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.73, #12)
Fluoride-induced ultrastructural changes in exocrine pancreas cells of rats: fluoride disrupts the export of zymogens from the rough endoplasmic reticulum (rER) by Saburou Matsuo; Hiroshi Nakagawa; Ken-ichi Kiyomiya; Masaru Kurebe (pp. 611-617).
Influence of fluoride on exocrine pancreas cells was examined morphologically with traditional and prolonged osmium fixation techniques for electron microscopy in the enamel fluorosis model rats injected subcutaneously twice a day with 20 mg/kg body weight of sodium fluoride. Although the rough endoplasmic reticulum (rER) of exocrine pancreas cells in control rats was laminated and oriented parallel to the circumference of the nucleus, the rER of the cells in NaF-treated rats was dilated, disrupted the laminated arrangement, and changed to the globular-shape rER. Many intracisternal granules were formed in these globular-shape rER of the cells exposed to fluoride. Lots of autophagosomes were also seen in the exocrine cells with NaF treatment. The autophagosomes were limited with a double or multiple membranes, and contained cytoplasmic organelles and/or the intracisternal granules. The outer and inner leaflets of double membranes of the autophagosomes were usually separated by a distinct electron-lucent area. In prolonged osmium fixation, the area between the double membranes of the autophagosome was filled with osmiun reaction deposits. Many autophagosomes were encircled with the single or multiple osmiophilic layers. In some cases, the osmium positive saccules also surrounded the free surface of the globular-shape rER containing intracisternal granules. These findings indicate that fluoride disrupts the export of zymogens from the rER, resulting in formation of intracisternal granules and autophagosomes, and that the osmiophilic saccules participate in sequestration of cytoplasmic organelles in forming autophagosomes.
Keywords: Key words Autophagosome; Exocrine pancreas cell; Fluoride; Intracellular transport
CYP2E1 expression in bone marrow and its intra- and interspecies variability: approaches for a more reliable extrapolation from one species to another in the risk assessment of chemicals by Ulrike Bernauer; Bärbel Vieth; Rainer Ellrich; Barbara Heinrich-Hirsch; Gerd-Rüdiger Jänig; Ursula Gundert-Remy (pp. 618-624).
When characterizing the health risks for man by exposure to chemicals, species-specific differences have to be taken into consideration, otherwise extrapolation from animal data to the human situation would be inadequate. The site-specific toxicity of chemicals may be explained by the following alternatives: (1) reactive metabolites are generated in the liver and subsequently transported to the target tissue(s); (2) metabolism of the parent compound occurs in the target tissue, a pathway by which the enzymes necessary for activation must be expressed in the target tissue. Cytochrome P450 2E1 (CYP2E1) is an important phase-I enzyme activating several chemicals. In the study described in this paper, myeloid intra- and interspecies variability in the expression of CYP2E1 has been investigated in rats, rabbits and man, because the bone marrow represents an important target organ for toxic effects of several chemicals, e.g. benzene. CYP2E1 at the protein level was detected by Western blotting and enzyme activities were determined by CYP2E1-dependent hydroxylation of chlorzoxazone (CLX). In the bone marrow of Wistar rats, the CLX hydroxylase activities were within the same order of magnitude (range: 0.1–0.4 pmol/mg protein per min) as previously described for mice (range 0.2–0.8 pmol/mg protein per min), whereas the CYP2E1 activities in two strains of rabbits were significantly higher (range: 1.7–4.7 pmol/mg protein per min) than in the rodents (P < 0.05). In human CD34+ bone marrow stem cells, CYP2E1 could also be detected on the protein level by Western blotting. The data demonstrate a presence of CYP2E1 in the bone marrow of all species investigated, thus supporting the hypothesis of CYP2E1-dependent local metabolism of several chemicals as a factor possibly contributing to their myelotoxicity and haematotoxicity. The data show that intraspecies/intrastrain variability of CYP2E1 activity in rodents is small. However, CYP2E1 activity between rodents and a non-rodent species was quite different indicating considerable interspecies variability.
Keywords: Key words Risk assessment; Species extrapolation; Local metabolism; CYP2E1; Variability
Effect of 4-tert-octylphenol on cytochrome P450 enzymes in rat liver by Nobumitsu Hanioka; Hideto Jinno; Youn-Son Chung; Tetsuji Nishimura; Toshiko Tanaka-Kagawa; Masanori Ando (pp. 625-631).
