Early activation signals in endothelial cells. Stimulation by cytokines

Cancer cells produce liver metastasis via gap formation in sinusoidal endothelial cells through proinflammatory paracrine mechanisms

Intracellular gap (iGap) formation in liver sinusoidal endothelial cells (LSECs) is caused by the destruction of fenestrae and appears under pathological conditions; nevertheless, their role in metastasis of cancer cells to the liver remained unexplored. We elucidated that hepatotoxin-damaged and fibrotic livers gave rise to LSECs-iGap formation, which was positively correlated with increased numbers of metastatic liver foci after intrasplenic injection of Hepa1-6 cells. Hepa1-6 cells induced interleukin-23-dependent tumor necrosis factor-α (TNF-α) secretion by LSECs and triggered LSECs-iGap formation, toward which their processes protruded to transmigrate into the liver parenchyma. TNF-α triggered depolymerization of F-actin and induced matrix metalloproteinase 9 (MMP9), intracellular adhesion molecule 1, and CXCL expression in LSECs. Blocking MMP9 activity by doxycycline or an MMP2/9 inhibitor eliminated LSECs-iGap formation and attenuated liver metastasis of Hepa1-6 cells. Overall, this study revealed that cancer cells induced LSEC-iGap formation via proinflammatory paracrine mechanisms and proposed MMP9 as a favorable target for blocking cancer cell metastasis to the liver.

Pathogenesis of atherosclerosis in the tunica intima, media, and adventitia of coronary arteries: An updated review

Atherosclerosis is a chronic inflammatory disease of arteries and it affects the structure and function of all three layers of the coronary artery wall. Current theories suggest that the dysfunction of endothelial cells is one of the initial steps in the development of atherosclerosis. The view that the tunica intima normally consists of a single layer of endothelial cells attached to the subendothelial layer and internal elastic membrane has been questioned in recent years. The structure of intima changes with age and it becomes multilayered due to migration of smooth muscle cells from the media to intima. At this stage, the migration and proliferation of smooth muscle cells do not cause pathological changes in the intima. The multilayering of intima is classically considered to be an important stage in the development of atherosclerosis, but in fact atherosclerotic plaques develop only focally due to the interplay of various processes that involve the resident and invading inflammatory cells. The tunica media consists of multiple layers of smooth muscle cells that produce the extracellular matrix, and this layer normally does not contain microvessels. During the development of atherosclerosis, the microvessels from the tunica adventitia or from the lumen may penetrate thickened media to provide nutrition and oxygenation. According to some theories, the endothelial dysfunction of these nutritive vessels may significantly contribute to the atherosclerosis of coronary arteries. The adventitia contains fibroblasts, progenitor cells, immune cells, microvessels, and adrenergic nerves. The degree of inflammatory cell infiltration into the adventitia, which can lead to the formation of tertiary lymphoid organs, correlates with the severity of atherosclerotic plaques. Coronary arteries are surrounded by perivascular adipose tissue that also participates in the atherosclerotic process.

Inhibition of endocytosis exacerbates TNF-α-induced endothelial dysfunction via enhanced JNK and p38 activation

Tumor necrosis factor-α (TNF-α) is a pro-inflammatory cytokine that causes endothelial dysfunction. Endocytosis of TNF-α receptors (TNFR) precedes endosomal reactive oxygen species (ROS) production, which is required for NF-κB activation in vascular smooth muscle cells. It is unknown how endocytosis of TNFRs impacts signaling in endothelial cells. We hypothesized that TNF-α-induced endothelial dysfunction is induced by both endosomal and cell surface events, including NF-κB and mitogen-activated protein kinases (MAPKs) activation, and endocytosis of the TNFR modifies signaling. Mesenteric artery segments from C57BL/6 mice were treated with TNF-α (10 ng/ml) for 22 h in tissue culture, with or without signaling inhibitors (dynasore for endocytosis, SP600125 for JNK, SB203580 for p38, U0126 for ERK), and vascular function was assessed. Endothelium-dependent relaxation to acetylcholine (ACh) was impaired by TNF-α, and dynasore exacerbated this, whereas JNK or p38 inhibition prevented these effects. In cultured endothelial cells from murine mesenteric arteries, dynasore potentiated JNK and p38 but not ERK phosphorylation and promoted cell death. NF-κB activation by TNF-α was decreased by dynasore. JNK inhibition dramatically increased both the magnitude and duration of TNF-α-induced NF-κB activation and potentiated intercellular adhesion molecule-1 (ICAM-1) activation. Dynasore still inhibited NF-κB activation in the presence of SP600125. Thus TNF-α-induced endothelial dysfunction is both JNK and p38 dependent. Endocytosis modulates the balance of NF-κB and MAPK signaling, and inhibition of NF-κB activation by JNK limits this pro-proliferative signal, which may contribute to endothelial cell death in response to TNF-α.

