Trovafloxacin attenuates neuroinflammation and improves outcome after traumatic brain injury in mice
Trovafloxacin is a broad-spectrum antibiotic, recently identified as an inhibitor of pannexin-1 (Panx1) channels. Panx1 channels are important conduits for the adenosine triphosphate (ATP) release from live and dying cells that enhances the inflammatory response of immune cells. Elevated extracellular levels ATP released upon injury activate purinergic pathways in inflammatory cells that promote migration, proliferation, phagocytosis, and apoptotic signals. Here, we tested whether trovafloxacin administration attenuates the neuroinflammatory response and improves outcomes after brain trauma.
The murine controlled cortical impact (CCI) model was used to determine whether in vivo delivery of trovafloxacin has anti-inflammatory and neuroprotective actions after brain trauma. Locomotor deficit was assessed using the rotarod test. Levels of tissue damage markers and inflammation were measured using western blot, qPCR, and immunofluorescence. In vitro assays were used to evaluate whether trovafloxacin blocks ATP release and cell migration in a chemotactic-stimulated microglia cell line.
Trovafloxacin treatment of CCI-injured mice significantly reduced tissue damage markers and improved locomotor deficits. In addition, trovafloxacin treatment significantly reduced mRNA levels of several pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), which correlates with an overall reduction in the accumulation of inflammatory cell types (neutrophils, microglia/macrophages, and astroglia) at the injury zone. To determine whether trovafloxacin exerted these effects by direct action on immune cells, we evaluated its effect on ATP release and cell migration using a chemotactic-stimulated microglial cell line. We found that trovafloxacin significantly inhibited both ATP release and migration of these cells.
Our results show that trovafloxacin administration has pronounced anti-inflammatory and neuroprotective effects following brain injury. These findings lay the foundation for future studies to directly test a role for Panx1 channels in pathological inflammation following brain trauma.
KeywordsBrain injury Neuroinflammation Microglia Pannexin Hemichannel
Brilliant Blue FCF
Controlled cortical impact
Cluster of differentiation
Dulbecco ‘s Modified Eagle Medium
Glial fibrillary acidic protein
Glyceraldehyde 3-phosphate dehydrogenase
Ionized calcium-binding adapter molecule 1
Matrix metalloproteinase 9
Traumatic brain injury
Tumor necrosis factor alpha
Trovafloxacin is a fluoroquinolone antibiotic that exerts bactericidal activity by inhibiting prokaryotic topoisomerase enzymes, which are important for cellular division . Recently, trovafloxacin was demonstrated to target human pannexin 1 (Panx1) channels at therapeutic concentrations reached in blood plasma . Studies in mice have shown that Panx1 inhibition by trovafloxacin leads to dysregulated fragmentation of dying cells and blockade of ATP release . Panx1 channels are large transmembrane pores that, besides ions, are permeable to small molecules such as ATP; they are expressed in various cell types [3, 4]. Recently, Panx1 channels have emerged as important players in response to injury and inflammation [5, 6, 7]. ATP release via Panx1 channels enhances inflammatory responses in peripheral immune cells and is implicated in the activation of the inflammasome [4, 6, 8]. Additionally, Panx1 channels expressed in endothelial cells can regulate the acute vascular inflammation by potentiating leukocyte emigration via ATP release . In the brain, neuronal Panx1 channel activation during ischemia or cortical spreading depression is thought to be an important mechanism for mediating neuronal dysfunction and death [10, 11, 12, 13]. Although it is likely that Panx1 channels also contribute to neuroinflammatory responses upon brain injury, their potential as therapeutic targets in traumatic brain injury (TBI) remains elusive.
