Biomedical subjects

W Bal

Publications and source records attributed to W Bal.

At least 19 recordsLinked to original sources

PubMed2003

Cu(II) complexation potentiates arginine vasopressin action on nonpregnant human myometrium in vitro.

Copper may influence in vivo and in vitro uterine activity. Recent evidence has shown that cupric ions can easily form complexes with oligopeptides like arginine vasopressin (AVP). The high complex stability in vitro suggests a possibility of complex formation in vivo, in the uterus of intrauterine device users. In vitro isometric contractions were recorded in uterine tissues from nonpregnant premenopausal women undergoing hysterectomy and the effect of Cu-AVP complex on isolated human nonpregnant myometrium was investigated. The addition of the Cu(II)-AVP complex to the bath medium led to a concentration-dependent increase of the contractile activity. The activity was somewhat lower for the complex (-log EC(50) of 8.5 +/- 0.2, n = 7) than for AVP, but the difference was not statistically significant (p = 0.11). The maximal responses (E(max)) of the myometrium strips treated with AVP and the Cu (II)-AVP complex did not differ significantly. To assess the effect of presence of Cu (II) in the medium on tissue response to AVP, myometrium strips were preincubated for 20 min in the medium containing 10(-6) mol/L Cu(II) prior to the administration of AVP. The chosen Cu (II) concentration was below the threshold of effect on the spontaneous contractile activity in our experiments. The presence of cupric ions in the bath caused a significant leftward shift in the concentration-response curve to AVP.

Adult↗

PubMed2001

Coordination of heavy metals by dithiothreitol, a commonly used thiol group protectant.

D,L-Dithiothreitol (DTT), known also as Cleland reagent, is a thiol group protectant, used commonly in peptide and protein chemistry. Therefore, it is often added at high concentrations in preparations of proteins relevant to heavy metal biochemistry. The coordination of five of these metal ions, Zn(II), Cd(II), Pb(II), Ni(II) and Cu(I) to DTT was studied by means of potentiometric titrations, and UV-Vis and NMR spectroscopies. It was found that DTT forms specific and very stable polymeric and monomeric complexes with all of these metal ions, using both of its sulfur donors. The quantitative description of these complexes in solution and the solid state provides the basis for predictions of interference from DTT in studies of metal ion binding of thiol-containing biomolecules.

Chelating Agents↗

PubMed2001

Copper(II)-lincomycin: complexation pattern and oxidative activity.

Coordination of Cu(II) to lincomycin was studied by potentiometry, UV-Vis, circular dichroism (CD), EPR, NMR, cyclic voltammetry (CV) and ESI-MS. Only mononuclear complexes of stoichiometries ranging from CuL to CuH(-3)L were found. In the main species present at neutral pH, CuH(-2)L, lincomycin bonds Cu(II) through both of its nitrogen donors, and a deprotonated oxygen donor at C4 of the sugar moiety. High pressure liquid chromatography (HPLC) of products of 2'-deoxyguanosine (dG) oxidation and agarose gel electrophoresis of plasmid DNA confirmed that lincomycin complexes effectively facilitate dG oxidation by H2O2, but are not able to cleave double-stranded plasmid DNA.

Anti-Bacterial Agents↗

PubMed2001

Stray Cu(II) may cause oxidative damage when coordinated to the -TESHHK- sequence derived from the C-terminal tail of histone H2A.

CH(3)CO-Thr-Glu-Ser-His-His-Lys-NH(2), a hexapeptide representing the 120-125 sequence of histone H2A, coordinates Cu(II) ions efficiently. Monomeric complexes are formed. In the major complex at physiological pH, CuH(-1)L, Cu(II) is coordinated equatorially through the imidazole nitrogen of the His-4 residue and the amide nitrogens of the Ser-3 and His-4 residues, and axially through the imidazole nitrogen of the His-5 residue. This complex reacts with H(2)O(2) and the resulting reactive oxygen intermediate efficiently oxidizes 2'-deoxyguanosine. The underlying mechanism involves the formation of Cu(III) and a metal-bound hydroxyl radical species.

Copper↗

PubMed2001

Molecular mechanism of hydrogen peroxide conversion and activation by Cu(II)-amikacin complexes.

