Check out our New Publishers' Select for Free Articles

Archives of Toxicology (v.73, #2)

Roles of CYP2A6 and CYP2B6 in nicotine C-oxidation by human liver microsomes by Hiroshi Yamazaki; Kiyoshi Inoue; Masafumi Hashimoto; Tsutomu Shimada (pp. 65-70).

Nicotine C-oxidation by recombinant human cytochrome P450 (P450 or CYP) enzymes and by human liver microsomes was investigated using a convenient high-performance liquid chromatographic method. Experiments with recombinant human P450 enzymes in baculovirus systems, which co-express human nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH)-P450 reductase, revealed that CYP2A6 had the highest nicotine C-oxidation activities followed by CYP2B6 and CYP2D6; the K _m values by these three P450 enzymes were determined to be 11.0, 105, and 132 μM, respectively, and the V _max values to be 11.0, 8.2, and 8.6 nmol/min per nmol P450, respectively. CYP2E1, 2C19, 1A2, 2C8, 3A4, 2C9, and 1A1 catalysed nicotine C-oxidation only at high (500 μM) substrate concentration. CYP1B1, 2C18, 3A5, and 4A11 had no measurable activities even at 500 μM nicotine. In liver microsomes of 16 human samples, nicotine C-oxidation activities were correlated with CYP2A6 contents at 10 μM substrate concentration, whereas such correlation coefficients were decreased when the substrate concentration was increased to 500 μM. Contribution of CYP2B6 (as well as CYP2A6) was demonstrated by experiments with the effects of orphenadrine (and also coumarin and anti-CYP2A6) on the nicotine C-oxidation activities by human liver microsomes at 500 μM nicotine. CYP2D6 was found to have minor roles since quinidine did not inhibit microsomal nicotine C-oxidation at both 10 and 500 μM substrate concentrations. These results support the view that CYP2A6 has major roles for nicotine C-oxidation at lower substrate concentration and both CYP2A6 and 2B6 play roles at higher substrate concentrations in human liver microsomes.

Keywords: Key words Nicotine; CYP2A6; CYP2B6; Human P450; Liver microsomes

Enzyme-mediated dichloromethane toxicity and mutagenicity of bacterial and mammalian dichloromethane-active glutathione S-transferases by Daniel Gisi; Thomas Leisinger; Stéphane Vuilleumier (pp. 71-79).

The kinetic properties of bacterial and rat liver glutathione S-transferases (GST) active with dichloromethane (DCM) were compared. The theta class glutathione S-transferase (rGSTT1-1) from rat liver had an affinity for dihalomethanes lower by three orders of magnitude (K _app > 50 mM) than the bacterial DCM dehalogenase/GST from Methylophilus sp. DM11. Unlike the bacterial DCM dehalogenase, the rat enzyme was unable to support growth of the dehalogenase minus Methylobacterium sp. DM4-2cr mutant with DCM. Moreover, the presence of DCM inhibited growth with methanol of the DM4-2cr transconjugant expressing the rat liver GSTT1-1. In Salmonella typhimurium TA1535, expression of rat and bacterial DCM-active GST from a plasmid in the presence of DCM yielded up to 5.3 times more reversions to histidine prototrophy in the transconjugant expressing the rat enzyme. Under the same conditions, however, GST-mediated conversion of DCM to formaldehyde was lower in cell-free extracts of the transconjugant expressing the rat GSTT1 than in the corresponding strain expressing the bacterial DCM dehalogenase. This provided new evidence that formaldehyde was not the main toxicant associated with GST-mediated DCM conversion, and indicated that an intermediate in the transformation of DCM by GST, presumably S-chloromethylglutathione, was responsible for the observed effects. The marked differences in substrate affinity of rat and bacterial DCM-active GST, as well as in the toxicity and genotoxicity associated with expression of these enzymes in bacteria, suggest that bacterial DCM dehalogenases/GST have evolved to minimise the toxic effects associated with glutathione-mediated catalysis of DCM conversion.

Keywords: Key words Dichloromethane; Dichloromethane dehalogenase; Formaldehyde; Glutathione S-transferase; Bacterial genotoxicity

Glutathione S-transferase (GST) M1 and GST T1 genotypes and hematopoietic effects of benzene exposure by Ling-Ling Hsieh; Saou-Hsing Liou; Li-Ling Chiu; Yeong-Hwang Chen (pp. 80-82).

This study investigated whether or not the genotypes glutathione S-transferase θ (GST T1) and μ (GST M1) correlated with low white blood cell (WBC) count found in benzene exposed workers. We found that individuals with genotypes positive for both GST T1 and GST M1 showed the highest prevalence of low WBC [odds ratio (OR) = 4.67, P = 0.046, 95% confidence interval (CI) = 1.02–24.15] when the benzene exposure was high. Multiple logistic regression showed that benzene exposure (OR = 2.81, P = 0.062, 95% CI = 0.96–8.30) was associated with increased OR on low WBC and interactions between the benzene exposure and the genotype of GST T1 were also observed. These observations suggest that GST T1 and GST M1 may play important roles in the biotransformation of benzene, the effect which leads to its hematotoxicity.