TNF-α response of vascular endothelial and vascular smooth muscle cells involve differential utilization of ASK1 kinase and p73

Atherosclerosis involves a specialized inflammatory process regulated by an intricate network of cytokine and chemokine signaling. Atherosclerotic lesions lead to the release of cytokines that can have multiple affects on various vascular cell functions either promoting lesion expansion or alternatively retard progression. Tumor necrosis factor-α (TNF-α) is one such cytokine that can activate both cell survival and cell death mechanisms simultaneously. Here we show that TNF-α induces apoptosis in human aortic endothelial cells (HAECs), while it promotes the proliferation of vascular smooth muscle cells (VSMCs). Both events involved the activation of the Rb-E2F1 transcriptional regulatory pathway. Stimulation of HAECs with TNF-α led to an increased expression of p73 protein and a reduction in the levels of p53. This involved apoptosis signal-regulating kinase 1 (ASK1)- mediated inactivation of Rb and its dissociation from the p73 promoter. In contrast, TNF-α stimulation of VSMCs enhanced the association of E2F1 with proliferative promoters like thymidylate synthase and cdc25A, while Rb was dissociated. ASK1 kinase has a critical role in the apoptotic process, as its depletion or dissociation from Rb reduced TNF-α-induced apoptosis. These results show that the cytokine TNF-α can elicit diametrically opposite responses in vascular endothelial cells and VSMCs, utilizing the Rb-E2F pathway.

Role of tumor necrosis factor-alpha and matrix metalloproteinase-9 in blood-brain barrier disruption after peripheral thermal injury in rats

OBJECT

A relationship has been found between peripheral thermal injury and cerebral complications leading to injury and death. In the present study, the authors examined whether tumor necrosis factor-alpha (TNF-alpha) and matrix metalloproteinase-9 (MMP-9) play a causative role in blood-brain barrier (BBB) disruption after peripheral thermal injury.

METHODS

Thirty-two male Sprague-Dawley rats were subjected to thermal injury. One hour later, 8 rats were injected with TNF-alpha neutralizing antibody, and 8 were injected with doxycycline, an inhibitor of the MMP family proteins; 16 rats did not receive any treatment. Brain tissue samples obtained 7 hours after injury in the treated animals were examined for BBB function by using fluorescein isothiocyanate-dextran and by assessing parenchymal water content. Protein expression of basement membrane components (collagen IV, laminin, and fibronectin) was quantified on Western blot analysis, and MMP-9 protein expression and enzyme activity were determined using Western blot and gelatin zymography. Thermally injured rats that did not receive treatment were killed at 3, 7, or 24 hours after injury and tested for BBB functioning at each time point. Histological analysis for basement membrane proteins was also conducted in untreated rats killed at 7 hours after injury. Results of testing in injured rats were compared with those obtained in a control group of rats that did not undergo thermal injury.

RESULTS

At 7 hours after thermal injury, a significant increase in the fluorescein isothiocyanate-dextran and water content of the brain was found (p < 0.05), but BBB dysfunction was significantly decreased in the rats that received TNF-alpha antibody or doxycycline (p < 0.05). In addition, the components of the basal lamina were significantly decreased at 7 hours after thermal injury (p < 0.01), and there were significant increases in MMP-9 protein expression and enzyme activity (p < 0.05). The basal lamina damage was reversed by inhibition of TNF-alpha and MMP-9, and the increase in MMP-9 protein was reduced in the presence of doxycycline (p < 0.05). The authors found that MMP-9 enzyme activity was significantly increased after thermal injury (p < 0.01) but decreased in the presence of either TNF-alpha antibody or doxycycline (p < 0.01).

CONCLUSIONS

The dual, inhibitory activity of both TNF-alpha and MMP-9 in brain injury suggests that a TNF-alpha and MMP-9 cascade may play a key role in BBB disruption. These results offer a better understanding of the pathophysiology of burn injuries, which may open new avenues for burn treatment beyond the level of current therapies.

Invasive amebiasis: a microcirculatory disorder?

The two current models of invasive amebiasis both hold that direct contact of toxic molecules and amebas with tissue produces the necrotic areas characteristic of this disorder. Whereas one model characterizes these toxic molecules as amebic products (e.g., lectins, amebapores, cysteine proteinases and other proteolytic enzymes), the other describes them as products of the inflammatory response (e.g., cytokines, nitric oxide, reactive oxygen intermediates and cytotoxic granules). Both these models can account for necrotic areas with many amebas present and with acute inflammation, but not those with few or no amebas present or with scarce inflammation. A new model poses that an inadequate immune response leads to a continuous and prolonged activation of endothelial cells (ECs) by amebas, amebic molecules and cytokines, which triggers the mechanisms leading to necrosis. Other toxic molecules later contribute to EC activation: nitric oxide, reactive oxygen intermediates, the activated complement and proteases. Hyperactivated endothelial cells continuously express adhesion molecules (e.g., ICAM-1 and E-selectin), pro-coagulant molecules (e.g., tissue factor, von Willebrand factor, and the plasminogen activator inhibitor), resulting in ever greater inflammation and thrombosis, which eventually reduces or blocks blood flow in some vessels and starves certain tissue areas of an adequate oxygen and nutrient supply. When necrotic areas first develop, they are surrounded by inflammatory cells due to the acute inflammation at this stage. However, these cells are starved of oxygen and essential nutrients by the same microcirculatory dysfunction. The increasing concentration of nitric oxide during amebiasis eventually has an anti-inflammatory and vasodilating effect, creating a new mechanism for the microcirculatory dysfunction. This local microcirculatory dysfunction can explain necrotic areas in the presence of many, few, or no amebas, with abundant or scarce inflammation.

