Rosenquist T H, Ratashak S A, Selhub J
Department of Cell Biology and Anatomy, University of Nebraska Medical Center, Omaha 68198-6395, USA.
Proc Natl Acad Sci U S A. 1996 Dec 24;93(26):15227-32. doi: 10.1073/pnas.93.26.15227.
The biological basis or mechanism whereby folate supplementation protects against heart and neural tube defect is unknown. It has been hypothesized that the amino acid homocysteine may be the teratogenic agent, since serum homocysteine increases in folate depletion; however, this hypothesis has not been tested. In this study, avian embryos were treated directly with D,L-homocysteine or with L-homocysteine thiolactone, and a dose response was established. Of embryos treated with 50 microliters of the teratogenic dose (200 mM D,L-homocysteine or 100 mM L-homocysteine thiolactone) on incubation days 0, 1, and 2 and harvested at 53 h (stage 14), 27% showed neural tube defects. To determine the effect of the teratogenic dose on the process of heart septation, embryos were treated during incubation days 2, 3, and 4; then they were harvested at day 9 following the completion of septation. Of surviving embryos, 23% showed ventricular septal defects, and 11% showed neural tube defects. A high percentage of the day 9 embryos also showed a ventral closure defect. The teratogenic dose was shown to raise serum homocysteine to over 150 nmol/ml, compared with a normal level of about 10 nmol/ml. Folate supplementation kept the rise in serum homocysteine to approximately 45 nmol/ml, and prevented the teratogenic effect. These results support the hypothesis that homocysteine per se causes dysmorphogenesis of the heart and neural tube, as well as of the ventral wall.
叶酸补充剂预防心脏和神经管缺陷的生物学基础或机制尚不清楚。有人提出，氨基酸同型半胱氨酸可能是致畸剂，因为在叶酸缺乏时血清同型半胱氨酸会升高；然而，这一假说尚未得到验证。在本研究中，直接用D，L-同型半胱氨酸或L-同型半胱氨酸硫内酯处理鸡胚，并建立剂量反应关系。在孵化第0、1和2天用50微升致畸剂量（200 mM D，L-同型半胱氨酸或100 mM L-同型半胱氨酸硫内酯）处理鸡胚，并在53小时（第14阶段）收获，27%的鸡胚出现神经管缺陷。为了确定致畸剂量对心脏分隔过程的影响，在孵化第2、3和4天处理鸡胚；然后在分隔完成后的第9天收获。在存活的鸡胚中，23%出现室间隔缺损，11%出现神经管缺陷。第9天的鸡胚中有很大比例还出现腹侧闭合缺陷。与正常水平约10 nmol/ml相比，致畸剂量可使血清同型半胱氨酸升高至超过150 nmol/ml。补充叶酸可使血清同型半胱氨酸升高至约45 nmol/ml，并预防致畸作用。这些结果支持了同型半胱氨酸本身会导致心脏、神经管以及腹侧壁畸形发生的假说。
