Histamine as an activator of cell growth and extracellular matrix reconstruction for human vascular smooth muscle cells

The Inhibition of Prolyl Oligopeptidase as New Target to Counteract Chronic Venous Insufficiency: Findings in a Mouse Model

(1) Background: Chronic venous insufficiency (CVI) is a common disorder related to functional and morphological abnormalities of the venous system. Inflammatory processes and angiogenesis alterations greatly concur to the onset of varicose vein. KYP-2047 is a selective inhibitor of prolyl oligopeptidase (POP), a serine protease involved in the release of pro-angiogenic molecules. The aim of the present study is to evaluate the capacity of KYP-2047 to influence the angiogenic and inflammatory mechanisms involved in the pathophysiology of CVI. (2) Methods: An in vivo model of CVI-induced by saphene vein ligation (SVL) and a tissue block culture study were performed. Mice were subjected to SVL followed by KYP-2047 treatment (intraperitoneal, 10 mg/kg) for 7 days. Histological analysis, Masson's trichrome, Van Gieson staining, and mast cells evaluation were performed. Release of cytokines, nitric oxide synthase production, TGF-beta, VEGF, α-smooth muscle actin, PREP, Endoglin, and IL-8 quantification were investigated. (3) Results: KYP-2047 treatment ameliorated the histological abnormalities of the venous wall, reduced the collagen increase and modulated elastin content, lowered cytokines levels and prevented mast degranulation. Moreover, a decreased expression of TGF-beta, eNOS, VEGF, α-smooth muscle actin, IL-8, and PREP was observed in in vivo study; also a reduction in VEGF and Endoglin expression was confirmed in tissue block culture study. (4) Conclusions: For the first time, this research, highlighting the importance of POP as new target for vascular disorders, revealed the therapeutic potential of KYP-2047 as a helpful treatment for the management of CVI.

Critical in vivo roles of histamine and histamine receptor signaling in animal models of metabolic syndrome

Histamine, a classic low-molecular-weight amine, is synthesized from L-histidine by histidine decarboxylase (HDC), and histamine-specific receptors (HRs) are essential for its actions. Our serial in vivo studies have uniquely reported that expression of histamine/HRs is variably identified in atherosclerotic lesions, and that HDC-gene knockout mice without histamine/HRs signaling show a marked reduction of atherosclerotic progression. These data have convinced us that histamine plays a pivotal role in the pathogenesis of atherosclerosis. Among four subclasses of HRs, the expression profile of the main receptors (H1/2R) has been shown to be switched from H2R to H1R during monocyte to macrophage differentiation, and H1R is also predominant in smooth muscle and endothelial cells of atheromatous plaque. Using various animal models of H1/2R-gene knockout mice, H1R and H2R were found to reciprocally but critically regulate not only hypercholesterolemia-induced atherosclerosis and injury-induced arteriosclerosis, but also hyperlipidemia-induced nonalcoholic fatty liver disease (NAFLD). Metabolic syndrome manifests obesity, dyslipidemia, insulin resistance, atherosclerosis, and/or NAFLD, i.e. the dysregulation of lipid/bile acid/glucose metabolism. Therefore, although its etiology is complicated and multifactorial, histamine/HRs signaling has a close relationship with the development of metabolic syndrome. We herein review diverse, key in vivo roles of histamine/HR signaling in the pathogenesis of metabolic syndrome.

Oxidized low-density lipoprotein contributes to atherogenesis via co-activation of macrophages and mast cells

Oxidized low-density lipoprotein (OxLDL) is a risk factor for atherosclerosis, due to its role in endothelial dysfunction and foam cell formation. Tissue-resident cells such as macrophages and mast cells release inflammatory mediators upon activation that in turn cause endothelial activation and monocyte adhesion. Two of these mediators are tumor necrosis factor (TNF)-α, produced by macrophages, and histamine, produced by mast cells. Static and microfluidic flow experiments were conducted to determine the number of adherent monocytes on vascular endothelium activated by supernatants of oxLDL-treated macrophages and mast cells or directly by oxLDL. The expression of adhesion molecules on activated endothelial cells and the concentration of TNF-α and histamine in the supernatants were measured by flow cytometry and enzyme-linked immunosorbent assay, respectively. A low dose of oxLDL (8 μg/ml), below the threshold for the clinical presentation of coronary artery disease, was sufficient to activate both macrophages and mast cells and synergistically increase monocyte-endothelium adhesion via released TNF-α and histamine. The direct exposure of endothelial cells to a much higher dose of oxLDL (80 μg/ml) had less effect on monocyte adhesion than the indirect activation via oxLDL-treated macrophages and mast cells. The results of this work indicate that the co-activation of macrophages and mast cells by oxLDL is an important mechanism for the endothelial dysfunction and atherogenesis. The observed synergistic effect suggests that both macrophages and mast cells play a significant role in early stages of atherosclerosis. Allergic patients with a lipid-rich diet may be at high risk for cardiovascular events due to high concentration of low-density lipoprotein and histamine in arterial vessel walls.

