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.

Importance of genetic polymorphisms of drug-metabolizing enzymes for the interpretation of biomarkers of exposure to styrene

The objective of this study was to test the infiuence of genetic polymorphisms for metabolic enzymes (CYP2E1, mEH, GSTM1 and GSTT1) implicated in the biotransformation of styrene in humans on the interpretation of urinary biomarkers of exposure. Thirty workers from a fibreglass-reinforced plastics factory took part in the study. Ambient styrene concentration was determined during the whole workshift by passive sampling. Urine was collected at the end of the shift for the determination of mandelic acid (MA) and phenylglyoxylic acid (PGA) (major biotransformation pathway), N-acetyl-S-(1-phenyl-2-hydroxy)ethyl-L-cysteine (M1) and N-acetyl-S-(2-phenyl-2-hydroxy)ethyl-L-cysteine (M2) (minor metabolic pathway) and creatinine. The average airborne styrene concentration of 18.2 ppm (range: 0.9-68.9 ppm) was very close to the current threshold limit value (TLV-TWA) recently adjusted by ACGIH from 50 to 20 ppm. There was a better correlation between external and internal exposure as estimated by urinary MA + PGA (r=0.92; p<0.0001) compared with urinary M1 + M2 (r=0.74; p<0.0001). To investigate to what extent genetic polymorphisms in metabolic enzymes could explain interindividual variations observed in the concentration of urinary biomarkers related to a given external exposure, two 'metabolic indexes' (derived from the ratio between the sum of urinary metabolites for a specific pathway and ambient styrene concentration) were calculated for each worker and compared for different allelic combinations. Monovariate analyses showed that GSTM1 polymorphism was clearly the most significant parameter infiuencing urinary concentrations of mercapturic acids. Based on GSTM1 allelic status, two different biological exposure indexes (BEIs) for M1 + M2 in post-shift urinary samples corresponding to a 20 ppm styrene concentration are proposed (GSTM1null: 1330 µg g(-1) creatinine, GSTM1+: 2878 µg g(-1) creatinine). Multivariate regression analyses were also performed and revealed that the presence of the rare CYP2E1*1B allele linked to TaqI polymorphism (A1/A2) was associated with increased urinary concentrations of metabolites from both pathways. Two previously described polymorphisms for the EPHX gene were also tested but seemed not really relevant for interpretation of biomarkers. In conclusion, while CYP2E1 genotyping, particularly assessment of the CYP2E1*1B allelic status, is useful for a more accurate interpretation of the concentration of urinary biomarkers, GSTM1 genotyping is absolutely necessary when considering a biological monitoring programme based on determination of urinary mercapturic acids.

Co-exposure to lead increases the renal response to low levels of cadmium in metallurgy workers

PURPOSE

Research on the effect of co-exposure to Cd and Pb on the kidney is scarce. The objective of the present study was to assess the effect of co-exposure to these metals on biomarkers of early renal effect.

METHODS

Cd in blood (Cd-B), Cd in urine (Cd-U), Pb in blood (Pb-B) and urinary renal biomarkers, i.e., microalbumin (μ-Alb), beta-2-microglobulin (β₂-MG), retinol binding protein (RBP), N-acetyl-β-d-glucosaminidase (NAG), intestinal alkaline phosphatase (IAP) were measured in 122 metallurgic refinery workers examined in a cross-sectional survey.

RESULTS AND CONCLUSIONS

The median Cd-B, Cd-U, Pb-B were: 0.8 μg/l (IQR = 0.5, 1.2), 0.5 μg/g creatinine (IQR = 0.3, 0.8) and 158.5 μg/l (IQR = 111.0, 219.3), respectively. The impact of Cd-B on the urinary excretion of NAG and IAP was only evident among workers with Pb-B concentrations ≥ 75th percentile. The association between Cd-U and the renal markers NAG and RBP was also evidenced when Pb-B ≥ 75th percentile. No statistically significant interaction terms were observed for the associations between Cd-B or Cd-U and the other renal markers under study (i.e., μ-Alb and β2-MG). Our findings indicate that Pb increases the impact of Cd exposure on early renal biomarkers.

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.

Carcinogenic potential of formaldehyde in occupational settings: a critical assessment and possible impact on occupational exposure levels

OBJECTIVES

To review epidemiological studies which led to a change in the classification of formaldehyde by the International Agency for Research on Cancer (IARC) in 2004 as well as studies published thereafter, with the objective to examine whether occupational exposure levels for formaldehyde should be adapted.

