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

Macrophages, Endothelial Cells, and Lipoprotein Oxidation in the Pathogenesis of Atherosclerosis*

One of the earliest phenomena in the atherogenic process in cholesterol-fed rabbits appears to be the trapping of low density lipoproteins (LDL) at lesion-prone sites in the aorta. The resulting increase in residence time may facilitate oxidation of the lipoproteins, which, in turn, may be a chemotactic signal for monocytes to enter the intima. Oxidized lipoproteins may also be the major source of the cholesterol that the cells accumulate during their transformation into macrophage-derived foam cells (MFC). Adherent monocytes appear to cluster over small groups of subendothelial foam cells, perhaps in response to the enhanced expression of specific adhesion molecules on the surface of endothelial cells and/or monocytes following activation by oxidized lipoproteins. Lipoproteins oxidized by MFC may also injure endothelial cells causing them to retract or rupture. The resulting exposure of the MFC facilitates the formation of mural thrombi. MFC contain oxidation-specific lipid-protein adducts and specifically express the mRNA for 15-lipoxygenase, an enzyme potentially involved in lipoprotein oxidation. MFC isolated from atherosclerotic lesions and containing up to 600 μg cholesterol/mg protein are still capable of binding and degrading modified lipoproteins and affecting the oxidation of LDL.

High density lipoproteins are modulators of protease activity: Implications in inflammation, complement activation, and atherothrombosis

High density lipoproteins (HDL) represent a compositionally diverse population of particles in the circulation, containing a wide variety of lipids and proteins. Gene ontology functional analysis of the 96 commonly identified HDL binding proteins reveals that almost half of these proteins are either proteases or have known roles in protease regulation. Here, we discuss the activities of some of these proteins in regard to their roles in regulating proteases involved in inflammation, coagulation, and complement activation, particularly in the context of atherosclerosis. The overall goal of this review is to discuss potential functional roles of HDL in protease regulatory pathways based on current literature and known functions of HDL binding proteins and to promote the consideration of HDL as a global modulator of proteolytic equilibrium.

Rosuvastatin Alters the Proteome of High Density Lipoproteins: Generation of alpha-1-antitrypsin Enriched Particles with Anti-inflammatory Properties

Statins lower plasma cholesterol by as much as 50%, thus reducing future cardiovascular events. However, the physiological effects of statins are diverse and not all are related to low density lipoprotein cholesterol (LDL-C) lowering. We performed a small clinical pilot study to assess the impact of statins on lipoprotein-associated proteins in healthy individuals (n = 10) with normal LDL-C (<130 mg/dL), who were treated with rosuvastatin (20 mg/day) for 28 days. Proteomic analysis of size-exclusion chromatography isolated LDL, large high density lipoprotein (HDL-L), and small HDL (HDL-S) fractions and spectral counting was used to compare relative protein detection before and after statin therapy. Significant protein changes were found in each lipoprotein pool and included both increases and decreases in several proteins involved in lipoprotein metabolism, complement regulation and acute phase response. The most dramatic effect of the rosuvastatin treatment was an increase in α-1-antirypsin (A1AT) spectral counts associated with HDL-L particles. Quantitative measurement by ELISA confirmed an average 5.7-fold increase in HDL-L associated A1AT. Molecular modeling predictions indicated that the hydrophobic reactive center loop of A1AT, the functional domain responsible for its protease inhibitor activity, is likely involved in lipid binding and association with HDL was found to protect A1AT against oxidative inactivation. Cell culture experiments, using J774 macrophages, demonstrated that the association of A1AT with HDL enhances its antiprotease activity, preventing elastase induced production of tumor necrosis factor α. In conclusion, we show that statins can significantly alter the protein composition of both LDL and HDL and our studies reveal a novel functional relationship between A1AT and HDL. The up-regulation of A1AT on HDL enhances its anti-inflammatory functionality, which may contribute to the non-lipid lowering beneficial effects of statins.

Platelet activating factor in heart failure: potential role in disease progression and novel target for therapy

Heart failure (HF) is a complex syndrome with cardiac, renal, neurohormonal and sympathetic nervous system's manifestations, the pathogenesis of which among others is connected to inflammation. PAF has local and systemic effects pertaining to HF progression since it causes a negative inotropic effect, it induces arrhythmias, it induces apoptosis and it is involved in inflammation and atherosclerosis. In the present review the role of PAF in HF will be thoroughly presented along with the relevant data on PAF enzymes and the potential role of PAF metabolic circuit as a novel pharmacological target.

Receptor-independent fluid-phase pinocytosis mechanisms for induction of foam cell formation with native low-density lipoprotein particles

PURPOSE OF REVIEW

Because early findings indicated that native low-density lipoprotein (LDL) did not substantially increase macrophage cholesterol content during in-vitro incubations, investigators presumed that LDL must be modified in some way to trigger its uptake by the macrophage. The purpose of this review is to discuss recent findings showing that native unmodified LDL can induce massive macrophage cholesterol accumulation mimicking macrophage foam cell formation that occurs within atherosclerotic plaques.

RECENT FINDINGS

Macrophages that show high rates of fluid-phase pinocytosis also show similar high rates of uptake of native unmodified LDL through nonreceptor mediated uptake within both macropinosomes and micropinosomes. Nonsaturable fluid-phase uptake of LDL by macrophages converts the macrophages into foam cells. Different macrophage phenotypes demonstrate either constitutive fluid-phase pinocytosis or inducible fluid-phase pinocytosis. Fluid-phase pinocytosis has been demonstrated by macrophages within mouse atherosclerotic plaques indicating that this pathway contributes to plaque macrophage cholesterol accumulation.

SUMMARY

Contrary to what has been believed previously, macrophages can take up large amounts of native unmodified LDL by receptor-independent, fluid-phase pinocytosis converting these macrophages into foam cells. Thus, targeting macrophage fluid-phase pinocytosis should be considered when investigating strategies to limit macrophage cholesterol accumulation in atherosclerotic plaques.

Protein kinase C β and δ isoenzymes mediate cholesterol accumulation in PMA-activated macrophages

Previously, we showed that PMA activation of human monocyte-derived macrophages stimulates macropinocytosis (i.e., fluid-phase endocytosis) of LDL and transforms these macrophages into foam cells. The current study aimed to learn which PKC isoenzymes mediate cholesterol accumulation in PMA-activated human macrophages incubated with LDL. Cholesterol accumulation by PMA-activated macrophages incubated with LDL was nearly completely inhibited (>85%) by the pan PKC inhibitors Go6850, Go6983, and RO 32-0432, but only was inhibited about 50% by the classical group PKC inhibitor, Go6976. This indicated that cholesterol accumulation was mediated by both a classical group and some other PKC isoenzyme. PKC beta was determined to be the classical group isoenzyme that mediated PMA-stimulated cholesterol accumulation. A pseudosubstrate myristoylated peptide inhibitor of PKC alpha and beta showed partial inhibition (congruent with 50%) of cholesterol accumulation. However, a small molecule inhibitor of PKC alpha, HBDDE, show minimal inhibition of cholesterol accumulation while a small molecule inhibitor of PKC beta, LY333513, could completely account for the inhibition of cholesterol accumulation by the classical group PKC isoenzyme. Thus, our findings show that beta and some other PKC isoenzyme, most likely delta, mediate cholesterol accumulation when macropinocytosis of LDL is stimulated in PMA-activated human monocyte-derived macrophages.

Adipophilin increases triglyceride storage in human macrophages by stimulation of biosynthesis and inhibition of beta-oxidation

Lipid accumulation alters macrophage biology and contributes to lipid retention within the vessel wall. In this study, we investigated the role of adipophilin on triglyceride accumulation and lipid-droplet formation in THP-1-derived macrophages (THP-1 macrophages). In the presence of acetylated low-density lipoprotein, macrophages infected with an adenovirus expressing human adipophilin showed a 31% increase in triglyceride content and a greater number of lipid droplets compared with control cells. Incubation of macrophages with very low-density lipoprotein (VLDL) dramatically increased cellular triglyceride content similarly in control and adipophilin-overexpressing cells. By itself, VLDL increased adipophilin expression, which explains the lack of effect of adipophilin overexpression on cellular triglyceride content in macrophages loaded with VLDL. The lipid-droplet content of macrophages was increased by overexpression of adipophilin and/or loading with VLDL. In contrast, inhibition of adipophilin expression using siRNA prevented lipid-droplet formation and significantly reduced intracellular triglyceride content. Using inhibitors of beta-oxidation and acyl-coenzyme A synthetase, results were obtained which suggest that adipophilin elevates cellular lipids by inhibition of beta-oxidation and stimulation of long-chain fatty acid incorporation into triglycerides. Adipophilin expression in THP-1 macrophages altered the cellular content of different lipids and enhanced the size of lipid droplets, consistent with a role for adipophilin in human foam cell formation.

Constitutive receptor-independent low density lipoprotein uptake and cholesterol accumulation by macrophages differentiated from human monocytes with macrophage-colony-stimulating factor (M-CSF)

Recently, we have shown that macrophage uptake of low density lipoprotein (LDL) and cholesterol accumulation can occur by nonreceptor mediated fluid-phase macropinocytosis when macrophages are differentiated from human monocytes in human serum and the macrophages are activated by stimulation of protein kinase C (Kruth, H. S., Jones, N. L., Huang, W., Zhao, B., Ishii, I., Chang, J., Combs, C. A., Malide, D., and Zhang, W. Y. (2005) J. Biol. Chem. 280, 2352-2360). Differentiation of human monocytes in human serum produces a distinct macrophage phenotype. In this study, we examined the effect on LDL uptake of an alternative macrophage differentiation phenotype. Differentiation of macrophages from human monocytes in fetal bovine serum with macrophage-colony-stimulating factor (M-CSF) produced a macrophage phenotype demonstrating constitutive fluid-phase uptake of native LDL leading to macrophage cholesterol accumulation. Fluid-phase endocytosis of LDL by M-CSF human macrophages showed non-saturable uptake of LDL that did not down-regulate over 48 h. LDL uptake was mediated by continuous actin-dependent macropinocytosis of LDL by these M-CSF-differentiated macrophages. M-CSF is a cytokine present within atherosclerotic lesions. Thus, macropinocytosis of LDL by macrophages differentiated from monocytes under the influence of M-CSF is a plausible mechanism to account for macrophage foam cell formation in atherosclerotic lesions. This mechanism of macrophage foam cell formation does not depend on LDL modification or macrophage receptors.

