Toxicity, mutagenicity and teratogenicity of lead

The effects of lead on the development of somites in chick embryos (Gallus gallus domesticus) under in vitro conditions: a histological study

Lead (Pb) is one of the most abundant toxic metals in the environment that can cause a variety of harmful effects. During embryonic development of vertebrates, somites are temporary organs that give rise to skeletal muscle, cartilage, tendon, endothelial cells, and dermis. In this study, we investigated the effects of lead on the development of somites and their derivatives in chick embryos under in vitro conditions. For this propose, fertilized eggs of Gallus gallus domesticus were incubated until they reached the stage of 15-20 somites. The somites and notochord were isolated and treated with different concentrations of lead acetate (500, 1000, 2000, and 4000 ng ml-1) for 72 h. Our results indicated that high concentrations of lead reduced the nucleus diameter, reduced the synthesis of collagen, inhibited the formation of the cartilage matrix in somite cells, and disturbed the formation and order of myotubes. In conclusion, the results of the current study for the first time indicated the disturbing effects of lead on the development of somites in the chick embryo. Our results revealed that lead disturbed the development of somites in the chick embryo, which suggested that at high concentrations it can cause a serious mortal danger to life.

Different exposure profile of heavy metal and health risk between residents near a Pb-Zn mine and a Mn mine in Huayuan county, South China

Heavy metal contamination of environmental media in mining area is a global major concern because of its potential threat for human health through food chain. However, the comparison of exposure level and health risk is scarce among people living in the vicinity of mining area with different pollution source. In this study, the concentrations of Mn, Cd, As, Pb, Cu, Zn, Cr and Ni in soil, air, water, rice, vegetable, fish, poultry meat and pork from a Pb-Zn mining area and a Mn mining area in Huayuan county, China were determined by inductively coupled plasma mass spectrometry. Results showed that the environmental media and foodstuffs in the two areas were contaminated by Cd, Pb, Zn, Cu, Cr and Ni. However, the pollution was more serious in Pb-Zn mining area than Mn mining area. The total hazard index (HI) was 6.59 and 4.55 in Pb-Zn mining area and Mn mining area, respectively, indicating a moderate non-carcinogenic risk of local people. As intake via rice ingestion was the predominant contributor to the total HI in the two mining areas, accounting for 25% and 35%, respectively. For Pb-Zn mining area, Cd intake through vegetable consumption and Mn intake via air inhalation appeared to be another two important components contributing to HI. This study highlights the multi-element and multi-pathway exposure assessment to evaluate the potential health risk and emphasizes concerns to reduce As and Cd in agricultural products as well as Mn in air to decrease the detrimental health effects of local resident.

Citric acid enhanced the antioxidant defense system and chromium uptake by Lemna minor L. grown in hydroponics under Cr stress

Phytoextraction is a cost-effective and eco-friendly technique for the removal of pollutants, mainly heavy metal(loids) especially from polluted water and metal-contaminated soils. The phytoextraction of heavy metals is, in general, limited due to the low availability of heavy metals in the growth medium. Organic chelators can help to improve the phytoextraction by increasing metal mobility and solubility in the growth medium. The present research was carried out to examine the possibility of citric acid (CA) in improving chromium (Cr) phytoextraction by Lemna minor (duckweed). For this purpose, healthy plants were collected from nearby marsh and grown in hydroponics under controlled conditions. Initial metal contents of both marsh water and plant were measured along with physico-chemical properties of the marsh water. Different concentrations of Cr and CA were applied in the hydroponics in different combinations after defined intervals. Continuous aeration was supplied and pH maintained at 6.5 ± 0.1. Results showed that increasing concentration of Cr significantly decreased the plant biomass, photosynthetic pigments, leaf area, and antioxidant enzyme activities (like catalase, ascorbate peroxidase, superoxide dismutase, peroxidase). Furthermore, Cr stress increased the Cr concentrations, electrolyte leakage, hydrogen peroxide, and malondialdehyde contents in plants. The addition of CA alleviated the Cr-induced toxicity in plants and further enhanced the Cr uptake and its accumulation in L. minor. The addition of CA enhanced the Cr concentration in L. minor by 6.10, 26.5, 20.5, and 20.2% at 0, 10, 100, and 200 μM Cr treatments, respectively, compared to the respective Cr treatments without CA. Overall, the results of the present study showed that CA addition may enhance the Cr accumulation and tolerance in L. minor by enhancing the plant growth and activities of antioxidant enzymes.

Ameliorative effects of curcumin against lead induced toxicity in human peripheral blood lymphocytes culture

Lead, a heavy metal and multifaceted toxicant, is well studied for its distribution and toxicity in ecosystem, yet there is no consensus on its amelioration by any synthetic or phytochemical compounds. Curcumin, a known antioxidant and dietary element, is a well-known herb, for its therapeutic uses and having a wide spectrum of its beneficial properties against several adverse effects. Hence, the current study was taken into consideration to evaluate the ameliorative effects of curcumin (3.87 μM, i.e. 1.43 μg/ml) against lead acetate (doses: 10^-6 M, i.e. 0.379 μg/ml and 10^-4 M, i.e. 37.9 μg/ml, durations: 24 h and 69 h) induced genotoxicity and oxidative stress in human peripheral blood lymphocyte cultures (PBLC). On one hand, antigenotoxic and antioxidative potentials of curcumin against lead were simultaneously evaluated by the array of genotoxicity and oxidative stress indices. The result postulated that lead acetate showed dose- and duration-dependent increase in both genotoxicity and oxidative stress whereas curcumin, when added along with lead acetate, showed the significant amelioration in all genotoxic and oxidative stress-related indices. The study indicated that, due to alteration in antioxidant defense system, there is an adverse genotoxic effect of lead. On the other hand, curcumin, a potent antidote, can protect chromatin material against lead -mediated genotoxicity by balancing the activity of antioxidant defense system.

