Mutation frequency in the lacI gene of liver DNA from lambda/lacI transgenic mice following the interaction of PCBs with iron causing hepatic cancer and porphyria

The association between chemical-induced porphyria and hepatic cancer

The haem biosynthetic pathway is of fundamental importance for cellular metabolism both for the erythroid and nonerythroid tissues. There are several genetic variants of the pathway in the human population that cause dysfunction of one or other of the enzymes resulting in porphyrias of varying severity. Serious chronic hepatic and systemic diseases may result. Some of these can be precipitated by exposure to drugs including hormones, barbiturates and antibiotics, as well as alcohol and particular chlorinated aromatic chemicals. In experimental animals some of the steps of this pathway can also be severely disrupted by a variety of environmental chemicals, potential drugs and pesticides, especially in the liver, leading to the accumulation of uroporphyrins derived from the intermediate uroporphyrinogens or protoporphyrin IX, the immediate precursor of haem. With some of these chemicals this also leads to cholestasis and liver cell injury and eventually hepatic tumours. The review evaluates the available evidence linking hepatic porphyria with carcinogenesis in naturally occurring human genetic conditions and in chemically-induced porphyrias in laboratory animals. The existing data showing gender, strain, and species differences in sensitivity to the chemical-induced porphyrias, liver injury and liver tumours are discussed and the role that transgenically altered mouse models have played in defining the varying mechanisms. Finally, the review proposes a novel, unifying hypothesis linking the hepatotoxicity induced by the accumulation of various porphyrins, with the increased risk of developing hepatic cancer as a long term consequence.

Effects of estradiol, PCB3, and their hydroxylated metabolites on proliferation, cell cycle, and apoptosis of human breast cancer cells

Certain estradiol metabolites and industrial pollutants, like polychlorinated biphenyls, may play a more important role in enhancing breast cancer risk than 17β-estradiol. The aim of this study was to compare the effects of 17β-estradiol (E2) with that of the air pollutant 4-chlorobiphenyl (PCB3) and four of their hydroxylated metabolites on cell cycle, proliferation, and apoptosis in MCF-7 human breast cancer cells at concentrations of 0.1-10nM (E2, 2-OH-E2, and 4-OH-E2) and 0.3-300nM (PCB3, 4-OH-PCB3, and 3, 4-diOH-PCB3) and 24-260h of exposure. E2 increased cell proliferation and cells in S-phase at all time points. 2-OH-E2 and 4-OH-E2 had no effect on the cell cycle, but a stimulatory action on cell proliferation from 72 to 260h of exposure to 4-OH-E2 and at 260h to 2-OH-E2 was seen. E2 and its metabolites had no effect on apoptosis. PCB3 and 4-OH-PCB3 showed no effect on proliferation, apoptosis or cell cycle distribution at any concentration and time point. Longer time exposures to 3,4-di-OH-PCB at 300nM caused a decrease of cells and an increase in G2/M and apoptotic cells. These results confirm the proliferative effect of E2 and its metabolite 4-OH-E2 in estrogen receptor positive breast cancer cells, but show no mitogenic activity for PCB3 and 4-OH-PCB3. However, the cell cycle and apoptosis effects of 3,4-diOH-PCB3 need further analysis.

Uroporphyria and hepatic carcinogenesis induced by polychlorinated biphenyls–iron interaction: Absence in the Cyp1a2(−/−) knockout mouse

Aryl hydrocarbon receptor ligands, such as polychlorinated biphenyls (PCBs), cause inhibition of the heme biosynthesis enzyme, uroporphyrinogen decarboxylase; this leads to uroporphyria and hepatic tumors, which are markedly enhanced by iron overload in C57BL/10 and C57BL/6 strains of mice. Cyp1a2(-/-) knockout mice were used to compare the effects of CYP1A2 expression on uroporphyria and liver carcinogenesis. PCBs in the diet (100ppm) of Cyp1a2(+/+) wild-type mice caused hepatic uroporphyria, which was strongly increased by iron-dextran (800mg Fe/kg). In contrast, uroporphyria was not detected in Cyp1a2(-/-) knockout mice, although expression of CYP1A1 and CYP2B10 was greatly induced. After 57 weeks on this diet, hepatic preneoplastic foci and tumors were seen in the Cyp1a2(+/+) mice; numbers and severity were enhanced by iron. No foci or tumors were detected in Cyp1a2(-/-) mice, although evidence for other forms of liver injury was observed. Our findings suggest a link not only between CYP1A2, iron metabolism, and the induction of uroporphyria by PCBs, but also with subsequent hepatocarcinogenesis.