Mast cells: multipotent local effector cells in atherothrombosis

High-Density Lipoprotein Metabolism and Function in Cardiovascular Diseases: What about Aging and Diet Effects?

Cardiovascular diseases (CVDs) have become the leading global cause of mortality, prompting a heightened focus on identifying precise indicators for their assessment and treatment. In this perspective, the plasma levels of HDL have emerged as a pivotal focus, given the demonstrable correlation between plasma levels and cardiovascular events, rendering them a noteworthy biomarker. However, it is crucial to acknowledge that HDLs, while intricate, are not presently a direct therapeutic target, necessitating a more nuanced understanding of their dynamic remodeling throughout their life cycle. HDLs exhibit several anti-atherosclerotic properties that define their functionality. This functionality of HDLs, which is independent of their concentration, may be impaired in certain risk factors for CVD. Moreover, because HDLs are dynamic parameters, in which HDL particles present different atheroprotective properties, it remains difficult to interpret the association between HDL level and CVD risk. Besides the antioxidant and anti-inflammatory activities of HDLs, their capacity to mediate cholesterol efflux, a key metric of HDL functionality, represents the main anti-atherosclerotic property of HDL. In this review, we will discuss the HDL components and HDL structure that may affect their functionality and we will review the mechanism by which HDL mediates cholesterol efflux. We will give a brief examination of the effects of aging and diet on HDL structure and function.

Chymase Inhibition Resolves and Prevents Deep Vein Thrombosis Without Increasing Bleeding Time in the Mouse Model

Background Deep vein thrombosis (DVT) is the primary cause of pulmonary embolism and the third most life-threatening cardiovascular disease in North America. Post-DVT anticoagulants, such as warfarin, heparin, and direct oral anticoagulants, reduce the incidence of subsequent venous thrombi. However, all currently used anticoagulants affect bleeding time at various degrees, and there is therefore a need for improved therapeutic regimens in DVT. It has recently been shown that mast cells play a crucial role in a DVT murine model. The underlying mechanism involved in the prothrombotic properties of mast cells, however, has yet to be identified. Methods and Results C57BL/6 mice and mouse mast cell protease-4 (mMCP-4) genetically depleted mice (mMCP-4 knockout) were used in 2 mouse models of DVT, partial ligation (stenosis) and ferric chloride-endothelial injury model of the inferior vena cava. Thrombus formation and impact of genetically repressed or pharmacologically (specific inhibitor TY-51469) inhibited mMCP-4 were evaluated by morphometric measurements of thrombi immunochemistry (mouse and human DVT), color Doppler ultrasound, bleeding times, and enzymatic activity assays ex vivo. Recombinant chymases, mMCP-4 (mouse) and CMA-1 (human), were used to characterize the interaction with murine and human plasmin, respectively, by mass spectrometry and enzymatic activity assays. Inhibiting mast cell-generated mMCP-4, genetically or pharmacologically, resolves and prevents venous thrombus formation in both DVT models. Inferior vena cava blood flow obstruction was observed in the stenosis model after 6 hours of ligation, in control- but not in TY-51469-treated mice. In addition, chymase inhibition had no impact on bleeding times of healthy or DVT mice. Furthermore, endogenous chymase limits plasmin activity in thrombi ex vivo. Recombinant mouse or human chymase degrades/inactivates purified plasmin in vitro. Finally, mast cell-containing immunoreactive chymase was identified in human DVT. Conclusions This study identified a major role for mMCP-4, a granule-localized protease of chymase type, in DVT formation. These findings support a novel pharmacological strategy to resolve or prevent DVT without affecting the coagulation cascade through the inhibition of chymase activity.

The role of phosphoinositide 3-kinases in immune-inflammatory responses: potential therapeutic targets for abdominal aortic aneurysm

The pathogenesis of abdominal aortic aneurysm (AAA) includes inflammatory responses, matrix metalloproteinases (MMPs) degradation, VSMC apoptosis, oxidative stress, and angiogenesis, among which the inflammatory response plays a key role. At present, surgery is the only curing treatment, and no effective drug can delay AAA progression in clinical practice. Therefore, searching for a signaling pathway related to the immune-inflammatory response is an essential direction for developing drugs targeting AAA. Recent studies have confirmed that the PI3K family plays an important role in many inflammatory diseases and is involved in regulating various cellular functions, especially in the immune-inflammatory response. This review focuses on the role of each isoform of PI3K in each stage of AAA immune-inflammatory response, making available explorations for a deeper understanding of the mechanism of inflammation and immune response during the formation and development of AAA.

Monocyte subsets, T cell activation profiles, and stroke in men and women: The Multi-Ethnic Study of Atherosclerosis and Cardiovascular Health Study

BACKGROUND AND AIMS

Despite mechanistic data implicating unresolving inflammation in stroke pathogenesis, data regarding circulating immune cell phenotypes - key determinants of inflammation propagation versus resolution - and incident stroke are lacking. Therefore, we aimed to comprehensively define associations of circulating immune phenotypes and activation profiles with incident stroke.

METHODS

We investigated circulating leukocyte phenotypes and activation profiles with incident adjudicated stroke in 2104 diverse adults from the Multi-Ethnic Study of Atherosclerosis (MESA) followed over a median of 16.6 years. Cryopreserved cells from the MESA baseline examination were thawed and myeloid and lymphoid lineage cell subsets were measured using polychromatic flow cytometry and intracellular cytokine activation staining. We analyzed multivariable-adjusted associations of cell phenotypes, as a proportion of parent cell subsets, with incident stroke (overall) and ischemic stroke using Cox regression models.

RESULTS

We observed associations of intermediate monocytes, early-activated CD4⁺ T cells, and both CD4⁺ and CD8⁺ T cells producing interleukin-4 after cytokine stimulation (T_h2 and T_c2, respectively) with higher risk for incident stroke; effect sizes ranged from 35% to 62% relative increases in risk for stroke. Meanwhile, differentiated and memory T cell phenotypes were associated with lower risk for incident stroke. In sex-stratified analyses, positive and negative associations were especially strong among men but null among women.

CONCLUSIONS

Circulating IL-4 producing T cells and intermediate monocytes were significantly associated with incident stroke over nearly two decades of follow-up. These associations were stronger among men and not among women. Further translational studies are warranted to define more precise targets for prognosis and intervention.

