Progress of renal dysfunction in inhabitants environmentally exposed to cadmium

Current Situation and Causes Analysis of Cadmium Pollution in the Kakehashi River Basin

Cadmium (Cd) pollution is a public environmental problem worthy of attention. Long-term exposure to Cd may have adverse effects on human health. Our previous study showed that urinary concentration of Cd (U-Cd) in the residents decreased when Cd-polluted paddy soil was removed. However, from 2008 to 2014, the concentration of U-Cd increased. At the same time, the concentration of urinary β2-microglobulin (β2-MG), which is considered to be an early sign of cadmium-induced renal dysfunction, increased continuously. To find the cause of elevated urinary cadmium (U-Cd) in residents of cadmium-contaminated areas, we measured the concentration of cadmium in the blood (B-Cd) of 29 elderly residents (15 female and 14 male) and edible rice (R-Cd), and correlations between R-Cd, B-Cd, and U-Cd were analyzed in the formerly cadmium-polluted areas (the Kakehashi River basin). In 2016, we collected blood, urine, and rice samples from each participant. The analysis showed a significant correlation between age and B-Cd, U-Cd, and β2-MG. However, there was no significant correlation between R-Cd and U-Cd, B-Cd, or β2-MG concentrations. Although we found a slightly higher level of Cd in rice and urine than reported in 2008, we cannot be sure that it indicates an increased Cd contamination in the Kakehashi River basin because larger studies are required for such a conclusion. The increased urinary Cd concentrations in this area may be because Cd in tissues and organs returns to blood and urine as participants age, which leads to an increasing trend.

A 30-year follow-up study in a former cadmium-polluted area of Japan: the relationship between cadmium exposure and β2-microglobulin in the urine of Japanese people

Cadmium (Cd) is an environmental pollutant. Long-term exposure to Cd may lead to adverse health effects in humans. Our epidemiological studies showed that urinary Cd (U-Cd) concentrations increased from 2008 through 2014, although they decreased from 1986 through 2008. The aim of this study was to elucidate the long-term effects of the changing trend of cadmium exposure levels (U-Cd) on residents' renal function within 30 years after Cd exposure ceased. In 2016, urine samples were collected from each subject by visiting 20 elderly Japanese people (9 females and 11 males) living in the Kakehashi River basin, a previously Cd-polluted area in Ishikawa, Japan. The geometric means of the β₂-microglobulin (β₂-MG) and urinary Cd (U-Cd) continued to increase from 2014 until 2016. Furthermore, Cd concentration and β₂-MG in urine were still higher than those in the non-polluted areas in Japan. Multivariate linear regression was performed to associate β₂-MG (dependent variable) and U-Cd with sex and age (independent variables). Significant correlations were found among age, U-Cd, and β₂-MG, and these were clearer in females than in males. In summary, we propose that three decades after Cd exposure ceased, age is associated with β₂-MG more strongly than Cd for bodily impact. Moreover, renal tubular dysfunction is irreversible and worsens after exposure to Cd, with females being more sensitive to exposure.

Cadmium body burden and health effects after restoration of cadmium-polluted soils in cadmium-polluted areas in the Jinzu River basin

BACKGROUND

Itai-itai disease is caused by environmental cadmium (Cd) pollution in the Jinzu River basin in Japan. To reduce the Cd contamination of rice, soil restoration of paddy fields was carried out. We evaluated the effect of soil restoration on the health status of residents of the former Cd-polluted area.

METHODS

Participants were 1,030 men and 944 women who lived in the area of restoration of Cd-polluted rice paddies. First morning urine was collected and urinary Cd, β2-microglobulin (β2MG), and N-acetyl-β-D-glucosaminidase (NAG) levels were measured. Associations among age, years of residence before and after soil restoration, and urinary Cd, β2MG, and NAG levels were evaluated by multiple regression analysis.

RESULTS

The geometric mean (interquartile range) of urinary Cd (µg/g Cr) was 1.00 (0.58-1.68) in men and 1.67 (1.02-2.91) in women. The geometric means of urinary β2MG (µg/g Cr) and NAG (U/g Cr) were 174.6 (92.6-234.2) and 1.47 (0.72-3.14) in men, and 217.6 (115.3-28.7) and 1.48 (0.73-2.96) in women, respectively. Urinary Cd, β2MG, and NAG were significantly positively correlated (p < 0.01 all). Age and duration of residence in the Cd-polluted area before soil restoration were independently associated with urinary Cd, β2MG, and NAG. Among the 916 participants who had resided in the area before the soil restoration, urinary Cd concentrations were significantly higher, thus by 1.03-fold (95% CI, 1.01-1.04) in men and 1.03-fold (95% CI, 1.01-1.05) in women, when the years of residence before soil restoration by each 5-years increment. By contrast, urinary Cd concentrations were significantly lower, thus 0.97-fold (95% CI, 0.96-0.99) lower in men and 0.97-fold (95% CI, 0.95-0.99) lower in women, by each 5-year increment of residence after soil restoration. A similar association was observed for urinary β2MG concentration, and no significant association was observed for urinary NAG levels in men or women.

CONCLUSIONS

Cd exposure and associated renal tubular dysfunction in residents of a former Cd-polluted area were influenced by Cd exposure from the environment prior to soil restoration. Soil restoration in Cd-polluted areas reduced the Cd exposure of local residents.

Effect of Picroliv on cadmium-induced hepatic and renal damage in the rat

The therapeutic efficacy of Picroliv-a standardized-was investigated in male rats exposed to CdCl2 (0.5 mg/kg, sc), 5 days/week for 18 weeks. Picroliv at two doses (6 and 12 mg/kg, po) was given to the cadmium (Cd)-administered group for the last 4 weeks (ie, weeks 15 -18). The Cd altered oxidative stress indices, such as increased lipid peroxidation and membrane fluidity, reduced levels of non-protein sulphydryls (NPSHs), and Na-K-ATPase activity in the liver and kidney were found close to the control values by Picroliv treatment, suggesting its antioxidant potential. The hepatoprotective action of Picroliv was evident by its ability to lower the Cd-induced liver function parameters-the serum enzymes, such as alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), g-glutamyl transpeptidase (GGT) and lactate dehydrogenase (LDH). Bile flow and biliary Cd also increased as a result of Picroliv's choleretic property. The Cd-induced serum urea and urinary excretion of proteins, calcium (Ca), Cd and enzymes, such as Nacetyl-b-D-glucosaminidase (NAG) and LDH, were less marked on Picroliv treatment, indicating recovery from nephrotoxicity. Organ uptake of Cd and essential metals by Cd exposure was reduced on Picroliv treatment. Cdinduced hepatic metallothionein (MT) was lowered by Picroliv, whereas renal MT was unaltered. Cd-induced hepatic damage was also minimized. However, the renal morphological changes were marginally protected by Picroliv. The 12-mg Picroliv dose was more effective than the 6-mg dose in causing amelioration of the above parameters. This study has provided clear evidence for the hepato-and renal protective efficacy of Picroliv against experimental Cd toxicity.

