Effects of Sample Preparation on Chemistry, Cytotoxicity, and Inflammatory Responses Induced by Air Particulate Matter

Abstract

Methanol is used for high-efficiency extraction of air particulate (PM) mass from the sampling substrate in the high-volume cascade impactor. Sonication is needed during extraction and when dissolving dried PM samples in liquids used in exposure studies. We investigated the effects of these procedures on the PM chemistry and PM-induced cytotoxic and inflammatory responses in mouse macrophages. Untreated and methanol-treated ambient air reference PM samples (SRM1649a, EHC-93) and diesel PM (SRM1650) were tested after different sonication durations (5–30 min). Furthermore, the time dependency of the responses to SRM1649a, EHC-93, and a fine PM sample from Helsinki was investigated. Methanol pretreatment increased on average by 24% and 21% the recovery of water-soluble metals from SRM1649a and EHC-93, but not SRM1650. It had no systematic effect on the recoveries of inorganic secondary ions (NO₃^-, SO₄^2-, NH₄⁺) or the sum of genotoxic PAH compounds from the three reference samples. Nitric oxide (NO) response to SRM1650 was strongly enhanced by methanol pretreatment, whereas the cytotoxic or inflammatory responses to the ambient air PM samples (EHC-93, SRM1649a) were only slightly modified. Sonication duration was a modifying factor only in connection to SRM1650. Maximal interleukin (IL)-1 production was observed earlier (8 h) than maximal tumor necrosis factor (TNF) α and IL-6 productions (24 h), which indicates the importance to know the optimal time points for measurement of the selected response parameters. In conclusion, methanol extraction and reasonable sonication duration are not likely to modify the cytotoxic and inflammatory potency of ambient air PM samples, but some responses to air PM, rich in organic compounds, can be modified.

Notes

This study was conducted within the framework of the project “Chemical and biological characterisation of ambient air coarse, fine, and ultrafine particles for human health risk assessment in Europe” (PAMCHAR), coordinated by the National Public Health Institute of Finland (more information: http://www.pamchar.org). The authors are grateful to the following persons for skilful laboratory analyses and tests: Karri Saarnio, MSc, for IC analyses; Ulla Makkonen, MSc, for ICP-MS analyses; Sirpa Himberg, for PAH analyses; and Arja Rönkkö and Reetta Tiihonen, for cytokine analyses. The financial support of the EC-FP5 Quality of Life and Management of Living Resources Programme (contract QLK4-CT-2001-00423), the Academy of Finland (FINE, contract 201701) and the Center of Excellence Program 2002–2007 of the Academy of Finland (contract 53307), and the National Technology Agency (TEKES, contract 40715/01) is also highly appreciated.