lead concentrations (r=0.45; p<0.01) and between urinary albumin excretion and blood lead concentrations (r=0.71; p<0.001) were noted. Conclusions: Use of renal scintigraphy in present study revealed measurable alterations of renal function under the conditions of low-level lead exposure and suggest that increased glomer-ular filtration may be an early indicator of kidney damage in subjects occupationally exposed to lead.
(J Occup Health 2015; 57: 91–99)
Key words: Lead, Occupational exposure, Renal scintigraphy
Lead absorbed in the body is mainly excreted through kidneys, and longstanding exposure to exces-sive lead concentrations may cause chronic nephrotox-ic effects such as interstitial nephritis, tubular damage, and at later stages glomerular damage leading to the chronic renal failure1, 2). Observational studies
have repeatedly reported an association between lead exposure and an increased risk of renal disease, but the intensity of exposure, which ultimately produces renal damage, is still a matter of debate3, 4). Up to the
present, severe adverse effects of lead on the kidney have been reported chiefly in subjects occupation-ally exposed in a working environment, which is the major source of heavy lead exposure3, 5, 6). Bases on
these results, the WHO Task Group on Environmental Health Criteria for Inorganic Lead concluded that renal dysfunction occurs in lead-exposed workers mainly at blood levels exceeding 600 µg/l7). While most studies
have failed to detect major adverse effects on kidney integrity in workers moderately exposed to lead, more subtle alterations manifesting as increased urinary excretion of sensitive tubular damage indicators such as α1-microglobulin (α1M), β2-microglobulin (β2M) or N-acetyl-β -glucosaminidase (NAG) have repeatedly Abstract: Scintigraphic assessment of renal
func-tion in steel plant workers occupafunc-tionally exposed to lead:Teresa WROŃSKA-NOFER, et al. Department of
Toxicology and Carcinogenesis, Nofer Institute of Occupational Medicine, Poland—Objectives: Occu-pational exposure to lead may produce kidney damage, but existing data on the dose range associated with nephrotoxicity are inconclusive. We here assessed renal function under conditions of low to moderate lead expo-sure using renal scintigraphy. Methods: Fifty-three male foundrymen (exposed group) and fourty male office workers (control group) from a steel plant were included in the study. Glomerular and tubular renal function were assessed by means of 99mTc-DTPA and 99mTc-EC clearance, respectively. Urinary markers of
glomerular dysfunction (albumin) and tubular damage (α1-microglobulin (α1M), β2-microglobulin (β2M), retinol-binding protein (RBP), N-acetyl-β-glucosaminidase (NAG) activity) were determined using latex beads tests or colorimetry. The lead concentration in blood was measured with atomic absorption spectrometry. Results: The blood lead concentrations were 145.8 (121.3−175.3) and 39.3 (35.1−44.1) µg/l (geometric mean, 95th CI, p<0.001) in the exposed and control
groups, respectively. Subjects exposed to lead presented with increased 99mTc-DTPA clearance (158.3
(148.4−168.8) vs. 135.9 (127.9−144.4) ml/min; p<0.01) and urinary albumin excretion (7.61 (6.28−9.22) vs. 4.78 (4.05−5.65) mg/g creatinine; p<0.001). 99mTc-EC
clear-ance and excretion of α1M, β2M, RBP and NAG were
not significantly different between the groups. Significant correlations between 99mTc-DTPA clearance and blood
Scintigraphic assessment of renal function in steel plant
workers occupationally exposed to lead
Teresa Wron´ska-Nofer
1, Anna Pisarska
1,2, Małgorzata Trzcinka-Ochocka
1,
Tadeusz Hałatek
1, Jan Stetkiewicz
3, Janusz Braziewicz
2,4, Jerzy-Roch Nofer
5and
Wojciech Wa˛sowicz
11Department of Toxicology and Carcinogenesis, Nofer Institute of Occupational Medicine, Poland, 2Department of Nuclear Medicine, Holycross Cancer Center, Poland, 3Department of Pathology, Nofer Institute of Occupational Medicine, Poland, 4Institute of Physics, Jan Kochanowski University, Poland and 5Center for Laboratory Medicine, University Hospital Münster, Germany
J Occup Health 2015; 57: 91–99
Journal of
Occupational Health
Received May 19, 2014; Accepted Oct 31, 2014 Published online in J-STAGE Jan 10, 2015
Correspondence to: J.-R. Nofer, Centrum für Laboratoriumsmedizin Universitätsklinikum Münster, Albert Schweizer Campus 1, Gebäude A1, 48149 Münster, Germany (e-mail: nofer@uni-muenster.de)
been detected in subjects, in whom the blood lead concentrations did not regularly exceed 600 µg/l3, 8−17).
