Abstract
Abstract. Several automated instruments exist to measure the acellular oxidative potential (OP) of ambient particulate matter (PM). However, cellular OP of the ambient PM is still measured manually, which severely limits the comparison between two types of assays. Cellular assays could provide a more comprehensive assessment of the PM-induced oxidative stress, as they incorporate more biological processes involved in the PM-catalyzed reactive oxygen species (ROS) generation. Considering this need, we developed a semi-automated instrument, the first of its kind, for measuring the cellular OP based on a macrophage ROS assay using rat alveolar macrophages. The instrument named SCOPE – semi-automated instrument for cellular oxidative potential evaluation – uses dichlorofluorescein diacetate (DCFH-DA) as a probe to detect the OP of PM samples extracted in water. SCOPE is capable of analyzing a batch of six samples (including one negative and one positive control) in 5 h and is equipped to operate continuously for 24 h with minimal manual intervention after every batch of analysis, i.e., after every 5 h. SCOPE has a high analytical precision as assessed from both positive controls and ambient PM samples (coefficient of variation (CoV)<17 %). The results obtained from the instrument were in good agreement with manual measurements using tert-butyl hydroperoxide (t-BOOH) as the positive control (slope =0.83 for automated vs. manual, R2=0.99) and ambient samples (slope =0.83, R2=0.71). We further demonstrated the ability of SCOPE to analyze a large number of both ambient and laboratory samples and developed a dataset on the intrinsic cellular OP of several compounds, such as metals, quinones, polycyclic aromatic hydrocarbons (PAHs) and inorganic salts, commonly known to be present in ambient PM. This dataset is potentially useful in future studies to apportion the contribution of key chemical species in the overall cellular OP of ambient PM.
Highlights
Based on several experiments conducted in our lab, we found it is difficult to detect a signal for a particulate matter (PM) extract with concentration below 20 μg mL−1, which could be considered as a rough measure of the detection limit for semiautomated instrument for cellular oxidative potential evaluation (SCOPE)
We have described the development of SCOPE for assessing the oxidative potential (OP) of water-soluble extracts of ambient PM in rat alveolar macrophages
The promising results of this instrument could pave the way for further development in automating other cellular assays
Summary
Epidemiological models have traditionally relied on mass of the particulate matter (PM) as a metric to associate health effects such as wheeze (Doiron et al, 2017; Karakatsani et al, 2012), asthma (Holm et al, 2018; Wu et al, 2019; Zmirou et al, 2002), myocardial infarction and coronary heart disease (Yang et al, 2019), ischemic heart disease and dysrhythmias (Pope et al, 2004) and heart rate variability (Breitner et al, 2019; Pieters et al, 2012; Riojas-Rodríguez et al, 2006) with the inhalation of ambient and indoor PM. Mass is not a wholesome metric as it does not capture the diverse range of particle physicochemical characteristics. We need a metric of the PM along with mass that can provide some relevant information to assess its toxicity. Oxidative stress has emerged as one such metric which has been identified as a crucial step in the progression of many human diseases
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