Identification of metallothionein subisoforms in HPLC using accurate mass and online sequencing by electrospray hybrid linear ion trap-orbital ion trap mass spectrometry

Nickel Nanoparticles Induce the Synthesis of a Tumor-Related Polypeptide in Human Epidermal Keratinocytes

Although nickel allergy and carcinogenicity are well known, their molecular mechanisms are still uncertain, thus demanding studies at the molecular level. The nickel carcinogenicity is known to be dependent on the chemical form of nickel, since only certain nickel compounds can enter the cell. This study investigates, for the first time, the cytotoxicity, cellular uptake, and molecular targets of nickel nanoparticles (NiNPs) in human skin cells in comparison with other chemical forms of nickel. The dose-response curve that was obtained for NiNPs in the cytotoxicity assays showed a linear behavior typical of genotoxic carcinogens. The exposure of keratinocytes to NiNPs leads to the release of Ni²⁺ ions and its accumulation in the cytosol. A 6 kDa nickel-binding molecule was found to be synthesized by cells exposed to NiNPs at a dose corresponding to medium mortality. This molecule was identified to be tumor-related p63-regulated gene 1 protein.

An insight into the complex roles of metallothioneins in malignant diseases with emphasis on (sub)isoforms/isoforms and epigenetics phenomena

Metallothioneins (MTs) belong to a group of small cysteine-rich proteins that are ubiquitous throughout all kingdoms. The main function of MTs is scavenging of free radicals and detoxification and homeostating of heavy metals. In humans, 16 genes localized on chromosome 16 have been identified to encode four MT isoforms labelled by numbers (MT-1-MT-4). MT-2, MT-3 and MT-4 proteins are encoded by a single gene. MT-1 comprises many (sub)isoforms. The known active MT-1 genes are MT-1A, -1B, -1E, -1F, -1G, -1H, -1M and -1X. The rest of the MT-1 genes (MT-1C, -1D, -1I, -1J and -1L) are pseudogenes. The expression and localization of individual MT (sub)isoforms and pseudogenes vary at intra-cellular level and in individual tissues. Changes in MT expression are associated with the process of carcinogenesis of various types of human malignancies, or with a more aggressive phenotype and therapeutic resistance. Hence, MT (sub)isoform profiling status could be utilized for diagnostics and therapy of tumour diseases. This review aims on a comprehensive summary of methods for analysis of MTs at (sub)isoforms levels, their expression in single tumour diseases and strategies how this knowledge can be utilized in anticancer therapy.

LC coupled to ESI, MALDI and ICP MS - A multiple hyphenation for metalloproteomic studies

A new multiple detection arrangement for liquid chromatography (LC) that supplements conventional electrospray ionization (ESI) mass spectrometry (MS) detection with two complementary detection techniques, matrix-assisted laser desorption/ionization (MALDI) MS and substrate-assisted laser desorption inductively coupled plasma (SALD ICP) MS has been developed. The combination of the molecular and elemental detectors in a single separation run is accomplished by utilizing a commercial MALDI target made of conductive plastic. The proposed platform provides a number of benefits in today's metalloproteomic applications, which are demonstrated by analysis of a metallothionein mixture. To maintain metallothionein complexes, separation is carried out at a neutral pH. The effluent is split; a major portion is directed to ESI MS while the remaining 1.8% fraction is deposited onto a plastic MALDI target. Dried droplets are overlaid with MALDI matrix and analysed consecutively by MALDI MS and SALD ICP MS. In the ESI MS spectra, the MT isoform complexes with metals and their stoichiometry are determined; the apoforms are revealed in the MALDI MS spectra. Quantitative determination of metallothionein isoforms is performed via determination of metals in the complexes of the individual protein isoforms using SALD ICP MS.

