Intravenous indocyanine green dye is insufficient for robust immune cell labelling in the human retina

Mechanisms of delayed indocyanine green fluorescence and applications to clinical disease processes

BACKGROUND

Delayed indocyanine green fluorescence imaging is under investigation in various clinical disease processes. Understanding the mechanisms of indocyanine green accumulation and retention is essential to correctly interpreting and analyzing imaging data. The purpose of this scoping review was to synthesize what is known about the mechanism of indocyanine green retention at the cellular level to better understand the clinical nuances of delayed indocyanine green imaging and identify critical gaps in our knowledge to guide future studies.

METHODS

We performed a scoping review of 7,087 citations after performing database searches of PubMed, Scopus, the Cochrane Library, and the Web of Science Core Collection electronic databases. Studies were eligible for inclusion if they were peer-reviewed original research discussing the mechanism of indocyanine green retention in the results section in disease processes involving inflammation and/or necrosis, including cancer, and were available in English. Data were extracted using Covidence software.

RESULTS

Eighty-nine studies were included in the final analysis. Several features of indocyanine green retention were identified.

CONCLUSION

We identified several mechanistic features involved in indocyanine green accumulation in diseased tissue that overall had distinct mechanisms of indocyanine green retention in tumors, nontumor inflammation, and necrosis. Our study also reveals new insights on how inflammatory infiltrate influences indocyanine green fluorescence imaging. These findings are noteworthy because they add to our understanding of how fluorescence-guided surgery may be optimized based on the pathology of interest via specific indocyanine green dosing and timing of image acquisition.

From bone to nanoparticles: development of a novel generation of bone derived nanoparticles for image guided orthopedic regeneration

Bone related diseases such as osteoporosis, osteoarthritis, metastatic bone cancer, osteogenesis imperfecta, and Paget's disease, are primarily treated with pharmacologic therapies that often exhibit limited efficacy and substantial side effects. Bone injuries or fractures are primarily repaired with biocompatible materials that produce mixed results in sufficiently regenerating healthy and homogenous bone tissue. Each of these bone conditions, both localized and systemic, use different strategies with the same goal of achieving a healthy and homeostatic bone environment. In this study, we developed a new type of bone-based nanoparticle (BPs) using the entire organic extracellular matrix (ECM) of decellularized porcine bone, additionally encapsulating indocyanine green dye (ICG) for an in vivo monitoring capability. Utilizing the regenerative capability of bone ECM and the functionality of nanoparticles, the ICG encapsulated BPs (ICG/BPs) have been demonstrated to be utilized as a therapeutic option for localized and systemic orthopedic conditions. Additionally, ICG enables an in situ monitoring capability in the Short-Wave Infrared (SWIR) spectrum, capturing the degradation or the biodistribution of the ICG/BPs after both local implantation and intravenous administration, respectively. The efficacy and safety of the ICG/BPs shown within this study lay the foundation for future investigations, which will delve into optimization for clinical translation.

Indocyanine Green-Labeled Platelets for Survival and Recovery Studies

Introduction

Before being implemented in daily clinical routine, new production strategies for platelet concentrates (PCs) must be validated for their efficacy. Besides in vitro testing, the establishment of new methods requires the labeling of platelets for in vivo studies of platelets' survival and recovery. Indocyanine green (ICG) is a Food and Drug Administration-approved near-infrared (NIR) fluorescent dye for diagnostic use in vivo, suitable for non-radioactive direct cell labeling of platelets.

Methods

Platelets from PCs in storage solutions with different plasma concentrations were labeled with ICG up to concentrations of 200 μm. Whole blood (WB) was used as an ex vivo matrix to monitor the labeling stability of ICG-labeled platelets. The impact of labeling processes was assessed by the quantification of CD62P expression and PAC-1 binding as platelet function markers. Platelet aggregation was analyzed by light transmission aggregometry. ICG-labeling efficiency and stability of platelets were determined by flow cytometry.

Results

Platelets from PCs could be successfully labeled with 10 μm ICG after 1 and 4 days of storage. The best labeling efficiency of 99.8% ± 0.1% (immediately after labeling) and 81% ± 6.2% (after 24 h incubation with WB) was achieved by plasma replacement by 100% platelet additive solution for the labeling process. Since the washing process slightly impaired platelet function, ICG labeling itself did not affect platelets. Immediately after the ICG-labeling process, plasma was re-added, resulting in a recovered platelet function.

