Showing papers on "Lead acetate published in 2001"

Is the capacity of lead acetate and cadmium chloride to induce genotoxic damage due to direct DNA–metal interaction?

Abstract: Even though the toxic effects of lead and cadmium compounds have been studied over many years, inconsistent results have been obtained about their mutagenic, clastogenic and carcinogenic properties. However, these metals are considered to be potential human carcinogens. The mechanism of metal-induced carcinogenesis is still unknown, but one possible pathway may involve the interaction of metals with DNA, either directly or indirectly. In this work we explore the capacity of lead, cadmium or a mixture of both metals to interact with acellular DNA, by employing a variant of the comet assay. Our results, using low non-cytotoxic metal concentrations (0.01, 0.1 and 1.0 microM) with the standard protocol for the acellular assay, showed an induction of DNA damage in cells of all organs studied; however, basal DNA damage was different in each organ. To confirm that we were working with pure DNA, proteinase K was added to the lysis solution. With this enriched-lysis solution we found a negative response in the induction of DNA damage in cells derived from the liver, kidney and lung of CD-1 male mice. To support the results obtained by the enriched-acellular assay, we studied the capacity of lead and cadmium (0.1 microM) to induce breaks in pooled genomic DNA in cells of the same organs, with negative results. Consistent with these findings, these metals do not induce DNA breaks in the plasmid pUSE amp+. On the whole, we did not detect direct induction of DNA strand breaks by lead acetate, cadmium chloride or a mixture of both metals, all at low non-cytotoxic concentrations. However, we found an induction of lipid peroxidation and an increase in free radical levels in the different organs of CD-1 male mice after inhalation of lead acetate (0.0068 microg/cc) or cadmium chloride (0.08 microg/cc) for 1 h, suggesting the induction of genotoxicity and carcinogenicity by indirect interactions, such as oxidative stress.

Antioxidant effect of taurine against lead-induced oxidative stress.

Abstract: Oxidative stress is proposed as a molecular mechanism in lead toxicity, which suggests that antioxidants might play a role in the treatment of lead poisoning. The present study was designed to investigate whether taurine has a beneficial effect both on Chinese hamster ovary (CHO) cells and on Fisher 344 (F344) rats following lead exposure. Therefore, oxidative stress parameters (glutathione, malondialdehyde levels, catalase, and glucose-6-phosphate dehydrogenase [G6PD] activities) of lead-exposed CHO cells and F344 rats were determined following taurine treatment. Taurine was found to be effective in (1) increasing glutathione levels that had been diminished by lead; (2) reducing malondialdehyde levels, an end-product of lipid peroxidation; (3) decreasing catalase and erythrocyte G6PD activity, which had been increased by lead exposure; and (4) improving cell survival of CHO cells. However, taurine had no effect on blood and tissue lead levels when 1.1 g/kg/day taurine was administered to F344 rats for 7 days, following 5 weeks of lead exposure (2,000 ppm lead acetate). As a result, taurine seems to be capable of fortifying cells against lead-induced oxidative attack without decreasing lead levels. Therefore, administration of taurine, accompanied by a chelating agent, might increase its effectiveness in the treatment of lead poisoning.

Compensatory Up-Regulation of Nitric-Oxide Synthase Isoforms in Lead-Induced Hypertension; Reversal by a Superoxide Dismutase-Mimetic Drug

Abstract: Chronic exposure to low levels of lead causes hypertension (HTN) that is, in part, due to increased inactivation of nitric oxide (NO) by reactive oxygen species (ROS). The latter results in functional NO deficiency and compensatory up-regulation of NO synthase (NOS). We have previously shown evidence for increased hydroxyl radical ( ⋅ OH) activity in rats with lead-induced HTN. Since in the biological systems ⋅ OH is primarily derived from superoxide (O⨪ 2 ) we hypothesize that lead-induced oxidative stress and HTN must be due to increased O⨪ 2 production and as such could be ameliorated by administration of a cell-permeable O⨪ 2 scavenger. We, therefore, studied the effects of the superoxide dismutase (SOD)-mimetic drug tempol (15 mmol/kg/day i.p. × 2 weeks) and placebo in lead-exposed (given lead acetate, 100 ppm in the drinking water for 12 weeks) and normal control rats. Lead exposure resulted in a marked elevation of blood pressure, a significant reduction in urinary NO metabolites (NO χ ) excretion, and up-regulations of endothelial and inducible NOS abundance in the kidney, aorta, and heart and of neuronal NOS in the cerebral cortex and brain stem. Administration of tempol ameliorated HTN, increased urinary NO χ excretion, and reversed the compensatory up-regulation of NOS isoforms in rats with lead-induced HTN. These abnormalities recurred within 2 wk after discontinuation of tempol. In contrast to the lead-exposed rats, the normal control rats showed no change in either blood pressure, urinary NO χ excretion, or tissue NOS expression in response to either administration or discontinuation of tempol. Thus, the study supports the presence of increased O⨪ 2 activity and its role in the pathogenesis of HTN and altered NO metabolism in lead-exposed animals.

