Check out our New Publishers' Select for Free Articles

Archives of Toxicology (v.86, #2)

Molecular mechanisms of pyrethroid insecticide neurotoxicity: recent advances by David M. Soderlund (pp. 165-181).

Synthetic pyrethroid insecticides were introduced into widespread use for the control of insect pests and disease vectors more than three decades ago. In addition to their value in controlling agricultural pests, pyrethroids are at the forefront of efforts to combat malaria and other mosquito-borne diseases and are also common ingredients of household insecticide and companion animal ectoparasite control products. The abundance and variety of pyrethroid uses contribute to the risk of exposure and adverse effects in the general population. The insecticidal actions of pyrethroids depend on their ability to bind to and disrupt voltage-gated sodium channels of insect nerves. Sodium channels are also important targets for the neurotoxic effects of pyrethroids in mammals but other targets, particularly voltage-gated calcium and chloride channels, have been implicated as alternative or secondary sites of action for a subset of pyrethroids. This review summarizes information published during the past decade on the action of pyrethroids on voltage-gated sodium channels as well as on voltage-gated calcium and chloride channels and provides a critical re-evaluation of the role of these three targets in pyrethroid neurotoxicity based on this information.

Keywords: Pyrethroid; Insecticide; Neurotoxicity; Voltage-gated sodium channel; Voltage-gated calcium channel; Voltage-gated chloride channel

4-Methylsulfanyl-3-butenyl isothiocyanate derived from glucoraphasatin is a potent inducer of rat hepatic phase II enzymes and a potential chemopreventive agent by Ahmed Faizal Abdull Razis; Gina Rosalinda De Nicola; Eleonora Pagnotta; Renato Iori; Costas Ioannides (pp. 183-194).

The objective of this study was to establish whether the phytochemical glucoraphasatin, a glucosinolate present in cruciferous vegetables, and its corresponding isothiocyanate, 4-methylsulfanyl-3-butenyl isothiocyanate, up-regulate enzymes involved in the detoxification of carcinogens and are thus potential chemopreventive agents. Glucoraphasatin and myrosinase were isolated and purified from Daikon sprouts and Sinapis alba L., respectively. Glucoraphasatin (0–10 μM) was incubated for 24 h with precision-cut rat liver slices in the presence and absence of myrosinase, the enzyme that converts the glucosinolate to the isothiocyanate. The intact glucosinolate failed to influence the O-dealkylations of methoxy- and ethoxyresorufin or the apoprotein expression of CYP1 enzymes. Supplementation with myrosinase led to an increase in the dealkylation of methoxyresorufin, but only at the highest concentration of the glucosinolate, and CYP1A2 expression. In the absence of myrosinase, glucoraphasatin caused a marked increase in epoxide hydrolase activity at concentrations as low as 1 μM paralleled by a rise in the enzyme protein expression; at the highest concentration only, a rise was also observed in glucuronosyl transferase activity, but other phase II enzyme systems were unaffected. Addition of myrosinase to the glucoraphasatin incubation maintained the rise in epoxide hydrolase and glucuronosyl transferase activities, further elevated quinone reductase and glutathione S-transferase activities, and increased total glutathione concentrations. It is concluded that at low concentrations, glucoraphasatin, either intact and/or through the formation of 4-methylsulfanyl-3-butenyl isothiocyanate, is a potent inducer of hepatic enzymes involved in the detoxification of chemical carcinogens and merits further investigation for chemopreventive activity.

Keywords: Glucoraphasatin; Isothiocyanates; Glucosinolates; Cruciferous vegetables; Chemoprevention

Urinary bladder cancer risk in relation to a single nucleotide polymorphism (rs2854744) in the insulin-like growth factor-binding protein-3 (IGFBP3) gene by Silvia Selinski; Marie-Louise Lehmann; Meinolf Blaszkewicz; Daniel Ovsiannikov; Oliver Moormann; Christoph Guballa; Alexander Kress; Michael C. Truß; Holger Gerullis; Thomas Otto; Dimitri Barski; Günter Niegisch; Peter Albers; Sebastian Frees; Walburgis Brenner; Joachim W. Thüroff; Miriam Angeli-Greaves; Thilo Seidel; Gerhard Roth; Frank Volkert; Rainer Ebbinghaus; Hans-Martin Prager; Cordula Lukas; Hermann M. Bolt; Michael Falkenstein; Anna Zimmermann; Torsten Klein; Thomas Reckwitz; Hermann C. Roemer; Mark Hartel; Wobbeke Weistenhöfer; Wolfgang Schöps; S. Adibul Hassan Rizvi; Muhammad Aslam; Gergely Bánfi; Imre Romics; Katja Ickstadt; Jan G. Hengstler; Klaus Golka (pp. 195-203).

