Fluorescently-tagged anti-ganglioside antibody selectively identifies peripheral nerve in living animals

Fluorescence imaging of peripheral nerve function and structure

Peripheral nerve injuries are common and can cause catastrophic consequences. Although peripheral nerves have notable regenerative capacity, full functional recovery is often challenging due to a number of factors, including age, the type of injury, and delayed healing, resulting in chronic disorders that cause lifelong miseries and significant financial burdens. Fluorescence imaging, among the various techniques, may be the key to overcome these restrictions and improve the prognosis because of its feasibility and dynamic real-time imaging. Intraoperative dynamic fluorescence imaging allows the visualization of the morphological structure of the nerve so that surgeons can reduce the incidence of medically induced injury. Axoplasmic transport-based neuroimaging allows the visualization of the internal transport function of the nerve, facilitating early, objective, and accurate assessment of the degree of regenerative repair, allowing early intervention in patients with poor recovery, thereby improving prognosis. This review briefly discusses peripheral nerve fluorescent dyes that have been reported or could potentially be employed, with a focus on their role in visualizing the nerve's function and anatomy.

Improving precision surgery: A review of current intraoperative nerve tissue fluorescence imaging

Iatrogenic nerve injury represents one of the most feared surgical complications and remains a major morbidity across many surgical specialties. Currently, no clinically approved technique can directly enhance intraoperative nerve visualization, where intraoperative nerve identification continues to challenge even experienced surgeons. Fluorescence-guided surgery (FGS) has been successfully integrated into clinical medicine to improve safety and efficacy in the surgical arena. A number of tissue- and disease-specific contrast agents are in the clinical translation pipeline for future FGS integration. Within this context, a diverse repertoire of fluorescent tracers have been developed to improve surgeons' intraoperative vision. This review aims to convey the recent developments for nerve-specific FGS and its potential for clinical translation.

Advances in optical molecular imaging for neural visualization

Iatrogenic nerve injury is a significant complication in surgery, which can negatively impact patients' quality of life. Currently, the main clinical neuroimaging methods, such as computed tomography, magnetic resonance imaging, and high-resolution ultrasonography, do not offer precise real-time positioning images for doctors during surgery. The clinical application of optical molecular imaging technology has led to the emergence of new concepts such as optical molecular imaging surgery, targeted surgery, and molecular-guided surgery. These advancements have made it possible to directly visualize surgical target areas, thereby providing a novel method for real-time identification of nerves during surgery planning. Unlike traditional white light imaging, optical molecular imaging technology enables precise positioning and identifies the cation of intraoperative nerves through the presentation of color images. Although a large number of experiments and data support its development, there are few reports on its actual clinical application. This paper summarizes the research results of optical molecular imaging technology and its ability to realize neural visualization. Additionally, it discusses the challenges neural visualization recognition faces and future development opportunities.

GAP-43 targeted indocyanine green-loaded near-infrared fluorescent probe for real-time mapping of perineural invasion lesions in pancreatic cancer in vivo

OBJECTIVE

Perineural invasion (PNI) is associated with local recurrence, distant metastasis, and a poor prognosis in pancreatic cancer. However, rare attempt was made to identified the PNI intraoperative. To facilitate precise R0 excision of the tumor, we planned to develop a fluorescent probe for intraoperative imaging of the PNI using GAP-43 as the target and indocyanine green (ICG) as the carrier.

METHODS

The probe was created by binding peptide antibody and ICG. Its targeting was tested in vitro and in vivo using a co-culture model of PC12 and tumor cells to create an in vitro neural invasion model and a mouse sciatic nerve invasion model. The small animal imaging system and surgical navigation system confirmed the probe's potential clinical applicability. The sciatic nerve damage model was created to confirm the probe's targeting.

RESULTS

We used the pancreatic cancer samples and the public database to confirm that GAP-43 was preferentially overexpressed in pancreatic cancer, particularly in PNI. PC12 cells showed high GAP-43RA-PEG-ICG probe-specific absorption after being co-cultured with tumor cells in vitro. In the sciatic nerve invasion experiment, animals in probe group displayed a significantly stronger fluorescence signal at the PNI compared to ICG-NP and the contralateral normal nerves groups. Although only 60 % of mice appeared to have R0 resections by the naked eye, small animal imaging systems and surgical fluorescence navigation systems could remove the tumor with R0 precision. The injury model used in the probe imaging experimental trials demonstrated that the probe was specifically targeted to the injured nerve, regardless of whether the injury was infiltrated by a tumor or physical.

