Grants and Contracts Details
Description
Following spinal cord injury (SCI), intraspinal inflammation takes place through the activation of
endogenous glia and due to the destruction of microvasculature, leading to an influx of blood-
derived inflammatory cells such as neutrophils and monocyte-derived macrophages.
Macrophages, derived from microglia and monocytes, play different roles in SCI, ranging from
potentiating secondary injury (proinflammatory phenotype) to facilitating recovery and wound
healing (reparative phenotype). While macrophages of mixed phenotypes respond to SCI,
reparative macrophages are quickly overwhelmed by pro-inflammatory macrophages. Pro-
inflammatory macrophages persist after SCI hindering the healing process (1). Finding
therapies that can modulate macrophage function and harness their reparative potential
remains a challenge for the SCI field.
Previous work in the Gensel lab has identified azithromycin (AZM), an antibiotic commonly
prescribed to SCI individuals (2), as an immunomodulator therapy with clear clinical viability. In
SCI mice, oral AZM administration (160 mg/kg) after SCI increases reparative macrophage
activation leading to significant locomotor recovery and tissue sparing compared to animals
treated with vehicle (3). Further, when administered 30 minutes after SCI, lower doses (10
mg/kg) of AZM drive reparative macrophage activation (4). Later studies confirmed that post-
SCI AZM treatment – 160mg/kg 30 minutes or 3 hours after SCI – significantly improves motor
function (5). Subsequently, the efficacy of AZM for SCI has been independently replicated in
rats [7].
However, due to the possible side effects of systemic administration of antibiotics, this therapy
would benefit from a system that allows a more specific drug delivery. Specifically, free AZM
can upset the gastrointestinal (GI) system and may have negative cardiac effects (6). It has
already been demonstrated that L-AZM successfully targets immune cells over cardiomyocytes
in vitro and, in vivo, L-AZM significantly decreases mortality relative to an equivalent dose of
free AZM or vehicle in a mouse model of cardiac ischemia (7).
Most liposomal drug formulations attach polymers, commonly polyethylene glycol (PEG), to
increase liposome circulation and half-life [8]. PEG protects the liposome from uptake and
degradation by immune cells, primarily macrophages [9]. In our case, macrophage uptake is
desired, therefore, I will utilize non-PEGylated L-AZM developed by our collaborator Dr. Venditto
(7).
I hypothesize that L-AZM will polarize macrophages toward a pro-regenerative phenotype at a
lower dose and with fewer side effects with a broader therapeutic window than free AZM. I will
test this hypothesis through two specific aims:
Aim 1: Identify the optimal dose of L-AZM after SCI to alter macrophage phenotype.
Aim 2: Determine the therapeutic window of L-AZM administration for improving SCI recovery.
In Aim 1, I will perform dose-response studies comparing L-AZM and free AZM. The primary
outcome will be intraspinal macrophage gene expression using a similar approach developed in
the Gensel and Venditto labs (4, 7). I will also assess the gut microbiome of treated animals in
terms of composition, diversity, and expression of antibiotic-resistance genes (ARGs). Primary
selection criteria will be the lowest dose that results in significant changes in gene expression
towards a reparative macrophage phenotype. The secondary selection criteria will be the dose
that doesn’t lead to expression of ARGs and that does not significantly change the gut
microbiome, in that order.
Considering the clinical feasibility of drug administration after an SCI, it is desirable to have a
treatment with a broad therapeutic window. I hypothesize that the use of liposomes as a drug
delivery system will increase AZM’s therapeutic window since L-AZM will be administered I.V.
and will get to circulating macrophages sooner. This hypothesis is supported by clodronate
studies demonstrating that liposomal encapsulation is effective when initial administration is
delayed until 1 day after SCI (8). In Aim 2, I will administer the optimal dose selected in Aim 1 at
1 (proof-of-concept), 8 (earliest feasible clinical dose), or 24 hours (feasible dosing for most SCI
individuals) after the SCI. A battery of functional and anatomical assays will be used to
determine the optimal therapeutic window of L-AZM administration that leads to wound repair
and functional recovery.
Dr. John Gensel has extensive expertise in SCI neuroinflammation and AZM therapeutic
strategies, and he will supervise my training. He has mentored 3 postdocs into academic
research positions (100%). The proposed study will allow me to gain experience in SCI surgery
in mice, I.V. drug administration, microbiome assessment, tissue processing and analysis as
well as functional assays. This will complement my PhD training in nanoparticle administration
after rat SCI and gene expression analysis. This work will be crucial in my path toward
becoming an independent scientist with a focus on SCI immune modulation and will have a
meaningful impact in the field.
Status | Active |
---|---|
Effective start/end date | 7/1/24 → 6/30/26 |
Funding
- Wings for Life Spinal Cord Research Foundation: $144,200.00
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