Experimental model of lead nephropathy. I. Continuous high-dose lead administration

Sex-Specific Associations of Urinary Metals with Renal Function: a Cross-sectional Study in China

BACKGROUND

Extensive studies have revealed the link between heavy metals and CKD. Compared to single meta-elements, mixture of metals reflect real-life metals exposure scenarios and are of interest. However, the mechanism of action of metal mixture on renal function is unclear.

METHODS

This study aimed to explore the potential relationship between urinary arsenic (As), cadmium (Cd), lead (Pb), manganese (Mn), and chromium (Cr) contents with estimated glomerular filtration rate (eGFR) levels in 2775 participants. The levels of metals in urine were determined by inductively coupled plasma-mass spectrometry. We used linear regression models and the Bayesian kernel machine regression (BKMR) to evaluate the association between metals and eGFR levels.

RESULTS

In linear regression analysis, urinary As (β = 2.723, 95%CI: 0.29, 5.157) and Pb (β = 3.081, 95%CI: 1.725, 4.438) were positively associated with eGFR in the total population. In the BKMR model, a mixture of the five metals had a positive joint effect on eGFR levels, while Pb (PIP = 0.996) contributed the most to eGFR levels. Pb was positively associated with eGFR levels in the total participants and women. As was positively correlated with eGFR levels in women. Pb and eGFR levels were positively correlated when the other metals were set at 25th, 50th, and 75th percentiles.

CONCLUSIONS

To the best of our knowledge, all five metals mixed exposure was positively associated with eGFR. Pb showed more important effects than the other four metals in the mixture, especially in women.

Associations of nickel exposure and kidney function in U.S. adults, NHANES 2017-2018

BACKGROUNDS

Nickel (Ni) is a ubiquitous heavy metal, but epidemiological studies on the association between Ni and kidney function are limited and controversial.

AIM

We aimed to explore the relationship between urinary Ni concentrations and kidney function in U.S. adults.

METHODS

This was a cross-sectional study based on the 2017-2018 National Health and Nutrition Examination Survey (NHANES) (n = 1588). Multiple linear regression models, logistic regression models, and restricted cubic spline models (RCS) were fitted to explore the associations between urinary Ni and estimated glomerular filtration rate (eGFR), urinary albumin-creatinine ratio (UACR), and the odds of impaired kidney function, which was defined as an eGFR ≤ 60 mL/min per 1.73 m², or UACR ≥ 30.0 mg/g. Bayesian kernel machine regression (BKMR) was used to account for joint-metal effects.

RESULTS

Compared with the lowest quartile, urinary Ni at the third quartile was associated with increased eGFR (β = 2.42, 95 % CI: 0.23-4.19); the highest quartile of urinary Ni was correlated with increased UACR (β = 0.10, 95 % CI: 0.02-0.18), as well as higher odds of impaired kidney function (OR=1.65, 95 % CI:1.08-2.54). Urinary Ni had a nonlinear inverted U-shape relationship with eGFR (P_nonlinear = 0.007), and linear J-shape associations with UACR (P_nonlinear = 0.063) and impaired kidney function (P_nonlinear= 0.215). Metal interaction of urinary Ni with cadmium (Cd) on eGFR was observed.

CONCLUSIONS

Our findings provided evidence that Ni exposure linked with declined kidney function and might interact with Cd exposure. Considering the cross-sectional design of the NHANES study, further prospective studies are necessary.

Developmental Exposure to Endocrine Disrupting Chemicals and Its Impact on Cardio-Metabolic-Renal Health

Developmental origin of health and disease postulates that the footprints of early life exposure are followed as an endowment of risk for adult diseases. Epidemiological and experimental evidence suggest that an adverse fetal environment can affect the health of offspring throughout their lifetime. Exposure to endocrine disrupting chemicals (EDCs) during fetal development can affect the hormone system homeostasis, resulting in a broad spectrum of adverse health outcomes. In the present review, we have described the effect of prenatal EDCs exposure on cardio-metabolic-renal health, using the available epidemiological and experimental evidence. We also discuss the potential mechanisms of their action, which include epigenetic changes, hormonal imprinting, loss of energy homeostasis, and metabolic perturbations. The effect of prenatal EDCs exposure on cardio-metabolic-renal health, which is a complex condition of an altered biological landscape, can be further examined in the case of other environmental stressors with a similar mode of action.

Associations of Blood Heavy Metals with Uric Acid in the Korean General Population: Analysis of Data from the 2016-2017 Korean National Health and Nutrition Examination Survey

We hypothesized that blood heavy metal levels such as lead, cadmium, and mercury were associated with uric acid level and hyperuricemia, and that this association remains significant after adjustment for other metals. We tested this hypothesis using the Korean National Health and Nutrition Examination Survey data. Beta coefficients and 95% confidence intervals (95% CIs) were calculated using multiple linear regression, and odds ratios (ORs) and 95% CIs were calculated using logistic regression in the cross-sectional study design. Relative to women, men had a higher geometric mean (GM) of lead (1.95 vs. 1.50 μg/dL) and mercury (3.94 vs. 2.77 μg/L), a lower GM of cadmium (0.80 vs. 1.04 μg/L), and a higher arithmetic mean (AM) of uric acid (5.84 vs. 4.40 mg/dL). Women had significant positive associations of log uric acid level with doubling of lead and mercury, and negative association with cadmium. Logistic regression analysis indicated the inverse association of serum hyperuricemia with doubling of blood metals was only significant for cadmium in women (OR = 0.641, 95% CI = 0.463 to 0.886) and the associations of serum hyperuricemia in the highest versus lowest quartiles of heavy metals were only significant for cadmium in women (OR = 0.495, 95% CI = 0.246 to 0.998). For both genders, age and estimated glomerular filtration rate (e-GFR) had negative associations with uric acid, but hypertension and triglycerides had positive associations with uric acid. In conclusion, blood lead and mercury levels were positively associated with uric acid level, but blood cadmium level was inversely associated with uric acid level and hyperuricemia in women.

Association of co-exposure to heavy metals with renal function in a hypertensive population

BACKGROUND

Chronic kidney disease (CKD) is an increasing health problem worldwide. Recent studies have suggested the potential associations between exposure to metals and CKD events, particularly in participants with hypertension. However, relevant studies are limited.

OBJECTIVES

We aimed to explore the associations of metal exposure with renal function in participants with essential hypertension.

METHODS

Nine hundred and thirty-four participants with essential hypertension were recruited at the Department of Cardiology, Union Hospital, Wuhan, China. We measured the levels of chromium, cadmium, thallium and uranium in urine and calculated the estimated glomerular filtration rate (eGFR) for renal function. Multivariable linear regression models adjusted for potential confounders were applied.

RESULTS

After adjusting for potential confounders and other metals, doubling of urinary chromium or uranium levels decreased eGFR by 2.90 (95% confidence interval, 2.04 to 3.76) and 1.87 (0.58 to 3.15) mL/min per 1.73m², respectively. Co-exposure to chromium and uranium was found to greatly decrease eGFR, particularly in women. Compared with those in the low exposure group, women with high exposure to chromium and uranium had a 11.36 (3.66 to 19.07) mL/min per 1.73m² adjusted decline in eGFR. Higher urinary thallium levels were positively related to elevated eGFR in men. The adjusted increase in eGFR with doubling of thallium levels was 3.12 (1.14 to 5.10) mL/min per 1.73m². Sex-difference in the associations of exposure to heavy metals with eGFR was also suggested.

CONCLUSIONS

Our findings suggest that environmental exposure to chromium and uranium might contribute to a decline in eGFR in individuals with hypertension. The associations of exposure to heavy metals with eGFR might be sex-different. Further studies are warranted to confirm our findings and clarify the underlying mechanisms.