In addition, moderate exposure to lead was found to produce increased plasma levels of uric acid arising as a consequence of defective tubular secretion and/or excessive tubular reabsorption15, 18, 19).
Previous investigations in subjects occupationally exposed to lead have usually employed traditional clinical parameters for the assessment of renal func-tion such as blood urea nitrogen (BUN), serum creatinine, creatinine clearance, or urinary excretion of low-weight proteins, which are inaccurate and do not allow the functional impairment related to tubular damage to be clearly distinguished from that related to glomerular damage. In the present study, we applied dynamic scintigraphy with technetium-99m diethylenetriamine pentaacetic acid (99mTc-DTPA) and
technetium-99m ethylenedicysteine (99mTc-EC) along
with early markers of renal damage for the first time in a group of foundrymen and crane operators chroni-cally exposed to lead in the ambient air at low to moderate levels. Renal scintigraphy is characterized by enhanced precision and enables complex assess-ment of various kidney functions including glomerular filtration, tubular excretion and urine outflow20, 21).
Our results suggest that even low to moderate occu-pational exposure to lead may give rise to measur-able alterations in kidney functions, which encompass glomerular hyperfiltration and increased albumin excretion.
Material and Methods
Study subjects
This study recruited 93 male employees of steel plant located in the south-eastern part of Poland that produces steel in an electric arc furnace (EAF) process using metal scrap as the sole charge. All included subjects were between 35 and 56 years of age and had employment histories of 11 to 36 years. The exposed group was made up of 53 foundrymen and crane operators participating in continuous steel casting and having contact with various impurities (dust and toxic chemicals including lead). As a rule, they used to stay in the polluted melt-shop area not less than 8 hours and worked for the entire period of their occupational activities in an environment polluted with heavy metals. While operating furnaces, foundry-men used half-masks equipped with a dust-absorbing filter. Monitoring conducted by the environmental health and safety (EHS) department of the steel plant revealed this group to be the most exposed among the staff. The control group consisted of 40 workers of the same steel plant allocated to administration, who have never been occupationally exposed to dust and/ or heavy metals in the courses of their professional
careers. All examined subjects received information on the purpose of the study and signed a participa-tion consent form. The protocol was approved by the local ethics committee. Each subject underwent a general medical examination, and information concerning smoking and medication within the past 12 months was collected. Subjects with known hema-tological or kidney diseases or apparent symptoms of health deterioration (n=2) were excluded. Except for minor illnesses, subjects in both examined groups were in a good health and were examined once during the course of the study.
Blood and urine sample collection
Blood was collected in an outpatient station loca-ted outside the melt-shop area simultaneously in both groups during the working shift one day before the first renal scintigraphy was performed. Blood samp-les for lead analysis were obtained using heavy metal-free disposable syringes (Venosafe® Li-Heparine,
Terumo-Europe, Leuven, Belgium) certified for metal determination and stored until analysis at −20°C in lead-free bottles for the maximum period of 6 months. Serum was separated by centrifugation immedi-ately after blood collection and stored as described above. Overnight urine samples were collected in the morning before a shift and temporarily stored at 4°C for no longer than 3 hours. To avoid contamination, polyethylene tubes were soaked in nitric acid (25%, v/v) for several hours and rinsed with ultrapure water prior to urine collection. Spot urine samples for cadmium determination (5.0 ml) were acidified with ultrapu-re nitric acid (0.05 ml, 50% v/v, Merck, Darmstadt, Germany). For the NAG and creatinine determina-tion, samples were stored without any preservation. For determinations of β2M, α1M and retinol-binding protein (RBP), 0.5 ml of phosphate buffer (0.4 mol/l, pH 7.4) containing 1% sodium azide was added to 4.5 ml urine. Preliminary experiments revealed that such handling is sufficient to avoid degradation of β2M, which was reported to be unstable in a low pH environment22). Thereafter, samples were divided
into aliquots and kept frozen at −20°C until analysis. According to previous studies23) and our own
observa-tions, urine storage at −20°C leads to marginal protein degradation, which is comparable to that seen at −70°C.