Bay w 9798, a dihydropyridine structurally related to nifedipine with no calcium channel-blocking properties, inhibits tumour necrosis factor-alpha-induced vascular cell adhesion molecule-1 expression in endothelial cells by suppressing reactive oxygen species generation

Dihydropyridine-based calcium antagonists (DHPs) are widely used to treat hypertension. We have previously shown that nifedipine, one of the most popular DHPs, blocks tumour necrosis factor-alpha (TNF-alpha)-induced monocyte chemoattractant protein-1 as well as vascular cell adhesion molecule-1 (VCAM-1) expression in endothelial cells by suppressing reactive oxygen species generation (ROS). The molecular mechanism is still to be elucidated, however, because endothelial cells do not possess voltage-operated L-type calcium channels. The aim of this study was to determine in TNF-alpha-exposed human umbilical vein endothelial cells (HUVECs) whether and how Bay w 9798, a dihydropyridine structurally related to nifedipine with no calcium antagonistic properties, may suppress VCAM-1 expression, a key molecule which mediates the adhesion of monocytes to vasculature in the early stages of atherosclerosis. In HUVECs, 10 ng/ml TNF-alpha for 4 h stimulated ROS generation and subsequently upregulated VCAM-1 mRNA levels, both of which were dose-dependently blocked by Bay w 9798. The results demonstrated that Bay w 9798 inhibited VCAM-1 expression in TNF-alpha-exposed cells by suppressing ROS generation. They suggest that the anti-inflammatory and anti-oxidative properties of nifedipine and Bay w 9798 may be ascribed to the dihydropyridine structure, which is common to both molecules and has no calcium antagonistic ability.

Azelnidipine, a new long-acting calcium-channel blocker, inhibits tumour necrosis factor-alpha-induced monocyte chemoattractant protein-1 expression in endothelial cells

Dihydropyridine-based calcium antagonists are among the most widely used drugs for the treatment of hypertension. Since azelnidipine is a highly lipid-soluble dihydropyridine-based calcium antagonist with high vascular affinity, it is conceivable that azelnidipine could play a protective role against atherosclerosis. The aim of this study was to determine whether azelnidipine could suppress the expression of monocyte chemoattractant protein-1, a principal chemokine which mediates the recruitment of monocytes to the vasculature, in tumour necrosis factor (TNF)-alpha-exposed human umbilical vein endothelial cells. TNF-alpha, at a concentration of 10 ng/ml, upregulated monocyte chemoattractant protein-1 mRNA levels about seven-fold. Azelnidipine, 10 nmol/l, was found to inhibit the TNF-alpha-induced upregulation of monocyte chemoattractant protein-1 mRNA levels in human umbilical vein endothelial cells significantly. Furthermore, azelnidipine suppressed TNF-alpha-induced monocyte chemoattractant protein-1 production by human umbilical vein endothelial cells. This study demonstrates a novel beneficial aspect of azelnidipine, whereby azelnidipine could play a protective role against atherosclerosis by suppressing monocyte chemoattractant protein-1 overexpression in endothelial cells.

The Mediterranean and CHO diets decrease VCAM-1 and E-selectin expression induced by modified low-density lipoprotein in HUVECs

BACKGROUND AND AIM

The oxidative modifications of low-density lipoprotein (LDL) are crucial for the atherosclerosis process. The aim of this study was to determine if the minimally modified LDL, obtained after the ingestion of three different diets, produce differential effects on the vascular cell adhesion molecule-1 (VCAM-1) and E-selectin expression in human umbilical endothelial cells (HUVECs).

METHODS AND RESULTS

Twenty healthy young males were exposed to three dietary periods. Each period lasted four weeks. During the first period, all subjects consumed a saturated fat (SFA) enriched diet (38% fat, 20% SFA). The second and third dietary periods were administered following a randomized crossover design: a low fat high carbohydrates diet (CHO diet) and a Mediterranean diet. LDL particles, isolated during each dietary period, were oxidized by exposure to UV light and incubated for 48 h with HUVEC. Thereafter, 100 U/mL of TNF-alpha was added and incubation continued for 6 h. Cellular ELISA determined adhesion molecules expression. Lag time, propagation rate and total amounts of formed conjugated dienes were calculated in LDL incubated with 10mumol/L Cu(2+). When compared to the SFA diet, LDL isolated from the Mediterranean and CHO diets induced a lower expression of VCAM-1 and E-selectin in HUVECS (P<0.007). There were no differences between both lipid lowering diets. However, lag time of LDL from the Mediterranean diet was higher than with the CHO diet (P<0.042). This parameter was inversely correlated with E-selectin expression (r=-0.497; P<0.04).

CONCLUSION

Our results suggest that both the Mediterranean and CHO diets may decrease the pro-inflammatory environment induced by modified LDL in endothelial cells.

