Granulocyte-macrophage colony-stimulating factor prevents the progression of atherosclerosis via changes in the cellular and extracellular composition of atherosclerotic lesions in watanabe heritable hyperlipidemic rabbits

Utility of atherosclerosis-associated serum antibodies against colony-stimulating factor 2 in predicting the onset of acute ischemic stroke and prognosis of colorectal cancer

Introduction

Autoantibodies against inflammatory cytokines may be used for the prevention of atherosclerosis. Preclinical studies consider colony-stimulating factor 2 (CSF2) as an essential cytokine with a causal relationship to atherosclerosis and cancer. We examined the serum anti-CSF2 antibody levels in patients with atherosclerosis or solid cancer.

Methods

We measured the serum anti-CSF2 antibody levels via amplified luminescent proximity homogeneous assay-linked immunosorbent assay based on the recognition of recombinant glutathione S-transferase-fused CSF2 protein or a CSF2-derived peptide as the antigen.

Results

The serum anti-CSF2 antibody (s-CSF2-Ab) levels were significantly higher in patients with acute ischemic stroke (AIS), acute myocardial infarction (AMI), diabetes mellitus (DM), and chronic kidney disease (CKD) compared with healthy donors (HDs). In addition, the s-CSF2-Ab levels were associated with intima-media thickness and hypertension. The analyzes of samples obtained from a Japan Public Health Center-based prospective study suggested the utility of s-CSF2-Ab as a risk factor for AIS. Furthermore, the s-CSF2-Ab levels were higher in patients with esophageal, colorectal, gastric, and lung cancer than in HDs but not in those with mammary cancer. In addition, the s-CSF2-Ab levels were associated with unfavorable postoperative prognosis in colorectal cancer (CRC). In CRC, the s-CSF2-Ab levels were more closely associated with poor prognosis in patients with p53-Ab-negative CRC despite the lack of significant association of the anti-p53 antibody (p53-Ab) levels with the overall survival.

Conclusion

S-CSF2-Ab was useful for the diagnosis of atherosclerosis-related AIS, AMI, DM, and CKD and could discriminate poor prognosis, especially in p53-Ab-negative CRC.

Integral role of receptor for advanced glycation end products (RAGE) in nondiabetic atherosclerosis

An advanced glycation end products (AGE)/a receptor for AGE (RAGE) axis plays a central role in the pathogenesis of diabetic vascular remodeling. This study was conducted to clarify the role of RAGE in nondiabetic atherosclerosis. We used the aortic and coronary atherosclerotic lesions of Watanabe heritable hyperlipidemic (WHHL) rabbits prone to myocardial infarction (WHHLMI) at 1 to 14 months. Immunohistochemistry demonstrated the significant expression of RAGE as early as at 1 month with the stronger expression at 3 and 7 months, which was remarkably diminished at 14 months. RAGE expression was concordant with AGE accumulation. The major original sources of RAGE expression were macrophages and smooth muscle cells in addition to endothelial cells, and RAGE expression was distributed in the areas of phospholipid products, a component of oxidized LDL and nitrotyrosine. The concentrations of serum AGE did not alter significantly with aging. These findings suggested the expression of RAGE was induced by hyperlipidemia and oxidative stress independent of diabetes in WHHLMI rabbits. Additionally, our in vitro study showed that silencing of RAGE tended to attenuate oxidized-LDL-triggered PAI-1 expression in human cultured macrophages, as well as oxidized-LDL-induced tissue factor expression in peritoneal macrophages, suggesting a possible role of RAGE in prothrombogenic molecular regulation. In conclusion, the present study provides in vivo evidence that RAGE plays an integral role in the initiation and progression of nondiabetic atherosclerosis, suggesting that RAGE may be a novel target for treating not only diabetic but also nondiabetic vascular complications.

The History of the WHHL Rabbit, an Animal Model of Familial Hypercholesterolemia (II) - Contribution to the Development and Validation of the Therapeutics for Hypercholesterolemia and Atherosclerosis

A number of effective drugs have been developed through animal experiments, contributing to the health of many patients. In particular, the WHHL rabbit family (WHHL rabbits and its advanced strains (coronary atherosclerosis-prone WHHL-CA rabbits and myocardial infarction-prone WHHLMI rabbits) developed at Kobe University (Kobe, Japan) contributed greatly in the development of cholesterol-lowering agents. The WHHL rabbit family is animal models for human familial hypercholesterolemia, coronary atherosclerosis, and coronary heart disease. At the end of breeding of the WHHL rabbit family, this review summarizes the contribution of the WHHL rabbit family to the development of lipid-lowering agents and anti-atherosclerosis agents. Studies using the WHHL rabbit family demonstrated, for the first time in the world, that lowering serum cholesterol levels or preventing LDL oxidation can suppress the progression and destabilization of coronary lesions. In addition, the WHHL rabbit family contributed to the development of various compounds that exhibit lipid-lowering and anti-atherosclerotic effects and has also been used in studies of gene therapeutics. Furthermore, this review also discusses the causes of the increased discrepancy in drug development between the results of animal experiments and clinical studies, which became a problem in recent years, and addresses the importance of the selection of appropriate animal models used in studies in addition to an appropriate study design.

Immune therapy in sepsis: Are we ready to try again?

Immune therapy to ease the burden of sepsis has thus far failed to consistently improve patient outcomes. Advances in cancer immune therapy and awareness that prolonged immune-suppression in sepsis can leave patients vulnerable to secondary infection and death have driven resurgence in the field of sepsis immune-therapy investigation. As we develop and evaluate these novel therapies, we must learn from past experiences where single-mediator targeted immune therapies were blindly delivered to heterogeneous patient cohorts with complex and evolving immune responses. Advances in genomics, proteomics, metabolomics, and point-of-care technology, coupled with a better understanding of sepsis pathogenesis, have meant that personalised immune-therapy is on the horizon. Here, we review the complex immune pathogenesis in sepsis and the contemporary immune therapies that are being investigated to manipulate this response. An outline of the immune biomarkers that may be used to support this approach is also provided.

Heat shock protein 27-derived atheroprotection involves reverse cholesterol transport that is dependent on GM-CSF to maintain ABCA1 and ABCG1 expression in ApoE-/- mice

Recently, we demonstrated that heat shock protein (HSP)-27 is protective against the development of experimental atherosclerosis, reducing plaque cholesterol content by more than 30%. Moreover, elevated HSP-27 levels are predictive of relative freedom from clinical cardiovascular events. HSP-27 signaling occurs via the activation of NF-κB, which induces a marked up-regulation in expression of granulocyte-monocyte colony-stimulating factor (GM-CSF), a cytokine that is known to alter ABC transporters involved in reverse cholesterol transport (RCT). Therefore, we hypothesized that HSP-27-derived GM-CSF has a potent role in impeding plaque formation by promoting macrophage RCT and sought to better characterize this pathway. Treatment of THP-1 cells, RAW-Blue cells, and primary macrophages with recombinant HSP-27 resulted in NF-κB activation via TLR-4 and was inhibited by various pharmacologic blockers of this pathway. Moreover, HSP-27-induced upregulation of GM-CSF expression was dependent on TLR-4 signaling. Recombinant (r)HSP-27 treatment of ApoE^-/- female (but not male) mice for 4 wk yielded reductions in plaque area and cholesterol clefts of 33 and 47%, respectively, with no effect on GM-CSF^-/-ApoE^-/- mice. With 12 wk of rHSP-27 treatment, both female and male mice showed reductions in plaque burden (55 and 42%, respectively) and a 60% reduction in necrotic core area but no treatment effect in GM-CSF^-/-ApoE^-/- mice. In vitro functional studies revealed that HSP-27 enhanced the expression of ABCA1 and ABCG1, as well as facilitated cholesterol efflux in vitro by ∼10%. These novel findings establish a paradigm for HSP-27-mediated RCT and set the stage for the development of HSP-27 atheroprotective therapeutics.-Pulakazhi Venu, V. K., Adijiang, A., Seibert, T., Chen, Y.-X., Shi, C., Batulan, Z., O'Brien, E. R. Heat shock protein 27-derived atheroprotection involves reverse cholesterol transport that is dependent on GM-CSF to maintain ABCA1 and ABCG1 expression in ApoE^-/- mice.