Determination of occupational exposure indices
For lead determination, blood samples (4.0 ml) were deproteinized with 1.6 ml nitric acid(5.0%, v/v). Samples were left for at least 1 hour at room tempera-ture and centrifuged (11.500 rpm, 15 minutes, 4°C), and the supernatant was then transferred to autosamp-ler tubes. Urine samples were diluted 1:1 (v/v) with a matrix modifier containing diammonium hydrogen
phosphate (0.5%, w/v) and magnesium nitrate (0.03%, w/v), and transferred to autosampler tubes. All vessels used during the analysis were washed with nitric acid (20.0%, v/v) and deionized water. The concentrations of lead in blood and cadmium in urine were determined using a graphite-furnace atomic-absorption spectrometer equipped with a transverse heated graphite atomizer and longitudinal Zeeman-effect background correction (Perkin-Elmer 4100ZL, Perkin Elmer, Palo Alto, CA, USA) as described previously24, 25). Signals for lead and cadmium were
monitored at 283.3 and 228.8 nm, respectively, using a slit width of 0.7 nm. The electrodeless discharge lamp was operated at 10 mA and 4 mA, respectively. The injection temperature was 100°C, the argon flow was 0.25 l/min, and the read time was 3 seconds for both parameters. The graphite furnace temperature program is shown in Table 1. The precisions of lead and cadmium determination were estimated to be 5.0 and 6.1%, respectively. The limit of detection (LoD) and limit of quantitation (LoQ) were, respec-tively, 1.0 µg/l and 2.0 µg/l for lead and 0.10 µg/l and 0.18 µg/l for cadmium. External quality control was carried out under the UK National External Quality Assessment Scheme (UK NEQAS). The laboratory was accredited according to PN/EN ISO/IEC 17025 to perform measurements of lead in blood and cadmium in urine for occupational medicine purposes.
Early biomarkers of renal damage
The concentrations of β2M, α1M, RBP and albumin in urine were measured with latex immunoassays as described previously26). These methods involve
agglu-tination of latex particles coated by specific antibodies provided by Dako Polska (Gdynia, Poland), and the results were verified against respective determinations by external laboratories. NAG activity in urine was measured using a commercially available colorimetric assay (Roche Diagnostics, Warsaw, Poland) according to the manufacturer’s instructions. Urine creatinine was measured according to the picrate method (Jaffe)
using a commercially available assay (Aqua-Med, Lodz, Poland).
Renal scintigraphy
Dynamic renal imaging was carried out in the Department of Nuclear Medicine, Holycross Cancer Center, Kielce, Poland. The first renal scan was performed with 99mTc-EC (tubular damage indicator),
and two weeks later the same subjects underwent imaging with 99mTc-DTPA (glomerular damage
indica-tor). Both renal scintigraphies were performed in the same way. Prior to examination, the subjects were asked to drink ~0.5 l of water (7.0 ml/kg). 99m
Tc-EC and 99mTc-DTPA dynamic images were acquired
with patients in the supine position and with the gamma camera head placed in a posterior view immediately after the intravenous administration of 370 MBq of the radiopharmaceutical. Data were acquired using a Multispect 2 or E-CAM gamma-camera (both from Siemens, Eschborn, Germany). The images were recorded in the energy window of 140 keV in 3 phases: vascular phase (0−2 minutes, image registration at 0.5 seconds intervals), filtration phase (2−5 minutes, image registration at 5 seconds intervals), excretion phase (5−25 minutes, image regis-tration at 30 seconds intervals). The preinjection and postinjection syringes were counted on the camera, and counts for the postinjection syringe were correc-ted for decay and subtraccorrec-ted from the counts for the preinjection syringe to determine counts injected. Acquired data were processed using the ICON soft-ware (Siemens) and automatically normalized for age and body height and mass. In all subjects, clearances of 99mTc-EC or 99mTc-DTPA were estimated using the
radiopharmaceutical administered for dynamic exami-nation. The absolute value of 99mTc-EC clearance
was determined according to the method of Bubeck27).
The value of 99mTc-DTPA clearance (GFR) was
esti-mated without blood sampling according to the meth-od of Gates28).
Table 1. Furnace programs used for metal determination in blood and urine
Step Lead Cadmium Gas flow rate (ml/min) Read Furnace temp (°C) Time(s) Furnace temp (°C) Time(s)
Ramp Hold Ramp Hold
1 110 3.0 20.0 110 1.0 20.0 250
2 170 10.0 30.0 170 10.0 30.0 250
3 500 5.0 30.0 250 30.0 30.0 250
4 1,350 0 3.0 1,450 0 3.0 0 ON
Statistical analysis
Exploratory statistics were performed using the MedCalc Statistical Software version 12.7.7 (MedCalc Software bvba, Ostend, Belgium). The distribution of variables was assessed for normality using the Shapiro-Wilk test. Non-normally distributed param-eters were analyzed after logarithmic transforma-tion. The Student’s t-test (2-sided) or Welch’s t-test were used for comparison of means. Fisher’s exact test was used for analysis of categorical variables. Pearson correlation coefficients (r) were calculated on log-transformed data for the relationship between plas-ma lead concentrations and other variables. Stepwise multiple regression analysis was used to determine independent factors affecting dependent variables reflecting renal function. The following confounding variables were sequentially entered into the model: age, employment duration, smoking, systolic and diastolic blood pressure and cadmium concentration in urine. The results are expressed as percentages or means ± SD. Non-normally distributed variables are presented as geometric means (95% CI for the mean) back-transformed after logarithmic transformation. Differences or correlations with a p value <0.05 were considered significant.