CONCLUSION

We developed the GAP-43Ra-ICG-PEG, an active-targeting near-infrared fluorescent (NIF) probe, that specifically binds to GAP-43-positive neural cells in an in vitro model of PNI. The probe efficiently visualized PNI lesions in pancreatic cancer in preclinical models, opening up new possibilities for NIRF-guided pancreatic surgery, particularly for PNI patients.

Turn-On Fluorescent Probe Based on a Dansyl Triarginine Peptide for Ganglioside Imaging

Gangliosides play pivotal biological roles in the animal cell membranes, and it is vital to develop fluorescent probes for imaging them. To date, various artificial receptors for ganglioside imaging have been developed; however, turn-on fluorescence imaging for gangliosides with high contrast has not been achieved. We developed a simple fluorescent probe on the basis of a dansyl triarginine peptide for turn-on ganglioside imaging on the liposome membrane. The probe bound to monosialyl gangliosides and other anionic lipids with association constants was 10⁵ M^-1, which enhanced from 6-fold to 7-fold the fluorescence intensity. Upon binding to monosialyl ganglioside-containing giant liposomes, the turn-on probe selectively enhanced the fluorescence intensity compared with the other anionic lipids. This simple peptide probe for turn-on fluorescence imaging of gangliosides would provide a novel molecular tool for chemical biology.

Nerve spectroscopy: understanding peripheral nerve autofluorescence through photodynamics

BACKGROUND

Being able to accurately identify sensory and motor nerves is crucial during surgical procedures to prevent nerve injury. We aimed to (1) evaluate the feasibility of performing peripheral human nerve visualization utilizing nerves' own autofluorescence in an ex-vivo model; (2) compare the effect of three different nerve fiber fixation methods on the intensity of fluorescence, indicated as the intensity ratio; and (3) similarly compare three different excitation ranges.

METHODS

Samples from various human peripheral nerves were selected postoperatively. Nerve fibers were divided into three groups: Group A nerve fibers were washed with a physiologic solution; Group B nerve fibers were fixated with formaldehyde for 6 h first, and then washed with a physiologic solution; Group C nerve fibers were fixated with formaldehyde for six hours, but not washed afterwards. An Olympus IX83 inverted microscope was used for close-up image evaluation. Nerve fibers were exposed to white-light wavelength spectrums for a specific time frame prior to visualization under three different filters-Filter 1-LF405-B-OMF Semrock; Filter 2-U-MGFP; Filter 3-U-MRFPHQ Olympus, with excitation ranges of 390-440, 460-480, and 535-555, respectively. The fluorescence intensity of all images was subsequently analyzed using Image-J Software, and results compared by analysis of variance (ANOVA).

RESULTS

The intensity ratios observed with Filter 1 failed to distinguish the different nerve fiber groups (p = 0.39). Conversely, the intensity ratios seen under Filters 2 and 3 varied significantly between the three nerve-fiber groups (p = 0.021, p = 0.030, respectively). The overall intensity of measurements was greater with Filter 1 than Filter 3 (p < 0.05); however, all nerves were well visualized by all filters.

CONCLUSION

The current results on ex vivo peripheral nerve fiber autofluorescence suggest that peripheral nerve fiber autofluorescence intensity does not greatly depend upon the excitation wavelength or fixation methods used in an ex vivo setting. Implications for future nerve-sparing surgery are discussed.

Targeting Glycans and Heavily Glycosylated Proteins for Tumor Imaging

Simple Summary

Distinguishing malignancy from healthy tissue is essential for oncologic surgery. Targeted imaging during an operation aids the surgeon to operate better. The present tracers for detecting cancer are directed against proteins that are overexpressed on the membrane of tumor cells. This review evaluates the use of tumor-associated sugar molecules as an alternative for proteins to image cancer tissue. These sugar molecules are present as glycans on glycosylated membrane proteins and glycolipids. Due to their location and large numbers per cell, these sugar molecules might be better targets for tumor imaging than proteins.

