Interaction of Cd and Zn with biologically important ligands characterized using solid-state NMR and ab initio calculations

Solid-state NMR spectroscopic analysis for structure determination of a zinc-bound catalytic amyloid fibril

Zinc ions are commonly involved in enzyme catalysis and protein structure stabilization, but their coordination geometry of zinc-protein complex is rarely determined. Here, in this chapter, we introduce a systematic solid-state NMR approach to determine the oligomeric assembly and Zn2+ coordination geometry of a de novo designed amyloid fibrils that catalyze zinc dependent ester hydrolysis. NMR chemical shifts and intermolecular contacts confirm that the peptide forms parallel-in-register β-sheets, with the two forms of Zn2+ bound histidines in each peptide. The amphiphilic parallel β-sheets assemble into stacked bilayers that are stabilized by hydrophobic side chains between β-sheets. The conformations of the histidine side chains, determined by 13C-15N distance measurements, reveal how histidines protrude from the β-sheet. 1H-15N correlation spectra show that the single-Zn2+ coordinated histidine associated with dynamic water. The resulting structure provides insight into how metal ions contribute to stabilizing the protein structure and driving its catalytic reactivity.

Hesperidin protects against cadmium-induced pancreatitis by modulating insulin secretion, redox imbalance and iNOS/NF-ĸB signaling in rats

AIM

Cadmium is a persistent ubiquitous environmental toxicant that elicits several biological defects on delicate body organs. Growing evidence suggests that cadmium (Cd) may perturb signaling pathways to induce oxidative pancreatitis. Thus, we explored whether hesperidin, a flavonone, could mitigate Cd-induced oxidative stress-mediated inflammation and pancreatitis in Wistar rats.

MAIN METHODS

Forty (40) rats randomly assigned to 5 groups (n = 8) were administered normal saline or hesperidin (Hsp) followed by Cd intoxication for 28 days.

KEY FINDINGS

Cadmium accumulated in the pancreas of rats, and markedly decreased insulin, pancreatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities and glutathione (GSH) level. Cadmium considerably increased malondialdehyde (MDA), serum lipase and amylase activities. Cadmium induced pancreatic pro-inflammation via over-expression of inducible nitric oxide synthase (iNOS), nuclear factor-ĸB (NF-κB), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), along with histopathological alterations. Hesperidin prominently decreased serum amylase and lipase activities, and markedly increased insulin level, pancreatic antioxidant defense mechanism, whereas iNOS, NF-κB, IL-6 and TNF-α levels significantly decreased. Changes in histology confirmed our biochemical findings.

SIGNIFICANCE

Our findings suggest that Cd induced pancreatitis via pro-inflammation and oxidative stress; Hsp, thus, protects against Cd-induced pancreatitis via attenuation of oxidative stress and proinflammatory responses in pancreas.

Zinc(II) Complexes with Amino Acids for Potential Use in Dermatology: Synthesis, Crystal Structures, and Antibacterial Activity

The multifunctional profile of Zn²⁺ has influenced its great popularity in various pharmaceutical, food, and cosmetic products. Despite the use of different inorganic and organic zinc derivatives, the search for new zinc-containing compounds with a safer skin profile still remains an open issue. The present paper describes the synthesis, structural characterization, and antibacterial activity of zinc(II) complexes with proteinogenic amino acids as potential candidates for dermatological treatments. The obtained complexes are of the general formula [Zn(AA)₂], where AA represents an amino acid (L-Glu, Gly, L-His, L-Pro, L-Met, and L-Trp). Their synthesis was designed in such a way that the final bis(aminoacidate) zinc(II) complexes did not contain any counter-ions such as Cl⁻, NO₃⁻, or SO₄²⁻ that can cause some skin irritations. The chemical structure and composition of the compounds were identified by ¹H NMR spectroscopy and elemental analysis, and four were also characterized by single-crystal X-ray diffraction. The Hirshfeld surface analysis for the Zn²⁺ metallic center helped to determine its coordination number and geometry for each complex. Finally, the antibacterial properties of the complexes were determined with respect to three Gram-positive strains, viz. Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, and Streptococcus pyogenes ATCC 19615, and two Gram-negative bacteria, viz. Escherichia coli ATCC 25992 and Pseudomonas aeruginosa ATCC 27853, and were compared with the activity of zinc 2-pirrolidone 5-carboxylate (ZnPCA), commonly applied in dermatology. It was found that the Zn(II) complexes with methionine and glycine exhibited a higher antibacterial activity than the tested standard, and the antimicrobial properties of complex with Trp were satisfactory. The results of the antimicrobial activity examination allow us to postulate that the obtained zinc complexes might become new active substances for use in dermatological products.

