Study of tungstate–protein interaction in human serum by LC–ICP-MS and MALDI-TOF

Rapid determination of toxic and essential metal binding proteins in biological samples by size exclusion chromatography-inductively coupled plasma tandem mass spectrometry

Metalloproteins binding with trace elements play a crucial role in biological processes and on the contrary, those binding with exogenous heavy metals have adverse effects. However, the methods for rapid, high sensitivity and simultaneous analysis of these metalloproteins are still lacking. In this study, a fast method for simultaneously determination of both essential and toxic metal-containing proteins was developed by coupling size exclusion chromatography (SEC) with inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). After optimization of the separation and detection conditions, seven metalloproteins with different molecular weight (from 16.0 to 443.0 kDa) were successfully separated within 10 min and the proteins containing iron (Fe), copper (Cu), zinc (Zn), iodine (I) and lead (Pb) elements could be simultaneously detected with the use of oxygen as the collision gas in ICP-MS/MS. Accordingly, the linear relationship between log molecular weight and retention time was established to estimate the molecular weight of unknown proteins. Thus, the trace metal and toxic metal containing proteins could be detected in a single run with high sensitivity (detection limits in the range of 0.0020-2.5 μg/mL) and good repeatability (relative standard deviations lower than 4.5 %). This method was then successfully used to analyze metal (e.g., Pb, Zn, Cu and Fe) binding proteins in the blood of Pb-intoxicated patients, and the results showed a negative correlation between the contents of zinc and lead binding proteins, which was identified to contain hemoglobin subunit. In summary, this work provided a rapid and sensitive tool for screening metal containing proteins in large number of biological samples.

Evaluation of biodistribution and kinetics of tungsten disulphide quantum dots by Inductively coupled plasma mass spectroscopy: A detailed in vivo QD-bio interactions study

WS₂ QDs are inorganic semiconductor nanocrystals which belong to the family of transition metal dichalcogenides (TMDC). As toxic heavy metal free quantum dots, TMDC based QDs is gaining attention due to excellent chemical stability, good thermal conductivity and stable optical properties. In the present study, bright green emissive and excellent WS₂ QDs was synthesized by solvothermal liquid exfoliation method using NMP solvent. The size and morphology were confirmed by HRTEM (3-4 nm, spherical). Illumination by 370 nm UV source showed bright green fluorescence due to the excellent quantum confinement effect. The as synthesised WS₂ QDs exhibits excellent properties such as stable dispersion, extreme low cytotoxicity as well as fluorescent properties, which makes them suitable candidates for optoelectronic and biological applications. Cytotoxicity analysis via NRU assay confirmed the low cytotoxic potential. Subcellular localization confirmed the distribution of WS₂ QDs around the nucleus. Spleenocyte proliferation via radioactivity measurement showed lack of any immune response. ICP-MS analysis showed that a significant amount of the administered WS₂ QDs was found in the urine samples when compared to feces, which confirmed the renal excretion route of the material. WS₂ QDs didnot evoke any evident toxic response upto 10 mg/kg body weight i.p administration. Excellent fluorescence property shown by this material marked its prominence in in vitro/ in vivo imaging and other biomedical applications. The study proved that WS₂ QDs are excellent candidate materials validated to be safe material for biomedical applications.

Protein ion yield enhancement in matrix-assisted laser desorption/ionization mass spectrometry after sample and matrix low-pressure glow discharge plasma irradiation

RATIONALE

Plasma-assisted ionization is widely used in mass spectrometry; in this study, a low-pressure glow discharge is introduced as a new method to improve the detection of large proteins, and bovine serum albumin (BSA) is used as a protein model. The treatment of analyte, matrix, and the matrix/analyte mixture is evaluated under optimal conditions.

METHODS

Low-pressure radio-frequency capacitively coupled plasma (RF-CCP) treatment is utilized in the sample preparation step of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to enhance the protein MALDI ion signal. Plasma treatment can be an effective tool for enhancing the non-covalent binding of the analyte with the matrix, incorporation of the analyte into the matrix, production of matrix/analyte crystals, and analyte protonation through plasma activation, resulting in an improved MALDI ion signal.

