Abstract 5649: Human Alanine: Glyoxylate Aminotransferase 2 Lowers ADMA and Protects From ADMA-induced Impairment in Nitric Oxide Production

Abstract

Elevated blood concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, are found in association with diabetes, hypertension, congestive heart failure and atherosclerosis. ADMA levels are controlled by dimethylarginine dimethyl-aminohydrolases, cytosolic enzymes which hydrolyze ADMA to citrulline and dimethylamine. ADMA also has been proposed to be regulated through an alternative pathway by alanine-glyoxylate aminotransferase 2 (AGXT2), an aminotransferase expressed primarily in the kidney. Little is known about the intracellular localization or activity of human AGXT2. The goal of this study was to define the subcellular localization of human AGXT2 and test the hypothesis that overexpression of human AGXT2 protects from ADMA-induced inhibition in nitric oxide (NO) production. AGXT2 was cloned from a human kidney cDNA library and overexpressed with a C-terminal FLAG epitope tag in COS-7 cells. Mitochondrial localization of human AGXT2 was demonstrated by confocal microscopy. A 41 amino acid N-terminal mitochondrial cleavage sequence was delineated by N-terminal sequencing of the mature protein. To determine the effect of AGXT2 on NO metabolism, human AGXT2 was overexpressed in MS-1 murine endothelial cells. Overexpression of AGXT2 protected MS-1 cells from ADMA-mediated inhibition of NO production. To determine the effect of AGXT2 on ADMA metabolism in vivo , human AGXT2 was overexpressed in the liver of C57BL/6 mice using an adenoviral expression vector. Four days after intravenous injection of the AGXT2 or control adenoviral vectors, mice receiving the AGXT2 vector had significantly lower levels of plasma and tissue ADMA compared with mice receiving the control vector (P<0.05). We conclude that mitochondrially localized human AGXT2 lowers ADMA and protects from ADMA-induced impairment in NO production.