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A J Valente

Publications and source records attributed to A J Valente.

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

Cultured human liver fat-storing cells produce monocyte chemotactic protein-1. Regulation by proinflammatory cytokines.

Monocytes infiltrate the portal space during chronic liver inflammation. Monocyte chemotactic protein-1 (MCP-1) is a cytokine that induces monocyte chemotaxis and activation. We investigated if human liver fat-storing cells (FSC) secrete MCP-1, and the mechanisms that regulate MCP-1 production. Unstimulated FSC secrete MCP-1 as measured by radioimmunoassay as well as a chemotactic assay and express mRNA that encodes for this cytokine. A two- to threefold increase in MCP-1 secretion was observed when FSC were treated with either interleukin-1 alpha (IL-1 alpha) or interferon-gamma (IFN-gamma). Tumor necrosis factor-alpha (TNF alpha) also increased MCP-1 secretion, although to a lesser extent (1.6-fold). Northern blot analysis showed that IL-1 alpha and IFN-gamma strongly increase the levels of mRNA that encodes for MCP-1, whereas TNF alpha appears to be a weaker stimulus. Analysis of FSC-conditioned medium by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting revealed three bands of MCP-1 that most likely represent isoforms of different apparent molecular weights. Pretreatment of FSC with H-7, a protein kinase C inhibitor, blocked cytokine-induced increase in both MCP-1 gene expression and secretion. To determine the potential role of MCP-1 in vivo, we also analyzed normal and pathologic human liver tissue. Northern blot analysis showed that MCP-1 mRNA expression is more abundant in liver tissue obtained from patients with chronic active hepatitis compared with normal liver tissue. These studies indicate that MCP-1 secreted by FSC is stimulated by proinflammatory cytokines and that MCP-1 gene expression is upregulated in chronic inflammatory liver disease. MCP-1 released by FSC may participate in the recruitment and activation of monocytes at sites of liver injury.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

Human monocyte colony-stimulating factor stimulates the gene expression of monocyte chemotactic protein-1 and increases the adhesion of monocytes to endothelial monolayers.

The stimulation of the human umbilical vein endothelial cell (HUVEC) with recombinant human monocyte-derived colony-stimulating factor (MCSF) increased the gene expression of monocyte chemotactic protein (MCP-1). Northern blot analysis indicated that 50 U/ml of MCSF is the optimal concentration for this effect. The elevation of MCP-1 mRNA started as early as 1 h after stimulation and was maintained for at least 8 h. An increased MCP-1 level in MCSF-treated HUVEC was also demonstrated at the protein level by immunocytochemical staining using a polyclonal MCP-1-specific antibody. HUVEC activated by 50 U/ml of MCSF for 5 h showed a stronger immunofluorescence staining than control cells. Micropipette separation of THP-1 monocytes from HUVEC showed that the activation of both THP-1 and endothelium by MCSF led to an increase in the separation force by more than three times (36.2 +/- 6.7 x 10(-4) vs. 9.6 +/- 3.6 x 10(-4) dyn). An increased adhesiveness was also observed after MCSF activation of peripheral blood monocytes and HUVEC (16.7 +/- 2.7 x 10(-4) vs. 5.2 +/- 0.9 x 10(-4) dyn). The increased adhesive force in both systems was blocked by the use of anti-MCP-1 (5.5 +/- 0.8 x 10(-4) and 6.8 +/- 1.1 x 10(-4) dyn). Similar results were obtained in experiments in which only HUVEC, but not monocytes, were activated by MCSF. This increased adhesion of untreated monocytes to MCSF-activated HUVEC was also blocked by the addition of anti-MCP-1. In contrast, experiments in which only THP-1 or peripheral blood monocytes, but not HUVEC, were treated with MCSF did not show a significant increase of adhesion between these cells. These results indicate that MCSF augments monocyte-endothelium interaction primarily by its action on the endothelial cell and that this function is probably mediated through an increased expression of MCP-1. The MCSF/MCP-1-dependent adhesive mechanism might be operative in the arterial wall in vivo to lead to the trapping of the infiltrated monocyte-macrophage in the subendothelial space during atherogenesis.

