Different mutation patterns of mitochondrial DNA displacement-loop in hepatocellular carcinomas induced by N-nitrosodiethylamine and a choline-deficient l-amino acid-defined diet in rats

Development of a novel mouse model of hepatocellular carcinoma with nonalcoholic steatohepatitis using a high-fat, choline-deficient diet and intraperitoneal injection of diethylnitrosamine

Background

The incidence of hepatocellular carcinoma with nonalcoholic steatohepatitis is increasing, and its clinicopathological features are well established. Several animal models of nonalcoholic steatohepatitis have been developed to facilitate its study; however, few fully recapitulate all its clinical features, which include insulin resistance, inflammation, fibrosis, and carcinogenesis. Moreover, these models require a relatively long time to produce hepatocellular carcinoma reliably. The aim of this study was to develop a mouse model of hepatocellular carcinoma with nonalcoholic steatohepatitis that develops quickly and reflects all clinically relevant features.

Methods

Three-week-old C57BL/6J male mice were fed either a standard diet (MF) or a choline-deficient, high-fat diet (HFCD). The mice in the MF + diethylnitrosamine (DEN) and HFCD + DEN groups received a one-time intraperitoneal injection of DEN at the start of the respective feeding protocols.

Results

The mice in the HFCD and HFCD + DEN groups developed obesity early in the experiment and insulin resistance after 12 weeks. Triglyceride levels peaked at 8 weeks for all four groups and decreased thereafter. Alanine aminotransferase levels increased every 4 weeks, with the HFCD and HFCD + DEN groups showing remarkably high levels; the HFCD + DEN group presented the highest incidence of nonalcoholic steatohepatitis. The levels of fibrosis and steatosis varied, but they tended to increase every 4 weeks in the HFCD and HFCD + DEN groups. Computed tomography scans indicated that all the HFCD + DEN mice developed hepatic tumors from 20 weeks, some of which were glutamine synthetase-positive.

Conclusions

The nonalcoholic steatohepatitis-hepatocellular carcinoma model we describe here is simple to establish, results in rapid tumor formation, and recapitulates most of the key features of nonalcoholic steatohepatitis. It could therefore facilitate further studies of the development, oncogenic potential, diagnosis, and treatment of this condition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12876-016-0477-5) contains supplementary material, which is available to authorized users.

Convergent mechanisms for dysregulation of mitochondrial quality control in metabolic disease: implications for mitochondrial therapeutics

Mitochondrial dysfunction is associated with a broad range of pathologies including diabetes, ethanol toxicity, metabolic syndrome and cardiac failure. It is now becoming clear that maintaining mitochondrial quality through a balance between biogenesis, reserve capacity and mitophagy is critical in determining the response to metabolic or xenobiotic stress. In diseases associated with metabolic stress, such as Type II diabetes and non-alcoholic and alcoholic steatosis, the mitochondria are subjected to multiple 'hits' such as hypoxia and oxidative and nitrative stress, which can overwhelm the mitochondrial quality control pathways. In addition, the underlying mitochondrial genetics that evolved to accommodate high-energy demand, low-calorie supply environments may now be maladapted to modern lifestyles (low-energy demand, high-calorie environments). The pro-oxidant and pro-inflammatory environment of a sedentary western lifestyle has been associated with modified redox cell signalling pathways such as steatosis, hypoxic signalling, inflammation and fibrosis. These data suggest that loss of mitochondrial quality control is intimately associated with the aberrant activation of redox cell signalling pathways under pathological conditions. In the present short review, we discuss evidence from alcoholic liver disease supporting this concept, the insights obtained from experimental models and the application of bioenergetic-based therapeutics in the context of maintaining mitochondrial quality.

Mitochondrial mutations in hepatocellular carcinomas and fibrolamellar carcinomas

Mitochondrial mutations are well documented in hepatocellular carcinoma, but their role in carcinogenesis remains unclear. To clarify their significance, a comprehensive analysis was performed of hepatocellular carcinomas (N=24), including quantifying the total mitochondrial DNA levels, quantifying the levels of mitochondrial DNA with the common deletion, and complete sequencing of the mitochondrial control region. In addition, these studies were expanded and reinforced by analysis of fibrolamellar carcinomas (N=15), a unique type of liver carcinoma that has increased numbers of mitochondria on electron microscopy. Overall, approximately 50% of hepatocellular carcinomas had lower levels of total mitochondrial DNA than paired non-neoplastic tissues. Interestingly, despite their increased numbers of mitochondria, primary fibrolamellar carcinomas had lower levels of total mitochondrial DNA. In contrast, metastatic fibrolamellar carcinomas had greatly increased mitochondrial DNA levels. Overall, deletions in the control region were associated with lower total DNA levels in typical hepatocellular carcinoma, but somatic single base pair mutations were not. In fact, almost all single base pair mutations were either reversions to the wild-type sequence or known population polymorphisms, strongly suggesting they are not directly oncogenic. Complete sequencing of the entire mitochondrial genome in fibrolamellar carcinomas identified several somatic mutations, but no consistent pattern of mutations was found. Overall, the levels of the common deletion were highest in tissues with lower total mitochondrial DNA. In conclusion, control region deletions, but not somatic mutations, may influence total DNA copy numbers. Somatic control region mutations in hepatocellular carcinoma are not directly oncogenic but instead may be adaptive.

A rodent model of NASH with cirrhosis, oval cell proliferation and hepatocellular carcinoma

BACKGROUND/AIMS

Hepatocellular carcinoma (HCC) is a well recognized complication of advanced NASH (non-alcoholic steatohepatitis). We sought to produce a rat model of NASH, cirrhosis and HCC.

METHODS

Adult Sprague-Dawley rats, weighing 250-300g, were fed a choline-deficient, high trans-fat diet and exposed to DEN in drinking water. After 16 weeks, the animals underwent liver ultrasound (US), sacrifice and assessment by microscopy, immunohistochemistry and transmission electron microscopy (TEM).

RESULTS

US revealed steatosis and focal lesions in 6 of 7. All had steatohepatitis defined as inflammation, advanced fibrosis and ballooning with Mallory-Denk bodies (MDB) with frank cirrhosis in 6. Areas of more severe injury were associated with anti-CK19 positive ductular reaction. HCC, present in all, were macro-trabecullar or solid with polyhedral cells with foci of steatosis and ballooned cells. CK19 was positive in single or solid nests of oval cells and in neoplastic hepatocytes. TEM showed ballooning with small droplet fat, dilated endoplasmic reticulum and MDB in non-neoplastic hepatocytes and small droplet steatosis in some cancer cells.

CONCLUSIONS

This model replicated many features of NASH including steatohepatitis with ballooning, fibrosis, cirrhosis and hepatocellular carcinoma. Oval cell proliferation was evident and the presence anti-CK 19 positivity in the cancer suggests oval cell origin of the malignancy.