Cellular and molecular mechanisms of NiONPs toxicity on eel hepatocytes HEPA-E1: An illustration of the impact of Ni release from mining activity in New Caledonia.

Anthropic activities such as open pit mining, amplify the natural erosion of metals contained in the soils, particularly in New Caledonia, leading to atmospheric emission of nickel oxide nanoparticles (NiONPs). These particles are produced during extraction end up in aquatic ecosystems through deposition or leaching in the rivers. Despite alarming freshwater Ni concentrations, only few studies have focused on the cellular and molecular mechanisms of NiONPs toxicity on aquatic organisms and particularly on eels. Those fish are known to be sensitive to metal contamination, especially their liver, which is a key organ for lipid metabolism, detoxification and reproduction. The objective of this study was to assess in vitro the cytotoxic effects of NiONPs on Anguilla japonica hepatocytes, HEPA-E1. HEPA-E1 were exposed to NiONPs (0.5-5 µg/cm2) for 4 or 24 h. Several endpoints were studied: (i) viability, (ii) ROS production, SOD activity and selected anti-oxidant genes expression, (iii) inflammation, (iv) calcium signalling, (v) mitochondrial function and (vi) apoptosis. The results evidenced that NiONPs induce a decrease of cell viability and an increase in oxidative stress with a significant superoxide anion production. An increase of mitochondrial calcium concentration and a decrease of mitochondrial membrane potential were observed, leading to apoptosis. These results underline the potential toxic impact of NiONPs on eels living in mining areas. Therefore, eel exposure to NiONPs can affect their migration and reproduction in New Caledonia.

NiONPs-induced alteration in calcium signaling and mitochondrial function in pulmonary artery endothelial cells involves oxidative stress and TRPV4 channels disruption.

In New Caledonia, anthropic activities, such as mining, increase the natural erosion of soils in nickel mines, which in turn, releases nickel oxide nanoparticles (NiONPs) into the atmosphere. Pulmonary vascular endothelial cells represent one of the primary targets for inhaled nanoparticles. The objective of this in vitro study was to assess the cytotoxic effects of NiONPs on human pulmonary artery endothelial cells (HPAEC). Special attention will be given to the level of oxidative stress and calcium signaling, which are involved in the physiopathology of cardiovascular diseases. HPAEC were exposed to NiONPs (0.5-150 µg/cm2) for 4 or 24 h. The following different endpoints were studied: (i) ROS production using CM-H2DCF-DA probe, electron spin resonance, and MitoSOX probe; the SOD activity was also measured (ii) calcium signaling with Fluo4-AM, Rhod-2, and Fluo4-FF probes; (iii) inflammation by IL-6 production and secretion and, (iv) mitochondrial dysfunction and apoptosis with TMRM and MitoTracker probes, and AnnexinV/PI. Our results have evidenced that NiONPs induced oxidative stress in HPAEC. This was demonstrated by an increase in ROS production and a decrease in SOD activity, the two mechanisms seem to trigger a pro-inflammatory response with IL-6 secretion. In addition, NiONPs exposure altered calcium homeostasis inducing an increased cytosolic calcium concentration ([Ca2+]i) that was significantly reduced by the extracellular calcium chelator EGTA and the TRPV4 inhibitor HC-067047. Interestingly, exposure to NiONPs also altered TRPV4 activity. Finally, HPAEC exposure to NiONPs increased intracellular levels of both ROS and calcium ([Ca2+]m) in mitochondria, leading to mitochondrial dysfunction and HPAEC apoptosis.