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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.

Usefulness of biomarkers of exposure to inorganic mercury, lead, or cadmium in controlling occupational and environmental risks of nephrotoxicity

A successful prevention of renal diseases induced by occupational or environmental exposure to toxic metals such as mercury (Hg), lead (Pb), or cadmium (Cd) largely relies on the capability to detect nephrotoxic effects at a stage when they are still reversible or at least not yet compromising renal function. The knowledge of dose-effect/response relations has been useful to control nephrotoxic effects of these metals through a "biological monitoring of exposure approach". Chronic occupational exposure to inorganic mercury (mainly mercury vapor) may result in renal alterations affecting both tubules and glomeruli. Most of the structural or functional renal changes become significant when urinary mercury (HgU) exceeds 50 micrograms Hg/g creatinine. However, a marked reduction of the urinary excretion of prostaglandin E2 was found at a HgU of 35 micrograms Hg/g creatinine. As renal changes evidenced in moderately exposed workers were not related to the duration of Hg exposure, it is believed that those changes are reversible and mainly the consequence of recently absorbed mercury. Thus, monitoring HgU is useful for controlling the nephrotoxic risk of overexposure to inorganic mercury; HgU should not exceed 50 micrograms Hg/g creatinine in order to prevent cytotoxic and functional renal effects. Several studies on Pb workers with blood lead concentrations (PbB) usually below 70 micrograms Pb/dl have disclosed either no renal effects or subclinical changes of marginal or unknown health significance. Changes in urinary excretion+ of eicosanoids was not associated with deleterious consequences on either the glomerular filtration rate (GFR)--estimated from the creatinine clearance (C(Cr))--or renal hemodynamics if the workers' PbB was kept below 70 micrograms Pb/dL. The health significance of a slight renal hyperfiltration state in Pb workers is yet unknown. In terms of Pb body burden, a mean tibia Pb concentration of about 60 micrograms Pb/g bone mineral (that is 5 to 10 times the average "normal" concentration corresponding to a cumulative PbB index of 900 micrograms Pb/dL x year) did not affect the GFR in male workers. This conclusion may not necessarily be extrapolated to the general population, as recent studies have disclosed inverse associations between PbB and GFR at low-level environmental Pb exposure. A 10-fold increase in PbB (e.g., from 4 to 40 micrograms Pb/dL) was associated with a reduction of 10-13 mL/min in the C(Cr) and the odds ratio of having impaired renal function (viz. C(Cr) < 5th percentile: 52 and 43 mL/min in men and women, respectively) was 3.8 (CI 1.4-10.4; p = 0.01). However, the causal implication of Pb in this association remains to be clarified. The Cd concentration in urine (CdU) has been proposed as an indirect biological indicator for Cd accumulation in the kidney. Several biomarkers for detecting nephrotoxic effects of Cd at different renal sites were studied in relation to CdU. In occupationally exposed males, the CdU thresholds for significant alterations of renal markers ranged, according to the marker, from 2.4 to 11.5 micrograms Cd/g creatinine. A threshold of 10 micrograms Cd/g creatinine (corresponding to 200 micrograms Cd/g renal cortex: the critical Cd concentration in the kidney) is confirmed for the occurrence of low-molecular-mass proteinuria (functional effect) and subsequent loss of renal filtration reserve capacity. In workers, microproteinuria was found reversible when reduction or cessation of exposure occurred timely when tubular damage was still mild (beta(2)-microglobulinuria < 1500 micrograms/g creatinine) and CdU had never exceeded 20 micrograms Cd/g creatinine. As the predictive significance of other renal changes (biochemical or cytotoxic) is still unknown, it seems prudent to recommend that occupational exposure to Cd should not allow that CdU exceeds 5 micrograms Cd/g creatinine.(ABSTRACT TRUNCATED)

The assessment of biomarkers to detect nephrotoxicity using an integrated database

Groups of industrial workers exposed to heavy metals (cadmium, mercury, and lead) or solvents were studied together with corresponding control groups. The cohorts were collected from several European centers (countries). Eighty-one measurements were carried out on urine, blood, and serum samples and the results of these analyses together with questionnaire information on each individual were entered into a central database using the relational database package Rbase. After the completion of the database construction phase, the data were exported in a format suitable for analysis by the statistical package SAS. The potential value of each test as an indicator of nephrotoxicity was then assessed. Rigorous exclusion criteria were applied which resulted in the elimination of some tests and samples from the dataset. The measurable contributions of smoking, gender, metal exposure, and site were either singly or in combination assessed by biomarkers for nephrotoxicity. The parameters measured included three urinary enzymes, six specific proteins, total protein, two extracellular matrix markers, four prostaglandins and anti-GBM antibodies, and beta 2-microglobulin in serum. The most sensitive renal tests included the urinary enzymes N-acetyl-beta-D-glucosaminidase (NAG) and intestinal alkaline phosphatase (IAP), brush border antigens, and urinary low-molecular-weight proteins. Of the newer tests investigated the prostaglandins were the most promising. Different patterns of biomarker excretion were observed following exposure to lead, cadmium, or mercury. The dataset provides a unique repository of data which could provide the basis of an enlarging source of information on normal human reference ranges and on the effects of exposure to toxins and the use of biomarkers for monitoring nephrotoxicity.