On the question of the pathogenetic importance of cobalt for hard metal fibrosis of the lung

Matrix metalloproteinase-2 and -9 are induced differently by metal nanoparticles in human monocytes: The role of oxidative stress and protein tyrosine kinase activation

Recently, many studies have shown that nanoparticles can translocate from the lungs to the circulatory system. As a particulate foreign body, nanoparticles could induce host responses such as reactive oxygen species (ROS) generation, inflammatory cytokine and matrix metalloproteinase (MMP) release which play a major role in tissue destruction and remodeling. However, the direct effects of nanoparticles on leukocytes, especially monocytes, are still unclear. The objective of the present study was to compare the ability of Nano-Co and Nano-TiO(2) to cause alteration of transcription and activity of MMPs and to explore possible mechanisms. We hypothesized that non-toxic doses of some transition metal nanoparticles stimulate an imbalance of MMP/TIMP that cause MMP production that may contribute to their health effects. To test this hypothesis, U937 cells were treated with Nano-Co and Nano-TiO(2) and cytotoxic effects and ROS generation were measured. The alteration of MMP-2 and MMP-9 expression and activity of MMP-2 and MMP-9 after exposure to these metal nanoparticles were subsequently determined. To investigate the potential signaling pathways involved in the Nano-Co-induced MMP activation, the ROS scavengers or inhibitors, AP-1 inhibitor, and protein tyrosine kinase (PTK) inhibitors were also used to pre-treat U937 cells. Our results demonstrated that exposure of U937 cells to Nano-Co, but not to Nano-TiO(2), at a dose that does not cause cytotoxicity, resulted in ROS generation and up-regulation of MMP-2 and MMP-9 mRNA expression(..) Our results also showed dose- and time-related increases in pro-MMP-2 and pro-MMP-9 gelatinolytic activities in conditioned media after exposure of U937 cells to Nano-Co, but not to Nano-TiO(2). Nano-Co-induced pro-MMP-2 and pro-MMP-9 activity increases were inhibited by pre-treatment with ROS scavengers or inhibitors. We also demonstrated dose- and time-related decreases in tissue inhibitors of metalloproteinases 2 (TIMP-2) in U937 cells after exposure to Nano-Co, but not to Nano-TiO(2). However, neither Nano-Co nor Nano-TiO(2) exposure led to any transcriptional change of TIMP-1. The decrease of TIMP-2 after exposure to Nano-Co was also inhibited by pre-treatment with ROS scavengers or inhibitors. Our results also showed that pre-treatment of U937 cells with AP-1 inhibitor, curcumin, or the PTK specific inhibitor, herbimycin A or genistein, prior to exposure to Nano-Co, significantly abolished Nano-Co-induced pro-MMP-2 and-9 activity. Our results suggest that Nano-Co causes an imbalance between the expression and activity of MMPs and their inhibitors which is mediated by the AP-1 and tyrosine kinase pathways due to oxidative stress.

Tumor necrosis factor-alpha release from rat pulmonary leukocytes exposed to ultrafine cobalt:in vivo andin vitro studies

Ultrafine cobalt (Uf-Co), one of the new category of ultrafine particles, is generated in some industrial situations and it also exists in environmental particles. The aim of this study was to investigate the ability of rat pulmonary leukocytes to release tumor necrosis factor alpha (TNF-alpha) after exposure to Uf-Coin vivo andin vitro. Rats were intratracheally instilled with 1 mg of Uf-Co, and then wet lung weight and bronchoalveolar lavage fluid (BALF) profile were analysed 1, 3, 7, 15, and 30 days later. The effects of Uf-Co on indices that can be presumed to reflect epithelial injury and permeability (lactate dehydrogenase (LDH) and total protein (TP)) were increased throughout the 30 day post-exposure period. Furthermore, at 3 days after exposure, leukocytes were collected by bronchoalveolar lavage (BAL). After 3, 6, 12, 24, 48, and 72 hours of incubation, TNF-alpha in supernatants were determined by ELISA method. The results showed that TNF-alpha secretion by activated leukocytes from rats instilled with Uf-Co was significantly higher than that of the controls. BAL leukocytes from the lung of exposed rats revealed time-arid dose-related increases in TNF-alpha release. In conclusion, our results reveal, for the first time to our knowledge, that exposure to Uf-Co can stimulate leukocytes to secrete TNF-alpha. These data suggest that the TNF- alpha release from pulmonary leukocytes probably plays a role in the pathogenesis of "cobalt lung".

