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Azithromycin drives alternative macrophage activation and improves recovery and tissue sparing in contusion spinal
Bei Zhang1, William M Bailey2, Timothy J Kopper3,4
1Spinal Cord and Brain Injury Research Center, Department of Physiology, University of Kentucky, Lexington, KY, 40536, USA. bei.zhang@uky.edu.
Background:
Macrophages 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.
Methods:
We 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.
Results:
In 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.
Conclusions:
Taken 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.
Insights
Azithromycin (AZM) treatment shifts macrophages to an anti-inflammatory state, improving tissue sparing and locomotor function after spinal cord injury (SCI). This suggests AZM is a promising therapy for SCI and neuroinflammatory conditions.
Area of Science:
- Neuroscience
- Immunology
- Pharmacology
Background:
- Macrophages are crucial in spinal cord injury (SCI), with pro-inflammatory (M1) types causing tissue loss and anti-inflammatory (M2) types promoting repair.
- Targeting macrophage phenotype offers a promising therapeutic strategy for SCI.
- Azithromycin (AZM), an antibiotic, has shown anti-inflammatory effects in other models.
Purpose of the Study:
- To investigate if AZM treatment can modify macrophage response to SCI and reduce progressive tissue damage.
- To assess AZM's impact on macrophage polarization and functional recovery after SCI.
Main Methods:
- Mice received AZM or vehicle orally before and after moderate-severe thoracic contusion SCI.
- Flow cytometry and rtPCR analyzed immune cell activation and macrophage phenotype.
- Locomotor function was assessed using the Basso Mouse Scale and gridwalk task.
- In vitro studies with bone marrow-derived macrophages (BMDMs) determined AZM's direct effects on macrophage phenotype.
Main Results:
- AZM treatment significantly increased anti-inflammatory (M2) and decreased pro-inflammatory (M1) macrophage activation in SCI mice.
- Improved tissue sparing and recovery of locomotor function were observed in AZM-treated mice.
- AZM altered macrophage phenotype in vitro and reduced the neurotoxic potential of M1 macrophages.
Conclusions:
- Pharmacological intervention with AZM effectively shifts macrophage polarization towards a beneficial phenotype post-SCI.
- AZM treatment may limit secondary injury processes and offers a novel therapeutic approach for SCI.
- AZM's non-invasive and clinical viability makes it a potential treatment for SCI and other neuroinflammatory diseases.
