Imaging of Vanadium in Microfossils: A New Potential Biosignature

The inability to unambiguously distinguish the biogenicity of microfossil-like structures in the ancient rock record is a fundamental predicament facing Archean paleobiologists and astrobiologists. Therefore, novel methods for discriminating biological from nonbiological chemistries of microfossil-like structures are of the utmost importance in the search for evidence of early life on Earth. This, too, is important for the search for life on Mars by in situ analyses via rovers or sample return missions for future analysis here on Earth. Here, we report the application of synchrotron X-ray fluorescence imaging of vanadium, within thermally altered organic-walled microfossils of bona fide biological origin. From our data, we demonstrate that vanadium is present within microfossils of undisputable biological origin. It is well known in the organic geochemistry literature that elements such as vanadium are enriched and contained within crude oils, asphalts, and black shales that have been formed by diagenesis of biological organic material. It has been demonstrated that the origin of vanadium is due to the diagenetic alteration of precursor chlorophyll and heme porphyrin pigment compounds from living organisms. We propose that, taken together, microfossil-like morphology, carbonaceous composition, and the presence of vanadium could be used in tandem as a biosignature to ascertain the biogenicity of putative microfossil-like structures. Key Words: Microfossils-Synchrotron micro-X-ray fluorescence-Vanadium-Tetrapyrrole-Biosignature. Astrobiology 17, 1069-1076.

Glutathione transferase P1-1 as an arsenic drug-sequestering enzyme

Arsenic-based compounds are paradoxically both poisons and drugs. Glutathione transferase (GSTP1-1) is a major factor in resistance to such drugs. Here we describe using crystallography, X-ray absorption spectroscopy, mutagenesis, mass spectrometry, and kinetic studies how GSTP1-1 recognizes the drug phenylarsine oxide (PAO). In conditions of cellular stress where glutathione (GSH) levels are low, PAO crosslinks C47 to C101 of the opposing monomer, a distance of 19.9 Å, and causes a dramatic widening of the dimer interface by approximately 10 Å. The GSH conjugate of PAO, which forms rapidly in cancerous cells, is a potent inhibitor (K_i  = 90 nM) and binds as a di-GSH complex in the active site forming part of a continuous network of interactions from one active site to the other. In summary, GSTP1-1 can detoxify arsenic-based drugs by sequestration at the active site and at the dimer interface, in situations where there is a plentiful supply of GSH, and at the reactive cysteines in conditions of low GSH.

Mechanisms of murine cerebral malaria: Multimodal imaging of altered cerebral metabolism and protein oxidation at hemorrhage sites

Using a multimodal biospectroscopic approach, we settle several long-standing controversies over the molecular mechanisms that lead to brain damage in cerebral malaria, which is a major health concern in developing countries because of high levels of mortality and permanent brain damage. Our results provide the first conclusive evidence that important components of the pathology of cerebral malaria include peroxidative stress and protein oxidation within cerebellar gray matter, which are colocalized with elevated nonheme iron at the site of microhemorrhage. Such information could not be obtained previously from routine imaging methods, such as electron microscopy, fluorescence, and optical microscopy in combination with immunocytochemistry, or from bulk assays, where the level of spatial information is restricted to the minimum size of tissue that can be dissected. We describe the novel combination of chemical probe-free, multimodal imaging to quantify molecular markers of disturbed energy metabolism and peroxidative stress, which were used to provide new insights into understanding the pathogenesis of cerebral malaria. In addition to these mechanistic insights, the approach described acts as a template for the future use of multimodal biospectroscopy for understanding the molecular processes involved in a range of clinically important acute and chronic (neurodegenerative) brain diseases to improve treatment strategies.

Reactivity and Speciation of Anti-Diabetic Vanadium Complexes in Whole Blood and Its Components: The Important Role of Red Blood Cells

