α1-Microglobulin as a promising marker of cadmium-induced tubular dysfunction, possibly better than β2-microglobulin

Evaluation of Renal Function in Children with Congenital Scoliosis and Congenital Anomalies of the Kidney and Urinary Tract

Background

The aim of this study was to compare renal function in children with congenital scoliosis and congenital anomalies of the kidney and urinary tract, with healthy children.

Material/Methods

Biochemical tests were performed before surgery (pre-therapy) and after surgery (post-therapy) in 16 children with congenital scoliosis and congenital anomalies of the kidney and urinary tract. Thirty-two healthy children were matched for age, sex, and weight (healthy controls). General renal function tests included serum electrolytes, creatinine, urea, cystatin C, and estimated glomerular filtration rate (eGFR). Tests for early renal changes included N-acetyl-beta-D-glucosaminidase (NAG), urine microalbumin, serum transferrin, immunoglobulin G (IgG), urinary alpha-1-microglobulin (A1M), and beta-2-microglobulin (B2M).

Results

Sixteen patients with congenital anomalies of the kidney and urinary tract included eight boys (mean age, 11.38±2.00 years) and eight girls (mean age, 11.00±2.78 years). There were no significant differences in renal function between the pre-therapy and post-therapy groups (P>0.05), or between the three groups (pre-therapy, post-therapy, and healthy controls). In the pre-therapy group, there were significant differences in IgG, A1M, NAG, and serum phosphate levels between boys and girls, urine microalbumin was significantly increased in girls, but not boys (P<0.05). There were no significant differences between the pre-therapy group and post-therapy group (P>0.05).

Conclusions

Routine tests of renal function were normal in children with congenital scoliosis and congenital anomalies of the kidney and urinary tract, but early changes in renal function occurred before surgical treatment, indicating long-term follow-up of renal function is recommended.

Application of the Benchmark Dose (BMD) Method to Identify Thresholds of Cadmium-Induced Renal Effects in Non-Polluted Areas in China

The benchmark dose (BMD) method has been increasingly used to assess the health risks of cadmium (Cd) in epidemiological studies. The aim of our study was to estimate the threshold levels of urinary Cd (UCd) using the BMD method in a general population of Jiangshan City, Zhejiang Province of China. In our study, a total of 934 people (469 men, 465 women) were recruited and morning urine samples were collected from all the participants. Levels of Cd, creatinine, and renal dysfunction indicators such as retinol binding protein (RBP), β2-microglobulin (β2-MG), and N-acetyl-b-glucosaminidase (NAG) in urine were detected for analysis of BMD and BMD low (BMDL) of UCd. RBP, β2-MG, and NAG in urine all correlated significantly (P < 0.001) with UCd except of age (P = 0.767). When the benchmark response (BMR) was 5%, the BMD/BMDL of UCd for RBP, β2-MG, and NAG was 1.69/ 0.89, 1.24/0.62, 0.85/0.49 μg/g Cr in men and 1.70/0.76, 1.35/0.64, 1.36/0.65 μg/g Cr in women, respectively. If the BMR was set at 10%, the BMD/BMDL of UCd for RBP, β2-MG, and NAG was 2.44/1.59, 2.09/1.30, 1.80/1.04 μg/g Cr in men and 2.43/1.53, 2.10/1.34, 2.31/1.37 μg/g Cr in women, respectively. Our results provided evidence for Cd-induced tubular effects in cadmium non-polluted areas in China. Both β2-MG and NAG were more sensitive than RBP in response to Cd exposure. But β2-MG was the most sensitive indicator in women, and NAG was the most sensitive one in men.

