Check out our New Publishers' Select for Free Articles

Archives of Toxicology (v.82, #10)

Failure in drug development: the role of inhibition and induction of cytochrome P450 enzymes by J. G. Hengstler; H. M. Bolt (pp. 665-666).

Inhibition and induction of human cytochrome P450 enzymes: current status by Olavi Pelkonen; Miia Turpeinen; Jukka Hakkola; Paavo Honkakoski; Janne Hukkanen; Hannu Raunio (pp. 667-715).

Variability of drug metabolism, especially that of the most important phase I enzymes or cytochrome P450 (CYP) enzymes, is an important complicating factor in many areas of pharmacology and toxicology, in drug development, preclinical toxicity studies, clinical trials, drug therapy, environmental exposures and risk assessment. These frequently enormous consequences in mind, predictive and pre-emptying measures have been a top priority in both pharmacology and toxicology. This means the development of predictive in vitro approaches. The sound prediction is always based on the firm background of basic research on the phenomena of inhibition and induction and their underlying mechanisms; consequently the description of these aspects is the purpose of this review. We cover both inhibition and induction of CYP enzymes, always keeping in mind the basic mechanisms on which to build predictive and preventive in vitro approaches. Just because validation is an essential part of any in vitro–in vivo extrapolation scenario, we cover also necessary in vivo research and findings in order to provide a proper view to justify in vitro approaches and observations.

Keywords: Cytochrome P450 (CYP); Inhibition; Induction

Human CYP2E1 mediates the formation of glycidamide from acrylamide by Eva Settels; Ulrike Bernauer; Richard Palavinskas; Horst S. Klaffke; Ursula Gundert-Remy; Klaus E. Appel (pp. 717-727).

Regarding the cancer risk assessment of acrylamide (AA) it is of basic interest to know, as to what amount of the absorbed AA is metabolized to glycidamide (GA) in humans, compared to what has been observed in laboratory animals. GA is suspected of being the ultimate carcinogenic metabolite of AA. From experiments with CYP2E1-deficient mice it can be concluded that AA is metabolized to GA primarily by CYP2E1. We therefore examined whether CYP2E1 is involved in GA formation in non-rodent species with the focus on humans by using human CYP2E1 supersomes™, marmoset and human liver microsomes and in addition, genetically engineered V79 cells expressing human CYP2E1 (V79h2E1 cells). Special emphasis was placed on the analytical detection of GA, which was performed by gas chromatography/mass spectrometry. The results show that AA is metabolized to GA in human CYP2E1 supersomes™, in marmoset and human liver microsomes as well as in V79h2E1 cells. The activity of GA formation is highest in supersomes™; in human liver it is somewhat higher than in marmoset liver. A monoclonal CYP2E1 human selective antibody (MAB-2E1) and diethyldithiocarbamate (DDC) were used as specific inhibitors of CYP2E1. The generation of GA could be inhibited by MAB-2E1 to about 80% in V79h2E1 cells and to about 90% in human and marmoset liver microsomes. Also DDC led to an inhibition of about 95%. In conclusion, AA is metabolized to GA by human CYP2E1. Overall, the present work describes (1) the application and refinement of a sensitive methodology in order to determine low amounts of GA, (2) the applicability of genetically modified V79 cell lines in order to investigate specific questions concerning metabolism and (3) the involvement, for the first time, of human CYP2E1 in the formation of GA from AA. Further studies will compare the activities of GA formation in genetically engineered V79 cells expressing CYP2E1 from different species.

Keywords: Acrylamide; Glycidamide; Human CYP2E1; Metabolism; Risk assessment

Modulation of serum concentrations and hepatic metabolism of 17β-estradiol and testosterone by amitraz in rats by Chen-Ping Chou; Shui-Yuan Lu; Tzuu-Huei Ueng (pp. 729-737).