Reactions with blood components are crucial for controlling the antidiabetic, anticancer, and other biological activities of V(V) and V(IV) complexes. Despite extensive studies of V(V) and V(IV) reactions with the major blood proteins (albumin and transferrin), reactions with whole blood and red blood cells (RBC) have been studied rarely. A detailed speciation study of Na3[V(V)O4] (A), K4[V(IV)2O2(citr)2]·6H2O (B; citr = citrato(4-)); [V(IV)O(ma)2] (C; ma = maltolato(-)), and (NH4)[V(V)(O)2(dipic)] (D; dipic = pyridine-2,6-dicarboxylato(2-)) in whole rat blood, freshly isolated rat plasma, and commercial bovine serum using X-ray absorption near-edge structure (XANES) spectroscopy is reported. The latter two compounds are potential oral antidiabetic drugs, and the former two are likely to represent their typical decomposition products in gastrointestinal media. XANES spectral speciation was performed by principal component analysis and multiple linear regression techniques, and the distribution of V between RBC and plasma fractions was measured by electrothermal atomic absorption spectroscopy. Reactions of A, C, or D with whole blood (1.0 mM V, 1-6 h at 310 K) led to accumulation of ∼50% of total V in the RBC fraction (∼10% in the case of B), which indicated that RBC act as V carriers to peripheral organs. The spectra of V products in RBC were independent of the initial V complex, and were best fitted by a combination of V(IV)-carbohydrate (2-hydroxyacid moieties) and/or citrate (65-85%) and V(V)-protein (15-35%) models. The presence of RBC created a more reducing environment in the plasma fraction of whole blood compared with those in isolated plasma or serum, as shown by the differences in distribution of V(IV) and V(V) species in the reaction products of A-D in these media. At physiologically relevant V concentrations (<50 μM), this role of RBC may promote the formation of V(III)-transferrin as a major V carrier in the blood plasma. The results reported herein have broad implications for the roles of RBC in the transport and speciation of metal pro-drugs that have broad applications across medicine.

Localization of the Trace Elements Iron, Zinc and Selenium in Relation to Anatomical Structures in Bovine Ovaries by X-Ray Fluorescence Imaging

X-ray fluorescence (XRF) was used to image 40 histological cross-sections of bovine ovaries (n=19), focusing on structures including: antral follicles at different stages of growth or atresia, corpora lutea at three stages of development (II-IV), and capillaries, arterioles, and other blood vessels. This method identified three key trace elements [iron (Fe), zinc (Zn), and selenium (Se)] within the ovarian tissue which appeared to be localized to specific structures. Owing to minimal preprocessing of the ovaries, important high-resolution information regarding the spatial distribution of these elements was obtained with elemental trends and colocalizations of Fe and Zn apparent, as well as the infrequent appearance of Se surrounding the antrum of large follicles, as previously reported. The ability to use synchrotron radiation to measure trace element distributions in bovine ovaries at such high resolution and over such large areas could have a significant impact on understanding the mechanisms of ovarian development. This research is intended to form a baseline study of healthy ovaries which can later be extended to disease states, thereby improving our current understanding of infertility and endocrine diseases involving the ovary.

Biotransformations of Antidiabetic Vanadium Prodrugs in Mammalian Cells and Cell Culture Media: A XANES Spectroscopic Study

The antidiabetic activities of vanadium(V) and -(IV) prodrugs are determined by their ability to release active species upon interactions with components of biological media. The first X-ray absorption spectroscopic study of the reactivity of typical vanadium (V) antidiabetics, vanadate ([V^VO₄]^3–, A) and a vanadium(IV) bis(maltolato) complex (B), with mammalian cell cultures has been performed using HepG2 (human hepatoma), A549 (human lung carcinoma), and 3T3-L1 (mouse adipocytes and preadipocytes) cell lines, as well as the corresponding cell culture media. X-ray absorption near-edge structure data were analyzed using empirical correlations with a library of model vanadium(V), -(IV), and -(III) complexes. Both A and B ([V] = 1.0 mM) gradually converged into similar mixtures of predominantly five- and six-coordinate V^V species (∼75% total V) in a cell culture medium within 24 h at 310 K. Speciation of V in intact HepG2 cells also changed with the incubation time (from ∼20% to ∼70% V^IV of total V), but it was largely independent of the prodrug used (A or B) or of the predominant V oxidation state in the medium. Subcellular fractionation of A549 cells suggested that V^V reduction to V^IV occurred predominantly in the cytoplasm, while accumulation of V^V in the nucleus was likely to have been facilitated by noncovalent bonding to histone proteins. The nuclear V^V is likely to modulate the transcription process and to be ultimately related to cell death at high concentrations of V, which may be important in anticancer activities. Mature 3T3-L1 adipocytes (unlike for preadipocytes) showed a higher propensity to form V^IV species, despite the prevalence of V^V in the medium. The distinct V biochemistry in these cells is consistent with their crucial role in insulin-dependent glucose and fat metabolism and may also point to an endogenous role of V in adipocytes.

The first detailed speciation study of typical antidiabetic vanadium(V/IV) complexes in mammalian cell culture systems showed that the complexes decomposed rapidly in cell culture media and were further metabolized by the cells, which included interconversions of V^V and V^IV species.

