Cobalt and its compounds: update on genotoxic and carcinogenic activities.

This article summarizes recent experimental and epidemiological data on the genotoxic and carcinogenic activities of cobalt compounds. Emphasis is on the respiratory system, but endogenous exposure from Co-containing alloys used in endoprostheses, and limited data on nanomaterials and oral exposures are also considered. Two groups of cobalt compounds are differentiated on the basis of their mechanisms of toxicity: (1) those essentially involving the solubilization of Co(II) ions, and (2) metallic materials for which both surface corrosion and release of Co(II) ions act in concert. For both groups, identified genotoxic and carcinogenic mechanisms are non-stochastic and thus expected to exhibit a threshold. Cobalt compounds should, therefore, be considered as genotoxic carcinogens with a practical threshold. Accumulating evidence indicates that chronic inhalation of cobalt compounds can induce respiratory tumors locally. No evidence of systemic carcinogenicity upon inhalation, oral or endogenous exposure is available. The scarce data available for Co-based nanosized materials does not allow deriving a specific mode of action or assessment for these species.

Worrying exposure to trace elements in the population of Kinshasa, Democratic Republic of Congo (DRC).

BACKGROUND AND OBJECTIVES: The particularly high rate of urbanization in Kinshasa (Democratic Republic of Congo) is associated with environmental degradation. Outdoor and indoor air pollution, as well as water pollution and waste accumulation, are issues of major concern. However, little documented information exists on the nature and extent of this pollution. A biomonitoring study was conducted to document exposure to trace elements in a representative sample of the population in Kinshasa. METHODS: Fifteen trace elements were measured by ICP-MS, CV-AAS, or HG-AFS in spot urine samples from 220 individuals (50.5% women) aged 6-70 years living in the urban area and from 50 additional subjects from the rural area of Kinshasa. Data were compiled as geometric means and selected percentiles, expressed without (µg/L) or with creatinine adjustment (µg/g cr). RESULTS: Overall, living in urban Kinshasa was associated with elevated levels of several parameters in urine as compared to the population living in the rural area (Asi, Ba, Cd, Cr, and V) as well as compared to an urban population of the southeast of Congo (Al, As, Cd, Cr, Cu, Pb, Mn, Ni, Se, V, and Zn). Elevated levels were also found by comparison with the reference values in databases involving American, Canadian, French, or German populations. CONCLUSIONS: This study provides the first biomonitoring database in the population of Kinshasa, revealing elevated levels for most urinary TE as compared to other databases. Toxicologically relevant elements such as Al, As, Cd, Pb, and Hg reach levels of public health concern.

Genotoxicity surveillance programme in workers dismantling World War I chemical ammunition.

PURPOSE: To evaluate the effectiveness of personal protective measures in a dismantling plant for chemical weapons from World War I of the Belgian Defence. METHODS: Seventeen NIOSH level B-equipped plant workers exposed to arsenic trichloride (AsCl(3)) in combination with phosgene or hydrogen cyanide (HCN) were compared to 24 NIOSH level C-protected field workers occasionally exposed to genotoxic chemicals (including AsCl(3)-phosgene/HCN) when collecting chemical ammunition, and 19 matched referents. Chromosomal aberrations (CA), micronuclei (MNCB and MNMC), sister chromatid exchanges (SCE) and high frequency cells (HFC) were analysed in peripheral blood lymphocytes. Urinary arsenic levels and genetic polymorphisms in major DNA repair enzymes (hOGG1(326), XRCC1(399), XRCC3(241)) were also assessed. RESULTS: SCE and HFC levels were significantly higher in plant-exposed versus referent subjects, but MNCB and MNMC were not different. MNCB, SCE and HFC levels were significantly higher and MNMC levels significantly lower in field-exposed workers versus referents. AsCl(3) exposure was not correlated with genotoxicity biomarkers. CONCLUSIONS: Protective measures for plant-exposed workers appear adequate, but protection for field-exposed individuals could be improved.

Hydroxyl radicals and oxidative stress: the dark side of Fe corrosion.

