Giovanni Camussi

The Future Role of Anti-Tumour Necrosis Factor (TNF) Products in the Treatment of Rheumatoid Arthritis

SummaryTumour necrosis factor-α (TNFα) is a pleiotropic cytokine which is overproduced in rheumatoid joints primarily by macrophages. This cytokine has a potentialpathogenic role in the establishment of rheumatoid synovitis, in the formationof pannus tissue and in the process of joint destruction, as it increases synoviocyte proliferation and triggers a cascade of secondary mediators involved in the recruitment of inflammatory cells, in neo-angiogenesis and in the process of joint destruction. These findings made TNFα a potential target for anticytokine therapy.Experimental studies have shown that TNFα blockade by monoclonal antibodies or by soluble TNF receptor reduced the extent and severity of arthritis bothin collagen-induced arthritis in mice and in transgenic mice overexpressingTNFα, which develop a rheumatoid-like destructive arthritis. Clinical studiesbased on the use of anti-TNFα antibodies or soluble receptors have suggested a potential beneficial effect of TNFα-blocking therapy in inducing amelioration of inflammatory parameters in patients with long-standing active disease. In these patients anti-TNFα therapy induces a rapid improvement in multiple clinical assessment of disease activity, including morning stiffness, pain score, Ritchie articular index and swollen joint count. The clinical benefits are associated withan improvement in some serological parameters, such as C-reactive protein and serum amyloid-A, erythrocyte sedimentation rate, blood cytokine levels, haemoglobin, white cells and platelet counts, rheumatoid factor titre and histological features of the synovium. However, it remains to be determined whether anti-TNFα therapy may be useful in the long term management of rheumatoid patients and in the achievement of better outcomes of disease. Because TNFα production also serves a specific function in host defence against infections and tumours, the adverse effects of long term anti-TNFα therapy must be carefully evaluated. In addition, targeting a single mediator may be not sufficient to block the complex inflammatory response in rheumatoid arthritis. For these reasons therapeutic strategies aimed at concomitantly interfering with multiple pathogenic pathways are currently under investigation.

Role of soluble mediators in angiogenesis

‘Dipartimento di Genetica, Biologia e Chimica Medica, University of Torino, Via Santena 5bis, 10126 Torino; ‘Istituto Nazionale per la Ricerca sul Cancro, Genova; ‘Dipartimento di Scienze Cliniche e Biologiche, University of Pavia at Varese; 4Dipat-timento di Scienze Biomediche e Biotecnologiche, University of Brescia; ‘Istituto dei Tumori “Fondazione G. Pascale”, Napoli; 6Dipartimento di Farmacologia Preclinica e Clinica, University of Florence, Florence; and 61stituto Internazionale di Genetica e Biofisica, C.N.R. Naples, Italy

Release of Platelet-Activating Factor in Systemic Lupus erythematosus

The biologically active 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (platelet-activating factor; PAF) is inactivated in plasma mainly by a specific PAF acetylhydrolase (1-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine acetylhydrolase; EC 3.1.1.48). In the present study, PAF was released in detectable amounts (5.4 +/- 2.9 ng/ml; mean +/- 1 SD) in the plasma of 8 out of 10 patients with systemic lupus erythematosus (SLE) during the most active phases of the disease. PAF was never detectable in the plasma of patients with inactive SLE or of healthy subjects. PAF acetylhydrolase activity was markedly reduced in sera of 10 patients with active SLE as compared to 7 patients with inactive SLE, 16 patients with rheumatoid arthritis (RA), 5 patients with nephrotic syndrome (NS) and 15 healthy subjects. A kinetic study of the enzyme in patients with active SLE suggested an overall reduced activity rather than an intrinsic defect of the enzyme. PAF acetylhydrolase in sera of patients with active SLE shared with that of healthy subjects the same substrate specificity, sensitivity to enzymatic and chemicophysical treatments and association to low-density lipoprotein (LDL), acting as carrier of PAF acetylhydrolase in plasma. However, the protein concentration of LDL was significantly reduced in patients with active SLE as compared to patients with inactive SLE, RA and NS and to healthy subjects, thereby suggesting that the reduction of PAF acetylhydrolase activity in active SLE might be due at least in part to a carrier defect related to the activity of the disease. In addition, experiments in which serum of patients with active SLE and serum of healthy subjects were mixed in different combinations indicated the absence of factors inhibiting PAF acetylhydrolase activity in SLE patients.