Vanadium(V) and -(IV) complexes of anionic polysaccharides: Controlled release pharmaceutical formulations and models of vanadium biotransformation products

Uncontrolled reactions in biological media are a main obstacle for clinical translation of V-based anti-diabetic or anti-cancer pro-drugs. We investigated the use of controlled-release pharmaceutical formulations to ameliorate this issue with a series of V(V) and (IV) complexes of anionic polysaccharides. Carboxymethyl cellulose, xanthan gum, or alginic acid formulations were prepared by the reactions of [VO4](3-) with one or two molar equivalents of biological reductants, L-ascorbic acid (AA) or L-cysteine (Cys), in the presence of excess polysaccharide at pH~7 or pH~4. XANES studies with the use of a previously developed library of model V(V), V(IV) and V(III) complexes showed that reactions in the presence of AA led mostly to the mixtures of five- and six-coordinate V(IV) species, while the reactions in the presence of Cys led predominantly to the mixtures of five- and six-coordinate V(V) species. The XANES spectra of some of these samples closely matched those reported previously for [VO4](3-) biotransformation products in isolated blood plasma, red blood cells, or cultured adipocytes, which supports the hypothesis that modified polysaccharides are major binders of V(V) and V(IV) in biological systems. Studies by EPR spectroscopy suggested predominant V(IV)-carboxylato binding in complexes with polysaccharides. One of the isolated products (a V(IV)-alginato complex) showed selective release of low-molecular-mass V species at pH~8, but not at pH~2, which makes it a promising lead for the development of V-containing formulations for oral administration that are stable in the stomach, but release the active ingredient in the intestines.

XAS studies of Se speciation in selenite-fed rats

The biological activity of selenium is dependent on its chemical form. Therefore, knowledge of Se chemistry in vivo is required for efficacious use of selenium compounds in disease prevention and treatment. Using X-ray absorption spectroscopy, Se speciation in the kidney, liver, heart, spleen, testis and red blood cells of rats fed control (∼0.3 ppm Se) or selenite-supplemented (1 ppm or 5 ppm Se) diets for 3 or 6 weeks, was investigated. X-ray absorption spectroscopy revealed the presence of Se-Se and Se-C species in the kidney and liver, and Se-S species in the kidney, but not the liver. X-ray absorption near edge structure (XANES) spectra showed that there was variation in speciation in the liver and kidneys, but Se speciation was much more uniform in the remaining organs. Using principal component analysis (PCA) to interpret the Se K-edge X-ray absorption spectra, we were able to directly compare the speciation of Se in two different models of selenite metabolism--human lung cancer cells and rat tissues. The effects of Se dose, tissue type and duration of diet on selenium speciation in rat tissues were investigated, and a relationship between the duration of the diet (3 weeks versus 6 weeks) and selenium speciation was observed.

Correction: X-Ray fluorescence imaging and other analyses identify selenium and GPX1 as important in female reproductive function

Correction for 'X-Ray fluorescence imaging and other analyses identify selenium and GPX1 as important in female reproductive function' by M. J. Ceko et al., Metallomics, 2014, DOI: .

X-Ray fluorescence imaging and other analyses identify selenium and GPX1 as important in female reproductive function

Studies of selenium (Se) status indicate that Se is necessary for fertility but how precisely is not known. We aimed to show that Se was important in bovine female reproductive function. The elemental distribution in the bovine ovary (n = 45 sections) was identified by X-ray fluorescence (XRF) imaging. Se was consistently localized to the granulosa cell layer of large (>10 mm) healthy follicles. Inductively Coupled Plasma - Mass Spectrometry revealed tenfold higher Se in the bovine follicle wall compared to corpora lutea. Gene expression analysis of selenoprotein genes GPX1, GPX3, VIMP and SELM in bovine granulosa cells revealed that only GPX1 was significantly up-regulated in large healthy follicles compared to the small healthy or atretic follicles (P < 0.05). Western immunoblotting identified GPX1 protein in bovine granulosa cells of large healthy follicles, but not of small healthy follicles. To assess if GPX1 was important in human follicles, cumulus cells from women undergoing IVF/ICSI with single embryo transfer were collected. Oocytes and embryos were cultured and transferred independently in 30 patients undergoing elective single embryo transfer. Gene expression of GPX1 was significantly higher in human cumulus cells from cumulus-oocyte complexes yielding a pregnancy (P < 0.05). We present the first XRF imaging of mammalian ovaries showing that Se is consistently localized to the granulosa cells of large healthy follicles. We conclude that Se and selenoproteins are elevated in large healthy follicles and may play a critical role as an antioxidant during late follicular development.