The interactions between Cu(II)-amikacin complexes [Cu(II)-Ami] and hydrogen peroxide were studied by spectroscopy (EPR, UV-vis, CD, XAS) and cyclic voltammetry. A monomer-dimer equilibrium was detected at complex concentrations above 5 mM (log K(dim) = 1.84 +/- 0.03). The dimeric complex undergoes easy, although irreversible oxidation (ca. 0.5-0.6 V) to a Cu(III) species on platinum electrode. However, the monomeric complexes are able to catalyze hydrogen peroxide disproportionation reaction at pH 7.4 in a multistep process, mediated by hydroxyl radicals and involving both Cu(I)/Cu(II) and Cu(II)/Cu(III) redox pairs.

Amikacin↗

PubMed2001

Differential zinc and DNA binding by partial peptides of human protamine HP2.

The Zn(II) binding by partial peptides of human protamine HP2: HP2(1-15); HP2(1-25), HP2(26-40), HP2(37-47), and HP2(43-57) was studied by circular dichroism (CD). Precipitation of a 20-mer DNA by these partial peptides and the effects of Zn(II) thereon were investigated using polyacrylamide gel electrophoresis (GE). The results of this study suggest that reduced HP2 (thiol groups intact) can bind Zn(II) at various parts of the molecule. In the absence of DNA, the primary Zn(II) binding site in reduced HP2 is located in the 37-47 sequence (involving Cys-37, His-39, His-43, and Cys-47), while in the presence of DNA, the strongest Zn(II) binding is provided by sequences 12-22 (by His-12, Cys-13, His-19, and His-22) and 43-57 (His-43, Cys-47, Cys-53, and His-57). In its oxidized form, HP2 can bind zinc through His residues of the 7-22 sequence. Zn(II) markedly enhances DNA binding by all partial peptides. These findings suggest that Zn(II) ions may be a regulatory factor for sperm chromatin condensation processes.

Binding Sites↗

PubMed2000

Lead effects on protamine-DNA binding.

BACKGROUND: Lead impairs male fertility and may affect offspring of exposed males, but the mechanisms for this impairment are not completely clear. Protamine P1 and P2 families pack and protect mammalian sperm DNA. Human HP2 is a zinc-protein and may have an important role in fertility. As lead has affinity for zinc-containing proteins, we evaluated its ability in vitro to bind to HP2 and its effects on HP2-DNA binding. Methods and Results UV/VIS spectroscopic data indicated that HP2 binds both Pb(2+) and Zn(2+)(as chloride salts). They also provided evidence that thiol groups mainly participate for Zn(2+)-binding; however, HP2 has additional binding sites for Pb(2+). The mobility shift assay showed that lead interaction with HP2 caused a dose-dependent decrease on HP2 binding to DNA, suggesting that lead may alter chromatin stability. CONCLUSIONS: These in vitro results demonstrate that lead can interact with HP2 altering the DNA-protamine binding. This chemical interaction of lead with protamines may result in chromatin alterations, which in turn may lead to male fertility problems and eventually to DNA damage.

Chromatin↗

PubMed2000

Molecular models in nickel carcinogenesis.

Nickel compounds are known human carcinogens, but the exact molecular mechanisms of nickel carcinogenesis are not known. Due to their abundance, histones are likely targets for Ni(II) ions among nuclear macromolecules. This paper reviews our recent studies of peptide and protein models of Ni(II) binding to histones. The results allowed us to propose several mechanisms of Ni(II)-inflicted damage, including nucleobase oxidation and sequence-specific histone hydrolysis. Quantitative estimations of Ni(II) speciation, based on these studies, support the likelihood of Ni(II) binding to histones in vivo, and the protective role of high levels of glutathione. These calculations indicate the importance of histidine in the intracellular Ni(II) speciation.

Amino Acid Sequence↗

PubMed2000

Lead interaction with human protamine (HP2) as a mechanism of male reproductive toxicity.