Currently, twelve validated genetic variants have been identified that are associated with urinary bladder cancer (UBC) risk. However, those validated variants explain only 5–10% of the overall inherited risk. In addition, there are more than 100 published polymorphisms still awaiting validation or disproval. A particularly promising of the latter unconfirmed polymorphisms is rs2854744 that recently has been published to be associated with UBC risk. The [A] allele of rs2854744 has been reported to be associated with a higher promoter activity of the insulin-like growth factor-binding protein-3 (IGFBP3) gene, which may lead to increased IGFBP-3 plasma levels and cancer risk. Therefore, we investigated the association of rs2854744 with UBC in the IfADo case–control series consisting of 1,450 cases and 1,725 controls from Germany, Hungary, Venezuela and Pakistan. No significant association of rs2854744 with UBC risk was obtained (all study groups combined: unadjusted P = 0.4446; adjusted for age, gender and smoking habits P = 0.6510), besides a small effect of the [A] allele in the Pakistani study group opposed to the original findings (unadjusted P = 0.0508, odds ratio (OR) = 1.43 for the multiplicative model) that diminished after adjustment for age, gender and smoking habits (P = 0.7871; OR = 0.93). Associations of rs2854744 with occupational exposure to urinary bladder carcinogens and smoking habits were also not present. A meta-analysis of all available case–control series including the original discovery study resulted in an OR of 1.00 (P = 0.9562). In conclusion, we could not confirm the recently published hypothesis that rs2854744 in the IGFBP3 gene is associated with UBC risk.

Keywords: Insulin growth factor 1 (IGF1); Genome-wide association study (GWAS); Single nucleotide polymorphism (SNP); Ethnic differences; Validation study

2,5-Hexanedione induces human ovarian granulosa cell apoptosis through BCL-2, BAX, and CASPASE-3 signaling pathways by Yan Sun; Yuan Lin; Hong Li; Jin Liu; Xiaohua Sheng; Wenchang Zhang (pp. 205-215).

Studies have shown that 2,5-hexanedione (2,5-HD) is the main active metabolite of n-hexane in the human body. The toxicity of n-hexane and 2,5-hexanedione has been extensively researched, but toxicity to the reproductive system, especially the impact on female reproductive function, has been less frequently reported. In this study, we exposed human ovarian granulosa cells to 0, 16, 64, and 256 μM 2,5-HD in vitro for 24 h. Through hematoxylin–eosin (HE) staining, Hoechst 33342 staining, transmission electron microscopy, and flow cytometry using FITC-Annexin V/PI double staining, 2,5-HD was demonstrated to cause significant apoptosis of human ovarian granulosa cells in a dose-dependent manner. As part of our continuing studies, we investigated the underlying apoptosis mechanism of human ovarian granulosa cells exposed to 0, 16, 64, and 256 μM 2,5-HD in vitro for 24 h. Real-time quantitative PCR and Western blot analysis were used to detect changes in the expression of the apoptosis-related BCL-2 family (BCL-2, BAX) and CASPASE family (CASPASE-3) with increasing 2,5-HD concentration. The results showed that with increasing 2,5-HD doses, the expression of BCL-2 decreased. However, a marked dose-dependent increase in the expression of BAX and active CASPASE-3 (p17) was observed in human ovarian granulosa cells. These results suggest that the mechanisms of 2,5-HD causing increased apoptosis in human ovarian granulosa cells might be through BCL-2, BAX, and CASPASE-3 signaling pathways.

Keywords: 2,5-Hexanedione; Granulosa cells; Ovarian; Apoptosis; BCL-2; BAX; CASPASE-3

Diphenyl ditelluride induces hypophosphorylation of intermediate filaments through modulation of DARPP-32-dependent pathways in cerebral cortex of young rats by Luana Heimfarth; Samanta Oliveira Loureiro; Karina Pires Reis; Bárbara Ortiz de Lima; Fernanda Zamboni; Sabrina Lacerda; Ângela Kronbauer Soska; Luisa Wild; João Batista Teixeira da Rocha; Regina Pessoa-Pureur (pp. 217-230).

