Chief Investigator: Professor Bevyn Jarrott
Associate Investigators: Mr Robert Weston
Steering Committee: Dr Henry De Aizpurua, Professor Peter McIntyre, Professor John Furness
Lead Organisation: Howard Florey Institute
VNI Funding: $126,341
Project Dates: 1 December 2006 - 30 November 2007

Project Summary:

HFI-1 proves more efficacious than mexiletine in decreasing recovery time and damage in a reversible spinal cord injury model in rats.

Background:

Spinal cord injury (SCI) predominantly occurs in young adults and, depending upon the spinal level of the injury, results in a variety of complications including motor and sensory deficits, respiratory distress, autonomic and sexual dysfunction and neuropathic pain. Our research focuses on developing drugs to minimise the effects of SCI.

Aims:

Thus we undertook a study of a mexiletine analog, HFI-1, which has both sodium channel blocking and antioxidant properties, to assess its efficacy as a neuroprotectant following SCI and compare its effects to mexiletine.

Methods:

Male Hooded Wistar rats were anaesthetised, and laminectomy performed at spinal level T12. An inflatable balloon catheter was inserted rostral, underneath the vertebra, to T10 and inflated for 5 minutes, causing reversible paraplegia.¹ This model demonstrates a slow, graded return of hindlimb motor function over 15 days, which has allowed us to assess the ability of putative neuroprotective drugs such as minocycline and AM-36 to accelerate recovery.² Mexiletine (12.5mg/kg, i.p.; n=8), HFI-1 (6mg/kg; 30mg/kg, i.p.; n=10 & 9) or vehicle controls (n=11) were administered at 3h after the injury and twice daily thereafter, until killed. Behavioural tests were conducted every 3 days. At 15d post-injury, rats were anaesthetised and transcardially perfused, to fix the spinal cords. Sections were cut and processed to examine the size of the cyst and modulatory effects of HFI-1 on lesion formation. An additional cohort was utilised to examine the effects of mexiletine and HFI-1 on caspase-3 expression and axonal damage using ELISA assays. In a more severe SCI model, using a spinal cord impactor, the effects of mexiletine and HFI-1 on neuropathic pain were examined using the plantar test.

Results:

All rats had almost complete functional recovery by 15d. HFI -1 treatment significantly decreased recovery time in behavioural outcomes following SCI, as seen in the ladder walking test, BBB scale and inclined ledged beam; with differences from untreated rats at 9d and 12d. Vehicle-treated rats only showed significantly improved function in the behavioural outcomes at 12d and 15d post-SCI. Mexiletine and HFI-1 reduced volume of damage following SCI by ~25% and ~50%, whilst axonal damage, assessed by sera phosphorylated neurofilament-H levels, was significantly reduced following HFI-1 (~70%) and mexiletine (~30%) treatment. Additionally, mexiletine and HFI-1 significantly reduced neuronal cell loss, glial reactivity and caspase-3 expression following transient SCI and reduced neuropathic pain following SCI induced with the spinal cord impactor. HFI-1 at the higher dose of 25mg/kg was more potent and efficacious than mexiletine, affording significantly greater protection following SCI.

Conclusions:

These data indicate that HFI-1 affords significantly greater protection than mexiletine and may be a potential neuroprotective drug for the treatment of SCI.

References:
1. Feldblum, S. et al (2000) Journal of Neurotrauma, 17:1079-1093.
2. Weston, R.M. et al (2004) International Neurotrauma Symposium 7: PB-61.

Researchers on this project attended the following conferences through the VNI conference support scheme:
Professor Bevyn Jarrott, Howard Florey Institute

- Neuroscience 2007, San Diego, California, 7 November, 2007

Mr Robert Weston, University of Melbourne

- 28th Annual Meeting for the Australian Neuroscience Society, Hobart, Tasmania, 27-30 January 2008

Awards:

Best poster, Neurological disease category, 2008 Australian Neuroscience Society Conference in Hobart.
WESTON RM, JARROTT B. HFI-1 decreases recovery time and reduces neurological damage in a partially reversible SCI model in rats.