Effect of lead on nitric oxide synthase expression in coronary endothelial cells: role of superoxide.

Abstract: Chronic exposure to low levels of lead causes hypertension (HTN) in humans and animals. We have previously shown that increased reactive oxygen species (ROS) leads to enhanced NO inactivation, depressed NO bioavailability, and compensatory upregulation of NO synthases (NOSs) in rats with lead-induced HTN. We have further demonstrated increased ROS generation with lead exposure in cultured endothelial cells. In the present study, we tested the effect of lead (medium containing lead acetate, 1 ppm) alone and with either the superoxide dismutase-mimetic agent tempol or a potent antioxidant lazaroid compound (both at 10(-8) and 10(-7) mol/L) on endothelial NOS expression and NO production in cultured human coronary endothelial cells. Lead-treated cells showed a significant upregulation of endothelial NOS (eNOS) protein abundance (P:<0.002) and a significant increase in the production of NO metabolites (NO(2)(-) +NO(3)(-)=NOx, P:<0.01). Cotreatment with either tempol or lazaroid abrogated the lead-induced upregulation of eNOS protein and NO(x) production. In contrast, tempol and lazaroid had no effect on either eNOS protein expression or NO(x) production in the control cells. Thus, lead exposure upregulated eNOS expression in vitro, simulating the results of our previous in vivo studies. This phenomenon points to a direct as opposed to an indirect (eg, HTN-mediated) effect of lead on NO metabolism. The reversal of lead effect by lazaroid and the cell-permeable superoxide dismutase-mimetic agent tempol suggests that lead exposure increases generation and/or reduces dismutation of superoxide, which in turn promotes oxidative stress, enhances NO inactivation, and elicits a compensatory upregulation of eNOS whose expression is negatively regulated by NO.

Alteration of the soluble guanylate cyclase system in the vascular wall of lead-induced hypertension in rats.

Abstract: Low-level lead exposure is a known cause of hypertension that has been associated with increased reactive oxygen species activity and endothelial-dependent vasorelaxation impairment. The effect of lead exposure on the vascular nitric oxide (NO)/cyclic guanocine monophosphate (cGMP) system was analyzed. Wistar rats were exposed to 5 ppm lead acetate in the drinking water during 30 d. Mean arterial BP increased significantly in the lead-treated rats. Relaxation to both acetylcholine and sodium nitroprusside (SNP) was reduced in lead-treated rats; however, the vascular wall of lead-administered rats showed an increased expression of endothelial NO synthase. The expression of both subunits (alpha(1) and beta(1)) of soluble guanylate cyclase (sGC) and the cGMP accumulated in the vascular wall were decreased in lead-treated rats. Cotreatment of lead with vitamin C (3 mmol/L) prevented the increase on mean arterial BP, improved the relaxation to both acetylcholine and sodium nitroprusside, and restored the normal expression of endothelial NO synthase and sGC proteins in the vascular wall. In conclusion, lead exposure altered both the endothelium-dependent and -independent relaxing response and induced a reduced expression of sGC in the vascular wall. These effects were abrogated with the antioxidant vitamin C, which suggests the involvement of reactive oxygen species in the regulation of the NO/cGMP relaxing system in the vascular wall of lead-treated rats.