We studied the effect of different concentrations of diphenyl ditelluride (PhTe)₂ on the in vitro phosphorylation of glial fibrillary acidic protein (GFAP) and neurofilament (NF) subunits from cerebral cortex and hippocampus of rats during development. (PhTe)₂-induced hypophosphorylation of GFAP and NF subunits only in cerebral cortex of 9- and 15-day-old animals but not in hippocampus. Hypophosphorylation was dependent on ionotropic glutamate receptors, as demonstrated by the specific inhibitors 10 μM DL-AP5 and 50 μM MK801, 100 μM CNQX and 100 μM DNQX. Also, 10 μM verapamil and 10 μM nifedipine, two L-voltage-dependent Ca²⁺ channels (L-VDCC) blockers; 50 μM dantrolene, a ryanodine channel blocker, and the intracellular Ca²⁺ chelator Bapta-AM (50 μM) totally prevented this effect. Results obtained with 0.2 μM calyculin A (PP1 and PP2A inhibitor), 1 μM Fostriecin a potent protein phosphatase 2A (PP2A) inhibitor, 100 μM FK-506 or 100 μM cyclosporine A, specific protein phosphatase 2B inhibitors, pointed to PP1 as the protein phosphatase directly involved in the hypophosphorylating effect of (PhTe)₂. Finally, we examined the activity of DARPP-32, an important endogenous Ca²⁺-mediated inhibitor of PP1 activity. Western blot assay using anti-DARPP-32, anti-pThr34DARPP-32, and anti-pThr75DARPP-32 antibodies showed a decreased phosphorylation level of the inhibitor at Thr34, compatible with inactivation of protein kinase A (PKA) by pThr75 DARPP-32. Decreased cAMP and catalytic subunit of PKA support that (PhTe)₂ acted on neuron and astrocyte cytoskeletal proteins through PKA-mediated inactivation of DARPP-32, promoting PP1 release and hypophosphorylation of IF proteins of those neural cells. Moreover, in the presence of Bapta, the level of the PKA catalytic subunit was not decreased by (PhTe)₂, suggesting that intracellular Ca²⁺ levels could be upstream the signaling pathway elicited by this neurotoxicant and targeting the cytoskeleton.

Keywords: Diphenyl ditelluride; Cytoskeleton; Calcium; Protein phosphatase 1; Protein kinase A; DARPP-32

Diallyl disulfide induces Ca²⁺ mobilization in human colon cancer cell line SW480 by Chung-Yi Chen; Chien-Fu Huang; Ya-Ting Tseng; Soong-Yu Kuo (pp. 231-238).

Diallyl disulfide (DADS), one of the major organosulfur compounds of garlic, is recognized as a group of potential chemopreventive compounds. In this study, we examines the early signaling effects of DADS on human colorectal cancer cells SW480 loaded with Ca²⁺-sensitive dye fura-2. It was found that DADS caused an immediate and sustained rise of [Ca²⁺]_i in a concentration-dependent manner (EC₅₀ = 232 μM). DADS also induced a [Ca²⁺]_i elevation when extracellular Ca²⁺ was removed, but the magnitude was reduced by 45%. Depletion of intracellular Ca²⁺ stores with 2 μM carbonylcyanide m-chlorophenylhydrazone, a mitochondrial uncoupler, didn’t affect DADS’s effect. In Ca²⁺-free medium, the DADS-induced [Ca²⁺]_i rise was abolished by depleting stored Ca²⁺ with 1 μM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor). DADS-caused [Ca²⁺]_i rise in Ca²⁺-containing medium was not affected by modulation of protein kinase C activity. The DADS-induced Ca²⁺ influx was blocked by nicardipine (10 μM). U73122, an inhibitor of phospholipase C, abolished ATP (but not DADS)-induced [Ca²⁺]_i rise. These findings suggest that DADS induced a significant rise in [Ca²⁺]_i in SW480 colon cancer cells by stimulating both extracellular Ca²⁺ influx and thapsigargin-sensitive intracellular Ca²⁺ release via as yet unidentified mechanisms.

Keywords: Ca²⁺ signaling; Diallyl disulfide (DADS); Fura-2; Garlic; SW480

Isoeugenol destabilizes IL-8 mRNA expression in THP-1 cells through induction of the negative regulator of mRNA stability tristetraprolin by Valentina Galbiati; Alice Carne; Montserrat Mitjans; Corrado Lodovico Galli; Marina Marinovich; Emanuela Corsini (pp. 239-248).

