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

Metallobiochemistry of ultratrace levels of bismuth in the rat I. Metabolic patterns of 205+206Bi3+ in the blood

BACKGROUND

The number of the applications of bismuth (Bi) is rapidly and remarkably increasing, enhancing the chance to increase the levels to which humans are normally daily exposed. The interest to Bi comes also from the potential of Bi-based nanoparticles (BiNPs) for industrial and biomedical purposes. Like other metal-based NPs used in nanomedicine, BiNPs may release ultratrace amounts of Bi ions when injected. The metabolic fate and toxicity of these ions still needs to be evaluated. At present, knowledge of Bi metabolism in laboratory animals refers almost solely to studies under unnatural "extreme" exposures, i.e. pharmacologically relevant high-doses (up to thousand mg kg^-1) in relation to its medical use, or infinitesimal-doses (pg kg^-1 as non-carrier-added Bi radioisotopes) for radiobiology protection, diagnostic and radiotherapeutic purposes. No specific study exists on the "metabolic patterns" in animal models exposed to levels of Bi, i.e. at "environmental dose exposure" that reflect the human daily exposure (μg kg^-1).

METHODOLOGY

Rats were intraperitoneally injected with 0.8 μg Bi kg^-1 bw as ^205+206Bi(NO)₃ alone or in combination with ⁵⁹Fe for radiolabelling of iron proteins. The use of ^205+206Bi radiotracers allowed the detection and measurement down to pg fg^-1 of the element in the blood biochemical compartments and protein fractions as isolated by differential centrifugation, size exclusion- and ion exchange chromatography, electrophoresis, solvent extraction, precipitation and dialysis.

RESULTS

24 h after the administration, the blood concentration of Bi was 0.18 ng mL^-1, with a repartition plasma/red blod cells (RBC) in a ratio of 2:1. Elution profiles of plasma from gel filtration on Sephadex G-150 showed four pools of Bi-binder proteins with different molecular sizes (> 300 kDa, 160 kDa, 70 kDa and < 6.5 kDa). In the 70 kDa fraction transferrin and albumin were identified as biomolecule carriers for Bi. In red blood cells, Bi was distributed between cytosol and membranes (ghosts) in a ratio of about 5:1. In the cytosol, low molecular components (LMWC) and the hemoglobin associated the Bi in a ratio of about 1.8:1. In the hemoglobin molecule, Bi was bound to the beta polypeptide chain of the globin. In the ghosts, Bi was detected at more than one site of the protein fraction, with no binding with lipids. Dialysis experiments and the consistently high recovery (80-90 %) of ²⁰⁶Bi from chromatography of ²⁰⁶Bi-containing biocomponents suggest that Bi was firmly complexed at physiological pH with a low degree of breaking during the applications of experimental protocols for the isolation of the ²⁰⁶Bi-biocomplexes. These latter were sensitive to acid buffer pH 5, and to the presence of complexing agents in the dialysis fluid.

CONCLUSIONS

On the basis of an environmental biochemical toxicology approach, we have undertaken a study on the metabolic patterns of Bi³⁺ ions in rats at tissue, subcellular and molecular level with the identification of cellular Bi-binding components. As a first part of the study the present work reports the results concerned with the metabolic fate of ultratrace levels of ^205+206Bi(NO)₃ in the blood.

Determination of Renal Distribution of Zinc, Copper, Iron, and Platinum in Mouse Kidney Using LA-ICP-MS

The main dose-limiting side effect of cisplatin is nephrotoxicity. The utilization of cisplatin is an issue of balancing tumour toxicity versus platinum-induced nephrotoxicity. In this study, we focused on intraorgan distribution of common essential trace elements zinc, copper, and iron in healthy mouse kidneys and distribution of platinum after cisplatin treatment. Renal distribution in 12 nontreated Nu-Nu mice (males) was assessed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Furthermore, 9 Nu-Nu mice were treated with cisplatin. The order of elements concentration in kidneys was as follows: Fe > Zn > Cu. All three metals showed the higher concentrations at the cortex and medulla (28.60, 3.35, and 93.83 μg/g for Zn, Cu, and Fe, respectively) and lower concentration at the pelvis and the urinary tract (20.20, 1.93, and 62.48 μg/g for Zn, Cu, and Fe, respectively). No statistically significant difference between cortex and medulla was observed for these elements. After platinum treatment, the concentration of platinum in kidneys was enhanced more than 60-times, p < 0.001. Platinum significantly showed the highest accumulation in cortex (2.11 μg/g) with a gradient distribution. Platinum was less accumulated in medulla and pelvis than in cortex, and the lowest accumulation occurred in the urinary tract (1.13 μg/g). Image processing has been successfully utilized to colocalize metal distribution using LA-ICP-MS and histological samples images.

