Immunological mechanisms in atherosclerosis

Immunotherapy for the Prevention of Myointimal Hyperplasia After Experimental Balloon Injury of the Rat Carotid Artery

We assessed the effect of novel immunotherapeutic heat-killed bacterial (Actinomycetales) preparations on the development of myointimal hyperplasia (MIH) in a rat carotid balloon trauma model and the effect on the immune response by measuring the expression of interferon γ (IFN-γ; (Th1) and interleukin 4 (IL-4; Th2). There was a significant reduction (P < .001) in intima/media ratios (mean ± SEM) in the rats treated by immunomodulation (0.52 ± 0.03 Gordonia bronchialis, 0.60 ± 0.03 Rhodococcus coprophilus, 0.43 ± 0.03 Tsukamurella inchonensis, 0.37 ± 0.03 Mycobacterium vaccae), in comparison with untreated controls (0.91 ± 0.05). Postballoon trauma G bronchialis increased messenger RNA (mRNA) IFN-γ (P < .02) and reduced mRNA IL-4 (P < .05). R coprophilus, T inchonensis, and M vaccae significantly increased production of mRNA IFN-γ (P < .001). R coprophilus and M vaccae also decreased production of mRNA IL-4 (P < .05, P < .01). Treatment with heat-killed Actinomycetales inhibits MIH through a combination of enhanced Th1 and attenuated Th2 response. Immunomodulation may provide a novel therapeutic option to prevent restenosis.

Lysophosphatidic acid-3 receptor-mediated feed-forward production of lysophosphatidic acid: an initiator of nerve injury-induced neuropathic pain

BACKGROUND

We previously reported that intrathecal injection of lysophosphatidylcholine (LPC) induced neuropathic pain through activation of the lysophosphatidic acid (LPA)-1 receptor, possibly via conversion to LPA by autotaxin (ATX).

RESULTS

We examined in vivo LPA-induced LPA production using a biological titration assay with B103 cells expressing LPA1 receptors. Intrathecal administration of LPC caused time-related production of LPA in the spinal dorsal horn and dorsal roots, but not in the dorsal root ganglion, spinal nerve or sciatic nerve. LPC-induced LPA production was markedly diminished in ATX heterozygotes, and was abolished in mice that were deficient in LPA3, but not LPA1 or LPA2 receptors. Similar time-related and LPA3 receptor-mediated production of LPA was observed following intrathecal administration of LPA. In an in vitro study using spinal cord slices, LPA-induced LPA production was also mediated by ATX and the LPA3 receptor. Intrathecal administration of LPA, in contrast, induced neuropathic pain, which was abolished in mice deficient in LPA1 or LPA3 receptors.

CONCLUSION

These findings suggest that feed-forward LPA production is involved in LPA-induced neuropathic pain.

Quantum dot mediated imaging of atherosclerosis

The progression of atherosclerosis is associated with leukocyte infiltration within lesions. We describe a technique for the ex vivo imaging of cellular recruitment in atherogenesis which utilizes quantum dots (QD) to color-code different cell types within lesion areas. Spectrally distinct QD were coated with the cell-penetrating peptide maurocalcine to fluorescently-label immunomagnetically isolated monocyte/macrophages and T lymphocytes. QD-maurocalcine bioconjugates labeled both cell types with a high efficiency, preserved cell viability, and did not perturb native leukocyte function in cytokine release and endothelial adhesion assays. QD-labeled monocyte/macrophages and T lymphocytes were reinfused in an ApoE(-/-) mouse model of atherosclerosis and age-matched controls and tracked for up to four weeks to investigate the incorporation of cells within aortic lesion areas, as determined by oil red O (ORO) and immunofluorescence ex vivo staining. QD-labeled cells were visible in atherosclerotic plaques within two days of injection, and the two cell types colocalized within areas of subsequent ORO staining. Our method for tracking leukocytes in lesions enables high signal-to-noise ratio imaging of multiple cell types and biomarkers simultaneously within the same specimen. It also has great utility in studies aimed at investigating the role of distinct circulating leukocyte subsets in plaque development and progression.

Autotaxin, a synthetic enzyme of lysophosphatidic acid (LPA), mediates the induction of nerve-injured neuropathic pain