Fe-based materials are considered for the manufacture of temporary implants that degrade through the corrosion of Fe by oxygen. Here we document the generation of hydroxyl radicals (HO) during this corrosion process, and their deleterious impacts on human endothelial (ECs) and smooth muscle cells (SMCs) in vitro. The generation of HO was documented by two independent acellular assays, terephtalic acid hydroxylation (fluorescence) and spin trapping technique coupled with electron paramagnetic resonance spectroscopy. All Fe-based materials tested exhibited a strong potential to generate HO. The addition of catalase prevented the formation of HO. Cellular responses were assessed in two ECs and SMCs lines using different cytotoxicity assays (WST-1 and CellTiter-Glo). Cells were exposed directly to Fe powder in the presence/absence of catalase, or to extracts obtained from the corrosion of Fe. Cell viability was dose-dependently affected by the direct contact with Fe materials, but not in the presence of catalase or after indirect exposure to cell extracts. The deleterious effect of HO on ECs and SMCs was confirmed by the dose-dependent increase of the transcripts of the oxidative stress gene heme oxygenase-1 4 h or 6 h after direct exposure to the particles, but not in presence of catalase or after indirect exposure. The demonstration of HO production during corrosion and consequent oxidative stress on human ECs and SMCs newly reveals a deleterious consequence of Fe-corrosion that should be integrated in the assessment of the biocompatibility of Fe-based alloys.

Endothelial dysfunction induced by hydroxyl radicals - the hidden face of biodegradable Fe-based materials for coronary stents.

Fe-based materials are currently considered for manufacturing biodegradable coronary stents. Here we show that Fe has a strong potential to generate hydroxyl radicals (HO) during corrosion. This HO generation, but not corrosion, can be inhibited by catalase. Oxidative stress was observed (increased HO-1 expression) in aortic rings after direct exposure to Fe, but not in the presence of catalase or after indirect exposure. This oxidative stress response induced an uncoupling of eNOS in, and a consequent reduced NO production by endothelial cells exposed to Fe. In isolated rat aortic rings NO production was also reduced by HO generated during Fe corrosion, as indicated by the protective role of catalase. Finally, all these mechanisms contributed to impaired endothelium-dependent relaxation in aortic rings caused by HO generated during the direct contact with Fe. This deleterious impact of Fe corrosion on the endothelial function should be integrated when considering the use of biodegradable Fe-based alloys for vascular implants.

Sputum eosinophilia: an early marker of bronchial response to occupational agents.

BACKGROUND: False-negative responses to specific inhalation challenge (SIC) with occupational agents may occur. We explored whether assessing changes in sputum cell counts would help improve the identification of bronchial reactivity to occupational agents during SICs. METHODS: The predictive value of the changes in sputum cell counts after a negative FEV(1) response to a first challenge exposure to an occupational agent was determined using the changes in airway calibre observed during repeated challenges as the 'gold standard'. The study included 68 subjects investigated for work-related asthma in a tertiary centre. After a control day, the subjects were challenged with the suspected occupational agent(s) for up to 2 h. All subjects who did not show an asthmatic reaction were re-challenged on the following day. Additional challenges were proposed to those who demonstrated a > or = 2% increase in sputum eosinophils or an increase in nonspecific bronchial hyperresponsiveness to histamine after the second challenge day. RESULTS: Six of the 35 subjects without changes in FEV(1) on the first challenge developed an asthmatic reaction on subsequent challenges. ROC analysis revealed that a >3% increase in sputum eosinophils at the end of the first challenge day was the most accurate parameter for predicting the development of an asthmatic response on subsequent challenges with a sensitivity of 67% and a specificity of 97%. CONCLUSIONS: An increase in sputum eosinophils is an early marker of specific bronchial reactivity to occupational agents, which may help to identify subjects who will develop an asthmatic reaction only after repeated exposure.

Absence of genotoxic impact assessed by micronucleus frequency in circulating lymphocytes of workers exposed to cadmium.

PURPOSE: Cd is considered as a genotoxic carcinogen for which a threshold can be identified. This threshold has, however, not been established and the shape of the relationship between Cd exposure and genotoxic effects is unknown. The aim of the present study was to analyse the shape of the dose-response relationship for the genotoxic effects of Cd in occupational settings. METHODS: The study has a cross-sectional design and includes 60 healthy male and female workers with known Cd exposure selected from two plants manufacturing or recycling nickel-Cd batteries. The frequency of MN was measured in circulating lymphocytes, and related to internal Cd doses (Cd-B, Cd-U). Determinants of MN frequency were traced by multivariate regression analysis. RESULTS: Cd exposure covered a wide range as measured by Cd-B (0.02-1.26 µg/dL), Cd-U (0.26-15.80 µg/g creat) and seniority in the plant (1-42 years). Gender was the only parameter significantly associated with MN frequency, women having on average 8.5 additional MN/1000 BN cells compared to men. Cd-B, Cd-U or Ni-U did not influence MN frequency when adjusted for gender and other potential confounders. CONCLUSION: This finding is consistent with the existing knowledge on the mechanisms governing the genotoxic activity of Cd, which are all non-stochastic and thresholded. The threshold for systemic genotoxic effects of Cd is thus beyond the range of internal exposure considered in the present investigation.

