Renal tubular function of workers exposed to low levels of cadmium

Cadmium Monitoring at the Workplace: Effectiveness of a Combination of Air- and Biomonitoring

Inhalation exposure to cadmium at the workplace has been associated with an increased risk of lung cancer and non-cancer respiratory effects. To ensure levels of cadmium remain below effect levels, air quality is monitored and regulations specifying an air limit value are implemented. The EU Carcinogens and Mutagens Directive of 2019 recommended values for the inhalable fraction and the respirable fraction but the latter only for a transitional period. Cadmium exposure has also been associated with systemic effects, following its storage in the kidneys and due to its long half-life. The accumulation of cadmium occurs via different exposure routes and from different sources, including workplace dust and fumes, food, and smoking. Biomonitoring (in blood, urine) has been identified as the most appropriate method to follow up cumulative exposure and total cadmium body burden, as it conveniently reflects intakes by all routes. However, it is not systematically implemented. This paper has a double objective: first, proposing a possible limit value for the respirable fraction, using an approach integrating epidemiological data. Secondly, demonstrating that the implementation of both air and biological limit values is key to protecting workers' health in occupational settings. The paper summarizes the current knowledge on cadmium health effects and how biomarkers reflect those. It presents an approach to derive a respirable value, using recent human data, and describes how the combination of air monitoring and biomonitoring is applied by the EU industry to protect the workforce. While a respirable fraction value helps protect workers against local respiratory adverse health effects, air monitoring alone is not sufficient to protect workers against systemic effects of cadmium. Therefore, complementary biomonitoring and the implementation of a biological limit value is recommended.

Nephrotoxic Biomarkers with Specific Indications for Metallic Pollutants: Implications for Environmental Health

Environmental and occupational exposure to heavy metals and metalloids is a major global health risk. The kidney is often a site of early damage. Nephrotoxicity is both a major consequence of heavy metal exposure and potentially an early warning of greater damage. A paradigm shift occurred at the beginning of the 21st century in the field of renal medicine. The medical model of kidney failure and treatment began to give way to a social model of risk factors and prevention with important implications for environmental health. This development threw into focus the need for better biomarkers: markers of exposure to known nephrotoxins; markers of early damage for diagnosis and prevention; markers of disease development for intervention and choice of therapy. Constituents of electronic waste, e-waste or e-pollution, such as cadmium (Cd), lead (Pb), mercury (HG), arsenic (As) and silica (SiO₂) are all potential nephrotoxins; they target the renal proximal tubules through distinct pathways. Different nephrotoxic biomarkers offer the possibility of identifying exposure to individual pollutants. In this review, a selection of prominent urinary markers of tubule damage is considered as potential tools for identifying environmental exposure to some key metallic pollutants.

Estimation of Benchmark Dose of Cumulative Cadmium Exposure for Renal Tubular Effect

Objectives: The aim of this study was to determine the no observed adverse effect level (NOAEL), the lowest observed adverse effect level (LOAEL) and the benchmark dose low (BMDL) of cadmium exposure by re-evaluation of the dose–response relationship between cumulative cadmium exposure and renal tubular damage reported previously. Methods: The participants were workers (326 men and 114 women) employed for at least three months between 1931 and 1982. Blood cadmium (Cd-B) and air cadmium (Cd-A) were collected at regular intervals with urinary β2-microglobulin as the tubular effect marker. Cumulative Cd-A and Cd-B were estimated by multiplying concentration and working period. The BMDL was calculated using Benchmark Dose Software (version 3.1.2). The benchmark response (BMR) was set at 5% or 10%. Results: By logistic regression, the NOAEL of mean cumulative Cd-B was 7122 months nmol/L. The LOAEL of cumulative Cd-A and least-squares cumulative Cd-B was 691 yrs μg/m³ and 8586 months nmol/L, respectively. Among various models for dose–response relationships, a probit model was adopted as the best fitting model. The obtained BMDLs of cumulative Cd-A were 272.3 yrs µg/m³ (BMR5%) and 707.5 yrs µg/m³ (BMR10%). The BMDLs of mean cumulative Cd-B were 3967.2 months nmol/L (BMR5%) and 7798.1 months nmol/L (BMR10%). The BMDLs of least-squares cumulative Cd-B were 3588.6 months nmol/L (BMR5%) and 8616.3 months nmol/L (BMR10%). Assuming a working period of 40 years, the BMDLs for BMR10% corresponded to 17.7 µg/m³ (Cd-A) and 1.8~2.0 µg/L (Cd-B). Discussion: This study provides new valuable information to enhance the reliability of limit values and thereby make a significant contribution to preventing the health effects of Cd in exposed workers.

