Elemental analysis of renal slices by proton-induced X-ray emission

Monitoring trace elements generated by automobiles: air pollutants with possible health impacts

Major transformations in the environmental composition are principally attributable to the combustion of fuels by automobiles. Motorized gasoline-powered two-stroke auto-rickshaws (TSA) and compressed natural gas (CNG)-powered four-stroke auto-rickshaws (FSA) are potential source of air pollution in south Asia and produce toxic amount of particulate matter (PM) to the environment. In this study, we attempted to characterize elemental pollutants from the PM of TSA and FSA using proton-induced X-ray emission (PIXE) analysis. The observations of the existing investigation recognized significant increase in Al (P < 0.05), P (P < 0.01), and Zn (P < 0.01) from the PM samples of FSA. In addition, the concentrations of Cu, Fe, K, Mg, Na and S were also observed exceeding the recommended National Institute for Environmental Studies limits. On the contrary, increased concentration of Sr and V were observed in the PM samples from TSA. It is generally believed that FSA generates smaller amount of PM but data obtained from FSA are clearly describing that emissions from FSA comprised potentially more toxic substances than TSA. The current research is specific to metropolitan population and has evidently revealed an inconsistent burden of exposure to air pollutants engendered by FSA in urban communities, which could lead to the disruption of several biological activities and may cause severe damage to entire ecological system.

Surface interactions of a W-DLC-coated biomedical AISI 316L stainless steel in physiological solution

The corrosion stability of a W-DLC coated surgical AISI 316L stainless steel in Hanks' solution has been evaluated. Particle induced X-ray emission (PIXE) measurements were performed to evaluate the incorporation of potentially bioactive elements from the physiological solution. The film structure was analyzed by X-ray diffractometry and micro-Raman spectroscopy. The wear behavior was assessed using the sphere-on-disc geometry. The in vitro biocompatibility of the W-DLC film was evaluated by cytotoxicity tests. The corrosion resistance of the stainless steel substrate decreased in the presence of the PVD layer. EIS measurements suggest that this behavior was closely related to the corrosion attack through the coating pores. PIXE measurements revealed the presence of Ca and P in the W-DLC film after immersion in Hanks' solution. This result shows that the PIXE technique can be applied to identify and evaluate the incorporation of bioactive elements by W-DLC films. The film showed good wear resistance and biocompatibility.

Interseasonal distribution and partitioning of heavy metals in subtidal sediment of Qua Iboe Estuary and associated Creeks, Niger Delta (Nigeria)

An analysis of the distribution and chemical forms of selected metals: cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and lead (Pb) in subtidal sediments of Qua Iboe Estuary and adjourning creeks, collected between June 2000 and January 2001, were studied using a sequential chemical extraction method. The concentration of metals in each extracted fraction was determined using inductively coupled plasma spectrometer (ICP-AES). Pb, Cd and Cu appear to be the most abundant metal in the sediments of the systems, and are predominantly associated with the residual, organic and oxidisable phases. Results indicate that there are also insignificant components that are bound to both the exchangeable and carbonates fractions. Ni is largely associated with bioavailable phases with insignificant bound to organic matter and residual fractions. In general, an insignificant component of Cd and Pb are bound to organic matter phase. Moreover, speciation results indicate that metal contamination in the ecosystems investigated primarily comes from human-mediated sources. Thus, based on index of geoaccumulation calculated, sediments of these ecosystems have been classified as uncontaminated by Cr, Cu and Ni, strongly contaminated by Pb and extremely contaminated by Cd.

