The research project was funded under New Investigator grant from the National Medical Research Council (NMRC), Singapore. The team will like to acknowledge the research training provided to Dr Agrawal at Institute of Ophthalmology (IoO), University College London (UCL) under National Medical Research Council (NMRC) Overseas Research Training Fellowship from November 2012 till October 2014 under mentorship of Prof. David Shima. Dr. Agrawal acquired the concept and skills for labelling the cells and live imaging in Dr. Shima&#39;s lab. The team will hence like to acknowledge supervision and guidance during the training fellowship from Prof. David Shima, Pro.f Kenith Meissner, Dr. Peter Lundh and Dr. Daiju Iwata.

The animal protocols used in this study were approved by the Institutional Animal Care and Use Committee of SingHealth, Singapore and are in accordance to the guidelines of the Association for Research in Vision and Ophthalmology (ARVO) Statement for the Use of Animals in Ophthalmic and Vision Research.
1. Labeling of Erythrocytes and Leukocytes with Fluorescent Dyes
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	<li>Preparation of reagents
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		<li>Prepare ICG (1.5 mg/mL) by dissolving 3 mg of ICG in 1800 &#181;L of sterilized dist...

Studying the hemodynamics in the retinal and choroidal circulation is vital for understanding the pathophysiology of many ocular diseases. The blood flow dynamics in the retinal circulation can be studied by Fourier-domain optical coherence tomography (FD-OCT), laser speckle flowgraphy (LSFG) and retinal oximetry. Although these methods use different approaches to study the total blood flow in the retinal circulation40,41,42<sup...

Studying the flow dynamics of the blood cells in the retinal and choroidal circulation is imperative to understanding the pathogenesis of potentially vision-threatening ocular diseases and other ocular inflammatory conditions. However, the conventional angiography techniques, which involve the binding of fluorescent dyes to plasma proteins, do not provide any information regarding the dynamics of the erythrocytes or leukocytes1. The erythrocyte retinal flow dynamics are important for studying metabolically efficient circulation in the retina, and the leukocyte flow dynamics, for understanding the cell migration, recognition, adhesion and destruction in various inflammatory conditions2. There are several fluorescent molecules used in the identification and characterization of various cell types3. The hemodynamics of the blood cells can be measured by staining them with the appropriate fluorescent dyes and applying the proper imaging techniques4.
The presence of inflammatory responses in intraocular diseases like age-related macular degeneration (AMD) and diabetic retinopathy (DR) involve the accumulation of lymphocytes in the diseased area5,6. Tracking the immune cells in the tissues can help understand the complex events involved in the mechanism of disease pathogenesis. Radioactive isotopes like 51Cr and 125I were used as cell tracers in early studies. These dyes are toxic and affect the cell viability. Although the radioactive markers 3H and 14C are less toxic to the cells, due to their lower emission energies, it is difficult to detect their signals in the system7,8. A number of fluorochrome dyes were introduced to overcome the potential problems associated with radioactive markers and track lymphocyte migration in vitro using fluorescent microscopy and flow cytometry9,10. Hoechst 33342 and thiazole orange are DNA binding fluorescent dyes, which are used to track lymphocytes in vivo. Hoechst 33342 binds to AT-rich regions in the DNA, is membrane permeable, retains fluorescent signals for 2 - 4 days and is resistant to quenching9,10. The disadvantages of Hoechst 33342 and thiazole orange are the inhibition of lymphocyte proliferation11 and the short half-life, respectively9.
Calcein-AM, fluorescein diacetate (FDA), 2&#8242;,7&#8242;-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM), 5-(and-6)-carboxyfluorescein diacetate (CFDA), and 5-(and-6)-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) are the cytoplasmic fluorescent dyes used for lymphocyte migration studies. However, FDA, CFDA and CFDA-AM have lower retention in the cells9. BCECF-AM reduces the proliferative response and influences the chemotaxis and superoxide production9,12. Calcein-AM is a fluorescent dye and useful for short-term in vivo lymphocyte migration studies. It emits strong fluorescent signals, does not interfere with most of the cellular functions and retains fluorescent signals for up to 3 days12,13. Fluorescein isothiocyanate (FITC) and carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) are covalent coupling fluorescent dyes, which are used for lymphocyte migration studies. FITC exhibits no effect on the cell viability and has a stronger affinity with B lymphocytes than T lymphocytes14,15. The CFDA-SE labeled lymphocytes can be tracked in vivo for more than 8 weeks and up to 8 cell divisions9,16. C18 DiI (1,1&#39;-dioctadecyl-3,3,3&#39;,3&#39;-tetramethylindocarbocyanine perchlorate), DiO (3,3&#39;-dioctadecyloxacarbocyanine perchlorate), Paul Karl Horan (PKH)2, PKH3, and PKH26 are membrane-inserting fluorescent lipophilic carbocyanine dyes used to label leukocytes and erythrocytes. C18 Dil and DiO exhibit higher signals when incorporated into the cell membrane and are relatively non-toxic12,17. PKH2, PKH3 and PKH26 labeled cells exhibit a good retention of the fluorescent signals with less toxicity18,19,20,21,22. However, PKH2 down regulates the CD62L expression and reduces the lymphocyte viability23.
Most of the above-mentioned studies have been performed for tracking the lymphocyte migration and proliferation in the lymphatics and studying the labeled erythrocytes in the non-ocular circulation. There are very few studies applying the labeling techniques to study the blood cells in the ocular circulation. Application of scanning laser ophthalmoscopy (SLO) has a great advantage in studying the labeled cells in the retinal and choroidal circulation in vivo by fundus angiography24. There are several fluorescent dyes, such as ICG, acridine orange, FITC, sodium fluorescein, and CFDA that are used to study the leukocytes in the retinal circulation by SLO25,26,27,28,29,30,31,32,33,34. The phototoxicity and carcinogenicity of acridine orange26,27, the interference of FITC with the cellular activity, and the requirement of an intravascular contrast agent for the resolution of the retinal and choroidal blood vessels limits their application in in vivo animal experiments29. Sodium fluorescein and ICG are non-toxic, approved by the Food and Drug Administration, and safe for testing on humans32,35. Most of the flow dynamic studies are related to the labeling of the leukocytes or erythrocytes and its visualization in the retinal and choroidal blood vessels36,37,38,39. Here, we describe a standardized protocol of ICG labeling of the erythrocytes, sodium fluorescein labeling of the leukocytes, and tracking the visualized labeled cells in the mouse retinal circulation using SLO.

