3rd Annual BMRP Investigator Meeting - Abstract

Effect of Dietary Microparticles on Macrophage Function in Crohn’s Disease

Matt Butler^1,a, Joseph Boyle², Jonathan Powell³, Robert Lechler⁴ and Subrata Ghosh^1,b

¹Department of Gastroenterology and ²Department of Histopathology, Imperial College London (London, England); ³GI Lab, The Rayne Institute, St Thomas’ Hospital (London, England); ⁴Department of Immunology, Imperial College London (London, England)

Western diets regularly expose the gastrointestinal tract to a large quantity of man-made, micron-sized, particles (>10¹²/day) derived from food additives. These are taken up by M cells and accumulate in gut macrophages where they are resistant to degradation. Microparticles also have charged surfaces that readily adsorb luminal biomolecules such as LPS. Binding of luminal antigens or toxins to microparticles and delivery to intestinal macrophages in a particulate form could potentially overcome tolerogenic process in susceptible individuals and lead to inflammatory bowel diseases such as Crohn’s.

We investigated the effect of two types of common dietary microparticles (aluminium silicates and titanium dioxide) on macrophage function in vitro. Monocyte-derived macrophages from active Crohn’s patients or healthy controls were incubated with microparticles for 24 hours before being assayed for cytokine production (IL-1β, IL-8, TNFα, IL-10, and TGFβ), phagocytosis (beads or apoptotic cells) and T cell stimulatory capacity (mixed lymphocyte reaction). Microparticles had little effect on macrophage function unless given at very high (toxic) doses (>10μg/ml). However, in the presence of LPS, microparticles appeared to have a slight adjuvant effect – improving cytokine responses to LPS by ~10%. This apparently resulted from adsorption of LPS to the surface of microparticles in the presence of calcium (Ca²⁺). Microparticles had negligible effects on phagocytosis and stimulatory capacity at doses up to 10μg/ml and cells from Crohn’s patients were no more susceptible to the presence of microparticles than cells from healthy controls. Thus, although they are immunologically ‘inert’ on their own, adsorption of luminal biomolecules to the surfaces of dietary microparticles could turn them into strong inflammatory stimuli.

In a related line of investigation, we took advantage of the fact that titanium dioxide (TiO2) microparticles readily adsorb biomolecules to generate microparticles coated with the anti-TNFα therapy, Infliximab. We hoped that these complexes might provide a more effective treatment of Crohn’s disease by targeting activated intestinal macrophages. Early in vitro experiments indicate that TiO2-Ca²⁺-Infliximab complexes are, indeed, more effective at blocking TNFα and preventing the subsequent inflammatory cytokine cascade and could be used as part of a novel treatment of Crohn’s disease.

^aCo-investigator and Presenter; bPrincipal Investigator