Polystyrene Microplastics of Varying Sizes and Shapes Induce Distinct Redox and Mitochondrial Stress Responses in a Caco-2 Monolayer

Abstract

Currently, we lack crucial knowledge on how the physicochemical properties of particles affect cellular health, resulting in an important gap in our understanding of the human toxicity of microplastics (MPs). Our aim was to evaluate the impact of the size and the shape of MPs on uptake and the intracellular effects in a human epithelial colorectal adenocarcinoma (Caco-2) cell line. Spherical (200 nm and 2 µm) and fibre-/fragment-shaped (8.9 ± 10.1 µm by 1.14 ± 0.97 µm) polystyrene microplastics (PS-MPs) were used to study their uptake and the potential to induce redox and mitochondrial stress responses after 24 h of exposure. We demonstrated the cellular uptake of both spherical and fibre-/fragment-shaped MPs in a size-dependent manner. In response to 2 µm spheres, we observed differential expressions of redox-related genes, including HMOX1, CAT, and GPX1. All PS-MPs decreased the intracellular H2O2 levels, which can be attributed to mitochondrial stress responses, such as increased mitochondrial DNA content, footprint, and morphology. Altogether, we demonstrated uptakes and changes in redox and mitochondrial parameters for all PS-MPs, with the 200 nm spheres showing the most profound effects. This suggests that the induction of defensive responses in Caco-2 cells mainly correlates with the number of particles taken up.

Microplastics and Oxidative Stress—Current Problems and Prospects

“…Predicting the cytotoxicity of plastic particles requires an understanding of how they interact with cells (Table 1). Therefore, an examination of how MPs affect specific cellular organelles may be beneficial (Figure 3) [68][69][70][71][72]118,119]. A549-human lung adenocarcinoma; Caco-2-human colorectal adenocarcinoma cell; CCD841CoN-cells isolated from normal human colon tissue; HaCaT-human keratinocyte; HeLa cells-immortalized cell line; HEK293 cells-immortalized human embryonic kidney cells; HIEC-6-human intestinal epithelial cell-6; HT-29-human colorectal adenocarcinoma cell; Jurkat cell-an immortalized line of human T lymphocyte cells; THP-1-a human monocytic cell line derived from an acute monocytic leukemia patient; T98G cells-a glioblastoma cell line; U937-a cell line exhibiting monocyte morphology; B cells-secondary antigen-presenting cells, typically known to secrete antibodies; NK cells-natural killer cells; GC-2 cells-a mouse spermatocyte line; RTG-2 cells-the rainbow trout ovary cell line; RTgill-W1-the rainbow trout gill cell line; RTL-W1-the rainbow trout liver cell line; PS-polystyrene; PTFE-polytetrafluoroethylene; PE-polyethylene; PVC-poly(vinyl chloride); ROS-reactive oxygen species; MAPK-mitogen-activated protein kinase; IL-6-interleukin-6; CAT-catalase; HMOX1-Heme oxygenase 1; GPx1-Glutathione peroxidase 1; GSSG-oxidized glutathione; ATP-adenosine triphosphate; GSH-glutathione; NLRP3-the pyrin domain-containing protein 3; IL-1β-interleukin-1β; MIP-1β-macrophage inflammatory protein-1 beta; IFN-γ-interferon-gamma; TNF-α-tumor necrosis factor-α; IL-33-interleukin 33; IL-4-interleukin 4; IL-5-interleukin 5; IL-10-interleukin 10; IL-18-interleukin 18; TGF-β1-transforming growth factor β1; h-hour; d-day.…”

“…The swelling of the mitochondria, weakening of the myelin substance in the mitochondrial membrane, reduction or disappearance of crista, decreased enzyme activity in the mitochondria, altered permeability of the mitochondrial membrane, and damage to the mitochondrial DNA are all morphological manifestations of MP damage [119,138,139].…”

“…Currently, information on adverse effects from available literature sources is very limited. In the case of cell-based assays, Caco-2 was most commonly studied [68,119,120]. A frequently occurring endpoint was the increase in ROS observed at MPs' concentrations of 10-100 µg/mL [68,120].…”