Carcinogenicity of iron in conjunction with a chlorinated environmental chemical, hexachlorobenzene, in C57BL/10ScSn mice

The therapeutic potential of curcumin in alleviating N-diethylnitrosamine and iron nitrilotriacetate induced renal cell tumours in mice via inhibition of oxidative stress: Implications for cancer chemoprevention

This study was designed to reveal the protective effects of dietary supplementation of curcumin against renal cell tumours and oxidative stress induced by renal carcinogen iron nitrilotriacetate (Fe-NTA) in ddY male mice. The results showed that mice treated with a renal carcinogen, Fe-NTA, a 35% renal cell tumour incidence was noticed, whereas renal cell tumour occurrence was elevated to 80% in Fe-NTA promoted and N-diethylnitrosamine (DEN)-initiated mice as compared with saline- treated mice. No incidence of tumours has been observed in DEN-initiated non-promoted mice. Diet complemented with 0.5% and 1.0% curcumin fed prior to, during and after treatment with Fe-NTA in DEN-initiated animals, tumour incidence was reduced dose-dependently to about 45% and 30% respectively. Immunohistochemical studies also revealed the increased formation of 4-hydroxy-2-nonenal (HNE)-modified protein adducts and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in kidney tissue of mice treated with an intraperitoneal injection of Fe-NTA (6.0 mg Fe/kg body weight.). Furthermore, Fe-NTA treatment of mice also resulted in significant elevation of malondialdehyde (MDA), serum urea, and creatinine and decreases renal glutathione. However, the changes in most of these parameters were attenuated dose-dependently by prophylactic treatment of animals with 0.5% and 1% curcumin diet, this may be due to its antioxidative impact of curcumin. These results suggest that intake of curcumin is beneficial for the prevention of renal cell tumours and oxidative stress damage mediated by renal carcinogen, Fe-NTA.

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.

Epidemiological and nonclinical studies investigating effects of iron in carcinogenesis--a critical review

The efficacy and tolerability of intravenous (i.v.) iron in managing cancer-related anemia and iron deficiency has been clinically evaluated and reviewed recently. However, long-term data in cancer patients are not available; yet, long-term i.v. iron treatment in hemodialysis patients is not associated with increased cancer risk. This review summarizes epidemiological and nonclinical data on the role of iron in carcinogenesis. In humans, epidemiological data suggest correlations between certain cancers and increased iron exposure or iron overload. Nonclinical models that investigated whether iron can enhance carcinogenesis provide only limited evidence relevant for cancer patients since they were typically based on high iron doses as well as injection routes and iron formulations which are not used in the clinical setting. Nevertheless, in the absence of long-term outcome data from prospectively defined trials in i.v. iron-treated cancer patients, iron supplementation should be limited to periods of concomitant anti-tumor treatment.

Absolute requirement for iron in the development of chemically induced uroporphyria in mice treated with 3-methylcholanthrene and 5-aminolevulinate

Accumulating evidence, including experiments using cytochrome P450 1a2 (Cyp1a2) gene knock-out mice (Cyp1a2(-/-)), indicates that the development of chemically induced porphyria requires the expression of CYP1A2. It has also been demonstrated that iron enhances and expedites the development of experimental uroporphyria, but that iron alone without CYP1A2 expression, as in Cyp1a2(-/-) mice, does not cause uroporphyria. The role of iron in the development of porphyria has not been elucidated. We examined the in vivo effect of iron deficiency on hepatic URO accumulation in experimental porphyria. Mice were fed diets containing low (iron-deficient diet (IDD), 8.5 mg iron/kg) or normal (normal diet (ND), 213.7 mg iron/kg) levels of iron. They were treated with 3-methylcholanthrene (MC), an archetypal inducer of CYP1A, and 5-aminolevulinate (ALA), precursors of porphyrin and heme. We found that uroporphyrin (URO) levels and uroporphyrinogen oxidation (UROX) activity were markedly increased in ND mice treated with MC and ALA, while the levels were not raised in IDD mice with the same treatments. CYP1A2 levels and methoxyresorufin O-demethylase (MROD) activities, the CYP1A2-mediated reaction, were markedly induced in the livers of both ND and IDD mice treated with MC and ALA. UROX activity, supposedly a CYP1A2-dependent activity, was not enhanced in iron-deficient mice in spite of the fact of induction of CYP1A2. We showed that a sufficient level of iron is essential for the development of porphyria and UROX activity.