Recently, we reported that lysophosphatidic acid (LPA) induces long-lasting mechanical allodynia and thermal hyperalgesia as well as demyelination and upregulation of pain-related proteins through one of its cognate receptors, LPA₁. In addition, mice lacking the LPA₁ receptor gene (lpa₁^-/- mice) lost these nerve injury-induced neuropathic pain behaviors and phenomena. However, since lpa₁^-/- mice did not exhibit any effects on the basal nociceptive threshold, it is possible that nerve injury-induced neuropathic pain and its machineries are initiated by LPA via defined biosynthetic pathways that involve multiple enzymes. Here, we attempted to clarify the involvement of a single synthetic enzyme of LPA known as autotaxin (ATX) in nerve injury-induced neuropathic pain. Wild-type mice with partial sciatic nerve injury showed robust mechanical allodynia starting from day 3 after the nerve injury and persisting for at least 14 days, along with thermal hyperalgesia. On the other hand, heterozygous mutant mice for the autotaxin gene (atx^+/-), which have 50% ATX protein and 50% lysophospholipase D activity compared with wild-type mice, showed approximately 50% recovery of nerve injury-induced neuropathic pain. In addition, hypersensitization of myelinated Aβ˜- or Aδ-fiber function following nerve injury was observed in electrical stimuli-induced paw withdrawal tests using a Neurometer^®. The hyperalgesia was completely abolished in lpa₁^-/- mice, and reduced by 50% in atx^+/- mice. Taken together, these findings suggest that LPA biosynthesis through ATX is the source of LPA for LPA₁ receptor-mediated neuropathic pain. Therefore, targeted inhibition of ATX-mediated LPA biosynthesis as well as LPA₁ receptor and its downstream pathways may represent a novel way to prevent nerve injury-induced neuropathic pain.

Lysophosphatidylcholine induces neuropathic pain through an action of autotaxin to generate lysophosphatidic acid

Lysophosphatidic acid receptor (LPA(1)) signaling initiates neuropathic pain and several pathological events in a partial sciatic nerve injury model. Recently, we reported that lysophosphatidic acid (LPA) induces neuropathic pain as well as demyelination and pain-related protein expression changes via LPA(1) receptor signaling. Lysophosphatidylcholine (LPC), also known as lysolecithin, which is hydrolyzed by autotaxin/ATX into LPA, induces similar plastic changes. Here, we attempted to clarify whether ATX and LPA(1) receptor signaling is involved in the LPC-induced neuropathic pain. In wild-type mice, a single intrathecal (i.t.) injection of LPC induced mechanical allodynia and thermal hyperalgesia 2 days after injection; this persisted for 7 days at least. On the other hand, LPC-induced mechanical allodynia and thermal hyperalgesia were completely abolished in mice lacking an LPA(1) receptor gene. Furthermore, the LPC-induced response was also significantly, but partially reduced in heterozygous mutant mice for the ATX gene. These findings suggest that intrathecally-injected LPC is converted to LPA by ATX, and this LPA activates the LPA(1) receptor to initiate neuropathic pain.

The dysregulated adipose tissue: a connecting link between insulin resistance, type 2 diabetes mellitus and atherosclerosis

An emerging paradigm supports the view that adipose tissue (AT) dysregulation might play a crucial role in the pathogenesis of insulin-resistance and atherosclerosis. The net result of such a dysregulation is a state of low-grade, chronic, systemic inflammation that, in turn, links both the metabolic and the vascular pathologies. Overwhelming evidence shows that high circulating levels of markers of chronic inflammation predict the development of T2DM and atherosclerotic manifestations. Therefore, atherosclerotic cardiovascular disease and T2DM seem to arise from a "common soil", and chronic inflammation is a candidate. In this scenario, the dysfunctional AT provide a common hallmark for these apparently divergent disorders. An important question then is whether dysregulated and inflamed AT can be converted to healthy fat and, consequently, the development or the progression of metabolic and vascular impairment can be prevented or reversed by the modulation of the inflammatory profile. The beneficial effects of weight loss on obesity-related complications are clearly associated with the modification of the inflammatory profile in the AT. Furthermore, the thiazolidinediones (TZDs) possess both anti-inflammatory and anti-atherogenic properties. Intriguingly, in contrast to the paradoxical weight gain, TZDs influence favorably the pattern of adipokines. In conclusion, accepting the paradigm of AT dysfunction, the use of TZDs will represent an additional therapeutic approach that, in association with lifestyle interventions, would improve inflammation, ameliorate insulin sensitivity, and alleviate the related risk of atherosclerosis.

The antiatherogenic potential of oat phenolic compounds

Avenanthramides are phenolic antioxidants, which are present in oats. Avenanthramides A, B, and C are the major constituents of the total soluble antioxidant phenolic compounds in oats. We tested the potential antiatherogenic activity of partially purified avenanthramides from oats by examining their effects on adhesion of monocytes to human aortic endothelial cell (HAEC) monolayers, expression of adhesion molecules, and production of proinflammatory cytokines and chemokines by HAEC. The oat avenanthramides mixture was prepared and partially purified by column chromatography. This avenanthramide-enriched mixture (AEM) had no toxicity to HAEC as tested up to 40 ng/ml. The pre-incubation of HAEC with 4, 20, and 40ng/ml AEM for 24h significantly decreased adhesion of U937 monocytic cells to interleukin (IL)-1beta-stimulated HAEC in a concentration-dependent manner. Pre-incubation of HAEC with AEM at 20 and 40 microg/ml, but not at 4 microg/ml, for 24h significantly suppressed IL-1beta-stimulated expressions of intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin and the secretion of proinflammatory cytokines IL-6, chemokines IL-8 and monocyte chemoattractant protein (MCP)-1. These data provide evidence for the potential anti-inflammatory and antiatherogenic effects of antioxidant avenanthramides present in oats.

