Selective inhibition of E-selectin, ICAM-1, and VCAM in endothelial cells

NF-kappaB independent activation of a series of proinflammatory genes by hydrogen sulfide

A stress response has the potential to induce greater resistance to subsequent stress damage. We tested whether hydrogen sulfide (H(2)S), an important signaling molecule, also used therapeutically, and known for detrimental effects, might induce a protective stress response. Therefore, the response of fibroblast-like synoviocytes (FLS) treated with sodium hydrosulfide and mice exposed to H(2)S were examined. In both cases a profound and long lasting induction of the stress-response could be detected. However, despite the sustained presence of large levels of HO-1 and HSP-70, proinflammatory effects of exposure to IL-1beta or H(2)S itself were not ameliorated. On the contrary, at H(2)S concentrations significantly lower than 10 ppm-the current maximal allowable concentration of H(2)S in many countries-COX-2, IL-8, IL-1alpha, IL-1beta and TNFalpha were dose dependently elevated. Importantly, in FLS, short-term exposure to H(2)S resulted in the activation of all three MAPK. In addition, mitochondrial activity was also significantly impaired at relatively low H(2)S concentrations. The transcription factor NF-kappaB is essential for the activation of most proinflammatory genes. However, the data presented imply that H(2)S activates proinflammatory genes in FLS through non-NF-kappaB-dependent pathways. Stress proteins reportedly act by blocking NF-kappaB activation, a mechanism that would explain the inability of stress proteins to prevent H(2)S mediated inflammatory processes. The presented data, showing MAPK activation, NF-kappaB-independent activation of a number of proinflammatory genes and mitochondrial damage, help to provide a better understanding of the biological and pathophysiological effects of exposure to H(2)S.

Hyaluronan production in synoviocytes as a consequence of viral infections: HAS1 activation by Epstein-Barr virus and synthetic double- and single-stranded viral RNA analogs

One of the hallmarks of arthritis is swollen joints containing unusually high quantities of hyaluronan. Intact hyaluronan molecules facilitate cell migration by acting as ligands for CD44. Hyaluronan degradation products, readily formed at sites of inflammation, also fuel inflammatory processes. Irrespective of whether viruses could be a cause of rheumatoid arthritis, there is clear evidence that links viral infections to this debilitating disease. For this study, live Epstein-Barr virus and a number of double- and single-stranded synthetic viral analogs were tested for their effectiveness as activators of hyaluronan (HA) synthesis. As shown herein, Epstein-Barr virus-treated fibroblast-like synoviocytes significantly increase HA production and release. Real time reverse transcription-PCR data show that HAS1 mRNA levels are significantly elevated in virus-treated cells, whereas mRNA levels for the genes HAS2 and HAS3 remain unchanged. As to the mechanism of virus-induced HAS1 transcription, data are presented that imply that among the double- and single-stranded polynucleotides tested, homopolymeric polycytidylic structures are the most potent inducers of HAS1 transcription and HA release, whereas homopolymeric polyinosinic acid is without effect. Analyses of virus-induced signal cascades, utilizing chemical inhibitors of MAPK and overexpressing mutated IKK and IkappaB, revealed that the MAPK p38 as well as the transcription factor NF-kappaB are essential for virus-induced activation of HAS1. The presented data implicate HAS1 as the culprit in unfettered HA release and point out targets in virus-induced signaling pathways that might allow for specific interventions in cases of unwanted and uncontrolled HA synthesis.

Apis mellifera venom and melittin block neither NF-kappa B-p50-DNA interactions nor the activation of NF-kappa B, instead they activate the transcription of proinflammatory genes and the release of reactive oxygen intermediates

Many alternative treatment approaches, originating from Asia, are becoming increasingly popular in the Western hemisphere. Recently, an article published in a renowned journal reported that venom of apis mellifera (bee venom (BV)) and melittin mediate immune-modulating effects by blocking the activation of the transcription factor NF-kappaB. Such a modus operandi would corroborate the many claims of beneficial effects of BV treatment and give immediate credit to this form of therapy. Fibroblast-like synoviocytes from rheumatoid arthritis patients and dermal fibroblast cells and white blood cells from healthy volunteers were used to study the effects of BV and melittin on the activation of NF-kappaB and a series of genes that are markers of inflammation. EMSAs demonstrate that neither BV nor melittin blocked IL-1beta-induced NF-kappaB activation; neither did they affect phosphorylation or degradation of IkappaB. Contrary to published data, even high concentrations of BV and melittin were without any effect on NF-kappaB-p50-DNA interactions. More importantly, in fibroblast-like synoviocytes, but also in dermal fibroblasts as well as in mononuclear cells exposed to BV or melittin, mRNA levels of several proinflammatory genes are significantly increased, and Western blot data show elevated cyclooxygenase-2 protein levels. Furthermore, exposure to BV higher than 10 mug/ml resulted in disintegration of all cell types tested. In addition, large quantities of oxygen radicals are produced in a dose-dependent manner in leukocytes exposed to BV. Taken together, data presented in this work do not corroborate an earlier report regarding the effectiveness of BV as an inhibitor of the transcription factor NF-kappaB.

