The hypotransferrinaemic mouse: Ultrastructural and laser microprobe analysis observations

Homozygote hypotransferrinaemic mice (hpx/hpx) have cytopathological features similar to those of human congenital atransferrinaemia, genetic haemochromatosis, and neonatal haemochromatosis. These conditions all have in common high levels of cytotoxic non‐transferrin‐bound serum iron. This study describes the ultrastructural features of iron overload in liver, pancreas, heart, and small intestine of 2‐ and 12‐month‐old hypotransferrinaemic mice. Electron microscopic studies of unstained sections showed early parenchymal cell siderosis, with accumulation of numerous ferritin particles and clusters in the cytosol, as well as ferritin and haemosiderin in lysosomes (siderosomes). In the 12‐month‐old animals, iron was also found in Kupffer cells and macrophages in other tissues. In addition, there were conspicuous iron‐containing compounds in the bile canaliculi, and marked iron deposition in the pancreas and heart. Laser microprobe mass analysis (LAMMA) enabled localization and relative quantitation of iron deposition in subcellular compartments providing in situ documentation of iron accumulation in siderosomes and contributed in assessing total cytosolic iron in various cell types. Moreover, it demonstrated the importance and magnitude of the biliary route for iron excretion in these animals.