Check out our New Publishers' Select for Free Articles

Archives of Toxicology (v.77, #6)

Difference in uptake and toxicity of trivalent and pentavalent inorganic arsenic in rat heart microvessel endothelial cells by Seishiro Hirano; Xing Cui; Song Li; Sanae Kanno; Yayoi Kobayashi; Toru Hayakawa; Amjad Shraim (pp. 305-312).

Intake of inorganic arsenic is known to cause vascular diseases as well as skin lesions and cancer in humans. We investigated the differences in cytotoxicity, uptake rate of arsenic, and gene expression of antioxidative enzymes between arsenite (As³⁺)- and arsenate (As⁵⁺)-exposed rat heart microvessel endothelial cells. As³⁺ was more cytotoxic than As⁵⁺, and LC₅₀ values were calculated to be 36 and 220 µM, respectively. As³⁺ (1–25 µM) increased mRNA levels of antioxidant enzymes such as heme oxygenase-1 (HO-1), thioredoxin peroxidase 2, NADPH dehydrogenase, and glutathione S-transferase P subunit. HO-1 mRNA levels showed the most remarkable increase in response to As³⁺. cDNA microarray analysis indicated that there was no prominent difference in arsenic-induced transcriptional changes between As³⁺- and As⁵⁺-exposed cells, when the cells were exposed to one-fourth the LC₅₀ concentration of arsenic (9 and 55 µM for As³⁺ and As⁵⁺, respectively). N-acetyl-l-cysteine (NAC) reduced both the cytotoxicity of inorganic arsenic and the HO-1 mRNA level, and buthionine sulfoximine enhanced cytotoxicity of inorganic arsenic. As³⁺ was taken up by the endothelial cells 6–7 times faster than As⁵⁺, and the presence of NAC in the culture medium did not change the uptake rate of As³⁺.These results suggest that the effects of NAC on arsenic-induced cytotoxicity and oxidative stress were due to the antioxidative role of non-protein thiols and not to chelation of arsenic in the culture medium. The difference in cellular uptake of arsenic between As³⁺ and As⁵⁺ appeared not to be due to the ionic charge on arsenic (at physiological pH, trivalent arsenic is neutral whereas pentavalent arsenic is negatively charged). These results suggest that the higher toxicity of As³⁺ compared with that of As⁵⁺ is probably due to the faster uptake of As³⁺ by endothelial cells, and inorganic arsenic exerts its toxicity at least in part via intracellular oxidative stress.

Keywords: Arsenite Arsenate Buthionine sulfoximine N-Acetyl-l-cysteine Endothelial cell Heme oxygenase-1

Do multiple cytochrome P450 isoforms contribute to parathion metabolism in man? by Elaine Mutch; Ann K. Daly; Julian B. S. Leathart; Peter G. Blain; Faith M. Williams (pp. 313-320).

Phosphorothioate compounds are widely used in agriculture and public health for the control of unwanted pests. The phosphorothioate parathion was metabolised to the toxic metabolite paraoxon (0.038–0.683 nmol/min per mg protein) and p-nitrophenol (0.023–2.10 nmol/min per mg protein) by human liver microsomes (n=27) in an NADPH-dependent reaction. There was a significant correlation (P<0.02) between nifedipine oxidation and paraoxon formation from parathion (200 µM) by human liver microsomes and with cytochrome P450 (CYP) 3A4/5 expression (P<0.05), although not with midazolam 1′-hydroxylation or testosterone 6β-hydroxylation. Paclitaxel 6′-hydroxylation and CYP2C8 expression correlated with paraoxon formation (P<0.01), indicating CYP2C8 involvement. Of nine recombinant P450 isoforms, CYPs 3A4, 3A5, 1A2 and 2D6 activated parathion to paraoxon at the highest rates (6.5, 8.5, 5.7 and 6.2 pmol/pmol P450 per h) with K _m values of 12.6, 2.7, 1.5 and 9.2 µM, respectively. Similar K _m values were seen with the human liver microsomes. These data indicate that CYP3A4/5 and CYP2C8, which constitute up to 40% of human liver P450s, are the most significant participants in the metabolism of parathion. However, several other isoforms could play an important role when CYP3A and CYP2C8 are poorly expressed due to environmental factors or the presence of a genetic polymorphism.

