Lyons J, Rauh-Pfeiffer A, Yu Y M, Lu X M, Zurakowski D, Tompkins R G, Ajami A M, Young V R, Castillo L
Laboratory of Human Nutrition and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.
Proc Natl Acad Sci U S A. 2000 May 9;97(10):5071-6. doi: 10.1073/pnas.090083297.
The availability of cysteine is thought to be the rate limiting factor for synthesis of the tripeptide glutathione (GSH), based on studies in rodents. GSH status is compromised in various disease states and by certain medications leading to increased morbidity and poor survival. To determine the possible importance of dietary cyst(e)ine availability for whole blood glutathione synthesis in humans, we developed a convenient mass spectrometric method for measurement of the isotopic enrichment of intact GSH and then applied it in a controlled metabolic study. Seven healthy male subjects received during two separate 10-day periods an L-amino acid based diet supplying an adequate amino acid intake or a sulfur amino acid (SAA) (methionine and cysteine) free mixture (SAA-free). On day 10, L-[1-(13)C]cysteine was given as a primed, constant i.v. infusion (3 micromol x kg(-1) x h(-1)) for 6 h, and incorporation of label into whole blood GSH determined by GC/MS selected ion monitoring. The fractional synthesis rate (mean +/- SD; day(-1)) of whole blood GSH was 0.65 +/- 0.13 for the adequate diet and 0.49 +/- 0.13 for the SAA-free diet (P < 0.01). Whole blood GSH was 1,142 +/- 243 and 1,216 +/- 162 microM for the adequate and SAA-free periods (P > 0.05), and the absolute rate of GSH synthesis was 747 +/- 216 and 579 +/- 135 micromol x liter(-1) x day(-1), respectively (P < 0.05). Thus, a restricted dietary supply of SAA slows the rate of whole blood GSH synthesis and diminishes turnover, with maintenance of the GSH concentration in healthy subjects.
基于对啮齿动物的研究，半胱氨酸的可利用性被认为是三肽谷胱甘肽（GSH）合成的限速因素。在各种疾病状态下以及某些药物的作用下，GSH状态会受到损害，从而导致发病率增加和生存率降低。为了确定膳食中半胱氨酸的可利用性对人体全血谷胱甘肽合成的潜在重要性，我们开发了一种便捷的质谱方法来测量完整GSH的同位素富集情况，然后将其应用于一项对照代谢研究中。七名健康男性受试者在两个独立的10天期间分别接受了一种基于L-氨基酸的饮食，该饮食提供足够的氨基酸摄入量，或者接受了一种不含硫氨基酸（SAA）（蛋氨酸和半胱氨酸）的混合物（无SAA）。在第10天，给予L-[1-（13）C]半胱氨酸作为首剂量、持续静脉输注（3微摩尔×千克（-1）×小时（-1）），持续6小时，并通过气相色谱/质谱选择离子监测法测定标记物掺入全血GSH的情况。对于充足饮食组，全血GSH的分数合成率（平均值±标准差；天（-1））为0.65±0.13，对于无SAA饮食组为0.49±0.13（P<0.01）。充足饮食期和无SAA期的全血GSH分别为1142±243和1216±162微摩尔（P>0.05），GSH合成的绝对速率分别为747±216和579±135微摩尔×升（-1）×天（-1）（P<0.05）。因此，膳食中SAA供应受限会减慢全血GSH的合成速率并减少周转率，同时维持健康受试者的GSH浓度。
