Combinational Spinal GAD65 Gene Delivery and Systemic GABA-Mimetic Treatment for Modulation of Spasticity

Abstract

BackgroundLoss of GABA-mediated pre-synaptic inhibition after spinal injury plays a key role in the progressive increase in spinal reflexes and the appearance of spasticity. Clinical studies show that the use of baclofen (GABAB receptor agonist), while effective in modulating spasticity is associated with major side effects such as general sedation and progressive tolerance development. The goal of the present study was to assess if a combined therapy composed of spinal segment-specific upregulation of GAD65 (glutamate decarboxylase) gene once combined with systemic treatment with tiagabine (GABA uptake inhibitor) will lead to an antispasticity effect and whether such an effect will only be present in GAD65 gene over-expressing spinal segments.Methods/Principal FindingsAdult Sprague-Dawley (SD) rats were exposed to transient spinal ischemia (10 min) to induce muscle spasticity. Animals then received lumbar injection of HIV1-CMV-GAD65 lentivirus (LVs) targeting ventral α-motoneuronal pools. At 2–3 weeks after lentivirus delivery animals were treated systemically with tiagabine (4, 10, 20 or 40 mg/kg or vehicle) and the degree of spasticity response measured. In a separate experiment the expression of GAD65 gene after spinal parenchymal delivery of GAD65-lentivirus in naive minipigs was studied. Spastic SD rats receiving spinal injections of the GAD65 gene and treated with systemic tiagabine showed potent and tiagabine-dose-dependent alleviation of spasticity. Neither treatment alone (i.e., GAD65-LVs injection only or tiagabine treatment only) had any significant antispasticity effect nor had any detectable side effect. Measured antispasticity effect correlated with increase in spinal parenchymal GABA synthesis and was restricted to spinal segments overexpressing GAD65 gene.Conclusions/SignificanceThese data show that treatment with orally bioavailable GABA-mimetic drugs if combined with spinal-segment-specific GAD65 gene overexpression can represent a novel and highly effective anti-spasticity treatment which is associated with minimal side effects and is restricted to GAD65-gene over-expressing spinal segments.

Intramuscular Neurotrophin-3 normalizes low threshold spinal reflexes, reduces spasms and improves mobility after bilateral corticospinal tract injury in rats

“…Although it may result in adverse systemic side effects and increasing tolerance during long-term treatment, it is evident that increasing inhibition in the spinal cord is an effective treatment for spasticity. Spasticity is associated with a decrease of inhibitory synapses and inhibitory post-synaptic potentials in motor neurons ( Kapitza et al, 2012 ; Kakinohana et al, 2012 ; Boulenguez et al, 2010 ) plus concurrent increase of excitatory synapses upon and persistent inward currents in motor neurons ( Tan et al, 2012 ; Toda et al, 2014 ; Bennett et al, 2001 ; Hultborn et al, 2013 ). We give evidence that there is an increase of vGluT1 boutons from proprioceptive afferents onto motor neurons and less presynaptic inhibition of proprioceptive afferents in the cervical spinal cord after bilateral pyramidotomy.…”

“…This reorganization can involve maladaptation causing functional abnormalities such as spasticity. Proposed mechanisms of spasticity include increased activity and connectivity between proprioceptive Ia muscle afferents and motor neurons, reduced presynaptic inhibition of Ia afferents by spinal interneurons ( Toda et al, 2014 ; Kakinohana et al, 2012 ), reduced autogenic inhibition from Golgi tendon organs (via Ib afferents and inhibitory interneurons), reduced reciprocal inhibition by Ia afferents from antagonist muscles and modified excitation and inhibition from muscle spindle group II afferents reviewed in [ Nielsen et al, 2007 ; Dietz, 2002 ]) as well as intrinsic changes in motor neurons such as altered ion channels, serotonergic receptors and transporter concentrations in the membranes ( Boulenguez et al, 2010 ; Murray et al, 2011 ) and an increase in persistent inward currents in motor neurons ( Hultborn et al, 2013 ; Boulenguez et al, 2010 ; Bennett et al, 2001 ; ElBasiouny et al, 2010 ) which together cause an increase in motor neuron excitability.…”

Amelioration of motor/sensory dysfunction and spasticity in a rat model of acute lumbar spinal cord injury by human neural stem cell transplantation

“…While under specific pathological conditions (such as inflammatory or neuropathic pain) spinal GABA can have excitatory effects due to reduced expression of the potassium-chloride exporter KCC2 [75,76], systematic experimental but also clinical studies have demonstrated a potent anti-spasticity effect after intrathecal treatment with the GABA B receptor agonist baclofen, suggesting continuing inhibitory GABA B receptor-mediated action [77,78]. In addition, we have recently demonstrated an effective anti-spastic effect after spinal parenchymal GAD65 (glutamate decarboxylase) upregulation if combined with systemic tiagabine (GABA uptake inhibitor) treatment in animals with spinal ischemia-induced muscle spasticity [79]. Jointly, these data suggest the anti-spasticity effect observed in our current study can be mediated by a synaptically coupled GABA-inhibitory effect.…”

Thoracic 9 Spinal Transection-Induced Model of Muscle Spasticity in the Rat: A Systematic Electrophysiological and Histopathological Characterization

“…Using this system coupled with rat models of spinal ischemic injury, L3 compression injury or spinal air-embolism-induced injury we have demonstrated the presence of velocity-dependent increase in muscle resistance which correlates with an increased EMG activity in gastrocnemius muscle [ 28 – 30 ]. In subsequent studies using the spinal ischemic model and spinal air embolism model of muscle spasticity we have demonstrated: i) a potent anti-spastic effect after spinal or systemic treatment with baclofen [ 31 ], tizanidine [ 32 ], NGX424 [ 13 ], ii) the effect of a combined anti-spastic therapy after spinal upregulation of GAD65 gene and systemic treatment with tiagabine [ 33 ], and, iii) development of baclofen tolerance in rats infused intrathecally with baclofen using a miniosmotic pump [ 34 ] and effective suppression of spasticity in baclofen-tolerant animals after systemic treatment with AMPA receptor antagonist NGX424 [ 35 ].…”