Ca(2+) signals evoked by histamine H1 receptors are attenuated by activation of prostaglandin EP2 and EP4 receptors in human aortic smooth muscle cells

BACKGROUND AND PURPOSE

Histamine and prostaglandin E2 (PGE2 ), directly and via their effects on other cells, regulate the behaviour of vascular smooth muscle (VSM), but their effects on human VSM are incompletely resolved.

EXPERIMENTAL APPROACH

The effects of PGE2 on histamine-evoked changes in intracellular free Ca(2+) concentration ([Ca(2+) ]i ) and adenylyl cyclase activity were measured in populations of cultured human aortic smooth muscle cells (ASMCs). Selective ligands of histamine and EP receptors were used to identify the receptors that mediate the responses.

KEY RESULTS

Histamine, via H1 receptors, stimulates an increase in [Ca(2+) ]i that is entirely mediated by activation of inositol 1,4,5-trisphosphate receptors. Selective stimulation of EP2 or EP4 receptors attenuates histamine-evoked Ca(2+) signals, but the effects of PGE2 on both Ca(2+) signals and AC activity are largely mediated by EP2 receptors.

CONCLUSIONS AND IMPLICATIONS

Two important inflammatory mediators, histamine via H1 receptors and PGE2 acting largely via EP2 receptors, exert opposing effects on [Ca(2+) ]i in human ASMCs.

Histamine induces activation of protein kinase D that mediates tissue factor expression and activity in human aortic smooth muscle cells

Histamine, an inflammatory mediator, has been shown to influence the pathogenesis of vascular wall cells. However, the molecular basis of its influence is not well understood. Our data reveal that histamine markedly induces protein kinase D (PKD) activation in human aortic smooth muscle cells. PKD belongs to a family of serine/threonine protein kinases, and its function in vascular disease is largely unknown. Our data show that histamine-induced PKD phosphorylation is dependent on the activation of histamine receptor 1 and protein kinase C (PKC). To determine the role of PKD in the histamine pathway, we employed a small-interfering RNA approach to downregulate PKD expression and found that PKD1 and PKD2 are key mediators for expression of tissue factor (TF), which is the key initiator of blood coagulation and is important for thrombosis. Our results show that PKD2 predominantly mediates histamine-induced TF expression via the p38 mitogen-activated protein kinase (MAPK) pathway, whereas PKD1 mediates histamine-induced TF expression through a p38 MAPK-independent pathway. We demonstrate that histamine induces TF expression via the PKC-dependent PKD activation. Our data provide the first evidence that PKD is a new component in histamine signaling in live cells and that PKD has a novel function in the histamine signaling pathway leading to gene expression, as evidenced by TF expression. Importantly, our data reveal a regulatory link from histamine to PKD and TF, providing new insights into the mechanisms of coagulation and the development of atherothrombosis.

Histamine H1 receptor promotes atherosclerotic lesion formation by increasing vascular permeability for low-density lipoproteins

OBJECTIVE

Enhanced endothelial permeability leading to intimal accumulation of low-density lipoproteins (LDL) stimulates the formation of atherosclerotic lesions. Histamine is known to increase vascular permeability. Whether this affects the formation of atherosclerotic lesions, however, remains elusive.

METHODS AND RESULTS

Apolipoprotein E-null (ApoE(-/-)) mice treated with a histamine H1 receptor but not an H2 receptor antagonist developed 40% fewer atherosclerotic lesions in the aorta than placebo-treated controls. Similarly, genetic deletion of the H1 but not the H2 receptor resulted in a 60% reduction of lesions compared with ApoE(-/-) controls. The H1 receptor enhanced LDL permeability and lipid accumulation in the aorta, whereas plasma lipoprotein levels remained unaltered. In contrast, the H1 receptor did not affect proliferation and migration of vascular smooth muscle cells. Bone marrow transplantation confirmed that the formation of atherosclerotic lesions depended on the H1 receptor in vascular cells, whereas its presence in bone marrow-derived cells was irrelevant for plaque development. Mice expressing the H1 receptor exhibited higher levels of the chemokine (C-C motif) ligand 5 and higher numbers of macrophages and T-helper lymphocytes in plaques, higher numbers of circulating lymphocytes, and larger spleens.