The linker region plays a key role in the adaptation to cold of the cellulase from an Antarctic bacterium

The psychrophilic cellulase, Cel5G, from the Antarctic bacterium Pseudoalteromonas haloplanktis is composed of a catalytic module (CM) joined to a carbohydrate-binding module (CBM) by an unusually long, extended and flexible linker region (LR) containing three loops closed by three disulfide bridges. To evaluate the possible role of this region in cold adaptation, the LR was sequentially shortened by protein engineering, successively deleting one and two loops of this module, whereas the last disulfide bridge was also suppressed by replacing the last two cysteine residue by two alanine residues. The kinetic and thermodynamic properties of the mutants were compared with those of the full-length enzyme, and also with those of the cold-adapted CM alone and with those of the homologous mesophilic enzyme, Cel5A, from Erwinia chrysanthemi. The thermostability of the mutated enzymes as well as their relative flexibility were evaluated by differential scanning calorimetry and fluorescence quenching respectively. The topology of the structure of the shortest mutant was determined by SAXS (small-angle X-ray scattering). The data indicate that the sequential shortening of the LR induces a regular decrease of the specific activity towards macromolecular substrates, reduces the relative flexibility and concomitantly increases the thermostability of the shortened enzymes. This demonstrates that the long LR of the full-length enzyme favours the catalytic efficiency at low and moderate temperatures by rendering the structure not only less compact, but also less stable, and plays a crucial role in the adaptation to cold of this cellulolytic enzyme.

Toxicity and transport of three synthesized mercury-thiol-complexes in isolated rabbit renal proximal tubule suspensions

Previous work has suggested that endogenous sulfhydryls, such as glutathione (GSH) and cysteine, are involved in the uptake and toxicity of HgCl2. To study this possibility, uptake and toxicity of synthesized Hg(SG)2, Hg(cysteinylglycine)2 [Hg(CYS-GLY)2] and Hg(CYS)2 were investigated in rabbit renal proximal tubule suspensions (RPT). The intracellular K+ was used as a toxicity indicator, and the mercury content in the tubules was measured by proton induced x-ray emission analysis. The toxicity rank order of the three synthesized mercury-thiol-complexes from the highest to the lowest was: Hg(CYS)2 > Hg(CYS-GLY)2 > Hg(SG)2. However, no significant difference among the mercury contents in the tubules exposed to these synthesized mercury-thiol-complexes was detected. Acivicin (0.25 mM), an inhibitor of gamma-glutamyltranspeptidase (GGT), decreased the toxicity of Hg(SG)2 in a manner that did not decrease the uptake of mercury in the tubules. This suggests that the toxicity of Hg(SG)2 requires processing to Hg(CYS-GLY)2 or Hg(CYS)2, while Hg(SG)2 may be taken up by the tubules via Na(+)-dependent GSH transporter since 10 mM acivicin, an inhibitor of this transporter dramatically decreased the uptake of Hg(SG)2. Organic anion transporter plays a minor role, if any, in the toxicity and uptake of Hg(SG)2 and Hg(CYS)2 since p-aminohippuric acid (PAH), an inhibitor of organic anion transporter, did not have significant effect on their uptake and toxicity. L-phenylalanine, an inhibitor of the neutral amino acid decreased the uptake of mercury, but to a lesser extent. This suggested that neutral amino acid transporter seemed to play a role, in part, in the toxicity and uptake of synthesized Hg(CYS)2. In summary, the data suggested that basolateral transport is important for the toxicity of the three synthesized mercury-thiol-complexes, and a variety of mechanisms are involved in the toxicity and uptake of these complexes in isolated rabbit RPT.

Use of the Caco-2 cell model to assess the relative lead-chelating ability of diasterioisomers of 2,3-dimercaptosuccinic acid

The purpose of this study was to examine the mechanisms of lead (Pb) uptake by human intestinal cells and to compare the intestinal transport and relative lead-chelating ability of two diastereoisomeric forms (i.e., meso and racemic) of 2, 3-dimercaptosuccinic acid (DMSA). The model used was the human adenocarcinoma (Caco-2) cell monolayer. The Caco-2 cells were cultured in flasks for examination of cellular uptake of lead and subsequent chelation of the lead by the DMSA isomers. For assessment of the comparative intestinal transport of the diastereoisomers, the Caco-2 cells were cultured on semipermeable supports. The effects of N-ethylmaleimide and 1,25-dihydroxyvitamin D3 (vitamin D3) on the uptake of lead by the Caco-2 monolayer were examined to determine the contributions of sulfhydryl-binding and calcium-binding protein, respectively, to the lead uptake process. Analysis of lead was performed using both macro- and micro-proton-induced X-ray emission (PIXE), and DMSA was measured spectrophotometrically following derivatization with 5,5'-dithiobis-2-nitrobenzoic acid. Results from micro-PIXE imaging suggest that lead is bound on the surface of the cell, and that sulfhydryl binding may be an important step in the uptake of lead by the Caco-2 cells. Macro-PIXE results indicate that the racemic form of DMSA may be more effective in chelating lead from within the cell. Comparison of the transport of the two DMSA diastereoisomers indicates that the racemic form is transported across the Caco-2 monolayer more readily than the meso form.