Influence of hOGG1, XRCC1 and XRCC3 genotypes on biomarkers of genotoxicity in workers exposed to cobalt or hard metal dusts.

Identification of genetic polymorphisms responsible for reduced DNA repair capacity may allow better cancer prevention. We examined whether variations in genes involved in base-excision (hOGG1, XRCC1) and double strand break (XRCC3) DNA repair contribute to inter-individual differences in genotoxic effects induced in the lymphocytes of 21 cobalt (Co) exposed, 26 hard metal (WC-Co) exposed and 26 matched control male workers. Genotyping was performed by PCR-RFLP. DNA single strand breaks and alkali-labile sites were measured by the alkaline Comet assay. Chromosomal rearrangements resulting from chromosome loss or acentric fragments were assessed as micronucleated mononucleates (MNMC) and binucleates (MNCB) with the cytokinesis-block micronucleus test. Urinary 8-hydroxydeoxyguanosine (8-OHdG) levels were used as an indicator of systemic oxidative DNA damage. A significantly higher frequency of MNMC was observed in WC-Co exposed workers with variant hOGG1(326) genotype. Multivariate analysis performed with genotypes, age, exposure status, type of plant, smoking and their interaction terms as independent variables indicated that MNMC and Comet tail DNA (TD) were influenced by genetic polymorphisms. In the exposed and total populations, workers variant for both XRCC3 and hOGG1 had elevated MNMC frequencies. Further studies will demonstrate whether genotyping for hOGG1 and XRCC3 polymorphisms is useful for a better individual monitoring of workers.

Plasminogen activator activity of cultured murine macrophages and effects of isopropylmethylphosphonofluoridate (sarin).

Casein-elicited mouse peritoneal macrophages cultured in the presence of phorbol 12-myristate 13-acetate (PMA) express u-PA. Induction is maximal after 4 hr of stimulation and u-PA activity is mainly recovered with the membrane fraction of the cellular lysate. This enzymatic activity is inhibited by isopropylmethylphosphonofluoridate after stimulation by PMA. The presence of the organophosphorus compound before stimulation does not affect the activity. The results of the present study on the kinetics of u-PA activity in cultured macrophages, its subcellular localization and the effect of an organophosphorus ester are consistent with the concept that the development of pericellular proteolysis proceeds through a series of stages, namely, (a) synthesis of pro-u-PA, (b) binding to membrane receptors, (c) activation to a double-chain u-PA, and (d) conversion of plasminogen into plasmin. The assay procedure developed here provides a sensitive tool to investigate the mechanism of interference of chemicals with several steps of induction of this enzymatic activity in macrophages.

Comparison of the effects of auranofin and retinoic acid on plasminogen activator activity of peritoneal macrophages and Lewis lung carcinoma cells.

Urokinase-type plasminogen activator, a neutral proteinase, seems to play a central role in the degradation of the extracellular matrix that accompanies a number of biological phenomena including inflammatory reactions and neoplasia. The effect of auranofin and retinoic acid on the plasminogen activator activity expressed by two cell types, i.e. murine macrophages and Lewis lung carcinoma cells, has been investigated. Low concentrations of both drugs (10(-6)-10(-7) M) can inhibit in vitro the induction of plasminogen activator in macrophages stimulated by phorbol 12-myristate 13-acetate. This action occurs rapidly (15 min), is irreversible and is independent of a global cytotoxic effect. Auranofin and retinoic acid remain without effect in macrophages when added after stimulation by the phorbol ester. Both drugs are thus potent inhibitors of the induction of plasminogen activator activity in macrophages, possibly through an interaction with the protein kinase C system. The plasminogen activator activity of Lewis lung carcinoma cells, which is apparently not dependent on a protein kinase C pathway, is not influenced by auranofin or retinoic acid. These observations may contribute to explain: (1) the activity of auranofin and retinoic acid in rheumatoid arthritis, and (2) the antitumor promoting activity of retinoic acid. It would be relevant to assess whether auranofin may exhibit, like retinoic acid, an antitumor-promoting activity.

