A Complex Methodological Approach for the Screening of Efficient and Safe Cobalt Chelators

Abstract

Background:: Cobalt is an essential trace element, but it can also rarely cause cobalt toxicity due to its release from cobalt-containing medical devices. Currently, there are no approved selective cobalt chelators which would represent an optimal treatment modality. Objective:: This study aimed to develop a simple and complex methodological approach for screening potential cobalt chelators along with evaluating their potential toxicity. Methods:: Firstly, a simple spectrophotometric assay employing 1-nitroso-2-naphthol-3,6- disulfonic acid disodium salt (NNDSA) for screening cobalt chelation was standardized at a pathophysiologically relevant range of pH 4.5-7.5. Then, the suitability of the method was verified using four known metal chelators (EDTA, 8-hydroxyquinoline, chloroxine and nitroxoline). As cobalt can catalyse the Fenton reaction, the potential toxicity of cobalt-chelator complexes was also determined by employing a novel HPLC method with coulometric detection. The effect on erythrocyte haemolysis was tested as well. Results:: The NNDSA method had high sensitivity enabling the detection of 25-200 nM of cobalt ions depending on pH conditions. Measurements could be carried out on a wide range of wavelengths from 470 to 540 nm. All tested complexes of the selected chelators decreased the rate of the Fenton reaction. Interestingly, chloroxine mixed with cobalt ions caused a marked lysis of erythrocytes in contrast to the other compounds. Conclusion:: The described complex methodological approach could serve as a simple, yet precise tool for making an evaluation of novel, effective and safe cobalt chelators.

3-Hydroxyflavone is a mildly active and safe cobalt chelator while cobalt markedly enhances baicalein toxicity toward erythrocytes

“…Both wavelengths were selected based on our previous study. 44 The results were essentially similar to few small differences (ESI Fig. 2 † ).…”

“…The degree of cobalt chelation was determined by a spectrophotometric method with the indicator NNDSA, as much recently reported by us. 44 The principle of this method is that if a avonoid is able to chelate cobalt, the amount of free cobalt ions in the solution decreases and these free, i.e., nonchelated, cobalt ions bind to the indicator NNDSA. Then, this complex of NNDSA-Co was measured spectrophotometrically.…”

“…The complete methodology has been previously published. 44 Two pathologically/physiologically relevant pH values (pH 6.8 and 7.5) were assessed. Shortly, 700 μL of TRIS buffer (pH 6.8 and 7.5) was mixed with 200 μL of methanol (blank), or different concentrations of a tested compound.…”

“…This experiment was performed according to previous studies 47 with some modifications. 44 Blood was obtained from adult rats (Wistar Han, Velaz, s.r.o., Czech Republic) by exsanguination into heparinized tubes. The exsanguination was performed by a trained researcher in accordance with The Guide for the Care and Use of Laboratory Animals published by the American National Institutes of Health (8th edition, revised 2011, ISBN-13: 978-0-309-15400-0).…”

“…43 For the aforementioned reasons, the aim of our study was to analyse the interaction of 23 structurally related avonoids with cobalt via a complex methodological approach developed by us. 44 First, their ability to chelate cobalt ions was compared under four (patho)physiologically relevant pH conditions. To cover different structural features, we involved a relatively large series of avonoids including some that were not expected to chelate cobalt.…”