Effect of Chronic Lead Exposure on Kidney Function in Male and Female Rats: Determination of a Lead Exposure Biomarker

Abstract: Several cytotoxic chemical pollutants inducing peroxidative damages are liable to induce kidney failure. Among these pollutants we find heavy metals such as: lead, nickel, cadmium, vanadium and mercury. Lead is one of the most dangerous metals because it is widely spread in the environment, and because it may be a source of several nervous diseases. The aim of this study is to provide evidence concerning the effect of this metal on the renal function and to try to determine a storage corner in the organism which serves as an indicator of a lead intoxication. Lead acetate was administered by oral route in the drinking water to adult rats aged three months at the rate of 0.3% (P1) and 0.6% (P2). Reference rats received distilled water to drink under the same conditions. The treatment continued for 15, 30, 45, 60 and 90 days. The creatinemia, uremia, glycemia and creatinuria are determined by colorimetric techniques. Lead concentration in blood as well as the lead content of the tail are determined by atomic absorption after nitroperchloric mineralization at the liquid stage. The results showed an increase of creatinemia on the 30th day of the experiment for both sexes in (P1 and P2). The same happened for ureamia. The increase of these two parameters would indicate a renal deficiency which is confirmed by a decrease of creatinuria and urinary pH observed mainly on and after the 45th day of the experiment. An increase of the renal relative weight was noticed in P1 and P2 on the 30th day of the treatment. The determination of the concentration of lead in the blood shows that this factor increases among treated subjects in a constant way, independently of the dose and the duration of the treatment. Nevertheless, the rate increase of lead in the tail seems to be dose-dependent. In conclusion, lead administered by oral route causes a renal deficiency to the rat without distinction between males and females. In addition, the tail seems to be a reliable exposure biomarker that demonstrates lead intoxication. The tail seems to be a dosimeter of lead bio-accumulation. It constitutes an endogenous source of lead impregnation. The concentration of lead in the blood is only an indicator of recent exposure.

Lead accumulation in human ovarian follicular fluid, and in vitro effect of lead on progesterone production by cultured human ovarian granulosa cells.

Abstract: Lead content of ovarian follicular fluid obtained from 23 women was determined by atomic absorption spectrophotometry. In an in vitro experiment the direct effect of lead on the morphology and on progesterone (P) production by cultured granulosa cells of six women was investigated. Follicular fluid and granulosa cells were obtained from follicular aspirates of women undergoing in vitro fertilization (IVF) and embryo transfer (ET). Granulosa cells were cultured for 48 h to form monolayers in the presence or absence of lead acetate (100-1600 µ M). The effect of the metal proved to be concentration dependent. While 100-400 µ M lead had no effect on the integrity of the monolayer, concentrations as high as 800 µ M or higher inhibited cell adhesion and induced detachment of cells. The lead levels found in follicular fluid were 11.29 - 1.38 µg/L (0.056 - 0.007 µ M). With lead in vitro at 1600 µ M (331.5 mg/L) there resulted a significant decrease in P production by granulosa cells. This concentration is very mu...

Inorganic lead stimulates DNA synthesis in human astrocytoma cells: role of protein kinase Cα

Abstract: As lead has been shown to activate protein kinase C (PKC), and gliomas are reported to be highly dependent on PKC for their proliferation, this study was undertaken to investigate whether lead may act as a mitogen in human astrocytoma cells, and to determine the role of PKC in this effect. Lead acetate (from 100 nM to 100 microM) induced a concentration- and time-dependent increase in DNA synthesis, as measured by incorporation of [methyl-3H]thymidine into cell DNA, without causing any cytotoxicity. Flow cytometric analysis showed that lead was able to stimulate the cell cycle transition from the G0/G1 phase to the S/G2 phase, resulting in increased percentage of cells in the latter phase. Western blot analyses showed that lead induced translocation of PKCalpha, but not of PKCepsilon or PKCzeta, from the cytosolic to the particulate fraction, with a concomitant increase in PKC enzyme activity. Prolonged exposure to lead caused down-regulation of PKCalpha, but not of PKCepsilon. The effect of lead on DNA synthesis was mediated through PKC as evidenced by the finding that two PKC inhibitors, GF 109203X and staurosporine, as well as down-regulation of PKC through prolonged treatment with 12-O-tetradecanoylphorbol 13-acetate, blocked lead-induced DNA synthesis. Further experiments using a pseudosubstrate peptide targeting classical PKCs and selective down-regulation of specific PKC isoforms indicated that the effect of lead on DNA synthesis was mediated by PKCalpha. Altogether, these results suggest that lead stimulates DNA synthesis in human astrocytoma cells by a mechanism that involves activation of PKCalpha.

