The Source and Pathophysiologic Significance of Excreted Cadmium

Urinary N-acetylglucosaminidase in People Environmentally Exposed to Cadmium Is Minimally Related to Cadmium-Induced Nephron Destruction

Exposure to even low levels of the environmental pollutant cadmium (Cd) increases the risk of kidney damage and malfunction. The body burden of Cd at which these outcomes occur is not, however, reliably defined. Here, multiple-regression and mediation analyses were applied to data from 737 non-diabetic Thai nationals, of which 9.1% had an estimated glomerular filtration rate (eGFR) ≤ 60 mL/min/1.73 m2 (a low eGFR). The excretion of Cd (ECd), and renal-effect biomarkers, namely β2-microglobulin (Eβ2M), albumin (Ealb), and N-acetylglucosaminidase (ENAG), were normalized to creatinine clearance (Ccr) as ECd/Ccr Eβ2M/Ccr, Ealb/Ccr, and ENAG/Ccr. After adjustment for potential confounders, the risks of having a low eGFR and albuminuria rose twofold per doubling ECd/Ccr rates and they both varied directly with the severity of β2-microglobulinuria. Doubling ECd/Ccr rates also increased the risk of having a severe tubular injury, evident from ENAG/Ccr increments [POR = 4.80, p = 0.015]. ENAG/Ccr was strongly associated with ECd/Ccr in both men (β = 0.447) and women (β = 0.394), while showing a moderate inverse association with eGFR only in women (β = -0.178). A moderate association of ENAG/Ccr and ECd/Ccr was found in the low- (β = 0.287), and the high-Cd body burden groups (β = 0.145), but ENAG/Ccr was inversely associated with eGFR only in the high-Cd body burden group (β = -0.223). These discrepancies together with mediation analysis suggest that Cd-induced nephron destruction, which reduces GFR and the tubular release of NAG by Cd, involves different mechanisms and kinetics.

Modulation of Adverse Health Effects of Environmental Cadmium Exposure by Zinc and Its Transporters

Zinc (Zn) is the second most abundant metal in the human body and is essential for the function of 10% of all proteins. As metals cannot be synthesized or degraded, they must be assimilated from the diet by specialized transport proteins, which unfortunately also provide an entry route for the toxic metal pollutant cadmium (Cd). The intestinal absorption of Zn depends on the composition of food that is consumed, firstly the amount of Zn itself and then the quantity of other food constituents such as phytate, protein, and calcium (Ca). In cells, Zn is involved in the regulation of intermediary metabolism, gene expression, cell growth, differentiation, apoptosis, and antioxidant defense mechanisms. The cellular influx, efflux, subcellular compartmentalization, and trafficking of Zn are coordinated by transporter proteins, solute-linked carriers 30A and 39A (SLC30A and SLC39A), known as the ZnT and Zrt/Irt-like protein (ZIP). Because of its chemical similarity with Zn and Ca, Cd disrupts the physiological functions of both. The concurrent induction of a Zn efflux transporter ZnT1 (SLC30A1) and metallothionein by Cd disrupts the homeostasis and reduces the bioavailability of Zn. The present review highlights the increased mortality and the severity of various diseases among Cd-exposed persons and the roles of Zn and other transport proteins in the manifestation of Cd cytotoxicity. Special emphasis is given to Zn intake levels that may lower the risk of vision loss and bone fracture associated with Cd exposure. The difficult challenge of determining a permissible intake level of Cd is discussed in relation to the recommended dietary Zn intake levels.

Is Chronic Kidney Disease Due to Cadmium Exposure Inevitable and Can It Be Reversed?

