The association between dietary cadmium exposure and renal dysfunction - the benchmark dose estimation of reference levels: the ChinaCad study

Estimation of urinary cadmium benchmark dose thresholds for preschool children in a cadmium-polluted area based on Bayesian model averaging

Urinary cadmium (U-Cd) values are indicators for determining chronic cadmium toxicity, and previous studies have calculated U-Cd indicators using renal injury biomarkers. However, most of these studies have been conducted in adult populations, and there is a lack of research on U-Cd thresholds in preschool children. We aimed to apply benchmark dose (BMD) analysis to estimate the U-Cd threshold level associated with renal impairment in preschool children in the cadmium-polluted area. 518 preschool children aged 3-5 years were selected by systematic sampling (275 boys, 243 girls). Urinary cadmium and three biomarkers of early renal injury (urinary N-acetyl-β-D-glucosaminidase, UNAG; urinary β2-microglobulin, Uβ2-MG; urinary retinol-binding protein, URBP) were determined. Bayesian model averaging estimated the BMD and lower confidence interval limit (BMDL) of U-Cd. The medians U-Cd levels in both boys and girls exceeded the recommended national standard threshold (5 μg/g cr) and U-Cd levels were higher in girls than in boys. Urinary N-acetyl-β-D-glucosaminidase (UNAG) was the most sensitive biomarker of renal effects in preschool children. The overall BMDL5 (BMDL at a benchmark response value of 5) was 2.76 μg/g cr. In the gender analysis, the BMDL5 values were 1.92 μg/g cr for boys and 4.12 μg/g cr for girls. This study shows that the U-Cd threshold (BMDL5) is lower than the national standard (5 μg/g cr) and boys' BMDL5 was lower than the limit set by the European Parliament and Council in 2019 (2 μg/g cr), which provides a reference point for making U-Cd thresholds for preschool children.

The Association Between Environmental Cadmium Exposure and Parathyroid Hormone Levels

Cadmium exposure is associated with renal dysfunction and bone damage. Chronic kidney disease and bone loss are also related to parathyroid hormone (PTH). However, whether cadmium exposure affect PTH level is not completely understood. In this study, we observed the association between environmental cadmium exposure and PTH levels in a Chinese population. A ChinaCd study was performed in China in 1990s which included 790 subjects living in heavily, moderately and low cadmium polluted area. 354 of them (121 men and 233 women) also had the data of serum PTH. The cadmium levels in blood (BCd) and urine (UCd) were determined by flame atomic absorption spectrometry. Serum PTH was detected by immunoradiometric assay. Renal function was assessed based on urinary N-acetyl-β-d-glucosaminidase (UNAG), β2-microglobulin (UBMG) and urinary albumin (UALB). The median BCd and UCd levels were 4.69 μg/L and 5.50 μg/g creatinine. The BCd, UCd, UNAG, UBMG and UALB levels in subjects with low PTH (< 5.0 ng/L) were significantly higher than those with PTH ≥ 5.0 ng/L (p < 0.05 or p < 0.01). Spearman correlation analysis also showed that UCd level was negatively correlated to PTH levels (r = -0.17, p = 0.008) in women. A weak correlation was also observed between PTH level and BCd in women (r = -0.11, p = 0.09) and UBMG in total population (r = -0.114, p = 0.07). Univariable and mutivariable logistic regression analysis both demonstrated that high BCd (> 10 μg/L) (odds ratio (OR) = 2.26, 95% confidence interval (CI):1.10-4.63; OR = 2.36, 95%CI: 1.11-5.05) and UCd level (> 20 μg/g cr) (OR = 2.84, 95% CI:1.32-6.10; OR = 2.97, 95%CI: 1.25-7.05) were associated with high risk of low PTH. Our data showed that environmental cadmium exposure was associated with low PTH level.

The Protective Potential of Aronia melanocarpa L. Berry Extract against Cadmium-Induced Kidney Damage: A Study in an Animal Model of Human Environmental Exposure to This Toxic Element

The impact of cadmium (Cd) on the function and structure of the kidney and the potential protective effect of an extract from Aronia melanocarpa L. berries were investigated in a rat model of low- and moderate-level environmental exposure to this heavy metal (1 and 5 mg Cd/kg feed for up to 24 months). The sensitive biomarkers of Cd-induced damage to the kidney tubules (N-acetyl-β-D-glucosaminidase (NAG), alkaline phosphatase (ALP), β2-microglobulin (β2-MG), and kidney injury molecule-1 (KIM-1) in the urine), clinically relevant early markers of glomerular damage (albumin in the urine and creatinine clearance), and other markers of the general functional status of this organ (urea, uric acid, and total protein in the serum and/or urine) and Cd concentration in the urine, were evaluated. The morphological structure of the kidney and inflammatory markers (chemerin, macrophage inflammatory protein 1 alpha (MIP1a), and Bcl2-associated X protein (Bax)) were also estimated. Low-level and moderate exposure to Cd led to damage to the function and structure of the kidney tubules and glomeruli. The co-administration of A. melanocarpa berry extract significantly protected against the injurious impact of this toxic element. In conclusion, even low-level, long-term exposure to Cd poses a risk of kidney damage, whereas an intake of Aronia berry products may effectively protect from this outcome.

Current Levels of Environmental Exposure to Cadmium in Industrialized Countries as a Risk Factor for Kidney Damage in the General Population: A Comprehensive Review of Available Data

The growing number of reports indicating unfavorable outcomes for human health upon environmental exposure to cadmium (Cd) have focused attention on the threat to the general population posed by this heavy metal. The kidney is a target organ during chronic Cd intoxication. The aim of this article was to critically review the available literature on the impact of the current levels of environmental exposure to this xenobiotic in industrialized countries on the kidney, and to evaluate the associated risk of organ damage, including chronic kidney disease (CKD). Based on a comprehensive review of the available data, we recognized that the observed adverse effect levels (NOAELs) of Cd concentration in the blood and urine for clinically relevant kidney damage (glomerular dysfunction) are 0.18 μg/L and 0.27 μg/g creatinine, respectively, whereas the lowest observed adverse effect levels (LOAELs) are >0.18 μg/L and >0.27 μg/g creatinine, respectively, which are within the lower range of concentrations noted in inhabitants of industrialized countries. In conclusion, the current levels of environmental exposure to Cd may increase the risk of clinically relevant kidney damage, resulting in, or at least contributing to, the development of CKD.

A systematic review of adverse health effects associated with oral cadmium exposure

Scientific data characterizing the adverse health effects associated with dietary cadmium (Cd) exposure were identified in order to make informed decisions about the most appropriate toxicological reference value (TRV) for use in assessing dietary Cd exposure. Several TRVs are available for Cd and regulatory organizations have used epidemiologic studies to derive these reference values; however, risk of bias (RoB) evaluations were not included in the assessments. We performed a systematic review by conducting a thorough literature search (through January 4, 2020). There were 1714 references identified by the search strings and 328 studies identified in regulatory assessments. After applying the specific inclusion and exclusion criteria, 208 studies (Human: 105, Animal: 103) were considered eligible for further review and data extraction. For the epidemiologic and animal studies, the critical effects identified for oral Cd exposure from the eligible studies were a decrease in bone mineral density (BMD) and renal tubular degeneration. A RoB analysis was completed for 49 studies (30 epidemiological and 19 animal) investigating these endpoints. The studies identified through the SR that were considered high quality and low RoB (2 human and 5 animal) can be used to characterize dose-response relationships and inform the derivation of a Cd TRV.

The Beneficial Impact of Zinc Supplementation on the Vascular Tissue of the Abdominal Aorta under Repeated Intoxication with Cadmium: A Study in an In Vivo Experimental Model

In an in vivo rat model of human exposure to cadmium (Cd; 5 and 50 mg/L, 6 months), whether the supplementation with zinc (Zn; 30 and 60 mg/L, increasing its daily intake by 79% and 151%, respectively) protects against the unfavourable impact of this xenobiotic on the vascular tissue of the abdominal aorta was investigated. The treatment with Cd led to oxidative stress and increased the concentrations of pro-inflammatory interleukin 1β (IL-1β), total cholesterol (TC), triglycerides (TG), and endothelial nitric oxide synthase (eNOS) and decreased the concentration of anti-inflammatory interleukin 10 (IL-10) in the vascular tissue. Cd decreased the expression of intercellular adhesion molecule-1 (ICAM-1), platelet endothelial cell adhesion molecule-1 (PECAM-1), and L-selectin on the endothelial cells. The administration of Zn prevented most of the Cd-induced alterations or at least weakened them (except for the expression of adhesive molecules). In conclusion, Zn supplementation may protect from the toxic impact of Cd on the blood vessels and thus exert a beneficial influence on the cardiovascular system. The increase in the intake of Zn by 79% may be sufficient to provide this protection and the effect is related to the antioxidative, anti-inflammatory, and antiatherogenic properties of this essential element.

Dose-response evaluation of urinary cadmium and kidney injury biomarkers in Chinese residents and dietary limit standards

BACKGROUND

Cadmium (Cd) is a common heavy metal that mainly causes renal damage. There is a lack of research on the large-scale and systematic evaluation of the association between urinary Cd (U-Cd) and various effect biomarkers among Chinese residents.

METHODS

Based on the establishment process of dietary Cd limit standards by European Food Safety Authority (EFSA), the dose-response relationships between U-Cd and four biomarkers, β2-microglobulin (β2-MG), N-acetyl-β-glucosidase (NAG), microalbumin (mALB), and retinol binding Protein (RBP) were explored, respectively. Toxicokinetic model was used to derive the dietary Cd exposure limit for Chinese residents after critical U-Cd concentration was calculated.

RESULTS

As the sensitive biomarkers of renal injury, β2-MG and NAG were selected to estimate the 95% confidence interval lower limit of the U-Cd benchmark dose (BMDL5) to be 3.07 and 2.98 μg/g Cr, respectively. Dietary Cd exposure limit was calculated to be 0.28 μg/kg bw/day (16.8 μg/day, based on the body weight of 60 kg), which was lower than the average Chinese Cd exposure (30.6 μg/day) by the China National Nutrient and Health Survey.

CONCLUSION

This study established an overall association between U-Cd and renal injury biomarkers, and explored the Chinese dietary Cd exposure limits, which helps improve Chinese Cd exposure risk assessment and provides a reference basis for formulating reasonable exposure standards.

The association between life-time dietary cadmium intake from rice and chronic kidney disease

The association between internal cadmium exposure and chronic kidney disease (CKD) has been investigated before. However, few studies have shown the association between dietary cadmium intake and CKD. In this study, we show the association between life-time dietary cadmium intake and CKD based on a follow-up study. At baseline, we collected blood and urine samples for assays of cadmium and renal effect biomarkers. A questionnaire and food survey was given to each subject to collect diet and lifestyle information for the estimation of cadmium intake. Dietary cadmium, cadmium in blood and urine were regarded as exposure markers. Life-time dietary cadmium intake was estimated based on an individual's daily cadmium intake and exposure time. At follow-up, 467 persons (163 men and 304 women) were finally included. CKD at follow-up was considered if the estimated glomerular filtration rate (eGFR) was less than 60 mL/min/1.73 m². The eGFR level in subjects in the highest quartile of total dietary cadmium intake (>9.34 g) was significantly lower than in those with a moderate or low intake (p < 0.01). eGFR was negatively associated with total dietary cadmium intake (β = -0.42, 95% confidence interval (CI): -0.77 to -0.07) after adjustment with confounders. Logistic regression further showed that the risk of CKD in subjects with a high total dietary cadmium intake (>2.2 g) was higher than in those with a low intake (odds ratio (OR) = 18.16, 95%CI: 1.75-188.85). A similar association was found between the baseline urinary albumin (UALB) level and CKD incidence. A predictive model based on UALB and life-time dietary cadmium intake showed an acceptable performance (the area under the curve was 0.77 (95%CI: 0.65-0.88)). Our data show that high dietary cadmium exposure was associated with CKD after controlling for renal tubular dysfunction and internal cadmium exposure.

A nomogram for predicting the renal dysfunction in a Chinese population with reduction in cadmium exposure based on an 8 years follow up study

Cadmium exposure is associated with renal dysfunction. However, the outcome of renal function in subjects who have had a reduction in cadmium exposure for years has not been completely clarified, particularly for individuals with normal baseline renal function. In this study, we used a nomogram model to predict renal dysfunction after a reduction in cadmium exposure in subjects with normal baseline renal function. In 1998, a survey was performed in 790 subjects living in control and cadmium-polluted areas. A total of 497 subjects was followed up in 2006. 404 subjects with normal baseline urinary β₂-microglobulin (UBMG), 373 subjects with normal baseline urinary N-acetyl-β-d-glucosaminidase (UNAG) and 407 subjects with normal baseline urinary albumin (UALB) were included in this analysis. Cadmium in the blood (BCd) and urine (UCd) was detected using graphite-furnace atomic absorption spectrometry. A logistic regression model was used to identify potential predicting factors of renal function at follow-up. Nomograms were developed based on those predictive factors. Bootstrap self-sampling, calibration curves and receiver operating characteristic (ROC) curves were performed to quantify our modeling strategy. Adjusted and unadjusted logistic regression models both showed that age, BCd and UBMG or UNAG at baseline were independent risk factors for renal tubular dysfunction. Baseline age, sex, BCd and UNAG or UBMG or UALB were used to construct the nomogam. The internal validation showed that the C-index was 0.70-0.74 for predicting renal dysfunction. The area under the curve of the nomogram was 0.70-0.74. Decision curve analysis verified the predictive value of the nomogram. A nomogram may be a useful risk assessment tool for predicting the progress of renal function in a cadmium-exposed population with normal baseline kidney function.

The Association Between Alcohol Consumption and Renal Tubular Dysfunction Induced by Cadmium Exposure

Alcohol consumption is inversely associated with the risk of chronic kidney diseases. However, this association has not been reported in populations exposed to cadmium. In the present study, we examined the association between alcohol consumption and renal tubular dysfunction in populations living in cadmium-polluted areas. A total of 446 subjects (170 men and 276 women) were finally included in our analysis. The urinary cadmium (UCd) and cadmium in blood (BCd) were determined as the exposure biomarkers. Urinary N-acetyl-β-D-glucosaminidase (UNAG) and β₂-microgloblin (UBMG) were measured as renal indicators. Alcohol drinking patterns were obtained from a questionnaire and divided into four categories: non-drinking, light drinking (< 3 drinks/week), moderate drinking (3-7 drinks/week), and heavy drinking (> 7 drinks /week). If UNAG was the indicator of renal dysfunction, the prevalence of renal tubular dysfunction was decreased in subjects with alcohol consumption both in men (χ² = 8.5, p < 0.01) and women (χ² = 8.3, p < 0.01). The odds ratio (OR) of subjects with light and moderate alcohol drinking was 0.31 (95% confidence interval (CI), 0.1-0.99) and 0.30 (95%CI, 0.1-0.96), respectively, compared with those of non-drinkers after adjusting with the confounders in men. Similar results were observed in women with light drinking (OR = 0.33, 95%CI, 0.15-0.70). Similar trends were observed in those subjects with high BCd (> 3.0 μg/L) or UCd (> 5.0 μg/g creatinine). Our data show that alcohol consumption is inversely associated with cadmium-induced renal tubular dysfunction.

Sirtuin-1 ameliorates cadmium-induced endoplasmic reticulum stress and pyroptosis through XBP-1s deacetylation in human renal tubular epithelial cells

Cadmium (Cd), an occupational and environmental pollutant, induces nephrotoxicity by primarily damaging renal proximal tubular cells. In this study, we hypothesized that pyroptosis, a caspase-1-dependent inflammatory programmed cell death mechanism, mediates Cd-induced nephrotoxicity. Human proximal tubular epithelial HK-2 cells were treated with 0-10 µM CdCl₂ for 48 h. We found that Cd dose-dependently caused cytotoxicity, which correlated with activation of the NLRP3 inflammasome, increases in the expression and secretion of pro-inflammatory cytokines and upregulation of pyroptosis-related genes in HK-2 cells or/and in kidneys of Cd-treated mice. These effects were significantly abrogated by inhibiting caspase-1 activity with inhibitor YVAD or silencing NLRP3 with siRNA in vitro, suggesting that Cd induces caspase-1- and NLRP3-inflammasome-dependent pyroptosis. Moreover, Cd treatment also activated three branches (ATF6, PERK and IRE-1α) of endoplasmic reticulum stress. Selective inhibition of the IRE-1α/XBP-1s branch by a pharmacological inhibitor STF-083010 or by genetic silencing of XBP-1 significantly attenuated Cd-induced NLRP3 inflammasome activation and pyroptosis. Mechanistically, Cd suppressed deacetylase Sirtuin-1 (SIRT-1) protein expression and activity leading to decrease in physical binding with XBP-1s protein, and thus the accumulation of acetylated XBP-1s levels. Activation of SIRT1 using a pharmacological agonist resveratrol or genetic SIRT1 overexpression significantly abolished Cd-induced activation of the IRE-1α/XBP-1s pathway and the NRLP3 inflammasome as well as pyroptosis, which were counteracted by co-overexpression of both SIRT1 and XBP-1s. Collectively, our findings indicate that SIRT1 activity protects against Cd-induced pyroptosis through deacetylating XBP-1s, and thus inhibiting the IRE-1α/XBP-1s pathway in HK-2 cells. These results provide a novel mechanism for Cd-induced nephrotoxicity.