Modification Of Metallothionein Polymorphism On Renal Dysfunction In Lead Exposed Workers

Lead (Pb), is one of heavy metal elements, which has been considered as a harmful pollutant of world wide concern. Lead is excreted through kidney, so it is the major target organ of lead. Blood lead can reflects the recent exposure to lead, for example, people subject to renal impact when their blood lead climbed up to over 1.9μmol/L (400μg/L), on the other hand, it has high renal dysfunction mortality when it turned to low-dose and long-term lead exposureThe purpose of this study are:To investigate renal dysfunction in lead exposed workers using epidemiological study, particularly estimating bench mark dose in order to characterize the relationship between lead exposure dose and lead induced renal dysfunction, to examine the the possibility using urinary metallothionein as the biomarker in lead exposed workers and to identify the role of metallothionein gene polymorphism on the modification of renal dysfunction in the whole course.The target population comprised people who worked in a storage battery plant and a kitchenware factory in Zhejiang Province. The exposure group consisted of 237 workers (male 172, female 67); the control group consisted of 76 workers (male 50, female 26), who have not joined the job exposed to lead. The lead worker has lead related work history from less than 1 year to 5years,1.23 years averagely. Two groups are comparable in age, work history, height, weight, BP and daily habits (smoking, alcohol).We collected the documents of air lead (2005～2007) of the storage battery plant, according to which the external dose of lead was calculated for every worker. The lead exposure indicators (blood lead, urinary lead) and effect biomarkers (UNAG, UALB), plus UMT were measured at the same time. Then the relationship among the parameters mentioned above were analyzed and bench mark dose (BMD), the lower confidence limit of the bench mark dose (BMDL) were estimated for the adverse effect of renal system. After choosing 4 SNPs in MT-1A and MT-2A gene, the genotype for each subject was detected using real time PCR technique, following which the modification of each SNPs were evaluated.According to the exposure assessment, it was found that:the external dose was well correlated to internal dose, it was much higher in exposure group than that in control group and was higher in male workers than that in the female. The internal dose, both blood lead and urinary lead, was significantly higher in both men and women of exposure group than that in control group. Blood lead was similar in men to women when they were in a same group, while their urinary lead was totally different, it was significantly higher in women than that in men. In addition, it seems that age could not influence internal dose, but length of working history was correlated to lead body burden and smoking could affect the status when people exposure to lower lead dose.Concerning renal dysfunction, when the air lead was over lmg-month, the level of UNAG raised up then, especially for women. Once the body burden climbed over the GB for lead absorption, both of UNAG and UALB increased significantly. In each group of blood lead or urinary lead, UNAG increased gradually, UALB showed the same trend in each group of urinary lead, while this trend was not obvious in groups f blood lead. We then defined the cutoff point based on the 95th percentile value for UNAG, and UALB. The cutoff points of UNAG and UALB of subjects were 10 U/g Cr and 25mg/g Cr, respectively. The prevalence of hyperNAGuria and hyperALBuria at internal dose of lead were calculated in all subjects. In general, the results showed the significantly increased prevalence of hyperNAGuria and hyperALBuria. The prevalence of hyperNAGuria of subjects showed significant increasing trend with the increase of of BPb in lead exposed groups. The prevalence of hyperALBuria has significant increasing trend in total group and the female. As far as BMD was concerned, the B-Pb BMDL of UNAG in men, women and the total were 402.03,264.67,362.56μg/L respectively, and 81.80,71.52,78.79μg/gCr for U-Pb BMDL; in terms of UALB, they were 962.44,285.44,607.76μg/L respectively for B-Pb and 153.37,75.71,117.79μg/gCr for U-Pb. It was obvious that BMDL of UANG was always lower than that of UALB, while the BMDL of UALB and UNAG were lower in women than those in men.The study of metallothionein in urine told us:urinary metallothionein (UMT) was well correlated with lead body burden. Its level increased following the increased exposure. The cutoff point was also calculated for it in the same way that mentioned above. The prevalence of hyperMTuria showed significant increasing trend in external and internal