Protection by selenium of lead-acetate-induced alterations on rat submandibular gland function.

Abstract: Pure submandibular saliva was collected intraorally by micro polyethylene cannulation of anaesthetized rats using pilocarpine as a secretagogue. Twenty-four days treatment with lead acetate 0.05% i...

In vitro effect of lead acetate on human erythropoietic progenitors.

Abstract: Lead is known to induce hematological disturbances resulting from abnormalities in cell differentiation and hemoglobin synthesis during hematopoiesis. The aim of the present work was to study human erythropoiesis in vitro in the presence of lead. Human erythroblastic progenitors, burst-forming units-erythroid (BFU-E), were exposed to lead acetate at increasing concentrations during 14 days of culture. Hematotoxicity was evaluated in vitro according to proliferation and differentiation of cell colonies arising from BFU-E development. The ability of cells to synthesize proteins, porphyrins, and hemoglobin was measured by spectrophotometric tests and by high-pressure liquid chromatography (HPLC). Results showed that in the presence of 10(-3) mol/L lead acetate, no hemoglobinized cells were observed in culture and no fluorescent porphyrins were detected in cells. Up to 10(-3) mol/L, lead acetate is not cytotoxic, i.e., it does not induce cell destruction. The present work demonstrates that lead acetate interferes with the porphyrin synthesis of human erythroblastic progenitors in vitro. The decrease of porphyrin content with 10(-5) mol/L lead acetate suggest that delta-aminolevulinic acid dehydratase can be inhibited by lead acetate during in vitro erythropoiesis. In vivo erythropoiesis occurs in the bone marrow. As about 95% of the body burden of lead in adults is located in the bones with a biological half-life of some years, the concentration of lead acetate found to block porphyrin synthesis in vitro has to be compared with in situ bone marrow lead concentrations.

The accumulation effect of lead on DNA damage in mice blood cells of three generations and the protection of selenium.

Abstract: The accumulation effect of lead on DNA damage and the protection of selenium against lead were studied in mice blood cells of three generations. The test animals were divided into four groups: controls, Pb group, Se group, Pb + Se group. Lead and Selenium were administered to mice in the drinking water. The concentrations of lead (in form of lead acetate) and selenium (in form of Kappa-selenocarrageenan) used in this paper were 1 microgram/ml and 0.25 microgram/ml respectively. The percentage of damaged cells (DNA comets) was examined and detected conveniently by the single-cell gel electrophoresis (comet) assay. Results showed that 1 microgram/ml lead did not damage the female mice blood cells of the first generation seriously. However, there was a significant damage effect in both sexes of the second and third generations, suggesting the accumulation effect of lead was very significant starting from the second generation. In addition, under normal physiological conditions, Kappa-Se did not appear to enhance the protective ability on DNA damage significantly, whereas under lead exposure conditions, administration of Kappa-Se displayed the occurrence of a good protection against lead intoxication which was started from the female mice of the second generation.

Influence of Garlic on the Disposition and Toxicity of Lead and Cadmium in the Rat

Abstract: Garlic (Allium sativum L., Liliaceae) was investigated for its potential to prevent the accumulation of lead or cadmium, major environmental pollutants, and to reduce their toxic effects in rats. The oral feeding of minced fresh garlic during intraperitoneal injection of lead acetate or cadmium chloride, daily for 6 weeks significantly decreased the accumulation of these toxic metals and prevented the metal sensitive biochemical alterations in blood, liver and kidney. The ability of garlic to provide glutathione, biosynthesize metallothionein or similar protein, and its antioxidant properties appear to protect against potential oxidative damage to tissues by lead or cadmium. The regular intake of garlic may be beneficial in reducing the toxic effects of these heavy metals in the exposed population.

Lead inhibits growth and induces apoptosis in normal rat fibroblasts.

