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Background Environmental pollutants can affect N6-methyladenosine (m6A) level in the body, but the change of m6A level in kidney after being exposed to cadmium (Cd) and the molecular mechanism of renal injury need to be further studied. Objective To analyze the associations of m6A modification and methyltransferases/demethylases with microRNA-21 (miR-21) and transforming growth factor- β1 (TGF - β1) in kidney of rats exposed to Cd. Methods Twenty-four SPF male SD rats were divided into 4 groups, with 6 rats in each group, and were exposed to Cd by subcutaneous injection of 2.0, 1.0, and 0.5 mg·kg−1 cadmium chloride (CdCl2) and equal volume of normal saline for 2 weeks, 7 d a week, respectively. The levels of N-acetyl-β-D-glucosidase (UNAG) and albumin (UALB) in urine, and the levels of m6A methylation and TGF-β1 in kidney were detected by enzyme-linked immunosorbent assay (ELISA). The level of blood urea nitrogen (BUN) was measured by urease method. The levels of renal oxidative stress indicators such as malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) were detected by total bile acid method, water-soluble tetrazolium asssay, and colorimetric method respectively. The relative levels of TGF-β1, methyltransferases, and demethylases in kidney were measured by reverse transcription-polymerase chain reaction. The expression of miR-21 in kidney was detected by fluorescent quantitative polymerase chain reaction. Results After 2 weeks of exposure to Cd, the body weights of rats in the 2.0 and 1.0 mg·kg−1 cadmium chloride groups decreased, and the ratio of kidney/body weight and the levels of BUN, UNAG, and TGF-β1 mRNA and protein increased in the 2.0 mg·kg−1 cadmium chloride group (P<0.05). The expression levels of m6A modification, methyltransferases METTL3, METTL14, Wilms’ tumor 1-associated protein (WTAP), and miR-21 were increased both in the 2.0 and 1.0 mg·kg−1 cadmium chloride groups, with significant differences compared with the control group (P<0.05). The results of correlation analysis showed that the m6A modification level was negatively correlated with SOD (r=−0.4489, P<0.05) and GSH-Px (r=−0.4874, P<0.05), METTL3 was negatively correlated with MDA (r=−0.5158, P<0.05), while there was a positive correlation between FTO and GSH-Px (r=0.4802, P<0.05). In addition, miR-21 was positively correlated with METTL3 (r=0.7491), METTL14 (r=0.6157), and WTAP (r=0.6660) (P<0.05), TGF-β1 was positively correlated with METTL3 (r=0.5025, P<0.05) but negatively correlated with FTO (r=−0.5634, P<0.05) . Conclusion Cd can induce m6A methylation and up-regulation of METTL3, METTL14, WTAP, and miR-21 expression levels in rat kidney tissues, indicating that m6A and miR-21 may be associated with Cd-induced renal fibrosis.
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Background Individual lead or cadmium exposure can cause abnormal blood glucose level and changes in telomere length, and the role of telomere length in the relationship between heavy metal joint exposure and blood glucose level is still unclear. Objective To explore the role of telomere length in the relationship between lead and cadmium coexposure and blood glucose. Methods A cross-sectional study was conducted. By convenient sampling method, 600 residents living in two communities in a city in North China were selected as participants from April to June 2016. Face-to-face interviews were performed to collect general demographics and lifestyles of the participants. The peripheral blood samples of the participants were collected for blood glucose and telomere length detection, the urine samples were collected for urinary cadmium, urinary lead, and urinary creatinine measurement, and both urinary cadmium and urinary lead were corrected by urinary creatinine. The included participants were divided into a control group, a high-cadmium and low-lead group, a high-lead and low-cadmium group, and a high-lead and high-cadmium group, according to the median levels of urinary cadmium and urinary lead. A restricted cubic spline model was constructed to analyze the relationship between urinary lead/cadmium levels and blood glucose concentrations in the four groups and the relationship between cadmium exposure and telomere length in the high-lead and high-cadmium group. Intermediary model test was conducted to analyze the effect of telomere length on the relationship between exposures to lead and cadmium and blood glucose. Results The included participants were divided into the control group (n=99), the high-cadmium and low-lead group (n=91), the high-lead and low-cadmium group (n=145), and the high-lead and high-cadmium group (n=265). The differences in age, education level, per capita monthly household income, smoking, blood glucose, and telomere length were statistically significant among the four groups (P＜0.05). The high-lead and high-cadmium group had the highest blood glucose concentration, (5.63±1.68) mmol·L−1, and the shortest telomere length, (2.63±1.05) Kb. The restricted cubic spline results showed that urinary cadmium level was correlated with blood glucose concentration in the high-lead and high-cadmium group (F=3.45, P=0.037), and there was a non-linear association (F=6.91, P=0.002); the association between urinary cadmium level and telomere length was also non-linear (F=5.93, P=0.043). The intermediary model test results showed that telomere length was a mediating variable between urinary cadmium level and blood glucose concentration, and the mediating effect size was 0.0192 (95%CI: 0.0007-0.0563), with a mediation ratio of 15.57%. Conclusion Correlations between urinary cadmium and blood glucose and between urinary cadmium and telomere length were observed in the high-lead and high-cadmium coexposure group, and telomere length may play a mediating role in the relationship between them.
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Background Exposure to environmental lead can cause kidney damage and telomere wear. However, the relationship among lead, peripheral blood telomere length, and glomerular filtration rate (eGFR) are unclear. Objective This study is conducted to investigate the relationships of urinary lead level with peripheral blood telomere length and renal function index eGFR, and further explore whether peripheral blood telomere length plays an intermediary role in the relationship between urinary lead level and eGFR. Methods A case-control study was conducted to select 497 residents from two communities in a city, including 230 in the control group (eGFR≥80 mL·min−1) and 267 in the abnormal eGFR group (eGFR<80 mL·min−1). Basic information and health information of the subjects were collected through a face-to-face questionnaire survey. Fasting morning urine was collected, and urinary lead and urinary creatinine (UCr) were detected. Fasting peripheral venous blood was collected to detect telomere length and serum creatinine (SCr) in peripheral blood leukocytes. eGFR was estimated by the Levey formula. After further adjusting for age, gender, education level, family per capita monthly income, smoking, and drinking the relationship among urinary lead level, peripheral blood telomere length, and renal function index eGFR was evaluated by mediating effect analysis. Results The overall level of creatinine-adjusted urinary lead [M (P25, P75)] in the abnormal eGFR group was 3.85 (1.56, 7.34) μg·g−1 which was higher than that in the control group, 1.57 (0.60, 3.62) μg·g−1(P<0.001). In addition, the overall level of peripheral blood telomere length in the abnormal eGFR group was 2.42 (1.89, 3.10) Kb, lower than that in the control group, 2.69 (2.09, 3.64) Kb (P<0.001). The results of mediating effect analysis showed that the magnitude of mediating effect by peripheral blood telomere length was −0.276 (95%CI: −0.708-−0.001) and it contributed 3.35% to the relationship between urinary lead level and eGFR. In women, the magnitude of mediating effect by peripheral blood telomere length was −0.484 (95%CI: −1.160-−0.023) between urinary lead level and eGFR, and the proportion of the mediating effect was 5.34%. In men, no mediating role of peripheral blood telomere length was found between urinary lead and eGFR. Conclusion Urinary lead level is closely related to renal function index eGFR and telomere length in peripheral blood. Peripheral blood telomere length plays a mediating role in the relationship between female urinary lead and eGFR in women.