Fe(II) interaction with cement phases: Method development, wet chemical studies and X-ray absorption spectroscopy.

Fe(II) interaction with cement phases was studied by means of co-precipitation and sorption experiments in combination with X-ray absorption fine structure (XAFS) spectroscopy. Oxidation of Fe(II) was fast in alkaline conditions and therefore, a methodology was developed which allowed Fe(II) to be stabilised in the sorption experiments and to prepare samples for spectroscopy. X-ray diffraction (XRD) of the co-precipitation samples showed uptake of a small portion of Fe(II) by calcium-silicate-hydrates (C-S-H) in the interlayer indicated by an increase in the interlayer spacing. Fe(II) incorporation by AFm phases was not indicated. Wet chemical experiments using 55Fe radiotracer revealed linear sorption of Fe(II) irrespective of the Ca/Si ratio of C-S-H and equilibrium pH. The Kd values for Fe(II) sorption on C-S-H are more than three orders of magnitude lower as compared to Fe(III), while they are comparable to those of other bivalent metal cations. XAFS spectroscopy showed Fe(II) binding by C-S-H in an octahedral coordination environment. The large number of neighbouring atoms rules out the formation of a single surface-bound Fe(II) species. Instead the data suggest presence of Fe(II) in a structurally bound entity. The data from XRD and XAFS spectroscopy suggests the presence of both surface- and interlayer-bound Fe(II) species.

Determination of ultra-low concentrations of gaseous 14C-bearing hydrocarbons produced during corrosion of irradiated steel using accelerator mass spectrometry.

Compound-specific radiocarbon analysis (CSRA) was developed to identify and quantify gaseous 14C-bearing carbon compounds at the pico- to femtomolar concentration range and employed in a corrosion experiment with small specimens of irradiated steel. The approach is based on gas chromatographic separation of single 14C-bearing carbon compounds, their oxidation to 14CO2, sampling with a custom-made fraction collector and quantification by accelerator mass spectrometry (AMS). In addition to CSRA, a method allowing the quantification of the total 14C content of the gas phase was developed and tested. After validation of the two set-ups with standards, the gaseous 14C-bearing carbon compounds produced during alkaline anoxic corrosion of irradiated steel were quantified. Small hydrocarbons (HCs) like methane (14CH4) and ethane (14C2H6) were the only 14C-bearing compounds identified in the gas phase above the detection limit. 14CH4 was the main species (on average 5.4 × 10-14 mol L-1 gas) and contributed >90% to the total 14C content, whereas the concentration of 14C2H6 was much lower (7.9 × 10-16 mol L-1 gas). To our knowledge, this is the first study reporting CSRA of gaseous 14C-bearing HCs produced during anoxic corrosion of irradiated metallic radioactive waste at ultra-low concentrations.

Analysis of 14C-bearing compounds released by the corrosion of irradiated steel using accelerator mass spectrometry.

The combination of ion chromatography (IC) with accelerator mass spectrometry (AMS) was developed to determine the speciation of 14C-(radiocarbon) bearing organic compounds in the femto to pico molar concentration range. The development of this compound-specific radiocarbon analysis (CSRA) of carboxylic acids is reported and the application of the method on a leaching solution from neutron-irradiated steel is demonstrated. The background and the dynamic range of the AMS-based method were quantified. On using 14C-labelled standards, the measurements demonstrate the repeatability of the analytical method and the reproducible recovery of the main target carboxylic acids (i.e., acetate, formate, malonate, and oxalate). The detection limit was determined to be in the mid fmol 14C per L level while the dynamic range of the analytical method covers three orders of magnitude from the low fmol to the mid pmol 14C per L level. Cross contamination was found to be negligible during IC fractionation and was accounted for during eluate processing and 14C detection by AMS. The 14C-bearing carboxylates released from an irradiated steel nut into an alkaline leaching solution were analysed using the CSRA-based analytical method with the aim to check the applicability of the approach and develop appropriate sample preparation. The concentrations of 14C-bearing formate and acetate, the main organic corrosion products, were at a low pmol 14C per L level for convenient dimensions of the alkaline leaching experiment which demonstrates that compound-specific 14C AMS is an extremely sensitive analytical method for analysing 14C-bearing compounds. The content of total organic 14C in solution (TO14C) determined by the direct measurement of an aliquot of the leaching solution agrees well with the sum of the 14C concentrations of the individual carboxylates within the uncertainty of the data. Furthermore, the TO14C content is in good agreement with the calculated value using the corrosion rate determined from the 60Co release and the 14C inventory of the irradiated steel specimen.