Design of the START-trial: STimulation of ARTeriogenesis using subcutaneous application of GM-CSF as a new treatment for peripheral vascular disease. A randomized, double-blind, placebo-controlled trial

Peripheral arterial disease (PAD) affects a large percentage of the elderly population. Standard invasive treatment, apart from risk factor modulation, consists of bypass surgery or percutaneous transluminal angioplasty. However, symptomatic recurrence rates are high for both procedures and a substantial part of the patient population with PAD is not a candidate for invasive revascularization due to complexity of the lesion and/or co-morbidity. Therapeutic arteriogenesis has been proposed as an alternative treatment option. The present paper describes the design of the START-trial. This trial aims to determine the potential of the proarteriogenic substance granulocyte/macrophage colony stimulating factor (GM-CSF) to increase maximal walking distance in patients with intermittent claudication. A double-blinded, randomized, placebo-controlled study will be performed in 40 patients with peripheral obstructive arterial disease Rutherford grade I, category 2 or 3, that are candidates for bypass surgery or percutaneous transluminal angioplasty. Based on pharmacokinetic and toxicologic studies, a dose of 10 mg/kg will be used. Patients will be treated for a period of 14 days on each consecutive day, with the last injection applied on day 12. The primary endpoint will be the change in walking distance from day 0 to day 14 as assessed by an exercise treadmill test. Secondary endpoints will be the ankle-brachial index at rest and after exercise, the pain-free walking distance and cutaneous microcirculatory alterations as assessed by laser Doppler fluxmetry. Iliac flow reserve and conductance will be measured by magnetic resonance imaging.

Interleukin-33 stimulates GM-CSF and M-CSF production by human endothelial cells

Interleukin (IL)-33, a member of the IL-1 family of cytokines, is involved in various inflammatory conditions targeting amongst other cells the endothelium. Besides regulating the maturation and functions of myeloid cells, granulocyte macrophage-colony stimulating factor (GM-CSF) and macrophage-CSF (M-CSF) have been shown to play a role in such pathologies too. It was the aim of our study to investigate a possible influence of IL-33 on GM-CSF and M-CSF production by human endothelial cells. IL-33, but not IL-18 or IL-37, stimulated GM-CSF and M-CSF mRNA expression and protein production by human umbilical vein endothelial cells (HUVECs) and human coronary artery ECs (HCAECs) through the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway in an IL-1-independent way. This effect was inhibited by the soluble form of ST2 (sST2), which is known to act as a decoy receptor for IL-33. The 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor fluvastatin could also be shown to moderately reduce the IL-33-mediated effect on M-CSF, but not on GM-CSF expression. In addition, IL-33, IL-1β, GM-CSF and M-CSF were detected in endothelial cells of human carotid atherosclerotic plaques using immunofluorescence. Upregulation of GM-CSF and M-CSF production by human endothelial cells, an effect that appears to be mediated by NF-κB and to be independent of IL-1, may be an additional mechanism through which IL-33 contributes to inflammatory activation of the vessel wall.

A Review of GM-CSF Therapy in Sepsis

Determine what clinical role, if any, GM-CSF may have in the clinical treatment of sepsis in the adult patient. Advancements in the management of sepsis have led to significant decreases in early mortality; however, sepsis remains a significant source of long-term mortality and disability which places strain on healthcare resources with a substantial growing economic impact. Historically, early multiple organ failure (MOF) and death in patients with severe sepsis was thought to result from an exaggerated proinflammatory response called the systemic inflammatory response syndrome (SIRS). Numerous prospective randomized controlled trials (PRCTs) tested therapies aimed at decreasing the organ injury associated with an exaggerated inflammatory response. With few exceptions, the results from these PRCTs have been disappointing, and currently no specific therapeutic agent is approved to counteract the early SIRS response in patients with severe sepsis. It has long been recognized that there is a delayed immunosuppressive state that contributes to long-term morbidity. However, recent findings now support a concurrent proinflammatory and anti-inflammatory response present throughout sepsis. Multiple immunomodulating agents have been studied to combat the immunosuppressive phase of sepsis with the goal of decreasing secondary infection, reducing organ dysfunction, decreasing ICU stays, and improving survival. Granulocyte-macrophage colony stimulating factor (GM-CSF), a myelopoietic growth factor currently used in patients with neutropenia secondary to chemotherapy-induced myelosuppression, has been studied as a potential immune-activating agent. The applicability of GM-CSF as a standard therapy for generalized sepsis is still largely understudied; however, small-scale studies available have demonstrated some improved recovery from infection, decreased hospital length of stay, decreased days requiring mechanical ventilation, and decreased medical costs.

The future of collateral artery research

In the event of obstructive coronary artery disease, collateral arteries have been deemed an alternative blood source to preserve myocardial tissue perfusion and function. Monocytes play an important role in modulating this process, by local secretion of growth factors and extracellular matrix degrading enzymes. Extensive efforts have focused on developing compounds for augmenting the growth of collateral vessels (arteriogenesis). Nonetheless, clinical trials investigating the therapeutic potential of these compounds resulted in disappointing outcomes. Previous studies focused on developing compounds that stimulated collateral vessel growth by enhancing monocyte survival and activity. The limited success of these compounds in clinical studies, led to a paradigm shift in arteriogenesis research. Recent studies have shown genetic heterogeneity between CAD patients with sufficient and insufficient collateral vessels. The genetic predispositions in patients with poorly developed collateral vessels include overexpression of arteriogenesis inhibiting signaling pathways. New directions of arteriogenesis research focus on attempting to block such inhibitory pathways to ultimately promote arteriogenesis. Methods to detect collateral vessel growth are also critical in realizing the therapeutic potential of newly developed compounds. Traditional invasive measurements of intracoronary derived collateral flow index remain the gold standard in quantifying functional capacity of collateral vessels. However, advancements made in hybrid diagnostic imaging modalities will also prove to be advantageous in detecting the effects of pro-arteriogenic compounds.

Identification of a non-growth factor role for GM-CSF in advanced atherosclerosis: promotion of macrophage apoptosis and plaque necrosis through IL-23 signaling

RATIONALE

Granulocyte macrophage colony-stimulating factor (GM-CSF, Csf2) is a growth factor for myeloid-lineage cells that has been implicated in the pathogenesis of atherosclerosis and other chronic inflammatory diseases. However, the role of GM-CSF in advanced atherosclerotic plaque progression, the process that gives rise to clinically dangerous plaques, is unknown.

