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

Uranium exposure and kidney tubule biomarkers in the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

Experimental studies indicate that uranium exposure is toxic to the kidney tubules. We evaluated the association of urinary uranium concentrations with biomarkers of tubule cell dysfunction (alpha-1-microglobulin [A1M], uromodulin [UMOD], epidermal growth factor [EGF]), and tubule cell injury (kidney injury molecule-1 [KIM-1], monocyte chemoattractant protein-1 [MCP-1], and chitinase-3-like protein 1 [YKL-40]), as well as with albuminuria and estimated glomerular filtration rate (eGFR) among participants in the Multi-Ethnic Study of Atherosclerosis (MESA).

METHODS

We conducted a cross-sectional study that included 461 participants selected for the absence of diabetes, chronic kidney disease (CKD), and cardiovascular disease, evaluated with six kidney tubule biomarker measurements. Urinary uranium concentrations were measured using inductively coupled plasma mass spectrometry in spot urine samples. Linear models were used to determine associations of urinary uranium concentrations with each kidney tubule biomarker, calculated by the geometric mean ratio (GMR), after adjustment for participant's urinary creatinine concentrations, age, sex, race/ethnicity, MESA field center, highest level of education completed, cigarette smoking status, alcohol consumption, body mass index (BMI), albuminuria levels, and eGFR.

RESULTS

Median (interquartile range) urinary uranium concentration was 5.2 (2.9, 10.4) ng/L, and mean (standard deviation) eGFR was 99 (16) mL/min/1.73 m2. The adjusted GMRs (95%CI) of KIM-1 and MCP-1 were 1.11 (1.01, 1.22) and 1.10 (1.01, 1.20), respectively per 7.5 ng/L (interquartile range) higher urinary uranium concentration, while no statistically significant associations were observed for YKL-40, A1M, UMOD, EGF, albuminuria, or eGFR. In flexible dose-response models, the associations were positive and largely linear between urinary uranium concentrations and higher KIM-1 and MCP-1.

CONCLUSIONS

Among healthy community-living individuals, chronic low-level uranium exposure, as measured in urine, was associated with markers of kidney tubule cell injury. Chronic low-level uranium exposure observed in contemporary US urban centers may adversely affect kidney tubule health and related outcomes.

A Comparative Study on the Paradoxical Relationship Between Heavy Metal Exposure and Kidney Function

Introduction: Korea has higher levels of heavy metals compared to other countries, raising the need to study the health impacts on vulnerable populations. This study examined the effects of heavy metal exposure-lead, mercury, and cadmium-on kidney function in residents of environmentally vulnerable areas compared to the general population in Korea. Methods: Epidemiological studies in vulnerable areas and official data from the Fourth Korean National Environmental Health Survey were analyzed to assess blood levels of lead and mercury and urinary cadmium. An integrated heavy metal concentration was calculated, combining the levels of these metals. Kidney function was evaluated using the estimated glomerular filtration rate (eGFR), classified into normal, mildly reduced, and impaired. Correlation and logistic regression analyses were used to examine relationships between heavy metal levels and eGFR. Results: The integrated heavy metal concentration in vulnerable areas was higher than in the general population. In the general population, increased heavy metal levels were associated with a decrease in eGFR, whereas in vulnerable areas, eGFR increased with higher heavy metal levels. In the general population, a rise in urinary cadmium increased the risk of eGFR decline by 19.9%, while in vulnerable areas, higher urinary cadmium reduced this risk by 23.3%. Conclusions: Contrasting relationships between heavy metal exposure and eGFR in vulnerable areas versus the general population may be due to long-term exposure and reduced renal excretion. This study underscores the need for continued monitoring in vulnerable areas, and future research should identify eGFR thresholds that correlate with heavy metal level shifts.

Analysis of relationship between mixed heavy metal exposure and early renal damage based on a weighted quantile sum regression and Bayesian kernel machine regression model

BACKGROUND

Occupation, environmental heavy metal exposure, and renal function impairment are closely related. The relationship between mixed metal exposure and chronic renal injury is inadequately described, and the interaction between each metal is poorly explored.

OBJECTIVE

This cross-sectional study assessed mixed heavy metal exposure in the general population and their relationship with early renal impairment, as well as possible interactions between metals.

METHODS

The study was conducted in two communities in Taiyuan City in northern China. Multiple linear regression, weighted quantile sum (WQS) and bayesian kernel machine regression (BKMR) regression were used to explore the relationship of mixed heavy metal exposure with indicators of early kidney injury (N-acetyl-β-D- glucosidase (UNAG), urinary albumin (UALB)). Meanwhile, BKMR was used to explore the possible interactions between mixed heavy metal and indicators of early kidney injury.

RESULTS

Based on the WQS regression results, we observed adjusted WQS coefficient β (β-WQS) of 0.711 (95% CI: 0.543, 0.879). Notably, this change was primarily driven by As (35.6%) and Cd (22.5%). In the UALB model, the adjusted β-WQS was 0.657 (95% CI: 0.567, 0.747), with Ni (30.5%), Mn (22.1%), Cd (21.2%), and As (18.6%) exhibiting higher weights in the overall effect. The BKMR results showed a negative interaction between As and other metals in the UNAG and UALB models, a positive interaction between Mn and Ni and other metals. No significant pairwise interaction was observed in the association of metals with indicators of early kidney injury.

CONCLUSION

Through multiple linear regression, WQS regression, and BKMR analyses, we found that exposure to mixed heavy metals such as Cd, Cr, Pb, Mn, As, Co and Ni was positively correlated with UNAG and UALB. Moreover, there are complex interactions between two or more heavy metals in more than one direction.

The Impact of Thallium Exposure in Public Health and Molecular Toxicology: A Comprehensive Review

This review offers a synthesis of the current understanding of the impact of low-dose thallium (Tl) on public health, specifically emphasizing its diverse effects on various populations and organs. The article integrates insights into the cytotoxic effects, genotoxic potential, and molecular mechanisms of thallium in mammalian cells. Thallium, a non-essential heavy metal present in up to 89 different minerals, has garnered attention due to its adverse effects on human health. As technology and metallurgical industries advance, various forms of thallium, including dust, vapor, and wastewater, can contaminate the environment, extending to the surrounding air, water sources, and soil. Moreover, the metal has been identified in beverages, tobacco, and vegetables, highlighting its pervasive presence in a wide array of food sources. Epidemiological findings underscore associations between thallium exposure and critical health aspects such as kidney function, pregnancy outcomes, smoking-related implications, and potential links to autism spectrum disorder. Thallium primarily exerts cellular toxicity on various tissues through mitochondria-mediated oxidative stress and endoplasmic reticulum stress. This synthesis aims to shed light on the intricate web of thallium exposure and its potential implications for public health, emphasizing the need for vigilant consideration of its risks.