GM-CSF activates RhoA, integrin and MMP expression in human monocytic cells

Monocyte migration is one of the key events occurring in the early stage of atherosclerosis. This process includes monocytic adhesion to and penetration through the arterial intima. In such an environment, many factors stimulate the monocytes to enhance integrin activation and extracellular matrix degradation. To investigate the coordinative operation of these two events in relation to monocyte migration, we paid particular attention to the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on monocytes in terms of RhoA activation and matrix metalloproteinase (MMP) expression. RhoA and integrin clustering were activated by GM-CSF, monocyte chemoattractant protein-1 (MCP-1) and platelet-derived growth factor-BB (PDGF-BB) in human monocytic cell lines. Furthermore, enhancement of migration was observed with stimulation by MCP-1 and PDGF-BB. Granulocyte-macrophage colony-stimulating factor did not enhance the migration, even though it activated RhoA and integrin. However, GM-CSF is known to stimulate monocytes to express MCP-1, suggesting the presence of an indirect mechanism for GM-CSF-mediated migratory activity. In contrast, only GM-CSF enhanced the expression of MMP-1 and MMP-9. These results provide evidence that GM-CSF has multiple functions enhancing monocytic migration via RhoA and integrin activation, and via MMP expression.

Platelet phagocytosis and processing of beta-amyloid precursor protein as a mechanism of macrophage activation in atherosclerosis

In human occluded saphenous vein grafts, we previously demonstrated cytotoxic foam cells, presumably derived from macrophages engulfing platelets. In the present study, we investigated whether platelet phagocytosis occurs in human atherosclerotic plaques, whether this activates macrophages, and whether the platelet constituent, amyloid precursor protein (APP), was involved. Immunohistochemistry documented the presence of APP, beta-amyloid peptide (Abeta, cleaved from APP), and platelets (CD9), along with inducible NO synthase (iNOS) and cyclooxygenase-2, two markers of macrophage activation, around microvessels in advanced human carotid artery plaques (n=18). Abeta colocalized with iNOS-expressing macrophages that were often surrounded by platelets. In vitro, murine J774 and human THP-1 macrophages were incubated with or without washed human platelets. Coincubation of macrophages and platelets led to platelet phagocytosis (electron and confocal microscopy) and formation of lipid-, APP-, and Abeta-containing foam cells. These expressed iNOS mRNA (reverse transcription-polymerase chain reaction) and protein and produced nitrite and tumor necrosis factor-alpha (ELISA). Macrophage pretreatment with 4-(2-aminoethyl)benzenesulfonyl fluoride, a protease inhibitor, reduced APP processing and inhibited NO biosynthesis induced by platelet phagocytosis but not by lipopolysaccharides. Human atherosclerotic plaques and J774 and THP-1 macrophages contained mRNA of the APP-cleaving enzyme beta-secretase. This is the first demonstration of Abeta, a peptide extensively studied in Alzheimer's disease, in human atherosclerotic plaques. It was present in activated iNOS-expressing perivascular macrophages that had phagocytized platelets. In vitro studies indicate that platelet phagocytosis leads to macrophage activation and suggest that platelet-derived APP is proteolytically processed to Abeta, resulting in iNOS induction. This represents a novel mechanism for macrophage activation in atherosclerosis.

Humoral markers of inflammation and endothelial dysfunction in relation to adiposity and in vivo insulin action in Pima Indians

Several studies have shown that humoral markers of inflammation and endothelial dysfunction are predictive of macrovascular events, and correlated with indirect measures of adiposity and insulin action, thus providing a possible link between obesity, insulin resistance and atherosclerosis. We examined the relationship between humoral markers of inflammation and endothelial dysfunction and direct measures of adiposity and insulin action in Pima Indians, a population with a very high prevalence of obesity and insulin resistance, but a relatively low propensity for atherosclerotic disease. Fasting plasma concentrations of the inflammatory markers C-reactive protein (CRP), secretory phospholipase A2 (sPLA2) and soluble intercellular adhesion molecule-1 (sICAM-1) and of the endothelial markers E-selectin and von Willebrand factor (vWF) were measured in 32 non-diabetic Pima Indians (18 M/14 F, age 27+/-1 years) in whom percent body fat and insulin-stimulated glucose disposal (M) were assessed by DEXA and a hyperinsulinemic clamp, respectively. CRP, sPLA2, and sICAM-1 were all positively correlated with percent body fat (r=0.71, 0.57, and 0.51, all P<0.01). E-selectin and vWF were not correlated with percent body fat, but were negatively correlated with M (r= -0.65 and -0.46, both P<0.001) and positively correlated with CRP (r=0.46, and 0.33, both P<0.05). These findings indicate that humoral markers of inflammation increase with increasing adiposity in Pima Indians whereas humoral markers of endothelial dysfunction increase primarily in proportion to the degree of insulin resistance and inflammation. Thus, obesity and insulin resistance appear to be associated with low-grade inflammation and endothelial dysfunction, respectively, even in an obesity- and diabetes-prone population with relatively low propensity for atherosclerosis.