Assessment of lipid peroxidation associated with lung damage induced by oxidative stress. In vivo and in vitro studies.

The lung thiobarbituric acid-reactive substances (TBA-RS) content and the amount of ethane exhaled, two potential markers of the lipid peroxidation process, were measured in rats following intratracheal administration of chemicals stimulating the production of free radicals, i.e. paraquat, phorbol myristate acetate and ferrous ions. Five hours after treatment, autopsy revealed gross pulmonary damage but the lung TBA-RS and the ethane exhalation were not different from control animals. On the contrary, a large increase in ethane production was observed 2 hr after intraperitoneal administration of the hepatotoxic carbon tetrachloride. In vitro, incubation of lung and liver homogenates from control rats with ferrous iron led to the development of a lipid peroxidation process in both tissues but the accumulation of TBA-RS and ethane was much lower with homogenates from lung as compared to liver tissue. Those results suggest that the lung may be more resistant than the liver to the initiation and/or propagation of a lipid peroxidation process. The possibility that others markers than ethane and TBA-RS are more appropriate to detect this process in the lung must also be considered.

Plasminogen activator activity of normal and retinoic acid-treated post-implantation embryos.

Urokinase-type plasminogen activator (uPA) has been implicated in cellular migration accompanying different biological phenomena including organogenesis. An increase in uPA activity was observed in mouse post-implantation embryos during the early organogenesis period. Since we have previously shown that all-trans retinoic acid (RA) prevented the induction of uPA in mouse peritoneal macrophages, we have now assessed whether teratogenic doses of this agent could also interfere with uPA activity in mouse embryo in vitro and in vivo. Post-implantation embryos (8.5 days) were incubated for up to 24 hr with micromolar concentration of RA resulting in the occurrence of malformations. No significant difference in uPA activity was found between control and treated embryos. Likewise, uPA activity was not altered in embryos explanted on day 9.5 from dams treated 24 hr before with a teratogenic dose of RA. This study indicates that the teratogenic activity of RA is not caused by an inhibition of the induction of uPA in embryos.

Absence of significant genotoxicity in lymphocytes and urine from workers exposed to moderate levels of cobalt-containing dust: a cross-sectional study.

Mortality studies have shown that, in the past, lung cancer occurred after exposure to mixtures of cobalt metal and metallic carbide particles, the main constituents of hard metals, but apparently not when exposure was to cobalt alone. The major objective of this biomonitoring study was to assess genotoxic effects as a measure for carcinogenic risk in workers from cobalt refineries and hard metal plants currently exposed to the threshold limit value/time-weighted average (TLV-TWA) for cobalt-containing dust. The study comprised three groups of workers: 35 workers exposed to cobalt dust from three refineries, 29 workers exposed to hard metal dust from two producing plants, and 35 matched control subjects recruited from the respective plants. The study design integrated complementary methodologies to assess biomarkers of effects that represent both initial DNA damage (8-hydroxydeoxyguanosine [8-OHdG] in urine and comet assay on lymphocytes) and definitive chromosome breakage/loss (micronuclei in lymphocytes). Cobalt and cotinine were determined in urine as a measure for cobalt exposure and recent smoking, respectively. No significant increase of genotoxic effects was detected in workers exposed to cobalt-containing dust as compared to controls. No difference in any genotoxicity biomarker was found between workers exposed to cobalt and hard metal dusts. Multiple regression analysis indicated that workers who smoked and were exposed to hard metal dusts had elevated 8-OHdG and micronuclei values. Because this observation is in line with a previous epidemiological study of an increased risk of dying from lung cancer in workers from the hard metal industry who smoked, it is concluded that this specific occupational group needs closer medical surveillance.

Acute and subacute organophosphate poisoning in the rat.

