Reply to Correspondence Regarding “Inflammatory Effects of Microplastics and Nanoplastics on Nasal Airway Epithelial Cells”

To the Editor: We thank Dr. Hyun Jin Min for the thoughtful correspondence regarding our manuscript, “Inflammatory Effects of Microplastics and Nanoplastics on Nasal Airway Epithelial Cells,” and we appreciate his engagement with both the methodology and broader implications of the work. We also recognize Dr. Min's important contributions to the field, in particular the identification and characterization of microplastics in human nasal samples [1], which help contextualize why the upper airway is a biologically plausible site for exposure and effects. Regarding controls and potential artifacts, we agree that rigorous design is essential in this type of research, alongside the recommendations outlined by Petersen et al. [2]. Our PBS-treated cells as a baseline control condition utilized all of the same vehicle solutions as well as instrumentation and disposables. That said, we recognize that control is question-dependent and that future studies (particularly environmentally representative models) will require additional strategies given the ubiquity and heterogeneity of environmental microplastics, as well as contaminant plastics in any experimental setup. We aim to incorporate nonplastic comparators (e.g., silica) and systematically expand across plastic types and environmentally relevant particle properties. Furthermore, a filtrate-only control is something we are looking to incorporate into our future experiments. Despite very significant dilution of commercially prepared solutions (from ∼10% plastics w/vol in water), it will still be important to assess the effects of any excipient materials. With respect to exposure route, we applied particles exclusively to the apical compartment of air–liquid interface (ALI) cultures to model inhalational exposure at the air-facing epithelial interface. This is arguably the most direct analogue to deposition of airborne particulates in vivo. We agree with Dr. Min that detection of microplastics and nanoplastics within human nasal tissues raises important questions about translocation and potential for basolateral exposure or signaling consequences, and we view this as a key area for future work. A direct apical versus basolateral comparison could be informative for understanding route-specific impacts, but hematogenous delivery rather than primary inhalational contact was not our original investigative interest. Finally, we appreciate the clarification of timing along assays. Our time points reflected both readout-specific considerations and practical constraints to maintaining ALI cultures (especially in a dosing exposure model), with a focus on capturing acute-to-subacute responses, as well as transcriptomics for a more stabilized exposure response. Shorter- (< 48 h) and longer-term (> 14 day) exposure paradigms may reveal additional biology. Additionally, the residence time of plastics on the apical surface of the ALI cultures may be prolonged relative to an in vivo exposure where mucociliary clearance would play a greater role.