Cadmium (Cd) is a metal with no nutritional value or physiological role. However, it is found in the body of most people because it is a contaminant of nearly all food types and is readily absorbed. The body burden of Cd is determined principally by its intestinal absorption rate as there is no mechanism for its elimination. Most acquired Cd accumulates within the kidney tubular cells, where its levels increase through to the age of 50 years but decline thereafter due to its release into the urine as the injured tubular cells die. This is associated with progressive kidney disease, which is signified by a sustained decline in the estimated glomerular filtration rate (eGFR) and albuminuria. Generally, reductions in eGFR after Cd exposure are irreversible, and are likely to decline further towards kidney failure if exposure persists. There is no evidence that the elimination of current environmental exposure can reverse these effects and no theoretical reason to believe that such a reversal is possible. This review aims to provide an update on urinary and blood Cd levels that were found to be associated with GFR loss and albuminuria in the general populations. A special emphasis is placed on the mechanisms underlying albumin excretion in Cd-exposed persons, and for an accurate measure of the doses-response relationships between Cd exposure and eGFR, its excretion rate must be normalised to creatinine clearance. The difficult challenge of establishing realistic Cd exposure guidelines such that human health is protected, is discussed.

Is Environmental Cadmium Exposure Causally Related to Diabetes and Obesity?

Cadmium (Cd) is a pervasive toxic metal, present in most food types, cigarette smoke, and air. Most cells in the body will assimilate Cd, as its charge and ionic radius are similar to the essential metals, iron, zinc, and calcium (Fe, Zn, and Ca). Cd preferentially accumulates in the proximal tubular epithelium of the kidney, and is excreted in urine when these cells die. Thus, excretion of Cd reflects renal accumulation (body burden) and the current toxicity of Cd. The kidney is the only organ other than liver that produces and releases glucose into the circulation. Also, the kidney is responsible for filtration and the re-absorption of glucose. Cd is the least recognized diabetogenic substance although research performed in the 1980s demonstrated the diabetogenic effects of chronic oral Cd administration in neonatal rats. Approximately 10% of the global population are now living with diabetes and over 80% of these are overweight or obese. This association has fueled an intense search for any exogenous chemicals and lifestyle factors that could induce excessive weight gain. However, whilst epidemiological studies have clearly linked diabetes to Cd exposure, this appears to be independent of adiposity. This review highlights Cd exposure sources and levels associated with diabetes type 2 and the mechanisms by which Cd disrupts glucose metabolism. Special emphasis is on roles of the liver and kidney, and cellular stress responses and defenses, involving heme oxygenase-1 and -2 (HO-1 and HO-2). From heme degradation, both HO-1 and HO-2 release Fe, carbon monoxide, and a precursor substrate for producing a potent antioxidant, bilirubin. HO-2 appears to have also anti-diabetic and anti-obese actions. In old age, HO-2 deficient mice display a symptomatic spectrum of human diabetes, including hyperglycemia, insulin resistance, increased fat deposition, and hypertension.

Estimation of the Cadmium Nephrotoxicity Threshold from Loss of Glomerular Filtration Rate and Albuminuria

Cadmium (Cd) is a pervasive, toxic environmental pollutant that preferentially accumulates in the tubular epithelium of the kidney. Current evidence suggests that the cumulative burden of Cd here leads to the progressive loss of the glomerular filtration rate (GFR). In this study, we have quantified changes in estimated GFR (eGFR) and albumin excretion (Ealb) according to the levels of blood Cd ([Cd]b) and excretion of Cd (ECd) after adjustment for confounders. ECd and Ealb were normalized to creatinine clearance (Ccr) as ECd/Ccr and Ealb/Ccr. Among 482 residents of Cd-polluted and non-polluted regions of Thailand, 8.1% had low eGFR and 16.9% had albuminuria (Ealb/Ccr) × 100 ≥ 20 mg/L filtrate. In the low Cd burden group, (ECd/Ccr) × 100 < 1.44 µg/L filtrate, eGFR did not correlate with ECd/Ccr (β = 0.007) while an inverse association with ECd/Ccr was found in the medium (β = -0.230) and high burden groups (β = -0.349). Prevalence odds ratios (POR) for low eGFR were increased in the medium (POR 8.26) and high Cd burden groups (POR 3.64). Also, eGFR explained a significant proportion of Ealb/Ccr variation among those with middle (η2 0.093) and high [Cd]b tertiles (η2 0.132) but did not with low tertiles (η2 0.001). With an adjustment of eGFR, age and BMI, the POR values for albuminuria were increased in the middle (POR 2.36) and high [Cd]b tertiles (POR 2.74) and those with diabetes (POR 6.02) and hypertension (2.05). These data indicate that (ECd/Ccr) × 100 of 1.44 µg/L filtrate (0.01-0.02 µg/g creatinine) may serve as a Cd threshold level based on which protective exposure guidelines should be formulated.