Effects of Primary Mast Cell Disease on Hemostasis and Erythropoiesis

Mast cell disease is an epigenetically and genetically determined disease entity with very diverse clinical manifestations in potentially every system and tissue due to inap pro priate release of variable subsets of mast cell mediators together with accumulation of either morphologically normal or altered mast cells. Easy bruising, excessive bleeding, and aberrancies of erythropoiesis can frequently be observed in patients with mast cell disease. A thorough history, including a family history, will guide the appropriate work-up, and laboratory evaluations may provide clues to diagnosis. In recent years, our understanding of the involvement of coagulation and anticoagulant pathways, the fibrinolytic system, and erythropoiesis in the pathophysiology of mast cell disease has increased considerably. This review summarizes current knowledge of the impact of the disturbed hemostatic and erythropoietic balance in patients with mast cell disease and describes options of treatment.

General Perspectives for the Treatment of Atherosclerosis

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Atherosclerosis, a cardiovascular disease, is at the top of the list among the diseases leading to death. Although the biochemical and pathophysiological cascades involved within the development of atherosclerosis have been identified clearly, its nature is quite complex to be treated with a single agent targeting a pathway. Therefore, many natural and synthetic compounds have been suggested for the treatment of the disease. The majority of the drugs employed target one of the single components of the pathological outcomes, resulting in many times less effective and longterm treatments. In most cases, treatment options prevent further worsening of the symptoms rather than a radical treatment. Consequently, the current review has been prepared to focus on the validated and non-validated targets of atherosclerosis as well as the alternative treatment options such as hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors, acyl-CoA cholesterol acyl transferase (ACAT) inhibitors, lipoprotein lipase stimulants, bile acid sequestrants, and some antioxidants. Related to the topic, both synthetic compounds designed employing medicinal chemistry skills and natural molecules becoming more popular in drug development are scrutinized in this mini review.

Is atopic sensitization associated with indicators of early vascular ageing in adolescents?

Background

Chronic systemic inflammation accelerates early vascular ageing. Atopic sensitization and allergic diseases may involve increased inflammatory activity. This study aimed to assess whether atopic sensitization and allergic diseases were associated with altered vascular biomarkers in Norwegian adolescents.

Methods

Distensibility coefficient of the common carotid arteries, carotid intima-media thickness and atopic sensitization (serum total and specific IgEs) were assessed in 95 Norwegian adolescents, who participated in the RHINESSA generation study. Symptoms of allergic disease were assessed by an interviewer-led questionnaire.

Results

Atopic sensitization was found in 33 (34.7%) of the adolescents. Symptomatic allergic disease was found in 11 (33.3%) of those with atopic sensitization. Distensibility coefficient of the common carotid arteries appeared to be lower in participants with atopic sensitization than in those without (46.99±8.07*10⁻³/kPa versus 51.50±11.46*10⁻³/kPa; p>0.05), while carotid intima-media thickness did not differ between these groups (0.50±0.04mm versus 0.50±0.04mm; p>0.05). Crude, as well as age- and sex-adjusted multiple regression, revealed no significant association, neither of atopic sensitization nor of allergic disease, with distensibility coefficient of the common carotid arteries and carotid intima-media thickness.

Conclusions

Our results do not support the assumption of an adverse impact of atopic sensitization and/or allergic disease on distensibility coefficient of the common carotid arteries and carotid intima-media thickness in Norwegian adolescents. Further research is necessary to study whether the clinical severity of allergic diseases might be more important than the status of allergic disease or atopic sensitization.

Mast cell tryptase - Marker and maker of cardiovascular diseases

Mast cells are tissue-resident cells, which have been proposed to participate in various inflammatory diseases, among them the cardiovascular diseases (CVDs). For mast cells to be able to contribute to an inflammatory process, they need to be activated to exocytose their cytoplasmic secretory granules. The granules contain a vast array of highly bioactive effector molecules, the neutral protease tryptase being the most abundant protein among them. The released tryptase may act locally in the inflamed cardiac or vascular tissue, so contributing directly to the pathogenesis of CVDs. Moreover, a fraction of the released tryptase reaches the systemic circulation, thereby serving as a biomarker of mast cell activation. Actually, increased levels of circulating tryptase have been found to associate with CVDs. Here we review the biological relevance of the circulating tryptase as a biomarker of mast cell activity in CVDs, with special emphasis on the relationship between activation of mast cells in their tissue microenvironments and the pathophysiological pathways of CVDs. Based on the available in vitro and in vivo studies, we highlight the potential molecular mechanisms by which tryptase may contribute to the pathogenesis of CVDs. Finally, the synthetic and natural inhibitors of tryptase are reviewed for their potential utility as therapeutic agents in CVDs.

The Relationship of Serum Antigen-Specific and Total Immunoglobulin E with Adult Cardiovascular Diseases

Background: The relationship of serum antigen-specific immunoglobulin E (IgE) with cardiovascular diseases (CVDs) remains poorly understood. This study aimed to explore the association of antigen-specific and total IgE with CVDs using data derived from the National Health and Nutrition Examination Survey (NHANES) 2005-2006. Methods and Results: The association of serum total or antigen-specific IgE levels with CVDs was analyzed by survey-weighted logistic regression modeling, adjusted by age, sex, race, education, body mass index, blood pressure, total cholesterol, C-reactive protein, homocysteine, diabetes, smoking, and alcohol consumption. 4953 subjects were included. Coronary heart disease was significantly related to serum total IgE levels. The association of serum total IgE levels with coronary heart disease was further validated by negative, ≥1 and 1-6 positive antigen-specific IgE. Myocardial infarction was positively associated with serum total IgE levels only when all antigen-specific IgE were negative, but inversely associated with serum total IgE when plant-specific IgE test results were positive. More specifically, myocardial infarction was also inversely related to positive oak, birch, or peanut-specific IgE. In addition, serum total IgE are positively associated with angina when at least one specific IgE were positive. Conclusions: Serum antigen-specific IgE, as well as total IgE, is significantly associated with CVDs independently of a long list of established cardiovascular risk factors, which is more informative than total IgE per se.

Evaluation of Lipid Profile in Patients with Cherry Angioma: A Case-Control Study in Guilan, Iran

BACKGROUND

Cherry angioma is the most common type of acquired cutaneous vascular proliferation which would increase with aging due to some angiogenic factors but the exact pathogenesis is unknown. Usually angiogenic factors are synthesized in human body to compensate occlusive effects of atherogenic agents such as serum lipids. Our hypothesis was that increased levels of these angiogenic factors could be a trigger for development of cherry angioma. This study has been designed to compare frequency of dyslipidemia in subjects with and without cutaneous cherry angioma.

METHODS

In this case-control study, 122 cases with cherry angioma and 122 control subjects without cherry angioma were enrolled. Demographic characteristics, number of the cherry angioma lesions, and serum lipid profile were collected for all subjects. The data was analyzed using SPSS 18 software.

RESULTS

Mean levels of the total cholesterol, triglyceride, low-density lipoprotein, and high-density lipoprotein were higher in patients with cherry angioma compared to control subjects in which differences were significant for total cholesterol, low-density lipoprotein, and triglyceride (P < 0.05) but not for high-density lipoprotein level.

