Interacting effects of atmospheric CO2 enrichment and solar radiation on growth of the aquatic fern Azolla filiculoides

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Membrane properties of oxysterols. Interfacial orientation, influence on membrane permeability and redistribution between membranes

The membrane properties of cholesterol auto-oxidation products, 7-ketocholesterol, 7 beta-hydroxycholesterol, 7 alpha-hydroxycholesterol and 25-hydroxycholesterol were examined. Monolayer studies show that these oxysterols are perpendicularly orientated at the interphase. Only 7 beta-hydroxycholesterol and 7 alpha-hydroxycholesterol are tilted at low surface pressures. In mixed monolayers with dioleoylphosphatidylcholine, 7-ketocholesterol, 7 beta-hydroxycholesterol and 7 alpha-hydroxycholesterol show a condensing effect in this order, although to a lesser extent that that observed for cholesterol. In liposomes these oxysterols also reduce glucose permeability and in the same order as their condensing effect. On the other hand 25-hydroxycholesterol shows no condensing effect in monomolecular layers whereas glucose permeability in liposomes is enormously increased. The permeability increase is already maximal at 2.5 mol% 25-hydroxycholesterol. Differential scanning calorimetry experiments reveal that all four oxysterols tested reduce the heat content of the gel----liquid-crystalline phase transition. It is concluded that 7-ketocholesterol, 7 beta-hydroxycholesterol and 7 alpha-hydroxycholesterol have a cholesterol like effect, although less efficient than cholesterol, whereas 25-hydroxycholesterol showing no condensing effect acts as a spacer molecule. Packing defects in the hydrophobic core of the bilayer due to the presence of the C-25 hydroxyl group are believed to cause the permeability increase. The transfer of radiolabelled (oxy)sterols from the monolayer to lipoproteins or vesicles in the subphase was studied. The transfer rate increases in the following order 7-ketocholesterol, 7 beta-hydroxycholesterol, 7 alpha-hydroxycholesterol, 25-hydroxycholesterol. The difference in rate between 7-ketocholesterol and 25-hydroxycholesterol is 20-fold. A higher rate of transfer is observed in the presence of high density lipoproteins and small unilamellar vesicles. A transfer rate for cholesterol is hardly measurable under these conditions. The transfer measured is consistent with the involvement of a water-soluble intermediate.     

The effect of a water-soluble tris-galactoside-terminated cholesterol derivative on the fate of low density lipoproteins and liposomes

A triantennary galactose-terminated cholesterol derivative, N-(tris(beta-D-galactopyranosyloxymethyl) methyl)-N alpha-(4-(5-cholesten-3 beta-yloxy)succinyl)glycinamide (Tris-Gal-Chol), which dissolves easily in water, was added to human low density lipoproteins (LDL) in varying quantities. Upon addition to LDL, Tris-Gal-Chol was immediately incorporated, and after intravenous injection into rats, the iodine-labeled apolipoprotein B radioactivity was readily associated with the liver. The incorporation of 5 or 13 micrograms of Tris-Gal-Chol into LDL (20 micrograms of protein) stimulates the parenchymal cell association of LDL 6- and 10-fold, respectively, at 10 min after injection. For non-parenchymal cells, the cell association is 60- and 70-fold stimulated, respectively. It can be calculated that non-parenchymal cells (mainly Kupffer cells) are for 80-90% responsible for the increased, galactose-mediated, interaction of Tris-Gal-Chol LDL with the liver. The increased interaction of LDL with the cells upon Tris-Gal-Chol incorporation is followed by degradation of the apolipoprotein B in the lysosomes. Incorporation of Tris-Gal-Chol into unilamellar liposomes (10 mol %) leads to an increased cell association of the enclosed [3H]inulin to parenchymal cells (1.4-fold) and non-parenchymal cells (11.8-fold). It is concluded that Tris-Gal-Chol incorporation into LDL leads to a markedly increased catabolism of LDL by the liver which might be used for lowering serum LDL levels. The possibility of increasing the interaction of LDL or liposomes with specific liver cell types by Tris-Gal-Chol might also have an application for targeting drugs or other compounds of interest to these cells.     

