Faculty Bibliography

The fluorescence quenching of calcein (CA) is not iron specific and results in a negative calibration curve. In the present study, deferoxamine (DFO), a strong iron chelator, was used to regenerate the fluorescence quenched by iron. Therefore, the differences in fluorescence reading of the same sample with or without addition of DFO are positively and specifically proportional to the amounts of iron. We found that the same iron species but different anions (e.g. ferric sulfate or ferric citrate) differed in CA fluorescence quenching, so did the same anions but different iron (e.g. ferrous or ferric sulfates). Excessive amounts of citrate competed with CA for iron and citrate could be removed by barium precipitation. After optimizing the experimental conditions, the sensitivity of the fluorescent CA assay is 0.02 microM of iron, at least 10 times more sensitive than the colorimetric assays. Sera from 6 healthy subjects were tested for low molecular weight (LMW) chelator bound iron in the filtrates of 10 kDa nominal molecular weight limit (NMWL). The LMW iron was marginally detectable in the normal sera. However, increased levels of LMW iron were obtained at higher transferrin (Tf) saturation (1.64-2.54 microM range at 80% Tf saturation, 2.77-3.15 microM range at 100% Tf saturation and 3.09-3.39 microM range at 120% Tf saturation). The application of the assay was further demonstrated in the filtrates of human liver HepG2 and human lung epithelial A549 cells treated with iron or iron-containing dusts

Marked regional differences in prevalence of pneumoconiosis are apparent in the US despite comparable dust exposure. In the present study, we examined the ability of 28 coal samples to release bioavailable iron (BAI) and calcium, as well as other metals such as Cr, Ni, Cu, and Co, from three coal mine regions in Utah (UT), West Virginia (WV), and Pennsylvania (PA), respectively. BAI is defined as iron (both Fe2+ and Fe3+) released by the coals in 10 mM phosphate solution, pH 4.5, which mimics conditions of the phagolysosomes in cells. We found that coals from the UT, WV, and PA regions released average levels of BAI of 9.6, 4658.8, and 12149 parts per million (ppm, w/w), respectively, which correlated well with the prevalence of pneumoconiosis from that region (correlation coefficient r = 0.92). The low levels of BAI in the UT coals were due to the presence of calcite (CaCO3), which was shown to be preferentially acid solubilized before iron compounds. Release of iron by two coal samples from the PA and UT regions was further examined in vitro in human lung epithelial A549 cells. We found that the coal from PA, with a high prevalence of pneumoconiosis, released BAI in a dose-dependent manner, both in tissue culture media and in A549 cells. At 2 microg/cm2, levels of lipid peroxidation induced by the PA coal were increased 112% over control cells at 24 h treatment, and were sustained at this level for 3 days. The coal from UT, with a low prevalence of pneumoconiosis, induced a marginal increase in cellular iron at 5 and 10 microg/cm2 treatments and had no effect on lipid peroxidation. Calcium levels in the cells treated with the PA and UT coals were 8.6 and 11.5 micromoles/10(6) cells, respectively, and were significantly higher than that in the controls (5.3 micromoles/10(6) cells) [corrected]. Our results suggest that the differences in the BAI content in the coals may be responsible for the observed regional differences in the prevalence of pneumoconiosis. Therefore, BAI may be a useful characteristic of coal for predicting coal's toxicity

Ferrous ion (Fe(2+)) is long thought to be the most likely active species, producing oxidants through interaction of Fe(2+) with oxygen (O(2)). Because current iron overload therapy uses only Fe(3+) chelators, such as desferrioxamine (DFO), we have tested a hypothesis that addition of a Fe(2+) chelator, 2,2'-dipyridyl (DP), may be more efficient and effective in preventing iron-induced oxidative damage in human liver HepG2 cells than DFO alone. Using ferrozine as an assay for iron measurement, levels of cellular iron in HepG2 cells treated with iron compounds correlated well with the extent of lipid peroxidation (r = 0.99 after log transformation). DP or DFO alone decreased levels of iron and lipid peroxidation in cells treated with iron. DFO + DP together had the most significant effect in preventing cells from lipid peroxidation but not as effective in decreasing overall iron levels in the cells. Using ESR spin trapping technique, we further tested factors that can affect oxidant-producing activity of Fe(2+) with dissolved O(2) in a cell-free system. Oxidant formation enhanced with increasing Fe(2+) concentrations and reached a maximum at 5 mM of Fe(2+). When the concentration of Fe(2+) was increased to 50 mM, the oxidant-producing activity of Fe(2+) sharply decreased to zero. The initial ratio of Fe(3+):Fe(2+) did not affect the oxidant producing activity of Fe(2+). However, an acidic pH (< 3.5) significantly slowed down the rate of the reaction. Our results suggest that reaction of Fe(2+) with O(2) is an important one for oxidant formation in biological system, and therefore, drugs capable of inhibiting redox activity of Fe(2+) should be considered in combination with a Fe(3+) chelator for iron overload chelation therapy