CONCLUSION

Serum lipids may have a role in producing angiogenic factors and development of cherry angioma and it seems logical to evaluate lipid profile in these cases.

Oxidized phospholipids stimulate production of stem cell factor via NRF2-dependent mechanisms

Receptor tyrosine kinase c-Kit and its ligand stem cell factor (SCF) regulate resident vascular wall cells and recruit circulating progenitors. We tested whether SCF may be induced by oxidized palmitoyl-arachidonoyl-phosphatidylcholine (OxPAPC) known to accumulate in atherosclerotic vessels. Gene expression analysis demonstrated OxPAPC-induced upregulation of SCF mRNA and protein in different types of endothelial cells (ECs). Elevated levels of SCF mRNA were observed in aortas of ApoE^-/- knockout mice. ECs produced biologically active SCF because conditioned medium from OxPAPC-treated cells stimulated activation (phosphorylation) of c-Kit in naïve ECs. Induction of SCF by OxPAPC was inhibited by knocking down transcription factor NRF2. Inhibition or stimulation of NRF2 by pharmacological or molecular tools induced corresponding changes in SCF expression. Finally, we observed decreased levels of SCF mRNA in aortas of NRF2 knockout mice. We characterize OxPLs as a novel pathology-associated stimulus inducing expression of SCF in endothelial cells. Furthermore, our data point to transcription factor NRF2 as a major mediator of OxPL-induced upregulation of SCF. This mechanism may represent one of the facets of pleiotropic action of NRF2 in vascular wall.

Mast cells emerge as mediators of atherosclerosis: Special emphasis on IL-37 inhibition

In atherosclerosis lipoproteins stimulate the innate immune response, leading to the release of inflammatory cytokines and chemokines. Hypercholesterolemia may activate the synthesis and release of inflammatory cytokines such as IL-1, which induces TNF release in mast cells (MCs). IL-1 and IL-1 family members orchestrate a broadening list of inflammatory diseases, including atherosclerosis. MCs are implicated in the pathophysiology of several diseases including allergy and inflammation. Activated MCs, located perivascularly, contribute to inflammation in atherosclerosis by producing inflammatory cytokines. MC IL-1-activation leads to the immediate release of inflammatory chemical mediators and TNF, and late inflammatory compounds such as cytokines. MCs can be activated by exogenous cytokines, antigens, microbial products (LPS) and neurotransmitters and generate IL-1 beta, TNF and several other inflammatory cytokines/chemokines along with PGD2, leukotrienes, histamine and proteases. MCs activated with IL-1 induce selective release of IL-6 without degranulation. TNF emerges as one of the most potent inflammatory cytokines involved in the response due to LDL. Cytokines, such as IL-1, IL-6, IL-33 and TNF, are generated in the inflammatory sites by both macrophages and MCs, mediating atherosclerosis. IL-37 (IL-1 family member 7) binds IL-18Ra chain and acts by an intracellular mechanism down-regulating the expression of pro-inflammatory signals cJun, MAP kinase p38a, STAT transcription factors and p53. Blocking IL-1 with IL-37 alleviates the symptoms in patients with inflammatory diseases including arteriosclerosis. The impact of IL-37 on inflammatory cytokines mediating atherosclerosis is beneficial and protective. However, more studies are needed to better define this mechanism and the safety and tolerability of IL-37.

Nicotine Accelerates Atherosclerosis in Apolipoprotein E-Deficient Mice by Activating α7 Nicotinic Acetylcholine Receptor on Mast Cells

OBJECTIVE

Cigarette smoking is an independent risk factor for atherosclerosis. Nicotine, the addictive component of cigarettes, induces mast cell (MC) release and contributes to atherogenesis. The purpose of this study was to determine whether nicotine accelerates atherosclerosis through MC-mediated mechanisms and whether MC stabilizer prevents this pathological process.

APPROACH AND RESULTS

Nicotine administration increased the size of atherosclerotic lesions in apolipoprotein E-deficient (Apoe^-/-) mice fed a fat-enriched diet. This was accompanied by enhanced intraplaque macrophage content and lipid deposition but reduced collagen and smooth muscle cell contents. MC deficiency in Apoe^-/- mice (Apoe^-/-Kit^W-sh/W-sh) diminished nicotine-induced atherosclerosis. Nicotine activated bone marrow-derived MCs in vitro, which was inhibited by a MC stabilizer disodium cromoglycate or a nonselective nicotinic acetylcholine receptor blocker mecamylamine. Further investigation revealed that α7 nicotinic acetylcholine receptor was a target for nicotine activation in MCs. Nicotine did not change atherosclerotic lesion size of Apoe^-/-Kit^W-sh/W-sh mice reconstituted with MCs from Apoe^-/-α7nAChR^-/- animals.

CONCLUSIONS

Activation of α7 nicotinic acetylcholine receptor on MCs is a mechanism by which nicotine enhances atherosclerosis.

Perivascular Mast Cells Govern Shear Stress-Induced Arteriogenesis by Orchestrating Leukocyte Function

The body has the capacity to compensate for an occluded artery by creating a natural bypass upon increased fluid shear stress. How this mechanical force is translated into collateral artery growth (arteriogenesis) is unresolved. We show that extravasation of neutrophils mediated by the platelet receptor GPIbα and uPA results in Nox2-derived reactive oxygen radicals, which activate perivascular mast cells. These c-kit(+)/CXCR-4(+) cells stimulate arteriogenesis by recruiting additional neutrophils as well as growth-promoting monocytes and T cells. Additionally, mast cells may directly contribute to vascular remodeling and vascular cell proliferation through increased MMP activity and by supplying growth-promoting factors. Boosting mast cell recruitment and activation effectively promotes arteriogenesis, thereby protecting tissue from severe ischemic damage. We thus find that perivascular mast cells are central regulators of shear stress-induced arteriogenesis by orchestrating leukocyte function and growth factor/cytokine release, thus providing a therapeutic target for treatment of vascular occlusive diseases.

Leukocytes Link Local and Systemic Inflammation in Ischemic Cardiovascular Disease: An Expanded "Cardiovascular Continuum"

Physicians have traditionally viewed ischemic heart disease in a cardiocentric manner: plaques grow in arteries until they block blood flow, causing acute coronary and other ischemic syndromes. Recent research provides new insight into the integrative biology of inflammation as it contributes to ischemic cardiovascular disease. These results have revealed hitherto unsuspected inflammatory signaling networks at work in these disorders that link the brain, autonomic nervous system, bone marrow, and spleen to the atherosclerotic plaque and to the infarcting myocardium. A burgeoning clinical published data indicates that such inflammatory networks-far from a mere laboratory curiosity-operate in our patients and can influence aspects of ischemic cardiovascular disease that determine decisively clinical outcomes. These new findings enlarge the circle of the traditional "cardiovascular continuum" beyond the heart and vessels to include the nervous system, the spleen, and the bone marrow.