Keywords: Parathion Paraoxon Phosphorothioate CYP 3A4/5 CYP 2C8 CYP 1A2 Interindividual variations

Fractional contribution of lung, nasal and gastrointestinal absorption to the systemic level following nose-only aerosol exposure in rats: a case study of 3.7-µm fluorescein aerosols by Masahiro Sakagami; Wataru Kinoshita; Kiyoyuki Sakon; Yuji Makino (pp. 321-329).

Because absorption takes place from multiple sites of aerosol deposition, it is generally difficult to interpret systemic levels following nose-only inhalation in laboratory rodents. Therefore, this study attempted to determine the fractional contribution of lung, nasal and gastrointestinal (GI) absorption to the observed systemic level following nose-only aerosol exposure in rats using fluorescein as a model powder solute. Rats were treated orally with vehicle or activated charcoal, the latter diminishing GI absorption of fluorescein, and were subsequently nose-only exposed to 3.7-µm fluorescein aerosols at 25.2 µg/l_air for 10 min. While fluorescein similarly disappeared from the lung at a half-life of 0.23 hr, its plasma concentrations in the charcoal-treated group were significantly lower than those in the charcoal-untreated (vehicle) group. This suggests that significant portions of fluorescein were transported by nasopharyngeal and tracheobronchial mucociliary clearances following aerosol exposure and were absorbed from the GI tract. Despite the lack of GI absorption in the charcoal-treated animals, it was estimated that this nose-only exposure of fluorescein allowed 25.7 and 82.5 µg/kg of simultaneous lung and nasal deposition, respectively, followed by their absorption composing the observed systemic level in this group (AUC_0–∞ 137.49 ng/ml h). Thus, assuming linear pharmacokinetics of fluorescein, the extent of absorption (AUC_0–∞) due to such nasal deposit (82.5 µg/kg) was estimated to be 47.00 ng/ml h using the AUC_0–∞ obtained in an independent study of intranasal powder insufflation at 34.5 µg/kg in the charcoal-treated rats (AUC_0–∞ 19.66 ng/ml h). As a result, the AUC_0–∞ due to 25.7 µg/kg of the lung deposit was deconvoluted to be 90.49 ng/ml h and finally, the absolute bioavailability (F%) of the "lung-region-specific" deposition and absorption of fluorescein was estimated to be 55.0%. It is observed therefore, that lung, nasal and GI absorption accounted for 24.2, 12.5 and 63.3% of the total fluorescein absorption, respectively, following nose-only exposure of 3.7-µm aerosols. This study addresses the common methodological insufficiency of nose-only inhalation studies in rodents, which have been neglected in most cases, and provides the appropriate kinetic interpretation for their observed systemic level.

Keywords: Inhalation Toxicokinetics Aerosols Nose-only exposure Disposition

Toxicokinetics of cyanide in rats, pigs and goats after oral dosing with potassium cyanide by Altamir B. Sousa; Helena Manzano; Benito Soto-Blanco; Silvana L. Górniak (pp. 330-334).

The aim of the present study was to determine the effect of the species on the toxicokinetics of cyanide and its main metabolite, thiocyanate. Forty-two rats, six pigs and six goats were dosed orally with 3.0 mg KCN/kg body weight, and cyanide and thiocyanate concentrations in blood were measured within 24 h. After the single oral dose, KCN was rapidly absorbed by rats and goats, with a time of peak concentration (T _max) of 15 min. The maximum plasma concentration (C _max) of cyanide was observed in goats (93.5 µmol/l), whereas the C _max of thiocyanate was higher in rats (58.1 µmol/l). The elimination half-life (t _1/2) and volume of distribution (Vd_area) of both cyanide and thiocyanate were higher in goats (1.28 and 13.9 h, and 0.41 and 1.76 l/kg, respectively). Whereas the area under the curve (AUC) of cyanide was significantly higher in goats (234.6 µmol.l/h), the AUC of thiocyanate was higher in rats (846.5 µmol.l/h). In conclusion, the results of the present study support the hypothesis that the metabolism of cyanide and its main metabolite, thiocyanate, is species-linked, with the goat being more sensitive to the toxic effects of cyanide/thiocyanate.

Keywords: Cyanide Thiocyanate Toxicokinetics Rats Pigs Goats

A role of aryl hydrocarbon receptor in the antiandrogenic effects of polycyclic aromatic hydrocarbons in LNCaP human prostate carcinoma cells by Ryoichi Kizu; Kazumasa Okamura; Akira Toriba; Hiroshi Kakishima; Atsushi Mizokami; Kerry L. Burnstein; Kazuichi Hayakawa (pp. 335-343).

