European Journal of Pharmacology: Environmental Toxicology and Pharmacology最新文献

Risk evaluation of complex environmental mixtures of polychlorinated dibenzo-p-dioxins and related halogenated aromatic hydrocarbons (polychlorinated dibenzofurans, azo- and azoxybenzenes, naphthalenes and some of the biphenyls) is currently carried out by measuring the concentration of each congener in the mixture and then multiplying every figure by its specific constant, toxic equivalency factor (TEF). All congeners are thought to produce highly similar effects albeit at different doses, and the TEFs are believed to represent the potencies of the congeners relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), considered the most toxic derivative of this class of environmental contaminants. Here we compared the acute toxicities of TCDD, 1,2,3,7,8-penta-, 1,2,3,4,7,8-hexa- and 1,2,3,4,6,7,8- heptachloro-dibenzo-p-dioxin in the most TCDD-susceptible (Long-Evans Turku AB; L-E) and the most TCDD-resistent (Han/Wistar Kuopio; H/W) rat strain. While L-E rats exhibited the expected rank order of sensitivities to the four dioxins, the higher chlorinated dioxins were more toxic than TCDD (in terms of acute lethality) to H/W rats, with the hexachlorodioxin showing the greatest potency. Even if the doses were adjusted according to the LD₅₀ values, both biochemical and morphological effects elicited by the dioxins turned out to depend, often critically, on strain, congener or the interaction of these two determinants. These findings demonstrate that the dioxins have distinct profiles of acute toxicities and underscore the importance of response and test organism in defining the TEFs.

Using recombinant cell lines showing Ah receptor-controlled expression of a luciferase reporter gene, the interaction of di-ortho-substituted polychlorinated biphenyls (PCBs) with Ah receptor agonists was studied. In the recombinant Hepa1c1c7 mouse hepatoma (H1L1.1c7) cells strong antagonistic interaction of 2,2′,5,5′-tetrachlorobiphenyl (PCB52) with luciferase expression induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 3,3′,4,4′-tetrachlorobiphenyl (PCB77) was observed, and similarly, between 2,2′,3,3′,4,4′-hexachlorobiphenyl (PCB128) and PCB77. Accordingly, PCB52 was found to inhibit ethoxyresorufin-O-deethylase (EROD) induction by PCB77 in wild-type Hepa1c1c7 cells. In contrast, the antagonistic effect of PCB52 on TCDD-induced luciferase expression was only minor in recombinant guinea pig GPC16 colon adenocarcinoma (G16L1.1c8) and human HepG2 hepatoma (HG2L1.1c3) cells, and intemediate in recombinant H4IIE rat hepatoma (H4L1.1c4) cells. Gel retardation studies using a ³²P-labelled dioxin responsive element (DRE)-containing oligonucleotide, and ligand binding studies using [³H]TCDD, demonstrated that the species-specific antagonistic activity of PCB52 on Ah receptor-controlled luciferase expression is due to inhibition of Ah receptor ligand and DNA binding. We conclude, that Ah-mediated luciferase expression provides a useful tool to study the species specificity of Ah receptor (ant)agonists.

The hepatic expression of xenobiotic-metabolising cytochrome P450 isoforms in the genetically obese Zucker rat, a model of obesity, was compared to that of its lean littermate. Cytochrome P450 (CYP) levels were determined using diagnostic substrates and/or immunologically in Western blot analyses. When compared with the lean Zucker rat, the obese animal exhibited hyperglycaemia, hypercholesterolaemia, marked hyperinsulinaemia and hypertriglyceridaemia but was normoketonaemic. CYP3A and CYP1A2 levels were higher in the obese Zucker rat when compared with the lean littermate but, in contrast, a protein recognised by human CYP2D6 and, to a lesser extent, CYP2C11 levels were lower. Pretreatment with acetone, dexamethasone and clofibrate resulted in enhanced p-nitrophenol hydroxylase (CYP2E), erythromycin N-demethylase (CYP3A) and lauric acid hydroxylase (CYP4A) activities respectively in the liver of the lean Zucker rat but, in contrast, the obese Zucker rat was refractive to such treatment; similarly, hepatic apoprotein levels of the CYP2E and CYP4A subfamilies were increased markedly only in the lean Zucker rat. It is concluded that CYP2E, CYP3A and CYP4A subfamilies are poorly expressed in the obese Zucker rat, and this rat strain may serve as a good model for elucidating the molecular mechanisms of induction of these cytochrome P450 proteins.

We have studied the hypothesis that 6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) is neurotoxic. Salsolinol induced a significant time and dose related inhibition of 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide; thiazoyl blue (MTT) reduction, and increased lactate dehydrogenase release (LDH) release from human SH-SY5Y neuroblastoma cells, at concentrations within the range of 1-methyl-4-phenylpyridinium (MPP⁺) cytotoxicity, in vitro. Cytotoxicity was not inhibited by the addition of antioxidants, monoamine oxidase inhibitors or imipramine. In confluent monolayers, salsolinol stimulated catecholamine uptake with EC₅₀ values of 17 μM and 11 μM, for noradrenaline and dopamine, respectively. Conversely, at concentrations above 100 μM, salsolinol inhibited the uptake of noradrenaline and dopamine, with IC₅₀ values of 411 μM and 379 μM, respectively. The inhibition of catecholamine uptake corresponded to the increased displacement of [³H]nisoxetine from the uptake₁ site by salsolinol, as the K_i (353 μM) for displacement was similar to the IC₅₀ (411 and 379 μM) for uptake. Salsolinol stimulated catecholamine uptake does not involve the uptake recognition site, or elevation of cAMP, cGMP, or inhibition of protein kinase C. Salsolinol also inhibited both carbachol (1 mM) and K⁺ (100 mM, Na⁺ adjusted) evoked release of noradrenaline from SH-SY5Y cells, with IC₅₀ values of 500 μM and 120 μM, respectively. In conclusion, salsolinol appears to be cytotoxic to SH-SY5Y cells, via a mechanism that does not require uptake₁, bioactivation by monoamine oxidase, or membrane based free radical damage. The effects of salsolinol on catecholamine uptake, and the mechanism of toxicity require further investigation.

