Mobilization of mercury by DMPS in occupationally exposed workers and in model experiments on rats: evaluation of body burden.

The aim of the study was to evaluate the efficacy of DMPS (sodium-2,3-dimercapto-1-propane sulfonate) (Dimaval) administration for mobilizing mercury from the body in occupationally exposed people and experimental animals. Two doses of DMPS were administered at a 24-h interval to: (a) groups of people occupationally exposed to merkury--workers of the chloralkali industry (n = 43), and dentists (n = 12), (b) non-exposed individuals (n = 20), and (c) rats chronically exposed to mercury vapour at the concentration of 0.8 mg/m3 Hg degree (6 h/day, 5 days/week) for 15 weeks. In an out-patient mobilizing test, the urinary excretion of mercury 48 h after the administration of the first dose reached 1513 micrograms in the group of industrial workers, 132.6 micrograms in dentists, and 3.78 micrograms in controls. In rats, two consecutive doses of DMPS decreased kidney content of mercury by about 30% and 50% after oral and intraperitoneal administration, respectively. Kidney mercury burden was calculated on the basis of the data from animal and human studies of the mobilization of mercury via urine after DMPS treatment: 61, 2800 and 28,000 ng/g in controls, dentists and workers, respectively. It was estimated that two doses of DMPS mobilized 17-20% (after oral administration) and 25-30% (after intramuscular administration) of kidney mercury burden, both in the control and exposed subjects.

Neurological and electrophysiological examinations on three groups of workers with different levels of exposure to mercury vapors.

The authors performed neurological, visual evoked potentials (VEP) and electroneurography (ENG) examinations on three groups of workers with occupational exposure to mercury vapors (Hg(0)), and on a control group. The exposure of dental professionals (n = 36) was mild, that of chloralkali plant workers (n = 36) was intermediate, and that of workers from mercury works (n = 77) was very high. Symptoms and signs of micromercurialism were observed only in the group with the highest exposure to Hg(0). In comparison with the control group, a shortening of VEP latency and a decrease in amplitude were found in the exposed groups. The VEP changes correlated with Hg(0) excreted in urine after administration of a chelating agent - sodium 2,3-dimercapto-1-propan sulfonate (DMPS). The frequency of abnormal VEP results increased with increasing levels of exposure. ENG changes were observed only in the group with the highest exposure to Hg(0). An isolated decrease of sural nerve conduction velocity was observed in 18% of total workers. In 70% of the cases, this was associated with an abnormality in VEP. The combination of a decrease in sural nerve conduction velocity and an abnormality of VEP seems to be a characteristic pattern of electrophysiological changes in persons exposed to mercury vapors.

Biliary iron excretion in rats following treatment with analogs of pyridoxal isonicotinoyl hydrazone.

Iron overload is a major life-threatening complication of thalassemia major and other iron-loading anemias treated by regular blood transfusions. Although the clinical manifestations of iron overload may be prevented by desferrioxamine, the only iron-chelating drug in routine clinical use, this treatment requires subcutaneous infusion of desferrioxamine for 12 hours each day. New orally effective iron chelators are urgently needed, and pyridoxal isonicotinoyl hydrazone (PIH), which was first recognized as an effective iron chelator in vitro and subsequently in vivo, shows promise for the treatment of iron overload. More recently, over 40 analogs of PIH were synthesized, and some of them proved to be very potent in mobilizing 59Fe in vitro from 59Fe-labeled cells. In this study, we show that PIH analogs such as pyridoxal benzoyl hydrazone, pyridoxal p-methoxybenzoyl hydrazone (PMBH), pyridoxal m-fluorobenzoyl hydrazone (PFBH), and pyridoxal-2-thiophenecarboxyl hydrazone, compounds previously shown to mobilize iron from cells in vitro, are also effective in vivo. All of these chelators significantly enhanced biliary excretion of iron (measured by atomic absorption spectrophotometry) following their intraperitoneal (IP) and/or oral administration to rats. The most effective was PFBH, which increased iron concentration in the bile about 150-fold, as compared with basal biliary iron concentration, within 1 hour following a single IP dose of 0.2 mmol/kg body weight. In contrast, desferrioxamine increased the biliary iron concentration only 20-fold to 30-fold under the same conditions. Moreover, while control rats excreted approximately 0.8 microg Fe in 2 hours, treatment with PFBH, PMBH, and desferrioxamine resulted in cumulative excretions of 87, 59, and 22 microg Fe, respectively, in the same period of time. Interestingly, PMBH was also quite effective following gastric administration, resulting in a 6-hour cumulative value of 34 microg Fe. These compounds are nontoxic and are inexpensive and easy to make. Their further evaluation as candidate drugs for the treatment of iron overload is warranted.