Glucocorticoids Alter the Balance Between Pro- and Anti-inflammatory Mediators in the Myocardium in a Porcine Model of Brain Death

BACKGROUND

Cardiac dysfunction after brain death (BD) limits donors for cardiac transplantation. Glucocorticoids ameliorate brain death-induced donor heart dysfunction. We hypothesized that glucocorticoid therapy alleviates myocardial depression through altering the balance between pro- and anti-inflammatory mediators via the nuclear factor-kappaB (NF-kappaB)/inhibitor of kappaB-alpha (IkappaBalpha) pathway and/or by preserving beta-adrenergic receptor (betaAR) signaling in the heart.

METHODS

Crossbred pigs (25 to 35 kg) were randomly assigned to the following groups (n = 5/treatment): sham (Group 1); BD (Group 2); and BD with glucocorticoids (30 mg/kg methylprednisolone), either 2 hours before (Group 3) or 1 hour after BD (Group 4). Tumor necrosis factor-alpha (TNF-alpha) levels were measured in plasma at baseline and 1 hour and 6 hours after BD. Protein levels were measured in left ventricular homogenates procured 6 hours after BD.

RESULTS

Pro-inflammatory proteins (TNF-alpha) and interleukin-6 were lower in Group 3 and Group 4 compared with Group 2 at 6 hours after BD (p < 0.01). Intracellular adhesion molecule-1 was also lower in Group 4 compared with Group 2 (p = 0.001). Interleukin-10, an anti-inflammatory mediator, was lower in Group 4 than in Group 2 (p < 0.001), but not different between Groups 2 and 3. At 6 hours after BD, neither NF-kappaB activity nor basal adenylate cyclase activity differed between Groups 3 and 4 compared with Group 2.

CONCLUSIONS

Glucocorticoids maintained myocardial function and shifted the balance of pro- and anti-inflammatory mediators after BD. The mechanisms by which glucocorticoids preserve myocardial function, however, do not appear to involve the NF-kappaB pathway or betaAR signaling.

Short-term hyperthermia prevents activation of proinflammatory genes in fibroblast-like synoviocytes by blocking the activation of the transcription factor NF-κB

Fibroblast-like synoviocytes (FLS) play a key role in the genesis of rheumatoid arthritis (RA). FLS are among the most versatile cells with the potential to activate an array of genes that are able to initiate and propagate inflammation in RA-affected joints. Controlling activation of FLS might hold the key to restraining inflammation in RA-affected joints. In this study, we investigate the effect and mechanisms of short-term hyperthermia on a series of proinflammatory genes in FLS. In vitro experiments demonstrate that exposure of FLS to elevated temperatures for the duration of 30 min prevents activation of a series of genes with proinflammatory properties. Exposure to hyperthermia reduces IL-1beta-induced prostaglandin E2 release, suppresses activation of the adhesion molecules VCAM-1, ICAM-1, the cytokines TNFalpha, IL-1alpha, IL-1beta, IL-8 as well as COX-2 protein synthesis. Real time reverse transcriptase-polymerase chain reaction showed that hyperthermia altered gene expression at the transcriptional level. The amount and the duration of inhibition is gene-specific and lasts for up to 25 h. As to the mechanism of inhibition, electrophoretic mobility shift assay experiments demonstrated that exposure of FLS to hyperthermia prevents IL-1beta-induced NF-kappaB translocation and subsequent DNA binding. Many mechanisms have been shown to be involved in hyperthermia-mediated effects on NF-kappaB-DNA interactions. We demonstrate by Western blot experiments that in FLS, hyperthermia prevents the phosphorylation and subsequent degradation of IkappaBalpha, therefore retaining the NF-kappaB complex in the cytoplasm. Carefully controlled in vivo tests are certainly needed before one can take full advantage of those phenomena; however, the ease by which the temperature in joints can be modulated might offer an opportunity for manipulating inflammatory processes in joints by simple balneological means.