Retention of selenium by calcium aluminate hydrate (AFm) phases under strongly-reducing radioactive waste repository conditions.

Safety assessment studies of future nuclear waste repositories carried out in many countries predict selenium-79 to be a critical radionuclide due to its presence as anion in three relevant oxidation states (vi, iv, -ii) resulting in weak retardation by most common rock minerals. This assumption, however, ignores its potential uptake by AFm phases, positively charged anion exchangers, which are present in significant quantities in the cementitious materials used in artificial barriers. Here we report for the first time wet chemistry and spectroscopic data on the interaction of the most relevant selenium anion species under the expected strongly reducing conditions, i.e. HSe-, with two AFm phases commonly found in cement, monocarbonate (AFm-MC) and hemicarbonate (AFm-HC). Batch sorption experiments showed that HSe- is retained much more strongly by AFm-HC (solid-liquid distribution ratio, Rd, of 100 ± 50 L kg-1) than by AFm-MC (Rd = 4 ± 2 L kg-1) at the equilibrium pH (∼12). X-ray absorption fine-structure (XAFS) spectroscopy revealed that the larger d-spacing in AFm-HC (d-spacing = 8.2 Å) provides easy access for HSe- to the AFm interlayer space for sorption, whereas the smaller d-spacing of AFm-MC (d-spacing = 7.55 Å) hinders interlayer access and limits HSe- sorption mostly to the outer planar surfaces and edges of the latter AFm phase. XAFS spectra further demonstrated that Se(-ii) prevalently sorbed in the interlayers of AFm-HC, is better protected from oxidation than Se(-ii) prevalently sorbed onto the outer surfaces of AFm-MC. The quantitative sorption data along with the molecular-scale process understanding obtained from this study provide crucial insight into the Se retention by the cementitious near-field of a radioactive waste repository under reducing conditions.

Donor-Derived Cell-Free DNA Is a Novel Universal Biomarker for Allograft Rejection in Solid Organ Transplantation.

BACKGROUND: In solid organ transplantation, sensitive real-time biomarkers to assess the graft health are desirable to enable early intervention, for example, to avoid full-blown rejections. During rejection, high amounts of graft-derived cell-free DNA (GcfDNA) are shed into the blood stream. The quantification of this GcfDNA in allotransplantation is considered to fulfill this need, because it can be measured with great precision and at reasonable cost. PATIENTS AND METHODS: Patients from 2 ongoing studies in kidney (KTx) and heart (HTx) transplantation were monitored blinded on a scheduled basis, by means of a published universal droplet digital polymerase chain reaction to quantify the GcfDNA. RESULTS: Immediately after engraftment, GcfDNA reaches high values (>5% of total cfDNA), with a rapid decrease to values of <0.5% within 1 week. Living-related KTx recipients show lower initial values, reflecting the absence of preservation injury. Episodes of rejection in KTx and HTx are accompanied by a significant increase of GcfDNA (>5-fold) above values in patients without complications, occurring earlier than clinical or biochemical hints to rejection. One case of rejection, which became clinically suspect after 1 year and was proven with biopsy, showed a significant 10-fold increase 3 months earlier. CONCLUSIONS: The quantification of GcfDNA has the potential to detect rejection episodes at early stages, when other means of diagnosis are not effective. The method's noninvasiveness enables the monitoring recipients at intervals that are desired to catch rejections at early actionable stages to prevent full-blown rejection. This biomarker will be particularly valuable in regimens to minimize immunosuppression.

Total and free plasma concentrations of the active metabolite of leflunomide in relation to therapeutic outcome in kidney transplant recipients with BK-virus nephropathy.