CONCLUSION

These data indicate that H1 but not H2 receptor activation drives the formation of atherosclerotic lesions through an increased vascular permeability for LDL, which is associated with an enhanced secondary aortic and systemic inflammation. These data open novel perspectives for the prevention and treatment of atherosclerotic vascular disease.

Histamine induces Egr-1 expression in human aortic endothelial cells via the H1 receptor-mediated protein kinase Cdelta-dependent ERK activation pathway

Histamine, a potent inflammatory mediator, has multiple effects on the pathogenesis of atherosclerosis. This study investigates the effect of histamine on the expression of early growth response factor 1 (Egr-1), a master transcription factor that regulates the expression of an array of atherogenic genes in atherosclerotic lesions. Histamine markedly and rapidly induces Egr-1 mRNA and protein expression in primary human aortic endothelial cells (HAECs). Histamine-induced Egr-1 expression is dependent on the activation of the H1 receptor. Histamine also rapidly and transiently activates protein kinase C-delta (PKCdelta), extracellular signal-regulated kinase (ERK)1/2, p38 kinase, and c-Jun N-terminal kinase (JNK) prior to Egr-1 induction. Using specific pharmacological inhibitors and small interfering RNA technology, we determined that PKCdelta and ERK, but not p38 and JNK, mediate histamine-induced Egr-1 expression. Our data provide the first evidence that histamine regulates expression of Egr-1 in mammalian cells and demonstrate a novel role of PKCdelta in up-regulation of Egr-1 expression. The present study reveals the following regulatory mechanism: histamine up-regulates Egr-1 expression in primary HAECs via the H1 receptor and the PKCdelta-dependent ERK activation pathway. Our data also imply that CREB, a downstream component of the ERK pathway, regulates Egr-1 expression in HAECs. Importantly, these results suggest a central role of Egr-1 in histamine-induced gene expression and in histamine-induced vascular disease.

Histamine upregulates the expression of inducible nitric oxide synthase in human intimal smooth muscle cells via histamine H1 receptor and NF-kappaB signaling pathway

OBJECTIVE

Histamine increases endothelial nitric oxide (NO) production as an endothelium-dependent vasodilator, which acts as a vasoconstrictor in atherosclerotic coronary arteries. To investigate the relation between histamine and NO production in intimal smooth muscle cells (SMCs), we studied the effect of histamine on inducible NO synthase (iNOS) expression in the SMCs.

METHODS AND RESULTS

In cultured human intimal SMCs, histamine increased NO production, iNOS expression, and NF-kappaB nuclear translocation, which were inhibited by histamine H1 blocker and NF-kappaB inhibitor. Luciferase assay using -8.3 kb upstream of human iNOS promoter region and electrophoretic mobility shift assay suggested that a NF-kappaB motif located at -3922 to -3914 would be necessary for histamine-inducible promoter activity. In addition, H1 blocker, NF-kappaB inhibitor, and dominant negative IkappaB alpha or IkappaB kinase beta downregulated the histamine-induced iNOS promoter activity. In the human aorta, histamine content was estimated to be 310+/-66 pmol/mg protein in the atherosclerotic intima, while that was to be 43+/-22 pmol/mg protein in the media (P<0.001).

CONCLUSIONS

Histamine stimulates intimal SMCs to increase iNOS expression via H1 receptors and NF-kappaB signaling pathway. Histamine could be one of NO-regulating factors, by inducing iNOS expression in intimal SMCs, and may be related to atherogenesis.

Stimulation of histamine H1 receptor up-regulates histamine H1 receptor itself through activation of receptor gene transcription

Histamine is a major mediator in allergy acting mainly through the histamine H(1) receptor (H1R). Although H1R up-regulation has been suggested as an important step for induction of allergic symptoms, little is known about the regulation of H1R level. Here we report that the activation of H1R up-regulates H1R through augmentation of H1R mRNA expression in HeLa cells. Histamine stimulation significantly increased both H1R promoter activity and mRNA level without alteration in mRNA stability. H1R protein was also up-regulated by histamine. An H1R antagonist but not histamine H(2) receptor antagonist blocked histamine-induced up-regulation of both promoter activity and mRNA expression. A protein kinase C (PKC) activator, phorbol-12-myristate-13-acetate, increased H1R mRNA expression, whereas an activator of PKA or PKG (8-Br-cAMP or 8-Br-cGMP, respectively) did not. Furthermore, histamine-induced up-regulation of both promoter activity and mRNA level were completely suppressed by the PKC inhibitor Ro-31-8220. H1R antagonists have long been thought to block H1R and inhibit immediate allergy symptoms. In addition to this short-term effect, our data propose their long-term inhibitory effect against allergic diseases by suppressing PKC-mediated H1R gene transcription. This finding provides new insights into the therapeutic target of H1R antagonist in allergic diseases.

