Name: an acute retinal model for evaluating blood retinal barrier breach and potential drugs for treatment
Uploaded: 2016-09-13T15:00:00
Description: Watch this Scientific Journal Video about An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment at JoVE.com

Bringhurst Meats (Berlin, NJ) is acknowledged for their genuine help in providing the swine eyeballs.

All protocols were carried out in compliance with the policies of the Institutional Animal Care and Use Committee where applicable.
1. Preparation
<ol>
	<li>Prepare the stabilization media with 75% Dulbecco&#39;s Modified Eagle Medium (DMEM), 25% Hanks&#39; Balanced Salt Solution (HBSS). Mix well, aliquot and store at -20 &#176;C until use.</li>
	<li>Prepare the Phosphate Buffered Saline (PBS) and sterilize by autoclaving. Store the solution at room temperature. Warm the PBS to 37 &#176;C be...

<ol>
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In this report, we present a powerful ex vivo acute retinal model of BRB dysfunction using the swine retina. This model system does not require special instruments and can be easily adapted under most laboratory settings. However, to obtain a successful result, several steps require close attention. After obtaining the eyeballs from the source, they must be kept at 4 &#176;C or on ice and processed as soon as possible. When the effect of a treatment is being analyzed, two halves of the same retina must be used -...

A growing body of evidence supports the existence of blood retinal barrier (BRB)1-5 and its similarity to the blood brain barrier (BBB)6,7. Compromise of the BBB has been tightly linked causally or as a diagnostic marker to chronic neurodegenerative diseases such as Alzheimer&#39;s disease (AD)8,9 and acute conditions such as delirium10. Mechanistic insights into these pathologies and discoveries for potential drug targets are generally hampered by the limited accessibility and network intricacy of the brain. Alternatives such as in vivo imaging11, brain organotypic culture12, primary cell cultures13,14 and co-culture systems15 have been generated. However, most of these models require special instruments, long experimental periods or multiple markers to identify cells. Functional and structural similarities between BBB and BRB as well as a correlation between the dysfunctions of the two have been argued16-19. In addition, easier access, well-defined cell types and a layered structure have allowed the well-characterized retina as a window to the brain. The structural and functional identities of the BBB and BRB remain to be compared in detail. However, retinal pathologies, especially the BRB breach, have also been tightly associated with the progression of various diseases, including diabetes18-19 and AD21,22. Thus, it is of interest to establish a BRB dysfunction system not only to delineate the mechanism but also to screen potential drugs. In this report, a protocol enabling BRB dysfunction using a simple acute retinal culture is developed and presented.
Increased BBB permeability and AD-like pathological changes have been established in a brain organotypic culture incubated with histamine, a pro-inflammatory mediator12. Therefore, in the presented system, histamine was applied to the ex vivo retinal culture to induce BRB dysfunction. Retinas from several species, such as Mus musculus and Bos Taurus, have been tested. Due to their commercial availability and resemblance to human tissue, fresh swine eyeballs were utilized to provide the data reported here. After incubating with histamine and/or other drugs, the retinas were processed for evaluation by immunostaining for several proteins12, such as Immunoglobulin G (IgG), one of the major components of the blood; glial fibrillary acidic protein (GFAP), a well-known marker for glial activation; and microtubule-associated protein 2 (MAP2), a neuron-specific cytoskeletal protein essential for microtubule assembly. Furthermore, the layered structure of the retina allows a detailed analysis of the processes of M&#252;ller cells and ganglion cells, such as changes in their width and continuity. Thus several additional parameters are available to assess the consequences of the BRB breach at an early stage and to evaluate the reversal effects of potential treatments as well.
In this protocol, potential reversal effects of screened drugs are evaluated from three perspectives: the leakage of blood vessels (BVs), the activation of glial cells and the damage-response of neuronal cells. Several quantification methods are utilized, for instance, the expression level shown by intensity of the immunostaining, width measurement of a process and continuity of neuronal processes shown by an enhancement filter. To better illustrate the method and to help interpret results, lipoxin A4 (LXA4), a compound endogenously synthesized in response to inflammatory injury and attenuating endothelial dysfunction23, has been chosen for demonstration purposes.