Potential angiogenic role of platelet-activating factor in human breast cancer.

This study investigated the presence of platelet-activating factor (PAF) in the lipid extracts of 18 primary breast carcinomas and 20 control breast tissues. The amount of PAF detected in breast carcinomas was significantly higher than in controls. The mass spectrometric analysis of PAF-bioactive lipid extract from breast carcinomas showed the presence of several molecular species of PAF, including C16-alkylPAF, C18-lysophosphatidylcholine (LPC), C16-LPC, lyso-PAF, and C16-acylPAF. The amount of bioactive PAF extracted from breast specimens significantly correlated with tumor vascularization revealed by the number of CD34-and CD31-positive cells. As C16-alkylPAF was previously shown to induce angiogenesis in vivo, we evaluated whether the thin layer chromatography-purified lipid extracts of breast specimens elicited neoangiogenesis in a murine model of subcutaneous Matrigel injection. The lipid extracts from specimens of breast carcinoma containing high levels of PAF bioactivity, but not from breast carcinomas containing low levels of PAF bioactivity or from normal breast tissue, induced a significant angiogenic response. This angiogenic response was significantly inhibited by the PAF receptor antagonist WEB 2170. T47D and MCF7 breast cancer cell lines, but not an immortalized nontumor breast cell line (MCF10), released PAF in the culture medium. A significant in vivo neoangiogenic response, inhibited by WEB 2170, was elicited by T47D and MCF7 but not by MCF10 culture medium. These results indicate that an increased concentration of PAF is present in tumors with high microvessel density and that PAF may account for the neoangiogenic activity induced in mice by the lipid extracts obtained from breast cancer. A contribution of PAF in the neovascularization of human breast cancer is suggested.

Biosynthesis and Release of Platelet-Activating Factor from Human Monocytes

The aim of the present study was to investigate the pathways of platelet-activating factor (PAF) production and release from human monocytes. For this purpose, both phagocytic stimuli and stimuli induced by soluble agents were used. The phagocytic stimuli exerted their effect in a receptor-specific mechanism related to surface Fc, C3b and C3d receptors. Stimuli induced by soluble agents, such as A23187 and pH 10.6, which do not require interaction with specific receptors, were also effective in inducing PAF release. In contrast, C5a, a soluble agent which induces a receptor-mediated release of PAF from neutrophils, failed to induce PAF release from monocytes. PAF release from monocytes could be dissociated from phagocytosis and from release of lysozyme. The PAF release required the presence of extracellular cations, the activation of membrane esterase and phospholipase A2 and the integrity of the microfilament system. Moreover, PAF release was modulated by lipoxygenase and intracellular cAMP levels. The relevance of an acetylation process in the biosynthesis of PAF was suggested by the increase of PAF yields in the presence of sodium acetate and by the incorporation of 14C-sodium acetate into molecules of active PAF.

Plasmin Promotes an Endothelium-Dependent Adhesion of Neutrophils Involvement of Platelet Activating Factor and P-Selectin