Prostaglandin E2: a potent activator of hyaluronan synthase 1 in type-B-synoviocytes

We demonstrated earlier that the gene HAS1 is inactive in resting type-B-synoviocytes but can be readily activated by a series of proinflammatory cytokines including IL-1beta. Here we show that in type-B-synoviocytes mRNA levels for the gene COX-2 increase more than 200-fold in response to IL-1beta treatment, whereas COX-1 mRNA levels remain virtually unchanged. We tested a series of eicosanoids and demonstrate that PGE(2) is a very potent activator of HAS1 in synoviocytes. While mumol concentrations of PGI(2) are required to activate HAS1, low nmol concentrations of PGE(2) are sufficient. In addition, while two thromboxane A(2) analogs moderately activated HAS1 at higher concentrations, the lipoxygenase pathway product LTB(4) was without effect. A series of COX inhibitors blocked IL-1beta induced HAS1 activation. Similarly, sodium salicylate (NaSal) also suppressed IL-1beta induced HAS1 activation. Furthermore, electrophoretic mobility shift assays and PGE(2) ELISA experiments demonstrate that NaSal completely prevents PGE(2) release but does not interfere with NF-kappaB translocation. PGE(2) is a very powerful activator of HAS1 transcription and translation. Such data indicate that the effect of IL-1beta on HAS1 is mediated by prostaglandins. Additionally, NaSal is a potent suppressor of HAS1 activation. These findings point towards HAS1 as a gene of importance in inflammation.

Adenovirus-mediated gene transfer of mutated IkappaB kinase and IkappaBalpha reveal NF-kappaB-dependent as well as NF-kappaB-independent pathways of HAS1 activation

It has become increasingly clear that hyaluronan is more than the simple matrix molecule it was once thought to be but instead takes part in a multitude of biological functions. Three genes encode for hyaluronan synthases (HAS). We demonstrated earlier that HAS2 and HAS3 are constitutively activated in type-B synoviocytes (fibroblast-like synoviocytes) and, furthermore, that the only gene that readily responds to stimulation with a series of proinflammatory cytokines is HAS1. Here we probe the involvement of the transcription factor NF-kappaB in induced and noninduced HAS activation. Transforming growth factor (TGF) beta1 as well as interleukin (IL)-1beta are both strong inducers of HAS1 transcription. Stimulation of fibroblast-like synoviocytes with IL-1beta resulted in rapid degradation of IkappaBalpha, an event that was preceded by IkappaBalpha phosphorylation. Interestingly, TGFbeta1 neither affected IkappaBalpha levels, nor did it cause phosphorylation of IkappaBalpha. In addition, TGFbeta1 had no effect on IkappaBbeta and IkappaBepsilon levels. Electrophorectic mobility shift assays demonstrate that IL-1beta is a potent inducer of NF-kappaB translocation; however, TGFbeta1 treatment did not result in shifting bands. Two adenovirus constructs were used to further clarify differences in TGFbeta1- and IL-1beta-induced HAS1 activation. Overexpressing IkappaBalpha completely abolished the IL-1beta effect on HAS1 but did not interfere with TGFbeta1-induced HAS1 mRNA accumulation. Identical results were obtained when a dominant negative IKK was overexpressed. Interestingly, neither overexpression of IkappaBalpha nor of IKK had any effect on HAS2 and HAS3 mRNA levels. Taken together, HAS1 can be activated by distinct pathways; IL-1beta utilizes NF-kappaB, and TGFbeta1 does not. Furthermore, HAS2 and HAS3 are activated without the involvement of NF-kappaB.

Antioxidant protein 2 prevents methemoglobin formation in erythrocyte hemolysates

Antioxidant protein 2 (AOP2) is a member of a family of thiol-specific antioxidants, recently renamed peroxiredoxins, that evolved as part of an elaborate system to counteract and control detrimental effects of oxygen radicals. AOP2 is found in endothelial cells, erythrocytes, monocytes, T and B cells, but not in granulocytes. AOP2 was found solely in the cytoplasm and was not associated with the nuclear or membrane fractions; neither was it detectable in plasma. Further experiments focused on the function of AOP2 in erythrocytes where it is closely associated with the hemoglobin complex, particularly with the heme. An investigation of the mechanism of this interaction demonstrated that the conserved cysteine-47 in AOP2 seems to play a role in AOP2-heme interactions. Recombinant AOP2 prevented induced as well as noninduced methemoglobin formation in erythrocyte hemolysates, indicating its antioxidant properties. We conclude that AOP2 is part of a sophisticated system developed to protect and support erythrocytes in their many physiological functions.