Reactivity-activity relationships of oral anti-diabetic vanadium complexes in gastrointestinal media: an X-ray absorption spectroscopic study

The reactions of oral V(V/IV) anti-diabetic drugs within the gastrointestinal environment (particularly in the presence of food) are a crucial factor that affects their biological activities, but to date these have been poorly understood. In order to build up reactivity-activity relationships, the first detailed study of the reactivities of typical V-based anti-diabetics, Na3V(V)O4 (A), [V(IV)O(OH2)5](SO4) (B), [V(IV)O(ma)2] (C, ma = maltolato(-)) and (NH4)[V(V)(O)2(dipic)] (D, dipic = pyridine-2,5-dicarboxylato(2-)) with simulated gastrointestinal (GI) media in the presence or absence of food components has been performed by the use of XANES (X-ray absorption near edge structure) spectroscopy. Changes in speciation under conditions that simulate interactions in the GI tract have been discerned using correlations of XANES parameters that were based on a library of model V(V), V(IV), and V(III) complexes for preliminary assessment of the oxidation states and coordination numbers. More detailed speciation analyses were performed using multiple linear regression fits of XANES from the model complexes to XANES obtained from the reaction products from interactions with the GI media. Compounds B and D were relatively stable in the gastric environment (pH ∼ 2) in the absence of food, while C was mostly dissociated, and A was converted to [V10O28](6-). Sequential gastric and intestinal digestion in the absence of food converted A, B and D to poorly absorbed tetrahedral vanadates, while C formed five- or six-coordinate V(V) species where the maltolato ligands were likely to be partially retained. XANES obtained from gastric digestion of A-D in the presence of typical food components converged to that of a mixture of V(IV)-aqua, V(IV)-amino acid and V(III)-aqua complexes. Subsequent intestinal digestion led predominantly to V(IV) complexes that were assigned as citrato or complexes with 2-hydroxyacidato donor groups from other organic compounds, including certain carbohydrates. The absence of strong reductants (such as ascorbate) in the food increased the V(V) component in gastrointestinal digestion products. These results can be used to predict the oral bioavailability of various types of V(V/IV) anti-diabetics, and the effects of taking such drugs with food.

Speciation of copper in a range of food types by X-ray absorption spectroscopy

Copper (Cu) is an essential element and the effects of diets deficient in it are well established. However, the effects of long-term high copper intake are less clear. The chemical form of copper from food sources and its resultant bioavailability is a potentially important factor in its biological activity. X-ray Absorption Near-Edge Structure (XANES) was used to determine the chemical forms of Cu in a range of foods that would make significant contributions to total copper absorption in a standard diet, as well as a chlorinated tap water sample. Analysis of the Cu K-edge XANES spectra suggested that Cu existed in both Cu(I) and Cu(II) forms, with the following five model compounds: Cu(I) acetate; Cu(II) acetate; Cu(I)-glutathione; Cu(I)-cysteine; and, Cu(II)-histidine being fitted to the sample spectra. This research suggested that the absorption of dietary copper could vary markedly dependent on the types of food consumed and the different bioavailability of the Cu species they contain.

Parkinson's disease-linked human PARK9/ATP13A2 maintains zinc homeostasis and promotes α-Synuclein externalization via exosomes

α-Synuclein plays a central causative role in Parkinson's disease (PD). Increased expression of the P-type ATPase ion pump PARK9/ATP13A2 suppresses α-Synuclein toxicity in primary neurons. Our data indicate that ATP13A2 encodes a zinc pump; neurospheres from a compound heterozygous ATP13A2(-/-) patient and ATP13A2 knockdown cells are sensitive to zinc, whereas ATP13A2 over-expression in primary neurons confers zinc resistance. Reduced ATP13A2 expression significantly decreased vesicular zinc levels, indicating ATP13A2 facilitates transport of zinc into membrane-bound compartments or vesicles. Endogenous ATP13A2 localized to multi-vesicular bodies (MVBs), a late endosomal compartment located at the convergence point of the endosomal and autophagic pathways. Dysfunction in MVBs can cause a range of detrimental effects including lysosomal dysfunction and impaired delivery of endocytosed proteins/autophagy cargo to the lysosome, both of which have been observed in cells with reduced ATP13A2 function. MVBs also serve as the source of intra-luminal nanovesicles released extracellularly as exosomes that can contain a range of cargoes including α-Synuclein. Elevated ATP13A2 expression reduced intracellular α-Synuclein levels and increased α-Synuclein externalization in exosomes >3-fold whereas ATP13A2 knockdown decreased α-Synuclein externalization. An increased export of exosome-associated α-Synuclein may explain why surviving neurons of the substantia nigra pars compacta in sporadic PD patients were observed to over-express ATP13A2. We propose ATP13A2's modulation of zinc levels in MVBs can regulate the biogenesis of exosomes capable of containing α-Synuclein. Our data indicate that ATP13A2 is the first PD-associated gene involved in exosome biogenesis and indicates a potential neuroprotective role of exosomes in PD.