Urine metabolomics of women from small villages exposed to high environmental cadmium levels

The present study aimed to identify urine metabolites in women exposed to high cadmium (Cd) levels. Twenty-one women exposed to environmental Cd and 12 age-matched controls were categorized as high exposure (urine Cd ≥ 15 μg/g creatinine; n = 9) or low exposure (15 μg/g creatinine > urine Cd > 5 μg/g creatinine; n = 12). Low-molecular weight metabolites in urine were analyzed by gas chromatography and mass spectrometry after derivatization. An orthogonal partial least-squares discriminant analysis model was constructed, and metabolites from the dimensional model were selected according to the variable importance in projection (>1). Metabolites differing significantly in abundance between different exposure groups were identified by searching mass spectral databases, and related pathways were analyzed using the Kyoto Encyclopedia of Genes and Genomes. Approximately 110 significantly different metabolites were detected with variable importance in projection > 1, and 48 of them were found to differ markedly in abundance among the 3 groups. Twenty-seven matched with known metabolites, including 22 significantly increased and 5 markedly decreased in the high-exposure group (p < 0.01). Kyoto Encyclopedia of Genes and Genomes results indicated that carbohydrate, amino acid, bone, and intestinal flora metabolism and the tricarboxylic acid cycle were affected by Cd exposure. The present study identified metabolites that differed in abundance in response to Cd exposure. Further studies may connect these biomarkers to early damage caused by Cd.

A 28-year observational study of urinary cadmium and β2 -microglobulin concentrations in inhabitants in cadmium-polluted areas in Japan

The biological half-life of cadmium (Cd) is as long as 10-30 years. Exposure to this element induces renal tubular dysfunction, which is considered irreversible. β₂ -microglobulin (β₂ -MG) is a low-molecular-weight protein, and urinary β₂ -MG is one of the most useful and critical indicators for the early detection of renal tubular dysfunction. However, very little research has been published concerning the long-term observation of Cd-induced adverse health effects. As such, this follow-up study was conducted for 28 years to clarify the relationship between the concentration of Cd and β₂ -MG in the urine of 28 inhabitants (14 male and 14 female) living in the Kakehashi River basin, Ishikawa prefecture (Japan), previously one of the most highly Cd-polluted regions in this country. All subjects were over 60 years old in 2014 and participated in all six health examinations conducted over 28 years (1986-2014). Urine was collected at the appropriate time and kept frozen to analyze urinary Cd and β₂ -MG concentrations. The urinary Cd concentration was found to decrease by nearly half between 1986 and 2008 in both male and female subjects, whereas it increased significantly from 2008 to 2014 in males. In contrast, urinary β₂ -MG concentrations tended to increase over the 28-year study period in both sexes. Urinary Cd and β₂ -MG concentrations in females were significantly higher than those in males in this Cd-polluted region. Age is more strongly associated with urinary β₂ -MG concentration than recent Cd body burden. Copyright © 2016 John Wiley & Sons, Ltd.

Estimation of the benchmark dose of urinary cadmium as the reference level for renal dysfunction: a large sample study in five cadmium polluted areas in China

BACKGROUND

Itai-itai disease primarily results from cadmium (Cd) exposure and is known as one of the four major pollution diseases in Japan. Cd pollution is more serious in several areas of China than in Japan. However, there is still a lack of information regarding the threshold level of Cd exposure for the adverse health effects in the general Chinese population. This study aims to evaluate the reference value of urinary Cd (UCd) for renal dysfunction in a Chinese population as the benchmark dose lower confidence limit (BMDL) based on a large sample survey.

METHODS

A total of 6103 participants who lived in five Cd polluted areas of China participated in this study. We analyzed UCd levels as a biomarker of exposure and urinary β2-microglobulin (Uβ2-MG) levels as a renal tubular effect biomarker. The BMD studies were performed using BMD software. The benchmark response (BMR) was defined as a 10% additional risk above the background.

RESULTS

There was a positive correlation between the UCd levels and the prevalence of Uβ2-MG. The BMD of UCd for Uβ2-MG was estimated for each province. The findings showed that the BMD levels were related to the participants' geographic region, which may be partially due to the large differences in Cd exposure level, ethnic group, lifestyle and diet of the sample population in these study areas. The reference level of UCd for the renal effects was further evaluated by combining the five sets of data from all 6103 subjects. The overall BMDLs of UCd for Uβ2-MG with an excess risk of 10% were 2.00 μg/g creatinine (μg/g cr) in males and 1.69 μg/g cr in females, which were significantly lower than the World Health Organization (WHO) threshold level of 5 μg/g cr for Cd-related renal effects.

CONCLUSIONS

The selection of the sample population and geographic region affected the BMDL evaluation. Based on the findings of this survey of a large sample population, the UCd BMDLs for Uβ2-MG in males with BMRs at 10% were 2.00 μg/g cr. The BMD was slightly lower in females, which indicated that females may be relatively more sensitive to Cd exposure than males.

Benchmark Dose for Urinary Cadmium based on a Marker of Renal Dysfunction: A Meta-Analysis

Background

Low doses of cadmium can cause adverse health effects. Benchmark dose (BMD) and the one-sided 95% lower confidence limit of BMD (BMDL) to derive points of departure for urinary cadmium exposure have been estimated in several previous studies, but the methods to derive BMD and the estimated BMDs differ.

Objectives

We aimed to find the associated factors that affect BMD calculation in the general population, and to estimate the summary BMD for urinary cadmium using reported BMDs.

Methods

A meta-regression was performed and the pooled BMD/BMDL was estimated using studies reporting a BMD and BMDL, weighted by sample size, that were calculated from individual data based on markers of renal dysfunction.

Results

BMDs were highly heterogeneous across studies. Meta-regression analysis showed that a significant predictor of BMD was the cut-off point which denotes an abnormal level. Using the 95th percentile as a cut off, BMD5/BMDL5 estimates for 5% benchmark responses (BMR) of β2-microglobulinuria (β2-MG) estimated was 6.18/4.88 μg/g creatinine in conventional quantal analysis and 3.56/3.13 μg/g creatinine in the hybrid approach, and BMD5/BMDL5 estimates for 5% BMR of N-acetyl-β-d-glucosaminidase (NAG) was 10.31/7.61 μg/g creatinine in quantal analysis and 3.21/2.24 g/g creatinine in the hybrid approach. However, the meta-regression showed that BMD and BMDL were significantly associated with the cut-off point, but BMD calculation method did not significantly affect the results. The urinary cadmium BMDL5 of β2-MG was 1.9 μg/g creatinine in the lowest cut-off point group.

Conclusion

The BMD was significantly associated with the cut-off point defining the abnormal level of renal dysfunction markers.

Benchmark dose estimation for cadmium-induced renal tubular damage among environmental cadmium-exposed women aged 35-54 years in two counties of China

BACKGROUND

A number of factors, including gender, age, smoking habits, and occupational exposure, affect the levels of urinary cadmium. Few studies have considered these influences when calculating the benchmark dose (BMD) of cadmium. In the present study, we aimed to calculate BMDs and their 95% lower confidence bounds (BMDLs) for cadmium-induced renal tubular effects in an age-specific population in south-central China.

METHODS

In this study, urinary cadmium, β2-microglobulin, and N-acetyl-β-D-glucosaminidase levels were measured in morning urine samples from 490 randomly selected non-smoking women aged 35-54 years. Participants were selected using stratified cluster sampling in two counties (counties A and B) in China. Multiple regression and logistic regression analyses were used to investigate the dose-response relationship between urinary cadmium levels and tubular effects. BMDs/BMDLs corresponding to an additional risk (benchmark response) of 5% and 10% were calculated with assumed cut-off values of the 84th and 90th percentile of urinary β2-microglobulin and N-acetyl-β-D-glucosaminidase levels of the controls.

