Hydramethylnon-induced pulmonary toxicity associated with necroptosis signaling and mitochondrial dysfunction in human bronchial epithelial cells.

Insecticides have been applied in various household products, and our previous study showed that hydramethylnon (HM), among five classes tested, showed significant pulmonary toxicity in rats and human A549 cells. In this study, we investigated the underlying molecular mechanisms of HM-induced toxicity in human bronchial epithelial cells (HBECs) using BEAS-2B and 16HBE14o cells. In addition, these mechanisms were further confirmed in mice using an intratracheal instillation model. HM treatment induced cytotoxicity in both cell lines, characterized by cell cycle arrest, inhibition of cell proliferation, and cell death with apoptotic features. Notably, HM treatment triggered a rapid increase in necroptosis signaling, as evidenced by phosphorylation of receptor-interacting protein kinase (RIPK) 1 and mixed lineage kinase domain-like (MLKL), and subsequent necroptosis signaling at mitochondria. This activation disrupted mitochondrial homeostasis as evidenced by a reduction in mitochondrial content, as assessed by decreased translocase of outer mitochondrial membrane 20 (TOM20) fluorescence intensity, loss of mitochondrial DNA, reduced electron transport chain complex proteins, adenosine triphosphate (ATP) depletion, increased reactive oxygen species (ROS), and induction of mitophagy. This necroptosis-associated mitochondrial dysfunction ultimately resulted in cell death with apoptotic features of HBECs. Consistently, intratracheal instillation of HM in mice induced acute lung injury with pronounced necroptosis signaling, mitochondrial loss in airway bronchial epithelial cells, and increased cell death with apoptotic features. These findings demonstrate that HM induces cytotoxicity in bronchial epithelial cells associated with necroptosis signaling and mitochondrial dysfunction in vitro and in vivo, revealing a novel mechanism of inhalation toxicity and highlighting the potential risks of HM-containing household products.