Localized expression of histamine H1 receptors in syncytiotrophoblast cells of human placenta

The previous Northern blot analysis and in situ hybridization studies showed that histamine H1-receptor (H1R) mRNA is expressed in human placenta and suggested that H(1)R plays some roles in the function of placenta in pregnancy. To investigate further, it is essential to show the precise location of H1R in the placenta. In the present study, we investigated H1R expression in human placenta by radioligand binding assay and immunohistochemical study using an antibody against human H1R. Placentas were obtained from normal uncomplicated deliveries. Membranes prepared from the tissue exhibited saturable [3H]mepyramine binding (K(d) = 4.0 +/- 0.6 nM and B(max) = 91.4 +/- 4.9 fmol/mg of protein). Stereoisomers of chlorpheniramine inhibited [(3)H]mepyramine binding; d-chlorpheniramine inhibited more potently than l-chlorpheniramine, K(i) values being 1.1 +/- 0.4 and 270 +/- 170 nM, respectively. The placenta tissues were positively immunostained with anti-H1R antibody only in the region of the syncytiotrophoblast of chorionic villus. The tissues were double stained with anti-H1R antibody and an antibody against human chorionic gonadotoropin (hCG) that is solely expressed in placental syncytiotrophoblast cells. The results showed that H1R and hCG were expressed on the same cells, that is, syncytiotrophoblast cells. These results indicate that H1Rs are specifically expressed in syncytiotrophoblast cells of human placenta organ.

Histamine Network in Atherosclerosis

Histamine is a low-molecular-weight amine, synthesized from l-histidine by histidine decarboxylase. It has been suggested that the histamine is produced in the atherosclerotic lesion although the activity of histamine has not been clarified completely. To avoid the pharmacologic problems, genetically engineered mice are useful. We recently observed the histidine decarboxylase-gene knockout mice ameliorates' atherosclerotic region, compared with that of the wild-type control mice. The source of histamine in atherosclerotic lesion should be clarified in details; however, it could be macrophage, endothelial cells, and mast cells. All four types of histamine receptors (H1-H4) have the possibilities to be involved in the atherosclerotic regions. Because H1 and H2 receptors are discovered previously, the activities through those receptors are investigated relatively well, but as the other two types of receptors have been cloned recently, their involvement in atherosclerotic lesion should be investigated further.

Marked increase in the histamine content of neointima after stent implantation of pig coronary artery and growth-promoting effects of histamine in cultured smooth muscle cells

After coronary stent implantation, the unfavorable in-stent restenosis often occurs by the formation of neointima due to the proliferation of smooth muscle cells. Platelet-derived growth factor (PDGF) and other peptide growth factors contribute to this process, but little is known about the role of non-peptide factors in this process. In the present study, the role of histamine, a non-peptide factor, in the formation of neointima was investigated using a pig coronary model of in-stent restenosis and a culture system of coronary smooth muscle cells. A Palmaz-Schatz stent was implanted in the left anterior descending coronary artery of male pigs. At 1, 2 and 4 weeks after stenting, the histamine content of neointima was determined to be 326 +/- 82, 1427 +/- 280 and 440 +/- 69 pmol/mg protein, respectively, by HPLC fluorometry. In contrast, the histamine content of arterial media from the untreated control arteries was only 15.3 +/- 1.6 pmol/mg protein. These results demonstrate that the histamine content of neointima is about 20 to 90-fold that of the normal media. In vitro, histamine by itself did not stimulate the proliferation of cultured smooth muscle cells, but potentiated the PDGF-stimulated proliferation of the cultured cells via a mechanism independent of H1 and H2 histamine receptors. Thus, histamine may be an important non-peptide factor in the pathogenesis of in-stent restenosis.

Role of histamine produced by bone marrow-derived vascular cells in pathogenesis of atherosclerosis

To clarify the role of histamine-producing cells and its origin in atherosclerosis, we investigated histidine decarboxylase (HDC; histamine-producing enzyme) expression in murine arteries with vascular injuries after the animal had received transplanted bone marrow (BM) from green fluorescent protein (GFP)-transgenic mice. The neointima in the ligated carotid arteries contained BM-derived HDC+ cells that expressed macrophage (Mac-3) or smooth muscle cell antigen (alpha-SMA). In contrast, the HDC+ BM-derived cells, which were positive for Mac-3, were mainly located in the adventitia in the cuff replacement model. In apolipoprotein E-knockout mice on a high cholesterol diet, BM-derived cells expressing Mac-3 in the atheromatous plaques were also positive for HDC. In comparison with wild-type mice, HDC-/- mice showed reduced neointimal thickening and a decreased intima-to-media ratio after ligation and cuff replacement. These results indicate that histamine produced from BM-derived progenitor cells, which could transdifferentiate into SMC- or macrophage-like cells, are important for the formation of neointima and atheromatous plaques.