Results
Characteristics of the studied groups
Characteristics of the exposed and control groups are shown in Table 2. Neither group differed signifi-cantly with respect to age, employment duration, and smoking habit. No significant differences were noted with respect to systolic and diastolic blood pressures.
Assessment of occupational exposure to air pollutants
Retrospective information regarding occupational exposure to air pollutants was obtained from the EHS department of the steel plant. In the years 1991−2000, the lead concentrations in the foundry working environment amounted up to 0.11 mg/m3 and
exceeded the occupational exposure limit (OEL) of 0.05 mg/m3. Assuming that exposure to 0.1 µg/m3 lead in
the ambient air produces an increase in the blood lead concentration of between 0.27 and 0.53 µg/dl29–31), the
blood lead levels of the foundrymen remained below or around 600 µg/l in this period. Due to changes in smelting technology, exposure to lead in the ambi-ent air was reduced down to 0.04 mg/m3 from 2001
onwards, and the estimated blood lead concentration was 108–212 µg/l. In contrast to lead, exposure to other heavy metals including Cd, Fe, Mn, Cr and Ni, toxic gases such as CO and NO and total and respi-rable dust in the ambient air was below their respec-tive OELs beginning in 1991. No information regard-ing the occupational exposure to air pollutants before 1991 was available.
At the time of the study (2008), the average blood lead concentrations were 145.8 (121.3−175.3) µ g/l and 39.3 (35.1−44.1) µg/l in the exposed and control groups, respectively (p<0.001). By contrast, the urine excretion of Cd was comparable in both groups (1.5 ± 0.6 vs. 2.0 ± 0.8 µg/g creatinine; n.s.).
Determination of biochemical nephrotoxicity markers
To assess the potential effect of occupational expo-sure to lead on renal integrity and function, we first examined urine concentrations of several nephrotox-icity biomarkers in the exposed and control groups. As shown in Table 3, no significant differences were observed between the groups with respect to biomark-ers reflecting tubular function and/or early tubular epithelial damage such as α1M, β2M, RBP and NAG activity. However, significantly higher concentrations of urine albumin, which reflects impaired glomeru-lar function, were observed in the exposed group. Analysis of the distribution of nephrotoxicity markers in both examined groups revealed that 48% of found-rymen presented with urine albumin concentrations above the 90th percentile of the control group (p<0.001;
see Table 4). By contrast, the percentage of
individu-Table 2. General characteristics of study subjects
Controls (n=40) Exposed subjects (n=53) Significance (p) Age 45.3 ± 17.5 45.5 ± 16.8 n.s. Employment duration 19.2 ± 11.8 15.8 ± 7.3 n.s. Smokers (>10 cigarettes/day) 52.3 49.2 n.s.
Diastolic blood pressure 79.8 ± 8.1 81.8 ± 7.9 n.s.
Systolic blood pressure 126.9 ± 17.8 130.9 ± 18.8 n.s.
Values shown are means ± SD. Age and employment duration are given as years. Blood pressure is given as mmHg. For smokers, values represent % of examined population. Significance was determined by the Student’s t-test or Fischer’s exact test. n.s.: not sig-nificant.
als with tubular toxicity markers exceeding the 90th
percentile of the control group was not significantly different between the exposed and control groups.
Scintigraphic assessment of renal function
Renal scintigraphy with 99mTc-DTPA and 99mTc-EC
was employed for detailed assessment of renal func-tion in both examined groups. Table 3 shows that Tmax—the time reflecting the intrarenal radio marker transit—was significantly increased for both 99m
Tc-DTPA and 99mTc-EC in the exposed group. Moreover,
the 99mTc-DTPA clearance corresponding to the
glomerular filtration rate (GFR) was elevated in the exposed group. By contrast, the 99mTc-EC clearance,
which reflects the secretory function of proximal tubuli, was comparable between the exposed and the control group. Assessment of the urine outflow from the kidneys as reflected by the radioactivity decline in the kidneys 25 min after administration of radio markers revealed decreased 99mTc-DTPA outflow index
in the exposed group and no significant differences between the exposed and control groups with respect to the 99mTc-EC outflow index. Analysis of the
frequency of scintigraphic markers in both examined groups showed that a significantly higher percentage of the foundryman population presented with 99m
Tc-DTPA and 99mTc-EC clearances, 99mTc-DTPA T max
values and outflow index above the 90th percentiles of
the control group (Table 4).
