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

To the Editor: I read with great interest the recent article by Kahan et al. [1] titled “Inflammatory Effects of Microplastics and Nanoplastics on Nasal Airway Epithelial Cells.” This study investigates the inflammatory responses of nasal airway epithelial cells following exposure to microplastics and nanoplastics. The authors demonstrate that microplastics and nanoplastics induce pro-inflammatory cytokine expression and cellular alterations in nasal epithelial cells, suggesting disruption of epithelial homeostasis. Furthermore, the study is particularly valuable in that it systematically compares the effects of polystyrene microplastics and nanoplastics on nasal epithelial cells according to particle size and surface charge, providing insight into how these physicochemical properties modulate cellular responses. These findings indicate that inhaled micro- and nanoplastics may contribute to upper airway inflammation and represent a potential risk to respiratory health. Based on my previous experience conducting research on the detection of microplastics in the human nasal epithelium and nasal cavity [2-4], I found this study particularly intriguing. After reading the manuscript, I would like to raise several points for discussion with the authors, which are outlined below. First, previous studies have emphasized that experiments involving microplastics and nanoplastics require carefully designed control measurements to identify potential artifacts, and that experimental protocols may need to be adjusted to minimize or eliminate such artifacts [5]. In the present study, the authors employed PBS-treated cells as the control condition; however, I would be interested in the authors’ perspective on what they consider to be the most appropriate control settings for future studies in this field. In addition, I wonder whether the inclusion of a positive control or the parallel testing of other types of plastic particles could contribute to establishing a more rigorous and biologically relevant true control. Next, in experiments using primary nasal epithelial cells, the authors state that microplastics and nanoplastics were applied exclusively to the apical compartment. I would be interested to know the rationale for not applying these particles to the basolateral compartment as part of the treatment protocol. In our previous work, we reported the detection of microplastics within human nasal epithelial tissues [4]. Based on these findings, I consider that the possibility of microplastics being released toward the basolateral side and subsequently influencing nasal epithelial cells cannot be entirely excluded. In this context, I wonder whether basolateral exposure to microplastics and nanoplastics might have induced different effects on transcriptomic profiles or transepithelial electrical resistance (TEER), and I would appreciate the authors’ perspectives on this possibility. Finally, this study employs a wide range of experimental approaches, and it appears that slightly varying exposure time points were applied across assays. For example, transcriptional changes were assessed after 10 days of treatment, cytokine alterations after 4 and 10 days, and electron microscopy analyses after 4–6 days. I would be interested to learn more about the considerations that guided the selection of these specific time points. In addition, I am curious whether the authors have experience with shorter exposures (within 2 days) or longer-term exposures exceeding 14 days to microplastics and nanoplastics, and if so, whether such conditions yielded qualitatively different outcomes. This work provides novel and important insights into the size- and surface charge–dependent effects of microplastics and nanoplastics on nasal epithelial cells. These observations, which have not been previously described, are of particular importance as they offer valuable insights that may facilitate diverse future investigations. I commend the authors for their considerable efforts and for the comprehensive use of diverse experimental approaches to substantiate their findings. I sincerely commend the authors for their outstanding work and thank them for sharing these valuable and insightful results with the scientific community. Sincerely, Hyun Jin Min The author declares no conflict of interest.