RESULTS

Urinary levels of β2-microglobulin and N-acetyl-β-D-glucosaminidase increased significantly with increasing levels of urinary cadmium. Age was not associated with urinary cadmium levels, possibly because of the narrow age range included in this study. Based on urinary β2-microglobulin and N-acetyl-β-D-glucosaminidase, BMDs and BMDLs of urinary cadmium ranged from 2.08 to 3.80 (1.41-2.18) µg/g cr for subjects in county A and from 0.99 to 3.34 (0.74-1.91) µg/g cr for those in county B. The predetermined benchmark response of 0.05 and the 90th percentiles of urinary β2-microglobulin and N-acetyl-β-D-glucosaminidase levels of the subjects not exposed to cadmium (i.e., the control group) served as cut-off values.

CONCLUSIONS

The obtained BMDs of urinary cadmium were similar to the reference point of 1 µg/g cr, as suggested by the European Food Safety Authority, indicating that cadmium exposure must be reduced to protect human health.

Renal function after reduction in cadmium exposure: an 8-year follow-up of residents in cadmium-polluted areas

BACKGROUND AND OBJECTIVE

Long-term exposure to cadmium (Cd) causes renal dysfunction, but the change in renal function with exposure is unknown. We assessed the evolution of Cd-induced renal effects after a reduction in dietary exposure to Cd in rice.

METHODS

Four hundred twelve residents in previously Cd-polluted and nonpolluted areas were examined twice, in 1998 and in 2006. Changes in blood Cd, urinary Cd, and kidney function [N-acetyl-β-d-glucosaminidase (NAG), β2-microglobulin, and albumin in urine] were measured.

RESULTS

In the most polluted area, mean blood Cd was 8.9 μg/L and 3.3 μg/L in 1998 and in 2006, respectively, and urinary Cd was 11.6 and 9.0 μg/g creatinine. Urinary albumin in 1998 increased with urinary Cd, but no such exposure-response relation appeared for 2006 albumin versus urinary Cd 1998, indicating recovery. Other biomarkers of kidney function were also elevated in 1998. Partial recovery was observed for NAG among women and was suggested for β2-microglobulin among young individuals. The probability of having β2-microglobulin levels above the 95th percentile in 2006 was high in those with elevated β2-microglobulin in 1998 [odds ratio (OR) = 24.8; 95% confidence interval (CI): 11.2, 55.3] compared with albumin (OR = 3.0; 95% CI: 1.2, 7.5) and NAG (OR = 2.6; 95% CI: 1.6, 4.4).

CONCLUSIONS

Results suggest that a Cd-mediated increase in urinary albumin excretion is reversible upon substantial reduction of exposure. For markers of tubular effects, we observed a tendency toward improvement but not complete recovery. Data from repeated observations suggest that β2-microglobulin may be more informative than NAG as an indicator for an individual's future tubular function.

Bone-prognostic status after cessation of cadmium exposure for one month in male rats

This study investigated bone status after decreased cadmium (Cd) exposure in male rats. Sprague-Dawley male rats were randomly divided into three groups. One group was injected subcutaneously with sodium chloride as control. The others were given CdCl2 by subcutaneous injection at doses of 0.5 mg Cd/kg body weight (bw) for 2 months (Cd+2m) and for 3 months (Cd+3m). For the Cd+2m group, the rats were shifted to cessation of Cd injection for 1 month after 2 months' exposure. At month 3, micro-computed tomography (micro-CT) analyses were performed on the proximal tibia and lumbar spine, and urine was collected from all rats. Rats were then killed and blood collected for metabolic-marker measurement and Cd assay. Bone tissues were also collected for bone-mass assay, biomechanical test, and bone-histology analysis. Cd burdens of rats in the Cd+2m and Cd+3m groups were both significantly greater than those in the control group. Cd burdens of rats were lower in the Cd+2m group compared with the Cd+3m group. Bone damage occurred in the Cd+2m and Cd+3m groups compared with the control group (p<0.05), but no significant improvement was found in the Cd+2m group compared with the Cd+3m group. Cd damage to bone could not be reversed over the short term. More attention should be paid to Cd's toxic effects on bone after decreased exposure.

Bone mineral density is related with previous renal dysfunction caused by cadmium exposure

Relationship between bone mineral density (BMD) and previous renal dysfunction caused by cadmium exposure was investigated. A total of 457 persons, living in polluted and control areas, were followed up in this study. The inhabitants living in exposure areas ceased ingesting cadmium-contaminated rice in 1996. Blood and urinary cadmium levels and BMD in 1998 and 2006 were measured. Urinary N-acetyl-β-d-glucosaminidase and albumin determined in 1998 and 2006 were used to evaluate kidney status. BMD of subjects with tubular damage was significant lower than those without damage in female (p < 0.05). The prevalence of osteoporosis was significantly different between those with and without kidney damage (p = 0.003, in total population; p = 0.039, in female) and those with and without tubular damage (p = 0.0005, in total population; p = 0.007, in female). The results suggested that BMD was correlated with previous kidney impairment caused by cadmium exposure, especially to tubular damage and especially for female.

Seventeen-year observation on urinary cadmium and beta2-microglobulin in inhabitants after cessation of cadmium-exposure in Japan

The purpose of this study was to clarify the change and relationship of urinary cadmium (Cd) and beta(2)-microglobulin (beta(2)-MG) concentrations of inhabitants in Cd-polluted areas after soil restoration. The urinary Cd and beta(2)-MG concentrations of 25 males and 28 females did not show a significant change, 22 years after the Cd-polluted soil was restored. Once exposed to Cd, it was found to remain in the body, 22 years after the Cd -polluted soil was restored. However, this did not influence renal tubular dysfunction in most of the younger generation compared with elders heavily exposed to Cd.

Increased hepatic and decreased urinary metallothionein in rats after cessation of oral cadmium exposure

We investigated the role of metallothionein (MT) in tissues after cessation of cadmium (Cd) exposure. Wistar rats of both genders were given CdCl(2) in drinking water at daily doses of 0, 2.5, 5.0 or 10.0 mg Cd/kg body-weight for 12 weeks. Half of the animals were then killed; the others were given Cd-free water for the following 16 weeks, i.e. until 28 weeks after start of the experiment (28-week rats). We observed dose-dependent increases in the levels of MT in the tissues of rats 12 weeks after beginning the experiment (12-week rats). After the exposure ceased, levels of MT in the 28-week rats changed in three ways: an increase in the liver, persistence in the kidney cortex and a decrease in the medulla, relative to those levels in their 12-week counterparts. Biomarkers of kidney dysfunction were determined to be urinary MT (UMT) and urinary N-acetyl-beta-D-glucosaminidase (UNAG). After 12 weeks, we observed dose-related statistically significant increases in UMT and UNAG in all of the Cd-exposed groups. A statistically significant decrease for UNAG between the 12- and 28-week rats occurred among males at the lowest Cd dose and for UMT in all of the Cd-exposed groups. The unchanged tissue levels of MT in the kidney cortex suggest that decreased UMT is a sign either of (i) decreased transport of Cd-MT from the liver via blood plasma to the renal tubules or (ii) increased tubular reabsorption and recovery of renal tubular function.