The association between urinary metals/metalloids and chronic kidney disease among general adults in Wuhan, China

The relation between exposure to single metal/metalloid and the risk of chronic kidney disease (CKD) remains unclear. We aimed to determine the single and mixed associations of 21 heavy metals/metalloids exposure and the risk of CKD. We performed a cross-sectional study that recruited 4055 participants. Multivariate logistic regression, linear regression and weighted quantile sum (WQS) regression were conducted to explore the possible effects of single and mixed metals/metalloids exposure on the risk of CKD, the risk of albuminuria and changes in the estimated glomerular filtration rate (eGFR). In single-metal models, Cu, Fe, and Zn were positively associated with increased risks of CKD (P-trend < 0.05). Compared to the lowest level, the highest quartiles of Cu (OR = 2.94; 95% CI: 1.70, 5.11; P-trend < 0.05), Fe (OR = 2.39; 95% CI: 1.42, 4.02; P-trend < 0.05), and Zn (OR = 2.35; 95% CI: 1.31, 4.24; P-trend < 0.05) were associated with an increased risk of CKD. After multi-metal adjustment, the association with the risk of CKD remained robust for Cu (P < 0.05). Weighted quantile sum regression revealed a positive association between mixed metals/metalloids and the risk of CKD, and the association was largely driven by Cu (43.7%). Specifically, the mixture of urinary metals/metalloids was positively associated with the risk of albuminuria and negatively associated with eGFR.

A State-of-the-Science Review on Metal Biomarkers

PURPOSE OF REVIEW

Biomarkers are commonly used in epidemiological studies to assess metals and metalloid exposure and estimate internal dose, as they integrate multiple sources and routes of exposure. Researchers are increasingly using multi-metal panels and innovative statistical methods to understand how exposure to real-world metal mixtures affects human health. Metals have both common and unique sources and routes of exposure, as well as biotransformation and elimination pathways. The development of multi-element analytical technology allows researchers to examine a broad spectrum of metals in their studies; however, their interpretation is complex as they can reflect different windows of exposure and several biomarkers have critical limitations. This review elaborates on more than 500 scientific publications to discuss major sources of exposure, biotransformation and elimination, and biomarkers of exposure and internal dose for 12 metals/metalloids, including 8 non-essential elements (arsenic, barium, cadmium, lead, mercury, nickel, tin, uranium) and 4 essential elements (manganese, molybdenum, selenium, and zinc) commonly used in multi-element analyses.

RECENT FINDINGS

We conclude that not all metal biomarkers are adequate measures of exposure and that understanding the metabolic biotransformation and elimination of metals is key to metal biomarker interpretation. For example, whole blood is a good biomarker of exposure to arsenic, cadmium, lead, mercury, and tin, but it is not a good indicator for barium, nickel, and uranium. For some essential metals, the interpretation of whole blood biomarkers is unclear. Urine is the most commonly used biomarker of exposure across metals but it should not be used to assess lead exposure. Essential metals such as zinc and manganese are tightly regulated by homeostatic processes; thus, elevated levels in urine may reflect body loss and metabolic processes rather than excess exposure. Total urinary arsenic may reflect exposure to both organic and inorganic arsenic, thus, arsenic speciation and adjustment for arsebonetaine are needed in populations with dietary seafood consumption. Hair and nails primarily reflect exposure to organic mercury, except in populations exposed to high levels of inorganic mercury such as in occupational and environmental settings. When selecting biomarkers, it is also critical to consider the exposure window of interest. Most populations are chronically exposed to metals in the low-to-moderate range, yet many biomarkers reflect recent exposures. Toenails are emerging biomarkers in this regard. They are reliable biomarkers of long-term exposure for arsenic, mercury, manganese, and selenium. However, more research is needed to understand the role of nails as a biomarker of exposure to other metals. Similarly, teeth are increasingly used to assess lifelong exposures to several essential and non-essential metals such as lead, including during the prenatal window. As metals epidemiology moves towards embracing a multi-metal/mixtures approach and expanding metal panels to include less commonly studied metals, it is important for researchers to have a strong knowledge base about the metal biomarkers included in their research. This review aims to aid metals researchers in their analysis planning, facilitate sound analytical decision-making, as well as appropriate understanding and interpretation of results.

Plasma Thallium Concentration, Kidney Function, Nephrotoxicity and Graft Failure in Kidney Transplant Recipients

The nephrotoxic effects of heavy metals have gained increasing scientific attention in the past years. Recent studies suggest that heavy metals, including cadmium, lead, and arsenic, are detrimental to kidney transplant recipients (KTR) even at circulating concentrations within the normal range, posing an increased risk for graft failure. Thallium is another highly toxic heavy metal, yet the potential consequences of the circulating thallium concentrations in KTR are unclear. We measured plasma thallium concentrations in 672 stable KTR enrolled in the prospective TransplantLines Food and Nutrition Biobank and Cohort Study using inductively coupled plasma mass spectrometry. In cross-sectional analyses, plasma thallium concentrations were positively associated with kidney function measures and hemoglobin. We observed no associations of thallium concentration with proteinuria or markers of tubular damage. In prospective analyses, we observed no association of plasma thallium with graft failure and mortality during a median follow-up of 5.4 [interquartile range: 4.8 to 6.1] years. In conclusion, in contrast with other heavy metals such as lead, cadmium, and arsenic, there is no evidence of tubular damage or thallium nephrotoxicity for the range of circulating thallium concentrations observed in this study. This is further evidenced by the absence of associations of plasma thallium with graft failure and mortality in KTR.

Environmental exposure to lead, mercury, and cadmium is not associated with abnormal kidney function in Korean adolescents

BACKGROUND

We aimed to elucidate the relationship between environmental exposure to lead (Pb), mercury (Hg), and cadmium (Cd) which were measured in blood and the kidney function of adolescents.

METHODS

Cross-sectional study was conducted using data from the Korea National Health and Nutrition Examination Survey from 2010 to 2017. Statistical procedures were performed to analyze the Korean population of adolescents aged 12-17 years. Regression analysis was performed, and covariates included age, sex, body mass index, smoking status, and other heavy metal levels.

RESULTS

The median blood levels of Pb, Hg, and Cd were 1.165 μg/dL, 1.805 μg/L, and 0.304 μg/L, respectively. Adolescents with Pb levels in the highest quartile (> 1.454 μg/dL) had a 3.35 mL/min/1.73 m²-lower estimated glomerular filtration rate using creatinine (eGFR_cr) (95% confidence interval (CI), -6.03 to -0.68 mL/min/1.73 m²) compared to those in the lowest quartile (< 0.856 μg/dL) in the unadjusted model. However, there was no association between the blood Pb level and eGFR_cr in the adjusted model. Levels of Hg and Cd were not associated with eGFR_cr in either model. High blood levels of all three heavy metals were not associated with the risk of hypertension.