Prevention of experimental myointimal hyperplasia by immunomodulation

INTRODUCTION

we have tested the hypothesis that treatment with a mycobacterial preparation that modulates the antibody response, would diminish restenosis in a rat angioplasty model.

MATERIALS/METHODS

male Sprague-Dawley rats were used. All immunisations were given subcutaneously. Group A (control) received normal saline on days 0, 21, and 42. Group B received SRL172 on days 0, 21, and 42. Group C received SRL172 on days 0, 21, and 42, and hsp65/Incomplete Freund's on days 21 and 42. Group D received hsp65/Freund's on days 21 and 42. Right common carotid arteries were balloon-injured on day 63 using a standard technique known to produce MIH and animals were sacrificed on day 77. For each carotid 6 microm cross sections were cut from paraffin blocks. Cross-sectional areas were measured by computerised planimetry.

RESULTS

balloon injury resulted in MIH in all animals. Data represents mean+/-SEM for the percentage of area enclosed within the internal elastic lamina occupied by MIH (% MIH); which for groups A, B, C, and D was 85+/-11, 24+/-3, 27+/-7, and 17+/-3 respectively. All the treatment groups had significantly less MIH when compared to the control group but no statistically significant difference was found between any of the treatment groups.

CONCLUSIONS

this is the first report that immunomodulation with mycobacterial material suitable for use in man, can reduce MIH. Since such modulation has low risk, this raises the prospect of an important new therapeutic modality to combat restenosis.

Sphingosylphosphorylcholine and lysophosphatidylcholine are ligands for the G protein-coupled receptor GPR4

Sphingosylphosphorylcholine (SPC) and lysophosphatidylcholine (LPC) are bioactive lipid molecules involved in numerous biological processes. We have recently identified ovarian cancer G protein-coupled receptor 1 (OGR1) as a specific and high affinity receptor for SPC, and G2A as a receptor with high affinity for LPC, but low affinity for SPC. Among G protein-coupled receptors, GPR4 shares highest sequence homology with OGR1 (51%). In this work, we have identified GPR4 as not only another high affinity receptor for SPC, but also a receptor for LPC, albeit of lower affinity. Both SPC and LPC induce increases in intracellular calcium concentration in GPR4-, but not vector-transfected MCF10A cells. These effects are insensitive to treatment with BN52021, WEB-2170, and WEB-2086 (specific platelet activating factor (PAF) receptor antagonists), suggesting that they are not mediated through an endogenous PAF receptor. SPC and LPC bind to GPR4 in GPR4-transfected CHO cells with K(d)/SPC = 36 nm, and K(d)/LPC = 159 nm, respectively. Competitive binding is elicited only by SPC and LPC. Both SPC and LPC activate GPR4-dependent activation of serum response element reporter and receptor internalization. Swiss 3T3 cells expressing GPR4 respond to both SPC and LPC, but not sphingosine 1-phosphate (S1P), PAF, psychosine (Psy), glucosyl-beta1'1-sphingosine (Glu-Sph), galactosyl-beta1'1-ceramide (Gal-Cer), or lactosyl-beta1'1-ceramide (Lac-Cer) to activate extracellular signal-regulated kinase mitogen-activated protein kinase in a concentration- and time-dependent manner. SPC and LPC stimulate DNA synthesis in GPR4-expressing Swiss 3T3 cells. Both extracellular signal-regulated kinase activation and DNA synthesis stimulated by SPC and LPC are pertussis toxin-sensitive, suggesting the involvement of a G(i)-heterotrimeric G protein. In addition, GPR4 expression confers chemotactic responses to both SPC and LPC in Swiss 3T3 cells. Taken together, our data indicate that GPR4 is a receptor with high affinity to SPC and low affinity to LPC, and that multiple cellular functions can be transduced via this receptor.

Neuro-immune-endocrine functional system and vascular pathology

A new interpretation of the response to injury by the nervous, immune and endocrine system is proposed, in order to integrate biochemical knowledge into the respective clinical areas. The discovery that the signaling molecules of the classical nervous, immune and endocrine systems, that is, the neurotransmitters, cytokines and hormones, respectively, are expressed and perceived by the three systems, has enabled us to establish a functional concept of these systems. The hypothetical integration of different pathological processes in a functional response made up by three phases, the immediate or nervous, intermediate or immune and late or endocrine ones, makes it possible to consider that all of them represent different forms of expression of a functional response whose meaning is always the same, that is, inflammation. If the functions that characterize each one of these three phases represent the activity of the nervous, immune and endocrine systems, the biochemical knowledge could be integrated into the functional meaning of each system.

