Studies on mode of action of hexaammine co(III) chloride against diethylnitrosamine‐induced hepatocarcinogenesis in mice

We recently reported the anticarcinogenic potential of hexaammine cobalt(III) chloride, a synthetic complex of cobalt, on diethylnitrosamine (DENA)‐induced carcinogenesis. The present study was conducted to ascertain the possible mode of action of this compound on DENA‐induced hepatocarcinogenesis in male BALB/c mice. Time course evaluation of liver injury markers showed that the low dose of the compound is more effective in ameliorating DENA‐induced changes when administered for longer duration of time. Long‐term exposure of the compound significantly reversed the levels of diacylgylcerol (DAG) and nitric oxide synthase (NOS) induced by DENA, thus suggesting that the compound may hinder the process of chemical carcinogenesis potentially by downregulating the signal transduction mechanism involving DAG and NOS. Furthermore, short‐term intraperitoneal injection of the compound to mice 26 weeks after DENA initiation reduced the cell viability count in preneoplstic liver lesions in a dose‐dependent manner. In conclusion, our results showed that anticarcinogenic effects of hexaammine cobalt(III) chloride result from its influence on signal transduction events mediated through DAG together with its direct cytotoxic action against preneoplastic hepatic lesions induced by DENA in mice. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:193–201, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20280     

Anticarcinogenic effect of brucine in diethylnitrosamine initiated and phenobarbital-promoted hepatocarcinogenesis in rats

We evaluated the effects of brucine on N-nitrosodiethylamine (DENA)-induced hepatocarcinogenesis in rats. Initiation of hepatocarcinogenesis was done by intraperitoneal injection of diethylnitrosamine (DENA) followed by promotion with phenobarbital. The rats were exposed to dietary brucine for 4 weeks prior to initiation, and the treatment was continued for 22 consecutive weeks. Brucine decreased the incidence, total number, multiplicity, size and volume of preneoplastic hepatic nodules in a dose-dependent manner. Administration of DENA induced hepatocellular carcinoma (HCC), as evidenced by changes in histopathological architecture, increased activity of cytochrome P450, decreased activity of glutathione Stransferase (GST) as well as decreased antioxidant status, enhanced lipid peroxidation, increased liver marker enzymes. Western blot analysis showed decreased expression of cyclin D1 and Bcl-2 with activation of caspase-3 and increased expression of Bax. Immunohistochemical demonstrated the decreased expression of the PCNA and VEGF. These results indicate that brucine prevents lipid peroxidation and hepatic cell damage and also protects the antioxidant system in DENA-induced hepatocarcinogenesis.     

Decrease in the level and enzymatic activity of cytochrome P-450 during diethylnitrosamine metabolism in vivo and in vitro

Diethylnitrosamine (DENA) intoxication of rats was accompanied by a reduction of cytochrome P-450 content in the liver, which correlated well with inactivation of cytochrome P-450 during metabolism of DENA in the liver microsomes.     

枯否细胞在实验性肝癌细胞凋亡中的作用研究

探讨Kupffer细胞在大鼠实验性肝癌细胞凋亡中的作用。应用免疫组化方法和TUNEL法对单用二乙基亚硝胺（DENA）诱发的肝癌及用氯化钆（GC）或酶母多糖（ZM）分别阻塞或激活Kupffer细胞后,给以DENA所引起的大鼠肝癌中的增殖细胞核抗原（PCNA）、bax、bcl-2蛋白表达和肝癌细胞的凋亡进行了对比研究,结果显示：肝癌组织的增殖指数在ZM＋DENA组、DENA组、GC＋DENA组依次增高,而凋亡指数在上述各组依次降低。Bax阳性率在ZM＋DENA组明显高于DENA组（P＜0.05）,而ZM＋DENA组bcl-2阳性率明显低于DENA组（P＜0.05）。结果提示：Kupffer细胞可促进实验性肝部细胞凋亡。     

Adrenergic component in the hepatotropic, carcinogenic effect of diethylnitrosamine]