XAS and XFM studies of selenium and copper speciation and distribution in the kidneys of selenite-supplemented rats

Se and Cu were colocalised in the kidneys of selenite-fed rats, but there was no evidence of Se–Cu bonding.

High mitochondrial accumulation of new gadolinium(III) agents within tumour cells

The first bifunctional Gd(III) complexes covalently bound to arylphosphonium cations and the first tumour-cell selective mitochondrial agents designed for potential application in binary cancer therapies are reported. The highest in vitro cellular uptake for any Gd complex reported to date is described, with levels exceeding 10(10) Gd atoms per tumour cell.

X-ray fluorescence imaging of single human cancer cells reveals that the N-heterocyclic ligands of iodinated analogues of ruthenium anticancer drugs remain coordinated after cellular uptake

Analogues of KP1019 containing iodinated indazole ligands were prepared to investigate the biological fate of the Ru-N-heterocycle bond in this class of anticancer agents. The new complexes, 5-iodoindazolium trans-tetrachloridobis(5-iodoindazole)ruthen(III)ate (1) and 5-iodoindazolium trans-tetrachlorido(dimethyl sulfoxide)(5-iodoindazole)ruthen(III)ate (3), were characterized by elemental analysis, mass spectrometry and UV-vis spectrophotometry. Tetramethylammonium salts of these complexes (2 and 4) were synthesized and characterized in a similar manner. Half-maximum inhibitory concentrations of 2 and 4 with regard to A549 cells at 24 h were determined on the basis of the dose-response curves derived from real-time cell adhesion impedance measurements and were shown to be in the same range as those determined for KP1019 and NAMI-A using the same method. X-ray fluorescence imaging of single cultured A549 cells treated with 2 or 4 showed that, in both cases, the distribution of ruthenium and iodine was identical, indicating that the Ru-N bonds in the anionic complexes remained intact after incubation in culture medium and subsequent cellular uptake and processing.

Selenium metabolism in cancer cells: the combined application of XAS and XFM techniques to the problem of selenium speciation in biological systems

Determining the speciation of selenium in vivo is crucial to understanding the biological activity of this essential element, which is a popular dietary supplement due to its anti-cancer properties. Hyphenated techniques that combine separation and detection methods are traditionally and effectively used in selenium speciation analysis, but require extensive sample preparation that may affect speciation. Synchrotron-based X-ray absorption and fluorescence techniques offer an alternative approach to selenium speciation analysis that requires minimal sample preparation. We present a brief summary of some key HPLC-ICP-MS and ESI-MS/MS studies of the speciation of selenium in cells and rat tissues. We review the results of a top-down approach to selenium speciation in human lung cancer cells that aims to link the speciation and distribution of selenium to its biological activity using a combination of X-ray absorption spectroscopy (XAS) and X-ray fluorescence microscopy (XFM). The results of this approach highlight the distinct fates of selenomethionine, methylselenocysteine and selenite in terms of their speciation and distribution within cells: organic selenium metabolites were widely distributed throughout the cells, whereas inorganic selenium metabolites were compartmentalized and associated with copper. New data from the XFM mapping of electrophoretically-separated cell lysates show the distribution of selenium in the proteins of selenomethionine-treated cells. Future applications of this top-down approach are discussed.

Synchrotron X-ray fluorescence studies of a bromine-labelled cyclic RGD peptide interacting with individual tumor cells

The first example of synchrotron X-ray fluorescence imaging of cultured mammalian cells in cyclic peptide research is reported. The study reports the first quantitative analysis of the incorporation of a bromine-labelled cyclic RGD peptide and its effects on the biodistribution of endogenous elements (for example, K and Cl) within individual tumor cells.