Modulating effects of cholesterol feeding and simvastatin treatment on platelet-activating factor acetylhydrolase activity and lysophosphatidylcholine concentration

BACKGROUND

Platelet-activating factor acetylhydrolyse (PAF-AH) is an enzyme that degrades PAF and bioactive oxidized lipids. However, it has been reported to be a risk factor for coronary heart disease. The present study examined the effects of cholesterol feeding and simvastatin treatment on plasma PAF-AH activity.

METHODS

Japanese White rabbits (n=22) were fed a diet containing 0.3% cholesterol and 3% corn oil for 1 month, and then divided into two groups that continued to receive this diet with (treated) or without (control) treatment with simvastatin (0.01%) for another 2 months.

RESULTS

Cholesterol feeding increased and simvastatin treatment decreased apolipoprotein (apo) B-containing lipoprotein subfractions as characterized by capillary isotachophoresis, serum levels of total cholesterol, phospholipids, LDL-C, apoE, plasma and LDL-associated PAF-AH (LDL-PAF-AH) activities, and plasma lyso-PC concentration. Cholesterol feeding also increased apoB levels but decreased the LDL-PAF-AH/LDL-C ratio and did not change the plasma PAF-AH/lyso-PC ratio. Simvastatin treatment did not affect apoB levels and only slightly increased the LDL-PAF-AH/LDL-C ratio. Secretion of PAF-AH activity from monocyte-derived macrophages was increased by cholesterol feeding but not affected by simvastatin treatment. These results indicate that PAF-AH activity is increased by cholesterol feeding due to increased secretion of PAF-AH activity from macrophages and that PAF-AH activity is decreased by simvastatin due to increased removal of lipid and enzyme contents of LDL particles.

CONCLUSION

Cholesterol elevation by cholesterol feeding and cholesterol-lowering by simvastatin modulate plasma PAF-AH activity by different mechanisms.

Macropinocytosis Is the Endocytic Pathway That Mediates Macrophage Foam Cell Formation with Native Low Density Lipoprotein

Previously, we reported that fluid-phase endocytosis of native LDL by PMA-activated human monocytederived macrophages converted these macrophages into cholesterol-enriched foam cells (Kruth, H. S., Huang, W., Ishii, I., and Zhang, W. Y. (2002) J. Biol. Chem. 277, 34573-34580). Uptake of fluid by cells can occur either by micropinocytosis within vesicles (<0.1 microm diameter) or by macropinocytosis within vacuoles ( approximately 0.5-5.0 microm) named macropinosomes. The current investigation has identified macropinocytosis as the pathway for fluid-phase LDL endocytosis and determined signaling and cytoskeletal components involved in this LDL endocytosis. The phosphatidylinositol 3-kinase inhibitor, LY294002, which inhibits macropinocytosis but does not inhibit micropinocytosis, completely blocked PMA-activated macrophage uptake of fluid and LDL. Also, nystatin and filipin, inhibitors of micropinocytosis from lipid-raft plasma membrane domains, both failed to inhibit PMA-stimulated macrophage cholesterol accumulation. Time-lapse video phase-contrast microscopy and time-lapse digital confocal-fluorescence microscopy with fluorescent DiI-LDL showed that PMA-activated macrophages took up LDL in the fluid phase by macropinocytosis. Macropinocytosis of LDL depended on Rho GTPase signaling, actin, and microtubules. Bafilomycin A1, the vacuolar H+-ATPase inhibitor, inhibited degradation of LDL and caused accumulation of undegraded LDL within macropinosomes and multivesicular body endosomes. LDL in multivesicular body endosomes was concentrated >40-fold over its concentration in the culture medium consistent with macropinosome shrinkage by maturation into multivesicular body endosomes. Macropinocytosis of LDL taken up in the fluid phase without receptor-mediated binding of LDL is a novel endocytic pathway that generates macrophage foam cells. Macropinocytosis in macrophages and possibly other vascular cells is a new pathway to target for modulating foam cell formation in atherosclerosis.

Serum matrix metalloproteinase-3 and tissue inhibitor of metalloproteinases-1 as potential markers of carotid atherosclerosis in infraclinical hyperlipidemia

The proteolytic activity of proinflammatory matrix metalloproteinases (MMPs) is elevated in lipid-rich atherosclerotic plaques, thereby contributing to plaque fragility and rupture. We hypothesized that changes in circulating levels of MMPs and their specific inhibitors (TIMPs) could reflect the atherosclerotic process occurring within the arterial wall. We determined serum levels of MMP-3, MMP-9, TIMP-1 and TIMP-2 in dyslipidemic subjects and compared them to those of age- and sex-matched normolipidemic healthy controls. Serum levels of MMP-3, MMP-9 and TIMP-1 were significantly increased in hyperlipidemic subjects versus controls (+54, +29 and +15%, respectively; P<0.001). We also noted a trend to elevated serum MMP-3 levels in patients with atherosclerotic lesions when compared to patients free of atherosclerosis (P=0.07). Circulating levels of MMPs and TIMPs were associated neither with those of C-reactive protein, nor with those of alpha2-macroglobulin (a nonspecific MMP inhibitor), nor with intima-media thickness values. Nonetheless, when divided into tertiles, MMP-3 and TIMP-1 levels in the highest tertile were positively associated with the presence of carotid artery lesions (odds ratios=3.4 and 2.0, confidence intervals 1.7-13.9 and 1.3-7.9, respectively). Thus, serum levels of MMP-3, -9 and TIMP-1 are significantly elevated in asymptomatic hyperlipidemic subjects at high cardiovascular risk; however, MMP-3 and TIMP-1 levels are strongly positively associated with the presence of carotid lesions. Such elevations might reflect enhanced vascular matrix remodeling, a key feature of the progression of atherosclerotic disease.

VLDL-induced triglyceride accumulation in human macrophages is mediated by modulation of LPL lipolytic activity in the absence of change in LPL mass

Mixed dyslipidemia of phenotype IIB is characterized by elevated levels of very low density lipoprotein (VLDL)-1 and VLDL-2 subfractions and of low density lipoprotein (LDL), which are associated with premature formation of atherosclerotic plaques, characterized by the presence of lipid-rich macrophage foam cells. Lipoprotein lipase (LPL) is a key factor in mediating macrophage lipid accumulation and foam-cell formation from native VLDL particles. The action of macrophage-derived LPL in the induction of intracellular lipid accumulation from triglyceride-rich lipoprotein (TRL) subfractions (VLDL-1, VLDL-2) is, however, indeterminate, as is the potential role of VLDL-1 and VLDL-2 in modulating macrophage LPL expression. We evaluated the role of LPL in the interaction of type IIB VLDL-1 and VLDL-2 with human macrophages. Both VLDL-1 and VLDL-2 subfractions induced significant accumulation of triglyceride (9.8-fold, P<0.0001, and 4.8-fold, P<0.0001, respectively) and of free cholesterol content (1.4-fold, P<0.001, and 1.2-fold, P=0.02, respectively). Specific inhibition (90%) of the lipolytic activity of endogenous LPL by tetrahydrolipstatin (THL) in the presence of VLDL-1 or VLDL-2 resulted in marked reduction in cellular loading of both triglycerides (-89%, P=0.008, and -89%, P=0.015, respectively) and free cholesterol (-76%, P=0.02, and -55%, P=0.06 respectively). Furthermore, VLDL-1 and VLDL-2 induced marked increase in macrophage-derived LPL enzyme activity (+81%, P=0.002, and +45%, P=0.02), but did not modulate macrophage-derived LPL mRNA and protein expression; consequently, LPL specific activity was significantly increased from 1.6 mU/microg at baseline to 4.1 mU/microg (P=0.01) and 3.1 mU/microg (P=0.05), in the presence of VLDL-1 and VLDL-2, respectively. We conclude that type IIB VLDL-1 and VLDL-2 induce triglyceride accumulation in human monocyte-macrophages primarily via the lipolytic action of LPL, which may involve stabilization and activation of the macrophage-secreted enzyme, rather than via modulation of enzyme production.

Effect of peroxisome proliferator-activated receptor gamma on thromboxane A(2) and prostaglandin E(2) production in macrophage cell lines

We studied the effect of peroxisome proliferator-activated receptor gamma (PPARgamma) activation on thromboxane A(2)(TXA(2)) and prostaglandin E(2)(PGE(2)) production in monocyte/macrophage cell lines. In present experiment, we used human peripheral blood monocyte (PBMC), monocyte-cell line THP-1 and mouse macrophage-like cell line RAW264.7. The expression of PPARgamma is reported in PBMC and THP-1. Synthetic PPARgamma ligands (troglitazone or BRL49653) inhibited TXA(2) production and enhanced PGE(2) production of PBMC and THP-1. When treated with 0.5-10 microM of troglitazone, there were no significant changes of TXA(2) and PGE(2) production of RAW264.7 cells, which express very low levels of PPARgamma. When RAW264.7 cells was transfected with PPARgamma expression plasmid and treated with troglitazone, PPARgamma was activated in a dose-dependent manner. In PPARgamma-transfected RAW264.7, TXA(2) production was decreased and PGE(2) production was increased by troglitazone treatment. But it needs high concentration of troglitazone (10 microM) for increasing PGE(2) production. These results suggest that PPARgamma may have negative effect on TXA(2) production, and also have slightly positive effect on PGE(2) production of macrophage.

