Hydroxproline Catabolism and Hyperoxaluria

描述（由申请人提供）：原发性高草酸尿I型和2型（PH1和PH2）的特征是由于丙氨酸-乙醛酸氨基转移酶和乙醛酸还原酶的功能缺陷而无法有效代谢乙醛酸盐。过量的草酸合成导致并最终可能导致肾功能衰竭。到目前为止，还没有一种疗法可以专门减少草酸盐的合成。羟脯氨酸代谢是迄今为止唯一被确认的乙醛酸盐的来源。我们假设饮食和内源性羟脯氨酸的分解有助于PH1和PH2患者合成大量草酸盐。这一假设的证实表明，抑制羟脯氨酸降解可能是减少PH患者内源性草酸产生的重要治疗机会。作为验证这一假设的第一步，我们已经合成了均匀标记的13c -羟脯氨酸，并验证了它可以使用色谱技术结合质量检测来跟踪羟脯氨酸降解为草酸盐、乙醇酸盐、乳酸盐和甘氨酸。本研究的具体目的是：(1)利用均匀标记的Hyp， 13c5 -羟脯氨酸作为代谢示踪剂，定量测定正常人和PH患者羟脯氨酸代谢对内源性草酸合成的贡献；(2)利用13c5 -羟脯氨酸定量测定PH小鼠KO模型（Agxt和Grhpr KO）中羟脯氨酸代谢对内源性草酸合成的贡献。通过对代谢物中同位素标记的定量和跟踪，我们将能够证明羟脯氨酸的降解是否有助于内源性乙醇酸和草酸的合成。此外，小鼠数据将基准羟脯氨酸的贡献尿乙醇酸和草酸在每个遗传设置。后一种数据将是无价的治疗方法的未来测试针对羟脯氨酸降解途径的独特酶。

DESCRIPTION (provided by applicant): Primary hyperoxaluria types I and 2 (PH1 and PH2) are characterized by an inability to efficiently metabolize glyoxylate as a consequence of functional defects in alanine-glyoxylate aminotransferase and glyoxylate reductase, respectively. Excessive oxalate synthesis results and may ultimately cause renal failure. To date, there are no therapies that can specifically reduce oxalate synthesis. Hydroxyproline metabolism is the only recognized source of glyoxylate that has been identified to date. We hypothesize that the breakdown of dietary and endogenous hydroxyproline contributes to the bulk of the oxalate synthesized in PH1 and PH2 patients. Confirmation of this hypothesis would suggest that the inhibition of hydroxyproline degradation may be a significant therapeutic opportunity for diminishing endogenous oxalate production in PH patients. As a first step toward testing this hypothesis, we have synthesized homogeneously labeled 13C-hydroxyproline and verified that it can be used to follow the degradation of hydroxyproline to oxalate, glycolate, lactate, and glycine using chromatographic techniques coupled to mass detection. The specific aims of the proposed research are: (1) to quantitate the contribution of hydroxyproline metabolism to endogenous oxalate synthesis in normal human subjects and patients with PH using homogeneously-labeled Hyp, 13C5-hydroxyproline, as a metabolic tracer; (2) to quantitate the contribution of hydroxyproline metabolism to endogenous oxalate synthesis in mouse KO models of PH (Agxt and Grhpr KO) using 13C5-hydroxyproline. Through the quantitation and tracking of the isotopic label within metabolites, we will be able to demonstrate whether or not hydroxyproline degradation contributes to endogenous glycolate, and oxalate synthesis. Moreover, the mouse data will benchmark the contribution of hydroxyproline to urinary glycolate and oxalate in each genetic setting. This latter data will be invaluable for the future testing of therapeutics targeting the unique enzymes of the hydroxyproline degradation pathway. PUBLIC HEALTH RELEVANCE: The synthesis of oxalate, a key component of kidney stones, is influenced by glyoxylate levels. Glyoxylate is produced from hydroxyproline during the normal degradation of collagen within the body and that consumed in the diet. The purpose of this study is to determine whether or not hydroxyproline degradation contributes adversely to the elevated levels of glyoxylate and oxalate production observed in primary hyperoxaluria patients.