Chronic Low-Dose Cadmium Exposure Impairs Cutaneous Wound Healing With Defective Early Inflammatory Responses After Skin Injury

Impairment of the immune system is a developing concern in evaluating the toxicity of cadmium (Cd). In the present study, we investigated if Cd could impair cutaneous wound healing through interfering with inflammation after injury. We found that exposure of mice to CdCl2 through drinking water at doses of 10, 30, and 50 mg/l for 8 weeks significantly impaired cutaneous wound healing. Chronic 30 mg/l CdCl2 treatment elevated murine blood Cd level comparable to that of low dose Cd-exposed humans, had no effect on blood total and differential leukocyte counts, but reduced neutrophil infiltration, chemokines (CXCL1 and CXCL2), and proinflammatory cytokines (TNFα, IL-1β, and IL-6) expression in wounded tissue at early stage after injury. Wounded tissue homogenates from CdCl2-treated mice had lower chemotactic activity for neutrophils than those from untreated mice. Mechanistic studies showed that chronic Cd treatment suppressed ERK1/2 and NF-κB p65 phosphorylation in wounded tissue at early stage after injury. Compared with neutrophils isolated from untreated mice, neutrophils from CdCl2 treated mice and normal neutrophils treated with CdCl2 invitro both had lower chemotactic response, calcium mobilization and ERK1/2 phosphorylation upon chemoattractant stimulation. Collectively, our study indicate that chronic low-dose Cd exposure impaired cutaneous wound healing by reducing neutrophil infiltration through inhibiting chemokine expression and neutrophil chemotactic response, and suppressing proinflammatory cytokine expression. Cd may suppress chemokine and proinflammatory expression through inactivating ERK1/2 and NF-κB, and inhibit neutrophil chemotaxis by attenuating calcium mobilization and ERK1/2 phosphorylation in response to chemoattractants.

Effect of Occupational Cadmium Exposure on Parathyroid Gland

BACKGROUND

Cadmium (Cd) is used in many industries. High-level exposure is associated with severe kidney and bone damage.

AIM

This study investigates the possible effect of occupational cadmium exposure on parathyroid gland and some minerals in workers.

METHODS

Environmental air monitoring of cadmium was done. Serum and urine cadmium levels, kidney function, some minerals, and plasma parathormone were estimated in the studied groups.

RESULTS

The exposed workers had significantly higher Cd concentration in serum and urine than controls. The mean levels of plasma parathyroid hormone, serum phosphorus and magnesium were significantly lower among the exposed group. However, the mean levels of serum creatinine and calcium were significantly higher in the same group when compared to referents. There was a significant positive correlation between Cd concentration in the serum and urine for the exposed group. The biological Cd exposure indices correlated positively with serum calcium and negatively with plasma PTH level. The prevalence of musculoskeletal complaints, bone ache, joint pain and muscle spasm were more prevalent among the exposed workers compared with the controls with odds ratio 4.316, 3.053 and 3.103 respectively.

CONCLUSIONS

Occupational cadmium exposure has an adverse effect on PTH level and serum human minerals.

Possible influence of delta-aminolevulinic acid dehydratase polymorphism and susceptibility to renal toxicity of lead: a study of a Vietnamese population

We examined six newly identified polymorphisms in the delta-aminolevulinic acid dehydratase (ALAD) single-nucleotide polymorphisms (SNPs) to determine if these SNPs could modify the relationship between blood lead (PbB) and some renal parameters. This is a cross-sectional study of 276 lead-exposed workers in Vietnam. All workers were measured for PbB, urinary retinol-binding protein (URBP), urinary alpha1-microglobulin (Ualpha1m), urinary beta2-microglobulin (Ubeta 2m), urinary N-acetyl-beta -d-glucosaminidase (NAG), urinary aminolevulinic acid (ALAU), serum alpha1-microglobulin (Salpha1m), serum beta2-microglobulin (Sbeta 2m), and urinary albumin (Ualb). The six SNPs were Msp and Rsa in exon 4, Rsa39488 in exon 5, HpyIV and HpyCH4 in intron 6, and Sau3A in intron 12. Analysis of covariance (ANCOVA) with interaction of PbB times SNPs were applied to examine modifying effect of the SNPs on the association of renal parameters and PbB, adjusting for potential confounders of age, gender, body mass index, and exposure duration. HpyCH4 was found to be associated with certain renal parameters. For HpyCH4 1-1, an increase of 1 microg/dL PbB caused an increase of 1.042 mg/g creatinine (Cr) U alpha1m, 1.069 mg/g Cr Ubeta 2m, 1.038 mg/g Cr URBP, and 1.033 mg/g Cr Ualb, whereas in HpyCH4 1-2, an increase of 1 microg/dL PbB resulted in an increase of only 1.009 mg/g Cr Ualpha1m, 1.012 mg/g Cr Ubeta 2m, 1.009 mg/g Cr URBP, and 1.007 mg/g Cr Ualb. HpyCH4 SNP appeared to modify the lead toxicity to kidney with wild-type allele being more susceptible than variants. The mechanism for this effect is not clear. Further studies are needed to confirm this observation.

