Uranium interaction with two multi-resistant environmental bacteria: Cupriavidus metallidurans CH34 and Rhodopseudomonas palustris

Depending on speciation, U environmental contamination may be spread through the environment or inversely restrained to a limited area. Induction of U precipitation via biogenic or non-biogenic processes would reduce the dissemination of U contamination. To this aim U oxidation/reduction processes triggered by bacteria are presently intensively studied. Using X-ray absorption analysis, we describe in the present article the ability of Cupriavidus metallidurans CH34 and Rhodopseudomonas palustris, highly resistant to a variety of metals and metalloids or to organic pollutants, to withstand high concentrations of U and to immobilize it either through biosorption or through reduction to non-uraninite U(IV)-phosphate or U(IV)-carboxylate compounds. These bacterial strains are thus good candidates for U bioremediation strategies, particularly in the context of multi-pollutant or mixed-waste contaminations.

Uptake, localization, and speciation of cobalt in Triticum aestivum L. (wheat) and Lycopersicon esculentum M. (tomato)

The root-to-shoot transfer, localization, and chemical speciation of Co were investigated in a monocotyledon (Triticum aestivum L., wheat) and a dicotyledon (Lycopersicon esculentum M., tomato) plant species grown in nutrient solution at low (5 muM) and high (20 muM) Co(II) concentrations. Cobalt was measured in the roots and shoots by inductively coupled plasma-mass spectrometry. X-ray absorption spectroscopy measurements were used to identify the chemical structure of Co within the plants and Co distribution in the leaves was determined by micro-PIXE (particle induced X-ray emission). Although the root-to-shoot transport was higher for tomato plants exposed to excess Co, both plants appeared as excluders. The oxidation state of Co(II) was not transformed by either plant in the roots or shoots and Co appeared to be present as Co(II) in a complex with carboxylate containing organic acids. Cobalt was also essentially located in the vascular system of both plant species indicating that neither responded to Co toxicity via sequestration in epidermal or trichome tissues as has been observed for other metals in metal hyperaccumulating plants.

Inactivation by oxidation and recruitment into stress granules of hOGG1 but not APE1 in human cells exposed to sub-lethal concentrations of cadmium

The induction of mutations in mammalian cells exposed to cadmium has been associated with the oxidative stress triggered by the metal. There is increasing evidence that the mutagenic potential of Cd is not restricted to the induction of DNA lesions. Cd has been shown to inactivate several DNA repair enzymes. Here we show that exposure of human cells to sub-lethal concentrations of Cd leads to a time- and concentration-dependent decrease in hOGG1 activity, the major DNA glycosylase activity responsible for the initiation of the base excision repair (BER) of 8-oxoguanine, an abundant and mutagenic form of oxidized guanine. Although there is a slight effect on the level of hOGG1 transcripts, we show that the inhibition of the 8-oxoguanine DNA glycosylase activity is mainly associated with an oxidation of the hOGG1 protein and its disappearance from the soluble fraction of total cell extracts. Confocal microscopy analyses show that in cells exposed to Cd hOGG1-GFP is recruited to discrete structures in the cytoplasm. These structures were identified as stress granules. Removal of Cd from the medium allows the recovery of the DNA glycosylase activity and the presence of hOGG1 in a soluble form. In contrast to hOGG1, we show here that exposure to Cd does not affect the activity of the second enzyme of the pathway, the major AP endonuclease APE1.

Size-, composition- and shape-dependent toxicological impact of metal oxide nanoparticles and carbon nanotubes toward bacteria

Ecotoxicological effects of nanoparticles (NP) are still poorly documented while their commercialization for industrial and household applications increases. The aim of this study was to evaluate the influence of physicochemical characteristics on metal oxide NP and carbon nanotubes toxicological effects toward bacteria. Two strains of bacteria, Cupriavidus metallidurans CH34 and Escherichia coli MG1655 were exposed to TiO(2) or Al(2)O(3) NP or to multiwalled-carbon nanotubes (MWCNT). Particular attention was paid on optimizing NP dispersion to obtain nonagglomerated suspensions. Our results show that NP toxicity depends on their chemical composition, size, surface charge, and shape but not on their crystalline phase. MWCNT toxicity does not depend on their purity. Toxicity also depends on the bacterial strain: E. coli MG1655 is sensitive to NP, whereas C. metallidurans CH34 is not. Interestingly, NP are accumulated in both bacterial strains, and association between NP and bacteria is necessary for bacterial death to occur. NP may then represent a danger for the environment, causing the disappearance of some sensitive bacterial strains such as E. coli MG1655, but also being mobilized by nonsensitive strains such as C. metallidurans CH34 and transported through the whole ecosystem.