dose of lead exposed group. BMDL value was also calculated for UMT. The B-Pb BMDL of UNAG in men, women and the total were 411.85,310.99, and 398.60μg/L, respectively, and 76.96,87.29 and 87.37μg/gCr for U-Pb BMDL. The B-Pb BMDL of UMT was higher than UNAG for men, women and the total and women's B-Pb BMDL of UMT was higher than UALB, but men's B-Pb BMDL of UMT was lower than UALB; on the other hand, women's U-Pb BMDL of UMT was higher than UNAG and UALB while it demonstrated opposite feature in men.In the research of MT1A and MT2A polymorphism, we found that:people's susceptibility to lead absorption and lead induced renal dysfunction could be modified by polymorphism of MT gene. Three genotype of each SNPs (totally 4 SNPs) were all found in our target population. SNP of MT1A-rs11076161 had modification to B-Pb and U-Pb for the whole population because people who carried with genotype AA showed lower body burden than the remains. When the population was divided into two groups according to their exposure level, the results became as follows:in the lower exposure group, workers with rs28366003-GG got higher B-Pb than AA+AG, while women who took rs28366003-AA had higher B-Pb and men who took rs11076161-AA had lower U-Pb. As a whole group, workers in higher exposure had lower body burden when they carried with rs10636-GG. But it was different in different gender:men with rs10636-GG or rs1610216-CC had lower body burden while women had not got this feature, if they carried with these genotype, they showed higher body burden yet. When it came to the relationship between MT gene polymorphism and lead induced renal dysfunction, it was found that:the level of UNAG was lower in workers with rs10636-GG or rs1610216-CC for the whole subjects. In lower exposure group, the level of UNAG and UALB in women with rs11076161-AA was lower than the remains. In higher exposure group, workers as a whole had lower UNAG if they carried with rs10636-GG, and it showed the same result in male workers but not in female workers. Women got higher UNAG if they carried with rs28366003-AA while they would get higher UALB when they carried with rs28366003-GG. Men with rs1610216-CC got lower UANG level while women with the same genotype didn't show the same phenomenon. In the course of analysis, smoking and drinking were considered in the model, but neither of which influenced the modification of the 4 SNPs.It could be concluded:①the air lead could be used as a reference parameter of lead exposure for short term-high level lead workers.②people could got renal damage when they expose to high dose of leadwith short term. In the course of damage, tubular dysfunction was earlier than glomerular.③UMT showed significant dose-effect and dose-response relationship with internal dose of lead, which implied that it can be considered as an biomarker for lead induced renal dysfunction.④in the condition of higher air lead for women, they got similar blood lead as men and much higher urinary lead than men, at the same time, they even had higher renal dysfunction indicators than men, both of which implied that women was inclined to collect lead and be more sensitive to lead.⑤MT1A and MT2A subtypes were susceptible genes in MT gene family. In the same external exposure of lead, MT1A-rs11076161-AA could modify the lead body burden, its takers had lower lead body burden than the others. MT2A-rs28366003-GG could increase the level of lead absorption under lower lead exposure. For the subjects as a whole, MT2A-rs10636-GG and MT2A-rs1610216-CC could protect body from the impact of tubular impact of lead.⑥the modification of MT gene polymorphism was different to different gender. Under lower lead exposure, MT1A-rs11076161-AA could increase the storage of lead in urine for men while it may decrease the renal dysfunction indicator's level for women. Under lower lead exposure, MT2A-rs10636-GG could release men from both lead absorption and renal impact to some extent. MT2A-rs1610216-CC could release the body burden for men but increase that for women; furthermore, this genotype could also protect men's kidney but would make kidney impact more serious for women.⑦the lead absorption and kidney impact induced by lead in this target population and different workers were modified by MT2A-rs10636, workers who took CC+CG had higher UNAG level than GG. After further comparison, the B-Pb BMDL of the two groups were 300.88,378.68μg/L respectively, which indicated the former group was susceptible to renal dysfunction induced by lead. What's more, the former group account 45.05% in the population, which implied almost half of our whole population susceptible to lead nephropathy. As a result, this genotype has great practical significance for occupational work.