Serial follow-up study on renal handling of calcium and phosphorus after soil replacement in Cd-polluted rice paddies estimated using a general linear mixed model

A 10-year follow-up study was conducted to investigate the effects of renal handling of calcium (Ca) and phosphorus (P) after the removal of cadmium-polluted soil in rice paddies and replacing it with nonpolluted soil. Using a general linear mixed model, serial changes of Ca and P concentrations in urine and serum (Ca-U/S, P-U/S), fractional excretion of Ca (FECa), and percent tubular reabsorption of P (%TRP) were determined in 37 persons requiring observation in the Cd-polluted Kakehashi River Basin, Japan. Ca-U and Ca-S remained within the normal range in both sexes. FECa in men returned to the normal level within 3.3 years from the completion of soil replacement. Overall, it is suggested that the renal handling of Ca showed no or only a slight change throughout the observation period in both sexes. P-U decreased gradually. P-S showed lower than normal values in the men and values at the lower end of the normal range in women, although the values recovered gradually to normal. %TRP values remained low throughout the observation period and the values did not recover in either sex. However, the results of P-U and P-S suggested that the renal handling of P may recover after the completion of soil replacement.

Renal effects evolution in a Chinese population after reduction of cadmium exposure in rice

Cadmium is a well-known nephrotoxic agent with extremely long biological half-time of 10-30 years in human. To investigate the evolution of cadmium-induced renal effects in the population, a number of 148 residents who lived in cadmium-polluted area were followed-up for 3 years after the reduction of cadmium exposure in rice. Urinary cadmium (UCd), beta(2)-microglobulin (B2M) and albumin (ALB) were analyzed in 1995 and 1998, respectively. The results demonstrated that the changes of renal effects of residents depended on the levels of UCd before inflow of cadmium to human body declined. In cases where UCd were less than 10 microg/g creatinine in 1995, evidence was found indicating significant decreases in proteinuria (i.e., B2M and ALB) 3 years later, whereas, in cases where the excretion of UCd exceeded 10 microg/g creatinine in 1995, progression was observed. The study of dose-response relationships between UCd and B2M or ALB also showed that the cadmium-induced renal dysfunction might be reversible if UCd concentration was low-level before exposure decreasing, otherwise it might be irreversible or aggravated.

Changes in renal tubular and glomerular functions and biological Acid-base balance after soil replacement in Cd-polluted rice paddies calculated with a general linear mixed model

Using a general linear mixed model, we conducted a 10-year follow-up investigation of 29 persons requiring observation in the cadmium (Cd)-polluted Kakehashi River basin to determine serial changes in biological parameters after removal of Cd-polluted soil present in rice paddies. In particular, we investigated changes in urinary Cd, urinary total protein, biological acid-base balance based on arterial blood pH, carbon dioxide tension (Pa(CO2)), base excess (BE), serum chloride ion (SCl(-)), and renal glomerular function based on serum creatinine (SCr) and creatinine clearance (C(Cr)). In both sexes, urinary Cd concentrations decreased and total protein concentrations increased with increasing number of years elapsed, with the partial regression coefficients statistically significant in the women. Partial regression coefficients showed positive values for SCl(-), with statistical significance in both sexes. The value for Pa(CO2) was significantly negative in men. Given the serial changes in arterial blood pH, Pa(CO2), BE, SCl(-), it is suggested that the biological acid-base balance will progress to metabolic acidosis with hyperchloremia. Moreover, glomerular dysfunction as indicated by an increase in SCr and a decrease in C(Cr) will continue to progress even after soil replacement. Interventions such as soil replacement appear to be too late to prevent progressive renal failure in Cd-exposed populations.

Biological variations in cadmium, alpha 1-microglobulin, beta 2-microglobulin and N-acetyl-beta-D-glucosaminidase in adult women in a non-polluted area

OBJECTIVES

This study was initiated to investigate the extents of biological variations in cadmium and three common tubular dysfunction marker levels in blood and urine through repeated sampling.

METHODS

A 12-month survey and a 10-week survey were conducted in an area with no known cadmium pollution. In the 12-month survey, five adult women offered urine samples once every month and blood samples once in every season, respectively. In the 10-week survey, 17 adult women gave urine samples once every week. Blood and urine samples were analyzed for cadmium (Cd-B and Cd-U) by graphite-furnace atomic absorption spectrometry, and urine samples were analyzed also for alpha 1-microglobulin (alpha 1-MG-U), beta 2-microglobulin (beta 2-MG-U) and N-acetyl-beta-D-glucosaminidase (NAG-U) by conventional methods, all under strict quality control. The results were subjected to statistical analysis to examine the extents of biological variations through-out the study periods.

RESULTS

Variations in geometric means (GMs) for Cd-B, Cd-U, alpha 1-MG-U, beta 2-MG-U, and NAG-U were all small; the ratio of the largest GM over the lowest GM was 1.1 for Cd-B, 2 for Cd-U and 2 to 3 for alpha 1-MG-U, beta 2-MG-U, and NAG-U in the 12-month survey, and 1.7 at largest for all parameters in the 10-week survey. The within-subject variations during the 12-month or 10-week periods were however large, i.e., more than 4-5-fold difference between the smallest and the largest values obtained for the same subject. Effects of the correction for urine density to reduce the variations were limited. In contrast, within-subject variation in Cd-B was small with a ratio of 1.3.

CONCLUSIONS

Variations in GM values for Cd-U, alpha 1-MG-U, beta 2-MG-U, and NAG-U at different time of sampling are small so that single measurement would be acceptable as far as the evaluation on a group basis is the study objective. Within-subject variations are wide however, the ratio of the largest value over the smallest value being 4-5 or more, irrespective of correction for urine density. Therefore, care should be practiced when evaluation on an individual basis is intended. Very low within-subject variation in Cd-B may suggest the advantage of Cd-B over Cd-U for individual evaluation among general populations if blood sampling is accepted.

Estimation of benchmark doses for urinary cadmium based on beta2-microglobulin excretion in cadmium-polluted regions of the Kakehashi River basin, Japan

A benchmark dose low (BMDL) is used as a replacement for the no observed adverse effect level. The threshold levels of urinary cadmium (Cd) as BMDL were estimated using data from the Kakehashi River basin. The target population (>or=50 years) comprised 3178 and 294 participants inhabiting Cd-polluted and non-polluted areas, respectively. Cut-off values for beta2-MG-uria were defined as the 84 and 95% upper limit values calculated from control subjects, and 1000 microg/l or microg/g cr of beta2-MG. Using these cut-off values, the BMDL at which the excess risk is 0.05 was determined to be 2.9 - 4.0 microg/g cr (males) and 1.5 - 3.6 microg/g cr (females). The present study demonstrated that a BMD approach is useful to estimate the threshold level of urinary Cd in Cd-exposed subjects and people living in general environment without any known Cd-pollution since a BMD approach does not need abnormality rates of urinary findings in the controls.

