Wim A. Buurman

Tumor necrosis factor (TNF)-alpha inhibits insulin signaling through stimulation of the p55 TNF receptor and activation of sphingomyelinase.

Tumor necrosis factor (TNF)-α plays a central role in the state of insulin resistance associated with obesity. It has previously been shown that one important mechanism by which TNF-α interferes with insulin signaling is through the serine phosphorylation of insulin receptor substrate-1 (IRS-1), which can then function as an inhibitor of the tyrosine kinase activity of the insulin receptor (IR). However, the receptors and the signaling pathway used by TNF-α that mediate the inhibition of IR activity are unknown. We show here that human TNF-α, which binds only to the murine p55 TNF receptor (TNFR), is as effective at inhibiting insulin-dependent tyrosine phosphorylation of IR and IRS-1 in adipocytes and myeloid 32D cells as murine TNF-α, which binds to both p55 TNFR and p75 TNFR. Likewise, antibodies that are specific agonists for p55 TNFR or p75 TNFR demonstrate that stimulation of p55 TNFR is sufficient to inhibit insulin signaling, though a small effect can also be seen with antibodies to p75 TNFR. Exogenous sphingomyelinase and ceramides, known to be formed by activation of p55 TNFR, inhibit IR and IRS-1 tyrosine phosphorylation and convert IRS-1 into an inhibitor of IR tyrosine kinase in vitro. Myeloid 32D cells expressing IR and IRS-1 are sensitive to this inhibition, but cells expressing IR and IRS-2 are resistant, pointing to an important difference in the biological function between IRS-1 and IRS-2. These data strongly suggest that TNF-α inhibits insulin signaling via stimulation of p55 TNFR and sphingomyelinase activity, which results in the production of an inhibitory form of IRS-1.

Long term anti-tumour necrosis factor alpha monotherapy in rheumatoid arthritis: effect on radiological course and prognostic value of markers of cartilage turnover and endothelial activation.

Objectives: To investigate the effect of prolonged neutralisation of tumour necrosis factor α (TNFα) on the radiological course in rheumatoid arthritis (RA). To assess whether the radiological course can be predicted by clinical variables or biological markers of cartilage and synovium turnover and of endothelial activation. Patients and methods: Forty seven patients with active RA enrolled at our centre in monotherapy trials with adalimumab (D2E7), a fully human anti-TNFα monoclonal antibody, were studied for two years. Radiographs of hands and feet obtained at baseline and after one and two years were scored in chronological order by a single, blinded observer using the modified Sharp method. Radiological course was classified as stable or progressive using the smallest detectable difference as cut off point. The relation between radiological course and serum markers of cartilage and synovium turnover (metalloproteinases (MMP-1 and MMP-3), cartilage oligomeric matrix protein (COMP), human cartilage glycoprotein-39 (HC gp-39)), endothelial activation (soluble E-selectin and intercellular adhesion molecule (ICAM-1)), and integrated measures of disease activity were assessed using univariate and multivariate analysis. Results: Radiological evaluation was performed in 36 patients with paired sets of radiographs at baseline and two years. After two years a total of 15/36 (42%) presented no radiological progression. More patients with stable radiological course were still receiving anti-TNFα treatment after two years (13/15 (87%) v 11/21 (52%); p=0.03) and had lower baseline COMP and sICAM-1 levels (p=0.01 and 0.04, respectively) than those in the group with progressive disease. In a logistic regression model the combination of sustained TNF neutralisation and baseline COMP and sICAM-1 levels was predictive for radiological outcome (p=0.03). C reactive protein and disease activity score area under the curve were significantly correlated with changes in radiological scores after two years (r=0.40 and 0.37, p<0.05). Long term TNFα neutralisation decreased the levels of COMP, sICAM, MMPs, and HC gp-39, but not sE-selectin. Conclusion: The results suggest that long term monotherapy with anti-TNFα has a positive effect on radiological outcome and modulates cartilage and synovium turnover as measured by biological markers. Baseline serum sICAM-1 levels and COMP levels may be helpful to identify patients with progressive or non-progressive radiological outcome.

