Molecular Changes in the Dorsal Root Ganglion during the Late Phase of Peripheral Nerve Injury-induced Pain in Rodents: A Systematic Review.

The dorsal root ganglion is widely recognized as a potential target to treat chronic pain. A fundamental understanding of quantitative molecular and genomic changes during the late phase of pain is therefore indispensable. The authors performed a systematic literature review on injury-induced pain in rodent dorsal root ganglions at minimally 3 weeks after injury. So far, slightly more than 300 molecules were quantified on the protein or messenger RNA level, of which about 60 were in more than one study. Only nine individual sequencing studies were performed in which the most up- or downregulated genes varied due to heterogeneity in study design. Neuropeptide Y and galanin were found to be consistently upregulated on both the gene and protein levels. The current knowledge regarding molecular changes in the dorsal root ganglion during the late phase of pain is limited. General conclusions are difficult to draw, making it hard to select specific molecules as a focus for treatment.

Capsaicin-Induced Skin Desensitization Differentially Affects A-Delta and C-Fiber-Mediated Heat Sensitivity.

Localized neuropathic pain can be relieved following the topical application of high-concentration capsaicin. This clinical effect is thought to be related to the temporary desensitization of capsaicin- and heat-sensitive epidermal nociceptors. The objective of the present study was to examine whether the changes in thermal sensitivity induced by high-concentration topical capsaicin can be explained entirely by desensitization of capsaicin-sensitive afferents. For this purpose, we characterized, in 20 healthy human volunteers, the time course and spatial extent of the changes in sensitivity to thermal stimuli preferentially activating heat-sensitive A-fiber nociceptors, heat-sensitive C-fiber afferents, and cool-sensitive A-fiber afferents. The volar forearm was treated with a high-concentration capsaicin patch for 1 h. Transient heat, warm and cold stimuli designed to activate Aδ- and C-fiber thermonociceptors, C-fiber warm receptors, and Aδ-fiber cold receptors were applied to the skin before and after treatment at days 1, 3, and 7. Reaction times, intensity ratings, and quality descriptors were collected. The stimuli were applied both within the capsaicin-treated skin and around the capsaicin-treated skin to map the changes in thermal sensitivity. We found that topical capsaicin selectively impairs heat sensitivity without any concomitant changes in cold sensitivity. Most interestingly, we observed a differential effect on the sensitivity to thermal inputs conveyed by Aδ- and C-fibers. Reduced sensitivity to Aδ-fiber-mediated heat was restricted to the capsaicin-treated skin, whereas reduced sensitivity to C-fiber-mediated heat extended well beyond the treated skin. Moreover, the time course of the reduced sensitivity to C-fiber-mediated input was more prolonged than the reduced sensitivity to Aδ-fiber-mediated input.

Dense fibroadhesive scarring and poor blood vessel-maturation hamper the integration of implanted collagen scaffolds in an experimental model of spinal cord injury.

Severe spinal cord injury (SCI) results in permanent functional deficits, which despite pre-clinical advances, remain untreatable. Combinational approaches, including the implantation of bioengineered scaffolds are likely to promote significant tissue repair. However, this critically depends on the extent to which host tissue can integrate with the implant. In the present paper, blood vessel formation and maturation were studied within and around implanted micro-structured type-I collagen scaffolds at 10 weeks post implantation in adult rat mid-cervical spinal cord lateral funiculotomy injuries. Morphometric analysis revealed that blood vessel density within the scaffold was similar to that of the lateral white matter tracts that the implant replaced. However, immunohistochemistry for zonula occludens-1 (ZO-1) and endothelial barrier antigen revealed that scaffold microvessels remained largely immature, suggesting poor blood-spinal cord barrier (BSB) reformation. Furthermore, a band of intense ZO-1-immunoreactive fibroblast-like cells isolated the implant. Spinal cord vessels outside the ZO-1-band demonstrated BSB-formation, while vessels within the scaffold generally did not. The formation of a double-layered fibrotic and astroglial scar around the collagen scaffold might explain the relatively poor implant-host integration and suggests a mechanism for failed microvessel maturation. Targeted strategies that improve implant-host integration for such biomaterials will be vital for future tissue engineering and regenerative medicine approaches for traumatic SCI.