Utilization of renal slices to evaluate the efficacy of chelating agents for removing mercury from the kidney

Mercury is an environmental contaminant that preferentially accumulates in the kidney. It has been previously shown using proton-induced X-ray emission analysis that mercury (HgCl2) accumulated in precision-cut rabbit renal cortical slices. In this study, the efficacy of seven chelating agents for the removal of Hg from renal slices has been examined. Rabbits were injected with HgCl2 (10 mg/kg) and 3 h later kidneys were sliced, or renal slices were exposed in vitro to a mildly toxic concentration of HgCl2 (5 x 10(-5)M, 4 h). The slices were then treated in vitro with 10 mM concentrations of EDTA, lipoic acid (LA), penicillamine (PA), glutathione (GSH), 1,4-dithiothreitol (DTT), DMSA, or DMPS. DMPS proved to be the most effective in mobilizing Hg from in vivo or in vitro HgCl2-exposed renal tissue ( > 85% of control after 3 h incubation). Relative efficacies for the seven agents were DMPS > DMSA, PA > DTT, GSH > LA, EDTA. The use of renal slices appears to be a useful in vitro tool for assessing the efficacy of chelating agents on mobilizing accumulated Hg from renal tissue.

Use of tissue slices in chemical mixture toxicology and interspecies investigations

Precision-cut tissue slices have proven to be a useful in vitro system for biotransformation and toxicity studies. Since tissue slices can be readily prepared from a variety of tissues and species, they can easily be used for interspecies investigations and comparisons. Furthermore, slices can be readily prepared from human tissue, thus comparisons (extrapolation) can be made between laboratory animals and humans. Slices can also be used to examine the toxic interactions of chemicals in vitro. It is important to use the correct experimental design to demonstrate toxic interactions and to assure that the tissue slices are properly exposed to the chemicals. Overall, tissue slices offer a valid in vitro system for performing species comparisons and chemical-chemical interaction studies.

Interaction of metals during their uptake and accumulation in rabbit renal cortical slices

The uptake and accumulation of metals occurs in the kidney, which is a key site for interaction between metal nephrotoxicants. The uptake/accumulation and interaction of CdCl2, HgCl2, K2Cr2O7, and NaAsO2 was examined in precision-cut rabbit renal cortical slices. Slices were incubated with 10(-6) to 10(-3) M of a single metal toxicant or combinations of metal toxicants for 12 hr in DME-F12 media. Slices were blotted and sandwiched between two mylar films stretched across XRF sample cups. Quantitation of the metal in the slices was performed by proton-induced X-ray emission analysis (PIXE). The uptake of the metals was rapid, often reaching a maximum between 3 to 6 hr; the accumulation of Hg was highest, followed in order by Cd, Cr, and As. When two metals were present together, substantial alterations were observed in the uptake of the metals in the slices. HgCl2 hindered the uptake of K2Cr2O7, NaAsO2, CdCl2 (in this order), whereas these metals facilitated the uptake of HgCl2. However, a decreased uptake of both metals was often noted after exposure to other combinations of metals. PIXE analysis of metal content in slices is attractive since all elements (atomic number > 20) can be determined simultaneously. This information will be particularly useful in studying potential toxic interactions.