Toxicité de l'hexachlorobenzène chez Meriones unguiculatus : effets sur la thyroïde et le foie

The effect of in vivo administered hexachlorobenzene (HCB) on liver and thyroid was studied on Meriones unguiculatus. HCB (1.6, 4, and 16 mg/kg of body weight) has been administered orally to meriones for 30 days. At the end of the experiment, the body weight of the animals did not show significant change. However, the higher dose of HCB treatment led to a pronounced hepatic hypertrophy comparatively to controls. Histological observations revealed many cytomorphological alterations. Cellular necrosis, periportal, and centrolobular vein congestion and cytoplasmic vacuolisation were noted and correlated with the administered doses of HCB. The higher dose of HCB induced modifications in the activities of hepatic transaminases and on thyroid hormones levels: ALAT activity level was more pronounced in males (170+/-24.7 U/l vs. 52.66+/-8.29 U/l in controls) than in females (120+/-12.47 U/l vs. 56+/-5 U/l in controls). However, ASAT activity increased significantly only in females (259+/-29 U/l vs. 244.66+/-18 U/l in controls). Plasma total triiodothyronine (TT3) and total thyroxine (TT4) levels seemed to be sex-dependent in intoxicated animals, since TT4 decreased significantly in males (21.95+/-7.46 nmol/l vs. 40.59+/-1.08 nmol/l in controls) and TT3 in females (1.42+/-0.11 nmol/l vs. 3.96+/-0.48 nmol/l in controls).

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.

Progressive iron overload enhances chemically mediated tumor promotion in murine skin

Iron overload has been shown to enhance chemically mediated cutaneous tumor promotion in animals. However, the majority of these animal studies have used high concentrations of iron before initiating tumor development. The current study was designed to evaluate the effect of small doses of iron on the promotion stage of chemically mediated cutaneous carcinogenesis. We found an increased tumor response in mice initiated with dimethylbenz(a)anthracene (DMBA) when iron at the dose levels of 0.5, 1.0, and 1.5mg/mouse was injected (intramuscularly) once a week into mice at the promotion stage of skin carcinogenesis, employing 12-O-tetradecanoyl phorbol-13-acetate (TPA)/benzoyl peroxide (BPO) as tumor promoter. The appearance of first papilloma and the number of tumors/mouse were recorded weekly. When compared to the control (non-iron-treated) group, the iron-treated groups showed an augmented incidence of tumors and number of tumors/mouse. In iron-treated mice, tumors appeared earlier than in the control group. TPA/BPO treatment resulted in a significant decrease in the activities of antioxidant enzymes and depletion in the level of epidermal reduced glutathione (GSH). TPA treatment in non-iron-treated mice resulted in approximately 20-40% decrease in GSH level and in the activities of antioxidant enzymes, whereas 1.5-mg iron treatment along with TPA treatment resulted in about approximately 30-70% decrease in GSH level and in the activities of antioxidant enzymes. Similarly, treatment of iron along with BPO treatment resulted in a dose-dependent higher depletion of GSH and the antioxidant enzymes as compared to non-iron-treated animals treated with BPO. Further, TPA/BPO-mediated induction in ornithine decarboxylase activity and [3H]thymidine incorporation in cutaneous DNA was approx two- to threefold higher in mice treated with iron as compared to non-iron-treated mice. Cutaneous lipid peroxidation and iron levels were also higher in mice treated with iron as compared to non-iron-treated mice. These data suggest that progressive iron overload can enhance the tumor promotion ability of TPA/BPO in DMBA-initiated murine skin.

Relative Roles of CYP2E1 and CYP1A2 in Mouse Uroporphyria Caused by Acetone

Porphyria cutanea tarda is a liver disease characterized by excess production of uroporphyrin. We previously reported that acetone, an inducer of CYP2E1, enhances hepatic uroporphyrin accumulation in mice treated with iron dextran (Fe) and 5-aminolevulinic acid (ALA). Cyp2e1(-/-) mice treated with Fe and ALA were used to investigate whether CYP2E1 is required for the acetone effect. Hepatic uroporphyrin accumulation was stimulated by acetone in Cyp2e1(-/-) mice to the same extent as in wild-type mice. In the absence of acetone, uroporphyrin accumulated in Cyp2e1(-/-) mice treated with Fe and ALA, but less than in wildtype mice. However, in Cypla2(-/-) mice, uroporphyrin accumulation caused by Fe and ALA, with or without acetone, was completely prevented. Acetone was not an inducer of hepatic CYP1A2 in the wild-type mice. Although acetone is an inducer of CYP2E1, CYP1A2 appears to have the essential role in acetone-enhancement of uroporphyria.

Animal studies addressing the carcinogenicity of TCDD (or related compounds) with an emphasis on tumour promotion

Dioxin and certain structurally related compounds increase the incidence of liver neoplasms in rodents upon chronic bioassay. Short-term studies indicate the lack of direct DNA-damaging effects including covalent binding to DNA; however, secondary mechanisms may be important in the observed carcinogenicity as these chemicals affect a number of pathways necessary for maintenance of normal growth control and differentiation status. Studies with TCDD in the mouse skin support a lack of initiating activity but an ability to promote the growth of previously initiated lesions indicative of a promoting agent. Mouse skin tumour promotion studies indicate that Ah receptor activation may be involved in promotion by TCDD and selected structurally related compounds. While the mechanism of carcinogenicity induced by TCDD is unknown, the processes involved have a no-effect level, which in the rat liver is at an exposure level below 10 ng TCDD/kg/day. At least for the rodent liver, the relative effective dose for cytochrome P450 induction is not a good indicator of promotion potency. Studies on liver tumour promotion in the female rat liver support a non-genotoxic mechanism for the induction of neoplasms by TCDD. The ability of TCDD to enhance proliferation and inhibit apoptotic processes in focal hepatic lesions further supports an indirect mechanism of carcinogenicity.

