Comparison of the cytotoxic,pro-oxidant and pro-inflammatory characteristics of different oxysterols

Oxidized low-density lipoproteins play important roles in the development of atherosclerosis and contain several lipid-derived, bioactive molecules which are believed to contribute to atherogenesis. Of these, some cholesterol oxidation products, refered to as oxysterols, are suspected to favor the formation of atherosclerotic plaques involving cytotoxic, pro-oxidant and pro-inflammatory processes. Ten commonly occurring oxysterols (7α-, 7β-hydroxycholesterol, 7-ketocholesterol, 19-hydroxycholesterol, cholesterol-5α,6α-epoxide, cholesterol-5β,6β-epoxide, 22R-, 22S-, 25-, and 27-hydroxycholesterol) were studied for both their cytotoxicity and their ability to induce superoxide anion production (O₂^{⋅ −}) and IL-8 secretion in U937 human promonocytic leukemia cells. Cytotoxic effects (phosphatidylserine externalization, loss of mitochondrial potential, increased permeability to propidium iodide, and occurrence of cells with swollen, fragmented and/or condensed nuclei) were only identified with 7β-hydroxycholesterol, 7-ketocholesterol and cholesterol-5β,6β-epoxide, which also induce lysosomal destabilization associated or not associated with the formation of monodansylcadaverine-positive cytoplasmic structures. No relationship between oxysterol-induced cytotoxicity and HMG-CoA reductase activity was found. In addition, the highest O₂^{⋅ −} overproduction quantified with hydroethidine was identified with 7β-hydroxycholesterol, 7-ketocholesterol and cholesterol-5β,6β-epoxide, with cholesterol-5α, 6α-epoxide and 25-hydroxycholesterol. The highest capacity to simultaneously stimulate IL-8 secretion (quantified by ELISA and by using a multiplexed, particle-based flow cytometric assay) and enhance IL-8 mRNA levels (determined by RT-PCR) was observed with 7β-hydroxycholesterol and 25-hydroxycholesterol. None of the effects observed for the oxysterols were detected for cholesterol. Therefore, oxysterols may have cytotoxic, oxidative, and/or inflammatory effects, or none whatsoever.     

Reactive oxygen species induce signals that lead to apoptotic DNA degradation in primary CD4+ T cells

Reactive oxygen species are toxic to cells but they may also have active roles in transducing apoptotic events. To study the role of reactive oxygen species in growth factor depletion induced apoptosis of human primary CD4+ T cells, we used a synthetic manganese porphyrin superoxide dismutase mimetic to detoxify superoxide anions formed during apoptosis. Apoptosis of primary CD4+ T cells was characterized by generation of superoxide anions, plasma membrane phosphatidyl-serine translocation, loss of mitochondrial membrane potential, activation of caspase 3, condensation of chromatin, as well as DNA degradation. The detoxification of superoxide anions did not influence plasma membrane phosphatidyl-serine translocation, or chromatin condensation, and only marginally inhibited the loss of mitochondrial membrane potential and the formation of DNA strand breaks. In contrast, the detoxification of superoxide anions significantly reduced caspase 3 activity and almost completely inhibited the apoptotic decrease in total cellular DNA content as measured by propidium iodide staining. Our results indicate that reactive oxygen anions induce signals leading to efficient DNA degradation after the initial formation of DNA strand breaks. Thus, reactive oxygen anions have active roles in signaling that lead to the apoptotic events.     

Structural basis of alpha-amylase activation by chloride

To further investigate the mechanism and function of allosteric activation by chloride in some alpha-amylases, the structure of the bacterial alpha-amylase from the psychrophilic micro-organism Pseudoalteromonas haloplanktis in complex with nitrate has been solved at 2.1 A degrees, as well as the structure of the mutants Lys300Gln (2.5 A degrees ) and Lys300Arg (2.25 A degrees ). Nitrate binds strongly to alpha-amylase but is a weak activator. Mutation of the critical chloride ligand Lys300 into Gln results in a chloride-independent enzyme, whereas the mutation into Arg mimics the binding site as is found in animal alpha-amylases with, however, a lower affinity for chloride. These structures reveal that the triangular conformation of the chloride ligands and the nearly equatorial coordination allow the perfect accommodation of planar trigonal monovalent anions such as NO3-, explaining their unusual strong binding. It is also shown that a localized negative charge such as that of Cl-, rather than a delocalized charge as in the case of nitrate, is essential for maximal activation. The chloride-free mutant Lys300Gln indicates that chloride is not mandatory for the catalytic mechanism but strongly increases the reactivity at the active site. Disappearance of the putative catalytic water molecule in this weakly active mutant supports the view that chloride helps to polarize the hydrolytic water molecule and enhances the rate of the second step in the catalytic reaction.     

