Katherine B. Santosa

Acellular nerve allografts in peripheral nerve regeneration: A comparative study

Introduction: Processed nerve allografts offer a promising alternative to nerve autografts in the surgical management of peripheral nerve injuries where short deficits exist. Methods: Three established models of acellular nerve allograft (cold‐preserved, detergent‐processed, and AxoGen‐processed nerve allografts) were compared with nerve isografts and silicone nerve guidance conduits in a 14‐mm rat sciatic nerve defect. Results: All acellular nerve grafts were superior to silicone nerve conduits in support of nerve regeneration. Detergent‐processed allografts were similar to isografts at 6 weeks postoperatively, whereas AxoGen‐processed and cold‐preserved allografts supported significantly fewer regenerating nerve fibers. Measurement of muscle force confirmed that detergent‐processed allografts promoted isograft‐equivalent levels of motor recovery 16 weeks postoperatively. All acellular allografts promoted greater amounts of motor recovery compared with silicone conduits. Conclusion: These findings provide evidence that differential processing for removal of cellular constituents in preparing acellular nerve allografts affects recovery in vivo. Muscle Nerve, 2011

NERVE ALLOGRAFTS SUPPLEMENTED WITH SCHWANN CELLS OVEREXPRESSING GLIAL-CELL-LINE-DERIVED NEUROTROPHIC FACTOR

We sought to determine whether supplementation of acellular nerve allografts (ANAs) with Schwann cells overexpressing GDNF (G‐SCs) would enhance functional recovery after peripheral nerve injury.

Schwann cells seeded in acellular nerve grafts improve functional recovery

Introduction: This study evaluated whether Schwann cells (SCs) from different nerve sources transplanted into cold‐preserved acellular nerve grafts (CP‐ANGs) would improve functional regeneration compared with nerve isografts. Methods: SCs isolated and expanded from motor and sensory branches of rat femoral and sciatic nerves were seeded into 14mm CP‐ANGs. Growth factor expression, axonal regeneration, and functional recovery were evaluated in a 14‐mm rat sciatic injury model and compared with isografts. Results: At 14 days, motor or sensory‐derived SCs increased expression of growth factors in CP‐ANGs versus isografts. After 42 days, histomorphometric analysis found CP‐ANGs with SCs and isografts had similar numbers of regenerating nerve fibers. At 84 days, muscle force generation was similar for CP‐ANGs with SCs and isografts. SC source did not affect nerve fiber counts or muscle force generation. Conclusions: SCs transplanted into CP‐ANGs increase functional regeneration to isograft levels; however SC nerve source did not have an effect. Muscle Nerve 49: 267–276, 2014

Transcardial perfusion versus immersion fixation for assessment of peripheral nerve regeneration

Accurate assessment of peripheral nerve regeneration requires fixation techniques that preserve tissue in a natural state with minimal artifact. While transcardial perfusion fixation is accepted as the gold standard for tissue fixation, the less cumbersome approach of immersion fixation has been criticized for introducing artifacts in brain tissue. We investigated whether immersion fixation increased artifact compared to perfusion fixation in the rat sciatic nerve. Eighteen Lewis rats were randomized into three groups: glutaraldehyde immersion fixation; glutaraldehyde transcardial perfusion; and paraformaldehyde transcardial perfusion. All animals underwent sciatic nerve transection and repair followed by tissue harvest and fixation at three weeks. Qualitative assessment of neural architecture and histological features was followed by quantitative analysis of nerve regeneration parameters. Outcome measures included quantitative histomorphometry, analysis of axon/myelin ratios, assessment of fiber distributions, and ultrastructural analysis. No qualitative or quantitative differences were observed with immersion fixation when compared to the transcardial perfusion fixation methods. Immersion fixation is a valid method for assessment of peripheral nerve regeneration in a rat model.

A systematic evaluation of Schwann cell injection into acellular cold-preserved nerve grafts.