Carbonyl-iron supplementation induces hepatocyte nuclear changes in BALB/CJ male mice

BACKGROUND/AIMS

In humans, chronic iron excess may induce hepatic fibrosis and/or hepatocellular carcinoma. This work was undertaken to investigate hepatic iron overload outcome in iron-overloaded mice.

METHODS

BALB/cJ male mice received supplements of 0, 0.5, 1.5 and 3% carbonyl-iron for 2, 4, 8 and 12 months. Histological staining, immunohistochemistry using ferritin antibodies and electron microscopic studies were performed on liver. Liver iron concentration was measured biochemically. Mitotic index and hepatocyte nuclear size were evaluated on Feulgen-stained slides.

RESULTS

Liver iron concentration was increased, reaching 13 times control value after 12 months in 3% iron-overloaded mice, and iron was found predominantly in hepatocytes, with a porto-centrolobular decreasing gradient. Neither hepatic fibrosis nor hepatocellular carcinoma was found. Perls' stain positive inclusions containing ferritin were found within hepatocyte nuclei in 3%-overloaded mice. Electron microscopy disclosed that inclusions consisted of ferritin particle aggregates without a limiting membrane. Mice overloaded with 3% iron for 12 months showed larger hepatocyte nuclei than control mice and a mitotic index increase with presence of abnormal tripolar mitotic figures. In addition, some iron-free hepatocytes were observed.

CONCLUSIONS

Carbonyl-iron supplementation produces significant iron overload in mice but does not result in liver fibrosis or hepatocellular carcinoma after 12 months. However, nuclear changes were produced in hepatocytes, and occasional iron-free hepatocytes were observed: these may represent preneoplastic changes caused by iron overload.

Liver preneoplastic changes in mice treated with the herbicide fomesafen

1. Effect of the diphenyl ether herbicide fomesafen on liver preneoplastic changes and porphyrin biosynthesis was examined in male C57BL/6J mice (0.23% in the diet for 14 months) and ICR mice (0.3% in the diet for 50 weeks). Fomesafen treatment resulted in preneoplastic changes (liver nodules and foci of altered hepatocytes) in both strains, uroporphyria developed only in ICR mice. 2. Iron pretreatment (600 mg/kg as a single dose) accelerated the development of fomesafen-induced preneoplastic changes in both mouse strains. The number of foci containing altered hepatocytes, as well as the number and size of liver nodules, were increased in iron-pretreated animals. 3. A single injection of iron induced marked uroporphyria in C57BL/6J mice after 14 months (liver porphyrin content 102 nmol/g). This uroporphyria was further potentiated by fomesafen administration (208 nmol/g). 4. In ICR mice, liver histology was apparently normal after a 3 month recovery from fomesafen treatment (0.32% for 9 months). Liver porphyrin content (260 nmol/g) started to decrease immediately after fomesafen withdrawal, but was still significantly elevated after 3 months (5 nmol/g), as compared to controls (1 nmol/g). 5. It is concluded that the toxicological evaluation of fomesafen should focus on liver porphyrin biosynthesis.

Alterations in total iron, zinc, and calcium levels and their influence on the hepatic activities of gamma-glutamyl transferase and glucose-6-phosphatase in the host bearing transplantable murine lymphoma

The levels of iron, zinc, and calcium in liver as well as serum, together with the enzymatic activities of gamma-glutamyl transferase (GGT, EC 2.3.2.2) and glucose-6-phosphatase (G-6-Pase, EC 3.1.3.9) in liver, were critically monitored over various periods in male Swiss albino mice bearing Dalton's lymphoma (DL), a transplantable ascites-producing tumor. Both hepatic and serum contents of iron, zinc, and calcium were found to be maximally elevated (p < 0.001) on day 15 after tumor transplantation as compared with their contents in normal animals. There was a gradual increase in the activity of GGT in liver in lymphoma-bearing mice in comparison with their normal counterparts, which showed a maximum peak (p < 0.001) on day 15, followed by a continuous and sharp fall. Hepatic G-6-Pase activity was found to decrease continuously throughout the progression of lymphoma as compared with its levels to normal animals. Tumor-cell counts in peritoneal lymph fluids of mice containing DL yielded a maximum count of 155.7 x 10(3) cells/mm3 on day 15. A significant correlation was observed among the levels of different metals, enzymatic activities, and tumor-cell counts at different periods of study. From these results, it can be concluded that the metals studied may have a role in initiating and controlling cellular proliferations, through their effects on modulating the activities of the possibly preneoplastic and neoplastic marker enzymes named above.