Treatment with the platelet-activating factor antagonist TCV-309 in patients with severe systemic inflammatory response syndrome: a prospective, multi-center, double-blind, randomized phase II trial.

In a prospective randomized, double-blind, placebo-controlled clinical study, the safety and efficacy of the platelet-activating factor antagonist TCV-309 in the treatment of systemic inflammatory response syndrome was studied. In total 29 patients were treated with 1.0 mg/kg TCV-309 twice daily during 7 days or with placebo. Study parameters were as follows: adverse events, 28 and 56 day all cause mortality, multi-organ failure scores, and the inflammatory mediators tumor necrosis factor, interleukin 6, interleukin 8, and soluble E-selectin. There was no difference in number and severity of adverse events between TCV-309- and placebo-treated patients. Day 28 and day 56 mortality was similar in both groups (day 56: 7/12 TCV-309 vs. 9/16 placebo, NS). Pulmonary and hematological failure scores improved significantly in TCV-309-treated patients (p < .05). There was no difference in inflammatory mediator levels between TCV-309- and placebo-treated patients. Treatment with TCV-309 appears to be safe in patients with systemic inflammatory response syndrome and does improve organ failure significantly.

Transient induction of E-selectin expression following TNF alpha-based isolated limb perfusion in melanoma and sarcoma patients is not tumor specific.

Endothelial injury of the tumor microvasculature after isolated limb perfusion (ILP) with TNF-α and melphalan is considered to play an important role in the pathogenesis of tumor necrosis. It is thought to follow endothelial cell activation and subsequent attraction of polymorphonuclear cells (PMNs). The observed selectivity for the tumor could be due to preferential overex-pression of cell-adhesion molecules by the tumor vasculature. We tested this proposition by analyzing sequential biopsies from both tumor and normal distant skin, taken from melanoma and sarcoma patients before ILP and at 30 min and 24 h after ILP. Histopathologically confirmed complete response was observed in six of seven melanoma patients, 1–8 months after ILP. By using immunohistochemistry on the light- and electron-microscopic level, the expression patterns of intercellular adhesion molecules-1 (ICAM-1), E-selectin (ELAM-1), VCAM-1, and PECAM-1 were examined. In addition, the results were compared with the effects on HUVECs (human umbilical vein endothelial cells) in vitro of transient exposure of the agents used during ILP. ICAM-1 and PECAM-1 were constitutively expressed on vascular endothelial cells, both in normal tissues and in the tumor lesions. In biopsies taken 30 min after termination of the perfusion, a moderate induction of E-selectin expression on the vascular endothelium in the tumors and a marked expression on the vasculature in the perfused normal skin were observed. It decreased within 24 h after perfusion in both normal skin and in the tumor. The upregulation of E-selectin was accompanied neither by an influx of neutrophils nor by hemorrhagic necrosis. There were no drastic changes in the expression of VCAM-1, ICAM-1, or PECAM-1. These findings imply that the upregulation of E-selectin after ILP is not restricted to the tumor microvasculature and that, therefore, these microvascular events seem not to be the decisive pathomechanism responsible for tumor regression.

Platelet-Activating Factor

Research leading to the discovery of platelet-activating factor (PAF) came from studying a reaction that triggered platelets to release histamine. It was attributed to a factor actively released from leukocytes. Platelet-activating factor was first identified by Benveniste et al. in 1972.1 Later it was recognized that this phospholipid mediator is also released from a number of other cell types, such as macrophages, basophils, and mast cells and that it displayed diverse immunomodulatory actions. The role PAF plays in the process leading to sepsis has especially attracted attention. PAF was identified as an important factor in sepsis leading to the release of many other inflammatory mediators.2