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Biomedical subjects

P Libby

Publications and source records attributed to P Libby.

At least 91 records · Page 5Linked to original sources
PubMed1999

Angiotensin induces inflammatory activation of human vascular smooth muscle cells.

Multiple data suggest that the renin-angiotensin system contributes to the pathogenesis of atherosclerosis. The atherogenic effect of the renin-angiotensin system can only in part be explained by the influence of its effector angiotensin II on blood pressure, smooth muscle cell (SMC) growth, or antifibrinolytic activity. Because chronic inflammation of the vessel wall is a hallmark of atherosclerosis, we hypothesized that angiotensin II may elicit inflammatory signals in vascular SMCs. Human vascular SMCs were stimulated with angiotensin. Inflammatory activation was assessed by determination of interleukin-6 (IL-6) release into the culture medium, detection of IL-6 mRNA by RT-PCR, and demonstration of activation of nuclear factor-kappaB in electrophoretic mobility shift assays. Angiotensin II concentration-dependently (1 nmol/L to 1 micromol/L) stimulated IL-6 production by SMCs via activation of the angiotensin II type 1 receptor (demonstrated by the inhibitory action of the receptor antagonist losartan). Angiotensin I increased IL-6 production by SMCs, too. This effect was inhibited by captopril and ramiprilat, suggesting conversion of angiotensin I to angiotensin II by angiotensin-converting enzyme in SMCs. Steady-state mRNA for IL-6 was augmented after stimulation with angiotensin II, suggesting regulation of angiotensin-induced IL-6 release at the pretranslational level. Moreover, the proinflammatory transcription factor nuclear factor-kappaB, which is necessary for transcription of most cytokine genes, was also activated by angiotensin II. Pyrrolidine dithiocarbamate suppressed angiotensin II-induced IL-6 release, a finding compatible with involvement of reactive oxygen species as second messengers in cytokine production mediated by angiotensin. The data demonstrate the ability of angiotensin to elicit an inflammatory response in human vascular SMCs by stimulation of cytokine production and activation of nuclear factor-kappaB. Inflammatory activation of the vessel wall by a dysregulated renin-angiotensin system may contribute to the pathogenesis of atherosclerosis.

Angiotensin II↗
PubMed1999

Plasma concentrations of interleukin-6 and abdominal aortic diameter among subjects without aortic dilatation.

Previous studies suggest that cytokine-induced tissue inflammation may participate in the pathogenesis of abdominal aortic aneurysms. Serum inflammatory markers may reflect arterial inflammation in asymptomatic phases of the aneurysmal disease. We studied 120 outpatients (62 men; age, 65+/-9 years) by ultrasound evaluation of the abdominal aorta to evaluate the association of circulating levels of interleukin-6 (IL-6) with abdominal aortic diameter in subjects with normal aortic size. Aortic diameter was measured at the infrarenal level and indexed for body surface area. Seven patients with abdominal aortic dilatation (indexed aortic diameter, >1.3 cm/m2) were also identified. Plasma concentrations of IL-6, serum amyloid A (SAA), C-reactive protein (CRP), total homocysteine, and lipids were measured. Among the 113 subjects without aortic dilatation, indexed aortic diameter was positively associated with serum levels of IL-6 (P<0.01), SAA (P<0.01), and total homocysteine (P=0.01). IL-6 levels increased in a stepwise fashion among dichotomized groups of aortic size (low and high aortic diameters) and peaked in patients with aortic dilatation (2.3+/-1.2 versus 2. 7+/-0.9 versus 3.2+/-0.9 pg/mL, respectively; P for trend=0.039). None of the serum lipid measurements correlated with abdominal aortic diameter. Although CRP levels were associated with SAA levels (r=0.60; P<0.001), associations between CRP and aortic diameter were nonsignificant. In multivariate analysis, levels of IL-6 (P=0.02), SAA (P=0.001), and total homocysteine (P<0.001) were independent correlates of indexed aortic diameter. In conclusion, circulating levels of IL-6, SAA, and total homocysteine may reflect processes involved in the early phases of abdominal aortic aneurysm formation, before dilation of the abdominal aorta is established. These data support a role for chronic inflammation in the progression of asymptomatic aortic disease.