Heavy metal concentrations in female wild mink (Neovison vison) in Sweden: Sources of variation and associations with internal organ weights

The American mink is an invasive species in Sweden, and it is legally hunted all year. Therefore, the mink is well suited as a sentinel species for environmental monitoring. In the present study female mink (n = 91) from 6 different areas in Sweden were analyzed for the concentrations of silver, cadmium, mercury and lead in liver tissue using inductively coupled plasma mass spectrometry. The wet concentrations in liver tissue were 42.6 ± 52.7 ng/g for silver, 99.5 ± 100 ng/g for cadmium, 652 ± 537 ng/g for mercury, and 196 ± 401 ng/g for lead (expressed as mean ± standard deviation). There were associations between the sample area and the concentrations of silver, lead, and mercury. The concentrations of lead and cadmium varied with season of capture and lead, cadmium, and mercury were positively associated with increasing age. Relative liver weight was positively associated with concentrations of mercury and negatively associated with lead and cadmium. Relative kidney weight was negatively associated with lead concentrations. In summary, it is of importance to take age and season of capture into account when assessing levels of heavy metals in wild mink. Also, liver and kidneys seem to be potential targets for heavy metal toxicity in wild female mink in Sweden. Environ Toxicol Chem 2017;36:2030-2035. © 2016 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Susceptibility of Overweight Mice to Liver Injury as a Result of the ZnO Nanoparticle-Enhanced Liver Deposition of Pb2

The prevalence of the applications of nanomaterials in consumer products and water treatment facilities increases the chance that humans will be exposed to both nanoparticles and environmental pollutants such as heavy metals. Co-exposure to nanoparticles and heavy metals may adversely affect human health, especially in susceptible populations such as overweight subjects. To evaluate the impact of such co-exposures, we orally administered zinc oxide nanoparticles (ZNPs; 14 or 58 nm) and/or Pb(Ac)₂ at tolerable doses to both healthy overweight and healthy normal weight mice. The ZNPs enhanced the deposition of Pb in all major organs in the overweight mice compared with that in the normal mice. As a result, higher levels of hepatic reactive oxygen species, pro-inflammatory cytokines, and liver injury were observed in the overweight mice but not in the normal weight mice. Our findings underscore a potentially enhanced risk of nanoparticle/heavy metal co-exposure in the susceptible overweight population.

Toxic environmental exposures and kidney health in children

High-level exposures to a number of agents are known to have direct nephrotoxic effects in children. A growing body of literature supports the hypothesis that chronic, relatively low-level exposure to various nephrotoxicants may also increase the risk for chronic kidney disease (CKD) or accelerate its progression. In this review we highlight several environmental nephrotoxicants and their association with CKD in children and adolescents. We also discuss unique epidemiological challenges in the use of kidney biomarkers in environmental nephrotoxicology.

Temporal stability of chemical hormesis (CH): Is CH just a temporary stop on the road to thresholds and toxic responses?

Chemical hormesis (CH) is currently described as a nonmonotonic, bidirectional dose-response relationship for chemicals, where a stimulatory, (beneficial?) response at low dose or exposure is followed by an inhibitory response at higher doses/exposures (or vice-versa). CH is depicted as U(J)-shaped or inverse U(J)-shaped curves, i.e., curve slopes change sign. Some describe CH as a homeostasis-preserving response; others view CH as adaptive or (pre)conditioning responses to chemical stress. One aspect of CH and stress hormesis in general that has not been researched is its temporal stability, i.e., persistence, particularly in experimental animals and humans having long-term chemical stressing. Once maximized, does the CH response remain operative over the entire time of chemical exposure? One possible reason for the question's neglect is that temporal stability, e.g., 'steady-state hormesis,' has been assumed. Another is that CH temporality is not well understood or has been under-appreciated as to its importance. Available data, mainly for simpler biological systems, describe cases of transitory CH. Other examples, in human and experimental animal studies, show transitory existence of CH and, in some specialized cases, persisting CH. Also, certain disease state-induced hormetic responses are transitory over time in humans. The question requires resolution if CH is to be considered (i) a stable and beneficial or adverse response, (ii) a stable dose-response model competitive with stable threshold and linear, nonthreshold (LNT) dose-response models, and (iii) a model having any impact on, or role in, regulatory and public health policies.

Urinary and blood cadmium and lead and kidney function: NHANES 2007-2012

BACKGROUND

Cadmium (Cd) and lead (Pb) are widespread environmental contaminants that are known nephrotoxins. However, their nephrotoxic effects at low-environmental exposure levels are debated.

OBJECTIVE

We examined the association of blood Pb (B-Pb), blood Cd (B-Cd), urinary Pb (U-Pb) and urinary Cd (U-Cd) with estimated glomerular filtration rate (eGFR) and urinary albumin (ALB).

METHODS

We used multivariate linear regression to analyze the association between B-Pb, B-Cd, U-Pb, and U-Cd with eGFR and ALB in adult participants (≥20 years of age) in NHANES 2007-2012. The dataset was limited to NHANES individuals with both blood and urinary metal measurements.

RESULTS

We found a statistically significant inverse association between eGFR and B-Cd and statistically significant positive associations between eGFR and both U-Cd and U-Pb, as well as statistically significant associations between ALB and the 3rd and 4th quartiles of U-Cd.

CONCLUSIONS

The inverse association between eGFR and B-Cd, in conjunction with positive associations between eGFR and ALB with U-Cd, suggest that U-Cd measurement at low levels of exposure may result from changes in renal excretion of Cd due to kidney function and protein excretion. However, renal effects such as hyperfiltration from Cd-mediated kidney damage or creatinine-specific Cd effects cannot be excluded with this cross-sectional design.

Challenges for environmental epidemiology research: are biomarker concentrations altered by kidney function or urine concentration adjustment?

Biomonitoring has become a standard approach for exposure assessment in occupational and environmental epidemiology. The use of biological effect markers to identify early adverse changes in target organs has also become widely adopted. However, the potential for kidney function to affect biomarker levels in the body and the optimal approach to adjustment of biomarker concentrations in spot urine samples for hydration status are two important but underappreciated challenges associated with biomarker use. Several unexpected findings, such as positive associations between urine nephrotoxicant levels and estimated glomerular filtration rate (eGFR), have been reported recently in research using biomarkers. These and other findings, discussed herein, suggest an impact of kidney glomerular filtration or tubule processing on biomarker levels. This is more commonly raised in the context of decreased kidney filtration, traditionally referred to as reverse causality; however, recent data suggest that populations with normal kidney filtration may be affected as well. Misclassification bias would result if biomarkers reflect kidney function as well as either exposures or early biological effect outcomes. Furthermore, urine biomarker associations with eGFR that differ markedly by approach used to adjust for urine concentration have been reported. Associations between urine measures commonly used for this adjustment, such as urine creatinine, and specific research outcomes could alter observed biomarker associations with outcomes. Research recommendations to address the potential impact of kidney function and hydration status adjustment on biomarkers are provided, including a range of approaches to study design, exposure and outcome assessment, and adjustment for urine concentration.

Curcumin Ameliorates Lead (Pb(2+))-Induced Hemato-Biochemical Alterations and Renal Oxidative Damage in a Rat Model

This study aims to evaluate the protective role of curcumin (Curc) against hematological and biochemical changes, as well as renal pathologies induced by lead acetate [Pb (CH3COO)2·3H2O] treatment. Male albino rats were intraperitoneally treated with Pb(2+) (25 mg of lead acetate/kg b.w., once a day) alone or in combination with Curc (30 mg of Curc/kg b.w., twice a day) for 7 days. Exposure of rats to Pb(2+) caused significant decreases in hemoglobin (Hb) content, hematocrit (Ht) value, and platelet (Plt) count, while Pb(2+)-related leukocytosis was accompanied by absolute neutrophilia, monocytosis, lymphopenia, and eosinopenia. A significant rise in lipid peroxidation (LPO) and a marked drop of total antioxidant capacity (TAC) were evident in the kidney, liver, and serum of Pb(2+) group compared to that of control. Furthermore, significantly high levels of total cholesterol (TC), triglycerides (TGs), and low-density lipoprotein cholesterol (LDL-C), and a sharp drop in serum high-density lipoprotein (HDL-C) level were also seen in blood after injection of Pb(2+). Additionally, hepatorenal function tests were enhanced. Meanwhile, Pb(2+) produced marked histo-cytological alterations in the renal cortex. Co-administration of Curc to the Pb(2+)-treated animals restored most of the parameters mentioned above to near-normal levels/features. In conclusion, Curc appeared to be a promising agent for protection against Pb(2+)-induced toxicity.

