Response to “Asymmetric Dimethylarginine and DDAH1 Transcript Variants in Cardiovascular and Cerebrovascular Diseases”

To the Editor: This letter is in response to “Letter to the Editor: Asymmetric Dimethylarginine and DDAH1 Transcript Variants in Cardiovascular and Cerebrovascular Diseases” by Tsuda. In our recently published article, we described a novel DDAH1 transcript designated as DDAH-V3 in humans and observed that only the DDAH1-V1 transcript was correlated with asymmetric dimethylarginine (ADMA) metabolic activity in primarily cultured human umbilical vein endothelial cells (HUVECs).1 We also observed decreased DDAH1-V2 and DDAH1-V3 mRNA expression in peripheral blood mononuclear cells (PBMCs) from patients with acute ischemic stroke (AIS) or acute myocardial infarction (AMI).1 However, considering that circulation ADMA is derived mainly from the vascular endothelium and the abundance of DDAH1 is low in PBMCs, as we observed (Figure 1A), we failed to report the relationship between the expression levels of DDAH1 transcripts in PBMCs and plasma ADMA levels in patients in our study. Chen et al. reported that plasma ADMA levels are elevated within 7 days after AIS onset.2 A cross-sectional study in patients with documented MI also indicated that the ADMA peak levels (between 06:00 a.m. and 7:59 a.m.) precede the AMI peak in symptom onset (between 10:00 a.m. and 11:59 a.m.), which suggests a possible causal relationship between ADMA and AMI.3 An inverse relationship between plasma ADMA and high-density lipoprotein (HDL), which is a risk factor of AMI, is also observed in AMI patients within 24 hours after symptom onset.4 These findings indicate increased plasma ADMA levels in patients with ischemic cardiovascular and cerebrovascular diseases during the clinical stages. The effects of TNF-α treatment on DDAH1 transcript mRNA and protein expression in cultured HUVECs. DDAH1 protein expression in HUVEC-C cell line, primarily cultured HUVECs, and PBMCs (A). Effects of TNF-α treatment on mRNA expression of DDAH1 transcript variants at concentrations of 25ng/ml, 50ng/ml, and 100ng/ml, respectively; n = 3, *P < 0.05, **P < 0.01, as compared with the control group (B). Effects of TNF-α treatment on DDAH1 protein expression at concentrations of 25ng/ml, 50ng/ml, and 100ng/ml, respectively; n = 3, *P < 0.05, as compared with the control group (C). Abbreviations: DDAH1, dimethylarginine dimethylaminohydrolase 1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HUVEC, human umbilical vein endothelial cell; PBMCs, peripheral blood mononuclear cells; TNF-α, tumor necrosis factor α. We are in agreement with Dr. Tsuda that it is meaningful to clarify whether mRNA expression levels of DDAH1 transcript variants precede the changes in plasma ADMA levels. We believe that further cross-sectional studies will be needed to answer this question. Inflammation is a characteristic event for both AIS and AMI, which are two critical clinical stages of cardiovascular and cerebrovascular diseases. Increased plasma levels of inflammatory cytokines such as tumor necrosis factor-α (TNF-α) are observed in AIS and AMI. Our recent study showed that the mRNA expression of both DDAH1-V1 and DDAH1-V2 were decreased significantly at 24 hour after TNF-α treatment at a relatively high concentration (100ng/ml) in cultured HUVECs (Figure 1B). At the same time, DDAH1-V3 mRNA expression was decreased significantly by TNF-α treatment at concentration of 25ng/ml and in a concentration-dependent manner (Figure 1B). We also observed that 37 kD DDAH1 protein expression (encoded by the common DDAH1-V1 transcript) was decreased by 24-hour TNF-α treatment at concentrations of both 50ng/ml and 100ng/ml in HUVECs (Figure 1C). Our data indicate that DDAH1 protein expression might be decreased in clinical stages of AIS and AMI at least partially by TNF-α and that this may lead to an increase in plasma ADMA during the onset of these diseases. Of course, further clinical studies are warranted. The authors declared no conflict of interest. This work was supported by Chinese National Science Foundation (No.81170091 and No. 81373489), funds for the Central University (2011JQ016), and Hunan Provincial Natural Science Foundation of China (13JJ1010).