Cobalt and possible oxidant-mediated toxicity

Transplacental transfer of cobalt: Evidence from a study of mothers and their neonates in the African Copperbelt

BACKGROUND

Transfer of the trace metal cobalt (Co) from mother to foetus has not been documented in populations with high environmental exposure to Co, as is the case in the African Copperbelt mining region. We analysed data obtained from 246 mother-infant pairs included (at delivery) in a previously published case-control study on birth defects, done in Lubumbashi (Democratic Republic of Congo) between March 1, 2013, and Feb 28, 2015.

METHODS

Co was measured by Inductively Coupled Plasma Mass Spectrometry in maternal blood, maternal urine, umbilical cord blood and placental tissue, as available.

RESULTS

The Co concentrations [geometric mean (GM) with interquartile range (IQR)] in maternal blood (GM 1.77 µg/L, IQR 1.07-2.93) and urine (GM 7.42 µg/g creatinine, IQR 4.41-11.0) were highly correlated (Spearman r = 0.71, n = 166; p < 0.001) and considerably higher than reference values determined for general populations elsewhere in the world. The concentrations of Co in umbilical cord blood (GM 2.41 µg/L) were higher (Wilcoxon test, p < 0.001) than in maternal blood (GM 1.37 µg/L), with a correlation between both values (Spearman r = 0.34; n = 127, p < 0.001). Co concentrations in placental tissue (geometric mean 0.02 µg/g wet weight) correlated with concentrations in maternal blood (Spearman r = 0.50, n = 86, p < 0.001) and in neonatal blood (Spearman r = 0.23, n = 83, p = 0.039).

CONCLUSION

This first study of maternal and neonatal Co concentrations in the African Copperbelt provides strong evidence of a high transfer of Co from mother to foetus.

High human exposure to cobalt and other metals in Katanga, a mining area of the Democratic Republic of Congo

BACKGROUND AND OBJECTIVES

The human health impact of the historic and current mining and processing of non-ferrous metals in the African Copperbelt is not known. This study assessed the exposure to metals in the population of Katanga, in the south east of the Democratic Republic of Congo, using biomonitoring.

METHODS

Seventeen metals (including Cd, Co, Cu, Pb, U) and non-metals (including As) were measured by ICP-MS in urine spot samples from 351 subjects (32% women), aged 2-74 yr (mean 33 yr). Forty subjects (controls) lived 400 km outside the mining area; 311 subjects lived in the mining area, either very close (< 3 km) (n=179; 6 communities) or moderately close (3-10 km) (n=132; 4 communities) to mines or smelting plants.

RESULTS

For all metals (except Ni) urinary concentrations were significantly higher in subjects from the mining area than in control subjects. In subjects living very close to mines or smelting plants, the geometric means (25th-75th percentile) of urinary concentrations, expressed as microg/g creatinine, were 17.8 (10.9-29.0) for As, 0.75 (0.38-1.16) for Cd, 15.7 (5.27-43.2) for Co, 17.1 (8.44-43.2) for Cu, 3.17 (1.47-5.49) for Pb and 0.028 (0.013-0.065) for U, these values being significantly higher than those of subjects living 3-10 km from mines or industrial operations. Urinary Co concentrations were markedly elevated, exceeding 15 microg/g creatinine in 53% of the subjects, and even 87% of children (<14 yr), living very close to the mining areas. Urinary As was also high (79% above 10 microg/g creatinine in subjects living very close to the mining areas). Compared with background values from the US general population, subjects living very close to areas of mining or refining had 4-, 43-, 5- and 4-fold higher urinary concentrations of Cd, Co, Pb and U, respectively.

CONCLUSIONS

This first biomonitoring study of metal exposure in the African Copperbelt reveals a substantial exposure to several metals, especially in children. The urinary Co concentrations found in this population are the highest ever reported for a general population. The pathways of exposure and health significance of these findings need to be further investigated.