The primary damage induced by mechanical brain trauma results in necrotic death of neurons, glial cells, and blood vessels [14, 15, 16]. The dying tissue produces damage-associated molecular pattern molecules (DAMPs, including ATP), which initiate and maintain an inflammatory response. The neuroinflammatory response is characterized by activation and migration of microglia and glial cells, leukocyte infiltration, and upregulation of inflammatory mediators [17, 18]. Elevated extracellular levels of ATP released upon injury have been shown to enhance the inflammatory response [19, 20]. ATP activates the purinergic pathway in inflammatory cells, thus playing an important role in migration, proliferation, phagocytosis, and apoptotic signals [21, 22, 23, 24]. There is compelling evidence demonstrating that Panx1 channels, in part, represent a cellular mechanism for ATP release to the external milieu during inflammation [7, 25].
By taking advantage of previous work assessing the pharmacological properties of trovafloxacin in mice [2, 26, 27], we aimed to evaluate the potential role of trovafloxacin administration on curtailing inflammation in the controlled cortical impact (CCI) model of TBI. We found that in vivo administration of trovafloxacin significantly attenuated the inflammatory response in CCI injured mice. In addition, it decreased tissue damage and improved locomotor deficits. Our results also indicate that trovafloxacin diminish the accumulation of microglia and macrophages at the injury zone. In vitro studies showed that trovafloxacin as well as other Panx1 channel blockers inhibited ATP release and cell migration of a stimulated microglia cell line. We propose that a reduced number of pro-inflammatory cells at the injury site in trovafloxacin treated mice might be related to lesser migration and could contribute to improve outcomes after TBI.
Animal handling and CCI
All procedures were performed in accordance with the institutional guidelines and approved by the Institutional Animal Care and Use Committee of Rutgers-New Jersey Medical School. C57BL/6 mice (Charles River, USA) were housed two per cage during pre- and post-operative procedures with a 12-h light-dark cycle with ad libitum access to water and chow.
Ten-week-old-male mice were subjected to CCI injury using the stereotaxic impactor Impact One™ (Leica Biosystems, USA). Animals were secured in a stereotaxic frame and anesthetized with isoflurane (induction at 3% and maintenance at 2%) administered through a nose mask. A midline incision was made over the skull. A unilateral craniectomy was performed between Bregma and Lambda using a hand drill with a 5-mm-diameter trephine. Special care was taken to prevent any damage to the dura mater, therefore assuring it was intact after each craniotomy. Animals were impacted using a 4.0-mm stainless steel flat impactor tip, at stereotaxic coordinates AP − 2.26, ML + 2.0 and 0.65 mm deep at a rate of 4.0 m/s and a dwell time of 200 ms, at an angle of 0.4°. After injury, any bleeding was cleaned up, the incision was sutured with clips, and the animals were immediately removed from anesthesia. Post-surgery, the mouse was placed on its back in a cage, which was set over a heating pad. The recovery of each mouse was observed until they were standing on their four paws. Sham animals went through the same procedures as CCI-injured animals, including anesthesia and skin incision over the skull, but not craniotomy, as it has been shown that the craniotomy procedure alone stimulates production of pro-inflammatory cytokines at 24 h after surgery , which would confound our analyses. The stock of trovafloxacin (100 mM) was prepared in DMSO and was then diluted to 1:10 in saline. Trovafloxacin-treated group was given intraperitoneal injections of 60 mg/kg at 1, 24, and 48 h post-CCI injury. Non-treated CCI-injured animals received vehicle only.
Total RNA extraction, reverse transcription, and real-time PCR (RT-qPCR)
Injured cortex was carefully dissected from the ipsilateral hemisphere using an adult mouse brain slicer. Total RNA was isolated using Trizol (Thermo Fisher scientific, USA) according to the manufacturer’s protocol. Two micrograms of RNA was reverse transcribed using High Capacity RNA-to-cDNA kit (Thermo Fisher scientific, USA). TaqMan® Universal PCR Master Mix and TaqMan® FAM™ conjugated primers (Thermo Fisher Scientific, USA) were used to evaluate mRNA using the ABI 7500 Sequence Detection System (Applied Biosystems, USA). mRNA expression was normalized to GAPDH as endogenous control, and the relative fold difference in expression was calculated using the comparative 2−ΔΔCT, a widely used method to present relative expression respect to controls (shams) [29, 30]. The following primer genes were assessed: IL-1β (Accession#Mm00434228_m1), TNF-α (Accession#Mm00443258_m1), IL-6 (Accession #Mm00446190_m1), MPO (Accession #Mm01298424_m1), GAFP (Accession #Mm01253033_m1), CD68 (Accession #Mm03047343_m1), and Iba1 (Accession #Mm00520165_m1). GAPDH (Accession #Mm99999915_g1) was used as an endogenous control. The ΔΔCT method was used to calculate the relative gene expression levels respect to shams.
