The metallobiochemistry of ultratrace levels of platinum group elements in the rat

Abstract

The use of platinum, palladium and rhodium (Platinum Group Elements – PGEs) and the possibility of exposure to their ultratrace levels is increasing. In fact, the exponential development of metallic PGE-based nanoparticles (<100 nm in size) opens extraordinary perspectives in the areas of electrocatalysts and catalytic converters, magnetic nanopowders, polymer membranes, cancer therapy, coatings, plastics, nanofibres and textiles. Like other metal-based nanoparticles, exposure to PGEs nanoparticles may result in a release of ultratrace amounts of Pt, Pd, Rh ions in the body whose metabolic fate and toxicity still need to be evaluated. Furthermore, PGEs can act as allergic sensitizers by acting as haptens and inducing both type I and IV allergic reactions. In this work we studied the in vivo metabolic patterns of ultratrace levels of potent allergens and sensitizers PGE halogenated salts. ¹⁹¹Pt, ¹⁰³Pd and ^101mRh radioisotopes were prepared via cyclotron irradiation and used for radiolabelling Na₂¹⁹¹PtCl₄, Na₂¹⁰³PdCl₄ and Na₂^101mRhCl₆ salts. These anionic chlorocomplexes were intraperitoneally injected into rats (114 ng Pt kg⁻¹ bodyweight; 24 ng Pd kg⁻¹ b.w.; 16 ng Rh kg⁻¹ b.w.). At 16 h post-exposure, PGEs were poorly but significantly retained in all tissues analysed. Kidneys, spleen, adrenal gland, liver, pancreas and small intestine were the organs with the highest Pt, Pd, Rh concentrations. In the blood 30–35% of ¹⁰³Pd and ¹⁹¹Pt and 10% of ^101mRh were recovered in the plasma, mainly bound to albumin and to a less extent to transferrin. The hepatic and renal intracellular distribution showed the highest recovery of ¹⁹¹Pt, ¹⁰³Pd and ^101mRh in the nuclear fraction (liver) and in the cytosol (kidney). Chromatographic separation and ultrafiltration experiments on kidney and liver cytosols showed the strong ability of biochemical macromolecules to bind ¹⁹¹Pt, ¹⁰³Pd and ^101mRh, and being responsible for the retention of the three elements in the body. The link to macromolecules is the basis for the sensitizing capacity of PGEs.