Preparation of phosphines through C-P bond formation

Phosphines are an important class of ligands in the field of metal-catalysis. This has spurred the development of new routes toward functionalized phosphines. Some of the most important C–P bond formation strategies were reviewed and organized according to the hybridization of carbon in the newly formed C–P bond.

Modelling the behaviour of uranium-series radionuclides in soils and plants taking into account seasonal variations in soil hydrology

In a previous paper, a mathematical model for the behaviour of (79)Se in soils and plants was described. Subsequently, a review has been published relating to the behaviour of (238)U-series radionuclides in soils and plants. Here, we bring together those two strands of work to describe a new mathematical model of the behaviour of (238)U-series radionuclides entering soils in solution and their uptake by plants. Initial studies with the model that are reported here demonstrate that it is a powerful tool for exploring the behaviour of this decay chain or subcomponents of it in soil-plant systems under different hydrological regimes. In particular, it permits studies of the degree to which secular equilibrium assumptions are appropriate when modelling this decay chain. Further studies will be undertaken and reported separately examining sensitivities of model results to input parameter values and also applying the model to sites contaminated with (238)U-series radionuclides.

A review of the behaviour of U-238 series radionuclides in soils and plants

The U-238 series of radionuclides is of relevance in a variety of environmental contexts ranging from the remediation of former uranium mining and milling facilities to the deep geological disposal of solid radioactive wastes. Herein, we review what is known concerning the behaviour of radionuclides from the U-238 decay chain in soils and plants. This review is intended to provide a single comprehensive source of information to anyone involved in undertaking environmental impact assessment studies relating to this decay chain. Conclusions are drawn relating to values and ranges of distribution coefficients appropriate to uranium, thorium, radium, lead and polonium in different soil types and under various environmental conditions. Similarly, conclusions are drawn relating to plant:soil concentration ratios for these elements for different plant and soil types, and consideration is given to the distribution of these elements within plants following both root uptake and foliar application.

Kinetics and mechanism of G-quadruplex formation and conformational switch in a G-quadruplex of PS2.M induced by Pb²⁺

DNA sequences with guanine repeats can form G-quartets that adopt G-quadruplex structures in the presence of specific metal ions. Using circular dichroism (CD) and ultraviolet-visible (UV–Vis) spectroscopy, we determined the spectral characteristics and the overall conformation of a G-quadruplex of PS2.M with an oligonucleotide sequence, d(GTG₃TAG₃CG₃TTG₂). UV-melting curves demonstrate that the Pb²⁺-induced G-quadruplex formed unimolecularly and the highest melting temperature (T_m) is 72°C. The analysis of the UV titration results reveals that the binding stoichiometry of Pb²⁺ ions to PS2.M is two, suggesting that the Pb²⁺ ions coordinate between adjacent G-quartets. Binding of ions to G-rich DNA is a complex multiple-pathway process, which is strongly affected by the type of the cations. Kinetic studies suggest that the Pb²⁺-induced folding of PS2.M to G-quadruplex probably proceeds through a three-step pathway involving two intermediates. Structural transition occurs after adding Pb(NO₃)₂ to the Na⁺- or K⁺-induced G-quadruplexes, which may be attributed to the replacement of Na⁺ or K⁺ by Pb²⁺ ions and the generation of a more compact Pb²⁺–PS2.M structure. Comparison of the relaxation times shows that the Na⁺→Pb²⁺ exchange is more facile than the K⁺→Pb²⁺ exchange process, and the mechanisms for these processes are proposed.

Genotoxic effects of lead: an updated review

Lead is a ubiquitous toxic heavy metal with unique physical and chemical properties that make it suitable for a great variety of applications. Because of its high persistence in the environment and its use since ancient times for many industrial activities, lead is a common environmental and occupational contaminant widely distributed around the world. Even though the toxic effects of lead and its compounds have been investigated for many years in a variety of systems, the data existing with regard to its mutagenic, clastogenic and carcinogenic properties are still contradictory. The International Agency for Research on Cancer has classified lead as possible human carcinogen (group 2B) and its inorganic compounds as probable human carcinogens (group 2A). Furthermore, although the biochemical and molecular mechanisms of action of lead remain still unclear, there are some studies that point out indirect mechanisms of genotoxicity such as inhibition of DNA repair or production of free radicals. This article reviews the works listed in the literature that use different parameters to evaluate the genotoxic effects of lead in vitro, in vivo and in epidemiological studies.