Macrophage foam cell formation with native low density lipoprotein

This investigation has elucidated a mechanism for development of macrophage foam cells when macrophages are incubated with native low density lipoprotein (LDL). LDL is believed to be the main source of cholesterol that accumulates in monocyte-derived macrophages within atherosclerotic plaques, but native LDL has not previously been shown to cause substantial cholesterol accumulation when incubated with macrophages. We have found that activation of human monocyte-derived macrophages with phorbol 12-myristate 13-acetate (PMA) stimulates LDL uptake and degradation and acyl-CoA:cholesterol acyltransferase-mediated esterification of LDL-derived cholesterol, resulting in massive macrophage cholesterol accumulation that could exceed 400 nmol/mg of cell protein. Cholesterol accumulation showed a biphasic linear LDL concentration dependence with LDL levels as high as 4 mg/ml, similar to LDL levels in artery intima. Protein kinase C mediated the PMA-stimulated macrophage uptake of LDL because the protein kinase C inhibitors, Gö6983 and GF109203X, inhibited cholesterol accumulation. LDL receptors did not mediate macrophage cholesterol accumulation because accumulation occurred with reductively methylated LDL and in the presence of an anti-LDL receptor-blocking monoclonal antibody. LDL-induced cholesterol accumulation was not inhibited by antioxidants, was not accompanied by increased LDL binding to macrophages, did not depend on the apoB component of LDL, and was not down-regulated by prior cholesterol enrichment of macrophages. We have shown that the mechanism of LDL uptake by macrophages was PMA-stimulated endocytosis of LDL taken up as part of the bulk phase fluid (i.e. fluid phase endocytosis). The amount of LDL taken up with the bulk phase fluid was measured with [(3)H]sucrose and accounted for a minimum of 83% of the LDL cholesterol delivery and accumulation in PMA-activated macrophages. This novel mechanism of macrophage cholesterol accumulation shows that modification of LDL is not necessary for foam cell formation to occur. In addition, the findings direct attention to macrophage fluid phase endocytosis as a relevant pathway to target for modulating macrophage cholesterol accumulation in atherosclerosis.

Extracellular matrix metalloproteinase inducer (EMMPRIN) is induced upon monocyte differentiation and is expressed in human atheroma

OBJECTIVE

Because extracellular matrix metalloproteinase inducer (EMMPRIN), a tumor cell-derived protein, induces matrix metalloproteinases (MMPs) in fibroblasts and because MMPs are important in atheroma formation, we investigated if EMMPRIN was expressed in granulocyte/macrophage-colony stimulating factor (GM-CSF)-differentiated human peripheral blood monocytes (HPBM) and macrophage foam cells. In addition, EMMPRIN was studied for its expression in human atheroma.

METHODS AND RESULTS

After 10 days of GM-CSF-induced monocyte differentiation, EMMPRIN mRNA increased 5- to 8-fold relative to undifferentiated monocytes. GM-CSF treatment of HPBM revealed that both EMMPRIN mRNA and protein were upregulated by day 2 over undifferentiated monocytes. GM-CSF-differentiated HPBM showed characteristic macrophage phenotype by showing increases in pancake-like morphology and increases in biochemical markers such as apolipoprotein E, MMP-9, and cholesterol ester (CE). While acetylated LDL treatment of the 10-day GM-CSF-differentiated HPBM increased CE mass 13- to 321-fold, EMMPRIN expression was unchanged relative to nonlipid-loaded macrophages. In human coronary atherosclerotic samples, EMMPRIN was observed in CD68(+) macrophage-rich areas as well as areas of MMP-9 expressions.

CONCLUSIONS

Based on these data, we conclude that monocyte differentiation induces EMMPRIN expression, CE enrichment of foam cells has no further effect on EMMPRIN expression, and EMMPRIN is present in human atheroma. Therefore, EMMPRIN may play a role in atherosclerosis development.

Inhibition of p70(S6) kinase during transforming growth factor-beta 1/vitamin D(3)-induced monocyte differentiation of HL-60 cells allows tumor necrosis factor-alpha to stimulate plasminogen activator inhibitor-1 synthesis

We investigated intracellular mechanisms involved in the up-regulation of plasminogen activator inhibitor I (PAI-1) synthesis by human recombinant tumor necrosis factor-alpha (TNF) during monocyte differentiation of HL-60 cells triggered by the transforming growth factor-beta1/vitamin D(3) (TGF/D3) mixture. TGF/D3-treated cells expressed surface monocytic markers and produced noticeable amounts of PAI-1 but stopped to proliferate. A reduced p70 S6 kinase (p70(S6K)) phosphorylation was also observed and, in this situation, TNF dramatically enhanced PAI-1 synthesis. Similarly, TNF significantly up-regulated PAI-1 synthesis when p70(S6K) phosphorylation was inhibited by rapamycin. This phenomenon was not due to a general decrease in protein synthesis but involved the activation of gene transcription rather than PAI-1 mRNA stabilization. The level of the transcriptional regulator factor E2F1, a repressor of PAI-1 gene expression, was shown to be down-modulated in TGF/D3- as well as in rapamycin-treated cells. Furthermore, the apoptotic effect of TNF in HL-60 cells appeared to be prevented by the addition of either TGF/D3 or rapamycin. In conclusion, these results indicate that inhibition of p70(S6K) phosphorylation during TGF/D3-induced monocyte differentiation of HL-60 cells is a determinant factor that allows TNF to exert its up-regulating effect on PAI-1 synthesis while protecting cells from apoptosis.

Oxidized low-density lipoprotein and peroxisome-proliferator-activated receptor alpha down-regulate platelet-activating-factor receptor expression in human macrophages

Regulation of the expression of platelet-activating factor (PAF) receptor by atherogenic lipoproteins might contribute to atherogenesis. We show that progressive oxidation of low-density lipoprotein (LDL) gradually inhibits PAF receptor expression on the macrophage cell surface. We tested the effect of oxidized LDL (oxLDL) on PAF receptor expression in human monocytes that do not contain peroxisome-proliferator-activated receptor gamma (PPARgamma), a nuclear receptor activated by oxLDL. OxLDL decreased by 50% (P < or = 0.001) and by 29% (P < or = 0.05) the binding of PAF and the expression of PAF receptor mRNA respectively. Next we demonstrated that progressive oxidation of LDLs significantly activated PPARalpha-dependent transcription in transfected mouse aortic endothelial cells. Finally we demonstrated, in mature macrophages, that fenofibrate (20 microM), a specific PPARalpha agonist, but not the specific PPARgamma agonist BRL49653 (20 nM), significantly decreased both PAF binding and PAF receptor mRNA expression, by 65% and 40% (P < or = 0.001) respectively. Additionally, another PPARalpha agonist, Wy14,643, decreased PAF receptor promoter activity by 70% (P < or = 0.05) in transfected THP-1 cells, suggesting the involvement of the proximal promoter region (-980 to -500) containing a series of four nuclear factor (NF)-kappaB motifs. Thus PPARalpha might be involved in the down-regulation of PAF receptor gene expression by oxLDLs in human monocytes/macrophages. The oxidation of one or more lipid components of LDLs might result in the formation of natural activators of PPARalpha. It is hypothesized that such activators might modulate inflammation and apoptosis upon atherogenesis by decreasing the expression of PAF receptor.

Expression of platelet-activating factor receptor in human carotid atherosclerotic plaques: relevance to progression of atherosclerosis

BACKGROUND

Human monocyte-derived macrophages synthesize numerous proinflammatory and prothrombotic substances, including lipid mediators, such as platelet-activating factor (PAF), which may play a major role in the onset and perpetuation of atherosclerotic lesions. In addition, both monocytes and macrophages express PAF receptors (PAF-R). The expression of PAF-R is transcriptionally downregulated by oxidized LDL in in vitro primary cultures of monocyte/macrophages. In this study, we evaluated the expression of PAF-R in human carotid plaque tissue, in foam cells isolated from human carotid plaques, and in primary cultures of umbilical smooth muscle cells (SMCs).

METHODS AND RESULTS

We show that PAF-R was expressed at low levels in foam cells compared with monocyte/macrophages in plaques, as assessed by immunohistochemical staining and in situ hybridization. In addition, low levels of mRNA were also detected by RT-PCR in isolated human carotid foam cells. A prominent finding of our study was the demonstration that contractile SMCs were positive for PAF-R, and its mRNA was extracted from primary cultures of umbilical SMCs.

CONCLUSIONS

As macrophages loose their inflammatory phenotype on transformation into foam cells, they may equally loose their capacity of defense against aggression. We postulate that the diminished expression of PAF-R may be deleterious in the context of plaque formation and progression. The observation that arterial SMCs of contractile phenotype express PAF-R opens new avenues concerning the migration of these cells from media to intima and atherosclerotic plaque formation.

CLA-1/SR-BI is expressed in atherosclerotic lesion macrophages and regulated by activators of peroxisome proliferator-activated receptors

BACKGROUND

The scavenger receptors are cell-surface receptors for native and modified lipoproteins that play a critical role in the accumulation of lipids by macrophages. CLA-1/SR-BI binds HDL with high affinity and is involved in the cholesterol reverse-transport pathway. Peroxisome proliferator-activated receptors (PPARs) are transcription factors regulating the expression of genes implicated in lipid metabolism, cellular differentiation, and inflammation. Here, we investigated the expression of CLA-1/SR-BI in macrophages and its regulation by PPARs.

