Abstract 19058: Role of Agxt2 in Metabolism of Adma in the Settings of Acute Elevation of Systemic Adma Levels

Abstract

Background: Endogenous inhibitor of nitric oxide synthases asymmetric dimethylarginine (ADMA) has been proposed to serve as an independent cardiovascular risk factor. The major pathway of ADMA degradation is hydrolysis catalyzed by dimethylarginine dimethylaminohydrolase (DDAH). ADMA can also be metabolized through a different pathway, by alanine:glyoxylate aminotransferase 2 (AGXT2), with the formation of α-keto-δ-(N,N-dimethylguanidino)valeric acid (DMGV). The goal of this study was to better characterize the role of the AGXT2 pathway in metabolism of ADMA in vivo using a recently developed assay for detection of DMGV in biological samples. Methods: ADMA (250 μmol x kg-1 x d-1) was infused in C57/BL6 mice for 3 days using osmotic minipumps implanted intraperitoneally. We performed bilateral nephrectomy in some of the mice 24 hours before the end of ADMA infusion and sample collection. Measurements of ADMA and DMGV were performed LC-MS/MS. Results: Infusion of ADMA for 3 days resulted in a 3.4 fold increase in plasma and in a 5.2 fold increase in urine ADMA levels. Elevation of ADMA concentration coincided with elevation of plasma and urine DMGV levels (2.9 and 3.9 folds respectively). Bilateral nephrectomy in the mice, which did not undergo ADMA infusion, did not increase plasma ADMA levels, while bilateral nephrectomy in the mice, which underwent ADMA infusion, led to a 1.7 fold increase in plasma ADMA levels and a 17.6 fold increase in DMGV levels. Neither bilateral nephrectomy nor infusion of ADMA for 3 days changed the AGXT2 mRNA levels in the liver. Conclusions: Infusion of ADMA leads to increased flux through the AGXT2 pathway of ADMA metabolism in vivo. The observation that each 1 μmol / mmol creatinine increase in ADMA level in urine leads to about 1 μmol / mmol creatinine increase in urine DMGV level suggests that AGXT2 is a major enzyme regulating ADMA levels in urine. The marked increase in DMGV levels in the mice lacking both kidneys suggests significant extrarenal production of DMGV in addition to absent renal excretion. Lack of increase in plasma ADMA levels after nephrectomy in mice infused with saline suggests that ADMA-metabolyzing ezymes are able to compensate for lack of renal excretion of ADMA in our model.