Metal-binding cyclodextrins: Synthesis and complexation with Zn2+ and Ga3+ cations towards antimicrobial applications

Highly resistant bacteria producing metallo-β-lactamases (MBLs) to evade β-lactam antibiotics, constitute a major cause of life-threatening infections world-wide. MBLs exert their hydrolytic action via Zn2+ cations in their active center. Presently, there are no approved drugs to target MBLs and combat the associated antimicrobial resistance (AMR). Towards this issue, we have prepared a family of cyclodextrins substituted with iminodiacetic acid (IDA) on their narrow side, while the wider side is either unmodified or per-2,3-O-methylated. The molecules form strong coordination complexes with Zn2+ or Ga3+ cations in aqueous solution. Free and metal-complexed compounds have been thoroughly characterized regarding structures, pH-dependent ionization states, distribution of species in solution, pKa values and metal-binding constants. At neutral pH the multi-anionic hosts bind up to four Zn2+ or Ga3+ cations. In vitro, 50 μΜ of the compounds achieve complete re-sensitization of MBL-producing Gram-negative clinical bacterial strains resistant to the carbapenems imipenem and meropenem. Moreover, the radioactive complex [67Ga]Ga-β-IDACYD prepared, displays high radiochemical purity, sufficient stability both overtime and in the presence of human plasma apo-transferrin, thus providing an invaluable tool for future biodistribution and pharmacokinetic studies of β-IDACYDin vivo, prerequisites for the development of therapeutic protocols.

Iminodiacetic acid-functionalized porous polymer for removal of toxic metal ions from water

The design of efficient adsorbent with abundant binding sites for heavy metal ions is crucial for developing innovative materials that will remove pollutant metal ions. The high uptake capacity, kinetics, and affinity towards the toxic metals are the key requirements that the materials under invesigation should accomplish. Here we report the synthesis of iminodiacetic acid-functionalized hypercrosslinked polymer (IDA-HCP) for purification of water polluted by toxic metal ions via coordination of carboxylate and amino active sites on the surface of porous polymer. The obtained porous polymer is stable under harsh conditions and the structural features on the polymer work together to help the removal of Pb(II) with 1138 mg g^-1 uptake capacity. In the meanwhile, the IDA-HCP reveals reuseability and very promising capture efficiency not only for Pb²⁺, but also for Hg²⁺ and Cd²⁺ from a mixture of Pb²⁺, Hg²⁺, Cd²⁺, Co²⁺, Fe³⁺, Zn²⁺, Mg²⁺, and Na⁺ metal ions. This result gives us confidence that the polymer material can solve the pollution problem caused by various metal ions.

Proteomics analysis of host cell proteins after immobilized metal affinity chromatography: Influence of ligand and metal ions

Different degrees of protein purity have been observed in immobilized metal affinity chromatography ranging from extremely high purity to moderate and low purity. It has been hypothesized that the host cell protein composition and the metal ligands are factors governing the purity of a protein obtained after immobilized metal affinity chromatography (IMAC). Ni nitrilotriacetic acid (NTA) has become the first choice for facile His-tagged protein purification, but alternative ligands such as iminodiacetic acid (IDA) with other immobilized metal ions such as Zn, Cu and Co are valuable options when the expected purity or binding capacity is not reached. Especially Cu and Zn are very attractive, due to their reduced environmental and safety concerns compared to Ni. Co and Zn are more selective than Ni and Cu. This increased selectivity comes at the cost of weaker binding. In this work, the influence of ligand choice on protein purity after IMAC was evaluated by several methods, including peptide mapping. His-tagged GFP was used as model protein. We found that host cell protein (HCP) content varies drastically between ligands, as IDA eluates generally showing higher HCP concentrations than NTA. The relative content of the key amino acids His, Cys and Trp in the sequence of the co-eluted protein does not suffice to explain co-eluting propensity. The co-elution of HCPs is mostly influenced by metal binding clusters on the protein surface and not by total content or surface concentration of metal interacting amino acids. Prediction of co-elution is not dependent on these clusters alone, due to protein-protein interactions, indicted by a relative low metal binding cluster score but high co-elution propensity and in a lot of cases these proteins are often part of complex such as ribosome and chaperones. The different co-eluting proteins were presented by a heatmap with a dendrogram. Ward's linkage method was used to calculate the distance between groups of co-eluting proteins. Clustering of co-eluting HCPs was observed according to ligand and by metal ions, with Zn and Co forming one cluster and Ni and Cu another. The co-elution of host cell proteins can be explained by clusters of metal interacting amino acids on the protein surface and by protein-protein interactions. While Ni NTA still appears to be highly advantageous, it might not be the cure-all for all applications.

