Hydroxyapatite nanoparticle-induced mitochondrial energy metabolism impairment in liver cells: in vitro and in vivo studies.

Hydroxyapatite nanoparticles (HAP-NPs) have been extensively developed as drug carriers, bone implants, coating materials, etc. in the human body. However, research focusing on the potential side effects of HAP-NPs on the mitochondria-associated energy metabolism in liver cells is lacking. In this study, HAP-NPs with a long diameter of 80 nm and a short diameter of 20 nm were evaluated for their ability to induce mitochondrial energy metabolism dysfunction in vitro and in vivo. In the in vitro system, the buffalo rat hepatocyte (BRL) cell line was directly exposed to the HAP-NPs. The results of these experiments showed that the HAP-NPs induced inhibition of mitochondrial dehydrogenase activity, which was accompanied by a decrease in the mitochondrial membrane potential (MMP). In addition, HAP-NPs elevated the hepatic levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and decreased the levels of GSH and SOD. These data indicated that HAP-NPs induced a lowered rate of electron transfer in the mitochondrial respiratory chain, accompanied by a decrease in the activity of the mitochondrial respiratory chain complexes I, II and III. Furthermore, HAP-NPs induced a decline in the enzymatic expression in the Krebs cycle. We also investigated the role of Kupffer cells (KCs, rat-derived) in the effects induced by the HAP-NPs. The supernatant from the HAP-NP-treated KCs was used to stimulate the BRL cells. We observed that the HAP-NPs had the ability to induce KC activation. The activation of KCs then led to the release of tumor necrosis factor-α (TNF-α), nitric oxide (NO) and reactive oxygen species (ROS), and induced the inhibition of mitochondrial respiratory chain complexes I, II and III in the BRL cells. In the in vivo study, the TEM examination revealed mitochondrial swelling and vacuolar degeneration in the HAP-NP-treated hepatocytes. In addition, the amount of succinate (Suc), an intermediate in the mitochondrial Krebs cycle, also declined in the 1 H NMR spectroscopic measurements.