Differential effect of oxpentifylline on tumour necrosis factor and interleukin-6 production

Tumour necrosis factor alpha production by rat blood and its ex vivo pharmacological modulation

Rat blood was investigated as a suitable test system for the discovery of inhibitors of tumour necrosis factor alpha (TNF alpha) biosynthesis. Lipopolysaccharide (LPS) caused a concentration- and time-dependent stimulation of TNF alpha production by heparinised rat blood with peak levels (1000-5000 U/ml; L929 bioassay) at 6 h. Bioactive material was neutralised with a polyclonal rabbit anti-murine TNF alpha antibody which cross-reacts with rat TNF alpha. Dexamethasone, pentoxifylline and denbufylline inhibited TNF alpha production with IC50s of 6.0 +/- 2.0 nM, 20.6 +/- 8.00 microM and 138.0 nM, respectively. When rats were dosed p.o. with dexamethasone or pentoxifylline or i.p. with denbufylline and 1.5 h later TNF alpha production was assessed ex vivo by LPS-stimulated blood, a dose-related inhibition of TNF alpha production occurred with ID50s of approximately 0.08, 250.0 and 5.0 mg/kg, respectively. These results demonstrate that rat blood provides a useful test system for the detection and ex vivo evaluation of inhibitors of TNF alpha biosynthesis.

The specific type III and IV phosphodiesterase inhibitor zardaverine suppresses formation of tumor necrosis factor by macrophages

Murine resident peritoneal macrophages were stimulated with lipopolysaccharide and treated with phosphodiesterase (PDE) inhibitors zardaverine, rolipram and motapizone. The PDE inhibitors suppressed the formation of tumor necrosis factor (TNF) by macrophages. The mono-selective PDE IV inhibitor rolipram and the dual-selective PDE III/IV inhibitor zardaverine had equal inhibitory potency, whereas the PDE III inhibitor motapizone was of lower inhibitory potency. All PDE inhibitors acted in synergy with the adenylate cyclase activators prostaglandin E2 and CG 4203, a prostacyclin analog, and super-additive effects of combinations were observed. The PDE inhibitors also blocked the formation of leukotriene C4 (LTC4); however, substantially higher doses were needed than for blockade of TNF synthesis. Furthermore, no additive or synergistic effects were observed upon combined treatment with adenylate cyclase activators. It is suggested that the suppression of TNF formation by PDE inhibitors is mediated mainly by a PDE isoenzyme of type IV. The effect of PDE inhibitors on LTC4 synthesis appears to be mediated by a different mechanism.

Pentoxifylline at clinically achievable levels inhibits FMLP-induced neutrophil responses, but not priming, upregulation of cell-adhesion molecules, or migration induced by GM-CSF

Pentoxifylline (PTX) administered after bone-marrow transplantation reduces procedure-related organ damage mediated by TNF alpha. GM-CSF is also given post-transplant to stimulate earlier neutrophil recovery. Because PTX has been shown to inhibit neutrophil function, we sought to determine whether it also inhibited the effects of GM-CSF on neutrophil activity. The study confirmed that PTX at clinically achievable concentration (5-10 mumol/l) attenuated the responses of human neutrophils to chemotactic peptide, whereas it did not inhibit the effect of GM-CSF on neutrophil function even at high concentrations. In experiments with human neutrophils, neither the direct effects of GM-CSF such as stimulation of migration and increased expression of CD11b, nor the priming effects of GM-CSF on the respiratory burst, were inhibited by PTX. In experiments with monkeys, intravenous administration of PTX did not block subsequent GM-CSF-induced neutrophil CD11b upregulation or phagocyte margination, even when near millimolar plasma levels of pentoxifylline were obtained. The retention of cytokine-stimulated activities suggests that PTX will not compromise the response of neutrophils to stimuli from infectious foci.

Tumor necrosis factor activities and cancer therapy--a perspective

Tumor necrosis factor (TNF) is a multifunctional cytokine which has excited and fascinated numerous investigators and commercial entities due to its promise as a therapeutic agent against cancer and as a target for drugs treating septic shock. TNF is a protein having cytotoxic, cytostatic, immunomodulatory as well as several other activities and is also involved in septic shock. This review covers the structure of TNF and its receptors, various in vitro activities and in vivo activities based on studies in animal model systems. The role of TNF as an anticancer therapeutic agent, based on various phase I and phase II clinical studies, has also been considered. The review concludes with several considerations for increasing the therapeutic utility of TNF in terms of targeting, toxicity and half-life.

Pentoxifylline and other methyl xanthines inhibit interleukin-2 receptor expression in human lymphocytes

Addition of pentoxifylline to lymphocytes caused a dose-dependent decrease in PHA-induced interleukin-2 receptor (IL-2R) expression. Expression of IL-2R protein and mRNA were inhibited by 60% at a concentration of 1 mM. Pentoxifylline also inhibited release of IL-2R into the medium by 85%. Treatment with recombinant IL-2 (50 U/ml) did not abrogate the effect of pentoxifylline. In addition to inhibition of IL-2R expression, pentoxifylline also decreased the expression of transferrin receptors and class I MHC antigens. Pentoxifylline also inhibited cell proliferation. However, aphidicolin, an inhibitor of DNA polymerase alpha inhibited cell proliferation to the same extent as pentoxifylline, but had no effect on IL-2R expression, indicating that inhibition of cell proliferation does not necessarily lead to inhibition of IL-2R expression. The inhibitory effect on IL-2R expression was also noted with other methylxanthines, theophylline and isobutylmethylxanthine, and with dbcAMP and forskolin. The inhibitory activity of pentoxifylline was prevented by W-13, a calmodulin antagonist, but not by HA-1004, a cyclic AMP-dependent protein kinase inhibitor. This suggests that pentoxifylline might act in part through a Ca2+/calmodulin-dependent mechanism. Pentoxifylline and other methylxanthines may prove useful in delineating the biochemical pathways involved in induction and expression of cell surface receptors.