Keywords: Key words Benzene; Glutathione S-transferases; Hematotoxicity

Effect of d-amphetamine repeated administration on rat antioxidant defences by Félix Carvalho; Eduarda Fernandes; Fernando Remião; Maria Lourdes Bastos (pp. 83-89).

The purpose of this study was to evaluate rat tissue antioxidant status after repeated administration of d-amphetamine. Three groups of four rats each were used: control, d-amphetamine sulphate dosed (s.c., 20 mg/kg per day), and pair-fed. After 14 days of d-amphetamine daily administration, superoxide dismutase (CuZnSOD and MnSOD), catalase, glutathione peroxidase (GPx), glutathione reductase (GRed), glutathione-S-transferase (GST), glutathione (GSH), cysteine and thiobarbituric acid reactive substances (TBARS) were measured in liver, kidney, and heart. Various serum and urine parameters were also analysed. d-Amphetamine treatment induced an increase of liver GSH, as well as a decrease of cysteine and MnSOD levels in this organ. A small increase in serum transaminases was also observed in comparison to the pair-fed group. Hepatic levels of TBARS, GPx, GRed and CuZnSOD were found to be similar among the three groups of rats. d-Amphetamine treatment induced an increase of kidney GST, GRed and catalase levels, and an elevation of N-acetyl-β-d-glucosaminidase efflux to the urine, accompanied by a decrease in urinary creatinine, compared to the pair-fed group. In d-amphetamine treated animals, heart cysteine levels were significantly depleted when compared to the pair-fed group, but all three groups of rats were found to have similar heart antioxidant enzyme levels. These results indicate that repeated administration of d-amphetamine caused a certain degree of stress in liver and kidney, which was followed by adaptations of antioxidant defences. The mechanisms involved in d-amphetamine-induced toxicity may explain the different adaptations observed for the studied organs.

Keywords: Key wordsd-Amphetamine; Oxidative; stress; Glutathione; Antioxidant enzymes; Rat tissues

Altered activity of heme biosynthesis pathway enzymes in individuals chronically exposed to arsenic in Mexico by Araceli Hernández-Zavala; Luz M. Del Razo; Gonzalo G. García-Vargas; Carolina Aguilar; Victor H. Borja; Arnulfo Albores; Mariano E. Cebrián (pp. 90-95).

Our objective was to evaluate the activities of some enzymes of the heme biosynthesis pathway and their relationship with the profile of urinary porphyrin excretion in individuals exposed chronically to arsenic (As) via drinking water in Region Lagunera, Mexico. We selected 17 individuals from each village studied: Benito Juarez, which has current exposure to 0.3 mg As/l; Santa Ana, where individuals have been exposed for more than 35 years to 0.4 mg As/l, but due to changes in the water supply (in 1992) exposure was reduced to its current level (0.1 mg As/l), and Nazareno, with 0.014 mg As/l. Average arsenic concentrations in urine were 2058, 398, and 88 μg As/g creatinine, respectively. The more evident alterations in heme metabolism observed in the highly exposed individuals were: (1) small but significant increases in porphobilinogen deaminase (PBG-D) and uroporphyrinogen decarboxylase (URO-D) activities in peripheral blood erythrocytes; (2) increases in the urinary excretion of total porphyrins, mainly due to coproporphyrin III (COPROIII) and uroporphyrin III (UROIII); and (3) increases in the COPRO/URO and COPROIII/COPROI ratios. No significant changes were observed in uroporphyrinogen III synthetase (UROIII-S) activity. The direct relationships between enzyme activities and urinary porphyrins, suggest that the increased porphyrin excretion was related to PBG-D, whereas the increased URO-D activity would enhance coproporphyrin synthesis and excretion at the expense of uroporphyrin. None of the human studies available have reported the marked porphyric response and enzyme inhibition observed in rodents. In conclusion, chronic As exposure alters human heme metabolism; however the severity of the effects appears to depend on characteristics of exposure not yet fully characterized.

Keywords: Key words Arsenic; Chronic exposure; Porphyrins; Porphobilinogen deaminase; Uroporphyrinogen decarboxylase

Age-related changes in rat testicular oxidative stress parameters by hexachlorocyclohexane by Luna Samanta; Arjun Sahoo; G. B. N. Chainy (pp. 96-107).

Effect of repeated oral administration of hexachlorocyclohexane (HCH; 10 and 20 mg/kg body weight per day for 7, 15 and 30 days) on antioxidant defence system and lipid peroxidation (LPX) in the testis was compared between immature (15-day-old) and mature (90-day-old) rats. In both age-groups of rats, the pesticide elicited a significant decrease in the activities of cytosolic superoxide dismutase (SOD; total and CN⁻-resistant) and catalase, and ascorbic acid content together with an increase in the levels of LPX (both in crude homogenate and subcellular fractions) and H₂O₂. Testicular glutathione peroxidase (GPx; total and non-selenium-dependent) activity was enhanced in both the age-groups of rats while the testicular glutathione content as well as glutathione reductase activity remained unaltered. HCH treatment resulted in a decrease of total epididymal sperm number with a higher incidence of dead and damaged spermatozoa, and sperms having anomalous head. Statistical analyses suggest that the alterations in the testicular antioxidant defence profile in the rat are not only dependent on the duration of pesticide treatment, but also influenced by age.