Human toxicity of cobalt-containing dust and experimental studies on the mechanism of interstitial lung disease (hard metal disease)

In the industry, the potential for exposure to cobalt metal dust is particularly important during the production of cobalt powder and the processing and use of hard metals and other cobalt-containing alloys. The different adverse health effects reported in these workers are reviewed. One of the main target organs is the respiratory tract, and this article concentrates on the lung parenchymal reactions induced by cobalt-containing dust. Clinical and epidemiological data indicate that this manifestation is rarely, if ever, induced by pure cobalt metal dust alone, but requires the concomitant inhalation of other compounds such as tungsten carbide in the hard metal industry (hard metal disease). Experimental studies demonstrate that cobalt metal and metallic carbides interact to produce an elective lung toxicity. Recent work on the mechanism of this interaction, which is based on the production of activated oxygen species, is reviewed. A practical implication in industrial hygiene should be that permissible exposure levels to Co dust might have to be different when exposure is to pure Co particles or an association with carbides.

Health risks associated with cobalt exposure--an overview

Cobalt is an essential oligoelement which enters in the composition of vitamin B12. For the general population, food and beverages represent the main source of cobalt exposure. Traces of cobalt are also present in cement and various household products. In industry, the potential for exposure to cobalt is particularly important during the production of cobalt powder, the production, processing and use of hard metals, the polishing of diamonds with cobalt containing disks and the processing of cobalt alloys. Except in the production of cobalt powders, these activities involve exposure not only to cobalt but also to other substances such as tungsten carbide, iron and diamond which may modulate the biological reactivity of cobalt. Cobalt salts are used for the preparation of enamels and pigments. Cobalt is mainly absorbed from the pulmonary and the gastrointestinal tracts. Absorption through the skin can occur but is low. Concomitant exposure to tungsten carbide increases the pulmonary absorption rate of cobalt metal. Cobalt is not a cumulative toxin and is mainly excreted in urine and to a lesser extent via faeces. Cobalt in blood and urine mainly reflects recent exposure. In the past, outbreaks of cardiomyopathy occurred among heavy consumers of cobalt fortified beer. It is likely that poor nutrition and ethanol had played a synergistic role. Toxic manifestations, however, have mainly been reported following inhalation of cobalt containing dusts in industry. The two main target organs are the skin and the respiratory tract. Cobalt itself may cause allergic dermatitis, rhinitis and asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation and comparison of the levels of occupational exposure to cobalt during dry and/or wet hard metal sharpening. Environmental and biological monitoring

To investigate risks to hard metal tool sharpeners, 80 factories in the Lombardia Region (North Italy) were selected and examined. The scope of the survey consisted of verifying and quantifying that risk, so as to be able to control it and reduce it as far as is possible. We singled out a group of 12 factories, comprising approximately 750 workers 60 of whom were exposed to cobalt, in which operations such as sharpening with diamond grinding stones are normally carried out. In those factories, the risk was quantified by determining the concentration of cobalt in dust, collected by means of personal and fixed samplers (23 measurements) during sharpening operations. The station had no local ventilation device; sharpening is mainly performed wet and has been found to present a greater risk than those where sharpening is exclusively performed dry. Results were confirmed by biological monitoring which showed the presence of cobalt excreted in exposed workers' urine collected at the end of the work shift.

