Expression of elastase activity by human monocyte-macrophages is modulated by cellular cholesterol content, inflammatory mediators, and phorbol myristate acetate

Protective effect of oleoyl peptide conjugates against elastolysis by neutrophil elastase and kappa elastin-induced monocyte chemotaxis

Elastin can impair the human neutrophil elastase (HNE) inhibitory capacity of elastase inhibitors. We synthesized oleoyl-alanyl-alanyl-prolyl-valine (Ol-Ala-Ala-Pro-Val-OH) (oleoyl peptide) and the amides (NH2 and NH-C3H7) of this peptide and studied their HNE-inhibitory potencies using succinyl-alanyl-alanyl-alanine-p-nitroanilide (Suc-Ala-Ala-Ala-pNA) or 3H-labeled elastin as substrates, as well as cryostat sections of rabbit skin as an ex vivo substrate. Using Suc-Ala-Ala-Ala-pNA, Ol-Ala-Ala-Pro-Val-OH had an IC50 of 3 microM. When the COOH terminal of the oleoyl peptide was derivatized to amide forms, the compound lost its ability to interact with HNE while keeping its elastin-protecting function: IC50 values for NH2 and NH-C3H7 derivatives were 22 and 17 microM, respectively. Also, the HNE-inhibitory capacity of Ol-Ala-Ala-Pro-Val-OH was only reduced 2-fold by using elastin as a substrate. This decrease was much lower than those determined with other HNE inhibitors of similar potency and could be accounted for by the ability of oleoyl peptide to bind to elastin. Cryostat sections of rabbit skin were also used as an ex vivo substrate for assessing the elastin-protecting property of Ol-Ala-Ala-Pro-Val-OH. Preincubating HNE and oleoyl peptide before application to tissue sections led to an IC50 of 8 microM, close to the value determined with elastin as a substrate. Treatment of sections with oleoyl peptide before adding HNE gave a lower IC50 (4 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Uptake of exogenous free cholesterol induces upregulation of tissue factor expression in human monocyte-derived macrophages

Lipid-laden macrophages present as foam cells may contribute to the hyperthrombotic state of human atherosclerotic lesions by the production of tissue factor (TF). We investigated the effect of exogenous nonlipoprotein cholesterol on the expression of TF by human monocyte-derived macrophages in culture. Nonlipoprotein cholesterol at 50 micrograms/ml increased TF activity 4-fold; TF induction was dose- and time-dependent. Expression of TF activity was positively correlated with the free cholesterol content of monocyte-derived macrophages, was increased upon inhibition of cholesterol esterification, and reflected de novo synthesis of TF protein. TF expression in cholesterol-loaded macrophages remained sensitive to stimulation (approximately 12-fold) by bacterial lipopolysaccharide, indicating that intracellular free cholesterol and lipopolysaccharide act by distinct mechanisms in inducing TF procoagulant activity. Our results suggest that loading human monocyte-derived macrophages with free cholesterol induces upregulation of TF expression, thereby contributing to thrombus formation at sites of plaque rupture.

Pathogenesis of acquired aneurysms of the abdominal aorta

The incidence of abdominal aortic aneurysm has recently increased. There is still no accurate definition of abdominal aortic aneurysm. The diameter of abdominal aortic aneurysms is the only factor permitting evaluation of the risk of rupture of aneurysms whose growth remains unpredictable. Abdominal aortic aneurysm is a multi-factorial disease associated with aortic aging and atheroma. It differs from stenotic disease by the intensity of degenerative or destructive phenomena in the media. Particular hemodynamic conditions in the infrarenal abdominal aorta seem to enhance the development of aneurysm at this level. While certain constitutional anomalies of the extracellular matrix of proteins seem to enhance the development of abdominal aortic aneurysm, protease activity of as yet undetermined origin also seems to play a prominent role. Family cases of abdominal aortic aneurysms have been reported but the mechanisms responsible remain to be determined. Several genetic markers have been suggested. The most reliable marker of aortic aneurysm is arteriomegaly.

Ultrastructure appearance of atherosclerosis in human and experimentally-induced animal models

We describe here the basic structure of the aorta, the changes with aging and ultrastructural appearance of atherosclerosis of human and animal models. The architecture of the aortic wall is highly organized, for adaptation to changes of blood pressure. The main cells composing the vessel are endothelial cells and smooth muscle cells. They maintain the integrity and homeostasis of the aorta along with the extracellular matrix of collagen fibrils, elastic fibers and glycosaminoglycans. The structural changes with aging and atherogenesis are a compensative or degenerative phenomenon caused by many factors. Three major cells are the endothelial cell, smooth muscle cell and monocyte-derived macrophages (as well as platelets) all of which are involved in atherogenesis. Foam cells in atheromatous lesions are derived from macrophages and smooth muscle cells. Recently, the molecular biological nature and function of these cells and their derived-factors have been thoroughly investigated in cell culture and in experimental animal models caused by a mechanical injury of the endothelium or by a dietary induced hypercholesterolemia. However, the mechanism of the endothelial injury in vivo as well as formation of atheromatous cores of human atherosclerosis is not exactly understood. Some structural and functional changes inherent to the arterial wall during aging may play an important role in initiation or progression of human atherosclerosis.