Assessment of uranium and selenium speciation in human and bacterial biological models to probe changes in their structural environment

This study illustrates the potential of physicochemical techniques to speciate uranium (U) and selenium (Se) in biological samples. Speciation, defined here as the study of structural environment, of both toxic elements, was characterized at several levels in biological media and directly in human cells or bacteria once the metal(loid)s were internalized. External speciation that is extracellular speciation in culture media was predicted by thermodynamic equilibrium computer modelling using the JChess software and validated by spectroscopic measurements (XANES and EXAFS). Internal speciation that is intracellular speciation in eukaryotic and prokaryotic cells was studied in vitro with a soil bacterium Cupriavidus metallidurans CH34 and ROS 17/2.8 osteoblasts, human cells responsible for bone formation. XANES, EXAFS, HPLC-ICP-MS and SDS-PAGE coupled to particle induced X-ray emission (PIXE) permitted the identification and quantification of complexes formed with organic or inorganic molecules and/or larger proteins.

Intracerebral delivery of 5-iodo-2'-deoxyuridine in combination with synchrotron stereotactic radiation for the therapy of the F98 glioma

Iodine-enhanced synchrotron stereotactic radiotherapy takes advantage of the radiation dose-enhancement produced by high-Z elements when irradiated with mono-energetic beams of synchrotron X-rays. In this study it has been investigated whether therapeutic efficacy could be improved using a thymidine analogue, 5-iodo-2'-deoxyuridine (IUdR), as a radiosentizing agent. IUdR was administered intracerebrally over six days to F98 glioma-bearing rats using Alzet osmotic pumps, beginning seven days after tumor implantation. On the 14th day, a single 15 Gy dose of 50 keV synchrotron X-rays was delivered to the brain. Animals were followed until the time of death and the primary endpoints of this study were the mean and median survival times. The median survival times for irradiation alone, chemotherapy alone or their combination were 44, 32 and 46 days, respectively, compared with 24 days for untreated controls. Each treatment alone significantly increased the rats' survival in comparison with the untreated group. Their combination did not, however, significantly improve survival compared with that of X-irradiation alone or chemotherapy alone. Further studies are required to understand why the combination of chemoradiotherapy was no more effective than X-irradiation alone.

Potential phytoavailability of anthropogenic cobalt in soils as measured by isotope dilution techniques

Isotope dilution is a useful technique to determine the potential phytoavailability of an element in soil. This method involves equilibrating an isotope with soil and then sampling the labile metal pool by analysis of the soil solution (E value) or plants growing in the soil (L value). The work reported here was conducted to evaluate the distribution coefficient (Kd), and the potential phytoavailability (E value) of cobalt (Co) in eight soils subjected to the atmospheric deposition of anthropogenic Co. Multiple regression analyses demonstrated that the K(d) of isotopically exchangeable Co in these soils was best modelled with two parameters: soil pH and organic carbon (OC) content (log Kd=0.85(pH)+1.1(logOC)-5.0, R2=0.94, p<0.01). Cobalt E values ranged from 1.5 to 37% of total soil Co concentrations. No evidence was obtained to suggest that Co(III), if present, was isotopically exchangeable in these soils and it was concluded that the Co E values consisted solely of Co(II). Cobalt L values, measured with Triticum aestivum L. (46 days), of two of these soils (varying in soil pH, e.g. 5.0 and 7.2) were statistically (p<0.05) different to E values. However, when changes of bulk soil pH on Co E values were considered, the two values were statistically (p<0.05) similar indicating that processes affecting soil pH during plant growth can alter isotopically exchangeable concentrations of Co.