Puerarin protects rat liver and kidney against cadmium-induced oxidative stress

Oxidative stress is thought to be involved in cadmium (Cd) induced toxicity. This study examined the possible protective effect of puerarin on cadmium chloride (CdCl2, 2 mg/kg b.w.) induced toxicity in male rats. Male SD rats were treated with either intraperitoneal Cd and/or oral puerarin (100 mg/kg. b.w.) for 4 weeks. The results demonstrated that exposure to Cd led to an increase in the level of BUN, ALT and AST in serum. Cadmium raised the concentrations of MDA and GSH, and decreased antioxidants activities (SOD, CAT, and GSH-Px) in the liver and kidney. Conversely, administration of puerarin markedly attenuated Cd-induced biochemical alterations in serum, liver, and kidney tissues. These results suggest that puerarin exerts protective effects against Cd toxicity attributable to its antioxidant actions.

A DFT/ZORA Study of Cadmium Magnetic Shielding Tensors: Analysis of Relativistic Effects and Electronic-State Approximations

Theoretical considerations are discussed for the accurate prediction of cadmium magnetic shielding tensors using relativistic density functional theory (DFT). Comparison is made between calculations that model the extended lattice of the cadmium-containing solids using periodic boundary conditions and pseudopotentials with calculations that use clusters of atoms. The all-electron cluster-based calculations afford an opportunity to examine the importance of (i) relativistic effects on cadmium magnetic shielding tensors, as introduced through the ZORA Hamiltonian at either the scalar (SC) or spin-orbit (SO) levels and (ii) variation in the class of the DFT approximation. Twenty-three combinations of pseudopotentials or all-electron methods, DFT functionals, and relativistic treatments are assessed for the prediction of the principal components of the magnetic shielding tensors of 30 cadmium sites. We find that the inclusion of SO coupling can increase the cadmium magnetic shielding by as much as ca. 1100 ppm for a certain principal values; these effects are most pronounced for cadmium sites featuring bonds to other heavy atoms such as cadmium, iodine, or selenium. The best agreement with experimental values is found at the ZORA SO level in combination with a hybrid DFT method featuring a large admixture of Hartree-Fock exchange such as BH&HLYP. Finally, a theoretical examination is presented of the magnetic shielding tensor of the Cd(I) site in Cd₂(AlCl₄)₂.

Osteocyte viability and bone density in cadmium chloride-induced osteoporosis ameliorated with Pilostigma thonningii stem bark-extracted D-3-O-methy-chiroinositol

BACKGROUND

This study examined the ameliorative effect of D-3-O-methyl-chiroinositol, isolated from the stem bark of Piliostigma thonningii, on cadmium chloride-induced osteoporosis in male Wistar rats.

METHODS

Thirty-six rats were assigned to three treatment groups (n = 12). Group A (2 mL distilled water), group B: (2.5 mg/kg b.w. CdCl2) and group C: (2.5 mg/kg b.w. CdCl2 and D-3-O-methyl-chiroinositol 2 mg/kg b.w.). Bone ash, calcium, phosphate, magnesium, and zinc content, as well as bone histological changes were determined at the end of months 1, 2, and 3.

RESULTS

There were significant differences (P ≤ 0.05) in the weight of the cervical, tibia, and femoral bones in all groups. The serum concentration of CdCl2 was significantly different across the three groups with time. There was significant variation (P < 0.005) in the mean bone ash across groups. The concentration of OH-proline was significantly different (P < 0.0001) across groups. There were significant differences (P < 0.0001) in bone calcium, magnesium, zinc, and phosphorus concentrations. Histology revealed high levels of bone mineralisation in the CdCl2-treated group, indicative of osteoporosis with hypertrophied osteocytes, while the femur of Wistar rats treated with D-3-O-methyl-chiroinositol showed bone trabeculae and viable osteocytes.

CONCLUSION

The study concluded that D-3-O-methyl-chiroinositol extract from Piliostigma thionningii stem bark ameliorated cadmium chloride-induced osteoporosis in male Wistar rats.

Preferential intermolecular interactions lead to chiral recognition: enantioselective gel formation and collapse

Enantioselective recognition of chiral amines through gel formation and collapse.