Aged↗
PubMed1999

Hyperlipidemia and atherosclerotic lesion development in LDL receptor-deficient mice fed defined semipurified diets with and without cholate.

Past studies of atherosclerosis in mice have used chow-based diets supplemented with cholesterol, lipid, and sodium cholate to overcome species resistance to lesion formation. Similar diets have been routinely used in studies with LDL receptor-deficient (LDLR(-/-)) mice. The nonphysiological nature and potential toxicity of cholate-containing diets have led to speculation that atherogenesis in these mice may not accurately reflect the human disease process. We have designed a semipurified AIN-76A-based diet that can be fed in powdered, pelleted, or liquid form and manipulated for the precise evaluation of diet-genetic interactions in murine atherosclerosis. LDLR(-/-) mice were randomly assigned among 4 diets (n=6/diet) as follows: 1, control, 10% kcal lipid; 2, high fat (40% kcal), moderate cholesterol (0.5% by weight); 3, high fat, high cholesterol (1.25% by weight); and 4, high fat, high cholesterol, and 0.5% (wt/wt) sodium cholate. Fasting serum cholesterol was increased in all cholesterol-supplemented mice compared with controls after 6 or 12 weeks of feeding (P<0.01). The total area of oil red O-stained atherosclerotic lesions was determined from digitally scanned photographs. In contrast to the control group, all mice in cholesterol-supplemented dietary groups 2 to 4 had lesions involving 7.01% to 12.79% area of the thoracic and abdominal aorta at 12 weeks (P<0.002, for each group versus control). The distribution pattern of atherosclerotic lesions was highly reproducible and comparable. The histological features of lesions in mice fed cholate-free or cholate-containing diets were similar. This study shows that sodium cholate is not necessary for the formation of atherosclerosis in LDLR(-/-) mice and that precisely defined semipurified diets are a valuable tool for the examination of diet-gene interactions.

Animal Feed↗
PubMed1999

MRI of rabbit atherosclerosis in response to dietary cholesterol lowering.

Direct imaging of the atherosclerotic plaque, rather than the angiographic lumen, may provide greater insight into the response of atherosclerosis to cholesterol-lowering therapy. Aortic plaque was studied in vivo by MRI in rabbits undergoing dietary cholesterol intervention. Thirty-one rabbits underwent aortic balloon injury and high-cholesterol diet for 4 months and then were assigned to low-cholesterol versus continued high-cholesterol diet for up to an additional 16 months. High-resolution (310 micrometer) fast spin-echo MRI of the abdominal aorta was performed at 4, 12, and 20 months and compared with histology. MRI demonstrated a significant reduction in % area stenosis in rabbits placed on low-cholesterol diet (44.6+/-2. 1% at 20 months versus 55.8+/-1.5% at 4 months, P=0.0002). In contrast, % area stenosis increased in rabbits maintained on high-cholesterol diet (69.8+/-3.8% at 20 months versus 55.8+/-1.5% at 4 months, P=0.001). Similarly, plaque thickness decreased significantly in the low-cholesterol group (0.60+/-0.05 mm at 20 months versus 0.85+/-0.06 mm at 4 months, P=0.006), with a trend toward increase in the high-cholesterol group (1.02+/-0.08 mm at 20 months versus 0.85+/-0.06 mm at 4 months, P=0.1). Thus, in rabbits undergoing dietary cholesterol lowering, MRI detected regression of aortic atherosclerotic plaque in vivo. Plaque progression was seen with maintenance of high-cholesterol diet. MRI is a promising noninvasive technology for directly imaging atherosclerosis and its response to therapeutic interventions.

Animals↗
PubMed1999

Chlamydial and human heat shock protein 60s activate human vascular endothelium, smooth muscle cells, and macrophages.