METHOD

Cohort and case-control studies investigating the association between occupational exposure to formaldehyde and nasopharyngeal cancer (NPC) and reporting estimates of formaldehyde exposure as well as the most recent meta-analyses, published after 1994, were reviewed.

RESULTS

Evidence of an association between occupational formaldehyde exposure and NPC appears debatable. Results of the cohort studied by Hauptmann et al. (Am J Epidemiol 159(12):1117-1130, 2004) were key findings in the IARC evaluation. In this study, mortality from NPC was elevated compared with that of the US general population. However, internal comparison analysis using alternative categorization revealed that none of the relative risk for NPC was statistically significantly increased in any category of exposure (Marsh and Youk in Regul Toxicol Pharmacol 42(3):275-283, 2005) and re-analyses of the data highlighted the inappropriateness of the exposure assessment used by Hauptmann et al. (Am J Epidemiol 159(12):1117-1130, 2004) and Marsh et al. (Regul Toxicol Pharmacol 47(1):59-67, 2007). Two other cohorts (Coggon et al. in J Natl Cancer Inst 95(21):1608-1615, 2003; Pinkerton et al. in Occup Environ Med 61(3)193-200, 2004) reported no increase in NPC. Two case-control studies brought some evidence of an increased risk of NPC but the assessment of exposure levels was uncertain.

DISCUSSION

Human studies fail to raise a convincing conclusion concerning the carcinogenicity of formaldehyde and are not helpful to delineate a possible dose-response relationship. Experimental data indicate that in rats, the carcinogenic activity of formaldehyde is associated with cytotoxic/proliferative mechanisms. Therefore protecting from these effects associated with formaldehyde exposure should be sufficient to protect from its potential carcinogenic effects, if any in humans.

CONCLUSION

Current occupational exposure levels to formaldehyde, set to protect against local irritation, should not be adapted.

CYP3A5 and ABCB1 polymorphisms and tacrolimus pharmacokinetics in renal transplant candidates: guidelines from an experimental study

Genetic polymorphisms in biotransformation enzyme CYP3A5 (6986G > A, CYP3A5*3; 14690A > G, CYP3A5*6) and drug transporter ABCB1 (1236C > T; 2677G > T/A; 3435C > T) are known to influence tacrolimus (Tac) dose requirements and trough blood levels in stable transplant patients. In a group of 19 volunteers selected with relevant genotypes among a list of 221 adult renal transplant candidates, we evaluated whether consideration of CYP3A5 and ABCB1 genetic polymorphisms could explain the interindividual variability in Tac pharmacokinetics after the first administration of a standard dose (0.1 mg/kg body weight twice a day). Lower area under the time versus blood concentration curves (AUC) or lower trough concentrations were observed among CYP3A5 expressors (n = 9) than among nonexpressors (n = 10) using two different analytical methods for Tac determination (liquid chromatography with tandem mass spectrometry (LC-MS/MS) and immunoassay). The median AUC(0-infinity) was 2.6- and 2.1-fold higher in nonexpressors for LC-MS/MS and immunologic methods, respectively. No difference was observed in Tac pharmacokinetic parameters in relation to ABCB1 polymorphisms. In conclusion, our study confirms the very significant effect of CYP3A5 polymorphism early after the first administration of Tac. It also provides a strong argument for a doubling of the loading dose in patients early identified a priori on the transplantation list as possessing at least one CYP3A5*1 allele.

Cadmium, lead and endometriosis

OBJECTIVES

Cadmium (Cd) and lead (Pb) have been demonstrated to exert endocrine disrupting activities. Their possible role in endometriosis, an oestrogen-dependent disease, is unknown.

METHODS

We compared cadmium urinary excretion (CdU) and blood concentration of cadmium (CdB) and lead (PbB) in 119 patients with peritoneal endometriosis and/or deep endometriotic (adenomyotic) nodules of the rectovaginal septum and 25 controls.

RESULTS

The mean levels of cadmium in urine and blood did not differ among the groups. Women suffering from endometriotic diseases showed lower levels of PbB than controls.

CONCLUSIONS

These data do not support a role for cadmium in the onset or the growth of endometriotic diseases but suggest a possible relationship with lead.