Estimation of benchmark dose as the threshold levels of urinary cadmium, based on excretion of total protein, beta2-microglobulin, and N-acetyl-beta-D-glucosaminidase in cadmium nonpolluted regions in Japan

Previously, we investigated the association between urinary cadmium (Cd) concentration and indicators of renal dysfunction, including total protein, beta2-microglobulin (beta2-MG), and N-acetyl-beta-D-glucosaminidase (NAG). In 2778 inhabitants 50 years of age (1114 men, 1664 women) in three different Cd nonpolluted areas in Japan, we showed that a dose-response relationship existed between renal effects and Cd exposure in the general environment without any known Cd pollution. However, we could not estimate the threshold levels of urinary Cd at that time. In the present study, we estimated the threshold levels of urinary Cd as the benchmark dose low (BMDL) using the benchmark dose (BMD) approach. Urinary Cd excretion was divided into 10 categories, and an abnormality rate was calculated for each. Cut-off values for urinary substances were defined as corresponding to the 84% and 95% upper limit values of the target population who have not smoked. Then we calculated the BMD and BMDL using a log-logistic model. The values of BMD and BMDL for all urinary substances could be calculated. The BMDL for the 84% cut-off value of beta2-MG, setting an abnormal value at 5%, was 2.4 microg/g creatinine (cr) in men and 3.3 microg/g cr in women. In conclusion, the present study demonstrated that the threshold level of urinary Cd could be estimated in people living in the general environment without any known Cd-pollution in Japan, and the value was inferred to be almost the same as that in Belgium, Sweden, and China.

Low-level cadmium exposure in Toyama City and its surroundings in Toyama prefecture, Japan, with references to possible contribution of shellfish intake to increase urinary cadmium levels

OBJECTIVES

This study was initiated to examine if exposure to cadmium (Cd) was high also outside of the previously identified Itai-itai disease endemic region in the Jinzu River basin in Toyama prefecture in Japan.

METHODS

Morning spot urine samples were collected in June-August 2004 from 651 adult women (including 535 never-smokers) in various regions in Toyama prefecture, and subjected to urinalyses for cadmium (Cd), alpha1-microglobulin (alpha1-MG), beta2-microglobulin (beta2-MG), N-acetyl-beta-D-glucosaminidase (NAG), specific gravity (SG or sg) and creatinine (CR or cr). Three months later, the second urine samples were collected from those with elevated Cd in urine (e.g., > or =4 microg/g cr), together with answers to questionnaires on shellfish consumption.

RESULTS

The geometric mean (GM) Cd, alpha1-MG, beta2-MG and NAG (after correction for CR) for the total participants were 2.0 microg/g cr, 2.4 mg/g cr, 104 microg/g cr and 2.8 units/g cr, respectively; further analysis with never-smoking cases only did not induce significant changes in these parameters. Analyses of the second urine samples from the high Cd subjects showed that there was substantial decrease (to about a half) in Cd in the 3-month period, and that the decrease was accompanied by reduction in alpha1-MG and NAG (beta2-MG did not show elevation even in the first samples). The urinalysis results in combination with the results of the questionnaire survey suggest that the high urinary Cd was temporary and might be induced by intake of shellfish that is edible whole.

CONCLUSIONS

The overall findings appear to suggest that Cd exposure in Toyama populations (outside of the Itai-itai disease endemic region) was at the levels commonly observed on the coast of the Sea of Japan, and that the Cd level in urine might be modified by the intake of some types of seafood. Further studies are necessary to elucidate the relation of urinary Cd with seafood intake.

Meta-analysis for deriving age- and gender-specific dose-response relationships between urinary cadmium concentration and beta2-microglobulinuria under environmental exposure

A meta-analysis was conducted to derive age- and gender-specific dose-response relationships between urinary cadmium (Cd) concentration and beta2-microglobulinuria (beta2MG-uria) under environmental exposure. beta2MG-uria was defined by a cutoff point of 1000 microg beta2-microglobulin/g creatinine. We proposed a model for describing the relationships among the interindividual variabilities in urinary Cd concentration, the ratio of Cd concentrations in the target organ and in urine, and the threshold Cd concentration in the target organ. The parameters in the model were determined so that good agreement might be achieved between the prevalence rates of beta2MG-uria reported in the literature and those estimated by the model. In this analysis, only the data from the literature on populations environmentally exposed to Cd were used. Using the model and estimated parameters, the prevalence rate of beta2MG-uria can be estimated for an age- and gender-specific subpopulation for which the distribution of urinary Cd concentrations is known. The maximum permissible level of urinary Cd concentration was defined as the maximum geometric mean of the urinary Cd concentration in an age- and gender-specific subpopulation that would not result in a statistically significant increase in the prevalence rate of beta2MG-uria. This was estimated to be approximately 3 microg/g creatinine for a population in a small geographical area and approximately 2 microg/g creatinine for a nationwide population.

Elevated levels of cadmium and zinc in paddy soils and elevated levels of cadmium in rice grain downstream of a zinc mineralized area in Thailand: implications for public health

Prolonged consumption of rice containing elevated cadmium (Cd) levels is a significant health issue particularly in subsistence communities that are dependent on rice produced on-farm. This situation is further exacerbated in areas of known non-ferrous mineralization adjacent to rice-based agricultural systems where the opportunity for contamination of rice and its eventual entry into the food chain is high. In the current study, an assessment of the degree of soil Cd and Zn contamination and associated rice grain Cd contamination downstream of an actively mined zone of Zn mineralization in western Thailand was undertaken. Total soil Cd and Zn concentrations in the rice-based agricultural system investigated ranged from 0.5 to 284 mg kg(-1) and 100 to 8036 mg kg(-1), respectively. Further, the results indicate that the contamination is associated with suspended sediment transported to fields via the irrigation supply. Consequently, the spatial distribution of Cd and Zn is directly related to a field's proximity to primary outlets from in-field irrigation channels and inter-field irrigation flows with 60-100% of the Cd and Zn loading associated with the first three fields in irrigation sequence. Rice grain Cd concentrations in the 524 fields sampled, ranged from 0.05 to 7.7 mg kg(-1). Over 90% of the rice grain samples collected contained Cd at concentrations exceeding the Codex Committee on Food Additives and Contaminants (CCFAC) draft Maximum Permissible Level for rice grain of 0.2 mg Cd kg(-1). In addition, as a function of demographic group, estimated Weekly Intake (WI) values ranged from 20 to 82 mug Cd per kg Body. This poses a significant public health risk to local communities. The results of this study suggest that an irrigation sequence-based field classification technique in combination with strategic soil and rice grain sampling and the estimation of WI values via rice intake alone may be a useful decision support tool to rapidly evaluate potential public health risks in irrigated rice-based agricultural systems receiving Cd contaminated irrigation water. In addition, the proposed technique will facilitate the cost effective strategic targeting of detailed epidemiological studies thus focusing resources to specific 'high risk' areas.

Markers of cadmium exposure in workers in a cadmium pigment factory after changes in the exposure conditions

The objective of this study was to assess changes in concentrations of cadmium in the blood (Cd-B), cadmium in the urine (Cd-U), beta2-microglobulin in the serum (beta2-mG-S) and beta2-microglobulin in the urine (beta2-mG-U) of workers at a cadmium (Cd) pigment factory in Japan in which exposure conditions improved. We evaluated reversibility of these markers in continuously employed workers in relation to changes in exposure levels resulting from improvements in the workplace and the reduced production of Cd. Our study involved both environmental and biological monitoring. Data were collected for four years. We measured the Cd concentration in the air of each work area, using the time-weighted average (TWA). Cd-B and Cd-U were measured in workers as direct indices of Cd exposure. beta2-mG-S and beta2-mG-U were measured as markers of renal tubular function. Exposure levels were high in all work areas, according to the criteria set by the American Conference of Governmental Industrial Hygienists (ACGIH). Workers' Cd-B and Cd-U concentrations reflected high levels of exposure. Correlation was found between these direct indices and beta2-mG-S concentrations. Since the second year, ambient Cd concentrations decreased and reacted markers have been improved. Our results suggest that Cd-B, Cd-U, beta2-mG-S and beta2-mG-U are appropriate markers for monitoring both the level of Cd exposure and the tubular function of workers. Reversibility of urinary low molecular weight protein was observed in the workers over the four years.