Effects of quinacrine on endothelial cell morphology and transcription factor-DNA interactions

Quinacrine has been used for decades and the beneficial effects of this drug are as numerous as its toxic effects. Since endothelial cells (EC) are in many cases the first cells coming in contact with drugs, the effect of quinacrine on certain aspects of EC biology were studied. The presented data demonstrate that quinacrine can have a marked impact on the integrity on EC monolayer without grossly interfering with cell viability. The described impact of quinacrine on EC might explain, at least in part, the toxic effects of this drug observed in the past. Furthermore, quinacrine profoundly effects gene regulation in EC. Quinacrine binds to DNA in a sequence-specific manner. While NF-kappa B-DNA interactions are not effected, AP-1-DNA binding is blocked by quinacrine. Such differential effects are presumably due to intercalation of quinacrine into the AP-1 consensus element. Preincubation of oligonucleotides resembling this sequence blocked the subsequent binding of nuclear extract containing AP-1 protein(s). Taken together, these data suggest that quinacrine interferes with EC physiology and alters the repertoire of EC to respond to stimuli. Furthermore, the differential effects of quinacrine might be exploited to study and gain additional insight in the involvement of AP-1 and NF-kappa B in gene regulation.

Activation and regulation of Hsp32 and Hsp70

Endothelial cells (EC) play a key role in the propagation of inflammatory responses. Better understanding of inflammatory processes in EC might provide new ways of controlling inflammation. We report here that the known antioxidant pyrrolidinedithiocarbamate (PDTC) leads to time and dose dependent activation of heat-shock protein 70 (Hsp70) as well as Hsp32 in EC. We further demonstrate that PDTC activates heat-shock factor 1 (HSF1), one of several transcription factor involved in the upregulation of heat-shock proteins. And more importantly, we demonstrate that Hsp32 as well as Hsp70 can be upregulated independently of the transcription factor nuclear factor kappaB (NF-kappaB). The presented data provide further insight into the mechanism of Hsp32 and Hsp70 regulation, as well as further distinguishing these genes from other so called 'protective genes' whose upregulation depends on the activation of NF-kappaB. These findings indicate that Hsp32 and Hsp70 might be ideal candidates among protective genes. Hsp32 and Hsp70 provide many desirable protective effects but, being independent of NF-kappaB, would leave open the option to interfere with the upregulation of proinflammatory genes by modulating the activation of NF-kappaB.

Camouflaging endothelial cells: does it prolong graft survival?

Camouflaging antigens on the surface of cells seems an appealing way to prevent activation of the immune system. We explored the possibility of preventing hyperacute rejection by chemically camouflaging endothelial cells (EC). In vitro as well as in vivo experiments were performed. First, the ability of mPEG coating to prevent antibody-antigen interactions was evaluated. Second, we tested the degree to which mPEG coating prevents activation of EC by stimuli such as TNF-alpha and LPS. Third, in vivo experiments were performed to test the ability of mPEG coating to prolong xenograft survival. We demonstrate that binding of several antibodies to EC or serum proteins can be inhibited by mPEG. Furthermore, binding of TNF-alpha as well as LPS to EC is blocked since mPEG treatment of EC inhibits the subsequent up-regulation of E-selectin by these stimuli. However, in vivo experiments revealed that currently this method alone is not sufficient to prevent hyperacute rejection.

Membrane-associated lymphotoxin on natural killer cells activates endothelial cells via an NF-kappaB-dependent pathway

BACKGROUND

Inhibition of complement in small animal models of xenotransplantation has demonstrated graft infiltration with natural killer (NK) cells and monocytes associated with endothelial cell (EC) activation. We have previously demonstrated that human NK cells activate porcine EC in vitro, which results in adhesion molecule expression and cytokine secretion. In this study, we used the NK cell line NK92 to define the molecular and cellular basis of NK cell-mediated EC activation.

METHODS

EC were transfected with either reporter constructs containing the luciferase gene driven either by E-selectin or interleukin (IL)-8 promoters or a synthetic NF-kappaB-dependent promoter. In addition, a dominant-negative mutant tumor necrosis factor receptor I (TNFRI) expression vector was co-transfected in inhibition studies. Forty-eight hours after transfection, EC were stimulated with NK cells or NK cell membrane extracts for 7 hr and activation was measured by a luciferase assay.

RESULTS

Co-culture of NK cells with transfected EC enhanced E-selectin, IL-8, and NF-kappaB-dependent promoter activity. NK cell membrane extracts retained the capacity to activate EC and induced nuclear translocation of NF-kappaB (p50 and p65). Western blotting of NK cell and membrane extracts detected the presence of Lymphotoxin-alpha (LTalpha) but not tumor necrosis factor-alpha. Furthermore, LTalpha was secreted in NK:EC co-cultures. Co-transfection with dominant-negative mutant TNFRI inhibited EC activation by NK cell membrane extracts and by NK cells by 80% and 47%, respectively. The same pattern of inhibition was observed using anti-human LT sera.

CONCLUSIONS

Human NK cell membrane-bound LT signals across species via TNFRI, leading to NF-kappaB nuclear translocation and transcription of E-selectin and IL-8, which results in EC activation. The discrepancy in the degree of inhibition by membrane extracts and NK cells with mutant TNFRI suggests that additional pathways are utilized by NK cells to activate EC.