Association between occupational exposure to lead and renal function
To more specifically address the influence of
occupational exposure to lead on renal function, correlations between lead concentrations in blood and biochemical and scintigraphic indicators of renal function were examined in the combined groups. As shown in Table 5, there were significant correla-tions between albumin excretion and the blood lead concentrations, between the 99mTc-DTPA T
max,
clear-ance and outflow index and between the 99mTc-EC
Tmax and blood lead concentrations. Other biochemi-cal or scintigraphic parameters reflecting renal func-tion showed no significant correlafunc-tions with blood lead concentrations. To examine associations between blood lead concentrations and each kidney outcome with adjustment for both kidney and lead confound-ers, a stepwise multiple linear regression analysis was
performed with the blood lead concentration, age, employment duration, smoking, systolic and diastolic blood pressure and cadmium concentration in urine as explanatory variables. For albumin excretion, the best predictor was plasma lead concentration (β=0.55,
p<0.01) followed by age (β=0.47, p<0.05) explaining, respectively, 30 and 21% of the albumin concentration in urine. For 99mTc-DTPA clearance, the best
predic-tor was plasma lead concentration (β =0.49 p<0.01) followed by diastolic pressure (β =−0.39, p<0.05) explaining, respectively, 24 and 15% of 99mTc-DTPA
excretion. No covariates were retained in models assessing the influence of the above exploratory vari-ables on other renal function/injury parameters.
Discussion
It has been recognized for many years that occu-pational exposure to excessive lead concentrations in
Table 3. Biochemical and scintigraphic evaluation of renal function in study subjects
Controls (n=40) Exposed subjects (n=53) Significance (p) Albumin (mg/g creatinine) 4.78 (4.05−5.65) 7.61 (6.28−9.22) <0.001 α1-microglobulin (µg/g creatinine) 2.95 (2.46−3.53) 3.48 (2.94−4.12) n.s. β2-microglobulin (µg/g creatinine) 34.6 (24.5−48.7) 34.9 (22.4−54.4) n.s.
Retinol-binding protein (µg/g creatinine) 43.1 (33.1−56.1) 56.5 (45.2−70.3) n.s. N-acetyl-β-glucosaminidase (IU/g creatinine) 1.26 (1.09−1.45) 1.41 (1.15−1.71) n.s. 99mTc-DTPA Tmax (s) 208.9 (200.9−217.2) 289.3 (258.5−323.6) <0.001 Clearance (ml/min) 135.9 (127.9−144.4) 158.3 (148.4−168.8) <0.01 Outflow index (%) 57.9 (56.8−59.1) 52.1 (49.2−52.1) <0.01 99mTc-EC Tmax (s) 193.6 (181.2−206.2) 231.1 (211.7−252.3) <0.01 Clearance (ml/min) 346.9 (331.2−362.5) 346.1 (338.6−355.3) n.s. Outflow index (%) 79.2 (77.6−80.7) 78.1 (74.3−82.1) n.s.
Values shown are geometric means (95% CI for the mean) back-transformed after logarithmic transformation. Significance was determined by the Student’s t-test or Welch’s t-test. n.s.: not significant.
ambient air may produce nephrotoxic effects such as interstitial nephritis or tubular damage and may ulti-mately result in renal failure. However, the role of low-level lead exposure as the cause of chronic kidney disease remains unsettled. Previous studies explor-ing renal effects of lead have frequently used param-eters such as blood urea nitrogen, serum creatinine, or GFR for estimation of kidney function, which are inaccurate and do not allow for clearly discriminating between disturbances of glomerular and tubular func-tions. In addition, due to the great reserve capacity of the kidney, these measures of excretory functions may be normal despite considerable impairment of renal
function. To circumvent these difficulties, we deter-mined here for the first time 99mTc-DTPA and 99m
Tc-EC clearances in subjects chronically exposed to low to moderate lead concentrations in ambient air. The radioisotopic methods applied in the present study are more precise, enable direct estimation of glomerular and tubular clearance, and are often used as reference methods for the assessment of renal function32,33). Our
results document two measurable aberrances of kidney function in the lead-exposed group. First, elevated
99mTc-DTPA clearance was observed in this group.