Evidence Linking Cadmium Exposure and β2-Microglobulin to Increased Risk of Hypertension in Diabetes Type 2

The most common causes of chronic kidney disease, diabetes, and hypertension are significant public health issues worldwide. Exposure to the heavy metal pollutant, cadmium (Cd), which is particularly damaging to the kidney, has been associated with both risk factors. Increased levels of urinary β₂-microglobulin (β₂M) have been used to signify Cd-induced kidney damage and circulating levels have been linked to blood pressure control. In this study we investigated the pressor effects of Cd and β₂M in 88 diabetics and 88 non-diabetic controls, matched by age, gender and locality. The overall mean serum β₂M was 5.98 mg/L, while mean blood Cd and Cd excretion normalized to creatinine clearance (C_cr) as E_Cd/C_cr were 0.59 µg/L and 0.0084 µg/L of filtrate (0.95 µg/g creatinine), respectively. The prevalence odds ratio for hypertension rose by 79% per every ten-fold increase in blood Cd concentration. In all subjects, systolic blood pressure (SBP) showed positive associations with age (β = 0.247), serum β₂M (β = 0.230), and E_Cd/C_cr (β = 0.167). In subgroup analysis, SBP showed a strong positive association with E_Cd/C_cr (β = 0.303) only in the diabetic group. The covariate-adjusted mean SBP in the diabetics of the highest E_Cd/C_cr tertile was 13.8 mmHg higher, compared to the lowest tertile (p = 0.027). An increase in SBP associated with Cd exposure was insignificant in non-diabetics. Thus, for the first time, we have demonstrated an independent effect of Cd and β₂M on blood pressure, thereby implicating both Cd exposure and β₂M in the development of hypertension, especially in diabetics.

Chronic Kidney Disease Induced by Cadmium and Diabetes: A Quantitative Case-Control Study

Kidney disease associated with chronic cadmium (Cd) exposure is primarily due to proximal tubule cell damage. This results in a sustained decline in glomerular filtration rate (GFR) and tubular proteinuria. Similarly, diabetic kidney disease (DKD) is marked by albuminuria and a declining GFR and both may eventually lead to kidney failure. The progression to kidney disease in diabetics exposed to Cd has rarely been reported. Herein, we assessed Cd exposure and the severity of tubular proteinuria and albuminuria in 88 diabetics and 88 controls, matched by age, gender and locality. The overall mean blood and Cd excretion normalized to creatinine clearance (C_cr) as E_Cd/C_cr were 0.59 µg/L and 0.0084 µg/L filtrate (0.96 µg/g creatinine), respectively. Tubular dysfunction, assessed by β₂-microglobulin excretion rate normalized to C_cr(E_β2M/C_cr) was associated with both diabetes and Cd exposure. Doubling of Cd body burden, hypertension and a reduced estimated GFR (eGFR) increased the risks for a severe tubular dysfunction by 1.3-fold, 2.6-fold, and 84-fold, respectively. Albuminuria did not show a significant association with E_Cd/C_cr, but hypertension and eGFR did. Hypertension and a reduced eGFR were associated with a 3-fold and 4-fold increases in risk of albuminuria. These findings suggest that even low levels of Cd exposure exacerbate progression of kidney disease in diabetics.

Cadmium-Induced Tubular Dysfunction in Type 2 Diabetes: A Population-Based Cross-Sectional Study

