Size-dependent effects of polystyrene microplastics on cytotoxicity and efflux pump inhibition in human Caco-2 cells

Microplastics in the environment may gain entry the human gastrointestinal tract through the food chain. However, information on different adverse effects of microplastics at nanometer or micrometer scales in human intestine cells is limited. This study compared the cytotoxicity and efflux pump inhibition ability of 0.1 μm and 5 μm polystyrene microplastics (PS-MPs) in the human colon adenocarcinoma Caco-2 cells. Both PS-MP sizes exhibited low toxicity on cell viability, oxidative stress, and membrane integrity and fluidity. However, the mitochondrial membrane potential was disrupted by both sizes of PS-MPs, and the 5 μm PS-MPs induced higher effects than 0.1 μm PS-MPs. Furthermore, 0.1 μm (≥20 μg/mL) or 5 μm (≥80 μg/mL) PS-MPs inhibited plasma membrane ATP-binding cassette (ABC) transporter activity and increased arsenic (one substrate of ABC transporter) toxicity. The 0.1 μm PS-MPs might act as substrates of ABC transporter to reduce the transport capacity of other substrates. However, high concentrations of 5 μm PS-MPs might reduce ABC transporter activity through induction of mitochondrial depolarization and potential depletion of ATP. This study provides basic information on the toxicity of 0.1 μm and 5 μm PS-MPs in human intestine cells, which are useful for assessing the risk of PS-MPs in humans.