Antibodies↗
PubMed1992

Elevated expression of monocyte chemoattractant protein 1 by vascular smooth muscle cells in hypercholesterolemic primates.

Atherosclerosis is marked by an overt inflammatory infiltrate, with enhanced recruitment of monocytes/macrophages observed in both human and experimental atherosclerosis. We previously determined that monocyte chemoattractant protein 1 (MCP-1) accounts for virtually all of the chemotactic activity produced by vascular (aortic) smooth muscle cells in culture. We now report that arteries from a primate model of atherosclerosis with dietary-induced hypercholesterolemia exhibit increased levels of MCP-1 mRNA expression in vivo, whereas their normal counterparts demonstrate minimal MCP-1 expression. Furthermore, immunohistochemistry and in situ hybridization clearly indicate that the expression of MCP-1 protein and mRNA is in the smooth muscle cells of the medial layer of the artery and in monocyte-like and smooth muscle-like cells found in the overlying intimal lesion. These studies indicate that one of the responses to dietary hypercholesterolemia is the expression of MCP-1 by vascular smooth muscle cells. This expression, when augmented with other cellular and molecular factors, could significantly contribute to the recruitment of monocytes/macrophages to the vessel wall.

Animals↗
PubMed1992

Expression of monocyte chemoattractant protein 1 mRNA in human idiopathic pulmonary fibrosis.

Macrophages are thought to play an important role in the pathologic changes associated with idiopathic pulmonary fibrosis (IPF). The mechanisms for increased monocyte/macrophage recruitment in IPF are unknown. Monocyte chemoattractant protein 1 (MCP-1) is the predominant monocyte chemoattractant secreted by a variety of different cell types in culture. We examined the expression of MCP-1 mRNA and its protein product in vivo in IPF and non-IPF lung specimens by in situ hybridization and immunocytochemistry. The cell types expressing MCP-1 in vivo were identified by immunostaining with specific antibodies. We demonstrated the expression of MCP-1 mRNA in pulmonary epithelial cells, in monocytes/macrophages, and in vascular endothelial and smooth muscle cells. Lung epithelial cells in patients with IPF strongly expressed MCP-1 mRNA and its protein product. In contrast, epithelial cells in non-IPF specimens did not express MCP-1 mRNA. Macrophages and vascular endothelial and smooth muscle cells were shown to express MCP-1 in both IPF and non-IPF lung specimens. These findings provide a basis for the understanding of the in vivo physiologic processes that mediate monocyte/macrophage recruitment and infiltration in the lung interstitium and the pathologic state contributing to an increased alveolar monocyte/macrophage population and inflammation in IPF.

Arteries↗
PubMed1992

Pathogenesis of the atherosclerotic lesion. Implications for diabetes mellitus.

In this review, we have highlighted pivotal cellular and molecular events in the initiation and progression of atherosclerosis. Key components of lesion initiation are an enhanced focal intimal influx and accumulation of lipoproteins, including LDL in hemodynamically determined lesion-prone areas, focal monocyte-macrophage recruitment, intimal generation of ROS, and oxidative modification of lipoproteins (including LDL [Ox-LDL]). Modified lipoproteins are taken up by the non-downregulating macrophage scavenger receptor, with foam cell formation and the development of the so-called fatty streak. One transitional event in lesion progression is foam cell necrosis, likely attributable to the cytotoxicity of both intimal free radicals and Ox-LDL, with development of an extracellular metabolically inert lipid core. Another is the migration to and proliferation within the intima of medial SMCs, leading to the synthesis of plaque collagens, elastin, and proteoglycans. Mural thrombosis plays a significant role in the late-stage progression of lesions. Regression of lesions is considered a function of the dynamic balance among components of initiation, progression, plaque stabilization, and removal of plaque constituents--the so-called regression quartet. Here, we critically examine how components of diabetes mellitus might impact not only lesion development, but also lesion regression. It is concluded that some components of diabetes mellitus augment key mechanisms in lesion initiation and progression and will likely retard the processes of plaque regression. Specifically, we focus on the various influences of diabetes mellitus on lipoprotein influx and accumulation, free radical generation and Ox-LDL, monocyte-macrophage recruitment, thrombosis and impaired fibrinolysis, and the reverse cholesterol transport system. The importance of nonenzymatic protein glycosylation in modifying a number of these processes is emphasized.