Introduction of organic/hydro-organic matrices in inductively coupled plasma optical emission spectrometry and mass spectrometry: a tutorial review. Part II. Practical considerations

Inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are increasingly used to carry out analyses in organic/hydro-organic matrices. The introduction of such matrices into ICP sources is particularly challenging and can be the cause of numerous drawbacks. This tutorial review, divided in two parts, explores the rich literature related to the introduction of organic/hydro-organic matrices in ICP sources. Part I provided theoretical considerations associated with the physico-chemical properties of such matrices, in an attempt to understand the induced phenomena. Part II of this tutorial review is dedicated to more practical considerations on instrumentation, instrumental and operating parameters, as well as analytical strategies for elemental quantification in such matrices. Two important issues are addressed in this part: the first concerns the instrumentation and optimization of instrumental and operating parameters, pointing out (i) the description, benefits and drawbacks of different kinds of nebulization and desolvation devices and the impact of more specific instrumental parameters such as the injector characteristics and the material used for the cone; and, (ii) the optimization of operating parameters, for both ICP-OES and ICP-MS. Even if it is at the margin of this tutorial review, Electrothermal Vaporization and Laser Ablation will also be shortly described. The second issue is devoted to the analytical strategies for elemental quantification in such matrices, with particular insight into the isotope dilution technique, particularly used in speciation analysis by ICP-coupled separation techniques.

An insight into silver nanoparticles bioavailability in rats

A comprehensive study of the bioavailability of orally administered silver nanoparticles (AgNPs) was carried out using a rat model. The silver uptake was monitored in liver and kidney tissues, as well as in urine and in feces. Significant accumulation of silver was found in both organs, the liver being the principal target of AgNPs. A significant (∼50%) fraction of silver was found in feces whereas the fraction excreted via urine was negligible (< 0.01%). Intact silver nanoparticles were found in feces by asymmetric flow field-flow fractionation (AsFlFFF) coupled with UV-Vis analysis. Laser ablation-ICP MS imaging showed that AgNPs were able to penetrate into the liver, in contrast to kidneys where they were retained in the cortex. Silver speciation analysis in cytosols from kidneys showed the metallothionein complex as the major species whereas in the liver the majority of silver was bound to high-molecular (70-25 kDa) proteins. These findings demonstrate the presence of Ag(i), released by the oxidation of AgNPs in the biological environment.

Quantitation of human metallothionein isoforms: a family of small, highly conserved, cysteine-rich proteins

Human metallothioneins (MTs) are important regulators of metal homeostasis and protectors against oxidative damage. Their altered mRNA expression has been correlated with metal toxicity and a variety of cancers. Current immunodetection methods lack the specificity to distinguish all 12 human isoforms. Each, however, can be distinguished by the mass of its acetylated, cysteine-rich, hydrophilic N-terminal tryptic peptides. These properties were exploited to develop a bottom-up MALDI-TOF/TOF-MS-based method for their simultaneous quantitation. Key features included enrichment of N-terminal acetylated peptides by strong cation exchange chromatography, optimization of C18 reversed-phase chromatography, and control of methionine oxidation. Combinations of nine isoforms were identified in seven cell lines and two tissues. Relative quantitation was accomplished by comparing peak intensities of peptides generated from pooled cytosolic proteins alkylated with ¹⁴N- or ¹⁵N-iodoacetamide. Absolute quantitation was achieved using ¹⁵N-iodoacetamide-labeled synthetic peptides as internal standards. The method was applied to the cadmium induction of MTs in human kidney HK-2 epithelial cells expressing recombinant MT-3. Seven isoforms were detected with abundances spanning almost 2 orders of magnitude and inductions up to 12-fold. The protein-to-mRNA ratio for MT-1E was one-tenth that of other MTs, suggesting isoform-specific differences in protein expression efficiency. Differential expression of MT-1G1 and MT-1G2 suggested tissue- and cell-specific alternative splicing for the MT-1G isoform. Protein expression of MT isoforms was also evaluated in human breast epithelial cancer cell lines. Estrogen-receptor-positive cell lines expressed only MT-2 and MT-1X, whereas estrogen-receptor-negative cell lines additionally expressed MT-1E. The combined expression of MT isoforms was 38-fold greater in estrogen-receptor-negative cell lines than in estrogen-receptor-positive cells. These findings demonstrate that individual human MT isoforms can be accurately quantified in cells and tissues at the protein level, complementing and expanding mRNA measurement as a means for evaluating MTs as potential biomarkers for cancers or heavy metal toxicity.