The intermediate syndrome in organophosphate poisoning is clinically characterized by weakness in the territory of cranial nerves, weakness of respiratory, neck and proximal limb muscles, and depressed deep tendon reflexes. It occurs between the acute cholinergic crisis and the usual onset of organophosphate-induced delayed neurotoxicity. The weakness has been ascribed to muscle fiber necrosis. Fenthion has been the most common cause. This study assesses the occurrence of the necrotizing myopathy in rats in relation to the clinical course and the acetylcholinesterase (AChE) inhibition after poisoning with organophosphates representative for each of the major types of organophosphate-related neurotoxicity. Marked differences are noted in the duration of cholinergic symptoms and of AChE inhibition after either paraoxon and mipafox, or fenthion poisoning. The necrotizing myopathy begins shortly after the initial decline in AChE activity with all organophosphates studied. Maximal muscle involvement occurs within the first 2 days of the poisoning with all organophosphates studied. The myopathy is not aggravated by a further decline in AChE activity in fenthion poisoning. Our data argues against the monophasic necrotizing myopathy being the cause of the intermediate syndrome, and is suggestive of persistent AChE inhibition being involved.

Prospective study on the reversibility of neurobehavioral effects in workers exposed to manganese dioxide.

In 1987, a cross-sectional study in a dry-alkaline battery plant in Belgium revealed subclinical neurobehavioral dysfunctions associated with inhalation exposure to manganese dioxide (MnO2) particulate. The overall geometric mean of the time-weighted average concentration of manganese (Mn) in "total" dust (MnT) amounted, at that time, to 1 mg Mn/m3 and the duration of exposure was 5.5 years on average. An 8-year longitudinal investigation was conducted in this cohort (n = 92) in order to find out whether early effects on eye-hand coordination (EHC), hand steadiness (HST), and simple visual reaction time (VRT) were reversible when the airborne manganese concentration at the workplace was abated. During the observation period from 1988 to 1995, MnT monitoring was implemented on a monthly basis producing more than 1300 personal air samples, EHC tests were given yearly to assess the precision of the hand-forearm movement (PN1), and HST and VRT tests were carried out yearly since 1991. By the end of the study, the cohort size had dropped to 34 subjects. The model of unbalanced repeated measurements with unstructured covariance matrix and a time-varying covariate (log MnT) was the most appropriate to analyze the data. Wald chi 2 statistic was used for testing time-trends. The reduction of MnT over time was significantly associated with an improvement of the PN1 values (total cohort: Wald chi 2 = 8.5, p = 0.004; beta log MnT = -6.098 +/- 2.096). Like in the total cohort, time-trends were also found in the three exposure subgroups which could be identified in the cohort (average MnT over 1987-1992 were about 400, 600, and 2000 micrograms Mn/m3 for the low, medium, and high exposure subgroups, respectively). Only in the low exposure subgroup the PN1 value normalized when MnT (provisional estimates) decreased from about 400 to 130 micrograms Mn/m3 by the end of the study. Solely the reduction in MnT explained these findings on PN1, while a "healthy-worker-effect" mechanism was unlikely to have operated. The prognosis for the medium and high exposure subgroups remains uncertain as the improvement of their EHC performance may have been affected by past MnO2 exposure to such an extent that the persistence of a partial loss of EHC ability is suggested. The time courses of the HST and VRT test results, however, indicated the absence of any improvement, suggesting irreversible impairment of hand stability (postural tremor) and simple visual reaction time. A separate examination in a group of 39 control subjects, re-tested 10 years after the first test in 1987, virtually precluded age as confounding factor in this prospective study. The findings of the longitudinal study are corroborated by the outcome of a separate follow-up study in a group of 24 ex-Mn employees, who showed in 1996 a significant improvement of eye-hand coordination after at least three years with no MnO2 exposure; as to HST and VRT, there was no significant change in the deficit of these two neurobehavioral markers.

Cadmium: a possible etiological factor in peripheral polyneuropathy.

Uncovering the exact cause of polyneuropathies seems to be impossible in up to 24% of the cases. Experimental studies have shown that cadmium (Cd), which is a well-known occupational and environmental hazard, can be a potent neurotoxicant for the peripheral nervous system. Moreover, Cd has a half-life of more than 15 years in humans. We hypothesize that older workers may be more susceptible to an increased Cd body burden, and may develop a peripheral polyneuropathy (PNP) over time. A blinded epidemiological survey was performed in 13 retired, long-term Cd-exposed workers and 19 age-matched controls. Historical Cd biomonitoring data were available over the last two decades. A neurological clinical examination, nerve conduction studies, and needle EMG were performed, and a standardized questionnaire was given to evaluate polyneuropathy complaints. If two of the following four criteria, i.e. complaints of polyneuropathy, neurophysiological changes compatible with polyneuropathy, distal symmetrical areflexia, or distal symmetrical anesthesia for vibration sense, temperature or blunt-sharp discrimination were present, the diagnosis of PNP was made. Two (11%) of the control and seven (54%) of the retired Cd workers met the PNP criteria OR: 9.92 (95%CI 1.60-61.6), Fisher exact test p=0.015. The existence of a polyneuropathy was related to the level of the Cd body burden as reflected by urinary Cd multiple logistic regression p=0.016, OR=1.26, (95%CI, 1.04-1.51), but not to blood lead (p=0.352). Our findings favour the hypothesis of a promoting role of increased cadmium body burden in the development of PNP at older age.