Uroporphyria produced in mice by iron and 5-aminolaevulinic acid does not occur in Cyp1a2(-/-) null mutant mice

In the present study we have investigated the putative requirement for the cytochrome P-450 isoform CYP1A2 in murine uroporphyria, by comparing Cyp1a2(-/-) knockout mice with Cyp1a2(+/+) wild-type mice. Uroporphyria was produced by injecting animals with iron-dextran and giving the porphyrin precursor 5-aminolaevulinic acid in the drinking water. Some animals also received 3-methylcholanthrene (MC) to induce hepatic CYP1A2. In both protocols, uroporphyria was elicited by these treatments in the Cyp1a2(+/+) wild-type mice, but not in the null mutant mice. Uroporphyrinogen oxidation activity in hepatic microsomes from untreated Cyp1a2(+/+) mice was 2.5-fold higher than in Cyp1a2(-/-) mice. Treatment with MC increased hepatic CYP1A1 in both mouse lines and hepatic CYP1A2 only in the Cyp1a2(+/+) line, as determined by Western immunoblotting. MC increased hepatic ethoxy- and methoxy-resorufin O-dealkylase activities in both mouse lines, but increased uroporphyrinogen oxidation activity in the Cyp1a2(+/+) wild-type mice only. These results indicate the absolute requirement for hepatic CYP1A2 in causing experimental uroporphyria under the conditions used.

Residues of chlorinated hydrocarbon insecticides in human milk of Jordanian women

A total of 411 milk samples were screened for the residues of the following chlorinated hydrocarbon insecticides using chromatographic methods: DDT insecticides (P,P'-DDT, P,P'-DDE, P,P'-DDD, O,P' -DDT); cyclodiene insecticides (aldrin, endrin, dieldrin, heptachlor, heptachlorepoxide, cis-and trans-chlordane); hexachlorocyclohexane (alpha-HCH, gamma-HCH) and hexachlorobenzene (HCB). The milk samples were obtained from lactating women selected randomly from five different geographical regions in Jordan. These regions were North and Middle Jordan Valley, Amman, Irbid and Zarqa. All of the studied insecticides were found to contaminate human milk in Jordan, but with high variations in the concentration and percentage of population occurrence. P,P'-DDE was the predominant contaminant occurring in 80.3% of studied population, followed by P,P'-DDT occurring in 53.5%. The regional results showed that the DDT residues were also the predominant contaminant in all regions and that the North and Middle Jordan Valley regions were the most affected. Infant's age (i.e. lactation period) had a significant inverse relationship with the concentration of insecticides in the milk fat.

Iron-induced carcinogenesis: the role of redox regulation

Redox cycling is a characteristic of transition metals such as iron. Iron is hypothesized to have been actively involved in the birth of primitive life on earth through the generation of reducing equivalents in the presence of UV light. Iron is an essential metal in mammals for oxygen transport by hemoglobin and for the function of many enzymes including catalase and cytochromes. However, the "free" or "catalytic" form of iron mediates the production of reactive oxygen species via the Fenton reaction and induces oxidative stress. Serum "free" iron is observed in rare situations such as in severe hemochromatosis in which serum transferrin is saturated. However, it is known that superoxide can release "free" iron from ferritin and hemosiderin in the cell. "Free" iron is quite cytotoxic as well as mutagenic and carcinogenic. Iron compounds were first reported to induce sarcomas in rats by Richmond in 1959. Thereafter, several iron-induced carcinogenesis models were established, including the ferric nitrilotriacetate model by Okada and colleagues. Iron may have a role in the carcinogenic process of other transition metals such as copper and nickel, or other kinds of carcinogens such as nitrosamine and even virus-induced carcinogenesis. In humans, genetic hemochromatosis and asbestosis are two major diseases associated with iron-induced carcinogenesis. There is an increasing number of reports of an association between increased body iron stores and increased risk of cancer. Iron-induced oxidative stress results in two possible consequences: (1) redox regulation failure that leads to lipid peroxidation and oxidative DNA and protein damage; (2) redox regulation that activates a variety of reducing and oxystress-protective mechanisms via signal transduction. Both consequences appear to play a role in iron-induced carcinogenesis.

Synergy of iron in the toxicity and carcinogenicity of polychlorinated biphenyls (PCBs) and related chemicals

In Ah-responsive C57BL/10ScSn mice a single dose of iron significantly potentiated the property of the polychlorinated biphenyl (PCB) mixture Aroclor 1254 to induce porphyria by inhibition at the uroporphyrinogen decarboxylase stage of hepatic haem biosynthesis. The induction of liver tumors and other lesions were also enhanced markedly by iron overload suggesting a link between porphyria and cancer. The cellular, molecular and biochemical processes involved have been investigated in attempts to explain these phenomena by an iron-catalysed 'oxidative stress' mechanism.

Pathological mechanisms of hepatic tumour formation in rats exposed chronically to dietary hexachlorobenzene

The chronic dietary administration of hexachlorobenzene (HCB) to rats for a year or more results in the formation of liver tumours described as hepatocellular carcinomas, hepatomas or haemangiomas. The hepatotoxicity of HCB, which is greatest in hamsters and rats, gives rise to peliosis and necrosis with haemosiderosis. This pattern of hepatotoxicity indicates vascular damage, which through haemosiderosis could increase not only the toxic effect of HCB to hepatocytes but also its tumourogenic potential. The present study confirmed vascular damage by the identification of widespread fibrin deposits in the livers of rats chronically exposed to HCB, using an antibody to rat fibrin. Based on our study we suggest that the formation of hepatomas and haemangiomas with elements of peliosis (cystic blood-filled cavities) could be explained by the compensatory hyperplastic responses to hepatocellular necrosis and by the simultaneous loss of hepatocellular cords. The accumulation of iron in the liver would strongly potentiate the development of hepatic tumours, as has been found in HCB and polychlorinated biphenyl-treated mice with iron overload. The implications of this non-genotoxic mechanism of hepatoma formation for the assessment of human health risk are discussed.