Metabolism and turnover of cell surface-associated heparan sulfate proteoglycan and chondroitin sulfate proteoglycan in normal and cholesterol-enriched macrophages

Analysis of sulfur-35-labeled proteoglycans indicated that cholesterol-enriched pigeon peritoneal macrophages synthesized 42% more 35S-labeled proteoglycan when compared with control macrophages during a 24-hour incubation. Proteoglycan turnover was subsequently studied in radiolabeled macrophage cultures after a 1-, 3-, 6-, 12-, or 24-hour chase with fresh media. During the chase, intracellular proteoglycan disappeared rapidly, whereas there was a small accumulation of 35S-labeled proteoglycan in the media that plateaued at about 6 hours and remained relatively constant thereafter. Pericellular heparan sulfate proteoglycan and chondroitin sulfate proteoglycan disappeared throughout the chase and did not appear to accumulate in the media or in the intracellular compartment. The rapid disappearance of intracellular proteoglycans along with the relative lack in metabolism of media proteoglycans indicated that the majority of pericellular proteoglycans were metabolized via an intracellular degradative pathway. Kinetic analysis of pericellular proteoglycans revealed the presence of a single pool of heparan sulfate proteoglycan (half-life [t1/2] = 6.9 hours) and a single pool of chondroitin sulfate proteoglycan (t1/2 = 11.5 hours) in control macrophage cultures. Cholesterol-enriched macrophage cultures also contained a single pool of pericellular heparan sulfate proteoglycan (t1/2 = 7.3 hours) but contained two pools of chondroitin sulfate proteoglycan (t1/2 = 0.8 hour and 25.9 hours).

Localization of stromelysin gene expression in atherosclerotic plaques by in situ hybridization

The stromelysins are members of a family of extracellular matrix metalloproteinases. These enzymes may erode the connective tissue in atherosclerotic plaques, leading to fissuring and acute thrombotic events. Cell-specific stromelysin expression in human atherosclerotic plaques was studied by in situ hybridization and immunocytochemistry. Sections were taken from nine coronary arteries: eight with well-established plaques and one normal. Unambiguous signals were seen in five plaques, two were inconclusive, and the remaining sample was negative, as was the normal coronary artery. Stromelysin mRNA transcripts were localized to isolated individual cells, some of which were smooth muscle, in the plaque cap, intima, and adventitia, but not the media. Expression was also seen in large clusters of macrophages that contained intracellular lipid deposits. The isolated expression of stromelysin by smooth muscle cells may reflect local connective tissue remodeling associated with growth and the formation of the plaque, whereas the more extensive expression associated with macrophages may be of greater pathological significance, contributing to the destabilization of the extracellular matrix and eventual plaque rupture.

A standardised method of culturing aortic explants, suitable for the study of factors affecting the phenotypic modulation, migration and proliferation of aortic smooth muscle cells

The study of factors affecting phenotypic change and growth of aortic smooth muscle cells (SMC) typically involves either the isolation of SMC by enzymatic dissociation or observation of outgrowth of cells from primary explants of vascular tissue. Explants provide a system in which the growth of cells can be investigated without dissociating them totally from their normal environment and avoids some of the problems of variability associated with enzymatic digestion. We describe here a standardised method for the preparation of medial explants of arterial tissue using a McIlwain tissue chopper, which is both fast and reproducible. Measurement was made of the percentage of explants showing outgrowth and of the distance migrated by cells at various times after plating explants singly into wells of a 96-well plate. Using this method, by 12 days after explanting, more than 95% of explants from normal rabbit aorta had shown outgrowth, in contrast to only 50% of explants prepared using a scalpel blade. Explants from atherosclerotic rabbit aorta showed a shorter lag phase before outgrowth commenced than explants from normal rabbit aorta of a similar age, but the subsequent rate of growth was the same. In contrast, when explants of normal rabbit aorta were grown in hyperlipidic rabbit serum, the lag phase was the same as for normal serum, but the subsequent rate of growth was greater. Explants from normal rabbit aorta treated with heparin showed an increased lag phase but reduced rate of growth. Treatment with heparinase decreased the lag phase and increased the rate of growth as did elastase.

Evidence for generation of a large amount of nitric oxide-like vascular smooth muscle relaxant by cholesterol-rich neutrophils

To determine the effect of cholesterol incorporation on the ability of neutrophils to generate superoxide radicals and nitric oxide-like vasorelaxant material, isolated human neutrophils were incubated with cholesterol-rich liposomes, which increased total cholesterol content by 141% and esterified cholesterol content by 523%. Cholesterol loading resulted in 5 to 7 fold increase in cytosolic calcium in resting as well as in PMA or f-MLP-stimulated cells, but a marked (P less than 0.01) reduction in both PMA- and f-MLP-stimulated superoxide radical generation by these cells. Nitric oxide-like activity measured as relaxation of rat aortic rings was more pronounced (P less than 0.02) in cholesterol-rich than in cholesterol-poor cells. The greater relaxation of aortic rings in response to cholesterol-rich neutrophils was observed in rings with or without intact endothelium, and was potentiated by superoxide dismutase and inhibited by oxyhemoglobin as well as L-NMMA, thus suggesting that the vasorelaxant material was nitric oxide. The greater generation of nitric oxide by cholesterol-rich neutrophils occurs perhaps in response to increased cytosolic calcium.