Total protein extraction and western blot analysis
Brain tissues enclosing the injury were carefully dissected from the ipsilateral cortex under a dissecting microscope and then homogenized in buffer containing M-PER Mammalian protein extraction reagent 5 mM Na3VO4, 1 mM NaF, 1 mM Na2P2O7, 1 mM Bezamidine, 5 mM EDTA, and Halt Protease Inhibitor Cocktail (Thermo Fisher scientific, USA). Protein concentrations were estimated using a BCA kit (Pierce, USA). Equal amounts of protein (20 μg) per sample was separated on 4–20% gradient gels (Bio-Rad, USA) and run under the same experimental conditions, transferred to PVDF membranes, and probed with the following antibodies: GFAP (Cell Signaling, USA), CD68 (Abcam, USA), α–ΙΙ spectrin (Santa Cruz Biotechnology, USA), MMP-9 (NeuroMab, USA), and GAPDH (Cell Signaling, USA). Blots were developed using enhanced chemiluminescence, and densitometric analysis was performed using Fuji Images or Bio-Rad Image Lab software.
BV-2 cell line was previously generated by others through infection of murine primary microglial cells with a v-raf/v-myc oncogene carrying retrovirus . This cell line has been found to retain some of the morphological, phenotypical, and functional properties of freshly isolated microglial cells and is considered immortalized microglial cells . BV-2 cells were seeded at a density of 7.5 × 105 cells/ml and maintained in DMEM/F-12 supplemented with 5% FBS, penicillin 100 IU/ml, and streptomycin 100 μg/mL. Cell cultures were kept in a cell incubator at 37 °C with 95% air and 5% CO2 and saturated humidity.
ATP release measurements
Extracellular ATP release was measured using the ATP bioluminescence assay kit (Molecular Probe, USA) following the manufacturer’s instructions. BV-2 cells were seeded in 24-well culture plates at a cell density of 1.5 × 105 cells/well in serum-free DMEM media supplemented with 4 mM L-glutamine. After 24 h, cells were treated with C5a (10 nM) in the presence or absence of Panx1 channel blockers trovafloxacin (1 μM), Brilliant Blue FCF (5μM) or 10Panx1 (200 μM) in serum-free DMEM medium. Extracellular ATP was measured before C5a stimulation and every 10 min thereafter. At the indicated time points, 10 μl aliquots from a total volume of 300 μl were collected from the culture supernatants for ATP determinations.
Migration assay was performed using 24-well plates and 8.0-μm pore size transwell inserts (Corning Costar, NY, USA). BV-2 cells suspended in serum-free medium were seeded at a density of 1.5 × 105 cells/ml/well in the upper chamber of the transwell insert. Cells were allowed to attach overnight. Then, the cells were stimulated with C5a (10 nM) or ATP (200 μM) in the presence or absence of pannexin channel blockers trovafloxacin (1 μM), Brilliant Blue FCF (5μM) or 10Panx1 (200 μM). At 4 or 24 h post treatment, cells were fixed with 4% paraformaldehyde (PFA) and stained with 0.05% crystal violet. BV-2 cells that did not migrate were removed from upper chamber by wiping with cotton swabs. Cells that migrated to the bottom of the filters were quantified from at least 5 images taken from different fields taken at 20× using an Olympus AX70 microscope.