Lead contamination results in late and slowly repairable DNA double-strand breaks and impacts upon the ATM-dependent signaling pathways

Despite a considerable amount of data, evaluation of the potential genotoxicity and cancer proneness of lead compounds remains unclear, probably due to the plethora of experimental procedures, biological endpoints and cellular models used. In parallel, the understanding in DNA damage formation, repair and signaling has considerably progressed all along these last years, notably for DNA double-strand breaks (DSBs). Here, were examined DNA damage formation and repair in human cells exposed to lead nitrate (Pb(NO(3))(2)) and their consequences upon the ATM-dependent stress signaling, cell cycle progression and cell death. As observed with anti-pH2AX immunofluorescence, exposure to Pb(NO(3))(2) results in formation of late DSBs, that would not originate from conversion of nucleotide damage but likely by a direct production of single-strand breaks. Lead contamination inhibits non-homologous end-joining repair process by preventing the DNA-PK kinase activity whereas the MRE11-dependent repair pathway is exacerbated. Lead contamination triggers successive synchronization of cells in G2/M phase in which the RAD51-dependent homologous recombination was found to be activated. Altogether, our findings support that lead contamination generates late unrepairable DSBs that impact upon the ATM-dependent stress signaling pathway by favoring propagation of errors. Such findings should help to consider more carefully the biological action of lead compounds in the frame of public and occupational exposures.

Protective effect of volatile oil, alcoholic and aqueous extracts of Origanum majorana on lead acetate toxicity in mice

Natural dietary antioxidants are extensively studied for their ability to protect cells from miscellaneous damages. Origanum majorana L., Lamiaceae, is a potent antioxidant. The effect of administration of O. majorana (volatile oil, alcoholic and aqueous extracts) on oral administration of lead acetate in the diet of mice at concentration 0.5% (W/W) for one month were studied by measuring serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), urea and creatinine, histopathological changes of the liver and kidney and genotoxicity including, rate of micronucleus and chromosomal aberrations in bone marrow cells. Mice were treated with the 3 different forms of O. majorana, one month before and maintained with lead acetate administration. The 3 forms of O. majorana induced a significant decrease in serum activities of transaminases (AST & ALT), ALP, urea and creatinine and improved the liver and kidney histology in comparison with lead acetate treated group. Alcoholic extracts of O. majorana significantly reduced the rate of micronucleus, number of aberrant cells and different kinds of chromosomal aberrations. Volatile oil extract significantly reduced the rate of micronucleus and chromosomal fragments. Aqueous extract and volatile oil also of O. majorana significantly reduced number of gaps, ring chromosome and stickiness. It could be concluded that O. majorana plays an important role in ameliorating liver and kidney functions and genotoxicity induced by lead toxicity.

Characterization of an unusual folding pattern in a catalytically active guanine quadruplex structure

In the presence of certain metal ions, DNA and RNA can form guanine quadruplex structures, which have been proposed to play a functional role in a variety of biological processes. An 18-nucleotide DNA oligomer, PS2.M, d(GTG3TAG3CG3T2G2), was previously reported to bind hemin and the resulting complex exhibited peroxidase activity. It was proposed that PS2.M folds unimolecularly into an antiparallel quadruplex with unusual, single-base loops and terminal guanines positioned in adjacent quartets. Here we describe structural and stability properties of PS2.M alone in different buffers and metal ions, using gel electrophoresis, circular dichroism (CD), ultraviolet (UV)-visible spectroscopies, and one-dimensional 1H nuclear magnetic resonance (NMR). Native gel behavior of PS2.M in the presence of either Na+ or Pb2+ suggests the formation of unimolecular structures but, in the presence of K+, both unimolecular and multistranded structures are observed. In the presence of Pb2+ ions, PS2.M forms a unimolecular quadruplex containing three guanine quartets. CD titrations reveal that binding of Pb2+ ions to PS2.M is stoichiometric, and a single lead cation suffices to fully fold PS2.M. The PS2.M-Na+ system also forms a similar unimolecular quadruplex. In the presence of K+, the PS2.M-K+ system forms mixed species. With increasing time and PS2.M concentration, the contribution of unimolecular species decreases while that of multimolecular species increases, and this behavior is independent of buffer media. These results suggest that the catalytically active form, studied in the presence of K+, may be a parallel, multistranded quadruplex rather than an antiparallel, unimolecular quadruplex.

The evaluation of micronucleus frequency by acridine orange fluorescent staining in peripheral blood of rats treated with lead acetate

The data concerning the mutagenic, clastogenic and carcinogenic properties of inorganic lead compounds have been conflicting. Here, we evaluated the frequency of micronuclei in the peripheral blood of female rats treated with three different lead acetate doses. Outbred female Wistar rats were treated by gavage once per week for 10 weeks with cumulative doses of 140, 250 and 500 mg/kg body weight (body wt) of lead acetate. Mitomycin C (MMC) 2 mg/kg body wt was used as a positive control. The aim of the present study was to investigate the possible cytotoxic and genotoxic effects of lead acetate on peripheral blood reticulocytes using the micronucleus test following chronic exposure. The results show the effects of lead acetate in peripheral blood reticulocytes. These effects are both cytotoxic and genotoxic because of a decrease in the number of polychromatic erythrocytes in the peripheral blood and an increase in frequency of micronucleated reticulocytes, respectively.