Biological monitoring of child lead exposure in the Czech Republic.

The area around the Pribram lead smelter has been recognized to be heavily contaminated by lead (Pb). In the early 1970s, several episodes of livestock lead intoxication were reported in this area; thereafter, several epidemiological and ecological studies focused on exposure of children. In contrast to earlier studies, the recent investigation (1992-1994) revealed significantly lower exposure to lead. From 1986-1990, recorded average blood lead levels were about 37.2 micrograms lead (Pb)/100 ml in an elementary school population living in a neighborhood close to the smelter (within 3 km of the plant). The present study, however, has found mean blood lead levels of 11.35 micrograms/100 ml (95% CI = 9.32; 13.82) among a comparable group of children. In addition to blood lead, tooth lead was used to assess exposure among children. Statistically significant differences (p < 0.05) were observed between the geometric mean tooth lead level of 6.44 micrograms Pb/g (n = 13; 95% CI = 3.95; 10.50) in the most contaminated zone and 1.43 micrograms Pb/g (n = 35; 95% CI = 1.11; 1.84) in zones farther away from the point source. Both biomarkers, blood and tooth lead levels, reflect a similar pattern of lead exposure in children. This study has attempted a quantitative assessment of risk factors associated with elevated lead exposure in the Czech Republic. Content of lead in soil, residential distance from the smelter, consumption of locally grown vegetables or fruits, drinking water from local wells, the mother's educational level, cigarette consumption among family members, and the number of children in the family were factors positively related (p < 0.05) to blood lead levels. The resulting blood lead level was found to be inversely proportional to the child's age.

In vivo and in vitro efficacy of a new carbodithioate for the mobilization of cadmium.

Female Wistar rats with chronic cadmium intoxication (oral exposure to low dosages of CdCl2 in drinking water over a period of 90 d) were used to examine the in vivo ability of a newly developed chelator, sodium N-(4-methylbenzyl)-4-O-(beta-D-galactopyranosyl)-D-glucamine-N- carbodithioate (MeBLDTC), singly and in combination with sodium 4-carboxy-amidopiperidine-N-carbodithioate (INADTC) as agents to induce the biliary and urinary excretion of cadmium. The combined administration of the two dithiocarbamates, which differ greatly in molecular weight and structural features, led to a synergistic increase in the biliary excretion of cadmium and an enhanced reduction of renal cadmium levels. The use of such a coadministration produced an increase in the biliary excretion of cadmium that was more than double that expected if the compounds acted in an additive fashion. Such mixed-chelation therapy has potential utility in the treatment of human chronic cadmium intoxication. The hepatocytes isolated from chronically Cd-intoxicated rats were used as an in vitro screening model system for the new chelator. The plasma membrane integrity study with MeBLDTC at 0.48 mmol/20 ml of hepatocyte incubate using the trypan blue exclusion test and lactate dehydrogenase (LDH) leakage test revealed no differences in the cell viability with or without chelator. The cellular metabolic competence measured as the rate of urea synthesis also did not show any marked deviation from that of controls when incubated with MeBLDTC at three different concentrations. In the hepatocyte cultures, MeBLDTC induced a significant removal of cadmium from the hepatocytes at concentrations as low as 0.04 mmol/20 ml.

Distribution and excretion of cadmium and nickel after simultaneous exposure and the effect of N-benzyl-D-glucamine dithiocarbamate on their biliary and urinary excretion.

A rat model for combined exposure to cadmium and nickel is presented that involves the administration of drinking water containing these elements over a period of 90 d. Coadministration of these two ions in drinking water leads to brain levels of both elements that are significantly higher than results from the administration of equal doses of the metals individually. The enhanced biliary excretion of cadmium in rats given sodium N-benzyl-D-glucamine dithiocarbamate (BGDTC) is almost twice as great in those animals given cadmium and nickel as in those animals given cadmium only. The excretion of nickel is reduced by the administration of this chelating agent. Although equal amounts of nickel and cadmium were administered to these animals, liver and kidney cadmium levels were approximately 100 times greater than the corresponding nickel levels. The results suggest that combined exposure to these elements may lead to enhanced levels of nickel and cadmium in the brain and a level of nervous system damage not predictable from information obtained under conditions of exposure to only one of these elements.

[Xenobiotic and biochemical parameters of isolated rat hepatocytes]. / Ksenobiotici i biohemijski parametri izolovanih hepatocita pacova.

