Immunotoxic and Genotoxic Responses Induced by Emitted Particles from Pellet Boiler and Conventional Masonry Heater in RAW264.7 Macrophages

MAIJA TAPANAINEN (1,2), Pasi I. Jalava (1,2), Mikko S. Happo (1,2), Jorma Mäki-Paakkanen (1), Raimo O. Salonen (1), Heikki Lamberg (2), Jarno Ruusunen (2), Jarkko Tissari (2), Pasi Yli-Pirilä (2), Kati Nuutinen (2), Jorma Jokiniemi (2,3), Maija-Riitta Hirvonen (1,2)

(1) National Institute for Health and Welfare (THL), Kuopio, Finland, (2) University of Eastern Finland, Kuopio, Finland, (3) VTT Technical Research Centre of Finland, Espoo, Finland

     Abstract Number: 51
     Last modified: October 9, 2009

Abstract
Residential biomass combustion appliances emit significant amounts of fine particle mass which is suspected to cause a substantial health burden. Exposure to wood smoke is associated with asthma attacks, respiratory symptoms, increased hospital admissions and daily mortality. However, health effects cannot be predicted only on the basis of source-related particle mass emissions. Instead, chemical composition is likely to determine toxic properties of the emitted particles. The aim of the present study was to identify cellular immuno- and genotoxic responses induced by the particles emitted from a pellet boiler and a conventional masonry heater, and thereafter to compare the detected cellular responses with the chemical composition of particles.

Fine particulate samples (aerodynamic diameter less than 1 micro-meter) were collected from diluted flue gas of the combustion using Dekati gravimetric impactor. The physicochemical properties of particles emitted from the combustion appliances are presented by Lamberg et al. (ibid). Mouse RAW264.7 macrophages were exposed for 24 hours to four doses (15, 50, 150 and 300 micro-grams / millilitre) of the emission particles suspended in pyrogen free water. Cell viability, programmed cell death, production of proinflammatory cytokine TNF-alpha and chemokine MIP-2 as well as DNA damage were measured from the exposed cells. The pellet boiler emitted substantially less particle mass than the conventional masonry heater suggesting more complete combustion process. Appliance type had a large effect on the content of known genotoxic PAHs in the particles (Lamberg et al. ibid).

The MTT test indicated a dose-dependent decrease in cell viability after the exposure to the particulate samples. Interestingly, particulate samples from the pellet boiler were more potent inducers of acute cell death (up to 57%) than the samples from the conventional masonry heater (up to 19%). However, a flow cytometric analysis of programmed cell death revealed that particles from the conventional masonry heater induced a two-fold increase in the amount of apoptotic cells compared to those from the pellet boiler. Particles from the conventional masonry heater were more potent inducers of DNA damage in the Comet assay than the pellet boiler derived particles, which caused only minor DNA damage. This may be due to the very different concentrations of genotoxic PAH compounds in the particulate samples. In addition, the results on programmed cell death were well in line with the genotoxic responses. The particulate samples from both combustion appliances triggered only slight, but dose-dependently increasing productions of inflammatory mediators measured with the ELISA immunoassay. The low inflammatory activity of the particles may be, at least partially, due to their high cytotoxicity.

The present results suggest that particles emitted from the pellet boiler induce cell death by different mechanisms than particles emitted from the conventional masonry heater. In addition, particles from more complete wood combustion are considered to be less genotoxic than those from incomplete combustion.