The global prevalence of diabetes, and its major complication, diabetic nephropathy, have reached epidemic proportions. The toxic metal cadmium (Cd) also induces nephropathy, indicated by a sustained reduction in the estimated glomerular filtration rate (eGFR) and the excretion of β₂-microglobulin (β₂M) above 300 µg/day, which reflects kidney tubular dysfunction. However, little is known about the nephrotoxicity of Cd in the diabetic population. Here, we compared Cd exposure, eGFR, and tubular dysfunction in both diabetics (n = 81) and non-diabetics (n = 593) who were residents in low- and high-Cd exposure areas of Thailand. We normalized the Cd and β₂M excretion rates (E_Cd and E_β2M) to creatinine clearance (C_cr) as E_Cd/C_cr and E_β2M/C_cr. Tubular dysfunction and a reduced eGFR were, respectively, 8.7-fold (p < 0.001) and 3-fold (p = 0.012) more prevalent in the diabetic than the non-diabetic groups. The doubling of E_Cd/C_cr increased the prevalence odds ratios for a reduced eGFR and tubular dysfunction by 50% (p < 0.001) and 15% (p = 0.002), respectively. In a regression model analysis of diabetics from the low-exposure locality, E_β2M/C_cr was associated with E_Cd/C_cr (β = 0.375, p = 0.001) and obesity (β = 0.273, p = 0.015). In the non-diabetic group, E_β2M/C_cr was associated with age (β = 0.458, p < 0.001) and E_Cd/C_cr (β = 0.269, p < 0.001). However, after adjustment for age, and body mass index (BMI), E_β2M/C_cr was higher in the diabetics than non-diabetics of similar E_Cd/C_cr ranges. Thus, tubular dysfunction was more severe in diabetics than non-diabetics of similar age, BMI, and Cd body burden.

Estimation of health risks associated with dietary cadmium exposure

In much of the world, currently employed upper limits of tolerable intake and acceptable excretion of cadmium (Cd) (ECd/Ecr) are 0.83 µg/kg body weight/day and 5.24 µg/g creatinine, respectively. These figures were derived from a risk assessment model that interpreted β2-microglobulin (β2MG) excretion > 300 μg/g creatinine as a "critical" endpoint. However, current evidence suggests that Cd accumulation reduces glomerular filtration rate at values of ECd/Ecr much lower than 5.24 µg/g creatinine. Low ECd/Ecr has also been associated with increased risks of kidney disease, type 2 diabetes, osteoporosis, cancer, and other disorders. These associations have cast considerable doubt on conventional guidelines. The goals of this paper are to evaluate whether these guidelines are low enough to minimize associated health risks reliably, and indeed whether permissible intake of a cumulative toxin like Cd is a valid concept. We highlight sources and levels of Cd in the human diet and review absorption, distribution, kidney accumulation, and excretion of the metal. We present evidence for the following propositions: excreted Cd emanates from injured tubular epithelial cells of the kidney; Cd excretion is a manifestation of current tissue injury; reduction of present and future exposure to environmental Cd cannot mitigate injury in progress; and Cd excretion is optimally expressed as a function of creatinine clearance rather than creatinine excretion. We comprehensively review the adverse health effects of Cd and urine and blood Cd levels at which adverse effects have been observed. The cumulative nature of Cd toxicity and the susceptibility of multiple organs to toxicity at low body burdens raise serious doubt that guidelines concerning permissible intake of Cd can be meaningful.

The Validity of Benchmark Dose Limit Analysis for Estimating Permissible Accumulation of Cadmium

Cadmium (Cd) is a toxic metal pollutant that accumulates, especially in the proximal tubular epithelial cells of kidneys, where it causes tubular cell injury, cell death and a reduction in glomerular filtration rate (GFR). Diet is the main Cd exposure source in non-occupationally exposed and non-smoking populations. The present study aimed to evaluate the reliability of a tolerable Cd intake of 0.83 μg/kg body weight/day, and its corresponding toxicity threshold level of 5.24 μg/g creatinine. The PROAST software was used to calculate the lower 95% confidence bound of the benchmark dose (BMDL) values of Cd excretion (ECd) associated with injury to kidney tubular cells, a defective tubular reabsorption of filtered proteins, and a reduction in the estimated GFR (eGFR). Data were from 289 males and 445 females, mean age of 48.1 years of which 42.8% were smokers, while 31.7% had hypertension, and 9% had chronic kidney disease (CKD). The BMDL value of ECd associated with kidney tubular cell injury was 0.67 ng/L of filtrate in both men and women. Therefore, an environmental Cd exposure producing ECd of 0.67 ng/L filtrate could be considered as Cd accumulation levels below which renal effects are likely to be negligible. A reduction in eGFR and CKD may follow when ECd rises from 0.67 to 1 ng/L of filtrate. These adverse health effects occur at the body burdens lower than those associated with ECd of 5.24 µg/g creatinine, thereby arguing that current health-guiding values do not provide a sufficient health protection.

