Stereoisomeric selectivity of 2,3-dimercaptosuccinic acids in chelation therapy for lead poisoning

Synthesis, structural characterization, computational studies and stability evaluations of metal ions and ZnONPs complexes with dimercaptosuccinic acid

Meso-2,3-dimercaptosuccinic acid (DMSA) is one of the efficient chelating reagents for treating the toxicity of several heavy metals. Currently, nanomaterial have been applied to various parts including zinc Oxide nanoparticles (ZnONPs). ZnONPs have several properties and are used as many applications. An increasing the amount of ZnONPs in commercial products causes risks related to free radicals or reactive oxygen species (ROS) in the body, leading to oxidative stress and eventually to the cancer process. In the present work, we mainly focused on the study of DMSA complexes in term of metal ions and nanoparticles. The synthesis of DMSA-ZnONPs by the co-precipitation method were determined, followed by Scanning Electron Microscope, Fourier Transform Infrared Spectroscopy and UV-Vis spectrophotometry confirming successful synthesis process. The stability study of the DMSA complexes with metal ions and ZnONPs were determined and evaluated the stability constant (K), with the Benesi- Hildebrand equation. All complexes with DMSA were formed at a 1:2 ratio by the dithiol group and the carboxyl group with different stability constants. Therefore, these results can help of an understanding of the interaction and its behavior between DMSA with heavy metal ion and ZnONPs. In addition, the stable structure of DMSA and metal ion complexes were predicted using the B3LYP and the 6-31G (d,p) basis set which the most stable structure of meso-DMSA was 2R,3S conformation and the metal ions and DMSA complexes was complex 2a with the binding energy of -1553.46 kcal mol^-1.

Whole-cell bioreporters and risk assessment of environmental pollution: A proof-of-concept study using lead

As the world burden of environmental contamination increases, it is of the utmost importance to develop streamlined approaches to environmental risk assessment in order to prioritize mitigation measures. Whole-cell biosensors or bioreporters and speciation modeling have both become of increasing interest to determine the bioavailability of pollutants, as bioavailability is increasingly in use as an indicator of risk. Herein, we examine whether bioreporter results are able to reflect expectations based on chemical reactivity and speciation modeling, with the hope to extend the research into a wider framework of risk assessment. We study a specific test case concerning the bioavailability of lead (Pb) in aqueous environments containing Pb-complexing ligands. Ligands studied include ethylene diamine tetra-acetic acid (EDTA), meso-2,3 dimercaptosuccinic acid (DMSA), leucine, methionine, cysteine, glutathione, and humic acid (HA), and we also performed experiments using natural water samples from Lake Tai (Taihu), the third largest lake in China. We find that EDTA, DMSA, cysteine, glutathione, and HA amendment significantly reduced Pb bioavailability with increasing ligand concentration according to a log-sigmoid trend. Increasing dissolved organic carbon in Taihu water also had the same effect, whereas leucine and methionine had no notable effect on bioavailability at the concentrations tested. We find that bioreporter results are in accord with the reduction of aqueous Pb²⁺ that we expect from the relative complexation affinities of the different ligands tested. For EDTA and HA, for which reasonably accurate ionization and complexation constants are known, speciation modeling is in agreement with bioreporter response to within the level of uncertainty recognised as reasonable by the United States Environmental Protection Agency for speciation-based risk assessment applications. These findings represent a first step toward using bioreporter technology to streamline the biological confirmation or validation of speciation modeling for use in environmental risk assessment.

Lead(II) binding to the chelating agent D-penicillamine in aqueous solution

A spectroscopic investigation of the complexes formed between the Pb(II) ion and D-penicillamine (H2Pen), a chelating agent used in the treatment of lead poisoning, was carried out on two sets of alkaline aqueous solutions with CPb(II) ≈ 10 and 100 mM, varying the H2Pen/Pb(II) molar ratio (2.0, 3.0, 4.0, 10.0). Ultraviolet-visible (UV-vis) spectra of the 10 mM Pb(II) solutions consistently showed an absorption peak at 298 nm for S(-) → Pb(II) ligand-to-metal charge-transfer. The downfield (13)C NMR chemical shift for the penicillamine COO(-) group confirmed Pb(II) coordination. The (207)Pb NMR chemical shifts were confined to a narrow range between 1806 ppm and 1873 ppm for all Pb(II)-penicillamine solutions, indicating only small variations in the speciation, even in large penicillamine excess. Those chemical shifts are considerably deshielded, relative to the solid-state (207)Pb NMR isotropic chemical shift of 909 ppm obtained for crystalline penicillaminatolead(II) with Pb(S,N,O-Pen) coordination. The Pb LIII-edge extended X-ray absorption fine structure (EXAFS) spectra obtained for these solutions were well-modeled with two Pb-S and two Pb-(N/O) bonds with mean distances 2.64 ± 0.04 Å and 2.45 ± 0.04 Å, respectively. The combined spectroscopic results, reporting δ((207)Pb) ≈ 1870 ppm and λmax ≈ 298 nm for a Pb(II)S2NO site, are consistent with a dominating 1:2 lead(II):penicillamine complex with [Pb(S,N,O-Pen)(S-HnPen)](2-n) (n = 0-1) coordination in alkaline solutions, and provide useful structural information on how penicillamine can function as an antidote against lead toxicity in vivo.

Comparative in vivo lead mobilization of meso- and rac-2,3-dimercaptosuccinic acids in albino Wistar rats

Comparison of the racemic and meso forms of 2,3-dimercaptosuccinic acid (DMSA) in lead mobilization from lead-loaded albino Wistar rats demonstrates that the racemic form is significantly more effective in reducing femur lead levels. After four oral doses at 0.5 mmol/kg, femur lead levels were reduced to 87% of control values by meso-DMSA and to 50% of control levels by rac-DMSA. Similarly, when the dose was increased to 1.0 mmol/kg, femur lead levels were reduced to 69% of control levels by meso-DMSA and to 45% of control levels by rac-DMSA. A similar pattern was found for renal lead levels. Brain lead concentrations were significantly lower in treated groups than in control groups, but no differences were found between rac- and meso-DMSA. Rac-DMSA is more soluble than meso-DMSA in acetonitrile, ethyl acetate, and ethyl ether. The partition coefficient of rac-DMSA in the n-octanol/water system was found to be about 2.8. These results indicate that rac-DMSA deserves further attention as a possible substitute for meso-DMSA.

Preparation of radioactive lead complexes utilizing Chelex methodology

The use of Chelex resin for the synthesis of radioactive lead complexes has been explored. The process involved immobilization of 203Pb on the resin and subsequent elution of complexed lead by chelating agents. 203Pb complexes derived from meso- and racemic dimercaptosuccinic acid (meso-DMSA, rac-DMSA) were prepared and assessed for stability in vitro.