Arteriosclerosis↗
PubMed1992

Atherosclerosis. Potential targets for stabilization and regression.

Reviewed are various aspects of atherosclerotic plaque stabilization and regression in humans and experimental animals. Plaque regression is a function of the dynamic balance among initiation, progression, stabilization, and removal of plaque constituents. Pseudoregression, the result of the triad thrombolysis, age- or lesion-dependent arterial dilatation, and relaxation of vasospasm, may readily give rise to angiographic misinterpretation. Although lowering of plasma cholesterol and low density lipoprotein-cholesterol has demonstrated significant clinical benefits in a number of clinical trials, the magnitude of angiographic regressive changes is relatively small despite aggressive lipid-lowering regimens. The emerging need for alternative or complementary therapeutic interventions has been emphasized. In particular, they should be targeted to pivotal cellular or molecular mechanisms in initiation, progression, or stabilization. Potentially important therapeutic targets include the use of antioxidants or free radical scavengers such as Probucol or its analogues, butylated hydroxytoluene, tocopherols, and possibly the tocotrienols. Other therapeutic targets include intimal monocyte-macrophage recruitment, macrophage cholesterol acyltransferase inhibition, stimulation of the high density lipoprotein-mediated reverse cholesterol transport system, smooth muscle cell migration to and proliferation in the arterial intima, and intimal connective tissue synthesis. Whether the isoprenylated proteins associated with the cholesterol biosynthetic pathway will give rise to compounds regulating smooth muscle cell growth has yet to be determined. Because of the importance of thrombosis in the pathogenesis and progression of lesions, the need to develop interventional strategies targeted at endothelial cell thromboresistance and thromboregulation must assume a high priority in future research and development. Other areas of therapeutic promise include the calcium channel blockers and angiotensin converting enzyme inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Mechanisms in intimal monocyte-macrophage recruitment. A special role for monocyte chemotactic protein-1.

This article briefly addresses the role of the monocyte-macrophage in atherogenesis and the potential mechanisms participating in intimal blood monocyte recruitment. The obligatory components of the recruitment process, i.e., contact with the vascular endothelium, attachment, and migration into the subendothelial space, are addressed with reference to the influence of blood flow, plasma proteins (particularly low density lipoprotein), and inflammatory mediators and cytokines. The potentially important role of monocyte chemotactic protein-1 in regulating monocyte recruitment in plaque pathogenesis is discussed.

Arteriosclerosis↗
PubMed1991

Initial characterization of the carbohydrate structure of MCP-1.

MCP-1 is the principle monocyte chemoattractant produced by tumor cells in vitro. We previously identified different isoforms of MCP-1. Here we report that two predominant isoforms of MCP-1 (13 kD and 9 kD) can be distinguished by lectin binding. The results indicate that the disaccharide galactose-beta 1-3D-N-acetyl galactosamine is present on the 13 kD MCP-1 isoform but not the 9 kD isoform. Glycosylation of the 13 kD MCP-1 isoform does not appear to significantly change its antigenic properties and also does not affect its capacity to induce monocyte migration.

Carbohydrate Sequence↗
PubMed1991

Characterization of monocyte chemotactic protein-1 binding to human monocytes.

Monocyte chemotactic protein-1 (MCP-1) stimulates chemotaxis of peripheral blood monocytes. In order to understand the biologic basis of this specific activity, binding studies of 125I-MCP-1 were undertaken. MCP-1 showed saturable binding to monocytes. Scatchard analysis of the monocyte binding data indicate that there are approximately 1,600 high affinity binding sites per monocyte with a Kd = 1.1 nM. Studies with synthetic peptides constructed according to the MCP-1 amino acid sequence indicate that a synthetic peptide, MCP-1[13-35], stimulates monocyte migration and competes with native MCP-1 for binding sites. Inhibition of MCP-1 binding was tested with chemotactic connective tissue proteins. No inhibition of MCP-1 binding was observed with either collagen, elastin-derived peptides or fibronectin. These results identify a single class of unique high affinity MCP-1 binding sites that are likely to recognize a peptide domain on MCP-1 which include the amino acids within the region, 13-35.