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		<tr height="21">
			<td height="21" style="height:21px;width:291px;">DMEM</td>
			<td style="width:269px;">Life Technologies&#160;</td>
			<td style="width:119px;">11965-092</td>
			<td style="width:305px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">HBSS</td>
			<td style="width:269px;">Life Technologies&#160;</td>
			<td style="width:119px;">14170-112</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Sucrose</td>
			<td style="width:269px;">J.T.Baker</td>
			<td style="width:119px;">4072-05</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Histamine&#160;</td>
			<td style="width:269px;">Sigma</td>
			<td style="width:119px;">H7125-1G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Penicillin-Streptomycin&#160;</td>
			<td style="width:269px;">Invitrogen</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">PFA</td>
			<td style="width:269px;">Electron Microscopy Sciences</td>
			<td style="width:119px;">15710</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Freezing Media&#160;</td>
			<td style="width:269px;">Triangle Biomedical Sciences</td>
			<td style="width:119px;">TFM-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Normal Goat Serum&#160;</td>
			<td style="width:269px;">Rockland</td>
			<td style="width:119px;">D104-00-0050</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">Triton X-100</td>
			<td style="width:269px;">Sigma</td>
			<td style="width:119px;">T8787</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">GFAP Antibody</td>
			<td style="width:269px;">Millipore</td>
			<td style="width:119px;">AB5804</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">MAP2 Antibody</td>
			<td style="width:269px;">EMD Millipore</td>
			<td style="width:119px;">MAB3418</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:291px;">FITC conjugated Donkey anti-rabbit IgG</td>
			<td style="width:269px;">Jackson ImmunoResearch Laboratories, Inc.</td>
			<td style="width:119px;">711-095-152</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:291px;">Cy3 conjugated Donkey anti-mouse IgG</td>
			<td style="width:269px;">Jackson ImmunoResearch Laboratories, Inc.</td>
			<td style="width:119px;">715-165-150</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">mounting medium containing DAPI</td>
			<td style="width:269px;">Vector Laboratories, Inc.</td>
			<td style="width:119px;">H-1200</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:291px;">Laser Confocal Microscope</td>
			<td style="width:269px;">Nikon</td>
			<td style="width:119px;">Eclipse Ti microscope</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:291px;">ImageJ</td>
			<td style="width:269px;">National Institutes of Health</td>
			<td style="width:119px;">1.45s</td>
			<td></td>
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an acute retinal model for evaluating blood retinal barrier breach and potential drugs for treatment

A low-cost, easy-to-use and powerful model system is established to evaluate potential treatments that could ameliorate blood retinal barrier breach. An inflammatory factor, histamine, is demonstrated to compromise vessel integrity in the cultured retina through positive staining of IgG outside of the blood vessels. The effects of histamine itself and those of candidate drugs for potential treatments, such as lipoxin A4, are assessed using three parameters: blood vessel leakage via IgG immunostaining, activation of M&#252;ller cells via GFAP staining and change in neuronal dendrites through staining for MAP2. Furthermore, the layered organization of the retina allows a detailed analysis of the processes of M&#252;ller and ganglion cells, such as changes in width and continuity. While the data presented is with swine retinal culture, the system is applicable to multiple species. Thus, the model provides a reliable tool to investigate the early effects of compromised retinal vessel integrity on different cell types and also to evaluate potential drug candidates for treatment.

We present a low-cost, time-efficient and easy-to-use system to evaluate potential treatments that could protect against the BRB breach induced by histamine. IgG is constrained within the vessels in control retina (Figure 1A), but leaks out of the blood vessels upon histamine exposure (Figure 1B), confirming that the model is successfully established.
LXA4 was chosen to demonstrate the screening...