Keywords: Key words Hexachlorocyclohexane; Lipid peroxidation; Antioxidant defence; Histopathology; Rat testis

Selective toxicity of ochratoxin A in primary cultures from different brain regions by Abdelhak Belmadani; Pieter S. Steyn; Gerard Tramu; Anne-Marie Betbeder; Isabelle Baudrimont; Edmond E. Creppy (pp. 108-114).

Ochratoxin A (OTA) is a mycotoxin produced by moulds from the Aspergillus and Penicillium genera. It is a natural contaminant of a wide variety of both human and animal foodstuffs. Via dietary intake, OTA passes into the blood of both humans and animals and accumulates in several organs, such as the kidney and the brain with selective toxicity in the ventral mesencephalon and in the cerebellum. In order to confirm the regional selectivity to OTA cytotoxicity in rat brain, investigations were designed to study the mechanism of the cytotoxicity of OTA in primary cultures of the above-mentioned structures (ventral mesencephalon and cerebellum), and to compare their sensitivity to the toxin. Protein and DNA synthases, lactate dehydrogenase (LDH) release and production of malondialdehyde (MDA) were assayed in astrocytes and neurones of the selected structures in the presence of OTA. After 48 h incubation, OTA (10–150 μM) induced an inhibition of protein and DNA syntheses in a concentration-dependent manner with a selective higher toxicity in the cells of the ventral mesencephalon [50% inhibitory concentrations (IC₅₀) of protein and DNA syntheses were 14 ± 2 μM for neurones and 40 ± 5 μM for astrocytes] compared to the cerebellum values (24 ± 7 μM for neurones and 69 ± 9 μM for astrocytes). In parallel, a significant increase in levels of MDA and LDH release were noted. Altogether these results indicate that OTA is also a neurotoxic substance in addition to its well-documented nephrotoxicity and that the effects are likely to be restricted within particular structures of the brain.

Keywords: Key words Ochratoxin A; Selective cytoxicity; Primary cultures; Rat brain

Acute soman poisoning in primates neither pretreated nor receiving immediate therapy: value of gacyclidine (GK-11) in delayed medical support by Guy Lallement; Didier Clarençon; Monique Galonnier; Dominique Baubichon; Marie-France Burckhart; Michel Peoc'h (pp. 115-122).

Organophosphorus (OP) nerve agents are still used as warfare and terrorism compounds. Classical delayed treatment of victims of organophosphate poisoning includes combined i.v. administration of a cholinesterase reactivator (an oxime), a muscarinic cholinergic receptor antagonist (atropine) and a benzodiazepine anticonvulsant (diazepam). The objective of this study was to evaluate, in a realistic setting, the therapeutic benefit of administration of GK-11 (gacyclidine), an antiglutamatergic compound, as a complement to the above therapy against organophosphate poisoning. Gacyclidine was injected (i.v.) in combination with atropine/diazepam/pralidoxime at man-equivalent doses after a 45- or 30-min latency period to intoxicated primates (2 LD₅₀). The effects of gacyclidine on the animals' survival, electroencephalographic (EEG) activity, signs of toxicity, recovery after challenge and central nervous system histology were examined. The present data demonstrated that atropine/diazepam/pralidoxime alone or combined with gacyclidine did not prevent signs of soman toxicity when treatment was delayed 45 min after poisoning. Atropine/diazepam/pralidoxime also did not control seizures or prevent neuropathology in primates exhibiting severe signs of poisoning when treatment was commenced 30 min after intoxication. However, in this latter case, EEG recordings revealed that additional treatment with gacyclidine was able to stop soman-induced seizures and restore normal EEG activity. This drug also totally prevented the neuropathology observed 5 weeks after soman exposure in animals treated with atropine/diazepam/pralidoxime alone. Overall, in the case of severe OP-poisoning, gacyclidine represents a promising adjuvant therapy to the currently available polymedication to ensure optimal management of organophosphate poisoning in man. This drug is presently being evaluated in a human clinical trial for a different neuroprotective indication. However, it should always be kept in mind that, in the case of severe OP-poisoning, medical intervention must be conducted as early as possible.

Keywords: Key words Organophosphate poisoning; Seizures; Neuropathology; Gacyclidine; Primates

The interaction of sarin and soman with plasma proteins: the identification of a novel phosphonylation site by Robin M. Black; John M. Harrison; Robert W. Read (pp. 123-126).

Incubation of both sarin and soman with human plasma has shown that binding occurs to a tyrosine residue. Similar binding occurs when sarin and soman are incubated with human serum albumin. This binding may provide an important biological marker, which retains full structural information concerning the identity of the agent, in cases of allegations of chemical warfare use.

Keywords: Key words Sarin; Soman; Protein binding; Tyrosine residue; Biomarker

Sections

Personal tools

Archives of Toxicology (v.73, #2)

Sections

Personal tools

Local resources

Archives of Toxicology (v.73, #2)