Animals↗
PubMed1991

Monocyte chemotactic proteins from human tumor cells.

The production of the monocyte chemoattractant MCP-1 suggests a common mechanism for the recruitment of monocytes/macrophages and provides an explanation for monocyte/macrophage infiltration frequently observed in solid tumors. The regulated production of MCP-1 by non-transformed cells further substantiates the suggestion that MCP-1 is an important inflammatory mediator and is involved in the recruitment of monocytes in a number of pathologic or physiologic conditions.

Animals↗
PubMed1991

The pathogenesis of atherosclerosis: an overview.

In this unifying hypothesis directed to the etiology and pathogenesis of atherosclerosis, the importance of focal arterial lesion-prone sites has been emphasized. Key initial participants in these sites include the focal intimal influx and accumulation of low-density lipoprotein (LDL) and a preferential recruitment of blood monocytes. Both are further enhanced in the presence of hyperlipidemia, when the quantity of intimal LDL and the oxidative potential of the intima exceed the capacity of macrophages to remove, via the non-down-regulating scavenger receptor, cytotoxic anionic (Ox-LDL) macromolecules. Foam cells, pathognomonic of the fatty streak, form during the receptor-mediated uptake of Ox-LDL by the macrophages. Interstitial free radicals and the excess of Ox-LDL particles injure and kill cells, including the foam cells, with the formation of the necrotic extracellular lipid core, a key transitional step in lesion progression. Monocyte-macrophage recruitment to the intima is likely to be regulated not only by a multiplicity of endothelial adhesive cytokines, integrins, and selectins, but also by the monocyte-specific chemoattractant, MCP-1, constitutively synthesized and secreted by intimal smooth muscle and endothelial cells. Its synthesis and secretion is augmented by mildly oxidized LDL. Free radicals, pivotal in the oxidation of LDL, and derived from activated macrophages, and also endothelial and smooth muscle cells. Smooth muscle cells migrate from the media through the intimal endothelial layer (IEL) and proliferate under the regulation of a number of mitogens, including platelet-derived growth factor (PDGF). Collagen synthesis by smooth muscle cells is substantial. Lymphocytes, as a source of interferons, invade the plaque and are present in the adventitia in substantial numbers, likely representing an autoimmune response in the later stages of plaque development. Platelets and mural thrombosis directly contribute to subsequent plaque growth, particularly after plaque rupture or fissure and disruption of the thromboresistant endothelial cells (EC). Plaque regression in all likelihood involves the conversion of the inert pool of extracellular lipid to a metabolically active intracellular pool and subsequent clearance by the high-density lipoprotein mediated reverse cholesterol transport system. The atherogenic cascades so described conceptually represent arterial inflammatory and healing processes occurring in a hyperlipidemic environment. Many components of pathogenesis are the targets for modulation by genetic, hemodynamic and selected risk factors. The prevention and treatment of the disease should logically target reduction in plasma LDL levels, the inhibition of the oxidative modification of lipoproteins, including LDL, by free radical scavengers, and augmentation of the reverse cholesterol transport system.

Animals↗
PubMed1991

Red blood cells are a sink for interleukin 8, a leukocyte chemotaxin.

IL-8 (also known as neutrophil-activating peptide 1) is recognized as a potent effector of neutrophil functions. Several different cell types that contact blood, namely T lymphocytes, monocytes, and endothelial cells, secrete this polypeptide following stimulation by cytokines, or lipopolysaccharide. Here we show that when IL-8 is added to blood it rapidly partitions from the plasma fluid to the blood cells and that erythrocytes account for the vast majority of this binding. Analysis of 125I-IL-8 binding [( ala-IL-8]77 form) to human red cells indicates a single, 5 nM Kd affinity class of binding sites, present at approximately 2,000 per red cell representing approximately 15 nmol of red cell IL-8 binding sites per liter of blood. These sites are protease sensitive. Their binding of IL-8 is rapidly reversible and does not result in receptor internalization, although bound IL-8 is resistant to extraction by pH 3 buffer at 5 degrees C. 125I-IL-8 binding to red cells was not inhibited by epidermal growth factor or interleukin 1, but was inhibited by monocyte chemotactic peptide-1, which is not a neutrophil chemotaxin, but is a member of the same family of polypeptides as IL-8. FACS analysis of IL-8-mediated mobilization of Ca2+ in neutrophils indicates that the IL-8 bound to red cells is incapable of stimulating neutrophils. Thus, red cell absorption of IL-8 may function to limit stimulation of leukocytes by IL-8 released into blood.

