Effects of lead acetate on DNA and RNA synthesis by intact HeLa cells, isolated nuclei and purified polymerases

Preparation of Porous Hydroxyapatite Using Cetyl Trimethyl Ammonium Bromide as Surfactant for the Removal of Lead Ions from Aquatic Solutions

In the present study, a new low-cost bioceramic nanocomposite based on porous hydroxyapatite (HAp) and cetyl trimethyl ammonium bromide (CTAB) as surfactant was successfully obtained by a simple chemical co-precipitation. The composition and structure of the HAp-CTAB were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) spectrometer, and N2 adsorption/desorption analysis. The capacity of HAp-CTAB nanocomposites to remove the lead ions from aqueous solutions was studied by adsorption batch experiments and proved by Langmuir and Freundlich models. The Pb2+ removal efficiency of HAp-CTAB biocomposite was also confirmed by non-destructive ultrasound studies. The cytotoxicity assays showed that the HAp-CTAB nanocomposites did not induce any significant morphological changes of HeLa cells after 24 h of incubation or other toxic effects. Taken together, our results suggests that the obtained porous HAp-CTAB powder could be used for the decontamination of water polluted with heavy metals, such as Pb2+.

Assessment of abnormal DNA repair responses and genotoxic effects in lead exposed workers

BACKGROUND

One of the main sources of occupational exposure to lead (Pb) in Turkey is in workers of battery industries. Genotoxic studies in human populations exposed to this metal have had conflicting results.

METHODS

Genotoxic effects of Pb were studied in blood cell samples from workers of battery manufactures exposed to Pb compounds by chromosomal aberration (CA) assay and X-ray induced challenge (XRC) assay to assess DNA damage and interference with DNA repair processes after an in vitro exposure of X-ray (1 Gy). The battery manufacturers (n=23) and 23 people who were not occupationally exposed to lead compounds were selected as a control group and classified into categories according to their blood lead levels.

RESULTS

The CA frequencies in the exposed and control group were not significantly different (P>0.05) by conventional CA (CCA) assay, however, the XRC assay demonstrated significantly elevated CAs (P<0.05). Statistically non-significant but reduced DNA repair responses have also been observed in lead exposed workers.

CONCLUSION

The results of this study showed significant increases in the CAs by XRC assay in Pb exposed workers compared to CCA assay. Our data suggests that Pb exposure may cause reduction in DNA repair capacity and these individuals will be more prone to DNA damage. Therefore, preventive measures should be improved against genotoxic risk in workplaces.

In vivo genotoxic effects of smoking and occupational lead exposure in printing press workers

The objective of the present study was to evaluate the genotoxicity of a combination exposure to lead and smoking in workers from the printing industry and also to examine the possible interaction between the two agents. Individuals were classified into 4 different groups: control group, lead-exposed group, smokers and the double-exposure group. Chromosomal analysis was carried out according to conventional methods. Our preliminary study shows that lead-exposed individuals had a significantly increased frequency of sister chromatid exchanges. Further, double exposure to smoking and lead inhibits mitosis.

Immunotoxicity of particulate lead: in vitro exposure alters pulmonary macrophage tumor necrosis factor production and activity

Rabbit pulmonary macrophages were exposed in vitro to particulate lead oxide (PbO) for periods of up to 72 h and then assayed for the activity of tumor necrosis factor-alpha (TNF alpha) released after stimulation with lipopolysaccharide (LPS). The levels of TNF alpha obtained from PbO-treated cells were decreased in a dose-dependent manner as compared with metal-free control cells for each time point examined. Cells treated simultaneously with both LPS and PbO yielded less monokine than did cells receiving LPS alone. In addition, incubation of cell-free TNF alpha with PbO resulted in a diminution of cytotoxicity directed against TNF alpha-sensitive tumor target cells. Macrophage burdens of PbO particles increased with both the length of incubation and concentration of PbO used; increases in cellular lead burdens were paralleled by reductions in cell viability. Thus, under in vitro conditions, PbO affects the levels of the immunoregulatory monokine TNF alpha and also disrupts its cytotoxic properties after release from activated macrophages.