Pigment epithelium-derived factor (PEDF) blocks the interleukin-6 signaling to C-reactive protein expression in Hep3B cells by suppressing Rac-1 activation

There is a growing body of evidence to show that that C-reactive protein (CRP), an acute phase reactant, is one of the most valuable predictors of future cardiovascular events. Since CRP proteins directly contribute to the development and progression of atherosclerosis as well, reduction of CRP levels may be a novel therapeutic target for the treatment of cardiovascular disease. In this study, we examined whether pigment epithelium-derived factor (PEDF) could block the interleukin-6-induced CRP expression in cultured human hepatoma cells and the way that it might achieve this effect. PEDF inhibited the IL-6-induced CRP expression in Hep3B cells at both mRNA and proteins levels. PEDF suppressed the intracellular reactive oxygen species generation in IL-6-exposed Hep3B cells. Anti-oxidants mimicked the effects of PEDF. PEDF was also found to inhibit the IL-6-elicited Rac-1 activation, whereas dominant-negative Rac-1 dose-dependently decreased the CRP mRNA levels. PEDF blocked the IL-6-induced STAT3 phosphorylations and NF-kappaB p65 activity in Hep3B cells. Our present study suggests that PEDF could be one of the potent suppressors of CRP production by the liver and may play a protective role against atherosclerosis.

Early inflammatory response in rat brain after peripheral thermal injury

Previous studies have shown that the cerebral complications associated with skin burn victims are correlated with brain damage. The aim of this study was to determine whether systemic thermal injury induces inflammatory responses in the brain. Sprague Dawley rats (n=28) were studied in thermal injury and control groups. Animals from the thermal injury (n=14) and control (n=14) group were anesthetized and submerged to the neck vertically in 85 degrees C water for 6 s producing a third degree burn affecting 60-70% of the animal body surface area. The controls were submerged in 37 degrees C water for 6 s. Early expression of tumor necrosis factor-alpha (TNF-alpha), interleukin 1-beta (IL-1beta), and intracellular cell adhesion molecules (ICAM-1) protein levels in serum were determined at 3 (n=7) and 7 h (n=7) by enzyme-linked immunoabsorbent assay (ELISA). mRNA of TNF-alpha, IL-1beta, and ICAM-1 in the brain was measured at the same time points with a real-time reverse transcriptase-polymerase chain reaction (RT-PCR). An equal animal number was used for controls. Systemic inflammatory responses were demonstrated by dramatic up-regulations (5-50 fold) of TNF-alpha, IL-1beta, and ICAM-1 protein level in serum at 7 h after the thermal injury. However, as early as 3 h after peripheral thermal injury, a significant increase (3-15 fold) in mRNA expression of TNF-alpha, IL-1beta and ICAM-1 was observed in brain homogenates, with increased levels remaining at 7 h after injury. This study demonstrated an early inflammatory response in the brain after severe peripheral thermal injury. The cerebral inflammatory reaction was associated with expression of systemic cytokines and an adhesion molecule.

Brain microvessel endothelial cell responses to tumor necrosis factor-alpha involve a nuclear factor kappa B (NF-κB) signal transduction pathway

The involvement of nuclear factor kappa B (NF-kappaB) in TNF-induced increases in cerebral microvascular permeability was evaluated both in vitro, using primary cultured bovine brain microvessel endothelial cells (BBMEC), and in vivo, using the rat cranial window model. In primary cultured BBMEC, TNF exposure resulted in an increased appearance of the Rel A subunit of NF-kappaB in immunoblots of cell lysates. Increases in the Rel A subunit of NF-kappaB were observed as early as 30-min after administration of TNF. The increased permeability and the secretion of prostaglandin E2 in response to TNF exposure in BBMEC monolayers were significantly reduced by several different NF-kappaB inhibitors, including PDTC, CAPE, BAY 11-7085, and lactacystin. Similar results were also obtained in the rat cranial window model where treatment with the COX-2 inhibitor, NS-398 (0.1 microM), or the NF-kappaB inhibitor, PDTC (10 microM), significantly reduced the permeability increases produced by TNF. These studies suggest that the increases in BBB permeability following TNF exposure are attributable to activation of an NF-kappaB-mediated signaling pathway in the cerebral microvasculature.

Platelet activation status decreases after menopause

OBJECTIVE

The aim of the study was to investigate the impact of the climacterium (before and after menopause) on platelet activation.

BACKGROUND

Platelet activation has been associated to the risk of cardiovascular disease. There is much speculation about the relationship between platelet function and sex steroids, due to peculiarities of platelet action between the genders, including concerns about the influence of low estradiol status in menopausal women.

METHODS

By means of a cross-sectional study design, 37 female patients divided into two groups were compared. Group A consisted of ten women, mean age 43.9 years, in the premenopausal period, with normal estrogen levels; and Group B comprised 27 patients, mean age 53.0 years, who had all reached menopause. Platelet activation markers, namely P-selectin and glycoprotein IIb-IIIa complex (GPIIb-IIIa), were evaluated by flow cytometry with monoclonal antibodies. A binding index was calculated for both parameters (percentage of positive platelets x mean fluorescence of positive platelets). Also, thromboxane A2 was quantified by means of its main plasma metabolite, thromboxane B2, by enzyme immunoassay.

RESULTS

P-selectin and GPIIb-IIIa expression results revealed lower platelet activation status after menopause, as there was a decrease in both the percentage of P-selectin+ platelets and of GPIIb-IIIa mean fluorescence of positive platelets, lowering both binding indices. P-selectin binding index differed significantly between Group A (12.3 +/- 3, n = 10) and Group B (6.2 +/- 2.9, n = 27; mean +/- standard deviation (SD), p < 0.001). GPIIb-IIIa binding index also differed significantly between both groups (Group A: 18.8 +/- 2.3, n = 10 vs. Group B: 16.2 +/- 3.1, n = 27; mean +/- SD, p < 0.0018). Plasma concentration of thromboxane B2 was 1.07 +/- 0.5 pg/well before menopause (Group A, n = 10) and 1.9 +/- 4.1 pg/well after menopause (Group B, n = 27), not significantly different (mean +/- SD, baseline x therapy, p = 0.85).