Both chlamydial and human heat shock protein 60s (HSP 60), which colocalize in human atheroma, may contribute to inflammation during atherogenesis. We tested the hypothesis that chlamydial or human HSP 60 activates human endothelial cells (ECs), smooth muscle cells (SMCs), and monocyte-derived macrophages. We examined the expression of adhesion molecules such as endothelial-leukocyte adhesion molecule-1 (E-selectin), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1), and the production of the proinflammatory cytokine interleukin-6 (IL-6). We also tested whether either HSP 60 induces nuclear factor-kappaB (NF-kappaB), which contributes to the gene expression of these molecules. Either chlamydial or human HSP 60 induced E-selectin, ICAM-1, and VCAM-1 expression on ECs similar to levels induced by Escherichia coli lipopolysaccharide (LPS). Each HSP 60 also significantly induced IL-6 production by ECs, SMCs, and macrophages to an extent similar to that induced by E. coli LPS, as assessed by enzyme-linked immunosorbent assay (ELISA). In ECs, either HSP 60 triggered activation of NF-kappaB complexes containing p65 and p50 Rel proteins. Heat treatment abolished all these effects, but did not alter the ability of E. coli LPS to induce these functions. Chlamydial and human HSP 60s therefore activate human vascular cell functions relevant to atherogenesis and lesional complications. These findings help to elucidate the mechanisms by which a chronic asymptomatic chlamydial infection might contribute to the pathophysiology of atheroma.

Cells, Cultured↗
PubMed1999

Differential expression of three T lymphocyte-activating CXC chemokines by human atheroma-associated cells.

Activated T lymphocytes accumulate early in atheroma formation and persist at sites of lesion growth and rupture, suggesting that they may play an important role in the pathogenesis of atherosclerosis. Moreover, atherosclerotic lesions contain the Th1-type cytokine IFN-gamma, a potentiator of atherosclerosis. The present study demonstrates the differential expression of the 3 IFN-gamma-inducible CXC chemokines--IFN-inducible protein 10 (IP-10), monokine induced by IFN-gamma (Mig), and IFN-inducible T-cell alpha chemoattractant (I-TAC)--by atheroma-associated cells, as well as the expression of their receptor, CXCR3, by all T lymphocytes within human atherosclerotic lesions in situ. Atheroma-associated endothelial cells (ECs), smooth muscle cells (SMCs), and macrophages (MO) all expressed IP-10, whereas Mig and I-TAC were mainly expressed in ECs and MO, as detected by double immunofluorescence staining. ECs of microvessels within lesions also expressed abundant I-TAC. In vitro experiments supported these results and showed that IL-1beta, TNF-alpha, and CD40 ligand potentiated IP-10 expression from IFN-gamma-stimulated ECs. In addition, nitric oxide (NO) treatment decreased IFN-gamma induction of IP-10. Our findings suggest that the differential expression of IP-10, Mig, and I-TAC by atheroma-associated cells plays a role in the recruitment and retention of activated T lymphocytes observed within vascular wall lesions during atherogenesis.

Animals↗
PubMed1999

Cystatin C deficiency in human atherosclerosis and aortic aneurysms.

The pathogenesis of atherosclerosis and abdominal aortic aneurysm involves breakdown of the elastic laminae. Elastolytic cysteine proteases, including cathepsins S and K, are overexpressed at sites of arterial elastin damage, but whether endogenous local inhibitors counterbalance these proteases is unknown. We show here that, whereas cystatin C is normally expressed in vascular wall smooth muscle cells (SMCs), this cysteine protease inhibitor is severely reduced in both atherosclerotic and aneurysmal aortic lesions. Furthermore, increased abdominal aortic diameter among 122 patients screened by ultrasonography correlated inversely with serum cystatin C levels. In vitro, cytokine-stimulated vascular SMCs secrete cathepsins, whose elastolytic activity could be blocked when cystatin C secretion was induced by treatment with TGF-beta(1). The findings highlight a potentially important role for imbalance between cysteine proteases and cystatin C in arterial wall remodeling and establish that cystatin C deficiency occurs in vascular disease.

Aorta↗
PubMed1998

Peroxisome proliferator-activated receptor gamma activators inhibit gene expression and migration in human vascular smooth muscle cells.

