Division of Space Life Sciences, Universities Space Research Association, Houston, TX, USA.
J Nutr. 2012 Mar;142(3):427-31. doi: 10.3945/jn.111.154245. Epub 2012 Feb 1.
Approximately 20% (7 of 38) of astronauts on International Space Station (ISS) missions have developed measurable ophthalmic changes after flight. This study was conducted to determine if the folate- and vitamin B-12-dependent 1-carbon metabolic pathway is altered in these individuals. Since 2006, we have conducted experiments on the ISS to evaluate nutritional status and related biochemical indices of astronauts before, during, and after flight. Data were modeled to evaluate differences between individuals with ophthalmic changes (n = 5) and those without them (n = 15), all of whom were on ISS missions of 48-215 d. We also determined whether mean preflight serum concentrations of the 1-carbon metabolites and changes in measured cycloplegic refraction after flight were associated. Serum homocysteine (Hcy), cystathionine, 2-methylcitric acid (2MCA), and methylmalonic acid concentrations were 25-45% higher (P < 0.001) in astronauts with ophthalmic changes than in those without them. These differences existed before, during, and after flight. Preflight serum concentrations of Hcy and cystathionine, and mean in-flight serum folate, were correlated with change (postflight relative to preflight) values in refraction (P < 0.05), and preflight serum concentrations of 2MCA tended to be associated (P = 0.06) with ophthalmic changes. The biochemical differences observed in crewmembers with vision issues strongly suggest that their folate- and vitamin B-12-dependent 1-carbon transfer metabolism was affected before and during flight. The consistent differences in markers of 1-carbon metabolism between those who did and those who did not develop changes in vision suggest that polymorphisms in enzymes of this pathway may interact with microgravity to cause these pathophysiologic changes.
约 20%（38 人中的 7 人）执行国际空间站（ISS）任务的宇航员在飞行后出现可测量的眼部变化。本研究旨在确定叶酸和维生素 B12 依赖性 1 碳代谢途径是否在这些个体中发生改变。自 2006 年以来，我们一直在 ISS 上进行实验，以评估宇航员在飞行前、飞行中和飞行后的营养状况和相关生化指标。对数据进行建模，以评估眼部变化者（n = 5）和无眼部变化者（n = 15）之间的差异，所有这些人都在 48-215 天的 ISS 任务中。我们还确定了飞行前血清中 1 碳代谢物的平均浓度与飞行后测量的睫状肌麻痹折射变化之间是否存在关联。与无眼部变化者相比，有眼部变化者的血清同型半胱氨酸（Hcy）、胱硫醚、2-甲基柠檬酸（2MCA）和甲基丙二酸浓度高 25-45%（P < 0.001）。这些差异在飞行前、飞行中和飞行后均存在。Hcy 和胱硫醚的飞行前血清浓度以及飞行中的平均血清叶酸与折射的变化（与飞行前相比）值相关（P < 0.05），并且 2MCA 的飞行前血清浓度趋于与眼部变化相关（P = 0.06）。在视力问题的机组人员中观察到的生化差异强烈表明，他们的叶酸和维生素 B12 依赖性 1 碳转移代谢在飞行前和飞行中受到影响。在出现和未出现视力变化的人员之间，1 碳代谢标志物的差异一致，这表明该途径中酶的多态性可能与微重力相互作用，导致这些病理生理变化。