METHODS AND RESULTS

CLA-1 is undetectable in human monocytes and is induced upon differentiation into macrophages. Immunohistological analysis on human atherosclerotic lesions showed high expression of CLA-1 in macrophages of the lipid core colocalizing with PPARalpha and PPARgamma staining. Activation of PPARalpha and PPARgamma resulted in the induction of CLA-1 protein expression in monocytes and in differentiated macrophages. Finally, SR-BI expression is increased in atherosclerotic lesions of apoE-null mice treated with either PPARgamma or PPARalpha ligands.

CONCLUSIONS

Our data demonstrate that CLA-1/SR-BI is expressed in atherosclerotic lesion macrophages and induced by PPAR activation, identifying a potential role for PPARs in cholesterol homeostasis in atherosclerotic lesion macrophages.

Enhanced macrophage uptake of elastase-modified high-density lipoproteins

Incubation of human HDL (d = 1.063-1.21 g/ml) with monocyte-derived elastase causes selective proteolysis of apoA-II and apoA-I apolipoproteins. We have found that elastase-digested HDL (ED-HDL) bind to J774-A1 murine macrophages with enhanced affinity and are internalized and degraded at a rate threefold higher than that of native HDL. Unlike oxidized LDL and HDL and proteolytically modified LDL, the uptake of ED-HDL lipoproteins does not affect the cellular lipid biosynthesis nor modify the cell lipid content. The cell surface binding of (125)I-ED-HDL can be competed by native HDL but not by acetylated LDL, consistent with the idea that ED-HDL are recognized by the class B type I scavenger receptor. The liberation of elastase by lipid-engorging macrophages is regarded as an important event during atherogenesis. By enhancing the cellular uptake of HDL this process can lead to a local decrease of antiatherogenic HDL particles.

Molecular mechanisms in intimal hyperplasia

Intimal hyperplasia is the process by which the cell population increases within the innermost layer of the arterial wall, such as occurs physiologically during closure of the ductus arteriosus and during involution of the uterus. It also occurs pathologically in pulmonary hypertension, atherosclerosis, after angioplasty, in transplanted organs, and in vein grafts. The underlying causes of intimal hyperplasia are migration and proliferation of vascular smooth muscle cells provoked by injury, inflammation, and stretch. This review discusses, at a molecular level, both the final common pathways leading to smooth muscle migration and proliferation and their (patho)-physiological triggers. It emphasizes the key roles played by growth factors and extracellular matrix-degrading metalloproteinases, which act in concert to remodel the extracellular matrix and permit cell migration and proliferation.

Effects of macrophage colony-stimulating factor (M-CSF) on protease production from monocyte, macrophage and foam cell in vitro: a possible mechanism for anti-atherosclerotic effect of M-CSF

M-CSF is a growth factor that stimulates proliferation and differentiation of monocyte/macrophage-lineage cells. In our previous studies, M-CSF regresses atherosclerotic lesions preformed in aorta of high cholesterol-fed rabbit. Immunohistochemical analysis indicated that extracellular matrix (ECM), such as collagen, was especially eliminated in the intima of atherosclerotic lesion. To define the collagen-lowering potential of M-CSF, we have studied the effects of M-CSF on production of collagen-degrading proteases, such as MMP-1, -9 and urokinase in vitro. Monocytes freshly isolated from human peripheral blood produced MMP-9, but not urokinase, and M-CSF enhanced MMP-9 production. Macrophages were prepared by culturing monocytes for 10 days in the presence or absence of M-CSF, and protease production was assayed. M-CSF augmented production of MMP-9 and urokinase in a dose-dependent manner. M-CSF also enhanced MMP-1 production of macrophages, but not significantly. Foam cells were prepared by culturing macrophages in the presence of acetyl LDL, and protease production from these cells were also elevated by M-CSF. These results suggest that M-CSF exogenously administered in atherosclerotic rabbits might regress the thickened intima by activating macrophages to degrade collagen accumulated in the lesion.

Oxidized LDL-containing immune complexes induce Fc gamma receptor I-mediated mitogen-activated protein kinase activation in THP-1 macrophages

Our previous studies have shown that Fc gamma receptor (FcgammaR)-mediated uptake of LDL-containing immune complexes (oxLDL-ICs) by human monocyte-derived macrophages leads to not only transformation of macrophages into foam cells but also macrophage activation and release of cytokines. It has been shown that cross-linking of FcgammaR triggers activation of signal transduction pathways that alter gene expression in macrophages. In this study, we determined whether engagement of FcgammaR by oxLDL-ICs leads to activation of mitogen-activated protein (MAP) kinase pathway, a signaling cascade serving many important functions, including the regulation of gene expression, in THP-1 macrophage-like cells. Our results from immunoblotting, using specific anti-phosphorylated MAP kinase antibodies, showed that oxLDL-ICs induced extracellular signal regulated kinase 2 (ERK2) MAP kinase phosphorylation in THP-1 macrophage-like cells in time- and dose-dependent manners. Cholesterol loading before stimulation led to a longer phosphorylation of ERK2. Nuclear translocation of phosphorylated ERK was markedly increased after the stimulation. Moreover, our data showed that oxLDL-IC induction of MAP kinase was prevented by human monomeric IgG1, suggesting that the specific engagement of type I FcgammaR by oxLDL-IC is responsible for the MAP kinase activation. Finally, we showed that human anti-oxLDL autoantibody-containing immune complexes immobilized on type I collagen induced MAP kinase activation in THP-1 cells. These results strongly suggest that oxLDL-IC, which has been detected in atherosclerotic plaques, may play an important role in macrophage activation and atherogenesis.

Oxidized low-density lipoprotein regulates matrix metalloproteinase-9 and its tissue inhibitor in human monocyte-derived macrophages

BACKGROUND

Macrophages in human atherosclerotic plaques produce a family of matrix metalloproteinases (MMPs), which may influence vascular remodeling and plaque disruption. Because oxidized LDL (ox-LDL) is implicated in many proatherogenic events, we hypothesized that ox-LDL would regulate expression of MMP-9 and tissue inhibitor of metalloproteinase-1 (TIMP-1) in monocyte-derived macrophages. MWRHOSA AND RESULTS: Mononuclear cells were isolated from normal human subjects with Ficoll-Paque density gradient centrifugation, and adherent cells were allowed to differentiate into macrophages during 7 days of culture in plastic dishes. On day 7, by use of serum-free medium, the macrophages were incubated with various concentrations of native LDL (n-LDL) and copper-oxidized LDL. Exposure to ox-LDL (10 to 50 microg/mL) increased MMP-9 mRNA expression as analyzed by Northern blot, protein expression as measured by ELISA and Western blot, and gelatinolytic activity as determined by zymography. The increase in MMP-9 expression was associated with increased nuclear binding of transcription factor NF-kappaB and AP-1 complex on electromobility shift assay. In contrast, ox-LDL (10 to 50 microg/mL) decreased TIMP-1 expression. Ox-LDL-induced increase in MMP-9 expression was abrogated by HDL (100 microg/mL). n-LDL had no significant effect on MMP-9 or TIMP-1 expression.

CONCLUSIONS

These data demonstrate that unlike n-LDL, ox-LDL upregulates MMP-9 expression while reducing TIMP-1 expression in monocyte-derived macrophages. Furthermore, HDL abrogates ox-LDL-induced MMP-9 expression. Thus, ox-LDL may contribute to macrophage-mediated matrix breakdown in the atherosclerotic plaques, thereby predisposing them to plaque disruption and/or vascular remodeling.

Tissue factor pathway inhibitor is expressed by human monocyte-derived macrophages : relationship to tissue factor induction by cholesterol and oxidized LDL

Lipid-laden macrophages express tissue factor (TF), which may activate the extrinsic coagulation pathway on rupture of the atherosclerotic plaque. Tissue factor pathway inhibitor (TFPI) is a major regulator of TF-induced coagulation. We evaluated the possibility that monocyte-derived macrophages express this protein, thereby contributing to regulation of TF activity (TFact). Equally, we investigated the effect of cholesterol and of oxidized LDL (Ox-LDL) on the expression of TFPI and TF by human monocyte-derived macrophages (HMDMs). Northern blot analysis of TFPI mRNA from cultured HMDMs revealed a single band at 4.2 kb with weak intensity; this finding was confirmed by reverse transcription-polymerase chain reaction. Gel filtration of HMDM supernatants showed the presence of an active 100-kDa form of TFPI, which was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions; under reducing conditions, however, the immunoblot revealed a 40-kDa form of TFPI. The TFPI in HMDM supernatants possessed heparin-binding affinity, suggesting potential interaction of TFPI with heparan sulfate proteoglycans. Stimulation of foam cell formation by incubation of macrophages for 48 hours with exogenous free cholesterol indicated that neither the biological activity nor the de novo synthesis of TFPI protein was affected. In contrast, cholesterol loading with exogenous free cholesterol induced significant upregulation of total TFact (2.6-fold: 25.0 versus 9.4 mU/mg cell protein, cholesterol-treated versus control cells; P<0. 05); such induction was not correlated with an elevation in TF antigen (8.5 versus 7.8 ng/mg cell protein, cholesterol-treated versus control cells). Similarly, cholesterol-rich Ox-LDL induced an increase in TFact (1.9-fold: 18.9 versus 10.0 mU/mg cell protein, Ox-LDL-treated versus control cells; P<0.05); by contrast, the amount of TF antigen remained unchanged (7.1 versus 7.9 ng/mg cell protein, Ox-LDL-treated versus control cells). Our data indicate that enhancement of the procoagulant activity of TF in macrophage-derived foam cells is not counterbalanced by upregulation of TFPI activity, suggesting that lesion foam cells are in a procoagulant state; they may therefore contribute to thrombus generation on plaque rupture.