Absorption↗
PubMed1991

Monocyte transmigration induced by modification of low density lipoprotein in cocultures of human aortic wall cells is due to induction of monocyte chemotactic protein 1 synthesis and is abolished by high density lipoprotein.

Incubation of cocultures of human aortic endothelial (HAEC) and smooth muscle cells (HASMC) with LDL in the presence of 5-10% human serum resulted in a 7.2-fold induction of mRNA for monocyte chemotactic protein 1 (MCP-1), a 2.5-fold increase in the levels of MCP-1 protein in the coculture supernatants, and a 7.1-fold increase in the transmigration of monocytes into the subendothelial space of the cocultures. Monocyte migration was inhibited by 91% by antibody to MCP-1. Media collected from the cocultures that had been incubated with LDL induced target endothelial cells (EC) to bind monocyte but not neutrophil-like cells. Media collected from cocultures that had been incubated with LDL-induced monocyte migration into the subendothelial space of other cocultures that had not been exposed to LDL. In contrast, media from separate cultures of EC or smooth muscle cells (SMC) containing equal number of EC or SMC compared to coculture and incubated with the same LDL did not induce monocyte migration when incubated with the target cocultures. High density lipoprotein HDL, when presented to cocultures together with LDL, reduced the increased monocyte transmigration by 91%. Virtually all of the HDL-mediated inhibition was accounted for by the HDL2 subfraction. HDL3 was essentially without effect. Apolipoprotein AI was also ineffective in preventing monocyte transmigration while phosphatidylcholine liposomes were as effective as HDL2 suggesting that lipid components of HDL2 may have been responsible for its action. Preincubating LDL with beta-carotene or with alpha-tocopherol did not reduce monocyte migration. However, pretreatment of LDL with probucol or pretreatment of the cocultures with probucol, beta-carotene, or alpha-tocopherol before the addition of LDL prevented the LDL-induced monocyte transmigration. Addition of HDL or probucol to LDL after the exposure to cocultures did not prevent the modified LDL from inducing monocyte transmigration in fresh cocultures. We conclude that cocultures of human aortic cells can modify LDL even in the presence of serum, resulting in the induction of MCP-1, and that HDL and antioxidants prevent the LDL induced monocyte transmigration.

Antioxidants↗
PubMed1990

Post-translational modification of a monocyte-specific chemoattractant synthesized by glioma, osteosarcoma, and vascular smooth muscle cells.

Chemotaxis is an important step in monocyte recruitment in inflammation, wound healing, and tumor growth. We reported previously that monocyte chemotactic activity secreted by malignant cells and normal smooth muscle cells is associated with a protein or family of proteins that are related to the monocyte-specific smooth muscle cell-derived chemotactic factor (SMC-CF) (Graves, D. T., Jiang, Y. L., Williamson, M. J., and Valente, A. J. (1989) Science 245, 1490-1493). Similar monocyte chemotactic proteins (MCP-1) produced by U-105MG human glioma cells have also been identified (Yoshimura, T., Robinson, E. A., Tanaka, S., Appella, E., Kuratsu, J., and Leonard, E. J. (1989) J. Exp. Med. 169, 1449-1459). We now report that the MCP-1 gene is expressed in MG-63 human osteosarcoma and vascular smooth muscle cells and that SMC-CF antiserum specifically immunoprecipitates proteins synthesized by U-105MG glioma cells. Experiments were undertaken to elucidate the processing pathway of MCP-1/SMC-CF-like proteins in each of these cell types. These experiments demonstrate that larger MCP-1/SMC-CF-like proteins are derived from a Mr = 9000 precursor. Post-translational modification involves the addition of O-linked carbohydrates and sialic acid residues. Differences in carbohydrate processing account for the heterogeneity in MCP-1/SMC-CF-like proteins produced by different cell types. Secretion of these proteins occurs rapidly following processing events in the endoplasmic reticulum-Golgi compartment.