Watch this Scientific Journal Video about An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment at JoVE.com

An Acute Retinal Model for Evaluating Blood Retinal Barrier Breach and Potential Drugs for Treatment

A low-cost, easy-to-use and powerful system is established to evaluate potential treatments that could ameliorate blood retinal barrier breach induced by histamine. Blood vessel leakage, M&#252;ller cell activation and the continuity of neuronal processes are utilized to assess the damage response and its reversal with a potential drug, lipoxin A4.

A low-cost, easy-to-use and powerful model system is established to evaluate potential treatments that could ameliorate blood retinal barrier breach. An ...

The overall goal of this ex vivo retinal model system is to screen drugs, that ameliorate the blood neural barrier breach. This method can answer several key questions in the field of neural degenerative diseases, like what are the early events, and how can we screen for drugs that can help treat those patients. The main advantage of this technique is that it is low-cost, easy to use, fast and adaptable.Generally individuals new to this method will struggle because obtaining reliable and reproducible data depends on the technical skills to generate good samples. First swine retinas, obtained from a commercial source, are used here. After procurement from the source, the eyeballs must be kept at four degree, or on ice, and processed as soon as possible.Begin the dissection in a tissue culture hood by cutting around the lens to open the eye cap. Then using a brush, gently remove the vitreous humor, without pulling on the retina. Use a brush to gently detach the retina from the cut edge, to expose the optic disc.Sever the optic nerve with a razor and release the retina. Transfer the retina into a petri dish and carefully rinse the retina once using cold HBSS. Place the sample in HBSS on ice.Next, use a razor to cut the retina in half symmetrically. When treatments are required, one half of the retina is treated, while the other half of the same retina must be processed to set the baseline and to correct for the animal variations. Gently transfer the samples to a six-well plate containing three milliliters of stabilization medium per well.Equilibrate the retinas for 30 minutes at 37 degrees Celsius in an incubator with the atmosphere containing 5%carbon dioxide. After the incubation, carefully aspirate the stabilization medium, and add three milliliters of medium containing histamine and LXA4 to each well. Incubate the samples for another hour.After rinsing with warm sterile PBS, add three milliliters of 4%PFA to each well and incubate for 15 minutes at room temperature. Once the incubation time has elapsed, quickly aspirate the PFA and rinse the samples once with PBS. Add 10%sucrose to the wells and incubate for two to four hours at four degrees Celsius.Next, replace the 10%sucrose with 30%sucrose and incubate overnight at four degrees Celsius. Then mix one part commercial freezing medium with two parts 20%sucrose, to make working freezing medium. Leave at four degrees Celsius overnight or longer until the air bubbles disappear.The next day, replace the 30%sucrose with working freezing medium, and allow it to equilibrate for five minutes at room temperature. After equilibration, trim each retina into three millimeter by five millimeter rectangles, then freeze the retina slices by placing them into freezing medium, contained in a cylinder of aluminium foil. Ensure that the retinal slices are vertical to provide a cross-section of the retina upon sectioning, and freeze them in liquid nitrogen.Section each block on a cryostat into 14 micron slices, and mount the sections on glass slides. Store the slides at negative 80 degree Celsius until use. Begin immunostaining by washing the sections with 5%sucrose phosphate buffer, or SPB.Then block the non-specific binding sites, by incubating the sections and blocking buffer for one hour at room temperature. Next incubate the sections with the appropriate primary antibody for one hour. Once the hour has elapsed, aspirate the solution and wash the sections three times in 5%SPB.Then incubate the sections with the corresponding secondary antibodies for one hour, while protected from light. After washing the sections three times with 5%SPB, prepare the samples for microscopy by mounting them in medium containing DAPI, and covering with cover slips. Finally, capture images using a confocal microscope.To measure the width of the process, use the magnifying glass tool to choose an area of the section where the processes are gesting, such as the outer nuclear layer. Then choose an optical field where such processes are visible and continuous. Click the analyze tool in the main menu and then click set scale on the submenu, to set the scale bar according to the microscopic setting.Select the line function in the main menu and draw a line across the process. Click analyze in the main menu, and then click measure in the submenu, to perform the measurement. To analyze the continuity of the process, return to the main menu and use the polygon function to select the inner plexiform layer as the region of interest.Measure the area by clicking analyze and then measure. Click process, filter and then variants, to enhance the edges in the image by replacing each pixel with its neighborhood variant. Then automatically adjust the contrast and brightness by clicking image, adjust, brightness and contrast, and then auto in the submenu.Then count the lines. In these images, IGG immunoreactivity is seen in red. In control groups, IGG is restricted within the blood vessels.In the histamine group, IGG is detected out of the blood vessels, where it forms leakage clouds indicated by dotted circles. In the LXA4 treated groups, IGG is again restricted within the blood vessels. Further addition of LXA4 rescues the vessels'function induced by histamine.This histogram shows the percentage of leaky blood vessels across the tested groups. In these images immunostaining for GFAP, which stains Muller cells, is presented. Positive staining is obtained in the processes of Muller cells, across the retina, and around the blood vessels.The width of the Muller cell processes, from all groups are presented. Treatment with histamine, or LXA4 alone, reduced process width. But when both reagents were applied together, process width was rescued.In these images, immunostaining for MAP2 is presented. Positive staining from the processes and cell bodies of ganglion cells is observed. The density of continuous MAP2 positive ganglion cell processes from all groups are presented.Treatment with histamine decreases the continuity of dendritic processes, while LXA4 has no significant effects. Once mastered, this experiment can be done in three to five days, if performed properly, with five minutes per retina for dissection, six minutes for treatment, followed by sectioning, immunostaining, and analysis. While attempting this procedure, it is important to use fresh tissue and proper controls.Following this procedure, other methods such as live imaging, can be added, to track real-time changes in levels of calcium and mitochondrial properties. After watching this video, you should have a good understanding of how to use this ex vivo acute retinal culture model, to create a BRB dysfunction, to assess the damage, and to screen for potential drugs. Thank you very much for watching and all the best with your experiments.