The NOAEL Equivalent of Environmental Cadmium Exposure Associated with GFR Reduction and Chronic Kidney Disease

Cadmium (Cd) is a highly toxic metal pollutant present in virtually all food types. Health guidance values were established to safeguard against excessive dietary Cd exposure. The derivation of such health guidance figures has been shifted from the no-observed-adverse-effect level (NOAEL) to the lower 95% confidence bound of the benchmark dose (BMD), termed BMDL. Here, we used the PROAST software to calculate the BMDL figures for Cd excretion (ECd) associated with a reduction in the estimated glomerular filtration rate (eGFR), and an increased prevalence of chronic kidney disease (CKD), defined as eGFR ≤ 60 mL/min/1.73 m2. Data were from 1189 Thai subjects (493 males and 696 females) mean age of 43.2 years. The overall percentages of smokers, hypertension and CKD were 33.6%, 29.4% and 6.2%, respectively. The overall mean ECd normalized to the excretion of creatinine (Ecr) as ECd/Ecr was 0.64 µg/g creatinine. ECd/Ecr, age and body mass index (BMI) were independently associated with increased prevalence odds ratios (POR) for CKD. BMI figures ≥24 kg/m2 were associated with an increase in POR for CKD by 2.81-fold (p = 0.028). ECd/Ecr values of 0.38-2.49 µg/g creatinine were associated with an increase in POR for CKD risk by 6.2-fold (p = 0.001). The NOAEL equivalent figures of ECd/Ecr based on eGFR reduction in males, females and all subjects were 0.839, 0.849 and 0.828 µg/g creatinine, respectively. The BMDL/BMDU values of ECd/Ecr associated with a 10% increase in CKD prevalence were 2.77/5.06 µg/g creatinine. These data indicate that Cd-induced eGFR reduction occurs at relatively low body burdens and that the population health risk associated with ECd/Ecr of 2.77-5.06 µg/g creatinine was not negligible.

Mitigation of Cadmium Toxicity through Modulation of the Frontline Cellular Stress Response

Cadmium (Cd) is an environmental toxicant of public health significance worldwide. Diet is the main Cd exposure source in the non-occupationally exposed and non-smoking populations. Metal transporters for iron (Fe), zinc (Zn), calcium (Ca), and manganese (Mn) are involved in the assimilation and distribution of Cd to cells throughout the body. Due to an extremely slow elimination rate, most Cd is retained by cells, where it exerts toxicity through its interaction with sulfur-containing ligands, notably the thiol (-SH) functional group of cysteine, glutathione, and many Zn-dependent enzymes and transcription factors. The simultaneous induction of heme oxygenase-1 and the metal-binding protein metallothionein by Cd adversely affected the cellular redox state and caused the dysregulation of Fe, Zn, and copper. Experimental data indicate that Cd causes mitochondrial dysfunction via disrupting the metal homeostasis of this organelle. The present review focuses on the adverse metabolic outcomes of chronic exposure to low-dose Cd. Current epidemiologic data indicate that chronic exposure to Cd raises the risk of type 2 diabetes by several mechanisms, such as increased oxidative stress, inflammation, adipose tissue dysfunction, increased insulin resistance, and dysregulated cellular intermediary metabolism. The cellular stress response mechanisms involving the catabolism of heme, mediated by heme oxygenase-1 and -2 (HO-1 and HO-2), may mitigate the cytotoxicity of Cd. The products of their physiologic heme degradation, bilirubin and carbon monoxide, have antioxidative, anti-inflammatory, and anti-apoptotic properties.