Influence of plasma fibrinogen levels on the incidence of myocardial infarction and death is modified by other inflammation-sensitive proteins: a long-term cohort study

Inflammation may play an important role in atherosclerotic disease. Plasma fibrinogen is an established predictor of cardiovascular events. The aim of this study was to evaluate whether other inflammation-sensitive plasma proteins modify this prediction. We studied the incidence of cardiac events and death in men in relation to fibrinogen levels alone and in combination with other proteins. The study was based on 6075 men, who were, on average, 46 years old at the time of the screening examination, which included the quantitative assessment of plasma levels of fibrinogen, orosomucoid, alpha(1)-antitrypsin, haptoglobin, and ceruloplasmin. The concentration of each protein was divided into quartiles for each. This classification made it possible to identify 4 groups, ie, men in the first fibrinogen quartile and at the same time either not belonging to the fourth quartile of any of the other proteins (Q1/No group) or also belonging to the fourth quartile of >/=1 of the additional proteins (Q1/Yes group) and corresponding groups in the fourth fibrinogen quartile (Q4/No and Q4/Yes groups). During the follow-up, which occurred at an average of 16 years, 439 (7.2%) men experienced a cardiac event, and 653 (10.7%) died; 278 of these men died of cardiovascular diseases, with 206 deaths attributed to ischemic heart disease. From the lowest to the highest quartile, there was for each protein a stepwise increase in the incidence of cardiac events and mortality. All-cause mortality and cardiovascular mortality were significantly higher in the Q4/Yes group compared with the Q4/No group, but they were similar in the Q4/No and Q1/Yes groups. The incidence of cardiac events was significantly higher in the Q1/Yes and Q4/Yes groups compared with the Q1/No and Q4/No groups, respectively. The increased cardiovascular mortality and cardiac event rates remained after adjustment for several confounders when the Q4/Yes and Q4/No groups were compared. The results suggest that the incidence of cardiac events and death due to cardiovascular diseases in middle-aged men predicted by plasma levels of fibrinogen is modified by other inflammation-sensitive proteins.

Beneficial effects of fluvastatin on myocardial blood flow at two time-points in hypercholesterolemic patients with coronary artery disease

Hypercholesterolemia is a major risk factor initiating and accelerating atherosclerosis and leading to severe stages of coronary artery disease (CAD) with a high risk of cardiovascular events. We investigated the impact of lipid lowering in patients with hypercholesterolemia and evident CAD on clinically relevant parameters like myocardial perfusion. Myocardial imaging was performed with thallium-201 single photon-emission computed tomography at rest and after maximal bicycle exercise in 22 patients after a 4-week lead-in period, and after 12 and 24 weeks of therapy with fluvastatin. Perfusion defects occurred in all patients, indicating stress-induced myocardial ischemia. After 12 weeks of therapy, the perfusion of the ischemic segments increased by 26% (277+/-99 to 349+/-96 cpm; p < 0.001), whereas the value of the normal segments was augmented only by 4% (478+/-44 to 497+/-28 cpm; p < 0.05). The results slightly improved further after 24 weeks. Moreover, a subgroup analysis elucidated a more pronounced effect in patients without lipid-lowering premedication. This nonpretreated group (n = 11) revealed an improvement of ischemic segments at stress by 42% at week 24. In contrast, pretreated patients had an increase of only 18% (between groups, p < 0.05), indicating a carryover effect of premedication. In conclusion, short-term therapy with fluvastatin acts beneficially on impaired vascular function in hypercholesterolemic patients with CAD.

Inflammation, insulin resistance, infection, diabetes, and atherosclerosis

OBJECTIVE

To review the relationship between poor control of blood glucose in patients with diabetes and potential for occurrence of the acute coronary syndrome.

METHODS

The role of advanced glycosylated end products in endothelial dysfunction is discussed, and the possible contributions of inflammation and infection in the rupture of atheromatous plaques are described.

RESULTS

Hyperglycemia predisposes to infection by decreasing the efficacy of leukocytes and allowing increased formation of advanced glycosylated end products. The associated endothelial permeability facilitates bacterial infiltration of atheromatous plaques. Reported associations between chronic infection and coronary artery disease have involved primarily Chlamydia pneumoniae. The insulin resistance syndrome is also characterized by compromised endothelial function, which may predispose patients to unstable plaques and cardiac events.

CONCLUSION

In patients with diabetes, poor glycemic control may lead to excessive advanced glycosylated end products, inflammation and infection of atheromatous plaques, and plaque rupture that can cause angina or myocardial infarction.