Granulocyte Macrophage–Colony Stimulating Factor Increases the Expression of Histamine and Histamine Receptors in Monocytes/Macrophages in Relation to Arteriosclerosis

OBJECTIVE

To study the effect of granulocyte macrophage-colony-stimulating factor (GM-CSF) on histamine metabolism in arteriosclerosis, the expression of histidine decarboxylase (HDC; histamine-producing enzyme), histamine receptors 1 and 2 (HH1R and HH2R), and GM-CSF was investigated in human and mouse arteriosclerotic carotid arteries. Furthermore, the molecular mechanisms of GM-CSF-induced HDC and HH1R expression in monocytic U937 cells were investigated.

METHODS AND RESULTS

Immunohistochemistry showed that atherosclerotic human coronary and mouse ligated carotid arteries contained HDC-expressing macrophages. Gene expression of HDC, HH1R, HH2R, and GM-CSF was also detected in the lesions. In U937 cells, GM-CSF enhanced histamine secretion and gene expression of HDC and HH1R. A promoter assay showed that GM-CSF enhanced gene transcription of HDC and HH1R but not HH2R.

CONCLUSIONS

The present results indicate that HDC and HHR are expressed in arteriosclerotic lesion, and that GM-CSF induces HDC and HH1R expression in monocytes. Locally produced histamine might participate in atherogenesis by affecting the expression of atherosclerosis-related genes in monocytes and smooth muscle cells. The presence of histamine-producing macrophages and gene expression of histamine receptors and GM-CSF was demonstrated in arteriosclerotic lesions. In monocytic U937 cells, GM-CSF upregulated the expression of histamine and HH1R. Coordinated expression of histamine and its receptors by GM-CSF would participate in atherogenesis by affecting monocytic and SMC gene expression.

Acute inflammatory reactions caused by histamine via monocytes/macrophages chronically participate in the initiation and progression of atherosclerosis

Previously we demonstrated that histidine decarboxylase (HDC), which produces histamine from l-histidine, was detected in monocytes/macrophages located in human atherosclerotic lesions. As monocytic migration is a key event of atherogenesis, we investigated whether histamine induces monocytic expression of monocyte chemoattractant protein (MCP)-1 and its receptors CCR2-A and -B, and also endothelial expression of ICAM-1 and VCAM-1. Furthermore, we studied the effect of interleukin (IL)-4, which inhibits the HDC expression, on the expression of MCP-1 and CCR2. Histamine stimulated monocytes, but not macrophages, to express MCP-1 and CCR2-A and -B. The expression of MCP-1 was inhibited by histamine H2 blocker. In contrast, IL-4 enhanced CCR2 expression but not MCP-1. Histamine stimulated endothelial cells to express ICAM-1 and VCAM-1. These results indicate that histamine and IL-4, which are both synthesized in the arterial intima, chronically participates in the pathogenesis of atherosclerosis via the enhanced expression of monocytic MCP-1, CCR2 and endothelial adhesion molecules.

Role of macrophage-derived histamine in atherosclerosis-- chronic participation in the inflammatory response --

The atherosclerotic intimal lesion contains endothelial cells, smooth muscle cells, monocytes/macrophages and T lymphocytes, which constitute a histamine-cytokine network that participates in chronic inflammatory responses. Monocytes/macrophages and T lymphocytes express the histamine-producing enzyme histidine decarboxylase (HDC), and specific histamine receptors (HHR), which are switched from HH2R to HHR1 during macrophage differentiation. Endothelial and smooth muscle cells also express HHR in response to histamine. The effects of histamine on these cells include a regulation of atherosclerosis-related events such as cell proliferation, expression of matrix metalloproteinase, adhesion molecules and cytokines. Furthermore, recent studies have indicated that histamine and the activation of its specific receptors modulate the Th1/Th2 balance in inflammatory lesions through the regulation of cytokine production from inflammatory cells. The histamine-cytokine network in the atherosclerotic intima could regulate inflammatory and immune responses, including Th1/Th2 balance, and contribute to atherogenesis.