[Immunohistochemical study of the role of mast cells and macrophages in the process of angiogenesis in the atherosclerotic plaques in patients with metabolic syndrome]

OBJECTIVE

to analyze the histotopographic distribution of neogenic vessels, the degree of mast cell degranulation, the expression of markers of macrophages in different types of plaques in different stages and in different arterial vessels in patients with atherosclerosis and in those with metabolic syndrome associated with atherosclerosis and to establish the role of mast cells and macrophages in the development of stages of atherosclerosis along with their diagnostic and prognostic value.

MATERIAL AND METHODS

Fragments of the thoracic and abdominal aorta, middle cerebral, carotid, renal, and iliac, and vertebral arteries from 34 persons who had died from atherosclerosis (n=17) and atherosclerotic complications due to metabolic syndrome (n=17) were examined. The investigators employed standard techniques, such as hematoxylin-eosin or orcein staining; silver impregnation. They used immunohistochemical staining with anti-mast cell tryptase (anti-MCT) for the determination of mast cells, the specific markers CD68 for macrophages, and CD105 (endoglin) for neogenic vessels.

RESULTS

The immunohistochemical technique is effective in identifying mast cells, macrophages, and neogenic vessels in atherosclerotic plaques. They were found in many types of atherosclerotic plaques, advantium, and subendothelial layers in the immediate vicinity of the plaques. There was a statistical correlation between the types of plaques and clinical data, which is of importance in elucidating the specific features of the pathogenesis of atherosclerosis in patients with metabolic syndrome.

CONCLUSION

CD105 is a sensitive marker for neogenic endothelial cells, an effective indicator of microvascular activation and proliferation in the atherosclerotic plaques. Neovascularization in the plaques frequently begins in the intima, progresses, and gives rise to their further destabilization. Anti-MCT staining used to reveal mast cells and CD68 for macrophages can elucidate the important patterns of development of atherosclerosis and its complications in patients with metabolic disturbances.

Smooth Muscle Cell Foam Cell Formation, Apolipoproteins, and ABCA1 in Intracranial Aneurysms: Implications for Lipid Accumulation as a Promoter of Aneurysm Wall Rupture

Saccular intracranial aneurysm (sIA) aneurysm causes intracranial hemorrhages that are associated with high mortality. Lipid accumulation and chronic inflammation occur in the sIA wall. A major mechanism for lipid clearance from arteries is adenosine triphosphate-binding cassette A1 (ABCA1)-mediated lipid efflux from foam cells to apolipoprotein A-I (apoA-I). We investigated the association of wall degeneration, inflammation, and lipid-related parameters in tissue samples of 16 unruptured and 20 ruptured sIAs using histology and immunohistochemistry. Intracellular lipid accumulation was associated with wall remodeling (p = 0.005) and rupture (p = 0.020). Foam cell formation was observed in smooth muscle cells, in addition to CD68- and CD163-positive macrophages. Macrophage infiltration correlated with intracellular lipid accumulation and apolipoproteins, including apoA-I. ApoA-I correlated with markers of lipid accumulation and wall degeneration (p = 0.01). ApoA-I-positive staining colocalized with ABCA1-positive cells particularly in sIAs with high number of smooth muscle cells (p = 0.003); absence of such colocalization was associated with wall degeneration (p = 0.017). Known clinical risk factors for sIA rupture correlated inversely with apoA-I. We conclude that lipid accumulation associates with sIA wall degeneration and risk of rupture, possibly via formation of foam cells and subsequent loss of mural cells. Reduced removal of lipids from the sIA wall via ABCA1-apoA-I pathway may contribute to this process.

Chymase inhibition protects diabetic rats from renal lesions

The present study aimed to investigate the effects of a chymase inhibitor on renal injury in diabetic rats. A total of 24 Sprague-Dawley rats were randomly divided into the following groups: The control group (n=7), the diabetes group (DM group; n=7), and the DM + chymase inhibitor group (DM + Chy-I group; n=10). Diabetes was induced via an intraperitoneal injection of streptozotocin (65 mg/kg). Rats in the DM + Chy-I group were administered 1 mg/kg chymase inhibitor [Suc-Val-Pro-Phe^P-(OPh)₂] daily for 12 weeks by intraperitoneal injection. Subsequently, kidney weight, various biochemical parameters and blood pressure were measured. In addition, the expression levels of fibronectin (FN), type IV collagen (ColIV), transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF) were determined by immunohistochemistry and reverse transcription polymerase chain reaction. Compared with in the DM group, the levels of serum cholesterol and urinary albumin/creatinine were decreased in the DM + Chy-I group (P<0.05). Furthermore, chymase inhibition reduced the overexpression of FN, ColIV, TGF-β1 and VEGF (P<0.05) in the renal tissue of diabetic rats. These results indicated that chymase inhibition may reduce the excretion of urinary albumin and the deposition of extracellular matrix components in the kidney of diabetic rats. These effects may be mediated by altered expression of the VEGF and TGF-β1 pathways. In conclusion, chymase inhibition may be considered a potential method for the treatment of renal damage.

Perivascular mast cells regulate vein graft neointimal formation and remodeling

Objective. Emerging evidence suggests an important role for mast cells in vein graft failure. This study addressed the hypothesis that perivascular mast cells regulate in situ vascular inflammatory and proliferative responses and subsequent vein graft neointimal lesion formation, using an optimized local mast cell reconstitution method.

Methods and Results. Neointimal hyperplasia was induced by insertion of a vein graft into the right carotid artery in wild type and mast cell deficient Kit^{W−sh/W−sh} mice. In some experiments, mast cells were reconstituted systemically (tail vein injection of bone marrow-derived mast cells) or locally (directly into the right neck area) prior to vein grafting. Vein graft neointimal lesion formation was significantly (P < 0.05) reduced in Kit^{W−sh/W−sh} mice. Mast cell deficiency reduced the number of proliferating cells, and inhibited L-selectin, CCL2, M-CSF and MIP-3α expression in the vein grafts. Local but not systemic mast cell reconstitution restored a perivascular mast cell population that subsequently promoted neointimal formation in mast cell deficient mice.

Conclusion. Our data demonstrate that perivascular mast cells play a key role in promoting neointima formation by inducing local acute inflammatory and proliferative responses. These results suggest that ex vivo intraoperative targeting of mast cells may have therapeutic potential for the prevention of pathological vein graft remodeling.