Detection of proteins by hyphenated techniques with endogenous metal tags and metal chemical labelling

The absolute and relative quantitation of proteins plays a fundamental role in modern proteomics, as it is the key to understand still unresolved biological questions in medical and pharmaceutical applications.

Hemoglobin as a major binding protein for methylmercury in white-sided dolphin liver

As methylmercury (MeHg) can be bioaccumulated and biomagnified in the trophic web, its toxicity for marine mammals is of major concern. Mercury speciation in marine biota has been widely studied, mainly focused on the discrimination and quantification of inorganic Hg and MeHg. Less attention has been paid to the interactions of Hg with biomolecules and the characterization of its specific binding, which play a key role in metabolic pathways controlling its uptake, transformation, and toxicity. In the studied white-sided dolphin (Lagenorhynchus acutus) liver homogenate (QC04LH4) sample, approximately 60% of the total MeHg was found in the water soluble fraction, specifically associated with high molecular weight biomolecules. The identity of the involved proteins was investigated (after tryptic digestion of the fraction) by μRPLC with parallel detection by ICP-MS and ESI-MS/MS. Molecular mass spectrometry experiments were carried out at high resolution (100000) to ensure accurate protein identification and determination of the MeHg binding sites. Cysteine residue on the dolphin hemoglobin β chain was found to be the main MeHg binding site, suggesting that hemoglobin is a major MeHg binding protein in this marine mammal and could be a potential carrier of this MeHg from blood to liver prior to its degradation in this organ. In parallel, a significant proportion of selenium was found to be present as selenoneine and a potential role for this compound in Hg detoxification is discussed.

Evolution of metallotionein isoforms complexes in hepatic cells of Mus musculus along cadmium exposure

Characterization of Cd-binding proteins has great analytical interest due to the high toxicity of Cd to living organisms. Metallothioneins (MTs), as Cd(II)-binding proteins are of increasing interest, since they form very stable Cd chelates and are involved in many detoxification processes. In this work, inductively coupled plasma octopole reaction cell mass spectrometry and nanospray ionization time-of-flight mass spectrometry were used in parallel and combined with two-dimensional chromatography: size exclusion followed by reversed-phase high performance liquid chromatography, to study metal complexes of MT isoforms produced in hepatic cytosols of Mus musculus during exposure experiments to Cd. Exposure experiments were carried out by subcutaneous injection of a growing dose of the toxic element ranging from 0.1 to 1.0 mg of Cd per kg of body weight per day during 10 days. A control group and three exposure groups at days 2, 6 and 10 of exposure were studied, and different cadmium, copper and zinc complexes with MTs isoforms were isolated and characterized from the two most exposed groups. The results allow gaining insight into the mechanisms involved in metal detoxification by MTs, showing the changes in the stoichiometry of metal complexes-MTs along cadmium exposure.

