblasts occurred by free radical mechanisms, and if so, which of the common free radical oxygen species were involved. The selective free radical blockers or scavengers employed included superoxide dismutase for superoxide, catalase for hydrogen peroxide, dimethylfuran for singlet molecular oxygen, and mannitol for hydroxyl radical. The presence during lipoprotein preparation of general free radical scavengers (vitamin E, butylated hydroxytoluene) or the divalent cation chelator ethylenediamine tetraacetic acid prevented the formation of cytotoxic low density lipoprotein, while the simultaneous presence of superoxide dismutase and catalase partially inhibited its formation. The results indicate that superoxide and/or hydrogen peroxide are involved in the formation of the toxic LDL lipid. The toxic action of oxidized LDL could not be prevented by inclusion of antioxidants in the culture medium, indicating that an oxidized lipid was responsible for cell injury rather than free radicals generated in culture by the action of oxidized LDL. Three separate assays for cell injury (enumeration of attached cells, cell loss of lactate dehydrogenase into the culture medium, and trypan blue uptake) indicated a sequence of events in which the fibroblasts are injured, die, and then detach.

Cell Survival↗
PubMed1980

A simple rapid method for the preparation of en face endothelial (Häutchen) monolayers from rat and rabbit aortas.

This report describes a new method for preparing Häutchen monolayers for autoradiography with photographic emulsion contacting either the abluminal or luminal endothelial surface. Included is a means for monitoring completeness of the monolayer and retrieving cells which fail to adhere to it. Cell retrieval may be important in studies requiring autographic evaluation of endothelial cell populations. The procedure has been applied to endothelium containing newly reendothelialized aortic regions.

Animals↗
PubMed1979

LDL-induced cytotoxicity and its inhibition by HDL in human vascular smooth muscle and endothelial cells in culture.

Human aortic medial smooth muscle cells (SMC) and umbilical vein endothelial cells (EC) in culture were exposed to various concentrations of plasma low density (LDL) and high density (HDL) lipoproteins prepared from normolipemic donors in order to assess their effects on cell growth. So that the effects of each lipoprotein could be evaluated separately and in combination, lipoproteins were added to culture medium containing lipoprotein deficient serum (LPDS, d greater than 1.25 g/ml at a protein concentration of 4.5 mg/ml of medium). The addition of LDL at cholesterol concentrations of 160 microgram/ml of culture medium, resulted in significant reductions in both the number of SMC and EC cells per dish within 3 days of exposure (P less than 0.001, SMC; P less than 0.01, EC), when compared with LPDS controls and the starting cell numbers. This cytotoxic phenomenon was dose-related, and only at LDL cholesterol concentrations equal to or below 50 microgram/ml were no marked changes observed. In contrast, HDL at all concentrations tested produced no such deleterious effects. Autoradiographic assessment of DNA synthesis confirmed these findings. After 48 h of continuous exposure to tritiated thymidine, labeling indexes reached much lower plateaus in the LDL-treated groups.

Aorta, Thoracic↗
PubMed1979

Distribution of glycosaminoglycans in consecutive layers of the rabbit aorta.

Transmural variations in various glycosaminoglycan (GAG) fractions were determined in adventitia-free thoracic aortas from rabbits. Total glycosaminoglycan concentration decreased from intima to outer media. These data are similar to total GAG concentration in bovine and human aortas as reported by others. There is a marked decrease in the concentration of the combined chondroitin sulfate-dermatan sulfate component with increasing distance from the endothelial surface. These transmural differences are linked to the possible variation of the diffusion coefficient of a diffusing solute as a function of distance, which can affect the concentration profile of the solute.

Animals↗
PubMed1977

The distribution of labeled albumin across the rabbit thoracic aorta in vivo.

125I-albumin was injected intravenously into normal conscious rabbits. The rabbits were killed after 10 minutes to 24 hours, and the descending thoracic aorta was excises immediately, opened longitudinally, rinsed, and frozen. Samples of frozen aorta were sectioned paralled to the intimal surface and washed with trichloroacetic acid (TCA) prior to counting. TCA-soluble tissue radioactivity slowly increased with time, suggesting that 125I was cleaved gradually from the labeled albumin within the aortic wall. At up to 4 hours, transmural concentration profiles of TCA-precipitable radioactivity had steep gradients near the intimal surface, moderate gradients near the medial-advential border, and were relatively falt in the middle of the media. After 24 hours, the steep intimal gradient had disappeared. Concentrations were otherwise comparable to those at 4 hours. The rate of accumulation of TCA-precipitable radioactivity was rapid initially (measurable concentrations were found throughout the media after only 10 minutes) and decreased with time. The results are consistent with entry of 125I-albumin into the media from both the luminal and adventitial sides. Approximate calculations indicate that the albumin mass transfer resistance associated with the intimal endothelium is about 1 order of magnitude greater than that associated with the media.

Animals↗
PubMedDate not supplied

Modification of human serum low density lipoprotein by oxidation--characterization and pathophysiological implications.

Plasma low density lipoprotein (LDL) can undergo free radical oxidation either catalyzed by divalent cations, such as Cu2+ or Fe2+ or promoted by incubation with cultured cells such as endothelial cells, smooth muscle cells and monocytes. The content of vitamin E, beta-carotene and unsaturated fatty acids is decreased in oxidized LDL. A breakdown of apolipoprotein-B (apoB), hydrolysis of the phospholipids, an increase of thiobarbituric acid reactive substances and the generation of aldehydes also occur. Changes in the ratio of lipid to protein, the electrophoretic mobility and the fluorescent properties have also been reported to accompany oxidation of this lipoprotein. The functional changes of oxidized LDL include its recognition by the scavenger receptor on macrophages, its cytotoxicity especially to proliferating cells, its chemotactic properties with respect to monocyte-macrophages and its regulation of platelet-derived growth factor-like protein (PDGFc) production by endothelial cells. In this article we summarize some of the contributions to this topic and present speculations relating oxidized LDL to pathological conditions such as atherosclerosis.

Free Radicals↗