We previously demonstrated in the human promyelocytic cell line THP-1 that all allergens tested, with the exception of the prohapten isoeugenol, induced a dose-related release of interleukin-8 (IL-8). In the present study, we investigated whether this abnormal behavior was regulated by the AU-rich element–binding proteins HuR and tristetraprolin (TTP) or by the downstream molecule suppressor of cytokine signaling (SOCS)-3. The contact allergens isoeugenol, diethylmaleate (DEM), and 2,4-dinitrochlorobenzene (DNCB), and the irritant salicylic acid were used as reference compounds. Chemicals were used at concentrations that induced a 20% decrease in cell viability as assessed by propidium iodide staining, namely 100 μg/ml (0.61 mM) for isoeugenol, 100 μg/ml (0.58 mM) for DEM, 3 μg/ml (14.8 μM) for DNCB, and 250 μg/ml (1.81 mM) for salicylic acid. Time course experiments of IL-8 mRNA expression and assessment of IL-8 mRNA half-life, indicated a decreased IL-8 mRNA stability in isoeugenol-treated cells. We could demonstrate that a combination and regulation of HuR and TTP following exposure to contact allergens resulted in a different modulation of IL-8 mRNA half-life and release. The increased expression of TTP in THP-1 cells treated with isoeugenol results in destabilization of the IL-8 mRNA, which can account for the lack of IL-8 release. In contrast, the strong allergen DNCB failing to up-regulate TTP, while inducing HuR, resulted in longer IL-8 mRNA half-life and protein release. SOCS-3 was induced only in isoeugenol-treated cells; however, its modulation did not rescue the lack of IL-8 release, indicating that it is unlikely to be involved in the lack of IL-8 production. Finally, the destabilization effect of isoeugenol on IL-8 mRNA expression together with SOCS-3 expression resulted in an anti-inflammatory effect, as demonstrated by the ability of isoeugenol to modulate LPS or ionomycin-induced cytokine release.

Keywords: Hypersensitivity; Dendritic cells; Cytokines; In vitro toxicology; Alternative method; mRNA stability

Cocaine-induced kidney toxicity: an in vitro study using primary cultured human proximal tubular epithelial cells by Maria João Valente; Rui Henrique; Vânia Vilas-Boas; Renata Silva; Maria de Lourdes Bastos; Félix Carvalho; Paula Guedes de Pinho; Márcia Carvalho (pp. 249-261).

Renal failure resulting from cocaine abuse has been well documented, although the underlying mechanisms remain to be investigated. In the present study, primary cultured human proximal tubular epithelial cells (HPTECs) of the kidney were used to investigate its ability to metabolize cocaine, as well as the cytotoxicity induced by cocaine and its metabolites benzoylecgonine (BE), ecgonine methyl ester (EME) and norcocaine (NCOC). Gas chromatography/ion trap-mass spectrometry (GC/IT-MS) analysis of HPTECs exposed to cocaine (1 mM) for 72 h confirmed its metabolism into EME and NCOC, but not BE. EME levels increased along the exposure time to cocaine, while NCOC concentration diminished after reaching a maximum at 6 h, indicating a possible secondary metabolism for this metabolite. Cocaine promoted a concentration-dependent loss of cell viability, whereas BE and EME were found to be non-toxic to HPTECs at the tested conditions. In contrast, NCOC revealed to have higher intrinsic nephrotoxicity than the parent compound. Moreover, cocaine-induced cell death was partially reversed in the presence of ketoconazole (KTZ), a potent CYP3A inhibitor, supporting the hypothesis that NCOC may play a role in cocaine-induced nephrotoxicity. Cocaine-induced cytotoxicity was found to involve intracellular glutathione depletion at low concentrations and to induce mitochondrial damage at higher concentrations. Under the present experimental conditions, HPTECs death pathway followed an apoptotic pattern, which was evident for concentrations as low as 0.1 mM.

Keywords: Cocaine; Nephrotoxicity; Human renal proximal tubular cells; Metabolism; Apoptosis

Fisetin induces apoptosis in human cervical cancer HeLa cells through ERK1/2-mediated activation of caspase-8-/caspase-3-dependent pathway by Tsung-Ho Ying; Shun-Fa Yang; Su-Ju Tsai; Shu-Ching Hsieh; Yi-Chang Huang; Da-Tian Bau; Yi-Hsien Hsieh (pp. 263-273).