The present study has investigated the ability of amitraz, a widely used formamidine pesticide, to modulate serum concentrations and liver microsomal metabolism of 17β-estradiol (E2) and testosterone in rats. Amitraz was administered intraperitoneally to male rats for 4 days and to intact female rats or ovariectomized (OVX) and 0.5 mg/kg E2-supplemented female rats for 7 days. E2 and metabolites were analyzed by gas chromatography-electron capture detection and testosterone and metabolites were analyzed by high-pressure liquid chromatography. In OVX and E2-supplemented females, 50 mg/kg amitraz caused an 85% decrease of serum E2 concentration and a marked increase of 2-OH-E2 concentration. Amitraz at 25 and 50 mg/kg produced 9.0-fold or greater increases of serum testosterone and 2β-OH-testosterone levels in males. Amitraz at 25 mg/kg resulted in no or minimal increases of liver microsomal formation of E2 or testosterone metabolites. Amitraz at 50 mg/kg produced 1.4- to 3.6-fold increases of 2-OH-E2; estrone; 2β-, 6β-, and 16α-OH-testosterone; and androstenedione formation in males and intact females. Amitraz at 50 mg/kg preferentially increased intact female 16β-OH-testosterone production by 8.6-fold. In OVX females, E2 supplement alone or cotreatment with E2 and 50 mg/kg amitraz produced 1.3- to several-fold increases of 2- and 4-OH-E2 formation and 2β- and 16α-OH-testosterone production. The cotreatment increased 6β- and 16β-OH-testosterone formation by 1.8- and 1.6-fold, respectively. The present findings show that amitraz induces hepatic E2 and testosterone metabolism in male and female rats, decreases serum E2 concentration in OVX and E2-supplemented females, but increases serum testosterone in males.

Keywords: Amitraz; Estrogen; Testosterone; Metabolism; Serum steroid; Endocrine disruptor

In vivo and in vitro percutaneous absorption of [¹⁴C]pyrene in Sprague Dawley male rats: skin reservoir effect and consequence on urinary 1-OH pyrene excretion by Jean-Paul Payan; Michel Lafontaine; Patrice Simon; Fabrice Marquet; Catherine Champmartin-Gendre; Dominique Beydon; Elisabeth Ferrari (pp. 739-747).

The skin reservoir effect of [¹⁴C]pyrene (in vivo and in vitro) on percutaneous absorption was determined in male Sprague Dawley rats. The urinary 1-OHpyrene (1-OHPy) excretion was compared between dermal exposure and intravenous administration. In vivo, the percutaneous absorption flux of [¹⁴C]pyrene (200 μg/cm²; 50 μL/cm² of ethanol) determined by sacrificing batches of rats after different exposure times over 4.5 h was 1.0 ± 0.1 μg/cm² h⁻¹. During exposure, penetration flux was twofold higher than absorption flux, indicating a gradual accumulation of pyrene in the skin. [¹⁴C] skin content at the end of exposure was 16 μg/cm², which decreased gradually over time to 2 μg/cm² 68 h after the end of exposure. The total absorbed dose during exposure was threefold lower than that after exposure, indicating a high contribution of pyrene skin content to the systemic availability of the compound. Similar results were obtained in vitro. The apparent elimination rate of [¹⁴C]pyrene (23 h) contained in the skin after an exposure of 4.5 h was similar to the apparent urinary excretion half life of 1-OHPy (21 h). These values are threefold higher than the urinary excretion half life of 1-OHPy after an intravenous administration of pyrene (0.5 mg/kg). In conclusion, absorbed dose and percutaneous absorption flux were well estimated from the 1-OHPy urinary excretion rate. For risk assessment purposes, the penetration flux rather than the absorption flux should be taken into account for topical pyrene exposure.

Keywords: Pyrene; 1-Hydroxypyrene; Percutaneous absorption; Skin reservoir; Biomarker

Piperonyl butoxide activates c-Jun and ATF-2 in the hepatocytes of mice by Masako Muguruma; Katsuhiko Arai; Mitsuyoshi Moto; Jihei Nishimura; Yasuaki Dewa; Kunitoshi Mitsumori (pp. 749-753).