Land contamination and urinary abnormalities: cause for concern?

AIMS

To determine the prevalence of proteinuira and enzymuria among a cohort of subjects exposed to hexachlorobutadiene (HCBD) in their homes and to determine whether there was a change in observed effects when exposure ceased.

METHODS

Residents underwent a health check, which included a panel of urinary markers of both glomerular and tubular origin, within two months of cessation of long term exposure to HCBD and again at least 10 months after exposure ceased. Analysis of the results was performed to determine if there was any early evidence of renal effects, and to ascertain whether changes in these parameters occurred after exposure to HCBD ceased.

RESULTS

Tubular proteinuria and enzymuria were increased in the initial health check and significantly decreased after the residents had left their homes for about 10 months. As the early renal tubular markers improved when exposure ceased it is anticipated that the long term nephrotoxic risk will be minimal, but the carcinogenic risk remains unknown.

CONCLUSIONS

Results show there was a renal effect which improved when subjects left their homes. This suggests there was a local environmental factor responsible for the observations. This is consistent with the predicted toxicological effects of HCBD from animal studies.

Effects of exposure to low levels of environmental cadmium on renal biomarkers

We conducted a study among residents of a small community contaminated with heavy metals from a defunct zinc smelter and residents from a comparison community to determine whether biologic measures of cadmium exposure were associated with biomarkers of early kidney damage. Creatinine-adjusted urinary cadmium levels did not differ between the smelter and comparison communities; thus we combined individuals from both communities (n = 361) for further analyses. The overall mean urinary cadmium level was low, 0.26 microg/g creatinine, similar to reference values observed in the U.S. general population. For children ages 6-17 years, urinary concentration of N-acetyl-beta-D-glucosaminidase (NAG), alanine aminopeptidase (AAP), and albumin were positively associated with urinary cadmium, but these associations did not remain statistically significant after adjusting for urinary creatinine and other potential confounders. For adults ages 18 or older, urinary concentration of NAG, AAP, and albumin were positively associated with urinary cadmium. The associations with NAG and AAP but not with albumin remained statistically significant after adjusting for creatinine and other potential confounders. We found a positive dose-effect relationship between levels of creatinine-adjusted urinary cadmium and NAG and AAP activity, and statistically significant differences in mean activity for these two enzymes between the highest (> or =1.0 microg cadmium/g creatinine) and the lowest (< or =0.25 microg cadmium/g creatinine) exposure groups. The findings of this study indicate that biologic measures of cadmium exposure at levels below 2.0 microg/g creatinine may produce measurable changes in kidney biomarkers.

New approaches for detecting thresholds of human nephrotoxicity using cadmium as an example

Damage to the kidneys is one of the primary toxic actions of metals. Nephrotoxic substances not only cause renal disease directly, but they can also destroy renal reserve capacity, potentially placing those people with additional risk factors, such as diabetes, hypertension, cardiovascular disease, and genetic predispositions, at greater risk. To detect nephrotoxicity in people at a stage where intervention can be effective, sensitive methods are needed. One of the major advantages of using sensitive biomarkers of renal damage is that people who may be particularly susceptible to renal damage can be identified early, at a reversible stage of damage, and the progression to end-stage renal disease may be halted or delayed. Various categories of tests can be used to detect effects of nephrotoxic substances on the kidney. Through the use of biomarkers of damage to various parts of the nephron, U.S. and European studies have both shown a similar pattern of damage among men occupationally exposed to cadmium. These studies indicate various thresholds of renal effects, which researchers suggest represent a cascade of progressively severe damage to the kidney. Research into new biomarkers of damage caused by exposure to nephrotoxic substances centers around mechanisms of cell death, including necrosis and apoptosis; mechanisms of cell growth, regeneration, and proliferation, including factors that control cell cycle, influence gene expression, and modulate nucleic acid synthesis; and genetic factors that increase susceptibility to renal disease. Examples of types of candidate biomarkers include cytokines, lipid mediators, growth factors, transcription factors and protooncogenes, extracellular matrix components (collagen, glycoproteins, and proteoglycans), and cell adhesion molecules. Research into new categories of biomarkers may provide additional insights into the mechanisms of damage caused by nephrotoxins.