Interleukin-8 mediates downregulation of tissue inhibitor of metalloproteinase-1 expression in cholesterol-loaded human macrophages: relevance to stability of atherosclerotic plaque

BACKGROUND

The accumulation of macrophage-derived foam cells in atherosclerotic lesions correlates with increased local release of matrix-degrading metalloproteinases (MMPs) and a thin fibrous cap. The activity of these enzymes is controlled by specific tissue inhibitors of metalloproteinases (TIMPs).

METHODS AND RESULTS

Because oxidized low-density lipoprotein (OxLDL) modulates gene expression, we investigated the effect of these particles on the levels of MMP-1, MMP-3, MMP-9, TIMP-1, and TIMP-2 in the culture media of human monocyte-derived macrophages. OxLDL but not native LDL or high-density lipoprotein reduced the level of TIMP-1 in a dose-dependent manner with maximal effect (60% of control) at approximately 100 microg protein/mL. In addition, Northern blotting revealed marked reduction in the abundance of TIMP-1 mRNA in OxLDL-treated cells. Evaluation of the effect of oxysterol components of OxLDL on TIMP-1 production revealed that 25-hydroxycholesterol (1 microg/mL) was the most potent inhibitor ( approximately 30% of control). Such inhibition was partially mediated by interleukin (IL)-8. Indeed, IL-8 (2.5 ng/mL) induced maximal inhibition of TIMP-1 accumulation (30% of control) in 4 of 6 cell preparations. In addition, the inhibitory effect of OxLDL-treated cells in the presence of an anti-IL-8 neutralizing antibody was partially reversed.

CONCLUSIONS

Immunohistochemical analyses of human atherosclerotic plaques revealed the expression of TIMP-1 in some but not all macrophage-rich and IL-8-rich areas. Therefore, IL-8 may play a potential atherogenic role by inhibiting local TIMP-1 expression, thereby leading to an imbalance between MMPs and TIMPs at focal sites in the atherosclerotic plaque.

Activation of proliferator-activated receptors alpha and gamma induces apoptosis of human monocyte-derived macrophages

Peroxisome proliferator-activated receptors (PPARs) have been implicated in metabolic diseases, such as obesity, diabetes, and atherosclerosis, due to their activity in liver and adipose tissue on genes involved in lipid and glucose homeostasis. Here, we show that the PPARalpha and PPARgamma forms are expressed in differentiated human monocyte-derived macrophages, which participate in inflammation control and atherosclerotic plaque formation. Whereas PPARalpha is already present in undifferentiated monocytes, PPARgamma expression is induced upon differentiation into macrophages. Immunocytochemistry analysis demonstrates that PPARalpha resides constitutively in the cytoplasm, whereas PPARgamma is predominantly nuclear localized. Transient transfection experiments indicate that PPARalpha and PPARgamma are transcriptionally active after ligand stimulation. Ligand activation of PPARgamma, but not of PPARalpha, results in apoptosis induction of unactivated differentiated macrophages as measured by the TUNEL assay and the appearance of the active proteolytic subunits of the cell death protease caspase-3. However, both PPARalpha and PPARgamma ligands induce apoptosis of macrophages activated with tumor necrosis factor alpha/interferon gamma. Finally, PPARgamma inhibits the transcriptional activity of the NFkappaB p65/RelA subunit, suggesting that PPAR activators induce macrophage apoptosis by negatively interfering with the anti-apoptotic NFkappaB signaling pathway. These data demonstrate a novel function of PPAR in human macrophages with likely consequences in inflammation and atherosclerosis.

Inhibition of LPL expression in human monocyte-derived macrophages is dependent on LDL oxidation state: a key role for lysophosphatidylcholine

The regulation of macrophage lipoprotein lipase (LPL) secretion and mRNA expression by atherogenic lipoproteins is of critical relevance to foam cell formation. LPL is present in arterial lesions and constitutes a bridging ligand between lipoproteins, proteoglycans, and cell receptors, thus favoring macrophage lipoprotein uptake and lipid accumulation. We investigated the effects of native and of oxidized lipoproteins on the expression of LPL in an in vitro human monocyte-macrophage system. Exposure of mature macrophages (day 12) to highly copper-oxidized human low density lipoprotein (LDL) (100 microg protein per milliliter) led to marked reduction in the expression of LPL activity (-62%, P<0.01) and mRNA level (-47%, P<0.05); native LDL, acetylated LDL, and LDL oxidized for <6 hours were without effect. The reduction in LPL activity became significant at a threshold of 6 hours of LDL oxidation (-31%, P<0.05). Among the biologically active sterols formed during LDL oxidation, only 7beta-hydroxycholesterol (5 microg/mL) induced a minor reduction in macrophage LPL activity, whereas 25-hydroxycholesterol was without effect. By contrast, lysophosphatidylcholine, whose LDL content increased in parallel with the degree of oxidation, induced significant reductions in LPL activity and mRNA levels at concentrations of 2 to 20 micromol/L (-34% to -53%, P<0.01). Our results demonstrate that highly oxidized LDL (>6-hour oxidation) exerts negative feedback on LPL secretion in human monocytes-macrophages via a reduction in mRNA levels. By contrast, native LDL and mildly oxidized LDL (<6-hour oxidation) did not exert a feedback effect on LPL expression. We speculate that the content of lysophosphatidylcholine and, to a lesser degree, of 7beta-hydroxycholesterol in oxidized LDLs is responsible for the downregulation of LPL activity and mRNA abundance in human monocyte-derived macrophages and may therefore modulate LPL-mediated pathways of lipoprotein uptake during conversion of macrophages to foam cells.

Expression and localization of matrix metalloproteinase-12 in the aorta of cholesterol-fed rabbits: relationship to lesion development

Degradation of extracellular matrix (ECM) proteins in the aorta is a critical step for the development of atherosclerosis. Expression of matrix metalloproteinase (MMP)-12 (macrophage elastase), an elastin-degrading proteinase in the MMP family, was investigated in the thoracic aorta of rabbits fed a 1% cholesterol-containing diet for 16 weeks. In the atherosclerotic lesions, MMP-12 was produced abundantly at both the mRNA and protein levels, whereas no expression was observed in the normal rabbit aortas. The principal source of MMP-12 was macrophage foam cells (MFCs) that had infiltrated the atherosclerotic intima; this was demonstrated in both in vitro culture studies of MFCs purified from atherosclerotic lesions and immunohistochemical studies of aortic lesions. Additional biochemical studies using recombinant rabbit MMP-12 revealed that MMP-12 digested elastin, type IV collagen, and fibronectin and also activated MMP-2 and MMP-3. Expression of MMP-12 by human macrophage cell lines was increased by stimulation with acetylated low-density lipoprotein, implying augmentation of MMP-12 production during foam cell formation. Increased expression of MMP-12 in atherosclerotic lesions, concomitant with foam cell generation, which triggers the acceleration of ECM breakdown, is likely to be a critical step in the initiation and progression of the atherosclerotic cascade.

Endothelial and serum factors which include apolipoprotein A1 tether elastin to smooth muscle cells inducing serine elastase activity via tyrosine kinase-mediated transcription and translation

We previously reported that serine elastase activity is induced in cultured porcine pulmonary artery (PA) smooth muscle cells (SMC) following serum stimulation by a mechanism involving adhesion of elastin to an elastin binding protein and tyrosine kinase activity. The present study demonstrates that a PA endothelial cell factor also promotes a fourfold increase in elastin adhesion to PA SMC and a twofold increase in serine elastase activity. The mechanism involves tethering of the factor to SMC, since [3H]-elastin pre-incubated with serum or endothelial cell (EC)-conditioned medium or SMC pre-treated with serum accelerates binding of elastin and tyrosine-kinase related elastase activity. The serum factor appears to interact with integrins as elastase induction is partially inhibited by RGD peptides. The elastase-inducing properties of serum could not, however, be attributed to several RGD-containing proteins. While a 120 kD fibronectin fragment partially reproduced the effect, it was not found in the serum fraction containing elastase-inducing activity. Instead, a 27 kD serum protein was enriched by elastin affinity chromatography, identified as apolipoprotein (Apo) A1 by microsequence analysis, and found to have about 50% of the elastase-inducing activity of serum. Elastase induction is inhibited by actinomycin and cycloheximide, suggesting a requirement for mRNA transcription and protein synthesis. Our results suggest a novel cell-extracellular matrix interaction whereby a soluble factor, in this case a lipoprotein, binds and tethers a matrix component to the cell surface and induces tyrosine kinase-dependent transcription of mRNA culminating in substrate proteolysis.

