Reply

Abstract

Reply We are responding to concerns raised in this Letter to the Editor that the solvent used during delivery of the specific caspase 1 inhibitor, AC-YVAD-cmk, to mice may have contributed to the observation that caspase 1 inhibition significantly increased the mortality in burn mice. We understand their concerns but wish to assure them and other readers that the concentration of solvent used in our studies was significantly lower than what has been reported to cause inflammation and increases in immune cell apoptosis in mice. The referenced study used 8 mg/kg of dimethyl sulfoxide (DMSO) before significant changes in immune cell apoptosis were observed (1). The amount of DMSO given with our AC-YVAD-cmk treatment was 0.5 mg/kg (2). This is 16-fold less than what was reported to cause apoptosis in mice. Other studies using DMSO to study changes in inflammatory cytokine production were done in vitro or at higher doses than what we used to deliver AC-YVAD-cmk (1, 3). Also, the stimulus used to induce inflammation was bacterial lipopolysaccharide (LPS), and the inflammatory reactions caused by LPS and trauma are not similar. In addition, one of the cytokines reported to be induced by DMSO exposure and LPS was interleukin 1β (IL-1β) (3). It is important to restate in this letter that we clearly showed that giving AC-YVAD-cmk in DMSO potently blocked injury-induced IL-1β production in vivo (2). Moreover, we performed in vivo dosing studies to demonstrate that giving AC-YVAD-cmk in DMSO to mice at doses that specifically reduced injury-induced caspase 1 activation led to significant mortality in burn mice. Finally, in control experiments comparing saline to vehicle (0.5 mg/kg DMSO), we found no measurable effect on mortality (n = 10 mice/group over 7 days) or systemic levels of injury-induced IL-6 production. We thank them for their opinions and interest in our research report. In closing, based on our findings, we are currently expanding our efforts to determine how inflammasome activation by injury protects mice from injury-induced complications. We recently found that caspase 1−/− mice also showed an enhanced inflammatory phenotype at 1 day after injury. Furthermore, a recent study using caspase 1−/− mice confirmed our findings showing that that caspase 1 was protective in a trauma mouse model of hemorrhagic shock with combined femur fracture (4). Thus, we are keenly interested in determining if stimulating inflammasome or caspase 1 activation could be used to protect from the acute complications of traumatic injuries. Akinori Osuka Marc Hanschen Veit Stoecklein James Lederer Brigham and Women’s Hospital Biomedical Research Institute and Harvard Medical School Boston, Massachusetts