T cells reactive to an inducible heat shock protein induce disease in toxin-induced interstitial nephritis

T cells reactive against immunodominant regions of inducible heat shock proteins (HSPs) have been identified in the chronic inflammatory lesions of several experimental autoimmune diseases. Since HSPs are known to be induced by a number of renal tubular epithelial cell toxins associated with chronic interstitial nephritis, we investigated the relevance of HSP expression and T cell reactivity to HSP70 in a model of progressive inflammatory interstitial nephritis. Chronic administration of cadmium chloride (CdCl2) to SJL/J mice induces HSP70 expression in renal tubular cells 4-5 wk before the development of interstitial mononuclear cell infiltrates. CdCl2 also induces HSP70 expression in cultured tubular epithelial cells from SJL/J mice. CD4+, TCR-alpha/beta+ T cell lines specific for an immunodominant HSP peptide are cytotoxic to heat stressed or CdCl2-treated renal tubular cells. Such HSP-reactive T cells mediate an inflammatory interstitial nephritis after adoptive transfer to CdCl2-treated mice at a time when immunoreactive HSP70 is detectable in the kidneys, but before the development of interstitial mononuclear cell infiltrates. T cells isolated from the nephritic kidneys of mice treated with CdCl2 for 13 wk are also cytotoxic to heat shocked or cadmium-treated tubular cells. These kidney-derived T cells additionally induced interstitial nephritis after passive transfer, indicating their pathogenic significance. Our studies strongly support a role for HSP-reactive T cells in CdCl2-induced interstitial nephritis and suggest that the induction of HSPs in the kidney by a multitude of "non-immune" events may initiate or facilitate inflammatory damage by HSP-reactive lymphocytes.

Urinary N-acetyl-beta-D-glucosaminidase activity in workers exposed to inorganic lead

Urinary N-acetyl-beta-D-glucosaminidase (NAG) had been shown to be a useful early marker of renal injury. In workers exposed to lead it seems to be the only early marker but the dose response and dose effect relations are weak. Furthermore, the significance and underlying mechanism of increased urinary NAG activity is far from clear. By studying the isoenzyme profiles of urinary NAG, the significance and underlying mechanism may be further clarified. The heat labile (NAG-A) and heat stable (NAG-B) isoenzyme profiles of 128 workers exposed to lead from a lead stabiliser factory were analysed. NAG activity was expressed as total NAG, NAG-A, and NAG-B activity as well as ratios (NAG-B/total NAG and NAG-B/NAG-A). Exposure indices included the recent concentration of blood lead (BPb), a cumulative blood lead index (TBPb), and the recent change in concentration of blood lead (CBPb). The NAG indices correlated best with CBPb. Nearly 50% of the variation in NAG-B activity could be explained by the combination of all three exposure indices but only the CBPb was highly significant. When these exposure indices were entered separately into the regression equation, CBPb accounted for 36.3% of the variation in NAG-B activity, 5.7% was accounted for by TBPb and 2.7% by BPb. There was also no dose-effect or dose-response relation between the NAG variables and BPb or TBPb groups. With CBPb, there were dose-effect and dose-response relations. With CBPb, there was an increase in NAG variables in the group with more than 25% increase in blood lead over the past six months. The increase in NAG activity in this study is likely to be due to a recent increase in concentration of blood lead and hence presumably a recent rise in renal burden of inorganic lead. This suggests that the increase in urinary NAG activity is a form of acute response to a sharp increase in renal burden of lead, rather than to a cumulative dose. Heat stable NAG is part of the lysosomal membrane and is present in the urine when there is breakdown of lysosomes. Our data therefore contradict suggestions that the increase in urinary NAG activity is due to exocytosis.