Association of arsenic with kidney function in adolescents and young adults: Results from the National Health and Nutrition Examination Survey 2009-2012

BACKGROUND

Long-term exposure to arsenic is a major public health concern. Emerging evidence suggests adverse health effects even at low levels of exposure. This study examined the association of arsenic exposure with estimated glomerular filtration rate (eGFR) and compared methods of adjustment for urinary dilution in a representative sample of U.S. adolescents and young adults.

METHODS

We performed a cross-sectional study of 1253 participants ages 12-30 years in the 2009-2012 National Health and Nutrition Examination Survey (NHANES) with available urinary arsenic and eGFR measures. Multivariable linear regression was used to model the association of urinary total arsenic and dimethylarsinate (DMA) with eGFR.

RESULTS

The median urinary total arsenic and DMA concentrations were 6.3 μg/L (IQR 3.3-12.7 μg/L) and 3.3 μg/L (IQR 1.7-5.7 μg/L), respectively. Median eGFR was 109 mL/min/1.73 m(2). Adjusting arsenic for urine concentration with urinary creatinine, eGFR was 4.0 mL/min/1.73 m(2) higher (95% confidence interval [CI] 1.0-7.1 mL/min/1.73 m(2)) and 4.3mL/min/1.73 m(2) higher (95% CI 0.5-8.0 mL/min/1.73 m(2)) per log-unit increase in total arsenic and DMA, respectively. When using urine osmolality to adjust for urine concentration, a log-unit increase in total arsenic and DMA was associated with a 0.4 mL/min/1.73 m(2) (95% CI -1.8 to 1.1 mL/min/1.73 m(2)) and 0.01 (95% CI -1.9 to 1.9 mL/min/1.73 m(2)) lower eGFR, respectively.

CONCLUSIONS

Discordant associations were observed between arsenic and eGFR levels depending on whether urinary creatinine or osmolality was used to adjust for urine concentration. Further study should be dedicated to validating the best approach to account for urinary dilution in research in toxicants, and this may have implications for all studies which examine urinary biomarkers.

Impact of urine concentration adjustment method on associations between urine metals and estimated glomerular filtration rates (eGFR) in adolescents

Positive associations between urine toxicant levels and measures of glomerular filtration rate (GFR) have been reported recently in a range of populations. The explanation for these associations, in a direction opposite that of traditional nephrotoxicity, is uncertain. Variation in associations by urine concentration adjustment approach has also been observed. Associations of urine cadmium, thallium and uranium in models of serum creatinine- and cystatin-C-based estimated GFR (eGFR) were examined using multiple linear regression in a cross-sectional study of adolescents residing near a lead smelter complex. Urine concentration adjustment approaches compared included urine creatinine, urine osmolality and no adjustment. Median age, blood lead and urine cadmium, thallium and uranium were 13.9 years, 4.0 μg/dL, 0.22, 0.27 and 0.04 g/g creatinine, respectively, in 512 adolescents. Urine cadmium and thallium were positively associated with serum creatinine-based eGFR only when urine creatinine was used to adjust for urine concentration (β coefficient=3.1 mL/min/1.73 m(2); 95% confidence interval=1.4, 4.8 per each doubling of urine cadmium). Weaker positive associations, also only with urine creatinine adjustment, were observed between these metals and serum cystatin-C-based eGFR and between urine uranium and serum creatinine-based eGFR. Additional research using non-creatinine-based methods of adjustment for urine concentration is necessary.

Ameliorating activity of ginger (Zingiber officinale) extract against lead induced renal toxicity in male rats

Lead poisoning has been known to be associated with structural and functional abnormalities of multiple organ systems of human body. The aim of this investigation was to study the renal protective effects of ginger (Zingiber officinale) extract in lead induced toxicity rats. In this study renal glutathione (GSH) level, glutathione peroxidase (GPX), glutathione-s-transferase (GST), and catalase enzymes were measured in lead nitrate (300 mg/kg BW), and lead nitrate plus ginger extract (150 mg/kg BW) treated rat groups for 1 week and 3 weeks respectively. The glutathione level and GSH dependent antioxidant enzymes such as glutathione peroxidase, glutathione-s-transferase, and catalase significantly (P < 0.05) increased in ginger extract treated rat groups. In addition, histological studies showed lesser renal changes in lead plus ginger extract treated rat groups than that of lead alone treated rat groups. These results indicate that ginger extract alleviated lead toxic effects by enhancing the levels of glutathione, glutathione peroxidase, glutathione-s-transferase and catalase.

Blood lead level and measured glomerular filtration rate in children with chronic kidney disease

BACKGROUND

The role of environmental exposure to lead as a risk factor for chronic kidney disease (CKD) and its progression remains controversial, and most studies have been limited by a lack of direct glomerular filtration rate (GFR) measurement.

OBJECTIVE

We evaluated the association between lead exposure and GFR in children with CKD.

METHODS

In this cross-sectional study, we examined the association between blood lead levels (BLLs) and GFR measured by the plasma disappearance of iohexol among 391 participants in the Chronic Kidney Disease in Children (CKiD) prospective cohort study.

RESULTS

Median BLL and GFR were 1.2 µg/dL and 44.4 mL/min per 1.73 m2, respectively. The average percent change in GFR for each 1-µg/dL increase in BLL was -2.1 (95% CI: -6.0, 1.8). In analyses stratified by CKD diagnosis, the association between BLL and GFR was stronger among children with glomerular disease underlying CKD; in this group, each 1-µg/dL increase in BLL was associated with a -12.1 (95% CI: -22.2, -1.9) percent change in GFR. In analyses stratified by anemia status, each 1-µg/dL increase in BLL among those with and without anemia was associated with a -0.3 (95% CI: -7.2, 6.6) and -4.6 (95% CI: -8.9, -0.3) percent change in GFR, respectively.

CONCLUSIONS

There was no significant association between BLL and directly measured GFR in this relatively large cohort of children with CKD, although associations were observed in some subgroups. Longitudinal analyses are needed to examine the temporal relationship between lead and GFR decline, and to further examine the impact of underlying cause of CKD and anemia/hemoglobin status among patients with CKD.

Dietary flaxseed oil supplementation mitigates the effect of lead on the enzymes of carbohydrate metabolism, brush border membrane, and oxidative stress in rat kidney tissues

Lead is a heavy metal widely distributed in the environment. Lead is a ubiquitous environmental toxin that is capable of causing numerous acute and chronic illnesses. Human and animal exposure demonstrates that lead is nephrotoxic. However, attempts to reduce lead-induced nephrotoxicity were not found suitable for clinical use. Recently, flaxseed oil (FXO), a rich source of ω-3 fatty acids and lignans, has been shown to prevent/reduce the progression of certain types of cardiovascular and renal disorders. In view of this, the present study investigates the protective effect of FXO on lead acetate (PbAc)-induced renal damage. Rats were pre-fed normal diet and the diet rich in FXO for 14 days, and then, four doses of lead acetate (25 mg/kg body weight) were administered intraperitoneally while still on diet. Various serum parameters, enzymes of carbohydrate metabolism, brush border membrane (BBM), and oxidative stress were analyzed in rat kidney. PbAc nephrotoxicity was characterized by increased serum creatinine and blood urea nitrogen. PbAc increased the activities of lactate dehydrogenase and NADP-malic enzyme, whereas it decreased malate and glucose-6-phosphate dehydrogenase, glucose-6-phosphatase, fructose-1, 6-bisphosphatase, and BBM enzyme activities. PbAc caused oxidant/antioxidant imbalances as reflected by increased lipid peroxidation and decreased activities of superoxide dismutase, glutathione peroxidase, and catalase. In contrast, FXO alone enhanced the enzyme activities of carbohydrate metabolism, BBM, and antioxidant defense system. FXO feeding to PbAc-treated rats markedly enhanced resistance to PbAc-elicited deleterious effects. In conclusion, dietary FXO supplementation ameliorated PbAc-induced specific metabolic alterations and oxidative damage by empowering antioxidant defense mechanism and improving BBM integrity and energy metabolism.