The Threshold Cadmium Level That Causes a Substantial Increase in .BETA.2-Microglobulin in Urine of General Populations

Cadmium (Cd) is a toxic element ubiquitous in the environment, and general populations have been exposed to this element primarily via foods. Thus, the critical level of non-occupational Cd exposure to cause any health effects among general populations is of public health as well as toxicological concern. The objectives of the present study were to examine the quantitative relationship between cadmium (Cd-U) and beta2-microglobulin in urine (beta2-MG-U) as a marker of exposure to Cd and as a marker of renal tubular dysfunction, respectively, and to identify a threshold Cd-U, if present, in causing a substantial increase in beta2-MG-U. Thus, paired data on geometric mean (GM) Cd-Ucr (i.e., Cd-U as corrected for creatinine [cr] concentration) and GM beta2-MG-Ucr (beta2-MG-U as corrected for cr) of residents in polluted as well as nonpolluted areas in Japan were retrieved in international and domestic sources. In practice, 245 cases of the data pairs were obtained in 51 articles published since 1975. Statistical analysis on ordinary scales disclosed that beta2-MG-Ucr increased markedly when Cd-Ucr exceeded a certain level. The relation between the two parameters after double-logarithmic conversion was in a shape of the letter J or a stick for ice hockey. Analysis for Cd-Ucr at the flexion point gave Cd-Ucr of 4 (on double logarithmic scales) or 7 microg/g cr (on ordinary scales). Cd-Ucr levels that correspond to a beta2-MG-Ucr of 1,000 microg/g cr were estimated to be 8-9 microg/g cr, by ordinary and logarithmic assumption as well as by the 3rd degree regression analysis. Thus, it is concluded that there is a threshold Cd-Ucr level that leads to a substantial increase in beta2-MG-Ucr, and that the threshold level is greater than 4 microg/g cr.

Threshold levels of urinary cadmium in relation to increases in urinary beta2-microglobulin among general Japanese populations

Through literature survey, paired data on cadmium (Cd) and beta(2)-microglobulin (beta(2)-MG) levels (as corrected for creatinine concentration) in urine (i.e., Cd-Ucr and beta(2)-MG-Ucr) among Japanese populations were available for 32 groups of men and 58 groups of women in 12 publications. Plotting of the Cd-Ucr and beta(2)-MG-Ucr data for the groups of women showed that beta(2)-MG-Ucr stayed unchanged when Cd-Ucr was at lower levels, whereas beta(2)-MG-Ucr increased sharply when Cd-Ucr was in excess of 10-20 microg/g cr. Regression analysis was made for groups of women with no elevation in beta(2)-MG-Ucr, and those with >400 or >1000 microg beta(2)-MG-U/g cr. A threshold Cd-Ucr level in relation to an increase in beta(2)-MG-Ucr was estimated as Cd-Ucr at the point of intercept of the two regression lines, one with no beta(2)-MG-Ucr elevation, and the other with >400 or >1000 microg beta(2)-MG-U/g cr. Cd-Ucr at the point of flexion thus calculated was 11-12 microg/g cr. Such observation was quantitatively reproduced by the analysis of data for men, giving 10-11 microg Cd-U/g cr at the point of flexion. This study suggests that the relationship of beta(2)-MG-Ucr with Cd-Ucr is not linear but in the shape of letter 'J', i.e., beta(2)-MG-Ucr increases sharply when Cd-Ucr is in excess of 10-12 microg/g cr.

Cadmium toxicity among wildlife in the Colorado Rocky Mountains

Cadmium is known to be both extremely toxic and ubiquitous in natural environments. It occurs in almost all soils, surface waters and plants, and it is readily mobilized by human activities such as mining. As a result, cadmium has been named as a potential health threat to wildlife species; however, because it exists most commonly in the environment as a trace constituent, reported incidences of cadmium toxicity are rare. Here we have measured trace metals in the food web and tissues of white-tailed ptarmigan (Lagopus leucurus) in Colorado. Our results suggest that cadmium toxicity may be more common among natural populations of vertebrates than has been appreciated to date and that cadmium toxicity may often go undetected or unrecognized. In addition, our research shows that ingestion of even trace quantities of cadmium can influence not only the physiology and health of individual organisms, but also the demographics and the distribution of species.

Renal effects of low-level environmental cadmium exposure: 5-year follow-up of a subcohort from the Cadmibel study

BACKGROUND

The clinical relevance of renal effects of cadmium in people exposed in the environment remains uncertain. This study examined the evolution of renal effects observed in a population exposed to cadmium in the environment.

METHODS

208 men and 385 women surveyed in 1985-89 (Cadmium in Belgium study [Cadmibel]; baseline) were re-examined on average 5 years later (Public health and environmental exposure to cadmium study [PheeCad]; follow-up). Urinary and blood cadmium and markers of renal tubular dysfunction and glomerular effects were measured. The association between cadmium body burden and renal factors was examined by multivariate logistic and linear regression.

FINDINGS

In men, mean urinary cadmium excretion and blood cadmium concentration measured at follow-up were 7.5 nmol/24 h (SD 1.9) and 6.1 nmol/L (2.2), reductions of 16% and 35% from baseline, respectively. In women, the corresponding values were 7.6 nmol/24 h (1.9) and 7.8 nmol/L (2.1), reductions of 14% and 28% from baseline. No indication of progressive renal damage was found and the overall results suggest that the effects of low environmental exposure to cadmium on the kidney are weak, stable, or reversible.

INTERPRETATION

Subclinical renal effects that have been reported in Belgium in patients with increased cadmium body burden are not associated with progressive renal dysfunction and most likely represent non-adverse manifestations.

Excursions of intake above ADI: case study on cadmium

High oral intake of cadmium via food or drink in a single dose by humans gives rise to vomiting, abdominal pain, and diarrhea. Concentrations of cadmium in drinks giving rise to such symptoms have been 16 mg/liter and higher corresponding to doses of 3 mg and higher. Longer term intakes of food (rice) with concentrations around 1 mg/kg corresponding to daily intakes of 600 micrograms have given rise to some less pronounced symptoms including signs of malabsorption. Reproductive and developmental effects have been observed in animal experiments at oral and other exposures. The present provisional tolerable weekly intake (PTWI) for Cd is 500 micrograms (a weekly intake of 7 micrograms/kg body wt), corresponding to a daily intake of 70 micrograms or 1 microgram per kg body wt. Recent data demonstrating renal dysfunction in humans at even lower lifelong oral exposures indicate that the PTWI needs to be lowered in the future. An estimated lowest-observed-adverse-effect level (LOAEL) for symptoms from the gastrointestinal tract in humans after intake of a single oral dose is 43 micrograms/kg body wt. If a safety factor of 3-10 is used based on LOAEL, a tolerable single dose would be 0.3-1 mg (4 to 14 micrograms/kg body wt). For longer time exposures (months-a few years) daily intakes of 200 micrograms (3 micrograms/kg body wt) may be tolerated without obvious gastrointestinal symptoms or signs. At present, there is no convincing human evidence that such doses can cause reproductive or developmental effects, but since such effects have been reported in animals, it may be advisable not to exceed a daily intake of 1 microgram/kg body wt for such potentially sensitive subsections of the population as children and women who are pregnant or lactating. Any excursions above the PTWI need to be compensated for by a corresponding period with intake below the PTWI in order for the cumulative dose to be low enough to avoid the long-term effects of cadmium on the kidney.

