Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Archives of Toxicology (v.75, #6)
No Title by Marta Biagioli; Wim Wätjen; Detmar Beyersmann; Roberto Zoncu; Chiara Cappellini; Matilde Ragghianti; Federico Cremisi; Stefania Bucci (pp. 313-320).
We investigated the induction of apoptosis by cadmium in NIH 3T3 murine fibroblasts. Apoptosis was triggered effectively by 10 µM CdCl2 within 24 h, under which conditions cell viability was reduced by 50%. Cadmium-induced apoptosis was demonstrated by both morphological and biochemical analysis. We have shown that cadmium concentrations of 5–20 µM caused nuclear fragmentation. Moreover, internucleosomal DNA fragmentation was evoked by 10–25 µM CdCl2 within 24 h, as detected by the formation of ladder patterns in DNA electrophoresis. Since the induction of programmed cell death occurs together with modifications in the cell cycle, we examined the ability of cadmium to block cell divisions by using a 5-bromo-2-deoxy-uridine incorporation assay. Our results indicate that about 40% of treated cells are blocked in G0-G1 phase when exposed to 10 µM cadmium for 27 h. Finally, we addressed the question of whether the effect of cadmium could be prevented by suppressing apoptosis. Over-expression of the anti-apoptotic protein Bcl-2 in NIH 3T3 cells protects against cadmium toxicity, thus suggesting a role for Bcl-2 in the regulation of cadmium-induced apoptosis.
Keywords: Cadmium Apoptosis NIH 3T3 murine fibroblasts Bcl-2 Retroviral gene transfer
No Title by Paraskevi Boutsiouki; John P. Thompson; Geraldine F. Clough (pp. 321-328).
Malathion [O,O-dimethyl-S-(1,2-dicarbethoxyethyl)phosphorodithioate] is an organophosphorus insecticide widely used in veterinary medicine and in humans for the treatment of lice. In this study, the rate of the percutaneous absorption of malathion has been measured in human skin, in vivo, using microdialysis. Malathion was detected in tissue dialysate within 30 min of its topical application to the skin of the volar surface of the forearm of healthy volunteers. The concentration of malathion in dialysate increased with lengthening duration of exposure to reach a steady state concentration at 2 h. Prolonged exposure to malathion caused a marked and long-lasting erythema localized to the area of contact. There was no evidence of local tissue oedema or of a neurogenically mediated flare or itch response following topical application. Reducing skin blood flow by the addition of the vasoconstrictor noradrenaline to the dialysis probe perfusate caused an eight-fold increase in the recovery of malathion in the dialysate, which failed to reach a steady state within 5 h. Together, these data confirm that malathion can be absorbed percutaneously and that its distribution within the cutaneous tissue space is influenced by local skin blood flow. They suggest that the increase in skin blood flow caused by malathion may itself play a significant role in enhancing its systemic uptake.
Keywords: Organophosphates Malathion Skin Blood flow Microdialysis Laser Doppler imaging
No Title by Jim E. Riviere; Guilin Qiao; Ronald E. Baynes; James D. Brooks; Moiz Mumtaz (pp. 329-334).
Interactions between chemicals in a mixture and interactions of mixture components with the skin can significantly alter the rate and extent of percutaneous absorption, as well as the cutaneous disposition of a topically applied chemical. The predictive ability of dermal absorption models, and consequently the dermal risk assessment process, would be greatly improved by the elucidation and characterization of these interactions. Pentachlorophenol (PCP), a compound known to penetrate the skin readily, was used as a marker compound to examine mixture component effects using in vitro porcine skin models. PCP was administered in ethanol or in a 40% ethanol/60% water mixture or a 40% ethanol/60% water mixture containing either the rubefacient methyl nicotinate (MNA) or the surfactant sodium lauryl sulfate (SLS), or both MNA and SLS. Experiments were also conducted with 14C-labelled 3,3',4,4'-tetrachlorobiphenyl (TCB) and 3,3',4,4',5-pentachlorobiphenyl (PCB). Maximal PCP absorption was 14.12% of the applied dose from the mixture containing SLS, MNA, ethanol and water. However, when PCP was administered in ethanol only, absorption was only 1.12% of the applied dose. There were also qualitative differences among the absorption profiles for the different PCP mixtures. In contrast with the PCP results, absorption of TCB or PCB was negligible in perfused porcine skin, with only 0.14% of the applied TCB dose and 0.05% of the applied PCB dose being maximally absorbed. The low absorption levels for the PCB congeners precluded the identification of mixture component effects. These results suggest that dermal absorption estimates from a single chemical exposure may not reflect absorption seen after exposure as a chemical mixture and that absorption of both TCB and PCB are minimal in this model system.