Conclusion

We developed a Good Manufacturing Practice compatible protocol for ICG fluorescent platelet labeling suitable for survival and recovery studies in vivo as a non-radioactive labeling alternative.

ICG-based laser treatments for ophthalmic diseases: Toward their safe and rapid strategy

The eye is a very important organ, and keratitis, corneal neovascularization, floaters, age-related macular degeneration, and other vision problems have seriously affected people's quality of life. Among the ophthalmic treatments, laser photocoagulations have been proposed and have shown therapeutic effects in clinical settings. However, corneal thinning and bleeding lesions induced by laser damage have led to limit its applications. To treat the issues of traditional hyperthermia treatments, photosensitizers [e.g., indocyanine green (ICG)] have been investigated to increase the therapeutic effects of corneal neovascularization and choroidal neovascularization. In the recent study, with the help of ICG, laser-induced nanobubble was proposed to treat vitreous opacities. The developed strategies could enlarge the effect of laser irradiation and reduce the side effects, so as to expand the scope of laser treatments in clinical ophthalmic diseases.

INDOCYANINE GREEN ANGIOGRAPHY OF TYPE 1 MACULAR NEOVASCULARIZATION IN AGE-RELATED MACULAR DEGENERATION AND CENTRAL SEROUS CHORIORETINOPATHY REVEALS DIFFERENT DISEASE MECHANISMS

PURPOSE

To assess the rate of late phase hyperfluorescent plaque (LPHP) in Type 1 macular neovascularization (MNV) in central serous chorioretinopathy (CSCR) and age-related macular degeneration (AMD) and to evaluate its prognostic value.

METHODS

Retrospective study including Type 1 MNV in AMD and CSCR, from 2012 to 2020. Eyes with a late indocyanine green angiography image (>20 minutes) and clear visualization of MNV on optical coherence tomography angiography (OCTA) were included. Quantitative and qualitative parameters on optical coherence tomography and best-corrected visual acuity were recorded at baseline and after three monthly antivascular endothelial growth factor injections.

RESULTS

Eighty-three eyes were included, 35 with CSCR and 48 with AMD. Patients in the CSCR group were significantly younger than in the AMD group (61.3 ± 10.4 vs. 80.2 ± 6.8 years, respectively, P < 0.001), predominantly male (68.6% CSCR vs. 35.4% AMD; P = 0.003), and with a thicker choroid (379 ± 93.3 µ m vs. 204.2 ± 93.2 µ m; P < 0.001). Type 1 MNV in CSCR showed fewer LPHP compared with AMD (31.4% vs. 77.1%; P < 0.001). The baseline visual acuity was lower in patients with LPHP (0.37 ± 0.22 vs. 0.27 ± 0.28 logarithm of the minimum angle of resolution, P = 0.03). On multivariate analysis, AMD was associated with the presence of LPHP ( P < 0.001). No significant difference in the response to antivascular endothelial growth factor was observed.

CONCLUSION

Leakage of macromolecules from MNV and accumulation in the retinal pigment epithelium and/or in the stroma imaged by the LPHP is less common in eyes with Type 1 MNV in CSCR than in AMD. Late phase indocyanine green angiography imaging offers an insight into the metabolism of the dye and the environment surrounding the neovascular membrane.

Triazole-derivatized near-infrared cyanine dyes enable local functional fluorescent imaging of ocular inflammation

Near-infrared (NIR) chemical fluorophores are promising tools for in-vivo imaging in real time but often succumb to rapid photodegradation. Indocyanine green (ICG) is the only NIR dye with regulatory approval for ocular imaging in humans; however, ICG, when employed for applications such as labelling immune cells, has limited sensitivity and does not allow precise detection of specific inflammatory events, for example leukocyte recruitment during uveitic flare-ups. We investigated the potential use of photostable novel triazole NIR cyanine (TNC) dyes for detecting and characterising activated T-cell activity within the eye. Three TNC dyes were evaluated for ocular cytotoxicity in-vitro using a MTT assay and optimised concentrations for intraocular detection within ex-vivo porcine eyes after topical application or intracameral injections of the dyes. TNC labelled T-cell tracking experiments and mechanistic studies were also performed in-vitro. TNC-1 and TNC-2 dyes exhibited greater fluorescence intensity than ICG at 10 μM, whereas TNC-3 was only detectable at 100 μM within the porcine eye. TNC dyes did not demonstrate any ocular cell toxicity at working concentrations of 10 μM. CD4⁺T-cells labelled with TNC-1 or TNC-2 were detected within the porcine eye, with TNC-1 being brighter than TNC-2. Detection of TNC-1 and TNC-2 into CD4⁺T-cells was prevented by prior incubation with dynole 34-2 (50 μM), suggesting active uptake of these dyes via dynamin-dependent processes. The present study provides evidence that TNC dyes are suitable to detect activated CD4⁺T-cells within the eye with potential as a diagnostic marker for ocular inflammatory diseases.