In order to clarify the possible mechanism of hepatocarcinogenesis induced by piperonyl butoxide, we attempted to identify the transcription factor activated by piperonyl butoxide in the male ICR mouse liver. Administration of 0.6% piperonyl butoxide for 24 h elevated the level of liver nuclear proteins that bind to an AP-1 consensus oligonucleotide, and these proteins demonstrated a supershift with the anti-c-Jun antibody. Additionally, immunoblot analysis revealed that piperonyl butoxide induced c-Jun phosphorylation within 8 h of administration, and phosphorylated ATF-2 was detected after 24 h of piperonyl butoxide treatment. Immunohistochemical analysis also demonstrated the presence of phosphorylated ATF-2 in the hepatocyte nuclei of mice fed with 0.6% piperonyl butoxide for 24 h. Furthermore, piperonyl butoxide induced ATF-2 phosphorylation in TLR-3, a mouse immortalized hepatocyte cell line. These results indicated that piperonyl butoxide activated c-Jun and ATF-2 in mouse hepatocytes during the early stage of hepatocarcinogenesis.

Keywords: ATF-2; c-Jun; Mouse; Liver; Piperonyl butoxide

Antioxidant properties of oxime 3-(phenylhydrazono) butan-2-one by Gustavo Orione Puntel; Priscila Gubert; Gisele Louro Peres; Leandro Bresolin; João Batista Teixeira Rocha; Maria Ester Pereira; Vanessa Santana Carratu; Félix A. Antunes Soares (pp. 755-762).

Oximes are a class of compounds normally used to reverse the acetylcholinesterase (AChE) inhibition caused by organophosphates (OPs). Conversely, researches focusing on the possible antioxidant properties of these compounds are lacking in the literature. The aim of this study was to investigate the potential antioxidant and toxic properties of 3-(phenylhydrazono) butan-2-one oxime in mice. In vitro, hydrogen peroxide-induced lipid peroxidation was decreased by low concentrations of the oxime (0.1–1.0 μM); (P < 0.05). Similarly, lipoperoxidation induced by malonate and iron (Fe²⁺) was significantly decreased by the oxime (0.4–1.0 μM) (P < 0.05). Oxime pre-treatment did not modify the basal peroxidation level nor prevented the induced lipid peroxidation determined ex-vivo. The present results suggest that 3-(phenylhydrazono) butan-2-one oxime could be a good antioxidant compound. The absence of toxicity signs after in vivo administration of 3-(phenylhydrazono) butan-2-one oxime to mice may indicate that it could be a safe drug for further studies.

Keywords: Oximes; Antioxidant; Oxygen reactive species

Methotrexate-induced nitrosative stress may play a critical role in small intestinal damage in the rat by Viswa Kalyan Kolli; Premila Abraham; Suganthy Rabi (pp. 763-770).

Methotrexate (MTX), a structural analogue of folic acid, is widely used as a chemotherapeutic agent for leukemia and other malignancies. One of the major toxic effects of MTX is intestinal injury and enterocolitis .The mechanism of gastrointestinal toxicity of methotrexate has not been investigated completely. Therefore cancer chemotherapy has to be accompanied by symptomatic therapy such as antibiotics and anti-diarrheal drugs. It is important to investigate the mechanism by which methotrexate induces intestinal damage in order to perform cancer chemotherapy effectively by preventing the side effects. This study aimed at investigating whether nitrosative stress plays a role in methotrexate induced small intestinal damage using a rat model. Adult male rats were administered methotrexate at the dose of 7 mg/kg body weight intraperitoneally for 3 consecutive days and sacrificed 12 or 24 h after the final dose of methotrexate. Vehicle treated rats served as control. The intestinal tissue was used for light microscopic studies and markers of nitrosative stress including tissue nitrite level and nitrotyrosine. Myeloperoxidase (MPO) activity, a marker of neutrophil infiltration was also measured in intestinal homogenates. The villi were damaged at 12 h and the damage progressed and became severe at 24 h after the final dose of MTX. Biochemically, tissue nitrate was elevated fivefold at 12 h and fourfold at 24 h after the final dose of MTX as compared with control. Nitrotyrosine, measured immunohistochemically was detected in all the parts of the small intestine. Duodenum stained the most for nitrotyrosine, followed by ileum and then jejunum. The staining for nitrotyrosine was more intense at 24 h as compared with 12 h after the final dose of methotrexate. There was marked neutrophil infiltration as evidenced by increase in MPO activity in the small intestines. In conclusion, the results of the present study reveal that nitrosative stress may play a critical role in methotrexate induced small intestinal damage. Intervention studies using nitric oxide synthase inhibitors is being carried out in order to confirm the role of nitrosative stress in methotrexate induced small intestinal damage.