Mercapturic acids revisited as biomarkers of exposure to reactive chemicals in occupational toxicology: a minireview

A minireview is presented concerning the use of mercapturic acids as biological exposure index for electrophilic chemicals. Besides pure analytical aspects, this minireview considers possible issues in relation to (a) the added value of mercapturic acids as compared to other well validated biomarkers of exposure and (b) the high inter-individual variability in mercapturic acids excretion. Recent field and/or experimental studies confirm the usefulness of mercapturic acids as biological exposure index for electrophilic chemicals and suggest the interest of a toxicogenetic approach for a better interpretation of the results of biological monitoring.

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.

Kinetics of an intratracheally administered chromium catalyst in rats

Chromium-based catalysts are used for the synthesis of polyethylene, but little is known about the hazard and biomonitoring possibilities of this type of chromium for workers who may be occupationally exposed to such compounds. Therefore, the bioavailability and toxicokinetics of chromium were studied in male Wistar rats after a single intratracheal instillation (2 ml/kg body weight) of various doses (1, 5, or 25 mg/kg body weight) of the catalyst (approximately 1% chromium bound to an amorphous silica matrix), either before (CAT-Cr[III]) or after (CAT-Cr[VI]) heat treatment. The results were compared with those of equivalent amounts of two chromium salts (CrCl(3) and K(2) Cr(2) O (7). Each dose group was composed of three rats. The concentration of chromium was determined by atomic absorption spectrometry in urine (collected daily for 7 d) and in plasma, erythrocytes, lung, and liver tissue obtained 2 d (only highest concentration) and 7 d after dosing. On d 2, a significant increase in lung weight was found in the animals treated with the highest dose of the hexavalent Cr products. On d 7, on the basis of body weights, lung weights, and lung histology, there was no overt toxicity, except after the highest dose of CAT-Cr(VI). The elimination of all forms of chromium was apparently monoexponential, with calculated half-life elimination times in urine of 4-11 h for Cr(III) (CAT-Cr[III] and CrCl3 ) and 8-21 h for Cr(VI) (CAT-Cr[VI] and K(2) Cr(2) O(7). On d 2, the erythro-cytes Cr concentrations were significantly higher for the hexavalent Cr products than for the trivalent Cr products. After 7 d, the erythrocytes Cr concentrations were significantly increased above control values (3 microg/L) only in rats treated with the 2 highest doses of Cr( VI) compounds (12 and 64 microg/L for K(2) Cr(2) O(7), and 14 and 79 microg/L for CAT-Cr[VI]). The present study shows that intratracheally instilled Cr(VI) and Cr(III) have different toxicokinetic profiles and that the Cr(VI) catalyst has the same bioavailability and excretion kinetics as a water-soluble Cr(VI) salt. Exposure to chromium compounds could be monitored by measuring Cr concen-trations in urine (shortly after exposure) and in erythrocytes (also at later time points after high Cr[VI] exposure).

[Recent findings on the role of cytokines in the pathogenesis of interstitial pulmonary fibrosis]

Cytokines are important mediators of the pathogenesis of lung fibrosis. The experimental studies carried out in our laboratory have used a murine model of lung silicosis to explore the activity of interleukin-9, -10 and -12. The data presented in this short overview illustrate the pro-fibrotic activity of anti-inflammatory cytokines (IL-10), and the role of type 2 immune polarisation, as illustrated by the paradoxical effect of IL-9 and the activity of IL-12 p40 subunit.

The Coca-Cola incident in Belgium, June 1999

The present paper describes the outbreak of health complaints that occurred in Belgium, in June 1999, among schoolchildren and members of the general public in relation to the consumption of Coca-Cola and other soft drinks. The outbreak took place in the wake of a major food crisis, caused by PCB/dioxin contamination of animal feed, that had erupted shortly before. The clinical features (absence of serious poisoning) and epidemiological characteristics of the Coca-Cola outbreak pointed to mass sociogenic illness, and no subsequent toxicological or other data have refuted this hypothesis.

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.

Update on the genotoxicity and carcinogenicity of cobalt compounds

OBJECTIVE

To integrate recent understandings of the mechanisms of genotoxicity and carcinogenicity of the different cobalt compounds.

METHOD

A narrative review of the studies published since the last IARC assessment in 1991 (genotoxicity, experimental carcinogenesis, and epidemiology).

