Differential response of SNU-1826 colon cells on the autophagy, ER stress, and inflammation during the regulation of microplastic internalization

The internalization mechanism of microplastics (MPs) into human cells has attracted considerable attention because these mechanisms are closely related to the physical and chemical properties of MPs. This study examined the response of human colon cells to autophagy, ER stress, and inflammation during the regulation on the internalization of polystyrene (PS)-MPs (0.4-0.6 μm size). To achieve this, changes in their key markers were analyzed in MPs-treated SNU-1826 cells after a cotreatment with uptake inhibitors or stimulators. The internalization of MPs was significantly higher in SNU-1826 cells than in other cells originated from differential tissues, such as the small intestine, kidneys, and nerves. On the other hand, the internalization of MPs into SNU-1826 cells was suppressed by cytochalasin D (CD) but not by pitstop (Pt). During this inhibition, the levels of the key parameters for autophagy (Light Chain 3-I/II (LC3-I/II) and Beclin1), ER stress (eukaryotic translation initiation factor 2 subunit alpha (EIF2α) and inositol-requiring kinase 1 alpha (IRE1α)), and inflammation (inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), tumor necrosis factor alpha (TNF-α), and interleukin (IL)-6) were suppressed in MPs+CD-treated SNU-1826 cells. In addition, the internalization of MPs into SNU-1826 cells was stimulated by a ZnSO₄ treatment, not by CaCl₂. These stimulation effects were reflected in the alteration of the critical parameters for autophagy, ER stress, and inflammation. Furthermore, the positive correlation was detected between MPs internalization and most parameters for cellular responses although their inhibition is stronger than stimulation. These results suggest that the internalization of MPs into SNU-1826 cells may be strongly associated with the changes in autophagy, ER stress, and inflammation during the regulation of CD and ZnSO₄.