The effect of norepinephine, an adrenomietic drug, and of pyrroxane, its antagonist, on diethylnitrosoamine (DENA) hepatocarcinogenesis was studied in albino rats. Norepinephrine was found to stimulate carcinogenesis, whereas pyrroxane--to inhibit this process; the latter drug decreased the incidence of multicentric tumours of the liver. In vitro experiments on the isolated rat atria showed low DENA concentrations (1x10(-6) to 1x10(-8) M) to sensitize the atrium adrenoreceptors to the endogenous and exogenous norepinephrine. A new hypothesis on the adrenergic component in the DENA carcinogenic effect caused by the endogenous norepinephrine is presented.     

The most important stages of the mechanism of action in vivo of carcinogen diethylnitrosoamine and its effect on the synthesis of RNA,proteins, DNA,and deoxyribonucleotides

The mechanisms of nitric oxide (NO) generation from exogenous and endogenous sources, induced by the addition of the carcinogen diethylnitrosoamine (DENA) to rat organism have been studied. Within 15 h after the addition of DENA, the carcinogen itself acts as an exogenous NO donor. The products of protein degradation (the process induced by DENA) act as endogenous donors of NO. It was shown that the generation of NO from DENA leads to deep hemic and tissue hypoxia and induces the inactivation of oxygen-dependent enzymes, including ribonucleotide reductase, and the inhibition of ATP synthesis. Under these conditions, the protein synthesis and as a consequence the synthesis of deoxyribonucleotides and DNA are strongly suppressed; i.e., DENA produces the effect similar to the action of the antibiotic cycloheximide, an inhibitor of translation. The administration of cycloheximide to the animal organism also led to the appearance of a considerable amount of NO in the blood. It is assumed that NO initiates (on the administration of the carcinogen) or at least enhances (on the administration of cycloheximide) the blockage of the synthesis of the protein, deoxyribonucleotides, and DNA. In response to the disturbance of protein synthesis, the complex of enzymes is activated that accomplish the utilization of the degradation products of proteins, including the inducible form of NO synthase.     

Effects of administration of Embelin and Curcumin on lipid peroxidation, hepatic glutathione antioxidant defense and hematopoietic system during N-nitrosodiethylamine/Phenobarbital-induced hepatocarcinogenesis in Wistar rats

The effects of administration of Embelin (EMB) and Curcumin (CUR) on lipid peroxidation, hepatic glutathione antioxidant defense and hematopoietic cells were examined during N-nitrosodiethylamine (DENA-200 mg kg⁻¹body wt, single I.P injection) initiated and Phenobarbital (PB-0.05% in drinking water orally for 13 weeks) promoted hepatocarcinogenesis in Wistar strain male albino rats. DENA/PB-induced hepatic damage was manifested by a significant drop in the hepatic glutathione antioxidant defense, increased lipid peroxidation and histological alterations like dysplasia, and atypical cells with abnormal chromatin pattern. Treatment with Curcumin (100 mg kg⁻¹body wt) and Embelin (50 mg kg⁻¹body wt) prevented the drop in hepatic glutathione antioxidant defense, decreased lipid peroxidation, minimized the histological alterations induced by DENA/PB, but showed toxic effects on the hematopoietic cells. Results indicate the beneficial effects of Embelin and Curcumin against oxidative tissue damage during chemically-induced hepatocarinogenesis in rats.     

Liver cancer is induced by a subnecrogenic dose of DENA when associated with fasting/refeeding: role of glutathione-transferase and lipid peroxidation.

