Preneoplastic foci of altered hepatocytes induced in rats by irradiation with alpha-particles of Thorotrast and neutrons

Gene expression profiles in mouse liver cells after exposure to different types of radiation

The liver is one of the target organs of radiation-induced cancers by internal exposures. In order to elucidate radiation-induced liver cancers including Thorotrast, we present a new approach to investigate in vivo effects of internal exposure to alpha-particles. Adopting boron neutron capture, we separately irradiated Kupffer cells and endothelial cells in mouse liver in vivo and analyzed the changes in gene transcriptions by an oligonucleotide microarray. Differential expression was defined as more than 3-fold for up-regulation and less than 1/3 for under-regulation, compared with non-irradiated controls. Of 6,050 genes examined, 68 showed differential expression compared with non-irradiated mice. Real-time polymerase chain reaction validated the results of the microarray analysis. Exposure to alpha-particles and gamma-rays produced different patterns of altered gene expression. Gene expression profiles revealed that the liver was in an inflammatory state characterized by up-regulation of positive acute phase protein genes, irrespective of the target cells exposed to radiation. In comparison with chemical and biological hepatotoxicants, inductions of Metallothionein 1 and Hemopexin, and suppressions of cytochrome P450s are characteristic of radiation exposure. Anti-inflammatory treatment could be helpful for the prevention and protection of radiation-induced hepatic injury.

Investigating the Formation and Growth of α-Particle Radiation-Induced Foci of Altered Hepatocytes: A Model-Based Approach

The effect of alpha-particle radiation on the formation and increase in volume of preneoplastic liver lesions was investigated in an animal experiment. Mice were divided into four groups; two groups received different doses of the alpha-particle-labeled antibody (213)Bi-anti CD19 ((213)Bi-CD19), Thorotrast was administered to one group, and one group was left untreated. Hematoxylin and eosin-stained liver sections were evaluated for preneoplastic foci of altered hepatocytes 6, 12 and 17 months after treatment. The density and size distribution of focal transections were described by a mechanistic model for the formation and growth of foci of altered hepatocytes. The negative control and the (213)Bi-CD19 groups were combined to investigate the dose-response relationship for model parameters describing the formation and growth of foci of altered hepatocytes. Although (213)Bi-CD19 was given by single injection, the effect on formation of foci of altered hepatocytes lasted for the entire experiment. Likelihood-ratio tests comparing nested models showed that (213)Bi-CD19 increases the rates of both the formation and growth of foci of altered hepatocytes. Comparing the effects of Thorotrast with those of (213)Bi-CD19 revealed that Thorotrast had an effect similar to that of a low dose of (213)Bi-CD19, but the effect on focus formation was slightly smaller whereas the effect on focus growth was slightly higher for Thorotrast, in contrast to a low dose of (213)Bi-CD19.

A biologically based model for liver cancer risk in the Swedish thorotrast patients

Data on liver tumors among 416 Swedish patients who were exposed to Thorotrast between 1930 and 1950 were analyzed with the biologically based two-step clonal expansion (TSCE) model. For background data, the Swedish Cancer Register for the follow-up period 1958 to 1997 was used. Effects of radiation on the initiating mutation and on the clonal expansion rate explained the observed patterns well. The TSCE model permits the deduction of several kinetic parameters of the postulated tumorigenesis process. Dose rates of 5 mGy/year double the spontaneous initiation rate. The clonal expansion rate is doubled by 80 mGy/year, and for females it reaches a plateau at dose rates beyond 240 mGy/year. For males the plateau is not significant. The magnitude of the estimated promoting effect of radiation can be explained with a moderate increase in the cell replacement probability for the intermediate cells in the liver, which is strikingly similar to the situation in lung tumorigenesis.

Early bioenergetic changes in hepatocarcinogenesis: preneoplastic phenotypes mimic responses to insulin and thyroid hormone

Biochemical and molecular biological approaches in situ have provided compelling evidence for early bioenergetic changes in hepatocarcinogenesis. Hepatocellular neoplasms regularly develop from preneoplastic foci of altered hepatocytes, irrespective of whether they are caused by chemicals, radiation, viruses, or transgenic oncogenes. Two striking early metabolic aberrations were discovered: (1) a focal excessive storage of glycogen (glycogenosis) leading via various intermediate stages to neoplasms, the malignant phenotype of which is poor in glycogen but rich in ribosomes (basophilic), and (2) an accumulation of mitochondria in so-called oncocytes and amphophilic cells, giving rise to well-differentiated neoplasms. The metabolic pattern of human and experimentally induced focal hepatic glycogenosis mimics the phenotype of hepatocytes exposed to insulin. The conversion of the highly differentiated glycogenotic hepatocytes to the poorly differentiated cancer cells is usually associated with a reduction in gluconeogenesis, an activation of the pentose phosphate pathway and glycolysis, and an ever increasing cell proliferation. The metabolic pattern of preneoplastic amphophilic cell populations has only been studied to a limited extent. The few available data suggest that thyromimetic effects of peroxisomal proliferators and hepadnaviral infection may be responsible for the emergence of the amphophilic cell lineage of hepatocarcinogenesis. The actions of both insulin and thyroid hormone are mediated by intracellular signal transduction. It is, thus, conceivable that the early changes in energy metabolism during hepatocarcinogenesis are the consequence of alterations in the complex network of signal transduction pathways, which may be caused by genetic as well as epigenetic primary lesions, and elicit adaptive metabolic changes eventually resulting in the malignant neoplastic phenotype.