Cellular accumulation and distribution of uranium and lead in osteoblastic cells as a function of their speciation

Uranium (U) and lead (Pb) are accumulated and fixed for long periods in bone, impairing remodeling processes. Their toxicity to osteoblasts, the cells responsible for bone formation, is poorly documented. It has been previously shown that cytotoxicity and phenotypic effects of both metals on osteoblasts are highly influenced by metal speciation. Differences in sensitivity between cell types have been underlined as well. In this paper, cellular accumulation of U and Pb in cultured and primary osteoblastic cells was assessed by trace element analysis. Distribution of different species at the cell scale was investigated by electron microscopy. Internalization of both metals was shown to be correlated to cytotoxicity and population growth recovery after exposure. For each metal, the amount of metal uptake leading to 50% cell death was shown to be speciation-dependent. Scanning and transmission electron microscopy showed the formation of precipitates with phosphate in lysosomes for both metals, whose role in toxicity or cell defence remains to be clarified. Although a clear link was established between cytotoxicity and accumulation, differences in sensitivity observed in terms of speciation could not be fully explained and other studies seem necessary.

Novel pattern of foliar metal distribution in a manganese hyperaccumulator

The primary sequestration of foliar manganese (Mn) in Mn-hyperaccumulating plants can occur in either their photosynthetic or non-photosynthetic tissues, depending on the species. To date, only non-photosynthetic tissues have been found to be the major sinks in other hyperaccumulators. Here, electron (SEM) and proton (PIXE) microprobes were used to generate qualitative energy dispersive (EDS) X-ray maps of leaf cross sections. Two Mn hyperaccumulators, Garcinia amplexicaulis Vieill. (Clusiaceae) and Maytenus fournieri (Panch. and Sebert) Loesn. (Celastraceae), and the Mn accumulator Grevillea exul Lindley (Proteaceae) were studied. PIXE/EDS data obtained here for M. fournieri were in agreement with existing SEM/EDS data showing that the highest localised foliar Mn concentrations were in the epidermal tissues. However, this is the first in situ microprobe investigation of G. amplexicaulis and G. exul. The Mn X-ray maps of G. amplexicaulis revealed a previously undescribed third spatial distribution pattern among Mn-hyperaccumulating species. Manganese was relatively evenly distributed throughout the leaf photosynthetic and non-photosynthetic tissues, while in G. exul it was most highly concentrated in the epidermal cells.

Resistance, accumulation and transformation of selenium by the cyanobacterium Synechocystis sp. PCC 6803 after exposure to inorganic SeVI or SeIV

Our purpose was to investigate the ability of Synechocystis sp . PCC 6803, a photosynthetic prokaryote isolated from fresh water, to resist, incorporate and reduce the oxidized forms of selenium including selenite and selenate, the major selenium species present in aquatic systems. Selenium speciation and the chemical intermediates during selenium transformation were determined by X-ray absorption near edge structure (XANES) spectroscopy. The possible internalisation pathways involving selenium and the metabolic fate of selenate and selenite were examined. Selenate metabolism seemed to proceed via the sulfate reduction pathway resulting in the formation of the R-Se-H, R-Se-R and R-Se-Se-R species. The transformation of selenate to toxic amino acids may explain the high sensitivity of Synechocystis to selenate. Several mechanisms of selenium reduction seem to compete during selenite assimilation. A specific mechanism may transform internalised selenite into selenide and, subsequently induce the biosynthesis of selenoproteins. A non-specific mechanism may interfere with thiols, such as glutathione in the cell cytoplasm, or with proteins in the periplasm of the bacteria, notably thioredoxins. Several hypotheses concerning the complex transformation of selenium in Synechocystis could therefore be proposed.

Bioavailability and microbial adaptation to elevated levels of uranium in an acid, organic topsoil forming on an old mine spoil

An old mine spoil at a 19th-century mining site with considerable residues of uranium (400-800 mg U/kg) was investigated with respect to U concentrations in soil and plants and tolerance to U in the soil microbial community in order to describe the bioavailability of U. Measurements of soil fractions representing water-soluble U, easily exchangeable U, and U bound to humified organic matter showed that all fractions contained elevated concentrations of U. Plant U concentrations were only 10 times higher at the mine spoil site compared to the reference site (3 mg U/kg vs 0.3 mg U/kg), while the most easily available soil fractions contained 0.18 to 0.86 mg U/kg soil at the mine spoil. An ecotoxicity bioassay using incorporation of [3H]thymidine into the indigenous microbial communities of the two soils in the presence of increasing U concentrations showed that microorganisms at the mining site were sensitive to U but also that they had acquired a substantial tolerance toward U (EC50, the effective concentration reducing activity by 50% of UO2-citrate was approximately 120 microM as compared to 30 microM in the reference soil). In the assay, more than 40% of the microbial activity was maintained in the presence of 1 mM UO2-citrate versus 3% in the reference soil. We conclude that U-enriched mining waste can contain sufficiently elevated concentrations of bioavailable U to affect indigenous microorganisms and that bioavailable U imposes a selection pressure that favors the development of a highly uranium-tolerant microbial community, while plant uptake of U remains low.

