Renal function of workers with low-level cadmium exposure

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.

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.

Efficacy of Crocus sativus L. on reduction of cadmium-induced toxicity on spermatogenesis in adult rats

Cadmium is a toxic heavy metal element, which probably cause infertility by impairment in spermatogenesis. The present work aimed (i) to study the toxic effect of cadmium on spermatogenesis in rat, as well as (ii) the protective effect of Crocus sativus L. on cadmium-intoxicated rats. Cadmium chloride was administered intraperitoneally during 16 days at intervals of 48 h between subsequent treatments. Crocus sativus L. was pre-treated in both of control and cadmium-injected rats. Animals were sacrificed on day 17 after the first treatment. The left cauda epididymis was removed and immediately immersed into Hank's balanced salt solution for the evaluation of sperm count and viability, and left testis was fixed in 10% formalin for histological evaluation. Following contamination with cadmium, a decrease was observed in the number and viability of cauda epididymis sperm, which were increased by Crocus sativus L. pre-treatment (P < 0.05). In addition, cadmium decreased both cell proliferation and Johnsen Scores in the seminiferous tubules, which were reversed by Crocus sativus pre-treatment (P < 0.05). Furthermore, cadmium-induced decrease in the amount of free serum testosterone as well as an increase in lipid peroxidation activity in the testicular tissue was reversed by Crocus sativus L. (P < 0.05). These findings may support the concept that Crocus sativus L. can improve the cadmium toxicity on spermatogenesis.

Effects of alpha-tocopherol on cadmium-induced toxicity in rat testis and spermatogenesis

Cadmium is known to exert toxic effects on multiple organs, including the testes. To determine if alpha-tocopherol, an antioxidant, could protect testicular tissues and spermatogenesis from the toxic effects of cadmium, six-week old male Sprague-Dawley rats were randomized to receive cadmium at doses of 0 (control), 1, 2, 4 or 8 mg/kg by the intraperitoneal route (Group A) or alpha-tocopherol for 5 days before being challenged with cadmium (Group B) in an identical dose-dependent manner. When both groups received cadmium at 1 mg/kg, there were no changes in testicular histology relative to controls. When Group A received cadmium at 2 mg/kg, undifferentiated spermatids and dead Sertoli cells increased in the seminiferous tubules while interstitial cells decreased and inflammatory cells increased in the interstitial tissues. On flow cytometric analysis, the numbers of elongated spermatids (M1) and round spermatids (M2) decreased while 2c stage cells (M3, diploid) increased. In contrast, when Group B received cadmium at 2 mg/kg, the histological insults were reduced and the distribution of the germ cell population remained comparable to controls. However, alpha-tocopherol had no protective effects with higher cadmium doses of 4 and 8 mg/kg. These findings indicate that alpha-tocopherol treatment can protect testicular tissue and preserve spermatogenesis from the detrimental effects of cadmium but its effectiveness is dependent on the dose of cadmium exposed.

Effect of chronic cadmium exposure on VEP and EEG spectral components

Pregnant swiss albino rats were divided to three groups as control (C), cadmium (Cd) and non-cadmium (NCd) groups. Control animals were received tap water while the rats of Cd group were received Cd as CdC12 in their drinking water during the experimental period. On the other hand, the NCd group was given Cd during pregnancy, but given tap water after birth. Twenty-two days after birth, fourteen rats (for each group) were taken from their mothers and continued to be treated with Cd (Cd group) or tap water (C and NCd groups) for an additional 38 days. After the experimental period, flash VEPs and EEGs of three groups were recorded and amplitude spectral analysis was computed by Transient Response-Frequency characteristics (TRFC) method. The mean amplitude (dB) of 1-3.5 and 14-20 Hz frequency bands for right response whereas 1-3.5, 4-7, 8-13 and 14-20 Hz frequency bands for left response of VEPs were decreased in Cd group compared with control group. On the other hand, significant differences were observed between Cd and control groups in all the frequency bands of EEGs except 6-8 Hz.

Cadmium induced alterations in somatosensory evoked potentials

Pregnant Swiss albino rats were divided into three groups: control (C), cadmium (Cd) and non-cadmium (NCd) groups. Control animals received tap water; the Cd rats received Cd as CdCl2 in their drinking water during the experimental period, while the NCd group was given Cd during pregnancy, and given tap water after birth. Twenty-two days after birth, 15 rats (for each group) were taken from their mothers and continued to be treated with Cd (Cd group) or tap water (C and NCd groups) for an additional 38 days. After the treatment period, somatosensory evoked potentials (SEPs) of the three groups were recorded from central (Cz) referenced to frontal (Fz) following left posterior tibial nerve (PTN) stimulation. Amplitude spectra of SEPs were computed by fast Fourier transform (FFT) algorithm. There was a significant amplitude decrease in 1-3.5 Hz in the NCd group and 1-3.5 and 14-20 Hz frequency bands of the Cd group compared with the control group.