Fisetin is a naturally occurring flavonoid that has been reported to inhibit the proliferation and to induce apoptotic cell death in several tumor cells. However, the apoptosis-inducing effect of fisetin on tumor cell lines was investigated besides HeLa cells. In this study, we found that fisetin induced apoptosis of HeLa cells in a dose- and time-dependent manner, as evidenced by nuclear staining of 4′-6-Diamidino-2-phenylindole (DAPI), flow cytometry assay, and Annexin-V/PI double-labeling. In addition, fisetin triggered the activations of caspases-3 and -8 and the cleavages of poly (ADP-ribose) polymerase, resulting in apoptosis induction. Moreover, treatment of HeLa cells with fisetin induced a sustained activation of the phosphorylation of ERK1/2, and inhibition of ERK1/2 by PD98059 (MEK1/2 inhibitor) or transfection with the mutant ERK1/2 expression vector significantly abolished the fisetin-induced apoptosis through the activation of caspase-8/-3 pathway. The in vivo xenograft mice experiments revealed that fisetin significantly reduced tumor growth in mice with HeLa tumor xenografts. In conclusion, our results indicated that fisetin exhibited anti-cancer effect and induced apoptosis in HeLa cell lines both in vitro and in vivo.

Keywords: Fisetin; Apoptosis; Cervical cancer; Caspase; ERK1/2; HeLa cell

Inhibition of autophagy by 3-methyladenine protects 1321N1 astrocytoma cells against pyocyanin- and 1-hydroxyphenazine-induced toxicity by Amelia J. McFarland; Shailendra Anoopkumar-Dukie; Anthony V. Perkins; Andrew K. Davey; Gary D. Grant (pp. 275-284).

Central nervous system (CNS) infections due to Pseudomonas aeruginosa are difficult to treat and have a high mortality rate. Pyocyanin, a virulence factor produced by P. aeruginosa, has been shown to be responsible for the majority of P. aeruginosa’s pathogenicity in mammalian cells. Several lines of evidence in respiratory cells suggest that this damage is primarily mediated by pyocyanin’s ability to generate ROS and deplete host antioxidant defense mechanisms. However, it has yet to be established whether pyocyanin or 1-hydroxyphenazine have potential toxicity to the CNS. Therefore, the aim of this study was to compare the CNS toxicity of pyocyanin and 1-hydroxyphenazine in vitro and to provide insight into mechanisms that underlie this toxicity using 1321N1 astrocytoma cells. To achieve this, we investigated the contribution of oxidative stress and other mediators of cell death including autophagy, senescence and apoptosis. We show that oxidative stress is not a primary mediator of pyocyanin (0–100 μM) and 1-hydroxyphenazine (0–100 μM) induced toxicity in 1321N1 cells. Instead, our results suggest that autophagy may play a central role. The autophagy inhibitor 3-methyladenine (5 mM) protected 1321N1 astrocytoma cells against both pyocyanin and 1-hydroxyphenazine-induced cell injury and increased accumulation of acidic vesicular organelles, a hallmark of autophagy. Furthermore, apoptosis and senescence events may be secondary to autophagy in pyocyanin and 1-hydroxyphenazine-mediated cell injury. In conclusion, this study provides the first evidence on mechanisms underlying the toxicity of both pyocyanin and 1-hydroxyphenazine to astrocytoma cells and provides novel evidence suggesting that this toxicity may be mediated by the formation of acidic vesicular organelles, a hallmark of autophagic cell death.

Keywords: Pyocyanin; 1-hydroxyphenazine; 3-methyladenine; Astrocytes; Acidic vesicular organelle (AVO)

Acute airway irritation of methyl formate in mice by Søren T. Larsen; Gunnar D. Nielsen (pp. 285-292).

