Hepatocarcinogenesis in the context of strain differences in energy metabolism between inbred strains of mice (C57BL/6J and C3H/He)

In utero arsenic exposure in mice and early life susceptibility to cancer

In its review of the U.S. Environmental Protection Agency's toxicological review of inorganic arsenic (iAs), the National Academy of Sciences identified carcinogenic endpoints among the highest priority health effects of concern and stated the need to consider evidence that early life exposures may increase the risk of adverse health effects. Recent studies in mice suggest that in utero exposure to arsenic increases susceptibility to cancer later in life. These data are striking in light of the general lack of evidence for carcinogenicity in rodents exposed to iAs. To evaluate the transplacental carcinogenic potential of iAs, a detailed analysis of the toxicology literature evaluating the role of in utero arsenic exposure in carcinogenesis was conducted. Bladder, lung, and skin tumors, which are the tumor types most consistently reported in humans exposed to high arsenic levels, were not consistently increased in mouse studies. There was also a lack of concordance across studies for other tumor types not typically reported in humans. Therefore, we considered methodological and other critical issues that may have contributed to variable results and we suggest additional studies to address these issues. It was concluded that the available data do not provide evidence of a causal link between in utero arsenic exposure and cancer or indicate early life-stage susceptibility to arsenic-induced cancer, particularly at environmentally relevant doses.

The role of triiodothyronine-induced substrate cycles in the hepatic response to overnutrition: thyroid hormone as an antioxidant

Overnutrition, by generating reactive oxygen species (ROS), produces oxidative stress - an important cause of cellular injury. In the liver, overnutrition begins in the perivenous hepatocytes. To prevent injury, cells must protect themselves against ROS accumulation. Overnutrition also activates the enzyme deiodinase-1 (D1), which catalyzes the conversion of T4 to T3. D1 is primarily located in the PV region of the liver. Thyroid hormone is known to generate substrate cycling. The hypothesis of this paper is that a nutrient-induced increase in intracellular T3 acts as an antioxidant by inducing substrate cycles that reduce ROS accumulation. These cycles do this by: (i) reducing ROS formation by hydrolyzing excess ATP, thus enhancing oxidative phosphorylation and reducing the proton motive force on the electron transport chain (ETC), and; (ii) enhancing the removal (reduction) of ROS by producing the NADPH required for regeneration of reduced glutathione, a potent endogenous antioxidant. Oxidative stress is an important factor in the etiology of a number of hepatic injuries, including nonalcoholic steatohepatitis (NASH) and hepatocarcinogenesis. In the latter, the frequency of mutations in thyroid hormone receptors (TRs) supports the concept that thyroid hormone acts as a tumor suppressor by reducing oxidative stress. This paper reviews the substrate cycles involved in this process. It also describes other mechanisms that permit rapid availability of T3 to cells undergoing oxidative stress.

Genomic instability of murine hepatocellular carcinomas with low and high metastatic capacities

AIM: To investigate the frequency of genomic instability in murine hepatocellular carcinoma (HCC) cell lines Hca/A2-P(P) and Hca/163-F(F) with low and high metastatic capacity, and to explore its association with the occurrence and metastasis of hepatocellular carcinomas.

METHODS: Forty microsatellite markers were randomly selected to examine P and F cells for genomic instability using PCR-simple sequence length polymorphism (PCR-SSLP) analysis.

RESULTS: Allelic genes on the chromosomes of P cell line with thirty informative microsatellite loci were paralleled to those of inbred strain C₃H mouse, while those of F cell line with 28 loci were paralleled to those of inbred strain C₃H mice. The frequency of microsatellite alterations was 37.5% and 42.5% in P cell line and F cell line, respectively. There were different alterations of allelic band 9 at loci between P and F cells, among which, the frequency of microsatellite alterations was most commonly seen on chromosomes 3, 7, 11 and 16.

CONCLUSION: Genomic instability in mouse chromosomes 3, 7, 11 and 16 may play a more important role in the development and progression of HCC in mice. It is suggested that these two sub-clones derived from a same hepatic tumor in homozygous mouse present different genetic features.