Novel regenerative drug, SPG302 promotes functional recovery of diaphragm muscle activity after cervical spinal cord injury.

Spinal cord hemisection at C 2 (C 2 SH), sparing the dorsal column is widely used to investigate the effects of reduced phrenic motor neuron (PhMN) activation on diaphragm muscle (DIAm) function, with reduction in DIAm activity on the injured side during eupnoea. Following C 2 SH, recovery of DIAm EMG activity may occur spontaneously over subsequent days/weeks. Various strategies have been effective at improving the incidence and magnitude of DIAm recovery during eupnoea, but little is known about the effects of C 2 SH on transdiaphragmatic pressure (P di ) during other ventilatory and non-ventilatory behaviours. We employ SPG302, a novel type of pegylated benzothiazole derivative, to assess whether enhancing synaptogenesis (i.e., enhancing spared local connections) will improve the incidence and the magnitude of recovery of DIAm EMG activity and P di function 14-days post C 2 SH. In anesthetized Sprague Dawley rats, DIAm EMG and P di were assessed during eupnoea, hypoxia/hypercapnoea and airway occlusion prior to surgery (C2SH or sham), immediately post-surgery and at 14-days post-surgery. In C 2 SH rats, 14 days of DMSO (vehicle) or SPG302 treatments (IP injection) occurred. At the terminal experiment, maximum P di was evoked by bilateral phrenic nerve stimulation. We show that significant EMG and P di deficits are apparent in C 2 SH compared to sham rats immediately after surgery. In C 2 SH rats treated with SPG302, recovery of eupneic, HH and occlusion DIAm EMG was enhanced compared to vehicle rats after 14 days. Treatment with SPG302 also ameliorated Pdi deficits following C 2 SH. In summary, SPG302 is an exciting new therapy to explore for use in spinal cord injuries. KEY POINTS: Despite advances in our understanding of the effects of cervical hemisection (C 2 SH) on diaphragm muscle (DIAm,) EMG activity, very little is understood about the impact of C 2 SH on the gamut of ventilatory and non-ventilatory transdiaphragmatic pressures (P di ). Recovery of DIAm activity following C 2 SH is improved using a variety of approaches, but very few pharmaceuticals have been shown to be effective. One way of improving DIAm recovery is to enhance the amount of latent local spared connections onto phrenic motor neurons. A novel pegylated benzothiazole derivatives enhances synaptogenesis in a variety of neurodegenerative conditions. Here, using a novel therapeutic SPG302, we show that 14 days of treatment with SPG302 ameliorated DIAm EMG and P di deficits compared to vehicle controls. Our results show that SPG302 is a compound with a very promising potential for use in improving functional outcomes post spinal cord injury. Abstract Figure Legend: Following a dorsal laminectomy, rats underwent a C 2 cervical hemisection surgery (C 2 SH, surgical field inset) or sham (laminectomy only), severing the right-sided spinal projections of the lateral and ventral funiculus (grey portion of transverse spinal cord) and sparing the dorsal funiculus and the entire left side of C 2 (green portion of transverse spinal cord). Following C 2 SH, rats were randomly assigned to either vehicle (DMSO-orange rats) or SPG302 (a novel pegylated benzothiazole derivatives-blue rats) treatments intraperitoneally for 14 days. Example diaphragm muscle (DIAm) RMS EMG on the injured side (grey) and uninjured (green) side from vehicle and SPG rats at 14-days post-C 2 SH are shown on the right hand end of the top row of figures. 14 days post-C 2 SH, DIAm RMS EMG, ventilatory transdiaphragmatic pressure (P di ), and maximum P di (P dimax ), evoked via bilateral phrenic nerve stimulation, was compared to pre-injury values (within each rat) and across groups between sham, vehicle and SPG302 treated rats. SPG302 increased the % of rats exhibiting recovery from C 2 SH compared to vehicle, with recovery defined as being >10% of the initial pre-injury DIAm RMS EMG during eupnoea. C 2 SH depressed P dimax , with SPG302 having improved P dimax compared to vehicle treated. In conclusion, SPG302 presents a promising potential therapeutic for use in spinal cord injury. This article is protected by copyright. All rights reserved.