Dose-Response Analysis of the Tubular and Glomerular Effects of Chronic Exposure to Environmental Cadmium

We retrospectively analyzed data on the excretion of cadmium (E_Cd), β₂-microglobulin (E_β2M) and N-acetyl-β-D-glucosaminidase (E_NAG), which were recorded for 734 participants in a study conducted in low- and high-exposure areas of Thailand. Increased E_β2M and E_NAG were used to assess tubular integrity, while a reduction in the estimated glomerular filtration rate (eGFR) was a criterion for glomerular dysfunction. E_Cd, E_β2M and E_NAG were normalized to creatinine clearance (C_cr) as E_Cd/C_cr, E_β2M/C_cr and E_NAG/C_cr to correct for interindividual variation in the number of surviving nephrons and to eliminate the variation in the excretion of creatinine (E_cr). For a comparison, these parameters were also normalized to E_cr as E_Cd/E_cr, E_β2M/E_cr and E_NAG/E_cr. According to the covariance analysis, a Cd-dose-dependent reduction in eGFR was statistically significant only when E_cd was normalized to C_cr as E_Cd/C_cr (F = 11.2, p < 0.001). There was a 23-fold increase in the risk of eGFR ≤ 60 mL/min/1.73 m² in those with the highest E_Cd/C_cr range (p = 0.002). In addition, doubling of E_Cd/C_cr was associated with lower eGFR (β = -0.300, p < 0.001), and higher E_NAG/C_cr (β = 0.455, p < 0.001) and E_β2M/C_cr (β = 0.540, p < 0.001). In contrast, a covariance analysis showed a non-statistically significant relationship between E_Cd/E_cr and eGFR (F = 1.08, p = 0.165), while the risk of low eGFR was increased by 6.9-fold only among those with the highest E_Cd/E_cr range. Doubling of E_Cd/E_cr was associated with lower eGFR and higher E_NAG/E_cr and E_β2M/E_cr, with the β coefficients being smaller than in the C_cr-normalized dataset. Thus, normalization of Cd excretion to C_cr unravels the adverse effect of Cd on GFR and provides a more accurate evaluation of the severity of the tubulo-glomerular effect of Cd.

Multiple Targets of Toxicity in Environmental Exposure to Low-Dose Cadmium

Dietary assessment reports and population surveillance programs show that chronic exposure to low levels of environmental cadmium (Cd) is inevitable for most people, and adversely impacts the health of children and adults. Based on a risk assessment model that considers an increase in the excretion of β₂-microglobulin (β₂M) above 300 μg/g creatinine to be the "critical" toxicity endpoint, the tolerable intake level of Cd was set at 0.83 µg/kg body weight/day, and a urinary Cd excretion rate of 5.24 µg/g creatinine was considered to be the toxicity threshold level. The aim of this review is to draw attention to the many other toxicity endpoints that are both clinically relevant and more appropriate to derive Cd exposure limits than a β₂M endpoint. In the present review, we focus on a reduction in the glomerular filtration rate and diminished fecundity because chronic exposure to low-dose Cd, reflected by its excretion levels as low as 0.5 µg/g creatinine, have been associated with dose-dependent increases in risk of these pathological symptoms. Some protective effects of the nutritionally essential elements selenium and zinc are highlighted. Cd-induced mitochondrial dysfunction is discussed as a potential mechanism underlying gonadal toxicities and infertility.

Effects of Environmental Exposure to Cadmium and Lead on the Risks of Diabetes and Kidney Dysfunction

Environmental exposure to cadmium (Cd) or lead (Pb) is independently associated with increased risks of type 2 diabetes, and chronic kidney disease. The aim of this study was to examine the effects of concurrent exposure to these toxic metals on the risks of diabetes and kidney functional impairment. The Cd and Pb exposure levels among study subjects were low to moderate, evident from the means for blood concentrations of Cd and Pb ([Cd]_b and [Pb]_b) of 0.59 µg/L and 4.67 µg/dL, respectively. Of 176 study subjects (mean age 60), 71 (40.3%) had abnormally high fasting plasma glucose levels. Based on their [Cd]_b and [Pb]_b, 53, 71, and 52 subjects were assigned to Cd and Pb exposure profiles 1, 2, and 3, respectively. The diagnosis of diabetes was increased by 4.2-fold in those with an exposure profile 3 (p = 0.002), and by 2.9-fold in those with the estimated glomerular filtration (eGFR) ≤ 60 mL/min/1.73 m² (p = 0.029). The prevalence odds ratio (POR) for albuminuria was increased by 5-fold in those with plasma glucose levels above kidney threshold of 180 mg/dL (p = 0.014), and by 3.1-fold in those with low eGFR) (p = 0.050). Collectively, these findings suggest that the Cd and Pb exposure profiles equally impact kidney function and diabetes risk.

