Check out our New Publishers' Select for Free Articles

Archives of Toxicology (v.68, #2)

Induction of hepatic microsomal CYP4A activity and of peroxisomal β-oxidation by two non-steroidal anti-inflammatory drugs by Eleni Rekka; Edward O. Ayalogu; David F. V. Lewis; Gordon G. Gibson; Costas Ioannides (pp. 73-78).

The effects of the non-steroidal anti-inflammatory drugs fenbufen and ibuprofen on hepatic cytochrome P450 activities and peroxisomal proliferation were investigated in the rat, following intraperitoneal administration at three dose levels. At the two highest doses, 30 and 150 mg/kg, ibuprofen stimulated lauric acid hydroxylase activity but no other dose-dependent effects on cytochrome P450 activities were evident. Fenbufen, at the highest dose of 150 mg/kg, decreased cytochrome P450 content and related activities, and this effect was attributed to the toxicity of the drug at this dose. Immunoblot studies employing solubilized microsomes from ibuprofen-treated rats revealed that ibuprofen increased the apoprotein levels of CYP4A1, at the two higher doses. The same treatment with ibuprofen, at the highest dose only, increased the β-oxidation of palmitoyl CoA, determined in liver homogenates, and immunoblott analysis showed an increase in the apoprotein levels of therans-2-enyol CoA hydratase trifunctional protein. Fenbufen did not influence palmitoyl β-oxidation. Computer graphic overlays with clofibric acid showed that ibuprofen, when compared with fenbufen, displayed a better overall fit to clofibric acid. Finally, interaction energies between the two drugs and the putative peroxisome proliferator-activated receptor lignad domain revealed that ibuprofen had a higher affinity for the receptor than fenbufen, but the difference was modes. It is concluded that ibuprofen, at doses far exceeding those employed clinically, is a weak inducer of both CYP4A1 activity and peroxisomal proliferation and these effects may be attributed to the presence of an aryl propionic acid moiety. These results are discussed with reference to the role of CYP4A induction and peroxisomal proliferation in the hepatotoxicity of this class od drugs.

Keywords: Cytochromes P450; Peroxisomal proliferation; Enzyme induction; Ibuprofen; Fenbufen; Nonsteroidal anti-inflammatory drugs

Bacterial mutagenicity of 2-chloro-1,3-butadiene (chloroprene) caused by decomposition products by Götz A. Westphal; Meinolf Blaszkewicz; Monika Leutbecher; Andreas Müller; Ernst Hallier; Hermann M. Bolt (pp. 79-83).

Since the literature on genotoxicity of 2-chloro-1,3-butadiene (chloroprene) is controversial, the mutagenicity of this compound was reinvestigated with respect to its chemical stability. Because of the volatility of chloroprene, Ames tests withS. typhimurium TA 100 were carried out with gas-tight preincubation. Propylene oxide, a volatile direct mutagen, served as a positive control. Benzo[a]pyrene was used as a control for an indirect mutagen. Using this experimental regimen, freshly distilled chloroprene was not mutagenic. However, a mutagenic effect occurred linearly with increasing age of the chloroprene distillates. Aged chloroprene gave the same positive results whether preincubation was gas-tight or not. Analysis by gas chromatography (GC) revealed several decomposition products in aged chloroprene distillates. The direct mutagenicity towards TA 100 correlated with the integrated amounts of four of these substances; these substances always occurred in the same relative ratio. When chloroprene was kept under anaerobic conditions, products occurred with time which were partly different from those obtained under aerobic conditions. The direct mutagenicity of anaerobically aged chloroprene was only weak, but the mutagenic effect was enhanced about two- to threefold by addition of S9 mix. Partial identification of chloroprene decomposition products was done by gas chromatography-mass spectrometry (GC-MS): major byproducts of chloroprene, probably responsible for mutagenic properties of aged chloroprene samples, were cyclic chloroprene dimers.

Keywords: Chloroprene; 2-Chloro-1,3-butadiene; Mutagenicity; Ames test

Effect of cadmium pretreatment on liver regeneration after partial hepatectomy in rats by A. Margeli; S. Theocharis; S. Skaltsas; A. Skopelitou; C. Kittas; M. Mykoniatis; D. Varonos (pp. 85-90).

Toxicity and chemical form of selenium in the liver of mice orally administered selenocystine for 90 days by Tatsuya Hasegawa; Shinjiro Taniguchi; Makoto Mihara; Katsuhiko Nakamuro; Yasuyoshi Sayato (pp. 91-95).