Limits to chemical hormesis as a dose-response model in health risk assessment

This review presents and discusses the extent to which chemical hormesis meets five important requirements for performance of any dose-response model in the toxicological and regulatory sciences. These include (1) the requirement that there be a documented and accepted mechanistic basis for the dose-response model's plausible role and use in health risk assessment; (2) the requirement that any newly proposed dose-response methodology can be compared with current models as to reliability and scientific validity; (3) the requirement that the underlying reliability and stability of the model be established as to its temporal aspects, that is, minimal temporal lag between stressor contact and biological or toxicological response and temporal stability expressed throughout the prevailing relationship; (4) the requirement that the dose-response model be as broadly applicable as other dose-response methodologies being applied in human health risk assessment; and, (5) the requirement that any dose-response model proposed as default methodology can be characterized as to variability and uncertainty and will have a minimal likelihood of harm to the health of impacted populations. This review includes a brief treatment of definitions of hormesis and its place in nonmonotonic dose-response relationships. Overall, critical evaluation of chemical hormesis as a dose-response model in risk assessment shows it to have significant limits within the five requirements. These limits will impede any acceptance of chemical hormesis as a default approach in health risk assessment.

Associations of blood lead, cadmium, and mercury with estimated glomerular filtration rate in the Korean general population: analysis of 2008-2010 Korean National Health and Nutrition Examination Survey data

INTRODUCTION

The objective of this study was to evaluate associations between blood lead, cadmium, and mercury levels with estimated glomerular filtration rate in a general population of South Korean adults.

METHODS

This was a cross-sectional study based on data obtained in the Korean National Health and Nutrition Examination Survey (KNHANES) (2008-2010). The final analytical sample consisted of 5924 participants. Estimated glomerular filtration rate (eGFR) was calculated using the MDRD Study equation as an indicator of glomerular function.

RESULTS

In multiple linear regression analysis of log2-transformed blood lead as a continuous variable on eGFR, after adjusting for covariates including cadmium and mercury, the difference in eGFR levels associated with doubling of blood lead were -2.624 mL/min per 1.73 m² (95% CI: -3.803 to -1.445). In multiple linear regression analysis using quartiles of blood lead as the independent variable, the difference in eGFR levels comparing participants in the highest versus the lowest quartiles of blood lead was -3.835 mL/min per 1.73 m² (95% CI: -5.730 to -1.939). In a multiple linear regression analysis using blood cadmium and mercury, as continuous or categorical variables, as independent variables, neither metal was a significant predictor of eGFR. Odds ratios (ORs) and 95% CI values for reduced eGFR calculated for log2-transformed blood metals and quartiles of the three metals showed similar trends after adjustment for covariates.

DISCUSSION

In this large, representative sample of South Korean adults, elevated blood lead level was consistently associated with lower eGFR levels and with the prevalence of reduced eGFR even in blood lead levels below 10 μg/dL. In conclusion, elevated blood lead level was associated with lower eGFR in a Korean general population, supporting the role of lead as a risk factor for chronic kidney disease.

Associations of multiple metals with kidney outcomes in lead workers

OBJECTIVES

Environmental exposure to multiple metals is common. A number of metals cause nephrotoxicity with acute and/or chronic exposure. However, few epidemiologic studies have examined the impact of metal coexposure on kidney function. Therefore, the authors evaluated associations of antimony and thallium with kidney outcomes and assessed the impact of cadmium exposure on those associations in lead workers.

METHODS

Multiple linear regression was used to examine associations between ln-urine thallium, antimony and cadmium levels with serum creatinine- and cystatin-C-based glomerular filtration measures and ln-urine N-acetyl-β-D-glucosaminidase (NAG).

RESULTS

In 684 participants, median urine thallium and antimony were 0.39 and 0.36 μg/g creatinine, respectively. After adjustment for lead dose, urine creatinine and kidney risk factors, higher ln-urine thallium was associated with higher serum creatinine- and cystatin-C-based estimates of glomerular filtration rate; associations remained significant after adjustment for antimony and cadmium (regression coefficient for serum creatinine-based estimates of glomerular filtration rate =5.2 ml/min/1.73 m2; 95% CI =2.4 to 8.0). Antimony associations with kidney outcomes were attenuated by thallium and cadmium adjustment; thallium and antimony associations with NAG were attenuated by cadmium.

CONCLUSIONS

Urine thallium levels were significantly associated with both serum creatinine- and cystatin-C-based glomerular filtration measures in a direction opposite that expected with nephrotoxicity. Given similarities to associations recently observed with cadmium, these results suggest that interpretation of urine metal values, at exposure levels currently present in the environment, may be more complex than previously appreciated. These results also support multiple metal analysis approaches to decrease the potential for inaccurate risk conclusions.

Antagonistic effects of cadmium on lead accumulation in pregnant and non-pregnant mice

People are frequently exposed to combinations of contaminants but there is a paucity of data on the effects of mixed contaminants at low doses. This study investigated the influence of cadmium (Cd) on lead (Pb) accumulation in pregnant and non-pregnant mice following exposure to contaminated soil. Exposure to Pb from contaminated soils increased Pb accumulation in both pregnant and non-pregnant mice compared to unexposed control animals (pregnant and non-pregnant). Lead accumulation in the liver and kidneys of exposure pregnant mice (40 ± 15 mg Pb kg(-1)) was significantly higher (P<0.05) than concentrations detected in control pregnant mice (<1 mg Pb kg(-1)). The presence of Cd in contaminated soil had a major effect on the Pb and Fe accumulation in the kidneys and liver, respectively. This study shows that Pb uptake is mediated by the presence of Cd in the co-contaminated soil and demonstrates that further research is required to investigate the influence of co-contaminants on human exposure at sub-chronic concentrations.

Assessment of some renal indices in people occupationally exposed to lead

Exposure to lead has been reported to have adverse health implications. An assessment of renal function in people occupationally exposed to lead was carried out using the following biochemical markers urea, creatinine, sodium, potassium, chloride and bicarbonate. A total of 53 test subjects (mean age 30.9 ± 7.7) were randomly selected among some workers occupationally exposed to lead in Osogbo city and 42 apparently healthy subjects (mean age 30.1 ± 1.2) were used as controls. The plasma urea, creatinine, chloride and bicarbonate concentration were determined using modified Berthelot method, Jaffe's reaction, Schales and Schales method and back titration methods, respectively. The plasma sodium and potassium concentrations were determined using flame emission spectrophotometry while blood lead level was also determined using atomic absorption spectrophotometry. The result showed significant increases in mean plasma concentration of creatinine (84.9 ± 13.6-97.4 ± 28.7 μmol/L), sodium (131.9 ± 3.9-134.8 ± 3.7 mmol/L) and chloride (98.2 ± 4.0-100.4 ± 3.9 mmol/L) in test subjects when compared with controls (p < 0.05). Furthermore, significant increases (p < 0.01) were observed in mean plasma concentration of urea (4.7 ± 1.2-5.7 ± 1.3 mmol/L) and blood lead levels (18.5 ± 3.5-69.7 ± 13.2 mg/L) in test subjects in comparison with controls. In contrast, there were no significant differences observed when mean plasma potassium and bicarbonate levels in test subjects were compared with controls (p > 0.05). These results indicate that occupational exposure to lead may compromise renal function.

Associations of blood lead with estimated glomerular filtration rate using MDRD, CKD-EPI and serum cystatin C-based equations

BACKGROUND

Low-level lead exposure is widespread and has been implicated as a chronic kidney disease (CKD) risk factor. However, studies evaluating associations of lead dose with newer, potentially more accurate, estimates of kidney function, in participants with a wide range of glomerular filtration rates (GFRs), are scarce.

METHODS

We compared associations of blood lead and estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and cystatin C single variable, multivariable and combined creatinine/cystatin C equations in 3941 adults who participated in the 1999-2002 National Health and Nutrition Examination Survey cystatin C subsample.