Selenium inhibits renal oxidation and inflammation but not acute kidney injury in an animal model of rhabdomyolysis

Acute kidney injury (AKI) is a manifestation of rhabdomyolysis (RM). Extracellular myoglobin accumulating in the kidney after RM promotes oxidative damage, which is implicated in AKI.

AIM

To test whether selenium (Se) supplementation diminishes AKI and improves renal function.

RESULTS

Dietary selenite increased Se in the renal cortex, as demonstrated by X-ray fluorescence microscopy. Experimental RM-stimulated AKI as judged by increased urinary protein/creatinine, clusterin, and kidney injury molecule-1 (KIM-1), decreased creatinine clearance (CCr), increased plasma urea, and damage to renal tubules. Concentrations of cholesterylester (hydro)peroxides and F₂-isoprostanes increased in plasma and renal tissues after RM, while aortic and renal cyclic guanidine monophosphate (cGMP; marker of nitric oxide (NO) bioavailability) decreased. Renal superoxide dismutase-1, phospho-P65, TNFα gene, MCP-1 protein, and the 3-chloro-tyrosine/tyrosine ratio (Cl-Tyr/Tyr; marker of neutrophil activation) all increased after RM. Dietary Se significantly decreased renal lipid oxidation, phospho-P65, TNFα gene expression, MCP-1 and Cl-Tyr/Tyr, improved NO bioavailability in aorta but not in the renal microvasculature, and inhibited proteinuria. However, CCr, plasma urea and creatinine, urinary clusterin, and histopathological assessment of AKI remained unchanged. Except for the Se++ group, renal angiotensin-receptor-1/2 gene/protein expression increased after RM with parallel increases in MEK1/2 inhibitor-sensitive MAPkinase (ERK) activity.

INNOVATION

We employed synchrotron radiation to identify Se distribution in kidneys, in addition to assessing reno-protection after RM.

CONCLUSION

Se treatment has some potential as a therapeutic for AKI as it inhibits oxidative damage and inflammation and decreases proteinuria, albeit histopathological changes to the kidney and some plasma and urinary markers of AKI remain unaffected after RM.

Biotransformations of anticancer ruthenium(III) complexes: an X-ray absorption spectroscopic study

An anti-metastatic drug, NAMI-A ((ImH)[Ru(III) Cl4 (Im)(dmso)]; Im=imidazole, dmso=S-bound dimethylsulfoxide), and a cytotoxic drug, KP1019 ((IndH)[Ru(III) Cl4 (Ind)2 ]; Ind=indazole), are two Ru-based anticancer drugs in human clinical trials. Their reactivities under biologically relevant conditions, including aqueous buffers, protein solutions or gels (e.g, albumin, transferrin and collagen), undiluted blood serum, cell-culture medium and human liver (HepG2) cancer cells, were studied by Ru K-edge X-ray absorption spectroscopy (XAS). These XAS data were fitted from linear combinations of spectra of well-characterised Ru compounds. The absence of XAS data from the parent drugs in these fits points to profound changes in the coordination environments of Ru(III) . The fits point to the presence of Ru(IV/III) clusters and binding of Ru(III) to S-donor groups, amine/imine and carboxylato groups of proteins. Cellular uptake of KP1019 is approximately 20-fold higher than that of NAMI-A under the same conditions, but it diminishes drastically after the decomposition of KP1019 in cell-culture media, which indicate that the parent complex is taken in by cells through passive diffusion.

X-ray-induced photo-chemistry and X-ray absorption spectroscopy of biological samples

As synchrotron light sources and optics deliver greater photon flux on samples, X-ray-induced photo-chemistry is increasingly encountered in X-ray absorption spectroscopy (XAS) experiments. The resulting problems are particularly pronounced for biological XAS experiments. This is because biological samples are very often quite dilute and therefore require signal averaging to achieve adequate signal-to-noise ratios, with correspondingly greater exposures to the X-ray beam. This paper reviews the origins of photo-reduction and photo-oxidation, the impact that they can have on active site structure, and the methods that can be used to provide relief from X-ray-induced photo-chemical artifacts.

A two-step valence tautomeric transition in a dinuclear cobalt complex

A dinuclear cobalt complex with cobalt centers bridged by a bis(dioxolene) ligand exhibits a rare two-step valence tautomeric transition.

