alpha-1-Microglobulin: epidemiological indicator for tubular dysfunction induced by cadmium?

Dietary Cadmium Intake and Its Effects on Kidneys

Cadmium (Cd) is a food-chain contaminant that has high rates of soil-to-plant transference. This phenomenon makes dietary Cd intake unavoidable. Although long-term Cd intake impacts many organ systems, the kidney has long been considered to be a critical target of its toxicity. This review addresses how measurements of Cd intake levels and its effects on kidneys have traditionally been made. These measurements underpin the derivation of our current toxicity threshold limit and tolerable intake levels for Cd. The metal transporters that mediate absorption of Cd in the gastrointestinal tract are summarized together with glomerular filtration of Cd and its sequestration by the kidneys. The contribution of age differences, gender, and smoking status to Cd accumulation in lungs, liver, and kidneys are highlighted. The basis for use of urinary Cd excretion to reflect body burden is discussed together with the use of urinary N-acetyl-β-d-glucosaminidase (NAG) and β2-microglobulin (β2-MG) levels to quantify its toxicity. The associations of Cd with the development of chronic kidney disease and hypertension, reduced weight gain, and zinc reabsorption are highlighted. In addition, the review addresses how urinary Cd threshold levels have been derived from human population data and their utility as a warning sign of impending kidney malfunction.

Associations between Urinary Excretion of Cadmium and Renal Biomarkers in Nonsmoking Females: A Cross-Sectional Study in Rural Areas of South China

OBJECTIVES

The aim of this study was to systematically evaluate the relationship between urinary excretion of cadmium (U-Cd) and biomarkers of renal dysfunction.

METHODS

One hundred eighty five non-smoking female farmers (aged from 44 to 71 years) were recruited from two rural areas with different cadmium levels of exposure in southern China. Morning spot urine samples were collected for detecting U-Cd, urinary creatinine (U-cre), β₂-microglobulin (β₂-MG), α₁-microglobulin (α₁-MG), metallothionein (MT), retinol binding protein (RBP), albumin (AB), N-acetyl-β-D-glucosaminidase (NAG), alkaline phosphatase (ALP), γ-glutamyl transpeptidase (GGT) and kidney injury molecule-1 (KIM-1). Spearman's rank correlation was carried out to assess pairwise bivariate associations between continuous variables. Three different models of multiple linear regression (the cre-corrected, un-corrected and cre-adjusted model) were used to model the dose-response relationships between U-Cd and nine urine markers.

RESULTS

Spearman's rank correlation showed that NAG, ALP, RBP, β₂-MG and MT were significantly associated with U-Cd for both cre-corrected and observed data. Generally, NAG correlated best with U-Cd among the nine biomarkers studied, followed by ALP and MT. In the un-corrected model and cre-adjusted model, the regression coefficients and R² of nine biomarkers were larger than the corresponding values in the cre-corrected model, indicating that the use of observed data was better for investigating the relationship between biomarkers and U-Cd than cre-corrected data.

CONCLUSIONS

Our results suggest that NAG, MT and ALP in urine were better biomarkers for long-term environmental cadmium exposure assessment among the nine biomarkers studied. Further, data without normalization with creatinine show better relationships between cadmium exposure and renal dysfunction.

Microarray-based identification of differentially expressed genes in families of turbot (Scophthalmus maximus) after infection with viral haemorrhagic septicaemia virus (VHSV)

Viral haemorrhagic septicaemia virus (VHSV) is one of the major threats to the development of the aquaculture industry worldwide. The present study was aimed to identify genes differentially expressed in several turbot (Scophthalmus maximus) families showing different mortality rates after VHSV. The expression analysis was conducted through genome-wide expression profiling with an oligo-microarray in the head kidney. A significant proportion of the variation in the gene expression profiles seemed to be explained by the genetic background, indicating that the mechanisms by which particular species and/or populations can resist a pathogen(s) are complex and multifactorial. Before the experimental infections, fish from resistant families (low mortality rates after VHSV infection) showed high expression of different antimicrobial peptides, suggesting that their pre-immune state may be stronger than fish of susceptible families (high mortality rates after VHSV infection). After infection, fish from both high- and low-mortality families showed an up-modulation of the interferon-induced Mx2 gene, the IL-8 gene and the VHSV-induced protein 5 gene compared with control groups. Low levels of several molecules secreted in the mucus were observed in high-mortality families, but different genes involved in viral entrance into target cells were down-regulated in low-mortality families. Moreover, these families also showed a strong down-modulation of marker genes related to VHSV target organs, including biochemical markers of renal dysfunction and myocardial injury. In general, the expression of different genes involved in the metabolism of sugars, lipids and proteins were decreased in both low- and high-mortality families after infection. The present study serves as an initial screen for genes of interest and provides an extensive overview of the genetic basis underlying the differences between families that are resistant or susceptible to VHSV infection.

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.

