Effect of n-propylthiouracil or thyroxine on arsenic trioxide toxicity in the liver of rat

Involvement of thyroid gland in the hepatotoxic manifestations of arsenic trioxide (As(III)) has been studied in rat. The effects of n-propylthiouracil (PTU) (a thyrotoxic compound) and L-thyroxine (a thyroid hormone) have been studied with reference to T(3) and T(4) values in the serum, arsenic concentration in the liver, Ca(2+) accumulation in the liver, aspartate transaminase, alanine transaminase and bilirubin values as the indicators of liver function, histopathological observations and finally the ultrastructural studies. It is concluded that hypothyroid condition protects against As(III) toxicity. Scavenging of reactive oxygen species (ROS) that significantly contribute in As(III) toxicity, by high intracellular concentration of reduced glutathione, as a consequence of PTU treatment is proposed as the plausible protective mechanism.     

Ontogenically regulated expression of metallothionein and its messenger RNA in chick liver

By electrophoretic and immunological assay the concentration of hepatic metallothionein in new born chick liver was found to be ontogenically modulated, reaching a peak accumulation per gram liver in fourth day of hatching and declining below the detection limit after second week postnatal. The protein was undetectable upto second week of incubation in egg-embryonic stage. The concentration of metallothionein mRNA shows drastic change during first few days after hatching. The greatest accumulation of metallothionein mRNA was detected in the one day new born chicks, which declined rapidly there after, and reduced to a barely detectable level. Metallothionein was also detected in the in vitro translated product of one day neonatal chick hepatic poly(A+) RNA by S-cysteine labelling and immunoprecipitation. The naturally occurring new-born chick liver metallothionein was found to be a zinc-metallothionein and the concentration of hepatic zinc in new-born chick was found to undergo drastic modulation during development, unlike some other chick tissues. Endogenous zinc ion mobilization can thus play a significant role in the developmental regulation of chick metallothionein expression.     

Binding of polonium-210 to liver metallothionein

The interactions of 210Po at the molecular level in biological systems have received little study even though this alpha-emitting radionuclide occurs widely in nature. Polonium-210 was given subcutaneously to rats and found to be incorporated into liver metallothionein as judged by a number of criteria including heat stability, acetone precipitation, and chromatography. In vitro studies confirmed this binding. The binding of 210Po to metallothionein has implications that may help explain some of the radiation damage 210Po causes intracellularly.     

Effect of stress,adrenalectomy and changes in glutathione metabolism on rat kidney metallothionein content: comparison with liver metallothionein

Eighteen hours of immobilization stress, accompanied by food and water deprivation, increased liver metallothionein (MT) but decreased kidney MT levels. Food and water deprivation alone had a significant effect only on liver MT levels. In contrast, stress and food and water deprivation increased both liver and kidney lipid peroxidation levels, indicating that the relationship between MT and lipid peroxidation levels (an index of free radical production) is unclear. Adrenalectomy increased both liver and kidney MT levels in basal conditions, whereas the administration of corticosterone in the drinking water completely reversed the effect of adrenalectomy, indicating an inhibitory role of glucocorticoids on MT regulation in both tissues. Changes in glutathione (GSH) metabolism produced significant effects on kidney MT levels. Thus, the administration of buthionine sulfoximine, an inhibitor of GSH synthesis, decreased kidney GSH and increased kidney MT content, suggesting that increased cysteine pools because of decreased GSH synthesis might increase kidney MT levels through an undetermined mechanism as it appears to be the case in the liver. However, attempts to increase kidney MT levels by the administration of cysteine or GSH were unsuccesful, in contrast to what is known for the liver. The present results suggest that there are similarities but also substantial differences between liver and kidney MT regulation in these experimental conditions.     

Effect of gamma irradiation on liver metallothionein synthesis and lipid peroxidation in rats.