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			<td height="42" style="height:42px;width:287px;">Cardiogreen polymethine dye (Indocyanine green)</td>
			<td style="width:179px;">Sigma Aldrich</td>
			<td style="width:119px;">12633-50MG</td>
			<td style="width:167px;"></td>
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			<td height="42" style="height:42px;width:287px;">Fluorescein 100 mg/mL</td>
			<td style="width:179px;">Novartis</td>
			<td style="width:119px;">U1705A/H-1330292</td>
			<td></td>
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			<td height="42" style="height:42px;width:287px;">10X Phosphate-buffered saline (PBS) Ultra Pure Grade</td>
			<td style="width:179px;">1st BASE</td>
			<td style="width:119px;">BUF-2040-10X1L</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Bovine serum albumin</td>
			<td style="width:179px;">Sigma Aldrich</td>
			<td style="width:119px;">A7906-100G</td>
			<td></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:287px;">Microtainer tubes with K2E (K2EDTA) - EDTA concentration - 1.8 mg/mL of blood</td>
			<td style="width:179px;">BD, USA</td>
			<td style="width:119px;">REF 365974</td>
			<td></td>
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			<td height="21" style="height:21px;width:287px;">Histopaque 1077 solution</td>
			<td style="width:179px;">Sigma Aldrich</td>
			<td style="width:119px;">10771</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Centrifuge 5810 R</td>
			<td style="width:179px;">Eppendorf</td>
			<td style="width:119px;">05-413-401</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Microcentrifuge tubes 2mL</td>
			<td style="width:179px;">Axygen</td>
			<td style="width:119px;">MCT-200-C-S</td>
			<td></td>
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			<td height="21" style="height:21px;width:287px;">Vortex mixer</td>
			<td style="width:179px;">Insta BioAnalytik pte. ltd</td>
			<td style="width:119px;">FINE VORTEX</td>
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			<td height="21" style="height:21px;width:287px;">Shaker incubator</td>
			<td style="width:179px;">Lab Tech</td>
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			<td height="42" style="height:42px;width:287px;">Ceva Ketamine injection (Ketamine hydrochloride 100mg/mL)</td>
			<td style="width:179px;">Ceva</td>
			<td style="width:119px;">KETALAB03</td>
			<td></td>
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			<td height="42" style="height:42px;width:287px;">ILIUM XYLAZIL-20 (Xylazine hydrochloride 20mg/Ml)</td>
			<td style="width:179px;">Troy Laboratories PTY. Limited</td>
			<td style="width:119px;">LI0605</td>
			<td></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:287px;">1% Mydriacyl 15 mL (Tropicamide 1%)</td>
			<td style="width:179px;">Alcon&#160;Laboratories, Inc. USA</td>
			<td style="width:119px;">NDC&#160;0998-0355-15</td>
			<td></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:287px;">2.5% Mydfrin 5 mL (Phenylephrine hydrochloride 2.5%)</td>
			<td style="width:179px;">Alcon&#160;Laboratories, Inc. USA</td>
			<td style="width:119px;">NDC&#160;0998-0342-05</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Terumo syringe with needle 1cc/mL Tuberculin</td>
			<td style="width:179px;">Terumo (Philippenes) Corporation, Philippines</td>
			<td style="width:119px;">SS-01T2613</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:287px;">Vidisic Gel 10G</td>
			<td style="width:179px;">Dr. Gerhard Mann, Chem.-Pharm, Fabrik Gmbh, Berlin, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="42" style="height:42px;width:287px;">Alcohol swabs</td>
			<td style="width:179px;">Assure medical disposables</td>
			<td style="width:119px;">7M-004-L-01</td>
			<td></td>
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			<td height="63" style="height:63px;width:287px;">Confocal laser scanning angiography system (Heidelberg Retina Angiograph 2)</td>
			<td style="width:179px;">Heidelberg Engineering, GmbH, Heidelberg, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="63">
			<td height="63" style="height:63px;width:287px;">Hiedelberg Spectralis Viewing Module software, v4.0</td>
			<td style="width:179px;">Heidelberg Engineering, GmbH, Heidelberg, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
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			<td height="42" style="height:42px;">Fluorescent microscope</td>
			<td style="width:179px;">ZEISS</td>
			<td style="width:119px;">Model: axio imager z1</td>
			<td></td>
		</tr>
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fluorescent dye labeling of erythrocytes and leukocytes for studying the flow dynamics in mouse retinal circulation