BACKGROUND The adhesion of leukocytes to the endothelium and the edema of vessel wall may cause vascular reocclusion after thrombolytic therapy. The aim of this study was to evaluate the role of platelet activating factor (PAF) and P-selectin on the adherence of polymorphonuclear neutrophils (PMN) to the endothelium and of PAF on the increased vascular permeability induced by tissue-type plasminogen activator, streptokinase, and plasmin. METHODS AND RESULTS We studied (1) the adhesion of 111Inlabeled PMN to human umbilical cord vein-derived cultured endothelial cells (HUVEC), (2) the transfer of 125I-labeled albumin across HUVEC monolayers, and (3) the adhesion of PMN to isolated bovine coronary arteries under flow conditions. It was found that the adhesion of PMN, induced by tissue-type plasminogen activator, streptokinase, and plasmin, correlated with the synthesis of PAF by HUVEC and was inhibited by WEB 2170, a PAF receptor antagonist. The adhesion of PMN was also inhibited by the treatment of HUVEC with anti-P-selectin antibodies or of PMN with soluble P-selectin or with anti-CD18 monoclonal antibodies. Plasmin also increased the permeability of HUVEC monolayers, an effect that was partially prevented by WEB 2170. Moreover, plasmin promoted the synthesis of PAF from isolated bovine coronary arteries and the adherence of PMN to the endothelium under flow conditions. The pretreatment of PMN with WEB 2170 or with soluble P-selectin prevented adhesion. CONCLUSIONS The synthesis of PAF by endothelial cells at the site of plasmin generation and the endothelial expression of P-selectin may render the endothelial cell surface proadhesive for neutrophils and may favor a local increase in vascular permeability.

Relevance of platelet-activating factor in inflammation and sepsis: mechanisms and kinetics of removal in extracorporeal treatments.

Sepsis can be considered a systemic inflammatory response syndrome (SIRS) caused by infection. When an excessive and/or persistent activation of humoral and cellular mechanisms of host defense is present, an exaggerated and generalized activation of inflammatory mechanisms can lead to a multiple organ dysfunction syndrome. Mediators thought to be involved in this syndrome include the major plasma cascade systems (complement, coagulation, and fibrinolytic systems) and soluble cell-derived mediators (cytokines, reactive oxygen species, platelet-activating factor (PAF), arachidonic acid metabolites, and nitric oxide and related compounds). Several findings indicate that among these mediators, PAF may exert an important role in the pathophysiology of septic shock. Evidence is accumulating that in human sepsis this scenario is far more complicated and that removal of inflammatory mediator excess from plasma, rather than blockade of their potentially beneficial local production, might provide a rationale for the use of continuous renal replacement therapy (CRRT). There is an emerging view that CRRT should be considered in the light of broader concept (ie, the use of blood purification for the treatment of sepsis). Recent studies, performed in an experimental model of continuous arteriovenous hemofiltration with exogenous PAF, demonstrated that polysulfone membranes can adsorb substantial amounts of biologically active PAF. These studies also showed that the removal of this mediator occurs by a two-step process involving early adsorption followed by ultrafiltration. Although the removal of cytokines, such as tumor necrosis factor-alpha (TNF-alpha), remains controversial, mainly because of differences in membrane used, operational conditions, and inter- and intra-assay variability, the crucial point is that no evidence has yet been given to show real benefit from CRRT in significantly reducing the plasma concentration of cytokines. The net advantage of CRRT, however, may not only be the removal of cytokines per se, but also the simultaneous elimination of cytokine-inducing substances. Experimental and human studies will be discussed as to whether extracorporeal treatments may remove an excess of circulating cytokines, either by increasing the turnover rate (the so-called high-volume hemofiltration), or by using sorbent systems to regenerate plasma filtrate.

Tumor necrosis factor alters cytoskeletal organization and barrier function of endothelial cells

Treatment of human umbilical cord vein endothelial cells with tumor necrosis factor results in marked changes in cell shape and cytoskeletal organization. After 4 h of treatment, these cells loose reciprocal contacts with the formation of intercellular gaps. This retraction reaches a maximum after 6 h when most stress fibers staining for F-actin disappear and vinculin becomes diffused in the cytoplasm. Such changes spontaneously reverse after 24 h in the presence of tumor necrosis factor or after 2 h of incubation in fresh medium. After treatment with tumor necrosis factor, endothelial monolayers become permeable to albumin because of gaps that form between cells. Normal human serum, plasma alpha 1-proteinase inhibitor and an anti-inflammatory peptide that decrease synthesis of platelet-activating factor inhibit the changes induced by tumor necrosis factor. Furthermore, receptor antagonists of platelet-activating factor have the same effect. These findings suggest that platelet-activating factor is a secondary mediator responsible for the changes in cell shape and cytoskeletal organization, and for the leakiness of endothelial monolayers.