Does occupational cobalt exposure determine early renal changes?

A cohort of workers occupationally exposed to cobalt (Co) dusts was examined to assess possible subclinical renal effects attributable to Co. Cross-sectional investigations involved 26 workers with a mean age of 34.2 (S.D., 8.3), chronically-exposed (median, 3.5 years; range, 0.9-11) to Co dusts in hard-metal manufacturing factories. Thirty-five healthy control workers, with a mean age of 32.4 (S.D., 4.6) were also examined. Individual interviews were used to exclude subjects with renal or systemic diseases, intake of nephrotoxic drugs, and exposure to known nephrotoxins. Exposure levels, assessed by ambient and biological monitoring, showed an estimated exposure approaching the ACGIH-recommended TLV of 50 micrograms/m3. Immunochemical methods were used to measure urinary albumin, retinol-binding protein (RBP), beta 2-microglobulin (beta 2m), and tubular brush-border antigens. The prevalence of abnormal values for early markers of renal dysfunction was similar in Co-exposed workers and in controls. However, within the reference interval, the cumulated frequency distribution for beta 2m was shifted towards higher values in the exposed group. No relationship was detected between renal markers and either intensity or duration of exposure. In spite of a limited number of observations, these findings suggest that the kidney is not a target organ during occupational exposure to Co.

Cobalt determination in serum and urine by electrothermal atomic absorption spectrometry

Cobalt determinations in biological fluids are of great interest in biological or toxicological research programs. Cobalturia is often chosen as an indicator for a biological monitoring program in occupational exposure to cobalt dusts. The method described here derives from the IUPAC reference method for nickel determination. It enables cobaltemia and cobalturia to be measured in small samples (1 mL). The mean usual values for cobalt in biological fluids are very low (2.7 nmol L-1 for serum and 6.7 nmol L-1 for urine), and therefore, thus require an analytical procedure with preconcentration and extraction. The sample is mineralized by wet acid digestion. After digestion, inorganic cobalt is extracted in form of ammonium pyrrolidine dithiocarbamate complex into isobutyl methyl ketone and measured in the organic layer by electrothermal atomic absorption spectrometry. The analytical parameters are described in detail. The extraction output is about 99%. The detection limits are 1.93 and 1.89 nmol L-1 for serum and urine, respectively. Sensitivity (expressed as the concentration that gives a 0.044 absorbance) is 3.4 nmol L-1 for serum and 3.3 nmol L-1 for urine. Within-run precision ranged between 3.9 and 2.5% (coefficients of variation) for serum and 4.2 and 1.1% for urine, at 87 and 136 nmol L-1 levels, respectively. Between-run precision ranged between 4.3 and 3.3% (coefficients of variation) for serum and 4.2 and 2.3% for urine, at 87 and 136 nmol L-1 levels, respectively. At very low concentration, 5.7 nmol L-1 for serum and 2.5 nmol L-1 for urine, the between-run precision is, respectively, 19.5 and 28%. Linearity is effective between 0 and 272 nmol L-1. Interferences and matrix effects are negligible for urine, serum, or plasma samples without hemoglobin. The method is easily applicable for routine determinations.

Epidemiological survey of workers exposed to cobalt oxides, cobalt salts, and cobalt metal