Genotoxicity of inorganic lead salts and disturbance of microtubule function

Lead compounds are known genotoxicants, principally affecting the integrity of chromosomes. Lead chloride and lead acetate induced concentration-dependent increases in micronucleus frequency in V79 cells, starting at 1.1 microM lead chloride and 0.05 microM lead acetate. The difference between the lead salts, which was expected based on their relative abilities to form complex acetato-cations, was confirmed in an independent experiment. CREST analyses of the micronuclei verified that lead chloride and acetate were predominantly aneugenic (CREST-positive response), which was consistent with the morphology of the micronuclei (larger micronuclei, compared with micronuclei induced by a clastogenic mechanism). The effects of high concentrations of lead salts on the microtubule network of V79 cells were also examined using immunofluorescence staining. The dose effects of these responses were consistent with the cytotoxicity of lead(II), as visualized in the neutral-red uptake assay. In a cell-free system, 20-60 microM lead salts inhibited tubulin assembly dose-dependently. The no-observed-effect concentration of lead(II) in this assay was 10 microM. This inhibitory effect was interpreted as a shift of the assembly/disassembly steady-state toward disassembly, e.g., by reducing the concentration of assembly-competent tubulin dimers. The effects of lead salts on microtubule-associated motor-protein functions were studied using a kinesin-gliding assay that mimics intracellular transport processes in vitro by quantifying the movement of paclitaxel-stabilized microtubules across a kinesin-coated glass surface. There was a dose-dependent effect of lead nitrate on microtubule motility. Lead nitrate affected the gliding velocities of microtubules starting at concentrations above 10 microM and reached half-maximal inhibition of motility at about 50 microM. The processes reported here point to relevant interactions of lead with tubulin and kinesin at low dose levels.

Toxicity of environmental lead and the influence of intestinal absorption in children

Exposure to metals, particularly lead, remains a widespread issue that is associated with historical and current industrial practices. Whereas the toxic properties of metals are well described, exposure to metals per se is only one of many factors contributing to elevated blood metal concentrations and their consequent health effects in humans. The absorbed dose of metal is affected by geochemical, biochemical, and physiological parameters that influence the rate and extent of absorption. In children, the interplay among these factors can be of critical importance, especially when biochemical and physiological processes might not have matured to their normal adult status. Such immaturity represents an elevated risk to metal-exposed children because they might be more susceptible to enhanced absorption, especially via the oral route. This review brings together the more recent findings on the physiological mechanisms of metal absorption, especially lead, and examines several models that can be useful in assessing the potential for metal uptake in children.

Estrogen-like activity of metals in MCF-7 breast cancer cells

The ability of metals to activate estrogen receptor-alpha (ERalpha) was measured in the human breast cancer cell line, MCF-7. Similar to estradiol, treatment of cells with the divalent metals copper, cobalt, nickel, lead, mercury, tin, and chromium or with the metal anion vanadate stimulated cell proliferation; by d 6, there was a 2- to 5-fold increase in cell number. The metals also decreased the concentration of ERalpha protein and mRNA by 40-60% and induced expression of the estrogen-regulated genes progesterone receptor and pS2 by1.6- to 4-fold. Furthermore, there was a 2- to 4-fold increase in chloramphenicol acetyltransferase activity after treatment with the metals in COS-1 cells transiently cotransfected with the wild-type receptor and an estrogen-responsive chloramphenicol acetyltransferase reporter gene. The ability of the metals to alter gene expression was blocked by an antiestrogen, suggesting that the activity of these compounds is mediated by ERalpha. In binding assays the metals blocked the binding of estradiol to the receptor without altering the apparent binding affinity of the hormone (K(d) = 10(-10) M). Scatchard analysis employing either recombinant ERalpha or extracts from MCF-7 cells demonstrated that (57)Co and (63)Ni bind to ERalpha with equilibrium dissociation constants of 3 and 9.5 x 10(-9) and 2 and 7 x 10(-9) M, respectively. The ability of the metals to activate a chimeric receptor containing the hormone-binding domain of ERalpha suggests that their effects are mediated through the hormone-binding domain. Mutational analysis identified amino acids C381, C447, E523, H524, N532, and D538 as potential interaction sites, suggesting that divalent metals and metal anions activate ERalpha through the formation of a complex within the hormone-binding domain of the receptor.

Effects of metallic mercury on the perimenstrual symptoms and menstrual outcomes of exposed workers

BACKGROUND

Mercury is an important environmental and industrial pollutant and its effect on perimenstrual symptoms and menstrual outcomes is unclear.

METHODS

A retrospective epidemiological investigation was conducted on 296 female workers exposed to mercury vapor and 394 female workers from food processing plants. Both groups included women of 18-44 years of age currently working since last at least 1 year when studied. Women who were currently pregnant, using oral contraceptives (Ocs), an intrauterine device (IUD), and steroid hormones were excluded.

RESULTS

The air concentration of mercury in the workplace ranged from 0.001-0.200 mg/m(3). The prevalence of abdominal pain in the exposed group was significantly higher than that in the control group (odds ratio (OR) = 1.47, 95% CI is 1.03-2.11). The prevalence of dysmenorrhea in the exposed group was significantly higher than that in the control group (OR = 1.66, 95% CI is 1.07-2.59).

CONCLUSIONS

An increased prevalence of abnormal menstruation was found in mercury-exposed workers in China. Dysmenorrhea may be a useful biomarker for assessing female exposure to mercury occupationally. These observations suggest that further studies and preventive measures are warranted.