Several studies have recently shown that metallothionein (MT), a protein characterized by a high thiol content and that binds Zn2+ and Cu+, might be involved in the protection against oxidative stress and can act as a free radical scavenger. Oxidative stresses, such as irradiation, increase lipid peroxidation (LP) and subsequent tissue damage through free radical production. The induction of hepatic MT synthesis by gamma-irradiation (20 Gy) at 8, 24, 30 and 48 hrs. post-irradiation in two different age groups of Sprague-Dawley rats (39-40 and 48-49 days old) was studied. LP measured by the thiobarbituric acid reactive substances (TBARS) assay and Cu and Zn levels in liver have also been determined. In the younger group, the gamma-irradiation induced hepatic MT synthesis and increased LP that peaked 24 hrs. after irradiation. During the first 30 hrs. post-irradiation, a positive and statistically significant correlation between hepatic MT content and LP level in liver was found. In the older group, liver MT synthesis was only increased 1.7-fold and LP levels were not altered at 24 hrs. post-irradiation compared with sham-irradiated rats.Therefore it appears that LP is not necessary for induction of MT synthesis by gamma-irradiation.     

The conversion of ethanolamine and of its metabolites to choline in human neuroblastoma clones: Effect of differentiation induced by retinoic acid

The sequential methylation of ethanolamine (Etn) or phosphorylethanolamine to the corresponding choline (Cho) derivatives was studied in both undifferentiated and retinoic acid (RA) differentiated human neuroblastoma clones LA-N-1 and LA-N-2. Conversion of Etn derivatives to the respective Cho metabolites was low in both cell types. However, after treatment of the cultures with ethanol or RA, the methylation of phosphoryl-Etn was stimulated while that of phosphatidyl-Etn was severely reduced in both cholinergic LA-N-2 and catecholaminergic LA-N-1 cells.Abbreviations Etn ethanolamine - MeEtn monomethylethanolamine - Me₂Etn dimethylethanolamine - Cho choline - PEtn phosphorylethanolamine - PtdEtn phosphatidylethanolamine - LPtdEtn lysophosphatidylethanolamine - RA retinoic acid     

Effect of nitric oxide synthesis inhibition on mouse liver and brain metallothionein expression

The role of nitric oxide (NO) production on metallothionein (MT) regulation in the liver and the brain has been studied in mice by means of the administration of nitric oxide synthase (NOS) inhibitors. Mice injected with either the arginine analog N^G-monomethyl-L-arginine (L-NMMA) or the heme binding compound 7-nitro indazole (7-NI) showed consistently increased liver MT-I mRNA and MT-I+II total protein levels, suggesting that NO is involved in the hepatic MT regulation. In agreement with the liver results, in situ hybridization analysis demonstrated a significant upregulation of the brain MT-I isoform in areas such as the cerebrum cortex, neuronal CA1-CA3 layers and dentate gyrus of the hippocampus, and Purkinje cell layer of the cerebellum, in 7-NI treated mice. The same trend was observed for the brain specific isoform, MT-III, but to a much lower extent. The effect of NOS inhibition was also evaluated in a MT-inducing condition, namely during immobilization stress. In both the liver and the brain, stress upregulated the MT-I isoform, and 7-NI significantly reduced or even blunted the MT-I response to stress, suggesting a mediating role of NO on MT-I regulation during stress. Stress also increased the MT-III mRNA levels in some brain areas, an effect blunted by the concomitant administration of 7-NI, which in some areas even decreased MT-III mRNA levels below the saline injected mice. Results in primary culture of neurons and astrocytes demonstrate significant effects of the NOS inhibitors in some experimental conditions. The present results suggest that NO may have some role on MT regulation in both the liver and the brain.     