Effect of the protoporphyrinogen oxidase-inhibiting herbicide fomesafen on liver uroporphyrin and heptacarboxylic porphyrin in two mouse strains

The effect of the protoporphyrinogen oxidase-inhibiting herbicide fomesafen on liver porphyrin accumulation was studied in long-term high-dose experiments. Fomesafen caused liver accumulation of uroporphyrin and heptacarboxylic porphyrin when fed at 0.25% in the diet to male ICR mice for 5 months (fomesafen-treated mice: 52 nmol uroporphyrin, 21 nmol heptacarboxylic porphyrin/g liver; control mice: traces of uroporphyrin, heptacarboxylic porphyrin not detected). Uroporphyrinogen decarboxylase activity was depressed to about 25% of control values. Iron treatment accelerated the development of this porphyria cutanea tarda-like experimental porphyria both in ICR and C57B1/6J mice. In contrast to other uroporphyrinogen decarboxylase inhibitors, fomesafen treatment did not increase the cytochrome P450IA-related activities and the amount of P450IA2 protein was shown to be significantly decreased by Western immunoblotting. Thus, fomesafen is a unique chemical that inhibits both the oxidation of protoporphyrinogen as well as the conversion of uroporphyrinogen to coproporphyrinogen. However, the accumulation of highly carboxylated porphyrins is evident only after prolonged treatment with high doses of the herbicide.

Influence of iron on the induction of hepatic tumors and porphyria by octachlorostyrene in C57BL/10ScSn mice

Octachlorostyrene (OCS) is an environmental contaminant, present in fish of Northern European waters and the Great Lakes of America. It has many distribution and toxic similarities to hexachlorobenzene (HCB). Administration of OCS at 0.01% of the diet to C57BL/10ScSn mice within iron overload for 18 months gave only a low incidence of hepatic nodular hyperplasia (2/10 survivors) and no hepatocellular adenomas or carcinomas. In contrast, with a similar regime, HCB causes severe liver cancer or nodules in all exposed mice. Whole body autoradiography of mice given [14C]OCS or [14C]HCB showed no gross variations in distribution or covalent binding of the radiolabelled compound to account for the difference between the chemicals in the development of tumours. In 12-week studies, the CYP1A subfamily was induced to a greater degree by HCB than OCS and iron-enhanced uroporphyria was significantly greater with HCB. The findings are consistent with the proposal that uroporphyria and liver cancer induced in mice by HCB are associated through related mechanisms, but occur to a significantly lesser extent with OCS.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Oxidative DNA damage--the effects of certain genotoxic and operationally non-genotoxic carcinogens

A wide variety of oxidative DNA lesions are commonly present in untreated human and animal DNA. One of these lesions, 8-hydroxydeoxyguanosine, has been shown to lead to base mispairing (mutation) on DNA replication. Other lesions remain to be investigated in this respect. Oxidative DNA lesions on cell replication may, in appropriate circumstances, lead to proto-oncogene activation. Oxidative DNA damage, on fixation, may also lead to cytotoxicity followed by regenerative proliferation. The probable or possible importance of oxidative DNA damage is reviewed for various classes of carcinogens and natural processes, including metal ions, high-energy radiation, miscellaneous chemicals, tumor-promoting agents, polyhydroxyphenols/quinones, lipid metabolism, peroxisome proliferators and thyroid function. It is concluded that although the evidence needs considerable strengthening in many of these examples, the available information indicates the potential importance of oxidative DNA damage in the induction of tumors by these agents. It is also possible that non-cancerous degenerative diseases associated with aging are the result of the accumulation of lesions resulting from unrepaired oxidative DNA damage.

Moderate elevation of body iron level and increased risk of cancer occurrence and death

The purpose of the study was to address the hypothesis that elevated body iron increases the risk of cancer occurrence and death, and to determine the dose response. Subjects were 3,287 men and 5,269 women participating in the first National Health and Nutrition Examination Survey who had a transferrin saturation determination at enrollment (1971-1975), who remained alive and cancer-free for at least 4 years, and who were followed to 1988 for cancer outcome. Among 379 men who developed cancer over the study period, the mean transferrin saturation at enrollment was 32.1% whereas among 2,908 who remained cancer-free it was 30.7%; the difference for mortality was 32.3% among 233 deaths vs. 30.8% among 3,054 men not dying of cancer. The mean differences among women were not significant. The mean differences in TIBC and serum iron among men were consistent with the findings for transferrin saturation, and all 3 differences were stable over time when examined by years since blood test. Men and women were divided into 5 groups on the basis of baseline transferrin saturation: 0 to 30%, 30-40%, 40-50%, 50-60%, and 60% and higher. Nineteen percent of men had a baseline transferrin saturation above 40% (the last 3 groups), whereas only 10 percent of women had transferrin saturation above 40%. For men and women combined, risk of cancer occurrence in each group relative to the first was 1.0, 0.95, 1.16, 1.38 and 1.81; for mortality the relative risks were 1.0, 0.96, 1.22, 1.29 and 1.73. There is evidence, in this cohort, of elevated cancer risk in those with moderately elevated iron level. This pattern was seen in women as well as in men.