RESULTS

Two different mechanisms of genotoxicity, DNA breakage induced by cobalt metal and especially hard metal particles, and inhibition of DNA repair by cobalt (II) ions contribute to the carcinogenic potential of cobalt compounds. There is evidence that soluble cobalt (II) cations exert a genotoxic and carcinogenic activity in vitro and in vivo in experimental systems but evidence in humans is lacking. Experimental data indicate some evidence of a genotoxic potential for cobalt metal in vitro in human lymphocytes but there is no evidence available of a carcinogenic potential. There is evidence that hard metal particles exert a genotoxic and carcinogenic activity in vitro and in human studies, respectively. There is insufficient information for cobalt oxides and other compounds.

CONCLUSION

Although many areas of uncertainty remain, an assessment of the carcinogenicity of cobalt and its compounds requires a clear distinction between the different compounds of the element and needs to take into account the different mechanisms involved.

Insertion polymorphism of CYP2E1 and urinary N-methylformamide after N,N- dimethylformamide exposure in Japanese workers

OBJECTIVES

This study examined whether consideration of the *1C/*1D CYP2E1 insertion polymorphism is important for interpreting the biological monitoring of exposure to N,N-dimethylformamide (DMF) in Japanese workers.

METHODS

The insertion genotype, airborne DMF exposure on the last day of a work week, and NMF in urine sampled just after the last workshift of the week were determined in 44 male and female Japanese workers.

RESULTS AND CONCLUSIONS

The allelic frequency of this CYP2E1 polymorphism was 0.261 in this Japanese population of workers. The CYP2E1 insertion polymorphism did not contribute to NMF levels even after consideration of BMI or alcohol intake. The results indicate that CYP2E1 insertion polymorphism does not appear to be an important determinant for the interpretation of biological exposure to DMF by the measurement of urinary NMF.

Interstitial lung disease induced by exogenous agents: factors governing susceptibility

The purpose of this review is to describe the present state of knowledge regarding host susceptibility factors that may determine the occurrence, development and severity of interstitial lung disease (ILD) caused by exogenous agents. First, host susceptibility may pertain to differences in the delivery and/or persistence of the noxious agent in the lung. The deposition and clearance of inhaled particles or fibres may vary depending on innate anatomical or physiological characteristics, and on acquired changes, such as nasal disease or smoking-induced alterations. Genetically- or environmentally-induced interindividual differences in the expression of pulmonary biotransformation enzymes may form the basis for, or contribute to the risk of, drug-induced interstitial lung disease. Secondly, there are genetic and acquired variations in various enzymatic and nonenzymatic defence systems that protect cells and tissues against oxidative stress, which is often involved in the pathogenesis of interstitial lung disease caused by particles, fibres, metals, organic agents and drugs. Thirdly, the occurrence of immunological sensitization is dependent on both genetic and environmental factors. This has been demonstrated in chronic beryllium lung disease and in hypersensitivity pneumonitis. Fourthly, the propensity of individuals to develop particular types of inflammation, such as granulomas, is probably under genetic control. The regulation and resolution of inflammation and fibrogenesis caused by dust particles are also partly determined by genetic factors, involving cytokine networks and growth factors. In conclusion, although the issue of genetics pervades the entire discussion of host susceptibility, genes are not the only determinants of health and disease. Environmental factors may be equally important in shaping host susceptibility. Therefore, research must be focused on both the genetic bases and the environmental determinants of interstitial lung disease, in order to provide mechanism-based prevention strategies, early detection of, and improved therapy for these conditions.

Investigations on the liver toxicity of a blend of HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane) and HCFC-124 (2-chloro-1,1,1,2-tetrafluoroethane) in guinea-pigs