CONCLUSIONS

There was no association between increased blood levels of Pb, Hg, and Cd; eGFR_cr; and increased risk of hypertension in Korean adolescents who were exposed to relatively low levels of heavy metals.

Prenatal Metal Exposures and Infants' Developmental Outcomes in a Navajo Population

Early-life exposure to environmental toxicants can have detrimental effects on children's neurodevelopment. In the current study, we employed a causal modeling framework to examine the direct effect of specific maternal prenatal exposures on infants' neurodevelopment in the context of co-occurring metals. Maternal metal exposure and select micronutrients' concentrations were assessed using samples collected at the time of delivery from mothers living across Navajo Nation with community exposure to metal mixtures originating from abandoned uranium mines. Infants' development across five domains was measured at ages 10 to 13 months using the Ages and Stages Questionnaire Inventory (ASQ:I), an early developmental screener. After adjusting for effects of other confounding metals and demographic variables, prenatal exposure to lead, arsenic, antimony, barium, copper, and molybdenum predicted deficits in at least one of the ASQ:I domain scores. Strontium, tungsten, and thallium were positively associated with several aspects of infants' development. Mothers with lower socioeconomic status (SES) had higher lead, cesium, and thallium exposures compared to mothers from high SES backgrounds. These mothers also had infants with lower scores across various developmental domains. The current study has many strengths including its focus on neurodevelopmental outcomes during infancy, an understudied developmental period, and the use of a novel analytical method to control for the effects of co-occurring metals while examining the effect of each metal on neurodevelopmental outcomes. Yet, future examination of how the effects of prenatal exposure on neurodevelopmental outcomes unfold over time while considering all potential interactions among metals and micronutrients is warranted.

Performance of urine, blood, and integrated metal biomarkers in relation to birth outcomes in a mixture setting

BACKGROUND

Studies on the health effects of metal mixtures typically utilize biomarkers measured in a single biological medium, such as blood or urine. However, the ability to evaluate mixture effects are limited by the uncertainty whether a unified medium can fully capture exposure for each metal. Therefore, it is important to compare and assess metal mixtures measured in different media in epidemiology studies.

OBJECTIVES

The aim of this study was to examine the mixture predictive performance of urine and blood metal biomarkers and integrated multi-media biomarkers in association with birth outcomes.

METHODS

In our analysis of 847 women from the Puerto Rico PROTECT Cohort, we measured 10 essential and non-essential metals in repeated and paired samples of urine and blood during pregnancy. For each metal, we integrated exposure estimates from paired urine and blood biomarkers into multi-media biomarkers (MMBs), using intraclass-correlation coefficient (ICC) and weighted quantile sum (WQS) approaches. Using Ridge regressions, four separate Environmental risk scores (ERSs) for metals in urine, blood, MMBICC, and MMBWQS were computed as a weighted sum of the 10 metal concentrations. We then examined associations between urine, blood, and multi-media biomarker ERSs and birth outcomes using linear and logistic regressions, adjusting for maternal age, maternal education, pre-pregnancy body mass index (BMI), and second-hand smoke exposure. The performance of each ERS was evaluated with continuous and tertile estimates and 95% confidence intervals of the odds ratio of preterm birth using area under the curve (AUC).

RESULTS

Pb was the most important contributor of blood ERS as well as the two integrated multi-media biomarker ERSs. Individuals with high ERS (3rd tertile) showed increased odds of preterm birth compared to individuals with low ERS (1st tertile), with 2.8-fold (95% CI, 1.49 to 5.40) for urine (specific gravity corrected); 3.2- fold (95% CI, 1.68 to 6.25) for blood; 3.9-fold (95% CI, 1.72 to 8.66) for multi-media biomarkers composed using ICC; and 5.2-fold (95% CI, 2.34 to 11.42) for multi-media biomarkers composed using WQS. The four ERSs had comparable predictive performances (AUC ranging from 0.64 to 0.68) when urine is examined with specific gravity corrected concentrations.

CONCLUSIONS

Within a practical metal panel, measuring metals in either urine or blood may be an equally good approach to evaluate the metals as a mixture. Applications in practical study design require validation of these methods with other cohorts, larger panels of metals and within the context of other adverse health effects of interest.

Nephrotoxic Metal Mixtures and Preadolescent Kidney Function

Exposure to metals including lead (Pb), cadmium (Cd), and arsenic (As), may impair kidney function as individual toxicants or in mixtures. However, no single medium is ideal to study multiple metals simultaneously. We hypothesized that multi-media biomarkers (MMBs), integrated indices combining information across biomarkers, are informative of adverse kidney function. Levels of Pb, Cd, and As were quantified in blood and urine in 4–6-year-old Mexican children (n = 300) in the PROGRESS longitudinal cohort study. We estimated the mixture effects of these metals, using weighted quantile sum regression (WQS) applied to urine biomarkers (Umix), blood biomarkers (Bmix), and MMBs, on the cystatin C-based estimated glomerular filtration rate (eGFR) and serum cystatin C assessed at 8–10 years of age, adjusted for covariates. Quartile increases in Umix and the MMB mixture were associated with 2.5% (95%CI: 0.1, 5.0) and 3.0% (95%CI: 0.2, 5.7) increased eGFR and −2.6% (95% CI: −5.1%, −0.1%) and −3.3% (95% CI: −6.5%, −0.1%) decreased cystatin C, respectively. Weights indicate that the strongest contributors to the associations with eGFR and serum cystatin C were Cd and Pb, respectively. MMBs detected mixture effects distinct from associations with individual metals or media-type, highlighting the benefits of incorporating information from multiple exposure media in mixtures analyses.

A case-control study of thallium exposure with the risk of premature ovarian insufficiency in women

Thallium exposure has been associated with female reproductive health, but little is known about its potential association with premature ovarian insufficiency (POI). In this study, a total of 169 patients with POI and 209 healthy women were recruited from Zhejiang province, China. Urinary thallium concentrations were significantly positively associated with the risk of POI [adjusted odds ratio (OR) = 1.63, 95% CI: 1.25-2.13, p < 0.001], geometric mean values of which were significantly higher in POI cases (0.213 μg/L, 0.302 μg/g for creatinine adjustment) than those of controls (0.153 μg/L, 0.233 μg/g for creatinine adjustment). Furthermore, the serum levels of follicle-stimulating hormone and luteinizing hormone were positively associated with urinary thallium concentrations, whereas anti-Mullerian hormone and estradiol were negatively correlated with thallium. To the best of our knowledge, this is the first study to provide evidence that thallium exposure at currently environmental levels is the potential risk factor for POI in women.