H1-receptor stimulation induces hyperalgesia through activation of the phospholipase C-PKC pathway

The supraspinal cellular events involved in H(1)-mediated hyperalgesia were investigated in a condition of acute thermal pain by means of the mouse hot-plate test. I.c.v. administration of the phospholipase C (PLC) inhibitors U-73122 and neomycin antagonized the hyperalgesia induced by the selective H(1) agonist FMPH. By contrast, U-73343, an analogue of U-73122 used as negative control, was unable to modify the reduction of the pain threshold induced by FMPH. In mice undergoing treatment with LiCl, which impairs phosphatidylinositol synthesis, or treatment with heparin, an IP(3)-receptor antagonist, the hyperalgesia induced by the H(1)-receptor agonist remained unchanged. Similarly, pretreatment with D-myo inositol did not alter the H(1)-induced hypernociceptive response. Neither i.c.v. pretreatment with TMB-8, a blocker of Ca(2+) release from intracellular stores, nor pretreatment with thapsigargin, a depletor of Ca(2+) intracellular stores, prevented the decrease of pain threshold induced by FMPH. On the other hand, i.c.v. pretreatment with the selective protein kinase C (PKC) inhibitors calphostin C and chelerytrine resulted in a dose-dependent prevention of the H(1)-receptor agonist-induced hyperalgesia. The administration of PKC activators, such as PMA and PDBu, did not produce any effect on FMPH effect. The pharmacological treatments employed did not produce any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate a role for the PLC-PKC pathway in central H(1)-induced hyperalgesia in mice. Furthermore, activation of PLC-IP(3) did not appear to play a major role in the modulation of pain perception by H(1)-receptor agonists.

Effects of histamine on functional maturation of dendritic cells

There is increasing evidence that histamine affects dendritic cell (DC) activation, maturation, and preference for Th1/Th2 differentiation. In this paper we report that histamine affects interleukin (IL)-12 and IL-6 production in an immature DC (iDC) line derived from murine spleen. Histamine treatment of iDC significantly increased the IL-12 p40 mRNA and protein levels compared to histamine untreated iDC. In the presence of tumor necrosis factor (TNF)-alpha histamine also increased IL-12 p40 and IL-6 production. However, histamine significantly decreased IL-12 p40 production by lipopolysaccharide (LPS)-stimulated DC in a concentration dependent manner. When expressions of histamine H1 (H1R) and H2 (H2R) receptors in DC were analyzed by RT-PCR, both receptors were down-regulated after LPS or TNF-alpha stimulation compared to unstimulated iDC. Histamine treatment significantly increased the expression of H2R mRNA in iDC and H1R mRNA in LPS-activated DC. However, histamine treatment decreased the expression of both histamine receptors in TNF-alpha-stimulated DC. Similar results were obtained by flow cytometry with FITC-conjugated histamine. These results demonstrate that histamine can regulate the expression of its own receptors and activate iDC, which may influence subsequent functional states of mature DC in a maturation signal-dependent manner. Consequently, histamine may contribute to an immune response outcome.

Histamine increases the expression of LOX-1 via H2 receptor in human monocytic THP-1 cells

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a member of the scavenger receptor family, and is known to be expressed in monocytes/macrophages. We investigated the effect of histamine on the expression of LOX-1 in cells of the human monocytic leukemia cell line THP-1. Histamine as well as forskolin and dibutyryl cyclic AMP (Bt2-cAMP) stimulated the THP-1 monocytes to express the LOX-1 gene at the transcription level. This histamine effect on LOX-1 gene expression, via the histamine H2 receptor-mediated cAMP signal transduction pathway, was reduced after differentiation of the cells into macrophages, even though forskolin and Bt2-cAMP still enhanced the gene expression. The alteration of the responsiveness of LOX-1 expression to histamine was related to suppressed expression of the H2 receptor in THP-1 macrophages. The switch of the predominant class of histamine receptors between H1 and H2 would modulate the effects of histamine on LOX-1 gene expression in monocytes and macrophages, and therefore, would play a certain role in the inflammatory aspects of atherogenesis.

Phosphatidylinositol 3-OH kinase-Akt/protein kinase B pathway mediates Gas6 induction of scavenger receptor a in immortalized human vascular smooth muscle cell line

The growth arrest-specific gene 6 encodes a secreted protein, Gas6, which was originally identified as the ligand of a receptor, Axl, with tyrosine kinase activity. The class A scavenger receptor (SRA) mediates lipid uptake into cells, leading to the formation of foam cells, an important step in atherogenesis. Although Gas6 induces SRA expression, the underlying mechanism is not clear. In this report, we show that the Gas6-induced expression of SRA was mediated by the phosphatidylinositol 3-OH kinase (PI3-kinase)-serine/threonine kinase (Akt/protein kinase B [PKB]) pathway involving Akt phosphorylation. This pathway was activated by exposure to Gas6. Furthermore, the effect of Gas6 was abrogated by wortmannin, a specific inhibitor of PI3-kinase. We also demonstrated that the constitutively active form of Akt enhanced activity of the SRA promoter but that the dominant-negative mutant of Akt completely abolished the expression of SRA after treatment with Gas6. These results show that the PI3-kinase-Akt/PKB pathway participates in Gas6-induced SRA expression and suggests that the activation of Akt/PKB plays an important role in Gas6-induced atherosclerosis and foam cell formation in human vascular smooth muscle cells.