The role of aryl hydrocarbon receptor (AhR) on the antiandrogenic effects of polycyclic aromatic hydrocarbons (PAHs) was studied in LNCaP cells. The PAHs used in this study were chrysene (Chr), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), anthracene (Ant) and pyrene (Pyr). Chr, BkF and BaP acted as AhR agonists in LNCaP cells, while Ant and Pyr did not. The antiandrogenic effects of the PAHs were evaluated on the basis of regulation of prostate-specific antigen (PSA) mRNA and protein levels by 5α-dihydrotestosterone (DHT). Chr, BkF and BaP exhibited an antiandrogenic effect, but Ant and Pyr did not. α-Naphthoflavone (α-NF), an AhR antagonist, reversed the antiandrogen action of Chr, BkF and BaP, suggesting a requirement for activated AhR. The antiandrogenic PAHs did not significantly decrease androgen receptor (AR) levels or cellular DHT concentrations. Gel mobility shift assays revealed that Chr, BkF and BaP inhibited the binding of AR in nuclear extracts to oligonucleotide probes containing the AR-responsive element (ARE), whereas Ant and Pyr had no effect. The antiandrogenic PAHs elevated mRNA levels of c-fos and c-jun. Since activator protein-1 (AP-1), a heterodimer of c-jun and c-fos proteins, is known to inhibit binding of AR to ARE by protein–protein interaction with AR, the findings in the present study suggest a possible involvement of AP-1 in the antiandrogenic effects of PAHs acting as AhR agonists. These results suggest that AhR can stimulate AP-1 expression resulting in inhibition of the binding of AR to ARE in the transcription regulatory region of target genes such as PSA.

Keywords: Polycyclic aromatic hydrocarbon Antiandrogenic effect Aryl hydrocarbon receptor Androgen receptor Activator protein-1

Changes in the structure and function of the kidney of rats chronically exposed to cadmium. I. Biochemical and histopathological studies by Małgorzata M. Brzóska; Marcin Kamiński; Dorota Supernak-Bobko; Krzysztof Zwierz; Janina Moniuszko-Jakoniuk (pp. 344-352).

The aim of this study was to assess the effects of chronic exposure to cadmium (Cd) on the structure and function of kidneys, as well as to establish the body burden of Cd at which the changes occur. For this purpose we have created an experimental model using rats intoxicated with Cd administered in drinking water at the concentration of 5 or 50 mg Cd/l for 6, 12 and 24 weeks. The degree of kidney damage was evaluated biochemically and histopathologically. Sensitive biomarkers of Cd-induced proximal tubular injury such as urinary total N-acetyl-β-d-glucosaminidase (NAG-T) and its isoenzyme B (NAG-B), and alkaline phosphatase (ALP) were used. Cd content in the kidney increased with the level and duration of exposure leading to dose- and time-dependent structural and functional renal failure. In rats exposed to 5 mg Cd/l, first symptoms of injury of the main tubules of long and short nephrons (structural damage to epithelial cells, increased urinary activities of NAG-T and NAG-B) were noted after 12 weeks of the experiment. The damage occurred at a low kidney Cd concentration amounting to 4.08±0.33 µg/g wet weight (mean ±SE) and a urinary concentration of 4.31±0.28 µg/g creatinine. On exposure to 50 mg Cd/l, damage to the main tubules (blurred structure of tubular epithelium, atrophy of brush border, partial fragmentation of cells with release of nuclei into tubular lumen as well as increased urinary activities of NAG-T, NAG-B and ALP) was already evident after 6 weeks with the kidney Cd concentration of 24.09±1.72 µg/g wet weight. In rats exposed to 50 mg Cd/l, a lack of regular contour of glomeruli was noted after 12 weeks, whereas after 24 weeks thickening of capillary vessels and widening of filtering space were evident. After 24 weeks of exposure to Cd, increased urea concentration in the serum with simultaneous decrease in its level in the urine, indicating decreased clearance of urea, and increased excretion of total protein were observed, but endogenous creatinine clearance remained unaffected. At the lower exposure, symptoms of structural, but not functional, damage to the glomeruli were also evident after 24 weeks of the experiment. Our results provide evidence that chronic exposure to Cd dose-dependently damages (structurally and functionally) the whole kidney. The injury affects the main resorptive part (proximal convoluted tubules and straight tubules) and the filtering part (glomeruli) of the nephron. But the target site for Cd action is the main tubule. We hypothesize that the threshold for Cd effects on the kidney is less than 4.08±0.33 µg/g wet kidney weight and greater than 2.40±0.15 µg/g (at this Cd concentration no symptoms of kidney damage were noted), and it may be close to the latter value. A very important finding of this study is that Cd acts on the whole kidney, especially on the main tubules, even at relatively low accumulation in this organ. It confirms the hypothesis that humans environmentally exposed to Cd, especially smokers, are at risk of tubular dysfunction.

