Recent Advances in Molecular Toxicology of Cadmium and Nickel

Cadmium (Cd) and nickel (Ni) are two toxic elements which are widespread in the human environment, but less recognized as hazardous by the general public. Herein, we describe molecular mechanisms of their toxicity towards humans, in the context of general chemical and toxicological properties of these metals. Following the introductory remarks, the routes of exposure are outlined. The next chapter covers the health hazards posed by cadmium and nickel with the main stress placed on diseases like cadmium induced nephropathy, reproductive disorders due to cadmium exposure, cadmium related COPD and cadmium carcinogenesis. In respect to nickel, acute toxicity, nickel allergy and nickel carcinogenicity were described. This overall description provides the basis for a detailed account of molecular mechanisms of cadmium and nickel toxicity. They include the involvement of metallothioneins and their role in the transport of Cd(II) ions, and the role of oxidative damage and DNA repair inhibition in cadmium carcinogenesis. The final issue covered in respect to molecular mechanisms of cadmium toxicity is its influence on cellular junctions. Molecular mechanisms of nickel toxicity are divided into subjects of nickel allergy and several mechanisms related to its carcinogenicity. The discussion is completed by the presentation of nickel and cadmium interactions with zinc fingers as a possible common ground of their molecular toxicity

Ternary Complex Formation and Competition Quench Fluorescence of ZnAF Family Zinc Sensors

Our current understanding of the intracellular thermodynamics and kinetics of Zn(II) ions is largely based on the application of fluorescent sensor molecules, used to study and visualize the concentration, distribution and transport of Zn(II) ions in real time. Such agents are designed for high selectivity for zinc in respect to other biological metal ions. However, the issue of their sensitivity to physiological levels of 10 low molecular weight Zn(II) ligands (LMWLs) has not been addressed. We followed the effects of eight such compounds on the fluorescence of ZnAF-1 and ZnAF-2F, two representatives of ZnAF family of fluorescein-based zinc sensors containing the N,N-bis(2-pyridylmethyl)ethylenediamine chelating unit. Fluorescence titrations of equimolar Zn(II)/ZnAF-1 and Zn(II)/ZnAF-2F solutions with acetate, phosphate, citrate, glycine, glutamic acid, histidine, ATP and GSH demonstrated strong fluorescence 15 quenching. These results are interpreted in terms of an interplay of the formation of the [ZnAF-Zn(II)- LMWL] ternary complexes and the competition for Zn(II) between ZnAF and LMWLs. UV-vis spectroscopic titrations revealed the existence of supramolecular interactions between the fluorescein moiety of ZnAF-1 and ATP and His, which, however, did not contribute to fluorescence quenching. Therefore, the obtained results show that the ZnAF sensors, other currently used zinc sensors containing 20 the N,N-bis(2-pyridylmethyl)ethylenediamine unit, and, in general, all sensors that do not saturate the Zn(II) coordination sphere, may co-report cellular metabolites and Zn(II) ions, leading to misrepresentations of the concentrations and fluxes of biological zinc

Effect of Common Buffers and Heterocyclic Ligands on the Binding of Cu(II) at the Multimetal Binding Site in Human Serum Albumin

Visible-range circular dichroism titrations were used to study Cu(II) binding properties of Multimetal Binding Site (MBS) of Human Serum Albumin (HSA). The formation of ternary MBS-Cu(II)-Buffer complexes at pH 7.4 was positively verified for sodium phosphate, Tris, and Hepes, the three most common biochemical buffers. The phosphate > Hepes > Tris order of affinities, together with strong spectral changes induced specifically by Tris, indicates the presence of both Buffer-Cu(II) and Buffer-HSA interactions. All complexes are strong enough to yield a nearly 100% ternary complex formation in 0.5 mM HSA dissolved in 100 mM solutions of respective buffers. The effects of warfarin and ibuprofen, specific ligands of hydrophobic pockets I and II in HSA on the Cu(II) binding to MBS were also investigated. The effects of ibuprofen were negligible, but warfarin diminished the MBS affinity for Cu(II) by a factor of 20, as a result of indirect conformational effects. These results indicate that metal binding properties of MBS can be modulated directly and indirectly by small molecules

The Reactions of H2_{2}O2_{2} and GSNO with the Zinc Finger Motif of XPA. Not A Regulatory Mechanism, but No Synergy with Cadmium Toxicity

Tetrathiolate zinc fingers are potential targets of oxidative assault under cellular stress conditions. We used the synthetic 37-residue peptide representing the tetrathiolate zinc finger domain of the DNA repair protein XPA, acetyl-DYVICEECGKEFMSYLMNHFDLPTCDNCRDADDKHK-amide (XPAzf) as a working model to study the reaction of its Zn(II) complex (ZnXPAzf) with hydrogen peroxide and S-nitrosoglutathione (GSNO), as oxidative and nitrosative stress agents, respectively. We also used the Cd(II) substituted XPAzf (CdXPAzf) to assess the situation of cadmium assault, which is accompanied by oxidative stress. Using electrospray mass spectrometry (ESI-MS), HPLC, and UV-vis and circular dichroism spectroscopies we demonstrated that even very low levels of H$_{2}$O$_{2}$ and GSNO invariably cause irreversible thiol oxidation and concomitant Zn(II) release from ZnXPAzf. In contrast, CdXPAzf was more resistant to oxidation, demonstrating the absence of synergy between cadmium and oxidative stresses. Our results indicate that GSNO cannot act as a reversible modifier of XPA, and rather has a deleterious effect on DNA repair