Review of lead toxicology relevant to the safety assessment of lead acetate as a hair colouring

The literature on lead toxicology has been critically reviewed to provide a safety assessment of lead acetate as a hair colouring. The main objectives were: (i) to determine the additional lead contribution from hair-colouring use to the total daily environmental lead intake; and (ii) to assess the toxicological significance of this additional contribution. The review also focuses attention on newer issues of concern over the effects of environmental lead on human health. Data available in animals and humans (including occupational exposure), mainly on lead acetate and other inorganic lead salts, have been presented and evaluated in respect of the following: absorption, distribution and excretion following ingestion; percutaneous absorption; carcinogenicity; genotoxicity; reproductive toxicity; neurological/behavioural status with particular reference to neuropsychological effects in children; and effects on other systems (e.g. cardiovascular). It is concluded that the absorption of lead from hair-colouring use represents about 0.5% of the lead absorption from the current average daily environmental lead intake. No convincing evidence could be found of any deleterious effect of current environmental lead levels on human health and thus the tiny contribution of lead acetate exposure from hair-colouring use can be regarded unequivocally as being toxicologically insignificant.

Lead impairs the production of osteocalcin by rat osteosarcoma (ROS 17/2.8) cells

The serum level of osteocalcin, a bone-specific protein produced by osteoblasts and an index of bone formation, is decreased in lead-intoxicated children. To elucidate the effect of lead on the hormonal regulation of osteocalcin production, ROS 17/2.8 cells were treated with 0, 5, 10, or 25 microM lead acetate for 24 hr, followed by an additional 24-hr lead treatment with or without 100 pg 1,25-dihydroxyvitamin D3/ml medium. At the end of this period a radioimmunoassay was conducted to determine the amount of osteocalcin present in the cells and secreted into the medium. 1,25-Dihydroxyvitamin D3 increased osteocalcin secretion in control cultures, but this increase was prevented by lead in a concentration-dependent manner. Osteocalcin secretion by cultures treated with 10 or 25 microM lead was even lower than in cultures not stimulated with 1,25-dihydroxyvitamin D3. Intracellular levels of osteocalcin were slightly elevated with 1,25-dihydroxyvitamin D3, and there was no lead effect on cellular levels. These data indicate that lead attenuates basal and 1,25-dihydroxyvitamin D3-stimulated production of osteocalcin in ROS 17/2.8 cells. Because osteocalcin appears to play a central role in bone mineralization, altered osteocalcin production may be a key event in the skeletal toxicity of lead.

Indirect mechanism of lead-induced genotoxicity in cultured mammalian cells

The data concerning the mutagenic, clastogenic and carcinogenic properties of inorganic lead compounds have been conflicting. To investigate whether the genotoxicity of lead is due to indirect effects such as interference with DNA-repair processes, the induction of mutations, sister-chromatid exchanges and strand breaks by lead ions alone as well as in combination with UV light as a standard mutagen were determined. Lead acetate alone does not induce DNA-strand breaks in HeLa cells or mutations at the HPRT locus and sister-chromatid exchanges in V79 Chinese hamster cells. However, at all endpoints tested, lead ions interfere with the processing of UV-induced DNA damage. They inhibit the closing of DNA-strand breaks after UV irradiation and enhance the number of UV-induced mutations and sister-chromatid exchanges, indicating an inhibition of DNA repair. These data point out the necessity to consider such indirect effects when assessing the genotoxicity of metal compounds. As possible mechanisms of repair inhibition we suggest either the interaction with repair enzymes such as polymerase or ligase or else the interaction with calcium-regulated processes, for example with calmodulin.

The effect of lead on protein and DNA metabolism of normal and lead-adapted rat kidney cells in culture

Cultures of epithelial rat kidney cells were used to investigate the effect of lead on protein and DNA metabolism. Lead-adapted cells were cultured in 5 and 10 microM Pb(NO3)2 for several months and subsequently showed the same growth characteristics but a higher resistance to increased lead doses than untreated cells. Both normal and adapted cell types were exposed to lead nitrate in concentrations from 5 to 1000 microM for incubation periods of from 1 to 24 h. 3H-leucine incorporation was increased in 10 microM lead by up to 140% in normal but not in adapted cells, pointing to a resistance forming mechanism. Not only is the overall rate of protein synthesis increased, but separations of cytosolic proteins by SDS-polyacrylamide electrophoresis indicate the novel or increased synthesis of several proteins. A difference could also be observed in the DNA metabolism, where normal cells show a very pronounced increase of up to 900% after 24 h of incubation. This was not observed in adapted cells.