The subacute oral toxicity of selenocystine and chemical form of selenium in the liver following exposure to this compound were assessed in ICR male mice. Animals were dosed 6 days/week for 30, 60 or 90 days with 0, 5, 10 or 15 mg/kg per day. Body weight gain decreased with dosage. The activities of aspartate aminotransferase and alanine aminotransferase in plasma were significantly elevated at the highest dose level after 60 days and at the two higher dose levels after 90 days of exposure. However, the level of selenium content in the liver was the same at the two higher dosages at both 60 and 90 days of exposure. The subcellular distribution of selenium in the liver from mice treated with selenocystine showed that the major part of the total selenium content, 68.3–72.1%, existed in the cytosolic fraction. Sephadex G-150 chromatograms of liver cytosol of the animals administered selenocystine revealed three selenium-containing fractions which involve glutathione peroxidase (molecular weight 80 000) high molecular (molecular weight 55 000–60 000) and low molecular (molecular weight <10 000) substances. Selenium content and acid-volatile selenium content in the high molecular weight fraction increased with exposure time to selenocystine. Thus, in a subacute toxicity study selenocystine given for 90 days caused hepatic damage in mice, depending on the acid-volatile selenium content in the liver cytosol.

Keywords: Selenium; Selenocystine; Subacute toxicity; Hepatic damage; Acid-volatile selenium; Chemical form of selenium

Gastrointestinal uptake and vascular transport of 2,4′-dichlorobiphenyl by David L. Busbee; Richard L. Ziprin (pp. 96-102).

Absorption from the gastrointestinal tract and subsequent vascular transport of [³H]-2,4′-dichlorobiphenyl (Aroclor 1232; DCB) was investigated in an ovine model system. Rapid uptake of DCB and transport as a component of blood plasma without prior occurrence in thoracic duct lymph indicates that DCB was absorbed directly via the gastric mucosa with water soluble compounds. [³H]-DCB did not circulate associated with plasma lipid fractions in vivo, and did not bind to or sequester within plasma lipids in vitro. HPLC analysis of plasma fractions treated in vitro showed DCB to elute within a molecular weight range consistent with unbound product. Further, [³H]-DCB-derived label was associated with low molecular weight plasma components in vivo. Essentially the same elution profile was seen for [³H]-DCB-derived label found in urine. Metabolism of DCB as a function of time resulted in the apparent formation of a biotransformed product(s) that circulated with a plasma fraction(s) at the low end of the albumin molecular size range. These data suggest that DCB was not absorbed and transported in a manner typical of polychlorinated biphenyls with a higher chlorine content; rather, that it was absorbed, transported within the vascular system, and excreted in a pattern typical of a water soluble compound.

Keywords: PCBs; Halogenated aromatic hydrocarbons; Vascular transport

Thyroxine pretreatment and halothane administration alter Ca²⁺ transport and transmembrane potential in rat liver mitochondria by Roberto Imberti; Mariapia Vairetti; Plinio Richelmi; Ivano Preseglio; Giorgio Bellomo (pp. 103-109).

Male rats pretreated with thyroid hormones and exposed to halothane in non-hypoxic conditions develop acute liver damage. In order to investigate the mechanisms leading to liver damage in this animal model, the effects of thyroxine (T₄) pretreatment and halothane administration on Ca²⁺ transport and transmembrane potential were studied in isolated rat liver mitochondria. Five-day T₄-pretreatment reduced the mitochondrial Ca²⁺ loading capacity and increased the rate of Ca²⁺ cycling across the mitochondrial membrane. Halothane administration further increased Ca²⁺ cycling and produced a time- and dose-dependent loss of transmembrane potential which was more pronounced in mitochondria from T₄-pretreated rats than in euthyroid animals. When mitochondria from T₄-pretreated rats were incubated in the presence of the Ca²⁺ chelator EGTA, membrane potential was well preserved. In contrast, when Ca²⁺ concentration in the extramitochondrial medium was increased, mitochondria deenergization occurred earlier. These findings confirm that alterations in Ca²⁺ transport and mitochondrial function can be interrelated events and suggest that a Ca²⁺-dependent, halothane-induced loss of transmembrane potential could participate in generating acute liver damage in hyperthyroid rats exposed to halothane in non-hypoxic conditions.

Keywords: Halothane; Rat; Thyroid hormones; Free calcium; Hepatotoxicity; Mitochondria; Membrane potential

Inhibition of mitochondrial respiration in vivo is an early event in acetaminophen-induced hepatotoxicity by Patty J. Donnelly; Robin M. Walker; William J. Racz (pp. 110-118).

Morphological changes in mitochondria are observed early in the course of acetaminophen (AA)-induced hepatotoxicity, and mitochondrial dysfunction has been observed both in vivo and in vitro following exposure to AA. This study examined the early effects of AA exposure in vivo on mitochondrial respiration and evaluated the effectiveness ofN-acetyl-L-cysteine (NAC) in protecting against respiratory dysfunction. Mitochondria were isolated from the livers of fasted, male CD-1 mice 0, 0.5, 1, 1.5 or 2 h after administration of a hepatotoxic dose of AA (750 mg/kg). Glutamate- and succinate-supported mitochondrial respiration were subsequently assessed by polarographic measurement of state 3 (ADP-stimulated) and state 4 (resting) rates of oxygen consumption and determination of the corresponding respiratory control ratios (RCR: state 3/state 4) and ADP:O ratios. Hepatotoxicity was assessed histologically and by measuring plasma alanine aminotransferase (ALT) activity. The earliest sign of mitochondrial dysfunction observed in this study was a significant decrease in the ADP:O ratio for the oxidation of glutamate 1 h post-dosing. At 1.5 and 2 h post-dosing the RCRs for both glutamate- and succinate-supported respiration were significantly decreased. All of the respiratory parameters measured in this study were significantly decreased, with the exception of succinate-supported state 4 respiration which was significantly increased, 2 h after AA administration. Thus, inhibition of mitochondrial respiration preceded overt hepatic necrosis, indicated by an elevation of ALT activity, which was not observed until 3 and 4 h post-dosing. In addition, mitochondrial respiratory dysfunction correlated with morphological alterations. Inhibition of mitochondrial respiration therefore appears to be an early event in the course of AA-induced hepatotoxicity. Cotreatment with NAC (1200 mg/kg) completely prevented the AA-induced impairment of mitochondrial respiration and the development of histopathologic damage. The protection afforded by NAC in these experiments indicates thatN-acetyl-p-benzoquinone imine (NAPQI), the reactive metabolite of AA, is responsible for the observed inhibitory effects, and suggests that mitochondrial dysfunction makes an important, if not essential, contribution to the development of AA-induced hepatotoxicity.

Keywords: Acetaminophen; N-Acetyl-L-cysteine; Mitochondrial respiration

The high sensitivity of the rabbit to the teratogenic effects of 13-cis-retinoic acid (isotretinoin) is a consequence of prolonged exposure of the embryo to 13-cis-retinoic acid and 13-cis-4-oxo-retinoic acid, and not of isomerization to all-trans-retinoic acid by Georg Tzimas; Heinrich Bürgin; Michael D. Collins; Hans Hummler; Heinz Nau (pp. 119-128).

Previous studies suggested that the rabbit is much more susceptible to the teratogenic action of 13-cis-retinoic acid (13-cis-RA) than the mouse or the rat, while the teratogenicity of all-trans-RA was comparable in these species. In the present study we investigated if pharmacokinetics can explain these species- and structure-related differences. The embryotoxic and teratogenic potential of all-trans-retinoid acid (all-trans-RA) and 13-cis-RA were evaluated in the Swiss hare rabbit after oral administration of daily doses of the two drugs throughout organogenesis, from gestation day (GD) 6 to 18 (plug day=GD 0). All-trans-RA was given at dose levels of 0.7, 2 or 6 mg/kg body weight per day and 13-cis-RA at 3, 7.5 or 10 mg/kg per day. The doses needed to elicit a minimum teratogenic response were found to be 6 mg/kg per day for all-trans-RA and 10 mg/kg per day for 13-cis-RA. Using these doses, transplacental pharmacokinetics of all-trans- and 13-cis-RA were performed. Pregnant rabbits were treated once daily from GD 7 to 12 and plasma and embryo samples were collected for HPLC analysis at various time intervals after the final dose. The main plasma metabolites of all-trans-and 13-cis-RA were all-trans-β-glucuronide (all-trans-RAG) and 13-cis-4-oxo-RA, respectively. The elimination of 13-cis-RA and its metabolites from maternal plasma were much slower than of all-trans-RA resulting in accumulation of the 13-cis-isomers in plasma. Marked differences in the placental transfer of the two drugs and their metabolites were observed. All-trans-RA and all-trans-4-oxo-RA were efficiently transferred to the rabbit embryo, reaching concentrations similar to the plasma levels. On the contrary, the 13-cis-isomers reached the embryo to a lesser extent. Despite its limited placental transfer, a considerable embryonic exposure to 13-cis-RA and 13-cis-4-oxo-RA was noticed after treatment with isotretinoin, as indicated by their area-under-the-concentration-time-curve (AUC) values in the embryo, which were in the same range as the corresponding AUC value of all-trans-RA after treatment with the all-trans-isomer. Our results suggest that the high sensitivity of the rabbit to the teratogenic effects of 13-cis-RA can be attributed mainly to the 13-cis-isomers and not to isomerization to all-trans-RA. The significant exposure of the rabbit embryo to 13-cis-RA and its 4-oxo metabolite is a result of their very slow excretion rates from the maternal organism. Furthermore, this study supports the view that embryonic AUC values should be considered as the most suitable pharmacokinetic correlate to retinoid induced teratogenesis.