Identification of Two Protein-Signaling States Delineating Transcriptionally Heterogeneous Human Medulloblastoma

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Het meten van angst om te vallen met de Falls Efficacy Scale-International (FES-I). Achtergrond en psychometrische kenmerken

The assessment of fear of falling with the Falls Efficacy Scale-International (FES-I). Development and psychometric properties in Dutch elderly. Fear of falling is common in older persons. Different methods have been developed to assess fear of falling. The most well-know measure is the 10-item Falls Efficacy Scale (FES). However, the FES items (a) focus on low functioning older persons and particularly on in-home activities, (b) do not comprise social activities, and (c) were developed from a US perspective so that translation in European languages is hampered. To solve these issues, the 16-item Falls Efficacy Scale-International (FES-I) was recently developed within the Prevention of Falls Network Europe (ProFaNE). In this article, the Dutch version of the FES-I is presented and the psychometric properties in 213 Dutch persons aged 70 years of age and over are described. The FES-I showed to be unidimensional and internally consistent; the Cronbach alpha coefficient was 0.96. The 4 week test-retest intra-class correlation coefficient was 0.82. The associations of the FES-I sumscores with age, gender, falls history and overall fear of falling was as expected, indicating construct validity. In addition, the FES-I discriminated in the same extent as the original 10-item FES scale. We conclude that the FES-I showed acceptable reliability and construct validity and may be useful in cross-national research. Future studies should focus on the sensitivity to change of FES-I.Tijdschr Gerontol Geriatr 2007; 38: 204-212     

Feedback inhibition of bile acid synthesis in cultured pig hepatocytes

Bile acid synthesis by cultured pig hepatocytes, as measured by conversion of [14C]cholesterol to bile acids, increased during the second and third day of culture. This rise was inhibited after addition of various conjugated and unconjugated bile acids in a concentration of 100 microM. It could be completely prevented by cycloheximide, indicating that de novo protein synthesis is required for the increase in bile acid formation. No effect of exogenous bile salts on LDH release to the medium or on cellular ATP content was observed, demonstrating that hepatocyte viability was not affected. During the period in which bile acid synthesis was inhibited, pig hepatocytes were able to accumulate taurocholic acid (100 microM) up to 7-18 nmol per mg cell protein (decreasing during culture time). It is concluded that feedback regulation of bile acid synthesis is exerted by direct action of bile acids on the hepatocyte.     

Binding of low-density lipoprotein to heparin-Sepharose: characterization and inhibition by serum high-molecular-weight components

In this study, the interaction of human serum low-density lipoprotein (LDL) with heparin immobilized on Sepharose was reinvestigated. Binding of isolated LDL (stabilized with human serum albumin (HSA] was compared with that of LDL in full serum. (1) Binding of isolated LDL was slightly decreased by CaCl2 and was not affected by MgCl2. In contrast, with full serum LDL binding was increased by these divalent cations. (2) In both situations, binding of LDL was saturable, but the maximum degree of binding that could be reached was much higher with isolated LDL than with LDL in full serum. This could be ascribed to an inhibitory action of a factor found in the d greater than 1.24 fraction of serum. (3) The effect of this factor was diminished in the presence of CaCl2 or MgCl2, which suggests that the stimulation of LDL binding by these cations in full serum is due to suppression of the inhibitory activity of this factor. (4) The inhibitory factor in the d greater than 1.24 fraction can be partially purified by absorption to heparin-Sepharose, followed by elution with 6 M guanidine chloride. The resulting preparation had a 30- to 50-fold higher specific activity. Attempts to purify the factor further resulted in loss of activity. (5) The activity is decreased upon treatment with trypsin and also upon acetylation or reduction with dithiothreitol, indicating that free amino groups and S-S bridges are essential.     

Quantitative determination of phenolsulfotransferase using 4-methylumbelliferone

The method presented here offers a rapid and reproducible technique for assay of the enzymic formation of MUS from MU, as use is made of the extremely intensive fluorescence of MU and of the possibility of quantitative separation of the product formed from the substrate by use of ion-exchange chromatography.     

Gas exchange patterns of Pterostichus niger (Carabidae) in dry and moist air

Gas exchange patterns of adult male Pterostichus niger Schaller after hydration (i.e. given access to food and water) are compared in dry air [5–7% relative humidity (RH)] and moist air (90–97% RH) by means of flow‐through CO₂ respirometry combined with infrared probe actography. Of thirty beetles examined, slightly more than 50% showed continuous gas exchange and are not considered further. Of the remaining beetles, the majority (approximately 71%) display a pattern of cyclic gas exchange in both dry and moist air (i.e. CO₂ gas is released in bursts, with a low level of CO₂ release during the interburst periods). A minority of the beetles (four out of 30) are found to exhibit discontinuous gas exchange in both dry and moist air; this is characterized by three clearly separated states of the spiracles: closed (C), flutter (F) and open (O) phases. The pattern of cyclic gas exchange is associated with weak abdominal pulsations. After switching from moist to dry air, a small modulation of the discontinuous gas exchange cycles (maximum mean CO₂ production rate) occurs, providing no clear support for the hygric theory of discontinuous gas exchange in this species (i.e. that it serves to restrict respiratory water loss).