Effects of histamine and interleukin-4 synthesized in arterial intima on phagocytosis by monocytes/macrophages in relation to atherosclerosis

We investigated the localization of histidine decarboxylase (HDC), which is the rate-limiting enzyme that generates histamine from histidine, in human aorta/coronary artery. RT-PCR and immunohistochemical staining revealed that the HDC gene was expressed in monocytes/macrophages and T cells in the arterial intima but not in smooth muscle cells in either the arterial intima or the media. A luciferase promoter assay with U937 and Jurkat cells demonstrated that interleukin-4 (IL-4) inhibited the expression of the HDC gene. In contrast, among a scavenger receptor family, IL-4 as well as histamine up-regulated U937 cells to express the LOX-1 gene but not the SR-A gene, which genes encode receptors that scavenge oxidized lipids. These findings suggest that histamine synthesized in the arterial wall participates in the initiation and progression of atherosclerosis and that IL-4 can act as an important inhibitory and/or stimulatory factor in the function of monocytes/macrophages modulated by histamine in relation to the process of atherosclerosis.

Role of protein kinase Calpha in signaling from the histamine H(1) receptor to the nucleus

Stimulation of histamine H(1) receptors produced a marked activation of inositol phospholipid hydrolysis, intracellular calcium mobilization, and stimulation of the c-fos promoter in CHO-H1 cells expressing the H(1) receptor at a level of 3 pmol/mg protein. The latter response was determined using a luciferase-based reporter gene (pGL3). This response to histamine was not sensitive to inhibition by pertussis toxin but could be completely attenuated by the protein kinase C (PKC) inhibitor Ro-31-8220, or by 24-h pretreatment with the phorbol esters phorbol 12,13-dibutyrate or phorbol-12-myristate-13-acetate. Several isoforms of PKC can be detected in CHO-H1 cells (alpha, delta, epsilon, mu, iota, zeta) but only PKCalpha and PKCdelta were down-regulated by prolonged treatment with phorbol esters. Of the two isoforms that were down-regulated, only protein kinase Calpha was translocated to CHO-H1 cell membranes after stimulation with either histamine or phorbol esters. The PKC inhibitor Gö 6976, which inhibits PKCalpha but not PKCdelta, was also able to significantly attenuate the c-fos-luciferase response to histamine. The mitogen-activated protein kinase kinase inhibitor PD 98059 markedly inhibited the response to histamine, suggesting that the likely major target for PKCalpha was the mitogen-activated protein kinase pathway. These data suggest that the histamine H(1) receptor can signal to the nucleus via PKCalpha after activation of phospholipase Cbeta.

Switch of histamine receptor expression from H2 to H1 during differentiation of monocytes into macrophages

It is known that histamine suppresses gene expression and synthesis of tumor necrosis factor alpha (TNF-alpha) induced by lipopolysaccharide (LPS) in human peripheral blood mononuclear monocytes (HPM) or alveolar macrophages via histamine H2 receptors. We investigated the effect of histamine and differentiation in macrophages on the expression and secretion of TNF-alpha, TNF-alpha-converting enzyme (TACE), and histamine H1 and H2 receptors by use of a leukemia cell line, U937, and HPM. Differentiation of U937 and HPM cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) enhanced the H1 receptor expression and rather suppressed the H2 receptor, resulting in up-regulation of the histamine-induced expression and secretion of TNF-alpha, modulated via TACE. Therefore, histamine failed to inhibit up-regulated expression of TNF-alpha induced by LPS in macrophages. The switch from H2 to H1 receptors during differentiation in the monocyte/macrophage lineage could participate in the pathogenic processes of atherosclerosis and inflammatory reactions in the arterial wall.

Therapeutic potential of matrix metalloproteinase inhibitors in atherosclerosis

The activity of matrix-degrading metalloproteinases (MMPs) is essential for many of the processes involved in atherosclerotic plaque formation, for example, infiltration of inflammatory cells, smooth muscle cell migration and proliferation and angiogenesis. Furthermore, matrix degradation by MMPs may cause the plaque instability and rupture that leads to the clinical symptoms of atherosclerosis; unstable angina, myocardial infarction and stroke. Together, the family of MMPs can degrade all of the components of the blood vessel extracellular matrix and their activity therefore, is tightly regulated in normal blood vessels. The increased MMP activity during atherosclerotic plaque development and instability must therefore be caused by increased cytokine and growth factor-stimulated gene transcription, elevated zymogen activation and an imbalance in the MMP:TIMP ratio. It is therefore conceivable that inhibition of MMPs or re-establishing the MMP:TIMP balance may be useful in treating the symptoms of atherosclerosis. Recent studies using synthetic MMP inhibitors and gene therapy have highlighted the potential of such an approach.