Association between NAG-B and cadmium in urine with no evidence of a threshold

OBJECTIVES

To explore the significance of the increase in urinary excretion of the lysosomal enzyme beta-N-acetylglucosaminidase (NAG) at low exposures to cadmium (Cd) that is frequently found in the absence of any other sign of renal dysfunction.

METHODS

The activity was measured of the two main isoenzymes of NAG (NAG-A secreted by exocytosis and NAG-B released with cell membranes) in the urine of 49 male workers employed in a Cd smelter and of 20 age matched controls.

RESULTS

An increased urinary excretion of low molecular weight proteins was noted only in subjects who excreted > 10 micrograms Cd/g creatinine. The urinary activity of NAG-B showed a dose related increase that was already significant in the group excreting 0.5-2 micrograms Cd/g creatinine. In multiple regression analysis the NAG-B activity correlated with the excretion of Cd but not with that of lead or mercury. The NAG-A activity was by contrast unaffected by exposure to Cd but correlated with the urinary excretion of lead and copper.

CONCLUSIONS

As NAG-B is considered to be the lesional form of NAG, the existence of a specific association between this enzyme and urinary Cd excretion with no detectable threshold suggests that this metal produces cellular alterations at exposures commonly found in the general population.

Role of lipid peroxidation in cadmium-induced impairment of the gastric mucosal barrier

Peroxidative tissue damage has been reported to contribute to several pathological disorders. Despite high exposure to both exogenous and endogenous oxidant stress, the strong cell defence mechanism of the gastric mucosa protects mucosal epithelial cells against these noxious stimuli. However, some environmental factors involved in lipid peroxidation (such as cadmium), which disrupt gastric mucosal protection, may impair the mucosal barrier and facilitate the occurrence of gastric ulcers. In an experimental study to investigate this hypothesis, the level of cadmium-induced lipid peroxidation products (TBARS) and an antioxidant enzyme (SOD) were investigated. The mucin content (P < 0.01) and prostaglandin levels (P < 0.05) of mucosa as components of the gastric mucosal barrier were found to be significantly reduced in rats exposed to 15 ppm of cadmium in water for 30 days when compared with those of unexposed controls. TBARS levels in blood (P < 0.05) and mucosa (P < 0.001) increased markedly in cadmium-exposed animals whereas blood SOD levels remained unchanged. The significant correlation between TBARS and mucosal cadmium (r = 0.664, P < 0.01), as well as between cadmium and PGE2 (r = -0.719, P < 0.01), led to the conclusion that cadmium-induced lipid peroxidation is involved in the increased vulnerability of gastric mucosa to injurious stimuli in rats. This susceptibility may be responsible for the high incidence of stress-induced gastric ulcer in the population.

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.

Subclinical affection of liver and kidney function and solvent exposure

The role of solvents as hepato- and nephrotoxic agents under present-day exposure levels is still unclear. The purpose of this study involving 99 metal degreasers was to examine dose-response relationships between long-term exposure of mainly trichloroethylene and a battery of liver function tests and one nephrotubular enzyme test. Serum gamma-glutamyltransferase and urinary N-acetyl-beta-glucosaminidase were elevated by increasing solvent exposure at bivariate level. The significance of this relationship, however, was not able to withstand a multiple regression analysis, with age and alcohol abuse as confounding variables. The conclusion is that of a nonsignificant association between solvent exposure and tests screening for early liver and kidney dysfunction.

Assessment of occupational exposure to cadmium in The Netherlands, 1980-1989

One thousand five hundred fifty urine samples and 1,295 blood samples, collected from 919 workers, were analyzed for cadmium (Cd). The workers were employed at 16 different types of workplaces. In about 7.5% of the samples, the concentration of Cd exceeded the biological limit values proposed by the Dutch Expert Committee for Occupational Standards. Levels higher than these values were measured in both urine samples and blood samples of workers involved in electrochemical plating, in production of Cd-stabilizers and enamels, and in soldering with silver-cadmium solder. Significantly higher concentrations of beta 2-microglobulin (MG) were found in urine samples with CdU greater than 10 micrograms/g creatinine. Cd levels in urine increased with age.