Effect of vitamin E on human aortic endothelial cell production of chemokines and adhesion to monocytes

Epidemiological and clinical studies indicate that vitamin E may reduce the risk of cardiovascular disease (CVD). Modulation of adhesion molecule expression and chemokine production by vitamin E may contribute to its beneficial effect. In this study we found that the enrichment of confluent human aortic endothelial cells (HAEC) or U937 monocytic cells with increasing doses of vitamin E (d-alpha-tocopherol, 20, 40, and 60 micromol/l for 20 h) inhibited their adhesion when either or both cell types were stimulated with interleukin (IL)-1beta. Enrichment of HAEC with the same doses of vitamin E suppressed IL-1beta-stimulated expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and endothelial leukocyte adhesion molecule-1 (E-selectin). Supplementation with increasing doses of vitamin E up to 60 micromol/l was not effective in preventing spontaneous production of monocyte chemoattractant protein-1 (MCP-1), but supplementation with vitamin E at 60 micromol/l reduced IL-8 production significantly. However, IL-1beta-induced productions of both MCP-1 and IL-8 were dose-dependently suppressed by enrichment of cells with vitamin E. Vitamin E, at the doses used, did not significantly change the spontaneous production but dose-dependently inhibited the IL-1beta-induced production of inflammatory cytokine IL-6. We concluded that vitamin E could inhibit production of chemokines and inflammatory cytokines, in addition to inhibiting adhesion of HAEC to monocytes by reducing expression of adhesion molecules when cells were activated with an inflammatory cytokine. These mediators are actively involved in the pathogenesis of atherosclerosis. Therefore, their inhibition by vitamin E may contribute to vitamin E's reported reduction in risk of CVD.

Chemokines and atherosclerosis

Chemokines or chemotactic cytokines represent an expanding family of structurally related small molecular weight proteins, recognised as being responsible for leukocyte trafficking and activation. Soon after the discovery of this class of cytokines, about a decade ago, monocyte chemoattractant protein-1 (MCP-1) was found to be highly expressed in human atherosclerotic lesions and postulated to be central in monocyte recruitment into the arterial wall and developing lesions. In this review, we will discuss our present knowledge about MCP-1 and its receptor CCR2 and their role in atherogenesis. Although less well established, other chemokines such as RANTES, MIP-1alpha and MIP-1beta have also been implicated in atherosclerotic lesion formation as are a number of more recently discovered chemokines like MCP-4, ELC and PARC. The role of these chemokines in the progression of atherosclerosis will be discussed as well as the emerging role of IL-8, mostly know for its effects on neutrophils. Particular attention will be given not only to the involvement of chemokines in the inflammatory recruitment of monocytes/macrophages, but also to their role in the related local immune responses and vascular remodelling which occur during the formation of unstable atherosclerotic plaques.

Expression and cellular localization of the CC chemokines PARC and ELC in human atherosclerotic plaques

Local immune responses are thought to play an important role in the development of atherosclerosis. Histological studies have shown that human atherosclerotic lesions contain T lymphocytes throughout all stages of development, many of which are in an activated state. A number of novel CC chemokines have been described recently, which are potent chemoattractants for lymphocytes: PARC (pulmonary and activation-regulated chemokine), ELC (EBI1-ligand chemokine), LARC (liver and activation-regulated chemokine), and SLC (secondary lymphoid-tissue chemokine). Using reverse transcriptase-polymerase chain reaction and in situ hybridization, we have found gene expression for PARC and ELC but not for LARC or SLC in human atherosclerotic plaques. Immunohistochemical staining of serial plaque sections with specific cell markers revealed highly different expression patterns of PARC and ELC. PARC mRNA was restricted to CD68+ macrophages (n = 14 of 18), whereas ELC mRNA was widely expressed by macrophages and intimal smooth muscle cells (SMC) in nearly all of the lesions examined (n = 12 of 14). ELC mRNA was also found to be expressed in the medial SMC wall of highly calcified plaques (n = 4). Very low levels of ELC mRNA expression could also be detected in normal mammary arteries but no mRNA expression for PARC was detected in these vessels (n = 4). In vitro, ELC mRNA was found to be up-regulated in aortic SMC stimulated with tumor necrosis factor-a and interferon-gamma but not in SMC stimulated with serum. Both PARC and ELC mRNA were expressed by monocyte-derived macrophages but not monocytes. The expression patterns of PARC and ELC mRNA in human atherosclerotic lesions suggest a potential role for these two recently described CC chemokines in attracting T lymphocytes into atherosclerotic lesions.