During spermatogenesis, histones are replaced by protamines, which condense and protect sperm DNA. In humans, zinc contributes to sperm chromatin stability and binds to protamine P2 (HP2). Chemical interactions with nuclear protamines, which prevent normal sperm chromatin condensation, may induce changes in the sperm genome and thus affect fertility and offspring development. Since lead has a high affinity for zinc-containing proteins, we investigated lead interactions with HP2 as a novel mechanism of its toxicity to sperm. UV/vis and CD spectroscopy results indicated that HP2 binds Pb(2+) at two different sites, causing a conformational change in the protein. They also provided evidence that thiol groups are primarily involved in Zn(2+) and Pb(2+) binding to HP2 and that HP2 may have additional binding sites for Pb(2+) not related to Zn(2+). HP2 affinities for Pb(2+) and Zn(2+) were very similar, suggesting that Pb(2+) can compete with or replace Zn(2+) in HP2 in vivo. This interaction of lead with HP2 resulted in a dose-dependent decrease in the extent of HP2-DNA binding, although lead interaction with DNA also contributed to this effect. Therefore, the ability of lead to decrease the level of HP2-DNA interaction may result in alterations to sperm chromatin condensation, and thus in reduced fertility.

Animals↗

PubMed2000

Ni(II) specifically cleaves the C-terminal tail of the major variant of histone H2A and forms an oxidative damage-mediating complex with the cleaved-off octapeptide.

The acetyl-TESHHK-amide peptide, modeling a part of the C-terminal "tail" of histone H2A, was found previously by us to undergo at pH 7. 4 a Ni(II)-assisted hydrolysis of the E-S peptide bond with formation of a stronger Ni(II) complex with the SHHK-amide product [Bal, W., et al. (1998) Chem. Res. Toxicol. 11, 1014-1023]. To further characterize the hydrolysis and test the resulting Ni(II) complex for redox activity, bovine histone H2A and three peptides were investigated: acetyl-LLGKVTIAQGGVLPNIQAVLLPKKTESHHKAKGK (H2A(34)), modeling the entire "C-tail" of H2A; SHHKAKGK (H2A(8)), modeling the cutoff product of hydrolysis; and acetyl-KTESHKAKGK (H2A(10)), modeling a putative Ni(II) binding site in a minor variant H2A.4 of human histone H2A. The Ni(II)-assisted hydrolysis of H2A and H2A(34) was found to proceed approximately 7-fold faster than that of the Ni(II)-acetyl-TESHHK-amide complex under comparable conditions. In both cases, the Ni(II) complex with H2A(8) was the smaller product of the hydrolysis, indicating a high site specificity of the reaction. Of three other metals tested with H2A(34), only Cu(II) cleaved the E-S bond, although much less efficiently than Ni(II); Co(II) and Zn(II) had no effect whatsoever. The H2A(10) peptide appeared to be fully resistant to hydrolytic cleavage and did not exhibit any redox activity versus H(2)O(2) in the presence of Ni(II) at pH 7.4. Likewise, redox-inactive was the Ni(II)-H2A(34) complex. In contrast, the Ni(II)-H2A(8) complex promoted oxidative damage of pUC19 DNA by H(2)O(2), evidenced by a significant increase in the number of single strand breaks and nucleobase modifications typical for a hydroxyl radical-like species attack on DNA. Interestingly, instead of 8-oxopurines, the corresponding formamidopyrimidines were the major products of the damage. The difference in redox activity between the Ni(II)-H2A(34) and Ni(II)-H2A(8) complexes is most likely associated with their different geometries: octahedral and square planar, respectively. Incubation of the Ni(II)-H2A(8) complex with H(2)O(2) also resulted in degradation of the peptide ligand, especially at its Ser and His residues. Thus, binding of Ni(II) to the ESHHK motif of the histone H2A C-tail is damaging to the histone C-terminal tail and to histone-associated DNA. The results support a dual mechanism of Ni(II)-induced carcinogenesis, including both genotoxic and epigenetic effects.

Amino Acid Sequence↗

PubMed2000

Induction of a secondary structure in the N-terminal pentadecapeptide of human protamine HP2 through Ni(II) coordination. An NMR study.

A solution structure of the Ni(II) complex with the N-terminal pentadecapeptide of human protamine HP2 (HP2(1)(-)(15)) was elucidated with the use of a range of one- and two-dimensional (1)H NMR techniques and molecular modeling. A striking double-loop conformation was found, exhibiting the interactions of the aromatic ring of the Tyr(8) residue with the Ni(II) coordination site at Arg(1), Thr(2), and His(3) residues and the side chain of the Arg(15) residue. In such a conformation, a tendency was found for all five positively charged arginine side chains to locate on one side of the molecule, making possible efficient contacts with the DNA double helix. These structural features, induced indirectly by Ni(II) coordination, are discussed in terms of a possible physiological function of the N-terminus of HP2 as a metal-binding site.