Biocompatibility Studies of Gadolinium Complexes with Iminodiacetic Acid Derivatives

Apart from using as radiopharmaceuticals, iminodiacetic acid derivatives, after complexation with gadolinium, have been also tested as MRI CAs (magnetic resonance imaging contrast agents) since they show high affinity to hepatocytes and therefore provide high-resolution MRI of the liver. The purpose of this study was to evaluate the biocompatibility of four gadolinium complexes with iminodiacetic acid (IDA) derivatives differing in substituent in aromatic ring by estimating their influence on plasma hemostasis, integrity of erythrocyte membrane, and toxicity towards human umbilical vein endothelial cells (HUVECs). The influence of gadolinium-based CAs on plasma hemostasis was evaluated by measuring PT (prothrombin time), APTT (activated partial tromboplastin time), and TT (thrombin time). The effects of tested compounds on RBCs (Red Blood Cells) were assessed using hemolysis assay and microscopy studies. The influence of gadolinium complexes on the barrier properties of HUVECs was assessed by means of real-time method based on the measurements of the impedance changes of the cells. Gadolinium complexes did not affect significantly PT and TT. APTT measurements revealed significant prolongation in the presence of all tested gadolinium complexes at the concentration higher than 0.5 μmol/mL. Hemolysis assay showed that compounds with alkyl substituents in benzene ring without halogen atom (1-3) do not exert unfavorable effect on the integrity of erythrocyte membrane over the entire concentration range. All gadolinium complexes at 1.0 μmol/mL contribute to the decrease in HUVEC viability and integrity. To conclude, the study describes biocompatibility studies of gadolinium-based CAs, provides additional insight into their potential toxicity associated with systemic administration, and underscores the necessity for further research.

Significant improvement of the nitrilase activity by semi-rational protein engineering and its application in the production of iminodiacetic acid

Iminodiacetic acid (IDA) is widely used as an intermediate in the manufacturing of chelating agents, glyphosate herbicides and surfactants. To improve activity and tolerance to the substrate for IDA production, Acidovorax facilis nitrilase was selected for further modification by the gene site saturation mutagenesis method. After screened by a two-step screening method, the best mutant (Mut-F168V/T201N/S192F/M191T/F192S) was selected. Compared to the wild-type nitrilase, Mut-F168V/T201N/S192F/M191T/F192S showed 136% improvement in specific activity. Co²⁺ stimulated nitrilase activity, whereas Cu²⁺, Zn²⁺ and Tween 80 showed a strong inhibitory effect. The V_max and k_cat of Mut-F168V/T201N/S192F/M191T/F192S were enhanced 1.23 and 1.23-fold, while the K_m was decreased 1.53-fold. The yield of Mut-F168V/T201N/S192F/M191T/F192S with 453.2 mM of IDA reached 71.9% in 5 h when 630 mM iminodiacetonitrile was used as substrate. This study indicated that mutant nitrilase obtained in this study is promising in applications for the upscale production of IDAN.

Affinity induced immobilization of adenylate cyclase from the crude cell lysate for ATP conversion

The development of an orientation immobilization technique via affinity between polyhistidine tags and metal ions aims at maintaining biocatalytic activity of the enzymes. In this work, to tackle the issue of the immobilization of adenylate cyclase (AC), a simple and effective approach of synthesizing iminodiacetic acid (IDA)-Ni²⁺ particles was applied for simultaneously purifying and immobilizing his-tagged AC. We chose agarose particles as carriers, and then decorated them with IDA, leading to the formation of a coordination combination of Ni²⁺. The porous carriers with a large pore size of 50 nm and a specific surface area of 45.8 m²/g exhibited favorable enzymatic activity and loading capacity. The optimal pH of the immobilized enzyme increased from 8.0 to 9.0 and the optimal temperature increased from 30 °C to 35 °C, compared to the free AC. Moreover, the immobilized AC retained a residual activity of approximately 80% after storing it at 25 °C for 48 h, whereas only 40% of the activity was left in the free AC at the same conditions. Maximum yield of cyclic adenosine-3', 5'- monophosphate (cAMP) reached up to the summit of the reaction. The immobilized AC by affinity adsorption will provide a promising route for the industrial production of cAMP.

