Hepatotoxicity and consequently increased cell proliferation are associated with flumequine hepatocarcinogenesis in mice

DNA modifications that do not cause gene mutations confer the potential for mutagenicity by combined treatment with food chemicals

Cell proliferation plays a key role in fixing mutations induced by DNA damage. We clarified whether this phenomenon occurred after combined treatment with chemicals in food. The effects of antibiotic flumequine (FL), a residue of veterinary medicinal products in foodstuffs, on mutagenicity in the liver were examined in mice treated with estragole (ES), a natural food flavouring compound. Gpt delta mice were orally administered 10 or 100 mg/kg/day ES and simultaneously fed a diet containing 0.4% FL for 4 weeks. Proliferating cell nuclear antigen-positive cells and cell cycle-related genes were additively increased in the livers of combined treatment groups as compared with high-dose ES or FL groups. Mutant frequencies (MFs) in gpt after cotreatment with low-dose ES and FL were significantly increased, although treatment with ES alone increased MFs only in the high-dose group. Sult1a1 mRNA levels were unchanged after FL treatment. Liquid chromatography with tandem-mass spectrometry analysis showed that FL did not affect the amount of ES-specific DNA adducts in the livers, indicating that FL treatment did not influence metabolic pathways of ES. Thus, enhancement of the mutagenic potential of a chemical by chemical-induced cell proliferation may occur as a result of the combined effects of chemicals in food.

Toxicological evaluation of flumequine in pubertal male rats after oral administration for six weeks

Introduction

Veterinarians use flumequine (FLU) widely but its toxicological effects are still unclear.

Material and Methods

FLU doses of 53, 200, or 750 mg/kg were administered orally for six weeks to pubertal male rats for evaluation of their toxicity.

Results

Weight gain was poorer after seven days of exposure to FLU 750, but relative weights of the brain, adrenal and thyroid glands, and testes were notably higher. Haematological and lipid profile parameters, cardiac markers, and inorganic phosphate significantly increased in the FLU 750 group. Blood glucose, oestradiol and serum concentrations of immunoglobulins G (IgG) and E (IgE) significantly decreased after treatment. The levels of interleukins 10 (IL-10) and 6 (IL-6) fell significantly in the FLU 200 and FLU 750 groups. Cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1) and cyclooxygenase-2 (Cox-2) expression amplified after treatment. Serum levels of free triiodothyronine (fT3) and free thyroxine (fT4) reduced in the FLU 200 and FLU 750 groups without changes in total T3 or T4 level. All doses of FLU significantly depressed concentrations of thyroid-stimulating hormone (TSH) and testosterone. Histopathology of thyroid glands from rats treated with FLU 750 showed degeneration and depletion of thyroid follicular epithelial cells. Expression of 8-hydroxydeoxyguanosine (8-OHdG) was increased in a dose-dependent manner in the brain, but decreased in the testes. Expression of CYP1A1 increased in the adrenal and pituitary glands.

Conclusion

The results of this study suggest that the toxicity of FLU in rats is an effect of its disruptive influence on the pituitary-thyroid hormonal system and on the dysfunction of the immune system.

Toxicological Evaluation of Flumequine in Pubertal Male Rats After Oral Administration for Six Weeks

INTRODUCTION

Veterinarians use flumequine (FLU) widely but its toxicological effects are still unclear.

MATERIAL AND METHODS

FLU doses of 53, 200, or 750 mg/kg were administered orally for six weeks to pubertal male rats for evaluation of their toxicity.

RESULTS

Weight gain was poorer after seven days of exposure to FLU 750, but relative weights of the brain, adrenal and thyroid glands, and testes were notably higher. Haematological and lipid profile parameters, cardiac markers, and inorganic phosphate significantly increased in the FLU 750 group. Blood glucose, oestradiol and serum concentrations of immunoglobulins G (IgG) and E (IgE) significantly decreased after treatment. The levels of interleukins 10 (IL-10) and 6 (IL-6) fell significantly in the FLU 200 and FLU 750 groups. Cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1) and cyclooxygenase-2 (Cox-2) expression amplified after treatment. Serum levels of free triiodothyronine (fT3) and free thyroxine (fT4) reduced in the FLU 200 and FLU 750 groups without changes in total T3 or T4 level. All doses of FLU significantly depressed concentrations of thyroid-stimulating hormone (TSH) and testosterone. Histopathology of thyroid glands from rats treated with FLU 750 showed degeneration and depletion of thyroid follicular epithelial cells. Expression of 8-hydroxydeoxyguanosine (8-OHdG) was increased in a dose-dependent manner in the brain, but decreased in the testes. Expression of CYP1A1 increased in the adrenal and pituitary glands.

