Multi-Modal Toxicological Evaluation of NiO nanoparticles and ionic nickel in a Human Lung-Cardiac Co-Culture System

Nickel is a widespread environmental and occupational contaminant associated with respiratory and cardiovascular toxicity, yet the mechanisms linking pulmonary exposure to adverse cardiac effects remain poorly understood. This study aimed to establish and evaluate a human in vitro lung–heart co-culture model for investigating cardiovascular responses following pulmonary exposure. Human alveolar epithelial A549 cells were exposed at the air–liquid interface to different concentrations of NiO nanoparticles or NiCl ₂ for 4- and 24-hours. Following cloud exposure, A549 cells were co-cultured with human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Cytotoxicity, metabolic activity, cytokine release, DNA damage, epigenetic alterations, and cardiac electrophysiological function were assessed. Nickel translocation across the epithelial barrier was quantified to facilitate interpretation of downstream cardiomyocyte effects. Exposure to both nickel forms induced cytotoxicity and resulted in measurable nickel translocation into the basolateral compartment. NiCl ₂ exhibited a time-dependent increase in basolateral nickel concentrations, whereas NiO translocation remained relatively stable over time. Cytokine profiling revealed selective induction of IL-8 and IL-18, with no significant changes in IL-1β, IL-6, IL-10, or TNF-α. Genotoxicity analyses demonstrated cell type-specific responses, characterized by delayed DNA strand breaks in A549 cells and early but transient DNA damage in hiPSC-CMs. Oxidative DNA damage was particularly pronounced in hiPSC-CMs following NiCl ₂ exposure. Global DNA methylation was reduced in hiPSC-CMs without corresponding changes in DNA methyltransferase activity. Electrophysiological assessment showed transient increases in conduction velocity, while beating frequency and field potential duration remained largely unaffected. Overall, the lung–heart co-culture model successfully captured both pulmonary and cardiac responses to nickel exposure and provided evidence for direct and indirect mechanisms of cardiotoxicity. Nickel translocation across the epithelial barrier, together with inflammatory and oxidative stress-related signalling, may contribute to downstream cardiac effects. These findings highlight the utility of this human-relevant platform for investigating systemic cardiovascular consequences of inhaled toxicants.