Plasma concentrations of A771726, the active moiety of leflunomide, have been suggested to be associated with antiviral efficacy and/or an increased risk of toxicity. A771726 is >99% bound to serum albumin, which can be relevant in kidney transplant recipients (KTRs) displaying impaired function, which leads to increased pharmacologically active free drug concentrations. This study investigated the relationship of total (t-) and free (f-) A771726 concentrations with clinical outcomes. The 20 KTRs displayed a median daily dose and time on leflunomide of 20 mg (range, 10-50) and 16.5 months (range, 2-28), respectively. A median of 6 (range, 1-15) trough concentrations were measured in each patient. All patients received steroids and a calcineurin inhibitor (CNI) as well as 4 of them, cidofovir. To evaluate therapeutic efficacy, we monitored viral loads in the urine and blood, serum creatinine, and kidney histology. To detect toxicity, we recorded blood and platelet counts, hematocrit, hemoglobin concentrations, liver enzymes (alanine aminotransferase [ALT], and aspartate aminotransferase [AST]), and skin diseases. The median t-A771726 concentration was 31.5 mg/L (interindividual range, 11.0-56.4); the median f-A771726 concentration and fraction were 55.8 µg/L and 0.19% (interindividual ranges, 27.9-148.4 µg/L and 0.12%-0.50%), respectively. A weak but significant inverse correlation was observed between the free drug fraction and both the glomerular filtration rate estimated by the Modification of Diet in Renal Disease formula (MDRD-GFR) (r = -0.202) and serum albumin (r = -0.358). Higher MDRD-GFRs were associated with greater t-A771726 concentrations. There were no significant associations between efficacy parameters and either the t- or f-A771726 concentration or between the t-A771726 concentration and toxicity parameters. In contrast, the f-A771726 concentration was significantly associated with leukopenia. These results indicated that f-A771726 concentrations may be more reliable than t-A771726 content to estimate the risk of leukopenia. Intensified elimination due to a higher free drug fraction and compromised absorption associated with a low GFR may have been responsible for the positive correlation between MDRD-GFR and t-A771726.

Lipoprotein apheresis--more than just cholesterol reduction?

Lipoprotein apheresis is a well-established extracorporeal treatment in modality of severe hyperlipoproteinemia. Besides the reduction of LDL cholesterol and modifications to physiology of lipoprotein and lipid metabolism, Lipoprotein apheresis may have crucial effects on many other atherogenic factors as vascular inflammation, rheology and gene expressions in blood cells. These different effects of lipoprotein apheresis treatments are reviewed with respect to oxidative stress in plasma, red and white blood cells and in consequence to progression of atherosclerosis. However, in consideration of these reviewed aspects as a factor of biocompatibility lipoprotein apheresis remains safe.

How to optimize lipoprotein apheresis treatment--a second look.

BACKGROUND: Lipoprotein apheresis (LA) is used in hypercholesterolemic patients suffering from cardiovascular disease (CHD) if a modified diet and lipid-lowering drug regimens had failed. During the first LA treatments LDL-cholesterol (LDL-C) and lipoprotein (a) (Lp(a)) can be decreased very effectively when using generally accepted formulas for calculating plasma (PV) (e.g. Pearson) or blood volumes (BV) as a basis for calculating treatment volume (e.g. Nadler). With respect to LDL-C and Lp(a) levels after LA treatment not all treated patients on steady state with apheresis treatment procedures may achieve the desired target concentrations for LDL-C (<70 mg/dl) and Lp(a) (<30 mg/dl). Are there further ways to increase the effectiveness of LA? METHODS: Over months or years of LA the treated volumes were stepwise increased in patients to achieve target cholesterol concentrations but not sufficiently in all cases. Therefore the patients' actual LA treatment volumes were compared to the calculated PV or BV. To possibly optimize the treatment capacity of LA procedures independent of calculated PV or BV the capacity threshold was determined in addition. During LA procedures every 20 min cholesterol, triglycerides, LDL-C, HDL-C and Lp(a) concentrations were determined and related to the hematocrit to exclude dilution effects. RESULTS: In patients undergoing regular LA treated volumes vs. calculated volumes were different: for PV 28 ± 18% (n = 7); for BV 28 ± 20% (n = 6). The mean treated volumes were 1.3 fold larger than the calculated volumes to achieve cholesterol target levels in most LA treatments. With respect to the capacity threshold we observed in only 1 of 13 patients an ineffective long treatment time. No LA procedure failed due to exhausted capacity. CONCLUSIONS: Lipoprotein apheresis treatment is a very effective treatment procedure in lowering LDL-C and Lp(a). However, not in all procedures the optimal treatment volume for LA patients may be calculated. However calculations of PV and BV are more or less error-prone. An increase of 1.3 fold in the calculated volumes may be the first step in optimizing individual LA treatment options. In addition, to exclude an exhaustion of LA procedures the determination of the individual capacity threshold in every LA patient may be further helpful to adjust treatment volumes. To substantiate our demand on changed treatment volumes further data are necessary.

