金屬硫蛋白與麩胺基硫轉移酶基因多型性與學齡前兒童血液中多種金屬元素濃度關係之探討

Abstract

當不同個體所暴露的金屬來源與劑量強度不一樣時，體內的金屬濃度分布就會有個體間的差異情形存在。儘管外在的環境金屬暴露是造成不同個體間金屬濃度差異的最主要因素，但當與金屬代謝解毒相關的金屬硫蛋白與麩胺基硫轉移酶等之調控基因發生變異時，也可能改變金屬在不同個體內的代謝能力及分布情形。鑒於現今一般生活環境中的金屬暴露型態應屬於低濃度多重金屬暴露，兒童又相對屬於金屬暴露較為敏感之族群，故本研究擬就MTs與GSTs之五種基因多型性與學齡前兒童血中多種金屬濃度之相關性作探討。 本研究在個案選擇是以行政等級為單位做分層抽樣，於民國一百年四月至十月間，隨機選取了全台44個區、市、鎮、鄉，總共707位學齡前兒童研究個案。問卷資料包括研究個案兒童個人與家庭背景資料、居住生活環境金屬暴露來源及出生與疾病資料等。個案血中鉛、鎘、砷、汞、錳、銅與鋅等金屬濃度之檢測分析使用感應耦合電漿質譜分析儀。MT2A(MT2A-5A/G與MT2A+838C/G)GSTs (GSTT1/GSTM1/GSTP1 Ile 105Val)之基因多型性分析則是透過高通量即時螢光定量聚合酶連鎖反應系統中的解鏈曲線分析來進行。 本研究個案兒童血中鉛平均濃度為20.7(±11.4) μg/L；鎘平均濃度為0.24(±0.21) μg/L；砷平均濃度為3.81(±3.31) μg/L；汞平均濃度為5.40(±3.67) μg/L；錳平均濃度為14.5(±4.3) μg/L，銅平均濃度為942.9(±202.5) μg/L；鋅平均濃度為4434.4(±899.7) μg/L。 當調整控制可能影響血中金屬濃度的相關變項後，本研究顯示MT2A-5A/G基因型為homozygous variant (G/G)或MT2A+838C/G基因型為homozygous variant (C/C)的個案，其血中汞濃度比起MT2A-5A/G homozygous wild-type (A/A)與MT2A+838C/G homozygous wild-type (G/G)個案皆顯著較高(p= 0.04及0.01)。MT2A +838C/G基因型為homozygous variant (C/C)的個案，其血中砷濃度比起homozygous wild-type (G/G)個案組顯著較高(p= 0.04)。而在GSTs方面，GSTM1基因型為無效基因型(null genotype)的個案其血中錳濃度比起有效基因型(present genotype)個案組顯著較低(p= 0.01)。GSTP1(Ile105Val)基因型為homozygous variant (G/G)的個案血中鉛濃度相對homozygous wild-type (A/A)個案組則顯著較高(p= 0.03)。 本研究發現學齡前兒童在MTs與GSTs的調控基因發生變異下，確實會與血中某些金屬濃度分布情形的改變有關，包括血中鉛、砷、錳與汞濃度等。然而，鑑於目前曾針對這些基因變異與金屬濃度間之相關性作探討的研究仍較少，因此本研究的結果仍需待後續更多的研究來加以佐證，進而能對於這些參與體內金屬代謝或解毒的相關酵素之基因變異效應與金屬濃度間的作用機制有更深入的瞭解。 此外，未來研究應也可調查其他與體內金屬代謝相關物質之調控基因多型性發生對體內特定金屬濃度分布的影響，如二價金屬運輸蛋白等，方能對於體內金屬濃度分布的基因影響因子作更廣泛完整的探討。

Different sources and levels of external exposure may contribute to the interindividual variation in human body metal levels, but polymorphisms in genes encoding functional enzymes and proteins such as metallothioneins(MTs) and glutathione S-transferases(GSTs), may also cause variation in biomarker for metal levels in humans. Besides, multiple metal exposure is one of the major types of environmental pollutant exposure and should be concerned, especially for the children who were regarded as a more susceptible group. Thus, in this study, we tried to investigate the relationship between some MTs and GSTs gene polymorphisms with multiple blood metal levels of the preschool children in Taiwan. Based on a stratified sampling strategy, 707 preschool children were recruited from kindergartens located in the randomly selected townships or city districts in Taiwan from April to October, 2011. Questionnaires were administered to get study subjects’ demographic information and environmental metal exposure factors. ICP-MS was applied to analyze lead, cadmium, arsenic, mercury, manganese, copper and zinc in blood sample. The genotyping of GSTs(GSTT1/GSTM1/GSTP1 Ile105Val) and MTs(MT2A-5A/G and MT2A+838C/G) gene polymorphisms were carried out using real-time PCR with melting curve analysis. The means of the blood Pb, Cd, As Hg, Mn, Cu and Zn levels were 20.7±11.4 μg/L, 0.24±0.21 μg/L, 3.81±3.31 μg/L, 5.40±3.67 μg/L, 14.5±4.3 μg/L, 942.9±202.5 μg/L and 4434.4±899.7 μg/L, respectively. The results showed that subjects with MT2A-5A/G GG genotype or MT2A+838C/G CC genotype had higher blood mercury levels than did those with MT2A-5A/G AA or MT2A+838C/G GG genotype (p = 0.04 and 0.01, respectively) after controlling for the potential exposure confounders. Subjects with MT2A+838C/G CC genotype had higher blood arsenic levels than subjects with MT2A+838C/G GG genotype (p=0.04). Regarding GSTs, subjects with GSTM1 null genotype (gene deletion) presented lower blood manganese level than subjects with present genotype (p= 0.01). In addition, blood lead level in subjects carrying GSTP1(Ile105Val) GG genotype were significantly higher than those with GSTP1 AA genotype (p= 0.03). Our findings suggested that gene variants of MTs and GSTs may be related to some toxic metals metabolism, including lead, arsenic, manganese and mercury. However, more evidences are warranted to confirm the association of these gene variants and metal levels for better understanding the mechanisms involved in metal toxicity and excretion while relevant studies concerning these issues are still limited. Besides, future studies may try to investigate the effect of other metal metabolism related gene variants such as divalent metal transporter 1 on toxic metal burden and trace element homeostasis in metal biomarkers.