RESULTS

Fourier-transform infrared (FTIR) spectroscopy allows us to distinguish between the functional groups of plasma-treated and control samples. In addition, optical emission spectroscopy (OES) determines the plasma species, and zeta potential analysis characterizes the potential difference between plasma-treated and control samples before MALDI-TOF MS analysis. Plasma-treated BSA can provide a five-times enhancement of ion intensity. The combination of the plasma-treated analyte with the plasma-treated matrix leads to an increase in the ion intensity by a factor of 14.

CONCLUSIONS

Low-pressure glow discharge plasma treatment greatly enhances MALDI ion signals, with a noticeable increase in incorporation, co-crystallization, protonation, and the concentration of the sample functional groups.

Serum-binding properties of isosteric ruthenium and osmium anticancer agents elucidated by SEC-ICP-MS

ABSTRACT

Size-exclusion chromatography-inductively coupled plasma-mass spectrometry (SEC-ICP-MS) was used to study the serum-binding preferences of two metallodrugs with anticancer activities in vivo, namely the organoruthenium compound plecstatin-1 and its isosteric osmium analog. The complexes were administered intraperitoneally into mice bearing a CT-26 tumor. Comparing the total metal content of mouse whole blood and serum underlined that the metallodrugs are mainly located in serum and not in the cellular fraction of the blood samples. In mouse serum, both compounds were not only found to bind extensively to the serum albumin/transferrin fraction but also to immunoglobulins. Free drug was not observed in any of the samples indicating rapid protein binding of the metallodrugs. These findings were validated by spiking human serum with the respective compounds ex vivo. An NCI-60 screen is reported for the osmium analog, which revealed a relative selectivity for cancer cell lines of the ovary and the central nervous system with respect to plecstatin-1. Finally, a COMPARE 170 analysis revealed disruption of DNA synthesis as a possible treatment effect of the osmium-based drug candidate.

GRAPHICAL ABSTRACT

Biological monitoring of welders' exposure to chromium, molybdenum, tungsten and vanadium

BACKGROUND

Welders are exposed to a number of metallic elements during work. Bioaccessability, that is important for element uptake, has been little studied. This study addresses bioaccessability and uptake of chromium (Cr), molybdenum (Mo), tungsten (W) and vanadium (V) among welders.

METHODS

Bioaccessability of Cr, Mo, V and W was studied in airborne particulate matter collected by personal sampling of the workroom air among shipyard welders by using the lung lining fluid simulant Hatch solution. Associations between concentrations of Hatch soluble and non-soluble elements (Hatch_sol and Hatch_non-sol) and concentrations of the four elements in whole blood, serum, blood cells and urine were studied.

RESULTS

Air concentrations of the four elements were low. Only a small fraction of Cr, V and W was Hatch_sol, while similar amounts of Mo were Hatch_sol and Hatch_non-sol. Welders (N=70) had statistically significantly higher concentrations of all four elements in urine and serum when compared to referents (N=74). Highly statistically significant associations were observed between urinary W and Hatch_sol W (p<0.001) and serum V and Hatch_sol V (p<0.001), in particular when air samples collected the day before collection of biological samples were considered.

CONCLUSIONS

Associations between Hatch_sol elements in air and their biological concentrations were higher than when Hatch_non-sol concentrations were considered. Associations were generally higher when air samples collected the day before biological sampling were considered as compared to air samples collected two days before.

