Study On Association Of Cadmium Exposure With Kidney Damage And Epigenetics In Population Aged 40-89 Of Typical Areas

Cadmium（Cd）,a toxic heavy metal,accumulates in the human body over the long term,with the kidneys serving as the primary storage and target organs.Consequently,Cd exposure may be a significant contributing factor to kidney damage.Previous research on the association between Cd exposure and kidney damage has yielded inconsistent results,with most studies merely investigating their correlation,and few providing a cutoff value for Cd exposure leading to kidney damage.Currently,the assessment of kidney damage relies on two main categories of biochemical markers:those reflecting glomerular function,such as estimated glomerular filtration rate（e GFR）and albumin-to-creatinine ratio（ACR）;and those reflecting changes in tubular function,such as urine N-acetyl-β-D-glucosaminidase（NAG）,urineβ₂-microglobulin（β₂-MG）,urineα1-microglobulin（α₁-MG）,and urine retinol-binding protein（RBP）.However,these markers are primarily utilized for the auxiliary diagnosis and screening of kidney damage,failing to meet the requirements for early prevention of kidney damage.In recent years,the development and optimization of high-resolution,high-throughput omics technologies have provided new technical capabilities for early intervention in kidney diseases.Objective1.This study aims to elucidate the relationship between urinary Cd and chronic kidney disease（CKD）as well as kidney damage markers,explore the cutoff value of urinary Cd causing CKD and abnormal kidney damage markers,and provide scientific evidence for the establishment of safe limits for Cd exposure in non-occupational populations in China.2.To investigate the differential effects of urinary Cd on kidney damage under various levels of Cd pollution in agricultural soil and rice,evaluate the current safety limits for Cd in agricultural soil and rice in China,and provide crucial scientific support for the revision of safe limits for Cd in agricultural soil and rice.3.Integrating DNA methylation data,this study systematically screens and identifies epigenetic biomarkers associated with Cd-induced kidney damage,identifies early intervention targets for Cd-induced kidney damage,and constructs a predictive model incorporating epigenetic information to provide a risk assessment tool for early intervention in Cd-induced kidney diseases.MethodsThis study’s data is derived from the Survey on the Impact of Soil Quality on Population Health in Typical Agricultural Areas in 2019.The project conducted a soil pollution survey in four representative regions nationwide,spanning four provinces in Southwest,East China,and Northeast China.Based on this information,the study focuses on three main areas.1.Association study of Cd exposure with CKD:Utilizing data from the survey of"Typical Area Agricultural Land Soil Quality and Its Impact on Population Health,"the research obtains urinary Cd levels among typical area populations in China and the prevalence of CKD at different stages.It employs methods such as multiple-factor Logistic regression models and restricted cubic splines to analyze the correlation between urinary Cd and CKD.Furthermore,using the R package"cutoff,"it deduces the cutoff value of Cd exposure causing CKD.According to the current safety limits for Cd in agricultural soil and rice in China,further exploration of the differential impact of urinary Cd on CKD in populations from areas with different levels of Cd in agricultural soil and rice is warranted.2.Association study of Cd exposure with kidney damage:Based on the detection of kidney damage marker data associated with the project,it gathers data on estimated e GFR,ACR,urine NAG,urineβ₂-MG,urineα₁-MG,and urine RBP levels and their abnormal rates among typical area populations in China.Using methods such as restricted cubic splines and multiple-factor Logistic regression models,it examines the dose-response relationship between urinary Cd and kidney damage markers and the correlation of kidney damage marker abnormalities.The study also uses the R package"cutoff"to deduce the Cd exposure cutoff value causing abnormalities in various kidney damage markers,identifying sensitive indicators of Cd-induced kidney damage.Based on the current safety limits for Cd in agricultural soil and rice in China,further exploration is needed to investigate the differential risk of urinary Cd on abnormal kidney damage indicators in populations from areas with different levels of Cd in agricultural soil and rice.3.Study on the Epigenetics of Cd Exposure and kidney damage:Utilizing blood DNA methylation data from 300 subjects,this research employs epigenome-wide association analysis to investigate the relationship between urinary Cd and DNA methylation.It identifies differential DNA methylation sites associated with urinary Cd and simultaneously examines the correlation between urinary Cd-related sites and kidney damage markers,pinpointing the overlapping differential DNA methylation sites between the two.Employing the R software package"mediation,"the study explores the mediating role of DNA methylation in the correlation between urinary Cd and kidney damage markers,identifying early intervention targets for Cd exposure-induced kidney damage.Additionally,it constructs a kidney damage predictive model incorporating epigenetic information using Logistic regression models and evaluates the model’s predictive performance using the concordance index（C-index）and calibration curves.Results1.Association study of Cd exposure with CKD.（1）In this study,the geometric mean of urinary Cd in the study population was2.39μg/g·cr,with a prevalence of CKD reaching 28.88%.As urinary Cd levels increased,the risk of CKD and its different stages gradually increased,with the cutoff value for Cd-induced CKD being 4.265μg/g·cr.