The retinal and choroidal blood flow dynamics may provide insight into the pathophysiology and sequelae of various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration (AMD) and other ocular inflammatory conditions. It may also help to monitor the therapeutic responses in the eye. The proper labeling of the blood cells, coupled with live-cell imaging of the labeled cells, allows for the investigation of the flow dynamics in the retinal and choroidal circulation. Here, we describe the standardized protocols of 1.5% indocyanine green (ICG) and 1% sodium fluorescein labeling of mice erythrocytes and leukocytes, respectively. Scanning laser ophthalmoscopy (SLO) was applied to visualize the labeled cells in the retinal circulation of C57BL/6J mice (wild type). Both methods demonstrated distinct fluorescently labeled cells in the mouse retinal circulation. These labeling methods can have wider applications in various ocular disease models.

Erythrocytes labeled with 1.5% ICG were visualized in the retinal circulation of C57BL/6J mice (wild type). Both 1% and 5% hematocrit of 1.5% ICG labeled erythrocytes were distinguishable in the retinal circulation. However, the individual labeled cells were more clearly visualized with 1% hematocrit of 1.5% ICG labeled erythrocytes (Figure 1). In 5% hematocrit, due to the large number of labeled cells in the retinal vessels, it was not possible to mark the i...

Watch this Scientific Journal Video about Fluorescent Dye Labeling of Erythrocytes and Leukocytes for Studying the Flow Dynamics in Mouse Retinal Circulation at JoVE.com

Fluorescent Dye Labeling of Erythrocytes and Leukocytes for Studying the Flow Dynamics in Mouse Retinal Circulation

Live-cell imaging of the labeled blood cells in ocular circulation can provide information about inflammation and ischemia in diabetic retinopathy and age-related macular degeneration. A protocol to label blood cells and image the labeled cells in the retinal circulation is described.

The retinal and choroidal blood flow dynamics may provide insight into the pathophysiology and sequelae of various ocular diseases, such as glaucoma, ...