RESULTS

Geometric mean blood lead was 1.7 μg/dL. After multivariable adjustment, differences [95% confidence interval (CI)] in mean eGFR for a doubling of blood lead were -1.9 (-3.2, -0.7), -1.7 (-3.0, -0.5) and -1.4 (-2.3, -0.5) mL/min/1.73 m(2), using the cystatin C single variable, multivariable and combined creatinine/cystatin C equations, respectively, reflecting lower eGFR with increased blood lead. The corresponding differences (95% CI) were -0.9 (-1.9, 0.02) and -0.9 (-1.8, 0.01) using the creatinine-based MDRD and CKD-EPI equations, respectively. In participants aged ≥60 years, differences in mean eGFR ranged from -3.0 to -4.5 mL/min/1.73 m(2), and odds of reduced eGFR (<60 mL/min/1.73 m(2)) were increased for all estimates of GFR.

CONCLUSIONS

These results support the inclusion of cystatin C-based eGFR in future lead research and provide additional evidence for environmental lead exposure as a CKD risk factor.

Associations of low-level urine cadmium with kidney function in lead workers

OBJECTIVES

Low-level cadmium exposure, resulting in, for example, urinary cadmium <2.0 μg/g creatinine, is widespread; recent data suggest nephrotoxicity even at these low levels. Few studies have examined the impact of low-level cadmium exposure in workers who are occupationally exposed to other nephrotoxicants such as lead.

METHODS

We evaluated associations of urine cadmium, a measure of cumulative dose, with four glomerular filtration measures and N-acetyl-β-D-glucosaminidase (NAG) in lead workers. Recent and cumulative lead doses were assessed via blood and tibia lead, respectively.

RESULTS

In 712 lead workers, mean (SD) blood and tibia lead values, urine cadmium values and estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease equation were 23.1 (14.1) μg/dl, 26.6 (28.9) μg Pb/g bone mineral, 1.15 (0.66) μg/g creatinine and 97.4 (19.2) ml/min/1.73 m(2), respectively. After adjustment for age, sex, body mass index, urine creatinine, smoking, alcohol, education, annual income, diastolic blood pressure, current or former lead worker job status, new or returning study participant, and blood and tibia lead, higher ln-urine cadmium was associated with higher calculated creatinine clearance, eGFR (β = 8.7 ml/min/1.73 m(2); 95% CI 5.4 to 12.1) and ln-NAG but lower serum creatinine.

CONCLUSIONS

Potential explanations for these results include a normal physiological response in which urine cadmium levels reflect renal filtration, the impact of adjustment for urine dilution with creatinine in models of kidney outcomes, and cadmium-related hyperfiltration.

Chronic renal failure from lead: myth or evidence-based fact?

In this mini review, we would like to challenge the well-established 'fact' that lead exposure causes chronic renal failure (CRF). Even though only scarce evidence exists of the relationship between lead and renal failure, a World Health Organization Environmental Health Criteria document summarizes that 'Lead has been a very common cause of acute or chronic renal failure'. It is also written and cited in textbooks and numerous publications that chronic lead nephropathy causes a slowly progressive interstitial nephritis manifested by a reduced glomerular filtration rate, and that there is a growing consensus that lead contributes to hypertension in the general population. We will argue that, when published reports are carefully scrutinized, such statements on lead and CRF are not evidence based but are rather founded on a few narrative reports on lead-exposed individuals and statistical associations between lead and serum creatinine (or urea) in a few population studies. We will, however, not argue that lead is not toxic and that lead does not cause other types of severe health effects where the evidence is unquestionable, but we do not believe that the kidneys are an early victim after lead exposure.

Protective effect of N-acetylcysteine on experimental chronic lead nephrotoxicity in immature female rats

Oxidative stress plays a key role in lead (Pb)-induced nephrotoxicity. N-acetylcysteine (NAC) is a potent oxygen free radicals scavenger and a metal chelator. In the present study, female Sprague-Dawley rats received PbAc(2) (300 mg/L, via drinking water) and/or NAC (100 mg/kg/day, by intraperitoneal injection) to investigate the protective effect of NAC on Pb-induced renal damage and oxidative stress as well as its mechanism of action. Renal toxicity was evaluated by measuring urinary excretion of total protein, beta(2)-microglobulin, albumin and urinary enzyme markers of tubular necrosis, as well as serum urea nitrogen level. Activities of antioxidant enzymes, contents of glutathione and malondialdehyde in kidney were also measured. Renal cell damage was assessed by electron microscopy. Animals that received both Pb and NAC showed a better renal function than those receiving Pb alone. Lead-induced tubular lesions and mitochondrial damage were markedly reduced in rats that also received NAC. Also, NAC significantly reduced the levels of lipid peroxidation and markedly restored the enzymic and non-enzymatic antioxidants levels in kidney of Pb-treated rats. Moreover, NAC administration significantly increased urinary Pb excretion and decreased its level in the serum and kidney. In conclusion, NAC treatment prevents renal tubular damage induced by chronic Pb administration, most probably through its antioxidant properties and chelating ability.

Blood lead level and kidney function in US adolescents: The Third National Health and Nutrition Examination Survey

BACKGROUND

Chronic, high-level lead exposure is a known risk factor for kidney disease. The effect of current low-level environmental lead exposure is less well known, particularly among children, a population generally free from kidney disease risk factors such as hypertension and diabetes mellitus. Therefore, in this study, we investigated the association between lead exposure and kidney function in a representative sample of US adolescents.

METHODS

Participants included 769 adolescents aged 12 to 20 years for whom whole blood lead and serum cystatin C were measured in the Third National Health and Nutrition Examination Survey, conducted from 1988-1994. The association between blood lead level and level of kidney function (glomerular filtration rate [GFR]), determined by cystatin C-based and creatinine-based estimating equations, was examined.

RESULTS

Median whole blood lead level was 1.5 microg/dL (to convert to micromoles per liter, multiply by 0.0483), and median cystatin C-estimated GFR was 112.9 mL/min/1.73 m(2). Participants with lead levels in the highest quartile (> or =3.0 microg/dL) had 6.6 mL/min/1.73 m(2)-lower estimated GFR (95% confidence interval, -0.7 to -12.6 mL/min/1.73 m(2)) compared with those in the first quartile (<1 microg/dL). A doubling of blood lead level was associated with a 2.9 mL/min/1.73 m(2)-lower estimated GFR (95% confidence interval, -0.7 to -5.0 mL/min/1.73 m(2)). Lead levels were also associated with lower creatinine-based estimated GFR levels, but the association was weaker than with cystatin C-based GFR and not statistically significant.

CONCLUSIONS

Higher blood lead levels in a range below the current Centers for Disease Control and Prevention-designated level of concern (10 microg/dL) were associated with lower estimated GFRs in a representative sample of US adolescents. This finding contributes to the increasing epidemiologic evidence indicating an adverse effect of low-level environmental lead exposure.

The alteration of glutathione peroxidase activity in rat organs after lead exposure

The activity response of the antioxidant enzymes glutathione peroxidase (GPx), glutathione reductase (GR) and the contents of thiobarbituric reactive substances (TBARS) were investigated in rats exposed to lead. The enzyme activities were determined in the liver, kidney and heart of male and female rats which were received 100 mg and 1000 mg of lead acetate per liter water for 18 weeks. The statistical analyses indicated the differences related to the organs and to the sex of animals. Administration of lead evoked decrease of GPx activity in the kidney of both male and female rats. On the contrary, GPx activity increased in the heart of female rats, while in the male rats the higher dose of lead evoked a decrease in activity. In the kidneys of male rats and in the heart of female rats thiobarbituric acid reactive substances (TBARS), an indicators of oxidative stress, significantly increased in rats which were given the high lead dose. Most likely the observed changes could be a compensatory response to different lead accumulation in the male and female organs and also the possible distinct mechanisms in ROS elimination.