2,2-Dichloro-1,1,1-trifluoroethane (HCFC-123) has been developed as a substitute for ozone-depleting chlorofluorocarbons (CFCs). It is a structural analogue of halothane and similarities in the metabolic pathways and liver toxicity of both compounds have been described. The present study was initiated after an accidental outbreak of hepatitis in an industrial setting to examine whether concomitant exposure to 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), which is not hepatotoxic, could enhance the liver toxicity of HCFC-123. Male Hartley guinea-pigs were exposed for 4 h to 5,000 ppm HCFC-123 alone or blended with 5,000 ppm HCFC-124, either once (single exposure) or on 5 consecutive days (repeated exposure). The animals were killed either 24 or 48 h after the last exposure. A transient cytolytic action of HCFC-123 was evident by increased mean serum levels of alanine aminotransferase at 24 h and isocitrate dehydrogenase at 24 and 48 h, both after a single or repeated exposure. The liver toxicity of HCFC-123 was confirmed by pathological examination of liver tissue, which showed mild (foci of necrotic hepatocytes) to moderate (multifocal random degeneration and necrosis) damage. Steatosis was also observed and was more pronounced after repeated exposure than after single. One animal out of 6 that were repeatedly exposed to the blend and sacrificed at 24 h showed liver lesions similar to halothane hepatitis. Although a few other animals responded markedly in the blend-treated group, on average, no significant difference in the biochemical or pathological lesions was found between the groups treated with HCFC-123 alone or with the blend. Urinary excretion of trifluoroacetic acid and chlorodifluoroacetic acid increased dose-dependently upon exposure to HCFC-123 and indicated accumulation after repeated exposure. No difference in metabolite excretion was found between animals treated with HCFC-123 alone or blended with HCFC-124. Treatment with HCFC-123 depleted hepatic glutathione levels by about 40 and 25% after single and repeated exposure, respectively; the amplitude of this reduction was not modified by co-exposure to HCFC-124. In conclusion, this study confirmed the hepatotoxicity of HCFC-123, based on biochemical, histopathological and metabolite studies, and found only very limited indication of a potentiation by HCFC-124 of this hepatotoxic effect.

Interleukin-9 reduces lung fibrosis and type 2 immune polarization induced by silica particles in a murine model

We examined the effect of interleukin (IL)-9, a cytokine active on B and T lymphocytes and associated with bronchial asthma, on the development of lung fibrosis induced by crystalline silica particles. Therefore, we compared the response to silica (1 and 5 mg/animal, intratracheally) in transgenic mice that constitutively express high levels of IL-9 (Tg5) and their wild-type counterparts (FVB). At 2 and 4 mo after treatment with silica, histologic examination and measurement of lung hydroxyproline content showed that the severity of fibrosis was significantly less important in Tg5 mice than in their wild-type counterparts. Intraperitoneal injection of IL-9 in C57BL/6 mice also reduced the amplitude of silica-induced lung fibrosis. The reduction of lung fibrosis by IL-9 was associated with a significant expansion of the B-lymphocyte population, both in bronchoalveolar lavage (BAL) and in the pulmonary parenchyma. In wild-type animals, silica-induced fibrosis correlated with markers of a T helper 2-like response such as upregulation of IL-4 levels in lung tissue and an increased immunoglobulin (Ig) G1/IgG2a ratio in BAL. Immunohistochemical studies demonstrated that the upregulation of IL-4 associated with the development of fibrosis was mainly localized in inflammatory alveolar macrophages. In transgenic mice, the level of IL-4 in lung homogenates was not significantly affected by silica treatment, and a reduced IgG1/IgG2a ratio was observed upon treatment with silica. The levels of interferon-gamma were significantly decreased after silica treatment in both strains. Together, these observations point to an antifibrotic effect of IL-9 in pulmonary fibrosis associated with a limitation of the type 2 polarization which accompanies lung fibrosis.

Clues and uncertainties in the risk assessment of arsenic in drinking water

On the basis of studies of the prevalence of skin cancer among users of As-rich well water in Taiwan, WHO experts recommended in 1984 a maximum As concentration of 50 microg/litre in drinking water. Since that time, a plethora of non-cancer as well as cancer effects has been observed in several other populations sustaining a chronic exposure to various As concentrations in drinking water. This prompted a revision of the standard and a provisional guideline of 10 microg/litre was recommended in 1993. While the uncertainty linked to the statistical inferences leading to the guideline are reduced by the fact that they are directly estimated from human data and result from extrapolations made relatively close to observed exposure levels, developed guideline depends strongly on the choice of the dose-response model (linear, quadratic, hockey-stick) and the accuracy of the exposure data. The potential exposure to As sources other than drinking water, dietary habits and genetic characteristics of the populations may also make more difficult the inference of a recommendation for As concentration in drinking water. Owing to the huge cost of strongly reducing the current As in water standard, many efforts are presently made to clarify the quantitative aspects of As-induced cancers, particularly at low dose levels. New data on the metabolism and carcinogenic mechanism of As in humans along with the results of epidemiological studies presently under way in several countries will help to reduce the uncertainty in the risk assessment of As.