The Effect of Cadmium on GFR Is Clarified by Normalization of Excretion Rates to Creatinine Clearance

Erroneous conclusions may result from normalization of urine cadmium and N-acetyl-β-D-glucosaminidase concentrations ([Cd]_u and [NAG]_u) to the urine creatinine concentration ([cr]_u). In theory, the sources of these errors are nullified by normalization of excretion rates (E_Cd and E_NAG) to creatinine clearance (C_cr). We hypothesized that this alternate approach would clarify the contribution of Cd-induced tubular injury to nephron loss. We studied 931 Thai subjects with a wide range of environmental Cd exposure. For x = Cd or NAG, E_x/E_cr and E_x/C_cr were calculated as [x]_u/[cr]_u and [x]_u[cr]_p/[cr]_u, respectively. Glomerular filtration rate (GFR) was estimated according to the Chronic Kidney Disease (CKD) Epidemiology Collaboration (eGFR), and CKD was defined as eGFR < 60 mL/min/1.73m². In multivariable logistic regression analyses, prevalence odds ratios (PORs) for CKD were higher for log(E_Cd/C_cr) and log(E_NAG/C_cr) than for log(E_Cd/E_cr) and log(E_NAG/E_cr). Doubling of E_Cd/C_cr and E_NAG/C_cr increased POR by 132% and 168%; doubling of E_Cd/E_cr and E_NAG/E_cr increased POR by 64% and 54%. As log(E_Cd/C_cr) rose, associations of eGFR with log(E_Cd/C_cr) and log(E_NAG/C_cr) became stronger, while associations of eGFR with log(E_Cd/E_cr) and log(E_NAG/E_cr) became insignificant. In univariate regressions of eGFR on each of these logarithmic variables, R² was consistently higher with normalization to C_cr. Our tabular and graphic analyses uniformly indicate that normalization to C_cr clarified relationships of E_Cd and E_NAG to eGFR.

Developmental toxicity of cadmium in infants and children: a review

Several millions of people are exposed to cadmium worldwide due to natural and anthropogenic activities that led to their widespread distribution in the environment and have shown potential adverse effects on the kidneys, liver, heart and nervous system. Recently human and animal-based studies have been shown that In utero and early life exposure to cadmium can have serious health issues that are related to the risk of developmental disabilities and other outcomes in adulthood. Since, cadmium crosses the placental barrier and reaches easily to the fetus, even moderate or high-level exposure of this metal during pregnancy could be of serious health consequences which might be reflected either in the children’s early or later stages of life. Mortality from various diseases including cancer, cardiovascular, respiratory, kidney and neurological problems, correlation with In utero or early life exposure to cadmium has been found in epidemiological studies. Animal studies with strong evidence of various diseases mostly support for the human studies, as well as suggested a myriad mechanism by which cadmium can interfere with human health and development. More studies are needed to establish the mechanism of cadmium-induced toxicity with environmentally relevant doses in childhood and later life. In this review, we provide a comprehensive examination of the literature addressing potential long- term health issues with In utero and early life exposure to cadmium, as well as correlating with human and animal exposure studies.

Maternal Urinary Metal and Metalloid Concentrations in Association with Oxidative Stress Biomarkers

Metal exposure has been associated with a wide range of adverse birth outcomes and oxidative stress is a leading hypothesis of the mechanism of action of metal toxicity. We assessed the relationship between maternal exposure to essential and non-essential metals and metalloids in pregnancy and oxidative stress markers, and sought to identify windows of vulnerability and effect modification by fetal sex. In our analysis of 215 women from the PROTECT birth cohort study, we measured 14 essential and non-essential metals in urine samples at three time points during pregnancy. The oxidative stress marker 8-iso-prostaglandin F2α (8-iso-PGF2α) and its metabolite 2,3-dinor-5,6-dihydro-15-15-F2t-IsoP, as well as prostaglandin F2α (PGF2α), were also measured in the same urine samples. Using linear mixed models, we examined the main effects of metals on markers of oxidative stress as well as the visit-specific and fetal sex-specific effects. After adjustment for covariates, we found that a few urinary metal concentrations, most notably cesium (Cs) and copper (Cu), were associated with higher 8-iso-PGF2α with effect estimates ranging from 7.3 to 14.9% for each interquartile range, increase in the metal concentration. The effect estimates were generally in the same direction at the three visits and a few were significant only among women carrying a male fetus. Our data show that higher urinary metal concentrations were associated with elevated biomarkers of oxidative stress. Our results also indicate a potential vulnerability of women carrying a male fetus.

Environmental Pollution and Chronic Kidney Disease

Chronic kidney disease (CKD) is a global public health problem associated with high rates of morbidity and mortality due to end-stage renal disease and cardiovascular disease. Safe and effective medications to reverse or stabilize renal function in patients with CKD are lacking, and hence it is important to identify modifiable risk factors associated with worsening kidney function. Environmental pollutants, including metals, air pollutant, phthalate and melamine can potentially increase the risk of CKD or accelerate its progression. In this review, we discuss the epidemiological evidence for the association between environmental pollution and kidney disease, including heavy metals, air pollution and other environmental nephrotoxicants in the general population.

The association between environmental endocrine disruptors and cardiovascular diseases: A systematic review and meta-analysis

BACKGROUND

Except for known cardiovascular risk factors, long-term exposure to environmental endocrine disruptors (EEDs) - a class of exogenous chemicals, or a mixture of chemicals, that can interfere with any aspect of hormone action - has been shown to increase the risk of cardiovascular diseases (CVDs), which are still controversial.

OBJECTIVE

To conduct a comprehensive systematic review and meta-analysis to estimate the association between EEDs, including nonylphenol (NP), bisphenol A (BPA), polychlorinated biphenyl (PCB), organo-chlorine pesticide (OCP) and phthalate (PAE) exposure and CVD risk.

METHODS

The heterogeneity between different studies was qualitatively and quantitatively evaluated using Q test and I² statistical magnitude, respectively. Subgroup analysis was performed using chemical homologs - a previously unused grouping method - to extract data and perform meta-analysis to assess their exposure to CVD.

RESULTS

Twenty-nine literatures were enrolled with a total sample size of 88891. The results indicated that exposure to PCB138 and PCB153 were the risk factors for CVD morbidity (odds ratio (OR) = 1.35, 95% confidence interval (CI): 1.10-1.66; OR = 1.35, 95% CI: 1.13-1.62). Exposure to organo-chlorine pesticide (OCP) (OR = 1.12, 95% CI: 1.00-1.24), as well as with phthalate (PAE) (OR = 1.11, 95% CI: 1.06-1.17) and BPA (OR = 1.19, 95% CI: 1.03-1.37) were positively associated with CVD risk, respectively. BPA exposure concentration had no correlation with total cholesterol (TC), or low-density lipoprotein (LDL), but exhibited a correlation with gender, waist circumference (WC), high-density lipoprotein (HDL), age, and body mass index (BMI) (standardized mean difference (SMD)) = 1.51; 95% CI: =(1.01-2.25); SMD = 0.16; 95% CI: (0.08-0.23); SMD = -0.19; 95% CI: (-0.27-0.12); SMD = -0.78; 95% CI: (-1.42-0.14); SMD = 0.08; 95% CI: (0.00-0.16).

CONCLUSIONS

EED exposure is a risk factor for CVD. Long-term exposure to EEDs can influence cardiovascular health in humans. A possible synergistic effect may exist between the homologs. The mechanism of which needs to be further explored and demonstrated by additional prospective cohort studies, results of in vitro and in vivo analyses, as well as indices affecting CVD.

Urinary Essential Elements of Young Children with Autism Spectrum Disorder and their Mothers

BACKGROUND

Even though the cause of autism spectrum disorders (ASD) remains unknown, the current understanding points towards complex interactions between environmental and genetic factors. One important environmental factor to consider is intake of toxic and essential elements, and their role in metabolism. Essential elements have received considerably less attention in the literature than the presence of toxins in urine.

METHOD

The purpose of this investigation is to comprehensively assess the association between urinary element compositions of 28 mothers who had young children with ASD and 29 mothers who had young typically developing (TD) children, and in a subset of their children (21 with ASD and 26 TD).

RESULTS

The results show that there are significant differences between the ASD and TD children cohorts' concentrations for four specific elements (sulfur, phosphorous, molybdenum, and tin). Utilizing multivariate statistical techniques (Fisher's discriminant analysis and support vector machines), it was possible to distinguish the ASD from the TD children groups with an 81% accuracy after cross-validation utilizing the four significantly different elements. However, among the mother cohorts assessed, there were no significant differences between those that had children with ASD and those with TD children. There was a significant correlation of levels of phosphorus and sulfur in the children with ASD (r = 0.63, p = 3.0E-3) and in the TD children (r = 0.47, p = 0.02).

CONCLUSIONS

Notable differences were observed between the elemental concentration in urine of children with ASD and their TD peers. Analyzing cellular pathways related to these elements are promising areas of future research.

Predictors of urinary and blood Metal(loid) concentrations among pregnant women in Northern Puerto Rico

Given the potential adverse health effects related to toxic trace metal exposure and insufficient or excessive levels of essential trace metals in pregnant women and their fetuses, the present study characterizes biomarkers of metal and metalloid exposure at repeated time points during pregnancy among women in Puerto Rico. We recruited 1040 pregnant women from prenatal clinics and collected urine, blood, and questionnaire data on demographics, product use, food consumption, and water usage at up to three visits. All samples were analyzed for 16 metal(loid)s: arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), copper (Cu), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), titanium (Ti), uranium (U), vanadium (V), and zinc (Zn). Urine samples were additionally analyzed for molybdenum (Mo), platinum (Pt), antimony (Sb), tin (Sn), and tungsten (W). Mean concentrations of most metal(loid)s were higher among participants compared to the general US female population. We found weak to moderate correlations for inter-matrix comparisons, and moderate to strong correlations between several metal(loid)s measured within each biological matrix. Blood concentrations of Cu, Zn, Mn, Hg, and Pb were shown to reflect reliable biomarkers of exposure. For other metals, repeated samples are recommended for exposure assessment in epidemiology studies. Predictors of metal(loid) biomarkers included fish and rice consumption (urinary As), fish and canned food (blood Hg), drinking public water (blood Pb), smoking (blood Cd), and iron/folic acid supplement use (urinary Cs, Mo, and Sb). Characterization of metal(loid) biomarker variation over time and between matrices, and identification of important exposure sources, may inform future epidemiology studies and exposure reduction strategies.

A Comparison of the Nephrotoxicity of Low Doses of Cadmium and Lead

Environmental exposure to moderate-to-high levels of cadmium (Cd) and lead (Pb) is associated with nephrotoxicity. In comparison, the health impacts of chronic low-level exposure to Cd and Pb remain controversial. The aim of this study was to therefore evaluate kidney dysfunction associated with chronic low-level exposure to Cd and Pb in a population of residents in Bangkok, Thailand. The mean age and the estimated glomerular filtration rate (eGFR) for 392 participants (195 men and 197 women) were 34.9 years and 104 mL/min/1.73 m², respectively, while the geometric mean concentrations of urinary Cd and Pb were 0.25 μg/L (0.45 μg/g of creatinine) and 0.89 μg/L (1.52 μg/g of creatinine), respectively. In a multivariable regression analysis, the eGFR varied inversely with blood urea nitrogen in both men (β = −0.125, p = 0.044) and women (β = −0.170, p = 0.008), while inverse associations of the eGFR with urinary Cd (β = −0.132, p = 0.043) and urinary Pb (β = −0.130, p = 0.044) were seen only in women. An increased urinary level of Cd to the median level of 0.38 μg/L (0.44 μg/g of creatinine) was associated with a decrease in the eGFR by 4.94 mL/min/1.73 m² (p = 0.011). The prevalence odds of a reduced eGFR rose 2.5-, 2.9- and 2.3-fold in the urinary Cd quartile 3 (p = 0.013), the urinary Cd quartile 4 (p = 0.008), and the urinary Pb quartile 4 (p = 0.039), respectively. This study suggests that chronic exposure to low-level Cd is associated with a decline in kidney function and that women may be more susceptible than men to nephrotoxicity due to an elevated intake of Cd and Pb.

Toxicity of Thallium at Low Doses: A Review

A mini review of the toxicity of Thallium (Tl) at low doses is herein presented. Thallium has severe toxicity. Although its acute biological effects have been widely investigated and are well known, its biological effects on human health and in cell cultures at low doses (<100 μg/L) due, for example, to Tl chronic exposure via consumption of contaminated water or foods, have often been overlooked or underestimated. Relatively few papers have been published on this topic and are herein reviewed to provide a focused scientific opinion in the light of current worldwide regulatory issues.

Urinary metabolites of organophosphate esters (OPEs) are associated with chronic kidney disease in the general US population, NHANES 2013-2014

Organophosphate esters (OPEs) have been widely used in building materials and consumer products as flame retardants and plasticizers. In vitro studies have suggested adverse effects of OPEs on the kidney. Despite accumulating evidence indicating widespread exposure to OPEs, their association with renal function in humans has not been evaluated. This study aims to investigate the association between OPEs exposure and chronic kidney disease (CKD) among the general US adult population by employing data from the US National Health and Nutrition Examination Survey (NHANES) 2013-2014. Among 1578 adults who were not currently pregnant, the associations of the urinary OPE metabolites with two CKD-related parameters, i.e., estimated glomerular filtration rate (eGFR) and albumin-to-creatinine ratio (ACR), and CKD were assessed. To account for urine dilution, in addition to conventional creatinine-adjustment, covariate-adjusted creatinine standardization, which controls for potential confounding by kidney function, was employed. Multi-pollutant models were also constructed to verify the associations observed in the models on individual OPE metabolites. The urinary bis(2-chloroethyl) phosphate (BCEP) level was negatively associated with eGFR only with the covariate-adjusted standardization method, but not with the conventional creatinine adjustment. In addition, both bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) and di-n-butyl phosphate (DNBP) were positively associated with the ACR, regardless of methods of urine dilution adjustment. These three compounds were also associated with CKD. Following adjusting urine dilution with the covariate-adjusted standardization method, the association became more evident. Moreover, similar results were observed in the secondary analysis with the multi-pollutant models. Among the US general population, several OPEs were identified as potential chemical determinants of CKD. Experimental studies are warranted to understand the potential mechanisms underlying this observation.

Combined exposure to lead, cadmium, mercury, and arsenic and kidney health in adolescents age 12-19 in NHANES 2009-2014

BACKGROUND

Occupational and environmental exposures to toxic metals are established risk factors for the development of hypertension and kidney disease in adults. There is some evidence of developmental metal nephrotoxicity in children and from animal studies; however, to our knowledge no previous studies have examined associations between co-exposure to nephrotoxic environmental metals and children's kidney health.

OBJECTIVE

The objective of this study was to assess the association between co-exposure to lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As), measured in urine and blood, and kidney parameters in US adolescents.

METHODS

We performed a cross-sectional analysis of a subsample of 2709 children aged 12-19 participating in the National Health and Nutrition Examination Survey (NHANES) between 2009 and 2014. We analyzed urine levels of 4 nephrotoxic metals selected a priori (As, Cd, Pb and Hg), U_mix, and 3 nephrotoxic metals in blood (Cd, Pb, and Hg), B_mix, using a weighted quantile sum (WQS) approach. We applied WQS regression to analyze the association of B_mix and U_mix with estimated glomerular filtration rate (eGFR), serum uric acid (SUA), urine albumin, blood urea nitrogen (BUN), and systolic blood pressure (SBP), adjusting for sex, race/ethnicity, age, head of household's education level, height, BMI, serum cotinine, and NHANES cohort year. U_mix and urine albumin models were also adjusted for urine creatinine, and B_mix models were also adjusted for fish consumption. Subanalyses included stratification by sex and an arsenic-only model including six speciated forms of As measured in urine.

RESULTS

In WQS regression models, each decile increase of U_mix was associated with 1.6% (95% CI: 0.5, 2.8) higher BUN, 1.4% (95% CI: 0.7, 2.0) higher eGFR, and 7.6% (95% CI: 2.4, 13.1) higher urine albumin. The association between U_mix and BUN was primarily driven by As (72%), while the association with eGFR was driven by Hg (61%), and Cd (17%), and the association with urine albumin was driven by Cd (37%), Hg (33%), and Pb (25%). There was no significant relationship between U_mix and SUA or SBP. In WQS models using the combined blood metals, B_mix, each decile increase of B_mix was associated with 0.6% (95% CI: 0.0, 1.3) higher SUA; this association was driven by Pb (43%), Hg (33%), and Cd (24%) and was marginally significant (p = 0.05). No associations were observed between B_mix and urine albumin, eGFR, BUN, or SBP.

CONCLUSIONS

The findings suggest metals including As, Pb, Hg, Cd and their combinations may affect renal parameters, although potential reverse causation cannot be ruled out due to the cross-sectional study design. Implications of early life low-level exposure to multiple metals on kidney function may have far-reaching consequences later in life in the development of hypertension, kidney disease, and renal dysfunction. Longitudinal studies should further evaluate these relationships.

Factors affecting interpretation of national biomonitoring data from multiple countries: BPA as a case study

INTRODUCTION

The use of biomonitoring data as an indicator of national levels of human exposure to environmental chemicals has grown in importance and prevalence. Nationally representative urinary bisphenol A (BPA) data are now available for Canada, the United States and Korea. Here we address the following questions: Are urinary BPA data from these countries comparable? What can be discerned regarding geographic and/or temporal similarities or differences? Are there generalizable lessons to be learned regarding comparison of biomonitoring results from different countries?

METHODS

We examined underlying methods and resultant urinary BPA data from national surveys of three countries: Canada (Canadian Health Measures Survey, CHMS, 2009-2015); United States (National Health and Nutrition Examination Survey, NHANES, 2009-2014); and Korea (Korean National Environmental Health Survey, KoNEHS, 2009-2014). We estimated BPA daily intakes on both a volume- and creatinine-adjusted basis.

RESULTS

The three countries use similar methods for analyzing urine samples for BPA and participate in external proficiency testing with acceptable results. Field blanks are only used in the CHMS program. There were program-specific differences in fasting times of participants. Median urinary BPA levels in Canada remained relatively constant over the three cycles (1.1-1.2 ng/ml), while US levels decreased (from 1.9 to 1.3 ng/ml) and Korean levels increased (from 0.7 to 1.1 ng/ml) over similar time periods. The most recent survey year data indicate that levels do not differ substantially across countries. Canadian urinary BPA levels have been stable; the subtle, non-significant decrease in intakes may be due to higher body weight in the more recent Canadian surveys. In contrast, the decrease in intakes in the US appears to be due to decreases in urinary BPA as body weights in the US have been stable. Estimated 95th percentile intakes are over an order of magnitude below current health-based guidance values.

DISCUSSION

Our assessment of urinary BPA data from Canada, the US and Korea indicates that methodological differences, methods for dilution adjustment, and population characteristics should be carefully considered when interpreting biomonitoring data. Despite the plethora of publications describing issues with use of creatinine levels for urinary dilution adjustment, there have been no major methodological advances that would assist in interpreting urinary chemical data. A combination of biomonitoring and traditional exposure assessment approaches may be needed to fully assess human exposures to BPA and other chemicals.

CONCLUSIONS

National biomonitoring surveys provide important information on population levels of chemicals such as BPA and can assist in understanding temporal and geographic similarities, differences, and trends. However, caution must be exercised when using these data to draw anything but broad conclusions, due to both intercountry methodological differences and factors affecting urinary chemical levels that are still poorly understood. While the issues raised in this paper do not appear to be a major concern specifically for the national-scale monitoring of BPA described here, they must be considered when comparing data for other chemicals measured as part of both national and smaller-scale biomonitoring-based research as well as for BPA data from other studies.

Associations of renal function with urinary excretion of metals: Evidence from NHANES 2003-2012

BACKGROUND

Urinary metals are considered measures of long-term exposures of metals, such as cadmium (Cd). Some studies indicate reduced renal function may affect the urinary excretion of several metals in general population making assessments difficult.

OBJECTIVES

To examine whether reduced renal function is associated with reduced urinary excretion of 12 metals or their metabolites and, in turn, an underestimated measure of Cd in general population.

METHODS

We conducted analyses using data from the National Health and Nutrition Examination Survey (NHANES) 2003-2012. Multiple linear regression models were used to examine the associations between urinary metal levels and estimated glomerular filtration rate (eGFR). Restricted cubic spline regression models were used to evaluate the nonlinearity.

RESULTS

Urinary metal levels significantly increased (p < 0.001) with increasing eGFR, except for antimony (p = 0.172). Urinary levels of arsenic, dimethylarsonic acid, cobalt, molybdenum and tungsten increased linearly with eGFR, while Cd, lead, mercury, barium, cesium and thallium increased nonlinearly (p < 0.001) with eGFR. Based on a restricted cubic spline regression model, we found, corresponding to a fixed blood Cd adverse cutpoint of 5 μg/L, predicted urinary Cd cutpoints substantially varied from 0.78-1.21 μg/g for urinary Cd between those aged <40 years and who had chronic kidney disease and those aged 60 years or over with normal renal function, respectively.

CONCLUSION

Reduced renal function is associated with reduced urinary metals; and associations are also observed across the eGFR range not just in the reduced range. Urinary abnormal cutpoints of metals are likely dependent on eGFR and age. The associations between urinary exposure of metals and disease risk are likely underestimated without considering the modifying effect of renal function.

Environmental exposures and pediatric kidney function and disease: A systematic review

BACKGROUND

Environmental chemical exposures have been implicated in pediatric kidney disease. No appraisal of the available evidence has been conducted on this topic.

METHODS

We performed a systematic review of the epidemiologic studies that assessed association of environmental exposures with measures of kidney function and disease in pediatric populations. The search period went through July 2016.

RESULTS

We found 50 studies that met the search criteria and were included in this systematic review. Environmental exposures reviewed herein included lead, cadmium, mercury, arsenic, fluoride, aflatoxin, melamine, environmental tobacco, bisphenol A, dental procedures, phthalates, ferfluorooctanoic acid, triclosan, and thallium/uranium. Most studies assessed environmental chemical exposure via biomarkers but four studies assessed exposure via proximity to emission source. There was mixed evidence of association between metal exposures, and other non-metal environmental exposures and pediatric kidney disease and other kidney disease biomarkers. The evaluation of causality is hampered by the small numbers of studies for each type of environmental exposure, as well as lack of study quality and limited prospective evidence.

CONCLUSION

There is a need for well-designed epidemiologic studies of environmental chemical exposures and kidney disease outcomes.

Cadmium and Alzheimer's disease mortality in U.S. adults: Updated evidence with a urinary biomarker and extended follow-up time

Cadmium has been linked to impaired cognitive function in adults and may cause behavioral, physiological and molecular abnormalities characteristic of Alzheimer's disease (AD) in animals. Evidence linking cadmium and AD in humans is limited, but supportive. In the most recent epidemiologic study, blood cadmium in U.S. adults was positively associated with elevated AD mortality 7-13 years later. The association between urinary cadmium - an arguably more appropriate biomarker for studying chronic diseases - and AD mortality has not yet been explored. Further study of cadmium and AD mortality in an independent population, with longer follow-up, and stratified by sex is also needed. We sought to answer these questions using the U.S. National Health and Nutrition Examination Survey (NHANES) (1999-2006 cycles) and NHANES III (interviews in 1988-1994) datasets, separately linked to AD mortality as of 2011. We used survey-weighted Cox regression models predicting age at AD death and adjusted for race/ethnicity, sex, smoking status, education and urinary creatinine. An interquartile range (IQR; IQR=0.51ng/mL) increase in urinary cadmium was associated with 58% higher rate of AD mortality (hazard ratio (HR)=1.58, 95% CI: 1.20, 2.09. p-value=0.0009, mean follow-up: 7.5 years) in NHANES 1999-2006 participants. In contrast, in NHANES III participants, an IQR (IQR=0.78ng/mL) increase in urinary cadmium was not associated with AD mortality (HR=0.85, 95% CI: 0.63, 1.17, p-value=0.31, mean follow-up: 13 years). Also in the NHANES III sample however, when the maximum follow-up time was restricted to 12.7 years (i.e. the same as NHANES 1999-2006 participants) and urinary creatinine adjustments were not made, urinary cadmium was associated with elevated AD mortality (HR=1.11, 95% CI: 1.02, 1.20, p-value=0.0086). Our study partially supported an association between cadmium and AD mortality, but the sensitivity of results to follow-up time and creatinine adjustments necessitate cautious interpretation of the association. Further studies, particularly those on toxicological mechanisms, are required to fully understand the nature of the "cadmium-AD mortality" association.

Is Urinary Cadmium a Biomarker of Long-term Exposure in Humans? A Review

Cadmium is a naturally-occurring element, and humans are exposed from cigarettes, food, and industrial sources. Following exposure, cadmium accumulates in the kidney and is slowly released into the urine, usually proportionally to the levels found in the kidneys. Cadmium levels in a single spot urine sample have been considered indicative of long-term exposure to cadmium; however, such a potentially exceptional biomarker requires careful scrutiny. In this review, we report good to excellent temporal stability of urinary cadmium (intraclass correlation coefficient 0.66-0.81) regardless of spot urine or first morning void sampling. Factors such as changes in smoking habits and diseases characterized by increased excretion of proteins may produce short-term changes in urinary cadmium levels. We recommend that epidemiologists use this powerful biomarker in prospective studies stratified by smoking status, along with thoughtful consideration of additional factors that can influence renal physiology and cadmium excretion.

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.

Urinary trace element concentrations in environmental settings: is there a value for systematic creatinine adjustment or do we introduce a bias?

Systematic creatinine adjustment of urinary concentrations of biomarkers has been a challenge over the past years because the assumption of a constant creatinine excretion rate appears erroneous and the issue of overadjustment has recently emerged. This study aimed at determining whether systematic creatinine adjustment is to be recommended for urinary concentrations of trace elements (TEs) in environmental settings. Paired 24-h collection and random spot urine samples (spotU) were obtained from 39 volunteers not occupationally exposed to TEs. Four models to express TEs concentration in spotU were tested to predict the 24-h excretion rate of these TEs (TEμg/24h) considered as the gold standard reference: absolute concentration (TEμg/l); ratio to creatinine (TEμg/gcr); TEμg/gcr adjusted to creatinine (TEμg/gcr-adj); and concentration adjusted to specific gravity (TEμg/l-SG). As, Ba, Cd, Co, Cr, Cu, Hg, Li, Mo, Ni, Pb, Sn, Sb, Se, Te, V and Zn were analyzed by inductively coupled argon plasma mass spectrometry. There was no single pattern of relationship between urinary TEs concentrations in spotU and TEμg/24h. TEμg/l predicted TEμg/24h with an explained variance ranging from 0 to 60%. Creatinine adjustment improved the explained variance by an additional 5 to ~60% for many TEs, but with a risk of overadjustment for the most of them. This issue could be addressed by adjusting TE concentrations on the basis of the regression coefficient of the relationship between TEμg/gcr and creatinine concentration. SG adjustment was as suitable as creatinine adjustment to predict TEμg/24h with no SG-overadjustment (except V). Regarding Cd, Cr, Cu, Ni and Te, none of the models were found to reflect TEμg/24h. In the context of environmental exposure, systematic creatinine adjustment is not recommended for urinary concentrations of TEs. SG adjustment appears to be a more reliable alternative. For some TEs, however, neither methods appear suitable.