Migration of vascular smooth muscle cells (VSMCs) plays an important role in atherogenesis and restenosis after arterial interventions. The expression of matrix metalloproteinases (MMPs), particularly MMP-9, contributes to VSMC migration. This process requires degradation of basal laminae and other components of the arterial extracellular matrix. Peroxisome proliferator-activated receptors (PPARs), members of the nuclear receptor family, regulate gene expression after activation by various ligands. Recent studies have suggested opposing effects of PPAR gamma (PPARgamma) activation on atherogenesis. The present study tested the hypotheses that human VSMCs express PPAR alpha (PPARalpha) and PPARgamma and that PPAR agonists in VSMCs modulate MMP-9 expression and activity, as well as VSMC migration. Human VSMCs expressed PPARalpha and PPARgamma mRNA and protein. Treatment of VSMCs with the PPARgamma ligands troglitazone and the naturally occurring 15-deoxy-Delta12, 14-prostaglandin J2 (15d-PGJ2) decreased phorbol 12-myristate 13-acetate-induced MMP-9 mRNA and protein levels, as well as MMP-9 gelatinolytic activity in the supernatants in a concentration-dependent manner. Six different PPARalpha activators lacked such effects. Addition of prostaglandin F2alpha, known to limit PPARgamma activity, diminished the MMP-9 inhibition seen with either troglitazone or 15d-PGJ2, further implicating PPARgamma in these effects. Finally, troglitazone and 15d-PGJ2 inhibited the platelet-derived growth factor-BB-induced migration of VSMCs in vitro in a concentration-dependent manner. PPARgamma activation may regulate VSMC migration and expression and activity of MMP-9. Thus, PPARgamma activation in VSMCs, via the antidiabetic agent troglitazone or naturally occurring ligands, may act to counterbalance other potentially proatherosclerotic PPARgamma effects.

Becaplermin↗
PubMed1998

Lipid lowering promotes accumulation of mature smooth muscle cells expressing smooth muscle myosin heavy chain isoforms in rabbit atheroma.

Smooth muscle cells (SMCs) in the atherosclerotic intima characteristically differ from those in the arterial media, for example, by reduced expression of SMC differentiation/maturation markers such as smooth muscle myosin heavy chain isoforms (SM1 and SM2). This study tested the hypothesis that lipid lowering promotes maturation of intimal SMCs in 33 rabbits subjected to balloon injury and cholesterol feeding (0.3%) for 4 months (Baseline group, n=15); some of which then were switched to a low-cholesterol diet for 8 months (Low group at 8 months, n=3) or 16 months (Low group at 16 months, n=10). The remaining rabbits continued to consume a high-cholesterol diet for 16 months (High group, n=5). We monitored SMC phenotype by expression of immunoreactive alpha-smooth muscle actin, SM1, and SM2. alpha-Actin is an early marker, and SM1 and SM2 are late markers for SMC differentiation/maturation. Only fully differentiated or mature SMCs express SM2. Data are reported as the percentage of the alpha-actin-positive intimal area occupied by smooth muscle myosin-positive SMCs determined by color image analysis of immunostained sections. Levels of SM1 and SM2, highly expressed by SMCs in the normal aortic media (n=5) decreased in the aortic intima of the Baseline and High groups, indicating a less mature phenotype. In contrast, SM1 and SM2 increased in the Low (16 months) group, indicating that intimal SMCs exhibit a more mature phenotype after lipid lowering. Electron microscopy also showed the presence of mature intimal SMCs with abundant myofilaments. Furthermore, lipid lowering reduced levels of platelet-derived growth factor-B in the arterial intima, a factor known to suppress smooth muscle myosin expression. These data demonstrate that lipid lowering favors accumulation of mature SMCs in the atherosclerotic intima in association with reduced levels of platelet-derived growth factor-B expression. Intimal SMCs in the Low group also displayed reduced expression of matrix metalloproteinases-3 and -9 compared with the Baseline and High groups. These findings shed new light on the effects of lipid lowering at the level of the vascular wall, which may influence the biology of the atheroma.

Actin Cytoskeleton↗
PubMed1998

Generation of biologically active IL-1 beta by matrix metalloproteinases: a novel caspase-1-independent pathway of IL-1 beta processing.