Human health implications of environmental contaminants in Arctic Canada: a review

This paper assesses the impact on human health of exposure to current levels of environmental contaminants in the Canadian Arctic, and identifies the data gaps that need to be filled by future human health research and monitoring. The concept of health in indigenous groups of the Arctic includes social, cultural, and spiritual dimensions. The harvesting, sharing and consumption of traditional foods are an integral component to good health among Aboriginal people influencing both physical health and social well-being. Traditional foods are also an economic necessity in many communities. Consequently, the contamination of country food raises problems which go far beyond the usual confines of public health and cannot be resolved by health advisories or food substitutions alone. The primary exposure pathway for the contaminants considered in this paper is through the traditional northern diet. For the Inuit, the OCs of primary concern at this time from the point of view of exposure are chlordane, toxaphene, and PCBs. Exposures are higher in the eastern than in the western region of the North. For Dene/Metis, exposure to OCs is in general below a level of concern. However, estimated intake of chlordane and toxaphene has been found to be elevated for certain groups and is a cause for concern if exposures are elevated on a regular basis. The developing foetus and breast-fed infant are likely to be more sensitive to the effects of OCs and metals than individual adults and are the age groups at greatest risk in the Arctic. Extensive sampling of human tissues in the Canadian north indicate that a significant proportion of Dene, Cree and Inuit had mean maternal hair mercury levels within the 5% risk-range proposed by the WHO for neonatal neurological damage. Based on current levels, lead does not appear to pose a health threat while cadmium is likely only a major risk factor for heavy smokers or consumers of large amounts of organ meats. Consumers of traditional foods are exposed to an approximately seven-fold higher radiation dose than non-consumers of traditional foods due predominantly to the bioaccumulation of natural radionuclides in the food chain. Risk determination for contaminants in country food involves a consideration of the type and amounts of food consumed and the sociocultural, nutritional, economic, and spiritual benefits associated with country foods. Risk management options that minimize the extent to which nutritional and sociocultural aspects of Aboriginal societies are compromised must always be considered.

Protection against chronic cadmium toxicity by glycine

A Japanese drug containing glycine, glycyrrhizin, and cysteine (Stronger Neo-Minophagen C) has been reported to protect against chronic cadmium (Cd) toxicity. The present study was conducted to evaluate which of the three constituents of this drug was the main antagonist for Cd toxicity and whether the mechanism of protection involved antioxidant action. Adult female Sprague-Dawley rats were injected sc with 5 micromol CdCl2/kg per day, five times per week, for 15 weeks. Four groups of Cd-injected animals received co-treatments with either 10 mg glycyrrhizin/kg, 100 mg glycine/kg, 5 mg cysteine/kg, or with a mixture of all three compounds, five times per week, starting from week 7. An additional Cd-injected group was co-treated with vitamin E (100 mg/kg, five times per week, starting from week 7) as a positive control. Only those animals that received vitamin E, Minophagen mixture, or glycine were protected against Cd-induced hepatotoxicity as well as nephrotoxicity. All three co-treatments suppressed Cd-induced hepatic and renal lipid peroxidation. We conclude that the reported beneficial effects of Stronger Neo-Minophagen C are due to glycine, which appears to protect against chronic Cd toxicity by reducing oxidative stress.

Treatment of chronic cadmium nephrotoxicity by N-acetyl cysteine

Chronic cadmium (Cd)-induced nephrotoxicity is believed to be irreversible at advanced stages and no treatment is currently available. This study examined the beneficial effect of N-acetyl cysteine (NAC) on Cd-induced nephrotoxicity. Female Sprague-Dawley rats were injected s.c. with 5 micromol CdCl2/kg per day, five times/week for up to 26 weeks. Nephrotoxicity was detected after 10 weeks by elevation in urinary lactate dehydrogenase activity and protein. NAC co-administration from week 13 prevented the progression of nephrotoxicity. In these animals, with low-level nephrotoxicity, discontinuation of Cd exposure at the end of week 22 resulted in gradual recovery over the next several weeks, without the need for treatment with NAC. On the other hand, discontinuation of NAC co-treatment at the end of week 22 resulted in quick progression of nephrotoxicity, indicating that NAC protection was short-lived. Resumption of NAC treatment and cessation of Cd exposure after 26 weeks resulted in rapid recovery from advanced nephrotoxicity. It is concluded that protection from Cd-induced nephrotoxicity is possible by continued co-administration of NAC and that recovery from advanced nephrotoxicity can also be achieved with NAC, provided that Cd exposure is stopped.

Association between renal effects and cadmium exposure in cadmium-nonpolluted area in Japan

Renal effects of cadmium exposure in people living in a cadmium-nonpolluted area in Japan were investigated. The population consisted of 1501 inhabitants (558 men and 743 women) over 50 years of age. Urinary cadmium was employed as an indicator of internal dose, and total urinary protein, beta 2-microglobulin, and N-acetyl-beta-glucosaminidase were used as indicators of renal dysfunction. Multiple regression analysis and a logistic regression analysis were performed to study the relationship between urinary cadmium excretion and these indicators of renal dysfunction. In both procedures, urinary cadmium concentrations were significantly associated with indicators of renal dysfunction. These results suggest the existence of renal dysfunction induced by exposure to environmental cadmium in a cadmium-nonpolluted area in Japan.

Reproducibility of urinary beta 2-microglobulin and cadmium excretion among residents in a cadmium-polluted area during a 3-year period

To assess the measurement error by using single exposure measurement in epidemiologic studies, reproducibility of urinary beta 2-microglobulin and cadmium excretion was evaluated among persons exposed to environmental cadmium. We measured urinary beta 2-microglobulin concentrations in 47 subjects four times and urinary cadmium concentrations in 48 subjects twice, during a 3-year period. Between-person and within-person variance components of these variables were estimated using a random-effects one-way analysis of variance model. The intraclass correlation coefficient (ICC) for urinary beta 2-microglobulin concentration, when expressed as microg/g creatinine and microg/l, was 0.92 and 0.89, respectively. The ICC for standardized urinary cadmium concentration (expressed as microg/g creatinine) was 0.81, while it decreased to 0.33 without standardization. The findings suggest that single measurement of urinary beta 2-microglobulin and cadmium, when expressed as a function of creatinine, can reliably estimate average levels over at least a 3-year period. Standardization of concentration using urinary creatinine improved reproducibility especially for urinary cadmium excretion.