Lipid droplets in activated mast cells - a significant source of triglyceride-derived arachidonic acid for eicosanoid production

Mast cells are potent effectors of immune reactions and key players in various inflammatory diseases such as atherosclerosis, asthma, and rheumatoid arthritis. The cellular defense response of mast cells represents a unique and powerful system, where external signals can trigger cell activation resulting in a stimulus-specific and highly coordinated release of a plethora of bioactive mediators. The arsenal of mediators encompasses preformed molecules stored in cytoplasmic secretory granules, as well as newly synthesized proteinaceous and lipid mediators. The release of mediators occurs in strict chronological order and requires proper coordination between the endomembrane system and various enzymatic machineries. For the generation of lipid mediators, cytoplasmic lipid droplets have been shown to function as a major intracellular pool of arachidonic acid, the precursor for eicosanoid biosynthesis. Recent studies have revealed that not only phospholipids in mast cell membranes, but also triglycerides in mast cell lipid droplets are a substrate source for eicosanoid formation. The present review summarizes current knowledge about mast cell lipid droplet biology, and discusses expansions and challenges of traditional mechanistic models for eicosanoid production.

Elevated Serum Tryptase and Endothelin in Patients with ST Segment Elevation Myocardial Infarction: Preliminary Report

An inflammatory response plays a crucial role in myocardial damage after an acute myocardial infarction.

OBJECTIVES

To measure serum concentrations of several mediators in patients with an acute myocardial infarction (STEMI) and to assess their potential relationship with a risk of coronary instability.

PATIENTS AND METHODS

The 33 patients with STEMI and 19 healthy volunteers were analyzed. The clinical data were obtained; as well serum concentrations of tryptase, endothelin (ET-1), angiogenin, soluble c-kit, and PDGF were measured.

RESULTS

Patients with STEMI had higher serum tryptase and ET-1 than healthy volunteers (2,5 ± 0,4 ng/mL versus 1,1 ± 0,4 ng/mL and 0,7 ± 0,1 ng/mL versus 0,3 ± 0,1 ng/mL, resp.). Subjects with significant lesion in left anterior descending artery (LAD) had lower serum ET-1 compared to those with normal LAD (0,6 ± 0,2 pg/mL versus 0,9 ± 0,4 pg/mL). Patients with three-vessel coronary artery disease (CAD) had higher level of soluble c-kit compared to those with one- or two-vessel CAD: 19,9 ± 24,1 ng/mL versus 5,6 ± 1,9 ng/mL.

CONCLUSIONS

Elevated serum tryptase and ET-1 may be markers of increased coronary instability; some cytokines may be related to the extension of CAD.

Randomized clinical trial of mast cell inhibition in patients with a medium-sized abdominal aortic aneurysm

Background

Abdominal aortic aneurysm (AAA) is thought to develop as a result of inflammatory processes in the aortic wall. In particular, mast cells are believed to play a central role. The AORTA trial was undertaken to investigate whether the mast cell inhibitor, pemirolast, could retard the growth of medium-sized AAAs. In preclinical and clinical trials, pemirolast has been shown to inhibit antigen-induced allergic reactions.

Methods

Inclusion criteria for the trial were patients with an AAA of 39–49 mm in diameter on ultrasound imaging. Among exclusion criteria were previous aortic surgery, diabetes mellitus, and severe concomitant disease with a life expectancy of less than 2 years. Included patients were treated with 10, 25 or 40 mg pemirolast, or matching placebo for 52 weeks. The primary endpoint was change in aortic diameter as measured from leading edge adventitia at the anterior wall to leading edge adventitia at the posterior wall in systole. All ultrasound scans were read in a central imaging laboratory.

Results

Some 326 patients (mean age 70·8 years; 88·0 per cent men) were included in the trial. The overall mean growth rate was 2·42 mm during the 12-month study. There was no statistically significant difference in growth between patients receiving placebo and those in the three dose groups of pemirolast. Similarly, there were no differences in adverse events.

Conclusion

Treatment with pemirolast did not retard the growth of medium-sized AAAs. Registration number: NCT01354184 (https://www.clinicaltrials.gov).

Expression and activity levels of chymase in mast cells of burn wound tissues increase during the healing process in a hamster model

The present study aimed to investigate the changes in the expression levels and activity of mast cell chymase in the process of burn wound healing in a hamster model of deep second-degree burn. The hamster model was established by exposing a ~3 cm diameter area of bare skin to hot water (75°C) for 0, 6, 8, 10 or 12 sec. Tissue specimens were collected 24 h after burning and histological analysis revealed that hot water contact for 12 sec was required to produce a deep second-degree burn. Quantitative polymerase chain reaction and a radioimmunoassay were used to the determine changes in chymase mRNA expression levels and activity. The mRNA expression levels and activity of chymase were increased in the burn wound tissues when compared with the normal skin. However, no statistically significant differences were observed in mast cell chymase activity amongst the various post-burn stages. Chymase mRNA expression levels peaked at day 1 post-burn, subsequently decreasing at days 3 and 7 post-burn and finally increasing again at day 14 post-burn. In summary, a hamster model of deep second-degree burn can be created by bringing the skin into contact with water at 75°C for 12 sec. Furthermore, the mRNA expression levels and activity of chymase in the burn wound tissues increased when compared with those in normal skin tissues.

Contribution of neovascularization and intraplaque haemorrhage to atherosclerotic plaque progression and instability

Atherosclerosis is a continuous pathological process that starts early in life and progresses frequently to unstable plaques. Plaque rupture leads to deleterious consequences such as acute coronary syndrome, stroke and atherothrombosis. The vulnerable lesion has several structural and functional hallmarks that distinguish it from the stable plaque. The unstable plaque has large necrotic core (over 40% plaque volume) composed of cholesterol crystals, cholesterol esters, oxidized lipids, fibrin, erythrocytes and their remnants (haeme, iron, haemoglobin), and dying macrophages. The fibrous cap is thin, depleted of smooth muscle cells and collagen, and is infiltrated with proinflammatory cells. In unstable lesion, formation of neomicrovessels is increased. These neovessels have weak integrity and leak thereby leading to recurrent haemorrhages. Haemorrhages deliver erythrocytes to the necrotic core where they degrade promoting inflammation and oxidative stress. Inflammatory cells mostly presented by monocytes/macrophages, neutrophils and mast cells extravagate from bleeding neovessels and infiltrate adventitia where they support chronic inflammation. Plaque destabilization is an evolutionary process that could start at early atherosclerotic stages and whose progression is influenced by many factors including neovascularization, intraplaque haemorrhages, formation of cholesterol crystals, inflammation, oxidative stress and intraplaque protease activity.