Pro-oxidative interactions of cobalt with human neutrophils

The primary objectives of this study were to investigate the effects of cobalt(II) chloride (Co, 1.5-25 microM) on the reactivity of hydrogen peroxide (H2O2, 100 microM) or oxidants generated by activated human neutrophils. The prooxidative interactions of Co with H2O2 or cells were measured by luminol-enhanced chemiluminescence (LECL), and according to the extent of oxidative inactivation of added alpha-1-proteinase inhibitor (API). Cobalt dramatically potentiated the oxidation of luminol and API by both H2O2 and neutrophils activated with phorbol 12-myristate 13-acetate (5 ng/ml), without affecting the assembly of NADPH oxidase or the magnitude of oxygen consumption by the cells. Using 5,5-dimethyl-pyrolline 1-oxide-based electron spin resonance spectroscopy we were unable to detect hydroxyl radical formation by Co in the presence of either H2O2 or activated neutrophils, while the corresponding LECL responses were unaffected by the hydroxyl radical scavengers benzoate and mannitol (50 mM). These observations indicate that Co potentiates the reactivity of neutrophil-derived oxidants, primarily H2O2, which if operative in vivo during exposure to the heavy metal may pose the risk of oxidant- and protease-mediated tissue injury.

Exhaled breath condensate as a suitable matrix to assess lung dose and effects in workers exposed to cobalt and tungsten

The aim of the present study was to investigate whether exhaled breath condensate (EBC), a fluid formed by cooling exhaled air, can be used as a suitable matrix to assess target tissue dose and effects of inhaled cobalt and tungsten, using EBC malondialdehyde (MDA) as a biomarker of pulmonary oxidative stress. Thirty-three workers exposed to Co and W in workshops producing either diamond tools or hard-metal mechanical parts participated in this study. Two EBC and urinary samples were collected: one before and one at the end of the work shift. Controls were selected among nonexposed workers. Co, W, and MDA in EBC were analyzed with analytical methods based on mass spectrometric reference techniques. In the EBC from controls, Co was detectable at ultratrace levels, whereas W was undetectable. In exposed workers, EBC Co ranged from a few to several hundred nanomoles per liter. Corresponding W levels ranged from undetectable to several tens of nanomoles per liter. A parallel trend was observed for much higher urinary levels. Both Co and W in biological media were higher at the end of the work shift in comparison with preexposure values. In EBC, MDA levels were increased depending on Co concentration and were enhanced by coexposure to W. Such a correlation between EBC MDA and both Co and W levels was not observed with urinary concentration of either element. These results suggest the potential usefulness of EBC to complete and integrate biomonitoring and health surveillance procedures among workers exposed to mixtures of transition elements and hard metals. Key words: cobalt, exhaled breath condensate, hard metals, lung, malondialdehyde, oxidative stress, tungsten.

Mitochondrial DNA damage and a hypoxic response are induced by CoCl(2) in rat neuronal PC12 cells

Generation of reactive oxygen species (ROS) and activation of a transcriptional program that mimics the hypoxic response have been documented in cultured cells in the presence of cobalt chloride. We found that in the presence of hypoxia-mimicking concentrations of CoCl(2), mitochondrial but not nuclear DNA damage is induced in rat neuronal, PC12 cells. To our knowledge, this is the first documentation of induction of mitochondrial DNA (mtDNA) damage under these conditions. Likewise, we provide the first evidence for elevation of MYH, the mammalian homolog of the Escherichia coli MutY DNA glycosylase, in mammalian cells. Recently, the human MYH was implicated in repair of oxidative DNA damage and shown to carry a mitochondrial localization sequence. Here, an induction of mtDNA damage and a time-dependent increase in the MYH level were detected with exposure of cells to 100 microM CoCl(2). In addition, the levels of proteins involved in cellular responses to hypoxia, ROS and nuclear DNA damage; hypoxia-inducible factor 1alpha(HIF-1alpha), p53, p21 and PCNA were also modulated temporally. Earlier studies suggested that the mtDNA is a primary target for oxidative damage. Our findings extend these observations and suggest that activation of DNA repair processes is associated with the presence of mtDNA damage.