Brain sample preparation for histology and immunofluorescence
For morphological analysis, CCI-injured mice were anesthetized with ketamine/xylazine at 6 days post-injury and transcardially perfused with RPMI media containing heparin (1000 USP units/ml) at a rate of 4 ml/min followed by 4% PFA in PBS, pH 7.4 at a rate of 5 ml/min. Once the animals were fixed, mice were decapitated and the whole brains were removed, taking care to keep the contusion region intact. After fixation, brains were immersed in 30% sucrose for 24 h and frozen − 80 °C until sectioning. Twenty micrometer coronal sections were made from whole brains using a cryostat.
Brain sections were taken at room temperature for 20 min. Then, they were washed twice with tris buffer 1× (TBS), pH 7.4 and permeabilized with 0.3% triton X-100 in TBS in a humid chamber at room temperature for 30 min. Sections were washed again with TBS and incubated in TBS buffer containing 10% BSA, 10% Normal Donkey Serum, pH 7.4 (TDB) in humid chamber at room temperature for 1 h. Primary antibody against CD68 (Bio-Rad, USA) diluted 1:300 in TDB diluent containing 20% TDB solution, 0.2% triton X-100, and 80% TBS pH 7.4 were applied to the slides and kept in a humid chamber at 4 °C for 12 h. The sections were washed for 5 min in TBS and then incubated with secondary antibodies (Cy3™ or Alexa Fluor 488 Donkey Anti-Rabbit IgG) from Jackson Immunoresearch (West Grove, USA) diluted 1:300 in TDB diluent were applied on the sections at room temperature for 2 h. Tissue slides were washed with 1× TBS buffer for 5 min. Samples were counterstained with 4′,6-diamidino-2-phenylindole (DAPI) for nuclear staining at 1:10,000 dilution for 10 min at room temperature in a humid chamber. Slides were rinsed twice with 1× TBS for 5 min each. Glass cover slips were mounted on the samples on glass slides with fluorescent mounting medium containing anti-fade (Gelvatol containing DABCO). Slides were left to dry at room temperature for 24 h and then stored at 4 °C. Images were captured using 10× objective in up-right fluorescence BX51 Olympus microscope and injury areas were evaluated using ImageJ software.
Quantification of areas for high-density immunofluorescence of CD68 positive microglial/macrophage cells
The core of the injury was morphologically identified as the region with the deepest damage in serial sections. At 6 days post injury, we identified a lesion zone with a bottom of approximately 600-μm diameter centered around the stereotactic coordinates of the epicenter (AP − 2.26, ML 2.0). This lesion zone was filled with a high density of CD68+ cells. The areas of high-density CD68+ cells were measured using the ImageJ 1× software . Using a slide scale under 4× objective in the fluorescence microscope, the pixels equivalent to 1 mm (388 pixels) were identified and set to scale in the ImageJ software. Using the polygon selection tool, high-density immunofluorescence of CD68+ cells were selected to enclose an area of injury. This area was measured in square millimeter and plotted against the distance from Bregma. To keep the fluorescence intensity levels uniform across all slides, they were stained all at the same time and images were acquired using the same settings and time exposure to minimize threshold bias.
Rotarod performance test
Mice were placed on a rotarod machine (IITC Life Sciences, USA) that has an accelerating rotating cylinder suspended over a platform. When the animal falls the platform is displaced and the machine records the latency in seconds for the animal to fall. This acquisition phase was performed at days 1, 3, and 5 after injury, (3 trials per day). Mice were trained in the rotarod for 3 days before CCI injury; last training day was considered the baseline testing. Sham, CCI vehicle, and CCI + trovafloxacin mice were evenly grouped on the basis of their average latency to fall.
One-way or two-way ANOVA followed by Tukey’s HSD (honest significant difference) test was used to determine statistical significance in migration assay and western blot analysis, respectively. Linear regression analysis was performed for time series of measurements using treatment and the interaction between treatment and time as factors. These analyses include ATP assays, RT-qPCR, and behavior. For immunofluorescence of CD68 analysis, linear regression was performed using treatment and the interaction of treatment and distance from Bregma as factors. Analyses were performed using SPSS 15.0 (IBM) or R statistical software. All experiments were performed at least three times. The values were expressed as the means ± SEM. The differences with p < 0.05 were considered statistically significant. Values are represented as means ± SEM. Differences with p values < 0.05 were considered statistically significant.