Several organs (lung, skin, thyroid, heart, bone marrow) are potential targets of cobalt (Co). Whereas there is no doubt that inhalation of Co alone may cause bronchial asthma, its role in the occurrence of hard metal disease is still controversial because most cases were reported in workers exposed not only to Co but also to other substances such as tungsten carbide, titanium carbide, iron, silica and diamond. To assess whether exposure to pure Co dust (metal, oxides, or salts) may lead to adverse health effects a cross sectional study was carried out among 82 workers in a Co refinery. The results were compared with those in a sex and age matched control group. The Co group had been exposed for 8.0 years on average (range 0.3-39.4). The geometric mean time weighted average exposure assessed with personal samplers (n = 82) was about 125 micrograms/m3 and 25% of the values were higher than 500 micrograms/m3. The concentrations of Co in blood and in urine after the shift were significantly correlated with those in air. Concentration of Co in urine increased during the workweek. A slight interference with thyroid metabolism (decreased T3, T4, and increased TSH), a slight reduction of some erythropoietic variables (red blood cells, haemoglobin, packed cell volume) and increased white cell count were found in the exposed workers. The exposed workers complained more often of dyspnoea and wheezing and had significantly more skin lesions (eczema, erythema) than control workers. Within the exposed group a dose-effect relation was found between the reduction of the forced expiratory volume in one second/vital capacity and the intensity of current exposure to Co assessed by the measurement of Co in air or in urine. The prevalence of dyspnoea was related to the dustiness of the workplace as reflected by statistically significant logistic regression between this symptom and the current levels of Co in air and in urine. No difference between lung volumes, ventilatory performances, carbon monoxide diffusing capacity, and serum myocardial creatine kinase and procollagen III peptide was found between the Co and control groups and no lung abnormalities were detected on the chest radiographs in both groups. The results suggest that exposure to high airborne concentrations of Co alone is not sufficient to cause pulmonary fibrosis. This finding is compatible with experimental studies indicating that interaction of other airborne pollutants with Co particles play a part in the pathogenesis of parenchymal lung lesions.

Inhalation of cobalt by sensitised guinea pigs: effects on the lungs

Two groups, each of six guinea pigs, were sensitised by the application of cobalt chloride (CoCl2) on the skin on day 0, 2, 7, and 9 and the establishment of contact allergy was confirmed by patch testing on day 21. A further six animals were not sensitised. Starting on day 42 one sensitised group and the non-sensitised group were exposed by inhalation to 2.4 (0.8) mg (mean (SD)) Co in the form of CoCl2 for six hours a day for two weeks. After exposure the lungs were lavaged and the cells obtained were studied by light and electron microscopy. In the sensitised exposed group much more lavage liquid was retained in the lungs than in the other two groups; although more liquid was instilled in the lungs of this group, on average only 5 (range 2.5-10) ml were recovered compared with 10 ml in all animals in the other two groups. In the sensitised exposed group, the percentage of neutrophils and eosinophils tended to be higher than in the non-sensitised exposed group. The results indicate that the lungs of guinea pigs allergic to contact with Co react differently to inhaled Co compared with those of non-sensitised ones.

Comparative study of the acute lung toxicity of pure cobalt powder and cobalt-tungsten carbide mixture in rat

Alveolitis progressing to lung fibrosis has been reported in workers exposed to cobalt containing dust (e.g., tungsten carbide-cobalt mixture as produced by the hard metal industry) but rarely following exposure to pure cobalt dust (e.g., in cobalt-producing factories). We have previously demonstrated that tungsten carbide-cobalt mixture is more toxic toward rat alveolar macrophages in vitro than pure cobalt metal powder. The present study was undertaken to compare in female rats the acute pulmonary response (lung weight, lung histology, cellular and biochemical analyses of bronchoalveolar lavage fluid, and mortality) following the intratracheal instillation of pure cobalt (Co) particles (median particle size, d50:4 microns), pure tungsten carbide (WC) particles (d50:2 microns), tungsten carbide-cobalt (WC-Co) powder (d50:2 microns; cobalt 6.3%, tungsten 84%, carbon 5.4%) and crystalline silica (d50 less than 5 micron) used as pneumotoxic reference material. WC alone (15.67 mg/100 g body wt) behaves as an inert dust producing only a mild accumulation of macrophages in the alveolar duct walls. Co alone (1.0 mg/100 g) only causes a moderate inflammatory response. An identical amount of Co given as WC-Co mixture (16.67 mg/100 g; corresponding to 1.0 mg Co/100 g) produces a severe alveolitis and fatal pulmonary edema. Cellular and biochemical characteristics of bronchoalveolar lavage fluid collected 24 hr after the intratracheal instillation of WC (1.0 mg/100 g) or Co (0.06 mg/100 g) are not significantly different from those of control animals instilled with sterile saline. On the contrary, bronchoalveolar lavage fluid changes following administration of the WC-Co mixture (1.0 mg/100 g; corresponding to 0.06 mg Co/100 g) are very similar to those induced by crystalline silica (1.0 mg/100 g). The amount of cobalt excreted in urine is significantly higher when the animals are exposed to WC-Co powder as compared to an equivalent amount of pure cobalt particles, suggesting an increased bioavailability of cobalt metal when combined with tungsten carbide. This study demonstrates that the acute lung toxicity of tungsten carbide-cobalt mixture is much higher than that of each individual component and may explain why lung fibrosis is rarely if ever induced by exposure to pure cobalt dust.