OBJECTIVE

To understand the role of GM-CSF in advanced atherosclerotic plaque progression.

METHODS AND RESULTS

Ldlr(-/-) mice and Csf2(-/-)Ldlr(-/-) mice were fed a Western-type diet for 12 weeks, and then parameters of advanced plaque progression in the aortic root were quantified. Lesions from the GM-CSF-deficient mice showed a substantial decrease in 2 key hallmarks of advanced atherosclerosis, lesional macrophage apoptosis and plaque necrosis, which indicates that GM-CSF promotes plaque progression. Based on a combination of in vitro and in vivo studies, we show that the mechanism involves GM-CSF-mediated production of interleukin-23, which increases apoptosis susceptibility in macrophages by promoting proteasomal degradation of the cell survival protein Bcl-2 (B-cell lymphoma 2) and by increasing oxidative stress.

CONCLUSIONS

In low-density lipoprotein-driven atherosclerosis in mice, GM-CSF promotes advanced plaque progression by increasing macrophage apoptosis susceptibility. This action of GM-CSF is mediated by its interleukin-23-inducing activity rather than its role as a growth factor.

Granulocyte colony-stimulating factor therapy is associated with a reduced incidence of acute rejection episodes or allograft vasculopathy in heart transplant recipients

BACKGROUND

We evaluated the potential effects of granulocyte colony-simulating factor (G- CSF) on the incidence of rejection and allograft vasculopathy in heart transplant recipients.

METHODS

Of 247 patients undergoing heart transplantation from 2000 to 2007, 52 (21%) developed leukopenia (white blood cell [WBC] <2.5 × 10(9) cells/L) in the absence of active infection, rejection, or malignancy. In 24 (46%) patients a clinical decision was made to treat the leukopenia with G-CSF (G-CSF group), and 28 (54%) Patients received no G-CSF (non-GCSF group). Patients followed up for 1 year after the period of leukopenia were assessed for allograft vasculopathy and acute rejection incidence.

RESULTS

At baseline, the G-CSF group and the non-GCSF group did not differ in age, gender, race, heart failure etiology, creatinine, left ventricular ejection fraction (LVEF) or immunosupressive regimen. During 1-year follow-up there were no deaths in the G-CSF group, and 1 death in the non-GCSF group (P = .34). The incidence of rejection or progressive allograft vasculopathy was lower in the G-CSF group when compared with the non-GCSF group (2 [8%] vs 15 [53%]; P < .01). Multivariate analysis identified both prior rejection episodes and G-CSF therapy as factors associated with the combined end-point of rejection or progressive allograft vasculopathy (odds ratio [OR] = 7.89 [1.67-37.2] and OR = 0.09 [0.02-0.52], respectively).

CONCLUSIONS

G-CSF therapy appears to be associated with a decreased incidence of acute rejection episodes or allograft vasculopathy in heart transplant recipients, suggesting a potential immunomodulatory effect of G-CSF.

The involvement of the monocytes/macrophages in chronic inflammation associated with atherosclerosis

Atherosclerosis is a progressive chronic disease of large and medium arteries, characterized by the formation of atherosclerotic plaques. Monocytes and macrophages are key factors in lesion development, participating to the processes that mediate the progression of the atherosclerotic plaque (lipid accumulation, secretion of pro-inflammatory and cytotoxic factors, extracellular matrix remodeling). The recruitment of the monocytes in the vascular wall represents a hallmark in the pathology of the atherosclerotic lesion. Monocyte adhesion and transmigration are dependent on the complementary adhesion molecules expressed on the endothelial surface, whose expression is modulated by chemical mediators. The atherosclerotic plaque is characterized by a heterogeneous population of macrophages reflecting the complexity and diversity of the micro-environment to which cells are exposed after entering the arterial wall. Within the atherosclerotic lesions, macrophages differentiate, proliferate and undergo apoptosis. Taking into account that their behavior has a direct and critical influence on all lesional stages, the development of therapeutic approaches to target monocytes/macrophages in the atherosclerotic plaque became a focal interest point for researchers in the field.

Role of Th17 cells in the pathogenesis of CNS inflammatory demyelination

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). The etiology of MS is not well understood, but it is believed that myelin-specific CD4(+) T cells play a central role in initiating and orchestrating CNS inflammation. In this scenario, CD4(+) T cells, activated in the periphery, infiltrate the CNS, where, by secreting cytokines and chemokines, they start an inflammatory cascade. Given the central role of CD4(+) T cells in CNS autoimmunity, they have been studied extensively, principally by using experimental autoimmune encephalomyelitis (EAE), an animal model of MS. In the late 1980s, CD4(+) T cells, based on their cytokine production, were divided into two helper lineages, Th1 and Th2 cells. It was postulated that Th1 cells, which produce IFN-γ, mediate inflammation of the CNS in MS/EAE, while Th2 cells, which produce IL-4, have a beneficial effect in disease, because of their antagonistic effect on Th1 cells. The Th1/Th2 paradigm remained the prevailing view of MS/EAE pathogenesis until 2005, when a new lineage, Th17, was discovered. In a relatively short period of time it became apparent that Th17 cells, named after their hallmark cytokine, IL-17A, play a crucial role in many inflammatory diseases, including EAE, and likely in MS as well. The Th17 paradigm developed rapidly, initiating the debate of whether Th1 cells contribute to EAE/MS pathogenesis at all, or if they might even have a protective role due to their antagonistic effects on Th17 cells. Numerous findings support the view that Th17 cells play an essential role in autoimmune CNS inflammation, perhaps mainly in the initial phases of disease. Th1 cells likely contribute to pathogenesis, with their role possibly more pronounced later in disease. Hence, the current view on the role of Th cells in MS/EAE pathogenesis can be called the Th17/Th1 paradigm. It is certain that Th17 cells will continue to be the focus of intense investigation aimed at elucidating the pathogenesis of CNS autoimmunity.

Granulocyte colony-stimulating factor promotes atherosclerosis in high-fat diet rabbits

Granulocyte-colony stimulating factor (G-CSF) has been reported to improve the function of infarcted heart, but its effects on atherosclerosis are unclear. Here we examined the effects and the potential mechanisms in the high-fat diet rabbit model. Six-month-old male New Zealand white rabbits, fed a high-cholesterol diet or a normal diet for 10 weeks, were treated with vehicle or G-CSF. G-CSF increased lesion area in the thoracic aorta and the plasma levels of total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C) at the early phase in the high-fat diet group. High-fat diet-induced arterial endothelium damage and apoptosis were greatly aggravated by G-CSF treatment. In vivo, G-CSF impaired apoptosis induced by oxidized low density lipoprotein (OX-LDL) but it had little effect on cultured endothelial cells (ECs) with vehicle treatment. Further research revealed that G-CSF promoted the upregulation of endothelin-1 (ET-1) and the downregulation of endothelial nitric oxide synthase (eNOS) of thoracic aortae induced by a high-fat diet. In vitro, the effects of G-CSF on expression of ET-1 and eNOS in cultured ECs were consistent with those in vivo. Our results suggested that G-CSF exacerbates lipid abnormity and endothelium damage in hyperlipidemia rabbits, thereby resulting in the deterioration of atherosclerosis and that the ET-1/eNOS system may regulate the progression.