Trovafloxacin improves locomotor recovery and reduces tissue damage in CCI-injured mice
To determinate whether the improvements observed in the behavioral outcome of trovafloxacin-treated mice correlate with neuroprotective actions after CCI, we analyzed protein levels of matrix metallopeptidase 9 (MMP9) and neuronal α–ΙΙ spectrin breakdown products (SBDPs) in CCI-injured mice treated with vehicle or trovafloxacin. MMP9 and SBDPs are general biomarkers for brain injury, such as TBI, in rodents and humans [34, 35]. Figure 1b shows that MMP-9 levels were sixfold higher in the CCI-injured group as compared to the sham group. Conversely, mice treated with a daily i.p. injection of trovafloxacin for up to 3 days post CCI showed a significant reduction in MMP-9 levels when compared to vehicle-treated CCI animals. The protein levels of full-length α–ΙΙ spectrin (250 kDa) and SBDP (140 and 120 kDa) were also examined at the cortex at 6 days post CCI (Fig. 1c). Full α–ΙΙ spectrin and SBDP 140 kDa remain unchanged in all three groups; conversely, the levels SBDP 120 kDa levels were noticeable higher in vehicle-treated CCI mice when compared to sham and trovafloxacin-treated mice. This suggests that brain injury-induced neuronal proteolysis in CCI-injured mice is reduced by trovafloxacin treatment. We also did not find differences in biomarker levels in sham mice treated with vehicle or trovafloxacin (Additional file 1: Figure S1).
Trovafloxacin decreases mRNA levels of pro-inflammatory cytokines and activated innate immune and glia cells after CCI
Microglia and macrophage accumulation is reduced in CCI -injured mice treated with trovafloxacin
Trovafloxacin inhibits ATP release and microglial migration in vitro by inhibition of Panx1 channels
In the present study, we found that administration of trovafloxacin to CCI-injured mice produced anti-inflammatory and neuroprotective effects and, importantly, ameliorated CCI-induced locomotor impairment. The beneficial effects of trovafloxacin treatment in this animal model of TBI are supported by (1) decreased tissue damage that correlated with improved locomotor behavioral outcomes; (2) significantly reduced mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) at their corresponding expression peaks; (3) reduced mRNA levels of infiltrating neutrophils (MPO), reactive astrocytes (GFAP), microglia and macrophage cells (CD68, Iba-1), which was corroborated by immunofluorescence, and western blot analyses; and (4) in vitro assays demonstrating a trovafloxacin-dependent reduction in migration of stimulated microglial cell lines via blockade of extracellular ATP release.
Although trovafloxacin was originally described as a broad-spectrum antibiotic, it has been recently shown that it is a blocker for Panx1 channels. Thus, it is possible to hypothesize that Panx1 channel activation after brain trauma enhances the neuroinflammatory responses via ATP release. Other potential routes of ATP release that are involved in stroke-induced neurodegeneration [11, 50] implicated Cx43 hemichannels or Panx2 channels; however, these channels are not blocked by trovafloxacin . Moreover, data from our laboratory indicate that trovafloxacin does not block other large ATP permeable pores including Cx26, Cx46, and CALHM-1 channels (unpublished results). It is important to note, however, that trovafloxacin was withdrawn from the market relatively soon after its release as a generic antibiotic due to the risk of hepatotoxicity . Trovafloxacin-induced hepatotoxicity appears to occur in conjunction with episodes of inflammatory stress associated with high levels of TNF-α in blood plasma. For example, a single trovafloxacin dose of 80 mg/kg or greater caused hepatotoxicity in LPS-treated mice, but 1000 mg/kg trovafloxacin in mice non-treated with LPS did not exert toxic effects . In the present study, we used daily doses of 60 mg/kg via i.p that was not extended for more than 3 days post-injury. Interestingly, this dosage was enough to attenuate TBI-induced neuroinflammatory events that peak at 6 days post-injury suggesting that early action of trovafloxacin is critical in affecting the later progression of the neuroinflammatory response.
