孕早期被动吸烟致胎儿神经管缺陷发生的风险及机制研究

Emerging evidence from questionnaire investigation suggests that women's passive smoking during early pregnancy may increase the risk of having a child with neural tube defects (NTD). We propose to conduct a human case-control study combined with rat experiment to examine the association of maternal passive smoking with the NTD risk in offspring and the two potential mechanisms: 1) folate metabolic disturbance, and 2) DNA oxidative damage. Epidemiological study will be conducted in the region of northern China with high NTD prevalence. The NTD cases and one matched control for each case will be recruited at the time of type-B ultrasound scanning in the second trimester of pregnancy. Women's hair samples, venous blood, information on women's passive smoking during early pregnancy and other variables will be collected in the recruitment. The recruited participants will be followed to verify the pregnancy outcome at delivery, and the final study subjects (200 pairs) will be confirmed at the time after exclusion of the subjects with false diagnosis by ultrasound scanning. Pregnant women's hair nicotine(Biomarker of passive smoking) in first trimester, blood folate and 8-hydroxydeoxyguanosine (Biomarker of DNA lesion) in second trimester, and relative genetic polymorphisms of metabolic enzymes will be measured. The association of maternal passive smoking with NTD risk and the potential mechanisms will be examined by analyzing the difference of hair nicotine, blood folate, and 8-hydroxydeoxyguanosine levels between case and control groups, and the correlation between these biomarkers. Rat passive smoking model will be established, together with measurement of various biomarkers, to directly and thoroughly verify the effects of passive smoking on NTD occurrence and the potential mechanisms by which passive smoking may result in NTD occurrence.

问卷调查研究提示，妇女孕早期被动吸烟可能增加胎儿神经管缺陷(NTD)发生风险。本研究拟以人群病例对照研究结合大鼠被动吸烟模型揭示孕早期被动吸烟与胎儿NTD发生风险的关系及两个可能的作用机制：1)叶酸代谢异常；2)DNA氧化损伤。人群研究在我国北方NTD高发地区进行。初选对象为孕中期B超筛查时发现的NTD疑似胎儿及配比选择的正常胎儿。采集孕妇发样和静脉血保存，收集孕早期被动吸烟及其它信息。随访妊娠结局，排除B超筛查错误的对象后，确定最终研究对象（200对）。通过测定和比较病例组和对照组之间孕早期发样尼古丁水平（被动吸烟标志物）、血液叶酸和8-羟基脱氧鸟苷水平（DNA氧化损伤标志物）、部分代谢酶多态性，以及各指标之间的相关性，揭示妇女被动吸烟与NTD发生的病因关联及可能的作用机制。通过构建大鼠孕早期被动吸烟模型及测定相关的生物标志物,直观、深入地验证被动吸烟致NTD发生的病因关联及作用机制。

研究目的：1）围孕期妇女被动吸烟是否显著增加子代神经管缺陷（NTDs）发生的危险性；2）如果风险增加，则探讨香烟烟雾暴露导致NTDs的机制如何？.方法：采用人群病例对照研究和大鼠被动吸烟模型进行研究。病例对照研究包括188例生育NTDs患儿母亲及256例正常对照母亲。调查了妇女怀孕前后被动吸烟及其它信息，采集妇女发样和静脉血。采用GC-MS进行定量测定发样尼古丁及可替宁（被动吸烟标志物），采用ICP-MS测定了发样中金属元素含量，微生物发测定了血样叶酸浓度。比较病例组和对照组各指标是否有显著差异。通过构建大鼠孕早期被动吸烟模型，进一步观察被动吸烟致NTD发生的效应及可能的作用机制。.结果：对照组被动吸烟率33%，病例组43%，调整混杂因素之后，自报被动吸烟妇女生育NTDs患儿的相对危险度为1.60；但对照组和NTDs病例组及各病例亚组妇女头发中尼古丁或可替宁浓度差异无统计学意义。自报被动吸烟妇女头发中尼古丁和可替宁浓度高于无暴露妇女。围孕期Ti暴露与神经管畸形的风险增加有关，Mg、Ca、Ni、Mo元素是神经管畸形的保护因素。动物实验发现高浓度被动吸烟组的NTD胚胎发生率为26.0%显著高于对照组3.5%（p<0.001），被动吸烟组Pax3表达显著降低(p<0.01)，促凋亡蛋白Bax表达量显著增高(p<0.001)，但血液叶酸水平并未显著降低。.结论：以头发中尼古丁或可替宁为标志物的人群病例对照研究尚不支持母亲在目前的香烟烟雾暴露水平显著增加NTDs发生的风险。既往大多数基于问卷调查得到的阳性结果可能是由于报告偏移导致的。动物实验说明，高浓度香烟烟雾的暴露可能增加NTDs发生风险增加，而Pax3表达降低进而引起神经上皮细胞过度凋亡可能是神经管闭合异常的主要机制。