Synergistic pulmonary toxicity of resorcinol bis(diphenylphosphate) and microplastics: Integrated proteomics and metabolomics approach reveals oxidative stress-inflammatory crosstalk

As a replacement for conventional brominated flame retardants, the environmental prevalence and toxicological implications of resorcinol bis(diphenylphosphate) (RDP), an emerging organophosphate ester flame retardants (OPFRs), remain inadequately characterized, particularly regarding its combinatorial effects with environmentally co-occurring micro/nanoplastics (MNPs). To address this knowledge gap, we established a murine inhalation exposure model featuring three experimental cohorts: low-dose group (0.1 mg/kg/day of RDP), high-dose group (10 mg/kg/day of RDP), and a co-exposure group (10 mg/kg/day of RDP and 10 mg/kg/day of polystyrene nanoplastics). Comprehensive mechanistic investigations employing histopathological evaluation, oxidative stress and inflammatory cytokine profiling, and integrated proteomic-metabolomic analyses revealed that: (1) Both RDP monotherapy and RDP-nanoplastics co-exposure elicited pulmonary lesions characterized by alveolar septal thickening and inflammatory cell infiltration, with the co-exposure group exhibiting exacerbated oxidative stress (2.4-fold elevation in malondialdehyde levels vs. controls, p < 0.05); (2) Proteomic perturbations demonstrated exposure-specific signatures: low-dose group preferentially disrupted cytoskeletal remodeling pathways (e.g., Myh4, Myh8 downregulation), suggesting subclinical mechanical compromise, whereas high-dose group impaired mitochondrial-nuclear crosstalk (Hspa9, Mtnd1 dysregulation). Crucially, the co-exposure group showed synergistic mitochondrial energy metabolism interference, activation of neuroinflammatory (Nrxn1, Nrp2 upregulation) and immunoregulatory pathways (Ildr2, Ighg2b upregulation); (3) Metabolomic perturbations in arachidonic acid metabolism, steroid hormone biosynthesis and tryptophan catabolism indicated systemic redox imbalance and inflammatory mediator dysregulation. This work provides the first experimental evidence of RDP-MNPs co-exposure inducing pulmonary toxicity through oxidative stress-inflammatory crosstalk, establishing a novel framework for assessing combinatorial risks of emerging pollutant mixtures.