Second, lead-exposed subjects excreted more urinary albumin as compared with controls. In addition,
Table 4. Distribution of biochemical and scintigraphic parameters of renal function in study subjects
90th percentile of control Controls (%) (n = 40) Exposed subjects (%) (n=53) Significance (p) Albumin (mg/g creatinine) 7.37 6 48 <0.001 α1-microglobulin (µg/g creatinine) 124 10 9 n.s. β2-microglobulin (µg/g creatinine) 5.94 10 19 n.s.
Retinol-binding protein (µg/g creatinine) 90.6 13 17 n.s.
N-acetyl-β-glucosaminidase (IU/g creatinine) 1.80 16 27 n.s.
99mTc-DTPA Tmax (s) 240 21 51 <0.01 Clearance (ml/min) 176 10 43 <0.01 Outflow index (%) 62.5 13 77 <0.001 99mTc-EC Tmax (s) 274 10 28 <0.05 Clearance (ml/min) 419 13 4 n.s. Outflow index (%) 84.1 10 17 n.s.
Values shown are percentages of parameter values exceeding the 90th percentile of the control. Significance was determined by the Fisher’s exact test. n.s.: not significant.
Table 5. Correlations between renal function parameters and lead exposure in study subjects
Correlation coefficient (r) Significance (p)
Albumin (mg/g creatinine) 0.71 <0.001
α1-microglobulin (µg/g creatinine) 0.11 n.s.
β2-microglobulin (µg/g creatinine) 0.16 n.s.
Retinol-binding protein (µg/g creatinine) −0.02 n.s.
N-acetyl-β-glucosaminidase (IU/g creatinine) 0.21 n.s.
99mTc-DTPA Tmax (s) 0.32 <0.05 Clearance (ml/min) 0.45 <0.01 Outflow index (%) −0.31 <0.05 99mTc-EC Tmax (s) 0.29 <0.05 Clearance (ml/min) 0.17 n.s. Outflow index (%) 0.10 n.s.
both 99mTc-DTPA clearance and albumin excretion
were correlated with lead concentrations in blood of exposed subjects.
In major contrast to several previous studies, the urinary excretion of biomarkers reflecting tubular damage including α1M, β2M, RBP and NAG activ-ity was normal in subjects occupationally exposed to lead. The missing effect of low-level lead exposure on tubular function was further underscored by deter-mination of 99mTc-EC clearance, which directly reflects
the excretory capacity of the nephron; the results were comparable between the exposed and control groups. However, the higher 99mTc-DTPA clearance observed
in the former group is highly suggestive of glomeru-lar hyperfiltration, which may be a consequence of increased proximal tubular volume reabsorption. Glomerular hyperfiltration is a condition often encoun-tered in various kidney pathologies (diabetes mellitus, polycystic kidney disease), where it precedes the dete-rioration of renal function and magnifies the risk of developing microalbuminuria33−36). Other diseases and
conditions such as sickle cell disease and hyperten-sion, in which elevated glomerular filtration is pres-ent, are also associated with a higher risk for subse-quent renal abnormalities including increased albumin excretion37, 38). In this context, it is worth noticing
that albumin excretion in five subjects (9%) in the lead-exposed group examined in this study exceeded the threshold of 24 mg/g creatinine, which defines microalbuminuria. Associations between increased GFR values estimated from creatinine clearance and higher lead exposure measures have been previously observed in subjects with long exposure histories and blood lead levels below 600 µg/l16, 17, 19, 39). In addition,
a positive association between GFR and blood lead concentration was reported in rodents exposed to 0.5% lead acetate in drinking water40). Together with these
previous studies, the present results suggest that the glomerular hyperfiltration may represent an early sign of renal dysfunction in prolonged low-level exposure to lead.
Several limitations of the present study have to be acknowledged. First, due to burdensome character of the radioisotope methods used for examination of glomerular and tubular functions, only small numbers of individuals could be included in the study, which limits its power. Second, the retrospective assessment of the occupational exposure to lead was mainly indi-rect, and the blood lead concentration in the period before the year 2000 was derived from the levels of this pollutant in the ambient air. Though blood lead concentrations estimated and measured at the time of the study were very close to each other, it cannot be entirely excluded that the levels of this metal in blood temporarily exceeded 600 µ g/dl, especially in the
early period of exposure. Third, though no signifi-cant difference in urine cadmium excretion was noted between the exposed and control groups at time of the study, limited retrospective information regarding the exposure to cadmium was available in the exam-ined population. This may be of importance, as even low-level cadmium exposure seems to modulate lead-induced nephrotoxicity and higher urinary excretion of cadmium was found to be associated with increased creatinine clearance and GFR41).