Expression of low-density lipoprotein receptors in peripheral blood and tonsil B lymphocytes

B lymphocytes, purified from peripheral leucocytes from young normolipaemic humans, expressed and internalized low-density lipoprotein receptors (LDLR). The expression was assessed by a monoclonal anti-LDLR. The internalization of LDL was assessed by LDL labelled with 125I (125I-LDL) and 1,1'-dioctadecyl-3,3,3',3' tetramethyl-indocarboxycyanine perchlorate (LDL-DiI). The expression of LDLR, assessed by anti-LDLR, was: 38 +/- 8% (n = 5) for fresh purified cells, 60 +/- 10% (n = 12) for non-stimulated cells, 79 +/- 5% (n = 10) for IL-2 (100 U/ml)-stimulated cells and 95 +/- 5% (n = 8) for pokeweed mitogen (PWM) (1:200 dilution)-stimulated cells. The optimal concentrations of agonist were 100 U/ml of IL-2, and 1:200 dilution of PWM. IL-2 and PWM increased the internalization of LDL-DiI by 1.5-fold. The internalization of LDL-DiI was maximal at 60 microg of protein/ml (48 +/- 8%). Scatchard analysis revealed a Kd of 3.2 +/- 0.22 x 10(-8) M and 2180 +/- 190 binding sites in non-stimulated cells, a Kd of 7.73 +/- 0.36 x 10(-9) M and 12,500 +/- 430 binding sites for IL-2 (100 U/ml)-stimulated cells, and a Kd of 7.2 +/- 0.43 x 10(-9) M and 13,250 +/- 450 binding sites for PWM (1:200 dilution)-stimulated cells. Lineweaver-Burk analysis of LDL binding (LDL-DiI) revealed that the apparent Kd for non-stimulated cells was 1.3 +/- 0.11 x 10(-8) M, and 9.2 +/- 0.2 x 10(-9) M and 7.5 +/- 0.25 x 10(-9) M for IL-2- and PWM-stimulated cells, respectively. B lymphocytes from tonsils also showed a high expression of LDLR assessed with anti-LDLR (70 +/- 6%). The high expression of LDLR and the avid internalization of LDL suggest that LDL may be important for B cell physiological responses.

Smooth muscle cells express granulocyte-macrophage colony-stimulating factor in the undiseased and atherosclerotic human coronary artery

Granulocyte-macrophage colony-stimulating factor (GM-CSF), one of a family of cytokines that regulate proliferation in macrophages and other types of cells, has been implicated in the inflammatory-fibroproliferative response of atherosclerosis. However, previous studies have been restricted to cultured cells and animal models. In the present study, we investigated GM-CSF expression in undiseased and atherosclerotic human coronary arteries at both the mRNA and protein levels. Dual in situ hybridization/cell-marking experiments demonstrated that subpopulations of intimal smooth muscle cells (SMCs) and endothelial cells express the cytokine in the histologically normal human coronary artery and that augmented expression occurs at these sites, and in macrophage accumulations and medial SMCs, in the atherosclerotic vessel. Corresponding data were obtained by in situ hybridization and reverse transcription-polymerase chain reaction and Northern analyses of cultured cells. Cultured human coronary arterial SMCs showed constitutive expression of GM-CSF in cells that had adopted an activated synthetic phenotype. Electron microscope immunocytochemistry revealed that GM-CSF is a protein localized in the cytoplasmic matrix of SMCs of both the undiseased and atherosclerotic vessel wall; extracellular matrix was largely unlabeled, with only occasional small patches of amorphous immunopositive material. The expression of GM-CSF by subpopulations of intimal SMCs in the undiseased artery and the marked upregulation of GM-CSF apparent in atherosclerotic lesions suggest roles for the cytokine in the cellular events underlying initiation and progression of the human atherosclerotic lesion.

Elevated circulating levels of inflammatory cytokines in patients with abdominal aortic aneurysm

The basic feature in the pathogenesis of abdominal aortic aneurysm (AAA) is the degradation of extracellular matrix components. This process is induced partly by cytokines secreted from inflammatory and mesenchymal cells. Circulating levels of inflammatory cytokines were studied in AAA patients and compared with subjects suffering from atherosclerotic disease only. Furthermore, the predictive value of cytokine concentrations was evaluated for aneurysm expansion rate. Circulating levels of interleukin 1 beta (IL-1 beta), interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) were measured in 50 AAA patients (40 men, 10 women), 42 patients with coronary heart disease (CHD) (23 men, 19 women), and 38 controls whose angiogram was normal (17 men, 21 women). No differences in cytokine concentrations were found between the CHD patients and the controls. AAA disease was found to be associated with significantly higher IL-1 beta and IL-6 concentrations in both male patients (median concentrations of 19.40 pmol/L and 6.45 pmol/L, respectively) and female patients (19.26 pmol/L and 7.99 pmol/L) than in either the CHD patients or the controls (P < .005). TNF-alpha levels were slightly higher in the AAA patients (1.64 pmol/L in the males and 1.59 pmol/L in the females) than in the other groups (P < .05). IFN-gamma levels were elevated significantly in the female AAA patients (3.75 pmol/L) compared with levels found in the other female (P < .05) or male (P < .01) patient groups. The measured cytokine concentrations were not related to the size of the aneurysm or the maximal thickness of the thrombus within the aneurysm. IFN-gamma concentration showed a significant positive correlation to the aneurysm expansion (R = .37, P < .02) and negative correlation to the concentration of aminoterminal propeptide of type III procollagen during 6-month follow up (R = -.42, P < .005). The results show that circulating levels of inflammatory cytokines are elevated in patients with AAA disease, suggesting that the production of these cytokines is increased in these patients compared with CHD patients and controls. Elevated INF-gamma concentrations seem to predict an increased rate of expansion in AAA.

