Differential toxicity in an alveolar epithelial cell line of fine particulate matter from brake wear, road wear, and diesel exhaust

Abstract

Introduction: Exposure to airborne fine particulate matter (diameter <2.5μm; PM2.5) is associated
with increasedmorbidity and mortality, but differential effects of PM2.5 from differentsources,
with differing compositions, are poorly understood.PM of this size is small enough to reach the alveoli, the functional unit of the lung. Carexhaust-derived PM release is decreasing, which has increased the relative contribution of non-exhaustPM, the major constituent of which is brake wearPM (BWPM), along with road and tyre wear. Non-exhaust PM emissions arepredicted to increase withheavier battery-electric vehicles. Importantly, non-exhaust PM emissions are currently unregulated by UK legislation, and hencethere is a lack of established mitigation strategies.Non-exhaust PM also tends to be rich in metals, which have been associated with
toxicity and are chemically heterogeneous, with PMcomposition differing considerably based on
the source. Lastly, their toxicological propertieshave been poorly studied compared to exhaust PM emissions. This study aimed to characterise boththe chemical and toxicological properties of PM2.5-0.1 from 4 brake pad types compared to roadwearand diesel exhaust PM. Methods: An alveolar type-II epithelial cell line(ATIIER:KRASV12) was exposed to 4-32 µg/cm2 (12.5 100 μg/ml)PM2.5-0.1 from 4 brake pad types: low-metallic, semi-metallic, non-asbestosorganic (NAO), and ceramic, or roadwear or dieselPM2.5-0.1 for 2-24h. PM composition was determined by ICP-MS. Cytotoxicity wasmeasured by LDH and MTT assays, inflammatory mediator release by ELISA, andgene expression by RT-qPCR and RNA-Seq. Protein expression was assessed usingwestern blotting, and luciferase reporter assays were used to assess transcriptionfactor binding activity. ATP production rates were assessed using a SeahorseATP-rate assay. Results: ICP-MS showed clear PM-specific composition; notablyNAO and ceramic BWPM were relatively enriched in copper, barium, titanium, andzirconium. RNA-Seq showed NAO and ceramic BWPM induced the greatest number ofdifferentially expressed genes vs. control, related to inflammatory, oxidativestress, heat-shock, metal-binding, and hypoxia responses, and also the greatestincreases in cytotoxicity and cytokine release, in all cases greater thanroadwear PM or diesel PM. Amelioration of responses by copper-chelatingtetraethylenepentamine implicated BWPM copper in this differential toxicity.NAO BWPM also induced an increase in HIF1α stabilisation in a copper- andoxidative stress-dependent manner and increased both the binding of the HIFtranscription factor complex to hypoxia response elements, and inhibition offactor inhibiting HIF (FIH). In further support of a hypoxic response areal-time metabolic assay
demonstrated an NAO BWPM-induced switch towardsglycolysis. Conclusions: This research demonstrated that epithelial cellresponses to vehicle-derived PM2.5-0.1 were dependent on source, with NAO andceramic BWPM proving the most potent across a range of endpoints. As copper wasimplicated in multiple toxicological responses, legislation to reduce coppercontent within brake pads could reduce the toxicity associated with theseemissions. Further research is needed to understand population exposure and healtheffects related to different non-exhaust PM types, especially chronicexposures, as well as the potential role of other components of non-exhaust PM.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata