Azithromycin drives alternative macrophage activation and improves recovery and tissue sparing in contusion spinal cord injury

Abstract

BackgroundMacrophages persist indefinitely at sites of spinal cord injury (SCI) and contribute to both pathological and reparative processes. While the alternative, anti-inflammatory (M2) phenotype is believed to promote cell protection, regeneration, and plasticity, pro-inflammatory (M1) macrophages persist after SCI and contribute to protracted cell and tissue loss. Thus, identifying non-invasive, clinically viable, pharmacological therapies for altering macrophage phenotype is a challenging, yet promising, approach for treating SCI. Azithromycin (AZM), a commonly used macrolide antibiotic, drives anti-inflammatory macrophage activation in rodent models of inflammation and in humans with cystic fibrosis.MethodsWe hypothesized that AZM treatment can alter the macrophage response to SCI and reduce progressive tissue pathology. To test this hypothesis, mice (C57BL/6J, 3-month-old) received daily doses of AZM (160 mg/kg) or vehicle treatment via oral gavage for 3 days prior and up to 7 days after a moderate-severe thoracic contusion SCI (75-kdyn force injury). Fluorescent-activated cell sorting was used in combination with real-time PCR (rtPCR) to evaluate the disposition and activation status of microglia, monocytes, and neutrophils, as well as macrophage phenotype in response to AZM treatment. An open-field locomotor rating scale (Basso Mouse Scale) and gridwalk task were used to determine the effects of AZM treatment on SCI recovery. Bone marrow-derived macrophages (BMDMs) were used to determine the effect of AZM treatment on macrophage phenotype in vitro.ResultsIn accordance with our hypothesis, SCI mice exhibited significantly increased anti-inflammatory and decreased pro-inflammatory macrophage activation in response to AZM treatment. In addition, AZM treatment led to improved tissue sparing and recovery of gross and coordinated locomotor function. Furthermore, AZM treatment altered macrophage phenotype in vitro and lowered the neurotoxic potential of pro-inflammatory, M1 macrophages.ConclusionsTaken together, these data suggest that pharmacologically intervening with AZM can alter SCI macrophage polarization toward a beneficial phenotype that, in turn, may potentially limit secondary injury processes. Given that pro-inflammatory macrophage activation is a hallmark of many neurological pathologies and that AZM is non-invasive and clinically viable, these data highlight a novel approach for treating SCI and other maladaptive neuroinflammatory conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-015-0440-3) contains supplementary material, which is available to authorized users.

Predictive screening of M1 and M2 macrophages reveals the immunomodulatory effectiveness of post spinal cord injury azithromycin treatment

“…Specifically, AZM doses ranging from 10–160 mg/kg decreased M1 gene expression in macrophages while both the lowest (10 mg/kg) and highest (160 mg/kg) doses administered increased M2 macrophage gene expression. Previously, we observed that this AZM-mediated shift in polarization following a pretreatment paradigm is associated with improved tissue sparing and functional recovery14. Therefore, these findings highlight the potential for AZM to serve as an effective treatment for SCI.…”

“…Previously we observed that AZM treatment, begun prior to SCI, alters macrophage activation and improves tissue repair and functional recovery14. The purpose of this study was to determine if AZM treatment, initiated after SCI, alters the macrophage response to injury.…”

“…Specifically, AZM treatment in rodent and human inflammatory conditions is associated with improved outcomes coincident with alterations in macrophage phenotype and function7891011. Further, AZM alters macrophage phenotype in experimental stroke1213 and we recently discovered that AZM alters macrophage phenotype and improves recovery when treatment is initiated prior to SCI14. AZM is commonly used to treat infections in SCI individuals1516 and is therefore safe for this patient population, however, its effectiveness when delivered post-SCI is unknown.…”

Age increases reactive oxygen species production in macrophages and potentiates oxidative damage after spinal cord injury

“…The lesion epicenter for each animals was identified as the tissue section with the least amount of axon and myelin staining on cross-sections double-stained with Eriochrome cyanine/neurofilament (EC/NF) as described previously (Zhang et al, 2015a; 2015b). …”

Ryanodine Receptor 2 Plays a Critical Role in Spinal Cord Injury via Induction of Oxidative Stress

“…We found that knockdown of RyR2 significantly promoted the recovery of structural and functional injury in spinal cord, as evidenced by reduction of lesion volume and increase of BBB and CBS scores. Inflammation plays an important role in the injury of spinal cord after trauma and reduction of inflammation was considered to be an important intervention for SCI therapy [23,24]. Since downregulation of RyR2 prohibited the increase of proinflammatory cytokines IL-1β and TNFα, it was indicated that RyR2 was involved in the development of inflammation, which contributed to traumatic injury of spinal cord.…”