Copper-catalyzed oxidation mediates PAF formation in human LDL subspecies. Protective role of PAF:acetylhydrolase in dense LDL

Free radical-mediated oxidation of cholesterol-rich LDL plays a key role in atherogenesis and involves the formation of oxidized phospholipids with proinflammatory biological activity. We evaluated the production of platelet-activating factor (PAF), a potent inflammatory mediator, in human LDL subspecies on copper-initiated oxidation (4 mumol/L CuCl2, 80 micrograms/mL for hours at 37 degrees C). PAF formation was determined by biological assay of HPLC-purified lipid extracts of copper-oxidized lipoproteins; chemical identity was confirmed by gas chromatographic and mass spectrometric analyses. PAF, characterized as the C16:0 molecular species, was preferentially produced in intermediate LDL (d = 1.029 to 1.039 g/mL) (8.6 +/- 5.7 pmol PAF/3 h per mg LDL protein) and light LDL (d = 1.019 to 1.029 g/mL), but was absent from dense LDL particles (d = 1.050 to 1.063 g/mL). As PAF:acetylhydrolase inactivates PAF and oxidized forms of phosphatidylcholine, we evaluated the relationship of lipoprotein-associated PAF:acetylhydrolase to PAF formation. We confirmed that PAF:acetylhydrolase activity was elevated in native, dense LDL (41.5 +/- 9.5 nmol/min per mg protein) but low in LDL subspecies of light and intermediate density (d 1.020 to 1.039 g/mL) (3.5 +/- 1.6 nmol/min per mg protein) [Tselepis et al, Arterioscler Thromb Vasc Biol. 1995;15:1764-1773]. On copper-mediated oxidation for 3 hours at 37 degrees C, dense LDL particles conserved 20 +/- 14% of their initial enzymatic activity; in contrast, PAF:acetylhydrolase activity was abolished in light and intermediate LDL subspecies. Clearly, the elevated PAF:acetylhydrolase activity of dense LDL efficiently diminishes the potential inflammatory role of endogenously formed PAF; nonetheless, formation of proatherogenic lysophospholipids results. In contrast, LDL particles of the light and intermediate subclasses can accumulate PAF on oxidative modification.

Expression of the PAF receptor in human monocyte-derived macrophages is downregulated by oxidized LDL: relevance to the inflammatory phase of atherogenesis

Human monocyte-derived macrophages play a major role in the initiation and progression of atherosclerotic lesions as a result of the production of a wide spectrum of proinflammatory and prothrombotic factors. Among such factors is a potent inflammatory phospholipid, platelet-activating factor (PAF), which is produced after macrophage activation. Because the cells involved in PAF biosynthesis are typically targets for the bioactions of PAF via specific cell surface receptors, we evaluated the expression of the PAF receptor in human monocyte-derived macrophages. Oxidized LDL (oxLDL) exerts multiple cellular effects that enhance lesion progression; we therefore investigated the potential modulation of expression of the macrophage PAF receptor by oxLDL. [3H]PAF bound to adherent human macrophages with a K(d) of 2.1 nmol/L and a B(max) of 19 fmol/10(6) cells; approximately 5300 binding sites per cell were detected. OxLDL (100 microg protein per milliliter) induced a twofold decrease in cellular PAF binding after 3 hours at 37 degrees C. Analysis of macrophage mRNA by reverse transcription-polymerase chain reaction (RT-PCR) revealed two forms corresponding to the PAF receptor, of which the leukocyte type (type 1 promoter) predominated. Expression of PAF receptor mRNA, evaluated by quantitative RT-PCR using an actin or a GAPDH mimic, was progressively reduced (up to 70%) by oxLDL up to 6 hours and remained low for at least 24 hours. Such downregulation was reversible after incubation of the cells for 24 hours in oxLDL-free medium. Addition of forskolin (3 micromol/L) or dibutyryl cAMP (1 mmol/L) to macrophage cultures reproduced the oxLDL-mediated inhibition of PAF receptor expression; carbamyl PAF reduced PAF binding and PAF mRNA to a similar degree (approximately 50%). These data demonstrate that atherogenic oxLDL downregulates the expression of both cellular PAF receptors and PAF receptor mRNA in macrophages, consistent with both a diminished bioresponse to PAF and decreased cell motility. Such diminished bioresponse to a powerful antacoid reflects the suppression of an acute inflammatory reaction, thereby leading to chronic, low-level inflammation, such as that characteristic of fatty streaks and more advanced atherosclerotic plaques.

Impact of a combination of a calcium antagonist and a beta-blocker on cell- and copper-mediated oxidation of LDL and on the accumulation and efflux of cholesterol in human macrophages and murine J774 cells

Calcium antagonists and beta-blockers may retard or inhibit atherogenesis. In the absence of data pertaining to the potential cardioprotective action of an association of such agents, we have investigated the impact of nifedipine and atenolol, alone or in combination, on the capacity of monocyte-macrophages (ex vivo) and copper ions (in vitro) to oxidize LDL and on intracellular metabolism and efflux of free and esterified forms of cholesterol in human macrophages and foam cells. At concentrations up to 100 micromol/L, atenolol had no effect on the oxidative resistance of LDL; on the contrary, nifedipine displayed a significant dose-dependent capacity to protect LDL during copper-mediated oxidation (100 micromol/L; P<.001). Using a DPPH radical generating system, nifedipine was shown to exert free radical-trapping activity (molar ratio of scavenging activity, nifedipine:alpha-tocopherol, 1:114). The addition of atenolol to nifedipine was without effect on the antioxidant activity of the calcium antagonist. In experiments in which oxidative modification was mediated by monocyte-macrophages, nifedipine but not atenolol conserved its antioxidant capacity. Furthermore, we demonstrated that association of atenolol with nifedipine did not modify the antioxidant properties of nifedipine itself. Using a human monocyte-derived macrophage culture system, nifedipine, atenolol, or a combination of the two drugs was ineffective in inhibiting foam cell formation induced by acetylated LDL or oxidized LDL. However, atenolol (100 micromol/L) increased cellular accumulation of cholesteryl ester (+17%; P<.05), whereas nifedipine (100 micromol/L) decreased total cholesterol (-37.4%; P<.05) accumulation induced by acetylated LDL in the mouse macrophage cell line J774. A combination of the two drugs neutralized these antagonistic effects. None of these results were reproduced during the oxidized LDL-induced transformation of murine J774 cells into foam cells. Furthermore, cholesterol efflux from preloaded human macrophages was equally unaffected by the addition of the drugs alone or in combination. It therefore seems unlikely that the beneficial effect of atenolol on coronary heart disease is mediated by changes in either LDL oxidizability or cholesterol metabolism in human macrophages and foam cells. Our findings with nifedipine suggest, however, that this calcium antagonist may potentially exert antiatherosclerotic properties via a reduction of the oxidative modification of LDL, thereby affecting a reduction in foam cell formation and in the pathophysiological cellular activities of oxidized lipids, rather than by inducing a direct reduction in cholesterol accumulation in human foam cells of macrophage origin.

Elastase-induced hydrolysis of synthetic solid substrates: poly(ester-urea-urethane) and poly(ether-urea-urethane)

Human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) were incubated with two radiolabelled model poly(urethane), a poly(ester-urea-urethane) containing [14C]toluene diisocyanate ([14C]TDI), poly(caprolactone)(PCL) and ethylenediamine (ED), and a poly(ether-urea-urethane) containing [14C]TDI, poly(tetramethylene oxide) (PTMO) and ED. Ten-fold more radioactive carbon was released when PPE was incubated with [14C]TDI/PCL/ED than when HNE was used. The PPE-induced radioactive carbon release was significantly reduced by a specific elastase inhibitor. Ten-fold less radioactive carbon was released when [14C]TDI/PTMO/ED was incubated with PPE as compared to [14C]TDI/PCL/ED. Since neutrophils, which contain elastolytic activity, are present during the inflammatory response, the stability of biomaterials used in implanted devices may be affected.

Matrilysin is expressed by lipid-laden macrophages at sites of potential rupture in atherosclerotic lesions and localizes to areas of versican deposition, a proteoglycan substrate for the enzyme

Certain matrix metalloproteinases (MMP) are expressed within the fibrous areas surrounding acellular lipid cores of atherosclerotic plaques, suggesting that these proteinases degrade matrix proteins within these areas and weaken the structural integrity of the lesion. We report that matrilysin and macrophage metalloelastase, two broad-acting MMPs, were expressed in human atherosclerotic lesions in carotid endarterectomy samples (n = 18) but were not expressed in normal arteries (n = 7). In situ hybridization and immunohistochemistry revealed prominent expression of matrilysin in cells confined to the border between acellular lipid cores and overlying fibrous areas, a distribution distinct from other MMPs found in similar lesions. Metalloelastase was expressed in these same border areas. Matrilysin was present in lipid-laden macrophages, identified by staining with anti-CD-68 antibody. Furthermore, endarterectomy tissue in organ culture released matrilysin. Staining for versican demonstrated that this vascular proteoglycan was present at sites of matrilysin expression. Biochemical studies showed that matrilysin degraded versican much more efficiently than other MMPs present in atherosclerotic lesions. Our findings suggest that matrilysin, specifically expressed in atherosclerotic lesions, could cleave structural proteoglycans and other matrix components, potentially leading to separation of caps and shoulders from lipid cores.

Interleukin 8 is induced by cholesterol loading of macrophages and expressed by macrophage foam cells in human atheroma

In order to identify novel genes expressed in macrophage-derived foam cells, we used a multigene assay to examine the expression of genes in control versus cholesterol-loaded macrophages. We compared THP-1 macrophages incubated with or without acetylated LDL (acLDL) +/- acyl-CoA:cholesterol O-acyltransferase (ACAT) inhibitor (compound 58035) for 20 h and assessed changes in mRNA of chemokines, growth factors, interleukins, and adhesion molecules. Among 49 genes examined, an increase in mRNA was observed only for interleukin 8 (IL-8) in THP-1 macrophages. Northern analysis confirmed a 3- to 4-fold increase of IL-8 mRNA and an enzyme-linked immunosorbent assay (ELISA) revealed a corresponding increase in IL-8 in conditioned medium. Oxidized LDL (oxLDL) also induced IL-8 mRNA, but native LDL had no effect. 58035 had a moderate effect on IL-8 induction by acLDL. AcLDL-induced IL-8 expression was concentration- and time-dependent. The time course of IL-8 induction paralleled that of cholesterol loading. MCP-1, a chemokine implicated in recruiting monocytes in atherogenesis, was also induced by acLDL. The induction of MCP-1, however, peaked at 1 h after addition of acLDL and returned to basal level by 20 h while IL-8 induction peaked at 8 h and was still 2-fold higher than basal level at 20 h. IL-8 induction was also observed in fresh human monocyte-derived macrophage cells treated with acLDL. Finally, immunohistochemistry and in situ hybridization studies using specimens of human coronary atheromas showed expression of IL-8 mRNA in a macrophage-rich area. We conclude that IL-8 is induced in macrophage foam cells as a response to cholesterol loading. The chemoattractant and/or mitogenic effects of IL-8 on neutrophils, T cells, smooth muscle, or vascular endothelial cells may contribute to the progression and complications of atherosclerosis.