Role of colony-stimulating factors in atherosclerosis

PURPOSE OF REVIEW

The varied effects of colony-stimulating factors (CSFs) on monocytes and macrophages during inflammation and atherosclerosis and its clinical presentation prompt the question whether the differing effects of CSFs dictate macrophage function and disease progression.

RECENT FINDINGS

CSFs can give rise to heterogeneous populations of monocyte-derived macrophages that are characterized by disparate expression of distinct molecules which dictate their ability to process lipid and regulate inflammatory and immune responses. The CSFs have been found within atherosclerotic plaques and in the circulation where their levels may act as predictive biomarkers of disease progression. Accordingly, differing exposure to these factors imparts divergent genomic signatures and functional properties on macrophages and may impact the multifactorial steps involved in atherogenesis, plaque progression and instability.

SUMMARY

Great interest in macrophage heterogeneity in the genesis and progression of atherosclerosis has led to the search for consistent markers of specific subsets in both animal models and humans. A better understanding of the overlap and competition between CSF regulation of macrophage phenotypes is therefore warranted, to allow their characterization in plaques. Subsequent targeted genetic and pharmacological intervention will facilitate the generation of therapeutic approaches to halt the progression and rupture of advanced atherosclerotic plaques.

Macrophage proliferation and apoptosis in atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is driven by cardiovascular risk factors that cause the recruitment of circulating immune cells beneath the vascular endothelium. Infiltrated monocytes differentiate into different macrophage subtypes with protective or pathogenic activities in vascular lesions. We discuss current knowledge about the molecular mechanisms that regulate lesional macrophage proliferation and apoptosis, two processes that occur during atherosclerosis development and regulate the number and function of macrophages within the atherosclerotic plaque.

RECENT FINDINGS

Lesional macrophages in early phases of atherosclerosis limit disease progression by phagocytizing modified lipoproteins, cellular debris and dead cells that accumulate in the plaque. However, macrophages in advanced lesions contribute to a maladaptive, nonresolving inflammatory response that can lead to life-threatening acute thrombotic diseases (myocardial infarction or stroke). Macrophage-specific manipulation of genes involved in cell proliferation and apoptosis modulates lesional macrophage accumulation and atherosclerosis burden in mouse models, and studies are beginning to elucidate the underlying mechanisms.

SUMMARY

Despite recent advances in our understanding of macrophage proliferation and apoptosis in atherosclerotic plaques, it remains unclear whether manipulating these processes will be beneficial or harmful. Advances in these areas may translate into more efficient therapies for the prevention and treatment of atherothrombosis.

Pentosan polysulfate inhibits atherosclerosis in Watanabe heritable hyperlipidemic rabbits: differential modulation of metalloproteinase-2 and -9

Pentosan polysulfate (PPS), a heparinoid compound essentially devoid of anticoagulant activity, modulates cell growth and decreases inflammation. We investigated the effect of PPS on the progression of established atherosclerosis in Watanabe heritable hyperlipidemic (WHHL) rabbits. After severe atherosclerosis developed on an atherogenic diet, WHHL rabbits were treated with oral PPS or tap water for 1 month. The aortic intima-to-media ratio and macrophage infiltration were reduced, plaque collagen content was increased, and plaque fibrous caps were preserved by PPS treatment. Plasma lipid levels and post-heparin hepatic lipase activity remained unchanged. However, net collagenolytic activity in aortic extracts was decreased, and the levels of matrix metalloproteinase (MMP)-2 and tissue inhibitor of metalloproteinase (TIMP) activity were increased by PPS. Moreover, PPS treatment decreased tumor necrosis factor α (TNFα)-stimulated proinflammatory responses, in particular activation of nuclear factor-κB and p38, and activation of MMPs in macrophages. In conclusion, oral PPS treatment prevents progression of established atherosclerosis in WHHL rabbits. This effect may be partially mediated by increased MMP-2 and TIMP activities in the aortic wall and reduced TNFα-stimulated inflammation and MMP activation in macrophages. Thus, PPS may be a useful agent in inhibiting the progression of atherosclerosis.

The effect of maternal hypercholesterolemia on the placenta and fetal arteries in rabbits

PURPOSE: To investigate the degree of placental permeability in dyslipidemic rabbits and the consequent vascular dysfunction in fetuses of female rabbits with high lipoprotein levels. METHODS: Fifteen adult females New Zealand White rabbits were divided into two groups. Group 1(n=5) - hypercholesterolemic diet with 0.5% cholesterol, and Group 2 (n=10) - control. On day 30, the levels of plasma lipoproteins and triglycerides were analyzed in the mothers, and the presence of collagen was analyzed in the placenta as well as in fetal coronary and aorta. Statistical analyses used the Student's t and the Mann-Whitney tests. RESULTS: Lipoprotein levels were significantly different (p=0.02 to p<0.001) in experimental and control groups. In the hypercholesterolemic group, total cholesterol levels were in average 793mg/dl; triglycerides were in average 257mg/dl; HDL-C was 48mg/dl, and LDL-C was in average 692mg/dl. The amount of collagen per micrometers square (mµ²) in samples from hypercholesterolemic animals was significantly higher than in the control group. CONCLUSIONS: The study confirmed placental permeability to lipoproteins, shown by increased amounts of collagen in fetal tissues. This alteration results in increased susceptibility to atherosclerosis in adult life, representing a risk factor for the early development of disease, which may appear even in the prenatal period.

Involvement of membrane type 1-matrix metalloproteinase (MT1-MMP) in RAGE activation signaling pathways

An advanced glycation end products (AGE)/a receptor for AGE (RAGE) axis plays a key role in diabetic vascular complications. Membrane type 1-matrix metalloproteinase (MT1-MMP) has been shown to function not only as a proteolytic enzyme but also as a signaling molecule. In this study, we investigated the role of MT1-MMP in the AGE/RAGE-triggered signaling pathways in cultured rabbit smooth muscle cells (SMCs) and the molecular interaction between RAGE and MT1-MMP in vitro and in vivo. In SMCs, AGE-activated Rac1 and p47(phox) within 1 min, NADPH oxidase activity and reactive oxygen species (ROS) generation within 5 min, and NF-κB phosphorylation within 15 min, thereby inducing redox-sensitive molecular expression. Silencing of RAGE by small-interfering RNA (siRNA) blocked the AGE-induced signaling pathways. AGE-induced geranylgeranyl transferase I (GGTase I) activity, Rac1·p47(phox) activation, NADPH oxidase activity, ROS generation, and molecular expression were also markedly attenuated by silencing of MT1-MMP. An inhibitor of GGTase I mimicked the effects of MT1-MMP-specific siRNA. Fluorescent immunohistochemistry revealed that MT1-MMP was partially co-localized with RAGE in SMCs, and RAGE was found to form a complex with MT1-MMP in both cultured SMCs and the aortae of diabetic rats by immunoprecipitation. Furthermore, MT1-MMP and RAGE formed a complex in the aortic atherosclerotic lesions of hyperlipidemic rabbits. We show that MT1-MMP plays a crucial role in RAGE-activated NADPH oxidase-dependent signaling pathways and forms a complex with RAGE in the vasculature, thus suggesting that MT1-MMP may be a novel therapeutic target for diabetic vascular complications.