CONCLUSION

The results of this study suggest that the toxicity of FLU in rats is an effect of its disruptive influence on the pituitary-thyroid hormonal system and on the dysfunction of the immune system.

Enhanced Susceptibility of Ogg1 Mutant Mice to Multiorgan Carcinogenesis

The role of deficiency of oxoguanine glycosylase 1 (Ogg1) Mmh homolog, a repair enzyme of the 8-hydroxy-2’-deoxyguanosine (8-OHdG) residue in DNA, was investigated using the multiorgan carcinogenesis bioassay in mice. A total of 80 male and female six-week-old mice of C57BL/6J background carrying a mutant Mmh allele of the Mmh/Ogg1 gene (Ogg1^−/−) and wild type (Ogg1^+/+) mice were administered N-diethylnitrosamine (DEN), N-methyl-N-nitrosourea (MNU), N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN), N-bis (2-hydroxypropyl) nitrosamine (DHPN) and 1,2-dimethylhydrazine dihydrochloride (DMH) (DMBDD) to induce carcinogenesis in multiple organs, and observed up to 34 weeks. Significant increase of lung adenocarcinomas incidence was observed in DMBDD-treated Ogg1^−/− male mice, but not in DMBDD-administered Ogg1^+/+ animals. Furthermore, incidences of lung adenomas were significantly elevated in both Ogg1^−/− males and females as compared with respective Ogg1^−/− control and DMBDD-treated Ogg1^+/+ groups. Incidence of total liver tumors (hepatocellular adenomas, hemangiomas and hemangiosarcomas) was significantly higher in the DMBDD-administered Ogg1^−/− males and females. In addition, in DMBDD-treated male Ogg1^−/− mice, incidences of colon adenomas and total colon tumors showed a trend and a significant increase, respectively, along with significant rise in incidence of simple hyperplasia of the urinary bladder, and a trend to increase for renal tubules hyperplasia in the kidney. Furthermore, incidence of squamous cell hyperplasia in the forestomach of DMBDD-treated Ogg1^−/− male mice was significantly higher than that of Ogg1^+/+ males. Incidence of small intestine adenomas in DMBDD Ogg1^−/− groups showed a trend for increase, as compared to the wild type mice. The current results demonstrated increased susceptibility of Ogg1 mutant mice to the multiorgan carcinogenesis induced by DMBDD. The present bioassay could become a useful tool to examine the influence of various targets on mouse carcinogenesis.

Contributions of flumequine and nitroarenes to the genotoxicity of river and ground waters

The SOS/umuC assay was performed in conjunction with analytical measurements to identify potential genotoxins in river and adjacent ground waters in the Jialu River basin, China. The major genotoxic activities of the river and adjacent ground waters occurred in the same two fractions (F4 and F11) when assayed using the Salmonella typhimurium strain TA1535/pSK1002. This indicates that ground water near the Jialu River was influenced by the river water. LC-MS/MS analysis indicated that flumequine accounted for 86% and 76% of the genotoxicity in fraction F11 of the river and adjacent ground waters, respectively. When HPLC fractions were tested using the strain NM3009, three fractions showed genotoxic activities for river water sample, while no fractions from ground water samples elicited genotoxic activities. The specific response to the strain NM3009 in one fraction compared with the strain TA1535/pSK1002 suggested the presence of nitroarenes. However, we failed to identify the exact nitroarenes when GC-MS analysis was used to analyze nitroarenes which are well detected in air and soil samples in previous papers.

Gene expression analysis on the dicyclanil-induced hepatocellular tumors in mice

Our previous studies showed the possibility that oxidative stress, including oxidative DNA damage, is involved in the mechanism of dicyclanil (DC)-induced hepatocarcinogenesis at the preneoplastic stage in mice. In this study, the expression analyses of genes, including oxidative stress-related genes, were performed on the tissues of hepatocellular tumors in a two-stage liver carcinogenesis model in mice. After partial hepatectomy, male ICR mice were injected with N-diethylnitrosamine (DEN) and given a diet containing 0 or 1500 ppm of DC for 20 weeks. Histopathological examinations revealed that the incidence of hepatocellular tumors (adenomas and carcinomas) significantly increased in the DEN + DC group. Gene expression analysis on the microdissected liver tissues of the mice in the DEN + DC group showed the highest expression levels of oxidative stress-related genes, such as Cyp1a1 and Txnrd1, in the tumor areas. However, no remarkable up-regulation of Ogg1-an oxidative DNA damage repair gene-was observed in the tumor areas, but the expression of Trail-an apoptosis-signaling ligand gene-was significantly down-regulated in the tumor tissues. These results suggest the possibility that the inhibition of apoptosis and a failure in the ability to repair oxidative DNA damage occur in the hepatocellular DC-induced tumors in mice.