Genotoxicity assessment of waste products of aluminum plasma etching with the SOS chromotest

We evaluated 36 characteristic waste products from the plasma etching of aluminum for genotoxicity with the SOS chromotest. The majority of the samples showed genotoxic activity in tester strain Escherichia coli PQ37 without metabolic activation using S9 mix. In the presence of S9, a deactivation of the samples was regularly observed. Comparable studies with the Salmonella/microsome (Ames) test using tester strains Salmonella typhimurium TA98 and TA100 indicated actual mutagenicity of waste products. Gas chromatograms of the organic constituents of all waste products were performed in parallel with the genotoxicity assays. In contrast to the similarity of the peak patterns of all chromatograms, the biological effects of individual waste samples showed large differences. Information on chemical composition and the SOS chromotest results of a representative sample recovered over a period of 2 years is given. For this sample, the influences of sample preparation and cytotoxic matrix effects on the test parameters are also shown.

Genetic variation of iron-induced uroporphyria in mice

Iron overload causes inhibition of hepatic uroporphyrinogen decarboxylase (UROD) and uroporphyria in C57BL/10ScSn but not DBA/2 mice [Smith, Cabral, Carthew, Francis and Manson (1989) Int. J. Cancer 43, 492-496]. We have investigated the induction of uroporphyria in 12 inbred strains of mice 25 weeks after iron treatment (600 mg/kg) to determine if there was any correlation with the Ah locus. Under these conditions, inhibition of UROD occurred to varying degrees in Ahd mice (SWR and AKR) as well as nominally Ahb-1 (C57BL/6J, C57BL/10ScSn and C57BL/10-cc) and Ahb-2 strains (BALB/c and C3H/HeJ). Five other Ahb or Ahd strains (C57BL/Ks, A/J, CBA/J, LP and DBA/2) were unaffected. Thus there appeared to be no correlation with the Ah phenotype and this illustrated that some other variable inherited factors are involved. Comparisons between another susceptible strain, A2G, and the congenic A2G-hr/+strain (carrying the recessive hr gene) showed a modulating influence associated with the hr locus. In contrast with individual mice of inbred strains, which showed consistent responses to iron, those of the outbred MF1 strain showed a spectrum of sensitivities as might be expected for a heterogeneic stock. The rate of porphyria development was accelerated by administration of 5-aminolaevulinic acid (5-ALA) in the drinking water, but this did not overcome strain differences. Among four strains the order of susceptibility was SWR > C57BL/10ScSn > C57B1/6J > DBA/2 (the last strain was completely resistant). With degrees of iron loading greater than 600 mg of Fe/kg (1200-1800 mg of Fe/kg) C57BL/10ScSn mice (after 20 weeks) and SWR mice (after 5 weeks which included 4 weeks of 5-ALA treatment) had less inhibition of UROD and a lower uroporphyric response, showing that there was an optimum level of liver iron concentration. Studies on selected microsomal enzyme activities associated with cytochrome P-450 showed no correlation with the propensities of strains to develop porphyria. These activities included the NADPH-dependent oxidation of uroporphyrinogen I to uroporphyrin I.

Lack of carcinogenicity of ferric chloride in F344 rats

The carcinogenicity of ferric chloride, a compound that is used as a food additive, a haemostatic or treatment for hypochromic anaemia, was examined in F344 rats of both sexes. It was dissolved in distilled water at levels of 0, 0.25 or 0.5%, and groups of 50 male and 50 female rats were given one of these solutions ad lib. as their drinking water for up to 2 yr. The mean body weights of the treated rats were lower than control group values for both males and females. A variety of tumours developed in all groups, including the control group, but all these neoplasms were histologically similar to those known to occur spontaneously in this strain of rats, and no statistically significant increase in the incidence of any tumour was found in the treated groups of either sex. Thus it is concluded that under the conditions of this experiment, ferric chloride exerts no carcinogenic potential in F344 rats.

Induction of cytochrome P450 activities by polychlorinated biphenyls in isolated mouse hepatocytes. Influence of Ah-phenotype and iron