Quercetin exerts preventive, ameliorative and prophylactic effects on cadmium chloride - induced oxidative stress in the uterus and ovaries of female Wistar rats

This study examined the possible protective effect of quercetin(QE) on cadmium chloride (CdCl₂) - induced reproductive toxicity in female rats. Cadmium (Cd) accumulated in the uterus and ovaries of rats, decreased antioxidants [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione (GSH)], and raised the concentrations of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in the uterus and ovaries of rats. Serum concentrations of estradiol, progesterone, follicle stimulating hormone and luteinizing hormone decreased significantly after CdCl₂ administration. Caspase-3 activity significantly increased in the ovaries, with an increase in Bax and a decrease in Bcl-2 protein expressions after CdCl₂ treatment. Histopathology of the ovaries revealed significant decrease in follicle number, while the uterus showed cyst-like endometrial glands. All three models of QE treatment [pre-treatment (QE + CdCl₂), post-treatment (CdCl₂+QE), simultaneous treatment (CdCl₂/QE)] decreased Cd accumulation, MDA, H₂O₂, and increased SOD, CAT and GPx activities in the uterus and ovaries, decreased apoptosis of follicular cells, and increased serum reproductive hormones. However, the QE pre-treated model offered better protection against CdCl₂ relative to the other two models. These results suggest that, QE exerts multi-mechanistic protective effects against cadmium toxicity attributable to its antioxidant and anti-apoptotic actions.

Zinc stabilization of prefibrillar oligomers of human islet amyloid polypeptide

The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in type II diabetes. Zinc present in secretory granules has been shown to affect this aggregation. A combination of EXAFS, NMR, and AFM experiments shows that the influence of zinc is most likely due to the stabilization of prefibrillar aggregates of hIAPP.

Effect of Cysteine vs. Histidine on the Electronic Structure of Zn2+Upon Complex Formation

The local electronic structure at Zn2+ions during complex formation with histidine and cysteine has been studied by near edge x-ray absorption fine structure spectroscopy at the Zn L-edge. At pH ≅ 5 both histidine and cysteine have carboxylate and amino groups able to form complexes with cations in solution such as Zn2+. Compared to histidine, cysteine has an extra thiolate group which can chelate Zn2+. This investigation shows that histidine is chelating the Zn2+ion mainly via the amino group, while cysteine chelates primarily via the thiolate group. The nature of the empty molecular orbitals involved in the transitions has been analyzed using density functional theory including the solvent effects. By comparing the calculated results with the experimental observations, we conclude that histidine affects primarily the Zn2+electronic states of d-symmetry, while cysteine affects both s- and d-states. This mechanism is important for understanding the zinc sulfhydryl bond in zinc finger proteins, where cysteine and histidine in the protein are chelating Zn2+.

NMR and EPR studies of membrane transporters

In order to fulfill their function, membrane transport proteins have to cycle through a number of conformational and/or energetic states. Thus, understanding the role of conformational dynamics seems to be the key for elucidation of the functional mechanism of these proteins. However, membrane proteins in general are often difficult to express heterologously and in sufficient amounts for structural studies. It is especially challenging to trap a stable energy minimum, e.g., for crystallographic analysis. Furthermore, crystallization is often only possible by subjecting the protein to conditions that do not resemble its native environment and crystals can only be snapshots of selected conformational states. Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy are complementary methods that offer unique possibilities for studying membrane proteins in their natural membrane environment and for investigating functional conformational changes, lipid interactions, substrate-lipid and substrate-protein interactions, oligomerization states and overall dynamics of membrane transporters. Here, we review recent progress in the field including studies from primary and secondary active transporters.

NMR studies of the Zn2+ interactions with rat and human beta-amyloid (1-28) peptides in water-micelle environment

Alzheimer's disease is a fatal neurodegenerative disorder involving the abnormal accumulation and deposition of peptides (amyloid-beta, Abeta) derived from the amyloid precursor protein. Here, we present the structure and the Zn2+ binding sites of human and rat Abeta(1-28) fragments in water/sodium dodecyl sulfate (SDS) micelles by using 1H NMR spectroscopy. The chemical shift variations measured after Zn2+ addition at T>310 K allowed us to assign the binding donor atoms in both rat and human zinc complexes. The Asp-1 amine, His-6 Ndelta, Glu-11 COO-, and His-13 Nepsilon of rat Abeta28 all enter the metal coordination sphere, while His-6 Ndelta, His-13, His-14 Nepsilon, Asp-1 amine, and/or Glu-11 COO- are all bound to Zn2+ in the case of human Abeta28. Finally, a comparison between the rat and human binding abilities was discussed.