Lack of in vivo mutagenicity and oxidative DNA damage by flumequine in the livers of gpt delta mice

Flumequine (FLU), an anti-bacterial quinolone agent, has been recognized as a non-genotoxic carcinogen for the mouse liver, but recent reports have suggested that some genotoxic mechanism involving oxidative DNA damage may be responsible for its hepatocarcinogenesis. In the present study, we investigated this possibility in the mouse liver using male and female B6C3F1 gpt delta mice fed diet containing 0.4% FLU, a carcinogenic dose, for 13 weeks. Measurements of 8-hydroxydeoxyguanosine levels in liver DNA, and gpt point and deletion mutations revealed no significant increases in any of these parameters in either sex. Histopathologically, centrilobular swelling of hepatocytes with vacuolation was apparent, however, together with significant increase in bromodeoxyuridine-labeling indices in the treated males and females. These results suggest that genotoxicity, including oxidative DNA damage, is not involved in mouse hepatocarcinogenesis by FLU, which might rather solely exert tumor-promoting effects in the liver.

Possible involvement of oxidative stress in dicyclanil-induced hepatocarcinogenesis in mice

Our previous study suggested the possibilities that dicyclanil (DC), a nongenotoxic carcinogen, produces oxidative stress in the liver of the two-stage hepatocarcinogenesis model of mice and the stress induced probably causes secondary oxidative DNA damage. However, clear evidences demonstrating the relationship between DC-induced hepatocarcinogenesis, oxidative stress, and oxidative DNA damage have not been obtained. To clarify the relationship, further investigations were performed in the liver of the partially hepatectomized (PH) mice maintained on diet containing 1,500 ppm of DC for 13 and 26 weeks after intraperitoneal injection of dimethylnitrosamine (DMN). Significant increases in mRNA expressions of some metabolism- and oxidative stress-related genes with a formation of gamma-glutamyltranspeptidase (GGT) positive foci were observed in the DMN + DC + PH group by the treatment of DC for 13 and 26 weeks. The levels of 8-hydroxy-deoxyguanosine (8-OHdG) in the liver DNA also significantly increased in mice of the DMN + DC + PH group at weeks 13 and 26 and mice given DC alone for 26 weeks. The in vitro measurement of reactive oxygen species (ROS) generation from the mouse liver microsomes showed a significant increase of ROS production in the presence of DC. These results suggest that DC induces oxidative stress which is probably derived from its metabolic pathway, partly, and support our previous speculation that oxidative stress plays one of the important roles in the DC-induced hepatocarcinogenesis in mice.

Gene expression analysis in mice liver on hepatocarcinogenesis by flumequine

mRNA expression profiles in the liver from mice treated with flumequine (FL) were analyzed in order to elucidate the mechanism of its tumor-promoting effect. The liver from a C3H/He mouse that received a diet containing 4,000 ppm of FL for 4 weeks was examined by cDNA microarray in comparison with an untreated mouse. Furthermore, to obtain a more comprehensive sequence, time-course changes in selected genes were determined by real-time RT-PCR. Microarray analysis revealed 15 upregulated and 9 downregulated genes in an FL-treated mouse. The upregulated genes included signal transducers and cell cycle regulators. In addition, the levels of stress response genes, particularly glutathione S-transferase (GST) alpha and GSTmu, were very high, indicating the generation of oxidative stress. On the other hand, the downregulated genes included phase I metabolic enzymes, such as cytochrome P450 (CYPs) enzymes, and apoptosis-associated proteins. These changes were confirmed by quantitative RT-PCR and were generally consistent with each other. Time-course observations revealed consistent results, particularly with regard to GSTalpha, GSTmu, ERK5, and CYP2E1. In addition, the expression of 8-oxoguanine DNA glycosylase 1 (OGG1) was increased in a time-dependent manner. These results suggest the possibility that responses against oxidative stress may play a major role in hepatocarcinogenesis by FL in mice.