In conclusion, the present study revealed measur-able alterations of renal function in low-level lead exposure and suggests that glomerular hyperfiltration may be an early indicator of functional impairments in subjects occupationally exposed to lead. Further prospective studies are necessary to clarify the clinical significance of this finding and to assess its utility in predicting nephrotoxicity in occupational exposure to lead.
Acknowledgments: The authors are most indebt-ed to Andrzej Sosnowski, M.Eng., Head of the Environmental Health and Safety Department, for his on-site help with recruitment and study organization. The technical assistance of Anna Kubiak is gratefully acknowledged. This study was supported by an intra-mural grant from the Nofer Institute of Occupational Medicine.
References
1) Sabath E, Robles-Osorio ML. Renal health and the environment: heavy metal nephrotoxicity. Nefrologia 2012; 32: 279−86.
2) Soderland P, Lovekar S, Weiner DE, Brooks DR, Kaufman JS. Chronic kidney disease associated with environmental toxins and exposures. Adv. Chronic Kidney Dis 2010; 17: 254−64.
3) Ekong EB, Jaar BG, Weaver VM. Lead-related nephrotoxicity: a review of the epidemiologic evidence. Kidney Int 2006; 70: 2074−84.
4) Evans M, Elinder CG. Chronic renal failure from lead: myth or evidence-based fact? Kidney Int 2011; 79: 272−9.
5) Loghman-Adham M. Renal effects of environmen-tal and occupational lead exposure. Environ Health Perspect 1997; 105: 928−38.
6) Roels HA, Hoet P, Lison D. Usefulness of biomark-ers of exposure to inorganic mercury, lead, or cadmium in controlling occupational and environ-mental risks of nephrotoxicity. Ren Fail 1999; 21, 251−62.
7) World Health Organisation (WHO). Inorganic Lead. In: Environmental Health Criteria 165 (Eds. International Program on Chemical Safety), WHO Geneva, 1995.
8) Cárdenas A, Roels H, Bernard AM, et al. Markers of early renal changes induced by industrial
pollut-ants. II. Application to workers exposed to lead. Br J Ind Med 1993; 50: 28−36.
9) Chia KS, Jeyaratnam J, Lee J, et al. Lead-induced nephropathy: relationship between various biological exposure indices and early markers of nephrotoxic-ity. Am J Ind Med 1995; 27: 883−95.
10) Ehrlich R, Robins T, Jordaan E, et al. Lead absorp-tion and renal dysfuncabsorp-tion in a South African battery factory. Occup Environ Med 1998; 55: 453−60.
11) Endo G, Konishi Y, Kiyota A, Horiguchi S. Urinary alpha 1 microglobulin in lead workers. Bull Environ Contam Toxicol 1993; 50: 744−9.
12) Garçon G, Leleu B, Zerimech F, et al. Biologic markers of oxidative stress and nephrotoxicity as studied in biomonitoring of adverse effects of occu-pational exposure to lead and cadmium. J Occup Environ Med 2004; 46: 1180−6.
13) Garçon G, Leleu B, Marez T, et al. Biomonitoring of the adverse effects induced by the chronic expo-sure to lead and cadmium on kidney function: usefulness of alpha-glutathione S-transferase. Sci Total Environ 2007; 377: 165−72.
14) Lim YC, Chia KS, Ong HY, Ng V, Chew YL. Renal dysfunction in workers exposed to inorganic lead. Ann Acad Med Singapore 2001; 30: 112−7.
15) Oktem F, Arslan MK, Dündar B, Delibas N, Gültepe M, Ergürhan Ilhan I. Renal effects and erythrocyte oxidative stress in long-term low-level lead-exposed adolescent workers in auto repair workshops. Arch Toxicol 2004; 78: 681−7.
16) Roels H, Lauwerys R, Konings J, et al. Renal func-tion and hyperfiltrafunc-tion capacity in lead smelter workers with high bone lead. Occup Environ Med 1994; 51; 505−12.
17) Weaver VM, Lee BK, Ahn KD, et al. Associations of lead biomarkers with renal function in Korean lead workers. Occup Environ Med 2003; 60: 551−62.
18) Wang VS, Lee MT, Chiou JY, et al. Relationship between blood lead levels and renal function in lead battery workers. Int Arch Occup Environ Health 2002; 75: 569−75.
19) Weaver VM, Jaar BG, Schwartz BS, et al. Associations among lead dose biomarkers, uric acid, and renal function in Korean lead workers. Environ Health Perspect 2005; 113: 36−42.
20) Itoh K, Tsushima S, Tsukamoto E, Tamaki N. Reappraisal of single-sample and gamma camera methods for determination of the glomerular filtra-tion rate with 99mTc-DTPA. Ann Nucl Med 2000; 14: 143−50.
