The effects of concentration, duration of exposure, size and surface function of polymethyl methacrylate micro/nanoplastics on human liver cells

Micro/nanoplastics (MP/NP) are pervasive contaminants that are detected throughout the environment in diverse matrices. Exposure to MP/NP have been demonstrated in humans by their presence in numerous body fluids and tissues. Due to the large quantity of production and broad applications, polymethyl methacrylate (PMMA) MP/NP have frequently been measured in surveys of microplastics in the environment. The effects of size, surface charge (aminated, carboxylated or non-functionalized), concentration, and exposure duration of PMMA particles in HepG2 human liver cells were evaluated in this study. The majority of PMMA MP/NP were non-cytotoxic. Some sporadic cytotoxicity was measured but it did not follow discernable trends. Confocal images revealed that 50, 100, and 1000 nm PMMA MP/NP were all taken up by HepG2 cells irrespective of surface charge. Particle size significantly affected caspase-3 release (p = 0.0002). Apoptosis was induced in only a small number of cells at 24 and 48 h for 50 nm and 1000 nm MP/NP. From 72 - 120 h, apoptosis increased in a time dependent manner for 50 nm beads at 100 µg/mL for all three surface functionalizations, with amine beads having the highest apoptosis at 120 h (36 %). Production of the pro-inflammatory interleukin-8 (IL-8) increased > 2x when the duration of exposure increased from 4 to 24 h irrespective of particle size, charge, or concentration. Collectively, PMMA MP/NP were not cytotoxic at the concentrations tested, but were able to translocate into HepG2 cells, release caspase-3, induce apoptosis, and produce IL-8 in a time dependent fashion.