Methyl formate (MF) is a volatile solvent with several industrial applications. The acute airway effects of MF were evaluated in a mouse bioassay, allowing the assessment of sensory irritation of the upper airways, airflow limitation of the conducting airways and deep lung (pulmonary) irritation. MF was studied at vapour concentrations of 202–1,168 ppm. Sensory irritation was the only effect observed, which developed slowly over the 30-min exposure period. The potency at steady state was at least 10-fold higher than expected from a hypothetically similar, but non-reactive compound. Methyl formate may be hydrolysed in vivo to formic acid, a potent sensory irritant, and methanol, a low-potent sensory irritant. Hydrolysis may be catalysed by carboxyesterases, and therefore, the role of the esterases was studied using the esterase inhibitor tri-ortho-cresyl phosphate (TOCP). TOCP pre-treatment reduced the irritation response of MF, suggesting that carboxyesterase-mediated hydrolysis plays a role in the irritative effect. However, even after administration of TOCP, MF was considerably more irritating than expected from a quantitative structure–activity relationship (QSAR) model. The slope of the concentration–effect relationship for formic acid was lower than that for the MF in the low-dose range, suggesting that different receptor activation mechanisms may occur, which may include an effect of MF itself, in addition to an effect of formic acid and potentially an effect from formaldehyde.

Keywords: Methyl formate; Airway irritation; BALB/c mice; Mechanisms of action

A potential human hepatocellular carcinoma inhibitor from Bauhinia purpurea L. seeds: from purification to mechanism exploration by Evandro Fei Fang; Clara Shui Fern Bah; Jack Ho Wong; Wen Liang Pan; Yau Sang Chan; Xiu Juan Ye; Tzi Bun Ng (pp. 293-304).

A 20-kDa Kunitz-type trypsin-chymotrypsin inhibitor, Bauhinia purpurea trypsin inhibitor (BPLTI), has been isolated from the seeds of B. purpurea L. by using liquid chromatography procedures that involved ion exchange chromatography on Sp-Sepharose and Mono S and gel filtration on Superdex 75. BPLTI demonstrated protease inhibitory activities of 7226 BAEE units/mg and 65 BTEE units/mg toward trypsin and α-chymotrypsin, respectively. BPLTI was relatively thermal (0–60°C) and pH (3–10) stable and its activity could be decreased by dithiothreitol treatment. BPLTI exhibited a wide spectrum of anti-proliferative and pro-apoptotic activities especially on human hepatocellular carcinoma Hep G2 cells. However, it was devoid of a significant antiproliferative effect on immortal human hepatic WRL 68 cells. We show here that BPLTI stimulates apoptosis in Hep G2 cells, including (1) evoking DNA damage including the production of chromatin condensation and apoptotic bodies; (2) induction of cell apoptosis/necrosis; (3) mitochondrial membrane depolarization; and (4) increasing the production of cytokines. Taken together, our findings show for the first time that purified protease inhibitor from B. purpurea L. seeds is a promising candidate for the treatment of human hepatocellular carcinoma.

Keywords: Bauhinia purpurea L.; Trypsin inhibitor; Liver cancer; Cytokine; Apoptosis

Carcinogenic potency of perfluorooctane sulfonate (PFOS) on Syrian hamster embryo (SHE) cells by N. Jacquet; M. A. Maire; Y. Landkocz; P. Vasseur (pp. 305-314).

Perfluorooctane sulfonate (PFOS) is the degradation product of many fluoroderivatives and a widespread environmental contaminant. Its persistence, its long half-life in humans and its toxicity explain high concerns on human health side effects in future. PFOS is suspected to be a non-genotoxic carcinogen. In the present work, we assessed carcinogenic potential of PFOS by studying morphological transformation in Syrian hamster embryo (SHE) cells; cell transformation of SHE cells is an in vitro assay recommended by the Organization for Economic Cooperation and Development to detect carcinogens, genotoxic or not. Genotoxicity of PFOS and expression of PPARs genes in SHE cells were also measured. PFOS was shown to induce cell transformation (P < 0.05) at non-cytotoxic concentrations (0.2 and 2 μg/mL) (P ≤ 0.01). No genotoxic effect was recorded in the range of PFOS concentrations tested (2 × 10⁻⁴ to 50 μg/mL) using the single-cell gel electrophoresis (comet) assay after 5 and 24 h of exposure. The expression of PPARs genes was measured by qPCR within the first 24 h and after 7 days of PFOS treatment. Results indicated an increased expression of ppar-β/δ isoform as early as 24 h. After 7 days, the increase of ppar-β/δ mRNA was significant at the concentrations inducing cell transformation (0.2 and 2 μg/mL), while overexpression of ppar-γ and ppar-α did not closely relate to effective concentrations. The results indicate that PFOS behave as a non-genotoxic carcinogen and impacted PPARs genes. Its cell transforming potential paralleled an increased expression of ppar-β/δ.

