Elevated Asymmetric Dimethylarginine Alters Lung Function and Induces Collagen Deposition in Mice

Abstract

Increasing evidence suggests that lung mechanics and structure are maintained in part by an intimate balance between the L-arginine-metabolizing enzymes nitric oxide synthase (NOS) and arginase. Asymmetric dimethylarginine (ADMA) is a competitive endogenous inhibitor of NOS. The role of ADMA in the regulation of NOS and arginase in the airways has not yet been explored. Our objective was to investigate the role of ADMA in lung physiology. A murine model of continuous subcutaneous ADMA infusion via osmotic minipump was used for assessment of elevated ADMA in vivo, and primary lung fibroblasts were used for in vitro assessments. Two weeks after minipump placement, animals were anesthetized and mechanically ventilated, and lung mechanical responses were evaluated. Lungs were assessed histologically and biochemically for collagen content, arginase activity, and arginase protein levels. Lung lavage fluid was assessed for cellularity, nitrite, urea, and cytokine concentrations. ADMA infusion resulted in significantly enhanced lung resistance and decreased dynamic compliance in response to methacholine. These physiologic changes were associated with significantly increased lung collagen content in the absence of inflammation. Significant decreases in lung fluid nitrite were accompanied by elevated lung fluid urea and arginase activity in lung homogenates. These changes were reversed in mice 4 weeks after completion of ADMA administration. In addition, treatment of primary mouse lung fibroblasts with ADMA stimulated arginase activity and collagen formation in vitro. These data support the idea that ADMA may play a role in airway diseases, including asthma and pulmonary fibrosis, through NOS inhibition and enhancement of arginase activity.

Asymmetric dimethyl-arginine metabolism in a murine model of cigarette smoke-mediated lung inflammation

“…Greiss reagents (1% sulfanilamide and 0.1% napthylethylenediamine in 5% phosphoric acid; Ricca Chemical, Pocomoke, MD) were used to measure the nitrite concentrations in the lavage fluid (WT, n ¼ 9-15; DDAH Tg, n ¼ 9) as previously described (Wells et al, 2009). Calibration curves were made with NaNO 2 (Sigma) dissolved in PBS.…”

“…L-Arginine deficiency leads to uncoupling of NOS and oxidant formation (Boger et al, 2000;. It is established that elevated ADMA contributes to endothelial dysfunction (Raptis et al, 2014), pulmonary inflammation (Klein et al, 2010), and fibrosis (Wells et al, 2009). …”

Asymmetric dimethylarginine and asthma: results from the Childhood Asthma Prevention Study

“…Recent studies have demonstrated a potential contribution of imbalances in L-arginine metabolism to the development of airway hyperresponsiveness and airflow obstruction in asthma [6][7][8]. ADMA is an endogenous inhibitor of all isoforms of NOS and is produced by the methylation of L-arginine residues by protein methyltransferases.…”

L-Arginine Metabolism in the Lung: Reciprocal Regulation of the NOS and Arginase Pathways

“…Additionally, exogenous administration of ADMA to lung epithelial cells in vitro has been demonstrated to lead to uncoupling of NOS, resulting in the formation of superoxide [72]. Furthermore, chronic (2-week) exogenous administration of ADMA to mice resulted in increased arginase activity, collagen deposition and increased airways responsiveness to methacholine [78]. Further studies from the same group have recently shown that infusion concurrent with an ovalbumin sensitization and challenge regimen potentiates allergic inflammation [79].…”