Studies on the rat liver following iron overload: an analysis of iron and lysosomal enzymes in isolated parenchymal and non-parenchymal cells

Ferritin in liver, plasma and bile of the iron-loaded rat

Rats were loaded with iron. With overload, up to a 10-fold increase of the iron and ferritin protein content of the livers was measured. The plasma ferritin concentration increased gradually with the ferritin concentration in the liver. The ferritin concentration in the bile increased also and was in the same range as in the plasma. The ratio plasma ferritin concentration to bile ferritin concentration in individual rats decreased in the case of considerable iron overload. After intravenous injection of liver ferritin, less than 2% of the ferritin concentration that disappeared from the blood was found to be in the bile. Isoelectric focussing revealed that the microheterogeneity of liver and bile ferritin were identical, but slightly different from plasma ferritin. These results indicate that ferritin was not solely leaking from the plasma to the bile. Together with ferritin, iron accumulated in the bile. The iron content of the bile ferritin was in the same range as in fully iron-loaded liver ferritin. It is likely that ferritin in the bile is excreted by the liver and consists of normal iron-loaded liver ferritin molecules. In all circumstances, the amount of iron in the bile was much higher than could be accounted for by transport by the bile ferritin. The ferritin protein to iron ratio in the bile was 0.1-1.2, which was in the same range as was measured in isolated lysosomal fractions of the liver. Those results agree with the supposition that ferritin and iron in the bile are excreted by the liver though lysosomal exocytosis.

Cadmium metabolism by rat liver endothelial and Kupffer cells

The metabolism of cadmium was investigated in Wistar-rat liver non-parenchymal cells. Kupffer and endothelial cells, the major cell populations lining the sinusoidal tracts, were isolated by collagenase dispersion and purified by centrifugal elutriation. At 20 h after subcutaneous injection of the metal salt (1.5 mg of Cd/kg body weight), endothelial cells accumulated 2-fold higher concentrations of Cd than did Kupffer or parenchymal cells. Most of the Cd in non-parenchymal cells was associated with cytosolic metallothionein (MT), the low-Mr heavy-metal-binding protein(s). When MT was quantified in cytosols from cells isolated from control rats by a 203Hg competitive-binding assay, low levels were found to be present in Kupffer, endothelial and parenchymal cells. Cd injection significantly increased MT levels in all three cell types. The induction of MT synthesis was investigated in vitro by using primary monolayer cultures. The incorporation of [35S]cysteine into MT increased 47% over constitutive levels in endothelial-cell cultures after the addition of 0.8 microM-Cd2+ to the medium for 10 h. MT synthesis in Kupffer cells was not observed. The lack of MT synthesis by monolayer cultures of Kupffer cells in vitro was associated with a decreased capacity of these cells to accumulate heavy metals from the extracellular medium. This apparent decreased ability to transport metals did not reflect a general defect in either cellular function or metabolic activity, since isolated Kupffer cells incorporated [3H]leucine into protein at rates comparable with those shown by liver parenchymal cells and readily phagocytosed particles.

Levels of malondialdehyde production in rat liver following loading and unloading with iron

Rats were given daily injections of an iron sorbitol citric acid complex in a total dose of 50 mg Fe3+/100 g of body weight and either killed immediately after iron loading, or investigated 2 months later. Among the latter animals, one group was subjected to weekly phlebotomies in order to mobilize iron from the stores, while another group was not further treated. Quantitation of iron and malondialdehyde production was performed on homogenates of liver, kidney and spleen from controls and rats in the different experimental groups, and the distribution of iron in granular form was studied in the livers by means of electron microscopy. The results showed substantially increased amounts of iron in the organs studied after iron-loading and also augmented malondialdehyde production in the liver and kidney (but not in the spleen). A decreased malondialdehyde production was recorded two months after iron-loading in the kidney and spleen of non-bled animals; this decrease was exaggerated in the same organs from bled animals. The production of malondialdehyde as well as the iron content in the livers of both bled and non-bled rats 2 months after iron loading was higher than in the controls. The evidence obtained suggested that the accumulation of iron in the liver was causally related to increased lipid peroxidation. Judging from the morphological appearances this change did not result in cell damage, the only pertinent morphologic alteration being the occurrence of iron particles in the lysosomal vacuome and the cell sap.