An ultrastructural study of the liver in erythropoietic protoporphyria

An ultrastructural investigation of the liver was performed in two patients with erythropoietic protoporphyria. There were many protoporphyrin crystals in the hepatocytes, Kupffer cells, bile canaliculi, epithelia of bile ducts, and sinusoidal endothelial cells and also free within sinusoids. In hepatocytes, these deposits were composed of granular amorphous materials and numerous slender, straight, or slightly curved needle-like crystals aligned in radial orientation. They were randomly distributed in the cytoplasm and completely replaced other cytoplasmic structures. Some crystals lay free in the cytoplasm and others were surrounded by a single membrane. In the bile canaliculi, severe alterations could be observed. Some of the bile canaliculi were filled with amorphous, noncrystalline pigments, and lumina were enlarged with loss of microvilli. In addition, despite the absence of protoporphyrin deposits, there were many dilated bile canaliculi. The microfilamentous network around such dilated bile canaliculi was no longer evident, suggesting the depolymerization of actin filaments, which could lead to bile excretory disturbances. The bile duct epithelia showed focal apical membrane bleb formation. The functional or structural alterations of the sinusoidal endothelial cells by the protoporphyrin crystals might lead to the hepatic disturbances. These ultrastructural findings of the liver might contribute to the understanding of the pathogenesis of complicated liver disease in erythropoietic protoporphyria.