Ventilatory function of workers exposed to cobalt and diamond containing dust

The ventilatory function of 48 workers occupied on the average for six years in a plant producing diamond-cobalt circular saws was compared with that of 23 control subjects. The geometric mean airborne cobalt concentrations in the two main work areas amounted to 15.2 and 135.5 micrograms/m3 respectively. The spirometric changes found in the exposed workers were compatible with a moderate restrictive syndrome and were correlated with duration of exposure.

Respiratory hazards in hard metal workers: a cross sectional study

A cross sectional study was conducted on 513 employees at three hard metal plants: 425 exposed workers (351 men, 74 women) and 88 controls (69 men, 19 women). Cough and sputum were more frequent in workers engaged in "soft powder" and presintering workshops compared with controls (12.5% and 16.5% v 3.5%). Spirometric abnormalities were more frequent among women in sintering and finishing workshops compared with control women (56.8% v 23.8%) and abnormalities of carbon monoxide test were more frequent in exposed groups than in controls; this difference was more pronounced in women (31.4% v 5.6%) than in men (18.5% v 13%). No significant correlation was observed between duration of exposure and age adjusted lung function tests. Slight abnormalities of chest radiographs (0/1, 1/1 according to ILO classification) were more frequent in exposed men than controls (12.8% v 1.9%) and mostly in soft powder workers. In subjects with abnormal chest radiographs FVC, FEV1 and carbon monoxide indices (fractional uptake of CO or CO transfer index or both) were lower compared with those with normal chest radiographs. Although relatively mild, the clinical, radiological, and functional abnormalities uncovered call for a regular supervision of workers exposed to hard metal dust.

Cobalt in the environment and its toxicological implications

Cobalt is an essential trace element which is widely distributed in nature. Most of cobalt consumed is used in the manufacture of alloys, and although not released extensively in the environment, it may represent a hazard to human health. In addition, excess dietary cobalt produces toxic effects in animals. Polycythemia and hyperglycemia with transitory damage to pancreatic alpha-cells have been widely reported after cobalt administration. Cobalt salts induce respiratory deficiency in yeast. CoCl2 increased sister chromatid exchange (SCE) in P388D1 cells and in lymphocytes from two donors. So far it has not been possible to induce cancer in experimental animals using cobalt by any other route than by injection. Ingestion of cobalt may lead to reproductive changes in the male rat such as loss of testicular volume and darkening of testicle color. On the other hand, oral administration of cobalt did not produce teratogenicity or significant fetotoxicity in the rat at daily doses as high as 100 mg CoCl2/kg. However, cobalt affected the period of late gestation as well as the postnatal development of the pups. Occupational toxicology of cobalt, hygienic and epidemiologic aspects, and treatment of cobalt poisoning are also topics of special interest. Cobalt is a metal with marked allergenic potential. Asthma, interstitial lung disease and combined asthma and alveolitis have been described as occupational health hazards. EDTA, DTPA, and N-acetyl-L-cysteine have been suggested as possible antidotes in cobalt intoxication.