Hepatotoxic and nephrotoxic effects of Cadmium in the frog Rana ridibunda

Histological and histochemical alterations in the liver and kidneys of the frog Rana ridibunda, which was exposed to 200 ppm aqueous solutions of cadmium for 4, 10 and 30 days, respectively were investigated. In both the liver and kidneys, essential changes appeared after 10 days' exposure, the maximum changes being apparent after 30 days of exposure. In the liver, what was very characteristic was an increase in the area occupied by Kupffer cells, with the area in the animals exposed to cadmium for 30 days being the largest observed. What was also apparent was karyomegaly, polyploidy and infiltration. In addition with regard the kidneys, Hyaline Globules (HG) and apoptotic bodies occurred at a higher rate. At 30 days' exposure, most of the above changes were enhanced. In comparison with 10 days' exposure, fibrosis around the blood vessels and between hepatocytes, as well as Proliferating Cell Nuclear Antigen (PCNA) reactivity and apoptotic bodies increased lightly in the liver. In the kidneys, the most pronounced changes were the increase in numbers of apoptotic bodies, PCNA reactivity and hyaline globules. It was concluded that the variability in positive reactions for various proteins in the hyaline globules may be an indication that these (and possibly other) proteins are synthesized by tumor cells, but, most probably, that they may represent liver damage, progressive nephropathy, or progressive glomerulonephropathy.

Molecular pathological analysis on the mechanism of liver carcinogenesis in dicyclanil-treated mice

To investigate the mechanism of hepatocarcinogenesis due to dicyclanil (DC), an insect growth regulator for sheep, histopathological and molecular biological analyses were performed in the liver of male ICR mice fed on a diet containing 1500 ppm of DC for 2 weeks (Experiment I; Exp. I). In gene expression analyses using a large-scale cDNA microarray and RT-PCR, fluctuations of expressions of metabolism-/oxidation-/reduction-related genes, such as CYP1A, aldehyde dehydrogenase family 1 subfamily A1 (Aldh1a1), and thioredoxin reductase 1 (Txnrd1), were predominantly observed in the liver of the DC-treated group. In Experiment II (Exp. II), small-scale and metabolism/oxidative stress-specific cDNA microarray, real-time RT-PCR, and measurement of NF-kappaB protein were performed in the mice liver using a two-stage hepatocarcinogenesis model, in which the male ICR mice were fed on a diet containing 1500 ppm of DC for 7 weeks after a single injection of dimethylnitrosamine (DMN). These mice were subjected to two-thirds partial hepatectomy (PH) at week 3. During histopathological examinations, a remarkable increase in gamma-glutamyltransferase-positive cells was observed in the DMN+DC+PH group. During the microarray and PCR analyses, the metabolism and oxidative stress-related genes, such as Cyp1a, P450 oxidoreductase (Por), and thioredoxin reductase 1 (Txnrd1); a few DNA damage/repair genes, such as 8-oxoguanine DNA-glycosylase 1 (Ogg1); and growth arrest and DNA-damage-inducible 45 alpha (Gadd45a), were fluctuated in this group, together with a slight increase in the concentration of activated NF-kappaB. These results suggest that DNA damages due to oxidative stress may be involved in the mechanism of DC-induced hepatocarcinogenesis in mice.

Susceptibility of liver proliferative lesions in heterozygous p53 deficient CBA mice to various carcinogens

To investigate the liver tumorigenic sensitivity to various carcinogens in heterozygous p53 deficient [p53 (+/-)] CBA mice and their wild-type littermates [p53 (+/+) mice], 71 p53 (+/-) and 74 p53 (+/+) CBA mice (male, 6-12 weeks of age) were given diet containing 4,000 or 0 ppm flumequine (FL) for 26 weeks or a single intraperitoneal injection of 5 mg/kg body weights dimethylnitrosamine (DMN) at start of the study in Exp. 1, diet containing 6,000 or 0 ppm di(2-ethylhexyl)-phthalate (DEHP) for 26 weeks in Exp. 2, or diet containing 12,000, 6,000 or 0 ppm phenolphthalein (PhP) for 26 weeks in Exp. 3. All surviving animals of these groups were killed after completion of treatment of the test substances for 26 weeks. In the FL groups, the incidences of hepatocellular altered foci in p53 (+/-) mice, the multiplicities of those in p53 (+/-) and p53 (+/+) mice were significantly increased as compared to the corresponding control groups. The incidences and multiplicities of altered foci in the DMN groups were higher than those in the corresponding control groups in p53 (+/-) and p53 (+/+) mice, but no significant differences were indicated between the groups. There were no significant differences in the incidences, multiplicities and proliferating cell nuclear antigen labeling indices of altered foci in the FL or DMN groups between p53 (+/-) and p53 (+/+) mice. There were no significant differences in the incidences and multiplicities of altered foci between the DEHP or PhP and control groups. The present results suggest that p53 gene knocked out heterozygously does not enhance the chemical hepatocarcinogenesis in CBA mice.