The authors investigated the effects of the inductors (griseofulvin and fenitoin) and the inhibitors of the cytochrome P-450 (metronidazole, chloramphenicol and phenylbutazone), the effects of the drugs with the purine structure (aminophylline, xanthinol-nicotinate, pentoxiphylline, azathioprine, thioguanine, 6-mercaptopurine), and the effects of several pesticides (lindane, binapicrile, parathion) on some biochemical parameters of the rat liver. The following parameters were determined: viability of hepatocytes, the content of glutathione and cytochrome P-450, and the activity of xanthinoxidase and lipoperoxidase. The experiments were performed in vivo and in vitro. The results showed that the cell viability as well as the other parameters studied, were most drastically affected by chloramphenicol, azathioprine and parathion, whereas the other substances elicited less intensive changes.

Mobilization of aged cadmium from isolated rat hepatocytes by sulfhydryl chelators.

Isolated hepatocytes appear to be a suitable in vitro model for the testing of the efficacy of chelating agents. In this study hepatocytes were isolated from rats exposed to CdCl2 (50 mg Cd2+/l) in drinking water for 3 months. The cells were incubated in a Krebs-Henseleit buffer for 2 hrs and the cytotoxicity was assessed using 5 types of parameters. N-benzyl-D-glucaminedithiocarbamate (BGDTC) and meso-2,3-dimercaptosuccinic acid (DMSA) were tested. Individual chelators in various concentrations were added to the incubation medium at the beginning of the experiment (t = 0). The concentration of Cd in the extracellular fluid was measured every 30 mins using flame AAS. Exposed hepatocytes did not show the signs of damage. Both chelators did not exhibit any cytotoxic effect. BGDTC was found to be efficient in the mobilization of Cd, while DMSA was ineffective.

The study of exposure to cadmium in the general population. I. Autopsy studies.

From 1982 to 1986 samples of materials (liver tissue, kidney cortex) were collected from 438 autopsies in Prague. The age of persons was over 50 years and residence time in the area was at least 10 years Concentrations of Cd and Zn were determined in the kidney cortex and the liver tissue using the AAS method. On the basis of the Questionnaire for Relatives, data on smoking habits, and occupational history of the investigated persons were obtained. The results of the study confirmed that the concentration of Cd in analyzed tissues did not exceed values reported in the literature for people of similar age living in Cd uncontaminated areas. In smokers significant increase of Cd in the kidney cortex was found in all age and sex groups. The body burden of Cd in smokers is significantly higher.

[Pesticides and liver biochemistry]. / Pesticidi i biohemizam jetre.

The effects of various pesticides (lindane, binapacrile and parathion) on the content of cytochrome P450 and glutathione, and on the activity of lipoperoxidase, xanthine oxidase and transaminases (SGOT and SPGT) were examined. Other parameters, such as the relative liver mass and hepatocyte viability were also estimated. All the studied parameters in the liver homogenate and in hepatocytes were changed by binapacrile, whereas in blood only the glutathione level was altered. Lindane produced an effect on all the parameters. In hepatocytes it did not affect only the lipoperoxidase activity. In the blood it changed only the level of glutathione content. Parathion, in the liver homogenate, changed all of the parameters examined, whereas in hepatocytes only lipoperoxidase activity remained unchanged. In the blood parathion caused a slight increase in the sulphhaemoglobin level and decreased the glutathione content.

Consequences of acrylonitrile metabolism in rat hepatocytes: effects on lipid peroxidation and viability of the cells.

Acrylonitrile caused thiobarbituric acid-positive reactants time- and concentration-dependently in isolated hepatocytes. This effect was markedly enhanced by gassing of the medium with 95% oxygen-5% CO2 gas mixture. Glycidonitrile, an acrylonitrile metabolite, proved more potent in this respect than the parent acrylonitrile or its end metabolite, cyanide anion. The latter decreased greatly the viability of isolated liver cells but caused thiobarbituric acid-positive reactants only in the presence of diethylmaleate. Acrylonitrile caused also a decrease in the concentration of nonprotein sulfhydryl groups but the oxidation of glutathione (GSH) to GSSG (oxidized glutathione) was not the major mechanism. This might indicate the consumption of GSH in the glutathione S-transferase catalyzed reactions. In contrast to cyanide anion-induced effects acrylonitrile did not affect markedly the viability of hepatocytes.

Acrylonitrile potentiation of oxygen toxicity in rats.

Single intraperitoneal injection of acrylonitrile, administered prior to the start, at the onset, or during oxygen exposure, respectively, in all cases significantly impaired the survival rate of rats exposed to 98% oxygen. Short periods of lung glutathione depletion by acrylonitrile accelerated the manifestation of O2 toxicity regardless of their timing with respect to the start of oxygen exposure, but in dependence on their intensity and duration. However, the effect of acrylonitrile was probably not solely glutathione-depletion-mediated, since O2 toxicity was enhanced even by acrylonitrile injection, given sufficiently in advance to allow the lung glutathione level to recover before the oxygen exposure started.

Acrylonitrile inhalation in rats: II. Excretion of thioethers and thiocyanate in urine.