Studies on lipid peroxidation in rat tissues following administration of low and moderate doses of cadmium chloride

The susceptibility to lipid peroxidation (LPO) of liver, kidneys, brains, lungs, heart, and testes was assessed in rats administered intraperitoneally with various doses of cadmium (Cd). Dose-response studies were carried out with male Long Evans rats (12-week-old; 300 +/- 33 g) injected with 25, 125, 500, and 1250 micrograms Cd/kg as CdCl2 and sacrificed after 24 h. In time-response studies, animals were administered with 25 and 500 micrograms Cd/kg as CdCl2 and sacrificed after 2, 6, 12, 24, and 72 h. Exposure of rats to low and moderate doses of Cd by the intraperitoneal route stimulated LPO in all the tissues investigated as assessed by the measurement of thiobarbituric acid reactive substances (TBARS). Lungs and brain were the most responsive, and these tissues and liver displayed early responses following Cd exposure. Comparison of LPO to various tissue indicators (for liver: alanine aminotransferase (ALT), sorbitol dehydrogenase (SDH), alkaline phosphatase (ALP); for lungs: ALP, gamma-glutamyl transpeptidase (GGT] suggested that low doses of Cd stimulated LPO without any evidence of acute damages. These results suggest that LPO is an early and sensitive consequence of Cd exposure as determined in various organs. Investigation of liver, lungs, and heart antioxidant defense system components (glutathione peroxidase (GPX), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PDH), superoxide dismutase (SOD] revealed that GPX might be considered as a potential modulator of the Cd-induced LPO reaction in lungs and heart tissues.

Assessment of urinary protein 1 and transferrin as early markers of cadmium nephrotoxicity

Transferrin and protein 1, a sex linked alpha 2-microprotein, were assayed in urine from 58 workers exposed to cadmium (Cd) in a non-ferrous smelter and from 58 age matched referents. These two new markers of nephrotoxicity were compared with urinary beta 2-microglobulin (beta 2-m), retinol binding protein (RBP), albumin, and beta-N-acetyl-glucosaminidase (NAG). The response of protein 1 to Cd tubulotoxicity was similar to that of beta 2-m, RBP, and NAG. In Cd workers, protein 1 had a correlation with urinary Cd (r = 0.56) similar to beta 2-m (r = 0.48), RBP (r = 0.58), and NAG (r = 0.49). Values of these three low molecular weight proteins and of NAG were increased only in workers with urinary Cd higher than 10 micrograms/g creatinine. Urinary transferrin and albumin were similarly affected by exposure to Cd. Their response, however, was clearly more sensitive than that of low molecular weight proteins. Prevalences of positive values of these two high molecular weight proteins were not only higher but also tended to rise at lower concentrations of Cd in urine or blood. This finding suggests that in some subjects subtle defects in glomerular barrier function may precede the onset of proximal tubular impairment after chronic exposure to Cd. It remains to be assessed whether these subjects are more at risk of developing renal insufficiency.

Significance of the excretion of urinary indicator proteins for a low level of occupational exposure to cadmium

Urinary cadmium (Cd), N-acetyl-beta-D-glucosaminidase (NAG), metallothionein (MT), beta 2-microglobulin (BMG), and blood cadmium were determined in 79 workers who had been employed at a Cd pigment factory in Japan. The workers who had been dealing with Cd pigment manufacturing processes were estimated to be exposed to cadmium pigment dust at a maximum concentration of 3.0 micrograms/m3/8 h for about 20 years. The urinary Cd level ranged from 0.2 to 9.7 micrograms/g creatinine with a geometric mean of 1.02 micrograms/g creatinine. Pearson's correlation coefficients between logarithm of urinary Cd and that of NAG, MT, and BMG in urine were 0.45, 0.62, and 0.05, respectively. The correlation coefficients between blood Cd and urinary NAG, MT, and BMG were 0.21, 0.40, and -0.074, respectively. When partial correlation coefficients were calculated to exclude the contribution of age factor, urinary Cd turned out to be significantly correlated with urinary MT (r = 0.55) and NAG (r = 0.52). The present results indicate that urinary Cd is more closely associated with urinary MT and NAG than with BMG, and suggest that MT and NAG could be good indicators of Cd absorption in a Cd-exposed population whose mean urinary Cd level is relatively low, or less than 10 micrograms/g creatinine.