Roles of the WHHL rabbit in translational research on hypercholesterolemia and cardiovascular diseases

Conquering cardiovascular diseases is one of the most important problems in human health. To overcome cardiovascular diseases, animal models have played important roles. Although the prevalence of genetically modified animals, particularly mice and rats, has contributed greatly to biomedical research, not all human diseases can be investigated in this way. In the study of cardiovascular diseases, mice and rats are inappropriate because of marked differences in lipoprotein metabolism, pathophysiological findings of atherosclerosis, and cardiac function. On the other hand, since lipoprotein metabolism and atherosclerotic lesions in rabbits closely resemble those in humans, several useful animal models for these diseases have been developed in rabbits. One of the most famous of these is the Watanabe heritable hyperlipidemic (WHHL) rabbit, which develops hypercholesterolemia and atherosclerosis spontaneously due to genetic and functional deficiencies of the low-density lipoprotein (LDL) receptor. The WHHL rabbit has been improved to develop myocardial infarction, and the new strain was designated the myocardial infarction-prone WHHL (WHHLMI) rabbit. This review summarizes the importance of selecting animal species for translational research in biomedical science, the development of WHHL and WHHLMI rabbits, their application to the development of hypocholesterolemic and/or antiatherosclerotic drugs, and future prospects regarding WHHL and WHHLMI rabbits.

Preventive effects of pravastatin on thrombin-triggered vascular responses via Akt/eNOS and RhoA/Rac1 pathways in vivo

AIMS

Small GTPases RhoA and Rac1 play crucial roles in endothelial dysfunction and reactive oxygen species (ROS) generation. We reported evidence that in thrombin-stimulated endothelial cells, rapid geranylgeranylation is an essential process for full activation of unprocessed RhoA, which is blocked by statin. In this study, we examined the effects of intravenous administration of pravastatin on thrombin-triggered vascular responses in vivo, as well as on the lipid modification of unprocessed forms of RhoA and Rac1 and their activation induced by thrombin.

METHODS AND RESULTS

Thrombin (50 U/kg) was intravenously injected with or without 0.3 mg/kg pravastatin into Wistar and spontaneously hypertensive rats. Coadministration of pravastatin prevented thrombin-induced impaired endothelium-dependent coronary vasodilation and down-regulated Akt/endothelial nitric oxide synthase (eNOS) phosphorylation within 1 h, as well as the down-regulation of eNOS protein expression within 4 h. In addition, thrombin increased Rac1/p47(phox)-dependent NAD(P)H oxidase activities of rat aortas within 1 h, resulting in ROS generation, which was prevented by the coadministration of pravastatin. Furthermore, the coadministration of pravastatin prevented thrombin-induced conversion of unprocessed RhoA and Rac1 into the geranylgeranylated forms as well as GTP-loading and membrane translocation within 1 h.

CONCLUSION

Intravenous injection of pravastatin prevents impaired NO-dependent vasodilation and Rac1/NAD(P)H oxidase-mediated-ROS generation by blocking the down-regulation of Akt/eNOS pathways and the full activation of unprocessed RhoA and Rac1 in vivo.

Blockade of renin-angiotensin system attenuates advanced glycation end products-mediated signaling pathways

AIM

Advanced glycation end products (AGE) and a receptor for AGE (RAGE) play a key role in diabetic vascular complications. Matrix metalloproteinases (MMPs) and apoptosis contribute to plaque instability. The renin-angiotensin system (RAS) is crucial for NADPH oxidase-dependent redox signaling pathways in the vascular wall. We investigated the effects of RAS blockade on AGE-triggered signaling pathways and its downstream events, including MMP-9 and apoptosis.

METHODS

We used cultured rabbit aortic smooth muscle cells (SMCs), which were stimulated with AGE in the presence or absence of temocaprilat or olmesartan.

RESULTS

Angiotensin converting enzyme (ACE) mRNA levels were increased 4 to 6 hours after adding AGE. AGE induced Rac1 and p47(phox) membrane translocation, reactive oxygen species (ROS) generation and NF-kappaB phosphorylation within 15 minutes, and various molecular expressions after 18 hours, which were attenuated by RAS blockade by temocaprilat or olmesartan. AGE-induced RAGE expression, as well as other molecules, including membrane type 1-MMP (MT1-MMP), monocyte chemoattractant protein-1 (MCP-1) and plasminogen activator inhibitor-1 (PAI-1), was NADPH oxidase signaling-dependent and blunted by temocaprilat and olmesartan. The parameters of plaque instability, including MMP-9 expression and activity, and apoptosis were up-regulated by AGE, which was markedly attenuated by temocaprilat or olmesartan. Using isolated human monocyte culture, AGE-induced ROS generation and molecular expression were also attenuated by RAS blockade.

CONCLUSION

The present study shows that AGE-triggered NADPH oxidase signaling pathways, including MMP-9 and apoptosis, were attenuated by RAS blockade, which may be an attractive strategy for treating plaque instability in diabetic vascular complications.

Advanced glycation end product-mediated matrix metallo-proteinase-9 and apoptosis via renin-angiotensin system in type 2 diabetes

AIM

Advanced glycation end products (AGE) play a key role in diabetic vascular complications, whereas matrix metalloproteinases (MMPs) and apoptosis contribute to plaque instability. This study was conducted to investigate the association of AGE-mediated MMP-9 and apoptosis with the renin-angiotensin system (RAS). We also examined the correlation between plasma HbA1c levels and plaque parameters.

METHODS

We used autopsy specimens from the aortae and coronary arteries of patients with or without diabetes (n=11, each group) for the immunohistochemistry of AGE, MMP-9, angiotensin-converting enzyme (ACE), and the receptor for AGE (RAGE). Apoptosis was determined by TUNEL staining.

RESULTS

The proportions of AGE accumulation, MMP-9 expression and apoptosis in intimal areas of both aortic and coronary specimens of diabetics were greater than in nondiabetics. MMP-9 expression and apoptosis were correlated with AGE accumulation. RAGE expression was significantly increased in diabetic specimens compared to nondiabetes. Interestingly, the expression of ACE in diabetic specimens was increased and also correlated with AGE accumulation, RAGE expression, MMP-9 expression, and apoptosis in all specimens from diabetics and nondiabetics. Plasma levels of HbA1c were linearly correlated with AGE accumulation, MMP-9, apoptosis, and ACE expression.

CONCLUSION

The present study shows that AGE/RAGE-related MMP-9 expression and apoptosis were correlated with ACE expression in diabetic plaques and that RAS may be involved in AGE-dependent diabetic vascular complications.

RhoA and Rac1 changes in the atherosclerotic lesions of WHHLMI rabbits

AIM

The activation of RhoA and Rac1 is crucial for the pathogenesis of atherosclerosis. This study investigated the changes of unprocessed and mature forms of RhoA and Rac1 in the progression of atherosclerosis.

METHODS

Unprocessed and geranylgeranylated forms of RhoA and Rac1 in aortic atherosclerotic lesions were separated by the Triton X-114 partition method using Watanabe heritable hyperlipidemic (WHHLMI) rabbits prone to myocardial infarction. The activation of RhoA and Rac1 was determined by membrane translocation and pull-down assays.

RESULTS

The levels of unprocessed RhoA and Rac1 of the aortas were higher at 7 months than 3 months, accompanied by increased levels of total RhoA and Rac1. Membrane-bound RhoA and Rac1 levels of the aortas at 7 months were significantly increased compared with those at 3 months, consistent with the results of GTP-loading. Unprocessed and activated forms of RhoA and Rac1 had gradually decreas at 15 and 24 months compared to 7 months.