Complement-Fixing Elicited Antibodies Are a Major Component in the Pathogenesis of Xenograft Rejection

Hamster to rat cardiac xenografts undergo delayed rejection as compared with the hyperacute rejection of discordant xenografts. Elicited xenoreactive Abs (EXA) are thought to initiate hamster to rat cardiac xenograft rejection. In this study, we demonstrate that following transplantation of a hamster heart, rats generated high levels of EXA. Adoptive transfer into naive recipients of purified IgM, IgG2b, or IgG2c, but not IgG1 or IgG2a EXA, induced xenograft rejection in a complement-dependent manner. Ability of EXA to cause rejection correlated with complement activation, platelet aggregation, and P-selectin expression in the xenograft endothelium. Cyclosporin A (CyA) administration, after transplantation, totally suppressed IgG1, IgG2a, IgG2b, and IgG2c EXA, and inhibited IgM EXA production, but failed to overcome rejection. Administration of cobra venom factor (CVF), 1 day before and at the time of transplantation, resulted in complement inhibition during 3 days after transplantation, which failed to overcome rejection. Combination of CyA and CVF, which we have previously shown to overcome rejection, resulted in suppression of IgG EXA production and in the return of IgM XNA to preimmunization serum levels, 3 to 7 days after xenotransplantation, while complement remained inhibited. Thus, under CyA/CVF treatment, complement activation by hamster cells was suppressed following xenotransplantation, and presumably for this reason xenograft rejection did not occur. In conclusion, our data demonstrate that EXA play a pivotal role in the pathogenesis of xenograft rejection and that CyA and CVF suppress xenograft rejection by preventing exposure of xenograft endothelial cells to complement activation by EXA.

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

BACKGROUND

Xenoreactive natural antibodies (XNAs) and complement mediate hyperacute rejection of discordant xenografts. Inhibition of complement alone results in some prolongation of graft survival, but delayed xenograft rejection still precludes long-term graft survival. In vitro data provide evidence for the direct proinflammatory activation of endothelial cells (ECs) by XNAs. These antibodies are primarily directed against galactose alpha(1-3)-galactose (alpha-gal), the major xenoantigen in the pig to primate xenotransplant model. Previous studies have shown EC activation by XNAs but failed to address the question of whether alpha-gal-specific ligands can induce EC activation. The aim of this study was to investigate whether agonist binding to the alpha-gal epitope by alpha-gal-specific lectins as compared with XNAs or elicited xenoreactive antibodies can directly elicit type II porcine aortic EC (PAEC) activation (i.e., activation that requires protein synthesis).

METHODS AND RESULTS

The tetravalent, alpha-gal-binding Bandeiraea simplicifolia lectin I (BS-I), the wholly alpha-gal-specific BS-I isolectin B4, and elicited primate anti-pig xenoreactive antibodies (decomplemented cynomolgus monkey anti-porcine serum) induced E-selectin protein expression in PAECs. This induction was alpha-gal-specific, as preincubation with synthetic alpha-gal carbohydrate or adsorption of lectin or serum to rabbit, but not human, red blood cells removed the activating component. E-selectin expression, induced by BS-I, was inhibited in the presence of genistein, a tyrosine kinase inhibitor, and by mepacrine, an inhibitor of phospholipase A2. Human and primate XNAs lacked this activity when tested at relevant concentrations; however, stimulation of PAECs with affinity-purified human XNA (IgM and IgG) resulted in slightly increased interleukin-8 and P-selectin mRNA levels but had no apparent effects on E-selectin transcription. BS-I strongly induced E-selectin, P-selectin, intercellular adhesion molecule-1, and interleukin-8 mRNA in an NF-kappaB-dependent manner.

CONCLUSIONS

Several agonists that specifically bind to alpha-gal can evoke type II EC activation. Hence, anti-Gal antibodies may contribute directly to xenograft rejection in the absence of complement activation.

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.

Low levels of tissue factor are compatible with development and hemostasis in mice

Tissue factor (TF) expression is associated with life-threatening thrombosis in a variety of human diseases, including sepsis, cancer, and atherosclerosis. Recently, it was shown that inactivation of the murine TF (mTF) gene results in embryonic lethality. To date, despite extensive studies on the regulation of the TF promoter in vitro, no studies have examined the cis-acting regulatory elements that control TF gene expression in vivo. Here we report that a human TF (hTF) minigene containing the human TF promoter and human TF cDNA directed a low level (approximately 1% relative to mouse TF) of both constitutive and LPS-inducible human TF expression in transgenic mice. Importantly, the human TF minigene rescued the embryonic lethality of murine TF null embryos, suggesting that human TF substituted for murine TF during embryogenesis. Rescued mice (mTF-/-, hTF+), which expressed low levels (approximately 1%) of TF activity, developed normally with no signs of a bleeding diathesis, suggesting that low TF expression can maintain hemostasis compatible with normal survival. These studies establish a novel mouse model system that can be used to examine the regulation of the human TF gene in vivo and the impact of low TF levels on the hemostatic balance in various thrombotic diseases.