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JoVE Journal

Medicine

Visualization and Analysis of Blood Flow and Oxygen Consumption in Hepatic Microcirculation: Application to an Acute Hepatitis Model

There is a considerable discrepancy between oxygen supply and demand in the liver because hepatic oxygen consumption is relatively high but about 70% of the hepatic blood supply is poorly oxygenated portal vein blood derived from the gastrointestinal tract and spleen. Oxygen is delivered to hepatocytes by blood flowing from a terminal branch of the portal vein to a central venule via sinusoids, and this makes an oxygen gradient in hepatic lobules. The oxygen gradient is an important physical parameter that involves the expression of enzymes upstream and downstream in hepatic microcirculation, but the lack of techniques for measuring oxygen consumption in the hepatic microcirculation has delayed the elucidation of mechanisms relating to oxygen metabolism in liver. We therefore used FITC-labeled erythrocytes to visualize the hepatic microcirculation and used laser-assisted phosphorimetry to measure the partial pressure of oxygen in the microvessels there. Noncontact and continuous optical measurement can quantify blood flow velocities, vessel diameters, and oxygen gradients related to oxygen consumption in the liver. In an acute hepatitis model we made by administering acetaminophen to mice we observed increased oxygen pressure in both portal and central venules but a decreased oxygen gradient in the sinusoids, indicating that hepatocyte necrosis in the pericentral zone could shift the oxygen pressure up and affect enzyme expression in the periportal zone. In conclusion, our optical methods for measuring hepatic hemodynamics and oxygen consumption can reveal mechanisms related to hepatic disease.

An optical system was developed to visualize hepatic microcirculation with FITC-labeled erythrocytes and to measure the partial pressure of oxygen in the microvessels with laser-assisted phosphorimetry. This method can be used to investigate physiological and pathological mechanisms by analyzing microvascular structure, diameter, blood flow velocity, and oxygen tension.