CONCLUSIONS

We show evidence of marked increases in unprocessed RhoA and Rac1 with enhanced activities in the progression of atherosclerosis in WHHLMI rabbits. This is important for better understanding of the pathogenesis of hyperlipidemia-dependent atherosclerosis.

Colony-stimulating factors in inflammation and autoimmunity

Although they were originally defined as haematopoietic-cell growth factors, colony-stimulating factors (CSFs) have been shown to have additional functions by acting directly on mature myeloid cells. Recent data from animal models indicate that the depletion of CSFs has therapeutic benefit in many inflammatory and/or autoimmune conditions and as a result, early-phase clinical trials targeting granulocyte/macrophage colony-stimulating factor and macrophage colony-stimulating factor have now commenced. The distinct biological features of CSFs offer opportunities for specific targeting, but with some associated risks. Here, I describe these biological features, discuss the probable specific outcomes of targeting CSFs in vivo and highlight outstanding questions that need to be addressed.

An overview of cytokine interactions in atherosclerosis and implications for peripheral arterial disease

Over the last three decades, a surge in research into the inflammatory pathophysiology of atherosclerosis has highlighted an array of cytokines and other inflammatory mediators associated with underlying inflammatory burden. The ability to identify and simultaneously measure multiple cytokines in peripheral blood highlights their potential as biomarkers of atherosclerosis. This has prompted much research in vascular medicine to identify the ;at-risk' groups for atherostenotic or atheroaneurysmal disease. This review is compiled with similar intentions and aims to discern the relevant evidence for cytokine profiling in peripheral arterial disease (PAD), where such information is lacking, while providing a holistic overview of cytokine interactions in atherosclerosis. This is pertinent given that cytokine profiles from coronary artery disease and aortic aneurysm studies cannot be directly extrapolated to PAD due to differences in inflammatory environments that exist in these conditions. Whilst plaque morphology and blood rheology play an important role in the cardiac manifestations of atherosclerosis, tissue thrombogenecity is very important in PAD. Further, cytokines act in concert rather than in isolation in a disease process, and no single cytokine in a cross-sectional model is able to serve as an absolute screening marker. Thus, it is essential to understand the regulation of cytokine production in atherosclerosis prior to evaluating the viability and merits of a multimarker approach for clinical risk stratification in PAD.

Imaging of atherosclerosis in WHHL rabbits using high-resolution ultrasound

Watanabe heritable hyperlipidemic (WHHL) rabbits provide an animal model of hypercholesterolemia and atherosclerotic progression. However, a large individual variation in plaque progression rate calls for serial investigations, as do treatment studies. In contrast to histopathology, transthoracic ultrasound imaging of the aortic arch is a noninvasive technique suitable for repeated investigations. We studied 34 WHHL rabbits by both techniques. Ultrasound correctly interpreted plaque morphology compared with histopathology of the same spot (location verified by needle puncture). Intima media thickness (IMT) measured by the two methods agreed well. Ultrasonic values were similar to the histopathologic average circumferential values when these were corrected for postmortem shrinkage. Finally, the transthoracic ultrasound technique demonstrated a significant increase in IMT over a 15-week period (p = 0.0002). We conclude that transthoracic ultrasound of aortic arch IMT in WHHL rabbits is a reliable and feasible technique for studies of plaque progression and the evaluation of interventions.

Specificity of vascular reactivity and remodeling after repeated endothelial injury in a swine model

We investigated the difference in vascular responses and remodeling between coronary and iliac arteries after repeated endothelial denudation. Endothelial denudation of the left anterior descending coronary artery (LAD) and the right common iliac artery (RIA) was repeated 4 times twice a month using a Fogarty catheter in 21 pigs. Vascular responses to vasoactive drugs were evaluated as % luminal diameter changes on contrast angiography 2 weeks after the last denudation. Corresponding nondenuded sites, ie, the left circumflex coronary artery (LCX) and the left common iliac artery (LIA), were used as references. Acetylcholine (1 microg/kg) did not constrict the LCX (0 +/- 1%) and the LAD (1 +/- 1%, P < 0.05), whereas it constricted the RIA (20 +/- 6%) but not the LIA (-3 +/- 3%, P < 0.01). Alternatively, serotonin (10 microg/kg) constricted the LAD strikingly (88 +/- 5%, P < 0.01 versus LCX and RIA), as well as the RIA (35 +/- 10%, P < 0.05 versus LIA). Vasodilator responses to substance P and isosorbide dinitrate were not different after injury in both arteries. The intima-to-media ratio and adventitia-to-media ratio of the relevant site in cross section of tissue sample from LAD were greater than those from LCX, and were more prominent than those from RIA. The results show that vascular tone regulation after the endothelial injury and vascular remodeling might be altered in a vessel-specific manner.

G-CSF prevents the progression of atherosclerosis and neointimal formation in rabbits

Granulocyte colony-stimulating factor (G-CSF) prevents left ventricular remodeling after myocardial infarction, but its effect on atherosclerosis is unknown. We examined two kinds of rabbit atherosclerosis models. Myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHL-MI) rabbits were treated with G-CSF or saline for 7 days from 14 months old. The vascular injury models were created by inflating angioplasty balloon in the iliac artery of rabbits and were divided into G-CSF and saline group. G-CSF significantly reduced the stenosis score of coronary artery and lipid plaque area of thoracic aorta in WHHL-MI rabbits at 4 weeks after the treatment. In the vascular injury model, G-CSF significantly prevented an increase in neointima/media ratio at 4 weeks after the treatment. G-CSF accelerated the reendothelialization of denuded arteries, and the pretreatment with nitric oxide synthase inhibitor significantly inhibited it. These results suggest that G-CSF has a therapeutic potential for the progression of atherosclerosis.

Alterations in the vascular extracellular matrix of granulocyte macrophage colony-stimulating factor (GM-CSF) -deficient mice

GM-CSF takes part in the cytokine network regulating the metabolism of extracellular matrix (ECM) during atherogenesis. Since data also point to an effect of GM-CSF on the vascular ECM in general, the vascular collagenous matrix was studied in wild-type and GM-CSF-deficient mice. Histological examination revealed a disorganized vascular ECM in GM-CSF-deficient mice involving the collagenous matrix and elastic fiber system. As shown by electron microscopy, collagen bundles were disrupted and reduced. The diameter of fibrils varied widely. mRNA expression of collagens and related molecules was studied. Fibrillar collagens were markedly reduced, alpha1(I)procollagen to 16.5% of control levels alpha1(III)procollagen was abolished whereas the expression level of network-forming alpha1(VIII)procollagen was not altered. As shown by in situ hybridization, the number of collagen-expressing cells was reduced. Matrix metalloproteinases and their inhibitor 1 were not affected by GM-CSF deficiency. Our studies demonstrate that GM-CSF plays a major role in the cytokine network regulating the metabolism of vascular collagens. GM-CSF deficiency leads to an altered composition of the vascular collagenous matrix, i.e., reduced amount of fibrillar collagen, altered ratio of fibrillar and network-forming collagen, and failures in the fibrillogenesis. We suggest that GM-CSF is a basic requirement for the maintenance of vessel wall integrity and resilience.