Gestational and lactational lead intoxication produces alterations in the hepatic system of rat pups

The effects of lead (Pb) intoxication during pregnancy and lactation were studied in the hepatic system of pups and young Wistar rats to test the hypothesis that gestational and lactational lead exposure alters the normal function of the liver in neonates. Lead acetate (300 mg/L) dissolved in distilled water was administered ad libitum to mothers during gestation and lactation. At days 12 and 21 postnatal (PN), pups were sacrificed, blood was collected, and livers were removed. Blood lead (PbB) levels were also measured. Although, histological evaluation revealed neither abnormalities in the liver structure nor depositions of lead, the toxicant produced biochemical alterations. Lead-intoxicated pups exhibited a decrease in hemoglobin, iron, and alkaline and acid phosphatase levels and an increase in PbB content. Protein, DNA, and lipid total amounts were reduced, and hepatic glycogen content was diminished at days 12 and 21 PN, with a higher level of glucose in the blood. Lead administration also resulted in a decrease in alkaline phosphatase in the liver of pups at day 21 PN, but acid phosphatase was unaltered. The findings of this study support the hypothesis that lead intoxication of mothers in gestation and lactation results in alterations in the hepatic system in neonates and pups.

Risk of birth defects in a population exposed to environmental lead pollution

To investigate the relation between environmental lead and risk of birth defects in humans, we examined the prevalence at birth of congenital anomalies in an industrial area of northern Italy heavily polluted with lead. Through a population-based registry of birth defects, we identified anomalies diagnosed during three consecutive periods characterized by decreasing environmental lead exposure, 1982-1986, 1987-1990 and 1991-1995. In the lead-polluted area, we observed an excess risk of cardiovascular defects which decreased from 2.59 [95% confidence interval (CI) 1.68-3.82] in the first period to 1.18 (95% CI 0.62-2.06) and 0.97 (95% CI 0.57-1.54) in the subsequent periods. We also found an excess risk of oral clefts and musculoskeletal anomalies, with decreasing trends over time. We could not identify homogeneous patterns of temporal variation for other congenital anomalies, neither did we detect cases of neural tube defects. These results appear to support an association between severe parental lead exposure and specific birth defects.

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

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 (100-1,600 microM). The effect of the metal proved to be concentration dependent. While 100-400 microM lead had no effect on the integrity of the monolayer, concentrations as high as 800 microM or higher inhibited cell adhesion and induced detachment of cells. The lead levels found in follicular fluid were 11.29 +/- 1.38 microg/L (0.056 +/- 0.007 microM). With lead in vitro at 1,600 microM (331.5 mg/L) there resulted a significant decrease in P production by granulosa cells. This concentration is very much higher than that measured in follicular fluid of IVF/ET patients, specifically nonexposed to lead, and even higher than mean blood levels reported by others in high exposure groups. In conclusion, lead seems not to exert a specific effect on the steroidogenesis by cultured human granulosa cells. Therefore, the lead levels measured in the ovarian follicular fluid seem not to pose a hazard with respect to progesterone secretion by the ovary.

Evaluation of occupational genotoxic risk in a Brazilian hospital

Many therapeutic, diagnostic and prophylactic procedures used in hospitals are of potential genetic risk. An evaluation was made of genotoxic occupational risk in 42 workers from the Hospital de Clínicas de Porto Alegre, RS, Brazil, who had been occupationally exposed to lead (solder), ethylene oxide (sterilization area), antineoplastic drugs (nurses and pharmacists) or ionizing radiation. They were compared with 42 unexposed individuals. There was an increase in the frequency of binucleated cytochalasin-blocked lymphocytes with micronuclei, though it was not significant (P = 0.058). The groups exposed to antineoplastic drugs and radiation had a significant increase in micronuclei frequency (P = 0.038 and P = 0.022, respectively). The high frequencies of dicentric bridges suggest the action of clastogenics in these two groups. These results suggest that the safety procedures adopted were very important to protect workers from exposure to mutagenic agents and should be improved in the radiological and chemotherapeutical areas.

Lead is unusually effective in sequence-specific folding of DNA

DNA quadruplex structures based on the guanine quartet are typically stabilized by monovalent cations such as K(+), Na(+), or NH(+)(3). Certain divalent cations can also induce quadruplex formation, such as Sr(2+). Here we show that Pb(2+) binds with unusually high affinity to the thrombin binding aptamer, d(GGTTGGTGTGGTTGG), inducing a unimolecular folded structure. At micromolar concentrations the binding is stoichiometric, and a single lead cation suffices to fold the aptamer. The lead-induced changes in UV and CD spectra are characteristic of folded quadruplexes, although the long wavelength CD maximum occurs at 312 nm rather than the typical value of 293 nm. The one-dimensional exchangeable proton NMR spectrum shows resonances expected for imino protons involved in guanine quartet base-pairing. Furthermore, two-dimensional NMR experiments reveal NOE contacts typically seen in folded structures formed by guanine quartets, such as the K(+) form of the thrombin aptamer. Only sequences capable of forming guanine quartets appear to bind Pb(+2) tightly and change conformation. This sequence-specific, tight DNA binding may be relevant to possible genotoxic effects of lead in the environment.