Current view: indications for extracorporeal lipid apheresis treatment.

BACKGROUND: One of the first investigations concerning extracorporeal treatment of hypercholesterolemia was performed in 1967 by plasma exchange in patients with homozygous or severe heterozygous familial hypercholesterolemia (FH). In the following decades, several specific lipid apheresis systems were developed to efficiently eliminate low-density lipoprotein (LDL) cholesterol and Lp(a) cholesterol in hypercholesterolemic patients. In the early 1980s, the main clinical indication has been homozygous FH including mainly children and pregnant women. In consideration of the current development of lipid-lowering regimens and scientific knowledge of preventing progression of cardiovascular diseases, the spectrum of indications to initiate lipid apheresis was extended due to still insufficient lipid-lowering therapy in some clinical cases. However, a generally accepted indication for lipid apheresis treatment is still under discussion. In Germany, the target-oriented distribution of increasingly limited healthcare resources demand data which support the benefit of established treatment procedures such as lipid apheresis. In recent years, the Federal Joint Committee (G-BA), a paramount decision-making body of the German Healthcare System, issued to reassess the approval of chronic lipid apheresis therapy for regular reimbursement. Therefore, in 2005, an interdisciplinary German Apheresis Working Group has been established by members of both the German societies of nephrology. One of the first goals of this working group was a revision of the indications for lipid apheresis corresponding to current guidelines and recommendations for the treatment of lipid disorders. In addition, recently new pathophysiological perceptions of the impact of lipoproteins on atherogenesis and thrombosis were also considered. METHODS AND RESULTS: Since 2005, the working group met on a regular basis to substantiate the first defined goals. The indications for lipid apheresis were critically revised with respect to actual results from clinical investigations, cardiovascular guidelines, and scientific knowledge and were accepted by the members of the apheresis working group. CONCLUSIONS: There is consensus between the medical societies and health insurance funds regarding the need for general accepted guidelines for lipid apheresis. Recommendations for the indications of lipid apheresis were developed, but additionally these results should be confirmed by medical societies to transform them to guidelines. However, due to limited data showing that lipid apheresis has effects on the progression of cardiovascular diseases all members of the apheresis working group support a project for creating a lipid apheresis registry. This apheresis registry has been developed and recently started. The primary goal is to substantiate prospective long-term data on clinical outcome of chronic lipid apheresis treatment and to support additional clinical research activities in this field. In addition, this registry should comply with the actual requests of the Federal Joint Committee (G-BA).

EXAFS study of Nd(III) uptake by amorphous calcium silicate hydrates (C-S-H).

Calcium silicate hydrate (C-S-H) phases control the immobilization of many metal cations in cementitious materials. In this study Nd binding to amorphous C-S-H phases with different Ca/Si (C/S) mol ratios (0.56, 0.87 and 1.54) and Nd loadings (7 and 35mumol/g), and which had been aged up to 270 days, has been investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters derived from EXAFS were compared with those predicted from bond-valence calculations. The study reveals that Nd may form several species in contact with C-S-H phases. The EXAFS parameters determined in samples after one day of reaction indicate the formation of inner-sphere surface complexes. The Nd-Ca and Nd-Si bond-distances tend to increase with time at both Nd loadings. Changes in the coordination numbers N(Si) and N(Ca) were found to be dependent on the (C/S) ratio. At the lowest C/S ratio the number of neighboring Si atoms tends to increase with time while the number of neighboring Ca atoms tends to increase with time at highest C/S ratio. No clear trend was observed for the medium C/S ratio. Nd incorporation into the structures of C-S-H phases is assumed to be the dominant immobilization process based on comparison with bond-distances predicted from structural considerations. After prolonged reaction times (45 days) Nd is expected to be predominantly incorporated into the Ca sheets of the C-S-H structure while small portions of Nd might also be taken up by the interlayer. The study suggests that, in the long term, amorphous C-S-H phases are capable of taking up Nd via exchange processes with Ca(2+) in the Ca sheets and the interlayer.