There is a considerable discrepancy between oxygen supply and demand in the liver because hepatic oxygen consumption is relatively high but about 70% of ...

Intravital Video Microscopy Measurements of Retinal Blood Flow in Mice

Alterations in retinal blood flow can contribute to, or be a consequence of, ocular disease and visual dysfunction. Therefore, quantitation of altered perfusion can aid research into the mechanisms of retinal pathologies. Intravital video microscopy of fluorescent tracers can be used to measure vascular diameters and bloodstream velocities of the retinal vasculature, specifically the arterioles branching from the central retinal artery and of the venules leading into the central retinal vein. Blood flow rates can be calculated from the diameters and velocities, with the summation of arteriolar flow, and separately venular flow, providing values of total retinal blood flow. This paper and associated video describe the methods for applying this technique to mice, which includes 1) the preparation of the eye for intravital microscopy of the anesthetized animal, 2) the intravenous infusion of fluorescent microspheres to measure bloodstream velocity, 3) the intravenous infusion of a high molecular weight fluorescent dextran, to aid the microscopic visualization of the retinal microvasculature, 4) the use of a digital microscope camera to obtain videos of the perfused retina, and 5) the use of image processing software to analyze the video. The same techniques can be used for measuring retinal blood flow rates in rats.

Intravital microscopy can be used in animals to visualize and measure retinal vascular diameters, bloodstream velocities, and total retinal blood flow.

Alterations in retinal blood flow can contribute to, or be a consequence of, ocular disease and visual dysfunction. Therefore, quantitation of altered ...

Oxygen-Glucose Deprivation and Reoxygenation as an In Vitro Ischemia-Reperfusion Injury Model for Studying Blood-Brain Barrier Dysfunction

Ischemia-Reperfusion (IR) injury is known to contribute significantly to the morbidity and mortality associated with ischemic strokes. Ischemic cerebrovascular accidents account for 80% of all strokes. A common cause of IR injury is the rapid inflow of fluids following an acute/chronic occlusion of blood, nutrients, oxygen to the tissue triggering the formation of free radicals.
Ischemic stroke is followed by blood-brain barrier (BBB) dysfunction and vasogenic brain edema. Structurally, tight junctions (TJs) between the endothelial cells play an important role in maintaining the integrity of the blood-brain barrier (BBB). IR injury is an early secondary injury leading to a non-specific, inflammatory response. Oxidative and metabolic stress following inflammation triggers secondary brain damage including BBB permeability and disruption of tight junction (TJ) integrity.
Our protocol presents an in vitro example of oxygen-glucose deprivation and reoxygenation (OGD-R) on rat brain endothelial cell TJ integrity and stress fiber formation. Currently, several experimental in vivo models are used to study the effects of IR injury; however they have several limitations, such as the technical challenges in performing surgeries, gene dependent molecular influences and difficulty in studying mechanistic relationships. However, in vitro models may aid in overcoming many of those limitations. The presented protocol can be used to study the various molecular mechanisms and mechanistic relationships to provide potential therapeutic strategies. However, the results of in vitro studies may differ from standard in vivo studies and should be interpreted with caution.

Oxygen-Glucose Deprivation and Reoxygenation as an In Vitro Ischemia-Reperfusion Injury Model for Studying Blood-Brain Barrier Dysfunction

Ischemia-Reperfusion (IR) injury is associated with a high rate of morbidity and mortality. The goal of the in vitro model of oxygen-glucose deprivation and reoxygenation (OGD-R) described here is to assess the effects of ischemia reperfusion injury on a variety of cells, particularly in blood-brain barrier (BBB) endothelial cells.

Ischemia-Reperfusion (IR) injury is known to contribute significantly to the morbidity and mortality associated with ischemic strokes. Ischemic ...

