Michio Mori

Progress from Chronic Hepatitis to Liver Cancer in Long-Surviving LEC Rats

In our previous papers, we reported on the clinical and pathological characteristics [1], pathogenesis [2], and combined immunodeficiency of spontaneous hepatitis in LEC rats.

High Susceptibility to Spontaneous Development of Hepatocellular Carcinoma in LEC Rats

Spontaneous hepatitis was first found in the LEC strain rat, which had been maintained conventionally at the Center for Experimental Plants and Animals, Hokkaido University [1]. The hepatitis appears suddenly in LEC rats at about 4 months after birth, and leads to a high mortality [2]. Characteristics of the disease are similar to those of fulminant hepatitis in humans, showing bilirubinuria, hyperbilirubinemia (frequently severe jaundice), subcutaneous bleeding, loss of body weight, increased levels of serum glutamic oxaloacetic transaminase, glutamic pyruvic transaminase and alkaline Phosphatase, and single-cell necrosis or spotty necrosis of liver tissues with faint inflammatory cell response. Genetic analysis by crossing tests indicated that the disease has an autosomal recessive mode of inheritance, being ruled by a single gene designated hts (symbol for hepatitis) [3]. Many rats died of submassive necrosis in liver tissues within 1 week after the onset of hepatitis. The remaining animals survived with chronic hepatitis more than 1 year and developed preneoplastic and neoplastic lesions of the liver [2]. Electron microscopic analysis failed to reveal any viral particles in the affected liver, and intraperitoneal injections of liver homogenates of jaundiced rats did not induce hepatitis in neonatal rats of another strain [2], although viral hepatitis has been reported to be associated with hepatocarcinogenesis in humans [4, 5], woodchucks [6], ground squirrels [7] and ducks [8]. Although the cause of hepatitis in LEC rats is different from that of viral hepatitis in the other cases, regenerative stimuli caused by hepatitis may promote development of liver tumors in all cases. In this report, the natural history of spontaneous hepatic lesions in LEC rats are described with regard to the anatomical and histopathological aspects. Furthermore, establishment and characterization of a hepatocellular carcinoma (hepatoma) cell line obtained from an LEC rat are reported.

Clinical and Pathological Characteristics of LEC Rats with Spontaneous Hepatitis

Currently, there are very few available animal models for the research of human hepatitis. We have known for many years that the marmoset and the chimpanzee are sensitive to hepatitis A and B viruses, respectively. It has been reported that the woodchunk (Marmota monax) shows a high incidence of persistent infection with woodchuck hepatitis virus (WHV), one of the hepadna viruses, and that the incidence of hepatocellular carcinomas in WHV-positive woodchucks is extremely high [1].

Combined Immunodeficiency in LEC Rats with Spontaneous Hepatitis

One of the abnormalities in the LEC rat is immunoglobulin G (IgG) formation, and a definite correlation has been found between suppressed IgG formation and the incidence of hepatitis [1, 2]. Therefore, we investigated both cellular and humoral immunological competence in relation to the incidence of hepatitis.

A case of adenofibroma of the uterus.

術前の子宮内膜細胞診で腫瘍細胞が検出された腺線維腫 (adenofibroma) の1例を経験したので報告した. 症例は45歳女性で, 月経過多と下腹部痛を主訴とし, 腹部超音波検査で, 子宮腔内に, 漿液を入れた嚢胞を含む腫瘍が発見された. 経過中, 膣より淡黄色の漿液の流出を認め, その後腫瘍が縮小, 症状が軽減したことから, 腫瘍内嚢胞の穿破が生じたものと考えられた. その後の子宮内膜細胞診で, 一部に線毛を伴う, 異型性に乏しい高円柱上皮細胞のシート状集塊を認めた. 摘出された腫瘍は組織学的に, 子宮内膜および筋層と明瞭に境され, 一層の高円柱上皮細胞で覆われた線維性結合組織の葉状, 乳頭状の増生からなっていた. 上皮, 問質成分のいずれにも, 細胞異型, 細胞分裂像は認められなかった. われわれの検索した限りでは, 内膜細胞診で腫瘍細胞を認めた子宮adenofibromaの報告はみられない.

Investigation of Infectious Agents Causing Spontaneous Hepatitis in LEC Rats

Two strains of Long-Evans rats, LEC and LEA were separated according to their coat colors. Acute hepatitis tends to occur spontaneously in the LEC rats after the 24th generation. As has been previously reported [1–3], the clinical course of the disease and the histopathological features closely resemble human fulminant hepatitis.

Genetic Analysis of Immunodeficiency and Hereditary Hepatitis in LEC Rats

The new mutant LEC rat suffers from hereditary hepatitis with severe jaundice, anemia, subcutaneous bleeding, weight loss, and oliguria at around 4 months after birth [1, 2]. About one-half of the LEC rats die within 1 week after the onset of hepatitis, whereas the remaining LEC rats survive much longer with chronic hepatitis and subsequently develop liver cancer at a high frequency [3, 4].

Replicative and Unscheduled DNA Synthesis of LEC Rat Hepatocytes: Relevance to Natural Development of Hepatocellular Carcinoma

The LEC rat is a new mutant inbred strain which suddenly displays coagulative necrosis of hepatocytes at around 4 months after birth [1], for which a single autosomal recessive gene (hts gene, [2]) is responsible. Those LEC rats surviving with chronic hepatitis eventually develop hepatocellular carcinomas as they become old [1, 3–5]. Since this hepatitishepatocellular carcinoma sequence is quite similar to the development of human liver cancer, LEC rats are expected to serve as an excellent animal model for the study of human hepatocarcinogenesis.

The Multistep Nature of Spontaneous Liver Cancer Development in the LEC Rat: Analysis of Incidence and Phenotype of Preneoplastic and Neoplastic Liver Lesions

The LEC rat has been established and characterized as a new mutant strain which spontaneously develops hepatitis and liver cancer at an extremely high incidence. The LEC rat manifests severe hereditary hepatitis with systemic jaundice and hemorrhagic tendency at around 4 months after birth. About 30%–40% of the rats die during the period of hepatitis because of submassive or massive necrosis of hepatocytes. The remaining rats recover from severe hepatitis and survive more than 1 year. Histopathological examination of the livers of the long-survived LEC rats shows development of preneoplastic and neoplastic lesions at a high incidence with continued hepatocyte death and regeneration (prolonged hepatitis) [1, 2].

Sensitivity of LEC Rats to the Hepatotoxic Effects of D-Galactosamine

Spontaneous hepatitis in the LEC rat is characterized by hyperbilirubinemia, increased levels of serum glutamic-oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) in laboratory examination and spotty coagulative necrosis of single hepatocyte without inflammatory cell response [1, 2]. Although a single autosomal recessive gene (hts) has been shown to be responsible for the hepatitis, the mechanism(s) of hepatocyte necrosis in the LEC rat remains obscure. The histological features of the liver reveal a certain resemblance between the hepatitis of LEC rats and the liver necrosis induced by the administration of D-galactosamine (GalN).