Correlations of DDAH1 Transcript Variants with Human Endothelial Asymmetric Dimethylarginine Metabolizing Activity

BACKGROUND Dimethylarginine dimethylaminohydrolases 1 (DDAH1) is the major enzyme responsible for inactivation of asymmetric dimethylarginine (ADMA). This study seeks to clarify the correlations between mRNA expression levels of DDAH1 transcript variants and the relationship with ADMA metabolizing activity in human. METHODS The mRNA expression levels of DDAH1 transcript variants in primarily cultured human umbilical vein endothelial cells (HUVECs) and peripheral blood mononuclear cells (PBMCs) from healthy control subjects and patients suffering from both acute ischemic stroke (AIS) and acute myocardial infarction (AMI) were determined by real-time polymerase chain reaction. ADMA metabolizing activity of the cell lysates from HUVECs was determined by enzyme-linked immunosorbent assay. RESULTS A novel DDAH1 transcript variant DDAH1-V3 was identified. DDAH1-V3 mRNA expression correlated significantly with that of both -V2 (R = 0.811; P = 0.000008) and -V1 (R = 0.454; P = 0.04) in HUVECs. In PBMCs from healthy subjects, significant correlation was observed only between DDAH1-V2 and -V3 (R = 0.571; P = 0.001; n = 36). Delta threshold cycle (DCT) values for both DDAH1-V2 and -V3 transcripts were increased significantly in PBMCs from AIS patients (P < 0.05, respectively). In PBMCs from patients suffering from both AIS and AMI, positive pairwise correlations between mRNA levels of DDAH1 transcripts were also observed as analyzed by partial correlation analysis (P < 0.05, respectively). However, only mRNA expression level of the DDAH1-V1 transcript correlated significantly with intracellular ADMA metabolizing activity in HUVECs (R = 0.805; P= 0.002). CONCLUSIONS This study demonstrated that although there are positive correlations between mRNA expression levels of DDAH1 transcript variants, only the DDAH1-V1 transcript is responsible for ADMA metabolism, and transcript specific primers are recommended to determine DDAH1 mRNA expression.