Mycophenolate mofetil administration reduces renal inflammation, oxidative stress, and arterial pressure in rats with lead-induced hypertension

Hypertension is a likely consequence of chronic lead exposure in humans, especially in association with reduced renal function and in high risk populations. Numerous studies have demonstrated that oxidative stress plays an important role in the pathogenesis of experimental lead-induced hypertension and we have shown recently that tubulointerstitial immune cell infiltration is a feature of chronic low-dose lead exposure. Since oxidative stress, renal inflammation, and angiotensin activity are closely linked characteristics in experimental models of hypertension, we decided to investigate whether lead-induced hypertension would be ameliorated by suppressing renal inflammation with the immunosuppressive drug mycophenolate mofetil (MMF). We studied rats exposed for 14 wk to lead acetate (100 ppm in the drinking water) that, in addition, received either MMF, 20 mg.kg(-1).day(-1) by gastric gavage (Pb.MMF group, n = 12) or vehicle (Pb group, n = 12). Control rats received MMF alone (n = 5) or neither lead nor MMF (n = 6). All rats were killed at the end of the experiment. Low-dose lead exposure resulted in mild to moderate tubular cell damage and a progressive increment in blood pressure, oxidative stress, interstitial accumulation of lymphocytes and macrophages, NF-kappaB activation, and increased renal angiotensin II level. The administration of MMF suppressed the tubulointerstitial accumulation of lymphocytes and macrophages and prevented the hypertension, oxidative stress, and NF-kappaB activation and reduced the heightened renal angiotensin content associated with chronic lead exposure. We conclude that interstitial inflammation plays an important role in lead-induced hypertension.

Benchmark dose approach for renal dysfunction in workers exposed to lead

Benchmark dose (BMD) and the lower confidence limit on the benchmark dose (BMDL) of blood lead were estimated to explore the biologic exposure limits for renal dysfunction caused by lead. One hundred thirty-five workers from one storage battery plant were selected as lead exposure group while 143 mechanics as the control. The relationship between the blood lead concentration and the urinary excretion of total protein (TP), beta2-microglobulin (beta2-MG), and N-acetyl-beta-D-glucosaminidase (NAG) was studied. The quantal linear logistic regression model (BMDS Version 1.3.1) was used to calculate BMD and BMDL of blood lead. The results showed that the levels of NAG, beta2-MG, and TP in lead-exposed workers were higher than those of control group and elevated along with rising length of employment. The levels of three indices for renal dysfunction increased with the elevated blood lead. The BMD and BMDL of blood lead for renal dysfunction were from 299.4 to 588.7 microg/L and from 253.4 to 402.3 microg/L, respectively. The BMDL of blood lead was ranged from high to low as TP, beta2-MG, and NAG. It is suggested that the urinary NAG activity could be a sensitive and early biomarker of renal tubular dysfunction induced by lead. When assessing renal function in workers occupationally exposed to lead, a blood lead level of 250 microg/L could serve as a warning signal.

Lead-related nephrotoxicity: a review of the epidemiologic evidence

Chronic kidney disease (CKD) represents a major global public health concern. Efforts to prevent and/or slow progression of CKD are essential. Lead nephropathy, characterized by chronic tubulointerstitial nephritis, is a well-known risk of chronic, high-level lead exposure. However, in recent years, lead exposure has declined sharply, particularly in developed countries. We reviewed epidemiologic research in general, occupational, and patient populations to assess whether lead, at current exposure levels, still contributes to nephrotoxicity. Other pertinent topics, such as risk in children, genetic susceptibility, and co-exposure to cadmium, are also considered. The data reviewed indicate that lead contributes to nephrotoxicity, even at blood lead levels below 5 microg/dl. This is particularly true in susceptible populations, such as those with hypertension (HTN), diabetes, and/or CKD. Low socioeconomic status is a risk factor for both lead exposure and diseases that increase susceptibility. Future public health risk for lead-related nephrotoxicity may be most significant in those rapidly developing countries where risk factors for CKD, including obesity and secondary HTN and diabetes mellitus, are increasing more rapidly than lead exposure is declining. Global efforts to reduce lead exposure remain important. Research is also needed to determine whether specific therapies, such as chelation, are beneficial in susceptible populations.

Effect modification 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

Genetic polymorphisms that affect lead toxicokinetics or toxicodynamics may be important modifiers of risk for adverse outcomes in lead-exposed populations. We recently reported associations between higher patella lead, which is hypothesized to represent a lead pool that is both bioavailable and cumulative, and adverse renal outcomes in current and former Korean lead workers. In the present study, we assessed effect modification by polymorphisms in the genes encoding for delta-aminolevulinic acid dehydratase (ALAD), the vitamin D receptor (VDR), and endothelial nitric oxide synthase on those associations. Similar analyses were conducted with three other lead biomarkers. Renal function was assessed via blood urea nitrogen, serum creatinine, measured and calculated creatinine clearances, urinary N-acetyl-beta-D-glucosaminidase, and retinol-binding protein. Mean (SD) blood, patella, tibia, and dimercaptosuccinic acid-chelatable lead values were 30.9 (16.7) microg/dl, 75.1 (101.1)and 33.6 (43.4) microg Pb/g bone mineral, and 0.63 (0.75) microg Pb/mg creatinine, respectively, in 647 lead workers. Little evidence of effect modification by genotype on associations between patella lead and renal outcomes was observed. The VDR polymorphism did modify associations between the other lead biomarkers and the serum creatinine and calculated creatinine clearance. Higher lead dose was associated with worse renal function in participants with the variant B allele. Models in two groups, dichotomized by median age, showed that this effect was present in the younger half of the population. Limited evidence of effect modification by ALAD genotype was observed; higher blood lead levels were associated with higher calculated creatinine clearance among participants with the ALAD(1-2) genotype. In conclusion, VDR and/or ALAD genotypes modified associations between all the lead biomarkers, except patella lead, and the renal outcomes.

Renal and neurologic effects of cadmium, lead, mercury, and arsenic in children: evidence of early effects and multiple interactions at environmental exposure levels

Lead, cadmium, mercury, and arsenic are common environmental pollutants in industrialized countries, but their combined impact on children's health is little known. We studied their effects on two main targets, the renal and dopaminergic systems, in > 800 children during a cross-sectional European survey. Control and exposed children were recruited from those living around historical nonferrous smelters in France, the Czech Republic, and Poland. Children provided blood and urine samples for the determination of the metals and sensitive renal or neurologic biomarkers. Serum concentrations of creatinine, cystatin C, and beta2-microglobulin were negatively correlated with blood lead levels (PbB), suggesting an early renal hyperfiltration that averaged 7% in the upper quartile of PbB levels (> 55 microg/L; mean, 78.4 microg/L). The urinary excretion of retinol-binding protein, Clara cell protein, and N-acetyl-beta-d-glucosaminidase was associated mainly with cadmium levels in blood or urine and with urinary mercury. All four metals influenced the dopaminergic markers serum prolactin and urinary homovanillic acid, with complex interactions brought to light. Heavy metals polluting the environment can cause subtle effects on children's renal and dopaminergic systems without clear evidence of a threshold, which reinforces the need to control and regulate potential sources of contamination by heavy metals. Key words: arsenic, biomarkers, cadmium, dopaminergic, heavy metals, interactions, lead, mercury, renal.

Chronic exposure to low doses of lead results in renal infiltration of immune cells, NF-kappaB activation, and overexpression of tubulointerstitial angiotensin II

Chronic exposure to low doses of lead results in generation of reactive oxygen species, reduced nitric oxide availability, and arterial hypertension. The present studies were done to define if other conditions associated with oxidative stress, such as renal interstitial inflammation, nuclear factor-kappaB (NF-kappaB) activation, and cells expressing angiotensin II, are, in fact, features of low-dose lead exposure. Male Sprague-Dawley rats were randomly assigned to the lead group (n = 8) or the control group (n = 9). The lead group received 100 ppm lead acetate in the drinking water for 14 weeks. At the end of this period of time, rats were killed under general anesthesia, and the kidneys were harvested for studies. The lead-exposed group presented focal tubulointerstitial damage and highly significant increments in nitrotyrosine immune staining, lymphocyte and macrophage infiltration, angiotensin II-positive cells, and intranuclear positive staining for the p65 DNA-binding subunit of NF-kappaB in tubulointerstitial cells. Tubulointerstitial inflammation, cells expressing angiotensin II, and NF-kappaB activation are consequences of a 3-month low-dose exposure to lead and likely play a role in the development of hypertension and chronic lead nephropathy.