An update to the toxicological profile for water-soluble and sparingly soluble tungsten substances

Tungsten is a relatively rare metal with numerous applications, most notably in machine tools, catalysts, and superalloys. In 2003, tungsten was nominated for study under the National Toxicology Program, and in 2011, it was nominated for human health assessment under the US Environmental Protection Agency's (EPA) Integrated Risk Information System. In 2005, the Agency for Toxic Substances and Disease Registry (ATSDR) issued a toxicological profile for tungsten, identifying several data gaps in the hazard assessment of tungsten. By filling the data gaps identified by the ATSDR, this review serves as an update to the toxicological profile for tungsten and tungsten substances. A PubMed literature search was conducted to identify reports published during the period 2004-2014, in order to gather relevant information related to tungsten toxicity. Additional information was also obtained directly from unpublished studies from within the tungsten industry. A systematic approach to evaluate the quality of data was conducted according to published criteria. This comprehensive review has gathered new toxicokinetic information and summarizes the details of acute and repeated-exposure studies that include reproductive, developmental, neurotoxicological, and immunotoxicological endpoints. Such new evidence involves several relevant studies that must be considered when regulators estimate and propose a tungsten reference or concentration dose.

A proteomic approach to identification of plutonium-binding proteins in mammalian cells

Plutonium can enter the body through different routes and remains there for decades; however its specific biochemical interactions are poorly defined. We, for the first time, have studied plutonium-binding proteins using a metalloproteomic approach with rat PC12 cells. A combination of immobilized metal ion chromatography, 2D gel electrophoresis, and mass spectrometry was employed to analyze potential plutonium-binding proteins. Our results show that several proteins from PC12 cells show affinity towards Pu(4+)-NTA (plutonium bound to nitrilotriacetic acid). Proteins from seven different spots in the 2D gel were identified. In contrast to the previously known plutonium-binding proteins transferrin and ferritin, which bind ferric ions, most identified proteins in our experiment are known to bind calcium, magnesium, or divalent transition metal ions. The identified plutonium interacting proteins also have functional roles in downregulation of apoptosis and other pro-proliferative processes. MetaCore™ analysis based on this group of proteins produced a pathway with a statistically significant association with development of neoplastic diseases.

Biospeciation of tungsten in the serum of diabetic and healthy rats treated with the antidiabetic agent sodium tungstate

It is known that oral administration of sodium tungstate preserves the pancreatic beta cell function in diabetic rats. Healthy and streptozotocin-induced diabetic rats were treated with sodium tungstate for one, three or six weeks, after which the species of W in serum, were analysed. An increase in serum W with treatment time was observed. After six weeks, the serum W concentration in diabetic rats (70 mg L(-1)) was about 4.6 times higher than in healthy specimens. This different behaviour was also observed for Cu accumulation, while the Zn pattern follows the contrary. The patterns observed in the retention of Cu and Zn may be attributable to a normalization of glycaemia. The speciation analysis of W was performed using 2D separations, including an immunoaffinity packing and a SEC (Size Exclusion Chromatography) column coupled to an ICP-MS (Inductively Coupled Plasma Mass Spectrometry) for elemental detection. Ultrafiltration data together with SEC-ICP-MS results proved that around 80% of serum W was bound to proteins, the diabetic rats registering a higher W content than their healthy counterparts. Most of the protein-bound W was due to a complex with albumin. An unknown protein with a molecular weight higher than 100 kDa was also found to bind a small amount of W (about 2%). MALDI-TOF (Matrix-Assisted Laser Desorption Ionization Time-of-Flight) analysis of the desalted and concentrated chromatographic fractions confirmed albumin as the main protein bound to tungstate in rat serum, while no binding to transferrin (Tf) was detected. The interaction between glutathione and W was also evaluated using standard solutions; however, the formation of complexes was not observed. The stability of the complexes between W and proteins when subjected to more stringent procedures, like those used in proteomic methodologies (denaturing with urea or SDS, boiling, sonication, acid media, reduction with β-mercaptoethanol (BME) or DTT (dithiotreitol) and alkylation with iodoacetamide (IAA), was also evaluated. Our results indicate that the stability of the complexes between W and proteins is not too high enough to remain unaltered during protein separation by SDS-PAGE in denaturing and reducing conditions. However, the procedures for in-solution tryptic digestion and for ESI-MS analysis in MeOH/H(2)O/with 0.1% formic acid could be used for protein identification without large loss of binding between W and proteins.