（2）In areas where Cd levels in agricultural soil exceed the screening values and rice Cd levels exceed the standards,the impact of urinary Cd levels on the risk of CKD was significantly higher compared to areas where these levels are within limits.However,even in areas where Cd levels in agricultural soil and rice do not exceed the standards,urinary Cd levels still have an impact on the risk of CKD.（3）Urinary Cd primarily affects the risk of CKD stage 1 in areas where Cd levels in agricultural soil and rice did not exceed the standards.In contrast,in areas where Cd levels in agricultural soil exceed the screening values and rice Cd levels exceed the standards,the impact of urinary Cd on CKD stages 2 and above was significantly higher than in areas where these levels are within limits.2.Association study of Cd exposure with kidney damage.（1）In this study,the percentages of abnormal e GFR,ACR,urinary NAG,urinaryβ₂-MG,urinaryα₁-MG,and urinary RBP were 9.39%,24.14%,34.24%,28.63%,31.09%,and 7.30%,respectively.The study found that as urinary Cd levels increased,the levels of urinary NAG,β₂-MG,α₁-MG,and RBP gradually increased.（2）The increase in urinary Cd levels could increase the risk of e GFR,ACR,urinary NAG,urinaryβ₂-MG,urinaryα₁-MG,and urinary RBP levels.Furthermore,the urinary Cd cutoff values causing abnormal e GFR,ACR,urinary NAG,urinaryβ₂-MG,urinaryα₁-MG,and urinary RBP were found to be 4.401μg/g·cr,2.990μg/g·cr,2.508μg/g·cr,3.068μg/g·cr,2.512μg/g·cr,and 4.343μg/g·cr,respectively.（3）In areas where Cd levels in agricultural soil exceed the screening values and rice Cd levels exceed the standards,the impact of urinary Cd levels on the risk of abnormal kidney damage markers was significantly higher compared to areas where these levels are within limits.However,even in areas where Cd levels in agricultural soil and rice did not exceed the standards,urinary Cd levels still have an impact on the risk of abnormal kidney damage markers.3.Study on the Epigenetics of Cd Exposure and kidney damage.（1）Epigenome-wide association analysis revealed that the methylation levels of27 CpG sites were associated with urinary Cd levels,annotated to 20 genes.Among these 27 CpG sites,urinary Cd levels were negatively correlated with the methylation of 14 CpG sites and positively correlated with the methylation of 13 CpG sites.（2）The study identified 17 CpG sites that were associated with both urinary Cd and kidney damage markers.（3）Mediation analysis revealed that cg16848624 mediated the effects of urinary Cd on urinaryβ₂-MG,urinaryα₁-MG,and urinary RBP,while cg26907612 mediated the effect of urinary Cd onβ₂-MG.（4）The predictive model for Cd-induced kidney damage included 10 influencing factors,including age,gender,and the methylation levels of 8 CpG sites.The predictive model had a C-index of 0.806,with an internally validated calibrated C-index of 0.779.The bias-adjusted calibration curve closely approximated the ideal distribution,and the predicted probability of kidney damage was highly consistent with the observed probability.The probability results of the prediction were accurate.Conclusions1.Urinary Cd was significantly associated with the risk of CKD and its different stages,with a critical urinary Cd cutoff value of 4.265μg/g·cr for the onset of CKD.2.Distinguished the CKD types mainly affected by urinary Cd under different levels of exposure to Cd in agricultural soil and rice.In areas where Cd levels in agricultural soil and rice did not exceed the screening values,urinary Cd primarily affects the risk of stage 1 CKD.However,in areas where Cd levels in agricultural soil exceed the screening values or rice Cd levels are above the standard,the impact of urinary Cd on stages 2 and above of CKD was significantly higher than in areas where they are not exceeded.3.The increase in urinary Cd levels could increase the risk of abnormal indicators such as e GFR,ACR,urinary NAG,urinaryβ₂-MG,urinaryα₁-MG,and urinary RBP,indicating that Cd affects the function of renal glomeruli and tubules.4.Urinary NAG was the most sensitive indicator of Cd-induced kidney damage in this study population,with a corresponding urinary Cd cutoff of 2.508μg/g·cr.These findings provided important scientific evidence for revising the urinary Cd safety limit for non-occupational populations in China.5.In areas where Cd levels in agricultural soil exceed the screening values or rice Cd levels were above the standard,the impact of urinary Cd on the risk of abnormal kidney damage indicators is significantly higher.However,even in areas where Cd levels in agricultural soil do not exceed the screening values or rice Cd levels are not above the standard,urinary Cd levels still affect the risk of abnormal kidney damage indicators,and the proportion of individuals with excessive urinary Cd levels remains relatively high.The research results did not support relaxing the current safety limit standards for Cd in agricultural soil and rice in China.6.Epigenome-wide association studies identified early intervention targets for preventing Cd exposure-induced kidney damage,evaluated the mediating effect of DNA methylation on the relationship between Cd exposure and kidney damage,and revealed the pathway of"Cd exposure-epigenetics-kidney damage."7.We have developed and validated a kidney damage risk prediction model that includes epigenetic information.Compared to other methods that use biochemical indicators or machine models to predict kidney damage,our prediction model has a stronger ability to predict the early risk of kidney damage.This prediction model provided a risk assessment tool for promoting early intervention in Cd induced kidney disease.