Keywords: Polychlorinated biphenyl Pentachlorophenol Dermal Absorption Mixtures
No Title by Dorothee M. Runge; Thomas W. Stock; Thomas Lehmann; Christiane Taege; Ulrike Bernauer; Donna Beer Stolz; Stefan Hofmann; Heidi Foth (pp. 335-345).
Serum-free primary cultures of human bronchial epithelial cells and freshly isolated samples of human bronchial epithelium were used to investigate basal expression of the cytochrome P450 enzyme CYP2E1 and its activation or induction by ethanol in bronchial epithelial cells. The cultures consisted of ≥95% cells of epithelial characteristics as determined by transmission electron microscopy and immunohistochemical staining. Monolayers were obtained from explants over a period of several months via transfer of tissue into new dishes ('generations' 1–5). Using RT-PCR analysis, basal expression of mRNAs coding for CYP2B7, CYP2F1 and CYP2E1 were detected in cultures from several donors. The basal expression of CYP2E1 protein and mRNA showed differences between the donors. The mRNA was detected even in cultures from higher generations and increased in some cultures over time. The CYP2E1 protein content was low and in most cultures of generations 2–5 could not be detected by immunoblot analysis of native protein extracts. Nevertheless, in some cases immunoreactive CYP2E1 protein was present in monolayers obtained from the fourth and fifth transfer (18-week 'generation' ). CYP2E1 activity was measured via 6-hydroxylation of chlorzoxazone either by a destructive assay using cell lysate or by a non-invasive assay using the medium of cell cultures. In short-term cultured isolated bronchial epithelium, ethanol treatment increased CYP2E1 activity by up to 5-fold within 4 days but with inter-individual differences. In cells up to 4 weeks in culture, CYP2E1 activity remained inducible by a single dose of ethanol. Differentiated primary human cells in culture may be useful tools as model systems for the evaluation of CYP2E1-driven processes in man.
Keywords: Human bronchial cell culture CYP2E1 Expression Activation Ethanol Chlorzoxazone
No Title by Ramesh C. Gupta; Dejan Milatovic; Wolf D. Dettbarn (pp. 346-356).
Acute effects of seizure-inducing doses of the organophosphate compound diisopropylphosphorofluoridate (DFP, 1.25 mg/kg s.c.) or the carbamate insecticide carbofuran (CF, 1.25 mg/kg s.c.) on nitric oxide (NO) were studied in the brain of rats. Brain regions (pyriform cortex, amygdala, and hippocampus) were assayed for citrulline as the determinant of NO and for high-energy phosphates (ATP and phosphocreatine) as well as their major metabolites (ADP, AMP, and creatine). Rats, anesthetized with sodium pentobarbital (50 mg/kg i.p.), were killed using a head-focused microwave (power, 10 kW; duration, 1.7 s). Analyses of brain regions of controls revealed significantly higher levels of citrulline in the amygdala (289.8±7.0 nmol/g), followed by the hippocampus (253.8±5.5 nmol/g), and cortex (121.7±4.3 nmol/g). Levels of energy metabolites were significantly higher in cortex than in amygdala or hippocampus. Within 5 min of CF injection, the citrulline levels were markedly elevated in all three brain regions examined, while with DFP treatment, only the cortex levels were elevated at this time. With either acetylcholinesterase (AChE) inhibitor, the maximum increase in citrulline levels was noted 30 min post-injection (>6- to 7-fold in the cortex, and >3- to 4-fold in the amygdala or hippocampus). Within 1 h following DFP or CF injection, marked declines in ATP (36–60%) and phosphocreatine (28–53%) were seen. Total adenine nucleotides and total creatine compounds were reduced (36–58% and 28–48%, respectively). The inverse relationship between the increase in NO and the decease in high-energy phosphates, could partly be due to NO-induced impaired mitochondrial respiration leading to depletion of energy metabolites. Pretreatment of rats with an antioxidant, the spin trapping agent N-tert-butyl-α-phenylnitrone (PBN, 200 mg/kg i.p.), prevented DFP- or CF-induced seizures, while the antioxidant vitamin E (100 mg/kg i.p. per day for 3 days) had no anticonvulsant effect. Both antioxidants, however, significantly prevented the increase of citrulline and the depletion of high-energy phosphates. It is concluded that seizures induced by DFP and CF produce oxidative stress due to a marked increase in NO, causing mitochondrial dysfunction, and thereby depleting neuronal energy metabolites. PBN pretreatment provides protection against AChE inhibitor-induced oxidative stress mainly by preventing seizures. Additional antioxidant actions of PBN may contribute to its protective effects. Vitamin E has direct antioxidant effects by preventing excessive NO production.