Quantitative determination of 5-hydroxy-N-methylpyrrolidone in urine for biological monitoring of N-methylpyrrolidone exposure.

The aim of this work was to validate a sensitive method for quantitative analysis of 5-hydroxy-N-methylpyrrolidone (5-HNMP) in urine. This compound has been recommended as a marker for biological monitoring of N-methylpyrrolidone (NMP) exposure. Different solvents and alternative methods of extraction including liquid-liquid extraction (LLE) on Chem Elut and solid-phase extraction (SPE) on Oasis HLB columns were tested. The most efficient extraction of 5-HNMP in urine was LLE with Chem Elut columns and dichloromethane as a solvent (consistently 22% of recovery). The urinary extracts were derivatized by bis(trimethylsilyl)trifluoroacetamide and analysed by gas chromatography-mass spectrometry (GC-MS) with tetradeutered 5-HNMP as an internal standard. The detection limit of this method is 0.017 mg/l urine with an intraassay precision of 1.6-2.6%. The proposed method of extraction is simple and reproducible. Four different m/z signal ratios of TMS-5-HNMP and tetralabelled TMS-5-HNMP have been validated and could be indifferently used in case of unexpected impurities from urine matrix.

Importance of biotransformation pathways for interpreting biological monitoring of exposure.

A detailed characterisation of the biotransformation pathways followed by the chemical of interest is, evidently, of primordial importance to design reliable biomonitoring programs. This short overview discusses some recent studies that are of potential interest for the development of new avenues of research. Four topics are addressed: tissue localisation of the metabolic process; importance of speciation; metabolic interactions and polymorphism and interindividual variability. While some of these studies offer new data that is directly useful for practical application, others raise mainly questions and indicate that there is still a large effort of research to be performed to improve the design and the interpretation of biomonitoring programs.

Study of the mechanism responsible for the elective toxicity of tungsten carbide-cobalt powder toward macrophages.

We have previously demonstrated that tungsten carbide-cobalt powder (WC-Co) is more toxic toward murine macrophages in vitro than pure cobalt metal particles and that the cellular uptake of cobalt is enhanced when the metal is present in the form of WC-Co mixture. The present study was undertaken to assess the possible mechanism(s) of this interaction. We found that solubilization of cobalt in the extracellular milieu was increased in the presence of WC. This phenomenon, however, is not the critical factor explaining the greater toxicity of the WC-Co mixture since increasing the amount of solubilized cobalt in the extracellular medium in the absence of WC did not result in increased toxicity. Moreover, the amount of cobalt solubilized from a toxic dose of WC-Co was insufficient to affect by itself macrophage viability. A toxic effect was only observed when the WC-Co mixture came directly in contact with the cells. The elective toxicity of WC-Co can also not be explained by stimulation of phagocytosis of cobalt metal particles due to the simultaneous presence of other particles (WC) in the extracellular fluid since stimulation of phagocytosis by latex beads or zymosan particles did not amplify the toxicity of cobalt metal particles. These results indicate that the toxicity of the WC-Co mixture does not simply result from an enhanced bioavailability of its cobalt component. This suggests that hard metal dust behaves as a specific toxic entity.

In vitro effect of mercury and vanadium on superoxide anion production and plasminogen activator activity of mouse peritoneal macrophages.

The in vitro effects of mercuric chloride and vanadate were examined on two functions of mouse peritoneal macrophages, i.e., the superoxide anion production and the plasminogen activator (PA) activity. Vanadate, at concentrations which do not affect the viability of the cells, does not seriously alter any of these functions. High concentrations of mercury depress the respiratory burst; this effect results from loss of the reducing properties of cellular NADPH. Low concentrations of mercury stimulate the effect of phorbol 12-myristate 13-acetate on PA activity. The mechanism of this stimulation does not involve the protein kinase C system. It is hypothesized that mercury could enhance the synthesis of PA, its translocation to the cell surface, or its binding to the membrane receptors.