Physiologic signaling and viability of the muscle cuff regenerative peripheral nerve interface (MC-RPNI) for intact peripheral nerves

Background. Robotic exoskeleton devices have become a promising modality for restoration of extremity function in individuals with limb loss or functional weakness. However, there exists no consistent or reliable way to record efferent motor action potentials from intact peripheral nerves to control device movement. Peripheral nerve motor action potentials are similar in amplitude to that of background noise, producing an unfavorable signal-to-noise ratio (SNR) that makes these signals difficult to detect and interpret. To address this issue, we have developed the muscle cuff regenerative peripheral nerve interface (MC-RPNI), a construct consisting of a free skeletal muscle graft wrapped circumferentially around an intact peripheral nerve. Over time, the muscle graft regenerates, and the intact nerve undergoes collateral axonal sprouting to reinnervate the muscle. The MC-RPNI amplifies efferent motor action potentials by several magnitudes, thereby increasing the SNR, allowing for higher fidelity signaling and detection of motor intention. The goal of this study was to characterize the signaling capabilities and viability of the MC-RPNI over time.Methods. Thirty-seven rats were randomly assigned to one of five experimental groups (Groups A-E). For MC-RPNI animals, their contralateral extensor digitorum longus (EDL) muscle was harvested and trimmed to either 8 mm (Group A) or 13 mm (Group B) in length, wrapped circumferentially around the intact ipsilateral common peroneal (CP) nerve, secured, and allowed to heal for 3 months. Additionally, one 8 mm (Group C) and one 13 mm (Group D) length group had an epineurial window created in the CP nerve immediately preceding MC-RPNI creation. Group E consisted of sham surgery animals. At 3 months, electrophysiologic analyses were conducted to determine the signaling capabilities of the MC-RPNI. Additionally, electromyography and isometric force analyses were performed on the CP-innervated EDL to determine the effects of the MC-RPNI on end organ function. Following evaluation, the CP nerve, MC-RPNI, and ipsilateral EDL muscle were harvested for histomorphometric analysis.Results. Study endpoint analysis was performed at 3 months post-surgery. All rats displayed visible muscle contractions in both the MC-RPNI and EDL following proximal CP nerve stimulation. Compound muscle action potentials were recorded from the MC-RPNI following proximal CP nerve stimulation and ranged from 3.67 ± 0.58 mV to 6.04 ± 1.01 mV, providing efferent motor action potential amplification of 10-20 times that of a normal physiologic nerve action potential. Maximum tetanic isometric force (F_o) testing of the distally-innervated EDL muscle in MC-RPNI groups producedF_o(2341 ± 114 mN-2832 ± 102 mN) similar to controls (2497 ± 122 mN), thus demonstrating that creation of MC-RPNIs did not adversely impact the function of the distally-innervated EDL muscle. Overall, comparison between all MC-RPNI sub-groups did not reveal any statistically significant differences in signaling capabilities or negative effects on distal-innervated muscle function as compared to the control group.Conclusions. MC-RPNIs have the capability to provide efferent motor action potential amplification from intact nerves without adversely impacting distal muscle function. Neither the size of the muscle graft nor the presence of an epineurial window in the nerve had any significant impact on the ability of the MC-RPNI to amplify efferent motor action potentials from intact nerves. These results support the potential for the MC-RPNI to serve as a biologic nerve interface to control advanced exoskeleton devices.

Autologous fat grafting for nerve regeneration and neuropathic pain: current state from bench-to-bedside

Despite recent advances in microsurgical techniques, functional recovery following peripheral nerve injury remains slow and inadequate. Poor peripheral nerve regeneration not only leaves patients with significant impairments, but also commonly leads to the development of debilitating neuropathic pain. Recent research has demonstrated the potential therapeutic benefits of adipose-derived stem cells, to enhance nerve regeneration. However, clinical translation remains limited due to the current regulatory burdens of the US FDA. A reliable and immediately translatable alternative is autologous fat grafting, where native adipose-derived stem cells present in the transferred tissue can potentially act upon regenerating axons. This review presents the scope of adipose tissue-based therapies to enhance outcomes following peripheral nerve injury, specifically focusing on their role in regeneration and ameliorating neuropathic pain.

Molecular Profiling to Determine Clonality of Serial Magnetic Resonance Imaging/Ultrasound Fusion Biopsies from Men on Active Surveillance for Low-Risk Prostate Cancer

Purpose: To determine whether MRI/ultrasound (MRI/US) fusion biopsy facilitates longitudinal resampling of the same clonal focus of prostate cancer and to determine whether high-grade cancers can evolve from low-grade clones.Experimental Design: All men on active surveillance who underwent tracking MRI/US fusion biopsy of Gleason 6 prostate cancer, on at least two distinct occasions, between 2012 and 2014 were enrolled. MRI/US fusion was used to track and resample specific cancer foci. IHC for ERG and targeted RNA/DNA next-generation sequencing (NGS) were performed on formalin-fixed paraffin-embedded prostate biopsy specimens to assess clonality.Results: Thirty-one men with median age and PSA of 65 years and 4.6 ng/mL, respectively, were analyzed. The median sampling interval was 12 months (range, 5-35). Of the 26 evaluable men, ERG IHC concordance was found between initial and repeat biopsies in 25 (96%), indicating resampling of the same clonal focus over time. Targeted NGS supported ERG IHC results and identified unique and shared driving mutations, such as IDH1 and SPOP, in paired specimens. Of the nine men (34.6%) who were found to have Gleason ≥7 on repeat biopsy, all displayed temporal ERG concordance. Prioritized genetic alterations were detected in 50% (13/26) of paired samples. Oncogenic mutations were detected in 22% (2/9) of Gleason 6 cancers prior to progression and 44% (4/9) of Gleason ≥7 cancers when progression occurred.Conclusions: Precise tracking of prostate cancer foci via MRI/US fusion biopsy allowed subsequent resampling of the same clonal focus of cancer over time. Further research is needed to clarify the grade progression potential of Gleason 6 prostate cancer. Clin Cancer Res; 23(4); 985-91. ©2016 AACR.