Epidermal Growth Factor Receptor (EGFR) Gene Polymorphism May be a Modifier for Cadmium Kidney Toxicity

The results of many studies indicate that cadmium (Cd) exposure is harmful to humans, with the proximal tubule of the kidney being the main target of Cd accumulation and toxicity. Studies have also shown that Cd has the effect of activating the pathway of epidermal growth factor receptor (EGFR) signaling and cell growth. The EGFR is a family of transmembrane receptors, which are widely expressed in the human kidney. The aim of this study was to investigate the kidney function estimated glomerular filtration rate (eGFR), and its relationship with plasma Cd level and EGFR gene polymorphism. Using data from Academia Sinica Taiwan biobank, 489 subjects aged 30-70 years were analyzed. The demographic characteristics was determined from questionnaires, and biological sampling of urine and blood was determined from physical examination. Kidney function was assessed by the eGFR with CKD-EPI formula. Plasma Cd (ug/L) was measured by inductively coupled plasma mass spectrometry. A total of 97 single-nucleotide polymorphisms (SNPs) were identified in the EGFR on the Taiwan biobank chip, however 4 SNPs did not pass the quality control. Multiple regression analyses were performed to achieve the study aim. The mean (±SD) plasma Cd level of the study subjects was 0.02 (±0.008) ug/L. After adjusting for confounding variables, rs13244925 AA, rs6948867 AA, rs35891645 TT and rs6593214 AA types had higher eGFR (4.89 mL/min/1.73 m² (p = 0.035), 5.54 mL/min/1.73 m² (p = 0.03), 4.96 mL/min/1.73 m² (p = 0.048) and 5.16 mL/min/1.73 m² (p = 0.048), respectively). Plasma cadmium and rs845555 had an interactive effect on eGFR. In conclusion, EGFR polymorphisms could be modifiers of Cd kidney toxicity, in which rs13244925 AA, rs6948867 AA, rs35891645 TT and rs6593214 AA may be protective, and Cd interacting with rs845555 may affect kidney function.

The Evolving Role for Zinc and Zinc Transporters in Cadmium Tolerance and Urothelial Cancer

Cadmium (Cd) is an environmental toxicant with serious public health consequences due to its persistence within arable soils, and the ease with which it enters food chains and then, accumulates in human tissues to induce a broad range of adverse health effects. The present review focuses on the role of zinc (Zn), a nutritionally essential metal, to protect against the cytotoxicity and carcinogenicity of Cd in urinary bladder epithelial cells. The stress responses and defense mechanisms involving the low-molecular-weight metal binding protein, metallothionein (MT), are highlighted. The efflux and influx transporters of the ZnT and Zrt-/Irt-like protein (ZIP) gene families are discussed with respect to their putative role in retaining cellular Zn homeostasis. Among fourteen ZIP family members, ZIP8 and ZIP14 mediate Cd uptake by cells, while ZnT1 is among ten ZnT family members solely responsible for efflux of Zn (Cd), representing cellular defense against toxicity from excessively high Zn (Cd) intake. In theory, upregulation of the efflux transporter ZnT1 concomitant with the downregulation of influx transporters such as ZIP8 and ZIP14 can prevent Cd accumulation by cells, thereby increasing tolerance to Cd toxicity. To link the perturbation of Zn homeostasis, reflected by the aberrant expression of ZnT1, ZIP1, ZIP6, and ZIP10, with malignancy, tolerance to Cd toxicity acquired during Cd-induced transformation of a cell model of human urothelium, UROtsa, is discussed as a particular example.

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.

Evaluation of the effect of serum cystatin-C and ACE I/D and ACE G2350A polymorphisms on kidney function among hypertensive sewage workers