Biologic activity of IL-1 beta requires processing of the inactive precursor, a function generally ascribed to IL-1 beta-converting enzyme (caspase-1). However, alternative mechanisms of IL-1 beta activation have been postulated in local inflammatory reactions. Expression of IL-1 beta and matrix metalloproteinases (MMPs) frequently occurs simultaneously at sites of inflammation. We describe here that stromelysin-1 (MMP-3), as well as the gelatinases A (MMP-2) and B (MMP-9), processes recombinant human IL-1 beta precursor (pIL-1 beta) into biologically active forms. Detection of both pIL-1 beta processing and biologic IL-1 beta activity demonstrated different processing capacities of the respective MMPs. Conversion of pIL-1 beta by stromelysin-1 required coincubation for at least 1 h, and biologic activity faded after 8 h to 24 h. Gelatinase A was less effective in processing pIL-1 beta, requiring at least 24 h of coincubation. In contrast, gelatinase B processed pIL-1 beta within minutes, resulting in immunoreactive products as well as biologic activity stable for 72 h. In addition, prolonged incubation of mature IL-1 beta with stromelysin-1, and to a lesser extent also with gelatinases, but not with interstitial collagenase, resulted in the degradation of mature IL-1 beta. None of the MMPs processed the second isoform of IL-1, IL-1 alpha. The present study indicates a biphasic regulation of IL-1 beta activity by MMPs: a caspase-1-independent pathway of IL-1 beta activation and inhibition of IL-1 beta activity by degrading the mature cytokine. The balance of the respective MMPs and pIL-1 beta might regulate the long term appearance of IL-1 beta activity at sites of acute or chronic inflammation.

Animals↗
PubMed1998

Expression of tissue inhibitor of metalloproteinases-3 in human atheroma and regulation in lesion-associated cells: a potential protective mechanism in plaque stability.

Atherosclerotic plaque stability depends on the structural integrity of its extracellular matrix skeleton. The balance between degradation by matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) may regulate plaque stability. Although MMP expression in atheroma is well documented, localization and control of expression of TIMPs in these lesions is incomplete. Extracts of atheroma (n= 14) had 5-fold higher levels of TIMP-3 than nonatherosclerotic tissue (n= 10). Plaques (n=24) contained abundant TIMP-1, -2, and -3 in macrophages in plaque shoulders, intimal-medial borders, and areas overlying the lipid core, as well as in medial smooth muscle cells, albeit in lesser amounts. These observations suggested that macrophages, a cell type not heretofore known to express TIMP-3, did so in atheroma in vivo. Further studies in vitro established the human macrophage as a novel source of TIMP-3 mRNA and protein. Human smooth muscle cells constitutively expressed TIMP-1, -2 and -3 proteins; platelet-derived growth factor and transforming growth factor-beta augmented levels of TIMP-1 and TIMP-3 but not TIMP-2. These findings suggest that regulated expression of TIMP-3, in addition to the presence of TIMP-1 and TIMP-2, counteracts MMP activity in atheroma and hence influences plaque stability.

Arteriosclerosis↗
PubMed1998

Expression of the elastolytic cathepsins S and K in human atheroma and regulation of their production in smooth muscle cells.

Formation of the atherosclerotic intima must involve altered metabolism of the elastin-rich arterial extracellular matrix. Proteases potentially involved in these processes remain unclear. This study examined the expression of the potent elastases cathepsins S and K in human atheroma. Normal arteries contained little or no cathepsin K or S. In contrast, macrophages in atheroma contained abundant immunoreactive cathepsins K and S. Intimal smooth muscle cells (SMC), especially cells appearing to traverse the internal elastic laminae, also contained these enzymes. Extracts of atheromatous tissues had approximately twofold greater elastase-specific activity than extracts of uninvolved arteries, mostly due to cysteine proteases. Cultured human SMC displayed no immunoreactive cathepsins K and S and exhibited little or no elastolytic activity when incubated with insoluble elastin. SMC stimulated with the atheroma-associated cytokines IL-1beta or IFN-gamma secreted active cathepsin S and degraded substantial insoluble elastin (15-20 microg/10(6) cells/24 h). A selective inhibitor of cathepsin S blocked > 80% of this elastolytic activity. The presence of cathepsins K and S at sites of vascular matrix remodeling and the ability of SMC and macrophages to use these enzymes to degrade elastin supports a role for elastolytic cathepsins in vessel wall remodeling and identifies novel therapeutic targets in regulating plaque stability.

Arteriosclerosis↗
PubMed1998

Chlamydial heat shock protein 60 localizes in human atheroma and regulates macrophage tumor necrosis factor-alpha and matrix metalloproteinase expression.

