Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS) and has been implicated in endothelial dysfunction. ADMA is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), with DDAH2 representing the predominant endothelial DDAH isoform. Symmetric dimethylarginine (SDMA), also originating from arginine methylation by protein arginine methyltransferases, is an inhibitor of intracellular arginine uptake. In both chronic pulmonary hypertensive rats and patients suffering from idiopathic pulmonary arterial hypertension (IPAH; NYHA class III and IV), a marked increase in plasma ADMA and SDMA levels, as well as tissue levels of asymmetric and symmetric dimethylated proteins, was observed. Moreover, when comparing lung tissue from pulmonary hypertensive rats and IPAH patients to corresponding normal lung tissue, expression of DDAH2 was found to be reduced at both the mRNA and the protein level with no significant changes in DDAH1 expression. These findings were further supported by demonstrating a decrease in DDAH2 function in the experimental pulmonary hypertension model. Immunohistochemistry in human and rat control tissue demonstrated both isoforms of DDAH in the endothelial layer and in the alveolar epithelium. In contrast, in pulmonary hypertensive tissue, the immunoreactivity of DDAH2 in pulmonary endothelium was significantly decreased compared with DDAH1. Therefore, altogether we can conclude that enhanced dimethylarginine levels may contribute to vascular abnormalities in pulmonary arterial hypertension. Suppression of endothelial DDAH2 expression and function represents an important underlying mechanism.

Background: The reliability of gene expression profiling-based technologies to detect transcriptional differences representative of the original samples is affected by the quality of the extracted RNA. It strictly depends upon the technique that has been employed. Hence, the present study aimed at systematically comparing silica-gel column (SGC) and guanidine isothiocyanate (GTC) techniques of RNA isolation to answer the question which technique is preferable when frozen, long-term stored or fresh lung tissues have to be evaluated for the downstream molecular analysis.

Circulating anucleate platelets contain minute amounts of residual megakaryocytic-derived mRNA. To study cell type-specific gene expression in platelets, an accurate and sensitive method to detect and quantify platelet mRNA that excludes contamination with leukocyte RNA is mandatory. Applying laser-assisted microdissection and manipulation (LMM) we could isolate platelets from hemalaun-stained cytospins under permanent visual control and after laser-photolysis of nucleated blood cells. For mRNA quantification, the platelet-specific mRNAs were subsequently measured by real time RT-PCR. High-copy beta3 integrin and low-copy a alpha2 integrin as well as tissue factor (TF) transcripts were analyzed in LMM-harvested platelets. In 91.2% (83/91) beta3 integrin was detectable with a mean threshold cycle (CT) value of 32.5+/-3.2 (< or =50,000 cells). The low-copy a 2 integrin mRNA was positive in 84.4% (38/45) with CT mean value of 36.9+/-1.3, indicating that the relative expression of alpha2 integrin mRNA in platelets was about 130 times lower than beta3. The TF transcript was undetectable in all samples. Comparing platelet mRNA from LMM isolation to that from limiting dilution series resulted in a high accordance for beta3 integrin transcript in both, recovery (91.2% vs. 95.2%) and CT value (32.5 vs. 32.8). These results demonstrate that the combination of LMM and real-time RT-PCR is a valuable tool for precise, platelet-specific mRNA analysis without contamination of other cells.

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS) and has been implicated in endothelial dysfunction. ADMA is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), with DDAH2 representing the predominant endothelial DDAH isoform. Symmetric dimethylarginine (SDMA), also originating from arginine methylation by protein arginine methyltransferases, is an inhibitor of intracellular arginine uptake. In both, chronic pulmonary hypertensive rats and patients suffering from idiopathic pulmonary arterial hypertension (IPAH; NYHA class III), a marked increase in plasma ADMA and SDMA levels as well as tissue levels of asymmetric and symmetric dimethylated proteins was observed. Moreover, when comparing lung tissue from pulmonary hypertensive rats and IPAH patients to corresponding normal lung tissue, expression of DDAH2 was found to be reduced at both, the mRNA and the protein level, with no significant changes in DDAH1 expression. These findings were further supported by demonstrating a decrease in DDAH2 function in the experimental pulmonary hypertension model. Immunohistochemistry in human and rat control tissue demonstrated both isoforms of DDAH in the endothelial layer and the in the alveolar epithelium. In contrast, in pulmonary hypertensive tissue, the immunoreactivity of DDAH2 in pulmonary endothelium was significantly decreased compared to DDAH1. Therefore, altogether we can conclude that enhanced dimethylarginine levels may contribute to vascular abnormalities in pulmonary arterial hypertension. Suppression of endothelial DDAH2 expression and function represent an important underlying mechanism.