Methylselenocysteine treatment leads to diselenide formation in human cancer cells: evidence from X-ray absorption spectroscopy studies

The selenoamino acids methylselenocysteine (MeSeCys) and selenomethionine (SeMet) have disparate efficacies as anticancer agents. Herein, we use X-ray absorption spectroscopy to determine the chemical form of selenium in human neuroblastoma cells. Cells treated with MeSeCys contain a significant diselenide component, which is absent from SeMet-treated cells and suggests that metabolites of MeSeCys are capable of altering the redox status of the cells. The differences in the speciation of Se in the selenoamino acid-treated cells may provide insight into the differing anticancer activities of MeSeCys and SeMet.

Metabolism of selenite in human lung cancer cells: X-ray absorption and fluorescence studies

Selenite is an inorganic form of selenium that has a cytotoxic effect against several human cancer cell lines: one or more selenite metabolites are considered to be responsible for its toxicity. X-ray absorption spectroscopy was used to monitor Se speciation in A549 human lung cancer cells incubated with selenite over 72 h. As anticipated, selenodiglutathione and elemental Se both comprised a large proportion of Se in the cells between 4 and 72 h after treatment, which is in accordance with the reductive metabolism of selenite in the presence of glutathione and glutathione reductase/NADPH system. Selenocystine was also present in the cells but was only detected as a significant component between 24 and 48 h concomitant with a decrease in the proportion of selenocysteine and the viability of the cells. The change in speciation from the selenol, selenocysteine, to the diselenide, selenocystine, is indicative of a change in the redox status of the cells to a more oxidizing environment, likely brought about by metabolites of selenite. X-ray fluorescence microscopy of single cells treated with selenite for 24 h revealed a punctate distribution of Se in the cytoplasm. The accumulation of Se was associated with a greater than 2-fold increase in Cu, which was colocalized with Se. Selenium K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy revealed Se-Se and Se-S bonding, but not Se-Cu bonding, despite the spatial association of Se and Cu. Microprobe X-ray absorption near-edge structure spectroscopy (μ-XANES) showed that the highly localized Se species was mostly elemental Se.

Studies of glutathione transferase P1-1 bound to a platinum(IV)-based anticancer compound reveal the molecular basis of its activation

Platinum-based cancer drugs, such as cisplatin, are highly effective chemotherapeutic agents used extensively for the treatment of solid tumors. However, their effectiveness is limited by drug resistance, which, in some cancers, has been associated with an overexpression of pi class glutathione S-transferase (GST P1-1), an important enzyme in the mercapturic acid detoxification pathway. Ethacraplatin (EA-CPT), a trans-Pt(IV) carboxylate complex containing ethacrynate ligands, was designed as a platinum cancer metallodrug that could also target cytosolic GST enzymes. We previously reported that EA-CPT was an excellent inhibitor of GST activity in live mammalian cells compared to either cisplatin or ethacrynic acid. In order to understand the nature of the drug-protein interactions between EA-CPT and GST P1-1, and to obtain mechanistic insights at a molecular level, structural and biochemical investigations were carried out, supported by molecular modeling analysis using quantum mechanical/molecular mechanical methods. The results suggest that EA-CPT preferentially docks at the dimer interface at GST P1-1 and subsequent interaction with the enzyme resulted in docking of the ethacrynate ligands at both active sites (in the H-sites), with the Pt moiety remaining bound at the dimer interface. The activation of the inhibitor by its target enzyme and covalent binding accounts for the strong and irreversible inhibition of enzymatic activity by the platinum complex.

Uptake and Distribution of a Platinum(II)-Carborane Complex Within a Tumour Cell Using Synchrotron XRF Imaging

Treatment of A549 human lung carcinoma cells with a DNA metallointercalator complex containing a PtII-terpy (terpy = 2,2′:6′,2′′-terpyridine) unit linked to a functionalized closo-carborane cage results in the uptake of the complex within the cells, as determined by synchrotron X-ray fluorescence (XRF) imaging. Although a significant cellular uptake of Pt existed, there was no significant accumulation of the element within the cell nuclei. Other statistically significant changes from the XRF data included an increase in Cl, K, and Cu and a decrease in Fe within the treated cells.