Amino Acid Sequence↗

PubMed2000

[Use of modern microscopic techniques for examining dialysis membrane properties].

The aim of the study was the microscopic evaluation of internal structure of cuprophane and polysulfone membrane and their surface analysis before and after reprocessing. The investigations were performed using an optical measurement system (Digital Instruments), a scanning electron microscope (SEM) and an atomic force microscope (AFM). We confirmed by SEM that reprocessing completely removed biofilm from both membranes surface. The analysis based on AFM visualized channels in the examined membrane. The diameter of the channels varied from 150 nm for cuprophane to 380 nm for polysulfone. The roughness expressed as root mean square (RMS) was higher for cuprophane than for polysulfone membrane. The physical differences between nanostrucure of the examined membranes might be responsible for lower biocompatibility of cuprophane.

Biocompatible Materials↗

PubMed1999

Interaction of Nickel(II) with histones: in vitro binding of nickel(II) to the core histone tetramer.

The absorption spectra of Ni(II) bound to the core histone tetramer, (H3-H4)2, of chicken erythrocytes in 500 mM NaCl + 100 mM phosphate (pH 7.4) were recorded. A charge transfer band was seen at 317 nm, characteristic of a bond between Ni(II) and the sulfur atom of Cys-110 of histone H3. The conditional affinity constants for Ni(II) binding at pH 7.4 for low and high Ni(II) saturation (log Kc = 4.26 +/- 0.02 and 5.26 +/- 0.11 M-1, respectively) were calculated from spectrophotometric titrations with the use of this band. The binding of Ni(II) to (H3-H4)2 is proposed to involve the Cys-110 and His-113 of different H3 molecules within the tetramer. The competition between histones and low-molecular-weight chelators for Ni(II) in the cell nucleus, histidine and glutathione, is discussed on the basis of the above results, indicating that histone H3 is very likely to bind Ni(II) dissolved intracellularly from phagocytosed particulate nickel compounds.

Animals↗

PubMed1999

Effects of Ni(II) and Cu(II) on DNA interaction with the N-terminal sequence of human protamine P2: enhancement of binding and mediation of oxidative DNA strand scission and base damage.

Epidemiological evidence suggests that certain paternal exposures to metals may increase the risk of cancer in the progeny. This effect may be associated with promutagenic damage to the sperm DNA. The latter is packed with protamines which might sequester carcinogenic metals and moderate the damage. Human protamine P2 has an amino acid motif at its N-terminus that can serve as a heavy metal trap, especially for Ni(II) and Cu(II). We have synthesized a pentadecapeptide modeling this motif, Arg-Thr-His-Gly-Gln-Ser-His-Tyr-Arg-Arg-Arg-His-Cys-Ser-Arg-amide (HP21-15) and described its complexes with Ni(II) and Cu(II), including their capacity to mediate oxidative DNA degradation [Bal et al. (1997) Chem. Res. Toxicol., 10, 906-914 and 915-921]. In the present study, effects of HP21-15 on Ni(II)- and Cu(II)-mediated DNA oxidation by H2O2 at pH 7.4 were investigated in more detail using the circular plasmid pUC19 DNA as a target, and the single/double-strand breaks and production of oxidized DNA bases, as end points. Ni(II) alone was found to promote oxidative DNA strand scission (mostly single strand breaks) and base damage, while Cu(II) alone produced the same effects, but to a much greater extent. Both metals were relatively more damaging to the pyrimidine bases than to purine bases. HP21-15 tended to increase the Ni(II)/H2O2-induced DNA breakage. In sharp contrast, the destruction of DNA strands by Cu(II)/H2O2 was almost completely prevented by HP21-15. The effect of HP21-15 on the oxidative DNA base damage varied from a limited enhancement (5-hydroxyhydantoin and thymine glycol) to slight suppression (5-hydroxycytosine, 5-hydroxyuracil, 8-oxoguanine, 8-oxoadenine, 2-hydroxyadenine, fapyguanine and fapyadenine) toward Ni(II)/H2O2. HP21-15 strongly suppressed the oxidative activity of Cu(II)/H2O2 in regard to all bases in DNA. Consistently with the above, the electron spin resonance/spin trap measurements revealed greater and more persistent generation of OH* and O2-*-like oxidants from H2O2 by the Ni(II)-HP21-15 complex than by the Cu(II)-HP21-15 complex (no O2-* was detected). Both complexes were also found to bind to DNA more strongly than HP21-15 alone. The results indicate that protamine P2 is capable of binding Ni(II) and Cu(II) and, in this way, attenuating the mediation of oxidative DNA damage by Cu(II), but not Ni(II). The effects found may be mechanistically involved in the reproductive toxicity and carcinogenicity of metals.