In previous studies, we reported that fasting/refeeding has a role in sustaining the initiation of liver cancer by a subnecrogenic (noninitiating) dose of diethylnitrosamine (DENA). This research investigated whether the metabolic alterations imposed by fasting/refeeding provide an imbalance between the generation of carcinogenic molecules and the scavenger defense mechanisms in rat liver. Metabolism of DENA, levels of reduced glutathione (GSH) and GSH transferase (GST) activity, as well as basal and stimulated malondialdehyde (MDA) production, were examined. Rats fasted for 4 days showed a decrease in the liver levels of GSH, GST activity, monounsaturated fatty acids and % of labeled nuclei. After 1 day of refeeding, at which point DENA was administered, the levels of GSH recovered, GST activity remained below control values, basal and stimulated MDA production and content of total polyunsaturated fatty acids in liver phospholipids decreased. One day after DENA treatment, MDA production further decreased, although the % of labeled nuclei increased. No significant changes in the content of arachidonic acid, the main target of peroxidation, were observed at any time. The results indicated that the induction of the hepatocellular carcinoma was associated with a depression of GST activity and lipid peroxidation when rats were given 20 mg/kg of DENA after 1 day of refeeding after 4-day fasting.     

Study of promutagen biotransformation in the Ames test. III. The role of conjugation with glucuronic acid and sulfate in the modification of mutagenic effect of nitrosomorpholine, diethylnitrosamine and cyclophosphamide

The role of reactions of conjugation with uridine diphosphoglucuronic acid (UDPGA) and with 3-phosphoadenosine-5-phosphosulfate (PAPS) in modification of the mutagenic effect of diethyl nitrosamine (DENA), nitrosomorpholine (NM) and cyclophosphane (CP) was studied by the Ames test. It was shown that adding UDPGA to the activating mixture significantly decreased the level of the mutagenic effect of DENA, NM and CP on bacteria Salmonella typhimurium TA 1950, when S9 and microsomal fractions of rat liver homogenate were used. Adding PAPS to the activating mixture when S9 and cytosole fractions were used, did not affect mutagenic action of DENA on S. typhimurium TA 1950 and TA 1535, enhancing the mutagenic effect of CP on TA 1535, with no such influence on TA 1950. Introduction of PAPS into the activating mixture elevated the mutagenic effect of NM on both bacterial strains using S9 fraction but not cytosole fraction.     

Comparative in vivo mutagenicity testing by SCE and micronucleus induction in mouse bone marrow

Summary The treatment of mice with repeated injections of BUdR and FUdR allows for the demonstration of differentially stained metaphases from bone marrow after FPG (fluorescence plus Giemsa; Perry and Wolff, 1974) treatment. Thus, it is possible to determine the number of SCE's under in vivo conditions, which appears as a very promising system for mutagenicity testing. We studied the response of this system in comparison to the micronucleus test using six mutagenic agents: triaziquone, cyclophosphamide (CP), dimethylphenyltriazene (PDMT), methylnitronitrosoguandine (MNNG), dimethylnitrosamine (DMNA), and diethylnitrosamine (DENA). With the exception of MNNG and DENA, all these agents induce both, SCE and micronuclei, MNNG and DENA being ineffective in both systems. The most potent SCE-inducing agent was triaziquone, followed by PDMT, CP, and DMNA. The quantitative comparison indicates that SCE are induced at 1/10–1/100 of the concentrations which are required for the detection of micronuclei.     

Antigenic divergence in a primary rat hepatocyte culture after exposure to the hepatic carcinogen N-diethylnitrosamine

Using the indirect immunofluorescence method, the appearance of membrane hetero-organic antigens of kidney origin associated with the Zajdela hepatoma cells was observed on the surface of cells of the rat liver primary culture following a single hepatocarcinogen N-diethylnitrosamine (DENA) treatment before and after explantation. A correlation of antigenic alterations after a single DENA treatment in vivo and in vitro was discovered. No antigens under investigation were discovered in cultured hepatocytes of intact adult rats.     

Early stages of hepatic carcinogenesis after vagotomy

Initial stages of hepatocarcinogenesis have been studied in nonoperated and vagotomized animals. As a carcinogenic substance diethylnitrosamine (DENA) has been used. In order to estimate manifestation of the changes, the histochemical method for revealing glucoso-6-phosphatase activity, adenosine triphosphatase and gamma-glutamyltranspeptidase in the liver has been applied. The disturbance of vagus innervation is stated to delay the course of early stages of hepatocarcinogenesis, induced with DENA.     