Fluoroquinoline antibiotics including alatrofloxacin and trovafloxacin have previously been shown to have immunosuppression effects in infected monocytes and macrophages [52, 53, 54]; however, no mechanisms of actions have been described. More recent work has shown that trovafloxacin might inhibit α-adrenoreceptors and suppress the activation of the peroxisome proliferator-activated receptor alpha (PPARα) in the liver [55, 56]. While the blockade of α-adrenoreceptors by trovafloxacin seems to be mediated by direct interactions, the mechanism by which trovafloxacin suppresses PPARα activation is still unclear. The role of these two receptors in brain trauma has also been well documented; crucially, it has been shown that activation, but not inhibition, of these receptors is neuroprotective after brain injury [57, 58, 59, 60]. For example, there is compelling evidence that activation of PPARα promotes anti-inflammatory and neuroprotective effects in several models of brain trauma [61, 62, 63, 64]. Moreover, blockade of α-adrenoreceptors increases behavioral deficits in traumatic brain injury . Therefore, it is unlikely that inhibition of α-adrenoreceptors and PPARα by trovafloxacin contributes to neuroprotection in our model of brain injury since, then, we would expect opposite results. Moreover, the fact that another Panx1 channel blocker like Brilliant Blue FCF has similar effects to trovafloxacin, at least at 1 day post-CCI supports the idea that trovafloxacin may have neuroprotective actions by inhibiting Panx1 channels. However, this hypothesis needs to be tested directly in future studies.
Several studies indicate that blockade or global deletion of Panx1 after stroke is neuroprotective [11, 12, 13, 65]. Panx1 is ubiquitously expressed in the brain, identified in both neurons and astrocytes. Also, leukocytes, microglia, and endothelial cells express Panx1 protein. Thus, it is possible that the beneficial effects exerted by trovafloxacin involve multiple neuronal and non-neuronal cell types. For instance, neuronal Panx1 activation via src-kinase has been recently shown to be deleterious in ischemia-induced excitotoxicity in vitro and in vivo [66, 67]. Moreover, endothelial Panx1 is also essential for leukocyte emigration in the acute inflammatory response by acting as a conduit for ATP release , whereas neuronal and astrocytic activation of Panx1 induces inflammasome activation in vitro .
Among the multiple cell types that could be targeted by trovafloxacin in our model of TBI, we focused on the accumulation of pro-inflammatory microglia and macrophages at the core of the injury site. In addition to cell proliferation, the accumulation of inflammatory cells requires infiltration of leukocytes (neutrophils and monocytes) and microglial migration. These events are mediated by activation of purinergic signaling via extracellular ATP and its byproducts . Several sources for ATP release upon injury have been described; an important contributor is the Panx1 pathway activated by dying cells. These cells function as a signal beacon to direct or point innate immune cells towards apoptotic cell death activity [24, 45]. Autocrine release of ATP from infiltrating innate immune cells is also associated with Panx1 channel activation and might contribute to cellular migration . Consistent with this idea, we found that trovafloxacin significantly reduced extracellular ATP release from C5a-stimulated BV-2 cells. It also prevented cell migration without affecting purinergic receptor activation and downstream signaling. Thus, our in vitro data may partially explain the decreased accumulation of leukocytes and microglial cells observed at the injury site of CCI animals treated with trovafloxacin. A reduction in the number of pro-inflammatory cells at the ipsilateral side in CCI mice treated with trovafloxacin also correlates with the lower mRNA levels detected for pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) when compared to vehicle-treated CCI mice. Accumulation of activated pro-inflammatory microglia and macrophage cells can promote the release of various pro-inflammatory factors, which in turn are detrimental to neuronal health and eventually causes cell death [69, 70]. Microglial cells in the activated state, in the cortical area, persist for at least 1 year in animal models of TBI, indicating a chronic inflammatory process induced by brain trauma . Indeed, the inflammatory-based progression of TBI in human postmortem studies shows that microglial activation remains for up to 17 years after TBI in subcortical brain areas [72, 73]. Thus, further studies are necessary to evaluate the role of Panx1 in the acute and chronic activation states of microglia and macrophage cells.