Mast cells in human health and disease

Mast cells are primarily known for their role in defense against pathogens, particularly bacteria; neutralization of venom toxins; and for triggering allergic responses and anaphylaxis. In addition to these direct effector functions, activated mast cells rapidly recruit other innate and adaptive immune cells and can participate in "tuning" the immune response. In this review we touch briefly on these important functions and then focus on some of the less-appreciated roles of mast cells in human disease including cancer, autoimmune inflammation, organ transplant, and fibrosis. Although it is difficult to formally assign causal roles to mast cells in human disease, we offer a general review of data that correlate the presence and activation of mast cells with exacerbated inflammation and disease progression. Conversely, in some restricted contexts, mast cells may offer protective roles. For example, the presence of mast cells in some malignant or cardiovascular diseases is associated with favorable prognosis. In these cases, specific localization of mast cells within the tissue and whether they express chymase or tryptase (or both) are diagnostically important considerations. Finally, we review experimental animal models that imply a causal role for mast cells in disease and discuss important caveats and controversies of these findings.

Immunoglobulin E (IgE) and ischemic heart disease. Which came first, the chicken or the egg?

Several lines of evidence demonstrate that the immune system plays a pivotal role in development and progression of ischemic heart disease (IHD). More recently, a series of biological and clinical investigations has generated new interest about the existence of a relationship between a specific class of immunoglobulin, that is immunoglobulin E (IgE), and IHD. Data obtained in several epidemiological studies have convincingly demonstrated that the concentration of total serum IgEs is significantly increased in patients with IHD and often correlates with the prognosis. The putative mechanisms are essentially mediated by a physiological interaction between IgEs and mast cells, which triggers the direct or indirect release of a variety of substances that are actively involved in the pathogenesis of myocardial ischemia and thrombosis. Regardless of these important evidences, a causality dilemma remains, since it is still unclear whether increased IgE levels are a consequence of IHD or, rather, IHD is an underlying cause of increased IgE levels. The answer would allow us to recognize whether total IgEs may be considered simple biomarkers or risk factors of IHD, thus paving the way to investigations focused on immunotherapy or avoidance of allergenic foods for reducing serum IgEs in patients at risk of IHD.

Role of bone-marrow- and non-bone-marrow-derived receptor for advanced glycation end-products (RAGE) in a mouse model of diabetes-associated atherosclerosis

RAGE (receptor for advanced glycation end-products) is expressed on multiple cell types implicated in the progression of atherosclerosis and plays a role in DAA (diabetes-associated atherosclerosis). The aim of the present study was to determine the relative role of either BM (bone marrow)- or non-BM-derived RAGE in the pathogenesis of STZ (streptozotocin)-induced DAA. Male ApoE (apolipoprotein E)-null (ApoE-/-:RAGE+/+) and ApoE:RAGE-null (ApoE-/-:RAGE-/-) mice at 7 weeks of age were rendered diabetic with STZ. At 8 weeks of age, ApoE-/- and ApoE-/-:RAGE-/- control and diabetic mice received BM from either RAGE-null or RAGE-bearing mice, generating various chimaeras. After 10 and 20 weeks of diabetes, mice were killed and gene expression and atherosclerotic lesion formation were evaluated respectively. Deletion of RAGE in either the BM cells or non-BM cells both resulted in a significant attenuation in DAA, which was associated with reduced VCAM-1 (vascular cell adhesion molecule-1) expression and translated into reduced adhesion in vitro. In conclusion, the results of the present study highlight the importance of both BM- and non-BM-derived RAGE in attenuating the development of DAA.

Activated human mast cells induce LOX-1-specific scavenger receptor expression in human monocyte-derived macrophages

Objective

Activated mast cells in atherosclerotic lesions degranulate and release bioactive compounds capable of regulating atherogenesis. Here we examined the ability of activated human primary mast cells to regulate the expression of the major scavenger receptors in cultured human primary monocyte-derived macrophages (HMDMs).

Results

Components released by immunologically activated human primary mast cells induced a transient expression of lectin-like oxidized LDL receptor (LOX-1) mRNA in HMDMs, while the expression of two other scavenger receptors, MSR1 and CD36, remained unaffected. The LOX-1-inducing secretory components were identified as histamine, tumor necrosis factor alpha (TNF-α), and transforming growth factor beta (TGF-β1), which exhibited a synergistic effect on LOX-1 mRNA expression. Histamine induced a transient expression of LOX-1 protein. Mast cell –induced increase in LOX-1 expression was not associated with increased uptake of oxidized LDL by the macrophages.

Conclusions

Mast cell-derived histamine, TNF-α, and TGF-β1 act in concert to induce a transient increase in LOX-1 expression in human primary monocyte-derived macrophages. The LOX-1-inducing activity potentially endows mast cells a hitherto unrecognized role in the regulation of innate immune reactions in atherogenesis.

Adipose triglyceride lipase regulates eicosanoid production in activated human mast cells

Human mast cells (MCs) contain TG-rich cytoplasmic lipid droplets (LDs) with high arachidonic acid (AA) content. Here, we investigated the functional role of adipose TG lipase (ATGL) in TG hydrolysis and the ensuing release of AA as substrate for eicosanoid generation by activated human primary MCs in culture. Silencing of ATGL in MCs by siRNAs induced the accumulation of neutral lipids in LDs. IgE-dependent activation of MCs triggered the secretion of the two major eicosanoids, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). The immediate release of PGD2 from the activated MCs was solely dependent on cyclooxygenase (COX) 1, while during the delayed phase of lipid mediator production, the inducible COX-2 also contributed to its release. Importantly, when ATGL-silenced MCs were activated, the secretion of both PGD2 and LTC4 was significantly reduced. Interestingly, the inhibitory effect on the release of LTC4 was even more pronounced in ATGL-silenced MCs than in cytosolic phospholipase A2-silenced MCs. These data show that ATGL hydrolyzes AA-containing TGs present in human MC LDs and define ATGL as a novel regulator of the substrate availability of AA for eicosanoid generation upon MC activation.

Adaptive (T and B cells) immunity and control by dendritic cells in atherosclerosis

Chronic inflammation in response to lipoprotein accumulation in the arterial wall is central in the development of atherosclerosis. Both innate and adaptive immunity are involved in this process. Adaptive immune responses develop against an array of potential antigens presented to effector T lymphocytes by antigen-presenting cells, especially dendritic cells. Functional analysis of the role of different T-cell subsets identified the Th1 responses as proatherogenic, whereas regulatory T-cell responses exert antiatherogenic activities. The effect of Th2 and Th17 responses is still debated. Atherosclerosis is also associated with B-cell activation. Recent evidence established that conventional B-2 cells promote atherosclerosis. In contrast, innate B-1 B cells offer protection through secretion of natural IgM antibodies. This review discusses the recent development in our understanding of the role of T- and B-cell subsets in atherosclerosis and addresses the role of dendritic cell subpopulations in the control of adaptive immunity.