The effects were studied of 4-tert-octylphenol (OP) on hepatic cytochrome P450 enzymes in rats. Rats were treated intraperitoneally with OP twice, at doses of 5, 10, and 20 mg/kg. Among the cytochrome P450-dependent monooxygenase activities, testosterone 2α-hydroxylase activity, which is associated with CYP2C11, was significantly decreased by OP at all doses. The level relative to control activity was 67–22%. CYP3A2-dependent monooxygenase, testosterone 6β-hydroxylase activity was also decreased by 51% by OP at 20 mg/kg. Furthermore, immunoblotting showed that OP (10 or 20 mg/kg) significantly decreased CYP2C11/6 and CYP3A2/1 protein levels. However, the reduction ratio of CYP2C11/6 and CYP3A2/1 protein levels by OP treatment was lower than that of testosterone 2α-hydroxylase and testosterone 6β-hydroxylase activities. The Cl int (V max/K m) value for testosterone 2α-hydroxylase was significantly decreased by OP at all doses, whereas the Cl int value for testosterone 6β-hydroxylase was only decreased by OP at 20 mg/kg. In addition, 7-ethoxycoumarin O-deethylase activity was significantly decreased by 32% by the highest dose of OP. By contrast, CYP1A1-, CYP1A2-, CYP2A1-, CYP2B1/2-, CYP2D1-, CYP2E1- and CYP4A1/2/3- dependent monooxygenase activities were not affected by OP at any dose. These results suggest that OP changes the male-specific cytochrome P450 isoforms in rat liver, and that these changes closely relate to the toxicity of OP.
Keywords: Key words Alkylphenol; 4-tert-Octylphenol; Cytochrome P450; Rat liver; Endocrine disruption
Biological monitoring of standardized exposure to ethylbenzene: evaluation of a biological tolerance (BAT) value by Udo Knecht; Antje Reske; Hans-Joachim Woitowitz (pp. 632-640).
The results of standardized 8 h lasting exposures of n=18 volunteers to ethylbenzene (EthBz) at levels of 25 and 100% of the maximum allowable concentrations at the workplace (MAK) value of 100 ppm as well as the results of field studies are considered to evaluate a biological tolerance (BAT) value for EthBz. On the basis of the relationship between the external and internal exposure a BAT value of 1.5 mg/l has been set for the EthBz concentration in blood as the most sensitive and specific parameter of exposure to this aromatic hydrocarbon. The interpretation of EthBz blood values has to take into account the short half-life of t 1/2=0.5 ± 0.08 h in the first hour after the end of exposure in which this aromatic hydrocarbon is eliminated from the blood. The additional determination of the EthBz metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA), respectively, excreted in post shift urine as well as in urine samples at the beginning of the next shift shows good correlations with the external exposure. The biological half-life of MA was calculated to t 1/2=5.3 ± 1.1 h. Because the time of sampling can vary the relationship between the levels of MA to PGA the total concentration of the excreted metabolites depends less on this influence and is therefore better suited for monitoring exposed persons. On the basis of the standardized experiments a BAT value has been proposed of 2 g MA plus PGA corrected per gram creatinine. Both BAT values are adjusted to data which result from earlier standardized exposures during 30 min to EthBz under physical activity of 50 watt on a bicycle ergometer.
Keywords: Key words Standardized exposures; MAK value; Biological monitoring; Ethylbenzene in blood; Mandelic and phenylglyoxylic acid in urine
Experimental exposure of rat skin to methyl bromide: a toxicokinetic and histopathological study by Osamu Yamamoto; Hajime Hori; Isamu Tanaka; Masakazu Asahi; Minoru Koga (pp. 641-648).
Methyl bromide was experimentally exposed to a 12 cm2 area of the back skin of Wistar rats for 30 s, and for 1, 3, and 5 min, and time courses of both changes in plasma bromide concentration and of histopathological changes were examined. To measure bromide ion, a head space gas chromatography was used. The concentration of plasma bromide ion showed a sharp increase immediately after the exposure in all exposed groups, reaching a peak level after 1 h, then decreased rapidly. The ion level gradually decreased after 72 h to 1 week, and returned to a normal level after 4 to 8 weeks. Calculating from a regressive curve, the biological half lives of plasma bromide ion were 5.0 days to 6.5 days. Histopathologically, the impairments to the epidermal cells, fibroblasts and blood vessels were observed in the early phase. These cellular changes could be due to the direct cytotoxicity of the compound. In the next phase, newly infiltrating cells showed degeneration and necrosis. Subsequently, an impairment of the collagen bundles was observed. Our experiments suggested an immediate permeation and rapid metabolization of methyl bromide in the skin and a multistep formation of the skin damage induced by the compound. These processes of methyl bromide-induced skin damage are quite different from chemical skin injuries caused by the representative causative agents such as alkaline and acid.