CONCLUSIONS

After the menopause, climacteric women--whose estradiol status is low--have a decreased activation platelet status compared with premenopausal women. Nevertheless, further studies on a larger sample are necessary for conclusive data regarding cardiovascular disease.

Pigment epithelium-derived factor inhibits TNF-alpha-induced interleukin-6 expression in endothelial cells by suppressing NADPH oxidase-mediated reactive oxygen species generation

Pigment epithelium-derived factor (PEDF) has recently been shown to be involved in the pathogenesis of proliferative diabetic retinopathy. Atherosclerosis is an inflammatory-fibroproliferative disease as well. Oxidative stress plays a major role in retinopathy and atherosclerosis. Accordingly, we investigated effects of PEDF on reactive oxygen species (ROS) generation, NF-kappaB activation and interleukin (IL)-6 expression in TNF-alpha-exposed HUVEC. TNF-alpha significantly increased intracellular ROS generation, which was completely blocked by PEDF or diphenylene iodonium, an inhibitor of NADPH oxidase. Further, PEDF completely prevented the TNF-alpha-induced increase in NADPH oxidase activity. PEDF or an antioxidant, N-acetylcysteine, significantly inhibited the TNF-alpha-induced NF-kappaB activation. PEDF inhibited TNF-alpha-induced expression of IL-6 at both mRNA and protein levels. Moreover, TNF-alpha downregulated PEDF mRNA levels. Ligand blot analysis revealed that HUVEC possessed a membrane protein with binding affinity for PEDF. The results demonstrated that PEDF inhibited TNF-alpha-induced NF-kappaB activation and subsequent IL-6 overexpression in HUVEC by suppressing NADPH oxidase-mediated ROS generation. Our present study suggests that PEDF may play an important role in the development and progression of atherosclerosis.

Azelnidipine, A Newly Developed Long-Acting Calcium Antagonist, Inhibits Tumor Necrosis Factor-α-Induced Interleukin-8 Expression in Endothelial Cells through its Anti-Oxidative Properties

Interleukin-8 (IL-8), a member of CXC chemokine family, has been found to play an important role in the pathogenesis of atherosclerosis. Tumor necrosis factor-alpha (TNF-alpha) is involved in the development and progression of atherosclerosis as well. In this study, we investigated whether and how azelnidipine, a newly developed long-acting calcium antagonist, could inhibit TNF-alpha-induced IL-8 expression in human umbilical vein endothelial cells (HUVEC). TNF-alpha significantly increased intracellular reactive oxygen species (ROS) generation in HUVEC, which was completely blocked by azelnidipine or apocynin, an inhibitor of NADPH oxidase. Azelnidipine also completely prevented TNF-alpha-induced increase in NADPH oxidase activity in HUVEC. Further, azelnidipine was found to significantly inhibit activator protein-1 (AP-1) promoter activity and IL-8 expression in TNF-alpha-exposed HUVEC. An inhibitor of AP-1, curcumin, or an anti-oxidant, N-acetylcysteine, also inhibited the TNF-alpha-induced IL-8 expression in HUVEC. These results demonstrated that azelnidipine inhibited TNF-alpha-induced IL-8 expression in HUVEC by blocking NADPH oxidase-mediated ROS generation and subsequent AP-1 activation. Our present study suggests that azelnidipine may play a protective role in the development and progression of atherosclerosis through its anti-oxidative properties.

The guanylate binding protein-1 GTPase controls the invasive and angiogenic capability of endothelial cells through inhibition of MMP-1 expression

Expression of the large GTPase guanylate binding protein-1 (GBP-1) is induced by inflammatory cytokines (ICs) in endothelial cells (ECs), and the helical domain of the molecule mediates the repression of EC proliferation by ICs. Here we show that the expression of GBP-1 and of the matrix metalloproteinase-1 (MMP-1) are inversely related in vitro and in vivo, and that GBP-1 selectively inhibits the expression of MMP-1 in ECs, but not the expression of other proteases. The GTPase activity of GBP-1 was necessary for this effect, which inhibited invasiveness and tube-forming capability of ECs in three-dimensional collagen-I matrices. A GTPase-deficient mutant (D184N-GBP-1) operated as a transdominant inhibitor of wild-type GBP-1 and rescued MMP-1 expression in the presence of ICs. Expression of D184N-GBP-1, as well as paracrine supplementation of MMP-1, restored the tube-forming capability of ECs in the presence of wild-type GBP-1. The latter finding indicated that the inhibition of capillary formation is specifically due to the repression of MMP-1 expression by GBP-1, and is not affected by the anti-proliferative activity of the helical domain of GBP-1. These findings substantiate the role of GBP-1 as a major regulator of the anti-angiogenic response of ECs to ICs.