New Metal-Organic Frameworks with Large Cavities: Selective Sorption and Desorption of Solvent Molecules

Five novel transition metal complexes [Cd(II) (3)(tpba-2)(2)(SCN)(6)].6 THF.3 H(2)O (1), [Cu(II) (3)(tpba-2)(2)(SCN)(6)].6 THF.3 H(2)O (2), [Ni(II) (3)(tpba-2)(2)(SCN)(6)].6 THF.3 H(2)O (3), [Cd(II) (2)(tpba-2)(SCN)(3)]ClO(4) (4), [Cu(I) (3)(SCN)(6)(H(3)tpba-2)] (5) [TPBA-2 = N',N'',N'''-tris(pyrid-2-ylmethyl)-1,3,5-benzenetricarboxamide, THF=tetrahydrofuran] were obtained by reactions of the corresponding transition metal salts with TPBA-2 ligand in the presence of NH(4)SCN using layering or solvothermal method, respectively. The results of X-ray crystallographic analysis showed that complexes 1, 2 and 3 are isostructural and have the same 2D honeycomb network structure with Kagomé lattice, in which all the M(II) (M = Cd, Cu, Ni) atoms are six-coordinated, and the TPBA-2 ligands adopt cis,cis,cis conformation while the thiocyanate anions act as terminal ligands. Capsule-like motifs are found in 1, 2 and 3, in which six THF molecules are hosted, and the results of XPRD and solid-state (13)C NMR spectral measurements showed that the compound 1 can selectively desorb and adsorb THF molecules occurring along with the re-establishment of its crystallinity. In contrast to 1, 2 and 3, complex 4 has different 2D network structure, resulting from TPBA-2 ligands with cis,trans,trans conformation, thiocyanate anions serving as end-to-end bridging ligands, and the incomplete replacement of perchlorate anions, which further link the 2D layers into 3D framework by the hydrogen bonds. In complex 5, the Cu(II) atoms are reduced to Cu(I) during the process of solvothermal reaction, and the Cu(I) atoms are connected by thiocyanate anions to form a 3D porous framework, in which the protonated TPBA-2 ligands are hosted in the cavities as templates.

Occupational exposure and effects on the male reproductive system

A significant increase in the incidence of male infertility has been described in the international literature, raising questions about its causes. Part of this effect may result from synthetic toxic substances acting on the endocrine system (endocrine disruptors), many of which are routinely used in work processes. We provide a critical review of the specialized literature on work-related chemical substances capable of causing male infertility. Pesticides such as DDT, linuron, and others, heavy metals like mercury, lead, cadmium, and copper, and substances from various industrial uses and residues such as dioxins, polychlorinated biphenyls (PCBs), ethylene dibromide (EDB), phthalates, polyvinyl chloride (PVC), and ethanol are among the main endocrine disruptors that can cause male infertility. Based on the literature, gonadal dysfunction and congenital malformation are the main alterations caused by these substances in the male reproductive system. We conclude that despite the relative lack of studies on this issue, the relevance of such risk calls for further studies as well as measures to prevent workers' exposure to the various substances.

First principle calculations of 113Cd chemical shifts for proteins and model systems

113Cd isotropic NMR shieldings are calculated for a number of metal ion binding sites in proteins, using the GIAO-B3LYP and GIAO-HF methods with the uncontracted (19s15p9d4f) polarized basis set of Kellö and Sadlej on cadmium and 6-31G(d) on the ligands. The results compare favorably with experimental data, indicating that first principle calculations are a useful tool for structural interpretation of (113)Cd chemical shift data from metal ion containing proteins. The effect of different ligand types (thiolate, imidazole, water, and monodentate carboxylate), coordination number, and deviations of the coordination geometry from ideal structures is evaluated. In particular, the ligand type and coordination number are important factors, but also changes in cadmium-ligand bond lengths may cause significant changes of the chemical shift.

Reactivity of 2-Pyridinecarboxylic Esters with Cadmium(II) Halides: Study of 113Cd NMR Solid State Spectra and Crystal Structures of Hexacoordinated Complexes [CdI2(C5H4NCOOMe)2] and [CdI2(C5H4NCOOPrn)2]

The series of complexes [CdX(2)(C(5)H(4)NCOOR)] (X = Cl or Br; R = Me, Et, Pr(n)() or Pr(i)()) and [CdX(2)(C(5)H(4)NCOOR)(2)] (X = I; R = Me, Et, Pr(n)(), or Pr(i)()) have been obtained by the addition reaction of esters of 2-pyridinecarboxylic acid to cadmium(II) halides. X-ray crystal structures of two complexes [CdI(2)(C(5)H(4)NCOOR)(2)], R = Me (10) and R = Pr(n)() (12), have been determined. In both cases, the structure consists of discrete neutral monomeric units where the cadmium atom has a distorted octahedral coordination with CdI(2)N(2)O(2) core, two halides being in cis disposition. Structural information is compared with that deduced from (113)Cd CPMAS NMR experiments. Chemical shift anisotropies are discussed in terms of distortions produced in cadmium octahedra. The orientation of the principal axes of (113)Cd shielding tensor is also analyzed and related to the disposition of ligands in the structures of two analyzed compounds.