da Costa Kerry-Ann, Gaffney Christopher E, Fischer Leslie M, Zeisel Steven H
Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Am J Clin Nutr. 2005 Feb;81(2):440-4. doi: 10.1093/ajcn.81.2.440.
Elevated concentrations of homocysteine in blood may be an independent risk factor for the development of atherosclerosis. Elevated homocysteine concentrations can be caused by decreased methylation of homocysteine to form methionine, as occurs in folate deficiency. A parallel pathway exists for methylation of homocysteine, in which choline, by way of betaine, is the methyl donor.
Our goal was to determine whether choline deficiency results in a decreased capacity to methylate homocysteine.
C57BL/6J mice were fed diets containing 0, 10, or 35 mmol choline/kg diet for 3 wk. We then administered an oral methionine load to the animals and measured plasma homocysteine concentrations. Also, in a pilot study, we examined 8 men who were fed a diet providing 550 mg choline/d per 70 kg body weight for 10 d, followed by a diet providing almost no choline, until the subjects were clinically judged to be choline deficient or for <or=42 d. A methionine load was administered at the end of each dietary phase.
Two hours after the methionine load, choline-deficient mice had plasma homocysteine concentrations twice those of choline-fed mice. Four hours after the methionine load, clinically choline-depleted men had plasma homocysteine concentrations that were 35% greater than those in men not choline depleted.
These results suggest that choline, like folate, plays an important role in the metabolism of homocysteine in humans and that response to a methionine load may be useful when assessing choline nutriture.
血液中同型半胱氨酸浓度升高可能是动脉粥样硬化发生的独立危险因素。同型半胱氨酸浓度升高可由同型半胱氨酸甲基化形成蛋氨酸减少所致，如叶酸缺乏时发生的情况。同型半胱氨酸甲基化存在一条平行途径，其中胆碱通过甜菜碱作为甲基供体。
我们的目标是确定胆碱缺乏是否会导致同型半胱氨酸甲基化能力下降。
给C57BL/6J小鼠喂食含0、10或35 mmol胆碱/千克饲料的饲料，持续3周。然后给动物口服蛋氨酸负荷，并测量血浆同型半胱氨酸浓度。此外，在一项初步研究中，我们检查了8名男性，他们先食用每70千克体重每天提供550毫克胆碱的饮食10天，然后食用几乎不含胆碱的饮食，直到临床判断受试者胆碱缺乏或持续≤42天。在每个饮食阶段结束时给予蛋氨酸负荷。
给予蛋氨酸负荷2小时后，胆碱缺乏小鼠的血浆同型半胱氨酸浓度是喂食胆碱小鼠的两倍。给予蛋氨酸负荷4小时后，临床胆碱缺乏的男性血浆同型半胱氨酸浓度比未缺乏胆碱的男性高35%。
这些结果表明，胆碱与叶酸一样，在人体同型半胱氨酸代谢中起重要作用，并且在评估胆碱营养状况时，对蛋氨酸负荷的反应可能有用。
