Genetic and pharmacological approaches to assess the therapeutic potential of DDAH1 inhibition in sepsis

Manasi Nandi1,2, Zhen Wang2, Raymond Stidwill2, Valerie Taylor2, James Leiper2. 1King’s College London, London, United Kingdom, 2University College London, London, United Kingdom.

Introduction: The leading cause of mortality in intensive care units is septic shock. The regulated release of nitric oxide (NO) plays an essential vasodilatory function in blood pressure regulation. However, following bacterial infection, inducible nitric oxide synthase (iNOS) is transcribed resulting in supranormal generation of NO, contributing to profound hypotension observed in septic shock. Asymmetric dimethylarginine (ADMA) is an endogenously produced competitive inhibitor of NOS. ADMA is metabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) of which there are 2 isoforms (DDAH1 and 2). We hypothesized that reducing DDAH1 activity would elevate endogenous ADMA and reduce excess NO production in septic shock. We used both pharmacological and genetic approaches to manipulate DDAH1 in in vivo models of septic shock (Lipopolysaccharide (LPS) induced endotoxemia).

Methods: Anesthetised rats (Wistar, male 250-350g) were instrumented with an arterial line for mean arterial blood pressure (MABP) recording. LPS was administered intravenously and MABP measured. Once MABP had fallen by 10-15% from baseline, the DDAH1 inhibitor or saline vehicle was administered at 3mg/kg or 30mg/kg and MABP recorded. DDAH1+/- mice and wild type littermates were instrumented with radiotelemetry devices for the measurement of conscious blood pressure. Mice were injected with LPS and conscious blood pressure monitored for 48 hours. Furthermore, the vascular responses to phenylephrine in endotoxic DDAH1+/- and wild type mice were assessed.

Results and conclusion: Both pharmacological inhibition and genetic haploinsufficiency of DDAH1 resulted in significant increases in ADMA. Administration of LPS in both the anesthetized and conscious septic shock models resulted in marked hypotension. However, rats administered with a pharmacological DDAH1 inhibitor or DDAH1+/- mice both displayed a significant attenuation of the observed hypotension and DDAH1+/- mice displayed enhanced contractile responses to phenylephrine. By utilising both pharmacological and genetic approaches, these results demonstrate that reducing DDAH1 activity may provide a novel mechanism to treat hypotension in septic shock.