Effect of mercury (Hg) dental amalgam fillings on renal and oxidative stress biomarkers in children

We examined the effect of mercury (Hg) associated with dental amalgam fillings on biomarkers of renal and oxidative stress in children between the ages of 5-15.5 years. Urine samples were analyzed for N-acetyl-β-D-glucosaminidase (NAG), α(1)-microglobulin (α(1)-MG), β(2)-microglobulin (β(2)-MG), retinol binding protein (RBP), albumin (ALB), 8-hydroxy-2-deoxyguanosine (8-OHdG) and malondialdehyde (MDA). The level of urinary Hg (UHg-C) was calculated as μg/g creatinine. Multiple regression analyses revealed that the excretion of urinary NAG was significantly associated with the presence of dental amalgam fillings (β=0.149, P=0.03) and the levels of UHg-C (β=0.531, P=0), with an interaction between the two (P=0). The increase in urinary NAG in relation to UHg-C levels had a dose-effect pattern. The lowest observed effect was seen at UHg-C levels above 1.452 μg/g creatinine, which is lower than previously reported. In contrast, α(1)-MG was negatively associated with the presence of dental amalgam fillings (β=-0.270, P=0), but positively with UHg-C levels (β=0.393, P=0). There were 7 children without, and one child with, dental amalgam fillings with urinary α(1)-MG levels above the reference limit of >7 mg/g creatinine. Even though α(1)-MG seems to be a reliable biomarker for early changes in renal functions, it might exert its effect only at a higher level of exposure. An inverse relationship was also observed between urinary 8-OHdG levels and the presence of dental amalgam fillings. This might suggest that the dental amalgam does not increase DNA damage but reduces the capacity to repair DNA, leading to lower urinary excretion of 8-OHdG. On the other hand, we found that Hg affected the excretion of urinary 8-OHdG in a dose-related pattern that was mostly associated with long-term exposure to low Hg levels. Urinary NAG levels were positively associated with urinary MDA levels (β=0.516, P=0) but not with 8-OHdG (β=0.134, P=0.078) after adjustment for potential confounders. Both UHg-C and the presence of dental amalgam fillings remained predictors of the NAG model. Our data provide evidence that low exposure to Hg from dental amalgam fillings exerts an effect on kidney tubular functions in children. Oxidative stress may have played a role in this mechanism. The results of this study would also suggest that urinary NAG is the most sensitive of all the investigated renal biomarkers. These results should be confirmed with further investigation.

Variation in benchmark dose (BMD) and the 95% lower confidence limit of benchmark dose (BMDL) among general Japanese populations with no anthropogenic exposure to cadmium

BACKGROUND

The use of benchmark dose (BMD) and the 95% lower confidence limit of benchmark dose (BMDL) have been gaining popularity not only in experimental studies but also in epidemiological studies including those on toxicology of cadmium (Cd), a ubiquitous hazardous element in the environment. However, the reproducibility of BMD and BMDL values has seldom been examined.

OBJECTIVES

This study was initiated to determine whether consistent BMD and BMDL values are obtained for similar non-exposed populations, i.e., the populations with no anthropogenic exposure to Cd in a single nation of Japan.

METHODS

Cd (an exposure marker), α(1)-microglobulin (α(1)-MG), β(2)-microglobulin (β(2)-MG) and N-acetyl-β-D-glucosaminidase (NAG) (three effect markers of tubular dysfunction) levels in the urine of adult Japanese women from five previous publications of this study group were examined. Overall, data were available for 17,375 cases (in 16 prefectures) regarding Cd, α(1)-MG and β(2)-MG, and 6,409 cases (in ten prefectures) regarding NAG. The data were used to calculate BMD and BMDL values taking advantage of the hybrid approach (Budtz-Jǿrgensen et al. in Biometrics 57:698-706, 2001). It was possible to calculate BMD and BMDL values for α(1)-MG and β(2)-MG for all of the 16 prefectures with 17,375 cases, whereas the values for NAG were successfully calculated for nine prefectures with 5,843 cases.

RESULTS

The application gave BMD values of 1.92, 2.46 and 2.32 μg Cd/g cr for α(1)-MG, β(2)-MG and NAG, respectively, and BMDL values of 1.83, 2.32 and 2.09 μg Cd/g cr. Large inter-prefectural variations were observed in the BMD and BMDL; there was about fourfold difference both in BMD and in BMDL calculated for α(1)-MG and β(2)-MG in 16 prefectures, and the variation was greater (i.e., by about sevenfold) in BMD and BMDL for NAG in nine prefectures. A survey of relevant literature revealed variation in BMD and BMDL values of similar folds as observed in the present analyses in five studies of Japanese populations. Multiple regression analyses taking BMD or BMDL as a dependent variable and age, CR concentration and Cd concentration as independent variables showed both BMD and BMDL were significantly influenced by Cd concentration in cases of α(1)-MG and β(2)-MG, whereas BMD and BMDL for NAG was by CR.