Keywords: Retinoic acid; Rabbit; Teratogenicity; Transplacental pharmacokinetics; Area-under-the concentration-time-curve (AUC)

Metabolic activation of aromatic and heterocyclicN-hydroxyarylamines by wild-type and mutant recombinant human NAT1 and NAT2 acetyltransferases by David W. Hein; Timothy D. Rustan; Ronald J. Ferguson; Mark A. Doll; Kevin Gray (pp. 129-133).

Recombinant human NAT1 and polymorphic NAT2 wild-type and mutantN-acetyltransferases (encoded byNAT2 alleles with mutations at 282/857, 191, 282/590, 341/803, 341/481/803, and 341/481) were expressed inEscherichia coli strains XA90 and/or JM105, and tested for their capacity to catalyze the metabolic activation (viaO-acetylation) of theN-hydroxy (N-OH) derivatives of 2-aminofluorene (AF), and the heterocyclic arylamine mutagens 2-amino-3-methylimidazo [4,5-f]quinoline (IQ), 2-amino-3,4-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Both NAT1 and NAT2 (including all mutant human NAT2s tested) catalyzed the metabolic activation of each of theN-hydroxyarylamines to products that bound to DNA. Metabolic activation of N-OH-AF was greater than that of the heterocyclicN-hydroxyarylamines. The relative capacity of NAT1 versus NAT2 to catalyze activation varied withN-hydroxyarylamine substrate. N-OH-MeIQx and N-OH-PhIP exhibited a relative specificity for NAT2. These results provide mechanistic support for a role of the genetic acetylation polymorphism in the metabolic activation of heterocyclic amine mutagens and carcinogens.

Keywords: HumanN-acetyltransferases; Acetylation polymorphism; O-Acetylation; N-Hydroxyarylamines; Heterocyclic arylamine carcinogens

Different distribution of paraquat and diquat in human poisoning cases after ingestion of a combined herbicide by Kiyoshi Ameno; Chiaki Fuke; Youichi Shirakawa; Shinji Ogura; Setsuko Ameno; Takahiro Kiriu; Hiroshi Kinoshita; Iwao Ijiri (pp. 134-137).

This report describes a slight difference in the rate of decrease of serum paraquat and diquat concentrations in eight human cases of poisoning by the herbicide PreegloxL (containing paraquatCl₂, 5% and diquatBr₂, 7%) and the distribution of each in three autopsied cases. There was no variation between the serum concentrations of paraquat and diquat within 24 h after ingestion, but paraquat remained at a slightly higher concentration than diquat after more than 24 h. The decrease of urinary paraquat and diquat concentrations was almost the same during the 24-h determination period. In three autopsied cases, diquat concentrations in the tissues were relatively lower than those of paraquat, except in bile. Paraquat and diquat were unevenly distributed in various tissues and fluids, but the distribution patterns of each in any particular tissues were quite similar. As no difference was observed in the decrease of urinary paraquat and diquat, the much higher concentration of diquat in bile indicates that bile may be one of the effective factors in lowering the concentration of diquat in serum and in tissues of the human body long after ingestion.

Keywords: Toxicology; Poisoning; Paraquat; Diquat; Human poisoning cases; Different distribution

The ambiguous effect of ascorbic acid on chromate induced proteinuria in rats by Dorothea Appenroth; Klaus Winnefeld; Heinz Schröter; Michael Rost (pp. 138-141).

The influence of ascorbic acid (AA, 5 g/kg body weight) on chromate (Cr, 10 mg/kg) induced proteinuria, which is a sensitive parameter of its nephrotoxicity, was investigated in adult female Wistar rats. The concentrations of Cr and ascorbic acid (AA) were determined in renal tissue. Cr nephrotoxicity is related to its intracellular reduction from Cr(VI) to Cr(III). Proteinuria was completely prevented by enhancement of extracellular reduction of Cr(VI) to Cr(III) followed by rapid renal excretion when Cr and AA were given concomitantly. With an interval up to 1 h between Cr and AA, proteinuria was decreased probably by the radical scavenging function of AA. At an interval of 3 h AA enhanced Cr toxicity by increased intracellular Cr reduction. If the interval was increased to 5 h or if Cr was given 24 h after AA, no influence of AA could be detected. Our results confirm that AA is a very effective reductant of Cr which can influence Cr nephrotoxicity in very high concentrations. It depends on the interval between Cr and AA administration whether or not there is a beneficial effect of AA in Cr nephrotoxicity.

Keywords: Nephrotoxicity; Proteinuria; Chromate; Ascorbic acid; Rat

Sections

Personal tools

Archives of Toxicology (v.68, #2)

Sections

Personal tools

Local resources

Archives of Toxicology (v.68, #2)