Serum tryptase: a new biomarker in patients with acute coronary syndrome?

BACKGROUND

Mast cell tryptase has recently been reported to be involved in atherosclerotic plaque destabilization. However, the results of these reports are conflicting.

METHODS

The aim of this study was to characterize the role of tryptase as a prognostic marker of patient cardiovascular complexity in acute coronary syndrome (ACS). Furthermore, its association with an angiographic scoring system [defined by the SYNergy between percutaneous coronary intervention (PCI) with the TAXUS drug-eluting stent and the cardiac surgery (SYNTAX) score] was examined. The serum tryptase was measured at admission in 65 consecutive ACS patients and in 35 healthy controls. In the patients with ACS, a composite measure of clinical and angiographic patient cardiovascular complexity was indicated by two of the following: clinical adverse events at hospitalization, at least 2 epicardial coronary arteries involved in the atherosclerotic disease, more than 1 stent implanted or more than 2 coronary artery disease risk factors.

RESULTS

The tryptase measurements were lower in patients without the composite measure (p < 0.0005). Linear regression showed a significant relationship between tryptase levels and the SYNTAX score (SX-score). Conversely, high-sensitivity troponin values did not correlate with either the composite outcome or the SX-score. The predictive accuracy of serum tryptase for the composite outcome was set at the cut-off point of 5.22 ng/ml (sensitivity 81% and specificity 95.7%).

CONCLUSION

In ACS patients, serum tryptase levels at admission may predict patient cardiovascular complexity more reliably than currently known biomarkers. Further studies are needed to demonstrate the long-term prognostic role of this biomarker in ACS.

A multimodal Darwinian strategy for alleviating the atherosclerosis pandemic

The conflict between our 'primitive' genes and 'modern' lifestyle probably lies at the root of several disorders that afflict modern man. Atherosclerosis, which is relatively unknown among contemporary hunter-gatherer populations, has reached pandemic proportions in recent times. Being an evolutionary problem with several inter-related pathologies, current therapeutic strategy for treating atherosclerosis has inherent limitations. Reviewing evolution-linked risk factors suggests that there are four aspects to the etiology of atherosclerosis namely, decreased intestinal parasitism, oversensitivity of evolutionarily redundant mast cells, chronic underactivation of AMPK (cellular energy sensor) and a deficiency of vitamin D. A combination of these four causes appear to have precipitated the atherosclerosis pandemic in modern times. Man and worms co-existed symbiotically in the past. Massive de-worming campaigns could have disrupted this symbiosis, increasing nutritional availability to man (pro-obesity) at the cost of decreased immunotolerance (pro-atherogenicity). A reduction in helminth-induced chronic TH2 activation could also have enhanced TH1 polarization, eventually disrupting the reciprocal regulation of TH1/TH2 balance and resulting in atherosclerosis. The riddance of helminth infestations may have rendered mast cells immunologically redundant, making them oversensitive to inflammatory stimuli, thereby playing a pro-atherogenic role. AMPK activation exerts pleiotropic anti-atherogenic effects, such as suppression of fatty acid, cholesterol, protein synthesis, reduction of vascular smooth muscle proliferation, etc. As energy deficit is the chief stimulus for AMPK activation, the over-nourished modern man appears to be suffering from chronic underactivation of AMPK, legitimising the unrivalled supremacy of metformin, the oldest prescribed antidiabetic drug. The fact that humans evolved in the sunny tropics suggests that humans are selected for high vitamin D levels. Vitamin D deficiency is now linked to several conditions including increased risk of CV disorders, diabetes, etc. The manifold decrease in vitamin D levels in modern man justifies a need for supplementation. We therefore hypothesize that a judicious combination of mast cell stabilization, AMPK activation, vitamin D supplementation, and moderation in hygiene practices could be an evolution-based multimodal strategy for both preventing and mitigating the pandemic of atherosclerosis.

Links between allergy and cardiovascular or hemostatic system

In addition to a well-known immunologic background of atherosclerosis and influences of inflammation on arterial and venous thrombosis, there is growing evidence for the presence of links between allergy and vascular or thrombotic disorders. In this interpretative review, five pretty well-documented areas of such overlap are described and discussed, including: (1) links between atherosclerosis and immunoglobulin E or atopy, (2) mutual effects of blood lipids and allergy, (3) influence of atopy and related disorders on venous thromboembolism, (4) the role of platelets in allergic diseases, and (5) the functions of protein C system in atopic disorders.

Immune mechanisms in atherosclerosis, especially in diabetes type 2

Atherosclerosis and ensuing cardiovascular disease (CVD) are major complications of diabetes type 2. Atherosclerosis is a chronic inflammatory condition involving immunocompetent cells of different types present in the lesions. Even though inflammation and immune activation may be more pronounced in atherosclerosis in diabetes type 2, there does not appear to be any major differences between diabetics and non-diabetics. Similar factors are thus implicated in atherosclerosis-associated immune activation in both groups. The cause of immune activation is not known and different mutually non-exclusive possibilities exist. Oxidized and/or enzymatically modified forms of low-density lipoprotein (OxLDL) and dead cells are present in atherosclerotic plaques. OxLDL could play a role, being pro-inflammatory and immunostimulatory as it activates T-cells and is cytotoxic at higher concentrations. Inflammatory phospholipids in OxLDL are implicated, with phosphorylcholine (PC) as one of the exposed antigens. Antibodies against PC (anti-PC) are anti-atherogenic in mouse studies, and anti-PC is negatively associated with development of atherosclerosis and CVD in humans. Bacteria and virus have been discussed as potential causes of immune activation, but it has been difficult to find direct evidence supporting this hypothesis, and antibiotic trials in humans have been negative or inconclusive. Heat shock proteins (HSP) could be one major target for atherogenic immune reactions. More direct causes of plaque rupture include cytokines such as interleukin 1β (IL-1β), tumor necrosis factor (TNF), and also lipid mediators as leukotrienes. In addition, in diabetes, hyperglycemia and oxidative stress appear to accelerate the development of atherosclerosis, one mechanism could be via promotion of immune reactions. To prove that immune reactions are causative of atherosclerosis and CVD, further studies with immune-modulatory treatments are needed.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Inflammation and immune system interactions in atherosclerosis

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, accounting for 16.7 million deaths each year. The underlying cause of the majority of CVD is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. Today's picture is far more complex. Atherosclerosis is considered a chronic inflammatory disease that results in the formation of plaques in large and mid-sized arteries. Both cells of the innate and the adaptive immune system play a crucial role in its pathogenesis. By transforming immune cells into pro- and anti-inflammatory chemokine- and cytokine-producing units, and by guiding the interactions between the different immune cells, the immune system decisively influences the propensity of a given plaque to rupture and cause clinical symptoms like myocardial infarction and stroke. In this review, we give an overview on the newest insights in the role of different immune cells and subtypes in atherosclerosis.

