Mouse model for protoporphyria. I. The liver and hepatic protoporphyrin crystals.

Outbred albino mice were rendered protoporphyric by a diet containing 2.5% (weight) of griseofulvin. There was a 5-fold increase in liver weight, hepatocellular degeneration and necrosis, cholestasis, ductular proliferation and cirrhosis. Liver protoporphyrin values were elevated and brown pigment granules were present in hepatocytes, Kupffer cells, and bile ducts. The granules showed red fluorescence, birefringence, and, at the ultrastructural level, consisted of aggregates of needle-like crystals. Crystals isolated from such livers showed solubility and absorption characteristics of protoporphyrin; in vitro recrystallization of protoporphyrin, extracted from protoporphyric mouse livers, yielded crystals identical with those observed in vivo, and commercial protoporphyrin exhibited similar morphologic features. The liver pathology and protoporphyrin crystals observed in these animals are identical to the liver pathology and crystals observed in the human disease, erythropoietic protoporphyria. In this mouse model, protoporphyrin crystals are intimately associated with hepatocellular injury and it appears that their accumulation within hepatocytes leads to hepatocellular destruction. A similar pathogenesis is postulated for the hepatic damage that occurs in some cases of erythropoietic protoporphyria.