Peripheral nerve regeneration after injury depends on environmental cues and trophic support. Schwann cells (SCs) secrete trophic factors that promote neuronal survival and help guide axons during regeneration. The addition of SCs to acellular nerve grafts is a promising strategy for enhancing peripheral nerve regeneration; however, inconsistencies in seeding parameters have led to varying results. The current work sought to establish a systematic approach to seeding SCs in cold-preserved acellular nerve grafts. Studies were undertaken to (1) determine the needle gauge for optimal cell survival and minimal epineurial disruption during injection, (2) track the seeded SCs using a commercially available dye, and (3) evaluate the seeding efficiency of SCs in nerve grafts. It was determined that seeding with a 27-gauge needle resulted in the highest viability of SCs with the least damage to the epineurium. In addition, Qtracker(®) dye, a commercially available quantum dot nanocrystal, was used to label SCs prior to transplantation, which allowed visualization of the seeded SCs in nerve grafts. Finally, stereological methods were used to evaluate the seeding efficiency of SCs in nerve grafts immediately after injection and following a 1- or 3-day in vitro incubation in SC growth media. Using a systematic approach, the best needle gauge and a suitable dye for SC visualization in acellular nerve grafts were identified. Seeding efficiency in these grafts was also determined. The findings will lead to improvements ability to assess injection of cells (including SCs) for use with acellular nerve grafts to promote nerve regeneration.

Effect of cold nerve allograft preservation on antigen presentation and rejection

OBJECT Nerve allotransplantation provides a temporary scaffold for host nerve regeneration and allows for the reconstruction of significant segmental nerve injuries. The need for systemic immunosuppression, however, limits the current clinical utilization of nerve allografts, although this need is reduced by the practice of cold nerve allograft preservation. Activation of T cells in response to alloantigen presentation occurs in the context of donor antigen presenting cells (direct pathway) or host antigen-presenting cells (indirect pathway). The relative role of each pathway in eliciting an alloimmune response and its potential for rejection of the nerve allograft model has not previously been investigated. The objective of this investigation was to study the effect of progressive periods of cold nerve allograft preservation on antigen presentation and the alloimmune response. METHODS The authors used wild type C57Bl/6 (B6), BALB/c, and major histocompatibility Class II-deficient (MHC-/-) C57Bl/6 mice as both nerve allograft recipients and donors. A nonvascularized nerve allograft was used to reconstruct a 1-cm sciatic nerve gap. Progressive cold preservation of donor nerve allografts was used. Quantitative assessment was made after 3 weeks using nerve histomorphometry. RESULTS The donor-recipient combination lacking a functional direct pathway (BALB/c host with MHC-/- graft) rejected nerve allografts as vigorously as wild-type animals. Without an intact indirect pathway (MHC-/- host with BALB/c graft), axonal regeneration was improved (p < 0.052). One week of cold allograft preservation did not improve regeneration to any significant degree in any of the donor-recipient combinations. Four weeks of cold preservation did improve regeneration significantly (p < 0.05) for all combinations compared with wild-type animals without pretreatment. However, only in the presence of an intact indirect pathway (no direct pathway) did 4 weeks of cold preservation improve regeneration significantly compared with 1 week and no preservation in the same donor-recipient combination. CONCLUSIONS The indirect pathway may be the predominant route of antigen presentation in the unmodified host response to the nerve allograft. Prolonged duration of cold nerve allograft preservation is required to significantly attenuate the rejection response. Cold preservation for 4 weeks improves nerve regeneration with a significant effect on indirect allorecognition.