Associations of patella lead and other lead biomarkers with renal function in lead workers

OBJECTIVE

We sought to compare associations of patella lead, which may represent a unique cumulative and bioavailable lead pool, with other lead measures in models of renal function.

METHODS

Renal function measures included blood urea nitrogen, serum creatinine, measured and calculated creatinine clearances, and urinary N-acetyl-beta-D-glucosaminidase (NAG) and retinol-binding protein.

RESULTS

In 652 lead workers, mean (SD) blood, patella, and tibia lead were 30.9 (16.7) microg/dL, 75.1 (101.1) and 33.6 (43.4) microg Pb/g bone mineral, respectively, and were correlated (Spearman's r = 0.51-0.74). Patella lead was associated (P < 0.05) with NAG in all lead workers. In models of effect modification by age, higher patella lead also was associated with higher serum creatinine in older participants. Similar associations were observed for blood and tibia lead.

CONCLUSIONS

Associations between patella lead and adverse renal outcomes were not unique; this may be due, in part, to high correlations among the lead biomarkers in this study.

Associations among lead dose biomarkers, uric acid, and renal function in Korean lead workers

Recent research suggests that both uric acid and lead may be nephrotoxic at lower levels than previously recognized. We analyzed data from 803 current and former lead workers to determine whether lead biomarkers were associated with uric acid and whether previously reported associations between lead dose and renal outcomes were altered after adjustment for uric acid. Outcomes included uric acid, blood urea nitrogen, serum creatinine, measured and calculated creatinine clearances, and urinary N-acetyl-ss-d-glucosaminidase (NAG) and retinol-binding protein. Mean (+/- SD) uric acid, tibia lead, and blood lead levels were 4.8 +/- 1.2 mg/dL, 37.2 +/- 40.4 microg/g bone mineral, and 32.0 +/- 15.0 microg/dL, respectively. None of the lead measures (tibia, blood, and dimercaptosuccinic-acid-chelatable lead) was associated with uric acid, after adjustment for age, sex, body mass index, and alcohol use. However, when we examined effect modification by age on these relations, both blood and tibia lead were significantly associated (ss = 0.0111, p < 0.01 and ss = 0.0036, p = 0.04, respectively) in participants in the oldest age tertile. These associations decreased after adjustment for blood pressure and renal function, although blood lead remained significantly associated with uric acid (ss = 0.0156, p = 0.01) when the population was restricted to the oldest tertile of workers with serum creatinine greater than the median (0.86 mg/dL). Next, in models of renal function in all workers, uric acid was significantly (p < 0.05) associated with all renal outcomes except NAG. Finally, in the oldest tertile of workers, associations between lead dose and NAG were unchanged, but fewer associations between the lead biomarkers and the clinical renal outcomes remained significant (p less than or equal to 0.05) after adjustment for uric acid. In conclusion, our data suggest that older workers comprise a susceptible population for increased uric acid due to lead. Uric acid may be one, but not the only, mechanism for lead-related nephrotoxicity.

Effects of smoking and lead exposure on proximal tubular integrity among Egyptian industrial workers

BACKGROUND

The hazards of occupational lead exposure are well documented. Tissue damage produced by lead is slow and progressive. The renal system is one of the systems primarily affected by lead. The present study aimed to evaluate renal proximal tubular functional and structural integrity among lead-exposed and cigarette-smoking male Egyptian workers. This study was extended to investigate the effect of lead exposure and cigarette smoking on urinary excretion of copper (Cu) and zinc (Zn).

METHODS

Participants included in the present study were 156 male workers grouped as follows: i) 75 lead non-exposed workers subgrouped into G1 that consisted of 36 non-smokers (age, 39.08+/-6.65 years) and G2, which included 39 smokers (age, 43.87+/-9.93 years); ii) 45 lead-exposed workers (work duration <20 years) subgrouped into G3 that consisted of 25 non-smokers (age, 37.40+/-3.76 years) and G4, which included 20 smokers (age, 38.40+/-4.95 years), and iii) 36 lead-exposed workers (work duration > or =20 years) subgrouped into G5 that consisted of 16 non-smokers (age, 45.94+/-4.19 years) and G6 which included 20 smokers (age, 45.70+/-2.25 years). Functional integrity of proximal tubules was studied by determining urinary level of low-molecular-weight protein alpha1-microglobulin (alpha1M), and structural integrity was investigated by measuring urinary activities of the lysosomal enzyme N-acetyl-beta-D-glucosaminidase (NAG) and the cytoplasmic enzyme glutathione S-transferase (GST). Urinary concentrations of Pb, Cu, Zn, and creatinine were also determined.

RESULTS

Data of the present investigation showed increased urinary excretion of all measured urinary parameters among lead-exposed workers in comparison with non-exposed workers whether they were non-smokers or smokers (G3 vs. G1, G5 vs. G1, G4 vs. G2, and G6 vs. G2), with greater elevation among lead-exposed smokers than among lead-exposed non-smokers (G4 vs. G3, G6 vs. G5). In addition, there was a greater increase in levels of all urinary parameters among workers with work duration > or =20 years than in those with <20 years' work duration (G6 vs. G4, G5 vs. G3).

CONCLUSIONS

Lead exposure in Egyptian workers causes damage to renal proximal tubules and results in its dysfunction. Cigarette smoking has a nephrotoxic effect and also is synergistic to lead nephrotoxicity on urinary excretion of GST and NAG, as well as Pb.

Therapeutic efficacy of lipoic acid in combination with dimercaptosuccinic acid against lead-induced renal tubular defects and on isolated brush-border enzyme activities

The combined therapeutic potentials of lipoic acid and dimercaptosuccinic acid were compared against their sole administrations in restoring the altered lead sensitive indices in urine and isolated renal brush-border preparations. Toxicity was induced in male albino rats (Wistar strain) by administering lead acetate (0.2%) in drinking water for 5 weeks, followed by therapy comprising lipoic acid (25 mg/kg body weight) and dimercaptosuccinic acid (20 mg/kg body weight) solely as well as combined during the 6th week. Changes in kidney weights encountered upon lead administration improved after therapy with lipoic acid and dimercaptosuccinic acid. Renal integrity was assessed by measuring the activities of alkaline phosphatase, acid phosphatase, lactate dehydrogenase, leucine aminopeptidase, N-acetyl-beta-D-glucosaminidase, gamma-glutamyl transferase and beta-glucuronidase in urine along with some urinary constituents (urea, uric acid, creatinine, protein and phosphorous). The effects of lead were also studied on isolated brush-border enzymes (alkaline phosphatase, acid phosphatase, gamma-glutamyl transferase and beta-glucuronidase) that showed a decline upon its administration. Increased activities of urinary enzymes were accompanied by increase in the urinary constituents. Increase in renal lead content was paralleled by a drastic fall in the renal delta-aminolevulinic acid dehydratase and a rise in urinary lead levels. Relative to the administration of lead, the combined therapy showed betterment on the renal integrity with respect to the functional parameters assessed, thereby indicating its efficacy over the monotherapies.

Associations of renal function with polymorphisms in the delta-aminolevulinic acid dehydratase, vitamin D receptor, and nitric oxide synthase genes in Korean lead workers

We analyzed data from 798 lead workers to determine whether polymorphisms in the genes encoding delta-aminolevulinic acid dehydratase (ALAD), endothelial nitric oxide synthase (eNOS), and the vitamin D receptor (VDR) were associated with or modified relations of lead exposure and dose measures with renal outcomes. Lead exposure was assessed with job duration, blood lead, dimercaptosuccinic acid (DMSA)-chelatable lead, and tibia lead. Renal function was assessed with blood urea nitrogen (BUN), serum creatinine, measured creatinine clearance, calculated creatinine clearance and urinary N-acetyl-beta-D-glucosaminidase (NAG), and retinol-binding protein. Mean (+/- SD) tibia lead, blood lead, and DMSA-chelatable lead levels were 37.2 +/- 40.4 microg/g bone mineral, 32.0 +/- 15.0 microg/dL, and 767.8 +/- 862.1 microg/g creatinine, respectively. After adjustment, participants with the ALAD(2) allele had lower mean serum creatinine and higher calculated creatinine clearance. We observed effect modification by ALAD on associations between blood lead and/or DMSA-chelatable lead and three renal outcomes. Among those with the ALAD(1-2) genotype, higher lead measures were associated with lower BUN and serum creatinine and higher calculated creatinine clearance. Participants with the eNOS variant allele were found to have higher measured creatinine clearance and BUN. In participants with the Asp allele, longer duration working with lead was associated with higher serum creatinine and lower calculated creatinine clearance and NAG; all were significantly different from relations in those with the Glu/Glu genotype except NAG (p = 0.08). No significant differences were seen in renal outcomes by VDR genotype, nor was consistent effect modification observed. The ALAD findings could be explained by lead-induced hyperfiltration.