Animals↗

PubMed1999

Coordination chemistry of glutathione.

The metal ion coordination abilities of reduced and oxidized glutathione are reviewed. Reduced glutathione (GSH) is a very versatile ligand, forming stable complexes with both hard and soft metal ions. Several general binding modes of GSH are described. Soft metal ions coordinate exclusively or primarily through thiol sulfur. Hard ones prefer the amino acid-like moiety of the glutamic acid residue. Several transition metal ions can additionally coordinate to the peptide nitrogen of the gamma-Glu-Cys bond. Oxidized glutathione lacks the thiol function. Nevertheless, it proves to be a surprisingly efficient ligand for a range of metal ions, coordinating them primarily through the donors of the glutamic acid residue.

Drug Stability↗

PubMed1998

Multi-metal binding site of serum albumin.

Circular dichroism and electron spin resonance spectroscopy are used to investigate the second specific metal binding site on human, bovine and porcine albumins. Ni(II), Zn(II) and Cd(II) can displace Cu(II) from the second Cu(II) site but not from the first strong site of human and bovine albumins (the N-terminal site). The second Cu(II) binds more strongly than the other metal ions to the second site of all three proteins, except Zn(II) binding to porcine albumin which is ca. 10 x stronger than Cu(II). The second Cu(II) site appears to be a tetragonal ¿2N, 4O¿ site.

Animals↗

PubMed1998

Interactions of Nickel(II) with histones: interactions of Nickel(II) with CH3CO-Thr-Glu-Ser-His-His-Lys-NH2, a peptide modeling the potential metal binding site in the "C-Tail" region of histone H2A.

A combined pH-metric and spectroscopic (UV/vis, CD, NMR) study of the Ni(II) binding to CH3CO-Thr-Glu-Ser-His-His-Lys-NH2 (AcTESHHKam), a blocked hexapeptide modeling a part of the C-terminal sequence of the major variant of histone H2A (residues 120-125), revealed the formation of a pseudo-octahedral NiHL complex in weakly acidic and neutral solutions. Ni(II) is bound to the peptide through imidazole nitrogens on both of its histidine residues and the carboxylate of the side chain of glutamic acid. At higher pH, a series of square-planar complexes are formed. This process is accompanied by hydrolytic degradation of the peptide. At pH 7.4, the peptide hydrolyzes in a Ni(II)-assisted fashion, yielding the square-planar Ni(II) complex of SHHKam as the sole product detected by CD, MALDI-TOF MS, and HPLC. Quantitative analysis of complex stabilities indicates that the -TESHHK- motif is a very likely binding site for carcinogenic Ni(II) ions in the cell nucleus. The Ni(II)-assisted hydrolysis of the C-terminal chain of histone H2A may provide a novel mechanism of genotoxicity combining the damage to the nucleosome with the generation of further toxic Ni(II) species.

Binding Sites↗

PubMed1997

Binding of nickel(II) and copper(II) to the N-terminal sequence of human protamine HP2.

A potentiometric and spectroscopic (UV/vis and CD) study of Cu(II) and Ni(II) binding to the N-terminal pentadecapeptide of human protamine HP2 (HP2(1-15)) was performed. The results indicate that the N-terminal tripeptide motif Arg-Thr-His is the exclusive binding site for both metal ions at a metal to HP2(1-15) molar ratio not higher than 1. The very high value of protonation-corrected stability constant (log *K) for Ni(II)-HP2(1-15) complex, -19.29, indicates that HP2 has the potential to sequester Ni(II) from other peptide and protein carriers, including albumin. The same is likely for Cu(II) (log *K = -13.13). The CD spectra of Cu(II) and Ni(II) complexes of HP2(1-15) indicate that the N-terminal metal binding affects the overall conformation of the peptide that, in turn, may alter interaction of HP2 with DNA. These results imply HP2 as a likely target for the toxic metals Ni(II) and Cu(II).

Amino Acid Sequence↗