Abstract

Real-time tumor imaging techniques are increasingly used in oncological surgery, but still need to be supplemented with novel targeted tracers, providing specific tumor tissue detection based on intra-tumoral processes or protein expression. To maximize tumor/non-tumor contrast, targets should be highly and homogenously expressed on tumor tissue only, preferably from the earliest developmental stage onward. Unfortunately, most evaluated tumor-associated proteins appear not to meet all of these criteria. Thus, the quest for ideal targets continues. Aberrant glycosylation of proteins and lipids is a fundamental hallmark of almost all cancer types and contributes to tumor progression. Additionally, overexpression of glycoproteins that carry aberrant glycans, such as mucins and proteoglycans, is observed. Selected tumor-associated glyco-antigens are abundantly expressed and could, thus, be ideal candidates for targeted tumor imaging. Nevertheless, glycan-based tumor imaging is still in its infancy. In this review, we highlight the potential of glycans, and heavily glycosylated proteoglycans and mucins as targets for multimodal tumor imaging by discussing the preclinical and clinical accomplishments within this field. Additionally, we describe the major advantages and limitations of targeting glycans compared to cancer-associated proteins. Lastly, by providing a brief overview of the most attractive tumor-associated glycans and glycosylated proteins in association with their respective tumor types, we set out the way for implementing glycan-based imaging in a clinical practice.

Intracellular G-actin targeting of peripheral sensory neurons by the multifunctional engineered protein C2C confers relief from inflammatory pain

The engineered multifunctional protein C2C was tested for control of sensory neuron activity by targeted G-actin modification. C2C consists of the heptameric oligomer, C2II-CI, and the monomeric ribosylase, C2I. C2C treatment of sensory neurons and SH-SY5Y cells in vitro remodeled actin and reduced calcium influx in a reversible manner. C2C prepared using fluorescently labeled C2I showed selective in vitro C2I delivery to primary sensory neurons but not motor neurons. Delivery was dependent on presence of both C2C subunits and blocked by receptor competition. Immunohistochemistry of mice treated subcutaneously with C2C showed colocalization of subunit C2I with CGRP-positive sensory neurons and fibers but not with ChAT-positive motor neurons and fibers. The significance of sensory neuron targeting was pursued subsequently by testing C2C activity in the formalin inflammatory mouse pain model. Subcutaneous C2C administration reduced pain-like behaviors by 90% relative to untreated controls 6 h post treatment and similarly to the opioid buprenorphene. C2C effects were dose dependent, equally potent in female and male animals and did not change gross motor function. One dose was effective in 2 h and lasted 1 week. Administration of C2I without C2II-CI did not reduce pain-like behavior indicating its intracellular delivery was required for behavioral effect.

Fluorescence Imaging of Nerves During Surgery

OBJECTIVE

This review details the agents for fluorescence-guided nerve imaging in both preclinical and clinical use to identify factors important in selecting nerve-specific fluorescent agents for surgical procedures.

BACKGROUND

Iatrogenic nerve injury remains a significant cause of morbidity in patients undergoing surgical procedures. Current real-time identification of nerves during surgery involves neurophysiologic nerve stimulation, which has practical limitations. Intraoperative fluorescence-guided imaging provides a complimentary means of differentiating tissue types and pathology. Recent advances in fluorescence-guided nerve imaging have shown promise, but the ideal agent remains elusive.

METHODS

In February 2018, PubMed was searched for articles investigating peripheral nerve fluorescence. Key terms used in this search include: "intraoperative, nerve, fluorescence, peripheral nerve, visualization, near infrared, and myelin." Limits were set to exclude articles exclusively dealing with central nervous system targets or written in languages other than English. References were cross-checked for articles not otherwise identified.