The overall goal of this procedure is to visualize retinal circulation of blood cells in the mouse using a scanning laser ophthalmoscope. This method can help answer key questions about retinal diseases such as what is the retinal floor dynamics of WBCs and RBCs and how can their flow dynamics contribute to disease pathogenesis. The main advantages of this technique is that it can refelct on different disease phenotypes and it is also very easy to perform.This procedure will be demonstrated by our team members, Praveen, Bo Bo, and Neha. To isolate the mouse blood cells layer freshly collected whole blood on top of a 1:1 polysucrose and sodium diatrizoatem solution in a two milliliter tube. Then centrifuge the tube for 30 minutes.Next aspirate and discard the plasma supernatant. Then carefully collect the buffy coat layer composed of leukocytes and the underlying layer of erythrocytes in separate tubes. Next wash the erythrocytes with 1XPBS to remove any contaminants and resuspend them in one volume of PBS.Then transfer half milliliter aliquots of the suspension into microcentrifuge tubes. Spin down the aliquots, discard the supernatant and add about 200 microliters of 40%1XPBS to the pelleted erythrocytes. Mix them well.And incubate them at room temperature for five minutes. After five minutes, add 100 microliters of ICG to each suspension. Mix the tubes using inversions and then incubate them at room temperature for five minutes.Next add 300 microliters of 1XPBS and incubate for an hour with gentle agitation at 37 degree Celsius. Then centrifuge the suspensions, keep the pelleted cells and resuspend them in one milliliter of 1XPBS. Keep washing the cells with 1XPBS until the supernatant is clear.After decanting the supernatant add back one volume of 1%BSA and PBS to achieve 50%hematocrit of ICG labeled erythrocytes. Next process the buffy coat collection. First wash the cells once with 10 milliliters of 1XPBS to remove any contaminants.Centrifuge the samples again and then resuspend the pellet in 900 microliters of 1XPBS. Next add 100 microliters of 10%sodium fluorescein and incubate the cells at room temperature for two minutes. Finally wash the labeled lymphocytes three times with 10 milliliters of 1XPBS.Centrifuge and resuspend them in 100 microliters of 1XPBS. To prepare the ICG labeled erythrocytes for injection first dilute an aliquot for injection down to a 5%or 1%hematocrit. Anesthetize the mouse and dilate its pupils.Then apply ophthalmic ointment to both eyes. And place a contact lens over one of the eyes. Now image the mouse using a confocal SLO camera with a positive 25 diopter lens to compensate for the eye's refraction.Fresh perfectly direct the cornea to the optical head of the SLO machine. Next switch on the imaging module and to maneuver it until the optic nerve is at the center of the imaging screen. Then at a 30 degree angle take the infrared fundus images.Next take an infrared fundus video. Turn on the 790 nanometer ICG filter set the camera mode to high speed addition keep the view angle at 15 to 30 degrees. Then set the ICG intensity to 85 for all readings.On the control panel, click on the acquire button to take a baseline video at 8.8 to 15 frames per second for one minute. Next load 100 microliters of ICG labeled erythrocytes into an insulin syringe with a 30 gauge needle and inject the cells into the tail vein or inject them retroorbitally. Immediately after the injection, take a new infrared fundus image and a new ICG filter video.After acquiring the videos export them in TIFF format for image analysis. Process the images using the freely available imaging software package, MHJ. After opening the file, set the frame interval of the image video for velocity measurements.Then open the MtrackJ plugin. From the menu, select tracking and toggle the option for moving to next timeframe index after adding a point. Now locate a cell of interest and track through each frame.From the menu, click add to add a new track and then click on the chosen cell. Then continue clicking on the current position of the cell as images advance from frame to frame. Once tracked change the display option for the trajectory from the displaying choices and choose to display only the track points at the current time.Continue clicking until the trajectory of the cell is displayed and then save the track. Now proceed with tracking the next cell starting with the add command and proceeding as with the first cell. After tracking all the cells of interest open the display of all the track measurements using the measure option.Then save the output for further analysis. Erythrocytes labeled with 1.5%ICG were visualized in the retinal circulation of C57 black 6J mice using 1%or 5%hematocrit, cells were distinguishable but in the 1%hematocrit the labeled cells were more easily visualized. With either injected concentration some erythrostasis was observable in the parapapillary region and it was more visible with the 5%hematocrit.Leukocytes were labeled with 1%sodium fluorescein and visualized as green labeled cells using fluorescence microscopy. Some clumping was observed. Once mastered, this technique can be done in six hours if performed properly.While attempting this procedure, it is important to dilate the eyes to acquire quality retinal images and videos.

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12.3K visualizações.  Tan Tock Seng Hospital. The overall goal of this procedure is to visualize retinal circulation of blood cells in the mouse using a scanning laser ophthalmoscope. This method can help answer key questions about retinal diseases such as what is the retinal floor dynamics of WBCs and RBCs and how can their flow dynamics contribute to disease pathogenesis. The main advantages of this technique is that it can refelct on different disease phenotypes and it is also very easy to perform.This procedure will be demonst...