A short-term assessment of tumor-promotion activity in the livers of rats treated with two genotoxic methylating agents: dimethylnitrosamine and methylnitrosourea

Can apricot kernels fatty acids delay the atrophied hepatocytes from progression to fibrosis in dimethylnitrosamine (DMN)-induced liver injury in rats?

Background and aims

The present study was aimed to analyze the chemical composition of ground apricot kernel (GAK) and examine its effect on hepatic fibrosis in vivo induced by dimethylnitrosamine (DMN) in rats.

Methods and results

Hepatic fibrosis was induced by intraperitoneal injections of 10 mg/kg DMN for 3 consecutive days each week over a period of 4 wk. The rats were randomly assigned to five groups of nine rats each: the negative control group (NC), the hepatic fibrosis group (PC), hepatic fibrosis supplemented with GAK (0.5 mg/kg/BW/rat), hepatic fibrosis supplemented with GAK (1 mg/kg/BW/rat) and hepatic fibrosis supplemented with GAK (1.5 mg/kg/BW/rat). Rats were killed, blood was collected and livers were excised for biochemical measurements and histological examination. Results indicate that the diet supplemented with GAK led to improving liver function, lipid peroxides, and liver CAT, SOD and GSH. These results were confirmed by liver histology. Hierarchically high levels f GAK (1.5 mg/kg/BW/rat) gave the best results compared to other tested levels.

Conclusion

This study demonstrates that GAK administration specifically (1.5 mg/kg/BW/rat) can effectively improve liver fibrosis caused by DMN, and may be used as a therapeutic option and preventive measure against hepatic fibrosis. Furthermore, a human trial would be applied specially GAK is a part of Egyptian diet. The act of why high amounts of GAK was improved biochemical values compared to low or moderate levels tested in this study may be due to increase levels of oleic acid and other polyphenols in apricot kernels

Collaborative study on fifteen compounds in the rat-liver Comet assay integrated into 2- and 4-week repeat-dose studies

A collaborative trial was conducted to evaluate the possibility of integrating the rat-liver Comet assay into repeat-dose toxicity studies. Fourteen laboratories from Europe, Japan and the USA tested fifteen chemicals. Two chemicals had been previously shown to induce micronuclei in an acute protocol, but were found negative in a 4-week Micronucleus (MN) Assay (benzo[a]pyrene and 1,2-dimethylhydrazine; Hamada et al., 2001); four genotoxic rat-liver carcinogens that were negative in the MN assay in bone marrow or blood (2,6-dinitrotoluene, dimethylnitrosamine, 1,2-dibromomethane, and 2-amino-3-methylimidazo[4,5-f]quinoline); three compounds used in the ongoing JaCVAM (Japanese Center for the Validation of Alternative Methods) validation study of the acute liver Comet assay (2,4-diaminotoluene, 2,6-diaminotoluene and acrylamide); three pharmaceutical-like compounds (chlordiazepoxide, pyrimethamine and gemifloxacin), and three non-genotoxic rodent liver carcinogens (methapyrilene, clofibrate and phenobarbital). Male rats received oral administrations of the test compounds, daily for two or four weeks. The top dose was meant to be the highest dose producing clinical signs or histopathological effects without causing mortality, i.e. the 28-day maximum tolerated dose. The liver Comet assay was performed according to published recommendations and following the protocol for the ongoing JaCVAM validation trial. Laboratories provided liver Comet assay data obtained at the end of the long-term (2- or 4-week) studies together with an evaluation of liver histology. Most of the test compounds were also investigated in the liver Comet assay after short-term (1-3 daily) administration to compare the sensitivity of the two study designs. MN analyses were conducted in bone marrow or peripheral blood for most of the compounds to determine whether the liver Comet assay could complement the MN assay for the detection of genotoxins after long-term treatment. Most of the liver genotoxins were positive and the three non-genotoxic carcinogens gave negative result in the liver Comet assay after long-term administration. There was a high concordance between short- and long-term Comet assay results. Most compounds when tested up to the maximum tolerated dose were correctly detected in both short- and long-term studies. Discrepant results were obtained with 2,6 diaminotoluene (negative in the short-term, but positive in the long-term study), phenobarbital (positive in the short-term, but negative in the long-term study) and gemifloxacin (positive in the short-term, but negative in the long-term study). The overall results indicate that the liver Comet assay can be integrated within repeat-dose toxicity studies and efficiently complements the MN assay in detecting genotoxins. Practical aspects of integrating genotoxicity endpoints into repeat-dose studies were evaluated, e.g. by investigating the effect of blood sampling, as typically performed during toxicity studies, on the Comet and MN assays. The bleeding protocols used here did not affect the conclusions of the Comet assay or of the MN assays in blood and bone marrow. Although bleeding generally increased reticulocyte frequencies, the sensitivity of the response in the MN assay was not altered. These findings indicate that all animals in a toxicity study (main-study animals as well as toxicokinetic (TK) satellite animals) could be used for evaluating genotoxicity. However, possible logistical issues with scheduling of the necropsies and the need to conduct electrophoresis promptly after tissue sampling suggest that the use of TK animals could be simpler. The data so far do not indicate that liver proliferation or toxicity confound the results of the liver Comet assay. As was also true for other genotoxicity assays, criteria for evaluation of Comet assay results and statistical analyses differed among laboratories. Whereas comprehensive advice on statistical analysis is available in the literature, agreement is needed on applying consistent criteria.

