Transgenerational impacts of dietary bioactive components on methyl group homeostasis

Abstract

背景 食品中許多研究顯示來自植物的活性物質具有表觀遺傳上之影響。例如特定植化素在癌細胞及疾病動物模型上皆會抑制DNA轉甲基酶或組蛋白去乙醯酶,進而降低或減緩癌症發生機率。也有研究顯示如果母體攝取特定食品活性物質會透過造表觀遺傳調節造成影響子代發育。硫-腺核苷甲硫胺酸為體內的甲基提供者,為單碳代謝途徑中的關鍵代謝物。本研究室先前研究顯示特殊食品活性成分會改變體內硫-腺核苷甲硫胺酸的含量。然而食品中特殊食品活性成分對於與單碳代謝影響尚未被全面性深入探討。本論文同時以細胞及動物模式探討食品活性成分對於單碳代謝之影響。同時本研究進一步探討不同生命週期-包含懷孕期、哺乳期或離乳後給予特殊食品活性成分探討不同生命週期對於子代單碳代謝之不同影響。 實驗設計 在體內與體外以穩定同位素標定的方法探討食品活性物質對甲基代謝相關路徑分流的變化。細胞模式中以有表達甘氨酸甲基轉移酶及硫-腺核苷甲硫胺酸合成酶之肝細胞為模型,探討食品活性物質在體外模式中對單碳代謝之影響。動物模式主要分為母代暴露於懷孕期、哺乳期、或離乳後。懷孕期主要探討母代老鼠在交配後至生產前給予食品活性物質補充之飼料,哺乳期為母代老鼠生產後開始給予食品活性物質補充之飼料四周,離乳組為子代離乳後給予子代含食品活性物質補充之飼料,其餘生命期則是給予正常飼料。老鼠子代皆在八周齡犧牲並進行分析。 結果 在動物模型中,無論食品活性物質暴露於哺乳期、懷孕期、或離乳後皆影響使老鼠子代肝臟硫-腺核苷甲硫胺酸的含量。此外,在懷孕期及哺乳期動物模型中給予特定食品活性物質補充會促進非依賴葉酸依賴之轉甲基之路徑。 另一方面,本研究發現在懷孕期給予母代或是離乳後給予子代補充特定食品活性物質會促進子代肝臟膽鹼有利用，並提升粒線體中特定單碳代謝路徑，進而有利於肝臟硫-腺核苷甲硫胺酸生成;但是哺乳期補充則不會影響此路徑。本論文是第一個發現母體孕期補充此種食品活性物質有利於肝臟特定單碳代謝路徑及甲基利用分流的研究。

關鍵字: 植化素、硫-腺核苷甲硫胺酸、單碳代謝、跨代研究。

Background. Bioactive food components including certain phytochemicals can cause epigenetic modifications such as DNA methylation and histone modifications. By modifying the gene expression they can have preventive effects on diseases such as cancer in offspring. Numerous epidemiological and animal studies demonstrate that specific phytochemical can inhibit DNA methyltransferase and histone deacetylase activity in cancer cells. S-adenosylmethionine is a universal methyl donor that plays an important role in epigenetic modifications. The present study aims to investigate how selected phytochemicals modulate S-adenosyl- methionine homeostasis and one carbon metabolic kinetics in vitro and in vivo. Study design. Stable isotope labeling experiments were performed in cells as well as in mice to investigate the methyl group fluxes. The impacts of gestational, lactational or post-weaning exposure of specific bioactive component B and S on one carbon metabolism were investigated in the offspring. In the gestation group, pregnant C57BL/6 mice received the specific phytochemical supplemented diet from gestational day 0 to day 18. In the lactation group, female C57BL/6 mice received a control or compound S supplemented diet from postnatal day 1 to day 28. In the post-weaning group, male and female offspring received a control or selected phytochemical S supplemented diet for 4 weeks after weaning. Finally a separate group of offspring mice receiving supplementation throughout the maternal gestation, lactation, and 4-week post weaning periods. Results. In our stable isotopic tracer experiments in vivo models, enrichments in methionine (Met+3) and S-adenosylmethionine+3 (adoMet+3) from [Trimethyl-2H9]-choline chloride increased by 32% (p=0.015) and 33% (p=0.076) when mice were supplemented with S during gestation. In addition, the enrichments in adoMet+3 tended to increase (by 19%) during lactation (p=0.083). Gestational supplementation of S promotes the methyl group utilization from choline for methionine and adoMet synthesis. On the other hand, the enrichments in S-adenosylmethionine+1 (adoMet+1) increased by 78% (P=0.006) in the S-gestation group, tended to increase by 83% (p=0.178) in the S-weaning group. However, they did not change in the S-lactation group. Conclusions. In conclusion, gestational exposure to S greatly promote cytosolic and mitochondrial choline utilization whereas lactational supplementation of S only promotes cytosolic choline utilization. The Impacts of S supplementation on DNA synthesis and global DNA methylation during gestation, lactation, and post-natal period were also investigated. Key words: phytochemicals, S-adenosylmethionine (adoMet), one carbon metabolism.