Research ArticleNERVE REGENERATION

Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates

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Science Translational Medicine  22 Jan 2020:
Vol. 12, Issue 527, eaav7753
DOI: 10.1126/scitranslmed.aav7753

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  • RE: In response to the article by Fadia et al. “Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates”
    • K Ming Chan, Physiatrist, University of Alberta
    • Other Contributors:
      • Douglas W. Zochodne, Neurologist, University of Alberta
      • Julie Shatto, Research assistant, University Hospital

    We read the paper by Fadia et al. entitled ‘Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates’ with interest. This is among a small handful of studies using non-human primates, a larger animal model that more closely approximates the clinical situation in human nerve repair. However, we have identified several concerns around the data and its interpretation.
    First, in the discussion section, the authors stated that “on the basis of the similar electrophysiological findings between the PGL/GDNF conduit and autograft, the PCL/GDNF conduit was as effective at regenerating the median nerve”. However, this interpretation runs counter to the data shown in Fig. 4G and 4H that the CMAP amplitudes in the PCL/GDNF were significantly lower than in the autograft group. Indeed, there was no significant difference between the PCL/GDNF and the PCL/Empty group. As the authors rightly pointed out that the CMAP amplitude serves as an estimate of motor unit numbers that regenerated, this is an important discrepancy as the interpretation is not supported by the data. Second, the authors have suggested that the degree of myelination, based on g-ratios, is better in the PCL/GDNF compared to the autograft group. However, based on the micrographs presented in Fig. 8, it appears that the axonal diameters in the PCL/GDNF were substantially smaller than those in the autograft and native nerve. This seems to run counter to the well-known f...

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    Competing Interests: None declared.
  • RE: In response to Shatto et al.’s Letter in response to “Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates”
    • Jacqueline M. Bliley, Graduate Student, Currently Carnegie Mellon University
    • Other Contributors:
      • Donald J. Crammond, Faculty, University of Pittsburgh
      • Neil B. Fadia, Medical Student, Now at University of South Florida
      • Kacey G. Marra, Faculty, University of Pittsburgh

    We thank Shatto et al. for their critical review of our paper, “Long-gap Peripheral Nerve Repair through Sustained Release of Neurotrophic Factor in Non-Human Primates.”

    We would like to first address the concern regarding the electrophysiology performed in our study. Shatto et al. state: “in the discussion section, the authors stated that “on the basis of the similar electrophysiological findings between the PGL/GDNF conduit and autograft, the PCL/GDNF conduit was as effective at regenerating the median nerve”. However, this interpretation runs counter to the data shown in Fig. 4G and 4H that the CMAP amplitudes in the PCL/GDNF were significantly lower than in the autograft group.” This is an important concern, and we acknowledge that this sentence can be interpreted in different ways. We stated that similar electrophysiological findings were observed between the PCL/GDNF and autograft group because we observed significantly increased nerve conduction velocity in the PCL/GDNF group and a positive APB CMAP response. However, as the authors of this letter have pointed out, we did observe a reduction in the APB CMAP amplitude compared to the autograft positive control suggesting that the autograft had reinnervated the APB to a larger extent. The similar CNAP amplitudes between autograft and PCL/GDNF group suggests that a similar number of axons completed regeneration in these two groups. Also note that the PCL/Empty group, on average, generated little to no CNAP res...

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    Competing Interests: None declared.

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