Cadmium (Cd) as nephrotoxicant metal exerts its potent effect mainly on renal tubules disturbing its functions. A cross-sectional study was conducted on 55 sewage workers occupationally exposed to Cd and 50 control subjects. The study aimed to assess the effect of low-level Cd exposure on blood pressure and renal function in terms of serum cystatin-C levels. The associations between genetic polymorphisms of ACEI/D and ACE G2350A and hypertension and tubular injury among workers were studied. We analyzed blood and urine Cd concentration (U-Cd), serum cystatin-C, ACE I/D polymorphisms, and ACE G2350A, and blood pressure was measured. Results recorded a significant rise in serum and U-Cd and cystatin-C levels in sewage workers compared with controls. Significant distribution in genotype frequency of ACE I/D and ACE G2350A gene was detected. An association in DD genotype of ACE I/D with a rise in serum and U-Cd was observed in workers. In wild type genotype GG of ACE G2350A gene, a significant rise in serum cystatin-C levels and diastolic pressure was found while in heterozygote genotype GA significant rise in U-Cd levels was detected. Also, the association of AA genotype of ACE G2350A gene with a significant rise in serum and U-Cd and cystatin-C levels was shown among workers compared with control groups. Our findings indicated an association of ACE DD polymorphism in conjugation with GG genotype of ACE2 with hypertension and tubular injury in sewage workers.

Cadmium and Lead Exposure, Nephrotoxicity, and Mortality

The present review aims to provide an update on health risks associated with the low-to-moderate levels of environmental cadmium (Cd) and lead (Pb) to which most populations are exposed. Epidemiological studies examining the adverse effects of coexposure to Cd and Pb have shown that Pb may enhance the nephrotoxicity of Cd and vice versa. Herein, the existing tolerable intake levels of Cd and Pb are discussed together with the conventional urinary Cd threshold limit of 5.24 μg/g creatinine. Dietary sources of Cd and Pb and the intake levels reported for average consumers in the U.S., Spain, Korea, Germany and China are summarized. The utility of urine, whole blood, plasma/serum, and erythrocytes to quantify exposure levels of Cd and Pb are discussed. Epidemiological studies that linked one of these measurements to risks of chronic kidney disease (CKD) and mortality from common ailments are reviewed. A Cd intake level of 23.2 μg/day, which is less than half the safe intake stated by the guidelines, may increase the risk of CKD by 73%, and urinary Cd levels one-tenth of the threshold limit, defined by excessive ß₂-microglobulin excretion, were associated with increased risk of CKD, mortality from heart disease, cancer of any site and Alzheimer's disease. These findings indicate that the current tolerable intake of Cd and the conventional urinary Cd threshold limit do not provide adequate health protection. Any excessive Cd excretion is probably indicative of tubular injury. In light of the evolving realization of the interaction between Cd and Pb, actions to minimize environmental exposure to these toxic metals are imperative.

Comparison of Methodologies to Estimate Dietary Cadmium Intake in an Italian Population

Cadmium is a metal that is toxic to humans, and the major source of cadmium exposure in the non-smoking general population is diet. To identify major food sources and lower exposure from diet, an accurate estimate of dietary cadmium intake is needed. Hence, the objectives of this study are to develop a method to assess dietary cadmium intake using a biomarker measurement and to improve the estimation of dietary cadmium intake when using a food frequency questionnaire (FFQ). In a random sample of an Italian population, we collected dietary habits by FFQ and measured cadmium in foods and beverages. These data were used to compute the estimated weekly dietary intake (WDI) of cadmium (µg) by kilogram (kg) of body weight (bw) (WDIFFQ). We also measured fasting serum cadmium levels by inductively-coupled plasma mass spectrometry. We used these data to develop a model for the estimation of the biomarker-derived dietary cadmium intake (WDIbio). In the 51 subjects recruited, the median level of serum cadmium was 0.041 µg/L (interquartile range (IQR): 0.030-0.054). The median WDIFFQ and WDIbio were 1.34 µg/kg bw/week (IQR: 0.86-1.70) and 0.72 µg/kg bw/week (IQR: 0.55-1.11), respectively. The correlation between the two estimates was low-to-moderate (r = 0.291). In exploratory analyses, the correlation was slightly higher in women and participants ages <50 years, and markedly higher in participants with body mass index <25 kg/m2 and smokers. Our approach allows for the dietary contribution to be isolated from the overall cadmium exposure measured with a biomarker; the estimated dietary cadmium intake was roughly similar to that estimated using the FFQ, especially in select subgroups. Future refinements to the biomarker-derived dietary cadmium intake approach should take into consideration additional sources of cadmium exposure, as well as factors affecting its absorption and metabolism.

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.