The pulmonary circulation in bronchopulmonary dysplasia

Abnormalities of the pulmonary circulation are increasingly being recognized as a major contributor to the high morbidity and mortality of bronchopulmonary dysplasia. Historically, studies have focused on the importance of pulmonary hypertension to the pathophysiology of BPD, with the assumption that pulmonary vascular abnormalities are a secondary consequence of primary injury to the airspace. Recent studies suggest, however, that abnormalities of the pulmonary vasculature, including altered growth and structure, may directly contribute to the abnormal alveolarization that characterizes the condition. In this article, we briefly outline mechanisms of pulmonary vascular injury in infants at risk of BPD. We then focus on the recognition and management of pulmonary hypertension in these infants. Finally, we review how disordered pulmonary vascular growth may contribute to the pathogenesis of BPD and emphasize the importance of the reciprocal development of the airspace and the pulmonary circulation.

In vitro evaluation of the role of platelet-activating factor and interleukin-8 in Mannheimia haemolytica-induced bovine pulmonary endothelial cell injury

OBJECTIVE

To develop an in vitro model of the bovine alveolar-capillary interface and to evaluate the roles of interleukin-8 (IL-8) and platelet-activating factor (PAF) in neutrophil-mediated endothelial injury induced by infection with Mannheimia haemolytica.

SAMPLE POPULATION

Cultured bovine pulmonary microvascular endothelial cells, freshly isolated bovine neutrophils, and monocyte-derived bovine macrophages.

PROCEDURE

A coculture system was developed in which endothelial cells were grown to confluence in tissue culture inserts, neutrophils were added to the inserts, and macrophages were added to tissue culture wells. Mannheimia haemolytica-derived lipopolysaccharide (LPS) or supernatant was added to activate macrophages, and inhibitors of PAF or IL-8 were added to the insert. Endothelial cell cytotoxicity and permeability (ie, albumin leakage) and neutrophil activation (ie, adhesion, degranulation [lactoferrin expression], and superoxide production) were assessed.

RESULTS

The addition of M haemolytica-derived LPS to bovine macrophages in the coculture system resulted in significant increases in endothelial cell cytotoxicity and permeability and neutrophil degranulation and adhesion. Inhibition of IL-8 reduced endothelial cell permeability and neutrophil degranulation induced by exposure to M haemolytica-derived supernatant, whereas inhibition of PAF decreased superoxide release by neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro activation of bovine macrophages by M haemolytica-derived LPS resulted in neutrophil activation and neutrophil-mediated endothelial damage. Neutrophil-mediated endothelial injury and neutrophil degranulation were, at least in part, mediated by IL8, whereas PAF promoted superoxide release by neutrophils in this in vitro system designed to mimic the in vivo events that occur during the early stages of bovine pneumonic pasteurellosis.

Chronic inflammation and protection from acute hepatitis in transgenic mice expressing TNF in endothelial cells

Endothelial activation is an important feature of many inflammatory diseases and has been implicated as the cause of vascular complications in disorders such as diabetes, atherosclerosis, and transplant rejection. One of the most potent activators of the endothelium is TNF, which can also be expressed by endothelial cells, causing a permanent, autocrine stimulatory signal. To establish a model of continuous endothelial activation and to elucidate the role of endothelial derived TNF in vivo, we generated transgenic mice expressing a noncleavable transmembrane form of TNF under the control of the endothelial-specific tie2 promoter. Adult tie2-transmembrane TNF-transgenic mice developed chronic inflammatory pathology in kidney and liver, characterized by perivascular infiltration of mononuclear cells into these organs. Along with the infiltrate, an up-regulation of the adhesion molecules ICAM-1 and VCAM-1, but not E-selectin, in the endothelium was observed. Despite predisposition to chronic inflammation these mice were protected from immune-mediated liver injury in a model of Con A-induced acute hepatitis. Although the blood levels of soluble TNF and IFN-gamma were increased in transgenic animals after challenge with Con A, no damage of hepatocytes could be detected, as assessed by the lack of increase in plasma transaminase activities and the absence of TUNEL staining in the liver. We conclude that expression of transmembrane TNF in the endothelium causes continuous endothelial activation, leading to both proinflammatory and protective events.

Sustained ERK phosphorylation is necessary but not sufficient for MMP-9 regulation in endothelial cells: involvement of Ras-dependent and -independent pathways

Endothelial expression of matrix metalloproteinase-9 (MMP-9), which degrades native type IV collagen, was implicated as a prerequisite for angiogenesis. Therefore, the aim of this study was to determine signaling requirements that regulate MMP-9 expression in endothelial cells. Both, primary and permanent human umbilical vein endothelial cells (HUVEC and ECV304, respectively) were stimulated with phorbol 12-myristate 13-acetate (PMA) and the cytokine tumor necrosis factor-(alpha) (TNF(alpha)) to induce MMP-9 expression. While both cell types responded to PMA at the protein, mRNA and promoter level by induction of MMP-9, TNF(alpha) caused this response only in ECV304. Inhibitors specific for mitogen-activated protein/ERK kinase 1/2 (MEK1/2), protein kinase C (PKC), and Ras and co-transfections of wild-type and mutant Raf were used to elucidate the signaling cascades involved. Thus, we could show that the Raf/MEK/ERK cascade is mainly responsible for MMP-9 induction in endothelial cells and that this cascade is regulated independently of PKC and Ras subsequent to TNF(alpha) stimulation and in a PKC-dependent manner as a result of PMA treatment. In addition, PMA triggers a Ras-dependent signal transduction pathway bypassing the phosphorylation of ERK. Finally, we provide evidence that sustained phosphorylation of ERK1/2 is necessary but not sufficient for expression of MMP-9.