Use of mild organic acid reagents to recover the Co and Li from spent Li-ion batteries

New organic acid mixtures have been investigated to recover the valuable metal ions from the cathode material of spent Li-ion batteries. The cathodic active material (LiCoO2) collected from spent Li-ion batteries (LIBs) is dissolved in mild organic acids, iminodiacetic acid (IDA) and maleic acid (MA), to recover the metals. Almost complete dissolution occurred in slightly excess (than the stoichiometric requirement) of IDA or MA at 80°C for 6h, based on the Co and Li released. The reducing agent, ascorbic acid (AA), converts the dissolved Co(III)- to Co(II)-L (L=IDA or MA) thereby selective recovery of Co as Co(II)-oxalate is possible. The formation of Co(III)- and Co(II)-L is evident from the UV-Vis spectra of the dissolved solution as a function of dissolution time. Thus, the reductive-complexing dissolution mechanism is proposed here. These mild organic acids are environmentally benign unlike the mineral acids.

Stability of erythrocyte membrane and overall hemostasis potential - A biocompatibility study of mebrofenin and other iminodiacetic acid derivatives

BACKGROUND

Intravenous injection seems to be the most convenient way of administering drugs and contrast agents, which makes components of the blood the first and usually unwanted target of their action. Binding of intravenously administered compounds to erythrocytes, blood platelets and vascular wall may have serious clinical implications. The aim of this study was to examine the influence of four iminodiacetic acid derivatives, potential ligands for gadolinium complexation, on the process of coagulation and fibrinolysis, activity of thrombin and hemolysis.

METHODS

Kinetic parameters of coagulation and fibrinolysis process were determined during an optical CL-test based on measurement of transmittance alterations. Thrombin (0.5 IU/mL) and t-PA (240 ng/mL) were used to obtain a clotting and lysis curve. The activity of thrombin was determined with a chromogenic substrate S-2238. Hemolysis was examined spectrophotometrically and expressed as a percentage of released hemoglobin.

RESULTS

Exposure to iminodiacetic acid derivatives resulted in a significant increase in the overall potential of clotting and lysis (CLAUC), as well as with the significant changes in the key parameters of these processes (thrombin time, initial plasma clotting velocity, clot stabilization time). Furthermore, iminodiacetic acid derivatives caused a significant decrease in the amidolytic activity of thrombin and enhanced hemolysis in a concentration-dependent manner.

CONCLUSION

Despite their influence on the process of coagulation and fibrinolysis, amidolytic activity of thrombin and hemolysis, iminodiacetic acid derivatives should be generally considered safe as the significant effects were observed mostly at 4 μmol/mL, which is about 10-fold higher than the theoretical plasma concentration of these compounds.

Evaluation of poly(amidoamine) dendrimers as potential carriers of iminodiacetic derivatives using solubility studies and 2D-NOESY NMR spectroscopy

The interactions between dendrimers and different types of drugs are nowadays one of the most actively investigated areas of the pharmaceutical sciences. The interactions between dendrimers and drugs can be divided into: internal encapsulation, external electrostatic interaction, and covalent conjugation. In the present study, we investigated the potential of poly(amidoamine) (PAMAM) dendrimers for solubility of four iminodiacetic acid derivatives. We reported that PAMAM dendrimers contribute to significant solubility enhancement of iminodiacetic acid analogues. The nature of the dendrimer–drug complexes was investigated by ¹H NMR and 2D-NOESY spectroscopy. The ¹H NMR analysis proved that the water-soluble supramolecular structure of the complex was formed on the basis of ionic interactions between terminal amine groups of dendrimers and carboxyl groups of drug molecules, as well as internal encapsulation. The 2D-NOESY analysis revealed interactions between the primary amine groups of PAMAM dendrimers and the analogues of iminodiacetic acid. The results of solubility studies together with ¹H NMR and 2D-NOESY experiments suggest that the interactions between PAMAM dendrimers of generation 1–4 and derivatives of iminodiacetic acid are based on electrostatic interactions and internal encapsulation.