Micro and nanoplastics pose a growing environmental threat with complex implications for human health. Despite the extensive research on the cytotoxicities of microplastics, gaps remain in understanding cellular responses to the interplay between environmental weathering and physiological processes. This study aims to fill this knowledge gap by evaluating and comparing the in vitro cellular responses to pristine polystyrene particles, particles weathered under UV light in DI water and seawater, and particles with subsequent incubation in simulated gastric fluid (SGF). In this study, Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were implemented to conduct surface chemistry and morphology characterizations of the particles. The combination of these techniques allowed a comprehensive understanding of surface morphology and chemistry alterations due to the weathering degradation and SGF incubation. Results showed nitrogen and carbonyl groups formed on weathered particles, and seawater-weathered particles showed a more pronounced weathering degree. After SGF incubation, stronger nitrogen and amide groups were detected on the surface of weathered particles, and more organic matter was attached. Two cell lines that are widely used for the evaluation of microplastic cytotoxicity were used, RAW264.7 macrophage and Caco-2 intestine epithelial cells. Results showed weathered and SGF-treated particles enhanced macrophage metabolic activity, viability, and pro-inflammatory effects compared to pristine particles. Elevated reactive oxygen species (ROS) generation was detected for all particle groups. Weathered particles caused higher cytotoxicity effects on Caco-2 cells and damaged tight junction integrity. The organic matter formation from the SGF incubation protected tight junction integrity and reduced cytotoxicity. These findings highlight the importance of taking both environmental and physiological factors into account for a more comprehensive assessment of microplastic toxicity.

中文翻译：

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风化和模拟胃液暴露对细胞对聚苯乙烯颗粒反应的影响


微塑料和纳米塑料对环境构成的威胁越来越大，对人类健康具有复杂的影响。尽管对微塑料的细胞毒性进行了广泛的研究，但在理解细胞对环境风化和生理过程之间相互作用的反应方面仍然存在差距。本研究旨在通过评估和比较体外细胞对原始聚苯乙烯颗粒、去离子水和海水中紫外光风化的颗粒以及随后在模拟胃液 （SGF） 中孵育的颗粒的反应来填补这一知识空白。本研究采用衰减全反射模式下的傅里叶变换红外光谱 （ATR-FTIR）、拉曼光谱、X 射线光电子能谱 （XPS） 和扫描电子显微镜-能量色散光谱 （SEM-EDS） 对颗粒进行表面化学和形貌表征。这些技术的结合可以全面了解由于风化降解和 SGF 孵育引起的表面形态和化学变化。结果表明，风化颗粒上形成氮基和羰基，海水风化颗粒表现出更明显的风化程度。SGF 孵育后，在风化颗粒表面检测到更强的氮基和酰胺基团，并附着更多的有机物。使用了两种广泛用于评估微塑料细胞毒性的细胞系，RAW264.7 巨噬细胞和 Caco-2 肠上皮细胞。结果显示，与原始颗粒相比，风化和 SGF 处理的颗粒增强了巨噬细胞代谢活性、活力和促炎作用。检测到所有颗粒组的活性氧 （ROS） 生成升高。 风化颗粒对 Caco-2 细胞造成更高的细胞毒性影响，并破坏了紧密连接的完整性。SGF 孵育形成的有机物保护了紧密连接的完整性并降低了细胞毒性。这些发现强调了同时考虑环境和生理因素对于更全面地评估微塑料毒性的重要性。