Blotting, Northern↗
PubMed1990

Minimally modified low density lipoprotein induces monocyte chemotactic protein 1 in human endothelial cells and smooth muscle cells.

After exposure to low density lipoprotein (LDL) that had been minimally modified by oxidation (MM-LDL), human endothelial cells (EC) and smooth muscle cells (SMC) cultured separately or together produced 2- to 3-fold more monocyte chemotactic activity than did control cells or cells exposed to freshly isolated LDL. This increase in monocyte chemotactic activity was paralleled by increases in mRNA levels for a monocyte chemotactic protein 1 (MCP-1) that is constitutively produced by the human glioma U-105MG cell line. Antibody that had been prepared against cultured baboon smooth muscle cell chemotactic factor (anti-SMCF) did not inhibit monocyte migration induced by the potent bacterial chemotactic factor f-Met-Leu-Phe. However, anti-SMCF completely inhibited the monocyte chemotactic activity found in the media of U-105MG cells, EC, and SMC before and after exposure to MM-LDL. Moreover, monocyte migration into the subendothelial space of a coculture of EC and SMC that had been exposed to MM-LDL was completely inhibited by anti-SMCF. Anti-SMCF specifically immunoprecipitated 10-kDa and 12.5-kDa proteins from EC. Incorporation of [35S]methionine into the immunoprecipitated proteins paralleled the monocyte chemotactic activity found in the medium of MM-LDL stimulated EC and the levels of MCP-1 mRNA found in the EC. We conclude that (i) SMCF is in fact MCP-1 and (ii) MCP-1 is induced by MM-LDL.

Aorta↗
PubMed1989

Pathophysiology of the atherogenic process.

Atherosclerosis is conceptually defined as the result of a multiplicity of interactive cascades among injurious stimuli and the healing responses of the arterial wall, occurring concurrently within a hyperlipidemic environment. In this discussion, the inflammatory nature of the disease is emphasized. Four aspects of the pathophysiology of atherogenesis are addressed: (1) The role(s) of fluid mechanical or hemodynamic stresses in the focal initiation and/or augmentation of lesions is discussed in terms of the influence of shear stress on endothelial cellular geometry, compliance, membrane anisotropy (r), low-density lipoprotein (LDL)-receptor expression, intracellular potential and replication; (2) mechanisms of blood monocyte recruitment to the arterial intima, including the roles of chemoattractants such as smooth muscle cell-derived chemotactic factor and oxidized LDL; (3) the alternate or "scavenger" receptor pathway of the macrophage and its pivotal roles in foam cell formation and plaque pathogenesis; and (4) the emerging significance of various lipoprotein modifications, and in particular, the oxidative modification of LDL, which facilitates the uptake of the cytotoxic oxidized LDL via the scavenger receptor, thus providing a non-down-regulating mechanism for foam cell formation and plaque development. Evidence indicates that the antioxidant drug probucol prevents the oxidative modification of LDL, thereby retarding atherogenesis independently of cholesterol reduction.

Animals↗
PubMed1989

Identification of monocyte chemotactic activity produced by malignant cells.

Human malignant cells secrete low molecular size proteins that attract peripheral blood monocytes and may be responsible for the accumulation of tumor-associated macrophages observed in vivo. Similar chemotactic proteins are secreted by cultured vascular smooth muscle cells. The predominant monocyte chemoattractants produced by tumor cells of differing origin were demonstrated to be related to smooth muscle cell-derived chemotactic factor. Thus, a single class of chemotactic proteins is produced by different cell types, which suggests a common mechanism for the recruitment of monocytes and macrophages. These results are significant in view of the potential of macrophages to affect tumor growth.

Animals↗