Arachidonic acid influences proinflammatory gene induction by stabilizing the inhibitor-kappaBalpha/nuclear factor-kappaB (NF-kappaB) complex, thus suppressing the nuclear translocation of NF-kappaB

Arachidonic acid (AA), through its myriad metabolites, is involved in inflammation in a number of ways. AA is produced and released by several cell types, including endothelial cells (EC), and acts on a variety of cells. EC activation plays a key role in inflammation presumably by modulating the immune response through up- or down-regulation of several genes. We have previously shown that AA and its nonmetabolizable analogue, 5,8,11,14-eicosatetraynoic acid (ETYA), inhibit up-regulation of proinflammatory genes in EC. In the present study we identify a mechanism to explain the inhibitory effects: AA and ETYA both inhibit the translocation of nuclear factor-kappaB (NF-kappaB) to the nucleus by blocking the degradation of the inhibitor of NF-kappaB (IkappaB) and thus stabilizing the IkappaB/NF-kappaB complex. To investigate the mechanism whereby AA inhibits up-regulation of genes encoding proinflammatory mediators, we examined the ability of ETYA to inhibit tumor necrosis factor-alpha (TNF-alpha) mediated phosphorylation and degradation of IkappaBalpha. Western blot analysis revealed that preincubation of EC with ETYA for 40 min prior to stimulation with TNF-alpha inhibits the phosphorylation and degradation of IkappaBalpha. These findings establish a mechanism by which AA inhibits nuclear translocation of NF-kappaB and thereby explaining its modulatory role in the induction of proinflammatory genes.

The effect of 5,8,11,14-eicosatetraynoic acid on endothelial cell gene expression

The endothelium plays a key role in inflammation, hemostasis and organ rejection. We report here that a synthetic polyunsaturated fatty acid, 5,8,11,14-eicosatetraynoic acid (ETYA), selectively inhibits the up-regulation of several genes on endothelial cells. ETYA suppresses endothelial cell activation by inhibiting the up-regulation of adhesion molecules like E-selectin. A runoff assay for E-selectin demonstrated that the suppression is at the level of transcription. The fact that ETYA inhibits E-selectin upon stimulation with a diverse group of stimuli like lipopolysaccharide, tumor necrosis factor-alpha or phorbol 12-myristate 13-acetate, suggests that ETYA does not exert its effect by modifying membrane-bound receptors. The messenger RNA for interleukin-8 and glyceraldehyde phosphate dehydrogenase are not affected. Pre-treatment of endothelial cells with ETYA also prevents the adherence of monocytes to tumor necrosis factor-alpha-stimulated cells.

Human monocytes activate porcine endothelial cells, resulting in increased E-selectin, interleukin-8, monocyte chemotactic protein-1, and plasminogen activator inhibitor-type-1 expression

Monocytes (Mo) are thought to be important effector cells in early xenograft rejection. Effects of Mo-endothelial cell (EC) interactions on EC activation in vitro were studied by coculturing human Mo or human monocytoid cell lines, U937 and THP-1, with porcine EC. Without preactivation, U937 cells and Mo induced mRNA for the EC-specific adhesion receptor, E-selectin, expressed only on activated cells, after 2 hr. Surface protein was maximal when equal numbers of EC and Mo were cocultured. Increased mRNA expression of the chemokines, interleukin-8 and monocyte chemotactic protein-1, and the antifibrinolytic protein plasminogen activator inhibitor type-1, confirmed EC activation. Like E-selectin, plasminogen activator inhibitor type-1 mRNA was rapidly induced and returned to baseline after 24 hr, whereas chemokine gene expression was slower and more prolonged. Interleukin-1 receptor antagonist failed to modulate induction of E-selectin. Soluble tumor necrosis factor (TNF) alpha receptor inhibited E-selectin induced by TNF alpha, but not by U937 cells, and mRNA and protein on EC in Mo-EC mixtures cocultured at 1:1 ratios were not significantly reduced. The TNF alpha inhibitor did reduce E-selectin expression (30-40%), as well as induced chemokine gene expression (80%), at higher Mo-EC ratios. Despite this, minimal TNF alpha was detectable in supernatants. These results, along with the transwell experiments that confirmed a requirement for Mo-EC contact, suggest that membrane-bound TNF alpha may be involved. Thus, Mo-EC interactions in the porcine to human combination activated several EC functions, suggesting that initial Mo contact with the vessel wall of a xenogeneic graft may promote leukocyte recruitment, inflammation, and maintenance of thrombus, resulting in eventual organ destruction.