A nine year follow up study of renal effects in workers exposed to cadmium in a zinc ore refinery

Renal changes with time have been studied in 14 workers engaged in the production of cadmium (Cd) in a zinc ore refinery. These workers were examined once a year in the period 1980 to 1985 and 13 of them also in 1989. Four of the workers (group A) had been employed in an old Cd plant before 1973 and had received higher exposures to Cd than the other workers (group B). Average urinary Cd concentrations over the whole study period in workers of group A ranged from 6.9 to 9.2 micrograms/g creatinine (median 8.4 micrograms/g) and in workers of group B from 0.64 to 7.1 micrograms/g creatinine (median 1.9 micrograms/g). Renal effects were assessed by the determination of urinary N-acetyl-beta-D-glucosaminidase (NAG), beta 2-microglobulin (beta 2-M), retinol binding protein, albumin, total protein, and serum creatinine concentrations and activity. Urinary beta 2-M concentrations in three of four workers of group A were close to or marginally above the upper normal limit during the study period. The beta 2-microglobinuria was not, however, progressive. No values outside normal limits were detected for any of the other renal tests in workers of groups A and B, related to exposure to Cd. Dose-response relations showed that urinary Cd correlated significantly with urinary NAG activity and total protein and beta 2-M. The earliest change induced by Cd was seen for urinary NAG activity within normal limits of NAG excretion. The regression lines were similar in the surveys between 1981 and 1989, indicative of no progression to higher values for any of the renal tests. The current biological exposure index (BEI) of 10 micrograms/g creatinine for workers exposed to Cd, set by the American Conference of Governmental Industrial Hygienists (ACGIH), therefore seems justified, although the safety margin is small. The World Health Organisation recommended limit and ACGIH (1992-3) proposed limit of 5 micrograms/g creatinine would provide a much larger safety margin, and could be regarded as an action point for increased health surveillance.

Markers of early renal changes induced by industrial pollutants. III. Application to workers exposed to cadmium

Cadmium (Cd) was the third heavy metal investigated in the European collaborative research project on the development and validation of new markers of nephrotoxicity. Fifty workers exposed to Cd and 50 control workers were examined. After application of selection criteria 37 workers (mean age 43) exposed to Cd for an average of 11.3 years; and 43 age matched referents were retained for final analysis. The average concentrations of Cd in blood (Cd-B) and urine (Cd-U) of exposed workers were 5.5 micrograms Cd/l and 5.4 micrograms Cd/g creatinine respectively. By contrast with lead and mercury, Cd had a broad spectrum of effects on the kidney, producing significant alterations in amounts of almost all potential indicators of nephrotoxicity that were measured in urine--namely, low and high molecular weight proteins, kidney derived antigens or enzymes, prostanoids, and various other biochemical indices such as glycosaminoglycans and sialic acid. An increase in beta 2-microglobulin and a decrease of sialic acid concentration were found in serum. Dose-effect/response relations could be established between most of these markers and Cd-U or Cd-B. The thresholds of Cd-U associated with a significantly higher probability of change in these indicators were estimated by logistic regression analysis. Three main groups of thresholds could be identified: one around 2 micrograms Cd/g creatinine mainly associated with biochemical alterations, a second around 4 micrograms Cd/g creatinine for high molecular weight proteins and some tubular antigens or enzymes, and a third one around 10 micrograms Cd/g creatinine for low molecular weight proteins and other indicators. The recent recommendation by the American Conference of Governmental Industrial Hygienists (ACGIH) of 5 micrograms Cd/g creatinine in urine as the biological exposure limit for occupational exposure to Cd appears thus justified, although for most of the effects occurring around this threshold the link with the subsequent development of overt Cd nephropathy is not established. In that respect, the very early interference with production of some prostanoids (threshold 2 micrograms Cd/g creatinine) deserves further investigation; although this effect might contribute to protect the filtration capacity of the kidneys, it might also play a part in the toxicity of Cd on bone.

Concentrations of heavy metals in maternal and umbilical cord blood

Concentrations of lead, cadmium, methylmercury and total mercury were measured in maternal and umbilical cord blood using graphite atomic absorption spectrometry. Two essential metals, copper and zinc, were also determined using ion chromatography. Lead, copper and zinc were found to be lower in the cord blood whereas methylmercury and total mercury were higher in cord blood than in maternal blood. Little differences were noted for cadmium in maternal and cord blood. Significant positive correlations were observed between the concentrations in maternal and cord blood with regard to lead (correlation coefficient, r = 0.44), copper (r = 0.34), zinc (r = 0.29), methylmercury (r = 0.44) and total mercury (r = 0.58). These results suggest that, like essential metals, most heavy metals can move rather freely across the human placenta. The potential health effects of heavy metal transfer from mothers to young infants cannot be discounted.