The Endothelium-Derived Hyperpolarizing Factor, H2O2, Promotes Metal-Ion Efflux in Aortic Endothelial Cells: Elemental Mapping by a Hard X-ray Microprobe

Hydrogen peroxide (H(2)O(2)) is a physiologic oxidant implicated in vascular cell signaling, although little is known about the biochemical consequences of its reaction with endothelial cells. Submicrometer-resolution hard X-ray elemental mapping of cultured porcine aortic endothelial cells (PAEC) has provided data on the global changes for intracellular elemental density within PAEC and indicates an efflux of metal ions and phosphorus from the cytoplasm after H(2)O(2) treatment. The synchrotron-radiation-induced X-ray emission experiments (SRIXE) show that H(2)O(2)-treated cells are irregularly shaped and exhibit blebbing indicative of increased permeability due to the damaged membrane. The SRIXE results suggest that H(2)O(2)-induced damage is largely restricted to the cell membrane as judged by the changes to membrane and cytoplasmic components rather than the cell nucleus. The SRIXE data also provide a mechanism for cell detoxification as the metal-ion efflux resulting from the initial H(2)O(2)-mediated changes to cell membrane potentially limits intracellular metal-mediated redox processes through Fenton-like chemistry. They may also explain the increased levels of these ions in atherosclerotic plaques, regardless of whether they are involved in plaque formation. Finally, the SRIXE data support the notion that cultured endothelial cells exposed to H(2)O(2) respond with enhanced cellular metal-ion efflux into the extracellular space.

Bonding in HNO-Myoglobin as Characterized by X-ray Absorption and Resonance Raman Spectroscopies

The EXAFS and resonance Raman spectra on the HNO-myoglobin adduct, 1, are consistent with the presence of HNO bound to a heme center. The three-dimensional structure about the heme center of 1 obtained from multiple-scattering (MS) analysis of the EXAFS of the heme protein yielded an Fe-N-O bond angle of 131 degrees and an Fe-N bond length of 1.82 A, which compare well with published values for model complexes containing RNO ligands. Resonance Raman spectra identified the nu(N=O) stretch at 1385 cm-1 (confirmed by 15N labeling), which corresponds well with those reported for small molecule HNO complexes. The wavelength of the nu(Fe-N) at 636 cm-1 of 1 is significantly higher than those of MbIINO and MbIIINO (554 and 595 cm-1, respectively). The XAFS, XANES, and resonance Raman data are all consistent with the structure deduced from the NMR experiments, providing more detail on the bonding between HNO and the metal center.

Determination of the nature of the heme environment in nitrosyl indoleamine 2,3-dioxygenase using Multiple-scattering analyses of X-ray absorption fine structure

Multiple-scattering analysis of X-ray absorption fine structure data on the NO adducts of indoleamine 2,3-dioxygenase (IDO) and analysis of X-ray absorption near-edge structure (XANES) have provided the first direct structural information about the iron center for this ubiquitous mammalian metalloprotein. The IDO(II)NO adduct, which is likely to play a physiological role in the immune system, differs from similar adducts such as Mb(II)NO and Lb(II)NO in that the Fe-His bond is essentially broken. At 10 K, the Fe-N(p)(av) bond length = 2.00(2) A, Fe-NO bond length = 1.75 A, and angle = 140 degrees, which are typical of five-coordinate Fe(II)NO species. The XANES is also closer to that of five-coordinate model complexes than six-coordinate species. In addition to the Fe(II)NO species, there was a minor component of the Fe(III)NO adduct because of incomplete reduction of the Fe(II) species. This was also a five-coordinate center and consists of a linear Fe(II)NO(+) moiety with the Fe-N(p)(av) bond length = 2.00(2) A, Fe-NO bond length = 1.63(3) A, and angle = 179 degrees. The results indicate that both the blocking of the heme site to O(2) binding and conformational changes induced by breaking the Fe-N(epsilon) bond may be important mechanisms by which NO inhibits IDO in vitro and in vivo.

Additional Hosts for the Ring Nematode, Criconemella xenoplax

Some common legumes and weeds indigenous to peach orchards in South Carolina were tested in greenhouse experiments to determine their host suitability for Criconemella xenoplax. Legumes that were hosts for the nematode were dwarf English trefoil (Lotus corniculatus var. arvensis), big trefoil (L. uliginosis), birdsfoot trefoil (L. corniculatus), narrowleaf birdsfoot trefoil (L. tenuis), ball clover (Trifolium nigrescens), rose clover (T. hirtum), subterranean clover (T. subterraneum), striate lespedeza (Lespedeza striata), and partridge pea (Cassiafasciculata). Most nonleguminous plants tested did not support population increases, but small increases were observed on orchardgrass (Dactylis glomerata), broadleaf signalgrass (Brachiaria platyphylla), purslane (Portulaca oleracea), and Carolina geranium (Geranium carolinianum). Results indicate that leguminous plants probably should not be used as ground cover or rotation crops for plants that are injured by C. xenopax.