Clinical significance of metallothioneins in cell therapy and nanomedicine

Mammalian metallothioneins (MTs) are low molecular weight (6–7 kDa) cysteine-rich proteins that are specifically induced by metal nanoparticles (NPs). MT induction in cell therapy may provide better protection by serving as antioxidant, anti-inflammatory, antiapoptotic agents, and by augmenting zinc-mediated transcriptional regulation of genes involved in cell proliferation and differentiation. Liposome-encapsulated MT-1 promoter has been used extensively to induce growth hormone or other genes in culture and gene-manipulated animals. MTs are induced as a defensive mechanism in chronic inflammatory conditions including neurodegenerative diseases, cardiovascular diseases, cancer, and infections, hence can serve as early and sensitive biomarkers of environmental safety and effectiveness of newly developed NPs for clinical applications. Microarray analysis has indicated that MTs are significantly induced in drug resistant cancers and during radiation treatment. Nutritional stress and environmental toxins (eg, kainic acid and domoic acid) induce MTs and aggregation of multilamellar electron-dense membrane stacks (Charnoly body) due to mitochondrial degeneration. MTs enhance mitochondrial bioenergetics of reduced nicotinamide adenine dinucleotide–ubiquinone oxidoreductase (complex-1), a rate-limiting enzyme complex involved in the oxidative phosphorylation. Monoamine oxidase-B inhibitors (eg, selegiline) inhibit α-synuclein nitration, implicated in Lewy body formation, and inhibit 1-methyl 4-phenylpyridinium and 3-morpholinosydnonimine-induced apoptosis in cultured human dopaminergic neurons and mesencephalic fetal stem cells. MTs as free radical scavengers inhibit Charnoly body formation and neurodegenerative α-synucleinopathies, hence Charnoly body formation and α-synuclein index may be used as early and sensitive biomarkers to assess NP effectiveness and toxicity to discover better drug delivery and surgical interventions. Furthermore, pharmacological interventions augmenting MTs may facilitate the theranostic potential of NP-labeled cells and other therapeutic agents. These unique characteristics of MTs might be helpful in the synthesis, characterization, and functionalization of emerging NPs for theranostic applications. This report highlights the clinical significance of MTs and their versatility as early, sensitive biomarkers in cell-based therapy and nanomedicine.

Combining chemical labeling, bottom-up and top-down ion-mobility mass spectrometry to identify metal-binding sites of partially metalated metallothionein

Metalation and demetalation of human metallothionein-2A (MT) with Cd(2+) is investigated by using chemical labeling and "bottom-up" and "top-down" proteomics approaches. Both metalation and demetalation of MT-2A by Cd(2+) are shown to be domain specific and occur as two distinct processes. Metalation involves sequential addition of Cd(2+) to the α-domain resulting in formation of an intermediate, Cd4MT. Chemical labeling with N-ethylmaleimide (NEM) and tandem mass spectrometry experiments clearly show that the four metal ions are located in the α-domain. In the presence of excess Cd(2+), the Cd4MT intermediate reacts to add Cd(2+) to the β-domain to yield the fully metalated Cd7MT. Demetalation occurs in the reverse order, i.e., Cd(2+) is removed (by EDTA) first from the β-domain followed by Cd(2+) removal from the α-domain. Metalation of human MT-2A is shown to be metal ion specific by comparing relative metal ion binding constants for Cd(2+) and Zn(2+).

Chemistry and biology of mammalian metallothioneins

Metallothioneins (MTs) are a class of ubiquitously occurring low molecular mass, cysteine- and metal-rich proteins containing sulfur-based metal clusters formed with Zn(II), Cd(II), and Cu(I) ions. In mammals, four distinct MT isoforms designated MT-1 through MT-4 exist. The first discovered MT-1/MT-2 are widely expressed isoforms, whose biosynthesis is inducible by a wide range of stimuli, including metals, drugs, and inflammatory mediators. In contrast, MT-3 and MT-4 are noninducible proteins, with their expression primarily confined to the central nervous system and certain squamous epithelia, respectively. MT-1 through MT-3 have been reported to be secreted, suggesting that they may play different biological roles in the intracellular and extracellular space. Recent reports established that these isoforms play an important protective role in brain injury and metal-linked neurodegenerative diseases. In the postgenomic era, it is becoming increasingly clear that MTs fulfill multiple functions, including the involvement in zinc and copper homeostasis, protection against heavy metal toxicity, and oxidative damage. All mammalian MTs are monomeric proteins, containing two metal-thiolate clusters. In this review, after a brief summary of the historical milestones of the MT-1/MT-2 research, the recent advances in the structure, chemistry, and biological function of MT-3 and MT-4 are discussed.