Novel nickel transport mechanism across the bacterial outer membrane energized by the TonB/ExbB/ExbD machinery

Nickel is a cofactor for various microbial enzymes, yet as a trace element, its scavenging is challenging. In the case of the pathogen Helicobacter pylori, nickel is essential for the survival in the human stomach, because it is the cofactor of the important virulence factor urease. While nickel transport across the cytoplasmic membrane is accomplished by the nickel permease NixA, the mechanism by which nickel traverses the outer membrane (OM) of this Gram-negative bacterium is unknown. Import of iron-siderophores and cobalamin through the bacterial OM is carried out by specific receptors energized by the TonB/ExbB/ExbD machinery. In this study, we show for the first time that H. pylori utilizes TonB/ExbB/ExbD for nickel uptake in addition to iron acquisition. We have identified the nickel-regulated protein FrpB4, homologous to TonB-dependent proteins, as an OM receptor involved in nickel uptake. We demonstrate that ExbB/ExbD/TonB and FrpB4 deficient bacteria are unable to efficiently scavenge nickel at low pH. This condition mimics those encountered by H. pylori during stomach colonization, under which nickel supply and full urease activity are essential to combat acidity. We anticipate that this nickel scavenging system is not restricted to H. pylori, but will be represented more largely among Gram-negative bacteria.

Uranium Induces Apoptosis and Is Genotoxic to Normal Rat Kidney (NRK-52E) Proximal Cells

Uranium (U) is a heavy metal used in the nuclear industry and for military applications. U compounds are toxic. Their toxicity is mediated either by their radioactivity or their chemical properties. Mammalian kidneys and bones are the main organs affected by U toxicity. Although the most characteristic response to U exposure is renal dysfunction, little information is available on the mechanisms of its toxicity at the molecular level. This report studied the genotoxicity of U. Apoptosis induction in normal rat kidney (NRK-52(E)) proximal cells was investigated as a function of exposure time or concentrations (0-800microM). In parallel, DNA damage was evaluated by several methods. In order to distinguish between the intrinsic and the extrinsic pathways of apoptosis, caspases-8, -9, -10 assays were conducted and the mitochondrial membrane potential was measured. Three methods were selected for their complementarities in the detection of genetic lesions. The comet assay was used for the detection of primary lesions of DNA. gamma-H2AX immunostaining was achieved to detect DNA double-strand breaks. The micronucleus assay was used to detect chromosomic breaks or losses. DNA damage and apoptosis were observed in a concentration-dependent manner. This study demonstrated that U is genotoxic from 300microM and induces caspase-dependent apoptosis cell death from 200microM mainly through the intrinsic pathway in NRK-52(E) cells. These results suggest that the DNA damage caused by U is reversible at low concentration (200-400microM) but becomes irreversible and leads to cell death for higher concentrations (500-800microM).

Citrate Does Not Change Uranium Chemical Speciation in Cell Culture Medium but Increases Its Toxicity and Accumulation in NRK-52E Cells

Uranium (U), as a heavy metal, is a strong chemical toxicant, which induces the damage to proximal tubule kidney cells. In order to reproduce U toxicity in vitro and to avoid precipitation, it is necessary to complex it with a strong ligand such as bicarbonate before dilution with cell culture medium. It was recently shown, in vitro on the NRK-52E normal renal tubular epithelial cells, that citrate increased the toxicity of U(VI)-bicarbonate complexes. This property was attributed to a change in U speciation, characterized by the occurrence of U(VI)-citrate complexes, which were supposed to be more toxic than U(VI)-bicarbonate. Here, we present the results of extended X-ray absorption fine structure spectroscopy (EXAFS) analyses of the media that were used to expose cells in vitro. Resulting data show that even when citrate is added to the exposure medium, the predominant species is U(VI)-bicarbonate. Nonetheless, citrate increases U(VI) toxicity and accelerates its intracellular accumulation kinetics, without inducing precipitation. This study emphasizes another parameter that modulates U(VI) toxicity for renal tubule cells and further characterizes the mechanisms of U(VI) toxicity.