NIDDM as a disease of the innate immune system: association of acute-phase reactants and interleukin-6 with metabolic syndrome X

Non-insulin-dependent diabetes mellitus (NIDDM) is commonly associated with hypertriglyceridaemia, low serum HDL-cholesterol concentrations, hypertension, obesity and accelerated atherosclerosis (metabolic syndrome X). Since a similar dyslipidaemia occurs with the acute-phase response, we investigated whether elevated acute-phase/stress reactants (the innate immune system's response to environmental stress) and their major cytokine mediator (interleukin-6, IL-6) are associated with NIDDM and syndrome X, and may thus provide a unifying pathophysiological mechanism for these conditions. Two groups of Caucasian subjects with NIDDM were studied. Those with any 4 or 5 features of syndrome X (n = 19) were compared with a group with 0 or 1 feature of syndrome X (n = 25) but similar age, sex distribution, diabetes duration, glycaemic control and diabetes treatment. Healthy non-diabetic subjects of comparable age and sex acted as controls. Overnight urinary albumin excretion rate, a risk factor for cardiovascular disease, was also assayed in subjects to assess its relationship to the acute-phase response. Serum sialic acid was confirmed as a marker of the acute-phase response since serum concentrations were significantly related to established acute-phase proteins such as alpha-1 acid glycoprotein (r = 0.82, p < 0.0001). There was a significant graded increase of serum sialic acid, alpha-1 acid glycoprotein, IL-6 and urinary albumin excretion rate amongst the three groups, with the lowest levels in non-diabetic subjects, intermediate levels in NIDDM patients without syndrome X and highest levels in NIDDM patients with syndrome X. C-reactive protein and cortisol levels were also higher in syndrome X-positive compared to X-negative patients and serum amyloid A was higher in both diabetic groups than in the control group. We conclude that NIDDM is associated with an elevated acute-phase response, particularly in those with features of syndrome X. Abnormalities of the innate immune system may be a contributor to the hypertriglyceridaemia, low HDL cholesterol, hypertension, glucose intolerance, insulin resistance and accelerated atherosclerosis of NIDDM. Microalbuminuria may be a component of the acute-phase response.

Secretion of cytokines by natural killer cells primed with interleukin-2 and stimulated with different lipoproteins

Natural killer (NK) cells were shown to secrete differentially interleukins (IL), IL-1 alpha, IL-1 beta, IL-2, IL-8, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), granulocyte-macrophage colony-stimulating factor (GM-CSF), and leukaemia inhibitory factor (LIF) upon stimulation with optimal concentrations of chylomicrons (CM), very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), high-density lipoprotein (HDL) or acetyl-modified low-density lipoprotein (AcLDL). CM, VLDL, LDL and AcLDL induced LIF secretion which was absent in nonstimulated cells. CM, VLDL, and LDL did not affect IL-1 alpha secretion. CM stimulated IL-8 > TNF-alpha > IL-1 alpha > IL-2 = IFN-gamma, and decreased seventeen-fold GM-CSF secretion. VLDL stimulated IL-8 secretion > IL-1 alpha = IL-2 > IFN-gamma > TNF-alpha and decreased fivefold GM-CSF secretion. LDL stimulated IL-8 secretion > IL-1 alpha > IL-2 = IFN-gamma, it did not modify TNF-alpha and inhibited five hundred-fold GM-CSF secretion. HDL stimulated IL-2 secretion = IFN-gamma > IL-8, it decreased GM-CSF secretion > IL-1 alpha > IL-1 beta > TNF-alpha without affecting LIF. AcLDL stimulated IL-8 secretion > TNF-alpha > IL-1 alpha > IL-2 = IFN-gamma = IL-1 beta, and decreased GM-CSF secretion eightfold. When NK cells were primed with 10, 100 or 500 IU/ml of IL-2 before the addition of lipoproteins, a decrease in the secretion of cytokines was observed as compared with cells primed with IL-2 only. Differences in cytokine secretion were observed among the diverse type of lipoproteins used for cell stimulus. Thus, lipoproteins may condition NK cytokine secretion and cell activation.