Differential proteomic analysis of lymphocytes treated with mycophenolic acid reveals caspase 3-induced cleavage of rho GDP dissociation inhibitor 2.

The antiproliferative immunosuppressive drug mycophenolic acid (MPA) is an uncompetitive inhibitor of inosine monophosphate dehydrogenase, a key enzyme in de novo synthesis of purine nucleotides. The latter are not only required for synthesis of DNA and RNA but also are essential for the regulation of numerous cellular signaling pathways modulated by guanine nucleotide binding proteins (G proteins). We undertook an analysis of the influence of MPA on protein expression in a T-lymphoblast cell line (CCRF-CEM), which displays concentration-dependent inhibition of proliferation by MPA to obtain insight into the influence of MPA on the cellular proteome. Cells were stimulated with phorbol myristate acetate/ionomycin and incubated in the presence or absence of MPA. Two-dimensional electrophoresis and densitometric imaging revealed 11 differentially expressed protein spots (P < 0.05) on MPA treatment, 6 with increased and 5 with decreased abundance. After in-gel tryptic digestion, proteins were identified by quadrupole time-of-flight mass spectrometry. Proteins displaying increased abundance after MPA treatment included splicing factor arginine/serine-rich 2, prostaglandin E synthase 3, peptidyl-prolyl cis-trans isomerase A, and deoxyuridine 5'-triphosphate nucleotidohydrolase. Endoplasmin, proliferating cell nuclear antigen, acidic leucine-rich nuclear phosphoprotein 32 family member A, and cofilin 1 showed decreased abundance after MPA treatment. Three separate spots (1 decreased and 2 increased abundance) were identified as Rho guanosine diphosphate dissociation inhibitor 2 (Rho GDI 2) proteins. Western blotting with a monoclonal antibody directed against the Rho GDI 2 site cleaved by caspase 3 demonstrated 1 spot with increased abundance to be the caspase 3-cleaved product of Rho GDI 2 lacking the first 19 amino acids. Rho GDI 2 plays a central regulatory role in the activation of Rho guanosine triphosphatases that function as molecular switches in cell signaling pathways affecting cell cytoskeletal dynamics and motility. Our data suggest that MPA can modulate Rho GDI 2 levels in T lymphocytes, thereby potentially disrupting cell signaling pathways important for T-cell function.

Prenatal dexamethasone exposure in the common marmoset monkey enhances gene expression of antioxidant enzymes in the aorta of adult offspring.

Human epidemiological studies have indicated that low birth weight associated with an adverse intrauterine environment is related to a greater incidence of cardiovascular disorders in later life. In the foetus, endogenous glucocorticoids generally increase if there is intrauterine nutrient deficiency. The consequent glucocorticoid hyperexposure has been hypothesised to cause in utero programming of atherogenic genes. We investigated the effect of oral treatment with the synthetic glucocorticoid dexamethasone during early or late pregnancy in marmoset monkeys on oxidative and antioxidant status in the offspring. Urinary concentrations of F(2)-isoprostanes were quantified as markers for in vivo oxidative stress. Expression of the mRNAs for the antioxidant enzymes cytosolic glutathione peroxidase (GPx-1), phospholipid hydroperoxide glutathione peroxidase (GPx-4), cytosolic Cu,Zn-superoxide dismutase (SOD1), mitochondrial Mn-superoxide dismutase (SOD2), glutathione reductase (GSR), modifier subunit of glutamate-cysteine ligase (GCLM) and catalase were determined in the aorta. Three groups of pregnant marmosets (10 animals per group) were treated orally for one week with vehicle, or with dexamethasone (5 mg/kg daily) during two gestation windows: early dexamethasone group, pregnancy day 42-48, and late dexamethasone group, pregnancy day 90-96. In one male sibling of each litter (10 males per group), aortas were taken at 2 years of age. In the late dexamethasone group a higher aortic mRNA expression for GPx-1 (p < 0.023), MnSOD (p < 0.016), GCLM (p < 0.019) and GSR (p < 0.014) in comparison to the controls was observed. Aortic expression in the early dexamethasone group was statistically significantly higher only for GSR mRNA (p < 0.038). No significant changes in urinary F(2)-isoprostane concentrations between controls, early and late dexamethasone groups at 2 years of age were observed. Hence, prenatal exposure to dexamethasone in the third trimester leads to increased mRNA expression of several aortic antioxidant enzymes in the offspring. This expression pattern was not temporally related to oxidative stress, and it may reflect in utero re-programming of aortic antioxidant gene expression during prenatal glucocorticoid exposure.