Assessment of isotope exchange methodology to determine the sorption coefficient and isotopically exchangeable concentration of selenium in soils and sediments

Isotope exchange methodology is invaluable to determine the solution-solid-phase distribution (Kd) and isotopically exchangeable concentration (Evalue) of elements in soils and sediments. This work examined the use of species-specific stable isotope exchange techniques to determine the Kd and E value of selenium (Se), as selenite (SeO3) and selenate (SeO4), in nine soils and sediments varying in concentration and source of Se. High-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) was used to quantify the isotope (e.g., 76Se, 78Se, 80Se, and 82Se) concentrations of the soluble Se oxyanions. The two Se oxyanions were detected in the solution phase of all of the soils and sediments. However, upon spiking the suspensions with stable isotope-labeled 78SeO3 and 76SeO4, it was observed that isotope self-exchange was insignificant to the derivation of Se oxyanion Kd and E values during 24 h (and up to 120 h in four of the samples). These results demonstrate that valid determinations of the Evalue of Se necessitate that the Se oxyanions are speciated in solution. This is clearly evident for these soils and sediments where it was observed that the Evalues of SeO3 and SeO4 represented, respectively, 5-97% and 3-95% of the total Se E value.

Actinide speciation in relation to biological processes

In case of accidental release of radionuclides into the environment, actinides represent a severe health risk to human beings following internal contamination (inhalation, ingestion or wound). For a better understanding of the actinide behaviour in man (in term of metabolism, retention, excretion) and in specific biological systems (organs, cells or biochemical pathways), it is of prime importance to have a good knowledge of the relevant actinide solution chemistry and biochemistry, in particular of the thermodynamic constants needed for computing actinide speciation. To a large extent, speciation governs bioavailability and toxicity of elements and has a significant impact on the mechanisms by which toxics accumulate in cell compartments and organs and by which elements are transferred and transported from cell to cell. From another viewpoint, speciation is the prerequisite for the design and success of potential decorporation therapies. The purpose of this review is to present the state of the art of actinide knowledge within biological media. It is also to discuss how actinide speciation can be determined or predicted and to highlight the areas where information is lacking with the aim to encourage new research efforts.

Redox regulation of human OGG1 activity in response to cellular oxidative stress

8-Oxoguanine (8-oxoG), a common and mutagenic form of oxidized guanine in DNA, is eliminated mainly through base excision repair. In human cells its repair is initiated by human OGG1 (hOGG1), an 8-oxoG DNA glycosylase. We investigated the effects of an acute cadmium exposure of human lymphoblastoid cells on the activity of hOGG1. We show that coinciding with alteration of the redox cellular status, the 8-oxoG DNA glycosylase activity of hOGG1 was nearly completely inhibited. However, the hOGG1 activity returned to normal levels once the redox cellular status was normalized. In vitro, the activity of purified hOGG1 was abolished by cadmium and could not be recovered by EDTA. In cells, however, the reversible inactivation of OGG1 activity by cadmium was strictly associated with reversible oxidation of the protein. Moreover, the 8-oxoG DNA glycosylase activity of purified OGG1 and that from crude extracts were modulated by cysteine-modifying agents. Oxidation of OGG1 by the thiol oxidant diamide led to inhibition of the activity and a protein migration pattern similar to that seen in cadmium-treated cells. These results suggest that cadmium inhibits hOGG1 activity mainly by indirect oxidation of critical cysteine residues and that excretion of the metal from the cells leads to normalization of the redox cell status and restoration of an active hOGG1. The results presented here unveil a novel redox-dependent mechanism for the regulation of OGG1 activity.

Seleno- l -Methionine Is the Predominant Organic Form of Selenium in Cupriavidus metallidurans CH34 Exposed to Selenite or Selenate

The accumulated organic form of selenium previously detected by X-ray absorption near-edge structure (XANES) analyses in Cupriavidus metallidurans CH34 exposed to selenite or selenate was identified as seleno- l -methionine by coupling high-performance liquid chromatography to inductively coupled plasma-mass spectrometry.