Associations of lead biomarkers with renal function in Korean lead workers

AIMS

To compare associations of lead biomarkers with renal function in current and former lead workers.

METHODS

Cross sectional analysis of first year results from a longitudinal study of 803 lead workers and 135 controls in South Korea. Clinical renal function was assessed by blood urea nitrogen (BUN), serum creatinine, and measured and calculated creatinine clearance. Urinary N-acetyl-beta-D-glucosaminidase (NAG) and retinol-binding protein were also measured.

RESULTS

Mean (SD) tibia lead, blood lead, and DMSA chelatable lead levels in lead workers were 37.2 (40.4) micro g/g bone mineral, 32.0 (15.0) micro g/dl, and 767.8 (862.1) micro g/g creatinine, respectively. Higher lead measures were associated with worse renal function in 16/42 models. When influential outliers were removed, higher lead measures remained associated with worse renal function in nine models. An additional five associations were in the opposite direction. Effect modification by age was observed. In 3/16 models, associations between higher lead measures and worse clinical renal function in participants in the oldest age tertile were significantly different from associations in those in the youngest age tertile which were in the opposite direction. Mean urinary cadmium (CdU) was 1.1 micro g/g creatinine (n = 191). Higher CdU levels were associated with higher NAG.

CONCLUSIONS

These data suggest that lead has an adverse effect on renal function in the moderate dose range, particularly in older workers. Associations between higher lead measures and lower BUN and serum creatinine and higher creatinine clearances may represent lead induced hyperfiltration. Environmental cadmium may also have an adverse renal impact, at least on NAG.

Interaction of dimercaptosuccinic acid (DMSA) with angiotensin II on calcium mobilization in vascular smooth muscle cells

Dimercaptosuccinic acid (DMSA) was shown to lower blood pressure in rat models of arterial hypertension. Thus, there is evidence that-besides its chelating properties-DMSA has a direct vascular effect, e.g. through scavenging of reactive oxygen species (ROS). We speculated that, in addition, intracellular calcium mobilization may be involved in this action. Therefore, the present study examined the effects of DMSA on Ca(2+) mobilization in cultured vascular smooth muscle cells (VSMCs) from rat aorta. Intracellular free Ca(2+) concentration ([Ca(2+)](i)) was measured with fura-2 AM. In a first series of experiments DMSA, 10(-11) to 10(-6)M, induced an immediate dose-dependent up to 4-fold rise of [Ca(2+)](i) (P<0.001) which was almost completely blunted by the calcium channel blocker verapamil or the intracellular calcium release blocker TMB-8. In a second series of experiments, when VSMCs were exposed acutely to DMSA (10(-11) to 10(-6)M), the angiotensin (ANG) II (10(-8)M)-induced rise in [Ca(2+)](i) to 295+/-40nM was attenuated at the average by 49% independent of the dose of DMSA. Preincubation of VSMCs with DMSA (10(-6)M) for 60min reduced basal [Ca(2+)](i) by 77% (P<0.001) and dose-dependently attenuated the ANG II (10(-8)M)-induced rise in [Ca(2+)](i) between 28 and 69% at concentrations between 10(-9) and 10(-5)M DMSA, respectively (P<0.05 and <0.01). In the presence of TMB-8, which attenuated the ANG II (10(-8)M)-induced rise in [Ca(2+)](i) by 66%, DMSA (10(-6)M) had no additional suppressive effect on [Ca(2+)](i). The results suggest that DMSA acutely raises [Ca(2+)](i) by stimulating transmembrane calcium influx via L-type calcium channels and by calcium release from intracellular stores followed by a decrease in [Ca(2+)](i) probably due to cellular calcium depletion. Thus, in addition to its action as scavenger of ROS, which in part mediate the vasoconstrictor response, e.g. to ANG II, DMSA may exert its hypotensive effect through decreasing total cell calcium, thereby attenuating the vasoconstrictor-induced rise in [Ca(2+)](i) in VSMCs.

Biomarkers of renal effects in children and adults with low environmental exposure to heavy metals

The health effects of chronic exposure to heavy metals such as lead, cadmium, and mercury are widely documented, yet few data exist about the renal impact of low environmental exposure to these metals, particularly in children. The aim of this study was to assess renal parameters in children and adults living in an environment known for its past heavy metal contamination around two nonferrous smelters in northern France (Noyelles-Godault and Auby) and to compare their results with age and gender-matched controls living in neighboring municipalities with unpolluted soil (total: 400 children, 600 adults, sex ratio = 1). The integrity of renal function was assessed by measuring the urinary excretion levels of total protein, albumin, transferrin, beta(2)-microglobulin, retinol-binding protein, brush border antigen, and the enzyme N-acetyl-beta-D-glucosaminidase (NAG). The mean blood concentrations of lead (Pb-B, children </=42.2 micro/L, adults </=71.3. micro/L) and of cadmium (Cd-B, children </=0.52 microg/L, adults 0.86 microg/L) were all relatively low, indicating a low uptake of these heavy metals from the environment despite relatively high levels in soil (between 100 and 1700 ppm for lead and 0.7 to 233 ppm for cadmium). Pb-B levels were, however, significantly increased in boys, girls, and women--but not men--living in the polluted area. Boys, men, and women living in the polluted area had also on average higher Cd-B levels. The concentrations of mercury in urine (Hg-U) were by contrast similar in control and exposed groups. None of the renal parameters studied showed a significant difference between control and exposed groups. The influence of heavy metals on renal parameters was further assessed by stepwise multiple regression, testing Pb-B, Cd-B, Hg-U, age, gender, body mass index (BMI), urinary creatinine levels, and area of residence as predictors in both children and adults, including first-order metal interaction terms, smoking habits, and alcohol consumption in adults. The only positive correlation was found between the urinary excretion of NAG activity (standardized for BMI and urinary creatinine) and Cd-B levels when taking the whole children population, indicating that even low cadmium burdens may produce subtle effects on the proximal tubule in children, although deleterious consequences are unlikely should exposure not increase. However, in the absence of other positive findings even after studying the smaller subgroups with higher levels of heavy metals, these results are clearly indicative of the minimal renal impact of living around nonferrous smelters that are currently complying with pollution regulations, even when soil contamination is still high.

Histological and histochemical alterations in the kidney induced by lead

BACKGROUND

Although lead intoxication is one of the most common forms of metal intoxication, the histochemical alterations in the renal tissues due to chronic lead exposure is limited and has not yet been well identified.

SUBJECTS AND METHODS

A total of 60 male Wistar albino rats (Rattus norvegicus) were exposed to lead acetate trihydrate (0.0, 0.25, 0.5, 1.0 and 2% for 1 to 12 months) in drinking water to investigate the histological and histochemical alterations in the renal tissues due to lead.

RESULTS

Chronic exposure to subtoxic doses of lead produced distinct progressive tubular, glomerular and interstitial damages. Tubular changes occurred earlier than glomerular and interstitial ones, and included anisokaryosis, nuclear pyknosis, karyomeglay, development of intranuclear and cytoplasmic inclusions together with tubular dilation, necrosis, vacuolization, tubular hyperplasia and solid tubular adenoma. The glomerular alterations were mainly mesangial hypercellularity, segmental proliferation, focal and segmental glomeruloscleriosis, glomerural hyalinization and glomerular tuft alterations.

CONCLUSIONS

The findings indicate that lead produces significant histological and histochemical changes in the kidney that lead to severe complications.