Effect of DENA induced hepatocarcinogenesis on neuroendocrine levels in male rats

Hepatocarcinogenesis was induced in Sprague Dawley rats by injecting diethylnitrosamine (DENA); 150 mg/kg body weight, ip, a well known liver carcinogen and a mutagenic agent. Concurrent with the induction of hepatocarcinoma, psychological stress was also elicited from the changes in brain neurotransmitters. Noradrenaline and dopamine, the neurotransmitters of sympathetic system were estimated from the whole brain and corresponding hormones T3, T4 and prolactin were estimated from the blood of such rats. The neuroendocrine cascade and the marker enzyme gamma glutamyl transferase were estimated at 7, 14, 21 and 30 weeks. A direct relationship between noradrenaline, T3 and T4 and a reciprocal relationship between dopamine and prolactin were observed, which may be correlated to the carcinogenic effect of DENA.     

Study of the process of promutagen biotransformation by the Ames test. I. The role of conjugation with glutathione in the modification of the mutagenic activity of nitrosomorpholine, diethylnitrosamine and cyclophosphamide

It is demonstrated that the level of the action of nitrosomorpholine (NM), diethyl nitrosoamine (DENA) and cyclophosphane (CP) promutagens on bacteria is lowered as a result of the Ames test modification by means of addition of reduced glutathione (G-SH) to the activating mixture. The data are presented on the dependence of this phenomenon on concentration of promutagens and G-SH, the period of bacteria preincubation with the compound under study and the activating mixture as well as on concentration of microsomal protein. No changes in the mutagenic effect of NM, DENA and CP were observed when G-SH was substituted for cysteine in equimolar concentration. This fact points to enzymic mechanism involved in elimination of the damaging effect of mutagenic metabolites of the compounds studied.     

Proton-Induced X-ray Emission (PIXE) Analysis and DNA-chain Break study in rat hepatocarcinogenesis: A possible chemopreventive role by combined supplementation of vanadium and beta-carotene

Combined effect of vanadium and beta-carotene on rat liver DNA-chain break and Proton induced X-ray emission (PIXE) analysis was studied during a necrogenic dose (200 mg/kg of body weight) of Diethyl Nitrosamine (DENA) induced rat liver carcinogenesis. Morphological and histopathological changes were observed as an end point biomarker. Supplementation of vanadium (0.5 ppm ad libitum) in drinking water and beta-carotene in the basal diet (120 mg/Kg of body weight) were performed four weeks before DENA treatment and continued till the end of the experiment (16 weeks). PIXE analysis revealed the restoration of near normal value of zinc, copper, and iron, which were substantially altered when compared to carcinogen treated groups. Supplementation of both vanadium and beta-carotene four weeks before DENA injection was found to offer significant (64.73%, P < 0.001) protection against generation of single-strand breaks when compared with the carcinogen control counter parts. A significant stabilization of hepatic architecture of the cells was observed as compared to carcinogen control in vanadium plus beta-carotene treated group. This study thus suggests that vanadium, a prooxidant but potential therapeutic agent yield safe and effective pharmacological formulation with beta-carotene, an antioxidant, in the inhibition of experimental rat hepatocarcinogenesis.     

Pituitary growth hormone and somatotrophs in rats bearing chemically induced hepatomas.

Measurement of pituitary growth hormone (GH) content by polyacrylamide gel electrophoresis (PAGE) showed that rats bearing diethylnitrosamine (DENA) induced hepatomas contained significantly less GH than age-related controls. Light microscopy of these pituitaries revealed many apparently dying somatotrophs in tumour bearing rats. By electron microscopy the somatotrophs of DENA hepatoma rats were relatively inactive and some clearly dying, which could account for the reduced hormone content. However, electron microscopy of somatotrophs of rats with 2-acetyl-aminofluorene (2-AAF) hepatic tumour nodules revealed many very active cells with greatly increased content of free ribosomes and many granules poised for imminent release. Other somatotrophs of these rats showed lysosomal activity indicating reduced secretion after an active phase.     