Keywords: Cadmium Nephrotoxicity markers Kidney structure Kidney function Rats

Consecutive administration of paraquat to rats induces enhanced cholesterol peroxidation and lung injury by Junko Adachi; Kenji Ishii; Masafumi Tomita; Tetsuo Fujita; Yudha Nurhantari; Yasushi Nagasaki; Yasuiro Ueno (pp. 353-357).

It is our hypothesis that as a consequence of increased oxidative stress, rats develop lung injury with increased cholesterol-derived hydroperoxides and oxysterols in lung after consecutive exposure of the rats to paraquat. To test this we administered 10 mg/kg of paraquat i.p. once or seven times (once a day) to Wistar rats. Rats were killed, and lung tissue was collected 24 h after the last paraquat injection. We found that in response to consecutive paraquat doses, there were significant increases in 7α- and 7β-hydroperoxycholest-5-en-3β-ol (7α-OOH and 7β-OOH; P=0.01) as well as 7α- and 7β-hydroxycholesterol (7α-OH and 7β-OH; P=0.01), and 7-ketocholesterol (7-keto; P=0.03). In addition, pulmonary hemorrhage, thickening of alveolar septum, and inflammatory cell infiltration of macrophages were observed. This is the first report showing enhanced cholesterol peroxidation and lung injury of rats due to consecutive doses of paraquat.

Keywords: Paraquat 7-Hydroperoxycholesterol Oxysterol Lung Rat

Effects of 2,3,7,8-TCDD and PCB 126 on human thymic epithelial cells in vitro by Kai Riecke; André Schmidt; Ralf Stahlmann (pp. 358-364).

2,3,7,8-Tetrachloro-dibenzo-p-dioxin (TCDD) is a ubiquitously distributed xenobiotic. The adverse effects of TCDD on the mammalian immune system have been studied for decades, but it is still unclear whether TCDD has direct effects on T-lymphocytes or whether it acts via the thymic microenvironment. We have studied the effects of TCDD on primary cultures of human thymic epithelial cells (TEC) focusing on differentiation markers, integrins and adhesion molecules involved in cell–cell and in cell–matrix interactions. TEC were treated with TCDD at concentrations of 0.001, 0.01, 0.1, 1.0 or 10.0 nM or with 100 nM PCB 126 (3,3',4,4',5-pentachlorobiphenyl) for 3 days, and were then analysed by flow cytometry for expression of surface antigens using monoclonal antibodies against Hassall's bodies (TE-8, TE-16) or against surface structures such as CD29, CD49b, CD49e, CD49f, CD51, CD54, CD58, CD61 and CD106. At TCDD concentrations as low as 0.01 nM we found a significant increase in terminally differentiated, TE-16-positive TEC; at a ten-fold greater concentration the number of cells marked with the TE-8 antibody was also increased. With both markers the most pronounced effect (approximately +15%) was observed at 1 nM TCDD. An increase of cells expressing the integrin α-chains CD49b, CD49e and CD51 as well as CD54 was observed at concentrations of 0.1 nM TCDD or higher. The proportion of cells expressing CD106 or CD49f decreased significantly upon treatment with TCDD. No effects on the integrin β-chains CD29 and CD61 could be detected. Overall, PCB 126 induced similar changes to TCDD. In summary, TCDD and a coplanar PCB induced terminal differentiation of human TEC along with changes of integrins and other adhesion molecules. These receptors and their interplay with the extracellular matrix have key functions in the maturation of T-lymphocytes and it is plausible that their alteration would be involved in TCDD-induced immunotoxicity.

Keywords: 2,3,7,8-Tetrachloro-dibenzo-p-dioxin PCB 126 Thymic epithelium Integrin Flow cytometry Hassall's bodies

Sections

Personal tools

Archives of Toxicology (v.77, #6)

Sections

Personal tools

Local resources

Archives of Toxicology (v.77, #6)