Pefabloc, 4-[2-aminoethyl]benzenesulfonyl fluoride, is a new, potent nontoxic and irreversible inhibitor of PAF-degrading acetylhydrolase

We report here that 4-[2-aminoethyl]benzenesulfonyl fluoride (Pefabloc SC, Pefabloc), a new irreversible serine proteinase inhibitor, efficiently inhibits both human and rat platelet activating factor (PAF)-degrading acetylhydrolase (acetylhydrolase). Indeed, low concentrations of Pefabloc (0.1 mM) rapidly and totally inactivate both human plasma-, VLDL-, IDL-, LDL- and HDL-associated acetylhydrolase, and in addition, acetylhydrolase synthesized and released by human adherent monocytes in culture, as well as rat brain cytosolic acetylhydrolase. By contrast, Pefabloc only minimally inhibited the phospholipase A2 (PLA2) activity from Naja naja and from porcine pancreas. In addition, Pefabloc is relatively nontoxic, stable and convenient to use. Henceforth, Pefabloc may replace both DFP and PMSF and therefore constitutes a useful and valuable tool in future studies of acetylhydrolase.

Phagocytic activation induces formation of platelet-activating factor in human monocyte-derived macrophages and in macrophage-derived foam cells. Relevance to the inflammatory reaction in atherogenesis

Monocyte-derived macrophages and macrophage-derived foam cells in arterial tissue may undergo phagocytic activation and thereby contribute to an inflammatory reaction. We have investigated the effect of phagocytic activation on the formation of platelet-activating factor (1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF-acether, PAF), a proinflammatory phospholipid, in human monocyte-derived macrophages (macrophages) and in cholesterol-loaded macrophage foam cells (foam cells). Adherent human monocyte-derived macrophages were transformed into foam cells upon incubation with acetylated low-density lipoproteins (Ac-LDL). Such foam cells characteristically displayed a markedly increased content of cholesteryl esters compared with macrophages (4.3 +/- 1.3 microgram/microgram DNA and 0.2 +/- 0.3 microgram/microgram DNA, n = 5, respectively). After phagocytic stimulation with serum-opsonized zymosan (OPZ), both macrophages and foam cells synthesized PAF transiently with maximal production (0.5-1.1 pmol PAF/microgram DNA, n = 5, corresponding to 4.0-8.8 pmol PAF/10(6) cells, as assessed by bioassay) occurring approximately 15 min after stimulation. A major fraction of the synthesized PAF remained cell-associated; such PAF was composed mainly of the hexadecyl (16:0 PAF, approximately 75%) and the octadecenyl (18:1 PAF) species and of trace amounts of octadecyl (18:0 PAF), as assessed by reverse-phase liquid chromatography. Addition of exogenous 16:0 lyso-PAF alone triggered PAF formation (0.9-1.7 pmol PAF/microgram DNA, after 15 min of cellular stimulation); simultaneous cellular stimulation with OPZ and 16:0 lyso-PAF increased PAF formation in an additive manner. Acetyltransferase, the enzyme which acetylates the precursor lyso-PAF and transforms it into PAF, displayed elevated activity both in macrophages and in foam cells, attaining 83-240 pmol PAF formed per min per mg DNA (n = 4); such elevated activity was not increased by OPZ-stimulation. The activity of acetylhydrolase, the PAF-degrading enzyme, was similar in macrophages and in foam cells, and varied between 120 pmol and 320 pmol PAF degraded per min per mg DNA (n = 5). Cell-associated acetylhydrolase activity was increased significantly by 40+/-15 % (P < 0.003, n = 5) after 15 - 30 min of activation with OPZ compared with non-stimulated cells and may account for the rapid decrease in cellular PAF content observed approximately 30 min after stimulation. These studies have established that metabolism of PAF in foam cells closely resembles that in macrophages, and thus PAF metabolism is largely independent of cellular cholesterol content. Moreover our data are consistent with the hypothesis that both macrophages and macrophage-derived foam cells upon phagocytic-activation constitute a significant transient source of PAF at inflammatory sites in the arterial intima where this phospholipidic mediator may exert potent proatherogenic and prothrombotic effects.

Phorbol myristate acetate ex vivo model of enhanced colonic epithelial permeability. Reactive oxygen metabolite and protease independence

The initiating mechanisms involved in colonic injury are currently unknown. The goal of the current study was to examine the role of the inflammatory mediators reactive oxygen metabolites and proteases in an ex vivo model of selective epithelial permeability. Rats were prepared with exteriorized colonic chambers to which the protein kinase C (PKC) activator phorbol myristate acetate (PMA) was added in doses ranging from 5 to 800 micrograms. PMA caused a dose-dependent transient increase in epithelial permeability, but had no significant effect on microvascular permeability. There was no accumulation of neutrophils and no apparent histological changes. PMA acts via a PKC-dependent mechanism, as assessed using the PKC-inactive phorbol analog 4 alpha-phorbol didecanoate, and the response is tachyphylactic. The mechanism is independent of reactive oxygen metabolites and proteases, as shown by the lack of effect of the free radical scavengers superoxide dismutase and catalase and the general serine protease inhibitor soybean trypsin inhibitor. The classic inflammatory process does not appear to be involved in the PMA-induced epithelial permeability changes. This finding suggests that noninflammatory mechanisms may regulate the increased epithelial permeability induced by PMA. Further study to elucidate these mechanisms is of importance for understanding both normal gastrointestinal physiology and initiation of pathology.

PAF-degrading acetylhydrolase is preferentially associated with dense LDL and VHDL-1 in human plasma. Catalytic characteristics and relation to the monocyte-derived enzyme

In human plasma, platelet activating factor (PAF)-degrading acetylhydrolase (acetylhydrolase) is principally transported in association with LDLs and HDLs; this enzyme hydrolyzes PAF and short-chain forms of oxidized phosphatidylcholine, transforming them into lyso-PAF and lysophosphatidylcholine, respectively. We have examined the distribution, catalytic characteristics, and transfer of acetylhydrolase activity among plasma lipoprotein subspecies separated by isopycnic density gradient ultracentrifugation; the possibility that the plasma enzyme may be partially derived from adherent monocytes has also been evaluated. In normolipidemic subjects with Lp(a) levels < 0.1 mg/mL, acetylhydrolase was associated preferentially with small, dense LDL particles (LDL-5; d = 1.050 to 1.063 g/mL) and with the very-high-density lipoprotein-1 subfraction (VHDL-1; d = 1.156 to 1.179 g/mL), representing 23.9 +/- 1.7% and 20.6 +/- 3.2%, respectively, of total plasma activity. The apparent Km values for PAF of the enzyme associated with such lipoproteins were 89.7 +/- 23.4 and 34.8 +/- 4.5 mumol/L for LDL-5 and VHDL-1, respectively: indeed, the Km value for LDL-5 was some 10-fold higher than that of the light LDL-1, LDL-2, and LDL-3 subspecies, whereas the Km of VHDL-1 was some twofold greater than those of the HDL-2 and HDL-3 subspecies. Furthermore, when expressed on the basis of unit plasma volume, the Vmax of the acetylhydrolase associated with LDL-5 was some 150-fold greater than that in LDL-1 (d = 1.019 to 1.023 g/mL). No significant differences in the pH dependence of enzyme activity or in sensitivity to protease inactivation, sulfydryl reagents, the serine protease inhibitor Pefabloc, or the PAF antagonist CV 3988 could be detected between apo B-containing and apo A-I-containing lipoprotein particle subspecies. Incubation of LDL-1 (Km = 8.4 +/- 2.6 mumol/L) and LDL-2 (d = 1.023 to 1.029 g/mL; Km = 8.4 +/- 3.3 mumol/L) subspecies with LDL-5, in which acetylhydrolase had been inactivated by pretreatment with Pefabloc, demonstrated preferential transfer of acetylhydrolase to LDL-5. Acetylhydrolase transferred to LDL-5 from the light LDL subspecies exhibited a Km of 9.4 +/- 2.2 mumol/L, a value characteristic of the particle donors. Finally, acetylhydrolase (Km = 23.4 +/- 7.6 mumol/L) released by adherent human monocytes in culture was found to bind preferentially to small, dense LDL subspecies upon incubation of Pefabloc-inactivated plasma with monocyte supernatant.(ABSTRACT TRUNCATED AT 400 WORDS)

The biologic behavior of balloon hyperinflation-induced arterial lesions in hypercholesterolemic pigs depends on the presence of foam cells