Keywords: Methotrexate; Small intestine; Nitrosative stress; Rat; Nitrotyrosine

Extremely weak tumor-promoting effect of troglitazone on splenic hemangiosarcomas in rasH2 mice induced by urethane by Meilan Jin; Sayaka Matsumoto; Yasuaki Dewa; Jihei Nishimura; Yukie Saekusa; Keiji Hasumi; Kunitoshi Mitsumori (pp. 771-777).

To examine the tumor-promoting effect of troglitazone (TRG), a novel thiazolidinedione insulin-sensitizing agent, on splenic hemangiosarcomas in rasH2 mice, histopathological and molecular analyses were performed in the spleen of female rasH2 mice fed a diet containing 6,000 or 0 ppm TRG for 16 weeks after 1,000 or 0 mg/kg urethane (UR) initiation. Histopathologically, splenic hemangiosarcomas were observed in the UR-alone and UR + TRG groups, but there was no significant difference in the incidence of splenic hemangiosarcomas between the UR-alone and UR+TRG groups. There were increasing tendencies in the number of positive cells for anti-PCNA antibody and gene expression in the UR + TRG group, but such a change was not statistically significant as compared to that in the UR-alone group. The gene expressions of VEGF, VEGFR1, VEGFC, VEGFR2 and Tie2 related to angiogenesis; c-fos related to MAPK cascade activation; and cyclin D1 related to cell cycle in the UR-alone and UR + TRG groups were significantly higher than those in the untreated control group. However, only the Tie2 gene in the UR + TRG group was significantly increased as compared to that in the UR-alone group. These results suggest that the vascular tumor-promoting activity of TRG in rasH2 mice is extremely low in the present experimental condition and a part of the gene related to angiogenesis probably contributes to the promotion of splenic hemangiosarcomas in rasH2 mice given TRG.

Keywords: Troglitazone; PPAR agonist; Urethane; rasH2 mouse

The response of Ty1 test to genotoxins by M. Pesheva; O. Krastanova; R. Stamenova; D. Kantardjiev; P. Venkov (pp. 779-785).

The Ty1 assay is a short-term test for detection of genotoxins based on induction of the transposition of a gene-engineered Ty1 retrotransposon in Saccharomyces cerevisiae cells. Here, we provide evidence that the Ty1 test responds positively in concentration-dependent manner to the carcinogenic genotoxins benz(a)anthracene, benzo(a)pyrene, chenodeoxycholic and taurodeoxycholic free bile acids and to environmental soil samples polluted with carcinogenic substances. The Ty1 test gives negative results with the noncarcinogenic mutagens benz(b)anthracene, benzo(e)pyrene, lithocholic and taurodeoxycholic conjugated bile acids and to soil samples not polluted with carcinogens. Presence or absence of genotoxins in soil samples was evidenced by chemical analysis. Several explanations for the sensitive differential test’s response to genotoxins are proposed and discussed. It is concluded that the Ty1 test can complement existing assays in laboratory and environmental studies showing high sensitivity to a wider spectrum of carcinogenic genotoxins.

Keywords: Ty1 test; Carcinogens; Soil samples

Sections

Personal tools

Archives of Toxicology (v.82, #10)

Sections

Personal tools

Local resources

Archives of Toxicology (v.82, #10)