Effects of potassium on the anion and cation contents of primary cultures of mouse astrocytes and neurons

Inastrocytes, as [K⁺]_o was increased from 1.2 to 10 mM, [K⁺]_i and [Cl^–]_i were increased, whereas [Na⁺]_i was decreased. As [K⁺]_o was increased from 10 to 60 mM, intracellular concentration of these three ions showed no significant change. When [K⁺]_o was increased from 60 to 122 mM, an increase in [K⁺]_i and [Cl^–]_i and a decrease in [Na⁺]_i were observed.Inneurons, as [K⁺]_o was increased from 1.2 to 2.8 mM, [Na⁺]_i and [Cl^–]_i were decreased, whereas [K⁺]_i was increased. As [K⁺]_o was increased from 2.8 to 30 mM, [K⁺]_i, [Na⁺]_i and [Cl^–]_i showed no significant change. When [K⁺]_o was increased from 30 to 122 mM, [K⁺]_i and [Cl^–]_i were increased, whereas [Na⁺]_i was decreased. Inastrocytes, pH_i increased when [K⁺]_o was increased. Inneurons, there was a biphasic change in pH_i. In lower [K⁺]_o (1.2–2.8 mM) pH_i decreased as [K⁺]_o increased, whereas in higher [K⁺]_o (2.8–122 mM) pH_i was directly related to [K⁺]_o. In bothastrocytes andneurons, changes in [K⁺]_o did not affect the extracellular water content, whereas the intracellular water content increased as the [K⁺]_o increased. Transmembrane potential (E_m) as measured with Tl-204 was inversely related to [K⁺]_o between 1.2 and 90 mM, a ten-fold increase in [K⁺]_o depolarized the astrocytes by about 56 mV and the neurons about 52 mV. The E_m values measured with Tl-204 were close to the potassium equilibrium potential (E_k) except those in neurons at lower [K⁺]_o. However, they were not equal to the chloride equilibrium potential (E_Cl) at [K⁺]_o lower than 30 mM in both astrocytes and neurons. Results of this study demonstrate that alteration of [K⁺]_o produced different changes in [K⁺]_i, [Na⁺]_i, [Cl^–]_i, and pH_i in astrocytes and neurons. The data show that astrocytes can adapt to alterations in [K⁺]_o, in such a way to maintain a more suitable environment for neurons.     

Potassium channel in rabbit corneal endothelium activated by external anions

Summary The apical membrane of the rabbit corneal endothelium contains a potassium-selective ionic channel. In patch-clamp recordings, the probability of finding the channel in the open state (P _o) depends on the presence of either HCO ₃ ^– or Cl^– in the bathing medium. In a methane sulfonate-containing bath,P _o is <0.05 at all physiologically relevant transmembrane voltages. With 0mm [HCO ₃ ^– ] _o at +60 mV,P _o was 0.085 and increased to 0.40 when [HCO ₃ ^– ] _o was 15mm. With 4mm [Cl^–] _o at +60 mV,P _o was 0.083 and with 150mm Cl^–,P _o increased to 0.36. LowP _o's are also found when propionate, sulphate, bromide, and nitrate are the primary bath anions. The mechanism of action of the anion-stimulated K⁺ channel gating is not yet known, but a direct action of pH seems unlikely. The alkalinization of cytoplasm associated with the addition of 10mm (NH₄)₂SO₄ to the bath and the acidification accompanying its removal do not result in channel activation nor does the use of Nigericin to equilibrate intracellular pH with that of the bath over the pH range of 6.8 to 7.8. Channel gating also is not affected by bathing the internal surface of the patch with cAMP, cGMP, GTP--s, Mg²⁺ or ATP. Blockers of Na/H⁺ exchange, Na⁺–HCO ₃ ^– cotransport, Na⁺–K⁺ ATPase and carbonic anhydrase do not block the HCO ₃ ^– stimulation ofP _o. Several of the properties of the channel could explain some of the previously reported voltage changes that occur in corneal endothelial cells stimulated by extracellular anions.     