Anion exchange liquid chromatography--inductively coupled plasma-mass spectrometry detection of the Co2+, Cu2+, Fe3+ and Ni2+ complexes of mugineic and deoxymugineic acid

Phytosiderophores, such as mugineic and deoxymugineic acid, are produced by graminaceous plant species in response to Fe deficiency conditions normally experienced in calcareous and alkaline non-calcareous soils. As these phytosiderophores have the ability to form thermodynamically stable complexes with other metal cations present in the growing medium, they have also been implicated in the transport and bioavailability of these metals in the environment. However, routine analytical methodology to detect the various metal complexes formed by these phytosiderophores is lacking. Therefore, as these complexes are negatively charged over a wide range of pH values, anion exchange liquid chromatography (AE LC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) was investigated as a means to separate and quantify these complexes. The metal-phytosiderophore complexes were prepared at pH 7 and separated by NaOH or NH4NO3 gradient elution on a Dionex AS11 anion exchange column. Of the metals tested only the Co2+ and Ni2+ complexes of mugineic and deoxymugineic acid were detected when using a 0-20mM NaOH gradient elution profile. However, the phytosiderophore complexes of Cu2+ and Fe3+ were also detected when using NH4NO3 as the mobile phase at pH 7. Base-assisted hydrolysis of the latter two complexes is proposed to explain their apparent 'instability' in the high pH NaOH mobile phase. The absolute detection limits of the developed methodologies for these metal complexes ranged from 0.1 to 2.8pmol. As phytosiderophore complexes with Cd2+ and Zn2+ were not detected, it was concluded that the dissociation kinetics of these metal-phytosiderophore complexes were too rapid for these complexes to be observed in the present chromatographic conditions.

Development of a single ion hit facility at the Pierre Sue Laboratory: a collimated microbeam to study radiological effects on targeted living cells

A single ion hit facility is being developed at the Pierre Süe Laboratory (LPS) since 2004. This set-up will be dedicated to the study of ionising radiation effects on living cells, which will complete current research conducted on uranium chemical toxicity on renal and osteoblastic cells. The study of the response to an exposure to alpha particles will allow us to distinguish radiological and chemical toxicities of uranium, with a special emphasis on the bystander effect at low doses. Designed and installed on the LPS Nuclear microprobe, up to now dedicated to ion beam microanalysis, this set-up will enable us to deliver an exact number of light ions accelerated by a 3.75 MV electrostatic accelerator. An 'in air' vertical beam permits the irradiation of cells in conditions compatible with cell culture techniques. Furthermore, cellular monolayer will be kept in controlled conditions of temperature and atmosphere in order to diminish stress. The beam is collimated with a fused silica capillary tubing to target pre-selected cells. Motorisation of the collimator with piezo-electric actuators should enable fast irradiation without moving the sample, thus avoiding mechanical stress. An automated epifluorescence microscope, mounted on an antivibration table, allows pre- and post-irradiation cell observation. An ultra thin silicon surface barrier detector has been developed and tested to be able to shoot a cell with a single alpha particle.

Chemical forms of selenium in the metal-resistant bacterium Ralstonia metallidurans CH34 exposed to selenite and selenate

Ralstonia metallidurans CH34, a soil bacterium resistant to a variety of metals, is known to reduce selenite to intracellular granules of elemental selenium (Se(0)). We have studied the kinetics of selenite (Se(IV)) and selenate (Se(VI)) accumulation and used X-ray absorption spectroscopy to identify the accumulated form of selenate, as well as possible chemical intermediates during the transformation of these two oxyanions. When introduced during the lag phase, the presence of selenite increased the duration of this phase, as previously observed. Selenite introduction was followed by a period of slow uptake, during which the bacteria contained Se(0) and alkyl selenide in equivalent proportions. This suggests that two reactions with similar kinetics take place: an assimilatory pathway leading to alkyl selenide and a slow detoxification pathway leading to Se(0). Subsequently, selenite uptake strongly increased (up to 340 mg Se per g of proteins) and Se(0) was the predominant transformation product, suggesting an activation of selenite transport and reduction systems after several hours of contact. Exposure to selenate did not induce an increase in the lag phase duration, and the bacteria accumulated approximately 25-fold less Se than when exposed to selenite. Se(IV) was detected as a transient species in the first 12 h after selenate introduction, Se(0) also occurred as a minor species, and the major accumulated form was alkyl selenide. Thus, in the present experimental conditions, selenate mostly follows an assimilatory pathway and the reduction pathway is not activated upon selenate exposure. These results show that R. metallidurans CH34 may be suitable for the remediation of selenite-, but not selenate-, contaminated environments.