BACKGROUND: Recent evidence has implicated Chlamydia pneumoniae in the aggravation of atherosclerosis. However, the mechanisms by which this agent affects atherogenesis remain poorly understood. Chlamydiae produce large amounts of heat shock protein 60 (HSP 60) during chronic, persistent infections, and C pneumoniae localizes predominantly within plaque macrophages. Several studies have furnished evidence that endogenous (human) HSP 60 may play a role in atherogenesis. We tested here the hypothesis that atheroma contains chlamydial HSP 60 and that this bacterial product might stimulate macrophage functions considered relevant to atherosclerosis and its complications, such as production of proinflammatory cytokines as tissue necrosis factor-alpha (TNF-alpha) and matrix-degrading metalloproteinases (MMPs). METHODS AND RESULTS: Surgical specimens of human carotid atherosclerotic arteries (n = 19) and normal arterial wall samples (n=7, 2 carotid arteries and 5 aortas) were tested immunohistochemically for the presence of chlamydial HSP 60 and human HSP 60. Macrophage localization of these antigens was assessed by double immunostaining. Murine peritoneal macrophages, maintained in serum-free conditions for 48 hours after harvesting, were incubated with C pneumoniae, chlamydial HSP 60, human HSP 60, or Escherichia coli lipopolysaccharide (LPS). Culture supernatants, collected at 24 hours for concentration-dependence experiments and at up to 72 hours for time-dependence experiments, were analyzed for TNF-alpha by ELISA and for MMP by gelatin zymography. Atherosclerotic lesions showed immunoreactive chlamydial HSP 60 in 47% (9 of 19) of the cases and human HSP 60 in 89% (17 of 19) of the cases. Chlamydial HSP 60 colocalized with human HSP 60 within plaque macrophages in 77% (7 of 9) of the cases. Nonatherosclerotic samples contained neither HSP. Both C pneumoniae and recombinant chlamydial HSP 60 induced TNF-alpha production by mouse macrophages in a concentration- and time-dependent fashion. E coli LPS and human HSP 60 produced similar effects. Similarly, C pneumoniae and HSPs induced MMPs in a concentration- and time-dependent manner. Heat treatment abolished the effect of C pneumoniae and HSPs on both TNF-alpha and MMP production, but it did not alter the ability of E coli LPS to induce these functions. CONCLUSIONS: Chlamydial HSP 60 frequently colocalizes with human HSP 60 in plaque macrophages in human atherosclerotic lesions. Chlamydial and human HSP 60 induce TNF-alpha and MMP production by macrophages. Chlamydial HSP 60 might mediate the induction of these effects by C pneumoniae. Induction of such macrophage functions provides potential mechanisms by which chlamydial infections may promote atherogenesis and precipitate acute ischemic events.

Animals↗
PubMed1998

Reduction of atherosclerosis in mice by inhibition of CD40 signalling.

Increasing amounts of evidence support the involvement of inflammation and immunity in atherogenesis, but mediators of communication between the major cell types in atherosclerotic plaques are poorly defined. Cells in human atherosclerotic lesions express the immune mediator CD40 and its ligand CD40L (also known as CD154 or gp39). The interaction of CD40 with CD40L figures prominently in both humoral and cell-mediated immune responses. CD40L-positive T cells accumulate in atheroma, and, by virtue of their early appearance, persistence and localization at sites of lesion growth and complication, activated T cells may coordinate important aspects of atherogenesis. Interruption of CD40L-CD40 signalling by administration of an anti-CD40L antibody limits experimental autoimmune diseases such as collagen-induced arthritis, lupus nephritis, acute or chronic graft-versus-host disease, multiple sclerosis and thyroiditis. Ligation of CD40 on atheroma-associated cells in vitro activates functions related to atherogenesis, including induction of proinflammatory cytokines, matrix metalloproteinases, adhesion molecules and tissue factor. However, the role of CD40 signalling in atherogenesis in vivo remains unknown. Here we determine whether interruption of CD40 signalling influences atherogenesis in vivo in hyperlipidaemic mice. Treatment with antibody against mouse CD40L limited atherosclerosis in mice lacking the receptor for low-density lipoprotein that had been fed a high-cholesterol diet for 12 weeks. This antibody reduces the size of aortic atherosclerotic lesions by 59% and their lipid content by 79%. Furthermore, atheroma of mice treated with anti-CD40L antibody contained significantly fewer macrophages (64%) and T lymphocytes (70%), and exhibited decreased expression of vascular cell adhesion molecule-1. These data support the involvement of inflammatory pathways in atherosclerosis and indicate a role for CD40 signalling during atherogenesis in hyperlipidaemic mice.