Keywords: Key words Methyl bromide; Wistar rat; Bromide ion; Head space gas chromatography; Histopathology
Measurement of furancarboxylic acid, a candidate for uremic toxin, in human serum, hair, and sweat, and analysis of pharmacological actions in vitro by Toshi Sassa; Hiroyuki Matsuno; Masayuki Niwa; Osamu Kozawa; Naohito Takeda; Toshimitu Niwa; Takashi Kumada; Toshihiko Uematsu (pp. 649-654).
3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF), a candidate for uremic toxin, was measured in human hair for examining a possible utility as indicator of renal dysfunction. The serum concentration of CMPF was much higher (32.3 ± 2.7 μg/ml, n=17; mean ± SEM) in uremic patients aged 40–55 years receiving hemodialysis treatment than in healthy younger subjects (3.61 ± 0.19 μg/ml, n=22), aged 18–23 years. However, the hair concentration of CMPF tended to be lower in the patients (6.8 ± 1.7 ng/10 mg hair) than in the healthy younger subjects (15.8 ± 4.5 ng/10 mg) and was significantly lower than that in the healthy age-matched subjects (22.4 ± 5.3 ng/10 mg, n=12), aged 40–47 years. Since CMPF was measurable in the sweat (4.4 ± 3.7 ng/mg) collected from six out of seven healthy subjects examined, it was suggested that the contribution of sweat to the measurement of CMPF in hair was considerable. The fact that the uremic patients undergoing hemodialysis therapy had less sweat than healthy subjects may explain the lower concentration of CMPF in the patients' hair. The pathophysiological roles of CMPF in the body were attempted to be explored by using excised guinea pig organs, and human platelets and neutrophils. CMPF showed no remarkable effects in the concentration range of ≤10−4 M except for only slight suppression of spontaneous contracture of guinea pig tenia coli at 10−4 M. As far as the organs and tissues examined in the present study are concerned, the biological activity of CMPF itself, if any, may be very weak. Precaution should be taken against the delivery of a substance through sweat to hair when a small amount of substance is attempted to be measured in hair by employing a sensitive analytical method.
Keywords: Key words Furancarboxylic acid; Uremic toxin; Hair; Sweat; GC/MS
The relevance of inhibitor-substrate interactions when measuring neuropathy target esterase inhibition by Angelo Moretto; Milan Jokanovic; Marcello Lotti (pp. 655-660).
Neuropathy target esterase (NTE), thought to be the target for organophosphate polyneuropathy, is operationally defined as that neural phenyl valerate esterase resistant to paraoxon (40 μM) and sensitive to mipafox (50 μM; 20 min, pH 8.0, 37°C). The time course of inhibition of particulate paraoxon pretreated esterases by mipafox showed that the lines indicating the rate of inhibition did not pass through the log 100% activity when extrapolated at zero time. Slopes of inhibition of NTE were not linearly related to the concentration of mipafox. Kinetic parameters derived from Wilkinson type plots were: K a=49–199 μM, k +2=0.24–0.64 min−1 and k a=3.1–5.0 mM−1 m−1. When mipafox was removed (either by dilution or centrifugation) before the addition of phenyl valerate intercepts below 100% disappeared. We confirm that the formation of Michaelis complex between NTE and mipafox is not prevented by phenyl valerate and that inhibition proceeds after addition of phenyl valerate. We compared inhibitions obtained with experiments by using the traditional method (sequential incubation with inhibitors and phenyl valerate) to those obtained with a method where mipafox is removed before the addition of substrate. When calculating fixed-time 50% inhibitory concentrations (IC50s) of some inhibitors for NTE, the longer the hydrolysis time, the lower were the IC50s. Therefore, the inhibitory potency of certain NTE inhibitors, is accurately assessed only when calculating second-order rate constants (k a).
Keywords: Key words Inhibition; Kinetics; Neuropathy target esterase; Organophosphates; Phenylvalerate