產前鄰苯二甲酸酯類暴露與發炎相關基因組蛋白修飾間之相關性探討

Abstract

背景及目的: 嬰兒和孩童一直以來都被視為易感受族群，無論是對於環境中的暴露物或是罹患疾病的風險，本研究的重點將放在母親懷孕期間，環境中鄰苯二甲酸酯類的暴露與胎盤中發炎相關基因的組蛋白修飾間之關聯性，並且進一步延伸到孩童罹患過敏相關疾病的風險。其中鄰苯二甲酸酯類包括鄰苯二甲酸二(2-乙基己基)酯 (DEHP)、鄰苯二甲酸二乙酯 (DEP)、鄰苯二甲酸二丁酯 (DBP)及鄰苯二甲酸丁苯甲酯 (BBzP)。過去流行病學研究指出，產前暴露不同種之鄰苯二甲酸酯類在導致孩童日後罹患過敏相關疾病風險提高上，都有發現一致的結果。而近年來，表觀遺傳學一直被視為一種潛在的調控機制，參與了整個致病過程，故本研究的目的為探討發炎相關基因之組蛋白修飾與產前暴露鄰苯二甲酸酯類間之關聯性探討。 方法: 本研究對象為2004年4月至2005年1月期間參與臺灣出生世代長期追蹤研究的母親與嬰兒配對。使用染色質免疫沉澱法來分析胎盤中過氧化物酶體增殖物活化受體α 、誘導型一氧化氮合成酶和干擾素γ 上之組蛋白修飾程度。再與第三孕期尿液中鄰苯二甲酸酯類代謝物、臍帶血中IgE、懷孕中之生活習慣和2歲孩童過敏反應，進行簡單線性迴歸和多重線性迴歸模式討論。 結果: 懷孕中使用塑膠袋盛裝熱食及孕婦尿液中MEHP有顯著的正相關(β = 0.54, p = 0.037)。PPARα組蛋白修飾程度和尿液MEHP濃度在簡單迴歸模式中發現快達到顯著相關(p=0.07)。然而，在iNOS、IFN-γ組蛋白修飾程度和MBP、MEHP及MBP中卻沒有發現顯著的相關性。兩歲孩童有無罹患氣喘和iNOS組蛋白修飾程度有顯著的正相關(crude OR, 3.28, 95%CI 1.0-10.8; adjusted OR, 4.62, 95%CI 1.01-20.94)。將發炎相關基因組蛋白修飾程度分為四組後，發現PPARα組蛋白修飾程度(>75%)和兩歲是否罹患異位性皮膚炎有顯著的正相關(OR, 1.69)。另外在環境因子中，懷孕時是否使用塑膠袋盛裝熱食、是否使用保養品或化妝品和懷孕前是否有吸菸等三個變項在四組IFN-γ組蛋白修飾程度中發現顯著差異且發現臍帶血中可丁尼濃度在四組IFN-γ組蛋白修飾程度中發現顯著差異。 結論: 本研究指出，產前暴露鄰苯二甲酸酯類和發炎相關基因的組蛋白修飾沒有顯著地相關，而可能的原因為目標片段的H3K4me3程度不足以發現顯著關聯性。本研究結果可以配合之前發炎相關基因甲基化的研究，進一步釐清表觀遺傳學是如何影響產前暴露鄰苯二甲酸酯類及孩童過敏反應間之作用機制。

Background/Aim: Phthalate esters (phthalates) could penetrate the placenta and expose fetuses through cord blood. Epidemiological investigations found out there were potent and consistent evidences that phthalates exposure could increase the risk of allergy and asthma on fetuses and children. In recent years, epigenetics have been described as a potential mediator between environmental exposures and diseases, especially the histone modification. The aim of the study was to investigate the association between histone modifications of inflammatory genes and allergic responses. Methods: A total of 486 mother-infant paired was recruited from April 2004 to January 2005 from Taiwan Birth Panel Study (TBPS), the cord blood IgE, phthalate metabolites concentration in maternal urine were measured, and placenta samples were collected. Cord blood IgE was used as a predictor of childhood allergic disorders. The levels of histone H3 at lysine 4 residue trimethylation (H3K4me3) on inflammatory genes were measured from placenta by using chromatin immunoprecipitation (ChIP). One hundred and fifty-six mother-infant pairs were included in the analyses, due to the availability of placenta samples and phthalate metabolites measurements. Results: A positive relationship was found between using plastic bags to contain hot foods during pregnancy and MEHP in maternal urine (β = 0.54, p = 0.037). The association of PPARα and MEP in crude model was of borderline significance (p=0.07). However, there was no significant linear associations were observed between MEP, MBP, MEHP, MBzP and H3K4me3 levels of PPARα, iNOS, and IFN-γ. The asthma at age 2 was significantly associated with the H3K4me3 level of iNOS (crude OR, 3.28,95%CI 1.0-10.8; adjusted OR, 4.62, 95%CI 1.01-20.94). H3K4me3 levels (>75%) of PPARα were significantly associated with AD at age2 (OR, 1.69) and environmental factors, including using plastic bags to contain hot foods, using cosmetics, and prenatal ETS exposure were all significantly different within four groups of H3K4me3 level of IFN-γ. Furthermore, cotinine in cord blood was significantly different in four groups of H3K4me3 level of IFN-γ. Conclusions: Our data suggested that prenatal phthalate exposures were not associated with histone modification of inflammatory genes and it might due to the insufficient H3K4me3 levels in PCR amplification region. With the previous DNA methylation study, we were capable to get a comprehensive view of how epigenetics influence the pathway of prenatal phthalate exposures and allergic responses.