Vascular collagens: spotlight on the role of type VIII collagen in atherogenesis

Collagens play a central role in maintaining the integrity and stability of the undiseased as well as of the atherosclerotic vessel wall. An imbalanced metabolism may lead to uncontrolled collagen accumulation reducing vessel wall velocity, frequently resulting in arterial occlusion or thrombosis. A reduced production of collagen and its uncontrolled degradation may affect the stability of the vessel wall and especially of the atherosclerotic plaques by making them prone to rupture and aneurysm. This review presents an overview on the four groups of vascular collagens and on their role in atherogenesis. The major focus was to highlight the extraordinary role and importance of the short chain network forming type VIII collagen in the extracellular matrix of undiseased arteries and of atherosclerotic plaques. The molecular structure of type VIII collagen, its cellular origin, its implication in atherogenesis, its temporal and spatial expression patterns in human and experimental models of atherogenesis, the factors modulating its expression, and--not at least--its potential function is discussed.

GM-CSF in inflammation and autoimmunity

Granulocyte macrophage-colony stimulating factor (GM-CSF) is now best viewed as a major regulator governing the functions of granulocyte and macrophage lineage populations at all stages of maturation. There is recent evidence for a key role for GM-CSF in inflammatory and autoimmune diseases, therefore making it worthy of consideration for targetting. Such evidence includes disease exacerbation following its administration and amelioration of disease in animal models by GM-CSF gene targetting or by anti-GM-CSF antibody blockade. The interdependence of GM-CSF formation and that of the important proinflammatory cytokines, interleukin-1 and tumour necrosis factor-alpha (TNF-alpha), is discussed, as is the greater disease suppression found in arthritis models following GM-CSF depletion compared with that observed in the absence of TNF-alpha.

Oxidized low-density lipoprotein receptor LOX-1 and apoptosis in human atherosclerotic lesions

BACKGROUND

Lectin-like oxidized LDL receptor-1 (LOX-1), a novel receptor for oxidized low-density lipoprotein, mediates oxidized low-density lipoprotein-induced apoptosis of endothelial cells, monocyte adhesion to endothelium, and phagocytosis of aged cells. The present study examined the role of LOX-1 and apoptosis in human atherosclerotic lesions.

METHODS AND RESULTS

Grafted vein (n = 8), human carotid artery endarterectomy (n = 11), and normal human internal mammary artery (n = 8) specimens were used to study the expression of LOX-1 and apoptosis. LOX-1 expression was determined by reverse transcriptase-polymerase chain reaction, Western analysis, and immunostaining. Presence of apoptosis was determined by fluorescent in situ nick end-labeling staining and by the presence of poly (ADP-ribose) polymerase protein (an apoptotic marker). Expression of LOX-1 was significantly increased in atherosclerotic grafted vein and carotid artery specimens compared with that in normal arteries. LOX-1 was expressed in endothelial cells, macrophages, and smooth muscle cells. LOX-1 was extensively expressed in the new blood vessels in the core of advanced atherosclerotic lesions. Double immunostaining showed LOX-1 expression to be colocalized with apoptotic cells. Fluorescent in situ nick end-labeling staining showed that the apoptotic cells were present mostly in the rupture-prone regions of the atherosclerotic plaque.

CONCLUSION

These observations indicate that LOX-1 is extensively expressed in the proliferated intima of grafted veins and in advanced atherosclerotic carotid arteries. Further, LOX-1 is colocalized with apoptotic cells. These observations may relate to the phenomenon of plaque rupture, and provide targets for developing new therapies.

Rho/Rho-kinase is involved in the synthesis of tissue factor in human monocytes

Monocytes and macrophages synthesize tissue factor (TF) which plays a role in thrombogenicity in coronary artery disease. This study was conducted to investigate the effect of Rho/Rho-kinase inhibition on the synthesis of TF in cultured human monocytes. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins), C3 exoenzyme and Rho-kinase inhibitors were added to isolated peripheral blood monocytes and the synthesis of TF was assessed by reverse transcriptase polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry. Rho activity was determined by measuring the GTP-bound form of Rho A. Cerivastatin and pravastatin reduced the levels of TF antigen and mRNA. The suppressive effect of statins on TF synthesis was reversed by geranylgeranylpyrophosphate (GGPP) and the restoring effect of GGPP was eliminated by C3 exoenzyme and Y-27632. Pravastatin decreased the activity of Rho A, suggesting that the suppression of TF synthesis by statins is mediated via inhibition of the geranylgeranylation of Rho. Moreover, inhibition of Rho and Rho-kinase downregulated the synthesis of TF. Our results suggest that Rho/Rho-kinase signaling is involved in the synthesis of TF in human monocytes and that inhibition of Rho/Rho-kinase may be useful for treating thrombogenicity in coronary artery disease.

Inhibition of Rho/Rho-kinase signaling downregulates plasminogen activator inhibitor-1 synthesis in cultured human monocytes

Increased production of plasminogen activator inhibitor-1 (PAI-1) in plaques plays a role in the pathogenesis of atherosclerosis. This study was conducted to investigate the effect of blockade of Rho/Rho-kinase signaling on the synthesis of PAI-1 in cultured human peripheral blood monocytes. HMG-CoA reductase inhibitors (statins) and inhibitors of Rho and Rho-kinase were added to monocyte cultures. The levels of PAI antigen and mRNA were determined by Western blotting and RT-PCR, respectively, and PAI-1 expression was assessed by immunohistochemistry. We performed pull-down assays to determine the activity of Rho by measuring the GTP-bound form of Rho A. In unstimulated and lipopolysaccharide (LPS)-stimulated cultured monocytes, statins reduced the levels of PAI-1 antigen and mRNA. The suppressive effects of statins on PAI-1 synthesis were reversed by geranylgeranylpyrophosphate (GGPP) and were mimicked by C3 exoenzyme. Immunohistochemistry confirmed the role of lipid modification by GGPP in suppressive effect of statins in PAI-1 synthesis. Pull-down assays demonstrated that statins decreased the levels of the GTP-bound form of Rho A. Our findings suggest that statins decrease the activity of Rho by inhibiting geranylgeranylation. Moreover, Rho-kinase inhibitors, Y-27632 and fasudil, suppressed the synthesis of PAI-1 in this culture system. We show that inhibition of Rho/Rho-kinase signaling downregulates the synthesis of PAI-1 in human monocytes.

GM-CSF: a strong arteriogenic factor acting by amplification of monocyte function

We investigated the role of the colony stimulating factor for monocytes (GM-CSF) to test the hypothesis whether prolongation of the monocyte's life cycle will support arteriogenesis (rapid growth of preexisting collateral arteries). This appeared logical in view of our discovery that circulating monocytes play an important part in the positive remodeling of small preexisting arterioles into arteries to compensate for arterial occlusions (arteriogenesis) and especially following our findings that MCP-1 markedly increases the speed of arteriogenesis. The continuous infusion of GM-CSF for 7 days into the proximal stump of the acutely occluded femoral artery of rabbits by osmotic minipump produced indeed a marked arteriogenic response as demonstrated by an increase (2-fold) in number and size of collateral arteries on postmortem angiograms and by the increase of maximal blood flow during vasodilation measured in vivo by blood pump perfusion of the hindquarter (5-fold). When GM-CSF and MCP-1 were simultaneously infused the effects on arteriogenesis were additive on angiograms as well as on conductance. GM-CSF was also able to widen the time window of MCP-1 activity: MCP-1 treatment alone was ineffective when given after the third week following occlusion. When administered together with GM-CSF about 80% of normal maximal conductance of the artery that was replaced by collaterals were achieved, a result that was not reached before by any other experimental treatment. Experiments with cells isolated from treated animals showed that monocyte apoptosis was markedly reduced. In addition we hypothesize that GM-CSF may aid in releasing pluripotent monocyte (stem-) cells from the bone marrow into the circulation. In contrast to MCP-1, GM-CSF showed no activity on monocyte transmigration through- and also no influence on monocyte adhesion to cultured endothelial cells. In conclusion we have discovered a new function of the hemopoietic stem cell factor GM-CSF, which is also a powerful arteriogenic peptide that acts via prolongation of the life cycle of monocytes/macrophages.

