Manganese ion interaction with glutamine synthetase from Escherichia coli: kinetic and equilibrium studies with xylenol orange and pyridine-2,6-dicarboxylic acid

Molecular and Nano-Structural Optimization of Nanoparticulate Mn2+-Hexarhenium Cluster Complexes for Optimal Balance of High T1- and T2-Weighted Contrast Ability with Low Hemoagglutination and Cytotoxicity

The present work introduces rational design of nanoparticulate Mn(II)-based contrast agents through both variation of the μ₃ (inner) ligands within a series of hexarhenium cluster complexes [{Re₆(μ₃-Q)₈}(CN)₆]⁴⁻ (Re₆Q₈, Q = S²⁻, Se²⁻ or Te²⁻) and interfacial decoration of the nanoparticles (NPs) K_4−2xMn_xRe₆Q₈ (x = 1.3 − 1.8) by a series of pluronics (F-68, P-123, F-127). The results highlight an impact of the ligand and pluronic for the optimal colloid behavior of the NPs allowing high colloid stability in ambient conditions and efficient phase separation under the centrifugation. It has been revealed that the K_4−2xMn_xRe₆Se₈ NPs and those decorated by F-127 are optimal from the viewpoint of magnetic relaxivities r₁ and r₂ (8.9 and 10.9 mM⁻¹s⁻¹, respectively, at 0.47 T) and low hemoagglutination activity. The insignificant leaching of Mn²⁺ ions from the NPs correlates with their insignificant effect on the cell viability of both M-HeLa and Chang Liver cell lines. The T₁- and T₂-weighted contrast ability of F-127–K_4−2xMn_xRe₆Q₈ NPs was demonstrated through the measurements of phantoms at whole body 1.5 T scanner.

From the Cover: Manganese Stimulates Mitochondrial H2O2 Production in SH-SY5Y Human Neuroblastoma Cells Over Physiologic as well as Toxicologic Range

Manganese (Mn) is an abundant redox-active metal with well-characterized mitochondrial accumulation and neurotoxicity due to excessive exposures. Mn is also an essential co-factor for the mitochondrial antioxidant protein, superoxide dismutase-2 (SOD2), and the range for adequate intake established by the Institute of Medicine Food and Nutrition Board is 20% of the interim guidance value for toxicity by the Agency for Toxic Substances and Disease Registry, leaving little margin for safety. To study toxic mechanisms over this critical dose range, we treated human neuroblastoma SH-SY5Y cells with a series of MnCl₂ concentrations (from 0 to 100 μM) and measured cellular content to compare to human brain Mn content. Concentrations ≤10 μM gave cellular concentrations comparable to literature values for normal human brain, whereas concentrations ≥50 μM resulted in values comparable to brains from individuals with toxic Mn exposures. Cellular oxygen consumption rate increased as a function of Mn up to 10 μM and decreased with Mn dose ≥50 μM. Over this range, Mn had no effect on superoxide production as measured by aconitase activity or MitoSOX but increased H₂O₂ production as measured by MitoPY1. Consistent with increased production of H₂O₂, SOD2 activity, and steady-state oxidation of total thiol increased with increasing Mn. These findings have important implications for Mn toxicity by re-directing attention from superoxide anion radical to H₂O₂-dependent mechanisms and to investigation over the entire physiologic range to toxicologic range. Additionally, the results show that controlled Mn exposure provides a useful cell manipulation for toxicological studies of mitochondrial H₂O₂ signaling.

Isolation of dipicolinic acid as an insecticidal toxin from Paecilomyces fumosoroseus

Several entomopathogenic fungi produce toxins that could be used as bioinsecticides in integrated pest management programs. Paecilomyces fumosoroseus is currently used for the biological control of the whiteflies Bemisia tabaci and B. argentifolii. Supernatants from submerged batch culture, where the fungus produced abundant dispersed mycelium, conidia and blastospores, were toxic to the whitefly nymphs. The most abundant metabolite was purified by HPLC and identified by mass spectrometry and NMR as dipicolinic acid. Both the dipicolinic acid produced by the fungus and the chemically synthesized compound had insecticidal activity against third-instar nymphs of the insect. Dipicolinic acid was toxic to the whitefly nymphs in bioassays involving topical applications. In submerged culture, the specific growth rate of P. fumosoroseus was 0.054 h-1, the specific glucose consumption rate was 0.1195 g g-1 h-1 and the specific dipicolinic acid production rate was 0.00012 g g-1 h-1. Dipicolinic acid was detected after 24 h when the fungus started growing; and dipicolinic acid production was directly correlated with fungal growth. Nevertheless, the yield was low and the maximal concentration was only 0.041 g l-1. The maximal concentrations of conidia and blastospores (per milliliter) were 1.4x10(8) and 7x10(7), respectively.

Thiobarbituric acid-reactive malondialdehyde formation during superoxide-dependent, iron-catalyzed lipid peroxidation: influence of peroxidation conditions

A systematic study of the influence of biological lipid peroxidation conditions on lipid hydroperoxide decomposition to thiobarbituric acid-reactive malondialdehyde is presented. A superoxide-dependent, iron-catalyzed peroxidation system was employed with xanthine oxidase plus hypoxanthine plus ferric iron-adenosine diphosphate complex as free radical generator. Purified cardiac membrane phospholipid (as liposomes) was the peroxidative target, and 15-hydroperoxy-eicosatetraenoic acid was used as a standard lipid hydroperoxide. Exposure of myocardial phospholipid to free radical generator at physiological pH (7.4) and temperature (37 degrees C) was found to support not only phospholipid peroxidation, but also rapid lipid hydroperoxide breakdown and consequent malondialdehyde formation during peroxidation. Under lipid peroxidation conditions, oxidative injury to the phospholipid polyunsaturated fatty acids required superoxide radical and ferric iron-adenosine diphosphate complex, whereas 37 degrees C temperature and trace iron were sufficient for lipid hydroperoxide decomposition to malondialdehyde. Harsh thiobarbituric acid-test conditions following peroxidation were not mandatory for either lipid hydroperoxide breakdown or thiobarbituric acid-reactive malondialdehyde formation. However, hydroperoxide decomposition that had begun in the peroxidation reaction could be completed during a subsequent thiobarbituric acid test in which no lipid autoxidation took place. Iron was more critical than heat in promoting the observed hydroperoxide decomposition to malondialdehyde during the lipid peroxidation reaction at 37 degrees C and pH 7.4. These data demonstrate that the radical generator, at physiological pH and temperature, serves a dual role as both initiator of membrane phospholipid peroxidation and promotor of lipid peroxide breakdown and thiobarbituric acid-reactive malondialdehyde formation.(ABSTRACT TRUNCATED AT 250 WORDS)