CONCLUSIONS

Even when the analysis was conducted in a single nation, both BMD and BMDL for the Cd effect markers varied by ca. fourfold when examining α(1)-MG or β(2)-MG and the values varied by ca. sevenfold for NAG among Cd-non-exposed populations. The most influential factors in the study population may include urine density and Cd levels in the urine.

N-acetyl-beta-D-glucosaminidase (NAG) as the most sensitive marker of tubular dysfunction for monitoring residents in non-polluted areas

Alpha(1)-microglobulin (alpha(1)-MG), beta(2)-microglobulin (beta(2)-MG) and N-acetyl-beta-D-glucosaminidase (NAG) are tubular dysfunction markers often used in cadmium (Cd) epidemiology. The purpose of the present study was to identify the best maker among the above-referred three that correlates most closely with Cd in urine of residents with no known Cd pollution. Survey was conducted in 2007-2008 in three prefectures in Japan. Adult women, 2163 in total, participated in the survey; they provided informed consents, offered spot urine samples and filled questionnaires on possible confounders of Cd burden. Urine samples were analyzed for Cd, alpha(1)-MG, beta(2)-MG and NAG together with calcium (Ca), magnesium (Mg), creatinine (CR) and specific gravity (SG). The analyte levels, as observed (e.g., Cd(ob)) or after correction for CR (e.g., Cd(cr)) or SG (e.g., Cd(sg)) were subjected to simple and multiple regression analysis. Correlation matrix analysis with observed values for total cases showed that the coefficients of correlation with Cd were highest for NAG, followed by alpha(1)-MG, and lowest for beta(2)-MG. Multiple regression analysis by three prefectures either separately or in combination (thus four analyses) disclosed that Cd was the independent variable most influential to NAG (as the dependent variable) throughout the four analysis conditions with high R(2) values (>0.3), whereas the most influential variables were not the same depending on the analysis conditions in cases with alpha(1)-MG and beta(2)-MG. When coefficients of correlation for the three dysfunction markers with Cd were compared among the observed, CR- and SG-corrected values, the coefficients for the observed values were higher than the counterpart values for CR- or SG-corrected values. In conclusion, NAG rather than alpha(1)-MG or beta(2)-MG should be recommended for monitoring Cd exposure-related tubular effects among general populations. Observed (i.e., un-corrected) values rather than CR- or SG-corrected values should be used.

Does the urinary excretion of alpha1-microglobulin and albumin predict clinical disease activity in ulcerative colitis?

INTRODUCTION

There remains some difficulty in determining disease activity during the development of inflammatory bowel disease (IBD). The excretion levels of some inflammatory response molecules increase as a result of the onset of this disease. We studied urinary alfa-1-microglobulin (alpha1-MG) and albumin levels in patients with active and inactive ulcerative colitis (UC) and investigated whether we could use these parameters as an activity index.

METHODS

The study was carried out at Gazi University Faculty of Medicine, Nephrology and Gastroenterology Departments, between December 2003 and March 2006. In total, 35 patients (male/female: 16/19, mean age: 38.3+/-2.4 years) and 13 healthy controls (male/female: 6/7, mean age: 35.8+/-2.8 years) were enrolled in the study. Nineteen patients had symptoms of active disease and the remaining 16 patients had inactive disease.

RESULTS

There was a significant difference in serum C-reactive protein (CRP), urinary albumin excretion, and alpha1-MG excretion levels between patients and controls. Patients with active disease had significantly higher serum CRP and alpha1-MG levels than those with inactive disease and controls. Patients with active disease had higher microalbuminuria levels than inactive patients, but this difference was not statistically significant. Urinary albumin and alpha1-MG excretion did not correlate with serum CRP levels.

