Sub-chronic exposure to nanoplastics in vitro disrupts hepatic lipid homeostasis in human hepatocytes.

Human exposure to micro- and nanoplastics is increasingly recognized as a global concern, yet their long-term effects on human health remain poorly understood. Defining the cellular consequences of chronic exposure is essential for reliable risk assessment and informed environmental and public health strategies. Here, we investigated the impact of prolonged culture in presence of nanoplastics, using an in vitro hepatocyte model (HepG2) exposed to environmentally relevant concentrations (10⁴ and 10⁶ particles/mL). After 28 days, no significant changes in morphology or cell viability were observed. Despite this apparent tolerance, prolonged exposure produced marked metabolic alterations. Cellular lipid content increased in a dose-dependent manner after 120 h, peaked at day 14 (120% ± 16 and 133% ± 12), remained stable until day 21, and declined thereafter. This response was accompanied by altered expression of key lipid metabolism regulators, including SREBP-1C, FABP1, PPAR-α, and PPAR-γ. Lipidomic analysis further revealed a shift in lipid composition from day 14 onward, with increased saturated fatty acids and reduced unsaturated lipids. Although total lipid accumulation partially resolved by day 28, suggesting adaptive responses, the lipidome continued to remodel toward a potentially pathological profile. This metabolic shift was paralleled by an inflammatory signal, as indicated by increased TNF-α expression after 7 days. Together, these findings show that prolonged exposure to low nanoplastic concentrations elicits substantial lipid remodeling, potentially predisposing hepatocytes to lipotoxic and inflammatory states.