Induction of Encystment in Acanthamoeba palestinensis. Factors Influencing Cyst Formation

SYNOPSIS. The effect of osmotic pressure, different electrolytes and organic compounds on cyst formation in Acanthamoeba palestinensis has been tested. The optimal osmolarity for encystment was similar to that of the growth medium. Iso-osmotic solutions of NaCl, KCl, MgCl₂, CaCl₂, glycine and sucrose led to maximum cyst formation. The involvement of various agents in the induction of encystment is discussed.     

An Ion-Permeable State of the Glycine Receptor Captured by Molecular Dynamics

1. Download high-res image (297KB)
2. Download full-size image

     

River and lake sediments as sources of infective Frankia (Alnus)

Exudation of carboxylic anions and protons by plant roots plays an important role in mobilizing soil P under P-deficiency conditions. The objective of this work was to quantify short-term (6 h) carboxylate and H⁺ exudation by tomato roots in response to P concentration (0, 0.1, 0.5 and 1.0 mt M P) in nutrient solution (C_p). The exudation rate of tri- and dicarboxylates decreased exponentially with increasing C_p, from 0.3 to 0.03 mol plant^–1 6h^–1. At low C_p the predominant exudates were fumarate, citrate and succinate, while at C_p=0.5 and 1.0 mt M the prevalent anions were succinate and citrate. The solution pH declined sharply as C_p was lowered from 0.1 (pH=4.2) to 0 mt M P (pH=3.7).     

Salinity and dissolved substances in the Vaal River at Balkfontein,South Africa

Seasonal variation and interrelationships between environmental variables and salinity in the Vaal River at Balkfontein were investigated between 1985 and 1989. The salinity levels were high (min. 108, max. 1032, average 512 mg 1^-1), and indications are that salinisation of the river water is continuing at a rate of 15 mg 1^t-1 a^-1. The concentration of major ions (mg 1^-1 or meq 1^-1) in the river water occurred in the proportions of cations, i.e. Ca²⁺ Na⁺ > Mg²⁺ > K⁺ and of anions, i.e. SO₄ ^2- > HCO₃ ^- > Cl^-. The high S0₄ concentration (average 212 mg 1^-1) indicated SO₄ pollution at Balkfontein. High Ca concentrations (average 59 mg 1^-1) evidently interfered with the solubility of phosphate (PO₄) which could play an important role in the availability of PO₄ to phytoplankton in the system. Measured electrical conductivity (EC) values can be used to estimate salinity (S, in mg 1^-1) in the Vaal River, i.e. e. S = 7.13 * EC - 27.8 (from regression analysis) or S = 6.72 * EC (from TDS:EC ratio). Salinity in the river tends to be higher during the dry season, i.e. winter months. All the dissolved ions (except Si) showed decreased concentrations with increased run-off. The main importance of the high salinity in the Vaal River is evidently its influence on turbidity and the possible clarification of the water-column, which results in a deeper euphotic zone and thus more favourable conditions for photosynthesis followed by a biomass build-up of phytoplankton.     

The effect of neutral salt anions on the oxidative deamination activity of plant glutamate dehydrogenase

Increasing concentrations of anions of the Hofmeister series decrease the activity of highly purified glutamate dehydrogenase (EC 1.4.1.2.) from Pisum sativum L. The extent of the inactivation, as estimated by the ion concentration which causes a 50% transformation of the native form to the low activity form of the enzyme (approximately halfmaximal activity), follows the ranking Cl^–––3 ^– –. Sulfate has a slightly activating effect. At salt concentrations higher than 1 M (with SCN^– higher than 200 mM), the activity decreases to a value from 3–6% of the initial activity and remains then stable over a wide range of higher anion concentrations. From kinetic investigations it is seen that the treatment of the enzyme with anions decreases the affinity for the cosubstrate NAD⁺ and the substrate L-glutamate (K _M-values increased) and also increases the dissociation constant for NAD⁺. The salt induced inactivation is reversible by dilution. From a mathematical treatment of the kinetic data of the inactivation, it is seen that increasing concentrations of the anions exert cooperative effects on the inactivation process.