Anticancer activity and tissue distribution of platinum (II) complex with lignin-derived polymer of benzene-poly-carboxylic acids

Platinum-containing antineoplastic agents with physiologically active ligands seem to be a promising direction in anticancer drug design. PDBA is a novel promising antineoplastic agent, containing polymer ligand of natural origin (international patent WO2013/143549 A1). Polymer ligand of PDBA has a highly functionalised polyphenolic backbone, which exerts its own pharmacological effect via immune modulation and regulation of gene expression. PDBA is a cis-diammineplatinum(II) complex, containing mono-deprotonated benzene-poly-carboxylic acids, derived from lignin, and hydroxyl group as O-donor ligands (approximate bulk formula C₈₃H₇₀N₂O₂₇Pt). The agent is being evaluated in Phase II controlled clinical trials in metastatic breast cancer patients. In the present study, tissue distribution and tumour growth inhibition effects of PDBA, cisplatin and carboplatin were compared in SHR female mice, bearing inoculated solid Ehrlich carcinoma. The agents were administered subcutaneously every second day for the period of 10days (5 injections) at 62.5mg/kg, 3.0mg/kg and 18.5mg/kg for PDBA, cisplatin and carboplatin, respectively. Experimental animals were sacrificed on the Days 11, 16 and 23 after the inoculation of the tumour. The doses of all studied drugs were selected to obtain similar antitumour efficacy with ca. 50% growth inhibition of the Ehrlich tumour at the end of the study. The efficacy of a single platinum reactive moiety [cis-diammineplatinum(II)] was shown to be the highest for cisplatin, followed by PDBA and finally carboplatin. However, the toxicity of PDBA was considerably lower than that of carboplatin and especially cisplatin. The drugs were mainly distributed in lungs, kidneys, liver, spleen and tumour tissue. PDBA showed quite high accumulation in the tumour tissue, possibly, owing to the effect of the lignin-derived ligand.

Pharmacokinetics and tissue distribution of novel platinum containing anticancer agent BP-C1 studied in rabbits using sector field inductively coupled plasma mass spectrometry

A method of platinum quantification in whole blood samples after microwave digestion using sector field inductively coupled plasma mass spectrometry has been developed. The following analytical figures of merit have been established: limit of detection 1.1 µg/L for blood samples, dynamic range 3.6–200 µg/L, intra‐day precision (relative standard deviation, n = 9) did not exceed 5%. Spiked samples were analyzed for method validation. The method was used for pharmacokinetics studies of a novel anti‐cancer drug BP‐С1, a complex of cis‐configured platinum and benzene‐poly‐carboxylic acids. Main pharmacokinetic parameters (area under curve, maximum concentration, clearance, half‐life times for α‐ and β‐phase) were estimated for two dosage forms of BP‐C1 0.05 and 0.125 mass %. Pharmacokinetic curves were assessed for single and course administration. Studies were performed using rabbits (n = 6) as a model. BP‐C1 was injected intramuscularly. The study established dose proportionality of the tested dosage forms and suggested clinical dosing schedule: 5 days of injections followed by 2 days’ break. Platinum tissue distribution was studied in tissue samples collected 20 days after the last injection. Predominant platinum accumulation was observed in kidneys, liver, and muscles near injection site. ‘Slow’ phase of platinum excretion kinetics may be related to the muscles at the injection site. © 2015 The Authors. Drug Testing and Analysis published by John Wiley & Sons Ltd.