Urinary mercury and biomarkers of early renal dysfunction in environmentally and occupationally exposed adults: a three-country study

We conducted a cross-sectional study in Sweden, Italy and Poland to assess environmental and occupational exposure to mercury from chloralkali (CA) plants and the potential association with biomarkers of early renal dysfunction. Questionnaire data and first-morning urine samples were collected from 757 eligible subjects. Urine samples were analysed for mercury corrected for creatinine (U-HgC), alpha-1-microglobulin (A1M), N-acetyl-beta-glucosaminidase (NAG) and albumin. Determinants of urinary mercury excretion were examined. Levels of kidney markers were compared in three U-HgC categories, and differences were tested taking age and other covariates into account. In the general population, the median U-HgC was higher in Italian (1.2 microg/gC) than in Polish (0.22 microg/gC) or Swedish (0.21 microg/gC) subjects, and no effect of living close to CA plants could be shown. Dental amalgam, chewing on amalgam, and fish consumption were positively associated with U-HgC. In subjects from the general population, no effects on the kidney markers could be detected, while in men, including workers occupationally exposed to mercury, U-HgC was positively associated with the kidney markers, especially with NAG, but to some extent also with A1M and albumin. Differences in urinary mercury and kidney markers in the general population between three studied countries could possibly be due to dietary factors, increased susceptibility to mercury at low selenium intake or co-exposure to other nephrotoxic metals.

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.

Pharmacokinetics/pharmacodynamics (PK/PD) modeling of risks of kidney toxicity from exposure to cadmium: estimates of dietary risks in the U.S. population

An analysis of epidemiological studies of associations between exposure to cadmium and kidney toxicity was conducted. Dose-response functions relating low-molecular-weight (LMW) proteinuria to various indices of cadmium dose (dietary cadmium intake, urinary cadmium excretion, or tissue cadmium burden) were obtained from 15 studies of diverse exposures (occupational, general environmental, environmental contamination). Estimates of the dose corresponding to probabilities of LMW proteinuria of 0.1, 0.15, or 0.2 were transformed from the reported dose units into corresponding estimates of target organ dose (microgram Cd/g renal cortex, RC) by simulation using a pharmacokinetics (PK) model. The median RC associated with a 0.1 probability (RC10M) of LMW proteinuria was predicted to be 153 micrograms Cd/g cortex (95% confidence interval [CI]: 84-263). The lower confidence limit on the RC10M (RC10L, 84 micrograms/g cortex) was predicted to be attained with a constant chronic intake of 1 microgram/kg/d in females or 2.2 micrograms/kg/d in males. The RC10L was 2.5-5 times higher than the median RCs predicted to result from dietary cadmium intake in U.S. nonsmokers (microgram Cd/g cortex: 33, females; 17, males) and 1.6-3 times higher than the corresponding 95th percentile RCs (53, females; 27, males). Additional exposure from smoking cigarettes (approximately 20 cigarettes/d, 3 micrograms Cd inhaled/d) was predicted to increase the median RC (microgram/g cortex) by approximately 45-70% (48, females; 29, males); however, predicted 95th percentile RCs for smokers (66, females; 38, males) were lower than the RC10L. These results indicate that, for most of the U.S. population, dietary-derived risks are likely to be negligible, in the absence of exposures from other sources.

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.

Environmental exposure of the pediatric age groups in Cairo City and its suburbs to cadmium pollution

In a trial to assess the exposure of subjects in the pediatric age group to cadmium (Cd) pollution, serum Cd was estimated by atomic absorption spectrometry in 405 subjects, birth-18 years old, from Cairo City and its suburbs. Serum Cd mean concentrations were: 0.92 microg/l in 32 neonates (birth-4 weeks); 1.33 microg/l in 70 infants (4 weeks-2 years); 1.11 microg/l in 100 children in the preschool period (2-6 years); 1.34 microg/l in 103 primary school children (6-12 years); and 1.24 microg/l in 100 adolescents (12-18 years). In neonates, serum Cd was higher in babies with weights and heights that remained below the 5th percentile for age. Breast-fed infants had a serum Cd geometric mean level (1.25 microg/l) that was not in accordance to that of their mothers' milk (0.52 microg/l, P < 0.001), suggesting alternative routes of exposure. Environmental tobacco-smoke exposure was the most important determinant of Cd status in the school-aged children, the geometric mean being 1.42 microg/l in passive smokers vs. 1.2 microg/l in non-exposed children (P < 0.05). Moreover, adolescents who were active smokers had a significantly higher serum Cd level (1.7 microg/l) as compared to non-smokers (1.2 microg/l). Gender did influence the Cd status in adolescents, being higher among males, probably related to smoking, or to the difference in lifestyle of adolescents according to gender in the community. Alpha-1-microglobulinuria was accompanied by a higher serum Cd concentration in the group of adolescents only, suggesting a subclinical renal effect after several years of cumulative exposure. The residential classification, whether urban or suburban, did not influence the serum Cd status; neither did the present or past history of bronchial asthma. These findings certainly justify further evaluation of the problem of Cd pollution among Cairene individuals, knowing the long-term consequences of exposure to it. Systematic efforts for the proper disposal of Cd wastes and prevention of smoking in public places are recommended.