Cytogenetic evaluation of arsenic trioxide toxicity in Sprague-Dawley rats

Acute exposure to arsenic trioxide has been reported to induce death and/or multiple organ damage with symptoms including nausea, vomiting, diarrhea, gastrointestinal hemorrhage, cerebral edema, tachycardia, dysrhythmias and hypovolemic shock. Its toxic effects are due to its ability to bind to sulfhydryl groups of proteins and to inhibit energy production. Although the chronic exposure to arsenic trioxide has been linked to various types of cancer, such as skin, liver, lung, bladder and kidney neoplasms, studies of its carcinogenic potential in animals have not been conclusive. In this study, we investigated the genotoxic potential of arsenic trioxide in bone-marrow cells obtained from Sprague-Dawley rats; using chromosomal aberrations (CA), mitotic index (MI) and micronuclei (MN) formation as the toxicological endpoints. Four groups of six male rats each, weighing approximately 60+/-2 g per rat, were injected intraperitoneally, once a day for 5 days with doses of 5, 10, 15 and 20 mg/kg body weight (BW) of arsenic trioxide dissolved in distilled water. A control group was also made of six animals injected with distilled water without chemical. All the animals were sacrificed at the end of the treatment period. Chromosome and micronuclei preparation was obtained from bone-marrow cells following standard protocols. Arsenic trioxide exposure significantly increased the number of structural chromosomal aberrations, the frequency of micronucleated cells and decreased the mitotic index in treated groups when compared with the control group. Our results demonstrate that arsenic trioxide has a clastogenic/genotoxic potential as measured by the bone-marrow CA and MN tests in Sprague-Dawley rats.     

Various tolerances to arsenic trioxide between human cortical neurons and leukemic cells

Arsenic trioxide (As₂O₃) is very effective for treatment of acute promyelocytic leukaemia (APL) but little can pass through the blood-brain-barrier (BBB), which limits its use in the prevention and treatment of central nervous system leukaemia (CNSL). Before creating a non-invasive method to help As₂O₃’s access, the safe and effective therapeutic concentration of As₂O₃ in the CNS ought to be known. The changes of apoptosis biomarkers, [Ca²⁺]_i and PKC activity of both leukaemia cells and human cortical neurons, were monitored before and after being treated with As₂O₃ in vitro with laser confocal microscopy and Western blot. NSE concentration, the neuron invasive biomarker, was monitored by enzyme immunoassay (NSE-EIA). This study revealed that cortical neuron was more tolerable to As₂O₃ compared to NB4. 1.0 μmol / L As₂O₃ showed little influence on cortical neuron but effectively promoted apoptosis and induced differentiation of NB4.     

Various tolerances to arsenic trioxide between human cortical neurons and leukemic cells

Arsenic trioxide (As2O3) is very effective for treatment of acute promyelocytic leukaemia (APL) but little can pass through the blood-brain-barrier (BBB),which limits its use in the prevention and treatment of central nervous system leukaemia (CNSL). Before creating a non-invasive method to help As2O3 ’s access,the safe and effective therapeutic concentration of As2O3 in the CNS ought to be known. The changes of apoptosis biomarkers,[Ca2 ]i and PKC activity of both leukaemia cells and human cortical neurons,were monitored before and after being treated with As2O3 in vitro with laser confocal microscopy and Western blot. NSE concentration,the neuron invasive biomarker,was monitored by enzyme immunoassay (NSE-EIA). This study revealed that cortical neuron was more tolerable to As2O3 compared to NB4. 1.0 μmol / L As2O3 showed little influence on cortical neuron but effectively promoted apoptosis and induced differentiation of NB4.     

Synergistic mitosis-arresting effects of arsenic trioxide and paclitaxel on human malignant lymphocytes

The treatment outcome of acute lymphoblastic leukemia (ALL) has improved steadily over the last 50 years. However, the cure rates are unlikely to be raised further with current therapies. Since increasing the dosage of chemotherapeutic agents could also elevate toxicity, a solution to how one could achieve maximum therapeutic effect with the minimum dosage possible is imminent. One possibility is the employment of combination drug therapies. Arsenic trioxide (ATO) is a widely used drug for acute promyelocytic leukemia (APL). Its combination with other drugs presented therapeutic activities in malignant cancers other than APL. Considering the fact that ATO induces mitotic arrest prior to apoptosis induction, we attempted to investigate the potential anti-cancer effects of ATO in combination with the microtubule-stabilizing agent, paclitaxel (PTX), using malignant lymphocytes as in vitro models. Three malignant lymphocytic cell lines and primary cells were treated with ATO and/or PTX. Using the Chou–Talalay analysis for evaluation of combined effect of ATO and PTX, we found a synergistic effect of the two drugs in the inhibition of cell growth. We also found that the combination of ATO and PTX at low concentrations synergistically induced mitotic arrest followed by apoptosis in malignant lymphocytes, which increased phosphorylated cyclin-dependent kinase 1 (Cdk1) on Thr¹⁶¹ and promoted the dysregulated activation of Cdk1. The ATO/PTX combination also significantly enhanced the activation of spindle checkpoint by inducing the formation of the inhibitory checkpoint complex BubR1/Cdc20. Our study provided the first in vitro demonstration that low concentrations of ATO and PTX synergistically induce mitotic arrest in malignant lymphocytes.     