RESULTS

Of the nonspecific agents, tracers that rely on axonal transport showed the greatest tissue specificity; however, neurovascular dyes already enjoy wide clinical use. Fluorophores specific to nerve moieties result in excellent nerve to background ratios. Although noteworthy findings on tissue specificity, toxicity, and route of administration specific to each fluorescent agent were reported, significant data objectively quantifying nerve-specific fluorescence and toxicity are lacking.

CONCLUSIONS

Fluorescence-based nerve enhancement has advanced rapidly over the past 10 years with potential for continued utilization and progression in translational research. An ideal agent would be easily administered perioperatively, would not cross the blood-brain barrier, and would fluoresce in the near-infrared spectrum. Agents administered systemically that target nerve-specific moieties have shown the greatest promise. Based on the heterogeneity of published studies and methods for reporting outcomes, it appears that the development of an optimal nerve imaging agent remains challenging.

Imaging in the repair of peripheral nerve injury

Surgical intervention followed by physical therapy remains the major way to repair damaged nerves and restore function. Imaging constitutes promising, yet underutilized, approaches to improve surgical and postoperative techniques. Dedicated methods for imaging nerve regeneration will potentially provide surgical guidance, enable recovery monitoring and postrepair intervention, elucidate failure mechanisms and optimize preclinical procedures. Herein, we present an outline of promising innovations in imaging-based tracking of in vivo peripheral nerve regeneration. We emphasize optical imaging because of its cost, versatility, relatively low toxicity and sensitivity. We discuss the use of targeted probes and contrast agents (small molecules and nanoparticles) to facilitate nerve regeneration imaging and the engineering of grafts that could be used to track nerve repair. We also discuss how new imaging methods might overcome the most significant challenges in nerve injury treatment.

Nerve-targeted probes for fluorescence-guided intraoperative imaging

A fundamental goal of many surgeries is nerve preservation, as inadvertent injury can lead to patient morbidity including numbness, pain, localized paralysis and incontinence. Nerve identification during surgery relies on multiple parameters including anatomy, texture, color and relationship to surrounding structures using white light illumination. We propose that fluorescent labeling of nerves can enhance the contrast between nerves and adjacent tissue during surgery which may lead to improved outcomes.

Methods: Nerve binding peptide sequences including HNP401 were identified by phage display using selective binding to dissected nerve tissue. Peptide dye conjugates including FAM-HNP401 and structural variants were synthesized and screened for nerve binding after topical application on fresh rodent and human tissue and in-vivo after systemic IV administration into both mice and rats. Nerve to muscle contrast was quantified by measuring fluorescent intensity after topical or systemic administration of peptide dye conjugate.

Results: Peptide dye conjugate FAM-HNP401 showed selective binding to human sural nerve with 10.9x fluorescence signal intensity (1374.44 ± 425.96) compared to a previously identified peptide FAM-NP41 (126.17 ± 61.03). FAM-HNP401 showed nerve-to-muscle contrast of 3.03 ± 0.57. FAM-HNP401 binds and highlight multiple human peripheral nerves including lower leg sural, upper arm medial antebrachial as well as autonomic nerves isolated from human prostate.

Conclusion: Phage display has identified a novel peptide that selectively binds to ex-vivo human nerves and in-vivo using rodent models. FAM-HNP401 or an optimized variant could be translated for use in a clinical setting for intraoperative identification of human nerves to improve visualization and potentially decrease the incidence of intra-surgical nerve injury.

Atomic Force Microscopy as a Tool to Assess the Specificity of Targeted Nanoparticles in Biological Models of High Complexity

The ability to design nanoparticle delivery systems capable of selectively target their payloads to specific cell populations is still a major caveat in nanomedicine. One of the main hurdles is the fact that each nanoparticle formulation needs to be precisely tuned to match the specificities of the target cell and route of administration. In this work, molecular recognition force spectroscopy (MRFS) is presented as a tool to evaluate the specificity of neuron-targeted trimethyl chitosan nanoparticles to neuronal cell populations in biological samples of different complexity. The use of atomic force microscopy tips functionalized with targeted or non-targeted nanoparticles made it possible to assess the specific interaction of each formulation with determined cell surface receptors in a precise fashion. More importantly, the combination of MRFS with fluorescent microscopy allowed to probe the nanoparticles vectoring capacity in models of high complexity, such as primary mixed cultures, as well as specific subcellular regions in histological tissues. Overall, this work contributes for the establishment of MRFS as a powerful alternative technique to animal testing in vector design and opens new avenues for the development of advanced targeted nanomedicines.