Activator protein 1 activation following hypoosmotic stress in HepG2 cells is actin cytoskeleton dependent

BACKGROUND

Following hypoosmotic stress-induced cell volume change, the actin cytoskeleton reorganizes itself. The role of this reorganization in the activation of the phosphatidylinositol 3-OH-kinase/protein kinase B/activator protein 1 (PI-3-K/PKB/AP-1) proliferative signaling cascade is unknown. Focal adhesion kinase (FAK) participates in the cytoskeleton-based activation of PI-3-K. We hypothesized that hypoosmotic stress-induced activation of PKB and AP-1 in HepG2 cells is dependent on an intact actin cytoskeleton and subsequent FAK phosphorylation.

METHODS

HepG2 cells were incubated for 1 h with or without 20 microM cytochalasin D, an actin disrupter, and were then exposed for up to 30 min to hypoosmotic medium (200 mOsm/L) to induce swelling. Tumor necrosis factor alpha (1.4 nM) and medium alone served as positive and negative controls, respectively. Western blots measured cytoplasmic phosphorylated or total FAK and PKB. EMSAs measured nuclear AP-1. All experiments were performed in triplicate.

RESULTS

Exposure to hypoosmotic stress resulted in activation of the following signaling messengers in a sequential fashion: (1) phosphorylation of FAK occurred by 2 min, (2) phosphorylation of PKB occurred by 10 min, (3) nuclear translocation of AP-1 occurred by 30 min. All three signaling events were abolished when these cells were pretreated with cytochalasin D.

CONCLUSION

Actin reorganization following hypoosmotic stress is essential for the FAK-mediated activation of the PI-3-K/PKB/AP-1 proliferative cascade. These data delineate a possible mechanism by which the cell swelling-induced cytoskeletal changes can initiate proliferative signal transduction in human liver cancer.

Age and organ dependent spontaneous generation of nuclear 8-hydroxydeoxyguanosine in male Fischer 344 rats

8-Hydroxydeoxyguanosine (8-OHdG) is a major oxidative DNA adduct playing roles in senescence, carcinogenesis and various disease processes. High-performance liquid chromatography with an electrochemical detection (HPLC-ECD) method has been widely used to assess organ levels of 8-OHdG, and a recently introduced immunohistochemical approach has made it possible to clarify intra-organ localization. In the present study, these methods were employed to reveal age-dependent changes in nuclear 8-OHdG within various tissues of male Fischer 344 rats between 18 fetal days and 104 weeks of age. 8-OHdG was detected in the nuclei of cerebellar small granule and small cortical cells, cerebral nerve cells, and choroid plexus epithelia of the brain and ependymal cells of the spinal cord; parenchymal cells in the anterior lobe of the pituitary and adrenal glands (mainly cortex); bronchial epithelium of the lung; intra-hepatic bile duct, pancreatic duct, glandular gastric and intestinal epithelial cells; renal tubular epithelial cells (mainly medulla); and spermatogonia and spermatocytes of the testis and seminal vesicle epithelia. The nuclear 8-OHdG levels were high (more than two lesions per 10(6) deoxyguanosines) from 7 days to 104 weeks of age in the brain, 3 to 6 weeks in the adrenal gland, 6 to 104 weeks in the lung, and 3 to 52 weeks in the testis. In the other organs, the nuclear 8-OHdG levels remained low throughout. These findings provide a basis for research dealing with oxidative stress by indicating organ-specific and age- but not aging-dependent changes in the localization of spontaneously generated nuclear 8-OHdG in intact rats. The immunohistochemical approach has advantages for assessing variation of 8-OHdG formation at the cellular level not accessible to the HPLC-ECD method.