Keywords: Anticholinesterase agent Diisopropylphosphorofluoridate Carbamate Citrulline Nitric oxide Nitric oxide synthase Energy-rich phosphates ATP Neuronal oxidative stress N-tert-Butyl-α-phenylnitrone Vitamin E
No Title by Susan Hasmall; Neil James; Kathryn Hedley; Kine Olsen; Ruth Roberts (pp. 357-361).
Peroxisome proliferators (PPs) are rodent nongenotoxic hepatocarcinogens that induce peroxisome proliferation and DNA synthesis, and suppress apoptosis in rodent hepatocytes. PPs act through the PP-activated receptor α (PPARα); tumour necrosis factor α (TNFα) and hepatic nonparenchymal cells (NPCs), the major source of TNF α in the liver, have also been implicated in mediating the rodent hepatic response to PPs. Here we investigate the interaction between PPARα and NPCs in regulating the response to PPs. Using normal hepatocyte cultures containing around 20% NPCs, the PP nafenopin (50 µM) induced DNA synthesis and suppressed transforming growth factor β1-induced apoptosis. However, when the NPCs were removed by differential centrifugation, nafenopin did not induce DNA synthesis or suppress apoptosis in the pure hepatocytes. Reconstitution of the normal hepatocyte cultures by mixing together the pure hepatocytes and the previously separated NPCs in the same proportions as the original cell preparation (17.7±8.7% NPCs) restored the response to nafenopin. Interestingly, nafenopin was still able to induce β-oxidation in the pure hepatocyte cultures, consistent with NPCs being required for PP-induced growth but not for peroxisome proliferation. Next, we evaluated the role of PPARα in the hepatocyte dependency upon NPCs. Interestingly, NPCs isolated from PPARα-null mice, like those isolated from the wild-type NPCs, restored the hepatocyte response to nafenopin. However, as expected, PPARα-null hepatocytes remained non-responsive to PPs, irrespective of the genotype of the added NPCs. These data support a role for NPCs in facilitating a response of hepatocytes to PPs that is ultimately dependent on the presence of PPARα in the hepatocyte.
Keywords: Peroxisome proliferators Apoptosis Proliferation Nonparenchymal Kupffer cells Tumour necrosis factor α
No Title by Lena Holm; Cecilia Berg; Björn Brunström; Yvonne Ridderstråle; Ingvar Brandt (pp. 362-368).
Eggshell thinning among wild birds has been an environmental concern for almost half a century and the underlying mechanisms are still not fully understood. Previously we showed that exposure of quail embryos to ethynylestradiol (EE2 ) caused disorganization of the tubular glands in the shell gland of adult birds. In this study, we have examined the effect of in ovo exposure to EE2 on carbonic anhydrase (CA) localization, especially in the shell gland, because CA is required for shell formation. In the control birds, CA was localized in the cell membranes of the tubular gland cells of the shell gland, whereas the surface epithelium was always devoid of CA. In ovo treatment with 20 ng EE2/g egg resulted in a loss of CA activity in the tubular glands while the surface epithelium showed strong induction of both membrane bound and cytoplasmic CA activity in 49±1% of the cells. The dose 2 ng EE2/g egg resulted in partial loss of tubular gland CA and strong induction of CA activity in 2.5±0.5% of the surface epithelial cells and weaker induction in 22±2% of the epithelial cells. In conclusion, this study shows that embryonic exposure to a xenoestrogen disrupts CA distribution in the adult shell gland. We propose that eggshell thinning in avian wildlife could reflect a functional malformation in the shell gland, already induced by xenoestrogen during embryonic development rather than being caused solely by exposure of the adult bird.
