Chronic Low-Dose Gold Nanoparticle Exposure Induces Persistent Alterations in Mitochondrial Respiration in a Physicochemical-Property Dependent Manner

Mitochondrial homeostasis is a central determinant of cellular health and disease. Gold nanoparticles (AuNPs) are widely developed for biomedical applications and have been explored as therapeutic tools for conditions associated with mitochondrial dysfunction. However, their long-term effects on mitochondrial health under more realistic, low-dose human exposure scenarios remain poorly understood. Here, we systematically investigated how low-dose exposure to well-characterized AuNPs impacts mitochondrial function in high-energy-demand primary human dermal fibroblasts. Cells were exposed to AuNPs with distinct physicochemical properties at a subcytotoxic concentration under acute and chronic conditions, followed by a recovery period in nanoparticle-free media. While acute AuNP exposure largely elicited adaptive mitochondrial responses, chronic exposure induced pronounced mitochondrial dysfunction in a physicochemical property-dependent manner. PEGylated AuNPs, largely considered biocompatible, were found free in the cytosol and disrupted mitochondrial membrane potential, increased mitochondrial reactive oxygen species, altered ATP production, and induced redox imbalance. Notably, nanoparticle shape governed the magnitude and persistence of mitochondrial stress as well as the adaptive mechanisms engaged. The absence of PEGylated AuNPs in cells restored several canonical indicators of mitochondrial health. However, mitochondrial respiration profiles remained persistently altered, indicating incomplete recovery of mitochondrial homeostasis and suggesting the potential for delayed cellular consequences. Collectively, these findings demonstrate that low-dose, chronic exposure to PEGylated AuNPs can lead to long-lasting changes in mitochondrial respiration without overt cytotoxicity. This work identifies mitochondria as highly sensitive targets of nanomaterial-induced stress, emphasizing the need to incorporate chronic exposure and postexposure recovery paradigms into safety assessments to guide the rational design of future nanotherapeutics.