Induction of vascular cell adhesion molecule-1 by low-density lipoprotein

Low-density lipoprotein (LDL) is a well-established risk factor for atherosclerosis. When endothelial cells are incubated with this lipoprotein in pathophysiologic amounts, the cells are activated. Among the documented cellular responses to LDL is increased recruitment of monocytes, which are believed to play a major role in promoting intimal plaque formation. The findings presented here link an atheogenic lipoprotein, LDL, with the induction of an adhesion molecule important in atherogenesis Human LDL induces the vascular cell adhesion molecule-1 (VCAM-1) transcriptionally with an increase in mRNA levels through activation of the VCAM promoter. This effect is blocked by anti-VCAM antibodies. After a 2-day incubation in LDL, the binding of NF-kappa B, which is believed to be a key oxidative-stress sensor for VCAM regulation, remains at basal level. In contrast, the binding activities of AP-1 and GATA, on the other hand, are increased by LDL. Thus, a component of LDL-enhanced endothelial recruitment of monocytes is attributed to VCAM-1 expression, which appears to be mediated through AP-1 and GATA. These data identify LDL as a VCAM-inducer possibly distinct from cytokines and endotoxin.

Adenoviral-mediated overexpression of I(kappa)B(alpha) in endothelial cells inhibits natural killer cell-mediated endothelial cell activation

Activated natural killer (NK) cells have been found in rejecting discordant xenografts and may contribute to endothelial cell (EC) activation and damage. The transcription of genes associated with EC activation, such as E-selectin and interleukin (IL)-8, is regulated by the transcription factor NF-kappaB. In resting EC, NF-kappaB is complexed within the cytoplasm to I(kappa)B(alpha), and EC activation leads to dissociation of the I(kappa)B(alpha)-NF-kappaB complex and nuclear translocation of NF-kappaB. We investigated whether overexpression of I(kappa)B(alpha) in EC, using adenoviral gene transfer, could block NF-kappaB translocation, thereby inhibiting NK cell-mediated EC activation. Co-culture of human NK cells with porcine EC resulted in a threefold increase in E-selectin expression after 4 hr and secretion of greater than 650 pg/ml porcine IL-8 over 24 hr. Overexpression of I(kappa)B(alpha) inhibited the NK cell-mediated induction of E-selectin expression and IL-8 secretion, whereas overexpression of P-galactosidase did not. The inhibition of EC activation was not due to variation in NK-EC adhesion, as the level of adhesion was similar between adenovirally infected and noninfected EC over 4 hr. The level of NK cell-mediated EC cytotoxicity was not significantly different after 4 hr of co-culture, but after 24 hr, cytotoxicity was increased in virally infected cells. Cytotoxicity was more marked in cells overexpressing I(kappa)B(alpha) than cells overexpressing beta-galactosidase. SLA class I and the induction of SLA class II antigen in response to interferon-gamma treatment were reduced in cells infected with adeno-I(kappa)B(alpha) and empty adenovirus, demonstrating that viral infection alone can influence EC biology. Overexpression of I(kappa)B(alpha) using adenovirus provides a novel approach to inhibiting NK cell-mediated EC activation, but additional strategies will be required to inhibit NK cell-mediated cytotoxicity.

Selective suppression of endothelial cell activation by arachidonic acid

Endothelial cell (EC) activation plays a key role in inflammation, thrombosis and organ rejection. Normally, EC are in a quiescent state in which their function is to prevent coagulation and thrombosis, and to participate in the regulation of leukocyte migration from the bloodstream into the tissue. Upon activation with cytokines or other stimuli, EC up-regulate a number of genes, including E-selectin (ELAM-1), intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-1, IL-8, tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1), MCP-1 (monocyte chemoattractant protein-1) and endothelial cell inducible gene (ECI-6). Arachidonic acid (AA) is produced by several cell types, including EC, and acts on various cells. We report here that AA inhibits the up-regulation of some, but not all genes that are induced with EC activation in a dose-dependent manner. AA suppresses TNF-alpha, IL-1 alpha, LPS or PMA-induced E-selectin expression, as well as mRNA accumulation of E-selectin, ICAM-1 and IL-8 stimulated by TNF-alpha. The inhibition appears to be at the level of transcription. At the same time under the same conditions AA does not, repress mRNA accumulation for PAI-1, ECI-6, MCP-1 and VCAM-1. We suggest that the induced expression of AA with EC activation may result in a negative feedback loop regulating further activation.