21) Petersen LJ, Petersen JR, Talleruphuus U, et al. Glomerular filtration rate estimated from the uptake phase of 99mTc-DTPA renography in chronic renal failure. Nephrol Dial Transplant 1999; 14: 1673−8. 22) Blumsohn A, Morris BW, Griffiths H, Ramsey CF.
Stability of beta 2-microglobulin and retinol binding protein at different values of pH and temperature in normal and pathological urine. Clin Chim Acta
1991; 195: 133−7.
23) MacNeil ML, Mueller PW, Caudill SP, Steinberg KK. Considerations when measuring urinary albu-min: precision, substances that may interfere, and conditions for sample storage. Clin Chem 1991; 37: 2120−3.
24) Razniewska G, Trzcinka-Ochocka M. Methods for determining lead and cadmium in blood; cadmium, copper, nickel and chromium in urine using flame-less atomic absorption spectrometry. Med Pr 1995; 66: 347−58.
25) Trzcinka-Ochocka M, Jakubowski M, Razniewska G, Halatek T, Gazewski A. The effects of environ-mental cadmium exposure on kidney function: the possible influence of age. Environ Res 2004; 95: 143−50.
26) Halatek T, Sinczuk-Walczak H, Rabieh S, Wasowicz W. Association between occupational exposure to arsenic and neurological, respiratory and renal effects. Toxicol Appl Pharmacol 2009; 239: 193−9. 27) Bubeck B. Renal clearance determination with one
blood sample: improved accuracy and universal applicability by a new calculation principle. Semin Nucl Med 1993; 23: 73−86.
28) Gates GF. Glomerular filtration rate: estimation from fractional renal accumulation of 99mTc-DTPA. Am J Roentgenol 1982; 138: 565−70.
29) Kentner M, Fischer T. Lead exposure in starter battery production: investigation of the correlation between air lead and blood lead levels. Int Arch Occup Environ Health 1994; 66: 223−8.
30) Lai JS, Wu TN, Liou SH, et al. A study of the relationship between ambient lead and blood lead among lead battery workers. Int Arch Occup Environ Health 1997; 69: 295−300.
31) Pierre F, Vallayer C, Baruthio F, et al. Specific relationship between blood lead and air lead in the crystal industry. Int Arch Occup Environ Health 2002; 75: 217−23.
32) Trimarchi H, Muryan A, Martino D, et al. Creatinine- vs. cystatin C-based equations compared with 99mTcDTPA scintigraphy to assess glomerular filtration rate in chronic kidney disease. J Nephrol 2012; 25: 1003−15.
33) White C, Akbari A, Hussain N, et al. Estimating glomerular filtration rate in kidney transplantation: a comparison between serum creatinine and cystatin C-based methods. J Am Soc Nephrol 2005; 16: 3763−70.
34) Amin R, Turner C, van Aken S, et al. The rela-tionship between microalbuminuria and glomerular filtration rate in young type 1 diabetic subjects: the Oxford regional prospective study. Kidney Int 2005; 68: 1740−9.
35) Helal I, Reed B, McFann K, et al. Glomerular hyperfiltration and renal progression in children with autosomal dominant polycystic kidney disease. Clin J Am Soc Nephrol 2011; 6: 2439−43.
36) Ruggenenti P, Porrini EL, Gaspari F, et al. GFR Study Investigators. Glomerular hyperfiltration
and renal disease progression in type 2 diabetes. Diabetes Care 2012; 35: 2061−8.
37) Aygun B, Mortier NA, Smeltzer MP, Hankins JS, Ware RE. Glomerular hyperfiltration and albumin-uria in children with sickle cell anemia. Pediatr Nephrol 2011; 26: 1285−90.
38) Palatini P, Mormino P, Dorigatti F, et al. HARVEST Study Group. Glomerular hyperfiltration predicts the development of microalbuminuria in stage 1 hypertension: the HARVEST. Kidney Int 2006; 70: 578−84.
39) Weaver VM, Lee BK, Todd AC, et al. Effect
modi-fication by delta-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase gene polymorphisms on associations between patella lead and renal function in lead workers. Environ Res 2006; 102: 61−9.
40) Khalil-Manesh F, Gonick HC, Cohen AH, et al. Experimental model of lead nephropathy. I. Continuous high-dose lead administration. Kidney Int 1992; 41: 1192−203.
41) Weaver VM, Kim NS, Jaar BG, et al. Associations of low-level urine cadmium with kidney function in lead workers. Occup Environ Med 2011; 68: 250−6.