Keywords: Perfluorooctane sulfonate (PFOS); Carcinogenicity; Cell transformation assay; Genotoxicity; PPARs gene

High incidence of acute promyelocytic leukemia specifically induced by N-nitroso-N-methylurea (NMU) in Sprague–Dawley rats by Yun-Ching Chang; Jeng-Dong Hsu; Wea-Lung Lin; Yi-Ju Lee; Chau-Jong Wang (pp. 315-327).

Carcinogenic agents such as N-methyl-N-nitrosourea can cause tumors. The aims of the present study were to evaluate and classify a subtype of AML (acute myeloid leukemia) that was induced by NMU. According to previous publications, NMU induces not only mammary cancer but also leukemia in Sprague–Dawley (S-D) rats. However, the subtype of leukemia involved in NMU-treated rats is unknown. We found that both organ weight and relative organ weights were significantly higher in NMU-exposed rats than in controls. Morphological changes of rat livers and spleens were assessed by histological evaluation (H&E staining), which found that these tissues were abnormal in appearance. Also, cytological examination of the blood showed immature white blood cells in a smear using Liu’s and Papanicolaou stains, indicating that gross abnormalities and histopathological changes were pathologically observed. NMU leukemia incidence was 97.1%. In this study, immunohistochemical (IHC) analysis was valuable in classifying the leukemia of poorly differentiated blasts induced by NMU. Paraffin blocks were stained for MPO, CD3, CD15, CD20, and CD34 markers. The NMU-induced group was positive for MPO, but negative for CD3, CD15, CD20, and CD34. These CD markers suggest that they are useful in helping diagnose APL (M3) leukemia. The model of NMU-induced leukemogenesis in an S-D rat suggests a more definite way to classify APL. This APL will provide an important tool for chemical carcinogenesis and leukemia studies.

Keywords: Acute promyelocytic leukemia; N-methyl-N-nitrosourea; CD marker; Histopathology; Alkylating agents

Role and interaction of p53, BAX and the stress-activated protein kinases p38 and JNK in benzo(a)pyrene-diolepoxide induced apoptosis in human colon carcinoma cells by Julia Donauer; Ilona Schreck; Urban Liebel; Carsten Weiss (pp. 329-337).

Polycyclic aromatic hydrocarbons are ubiquitous environmental pollutants formed during incomplete combustion of organic material. For example benzo[a]pyrene (B[a]P) is a constituent and contaminant of cigarette smoke, automobile exhaust, industrial waste and even food products. B[a]P is carcinogenic to rodents and humans. B[a]P induces its own metabolism, which generates different metabolites such as the highly reactive electrophilic genotoxin and ultimal carcinogen B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE). BPDE can bind to nucleophilic macromolecules such as proteins and DNA and causes mutations. Multiple defence mechanisms have evolved to protect the cell from DNA damage. Specific signalling pathways operate to detect and repair different kinds of lesions. In case, the damage is poorly removed expansion of damaged cells can be counteracted, e.g., by the inhibition of proliferation or triggering apoptosis. Examples of damage sensors and transducers are stress-activated protein kinases (SAPKs) and the tumour suppressor protein p53. Here, we studied the role of p53 and the pro-apoptotic protein BAX in BPDE-induced cell death by using wild-type- or knock-out-human colon carcinoma cells. As reported previously, we could reconfirm a critical role of p53 in BPDE-induced apoptosis. Furthermore, induced levels of total p53 and its transcriptional target p21 declined at higher BPDE concentrations correlating with reduced rates of apoptosis. Interestingly, increased phosphorylation of p53 at serine 15 remained elevated at higher BPDE concentrations thus disconnecting p53 phosphorylation from downstream apoptosis. Hence, phosphorylation of p53 seems not only to be a more sensitive biomarker of BPDE exposure but might serve other functions unrelated to apoptosis. In addition, we identify BAX as a novel and essential factor to trigger the intrinsic pathway of apoptosis in response to BPDE. Furthermore, BPDE in parallel activates the SAPKs p38 and JNK, which are as well involved in apoptosis. Although several routes of mutual regulation of p53 and SAPK have been described, we present evidence that the SAPK pathway in response to genotoxic stress can unexpectedly operate independently of p53 and controls apoptosis by a novel mechanism possibly downstream of caspases.

Keywords: Polycyclic aromatic hydrocarbons; p53; BAX; Stress-activated protein kinases; Apoptosis

Sections

Personal tools

Archives of Toxicology (v.86, #2)

Sections

Personal tools

Local resources

Archives of Toxicology (v.86, #2)