In the present study we investigated the influence of acute lead poisoning upon the expression of benzodiazepine receptors. In addition, we examined if administration of PK 11195, an isoquinoline carboxamide derivative, to lead-poisoned rats could modulate the changes in receptor binding properties achieved by lead alone. Lead poisoning was ascertained by determination of urine σ-aminolevulinic acid levels and lead levels in rat livers. Scatchard analysis of saturation curves of [³H]PK 11195 binding to liver membranes of rats treated with lead alone or with both lead and PK 11195 showed an approximately two-fold decrease in receptor density in comparison with control groups. Peripheral benzodiazepine receptor density in the kidneys and adrenals of poisoned rats was not changed by lead intoxication per se or by coadministration of PK 11195. Scatchard analysis of saturation curves of [³H]Ro 15-1788 binding in rat cerebral cortex tissue showed no difference in the receptor density between the various groups. The K_d values of all organs were in the nanomolar range (1–4 nM). We conclude that PK 11195 is not a protective agent of hepatic peripheral benzodiazepine receptors in lead intoxication. Moreover, it causes over-accumulation of lead in hepatocytes in an unknown mechanism of action.

The metabolism of inorganic arsenic (As) in native women in four Andean villages in north-western Argentina with elevated levels of As in the drinking water (2.5, 14, 31, and 200 μg/l, respectively) has been investigated. Collected foods contained 9–427 μg As/kg wet weight, with the highest concentrations in soup. Total As concentrations in blood were markedly elevated (median 7.6 μg/l) only in the village with the highest concentration in the drinking water. Group median concentrations of metabolites of inorganic As (inorganic As, methylarsonic acid (MMA) and dimethylarsinic acid (DMA) in the urine varied between 14 and 256 μg/l. Urinary concentrations of total As were only slightly higher (18–258 μg/l), indicating that inorganic As was the main form of As ingested. In contrast to all other populations studied so far, arsenic was excreted in the urine mainly as inorganic As and DMA. There was very little MMA in the urine (overall median 2.2%, range 0.0–11%), which should be compared to 10–20% of the urinary arsenic in all other populations studied. This may indicate the existence of genetic polymorphism in the control of the methyltransferase activity involved in the methylation of As. Furthermore, the percentage of DMA in the urine was significantly higher in the village with 200 μg As/l in the water, indicating an induction of the formation of DMA. Such an effect has not been observed in other studies on human subjects with elevated exposure to arsenic.

The present study demonstrated cardiorespiratory effects of a synthetic phosphorus-containing ichthyotoxic metabolite elaborated by the marine dinoflagellate Ptychodiscus brevis in anaesthetised cats. The metabolite at a dose of 0.25–1.5 mg/kg i.v., resulted in a dose-dependent fall in blood pressure and such vasodepressor effect was associated with bradycardia. There is initial respiratory apnoea ollowed by increased rate and depth of respiration (hyperapnoea) following the administration of the toxin. The hypotensive response was accompanied by a decrease in aortic baroreceptor activity. The ECG showed atrioventricular conduction block, arrhythmia and depression of S-T segment and T wave which indicated coronary insufficiency. Vasodepressive property of the toxin is presumably muscarinic in nature as atropine counteracted the vasodepression.

The neurobehavioral and hepatic effects following chronic endosulfan administration were studied in adult male and female rats. The neurobehavioral effect was determined by testing spontaneous motor activity, motor coordination and learning and memory processes in rats of either sex, 30 days after treating the animal orally with endosulfan (3.0 and 6.0 mg/kg per day). Mortality occurring during the treatment and body weight gain at the termination of treatment were also recorded. Liver weight and liver and serum concentrations of glutamic oxaloacetic transamine, glutamic pyruvic transaminase and acetylinesterase were measured in order to determine the hepatotoxic effect of endosulfan. Body weight gain, motor coordination and acetylcholinesterase activity were unaltered in either sex. Learning and memory processes were impaired in both groups indistinguishably. Liver weight and liver and serum transaminases concentrations were increased more markedly in female than in male animals. A 30% mortality occurred in female group that received 6 mg/kg of endosulfan. Endosulfan stimulated spontaneous motor activity more markedly in male than in female animals. These findings suggest that a sex-related difference seems to occur in the stimulation of spontaneous motor activity, liver injury and mortality that result from repeated exposure to sublethal doses of endosulfan in rats.

We studied the effects of ibuprofen on bronchial blood flow and myocordial function after inhalation injury. Sheep (n = 12) were chronically instrumented with cardiovascular and pulmonary catheters. After 5 days of recovery period, baseline data were collected and the sheep were divided into two groups. Group S (n = 6) were insufflated with 48 breaths of cotton smoke; while group I (n = 6) were pretreated with ibuprofen (12 mg/kg bolus followed by 3 mg/kg/h continuous infusion for 24 h) and challenged with the same dose of smoke. All the animals were studied for 24 h. Bronchial blood flow increased significantly in both groups throughout the experimental period; while stroke volume as well as right and left ventricular stroke work indices of both groups were significantly decreased (group I worse than group S) in the second half of the experimental period. These data suggest that vasodilatory prostaglandins do not play a major role in the bronchial vascular response to smoke inhalation injury and myocardial depression seen post injury is worse in animals treated with ibuprofen.