Animals↗
PubMed1998

Lipid lowering by diet reduces matrix metalloproteinase activity and increases collagen content of rabbit atheroma: a potential mechanism of lesion stabilization.

BACKGROUND: Proteolytic enzyme activity in lipid-rich atheroma may promote plaque rupture and precipitate acute coronary syndromes. This study tested the hypothesis that lipid lowering stabilizes plaques by reducing proteolytic activity. METHODS AND RESULTS: We produced experimental atheroma in 33 rabbits by balloon injury and an atherogenic diet (0.3% cholesterol and 4.7% coconut oil) for 4 months. At that time, 15 rabbits were killed (baseline group). The remaining animals were divided into two groups: a hyperlipemic group continued to consume a cholesterol-enriched diet (0.05% to 0.2%) for 16 more months (n=5) and a lipid-lowering group consumed a purified chow diet with no added cholesterol or fat for 8 (n=3) or 16 months (n=10). Macrophage accumulation and interstitial collagenase (matrix metalloproteinase-1, MMP-1) expression in the lesion were measured by quantitative image analysis of standardized sections of immunostained aortas. Baseline lesions expressed high levels of MMP-1 and contained many macrophages. These features of plaque instability persisted in the hyperlipemic group. However, the lipid-lowering group showed progressive reduction in both macrophage content and MMP- 1 immunoreactivity with time. Aortic rings of the baseline and hyperlipemic groups elaborated gelatinolytic, caseinolytic, and elastinolytic activity attributable to MMP-2, MMP-3, or MMP-9, monitored by SDS-PAGE zymography. Proteolytic activity decreased markedly in the lipid-lowering group. Aortic content of interstitial collagen, determined by sirius red staining, increased in the lipid-lowering group compared with the baseline or continued hyperlipemic groups, indicating that lipid lowering reinforced the fibrous skeleton of the atheroma. CONCLUSIONS: These results establish a mechanism by which lipid lowering may stabilize vulnerable plaques by reduced expression and activity of enzymes that degrade the arterial extracellular matrix and render atheroma less susceptible to disruption and thrombosis by favoring collagen accumulation in the fibrous cap.

Animals↗
PubMed1998

Heterozygous osteopetrotic (op) mutation reduces atherosclerosis in LDL receptor- deficient mice.

Previous studies of osteopetrotic (op) mice lacking macrophage colony-stimulating factor (M-CSF) have revealed an inhibition of atherosclerosis development in the apolipoprotein E (apo E)-deficient model and in a diet-induced model. Using LDL receptor-deficient mice, we now show that atheroma development depends on M-CSF concentration, as not only did homozygous osteopetrotic (op/op) mice have dramatically reduced lesions (approximately 0.3% of control lesion size) but heterozygous (op/+) mice had lesions < 1% of controls. Mice heterozygous for the op mutation (op/+) had plasma levels of M-CSF about half those in controls (+/+). The finding that an approximately 2-fold reduction in M-CSF expression reduced lesion size approximately 100-fold suggests the requirement for a threshold level of M-CSF. The effect of M-CSF on atherosclerosis did not appear to be mediated either by changes in plasma lipoprotein levels or alterations in the number of circulating monocytes, since both op/op and op/+ mice exhibited higher levels of atherogenic lipoprotein particles and (op/+) mice showed a near normal number of circulating monocytes. LDL receptor-null littermates of genotypes from op/op, op/+, to +/+ showed monocyte differentials of approximately 4.5, 8, and 10%, respectively. Taken together, these results suggest that the effects of M-CSF on atherogenesis may not be mediated by expression of M-CSF systemically or by modulation of the number of circulating monocytes. These studies support the conclusion that M-CSF participates critically in fatty streak formation and progression to a complex fibrous lesion.

Animals↗