Exposure of cultured primary hepatocytes from Ah-responsive male C57BL/10ScSn mice to a polychlorinated biphenyl (PCB) mixture (Aroclor 1254) at 0.1-20 micrograms/mL for up to 96 hr induced cytochrome P4501AI-mediated activity (ethoxyresorufin O-deethylase, EROD) up to 50-fold. In contrast, pentoxyresorufin O-dealkylase (PROD), which in some circumstances is a measure of phenobarbitone-induced cytochrome P450 isoenzymes, was induced only 5-fold. There were similar findings on EROD activities with the pure compounds 3,3',4,4',5,5'-hexachlorobiphenyl, 3,3',4,4',5,5'-hexabromobiphenyl and 3,3',4,4'-tetrachlorobiphenyl(TCB) and also beta-naphthoflavone but not with 2,2',4,4'-TCB or phenobarbitone. The higher concentrations of Aroclor 1254 were also associated with cytotoxicity as estimated by release of alanine aminotransferase (ALT) into the medium. Unlike in C57BL/10ScSn hepatocytes induction of EROD and cytotoxicity was minimal in hepatocytes from the Ah-non-responsive strain DBA/2. Although in vivo the hepatic toxicity and carcinogenicity of polyhalogenated aromatics are markedly potentiated by iron, no enhancement of the cytotoxicity of Aroclor 1254 towards C57BL/10ScSn hepatocytes by iron was observed in vitro. However, iron caused decreased EROD activities and possibly cytochrome P4501AI (as judged by Western blotting) as in vivo. Even in the presence of iron and the haem precursor 5-aminolaevulinic acid (5-ALA) there was no development of uroporphyria in this system although this occurs with Aroclor in vivo and is enhanced by iron. Accumulation of uroporphyrin did occur after extended culture of C57BL/10ScSn hepatocytes on matrigel for 8 days in the presence of 5-ALA and Aroclor 1254 but again no potentiation by iron was observed. Thus, although culture of Ah-responsive and -non-responsive hepatocytes mimics some aspects of the mechanisms of in vivo toxicity of PCBs, there is some unknown associated influence of iron metabolism which cannot, as yet, be produced in vitro but which is of importance in vivo.

Uroporphyria produced in mice by iron and 5-aminolevulinic acid

Porphyria cutanea tarda and the analogous hepatic uroporphyria produced in rodents by aromatic hydrocarbons result from inactivation of hepatic uroporphyrinogen decarboxylase (UROD). Inactivation appears to be iron-dependent and may require induction of cytochromes of the P450IA subfamily. To investigate the hypothesis that the mechanism of inactivation involves an intermediate of haem biosynthesis, we administered iron and the haem precursor, 5-aminolevulinate (ALA), to mice. Iron-overloaded male mice of the Ah-responsive C57BL/6 strain, given ALA solution as their only drink, developed severe uroporphyria after 49 days. ALA did not produce uroporphyria in iron-overloaded male mice of the Ah-nonresponsive DBA/2 strain. Iron or ALA alone did not produce porphyria in either strain. Hepatic iron concentrations and rates of ethoxyresorufin deethylation (an indicator of cytochrome P450IA-mediated activity) were similar in both strains. These experiments show that a haem precursor is involved in iron-dependent inactivation of UROD. They emphasize the importance of inherited factors in determining susceptibility to this type of porphyria, even in the absence of administration of compounds that act through the Ah locus to induce cytochromes of the P450IA subfamily.

Quercetin-induced lipid peroxidation and DNA damage in isolated rat-liver nuclei

The extent of lipid peroxidation and DNA damage induced by quercetin were studied under aerobic conditions in isolated rat-liver nuclei. The effects of iron and copper ions on these two toxic oxidative processes were also investigated. Quercetin induced significant (P less than 0.05) concentration-dependent nuclear lipid peroxidation concurrent with DNA degradation; these effects were enhanced by iron and copper ions. The results suggest that the reactive oxygen species generated by quercetin autoxidation, catalyzed by iron and copper ions, are responsible for the concurrent lipid peroxidation and DNA damage in isolated rat-liver nuclei.

A genotoxicological study of hexachlorobenzene and pentachloroanisole

The potential mutagenic activity of hexachlorobenzene (HCB) and pentachloroanisole (PCA) was investigated. No genotoxicity after application on Salmonella typhimurium (Ames test), Escherichia coli, and human peripheral blood lymphocytes in vitro was observed.

Characterization and accumulation of ferritin in hepatocyte nuclei of mice with iron overload

After a single subcutaneous dose of iron-dextran (600 mg of iron/kg), iron overload developed in C57BL/10ScSn mice. At 4, 24 and 78 wk liver nonheme iron concentrations were 67-, 42- and 21-fold higher than controls, respectively. Much of the iron was in macrophages, but hepatocytes were also strongly positive for Perls' stainable iron. One feature was the development of iron-positive nuclear inclusions in hepatocytes. After a delay of at least 8 wk when no stainable iron was evident, a maximum of 37% of periportal hepatocytes contained inclusions by 24 wk. Although this proportion remained constant for the remainder of the study, the size of the inclusions (which were not membrane-limited) increased to greater than 3 microns in diameter, occupying greater than 25% of the nuclear volume. The presence of iron in the inclusions was confirmed by energy dispersive x-ray microanalysis. Immunocytochemical studies showed that the iron was present as aggregates of ferritin. Quantitation of nonaggregated ferritin molecules by image analyses after electron microscopy demonstrated that within 4 wk ferritin levels in cytoplasm and nucleoplasm had greatly increased but that there was a concentration gradient of approximately one order of magnitude across the nuclear envelope. These findings are consistent with the hypothesis that in iron-loaded mouse hepatocytes there is a slow passage of ferritin-molecules through the nuclear pores; the gradient is maintained by the continual aggregation of ferritin within the nucleus. Intranuclear ferritin may provide a source of iron for catalyzing hydroxyl radical formation in nuclei during some toxic, carcinogenic and aging processes.