Singlet oxygen is the major species participating in the induction of DNA strand breakage and 8-hydroxydeoxyguanosine adduct by lead acetate

To investigate DNA damage induced by Pb2+ and its prevention by scavengers, we determined DNA strand breakage and the formation of 8-hydroxydeoxyguanosine (8-OHdG) in DNA using plasmid relaxation assay and HPLC with electrochemical detection, respectively. Lead acetate induced DNA strand breakage in 10 mM of Hepes buffer, pH 6.8, in a time- and dose-dependent manner. Compared with lead, zinc acetate did not significantly induce DNA breakage. The singlet oxygen scavengers NaN3 and 2,2,6,6-tetramethyl-4-piperidone (TEMP) inhibited lead-induced DNA breakage more efficiently than the hydroxyl radical scavengers mannitol and DMPO. Deuterium oxide (D2O), a singlet oxygen enhancer, potentiated lead-induced DNA breakage. At low ratios to Pb2+, NADPH, glutathione, and 2-mercaptoethanol enhanced lead-induced DNA breakage, whereas high ratios of these agents protected it. Catalase and superoxide dismutase (SOD) did not protect DNA breaks induced by Pb2+. Lead-induced DNA breakage was markedly enhanced by H2O2, and this induction was inhibited by NaN3, TEMP, EDTA, catalase, BSA, and glutathione. In contrast, mannitol and SOD potentiated Pb2+/H2O2-induced DNA breaks. The results indicate that singlet oxygen, lead, and H2O2 are all involved in the reaction system, whereas hydroxyl radical and superoxide did not. Lead could cause a small amount of 8-OHdG formation in calf thymus DNA and dose-dependently induced the formation of this adduct in the presence of H2O2. Singlet oxygen scavengers were more effective than hydroxyl radical scavengers in protection from lead/H2O2-induced 8-OHdG adducts. Taken together, these results suggest that lead may induce DNA damage through a Fenton-like reaction and that singlet oxygen is the principal species involved.

Biomonitoring of workers exposed to lead. Genotoxic effects, its modulation by polyvitamin treatment and evaluation of the induced radioresistance

A population monitoring study was performed, by using the micronucleus (MN) assay in human peripheral lymphocytes, to investigate whether occupational exposure to lead is genotoxic to workers. In addition to the exposed workers group, two more groups were studied, an external group from a factory without exposure to lead and an internal control group, from the same factory as the exposed workers, but that were not directly exposed to lead. Measures of lead levels at working place and in blood were calculated, and blood samples were collected to carry out a MN study. The results from these studies indicate that the blood from workers directly exposed contained high levels of lead, compared with the other groups, and a significant increase in the frequency of both the total number of MN and the number of binucleated cells carrying MN appeared. In addition, a study on the antimutagenic effects of a polyvitamin rich diet was conducted by measuring the frequency of MN after the workers had a four month daily intake of a polyvitamin-polymineral complex. These results clearly show a significant reduction of the MN frequency evaluated after this treatment, obtaining values that were even lower than those obtained in the internal control group. Finally, a challenge assay was carried out to determine response to gamma-radiation as indication of any kind of radiosensitivity or radioresistance. The results of this experiment did not show any significant variation in the increase of the frequency of MN after challenge irradiation in the lead exposed workers; nevertheless this increase was significantly reduced in the sample obtained after the polyvitamin treatment indicating a radioresistance response.

Study of alterations produced by cadmium and cadmium/lead administration during gestational and early lactation periods in the reproductive organs of the rat

Administration of cadmium (10 mg/liter) and cadmium+lead (300 mg/liter) via drinking water to Wistar rats during gestation and early lactation until delivery and (5 days after parturition) damaged pup reproductive systems. The effects are additive in the decreased gonad weight and additive or even synergistic in the reduced DNA gonadal content. The effects on protein reduction are similar for both cations. In the testes, the effects of cadmium are more important in the reduction of seminiferous tubule diameter, whereas the effects of lead are more overt in the reduction of the number of prospermatogonia.

A study of the cellular mechanism by which lead affects catecholamine secretion

Our purpose was to determine the role of protein kinases in the mediation of the stimulatory effects of lead on catecholamine secretion. Pheochromocytoma cells were incubated for 90 minutes with W-7 (calmodulin antagonist), calphostin C (protein kinase C inhibitor), Sp-cAMPS (cAMP agonist), Rp-cAMPS (cAMP antagonist), forskolin (activator of adenylyl cyclase), or lead nitrate. Catecholamines were measured by liquid chromatography. Lead had a stimulatory effect on catecholamine secretion, whereas W-7 was inhibitory. In the presence of both lead and W-7, the response was markedly decreased compared to that seen with lead alone. Calphostin C suppressed the secretion of catecholamines; however, in the presence of lead and calphostin C, the secretion was similar to that seen with lead alone. Compared to control, Sp-cAMPS was stimulatory. Co-incubation of Sp-cAMPS and lead had a slight synergistic effect. Rp-cAMPS decreased catecholamine secretion, but co-incubation of Rp-cAMPS and lead resulted in a slight reduction compared to lead alone. Forskolin markedly increased the secretion of catecholamines, and co-incubation of lead and forskolin resulted in a synergistic increase. In the absence of calcium, lead had no effect. We conclude that lead stimulates catecholamine secretion by acting through the calcium/calmodulin-dependent protein kinase II system and not through the protein kinase C or protein kinase A system, and requires the presence of calcium for its action.