Influence of Uranium Speciation on Normal Rat Kidney (NRK-52E) Proximal Cell Cytotoxicity

Uranium is a naturally occurring heavy metal. Its extensive use in the nuclear cycle and for military applications has focused attention on its potential health effects. Acute exposures to uranium are toxic to the kidneys where they mainly cause damage to proximal tubular epithelium. The purpose of this study was to investigate the biological consequences of acute in vitro uranyl exposure and the influence of uranyl speciation on its cytotoxicity. NRK-52E cells, representative of rat kidney proximal epithelium, were exposed to uranyl-carbonate and -citrate complexes, which are the major complexes transiting through renal tubules after acute in vivo contamination. Before NRK-52E cell exposure, these complexes were diluted in classical or modified cell culture media, which can possibly modify uranyl speciation. In these conditions, uranium cytotoxicity appears after 16 h of exposure. The CI50 cytotoxicity index, the uranium concentration leading to 50% dead cells after 24 h of exposure, is 500 microM (+/-100 microM) and strongly depends on uranyl counterion and cell culture medium composition. Computer modeling of uranyl speciation is reported, enabling one to draw a parallel between uranyl speciation and its cytotoxicity.

Impact of emerging technologies and regulations on the role of POCT

Point-of-care testing (POCT) can be introduced by laboratory directors or clinicians in response to the need for rapid results to guide treatment. The professional responsibility for ensuring reliable and accurate results is well-defined in some countries such as France, but the role and responsibility of the laboratory is less clear in many other places. When point-of-care instrument technology and the intrinsic design of the device leads to device-specific parameters or analytical differences from laboratory-based equipment, there is a risk of misinterpretation and erroneous treatment decisions. Laboratory staffs are more often aware of the interaction of analytical technology and result interpretation than clinicians, making it more rational to involve the laboratory in the selection of point-of-care equipment, procedures, and therapeutic decisions based on the results. The design control and risk-analysis provisions of emerging regulations such as the EU in vitro diagnostic medical device (IVD) can be interpreted as engaging the manufacturer's responsibility, even when the equipment is functioning according to specification. This is especially true of device-specific parameters in which cross-calibration or traceability to a reference material or method is not possible. This is a further argument for involvement of the laboratory in the selection and implementation of point-of-care testing devices.

Red cell effects on lithium measurements by ion-selective electrode

The possible interference of haematocrit was studied in an evaluation of the analytical performance of the NOVA 11 analyzer. For lithium concentrations between 0.56 and 0.68 mmol/L, the within-run imprecision was less than 1.06%, and less than 2.8% in day-to-day imprecision, measured in quality control solutions. Comparison of whole blood with plasma measurement showed satisfactory correlation with deviations up to 0.06 mmol/L for haematocrits from 35-53% (y = 0.73 x + 0.12). Measurement on a blood specimen not containing lithium, whose haematocrit was varied, allowed us to quantify a specific red cell interference. With samples from treated patients, and a sample spiked to various lithium concentrations, we obtained differences dependent on haematocrit and on lithium concentrations. In subtracting the specific red cell effect, we could systematically observe that apparent lithium levels diminish as haematocrit increases. This observation should allow development of an appropriate algorithm for obtaining exact values on whole blood samples.

[Determination of pH in the body: methodologic review]

The maintenance of a defined free H+ concentration within narrow limits is a prerequisite and feature of living organisms. In recent years the different disciplines of biological science have made considerable progress in the elucidation of the mechanisms involved in pH homeostasis. Recent advances have occurred also in the field of pH measurement. This review focuses mainly on the modern instruments for pH and blood gas analysis. The techniques of intracellular pH currently in general use are described together with some of the techniques for determination of pH in subcellular compartments.

Electrode measurement of glucose and urea in undiluted samples

The development of ion-selective electrodes (ISEs) for electrolyte measurements necessitates a re-evaluation of the biological and clinical interpretation of a result. In pathological situations (e.g., hyperlipidemia and hyperproteinemia) direct potentiometry is the method of choice for ion measurements in blood. However, the "plasma water effect" exists also in normal samples, requiring new reference values for physiological ranges. A compromise between medical and instrumentation workers retained the old reference values (flame photometry for Na+ and K+) by introducing correction factors into the ISE instruments, so that the results for direct ISE and flame photometry are the same for "normal" samples. Analyses of "abnormal" samples will reveal biases between the two methods. Now, a new generation of electrodes for assaying additional metabolites reopens the issue. Although classical methods measure a quantity of substance in a predetermined volume of sample, the majority of the substance is usually in the aqueous phase, and the volumes occupied by lipid and protein are not taken into consideration. In evaluating the NOVA 12 instrument (NOVA Biomedical), using electrodes for direct measurement in serum or plasma of Na, K, Cl, total CO2, urea, and glucose, we have demonstrated the inadequacy of classical measurements of urea and glucose, especially in pathological situations characterized by a large variation in the plasma water fraction.

