Ketamine inhibits tumor necrosis factor secretion by RAW264.7 murine macrophages stimulated with antibiotic-exposed strains of community-associated, methicillin-resistant Staphylococcus aureus

Thomas Spentzas,Mark S Rayburn,Lauren Lazar,B Keith English,Elizabeth Meals,Rebekah Kh Shapley,Carlos Acuna Aguirre,Brett S Walker

doi:10.1186/1471-2172-12-11

Abstract

BackgroundInfections caused by community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA) are associated with a marked and prolonged host inflammatory response. In a sepsis simulation model, we tested whether the anesthetic ketamine inhibits the macrophage TNF response to antibiotic-exposed CA-MRSA bacteria via its antagonism of N-methyl-D-aspartate (NMDA) receptors. RAW264.7 cells were stimulated for 18 hrs with 105 to 107 CFU/mL inocula of either of two prototypical CA-MRSA isolates, USA300 strain LAC and USA400 strain MW2, in the presence of either vancomycin or daptomycin. One hour before bacterial stimulation, ketamine was added with or without MK-801 (dizocilpine, a chemically unrelated non-competitive NMDA receptor antagonist), APV (D-2-amino-5-phosphono-valerate, a competitive NMDA receptor antagonist), NMDA, or combinations of these agents. Supernatants were collected and assayed for TNF concentration by ELISA.ResultsRAW264.7 cells exposed to either LAC or MW2 in the presence of daptomycin secreted less TNF than in the presence of vancomycin. The addition of ketamine inhibited macrophage TNF secretion after stimulation with either of the CA-MRSA isolates (LAC, MW2) in the presence of either antibiotic. The NMDA inhibitors, MK-801 and APV, also suppressed macrophage TNF secretion after stimulation with either of the antibiotic-exposed CA-MRSA isolates, and the effect was not additive or synergistic with ketamine. The addition of NMDA substrate augmented TNF secretion in response to the CA-MRSA bacteria, and the addition of APV suppressed the effect of NMDA in a dose-dependent fashion.ConclusionsKetamine inhibits TNF secretion by MRSA-stimulated RAW264.7 macrophages and the mechanism likely involves NMDA receptor antagonism. These findings may have therapeutic significance in MRSA sepsis.

Highlights

Infections caused by community-associated strains of methicillin-resistant Staphylococcus aureus (CAMRSA) are associated with a marked and prolonged host inflammatory response
community-associated strains of methicillin-resistant Staphylococcus aureus (CA-MRSA) strains MW2 and LAC stimulated less TNF secretion by RAW264.7 murine macrophages in the presence of daptomycin than in the presence of vancomycin As previously observed with two USA300 CA-MRSA strains isolated from Memphis children with invasive staphylococcal infections [11], macrophages exposed to either of the two prototypical CA-MRSA strains studied secreted significantly less TNF in the presence of daptomycin as compared with vancomycin
We previously reported similar findings in six S. aureus clinical isolates, suggesting that this effect of daptomycin is conserved in many different S. aureus isolates

Summary

Introduction

Infections caused by community-associated strains of methicillin-resistant Staphylococcus aureus (CAMRSA) are associated with a marked and prolonged host inflammatory response. CA-MRSA isolates express many virulence factors [7,8], including several cytolysins: a-toxin, g-toxin, Panton-Valentine leukocidin (PVL), phenol-soluble modulins (PSMs), δ-toxin and, unlike traditional hospital-associated (HA-MRSA) isolates, may express superantigens such as TSST-1 [9] These bacterial components can stimulate massive cytokine release and lead to septic shock, acute respiratory distress syndrome (ARDS) and death. We previously reported that RAW264.7 murine macrophages exposed to any of a series of six pediatric clinical isolates of S. aureus (two CA-MRSA, two HAMRSA, and two methicillin-susceptible strains) in the presence of daptomycin (vs vancomycin) secreted less TNF and accumulated less inducible nitric oxide synthase (iNOS) protein [11]. The rapid lysis of staphylococci, streptococci and other pyogenic bacteria exposed to cell-wall active antibiotics such as beta-lactams and vancomycin results in exaggerated release of bacterial products and an augmented and potentially harmful host inflammatory response [15,16]. Optimal treatment of sepsis and other severe bacterial infections might include the use of antibiotics and/or other medications that blunt the host inflammatory response and dampen the cytokine cascade [16]

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