Lead acetate mutagenicity and mutational spectrum in the hypoxanthine guanine phosphoribosyltransferase gene of Chinese hamster ovary K1 cells

The molecular nature of lead-induced mutations was examined in this study to more thoroughly understand lead mutagenesis. Chinese hamster ovary K1 cells were exposed to 0.5-3 mM lead acetate for 24 h. The median lethal dose (LD50) value was 1.5 mM, and the hypoxanthine guanine phosphoribosyltransferase (HPRT) mutant frequency increased linearly as lead concentrations were raised from 0.5 to 1.5 mM. We also amplified the HPRT cDNAs of 56 independent lead-induced mutants by reverse transcriptase-polymerase chain reaction (PCR). Forty-two mutant cDNAs were successfully amplified: 36 mutants had transcripts of normal or slightly smaller than normal size, and six mutants had large deletions. The other 14 mutants whose HPRT cDNA could not be amplified were subjected to genomic-DNA PCR analysis. All of those mutants had one or more exons missing from their genomic HPRT DNA. DNA sequencing of mutant cDNAs showed that 22 had single-base substitutions, four had small alterations, 10 had single-exon deletions, and six were missing two or three exons. Furthermore, DNA sequencing of the HPRT intron-exon boundaries in eight splice mutants revealed that all of them had single-base substitutions in their genomic DNA. G.C base substitutions occurred 3.3-fold more frequently than A.T base substitutions. Similar frequencies were observed for G.C-->A.T, G.C-->T.A, and G.C-->C.G mutations. These results suggest that G.C base pairs may be the primary target sites for lead mutagenesis.

Reproductive toxicity of chronic lead exposure in male and female mice

The reproductive toxicity of lead was investigated in NMRI mice exposed to 0.5% lead acetate in drinking water from day 1 of intra-uterine life until 60 days after birth. Compared with control mice, the weights of lead-exposed fetuses and subsequently of the lead-exposed weaned pups, male and female, diminished by 11 and 13% respectively. The lead-exposed male and female offspring of lead-exposed dams were mated with unexposed females and males, to examine the effect of lead exposure on reproductive function. Male fertility was not affected but reduced female fertility was observed: litters were smaller and a smaller number of implantation sites was found in lead-exposed females. In lead-exposed males, the weights of the body, testes and epididymes diminished by about 13%, and seminal vesicle and ventral prostate weights, by about 29%. Testicular histology and the number and morphology of epididymal spermatozoa were normal. The levels of plasma FSH, LH and testosterone, and of testicular testosterone, were not modified. These results suggest that the hypothalamic-pituitary-testicular axis is not adversely affected by the above lead exposure, and that therefore the decreased seminal vesicle and ventral prostate weights might not be the consequence of reduced testosterone levels. The hypothesis that lead has a direct effect on these organs as well as a secondary effect resulting from possibly reduced food consumption by lead-exposed mice cannot be excluded. Consequently, in male NMRI mice, exposure to lead might affect reproductive function by acting directly and/or indirectly on accessory sex organs.

Testicular alterations in rats due to gestational and early lactational administration of lead

A solution of lead acetate (300 mg/L) was administered via drinking water to pregnant Wistar rats from day 1 of pregnancy to delivery (Pb-treated day 0 group) or throughout gestation and early lactation (from day 1 to day 5 postnatal) (Pb-treated day 5 group). When the pups were born, four dams and their offspring in each group (control day 0, Pb-treated day 0, control day 5, and Pb-treated day 5) were sacrificed on day 0 (day 0 groups) or on day 5 (day 5 groups). Relative testicular weight and gross testicular structure were not altered by the treatment. The seminiferous tubule diameter and the number of prospermatogonia were reduced by the treatment. Determination of the n-ploidy stage of prospermatogonia indicates that these cells have more proliferative activity in Pb-treated rats than in control rats. On the other hand, the total DNA, RNA, and protein content of the testes in treated rats was significantly reduced, but the DNA: RNA ratio remained unaltered.

Perspectives on lead toxicity

Lead toxicity causes hematological, gastrointestinal, and neurological dysfunction in adults and children. Symptoms are usually noted with blood lead greater than 1.93 mumol/L. Severe or prolonged exposure may also cause chronic nephropathy, hypertension, and reproductive impairment. Lead inhibits enzymes; alters cellular calcium metabolism; stimulates synthesis of binding proteins in kidney, brain, and bone; and slows nerve conduction. Less severe exposure to lead, designated by blood lead levels of 0.48-0.96 mumol/L, has been implicated in poor pregnancy outcome, impaired neurobehavioral development, reduced stature in young children, and higher blood pressure in adults. Biochemical and systemic effects of high and low level lead toxicity are described. Dust, water, and paint chips are still major sources of lead but lead from folk remedies, cosmetics, food supplements, food preparation utensils, and improperly prepared infant formula has caused epidemic and sporadic severe lead toxicity. Screening for pediatric low level lead exposure requires measurement of blood lead.

Temporal changes in blood lead levels of hazardous waste workers in New Jersey, 1984-1987

The blood lead levels of 568 New Jersey hazardous waste workers were determined at least once in the period 1984-1987. Workers almost always wore protective clothing in the field, which should have prevented exposure to lead. Therefore, despite their occupation, these workers are probably representative of the New Jersey suburban population in the mid-1980s. Blood lead levels ranged from 2.0-20.7 µg/dL, with an arithmetic mean value of 5.8 µg/dL, representing a decline from levels measured a decade earlier, but there was no clear change over the four years of the study. Blood lead levels increased with age of the worker up to age 60. Women showed lower levels than men in every age group.