Immune effector mechanisms implicated in atherosclerosis: from mice to humans

According to the traditional view, atherosclerosis results from a passive buildup of cholesterol in the artery wall. Yet, burgeoning evidence implicates inflammation and immune effector mechanisms in the pathogenesis of this disease. Both innate and adaptive immunity operate during atherogenesis and link many traditional risk factors to altered arterial functions. Inflammatory pathways have become targets in the quest for novel preventive and therapeutic strategies against cardiovascular disease, a growing contributor to morbidity and mortality worldwide. Here we review current experimental and clinical knowledge of the pathogenesis of atherosclerosis through an immunological lens and how host defense mechanisms essential for survival of the species actually contribute to this chronic disease but also present new opportunities for its mitigation.

Role of mast cells in mucosal diseases: current concepts and strategies for treatment

Mast cells are well known for their role in type I hypersensitivity. However, their role in the immune system as well as their pathophysiological role in other diseases is underacknowledged. The role of mast cells in inflammatory bowel disease, allergic contact dermatitis and asthma is illustrated in this review. The contribution of mast cell activation in these diseases is controversial and two alternative means are proposed: activation via stress response pathways and immunoglobulin-free light chains. Activation of the mast cells leads to release of preformed mediators and to generation of other potent biological substances that have both physiological and pathophysiological effects. The role of these mediators in the aforementioned diseases is also outlined in this review. When the roles of mast cells are better understood, drugs specifically targeting mast cells may be developed to effectively treat a wide range of diseases.

Mast cells: from lipid droplets to lipid mediators

LDs (lipid droplets) are metabolically highly active intracellular organelles. The lipid and protein profiles of LDs are cell-type-specific, and they undergo dynamic variation upon changes in the physiological state of a cell. It is well known that the main function of the LDs in adipocytes is to ensure energy supply and to maintain lipid homoeostasis in the body. In contrast, LDs in inflammatory cells have been implicated in eicosanoid biosynthesis, particularly under inflammatory conditions, thereby enabling them to regulate immune responses. Human mast cells are potent effector cells of the innate immune system, and the triacylglycerol (triglyceride) stores of their cytoplasmic LDs have been shown to contain large amounts of arachidonic acid, the main precursor of pro-inflammatory eicosanoids. In the present review, we discuss the current knowledge about the formation and function of LDs in inflammatory cells with specific emphasis on arachidonic acid and eicosanoid metabolism. On the basis of findings reported previously and our new observations, we propose a model in which lipolysis of LD-triacylglycerols provides arachidonic acid for lipid mediator generation in human mast cells.

Tryptase promotes atherosclerotic plaque haemorrhage in ApoE-/- mice

Tryptase, the most abundant mast cell (MC) granule protein, plays an important role in atherosclerosis plaque development. To test the hypothesis that tryptase participates directly in atherosclerosis plaque haemorrhage, the gene sequence and siRNA for tryptase were cloned into a lentivirus carrier and atherosclerosis plaque haemorrhage models in ApoE-/- mice were constructed. After a cuffing-cervical artery operation, the mice were randomly divided into 6 groups. Hematoxylin and eosin(HE) staining showed that the cervical artery plaque area was much larger in the tryptase overexpression group compared to the other groups, and there was greater artery stenosis. The artery stenosis from the cuff-side in all groups was more than 90%, except the siRNA group. Tryptase promotes plaque haemorrhage distinctively because 50% of the mice in the tryptase overexpression group had plaque haemorrhage, while only 10% in the siRNA group did. The immunohistochemistry of the cervical artery plaque showed that plasminogen activator inhibitor-1 (PAI-1) expression was the lowest while tissue plasminogen activator (tPA), CD31, CD34 and VEGF was the highest in the tryptase overexpression groups. This observation was completely contrary to what was observed in the siRNA group. Tryptase promoted bEnd.3 cell growth, migration and capillary-like tube formation, which suggests that tryptase can promote microvessel angiogenesis. PAI-1 expression was inhibited, while tPA expression was increased by tryptase in bEnd.3 cells. Our in vivo and in vitro studies suggest that trypase can promote atherosclerotic plaque haemorrhage by promoting angiogenesis and regulating the balance of PAI-1 and tPA. Thus, regulating tryptase expression in MCs may provide a potential target for atherosclerosis treatment.

Mast cells and vascular diseases

Mast cells are increasingly being recognized as effector cells in many cardiovascular conditions. Many mast-cell-derived products such as tryptase and chymase can, through their enzymic action, have detrimental effects on blood vessel structure while mast cell-derived mediators such as cytokines and chemokines can perpetuate vascular inflammation. Mice lacking mast cells have been developed and these are providing an insight into how mast cells are involved in cardiovascular diseases and, as knowledge increase, mast cells may become a viable therapeutic target to slow progression of cardiovascular disease.

Tryptase serum levels in patients suffering from hepatocellular carcinoma undergoing intra-arterial chemoembolization: Possible predictive role of response to treatment

Tryptase is a serin protease stored in mast cell granules that has recently been found to be involved in tumor angiogenesis. Data from experimental tumor models have suggested that prior to the onset of angiogenesis mast cells were accumulated near tumor cells and were required for the macroscopic expansion and metastatic spread of primary tumor cells. Hepatocellular cancer (HCC) is a well-established, highly angiogenesis-dependent hypervascular tumor. The aim of this preliminary study was to assess tryptase serum levels in 30 HCC patients prior and subsequent to hepatic transarterial chemoembolization (TACE). In this study, patients with intermediate stage (B) HCC, according to the Barcelona Clinic Liver Cancer (BCLC) staging classification, were enrolled. Additional patient features were adequate liver functional reserve and A or B status, according to the Child-Pugh classification. Tryptase levels were measured using the UniCAP-Tryptase fluoroimmunoassay. TACE was performed by loading doxorubicin on microspheres. The mean ± standard deviation (SD) tryptase level pre-TACE was 7.74±3.62 μg/l, and post-TACE 4.67±2.79 μg/l. A statistically significant difference (P<0.001) was detected, using the Student's t-test, between pre- and post-TACE tryptase level concentrations. No correlations were found between tryptase levels and other important clinicopathological features of patients. This is the first preliminary study analyzing the potential significance of serum tryptase levels in HCC patients. The results demonstrated higher serum tryptase levels in HCC patients, suggesting tryptase release from HCC tissue. As expected, after TACE, serum tryptase levels were decreased. Therefore, we suggested that tryptase was a potential biomarker of response to TACE treatment in HCC patients.