Distinct cellular responses in liver macrophages to short- and long-term exposure to pristine and artificially aged polystyrene microplastic particles.

Microplastic particles (MPP) arise from mismanaged plastic waste, plastic degradation (i.e., agricultural films, textiles, or packaging), and direct use in products such as cosmetics. Their environmental persistence raises concerns for ecosystems, wildlife, and human health. However, most in vitro studies focus on pristine spherical particles and short-term exposure, limiting environmental relevance. Here, we conducted a comprehensive multi-parametric analysis of short- (24 h) and long-term (21 days) exposure of murine macrophages to pristine (PSpristine) and artificially weathered (PSaged) polystyrene (PS) MPP. PSpristine were largely non-toxic during short-term exposure but induced adaptive pro- and anti-inflammatory responses, with minimal cytotoxicity, after repeated long-term exposure. PSaged triggered acute oxidative stress, reduced metabolic activity, induced DNA damage, and elicited early pro-inflammatory activation, while long-term exposure resulted in pronounced cellular stress, functional impairment, and minimal macrophage polarization. These results demonstrate that particle ageing and exposure period critically shape macrophage responses and highlight the need for long-term in vitro studies using environmentally relevant, well-characterized MPP.