Heparin proteoglycans released from rat serosal mast cells inhibit proliferation of rat aortic smooth muscle cells in culture

-Mast cells are present in the human arterial intima. To study whether mast-cell degranulation influences the rate of proliferation of smooth muscle cells, we cocultured sensitized (IgE-bearing) rat serosal mast cells and rat aortic smooth muscle cells (SMCs). When sensitized mast cells were stimulated to degranulate with antigen, the rate of proliferation of the cocultured SMCs decreased sharply. This inhibitory effect was found to be due mainly to the very high molecular weight (Mr) heparin proteoglycans (average Mr 750 000) released from the stimulated mast cells. When the heparin proteoglycans were purified from mast-cell granule remnants and added to the SMC culture, they were found to block the cell cycle at the G0-->S transition and the exit from the G2/M phase, their inhibitory effect resembling that of commercial heparin. However, in contrast to the reported dependence of the inhibitory effect of commercial heparin on the release of transforming growth factor-beta from serum, the inhibitory effect of the mast cell-derived heparin proteoglycans in the presence of serum was not transforming growth factor-beta dependent. Moreover, the effect of the mast cell-derived heparin proteoglycans was more efficient than that of commercial heparins of high (average Mr 15 000) and low (average Mr 5000) molecular weight. We also purified heparin glycosaminoglycans (average Mr 75 000) from the mast cell-derived heparin proteoglycans and found that they also inhibited SMC growth efficiently, although less strongly than their parent heparin proteoglycans. These results reveal, for the first time, that mast cells are able to regulate SMC growth. Thus, activated mast cells, by releasing heparin proteoglycans, possibly participate in the regulation of SMC growth in the human arterial intima, the site of atherogenesis.

Tissue inhibitors of metalloproteinases and metalloproteinases in atherosclerosis

The ability of the metalloproteinases to degrade extracellular matrix proteins is essential for the matrix remodelling that occurs during infiltration of inflammatory cells, intimal thickening, angiogenesis and plaque rupture which are a result of atherosclerosis. Increased metalloproteinase activity therefore requires stimulation of metalloproteinase expression by cytokines and growth factors, activation of metalloproteinases, and downregulation of tissue inhibitors of metalloproteinases. In addition, metalloproteinases may influence atherosclerosis by processing of proteins involved in inflammation and cell growth and death and the tissue inhibitors of metalloproteinases may also play a less inhibitory role by influencing cell growth and apoptosis.

A role for interleukin 4 in production of matrix metalloproteinase 1 by human aortic smooth muscle cells

Effect of interleukin 4 (IL-4) on the production of matrix metalloproteinase 1 (MMP-1) by normal and immortalized human intimal smooth muscle cells (SMC) was investigated. The production of the precursors of MMP-1 by intimal SMC was enhanced in a dose-dependent manner by addition of IL-4 to the culture medium, whereas the cytokine also showed an inhibitory effect on DNA synthesis in the cells. In addition, mRNA of IL-4 was found in the atherosclerotic and nonatherosclerotic areas of the intima. Although the production of MMP-1 and the proliferation of SMC are thought to play an important role in reconstruction of the intima during atherogenesis, our results suggest a possible role of IL-4 induced MMP-1 in inhibiting tissue remodeling caused by a variety of arterial disorders including atherosclerosis.

Increased mast cell infiltration in varicose veins of the lower limbs: a possible role in the development of varices

BACKGROUND

This study shows increased infiltration of mast cells in the walls of varicose veins in the lower limbs as an explanation of the pathogenesis of varix formation.

METHODS

Great saphenous veins exhibiting varicosity were histologically examined after vein stripping surgery, and the numbers of mast cells in the varicose lesions were estimated in 20 high-power fields (x400). Normal-looking regions of the veins were referred to as controls, and normal saphenous veins were prepared during coronary artery bypass grafting and designated baseline controls.

RESULTS

The varicose lesions showed a greater extent of mast cell infiltration (15.0 +/- 8.4 cells; mean +/- standard deviation), whereas control veins (5.9 +/- 4.0) and baseline control veins (4.4 +/-2.9) had a smaller number of mast cells.

CONCLUSIONS

The study suggests that increased mast cell infiltration contributes to the development of varicose veins.