Evolving Patterns of Hyperfluorescent Fundus Autofluorescence Accompany Retinal Atrophy in the Rat and Mimic Atrophic Age-Related Macular Degeneration

Purpose

Complex two-dimensional (2D) patterns of hyperfluorescent short-wave fundus autofluorescence (FAF) at the border of geographic atrophy (GA) can predict its expansion in patients with late non-exudative “dry” AMD. However, preclinical models do not phenocopy this important feature of disease. We sought to describe the spatiotemporal changes in hyperfluorescent FAF patterns that occur following acute oxidative stress, potentially in association with GA expansion.

Methods

Sprague Dawley rats (n = 54) received systemic sodium iodate (25–45 mg/kg, n = 90 eyes) or saline (n = 18 eyes) and underwent serial full fundus imaging by confocal scanning laser ophthalmoscopy, including blue FAF and delayed near-infrared analysis. Composite images of the fundus were assembled, and the 2D patterns were described qualitatively and quantitatively. A subset of eyes underwent tissue analysis, and four underwent optical coherence tomography (OCT) imaging.

Results

Reproducibly changing, complex patterns of hyperfluorescent FAF emerge at the borders of toxin-induced damage; however, in the absence of GA expansion, they percolate inward within the region of retinal pigment epithelium loss, evolving, maturing, and senescing in situ over time. Unexpectedly, the late FAF patterns most closely resemble the diffuse tricking form of clinical disease. A five-stage classification system is presented.

Conclusions

Longitudinal, full-fundus imaging of outer retinal atrophy in the rat eye identifies evolving, complex patterns of hyperfluorescent FAF that phenocopy aspects of disease.

Translational Relevance

This work provides a novel tool to assess hyperfluorescent FAF in association with progressive retinal atrophy, a therapeutic target in late AMD.

Intraoperative Indocyanine Green Angiography for Assessing Flap Perfusion in Skull Base Reconstruction: A Systematic Review

Objective This study was aimed to study the current use of intraoperative indocyanine green (ICG) angiography during skull base reconstruction and understand its efficacy in predicting postoperative magnetic resonance imaging (MRI) enhancement and flap.

Study Design The Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, and Google Scholar databases were searched from the date of inception until August 2020 for studies of ICG flap perfusion assessment during skull base reconstruction. The primary outcome of interest was the development of cerebrospinal fluid (CSF) leak after skull base reconstruction. Secondary outcomes of interest included postoperative meningitis, flap MRI enhancement, flap necrosis, flap perfusion measurements, and total complications.

Results Search results yielded 189 studies, from which seven studies with a total of 104 patients were included in the final analysis. There were 44 nasoseptal flaps (NSF), two lateral nasal wall flaps (LNWF), 14 pericranial flaps (PCF), and 44 microvascular free flaps. The rates of CSF leak and postoperative MRI enhancement were 11 and 94%, respectively. There was one case of postoperative meningitis. Pooled analysis of the available data showed that intraoperative ICG flap perfusion was associated with flap enhancement on postoperative MRI (p = 0.008) and CSF leak (p = 0.315) by Fisher's exact test.

Conclusion The available literature suggests intraoperative ICG enhancement is associated with postoperative MRI enhancement. Given the small sample sizes in the literature and the rarity of complications associated with skull base reconstruction, intraoperative ICG enhancement has not been predictive of flap necrosis or postoperative complications such as CSF leak or meningitis.

Level of Evidence This study presents level 3 evidence as a systematic review of case studies, case reports, and retrospective and prospective trials with no blinding, controls, and inconsistently applied reference standards.