Tubular and glomerular kidney effects in the Chinese general population with low environmental cadmium exposure

Cadmium (Cd), a well-known nephrotoxic agent, has received a great deal of attention from the Chinese public because of reports of its presence in rice. But very few studies have assessed the renal risk of Cd exposure in children. In this cross-sectional study, we aimed to determine whether biologic measures of Cd exposure were associated with biomarkers of early kidney damage in children, adolescents and adults. A total of 1235 subjects (2-86.8 years old) participated in this study and provided samples of blood and urine. As a result, the median urinary Cd level was 0.38 μg g(-1) creatinine in adult men and 0.42 μg g(-1) creatinine in adult women, similar to reference values observed in the United States (median: 0.32-0.40 μg L(-1) in adults). Multiple linear regressions showed Cd in urine to be significantly positively associated with effects on renal tubule biomarkers (as indicated by increased levels of N-acetyl-β-D-glucosaminidase and β2-microglobulin) after adjusting for age, body mass index, blood lead, and urinary density, in all age groups including children. We also found positive associations between blood Cd and renal tubule biomarkers in children. In conclusion, adverse tubular renal effects might have occurred at the current low Cd levels in the study population, including children. These findings are particularly relevant assessing health risks associated with low environmental exposures to Cd.

Confusion about Cadmium Risks: The Unrecognized Limitations of an Extrapolated Paradigm

BACKGROUND

Cadmium (Cd) risk assessment presently relies on tubular proteinuria as a critical effect and urinary Cd (U-Cd) as an index of the Cd body burden. Based on this paradigm, regulatory bodies have reached contradictory conclusions regarding the safety of Cd in food. Adding to the confusion, epidemiological studies implicate environmental Cd as a risk factor for bone, cardiovascular, and other degenerative diseases at exposure levels that are much lower than points of departure used for setting food standards.

OBJECTIVE

The objective was to examine whether the present confusion over Cd risks is not related to conceptual or methodological problems.

DISCUSSION

The cornerstone of Cd risk assessment is the assumption that U-Cd reflects the lifetime accumulation of the metal in the body. The validity of this assumption as applied to the general population has been questioned by recent studies revealing that low-level U-Cd varies widely within and between individuals depending on urinary flow, urine collection protocol, and recent exposure. There is also evidence that low-level U-Cd increases with proteinuria and essential element deficiencies, two potential confounders that might explain the multiple associations of U-Cd with common degenerative diseases. In essence, the present Cd confusion might arise from the fact that this heavy metal follows the same transport pathways as plasma proteins for its urinary excretion and the same transport pathways as essential elements for its intestinal absorption.

CONCLUSIONS

The Cd risk assessment paradigm needs to be rethought taking into consideration that low-level U-Cd is strongly influenced by renal physiology, recent exposure, and factors linked to studied outcomes.

CITATION

Bernard A. 2016. Confusion about cadmium risks: the unrecognized limitations of an extrapolated paradigm. Environ Health Perspect 124:1-5; http://dx.doi.org/10.1289/ehp.1509691.

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.

Evaluation of cystatin C as an early biomarker of cadmium nephrotoxicity in the rat

Cadmium (Cd) is a nephrotoxic environmental pollutant that causes insidious injury to the proximal tubule that results in severe polyuria and proteinuria. Cystatin C is a low molecular weight protein that is being evaluated as a serum and urinary biomarker for various types of ischemic and nephrotoxic renal injury. The objective of the present study was to determine if cystatin C might be a useful early biomarker of Cd nephrotoxicity. Male Sprague-Dawley rats were given daily injections of Cd for up to 12 weeks. At 3, 6, 9 and 12 weeks, urine samples were analyzed for cystatin C, protein, creatinine, β2 microglobulin and kidney injury molecule-1. The results showed that Cd caused a significant increase in the urinary excretion of cystatin C that occurred 3-4 weeks before the onset of polyuria and proteinuria. Serum levels of cystatin C were not altered by Cd. Immunolabeling studies showed that Cd caused the relocalization of cystatin C from the cytoplasm to the apical surface of the epithelial cells of the proximal tubule. The Cd-induced changes in cystatin C labelling paralleled those of the brush border transport protein, megalin, which has been implicated as a mediator of cystatin C uptake in the proximal tubule. These results indicate that Cd increases the urinary excretion of cystatin C, and they suggest that this effect may involve disruption of megalin-mediated uptake of cystatin C by epithelial cells of the proximal tubule.

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.

Kidney function and blood pressure in preschool-aged children exposed to cadmium and arsenic--potential alleviation by selenium

BACKGROUND

Early-life exposure to toxic compounds may cause long-lasting health effects, but few studies have investigated effects of childhood exposure to nephrotoxic metals on kidney and cardiovascular function.

OBJECTIVES

To assess effects of exposure to arsenic and cadmium on kidney function and blood pressure in pre-school-aged children, and potential protection by selenium.

METHODS

This cross-sectional study was part of the 4.5 years of age (range: 4.4-5.4 years) follow-up of the children from a supplementation trial in pregnancy (MINIMat) in rural Bangladesh, and nested studies on early-life metal exposures. Exposure to arsenic, cadmium and selenium from food and drinking water was assessed by concentrations in children's urine, measured by ICP-MS. Kidney function was assessed by the estimated glomerular filtration rate (eGFR, n=1106), calculated from serum cystatin C, and by kidney volume, measured by ultrasound (n=375). Systolic and diastolic blood pressure was measured (n=1356) after five minutes rest.

RESULTS

Multivariable-adjusted regression analyzes showed that exposure to cadmium, but not arsenic, was inversely associated with eGFR, particularly in girls. A 0.5 µg/L increase in urinary cadmium among the girls (above spline knot at 0.12) was associated with a decrease in eGFR of 2.6 ml/min/1.73 m(2), corresponding to 0.2SD (p=0.022). A slightly weaker inverse association with cadmium was also indicated for kidney volume, but no significant associations were found with blood pressure. Stratifying on children's urinary selenium (below or above median of 12.6 µg/L) showed a three times stronger inverse association of U-Cd with eGFR (all children) in the lower selenium stratum (B=-2.8; 95% CI: -5.5, -0.20; p=0.035), compared to those with higher selenium (B=-0.79; 95% CI: -3.0, 1.4; p=0.49).

CONCLUSIONS

Childhood cadmium exposure seems to adversely affect kidney function, but not blood pressure, in this population of young children in rural Bangladesh. Better selenium status appears to be protective. However, it is important to follow up these children to assess potential long-term consequences of these findings.