Novel ALT Isoenzymes and Their Diagnositc Application

简介（申请人提供）：近五十年来，丙氨酸转氨酶（ALT）一直是临床广泛使用的急慢性肝损伤诊断标志物。虽然血清ALT升高是肝损伤的共同特征，但在其他疾病如肥胖、肌肉疾病和表面健康的人群中也可以观察到。在上述情况下导致ALT变化的细胞机制尚不清楚，这往往使ALT数据的解释存在问题。本申请中提出的工作是基于我们最近发现的一种新的人类ALT同源物，我们将其命名为ALT2。ALT2与ALT1（唯一已知的ALT）具有显著的同源性，在肽水平上具有69%的同源性和78%的相似性。重要的是，这两种同工酶由不同的基因编码，在组织分布上有显著差异；ALT2在肌肉、肾脏和脂肪组织中高表达，而ALT1主要在肝脏、肾脏和心脏组织中表达。由于目前测定血清ALT水平的方法是酶促的，它们不能区分ALT1和ALT2。血清中同工酶的测量可能比总酶活性更有诊断价值，如肌酸激酶- mb对心肌梗死和骨特异性碱性磷酸酶对骨病的诊断。我们假设ALT2在血清中循环，并对目前可用的临床检测中测量的总ALT活性有不同的贡献（取决于疾病病因）。此外，我们假设ALT2在脂肪肝和/或肥胖患者中会特别升高，因为ALT2而不是ALT1在脂肪组织中大量表达。为了检验这些假设，我们建议开发一种ALT同工酶特异性免疫测定。该试验将用于测量多种疾病状态下的血清ALT同工酶水平，包括肝病和肥胖（稳定和减肥期间）。我们预测脂肪肝或肥胖患者的血清ALT2水平会更高，这可能是脂肪肝和其他疾病状态的临床有用标志物。

DESCRIPTION (provided by applicant): For nearly fifty years, alanine transaminase (ALT) has been a widely used clinical diagnostic marker of acute and chronic hepatic injury. Although elevated serum ALT is a common feature of liver damage, it is also observed in other diseases such as obesity, muscle disease, and in apparently healthy people. The cellular mechanisms leading to ALT changes in the above situations are poorly understood, which often renders the interpretation of ALT data problematic. The work proposed in this application is based upon our recent discovery of a novel homologue of human ALT, which we have designated ALT2. ALT2 has significant homology to ALT1 (the only previously known ALT) with 69% identity and 78% similarity at the peptide level. Importantly, the two isoenzymes are encoded by distinct genes and differ significantly in tissue distribution; ALT2 is highly expressed in muscle, kidney and adipose tissue, whereas ALT1 is mainly expressed in liver, kidney and heart. Since current assays to measure serum ALT levels are enzymatic, they do not differentiate between ALT1 and ALT2. Measurement of an isoenzyme in serum may have more diagnostic value than total enzyme activity, as exemplified by creatine kinase-MB for cardiac infarction and bone-specific alkaline phosphatase for bone disease. We hypothesize that ALT2 circulates in serum and contributes variably (depending on disease etiology) to total ALT activity measured in currently available clinical assays. Furthermore, we hypothesize that ALT2 will be particularly elevated in patients with fatty liver and/or obesity, since ALT2, but not ALT1, is abundantly expressed in adipose tissue. To examine these hypotheses, we propose to develop an ALT isoenzyme-specific immunoassay. This assay will be used to measure serum levels of ALT isoenzymes in a host of disease states including liver disease and obesity (stable and during weight loss). We predict that serum ALT2 will be higher in patients with fatty liver or obesity and may be a clinically useful marker for this and other disease states.