Lack of a large-animal model of accelerated atherosclerosis has limited study of the biologic behavior of atherosclerotic lesions. We hypothesized that mechanical vascular trauma combined with diet-induced hypercholesterolemia would result in rapid development of complex atherosclerosis-like lesions. Accordingly, we induced deep injury to a carotid artery by repetitive balloon hyperinflations in minipigs that were fed either an atherogenic diet (n = 30) or a standard diet (controls, n = 4) and examined the resultant lesions 1 month later. The neointimal lesions that evolved in 23 patent vessels from cholesterol-fed animals were complex, exhibiting infiltration of smooth muscle and foam cells and evidence of organized thrombus, recent thrombus, hemorrhage, and calcification. Lesions were separable histologically into two groups: foam-cell rich (n = 12), with 33 +/- 10 foam cells per high-power field, and foam-cell poor (n = 11), with 4 +/- 1 foam cells per high-power field. Minipigs with foam cell-rich lesions had higher serum cholesterol levels than those with foam cell-poor lesions (712 +/- 178 vs 468 +/- 240 mg/dL, P < .02). The incidence of intralesional thrombus was also significantly greater in foam cell-rich than in foam cell-poor lesions (50% vs 9%, P < .04). In addition, the degree of luminal stenosis was greater in the presence of lesions containing thrombus compared with those without thrombus (60 +/- 38% vs 30 +/- 29%, P = .05). Lesions in the control animals were fibrocellular and lacked foam cells and thrombus. Thus, hypercholesterolemia appeared to affect lesion composition and behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary report: genetic variation in the human stromelysin promoter is associated with progression of coronary atherosclerosis

Stromelysin is a member of the family of metalloproteinases that degrade extracellular matrix. In situ hybridisation and histopathological studies suggest that stromelysin activity may be important in the connective tissue remodelling processes associated with atherogenesis and plaque rupture. Single strand conformation polymorphism analysis identified a common polymorphism in the stromelysin gene promoter located 1171 bp upstream from the start of transcription in which one allele has a run of six adenosines (6A) and another has five adenosines (5A). 72 men with coronary heart disease, were genotyped. They were participants in the St Thomas' Atherosclerosis Regression Study who were randomised to receive usual care (UC), dietary intervention (D), or diet plus cholestyramine (DC), with angiography at baseline and at 39 months. In these patients the frequency of the 5A allele was 0.49 (95% CI from 0.41 to 0.57) and was not significantly different from that in a sample of 354 healthy UK men. In the UC group, patients who were homozygous for the 6A allele showed greater progression of angiographic disease than those with other genotypes: the minimum absolute width of coronary segments decreased by 0.04 (SEM 0.10) mm for 5A5A, 0.20 (0.07) mm for 5A6A, and 0.67 (0.19) mm for 6A6A (P < 0.01). The findings were similar but slightly less significant for the change in mean absolute width of coronary segments (P < 0.05). No significant associations were seen in patients in the D or DC groups. In data pooled from the three treatment groups, the 6A6A genotype was significantly associated with greater progression of coronary atherosclerosis than other genotypes in patients with baseline percentage diameter stenosis less than 20% (P < 0.05), but not in those with baseline percentage diameter stenosis greater than or equal to 20%. These results provide the first evidence of a link between genetic variation in stromelysin and progression of coronary atherosclerosis and support the hypothesis that connective tissue remodeling mediated by metalloproteinases contribute to the pathogenesis of atherosclerosis.

Neutrophil-mediated degradation of segmented polyurethanes

The biostability of polyurethanes was evaluated using a human neutrophil cell culture. The polymers were synthesized with 14C radiolabelled components incorporated into the polyurethane chain and the amount of radiolabel released during exposure to cells and medium was used as a marker for material degradation. The effect of diisocyanate, soft segment and chain extender chemistry on the susceptibility of polymer degradation was examined. All polymers showed a release of material into the tissue culture medium which was unrelated to the cells. A significant cell-dependent release of radiolabel-containing material was found from one of the polymers (a polyester urea-urethane, TDI/PCL/ED) which increased linearly up to 96 h. The polyether-containing polyurethanes showed no significant cell-mediated degradation under similar conditions as measured by radiolabel release. Scanning electron microscopy (SEM) showed that the cells adhered to the different polyurethanes. However, no effect of neutrophils on polymer structure could be detected by this technique. The cellular response to each polymer was evaluated by measuring release of elastase-like activity (ELA) into the tissue culture media. After 24h TDI/PCL/ED showed the highest levels of ELA in the tissue culture medium. When TDI/PCL/ED was incubated with commercial elastase in vitro, a significant release of radiolabel was found which was comparable to the amount of radiolabelled material released from this polymer in contact with the neutrophils in culture. No significant amount of radiolabel was released from the corresponding polyether material (TDI/PTMO/ED) under similar conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Iron induces lipid peroxidation in cultured macrophages, increases their ability to oxidatively modify LDL, and affects their secretory properties

The present study demonstrates for the first time that iron ions can induce lipid peroxidation in intact macrophages without causing cell death. Macrophage lipid peroxidation increases cell-mediated oxidation of LDL, enhances the release of interleukin 1 and inhibits the release of apolipoprotein E from the macrophages. When cultured macrophages were exposed to ferrous ions (50 microM FeSO4) for 4 h at 37 degrees C, cellular lipid peroxidation (measured by analyses of malondialdehyde (MDA), conjugated dienes (CD), and lipid peroxides (PD)) increased 2-4-fold in comparison with non-treated cells. This process was iron-dose dependent, reached its maximum after 4 h of incubation, and was accompanied by 68% and 53% reductions in the content of the cellular linoleic (18:2), and arachidonic acid (20:4), respectively, and by 29% and 36% reductions of cellular vitamin E and vitamin A, respectively. Cell viability (measured by trypan blue exclusion, by [3H]thymidine incorporation into DNA, by analysis of the release of lactate dehydrogenase (LDH) or [3H]adenine), and cell morphology (studied by scanning electron microscopy) were not significantly affected by the iron-induced oxidative stress. Manitol and dimethylthiourea (DMTU), but not catalase or superoxide dismutase (SOD), significantly inhibited iron-induced cellular lipid peroxide formation, suggesting that hydroxyl radical, but not superoxides or hydrogen peroxides, mediated the iron-induced cellular lipid peroxidation. Incubation of LDL (0.2 mg of protein/ml) with oxidized macrophages resulted in LDL lipids peroxidation, as evidenced by an 8-fold increase in the LDL associated MDA in comparison with LDL that was incubated under similar conditions with non-oxidized macrophages. Furthermore, oxidation of LDL by oxidized macrophages in the presence of copper ions (10 microM CuSO4) was 2-fold higher in comparison with oxidation of LDL by non-oxidized macrophages. The release of apolipoprotein E from oxidized macrophages decreased by 50%, whereas macrophage release of beta-glucuronidase and of interleukin-1 beta increased by 83% and by a factor of 6, respectively. This study demonstrates for the first time that iron ions induce oxidation of the cellular polyunsaturated fatty acids in intact macrophages and that this cellular lipid peroxidation can subsequently induce LDL oxidation.

Serum-induced vascular smooth muscle cell elastolytic activity through tyrosine kinase intracellular signalling

In previous studies, we related increased elastolytic activity in pulmonary arteries (PA) with endothelial injury to the later development of PA hypertension in rats. As the mechanism causing the increased PA elastase was unknown, we hypothesized that serum factors which are accessible to vascular smooth muscle cells (SMC) following endothelial injury stimulate their elastolytic activity. To test this, we developed an in vitro assay in which we added [3H]-elastin to cultured vascular SMC after 24 h serum starvation and monitored elastolysis following a further 24 h incubation with fetal bovine serum (FBS). We observed that serum induced increased elastolytic activity in both PA and aorta-derived SMC but not in endothelial cells or SMC with low basal levels of elastolytic activity. Maximum stimulation of SMC elastolytic activity occurred with a concentration as low as 1% FBS and despite elastase inhibitors in serum, suggesting that the activity is confined to the immediate pericellular region where enzyme concentration is high. Serum-stimulated elastolytic activity was not reproduced by growth factors or cytokines known to be associated with vascular disease or to induce release of elastases in other cells. The serum inducing elastolytic activity was heat and acid labile. It was associated with increased elastin adhesion to the 67 kD elastin binding protein on SMC surfaces and was prevented by tyrosine kinase inhibitors but not protein kinase C or A inhibitors. Our studies therefore suggest a mechanism whereby serum induction of SMC elastase requires signalling through the elastin binding protein and activation of tyrosine kinase.

PAF-acether-degrading acetylhydrolase in plasma LDL is inactivated by copper- and cell-mediated oxidation

In peripheral blood, native low-density lipoprotein (LDL) is a major carrier of acetylhydrolase, the enzyme that hydrolyzes the sn-2 acetate of PAF-acether, converting it to lyso PAF-acether. By controlling the level of PAF-acether, the acetylhydrolase may regulate the biologic effects of this potent inflammatory and thrombotic mediator. The biologic oxidation of LDL appears to underlie its atherogenicity. We report here that oxidative modification of LDL led to progressive loss of associated acetylhydrolase activity. Reductions of approximately 90% and 40% of acetylhydrolase activity occurred respectively in LDL oxidized for 24 hours by copper ions (2.5 mumol/L) in phosphate-buffered saline and in LDL incubated with human monocyte-like THP1 cells in Ham's F-10 medium. Acetylhydrolase activity decreased as a function of the degree of LDL oxidation and was correlated with an increase in net negative charge and in the content of thiobarbituric acid-reactive substances (r = -.94 and r = -.88, respectively; P < or = .001). The acetylhydrolase of mildly oxidized LDL displayed a similar Km for PAF-acether compared with native LDL, whereas its Vmax was lower. Thus, acetylhydrolase conserved its affinity for PAF-acether, whereas a nondefined and noncompetitive inhibitor, apparently produced during oxidation, might account for the observed loss in enzymatic activity. Acetylhydrolase activity was totally recovered in LDL modified by both acetylation and malondialdehyde.(ABSTRACT TRUNCATED AT 250 WORDS)