Photographic Standards for Patients With Facial Palsy and Recommendations by Members of the Sir Charles Bell Society

Importance There is no widely accepted assessment tool or common language used by clinicians caring for patients with facial palsy, making exchange of information challenging. Standardized photography may represent such a language and is imperative for precise exchange of information and comparison of outcomes in this special patient population. Objectives To review the literature to evaluate the use of facial photography in the management of patients with facial palsy and to examine the use of photography in documenting facial nerve function among members of the Sir Charles Bell Society—a group of medical professionals dedicated to care of patients with facial palsy. Design, Setting, and Participants A literature search was performed to review photographic standards in patients with facial palsy. In addition, a cross-sectional survey of members of the Sir Charles Bell Society was conducted to examine use of medical photography in documenting facial nerve function. The literature search and analysis was performed in August and September 2015, and the survey was conducted in August and September 2013. Main Outcomes and Measures The literature review searched EMBASE, CINAHL, and MEDLINE databases from inception of each database through September 2015. Additional studies were identified by scanning references from relevant studies. Only English-language articles were eligible for inclusion. Articles that discussed patients with facial palsy and outlined photographic guidelines for this patient population were included in the study. The survey was disseminated to the Sir Charles Bell Society members in electronic form. It consisted of 10 questions related to facial grading scales, patient-reported outcome measures, other psychological assessment tools, and photographic and videographic recordings. Results In total, 393 articles were identified in the literature search, 7 of which fit the inclusion criteria. Six of the 7 articles discussed or proposed views specific to patients with facial palsy. However, none of the articles specifically focused on photographic standards for the population with facial palsy. Eighty-three of 151 members (55%) of the Sir Charles Bell Society responded to the survey. All survey respondents used photographic documentation, but there was variability in which facial expressions were used. Eighty-two percent (68 of 83) used some form of videography. From these data, we propose a set of minimum photographic standards for patients with facial palsy, including the following 10 static views: at rest or repose, small closed-mouth smile, large smile showing teeth, elevation of eyebrows, closure of eyes gently, closure of eyes tightly, puckering of lips, showing bottom teeth, snarling or wrinkling of the nose, and nasal base view. Conclusions and Relevance There is no consensus on photographic standardization to report outcomes for patients with facial palsy. Minimum photographic standards for facial paralysis publications are proposed. Videography of the dynamic movements of these views should also be recorded. Level of Evidence NA.

Costimulation blockade inhibits the indirect pathway of allorecognition in nerve allograft rejection.

Nerve allografts provide a temporary scaffold for host nerve regeneration. The need for systemic immunosuppression limits clinical application. Characterization of the immunological mechanisms that induce immune hyporesponsiveness may provide a basis for optimizing immunomodulating regimens. We utilized wild‐type and MHC class II–deficient mice, as both recipients and donors. Host treatment consisted of triple costimulatory blockade. Quantitative assessment was made at 3 weeks using nerve histomorphometry, and muscle testing was performed on a subset of animals at 7 weeks. Nerve allograft rejection occurred as long as either the direct or indirect pathways were functional. Indirect antigen presentation appeared to be more important. Nerve allograft rejection occurs in the absence of a normal direct or indirect immune response but may be more dependent on indirect allorecognition. The indirect pathway is required to induce costimulatory blockade immune hyporesponsiveness. Muscle Nerve, 2011

Abstract 91: Gender Imbalance in Invited Speakers at a National Plastic Surgery Meeting

PURPOSE: Participating in and attending scientific meetings within plastic and reconstructive surgery offers numerous benefits for practitioners at all levels. Not only are participants given the opportunity to learn about cuttingedge innovations, exchange new ideas with colleagues, and network with fellow surgeons, but meeting participation also affords recognition and respect for investigators’ work in the field. Studies suggest, however, that these opportunities are not made equally available for female researchers compared to their male counterparts.

Clinical relevance of terminal Schwann cells: An overlooked component of the neuromuscular junction

The terminal Schwann cell (tSC), a type of nonmyelinating Schwann cell, is a significant yet relatively understudied component of the neuromuscular junction. In addition to reviewing the role tSCs play on formation, maintenance, and remodeling of the synapse, we review studies that implicate tSCs in neuromuscular diseases including spinal muscular atrophy, Miller–Fisher syndrome, and amyotrophic lateral sclerosis, among others. We also discuss the importance of these cells on degeneration and regeneration after nerve injury. Knowledge of tSC biology may improve our understanding of disease pathogenesis and help us identify new and innovative therapeutic strategies for the many patients who suffer from neuromuscular disorders and nerve injuries.