Hack V, Schmid D, Breitkreutz R, Stahl-Henning C, Drings P, Kinscherf R, Taut F, Holm E, Dröge W
Department of Immunochemistry, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
FASEB J. 1997 Jan;11(1):84-92. doi: 10.1096/fasebj.11.1.9034170.
Patients with skeletal muscle catabolism (cachexia) fail to conserve the skeletal muscle protein and release large amounts of nitrogen as urea. Previous studies suggest that the threshold for the conversion of amino acids into other forms of chemical energy and the concomitant production of urea are regulated by the plasma cystine level and hepatic cysteine catabolism. Studies of plasma amino acid exchange rates in the lower extremities now show that healthy young subjects regulate their plasma cystine level in a process that may be described as controlled constructive catabolism. The term controlled describes the fact that the release of cystine and other amino acids from the peripheral tissue is negatively correlated with (certain) plasma amino acid levels. The term constructive describes the fact that the release of cystine is correlated with an increase of the plasma cystine level. The regulation of the plasma cystine level is disturbed in conditions with progressive skeletal muscle catabolism including cancer, HIV infection, and old age. These conditions show also a low plasma glutamine:cystine ratio indicative of an impaired hepatic cystine catabolism. In HIV+ patients and SIV-infected macaques, a decrease of the plasma cystine level was found to coincide with the decrease of CD4+ T cells.
患有骨骼肌分解代谢（恶病质）的患者无法保留骨骼肌蛋白质，并以尿素的形式释放大量氮。先前的研究表明，氨基酸转化为其他形式化学能以及随之产生尿素的阈值受血浆胱氨酸水平和肝脏半胱氨酸分解代谢的调节。现在对下肢血浆氨基酸交换率的研究表明，健康的年轻受试者在一个可被描述为受控的建设性分解代谢的过程中调节其血浆胱氨酸水平。“受控”一词描述了这样一个事实，即外周组织中胱氨酸和其他氨基酸的释放与（某些）血浆氨基酸水平呈负相关。“建设性”一词描述了这样一个事实，即胱氨酸的释放与血浆胱氨酸水平的升高相关。在包括癌症、HIV感染和老年在内的进行性骨骼肌分解代谢的情况下，血浆胱氨酸水平的调节受到干扰。这些情况还表现出血浆谷氨酰胺：胱氨酸比值较低，表明肝脏胱氨酸分解代谢受损。在HIV阳性患者和感染SIV的猕猴中，发现血浆胱氨酸水平的降低与CD4 + T细胞的减少同时出现。
