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

• PM-induced inflammation involves cellular release of a range of mediators.
• Adsorption of mediators to PM complicates the interpretation of mediator measurements.
• This adsorption might even influence the conclusions of a study.
• Adsorption of mediators to PM needs to be assessed to avoid misinterpretation of data.
• We provide a step-by-step method for correcting data for mediator adsorption to PM.

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.