Keywords: Carbonic anhydrase Endocrine disruption Ethynylestradiol Shell gland Quail
No Title by Mehdi Shakibaei; Philippe de Souza; David van Sickle; Ralf Stahlmann (pp. 369-374).
Quinolones are antibacterial agents that have the potential to induce Achilles tendon disorders – such as tendinitis or even ruptures – in patients treated with these drugs. We studied the effects of ciprofloxacin on several proteins of Achilles tendons from immature dogs, 10- to 11-weeks-old. The dogs were treated orally for 5 days with 30 or 200 mg ciprofloxacin/kg body weight or with the vehicle alone. Since quinolone-like alterations in joint cartilage were observed in magnesium-deficient animals, another group was fed a magnesium-deficient diet for 6 weeks. At necropsy, tendons (n=3 from each group) were frozen and stored until analysis when they were homogenized in a lysis buffer to release a soluble fraction of the tendon proteins. Densitometric analysis of the immunoblots with anti-collagen type I, anti-elastin, anti-fibronectin, and anti-integrin antibodies showed a significant reduction of all proteins. For example, collagen type I concentrations (mean ±SD, arbitrary densitometric units) were 3190±217 (controls), 1890±468 (30 mg/kg), 1695±135 (200 mg/kg) and 2053±491 in the magnesium-deficient dogs. The differences between concentrations in controls and all treated groups were statistically significant (P<0.01, t-test). Similarly, compared with control samples, relative concentrations of other proteins in tendons from ciprofloxacin-treated dogs (30 mg/kg) decreased by 73% (elastin), 88% (fibronectin), and 96% (β1 integrin) (data from low-dose group only). A very similar pattern of protein alterations was detected in samples from magnesium-deficient dogs. In conclusion, rather low doses of a fluoroquinolone or a diet-induced magnesium deficiency caused similar biochemical alterations in the soluble fraction of proteins from canine tendons. These findings support our hypothesis that quinolone-induced toxic effects on connective tissue structures are due to the magnesium-antagonistic effects of these antibacterial agents. They also indicate that patients with a latent magnesium deficiency could be at an increased risk of quinolone-induced tendon disorders.
Keywords: Ciprofloxacin Dog Tendon Magnesium Extracellular matrix
No Title by Philip Carthew; Peter N. Lee; Richard E. Edwards; Robert T. Heydon; Barbara M. Nolan; Elizabeth A. Martin (pp. 375-380).
Tamoxifen is a potent rat liver carcinogen, currently being used as a long-term chemopreventative for breast cancer in healthy women. The mechanism by which tamoxifen causes liver cancer in rats is known to be associated with the accumulation of tamoxifen DNA adducts in this organ. We have examined the dose-response relationship of tamoxifen-induced DNA adducts in the liver and the subsequent increase in the development of liver cancer, with and without phenobarbital promotion. Female Wistar (Han) rats were fed 420 ppm tamoxifen in the diet for 0, 1, 4, 8 or 12 weeks after which time rats were either examined immediately for hepatic tamoxifen-induced DNA damage using the 32P-postlabelling assay, or left for lifetime for tumour assessment. A proportion of rats left for lifetime study were given phenobarbital in their drinking water. There was a clear dose-response relationship with respect to duration of tamoxifen exposure for both accumulation of DNA adducts and lifetime risk of liver cancer. In the absence of phenobarbital promotion there was a threshold value for tamoxifen-induced DNA adducts (180 adducts/108 nucleotides) and the subsequent induction of liver cancer. This study demonstrates the relationship between the accumulation of hepatic tamoxifen-induced DNA adducts and the development of liver cancer and establishes the threshold for hepatocarcinogenesis in terms of DNA adduct formation. These data could provide useful information in interpreting the relevance of low levels of DNA adducts in humans.
Keywords: Liver cancer Tamoxifen Phenobarbital DNA adduct