SBPD 120 kDa and MMP9, two well-known biomarkers associated with the worsening of brain injury after trauma, were found at high levels in vehicle-treated CCI mice, but were significantly reduced in trovafloxacin-treated CCI mice. SBPD 120 kDa is a byproduct of the neuronally expressed α–ΙΙ spectrin and is generated from sequential cleavage by caspase-3 proteases, which are activated upon neuronal injury and indicative of apoptotic cell death [74, 75]. Furthermore, pathological activation of MMPs, in particular MMP-9, has been shown to promote detrimental outcomes after brain injury, including blood brain barrier disruption, hemorrhage, and neuronal apoptosis [76, 77]. Hence, a reduction of the levels of MMP-9 in CCI mice treated with trovafloxacin might also contribute to the smaller hematomas observed in fixed brain from this group when compared to those that were treated only with vehicle.
To further link the actions of trovafloxacin with the blockade of Panx1 channel, we used Brilliant blue FCF another well-known Panx1 channel blocker . As expected, Brilliant Blue FCF markedly reduced C5a-induced ATP release and migration in BV-2 cells in vitro further supporting a role for Panx1 channels. Importantly, Brilliant Blue FCF is a derivative of Brilliant Blue G; the latter has been shown to have anti-inflammatory and neuroprotective actions in mice and rats after traumatic brain injury [78, 79]. While Brilliant Blue G blocks both P2X7 channels and Panx1 channels, Brilliant Blue FCF only inhibits Panx1 channels . Here, we found that mice treated with Brilliant blue FCF 1 h post-injury showed significant reduction of mRNA levels of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α (Additional file 2: Figure S2). Lastly, our preliminary data show that mice treated daily with Brilliant Blue FCF (i.p. injection, 60 mg/kg) display a trend towards improved locomotor outcomes after 5 days post-injury (unpublished results). Unlike trovafloxacin, previous studies have shown that Brilliant Blue FCF is poorly absorbed from the gastrointestinal tract, and following absorption, it goes through extensive and rapid biliary and urinary excretion [80, 81]. Hence, further studies are necessary to find optimal doses and frequency of administration of Brilliant Blue FCF to establish a neuroprotective role in our model of brain trauma.
Trovafloxacin treatment reduces inflammation and brain damage in a model of moderate TBI. We propose that the anti-inflammatory and neuroprotective actions of trovafloxacin are linked to the blockade of Panx1 channels due to the known roles of Panx1 channels in neuronal death during ischemia and infiltration of leukocytes during acute inflammation [9, 67, 11]. It is therefore possible that opening of Panx1 channels might potentiate the secondary damage response triggered by brain trauma. Future studies addressing the cell-type specific role of Panx1 in TBI will enhance our understanding and contribute to the development of Panx1 channels as a therapeutic target to improve outcome after brain injury.
We thank Ms. Yu Liu for her technical support.
This research was supported by the New Jersey Commission for Brain Injury Research (Pre-doctoral CBIR14FEL006 to C. Garg, CBIR13IRG015 to F. Calderon, CBIR15IRG018 to J.E. Contreras) and Health Resources and Services Administration through grant D34HP26020 to New Jersey Medical School Hispanic Center of Excellence (to support F. Calderon and J.E. Contreras).
Availability of data and materials
The datasets analyzed during the current study are available from the corresponding author on reasonable request
Study concept and design were contributed by FC and JEC. Experiments were performed by CG, JHS, JR, and FC. Analysis and interpretation of data were contributed by CG, JHS, FC, and JEC. Statistical analyses were performed by JMH. The manuscript was written by FC and JEC. Study supervision was contributed by FC and JEC. All authors read and approved the final manuscript.
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