Metal speciation in environmental and biological systems

Metal ions form complexes with naturally occurring complexing agents or ligands released from industrial activity. The metal complexes are thereby mobilized and transported in environmental and biological systems. The impact of such metal complexes depends on the metal complex species that are kinetically and thermodynamically stable in these homogeneous and heterogeneous systems. The distribution of metal complex species in these complex systems can be calculated from available formation constant data. This article describes the importance of verifying the validity of these calculations by employing experimental techniques that can speciate metal complexes.

Glutathione effects on toxicity and uptake of mercuric chloride and sodium arsenite in rabbit renal cortical slices

The mechanism of renal uptake of nephrotoxic heavy metals such as HgCl2 and NaAsO2 is not clear. The metals are known to react with endogenous sulfhydryls such as glutathione (GSH), so metal-GSH conjugates may be delivered to the kidney. To study this possibility, renal cortical slices from male New Zealand white rabbits were incubated with 10(-4) M HgCl2 or 10(-3) M NaAsO2 +/- stoichiometric amounts (1-3x) of GSH; or synthetic metal-GSH conjugates [10(-4) M Hg(SG)2 or 10(-3) M As(SG)3]. Incubations were performed at 37 degrees C in DME-F12 buffer (95/5 O2/CO2) for 8 hr. Hg(SG)2 reduced slice K+/DNA content, as an indicator of viability, significantly less than HgCl2. As(SG)3 exhibited a 2-hr delay in K+/DNA content reduction compared to NaAsO2. This delay in toxicity was not correlated to changes in uptake. Arsenic and mercury accumulation, determined by proton-induced X-ray emission, were also identical between the metal salts and the metal-GSH conjugates. Exogenous GSH decreased HgCl2 cytotoxicity and was correlated to a decrease in Hg accumulation in the slice. Exogenous GSH had limited if any protective effects against cytotoxicity by NaAsO2 and a decrease in As accumulation was not observed. Complex metal-GSH interactions appear to exist and impact on the uptake and toxicity of these metals.

Measurements of environmental lead contamination and human exposure

The importance of accurate measurements of environmental lead exposure and toxicity is substantiated by analyses documenting the global contamination of the biosphere with industrial lead and the pervasiveness of measurable lead toxicity in human populations. Those data demonstrating environmental lead contamination and toxicity have, in part, led to regulations that limit the amount of lead in some products (e.g., paint, solder, and gasolines) in many industrialized countries. These regulations have resulted in a substantial reduction in some lead discharges to the environment. In spite of these reductions, current environmental lead levels are still often more than 10-fold, and sometimes more than 10,000-fold, higher than natural levels. Further, environmental lead concentrations are expected to remain elevated for a protracted period due to continued emissions of relatively large amounts of industrial lead to the environment and the persistence of contaminant lead in the environment. Discharges of contaminant lead have resulted in increases in organism and human lead levels comparable to increases documented in environmental matrices, as indicated by a recent estimate of the natural level of lead in blood of preindustrial humans (0.016 microgram/dL or 0.8 nM). This estimate is 175-fold lower than average blood lead levels in the United States (2.8 micrograms/dL or 140 nM) and 600-fold lower than the recently (1991) revised Centers for Disease Control (CDC) action level of concern for early toxic effects in children (10 micrograms/dL or 480 nM). The significance of these comparisons to public health is corroborated by numerous studies suggesting that there may be no lower threshold for sublethal toxicity in contemporary (i.e., lead-contaminated) humans. Those data also indicate that environmental lead concentrations that were previously considered innocuous may be deleterious to human health. It is apparent that the extent of sublethal lead toxicity in humans may be best addressed by studies that consider control populations possessing natural (i.e., preindustrial) lead burdens, as well as state-of-the-art, trace-metal-clean techniques and advanced instrumentation. Trace-metal-clean techniques are required to prevent the inadvertent lead contamination of samples, which has plagued many previous analyses of environmental and human lead levels. Advanced instrumentation is required to provide the sensitivity, accuracy, and precision that are needed to quantify the sublethal effects of lead concentrations at environmental levels of exposure. Fortunately, methodologies utilizing these advancements are now capable of addressing many of the important issues (e.g., lead biomolecular speciation, low exposure effects) in environmental and human lead toxicology.