Modulatory effect of interleukin‐10 on the production of platelet‐activating factor and superoxide anions by human leucocytes

We observed that human monocytes (MO) and polymorphonuclear neutrophils (PMN) stimulated by lipopolysaccharide (LPS) produce platelet‐activating factor (PAF) in a pattern characterized by an early and a delayed peak of synthesis. The early peak of PAF synthesis was due to a direct stimulation of these cells through mCD14 receptor as it was inhibited by anti‐CD14 monoclonal antibody. The delayed and sustained peak of PAF synthesis was dependent on protein synthesis and cytokine production as shown by the inhibitory effect of cycloheximide on both MO and PMN, and of anti‐tumour necrosis factor‐α (anti‐TNF‐α) and of anti‐interleukin‐8 (anti‐IL‐8) neutralizing antibodies on MO and PMN respectively. IL‐10 completely prevented this second, cytokine‐dependent peak of PAF synthesis. In contrast, IL‐10 markedly enhanced the first peak of PAF synthesis both in MO and PMN. Moreover, IL‐10 was shown to modulate the production of superoxide anions (O‐2) on both MO and PMN. As suggested by previous studies, IL‐10 inhibited the delayed production of O‐2. In the present study, we observed that IL‐10 directly stimulated an early production of O‐2. In addition, IL‐10 enhanced the synthesis of O‐2 by MO and PMN challenged with LPS. The IL‐10‐induced O‐2 production was dependent, at least in part, from its effect on PAF synthesis, as it was inhibited by the PAF receptor antagonist WEB 2170. These results suggest that IL‐10 may upregulate the early synthesis of PAF and O‐2 triggered by direct LPS stimulation, whereas it may downregulate the delayed production of these mediators.

Production of cytokines in hemodialysis.

Tumor necrosis factor (TNF-alpha) and interleukin-1 (IL-1 beta) are cytokines primarily produced by monocytes/macrophages when stimulated by endotoxin, complement-derived anaphylatoxins and the specific antigen. In the present study, the plasma levels of TNF-alpha and IL-1 beta were evaluated before and after hemodialysis with cuprophane membrane (in 9 patients) and hemodiafiltration (in 9 patients) using three high-permeability membranes such as polymethylmethacrylate, polyacrylonitrile (AN-69) and polysulfone. In vitro spontaneous production of TNF-alpha and IL-1 beta was evaluated in the supernatants from short-term cultured monocytes obtained before and after treatment. The predialytic levels of TNF-alpha and IL-1 beta were significantly higher (p less than 0.05) in the uremic population than in 21 healthy subjects taken as controls. The analysis of the uremic population regarding the mode of therapy indicated that in hemodialysis the predialytic plasma levels of TNF-alpha and IL-1 beta did not significantly differ from those of healthy subjects. In contrast, in hemodiafiltration with polymethylmethacrylate and AN-69, but not with polysulfone, the predialytic plasma levels of both cytokines were significantly (p less than 0.05) increased. No significant variation in plasma levels of both cytokines was observed after hemodialysis with cuprophane membranes. Hemodiafiltration with polymethylmethacrylate and AN-69, but not with polysulfone, brought about a consistent reduction in plasma levels of both cytokines. Detectable amounts of TNF-alpha and IL-1 beta were spontaneously produced by peripheral-blood monocytes 6 h after the end of hemodialysis but not of hemodiafiltration. These studies suggest a possible role of TNF-alpha and IL-1 beta in the biocompatibility of different extracorporeal treatments.