Abstract 220: Regulation of Dimethylamine Dimethylaminohydrolase in the Liver

Introduction: Nitric Oxide (NO) is a crucial molecule in cardiovascular biology. Abnormalities in NO are critical in atherosclerosis and impairment of the NO pathway increases risk of cardiovascular disease (CVD). A possible cause of endothelial dysfunction is an elevation (in plasma) of the endogenous inhibitor of NO synthase, asymmetric dimethylarginine (ADMA). ADMA was initially described in renal failure. 80% of ADMA is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) in the liver. DDAH-1 is widely distributed and felt to be the major determinant of circulating ADMA levels. Very little data is available regarding the cause and effects of DDAH dysregulation in the liver. Understanding the biology of DDAH represents a target for better understanding of CVD and for novel therapy. Hypothesis: Diabetes and related factors will alter DDAH expression/activity potentially modulating the amount of ADMA. Methods: Liver tissues from control and db/db mice were archival. Human skeletal muscle tissue was obtained from cardiovascular surgical patients. HepG2 cells were used for low/high glucose treatment studies (5mM/25mM). DDAH-1 expression was determined using Western immunoblotting. DDAH activity measurement used a colourimetric assay. Intra/extracellular ADMA were measured in HepG2 cells using an HPLC-MS/MS technique. Results: In skeletal muscle from diabetic cardiac surgery patients DDAH-1 protein expression is increased ( P < 0.05). Further to this, db/db mice livers versus control had a significant increase in DDAH expression and activity. Using HepG2 cells we specifically examined the effect of 25mM glucose on DDAH-1. Treatment increased expression and activity of DDAH-1 ( P Conclusion: These novel results report an alteration of DDAH-1 expression and activity in hepatic tissues and cells in response to elevated glucose - a result which has not been reported previously. This suggests a possible link between the DDAH/ADMA/NOS pathway, diabetes, and glycaemic dysregulation - key risk factors in CVD.