Clinical and biometrical 12-month follow-up in patients after reconstruction of the sural nerve biopsy defect by the collagen-based nerve guide Neuromaix.

Many new strategies for the reconstruction of peripheral nerve injuries have been explored for their effectiveness in supporting nerve regeneration. However only a few of these materials were actually clinically evaluated and approved for human use. This open, mono-center, non-randomized clinical study summarizes the 12-month follow-up of patients receiving reconstruction of the sural nerve biopsy defect by the collagen-based nerve guide Neuromaix. Neuromaix was implanted as a micro-structured, two-component scaffold bridging 20-40 mm nerve defects after sural nerve biopsy in twenty patients (eighteen evaluated, two lost in follow-up). Safety of the material was evaluated by clinical examination of wound healing. Performance was assessed by sensory testing of modalities, pain assessment, and palpation for the Hoffmann-Tinel's sign as well as demarcating the asensitive area at each follow-up visit. Every patient demonstrated uneventful wound healing during the complete 12-month time course of the study. Two patients reported complete return of sensation, whereas eleven out of eighteen patients reported a positive Hoffmann-Tinel's sign at the lower leg with simultaneous reduction of the asensitive area by 12 months. Our data show that Neuromaix can be implanted safely in humans to bridge sural nerve gaps. No procedure-related, adverse events, or severe adverse events were reported. These first clinical data on Neuromaix provide promising perspectives for the bridging of larger nerve gaps in combined nerves, which should be investigated more through extensive, multi-center clinical trials in the near future.

The proximal medial sural nerve biopsy model: a standardised and reproducible baseline clinical model for the translational evaluation of bioengineered nerve guides.

Autologous nerve transplantation (ANT) is the clinical gold standard for the reconstruction of peripheral nerve defects. A large number of bioengineered nerve guides have been tested under laboratory conditions as an alternative to the ANT. The step from experimental studies to the implementation of the device in the clinical setting is often substantial and the outcome is unpredictable. This is mainly linked to the heterogeneity of clinical peripheral nerve injuries, which is very different from standardized animal studies. In search of a reproducible human model for the implantation of bioengineered nerve guides, we propose the reconstruction of sural nerve defects after routine nerve biopsy as a first or baseline study. Our concept uses the medial sural nerve of patients undergoing diagnostic nerve biopsy (≥ 2 cm). The biopsy-induced nerve gap was immediately reconstructed by implantation of the novel microstructured nerve guide, Neuromaix, as part of an ongoing first-in-human study. Here we present (i) a detailed list of inclusion and exclusion criteria, (ii) a detailed description of the surgical procedure, and (iii) a follow-up concept with multimodal sensory evaluation techniques. The proximal medial sural nerve biopsy model can serve as a preliminary nature of the injuries or baseline nerve lesion model. In a subsequent step, newly developed nerve guides could be tested in more unpredictable and challenging clinical peripheral nerve lesions (e.g., following trauma) which have reduced comparability due to the different nature of the injuries (e.g., site of injury and length of nerve gap).

Human Schwann cells seeded on a novel collagen-based microstructured nerve guide survive, proliferate, and modify neurite outgrowth.

A variety of new bioartificial nerve guides have been tested preclinically for their safety and nerve regeneration supporting properties. So far, only a limited number of biomaterials have been tested in humans since the step from preclinical work to a clinical application is challenging. We here present an in vitro model with human Schwann cells (hSCs) as an intermediate step towards clinical application of the nerve guide Perimaix, a collagen-based microstructured 3D scaffold containing numerous longitudinal guidance channels for directed axonal growth. hSCs were seeded onto different prototypes of Perimaix and cultivated for 14 days. hSC adhered to the scaffold, proliferated, and demonstrated healthy Schwann cell morphology (spindle shaped cell bodies, bipolar oriented processes) not only at the surface of the material, but also in the deeper layers of the scaffold. The general well-being of the cells was quantitatively confirmed by low levels of lactate dehydrogenase release into the culture medium. Moreover, conditioned medium of hSCs that were cultivated on Perimaix was able to modify neurite outgrowth from sensory dorsal root ganglion neurons. Overall these data indicate that Perimaix is able to provide a matrix that can promote the attachment and supports process extension, migration, and proliferation of hSC.