Early and interdisciplinary physiotherapy in a patient in the intensive care unit with a bronchopulmonary fistula after thoracic fenestration: a case report

The aim of this study is to present the effects of the medical team’s therapy with particular focus on early physiotherapy in a patient subjected to elective pneumonectomy due to pleural empyema and chest fenestration. Our patient was 48 years old and underwent an elective pneumonectomy due to pleural empyema and cicatrization atelectasis as a result of complications. A lack of lung recoil after chest fenestration was the indication to transfer the patient to the intensive care unit (ICU) from the operating theater. Respective rehabilitation is necessary to restore the function of the respiratory system. It should be an integral part of the treatment plan, must be implemented in a timely manner, and should continue until the patient’s full recovery. This paper presents the effects of the medical team’s work with the emphasis on early physiotherapy in a patient in the ICU that resulted in a shorter hospitalization and a full return to functional capacity

The N-terminus of hepcidin is a strong and potentially biologically relevant Cu(II) chelator.

Hepcidin is an iron regulatory hormone, involved also in immune response in vertebrates. It contains the N-terminal Asp-Thr-His site able to bind Cu(II) ions. A significant discrepancy exist in the literature regarding Cu(II) affinity of this site in hepcidin. Our study focused on the model DTHFPI-NH2 hexapeptide reflecting the N-terminal motif of mature hepcidin Using potentiometry, UV-vis and CD spectroscopies we demonstrated that DTHFPI-NH2 is the strongest Cu(II) binding peptide discovered so far. A competition assay with human serum albumin (HSA) confirmed this high affinity and demonstrated that DTHFPI-NH2. withdraws all Cu(II) from HSA under equimolar concentrations. Based on these results we propose that hepcidin could exist as Cu(II) complex in blood, especially under inflammatory conditions, when its serum concentration is elevated

Interactions of Zn(II) Ions with Three His-Containing Peptide Models of Histone H2A

The interactions of Zn(ll) ions with the blocked hexapeptide models -TESHHK-, -TASHHK- and -TEAHHK- of the -ESHH- motif of the C-terminal of historic H2A were studied by using potentiometric and IH-NMR techniques. The first step of these studies was to compare the pKa values of the two His residues inside each hexapeptide calculated by potentiometric or H-NMR titrations. Hereafter, the potentiometric titrations in the pH range 5 11 suggest the formation of several monomeric Zn(ll) complexes. It was found that all hexapeptides bind to Zn(ll) ions initially through both imidazole nitrogens in weakly acidic and neutral solutions forming slightly distorted octahedral complexes. At higher pH values, the combination of potentiometric titrations and one and two dimensional NMR suggested no amide coordination in the coordination sphere of Zn(II) ions. Obviously, these studies support that the -ESHH- sequence of histone H2A is a potential binding site for Zn(II) ions similarly with the Cu(II) and Ni(ll) ions, presented in previous papers

Hierarchical binding of copperII to N-truncated Ab4–16 peptide

N-Truncated Ab4–42 displays a high binding affinity with CuII. A mechanistic scheme of the interactions between Ab4–42 and CuII has been proposed using a fluorescence approach. The timescales of different conversion steps were determined. This kinetic mechanism indicates the potential synaptic functions of Ab4–42 during neurotransmission

Overexpression of phytochelatin synthase in tobacco: distinctive effects of AtPCS1 and CePCS genes on plant response to cadmium

Phytochelatins, heavy-metal-binding polypeptides, are synthesized by phytochelatin synthase (PCS) (EC 2.3.2.15). Previous studies on plants overexpressing PCS genes yielded contrasting phenotypes, ranging from enhanced cadmium tolerance and accumulation to cadmium hypersensitivity. This paper compares the effects of overexpression of AtPCS1 and CePCS in tobacco (Nicotiana tabacum var. Xanthi), and demonstrates how the introduction of single homologous genes affects to a different extent cellular metabolic pathways leading to the opposite of the desired effect. In contrast to WT and CePCS transformants, plants overexpressing AtPCS1 were Cd-hypersensitive although there was no substantial difference in cadmium accumulation between studied lines. Plants exposed to cadmium (5 and 25 μM CdCl2) differed, however, in the concentration of non-protein thiols (NPT). In addition, PCS activity in AtPCS1 transformants was around 5-fold higher than in CePCS and WT plants. AtPCS1 expressing plants displayed a dramatic accumulation of γ-glutamylcysteine and concomitant strong depletion of glutathione. By contrast, in CePCS transformants, a smaller reduction of the level of glutathione was noticed, and a less pronounced change in γ-glutamylcysteine concentration. There was only a moderate and temporary increase in phytochelatin levels due to AtPCS1 and CePCS expression. Marked changes in NPT composition due to AtPCS1 expression led to moderately decreased Cd-detoxification capacity reflected by lower SH:Cd ratios, and to higher oxidative stress (assessed by DAB staining), which possibly explains the increase in Cd-sensitivity. The results indicate that contrasting responses to cadmium of plants overexpressing PCS genes might result from species-dependent differences in the activity of phytochelatin synthase produced by the transgenes