Co speciation in hardened cement paste: a macro- and micro-spectroscopic investigation.

Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposal of hazardous and radioactive wastes. Cement is used to condition and stabilize the waste materials and to construct the engineered barrier systems (container, backfill and liner materials) of repositories for radioactive waste. In this study, Co uptake by hardened cement paste (HCP) has been investigated with the aim of improving our understanding of the immobilization process of heavy metals in cement on the molecular level. X-ray-absorption spectroscopy (XAS) on powder material (bulk-XAS) was used to determine the local environment of Co in cement systems. Bulk-XAS investigations were complemented with micro-beam investigations to probe the inherent microscale heterogeneity of cement by using micro-X-ray-fluorescence (micro-XRF) and micro-XAS. Micro-XRF was used to gain information on the spatial heterogeneity of the Co distribution, whereas micro-XAS was employed to determine the speciation of Co on the microscale. The Co-doped HCP samples hydrated for time-scales from 1 hour up to 1 year were prepared under normal atmosphere, to simulate similar conditions as for waste packages. To investigate the role of oxygen, further samples were prepared in the absence of oxygen. The study showed that, for the samples prepared in air, Co(II) is oxidized to Co(III) after 1 hour of hydration time. Moreover, the relative amount of Co(III) increases with increasing hydration time. The study further revealed that Co(II) is predominately present as a Co-hydroxide-like phase and/or Co-phyllosilicates, whereas Co(III) tends to be incorporated into a CoOOH-like phase and/or Co-phyllomanganates. In contrast to samples prepared in air, XAS experiments with samples prepared in the absence of oxygen revealed solely the presence of Co(II). This finding indicates that oxygen plays an important role for Co oxidation in cement. Furthermore, the study suggests that Co(III) species or Co(III)-containing phases should be taken into account for an overall assessment of the Co release from Co-containing cement-stabilized waste under oxidizing conditions.

[Effects of LDL-apheresis--more than reduction of cholesterol?]. / Effekte der LDL-Apherese--Mehr als nur Cholesterinsenkung?

LDL apheresis is a safe and very effective extracorporeal treatment of refractory hypercholesterolemia. LDL cholesterol levels can be reduced with this procedure by more than 60%. C-reactive protein (CRP) is a known marker of inflammation in atherosclerosis. Interestingly CRP can be effectively removed by a single LDL apheresis, but further studies are needed to substantiate the effect of extracorporeal reduction of CRP on the progression of atherosclerosis. However, adhesion molecules and activities of inflammatory cells were also found to be reduced after a single LDL apheresis. The biochemical composition of newly formed LDL particles after apheresis is altered: LDL particles isolated after LDL apheresis had an increased resistance to oxidative stress in vitro. In addition, antioxidants are not depleted by LDL apheresis. The extracorporal method itself does not have a negative impact on the oxidative/antioxidative balance. A recent investigation showed that LDL-cholesterol had a more pronounced effect on blood rheology than fibrinogen. This observation may explain why a single LDL apheresis leads to better myocardial perfusion, as demonstrated by PET in patients with hypercholesterolemia. These additional effects have so far only been known with statins. Further investigations are needed to substantiate the observed potentially beneficial effects of LDLapheresis beyond its effect of lowering LDL.