Segal Stanton, Wehrli Suzanne, Yager Claire, Reynolds Robert
Metabolic Research Laboratory, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
Mol Genet Metab. 2006 Feb;87(2):92-101. doi: 10.1016/j.ymgme.2005.09.012. Epub 2005 Nov 2.
To determine if classic galactosemics have residual galactose-1-phosphate uridyltransferase (GALT) activity to explain their considerable ability to oxidize galactose over 24 h, we devised a method for assessing their ability to form hepatic UDPglucose (UDPglu), an intermediate in the normal Leloir pathway of galactose metabolism. The protocol involved the single oral administration of 7 mg/kg [2-13C]galactose concomitant with multiple small doses of acetaminophen with measurement of the extent of labeling of urinary acetaminophen glucuronide, the glucuronide moiety being formed from hepatic UDPglu. We performed the study lasting 24 h in two normal subjects and three classic galactosemics, two homozygous for the Q188R mutation and one compound for the Q188R/K258N mutation. The labeling and total excretion of acetaminophen glucuronide was measured in urine by nuclear magnetic resonance techniques. Concomitant with determination of label in the glucuronide measurement was made of galactose oxidation to 13CO2 and the 13C enrichment of plasma glucose. All of the galactosemic patients formed 13C enriched acetaminophen glucuronide indicating that they had converted the labeled galactose to [13C]UDPglu and that residual GALT or another pathway that forms UDPglu is present in hepatic tissue. Compared to the normal whose glucuronide labeling was rapid and short-lived that of the galactosemics was delayed and extended for a long period over 10 h. The extent of isotopic enrichment of glucuronide by galactosemics was comparable to the normals, resulting in a much greater conversion of galactose to UDPglu by the galactosemics. The labeling of the UDPglu pool was reflected by the rate of 13CO2 formation being rapid in the normal with peak labeling at 2-3 h with total oxidation of over 70% in 24 h. The oxidation of the galactosemics was slow with a broad peak of 13CO2 at 10 h and a total excretion of 25-39% of the [13C]galactose administered. The normal subjects formed highly enriched plasma glucose within 30 min while no enrichment of plasma glucose was detected until after 300 min in galactosemics. The exact pathway(s) of galactose metabolism by galactosemics to UDPglu remain to be determined. Their delineation may contribute to new approaches to therapeutic strategies for this enigmatic disorder.
为了确定典型半乳糖血症患者是否具有残余的1-磷酸半乳糖尿苷转移酶（GALT）活性，以解释他们在24小时内具有相当强的氧化半乳糖的能力，我们设计了一种方法来评估他们形成肝UDP葡萄糖（UDPglu）的能力，UDPglu是半乳糖代谢正常Leloir途径中的一种中间产物。该方案包括单次口服7mg/kg的[2-13C]半乳糖，并同时多次小剂量服用对乙酰氨基酚，然后测量尿中对乙酰氨基酚葡萄糖醛酸苷的标记程度，葡萄糖醛酸部分由肝UDPglu形成。我们在两名正常受试者和三名典型半乳糖血症患者中进行了为期24小时的研究，其中两名是Q188R突变纯合子，一名是Q188R/K258N突变复合杂合子。通过核磁共振技术测量尿中对乙酰氨基酚葡萄糖醛酸苷的标记和总排泄量。在测定葡萄糖醛酸苷标记的同时，还测定了半乳糖氧化为13CO2以及血浆葡萄糖的13C富集情况。所有半乳糖血症患者都形成了富含13C的对乙酰氨基酚葡萄糖醛酸苷，这表明他们已将标记的半乳糖转化为[13C]UDPglu，并且肝组织中存在残余的GALT或另一种形成UDPglu的途径。与正常受试者相比，正常受试者的葡萄糖醛酸苷标记迅速且短暂，而半乳糖血症患者的标记延迟且在10小时内持续较长时间。半乳糖血症患者葡萄糖醛酸苷同位素富集程度与正常受试者相当，这导致半乳糖血症患者将更多的半乳糖转化为UDPglu。正常受试者中UDPglu池的标记反映在13CO2形成速率上，在2-3小时达到标记峰值，24小时内总氧化率超过70%。半乳糖血症患者的氧化速度较慢，13CO2在10小时出现宽峰，[13C]半乳糖的总排泄量为给药量的25-39%。正常受试者在30分钟内形成高度富集的血浆葡萄糖，而半乳糖血症患者直到300分钟后才检测到血浆葡萄糖的富集。半乳糖血症患者将半乳糖代谢为UDPglu的确切途径仍有待确定。对其进行描述可能有助于为这种疑难病症开发新的治疗策略。