A Step by Step Protocol for Subretinal Surgery in Rabbits

Age related macular degeneration (AMD), retinitis pigmentosa, and other RPE related diseases are the most common causes for irreversible loss of vision in adults in industrially developed countries. RPE transplantation appears to be a promising therapy, as it may replace dysfunctional RPE, restore its function, and thereby vision.
Here we describe a method for transplanting a cultured RPE monolayer on a scaffold into the subretinal space (SRS) of rabbits. After vitrectomy xenotransplants were delivered into the SRS using a custom made shooter consisting of a 20-gauge metallic nozzle with a polytetrafluoroethylene (PTFE) coated plunger. The current technique evolved in over 150 rabbit surgeries over 6 years. Post-operative follow-up can be obtained using non-invasive and repetitive in vivo imaging such as spectral domain optical coherence tomography (SD-OCT) followed by perfusion-fixed histology.
The method has well-defined steps for easy learning and high success rate. Rabbits are considered a large eye animal model useful in preclinical studies for clinical translation. In this context rabbits are a cost-efficient and perhaps convenient alternative to other large eye animal models.

Retinal pigment epithelium (RPE) replacement strategies and gene-based therapy are considered for several retinal degenerative conditions. For clinical translation, large eye animal models are required to study surgical techniques applicable in patients. Here we present a rabbit model for subretinal surgery geared towards RPE transplantation, which is versatile and cost-efficient.

Age related macular degeneration (AMD), retinitis pigmentosa, and other RPE related diseases are the most common causes for irreversible loss of vision in ...

Improved Method for the Establishment of an In Vitro Blood-Brain Barrier Model Based on Porcine Brain Endothelial Cells

The aim of this protocol presents an optimized procedure for the purification and cultivation of pBECs and to establish in vitro blood-brain barrier (BBB) models based on pBECs in mono-culture (MC), MC with astrocyte-conditioned medium (ACM), and non-contact co-culture (NCC) with astrocytes of porcine or rat origin. pBECs were isolated and cultured from fragments of capillaries from the brain cortices of domestic pigs 5-6 months old. These fragments were purified by careful removal of meninges, isolation and homogenization of grey matter, filtration, enzymatic digestion, and centrifugation. To further eliminate contaminating cells, the capillary fragments were cultured with puromycin-containing medium. When 60-95% confluent, pBECs growing from the capillary fragments were passaged to permeable membrane filter inserts and established in the models. To increase barrier tightness and BBB characteristic phenotype of pBECs, the cells were treated with the following differentiation factors: membrane permeant 8-CPT-cAMP (here abbreviated cAMP), hydrocortisone, and a phosphodiesterase inhibitor, RO-20-1724 (RO). The procedure was carried out over a period of 9-11 days, and when establishing the NCC model, the astrocytes were cultured 2-8 weeks in advance. Adherence to the described procedures in the protocol has allowed the establishment of endothelial layers with highly restricted paracellular permeability, with the NCC model showing an average transendothelial electrical resistance (TEER) of 1249 &#177; 80 &#937; cm2, and paracellular permeability (Papp) for Lucifer Yellow of 0.90 10-6 &#177; 0.13 10-6 cm sec-1 (mean &#177; SEM, n=55). Further evaluation of this pBEC phenotype showed good expression of the tight junctional proteins claudin 5, ZO-1, occludin and adherens junction protein p120 catenin. The model presented can be used for a range of studies of the BBB in health and disease and, with the highly restrictive paracellular permeability, this model is suitable for studies of transport and intracellular trafficking.

Improved Method for the Establishment of an In Vitro Blood-Brain Barrier Model Based on Porcine Brain Endothelial Cells

The aim of the protocol is to present an optimized procedure for the establishment of an in vitro blood-brain barrier (BBB) model based on primary porcine brain endothelial cells (pBECs). The model shows high reproducibility, high tightness, and is suitable for studies of transport and intracellular trafficking in drug discovery.

The aim of this protocol presents an optimized procedure for the purification and cultivation of pBECs and to establish in vitro blood-brain barrier (BBB) ...