Inorganic particulates in pneumoconiotic lungs of hard metal grinders

Data from the analysis of lung dust in 16 metal grinders who had been exposed to hard metals between five and 44 years is reported. The mean latent time between the first exposure and analysis in biopsy or necropsy specimens was 33.6 years. Mineralogical and elementary analysis by a variety of techniques showed small or trace amounts of hard metal in all lungs. Many specimens, however, did not contain all hard metal components, cobalt, for example, being detected in four cases only. All the lungs contained quartz and silicates and in most of the necropsy cases carborundum and corundum could also be shown. Histologically no specific pattern was found. The appearances included mixed dust nodular pneumoconiosis, diffuse interstitial lung fibrosis, and foreign body and sarcoid like granulomatous changes. In view of the mixed dust exposure of the hard metal grinders and the variable histological appearance we think that the term "mixed dust pneumoconiosis in hard metal grinders" is more appropriate than "hard metal lung" to describe this condition.

Respiratory diseases in hard metal workers: an occupational hygiene study in a factory

A hygiene study of a hard metal factory was conducted from 1981 to 1984. All workers exposed to hard metal were medically examined and their exposure to cobalt measured. Eighteen employees had occupational asthma related to exposure to hard metal, a prevalence rate of 5.6%. Nine had a positive bronchial provocation test to cobalt and reactions of the immediate, late, or dual type were elicited. Exposure measurements suggest that asthma may be caused by cobalt at a mean time weighted average concentration below 0.05 mg/m3. Only two of the nine individuals with cobalt asthma had a positive patch test to cobalt. Chest radiographs of three workers showed diffuse shadows of category 1 or over. X ray microanalysis of lung biopsy specimens from two of these three workers showed the presence of tungsten, titanium, cobalt, nickel, and some minerals. One of the two was diagnosed as having pneumoconiosis due to exposure to silica in a steel industry and the other was suspected of having pulmonary fibrosis caused by dust generated from the carborundum wheels used to grind hard metal. There were no cases with interstitial pneumonitis in the factory.

Urinary cobalt as a measure of exposure in the hard metal industry

Twenty-six workers in a hard metal manufacturing plant were monitored by cobalt urinary and ambient air measurements during the first month after summer holidays. Cobalt determinations were performed utilizing AAS, with a preliminary chelation and extraction procedure for urinary samples. Almost all personal ambient air samples turned out to be under the cobalt dust TLV of 0.1 mg/m3. When restarting work after the holidays, urinary values did not differ from the control group. At the end of the first working week, urinary cobalt had increased four fold, then decreased to the original values on the following Monday before restarting work. Thereafter, the weekend was no longer sufficient to reduce the levels to normal urinary cobalt values. The values rose to the same level observed before the holidays, and dit not substantially decrease even after the weekend. End-shift urinary cobalt values showed a good relationship with present as well as with mean past exposure on the first and the fifth weekday, but the third day did not. The correlation was better with present exposure on Monday and with mean past exposure on Friday. The observed differences may be explained by the minor influence of recent exposure on present exposure on Monday. The highest values were found on Wednesday. We suggest the utilization of end-shift urinary cobalt determination as a measure of the present exposure on Monday, and of mean recent or preceding exposure on Friday.

Cobalt-induced bronchial asthma in diamond polishers

Three diamond workers had occupational asthma attributed to the inhalation of cobalt powder. The exposure originated from high speed polishing disks with an abrasive consisting of microdiamonds cemented in extra fine cobalt not alloyed to tungsten carbide. The bronchoconstriction progressed towards the end of working-days; it was especially pronounced in the absence of an adequate exhaust ventilation; and it could be accompanied by rhinitis and chest tightness. Cobalt inhalation challenge tests were positive in all three patients, and exposure to cobalt temporarily increased nonspecific hyperreactivity.