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The aerobic glycolysis rate and mitochondria-bound hexokinase activity of ascitic liver cancer cells are 8 and 50 times as high as those of the normal liver cells, and they can be inhibited by Na2SeO3 in concentration below 10 micrograms/ml. The inhibitory effect increases with selenium concentration. In contrast, Na2SeO3 at the same concentration does not significantly affect the glycolysis rate and mitochondria-bound hexokinase activity of the normal liver cells. The selective action of selenium on energy metabolism of the liver cancer cells may account for its inhibitory effect on cancer cells.

Sodium selenite in normal saline was administered intraperitoneally (1 mg/kg) into mice bearing ascitic hepatocarcinoma for 4 days. The cyclic AMP-dependent protein kinase isozymes (type I and type II) in normal liver and hepatocarcinoma cells were separated and assayed. The results show that the level of type I/II is markedly higher in hepatocarcinoma than in the normal liver cells. Sodium selenite is able to reduce it towards the normal level. Further analysis shows that the chief function of sodium selenite is to reduce the raised level of type I/II in hepatocarcinoma cells which, in fact, is due to the increase of total amount of type I cyclic AMP-dependent protein kinase. This paper presents the speculation that one of the mechanisms of the inhibitory effect of sodium selenite on carcinogenesis may be due to the selective action of this compound on the cyclic AMP-dependent protein kinase isozymes in tumor cells, thus inhibiting cancer cell division and facilitating differentiation and reversion.

After treating human lung adenocarcinoma cells by Na2SeO3 (1 microgram/ml) for 24 hours, its mitotic index decreased by 50%. The reduction rate was directly proportional to selenite concentration (1-5 micrograms/ml). In the meantime, the labelling index, growth rate and progression of the cell cycle were also inhibited. In contrast to the above observation, there was no marked change in the cell count, mitotic index, labelling index and the average silver granule number in the human embryonic lung diploid cells treated by Na2SeO3 (1-5 micrograms/ml) for 1-3 days. When human embryonic lung diploid cells were mix-cultured with human lung adenocarcinoma cells in the presence of 5 micrograms/ml Na2SeO3 for 24 hours, the former maintained a normal morphology, while the lung cancer cells showed heavily vacuolated cytoplasms and distorted nuclei.

Ascitic hepatoma cells of mice were incubated with three HPD. After the cell-bound HPD was treated by visible light, the product of membrane lipid peroxidation--malondialdehyde (MDA) was determined. The results showed that the MDA level increased with HPD concentration and exposure time, but it was unchanged in the control. Beta-carotene, a quencher of singlet oxygen, could inhibit the lipid photooxidation of the membrane of cell-bound HPD resulting in a decrease of MDA level which decreased with increase of beta-carotene concentration. Adding vitamin E in vitro and vivo, formation of the product of membrane lipid peroxidation of cell-bound HPD by light was inhibited and the MDA level decreased with the increase of vitamin E concentration. These results show that the singlet oxygen, produced by HPD bound cells following light activation, reacts directly with the polyunsaturated fatty acids on cell membrane to produce lipid peroxides leading to cellular damage.

The selenium (Se) level in barley and maize from 43 communes of Qidong county, a high risk area of liver cancer in China, were assayed. An inverse correlation between the Se level and the liver cancer incidence was observed. An inverse correlation was also observed between the blood Se level and liver cancer incidence of the local residents. When selenite solution was sprayed on the crops during their preflowering, the content of Se in barley and maize was increased by 6 fold over the control. It is suggested that the increase of blood Se level of the residents who live in the low-Se areas by this method be useful in the prevention of liver cancer.