Abstract 162: Detection of N-alpha-acetyltransferase Activity Towards Endogenous Inhibitor of Nitric Oxide Synthase Asymmetric Dimethylarginine in the Liver and Kidneys

Background: Endogenous inhibitor of nitric oxide synthase asymmetric dimethylarginine (ADMA) has been proposed as a risk factor and mediator of cardiovascular diseases. ADMA can undergo hydrolysis by dimethylarginine dimethylaminohydrolase or be processed through an alternative pathway by alanine:glyoxylate aminotransferase 2. We and other have also shown that ADMA can be N-acetylated to form asymmetrical Nα-acetyldimethylarginine (Ac-ADMA). The goal of the study was to characterize this novel pathway in vivo and identify the organs, which are responsible for the ADMA-acetylating activity. Results: We infused ADMA in mice for three days. Control mice received saline infusion. Half of the mice underwent bilateral nephrectomy 24 hours before completion of the infusion, the rest had a sham surgery. ADMA infusion resulted in a 3.5 fold rise in plasma Ac-ADMA levels in the sham-operated mice (1.35 ± 0.45 nmol/L vs. 4.77 ± 0.88 nmol/L). In nephrectomized mice plasma Ac-ADMA levels were markedly increased even after saline infusion (45.08 ± 9.25 nmol/L) and further raised 5-fold after ADMA infusion (229.65 ± 91.30 nmol/L). We assessed tissue distribution of Ac-ADMA in mice and found the highest levels in pancreas, small intestine, liver and kidney. We incubated the lysates of those organs with ADMA for 24 hours and estimated production of Ac-ADMA. Only liver and kidney lysates showed significant increase in Ac-ADMA levels upon addition of ADMA (from 0.03 ± 0.01 nmol/μg protein to 0.18 ± 0.06 nmol/μg protein and from 0.06 ± 0.01 nmol/μg protein to 0.11 ± 0.02 nmol/μg protein). Conclusions: We showed that overload of ADMA leads to increase in plasma Ac-ADMA levels. This observation is consistent with the hypothesis that Ac-ADMA is formed from ADMA in vivo. The striking rise in plasma Ac-ADMA concentrations after bilateral nephrectomy suggests that Ac-ADMA is predominantly eliminated via the kidneys. We demonstrated that liver and kidney are the organs, in which acetylation of ADMA takes place. The high levels of Ac-ADMA in pancreas and intestine may be due to accumulation of Ac-ADMA in those organs. In the next step we want to identify the enzyme responsible for acetylation of ADMA and explore the clinical implications of this novel pathway of ADMA metabolism.