Dimethylarginine Dimethylaminohydrolase 2 Regulates Nitric Oxide Synthesis and Hemodynamics and Determines Outcome in Polymicrobial Sepsis

Abstract

Objective— Nitric oxide is a key to numerous physiological and pathophysiological processes. Nitric oxide production is regulated endogenously by 2 methylarginines, asymmetric dimethylarginine (ADMA) and monomethyl- l -arginine. The enzyme that specifically metabolizes asymmetric dimethylarginine and monomethyl- l -arginine is dimethylarginine dimethylaminohydrolase (DDAH). The first isoform dimethylarginine dimethylaminohydrolase 1 has previously been shown to be an important regulator of methylarginines in both health and disease. This study explores for the first time the role of endogenous dimethylarginine dimethylaminohydrolase 2 in regulating cardiovascular physiology and also determines the functional impact of dimethylarginine dimethylaminohydrolase 2 deletion on outcome and immune function in sepsis. Approach and Results— Mice, globally deficient in Ddah2, were compared with their wild-type littermates to determine the physiological role of Ddah2 using in vivo and ex vivo assessments of vascular function. We show that global knockout of Ddah2 results in elevated blood pressure during periods of activity (mean [SEM], 118.5 [1.3] versus 112.7 [1.1] mm Hg; P =0.025) and changes in vascular responsiveness mediated by changes in methylarginine concentration, mean myocardial tissue asymmetric dimethylarginine (SEM) was 0.89 (0.06) versus 0.67 (0.05) μmol/L ( P =0.02) and systemic nitric oxide concentrations. In a model of severe polymicrobial sepsis, Ddah2 knockout affects outcome (120-hour survival was 12% in Ddah2 knockouts versus 53% in wild-type animals; P <0.001). Monocyte-specific deletion of Ddah2 results in a similar pattern of increased severity to that seen in globally deficient animals. Conclusions— Ddah2 has a regulatory role both in normal physiology and in determining outcome of severe polymicrobial sepsis. Elucidation of this role identifies a mechanism for the observed relationship between Ddah2 polymorphisms, cardiovascular disease, and outcome in sepsis.

Asymmetric and symmetric dimethylarginine as risk markers for total mortality and cardiovascular outcomes: A systematic review and meta-analysis of prospective studies

“…[72] Recent data from mice with impaired ADMA metabolism point in the same direction. [73] As expected, slight differences between studies were observed, with slightly smaller effects being reported in studies of higher quality (higher number of events, longer duration of followup and higher number of included confounders in the statistical analysis). In addition, associations were slightly stronger for studies that measured ADMA in plasma compared to studies measuring it in the serum.…”

Hypoxia causes increased monocyte nitric oxide synthesis which is mediated by changes in dimethylarginine dimethylaminohydrolase 2 expression in animal and human models of normobaric hypoxia

“…We postulate that this is one of the mechanisms by which animals deficient in DDAH2 demonstrate impaired monocyte function and elevated mortality in animal models of sepsis 31 and may in part explain the association between polymorphisms of the human DDAH2 gene and outcome in patients with septic shock 38 This study also highlights differing mechanisms in the synthesis of NO across species. In our murine studies, elevated iNOS was observed in isolated hypoxic primary murine macrophages consistent with previous studies of the impact of hypoxia on the inducible isoform of the enzyme 39 .…”

“…This suggests that DDAH2 regulation in hypoxia may be tissue specific and reflect differing adaptive responses to hypoxic stress. We have previously shown that global and macrophage specific knockout of DDAH2 in murine models of severe sepsis leads to a significant excess mortality which is mediated by impaired macrophage phagocytosis, bactericidal ability and NO synthesis 31 . Sepsis is a complex physiological insult in which multiple processes contribute to organ dysfunction and death.…”

“…We have previously shown that immune cells express only DDAH2 but not DDAH1 28,31 . See supplementary material for further details.…”

“…The two isoforms of DDAH have different tissue distributions 27,28 which lead to differing roles in both basal and pathological states. DDAH1 knockout or pharmacological inhibition leads to a hypertensive phenotype 29 and is protective in animal models of septic shock 30 whereas knockout of DDAH2 leads to minimal cardiovascular disturbance but profound immune dysfunction and excess mortality in sepsis 31 .…”