Effect of surgically induced cholestasis on the levels of hepatic zinc and metallothionein in rat liver

Early effects of experimental cholestasis on the homeostasis of zinc (Zn) and metallothionein (MT) were studied in rats which had undergone bile duct ligation for 0, 3, 6, 9, 12, 16, 20, and 24 h. Transient increases in hepatic Zn levels were observed at 9 h but returned to control values at 12 h. Serum Zn levels increased at 24 h. Cholestasis was confirmed by increased serum alkaline phosphatase (AP) activity. MT increased at 3 h and reached a maximum level at 12 h and remained elevated even at 24 h after the onset of experimental cholestasis. No hepatocellular damage was detected according to the results of alanine aminotransferase (ALT) activities in serum. These results shown that the increases in Zn observed in liver are related to bile stagnation rather than to a hepatocellular damage and that increased MT occurs concurrently with increased hepatic Zn. These observations suggest that the cellular levels of Zn in cholestasis is regulated by homeostatic mechanisms, of which one could be mediated by MT.     

Effect of thyrotropin on conversion of T4 to T3 in perfused rat liver

The present study was undertaken to elucidate the direct effect of thyrotropin (TSH) on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat liver. The liver was perfused without recirculation with a synthetic medium containing 10 micrograms/dl T4 and the effect of constant infusion of bovine TSH (125 or 250 microU/ml) on the conversion of T4 to T3 was examined. T4 uptake in the perfused liver was not changed by the addition of TSH. The release of T3 (10.3 +/- 1.4 ng/g/30min, mean +/- SD), tissue T3 production (99.5 +/- 21.4 ng/g/30min), net T3 production (102.6 +/- 20.2 ng/g/30min), and the conversion rate of T4 to T3 (14.8 +/- 3.5%) in the liver perfused with 250 microU/ml TSH were significantly higher than those in controls (8.1 +/- 1.2 ng/g/30min, 69.0 +/- 6.8 ng/g/30min, 69.9 +/- 6.1 ng/g/30min, and 10.0 +/- 0.8%), respectively. These results suggest that TSH may directly enhance hepatic conversion of T4 to T3 in rats in vitro.     

Effect of ethanol on the levels of dopamine and its metabolites in the brain of rats with different degree of sensitivity to stress

It was shown, that content of dopamine and its metabolites (DOPAC and HVA) are the same in two groups of rats with different time of immobilization in forced swimming test. One group of low active (LA) animals experienced the immobilization more than 300s, other high active (HA) rats for less than 120 s. Ethanol (2 g/kg per oris) increased the level of DA in the striatum and medial prefrontal cortex only in LA rats and besides, the concentration of dopamine after ethanol administration was higher in the n. accumbens of LA rats, than in that of HA rats. The authors suggest that differences in dopamine content between LA and HA rats are connected with different levels of voluntary alcohol consumption. The opportunity to use both groups of HA and LA rats for developing models of pathogenic heterogeneity of alcoholism is discussed.     

磷对土壤中砷吸附的影响

在黄壤、红壤和褐土中进行As的等温吸附实验表明,在不添加P的情况下,3种土壤对As的吸附能力随土壤pH的升高而降低,随土壤粘粒含量的降低而减弱,3种土壤吸附能力为黄壤>红壤>褐土,As在土壤中的吸附受P存在的影响,60mg·kg^-1的P可以降低黄壤和红壤对As最大吸附量．吸附质中P：As的比例不同,P对土壤吸附As的影响差异很大：吸附质中P：As=1：2时,土壤对As的吸附能力均强于P：As=1：1和P：As=2：1,后两者差异不显著,表明土壤中的吸附点位对As和P的亲和性具有一定的差异,Languir方程能很好地拟合所测得的土壤平衡溶液中As浓度。