An In Vivo Method for Evaluating the Gut-Blood Barrier and Liver Metabolism of Microbiota Products

The gut-blood barrier (GBB) controls the passage of nutrients, bacterial metabolites and drugs from intestinal lumen to the bloodstream. The GBB integrity is disturbed in gastrointestinal, cardiovascular and metabolic diseases, which may result in easier access of biologically active compounds, such as gut bacterial metabolites, to the bloodstream. Thus, the permeability of the GBB may be a marker of both intestinal and extraintestinal diseases. Furthermore, the increased penetration of bacterial metabolites may affect the functioning of the entire organism.
Commonly used methods for studying the GBB permeability are performed ex vivo. The accuracy of those methods is limited, because the functioning of the GBB depends on intestinal blood flow. On the other hand, commonly used in vivo methods may be biased by liver and kidney performance, as those methods are based on evaluation of urine or/and peripheral blood concentrations of exogenous markers. Here, we present a direct measurement of GBB permeability in rats using an in vivo method based on portal blood sampling, which preserves intestinal blood flow and is virtually not affected by the liver and kidney function. 
Polyurethane catheters are inserted into the portal vein and inferior vena cava just above the hepatic veins confluence. Blood is sampled at baseline and after administration of a selected marker into a desired part of the gastrointestinal tract. Here, we present several applications of the method including (1) evaluation of the colon permeability to TMA, a gut bacterial metabolite, (2) evaluation of liver clearance of TMA, and (3) evaluation of a gut-portal blood-liver-peripheral blood pathway of gut bacteria-derived short-chain fatty acids. Furthermore, the protocol may also be used for tracking intestinal absorption and liver metabolism of drugs or for measurements of portal blood pressure.

An In Vivo Method for Evaluating the Gut-Blood Barrier and Liver Metabolism of Microbiota Products

The access of nutrients, microbiota metabolites and medicines to the circulation is controlled by the gut-blood barrier (GBB). We describe a direct method for measuring the GBB permeability in vivo, which, in contrast to commonly used indirect methods, is virtually not affected by liver and kidney functions.

The gut-blood barrier (GBB) controls the passage of nutrients, bacterial metabolites and drugs from intestinal lumen to the bloodstream. The GBB integrity ...

Oxygen-Induced Retinopathy Model for Ischemic Retinal Diseases in Rodents

One of the commonly used models for ischemic retinopathies is the oxygen-induced retinopathy (OIR) model. Here we describe detailed protocols for the OIR model induction and its readouts in both mice and rats. Retinal neovascularization is induced in OIR by exposing rodent pups either to hyperoxia (mice) or alternating levels of hyperoxia and hypoxia (rats). The primary readouts of these models are the size of neovascular (NV) and avascular (AVA) areas in the retina. This preclinical in vivo model can be used to evaluate the efficacy of potential anti-angiogenic drugs or to address the role of specific genes in the retinal angiogenesis by using genetically manipulated animals. The model has some strain and vendor specific variation in the OIR induction which should be taken into consideration when designing the experiments.

Oxygen-induced retinopathy (OIR) can be used to model ischemic retinal diseases such as retinopathy of prematurity and proliferative diabetic retinopathy and to serve as a model for proof-of-concept studies in evaluating antiangiogenic drugs for neovascular diseases. OIR induces robust and reproducible neovascularization in the retina that can be quantified.

One of the commonly used models for ischemic retinopathies is the oxygen-induced retinopathy (OIR) model. Here we describe detailed protocols for the OIR ...