CONCLUSION

The present study suggests that, as with CRP, urinary levels of albumin and alpha1-MG increase during the active period of UC. During the inactive period, concentrations of these parameters are comparable to controls. The measurement of alpha1-MG and/or microalbuminuria could provide information on disease severity and response to treatment.

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.

Monitoring of cadmium toxicity in a Thai population with high-level environmental exposure

This study evaluated the utility of single and combined measurements of cadmium toxicity markers for surveillance purposes, using a sample of 224 individuals, 30-87 years of age, who were residents of cadmium polluted area in Mae Sot District, Tak Province, Thailand. Urinary cadmium levels excreted by them ranged between 1 and 58 microg/g creatinine with geometric mean of 8.2 microg/g creatinine which was 16-fold greater than the average for the general Thai population of 0.5 microg/g creatinine. The urinary markers evaluated were total protein, albumin, N-acetyl-beta-D-glucosaminidase (NAG), lysozyme, beta2-microglobulin (beta2-MG) and alpha1-microglobulin (alpha1-MG). Among these markers, only NAG showed a positive correlation with urinary cadmium in both male and female subjects with and without disease (r=0.43-0.71). Further, the prevalence rates for urinary NAG above 8 units/g creatinine (NAG-uria) increased with exposure levels in a dose dependent manner (p=0.05) among subjects with disease. In contrast, however, increased prevalence of beta2-MG above 0.4 mg/g creatinine (beta2-MG-uria) was associated with cadmium above 5 microg/g creatinine only in those without disease (POR=10.6 and 7.8 for 6-10 and >10 microg/g creatinine). Prevalence rates for abnormal excretion of all other markers, except albumin, were markedly increased among those having beta2-MG-uria with and without disease (chi2-test, p<or=0.001-0.02). Thus, urinary beta2-MG and NAG should be used together with urinary cadmium in the monitoring of renal toxicity in a population exposed to high-level cadmium coupled with high prevalence of chronic diseases.

Biological markers for metal toxicity

Exposure assessment is often considered the weakest link in risk assessment. It is important for investigators to continue to utilize the full potential of biomarkers for chemicals whose exposure is of global concern. This review is concerned with the biomarkers of metal toxicity, as the overall exposure to metals encountered occupationally or in the environment would continue causing indirect, delayed effects therefore ecoepidemiology, using designed molecular probes and noninvasive diagnostics will be the leading component for future management of environmental health. An attempt is made here at appraising the need for the development of more biomarkers for use in environmental epidemiology and health risk assessment.

Reproducibility of urinary cadmium, alpha1-microglobulin, and beta2-microglobulin levels in health screening of the general population

The present study examined whether levels of cadmium, and alphal- and beta2-microglobulin in urine (Cd-U, ac-MG-U, and beta2-MG-U, respectively) were reproducible in urine samples collected from the same subjects on multiple occasions. For this purpose, two databases on background exposure to cadmium in Japan-one from study I between 2000 and 2001 and the other from study II in 2002-were revisited to find 231 apparently healthy, nonpregnant, nonlactating adult women who participated in both studies and thus had provided two urine samples. The databases contained information on Cd-U, alphal,-MG-U, and beta2-MG-U, creatinine (CR), and specific gravity (SG) as well as smoking and other lifestyle factors. Of the 231 women, 195 who had never smoked were selected for the present analysis. Cd-U as well as alpha1-MG-U were reproducible (e.g., with correlation coefficients [r] between study I and II results of 0.4 to 0.6) when measured on two occasions 9 to 10 months apart. The r values were lower for beta2-MG-U (r0.3). Exclusion of urine samples with inadequate urine density(i.e., CR <0.5 or >3.0 g/L or SG <1.010 or >1.030) resulted in substantial improvement of the agreements between the two measures (e.g., r = 0.6 to 0.7 for Cd-U and alpha1-MG-U). CR and SG correlated closely with each other, especially in low-density urine samples (r >0.9), and therefore the effects of CR and SG could not be evaluated separately. In the overall evaluation,single determination (i.e., without repeated urine sampling) of Cd-U and alpha1-MG-U should be acceptable, and it may also be acceptable for beta2-MG-U. Use of samples with adequate urine density rather than application of density correction to low-density urine samples in recommended.