Evidence from surface tension and fluorescence data of a pyrene-assisted micelle-like assemblage of humic substances

Surface activity and fluorescence of humic substances (HS) and HS/pyrene solutions were monitored under various pH conditions. For HS alone the surface tension of the solutions decreased with increasing acidity, with a minimum at around pH 4. This effect, which is a consequence of an increase in the amphiphilic character of structures, is much more pronounced in humic (HA) than in fulvic acids (FA). The addition of pyrene (0.1 micromolL(-1)) results, for HA, in a marked reduction in the migration of amphiphilic species to the solution surface. FA profiles are not modified in presence of pyrene at that concentration. A decrease in the pyrene I1/I3 ratio in HS solutions shows that below pH 9 pyrene molecules react progressively to the change to a more hydrophobic environment, the greatest effect being observed at around pH 6 to 7. These signals are followed by a significant increase in the pyrene excimer fluorescence (lambda(exc)/lambda(em)=334 nm/450 nm), which is a consequence of the proximity of pyrene molecules. For FA, the I1/I3 decrease is less significant and no excimers develop. This set of effects is explained in view of conformational adjustments of HS, mainly HA, which become arranged in micelle-like domains in aqueous solution, the aromatic moieties being assembled around the pyrene molecules.     

Acute liver injury in rats by praseodymium nitrate (author''s transl)

After acute intoxication with praseodymium nitrate (10 mg/kg body weight i.v.), time functions of enzyme activities of GOT, GPT, ChE, AP and of free fatty acids concentration in rat serum were analysed and the results subjected to significance and correlation analysis. Time functions of free fatty acids concentration corresponded with those of enzyme activities of GOT and GPT. In the early state of intoxication serum concentrations of palmitoleinic and oleic acid were more increased than those of stearinic acid. There seems to be an alteration in the correlations of analysed measures with regard to their temporal changes parallel to the progress of intoxication.     

The effect of silymarin-N-methylglucamine salt and silybin-dihemisuccinate on (1-14C)-acetate incorporation in rat liver lipids (author''s transl)

60 min after i.v. application of 140.5 mg silymarin-N-methylglucamine salt/kg body weight dissolved in 4% polyvinylpyrrolidone solution, and 30 min after i.p. administration [1-14C]-acetate, compared to rats treated with solvent only, a statistically significant increase of specific radioactivities in total lipids, triglycerides, total phospholipids as well as in the phosphatidylcholine fraction and a decrease of specific activities in the free cholesterol fraction of the liver can be determined. 70 min after i.p. application of 140.5 mg silybin-dihemisuccinate/kg body weight dissolved in phosphate buffer, and 10 min after i.v. administration of [1-14C]-acetate in comparison with rats treated with solvent only, a statistically significant enhancement of specific activities of total liver lipids, free hepatic cholesterol, liver triglycerides, total liver phospholipids, and the hepatic fraction of phosphatidyl ethanolamine can be measured. Silybin also produces an increased specific radioactivity of the serum triglyceride fraction.     

Zum wirkungsmechanismus von betonverflüssigern auf der basis von wasserlöslichen melaminharzen

Measurements of the viscosity of limestone-, quartz- and cement-suspensions with and without admixtures of water soluble melamine resins indicate a mechanism for the melamine-resin-fluidifiers that results from the formation of gelatinous calcium-compounds on the surface of the cement particles.     

ROS-mediated genotoxicity of asbestos-cement in mammalian lung cells <Emphasis Type="Italic">in vitro</Emphasis>

Asbestos is a known carcinogen and co-carcinogen. It is a persisting risk in our daily life due to its use in building material as asbestos-cement powder. The present study done on V79-cells (Chinese hamster lung cells) demonstrates the cytotoxic and genotoxic potential of asbestos-cement powder (ACP) in comparison with chrysotile asbestos. A co-exposure of chrysotile and ACP was tested using the cell viability test and the micronucleus assay. The kinetochore analysis had been used to analyse the pathway causing such genotoxic effects. Thiobarbituric acid-reactive substances were determined as evidence for the production of reactive oxygen species. Both, asbestos cement as well as chrysotile formed micronuclei and induced loss of cell viability in a concentration- and time- dependent way. Results of TBARS analysis and iron chelator experiments showed induction of free radicals in ACP- and chrysotile exposed cultures. CaSO₄ appeared to be a negligible entity in enhancing the toxic potential of ACP. The co-exposure of both, ACP and chrysotile, showed an additive effect in enhancing the toxicity. The overall study suggests that asbestos-cement is cytotoxic as well as genotoxic in vitro. In comparison to chrysotile the magnitude of the toxicity was less, but co-exposure increased the toxicity of both.     