Relative efficiency of Phyllanthus emblica fruit extract and ascorbic acid in modifying lead and aluminium-induced sister-chromatid exchanges in mouse bone marrow

The identification of desmutagens and bioantimutagens in plants has prompted the search for additional plant extracts capable of modifying adverse cellular effects of environmental toxicants. The protective action of crude extracts of Phyllanthus emblica fruits (PFE) against lead (Pb) and aluminium (Al)-induced sister chromatid exchanges (SCEs) was studied in bone marrow cells of Mus musculus. The modifying effect of the crude extract was compared with that of comparable amounts of synthetic ascorbic acid (AA), a major component of the fruits. Oral administration of PFE or AA for 7 consecutive days before exposure of mice to the metals by intraperitoneal injections reduced the frequencies of SCEs induced by both metals. PFE afforded a more pronounced protective effect than AA in counteracting the genotoxicity induced by both Al and Pb: This difference was significant with Pb. The higher protection afforded by PFE may be attributed to the interaction of AA with other natural ingredients present in the crude fruit extract.

The genotoxicity of lead

Lead has been tested for genotoxic potential in a range of mutagenicity assays. Such studies report varying effects, and the results are equivocal. The reasons for this may be related to problems of the solubility of many lead compounds, their inability to dissolve in biological fluids, chemical interferences resulting in conflicting observations, the nonspecificity of the assays used, the delivery of toxic doses to specific genetic processes or the mediation of genotoxicity through indirect mechanisms. Occupational and environmental exposures to lead have also been associated with increases in chromosomal damage in humans at moderate to high exposures, although this evidence is contradictory. Where positive findings have been reported, many are related to exposure. The possibility that lead is genotoxic is by no means clear, but evidence is still accumulating.

Induction of chromosomal aberrations in Chinese hamster ovary cells by triethyllead acetate

Organolead compounds enter the environment primarily through the combustion of leaded gasoline and industrial discharge. Lead and lead-containing compounds have been shown to induce a broad spectrum of toxic effects, including hematopoietic, renal, neurologic, and carcinogenic effects. In this study, the mutagenic activity of triethyllead acetate (Et3PbAc) was determined by measuring the induction of chromosomal aberrations in Chinese hamster ovary cells. The results indicate that Et3PbAc is very cytotoxic and a potent clastogen. In preliminary cytotoxicity studies used to determine appropriate test concentrations for chromosomal aberration analysis, the LC50 of Et3PbAc was approximately 10 microM in the absence of metabolic activation, and 80 microM in the presence of metabolic activation. The maximal response was greater with metabolic activation than without. However, a much higher dose was required to elicit a significant response in the presence of metabolic activation than in its absence.

Occupational exposure and defects of the central nervous system in offspring: review

A study of published work was carried out in a search for evidence of a causal role for parental occupational exposure in the origin of structural and functional defects of the central nervous system (CNS) in children. Studies that consider this topic are scarce and mostly refer to broad categories of exposures and effects. Non-occupational studies referring to environmental exposure of humans and studies on experimental animals were also reviewed. The studies on animals provided straightforward evidence about morphological and behavioural abnormalities resulting from some agents used occupationally. The studies on humans yielded a scala of defects that could be ascribed to exposure to high doses of various agents in the environment. Evidence for a causal role of occupational exposure has not been found, but a highly probable influence on the developing CNS is hypothesised for lead, methyl mercury, and ionising radiation. Parental occupational exposure to cadmium, organic solvents, anaesthetics, and pesticides may also play a part in causing defects of the CNS. Well designed future research is needed to test the above hypotheses.

Urinary mutagenicity tests in lead-exposed workers

Urinary mutagenic activity detected by the bacterial fluctuation assay, using Salmonella typhimurium TA98 and Escherichia coli WP2 uvrA with and without metabolic activation (S9 mix), was studied in a group of 21 workers exposed to inorganic lead and a control group of 22 non-occupationally exposed subjects. Occupational exposure to inorganic lead had no effect on urinary mutagenicity in the strains considered, with or without metabolic activation. In smokers (exposed and non-exposed), urinary mutagenic activity appeared to increase compared to non-smokers (exposed and non-exposed), only with Salmonella typhimurium TA98 in the presence of S9 mix.

The interaction of triethyl lead with tubulin and microtubules

The impact of triethyl lead chloride was studied on: (i) the in vitro assembly and disassembly of microtubules from porcine brain by turbidometry and electron microscopy, (ii) the microtubule system of living mammalian cells using immunofluorescence microscopy, (iii) cell motility and chemotaxis employing the methods of phagokinetic track formation and the Boyden chamber assay, respectively, and (iv) thiol groups of the protein tubulin by their titration in the presence and absence of the organic lead compound. Triethyl lead chloride inhibited microtubule assembly and depolymerized preformed microtubules in vitro and in living cells. Random motility of cells was not markedly inhibited by triethyl lead chloride, whereas chemotaxis (directed cellular movement) was strongly inhibited. Triethyl lead chloride was found to interact with 2 thiol groups of the tubulin dimer. The interaction of triethyl lead chloride with the tubulin/microtubule system in vivo likely causes aneuploidy and is at least partly responsible for the cytotoxicity of the drug.