A benzothiophene-carboxamide is a potent inhibitor of IL-1beta induced VCAM-1 gene expression in human endothelial cells

Vascular endothelial cells respond to cytokines such as IL-1 beta or TNF-alpha by undergoing a number of functional alterations. Among these alterations is the induction of cell surface adhesion molecules, including VCAM-1. In this report, we investigated the effects of a 3-alkoxybenzo[beta]thiophene-2-carboxamide (BZT) on the cytokine induction of VCAM-1 expression and activation of the transcription factor NF-kappa B in human endothelial cells. BZT blocked the IL-1 beta induced cell surface expression of VCAM-1 in human endothelial cells but did not prevent nuclear translocation of NF-kappa B. This study demonstrates that BZT is a potent inhibitor of VCAM-1 expression in human endothelial cells.

Inhibition of endothelial cell activation by adenovirus-mediated expression of I kappa B alpha, an inhibitor of the transcription factor NF-kappa B

During the inflammatory response, endothelial cells (EC) transiently upregulate a set of genes encoding, among others, cell adhesion molecules and chemotactic cytokines that together mediate the interaction of the endothelium with cells of the immune system. Gene upregulation is mediated predominantly at the transcriptional level and in many cases involves the transcription factor nuclear factor (NF) kappa B. We have tested the concept of inhibiting the inflammatory response by overexpression of a specific inhibitor of NF-kappaB, I kappa B alpha. A recombinant adenovirus expressing I kappa B alpha was constructed (rAd.I kappa B alpha) and used to infect EC of human and porcine origin. Ectopic expression of IkappaBalpha resulted in marked, and in some cases complete, reduction of the expression of several markers of EC activation, including vascular cell adhesion molecule 1, interleukins 1, 6, 8, and tissue factor. Overexpressed I kappa B alpha inhibited NF-kappa B specifically since (a) in electrophoretic mobility shift assay, NF-kappa B but not AP-1 binding activity was inhibited, and (b) von Willebrand factor and prostacyclin secretion that occur independently of NF-kappa B, remained unaffected. Functional studies of leukocyte adhesion demonstrated strong inhibition of HL-60 adhesion to I kappa B alpha-expressing EC. These findings suggest that NF-kappa B could be an attractive target for therapeutic intervention in a variety of inflammatory diseases, including xenograft rejection.

Intercellular adhesion molecule-1

The intercellular adhesion molecule (ICAM) 1 is an Ig-like cell adhesion molecule expressed by several cell types, including leukocytes and endothelial cells. It can be induced in a cell-specific manner by several cytokines, for example, tumor necrosis factor-alpha, interleukin-1, and interferon-gamma, and inhibited by glucocorticoids. Its ligands are the membrane-bound integrin receptors LFA-1 and Mac-1 on leukocytes, CD43, the soluble molecule fibrinogen, the matrix factor hyaluronan, rhinoviruses, and Plasmodium falciparum malaria-infected erythrocytes. ICAM-1 expression is predominantly transcriptionally regulated. The ICAM-1 promoter contains several enhancer elements, among them a novel kappa B element which mediates effects of 12-O-tetradecanoylphorbol-13-acetate, interleukin-1, lipopolysaccharide, tumor necrosis factor-alpha, and glucocorticoids. Expression regulation is cell specific and depends on the availability of cytokine/hormone receptors, signal transduction pathways, transcription factors, and posttranscriptional modification. ICAM-1 plays a role in inflammatory processes and in the T-cell mediated host defense system. It functions as a costimulatory molecule on antigen-presenting cells to activate MHC class II restricted T-cells, and on other cell types in association with MHC class I to activate cytotoxic T-cells. ICAM-1 on endothelium plays an important role in migration of (activated) leukocytes to sites of inflammation. ICAM-1 is shed by the cell and detected in plasma as sICAM-1. Regulation and significance of sICAM-1 are as yet unclear, but sICAM-1 is increased in many pathological conditions. ICAM-1 may play a pathogenetic role in rhinovirus infections. Derangement of ICAM-1 expression probably contributes to the clinical manifestations of a variety of diseases, predominantly by interfering with normal immune function. Among these are malignancies (e.g., melanoma and lymphomas), many inflammatory disorders (e.g., asthma and autoimmune disorders), atherosclerosis, ischemia, certain neurological disorders, and allogeneic organ transplantation. Interference with ICAM-1 leukocyte interaction using mAbs, soluble ICAM-1, antisense ICAM-1 RNA, and in the case of melanoma mAb-coupled immunotoxin, may offer therapeutic possibilities in the future. Integration of knowledge concerning membrane-bound and soluble ICAM-1 into a single functional system is likely to contribute to elucidating the immunoregulatory function of ICAM-1 and its pathophysiological significance in various disease entities.