Abstract: The effects on normal rat fibroblasts of lead supplementation (as lead acetate) in the medium were examined. The amount of lead acetate ranged from 0.078 microM to 320 microM, at 14 concentrations. The normal level of lead in the medium was 0.060 microM, and the normal concentration of lead in the fibroblasts was 3.1 +/- 0.1 ng/10(7) cells: these represented the control conditions. On studying fibroblast proliferation and survival after incubation for 48 hours, a lead acetate dose-dependent inhibition of cell proliferation was observed, the results being shown to be significant by ANOVA (p < 0.01), and suggesting a significant dose-response relationship. Apoptosis, evaluated by quantifying cytoplasmic DNA fragments, differs significantly between the lead levels tested. The distribution in the cell cycle, evaluated by using a fluorescence-activated cell sorter, showed a dose-dependent accumulation of cells in the G0/G1 phase, with a compensatory decrease in the percentage of cells in the S phase. Moreover, the occurrence of a subdiploid peak confirmed that apoptosis was more evident when the medium was supplemented with lead acetate at concentrations of 5-20 microM. The inhibition of cell growth is probably due to a direct inhibition of cell proliferation.

Effects of lead and/or zinc exposure during the second stage of rapid postnatal brain growth on delta-aminolevulinate dehydratase and negative geotaxis of suckling rats

Abstract: Lead has been shown to produce cognitive and motor deficits in young rats that could be mediated, at least in part, by inhibition of the zinc-containing heme biosynthetic enzyme delta-aminolevulinate dehydratase (ALA-D). In the present study we investigated the effects of lead and/or zinc treatment during the second stage of rapid postnatal brain development on brain, kidney and blood ALA-D specific activity, as well as the negative geotaxis behavior of rats. Eight-day-old Wistar rats were injected intraperitoneally with saline, lead acetate (8 mg/kg) and/or zinc chloride (2 mg/kg) daily for five consecutive days. Twenty-four hours after treatment, ALA-D activity was determined in the absence and presence of DL-dithiothreitol (DTT). The negative geotaxis behavior was assessed in 9- to 13-day-old rats. Treatment with lead and/or zinc did not affect body, brain or kidney weights or brain- or kidney-to-body weight ratios of the animals. In spite of the absence of effect of any treatment on ALA-D specific activity in brain, kidney and blood, the reactivation index with DTT was higher in the groups treated with lead or lead + zinc than in the control group, in brain, kidney and blood (mean +/- SEM; brain: 33.33 +/- 4.34, 38.90 +/- 8.24, 13.67 +/- 3.41; kidney: 33.50 +/- 2.97, 37.60 +/- 2.67, 15.80 +/- 2.66; blood: 63.95 +/- 3.73, 56.43 +/- 5.93, 31.07 +/- 4.61, respectively, N = 9-11). The negative geotaxis response behavior was not affected by lead and/or zinc treatment. The results indicate that lead and/or zinc treatment during the second stage of rapid postnatal brain growth affected ALA-D, but zinc was not sufficient to protect the enzyme from the effects of lead in brain, kidney and blood.

Succimer treatment during ongoing lead exposure reduces tissue lead in suckling rats

Abstract: There is a concern that oral treatment with succimer (meso-2, 3-dimereaptosuceinic acid, DMSA) can promote gastrointestinal lead absorption if not performed in a lead-safe environment. The scope of our investigation was to evaluate the efficacy of oral DMSA treatment during oral lead exposure on tissue lead in suckling rats. Six-day-old Wistar rats of both genders were divided into two groups-untreated (Ph) and treated (Ph + DMSA)-with 10 animals per group. Lead (as acetate) was given orally at a dose of 2 mg kg(-1) body weight day(-1) for eight consecutive days (total dose 16 mg kg(-1), i.e. 0.08 mmol kg(-1)). During this period the treated group received a daily dose of 0.5 mmol DMSA kg(-1) body weight p.o. six times on days 1-3 and 6-8 of the experiment (total dose 3 mmol kg(-1)). Tissue lead was determined by means of atomic absorption spectrometry. The DMSA efficiently reduced the lead concentration in the analysed tissues (carcass, liver, kidneys and brain) by similar to 50% compared with untreated controls. The pups' growth and organ weights were not affected. In conclusion, our results indicate that DMSA is an efficient oral lead chelator in sucklings even if challenged with ongoing lead exposure. Copyright (C) 2001 John Wiley & Sons, Ltd. [References: 10]