Biological and hepatotoxic effects of palladium. An overview on experimental investigations and personal studies

New mechanistic approach of inorganic palladium toxicity: impairment in mitochondrial electron transfer

Human activities have increased the levels of palladium (Pd) that are progressively accumulating in the environment. The growing evidence of Pd toxicity has become the focus of serious concern for the environment, organisms and humans, with little data on the mechanism of Pd toxicity. Recent studies have suggested that mitochondria have a key role in Pd toxicity via mitochondrial membrane potential collapse and depletion of the cellular glutathione (GSH) level. Therefore, it was decided to determine the mechanistic toxicity of Pd towards isolated mitochondria via new and reliable methods. Isolated liver and kidney mitochondria were obtained by differential ultracentrifugation and incubated with different concentrations of Pd (100-400 μM). Our results showed that Pd induced mitochondrial dysfunction via an increase in mitochondrial ROS production and membrane potential collapse, which correlated to cytochrome c release. Also, increased disturbance in oxidative phosphorylation was also shown by the increase in ADP/ATP ratio in Pd-treated mitochondria, which indicates mitochondrial dysfunction in isolated liver and kidney mitochondria. Our results suggest that Pd-induced toxicity is the result of a disruptive effect on the mitochondrial respiratory chain, increasing the chance of cell death signaling. In addition, it is supposed that kidney tissue is more susceptible to Pd exposure than liver tissue.

Multiple parameter cytotoxicity index on dental alloys and pure metals

Palladium (Pd) is a metal frequently used for dental alloys. In order to elucidate controversial options about Pd concerning its biological performances, our study consists in the evaluation of commercial and experimental PFM and C&B precious and semi-precious dental alloys. This investigation was also designated to the establishment of a cytotoxicity index (CI) such as it was described for hemocompatibility testing. The following materials were tested: 36 commercial alloys (Au-, Pd- and Ag-base), 14 experimental alloys (Pd-base established by an experience plan) and pure metals (Ag, Au, Cu, Ni, Cr, In, Sn, Pt, Ti, Zn). The cells culture experiments were carried out with epithelial L132 cells and NIH 3T3 fibroblasts. In vitro cell viability tests show that Pt, Sn, In, Ti, Au and Pd have no cytotoxic effect; Cr, Cu and Ag are toxic, Ni, Zn, and Co are highly toxic. An identical ranking was found with the inflammatory and proliferation tests. Toxic and highly toxic metals induced slight or strong prosthetic dental restoration morphological alterations after 3-days cultures and mostly cell death after 6-days cultures. These effects are dependent on the leakage of the element into the culture medium as revealed by ICP. The addition of Au gives benefit to Pd-Ag alloys, but does not produce any major effect on Pd-Cu alloys. This qualitative ranking can quantitatively be confirmed by cytocompatibility testing after application of a CI.