Epidemiological survey of workers exposed to inorganic germanium compounds

OBJECTIVES

To assess occupational exposure to inorganic germanium (Ge) in workers from a producing plant, and to assess the health of these workers, with a special focus on respiratory, kidney, and liver functions.

METHODS

Cross sectional study of 75 workers exposed to Ge and 79 matched referents. Exposure was characterised by measuring air and urine concentrations of the element during a typical working week, and health was assessed by a questionnaire, clinical examination, lung function testing, chest radiography, and clinical chemistry in serum and urine, including high and low molecular weight urinary proteins.

RESULTS

Airborne concentrations of Ge (inhalable fraction) ranged from 0.03 to 300 micrograms/m, which was reflected by increased urinary excretion of Ge (0.12-200 micrograms/g creatinine, after the shift at the end of the working week). Lung, liver, and haematological variables were not significantly different between referents and workers exposed to Ge. A slightly higher urinary concentration of high molecular weight proteins (albumin and transferrin) was found in workers exposed to Ge, possibly reflecting subclinical glomerular changes. No relation was found between the intensity or duration of exposure and the urinary concentration of albumin. No difference between referents and workers exposed to Ge was found for other renal variables.

CONCLUSIONS

Measurement of urinary Ge can detect occupational exposure to inorganic Ge and its compounds. It is prudent to recommend the monitoring of renal variables in workers exposed to Ge.

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.

Renal effects of low-level environmental cadmium exposure: 5-year follow-up of a subcohort from the Cadmibel study

BACKGROUND

The clinical relevance of renal effects of cadmium in people exposed in the environment remains uncertain. This study examined the evolution of renal effects observed in a population exposed to cadmium in the environment.

METHODS

208 men and 385 women surveyed in 1985-89 (Cadmium in Belgium study [Cadmibel]; baseline) were re-examined on average 5 years later (Public health and environmental exposure to cadmium study [PheeCad]; follow-up). Urinary and blood cadmium and markers of renal tubular dysfunction and glomerular effects were measured. The association between cadmium body burden and renal factors was examined by multivariate logistic and linear regression.

FINDINGS

In men, mean urinary cadmium excretion and blood cadmium concentration measured at follow-up were 7.5 nmol/24 h (SD 1.9) and 6.1 nmol/L (2.2), reductions of 16% and 35% from baseline, respectively. In women, the corresponding values were 7.6 nmol/24 h (1.9) and 7.8 nmol/L (2.1), reductions of 14% and 28% from baseline. No indication of progressive renal damage was found and the overall results suggest that the effects of low environmental exposure to cadmium on the kidney are weak, stable, or reversible.

INTERPRETATION

Subclinical renal effects that have been reported in Belgium in patients with increased cadmium body burden are not associated with progressive renal dysfunction and most likely represent non-adverse manifestations.

Sulfur mustard upregulates the expression of interleukin-8 in cultured human keratinocytes

Although the morphological description of sulfur mustard (SM) injury is well characterised, little is known of the molecular mediators involved in cutaneous toxicity. Since infiltration by lymphocytes and PMNs represents one of the very first events observed in vivo upon exposure to SM, this study examined whether SM exposure can modify the expression by cultured human keratinocytes of interleukin-8, one of the most important chemoattractants for polymorphonuclear leukocytes (PMNs) in humans. Conditioned medium harvested from control keratinocyte cultures showed a gradual accumulation of this cytokine over time followed by a levelling off after 12 hours. Upon treatment with 10(-6) and 10(-5) M SM, no significant difference compared to the control situation was observed. After 6 h, a significantly higher amount of IL-8 was secreted by human keratinocytes treated with 10(-4) M SM and the accumulation of the cytokine persisted up to 24 h after exposure. The expression of IL-8 mRNA was assessed semi-quantitatively (RT-PCR) at the same time points in control and SM-treated (10(-4) M) human keratinocytes. When compared to control cultures, a clear upregulation of IL-8 mRNA levels was observed 6 and 12 h after SM exposure, which is consistent with the secretion pattern of the protein. The present observation indicates that increased secretion of IL-8 by human keratinocytes represents an early event of the inflammatory reaction following SM which is coherent with the reported delay in the recruitment of lymphocytes and PMNs observed in vivo.

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.