Abstract 219: Agxt2 Plays Important Role in Regulation of Urine Adma Levels After Acute Adma Loading in Mice
Background Multiple epidemiological studies demonstrated increased levels of an endogenous inhibitor of nitric oxide synthases asymmetric dimethylarginine (ADMA) in cardiovascular diseases. In addition to the well characterized pathway of ADMA hydrolysis by dimethylarginine dimethylaminohydrolase (DDAH) ADMA can also be metabolized through an alternative pathway by alanine:glyoxylate aminotransferase 2 (AGXT2), which converts ADMA to α-keto-δ-(N,N-dimethylguanidino)valeric acid (DMGV). The goal of this study was to better characterize the role of 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. Urine was collected for 24 hours in metabolic cages. Blood was collected by cardiac puncture. Measurements of ADMA and DMGV were performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS).
Results Intraperitoneal infusion of ADMA for 3 days resulted in an increase in plasma ADMA levels from 0.46±0.045 to 1.57±0.40 μM (p<0.05) and in urine ADMA levels from 36.4±3.4 to 188.6±31.5 μmol / mmol creatinine (p<0.05). Elevation of ADMA concentration coincided with elevation of plasma DMGV levels from 0.21±0.025 to 0.61±0.14 μM (p<0.05) and urine DMGV levels from 41.4±3.2 to 162.5±32.9 μmol / mmol creatinine (p<0.05). Bilateral nephrectomy in the mice, which underwent ADMA infusion, lead to a 1.7 fold increase in plasma ADMA levels and a 17.6 fold increase in DMGV levels compared with the mice from the sham group.
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 a ~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.
- © 2013 by American Heart Association, Inc.