Methicillin-resistant Staphylococcus aureus (MRSA) sepsis is a severe condition associated with vascular leakage and poor prognosis. The hemodynamic management of sepsis targets hypotension, but there is no specific treatment available for vascular leakage. Arginine vasopressin (AVP) has been used in sepsis to promote vasoconstriction by activating AVP receptor 1 (V(1)R). However, recent evidence suggests that increased fluid retention may be associated with AVP receptor 2 (V(2)R) activation worsening the outcome of sepsis. Hence, we hypothesized that inhibition of V(2)R activation ameliorates the severity of microvascular hyperpermeability during sepsis. The hypothesis was tested using a well-characterized and clinically relevant ovine model of MRSA pneumonia/sepsis and in vitro assays of human lung microvascular endothelial cells (HMVECs). In vivo experiments demonstrated that the treatment of septic sheep with tolvaptan (TLVP), an FDA-approved V(2)R antagonist, significantly attenuated the sepsis-induced fluid retention and markedly reduced the lung water content. These pathological changes were not affected by the treatment with V(2)R agonist, desmopressin (DDAVP). Additionally, the incubation of cultured HMVECs with DDAVP and DDAVP along with MRSA significantly increased the paracellular permeability. Finally, both the DDAVP and MRSA-induced hyperpermeability was significantly attenuated by TLVP. Subsequent protein and gene expression assays determined that the V(2)R-induced increase in permeability is mediated by phospholipase C beta (PLCβ) and the potent permeability factor angiopoietin-2. In conclusion, our results indicate that the activation of the AVP-V(2)R axis is critical in the pathophysiology of severe microvascular hyperpermeability during Gram-positive sepsis. The use of the antagonist TLVP should be considered as adjuvant treatment for septic patients. The results from this clinically relevant animal study are highly translational to clinical practice.