Increased plasminogen activator inhibitor-1 and apolipoprotein (a) in coronary atherectomy specimens in acute coronary syndromes

BACKGROUND

Although increased tissue factor expression is known in vulnerable plaques, there is no reported study to compare plaque fibrinolysis in stable and unstable plaques. This study investigates the extent of plasminogen activator inhibitor-1 (PAI-1) and apolipoprotein (a) [apo(a)] in the plaques of different types of coronary artery disease as well as the correlation between these molecules and infiltration of macrophages to plaques.

METHODS

Using immunohistochemical staining, we examined PAI-1 expression and apo(a) deposition in coronary atherosclerotic specimens obtained by directional coronary atherectomy from 19 patients with acute myocardial infarction (AMI), 12 with unstable angina pectoris (UAP), and 13 with stable angina pectoris (SAP). The percentages of the total areas of specimens stained with PAI-1 or apo(a) were estimated by an NIH image program. The proportion of macrophages as a percentage of all cells in plaques was calculated as the macrophage density.

RESULTS

We found significantly higher percentages of total areas of specimens stained with PAI-1 in AMI (25.5 +/- 8.6%, P < 0.001) and UAP (22.2 +/- 10.4%, P < 0.005) than in SAP (9.5 +/- 5.0%), as well as with apo(a) (AMI; 11.7 +/- 7.1%, P < 0.005, UAP; 11.1 +/- 5.5%, P < 0.01 versus SAP; 3.9 +/- 1.5%). Linear regression analysis of all the samples showed a correlation between PAI-1 or apo(a) and macrophage density (PAI-1: r = 0.75, P < 0.001 and apo(a): r = 0.56, P < 0.001).

CONCLUSIONS

Our results suggest a possible contribution of increased PAI-1 and apo(a) in plaques to the pathogenesis of acute coronary syndromes including impaired fibrinolysis.

Expression of very low density lipoprotein receptor mRNA in circulating human monocytes: its up-regulation by hypoxia

Although very low density lipoprotein (VLDL) receptor expression by macrophages has been shown in the vascular wall, it is not clear whether or not circulating monocytes express the VLDL receptor. We investigated the expression of VLDL receptor mRNA in human peripheral blood monocytes and monocyte-derived macrophages by reverse transcriptase polymerase chain reaction (RT-PCR) and nucleotide sequencing after subcloning of PCR product. VLDL receptor mRNA was detected both in peripheral blood monocytes and monocyte-derived macrophages. Expression of VLDL receptor mRNA was upregulated by hypoxia in monocytes, whereas treatment with oxidized LDL, interleukin-1beta or monocyte chemoattractant protein-1 did not affect the levels of VLDL receptor mRNA in monocytes and macrophages. The present study shows a novel response of VLDL receptor mRNA to hypoxia, suggesting a role for VLDL receptor in the metabolism of lipoproteins in the vascular wall and the development of atherosclerosis.

Effects of blockade of the renin-angiotensin system on tissue factor and plasminogen activator inhibitor-1 synthesis in human cultured monocytes

OBJECTIVES

To clarify the pathophysiological significance of the renin-angiotensin system (RAS) in monocytes, we examined the effect of its blockade on tissue factor and plasminogen activator inhibitor-1 (PAI-1) synthesis in human cultured monocytes.

METHODS

Monocytes were isolated from healthy volunteers and cultured. Tissue factor and PAI-1 antigens in culture medium and cells were measured by enzyme-linked immunosorbent assay and Western blotting, and mRNA levels were assessed by reverse-transcriptase polymerase chain reaction.

RESULTS

We show that the RAS is present in isolated human peripheral blood monocytes. Exogenous angiotensin II increased the levels of tissue factor antigen and mRNA in cultured monocytes, but not of PAI-1 synthesis. An angiotensin converting enzyme (ACE) inhibitor (captopril) and an angiotensin II type 1 (AT1) receptor antagonist (candesartan) decreased the levels of tissue factor protein and mRNA in cultured monocytes. These alterations were accompanied by a reduction in the levels of tumour necrosis factor-alpha protein and mRNA. The levels of PAI-1 protein were reduced by captopril, but not by candesartan. A bradykinin B2 receptor antagonist abolished the suppressive effect of captopril on PAI-1 antigen.

CONCLUSIONS

An ACE inhibitor and an AT1 receptor antagonist reduced tissue factor synthesis in these cells. We show different actions of these agents on PAI-1 synthesis. ACE inhibition decreased PAI-1 synthesis mediated by bradykinin production, but AT1 receptor inhibition had no effect.

Gene therapy and pharmaceutical modulation of apoptosis

Apoptosis is detectable in cardiovascular disease in various forms. Although the methods to detect apoptosis need improvement, and its magnitude is not known clearly, there is sufficient evidence to postulate that it might be important in progression of disease. Clinicians now have some specific compounds that can be used to modulate apoptosis. The preliminary data suggest that we can modulate apoptosis in animal models and that this is associated with obvious benefits in terms of tissue salvage and possibly improved function. There are no human data as yet. Many questions must be addresses before undertaking human studies. Despite these shortcomings, there is a tremendous potential for apoptotic modulation in preventing or ameliorating cardiovascular disease in the near future.

Postmenopausal changes in serum cytokine levels and hormone replacement therapy

OBJECTIVE

Our purpose was to investigate the effect of hormone replacement therapy on the postmenopausal changes in serum cytokine levels.

STUDY DESIGN

Fifteen cytokines were measured by an enzyme-linked immunosorbent assay in 97 untreated and hormone replacement-treated women. Thirteen women were examined before and during hormone replacement therapy.

RESULTS

Serum concentrations of macrophage colony-stimulating factor were significantly (P < .05) lower during the early postmenopausal period (< or = 10 years) than the values in premenopause and the elevated levels in the late postmenopausal period (< or = 30 years). A significant increase in tumor necrosis factor alpha and a decline in transforming growth factor beta1 were found in late postmenopausal women. Serum levels of macrophage colony-stimulating factor in women receiving hormone replacement therapy were significantly higher than those in untreated postmenopausal women. Furthermore, hormone replacement therapy induced a significant (P < .01) increase in serum levels of macrophage colony-stimulating factor, whereas serum levels of other cytokines were not affected.

CONCLUSION

It is well documented that macrophage colony-stimulating factor lowers serum cholesterol concentrations and prevents atherosclerosis. Inducing the production of macrophage colony-stimulating factor is a possible additional mechanism of hormone replacement therapy in mediating the antiatherogenic effect.