Isoform-specific expression of metallothionein mRNA in the developing and adult human kidney

The organization of the metallothionein (MT) gene family has been demonstrated to be much more complex in humans than in the mouse, and possibly rodents in general. For humans, the MTs are encoded by a family of genes located at 16q13 representing 10 functional and 7 non-functional MT isoforms. In the present study, the 5' and 3' untranslated region sequences of the highly conserved, functional MT genes were utilized to generate primer pairs for the analysis of isoform-specific MT mRNA using reverse transcriptase-polymerase chain reaction (RT-PCR). Human kidneys from 13 weeks gestation through adulthood were examined for the expression of MT protein and mRNA. Immunohistochemical analysis demonstrated MT immunoreactivity to be confined exclusively to the proximal tubules of the adult and developing kidney. For all MT-positive cells, MT was localized in the cytoplasm and nuclear localization was variable. There was no correlation between nuclear staining and stage of development. Of the 10 MT genes examined (MT-1A, MT-1B, MT-1E, MT-1F, MT-1G, MT-1H, MT-1X, MT-2A, MT-3, and MT-4), mRNAs representing the MT-1E, MT-1F, MT-1X, and MT-2A genes were consistently expressed in all samples regardless of gestational age. There was no indication of a 'fetal form' of MT analogous to that noted to occur in human liver. Messenger RNA for the MT-1A gene was detected in 2 of 6 renal samples without correlation to gestational age. In no instance was mRNA for the MT-1B, MT-1G, MT-1H, MT-3 or MT-4 genes detected. These studies detail the initial determination of MT gene expression in the human renal system and provide the PCR primers for testing and determination of MT gene expression in other organ systems.

Dose-response relationship between urinary cadmium concentration and beta2-microglobulinuria using logistic regression analysis

Logistic regression analysis was used to investigate the dose-response relationship for environmental cadmium exposure and to consider the effect age had on this association. The target population comprised 3178 inhabitants of Japan who were more than 50 y of age and who lived in a cadmium-polluted area and 1134 inhabitants who lived in nonpolluted areas of Japan. Logistic regression analysis was completed on the dose-response relationship between urinary cadmium concentration (i.e., an indicator of cadmium body burden) and beta2-microglobulinuria (i.e., an index of renal tubular dysfunction caused by exposure to cadmium). Both age and urinary cadmium concentration were associated significantly with beta2-microglobulinuria. Based on the relationship that was determined, we calculated, by age and sex, the values of urinary cadmium concentration that corresponded to the prevalence rates of beta2-microglobulinuria in the nonpolluted population. The resulting values were 1.6-3.0 micrograms/g creatinine for men and 2.3-4.6 micrograms/g creatinine for women.

Heterogeneity in the amount of ionic cadmium necessary to elicit cell death in independent cultures of human proximal tubule cells

Eleven separate isolates of human renal proximal tubule cells (HPT) were analyzed for toxic response to ionic cadmium exposure over a 16-day period in vitro. This study demonstrates a heterogeneous response to Cd2+ exposure in isolates from different individuals with some individuals nearly 3-times more sensitive to ionic cadmium exposure than others. There was no apparent correlation to the race, sex or age of the individuals in the response to cadmium. In addition, readily identifiable culture artifacts, i.e., culture age, passage number, had no influence on the response to Cd2+ exposure and the different isolates had homogeneous baseline HPT properties and morphology. This difference in response to Cd2+ may reflect a heterogeneous response within the human population to cadmium exposure.

Cell death and regeneration of renal proximal tubular cells in rats with subchronic cadmium intoxication

Male Sprague-Dawley rats were injected subcutaneously with 0.6 mg cadmium (Cd)/kg/day for 8 wk. The subsequent changes in renal proximal tubules were studied histologically, histochemically, and ultrastructurally. The urinary and tissue Cd concentrations were determined by atomic absorption spectrophotometry. After 4 wk of exposure, apoptosis was observed predominantly in segment S3 along with epithelial regeneration in the affected tubules, and these changes gradually became more pronounced as the experimental period was prolonged. The apoptotic cells were shed into the lumen and were found to contain a large quantity of Cd. Apoptotic cells were counted in paraffin sections after various periods of exposure to Cd. Nuclear bromodeoxyuridine uptake, mitotic count, and nuclear density were used as indicators of tubular regeneration. A correlation was found between the numerical increase of apoptotic cells and the rate of urinary Cd excretion, and the rate of increase in the tissue Cd concentration had a tendency to reduce after 4 wk as the rate of urinary Cd increased. These observations suggest that apoptosis might be helpful for the efficient excretion of Cd into urine. Progressive increases in the preceding indicators of regeneration were observed. From our results, it appears that Cd-induced tubular damage, i.e., cell deletion due to apoptosis, is reversible as a result of marked epithelial regeneration. On the basis of these histological changes, the critical concentration of Cd required to produce renal tubular damage was estimated to be 600 micrograms/g dry tissue.

Renal tubular function after reduction of environmental cadmium exposure: a ten-year follow-up

A prospective follow-up study was carried out to assess the prognosis of renal tubular function after reduction of environmental cadmium exposure. Time-related changes in urinary beta 2-microglobulin and cadmium excretion were followed from 1979 to 1989 in 102 residents of a cadmium-polluted area in Nagasaki, Japan. The average dietary cadmium intake among the study population was more than 200 micrograms/d in 1969, which decreased to approximately half that amount in 1983 because cadmium-polluted paddy fields were replaced with new soil in 1981. The geometric mean urinary beta 2-microglobulin concentration for 28 subjects aged 40 y or older in 1979 increased from 1,135.8 micrograms/g creatinine in 1979 to 1,999.7 micrograms/g creatinine in 1989. A similar tendency was also observed in 16 subjects with urinary beta 2-microglobulin concentrations greater than 1,000 micrograms/g creatinine in 1979, although the statistical significance of the difference did not reach the 5% level, probably because of the small sample size. In 48 persons examined in 1982, 1986, and 1989, the geometric mean of urinary cadmium concentration decreased from 8.49 micrograms/g creatinine in 1982 to 6.03 micrograms/g creatinine in 1989. The tendency for increasing beta 2-microglobulin excretion observed in the present study could not be explained by aging alone. Thus, it was concluded that renal tubular dysfunction caused by environmental cadmium was irreversible and slowly progressive, even after reduction of exposure. Six of 8 subjects who had severe renal dysfunction and who were included in the study died before 1986 and could not be followed. The implication of loss of subjects because of death is also discussed.

Biological monitoring of cadmium exposure in itai-itai disease epidemiology

Cadmium (Cd) concentrations in blood and urine were significantly higher in itai-itai disease patients, suspected patients and inhabitants in Cd-polluted areas in Japan. Urinary Cd concentrations were mainly related to the body burden of Cd and did not decrease for several years following cessation of Cd exposure. There was a close association between urinary Cd excretion and the occurrence of beta 2-microglobulinuria (beta 2-mg-uria). Probit regression analysis between urinary Cd excretion and, beta 2-mg-uria indicated that the threshold value may be set around 4 micrograms/g creatinine (cr.). Studies on inhabitants in Cd-polluted areas showed that urinary, beta 2-mg levels of more than 1000 micrograms/l or 1000 micrograms/g cr. were irreversible, while increased urinary excretion of beta 2-mg was associated with increased mortality. At present, beta 2-mg in urine is not a suitable indicator for monitoring renal tubular dysfunction in the general population since the significance of slightly increased excretion of urinary beta 2-mg has yet to be clarified.