Sphingosine kinase-mediated Ca2+ signalling by G-protein-coupled receptors

Formation of inositol 1,4,5-trisphosphate (IP3) by phospholipase C (PLC) with subsequent release of Ca2+ from intracellular stores, is one of the major Ca2+ signalling pathways triggered by G-protein-coupled receptors (GPCRs). However, in a large number of cellular systems, Ca2+ mobilization by GPCRs apparently occurs independently of the PLC-IP3 pathway, mediated by an as yet unknown mechanism. The present study investigated whether sphingosine kinase activation, leading to production of sphingosine-1-phosphate (SPP), is involved in GPCR-mediated Ca2+ signalling as proposed for platelet-derived growth factor and FcepsilonRI antigen receptors. Inhibition of sphingosine kinase by DL-threo-dihydrosphingosine and N,N-dimethylsphingosine markedly inhibited [Ca2+]i increases elicited by m2 and m3 muscarinic acetylcholine receptors (mAChRs) expressed in HEK-293 cells without affecting mAChR-induced PLC stimulation. Activation of mAChRs rapidly and transiently stimulated production of SPP in HEK-293 cells. Finally, intracellular injection of SPP induced a rapid and transient Ca2+ mobilization in HEK-293 cells which was not antagonized by heparin. We conclude that mAChRs utilize the sphingosine kinase-SPP pathway in addition to PLC-IP3 to mediate Ca2+ mobilization. As Ca2+ signalling by various, but not all, GPCRs in different cell types was likewise attenuated by the sphingosine kinase inhibitors, we suggest a general role for sphingosine kinase, besides PLC, in mediation of GPCR-induced Ca2+ signalling.     

Assessment of chelatable mitochondrial iron by using mitochondrion-selective fluorescent iron indicators with different iron-binding affinities

Chelatable cellular iron, and chelatable mitochondrial iron in particular, has yet to be well characterized, so the overall strength with which these "loosely bound" iron ions (presumably mainly Fe(II)) are intracellularly/intramitochondrially bound is unclear. We have previously reported the first selective mitochondrial iron indicator: rhodamine B 4-[(1,10-phenanthrolin-5-yl)aminocarbonyl]benzyl ester (RPA). With this compound as a model, we have now developed two additional mitochondrial iron indicators with very different iron-binding affinities and have applied these to the study of the chelatable iron pool in the mitochondria of isolated rat liver cells. With the new indicator rhodamine B 4-[(2,2'-bipyridin-4-yl)aminocarbonyl]benzyl ester (RDA), with 2,2'-bipyridine as chelating unit (log beta(3)=17.5), essentially the same iron concentration (16.0+/-1.9 microM) was determined as with RPA (log beta(3)=21.1), despite the four orders of magnitude difference in Fe(II)-binding affinity. This not only demonstrates the reliability of the procedure, but also confirms that iron complexation by these indicators does not induce any significant release of iron from the iron-storage proteins on the timescale of the experiment. In contrast, the indicator rhodamine B 4-[bis(pyridin-2-ylmethyl)aminomethyl]benzyl ester (PIRO), with an N,N-bis(pyridin-2-ylmethyl)amine group as chelating component (log beta(2)=12.2), could not compete against the array of endogenous ligands. The intramitochondrial concentrations of the three indicators were determined to be in the range of 100 microM: that is, about three orders of magnitude lower than the total concentration of endogenous compounds that might chelate iron ions. It is therefore estimated that chelatable mitochondrial iron ions are bound by endogenous ligands with apparent stability constants (log K(app)) of between 9 and 14.