In male Wistar rats, the inhalation exposure to acrylonitrile (AN), 271 mg X m-3, 8 hours a day, 5 days a week, did not affect protein sulfhydryl concentration in liver and blood and decreased glutathione concentration in the liver, but not in the brain at the end of the fifth exposure. The urinary excretion of the main AN metabolites, thioethers (AN-mercapturic acids) and thiocyanate was proportional to the inhaled AN concentration (57, 125, 271 mg X m-3, respectively) in a single exposure for 12 hours, and their mutual ratio was greatly different from that after injection of AN. The results revealed that the urinary excretion of thioethers is a very sensitive and dose-related indicator of exposure to AN and extrapolation of the results indicates that the exposure to AN concentration below 10 mg X m-3 could thus be demonstrated.

Acrylonitrile inhalation in rats: I. Effect on intermediary metabolism.

In male Wistar rats the inhalation exposure to acrylonitrile (AN), 280 mg X m-3, 8 hours a day for five days significantly decreased the serum concentration of cholesterol and triglycerides, but the liver concentrations of phospholipids, and esterified fatty acids were unchanged. The liver microsomal protein and cytochrome P-450 content decreased significantly. On the other hand the levels of glucose, lactate and pyruvate in the blood and brain significantly increased up to 250% of controls. A microscopic examination of the lungs, liver, kidneys and adrenals did not show structural changes and the numbers and enzyme activities of alveolar macrophages were also unaffected. In single 12-hour inhalation exposures the elevation of blood glucose was proportional to the inhaled concentration of AN (average concentrations 57, 125, or 271 mg X m-3); the effect was significant at the lowest AN concentration and was intensified in the glucose tolerance test. The elevation of blood glucose proved to be the most sensitive and dose-related indicator of AN exposure of those observed.

Acrylonitrile metabolism in the rat.

Acrylonitrile (AN) is metabolized by an oxidative pathway via glycidonitrile and glycolaldehyde cyanohydrin to cyanide (CN-), which is transformed to thiocyanate. The major route of AN metabolism (more than 2/3), however, proceeds via cyanoethylation of glutathione, to N-acetyl-S-(2-cyanoethyl)cysteine (AN-mercapturic acid) as a final product.

Two routes of acrylonitrile metabolism.

Acrylonitrile (AN) is metabolized in two different routes. The minor route of AN metabolism is its conversion to cyanide. In vitro experiments confirmed that this biotransformation proceeds via glycidonitrile (catalyzed by hepatic monooxygenases) and glycolaldehyde cyanohydrin (catalyzed by epoxide hydrase). Cyanohydrin is spontaneously decomposed to cyanide, which is then metabolized in vivo to thiocyanate by rhodanese. A major route of AN-metabolism (more than 2/3), however, proceeds via its conjugation with glutathione catalyzed by glutathione S-alkenetransferases, to N-acetyl-S-(2-cyanoethyl)cysteine as a final product.

Acrylonitrile biotransformation in rats, mice, and chinese hamsters as influenced by the route of administration and by phenobarbital, SKF 525-A, cysteine, dimercaprol, or thiosulfate.

Female wistar rats, conventional albino mice, and Chinese hamsters were given a single dose of acrylonitrile, 0.5 or 0.75 mM/kg body weight. The elimination in the urine of thiocyanate, which is the main metabolite of acrylonitrile, indicated a decreasing proportion of biotransformation after oral (over 20%), intraperitoneal, or subcutaneous (2 to 5%), and intravenous (1%) administration in rats. Oral administration of acrylonitrile in hamsters and mice was also followed by higher biotransformation than intraperitoneal administration. Pretreatment of rats with phenobarbital, SKF 525 A, cysteine, or dimercaprol did not significantly influence elimination of thiocyanate in the urine after the administration of acrylonitrile, but simultaneous administration of thiosulfate significantly increased the metabolized portion of acrylonitrile given intraperitoneally in rats (almost twice) and mice (more than three times). Acrylonitrile was found to be strongly bound in blood. The study confirmed the marked effect of distribution (first-pass metabolic phenomenon) on the metabolic fate of foreign compounds. The strong acrylonitrile binding and cyanoethylation are apparently responsible for the unusually high influence of the different routes of administration on the metabolic fate of acrylonitrile. Acrylonitrile was more effectively metabolized to thiocyanate in mice than in rats after oral, intraperitoneal, and intravenous administration. A greater response of acrylonitrile to thiocyanate metabolism and a larger decrease in its acute toxicity after thiosulfate in mice than in rats indicate possible differences in the mechanism of acrylonitrile toxicity in these animals. Cyanide apparently plays a minor role in the acrylonitrile toxicity in rats, but may play quite an important one in mice.