Rapid fluorescence imaging of spinal cord following epidural administration of a nerve-highlighting fluorophore

Iatrogenic spinal cord injury (SCI) is the most devastating complication of spine surgery, which usually results in permanent and serious disabilities of patients. Improvement of the visualization and discrimination of the spinal cord is critical for accuracy and safety during surgery; however, to date, there is no suitable technology to fulfill this clinical need. Here, we first show an efficient and rapid fluorescence imaging of the spinal cord in rabbit by epidural administration of a nerve-highlighting fluorophore, i.e. (E, E)-1,4-bis(p-aminostryl)-2-methoxy benzene (BMB). The BMB is firstly encapsulated into polymeric micelles to form a BMB-micelle (BMB-m) formulation with well-dispersion in normal saline solution. After epidural administration of BMB-m, BMB is transported by the flow of cerebrospinal fluid (CSF) and binds to the peripheral region of the white matter thus facilitating rapid staining of the spinal cord. Furthermore, this BMB imaging technology also holds great potential for visually monitoring the integrity of the spinal cord in real time and promptly identifying acute SCI during spine surgery.

Laminin targeting of a peripheral nerve-highlighting peptide enables degenerated nerve visualization

Target-blind activity-based screening of molecular libraries is often used to develop first-generation compounds, but subsequent target identification is rate-limiting to developing improved agents with higher specific affinity and lower off-target binding. A fluorescently labeled nerve-binding peptide, NP41, selected by phage display, highlights peripheral nerves in vivo. Nerve highlighting has the potential to improve surgical outcomes by facilitating intraoperative nerve identification, reducing accidental nerve transection, and facilitating repair of damaged nerves. To enable screening of molecular target-specific molecules for higher nerve contrast and to identify potential toxicities, NP41's binding target was sought. Laminin-421 and -211 were identified by proximity-based labeling using singlet oxygen and by an adapted version of TRICEPS-based ligand-receptor capture to identify glycoprotein receptors via ligand cross-linking. In proximity labeling, photooxidation of a ligand-conjugated singlet oxygen generator is coupled to chemical labeling of locally oxidized residues. Photooxidation of methylene blue-NP41-bound nerves, followed by biotin hydrazide labeling and purification, resulted in light-induced enrichment of laminin subunits α4 and α2, nidogen 1, and decorin (FDR-adjusted P value < 10^-7) and minor enrichment of laminin-γ1 and collagens I and VI. Glycoprotein receptor capture also identified laminin-α4 and -γ1. Laminins colocalized with NP41 within nerve sheath, particularly perineurium, where laminin-421 is predominant. Binding assays with phage expressing NP41 confirmed binding to purified laminin-421, laminin-211, and laminin-α4. Affinity for these extracellular matrix proteins explains the striking ability of NP41 to highlight degenerated nerve "ghosts" months posttransection that are invisible to the unaided eye but retain hollow laminin-rich tubular structures.

A four-dimensional snapshot hyperspectral video-endoscope for bio-imaging applications

Hyperspectral imaging has proven significance in bio-imaging applications and it has the ability to capture up to several hundred images of different wavelengths offering relevant spectral signatures. To use hyperspectral imaging for in vivo monitoring and diagnosis of the internal body cavities, a snapshot hyperspectral video-endoscope is required. However, such reported systems provide only about 50 wavelengths. We have developed a four-dimensional snapshot hyperspectral video-endoscope with a spectral range of 400–1000 nm, which can detect 756 wavelengths for imaging, significantly more than such systems. Capturing the three-dimensional datacube sequentially gives the fourth dimension. All these are achieved through a flexible two-dimensional to one-dimensional fiber bundle. The potential of this custom designed and fabricated compact biomedical probe is demonstrated by imaging phantom tissue samples in reflectance and fluorescence imaging modalities. It is envisaged that this novel concept and developed probe will contribute significantly towards diagnostic in vivo biomedical imaging in the near future.