Inactivation of PEMT2 in hepatocytes initiated by DENA in fasted/refed rats

Phosphatidylethanolamine N-methyltransferase (PEMT) is the enzyme that converts phosphatidylethanolamine (PE) into phosphatidylcholine. We have previously shown that PEMT suppressed hepatoma growth by triggering apoptosis. We investigate whether PEMT controlled cell death and cell proliferation triggered by fasting/refeeding and whether it is a marker of early preneoplastic lesions. The induction of programmed cell death and suppression of cell proliferation by fasting were associated with enhanced PEMT expression and activity, and with a decrease in CTP:phosphocholine cytidylyltransferase expression. Refeeding returned the liver growth and expression of CTP:phosphocholine cytidylyltransferase to control levels, while the expression of PEMT decreased to below control values. After DENA administration, PEMT protein, evaluated by Western blotting, slightly increased, but it remained below control levels. The treatment with 20 mg/kg DENA to refed rats induced the appearance of initiated hepatocytes that were negative for PEMT expression. Present findings indicate that PEMT is a novel tumour marker for early liver preneoplastic lesions.     

Rat liver foci study on coexposure with 50 Hz magnetic fields and known carcinogens

A study was performed to investigate possible interactions by magnetic fields (MF) with the processes of initiation and promotion of chemically induced preneoplastic lesions in rat liver. Male Sprague-Dawley rats were subjected to a 70% partial hepatectomy followed after 24 h by i.p. injection of diethylnitrosamine (DENA) as a tumour initiator. Starting one week after the DENA-treatment phenobarbital (PB) was given to promote growth of enzymatically altered foci of liver cells. MF was applied immediately after the partial hepatectomy and continued until sacrifice after 12 weeks of PB exposure. Homogenous horizontal AC magnetic fields with a frequency of 50 Hz and flux densities of 0.5 μT or 0.5 mT were used. The rats coexposed with MF and DENA plus PB did not gain weight as much as the rats exposed to the chemical agents only. The MF-exposure also resulted in a slight reduction in size and numbers of the focal lesions. The results suggest an interaction of MF with the processes of chemical carcinogenesis either as a result of stress or depending on effects on the proliferation of preneoplastic cells. © 1993 Wiley-Liss, Inc.     

Early induction of TGF-beta1 through a fasting-re-feeding regimen promotes liver carcinogenesis by a sub-initiating dose of diethylnitrosamine

We previously reported that a sub-necrogenic dose (20 mg/kg) of diethylnitrosamine (DENA) can induce the development of liver cancer when rats undergo a fasting-re-feeding regimen. The present study was undertaken to establish whether fasting followed by re-feeding builds up mechanisms able to trigger liver fibrosis, eventually leading to cirrhosis and cancer. Adult male rats, for fasted 4 days, were given 20 mg/kg of DENA after 1 day of re-feeding; in parallel, consistently fed animals receiving 20 mg/kg (sub-necrogenic) or 200 mg/kg (necrogenic dose) of DENA were used as negative and positive controls, respectively. All three groups were then subjected to the 2-acetylaminofluorene/carbon tetrachloride promoting regimen. Fasting induced moderate apoptosis in liver tissue, as evidenced by increased levels of transforming growth factor-beta1 (TGF-beta1) and Bax proteins and by a dramatic drop in the level of Bcl-2. Subsequent re-feeding caused all changes to revert except TGF-beta1 up-regulation. Histological findings of inflammation and fibrosis were consistently associated with increased production of TGF-beta1, the inflammatory cytokine with the most pronounced profibrogenic action. Thus, up-regulation of TGF-beta1 expression appears as a major mechanism by which the fasting-re-feeding regimen predisposes to initiation and promotion of liver carcinogenesis in rats. Avoiding fasting-re-feeding could be considered in the nutritional status of patients with liver fibrosis.