Sex-linked hepatic uroporphyria and the induction of cytochromes P450IA in rats caused by hexachlorobenzene and polyhalogenated biphenyls

A marked sex difference in the development of uroporphyria occurred after administration of polychlorinated and polybrominated biphenyls (PCBs and PBBs), as well as hexachlorobenzene (HCB), to F344 rats for 15 weeks. Thus the propensity of female rats to develop uroporphyria appears to be a general response to this class of halogenated chemicals. A heat-stable inhibitor(s) of liver uroporphyrinogen decarboxylase was extractable from uroporphyric livers. Although oxidation of uroporphyrinogen I to uroporphyrin I by hepatic microsomes from rats pretreated with porphyrogenic regimes of HCB and PCBs was induced, there was no correlation with the in vivo sex difference in porphyria development. Levels of total cytochrome P450 and pentoxyresorufin and benzyloxyresorufin dealkylase activities (associated with cytochrome P450IIB1) were greater in microsomes from control, HCB, PCB and PBB treated male rats than females. In contrast, ethoxyresorufin deethylase activity (associated with cytochrome P450IA1) was always significantly greater in females. These findings were confirmed by immunoblotting with polyclonal antibodies to cytochromes P450IA1, IA2 and IIB1. Immunocytochemical studies showed that, even after 30 weeks of HCB exposure, cytochromes P450IA1 and P450IA2 were still more highly induced in female liver, especially in the centrilobular region. The results are consistent with the association of cytochrome P450IA isoenzymes with uroporphyria development, although the sex difference in P450IA levels alone may not be marked enough to provide the complete explanation for the pronounced susceptibility of females to HCB.

Chlorinated biphenyls induce cytochrome P450IA2 and uroporphyrin accumulation in cultures of mouse hepatocytes

Previous enzymatic and immunological studies from this laboratory have indicated a critical role for cytochrome P450IA2-catalyzed uroporphyrinogen oxidation in the development of uroporphyria caused by halogenated aromatic hydrocarbons. To extend these studies, we investigated whether primary cultures of mammalian hepatocytes which are inducible for cytochrome P450IA2 are also inducible for chemically mediated uroporphyria. Hepatocytes were isolated from C57BL/6 mice and maintained on Matrigel, an extracellular matrix isolated from a mouse tumor. When these cultures were treated with 3,4,5,3',4',5'-hexachlorobiphenyl (HCB) and 5-aminolevulinic acid (ALA), they accumulated cytochrome P450IA2 as well as uroporphyrin (URO) and heptacarboxyporphyrin for up to 12 days. Cultures treated with ALA alone accumulated no P450IA2 and very little URO. Neither URO accumulation nor the level of P450IA2 was affected by addition of iron as the nitrilotriacetate complex. Other inducers of P450IA2 in vivo (3,4,5,3',4'-pentachlorobiphenyl, 3,4,3',4'-tetrachlorobiphenyl, and 3-methylcholanthrene) also increased P450IA2 in the cultures and caused URO accumulation in the presence of added ALA. The tetrachlorobiphenyl and methylcholanthrene caused these effects only when given repeatedly. Inducers of other forms of P450 failed to cause URO accumulation in the presence of ALA and iron. Cultures of hepatocytes from DBA mice (which are resistant to the uroporphyria in vivo) accumulated much less P450IA2 or URO when treated with HCB and ALA. These primary cultures of mammalian hepatocytes represent a new experimental model to investigate the role of cytochrome P450IA2 in the mechanism of chemically induced uroporphyria.

Oxidative injury mediated by the hepatic cytochrome P-450 system in conjunction with cellular iron. Effects on the pathway of haem biosynthesis

1. Some polyhalogenated aromatic chemicals such as 2,3,7,8-tetrachloro-p-dioxin, brominated and chlorinated biphenyls, and hexachlorobenzene cause in humans, animals and hepatocyte systems a partial block in haem biosynthesis leading to accumulation and excretion of uroporphyrin, the oxidation product of the unstable biosynthetic intermediate uroporphyrinogen. 2. The involvement of reactive toxic metabolites of the halogenated chemicals has previously been suggested. The evidence presented in this paper supports a different mechanism involving chronic induction of the microsomal cytochrome P-450 system, mobilization of hepatocellular iron and associated oxidative stress. Besides oxidation of uroporphyrinogen to uroporphyrin, an inhibitor of uroporphyrinogen decarboxylase may also be formed. 3. Studies with iron-loaded mice and chicken embryo hepatocytes show that under appropriate conditions iron alone, or chemicals such as beta-naphthoflavone which induce the same cytochromes P-450 isozymes as do the chlorinated aromatics, will cause a similar uroporphyria. These findings provide an experimental model for the human disease porphyria cutanea tarda, sometimes occurring in patients with liver damage. 4. Experiments with rats and iron-loaded mice indicate that there may also be an association between the induction of uroporphyria and the development of liver tumours after administration of polyhalogenated aromatic chemicals.