A very small, predominantly cytosolic pool of iron ions plays the central role in the cellular iron metabolism. It links the cellular iron uptake with the insertion of the metal in iron storage proteins and other essential iron-containing molecules. Furthermore, this transit ('labile') pool is essentially involved in the pathogenesis of a number of diseases. Due to its high physiological and pathophysiological significance, numerous methods for its characterization have been developed during the last five decades. Most of these methods, however, influence the size and nature of the transit iron pool artificially, as they are not applicable to viable biological material. Recently, fluorescence spectroscopic methods for measurements within viable cells have become available. Although these methods avoid the artifacts of previous methods, studies using fluorescent iron indicators revealed that the 'intracellular transit iron pool', which is methodically assessed as 'chelatable iron', is substantially defined by the method and/or the iron-chelating indicator applied for its detection, since the iron ions are bound to a large number of different ligands in different metabolic compartments. A more comprehensive characterization of the nature and the role of the thus not uniform cellular transit iron pool therefore requires parallel employment of different indicator molecules, which clearly differ in their intracellular distribution and their physico-chemical characteristics.

The intracellular pool of chelatable iron is considered to be a decisive pathogenetic factor for various kinds of cell injury. We therefore set about establishing a method of detecting chelatable iron in isolated hepatocytes based on digital fluorescence microscopy. The fluorescence of hepatocytes loaded with the fluorescent metal indicators, phen green SK (PG SK), phen green FL (PG FL), calcein, or fluorescein desferrioxamine (FL-DFO), was quenched when iron was added to the cells in a membrane-permeable form. It increased when cellular chelatable iron available to the probe was experimentally decreased by an excess of various membrane-permeable transition metal chelators. The quenching by means of the ferrous ammonium sulfate ؉ citrate complex and also the ''dequenching'' using 2,2Ј-dipyridyl (2,2Ј-DPD) were largest for PG. We therefore optimized the conditions for its use in hepatocytes and tested the influence of possible confounding factors. An ex situ calibration method was set up to determine the chelatable iron pool of cultured hepatocytes from the increase of PG SK fluorescence after the addition of excess 2,2Ј-DPD. Using this method, we found 9.8 ؎ 2.9 mol/L (mean ؎ SEM; n ‫؍‬ 18) chelatable iron in rat hepatocytes, which constituted 1.0% ؎ 0.3% of the total iron content of the cells as determined by atomic absorption spectroscopy. The concentration of chelatable iron in hepatocytes was higher than the one in K562 cells (4.0 ؎ 1.3 mol/L; mean ؎ SEM; n ‫؍‬ 8), which were used for comparison. This method allowed us to record time courses of iron uptake and of iron chelation by different chelators (e.g., deferoxamine, 1,10-phenanthroline) in single, intact cells. (HEPATOLOGY 1999;29: 1171-1179.)

A new type of nano-sized silicon/carbon composite was developed. It shows superior electrochemical cycling properties as negative electrode material for possible use in lithium-ion batteries with respect to high reversible and low irreversible capacity, and low fading.

When incubated at 4 degrees C, cultured rat hepatocytes or liver endothelial cells exhibit pronounced injury and, during earlier rewarming, marked apoptosis. Both processes are mediated by reactive oxygen species, and marked protective effects of iron chelators as well as the protection provided by various other antioxidants suggest that hydroxyl radicals, formed by classical Fenton chemistry, are involved. However, when we measured the Fenton chemistry educt hydrogen peroxide and its precursor, the superoxide anion radical, formation of both had markedly decreased and steady-state levels of hydrogen peroxide did not alter during cold incubation of either liver endothelial cells or hepatocytes. Similarly, there was no evidence of an increase in O2-/H2O2 release contributing to cold-induced apoptosis occurring on rewarming. In contrast to the release/level of O2- and H2O2, cellular homeostasis of the transition metal iron is likely to play a key role during cold incubation of cultured hepatocytes: the hepatocellular pool of chelatable iron, measured on a single-cell level using laser scanning microscopy and the fluorescent indicator phen green, increased from 3.1 +/- 2.3 microM (before cold incubation) to 7.7 +/- 2.4 microM within 90 min after initiation of cold incubation. This increase in the cellular chelatable iron pool was reversible on rewarming after short periods of cold incubation. The cold-induced increase in the hepatocellular chelatable iron pool was confirmed using the calcein method. These data suggest that free radical-mediated hypothermia injury/cold-induced apoptosis is primarily evoked by alterations in the cellular iron homeostasis/a rapid increase in the cellular chelatable iron pool and not by increased formation of O2-/H2O2.