The effect of carotenoids on the expression of cell surface adhesion molecules and binding of monocytes to human aortic endothelial cells

Several large epidemiological studies have shown a correlation between elevated plasma carotenoid levels and decreased risk of cardiovascular disease (CVD). One proposed mechanism for the beneficial effect of carotenoids is through functional modulation of potentially atherogenic processes associated with the vascular endothelium. To test this, we incubated confluent human aortic endothelial cell (HAEC) cultures (passages 4-8) for 24 h with each of the five most prevalent carotenoids in human plasma, which are alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, and lycopene, at an approximate concentration of 1 micromol/l. Carotenoids were solubilized in 0.7% (v/v) tetrahydrofuran and incorporated into FBS before adding to cell culture medium. Due to disparate solubilities in aqueous medium, final concentrations of alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, and lycopene were 1.7, 1.1, 0.7, 0.9, and 0.3 micromol/l and monolayers accumulated 647, 158, 7, 113, and 9 pmol/mg protein, respectively. Monolayers were then stimulated with IL-1beta (5 ng/ml) for 6 h with subsequent determination of cell surface expression of adhesion molecules as measured by an enzyme-linked immunosorbent assay (ELISA). To assess endothelial cell adhesion to monocytes, IL-1beta-stimulated monolayers were incubated for 10 min with 51Cr-labeled U937 monocytic cells and adhesion determined by isotope counting. Pre-incubation of HAEC with beta-carotene, lutein and lycopene significantly reduced VCAM-1 expression by 29, 28, and 13%, respectively. Pre-incubation with beta-carotene and lutein significantly reduced E-selectin expression by 38 and 34%, respectively. Pre-treatment with beta-carotene, lutein and lycopene significantly reduced the expression of ICAM-1 by 11, 14, and 18%, respectively. While other carotenoids were ineffective, lycopene attenuated both IL-1beta-stimulated and spontaneous HAEC adhesion to U937 monocytic cells by 20 and 25%, respectively. Thus, among the carotenoids, lycopene appears to be most effective in reducing both HAEC adhesion to monocytes and expression of adhesion molecules on the cell surface.

A role for c-Raf kinase and Ha-Ras in cytokine-mediated induction of cell adhesion molecules

Cytokines such as tumor necrosis factor (TNFalpha) play fundamental roles in the pathophysiology of inflammation and immunity-related diseases. Despite rapid advances in our understanding of cytokine biology in recent years, definitive knowledge of the cytokine cell signaling pathways remains elusive due to the enormous complexity of these pathways and the lack of specific biological tools and reagents. Using highly specific antisense oligonucleotides that target the mRNA encoding c-Raf kinase and Ha-Ras, we show here that inhibition of c-raf and Ha-ras expression blocks the up-regulation of E-selectin and vascular adhesion molecule-1 induced by TNFalpha in endothelial cells. Induction of intercellular adhesion molecule-1 was also reduced, although to a much lesser extent, by treatment with antisense oligonucleotides. We also show that inhibition of c-raf kinase expression decreased extracellular signal-regulated kinase and c-Jun N-terminal kinase (JNK) kinase stimulation by TNFalpha. Furthermore, antisense inhibition of JNK2 also blocked TNFalpha-mediated induction of E-selectin, whereas PD98059 (mitogen-activated protein kinase kinase 1 and 2 inhibitor) had no effect on this process. These results indicate that TNFalpha induction of E-selectin and vascular adhesion molecule-1 in endothelial cells occurs through signaling pathways that are, at least in part, dependent on c-Raf kinase, Ha-Ras, and JNK2.

Human endothelial cells regulate polymorphonuclear leukocyte degranulation

Neutrophil degranulation is an important event in inflammatory responses. We examined the regulation of neutrophil (PMN) degranulation by resting and activated human endothelial cells. Whereas PMNs adherent to endothelial cells that were stimulated to express P-selectin and platelet-activating factor did not release the specific granule marker lactoferrin or the primary granule enzyme, elastase, PMNs adherent to endothelial cells stimulated with interleukin-1 (IL-1) or tumor necrosis factor secreted both. PMN degranulation was dependent on the time of incubation of endothelial cells with the cytokine, its concentration, and the time of incubation of the PMNs with endothelial cells. Degranulation of PMNs and their adhesion to stimulated endothelial cells are correlated events, but they could be dissociated by blocking the tethering molecules used by the endothelial cells and neutrophils under these conditions. This suggested that paracrine signaling molecules that induce PMN degranulation are produced by cytokine-stimulated endothelial cells. We found that endothelial cells stimulated with IL-1 release newly synthesized degranulating factors that require transcription and translation. IL-8 was synthesized, released, and signaled granular secretion by PMNs. However, experiments with blocking antibodies indicated the presence of an additional degranulating factor not accounted for by IL-8. These experiments demonstrate that human endothelial cells regulate degranulation of neutrophils by generating signaling factors that are expressed differentially depending on the endothelial agonist and other features. Active modification of neutrophil granular secretion by endothelial cells can influence physiologic acute inflammatory responses but may also contribute to pathologic vascular and tissue damage.

