| 摘要: | 先前本實驗室已觀察到母鼠孕期攝食氧化炸油(oxidized frying oil; OFO)會造成子代畸形，由於OFO已知可活化PPARα，環境汙染物塑化劑 (DEHP)和鐵弗龍成分全氟辛酸(PFOA)與OFO一樣都是PPARα的活化劑，懷孕期間暴露於這些環境汙染物，也會造成子代的發育毒性，這些環境汙染物已證實部分與PPARα活化有關，但PPARα活化如何影響胎胚發育，其中機制有待釐清。
文獻指出PPARα活化劑clofibrate，會顯著影響參與維生素A酸(retinoic acid, RA)代謝相關基因表現。RA是胚胎發育時期重要的型態原(morphogen)，RA表現量過多或過少均會造成畸胎。胚胎發育期間RA的表現需要精確的時空 (Spatial-temporal) 調節，本研究假設母鼠孕期攝取OFO可能透過PPARα活化，影響母鼠與胚胎體內的RA合成及代謝，進而導致子代畸形，實驗分為二部份:1.探討孕期攝取OFO並添加RA是否可以降低畸胎率。若孕期攝食OFO使RA生成量減少而致畸胎，則補充RA應能成功降低其畸胎率; 反之則可能是RA生成過多。2.探討炸油畸胎性與PPARα活化及維生素A代謝干擾之關係。將炸油區分為極性(OFO-polar fraction；PO)與非極性區分物(OFO-nonpolar fraction；NP)，先前研究已知OFO的PPARα活化物存在於PO，若能證實PO不但放大PPARα活化，也放大其畸胎性及干擾RA代謝效應，則間接支持我們假說。
結果: 1. OFO補充RA顯著增加母鼠full-litter resorptions (FLR)、胎兒死亡及畸胎率、骨骼異常機率更甚於未補充RA組，可見補充RA不能挽救炸油致畸胎。2.分離自OFO的PO更加劇胎兒死亡率、畸胎率、骨骼發育不良機率，與PPARα活化，且不論母親或胚胎均發現PO組RA合成與分解相關酵素基因表現偏離正常對照組。結論: OFO畸胎性並非母鼠RA缺乏所造成，但OFO飲食的確在PPARα活化的同時，也干擾了RA合成與分解，至於畸胎性是否與PPARα活化有關則有待進一步研究證實。
In our previous study, we had observed a higher incidence of malformations in fetuses of dams receiving oxidized frying oil (OFO) during pregnancy. It has been reported that OFO can activate the peroxisome proliferator-activated receptor alpha (PPARα). Clofibrate, as a PPARα activator, has been shown to affect expression of genes participating in retinoic acid (RA) catabolism. Being regarded as a morphogen, excess or deficiency of RA during fetus development, both result in teratogenesis. Environmental contaminants such as plasticizer (di(2-ethylhexyl)
phthalate; DEHP), teflon components (perfluorooctanoic acid ; PFOA) activate PPARα as well. Exposure to these Environmental contaminants has been shown to cause developmental toxicity in the offspring during pregnancy, which is partly attributed to PPARα activation. However, the underlying mechanisms remain to be clarified.
RA is indispensible for the precisely spatial and temporal regulation during embryonic development. In this study, we hypothesized that the maternal ingestion of OFO during pregnancy, via PPARα activation, results in teratogenesis by interfering with maternal and embryonic RA synthesis/catabolism. To test this hypothesis, two experiments were included: in Expt. 1, we sought to investigate whether the OFO-mediated teratogenesis can be rescued by RA supplementation. If OFO-mediated teratogenesis is associated with RA deficiency in dams and their fetuses, supplementation of RA would successfully rescue the defects; otherwise, an exaggerated effect would be seen. In Expt. 2, the relevance of OFO teratogenic effect, PPARα activation and the interference of RA metabolism were explored. The OFO was fractionated into OFO-polar fraction (PO) and OFO-nonpolar fraction (NP). It is known that the PPARα activators in OFO are present in the PO fraction, rather than NP fraction. We expected our hypothesis would be supported indirectly if we could see the teratogenic effect of OFO, along with PPARα activation and RA metabolic interference was amplified in dams and their fetuses receiving PO during gestational period compared with their counterparts receiving NP or OFO.
As results of Expt. 1, supplementation of RA in OFO group significantly increased maternal full-litter resorptions (FLR), incidences of fetal death, birth defects, and skeletal abnormalities as compared to the OFO group without RA supplementation. It suggests that supplementation of RA did not rescue, but aggravate, the teratogenesis caused by OFO. In Expt. 2, the fetus mortality, incidences of birth defects and skeletal abnomalities, and PPARα activation consistently showed an order of PO>NP>SO (fresh soybean oil control) groups. In addition, the expression levels of genes encoding enzymes related with RA synthesis/catabolism in the liver of dams and their fetuses receiving PO diet were significantly different from those of their normal counterparts. Based on above results, we concluded that the OFO-mediated teratogenesis is not attributable to RA deficiency. However, dietary OFO does interfere with RA metabolism in accordance with PPARα activation. The role of PPARα in the OFO-mediated teratogengesis will be investigated in the future studies. |
