Acute axon damage and demyelination are mitigated by 4-aminopyridine (4-AP) therapy after experimental traumatic brain injury

Abstract

Damage to long axons in white matter tracts is a major pathology in closed head traumatic brain injury (TBI). Acute TBI treatments are needed that protect against axon damage and promote recovery of axon function to prevent long term symptoms and neurodegeneration. Our prior characterization of axon damage and demyelination after TBI led us to examine repurposing of 4-aminopyridine (4-AP), an FDA-approved inhibitor of voltage-gated potassium (Kv) channels. 4-AP is currently indicated to provide symptomatic relief for patients with chronic stage multiple sclerosis, which involves axon damage and demyelination. We tested clinically relevant dosage of 4-AP as an acute treatment for experimental TBI and found multiple benefits in corpus callosum axons. This randomized, controlled pre-clinical study focused on the first week after TBI, when axons are particularly vulnerable. 4-AP treatment initiated one day post-injury dramatically reduced axon damage detected by intra-axonal fluorescence accumulations in Thy1-YFP mice of both sexes. Detailed electron microscopy in C57BL/6 mice showed that 4-AP reduced pathological features of mitochondrial swelling, cytoskeletal disruption, and demyelination at 7 days post-injury. Furthermore, 4-AP improved the molecular organization of axon nodal regions by restoring disrupted paranode domains and reducing Kv1.2 channel dispersion. 4-AP treatment did not resolve deficits in action potential conduction across the corpus callosum, based on ex vivo electrophysiological recordings at 7 days post-TBI. Thus, this first study of 4-AP effects on axon damage in the acute period demonstrates a significant decrease in multiple pathological hallmarks of axon damage after experimental TBI.

Neuronal tau pathology worsens late-phase white matter degeneration after traumatic brain injury in transgenic mice

“…This time point of 8 weeks of age at the time of injury is matched to our prior studies characterizing the distinct s-TBI and r-mTBI injury models using neuropathology, electron microscopy, MRI, and behavior analyses [ 10 , 54 , 56 , 63 , 90 ]. The acute phase post-surgical and neuropathology data from these prior studies are similar to the results in the Tg2541 mice across wild-type, hemizygous, and homozygous genotypes.…”

“…Additional axon pathology is associated with disorganization of the molecular components of the node of Ranvier and the flanking paranodes, where myelin sheaths attach to axons. Node of Ranvier abnormalities have been identified in this s-TBI mouse model, in a swine rotational TBI model, and in human TBI cases [ 54 , 63 , 73 ]. Demyelination can lead to further neurodegeneration since myelination protects vulnerable denuded axons and provides bioenergetic and trophic support [ 50 , 66 ], which is of interest in neurodegenerative processes of Alzheimer’s disease [ 52 ].…”

“…Varied pathology, particularly the extent of corpus callosum axon damage in these two different injury models, was tested relative tau transgene dosage to inform interpretation of heterogeneous patient populations. As extensively characterized in adult wild-type mice, the s-TBI model produces traumatic axonal injury that progresses to corpus callosum atrophy, with features that model clinical findings of neuropathology and MRI of patients with TBI [ 10 , 33 , 54 , 56 , 63 , 73 ]. Similarly, the r-mTBI model has also been previously characterized in wild-type mice using neuropathology and MRI [ 90 ].…”

Chemical and biophysical characterization of novel potassium channel blocker 3-fluoro-5-methylpyridin-4-amine

“…Its mechanism of action involves binding to voltage-gated K + (K v ) channels exposed due to demyelination, reducing the aberrant efflux of K + ions and enhancing axonal conduction 4 – 13 . Additionally, 4AP has demonstrated potential clinical utility for spinal cord injury 14 – 19 , traumatic brain injury 20 , and other diseases involving demyelination 21 . Based on the mechanism of action of 4AP, it has been proposed that upregulated K + channels in demyelinated axons could be targeted for imaging demyelination using positron emission tomography (PET) 22 , 23 .…”