Bacterial lipopolysaccharide induces endothelial cells to synthesize a degranulating factor for neutrophils

Enzymes and other factors secreted by degranulating neutrophils (polymorphonuclear leukocytes, PMNs) mediate endothelial injury, thrombosis, and vascular remodeling. In bacteremia and sepsis syndrome and their consequent complications (including acute respiratory distress syndrome and systemic ischemia-reperfusion resulting from septic shock), neutrophil degranulation is an important mechanism of injury. In related studies, we found that human endothelial cells regulate neutrophil degranulation and that inflammatory cytokines induce synthesis of degranulating factors by human endothelial cells. Here we show that lipopolysaccharides (LPS) from gram-negative bacteria were the most potent agonists for release of degranulating activity by endothelial cells when compared to several cytokines and stimulatory factors. LPS also induced the release of degranulating signals for PMNs from a human endothelial cell line, EA.hy 926. Interleukin 8 (IL-8) is synthesized by endothelial and EA.hy 926 cells in response to LPS and induces neutrophil degranulation. However, complementary strategies using receptor desensitization, translation of messenger RNA by Xenopus laevis oocytes, and purification and analysis of factors from conditioned supernatants demonstrated that degranulating factors distinct from IL8 are generated in response to LPS. The characteristics of a partially purified degranulating factor isolated from conditioned supernatants distinguished it from known chemokines and other factors that induce PMN degranulation and are generated by endothelial cells in response to LPS. Thus, cultured human endothelial cells and endothelial cell lines synthesize several unique signaling molecules that can trigger neutrophil granular secretion. If produced in vivo in response to LPS or other pathologic agonists, these degranulating signals may activate PMNs in combination or in sequence, initiating or propagating vascular damage.

Alpha-galactosyl epitope-mediated activation of porcine aortic endothelial cells: type I activation

BACKGROUND

The galactose alpha(1-3)galactose (alpha-gal) epitope associated with membrane glycoproteins and glycolipids represents a major determinant recognized on porcine cells by human xenoreactive natural antibodies (XNA). Together, bound XNA and complement rapidly induce porcine aortic endothelial cell (PAEC) activation; this process is associated with cellular shape changes, transient development of intercellular gaps, and loss of ATDPase and thrombomodulin, with release of heparan sulfate. The aim of this study was to evaluate patterns of type I endothelial cell activation (i.e., activation that does not require protein synthesis) following ligation of alpha-gal epitopes with anti-Gal antibodies and alpha-gal-specific lectins.

METHODS AND RESULTS

PAEC incubated in the presence of the alpha-gal binding, Bandeiraea simplicifolia lectin (BS-I) underwent cellular shape changes associated with the formation of intercellular gaps. PAEC exposure to BS-I was also associated with the tyrosine phosphorylation of a protein (apparent molecular mass of approximately 130 kDa), not observed following lipopolysaccharide, tumor necrosis factor, or XNA stimulation. This lectin-induced tyrosine phosphorylation was not affected by cytochalasin D (inhibitor of actin filament polymerization), by genistein (inhibitor of tyrosine kinases), or by staurosporine (inhibitor of tyrosine phosphorylation and protein kinase C). In addition, incubation of PAEC with BS-I and monoclonal anti-Gal IgM induced p42/44 map kinase and activated the transcription factor NF-kappaB.

CONCLUSIONS

Agonist binding of alpha-gal can evoke endothelial cell activation independently of complement activation. These observations have implications for the survival of xenografts.

Differential effects of tumor necrosis factor-alpha and interleukin-1 on 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase expression in mouse Leydig cells

Immune-endocrine interactions are important to the regulation of Leydig cell steroidogenesis. We have shown previously that both tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1-beta) inhibit 8-bromo-cAMP-(8-Br-cAMP)-stimulated steroidogenesis in mouse Leydig cells. TNF and IL-1 both inhibit cAMP-stimulated testosterone production as well as mRNA and protein levels of cholesterol side chain cleavage enzyme (P450scc) and 17 alpha-hydroxylase/C17,20 lyase (P450c17) in mouse Leydig cells. Neither TNF nor IL-1 affects basal levels of P450scc mRNA and protein. In the present study, we tested the effects of TNF and IL-1 on basal testosterone production and 8-Br-cAMP-stimulated 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase (3 beta HSD) expression in Leydig cells. Purified and macrophage-depleted Leydig cells were cultured for 5 d with daily changes of media, and then treated with increasing concentrations of recombinant mouse TNF or IL-1 in the presence or absence of 8-Br-cAMP (50 microM) for 24 h. The media were collected for testosterone RIA and RNA and protein were extracted from cells. Basal testosterone production was inhibited by TNF, but not IL-1. Treatment of Leydig cells with 8-Br-cAMP alone caused a marked increase in 3 beta HSD mRNA, and protein levels. Both TNF and IL-1 inhibited cAMP-stimulated 3 beta HSD mRNA and protein levels, but only TNF inhibited basal 3 beta HSD expression. These results demonstrate that TNF and IL-1 have different effects on basal steroidogenesis in Leydig cells and suggest that TNF-mediated inhibition of basal testosterone production may be owing to the inhibition of basal 3 beta-HSD expression in Leydig cells.