Abstract 250: Kidney and Liver are the Main Organs of Alanine: Glyoxylate Aminotransferase 2 Expression in Humans

Abstract

Background: Numerous epidemiological studies have demonstrated an association between elevated levels of the endogenous inhibitor of nitric oxide synthases asymmetric dimethylarginine (ADMA) with cardiovascular diseases. ADMA can be hydrolysed by dimethylarginine dimethylaminohydrolase (DDAH). It can also be metabolized through a much less explored alternative pathway by alanine:glyoxylate aminotransferase 2 (AGXT2), which converts ADMA to α-keto-δ-(N,N-dimethylguanidino)valeric acid (ADGV). It has been shown in previous Northern Blot and in-situ RNA-hybridisation experiments that the kidney is the main organ of Agxt2 expression in rats, while RT-PCR and Western Blot studies suggested that Agxt2 is expressed in the mouse kidney and liver at comparable levels. The goal of the current study was to analyse the expression of the enzyme in human tissues. Methods and Results: We performed immunohistochemical staining using two rabbit polyclonal anti-AGXT2 antibodies in both frozen and paraformaldehyde-fixed samples from a normal tissue bank. We saw the strongest expression of AGXT2 using both of the antibodies in the proximal convoluted tubule of the kidney and in the liver with a homogenous pattern throughout all the samples. We also observed weak staining in the skeletal and heart muscle. Aorta, small intestine and lungs were negative for AGXT2 expression. We also confirmed our immunohistochemistry data by RT-PCR. Conclusions: Our current data suggest that both hepatocytes and kidney tubular epithelial cells are the major sources of AGXT2 in humans. We are currently designing experiments to show the direct localization of AGXT2 in a human cell.