Effects of palladium model nanoparticles emitted from car exhaust converters on peripheral blood mononuclear cells of palladium-sensitized women

Introduction
Today, the content of palladium (Pd) in catalytic converters is increasing. The high percentages of Pd sensitization detected in German children and in the Austrian and Italian population may reflect not only the presence of Pd in dental alloys but also the introduction of catalytic converters. Aim of this study is to evaluate the immune potential of Pd nanoparticles (in size of those emitted from car exhaust converters, Center (CeSI)"G. d'Annunzio" University Foundation, compared to that of a Pd salt (hexa-chloropalladate) on cytokine release and production from peripheral blood mononuclear cells (PBMCs) of control or Pd-sensitized non-atopic women .

Methods
TNF-, and IFN-??release and expression from PBMCs incubated in presence of 5-10nm Pd nanoparticles or potassium hexa-chloropalladate were determined by ELISA and RT-PCR. Transmission electronmicroscopy (TEM) was performed.

Results
In LPS-stimulated PBMCs from controls, Pd salt inhibited IFN-gamma release and production, whereas Pd nanoparticles enhanced IFN-gamma release and production and inhibited TNF-alpha secretion. In LPS-stimulated PBMCs from Pd-sensitized women showing high IFN-gamma release and production, Pd nanoparticles inhibited TNF-alpha release. TNF-alpha and IFN- gamma release and mRNA expression were correlated. TEM demonstrated that the mononuclear cells showed numerous markedly dilated endocytic vacuoles, filled with particulated nanometer-scale material. Often these vacuoles contained multi-lamellar bodies or intravacuolar membranous structures, suggesting autophagic processes. In addition, lysosomes, often in various stages of fusion with autophagosomes (autophagolysomes), were prominent. The mitochondria revealed dilated cristae. These data indicate that Pd nanoparticles are abundantly endocytosed by PBMCs and accumulate in the endocytic vacuolar compartment, exerting cell damaging effects that appear to activate autophagy.

Discussion
Pd ions and nanoparticles exert different effects in vitro on the expression and release of cytokines. Moreover, we could demonstrate that the Pd nanoparticles exert their effects, after intracellular uptake and accumulation within the endocytic vacuolar, stimulating autophagic activities.