Retinal Organoid Induction System for Derivation of 3D Retinal Tissues from Human Pluripotent Stem Cells

Retinal degenerative diseases are the main causes of irreversible blindness without effective treatment. Pluripotent stem cells that have the potential to differentiate into all types of retinal cells, even mini-retinal tissues, hold huge promises for patients with these diseases and many opportunities in disease modeling and drug screening. However, the induction process from hPSCs to retinal cells is complicated and time-consuming. Here, we describe an optimized retinal induction protocol to generate retinal tissues with high reproducibility and efficiency, suitable for various human pluripotent stem cells. This protocol is performed without the addition of retinoic acid, which benefits the enrichment of cone photoreceptors. The advantage of this protocol is the quantification of EB size and plating density to significantly enhance the efficiency and repeatability of retinal induction. With this method, all major retinal cells sequentially appear and recapitulate the main steps of retinal development. It will facilitate downstream applications, such as disease modeling and cell therapy.

Here we describe an optimized retinal organoid induction system, which is suitable for various human pluripotent stem cell lines to generate retinal tissues with high reproducibility and efficiency.

Retinal degenerative diseases are the main causes of irreversible blindness without effective treatment. Pluripotent stem cells that have the potential to ...

Retinal Pigment Epithelium Transplantation in a Non-human Primate Model for Degenerative Retinal Diseases

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These conditions include retinitis pigmentosa (RP) and advanced forms of age-related macular degeneration (AMD), such as geographic atrophy (GA). Together, these disorders represent a significant proportion of currently untreatable blindness globally. These unmet medical needs have generated heightened academic interest in developing methods of RPE replacement. Among the animal models commonly utilized for preclinical testing of therapeutics, the non-human primate (NHP) is the only animal model that has a macula. As it shares this anatomical similarity with the human eye, the NHP eye is an important and appropriate preclinical animal model for the development of advanced therapy medicinal products (ATMPs) such as RPE cell therapy.
This manuscript describes a method for the submacular transplantation of an RPE monolayer, cultured on a polyethylene terephthalate (PET) cell carrier, underneath the macula onto a surgically created RPE wound in immunosuppressed NHPs. The fovea-the central avascular portion of the macula-is the site of the greatest mechanical weakness during the transplantation. Foveal trauma will occur if the initial subretinal fluid injection generates an excessive force on the retina. Hence, slow injection under perfluorocarbon liquid (PFCL) vitreous tamponade is recommended with a dual-bore subretinal injection cannula at low intraocular pressure (IOP) settings to create a retinal bleb. 
Pretreatment with an intravitreal plasminogen injection to release parafoveal RPE-photoreceptor adhesions is also advised. These combined strategies can reduce the likelihood of foveal tears when compared to conventional techniques. The NHP is a key animal model in the preclinical phase of RPE cell therapy development. This protocol addresses the technical challenges associated with the delivery of RPE cellular therapy in the NHP eye.

The non-human primate (NHP) is an ideal model for studying human retinal cellular therapeutics due to the anatomical and genetic similarities. This manuscript describes a method for submacular transplantation of retinal pigment epithelial cells in the NHP eye and strategies to prevent intraoperative complications associated with macular manipulation.

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These ...

Retinal Pathophysiological Evaluation in a Rat Model

A posterior segment eye disease like diabetic retinopathy alters the physiology of the retina. Diabetic retinopathy is characterized by a retinal detachment, breakdown of the blood-retinal barrier (BRB), and retinal angiogenesis. An in vivo rat model is a valuable experimental tool to examine the changes in the structure and function of the retina. We propose three different experimental techniques in the rat model to identify morphological changes of retinal cells, retinal vasculature, and compromised BRB. Retinal histology is used to study the morphology of various retinal cells. Also, quantitative measurement is performed by retinal cell count and thickness measurement of different retinal layers. A BRB breakdown assay is used to determine the leakage of extraocular proteins from the plasma to vitreous tissue due to the breakdown of BRB. Fluorescence angiography is used to study angiogenesis and leakage of blood vessels by visualizing retinal vasculature using FITC-dextran dye.

Diabetic retinopathy is one of the leading causes of blindness. Histology, blood-retinal barrier breakdown assay, and fluorescence angiography are valuable techniques to understand the pathophysiology of the retina, which could further enhance the efficient drug screening against diabetic retinopathy.