Histopathological and biochemical effects of green tea and/or licorice aqueous extracts on thyroid functions in male albino rats intoxicated with dimethylnitrosamine

Objective

To investigate histopathological and biochemical effects of green tea and/or licorice aqueous extracts in thyroid functions in male albino rats intoxicated with Dimethylnitrosamine.

Methods

40 Male albino rats were divided into two main groups, 20 normal rats and 20 DMN intoxicated rats. Normal rats were subgrouped into 4 equal groups, group A without treatment (controls), group B treated with green tea, group C treated with licorice, group D treated with green tea and licorice. DMN intoxicated rats were subgrouped into 4 equal groups, group E treated with DMN, group F treated with DMN and green tea, group G treated with DMN and licorice, group H treated with DMN, green tea and licorice. The rats were permitted for free access to solubilized extracts of green tea and or licorice for 4 weeks. All rats in groups E, F, G, H were treated by intraperitoneal DMN (4 mg dissolved in 2.5 ml distilled water/kg body weight) seven times every 2 days in the first two weeks. Plasma total triiodothyronine and tetraiodothyronine were determined by radioimmunoassay. Thyroxine 5^-monodeiodinase activity of liver was determined by spectrophotometeric method. Plasma thyroid stimulating hormone was determined by chemiluminometric technique. Histopathological examination was conducted.

Results

Histopathologically thyroid gland of DMN intoxicated rats showed degeneration (DG)and desquamation (DS) of the lining epithelium and atrophy of many acini with hyperemia (H) in the stromal capillaries and In comparison with control, the administration of DMN alone induced decrease in plasma levels of T3 and T4 while it induced increase in plasma levels of TSH and hepatic activity of Thyroxine 5^-monodeiodinase. Coadminstration of DMN and green tea attenuated the lowering effect of DMN on plasma levels of T3 and T4 and induced increase in these levels but values are still below normal ones while Co administration of DMN with licorice or mixture did not affect these levels. Co administration of green tea and/or licorice with DMN attenuated the rising effect of DMN on hepatic activity of Thyroxine 5^--DI while augmented the rising effect of DMN on plasma level of TSH.

Conclusion

Aqueous extract of green tea may be effective in amelioration of biochemical effects and histopathological lesions induced by DMN.

Relationship between Hepatic Gene Expression Profiles and Hepatotoxicity in Five Typical Hepatotoxicant-Administered Rats

In the field of gene expression analysis, DNA microarray technology has a major impact on many different areas including toxicogenomics, such as in predicting the adverse effects of new drug candidates and improving the process of risk assessment and safety evaluation. In this study, we investigated whether there is relationship between the hepatotoxic phenotypes and gene expression profiles of hepatotoxic chemicals measured by DNA microarray analyses. Sprague-Dawley rats (6 weeks old) were administered five hepatotoxicants: acetaminophen (APAP), bromobenzene, carbon tetrachloride, dimethylnitrosamine, and thioacetamide. Serum biochemical markers for liver toxicity were measured to estimate the maximal toxic time of each chemical. Hepatic mRNA was isolated, and the gene expression profiles were analyzed by DNA microarray containing 1,097 drug response genes, such as cytochrome P450s, other phase I and phase II enzymes, nuclear receptors, signal transducers, and transporters. All the chemicals tested generated specific gene expression patterns. APAP was sorted to a different cluster from the other four chemicals. From the gene expression profiles and maximal toxic time estimated by serum biochemical markers, we identified 10 up-regulated genes and 10 down-regulated genes as potential markers of hepatotoxicity. By Quality-Threshold (QT) clustering analysis, we identified major up- and down-regulated expression patterns in each group. Interestingly, the average gene expression patterns from the QT clustering were correlated with the mean value profiles from the biochemical markers. Furthermore, this correlation was observed at any extent of hepatotoxicity. In this study, we identified 17 potential toxicity markers, and those expression profiles could estimate the maximal toxic time independently of the hepatotoxicity levels. This expression profile analysis could be one of the useful tools for evaluating a potential hepatotoxicant in the drug development process.

DNA adducts and liver DNA replication in rats during chronic exposure to N-nitrosodimethylamine (NDMA) and their relationships to the dose-dependence of NDMA hepatocarcinogenesis

Exposure of rats to the hepatocarcinogen N-nitrosodimethylamine (NDMA) (0.2-2.64 ppm in the drinking water) for up to 180 days resulted in rapid accumulation of N7- and O6-methylguanine in liver and white blood cell DNA, maximum adduct levels being reached within 1-7 days, depending on the dose. The levels of both adducts remained constant up to treatment day 28, subsequently declining slowly to about 40% of maximal levels for the liver and 60% for white blood cells by day 180. In order to elucidate the role of DNA replication in NDMA hepatocarcinogenesis, changes in liver cell labeling index (LI) were also measured on treatment days 21, 120 and 180. Although the time- and dose-dependence of the observed effects were complex, a clear trend towards increased rates of hepatocyte LI, as indicated by BrdU incorporation, with increasing NDMA doses was evident, particularly above 1 ppm, a concentration above which NDMA hepatocarcinogenicity is known to increase sharply. In contrast, no increase in Kupffer cell DNA replication was found at any of the doses employed, in accordance with the low susceptibility of these cells to NDMA-induced carcinogenesis. No significant increase in the occurrence of necrotic or apoptotic cells was noted under the treatment conditions employed. These results suggest that, in addition to the accumulation of DNA damage, alterations in hepatocyte DNA replication during the chronic NDMA exposure may influence the dose-dependence of its carcinogenic efficacy.