engleski

Nuclear iron deposits in carp hepatocytes: a histochemical and morphometrical study

Iron is a metal of vital importance for many organisms as it plays an essential role in numerous metabolic processes. It is an integral part of various proteins such as haemoglobin and myoglobin, where it participates in oxygen binding and transport, cytochromes, which enable the processes of cell respiration as well as of numerous enzymes such as catalases, peroxidases, dehydrogenases (succinate dehydrogenase, mitochondrial NADH dehydrogenase) and enzymes involved in DNA and RNA metabolisms. Although essential, iron can be toxic when present in excess as it can catalyse the generation of wide range of free radicals, including the hydroxyl radical, which can react with a wide spectrum of cell components, most notably the DNA, and can cause serious cellular damage. Previous investigations in our laboratory have shown that the exposure to even low concentrations of iron-dextran (FeD) (1mg/L) during a longer period of time (70 days) caused significant accumulation of iron in the carp liver. Iron was found in the cytoplasm of macrophages and hepatocytes but also in the nuclei of hepatocytes. Studies of intra-nuclear iron are rare so we set out to further analyse nuclear iron deposits and observe the earliest steps of iron accumulation in the nucleus. Iron deposits were monitored in the paraffin sections of liver tissue using the histochemical Perls method. The number, diameter and area of iron-positive depositions in the hepatocyte nuclei were quantified using an image analyser. The first reaction indicating presence of iron in hepatocyte nucleus was found at the same time as in cytoplasm, on the 14th day of the treatment, when only 0, 3% of nuclei contained round deposits with small diameters, occupying 0, 1-2, 9% of the nuclear area. Further treatment caused increase in the number of positive nuclei and the size of the deposits. On the 28th day, deposits that occupied 0, 1-4, 9% of areas were observed in 0, 97% of nuclei and on the 77th day 4, 38% nuclei had deposits that occupied 2, 9-10% of nuclear area. In some nuclei more than one deposit was observed. We also examined the chronic exposure of carp to iron gluconate (FeG) under the same conditions to compare nuclear iron accumulation using different iron salts. Like in the case of FeD exposure, continuous exposure of carp to low concentration of FeG over a longer period of time also caused the significant accumulation of iron (p<0, 05) in the liver. However, in the animals treated with FeG, nuclear iron deposits were not found. In conclusion, our results indicate that the slow passage of cytoplasmic ferritin through the nuclear pores might not be the mechanism by which iron accumulates in the nucleus as have been postulated by some authors. Further studies will be required to examine the exact mechanism of iron accumulation in the nucleus during chronic exposure to iron salts. Medical relevance will also be addressed.

iron; hepatocytes; nuclei; Perls reaction; morphometric; carp

znanstveni skup počinje 18.09.2005. i tada će sažetak biti objavljen