The challenge of obtaining correct data for cellular release of inflammatory mediators after in vitro exposure to particulate matter.

Exposure to ambient particulate matter (PM) has been associated with adverse cardiopulmonary effects where inflammation seems to play an important role. Cellular release of inflammatory mediators is therefore commonly measured in in vitro studies of PM-induced effects. However, adsorption of such mediators to PM may interfere with these measurements and thereby possibly also influence the conclusions of such studies. The aim of the present mini review is to provide the reader with an update on what is currently known about adsorption of inflammatory mediators to PM. We also present a step-by-step method for correction of in vitro results, based on mediator adsorption experiments. Moreover, mediator adsorption and its possible consequences are exemplified with a case study demonstrating adsorption of long pentraxin 3 (PTX3) and vascular endothelial growth factor (VEGF) to a selection of PM samples. The highest degree of adsorption was determined to be 65 and 95% for PTX3 and VEGF respectively, and for the various PM samples the degree of adsorption was highly variable. In conclusion, the data and results discussed in this review underscore the importance of assessing and correcting for mediator adsorption, especially in studies involving comparison of effects induced by several different PM samples.

Role of IL-1 beta and COX2 in silica-induced IL-6 release and loss of pneumocytes in co-cultures.

The pro-inflammatory cytokines IL-1 beta, TNF-alpha and IL-6 are of great importance in the development of silica-induced lung damage and repair. In this study we investigated the role of IL-1 beta, TNF-alpha and COX2 in silica-induced regulation of IL-6 release and pneumocyte loss in various mono- and co-cultures of monocytes, pneumocytes and endothelial cells. All co-cultures with monocytes, and especially cultures including endothelial cells, showed an increase of silica-induced release of IL-6 compared to the respective monocultures. Treatment with the antagonist IL-1 ra strongly decreased IL-1 beta and IL-6 release in contact co-cultures of monocytes and pneumocytes. COX2 up-regulation by silica and IL-1 beta was eliminated by IL-1 ra. Inhibition of COX2 markedly reduced both IL-1 beta and IL-6 release. IL-1 ra was more effective than COX2-inhibition in reduction of IL-6, but not of IL-1 beta. Silica-induced pneumocyte loss was reduced by IL-1 beta, but this effect was not counteracted by the IL-1 receptor antagonist. Our findings suggest that silica-induced IL-6 release from pneumocytes is mainly mediated via IL-1 beta release from the monocytes, via both COX2-dependent and -independent pathways. Notably, COX2-derived mediators seem crucial for a positive feed-back regulation of IL-1 beta release from the monocytes. In contrast to silica-induced IL-6, the reduction in pneumocyte loss by IL-1 beta does not seem to be regulated through an IL-1R1-dependent mechanism.

IL-1beta differently involved in IL-8 and FGF-2 release in crystalline silica-treated lung cell co-cultures.

BACKGROUND: Inhalation of crystalline silica particles is in humans associated with inflammation and development of fibrosis. The aim of the present study was to investigate the effect of crystalline silica on the release of the fibrosis- and angiogenesis-related mediator FGF-2 and the pro-inflammatory mediator IL-8, and how IL-1beta and TNF-alpha were involved in this release from various mono- and co-cultures of monocytes, pneumocytes and endothelial cells. RESULTS: Silica exposure induced an increase of IL-8 release from monocytes and from pneumocytes alone, and the FGF-2 level in the medium increased upon silica exposure of pneumocytes. Both the responses were enhanced in non-contact co-cultures with endothelial cells. The FGF-2 release seemed to increase with the silica-induced decrease in the number of pneumocytes. The release of IL-8 and FGF-2 was partially suppressed in cultures with pneumocytes in contact with monocytes compared to non-contact cultures. Treatment with anti-TNF-alpha and the IL-1 receptor antagonist revealed that release of IL-1beta, and not TNF-alpha, from monocytes dominated the regulation of IL-8 release in co-cultures. For release of FGF-2, IL-1ra was without effect. However, exogenous IL-1beta reduced the FGF-2 levels, strongly elevated the FGF-2-binding protein PTX3, and prevented the reduction in the number of pneumocytes induced by silica. CONCLUSION: IL-1beta seems to be differently involved in the silica-induced release of IL-8 and FGF-2 in different lung cell cultures. Whereas the silica-induced IL-8 release is regulated via an IL-1-receptor-mediated mechanism, IL-1beta is suggested only indirectly to affect the silica-induced FGF-2 release by counteracting pneumocyte loss. Furthermore, the enhanced IL-8 and FGF-2 responses in co-cultures involving endothelial cells show the importance of the interaction between different cell types and may suggest that both these mediators are important in angiogenic or fibrogenic processes.