Carbon monoxide, carbon disulfide, lead and cadmium--four examples of occupational toxic agents linked to cardiovascular disease

A variety of industrial agents to which large segments of the population are exposed have been linked to the development of cardiovascular disease. These toxic agents, which include carbon monoxide, carbon disulphide, lead, and cadmium, are produced by a wide variety of industrial processes and so are ubiquitous in the modern industrial environment. Although the mechanisms by which such toxins may contribute to cardiovascular disease are not well defined, there are at least four possible theories that have received clinical and experimental support. The postulated mechanisms by which such toxins may play a role in vascular disease are: (1) an increase in blood pressure; (2) an increase in the levels of blood cholesterol and/or an induction of lipid accumulation in vessel walls; (3) an induction of a lipid peroxidation process thereby increasing the tendency of blood clotting; and (4) a promotion of a mutation in the arterial cell wall.

Epidemiological application of early markers of nephrotoxicity

This paper is a review of epidemiological studies in which sensitive markers of nephrotoxicity have been used to detect the early effects of chemicals on the kidney. Most of the studies are cross-sectional, and their objective was either to identify potentially nephrotoxic chemicals (organic solvents, heavy metals) in the working or general environment or to establish dose-response/effect relationships from which safe exposure levels can be defined (e.g., for cadmium and mercury vapour). A few longitudinal studies were conducted to determine the persistence of renal disturbances and to get information on their predictive value (e.g., microproteinuria in cadmium workers). Nephrotoxicity tests, which have proved to be the most useful in these epidemiological studies, rely on the determination of specific urinary proteins which, according to their size, reflect the functional integrity of the proximal tubule (e.g., retinol-binding protein or beta 2-microglobulin) or the glomerulus (e.g., albumin, immunoglobulin G). An increased urinary excretion of the lysosomal enzyme N-acetyl-beta-D-glucosaminidase has been reported in several studies (e.g., in lead-exposed workers), but the pathological significance of this finding remains to be clarified, particularly when it is not associated with changes in the urinary excretion of specific proteins. Further work is needed to assess the usefulness of tests introduced more recently such as the assay of renal antigens in urine and the use of red-blood-cell membrane negative charges as an index of the glomerular polyanion. With the exception of microproteinuria observed in chronic cadmium poisoning, no epidemiological data are available on the prognostic value of subclinical renal effects caused by nephrotoxic chemicals.

Renal tubular function of workers exposed to low levels of cadmium

Cadmium induced renal tubular effects were examined in 65 female workers in a factory manufacturing nickel cadmium batteries. Urinary beta 2-microglobulin (beta 2m), urinary N-acetyl-D-glucosaminidase activity (NAG), and serum creatinine and serum urea concentrations were used to assess the renal effects. Of the four measures, only urinary NAG and urinary beta 2m showed a strong positive correlation with blood cadmium concentrations (r = 0.49 and 0.43 respectively); NAG showed a weaker correlation with urinary cadmium concentrations (r = 0.35). Urinary beta 2m has weak correlation with urinary cadmium (r = 0.04). Only urinary NAG showed a significant deterioration in renal function among the exposed group. NAG detects the largest proportion of abnormalities among the exposed group. Abnormal urinary beta 2m is detected in only 15.4% of the workers, half of whom have blood cadmium above 10 micrograms/l. The proportion of abnormalities detected by urinary NAG differs significantly from the proportion of abnormalities detected by urinary beta 2m (p less than 0.01). The age adjusted mean urinary NAG excretion showed a significant rise with urinary cadmium of above 3 micrograms/g creatinine. Urinary beta 2m failed to show any significant rise. With blood cadmium concentrations, the age adjusted mean urinary NAG excretion showed a rise from 1 microgram/l of blood cadmium followed by a plateau between blood cadmium concentrations of 3-10 micrograms/l. No significant rise in mean urinary excretion in beta 2m was seen until blood cadmium concentrations exceeded 10 micrograms/l.

Urinary mercury levels and early changes in kidney function in dentists and dental assistants

Mercury exposure and renal function parameters were examined in 68 dentists and 64 dental assistants. The levels of mercury in urine were low: only three individuals exceeded 20 micrograms/l. Increased excretion of urinary proteins and increased activity of urinary enzymes were observed. This enhanced prevalence of renal function changes appeared not to be related to the mercury urine level, age, sex, or smoking and drinking habits. Only for men was a positive relation between the level of mercury in urine and the activity of beta-galactosidase found. The proteinuria may be due to one or more potential nephrotoxic agents used in dental practice.