Electrode measurement of glucose and urea in undiluted samples

The development of ion-selective electrodes (ISEs) for electrolyte measurements necessitates a re-evaluation of the biological and clinical interpretation of a result. In pathological situations (e.g., hyperlipidemia and hyperproteinemia) direct potentiometry is the method of choice for ion measurements in blood. However, the "plasma water effect" exists also in normal samples, requiring new reference values for physiological ranges. A compromise between medical and instrumentation workers retained the old reference values (flame photometry for Na+ and K+) by introducing correction factors into the ISE instruments, so that the results for direct ISE and flame photometry are the same for "normal" samples. Analyses of "abnormal" samples will reveal biases between the two methods. Now, a new generation of electrodes for assaying additional metabolites reopens the issue. Although classical methods measure a quantity of substance in a predetermined volume of sample, the majority of the substance is usually in the aqueous phase, and the volumes occupied by lipid and protein are not taken into consideration. In evaluating the NOVA 12 instrument (NOVA Biomedical), using electrodes for direct measurement in serum or plasma of Na, K, Cl, total CO2, urea, and glucose, we have demonstrated the inadequacy of classical measurements of urea and glucose, especially in pathological situations characterized by a large variation in the plasma water fraction.

[Ionized calcium. An essential parameter for the study of calcium metabolism]

Calcium ions in plasma are either free (ionized calcium) or bound to protein and small anions. Ionized calcium is the physiologically active fraction. Several factors have recently been combined to change the measurement of ionized calcium from a specialized to a routine test. Reliable instrumentation, easy to maintain, is now available with simultaneous pH measurement. This paper focuses on both the analytical consideration required to perform reliable laboratory measurements and the clinical situations where ionized calcium has proved to provide a substantially different clinical interpretation than the measurement of total calcium.

A reliable potentiometric measurement of ionized calcium and pH on the ICA2 Radiometer in clinical practice

A second generation analyser for potentiometric measurement of ionized calcium and pH (ICA2 Radiometer, Copenhagen) was tested with respect to analytical performance in two different laboratories. Newly-developed aqueous buffered solutions were used at different Ca2+ concentrations as well as biological specimens prepared from human subjects. The overall precision of ICA2 was very good: CV = 0.0-0.4% for within-run and 0.4-1.7% for day-to-day precision with protein-free solutions and CV = 0.3-0.9% for within-run precision on biological specimens. The adjusted value of Ca2+ to pH 7.40 is an analytical advantage for which the calculation is correct but the assumption made for this algorithm may limit its clinical relevance. Measurements were comparable on ICA2 when performed on either whole blood, serum or plasma. Pre-analytical conditions should be observed such as the choice of anticoagulant and anaerobic conditions. Such a reliable and accurate instrument may promote the use of ionized calcium measurement in daily clinical practice.

Evaluation of Roche fructosamine test: use for diabetic patient monitoring

A fructosamine assay using commercially available reagents on an IL Multistat III centrifugal analyser was evaluated. Within- and between-batch precision were less than 4% (CV). Results were similar using serum or oxalated plasma, but were 5% lower than those using sodium heparinate. We compared serum fructosamine and Hb A1c results in insulin-dependent and non-insulin-dependent diabetics: serum fructosamine correlated with Hb A1c (r = 0.80) and gave at least as good a separation of patients from normal controls as did Hb A1c.

[Effect of constant rate enteral nutrition on gastrin secretion in children (author's transl)]]

The aim of this work was to study gastrin secretion in children receiving constant rate enteral nutrition (CREN) then avoiding intermittent stimulation induced by meals. Induced hypergastrinemia was performed in 12 children during CREN and compared with that in 8 children with intermittent oral feeding as a control group. Before stimulation by protein load there was no significant difference between the 2 groups; 20 minutes after stimulation, there was no change in the serum gastrin concentration in the CREN group, but a dramatic increase in the control group. The hypothetic role of gastrin and/or intestinal factors is advanced to explain the inhibition of gastrin secretory response during CREN. A progressive substitution from continuous to discontinuous intakes is suggested to avoid weaning complications of this nutritional technique.